Optical glass and optical element

Abstract

To provide an optical glass and an optical element, having a desired Abbe number νd and refractive index nd, and suitability for chromatic aberration correction.SOLUTION: An optical glass has an Abbe number νd of more than 25.20 and 29.00 or less. The refractive index nd is 1.80000 or more and 1.85000 or less. In terms of mass%, the content of SiO2 is 20 to 30%. The content of Nb2O5 is 35 to 55%. The mass ratio [SiO2 / Nb2O5] of the content of SiO2 to the content of Nb2O5 is 0.47 to 0.66.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to optical glass and optical elements.

Background Art

[0002] In the design of optical systems, optical glass with a high refractive index and high dispersibility is highly valuable for correcting chromatic aberration and enhancing the functionality and compactness of optical systems.

[0003] As a manufacturing method for such optical glass used in optical systems, there is the reheat press method in which the glass is reheated and molded. In this manufacturing method, in Si-Nb-based high refractive index and high dispersibility optical glass containing Si and Nb, phase separation is likely to occur during reheating. When phase separation occurs, the fluidity of the glass during reheating may deteriorate, and it may not be possible to mold it into the desired shape. Further, this phase separation causes crystal precipitation. That is, in Si-Nb-based high refractive index and high dispersibility optical glass containing Si and Nb, crystals are likely to precipitate during reheating. The crystals precipitated during reheating serve as the starting points of devitrification in the optical glass. Therefore, there is a need for Si-Nb-based high refractive index and high dispersibility optical glass in which crystal precipitation is suppressed during reheating.

[0004] In addition, in the design of optical systems, primary chromatic aberration is corrected by combining two types of lenses having different Abbe numbers. Therefore, optical glass having a desired Abbe number and refractive index is required.

[0005] Patent Documents 1 and 2 disclose Si-Nb-based high refractive index and high dispersibility optical glass. However, from the viewpoints of the Abbe number and refractive index, further improvement is required for correcting chromatic aberration in any of the glasses.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

[0007] In view of such circumstances, an object of the present invention is to provide an optical glass and an optical element having a desired Abbe number νd and refractive index nd and being suitable for chromatic aberration correction.

MEANS FOR SOLVING THE PROBLEMS

[0008] The gist of the present invention is as follows.

[0009] 〔1〕The Abbe number νd exceeds 25.20 and is 29.00 or less, the refractive index nd is 1.80000 or more and 1.85000 or less, in terms of mass%, the content of SiO2 is 20 to 30%, the content of Nb2O5 is 35 to 55%, the mass ratio [SiO2 / Nb2O5] of the content of SiO2 to the content of Nb2O5 is 0.47 to 0.66, the total content [SiO2+Nb2O5] of SiO2 and Nb2O5 is 60 to 75%, the mass ratio [B2O3 / SiO2] of the content of B2O3 to the content of SiO2 is 0.00 to 0.07, the content of Li2O is 6.20% or less, the content of K2O is 0.62% or more, the total content [Li2O+Na2O+K2O] of Li2O, Na2O, and K2O is 13.00 to 15.69%, the mass ratio [Li2O / (Li2O+Na2O+K2O)] of the content of Li2O to the total content of Li2O, Na2O, and K2O is 0.34 to 0.41, the mass ratio [Na2O / (Li2O+Na2O+K2O)] of the content of Na2O to the total content of Li2O, Na2O, and K2O is 0.33 to 0.50, The mass ratio of the content of K2O to the total content of Li2O, Na2O, and K2O [K2O / (Li2O + Na2O + K2O)] is 0.04 to 0.30, The mass ratio of the total content of SiO2 and Nb2O5 to the total content of Li2O, Na2O, and K2O [(SiO2 + Nb2O5) / (Li2O + Na2O + K2O)] is 4.00 to 5.02, The content of TiO2 is 0 to 11%, An optical glass in which the content of ZrO2 exceeds 0%.

[0010] 〔2〕 The optical glass according to 〔1〕, wherein the specific gravity d is 3.32 or more and 3.51 or less.

[0011] 〔3〕 Containing SiO2, Nb2O5, ZrO2, and alkali metal oxides, The Abbe number νd exceeds 25.20 and is 29.00 or less, The refractive index nd is 1.80000 or more and 1.85000 or less, After heating for 10 minutes at a temperature [Tg + 50°C] 50°C higher than the glass transition temperature Tg in the atmosphere, when heated for 10 minutes at a temperature [Tg + 240°C] 240°C higher than the glass transition temperature Tg, the number density of crystals with a maximum diameter of 1 μm or more that precipitate is 2000 pieces / kg or less. An optical glass.

[0012] 〔4〕 An optical element made of the optical glass according to any one of 〔1〕 to 〔3〕 above.

Advantages of the Invention

[0013] According to the present invention, it is possible to provide an optical glass and an optical element having a desired Abbe number νd and refractive index nd and suitable for chromatic aberration correction.

Modes for Carrying Out the Invention

[0014] Hereinafter, one aspect of the present invention will be described. In the present invention and this specification, the glass composition is expressed on an oxide basis unless otherwise specified. Here, the "glass composition on an oxide basis" refers to a glass composition obtained by converting all glass raw materials into oxides existing in the glass by being decomposed during melting, and the notation of each glass component follows the convention, such as being described as SiO2, TiO2, etc. The content, total content, and ratio of glass components are on a mass basis unless otherwise specified, and "%" means "mass%".

[0015] The content of the glass component can be quantified by known methods, such as methods like inductively coupled plasma atomic emission spectrometry (ICP - AES) and inductively coupled plasma mass spectrometry (ICP - MS). Also, in the present invention and this specification, when the content of a constituent component is 0%, it means that this constituent component is substantially not contained, and it is allowed that the component is contained at an inevitable impurity level.

[0016] Hereinafter, the optical glass according to this embodiment will be described in detail. First, the optical glass will be described from the perspective of the glass composition as the first embodiment. Next, the optical glass will be described from the perspective of the glass properties as the second embodiment.

[0017] First Embodiment The optical glass according to the first embodiment is such that the Abbe number νd exceeds 25.20 and is 29.00 or less, the refractive index nd is 1.80000 or more and 1.85000 or less, in terms of mass%, the content of SiO2 is 20 - 30%, the content of Nb2O5 is 35 - 55%, the mass ratio [SiO2 / Nb2O5] of the content of SiO2 to the content of Nb2O5 is 0.47 - 0.66, the total content [SiO2 + Nb2O5] of SiO2 and Nb2O5 is 60 - 75%, the mass ratio [B2O3 / SiO2] of the content of B2O3 to the content of SiO2 is 0.00 - 0.07. The content of Li2O is 6.20% or less, the content of K2O is 0.62% or more, the total content of Li2O, Na2O, and K2O [Li2O + Na2O + K2O] is 13.00 to 15.69%, the mass ratio of the content of Li2O to the total content of Li2O, Na2O, and K2O [Li2O / (Li2O + Na2O + K2O)] is 0.34 to 0.41, the mass ratio of the content of Na2O to the total content of Li2O, Na2O, and K2O [Na2O / (Li2O + Na2O + K2O)] is 0.33 to 0.50, the mass ratio of the content of K2O to the total content of Li2O, Na2O, and K2O [K2O / (Li2O + Na2O + K2O)] is 0.04 to 0.30, the mass ratio of the total content of SiO2 and Nb2O5 to the total content of Li2O, Na2O, and K2O [(SiO2 + Nb2O5) / (Li2O + Na2O + K2O)] is 4.00 to 5.02, the content of TiO2 is 0 to 11%, the content of ZrO2 exceeds 0%.

