JP7713809B2 - Optical glass, preforms and optical elements - Google Patents

Description

The present invention relates to optical glass, preforms, and optical elements.

In addition to digital cameras, projectors, and surveillance cameras, optical glass is increasingly being used as an optical element, such as the imaging lenses installed in in-vehicle cameras, as autonomous driving technology advances. For in-vehicle cameras, for example, those used outdoors require excellent chemical durability for the front lens, which is exposed to the outside air. Good chemical durability makes it less likely for the lens surface to corrode and become cloudy, enabling long-term use. Furthermore, in-vehicle cameras are prone to scratches on their lenses caused by dust particles in the air or pebbles caught in tires, so optical glass that is resistant to scratches caused by impacts is required. Furthermore, it is desirable for the optical elements incorporated into in-vehicle optical equipment to be inexpensive.

As a lens glass material for vehicle-mounted cameras, there is a growing demand for Class 6 glass materials that combine so-called high refractive index, high dispersion optical properties with a high refractive index (n _d ) of 1.75000 or more and an Abbe number (ν _d ) of 20.00 to 40.00, as well as excellent chemical durability and mechanical properties such as Knoop hardness. Glass compositions such as those described in Patent Documents 1 and 2 are known as materials used for such vehicle-mounted optical devices.

Japanese Patent Application Laid-Open No. 2008-233547 WO2017/175552 publication

However, while the optical glass disclosed in Patent Document 1 maintains a high refractive index, its chemical durability (acid resistance) measured by the powder method is grade 1 to 3, and its Knoop hardness is grade 6 or higher when measured according to the "JOGIS09-1975 Method for Measuring Knoop Hardness of Optical Glass" method. However, the optical glass contains Nb ₂ O ₅ and Gd ₂ O ₃ , which are expensive raw materials, and therefore has the problem of being expensive.

Furthermore, the optical glasses disclosed in Patent Documents 1 and 2 contain a large amount of _ZrO2 in order to have a high refractive index and to obtain powder-method acid resistance grades 1 to 3. However, the _ZrO2 component deteriorates devitrification resistance and raises the liquidus temperature, which causes problems such as a decrease in the melting and molding yield of the glass.

The present invention was made in consideration of the above problems, and its purpose is to provide an optical glass that has the optical properties of a high refractive index and high dispersion, has powder-method acid resistance of grades 1 to 3, and a Knoop hardness of grade 6 or higher, and is also inexpensive.

As _a result of extensive research and experimentation to solve the above problems, the present inventors have discovered that by minimizing the content of _Nb2O5 and _ZrO2 components and adjusting the contents of each component, including _B2O3 , _SiO2 , _ZnO , and _La2O3 , it is possible to produce an inexpensive glass material that combines good chemical durability and mechanical properties, _and have completed the present invention. Specifically, the present invention provides the following.

(1) in mass %,
_ZrO2 component 0.0 to 10.0%,
B ₂ O ₃ components more than 0.0% to 20.0%,
SiO ₂ components more than 0.0% to 30.0%
ZnO component 0.0 to 40.0%,
La ₂ O ₃ components 5.0 to 35.0%,
and the mass sum of Ta ₂ O ₅ +Nb ₂ O ₅ +WO ₃ +Gd ₂ O ₃ is 5.0% or less;
the mass ratio SiO ₂ /(SiO ₂ +B ₂ O ₃ +TiO ₂ ) is 0.15 to 0.45;
and
An optical glass characterized by having a result of measuring acid resistance of grade 1 to 3 by the powder method specified in the Japan Optical Glass Industry Association Standard (JOGIS06-2006), and a result of measuring Knoop hardness of grade 6 or higher by the measurement method specified in the Japan Optical Glass Industry Association Standard (JOGIS09-1975).

(2) The mass sum CaO + ZnO + TiO ₂ is 10.0 to 50.0% or less,
The optical glass of (1) has a mass ratio (BaO+ZnO)/La ₂ O ₃ of 0.5 to 2.1.

(3) having a refractive index (n _d ) of 1.78000 or more and 1.98000 or less, and an Abbe number (ν _d ) of 20.00 or more and 40.00 or less;
The optical glass of (1) or (2) has a mass ratio (CaO+ZnO+Li ₂ O)/BaO of 0.022 or more.

(4) A preform made of any of the optical glasses (1) to (3).

(5) An optical element made of any of the optical glasses (1) to (3).

(6) An optical device equipped with the optical element of (5).

The present invention provides inexpensive optical glass that has high refractive index and high dispersion optical properties, and exhibits acid resistance measured using the powder method specified in the Japan Optical Glass Industry Association Standard (JOGIS06-2006) of Grades 1 to 3, and Knoop hardness measured using the method specified in the Japan Optical Glass Industry Association Standard (JOGIS09-1975) of Grade 6 or higher. It also provides excellent chemical durability and resistance to impacts, and can be used to produce preforms and optical elements.

The optical glass of the present invention contains, by mass, 0.0 to 10.0% _ZrO2 , between 0.0 and _20.0 % _B2O3 , between 0.0 and 30.0% _SiO2 , between 0.0 and 40.0% _ZnO , and between 5.0 and 35.0% _La2O3 . By adjusting the contents of each component, including _ZrO2 , _B2O3 , _SiO2 , _ZnO , and _La2O3 , it is possible to obtain _an optical glass with a high refractive index and high dispersion, acid resistance of grades 1 to 3 by powder method, Knoop hardness of grade 6 or higher, low liquidus temperature, and low cost, particularly suitable for automotive glass. Furthermore, by keeping the _mass sum of _Ta2O5 + _Nb2O5 + _WO3 + _Gd2O3 to 5.0 _% or _less , raw material costs can be reduced.
By setting the mass ratio SiO ₂ /(SiO ₂ +B ₂ O ₃ +TiO ₂ ) to 0.15 to 0.45 or less, the liquidus temperature of the glass is lowered, and a stable glass can be obtained that satisfies the desired refractive index and Abbe number.

