JP7791079B2 - Molding glass material - Google Patents

Description

The present invention relates to a glass material for molding.

Optical glass differs from conventional silicate-based glasses such as window glass and bottle glass in that it not only has specific optical constants such as refractive index and Abbe number, but also has high light transmittance and uniform optical properties.

In recent years, in order to keep up with the trend toward higher definition imaging equipment, there has been a growing demand for higher performance imaging equipment, as well as a growing demand for lower height optical elements themselves. This has created a demand for optical glass that has a relatively high refractive index and excellent stability.

Here, examples of methods for manufacturing optical glass include a reheat press method, a round bar molding method, an extrusion molding method, etc. _, in which glass is reheated and shaped. In these manufacturing methods, silicate-based optical glass containing many components that improve optical properties, such as _Nb2O5 , _TiO2 , or _{La2O3 ,} tends to have a problem in that the stability of the glass tends to decrease, and crystallization tends to progress particularly when reheated.

It is known that melts of inorganic compounds that easily crystallize can be vitrified by rapid cooling. Therefore, the inorganic glass that is the subject of this invention is produced by cooling molten inorganic compounds at a rate faster than the rate at which crystallization progresses, thereby maintaining and freezing the disordered atomic arrangement in the molten state even at room temperature.

However, optical glass that does not absorb at least visible light does not have a high thermal conductivity even in a molten state, so the cooling rate of the entire glass decreases as the thickness of the glass increases, and the rapid cooling effect is limited. For example, as shown in Non-Patent Document 1, even if a cooling rate of 10 ² to 10 ³ °C/sec can be obtained by press-molding a 0.5 mm thick molten glass with a metal plate, the cooling rate when a 5 mm thick molten glass is press-molded with a metal plate is only 10 to 20 °C/sec. For this reason, the glass obtained by rapid cooling is said to be a "flake" as shown in Non-Patent Document 2.

Glass thick enough to be used to form optical elements is produced by continuously melting glass approximately 10 mm thick, with thicknesses as large as 30 mm or 40 mm. The presence of crystals inside the glass causes light scattering, making such glass unusable as optical elements. Even if one attempts to obtain glass by rapidly cooling the surface of glass of this thickness, the interior of the glass may not be cooled rapidly enough, resulting in the formation of crystals inside the glass. Furthermore, if the cooling conditions are too strong in an attempt to avoid such crystallization inside the glass, the surface of the glass will solidify before the interior, resulting in problems such as cracks or the glass breaking.

As such, when producing glass of a certain thickness, only the surface area can be vitrified without crystallization using the usual rapid cooling process. Furthermore, even if glass that has already crystallized internally is reheated, the tendency to crystallize does not disappear, and there is a high possibility that the glass will crystallize again during molding. Therefore, the glass material obtained in this way cannot be softened by heating to obtain the desired shape, and therefore cannot be used as optical glass for general industrial use.

On the other hand, Patent Document 1 discloses prior art that proposes unusual cooling conditions for optical glass. Specifically, it discloses that for silicate glass containing a large amount of _TiO2 , molten glass is cooled to room temperature and then annealed at a temperature lower than the glass transition temperature Tg to remove strain, thereby obtaining a glass material that can suppress the formation of crystals when reheated.

However, the optical glass obtained from the glass material in Patent Document 1 had low transmittance in the short wavelength region of visible light, especially blue light, and large partial dispersion ratios Pg and F, making it unable to meet the demands of modern optical design.

Japanese Patent Application Laid-Open No. 2003-192384

Sakuka Tadao, "Science of Amorphous Glass" (1983), p. 23 New Glass Forum, "Basic Lectures on New Glass" (1983), pp. 2-6

The present invention was made in consideration of these circumstances and aims to provide a glass material for molding that has excellent stability when reheated.

The gist of the present invention is as follows.
[1] A glass material for molding, in which the maximum value α _max of the linear expansion coefficient and the total content of SiO ₂ and ZrO ₂ expressed in mass % [SiO ₂ +ZrO ₂ ] satisfy the following formula (1):
α _max × [SiO ₂ + ZrO ₂ ]≦27900 (1)

[2] A glass material for molding, in which the maximum value α _max of the linear expansion coefficient, the average linear expansion coefficient α _100-300 at 100 to 300°C, and the total content of SiO ₂ and ZrO ₂ [SiO ₂ + ZrO ₂ ] expressed in mass% satisfy the following formula (4):
α _max /α _100-300 × [SiO ₂ +ZrO ₂ ]≦264 (4)

[3] A glass material for molding, the maximum value α _max of the linear expansion coefficient of which is smaller than the maximum value α _max (Tg) of the linear expansion coefficient of a glass material obtained by soaking the glass material for molding at the glass transition temperature Tg, followed by cooling at -30°C/hr for 4 hours, and then allowing it to cool.

[4] A glass material for molding described in [1] to [3], in which when an 11 mm x 11 mm x 10.5 mm sample is heat-treated for 5 minutes at a temperature 200°C higher than the glass transition temperature Tg, the number density D of crystals per 1 g of glass is less than 10 crystals/g.

[5] The glass material for molding according to any one of [1] to [4], wherein the TiO ₂ content [TiO ₂ ] and the Nb ₂ O ₅ content [Nb ₂ O ₅ ], expressed in mass%, satisfy the following formula (7):
{5×[TiO ₂ ]}/{3×[Nb ₂ O ₅ ]}≦3 (7)

[6] The glass material for molding according to any one of [1] to [5], wherein the wavelength λτ ₈₀ at which the internal transmittance of a 10 mm thick glass is 80% in the wavelength range of 280 to 700 nm is 395 nm or less.

[7] The glass material for molding according to any one of [1] to [6], wherein the Abbe number νd and the partial dispersion ratio Pg, F satisfy the following formula (8):
Pg,F≦-0.00286×νd+0.68700...(8)

[8] Optical glass made from the molding glass material described in [1] to [7] above.

The present invention provides a glass material for molding that has excellent stability when reheated.

1 is a graph showing the glass temperature during the manufacturing process of an example of a glass material for molding according to the present embodiment, with the vertical axis representing the glass temperature and the horizontal axis representing time (seconds) in logarithmic scale.

In the present invention and this specification, glass compositions are expressed on an oxide basis unless otherwise specified. Here, "glass composition on an oxide basis" refers to a glass composition obtained by converting the glass raw materials into oxides that are all decomposed during melting and exist in the glass, and each glass component is conventionally expressed as SiO ₂ , TiO ₂ , etc. Unless otherwise specified, the content and total content of glass components are on a mass basis, and "%" means "mass%". Furthermore, "glass material for molding" may be simply referred to as "glass" or "glass material".

The content of glass components can be quantified using known methods, such as inductively coupled plasma atomic emission spectroscopy (ICP-AES) and inductively coupled plasma mass spectrometry (ICP-MS). Furthermore, in this specification and the present invention, a content of 0% of a component means that the component is substantially absent, and it is acceptable for the component to be present at an unavoidable impurity level.

Below, the glass material for molding of the present invention will be described in three parts: a first embodiment, a second embodiment, and a third embodiment. The characteristics of the glass in the second and third embodiments are the same as those of the glass in the first embodiment. The actions and effects of each glass component in the second and third embodiments are the same as those of the glass component in the first embodiment. Therefore, in the second and third embodiments, matters that overlap with the explanation of the first embodiment will be omitted as appropriate.

First Embodiment The glass material for molding according to the first embodiment is
The maximum value α _max of the linear expansion coefficient and the total content of SiO ₂ and ZrO ₂ [SiO ₂ +ZrO ₂ ] expressed in mass % satisfy the following formula (1).
α _max × [SiO ₂ + ZrO ₂ ]≦27900 (1)

In the glass material for molding according to the first embodiment, the maximum value α _max of the linear expansion coefficient and the total content of SiO ₂ and ZrO ₂ expressed in mass % [SiO ₂ + ZrO ₂ ] satisfy the following formula (1), preferably the following formula (2), and more preferably the following formula (3). By satisfying the following formula, a glass material for molding with excellent stability during reheating can be obtained.
α _max × [SiO ₂ + ZrO ₂ ]≦27900 (1)
α _max × [SiO ₂ + ZrO ₂ ]≦27500 (2)
α _max × [SiO ₂ + ZrO ₂ ]≦27000 (3)

The maximum value α _max of the linear expansion coefficient can be controlled by adjusting the conditions for cooling the molten glass in the manufacturing process of the glass material described below.

The linear expansion coefficient is measured in accordance with the Japan Engineering Society Standard JOGIS08. The sample is a round bar measuring 20 mm ± 0.5 mm in length and 5 mm ± 0.5 mm in diameter. A load of 98 mN is applied to the sample, which is heated at a constant rate of 4°C per minute. The temperature and sample elongation are measured every second. The maximum linear expansion coefficient α _max is the maximum linear expansion coefficient between room temperature and the yield point (the temperature at which the sample yields and apparent elongation stops). Therefore, the linear expansion coefficient at the temperature at which the sample elongates most per unit temperature increase can be determined. The maximum linear expansion coefficient α _max may be calculated by taking a moving average of the linear expansion coefficients at 31 measurement points. The average linear expansion coefficient α _100-300 , described below, is the average linear expansion coefficient between 100°C and 300°C.

In this specification, the maximum linear expansion coefficient α _MAX and the average linear expansion coefficient α _100-300 are expressed to the first integer in units of 10 ⁻⁷ ° C ⁻¹ in accordance with the provisions of JOGIS08. In other words, the maximum linear expansion coefficient α _MAX and the average linear expansion coefficient α _100-300 are expressed as integers in units of [10 ⁻⁷ ° C ⁻¹ ].
In this specification, the average linear expansion coefficient α is expressed in units of [° C. ⁻¹ ], but the numerical value of the average linear expansion coefficient α is the same even when the unit is [K ⁻¹ ].

Non-limiting examples of properties and glass compositions other than those described above for the molding glass material of this embodiment are shown below.

In the glass material for molding according to the first embodiment, the maximum value α _max of the linear expansion coefficient, the average linear expansion coefficient α _100-300 at 100 to 300°C, and the total content of SiO ₂ and ZrO ₂ [SiO ₂ +ZrO ₂ ] expressed in mass% preferably satisfy the following formula (4), more preferably satisfy the following formula (5), and even more preferably satisfy the following formula (5). In order to obtain a glass material for molding that has excellent stability when reheating, it is preferable that the following formula be satisfied.
α _max /α _100-300 × [SiO ₂ +ZrO ₂ ]≦264 (4)
α _max /α _100-300 × [SiO ₂ + ZrO ₂ ]≦260 (5)
α _max /α _100-300 × [SiO ₂ + ZrO ₂ ]≦255 (6)

The maximum linear expansion coefficient α _max and the average linear expansion coefficient α _100-300 can be controlled by adjusting the conditions for cooling the molten glass in the manufacturing process of the glass material described below.

In the glass material for molding according to the first embodiment, the maximum value α _max of the linear expansion coefficient is preferably smaller than the maximum value α _max (Tg) of the linear expansion coefficient of a glass material obtained by soaking the glass material for molding at the glass transition temperature Tg, then cooling it at −30° C./hr for 4 hours, and then allowing it to cool. However, the maximum value α _max of the linear expansion coefficient may be slightly larger than the maximum value α _max (Tg) of the linear expansion coefficient. Therefore, the difference between α _max and α _max (Tg) [α _max (Tg) - α _max ], expressed to the first integer in units of 10 ^-7 · ° C ^-1 , is preferably -9 or more, and more preferably -4 or more, 0 or more, 5 or more, 10 or more, 20 or more, 40 or more, 60 or more, 80 or more, 100 or more, 120 or more, 140 or more, 160 or more, 180 or more, 200 or more, 250 or more, 300 or more, 350 or more, and 400 or more in that order. There are no particular limitations on the upper limit of the difference, but it is usually α _max (Tg), and preferably about α _max (Tg) - 100.

The maximum linear expansion coefficient α _max (Tg) is the maximum linear expansion coefficient of glass obtained by holding the glass material for molding so that it is soaked at the glass transition temperature Tg, and then cooling at -30°C/hr for 4 hours. The glass material for molding according to the first embodiment has a maximum linear expansion coefficient α _max but does not have a maximum linear expansion coefficient α _max (Tg). As will be described later, the glass material for molding according to the first embodiment is obtained by holding it at a temperature lower than the glass transition temperature Tg, and therefore has an α _max that is smaller than α _max (Tg).

When soaking at the glass transition temperature Tg, the glass material to be molded may be heated to a temperature above Tg and then cooled to the same temperature as Tg. Alternatively, the glass material to be molded may be gradually heated to the same temperature as Tg.

Fig. 1 is a graph showing the glass temperature in the manufacturing process for an example of a glass material for molding according to this embodiment. As will be described later, the glass material for molding according to this embodiment is held at a temperature lower than the glass transition temperature Tg in step 2. Here, the maximum linear expansion coefficient α _max (Tg) is the maximum linear expansion coefficient for glass obtained by holding at the glass transition temperature Tg in step 2, as in the comparative example (Tg1) in Fig. 1. Alternatively, the maximum linear expansion coefficient α _max (Tg) may be the maximum linear expansion coefficient for glass obtained by heating the glass material for molding from room temperature, soaking it at a temperature equal to Tg, and then cooling it, as in the comparative example (Tg2) in Fig. 1.

When a molding glass material is heated to a temperature higher than the glass transition temperature (Tg) and then cooled, the minimum time required for soaking at the glass transition temperature (Tg) is approximately 30 minutes after the glass surface temperature reaches Tg, depending on the size of the sample, but it can also be 1 hour, 2 hours, or 4 hours. There is no particular upper limit, and it is usually within 24 hours, preferably within 12 hours. The soaking time for the interior of the glass after reaching the Tg temperature can also be around 10 minutes.

When soaking glass material for molding, even if the surface temperature of the glass reaches the glass transition point Tg, this does not necessarily mean that the internal temperature has also reached Tg. Whether soaking is sufficient can be determined by its specific gravity. Glass obtained by sufficiently soaking at the glass transition temperature Tg and then cooling will have almost no change in specific gravity even if the time spent soaking at Tg is extended. On the other hand, glass obtained by cooling before being soaked at the glass transition temperature Tg, for example before the internal part of the glass reaches the glass transition temperature Tg, will have a different specific gravity than glass obtained by cooling after the internal part of the glass has been sufficiently soaked at Tg.

Therefore, for example, the absolute value of the change [d(t 1 ) - d(t ₁ + K)] between the specific gravity d(t ₁ ) of the glass obtained by heating a glass material for molding in a furnace so as to be soaked at the glass transition temperature Tg, holding the temperature for a holding time t ₁ (hr), and then cooling it, and the specific gravity d(t ₁ + K) of the glass obtained by heating the glass in a furnace, holding the temperature for a holding time t _{1 +} K (hr), and then cooling it, is preferably 0.002 or less. Here, the lower limit of the value of K is preferably 4, more preferably 8, and even more preferably 12.

When the above change is satisfied, it can be determined that the soaking of the glass is sufficient by heating for the holding time _t1 . In this case, the time required for soaking at the glass transition temperature Tg may be _t1 or more.

There are no particular restrictions on the method for cooling glass that has been soaked at the glass transition temperature Tg, as long as it is cooled at a cooling rate of -30°C/hr for 4 hours after soaking. For example, a temperature-programmable slow cooling furnace can be used. Note that if the temperature does not fall below the strain point of the glass even after cooling from the holding temperature Tg at a cooling rate of -30°C/hr for 4 hours, it may also be cooled from the holding temperature Tg at a cooling rate of -30°C/hr for 5 to 6 hours.

The heating temperature during reheating is usually the temperature at which the glass softens and deforms. Specific heating temperatures are expected to be low, about 50°C higher than the glass transition temperature Tg, and high, about 200-300°C higher than the glass transition temperature Tg. When the heating temperature during reheating is low, that is, when heating is performed at a temperature about 50°C higher than the glass transition temperature Tg, it is easier to ensure the stability of the glass and suppress the formation of crystals and devitrification.

However, if the reheating temperature is low, high pressure must be applied during molding. As a result, there is a higher chance of cracks occurring in the molded glass products (e.g., lenses, lens blanks, round bars, extrusion molded products, etc.) or the glass breaking. Therefore, if the reheating temperature is low, production yields are likely to decrease and the shapes of glass products that can be molded are likely to be limited.

On the other hand, if the heating temperature during reheating is high, i.e., if the glass is heated at a temperature approximately 200 to 300°C higher than the glass transition temperature Tg, deformation can be achieved in a shorter time and the degree of freedom in the shape of the molded product may be improved, but it becomes more difficult to ensure the stability of the glass, and crystallization and devitrification are more likely. For these reasons, in glasses with compositions such as those of the present invention, increasing the molding temperature makes crystals more likely to precipitate, and to avoid this crystal precipitation, the molding temperature must be lower than for conventional glasses, which increases the likelihood of deformation defects such as cracks and breakage.

In the glass material for molding according to the first embodiment, when an 11 mm x 11 mm x 10.5 mm sample is heat-treated for 5 minutes at a temperature 200°C higher than the glass transition temperature Tg, the number density D of crystals per 1 g of glass is preferably less than 10 crystals/g, with the upper limits being more preferably 9 crystals/g, 8 crystals/g, 7 crystals/g, 6 crystals/g, 5 crystals/g, 4 crystals/g, 3 crystals/g, 2 crystals/g, and 1 crystal/g, in that order. The number of crystals is most preferably 0 crystals/g.

The number of crystals used to calculate the number density D above is the number of bright spots that can be recognized as crystals using an optical microscope (100x magnification).

The above number density D is calculated using the following procedure.

[Sample preparation]
First, an optical microscope (100x magnification) was used to confirm that there were no visible foreign objects or crystals inside the glass. The glass was then cut and milled to obtain a rectangular sample measuring approximately 11 mm x 11 mm x 10.5 mm. The entire surface of this sample was ground with a grinding wheel of grit size #80 to #400 to create a sand-polished surface.

[Heat treatment furnace temperature uniformity]
The temperature is set to 200°C higher than the glass transition temperature Tg, and the material is heated in a heat treatment furnace with an internal space volume of approximately 25 cm x approximately 10 cm x approximately 10 cm that has been soaked for 15 minutes or more after the furnace temperature reaches Tg + 200°C.

In this case, the control thermometer of the heat treatment furnace should be installed approximately in the center of the internal space, and when the glass sample is heat treated, it should be positioned within 3 cm of the control thermometer sensor.

[Preheating the tray]
The tray is a rectangular hexahedron made of alumina and measuring approximately 10.5 cm x 3 cm x 1 cm. An anti-fusing agent such as powdered alumina or a solid lubricant such as BN is applied to the tip of the tray in an amount of 0.01 to 0.3 g, preferably 0.5 g to 0.15 g, and more preferably 0.1 g. The glass sample is then placed on top of the tray and heated in a heat treatment furnace. The tray is preheated in the heat treatment furnace for at least 15 minutes before testing.

[Heat treatment of glass samples]
The saucer is removed from the heat treatment furnace just before the glass sample is introduced, and the glass sample is immediately placed on the saucer at the position where the anti-fusing agent or solid lubricant was applied. The glass sample and the saucer are returned to their original position in the furnace. The time between removing the saucer and returning it to its original position is preferably within 10 seconds, more preferably within 8 seconds, and even more preferably within 6 seconds to avoid a drop in the temperature of the saucer. Five minutes after the glass sample is introduced, the glass and the saucer are removed, and the glass sample is then removed from the saucer and cooled at a cooling rate sufficient to prevent cracking. To ensure efficient cooling without affecting the stability of the glass, the glass sample is removed from the furnace and immediately (approximately 3±1 seconds later) rolled onto a ceramic fiber or similar material, covered with ceramic fiber or similar material to the extent that it does not compress the top surface of the sample, and then cooled to room temperature. After cooling, the edge of the glass sample is optically polished, and the interior of the glass sample is observed under an optical microscope (100x magnification). During optical polishing, preferably 80% or more, more preferably 85% or more of the softened glass sample remains as the observation volume. The number of crystals (bright spots) inside the glass sample is counted, and the weight of the sample after optical polishing is measured and converted into the number per gram.

In the glass material for molding according to the first embodiment, the TiO ₂ content [TiO ₂ ] and the Nb ₂ O ₅ content [Nb ₂ O ₅ ] expressed in mass % preferably satisfy the following formula (7).
{5×[TiO ₂ ]}/{3×[Nb ₂ O ₅ ]}≦3 (7)

The upper limit of the {5×[ _TiO2 ]}/{3×[ _Nb2O5 ]} is more preferably 2, and more preferably 1.25, 1.1, 1.0, 0.9, 0.8 _, 0.7, 0.6, and 0.5, in that order, for the purposes of further reducing Pg and F and achieving glass stability and/or a high refractive index. On the other hand, particularly from the viewpoint of reducing Pg and F and further improving the transmittance λτ80 in the blue region, the upper limit of the {5×[ _TiO2 ]}/ _{ 3×[ _Nb2O5 ]} is preferably 0.4, and more preferably 0.3 _, 0.2, and 0.1, in that order. The {5×[ _TiO2 ]}/{3×[ _Nb2O5 ]} may also be 0.0.

The above {5 × [TiO ₂ ]}/{3 × [Nb ₂ O ₅ ]} represents the abundance ratio of Ti ions to Nb ions in the glass material for molding. If there are too many Ti ions, the partial dispersion ratio Pg,F may increase. In addition, there is a risk that fine crystal nuclei may be generated when the molten glass is cooled, which may cause crystal growth under subsequent molding conditions, resulting in a decrease in optical quality and other problems that may hinder glass production. Therefore, it is preferable to satisfy the above formula in order to suppress an increase in the partial dispersion ratio Pg,F and suppress glass crystallization.

In the glass material for molding according to the first embodiment, the partial dispersion ratios Pg, F preferably satisfy the following formula (8), more preferably the following formula (9), even more preferably the following formula (10), particularly preferably the following formula (11), and most preferably the following formula (12). When the partial dispersion ratios Pg, F satisfy the following formula, an optical glass that is suitable for correcting chromatic aberration can be provided.
Pg,F≦-0.00286×νd+0.68700...(8)
Pg, F≦-0.00286×νd+0.68600 (9)
Pg, F≦-0.00286×νd+0.68500 (10)
Pg,F≦-0.00286×νd+0.68400 (11)
Pg, F≦-0.00286×νd+0.68300 (12)

The partial dispersion ratio Pg,F is expressed by the following formula (13) using the refractive indices ng, nF, and nC at the g-line, F-line, and C-line, respectively.
Pg,F=(ng-nF)/(nF-nC)...(13)

The partial dispersion ratio of Pg and F is the mass ratio [(Li ₂ O + Na ₂ O + K ₂ O + Cs ₂ O
)/(SiO ₂ +P ₂ O ₅ +B ₂ O ₃ )], mass ratio [(Li ₂ O +Na ₂ O +K ₂ O +Cs ₂ O)/(Nb ₂ O ₅ +TiO ₂ +WO ₃ +Bi ₂ O ₃ )], mass ratio [(SiO ₂ +P ₂ O ₅ +B ₂ O ₃ )/(Nb ₂ O ₅ +TiO ₂ +WO ₃ +Bi ₂ O ₃ )], mass ratio [ZrO ₂ /(Nb ₂ O ₅ +TiO ₂ +WO ₃ +Bi ₂ O ₃ )], mass ratio [P ₂ O ₅ /(SiO ₂ +P ₂ O ₅ +B ₂ O ₃ ) )] and the mass ratio [Nb ₂ O ₅ /(Nb ₂ O ₅ +TiO ₂ +WO ₃ +Bi ₂ O ₃ )].

Also, ΔPg,F is the deviation of Pg,F from the normal line and is calculated as shown in equation (14).
ΔPg,F=Pg,F-(0.6483-0.001802×νd)...(14)

The molding glass material according to the first embodiment can be high-dispersion glass with a relatively small partial dispersion ratio Pg,f. By reducing the values of Pg,f in high-dispersion glass, it becomes easier to suppress the occurrence of focal length shifts near the g-line, i.e., chromatic aberration in the short wavelength range, when performing achromatization (adjusting the focal length) focusing on the usual F-line and C-line. It also makes it easier to improve the contrast when enlarging an image captured with a camera. Furthermore, when recognizing digital images electronically, it becomes easier to recognize the edges of the subject, which is expected to reduce the computational load on the image engine.

The molding glass material according to this embodiment may have glass composition A, glass composition B, or glass composition C, as described in detail below.

(Glass Composition A)
The contents and ratios of the glass components and the glass properties when the glass material for molding according to this embodiment has glass composition A will be described below.

In the case of glass composition A, the glass material for molding according to this embodiment is preferably a silicate glass containing SiO ₂ primarily as a glass network-forming component. The lower limit of the SiO ₂ content is preferably 0%, and the larger the value, the more preferable in the order of 6%, 11%, and 16%. In particular, when thermal stability is more important than the refractive index of the glass, the lower limit of the SiO ₂ content is preferably 21%, and can also be 24%, 26%, or 28%. The upper limit of the SiO ₂ content is preferably 40%, and the smaller the value, the more preferable in the order of 38%, 35%, and 33%. In particular, when the refractive index is more important than the stability of the glass, the upper limit of the SiO ₂ content is preferably 30%, and can also be 28%, 26%, or 25%.

In glass composition A, _SiO2 serves as a glass network-forming component, improving the thermal stability, chemical durability, and weather resistance of the glass, increasing the viscosity of the glass melt, and making the glass melt easier to shape. It also increases thermal stability during reheating and has the effect of reducing the crystal number density D. On the other hand, if the _SiO2 content is high, the devitrification resistance of the glass tends to decrease, and Pg and F increase. Therefore, it is preferable that the _SiO2 content be within the above range.

The glass material for molding according to this embodiment, when _{it has glass composition A, preferably contains P2O5. The lower limit of the P2O5 content is preferably} 0%, and more preferably 0.2%, 0.4%, and 0.6%, in that order. The upper limit of _{the P2O5} content is preferably 10%, and more preferably 8%, 7%, 6%, 5%, and 4%, in that order.

In glass composition A, when the lower limit of the P ₂ O ₅ content satisfies the above, it has the effect of increasing thermal stability during reheating and reducing the crystal number density D. Furthermore, when the upper limit of the P ₂ O ₅ content satisfies the above, it is possible to suppress an increase in the partial dispersion ratios Pg, F and maintain stability during reheating.

In the glass material for molding according to this embodiment, in the case of glass composition A, the upper limit of the B ₂ O ₃ content is preferably 20%, and more preferably 14%, 9%, and 4%, in that order. The _{B 2} O ₃ content may be 0%.

In glass composition A, B ₂ O ₃ is a glass network-forming component that enhances the meltability of the glass and improves its thermal stability. On the other hand, if the B ₂ O ₃ content is too high, there is a risk that the amount of volatilization of glass components increases during glass melting, and high dispersion is hindered, tending to reduce devitrification resistance. Furthermore, there is a risk that the viscosity of the glass will be lowered compared to when the same amount of SiO ₂ is substituted. Furthermore, if introduced in excess, there is a risk that the thermal stability during reheating will be reduced. Therefore, it is preferable that the B ₂ O ₃ content be within the above range.

In the glass material for molding according to this embodiment, in the case of glass composition A, the upper limit of _{the Al2O3} content is preferably 20%, and more preferably 9%, 4%, 2%, and 1% in that order. The lower limit of _{the Al2O3} content is preferably 0%, and more preferably 0.02%, 0.04%, 0.08%, 0.12%, 0.14%, 0.16%, 0.2%, and 0.3% in that order. _{The Al2O3} content may even be 0%.

In glass composition A, Al ₂ O ₃ is a glass component that functions to improve the chemical durability and weather resistance of the glass, and can be considered as a network-forming component. On the other hand, if the Al ₂ O ₃ content increases, the devitrification resistance of the glass decreases. Furthermore, problems such as an increase in the glass transition temperature Tg and a decrease in thermal stability when cooling the molten glass are likely to occur. From the viewpoint of avoiding such problems, the Al ₂ O ₃ content is preferably within the above range. Furthermore, when a container and/or trough made of refractory bricks is used for melting or transporting the molten glass, the Al ₂ O ₃ content can be 0.02% or more.

In _the glass material for molding according to this embodiment, in the case of glass composition _A , the lower limit of the total content of _SiO2 and _P2O5 [ _SiO2 + _P2O5 ] is preferably 5%, and more preferably 11%, 16%, and 21% in that order. In particular, when stability is important, the lower limit of the total content is preferably 24%, and can also be 27% or 30%. Furthermore, the upper limit of the total content is preferably 40%, and more preferably 38%, 36%, 34%, and 33% in that order.

In glass composition A, when the lower limit of _the total content of _SiO2 and _P2O5 [ _SiO2 + _P2O5 ] satisfies the above range, it is possible to improve thermal stability during reheating and reduce _the crystal number density D. When the upper limit of the total content satisfies the above range, it is possible to suppress a decrease in the refractive index and an increase in the partial dispersion ratios Pg and F, and also to maintain the thermal stability of the glass.

In the glass material for molding according to this embodiment, in the case of glass composition A, the lower limit of the total content of SiO ₂ , P ₂ O ₅ , and B ₂ O ₃ [SiO ₂ + P ₂ O ₅ + B ₂ O ₃ ] is preferably 5%, and more preferably 10%, 15%, 18%, 21%, 22%, and 23% in that order. The upper limit of this total content is preferably 50%, and more preferably 45%, 40%, 37%, 35%, 34%, and 33% in that order. When refractive index is particularly important, the upper limit of this total content is preferably 30%, and can also be 28%, 26%, or 25%.

In glass composition A, from the viewpoint of maintaining stability during reheating, the total content [SiO ₂ +P ₂ O ₅ +B ₂ O ₃ ] is preferably within the above range.

In the glass material for molding according to this embodiment, in the case of glass composition A, the upper limit of the mass ratio of the content of B ₂ O ₃ to the content of SiO ₂ [B ₂ O ₃ /SiO ₂ ] is preferably 0.8.
The lower limit of the mass ratio is preferably 0, and more preferably 0.70, 0.60, 0.50, 0.40, 0.30, 0.20, 0.10, 0.05, and 0.03 in that order. The lower limit of the mass ratio is preferably 0, and more preferably 0.005, 0.01, 0.015, and 0.02 in that order. The mass ratio may even be 0.

In glass composition A, the mass ratio [B ₂ O ₃ /SiO ₂ ] is preferably in the above range, from the viewpoint of suppressing an increase in the specific gravity of the glass and suppressing an increase in coloration of the glass.

In the glass material for molding according to this embodiment, in the case of glass composition A, the lower limit of the mass ratio of the content of _P2O5 to the total content of _{SiO2 and P2O5} [ _P2O5 /( _SiO2 + _P2O5 )] is preferably 0.00, and more preferably 0.006 _, 0.011, 0.016, and _0.021 in _that order. The upper limit of this mass ratio is preferably 0.20, and more preferably 0.18, 0.16, 0.14, 0.12, and 0.11 in that order.

In glass composition A, if the mass ratio [P ₂ O ₅ /(SiO ₂ +P ₂ O ₅ )] is too low, stability during reheating may deteriorate, while if it is too high, the partial dispersion ratio Pg, F may increase. Therefore, the mass ratio is preferably within the above range.

In the glass material for molding according to this embodiment, in the case of glass composition A, the lower limit of the mass ratio of the content of _P2O5 to the total content of _{SiO2 , P2O5} , and _B2O3 [ _P2O5 /( _SiO2 + _P2O5 + _B2O3 )] is preferably 0.00, and more preferably 0.006 _, 0.011 _, 0.016, and 0.021 in that order. The upper limit of this mass ratio is preferably 0.20, and more preferably 0.18, 0.16 _, 0.14 _, 0.12, and _0.11 in that order.

In glass composition A, if the mass ratio [P ₂ O ₅ /(SiO ₂ +P ₂ O ₅ +B ₂ O ₃ )] is too high, there is a risk of an increase in the partial dispersion ratio Pg, F. Therefore, the mass ratio is preferably within the above range.

