Optical glass, preform, and optical element

Abstract

To provide an inexpensive optical glass having a low specific gravity to a refractive index and high devitrification resistance in spite of being a high refractive index (nd) glass.SOLUTION: In which SiO2, B2O3, La2O3, and TiO2 are essential components, in mass% on an oxides basis, SiO2 components are more than 0% and 15.0% or less, B2O3 components are more than 0% and 15.0% or less, La2O3 components are 20.0 to 40.0%, TiO2 components are 20.0 to 40.0%, and the sum of the contents of RO components (in the formula, R is one or more selected from the group consisting of Mg, Ca, Sr, Ba, and Zn) is more than 0% and 18.0% or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical glass, a preform, and an optical element. [Background technology]

[0002] Optical glass and optical elements can be used in applications such as combining lenses of different optical regions to improve the optical properties of cameras and imaging devices, or being incorporated into optical equipment to realize various optical designs. In particular, reducing the weight of optical glass and optical elements leads to more compact and lightweight optical equipment bodies, modules, etc. For example, in cameras with zoom and autofocus functions, lightweight optical elements allow for smoother power transmission between the actuator and lens, improving performance.

[0003] On the other hand, La-based glass described in Patent Document 1, P—Nb-based glass described in Patent Document 2, and Bi-based glass described in Patent Document 3 are known as glasses with high refractive index. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Publication number CN102745894 [Patent Document 2] Patent No. 4262256 [Patent Document 3] Japanese Patent Publication No. 2020-19710 Summary of the Invention [Problem to be solved by the invention]

[0005] In producing glass, the specific gravity tends to increase as the refractive index increases by increasing the content of components that increase the refractive index. The glasses disclosed in Patent Documents 1 and 2 contain large amounts of components with high specific gravity, such as rare earth components and Bi2O3 components, and therefore have a high specific gravity relative to the refractive index, and it cannot be said that the weight of the optical glass is sufficiently reduced.

[0006] In order to reduce the material costs of optical glass, it is desirable that the raw material costs of optical glass be as low as possible. However, the glass described in Patent Document 3 contains a large amount of Nb2O5, an expensive raw material, and therefore it is difficult to say that it fully meets this demand.

[0007] The present invention has been made in view of the above problems, and an object of the present invention is to provide an inexpensive optical glass which has a low specific gravity relative to its refractive index and is highly resistant to devitrification. [Means for solving the problem]

[0008] The present inventors have conducted extensive testing and research to solve the above problems, and as a result have discovered that when the SiO2 component, B2O3 component, La2O3 component, TiO2 and RO component are used in combination and the mass ratio is adjusted, an inexpensive optical glass having a low specific gravity relative to the refractive index and high resistance to devitrification can be obtained, which has led to the completion of the present invention. Specifically, the present invention provides the following:

[0009] (1) The essential components are SiO2, B2O3, La2O3, and TiO2. In mass % based on oxides, SiO2 content is more than 0% and less than 15.0%. B2O3 component is more than 0% and 15.0% or less, La2O3 component 20.0 to 40.0%, Contains 20.0 to 40.0% TiO2. the sum of the contents of RO components (wherein R represents one or more selected from the group consisting of Mg, Ca, Sr, Ba, and Zn) is more than 0% and 18.0% or less; The mass ratio SiO2 / (SiO2+B2O3) is 0.40 or more, Mass ratio (La2O3+TiO2) / (SiO2+B2O3) is 3.3 or more and 7.5 or less Optical glass.

[0010] (2) The optical glass according to (1), which has a refractive index (nd) of 1.95000 to 2.15000, an Abbe number (νd) of 20.00 to 30.00, and satisfies the relationship d≦7.494×nd−10.361, where d is the specific gravity and nd is the refractive index.

[0011] (3) The mass ratio SiO2 / (SiO2+B2O3) is 0.40 or more; Mass ratio (La2O3+TiO2) / (SiO2+B2O3) is 3.3 or more and 7.5 or less The optical glass of (1) or (2).

[0012] (4) The optical glass according to any one of (1) to (3), in which the Ta2O5 component is 2.0% or less by mass and the mass ratio Y2O3 / La2O3 is 0.40 or less.

[0013] (5) An optical element blank made of the optical glass according to any one of (1) to (4).

