Optical glass and optical element

Abstract

The invention provides optical glass and an optical element which have expected abbe number vd and refractive index nd and are suitable for color difference correction. The optical glass is characterized in that vd is more than 25.20 and less than or equal to 29.00, nd is more than or equal to 1.80000 and less than or equal to 1.85000, in terms of mass%, SiO2 is 20-30%, Nb2O5 is 35-55%, the mass ratio of SiO2 to Nb2O5 is 0.47-0.66, the total of SiO2 and Nb2O5 is 60-75%, [B2O3 / SiO2] is 0.00-0.07, Li2O is less than or equal to 6.20%, K2O is more than or equal to 0.62%, the total of Li2O, Na2O and K2O is 13.00-15.69%, the mass ratios of Li2O, Na2O and K2O are 0.34-0.41, 0.33-0.5, 0.04-0.30 and 4.00-5.02, respectively,

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 high refractive index and high dispersibility is highly useful for correcting chromatic aberration and making optical systems highly functional and compact.

[0003] As a method for manufacturing such optical glass used in optical systems, there is a reheat press method in which the glass is reheated and molded. In this manufacturing method, Si-Nb-based high refractive index and high dispersibility optical glass containing Si and Nb is prone to phase separation during reheating. If phase separation occurs, the fluidity of the glass during reheating may deteriorate, and it may not be possible to mold it into a desired shape. In addition, this phase separation causes crystal precipitation. That is, Si-Nb-based high refractive index and high dispersibility optical glass containing Si and Nb is prone to crystal precipitation during reheating. The crystals precipitated during reheating become 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 during reheating is suppressed.

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

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

[0006] Prior Art Documents

[0007] Patent Documents

[0008] Patent Document 1: Japanese Patent Application Laid-Open No. 2019-64898

[0009] Patent Document 2: Japanese Patent Application Laid-Open No. 2020-7214 Summary of the Invention

[0010] Problems to be Solved by the Invention

[0011] The present invention has been made in view of such actual circumstances, and an object thereof is to provide optical glass and optical elements having a desired Abbe number νd and refractive index nd and suitable for chromatic aberration correction.

[0012] Means for Solving the Problems

[0013] The gist of the present invention is as follows.

[0014] [1] An optical glass having an Abbe number νd exceeding 25.20 and being 29.00 or less, and a refractive index nd of 1.80000 or more and 1.85000 or less,

[0015] In terms of mass %,

[0016] The content of SiO2 is 20 - 30%,

[0017] The content of Nb2O5 is 35 - 55%,

[0018] The mass ratio [SiO2 / Nb2O5] of the content of SiO2 to the content of Nb2O5 is 0.47 - 0.66,

[0019] The total content [SiO2 + Nb2O5] of SiO2 and Nb2O5 is 60 - 75%,

[0020] The mass ratio [B2O3 / SiO2] of the content of B2O3 to the content of SiO2 is 0.00 - 0.07,

[0021] The content of Li2O is 6.20% or less,

[0022] The content of K2O is 0.62% or more,

[0023] The total content [Li2O + Na2O + K2O] of Li2O, Na2O and K2O is 13.00 - 15.69%,

[0024] The mass ratio [Li2O / (Li2O + Na2O + K2O)] of the content of Li2O to the total content of Li2O, Na2O and K2O is 0.34 - 0.41,

[0025] The mass ratio [Na2O / (Li2O + Na2O + K2O)] of the content of Na2O to the total content of Li2O, Na2O and K2O is 0.33 - 0.50,

[0026] The mass ratio [K2O / (Li2O + Na2O + K2O)] of the content of K2O to the total content of Li2O, Na2O and K2O is 0.04 - 0.30,

[0027] 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 - 5.02,

[0028] The content of TiO2 is 0 - 11%,

[0029] The content of ZrO2 exceeds 0%.

[0030] [2] The specific gravity d of the optical glass according to [1] is 3.32 or more and 3.51 or less.

[0031] [3] An optical glass comprising SiO2, Nb2O5, ZrO2 and an alkali metal oxide,

[0032] The Abbe number νd of the optical glass exceeds 25.20 and is 29.00 or less, and the refractive index nd is 1.80000 or more and 1.85000 or less.

[0033] When the optical glass 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 precipitated is 2000 pieces / kg or less.

[0034] [4] An optical element made of the optical glass according to any one of [1] to [3] above.

[0035] Effect of the Invention

[0036] According to the present invention, an optical glass and an optical element having a desired Abbe number νd and refractive index nd and suitable for chromatic aberration correction can be provided. Detailed Embodiments

[0037] Hereinafter, an embodiment of the present invention will be described. It should be noted that in the present invention and this specification, unless otherwise specified, the glass composition is expressed on an oxide basis. Here, the "glass composition on an oxide basis" means the glass composition obtained by converting according to the substances that are all decomposed when the glass raw materials are melted and exist in the glass in the form of oxides, and the expressions of the respective glass components are recorded as SiO2, TiO2, etc. according to custom. Unless otherwise specified, the content, total content, and ratio of the glass components are on a mass basis, and "%" means "mass%".

[0038] The content of the glass component can be quantified by a known method, such as inductively coupled plasma atomic emission spectrometry (ICP - AES), inductively coupled plasma mass spectrometry (ICP - MS), etc. In addition, in the present invention and this specification, a content of 0% of a constituent means that the constituent is substantially not contained, and it is allowed to contain the component at an unavoidable impurity level.

[0039] Hereinafter, the optical glass of the present embodiment will be described in detail. First, as the first embodiment, the optical glass will be described from the viewpoint of the glass composition. Next, as the second embodiment, the optical glass will be described from the viewpoint of the characteristics of the glass.

[0040] First Embodiment

[0041] The Abbe number νd of the optical glass of the first embodiment exceeds 25.20 and is 29.00 or less, and the refractive index nd is 1.80000 or more and 1.85000 or less.

[0042] In terms of mass%,

[0043] The content of SiO2 is 20 to 30%,

[0044] The content of Nb2O5 is 35 to 55%,

[0045] The mass ratio [SiO2 / Nb2O5] of the content of SiO2 to the content of Nb2O5 is 0.47 to 0.66.

[0046] The total content [SiO2+Nb2O5] of SiO2 and Nb2O5 is 60 to 75%.

[0047] The mass ratio [B2O3 / SiO2] of the content of B2O3 to the content of SiO2 is 0.00 to 0.07.

[0048] The content of Li2O is 6.20% or less.

[0049] The content of K2O is 0.62% or more.

[0050] The total content [Li2O+Na2O+K2O] of Li2O, Na2O and K2O is 13.00 to 15.69%.

