Optical Glass and Optical Elements

Abstract

[Problem] To provide an optical glass having a high refractive index and a relatively low specific gravity, and an optical element. [Solution] An optical glass which is a SiO2-TiO2-Nb2O5-based glass, and in which the content of SiO2 is 10% by mass or greater, the total content of Na2O, K2O, and Cs2O (Na2O+K2O+Cs2O)is 11.0% by mass or less, and the specific gravity and the refractive index nd thereof satisfy formula (1). (1): nd ≥ 0.2 × specific gravity + 1.18

Description

[Technical Field]

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

[0002] In recent years, with the advancement of AR (Augmented Reality) technology, goggle-type or eyeglass-type display devices have been developed as AR devices. For example, goggle-type display devices require lenses with a high refractive index and a low specific gravity, and there is an increasing demand for glass that can be used for such lenses.

[0003] High refractive index optical glasses are disclosed in Patent Documents 1 to 4. However, all of them have a problem in that their specific gravity is too high relative to their refractive index to be used as lenses for AR devices.

[0004] Therefore, there is a demand for optical glasses that have a reduced specific gravity while maintaining a high refractive index. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5766002 [Patent Document 2] Patent No. 5734587 [Patent Document 3] Japanese Patent Application Laid-Open No. 2016-88759 [Patent Document 4] Japanese Patent Application Publication No. 2019-34874 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention has been made in view of the above circumstances, and has as its object to provide an optical glass and an optical element that have a high refractive index and a relatively low specific gravity. [Means for solving the problem]

[0007] The gist of the present invention is as follows. (1) SiO2-TiO2-Nb2O5-based glass, The SiO2 content is 10 mass% or more, The total content of Na2O, K2O, and Cs2O [Na2O + K2O + Cs2O] is 11.0% by mass or less, An optical glass having a specific gravity and a refractive index nd that satisfy the following formula (1): nd≧0.2×specific gravity+1.18…(1)

[0008] (2) The SiO2 content is 1 to 50 mass%; The content of TiO2 is 1 to 50 mass%; The BaO content is 0 to 16.38 mass%; The content of Nb2O5 is 1 to 50 mass%; the total content of LiO, NaO, KO, and CsO [LiO + NaO + KO + CsO] is 0.1 to 20 mass%; the total content of La2O3, Gd2O3, and Y2O3 [La2O3 + Gd2O3 + Y2O3] is 0 to 10 mass%; The total content of TiO2 and Nb2O5 [TiO2 + Nb2O5] is 45 to 65 mass%; The mass ratio of the TiO2 content to the total content of TiO2 and Nb2O5 [TiO2 / (TiO2+Nb2O5)] is 0.3 or more, the mass ratio of the content of LiO to the total content of LiO, NaO, KO, and CsO [LiO / (LiO+NaO+KO+CsO)] is 0.1 to 1; the Abbe number νd is 25 or less, Optical glass having a refractive index nd of 1.86 or more.

[0009] (3) The SiO2 content is 1 to 50 mass%; The content of TiO2 is 1 to 50 mass%; The content of Nb2O5 is 1 to 50 mass%; The content of Na2O is 0 to 8 mass%; The total content of TiO2 and Nb2O5 [TiO2 + Nb2O5] is 40 to 80 mass%; The mass ratio of the TiO2 content to the total content of TiO2 and Nb2O5 [TiO2 / (TiO2+Nb2O5)] is 0.3 or more, The refractive index nd is 1.88 or more, Optical glass with a ratio of refractive index nd to specific gravity [refractive index nd / specific gravity] of 0.50 or more.

[0010] (4) The optical glass according to (3), wherein the BaO content is less than 16.0 mass %.

[0011] (5) The mass ratio of the LiO content to the total content of glass components other than SiO, B, P, and GeO [LiO / {100-(SiO+B+P+GeO)}] is 0.02 or more; the mass ratio of the TiO2 content to the total content of TiO2, Nb2O5, WO3, ZrO2, SrO, BaO, ZnO, La2O3, Gd2O3, Y2O3, Ta2O5, and Bi2O3 [TiO2 / (TiO2+Nb2O5+WO3+ZrO2+SrO+BaO+ZnO+La2O3+Gd2O3+Y2O3+Ta2O5+Bi2O3)] is 0.40 or more; Optical glass having a refractive index nd of 1.86 or more.

[0012] (6) An optical element made of the optical glass according to any one of (1) to (5) above.

[0013] (7) A light guide plate made of the optical glass according to any one of (1) to (5) above.

[0014] (8) The light guide plate according to (7), which has a diffraction grating on its surface.

[0015] (9) An image display device comprising an image display element and a light guide plate for guiding light emitted from the image display element, wherein the light guide plate is made of the optical glass according to any one of (1) to (5). [Effects of the Invention]

[0016] According to the present invention, an optical glass and an optical element having a high refractive index and a relatively low specific gravity can be provided. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a graph in which an example of the optical glass according to the first embodiment and the optical glasses disclosed in the examples of Patent Documents 1 to 4 are plotted on a graph with the refractive index nd on the vertical axis and the specific gravity on the horizontal axis. [Figure 2] FIG. 2 is a diagram showing the configuration of a head-mounted display using a light guide plate according to one embodiment of the present invention. [Figure 3] FIG. 3 is a side view schematically showing the configuration of a head-mounted display using a light guide plate according to one embodiment of the present invention. [Figure 4] FIG. 4 is a graph in which an example of the optical glass according to the fourth embodiment and the optical glasses disclosed in the examples of Patent Documents 1 to 4 are plotted with the mass ratio [LiO / {100-(SiO+B+P+GeO)}] on the vertical axis and the mass ratio [TiO / (TiO+Nb+WO+WO+ZrO+SrO+BaO+ZnO+La+Gd+Y+Ta+Bi)] on the horizontal axis. [Figure 5] FIG. 5 is a graph in which an example of the optical glass according to the fourth embodiment and the optical glasses disclosed in the examples of Patent Documents 1 to 4 are plotted, with the ratio of the refractive index nd to the specific gravity [refractive index nd / specific gravity] on the vertical axis and the mass ratio [TiO2 / (TiO2+Nb2O5+WO3+ZrO2+SrO+BaO+ZnO+La2O3+Gd2O3+Y2O3+Ta2O5+Bi2O3)] on the horizontal axis. [Figure 6] 1 is a photograph of a glass sample obtained in Comparative Example 1. [Figure 7] 1 is a photograph of a glass sample obtained in Comparative Example 2. [Figure 8] 1 is a photograph of a glass sample obtained in Comparative Example 4. [Figure 9]1 is a photograph of a glass sample obtained in Comparative Example 5. [Figure 10] 1 is a photograph of a glass sample obtained in Comparative Example 6. [Figure 11] 1 is a photograph of a glass sample obtained in Comparative Example 7. DETAILED DESCRIPTION OF THE INVENTION

[0018] In the present invention and this specification, glass compositions are expressed on an oxide basis unless otherwise specified. Here, "glass composition on an oxide basis" refers to a glass composition obtained by converting the glass raw materials into oxides that are present in the glass after they are all decomposed during melting. The total content of all glass components expressed on an oxide basis (excluding Sb (Sb2O3) and Ce (CeO2) added as fining agents) is 100 mass%. Following the convention, each glass component is expressed as SiO2, TiO2, etc. The contents and total contents of glass components are expressed on a mass basis unless otherwise specified, and "%" means "mass%."

[0019] The content of glass components can be quantified by known methods, such as inductively coupled plasma atomic emission spectroscopy (ICP-AES), inductively coupled plasma mass spectroscopy (ICP-MS), etc. In this specification and the present invention, a content of 0% of a component means that the component is substantially not contained, and it is acceptable for the component to be present at an unavoidable impurity level.

[0020] The present invention will be described below in terms of a first embodiment, a second embodiment, a third embodiment, and a fourth embodiment.

[0021] First embodiment The optical glass according to the first embodiment is It is a SiO2-TiO2-Nb2O5 type glass, The SiO2 content is 10 mass% or more, The total content of Na2O, K2O, and Cs2O [Na2O + K2O + Cs2O] is 11.0% by mass or less, The specific gravity and the refractive index nd satisfy the following formula (1). nd≧0.2×specific gravity+1.18…(1)

[0022] The optical glass according to the first embodiment is a SiO2-TiO2-Nb2O5-based glass. That is, the glass components include SiO2, TiO2, and Nb2O5. By using SiO2-TiO2-Nb2O5-based glass, it is possible to suppress a decrease in strength and chemical durability.

[0023] In the optical glass according to the first embodiment, the SiO2 content is 10% or more. The lower limit of the SiO2 content is preferably 12%, and more preferably 15%, 18%, and 20% in that order. The upper limit of the SiO2 content is preferably 40%, and more preferably 38%, 35%, 33%, and 30% in that order.

[0024] SiO2 is a glass network-forming component. By setting the SiO2 content within the above range, the thermal stability, chemical durability, and weather resistance of the glass can be improved, and the viscosity of the glass melt can be increased. On the other hand, if the SiO2 content is too high, the refractive index of the glass decreases, and the desired optical properties may not be obtained.

[0025] In the optical glass according to the first embodiment, the total content of Na2O, K2O, and Cs2O [Na2O + K2O + Cs2O] is 11.0% or less. The upper limit of this total content is preferably 10.0%, and more preferably 9.0%, 8.0%, 7.0%, and 6.0%, in that order. The lower limit of this total content is preferably 0%.

[0026] By setting the total content [Na2O+K2O+Cs2O] within the above range, it is possible to maintain a high refractive index while maintaining the thermal stability of the glass.

[0027] In the optical glass according to the first embodiment, the refractive index nd and specific gravity satisfy the following formula (1): Preferably, the following formula (2) is satisfied, and more preferably the following formula (3): When the refractive index nd and specific gravity satisfy the following formula, an optical glass having a high refractive index and a relatively low specific gravity can be obtained. nd≧0.2×specific gravity+1.18…(1) nd≧0.2×specific gravity+1.19…(2) nd≧0.2×specific gravity+1.20…(3)

[0028] Non-limiting examples of the contents, ratios, and properties of glass components other than those described above in the optical glass according to the first embodiment are given below.

[0029] In the optical glass according to the first embodiment, the upper limit of the P2O5 content is preferably 10%, and more preferably 8%, 5%, and 3%, in that order. The P2O5 content may be 0%.

[0030] In order to obtain an optical glass having a high refractive index and a reduced specific gravity, the content of P2O5 is preferably within the above range.

[0031] In the optical glass according to the first embodiment, the upper limit of the B2O3 content is preferably 10%, and more preferably 8%, 5%, and 3% in that order. The lower limit of the B2O3 content is preferably 0%, and more preferably 0.5%, 0.8%, and 1.0% in that order.

[0032] B2O3 is a glass network-forming component. B2O3 has the function of improving the thermal stability of the glass, but if the B2O3 content is too high, the refractive index may decrease. Therefore, it is preferable that the B2O3 content be within the above range.

[0033] In the optical glass according to the first embodiment, the upper limit of the Al2O3 content is preferably 10%, and more preferably 8%, 5%, and 3%, in that order. The Al2O3 content may be 0%.

[0034] Although Al2O3 has the function of increasing chemical durability, if the Al2O3 content is too high, the meltability of the glass may deteriorate, so it is preferable that the Al2O3 content be set within the above range.

[0035] In the optical glass according to the first embodiment, the lower limit of the total content of SiO2 and Al2O3 [SiO2 + Al2O3] is preferably 10%, and more preferably 13%, 15%, 18%, and 20% in that order. The upper limit of this total content is preferably 50%, and more preferably 45%, 40%, 35%, and 30% in that order.

[0036] In order to improve the thermal stability of the glass, the total content [SiO2 + Al2O3] is preferably within the above range.

[0037] In the optical glass according to the first embodiment, the lower limit of the mass ratio of the B2O3 content to the total content of SiO2 and Al2O3 [B2O3 / (SiO2+Al2O3)] is preferably 0.01, and more preferably 0.02, 0.03, and 0.04 in that order. The upper limit of this mass ratio is preferably 0.20, and more preferably 0.18, 0.15, 0.13, and 0.10 in that order.

[0038] From the viewpoint of improving chemical durability and thermal stability, it is preferable that the mass ratio [B2O3 / (SiO2+Al2O3)] is within the above range.

[0039] In the optical glass according to the first embodiment, the lower limit of the total content of B2O3 and P2O5 [B2O3 + P2O5] is preferably 0.5%, more preferably 0.8% and 1.0%, in that order, and the upper limit of this total content is preferably 10%, more preferably 8%, 5%, and 3%, in that order.

[0040] From the viewpoint of improving chemical durability and thermal stability, the total content [B2O3+P2O5] is preferably within the above range.

[0041] In the optical glass according to the first embodiment, the lower limit of the total content of B2O3 and SiO2 [B2O3 + SiO2] is preferably 10%, more preferably 15%, 18%, and 20%, in that order, and the upper limit of this total content is preferably 50%, more preferably 45%, 40%, and 35%, in that order.

[0042] In order to obtain an optical glass with a high refractive index, the total content [B2O3+SiO2] is preferably within the above range.

[0043] In the optical glass according to the first embodiment, the lower limit of the ZrO2 content is preferably 0%, and more preferably 0.1%, 0.5%, and 1.0%, in that order. The upper limit of the ZrO2 content is preferably 10%, and more preferably 8%, 5%, and 3%, in that order. The ZrO2 content may even be 0%.

[0044] ZrO2 is a component that contributes to a high refractive index. On the other hand, if the ZrO2 content is too high, the thermal stability may decrease and the specific gravity may increase. Therefore, it is preferable that the ZrO2 content be within the above range.

[0045] In the optical glass according to the first embodiment, the lower limit of the TiO2 content is preferably 10%, and more preferably 13%, 15%, 18%, and 20% in that order. The upper limit of the TiO2 content is preferably 50%, and more preferably 45%, 40%, and 35% in that order.

[0046] TiO2 is a component that contributes to a high refractive index and improves glass stability. It can also increase the refractive index without increasing the specific gravity. On the other hand, if the TiO2 content is too high, thermal stability may decrease. Therefore, it is preferable that the TiO2 content be within the above range.

[0047] In the optical glass according to the first embodiment, the lower limit of the Nb2O5 content is preferably 10%, and more preferably 13%, then 15%. The upper limit of the Nb2O5 content is preferably 50%, and more preferably 45%, then 40%, then 35%.

[0048] Nb2O5 is a component that contributes to increasing the refractive index and improves glass stability. However, if the Nb2O5 content is too high, the specific gravity may increase and the thermal stability may decrease. Therefore, it is preferable that the Nb2O5 content be within the above range.

[0049] In the optical glass according to the first embodiment, the lower limit of the total content of TiO2 and Nb2O5 [TiO2 + Nb2O5] is preferably 20%, more preferably 25%, 30%, and 35%, in that order. The upper limit of this total content is preferably 70%, more preferably 65%, 60%, and 55%, in that order.

[0050] TiO2 and Nb2O5 are components that contribute to increasing the refractive index, and therefore, in order to obtain glass with the desired optical properties, it is preferable that the total content of TiO2 and Nb2O5 be within the above range.

[0051] In the optical glass according to the first embodiment, the lower limit of the mass ratio of the TiO2 content to the total content of TiO2 and Nb2O5 [TiO2 / (TiO2+Nb2O5)] is preferably 0.20, and more preferably 0.25, 0.30, and 0.35 in that order. The upper limit of this mass ratio is preferably 0.80, and more preferably 0.75, 0.70, and 0.65 in that order.

[0052] In order to obtain an optical glass with a high refractive index and a reduced specific gravity, it is preferable that the mass ratio [TiO2 / (TiO2+Nb2O5)] is within the above range.

[0053] In the optical glass according to the first embodiment, the upper limit of the WO3 content is preferably 10%, and more preferably 8%, 5%, and 3%, in that order. The WO3 content may be 0%.

[0054] WO3 is a component that contributes to a high refractive index. On the other hand, if the WO3 content is too high, the thermal stability may decrease, the specific gravity may increase, and the coloring of the glass may increase, resulting in a decrease in transmittance. Therefore, it is preferable that the WO3 content be within the above range.

[0055] In the optical glass according to the first embodiment, the upper limit of the Bi2O3 content is preferably 10%, and more preferably 8%, 5%, and 3%, in that order. The lower limit of the Bi2O3 content is preferably 0%. The Bi2O3 content may be 0%.

[0056] When an appropriate amount of Bi2O3 is included, it improves the thermal stability of the glass. It is also a component that contributes to a high refractive index. On the other hand, if the Bi2O3 content is too high, the specific gravity increases. Furthermore, the coloring of the glass increases. Therefore, it is preferable that the Bi2O3 content be within the above range.

[0057] In the optical glass according to the first embodiment, the upper limit of the total content of TiO2, Nb2O5, WO3 and Bi2O3 [TiO2 + Nb2O5 + WO3 + Bi2O3] is preferably 80%, more preferably 70% and more preferably 60%, and the lower limit of this total content is preferably 20%, more preferably 25%, 30%, and more preferably 35%.

[0058] TiO2, Nb2O5, WO3 and Bi2O3 are all components that contribute to increasing the refractive index, so it is preferable that the total content [TiO2 + Nb2O5 + WO3 + Bi2O3] is within the above range.

