JP2012197217A - Optical glass - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide optical glass capable of satisfying all of following requirements: (1) the optical glass does not substantially contain environmentally unfavorable components; (2) the optical glass has a low glass transition point; (3) the optical glass has a high refractive index and low dispersion; and (4) the optical glass is excellent in devitrification resistance when forming preform glass.SOLUTION: The optical glass is characterized by including, in mass% as glass compositions, 0-21% SiO, 6.5-30% BO, 0-15.5% ZnO, 0-8% ZrO, 36.6-65% LaO, 0-16% GdO, 1-18% TaO, 0 to less than 8% NbO, 0.1-25% WOand 0.1-5% LiO, having a refractive index of 1.86 or more and substantially not containing lead, arsenic and F components.

Description

  The present invention relates to an optical glass. Specifically, the present invention relates to an optical glass suitable for an optical pickup lens of various optical disk systems, a video camera, a photographing lens of a general camera, and the like.

  Optical pickup lenses for CD, MD, DVD, and other various optical disk systems, video cameras, and photographing lenses for general cameras are generally manufactured as follows.

  First, molten glass is dropped from the tip of a nozzle to produce droplet glass (droplet molding), and grinding, polishing, and washing are performed to produce a preform glass. Alternatively, the molten glass is rapidly cast to produce a glass ingot, which is then ground, polished and washed to produce a preform glass. Subsequently, the preform glass is heated and softened, and pressure-molded with a precision-processed mold, and the surface shape of the mold is transferred to the glass to produce a lens. Such a molding method is generally called a mold press molding method.

  When adopting the mold press molding method, a glass having a glass transition point as low as possible (for example, 650 ° C. or lower) is required to precisely mold press mold the lens while suppressing deterioration of the mold. Various glasses have been proposed (see, for example, Patent Documents 1 to 3).

  If devitrification occurs when producing a preform glass, the basic performance as a lens cannot be obtained. Therefore, it is important that the glass has excellent devitrification resistance. Moreover, optical glass which does not use harmful substances, such as lead, in a glass component is desired from the heightened awareness of environmental issues. Furthermore, in recent years, with regard to optical lenses such as optical pickup lenses of various optical disc systems and photographing lenses, it has been studied to make the lenses thinner or reduce the number of lenses for the purpose of cost reduction. Therefore, a glass material having a high refractive index and low dispersion (a large Abbe number) is required.

JP 2003-267748 A JP 2003-248897 A JP 2006-16295 A

  In general, when an optical glass having a high refractive index is to be produced, the Abbe number tends to be small, that is, the glass tends to be highly dispersed. Further, when an attempt is made to produce a glass having a high refractive index and low dispersion, devitrification resistance tends to be lowered.

  Therefore, the present invention is (1) substantially free of environmentally undesirable components, (2) has a low glass transition point, (3) has a high refractive index and low dispersion, and (4) preform glass production. An object of the present invention is to provide an optical glass capable of satisfying all the requirements such as excellent devitrification resistance.

In the present invention, as a glass composition, SiO _{2 0 to} 21%, B ₂ O ₃ 6.5 to 30%, ZnO 0 to 15.5%, ZrO ₂ 0 to 8%, La ₂ O ₃ 36 by mass%. _{.6~65%, Gd 2 O 3 0~16} %, Ta 2 O 5 1~18%, Nb 2 O 5 less than _{0~8%, WO 3 0.1~25%,} Li 2 O 0.1~ The present invention relates to an optical glass containing 5%, having a refractive index of 1.86 or more, and substantially free of a lead component, an arsenic component, and an F component.

  As a result of various investigations, the present inventor has found that the above problems can be solved if the optical glass has the glass composition.

  Specifically, since the optical glass of the present invention can easily lower the glass transition point and can be press-molded at a low temperature, it can suppress deterioration of the mold during mold press molding. it can.

  Further, if the optical glass having the composition range, when the refractive index is equivalent to the conventional glass, it is possible to achieve a lower dispersion, and the Abbe number is equivalent to the conventional glass It is possible to achieve a higher refractive index. For this reason, it is possible to reduce the thickness of the lens and reduce the number of lenses necessary for the optical device, thereby reducing the component cost of the optical device.