In the glass material for molding according to this embodiment, in the case of glass composition A, the lower limit of the mass ratio of the _SiO2 content to the total content of SiO2, _P2O5 , and _{B2O3 [ SiO2} /( _SiO2 + _P2O5 + _B2O3 )] is preferably 0.100, and more preferably 0.200, 0.300, 0.400, 0.500, 0.600, 0.700, 0.800 _{, 0.820} , 0.840, and _0.860 in this order. The upper limit of this mass ratio is preferably 1.000, and more preferably 0.995, _0.990 , 0.985, 0.980, and 0.978 in this order.

In glass composition A, from the viewpoint of maintaining stability during reheating, the mass ratio [SiO ₂ /(SiO ₂ +P ₂ O ₅ +B ₂ O ₃ )] is preferably within the above range.

In the glass material for molding according to this embodiment, in the case of glass composition A, the lower limit of the _ZrO2 content is preferably 0%, and more preferably 2%, 3%, 4%, and 5%, in that order. In particular, when stability is more important than refractive index, the lower limit of the _ZrO2 content is preferably 6%, or can be 8%. Furthermore, the upper limit of the _ZrO2 content is preferably 15%, and more preferably 14%, 13%, 12%, 11%, and 10%, in that order.
In particular, when the refractive index is more important than stability, the upper limit of the ZrO ₂ content is preferably 9%, and can also be set to 8%, 7%, or 6%.

In glass composition A, when the lower limit of the _ZrO2 content satisfies the above, it is possible to obtain a glass that combines high refractive index and high dispersion with a high internal transmittance λτ of _80. Furthermore, when the upper limit of the _ZrO2 content satisfies the above, it is possible to suppress an increase in the partial dispersion ratio Pg,F, suppress the occurrence of defects as an optical element, and maintain the meltability and thermal stability of the glass.

In the glass material for molding according to this embodiment, in the case of glass composition A, the lower limit of the Nb ₂ O ₅ content is preferably 1%, and more preferably 11%, 21%, 26%, 31%, 34%, and 36% in this order. When the refractive index is particularly important over stability, the lower limit of the Nb ₂ O ₅ content is preferably 39%, and can also be 41%, 46%, 49%, or 50%. Furthermore, the upper limit of the Nb ₂ O ₅ content is preferably 80%, and more preferably 70%, 64%, 59%, 56%, and 54% in this order. When the stability is particularly important over refractive index, the upper limit of the Nb ₂ O ₅ content is preferably 51%, and can also be 47%, 44%, 43%, or 38%.

In glass composition A, by ensuring that the lower limit of the Nb ₂ O ₅ content satisfies the above, it is possible to obtain a high-refractive-index, high-dispersion glass with reduced partial dispersion ratios Pg and F. Nb ₂ O ₅ is also a glass component that improves the thermal stability and chemical durability of the glass. If the content is low, Pg and F may increase, while if it is contained in excess, the thermal stability of the glass may deteriorate. Therefore, by ensuring that the upper limit of the Nb ₂ O ₅ content satisfies the above, the thermal stability and chemical durability of the glass can be maintained well and the formability during reheating can be improved.

In the glass material for molding according to this embodiment, in the case of glass composition A, the lower limit of the _TiO2 content is preferably 0%, and more preferably 1%, 2%, 3%, and 4% in that order. The upper limit of the _TiO2 content is preferably 20%, and more preferably 15%, 11%, 8%, and 6% in that order.

_TiO2 is a component that contributes to a high refractive index and high dispersion in glass composition A. By coexisting _{with Nb2O5} , it improves glass stability while maintaining a high refractive index, and improves stability during reheating. On the other hand, if excessive _TiO2 is introduced, the partial dispersion ratio Pg,F increases and the transmittance of the glass in the short wavelength range may decrease. Furthermore, crystals may form in a temperature range lower than the deformation point of the glass, which may hinder the productivity of the glass. Therefore, it is preferable that the _TiO2 content be within the above range.

In the glass material for molding according to this embodiment, in the case of glass composition _A , the lower limit of the total content of _{Nb2O5 and TiO2} [ _Nb2O5 + _TiO2 ] is preferably 10%, and more preferably 20%, 30%, 35%, 38%, 39%, 40%, and 41% in this order. When the refractive index is particularly important over stability, the lower limit of the total content is preferably 45%, and can also be 48%, 51%, 53%, or 55%. Furthermore, the upper limit of the total content is preferably 80%, and more preferably 75%, 70%, 65%, 62%, 59%, and 56% in this order. When the stability is particularly important over the refractive index, the upper limit of the total content is preferably 53%, and can also be 50%, 47%, 44%, or 43%.

In glass composition A, from the viewpoint of improving glass stability while maintaining a high refractive index and improving stability during reheating, the total content [Nb ₂ O ₅ +TiO ₂ ] is preferably within the above range.

In the glass material for molding according to this embodiment, in the case of glass composition A, the upper limit of the mass ratio of the _{TiO2 content to the Nb2O5 content [ TiO2} / _Nb2O5 ] is preferably 0.50, and more preferably 0.40, 0.30, 0.20 _, 0.18, and 0.16 in that order. The lower limit of this mass ratio is preferably 0, and more preferably 0.02, 0.04, 0.06, 0.08, and 0.10 in that order. This mass ratio may even be 0.

In the glass composition A, from the viewpoint of suppressing an increase in the partial dispersion ratios Pg and F and increasing λτ80, the mass ratio [TiO ₂ /Nb ₂ O ₅ ] is preferably in the above range.

In the glass material for molding according to this embodiment, in the case of glass composition A, the lower limit of the mass ratio of _{the P2O5} content to _{the Nb2O5} content [ _P2O5 / _Nb2O5 ] is preferably 0.000, and more preferably 0.005, _{0.010 ,} 0.015, and 0.020 in that order. The upper limit of this mass ratio is preferably 0.200, and more preferably 0.150, 0.100, 0.090, and 0.080 in that order.

In the glass composition A, from the viewpoint of suppressing an increase in the partial dispersion ratios Pg and F, the mass ratio [P ₂ O ₅ /Nb ₂ O ₅ ] is preferably in the above range.

In the glass material for molding according to this embodiment, in the case of glass composition A, the lower limit of the mass ratio of the content of _P2O5 to the total content of _{Nb2O5 and TiO2} [ _P2O5 /( _Nb2O5 + _{TiO2 )} ] is preferably 0.000, and more preferably 0.005, 0.010, 0.015, and _0.018 in that order. The upper limit of this mass ratio is preferably 0.200, and more preferably 0.150, 0.100, 0.090 _, and 0.080 in that order.

In glass composition A, from the viewpoint of obtaining the desired high dispersibility, the mass ratio [P ₂ O ₅ /(Nb ₂ O ₅ +TiO ₂ )] is preferably in the above range.

In the glass material for molding according to this embodiment, in the case of glass composition A, the upper limit of the _WO3 content is preferably 20%, and more preferably 17%, 14%, 11%, 8%, 6%, 4%, 3%, 2%, 1%, 0.5%, and 0.2%, in that order. The lower limit of the _WO3 content is preferably 0%. The _WO3 content may be 0%.

_WO3 is a component that improves the stability of glass composition A during reheating. On the other hand, _WO3 increases the partial dispersion ratio Pg,F. It also tends to cause coloration of the glass and reduces λτ80. Therefore, the content of _WO3 is preferably within the above range.

In the glass material for molding according to this embodiment, in the case of glass composition A, the upper limit of _{the Bi2O3} content is preferably 20%, and more preferably 17%, 14%, 11%, 8%, 6%, 4%, 3%, 2%, 1%, 0.5%, and 0.2%, in that order. The lower limit of _{the Bi2O3} content is preferably 0%. _{The Bi2O3 content} may even be 0%.

When an appropriate amount _{of Bi2O3} is contained in glass composition A, it serves to improve the thermal stability of the glass. On the other hand, if _{the Bi2O3} content is too high, the partial dispersion ratio Pg,F increases. Furthermore, there is a risk that the coloring of the glass increases and λτ80 decreases. Therefore, it is preferable that _{the Bi2O3 content} be within the above range.

In the glass material for molding according to this embodiment, in the case of glass composition A, _the upper limit of the total content of _Nb2O5 , _TiO2 , _{WO3 ,} and _Bi2O3 [ _Nb2O5 + _TiO2 + _WO3 + _{Bi2O3 ]} is preferably 80%, and more preferably 75%, 70%, 65%, 62%, 59%, and 56% in this order. When stability is particularly important rather than refractive index _, the upper limit of this total content is preferably 53%, and can also be 50%, 47%, 44%, or 43%. The lower limit of this total content is preferably 10%, and more preferably 20%, 30%, 35%, 38%, 39%, 40%, and 41% in this order. In particular, when the refractive index is more important than stability, the lower limit of the total content is preferably 45%, and can also be set to 48%, 51%, 53%, or 55%.

In glass composition A, TiO ₂ , WO ₃ and Bi ₂ O ₃ are components that contribute to a high refractive index and high dispersion, together with Nb ₂ O _5. Therefore, the total content [Nb ₂ O ₅ + TiO ₂ + WO ₃ + Bi ₂ O ₃ ] is preferably within the above range.

Furthermore, in the glass material for molding according to this embodiment, in the case of glass composition A, the upper limit of the mass ratio [ _{Nb2O5 /} ( _Nb2O5 + _TiO2 + _WO3 + _{Bi2O3 )} ] of the content of _Nb2O5 to the total content of _{Nb2O5 , TiO2} , _WO3 , and _Bi2O3 is preferably ₁ , and more preferably 0.98, _0.96 , 0.94, and _0.92 , in order from the viewpoints of maintaining the thermal stability of the glass, increasing the λτ80 of the glass, and improving the stability during reheating. The lower limit of this mass ratio is preferably 0.1, and more preferably 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, and 0.8, in order.

Furthermore, in the glass material for molding according to this embodiment, in the case of glass composition A, the upper limit of the mass ratio [ _ZrO2 / _{( Nb2O5} + _TiO2 + _WO3 + _{Bi2O3 )} ] of the _ZrO2 content to the total content of _Nb2O5 , _TiO2 , _WO3 , and _Bi2O3 is preferably ₁ , and more preferably 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, and _0.25 in that order, from the viewpoint of maintaining the thermal stability of the glass. Furthermore, from the viewpoint of increasing λτ80 of the glass, the lower limit of the mass ratio [ _ZrO2 /( _Nb2O5 + _TiO2 + _WO3 + _Bi2O3 )] is preferably 001, and more preferably 0.03, 0.05, 0.08, 0.09 _{, 0.10} , and 0.11 in that order. Note that, from the viewpoint of maintaining high dispersibility of the glass, the upper limit of the mass ratio [ _{ZrO2 /} ( _Nb2O5 + _TiO2 + _WO3 + _Bi2O3 )] can also be set to 0.02, 0.01, or _0.00 .

In _the glass according to this embodiment, in the case of glass composition A, the upper limit _{of the mass ratio of the total content of SiO2, P2O5, and B2O3 to the total content of Nb2O5, TiO2, WO3, and Bi2O3 [ ( SiO2 + P2O5 + B2O3 ) / ( Nb2O5 + TiO2 + WO3} + _Bi2O3 )] is preferably 5, and more preferably ₄ , 3, ₂ , 1.5, 1.3, 1.1 _, 1.0, 0.9, and _0.8 , in that order. When emphasis is placed on the refractive index, the upper limit of this mass ratio is preferably 0.7, and can also be 0.6, 0.5, or 0.45. The lower limit of the mass ratio is preferably 0.013, and more preferably 0.10, 0.20, 0.30, 0.35, and 0.40 in that order. When stability is particularly important, the lower limit of the mass ratio is preferably 0.50, and can also be 0.60, 0.70, or 0.75.

In glass composition A, by setting the mass ratio [(SiO ₂ + P ₂ O ₅ + B ₂ O ₃ )/(Nb ₂ O ₅ + TiO ₂ + WO ₃ + Bi ₂ O ₃ )] within the above range, the refractive index of the glass can be adjusted and thermal stability can be maintained.

In the glass material for molding according to this embodiment, in the case of glass composition A, the upper limit of _{the Ta2O5} content is preferably 20%, and more preferably 15%, 10%, 8%, 6%, 4%, 2%, and 1% in that order. The lower limit of _{the Ta2O5} content is preferably 0%. _{The Ta2O5 content} may even be 0%.

_{Ta2O5 is} a glass component in glass composition A that functions to improve the thermal stability of the glass. On the other hand, if the content of _Ta2O5 increases, the thermal stability of the glass decreases, and when the glass is melted, unmelted glass raw materials tend to remain. In addition, _Ta2O5 is an expensive component, and there is a risk that _the manufacturing cost of the glass will increase. Therefore, the content of _Ta2O5 is preferably within the above range.

Furthermore, in the glass material for molding according to this embodiment, in the case of glass composition A, the _upper limit of the mass ratio of the content of _Ta2O5 to the total content of _Ta2O5 , _Nb2O5 , _{TiO2 , WO3, and Bi2O3 [Ta2O5 / ( Ta2O5 + Nb2O5 + TiO2 + WO3} + _Bi2O3 )] is preferably 0.9, and more preferably 0.7 _{, 0.5} , 0.3, 0.2 _, 0.1, and _0.05 in that order. The lower limit of this mass ratio is preferably 0.000.

In glass composition A, from the viewpoint of suppressing an increase in specific gravity and suppressing an increase in the manufacturing cost of the glass, the mass ratio [Ta ₂ O ₅ /(Ta ₂ O ₅ +Nb ₂ O ₅ +TiO ₂ +WO ₃ +Bi ₂ O ₃ )] is preferably in the above range.

In the glass material for molding according to this embodiment, in the case of glass composition A, the upper limit of the Li ₂ O content is preferably 10%, and more preferably 9%, 8%, 7%, and 6% in that order. The lower limit of the _{Li 2} O content is preferably 0%, and more preferably 1%, 2%, 3%, 3.5%, 4%, and 4.5% in that order.

In the glass material for molding according to this embodiment, in the case of glass composition A, the upper limit of the Na ₂ O content is preferably 30%, and more preferably 25%, 20%, 18%, 16%, 14, and 12% in that order. The lower limit of the _{Na 2} O content is preferably 0%, and more preferably 1%, 2%, 3%, 3.5%, 4%, 4.5%, and 5% in that order.

In the glass material for molding according to this embodiment, in the case of glass composition A, the upper limit of the K ₂ O content is preferably 30%, and more preferably 20%, 15%, 10%, 7%, and 4% in that order. The lower limit of the _{K 2} O content is preferably 0%, and more preferably 0.1%, 0.2%, 0.3%, 0.4%, and 0.5% in that order.

In glass composition A, Li ₂ O, Na ₂ O, and K ₂ O all function to lower the liquidus temperature and improve the thermal stability of the glass, but if their contents increase, the chemical durability and weather resistance decrease. Therefore, it is preferable that the contents of Li ₂ O, Na ₂ O, and K ₂ O are each within the above-mentioned ranges.

In the glass material for molding according to this embodiment, in the case of glass composition A, the lower limit of the total content of _Li2O , _Na2O , and _K2O [ _Li2O + _Na2O + _K2O ] is preferably 1%, and more preferably 5%, 8%, 10%, 12%, 13%, and 14% in this order. The upper limit of the total content is preferably 40%, and more preferably 35%, 30%, 25%, 22%, 20%, 19%, 18%, and 17% in this order.

In glass composition A, when the lower limit of the total content [Li ₂ O + Na ₂ O + K ₂ O] satisfies the above range, the meltability of the glass can be improved and an increase in the liquidus temperature can be suppressed. When the upper limit of the total content satisfies the above range, the viscosity of the glass can be increased, the crystallization rate of the glass melt can be reduced, and stability during reheating can be improved.

In the glass composition A of the molding glass material according to this embodiment, the lower limit of the mass ratio of the total content of _Li2O , _Na2O , _{and K2O} to the total content of _Nb2O5 and _TiO2 [( _Li2O + _Na2O + _K2O )/( _Nb2O5 + _TiO2 )] is preferably 0.10, and more preferably 0.15, _0.18 , 0.21, 0.23, and 0.25 in this order. The upper limit of this mass ratio is preferably 0.70, and more preferably 0.65, 0.60, 0.55, 0.50, and 0.45 in this order.

In glass composition A, from the viewpoint of obtaining desired optical constants while maintaining the melting characteristics and thermal stability of the glass, the mass ratio [(Li ₂ O + Na ₂ O + K ₂ O)/(Nb ₂ O ₅ + TiO ₂ )] is preferably in the above range.

In the glass material for molding according to this embodiment, in the case of glass composition A, the _upper limit of the mass ratio of the content of _P2O5 to the total content of _Li2O , _Na2O , _K2O , and _Nb2O5 [ _P2O5 /( _Li2O + _Na2O + _K2O + _Nb2O5 )] is preferably _0.500 , and more preferably 0.400, 0.300, 0.200, 0.100 _, 0.080, 0.070, and _0.060 in this order. The lower limit of this mass ratio is preferably 0, and more preferably 0.005, 0.010, 0.011, 0.012, 0.013, and 0.014 in this order.

In glass composition A, from the viewpoint of stabilizing the glass and suppressing an increase in the partial dispersion ratio Pg, F, the mass ratio [P ₂ O ₅ /(Li ₂ O + Na ₂ O + K ₂ O + Nb ₂ O ₅ )] is preferably in the above range.

In the glass material for molding according to this embodiment, in the case of glass composition A, the upper limit of the _Cs2O content is preferably 10%, and more preferably 8%, 6%, 4%, 3%, 2%, and 1% in that order. The lower limit of the _Cs2O content is preferably 0%.

In glass composition A, Cs ₂ O has the function of improving the thermal stability of the glass, but if its content increases, chemical durability and weather resistance decrease. Therefore, the content of Cs ₂ O is preferably within the above range.

In the glass material for molding according to this embodiment, in the case of glass composition A, the lower limit of the total content of _Li2O , _Na2O , _K2O , and _Cs2O [ _Li2O + _Na2O + _K2O + _Cs2O ] is preferably 1%, and more preferably 5%, 8%, 10%, 12%, 13%, and 14% in this order. The upper limit of the total content is preferably 40%, and more preferably 35%, 30%, 25%, 22%, 20%, 19%, 18%, and 17% in this order.

In glass composition A, from the viewpoint of maintaining stability during reheating, the total content [Li ₂ O + Na ₂ O + K ₂ O + Cs ₂ O] is preferably within the above range.

Furthermore, in the glass material for molding according to this embodiment, in the case of glass composition A, the upper limit of the mass ratio of the content of _Li2O to the total content of _Li2O , _Na2O , _K2O , and _Cs2O [ _Li2O /( _Li2O + _Na2O + _K2O + _Cs2O )] is preferably 1, and more preferably 0.9, 0.8, 0.7, 0.6, 0.5, 0.45, and 0.4, in order from the viewpoint of suppressing an increase in liquidus temperature and suppressing a decrease in weather resistance. The lower limit of this mass ratio is preferably 0, and more preferably 0.1, 0.2, 0.25, 0.29, 0.31, and 0.33, in order.

Furthermore, in the glass material for molding according to this embodiment, in the case of glass composition A, the upper limit of the mass ratio of the content of _Na2O to the total content of _Li2O , _Na2O , _K2O , and _Cs2O [ _Na2O /( _Li2O + _Na2O + _K2O + _Cs2O )] is preferably 1, and more preferably 0.95, 0.9, 0.85, 0.80, 0.75, 0.70, and 0.66, in order from the viewpoint of suppressing an increase in liquidus temperature and suppressing a decrease in weather resistance. The lower limit of this mass ratio is preferably 0, and more preferably 0.1, 0.2, 0.25, 0.29, 0.31, 0.33, and 0.34, in order.

In the glass material for molding according to this embodiment, in the case of glass composition A, the upper limit of the mass ratio of the content of _K2O to the total content of _Li2O , _Na2O , _K2O , and _Cs2O [ _K2O /( _Li2O + _Na2O + _K2O + _Cs2O )] is preferably 1, and more preferably 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.28, and 0.27, in order from the viewpoint of suppressing an increase in liquidus temperature and suppressing a decrease in weather resistance. The lower limit of this mass ratio is preferably 0, and more preferably 0.1, 0.15, 0.20, 0.22, 0.24, and 0.25, in order.

Furthermore, in the glass material for molding according to this embodiment, in the case of glass composition A, the upper limit of the mass ratio of the content of _P2O5 to _the total content of _Li2O , _Na2O , _K2O , _Cs2O , _Nb2O5 , _{TiO2 , WO3 ,} and _Bi2O3 [ _{P2O5 /} ( _Li2O + _Na2O + _K2O +Cs2O+ _Nb2O5 + _TiO2 + _WO3 + _Bi2O3 )] is preferably 1, and more preferably _0.5 , _0.3 , _0.1 , 0.08, 0.07, and 0.06 in this order. The lower limit of this mass ratio is preferably 0, and more preferably 0.005, 0.008, 0.011, and 0.012 in this order.

In glass composition A, the desired Abbe number vd and partial dispersion _ratio Pg, _F can be obtained by appropriately incorporating _Li2O , _Na2O , _K2O , _Cs2O , _Nb2O5 , _TiO2 , _WO3 , and _Bi2O3 as glass components. However, incorporating these components into silicate-based glass may deteriorate stability during reheating. On the other hand, _P2O5 is a component that improves stability during reheating. Therefore, _if the mass ratio [ _P2O5 /( _Li2O + _Na2O + _K2O + _Cs2O + _Nb2O5 + _TiO2 + _WO3 + _Bi2O3 )] is _too high, the stability of the glass may deteriorate and the partial dispersion ratio Pg,F may increase. Conversely, if _the mass _ratio is too low, the stability during reheating may deteriorate. Therefore, the mass ratio is preferably within the above range.

In the glass material for molding according to this embodiment, in the case of glass composition A, _the upper limit of the mass ratio of the total content of _Li2O , _Na2O , _K2O , and _Cs2O to the total content of _SiO2 , _P2O5 , and _B2O3 [( _Li2O + _Na2O + _K2O + _Cs2O )/( _SiO2 + _P2O5 + _B2O3 )] is preferably ₅ , and more preferably 4, 3, ₂ , 1.5, 1, 0.9, 0.8, 0.7, and _0.6 in that order. The lower limit of this mass ratio is preferably 0.02, and more preferably 0.1, 0.2, 0.3, 0.4, and 0.45 in that order.

In glass composition A, if the mass ratio _[ ( _Li2O + _Na2O + _K2O + _Cs2O )/( _SiO2 + _P2O5 + _B2O3 )] is too low, the glass transition temperature Tg increases, the meltability deteriorates, and there is a risk of an increase in the partial dispersion ratios Pg and F. On the other hand, if _it is too high, there is a risk of a decrease in the viscosity of the glass during melting, a decrease in the thermal stability of the melt, and a decrease in stability during reheating.

In the glass material for molding according to this embodiment, in the case of glass composition A, _{the upper} limit of the mass ratio of the total content of _Li2O , _Na2O , _K2O , and _Cs2O to the total content of _Nb2O5 , _TiO2 , _WO3, and _Bi2O3 [( _Li2O + _Na2O + _K2O + _Cs2O )/( _Nb2O5 + _TiO2 + _WO3 + _Bi2O3 )] is preferably 4, and more preferably 3, 2, 1.5, ₁ , 0.9, 0.8, _0.7 , 0.6, and 0.5 in that order. The lower limit of this mass ratio is preferably 0.015, and more preferably 0.100, 0.200, and 0.300 in that order.

In glass composition A, if the mass ratio _[ ( _Li2O + _Na2O + _K2O + _Cs2O )/( _Nb2O5 + _TiO2 + _WO3 + _Bi2O3 )] is too low, the partial dispersion ratio Pg,F increases and the transmittance may deteriorate. On the other hand, if _it is too high, the Abbe number increases, the refractive index decreases, and stability during reheating may deteriorate.

In the glass material for molding according to this embodiment, in the case of glass composition A, the upper limit of the MgO content is preferably 20%, and more preferably 14%, 9%, 4%, 2%, and 1%, in that order. The upper limit may be 0%. The lower limit of the MgO content is preferably 0%. In particular, when increasing the resistivity of the glass to improve melting efficiency, the lower limit of the MgO content is preferably 1%, and can also be 2%, 4%, or 6%.

In the glass material for molding according to this embodiment, in the case of glass composition A, the upper limit of the CaO content is preferably 20%, and more preferably 14%, 9%, 4%, 2%, and 1%, in that order. The upper limit may be 0%. The lower limit of the CaO content is preferably 0%. In particular, when increasing the resistivity of the glass to improve melting efficiency, the lower limit of the CaO content is preferably 1%, and can also be 2%, 4%, 6%, or 8%.

In the glass material for molding according to this embodiment, in the case of glass composition A, the upper limit of the SrO content is preferably 20%, and more preferably 14%, 9%, 4%, 2%, and 1%, in that order. The upper limit may be 0%. The lower limit of the SrO content is preferably 0%. In particular, when increasing the resistivity of the glass to improve melting efficiency, the lower limit of the SrO content is preferably 1%, and can also be 2%, 4%, 6%, or 8%.

In the glass material for molding according to this embodiment, in the case of glass composition A, the upper limit of the BaO content is preferably 20%, and more preferably 14%, 9%, 4%, 2%, and 1%, in that order. The upper limit may be 0%. The lower limit of the BaO content is preferably 0%. In particular, when increasing the resistivity of the glass to improve melting efficiency, the lower limit of the BaO content is preferably 1%, and can also be 2%, 4%, 6%, or 8%.

In glass composition A, MgO, CaO, SrO, and BaO are all glass components that improve the thermal stability and devitrification resistance of the glass. However, if the content of these glass components increases, the specific gravity increases, high dispersibility is impaired, and the thermal stability and devitrification resistance of the glass decrease. Therefore, it is preferable that the content of each of these glass components be within the above-mentioned ranges.

In the glass material for molding according to this embodiment, in the case of glass composition A, the upper limit of the ZnO content is preferably 20%, and more preferably 14%, 9%, 4%, 2%, and 1%, in that order. The upper limit may be 0%. The lower limit of the ZnO content is preferably 0%. In particular, when increasing the resistivity of the glass to improve melting efficiency or when lowering the glass transition point, the lower limit of the ZnO content is preferably 1%, and can also be 2%, 4%, or 6%.

ZnO is a glass component in glass composition A that improves the thermal stability of the glass. However, if the ZnO content is too high, the specific gravity may increase. Therefore, it is preferable that the ZnO content be within the above range.

In the glass material for molding according to this embodiment, in the case of glass composition A, the upper limit of the total content of MgO and CaO [MgO + CaO] is preferably 20%, and more preferably 14%, 9%, 4%, 2%, and 1%, in that order. The upper limit may be 0%. The lower limit of the total content is preferably 0%. From the viewpoint of maintaining thermal stability without interfering with high dispersion, it is preferable that the total content be within the above range.

Furthermore, in the glass material for molding according to this embodiment, in the case of glass composition A, the upper limit of the total content of MgO, CaO, SrO, BaO, and ZnO [MgO + CaO + SrO + BaO + ZnO] is preferably 20%, and more preferably 14%, 9%, 4%, 2%, and 1%, in that order. The upper limit may be 0%. The lower limit of this total content is preferably 0%. In particular, when increasing the resistivity of the glass to improve melting efficiency, the lower limit of this total content is preferably 1%, and can also be 2%, 4%, 6%, or 8%. From the viewpoints of suppressing an increase in specific gravity and maintaining thermal stability without hindering high dispersion, it is preferable that the total content be within the above range.

Furthermore, in the glass material for molding according to this embodiment, in the case of glass composition A, the upper limit of the mass ratio [(MgO + CaO + SrO + BaO + ZnO)/( _Li2O + _Na2O + _K2O + _Cs2O )] of the total content of MgO, CaO, SrO, BaO, and ZnO to the total content of _Li2O , _Na2O , _K2O , and _Cs2O ] is preferably 20, and more preferably 18, 16, and 14 in that order. The lower limit of this mass ratio is preferably 0, and more preferably 5, 8, 10, 12, and 13 in that order. This mass ratio may even be 0. From the viewpoints of suppressing an increase in the specific gravity of the glass, improving the filling rate of the glass to achieve a high refractive index and high dispersion while enhancing meltability, and appropriately maintaining the specific resistance of the glass, it is preferable that this mass ratio be in the above range.

In the glass material for molding according to this embodiment, in the case of glass composition A, the upper limit of _{the La2O3} content is preferably 20%, and more preferably 17%, 14%, and 12%, in that order. When stability is more important than refractive index, the upper limit of _{the La2O3} content can be 9%, 7%, 5%, 3%, 2%, or 1%. The upper limit may be 0%. Furthermore, the lower limit of _{the La2O3} content is preferably 0%. In particular, when the refractive index is increased while maintaining the content of the glass-forming components, the lower limit of _{the La2O3} content is preferably 1%, and can also be 2%, 4%, or 6%.

In glass composition A, if the content of La ₂ O ₃ is large, the high dispersion of the glass is suppressed and the thermal stability is reduced. Therefore, the content of La ₂ O ₃ is preferably within the above range.

In the glass material for molding according to this embodiment, in the case of glass composition A, the upper limit of the Y ₂ O ₃ content is preferably 20%, and more preferably 17%, 14%, and 12%, in that order. When stability is more important than refractive index, the upper limit of the Y ₂ O ₃ content can be 9%, 7%, 5%, 3%, 2%, or 1%. The upper limit may be 0%. Furthermore, the lower limit of the Y ₂ O ₃ content is preferably 0%. In particular, when the refractive index is increased while maintaining the content of the glass-forming components, the lower limit of the Y ₂ O ₃ content is preferably 1%, and can also be 2%, 3%, or 5%.

In glass composition A, if the content of Y ₂ O ₃ is too high, the high dispersion of the glass is suppressed, the thermal stability is reduced, and the glass is prone to devitrification during production. Therefore, the content of Y ₂ O ₃ is preferably within the above range.

In the glass material for molding according to this embodiment, in the case of glass composition A, the upper limit of _{the Sc2O3} content is preferably 3%, and more preferably 2%, 1.5%, 1%, and 0.5% in that order. The upper limit may be 0%. The lower limit of _{the Sc2O3} content is preferably 0%.

In the glass material for molding according to this embodiment, in the case of glass composition A, the upper limit of the _HfO2 content is preferably 3%, and more preferably 2%, 1.5%, 1%, and 0.5% in that order. The upper limit may be 0%. The lower limit of the _HfO2 content is preferably 0%.

Sc ₂ O ₃ and HfO ₂ have the function of increasing the dispersibility of the glass in glass composition A, but are expensive components. Therefore, the contents of Sc ₂ O ₃ and HfO ₂ are preferably within the above ranges.

Note that a certain amount of HfO ₂ may be contained in the ZrO ₂ raw material. Therefore, glass containing ZrO ₂ may also contain a certain amount of HfO _2. Therefore, in the glass material for molding according to the first embodiment, in the case of glass composition A, the mass ratio of the HfO ₂ content to the ZrO ₂ content [HfO ₂ /ZrO ₂ ] may also be within a predetermined range. For example, the lower limit of the mass ratio [HfO ₂ /ZrO ₂ ] may be 0.005, or even 0.010, 0.013, or 0.015. On the other hand, the upper limit of the mass ratio may be 0.05, or even 0.040, 0.030, 0.020, or 0.018. From the viewpoint of preventing components of the refractory brick from dissolving into the glass, it is preferable that the glass contain a small amount of ZrO ₂ , and therefore the HfO ₂ content is preferably within the above range.

In the glass material for molding according to this embodiment, in the case of glass composition _A , the upper limit of the content of _Lu2O3 is preferably 3%, and more preferably 2%, 1.5%, 1%, and 0.5% in that order. The upper limit may be 0%. The lower limit of the content _{of Lu2O3} is preferably 0%.

In glass composition A, _Lu2O3 has the function _of increasing the dispersibility of the glass, but also has a large molecular weight and is therefore a glass component that increases _the specific gravity of the glass. Therefore, the content of _Lu2O3 is preferably within the above range.

In the glass material for molding according to this embodiment, in the case of glass composition A, the upper limit of the _GeO2 content is preferably 3%, and more preferably 2%, 1.5%, 1%, and 0.5% in that order. The upper limit may be 0%. The lower limit of the _GeO2 content is preferably 0%.