Embodiments of the optical glass of the present invention are described in detail below. The present invention is not limited to the following embodiments, and can be implemented with appropriate modifications within the scope of the object of the present invention. Note that redundant explanations may be omitted where appropriate, but this does not limit the spirit of the invention.

[Glass components]
The composition ranges of each component constituting the optical glass of the present invention are described below. Throughout this specification, unless otherwise specified, the content of each component is expressed as mass % relative to the total mass of the composition calculated as oxide. Here, "composition calculated as oxide" refers to a composition expressed as the amount of each component contained in the glass, assuming that the oxides, composite salts, metal fluorides, etc. used as raw materials for the glass components of the present invention are all decomposed and converted to oxides during melting, with the total mass of the oxides produced being 100 mass %.

<Required and optional ingredients>
In the optical glass of the present invention, which contains a large amount _of rare earth oxides, the _B2O3 component is an essential component as a glass-forming _oxide . In particular, by making the content of the _B2O3 component greater than 0.0%, the devitrification resistance of the glass and the meltability of the glass can be improved. Therefore, the _lower limit of the content of the _B2O3 component is preferably greater than 0%, more preferably 1.5% or more, and even more preferably 2.0% or more.
On the other hand, by setting the content of the _B2O3 component to 20.0% or less, _a higher refractive index can be easily obtained and deterioration of chemical durability _can be suppressed. Therefore, the upper limit of the content of the _B2O3 component is preferably set to 20.0% or less, more preferably 18.0% or less, and even more preferably 15.0% or less.
As _{the B2O3 component, H3BO3, Na2B4O7, Na2B4O7.10H2O , BPO4 , etc. can be used as raw materials .}

The _SiO2 component is an essential component that increases the viscosity of the glass melt and increases the hardness of the glass when the content exceeds 0.0%. It also increases the stability of the glass, making it easier to obtain glass that can withstand mass production. Therefore, the lower limit of the _SiO2 component content is preferably greater than 0.0%, more preferably 2.0% or more, and more preferably 4.0% or more.
On the other hand, by keeping the content of the _SiO2 component at 30.0% or less, the viscosity becomes suitable for glass molding and a decrease in the refractive index is suppressed. Therefore, the upper limit of the content of the _SiO2 component is preferably set to 30.0% or less, more preferably 27.0% or less, and even more preferably 25.0% or less.
As the _SiO2 component, _SiO2 , _K2SiF6 , _{Na2SiF6 , etc.} can be used as raw materials.

When the _TiO2 component is contained in an amount of 5.0% or more, it increases the refractive index of the glass, increases the Abbe number, and increases the hardness of the glass. Therefore, the lower limit of the _TiO2 component content is preferably 5.0% or more, more preferably 6.5% or more, and even more preferably 8.0% or more.
On the other hand, by limiting the content of the _TiO2 component to 40.0% or less, devitrification due to excessive _TiO2 content can be reduced, and a decrease in the transmittance of the glass to visible light (particularly wavelengths of 500 nm or less) can be suppressed. This also prevents a decrease in the Abbe number. Therefore, the upper limit of the content of the _TiO2 component is preferably 40.0% or less, more preferably 38.0% or less, and even more preferably 35.0% or less.
As the _TiO2 component, TiO2 _or the like can be used as a raw material.

ZnO is an optional component that, when contained in an amount exceeding 0.0%, improves the meltability of the raw materials, increases the hardness of the glass, and enhances the stability of the glass. It is also a component that can improve chemical durability. Therefore, the lower limit of the ZnO content is preferably more than 0.0%, more preferably 0.5% or more, and even more preferably 1.0% or more.
On the other hand, by setting the content of the ZnO component to 40.0% or less, a decrease in the refractive index of the glass can be suppressed and devitrification due to an excessive decrease in viscosity can be reduced. Therefore, the upper limit of the content of the ZnO component is preferably set to 40.0% or less, more preferably 38.0% or less, and more preferably 35.0% or less.
As the ZnO component, ZnO, _ZnF2 , etc. can be used as raw materials.

The La ₂ O ₃ component is an optional component that increases the refractive index and Abbe number of the glass when the content exceeds 0.0%.
Therefore, when an optical glass having a refractive index of 1.75 or more is desired, the lower limit of the content of _{the La2O3} component is preferably 5.0% or more, more preferably 8.0% or more, and even more preferably 10.0% or more.
On the other hand, by setting the content of the _La2O3 component to 35.0% or less, the stability of the glass _can be improved, thereby reducing devitrification and suppressing an unnecessary increase in the Abbe number. Therefore, the upper limit is preferably set to 35.0% or less, more preferably 33.0% or less, and even more preferably 30.0% or less.