[0059] In the optical glass according to the first embodiment, the lower limit of the LiO content is preferably 0.0%, and more preferably 0.1%, 0.3%, 0.5%, 0.8%, 1.0%, 1.3%, and 1.5%, in that order. The upper limit of the LiO content is preferably 10%, and more preferably 9%, 8%, 7%, 6%, and 5%, in that order.

[0060] Li2O is a component that contributes to lowering the specific gravity and, among alkali metals, is a component that particularly contributes to increasing the refractive index. On the other hand, if the Li2O content is too high, the thermal stability may decrease. Therefore, it is preferable that the Li2O content be within the above range.

[0061] In the optical glass according to the first embodiment, the upper limit of the Na2O content is preferably 10%, and more preferably 9%, 8%, and 7%, in that order. The lower limit of the Na2O content is preferably 0%, and more preferably 0.5%, 1.0%, 1.5%, and 2.0%, in that order.

[0062] In the optical glass according to the first embodiment, the upper limit of the K2O content is preferably 10%, and more preferably 8%, then 5%. The lower limit of the K2O content is preferably 0%, and more preferably 0.5%, then 1.0%, then 1.5%, then 2.0%. The K2O content may even be 0%.

[0063] Na2O and K2O have the function of improving the meltability of glass. On the other hand, if their contents are too high, the refractive index may decrease and the thermal stability may also decrease. Therefore, it is preferable that the contents of Na2O and K2O are each within the above ranges.

[0064] In the optical glass according to the first embodiment, the upper limit of the Cs2O content is preferably 5%, and more preferably 3% and 1% in that order. The lower limit of the Cs2O content is preferably 0%.

[0065] Cs2O has the function of improving the thermal stability of the glass, but if its content increases, the chemical durability and weather resistance decrease, so the Cs2O content is preferably set within the above range.

[0066] In the optical glass according to the first embodiment, the lower limit of the mass ratio of the LiO content to the total content of LiO, NaO, and KO [LiO / (LiO+NaO+KO)] is preferably 0.00, and more preferably 0.10, 0.15, 0.20, and 0.25 in that order. The upper limit of this mass ratio is preferably 1.00, and more preferably 0.80, 0.75, 0.70, and 0.65 in that order.

[0067] In order to obtain an optical glass having a high refractive index and a reduced specific gravity, the mass ratio [Li2O / (Li2O+Na2O+K2O)] is preferably within the above range.

[0068] In the optical glass according to the first embodiment, the lower limit of the mass ratio of the LiO content to the total content of LiO, NaO, KO, and CsO [LiO / (LiO+NaO+KO+CsO)] is preferably 0.10, and more preferably 0.15, 0.20, and 0.25 in that order. The upper limit of this mass ratio is preferably 1.00, and more preferably 0.80, 0.75, 0.70, and 0.65 in that order.

[0069] In order to obtain an optical glass having a high refractive index and a reduced specific gravity, the mass ratio [Li2O / (Li2O+Na2O+K2O+Cs2O)] is preferably within the above range.

[0070] In the optical glass according to the first embodiment, the lower limit of the total content of Li2O, Na2O, K2O, and Cs2O [Li2O + Na2O + K2O + Cs2O] is preferably 1.5%, and more preferably 2%, 4%, and 6% in that order. The upper limit of this total content is preferably 15%, and more preferably 13% and 10% in that order.

[0071] In order to obtain an optical glass having excellent melting properties, the total content [Li2O+Na2O+K2O+Cs2O] is preferably within the above range.

[0072] In the optical glass according to the first embodiment, the upper limit of the MgO content is preferably 20%, and more preferably 15%, 10%, and 5%, in that order. The lower limit of the MgO content is preferably 0%.

[0073] In the optical glass according to the first embodiment, the lower limit of the CaO content is preferably 1%, and more preferably 3%, 5%, and 8%, in that order. The upper limit of the CaO content is preferably 20%, and more preferably 18%, 15%, and 13%, in that order.

[0074] MgO and CaO have the function of improving the meltability of glass. On the other hand, if their contents are too high, thermal stability may decrease. Therefore, it is preferable that the contents of MgO and CaO are each within the above ranges.

[0075] In the optical glass according to the first embodiment, the upper limit of the SrO content is preferably 10%, and more preferably 8%, 5%, and 3%, in that order. The lower limit of the SrO content is preferably 0%.

[0076] SrO improves the meltability of glass and increases the refractive index. However, if the SrO content is too high, the thermal stability may decrease and the specific gravity may increase. Therefore, it is preferable that the SrO content be within the above range.

[0077] In the optical glass according to the first embodiment, the upper limit of the BaO content is preferably 20%, and more preferably 17%, 15%, 13%, and 10%, in that order. The lower limit of the BaO content is preferably 0%.

[0078] BaO has the function of improving the meltability of the glass and increasing the refractive index. On the other hand, if the BaO content is too high, the thermal stability may decrease and the specific gravity may increase. Therefore, it is preferable that the BaO content be within the above range.

[0079] In the optical glass according to the first embodiment, the upper limit of the ZnO content is preferably 10%, and more preferably 8%, 5%, and 3%, in that order. The lower limit of the ZnO content is preferably 0%.

[0080] ZnO is a glass component that improves the thermal stability of glass. However, if the ZnO content is too high, the specific gravity increases. Therefore, 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.

[0081] In the optical glass according to the first embodiment, the upper limit of the total content of MgO, CaO, SrO, BaO, and ZnO [MgO + CaO + SrO + BaO + ZnO] is preferably 40%, more preferably 35%, 30%, and 25%, in that order. The lower limit of this total content is preferably 3%, more preferably 5%, 8%, and 10%, in that order. From the viewpoints of suppressing an increase in specific gravity and maintaining thermal stability without impeding high dispersion, it is preferable that the total content be within the above range.

[0082] In the optical glass according to the first embodiment, the upper limit of the Ta2O5 content is preferably 10%, and more preferably 8%, 5%, and 3%, in that order. The lower limit of the Ta2O5 content is preferably 0%.

[0083] Ta2O5 is a component that contributes to a high refractive index. It is also a glass component that improves the thermal stability of the glass and reduces Pg and F. On the other hand, if the Ta2O5 content is high, the thermal stability of the glass decreases, and when the glass is melted, the glass raw material is more likely to remain unmelted. In addition, the specific gravity increases. Therefore, it is preferable that the Ta2O5 content be within the above range.

[0084] In the optical glass according to the first embodiment, the upper limit of the La2O3 content is preferably 10%, and more preferably 8%, 5%, and 3%, in that order. The lower limit of the La2O3 content is preferably 0%.

[0085] La2O3 is a component that contributes to a high refractive index. If the content of La2O3 is too high, the specific gravity increases and the thermal stability of the glass decreases. Therefore, from the viewpoint of suppressing the increase in specific gravity and the decrease in the thermal stability of the glass, it is preferable that the content of La2O3 be within the above range.

[0086] In the optical glass according to the first embodiment, the upper limit of the Y2O3 content is preferably 10%, and more preferably 8%, 5%, and 3%, in that order. The lower limit of the Y2O3 content is preferably 0%.

[0087] Y2O3 is a component that contributes to a high refractive index. On the other hand, if the Y2O3 content is too high, the thermal stability of the glass decreases, making the glass more susceptible to devitrification during production. Therefore, from the viewpoint of preventing a decrease in the thermal stability of the glass, it is preferable that the Y2O3 content be within the above range.

[0088] In the optical glass according to the first embodiment, the Sc2O3 content is preferably 2% or less, and the lower limit of the Sc2O3 content is preferably 0%.

[0089] In the optical glass according to the first embodiment, the content of HfO2 is preferably 2% or less, and the lower limit of the content of HfO2 is preferably 0%.

[0090] Sc2O3 and HfO2 have the function of increasing the dispersibility of the glass, but are expensive components, so it is preferable that the contents of Sc2O3 and HfO2 are each within the above ranges.

[0091] In the optical glass according to the first embodiment, the content of Lu2O3 is preferably 2% or less, and the lower limit of the content of Lu2O3 is preferably 0%.

[0092] Lu2O3 has the function of increasing the dispersibility of the glass, but because it has a large molecular weight, it is also a glass component that increases the specific gravity of the glass, so the content of Lu2O3 is preferably within the above range.

[0093] In the optical glass according to the first embodiment, the GeO2 content is preferably 2% or less, and the lower limit of the GeO2 content is preferably 0%.

[0094] GeO2 has the function of increasing the high dispersibility of the glass, but is an extremely expensive component among commonly used glass components, so from the perspective of reducing the manufacturing cost of the glass, it is preferable that the GeO2 content be in the above range.

[0095] In the optical glass according to the first embodiment, the upper limit of the Gd2O3 content is preferably 3.0%, more preferably 2.0%, and the lower limit of the Gd2O3 content is preferably 0%.

[0096] Gd2O3 is a component that contributes to a high refractive index. However, if the Gd2O3 content is too high, the thermal stability of the glass decreases. Furthermore, if the Gd2O3 content is too high, the specific gravity of the glass increases, which is undesirable. Therefore, from the viewpoint of suppressing an increase in specific gravity while maintaining good thermal stability of the glass, it is preferable that the Gd2O3 content be within the above range.

[0097] In the optical glass according to the first embodiment, the Yb2O3 content is preferably 2% or less, and the lower limit of the Yb2O3 content is preferably 0%.

[0098] Yb2O3 has a larger molecular weight than La2O3, Gd2O3, and Y2O3, and therefore increases the specific gravity of the glass. This increases the specific gravity of the glass, which in turn increases the mass of the optical element. Therefore, it is desirable to reduce the Yb2O3 content to prevent the increase in the specific gravity of the glass.

[0099] Furthermore, if the Yb2O3 content is too high, the thermal stability of the glass decreases. From the viewpoint of preventing a decrease in the thermal stability of the glass and suppressing an increase in specific gravity, it is preferable that the Yb2O3 content be within the above range.

[0100] In the optical glass according to the first embodiment, the upper limit of the total content of La2O3, Gd2O3, and Y2O3 [La2O3 + Gd2O3 + Y2O3] is preferably 10%, and more preferably 8%, 5%, and 3%, in that order. The lower limit of this total content is 0%. This total content may even be 0%.

[0101] From the viewpoint of suppressing an increase in specific gravity and maintaining good thermal stability, the total content [La2O3+Gd2O3+Y2O3] is preferably within the above range.

[0102] In the optical glass according to the first embodiment, the mass ratio [LiO / {100-(SiO+B+P+GeO)}] of the LiO content to the total content of glass components other than SiO, B, O, P, and GeO is preferably 0.00, and more preferably 0.02, 0.03, 0.04, 0.05, and 0.06 in this order. The upper limit of this mass ratio is preferably 0.20, and more preferably 0.15, 0.13, and 0.10 in this order.

[0103] The total content of all glass components is 100% by mass. Therefore, the total content of glass components other than SiO2, B2O3, P2O5, and GeO2 is expressed as [100 - (SiO2 + B2O3 + P2O5 + GeO2)]. From the perspective of obtaining an optical glass with a high refractive index and a low specific gravity, it is preferable that the mass ratio [Li2O / {100 - (SiO2 + B2O3 + P2O5 + GeO2)}] be within the above range.

[0104] In the optical glass according to the first embodiment, the mass ratio of the TiO content to the total content of TiO, NbO, WO, ZrO, SrO, BaO, ZnO, LaO, GdO, YO, TaO, and BiO [TiO / (TiO + NbO + WO + ZrO + SrO + BaO + ZnO + LaO + GdO + YO + TaO + BiO)] is preferably 0.40, and more preferably 0.42, 0.44, 0.46, 0.48, and 0.50, in that order. The upper limit of this mass ratio is preferably 0.80, and more preferably 0.75, 0.70, and 0.65, in that order.

[0105] From the viewpoint of increasing the refractive index while suppressing an increase in specific gravity, it is preferable that the mass ratio [TiO2 / (TiO2+Nb2O5+WO3+ZrO2+SrO+BaO+ZnO+La2O3+Gd2O3+Y2O3+Ta2O5+Bi2O3)] be in the above range.

[0106] The optical glass according to the first embodiment is preferably composed primarily of the above-mentioned glass components, namely, Li2O and TiO2 as essential components and SiO2, P2O5, B2O3, Al2O3, ZrO2, Nb2O5, WO3, Bi2O3, Na2O, K2O, Cs2O, MgO, CaO, SrO, BaO, ZnO, Ta2O5, La2O3, Y2O3, Sc2O3, HfO2, Lu2O3, GeO2, Gd2O3, and Yb2O3 as optional components, and the total content of the above-mentioned glass components is preferably 95% or more, more preferably 98% or more, even more preferably 99% or more, and even more preferably 99.5% or more.

[0107] The optical glass according to the first embodiment is preferably composed essentially of the above glass components, but may contain other components as long as they do not impair the effects of the present invention. Furthermore, the present invention does not exclude the inclusion of unavoidable impurities.

[0108] (Other ingredients) Pb, As, Cd, Tl, Be, and Se are all toxic. Therefore, it is particularly preferable that the optical glass according to the first embodiment does not contain these elements as glass components. The content of each of the above elements, calculated as an oxide, is preferably less than 0.5%, and more preferably less than 0.1%, less than 0.05%, and less than 0.01%, in that order.

[0109] U, Th, and Ra are all radioactive elements. Therefore, it is particularly preferable that the optical glass according to the first embodiment does not contain these elements as glass components. The content of each of the above elements, calculated as an oxide, is preferably less than 0.5%, and more preferably less than 0.1%, less than 0.05%, and less than 0.01%, in that order.

[0110] V, Cr, Mn, Fe, Co, Ni, Cu, Pr, Nd, Pm, Sm, Eu, Tb, Dy, Ho, Er, and Tm increase the coloration of the glass and can be sources of fluorescence. Therefore, it is particularly preferable that the optical glass according to the first embodiment does not contain these elements as glass components. The content of each of the above elements, calculated as oxide, is preferably less than 0.5%, and more preferably less than 0.1%, less than 0.05%, and less than 0.01%, in that order.

[0111] Sb (Sb2O3) and Ce (CeO2) are elements that can be added as optional elements and function as fining agents. Of these, Sb (Sb2O3) is a fining agent with a large fining effect. Ce (CeO2) has a smaller fining effect than Sb (Sb2O3). Ce (CeO2) tends to intensify the coloring of glass when added in large amounts.

[0112] In this specification, the contents of Sb (Sb2O3) and Ce (CeO2) are expressed as exclusive percentages and are not included in the total content of all glass components expressed on an oxide basis. That is, in this specification, the total content of all glass components excluding Sb (Sb2O3) and Ce (CeO2) is taken to be 100 mass%.

[0113] The Sb2O3 content is expressed as an exclusive ratio. That is, in the optical glass according to the first embodiment, when the total content of all glass components other than Sb2O3 and CeO2 is taken as 100 mass%, the Sb2O3 content is preferably 1 mass% or less, and more preferably 0.1 mass% or less, 0.05 mass% or less, and 0.03 mass% or less. The Sb2O3 content may be 0 mass%.

[0114] The CeO2 content is also expressed as an exclusive ratio. That is, in the optical glass according to the first embodiment, when the total content of all glass components other than CeO2 and Sb2O3 is taken as 100 mass%, the CeO2 content is preferably 2 mass% or less, and more preferably 1 mass% or less, 0.5 mass% or less, and 0.1 mass% or less, in that order. The CeO2 content may be 0 mass%. By keeping the CeO2 content within the above range, the clarity of the glass can be improved.

[0115] (Glass characteristics) <Abbe number νd> In the optical glass according to the first embodiment, the Abbe number vd is preferably 15 to 30. The Abbe number vd may be 18 to 25, or may be 20 to 24. By setting the Abbe number vd within the above range, it is possible to obtain a glass with the desired dispersibility. The Abbe number vd can be controlled by adjusting the contents of TiO2, Nb2O5, WO3, and Bi2O3, which are glass components that contribute to high dispersion.

[0116] <Refractive index nd> In the optical glass according to the first embodiment, the lower limit of the refractive index nd is 1.86. The lower limit of the refractive index nd can also be 1.87, 1.88, 1.89, or 1.90. The upper limit of the refractive index nd can be 2.20, or even 2.15, 2.10, or 2.05. The refractive index can be controlled by adjusting the contents of TiO2, Nb2O5, WO3, Bi2O3, ZrO2, La2O3, Gd2O3, YO3, and Ta2O5, which are glass components that contribute to a high refractive index.

[0117] <Specific gravity of glass> The optical glass according to the first embodiment is a high refractive index glass, but does not have a high specific gravity. If the specific gravity of the glass can be reduced, the weight of the lens can be reduced. On the other hand, if the specific gravity is too low, thermal stability will be reduced.

[0118] Therefore, in the optical glass according to the first embodiment, the specific gravity is preferably 4.2 or less, and more preferably 4.0 or less, 3.8 or less, 3.6 or less, and 3.4 or less in that order.

[0119] The specific gravity can be controlled by adjusting the content of each glass component. In particular, by adjusting the content of Li2O and TiO2, the specific gravity can be reduced while maintaining a high refractive index.

[0120] In the optical glass according to the first embodiment, the ratio of the refractive index nd to the specific gravity [refractive index nd / specific gravity] is preferably 0.50 or greater, more preferably 0.52 or greater, and even more preferably 0.54 or greater. By keeping the ratio [refractive index nd / specific gravity] within the above range, an optical glass with a high refractive index and a relatively low specific gravity can be obtained.