In glass composition A, _GeO2 has the function of increasing the high dispersibility of the glass, but is an extremely expensive component among commonly used glass components. Therefore, from the viewpoint of reducing the manufacturing cost of the glass, it is preferable that the content of _GeO2 is in the above range.

In the glass material for molding according to this embodiment, in the case of glass composition A, the upper limit of _{the Gd2O3} content is preferably 3%, and more preferably 2%, 1.5%, 1%, and 0.5% in that order. The upper limit may be 0%. The lower limit of _{the Gd2O3} content is preferably 0%.

In glass composition A, if the Gd ₂ O ₃ content is too high, the thermal stability of the glass decreases. Furthermore, if the Gd ₂ O ₃ content is too high, the specific gravity of the glass increases, which is undesirable. Therefore, from the viewpoint of suppressing an increase in specific gravity while maintaining good thermal stability of the glass, the Gd ₂ O ₃ content is preferably within the above range.

In the glass material for molding according to this embodiment, in the case of glass composition A, the upper limit of the Yb ₂ O ₃ content is preferably 3%, and more preferably 2%, 1.5%, 1%, and 0.5% in that order. The upper limit may be 0%. The lower limit of the Yb ₂ O ₃ content is preferably 0%.

In glass composition A, _{Yb2O3 has a} larger molecular weight than _La2O3 , _Gd2O3 , _{and Y2O3 ,} and therefore increases the specific gravity of the glass. An increase in the specific gravity of the glass increases the mass of the optical element. For example, if a lens with a large mass is incorporated into an autofocus imaging lens, the power required to drive the lens during autofocusing increases, resulting in rapid battery consumption. Therefore, it is desirable to reduce _{the Yb2O3} content to suppress the increase in the specific gravity of the glass.

Furthermore, if the content of Yb ₂ O ₃ in glass composition A is too high, the thermal stability of the glass decreases and absorption in the near-infrared region tends to occur. From the viewpoints of maintaining the transmittance of the glass in the near-infrared region, preventing a decrease in thermal stability, and suppressing an increase in specific gravity, the content of Yb ₂ O ₃ is preferably within the above range.

In the case of glass composition A, the glass material for molding according to this embodiment mainly contains the above-mentioned glass components, namely, _SiO2 , _P2O5 , _{B2O3 , Al2O3, ZrO2, TiO2, Nb2O5, WO3, Bi2O3, Ta2O5, Li2O , Na2O , K2O , Cs2O , MgO , CaO , SrO , BaO , ZnO} , _La2O3 , _Y2O3 , _Sc2O3 , _{HfO2 , Lu2O3} , _{GeO2 , Gd2O3 , and Yb2O . 3} , and the lower limit of the total content of the above glass components is preferably 95.5%, and more preferably 96.0%, 96.5%, 97.0%, 97.5%, 98.0%, 98.5%, and 99.0% in that order.

The glass material for molding according to this embodiment is preferably composed primarily of the above glass components, but may contain other components as long as they do not interfere with the effects of the present invention. Furthermore, the present invention does not exclude the inclusion of unavoidable impurities.

(Other ingredients)
Pb, As, Cd, Tl, Be, and Se are all toxic, and therefore the glass material for molding according to this embodiment preferably does not contain these elements as glass components.

U, Th, and Ra are all radioactive elements. Therefore, it is preferable that the glass material for molding according to this embodiment does not contain these elements as glass components.

V, Cr, Mn, Fe, Co, Ni, Cu, Pr, Nd, Pm, Sm, Eu, Tb, Dy, Ho, Er, and Tm increase the coloration of the glass and can be sources of fluorescence. Therefore, it is preferable that the glass material for molding according to this embodiment does not contain these elements as glass components.

Sb (Sb ₂ O ₃ ) and Ce (CeO ₂ ) are elements that can be added as desired and function as fining agents. Of these, Sb (Sb ₂ O ₃ ) is a fining agent with a large fining effect, and when introduced in small amounts, it promotes the oxidation of easily reduced components and has the effect of increasing λτ80. Ce (CeO ₂ ) has a smaller fining effect than Sb (Sb ₂ O ₃ ). When added in large amounts, Ce (CeO ₂ ) tends to intensify the coloring of the glass.

The content of _Sb2O3 is expressed as an exclusive ratio. That is, when the total content of all glass components other than _{Sb2O3 and CeO2} is 100 mass% _, the upper limit of _{the Sb2O3 content} is preferably 1.000 mass%, and more preferably 0.500 mass%, 0.300 mass%, 0.100 mass%, 0.080 mass%, 0.060 mass%, and 0.040 mass% in that order. The lower limit of _{the Sb2O3 content} is preferably 0.000 mass%, and more preferably 0.001 mass%, 0.003 mass%, 0.005 mass%, 0.010 mass%, 0.015 mass%, and 0.020 mass% in that order. Since Sb ₂ O ₃ itself shifts the transmission/absorption edge of the glass to a longer wavelength, the content of Sb ₂ O ₃ may be 0.008 mass % or less, or may be 0.004 mass % or less, or may be 0.000 mass %, from the viewpoint of increasing the transmittance of the glass in the short wavelength region as much as possible.

The _CeO2 content is also expressed as an exclusive percentage. That _is , when the total content of all glass components other than _CeO2 and _Sb2O3 is 100 mass%, the upper limit of the _CeO2 content is preferably 1.000 mass%, and more preferably 0.500 mass%, 0.300 mass%, 0.100 mass%, 0.080 mass%, 0.060 mass%, and 0.040 mass% in that order. The lower limit of the _CeO2 content is preferably 0.000 mass%, and more preferably 0.005 mass%, 0.010 mass%, 0.015 mass%, and 0.020 mass% in that order. The _CeO2 content may be 0 mass%.

(Properties of glass having glass composition A)
<Abbe number νd>
In the glass material for molding according to this embodiment, in the case of glass composition A, the upper limit of the Abbe number vd is preferably 50, and may be 45, 40, 35, 33, 31, or 30. The lower limit of the Abbe number vd is preferably 15, and may be 17, 18, 19, 20, 21, 22, 23, or 24.

By setting the Abbe number νd within the above range, a highly dispersive glass can be obtained.
The Abbe number νd can be controlled by adjusting the contents of Nb ₂ O ₅ , TiO ₂ , WO ₃ and Bi ₂ O ₃ , which are glass components that contribute to high dispersion.

<Refractive index nd>
In the glass material for molding according to this embodiment, in the case of glass composition A, the lower limit of the refractive index nd can be 1.65, or even 1.70, 1.72, 1.74, 1.76, or 1.80. The upper limit of the refractive index nd can be 2.30, or even 2.10, 2.00, or 1.90. The refractive index can be controlled by adjusting the contents of _Nb2O5 , _TiO2 , _{WO3 ,} and _{Bi2O3 ,} which are glass components that contribute to increasing the refractive index.

<Glass transition temperature Tg>
In the glass material for molding according to this embodiment, in the case of glass composition A, the upper limit of the glass transition temperature Tg is preferably 700°C, 680°C, 670°C, 660°C, 650°C, 640°C, 630°C, 620°C, 610°C, 600°C, 590°C, and 580°C, in that order. The lower limit of the glass transition temperature Tg is not particularly limited, but is preferably 200°C, and more preferably 300°C, 400°C, and ₄₅₀ °C, in that order. The glass transition temperature Tg can be controlled by adjusting the mass ratio [( _Li2O + _Na2O + _K2O + _Cs2O )/( _Nb2O5 + _TiO2 + _WO3 + _Bi2O3 )] _, etc.

By satisfying the above upper limit of the glass transition temperature Tg, the increase in molding temperature and annealing temperature when reheating the glass can be suppressed, thereby reducing thermal damage to the reheating molding equipment and annealing equipment.

By satisfying the above lower limit of the glass transition temperature Tg, the glass of the present invention can have the desired Abbe number, refractive index, or transmittance while easily maintaining good formability and thermal stability of the glass when reheated.

<Specific gravity>
In the glass material for molding according to this embodiment, in the case of glass composition A, the upper limit of the specific gravity is preferably 4.3, and more preferably 4.1, 4.0, 3.9, 3.8, 3.7, and 3.6 in that order. The lower limit of the specific gravity is not particularly limited, but is usually 2.0, and preferably 2.5.

Specific gravity is measured using a method with repeatability accuracy in the range of ±0.001 to ±0.002.

<λτ80>
In the case of glass composition A, glass samples having thicknesses of 2.0 mm±0.1 mm and 10.0 mm±0.1 mm are used to measure the spectral transmittance in the wavelength range of 200 to 700 nm in accordance with JOGIS17 (Method for measuring the internal transmittance of optical glass), and the wavelength at which the internal transmittance at a thickness of 10 mm is 80% is defined as λτ80.

In the molding glass material according to this embodiment, for glass composition A, the upper limit of λτ80 is preferably 395 nm, and the smaller the value, the more preferable it is in the order of 390 nm, 385 nm, 380 nm, 375 nm, and 370 nm. The lower limit of λτ80 is not particularly limited, but is typically 250 nm. From the viewpoint of suppressing ultraviolet light transmittance, it may be 300 nm or even 320 nm.

<λ70>
In the case of glass composition A, the spectral transmittance is measured in the wavelength range of 200 to 700 nm for a glass sample having a thickness of 10.0 mm±0.1 mm, and the wavelength at which the external transmittance becomes 70% is defined as λ70.

In the molding glass material according to this embodiment, for glass composition A, the upper limit of λ70 is preferably 445 nm, and more preferably 440 nm, 430 nm, 420 nm, 410 nm, 400 nm, 390 nm, and 380 nm, in that order. The lower limit of λ70 is not particularly limited, but is typically 255 nm. From the viewpoint of suppressing the transmittance of ultraviolet light, it may be 305 nm or even 325 nm.

In the present invention, glass composition A has a high refractive index but a small partial dispersion ratio Pg,f. Therefore, even when the cooling rate of the glass in step 3 described below is reduced to one-tenth, fluctuations in the glass's dispersion can be suppressed. For example, in step 3, the change in Abbe number Δνd between the glass obtained at the cooling rate described below and the glass obtained when the cooling rate is reduced to one-tenth is preferably greater than -0.10, more preferably greater than -0.09, with the lower limits being -0.08, -0.07, -0.06, -0.05, -0.04, and -0.03, in that order. Furthermore, from the perspective of effectively correcting chromatic aberration when combined with a low-dispersion lens, the Abbe number νd of the glass material of this embodiment is preferably 50 or less. Therefore, the upper limit of the above Δνd is +0.10, with the order of +0.08, +0.06, +0.04, +0.02, and +0.01 being more preferable. In particular, when the Abbe number is 35 or less, preferably 30 or less, the upper limit of the Δνd is preferably +0.005, and can also be set to +0.00, −0.01, −0.02, or −0.03.

<Average linear expansion coefficient α _L >
In the glass material for molding according to this embodiment, in the case of glass composition A, the lower limit of the average linear expansion coefficient α _L at -30 to 70°C is preferably 0.70×10 ^-5 °C ^-1 , and is more preferably 0.71×10 ^-5 °C ^-1 , 0.72×10 ^-5 °C ^-1 , 0.73×10 ^-5 °C ^-1 , 0.74×10 ^-5 °C ^-1 , 0.75×10 ^-5 °C ^-1 , 0.76×10 ^-5 °C ^-1 , 0.77×10 ^-5 °C ^-1 , 0.78×10 ^-5 °C ^-1 , and 0.79×10 ^-5 °C ^-1 in this order. Furthermore, from the viewpoint of maintaining the stability of the glass and obtaining the desired optical properties, the upper limit of the average linear expansion coefficient _αL can be, for example, 1.10×10 ⁻⁵ ° C. ⁻¹ , and is preferably 1.05×10 ⁻⁵ ° C. ⁻¹ or less, with 1.00×10 ⁻⁵ ° C. ⁻¹ , 0.96×10 ⁻⁵ ° C. ⁻¹ , 0.92×10 ⁻⁵ ° C. ⁻¹ , 0.88×10 ⁻⁵ ° C. ⁻¹ , and 0.84×10 ⁻⁵ ° C. ⁻¹ being more preferred in this order.

In the case of glass composition A, by setting the average linear expansion coefficient _αL at −30 to 70° C. within the above range, it is possible to obtain a glass material for molding that can be used in a wide range of temperature environments.

The average linear expansion coefficient _αL is measured in accordance with the provisions of JOGIS16. The sample is a round bar with a length of 20 mm ± 0.5 mm and a diameter of 5 mm ± 0.5 mm. With a load of 98 mN applied to the sample, it is heated at a constant rate of 4°C per minute, and the temperature and sample elongation are measured in 1-second increments. The average linear expansion coefficient _αL is the average value of the linear expansion coefficient from -30 to 70°C.

It should be noted that JOGIS16 stipulates that "the average linear expansion coefficient shall be expressed in units of 10 ^-7 ° C ^-1 to the nearest integer," but in this specification, the average linear expansion coefficient α _L shall be expressed in units of [10 ^-5 · ° C ^-1 ].

In this specification, the average linear expansion coefficient α _L is expressed in units of [10 ⁻⁵ ·° C. ⁻¹ ], but the numerical value of the average linear expansion coefficient α _L is the same even when the unit is [10 ⁻⁵ ·K ⁻¹ ].

(Glass Composition B)
Next, the contents and ratios of the glass components and the glass properties when the glass material for molding according to this embodiment has glass composition B will be described.

In this embodiment, when the glass has glass composition B, the contents of the glass components SiO ₂ , B ₂ O ₃ , Al ₂ O ₃ , Li ₂ O, Na ₂ O, K ₂ O, Cs ₂ O, MgO, CaO, SrO, BaO, ZnO, La ₂ O ₃ , Gd ₂ O ₃ , Y ₂ O ₃ , ZrO ₂ , TiO ₂ , Nb ₂ O ₅ , WO ₃ , and Bi ₂ O ₃ expressed in mass % on an oxide basis are respectively set to C(SiO ₂ ), C(B ₂ O ₃ ), C(Al ₂ O ₃ ), C(Li ₂ O), C(Na ₂ O), C(K ₂ O), C(Cs _{2 O} ), O), C(MgO), C(CaO), C(SrO), C(BaO), C(ZnO), C( _La2O3 ), C( _{Gd2O3 )} , C( _Y2O3 ), C( _ZrO2 ), C _{( TiO2} ), _C ( _Nb2O5 ), _{C(WO3 ) ,} and C( _Bi2O3 ).

The contents _{of the glass components Ta2O5, Sc2O3, HfO2 , Lu2O3 , GeO2 , and Yb2O3} other than those described _above , expressed in mass%, _{are C(Ta2O5), C(Sc2O3), C(HfO2 ) , C} ( _Lu2O3 ), _C ( _GeO2 ), and C _{( Yb2O3 ) ,} respectively.

In this embodiment, when having glass composition B, the chemical formula amounts of SiO ₂ , BO _1.5 , AlO _1.5 , LiO _0.5 , NaO _0.5 , KO _0.5 , CsO _0.5 , MgO, CaO, SrO, BaO, ZnO, LaO _1.5 , GdO _1.5 , YO _1.5 , ZrO ₂ , TiO ₂ , NbO _2.5 , WO ₃ , and BiO _1.5 are M(SiO ₂ ), M(BO _1.5 ), M(AlO _1.5 ), M(LiO _0.5 ), M(NaO _0.5 ), M(KO _0.5 ), M(CsO _{0.5 )} , ), M(MgO), M(CaO), M(SrO), M(BaO), M(ZnO), M( _LaO1.5 ), M( _GdO1.5 ), M( _YO1.5 ), M( _ZrO2 ), M( _TiO2 ), M( _NbO2.5 ), M( _WO3 ), and M( _BiO1.5 ).

The chemical formula weights of the other glass components _TaO2.5 , _ScO1.5 , _HfO2 , _LuO1.5 , _GeO2 , and _YbO1.5 are M( _TaO2.5 ), M( _ScO1.5 ), M( _HfO2 ), M( _LuO1.5 ), M( _GeO2 ), and M( _YbO1.5 ), respectively.

That _is , in this embodiment, when having glass composition B, for example, the content _of oxide _XyOz expressed in mass % can be C( _XyOz ). Also, the chemical formula amount per mole of cation (cation "X" ₎ in oxide _XyOz , i.e., the chemical formula amount in XOz _/y , can be M( _XOz/y ). And, what is expressed by the formula {C( _XyOz )/M( _XOz/y )} is the content of cation "X" expressed in mol %, _i.e. , the content of "X" expressed in cation %.

In the glass material for molding according to this embodiment, in the case of glass composition B, when A1 = {C( _B2O3 )/M( _BO1.5 )}/{C( _B2O3 )/M( _BO1.5 )+C( _SiO2 )/M( _SiO2 )}, the lower limit of A1 is preferably 1/3, and more preferably 1.1/3 _{, 1.2} /3, 1.3/3, 1.4/3, 1.5/3, 1.6/3, 1.7/3, 1.8/3, and 1.9/3 in that order. The upper limit of A1 is preferably 3.0/3, and more preferably 2.9/3, 2.8/3, 2.7/3, 2.6/3, 2.5/3, 2.4/3, and 2.3/3 in that order.

In glass composition B, by setting A1 within the above range, a molding glass material with a large average linear expansion coefficient _αL at -30 to 70°C and low dispersion can be obtained. Furthermore, the temperature coefficient of the relative refractive index (dn/dT) of the glass can be reduced. Furthermore, even when a large amount of La ₂ O ₃ is contained, a decrease in the thermal stability of the glass can be suppressed. On the other hand, if A1 is too small, the glass may become unstable when it contains large amounts of La ₂ O ₃ and Y ₂ O ₃ , which are glass components that increase the refractive index nd and prevent a decrease in the average linear expansion coefficient _αL . Furthermore, if A1 is too large, the stability, chemical durability, and mechanical properties of the glass may be reduced.

In the glass material for molding according to this embodiment, in the case of glass composition B, B1 = {C(BaO)/M(BaO) + C(SrO)/M(SrO)}/{C( _Li2O )/M( _LiO0.5 ) + C( _Na2O )/M( _NaO0.5 ) + C( _K2O )/M( _KO0.5 ) + C( _Cs2O )/M( _CsO0.5) ) + C(MgO) / M(MgO) + C(CaO) / M(CaO) + C(SrO) / M(SrO) + C(BaO) / M(BaO)}, the lower limit of B1 is preferably 0.62, and more preferably 0.63, 0.65, 0.67, 0.69, 0.71, 0.73, 0.75, 0.77, 0.79, 0.81, 0.83, 0.85, and 0.87 in that order. The upper limit of B1 is preferably 1.00, and more preferably 0.99 and 0.98 in that order. B1 may be 1.00.

By setting B1 in the above range in glass composition B, a molding glass material with a large average linear expansion coefficient _αL and a high refractive index can be obtained. Furthermore, it is possible to suppress a decrease in thermal stability while increasing the average linear expansion coefficient _αL . On the other hand, if B1 is too small, the average linear expansion coefficient _αL and the refractive index nd decrease, and the stability of the glass may be impaired.

In the glass material for molding according to this embodiment, in the case of glass composition B, when C1 = {C(BaO)/M(BaO) + C( _Li2O )/M( _LiO0.5 )}/{C( _Na2O )/M( _NaO0.5 ) + C( _K2O )/M( _KO0.5 ) + C( _SiO2 )/M( _SiO2 ) + C(TiO2)/M( _TiO2 ) + C( _Nb2O5 )/M _{( NbO2.5} ) + C( _WO3 )/M( _WO3 )}, the lower limit of C1 is preferably 8/9, and more preferably 8.2/ ₉ , 8.4/9, 8.6/9, 8.8/9, 9.0/9, 9.2/9, 9.4/9, and 9.5/9 in that order. The upper limit of C1 is preferably 27/9, and more preferably 25/9, 23/9, 21/9, 19/9, 17/9, 15/9, 13/9, and 12/9 in that order.

In glass composition B, by setting C1 within the above range, a molding glass material with a large average linear expansion coefficient _αL and high refractive index and low dispersion can be obtained. Furthermore, the temperature coefficient of the relative refractive index (dn/dT) of the glass can be reduced. On the other hand, if C1 is too small, the average linear expansion coefficient _αL decreases, and the high refractive index and low dispersion properties of the glass may be lost. Furthermore, if C1 is too large, the stability of the glass may be reduced.

In the glass material for molding according to this embodiment, in the case of glass composition B, when D1 = C( _Gd2O3 ) + C( _ZnO ) + C(TiO2) + C( _Nb2O5 ) + C( _WO3 ) + C( _ZrO2 ), the upper limit of D1 is preferably 13.50, and more preferably 12.00, 11.00, 10.50, 10.00, _9.50 , 9.00, and 8.50 in that order. The lower limit of D1 is preferably 0, and more preferably 1, 2, ₃ , 4, 5, 6, 7, and 8 in that order. D1 may also be 0.

In glass composition B, by setting D1 within the above range, it is possible to suppress a decrease in the average linear expansion coefficient _αL . Furthermore, high dispersion is suppressed, and a glass material for molding with high refractive index and low dispersion is obtained. Furthermore, it has the effect of not increasing the temperature coefficient of the relative refractive index (dn/dT) of the glass. D1 may be 0, but D1 can also be made greater than 0 in order to adjust optical constants such as the Abbe number νd. On the other hand, if D1 is too large, the average linear expansion coefficient _αL decreases, and the high refractive index and low dispersion properties of the glass may be lost.

In the glass material for molding according to this embodiment, in the case of glass composition B, when E1 = {C( _La2O3 ) + C( _{Gd2O3 )} + C( _Y2O3 )}/{C( _SiO2 ) + C( _{B2O3 )} + C( _Al2O3 )}, the lower limit of E1 is preferably 1.25, and more preferably 1.30, 1.35, _1.40 , _1.45 , 1.50, 1.55, 1.60 _, 1.65, and 1.70 in that order. The upper limit of E1 is preferably 3.00, and more preferably 2.80, 2.60, 2.40, 2.20, and 2.10 in that order.

In glass composition B, by setting E1 within the above range, a molding glass material with a high refractive index and low dispersion can be obtained. On the other hand, if E1 is too small, the high refractive index and high dispersion properties of the glass may be lost, and the average linear expansion coefficient _αL may decrease. Furthermore, if E1 is too large, the thermal stability of the glass may decrease.

In the glass material for molding according to this embodiment, in the case of glass composition B, when F1 = {C( _Gd2O3 )/M _{(GdO1.5 )} + C(ZnO)/M(ZnO) + C( _TiO2 )/M( _TiO2 ) + C( _Nb2O5 )/M( _NbO2.5 ) + C( _WO3 )/M( _WO3 ) + C( _Bi2O3 )/M( _BiO1.5 )}/{C( _Y2O3 )/M( _YO1.5 )}, the upper limit of F1 is preferably 2.0, and more preferably 1.8, _1.6 , 1.4, 1.2, 1.1, 1.0, 0.9, 0.8 _{, and} 0.6 in that order. The lower limit of F1 is preferably 0, and more preferably 0.1, 0.2, 0.3, and 0.4 in that order. F1 may be 0.

In glass composition B, by setting F1 within the above range, a molding glass material with a large average linear expansion coefficient _αL can be obtained. Furthermore, a decrease in the thermal stability of the glass can be suppressed. F1 may be 0, but F1 can also be greater than 0 in order to adjust optical constants such as the Abbe number νd. On the other hand, if F1 is too large, the average linear expansion coefficient _αL decreases, and the high refractive index and low dispersion properties of the glass may be lost.

In the glass material for molding according to this embodiment, in the case of glass composition B, when G1 = C(BaO)/M(BaO) + C( _La2O3 )/M( _LaO1.5 ) + C( _Li2O )/M( _LiO0.5 ) + C( _Y2O3 )/M( _YO1.5 ), the lower limit of G1 is preferably 0.47, and more preferably _0.475 , 0.48, and 0.485 in that order. The upper limit of G1 is preferably 0.60, and more preferably 0.59 _, 0.58, 0.57, 0.56, 0.55, 0.54, and 0.53 in that order.

In glass composition B, it is preferable to set G1 within the above range from the viewpoint of suppressing a decrease in the average linear expansion coefficient _αL and obtaining a molding glass material with a high refractive index and low dispersion. On the other hand, if G1 is too small, the average linear expansion coefficient _αL decreases, and the high refractive index and low dispersion properties of the glass may be lost. Furthermore, if G1 is too large, the thermal stability of the glass may decrease.

In this embodiment, for glass composition B, the lower limit of {C( _B2O3 )/M( _BO1.5 )+C( _SiO2 )/M( _SiO2 )} is preferably _0.35 , and more preferably 0.37, 0.39, 0.41, 0.43, 0.45, and 0.47 in that order. The upper limit is preferably 0.75, and more preferably 0.73, 0.71, 0.69, 0.67, 0.65, 0.63, 0.61, and 0.59 in that order.

In glass composition B, from the viewpoint of obtaining a molding glass material having a large average linear expansion coefficient _αL and low dispersion, it is preferable that {C(B ₂ O ₃ )/M(BO _1.5 )+C(SiO ₂ )/M(SiO ₂ )} be in the above range.

In this embodiment, for glass composition B, the lower limit of {C(BaO)/M(BaO)+C(SrO)/M(SrO)} is preferably 0.15, and more preferably 0.16, 0.17, 0.18, 0.19, and 0.20 in that order. The upper limit is preferably 0.30, and more preferably 0.29, 0.28, 0.27, 0.26, 0.25, 0.24, and 0.23 in that order.

In glass composition B, from the viewpoint of obtaining a glass material for molding having a large average linear expansion coefficient _αL and a high refractive index, it is preferable that {C(BaO)/M(BaO)+C(SrO)/M(SrO)} be in the above range.

In this embodiment, in the case of glass composition B, the lower limit of {C( _Li2O )/M( _LiO0.5 ) + C( _Na2O )/M( _NaO0.5 ) + C( _K2O )/M( _KO0.5 ) + C( _Cs2O )/M( _CsO0.5 ) + C(MgO)/M(MgO) + C(CaO)/M(CaO) + C(SrO)/M(SrO) + C(BaO)/M(BaO)} is preferably 0.15, and more preferably 0.16, 0.17, 0.18, 0.19, and 0.20 in that order. The upper limit is preferably 0.35, and more preferably 0.34, 0.33, 0.32, 0.31, 0.30, 0.29, 0.28, 0.27, 0.26, 0.25, 0.24, and 0.23 in that order.

In glass composition B, from the viewpoint of obtaining a molding glass material having a large average linear expansion coefficient _αL and a high refractive index, it is preferable that {C( _Li2O )/M( _LiO0.5 ) + C( _Na2O )/M( _NaO0.5 ) + C( _K2O )/M( _KO0.5 ) + C( _Cs2O )/M( _CsO0.5 ) + C(MgO)/M(MgO) + C(CaO)/M(CaO) + C(SrO)/M(SrO) + C(BaO)/M(BaO)} be in the above range.

In this embodiment, in the case of glass composition B, the lower limit of {C(BaO)/M(BaO)+C( _Li2O )/M( _LiO0.5 )} is preferably 0.15, and more preferably 0.16, 0.17, 0.18, 0.19, and 0.20 in this order. The upper limit is preferably 0.35, and more preferably 0.34, 0.33, 0.32, 0.31, 0.30, 0.29, 0.28, 0.27, 0.26, 0.25, 0.24, and 0.23 in this order.

In glass composition B, from the viewpoint of obtaining a molding glass material having a large average linear expansion coefficient _αL and a high refractive index and low dispersion, it is preferable that {C(BaO)/M(BaO)+C(Li ₂ O)/M(LiO _0.5 )} be in the above range.

In this embodiment, in the case of glass composition B, the lower limit of {C( _Na2O )/M( _NaO0.5 ) + C( _K2O )/M( _KO0.5 ) + C( _SiO2 )/M( _SiO2 ) + C( _TiO2 )/M(TiO2) + C( _Nb2O5 )/M( _NbO2.5 ) + C( _WO3 )/M( _WO3 )} is preferably 0.05, and more preferably 0.06, 0.07, 0.08, 0.09, _0.10 , 0.11, _0.12 , 0.13, 0.14, 0.15, and 0.16 in that order. The upper limit is preferably 0.30, and more preferably 0.29, 0.28, 0.27, 0.26, 0.25, 0.24, 0.23, 0.22, and 0.21 in that order.

In glass composition B, from the viewpoint of obtaining a molding glass material having a large average linear expansion coefficient _αL and a high refractive index and low dispersion, it is preferable that {C(Na ₂ O)/M(NaO _0.5 )+C(K ₂ O)/M(KO _0.5 )+C(SiO ₂ )/M(SiO ₂ )+C(TiO ₂ )/M(TiO ₂ )+C(Nb ₂ O ₅ )/M(NbO _2.5 )+C(WO ₃ )/M(WO ₃ )} be in the above range.

In the glass material for molding according to this embodiment, in the case of glass composition B, the lower limit of the mass ratio [C(BaO)/{C( _SiO2 )+C( _TiO2 )+C( _Nb2O5 )+C _{( WO3} )}] is preferably 1.0, and more preferably 1.2, 1.4, 1.6, 1.8, 2.0, 2.2, and 2.4 in that order. The upper limit of this mass ratio is preferably 5.5, and more preferably 5.3, 5.1, 4.9, 4.7, 4.5, 4.3, 4.1, 3.9, 3.7, and 3.5 in that order.

In glass composition B, from the viewpoint of obtaining a molding glass material having a large average linear expansion coefficient _αL and a high refractive index and low dispersion, and from the viewpoint of reducing the temperature coefficient of the relative refractive index (dn/dT), it is preferable that the mass ratio [C(BaO)/{C(SiO ₂ )+C(TiO ₂ )+C(Nb ₂ O ₅ )+C(WO ₃ )}] be in the above range.

In the glass material for molding according to this embodiment, in the case of glass composition B, the lower limit of the mass ratio [C(BaO)/{C( _SiO2 )+C( _B2O3 )+C( _TiO2 )+C( _Nb2O5 )+C( _WO3 )}] is preferably 0.80, and more preferably 0.85, 0.90, 0.95, 1.00 _, 1.05, 1.10 _, 1.15, and 1.20 in this order. The upper limit of this mass ratio is preferably 1.70, and more preferably 1.65, 1.60, 1.55, 1.50, 1.45, 1.40, and 1.35 in this order.

In glass composition B, from the viewpoint of obtaining a molding glass material having a large average linear expansion coefficient _αL and a high refractive index and low dispersion, and from the viewpoint of reducing the temperature dependence of the temperature coefficient of the relative refractive index (dn/dT), it is preferable that the mass ratio [C(BaO)/{C(SiO ₂ )+C(B ₂ O ₃ )+C(TiO ₂ )+C(Nb ₂ O ₅ )+C(WO ₃ )}] be in the above range.

In the glass material for molding according to this embodiment, in the case of glass composition B, the lower limit of the mass ratio [{C(BaO)+C( _Li2O )+C(SrO)}/{C( _SiO2 )+C( _TiO2 )+C( _Nb2O5 )+C( _WO3 )}] is preferably 0.5, and more preferably 1.0, 1.5, 2.0 _, 2.2, and 2.4 in that order. The upper limit of this mass ratio is preferably 7.0, and more preferably 6.5, 6.0, 5.5, 5.0, 4.5, 4.0, and 3.5 in that order.

In glass composition B, from the viewpoint of obtaining a molding glass material having a large average linear expansion coefficient _αL and a high refractive index and low dispersion, it is preferable that the mass ratio [{C(BaO)+C(Li ₂ O)+C(SrO)}/{C(SiO ₂ )+C(TiO ₂ )+C(Nb ₂ O ₅ )+C(WO ₃ )}] be in the above range.

In the glass material for molding according to this embodiment, in the case of glass composition B, the lower limit of the mass ratio [{C( _Li2O )+C( _Na2O )+C( _K2O )+C( _Cs2O )+C(CaO)+C(SrO)+C(BaO)}/{C( _SiO2 )+C( _TiO2 )+C( _Nb2O5 )+C( _WO3 )}] is preferably 0.5, and more preferably 1.0, 1.5, _2.0 , 2.2, and 2.4 in that order. The upper limit of this mass ratio is preferably 7.0, and more preferably 6.5, 6.0, 5.5, 5.0, 4.5, 4.0, and 3.5 in that order.