The _ZrO2 component is an optional component that, when contained in an amount exceeding 0.0%, suppresses a decrease in acid resistance and increases the refractive index and Abbe number of the glass. The lower limit of the _ZrO2 content is preferably more than 0.0%, more preferably 0.5% or more, and even more preferably 1.0% or more.
On the other hand, by limiting the content of the _ZrO2 component to 10.0% or less, devitrification due to excessive inclusion of the _ZrO2 component can be reduced. Therefore, the upper limit of the content of the _ZrO2 component is preferably 10.0% or less, more preferably 8.0% or less, and even more preferably 5.3% or less.
As the _ZrO2 component, _ZrO2 , _ZrF4 , etc. can be used as raw materials.

The Nb ₂ O ₅ component is an optional component that can increase the refractive index of glass when contained in a content exceeding 0.0%. On the other hand, by limiting the content of the Nb ₂ O ₅ component to 5.0% or less, the material costs of the glass can be reduced. Furthermore, devitrification due to excessive inclusion of the Nb ₂ O ₅ component can be reduced, and a decrease in the transmittance of the glass for visible light (particularly wavelengths of 500 nm or less) can be suppressed. This also suppresses a decrease in the Abbe number. Therefore, the upper limit of the content of the Nb ₂ O ₅ component is preferably 5.0% or less, more preferably 4.0% or less, and even more preferably 3.0% or less. In particular, from the viewpoint of reducing material costs, it is most preferable that the Nb ₂ O ₅ component is not contained.
As the Nb ₂ O ₅ component, Nb ₂ O ₅ or the like can be used as a raw material.

The _WO3 component is an optional component that, when contained in an amount exceeding 0.0%, can increase the refractive index and improve resistance to devitrification while reducing the coloring of the glass due to other high refractive index components.
On the other hand, by limiting the content of the _WO3 component to 5.0% or less, the material cost of the glass can be reduced. Furthermore, the coloring of the glass caused by the _WO3 component can be reduced, thereby increasing the visible light transmittance. Therefore, the upper limit of the content of the _WO3 component is preferably 5.0% or less, more preferably 3.0% or less, and even more preferably 1.0% or less. In particular, from the viewpoint of reducing material costs, it is most preferable that the _WO3 component is not contained.
As the _WO3 component, _WO3 or the like can be used as a raw material.

The Y ₂ O ₃ component is an optional component that, when contained in an amount exceeding 0.0%, can reduce the material cost of the glass while maintaining the desired refractive index and Abbe number.
On the other hand, by setting the content of the Y ₂ O ₃ component to 10.0% or less, the decrease in the refractive index of the glass can be suppressed and the stability of the glass can be improved. Also, the deterioration of the meltability of the glass raw materials can be suppressed. Therefore, the upper limit of the content of the Y ₂ O ₃ component is preferably set to 10.0% or less, more preferably 5.0% or less, and even more preferably 3.5% or less.
As the Y ₂ O ₃ component, Y ₂ O ₃ , YF _{3 ,} etc. can be used as raw materials.

The Gd ₂ O ₃ component and the Yb ₂ O ₃ component are optional components that can increase the refractive index of the glass when contained in an amount exceeding 0.0%.
However, the raw material prices of _{the Gd2O3} component and _{the Yb2O3} component are high, and a high content of _these components increases production costs, thereby negating the effects of reducing the _Nb2O5 component, the _WO3 component, and the like. Furthermore, reducing the content of _{the Gd2O3} component and _{the Yb2O3} component can suppress an increase in the Abbe number of the glass. Therefore, the upper limits of the contents of _{the Gd2O3} component and the _Yb2O3 component are preferably 4.0% or _less , more preferably 2.0% or less, even more preferably 1.0% or less, even more preferably 0.5% or less, and even more preferably 0.1% or less. In particular, from the viewpoint of reducing material costs, it is most preferable that these components are not contained.
The Gd ₂ O ₃ component and the Yb ₂ O ₃ component can be prepared from Gd ₂ O ₃ , GdF ₃ , Yb ₂ O _{3 ,} or the like.

Ta ₂ O ₅ is an optional component that, when contained in an amount exceeding 0.0%, can increase the refractive index of the glass and improve the devitrification resistance.
However, the raw material price _{of Ta2O5} component is high, and if its content is high, the production cost increases, thereby negating the effect of reducing the _Nb2O5 component, _WO3 component, etc. Furthermore, by setting the content of _Ta2O5 component to 5.0% or less, the melting temperature of _the raw materials is lowered, and the energy required for melting the raw materials is reduced, thereby reducing the manufacturing cost of the optical glass. Therefore, the content of _Ta2O5 component is preferably _5.0 % or less, more preferably 3.0% or less, even more preferably 1.0% or less, even more preferably 0.5% or less, and even more preferably 0.1% or less as the upper limit. In particular, from the viewpoint _of reducing material costs, it is most preferable that the _Ta2O5 component _is not contained.
For the Ta ₂ O ₅ component, Ta ₂ O ₅ or the like can be used as a raw material.

The MgO component is an optional component that can improve the meltability of the glass raw materials and the devitrification resistance of the glass.
On the other hand, by limiting the content of the MgO component to 10.0% or less, it is possible to prevent a decrease in refractive index and a decrease in devitrification resistance due to an excessive content of these components. Therefore, the upper limit of the content of the MgO component is preferably set to 10.0% or less, more preferably 9.0% or less, and more preferably 8.0% or less.

The CaO component is an optional component that can increase the hardness of the glass and improve the meltability of the glass raw materials.
On the other hand, by limiting the CaO content to 20.0% or less, it is possible to prevent a decrease in refractive index and a decrease in devitrification resistance due to an excessive content of these components. Therefore, the upper limit of the CaO content is preferably set to 20.0% or less, more preferably 18.0% or less, and most preferably 15.0% or less.