[0121] <Glass transition temperature Tg> In the optical glass according to the first embodiment, the upper limit of the glass transition temperature Tg is preferably 690°C, and more preferably 680°C, 660°C, 650°C, 630°C, and 600°C in that order. There is no particular lower limit for the glass transition temperature Tg, but it is usually 500°C, and preferably 550°C.

[0122] The glass transition temperature Tg can be controlled by adjusting the total content of alkali metals.

[0123] By ensuring that the upper limit of the glass transition temperature Tg satisfies the above range, increases in the molding temperature and annealing temperature during glass reheat pressing can be suppressed, and thermal damage to the reheat press molding equipment and annealing equipment can be reduced.

[0124] When the lower limit of the glass transition temperature Tg satisfies the above range, it becomes easier to maintain good reheat press moldability and good thermal stability of the glass while maintaining the desired Abbe number and refractive index.

[0125] <Light transmittance of glass> The light transmittance of the optical glass according to the first embodiment can be evaluated by the coloring degrees λ80, λ70 and λ5. The spectral transmittance of a glass sample with a thickness of 10.0 mm ± 0.1 mm is measured in the wavelength range of 200 to 700 nm, and the wavelength at which the external transmittance is 80% is defined as λ80, the wavelength at which the external transmittance is 70% is defined as λ70, and the wavelength at which the external transmittance is 5% is defined as λ5.

[0126] The λ80 of the optical glass according to the first embodiment is preferably 700 nm or less, more preferably 650 nm or less, and even more preferably 600 nm or less. λ70 is preferably 600 nm or less, more preferably 550 nm or less, and even more preferably 500 nm or less. λ5 is preferably 500 nm or less, more preferably 450 nm or less, and even more preferably 400 nm or less.

[0127] (Optical glass manufacturing) The optical glass according to the first embodiment may be produced by blending glass raw materials to obtain the above-described predetermined composition, and then using the blended glass raw materials in accordance with a known glass manufacturing method. For example, a plurality of compounds may be blended and thoroughly mixed to form a batch raw material, which is then placed in a quartz crucible or platinum crucible and roughly melted (rough melted). The molten material obtained by rough melting is then rapidly cooled and pulverized to produce cullet. The cullet is then placed in a platinum crucible, heated, and remelted (remelted) to produce a glass melt, which is then clarified and homogenized, and then formed and slowly cooled to obtain the optical glass. Known methods may be used to form and slowly cool the glass melt.

[0128] The compounds used when preparing the batch raw materials are not particularly limited as long as they can introduce desired glass components into the glass to achieve desired contents. Examples of such compounds include oxides, carbonates, nitrates, hydroxides, and fluorides.

[0129] (Manufacturing of optical elements, etc.) To produce an optical element using the optical glass according to the first embodiment, a known method may be applied. For example, in the production of the optical glass, molten glass is poured into a mold and formed into a plate to produce a glass material made of the optical glass according to the present invention. The obtained glass material is cut, ground, and polished as appropriate to produce cut pieces of a size and shape suitable for press molding. The cut pieces are heated and softened, and press-molded (reheat pressed) using a known method to produce an optical element blank that approximates the shape of the optical element. The optical element blank is annealed, and then ground and polished using a known method to produce an optical element.

[0130] The optically functional surface of the fabricated optical element may be coated with an anti-reflection film, a total reflection film, or the like depending on the intended use.

[0131] According to one aspect of the present invention, an optical element made of the above optical glass can be provided. Examples of optical elements include lenses such as flat lenses, spherical lenses, and aspherical lenses, as well as prisms, diffraction gratings, and light guide plates. Examples of lens shapes include biconvex lenses, plano-convex lenses, biconcave lenses, plano-concave lenses, convex meniscus lenses, and concave meniscus lenses. Examples of uses for light guide plates include display devices such as augmented reality (AR) display type eyeglasses and mixed reality (MR) display type eyeglasses. Such light guide plates are plate-shaped glass attached to the frame of eyeglasses and made of the above optical glass. If necessary, a diffraction grating may be formed on the surface of the light guide plate to change the direction of propagation of light propagating through the light guide plate by repeated total reflection. The diffraction grating can be formed by a known method. When an eyeglass device having the above light guide plate is worn, light propagating through the light guide plate enters the pupil, thereby exhibiting augmented reality (AR) display or mixed reality (MR) display functions. Such eyeglass-type devices are disclosed, for example, in JP-A-2017-534352. The light guide plate can be produced by a known method. The optical element can be manufactured by a method including a step of processing a glass molded body made of the optical glass. Examples of processing include cutting, milling, rough grinding, fine grinding, and polishing. By using the glass described above during such processing, breakage can be reduced, enabling a stable supply of high-quality optical elements.

[0132] (Image display device) A light guide plate according to one embodiment of the present invention and an image display device using the same will be described in detail below with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals, and description thereof will not be repeated.

[0133] FIG. 2 illustrates the configuration of a head-mounted display 1 (hereinafter abbreviated as "HMD1") using a light guide plate 10 according to one embodiment of the present invention. FIG. 2(a) is a front perspective view of the HMD 1, and FIG. 2(b) is a rear perspective view of the HMD 1. As shown in FIGS. 2(a) and 2(b), eyeglass lenses 3 are attached to the front of an eyeglass-type frame 2 worn on the user's head. A backlight 4 for illuminating images is attached to a mounting portion 2a of the eyeglass-type frame 2. A signal processing device 5 for displaying images and a speaker 6 for reproducing sound are provided on the temples of the eyeglass-type frame 2. Flexible printed circuits (FPCs) 7, which constitute wiring extending from the circuit of the signal processing device 5, are routed along the eyeglass-type frame 2. A display element unit (e.g., a liquid crystal display element) 20 is routed by the FPC 7 to the center of the user's eyes and is held so that the approximate center of the display element unit 20 is aligned with the optical axis of the backlight 4. The imager unit 20 is fixed relatively to the light guide plate 10 so as to be located approximately in the center of the light guide plate 10. Furthermore, HOEs (Holographic Optical Elements) 32R and 32L (first optical elements) are closely fixed to the first surface 10a of the light guide plate 10 by adhesive or the like at locations located in front of the user's eyes. HOEs 52R and 52L are stacked on the second surface 10b of the light guide plate 10 at positions facing the imager unit 20 across the light guide plate 10.

[0134] FIG. 3 is a side view schematically illustrating the configuration of an HMD 1 according to one embodiment of the present invention. For clarity, FIG. 3 shows only the main components of the image display device, and the eyeglass-type frame 2 and other components are omitted. As shown in FIG. 3, the HMD 1 has a symmetrical structure with respect to a center line X connecting the center of the image display element 24 and the light guide plate 10. Furthermore, light of each wavelength incident on the light guide plate 10 from the image display element 24 is split into two beams, as will be described later, and guided to the right and left eyes of the user. The optical paths of the light of each wavelength guided to each eye are also approximately symmetrical with respect to the center line X.

[0135] As shown in FIG. 3, the backlight 4 includes a laser light source 21, a diffusion optical system 22, and a microlens array 23. The display element unit 20 is an image generating unit including an image display element 24, and is driven, for example, by a field sequential method. The laser light source 21 includes laser light sources corresponding to the wavelengths of R (wavelength 436 nm), G (wavelength 546 nm), and B (wavelength 633 nm), and sequentially irradiates light of each wavelength at high speed. The light of each wavelength is incident on the diffusion optical system 22 and the microlens array 23, where it is converted into a uniform, highly directional parallel beam of light with no unevenness in the amount of light, and is then incident perpendicularly on the display panel surface of the image display element 24.

[0136] The image display element 24 is, for example, a transmissive liquid crystal (LCDT-LCOS) panel driven by a field sequential method. The image display element 24 modulates light of each wavelength in accordance with an image signal generated by an image engine (not shown) of the signal processing device 5. The light of each wavelength modulated by the pixels in the effective area of ​​the image display element 24 is incident on the light guide plate 10 with a predetermined beam cross section (approximately the same shape as the effective area). Note that the image display element 24 can also be replaced with other types of display elements, such as a DMD (Digital Mirror Device), a reflective liquid crystal (LCOS) panel, a MEMS (Micro Electro Mechanical Systems), an organic EL (Electro-Luminescence), or an inorganic EL.

[0137] The image generating unit of the image display element 20 is not limited to a field sequential type image display element, but may be a simultaneous type image display element (a display element having a predetermined arrangement of RGB color filters in front of the light emitting surface). In this case, for example, a white light source is used as the light source.

[0138] As shown in Fig. 3, light of each wavelength modulated by the image display element 24 is sequentially incident on the first surface 10a into the light guide plate 10. HOEs 52R and 52L (second optical elements) are laminated on the second surface 10b of the light guide plate 10. HOEs 52R and 52L are, for example, rectangular reflective volume phase HOEs, each configured by laminating three photopolymer sheets on which interference fringes corresponding to light of each wavelength of R, G, and B are recorded. In other words, HOEs 52R and 52L are configured to have a wavelength selection function that diffracts light of each wavelength of R, G, and B and transmits light of other wavelengths.

[0139] The HOEs 32R and 32L are also reflective volume phase HOEs and have the same layer structure as the HOEs 52R and 52L. The HOEs 32R and 32L and the HOEs 52R and 52L may have, for example, approximately the same pitch of the interference fringe patterns.

[0140] The HOEs 52R and 52L are stacked with their centers aligned and with their interference fringe patterns inverted by 180°. They are then tightly fixed by adhesive or the like onto the second surface 10b of the light guide plate 10 so that their centers are aligned with the center line X. The light of each wavelength modulated by the image display element 24 is incident sequentially on the HOEs 52R and 52L via the light guide plate 10.

[0141] The HOEs 52R and 52L each diffract light of each wavelength incident sequentially at a predetermined angle to guide it to the right eye and left eye. The light of each wavelength diffracted by the HOEs 52R and 52L undergoes repeated total reflection at the interface between the light guide plate 10 and the air, propagates within the light guide plate 10, and is then incident on the HOEs 32R and 32L. The HOEs 52R and 52L impart the same diffraction angle to the light of each wavelength. Therefore, all light of all wavelengths incident at approximately the same position on the light guide plate 10 (or, in other words, emitted from approximately the same coordinates within the effective area of ​​the image display element 24) propagates along approximately the same optical path within the light guide plate 10 and is incident on approximately the same position on the HOEs 32R and 32L. From another perspective, the HOEs 52R and 52L diffract the light of each wavelength of RGB so that the pixel positional relationship within the effective area of ​​the image displayed on the effective area of ​​the image display element 24 is faithfully reproduced on the HOEs 32R and 32L.

[0142] Thus, in one aspect of the present invention, HOEs 52R and 52L each diffract light of all wavelengths emitted from approximately the same coordinates within the effective area of ​​image display element 24 so that it is incident on approximately the same position on HOEs 32R and 32L. Alternatively, HOEs 52R and 52L may be configured to diffract light of all wavelengths that would originally form the same pixel but are relatively shifted within the effective area of ​​image display element 24 so that it is incident on approximately the same position on HOEs 32R and 32L.

[0143] The light of each wavelength incident on the HOEs 32R and 32L is diffracted by the HOEs 32R and 32L and sequentially emitted approximately perpendicularly to the outside from the second surface 10b of the light guide plate 10. The light of each wavelength emitted as approximately parallel light in this manner forms a virtual image I of the image generated by the image display element 24 on the retina of the user's right eye and left eye, respectively. Alternatively, to allow the user to observe the virtual image I of the enlarged image, the HOEs 32R and 32L may be given a condenser effect. That is, light incident on the peripheral regions of the HOEs 32R and 32L may be emitted at an angle closer to the center of the pupil and formed on the user's retina. Alternatively, to allow the user to observe the virtual image I of the enlarged image, the HOEs 52R and 52L may diffract the light of each wavelength of RGB so that the pixel positional relationship on the HOEs 32R and 32L forms an enlarged, similar shape to the pixel positional relationship within the effective area of ​​the image displayed on the image display element 24.

[0144] The higher the refractive index, the shorter the air-equivalent optical path length of light traveling through the light guide plate 10, so by using the optical glass according to this embodiment, which has a high refractive index, it is possible to increase the apparent viewing angle relative to the width of the image display element 24. Furthermore, because the specific gravity is kept low despite the high refractive index, it is possible to provide a light guide plate that is lightweight yet achieves the above effects.

[0145] Note that the light guide plate according to one embodiment of the present invention can be used in a see-through transmissive head-mounted display, a non-transmissive head-mounted display, or the like.

[0146] These head-mounted displays have light guide plates made of the high-refractive-index, low-specific-gravity optical glass of this embodiment, which provides an excellent sense of immersion due to the wide viewing angle, and are suitable as image display devices for use in combination with information terminals, for providing AR (Augmented Reality), etc., or for providing movies, games, VR (Virtual Reality), etc.

[0147] Although the above description has been given taking a head-mounted display as an example, the light guide plate may be attached to other image display devices.

[0148] Second embodiment The optical glass according to the second embodiment is The SiO2 content is 1 to 50 mass%; The content of TiO2 is 1 to 50 mass%; The BaO content is 0 to 16.38 mass%; The content of Nb2O5 is 1 to 50 mass%; the total content of LiO, NaO, KO, and CsO [LiO + NaO + KO + CsO] is 0.1 to 20 mass%; the total content of La2O3, Gd2O3, and Y2O3 [La2O3 + Gd2O3 + Y2O3] is 0 to 10 mass%; The total content of TiO2 and Nb2O5 [TiO2 + Nb2O5] is 45 to 65 mass%; The mass ratio of the TiO2 content to the total content of TiO2 and Nb2O5 [TiO2 / (TiO2+Nb2O5)] is 0.3 or more, the mass ratio of the content of LiO to the total content of LiO, NaO, KO, and CsO [LiO / (LiO+NaO+KO+CsO)] is 0.1 to 1; the Abbe number νd is 25 or less, The refractive index nd is 1.86 or more.

[0149] In the optical glass according to the second embodiment, the SiO2 content is 1 to 50%. The lower limit of the SiO2 content is preferably 10%, and more preferably 12%, 15%, 18%, and 20% in that order. The upper limit of the SiO2 content is preferably 40%, and more preferably 38%, 35%, 33%, and 30% in that order.

[0150] SiO2 is a glass network-forming component. By setting the SiO2 content within the above range, the thermal stability, chemical durability, and weather resistance of the glass can be improved, and the viscosity of the glass melt can be increased. On the other hand, if the SiO2 content is too high, the refractive index of the glass decreases, and the desired optical properties may not be obtained.

[0151] In the optical glass according to the second embodiment, the TiO2 content is 1 to 50%. The lower limit of the TiO2 content is preferably 10%, and more preferably 13%, 15%, 18%, and 20% in that order. The upper limit of the TiO2 content is preferably 45%, and more preferably 40% and 35% in that order.

[0152] By setting the TiO2 content within the above range, the refractive index can be increased and the stability of the glass can be improved. Furthermore, the refractive index can be increased without increasing the specific gravity. On the other hand, if the TiO2 content is too high, the thermal stability may be reduced.

[0153] In the optical glass according to the second embodiment, the BaO content is 0 to 16.38%. The upper limit of the BaO content is preferably 15%, and more preferably 13% and 10%. The lower limit of the BaO content is preferably 0%.

[0154] By setting the BaO content within the above range, the meltability of the glass can be improved and the refractive index can be increased. On the other hand, if the BaO content is too high, the thermal stability may decrease and the specific gravity may increase.

[0155] In the optical glass according to the second embodiment, the Nb2O5 content is 1 to 50%. The lower limit of the Nb2O5 content is preferably 10%, and more preferably 13% and 15% in that order. The upper limit of the Nb2O5 content is preferably 50%, and more preferably 45%, 40%, and 35% in that order.

[0156] By setting the content of Nb2O5 within the above range, the refractive index can be increased and the stability of the glass can be improved. On the other hand, if the content of Nb2O5 is too high, the specific gravity may increase and the thermal stability may decrease.

[0157] In the optical glass according to the second embodiment, the total content of Li2O, Na2O, K2O, and Cs2O [Li2O + Na2O + K2O + Cs2O] is 0.1 to 20%. The lower limit of this total content is preferably 1.5%, and more preferably 2%, 4%, and 6%, in that order. The upper limit of this total content is preferably 15%, and more preferably 13% and 10%, in that order.

[0158] By setting the total content [Li2O+Na2O+K2O+Cs2O] within the above range, an optical glass with excellent melting properties can be obtained.

[0159] In the optical glass according to the second embodiment, the total content of La2O3, Gd2O3, and Y2O3 [La2O3 + Gd2O3 + Y2O3] is 0 to 10%. The upper limit of this total content is preferably 8%, with 5% and 3% being more preferred in that order. The lower limit of this total content is 0%. This total content may even be 0%.

[0160] From the viewpoint of suppressing an increase in specific gravity and maintaining good thermal stability, the total content [La2O3+Gd2O3+Y2O3] is preferably within the above range.

[0161] In the optical glass according to the second embodiment, the total content of TiO2 and Nb2O5 [TiO2 + Nb2O5] is 45 to 65%. The lower limit of this total content is preferably 20%, with 25%, 30%, and 35% being more preferred in that order. The upper limit of this total content is preferably 63%, with 61%, 59%, and 57% being more preferred in that order.

[0162] By setting the total content [TiO2 + Nb2O5] within the above range, it is possible to increase the refractive index and obtain glass having desired optical properties.