[0051] 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.

[0052] 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.

[0053] The mass ratio [K2O / (Li2O+Na2O+K2O)] of the content of K2O to the total content of Li2O, Na2O and K2O is 0.04 to 0.30.

[0054] 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.

[0055] The content of TiO2 is 0 to 11%.

[0056] The content of ZrO2 exceeds 0%.

[0057] <Abbe number νd>

[0058] Regarding the optical glass of 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 set to 25.40, 25.60 or 25.80. In addition, the upper limit of the Abbe number νd can be set to 28.80, 28.60, 28.40, 28.00, 27.50, 27.00, 26.60, 26.40 or 26.20.

[0059] 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.

[0060] <Refractive index nd>

[0061] Regarding the optical glass of 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 set to 1.80500, 1.81000, 1.81500, 1.82000, 1.82500 or 1.82800. In addition, the upper limit of the refractive index nd can be set to 1.84800, 1.84500 or 1.84000.

[0062] By setting the refractive index nd within the above range, a glass with high refractive index 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 high refractive index.

[0063] In the optical glass of the first embodiment, the content of SiO2 is 20 to 30%. The lower limit of the content of SiO2 is preferably 21.00%, and more preferably in the order of 22.00%, 23.30%, 23.40% further. In addition, the upper limit of the content of SiO2 is preferably 29.00%, and more preferably in the order of 28.00%, 27.00%, 26.00%, 25.00% further.

[0064] SiO2 is a network-forming component of the glass. By making the lower limit of SiO2 satisfy the above range, 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. In addition, by making the upper limit of SiO2 satisfy the above range, a decrease in the devitrification resistance of the glass can be suppressed.

[0065] In the optical glass of the first embodiment, the content of Nb2O5 is 35 to 55%. The lower limit of the content of Nb2O5 is preferably 36.00%, and more preferably in the order of 37.00%, 37.50%, 38.00%, 39.00%, 40.00%, 41.00%, 42.00%, 43.00%, 44.00%, 45.00%. In addition, the upper limit of the content of Nb2O5 is preferably 54.00%, and more preferably in the order of 53.00%, 52.00%, 51.00%, 50.00%, 49.00%, 48.00%, 47.00%.

[0066] By making the lower limit of the content of Nb2O5 satisfy the above range, a glass with high refractive index and high dispersion can be obtained. In addition, Nb2O5 is also a glass component that improves the thermal stability and chemical durability of the glass. By making the upper limit of the content of Nb2O5 satisfy the above range, the thermal stability and chemical durability of the glass can be maintained well, thereby suppressing the precipitation of crystals during reheating.

[0067] In the optical glass of the first embodiment, the mass ratio [SiO2 / Nb2O5] of the content of SiO2 to the content of Nb2O5 is 0.47 to 0.66. The lower limit of this mass ratio is preferably 0.48, and more preferably in the order of 0.49, 0.50, 0.51. In addition, the upper limit of this mass ratio is preferably 0.655, and more preferably in the order of 0.650, 0.630, 0.600, 0.590, 0.580, 0.570, 0.560.

[0068] By making the mass ratio [SiO2 / Nb2O5] within the above range, while reducing the specific gravity d of the glass, the desired optical constants (refractive index nd, Abbe number νd) can be maintained. It should be noted that if the specific gravity of the glass increases, the mass of the optical element increases. For example, if a lens with a large mass is introduced into an autofocus type camera lens, there is a risk that the power required for driving the lens increases and the battery consumption becomes severe during autofocus.

[0069] In the optical glass of the first embodiment, the total content of SiO2 and Nb2O5 [SiO2 + Nb2O5] is 60 to 75%. The lower limit of this total content is preferably 61.0%, and more preferably in the order of 62.0%, 62.5%, 62.9%, 63.0%, 64.0%, 65.0%, 66.0%, 67.0%, 68.0%, 69.0% in turn. The upper limit of this total content is preferably 74.0%, and more preferably in the order of 73.5%, 73.0%, 72.5%, 72.0%, 71.5% in turn.

[0070] By setting the total content [SiO2 + Nb2O5] within the above range, the liquidus temperature can be reduced and the thermal stability of the glass can be improved. In addition, the crystallization of the glass can be suppressed.

[0071] In the optical glass of the first embodiment, the mass ratio of the content of B2O3 to the content of SiO2 [B2O3 / SiO2] is 0.00 to 0.07. The upper limit of this mass ratio is preferably 0.06, and more preferably in the order of 0.05, 0.04, 0.03, 0.02 in turn. The lower limit of this mass ratio is preferably 0.01.

[0072] By making the mass ratio [B2O3 / SiO2] within the above range, an increase in the specific gravity d and the coloring of the glass can be suppressed.

[0073] In the optical glass of 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 in the order of 6.00%, 5.90%, 5.80% in turn. In addition, the lower limit of the content of Li2O is preferably 5.30%, and more preferably in the order of 5.35%, 5.40%, 5.45% in turn.

[0074] Li2O has the effect of reducing 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.

[0075] In the optical glass of 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 in the order of 1.00%, 1.20%, 1.40%, 1.80%, 2.20%, 2.40%, 2.60% in turn. In addition, the upper limit of the content of K2O is preferably 7.00%, and more preferably in the order of 6.50%, 6.00%, 5.50%, 5.00%, 4.50%, 4.20%, 3.90% in turn.

[0076] By setting the content of K2O within the above range, the liquidus temperature can be reduced, and the thermal stability of the glass can be improved. On the other hand, when the content of K2O increases, there is a risk of deterioration in chemical durability and weather resistance.

[0077] In the optical glass of the first embodiment, the total content of Li2O, Na2O and K2O [Li2O + Na2O + K2O] is 13.00 to 15.69%. The lower limit of this total content is preferably 13.20%, and more preferably in the order of 13.40%, 13.60%, 13.80%, 14.00%, 14.20%, 14.40%, 14.60% further. In addition, the upper limit of this total content is preferably 15.50%, and more preferably in the order of 15.40%, 15.30%, 15.20%, 15.10% further.

[0078] By making the lower limit of the total content [Li2O + Na2O + K2O] satisfy the above range, the meltability and thermal stability of the glass can be improved, and the liquidus temperature can be reduced. In addition, by making the upper limit of the total content [Li2O + Na2O + K2O] satisfy the above range, the precipitation of crystals during reheating can be suppressed, and the generation of internal defects of the glass such as cracks and striae can be suppressed.