[0014] (6) An optical element made of the optical glass according to any one of (1) to (4). [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a graph showing the relationship between refractive index (nd) and specific gravity (d) for glasses in examples of the present application. DETAILED DESCRIPTION OF THE INVENTION

[0016] The optical glass of the present invention is SiO2 content is more than 0% and less than 15.0%. B2O3 component is more than 0% and 15.0% or less, La2O3 component 20.0 to 40.0%, Contains 20.0 to 40.0% TiO2. the sum of the contents of RO components (wherein R represents one or more selected from the group consisting of Mg, Ca, Sr, Ba, and Zn) is more than 0% and 18.0% or less; The mass ratio SiO2 / (SiO2+B2O3) is 0.40 or more, The mass ratio (La2O3+TiO2) / (SiO2+B2O3) is 3.3 or more and 7.5 or less. According to the present invention, when the SiO2 component, B2O3 component, La2O3 component, TiO2 and RO component are used in combination and the mass ratio is adjusted, an inexpensive glass can be obtained that has a low specific gravity relative to the refractive index.

[0017] Hereinafter, embodiments of the optical glass of the present invention will be described in detail, but the present invention is not limited to the following embodiments and can be practiced 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.

[0018] [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 % of the total amount of glass material, calculated as an oxide. Here, "oxide-based composition" refers to the composition 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 amount of oxides produced being 100 mass %.

[0019] <Required and optional ingredients> The SiO2 component is an essential component that can increase the viscosity of the glass melt, reduce coloration of the glass, and improve devitrification resistance. Therefore, the content of the SiO2 component is preferably more than 0%, more preferably 1.0% or more, even more preferably 2.0% or more, even more preferably 3.0% or more, even more preferably 4.0% or more, and even more preferably 5.0% or more. On the other hand, by keeping the content of the SiO2 component at 15.0% or less, the decrease in refractive index can be suppressed and the specific gravity can be reduced. Therefore, the content of the SiO2 component is preferably 15.0% or less, more preferably 13.0% or less, even more preferably 11.0% or less, even more preferably 9.0% or less, even more preferably 7.0% or less, and even more preferably 6.0% or less. The SiO2 component can be made from SiO2, K2SiF6, Na2SiF6, or the like.

[0020] The B2O3 component is an essential component that is indispensable as a glass-forming oxide in the optical glass of the present invention that contains a large amount of rare earth oxides. In particular, by including more than 0% of the B2O3 component, the devitrification resistance of the glass can be improved and the specific gravity can be reduced. Therefore, the content of the B2O3 component is preferably more than 0%, more preferably 1.0% or more, even more preferably 2.0% or more, and still more preferably 3.0% or more. On the other hand, by keeping the content of the B2O3 component at 15.0% or less, it is possible to prevent a decrease in the refractive index, an increase in the Abbe number, and a deterioration in chemical durability. Therefore, the content of the B2O3 component is preferably 15.0% or less, more preferably 13.0% or less, even more preferably 12.0% or less, even more preferably 10.0% or less, even more preferably 8.0% or less, and even more preferably 6.0% or less. The B2O3 component can be obtained from raw materials such as H3BO3, Na2B4O7, Na2B4O7·10H2O, and BPO4.

[0021] The La2O3 component is an essential component that increases the refractive index and is also a component that is unlikely to color the glass. Therefore, the content of the La2O3 component is preferably 20.0% or more, more preferably 23.0% or more, even more preferably 25.0% or more, even more preferably more than 27.0%, and even more preferably 29.0% or more. On the other hand, by keeping the content of the La2O3 component at 40.0% or less, the stability of the glass can be improved, devitrification can be reduced, and an increase in specific gravity can be suppressed. Therefore, the content of the La2O3 component is preferably 40.0% or less, more preferably 38.0% or less, even more preferably 36.0% or less, and even more preferably 34.0% or less. The La2O3 component can be prepared from raw materials such as La2O3, La(NO3)3·XH2O (X is an arbitrary integer).

