JP4687010B2 - Glass for optical lenses - Google Patents

Description

The present invention relates to glass for optical lenses .

  Refractive index (nd) is 1.55-1.60, Abbe number (νd) for optical pickup lenses of various optical disk systems such as CD, MD, DVD, and optical lenses of video cameras, digital cameras, film cameras, etc. An optical glass of 57 or more is used.

Conventionally, glass having a high lead content (for example, see Patent Document 1) has been used as an optical glass for the purpose of increasing the refractive index. However, recently, SiO ₂ − containing no lead from the viewpoint of environmental problems. B ₂ O ₃ —RO—R ′ ₂ O-based glass (for example, see Patent Documents 2 to 4) is being switched. R ′ is one or more elements selected from the group consisting of Li, Na and K, and R is one or more elements selected from the group consisting of Mg, Ca, Sr, Ba and Zn It is. In this type of glass, B ₂ O ₃ is added to increase the Abbe number, and R ′ ₂ O is added to lower the softening point and facilitate molding.
JP 58-130136 A JP-A-6-107425 Japanese Patent Application Laid-Open No. 2000-302459 JP 2004-137145 A

  These optical pickup lenses and optical lenses are prepared by dripping molten glass from the tip of the nozzle, grinding, polishing, and washing, preform glass obtained by quenching or melting glass to produce a glass block, and also grinding, A so-called mold press molding method is widely used in which preform glass obtained by polishing and washing is softened by heating and the surface shape of a precision-processed mold is transferred to the glass.

  The optical glass used in the mold press molding method has the required optical properties (refractive index, Abbe number), as well as a low softening point, acid resistance, and weather resistance so as not to deteriorate the mold. Is required to be high.

  However, the optical glasses disclosed in Patent Documents 2 to 4 may not have sufficient acid resistance. For example, the processing of the optical lens includes cutting, polishing, and cleaning steps, but an acidic solution having a pH of 2 to 4 is used in order to efficiently remove the polishing powder. However, if the acid resistance is not sufficient, the glass surface is altered. When preform glass with surface alteration is molded by press, defects such as devitrification, cloudiness and bubbles are generated.

  Further, even if optical glass is processed and incorporated into a final product as a part, if the glass surface is exposed to a high-temperature and high-humidity environment for a long period of time, the glass surface may be denatured or discolored.

The objective of this invention is providing the glass for optical lenses which has sufficient acid resistance and a weather resistance, satisfy | filling an optical characteristic.

The present inventors have found that SiO ₂ —B ₂ O ₃ —RO—R ′ ₂ O-based glass contains a large amount of B ₂ O ₃ and R ′ ₂ O. Ascertains that the components may cause elution and cause part of B ₂ O ₃ to be replaced with SiO ₂ and part of R ′ ₂ O to be replaced with CaO, SrO and / or BaO. As a result, it has been found that the generation of cloudiness in the acid cleaning step and the alteration of the glass surface due to long-term use can be suppressed, and the present invention has been proposed.

That is, a glass optical lens of the present invention, in _{mass%, SiO 2 42~60%, B} 2 O 3 2~10%, CaO 0.5~11%, BaO 9.8 ~11.5%, SrO 0 to 10%, Li ₂ O 2 to 10%, ZrO ₂ 0 to 3%, La ₂ O ₃ 0 to 2.5% are contained, and the total amount of Li ₂ O, Na ₂ O and K ₂ O is 3 to 10% (excluding the case where Y ₂ O ₃ is 1 to 10% by mass).

Also, glass optical lens of the present invention has a refractive index of 1.55 to 1.60, an Abbe number of 57 or more, the acid dissolution amount is a less than 0.65 mass%, after high-temperature and high-humidity treatment The transmittance at a wavelength of 500 nm is 80% or more at a thickness of 10 mm, and the reduction in transmittance due to the treatment is 10% or less.

  The acid elution amount is based on Japan Optical Glass Industry Association Standard 06-1975, and a glass sample crushed to a particle size of 420 to 590 μm is weighed in a mass equal to its specific gravity and placed in a platinum bowl. The nitric acid was added and immersed in a boiling water bath for 60 minutes, and the mass reduction rate (mass%) of the glass sample was calculated.