[0079] In the optical glass of 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 this mass ratio is preferably 0.345, and more preferably in the order of 0.350, 0.355, 0.360 further. In addition, the upper limit of this mass ratio is preferably 0.405, and more preferably in the order of 0.400, 0.395, 0.390, 0.385 further.

[0080] By making the mass ratio [Li2O / (Li2O + Na2O + K2O)] within the above range, the thermal stability of the glass can be improved. In addition, the precipitation of crystals during reheating can be suppressed without impairing the network-forming effect of the glass.

[0081] In the optical glass of 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 this mass ratio is preferably 0.340, and more preferably in the order of 0.345, 0.350, 0.355 further. In addition, the upper limit of this mass ratio is preferably 0.490, and more preferably in the order of 0.480, 0.470, 0.460, 0.450, 0.440, 0.430, 0.425 further.

[0082] By making the mass ratio [Na2O / (Li2O + Na2O + K2O)] within the above range, the thermal stability of the glass can be improved. In addition, the precipitation of crystals during reheating can be suppressed without impairing the network-forming effect of the glass.

[0083] In the optical glass of the first embodiment, the mass ratio [K2O / (Li2O + Na2O + K2O)] of the content of K2O to the total content of Li2O, Na2O and K2O is 0.04 to 0.30. The lower limit of this mass ratio is preferably 0.05, and more preferably in the order of 0.06, 0.08, 0.12, 0.14, 0.16, 0.18, 0.20. In addition, the upper limit of this mass ratio is preferably 0.290, and more preferably in the order of 0.280, 0.275, 0.270.

[0084] By making the mass ratio [K2O / (Li2O + Na2O + K2O)] within the above range, the thermal stability of the glass can be improved. In addition, the precipitation of crystals during reheating can be suppressed without impairing the network-forming effect of the glass.

[0085] In the optical glass of 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 this mass ratio is preferably 4.10, and more preferably in the order of 4.15, 4.20, 4.25, 4.30, 4.35, 4.40, 4.45, 4.50, 4.55, 4.60. In addition, the upper limit of this mass ratio is preferably 4.95, and more preferably in the order of 4.90, 4.85, 4.80.

[0086] By making the mass ratio [(SiO2 + Nb2O5) / (Li2O + Na2O + K2O)] within the above range, the thermal stability of the glass can be improved. In addition, the precipitation of crystals during reheating can be suppressed without impairing the network-forming effect of the glass.

[0087] In the optical glass of the first embodiment, the content of TiO2 is 0 to 11%. The lower limit of the content of TiO2 is preferably 1%, and more preferably in the order of 2%, 3%, 4%. In addition, the upper limit of the content of TiO2 is preferably 10%, and more preferably in the order of 9%, 7%, 6%, 5%.

[0088] TiO2 is a component that contributes to high dispersion. By setting the content of TiO2 within the above range, the thermal stability of the glass can be improved, and in addition, the precipitation of crystals during reheating can be suppressed. On the other hand, if TiO2 is introduced in excess, there is a risk of increasing the relative partial dispersion Pg,F.

[0089] In the optical glass of the first embodiment, the content of ZrO2 exceeds 0%. The lower limit of the content of ZrO2 is preferably 1.00%, and more preferably in the order of 2.00%, 3.00%, 4.00%, 6.00% further. In addition, the upper limit of the content of ZrO2 is preferably 16.50%, and more preferably in the order of 15.00%, 13.00%, 11.00%, 9.00%, 7.00% further.

[0090] By making the lower limit of the content of ZrO2 satisfy the above range, a glass with high refractive index and high dispersibility can be obtained. In addition, by making the upper limit of the content of ZrO2 satisfy the above range, in addition to reducing the relative partial dispersion Pg,F and suppressing the generation of defects as optical elements, the meltability and thermal stability of the glass can also be maintained.

[0091] Regarding the content, ratio and glass properties of the glass components other than the above in the optical glass of the first embodiment, non-limiting examples are shown below.

[0092] In the optical glass of the first embodiment, the lower limit of the content of P2O5 is preferably 0.00%, and more preferably in the order of 0.20%, 0.40%, 0.60% further. In addition, the upper limit of the content of P2O5 is preferably 7.00%, and more preferably in the order of 5.00%, 4.00%, 3.00% further.

[0093] P2O5 is a network-forming component of the glass and has the effect of improving the thermal stability of the glass. On the other hand, when the content of P2O5 increases, there is a risk of reducing the thermal stability of the glass and easily precipitating crystals during reheating. Therefore, it is preferable to set the content of P2O5 within the above range.

[0094] In the optical glass of the first embodiment, the lower limit of the content of B2O3 is preferably 0.00%, and more preferably in the order of 0.02%, 0.04%, 0.06% further. In addition, the upper limit of the content of B2O3 is preferably 7.00%, and more preferably in the order of 5.00%, 3.00%, 1.00%, 0.50% further.

[0095] B2O3 is a network-forming component of the glass and has the effect of improving the thermal stability of the glass. On the other hand, when the content of B2O3 is high, there is a risk of an increase in the volatilization amount of the glass components during glass melting. In addition, when the content of B2O3 is high, there is a tendency to hinder high dispersion and reduce devitrification resistance. Therefore, it is preferable to set the content of B2O3 within the above range.

[0096] In the optical glass of the first embodiment, the content of Al2O3 is preferably 20% or less, and more preferably 10% or less, 5% or less, and 3% or less in this order. The content of Al2O3 may also be 0%.

[0097] Al2O3 is a glass component that has the effect of improving 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. In addition, 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 to set the content of Al2O3 within the above range.

[0098] In the optical glass of the first embodiment, the upper limit of the content of WO3 is preferably 20%, and more preferably 15%, 10%, and 5% in this order. In addition, the lower limit of the content of WO3 is preferably 0%.

[0099] 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. In addition, WO3 is likely to cause glass coloring and there is a risk of deteriorating the transmittance. Therefore, it is preferable to set the content of WO3 within the above range.

[0100] In the optical glass of the first embodiment, the upper limit of the content of Bi2O3 is preferably 20%, and more preferably 10%, 5%, and 3% in this order. In addition, the lower limit of the content of Bi2O3 is preferably 0%.

[0101] Bi2O3 has the effect of improving the thermal stability of the glass when contained in an appropriate amount. On the other hand, if the content of Bi2O3 is increased, there is a risk of increasing the specific gravity d. In addition, there is a risk of increasing the coloring of the glass. Therefore, it is preferable to set the content of Bi2O3 within the above range.

[0102] In the optical glass of the first embodiment, the lower limit of the content of Na2O is preferably 3.00%, and more preferably 3.50%, 4.00%, 4.50%, 5.00%, and 5.10% in this order. In addition, the upper limit of the content of Na2O is preferably 10.00%, and more preferably 9.00%, 8.50%, 8.00%, 7.00%, and 6.50% in this order.