The SrO component is an optional component that can improve the melting properties of the glass raw materials and the devitrification resistance of the glass.
On the other hand, by limiting the content of the SrO component to 10.0% or less, it is possible to prevent a decrease in refractive index and a decrease in devitrification resistance due to an excessive content of these components. Therefore, the upper limit of the content of the SrO component is preferably set to 10.0% or less, more preferably 9.0% or less, and most preferably 8.0% or less.

The BaO component is an optional component that, when contained in an amount exceeding 0.0%, increases the refractive index and Abbe number of the glass and decreases the liquidus temperature. The lower limit of the BaO content is preferably greater than 0.0%, more preferably 1.0% or more, and even more preferably 1.5% or more.
By keeping the BaO content at 40.0% or less, it is possible to prevent the reduction in refractive index, the reduction in devitrification resistance, and the deterioration in chemical durability (acid resistance) that would otherwise be caused by the excessive inclusion of these components. Therefore, the upper limit of the BaO content is preferably set to 40.0% or less, more preferably 35.0% or less, and most preferably 31.0% or less.

The Li ₂ O component, the Na ₂ O component and the K ₂ O component are optional components that can improve the meltability of the glass and lower the glass transition temperature when contained in an amount exceeding 0.0%.
On the other hand, by limiting each of the Li ₂ O component, Na ₂ O component, and K ₂ O component to 10.0% or less, the refractive index of the glass is less likely to decrease and devitrification of the glass can be reduced. Furthermore, deterioration of chemical durability (acid resistance) and reduction in hardness can be suppressed. Therefore, the upper limits of the contents of the Li ₂ O component, Na ₂ O component, and K ₂ O component are each preferably 10.0% or less, more preferably 5.0% or less, even more preferably 3.0% or less, and even more preferably 1.5% or less.
The Li ₂ O component, Na ₂ O component and K ₂ O component can be obtained from raw materials such as Li ₂ CO ₃ , LiNO ₃ , Li ₂ CO ₃ , Na ₂ CO ₃ , NaNO ₃ , NaF, Na ₂ SiF ₆ , K ₂ CO ₃ , KNO ₃ , KF, KHF ₂ , and K ₂ SiF _6.

The P ₂ O ₅ component is an optional component that, when contained in an amount exceeding 0.0%, can lower the liquidus temperature of the glass and improve the devitrification resistance.
On the other hand, by keeping the content of the _P2O5 component at 10.0% or less, deterioration of the chemical durability of _the glass, particularly water resistance, can be suppressed. Therefore, the upper limit of the content of _{the P2O5} component is preferably set to 10.0% or less, more preferably 5.0% or less, and even more preferably 3.0% or less.
As the _P2O5 component, Al( _PO3 ) ₃ , Ca( _PO3 ) ₂ , Ba( _PO3 ) ₂ , _BPO4 , _{H3PO4 , etc.} can be used as raw materials.

_GeO2 is an optional component that can increase the refractive index of the glass and improve the devitrification resistance when the content exceeds 0.0%.
However, _GeO2 is expensive as a raw material, and a high content of GeO2 increases production costs, thereby negating the effect of reducing _{the Gd2O3} component and _Ta2O5 component. Therefore, the upper limit of the content of the _GeO2 component is preferably 10.0% or less, _more preferably 5.0% or less, even more preferably 3.0% or less, even more preferably 1.0% or less, and even more preferably 0.1% or less. From the viewpoint of reducing material costs, the _GeO2 component does not need to be contained. _{GeO2 or} the like can be used as a raw material for the _GeO2 component.

The Al ₂ O ₃ component is an optional component that can improve the chemical durability of the glass and the devitrification resistance of the glass melt when contained in an amount of more than 0.0%. Therefore, the lower limit of the Al ₂ O ₃ component content is preferably more than 0.0%, more preferably 0.5% or more.
On the other hand, by setting the content of the Al ₂ O ₃ component to 15.0% or less, the liquidus temperature of the glass can be lowered and devitrification resistance can be improved. Therefore, the upper limit of the content of the Al ₂ O ₃ component is preferably set to 15.0% or less, more preferably 10.0% or less, even more preferably 9.0% or less, and still more preferably 8.0% or less.
As the Al ₂ O ₃ component, Al ₂ O ₃ , Al(OH) ₃ , AlF ₃ , etc. can be used as raw materials.

The Ga ₂ O ₃ component is an optional component that can improve the chemical durability of the glass and can also improve the devitrification resistance of the glass melt when the content exceeds 0.0%.
On the other hand, by setting the content of the _Ga2O3 component to 15.0% or less, the liquidus temperature of the glass _can be lowered and devitrification resistance can be improved. Therefore, the upper limit of the content of _{the Ga2O3} component is preferably set to 15.0% or less, more preferably 10.0% or less, even more preferably 5.0% or less, and still more preferably 3.0% or less.
As _{the Ga2O3} component, _Ga2O3 , Ga(OH) ₃ , etc. can be used as _raw materials.

The Bi ₂ O ₃ component is an optional component that can increase the refractive index and lower the glass transition point when it is contained in an amount exceeding 0.0%.
On the other hand, by limiting the content of the _Bi2O3 component to 5.0% or less, the liquidus temperature of the glass _can be lowered, improving devitrification resistance, and production costs _can be reduced due to the high cost of raw materials. Therefore, the upper limit of the content of the _Bi2O3 component is preferably 5.0% or less, more preferably 3.0% or less, and even more preferably 1.0% or less. In particular, from the viewpoint of reducing material costs, it is most preferable that _{the Bi2O3} component is not contained.
As the Bi ₂ O ₃ component, Bi ₂ O ₃ or the like can be used as a raw material.