  In the high-temperature and high-humidity treatment, a glass sample whose surfaces were mirror-finished so as to have a thickness of 10 mm was left in a high-temperature and high-humidity environment of 60 ° C. and 90% for 168 hours. In addition, the transmittance | permeability was measured using the spectrophotometer (Shimadzu UV-3100PC).

Since the glass for optical lenses of the present invention has the above composition, it has optical characteristics such as a refractive index of 1.55 to 1.60 and an Abbe number of 57 or more without substantially using lead. Excellent in acid resistance and weather resistance. Therefore, the glass surface does not deteriorate even if it is washed with an acidic solution in the washing step or exposed to a high temperature and humidity environment for a long period of time.

Glass optical lens of the present invention is preferably, acid elution amount is a less than 0.65 wt%, the transmittance at a wavelength of 500nm after the high-temperature and high-humidity treatment at least 80% in thickness 10 mm, The decrease in transmittance due to the treatment can be made within 10%.

When the acid elution amount is 0.65% by mass or more, when acid cleaning is performed, clouding and devitrification are generated, and it becomes difficult to function as glass for optical lenses .

  Further, in the high-temperature and high-humidity treatment, if the transmittance after treatment is lower than 80%, it is difficult to function as an optical component. Further, if the decrease in the transmittance due to the treatment is more than 10%, it is not preferable because it easily deteriorates with time.

The reason why the composition range of the optical lens glass is limited as described above will be described.

SiO ₂ is a component that constitutes the skeleton of the glass, is a component that has a large effect of increasing the Abbe number after B ₂ O ₃ , and is also a component that improves weather resistance. When the content of SiO ₂ is more than 60%, the refractive index tends to be low and the softening point tends to be high. On the other hand, if it is less than 42%, acid resistance and weather resistance tend to deteriorate. A preferable range of the content of SiO ₂ is 45 to 57%, and a more preferable range is 50 to 55%.

B ₂ O ₃ has an effect of increasing the Abbe number, but as mentioned above, when it is contained in a large amount, specifically more than 10%, the acid resistance tends to be lowered. On the other hand, when the content is less than 2%, it becomes difficult to make the Abbe number 57 or more. A preferable range of the content of B ₂ O ₃ is 5 to 9.5%, a more preferable range is 7 to 9.2%, and a further preferable range is 7 to 9%.

  CaO is a component that can increase the weather resistance and acid resistance by substituting an alkali metal component because it has the effect of lowering the softening point next to the alkali metal oxide. It also has the effect of increasing the refractive index. However, if contained in a large amount, the glass surface is likely to be altered when exposed to a high temperature and humidity environment for a long period of time. The range of preferable CaO content is 1 to 10%, and the more preferable range is 5 to 10%.

BaO is a component that improves weather resistance and increases the refractive index, and also improves workability by lowering the liquidus temperature of the glass. However, if contained in a large amount, the glass surface is likely to be altered when exposed to a high temperature and humidity environment for a long period of time. The range of preferable BaO content is 9.8 to 11.5 % .

  SrO, like BaO, is a component that increases weather resistance and increases the refractive index, and also improves workability by lowering the liquidus temperature of the glass. However, if contained in a large amount, the glass surface is likely to be altered when exposed to a high temperature and humidity environment for a long period of time. A preferable range of the SrO content is 3 to 10%, and a more preferable range is 5 to 10%.

Li ₂ O is used as an essential component because it has an effect of lowering the melting temperature and softening point and improving workability. A preferable range of Li ₂ O content is 3.5 to 9%, and a more preferable range is 5 to 9%. If it exceeds 10%, the phase separation is strong, the liquidus temperature becomes high, and the workability deteriorates. On the other hand, if it is less than 2%, the melting temperature tends to be high.

Li ₂ O, Na ₂ O and K ₂ O have the effect of lowering the melting temperature and softening point and improving workability, but the total amount is 3 to 10 %, preferably 5 to 10%. When the total amount of Li ₂ O, Na ₂ O and K ₂ O increases, the surface alteration tends to be easily altered in the cleaning process. In addition, the liquidus temperature rises, the working range is narrowed, and the mass productivity tends to be adversely affected. On the other hand, when the total amount thereof decreases, the softening point increases and the workability tends to be impaired.

Na ₂ O has the effect of lowering the melting temperature and softening point and improving workability in the same manner as Li ₂ O. However, if the amount is too large, the amount of volatile matter formed by B ₂ O ₃ —Na ₂ O at the time of melting the glass increases, which tends to promote the formation of striae. The Na ₂ O content is preferably 5% or less, particularly preferably 3% or less.