  Furthermore, since the optical glass of the present invention is unlikely to generate a devitrified substance that impairs transparency during the preparation of the preform glass, the basic performance as a lens is not impaired. Further, since it does not substantially contain lead components, arsenic components and F components which are harmful substances, it is an environmentally preferable glass.

  In the present invention, “substantially free of lead component, arsenic component and F component” means that these components are not intentionally contained in the glass, and completely exclude unavoidable impurities. It doesn't mean that. Objectively, it means that the content of these components including impurities is less than 0.1% by mass.

Secondly, the optical glass of the present invention, further, as a glass composition, in _{mass%, TiO 2 0~10%, Y} 2 O 5 0~10%, may contain _Yb 2 O 5 _0~10% preferable.

Third, the optical glass of the present invention preferably has La ₂ O ₃ + WO ₃ of 37 to 80%.

Fourth, it is preferable that the optical glass of the present invention has a mass ratio of La ₂ O ₃ / ZrO ₂ of 5 or more.

Fifth, the optical glass of the present invention preferably has (SiO ₂ + B ₂ O ₃ + La ₂ O ₃ ) / ZrO ₂ of 7 or more by mass ratio.

Sixth, the optical glass of the present invention preferably has a mass ratio of La ₂ O ₃ / Ta ₂ O ₅ of 2 or more.

Seventh, the optical glass of the present invention preferably has La ₂ O ₅ / Gd ₂ O ₃ of 3 or more in terms of mass ratio.

Eighth, in the optical glass of the present invention, it is preferable that La ₂ O ₅ / ZnO is 3 or more by mass ratio.

Ninth, it is preferable that the optical glass of the present invention has (La ₂ O ₅ + Gd ₂ O ₃ ) / (WO ₃ + TiO ₂ + Nb ₂ O ₅ ) of 2 or more in terms of mass ratio.

Tenth, the optical glass of the present invention preferably contains 15% or less of ZrO ₂ + ZnO.

Eleventh, in the optical glass of the present invention, TiO ₂ + Nb ₂ O ₅ is preferably less than 10%.

  Twelfth, the optical glass of the present invention is preferably for mold press molding.

The optical glass of the present invention has, as a glass composition, mass%, SiO _{2 0 to} 21%, B ₂ O ₃ 6.5 to 30%, ZnO 0 to 15.5%, ZrO ₂ 0 to 8%, La _{2. O 3 36.6~65%, Gd 2 O} 3 0~16%, Ta 2 O 5 1~18%, Nb 2 O 5 less than _{0~8%, WO 3 0.1~25%,} Li 2 O 0 0.1 to 5%, a refractive index of 1.86 or more, and substantially free of lead component, arsenic component and F component.

  Below, the reason which specified content of each component as mentioned above is demonstrated. Unless otherwise specified, “%” means “mass%” in the following description.

SiO ₂ is a component constituting the skeleton of the glass, and has an effect of suppressing devitrification and improving weather resistance. It also has the effect of increasing the Abbe number. The content of SiO ₂ is preferably 0 to 21%, 0.5 to 20%, 1 to 16%, particularly preferably 1.5 to 10%. When the content of SiO ₂ is too large, the refractive index is lowered, there is a tendency that the softening point increases. On the other hand, if the content of SiO ₂ is too small, the devitrification resistance of glass becomes unstable tends to decrease. In addition, there is a tendency that weather resistance such as acid resistance and water resistance is lowered due to phase separation.

B ₂ O ₃ is a component constituting the skeleton of the glass and has a large effect of increasing the Abbe number. The content of B ₂ O ₃ is preferably 6.5 to 30%, 7.5 to 25%, and particularly preferably 8.5 to 20%. If the B ₂ O ₃ content is too large, weather resistance along with the refractive index decreases tends to decrease. On the other hand, if the content of B ₂ O ₃ is too small, it is difficult to obtain a high Abbe number. Further, the glass becomes unstable and the devitrification resistance tends to decrease, and the coloring degree tends to decrease.