[0018] <Abbe number νd> In the optical glass according to the first embodiment, the Abbe number νd exceeds 25.20 and is 29.00 or less. The lower limit of the Abbe number νd can be 25.40, 25.60, or 25.80. Also, the upper limit of the Abbe number νd can be 28.80, 28.60, 28.40, 28.00, 27.50, 27.00, 26.60, 26.40, or 26.20.

[0019] By setting the Abbe number νd within the above range, a glass with high dispersibility can be obtained. The Abbe number νd can be controlled by adjusting the contents of glass components Nb2O5, TiO2, WO3, and Bi2O3 that contribute to high dispersion.

[0020] <Refractive index nd> In the optical glass according to the first embodiment, the refractive index nd is 1.80000 or more and 1.85000 or less. The lower limit of the refractive index nd can be 1.80500, 1.81000, 1.81500, 1.82000, 1.82500, or 1.82800. Also, the upper limit of the refractive index nd can be 1.84800, 1.84500, or 1.84000.

[0021] By setting the refractive index nd within the above range, a high-refractive-index glass can be obtained. The refractive index nd can be controlled by adjusting the contents of Nb2O5, TiO2, WO3, and Bi2O3, which are glass components that contribute to increasing the refractive index.

[0022] In the optical glass according to the first embodiment, the content of SiO2 is 20 to 30%. The lower limit of the content of SiO2 is preferably 21.00%, more preferably 22.00%, 23.30%, and 23.40% in that order. Also, the upper limit of the content of SiO2 is preferably 29.00%, more preferably 28.00%, 27.00%, 26.00%, and 25.00% in that order.

[0023] SiO2 is a network-forming component of the glass. By satisfying the lower limit of SiO2 as described above, the thermal stability, chemical durability, and weather resistance of the glass can be improved, the viscosity of the molten glass can be increased, and the molten glass can be easily formed. Also, by satisfying the upper limit of SiO2 as described above, a decrease in the devitrification resistance of the glass can be suppressed.

[0024] In the optical glass according to the first embodiment, the content of Nb2O5 is 35 to 55%. The lower limit of the content of Nb2O5 is preferably 36.00%, more preferably 37.00%, 37.50%, 38.00%, 39.00%, 40.00%, 41.00%, 42.00%, 43.00%, 44.00%, and 45.00% in that order. Also, the upper limit of the content of Nb2O5 is preferably 54.00%, more preferably 53.00%, 52.00%, 51.00%, 50.00%, 49.00%, 48.00%, and 47.00% in that order.

[0025] By satisfying the lower limit of the Nb₂O₅ content as described above, a glass with a high refractive index and high dispersibility can be obtained. Further, Nb₂O₅ is also a glass component that improves the thermal stability and chemical durability of the glass. By satisfying the upper limit of the Nb₂O₅ content as described above, the thermal stability and chemical durability of the glass can be maintained well, and the precipitation of crystals during reheating can be suppressed.

[0026] In the optical glass according to the first embodiment, the mass ratio [SiO₂ / Nb₂O₅] of the SiO₂ content to the Nb₂O₅ content is 0.47 to 0.66. The lower limit of the mass ratio is preferably 0.48, and more preferably 0.49, 0.50, 0.51 in that order. Also, the upper limit of the mass ratio is preferably 0.655, and more preferably 0.650, 0.630, 0.600, 0.590, 0.580, 0.570, 0.560 in that order.

[0027] By setting the mass ratio [SiO₂ / Nb₂O₅] within the above range, the specific gravity d of the glass can be reduced while maintaining the desired optical constants (refractive index nd, Abbe number νd). Note that when the specific gravity of the glass increases, the mass of the optical element increases. For example, when a lens with a large mass is incorporated into an autofocus type imaging lens, the power required for driving the lens during autofocus increases, and there is a risk of rapid battery consumption.

[0028] In the optical glass according to the first embodiment, the total content [SiO₂ + Nb₂O₅] of SiO₂ and Nb₂O₅ is 60 to 75%. The lower limit of the total content is preferably 61.0%, and more preferably 62.0%, 62.5%, 62.9%, 63.0%, 64.0%, 65.0%, 66.0%, 67.0%, 68.0%, 69.0% in that order. The upper limit of the total content is preferably 74.0%, and more preferably 73.5%, 73.0%, 72.5%, 72.0%, 71.5% in that order.

[0029] By setting the total content [SiO2 + Nb2O5] within the above range, the liquidus temperature can be lowered, and the thermal stability of the glass can be improved. Also, the crystallization of the glass can be suppressed.

[0030] In the optical glass according to the first embodiment, the mass ratio [B2O3 / SiO2] of the content of B2O3 to the content of SiO2 is 0.00 to 0.07. The upper limit of the mass ratio is preferably 0.06, and more preferably 0.05, 0.04, 0.03, 0.02 in that order. The lower limit of the mass ratio is preferably 0.01.

[0031] By setting the mass ratio [B2O3 / SiO2] within the above range, an increase in specific gravity d and coloring of the glass can be suppressed.

[0032] In the optical glass according to the first embodiment, the content of Li2O is 6.20% or less. The upper limit of the content of Li2O is preferably 6.10%, and more preferably 6.00%, 5.90%, 5.80% in that order. Also, the lower limit of the content of Li2O is preferably 5.30%, and more preferably 5.35%, 5.40%, 5.45% in that order.

[0033] Li2O has the function of lowering the liquidus temperature and improving the thermal stability of the glass. By setting the content of Li2O within the above range, a decrease in chemical durability and weather resistance can be suppressed.

[0034] In the optical glass according to the first embodiment, the content of K2O is 0.62% or more. The lower limit of the content of K2O is preferably 0.80%, and more preferably 1.00%, 1.20%, 1.40%, 1.80%, 2.20%, 2.40%, 2.60% in that order. Also, the upper limit of the content of K2O is preferably 7.00%, and more preferably 6.50%, 6.00%, 5.50%, 5.00%, 4.50%, 4.20%, 3.90% in that order.

[0035] By setting the content of K₂O within the above range, the liquidus temperature can be lowered, and the thermal stability of the glass can be improved. On the other hand, if the content of K₂O increases, there is a risk of deterioration in chemical durability and weather resistance.

[0036] In the optical glass according to the first embodiment, the total content of Li₂O, Na₂O, and K₂O [Li₂O + Na₂O + K₂O] is 13.00 to 15.69%. The lower limit of the total content is preferably 13.20%, more preferably 13.40%, 13.60%, 13.80%, 14.00%, 14.20%, 14.40%, 14.60% in this order. Also, the upper limit of the total content is preferably 15.50%, more preferably 15.40%, 15.30%, 15.20%, 15.10% in this order.

[0037] By satisfying the lower limit of the total content [Li₂O + Na₂O + K₂O] as described above, the meltability and thermal stability of the glass can be improved, and the liquidus temperature can be lowered. Also, by satisfying the upper limit of the total content [Li₂O + Na₂O + K₂O] as described above, the precipitation of crystals during reheating can be suppressed, and the occurrence of internal defects in the glass such as cracks and veins can be suppressed.

[0038] In the optical glass according to the first embodiment, the mass ratio of the content of Li₂O to the total content of Li₂O, Na₂O, and K₂O [Li₂O / (Li₂O + Na₂O + K₂O)] is 0.34 to 0.41. The lower limit of the mass ratio is preferably 0.345, more preferably 0.350, 0.355, 0.360 in this order. Also, the upper limit of the mass ratio is preferably 0.405, more preferably 0.400, 0.395, 0.390, 0.385 in this order.