In glass composition B, from the viewpoint of obtaining a molding glass material having a large average linear expansion coefficient _αL and a high refractive index and low dispersion, it is preferable that the mass ratio [{C(Li ₂ O) + C(Na ₂ O) + C(K ₂ O) + C(Cs ₂ O) + C(CaO) + C(SrO) + C(BaO)}/{C(SiO ₂ ) + C(TiO ₂ ) + C(Nb ₂ O ₅ ) + C(WO ₃ )}] be in the above range.

In the glass material for molding according to this embodiment, in the case of glass composition B, the lower limit of the total content [C(ZnO)+C( _Gd2O3 )+C( _TiO2 )+C( _Nb2O5 )+C( _WO3 )] is preferably 0, and more preferably 1 _, 2 _, 3, 4, and 5 in that order. The total content may be 0. The upper limit of the total content is preferably 15, and more preferably 14, 13, 12, 11, 10, 9, 8, 7, and 6 in that order.

In glass composition B, from the viewpoint of obtaining a glass material for molding having a large average linear expansion coefficient _αL and small variance, it is preferable that the total content [C(ZnO)+C(Gd ₂ O ₃ )+C(TiO ₂ )+C(Nb ₂ O ₅ )+C(WO ₃ )] be within the above range.

In the glass material for molding according to this embodiment, in the case of glass composition B, the lower limit of the total content [C(SiO ₂ )+C(ZnO)+C(Gd ₂ O ₃ )+C(TiO ₂ )+C(Nb ₂ O ₅ )+C(WO ₃ )] is preferably 5, and more preferably 6, 7, 8, and 9 in that order. The upper limit of the total content is preferably 25, and more preferably 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, and 14 in that order.

In glass composition B, from the viewpoint of obtaining a molding glass material having a large average linear expansion coefficient _αL and a high refractive index and low dispersion, it is preferable that the total content [C(SiO ₂ )+C(ZnO)+C(Gd ₂ O ₃ )+C(TiO ₂ )+C(Nb ₂ O ₅ )+C(WO ₃ )] be within the above range.

In the glass material for molding according to this embodiment, in the case of glass composition B, the lower limit of the total content [C( _SiO2 )+C(ZnO)+C( _Gd2O3 )+C( _ZrO2 )+C( _TiO2 )+C( _Nb2O5 )+C( _WO3 )] is preferably 5, and more preferably 6 _, 7, 8, and 9 in that order. The upper limit of the total content is preferably 25, and more preferably 24 _, 23, 22, 21, 20, 19, 18, 17, and 16 in that order.

In glass composition B, from the viewpoint of obtaining a molding glass material having a large average linear expansion coefficient _αL and a high refractive index and low dispersion, it is preferable that the total content [C(SiO ₂ ) + C(ZnO) + C(Gd ₂ O ₃ ) + C(ZrO ₂ ) + C(TiO ₂ ) + C(Nb ₂ O ₅ ) + C(WO ₃ )] be within the above range.

In the glass material for molding according to this embodiment, in the case of glass composition B, the lower limit of the total content [C( _Al2O3 )+C _{( SiO2} )+C(ZnO)+C( _Gd2O3 )+C( _ZrO2 )+C( _TiO2 )+C( _Nb2O5 )+C( _WO3 )] is preferably ₅ , and more preferably ₆ , 7, 8, and 9 in that order. The upper limit of the total content is preferably 25, and more preferably 24, 23, 22, 21, 20, 19, 18, 17, and 16 in that order.

In glass composition B, from the viewpoint of obtaining a molding glass material having a large average linear expansion coefficient _αL and a high refractive index and low dispersion, it is preferable that the total content [C(Al ₂ O ₃ ) + C(SiO ₂ ) + C(ZnO) + C(Gd ₂ O ₃ ) + C(ZrO ₂ ) + C(TiO ₂ ) + C(Nb ₂ O ₅ ) + C(WO ₃ )] be within the above range.

In the present embodiment, in the case of glass composition B, the lower limit of the total content [C( _La2O3 )+C( _Gd2O3 )+C( _Y2O3 )] is preferably 25, and more preferably 26, 27, 28, 29, 30, 31, 32 _, 33, 34, 35 _, 36, ₃₇ , and 38 in that order. The upper limit of the total content is preferably 50, and more preferably 49, 48, 47, 46, 45, 44, and 43 in that order.

In glass composition B, from the viewpoint of obtaining a molding glass material with a high refractive index and low dispersion, the total content [C(La ₂ O ₃ )+C(Gd ₂ O ₃ )+C(Y ₂ O ₃ )] is preferably within the above range.

In the present embodiment, in the case of glass composition B, the lower limit of the total content [C( _SiO2 ) + C( _B2O3 ) + C( _Al2O3 )] is preferably 15, and more preferably 16, 17, 18, and 19 in that order. The upper limit of the total content is preferably 30, and more preferably 29 _, 28 _, 27, 26, and 25 in that order.

In glass composition B, from the viewpoint of obtaining a high-refractive-index, low-dispersion glass material for molding without decreasing the refractive index as much as possible, it is preferable that the total content [C(SiO ₂ )+C(B ₂ O ₃ )+C(Al ₂ O ₃ )] be within the above range.

In the glass material for molding according to this embodiment, in the case of glass composition B, the lower limit of the mass ratio [{C( _La2O3 )+C( _Gd2O3 )+C( _Y2O3 )}/{2×C( _SiO2 )+C( _B2O3 )+C( _Al2O3 )}] is preferably 1.00, and more preferably 1.05 _, 1.10 _{, 1.15} , _{1.16 ,} 1.17, 1.18, 1.19, 1.20, and 1.21 in this order. The upper limit of this mass ratio is preferably 1.80, and more preferably 1.75, 1.70, 1.65, 1.60, 1.55, 1.54, 1.53, 1.52, 1.51, and 1.50 in this order.

In glass composition B, from the viewpoint _of obtaining a molding glass material with a high refractive index and low dispersion, it _{is preferable} that the mass ratio [{C( _La2O3 )+C( _Gd2O3 )+C( _Y2O3 )}/{2×C( _SiO2 )+C( _B2O3 )+C _{( Al2O3 )} }] be in the above range.

In the glass material for molding according to this embodiment, in the case of glass composition B, the lower limit of the total content [2×C(SiO ₂ )+C(B ₂ O ₃ )+C(Al ₂ O ₃ )] is preferably 20, and more preferably 21, 22, 23, 24, 25, and 26 in that order. The upper limit of the total content is preferably 45, and more preferably 44, 43, 42, 41, 40, 39, 38, 37, 36, and 35 in that order.

In glass composition B, from the viewpoint of obtaining a molding glass material with a large average linear expansion coefficient _αL and a high refractive index and low dispersion, it is preferable that the total content [2 × C(SiO ₂ ) + C(B ₂ O ₃ ) + C(Al ₂ O ₃ )] be in the above range.

In the glass material for molding according to this embodiment, in the case of glass composition B, the lower limit of the mass ratio [{C( _La2O3 )+C( _Y2O3 )}/{C( _B2O3 )+C(BaO)}] is preferably 0.50, and more preferably _0.55 , 0.60 _, 0.65, 0.70, 0.75, and 0.80 in that order. The upper limit of this mass ratio is preferably 1.30, and more preferably 1.25, 1.20, 1.15 _, 1.10, 1.05, 1.00, 0.95, and 0.92 in that order.

In glass composition B, from the viewpoint _of obtaining a molding glass material with a high refractive index and low dispersion, the mass ratio [{C( _La2O3 )+C( _Y2O3 )}/{C( _B2O3 )+C _{( BaO} )}] is preferably in the above range.

In this embodiment, in the case of glass composition B, the lower _limit of [C( _Gd2O3 )/M( _GdO1.5 ) + C(ZnO)/M(ZnO) + C( _TiO2 )/M( _TiO2 ) + C( _Nb2O5 )/M( _NbO2.5 ) + C( _WO3 )/M( _WO3 ) + C( _Bi2O3 )/M( _BiO1.5 )] is preferably 0, and more preferably 0.01, 0.02, _0.03 , _0.04 , 0.05, and 0.06 in this order. The value may be 0. The upper limit is preferably 0.30, and more preferably 0.25, 0.20, 0.18, 0.16, 0.14, 0.12, 0.10, and 0.08 in this order.

In glass composition B, from the viewpoint _of having a large average linear expansion coefficient _αL and suppressing a decrease in the thermal stability of the glass, it is preferable that [C( _Gd2O3 )/M( _GdO1.5 )+C(ZnO)/M(ZnO)+C( _TiO2 )/M _{( TiO2} )+C( _Nb2O5 )/M( _NbO2.5 )+C( _WO3 )/M( _WO3 )+C( _Bi2O3 )/M _{(BiO1.5 )} ] be in the above range.

In the glass material for molding according to this embodiment, in the case of glass composition B, the lower limit of the mass ratio [C(Y ₂ O ₃ )/{C(La ₂ O ₃ )+C(Y ₂ O ₃ )+C(Gd ₂ O ₃ )}] is preferably 0.20, and more preferably 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29, 0.30, 0.31, 0.32, 0.33, and 0.34 in that order. The upper limit of the mass ratio is preferably 0.60, and more preferably 0.59, 0.58, 0.57, 0.56, 0.55, 0.54, 0.53, 0.52, 0.51, 0.50, 0.49, 0.48, 0.47, and 0.46 in that order.

In glass composition B, from the viewpoint of having a large average linear expansion coefficient _αL and suppressing a decrease in the thermal stability of the glass, it is preferable that the mass ratio [C(Y ₂ O ₃ )/{C(La ₂ O ₃ )+C(Y ₂ O ₃ )+C(Gd ₂ O ₃ )}] be in the above range.

In the glass material for molding according to this embodiment, in the case of glass composition B, the lower limit of the mass ratio [C( _Y2O3 )/{C( _La2O3 )+C( _Y2O3 )+C( _TiO2 )}] is preferably 0.20, and more preferably 0.21, _{0.22 ,} 0.23, 0.24 _, 0.25, 0.26, 0.27, 0.28, 0.29, 0.30, 0.31, and 0.32 in this order. The upper limit of this mass ratio is preferably 0.50, and more preferably 0.49, 0.48, 0.47, 0.46, and 0.45 in this order.

In glass composition B, from the viewpoint of having a large average linear expansion coefficient _αL and suppressing a decrease in the thermal stability of the glass, it is preferable that the mass ratio [C(Y ₂ O ₃ )/{C(La ₂ O ₃ )+C(Y ₂ O ₃ )+C(TiO ₂ )}] be in the above range.

In the glass material for molding according to this embodiment, in the case of glass composition B, the lower limit of the total content [C(BaO)+C( _La2O3 )+C( _Y2O3 )] is preferably 50, and more preferably 52, 54, 56, 58, 60 _, 62, 64, 66, ₆₈ , and 70, in that order. The upper limit of the total content is preferably 85, and more preferably 83, 81, 79, 77, and 76, in that order.

In glass composition B, from the viewpoint of suppressing a decrease in the average linear expansion coefficient _αL and obtaining a molding glass material with a high refractive index and low dispersion, it is preferable that the total content [C(BaO)+C(La ₂ O ₃ )+C(Y ₂ O ₃ )] be within the above range.

In the glass material for molding according to this embodiment, in the case of glass composition B, the lower limit of the SiO ₂ content is preferably 3.0%, and more preferably 3.5%, 4.0%, 4.5%, 5.0%, 5.5%, 6.0%, 6.5%, and 7.0% in that order. The upper limit of the SiO ₂ content is preferably 15.0%, and more preferably 14.5%, 14.0%, 13.5%, 13.0%, 12.5%, 12.0%, 11.5%, 11.0%, 10.5%, and 10.0% in that order.

_SiO2 is a glass network-forming component in glass composition B, and functions to improve the thermal stability, chemical durability, and weather resistance of glass, increase the viscosity of molten glass, and make the molten glass easier to mold. Furthermore, _SiO2 has a stronger effect of increasing the value of ΔPg,F than, for example, _La2O3 , _BaO , and _{Y2O3 ,} which are contained in large amounts in glass composition B. On the other hand, if the _SiO2 content is high, the average linear expansion coefficient _αL is relatively likely to decrease and the refractive index nd may also decrease. Furthermore, if the _SiO2 content is too low, stability during reheating may deteriorate. Therefore, the _SiO2 content is preferably within the above range.

In the glass material for molding according to this embodiment, in the case of glass composition B, the lower limit of _{the B2O3 content} is preferably 8.0%, and more preferably 8.5%, 9.0%, 9.5%, 10.0%, 10.5%, 11.0%, 11.5%, and 12.0% in that order. The upper limit of _{the B2O3 content} is preferably 20.0%, and more preferably 19.5%, 19.0%, 18.5%, 18.0%, 17.5%, 17.0%, 16.5%, 16.0%, 15.5%, and 15.0% in that order.

_B2O3 is a network-forming component of glass in glass composition B and has the function of improving the thermal stability of the glass. Among the network-forming components, _B2O3 is a component that does not relatively reduce the average linear expansion coefficient _αL . Furthermore, from the viewpoint _{of obtaining a glass with a high refractive index nd without impairing low dispersion, the content of B2O3 can be set within the above range. On the other hand, if the content of B2O3 is too high} , the refractive index nd may decrease. Furthermore, if the content _{of B2O3 is} too low, the stability during reheating may deteriorate.

In the glass material for molding according to this embodiment, in the case of glass composition B, the upper limit of the Al ₂ O ₃ content is preferably 10%, and more preferably 8%, 6%, 4%, 2%, 1%, 0.5%, 0.2%, and 0.1% in that order. The lower limit of the Al ₂ O ₃ content is preferably 0%. The _{Al 2} O ₃ content may be 0%.

In glass composition B, Al ₂ O ₃ is a glass component that functions to improve the chemical durability and weather resistance of the glass, and can be considered as a network-forming component. On the other hand, if the content of Al ₂ O ₃ increases, the refractive index nd decreases, and the thermal stability and meltability of the glass may decrease. Therefore, the content of Al ₂ O ₃ is preferably within the above range.

In the glass material for molding according to this embodiment, in the case of glass composition _B , the upper limit of the _P2O5 content is preferably 10%, and more preferably 8%, 6%, 4%, 2%, 1%, 0.5%, 0.2%, and 0.1% in that order. The lower limit of _{the P2O5} content is preferably 0%. _{The P2O5 content} may be 0%.

P ₂ O ₅ is a component that reduces the refractive index nd in glass composition B and also reduces the thermal stability of the glass. Therefore, the content of P ₂ O ₅ is preferably within the above range.

In the glass material for molding according to this embodiment, in the case of glass composition B, the upper limit of the Li ₂ O content is preferably 10%, and more preferably 8%, 6%, 4%, 2%, 1%, 0.5%, 0.2%, and 0.1% in that order. The lower limit of the Li ₂ O content is preferably 0%. The Li ₂ O content may be 0%.

In glass composition B, Li ₂ O is a component that contributes to lowering the specific gravity of the glass, improves the meltability of the glass, and increases the average linear expansion coefficient _αL . Furthermore, it is a component that contributes to lowering the glass transition temperature Tg, and contributes to improving formability during precision press molding. Furthermore, from the viewpoint of obtaining a glass with a high refractive index nd without impairing low dispersion, the content of Li ₂ O can be set within the above range. On the other hand, if the content of Li ₂ O is too high, there is a risk that devitrification resistance and acid resistance will decrease. There is also a risk that low dispersion will be impaired.

In the glass material for molding according to this embodiment, in the case of glass composition B, the upper limit of the Na ₂ O content is preferably 10%, and more preferably 8%, 6%, 4%, 2%, 1%, 0.5%, 0.2%, and 0.1% in that order. The lower limit of the Na ₂ O content is preferably 0%. The _{Na 2} O content may be 0%.

In the glass material for molding according to this embodiment, in the case of glass composition B, the upper limit of the K ₂ O content is preferably 10%, and more preferably 8%, 6%, 4%, 2%, 1%, 0.5%, 0.2%, and 0.1% in that order. The lower limit of the K ₂ O content is preferably 0%. The K ₂ O content may be 0%.

In the glass material for molding according to this embodiment, in the case of glass composition B, the upper limit of the total content of Na ₂ O and K ₂ O is preferably 10%, and more preferably 8%, 6%, 4%, 2%, 1%, 0.5%, 0.2%, and 0.1% in that order. The lower limit of the total content is preferably 0%, and more preferably 0.001%, 0.01%, and 0.05% in that order.

In glass composition B, Na ₂ O and K ₂ O both function to improve the meltability of the glass. They also function to increase the average linear thermal expansion coefficient. On the other hand, if their contents increase, thermal stability, devitrification resistance, chemical durability, and weather resistance decrease. Therefore, it is preferable that the respective contents of Na ₂ O and K ₂ O and their total content are within the above ranges.

In the glass material for molding according to this embodiment, in the case of glass composition B, the upper limit of the _Cs2O content is preferably 10%, and more preferably 8%, 6%, 4%, 2%, 1%, 0.5%, 0.2%, and 0.1% in that order. The lower limit of the _Cs2O content is preferably 0%. The _Cs2O content may be 0%.

In glass composition B, Cs ₂ O has the function of improving the meltability of the glass, but if the content is too high, the thermal stability and refractive index nd of the glass will decrease, and volatilization of glass components during melting will increase, which may make it impossible to obtain the desired glass. Therefore, the content of Cs ₂ O is preferably within the above range.

In the glass material for molding according to this embodiment, in the case of glass composition B, the upper limit of the total content of Li ₂ O, Na ₂ O, K ₂ O, and Cs ₂ O is preferably 10%, and more preferably 8%, 6%, 4%, 2%, 1%, 0.5%, 0.2%, and 0.1%, in that order. The lower limit of the total content is preferably 0%. The total content may be 0%. From the viewpoint of suppressing an increase in the liquidus temperature of the glass, it is preferable that the total content of Li ₂ O, Na ₂ O, K ₂ O, and Cs ₂ O be within the above range.

In the glass material for molding according to this embodiment, in the case of glass composition B, the upper limit of the MgO content is preferably 10%, and more preferably 8%, 6%, 4%, 2%, 1%, 0.5%, 0.2%, and 0.1%, in that order. Furthermore, the lower limit of the MgO content is preferably 0%. The MgO content may be 0%.

In the glass material for molding according to this embodiment, in the case of glass composition B, the upper limit of the CaO content is preferably 10%, and more preferably 8%, 6%, 4%, 2%, 1%, 0.5%, 0.2%, and 0.1%, in that order. Furthermore, the lower limit of the CaO content is preferably 0%. The CaO content may be 0%.

In the glass material for molding according to this embodiment, in the case of glass composition B, the upper limit of the SrO content is preferably 10%, and more preferably 8%, 6%, 4%, 2%, 1%, 0.5%, 0.4%, and 0.3%, in that order. Furthermore, the lower limit of the SrO content is preferably 0%, and more preferably 0.05%, 0.10%, 0.15%, and 0.20%, in that order.

In the glass material for molding according to this embodiment, in the case of glass composition B, the upper limit of the total content of MgO, CaO, and SrO is preferably 10%, and more preferably 8%, 6%, 4%, 2%, 1%, 0.5%, 0.4%, and 0.3%, in that order. The lower limit of this total content is preferably 0%, and more preferably 0.05%, 0.10%, 0.15%, and 0.20%, in that order. The total content may even be 0%.

In glass composition B, MgO, CaO, and SrO are glass components that improve the meltability of the glass and also serve to relatively increase the average linear expansion coefficient. However, if the content of these glass components increases, the thermal stability and devitrification resistance of the glass decrease. Therefore, it is preferable that the individual contents and total content of these glass components be within the above ranges.

In the glass material for molding according to this embodiment, in the case of glass composition B, the lower limit of the BaO content is preferably 20%, and more preferably 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, and 31% in that order. Furthermore, the upper limit of the BaO content is preferably 45%, and more preferably 44%, 43%, 42%, 41%, 40%, 39%, 38%, 37%, 36%, 35%, and 34% in that order.

BaO is a glass component that functions to increase the average linear expansion coefficient _αL in glass composition B without impairing the high refractive index and low dispersion characteristics, and is also a component that relatively reduces the value of ΔPg,F. By setting the BaO content within the above range, a glass material for molding can be obtained that has a high refractive index and low dispersion and an improved average linear expansion coefficient _αL . On the other hand, if the BaO content is too high, the thermal stability of the glass may decrease, and the glass may be devitrified, and stability during reheating may also be impaired.

In _the glass material for molding according to this embodiment, in the case of glass composition B, the upper limit of the total content of _SiO2 and _B2O3 is preferably 30%, and more preferably 29%, 28%, 27%, 26%, 25%, 24%, 23%, 22%, 21%, and 20% in that order. The lower limit of the total content is preferably 13%, and more preferably 14%, 15%, 16%, 17%, and 18% in that order.

In glass composition B, the total content of SiO ₂ and B ₂ O ₃ is preferably within the above range, from the viewpoint of suppressing a decrease in the refractive index while maintaining the stability of the glass.

In the glass composition B of the molding glass material according to this embodiment, the upper limit of the mass ratio of the BaO content to the total content of _SiO2 and _B2O3 [BaO/( _SiO2 + _B2O3 )] is preferably 3.00, and more preferably _2.80 , 2.60, 2.40, 2.20, 2.00, _1.80 , and 1.70 in this order. The lower limit of this mass ratio is preferably 0.60, and more preferably 0.80, 0.90, 1.00, 1.10, 1.20, and 1.30 in this order.

In glass composition B, the mass ratio is preferably within the above range from the viewpoint of obtaining glass that maintains the stability of the glass and has a large average linear expansion coefficient _αL .

In the glass material for molding according to this embodiment, in the case of glass composition B, the upper limit of the ZnO content is preferably 10%, and more preferably 8%, 6%, 4%, 2%, 1%, 0.5%, 0.4%, 0.3%, 0.2%, 0.1%, 0.05%, 0.03%, 0.02%, and 0.01%, in that order. Furthermore, the lower limit of the ZnO content is preferably 0%. The ZnO content may be 0%.

ZnO is a glass component in glass composition B that functions to improve the meltability of the glass. However, if the ZnO content is too high, the specific gravity of the glass increases, and the average linear expansion coefficient _αL may decrease. The low dispersion of the glass may also be impaired. Furthermore, the glass transition temperature Tg may decrease. Therefore, the ZnO content is preferably within the above range.

In the glass material for molding according to this embodiment, in the case of glass composition B, the lower limit of _{the La2O3} content is preferably 15%, and more preferably 16%, 17%, 18%, 19%, 20%, 21%, and 22% in this order. The upper limit of _{the La2O3} content is preferably 40%, and more preferably 39%, 38%, 37%, 36%, 35%, 34%, 33%, 32%, 31%, 30%, 29%, and 28% in this order.

_La2O3 is a glass component in glass composition B that increases the refractive index while suppressing a decrease in the Abbe number vd. It is also a component that reduces the partial dispersion ratio Pg,F _, and has a stronger effect of reducing the value of ΔPg,F than BaO. Therefore, by setting _{the La2O3} content within the above range, a molding glass material can be obtained that has a high refractive index and low dispersion, suppresses a decrease in the average linear expansion coefficient _αL , and suppresses an increase in the temperature coefficient of the relative refractive index (dn/ _dT ). On the other hand, if the _La2O3 content is too high, the thermal stability and devitrification resistance of the glass may decrease, and stability during reheating may also deteriorate.

In the glass material for molding according to this embodiment, in the case of glass composition _B , the upper limit of the _Gd2O3 content is preferably 20%, and more preferably 15%, 10%, 5%, 4%, 3%, 2%, 1%, and 0.5% in that order. The lower limit of _{the Gd2O3 content} is preferably 0%. _{The Gd2O3} content may be 0%.

In glass composition B, Gd ₂ O ₃ is a component that has high refractive index and low dispersion and can suppress a decrease in the average linear expansion coefficient _αL . However, in the glass of this embodiment, which incorporates a large amount of BaO, if the Gd ₂ O ₃ content is too high, the thermal stability and devitrification resistance of the glass decrease, making the glass more susceptible to devitrification during production. Furthermore, if the Gd ₂ O ₃ content is too high, the specific gravity of the glass increases, which is undesirable. It is also disadvantageous from the viewpoint of reducing raw material costs. Therefore, it is preferable that the Gd ₂ O ₃ content be within the above range.

In the glass material for molding according to this embodiment, in the case of glass composition _B , the lower limit of the _Y2O3 content is preferably 5%, and more preferably 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, and 14% in that order. The upper limit of the _{Y2O3 content} is preferably 25%, and more preferably 24%, 23%, 22%, 21%, 20%, and 19% in that order.

Y ₂ O ₃ is a component that functions to increase the refractive index while suppressing a decrease in the Abbe number vd in glass composition B. Furthermore, in the glass of this embodiment, in which a relatively large amount of BaO or SrO is incorporated among the alkali and alkaline earth components, Y 2 O 3 is a component that is effective in suppressing a decrease in the average linear expansion coefficient _αL and imparting high refractive index and low dispersion characteristics. It also functions to improve the chemical durability and weather resistance of the glass and to increase the glass transition temperature. It is a component that reduces the partial dispersion ratio Pg,F and also functions to reduce the value of ΔPg,F. On the other hand, if the Y ₂ O ₃ content is too high, the thermal stability and devitrification resistance of the glass may decrease. Stability during reheating may also deteriorate. Therefore, the Y ₂ O ₃ content is preferably within the above range.

In the glass material for molding according to this embodiment, in the case of glass composition B, the upper limit of the _ZrO2 content is preferably 10%, and more preferably 9%, 8%, 7%, 6%, 5%, 4%, 3%, and 2.5% in that order. The lower limit of the _ZrO2 content is preferably 0%, and more preferably 0.005%, 0.01%, 0.05%, 0.1%, 0.5%, 1.0%, 1.5%, and 2.0% in that order. The _ZrO2 content may be 0%.

_ZrO2 is a component in glass composition B that increases the refractive index, and when contained in an appropriate amount, it also improves the thermal stability of the glass. However, _ZrO2 is a component that relatively reduces the average linear expansion coefficient _αL , and also increases the temperature dependence of the temperature coefficient of the relative refractive index (dn/dT). Furthermore, if the content is too high, there is a risk of a significant decrease in thermal stability. Therefore, it is preferable that the content of _ZrO2 be within the above range.

In the glass material for molding according to this embodiment, in the case of glass composition B, the upper limit of the _TiO2 content is preferably 15%, and more preferably 14%, 13%, 12%, 11%, 10%, 9%, 8%, 7%, and 6% in that order. The lower limit of the _TiO2 content is preferably 0%, and more preferably 1%, 2%, 3%, 4%, and 5% in that order. The _TiO2 content may be 0%.

_TiO2 is a component in glass composition B that increases the refractive index, and when included in an appropriate amount, it also improves the thermal stability of the glass. _TiO2 is a component that increases _the partial dispersion ratio Pg,F, and has a stronger effect of increasing the values of Pg,F and ΔPg,F compared to _Nb2O5 . On the other hand, if the _TiO2 content is too high, the average linear expansion coefficient _αL may decrease, the Abbe number νd may decrease, the coloring of the glass may become stronger, and the meltability may deteriorate. There is also a risk of deterioration in stability during reheating. Therefore, it is preferable that the _TiO2 content be within the above range.

In the glass material for molding according to this embodiment, in the case of glass composition B, the upper limit of _{the Nb2O5} content is preferably 20%, and more preferably 19%, 18%, 17%, 16%, 15%, 14%, 13%, 12%, 11%, 10%, 5%, 3%, 2%, and 1% in that order. The lower limit of _{the Nb2O5} content is preferably 0%, and more preferably 0.001%, 0.003%, 0.005%, 0.010%, 0.050%, 0.080%, and 0.100% in that order. _{The Nb2O5 content} may be 0%.

Nb ₂ O ₅ is a component in glass composition B that increases the refractive index, and when contained in an appropriate amount, it also improves the thermal stability of the glass. Nb ₂ O ₅ is also a component that increases the partial dispersion ratios Pg,F and ΔPg,F. On the other hand, if the Nb ₂ O ₅ content is too high, the average linear expansion coefficient _αL may decrease and the coloring of the glass may become stronger. There is also a risk of the stability during reheating being impaired. Therefore, the Nb ₂ O ₅ content is preferably within the above range.

In the glass material for molding according to this embodiment, in the case of glass composition B, the upper limit of the _WO3 content is preferably 10%, and more preferably 8%, 6%, 4%, 2%, 1%, 0.5%, and 0.1% in that order. The lower limit of the _WO3 content is preferably 0%. The _WO3 content may be 0%.

In glass composition B, _WO3 has the function of lowering the glass transition temperature Tg relative to other highly dispersive components, and therefore can be incorporated for the purpose of lowering the molding temperature in order to protect the molding die, its protective film, and the molding machine when softening and molding the glass, particularly when precision pressing is performed. On the other hand, from the viewpoints of increasing the transmittance of the glass and suppressing an increase in the temperature coefficient of the relative refractive index (dn/dT) of the glass, the content of _WO3 is preferably within the above range.

In the glass material for molding according to this embodiment, in the case of glass composition _B , the upper limit of the _Bi2O3 content is preferably 10%, and more preferably 8%, 6%, 4%, 2%, 1%, 0.5%, and 0.1% in that order. The lower limit of _{the Bi2O3} content is preferably 0%. _{The Bi2O3 content} may be 0%.

In the glass composition B, Bi ₂ O ₃ is a component that increases the refractive index nd while decreasing the Abbe number νd. It is also a component that tends to increase the coloration of the glass. Therefore, the content of Bi ₂ O ₃ is preferably within the above range.

In the glass material for molding according to this embodiment, in the case of glass composition _B , the upper limit of the content of _Ta2O5 is preferably 20%, and more preferably 15%, 13%, 10%, 5 _% , 3%, and 1% in that order. The lower limit of _the content of _Ta2O5 is preferably 0%. The content of _Ta2O5 may be 0%.

_Ta2O5 is _a glass component in glass composition B that improves the thermal stability and devitrification resistance of the glass. On the other hand, _Ta2O5 increases the refractive index and makes the glass highly dispersible. Furthermore, as _{the Ta2O5} content increases, the thermal stability of the glass decreases, making it more likely that glass raw materials will remain unmelted when melting the glass. _Ta2O5 is also a component that relatively reduces the average linear expansion coefficient _αL . Therefore, the _Ta2O5 content is preferably within the above range. Furthermore, _Ta2O5 is _an extremely expensive component compared to other glass components, and increasing the _Ta2O5 content increases _the production cost of the glass. Furthermore, because _Ta2O5 has a larger molecular weight than other glass components, it increases _the specific gravity of the glass, resulting in _an increase in the weight of the optical element.

In the glass material for molding according to this embodiment, in the case of glass composition B, the upper limit of the Sc ₂ O ₃ content is preferably 2%. The lower limit of the Sc ₂ O ₃ content is preferably 0%.

In the glass material for molding according to this embodiment, in the case of glass composition B, the upper limit of the HfO ₂ content is preferably 2%. The lower limit of the HfO ₂ content is preferably 0%.

In the glass composition B, Sc ₂ O ₃ and HfO ₂ both have the function of increasing the refractive index nd and are expensive components, so the contents of Sc ₂ O ₃ and HfO ₂ are preferably within the above ranges.

In the glass material for molding according to this embodiment, in the case of glass composition B, the upper limit of the Lu ₂ O ₃ content is preferably 2%. The lower limit of the Lu ₂ O ₃ content is preferably 0%.

_Lu2O3 has the function of increasing the refractive index nd in glass composition B. In addition, since _it has a large molecular weight, it is also a glass component that increases _the specific gravity of the glass. Therefore, the content of _Lu2O3 is preferably within the above range.

In the glass material for molding according to this embodiment, in the case of glass composition B, the upper limit of the GeO ₂ content is preferably 2%. The lower limit of the GeO ₂ content is preferably 0%.

_GeO2 has the function of increasing the refractive index nd in glass composition B, and is an extremely expensive component among commonly used glass components. Therefore, from the viewpoint of reducing the manufacturing cost of the glass, it is preferable that the content of _GeO2 is in the above range.

In the glass material for molding according to this embodiment, in the case of glass composition B, the upper limit of _{the La2O3} content is preferably 2%. The lower limit of _{the La2O3} content is preferably 0%. _{The La2O3 content} may be 0%.