SiO ₂ + B ₂ O ₃ is 8 to 25% or less, particularly preferably 10 to 20%. When SiO ₂ + _B 2 _{O 3} is too small, the liquid phase temperature tends to become high, hard high dispersion characteristics. In addition, weather resistance tends to decrease. On the other _hand, when the SiO _{2 +} B 2 _{O 3} is too large, the refractive index is lowered, there is a tendency that the softening point increases.

_{Incidentally,} B 2 _{O 3} as compared to SiO _2, less likely to increase the glass transition point. _Accordingly, B ₂ O 3 / SiO ₂ is preferably 0.5 or more. When the ratio is too small, it becomes difficult to achieve the characteristics of a high refractive index and a low softening point.

  ZnO is a component that lowers the glass viscosity without greatly changing the refractive index and Abbe number. Therefore, by adding ZnO, the glass transition point can be lowered, and the mold press molding temperature can be lowered. In addition, it is possible to obtain glass that is difficult to fuse with the mold during mold press molding. In addition, since ZnO does not have a strong devitrification tendency as compared with alkaline earth metal components (CaO, SrO, BaO, MgO), a homogeneous glass can be obtained even if contained in a large amount. The content of ZnO is preferably 0 to 15.5%, 0.5 to 12.5%, 1 to 10%, 2 to 7.5%, particularly 2.5 to 5%. When there is too much content of ZnO, there exists a tendency for a weather resistance to fall. In addition, volatilization during mold press molding increases, and striae tend to occur. On the other hand, when the content of ZnO is too small, it is difficult to achieve a low glass transition point and a high refractive index. Moreover, it becomes easy to fuse | melt with a metal mold | die at the time of mold press molding.

ZrO ₂ is a component that can increase the refractive index without substantially reducing the Abbe number. Further, since a glass skeleton is formed as an intermediate oxide, there is an effect of improving chemical durability. The content of ZrO ₂ is preferably 0 to 10%, 0.1 to 8%, 0.5 to 6%, particularly 1 to 5%. When the content of ZrO ₂ is too large, the glass transition temperature rises, press molding tends to decrease. Furthermore, devitrification composed mainly of ZrO ₂ and _La 2 _{O 3,} or devitrification mainly composed of ZrO 2, _Gd 2 _{O 3} and _Ta 2 _{O 5} is likely to precipitate.

La ₂ O ₃ is a component that can increase the refractive index without substantially reducing the Abbe number. La ₂ O ₃ is less homogenous than ZrO ₂ , Gd ₂ O ₃ , Ta ₂ O ₅ and Nb ₂ O ₅ , which also has the effect of increasing the refractive index. Glass can be obtained. The content of La ₂ O ₃ is 36.6 to 65%, 37 to 60%, 37.5 to 55%, 38 to 50%, 38.5 to 45%, particularly 39 to 42.5%. preferable. If the content of La ₂ O ₃ is too small, it is difficult to obtain a desired refractive index. On the other hand, when the content of _La 2 _{O 3} is too large, devitrification mainly during glass molding _B 2 _{O 3} and _La 2 _{O 3} is likely to generate.

Gd ₂ O ₃ is a component that increases the refractive index. Further, there is the effect of improving the devitrification resistance (B ₂ O ₃ and La ₂ O ₃ in devitrification suppression formed), a component capable of expanding the working temperature range. The content of Gd ₂ O ₃ is preferably 0 to 16%, 2 to 15%, particularly 4 to 12%. When the content of Gd ₂ O ₃ is too large, phase separation tendency becomes strong, homogeneous glass is hardly obtained. Further, the liquidus temperature rises, and a devitrified substance containing Gd ₂ O ₃ as a main component is likely to precipitate on the surface (surface devitrification). Furthermore, the Abbe number tends to decrease. However, it can be said that Gd ₂ O ₃ has a lower rate of decrease of the Abbe number compared to other components that lower the Abbe number (for example, Ta ₂ O ₅ , WO ₃ , TiO _2, etc.).