[0039] By setting the mass ratio [Li₂O / (Li₂O + Na₂O + K₂O)] within the above range, the thermal stability of the glass can be enhanced. Also, the precipitation of crystals during reheating can be suppressed without impairing the network-forming action of the glass.

[0040] In the optical glass according to the first embodiment, the mass ratio of the content of Na2O to the total content of Li2O, Na2O, and K2O [Na2O / (Li2O + Na2O + K2O)] is 0.33 to 0.50. The lower limit of the mass ratio is preferably 0.340, more preferably 0.345, 0.350, 0.355 in this order. Also, the upper limit of the mass ratio is preferably 0.490, more preferably 0.480, 0.470, 0.460, 0.450, 0.440, 0.430, 0.425 in this order.

[0041] By setting the mass ratio [Na2O / (Li2O + Na2O + K2O)] within the above range, the thermal stability of the glass can be enhanced. Also, the precipitation of crystals during reheating can be suppressed without impairing the network-forming action of the glass.

[0042] In the optical glass according to the first embodiment, the mass ratio of the content of K2O to the total content of Li2O, Na2O, and K2O [K2O / (Li2O + Na2O + K2O)] is 0.04 to 0.30. The lower limit of the mass ratio is preferably 0.05, more preferably 0.06, 0.08, 0.12, 0.14, 0.16, 0.18, 0.20 in this order. Also, the upper limit of the mass ratio is preferably 0.290, more preferably 0.280, 0.275, 0.270 in this order.

[0043] By setting the mass ratio [K2O / (Li2O + Na2O + K2O)] within the above range, the thermal stability of the glass can be enhanced. Also, the precipitation of crystals during reheating can be suppressed without impairing the network-forming action of the glass.

[0044] In the optical glass according to the first embodiment, the mass ratio [(SiO2 + Nb2O5) / (Li2O + Na2O + K2O)] of the total content of SiO2 and Nb2O5 to the total content of Li2O, Na2O, and K2O is 4.00 to 5.02. The lower limit of the mass ratio is preferably 4.10, and more preferably 4.15, 4.20, 4.25, 4.30, 4.35, 4.40, 4.45, 4.50, 4.55, 4.60 in this order. Also, the upper limit of the mass ratio is preferably 4.95, and more preferably 4.90, 4.85, 4.80 in this order.

[0045] By setting the mass ratio [(SiO2 + Nb2O5) / (Li2O + Na2O + K2O)] within the above range, the thermal stability of the glass can be enhanced. Also, the precipitation of crystals during reheating can be suppressed without impairing the network-forming action of the glass.

[0046] In the optical glass according to the first embodiment, the content of TiO2 is 0 to 11%. The lower limit of the TiO2 content is preferably 1%, and more preferably 2%, 3%, 4% in this order. Also, the upper limit of the TiO2 content is preferably 10%, and more preferably 9%, 7%, 6%, 5% in this order.

[0047] TiO2 is a component that contributes to high dispersion. By setting the TiO2 content within the above range, the thermal stability of the glass can be improved, and the precipitation of crystals during reheating can be suppressed. On the other hand, if TiO2 is introduced in excess, there is a possibility that the partial dispersion ratio Pg,F may increase.

[0048] In the optical glass according to the first embodiment, the content of ZrO2 exceeds 0%. The lower limit of the ZrO2 content is preferably 1.00%, and more preferably 2.00%, 3.00%, 4.00%, 6.00% in this order. Also, the upper limit of the ZrO2 content is preferably 16.50%, and more preferably 15.00%, 13.00%, 11.00%, 9.00%, 7.00% in this order.

[0049] By satisfying the lower limit of the ZrO₂ content as described above, a glass with a high refractive index and high dispersibility can be obtained. Further, by satisfying the upper limit of the ZrO₂ content as described above, the partial dispersion ratio Pg,F can be lowered, the occurrence of defects as an optical element can be suppressed, and the meltability and thermal stability of the glass can be maintained.

[0050] Regarding the contents, ratios, and glass properties of the glass components other than those described above in the optical glass according to the first embodiment, non-limiting examples are shown below.

[0051] In the optical glass according to the first embodiment, the lower limit of the P₂O₅ content is preferably 0.00%, more preferably 0.20%, 0.40%, and 0.60% in that order. Further, the upper limit of the P₂O₅ content is preferably 7.00%, more preferably 5.00%, 4.00%, and 3.00% in that order.

[0052] P₂O₅ is a glass network-forming component and has the function of improving the thermal stability of the glass. On the other hand, when the content of P₂O₅ increases, the thermal stability of the glass decreases, and there is a risk that crystals are likely to precipitate during reheating. Therefore, it is preferable that the content of P₂O₅ is within the above range.

[0053] In the optical glass according to the first embodiment, the lower limit of the B₂O₃ content is preferably 0.00%, more preferably 0.02%, 0.04%, and 0.06% in that order. Further, the upper limit of the B₂O₃ content is preferably 7.00%, more preferably 5.00%, 3.00%, 1.00%, and 0.50% in that order.

[0054] B₂O₃ is a glass network-forming component and has the function of improving the thermal stability of the glass. On the other hand, when the content of B₂O₃ is large, the volatilization amount of the glass components may increase during glass melting. Also, when the content of B₂O₃ is large, high dispersion is hindered, and the devitrification resistance tends to decrease. Therefore, it is preferable that the content of B₂O₃ is within the above range.

[0055] In the optical glass according to the first embodiment, the content of Al2O3 is preferably 20% or less, more preferably 10% or less, still more preferably 5% or less, and even more preferably 3% or less. The content of Al2O3 may be 0%.

[0056] Al2O3 is a glass component that functions to improve the chemical durability and weather resistance of the glass and can be considered as a network-forming component. On the other hand, when the content of Al2O3 increases, the devitrification resistance of the glass decreases. Also, problems such as an increase in the glass transition temperature Tg and a decrease in thermal stability are likely to occur. From the viewpoint of avoiding such problems, it is preferable that the content of Al2O3 be within the above range.

[0057] In the optical glass according to the first embodiment, the upper limit of the content of WO3 is preferably 20%, more preferably 15%, still more preferably 10%, and even more preferably 5%. Also, the lower limit of the content of WO3 is preferably 0%.

[0058] WO3 is a component that improves the thermal stability of the glass and suppresses the precipitation of crystals during reheating. On the other hand, WO3 is also a component that increases the specific gravity d. Also, WO3 is likely to cause coloring of the glass and may deteriorate the transmittance. Therefore, it is preferable that the content of WO3 be within the above range.

[0059] In the optical glass according to the first embodiment, the upper limit of the content of Bi2O3 is preferably 20%, more preferably 10%, still more preferably 5%, and even more preferably 3%. Also, the lower limit of the content of Bi2O3 is preferably 0%.

[0060] Bi2O3 has the function of improving the thermal stability of the glass when contained in an appropriate amount. On the other hand, when the content of Bi2O3 is increased, there is a risk that the specific gravity d will increase. Furthermore, there is a risk that the coloring of the glass will increase. Therefore, it is preferable that the content of Bi2O3 be within the above range.

[0061] In the optical glass according to the first embodiment, the lower limit of the Na2O content is preferably 3.00%, more preferably 3.50%, 4.00%, 4.50%, 5.00%, and 5.10% in that order. Also, the upper limit of the Na2O content is preferably 10.00%, more preferably 9.00%, 8.50%, 8.00%, 7.00%, and 6.50% in that order.

[0062] Na2O has the function of lowering the liquidus temperature and improving the thermal stability of the glass. On the other hand, when the content of Na2O increases, there is a risk of deterioration in chemical durability and weather resistance. Therefore, it is preferable that the content of Na2O be within the above range.