[0022] The TiO2 component is an essential component that can increase the refractive index, reduce the specific gravity, and improve devitrification resistance. Therefore, the content of the TiO2 component is preferably 20.0% or more, more preferably 22.0% or more, even more preferably 24.0% or more, even more preferably 26.0% or more, and still more preferably 28.0% or more. On the other hand, by keeping the content of the TiO2 component at 40.0% or less, devitrification due to excessive inclusion of the TiO2 component can be suppressed. Therefore, the content of the TiO2 component is preferably 40.0% or less, more preferably 38.0% or less, even more preferably 36.0% or less, even more preferably 34.0% or less, even more preferably 32.0% or less, and even more preferably less than 30.0%. As the TiO2 component, TiO2 or the like can be used as a raw material.

[0023] The sum of the masses of RO components (wherein R is one or more selected from the group consisting of Ca, Sr, Ba, and Zn) is preferably more than 0% and 18.0% or less. In particular, by making this mass sum exceed 0%, meltability during glass production and devitrification resistance can be improved. Therefore, this mass sum is preferably exceeding 0%, more preferably 1.5% or more, even more preferably 2.0% or more, even more preferably 3.5% or more, even more preferably 5.0% or more, and even more preferably 6.0% or more. On the other hand, by keeping this mass sum at 18.0% or less, a decrease in the refractive index can be suppressed. Therefore, this mass sum is preferably 18.0% or less, more preferably 16.0% or less, even more preferably 14.0% or less, and even more preferably 12.0% or less.

[0024] The mass ratio SiO2 / (SiO2+B2O3) is preferably 0.40 or more. In particular, by setting this mass ratio to 0.40 or more, the viscosity of the molten glass can be increased and devitrification resistance can be improved. Therefore, this mass ratio is preferably 0.40 or more, more preferably 0.45 or more, even more preferably 0.50 or more, and even more preferably 0.55 or more. On the other hand, by setting this mass ratio to 1.0 or less, the meltability during glass production can be improved and devitrification resistance can be increased. Therefore, this mass ratio is preferably set to 1.0 or less, more preferably 0.80 or less, even more preferably 0.75 or less, even more preferably 0.70 or less, and still more preferably 0.65 or less.

[0025] The mass ratio (La2O3 + TiO2) / (SiO2 + B2O3) is preferably 3.3 or more and 7.5 or less. In particular, by setting this mass ratio to 3.3 or more, a glass with a low specific gravity relative to the refractive index can be obtained. Therefore, this mass ratio is preferably 3.3 or more, more preferably 3.5 or more, and even more preferably 4.0 or more. On the other hand, devitrification resistance can be improved by setting this mass ratio to 7.5 or less, and therefore this mass ratio is preferably set to 7.5 or less, more preferably 7.0 or less, and even more preferably 6.5 or less.

[0026] The mass ratio Y2O3 / La2O3 is preferably 0.40 or less. In particular, by making this mass ratio greater than 0, a glass with a low specific gravity relative to the refractive index can be obtained. Therefore, this mass ratio is preferably greater than 0, more preferably 0.10 or greater, even more preferably 0.12 or greater, and even more preferably 0.14 or greater. On the other hand, devitrification resistance can be improved by setting this mass ratio to 0.40 or less, and therefore this mass ratio is preferably set to 0.40 or less, more preferably 0.38 or less, and even more preferably 0.36 or less.

[0027] The Nb2O5 component is an optional component that, when contained in an amount exceeding 0%, increases the refractive index of the glass and lowers the liquidus temperature of the glass, thereby improving devitrification resistance. Therefore, the content of the Nb2O5 component may be preferably 0% or more, more preferably 1.0% or more, even more preferably 3.0% or more, even more preferably 6.0% or more, and even more preferably 8.0% or more. On the other hand, by keeping the content of the Nb2O5 component at 18.0% or less, the material cost of the glass can be reduced and a decrease in the Abbe number can be suppressed. Furthermore, devitrification due to an excessive content of the Nb2O5 component 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. Therefore, the content of the Nb2O5 component is preferably 18.0% or less, more preferably 15.0% or less, even more preferably 13.0% or less, and even more preferably 10.0% or less.

[0028] The Y2O3 component is an optional component that, when contained at more than 0%, can reduce the material cost of the glass and the specific gravity of the glass while maintaining a high refractive index and a high Abbe number. Therefore, the content of the Y2O3 component may be preferably 0% or more, more preferably 1.0% or more, even more preferably 2.0% or more, and even more preferably 4.0% or more. On the other hand, by keeping the content of the Y2O3 component at 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. Furthermore, the deterioration of the melting properties of the glass raw materials can be suppressed. Therefore, the content of the Y2O3 component is preferably 15.0% or less, more preferably 12.0% or less, even more preferably 9.0% or less, and even more preferably 7.0% or less.