Ta ₂ O ₅ is a component that has an effect of improving the refractive index, chemical durability, and devitrification resistance (suppression of devitrified substances formed by B ₂ O ₃ and La ₂ O ₃ ). Ta ₂ O ₅ is a component having a large ratio of increasing the refractive index with respect to a decrease in Abbe number, and is an effective component for obtaining high refraction and low dispersion characteristics. The content of Ta ₂ O ₅ is preferably 1 to 18%, 4 to 17%, 7 to 17.5%, particularly preferably 10 to 17%. When the content of Ta ₂ O ₅ is too large, it decreases Abbe number, desired optical characteristics are difficult to obtain. In addition, the liquidus temperature rises, and devitrified substances containing Ta ₂ O ₅ as a main component are likely to precipitate. Furthermore, the cost is increased, which is not preferable from an economic viewpoint.

Nb ₂ O ₅ is a component having a large effect of increasing the refractive index. In the glass of relatively large containing _Ta 2 _{O 5,} serves to improve the devitrification resistance _{(La 2 O 3, Ta 2} O 5 and _B 2 _{O 3} in the suppression of devitrification to be formed) is there. Furthermore, it is a component that increases the refractive index with respect to the decrease in Abbe number, and is an effective component for obtaining high refractive index and low dispersion characteristics. The content of Nb ₂ O ₅ is preferably 0 to less than 8%, particularly preferably 0.1 to 5%. When the content of Nb ₂ O ₅ is too large, _Nb 2 _{O 5} and _La 2 _{O 3} as main components devitrification is likely to precipitate at the interface between the molten glass and the melting vessel or the like (in particular platinum member) It becomes easier to fuse with the mold during mold press molding.

WO ₃ has the effect of increasing the refractive index. In addition, since a glass skeleton is formed as an intermediate oxide, there is an effect of improving devitrification resistance (suppression of devitrified substances formed of B ₂ O ₃ and La ₂ O ₃ ). Furthermore, it is a component that increases the refractive index with respect to the decrease in Abbe number, and is an effective component for obtaining high refraction and low dispersion characteristics. In addition, since WO ₃ does not have a strong devitrification tendency as compared with Ta ₂ O ₅ and Nb ₂ O ₃ , a homogeneous glass can be obtained even if contained in a large amount. The content of WO ₃ is preferably 0.1 to 25%, 1 to 25%, 1.5 to 20%, 2 to 17.5%, particularly 2 to 15%. If the content of WO ₃ is too small, it is difficult to obtain the above effect. On the other hand, if the content of WO ₃ is too large, the Abbe number decreases, and it becomes difficult to obtain desired optical characteristics. Further, the absorption edge of the transmittance curve shifts to the long wavelength side, and the transmittance in the short wavelength region tends to decrease. Furthermore, it tends to be easily fused with the mold during mold press molding.

Li ₂ O is a component having the greatest effect of lowering the softening point among alkali metal oxides (R ′ ₂ O). The content of Li ₂ O is preferably 0.1 to 5%, 0.2 to 3%, particularly preferably 0.5 to 2% or less. Since Li ₂ O has a strong phase separation property, if the amount of Li ₂ O added is too large, the liquidus temperature becomes high, and devitrified substances containing B ₂ O ₃ and La ₂ O ₃ as main components tend to precipitate. As a result, workability tends to decrease. Moreover, there is a tendency that the volatile matter generated during mold press molding increases or the glass tends to be fused with the mold.

  In the optical glass of the present invention, in order to achieve high refractive index and low dispersion characteristics and improve devitrification resistance, it is preferable to appropriately adjust the total amount or ratio of each component as described below.

La ₂ O ₃ + WO ₃ is preferably 37 to 80%, 37.5 to 70%, particularly 38 to 60%. When La 2 _{O 3 +} WO 3 is too small, it becomes difficult to obtain the effect of improving resistance to devitrification becomes too large, difficult to achieve a high refractive index characteristic.

In terms of mass ratio, La ₂ O ₃ / ZrO ₂ is preferably 5 or more, 7 or more, particularly 10 or more. When the ratio is too small, it is difficult to obtain the effect of improving devitrification resistance.