[0063] In the optical glass according to the first embodiment, the upper limit of the Cs2O content is preferably 10%, more preferably 5%, 3%, and 1% in that order. The lower limit of the Cs2O content is preferably 0%.

[0064] Cs2O has the function of improving the thermal stability of the glass. On the other hand, when the content of Cs2O increases, there is a risk of deterioration in chemical durability and weather resistance. Therefore, it is preferable that the content of Cs2O be within the above range.

[0065] In the optical glass according to the first embodiment, the lower limit of the total content of alkali metal oxides is preferably 13.20%, more preferably 13.40%, 13.60%, 13.80%, 14.00%, 14.20%, 14.40%, and 14.60% in that order. Also, the upper limit of the total content of alkali metal oxides is preferably 15.50%, more preferably 15.40%, 15.30%, 15.20%, and 15.10% in that order.

[0066] The alkali metal oxide is preferably one or more oxides selected from the group consisting of Li2O, Na2O, K2O, and Cs2O.

[0067] From the perspective of improving the fusibility and thermal stability of the glass and reducing the liquidus temperature, it is preferable to set the lower limit of the total content of alkali metal oxides as described above. Also, from the perspective of suppressing the occurrence of defects as an optical element, it is preferable to set the upper limit of the total content of alkali metal oxides as described above.

[0068] In the optical glass according to the first embodiment, the upper limit of the content of MgO is preferably 20%, more preferably 10%, 5%, and 3% in that order. Also, the lower limit of the content of MgO is preferably 0%.

[0069] In the optical glass according to the first embodiment, the upper limit of the content of CaO is preferably 20%, more preferably 10%, 5%, and 3% in that order. Also, the lower limit of the content of CaO is preferably 0%.

[0070] In the optical glass according to the first embodiment, the upper limit of the content of SrO is preferably 20%, more preferably 10%, 5%, and 3% in that order. Also, the lower limit of the content of SrO is preferably 0%.

[0071] In the optical glass according to the first embodiment, the upper limit of the content of BaO is preferably 20%, more preferably 10%, 5%, and 3% in that order. Also, the lower limit of the content of BaO is preferably 0%, and it can also be 0.10% or 0.20%.

[0072] MgO, CaO, SrO, and BaO are all glass components that have the function of improving the thermal stability and devitrification resistance of the glass. However, when the content of these glass components increases, the specific gravity d increases, the high dispersibility is impaired, and the thermal stability and devitrification resistance of the glass decrease. Therefore, the content of each of these glass components is preferably within the above range.

[0073] In the optical glass according to the first embodiment, the upper limit of the ZnO content is preferably 20%, more preferably 10%, 5%, and 3% in this order. Further, the lower limit of the ZnO content is preferably 0%.

[0074] ZnO is a glass component that has the function of improving the thermal stability of the glass. However, when the ZnO content increases, the specific gravity d may increase. From the viewpoint of improving the thermal stability of the glass and maintaining the desired optical properties, it is preferable that the ZnO content be within the above range.

[0075] In the optical glass according to the first embodiment, the upper limit of the La2O3 content is preferably 20%, more preferably 10%, 5%, and 3% in this order. Further, the lower limit of the La2O3 content is preferably 0%.

[0076] When the La2O3 content increases, the specific gravity d increases and the thermal stability of the glass may decrease. Therefore, from the viewpoint of suppressing the increase in the specific gravity d and the decrease in the thermal stability of the glass, it is preferable that the La2O3 content be within the above range.

[0077] In the optical glass according to the first embodiment, the upper limit of the Y2O3 content is preferably 20%, more preferably 10%, 5%, and 3% in this order. Further, the lower limit of the Y2O3 content is preferably 0%.

[0078] If the Y2O3 content becomes too high, the thermal stability of the glass decreases and the glass is likely to devitrify during production. Therefore, from the viewpoint of suppressing the decrease in the thermal stability of the glass, it is preferable that the Y2O3 content be within the above range.

[0079] In the optical glass according to the first embodiment, the upper limit of the Ta2O5 content is preferably 20%, more preferably 10%, 5%, and 3% in this order. Further, the lower limit of the Ta2O5 content is preferably 0%.

[0080] Ta2O5 is a glass component that functions to improve the thermal stability of glass. Compared with Nb2O5, TiO2, WO3, and Bi2O3, it is a component that reduces the partial dispersion ratio Pg,F. On the other hand, when the content of Ta2O5 increases, the thermal stability of the glass decreases, and when melting the glass, the remaining unmelted glass raw materials are likely to occur. Also, there is a possibility that the specific gravity d increases. Therefore, it is preferable that the content of Ta2O5 be within the above range.

[0081] In the optical glass according to the first embodiment, the content of Sc2O3 is preferably 2% or less. Also, the lower limit of the content of Sc2O3 is preferably 0%.

[0082] In the optical glass according to the first embodiment, the content of HfO2 is preferably 2% or less. Also, the lower limit of the content of HfO2 is preferably 0%.

[0083] Sc2O3 and HfO2 function to enhance the high dispersibility of glass, but they are expensive components. Therefore, it is preferable that the respective contents of Sc2O3 and HfO2 be within the above range.

[0084] In the optical glass according to the first embodiment, the content of Lu2O3 is preferably 2% or less. Also, the lower limit of the content of Lu2O3 is preferably 0%.

[0085] Lu2O3 functions to enhance the high dispersibility of glass, but because of its large molecular weight, it is also a glass component that increases the specific gravity d of the glass. Therefore, it is preferable that the content of Lu2O3 be within the above range.

[0086] In the optical glass according to the first embodiment, the content of GeO2 is preferably 2% or less. Also, the lower limit of the content of GeO2 is preferably 0%.

[0087] GeO2 has the function of enhancing the high dispersibility of glass, but among the commonly used glass components, it is a particularly expensive component. Therefore, from the perspective of reducing the manufacturing cost of glass, it is preferable that the content of GeO2 is within the above range.

[0088] In the optical glass according to the first embodiment, the content of Gd2O3 is preferably 2% or less. Also, the lower limit of the content of Gd2O3 is preferably 0%.

[0089] If the content of Gd2O3 becomes too high, the thermal stability of the glass may decrease. Also, if the content of Gd2O3 becomes too high, the specific gravity d of the glass increases, which is not preferable. Therefore, from the perspective of maintaining good thermal stability of the glass while suppressing the increase in specific gravity d, it is preferable that the content of Gd2O3 is within the above range.

[0090] In the optical glass according to the first embodiment, the content of Yb2O3 is preferably 2% or less. Also, the lower limit of the content of Yb2O3 is preferably 0%.

[0091] Since Yb2O3 has a larger molecular weight compared to La2O3, Gd2O3, and Y2O3, there is a possibility of increasing the specific gravity d of the glass. Therefore, it is desirable to reduce the content of Yb2O3 to suppress the increase in the specific gravity d of the glass. Also, if the content of Yb2O3 is too high, the thermal stability of the glass may decrease. From the perspective of preventing the decrease in the thermal stability of the glass and suppressing the increase in specific gravity d, it is preferable that the content of Yb2O3 is within the above range.

[0092] The optical glass according to the first embodiment is mainly composed of the above glass components, that is, SiO2, Nb2O5, K2O, ZrO2 as essential components, and Li2O, TiO2, P2O5, B2O3, Al2O3, WO3, Bi2O3, Na2O, Cs2O, MgO, CaO, SrO, BaO, ZnO, La2O3, Y2O3, Ta2O5, Sc2O3, HfO2, Lu2O3, GeO2, Gd2O3, and Yb2O3 as optional components. Preferably, the total content of the above glass components is 95% or more, more preferably 98% or more, still more preferably 99% or more, and even more preferably 99.5% or more.