K ₂ O, like Na ₂ O, has the effect of lowering the melting temperature and softening point and improving workability. However, if the amount is too large, the amount of volatile matter formed by B ₂ O ₃ —K ₂ O at the time of melting the glass increases, which tends to promote the generation of striae. The content of K ₂ O is desirably 5% or less, particularly 3% or less.

ZrO ₂ is a component added to increase the refractive index and improve the weather resistance. However, as the content increases, the Abbe number tends to decrease and the tendency to devitrification also increases, so that a homogeneous glass cannot be obtained.

La ₂ O ₃ has the effect of increasing the refractive index without decreasing the Abbe number. However, since it will tend to devitrify if contained excessively, the content is preferably 2.5% or less. Further, when performing mold press molding, if the content is large, there is a tendency to fuse with the mold.

The glass for optical lenses of the present invention can contain Al ₂ O ₃ , MgO and / or ZnO for the purpose of improving the weather resistance.

Al ₂ O ₃ is a component constituting a glass skeleton together with SiO ₂ , has an effect of improving weather resistance, and can be contained up to 10%. Moreover, it has the remarkable effect which suppresses that the alkaline component in glass elutes in water. However, when the content of Al ₂ O ₃ increases, the refractive index tends to decrease and the softening point tends to increase. A preferable range of the content of Al ₂ O ₃ is 0 to 8%, and a more preferable range is 1 to 5%.

  MgO can be added up to 5% in order to increase the weather resistance and increase the refractive index. However, if the content is large, the tendency of phase separation is strong, and the liquidus temperature tends to be increased. A preferred range for the content of MgO is 4% or less, and a more preferred range is 3% or less.

  ZnO is a component added to increase the refractive index and improve the weather resistance, and can be contained up to 5%. However, as the content increases, the Abbe number tends to decrease, the tendency to devitrification also increases, and it becomes difficult to obtain a homogeneous glass. Therefore, the content is desirably 3% or less.

Components other than those described above can be added as appropriate to the optical lens glass of the present invention.

Since Sb ₂ O ₃ , As ₂ O ₃ , and SnO ₂ function as a fining agent, each can be added up to 0.5%. However, since As ₂ O ₃ is an environmentally hazardous substance, it is preferably not substantially contained.

Bi ₂ O ₃ is a component added to increase the refractive index. However, since there exists a tendency for glass to color when content increases, it is preferable that it is 5% or less.

P ₂ O ₅ is a component added to lower the liquidus temperature. However, as the content increases, the glass tends to phase-separate and the surface tends to become cloudy in the washing step, so the content is preferably 5% or less.

TiO ₂ and Nb ₂ O ₅ are effective components for increasing the refractive index, but on the other hand, they cause a significant decrease in the Abbe number, so the content of each of TiO ₂ and Nb ₂ O _{5 is} 0.3%. The following is preferable.

  PbO is an effective component for increasing the refractive index, but it is preferably not substantially contained since it is an environmental load substance.

The glass for optical lenses of the present invention preferably has a softening point of 630 ° C. or lower because it can be molded by a mold press, so that productivity can be improved. A softening point higher than 630 ° C. is not preferable because the surface of tungsten carbide most commonly used as a mold is likely to corrode.

In addition, since the glass for optical lenses of the present invention tends to have a density of 3 g / cm ³ or less, the weight of optical components is reduced, and further, the weight of equipment such as CDs, DVDs, and digital cameras equipped with the optical components is reduced. It is easy and preferable.

Next, the manufacturing method of optical components, such as a lens, using the glass for optical lenses of this invention is demonstrated.

  First, the glass raw material prepared so as to have a desired composition is melted at 1200 to 1400 ° C.

  Subsequently, the molten glass is poured out and formed into a predetermined shape.

  Finally, the glass piece molded into a predetermined shape is subjected to processing such as cutting, grinding and polishing, and washed and dried to produce an optical component.

  In addition, when mold press molding is possible, the molten glass is formed into a preform of a size that can be mold pressed, the preform is heated and softened, molded press and processed into a desired shape, and then washed and dried. To make optical components.

  As a method for forming a preform, it may be prepared by cutting out into a predetermined shape from a plate-like or lump-like glass piece and polishing and washing. However, a predetermined amount is dropped continuously before grinding, polishing and washing. It is preferable to use a droplet forming method because it can be easily formed.