SiO ₂ + B ₂ O ₃ + La ₂ O ₃ is preferably 35 to 75%, 37.5 to 70%, particularly preferably 38 to 65%. When _{SiO 2 + B 2 O 3 +} La 2 O 3 is too small, the effect is obtained hardly improving the devitrification resistance, difficult to achieve the characteristics of low dispersion and high transmittance. Moreover, there is a tendency that the volatile matter generated at the time of mold press molding increases, or the glass tends to be fused with the mold. On the other _hand, when the _{SiO 2 + B 2 O 3 +} La 2 O 3 is too large, it is difficult to achieve a low glass transition point.

In terms of mass ratio, (SiO ₂ + B ₂ O ₃ + La ₂ O ₃ ) / ZrO ₂ is preferably 7 or more, particularly preferably 10 or more. When the ratio is too small, it is difficult to obtain the effect of improving devitrification resistance.

In terms of mass ratio, La ₂ O ₃ / Ta ₂ O ₅ is preferably 2 or more, 2.1 or more, 2.3 or more, and particularly preferably 2.5 or more. When the ratio is too small, it becomes difficult to obtain a high Abbe number or the effect of improving devitrification resistance is difficult to obtain.

In terms of mass ratio, La ₂ O ₃ / Gd ₂ O ₃ is preferably 3 or more, particularly preferably 3.5 or more. When the ratio is too small, it is difficult to obtain the effect of improving devitrification resistance.

In terms of mass ratio, La ₂ O ₃ / ZnO is preferably 3 or more, particularly preferably 3.5 or more. When the ratio is too small, it is difficult to obtain the effect of improving devitrification resistance.

In terms of mass ratio, (La ₂ O ₃ + Gd ₂ O ₃ ) / (Ta ₂ O ₅ + WO ₃ + TiO ₂ + Nb ₂ O ₅ ) is preferably 2 or more, particularly preferably 2.5 or more. When the ratio is too large, it becomes difficult to obtain a high Abbe number or the effect of improving devitrification resistance is difficult to obtain. Moreover, it becomes easy to fuse | melt with a metal mold | die at the time of mold press molding.

ZnO + ZrO ₂ is preferably 1 to 20%, 2 to 15%, particularly preferably 3 to 12.5%. If there is too much ZnO + ZrO _2, it will be difficult to obtain the effect of improving devitrification resistance, and if it is too little, it will be difficult to achieve high refractive index characteristics.

TiO ₂ + Nb ₂ O ₅ is preferably less than 10%, 7.5% or less, particularly 5% or less. When TiO ₂ + _{Nb 2 O 5} is too large, a high Abbe number is difficult to obtain. Moreover, since the absorption in the ultraviolet region increases and the absorption edge in the transmittance curve shifts to the long wavelength side, the transmittance in the short wavelength region tends to decrease. Furthermore, it tends to be easily fused with the mold during mold press molding.

Further, the optical glass of the present invention, in addition to the above _components, may contain TiO _2, Y _{2 O 3} or _Yb 2 _{O 3.}

TiO ₂ is a component that increases the refractive index. Moreover, there is also an effect of decreasing the liquidus temperature and improving the devitrification resistance (suppression of devitrified materials formed of B ₂ O ₃ and La ₂ O ₃ ). Furthermore, it has the effect of improving the water resistance and acid resistance of the glass. The content of TiO ₂ is preferably 0 to 10%, 0.1 to 5%, particularly 1 to 2.5%. If the content of TiO ₂ is too large, the Abbe number tends to decrease. Moreover, the absorption edge in the transmittance curve is shifted to the long wavelength side, and the transmittance in the short wavelength region is likely to be lowered. Specifically, the transmittance at a wavelength of 390 to 440 nm is lowered, and there is a possibility that the use as a short wavelength lens may be hindered. Furthermore, it becomes easy to fuse | melt with a metal mold | die at the time of mold press molding.