[0093] It should be noted that the optical glass according to this embodiment is preferably basically composed of the above glass components, but other components can also be contained within a range that does not interfere with the effects of the present invention. In addition, the present invention does not exclude the inclusion of inevitable impurities.

[0094] (Other components) In addition to the above components, the optical glass can also contain a small amount of Sb2O3, CeO2, etc. as fining agents. The total amount (external addition amount) of the fining agent is preferably 0% or more and less than 1%, and more preferably 0% or more and 0.5% or less.

[0095] The external addition amount is the addition amount of the fining agent expressed as a weight percentage when the total content of all glass components excluding the fining agent is 100%.

[0096] Pb, Cd, As, Th, etc. are components with concerns about environmental impact. Therefore, the content of PbO, CdO, ThO2, and As2O3 is preferably 0 to 0.1% for each, more preferably 0 to 0.05%, still more preferably 0 to 0.01%, and particularly preferably substantially free of PbO, CdO, ThO2, and As2O3.

[0097] Furthermore, the above optical glass has a high transmittance over a wide range of the visible region. To take advantage of such characteristics, it is preferably free of coloring elements. Examples of coloring elements include Cu, Co, Ni, Fe, Cr, Eu, Nd, Er, V, etc. Any of these elements is preferably less than 100 ppm by mass, more preferably 0 to 80 ppm by mass, still more preferably 0 to 50 ppm by mass, and particularly preferably substantially not contained.

[0098] Also, Ga, Te, Tb, etc. are components that do not need to be introduced and are also expensive components. Therefore, the content ranges of Ga2O3, TeO2, and TbO2 in terms of mass% are all preferably 0 to 0.1%, more preferably 0 to 0.05%, still more preferably 0 to 0.01%, even more preferably 0 to 0.005%, yet even more preferably 0 to 0.001%, and particularly preferably substantially not contained.

[0099] (Glass properties) <Specific gravity d> The optical glass according to the first embodiment has a high refractive index and high dispersibility, while the specific gravity d is not large. Usually, if the specific gravity d of the glass can be reduced, the weight of the lens can be decreased. As a result, the power consumption of the autofocus drive of the camera lens equipped with the lens can be reduced. On the other hand, if the specific gravity d is reduced too much, there is a risk of reducing the thermal stability.

[0100] Therefore, in the optical glass according to the present embodiment, the lower limit of the specific gravity d is preferably 3.32, more preferably 3.34, 3.36, 3.38, 3.40 in this order. Also, the upper limit of the specific gravity d is preferably 3.51, more preferably 3.50, 3.49, 3.48, 3.46, 3.44 in this order. The specific gravity d can be controlled by appropriately adjusting the content of each glass component.

[0101] <Transmittance> The optical glass according to the first embodiment is an optical glass with extremely little coloring. Such optical glass is suitable as a material for imaging optical elements such as camera lenses and projection optical elements such as projectors.

[0102] Generally, the coloring degree of optical glass is represented by λ80, λ70, λ5, etc. For a glass sample with a thickness of 10.0 mm ± 0.1 mm, the spectral transmittance is measured in the wavelength range of 200 to 700 nm. The wavelength at which the external transmittance becomes 80% is λ80, the wavelength at which the external transmittance becomes 70% is λ70, and the wavelength at which the external transmittance becomes 5% is λ5.

[0103] In the optical glass according to the first embodiment, λ80 is preferably 500 nm or less, more preferably 490 nm or less, 480 nm or less, and 470 nm or less in that order. λ70 is preferably 440 nm or less, more preferably 430 nm or less, 420 nm or less, and 415 nm or less in that order. λ5 is preferably 365 nm or less, more preferably 364 nm or less, 363 nm or less, and 362 nm or less in that order. λ80, λ70, and λ5 can be controlled mainly by adjusting the amount of glass components that contribute to high refractive index and high dispersion.

[0104] <Workability> In the optical glass according to the first embodiment, the precipitation of crystals during reheating can be suppressed. The optical glass according to this embodiment suppresses the precipitation of crystals during reheating even when reheated in a wide temperature range, and internal defects such as cracks and veins and devitrification are less likely to occur.

[0105] The heating temperature during reheating press is, for example, the temperature at which normal glass softens and deforms. Specifically, as the heating temperature, a temperature about 50 °C higher than the glass transition temperature Tg in the lower case and a temperature about 200 - 300 °C higher than the glass transition temperature Tg in the higher case are assumed.

[0106] Generally, when the heating temperature during reheating press is low, that is, when heating at a temperature about 50 °C higher than the glass transition temperature Tg, phase separation is less likely to occur inside the glass. However, when the heating temperature during reheating press is low, it is necessary to apply a high pressure during press forming. As a result, in the process of cooling the pressed glass molded article (for example, a lens or a lens blank), the possibility of cracks or breakage occurring in the glass increases. Therefore, when the heating temperature during reheating press is low, the production yield is likely to decrease, and the shape of the glass molded article that can be press-formed is likely to be restricted.

[0107] On the other hand, when the heating temperature during reheating press is high, that is, when heating at a temperature about 200 - 300 °C higher than the glass transition temperature Tg, phase separation is likely to occur inside the glass and crystals are likely to precipitate. However, when the heating temperature during reheating press is high, it is not necessary to apply a high pressure during press forming, and cracks and the like are less likely to occur in the glass molded article. Therefore, a decrease in yield is suppressed, and the shape of the glass molded article is less likely to be restricted.

[0108] In the optical glass according to the first embodiment, by adjusting the glass composition, crystals are less likely to precipitate regardless of the assumed heating temperature during reheating press. In particular, even when reheating press is performed at a high temperature, crystals are less likely to precipitate and devitrification is less likely to occur, so problems such as a decrease in yield and shape restriction are also less likely to occur.

[0109] When the optical glass according to the first embodiment is heated in the air at a temperature [Tg + 50 °C] 50 °C higher than the glass transition temperature Tg for 10 minutes and then heated at a temperature [Tg + 240 °C] 240 °C higher than the glass transition temperature Tg for 10 minutes, the number density of crystals with a maximum diameter of 1 μm or more that precipitate is preferably 2000 pieces / kg or less, more preferably 1800 pieces / kg or less, still more preferably 1500 pieces / kg or less, and even more preferably 1000 pieces / kg or less.

[0110] (Manufacture of optical glass) The optical glass according to the embodiment of the present invention may be produced by preparing glass raw materials so as to have the above-described predetermined composition and using the prepared glass raw materials according to a known glass manufacturing method. For example, a plurality of types of compounds are prepared, sufficiently mixed to obtain a batch raw material, and the batch raw material is placed in a quartz crucible or a platinum crucible and roughly melted (rough melt). The melt obtained by the rough melting is rapidly cooled and pulverized to produce cullets. Further, the cullets are placed in a platinum crucible, heated, and remelted (remelt) to obtain molten glass. After further clarification and homogenization, the molten glass is formed and slowly cooled to obtain optical glass. Known methods may be applied to the forming and slow cooling of the molten glass.

[0111] Note that the compounds used when preparing the batch raw material are not particularly limited as long as the desired glass components can be introduced into the glass so as to have the desired contents. Examples of such compounds include oxides, carbonates, nitrates, hydroxides, fluorides, and the like.

[0112] (Manufacture of optical elements, etc.) To produce an optical element using the optical glass according to the embodiment of the present invention, a known method may be applied. For example, in the production of the above-described optical glass, the molten glass is poured into a mold and formed into a plate shape to produce a glass material made of the optical glass according to the present invention. The obtained glass material is appropriately cut, ground, and polished to produce a cut piece having a size and shape suitable for press forming. The cut piece is heated and softened, and press formed (hot press) by a known method to produce an optical element blank approximating the shape of the optical element. The optical element blank is annealed and ground and polished by a known method to produce an optical element.