Hereinafter, the glass for optical lenses of this invention is demonstrated in detail based on an Example.

Table 1 shows Examples 1 to 3, Reference Examples 1 and 2 , and Comparative Examples 1 to 3.

  Each sample was produced as follows.

  First, glass raw materials prepared so as to have the composition shown in Table 1 were put in a platinum crucible and melted at 1350 ° C. for 3 hours.

  Next, the molten glass was poured out on a carbon plate, cooled and solidified, and then annealed to prepare a sample.

  The refractive index was shown by the measured value at the d-line (wavelength: 587.6 nm) of a helium lamp using a refractometer (KPR-200, manufactured by Kalnew Optical Industry Co., Ltd.)

  The Abbe number was measured using a refractometer (KPR-200, manufactured by Kalnew Optical Industry Co., Ltd.) as described above for d line, hydrogen lamp F line (wavelength: 486.1 nm), and hydrogen lamp C line (wavelength: 656. The value obtained by measuring the refractive index at 3 nm) was set to {(nd-1) / (nF-nC)} when nd, nF, and nC were used.

  The softening point was measured using a fiber elongation method based on JIS R 3104.

  The density was measured by cutting the sample into a size of 10 × 10 × 20 mm and using the Archimedes method in water.

  The acid resistance is based on Japan Optical Glass Industry Association Standard 06-1975, and a glass sample crushed to a particle size of 420 to 590 μm is weighed in a mass equal to its specific gravity and placed in a platinum bowl. Nitric acid was added and immersed in a boiling water bath for 60 minutes, and the mass reduction rate (mass%) of the glass sample was calculated.

  As for weather resistance, a sample whose surfaces are mirror-finished so that the thickness is 10 mm is left in a high-temperature and high-humidity environment of 60 ° C. and 90% for 168 hours, and the transmittance at a wavelength of 500 nm before and after the treatment is measured with a spectrophotometer (Shimadzu Corporation). Manufactured by UV-3100PC) and evaluated by the difference between the transmittance after the treatment and the transmittance before and after the treatment.

As is clear from Table 1, Examples 1 to 3 had a refractive index of 1.5817 to 1.5853 and an Abbe number of 58.9 to 59.5 . The mass reduction rate indicating acid resistance is as good as 0.51% or less, and in weather resistance, the transmittance after treatment is 83.3% or more, and the difference in transmittance before and after treatment is 6.1. It was small and good at less than%. Further, since the softening point is 590 to 618 ° C., mold press molding is also possible.

  On the other hand, in Comparative Example 1, the mass reduction rate indicating acid resistance is 1.15%, and in Comparative Examples 2 and 3, the transmittance after treatment is 77.5% or less in weather resistance, and before and after treatment. The difference in transmittance was 11.7% or more.

The glass for optical lenses of the present invention is made of glass that does not substantially contain lead, has a refractive index of 1.55 to 1.60, an Abbe number of 57 or more, and has excellent acid resistance and weather resistance. It can be used for optical pickup lenses such as DVDs and optical lenses such as video cameras and digital cameras.

  Further, since the glass component is not easily volatilized even during the molding process due to its low softening point and the mold is not easily deteriorated, it is suitable as an optical glass for mold press molding.

Claims (4)

By _{mass%, SiO 2 42~60%, B} 2 O 3 2~10%, CaO 0.5~11%, BaO 9.8 ~11.5%, SrO 0~10%, Li 2 O 2~10 %, ZrO ₂ 0 to 3%, La ₂ O ₃ 0 to 2.5%, and the total amount of Li ₂ O, Na ₂ O and K ₂ O is 3 to 10% (provided that Y ₂ O ₃ Is 1 to 10% by mass).   The glass for optical lenses according to claim 1, wherein the softening point is 630 ° C or lower.   The glass for optical lenses according to claim 1, wherein the glass for optical lenses is used for mold press molding.   The refractive index is 1.55 to 1.60, the Abbe number is 57 or more, the acid elution amount is less than 0.65% by mass, and the transmittance at a wavelength of 500 nm after high temperature and high humidity treatment is 80% at a thickness of 10 mm. The optical lens glass according to any one of claims 1 to 3, wherein a reduction in transmittance due to the treatment is 10% or less.