[0103] Na2O has the effect of lowering the liquid phase temperature and improving the thermal stability of the glass. On the other hand, when the content of Na2O increases, there is a risk of reducing chemical durability and weather resistance. Therefore, it is preferable to set the content of Na2O within the above range.

[0104] In the optical glass of the first embodiment, the upper limit of the content of Cs2O is preferably 10%, and more preferably in the order of 5%, 3%, 1% further. The lower limit of the content of Cs2O is preferably 0%.

[0105] Cs2O has the effect of improving the thermal stability of the glass. On the other hand, when the content of Cs2O increases, there is a risk of reducing chemical durability and weather resistance. Therefore, it is preferable to set the content of Cs2O within the above range.

[0106] In the optical glass of the first embodiment, the lower limit of the total content of alkali metal oxides is preferably 13.20%, and more preferably in the order of 13.40%, 13.60%, 13.80%, 14.00%, 14.20%, 14.40%, 14.60% further. In addition, the upper limit of the total content of alkali metal oxides is preferably 15.50%, and more preferably in the order of 15.40%, 15.30%, 15.20%, 15.10% further.

[0107] The alkali metal oxide is preferably one or more oxides selected from Li2O, Na2O, K2O and Cs2O.

[0108] From the viewpoints of improving the meltability and thermal stability of the glass and lowering the liquid phase temperature, it is preferable to set the lower limit of the total content of alkali metal oxides as described above. In addition, from the viewpoint of suppressing the generation 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.

[0109] In the optical glass of the first embodiment, the upper limit of the content of MgO is preferably 20%, and more preferably in the order of 10%, 5%, 3% further. The lower limit of the content of MgO is preferably 0%.

[0110] In the optical glass of the first embodiment, the upper limit of the content of CaO is preferably 20%, and more preferably in the order of 10%, 5%, 3% further. The lower limit of the content of CaO is preferably 0%.

[0111] In the optical glass of the first embodiment, the upper limit of the content of SrO is preferably 20%, and more preferably in the order of 10%, 5%, 3% further. The lower limit of the content of SrO is preferably 0%.

[0112] In the optical glass of the first embodiment, the upper limit of the content of BaO is preferably 20%, and more preferably in the order of 10%, 5%, and 3% further. In addition, the lower limit of the content of BaO is preferably 0%, and it may be set to 0.10% or 0.20%.

[0113] MgO, CaO, SrO, and BaO are all glass components that have the effect 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 in addition, the thermal stability and devitrification resistance of the glass decrease. Therefore, the content of each of these glass components is preferably in the above range.

[0114] In the optical glass of the first embodiment, the upper limit of the content of ZnO is preferably 20%, and more preferably in the order of 10%, 5%, and 3% further. In addition, the lower limit of the content of ZnO is preferably 0%.

[0115] ZnO is a glass component that has the effect of improving the thermal stability of the glass. However, if the content of ZnO increases, there is a risk of an increase in the specific gravity d. From the viewpoint of improving the thermal stability of the glass and maintaining the desired optical properties, it is preferable to set the content of ZnO in the above range.

[0116] In the optical glass of the first embodiment, the upper limit of the content of La2O3 is preferably 20%, and more preferably in the order of 10%, 5%, and 3% further. In addition, the lower limit of the content of La2O3 is preferably 0%.

[0117] If the content of La2O3 increases, there is a risk of an increase in the specific gravity d and a decrease in the thermal stability of the glass. 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 to set the content of La2O3 in the above range.

[0118] In the optical glass of the first embodiment, the upper limit of the content of Y2O3 is preferably 20%, and more preferably in the order of 10%, 5%, and 3% further. In addition, the lower limit of the content of Y2O3 is preferably 0%.

[0119] If the content of Y2O3 becomes too much, the thermal stability of the glass decreases, and the glass is likely to devitrify during manufacturing. Therefore, from the viewpoint of suppressing the decrease in the thermal stability of the glass, it is preferable to set the content of Y2O3 in the above range.

[0120] In the optical glass of the first embodiment, the upper limit of the content of Ta2O5 is preferably 20%, and more preferably in the order of 10%, 5%, and 3% further. In addition, the lower limit of the content of Ta2O5 is preferably 0%.

[0121] Ta2O5 is a glass component that improves the thermal stability of glass. Compared with Nb2O5, TiO2, WO3, and Bi2O3, it is a component that reduces the relative partial dispersion Pg,F. On the other hand, when the content of Ta2O5 increases, the thermal stability of the glass decreases, and it is easy for the glass raw materials not to melt when melting the glass. In addition, there is a risk of an increase in the specific gravity d. Therefore, it is preferable to set the content of Ta2O5 within the above range.

[0122] In the optical glass of the first embodiment, the content of Sc2O3 is preferably 2% or less. In addition, the lower limit of the content of Sc2O3 is preferably 0%.

[0123] In the optical glass of the first embodiment, the content of HfO2 is preferably 2% or less. In addition, the lower limit of the content of HfO2 is preferably 0%.

[0124] Sc2O3 and HfO2 have the effect of improving the high dispersibility of glass, but they are expensive components. Therefore, it is preferable to set the respective contents of Sc2O3 and HfO2 within the above range.

[0125] In the optical glass of the first embodiment, the content of Lu2O3 is preferably 2% or less. In addition, the lower limit of the content of Lu2O3 is preferably 0%.

[0126] Lu2O3 has the effect of improving the high dispersibility of glass, but due to its large molecular weight, it is also a glass component that causes an increase in the specific gravity d of the glass. Therefore, it is preferable to set the content of Lu2O3 within the above range.

[0127] In the optical glass of the first embodiment, the content of GeO2 is preferably 2% or less. In addition, the lower limit of the content of GeO2 is preferably 0%.

[0128] GeO2 has the effect of improving the high dispersibility of glass, but among the commonly used glass components, it is an extremely expensive component. Therefore, from the viewpoint of reducing the manufacturing cost of the glass, it is preferable to set the content of GeO2 within the above range.

[0129] In the optical glass of the first embodiment, the content of Gd2O3 is preferably 2% or less. In addition, the lower limit of the content of Gd2O3 is preferably 0%.

[0130] If the content of Gd2O3 becomes excessive, there is a risk of a decrease in the thermal stability of the glass. In addition, if the content of Gd2O3 becomes excessive, the specific gravity d of the glass increases, which is not preferable. Therefore, from the viewpoint of maintaining the thermal stability of the glass well and suppressing the increase in the specific gravity d, it is preferable to set the content of Gd2O3 within the above range.