[0113] An antireflection film, a total reflection film, or the like may be coated on the optical functional surface of the produced optical element according to the purpose of use.

[0114] According to one aspect of the present invention, an optical element made of the above optical glass can be provided. Examples of the types of optical elements include lenses such as spherical lenses and aspherical lenses, prisms, diffraction gratings, and the like. Examples of the shapes of the lenses include various shapes such as biconvex lenses, plano-convex lenses, biconcave lenses, plano-concave lenses, convex meniscus lenses, and concave meniscus lenses. The optical element can be manufactured by a method including a step of processing a glass molded body made of the above optical glass. Examples of the processing include cutting, machining, rough grinding, fine grinding, polishing, and the like. When performing such processing, by using the above glass, breakage can be reduced, and high-quality optical elements can be stably supplied.

[0115] Second Embodiment The optical glass according to the second embodiment is composed of SiO2, Nb2O5, ZrO2, and alkali metal oxides, the Abbe number νd exceeds 25.20 and is 29.00 or less, the refractive index nd is 1.80000 or more and 1.85000 or less, when heated at a temperature [Tg + 50 °C] 50 °C higher than the glass transition temperature Tg in the atmosphere for 10 minutes and then heated at a temperature [Tg + 240 °C] 240 °C higher than the glass transition temperature Tg for 10 minutes, the number density of crystals having a maximum diameter of 1 μm or more that precipitate is 2000 pieces / kg or less.

[0116] The optical glass according to the second embodiment contains SiO2. The lower limit of the content of SiO2 is preferably 20%, and more preferably 21.00%, 22.00%, 23.30%, 23.40% in this order. The upper limit of the content of SiO2 is preferably 30%, and more preferably 29.00%, 28.00%, 27.00%, 26.00%, 25.00% in this order.

[0117] SiO2 is a network-forming component of glass. By including SiO2, the thermal stability, chemical durability, and weather resistance of the glass can be improved, the viscosity of the molten glass can be increased, and the molten glass can be easily formed. Also, from the viewpoint of suppressing a decrease in the devitrification resistance of the glass, it is preferable to set the upper limit of the content of SiO2 as described above.

[0118] The optical glass according to the second embodiment contains Nb2O5. The lower limit of the content of Nb2O5 is preferably 35%, more preferably 36.00%, 37.00%, 37.50%, 38.00%, 39.00%, 40.00%, 41.00%, 42.00%, 43.00%, 44.00%, 45.00% in this order. Also, the upper limit of the content of Nb2O5 is preferably 55%, more preferably 54.00%, 53.00%, 52.00%, 51.00%, 50.00%, 49.00%, 48.00%, 47.00% in this order.

[0119] By including Nb2O5, a glass with a high refractive index and high dispersion can be obtained. Nb2O5 is also a glass component that improves the thermal stability and chemical durability of the glass. Also, from the viewpoint of maintaining good thermal stability and chemical durability of the glass and suppressing the precipitation of crystals during reheating, it is preferable to set the upper limit of the content of Nb2O5 as described above.

[0120] The optical glass according to the second embodiment contains ZrO2. That is, in the optical glass according to the second embodiment, the content of ZrO2 exceeds 0%. The lower limit of the content of ZrO2 is preferably 1.00%, more preferably 2.00%, 3.00%, 4.00%, 6.00% in this order. Also, the upper limit of the content of ZrO2 is preferably 16.50%, more preferably 15.00%, 13.00%, 11.00%, 9.00%, 7.00% in this order.

[0121] By containing ZrO2, a glass with a high refractive index and high dispersibility can be obtained. Further, from the viewpoint of reducing the partial dispersion ratio Pg,F and suppressing the occurrence of defects as an optical element, and maintaining the meltability and thermal stability of the glass, it is preferable to set the upper limit of the content of ZrO2 as described above.

[0122] The optical glass according to the second embodiment contains an alkali metal oxide. The alkali metal oxide is preferably one or more oxides selected from the group consisting of Li2O, Na2O, K2O, and Cs2O. The lower limit of the total content of the alkali metal oxide is preferably 13.20%, more preferably 13.40%, 13.60%, 13.80%, 14.00%, 14.20%, 14.40%, 14.60% in this order. Further, the upper limit of the total content of the alkali metal oxide is preferably 15.50%, more preferably 15.40%, 15.30%, 15.20%, 15.10% in this order.

[0123] From the viewpoint of improving the meltability and thermal stability of the glass and lowering the liquidus temperature, it is preferable to set the lower limit of the total content of the alkali metal oxide as described above. Further, from the viewpoint of suppressing the occurrence of defects as an optical element, it is preferable to set the upper limit of the total content of the alkali metal oxide as described above.

[0124] <Abbe number νd> In the optical glass according to the second embodiment, the Abbe number νd exceeds 25.20 and is 29.00 or less. The lower limit of the Abbe number νd can be 25.40, 25.60, or 25.80. Further, the upper limit of the Abbe number νd can be 28.80, 28.60, 28.40, 28.00, 27.50, 27.00, 26.60, 26.40, or 26.20.

[0125] By setting the Abbe number νd within the above range, a glass with high dispersibility can be obtained. The Abbe number νd can be controlled by adjusting the contents of Nb2O5, TiO2, WO3, and Bi2O3, which are glass components contributing to high dispersion.

[0126] <Refractive index nd> <In the optical glass according to the second embodiment, the refractive index nd is 1.80000 or more and 1.85000 or less. The lower limit of the refractive index nd can be 1.80500, 1.81000, 1.81500, 1.82000, 1.82500, or 1.82800. Further, the upper limit of the refractive index nd can be 1.84800, 1.84500, or 1.84000.>

[0127] <By setting the refractive index nd within the above range, a high refractive index glass can be obtained. The refractive index nd can be controlled by adjusting the contents of Nb2O5, TiO2, WO3, and Bi2O3, which are glass components contributing to the increase in refractive index.>

[0128] <Workability> <When the optical glass according to the second embodiment is heated in the atmosphere at a temperature [Tg + 50°C] 50°C higher than the glass transition temperature Tg for 10 minutes and then heated at a temperature [Tg + 240°C] 240°C higher than the glass transition temperature Tg for 10 minutes, the number density of crystals with a maximum diameter of 1 μm or more that precipitate is 2000 pieces / kg or less. The number density is preferably 1800 pieces / kg or less, more preferably 1500 pieces / kg or less, and even more preferably 1000 pieces / kg or less in that order.>

[0129] <By setting the above number density within the above range, precipitation of crystals during reheating can be suppressed. Further, even when heat pressing is performed in a wide temperature range, precipitation of crystals during reheating can be suppressed, and internal defects such as cracks and veins and devitrification can also be suppressed.>

[0130] <In the optical glass according to the second embodiment, the lower limit of the mass ratio [SiO2 / Nb2O5] of the content of SiO2 to the content of Nb2O5 is preferably 0.47, more preferably 0.48, 0.49, 0.50, 0.51 in that order. Further, the upper limit of the mass ratio is preferably 0.66, more preferably 0.655, 0.650, 0.630, 0.600, 0.590, 0.580, 0.570, 0.560 in that order.>

[0131] From the viewpoint of reducing the specific gravity d of the glass while maintaining the desired optical constants (refractive index nd, Abbe number νd), it is preferable that the mass ratio [SiO2 / Nb2O5] be within the above range. Note that when the specific gravity of the glass increases, the mass of the optical element increases. For example, when a lens with a large mass is incorporated into an autofocus type imaging lens, the power required for driving the lens during autofocus increases, and there is a risk of rapid battery depletion.