_TeO2 is an optional component that can increase the refractive index and lower the glass transition point when contained in an amount exceeding 0.0%.
On the other hand, there is a problem that _TeO2 may form an alloy with platinum when melting glass raw materials in a platinum crucible or a melting tank whose parts in contact with the molten glass are made of platinum. Therefore, the content of the _TeO2 component is preferably set to an upper limit of 5.0% or less, more preferably 3.0% or less, and even more preferably 1.0% or less. In particular, from the viewpoint of reducing material costs, it is most preferable that the _TeO2 component is not contained.
The _TeO2 component can be made from TeO2 _or the like as a raw material.

The _SnO2 component is an optional component that, when contained in an amount exceeding 0.0%, reduces oxidation of the glass melt to clarify it and also increases the visible light transmittance of the glass.
On the other hand, by keeping the content of the _SnO2 component at 3.0% or less, it is possible to reduce coloration of the glass due to reduction of the glass melt and devitrification of the glass. Furthermore, alloying of the _SnO2 component with the melting equipment (especially precious metals such as Pt) is reduced, thereby extending the life of the melting equipment. Therefore, the upper limit of the content of the _SnO2 component is preferably 3.0% or less, more preferably 1.0% or less, even more preferably 0.5% or less, and even more preferably 0.1% or less.
As the _SnO2 component, SnO, _SnO2 , _SnF2 , _SnF4, etc. can be used as raw materials.

The Sb ₂ O ₃ component is an optional component that can degas the glass melt when its content exceeds 0.0%.
On the other hand, if the amount of Sb ₂ O ₃ is too large, the transmittance in the short wavelength region of the visible light region will be reduced. Therefore, the upper limit of the content of the Sb ₂ O ₃ component is preferably 1.0% or less, more preferably 0.5% or less, and even more preferably 0.3% or less.
As the Sb ₂ O ₃ component, Sb ₂ O ₃ , Sb ₂ O ₅ , Na ₂ H ₂ Sb ₂ O _{7.5H 2} O, etc. can be used as raw materials.

The component for fining and defoaming the glass is not limited to the above Sb ₂ O ₃ component, and any known fining agent, defoaming agent, or combination thereof in the field of glass manufacturing can be used.

The F component is an optional component that, when contained in an amount of more than 0.0%, can increase the Abbe number of the glass, lower the glass transition point, and improve the devitrification resistance.
However, if the content of the F component, i.e., the total amount of F in the fluorides that have substituted part or all of the oxides of one or more of the above-mentioned metal elements, exceeds 15.0%, the amount of volatilization of the F component increases, making it difficult to obtain stable optical constants and homogeneous glass, and also increasing the Abbe number more than necessary.
Therefore, the upper limit of the F content is preferably 15.0% or less, more preferably 10.0% or less, even more preferably 5.0% or less, and even more preferably 3.0% or less.
The F component can be contained in the glass by using, for example, ZrF ₄ , AlF ₃ , NaF, CaF ₂ or the like as a raw material.

By setting the mass ratio SiO ₂ /(SiO ₂ +B ₂ O ₃ +TiO ₂ ) to 0.15 to 0.45 or less, the liquidus temperature of the glass can be lowered, and stable glass can be obtained.
Therefore, the lower limit of the mass ratio SiO ₂ /(SiO ₂ +B ₂ O ₃ +TiO ₂ ) is preferably 0.15 or more, more preferably 0.16 or more, and even more preferably 0.17 or more.
On the other hand, the desired refractive index and Abbe number can be obtained by setting the _mass ratio _SiO2 /( _SiO2 + _B2O3 + _TiO2 ) to 0.45 or less. Therefore, the upper limit of the mass ratio _SiO2 / _{( SiO2} + _B2O3 + _TiO2 ) is preferably 0.45 or less, more preferably 0.44 or less, and even more preferably 0.43 or less.

The total content of _Ta2O5 , _Nb2O5 , _{WO3 ,} and _Gd2O3 is preferably 5.0% or less. In particular, by setting the total content to 5.0% or less, the contents _of these expensive components are reduced _, thereby reducing raw material costs.
Therefore, the upper limit of the mass sum (Ta ₂ O ₅ +Nb ₂ O ₅ +WO ₃ +Gd ₂ O ₃ ) is preferably 5.0% or less, more preferably 4.5% or less, and even more preferably 4.0% or less.

The total content of CaO, ZnO, and _TiO2 is preferably 10.0 to 50.0%. By setting the total content to 10.0% or more, the Knoop hardness can be increased. Therefore, the lower limit of the total content of CaO, ZnO, and _TiO2 is preferably 10.0% or more, more preferably 10.5% or more, and even more preferably 11.0% or more.
On the other hand, by setting the total content of CaO, ZnO, and _TiO2 to 50.0% or less, deterioration of devitrification resistance can be suppressed. Therefore, the upper limit of the total content of CaO, ZnO, and _TiO2 is preferably set to 50.0% or less, more preferably 49.0% or less, and even more preferably 48.0% or less.