In glass composition B, if the content of La ₂ O ₃ is large, the thermal stability and devitrification resistance of the glass will decrease, and the glass will be more likely to devitrify during production. Therefore, from the viewpoint of suppressing the decrease in thermal stability and devitrification resistance, the content of La ₂ O ₃ is preferably within the above range.

In the glass material for molding according to this embodiment, in the case of glass composition B, the upper limit of the content of Yb ₂ O ₃ is preferably 2%. Furthermore, the lower limit of the content of Yb ₂ O ₃ is preferably 0%.
%.

In glass composition B, if the Yb ₂ O ₃ content is too high, the thermal stability and devitrification resistance of the glass may decrease. Furthermore, Yb 2 O 3 is an expensive component among commonly used glass components. From the viewpoints of preventing a decrease in the thermal stability of the glass, suppressing an increase in specific gravity, and reducing the manufacturing cost of the glass, the Yb ₂ O ₃ content is preferably within the above range.

In the case of glass composition B, the glass material for molding according to this embodiment mainly _{contains the above-mentioned glass components SiO2, B2O3, Al2O3, P2O5, Li2O , Na2O , K2O , Cs2O , MgO} , CaO, _SrO , BaO, _ZnO , _La2O3 , _Gd2O3 , _{Y2O3 , ZrO2 , TiO2} , _{Nb2O5 , WO3 , Bi2O3} , _Ta2O5 , _Sc2O3 , _{HfO2 , Lu2O3} , _{GeO2 , and Yb2O .} The total content of the _above glass components is preferably 95% or more, more preferably 98% or more, even more preferably 99% or more, and even more preferably 99.5% or more.

In the glass material for molding according to this embodiment, the upper limit of the TeO ₂ content is preferably 2%. The lower limit of the TeO ₂ content is preferably 0%.

Since _TeO2 is toxic, it is preferable to reduce the content of _TeO2 . Therefore, the content of _TeO2 is preferably within the above range.

In the glass material for molding according to this embodiment, in the case of glass composition B, the fluorine (F) content is preferably 3% or less, with the upper limits being 1%, 0.5%, and 0.3%, in that order. The lower the F content, the more preferable it is, and the lower limit is preferably 0%. The F content may be 0%. Preferably, the glass is substantially free of fluorine (F).

In glass composition B, by setting the F content within the above range, volatilization during melting of the glass can be suppressed, and refractive index fluctuations and striae can be suppressed.

The glass material for molding according to this embodiment is preferably composed primarily of the above glass components, but may contain other components as long as they do not interfere with the effects of the present invention. Furthermore, the present invention does not exclude the inclusion of unavoidable impurities.

<Other ingredient composition>
Pb, As, Cd, Tl, Be, and Se are all toxic, and therefore it is preferable that the glass material for molding according to this embodiment does not contain these elements as glass components.

U, Th, and Ra are all radioactive elements. Therefore, it is preferable that the glass material for molding according to this embodiment does not contain these elements as glass components.

V, Cr, Mn, Fe, Co, Ni, Cu, Pr, Nd, Pm, Sm, Eu, Tb, Dy, Ho, Er, and Tm increase the coloration of the glass and can be sources of fluorescence. Therefore, it is preferable that the glass material for molding according to this embodiment does not contain these elements as glass components.

Sb (Sb ₂ O ₃ ) and Ce (CeO ₂ ) are elements that can be added as desired and function as fining agents, with Sb (Sb ₂ O ₃ ) being a fining agent with a significant fining effect.

_{The Sb2O3 content} is expressed as an exclusive percentage. That is _, when the total content of all glass components other than _{Sb2O3 and CeO2 is taken as 100 mass%, the Sb2O3 content is} preferably less than 1 mass%, more preferably less than 0.1 mass%. Furthermore, less than 0.05 mass%, less than 0.03 mass%, less than 0.02 mass%, and less than 0.01% are more preferable, in that order. _{The Sb2O3 content} may be 0 mass%.

The _CeO2 content is also expressed as an exclusive percentage. That _is , when the total content of all glass components other than _CeO2 and _Sb2O3 is taken as 100 mass%, the _CeO2 content is preferably less than 2 mass%, more preferably less than 1 mass%, even more preferably less than 0.5 mass%, and even more preferably less than 0.1 mass%. _{The CeO2} content may be 0 mass%. By setting the _CeO2 content within the above range, the clarity of the glass can be improved.

(Glass properties when glass composition B is used)
<Refractive index nd>
In the glass material for molding according to this embodiment, in the case of glass composition B, the refractive index nd is not particularly limited and can be, for example, 1.60 to 2.10, preferably 1.65 to 2.00, more preferably 1.70 to 1.88, and even more preferably 1.73 to 1.85. The lower limit of the refractive index nd may be 1.65, 1.74, 1.75, 1.76, 1.77, 1.78, or 1.79, and the upper limit of the refractive index nd may be 2.0, 1.9, 1.84, 1.83, or 1.82.

The refractive index nd can be adjusted to a desired value by appropriately adjusting the content of each glass component in glass composition B. Components that function to relatively increase the refractive index nd (refractive index-increasing components) include Nb ⁵⁺ , Ti ⁴⁺ , W ⁶⁺ , Bi ³⁺ , Ta ⁵⁺ , Zr ⁴⁺ , La ³⁺ _3, etc. (i.e., in terms of oxides, Nb ₂ O ₅ , TiO ₂ , WO ₃ , Bi ₂ O ₃ , Ta ₂ O ₅ , ZrO ₂ , La ₂ O _3, etc.). On the other hand, components that act to relatively lower the refractive index nd (refractive index lowering components) include P ⁵⁺ , Si ⁴⁺ , B ³⁺ , Li ⁺ , Na ⁺ , K ^{+ ,} etc. (i.e., in oxide terms, P ₂ O ₅ , SiO ₂ , B ₂ O ₃ , Li ₂ O, Na ₂ O, K ₂ O, etc.).
is.

<Abbe number νd>
In the glass material for molding according to this embodiment, in the case of glass composition B, the Abbe number vd can exhibit an Abbe number of 20 to 70, preferably 25 to 65, more preferably 30 to 60, and even more preferably 35 to 55. The lower limit of the Abbe number vd may be 23, 28, 32, 36, 37, 38, 39, or 40, and the upper limit of the Abbe number vd may be 67, 63, 57, 53, 51, 49, 47, 45, 43, or 42.

The Abbe number vd can be adjusted to a desired value by appropriately adjusting the content of each glass component in glass composition B. Components that relatively lower the Abbe number vd, i.e., high dispersion components, include Nb ⁵⁺ , Ti ⁴⁺ , W ⁶⁺ , Bi ³⁺ , Ta ⁵⁺ , and Zr ⁴⁺ (i.e., in oxide terms, Nb ₂ O ₅ , TiO ₂ , WO ₃ , Bi ₂ O ₃ , Ta ₂ O ₅ , and ZrO ₂ ). On the other hand, components that relatively increase the Abbe number vd, i.e., components that reduce dispersion, are P ⁵⁺ , Si ⁴⁺ , B ³⁺ , Li ⁺ , Na ⁺ , K ⁺ , La ³⁺ , Ba ²⁺ , Ca ²⁺ , Sr ^{2+ ,} etc. (i.e., in oxide terms, P ₂ O ₅ , SiO ₂ , B ₂ O ₃ , Li ₂ O, Na ₂ O, K ₂ O, La ₂ O ₃ , BaO, CaO, SrO, etc.).

In the glass material for molding according to this embodiment, in the case of glass composition B, the refractive index nd and the Abbe number vd preferably satisfy the following formula (1), more preferably the following formula (2), even more preferably the following formula (3), and particularly preferably the following formula (4). When the refractive index nd and the Abbe number vd satisfy the following formula, a glass material for molding having high refractive index and low dispersion properties can be obtained.
nd−(−0.0183 × Abbe number νd+2.502)≧0 … (1)
nd-(-0.0183 × Abbe number νd+2.512)≧0 ... (2)
nd−(−0.0183 × Abbe number νd+2.522)≧0 … (3)
nd-(-0.0183 × Abbe number νd+2.532)≧0 ... (4)

<Average linear expansion coefficient α _L >
In the glass material for molding according to this embodiment, in the case of glass composition B, the lower limit of the average linear expansion coefficient α _L at -30 to 70°C is preferably 0.80×10 ^-5 °C ^-1 , and is more preferably 0.81×10 ^-5 °C ^-1 , 0.82×10 ^-5 °C ^-1 , 0.83×10 ^-5 °C ^-1 , 0.84×10 ^-5 °C ^-1 , 0.85×10 ^-5 °C ^-1 , 0.86×10 ^-5 °C ^-1 , 0.87×10 ^-5 °C ^-1 , and 0.88×10 ^-5 °C ^-1 in this order. From the viewpoint of maintaining the stability of the glass and obtaining the desired optical properties, the upper limit of the average linear expansion coefficient _αL can be, for example, 1.20×10 ⁻⁵ ° C. ⁻¹ , and is preferably 1.10×10 ⁻⁵ ° C. ⁻¹ or less, with 1.00×10 ⁻⁵ ° C. ⁻¹ , 0.98×10 ⁻⁵ ° C. ⁻¹ , 0.96×10 ⁻⁵ ° C. ⁻¹ , 0.95×10 ⁻⁵ ° C. ⁻¹ , 0.94×10 ⁻⁵ ° C. ⁻¹ , and 0.93×10 ⁻⁵ ° C. ⁻¹ being more preferred in this order.

In the case of glass composition B, by setting the average linear expansion coefficient _αL at −30 to 70° C. within the above range, it is possible to obtain a glass material for molding that can be used in a wide range of temperature environments.

The average linear expansion coefficient _αL is measured in accordance with the provisions of JOGIS16. The sample is a round bar with a length of 20 mm ± 0.5 mm and a diameter of 5 mm ± 0.5 mm. With a load of 98 mN applied to the sample, it is heated at a constant rate of 4°C per minute, and the temperature and sample elongation are measured in 1-second increments. The average linear expansion coefficient _αL is the average value of the linear expansion coefficient from -30 to 70°C.

It should be noted that JOGIS16 stipulates that "the average linear expansion coefficient shall be expressed in units of 10 ^-7 ° C ^-1 to the nearest integer," but in this specification, the average linear expansion coefficient α _L shall be expressed in units of [10 ^-5 · ° C ^-1 ].

In this specification, the average linear expansion coefficient α _L is expressed in units of [10 ⁻⁵ ·° C. ⁻¹ ], but the numerical value of the average linear expansion coefficient α _L is the same even when the unit is [10 ⁻⁵ ·K ⁻¹ ].

<Average linear expansion coefficient α _100-300 >
In the glass material for molding according to this embodiment, in the case of glass composition B, the lower limit of the average linear expansion coefficient α _100-300 at 100 to 300° C. is preferably 90, and more preferably 92, 94, and 95 in that order. Furthermore, from the viewpoint of maintaining the stability of the glass and obtaining the desired optical properties, the upper limit of the average linear expansion coefficient α _100-300 can be, for example, 130, and is preferably 115, and more preferably 110, 106, and 104 in that order.

The average linear expansion coefficient α _100-300 is measured in accordance with the JOGIS08 standard. The sample is a round bar with a length of 20 mm ± 0.5 mm and a diameter of 5 mm ± 0.5 mm. With a load of 98 mN applied to the sample, it is heated at a constant rate of 4°C per minute, and the temperature and sample elongation are measured in 1-second increments. The average linear expansion coefficient α _100-300 is the average value of the linear expansion coefficient from 100 to 300°C.

In this specification, the average linear expansion coefficient α _100-300 is expressed to the first integer in units of 10 ⁻⁷ ° C ⁻¹ in accordance with the provisions of JOGIS08. That is, the average linear expansion coefficient α _100-300 is expressed as an integer in units of [10 ⁻⁷ · ° C ⁻¹ ].

<Temperature coefficient of relative refractive index dn/dT>
The temperature coefficient of the relative refractive index (dn/dT) of glass is measured in accordance with Japanese Industrial Standard JIS B7072-2 (Method for measuring the temperature coefficient of refractive index of optical glass - Part 2: Interferometry) by measuring the value of the temperature coefficient of the relative refractive index for light with a wavelength of 632.8 nm when the temperature is changed from -40°C to 110°C.
In this specification, the temperature coefficient of the relative refractive index (dn/dT) is expressed in units of [10 ⁻⁶ ·°C ⁻¹ ], but even if the unit is [10 ⁻⁶ ·K ⁻¹ ], the value of the temperature coefficient of the relative refractive index dn/dT will be the same.

In the glass material for molding according to this embodiment, in the case of glass composition B, the upper limit of the temperature coefficient of relative refractive index dn/dT is preferably 2.0×10 ⁻⁶ ° C ⁻¹ at a He—Ne laser wavelength (633 nm to 632.8 nm) and in a temperature range of 20 to 40° C., and is further more preferably 1.5×10 ⁻⁶ ° C ⁻¹ , 1.0×10 ⁻⁶ ° C ⁻¹ , 0.5×10 ⁻⁶ ° C ⁻¹ , 0.0×10 ⁻⁶ ° C ⁻¹ , −0.5×10 ⁻⁶ ° C ⁻¹ , and −1.0×10 ⁻⁶ ° C ⁻¹ in that order. Furthermore, there is no clear lower limit to the temperature coefficient of the relative refractive index dn/dT, but at a wavelength of a He—Ne laser (633 nm to 632.8 nm) and in a temperature range of 20 to 40° C., it is preferably −13.0×10 ⁻⁶ ° C. ⁻¹ , and more preferably −10.0×10 ⁻⁶ ° C. ⁻¹ , −9.0×10 ⁻⁶ ° C. ⁻¹ , −8.0×10 ⁻⁶ ° C. ⁻¹ , −7.0×10 ⁻⁶ ° C. ⁻¹ , and −6.5×10 ⁻⁶ ° C. ⁻¹ in that order.

By setting dn/dT within the above range and combining it with an optical element in which dn/dT is a positive value, or an optical element in which dn/dT is a negative value and the lens focal length has a different sign, the refractive index fluctuations are reduced even in environments where the temperature of the optical element fluctuates greatly, and the desired optical characteristics can be exhibited with high precision over a wider temperature range.

On the other hand, when high-energy light, such as laser light or light with wavelengths equivalent to those absorbed by glass, is incident on the glass, the extent of the temperature rise in the glass varies depending on the intensity of the light and the duration of irradiation. In this case, it may be necessary to minimize the temperature change in the refractive index of the glass of this embodiment alone.

In such a case, the upper limit of the temperature coefficient of the relative refractive index dn/dT is preferably 2.0×10 −6 ° C −1 , and more preferably 1.5×10 ⁻⁶ ° C ⁻¹ , 1.0×10 ⁻⁶ ° C ⁻¹ , 0.5×10 −6 ° C −1 , 0.3×10 ⁻⁶ ° C ⁻¹ , and 0.1×10 ⁻⁶ ° C ⁻¹ in this order, taking the wavelength of a He—Ne laser ⁽ 633 nm to ^632.8 nm) ^and a temperature range of 20 to ⁴⁰ ° C. as an example. The lower limit of the temperature coefficient of refractive index dn/dT is preferably -2.0×10 ^-6 ° C. ^-1 , and is more preferably -1.5×10 ^-6 ° C. ^-1 , -1.0×10 ^-6 ° C. ^-1 , -0.5×10 ^-6 ° C. ^-1 , -0.3×10 ^-6 ° C. ^-1 , and -0.1×10 ^-6 ° C. ^-1 in this order. The temperature coefficient of refractive index dn/dT can also be 0.0×10 ^-6 ° C. ^-1 . The value of the temperature coefficient of refractive index (dn/dT) of the glass material for molding according to this embodiment may be appropriately selected within the above-mentioned preferred range depending on the laser wavelength to be used, taking into consideration the description in this specification.

<Method for measuring temperature dependence of temperature coefficient of relative refractive index dn/dT>
The glass of this embodiment has a small temperature dependency of the temperature coefficient of the relative refractive index (dn/dT) in the case of glass composition B. The measurement method is as follows.

Measurement is performed using the interference method, a method described in Japan Optical Glass Industry Association Standard JOGIS18, "Method for measuring the temperature coefficient of refractive index of optical glass." The temperature is changed from -40°C to 80°C, and dn/dT (hereinafter referred to as dn/dT@632.8) at a wavelength of 632.8 nm is measured at temperatures of -30°C, -10°C, +10°C, +30°C, +50°C, and +70°C. An approximation line for the dn/dT@632.8 values versus temperature is determined using the least squares method, with the slope of the line defined as a and the intercept at a temperature of 0°C defined as b.

The closer the slope a is to 0, the smaller the change in dn/dT due to temperature, meaning that the change in the value of dn/dT per temperature change is smaller even in different temperature ranges. In other words, the shift in focal length per unit temperature change of the optical element is constant regardless of temperature, which simplifies the position adjustment mechanism on the light receiving element side and is effective for optical elements that require high-precision imaging.

Therefore, in the glass material for molding according to this embodiment, in the case of glass composition B, the range of the value of the slope a is preferably 10.0×10 ⁻⁹ to −10.0×10 ⁻⁹ , and more preferably 8.0×10 ⁻⁹ to −8.0×10 ⁻⁹ , 6.0×10 ⁻⁹ to −6.0×10 ⁻⁹ , 4.0×10 ⁻⁹ to −4.0×10 ⁻⁹ , and 3.0×10 ⁻⁹ to −3.0×10 ⁻⁹ , in that order.

Furthermore, the closer the intercept b is to 0.0 × 10 ^-6 , the smaller the value of dn/dT@632.8 at 0°C on the approximate line is, which means that the absolute value of dn/dT is smaller. Therefore, the amount of focal length shift per unit temperature change of a single optical element is smaller, which is effective for optical elements that require high-precision imaging.

Therefore, in the glass material for molding according to this embodiment, in the case of glass composition B, the range of the value of the intercept b is preferably 3.0×10 ^-6 to -3.0×10 ^-6 , and more preferably 2.0×10 ^-6 to -2.0×10 ^-6 , 1.0×10 ^-6 to -1.0×10 ^-6 , and 0.5×10 ^-6 to -0.5×10 ^-6 , in that order. Note that as long as the value of the slope a is controlled to a certain value or less, preferably near 0, the intercept b does not necessarily have to be 0. The intercept b can also be set near 0.

<Glass transition temperature Tg>
In the glass material for molding according to this embodiment, in the case of glass composition B, the upper limit of the glass transition temperature Tg is preferably 730°C, and more preferably 720°C, 710°C, and 700°C in that order. The lower limit of the glass transition temperature Tg is preferably 500°C, and more preferably 550°C, 560°C, 570°C, and 580°C in that order.

By ensuring that the upper limit of the glass transition temperature Tg satisfies the above range, increases in the molding and annealing temperatures of the glass can be suppressed, reducing thermal damage to press molding and annealing equipment. Furthermore, by ensuring that the lower limit of the glass transition temperature Tg satisfies the above range, it becomes easier to maintain the desired Abbe number and refractive index while maintaining the thermal stability of the glass. Furthermore, good moldability can be achieved when used as a precision press material.

On the other hand, the higher the glass transition temperature Tg, the smaller the amount of expansion per unit temperature change, which tends to reduce the degree of shape change due to thermal expansion per unit temperature change. Furthermore, if the temperature of the glass rises to near Tg or above the strain point due to heating, there is a risk that the optical performance will not return to its original state even if the glass is subsequently cooled. Therefore, it is preferable that the lower limit of Tg be within the above range.

<Specific gravity of glass>
In the glass material for molding according to this embodiment, when the glass has composition B, the specific gravity is preferably 5.50 or less, and more preferably 5.00 or less, and then 4.80 or less. If the specific gravity of the glass can be reduced, the weight of the lens can be reduced. As a result, the power consumption of the autofocus drive of the camera lens in which the lens is mounted can be reduced.

<Light transmittance of glass>
The light transmittance of the glass material for molding according to this embodiment can be evaluated by the coloring degrees λ5, λ70, and λ80.
In the case of glass composition B, the spectral transmittance is measured in the wavelength range of 200 to 700 nm for a glass sample having a thickness of 10.0 mm±0.1 mm, and the wavelength at which the external transmittance is 5% is defined as λ5, the wavelength at which the external transmittance is 70% is defined as λ70, and the wavelength at which the external transmittance is 80% is defined as λ80.

In the molding glass material of this embodiment, for glass composition B, λ5 is preferably 400 nm or less, more preferably 380 nm or less, even more preferably 360 nm or less, and particularly preferably 350 nm or less.

In the molding glass material of this embodiment, for glass composition B, λ70 is preferably 440 nm or less, more preferably 430 nm or less, and even more preferably 420 nm or less.

In the molding glass material of this embodiment, for glass composition B, λ80 is preferably 510 nm or less, more preferably 500 nm or less, and even more preferably 490 nm or less.

By using molding glass materials with λ5, λ70, and λ80 wavelengths shortened as described above, optical elements that enable favorable color reproduction can be provided.

(Glass Composition C)
Next, the contents and ratios of the glass components and the glass properties when the glass material for molding according to this embodiment has glass composition C will be described.

In the glass material for molding according to this embodiment, in the case of glass composition C, _SiO2 is an essential component that functions as a glass network-forming component to improve the thermal stability, reheat devitrification resistance, chemical durability, and weather resistance of the glass, to increase the viscosity of the glass melt, and to make _the glass melt easier to mold. From the above perspectives, the _SiO2 content, expressed in mass%, is preferably greater than the total content of _B2O3 and _{P2O5 .} In the case of glass composition C, silicate glass is preferred. In the case of glass composition C, the _SiO2 content is preferably 8.0% or more, and more preferably in the following order: 10.00% or more, 11.00% or more, 12.00% or more, 13.00% or more, 14.00% or more, 14.50% or more, 15.00% or more, 15.50% or more, 16.00% or more, 16.50% or more, and 16.60% or more.
In the glass material for molding according to this embodiment, in the case of glass composition C, from the viewpoint of improving the devitrification resistance, meltability, and partial dispersion characteristics of the glass, the SiO ₂ content is preferably 50.00% or less, and is more preferably 45.00% or less, 40.00% or less, 35.00% or less, 30.00% or less, 28.00% or less, 26.00% or less, 25.00% or less, 24.50% or less, 24.00% or less, 23.50% or less, 23.00% or less, 22.75% or less, 22.50% or less, and 22.00% or less in that order.

In the glass material for molding according to this embodiment, in the case of glass composition C, the total content of SiO ₂ and B ₂ O ₃ (SiO ₂ +B ₂ O ₃ ) is preferably 10.00% or more, and more preferably 12.00% or more, 14.00% or more, 15.00% or more, 16.00% or more, 17.00% or more, 17.75% or more, 18.00% or more, 18.25% or more, 18.50% or more, and 18.60% or more in that order, and is preferably 35.00% or less, and more preferably 32.00% or less, 30.00% or less, 28.00% or less, 27.00% or less, 26.50% or less, 26.00% or less, 25.50% or less, 25.00% or less, 24.50% or less, 24.40% or less, and 24.30% or less in that order.

In the glass material for molding according to this embodiment, in the case of glass composition C, _SiO2 and _B2O3 function to improve the thermal stability of the glass, but _an increase in the _SiO2 content tends to decrease the meltability of the glass. From the above viewpoints, the mass ratio of _SiO2 to the total content of SiO2 and _B2O3 ( _SiO2 /( _SiO2 + _{B2O3 )} ) is preferably _0.50 or more, and more preferably 0.55 or more, 0.60 or more, 0.65 or more, 0.70 or more, 0.75 or more, 0.77 or more, and 0.80 or more in that order _, and is preferably 1.00 or less, and more preferably 0.99 or less, 0.98 or less, 0.97 or less, 0.96 or less, 0.95 or less, 0.94 or less, 0.93 or less, 0.92 or less, 0.91 or less, 0.90 or less, 0.89 or less, and 0.88 or less in that order.

In the glass material for molding according to this embodiment, in the case of glass composition C, the mass ratio of the B ₂ O ₃ content to the SiO ₂ content (B ₂ O ₃ /SiO ₂ ) is preferably less than 1.00, from the viewpoints of improving chemical durability, reducing α _max , and improving reheat devitrification resistance, and is more preferably 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, 0.50 or less, 0.40 or less, 0.35 or less, 0.32 or less, 0.31 or less, 0.30 or less, 0.29 or less, 0.28 or less, 0.27 or less, 0.26 or less, and 0.25 or less in that order. From the viewpoint of improving thermal stability, the mass ratio (B ₂ O ₃ /SiO ₂ ) is preferably 0.00 or more, and more preferably 0.01 or more, 0.02 or more, 0.03 or more, 0.04 or more, 0.05 or more, 0.06 or more, 0.07 or more, 0.08 or more, 0.09 or more, 0.10 or more, 0.11 or more, 0.12 or more, 0.13 or more, 0.14 or more, and 0.15 or more in that order.

In the glass material for molding according to this embodiment, in the case of glass composition C, _{the B2O3} content is preferably 0.00% or more, more preferably more than 0.00%, and more preferably 0.10% or more, 0.20% or more, 0.30% or more, 0.35% or more, 0.37% or more, 0.39% or more, 0.40% or more, 0.41% or more, 0.42% or more, 0.43% or more, 0.44% or more, 0.45% or more, 0.46% or more, 0.47% or more, 0.48% or more, and 0.49% or more in that order. _{The B2O3} content is preferably 30.00% or less, and is more preferably 25.00% or less, 20.00% or less, 18.00% or less, 16.00% or less, 14.00% or less, 12.00% or less, 10.00% or less, 9.00% or less, 8.00% or less, 7.00% or less, 6.00% or less, 5.50% or less, 5.20% or less, 5.10% or less, 5.00% or less, 4.90% or less, and 4.80% or _{less in that order. By setting the B2O3 content} within the above range, the specific gravity of the glass can be further reduced and the thermal stability of the glass can be improved.

In the glass material for molding according to this embodiment, in the case of glass composition C, the CaO content is preferably 3.00% or more, more preferably 4.00% or more, from the viewpoint of improving the meltability and thermal stability of the glass, and more preferably 5.00% or more, 5.10% or more, 5.20% or more, 5.30% or more, 5.40% or more, 5.50% or more, 5.60% or more, 5.70% or more, 5.80% or more, and 5.90% or more in that order. From the same viewpoint, the CaO content is preferably 40.00% or less, and more preferably 35.00% or less, 30.00% or less, 28.00% or less, 26.00% or less, 24.00% or less, 22.00% or less, 21.50% or less, 21.00% or less, 20.50% or less, 20.25% or less, 20.00% or less, and 19.50% or less in that order.

In the molding glass material according to this embodiment, in the case of glass composition C, the total content of the alkaline earth metal oxides MgO, CaO, SrO, and BaO and ZnO (MgO + CaO + SrO + BaO + ZnO) is preferably 5.00% or more, and more preferably 7.00% or more, 10.00% or more, 11.00% or more, 12.00% or more, 13.00% or more, 13.50% or more, 14.00% or more, 14.50% or more, 15.00% or more, 15.30% or more, 15.50% or more, and 16.00% or more in that order. The total content (MgO+CaO+SrO+BaO+ZnO) is preferably 50.00% or less, and more preferably 45.00% or less, 40.00% or less, 39.00% or less, 38.00% or less, 37.00% or less, 36.50% or less, 36.00% or less, 35.50% or less, 35.00% or less, 34.50% or less, and 34.00% or less in that order. Having the total content (MgO+CaO+SrO+BaO+ZnO) in the above range is preferred from the viewpoint of maintaining thermal stability without interfering with further lowering the specific gravity and high dispersion.

In the glass material for molding according to this embodiment, in the case of glass composition C, among MgO, CaO, SrO, BaO, and ZnO, MgO and CaO are more effective components in suppressing the specific gravity of the glass than SrO, BaO, and ZnO. Therefore, from the viewpoint of further suppressing an increase in specific gravity, the mass ratio of the total content of ZnO, SrO, and BaO to the total content of MgO and CaO ((ZnO + SrO + BaO)/(MgO + CaO)) is preferably 2.78 or less, and more preferably 2.77 or less, 2.76 or less, 2.75 or less, 2.74 or less, and 2.73 or less in that order.
On the other hand, SrO, BaO, and ZnO work to improve partial dispersion characteristics more effectively than MgO and CaO. Therefore, from the viewpoint of improving partial dispersion characteristics, the mass ratio ((ZnO+SrO+BaO)/(MgO+CaO)) is preferably 0.17 or more, and more preferably 0.18 or more, 0.19 or more, and 0.20 or more in that order.

In the molding glass material according to this embodiment, in the case of glass composition C, the mass ratio of the CaO content to the total content of MgO, CaO, SrO, BaO and ZnO (CaO/(MgO+CaO+SrO+BaO+ZnO)) is preferably 0.35 or more, from the viewpoint of achieving an even higher refractive index and a further lower specific gravity, and is more preferably 0.36 or more, 0.37 or more, 0.38 or more, 0.39 or more, 0.40 or more, 0.41 or more, and 0.42 or more in that order. From the viewpoint of improving thermal stability, the mass ratio (CaO/(MgO+CaO+SrO+BaO+ZnO)) is preferably 1.00 or less, and more preferably 0.95 or less, 0.90 or less, 0.89 or less, 0.88 or less, 0.87 or less, 0.86 or less, 0.85 or less, 0.84 or less, 0.83 or less, 0.80 or less, and 0.78 or less in that order.

In the molding glass material according to this embodiment, in the case of glass composition C, the mass ratio of the total content of CaO and MgO to the total content of MgO, CaO, SrO, BaO and ZnO ((CaO + MgO)/(MgO + CaO + SrO + BaO + ZnO)) is preferably 0.35 or more from the viewpoint of further reducing the specific gravity, and more preferably 0.36 or more, 0.37 or more, 0.38 or more, 0.39 or more, 0.40 or more, 0.41 or more, and 0.42 or more in that order. From the viewpoint of improving thermal stability, the mass ratio ((CaO+MgO)/(MgO+CaO+SrO+BaO+ZnO) is preferably 1.00 or less, and is more preferably 0.95 or less, 0.90 or less, 0.89 or less, 0.88 or less, 0.87 or less, 0.86 or less, 0.85 or less, 0.84 or less, 0.83 or less, 0.80 or less, and 0.78 or less in that order.

In the glass composition C of the molding glass material according to this embodiment, the alkaline earth metal oxides MgO, CaO, SrO, BaO, and ZnO lower the liquidus temperature and improve thermal stability. On the other hand, increasing their contents tends to reduce chemical durability and _/ or weather resistance. Furthermore, _SiO2 and _B2O3 improve thermal stability and reheat devitrification, but increasing their contents tends to reduce meltability. From the above viewpoints, the mass ratio of the total content of _SiO2 and _B2O3 to _the total content of MgO, CaO, SrO, _BaO , and ZnO (( _SiO2 + _B2O3 ) / (MgO + CaO + SrO + BaO + ZnO)) is preferably 0.40 or more, more preferably 0.45 or more, 0.50 or more, 0.52 or more, 0.54 or more, 0.56 or more, 0.57 or more, 0.58 or more, 0.59 or more, 0.60 or more, 0.61 or more, 0.70 or more, 0.80 or more, 0.90 or more, 1.00 or more, and 1.10 or more in that order, and is preferably 2.00 or less, and more preferably 1.80 or less, 1.60 or less, 1.55 or less, 1.50 or less, 1.45 or less, 1.40 or less, and 1.35 or less in that order.

In the glass material for molding according to this embodiment, in the case of glass composition C, the MgO content is preferably 0.00% or more. Furthermore, the MgO content is preferably 15.00% or less, and more preferably 12.00% or less, 9.00% or less, 7.00% or less, 6.00% or less, 5.00% or less, 4.00% or less, 3.50% or less, 3.00% or less, 2.50% or less, and 2.10% or less, in that order.

In the glass material for molding according to this embodiment, in the case of glass composition C, the SrO content is preferably 0.00% or more, and more preferably 0.10% or more, 0.20% or more, 0.25% or more, 0.26% or more, 0.27% or more, 0.28% or more, 0.29% or more, 0.30% or more, and 0.31% or more in that order. Furthermore, the SrO content is preferably 15.00% or less, and more preferably 12.00% or less, 10.00% or less, 9.00% or less, 8.50% or less, 8.00% or less, 7.50% or less, 7.00% or less, 6.50% or less, and 6.00% or less in that order.