[0131] In the optical glass of the first embodiment, the content of Yb2O3 is preferably 2% or less. Additionally, the lower limit of the content of Yb2O3 is preferably 0%.

[0132] Yb2O3 has a larger molecular weight compared to La2O3, Gd2O3, and Y2O3. Therefore, there is a risk of increasing the specific gravity d of the glass. Thus, it is desirable to reduce the content of Yb2O3 to suppress the increase in the specific gravity d of the glass. Additionally, if the content of Yb2O3 is excessive, there is a risk of reducing the thermal stability of the glass. From the perspective of preventing the reduction of the thermal stability of the glass and suppressing the increase in the specific gravity d, it is preferable to set the content of Yb2O3 within the above range.

[0133] Preferably, the optical glass of the first embodiment mainly consists of the above glass components, namely, 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. The total content of the above glass components is preferably 95% or more, more preferably 98% or more, further preferably 99% or more, and even more preferably 99.5% or more.

[0134] It should be noted that the optical glass of this embodiment preferably consists essentially of the above glass components, but may also contain other components within the range that does not hinder the effects of the present invention. Additionally, in the present invention, the inclusion of unavoidable impurities is not excluded.

[0135] (Other components)

[0136] In addition to the above components, the above optical glass may also contain a small amount of Sb2O3, CeO2, etc. as fining agents. The total amount of fining agents (addition ratio addition amount) is preferably set to 0% or more and less than 1%, more preferably 0% or more and 0.5% or less.

[0137] The addition ratio addition amount refers to the addition amount of the fining agent expressed as a weight percentage when the total content of all glass components except the fining agent is set to 100%.

[0138] Pb, Cd, As, Th, etc. are components that may cause an environmental burden. Therefore, the content of PbO, CdO, ThO2, and As2O3 is preferably 0 - 0.1%, more preferably 0 - 0.05%, further preferably 0 - 0.01%, and particularly preferably substantially free of PbO, CdO, ThO2, and As2O3.

[0139] In addition, the above optical glass can achieve a high transmittance in a wide range of the visible region. To effectively utilize such an advantage, elements with coloring properties are preferably not contained. Examples of elements with coloring properties include Cu, Co, Ni, Fe, Cr, Eu, Nd, Er, V, etc. Each element is preferably less than 100 mass ppm, more preferably 0 to 80 mass ppm, further preferably 0 to 50 mass ppm, and particularly preferably substantially not contained.

[0140] In addition, 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 expressed in mass% are all preferably 0 to 0.1%, more preferably 0 to 0.05%, further preferably 0 to 0.01%, still further preferably 0 to 0.005%, even further preferably 0 to 0.001%, and particularly preferably substantially not contained.

[0141] (Glass properties)

[0142] <Specific gravity d>

[0143] The optical glass of the first embodiment has a high refractive index and high dispersibility, and the specific gravity d is not large. Generally, if the specific gravity d of the glass can be reduced, the weight of the lens can be reduced. 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 excessively reduced, there is a risk of reducing the thermal stability.

[0144] Therefore, in the optical glass of the present embodiment, the lower limit of the specific gravity d is preferably 3.32, and is further more preferably in the order of 3.34, 3.36, 3.38, 3.40. In addition, the upper limit of the specific gravity d is preferably 3.51, and is further more preferably in the order of 3.50, 3.49, 3.48, 3.46, 3.44. The specific gravity d can be controlled by appropriately adjusting the content of each glass component.

[0145] <Transmittance>

[0146] The optical glass of the first embodiment is an optical glass with extremely little coloring. Such an optical glass is suitable as a material for optical elements for imaging such as camera lenses and optical elements for projection such as projectors.

[0147] The coloring degree of the optical glass is generally represented by λ80, λ70, λ5, etc. For a glass specimen 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 reaches 80% is set as λ80, the wavelength at which the external transmittance reaches 70% is set as λ70, and the wavelength at which the external transmittance reaches 5% is set as λ5.

[0148] In the optical glass of 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 this order. λ70 is preferably 440 nm or less, more preferably 430 nm or less, 420 nm or less, and 415 nm or less in this order. λ5 is preferably 365 nm or less, more preferably 364 nm or less, 363 nm or less, and 362 nm or less in this order. λ80, λ70, and λ5 can be controlled by adjusting the amounts of glass components that mainly contribute to high refraction and high dispersion.

[0149] <Workability>

[0150] In the optical glass of the first embodiment, precipitation of crystals during reheating can be suppressed. Even when the optical glass of this embodiment is reheated and pressed within a wide temperature range, precipitation of crystals during reheating can be suppressed, and internal defects such as cracks and striae, or devitrification are less likely to occur.

[0151] The heating temperature during reheating and pressing is, for example, generally the temperature at which the glass softens and deforms. Specifically, as the heating temperature, in the case of a low temperature, it is assumed to be a temperature about 50 °C higher than the glass transition temperature Tg, and in the case of a high temperature, it is assumed to be a temperature about 200 - 300 °C higher than the glass transition temperature Tg.

[0152] Generally, when the heating temperature during reheating and pressing is low, that is, when heating is performed at a temperature about 50 °C higher than the glass transition temperature Tg, phase separation is less likely to occur inside the glass. However, if the heating temperature during reheating and pressing is low, a high pressure needs to be applied during press molding. As a result, during the cooling process of the pressed glass molded product (for example, a lens or a lens blank), the possibility of the glass cracking or the glass splitting increases. Therefore, when the heating temperature during reheating and pressing is low, the production yield is likely to decrease, and the shape of the glass molded product that can be press molded is easily restricted.

[0153] On the other hand, when the heating temperature during reheating and pressing is high, that is, when heating is performed 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, if the heating temperature during reheating and pressing is high, a high pressure does not need to be applied during press molding, and cracks and the like are less likely to occur in the glass molded product. Therefore, a decrease in the production yield can be suppressed, and the shape of the glass molded product is not easily restricted.

[0154] In the optical glass of the first embodiment, the glass composition is adjusted so that crystals are not likely to precipitate under reheating at any assumed heating temperature. In particular, even when reheating is performed at a high temperature, crystals are not likely to precipitate and devitrification is not likely to occur, so problems such as a decrease in the yield rate and shape limitations are not likely to occur.

[0155] When the optical glass of the first 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 precipitated is preferably 2000 pieces / kg or less, and more preferably 1800 pieces / kg or less, 1500 pieces / kg or less, and 1000 pieces / kg or less in that order.