[0163] In the optical glass according to the second embodiment, the mass ratio of the TiO2 content to the total content of TiO2 and Nb2O5 [TiO2 / (TiO2+Nb2O5)] is 0.3 or greater. The lower limit of this mass ratio is preferably 0.35, with 0.40 and 0.45 being more preferred. The upper limit of this mass ratio is preferably 0.80, with 0.75, 0.70, and 0.65 being more preferred.

[0164] By setting the mass ratio [TiO2 / (TiO2+Nb2O5)] within the above range, an optical glass with a high refractive index and a reduced specific gravity can be obtained.

[0165] In the optical glass according to the second embodiment, the mass ratio of the LiO content to the total content of LiO, NaO, KO, and CsO [LiO / (LiO + NaO + KO + CsO)] is 0.1 to 1. The lower limit of this mass ratio is preferably 0.15, and more preferably 0.20 and 0.25 in that order. The upper limit of this mass ratio is preferably 0.80, and more preferably 0.75, 0.70, and 0.65 in that order.

[0166] By setting the mass ratio [Li2O / (Li2O+Na2O+K2O+Cs2O)] within the above range, an optical glass with a high refractive index and a reduced specific gravity can be obtained.

[0167] <Abbe number νd> In the optical glass according to the second embodiment, the Abbe number vd is 25 or less. The Abbe number vd may be 15 to 25, 18 to 25, or 20 to 24. By setting the Abbe number vd within the above range, it is possible to obtain a glass with the desired dispersibility. The Abbe number vd can be controlled by adjusting the contents of TiO2, Nb2O5, WO3, and Bi2O3, which are glass components that contribute to high dispersion.

[0168] <Refractive index nd> In the optical glass according to the second embodiment, the refractive index nd is 1.86 or greater. The lower limit of the refractive index nd can be 1.87, or even 1.88, 1.89, or 1.90. The upper limit of the refractive index nd can be 2.20, or even 2.15, 2.10, or 2.05. The refractive index can be controlled by adjusting the contents of TiO2, Nb2O5, WO3, Bi2O3, ZrO2, La2O3, Gd2O3, YO3, and Ta2O5, which are glass components that contribute to a high refractive index.

[0169] Non-limiting examples of the contents, ratios, and properties of glass components other than those described above in the optical glass according to the second embodiment are given below.

[0170] In the optical glass according to the second embodiment, the upper limit of the P2O5 content is preferably 10%, and more preferably 8%, 5%, and 3%, in that order. The P2O5 content may be 0%.

[0171] In order to obtain an optical glass having a high refractive index and a reduced specific gravity, the content of P2O5 is preferably within the above range.

[0172] In the optical glass according to the second embodiment, the upper limit of the B2O3 content is preferably 10%, and more preferably 8%, 5%, and 3% in that order. The lower limit of the B2O3 content is preferably 0%, and more preferably 0.5%, 0.8%, and 1.0% in that order.

[0173] B2O3 is a glass network-forming component. B2O3 has the function of improving the thermal stability of the glass, but if the B2O3 content is too high, the refractive index may decrease. Therefore, it is preferable that the B2O3 content be within the above range.

[0174] In the optical glass according to the second embodiment, the upper limit of the Al2O3 content is preferably 10%, and more preferably 8%, 5%, and 3%, in that order. The Al2O3 content may be 0%.

[0175] Although Al2O3 has the function of increasing chemical durability, if the Al2O3 content is too high, the meltability of the glass may deteriorate, so it is preferable that the Al2O3 content be set within the above range.

[0176] In the optical glass according to the second embodiment, the lower limit of the total content of SiO2 and Al2O3 [SiO2 + Al2O3] is preferably 10%, and more preferably 13%, 15%, 18%, and 20% in that order. The upper limit of this total content is preferably 50%, and more preferably 45%, 40%, 35%, and 30% in that order.

[0177] In order to improve the thermal stability of the glass, the total content [SiO2 + Al2O3] is preferably within the above range.

[0178] In the optical glass according to the second embodiment, the lower limit of the mass ratio of the B2O3 content to the total content of SiO2 and Al2O3 [B2O3 / (SiO2+Al2O3)] is preferably 0.01, and more preferably 0.02, 0.03, and 0.04 in that order. The upper limit of this mass ratio is preferably 0.20, and more preferably 0.18, 0.15, 0.13, and 0.10 in that order.

[0179] From the viewpoint of improving chemical durability and thermal stability, it is preferable that the mass ratio [B2O3 / (SiO2+Al2O3)] is within the above range.

[0180] In the optical glass according to the second embodiment, the lower limit of the total content of B2O3 and P2O5 [B2O3 + P2O5] is preferably 0.5%, more preferably 0.8% and 1.0%, in that order, and the upper limit of this total content is preferably 10%, more preferably 8%, 5%, and 3%, in that order.

[0181] From the viewpoint of improving chemical durability and thermal stability, the total content [B2O3+P2O5] is preferably within the above range.

[0182] In the optical glass according to the second embodiment, the lower limit of the total content of B2O3 and SiO2 [B2O3 + SiO2] is preferably 10%, more preferably 15%, 18%, and 20%, in that order, and the upper limit of this total content is preferably 50%, more preferably 45%, 40%, and 35%, in that order.

[0183] In order to obtain an optical glass with a high refractive index, the total content [B2O3+SiO2] is preferably within the above range.

[0184] In the optical glass according to the second embodiment, the lower limit of the ZrO2 content is preferably 0%, and more preferably 0.1%, 0.5%, and 1.0%, in that order. The upper limit of the ZrO2 content is preferably 10%, and more preferably 8%, 5%, and 3%, in that order. The ZrO2 content may even be 0%.

[0185] ZrO2 is a component that contributes to a high refractive index. On the other hand, if the ZrO2 content is too high, the thermal stability may decrease and the specific gravity may increase. Therefore, it is preferable that the ZrO2 content be within the above range.

[0186] In the optical glass according to the second embodiment, the upper limit of the WO3 content is preferably 10%, and more preferably 8%, 5%, and 3%, in that order. The WO3 content may be 0%.

[0187] WO3 is a component that contributes to a high refractive index. On the other hand, if the WO3 content is too high, the thermal stability may decrease, the specific gravity may increase, and the coloring of the glass may increase, resulting in a decrease in transmittance. Therefore, it is preferable that the WO3 content be within the above range.

[0188] In the optical glass according to the second embodiment, the upper limit of the Bi2O3 content is preferably 10%, and more preferably 8%, 5%, and 3%, in that order. The lower limit of the Bi2O3 content is preferably 0%. The Bi2O3 content may be 0%.

[0189] When an appropriate amount of Bi2O3 is included, it improves the thermal stability of the glass. It is also a component that contributes to a high refractive index. On the other hand, if the Bi2O3 content is too high, the specific gravity increases. Furthermore, the coloring of the glass increases. Therefore, it is preferable that the Bi2O3 content be within the above range.

[0190] In the optical glass according to the second embodiment, the upper limit of the total content of TiO2, Nb2O5, WO3 and Bi2O3 [TiO2 + Nb2O5 + WO3 + Bi2O3] is preferably 80%, more preferably 70% and more preferably 60%, and the lower limit of this total content is preferably 20%, more preferably 25%, 30%, and more preferably 35%.

[0191] TiO2, Nb2O5, WO3 and Bi2O3 are all components that contribute to increasing the refractive index, so it is preferable that the total content [TiO2 + Nb2O5 + WO3 + Bi2O3] is within the above range.

[0192] In the optical glass according to the second embodiment, the lower limit of the LiO content is preferably 0.1%, and more preferably 0.3%, 0.5%, 0.8%, 1.0%, 1.3%, and 1.5%, in that order. The upper limit of the LiO content is preferably 10%, and more preferably 9%, 8%, 7%, 6%, and 5%, in that order.

[0193] Li2O is a component that contributes to lowering the specific gravity and, among alkali metals, is a component that particularly contributes to increasing the refractive index. On the other hand, if the Li2O content is too high, the thermal stability may decrease. Therefore, it is preferable that the Li2O content be within the above range.

[0194] In the optical glass according to the second embodiment, the upper limit of the Na2O content is preferably 10%, and more preferably 9%, 8%, and 7%, in that order. The lower limit of the Na2O content is preferably 0%, and more preferably 0.5%, 1.0%, 1.5%, and 2.0%, in that order.

[0195] In the optical glass according to the second embodiment, the upper limit of the K2O content is preferably 10%, and more preferably 8%, then 5%. The lower limit of the K2O content is preferably 0%, and more preferably 0.5%, then 1.0%, then 1.5%, then 2.0%. The K2O content may even be 0%.

[0196] Na2O and K2O have the function of improving the meltability of glass. On the other hand, if their contents are too high, the refractive index may decrease and the thermal stability may also decrease. Therefore, it is preferable that the contents of Na2O and K2O are each within the above ranges.

[0197] In the optical glass according to the second embodiment, the upper limit of the Cs2O content is preferably 5%, and more preferably 3%, and 1% in that order. The lower limit of the Cs2O content is preferably 0%.

[0198] Cs2O has the function of improving the thermal stability of the glass, but if its content increases, the chemical durability and weather resistance decrease, so the Cs2O content is preferably set within the above range.

[0199] In the optical glass according to the second embodiment, the lower limit of the mass ratio of the LiO content to the total content of LiO, NaO, and KO [LiO / (LiO+NaO+KO)] is preferably 0.10, and more preferably 0.15, 0.20, and 0.25 in that order. The upper limit of this mass ratio is preferably 1.00, and more preferably 0.80, 0.75, 0.70, and 0.65 in that order.

[0200] In order to obtain an optical glass having a high refractive index and a reduced specific gravity, the mass ratio [Li2O / (Li2O+Na2O+K2O)] is preferably within the above range.

[0201] In the optical glass according to the second embodiment, the lower limit of the total content of NaO, KO, and CsO [NaO + KO + CsO] is preferably 0%, and the upper limit of this total content is preferably 11.0%, and more preferably 10.0%, 9.0%, 8.0%, 7.0%, and 6.0%, in that order.

[0202] In order to maintain a high refractive index while maintaining the thermal stability of the glass, the total content [Na2O+K2O+Cs2O] is preferably within the above range.

[0203] In the optical glass according to the second embodiment, the upper limit of the MgO content is preferably 20%, and more preferably 15%, 10%, and 5%, in that order. The lower limit of the MgO content is preferably 0%.

[0204] In the optical glass according to the second embodiment, the lower limit of the CaO content is preferably 1%, and more preferably 3%, 5%, and 8%, in that order. The upper limit of the CaO content is preferably 20%, and more preferably 18%, 15%, and 13%, in that order.

[0205] MgO and CaO have the function of improving the meltability of glass. On the other hand, if their contents are too high, thermal stability may decrease. Therefore, it is preferable that the contents of MgO and CaO are each within the above ranges.

[0206] In the optical glass according to the second embodiment, the upper limit of the SrO content is preferably 10%, and more preferably 8%, 5%, and 3%, in that order. The lower limit of the SrO content is preferably 0%.

[0207] SrO improves the meltability of glass and increases the refractive index. However, if the SrO content is too high, the thermal stability may decrease and the specific gravity may increase. Therefore, it is preferable that the SrO content be within the above range.

[0208] In the optical glass according to the second embodiment, the upper limit of the ZnO content is preferably 10%, and more preferably 8%, 5%, and 3%, in that order. The lower limit of the ZnO content is preferably 0%.

[0209] ZnO is a glass component that improves the thermal stability of glass. However, if the ZnO content is too high, the specific gravity increases. Therefore, 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.

[0210] In the optical glass according to the second embodiment, the upper limit of the total content of MgO, CaO, SrO, BaO, and ZnO [MgO + CaO + SrO + BaO + ZnO] is preferably 40%, more preferably 35%, 30%, and 25%, in that order. The lower limit of this total content is preferably 3%, more preferably 5%, 8%, and 10%, in that order. From the viewpoints of suppressing an increase in specific gravity and maintaining thermal stability without impeding high dispersion, it is preferable that the total content be within the above range.

[0211] In the optical glass according to the second embodiment, the upper limit of the Ta2O5 content is preferably 10%, and more preferably 8%, 5%, and 3%, in that order. The lower limit of the Ta2O5 content is preferably 0%.

[0212] Ta2O5 is a component that contributes to a high refractive index. It is also a glass component that improves the thermal stability of the glass and reduces Pg and F. On the other hand, if the Ta2O5 content is high, the thermal stability of the glass decreases, and when the glass is melted, the glass raw material is more likely to remain unmelted. In addition, the specific gravity increases. Therefore, it is preferable that the Ta2O5 content be within the above range.

[0213] In the optical glass according to the second embodiment, the upper limit of the La2O3 content is preferably 10%, and more preferably 8%, 5%, and 3%, in that order. The lower limit of the La2O3 content is preferably 0%.

[0214] La2O3 is a component that contributes to a high refractive index. However, as the La2O3 content increases, the specific gravity increases and the thermal stability of the glass decreases. Therefore, from the viewpoint of suppressing the increase in specific gravity and the decrease in the thermal stability of the glass, it is preferable that the La2O3 content be within the above range.

[0215] In the optical glass according to the second embodiment, the upper limit of the Y2O3 content is preferably 10%, and more preferably 8%, 5%, and 3%, in that order. The lower limit of the Y2O3 content is preferably 0%.

[0216] Y2O3 is a component that contributes to a high refractive index. On the other hand, if the Y2O3 content is too high, the thermal stability of the glass decreases, making the glass more susceptible to devitrification during production. Therefore, from the viewpoint of preventing a decrease in the thermal stability of the glass, it is preferable that the Y2O3 content be within the above range.

[0217] In the optical glass according to the second embodiment, the Sc2O3 content is preferably 2% or less, and the lower limit of the Sc2O3 content is preferably 0%.

[0218] In the optical glass according to the second embodiment, the content of HfO2 is preferably 2% or less, and the lower limit of the content of HfO2 is preferably 0%.

[0219] Sc2O3 and HfO2 have the function of increasing the dispersibility of the glass, but are expensive components, so it is preferable that the contents of Sc2O3 and HfO2 are each within the above ranges.

[0220] In the optical glass according to the second embodiment, the content of Lu2O3 is preferably 2% or less, and the lower limit of the content of Lu2O3 is preferably 0%.

[0221] Lu2O3 has the function of increasing the dispersibility of the glass, but because it has a large molecular weight, it is also a glass component that increases the specific gravity of the glass, so the content of Lu2O3 is preferably within the above range.

[0222] In the optical glass according to the second embodiment, the GeO2 content is preferably 2% or less, and the lower limit of the GeO2 content is preferably 0%.

[0223] GeO2 has the function of increasing the high dispersibility of the glass, but is an extremely expensive component among commonly used glass components, so from the perspective of reducing the manufacturing cost of the glass, it is preferable that the GeO2 content be in the above range.

[0224] In the optical glass according to the second embodiment, the upper limit of the Gd2O3 content is preferably 3.0%, more preferably 2.0%, and the lower limit of the Gd2O3 content is preferably 0%.

[0225] Gd2O3 is a component that contributes to a high refractive index. However, if the Gd2O3 content is too high, the thermal stability of the glass decreases. Furthermore, if the Gd2O3 content is too high, the specific gravity of the glass increases, which is undesirable. Therefore, from the viewpoint of suppressing an increase in specific gravity while maintaining good thermal stability of the glass, it is preferable that the Gd2O3 content be within the above range.

[0226] In the optical glass according to the second embodiment, the content of Yb2O3 is preferably 2% or less, and the lower limit of the content of Yb2O3 is preferably 0%.

[0227] Yb2O3 has a larger molecular weight than La2O3, Gd2O3, and Y2O3, and therefore increases the specific gravity of the glass. This increases the specific gravity of the glass, which in turn increases the mass of the optical element. Therefore, it is desirable to reduce the Yb2O3 content to prevent the increase in the specific gravity of the glass.

[0228] Furthermore, if the Yb2O3 content is too high, the thermal stability of the glass decreases. From the viewpoint of preventing a decrease in the thermal stability of the glass and suppressing an increase in specific gravity, it is preferable that the Yb2O3 content be within the above range.

[0229] In the optical glass according to the second embodiment, the mass ratio [LiO / {100-(SiO+B+P+GeO)}] of the LiO content to the total content of glass components other than SiO, B, O, P, and GeO is preferably 0.02, and more preferably 0.03, 0.04, 0.05, and 0.06 in this order. The upper limit of this mass ratio is preferably 0.20, and more preferably 0.15, 0.13, and 0.10 in this order.

[0230] The total content of all glass components is 100% by mass. Therefore, the total content of glass components other than SiO2, B2O3, P2O5, and GeO2 is expressed as [100 - (SiO2 + B2O3 + P2O5 + GeO2)]. From the perspective of obtaining an optical glass with a high refractive index and a low specific gravity, it is preferable that the mass ratio [Li2O / {100 - (SiO2 + B2O3 + P2O5 + GeO2)}] be within the above range.

[0231] In the optical glass according to the second embodiment, the mass ratio of the TiO content to the total content of TiO, NbO, WO, ZrO, SrO, BaO, ZnO, LaO, GdO, YO, TaO, and BiO [TiO / (TiO + NbO + WO + ZrO + SrO + BaO + ZnO + LaO + GdO + YO + TaO + BiO)] is preferably 0.40, and more preferably 0.42, 0.44, 0.46, 0.48, and 0.50 in that order. The upper limit of this mass ratio is preferably 0.80, and more preferably 0.75, 0.70, and 0.65 in that order.