In the glass material for molding according to this embodiment, in the case of glass composition C, the BaO content is preferably 0.00% or more, and more preferably 0.10% or more, 0.20% or more, 0.30% or more, 0.40% or more, 0.50% or more, 0.60% or more, 0.70% or more, 0.80% or more, 0.90% or more, 1.00% or more, 1.10% or more, 1.20% or more, and 1.30% or more in that order. Furthermore, the BaO content is preferably 25.00% or less, and more preferably 22.00% or less, 20.00% or less, 19.00% or less, 18.00% or less, 17.00% or less, 16.50% or less, 16.00% or less, 15.50% or less, 15.25% or less, and 15.00% or less in that order.

MgO, CaO, SrO, and BaO are all glass components that improve the thermal stability and devitrification resistance of the glass. From the perspectives of high dispersibility and further reducing the specific gravity, as well as improving the thermal stability and devitrification resistance of the glass, it is preferable that the content of each of these glass components be within the above-mentioned ranges.

In the glass material for molding according to this embodiment, in the case of glass composition C, the ZnO content is preferably 0.00% or more. Furthermore, the ZnO content is preferably 10.00% or less, and more preferably 9.00% or less, 8.00% or less, 7.00% or less, 6.00% or less, 5.00% or less, 4.00% or less, 3.00% or less, and 2.00% or less, in that order. ZnO is a glass component that functions to improve the thermal stability of the glass. From the viewpoint of further reducing the specific gravity, improving the thermal stability of the glass, and obtaining more desirable optical constants, the ZnO content is preferably within the above range.

In the glass material for molding according to this embodiment, in the case of glass composition C, the total content of the rare earth oxides La ₂ O ₃ , Gd ₂ O ₃ and Y ₂ O ₃ (La ₂ O ₃ + Gd ₂ O ₃ + Y ₂ O ₃ ) is preferably more than 0% from the viewpoint of achieving a high refractive index and low dispersion, and more preferably 0.50% or more, 1.00% or more, 1.33% or more, 1.50% or more, 2.00% or more, 2.50% or more, and 3.00% or more, in that order. From the viewpoint of further reducing the specific gravity, the total content of _La2O3 , _{Gd2O3 and Y2O3} ( _{La2O3 + Gd2O3} + _Y2O3 ) is preferably 30.00% _or less, and is more preferably 29.00% _or less, 28.00% or less, _26.00 % or less, 24.00% or less, 22.00% or less, 20.00% _or less, 18.00% or less, 16.00% or less, 15.00% or less, 14.50% or less, 14.00% or less, 13.50% or less, 13.00% or less, 12.50% or less, and 12.00% or less in that order.

In the glass composition C of the molding glass material according to this embodiment, BaO and the rare earth oxides La ₂ O ₃ , Gd ₂ O ₃ and Y ₂ O ₃ are all components that contribute to low dispersion (i.e., increase the Abbe number νd), but as their contents increase, the specific gravity of the glass tends to increase. From _the above viewpoints, in the case of glass composition C, the total content of BaO and the rare earth oxides _La2O3 , _{Gd2O3 , and Y2O3} (BaO + _La2O3 + _Gd2O3 + _{Y2O3 )} is preferably 30.00% _or less, and more preferably 29.00% or less, 28.00% or less, 27.00% or less, 26.00% or less, 25.00% or less, 24.50% or less, 24.00% or less, 23.50% or less, and 23.00% or less in that _order . Furthermore, from the viewpoint of increasing the Abbe number vd, the total content of BaO, La ₂ O ₃ , Gd ₂ O ₃ and Y ₂ O ₃ (BaO + La ₂ O ₃ + Gd ₂ O ₃ + Y ₂ O ₃ ) is preferably more than 0%, and more preferably 1.00% or more, 2.00% or more, 3.00% or more, 4.00% or more, 5.00% or more, 6.00% or more, 7.00% or more, 7.50% or more, 8.00% or more, and 8.50% or more in that order.

In the glass material for molding according to this embodiment, in the case of glass composition C, both BaO and La ₂ O ₃ are low-dispersion components, but BaO has a smaller effect of increasing the refractive index than La ₂ O _3. Therefore, from the viewpoint of increasing the refractive index, the mass ratio of the BaO content to the La ₂ O ₃ content (BaO/La ₂ O ₃ ) is preferably 8.30 or less, and is more preferably 8.00 or less, 7.50 or less, 7.00 or less, 6.50 or less, 6.00 or less, 5.50 or less, 5.40 or less, 5.30 or less, 5.20 or less, 5.10 or less, 5.00 or less, 4.90 or less, 4.80 or less, and 4.70 or less in that order.
In the glass material for molding according to this embodiment, in the case of glass composition C, the mass ratio (BaO/La ₂ O ₃ ) may be 0 or 0.00 or more. From the viewpoint of maintaining the thermal stability of the glass, the mass ratio (BaO/La ₂ O ₃ ) is preferably more than 0.00, and is more preferably 0.01 or more, 0.02 or more, 0.03 or more, 0.04 or more, 0.05 or more, 0.06 or more, 0.07 or more, 0.08 or more, 0.09 or more, 0.10 or more, and 0.11 or more in that order.

In the glass composition C of _the molding glass material according to this embodiment, the rare earth oxides _La2O3 , _Gd2O3 , and _Y2O3 increase the refractive index and contribute to low dispersion, _but their contents tend to decrease thermal stability. Also _{, SiO2 and B2O3} improve thermal stability, but their contents tend to decrease meltability and the refractive index. From the above viewpoints, the mass ratio of the total content of _SiO2 and _B2O3 to the total content _{of La2O3} , _Gd2O3 , _{and Y2O3} (( _SiO2 + _B2O3 )/( _La2O3 + _Gd2O3 + _Y2O3 )) is preferably more than 0.00, _and is more preferably 0.25 or more, 0.50 or _more , _0.75 or more, _1.00 or more, _1.25 or more, _1.50 or more, 1.75 or more, 1.80 or more, and 1.85 or more in that order, and is preferably 7.47 or less, and more preferably 7.40 or less, 7.35 or less, 7.30 or less, and 7.25 or less in that order.

In the glass material for molding according to this embodiment, in the case of glass composition C, La ₂ O ₃ , Gd ₂ O ₃ , and Y ₂ O ₃ are all components that can increase the refractive index of the glass, but Gd ₂ O ₃ and Y ₂ O ₃ are components that increase the specific gravity compared to La ₂ O _3. Therefore, from the viewpoint of further reducing the specific gravity, the mass ratio of the La ₂ O ₃ content to the total content of La 2 O ₃ , Gd ₂ O ₃ , and Y ₂ O ₃ (La ₂ O ₃ / (La ₂ O ₃ + Gd ₂ O ₃ + Y _{2 O 3} )) is preferably more than 0.00, and more preferably 0.10 or more, 0.20 or more, 0.30 or more, 0.40 or more, 0.50 or more, 0.60 or more, 0.70 or more, and 0.75 or more, in that order. The mass ratio (La ₂ O ₃ /(La ₂ O ₃ +Gd ₂ O ₃ +Y ₂ O ₃ )) can be 1.00 or less.
From _the same viewpoint, in the case of glass _composition C, the mass ratio of the _Gd2O3 content to the total content of _La2O3 , _Gd2O3 , _{and Y2O3} ( _Gd2O3 /( _La2O3 + _Gd2O3 + _{Y2O3 )} ) is preferably less than 1.00, _{and is} more preferably 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, 0.50 or less, 0.40 _or less, 0.30 or less, _0.25 or less, and 0.20 or _less , in that order. The mass ratio ( _Gd2O3 /( _{La2O3 + Gd2O3 + Y2O3} )) can be 0.00 or _more .
From the same viewpoint, in the case of glass composition C, the mass ratio of the _{Y2O3 content to the total content of La2O3, Gd2O3, and Y2O3 ( Y2O3 / ( La2O3 + Gd2O3 + Y2O3 ) ) is preferably} less than 1.00, and is more preferably 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, 0.50 _or less, 0.40 or less _{, 0.30} or less, and 0.25 or less _, in that order. The mass ratio ( _Y2O3 /( _{La2O3 + Gd2O3} + _Y2O3 )) can be 0.00 or _more .

In the glass material for molding according to this embodiment, in the case of glass composition C, from the above viewpoint, the contents of the above components which are rare earth oxides are preferably in the following ranges.
_{The La2O3} content is preferably 0.00% or more, more preferably more than 0.00%, 0.50% or more, 1.00% or more, 1.33% or more, 1.50% or more, 2.00% or more, 2.50% or more, 2.75% or more, and 3.00% or more. _{The La2O3} content is preferably 30.00% or less, more preferably 25.00% or less, 20.00% or less, 18.00% or less, 16.00% or less, 15.00% or less, 14.00% or less, 13.50% or less, 13.00% or less, 12.50% or less, and 12.00% or less.
The _Gd2O3 content is preferably 0.00% or more. _{The Gd2O3} content _is preferably 10.00% or less, and more preferably 9.00% or less, 8.00% or less, 7.00% or less, 6.00% or less, 5.00% or less, 4.00% or less, 3.00% or less, and 2.00% or less in that order.
The _Y2O3 content is preferably 0.00% or more. _{The Y2O3 content is} preferably 10.00% or less, and more preferably 9.00% or less, 8.00% or less, 7.00% or less, 6.00% or less, 5.00% or less, 4.00% or less, 3.00% or less, and 2.00% or less in that order.

In the glass material for molding according to this embodiment, in the case of glass composition C, La ₂ O ₃ has the function of increasing the refractive index of the glass, and B ₂ O ₃ tends to decrease the refractive index of the glass. Therefore, from the viewpoint of achieving an even higher refractive index, the mass ratio of the La ₂ O ₃ content to the B ₂ O ₃ content (La ₂ O ₃ /B ₂ O ₃ ) is preferably 1.30 or more, and more preferably 1.35 or more, 1.40 or more, 1.45 or more, 1.50 or more, 1.55 or more, 1.60 or more, 1.65 or more, 1.70 or more, and 1.72 or more in that order. From the viewpoint of further reducing the specific gravity, the mass ratio (La ₂ O ₃ /B ₂ O ₃ ) is preferably 20.00 or less, and more preferably 18.00 or less, 16.00 or less, 14.00 or less, 13.00 or less, 12.00 or less, 11.50 or less, 11.00 or less, 10.50 or less, and 10.00 or less in that order.

In the glass material for molding according to this embodiment, in the case of glass composition _{C, the mass ratio of the B2O3 content to the La2O3 content (B2O3/La2O3 ) is preferably 0.79 or less ,} and more preferably 0.78 or less, 0.77 or less, 0.76 or less, 0.75 or less, 0.70 or less, 0.65 or less, 0.64 or less, 0.62 or less, 0.61 or less, 0.60 or less, 0.59 or less, 0.58 or less, _0.57 or less, and 0.50 or less _, in that order. The mass ratio ( _La2O3 / _B2O3 ) is preferably 0.00 or more, and more preferably greater than 0.00.

In the glass material for molding according to this embodiment, in the case of glass composition C, rare earth oxides can increase the refractive index of the glass, but as the content of rare earth oxides increases, the thermal stability decreases and the meltability of the glass tends to decrease. Therefore, from the viewpoint of further increasing the refractive index while maintaining the thermal stability of the glass, _the mass ratio of the total content of _La2O3 , _Gd2O3 , and _Y2O3 to the total content of _{BaO, La2O3 , Gd2O3} , _{and Y2O3 (} ( _La2O3 + _Gd2O3 + _{Y2O3 )} /(BaO + _La2O3 + _Gd2O3 + _{Y2O3 )} ) is preferably 1.00 or less, and is more preferably less than _1.00 , _0.99 or less, _0.98 or less, _0.97 or _less , 0.96 or less, _0.95 or less, 0.94 or less, 0.93 or less, 0.92 or less, 0.91 or less, and 0.90 or less, in that order. The _mass ratio ( _{( La2O3} + _Gd2O3 + _Y2O3 )/(BaO+ _La2O3 + _{Gd2O3 + Y2O3} )) is preferably more than _0.00 , _and is more preferably 0.05 or more, _0.06 or more, 0.07 or more, 0.08 or more, 0.09 or more, 0.10 or more, 0.11 or more, 0.12 or more, 0.13 or more, 0.14 or more, 0.15 or more, 0.16 or more, 0.17 or more, 0.18 or more, and 0.20 or more in that order.

In the glass material for molding according to this embodiment, in the case of glass composition C, rare earth oxides can increase the refractive index of the glass, but the meltability of the glass tends to decrease as their content increases. On the other hand, alkaline earth metal oxides can increase the meltability of the glass, but the refractive index tends to decrease as their content increases. Therefore, from the viewpoint of further increasing the refractive index while maintaining the meltability of the glass, the mass ratio of the total content of _La2O3 , _Gd2O3 , and _Y2O3 to the total content of _MgO , CaO, _SrO , _{BaO, ZnO, La2O3, Gd2O3 , and Y2O3 is ( ( La2O3} + _{Gd2O3 +Y2O3 ) /} (MgO+CaO+SrO+BaO+ _ZnO + _{La2O3 + Gd2O3 + Y2O3 )} )) is preferably more than 0.00, and is more preferably 0.01 or more, 0.02 or more, 0.03 or more, 0.04 or more, 0.05 or more, 0.06 or more, 0.07 or more, and 0.08 or more in that order, and is preferably 0.85 or less, and more preferably 0.80 or less, 0.75 or less, 0.70 or less, 0.65 or less, 0.60 or less, 0.55 or less, 0.50 or less, 0.45 or less, 0.44 or less, 0.43 or less, 0.42 or less, 0.41 or less, and 0.40 or less in that order.

In the glass material for molding according to this embodiment, in the case of glass composition C, rare earth oxides can increase the refractive index of the glass, but increasing their content tends to decrease the thermal stability of the glass. On the other hand, B ₂ O ₃ can increase the thermal stability of the glass, but increasing its content tends to decrease the refractive index. Therefore, from the viewpoint of further increasing the refractive index while maintaining the thermal stability of the glass, _the mass ratio of _{the B2O3} content to the total content of _BaO , _La2O3 , _Gd2O3 , and _Y2O3 ( _B2O3 /(BaO+ _La2O3 + _Gd2O3 + _{Y2O3 )} ) is preferably 0.00 or _more , more preferably more than 0.00, _0.01 or more, _0.02 or more, and 0.03 or more in that order, _and is preferably 1.00 or less, and more preferably 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, 0.55 or less, 0.50 or less, 0.45 or less, 0.40 or less, and 0.35 or less in that order.

In _the glass composition C of the molding glass material according to this embodiment, _La2O3 , _{Gd2O3 ,} and _Y2O3 function to increase the refractive index of the glass, but a high total content of these elements tends to decrease the thermal stability. On the other _hand , _B2O3 functions to improve _the thermal stability of the glass, but tends to decrease the refractive index. Therefore, from the viewpoint _of increasing _the refractive index while maintaining the thermal stability of the glass, the mass ratio of the total content of _La2O3 , _Gd2O3 , and _Y2O3 to the total content of _B2O3 , _La2O3 , _{Gd2O3 , and Y2O3 ( ( La2O3} + _Gd2O3 + _{Y2O3 )} /( _B2O3 + _La2O3 + _Gd2O3 + _Y2O3 )) is preferably _{0.57 or} more, and more preferably 0.58 or _more , _0.59 or _more , _0.60 or more, _{0.61 or} more, 0.62 or more, 0.63 or more, and 0.64 or more in that order. From the viewpoint of further reducing the specific gravity, the mass ratio (( _La2O3 + _Gd2O3 + _{Y2O3 )} /( _{B2O3 + La2O3} + _Gd2O3 + _Y2O3 )) is preferably 1.00 or less, and is _more preferably _less than 1.00, _{0.99 or less} , 0.98 or less, 0.97 or less, 0.96 or less, 0.95 or less, 0.94 or less, 0.93 or less, 0.92 or less, 0.91 or less, 0.90 or less, 0.89 or less, 0.88 or less, 0.87 or less, 0.86 or less, and 0.85 or less in that order.

In the glass material for molding according to this embodiment, in the case of glass composition C, _La2O3 , _Gd2O3 , _{Y2O3 ,} and _ZrO2 increase the refractive index and improve _the partial dispersion characteristics, but as the _ZrO2 content increases, the meltability of the glass tends to decrease. From the above viewpoints, _the mass ratio of the _ZrO2 content to the total content of _La2O3 , _Gd2O3 , _{Y2O3 ,} and _ZrO2 ( _ZrO2 /( _La2O3 + _Gd2O3 + _Y2O3 + _ZrO2 )) is preferably 0.01 or more, more preferably 0.02 or more, _0.03 or more, _{and 0.04} or more in _that order, and is preferably 5.00 or less, and more preferably 4.00 or less, 3.00 or less, _and 2.00 or less in that order.

In the glass composition C of the molding glass material according to this embodiment, La ₂ O ₃ , Gd ₂ O ₃ , Y ₂ O ₃ and ZrO ₂ are all components that increase the refractive index, but ZrO ₂ has a greater effect of increasing the refractive index and a greater effect of increasing dispersion (decreasing the Abbe number) than La ₂ O ₃ , Gd ₂ O ₃ and Y ₂ O ₃ . From _the viewpoint of maintaining low dispersion, the mass ratio of the content of _ZrO2 to the total content of _La2O3 , _{Gd2O3 ,} and _Y2O3 ( _ZrO2 /( _La2O3 + _Gd2O3 + _Y2O3 )) is preferably 3.30 or less, and more preferably _{3.00 or} less, _{2.90 or} less, 2.80 or less, 2.70 or less, 2.60 or less, 2.50 or less, 2.40 or less, 2.30 or less, 2.20 or less, 2.10 or less, 2.00 or less, 1.90 or less, 1.80 or less, 1.70 or less, 1.60 or less, 1.50 or less, 1.40 or less, 1.30 or less, and 1.25 or less, in that order. _The mass ratio ( _{ZrO2 /} ( _La2O3 + _Gd2O3 + _Y2O3 )) can be 0.00 or more, and from the viewpoint of further increasing the refractive index, _it is preferably more than 0.00, and more preferably 0.01 or more, 0.02 or more, 0.03 or more, 0.04 or more, 0.05 or more, and 0.06 or more in that order.

In the molding glass material according to this embodiment, in the case of glass composition C, the ZrO ₂ content is preferably 7.63% or less from the viewpoint of realizing desirable optical constants and improving partial dispersion characteristics, and is more preferably less than 7.63%, 7.60 or less, 7.50 or less, 7.40 or less, 7.30 or less, 7.20 or less, 7.10 or less, 7.00 or less, 6.90 or less, 6.80 or less, 6.70 or less, 6.60 or less, 6.50 or less, 6.40 or less, 6.30 or less, 6.20 or less, 6.10 or less, 6.00 or less, 5.95 or less, and 5.90 or less, more preferably, in this order, and particularly from the viewpoint of improving reheat devitrification resistance, 6.00 or less, 5.50 or less, 5.00 or less, 4.00 or less, 3.00 or less, and 2.50 or less are more preferable. Furthermore, from the viewpoint of realizing more desirable optical constants and further improving partial dispersion characteristics, the _ZrO2 content is preferably 0.00% or more, and more preferably more than 0.00%, 0.10% or more, 0.20% or more, 0.30% or more, 0.40% or more, 0.50% or more, 0.60% or more, 0.65% or more, 1.10% or more, and 1.60% or more, in that order.

In the glass composition C of the molding glass material according to this embodiment, MgO, CaO, SrO, _BaO , and ZnO have the function of improving the thermal stability of the glass, but as their contents increase, the refractive index tends to decrease. On the other _hand , _La2O3 , _Gd2O3 , and _Y2O3 have the function of increasing the refractive index, but as their contents increase _, the thermal stability tends to decrease. From the above perspectives, the mass ratio of the total content of MgO, CaO, _SrO , BaO _, and ZnO to the total content of _La2O3 , _Gd2O3 , and _Y2O3 ((MgO+CaO+ _SrO + _{BaO +} ZnO)/( _La2O3 + _Gd2O3 + _{Y2O3 )} )) is preferably more than 0.00, and is more preferably 0.10 or more, 0.20 or more, 0.30 or more, 0.40 or more, 0.50 or more, 0.60 or more, 0.70 or more, 0.80 or more, 0.90 or more, 1.00 or more, 1.10 or more, 1.20 or more, 1.30 or more, and 1.40 or more in that order, and is preferably 20.00 or less, and is more preferably 18.00 or less, 16.00 or less, 14.00 or less, 11.09 or less, 11.08 or less, 11.07 or less, 11.06 or less, 11.05 or less, 11.04 or less, 11.03 or less, 11.02 or less, 11.01 or less, and 11.00 or less in that order.

In _the glass material for molding according to this embodiment, in the case of glass composition C, SrO, BaO, _La2O3 , _{Gd2O3 , and Y2O3} are all components effective in maintaining low dispersion. Therefore, from the viewpoint of maintaining even lower dispersion, the total content of SrO, BaO, _La2O3 , _{Gd2O3 , and Y2O3} (SrO + BaO + _La2O3 + _Gd2O3 + _Y2O3 ) is preferably 9.00% or more, and more preferably _9.50 % or more, _10.00 % or _more , 10.50% or more, 11.00% or more, 11.50% or more, 12.00% or more, 12.50% or more, 13.00% or _more , and 13.50% or more in that order.
Furthermore, in the glass material for molding according to this embodiment, in the case of glass composition C, from the viewpoint of further reducing the specific gravity, the total content (SrO + BaO + La ₂ O ₃ + Gd ₂ O ₃ + Y ₂ O ₃ ) is preferably 45.00% or less, and more preferably 40.00% or less, 35.00% or less, 30.00% or less, 29.00% or less, 28.00% or less, 27.00% or less, 26.00% or less, and 25.00% or less in that order.

In the glass composition C of the molding glass material according to this embodiment, _La2O3 , _{Gd2O3 ,} and _Y2O3 are components that increase the refractive index, and _SiO2 is a component that maintains the thermal stability of the _glass . From _{the viewpoint of further} increasing the refractive index _, the mass ratio of the _total content of _La2O3 , _Gd2O3 , _{and Y2O3} to the total content of _La2O3 , _{Gd2O3 ,} and _{SiO2 (} ( _{La2O3 + Gd2O3} + _Y2O3 )/( _La2O3 + _Gd2O3 + _{Y2O3 + SiO2 )} ) is preferably 0.12 or more, and more preferably _0.13 or _more . From the viewpoint of maintaining _the thermal stability of the glass _{, the} mass ratio (( _La2O3 + _Gd2O3 + _Y2O3 )/( _La2O3 + _Gd2O3 + _Y2O3 + _SiO2 )) is preferably 0.70 _or less, and more preferably 0.60 or less, _0.50 or _less , 0.49 or less, 0.48 or less, 0.47 or less, 0.46 or less, 0.45 or less, 0.44 or less, 0.43 or less, 0.42 or less, and 0.41 or less in that order.

In the glass material for molding according to this embodiment, in the case of glass composition C, the mass ratio of the total content of _{SiO2 and CaO} to the total content of _TiO2 , _Nb2O5 , _Ta2O5 , _WO3 and _Bi2O3 (( _SiO2 + CaO)/( _TiO2 + _Nb2O5 + _Ta2O5 + _WO3 + _{Bi2O3 ) )} is such _that the denominator is the total content of components that have a significant effect of increasing the refractive index, and the numerator is the total content of components _that are effective in reducing dispersion and specific gravity. From the viewpoints of achieving a high refractive index, maintaining low dispersion, reducing specific gravity, and maintaining thermal stability, the mass ratio ₍ ( _SiO2 + CaO)/( _TiO2 + _Nb2O5 + _Ta2O5 + _WO3 + _{Bi2O3 )} ) is preferably 1.20 or less, and more preferably _1.09 or less, 1.08 or less, 1.07 or less, 1.06 or less, 1.05 or less, 1.04 or less, 1.03 or less, 1.02 or less, 1.01 or less, 0.99 or less, 0.94 or less, 0.89 or less, and 0.86 or less in that order. Furthermore, from the viewpoint of achieving a higher refractive index, maintaining even lower dispersion, and further reducing the specific gravity, _the mass ratio (( _SiO2 +CaO)/( _TiO2 + _Nb2O5 + _Ta2O5 + _WO3 + _Bi2O3 )) is preferably _{0.25 or} more, and more preferably 0.30 or more, 0.35 or more, 0.40 or more, 0.42 or more, 0.44 or more, 0.46 or more, 0.48 or more, 0.50 or more, 0.52 or more, 0.54 or more, and 0.55 or more in that order.

In the glass material for molding according to this embodiment, in the case of glass composition C, among the components _that increase the refractive index _{, ZrO2, TiO2, Nb2O5, Ta2O5 , WO3 , and Bi2O3 , ZrO2 has} a relatively small effect of increasing dispersion. Therefore, from the viewpoint of maintaining even lower dispersion, the mass ratio of the _ZrO2 content to the total content of _TiO2 , _{Nb2O5 , Ta2O5} , _{WO3 ,} and _Bi2O3 ( _ZrO2 / _{( TiO2} + _Nb2O5 + _Ta2O5 + _WO3 + _Bi2O3 )) is preferably 0.00 or more, and more preferably 0.01 _{or more} , _and more preferably 0.02 or more. From the viewpoint of maintaining the thermal stability of the glass and maintaining resistance to devitrification when the glass is heated, softened, and press-molded (stability during reheat press molding: also referred to _as reheat press moldability), the mass ratio ( _ZrO2 /( _TiO2 + _Nb2O5 + _Ta2O5 + _WO3 + _Bi2O3 )) is preferably 0.21 or less, and more preferably _{0.20 or} less, 0.19 or less, 0.18 or less, 0.17 or less, 0.16 or less, 0.15 or less, 0.12 or less, 0.10 or less, 0.08 or less, and 0.06 or less, in that order.

In the glass material for molding according to this embodiment, in the case of glass composition C, the lower limit of the total content of _Li2O , _Na2O , and _K2O [ _Li2O + _Na2O + _K2O ] is preferably 0.1%, and more preferably 0.2%, 0.5%, 1.0%, 1.2%, and 1.5% in that order. The upper limit of the total content is preferably 20%, and more preferably 15%, 10%, 8%, 6%, 4%, and 2% in that order.

In glass composition C, when the lower limit of the total content [Li ₂ O + Na ₂ O + K ₂ O] satisfies the above range, the meltability of the glass can be improved and an increase in the liquidus temperature can be suppressed. When the upper limit of the total content satisfies the above range, the viscosity of the glass can be increased, the crystallization rate of the glass melt can be reduced, and stability during reheating can be improved.

In the glass material for molding according to this embodiment, in the case of glass composition C, the alkali metal oxides Li ₂ O, Na ₂ O, K ₂ O, and Cs ₂ O have the function of improving partial dispersion characteristics, lowering the liquidus temperature, and improving the thermal stability of the glass. From these viewpoints, the total content of Li ₂ O, Na ₂ O, K ₂ O, and Cs ₂ O (Li ₂ O + Na ₂ O + K ₂ O + Cs ₂ O) is preferably 0.00% or more, and more preferably in the following order: more than 0.00%, 0.05% or more, 0.10% or more, 0.15% or more, 0.20% or more, 0.25% or more, 0.28% or more, 0.60% or more, 1.10% or more, 1.30% or more, and 1.60% or more. From the viewpoint of improving chemical durability and weather resistance, the total content ( _Li2O + _Na2O + _K2O + _Cs2O ) is preferably 20.00% or less, and more preferably 18.00% or less, 16.00% or less, 14.00% or less, 12.00% or less, 10.00% or less, 9.00% or less, 8.00% or less, 7.00% or less, 6.50% or less, 6.00% or less, 5.50% or less, 5.00% or less, 4.50% or less, 3.90% or less, 2.90% or less, and 2.40% or less in that order.

In the glass composition C of the molding glass material according to this embodiment, _the upper _{limit of} the mass ratio of the total content of _Li2O , _Na2O , _K2O , and _Cs2O to the total content of SiO2, _P2O5 , and _B2O3 [( _Li2O + _Na2O + _K2O + _Cs2O )/( _SiO2 + _P2O5 + _B2O3 )] is preferably 1.0, and more preferably 0.7, 0.5, _0.4, 0.3, 0.2, 0.1, 0.09, _{and 0.08} in this order. The lower limit of this mass ratio is preferably 0.001, and more preferably 0.01, 0.02, 0.03, 0.04, 0.05, and 0.06 in this order.

In glass composition C, _if the mass ratio [( _Li2O + _Na2O + _K2O + _Cs2O )/( _SiO2 + _P2O5 + _B2O3 )] is too low, the meltability may deteriorate. On the other hand, if it is too high, the viscosity of the glass during melting may decrease, the thermal stability of the melt may decrease, and _the stability during reheating may deteriorate.

In the glass composition C of the molding glass material according to this embodiment, _the upper limit of the mass ratio of the total content of _Li2O , _Na2O , _K2O , and _Cs2O to the total content of _Nb2O5 , _TiO2 , _WO3 , and _Bi2O3 [( _Li2O + _Na2O + _K2O + _Cs2O )/( _Nb2O5 + _TiO2 + _WO3 + _Bi2O3 )] is preferably 1.0, and more preferably 0.5, 0.3, _0.2 , 0.1, 0.09, _0.08 , 0.07, 0.06, and _0.05 in this order. The lower limit of this mass ratio is preferably 0.005, and more preferably 0.01, 0.02, 0.03, and 0.04 in this order.

In glass composition C, _if the mass ratio [( _Li2O + _Na2O + _K2O + _Cs2O )/( _Nb2O5 + _TiO2 + _WO3 + _Bi2O3 )] is too low, the partial dispersion ratio Pg,F increases and the transmittance may deteriorate. On the other hand, if _it is too high, the Abbe number increases, the refractive index decreases, and stability during reheating may deteriorate.

In the glass material for molding according to this embodiment, in the case of glass composition C, alkali metal oxides and alkaline earth metal oxides can contribute to maintaining the meltability and thermal stability of the glass, but as their contents increase, the meltability and thermal stability of the glass tend to decrease. Therefore, from the viewpoint of maintaining the meltability and thermal stability of the glass, it is necessary to select the total content of the alkali metal oxides Li 2 O, Na 2 O, K 2 O, and Cs 2 O and the alkaline earth metal oxides MgO, CaO, SrO, and BaO (Li 2 O + Na 2 O + K 2 O + Cs 2 O) as the total content of the alkali metal oxides Li ₂ O, Na ₂ O, K 2 O, and Cs 2 O and the alkaline earth metal oxides MgO, CaO, SrO, and BaO (Li 2 O + Na 2 O + K ₂ O + Cs ₂ O) as the total content of the alkali metal oxides Li 2 O, Na 2 O, K 2 O, and Cs 2 O as the total content of the alkaline earth metal oxides MgO, CaO, SrO, and BaO (Li 2 O + Na 2 O + K 2 O + Cs _{2 O)} as the total content of the alkali metal oxides Li ₂ O, Na ₂ O, K ₂ O, and Cs 2 O) as the total content of the alkali ... The total content of MgO, MgO, CaO, SrO, and BaO is preferably 5.00% or more, more preferably 7.00% or more, 9.00% or more, 10.00% or more, 12.00% or more, 14.00% or more, 15.00% or more, 16.00% or more, 17.00% or more, 18.00% or more, and 18.50% or more in that order, and is preferably 50.00% or less, and more preferably 48.00% or less, 46.00% or less, 44.00% or less, 43.00% or less, 42.00% or less, 41.00% or less, 40.00% or less, 39.00% or less, 38.00% or less, 37.00% or less, 36.00% or less, 35.00% or less, 34.50% or less, and 34.00% or less in that order.