[0029] The ZrO2 component is an optional component that, when contained at more than 0%, can increase the refractive index and Abbe number of the glass and improve devitrification resistance. Therefore, the content of the ZrO2 component may be preferably more than 0%, more preferably 1.0% or more, even more preferably more than 3.5%, even more preferably more than 5.0%, and even more preferably 6.5% or more. On the other hand, by keeping the content of ZrO2 at 15.0% or less, devitrification due to excessive inclusion of ZrO2 can be reduced. Therefore, the content of ZrO2 is preferably 15.0% or less, more preferably less than 12.0%, even more preferably less than 10.0%, and still more preferably less than 8.0%.

[0030] The Gd2O3 component, the Yb2O3 component, and the Lu2O3 component are optional components that can increase the refractive index and Abbe number of the glass when contained at more than 0%. However, the raw material prices of the Gd2O3 component, the Yb2O3 component, and the Lu2O3 component are high, and if their contents are high, the production costs and the specific gravity of the glass increase. Therefore, the contents of the Gd2O3 component, the Yb2O3 component, and the Lu2O3 component are each preferably 10.0% or less, more preferably 8.0% or less, even more preferably 7.0% or less, and even more preferably 4.0% or less. In particular, from the viewpoint of reducing material costs, it is most preferable that these components are not contained.

[0031] The Ta2O5 component is an optional component that, when contained in an amount exceeding 0%, can increase the refractive index of the glass and improve the devitrification resistance. However, the raw material price of the Ta2O5 component is high, and a high Ta2O5 content increases production costs. Furthermore, by limiting the Ta2O5 content to 10.0% or less, the melting temperature of the raw materials is lowered, reducing the energy required to melt the raw materials, thereby reducing the manufacturing costs of the optical glass. Therefore, the Ta2O5 content is preferably 10.0% or less, more preferably 5.0% or less, even more preferably 3.0% or less, and even more preferably 2.0% or less. From the perspective of reducing material costs in particular, it is most preferable to not include the Ta2O5 component.

[0032] The WO3 component is an optional component that, when contained in excess of 0%, can increase the refractive index, lower the glass transition temperature, and improve devitrification resistance while reducing the coloration of the glass caused by other high refractive index components. Therefore, the content of the WO3 component may be preferably 0% or more, more preferably 0.3% or more, and even more preferably 0.5% or more. On the other hand, by keeping the WO3 content at 10.0% or less, the material cost of the glass can be reduced, the Abbe number can be prevented from decreasing, and the specific gravity can be reduced. Furthermore, the coloring of the glass caused by the WO3 component can be reduced, and the visible light transmittance can be increased. Therefore, the WO3 content is preferably 10.0% or less, more preferably 5.0% or less, even more preferably 3.0% or less, and even more preferably 1.0% or less.

[0033] ZnO is an optional component that, when contained in an amount greater than 0%, can enhance the stability of the glass and reduce coloration. It also lowers the glass transition temperature and improves chemical durability. Therefore, the ZnO content may be preferably 0% or more, more preferably 0.3% or more, even more preferably 0.5% or more, and even more preferably 1.0% or more. On the other hand, by keeping the ZnO content at 15.0% or less, it is possible to prevent a decrease in the refractive index of the glass and reduce devitrification due to an excessive decrease in viscosity. Therefore, the ZnO content is preferably 15.0% or less, more preferably 12.0% or less, even more preferably 10.0% or less, still more preferably 8.0% or less, even more preferably 6.0% or less, and still more preferably 3.0% or less.

[0034] The MgO component, CaO component, SrO component, and BaO component are optional components that can adjust the refractive index, meltability, and devitrification resistance of the glass when contained in an amount greater than 0%. Therefore, the contents of the MgO component, CaO component, SrO component, and BaO component may be preferably 0% or more, more preferably 3.0% or more, even more preferably 5.0% or more, and even more preferably 7.0% or more. On the other hand, by setting the contents of the MgO, CaO, SrO, and BaO components to 18.0% or less, respectively, it is possible to suppress a decrease in the refractive index and reduce devitrification due to the excessive content of these components. Therefore, the contents of the MgO, CaO, SrO, and BaO components are each preferably set to 18.0% or less, more preferably 16.0% or less, even more preferably 14.0% or less, and even more preferably 12.0% or less.