[0232] From the viewpoint of increasing the refractive index while suppressing an increase in specific gravity, it is preferable that the mass ratio [TiO2 / (TiO2+Nb2O5+WO3+ZrO2+SrO+BaO+ZnO+La2O3+Gd2O3+Y2O3+Ta2O5+Bi2O3)] be in the above range.

[0233] The optical glass according to the second embodiment is preferably composed primarily of the above-mentioned glass components, namely, SiO2, TiO2, and Nb2O5 as essential components and BaO, P2O5, B2O3, Al2O3, ZrO2, WO3, Bi2O3, Li2O, Na2O, K2O, Cs2O, MgO, CaO, SrO, ZnO, Ta2O5, La2O3, Y2O3, Sc2O3, HfO2, Lu2O3, GeO2, Gd2O3, and Yb2O3 as optional components, and the total content of the above-mentioned glass components is preferably 95% or more, more preferably 98% or more, even more preferably 99% or more, and even more preferably 99.5% or more.

[0234] The optical glass according to the second embodiment is preferably composed essentially of the above glass components, but may contain other components as long as they do not impair the effects of the present invention. Furthermore, the present invention does not exclude the inclusion of unavoidable impurities.

[0235] (Other ingredients) Pb, As, Cd, Tl, Be, and Se are all toxic. Therefore, it is particularly preferable that the optical glass according to the second embodiment does not contain these elements as glass components. The content of each of the above elements, calculated as an oxide, is preferably less than 0.5%, and more preferably less than 0.1%, less than 0.05%, and less than 0.01%, in that order.

[0236] U, Th, and Ra are all radioactive elements. Therefore, it is particularly preferable that the optical glass according to the second embodiment does not contain these elements as glass components. The content of each of the above elements, calculated as an oxide, is preferably less than 0.5%, more preferably less than 0.1%, less than 0.05%, and even more preferably less than 0.01%, in that order.

[0237] V, Cr, Mn, Fe, Co, Ni, Cu, Pr, Nd, Pm, Sm, Eu, Tb, Dy, Ho, Er, and Tm increase the coloration of the glass and can be sources of fluorescence. Therefore, it is particularly preferable that the optical glass according to the second embodiment does not contain these elements as glass components. The content of each of the above elements, calculated as oxide, is preferably less than 0.5%, and more preferably less than 0.1%, less than 0.05%, and less than 0.01%, in that order.

[0238] Sb (Sb2O3) and Ce (CeO2) are elements that can be added as optional elements and function as fining agents. Of these, Sb (Sb2O3) is a fining agent with a large fining effect. Ce (CeO2) has a smaller fining effect than Sb (Sb2O3). Ce (CeO2) tends to intensify the coloring of glass when added in large amounts.

[0239] In this specification, the contents of Sb (Sb2O3) and Ce (CeO2) are expressed as exclusive percentages and are not included in the total content of all glass components expressed on an oxide basis. That is, in this specification, the total content of all glass components excluding Sb (Sb2O3) and Ce (CeO2) is taken to be 100 mass%.

[0240] The Sb2O3 content is expressed as an external percentage. That is, in the optical glass according to the second embodiment, when the total content of all glass components other than Sb2O3 and CeO2 is taken as 100 mass%, the Sb2O3 content is preferably 1 mass% or less, and more preferably 0.1 mass% or less, 0.05 mass% or less, and 0.03 mass% or less. The Sb2O3 content may be 0 mass%.

[0241] The CeO2 content is also expressed as an exclusive ratio. That is, in the optical glass according to the second embodiment, when the total content of all glass components other than CeO2 and Sb2O3 is taken as 100 mass%, the CeO2 content is preferably 2 mass% or less, and more preferably 1 mass% or less, 0.5 mass% or less, and 0.1 mass% or less, in that order. The CeO2 content may be 0 mass%. By keeping the CeO2 content within the above range, the clarity of the glass can be improved.

[0242] (Glass characteristics) <Specific gravity of glass> The optical glass according to the second embodiment is a high refractive index glass, but does not have a high specific gravity. If the specific gravity of the glass can be reduced, the weight of the lens can be reduced. On the other hand, if the specific gravity is too low, it will result in a decrease in thermal stability.

[0243] Therefore, in the optical glass according to the second embodiment, the specific gravity is preferably 4.2 or less, and more preferably 4.0 or less, 3.8 or less, 3.6 or less, and 3.4 or less in that order.

[0244] The specific gravity can be controlled by adjusting the content of each glass component. In particular, by adjusting the content of Li2O and TiO2, the specific gravity can be reduced while maintaining a high refractive index.

[0245] In the optical glass according to the second embodiment, the refractive index nd and the specific gravity preferably satisfy the following formula (1), more preferably the following formula (2), and even more preferably the following formula (3): When the refractive index nd and the specific gravity satisfy the following formula, an optical glass with a high refractive index and a relatively low specific gravity can be obtained. nd≧0.2×specific gravity+1.18…(1) nd≧0.2×specific gravity+1.19…(2) nd≧0.2×specific gravity+1.20…(3)

[0246] In the optical glass according to the second embodiment, the ratio of the refractive index nd to the specific gravity [refractive index nd / specific gravity] is preferably 0.50 or greater, more preferably 0.52 or greater, and even more preferably 0.54 or greater. By keeping the ratio [refractive index nd / specific gravity] within the above range, an optical glass with a high refractive index and a relatively low specific gravity can be obtained.

[0247] <Glass transition temperature Tg> In the optical glass according to the second embodiment, the upper limit of the glass transition temperature Tg is preferably 680°C, and more preferably 670°C, 660°C, 650°C, 630°C, and 600°C in that order. There is no particular lower limit to the glass transition temperature Tg, but it is usually 500°C, and preferably 550°C.

[0248] The glass transition temperature Tg can be controlled by adjusting the total content of alkali metals.

[0249] By ensuring that the upper limit of the glass transition temperature Tg satisfies the above range, increases in the molding temperature and annealing temperature during glass reheat pressing can be suppressed, and thermal damage to the reheat press molding equipment and annealing equipment can be reduced.

[0250] When the lower limit of the glass transition temperature Tg satisfies the above range, it becomes easier to maintain good reheat press moldability and good thermal stability of the glass while maintaining the desired Abbe number and refractive index.

[0251] <Light transmittance of glass> The light transmittance of the optical glass according to the second embodiment can be evaluated by the coloring degrees λ80, λ70 and λ5. The spectral transmittance of a glass sample with a thickness of 10.0 mm ± 0.1 mm is measured in the wavelength range of 200 to 700 nm, and the wavelength at which the external transmittance is 80% is defined as λ80, the wavelength at which the external transmittance is 70% is defined as λ70, and the wavelength at which the external transmittance is 5% is defined as λ5.

[0252] The λ80 of the optical glass according to the first embodiment is preferably 700 nm or less, more preferably 650 nm or less, and even more preferably 600 nm or less. λ70 is preferably 600 nm or less, more preferably 550 nm or less, and even more preferably 500 nm or less. λ5 is preferably 500 nm or less, more preferably 450 nm or less, and even more preferably 400 nm or less.

[0253] (Optical glass manufacturing) The optical glass according to the second embodiment may be produced by blending glass raw materials to obtain the above-described predetermined composition, and then using the blended glass raw materials in accordance with a known glass manufacturing method. For example, a plurality of compounds may be blended and thoroughly mixed to form batch raw materials, which are then placed in a quartz crucible or platinum crucible for rough melting. The molten material obtained by rough melting is then rapidly cooled and pulverized to produce cullet. The cullet is then placed in a platinum crucible, heated, and remelted to form a glass melt, which is then refined and homogenized, and then formed and slowly cooled to obtain the optical glass. Known methods may be used to form and slowly cool the glass melt.

[0254] The compounds used when preparing the batch raw materials are not particularly limited as long as they can introduce desired glass components into the glass to achieve desired contents. Examples of such compounds include oxides, carbonates, nitrates, hydroxides, and fluorides.

[0255] (Manufacturing of optical elements, etc.) To produce an optical element using the optical glass according to the second embodiment, a known method may be applied. For example, in the production of the optical glass, molten glass is poured into a mold and formed into a plate to produce a glass material made of the optical glass according to the present invention. The obtained glass material is cut, ground, and polished as appropriate to produce cut pieces of a size and shape suitable for press molding. The cut pieces are heated and softened, and press-molded (reheat pressed) by a known method to produce an optical element blank that approximates the shape of the optical element. The optical element blank is annealed, and then ground and polished by a known method to produce an optical element.

[0256] The optically functional surface of the fabricated optical element may be coated with an anti-reflection film, a total reflection film, or the like depending on the intended use.

[0257] According to one aspect of the present invention, an optical element made of the above optical glass can be provided. Examples of optical elements include lenses such as flat lenses, spherical lenses, and aspherical lenses, as well as prisms, diffraction gratings, and light guide plates. Examples of lens shapes include biconvex lenses, plano-convex lenses, biconcave lenses, plano-concave lenses, convex meniscus lenses, and concave meniscus lenses. Examples of uses for light guide plates include display devices such as augmented reality (AR) display type eyeglasses and mixed reality (MR) display type eyeglasses. Such light guide plates are plate-shaped glass attached to the frame of eyeglasses and made of the above optical glass. If necessary, a diffraction grating may be formed on the surface of the light guide plate to change the direction of propagation of light propagating through the light guide plate by repeated total reflection. The diffraction grating can be formed by a known method. When an eyeglass device having the above light guide plate is worn, light propagating through the light guide plate enters the pupil, thereby exhibiting augmented reality (AR) display or mixed reality (MR) display functions. Such eyeglass-type devices are disclosed, for example, in JP-A-2017-534352. The light guide plate can be produced by a known method. The optical element can be manufactured by a method including a step of processing a glass molded body made of the optical glass. Examples of processing include cutting, milling, rough grinding, fine grinding, and polishing. By using the glass described above during such processing, breakage can be reduced, enabling a stable supply of high-quality optical elements.

[0258] (Image display device) The image display device according to the second embodiment can be similar to that of the first embodiment.

[0259] Third embodiment The optical glass according to the third embodiment is The SiO2 content is 1 to 50 mass%; The content of TiO2 is 1 to 50 mass%; The content of Nb2O5 is 1 to 50 mass%; The content of Na2O is 0 to 8 mass%; The total content of TiO2 and Nb2O5 [TiO2 + Nb2O5] is 40 to 80 mass%; The mass ratio of the TiO2 content to the total content of TiO2 and Nb2O5 [TiO2 / (TiO2+Nb2O5)] is 0.3 or more, The refractive index nd is 1.88 or more, The ratio of refractive index nd to specific gravity [refractive index nd / specific gravity] is 0.50 or more.

[0260] In the optical glass according to the third embodiment, the SiO2 content is 1 to 50%. The lower limit of the SiO2 content is preferably 10%, and more preferably 12%, 15%, 18%, and 20% in that order. The upper limit of the SiO2 content is preferably 40%, and more preferably 38%, 35%, 33%, and 30% in that order.

[0261] SiO2 is a glass network-forming component. By setting the SiO2 content within the above range, the thermal stability, chemical durability, and weather resistance of the glass can be improved, and the viscosity of the glass melt can be increased. On the other hand, if the SiO2 content is too high, the refractive index of the glass decreases, and the desired optical properties may not be obtained.

[0262] In the optical glass according to the third embodiment, the TiO2 content is 1 to 50%. The lower limit of the TiO2 content is preferably 10%, and more preferably 13%, 15%, 18%, and 20% in that order. The upper limit of the TiO2 content is preferably 50%, and more preferably 45%, 40%, and 35% in that order.

[0263] By setting the TiO2 content within the above range, the refractive index can be increased and the stability of the glass can be improved. Furthermore, the refractive index can be increased without increasing the specific gravity. On the other hand, if the TiO2 content is too high, the thermal stability may be reduced.

[0264] In the optical glass according to the third embodiment, the Nb2O5 content is 1 to 50%. The lower limit of the Nb2O5 content is preferably 10%, and more preferably 13% and 15% in that order. The upper limit of the Nb2O5 content is preferably 50%, and more preferably 45%, 40%, and 35% in that order.

[0265] By setting the content of Nb2O5 within the above range, the refractive index can be increased and the stability of the glass can be improved. On the other hand, if the content of Nb2O5 is too high, the specific gravity may increase and the thermal stability may decrease.

[0266] In the optical glass according to the third embodiment, the Na2O content is 0 to 8%. The lower limit of the Na2O content is preferably 0.5%, and more preferably 1.0%, 1.5%, and 2.0% in that order. The upper limit of the Na2O content is preferably 7%, and more preferably 6.5%, 5.5%, and 4.5% in that order.

[0267] By setting the Na2O content within the above range, the meltability of the glass can be improved. On the other hand, if the Na2O content is too high, the refractive index may decrease and the thermal stability may also decrease.

[0268] In the optical glass according to the third embodiment, the total content of TiO2 and Nb2O5 [TiO2 + Nb2O5] is 40 to 80%. The lower limit of this total content is preferably 42%, with 44%, 46%, and 48% being more preferred in that order. The upper limit of this total content is preferably 70%, with 65%, 60%, and 55% being more preferred in that order.

[0269] By setting the total content [TiO2 + Nb2O5] within the above range, it is possible to increase the refractive index and obtain glass having desired optical properties.

[0270] In the optical glass according to the third embodiment, the mass ratio of the TiO2 content to the total content of TiO2 and Nb2O5 [TiO2 / (TiO2+Nb2O5)] is 0.3 or greater. The lower limit of this mass ratio is preferably 0.35, with 0.40 and 0.45 being more preferred. The upper limit of this mass ratio is preferably 0.80, with 0.75, 0.70, and 0.65 being more preferred.

[0271] By setting the mass ratio [TiO2 / (TiO2+Nb2O5)] within the above range, an optical glass with a high refractive index and a reduced specific gravity can be obtained.

[0272] In the optical glass according to the third embodiment, the refractive index nd is 1.88 or greater. The lower limit of the refractive index nd can be 1.89 or 1.90. The upper limit of the refractive index nd can be 2.20, or even 2.15, 2.10, or 2.05. The refractive index can be controlled by adjusting the contents of TiO2, Nb2O5, WO3, Bi2O3, ZrO2, La2O3, Gd2O3, YO3, and Ta2O5, which are glass components that contribute to a high refractive index.

[0273] In the optical glass according to the third embodiment, the ratio of the refractive index nd to the specific gravity [refractive index nd / specific gravity] is 0.50 or greater, preferably 0.52 or greater, and more preferably 0.54 or greater. By keeping the ratio [refractive index nd / specific gravity] within the above range, an optical glass with a high refractive index and a relatively low specific gravity can be obtained.

[0274] Non-limiting examples of the contents, ratios, and properties of glass components other than those described above in the optical glass according to the third embodiment are given below.

[0275] In the optical glass according to the third embodiment, the upper limit of the P2O5 content is preferably 10%, and more preferably 8%, 5%, and 3%, in that order. The P2O5 content may be 0%.

[0276] In order to obtain an optical glass having a high refractive index and a reduced specific gravity, the content of P2O5 is preferably within the above range.

[0277] In the optical glass according to the third embodiment, the upper limit of the B2O3 content is preferably 10%, and more preferably 8%, 5%, and 3% in that order. The lower limit of the B2O3 content is preferably 0%, and more preferably 0.5%, 0.8%, and 1.0% in that order.

[0278] B2O3 is a glass network-forming component. B2O3 has the function of improving the thermal stability of the glass, but if the B2O3 content is too high, the refractive index may decrease. Therefore, it is preferable that the B2O3 content be within the above range.

[0279] In the optical glass according to the third embodiment, the upper limit of the Al2O3 content is preferably 10%, and more preferably 8%, 5%, and 3%, in that order. The Al2O3 content may be 0%.

[0280] Although Al2O3 has the function of increasing chemical durability, if the Al2O3 content is too high, the meltability of the glass may deteriorate, so it is preferable that the Al2O3 content be set within the above range.

[0281] In the optical glass according to the third embodiment, the lower limit of the total content of SiO2 and Al2O3 [SiO2 + Al2O3] is preferably 10%, and more preferably 13%, 15%, 18%, and 20% in that order. The upper limit of this total content is preferably 50%, and more preferably 45%, 40%, 35%, and 30% in that order.

[0282] In order to improve the thermal stability of the glass, the total content [SiO2 + Al2O3] is preferably within the above range.

[0283] In the optical glass according to the third embodiment, the lower limit of the mass ratio of the B2O3 content to the total content of SiO2 and Al2O3 [B2O3 / (SiO2+Al2O3)] is preferably 0.01, and more preferably 0.02, 0.03, and 0.04 in that order. The upper limit of this mass ratio is preferably 0.20, and more preferably 0.18, 0.15, 0.13, and 0.10 in that order.

[0284] From the viewpoint of improving chemical durability and thermal stability, it is preferable that the mass ratio [B2O3 / (SiO2+Al2O3)] is within the above range.

[0285] In the optical glass according to the third embodiment, the lower limit of the total content of B2O3 and P2O5 [B2O3 + P2O5] is preferably 0.5%, more preferably 0.8% and 1.0%, in that order, and the upper limit of this total content is preferably 10%, more preferably 8%, 5%, and 3%, in that order.

[0286] From the viewpoint of improving chemical durability and thermal stability, the total content [B2O3+P2O5] is preferably within the above range.