The ratio of the total amount of BaO and ZnO to the content _{of La2O3} is preferably 0.5 to 2.1. In particular, by making this mass ratio (BaO + ZnO)/ _{La2O3 0.5} or more, the liquidus temperature of the glass is lowered, and the desired refractive index and Abbe number can be obtained.
Therefore, the lower limit of this mass ratio (BaO+ZnO)/La ₂ O ₃ is preferably 0.5 or more, more preferably 0.55 or more, and even more preferably 0.6 or more.
On the other hand, by setting this mass ratio (BaO + ZnO)/ _La2O3 to _2.1 or less, deterioration of the acid resistance by the powder method can be suppressed. Therefore, the upper _limit of (BaO + ZnO)/ _La2O3 is preferably set to 2.1 or less, more preferably 2.06 or less, and even more preferably 2.02 or less.

The ratio of the total amount of CaO, ZnO, and _Li2O to BaO is preferably 0.022 or more. In particular, by making this mass ratio (CaO+ZnO+ _Li2O )/BaO 0.022 or more, deterioration of powder-method acid resistance can be suppressed and a glass with high Knoop hardness can be obtained.
Therefore, the lower limit of this mass ratio (CaO+ZnO+Li ₂ O)/BaO is preferably 0.022 or more, more preferably 0.023 or more, and even more preferably 0.024 or more.
On the other hand, the ratio of the total amount of CaO, ZnO, and _Li2O to BaO is preferably 20.0 or less to prevent deterioration of the stability of the glass and a decrease in the refractive index. Therefore, the upper limit of the mass ratio (CaO + ZnO + _Li2O )/BaO is preferably 20.0 or less, more preferably 18.0 or less, and even more preferably 16.0 or less.

<Ingredients that should not be included>
Next, components that should not be contained in the optical glass of the present invention and components that are undesirable to contain will be explained.

Other components can be added as needed to the extent that they do not impair the properties of the glass of the present invention. However, transition metal components such as V, Cr, Mn, Fe, Co, Ni, Cu, Ag, and Mo (excluding Ti, Zr, Nb, W, La, Gd, Y, Yb, and Lu) tend to color the glass and absorb specific wavelengths in the visible range even when contained in small amounts, either alone or in combination. Therefore, it is preferable that they are substantially absent, particularly in optical glasses used with wavelengths in the visible range. Furthermore, it is preferable that Rb and Cs components are not contained, from the perspective of suppressing coloration of the glass.

Furthermore, lead compounds such as PbO and arsenic compounds such as As ₂ O ₃ are components that have a high environmental impact, and therefore it is desirable that they are not contained substantially, that is, that they are not contained at all except for unavoidable contamination.

Furthermore, in recent years, there has been a trend to reduce the use of Th, Cd, Tl, Os, Be, and Se, which are considered hazardous chemicals, and environmental measures are required not only in the glass manufacturing process, but also in the processing process and disposal after productization. Therefore, when environmental impact is a priority, it is preferable that these elements are substantially absent.

[Manufacturing method]
The optical glass of the present invention is produced, for example, as follows: High-purity raw materials for the above components, such as oxides, hydroxides, carbonates, nitrates, fluorides, and metaphosphate compounds, which are typically used in optical glass, are mixed uniformly so that the contents of each component fall within the specified ranges, the resulting mixture is placed in a platinum crucible, and melted and stirred in an electric furnace at a temperature ranging from 1000 to 1400°C for 1 to 10 hours depending on the melting difficulty of the glass raw materials, followed by homogenization by lowering the temperature to an appropriate level and then pouring the mixture into a mold and slowly cooling it.

In this case, it is preferable to use glass raw materials with high melting properties. This allows for melting at lower temperatures and in a shorter time, thereby increasing glass productivity and reducing production costs. In addition, volatilization of components and reaction with the crucible, etc. are reduced, making it easier to obtain glass with less coloration.

<Physical properties>
The optical glass of the present invention has a high refractive index and high dispersion.
In particular, the refractive index ( _nd ) of the optical glass of the present invention preferably has a lower limit of 1.78000 or more, more preferably 1.78500 or more, and even more preferably 1.79000 or more. The upper limit of this refractive index ( _nd ) may be preferably 1.98000 or less, more preferably 1.97000 or less, and even more preferably 1.96500 or less.
The Abbe number ( _νd ) of the optical glass of the present invention may have a lower limit of preferably 20.00 or more, more preferably 21.00 or more, and even more preferably 22.00 or more. The Abbe number ( _νd ) may have an upper limit of preferably 40.00 or less, more preferably 39.00 or less, and even more preferably 38.00 or less.

The optical glass of the present invention preferably has high visible light transmittance, particularly high transmittance for light on the short wavelength side of visible light, and therefore is less colored.
In particular, the optical glass of the present invention, when expressed in terms of glass transmittance, has an upper limit of the wavelength (λ ₇₀ ) at which a 10 mm thick sample exhibits a spectral transmittance of 70%, preferably 480 nm or less, more preferably 460 nm or less, more preferably 450 nm or less, and even more preferably 440 nm or less.
In the optical glass of the present invention, the shortest wavelength (λ ₅ ) at which a 10 mm thick sample exhibits a spectral transmittance of 5% is preferably 400 nm or less, more preferably 385 nm or less, and even more preferably 370 nm or less.