[0156] (Manufacture of optical glass)

[0157] The optical glass of the embodiment of the present invention is prepared by formulating glass raw materials so as to achieve the above-given composition, and the formulated glass raw materials are used to produce according to a well-known glass manufacturing method. For example, a variety of compounds are formulated and thoroughly mixed to form a batch raw material, and the batch raw material is placed in a quartz crucible or a platinum crucible for rough melting. The melt obtained by rough melting is rapidly cooled and pulverized to produce cullet. Further, the cullet is placed in a platinum crucible for heating and remelting to form molten glass. After clarification and homogenization, the molten glass is formed and slowly cooled to obtain the optical glass. The forming and slow cooling of the molten glass can be carried out by well-known methods.

[0158] It should be noted that as long as the desired glass components can be introduced into the glass and the desired content can be achieved, there is no particular limitation on the compounds used when formulating the batch raw material. Examples of such compounds include oxides, carbonates, nitrates, hydroxides, fluorides, etc.

[0159] (Manufacture of optical elements, etc.)

[0160] When an optical element is produced using the optical glass of the embodiment of the present invention, a well-known method can be adopted. For example, in the manufacture of the above optical glass, the molten glass is poured into a mold and formed into a plate shape to produce a glass material formed of the optical glass of the present invention. The obtained glass material is appropriately cut, ground, and polished to produce fragments having a size and shape suitable for press molding. The fragments are heated and softened, and press molding (reheating press) is carried out by a well-known method to produce an optical element blank having a shape approximate to that of the optical element. The optical element blank is annealed and ground and polished by a well-known method to produce the optical element.

[0161] Depending on the purpose of use, an antireflection film, a total reflection film, etc. can be coated on the optical functional surface of the fabricated optical element.

[0162] According to one embodiment of the present invention, an optical element made of the above optical glass can be provided. As the types of optical elements, lenses such as spherical lenses and aspherical lenses, prisms, diffraction gratings, etc. can be exemplified. As the shape of the lens, various shapes such as biconvex lenses, plano-convex lenses, biconcave lenses, plano-concave lenses, convex meniscus lenses, and concave meniscus lenses can be exemplified. The optical element can be manufactured by a method including a process of processing a glass molded body formed of the above optical glass. As the processing, cutting, machining, rough grinding, fine grinding, polishing, etc. can be exemplified. When performing such processing, by using the above glass, breakage can be reduced, and high-quality optical elements can be stably provided.

[0163] Second Embodiment

[0164] The optical glass of the second embodiment contains SiO2, Nb2O5, ZrO2, and an alkali metal oxide.

[0165] The Abbe number νd of this optical glass exceeds 25.20 and is 29.00 or less, and the refractive index nd is 1.80000 or more and 1.85000 or less.

[0166] When heated in the atmosphere at a temperature [Tg + 50 °C] 50 °C higher than the glass transition temperature Tg for 10 minutes and then 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 precipitated is 2000 pieces / kg or less.

[0167] The optical glass of the second embodiment contains SiO2. The lower limit of the content of SiO2 is preferably 20%, and more preferably in the order of 21.00%, 22.00%, 23.30%, 23.40% further. In addition, the upper limit of the content of SiO2 is preferably 30%, and more preferably in the order of 29.00%, 28.00%, 27.00%, 26.00%, 25.00% further.

[0168] SiO2 is a network-forming component of the glass. By containing 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. In addition, 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.

[0169] The optical glass of the second embodiment contains Nb2O5. The lower limit of the content of Nb2O5 is preferably 35%, and more preferably in the order of 36.00%, 37.00%, 37.50%, 38.00%, 39.00%, 40.00%, 41.00%, 42.00%, 43.00%, 44.00%, 45.00%. In addition, the upper limit of the content of Nb2O5 is preferably 55%, and more preferably in the order of 54.00%, 53.00%, 52.00%, 51.00%, 50.00%, 49.00%, 48.00%, 47.00%.

[0170] By containing Nb2O5, a glass with high refractive index and high dispersibility can be obtained. Nb2O5 is also a glass component that improves the thermal stability and chemical durability of the glass. In addition, from the viewpoint of maintaining the thermal stability and chemical durability of the glass well and suppressing the precipitation of crystals during reheating, it is preferable to set the upper limit of the content of Nb2O5 as described above.

[0171] The optical glass of the second embodiment contains ZrO2. That is, in the optical glass of the second embodiment, the content of ZrO2 exceeds 0%. The lower limit of the content of ZrO2 is preferably 1.00%, and more preferably in the order of 2.00%, 3.00%, 4.00%, 6.00%. In addition, the upper limit of the content of ZrO2 is preferably 16.50%, and more preferably in the order of 15.00%, 13.00%, 11.00%, 9.00%, 7.00%.

[0172] By containing ZrO2, a glass with high refractive index and high dispersibility can be obtained. In addition, from the viewpoints of reducing the relative partial dispersion Pg,F, suppressing the generation of defects as an optical element, and further 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.

[0173] The optical glass of the second embodiment contains alkali metal oxides. The alkali metal oxides are preferably one or more oxides selected from Li2O, Na2O, K2O, and Cs2O. The lower limit of the total content of the alkali metal oxides is preferably 13.20%, and more preferably in the order of 13.40%, 13.60%, 13.80%, 14.00%, 14.20%, 14.40%, 14.60%. In addition, the upper limit of the total content of the alkali metal oxides is preferably 15.50%, and more preferably in the order of 15.40%, 15.30%, 15.20%, 15.10%.

[0174] From the viewpoints 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 alkali metal oxides as described above. Further, from the viewpoint of suppressing the generation 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.

[0175] <Abbe number νd>

[0176] In the optical glass of 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 set to 25.40, 25.60, or 25.80. Further, the upper limit of the Abbe number νd can be set to 28.80, 28.60, 28.40, 28.00, 27.50, 27.00, 26.60, 26.40, or 26.20.

[0177] 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.

[0178] <Refractive index nd>

[0179] In the optical glass of 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 set to 1.80500, 1.81000, 1.81500, 1.82000, 1.82500, or 1.82800. Further, the upper limit of the refractive index nd can be set to 1.84800, 1.84500, or 1.84000.

[0180] By setting the refractive index nd within the above range, a glass with a high refractive index 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 high refractive index.

[0181] <Workability>

[0182] When the optical glass of the second embodiment is 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 with a maximum diameter of 1 μm or more precipitated is 2000 pieces / kg or less. This number density is preferably 1800 pieces / kg or less, and more preferably 1500 pieces / kg or less and 1000 pieces / kg or less in that order.