[0287] In the optical glass according to the third embodiment, the lower limit of the total content of B2O3 and SiO2 [B2O3 + SiO2] is preferably 10%, more preferably 15%, 18%, and 20%, in that order, and the upper limit of this total content is preferably 50%, more preferably 45%, 40%, and 35%, in that order.

[0288] In order to obtain an optical glass with a high refractive index, the total content [B2O3+SiO2] is preferably within the above range.

[0289] In the optical glass according to the third embodiment, the lower limit of the ZrO2 content is preferably 0%, and more preferably 0.1%, 0.5%, and 1.0%, in that order. The upper limit of the ZrO2 content is preferably 10%, and more preferably 8%, 5%, and 3%, in that order. The ZrO2 content may even be 0%.

[0290] ZrO2 is a component that contributes to a high refractive index. On the other hand, if the ZrO2 content is too high, the thermal stability may decrease and the specific gravity may increase. Therefore, it is preferable that the ZrO2 content be within the above range.

[0291] In the optical glass according to the third embodiment, the upper limit of the WO3 content is preferably 10%, and more preferably 8%, 5%, and 3%, in that order. The WO3 content may be 0%.

[0292] WO3 is a component that contributes to a high refractive index. On the other hand, if the WO3 content is too high, the thermal stability may decrease, the specific gravity may increase, and the coloring of the glass may increase, resulting in a decrease in transmittance. Therefore, it is preferable that the WO3 content be within the above range.

[0293] In the optical glass according to the third embodiment, the upper limit of the Bi2O3 content is preferably 10%, and more preferably 8%, 5%, and 3%, in that order. The lower limit of the Bi2O3 content is preferably 0%. The Bi2O3 content may be 0%.

[0294] When an appropriate amount of Bi2O3 is included, it improves the thermal stability of the glass. It is also a component that contributes to a high refractive index. On the other hand, if the Bi2O3 content is too high, the specific gravity increases. Furthermore, the coloring of the glass increases. Therefore, it is preferable that the Bi2O3 content be within the above range.

[0295] In the optical glass according to the third embodiment, the upper limit of the total content of TiO2, Nb2O5, WO3 and Bi2O3 [TiO2 + Nb2O5 + WO3 + Bi2O3] is preferably 80%, more preferably 70% and more preferably 60%, and the lower limit of this total content is preferably 20%, more preferably 25%, 30%, and more preferably 35%.

[0296] TiO2, Nb2O5, WO3 and Bi2O3 are all components that contribute to increasing the refractive index, so it is preferable that the total content [TiO2 + Nb2O5 + WO3 + Bi2O3] is within the above range.

[0297] In the optical glass according to the third embodiment, the lower limit of the LiO content is preferably 0.0%, and more preferably 0.1%, 0.3%, 0.5%, 0.8%, 1.0%, 1.3%, and 1.5%, in that order. The upper limit of the LiO content is preferably 10%, and more preferably 9%, 8%, 7%, 6%, and 5%, in that order.

[0298] Li2O is a component that contributes to lowering the specific gravity and, among alkali metals, is a component that particularly contributes to increasing the refractive index. On the other hand, if the Li2O content is too high, the thermal stability may decrease. Therefore, it is preferable that the Li2O content be within the above range.

[0299] In the optical glass according to the third embodiment, the upper limit of the K2O content is preferably 10%, and more preferably 8%, then 5%. The lower limit of the K2O content is preferably 0%, and more preferably 0.5%, then 1.0%, then 1.5%, then 2.0%. The K2O content may even be 0%.

[0300] K2O has the function of improving the meltability of glass. On the other hand, if the K2O content is too high, the refractive index may decrease and the thermal stability may also decrease. Therefore, it is preferable that the K2O content be within the above range.

[0301] In the optical glass according to the third embodiment, the upper limit of the Cs2O content is preferably 5%, and more preferably 3%, and 1% in that order. The lower limit of the Cs2O content is preferably 0%.

[0302] Cs2O has the function of improving the thermal stability of the glass, but if its content increases, the chemical durability and weather resistance decrease, so the Cs2O content is preferably set within the above range.

[0303] In the optical glass according to the third embodiment, the lower limit of the mass ratio of the LiO content to the total content of LiO, NaO, and KO [LiO / (LiO+NaO+KO)] is preferably 0.00, and more preferably 0.10, 0.15, 0.20, and 0.25 in that order. The upper limit of this mass ratio is preferably 1.00, and more preferably 0.80, 0.75, 0.70, and 0.65 in that order.

[0304] In order to obtain an optical glass having a high refractive index and a reduced specific gravity, the mass ratio [Li2O / (Li2O+Na2O+K2O)] is preferably within the above range.

[0305] In the optical glass according to the third embodiment, the lower limit of the total content of Na2O, K2O, and Cs2O [Na2O + K2O + Cs2O] is preferably 0%, and the upper limit of this total content is preferably 11.0%, and more preferably 10.0%, 9.0%, 8.0%, 7.0%, and 6.0%, in that order.

[0306] In order to maintain a high refractive index while maintaining the thermal stability of the glass, the total content [Na2O+K2O+Cs2O] is preferably within the above range.

[0307] In the optical glass according to the third embodiment, the lower limit of the total content of Li2O, Na2O, K2O, and Cs2O [Li2O + Na2O + K2O + Cs2O] is preferably 1.5%, more preferably 2%, 4%, and 6%, in that order. The upper limit of this total content is preferably 15%, more preferably 13% and 10%, in that order.

[0308] In order to obtain an optical glass having excellent melting properties, the total content [Li2O+Na2O+K2O+Cs2O] is preferably within the above range.

[0309] In the optical glass according to the third embodiment, the lower limit of the mass ratio of the LiO content to the total content of LiO, NaO, KO, and CsO [LiO / (LiO+NaO+KO+CsO)] is preferably 0.00, and more preferably 0.10, 0.15, 0.20, and 0.25 in that order. The upper limit of this mass ratio is preferably 1.00, and more preferably 0.80, 0.75, 0.70, and 0.65 in that order.

[0310] In order to obtain an optical glass having a high refractive index and a reduced specific gravity, the mass ratio [Li2O / (Li2O+Na2O+K2O+Cs2O)] is preferably within the above range.

[0311] In the optical glass according to the third embodiment, the upper limit of the MgO content is preferably 20%, and more preferably 15%, 10%, and 5%, in that order. The lower limit of the MgO content is preferably 0%.

[0312] In the optical glass according to the third embodiment, the lower limit of the CaO content is preferably 1%, and more preferably 3%, 5%, and 8%, in that order. The upper limit of the CaO content is preferably 20%, and more preferably 18%, 15%, and 13%, in that order.

[0313] MgO and CaO have the function of improving the meltability of glass. On the other hand, if their contents are too high, thermal stability may decrease. Therefore, it is preferable that the contents of MgO and CaO are each within the above ranges.

[0314] In the optical glass according to the third embodiment, the upper limit of the SrO content is preferably 10%, and more preferably 8%, 5%, and 3%, in that order. The lower limit of the SrO content is preferably 0%.

[0315] SrO improves the meltability of glass and increases the refractive index. However, if the SrO content is too high, the thermal stability may decrease and the specific gravity may increase. Therefore, it is preferable that the SrO content be within the above range.

[0316] In the optical glass according to the third embodiment, the BaO content is preferably 20% or less, and more preferably 17% or less, less than 16.0%, 15% or less, 13% or less, and 10% or less, in that order. The lower limit of the BaO content is preferably 0%.

[0317] By setting the BaO content within the above range, the meltability of the glass can be improved and the refractive index can be increased. On the other hand, if the BaO content is too high, the thermal stability may decrease and the specific gravity may increase.

[0318] In the optical glass according to the third embodiment, the upper limit of the ZnO content is preferably 10%, and more preferably 8%, 5%, and 3%, in that order. The lower limit of the ZnO content is preferably 0%.

[0319] ZnO is a glass component that improves the thermal stability of glass. However, if the ZnO content is too high, the specific gravity increases. Therefore, 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.

[0320] In the optical glass according to the third embodiment, the upper limit of the total content of MgO, CaO, SrO, BaO, and ZnO [MgO + CaO + SrO + BaO + ZnO] is preferably 40%, more preferably 35%, 30%, and 25%, in that order. The lower limit of this total content is preferably 3%, more preferably 5%, 8%, and 10%, in that order. From the viewpoints of suppressing an increase in specific gravity and maintaining thermal stability without impeding high dispersion, it is preferable that the total content be within the above range.

[0321] In the optical glass according to the third embodiment, the upper limit of the Ta2O5 content is preferably 10%, and more preferably 8%, 5%, and 3%, in that order. The lower limit of the Ta2O5 content is preferably 0%.

[0322] Ta2O5 is a component that contributes to a high refractive index. It is also a glass component that improves the thermal stability of the glass and reduces Pg and F. On the other hand, if the Ta2O5 content is high, the thermal stability of the glass decreases, and when the glass is melted, the glass raw material is more likely to remain unmelted. In addition, the specific gravity increases. Therefore, it is preferable that the Ta2O5 content be within the above range.

[0323] In the optical glass according to the third embodiment, the upper limit of the La2O3 content is preferably 10%, and more preferably 8%, 5%, and 3%, in that order. The lower limit of the La2O3 content is preferably 0%.

[0324] La2O3 is a component that contributes to a high refractive index. However, as the La2O3 content increases, the specific gravity increases and the thermal stability of the glass decreases. Therefore, from the viewpoint of suppressing the increase in specific gravity and the decrease in the thermal stability of the glass, it is preferable that the La2O3 content be within the above range.

[0325] In the optical glass according to the third embodiment, the upper limit of the Y2O3 content is preferably 10%, and more preferably 8%, 5%, and 3%, in that order. The lower limit of the Y2O3 content is preferably 0%.

[0326] Y2O3 is a component that contributes to a high refractive index. On the other hand, if the Y2O3 content is too high, the thermal stability of the glass decreases, making the glass more susceptible to devitrification during production. Therefore, from the viewpoint of preventing a decrease in the thermal stability of the glass, it is preferable that the Y2O3 content be within the above range.

[0327] In the optical glass according to the third embodiment, the Sc2O3 content is preferably 2% or less, and the lower limit of the Sc2O3 content is preferably 0%.

[0328] In the optical glass according to the third embodiment, the content of HfO2 is preferably 2% or less, and the lower limit of the content of HfO2 is preferably 0%.

[0329] Sc2O3 and HfO2 have the function of increasing the dispersibility of the glass, but are expensive components, so it is preferable that the contents of Sc2O3 and HfO2 are each within the above ranges.

[0330] In the optical glass according to the third embodiment, the content of Lu2O3 is preferably 2% or less, and the lower limit of the content of Lu2O3 is preferably 0%.

[0331] Lu2O3 has the function of increasing the dispersibility of the glass, but because it has a large molecular weight, it is also a glass component that increases the specific gravity of the glass, so the content of Lu2O3 is preferably within the above range.

[0332] In the optical glass according to the third embodiment, the GeO2 content is preferably 2% or less, and the lower limit of the GeO2 content is preferably 0%.

[0333] GeO2 has the function of increasing the high dispersibility of the glass, but is an extremely expensive component among commonly used glass components, so from the perspective of reducing the manufacturing cost of the glass, it is preferable that the GeO2 content be in the above range.

[0334] In the optical glass according to the third embodiment, the upper limit of the Gd2O3 content is preferably 3.0%, more preferably 2.0%, and the lower limit of the Gd2O3 content is preferably 0%.

[0335] Gd2O3 is a component that contributes to a high refractive index. However, if the Gd2O3 content is too high, the thermal stability of the glass decreases. Furthermore, if the Gd2O3 content is too high, the specific gravity of the glass increases, which is undesirable. Therefore, from the viewpoint of suppressing an increase in specific gravity while maintaining good thermal stability of the glass, it is preferable that the Gd2O3 content be within the above range.

[0336] In the optical glass according to the third embodiment, the Yb2O3 content is preferably 2% or less, and the lower limit of the Yb2O3 content is preferably 0%.

[0337] Yb2O3 has a larger molecular weight than La2O3, Gd2O3, and Y2O3, and therefore increases the specific gravity of the glass. This increases the specific gravity of the glass, which in turn increases the mass of the optical element. Therefore, it is desirable to reduce the Yb2O3 content to prevent the increase in the specific gravity of the glass.

[0338] Furthermore, if the Yb2O3 content is too high, the thermal stability of the glass decreases. From the viewpoint of preventing a decrease in the thermal stability of the glass and suppressing an increase in specific gravity, it is preferable that the Yb2O3 content be within the above range.

[0339] In the optical glass according to the third embodiment, the upper limit of the total content of La2O3, Gd2O3, and Y2O3 [La2O3 + Gd2O3 + Y2O3] is preferably 10%, and more preferably 8%, 5%, and 3%, in that order. The lower limit of this total content is 0%. This total content may even be 0%.

[0340] From the viewpoint of suppressing an increase in specific gravity and maintaining good thermal stability, the total content [La2O3+Gd2O3+Y2O3] is preferably within the above range.

[0341] In the optical glass according to the third embodiment, the mass ratio [LiO / {100-(SiO+B+P+GeO)}] of the LiO content to the total content of glass components other than SiO, B, O, P, and GeO is preferably 0.00, and more preferably 0.02, 0.03, 0.04, 0.05, and 0.06 in this order. The upper limit of this mass ratio is preferably 0.20, and more preferably 0.15, 0.13, and 0.10 in this order.

[0342] The total content of all glass components is 100% by mass. Therefore, the total content of glass components other than SiO2, B2O3, P2O5, and GeO2 is expressed as [100 - (SiO2 + B2O3 + P2O5 + GeO2)]. From the perspective of obtaining an optical glass with a high refractive index and a low specific gravity, it is preferable that the mass ratio [Li2O / {100 - (SiO2 + B2O3 + P2O5 + GeO2)}] be within the above range.

[0343] In the optical glass according to the third embodiment, the mass ratio of the TiO content to the total content of TiO, NbO, WO, ZrO, SrO, BaO, ZnO, LaO, GdO, YO, TaO, and BiO [TiO / (TiO + NbO + WO + ZrO + SrO + BaO + ZnO + LaO + GdO + YO + TaO + BiO)] is preferably 0.40, and more preferably 0.42, 0.44, 0.46, 0.48, and 0.50, in that order. The upper limit of this mass ratio is preferably 0.80, and more preferably 0.75, 0.70, and 0.65, in that order.

[0344] From the viewpoint of increasing the refractive index while suppressing an increase in specific gravity, it is preferable that the mass ratio [TiO2 / (TiO2+Nb2O5+WO3+ZrO2+SrO+BaO+ZnO+La2O3+Gd2O3+Y2O3+Ta2O5+Bi2O3)] be in the above range.

[0345] The optical glass according to the third embodiment is preferably composed primarily of the above-mentioned glass components, namely, SiO2, TiO2, and Nb2O5 as essential components, and Na2O, P2O5, B2O3, Al2O3, ZrO2, WO3, Bi2O3, Li2O, K2O, Cs2O, MgO, CaO, SrO, BaO, ZnO, Ta2O5, La2O3, Y2O3, Sc2O3, HfO2, Lu2O3, GeO2, Gd2O3, and Yb2O3 as optional components, and the total content of the above-mentioned glass components is preferably 95% or more, more preferably 98% or more, even more preferably 99% or more, and even more preferably 99.5% or more.

[0346] The optical glass according to the third embodiment is preferably composed essentially of the above glass components, but may contain other components as long as they do not impair the effects of the present invention. Furthermore, the present invention does not exclude the inclusion of unavoidable impurities.

[0347] (Other ingredients) Pb, As, Cd, Tl, Be, and Se are all toxic. Therefore, it is particularly preferable that the optical glass according to the third embodiment does not contain these elements as glass components. The content of each of the above elements, calculated as an oxide, is preferably less than 0.5%, and more preferably less than 0.1%, less than 0.05%, and less than 0.01%, in that order.

[0348] U, Th, and Ra are all radioactive elements. Therefore, it is particularly preferable that the optical glass according to the third embodiment does not contain these elements as glass components. The content of each of the above elements, calculated as an oxide, is preferably less than 0.5%, more preferably less than 0.1%, less than 0.05%, and even more preferably less than 0.01%, in that order.

[0349] V, Cr, Mn, Fe, Co, Ni, Cu, Pr, Nd, Pm, Sm, Eu, Tb, Dy, Ho, Er, and Tm increase the coloration of the glass and can be sources of fluorescence. Therefore, it is particularly preferable that the optical glass according to the third embodiment does not contain these elements as glass components. The content of each of the above elements, calculated as oxide, is preferably less than 0.5%, and more preferably less than 0.1%, less than 0.05%, and less than 0.01%, in that order.

[0350] Sb (Sb2O3) and Ce (CeO2) are elements that can be added as optional elements and function as fining agents. Of these, Sb (Sb2O3) is a fining agent with a large fining effect. Ce (CeO2) has a smaller fining effect than Sb (Sb2O3). Ce (CeO2) tends to intensify the coloring of glass when added in large amounts.

[0351] In this specification, the contents of Sb (Sb2O3) and Ce (CeO2) are expressed as exclusive percentages and are not included in the total content of all glass components expressed on an oxide basis. That is, in this specification, the total content of all glass components excluding Sb (Sb2O3) and Ce (CeO2) is taken to be 100 mass%.

[0352] The Sb2O3 content is expressed as an exclusive percentage. That is, in the optical glass according to the third embodiment, when the total content of all glass components other than Sb2O3 and CeO2 is taken as 100 mass%, the Sb2O3 content is preferably 1 mass% or less, and more preferably 0.1 mass% or less, 0.05 mass% or less, and 0.03 mass% or less. The Sb2O3 content may be 0 mass%.