The glass of the present invention preferably has high resistance to devitrification, more specifically, a low liquidus temperature. That is, the upper limit of the liquidus temperature of the glass of the present invention is preferably 1300°C or lower, more preferably 1250°C or lower, and even more preferably 1200°C or lower. This reduces crystallization of the produced glass even when the molten glass is flowed at a lower temperature, thereby reducing devitrification, particularly when the glass is formed from a molten state. Furthermore, because the glass can be formed even at a lower glass melting temperature, the energy consumed during glass forming can be reduced, thereby reducing glass production costs. On the other hand, the lower limit of the liquidus temperature of the glass of the present invention is not particularly limited, but the lower limit of the liquidus temperature of the glass obtained by the present invention may be preferably 950°C or higher, more preferably 980°C or higher, and even more preferably 1000°C or higher.
In this specification, the term "liquidus temperature" refers to the lowest temperature at which no crystals are observed when a 30 cc cullet-shaped glass sample is placed in a 50 ml platinum crucible, completely melted at 1350°C, cooled to a predetermined temperature, and maintained at that temperature for 12 hours. The sample is then removed from the furnace and cooled, and the presence or absence of crystals on the surface and in the glass is immediately observed.

The acid resistance of the glasses in the examples and comparative examples was measured in accordance with the Japan Optical Glass Industry Association standard "Method for Measuring the Chemical Durability of Optical Glass" JOGIS06-2006. Specifically, glass samples crushed to particle sizes of 425 to 600 μm were placed in a pycnometer and placed in a platinum cage. The platinum cage was placed in a quartz glass round-bottom flask containing 0.01 N aqueous nitric acid solution and treated in a boiling water bath for 60 minutes. The weight loss rate (mass%) of the glass sample after treatment was calculated, and the weight loss rate (mass%) was assigned a grade of 1 if it was less than 0.20, a grade of 2 if it was 0.20 to less than 0.35, a grade of 3 if it was 0.35 to less than 0.65, a grade of 4 if it was 0.65 to less than 1.20, a grade of 5 if it was 1.20 to less than 2.20, and a grade of 6 if it was 2.20 or greater. In this case, the smaller the class number, the better the acid resistance of the glass.
In the optical glass of the present invention, it is preferably 1 to 3 grades, more preferably 1 to 2 grades.

The optical glass of the present invention preferably has a Knoop hardness of grade 6 or higher when measured using a method conforming to "JOGIS09-1975 Method for Measuring Knoop Hardness of Optical Glass." This makes it less likely that the glass will be scratched or broken during polishing, or that the surface will be scratched during transportation, etc., resulting in an optical glass that has the desired surface condition and is easy to maintain. Therefore, the Knoop hardness of the optical glass of the present invention is preferably grade 6 or higher.

[Preform and optical element]
A glass molded body can be produced from the produced optical glass, for example, by using a polishing means or a mold press molding means such as reheat press molding or precision press molding. That is, the glass molded body can be produced by subjecting the optical glass to mechanical processing such as grinding and polishing, or by producing a preform for mold press molding from the optical glass, subjecting this preform to reheat press molding, and then polishing the preform to produce a glass molded body, or by subjecting a preform produced by polishing or a preform molded by known floating molding or the like to precision press molding to produce a glass molded body. Note that the means for producing the glass molded body are not limited to these means.

As such, the optical glass of the present invention is useful for a variety of optical elements and optical designs. It is particularly preferable to form a preform from the optical glass of the present invention and use this preform to produce optical elements such as lenses and prisms through reheat press molding or precision press molding. This makes it possible to form preforms with large diameters, allowing for larger optical elements while still achieving high-definition, high-precision imaging and projection characteristics when used in optical equipment.

Glass molded articles made from the optical glass of the present invention can be used for optical elements such as lenses, prisms, and mirrors, and can also be used in applications requiring good hardness and chemical durability, such as in-vehicle optical equipment such as in-vehicle cameras.

The compositions of the examples (No. 1 to No. 29) of the present invention, as well as the refractive index (n _d ), Abbe number (ν _d ), chemical durability (acid resistance) measured by the powder method, Knoop hardness, transmittance (λ ₅ , λ ₇₀ ), and liquidus temperature of these glasses are shown in Tables 1 to 4. Note that the following examples are for illustrative purposes only, and the present invention is not limited to these examples.

The glasses in the examples of the present invention were all made by selecting high-purity raw materials used in ordinary optical glass, such as the corresponding oxides, hydroxides, carbonates, nitrates, fluorides, and metaphosphate compounds, as the raw materials for each component. These were then weighed out and uniformly mixed to achieve the compositional ratios shown in the table for each example, then placed in a platinum crucible and melted in an electric furnace at a temperature range of 1000-1400°C for 1-10 hours, depending on the melting difficulty of the glass raw materials. The mixture was then stirred to homogenize, poured into a mold, and slowly cooled.

The refractive index (n _d ) and Abbe number (ν _d ) of the glasses of the examples and comparative examples were measured in accordance with the V-block method specified in JIS B 7071-2:2018. Here, the refractive index (n _d ) is shown as a measurement value for the d-line (587.56 nm) of a helium lamp. The Abbe number (ν _d ) was calculated from the formula Abbe number (ν _d ) = [(n _d -1)/(n F -n _C )] using the refractive index (n _d ) for the d-line of a helium lamp, the refractive index (n _F ) for the F-line (486.13 _nm ) of a hydrogen lamp, and the refractive index (n _C ) for the C-line (656.27 nm). These refractive indexes (n _d ) and Abbe number (ν _d ) were determined by measuring glasses obtained at a slow cooling rate of -25°C/hr.

The transmittance of the glasses in the examples was measured in accordance with Japan Optical Glass Industry Association standard JOGIS02-2003. In the present invention, the presence and degree of coloration of the glass was determined by measuring the transmittance of the glass. Specifically, the spectral transmittance of a 10±0.1 mm thick, parallel-polished specimen was measured in the range of 200 to 800 nm in accordance with JIS Z8722 to determine λ ₅ (wavelength at 5% transmittance) and λ ₇₀ (wavelength at 70% transmittance).