[0183] By setting the above-mentioned number density within the above-mentioned range, precipitation of crystals during reheating can be suppressed. In addition, even when reheating is performed within a wide temperature range, precipitation of crystals during reheating can be suppressed, and internal defects such as cracks and striae, and devitrification can also be suppressed.

[0184] In the optical glass of 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, and more preferably in the order of 0.48, 0.49, 0.50, 0.51. Further, the upper limit of this mass ratio is preferably 0.66, and more preferably in the order of 0.655, 0.650, 0.630, 0.600, 0.590, 0.580, 0.570, 0.560.

[0185] 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 to set the mass ratio [SiO2 / Nb2O5] within the above-mentioned range. It should be noted that if the specific gravity of the glass increases, the mass of the optical element increases. For example, if a lens with a large mass is introduced into an autofocus type imaging lens, there is a risk that the power required for driving the lens increases and the battery consumption becomes severe during autofocus.

[0186] In the optical glass of the second embodiment, the lower limit of the total content [SiO2+Nb2O5] of SiO2 and Nb2O5 is preferably 60%, and more preferably in the order of 61.0%, 62.0%, 62.5%, 62.9%, 63.0%, 64.0%, 65.0%, 66.0%, 67.0%, 68.0%, 69.0%. Further, the upper limit of this total content is preferably 75%, and more preferably in the order of 74.0%, 73.5%, 73.0%, 72.5%, 72.0%, 71.5%.

[0187] From the viewpoints of reducing the liquidus temperature, improving the thermal stability of the glass, and suppressing crystallization of the glass, it is preferable to set the total content [SiO2+Nb2O5] within the above-mentioned range.

[0188] In the optical glass of 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, and more preferably in the order of 0.06, 0.05, 0.04, 0.03, 0.02. Further, the lower limit of this mass ratio is preferably 0.00, and more preferably 0.01.

[0189] From the viewpoints of suppressing an increase in specific gravity d and coloring of the glass, it is preferable to set the mass ratio [B2O3 / SiO2] within the above-mentioned range.

[0190] In the optical glass of the second embodiment, the upper limit of the content of Li2O is preferably 6.20%, and more preferably in the order of 6.10%, 6.00%, 5.90%, and 5.80%. In addition, the lower limit of the content of Li2O is preferably 5.30%, and more preferably in the order of 5.35%, 5.40%, and 5.45%.

[0191] Li2O has the effect 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 to set the content of Li2O within the above range.

[0192] In the optical glass of the second embodiment, the lower limit of the content of K2O is preferably 0.62%, and more preferably in the order of 0.80%, 1.00%, 1.20%, 1.40%, 1.80%, 2.20%, 2.40%, and 2.60%. In addition, the upper limit of the content of K2O is preferably 7.00%, and more preferably in the order of 6.50%, 6.00%, 5.50%, 5.00%, 4.50%, 4.20%, 3.90%.

[0193] From the viewpoint of lowering the liquidus temperature and improving the thermal stability of the glass, it is preferable to set the content of K2O within the above range. On the other hand, when the content of K2O increases, there is a risk of decreasing chemical durability and weather resistance.

[0194] In the optical glass of the second embodiment, the lower limit of the total content [Li2O + Na2O + K2O] of Li2O, Na2O, and K2O is preferably 13.00%, and more preferably in the order of 13.20%, 13.40%, 13.60%, 13.80%, 14.00%, 14.20%, 14.40%, and 14.60%. In addition, the upper limit of the total content is preferably 15.69%, and more preferably in the order of 15.50%, 15.40%, 15.30%, 15.20%, and 15.10%.

[0195] From the viewpoints of improving the meltability and thermal stability of the glass and suppressing the liquidus temperature, it is preferable to set the lower limit of the total content [Li2O + Na2O + K2O] as described above. In addition, from the viewpoints of suppressing the precipitation of crystals during reheating and suppressing the generation of internal defects of the glass such as cracks and striae, it is preferable to set the upper limit of the total content [Li2O + Na2O + K2O] as described above.

[0196] In the optical glass of 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 in the order of 0.345, 0.350, 0.355, 0.360. Further, the upper limit of this mass ratio is preferably 0.41, and more preferably in the order of 0.405, 0.400, 0.395, 0.390, 0.385.

[0197] From the viewpoints of improving 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 make the mass ratio [Li2O / (Li2O + Na2O + K2O)] within the above range.

[0198] In the optical glass of 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 in the order of 0.340, 0.345, 0.350, 0.355. Further, the upper limit of this mass ratio is preferably 0.50, and more preferably in the order of 0.490, 0.480, 0.470, 0.460, 0.450, 0.440, 0.430, 0.425.

[0199] From the viewpoints of improving 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 make the mass ratio [Na2O / (Li2O + Na2O + K2O)] within the above range.

[0200] In the optical glass of the second embodiment, the lower limit of the mass ratio [K2O / (Li2O + Na2O + K2O)] of the content of K2O to the total content of Li2O, Na2O, and K2O is preferably 0.04, and more preferably in the order of 0.05, 0.06, 0.08, 0.12, 0.14, 0.16, 0.18, 0.20. Further, the upper limit of this mass ratio is preferably 0.30, and more preferably in the order of 0.290, 0.280, 0.275, 0.270.

[0201] From the viewpoints of improving 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 make the mass ratio [K2O / (Li2O + Na2O + K2O)] within the above range.

[0202] In the optical glass of the second embodiment, the lower limit of 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 preferably 4.00, and more preferably in the order of 4.10, 4.15, 4.20, 4.25, 4.30, 4.35, 4.40, 4.45, 4.50, 4.55, 4.60. Further, the upper limit of this mass ratio is preferably 5.02, and more preferably in the order of 4.95, 4.90, 4.85, 4.80.

[0203] From the viewpoint of improving 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 make the mass ratio [(SiO2 + Nb2O5) / (Li2O + Na2O + K2O)] within the above range.

[0204] In the optical glass of the second embodiment, the lower limit of the content of TiO2 is preferably 0%, and more preferably in the order of 1%, 2%, 3%, 4%. Further, the upper limit of the content of TiO2 is preferably 11%, and more preferably in the order of 10%, 9%, 7%, 6%, 5%.

[0205] TiO2 is a component that contributes to high dispersion. From the viewpoints of improving the thermal stability of the glass and suppressing the precipitation of crystals during reheating, it is preferable to set the content of TiO2 within the above range. On the other hand, if TiO2 is introduced in excess, there is a risk of causing an increase in the relative partial dispersion Pg,F.