[0035] The Li2O component, Na2O component, and K2O component are optional components that can improve the meltability of the glass and lower the glass transition point when contained in an amount exceeding 0%. On the other hand, by limiting each of the Li2O, Na2O, and K2O components to 10.0% or less, it is possible to prevent a decrease in the refractive index of the glass and reduce devitrification of the glass. Therefore, the contents of the Li2O, Na2O, and K2O components are each preferably 10.0% or less, more preferably 5.0% or less, even more preferably 3.0% or less, and even more preferably 1.0% or less.

[0036] The P2O5 component is an optional component that can act as a glass-forming component when its content exceeds 0%, and can lower the liquidus temperature of the glass and increase the devitrification resistance. On the other hand, by keeping the content of the P2O5 component at 10.0% or less, the chemical durability of the glass, particularly its water resistance, can be prevented from decreasing. Therefore, the content of the P2O5 component is preferably 10.0% or less, more preferably 5.0% or less, even more preferably 3.0% or less, and even more preferably 1.0% or less.

[0037] GeO2 is an optional component that, when contained in an amount exceeding 0%, can increase the refractive index of the glass and improve the devitrification resistance. However, GeO2 is expensive as a raw material, and a high GeO2 content increases production costs. Therefore, the GeO2 content is preferably 10.0% or less, more preferably 5.0% or less, even more preferably 3.0% or less, and even more preferably 1.0% or less. In particular, from the viewpoint of reducing material costs, the GeO2 component may not be contained.

[0038] The Al2O3 component and the Ga2O3 component are optional components that, when contained in an amount exceeding 0%, can improve the chemical durability of the glass and can also improve the devitrification resistance of the glass. On the other hand, by limiting the content of each of the Al2O3 component and the Ga2O3 component to 10.0% or less, devitrification due to excessive content can be suppressed. Therefore, the contents of the Al2O3 component and the Ga2O3 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 1.0% or less.

[0039] The Bi2O3 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%. On the other hand, by keeping the content of Bi2O3 component at 10.0% or less, an increase in specific gravity can be suppressed. Therefore, the content of Bi2O3 component is preferably 10.0% or less, more preferably 5.0% or less, even more preferably 3.0% or less, and even more preferably 1.0% or less. In particular, from the viewpoint of reducing specific gravity, the Bi2O3 component may not be contained.

[0040] The TeO2 component is an optional component that, when contained at more than 0%, can increase the refractive index and lower the glass transition point. On the other hand, TeO2 has the problem of alloying 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 TeO2 component is preferably 10.0% or less, more preferably 5.0% or less, even more preferably 3.0% or less, and even more preferably 1.0% or less.

[0041] The SnO2 component is an optional component that, when contained in an amount exceeding 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 SnO2 content at 3.0% or less, it is possible to reduce glass coloration and devitrification due to reduction of the glass melt. 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 SnO2 content is preferably 3.0% or less, more preferably 2.0% or less, and even more preferably 1.0% or less.

[0042] The Sb2O3 component is an optional component that can degas the glass melt when its content exceeds 0%. On the other hand, if the amount of Sb2O3 is too large, the transmittance in the short wavelength region of the visible light range will be poor. Therefore, the content of the Sb2O3 component is preferably 1.0% or less, more preferably 0.5% or less, and even more preferably 0.3% or less.

[0043] The component for clarifying and defoaming the glass is not limited to the above Sb2O3 component, but any known fining agent, defoaming agent or combination thereof in the field of glass manufacturing can be used.

[0044] Component F is an optional component that, when contained in an amount of more than 0%, can increase the Abbe number of the glass, lower the glass transition point, and improve the resistance to devitrification. 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 10.0%, the amount of volatilization of the F component increases, making it difficult to obtain stable optical constants and homogeneous glass. Therefore, the content of the F component is preferably 10.0% or less, more preferably 5.0% or less, even more preferably 3.0% or less, and even more preferably 1.0% or less.

[0045] <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.

[0046] Other components can be added as needed to the extent that they do not impair the properties of the glass of the present invention, but 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 alone or in combination, even in small amounts. Therefore, it is preferable that optical glasses used with wavelengths in the visible range are substantially free of these components.