In the examples, the liquidus temperature was determined by placing a 30cc cullet-shaped glass sample in a 50ml platinum crucible, completely melting it at 1350°C, lowering the temperature to the specified temperature and holding it there for 12 hours, removing it from the furnace and allowing it to cool. Immediately after cooling, the glass surface and interior were observed for the presence or absence of crystals, and the lowest temperature at which no crystals were observed was determined.

The chemical durability of the glass in the examples and comparative examples was measured in accordance with the Japan Optical Glass Industry Association standard, "Method for Measuring the Chemical Durability of Optical Glass," JOGIS06-2006. Specifically, glass samples crushed to particle sizes of 425 to 600 μm were placed in a pycnometer and placed in a platinum cage. The platinum cage was then placed in a quartz glass round-bottom flask containing 0.01 N aqueous nitric acid solution and treated in a boiling water bath for 60 minutes. The weight loss rate (mass%) of the glass sample after treatment was calculated, and the weight loss rate (mass%) was assigned a grade of 1 if it was less than 0.20, a grade of 2 if it was 0.20 to less than 0.35, a grade of 3 if it was 0.35 to less than 0.65, a grade of 4 if it was 0.65 to less than 1.20, a grade of 5 if it was 1.20 to less than 2.20, and a grade of 6 if it was 2.20 or greater. In this case, the smaller the class number, the better the acid resistance of the glass.

The Knoop hardness (Hk) of the glasses in the Examples (No. 1 to No. 29) and Comparative Example (A) was measured in accordance with the Japan Optical Glass Industry Association standard (JOGIS09-1975). Specifically, a diamond rhombic indenter (with diagonal angles of 172°30' and 130°) was pressed against the flat, polished surface of the sample with a load of 0.98 N (0.1 kgf) for 15 seconds to create an indentation, and the length of the longer diagonal of the indentation was measured and calculated using formula (1).

Knoop hardness = 1.451 F/l ² (1)
F: Load (N)
l: Length of the longer diagonal (mm)
Knoop hardness is classified as Grade 1 when it is less than 150, Grade 2 when it is 150 or more but less than 250, Grade 3 when it is 250 or more but less than 350, Grade 4 when it is 350 or more but less than 450, Grade 5 when it is 450 or more but less than 550, Grade 6 when it is 550 or more but less than 650, and Grade 7 when it is 650 or more, with the higher grade indicating harder glass.

As shown in the table, the chemical durability (acid resistance) of the optical glasses of the examples measured by the powder method was grade 3 or higher, which was within the desired range. On the other hand, the optical glasses of the comparative examples were grade 4.

Furthermore, the optical glasses of the Examples all had a refractive index ( _nd ) of 1.80000 or more, which was within the desired range, and the optical glasses of the Examples of the present invention all had an Abbe number (vd ₎ in the range of 20.00 to 40.00.

Furthermore, the optical glass of the examples of the present invention had a liquidus temperature of 1200°C or lower. This demonstrates that the optical glass of the examples of the present invention is a stable glass with excellent resistance to devitrification.

Furthermore, the optical glass in the examples of the present invention had a Knoop hardness of grade 6 or higher. This demonstrates that the optical glass in the examples of the present invention is hard glass.

Furthermore, a glass block was formed using the optical glass of the present invention, and this glass block was then ground and polished to form lenses and prisms. As a result, it was possible to stably form a variety of lens and prism shapes.

Although the present invention has been described in detail for purposes of illustration, it will be understood that this is for illustrative purposes only and that many modifications may be made by those skilled in the art without departing from the spirit and scope of the invention.

Claims (6)

In mass%,
_ZrO2 component 0.0 to 5.3%,
B ₂ O ₃ component more than 0.0% to 15.0%,
SiO ₂ component more than 0.0% to 30.0%,
ZnO component 0.0 to 40.0%,
La ₂ O ₃ component 5.0 to 30.0%,
_TiO2 component 8.0 to 40.0%,
CaO component 0.00-18.0%,
BaO component: More than 0.0 ~ 30.39 %
Contains
Does not contain PbO
The mass sum Ta ₂ O ₅ + Nb ₂ O ₅ + WO ₃ + Gd ₂ O ₃ is 5.0% or less,
the mass ratio SiO ₂ /(SiO ₂ +B ₂ O ₃ +TiO ₂ ) is 0.18 to 0.45;
the mass ratio (CaO+ZnO+Li ₂ O)/BaO is 0.024 or more;
An optical glass characterized by having a result of measuring acid resistance of grade 1 to 3 by the powder method specified in the Japan Optical Glass Industry Association Standard (JOGIS06-2006), and a result of measuring Knoop hardness of grade 6 or higher by the measurement method specified in the Japan Optical Glass Industry Association Standard (JOGIS09-1975). 2. The optical glass according to claim 1, wherein the mass sum of CaO+ZnO+TiO ₂ is 10.0 to 50.0% and the mass ratio (BaO+ZnO)/La ₂ O ₃ is 0.5 to 2.1. 3. The optical glass according to claim 1, which has a refractive index ( _nd ) of 1.78000 or more and 1.98000 or less, and an Abbe number ( _vd ) of 20.00 or more and 40.00 or less. A preform made of the optical glass according to any one of claims 1 to 3. An optical element made of the optical glass of any one of claims 1 to 3. An optical instrument comprising the optical element described in claim 5.