Y ₂ O ₃ and Yb ₂ O ₃ are components that can increase the refractive index without substantially reducing the Abbe number. For this reason, devitrification resistance can be improved by substitution with La ₂ O ₃ . It also has the effect of suppressing phase separation. The contents of Y ₂ O ₃ and Yb ₂ O ₃ are each preferably 10% or less, particularly preferably 8% or less. When Y ₂ O ₃ or _Yb 2 _{O 3} content is too large, easily devitrified, they tend to work temperature range is narrowed. In addition, striae are likely to occur in the glass. In order to sufficiently obtain the above effects, it is preferable that Y ₂ O ₃ or Yb ₂ O ₃ is contained in an amount of 0.1% or more, particularly 1% or more.

Furthermore, in addition to the above components, various components can be added as long as the characteristics of the optical glass of the present invention are not impaired. Examples of such components include Al ₂ O ₃ , CaO, BaO, SrO, Na ₂ O, K ₂ O, clarifiers, and the like.

Al ₂ O ₃ is a component constituting a glass skeleton together with SiO ₂ and B ₂ O ₃ . Moreover, there exists an effect which improves a weather resistance, and especially the effect which suppresses that the component in glass selectively elutes in water is remarkable. The content of Al ₂ O ₃ is preferably 0 to 10%, particularly preferably 0.1 to 5%. When the content of Al ₂ O ₃ is too large, it tends to be devitrified. Further, the meltability is lowered, and striae and bubbles remain in the glass, which may not satisfy the required quality as lens glass.

Alkaline earth metal oxides (RO) such as CaO, BaO and SrO act as fluxes and have the effect of increasing the refractive index without substantially reducing the Abbe number. If RO is too much, devitrified materials containing B ₂ O ₃ and La ₂ O ₃ as main components are likely to precipitate during the melting or forming process, and the liquid phase temperature is likely to increase, resulting in a narrow working range. . As a result, mass production tends to be difficult. In addition, the weather resistance tends to decrease, and the amount of glass components eluted into various cleaning solutions such as polishing cleaning water tends to increase, or the glass surface tends to be significantly altered in a hot and humid state. Therefore, the total amount of RO is preferably 0 to 20%, 0.1 to 10%, particularly 1 to 5%.

  In addition, preferable content of each component of RO is as follows.

  The content of CaO is preferably 0 to 10%, particularly preferably 0.1 to 5%.

  The BaO content is preferably 0 to 20%, particularly preferably 0.1 to 5%.

  The SrO content is preferably 0 to 20%, 0.1 to 10%, particularly preferably 1 to 5%.

  In order to increase the refractive index, MgO may be added as an RO component. The content of MgO is preferably 0 to 10%, particularly preferably 0.1 to 5%. When there is too much content of MgO, it will become easy to devitrify.

Na ₂ O is a component having an effect of lowering the softening point, like Li ₂ O. The content of Na ₂ O is preferably 0 to 10%, particularly preferably 0.1 to 5%. When the content of Na 2 _O is too large, volatiles increases mainly composed of B ₂ O ₃ and Na 2 _O at the time of melting, there is a tendency to promote the formation of striae. Further, the liquidus temperature becomes _high, devitrification of the B 2 _{O 3} and _La 2 _{O 3} as a main component is easily precipitated. Furthermore, there is a tendency that the amount of generated volatile matter increases during mold press molding, and it is easy to fuse with a mold.

K ₂ O is also a component having an effect of lowering the softening point, like Li ₂ O. The content of K ₂ O is preferably 0 to 10%, particularly preferably 0.1 to 5%. When the content of K 2 _O is too large, the weather resistance tends to lower. Further, the liquidus temperature becomes _high, devitrification of the B 2 _{O 3} and _La 2 _{O 3} as a main component is easily precipitated. Furthermore, there is a tendency that the amount of generated volatile matter increases during mold press molding, and it is easy to fuse with a mold.

For example, Sb ₂ O ₃ or SnO ₂ can be added as a clarifier. The contents of Sb ₂ O ₃ and SnO ₂ are preferably 0 to 1%, 0.001 to 0.5%, 0.01 to 0.1%, particularly 0.01 to 0.05%, respectively. When the content of Sb ₂ O ₃ or SnO ₂ is too large, coloring or tend or cause devitrification.

Lead components (eg, PbO), arsenic components (eg, As ₂ O ₃ ), and F components (eg, F ₂ ) should be avoided in substantial glass for environmental reasons. Therefore, the optical glass of the present invention does not substantially contain these components.