[0132] In the optical glass according to the second embodiment, the lower limit of the total content [SiO2+Nb2O5] of SiO2 and Nb2O5 is preferably 60%, more preferably 61.0%, 62.0%, 62.5%, 62.9%, 63.0%, 64.0%, 65.0%, 66.0%, 67.0%, 68.0%, 69.0% in that order. The upper limit of the total content is preferably 75%, more preferably 74.0%, 73.5%, 73.0%, 72.5%, 72.0%, 71.5% in that order.

[0133] From the viewpoint of lowering the liquidus temperature, improving the thermal stability of the glass, and suppressing the crystallization of the glass, it is preferable that the total content [SiO2+Nb2O5] be within the above range.

[0134] In the optical glass according to the second embodiment, the upper limit of the mass ratio [B2O3 / SiO2] of the content of B2O3 to the content of SiO2 is preferably 0.07, more preferably 0.06, 0.05, 0.04, 0.03, 0.02 in that order. The lower limit of the mass ratio is preferably 0.00, more preferably 0.01.

[0135] From the viewpoint of suppressing an increase in the specific gravity d and coloring of the glass, it is preferable that the mass ratio [B2O3 / SiO2] be within the above range.

[0136] In the optical glass according to the second embodiment, the upper limit of the Li2O content is preferably 6.20%, more preferably 6.10%, 6.00%, 5.90%, and 5.80% in this order. Further, the lower limit of the Li2O content is preferably 5.30%, more preferably 5.35%, 5.40%, and 5.45% in this order.

[0137] Li2O has the function of lowering the liquidus temperature and improving the thermal stability of the glass. From the viewpoint of suppressing the decrease in chemical durability and weather resistance, it is preferable that the Li2O content be within the above range.

[0138] In the optical glass according to the second embodiment, the lower limit of the K2O content is preferably 0.62%, more preferably 0.80%, 1.00%, 1.20%, 1.40%, 1.80%, 2.20%, 2.40%, and 2.60% in this order. Further, the upper limit of the K2O content is preferably 7.00%, more preferably 6.50%, 6.00%, 5.50%, 5.00%, 4.50%, 4.20%, and 3.90% in this order.

[0139] From the viewpoint of lowering the liquidus temperature and improving the thermal stability of the glass, it is preferable that the K2O content be within the above range. On the other hand, when the K2O content increases, there is a risk of deterioration in chemical durability and weather resistance.

[0140] In the optical glass according to the second embodiment, the lower limit of the total content of Li2O, Na2O, and K2O [Li2O + Na2O + K2O] is preferably 13.00%, more preferably 13.20%, 13.40%, 13.60%, 13.80%, 14.00%, 14.20%, 14.40%, and 14.60% in this order. Further, the upper limit of the total content is preferably 15.69%, more preferably 15.50%, 15.40%, 15.30%, 15.20%, and 15.10% in this order.

[0141] From the perspective of improving the fusibility and thermal stability of the glass and reducing the liquidus temperature, it is preferable to set the lower limit of the total content [Li2O + Na2O + K2O] as described above. Also, from the perspective of suppressing the precipitation of crystals during reheating and suppressing the occurrence of internal defects in the glass such as cracks and veins, it is preferable to set the upper limit of the total content [Li2O + Na2O + K2O] as described above.

[0142] In the optical glass according to the second embodiment, the lower limit of the mass ratio [Li2O / (Li2O + Na2O + K2O)] of the content of Li2O to the total content of Li2O, Na2O, and K2O is preferably 0.34, and more preferably 0.345, 0.350, 0.355, 0.360 in this order. Also, the upper limit of the mass ratio is preferably 0.41, and more preferably 0.405, 0.400, 0.395, 0.390, 0.385 in this order.

[0143] From the perspective of enhancing the thermal stability of the glass and suppressing the precipitation of crystals during reheating without impairing the network-forming action of the glass, it is preferable to set the mass ratio [Li2O / (Li2O + Na2O + K2O)] within the above range.

[0144] In the optical glass according to the second embodiment, the lower limit of the mass ratio [Na2O / (Li2O + Na2O + K2O)] of the content of Na2O to the total content of Li2O, Na2O, and K2O is preferably 0.33, and more preferably 0.340, 0.345, 0.350, 0.355 in this order. Also, the upper limit of the mass ratio is preferably 0.50, and more preferably 0.490, 0.480, 0.470, 0.460, 0.450, 0.440, 0.430, 0.425 in this order.

[0145] From the perspective of enhancing the thermal stability of the glass and suppressing the precipitation of crystals during reheating without impairing the network-forming action of the glass, it is preferable to set the mass ratio [Na2O / (Li2O + Na2O + K2O)] within the above range.

[0146] In the optical glass according to the second embodiment, the lower limit of the mass ratio of the content of K2O to the total content of Li2O, Na2O, and K2O [K2O / (Li2O + Na2O + K2O)] is preferably 0.04, and more preferably 0.05, 0.06, 0.08, 0.12, 0.14, 0.16, 0.18, 0.20 in this order. Further, the upper limit of the mass ratio is preferably 0.30, and more preferably 0.290, 0.280, 0.275, 0.270 in this order.

[0147] From the viewpoint of enhancing the thermal stability of the glass and suppressing the precipitation of crystals during reheating without impairing the network-forming action of the glass, it is preferable that the mass ratio [K2O / (Li2O + Na2O + K2O)] be within the above range.

[0148] In the optical glass according to the second embodiment, the lower limit of the mass ratio of the total content of SiO2 and Nb2O5 to the total content of Li2O, Na2O, and K2O [(SiO2 + Nb2O5) / (Li2O + Na2O + K2O)] is preferably 4.00, and more preferably 4.10, 4.15, 4.20, 4.25, 4.30, 4.35, 4.40, 4.45, 4.50, 4.55, 4.60 in this order. Further, the upper limit of the mass ratio is preferably 5.02, and more preferably 4.95, 4.90, 4.85, 4.80 in this order.

[0149] From the viewpoint of enhancing the thermal stability of the glass and suppressing the precipitation of crystals during reheating without impairing the network-forming action of the glass, it is preferable that the mass ratio [(SiO2 + Nb2O5) / (Li2O + Na2O + K2O)] be within the above range.

[0150] In the optical glass according to the second embodiment, the lower limit of the content of TiO2 is preferably 0%, and more preferably 1%, 2%, 3%, 4% in this order. Further, the upper limit of the content of TiO2 is preferably 11%, and more preferably 10%, 9%, 7%, 6%, 5% in this order.

[0151] TiO₂ is a component that contributes to high dispersion. From the viewpoint of improving the thermal stability of the glass and suppressing the precipitation of crystals during reheating, it is preferable that the content of TiO₂ be within the above range. On the other hand, if TiO₂ is introduced in excess, there is a risk that the partial dispersion ratio Pg,F will increase.

[0152] The contents, ratios, and glass properties of the glass components other than those described above in the second embodiment can be the same as those in the first embodiment. Also, the glass properties other than those described above in the second embodiment, the production of optical glass, and the production of optical elements, etc. can be the same as those in the first embodiment.

Examples

[0153] Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the embodiments shown in the examples.

[0154] (Example 1) Glass samples having the glass compositions shown in Tables 1 to 2 were prepared by the following procedure and various evaluations were performed.