[0047] Furthermore, since lead compounds such as PbO and arsenic compounds such as As2O3 are components that have a high environmental impact, it is desirable that they are not contained substantially, that is, that they are not contained at all except for unavoidable contamination.

[0048] Furthermore, in recent years, there has been a trend to reduce the use of Th, Cd, Tl, Os, Be, and Se as harmful chemical substances, and environmental measures are required not only in the glass manufacturing process but also in the processing process and disposal after commercialization. Therefore, when environmental impact is important, it is preferable that these elements are substantially not contained.

[0049] [Manufacturing method] The optical glass of the present invention is produced, for example, as follows: The above raw materials are mixed uniformly so that the respective components fall within the prescribed content range, the mixture is placed in a platinum crucible, and melted and stirred in an electric furnace at a temperature ranging from 1100 to 1500°C for 2 to 5 hours depending on the melting difficulty of the glass raw materials, and then the mixture is cooled to an appropriate temperature, poured into a mold, and slowly cooled.

[0050] [Physical Properties] The optical glass of the present invention preferably has a high refractive index and a high Abbe number (low dispersion). In particular, the refractive index (nd) of the optical glass of the present invention preferably has a lower limit of 1.95000, more preferably 2.00000, and even more preferably 2.05000. The upper limit of this refractive index (nd) may be preferably 2.15000, more preferably 2.13000, and even more preferably 2.11000. The Abbe number (νd) of the optical glass of the present invention preferably has a lower limit of 20.00, more preferably 20.50, and even more preferably 21.00, and preferably an upper limit of 30.00, more preferably 29.00, and even more preferably 28.00.

[0051] Here, the relationship between the refractive index (nd) and the specific gravity (d) of the optical glass of the present invention satisfies the relational expression (d≦7.494×nd−10.361). Glasses having a refractive index (nd) of 2.00 or higher and a low specific gravity have traditionally only been known as being expensive materials. In contrast, the optical glass of the present invention satisfies the above relational expression, thereby having a small specific gravity (d) relative to the refractive index (nd), which can contribute to reducing the weight of optical elements and optical devices. More specifically, the relationship between the refractive index (nd) and the specific gravity (d) of the optical glass of the present invention preferably satisfies the relational expression (d≦7.494×nd−10.361), more preferably satisfies the relational expression (d≦7.494×nd−10.561), and even more preferably satisfies the relational expression (d≦7.494×nd−10.761). On the other hand, if the specific gravity (d) is too small relative to the refractive index (nd), the devitrification tendency increases, making it difficult to obtain a stable glass. Therefore, the relationship between the refractive index (nd) and the specific gravity (d) preferably satisfies the relational expression (d≦7.494×nd−11.161), more preferably the relational expression (d≦7.494×nd−11.061), and even more preferably the relational expression (d≦7.494×nd−10.961).

[0052] From the viewpoint of contributing to weight reduction of optical elements and optical instruments, the upper limit of the specific gravity of the optical glass of the present invention is preferably 5.50, more preferably 5.30, and preferably 5.20. On the other hand, the specific gravity of the optical glass of the present invention is preferably approximately 4.30 or more, more specifically 4.50 or more, and even more specifically 4.70 or more. The specific gravity of the optical glass of the present invention is measured in accordance with Japan Optical Glass Industry Association Standard JOGIS05-1975 "Method for measuring the specific gravity of optical glass."

[0053] The optical 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 optical glass of the present invention is preferably 1350°C, more preferably 1320°C, even more preferably 1300°C, and even more preferably 1250°C. This reduces crystallization of the produced glass, even when the melted glass is poured out at a lower temperature. This reduces devitrification when the glass is formed from the molten state, thereby reducing the impact on the optical properties of optical elements using the glass. Furthermore, because the glass can be molded even at a lower melting temperature, the energy consumed during glass molding can be reduced, thereby reducing glass production costs. While there is no particular lower limit for the liquidus temperature of the optical glass of the present invention, the liquidus temperature of the glass obtained by the present invention is often generally 800°C or higher, specifically 850°C or higher, and more specifically 900°C or higher. In this specification, the term "liquidus temperature" refers to the lowest temperature at which no crystals are observed when a 5 cc cullet-shaped glass sample is placed in a 50 ml platinum crucible, completely melted at 1400°C, cooled to a predetermined temperature, held for 1 hour, removed from the furnace, cooled, and then immediately observed for the presence or absence of crystals on the glass surface and in the glass. The predetermined temperature for cooling is a temperature between 1350°C and 800°C in 10°C increments.