  The refractive index (nd) of the optical glass of the present invention is preferably 1.86 to 1.95, particularly 1.87 to 1.9. Moreover, it is preferable that the Abbe numbers ((nu) d) of the optical glass of this invention are 30-50, 32-45, especially 34-42. By satisfying these optical constants, it is suitable as an optical lens for a small optical device having a high refractive index, little chromatic dispersion, and a high function.

  The glass transition point of the optical glass of the present invention is preferably 650 ° C. or lower, 640 ° C. or lower, and particularly preferably 630 ° C. or lower. If the glass transition point is too high, the mold press molding temperature becomes high, and problems such as mold oxidation, mold contamination due to volatilization of glass components, and fusion between the glass and the mold tend to occur.

The liquid phase temperature of the optical glass of the present invention is preferably 1200 ° C. or lower, particularly preferably 1150 ° C. or lower. When the liquidus temperature exceeds 1200 ° C., it is difficult to achieve a liquidus viscosity of 10 ^0.5 dPa · s or more. For example, devitrification is likely to occur when droplet forming is performed.

The degree of coloration λ ₇₀ of the optical glass of the present invention is preferably less than 450 nm, 440 nm or less, 430 nm or less, particularly 420 nm or less. When the coloring degree λ ₇₀ is 450 nm or more, the transmittance in the visible region or near-ultraviolet region is inferior, making it difficult to use it in various optical lenses. “Coloring degree λ ₇₀ ” refers to a wavelength at which the transmittance is 70% in the transmittance curve.

In order to adjust the coloring degree λ ₇₀ within the above range, the mixing of impurities such as Fe, Ni, Cr, and Cu, which are coloring components, is suppressed, or the transmittance of Nb ₂ O ₅ , WO ₃ , TiO _2, etc. It is effective to reduce the content of components that lower the content.

  Next, the optical glass of the present invention and a method for producing an optical pickup lens, a photographing lens, etc. using the optical glass will be described.

  First, after preparing a glass raw material so that it may become a desired composition, it fuse | melts in a glass melting furnace. Next, molten glass is dropped from the tip of the nozzle and molded while cooling to obtain a preform glass. Alternatively, the molten glass is rapidly cast to prepare a glass block, which is then ground, polished and washed to obtain a preform glass.

  Subsequently, the preform glass is put into a precision-processed mold, and pressure molding is performed while heating until it becomes softened, and the surface shape of the mold is transferred to the glass (mold press molding). In this way, an optical pickup lens and a photographing lens can be obtained.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example, this invention is not limited to these Examples.

  Tables 1 to 6 show examples (Nos. 1 to 42, 46 to 53) and comparative examples (Nos. 43 to 45) of the present invention, respectively.

  Each sample was prepared as follows.

  First, the glass raw material was prepared so that it might become each composition shown to a table | surface, and it melted at 1300-1450 degreeC for 3 hours using the platinum crucible. After melting, the glass melt was poured onto a carbon plate, and after annealing, a sample suitable for each measurement was produced.

About the obtained sample, refractive index (nd), Abbe number ((nu) d), glass transition point (Tg), liquidus temperature (Tl), and coloring degree (lambda) ₇₀ were measured. The results are shown in Tables 1-6.

  In addition, the refractive index was shown by the measured value with respect to d line (587.6 nm) of a helium lamp.

  The Abbe number uses the refractive index value of the d-line and the refractive index of the F-line (486.1 nm) of the hydrogen lamp and the C-line (656.3 nm) of the hydrogen lamp, and the Abbe number (νd) = [(nd -1) / (nF-nC)].

  The glass transition point was evaluated by a value measured with a thermal expansion measuring device (dilatometer).

  The liquidus temperature was remelted in an electric furnace at 1350 ° C. for 0.5 hours, held in an electric furnace having a temperature gradient for 16 hours, then taken out of the electric furnace and allowed to cool in air. It measured by calculating | requiring the deposition position of a devitrification thing with a microscope.