In the glass material for molding according to this embodiment, in the case of glass composition C, alkali metal oxides and alkaline earth metal oxides have the function of lowering the liquidus temperature and improving thermal stability, but if their contents relative to the network-forming components of the glass increase, chemical durability and weather resistance tend to decrease. Also, _SiO2 and _B2O3 have _the function of improving thermal stability, but if their contents increase, meltability tends to decrease. From _these viewpoints, the mass ratio of the total content of _Li2O , _Na2O , _K2O , _Cs2O , MgO, CaO, _SrO , and BaO to the total content of SiO2 and _B2O3 ( _{( Li2O} +Na2O+ _K2O + _Cs2O +MgO+CaO+SrO+BaO)/( _SiO2 + _{B2O3 )} )) is preferably 0.50 or more, more preferably 0.52 or more, 0.54 or more, 0.56 or more, 0.58 or more, 0.60 or more, 0.62 or more, 0.64 or more, 0.66 or more, 0.68 or more, 0.70 or more, 0.72 or more, 0.74 or more, 0.75 or more, 0.76 or more, 0.77 or more, 0.78 or more, and 0.79 or more in that order, and is preferably 5.00 or less, more preferably 4.50 or less, 4.00 or less, 3.50 or less, 3.00 or less, 2.50 or less, 2.00 or less, 1.90 or less, 1.80 or less, 1.70 or less, 1.65 or less, and 1.60 or less in that order.

In the glass material for molding according to this embodiment, in the case of glass composition C, of Li ₂ O, Na ₂ O, and K ₂ O, Li ₂ O is the component that is least likely to lower the refractive index. Therefore, from the viewpoint of achieving a higher refractive index, the mass ratio of the Li ₂ O content to the total content of Li ₂ O, Na ₂ O, and K ₂ O (Li ₂ O/(Li ₂ O + Na ₂ O + K ₂ O)) is preferably 0.00 or more, and more preferably more than 0.00, 0.10 or more, 0.20 or more, 0.30 or more, 0.40 or more, and 0.45 or more in that order. On the other hand, the mass ratio (Li ₂ O/(Li ₂ O + Na ₂ O + K ₂ O)) can be, for example, 1.00 or less, and from the viewpoint of suppressing a decrease in reheat devitrification resistance, it can also be 0.99 or less, 0.98 or less, 0.95 or less, 0.90 or less, 0.80 or less, 0.70 or less, 0.65 or less, 0.60 or less, or 0.50 or less.

In the glass material for molding according to this embodiment, in the case of glass composition C, Li ₂ O, Na ₂ O, K ₂ O, MgO, CaO, SrO, BaO, and ZnO function to improve the thermal stability and meltability of the glass, but as the total content of Li ₂ O, Na ₂ O, and K ₂ O increases, the glass tends to exhibit high dispersibility. Therefore, from the viewpoint of obtaining more desirable dispersibility, the mass ratio of the total content of Li ₂ O, Na ₂ O, and K ₂ O to the total content of MgO, CaO, SrO, BaO, and ZnO ((Li ₂ O + Na ₂ O + K ₂ O) / (MgO + CaO + SrO + BaO + ZnO)) is preferably 0.00 or more, more preferably more than 0.00, 0.01 or more, 0.02 or more, 0.03 or more, 0.04 or more, and 0.05 or more in that order, and is preferably 4.00 or less, and more preferably 3.50 or less, 3.00 or less, 2.50 or less, 2.00 or less, 1.50 or less, 1.00 or less, 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, 0.50 or less, 0.40 or less, and 0.35 or less in that order.

In the glass material for molding according to this embodiment, in the case of glass composition C, the mass ratio of the total content of Li ₂ O, Na ₂ O, and K ₂ O to the total content of SiO ₂ and B ₂ O ₃ ((Li ₂ O + Na ₂ O + K ₂ O)/(SiO ₂ + B ₂ O ₃ )) is preferably 1.00 or less, and more preferably 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, 0.50 or less, 0.40 or less, 0.35 or less, 0.30 or less, and 0.25 or less, in that order, from the viewpoint of maintaining thermal stability and/or maintaining reheat press formability. From the viewpoint of maintaining meltability and/or reducing the partial dispersion ratio to provide a glass suitable for correcting high-order chromatic aberrations, the mass ratio ((Li ₂ O + Na ₂ O + K ₂ O)/(SiO ₂ + B ₂ O ₃ )) is preferably 0.00 or greater, and more preferably greater than 0.00, 0.01 or greater, 0.02 or greater, 0.03 or greater, 0.04 or greater, and 0.05 or greater in that order.

In the glass material for molding according to this embodiment, in the case of glass composition C, the Li ₂ O content is preferably 0.00% or more, and more preferably 0.05% or more, 0.10% or more, 0.15% or more, 0.20% or more, 0.25% or more, 0.30% or more, 0.40% or more, 0.50% or more, and 0.60% or more in this order. Furthermore, the Li ₂ O content is preferably 14.00% or less, and more preferably 12.00% or less, 10.00% or less, 8.00% or less, 7.00% or less, 6.50% or less, 6.00% or less, 5.50% or less, and 5.00% or less in this order. Setting the _{Li 2} O content within the above range is preferable from the viewpoint of realizing more desirable optical constants and from the viewpoint of maintaining chemical durability, weather resistance, and stability during reheating.

In the glass material for molding according to this embodiment, in the case of glass composition C, the Na ₂ O content is preferably 0.00% or more. The Na ₂ O content is preferably 10.00% or less, and more preferably 8.00% or less, 7.00% or less, 6.00% or less, 5.00% or less, 4.00% or less, 3.00% or less, and 2.00% or less, in that order. Setting the _{Na 2} O content within the above range is preferred from the viewpoint of improving partial dispersion characteristics.

In the glass material for molding according to this embodiment, in the case of glass composition C, the K ₂ O content is preferably 0.00% or more. The K ₂ O content is preferably 10.00% or less, and more preferably 8.00% or less, 7.00% or less, 6.00% or less, 5.00% or less, 4.00% or less, 3.00% or less, and 2.00% or less, in that order. Setting the _{K 2} O content within the above range is preferred from the viewpoint of improving the thermal stability of the glass.

In the glass material for molding according to this embodiment, in the case of glass composition C, the Cs ₂ O content is preferably 5.00% or less, and more preferably 4.00% or less, 3.00% or less, 2.00% or less, 1.00% or less, and 0.50% or less in that order, and may even be 0%.

In the glass material for molding according to this embodiment, in the case of glass composition C, the total content of TiO ₂ , Nb ₂ O ₅ , Ta ₂ O ₅ , WO ₃ and Bi ₂ O ₃ (TiO ₂ + Nb ₂ O ₅ + Ta ₂ O ₅ + WO ₃ + Bi ₂ O ₃ ) is preferably 30.00% or more from the viewpoint of achieving an even higher refractive index, and is more preferably 31.00% or more, 32.00% or more, 33.00% or more, 34.00% or more, 35.00% or more, 36.00% or more, 36.50% or more, 37.00% or more, and 37.55% or more in that order. From the viewpoint of further reducing the specific gravity and improving the thermal stability, the total content of TiO ₂ , Nb ₂ O ₅ , Ta ₂ O ₅ , WO ₃ and Bi ₂ O ₃ (TiO ₂ + Nb ₂ O ₅ + Ta ₂ O ₅ + WO ₃ + Bi ₂ O ₃ ) is preferably 60.00% or less, and more preferably 58.00% or less, 56.00% or less, 54.00% or less, 52.00% or less, 51.00% or less, 50.00% or less, 49.50% or less, 49.00% or less, and 48.50% or less, in that order.

In the glass material for molding according to this embodiment, in the case of glass composition C, the mass ratio of the total content of _{SiO2 and B2O3 to the total content of TiO2, Nb2O5, Ta2O5, WO3 , and Bi2O3 ( ( SiO2+B2O3)/(TiO2+Nb2O5 + Ta2O5 + WO3 + Bi2O3 ) ) is preferably} 0.75 _or less, from the viewpoint of obtaining a glass with a high refractive index while suppressing an increase in specific gravity. In addition to the above _, from the viewpoint of realizing _a desirable Abbe number vd, improving partial dispersion characteristics, and improving devitrification resistance, the mass ratio (( _SiO2 + _{B2O3 )} /( _TiO2 + _Nb2O5 + _{Ta2O5 + WO3 + Bi2O3 )} )) is preferably 0.16 or more, more preferably 0.20 or more, 0.25 or more, 0.30 or more, 0.35 or more, 0.36 or more, 0.37 or more, 0.38 or more, 0.39 or more, 0.40 or more, 0.41 or more, and 0.42 or more in that order, and is preferably 0.75 or less, more preferably 0.74 or less, 0.73 or less, 0.72 or less, 0.71 or less, 0.70 or less, 0.69 or less, 0.68 or less, 0.67 or less, 0.66 or less, 0.65 or less, and 0.64 or less in that order.

In _the molding glass material according to this embodiment, in the case of glass composition C, _SiO2 and _B2O3 act to decrease _{the refractive index and decrease the dispersion (increase the Abbe number), while TiO2, Nb2O5, Ta2O5, WO3 , Bi2O3 , and ZrO2 are high} -refractive-index _, high-dispersion components. From the viewpoint _of further increasing the refractive index, the mass ratio of the total content of _{SiO2 and B2O3} to _the total content of _TiO2 , _Nb2O5 , _Ta2O5 , _WO3 , _{Bi2O3 and ZrO2} (( _SiO2 + _B2O3 ) / ( _TiO2 + Nb2O5 + _Ta2O5 + _WO3 + _{Bi2O3 + ZrO2} )) is preferably 0.64 or less, and more preferably _{0.63 or} less, 0.62 or less, _0.61 or less, _0.60 or less, 0.59 or less, and 0.58 or less in that order.
On the other hand, in the case of glass composition C, from the viewpoint _{of suppressing high dispersion, the mass ratio ((SiO2 + B2O3 ) /} ( _TiO2 + _Nb2O5 + _Ta2O5 + _WO3 + _{Bi2O3 + ZrO2} )) is preferably 0.13 or more, and more preferably 0.15 _or more, _0.20 or more, 0.25 or more, 0.26 or more, 0.27 or more, 0.28 or more, 0.29 or more, 0.30 or more, 0.31 or more, 0.32 or more, 0.33 or more, 0.34 or more, 0.35 or more, 0.36 or more, 0.37 or more, and 0.38 or more in that order.

In the glass material for molding according to this embodiment, in the case of glass composition C _, the mass ratio of the total content of _Li2O , _{Na2O and K2O to the total content of TiO2, Nb2O5 , Ta2O5, WO3 and Bi2O3 ( ( Li2O + Na2O + K2O ) /} ( _TiO2 + _Nb2O5 + _Ta2O5 + _WO3 + _Bi2O3 )) is preferably 0.00 or more, and more preferably 0.01 or _{more ,} from the viewpoint of improving partial dispersion characteristics and _{transmittance} . From the viewpoint of maintaining the thermal stability and/or reheat press formability of the glass, the mass ratio (( _Li2O + _Na2O + _K2O )/( _TiO2 + _Nb2O5 + _Ta2O5 + _WO3 + _Bi2O3 )) is preferably 0.67 or less, and _more preferably 0.60 or less, 0.50 or less, 0.40 or less, _0.30 or less, 0.20 or less, 0.15 or less, _and 0.10 or less in that order.

In the glass composition C of the molding glass material according to this embodiment, MgO, CaO, SrO, BaO, and ZnO function to improve the thermal stability of the glass, but as their contents increase, the refractive index tends to decrease and the glass tends to have lower dispersion. On the other hand, TiO ₂ , Nb ₂ O ₅ , WO ₃ , and Bi ₂ O ₃ tend to increase the refractive index and make the glass more dispersive, but as their contents increase, the thermal stability tends to decrease. From the above viewpoints, the mass ratio of the total content of MgO, CaO, SrO, BaO and ZnO to the total content of TiO ₂ , Nb ₂ O ₅ , Ta ₂ O ₅ , WO ₃ and Bi ₂ O ₃ ((MgO + CaO + SrO + BaO + ZnO) / (TiO ₂ + Nb ₂ O ₅ + Ta ₂ O ₅ + WO ₃ + Bi ₂ O ₃ )) is preferably 0.09 or more, more preferably 0.10 or more, 0.15 or more, 0.20 or more, 0.21 or more, 0.22 or more, 0.23 or more, 0.24 or more, 0.25 or more, 0.26 or more, 0.27 or more, 0.28 or more, 0.29 or more, 0.30 or more, 0.31 or more, 0.32 or more, 0.35 or more, 0.40 or more, and 0.45 or more in that order, and is preferably 1.66 or less, and more preferably 1.60 or less, 1.50 or less, 1.40 or less, 1.30 or less, 1.20 or less, 1.10 or less, 1.00 or less, 0.95 or less, 0.90 or less, 0.88 or less, 0.80 or less, 0.70 or less, 0.60 or less, and 0.50 or less in that order.

In the glass material for molding according to this embodiment, in the case of glass composition C, among MgO, CaO, SrO, BaO, and ZnO, MgO and CaO are components that are more effective than SrO, BaO, and ZnO in suppressing an increase in the specific gravity of the glass and in reducing α _100-300 and α _max . Therefore, from the viewpoint of suppressing an increase in specific gravity, the mass ratio of the total content of ZnO, SrO, and BaO to the total content of MgO and CaO ((ZnO+SrO+BaO)/(MgO+CaO)) is preferably 1.98 or less, and more preferably 1.96 or less, 1.94 or less, 1.92 or less, 1.90 or less, 1.88 or less, 1.86 or less, 1.85 or less, 1.84 or less, 1.83 or less, 1.82 or less, 1.81 or less, 1.80 or less, 1.79 or less, 1.78 or less, 1.50 or less, 1.20 or less, 0.95 or less, 0.80 or less, 0.70 or less, 0.60 or less, and 0.50 or less in that order.

On the other hand, in the glass material for molding according to this embodiment, in the case of glass composition C, the introduction of small amounts of SrO, BaO, and ZnO increases the stability of the glass and also increases the refractive index. Therefore, from the viewpoint of maintaining low dispersion, the mass ratio ((ZnO + SrO + BaO)/(MgO + CaO)) is preferably 0.17 or greater, and more preferably 0.18 or greater, 0.19 or greater, 0.20 or greater, 0.25 or greater, and 0.30 or greater, in that order.

In the glass composition C of the molding glass material according to this embodiment, the lower limit of the mass ratio of the total content of _Li2O , _Na2O , _{and K2O} to the total content of _Nb2O5 and _TiO2 [( _Li2O + _Na2O + _K2O )/( _Nb2O5 + _TiO2 )] is preferably 0.001, and more preferably 0.01, _0.02 , 0.03, and 0.04 in this order. The upper limit of this mass ratio is preferably 1.00, and more preferably 0.50, 0.30, 0.20, 0.10, 0.08, and 0.06 in this order.

In glass composition C, from the viewpoint of obtaining desired optical constants while maintaining the melting characteristics, thermal stability, and stability during reheating of the glass, it is preferable that the mass ratio [(Li ₂ O + Na ₂ O + K ₂ O)/(Nb ₂ O ₅ + TiO ₂ )] be in the above range.

In the glass material for molding according to this embodiment, in the case of glass composition C, when TiO ₂ , Nb ₂ O ₅ , Ta ₂ O ₅ , WO ₃ and Bi ₂ O ₃ are compared with La ₂ O ₃ , Gd ₂ O ₃ and Y ₂ O ₃ in terms of their contribution to dispersibility, TiO ₂ , Nb ₂ O ₅ , Ta ₂ O ₅ , WO ₃ and Bi ₂ O ₃ tend to make the glass less dispersible, while La ₂ O ₃ , Gd ₂ O ₃ and Y ₂ O ₃ tend to make the glass more dispersible. From the viewpoint of obtaining desirable dispersibility, the mass ratio of the total content of _La2O3 , _{Gd2O3 ,} and _Y2O3 to the total content of _TiO2 , _Nb2O5 , _Ta2O5 , _WO3 , and _Bi2O3 (( _La2O3 + _Gd2O3 + _{Y2O3 )} /( _TiO2 + _{Nb2O5 + Ta2O5 + WO3} + _{Bi2O3 ) ) is preferably 0.5 to 1.0 .} )) is preferably more than 0.00, and is more preferably 0.01 or more, 0.02 or more, 0.03 or more, 0.04 or more, 0.05 or more, 0.06 or more, and 0.07 or more in that order, and is preferably 1.00 or less, and is more preferably 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, 0.50 or less, 0.45 or less, 0.40 or less, 0.35 or less, and 0.32 or less in that order.

In the glass material for molding according to this embodiment, in the case of glass composition C, the mass ratio of the _TiO2 content to the total content of _TiO2 , _Nb2O5 , _Ta2O5 , _WO3 , and _Bi2O3 ( _TiO2 /( _TiO2 + _Nb2O5 + _Ta2O5 + _WO3 + _{Bi2O3 )} ) is preferably _0.00 or _more from the viewpoint of achieving _a high refractive index and _a low specific gravity, _and is more preferably greater than 0.00, 0.01 or more, 0.02 or more, 0.03 or more, 0.04 or more, 0.05 or more, 0.06 or more, 0.07 or more, 0.08 or more, 0.09 or more, 0.15 or more, 0.20 or more, 0.25 or more, and 0.30 or more in that order. On the other hand, from the viewpoint of suppressing coloration of the glass and enhancing the stability of the glass, it is preferably 1.00 or less, and more preferably less than 1.00, 0.95 or less, 0.90 or less, 0.85 or less, 0.80 or less, 0.75 or less, 0.73 or less, 0.60 or less, 0.50 or less, 0.45 or less, and 0.40 or less in that order.

In the glass material for molding according to this embodiment, in the case of glass composition _C , the mass ratio of _{the Nb2O5 content to the total content of TiO2, Nb2O5, Ta2O5 , WO3 , and Bi2O3} ( _Nb2O5 /( _TiO2 + _Nb2O5 + _Ta2O5 + _WO3 + _Bi2O3 )) is preferably _{0.00 or more} from the viewpoint of improving partial dispersion characteristics, and is _more preferably greater than _{0.00 ,} 0.01 or more, 0.05 or more, 0.10 or more, 0.15 or more, 0.20 or more, 0.21 or more, 0.22 or more, 0.23 or more, 0.24 or more, 0.25 or more, 0.26 or more, and 0.27 or more in that order. On the other hand, in order to improve the thermal stability of the glass and to improve reheat devitrification resistance, the value is preferably 1.00 or less, and more preferably in the order of less than 1.00, 0.99 or less, 0.98 or less, 0.97 or less, 0.96 or less, 0.95 or less, 0.94 or less, 0.93 or less, 0.92 or less, 0.91 or less, 0.85 or less, 0.80 or less, 0.75 or less, 0.70 or less, and 0.66 or less.

In the glass material for molding according to _this embodiment, in the case of glass composition C _, the mass ratio of _{the Ta2O5} content to the total content of _TiO2 , _Nb2O5 , _Ta2O5 , _{WO3 ,} and _Bi2O3 ( _Ta2O5 /( _TiO2 + _Nb2O5 + _Ta2O5 + _{WO3 + Bi2O3} )) is preferably 1.00 _or less, in order of preference 0.80 or less, 0.60 or less, 0.40 or less, 0.30 or _less , 0.20 or less, and 0.10 or less, _and is particularly preferably 0.

In the molding glass material according to this embodiment, in the case of glass composition C, among the high refractive index, high dispersion components TiO ₂ , Nb ₂ O ₅ , Ta ₂ O ₅ , WO ₃ and Bi ₂ O ₃ , WO ₃ and Bi ₂ O ₃ have a large effect of increasing the specific gravity. _{Therefore, from the viewpoint of further reducing the specific gravity, the mass ratio of the WO3 content to the total content of TiO2, Nb2O5, Ta2O5, WO3 and Bi2O3 ( WO3 / ( TiO2 + Nb2O5 + Ta2O5 + WO3 + Bi2O3 )} ) is preferably 1.00 or less, more preferably 0.80 or less, _0.60 or less, 0.40 or less, _0.30 or less, 0.20 or less, and 0.10 or less in that order, _and is particularly preferably 0.
From _{the same viewpoint, in the case of glass composition C, the mass ratio of the Bi2O3 content to the total content of TiO2, Nb2O5, Ta2O5 , WO3 and Bi2O3 ( Bi2O3 / ( TiO2 + Nb2O5 + Ta2O5} + _WO3 + _Bi2O3 )) is preferably _1.00 or less, and more preferably 0.80 or less, _0.60 or less, 0.40 or less, _0.30 or less, 0.20 or less, and 0.10 or less, in that order _, is particularly preferable, and 0 is particularly preferable.

In _the glass composition C of the molding glass material according to this embodiment, _Li2O3 , _La2O3 , Gd2O3, _Y2O3 , _ZrO2 , _TiO2 , _Nb2O5 , _Ta2O5 , _{WO3 ,} and _Bi2O3 function to increase _the refractive index, while _SiO2 , _B2O3 , _Na2O , _K2O , _MgO , CaO, _SrO , _{BaO ,} and _ZnO tend to decrease _the refractive index. From the viewpoint of achieving a higher refractive index, _the mass _ratio of _SiO2 , _B2O3 , _{Na2O, K2O , MgO} , _CaO , _SrO , BaO, and _ZnO to the total content of Li2O3, La2O3, _Gd2O3 , _Y2O3 , _ZrO2 , _{TiO2 , Nb2O5} , _Ta2O5 , _{WO3 ,} and _Bi2O3 is (( _{SiO2 + B2O3} + _Na2O + _K2O + MgO + CaO + _SrO + BaO + ZnO ₎ / _{( Li2O + La2O3} + _Gd2O3 + _Y2O3 + _ZrO2 + _{TiO 2} +Nb ₂ O ₅ +Ta ₂ O ₅ +WO ₃ +Bi ₂ O ₃ )) is preferably 0.12 or more, more preferably 0.15 or more, 0.20 or more, 0.30 or more, 0.35 or more, 0.40 or more, 0.45 or more, 0.50 or more, and 0.55 or more in that order, and is preferably 2.83 or less, and more preferably 2.80 or less, 2.60 or less, 2.40 or less, 2.20 or less, 2.00 or less, 1.80 or less, 1.70 or less, 1.60 or less, 1.50 or less, 1.40 or less, 1.30 or less, 1.26 or less, 1.25 or less, and 1.24 or less in that order.

In the glass material for molding according to this embodiment, in the case of glass composition C, TiO ₂ , Nb ₂ O ₅ , Ta ₂ O ₅ , WO ₃ , Bi ₂ O ₃ and ZrO ₂ have the function of increasing the refractive index of the glass, but as the ZrO ₂ content increases, the meltability of the glass tends to decrease. From _the above viewpoints, the mass ratio of the _ZrO2 content to _the total content of _TiO2 , _Nb2O5 , _Ta2O5 , _WO3 , _Bi2O3 and _ZrO2 ( _ZrO2 /( _TiO2 + _Nb2O5 + _Ta2O5 + _WO3 + _Bi2O3 + _ZrO2 )) is preferably 0.00 _or more, more preferably 0.01 _or more and _0.02 or more in that order, and is preferably 0.17 or less, _and more preferably 0.16 or less, 0.15 or less, 0.14 or less, and 0.13 or less in that order.

In the glass composition C of the molding glass material according to this embodiment, TiO ₂ , Nb ₂ O ₅ , WO ₃ and ZnO tend to increase the refractive index and make the glass more highly dispersible, but when these are contained in large amounts, the thermal stability of the glass tends to decrease. On the other hand, MgO, CaO, SrO and BaO tend to make the glass more low-dispersible and have the function of improving the thermal stability, but when these are contained in large amounts, the refractive index tends to decrease. From the above viewpoints, the mass ratio of the total content of MgO, CaO, SrO and BaO to _the total content of _TiO2 , _Nb2O5 , _WO3 and ZnO ((MgO + CaO + SrO + BaO) / ( _TiO2 + _Nb2O5 + _WO3 + _ZnO )) is preferably 0.10 or more, more preferably 0.15 or more, 0.20 or more, 0.25 or more, 0.26 or more, 0.27 or more, 0.28 or more, 0.29 or more, 0.30 or more, 0.31 or more, and 0.32 or more in that order, and is preferably 1.50 or less, and more preferably 1.30 or less, 1.20 or less, 1.10 or less, 1.00 or less, 0.95 or less, 0.90 or less, and 0.87 or less in that order.

In the glass material for molding according to this embodiment, in the case of glass composition C, the TiO ₂ content is preferably 0.00% or more, more preferably more than 0.00%, 0.50% or more, 1.00% or more, 1.50% or more, 2.00% or more, 2.50% or more, 3.00% or more, 3.50% or more, 4.00% or more, and more preferably 50.00% or less, 45.0% or less, 40.00% or less, 38.00% or less, 36.00% or less, 35.00% or less, 34.00% or less, 32.00% or less, 31.00% or less, 30.00% or less, 29.50% or less, and 29.00% or less. The TiO ₂ content in the above range is preferable from the viewpoint of realizing more desirable optical constants and reducing the raw material cost of the glass.

In the glass material for molding according to this embodiment, in the case of glass composition C, _{the Nb2O5} content is preferably 0.00% or more, and more preferably in the order of more than 0.00%, 1.00% or more, 2.00% or more, 3.00% or more, 4.00% or more, 5.00% or more, 6.00% or more, 7.00% or more, 8.00% or more, 9.00% or more, 10.00% or more, and 10.50% or _more . Furthermore, the _Nb2O5 content is preferably 60.00% or less, and more preferably in the order of 58.00% or less, 56.00% or less, 54.00% or less, 52.00% or less, 50.00% or less, 49.00% or less, 48.00% or less, 47.00% or less, 46.00% or less, 45.00% or less, and 44.00% or less. The Nb ₂ O ₅ content within the above range is preferable from the viewpoint of realizing more desirable optical constants, further reducing the specific gravity, and improving the partial dispersion characteristics.

In the glass material for molding according to this embodiment, in the case of glass composition C, the _Ta2O5 content can be 0.00% or more. _{The Ta2O5} content is preferably _5.00 % or less, and more preferably 4.00% or less, 3.00% or less, 2.00% or less, 1.00% or less, and 0.50% or less in that order. _{A Ta2O5} content within the above range is preferred from the viewpoints of improving the thermal stability and melting property of the glass and further reducing the specific gravity.

In the glass material for molding according to this embodiment, in the case of glass composition C, the _WO3 content can be 0.00% or more. The _WO3 content is preferably 5.00% or less, and more preferably 4.00% or less, 3.00% or less, 2.00% or less, 1.00% or less, and 0.50% or less in that order. _{A WO3} content within the above range is preferred from the viewpoints of improving the transmittance of the glass, improving the partial dispersion characteristics, and further lowering the specific gravity.

In the glass material for molding according to this embodiment, in the case of glass composition C, the _Bi2O3 content can be 0.00% or more. _{The Bi2O3} content is preferably _5.00 % or less, and more preferably 4.00% or less, 3.00% or less, 2.00% or less, 1.00% or less, and 0.50% or less in that order. _{A Bi2O3} content within the above range is preferred from the viewpoints of improving the thermal stability of the glass, improving the partial dispersion characteristics, and further lowering the specific gravity.

In the glass material for molding according to this embodiment, in the case of glass composition C, _GeO2 functions to increase the refractive index but is a very expensive component. From the viewpoint of reducing the manufacturing cost of the glass, the _GeO2 content can be 0.00% or more, and is preferably 2.00% or less, with 1.50% or less, 1.00% or less, and 0.50% or less being more preferred in that order.

In the glass material for molding according to this embodiment, in the case of glass composition C, in addition to the above components, one or more of P ₂ O ₅ , Al ₂ O ₃ and the like may also be contained.
_{The P2O5 content} can be 0.00% or more, and is preferably 10.00% or less, and is more preferably 8.00% or less, 6.00% or less, 4.00% or less, 2.00% or less, 1.00% or less, and 0.50% or less in that order. _{A P2O5} content within the above range is preferred from the viewpoint of improving the thermal stability and partial dispersion characteristics of the glass.
_{The Al2O3} content can be 0.00% or more, and is preferably 10.00% or less, and is more preferably 8.00% or less, 6.00% or less, 4.00% or less, 2.00% or less, 1.00% or less, and 0.50% or less in that order. _{The Al2O3} content in the above range is preferred from the viewpoint of improving the devitrification resistance and thermal stability of the glass.

Pb, As, Cd, Tl, Be, and Se are each toxic, and therefore it is preferable not to include these elements, i.e., not to introduce these elements into the glass as glass components.
U, Th, and Ra are all radioactive elements, and therefore it is preferable not to include these elements, i.e., not to introduce these elements into the glass as glass components.
V, Cr, Mn, Fe, Co, Ni, Cu, Pr, Nd, Pm, Sm, Eu, Tb, Dy, Ho, Er, Tm, and Ce are undesirable elements to be contained in glass for optical elements because they increase the coloration of the glass or are sources of fluorescence. Therefore, it is preferable not to contain these elements, i.e., not to introduce these elements into the glass as glass components.

Sb and Sn are elements that can be added as desired and function as fining agents.
The amount of Sb added is converted to Sb ₂ O ₃ and, when the total content of glass components other than Sb ₂ O ₃ is taken as 100 mass %, is preferably in the range of 0 to 0.11 mass %, more preferably in the range of 0.01 to 0.08 mass %, and even more preferably in the range of 0.02 to 0.05 mass %.
The amount of Sn added is converted to _SnO2 and, when the total content of glass components other than _SnO2 is taken as 100 mass%, is preferably in the range of 0 to 0.50 mass%, more preferably in the range of 0 to 0.20 mass%, and even more preferably 0 mass%.

<Glass properties>
(Refractive index nd)
In the glass material for molding according to this embodiment, glass composition C can be used to produce glass with a high refractive index. In the case of glass composition C, the refractive index nd is preferably 1.860 or more, and is more preferably 1.865 or more, 1.870 or more, 1.875 or more, 1.880 or more, 1.885 or more, 1.890 or more, 1.895 or more, and 1.900 or more in that order. Furthermore, the refractive index nd can be, for example, 1.950 or less, 1.945 or less, 1.940 or less, 1.935 or less, 1.930 or less, or 1.925 or less. In the present invention and this specification, "refractive index" means "refractive index nd".

(Abbe number νd)
The Abbe number vd is a value that represents properties related to dispersibility, and is expressed as vd = (nd - 1) / (nF - nC) using the refractive indices nd, nF, and nC at the d-line, F-line, and C-line. In the glass material for molding according to this embodiment, in the case of glass composition C, from the viewpoint of usefulness as a material for optical elements, the Abbe number vd is preferably 22.00 or more, and more preferably in the order of 22.50 or more, 23.00 or more, 23.50 or more, 24.00 or more, 24.20 or more, 24.40 or more, 24.60 or more, 24.70 or more, 24.80 or more, 25.00 or more, 25.50 or more, 25.60 or more, 25.80 or more, and 26.00 or more. From the same viewpoint, the Abbe number vd is preferably 30.00 or less, and more preferably 29.50 or less, 29.00 or less, 28.50 or less, 28.40 or less, 28.30 or less, 28.20 or less, 28.10 or less, 28.00 or less, 27.90 or less, 27.80 or less, and 27.70 or less in that order.

Furthermore, in the glass material for molding according to this embodiment, in the case of glass composition C, from the viewpoint of usefulness as a material for optical elements, it is also preferable that the refractive index nd and the Abbe number νd satisfy one or more of the following relational expressions:
nd≧−0.0025νd+1.925
nd≧−0.0025νd+1.935
nd≦-0.0025νd+1.995
nd≦-0.0025νd+2.005

(specific gravity d)
The refractive power of the optical elements that make up an optical system is determined by the refractive index of the glass that makes up the optical element and the curvature of the optically functional surface of the optical element (the surface through which the light rays to be controlled enter and exit). Increasing the curvature of the optically functional surface also increases the thickness of the optical element. As a result, the optical element becomes heavier. In contrast, if glass with a high refractive index is used, a large refractive power can be obtained without increasing the curvature of the optically functional surface.
From the above, if the refractive index can be increased while suppressing an increase in the specific gravity of the glass, it will be possible to reduce the weight of an optical element having a certain refractive power.
From the above viewpoints, in the glass material for molding according to this embodiment, in the case of glass composition C, the specific gravity d is preferably 4.100 or less, and more preferably 4.095 or less, 4.090 or less, 4.085 or less, 4.080 or less, 4.050 or less, 4.000 or less, 3.995 or less, 3.990 or less, and 3.985 or less in that order. Since a lower specific gravity is preferable from the viewpoint of reducing the weight of the optical element, the lower limit of the specific gravity is not particularly limited. In one embodiment, the specific gravity can be 3.400 or more, 3.450 or more, 3.500 or more, 3.550 or more, 3.600 or more, 3.650 or more, 3.700 or more, or 3.750 or more.