[0353] The CeO2 content is also expressed as an exclusive ratio. That is, in the optical glass according to the third embodiment, when the total content of all glass components other than CeO2 and Sb2O3 is taken as 100 mass%, the CeO2 content is preferably 2 mass% or less, and more preferably 1 mass% or less, 0.5 mass% or less, and 0.1 mass% or less, in that order. The CeO2 content may be 0 mass%. By keeping the CeO2 content within the above range, the clarity of the glass can be improved.

[0354] (Glass characteristics) <Abbe number νd> In the optical glass according to the third embodiment, the Abbe number vd is preferably 15 to 30. The Abbe number vd may be 18 to 25, or may be 20 to 24. By setting the Abbe number vd within the above range, it is possible to obtain a glass with the desired dispersibility. The Abbe number vd can be controlled by adjusting the contents of TiO2, Nb2O5, WO3, and Bi2O3, which are glass components that contribute to high dispersion.

[0355] <Specific gravity of glass> The optical glass according to the third embodiment is a high refractive index glass, but does not have a high specific gravity. If the specific gravity of the glass can be reduced, the weight of the lens can be reduced. On the other hand, if the specific gravity is too low, it will result in a decrease in thermal stability.

[0356] Therefore, in the optical glass according to the third embodiment, the specific gravity is preferably 4.2 or less, and more preferably 4.0 or less, 3.8 or less, 3.6 or less, and 3.4 or less in that order.

[0357] The specific gravity can be controlled by adjusting the content of each glass component. In particular, by adjusting the content of Li2O and TiO2, the specific gravity can be reduced while maintaining a high refractive index.

[0358] In the optical glass according to the third embodiment, the refractive index nd and specific gravity preferably satisfy the following formula (1), more preferably the following formula (2), and even more preferably the following formula (3): When the refractive index nd and specific gravity satisfy the following formula, an optical glass with a high refractive index and a relatively low specific gravity can be obtained. nd≧0.2×specific gravity+1.18…(1) nd≧0.2×specific gravity+1.19…(2) nd≧0.2×specific gravity+1.20…(3)

[0359] <Glass transition temperature Tg> In the optical glass according to the third embodiment, the upper limit of the glass transition temperature Tg is preferably 690°C, and more preferably 680°C, 660°C, 650°C, 630°C, and 600°C in that order. There is no particular lower limit for the glass transition temperature Tg, but it is usually 500°C, and preferably 550°C.

[0360] The glass transition temperature Tg can be controlled by adjusting the total content of alkali metals.

[0361] By ensuring that the upper limit of the glass transition temperature Tg satisfies the above range, increases in the molding temperature and annealing temperature during glass reheat pressing can be suppressed, and thermal damage to the reheat press molding equipment and annealing equipment can be reduced.

[0362] When the lower limit of the glass transition temperature Tg satisfies the above range, it becomes easier to maintain good reheat press moldability and good thermal stability of the glass while maintaining the desired Abbe number and refractive index.

[0363] <Light transmittance of glass> The light transmittance of the optical glass according to the third embodiment can be evaluated by the coloring degrees λ80, λ70 and λ5. The spectral transmittance of a glass sample with a thickness of 10.0 mm ± 0.1 mm is measured in the wavelength range of 200 to 700 nm, and the wavelength at which the external transmittance is 80% is defined as λ80, the wavelength at which the external transmittance is 70% is defined as λ70, and the wavelength at which the external transmittance is 5% is defined as λ5.

[0364] The λ80 of the optical glass according to the first embodiment is preferably 700 nm or less, more preferably 650 nm or less, and even more preferably 600 nm or less. λ70 is preferably 600 nm or less, more preferably 550 nm or less, and even more preferably 500 nm or less. λ5 is preferably 500 nm or less, more preferably 450 nm or less, and even more preferably 400 nm or less.

[0365] (Optical glass manufacturing) The optical glass according to the third embodiment may be produced by blending glass raw materials to obtain the above-described predetermined composition, and then using the blended glass raw materials in accordance with a known glass manufacturing method. For example, a plurality of compounds may be blended and thoroughly mixed to form a batch raw material, which is then placed in a quartz crucible or platinum crucible and roughly melted (rough melted). The molten material obtained by rough melting is then rapidly cooled and pulverized to produce cullet. The cullet is then placed in a platinum crucible, heated, and remelted (remelted) to produce a glass melt, which is then further refined and homogenized, and then formed and slowly cooled to obtain the optical glass. Known methods may be used to form and slowly cool the glass melt.

[0366] The compounds used when preparing the batch raw materials are not particularly limited as long as they can introduce desired glass components into the glass to achieve desired contents. Examples of such compounds include oxides, carbonates, nitrates, hydroxides, and fluorides.

[0367] (Manufacturing of optical elements, etc.) To produce an optical element using the optical glass according to the third embodiment, a known method may be applied. For example, in the production of the optical glass, molten glass is poured into a mold and formed into a plate to produce a glass material made of the optical glass according to the present invention. The obtained glass material is cut, ground, and polished as appropriate to produce cut pieces of a size and shape suitable for press molding. The cut pieces are heated and softened, and press-molded (reheat pressed) using a known method to produce an optical element blank that approximates the shape of the optical element. The optical element blank is annealed, and then ground and polished using a known method to produce an optical element.

[0368] The optically functional surface of the fabricated optical element may be coated with an anti-reflection film, a total reflection film, or the like depending on the intended use.

[0369] According to one aspect of the present invention, an optical element made of the above optical glass can be provided. Examples of optical elements include lenses such as flat lenses, spherical lenses, and aspherical lenses, as well as prisms, diffraction gratings, and light guide plates. Examples of lens shapes include biconvex lenses, plano-convex lenses, biconcave lenses, plano-concave lenses, convex meniscus lenses, and concave meniscus lenses. Examples of uses for light guide plates include display devices such as augmented reality (AR) display type eyeglasses and mixed reality (MR) display type eyeglasses. Such light guide plates are plate-shaped glass attached to the frame of eyeglasses and made of the above optical glass. If necessary, a diffraction grating may be formed on the surface of the light guide plate to change the direction of propagation of light propagating through the light guide plate by repeated total reflection. The diffraction grating can be formed by a known method. When an eyeglass device having the above light guide plate is worn, light propagating through the light guide plate enters the pupil, thereby exhibiting augmented reality (AR) display or mixed reality (MR) display functions. Such eyeglass-type devices are disclosed, for example, in JP-A-2017-534352. The light guide plate can be produced by a known method. The optical element can be manufactured by a method including a step of processing a glass molded body made of the optical glass. Examples of processing include cutting, milling, rough grinding, fine grinding, and polishing. By using the glass described above during such processing, breakage can be reduced, enabling a stable supply of high-quality optical elements.

[0370] (Image display device) The image display device according to the third embodiment can be similar to that of the first embodiment.

[0371] Fourth embodiment The optical glass according to the fourth embodiment is the mass ratio of the LiO content to the total content of glass components other than SiO, B, P, and GeO [LiO / {100-(SiO+B+P+GeO)+GeO)] is 0.02 or more; the mass ratio of the TiO2 content to the total content of TiO2, Nb2O5, WO3, ZrO2, SrO, BaO, ZnO, La2O3, Gd2O3, Y2O3, Ta2O5, and Bi2O3 [TiO2 / (TiO2+Nb2O5+WO3+ZrO2+SrO+BaO+ZnO+La2O3+Gd2O3+Y2O3+Ta2O5+Bi2O3)] is 0.40 or more; The refractive index nd is 1.86 or more.

[0372] In the optical glass according to the fourth embodiment, the mass ratio [LiO / {100-(SiO+B+P+GeO)}] of the content of LiO to the total content of glass components other than SiO, B, O, P, and GeO is 0.02 or greater. The lower limit of this mass ratio is preferably 0.03, with 0.04, 0.05, and 0.06 being more preferred. The upper limit of this mass ratio is preferably 0.20, with 0.15, 0.13, and 0.10 being more preferred.

[0373] The total content of all glass components is 100% by mass. Therefore, the total content of glass components other than SiO2, B2O3, P2O5, and GeO2 is expressed as [100 - (SiO2 + B2O3 + P2O5 + GeO2)]. By keeping the mass ratio [Li2O / {100 - (SiO2 + B2O3 + P2O5 + GeO2)}] within the above range, optical glass with a high refractive index and low specific gravity can be obtained.

[0374] In the optical glass according to the fourth embodiment, the mass ratio of the TiO content to the total content of TiO, NbO, WO, ZrO, SrO, BaO, ZnO, LaO, GdO, YO, TaO, and BiO [TiO / (TiO + NbO + WO + ZrO + SrO + BaO + ZnO + LaO + GdO + YO + TaO + BiO)] is 0.40 or greater. The lower limit of this mass ratio is preferably 0.42, with 0.44, 0.46, 0.48, and 0.50 being more preferred. The upper limit of this mass ratio is preferably 0.80, with 0.75, 0.70, and 0.65 being more preferred.

[0375] By setting the mass ratio [TiO2 / (TiO2+Nb2O5+WO3+ZrO2+SrO+BaO+ZnO+La2O3+Gd2O3+Y2O3+Ta2O5+Bi2O3)] within the above range, it is possible to increase the refractive index while suppressing an increase in specific gravity.

[0376] Non-limiting examples of the contents of glass components in the optical glass according to the fourth embodiment and ratios other than those mentioned above are shown below.

[0377] In the optical glass according to the fourth embodiment, the lower limit of the SiO content is preferably 10%, and more preferably 12%, 15%, 18%, and 20% in that order. The upper limit of the SiO content is preferably 40%, and more preferably 38%, 35%, 33%, and 30% in that order.

[0378] SiO2 is a glass network-forming component. In order to improve the thermal stability, chemical durability, and weather resistance of the glass and to increase the viscosity of the glass melt, the SiO2 content is preferably within the above range. If the SiO2 content is too high, the refractive index of the glass will decrease, and the desired optical properties may not be obtained.

[0379] In the optical glass according to the fourth embodiment, the upper limit of the P2O5 content is preferably 10%, and more preferably 8%, 5%, and 3%, in that order. The P2O5 content may be 0%.

[0380] In order to obtain an optical glass having a high refractive index and a reduced specific gravity, the content of P2O5 is preferably within the above range.

[0381] In the optical glass according to the fourth embodiment, the upper limit of the B2O3 content is preferably 10%, and more preferably 8%, 5%, and 3% in that order. The lower limit of the B2O3 content is preferably 0%, and more preferably 0.5%, 0.8%, and 1.0% in that order.

[0382] B2O3 is a glass network-forming component. B2O3 has the function of improving the thermal stability of the glass, but if the B2O3 content is too high, the refractive index may decrease. Therefore, it is preferable that the B2O3 content be within the above range.

[0383] In the optical glass according to the fourth embodiment, the upper limit of the Al2O3 content is preferably 10%, and more preferably 8%, 5%, and 3%, in that order. The Al2O3 content may be 0%.

[0384] Although Al2O3 has the function of increasing chemical durability, if the Al2O3 content is too high, the meltability of the glass may deteriorate, so it is preferable that the Al2O3 content be set within the above range.

[0385] In the optical glass according to the fourth embodiment, the lower limit of the total content of SiO2 and Al2O3 [SiO2 + Al2O3] is preferably 10%, and more preferably 13%, 15%, 18%, and 20% in that order. The upper limit of this total content is preferably 50%, and more preferably 45%, 40%, 35%, and 30% in that order.

[0386] In order to improve the thermal stability of the glass, the total content [SiO2 + Al2O3] is preferably within the above range.

[0387] In the optical glass according to the fourth embodiment, the lower limit of the mass ratio of the B2O3 content to the total content of SiO2 and Al2O3 [B2O3 / (SiO2+Al2O3)] is preferably 0.01, and more preferably 0.02, 0.03, and 0.04 in that order. The upper limit of this mass ratio is preferably 0.20, and more preferably 0.18, 0.15, 0.13, and 0.10 in that order.

[0388] From the viewpoint of improving chemical durability and thermal stability, it is preferable that the mass ratio [B2O3 / (SiO2+Al2O3)] is within the above range.

[0389] In the optical glass according to the fourth embodiment, the lower limit of the total content of B2O3 and P2O5 [B2O3 + P2O5] is preferably 0.5%, more preferably 0.8% and 1.0%, in that order, and the upper limit of this total content is preferably 10%, more preferably 8%, 5%, and 3%, in that order.

[0390] From the viewpoint of improving chemical durability and thermal stability, the total content [B2O3+P2O5] is preferably within the above range.

[0391] In the optical glass according to the fourth embodiment, the lower limit of the total content of B2O3 and SiO2 [B2O3 + SiO2] is preferably 10%, more preferably 15%, 18%, and 20%, in that order, and the upper limit of this total content is preferably 50%, more preferably 45%, 40%, and 35%, in that order.

[0392] In order to obtain an optical glass with a high refractive index, the total content [B2O3+SiO2] is preferably within the above range.

[0393] In the optical glass according to the fourth embodiment, the lower limit of the ZrO2 content is preferably 0%, and more preferably 0.1%, 0.5%, and 1.0%, in that order. The upper limit of the ZrO2 content is preferably 10%, and more preferably 8%, 5%, and 3%, in that order. The ZrO2 content may even be 0%.

[0394] ZrO2 is a component that contributes to a high refractive index. On the other hand, if the ZrO2 content is too high, the thermal stability may decrease and the specific gravity may increase. Therefore, it is preferable that the ZrO2 content be within the above range.

[0395] In the optical glass according to the fourth embodiment, the lower limit of the TiO2 content is preferably 10%, and more preferably 13%, 15%, 18%, and 20% in that order. The upper limit of the TiO2 content is preferably 50%, and more preferably 45%, 40%, and 35% in that order.

[0396] TiO2 is a component that contributes to a high refractive index and improves glass stability. It can also increase the refractive index without increasing the specific gravity. On the other hand, if the TiO2 content is too high, thermal stability may decrease. Therefore, it is preferable that the TiO2 content be within the above range.

[0397] In the optical glass according to the fourth embodiment, the lower limit of the Nb2O5 content is preferably 10%, more preferably 13%, and more preferably 15%. The upper limit of the Nb2O5 content is preferably 50%, more preferably 45%, 40%, and more preferably 35%.

[0398] Nb2O5 is a component that contributes to increasing the refractive index and improves glass stability. However, if the Nb2O5 content is too high, the specific gravity may increase and the thermal stability may decrease. Therefore, it is preferable that the Nb2O5 content be within the above range.

[0399] In the optical glass according to the fourth embodiment, the lower limit of the total content of TiO2 and Nb2O5 [TiO2 + Nb2O5] is preferably 20%, more preferably 25%, 30%, and 35%, in that order, and the upper limit of this total content is preferably 70%, more preferably 65%, 60%, and 55%, in that order.

[0400] TiO2 and Nb2O5 are components that contribute to increasing the refractive index, and therefore, in order to obtain glass with the desired optical properties, it is preferable that the total content of TiO2 and Nb2O5 be within the above range.

[0401] In the optical glass according to the fourth embodiment, the lower limit of the mass ratio of the TiO2 content to the total content of TiO2 and Nb2O5 [TiO2 / (TiO2+Nb2O5)] is preferably 0.20, and more preferably 0.25, 0.30, and 0.35 in that order. The upper limit of this mass ratio is preferably 0.80, and more preferably 0.75, 0.70, and 0.65 in that order.

[0402] In order to obtain an optical glass with a high refractive index and a reduced specific gravity, it is preferable that the mass ratio [TiO2 / (TiO2+Nb2O5)] is within the above range.

[0403] In the optical glass according to the fourth embodiment, the upper limit of the WO3 content is preferably 10%, and more preferably 8%, 5%, and 3%, in that order. The WO3 content may be 0%.

[0404] WO3 is a component that contributes to a high refractive index. On the other hand, if the WO3 content is too high, the thermal stability may decrease, the specific gravity may increase, and the coloring of the glass may increase, resulting in a decrease in transmittance. Therefore, it is preferable that the WO3 content be within the above range.

[0405] In the optical glass according to the fourth embodiment, the upper limit of the Bi2O3 content is preferably 10%, and more preferably 8%, 5%, and 3%, in that order. The lower limit of the Bi2O3 content is preferably 0%. The Bi2O3 content may be 0%.

[0406] When an appropriate amount of Bi2O3 is included, it improves the thermal stability of the glass. It is also a component that contributes to a high refractive index. On the other hand, if the Bi2O3 content is too high, the specific gravity increases. Furthermore, the coloring of the glass increases. Therefore, it is preferable that the Bi2O3 content be within the above range.

[0407] In the optical glass according to the fourth embodiment, the upper limit of the total content of TiO2, Nb2O5, WO3 and Bi2O3 [TiO2 + Nb2O5 + WO3 + Bi2O3] is preferably 80%, more preferably 70% and more preferably 60%, and the lower limit of this total content is preferably 20%, more preferably 25%, 30%, and more preferably 35%.

[0408] TiO2, Nb2O5, WO3 and Bi2O3 are all components that contribute to increasing the refractive index, so it is preferable that the total content [TiO2 + Nb2O5 + WO3 + Bi2O3] is within the above range.