The degree of coloration λ ₇₀ is obtained by measuring the transmittance in a wavelength range of 200 to 800 nm at intervals of 0.5 nm using a spectrophotometer for an optically polished glass sample having a thickness of 10 mm ± 0.1 mm. The evaluation was based on a wavelength indicating 70%.

  Water resistance and acid resistance were evaluated by weight reduction of the glass after water resistance and acid resistance tests according to JOGIS (Japan Optical Glass Industry Association Standard: Powder Method) 06-1999. A water resistance of 0.10% or less and an acid resistance of 0.35% or less can be judged good.

As is clear from Tables 1 to 6, sample No. Glasses of 1 to 42 and 46 to 53 have desired optical properties such as a refractive index of 1.8527 to 1.9267, an Abbe number of 33.9 to 43.2, and a glass transition point of 648 ° C. or lower. It was low and suitable for mold press molding. Further, since the liquidus temperature is as low as 1200 ° C. or lower, it is considered suitable for droplet forming (devitrification hardly occurs). Furthermore, it can be seen that the coloring degree λ ₇₀ is 415 nm or less and the transmission characteristics in the visible region and the near ultraviolet region are excellent.

On the other hand, sample No. which is a comparative example. The glass No. 43 had a refractive index as low as 1.7910 and did not satisfy the desired optical properties. Sample No. Glass No. 44 had a high glass transition point of 690 ° C. and was not suitable for mold press molding. Moreover, coloring degree (lambda) ₇₀ was as high as 450 nm, and it was inferior to the permeation | transmission characteristic of a visible region and a near ultraviolet region. Sample No. Since glass No. 45 has a high liquidus temperature of 1260 ° C., it is considered to be inferior in devitrification resistance and not suitable for droplet forming (devitrification is likely to occur).

  The optical glass of the present invention is suitable as a glass material for mold press molding used in optical pickup lenses for CD, MD, DVD and other various optical disk systems, video cameras, photographing lenses for general cameras, and the like. It can also be used as a glass material formed by a method other than mold press molding.

Claims (12)

As a glass composition, in _{mass%, SiO 2 0~21%, B} 2 O 3 6.5~30%, ZnO 0~15.5%, ZrO 2 0~8%, La 2 O 3 36.6~65 %, Gd ₂ O ₃ 0-16%, Ta ₂ O ₅ 1-18%, Nb ₂ O ₅ 0-8%, WO ₃ 0.1-25%, Li ₂ O 0.1-5% And an optical glass having a refractive index of 1.86 or more and substantially free of a lead component, an arsenic component, and an F component. Further, as a glass composition, in _{mass%, TiO 2 0~10%, Y} 2 O 5 0~10%, the optical glass according to claim 1, characterized by containing _Yb 2 O 5 _0~10% . The optical glass according to claim 1 or 2, wherein the La ₂ O ₃ + WO ₃ is 37 to 80%. The optical glass according to any one of claims 1 to ₃ , wherein La ₂ O ₃ / ZrO ₂ is 5 or more by mass ratio. The optical glass according to any one of claims 1 to 4, wherein (SiO ₂ + B ₂ O ₃ + La ₂ O ₃ ) / ZrO ₂ is 7 or more by mass ratio. The optical glass according to any one of claims 1 to 5, wherein La ₂ O ₃ / Ta ₂ O ₅ is 2 or more by mass ratio. The optical glass according to any one of claims 1 to 6, wherein La ₂ O ₅ / Gd ₂ O ₃ is 3 or more by mass ratio. The optical glass according to any one of claims 1 to 7, wherein La ₂ O ₅ / ZnO is 3 or more in terms of mass ratio. The optical glass according to claim 1, wherein (La ₂ O ₅ + Gd ₂ O ₃ ) / (WO ₃ + TiO ₂ + Nb ₂ O ₅ ) is 20 or less by mass ratio. The optical glass according to claim 1, wherein ZrO ₂ + ZnO is 15% or less. The optical glass according to claim 1, wherein TiO ₂ + Nb ₂ O ₅ is less than 10%.   It is an object for mold press molding, The optical glass in any one of Claims 1-11 characterized by the above-mentioned.