(d/nd)
From the same viewpoint as described above regarding the specific gravity d, in the glass material for molding according to this embodiment, in the case of glass composition C, the value (d/nd) obtained by dividing the specific gravity d by the refractive index nd is preferably 4.35 or less, and more preferably in this order: 4.00 or less, 3.50 or less, 3.00 or less, 2.90 or less, 2.80 or less, 2.70 or less, 2.60 or less, 2.50 or less, 2.40 or less, 2.30 or less, 2.20 or less, and 2.15 or less. The smaller the value of (d/nd), the more preferable it is from the viewpoint of reducing the weight of the optical element, and therefore there is no particular lower limit for (d/nd). In one form, (d/nd) can be, for example, 1.74 or more, 1.76 or more, 1.78 or more, 1.80 or more, 1.82 or more, 1.84 or more, 1.85 or more, 1.86 or more, 1.87 or more, 1.88 or more, 1.89 or more, 1.90 or more, 1.91 or more, 1.92 or more, 1.93 or more, 1.94 or more, or 1.95 or more.

(Coloring degree λ5)
In the glass material for molding according to this embodiment, in the case of glass composition C, the light transmittance of the glass, specifically, the suppression of the shift of the optical absorption edge on the short wavelength side to longer wavelengths, can be evaluated by the coloring degree λ5. The coloring degree λ5 represents the wavelength at which the spectral transmittance (including surface reflection loss) of a 10 mm thick glass is 5% from the ultraviolet to visible range. In the case of glass composition C, the spectral transmittance is, for example, more specifically, the spectral transmittance obtained by using a glass sample having parallel flat surfaces polished to a thickness of 10.0±0.1 mm and illuminating light perpendicularly to the polished surface, i.e., Iout/Iin, where Iin is the intensity of light incident on the glass sample and Iout is the intensity of light transmitted through the glass sample.
The coloring degree λ5 allows quantitative evaluation of the absorption edge on the short wavelength side of the spectral transmittance. When cementing lenses together with an ultraviolet-curable adhesive to produce a cemented lens, the adhesive is cured by irradiating it with ultraviolet light through an optical element. From the viewpoint of efficiently curing the ultraviolet-curable adhesive, it is preferable that the absorption edge on the short wavelength side of the spectral transmittance is in a short wavelength range. The coloring degree λ5 can be used as an index for quantitatively evaluating this absorption edge on the short wavelength side. In the case of glass composition C, a λ5 of 400 nm or less can be preferably exhibited. λ5 is more preferably 395 nm or less, 390 nm or less, 385 nm or less, and 380 nm or less, in that order. A lower λ5 is preferable, and the lower limit is not particularly limited.

(Glass transition temperature Tg)
In the glass material for molding according to this embodiment, in the case of glass composition C, the glass transition temperature Tg is preferably 560°C or higher from the viewpoint of machinability. Glass with a high glass transition temperature is preferred because it tends to be less likely to break when mechanically processing the glass, such as cutting, milling, grinding, or polishing. From the viewpoint of machinability, the glass transition temperature Tg is more preferably 570°C or higher, and further preferably 580°C or higher, 590°C or higher, and 600°C or higher in this order. On the other hand, from the viewpoint of reducing the burden on the annealing furnace and the molding die, the glass transition temperature Tg is preferably 800°C or lower, and more preferably 790°C or lower, 780°C or lower, 770°C or lower, 760°C or lower, 750°C or lower, and 740°C or lower in this order.

The glass transition temperature (Tg) is determined as follows. In differential scanning calorimetry (DSC), when a glass sample is heated, an endothermic behavior associated with a change in specific heat, i.e., an endothermic peak, appears; further heating leads to an exothermic peak. DSC produces a differential scanning calorimetry curve (DSC curve), with the horizontal axis representing temperature and the vertical axis representing quantities corresponding to the sample's heat release and endothermic heat. The glass transition temperature (Tg) is determined by the intersection of the tangent to the point where the slope of this curve becomes maximum when an endothermic peak appears from the baseline. The glass transition temperature (Tg) can be measured by using a sample of glass that has been thoroughly crushed in a mortar or other container, using a differential scanning calorimeter, and heating the sample at a rate of 10°C/min.

(liquidus temperature)
The thermal stability of glass includes resistance to devitrification when molten glass is formed, and resistance to devitrification when glass that has been solidified is reheated.
The liquidus temperature LT can be used as a guide for determining devitrification resistance during molding of a glass melt. It can be said that the lower the liquidus temperature, the better the devitrification resistance. With glasses having a high liquidus temperature, the temperature of the glass melt, i.e., the glass melt, must be maintained at a high temperature to prevent devitrification, which can result in the volatilization of easily volatile components, promote corrosion of the crucible, and, particularly in the case of a crucible made of a precious metal, cause precious metal ions to dissolve in the glass melt, resulting in coloration of the glass. The viscosity during molding is reduced, making it difficult to mold a highly homogeneous glass. Therefore, for glass composition C, the liquidus temperature is preferably 1400°C or lower, and more preferably 1370°C or lower, 1340°C or lower, 1310°C or lower, 1280°C or lower, 1270°C or lower, 1260°C or lower, and 1250°C or lower, in that order. The liquidus temperature can be, for example, 1000° C. or higher, 1050° C. or higher, or 1100° C. or higher, but can also be higher than the values exemplified here.

The "liquidus temperature" in the present invention and this specification is determined by the following method.
Using a differential scanning calorimeter, approximately 0.02 ml of a crushed glass sample was heated to 1350°C at a heating rate of 10°C/min in a nitrogen atmosphere with a nitrogen flow rate of 0.3 L/min. The liquidus temperature was determined as the end point of the endothermic peak that occurs when crystals in the glass formed during the heating process melt in a temperature range higher than the glass transition temperature or crystallization temperature. Figure 1 is a schematic diagram showing a differential scanning calorimeter curve (DSC curve). The horizontal axis represents temperature, with higher temperatures moving to the right and lower temperatures moving to the left. The vertical axis corresponds to the heat generation and endothermic peaks of the sample, with the area above the baseline (dotted line) representing heat generation and the area below representing endothermic peaks. Crystal precipitation during the heating process corresponds to the exothermic peak, and melting of the precipitated crystals corresponds to the endothermic peak. The temperature at which the crystals melt into a molten liquid is the liquidus temperature. The liquidus temperature is determined as the temperature at the intersection of the tangent to the high-temperature side of the endothermic peak and the baseline.

(Glass material manufacturing)
Glass according to an embodiment of the present invention can be produced by blending glass raw materials to achieve the above-described predetermined composition. For example, multiple compounds are blended and thoroughly mixed to form batch raw materials, which are then placed in a quartz crucible or platinum crucible for rough melting. The resulting molten material is cooled and crushed to produce cullet. The cullet is then placed in a platinum crucible, heated, and remelted to form a glass melt. This is then cooled, clarified, and homogenized, and the glass melt is poured into a mold whose temperature has been adjusted so that the glass melt reaches a temperature Tx below Tg (Step 1), and maintained at Tx (Step 2). The glass is then cooled at a rate of −30° C./hr for 4 hours to ensure that the temperature is below the strain point of the glass (Step 3), and then allowed to cool at a slow cooling rate sufficient to prevent the glass from breaking, until it can be removed from the furnace (Step 4).

In addition, there are no particular restrictions on the compounds used when mixing the batch raw materials, as long as the desired glass components can be introduced into the glass in the desired content, but such compounds include oxides, carbonates, nitrates, hydroxides, fluorides, etc.

Steps 1 to 4 are explained below.

(Step 1)
In step 1, the molten glass is cast into a mold whose temperature has been adjusted to reach a temperature Tx below the glass transition temperature Tg. By controlling the temperature of the molten glass as described above, it is possible to reduce the thermal energy applied to the glass and suppress the movement of atoms within the glass. As a result, the movement of atoms is restricted before structural factors within the glass, such as the bond distances and bond angles between atoms, become homogenized. By maintaining a disordered glass structure similar to that in a molten state, a glass material with excellent stability when reheated can be obtained.

The temperature of the molten glass before step 1 is typically between the liquidus temperature and the melting temperature of the glass. In step 1, the glass temperature when the molten glass is poured into the mold is the temperature at which the glass melts, generally in the range of 1500°C to 1100°C, and preferably 1400°C to 1200°C. Therefore, in step 1, the molten glass is cooled before being poured into the mold. This cooling is typically achieved by allowing the glass to cool naturally in the air. However, if the cooling rate is too fast, some parts of the glass may become so viscous that they no longer flow, or may solidify. This can hinder the homogenization of the glass and may even cause cracks or breakage in the glass. Therefore, the lower limit of the cooling rate in step 1 is preferably approximately 1°C/sec, with 3°C/sec and 6°C/sec being more preferred. The upper limit of the cooling rate is preferably 20°C/sec, and more preferably 15°C/sec, 12°C/sec, and 10°C/sec in that order.

(Step 2)
In step 2, the glass melt is held at a temperature Tx. The holding temperature Tx in step 2 is preferably lower than the glass transition temperature Tg, with the upper limit being Tg-1°C, Tg-5°C, Tg-10°C, Tg-15°C, and Tg-20°C, in that order. By setting the upper limit of the holding temperature Tx within the above range, the disorder of the glass structure is increased, and a glass material with excellent stability when reheated can be obtained.

The lower limit of the holding temperature Tx in step 2 is preferably Tg - 100°C, and more preferably Tg - 90°C, Tg - 80°C, Tg - 70°C, Tg - 60°C, and Tg - 50°C in that order. In particular, it is preferable that Tx not be too far below the strain point, and it is even more preferable that it be at or above the strain point. By setting the lower limit of the holding temperature Tx within the above range, excess internal strain in the glass can be removed, and deterioration of the glass workability in subsequent steps can be suppressed or breakage of the glass bulk can be prevented. In processes where deterioration of the glass workability in subsequent steps is not an issue, the lower limit of the temperature in step 2 is not particularly specified.

The holding time in step 2 tends to be longer as the thickness of the glass increases and as the volume of the glass increases in order to soak the high-temperature glass cooled from the molten state, but is preferably 10 minutes or more, and can be 20 minutes or more, or 30 minutes or more. From the viewpoints of productivity and maintaining the thermal stability of the glass, the upper limit of the holding time is sufficient to be less than 3 hours, and may further be less than 2 hours, less than 1.5 hours, or less than 1.0 hour. If the holding time is too long, the disordered state of atomic arrangement in the molten state is not maintained, and the atomic arrangement becomes more ordered, which reduces the thermal stability of the glass and tends to increase α _max .

(Step 3)
In step 3, the glass is cooled at -30°C/hr for 4 hours to ensure that the temperature is below the strain point during annealing. When the temperature Tx is higher than the strain point, the time required for this cooling is preferably 4 hours or more, more preferably 5 hours or more, and even more preferably 6 hours or more. When the temperature Tx is lower than the strain point, the time required for cooling can be less than 4 hours.

(Step 4)
In step 4, the glass is cooled at a slow cooling rate that does not cause cracking to a temperature at which the glass can be removed from the furnace. The slow cooling rate in step 4 is preferably less than approximately -50°C/hr, and can be approximately -10°C/hr or -30°C/hr. A rate less than -1°C/hr may impair productivity. The temperature of the glass that can be removed from the furnace depends on the insulation conditions outside the furnace, but is preferably approximately 100°C or less, and more preferably 80°C or less, 60°C or less, 40°C or less, and 20°C or less in this order. Expressed in terms of the difference from room temperature, the upper limit of the temperature of the glass that can be removed from the furnace is preferably room temperature + 50°C, and more preferably room temperature + 40°C, room temperature + 30°C, room temperature + 20°C, and room temperature + 10°C in this order. The lower limit of the temperature of the glass that can be removed from the furnace may be room temperature.

To slowly cool the glass, any known method that can achieve the above temperature profile can be used, such as a temperature-programmable slow cooling furnace.

By setting the cooling rate in step 1 and the holding temperature Tx in step 2 within the above ranges, the disorder of the glass structure is increased, resulting in a glass material with excellent stability when reheated. Furthermore, by cooling and slowly cooling the glass as in steps 3 and 4, distortion in the glass can be removed, maintaining the workability of the glass in subsequent processes.

The molding glass material according to an embodiment of the present invention can be used as is as the optical glass according to an embodiment of the present invention.

(Manufacturing of optical elements, etc.)
To produce an optical element using the glass material for molding according to an embodiment of the present invention, a known method may be applied. For example, in the production of the glass material, molten glass is poured into a mold and molded into a plate to produce the glass material for molding according to the present invention. The obtained glass material is appropriately cut, ground, and polished to produce a molding precursor (also referred to as a cut piece) having a size and shape suitable for molding after reheating. The cut piece is heated and softened, and molded by a known method (reheat pressing, round bar molding, extrusion molding, etc.) to produce an optical element blank that approximates the shape of the optical element. The optical element blank is annealed, and then cut, ground, polished, etc. by a known method to produce an optical element.

The optically functional surfaces of the manufactured optical elements may be coated with anti-reflection films, total reflection films, etc. depending on the intended use.

According to one aspect of the present invention, an optical element made from the above optical glass can be provided. Examples of optical elements include lenses such as spherical lenses and aspherical lenses, prisms, and diffraction gratings. Examples of lens shapes include biconvex lenses, plano-convex lenses, biconcave lenses, plano-concave lenses, convex meniscus lenses, and concave meniscus lenses. The optical element can be manufactured by a method including a step of processing a glass molded body made from the above optical glass. Examples of processing include cutting, milling, rough grinding, fine grinding, and polishing. Using the above glass during such processing can reduce breakage and ensure a stable supply of high-quality optical elements.

Second embodiment The glass material for molding according to the second embodiment is
The maximum value α _max of the linear expansion coefficient, the average linear expansion coefficient α _100-300 at 100 to 300°C, and the total content of SiO ₂ and ZrO ₂ [SiO ₂ +ZrO ₂ ] expressed in mass% satisfy the following formula (4).
α _max /α _100-300 × [SiO ₂ +ZrO ₂ ]≦264 (4)

In the glass material for molding according to the second embodiment, the maximum value of the linear expansion coefficient α _max , the average linear expansion coefficient α _100-300 at 100 to 300°C, and the total content of SiO ₂ and ZrO ₂ [SiO ₂ +ZrO ₂ ] expressed in mass% satisfy the following formula (4), preferably the following formula (5), and more preferably the following formula (5). By satisfying the following formula, a glass material for molding that has excellent stability when reheating can be obtained.
α _max /α _100-300 × [SiO ₂ +ZrO ₂ ]≦264 (4)
α _max /α _100-300 × [SiO ₂ + ZrO ₂ ]≦260 (5)
α _max /α _100-300 × [SiO ₂ + ZrO ₂ ]≦255 (6)

The maximum linear expansion coefficient α _max and the average linear expansion coefficient α _100-300 can be controlled by adjusting the conditions for cooling the molten glass in the process of producing the glass material.

The maximum value α _max of the linear expansion coefficient and the average linear expansion coefficient α _100-300 can be measured in the same manner as in the first embodiment.

In the glass material for molding according to the second embodiment, the maximum value α _max of the linear expansion coefficient and the total content of SiO ₂ and ZrO ₂ expressed in mass % [SiO ₂ + ZrO ₂ ] preferably satisfy the following formula (1), more preferably satisfy the following formula (2), and even more preferably satisfy the following formula (3). From the viewpoint of obtaining a glass material for molding that has excellent stability when reheated, it is preferable that the following formula is satisfied.
α _max × [SiO ₂ + ZrO ₂ ]≦27900 (1)
α _max × [SiO ₂ + ZrO ₂ ]≦27500 (2)
α _max × [SiO ₂ + ZrO ₂ ]≦27000 (3)

The maximum value α _max of the linear expansion coefficient can be controlled by adjusting the conditions for cooling the molten glass in the process of producing the glass material.

In the glass material for molding according to the second embodiment, the properties and glass composition other than those described above can be the same as those of the first embodiment. Furthermore, the manufacturing of the glass material and the manufacturing of optical elements, etc. in the second embodiment can also be the same as those of the first embodiment.

Third embodiment The glass material for molding according to the third embodiment is
The maximum linear expansion coefficient α _max is smaller than the maximum linear expansion coefficient α max (Tg) of a glass material obtained by soaking the glass material for molding at the glass transition temperature _Tg , cooling it at −30° C./hr for 4 hours, and then allowing it to cool.

In the glass material for molding according to the third embodiment, the maximum linear expansion coefficient α _max is smaller than the maximum linear expansion coefficient α _max (Tg) of a glass material obtained by soaking the glass material for molding at the glass transition temperature Tg, then cooling it at −30° C./hr for 4 hours, and then allowing it to cool. However, the maximum linear expansion coefficient α _max may be slightly larger than the maximum linear expansion coefficient α _max (Tg). Therefore, the difference between α _max and α _max (Tg) [α _max (Tg) - α _max ], expressed to the first integer in units of 10 ^-7 · ° C ^-1 , is preferably -9 or more, and more preferably -4 or more, 0 or more, 5 or more, 10 or more, 20 or more, 40 or more, 60 or more, 80 or more, 100 or more, 120 or more, 140 or more, 160 or more, 180 or more, 200 or more, 250 or more, and 300 or more, in that order. There are no particular limitations on the upper limit of the difference, but it is usually α _max (Tg), and preferably about α _max (Tg) - 100.

In the glass material for molding according to the third embodiment, the method for measuring the maximum value α _max (Tg) is the same as in the first embodiment.

In the glass material for molding according to the third embodiment, the maximum value α _max of the linear expansion coefficient and the total content of SiO ₂ and ZrO ₂ expressed in mass % [SiO ₂ + ZrO ₂ ] preferably satisfy the following formula (1), more preferably satisfy the following formula (2), and even more preferably satisfy the following formula (3). From the viewpoint of obtaining a glass material for molding that has excellent stability when reheated, it is preferable that the following formula is satisfied.
α _max × [SiO ₂ + ZrO ₂ ]≦27900 (1)
α _max × [SiO ₂ + ZrO ₂ ]≦27500 (2)
α _max × [SiO ₂ + ZrO ₂ ]≦27000 (3)

The maximum value α _max of the linear expansion coefficient can be controlled by adjusting the conditions for cooling the molten glass in the process of producing the glass material.

In the glass material for molding according to the third embodiment, the properties and glass composition other than those described above can be the same as those of the first embodiment. Furthermore, the manufacturing of the glass material and the manufacturing of optical elements, etc. in the third embodiment can also be the same as those of the first embodiment.

The present invention will be described in more detail below using examples. However, the present invention is not limited to the embodiments shown in the examples.

(Example 1-1)
Glass samples having glass composition I shown in Table 1(1) were prepared by the following procedure, and the obtained glass samples were subjected to various evaluations. The results are shown in Tables 2(1) and 2(2).

[Production of glass samples]
First, oxides, hydroxides, carbonates, and nitrates corresponding to the constituent components of the glass were prepared as raw materials. These raw materials were weighed and blended so that the resulting optical glass had the glass composition shown in Table 1(1), and the raw materials were thoroughly mixed. The resulting blended raw materials (batch raw materials) were placed in a platinum crucible and heated at 1350°C to 1450°C for two hours to form a molten glass. The molten glass was then stirred to homogenize it and refined. The molten glass was then cast into a mold preheated to an appropriate temperature and rapidly cooled (Step 1). The cast glass was then held for 30 minutes at a holding temperature Tx, which was 25°C lower than the glass transition temperature Tg (Step 2). The glass was then cooled at a rate of −30°C/hr to a temperature 120°C lower than the holding temperature Tx of Step 2 (Step 3), and then allowed to cool to room temperature in a furnace (Step 4), yielding a glass sample. The amount of glass used here was 150 g.

Here, the holding temperature Tx in step 2 was set to 25°C lower than the glass transition temperature Tg (unit: °C), rounded to the nearest whole number, which was used as the Tg of the glass sample. Table 2 (2) shows the difference between the rounded Tg and the holding temperature Tx, which corresponds to this temperature difference. This allows the same holding temperature Tx to be set regardless of slight variations in the measured Tg values, and multiple samples can be held at the same time, thereby improving the production efficiency of the glass of the present invention.

[Confirmation of glass component composition]
The content of each glass component in the obtained glass sample was measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES), and it was confirmed that the composition was as shown in Table 1(1).

[Glass transition temperature Tg]
The glass transition temperature Tg was measured using a differential scanning calorimeter (DSC3300SA) manufactured by NETZSCH JAPAN at a temperature rise rate of 10° C./min.

[Stability test]
The obtained glass sample was confirmed to be free of internal foreign matter using an optical microscope (100x magnification), and then cut and milled to obtain a sample measuring 11 mm x 11 mm x 10.5 mm. This sample was placed in a heat treatment furnace set to a temperature 200°C higher than the Tg, heated, and then removed after 5 minutes, and the glass sample was cooled. After cooling, the edges of the glass sample were optically polished, and the interior of the glass sample was observed using an optical microscope (100x magnification). The number of crystals (bright spots) observed throughout the glass sample was counted and converted to the number per gram. The crystals were in the range of 1 to 300 μm in size. No cracks or striae were observed in the glass sample.

[Linear expansion coefficient]
The average linear expansion coefficient of the obtained glass samples was measured in accordance with the JOGIS08 standard. The samples were round bars with a length of 20 mm ± 0.5 mm and a diameter of 5 mm ± 0.5 mm. A load of 98 mN was applied to the samples, and they were heated at a constant rate of 4°C per minute. The temperature and sample elongation were measured every second. The maximum value of the linear expansion coefficient at the temperature at which the sample elongated most per unit temperature increase between room temperature and the yield point (the temperature at which the sample yielded and apparent elongation ceased) was defined as α _max . The maximum value obtained by moving average of the linear expansion coefficients at 31 measurement points was used for α _max . The average value of the linear expansion coefficients from 100 to 300°C was defined as the average linear expansion coefficient α _100-300 .

The maximum linear expansion coefficient α _max and the maximum linear expansion coefficient α _max (Tg) of the glass when the holding temperature Tx in step 2 was the glass transition temperature were measured, and the difference Q: α _max (Tg) - α _max was calculated.

[Average linear expansion coefficient α _L ]
The average linear expansion coefficient of the obtained glass samples was measured with reference to the provisions of JOGIS16. The average linear expansion coefficient was measured using a thermomechanical analyzer (TMA4000SE) manufactured by NETZSCH JAPAN. The sample was a round bar with a length of 20 mm ± 0.5 mm and a diameter of 5 mm ± 0.5 mm. First, the sample was cooled to -80°C or below using liquid nitrogen and held for 20 minutes before starting the measurement. During the measurement, a load of 98 mN was applied to the sample, and the temperature was raised to 320°C at a constant rate of 4°C per minute, while the temperature and sample elongation were measured every second. The average value of the linear expansion coefficients from -30 to 70°C was taken as the average linear expansion coefficient _αL .

[Measurement of optical properties]
The refractive indices nd, ng, nF and nC, the Abbe number vd, and the partial dispersion ratios Pg,F and ΔPg,F of the obtained glass samples were measured. The results are shown in Tables 2(1) and 2(2).

(i) Refractive indexes nd, ng, nF, nC and Abbe number νd
The refractive indices nd, ng, nF, and nC of the glass sample were measured by the refractive index measurement method of Japanese Industrial Standards JIS B 7071-1, and the Abbe number νd was calculated according to the following formula.
νd=(nd-1)/(nF-nC)

(ii) Partial dispersion ratio Pg,F, ΔPg,F
Using the refractive indices ng, nF, and nC at the g-line, F-line, and c-line, the partial dispersion ratios Pg,F and ΔPg,F were calculated based on the following formulas.
Pg,F=(ng-nF)/(nF-nC)...(13)
ΔPg,F=Pg,F-(0.6483-0.001802×νd)...(14)

[Evaluation of Light Transmittance]
(i) λτ80
Using glass samples with thicknesses of 2.0 mm ± 0.1 mm and 10.0 mm ± 0.1 mm, spectral transmittance was measured in the wavelength range of 200 to 700 nm in accordance with JOGIS17 (Method for measuring internal transmittance of optical glass). The wavelength at which the internal transmittance of a 10 mm thickness was 80% was defined as λτ80. The results are shown in Table 2(1).

(ii) λ70
The spectral transmittance of a glass sample having a thickness of 10.0 mm±0.1 mm was measured in the wavelength range of 200 to 700 nm. The wavelength at which the external transmittance was 70% was defined as λ70. The results are shown in Table 2(1).

[specific gravity]
The specific gravity was measured by Archimedes' method, and the results are shown in Table 2(1).

(Example 1-2)
In the production of the glass sample, a glass sample was obtained in the same manner as in Example 1-1, except that the holding temperature Tx in step 2 was set to a temperature 50° C. lower than the glass transition temperature Tg. Various evaluations were performed in the same manner as in Example 1-1.

(Examples 1-3)
In the production of the glass sample, a glass sample was obtained in the same manner as in Example 1-1, except that the holding temperature Tx in step 2 was set to a temperature 100° C. lower than the glass transition temperature Tg. Various evaluations were performed in the same manner as in Example 1-1.

(Example 2-1)
A glass sample having glass composition II shown in Table 1 (1) was produced. In producing the glass sample, raw materials were blended to obtain glass composition II, and the holding temperature Tx in step 2 was set to a temperature 60°C lower than the glass transition temperature Tg, and the glass sample was obtained in the same manner as in Example 1-1. Various evaluations were performed in the same manner as in Example 1-1.

(Comparative Example 1-1)
In the production of the glass sample, a glass sample was obtained in the same manner as in Example 1-1, except that the holding temperature Tx in step 2 was set to a temperature 30° C. higher than the glass transition temperature Tg. Various evaluations were performed in the same manner as in Example 1-1.

(Comparative Example 1-2)
In the production of the glass sample, a glass sample was obtained in the same manner as in Example 1-1, except that the holding temperature Tx in step 2 was set to the glass transition temperature Tg. Various evaluations were performed in the same manner as in Example 1-1. The maximum value of the linear expansion coefficient in Comparative Example 1-2 was designated as α _max (Tg), and this was compared with the maximum value of the linear expansion coefficient α _max in Examples 1-1, 1-2, and 1-3.

(Comparative Examples 1-3)
In the production of the glass sample, a glass sample was obtained in the same manner as in Example 1-1, except that the holding time in step 2 was 72 hours. Various evaluations were performed in the same manner as in Example 1-1. Note that, although a glass was obtained in Comparative Example 1-3, significant devitrification occurred in the stability test. Furthermore, the refractive index nd, Abbe number νd, partial dispersion ratios Pg,F, and ΔPg,F could not be measured.

(Comparative Example 2-1)
In the production of the glass sample, a glass sample was obtained in the same manner as in Example 2-1, except that the holding temperature Tx in step 2 was set to the glass transition temperature Tg. Various evaluations were performed in the same manner as in Example 2-1. The maximum value of the linear expansion coefficient in Comparative Example 2-1 was defined as α _max (Tg), and this was compared with the maximum value of the linear expansion coefficient α _max in Example 2-1.

(Example 3-1)
A glass sample having glass composition III shown in Table 1 (2) was produced. In producing the glass sample, raw materials were blended to obtain glass composition III, and the holding temperature Tx in step 2 was set to a temperature 60°C lower than the glass transition temperature Tg, and the glass sample was obtained in the same manner as in Example 1-1. Various evaluations were performed in the same manner as in Example 1-1.

(Example 3-2)
A glass sample having glass composition III shown in Table 1 (2) was produced. In producing the glass sample, raw materials were blended to obtain glass composition III, and the holding temperature Tx in step 2 was set to a temperature 100°C lower than the glass transition temperature Tg, and the glass sample was obtained in the same manner as in Example 1-1. Various evaluations were performed in the same manner as in Example 1-1.

(Example 4-1)
A glass sample having glass composition IV shown in Table 1 (3) was produced. In producing the glass sample, raw materials were blended to give glass composition IV, and the holding temperature Tx in step 2 was set to the same temperature as the glass transition temperature Tg, and other than that, the glass sample was obtained in the same manner as in Example 1-1. Various evaluations were performed in the same manner as in Example 1-1.

(Example 4-2)
A glass sample having glass composition IV shown in Table 1 (3) was produced. In the production of the glass sample, the raw materials were blended so as to obtain glass composition IV, and the glass sample was obtained in the same manner as in Example 1-1. Various evaluations were performed in the same manner as in Example 1-1.

Example 3
Lens blanks were prepared by known methods using the glass samples prepared in Examples 1-1, 1-2, 1-3, 2-1, 3-1, 3-2, 4-1, and 4-2, and various lenses were prepared by processing the lens blanks by known methods such as polishing.
The optical lenses produced include various lenses such as biconvex lenses, biconcave lenses, plano-convex lenses, plano-concave lenses, concave meniscus lenses, and convex meniscus lenses.
By combining various lenses with lenses made of other types of optical glass, it was possible to effectively correct secondary chromatic aberration.

In the same manner, prisms were manufactured using the various optical glasses prepared in Examples 1-1, 1-2, 1-3, 2-1, 3-1, 3-2, 4-1, and 4-2.

The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims.

For example, by adjusting the composition as described in the specification for the glass compositions exemplified above, an optical glass according to one aspect of the present invention can be produced.
Furthermore, it is of course possible to arbitrarily combine two or more of the items described in the specification as examples or preferred ranges.

Claims (6)

Molding glass material that satisfies the following requirements A or B:
A. It has the following composition I and the maximum linear expansion coefficient α _max is 925, 720 or 631, or has the following composition II, and α _max If is 615:
A. When a sample of 11 mm x 11 mm x 10.5 mm is heat-treated for 5 minutes at a temperature 200°C higher than the glass transition temperature Tg, the number density D of crystals per 1 g of glass is less than 10 crystals/g,
Maximum linear expansion coefficient α _max and SiO in mass% ₂ and ZrO ₂ The total content [SiO ₂ + ZrO ₂ ] satisfies the following formula (1),
α _max ×[SiO ₂ + ZrO ₂ ］≦27900 ... (1)
SiO ₂ Contains 6 to 40 mass% of
P ₂ O ₅ Contains 0 to 5 mass% of
SiO ₂ and P ₂ O ₅ The total content [SiO ₂ +P ₂ O ₅ ] is 5 to 40 mass %,
SiO ₂ , P ₂ O ₅ and B ₂ O ₃ The total content [SiO ₂ +P ₂ O ₅ +B ₂ O ₃ ] is 5 to 50 mass %,
TiO ₂ Contains 0 to 20 mass% of
Nb ₂ O ₅ and TiO ₂ The total content [Nb ₂ O ₅ + TiO ₂ ] is 10 to 80 mass %;
WO ₃ Contains 0 to 20 mass% of
ZrO ₂ The content is 2% by mass or more,
Bi ₂ O ₃ The content of is 20% by mass or less,
α _max If is between 925 and 615. In the case of A above,
2. The glass material for molding according to claim 1, wherein when a sample of 11 mm × 11 mm × 10.5 mm is heat-treated for 5 minutes at a temperature 200° C. higher than the glass transition temperature Tg, the number density D of crystals per 1 g of glass is less than 10 crystals/g. _3. The glass material for molding according to claim 1, wherein the _TiO2 content [ _TiO2 ] and the _Nb2O5 content [ _Nb2O5 ], expressed in mass%, satisfy the following formula (7): _TiO2 + Nb2O5 ...
{5×[TiO ₂ ]}/{3×[Nb ₂ O ₅ ]}≦3 (7) 4. The glass material for molding according to claim 1, wherein the wavelength λτ ₈₀ at which a glass having a thickness of 10 mm exhibits an internal transmittance of 80% in the wavelength range of 280 to 700 nm is 395 nm or less. 5. The glass material for molding according to claim 1, wherein the Abbe number νd and the partial dispersion ratio Pg, F satisfy the following formula (8):
Pg,F≦-0.00286×νd+0.68700...(8) A method for producing an optical element, comprising the step of heating, softening, and molding the glass material for molding according to any one of claims 1 to 5.