[0054] [Preforms and optical elements] 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.

[0055] Thus, the optical glass of the present invention is useful for various optical elements and optical designs. Among these, 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 by reheat press molding or precision press molding. This makes it possible to form preforms with large diameters, which allows for larger optical elements to be produced, while still achieving high-definition, high-precision imaging and projection characteristics when used in optical equipment such as cameras and projectors. [Example]

[0056] The compositions of the examples (No. 1 to No. 15) of the present invention and the comparative example (No. A), as well as the refractive index (nd), Abbe number (νd), liquidus temperature, and specific gravity of these glasses, are shown in Tables 1 and 2. Note that the following examples are for illustrative purposes only, and the present invention is not limited to these examples.

[0057] The glasses of the examples and comparative examples of the present invention were all prepared 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, weighing them out to obtain the composition ratios shown in the tables for each example, mixing them uniformly, and then placing them in a platinum crucible. Depending on the melting difficulty of the glass raw materials, the mixture was melted in an electric furnace at a temperature ranging from 1100 to 1500°C for 2 to 5 hours, and then stirred to homogenize the mixture before being poured into a mold or the like and slowly cooled.

[0058] The refractive index (nd) and Abbe number (νd) of the glasses in the examples were measured at the d-line (587.56 nm) of a helium lamp. The Abbe number (νd) was calculated from the formula (νd) = [(nd-1) / (nF-nC)] using the refractive index at the d-line, the refractive index (nF) at the F-line (486.13 nm) of a hydrogen lamp, and the refractive index (nC) at the C-line (656.27 nm). In addition, the relational expression (d≦7.494×nd−10.361) was calculated using the measured nd values.

[0059] The specific gravity d of the glasses in the examples and comparative examples was measured in accordance with the Japan Optical Glass Industry Association standard JOGIS05-1975 "Method for measuring the specific gravity of optical glass."

[0060] The liquidus temperatures of the glasses in the Examples and Comparative Examples were determined by placing a 5 cc cullet-shaped glass sample in a 50 ml platinum crucible, completely melting it at 1400°C, lowering the temperature to any of the temperatures set in 10°C increments between 1350°C and 800°C, holding the temperature for one hour, removing the sample from the furnace, and immediately observing the presence or absence of crystals on the glass surface and in the glass, to determine the lowest temperature at which no crystals were observed.

[0061] [Table 1]

[0062] [Table 2]

[0063] From the above examples, it has been found that the present invention is a high refractive index (nd) glass, but has a low specific gravity relative to the refractive index and is highly resistant to devitrification.

Claims

1. SiO 2 , B 2 O 3 , La 2 O 3 , TiO 2 The essential ingredients are In mass % based on oxides, SiO 2 Ingredients exceeding 0% and not exceeding 15.0%, B 2 O 3 Ingredients exceeding 0% and not exceeding 15.0%, La 2 O 3 Ingredients: 20.0-40.0%, TiO 2 Ingredients: 20.0-40.0%, The sum of the contents of RO components (wherein R is one or more selected from the group consisting of Mg, Ca, Sr, Ba, and Zn) is more than 0% and 18.0% or less. Optical glass.

2. 2. The optical glass according to claim 1, which has a refractive index (nd) of 1.95000 to 2.15000, an Abbe number (νd) of 20.00 to 30.00, and satisfies the relationship d≦7.494×nd−10.361, where d is the specific gravity and nd is the refractive index.

3. Mass ratio SiO 2 / (SiO 2 +B 2 O 3 ) is 0.40 or more, Mass ratio (La 2 O 3 + TiO 2 ) / (SiO 2 +B 2 O 3 ) is between 3.3 and 7.5 3. The optical glass of claim 1, wherein

4. Ta 2 O 5 The component is 2.0% or less, and the mass ratio Y 2 O 3 / La 2 O 3 4. The optical glass according to claim 1, wherein the refractive index is 0.40 or less.

5. An optical element blank made of the optical glass according to any one of claims 1 to 4.

6. An optical element made of the optical glass according to any one of claims 1 to 4.

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