[0155] [Production of optical glass] Oxides, hydroxides, carbonates, and nitrates corresponding to the constituent components of the glass were prepared as raw materials, and the raw materials were weighed and formulated so that the glass composition of the resulting optical glass would be each composition shown in Tables 1 to 2, and the raw materials were thoroughly mixed. The thus-obtained formulated raw materials (batch raw materials) were put into a platinum crucible, heated at 1350°C to 1400°C for 2 hours to obtain molten glass, stirred for homogenization, clarified, and then the molten glass was cast into a mold preheated to an appropriate temperature. The cast glass was heat-treated at a temperature lower than the glass transition temperature Tg for 30 minutes and allowed to cool to room temperature in the furnace to obtain glass samples.

[0156] [Confirmation of glass component composition] Regarding the obtained glass samples, the content of each glass component was measured by inductively coupled plasma atomic emission spectrometry (ICP-AES), and it was confirmed that the composition was as shown in Tables 1 to 2.

[0157] [Measurement of Optical Properties] The obtained glass sample was further annealed at around the glass transition temperature Tg for about 30 minutes to about 2 hours, and then cooled to room temperature in the furnace at a cooling rate of -30 °C / hour to obtain an annealed sample. For the obtained annealed sample, the refractive indices nd, ng, nF and nC, Abbe number νd, specific gravity d, glass transition temperature Tg, λ80, λ70 and λ5 were measured. The results are shown in Table 3. (i) Refractive indices nd, ng, nF, nC and Abbe number νd For the above annealed sample, the refractive indices nd, ng, nF, nC were measured by the refractive index measurement method of JIS standard JIS B 7071-1, and the Abbe number νd was calculated based on the following formula. νd = (nd - 1) / (nF - nC)

[0158] (ii) Specific gravity d The specific gravity d was measured by the Archimedes method.

[0159] (iii) Glass transition temperature Tg A sample obtained by sufficiently pulverizing the obtained optical glass sample in a mortar was used, and a differential scanning calorimeter (DSC8270) manufactured by Rigaku was used to measure the glass transition temperature Tg at a heating rate of 10 °C / min.

[0160] (iv) λ80, λ70, λ5 The above annealed sample was processed to have a thickness of 10 mm and flat surfaces that are parallel to each other and optically polished, and the spectral transmittance in the wavelength range from 200 nm to 700 nm was measured. The intensity of the light incident perpendicularly to one of the optically polished flat surfaces was defined as intensity A, and the intensity of the light exiting from the other flat surface was defined as intensity B, and the spectral transmittance B / A was calculated. The wavelength at which the spectral transmittance becomes 80% was defined as λ80, the wavelength at which the spectral transmittance becomes 70% was defined as λ70, and the wavelength at which the spectral transmittance becomes 5% was defined as λ5. Note that the spectral transmittance includes the reflection loss of light at the sample surface.

[0161]

Table 1

[0162]

Table 2

[0163]

Table 3

[0164] (Example 2) [Workability] The glass sample obtained in Example 1 was cut, sliced, polished on the entire surface with a #800 file, and chamfered on all sides. A test piece of 10 mm × 10 mm × 10 mm was obtained. This test piece was heated in a first test furnace set at a temperature [Tg + 50°C] 50°C higher than the glass transition temperature Tg for 10 minutes, and further heated in a second test furnace set at a temperature [Tg + 240°C] 240°C higher than the glass transition temperature Tg for 10 minutes. The test piece was heated on an alumina plate with a small amount of BN (boron nitride) powder for preventing fusion. After heating in the second test furnace, the test piece was wrapped with ceramic fibers having heat-resistant fire resistance such as kaowool to prevent cracking and allowed to cool to room temperature. The test piece was optically polished and the inside was observed with an optical microscope (40 - 200 times magnification). The number of crystals having a maximum diameter of 1 μm or more inside the test piece was counted and converted to the number per kg. The results are shown in Table 3. After heating in the second test furnace, the inside of all the test pieces was not cloudy, had no texture, and had no cracks or fractures.

[0165] (Example 3) Using each of the optical glasses produced in Example 1, lens blanks were produced by a known method, and various lenses were produced by processing the lens blanks by known methods such as polishing. The produced optical lenses are various lenses such as biconvex lenses, biconcave lenses, plano-convex lenses, plano-concave lenses, concave meniscus lenses, and convex meniscus lenses. By combining the various lenses with lenses made of other types of optical glass, chromatic aberration could be corrected well.

[0166] In addition, since the glass has a low specific gravity, the weight is smaller than that of lenses having the same optical characteristics and size, and it is suitable for use in various imaging devices, particularly autofocus type imaging devices for reasons such as energy saving. Similarly, prisms were fabricated using various optical glasses fabricated in Example 1.

[0167] It should be considered that all aspects of the embodiments disclosed this time are illustrative and not restrictive. The scope of the present invention is shown not by the above description but by the claims, and it is intended that all modifications within the meaning and scope equivalent to the claims are included.

[0168] For example, by performing the composition adjustment described in the specification on the glass composition exemplified above, an optical glass according to one aspect of the present invention can be fabricated. In addition, it is of course possible to arbitrarily combine two or more of the matters exemplified or described as preferred ranges in the specification.

Claims

1. The Abbe number νd exceeds 25.20 and is 29.00 or less, the refractive index nd is 1.80000 or more and 1.85000 or less, in terms of mass%, SiO 2 The content of which is 20 to 30%, Nb 2 O 5 The content thereof is 35 to 55%, Nb 2 O 5 The mass ratio [SiO 2 / Nb 2 O 2 O 5 of the content of SiO to the content of NbO is 0.47 to 0.66, and SiO 2 and Nb 2 O 5 The total content of 2 [SiO 2 + Nb 5 O] is 60 to 75%, and SiO 2 The mass ratio of the content of B 2 O 3 to the content of 2 O 3 / SiO 2 is 0.00 to 0.07, and Li 2 The content of O is 6.20% or less, K 2 The content of O is 0.62% or more, Li 2 O, Na 2 O, and K 2 The total content of O [Li 2 O + Na 2 O + K 2 O] is 13.00 to 15.69%, and Li 2 O, Na 2 O, and K 2 The mass ratio of Li to the total content of 2 O, [Li 2 O / (Li 2 O + Na 2 O + K 2 O)] is 0.34 to 0.41, and Li 2 O, Na 2 O, and K 2 Na content relative to total O content 2 Mass ratio of O content [Na 2 O / (Li 2 O+Na 2 O+K 2 O)] is 0.33 to 0.50, Li 2 O, Na 2 O, and K 2 The mass ratio of K 2 O content to the total content of K 2 O / (Li 2 O + Na 2 O + K 2 O)] is 0.04 to 0.30, Li 2 O, Na 2 O, and K 2 The mass ratio of SiO 2 and Nb 2 O 5 to the total content of 2 [(SiO 2 + Nb 5 O) / (Li 2 O + Na 2 O + K 2 O)] is 4.00 to 5.02, and TiO 2 The content thereof is 0 to 11%, ZrO 2 An optical glass having a ZrO content exceeding 0%.

2. The specific gravity d is 3.32 or more and 3.51 or less. The optical glass according to Claim 1.

3. SiO 2 , Nb 2 O 5 , ZrO 2 , and contains alkali metal oxides, The Abbe number νd exceeds 25.20 and is 29.00 or less, the refractive index nd is 1.80000 or more and 1.85000 or less, When heated at a temperature [Tg + 50°C] which is 50°C higher than the glass transition temperature Tg in the atmosphere for 10 minutes and then heated at a temperature [Tg + 240°C] which is 240°C higher than the glass transition temperature Tg for 10 minutes, the number density of crystals with a maximum diameter of 1 μm or more that precipitate is 2000 pieces / kg or less. The optical glass.

4. An optical element made of the optical glass according to any one of Claims 1 to 3.

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