[0206] The content, ratio, and glass properties of the glass components other than the above in the second embodiment can be set to be the same as those in the first embodiment. In addition, regarding the glass properties, the manufacture of the optical glass, and the manufacture of optical elements, etc., other than the above in the second embodiment, they can also be set to be the same as those in the first embodiment.

[0207] Examples

[0208] 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.

[0209] (Example 1)

[0210] Glass samples having the glass compositions shown in Tables 1 to 2 were produced in the following order, and various evaluations were performed.

[0211] [Manufacture of Optical Glass]

[0212] Oxides, hydroxides, carbonates, and nitrates corresponding to the constituent components of the glass were prepared as raw materials, and the above raw materials were weighed and formulated in such a way that the glass composition of the obtained optical glass reached 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 and heated at 1350 °C to 1400 °C for 2 hours to form molten glass, and stirred to achieve homogenization. After clarification, 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 then naturally cooled to room temperature in the furnace, thereby obtaining a glass sample.

[0213] [Confirmation of glass composition]

[0214] For the obtained glass sample, the contents of each glass component were measured by inductively coupled plasma atomic emission spectrometry (ICP-AES), and it was confirmed that they were consistent with each composition shown in Tables 1 to 2.

[0215] [Measurement of optical properties]

[0216] After 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, an annealed sample was obtained. The refractive indices nd, ng, nF, and nC, Abbe number νd, specific gravity d, glass transition temperature Tg, λ80, λ70, and λ5 of the obtained annealed sample were measured. The results are shown in Table 3.

[0217] (i) Refractive indices nd, ng, nF, nC, and Abbe number νd

[0218] For the above annealed sample, the refractive indices nd, ng, nF, and 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.

[0219] νd = (nd - 1) / (nF - nC)

[0220] (ii) Specific gravity d

[0221] The specific gravity d was measured by the Archimedes method.

[0222] (iii) Glass transition temperature Tg

[0223] The obtained optical glass sample was thoroughly pulverized with a mortar and used as a specimen, and the glass transition temperature Tg was measured using a differential scanning calorimeter (DSC8270) manufactured by Rigaku Corporation with a heating rate of 10 °C / min.

[0224] (iv) λ80, λ70, λ5

[0225] The above annealed samples were processed to have a thickness of 10 mm and parallel and optically polished planes, and the spectral transmittance in the wavelength range of 200 nm to 700 nm was measured. The intensity of the light perpendicularly incident on one optically polished plane was defined as intensity A, and the intensity of the light exiting from the other plane was defined as intensity B, and the spectral transmittance B / A was calculated. The wavelength at which the spectral transmittance reached 80% was defined as λ80, the wavelength at which the spectral transmittance reached 70% was defined as λ70, and the wavelength at which the spectral transmittance reached 5% was defined as λ5. It should be noted that the spectral transmittance also includes the reflection loss of the light on the surface of the specimen.

[0226] [Table 1]

[0227]

[0228] [Table 2]

[0229]

[0230] [Table 3]

[0231]

[0232] (Example 2)

[0233] [Workability]

[0234] The glass sample obtained in Example 1 was cut and machined, the entire surface was polished with a #800 file, and all edges were chamfered. A test piece of 10 mm × 10 mm × 10 mm was obtained. The 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. It should be noted that for the test piece, heating was carried out on an alumina plate on which a small amount of anti-sticking BN (boron nitride) powder was placed. For the test piece heated in the second test furnace, in order to prevent cracking, it was wrapped with heat-resistant and refractory ceramic fibers such as kaolin wool and naturally cooled to room temperature. The test piece was optically polished, and the inside was observed through an optical microscope (40 - 200 times). The number of crystals with a maximum diameter of 1 μm or more inside the test piece was counted and converted to the number per kg on average. The results are shown in Table 3. It should be noted that for the test pieces heated in the second test furnace, no cloudiness occurred inside, no ripple streaks were present, and no cracks or fractures occurred.

[0235] (Example 3)

[0236] Using each of the optical glasses produced in Example 1, lens blanks were produced by a known method, and the lens blanks were processed by known methods such as grinding to produce various lenses.

[0237] The optical lenses produced were various lenses such as biconvex lenses, biconcave lenses, plano-convex lenses, plano-concave lenses, concave meniscus lenses, and convex meniscus lenses.

[0238] For various lenses, by combining them with lenses made of other types of optical glass, chromatic aberration can be corrected well.

[0239] In addition, since the glass has a low specific gravity, each lens is lighter in weight than a lens having the same optical characteristics and size, and can be suitably used for various imaging devices. In particular, for reasons such as energy conservation, it is suitably used for the purpose of an autofocus imaging device. Similarly, prisms were produced using various optical glasses produced in Example 1.

[0240] It should be understood that the embodiments disclosed herein are exemplary in all respects and do not constitute a limitation. The scope of the present invention is defined by the claims, rather than the above description, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0241] For example, by making composition adjustments to the glass compositions exemplified above as described in the specification, an optical glass according to an embodiment of the present invention can be produced.

[0242] In addition, without doubt, any combination of two or more of the features exemplified in the specification or described as the preferred range can be made.

Claims

1. An optical glass having an Abbe number νd of more than 25.20 and not more than 29.00 and a refractive index nd of not less than 1.80000 and not more than 1.85000, Expressed in mass %, The content of SiO2 is 20-30%, The content of Nb2O5 is 35-55%, The mass ratio of SiO2 content to Nb2O5 content [SiO2 / Nb2O5] is 0.47 to 0.66, The total content of SiO2 and Nb2O5 [SiO2+Nb2O5] is 60-75%, The mass ratio of the content of B2O3 to the content of SiO2 [B2O3 / SiO2] is 0.00 to 0.07, The content of Li2O is less than 6.20%, The content of K2O is above 0.62%, The total content of Li2O, Na2O and K2O [Li2O+Na2O+K2O] is 13.00-15.69%, 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 0-11%, The content of ZrO2 exceeds 0%. 2 . The optical glass according to claim 1 , wherein the specific gravity d is 3.32 or more and 3.51 or less.

3. An optical glass comprising SiO2, Nb2O5, ZrO2 and an alkali metal oxide, The optical glass has an Abbe number νd of more than 25.20 and not more than 29.00, a refractive index nd of not less than 1.80000 and not more than 1.85000, When the optical glass is heated in the atmosphere at a temperature 50°C higher than the glass transition temperature Tg [Tg+50°C] for 10 minutes, and then heated at a temperature 240°C higher than the glass transition temperature Tg [Tg+240°C] for 10 minutes, the number density of crystals with a maximum diameter of 1 μm or more precipitated is less than 2000 pieces / kg. 4 . An optical element, comprising the optical glass according to claim 1 .

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