[0409] In the optical glass according to the fourth embodiment, the lower limit of the LiO content is preferably 0.1%, and more preferably 0.3%, 0.5%, 0.8%, 1.0%, 1.3%, and 1.5%, in that order. The upper limit of the LiO content is preferably 10%, and more preferably 9%, 8%, 7%, 6%, and 5%, in that order.

[0410] Li2O is a component that contributes to lowering the specific gravity and, among alkali metals, is a component that particularly contributes to increasing the refractive index. On the other hand, if the Li2O content is too high, the thermal stability may decrease. Therefore, it is preferable that the Li2O content be within the above range.

[0411] In the optical glass according to the fourth embodiment, the upper limit of the Na2O content is preferably 10%, and more preferably 9%, 8%, and 7%, in that order. The lower limit of the Na2O content is preferably 0%, and more preferably 0.5%, 1.0%, 1.5%, and 2.0%, in that order.

[0412] In the optical glass according to the fourth embodiment, the upper limit of the K2O content is preferably 10%, and more preferably 8%, then 5%. The lower limit of the K2O content is preferably 0%, and more preferably 0.5%, then 1.0%, then 1.5%, then 2.0%. The K2O content may even be 0%.

[0413] Na2O and K2O have the function of improving the meltability of glass. On the other hand, if their contents are too high, the refractive index may decrease and the thermal stability may also decrease. Therefore, it is preferable that the contents of Na2O and K2O are each within the above ranges.

[0414] In the optical glass according to the fourth embodiment, the upper limit of the Cs2O content is preferably 5%, and more preferably 3%, and 1% in that order. The lower limit of the Cs2O content is preferably 0%.

[0415] Cs2O has the function of improving the thermal stability of the glass, but if its content increases, the chemical durability and weather resistance decrease, so the Cs2O content is preferably set within the above range.

[0416] In the optical glass according to the fourth embodiment, the lower limit of the mass ratio of the LiO content to the total content of LiO, NaO, and KO [LiO / (LiO+NaO+KO)] is preferably 0.10, and more preferably 0.15, 0.20, and 0.25 in that order. The upper limit of this mass ratio is preferably 1.00, and more preferably 0.80, 0.75, 0.70, and 0.65 in that order.

[0417] In order to obtain an optical glass having a high refractive index and a reduced specific gravity, the mass ratio [Li2O / (Li2O+Na2O+K2O)] is preferably within the above range.

[0418] In the optical glass according to the fourth embodiment, the lower limit of the mass ratio of the LiO content to the total content of LiO, NaO, KO, and CsO [LiO / (LiO+NaO+KO+CsO)] is preferably 0.10, and more preferably 0.15, 0.20, and 0.25 in that order. The upper limit of this mass ratio is preferably 1.00, and more preferably 0.80, 0.75, 0.70, and 0.65 in that order.

[0419] In order to obtain an optical glass having a high refractive index and a reduced specific gravity, the mass ratio [Li2O / (Li2O+Na2O+K2O+Cs2O)] is preferably within the above range.

[0420] In the optical glass according to the fourth embodiment, the lower limit of the total content of Na2O, K2O, and Cs2O [Na2O + K2O + Cs2O] is preferably 0%, and the upper limit of this total content is preferably 11.0%, and more preferably 10.0%, 9.0%, 8.0%, 7.0%, and 6.0%, in that order.

[0421] In order to maintain a high refractive index while maintaining the thermal stability of the glass, the total content [Na2O+K2O+Cs2O] is preferably within the above range.

[0422] In the optical glass according to the fourth embodiment, the lower limit of the total content of Li2O, Na2O, K2O, and Cs2O [Li2O + Na2O + K2O + Cs2O] is preferably 1.5%, and more preferably 2%, 4%, and 6% in that order. The upper limit of this total content is preferably 15%, and more preferably 13% and 10% in that order.

[0423] In order to obtain an optical glass having excellent melting properties, the total content [Li2O+Na2O+K2O+Cs2O] is preferably within the above range.

[0424] In the optical glass according to the fourth embodiment, the upper limit of the MgO content is preferably 20%, and more preferably 15%, 10%, and 5%, in that order. The lower limit of the MgO content is preferably 0%.

[0425] In the optical glass according to the fourth embodiment, the lower limit of the CaO content is preferably 1%, and more preferably 3%, 5%, and 8%, in that order. The upper limit of the CaO content is preferably 20%, and more preferably 18%, 15%, and 13%, in that order.

[0426] MgO and CaO have the function of improving the meltability of glass. On the other hand, if their contents are too high, thermal stability may decrease. Therefore, it is preferable that the contents of MgO and CaO are each within the above ranges.

[0427] In the optical glass according to the fourth embodiment, the upper limit of the SrO content is preferably 10%, and more preferably 8%, 5%, and 3%, in that order. The lower limit of the SrO content is preferably 0%.

[0428] SrO improves the meltability of glass and increases the refractive index. However, if the SrO content is too high, the thermal stability may decrease and the specific gravity may increase. Therefore, it is preferable that the SrO content be within the above range.

[0429] In the optical glass according to the fourth embodiment, the upper limit of the BaO content is preferably 20%, and more preferably 17%, 15%, 13%, and 10%, in that order. The lower limit of the BaO content is preferably 0%.

[0430] BaO has the function of improving the meltability of the glass and increasing the refractive index. On the other hand, if the BaO content is too high, the thermal stability may decrease and the specific gravity may increase. Therefore, it is preferable that the BaO content be within the above range.

[0431] In the optical glass according to the fourth embodiment, the upper limit of the ZnO content is preferably 10%, and more preferably 8%, 5%, and 3%, in that order. The lower limit of the ZnO content is preferably 0%.

[0432] ZnO is a glass component that improves the thermal stability of glass. However, if the ZnO content is too high, the specific gravity increases. Therefore, 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.

[0433] In the optical glass according to the fourth embodiment, the upper limit of the total content of MgO, CaO, SrO, BaO, and ZnO [MgO + CaO + SrO + BaO + ZnO] is preferably 40%, more preferably 35%, 30%, and 25%, in that order. The lower limit of this total content is preferably 3%, more preferably 5%, 8%, and 10%, in that order. From the viewpoints of suppressing an increase in specific gravity and maintaining thermal stability without impeding high dispersion, it is preferable that the total content be within the above range.

[0434] In the optical glass according to the fourth embodiment, the upper limit of the Ta2O5 content is preferably 10%, and more preferably 8%, 5%, and 3%, in that order. The lower limit of the Ta2O5 content is preferably 0%.

[0435] Ta2O5 is a component that contributes to a high refractive index. It is also a glass component that improves the thermal stability of the glass and reduces Pg and F. On the other hand, if the Ta2O5 content is high, the thermal stability of the glass decreases, and when the glass is melted, the glass raw material is more likely to remain unmelted. In addition, the specific gravity increases. Therefore, it is preferable that the Ta2O5 content be within the above range.

[0436] In the optical glass according to the fourth embodiment, the upper limit of the La2O3 content is preferably 10%, and more preferably 8%, 5%, and 3%, in that order. The lower limit of the La2O3 content is preferably 0%.

[0437] La2O3 is a component that contributes to a high refractive index. However, as the La2O3 content increases, the specific gravity increases and the thermal stability of the glass decreases. Therefore, from the viewpoint of suppressing the increase in specific gravity and the decrease in the thermal stability of the glass, it is preferable that the La2O3 content be within the above range.

[0438] In the optical glass according to the fourth embodiment, the upper limit of the Y2O3 content is preferably 10%, and more preferably 8%, 5%, and 3%, in that order. The lower limit of the Y2O3 content is preferably 0%.

[0439] Y2O3 is a component that contributes to a high refractive index. On the other hand, if the Y2O3 content is too high, the thermal stability of the glass decreases, making the glass more susceptible to devitrification during production. Therefore, from the viewpoint of preventing a decrease in the thermal stability of the glass, it is preferable that the Y2O3 content be within the above range.

[0440] In the optical glass according to the fourth embodiment, the Sc2O3 content is preferably 2% or less, and the lower limit of the Sc2O3 content is preferably 0%.

[0441] In the optical glass according to the fourth embodiment, the content of HfO2 is preferably 2% or less, and the lower limit of the content of HfO2 is preferably 0%.

[0442] Sc2O3 and HfO2 have the function of increasing the dispersibility of the glass, but are expensive components, so it is preferable that the contents of Sc2O3 and HfO2 are each within the above ranges.

[0443] In the optical glass according to the fourth embodiment, the content of Lu2O3 is preferably 2% or less, and the lower limit of the content of Lu2O3 is preferably 0%.

[0444] Lu2O3 has the function of increasing the dispersibility of the glass, but because it has a large molecular weight, it is also a glass component that increases the specific gravity of the glass, so the content of Lu2O3 is preferably within the above range.

[0445] In the optical glass according to the fourth embodiment, the GeO2 content is preferably 2% or less, and the lower limit of the GeO2 content is preferably 0%.

[0446] GeO2 has the function of increasing the high dispersibility of the glass, but is an extremely expensive component among commonly used glass components, so from the perspective of reducing the manufacturing cost of the glass, it is preferable that the GeO2 content be in the above range.

[0447] In the optical glass according to the fourth embodiment, the upper limit of the Gd2O3 content is preferably 3.0%, more preferably 2.0%, and the lower limit of the Gd2O3 content is preferably 0%.

[0448] Gd2O3 is a component that contributes to a high refractive index. However, if the Gd2O3 content is too high, the thermal stability of the glass decreases. Furthermore, if the Gd2O3 content is too high, the specific gravity of the glass increases, which is undesirable. Therefore, from the viewpoint of suppressing an increase in specific gravity while maintaining good thermal stability of the glass, it is preferable that the Gd2O3 content be within the above range.

[0449] In the optical glass according to the fourth embodiment, the content of Yb2O3 is preferably 2% or less, and the lower limit of the content of Yb2O3 is preferably 0%.

[0450] Yb2O3 has a larger molecular weight than La2O3, Gd2O3, and Y2O3, and therefore increases the specific gravity of the glass. This increases the specific gravity of the glass, which in turn increases the mass of the optical element. Therefore, it is desirable to reduce the Yb2O3 content to prevent the increase in the specific gravity of the glass.

[0451] Furthermore, if the Yb2O3 content is too high, the thermal stability of the glass decreases. From the viewpoint of preventing a decrease in the thermal stability of the glass and suppressing an increase in specific gravity, it is preferable that the Yb2O3 content be within the above range.

[0452] In the optical glass according to the fourth embodiment, the upper limit of the total content of La2O3, Gd2O3, and Y2O3 [La2O3 + Gd2O3 + Y2O3] is preferably 10%, and more preferably 8%, 5%, and 3%, in that order. The lower limit of this total content is 0%. This total content may even be 0%.

[0453] From the viewpoint of suppressing an increase in specific gravity and maintaining good thermal stability, the total content [La2O3+Gd2O3+Y2O3] is preferably within the above range.

[0454] The optical glass according to the fourth embodiment is preferably composed primarily of the above-mentioned glass components, namely, Li2O and TiO2 as essential components and SiO2, P2O5, B2O3, Al2O3, ZrO2, Nb2O5, WO3, Bi2O3, Na2O, K2O, Cs2O, MgO, CaO, SrO, BaO, ZnO, Ta2O5, La2O3, Y2O3, Sc2O3, HfO2, Lu2O3, GeO2, Gd2O3, and Yb2O3 as optional components, and the total content of the above-mentioned glass components is preferably 95% or more, more preferably 98% or more, even more preferably 99% or more, and even more preferably 99.5% or more.

[0455] The optical glass according to the fourth embodiment is preferably composed essentially of the above glass components, but may contain other components as long as they do not impair the effects of the present invention. Furthermore, the present invention does not exclude the inclusion of unavoidable impurities.

[0456] (Other ingredients) Pb, As, Cd, Tl, Be, and Se are all toxic. Therefore, it is particularly preferable that the optical glass according to the fourth embodiment does not contain these elements as glass components. The content of each of the above elements, calculated as an oxide, is preferably less than 0.5%, and more preferably less than 0.1%, less than 0.05%, and less than 0.01%, in that order.

[0457] U, Th, and Ra are all radioactive elements. Therefore, it is particularly preferable that the optical glass according to the fourth embodiment does not contain these elements as glass components. The content of each of the above elements, calculated as an oxide, is preferably less than 0.5%, and more preferably less than 0.1%, less than 0.05%, and less than 0.01%, in that order.

[0458] V, Cr, Mn, Fe, Co, Ni, Cu, Pr, Nd, Pm, Sm, Eu, Tb, Dy, Ho, Er, and Tm increase the coloration of the glass and can be sources of fluorescence. Therefore, it is particularly preferable that the optical glass according to the fourth embodiment does not contain these elements as glass components. The content of each of the above elements, calculated as oxide, is preferably less than 0.5%, and more preferably less than 0.1%, less than 0.05%, and less than 0.01%, in that order.

[0459] Sb (Sb2O3) and Ce (CeO2) are elements that can be added as optional elements and function as fining agents. Of these, Sb (Sb2O3) is a fining agent with a large fining effect. Ce (CeO2) has a smaller fining effect than Sb (Sb2O3). Ce (CeO2) tends to intensify the coloring of glass when added in large amounts.

[0460] In this specification, the contents of Sb (Sb2O3) and Ce (CeO2) are expressed as exclusive percentages and are not included in the total content of all glass components expressed on an oxide basis. That is, in this specification, the total content of all glass components excluding Sb (Sb2O3) and Ce (CeO2) is taken to be 100 mass%.

[0461] The Sb2O3 content is expressed as an exclusive ratio. That is, in the optical glass according to the fourth embodiment, when the total content of all glass components other than Sb2O3 and CeO2 is taken as 100 mass%, the Sb2O3 content is preferably 1 mass% or less, and more preferably 0.1 mass% or less, 0.05 mass% or less, and 0.03 mass% or less, in that order. The Sb2O3 content may be 0 mass%.

[0462] The CeO2 content is also expressed as an exclusive ratio. That is, in the optical glass according to the fourth embodiment, when the total content of all glass components other than CeO2 and Sb2O3 is taken as 100 mass%, the CeO2 content is preferably 2 mass% or less, and more preferably 1 mass% or less, 0.5 mass% or less, and 0.1 mass% or less, in that order. The CeO2 content may be 0 mass%. By keeping the CeO2 content within the above range, the clarity of the glass can be improved.

[0463] (Glass characteristics) <Abbe number νd> In the optical glass according to the fourth embodiment, the Abbe number vd is preferably 15 to 30. The Abbe number vd may be 18 to 25, or may be 20 to 24. By setting the Abbe number vd within the above range, it is possible to obtain a glass with the desired dispersibility. The Abbe number vd can be controlled by adjusting the contents of TiO2, Nb2O5, WO3, and Bi2O3, which are glass components that contribute to high dispersion.

[0464] <Refractive index nd> In the optical glass according to the fourth embodiment, the lower limit of the refractive index nd is 1.86. The lower limit of the refractive index nd can also be 1.87, 1.88, 1.89, or 1.90. The upper limit of the refractive index nd can be 2.20, or even 2.15, 2.10, or 2.05. The refractive index can be controlled by adjusting the contents of TiO2, Nb2O5, WO3, Bi2O3, ZrO2, La2O3, Gd2O3, YO3, and Ta2O5, which are glass components that contribute to a high refractive index.

[0465] <Specific gravity of glass> The optical glass according to the fourth embodiment is a high refractive index glass, but does not have a high specific gravity. If the specific gravity of the glass can be reduced, the weight of the lens can be reduced. On the other hand, if the specific gravity is too low, thermal stability will be reduced.

[0466] Therefore, in the optical glass according to the fourth embodiment, the specific gravity is preferably 4.2 or less, and more preferably 4.0 or less, 3.8 or less, 3.6 or less, and 3.4 or less in that order.

[0467] The specific gravity can be controlled by adjusting the content of each glass component. In particular, by adjusting the content of Li2O and TiO2, the specific gravity can be reduced while maintaining a high refractive index.

[0468] In the optical glass according to the fourth embodiment, the refractive index nd and the specific gravity preferably satisfy the following formula (1), more preferably the following formula (2), and even more preferably the following formula (3): When the refractive index nd and the specific gravity satisfy the following formula, an optical glass having a high refractive index and a relatively low specific gravity can be obtained. nd≧0.2×specific gravity+1.18…(1) nd≧0.2×specific gravity+1.20…(2) nd≧0.2×specific gravity+1.22…(3)

[0469] In the optical glass according to the fourth embodiment, the ratio of the refractive index nd to the specific gravity [refractive index nd / specific gravity] is preferably 0.50 or greater, more preferably 0.52 or greater, and even more preferably 0.54 or greater. By keeping the ratio [refractive index nd / specific gravity] within the above range, an optical glass with a high refractive index and a relatively low specific gravity can be obtained.

[0470] <Glass transition temperature Tg> In the optical glass according to the fourth embodiment, the upper limit of the glass transition temperature Tg is preferably 660°C, and more preferably 650°C, 630°C, and 600°C in that order. There is no particular lower limit for the glass transition temperature Tg, but it is usually 500°C, and preferably 550°C.

[0471] The glass transition temperature Tg can be controlled by adjusting the total content of alkali metals.

[0472] By ensuring that the upper limit of the glass transition temperature Tg satisfies the above range, increases in the molding temperature and annealing temperature during glass reheat pressing can be suppressed, and thermal damage to the reheat press molding equipment and annealing equipment can be reduced.

[0473] When the lower limit of the glass transition temperature Tg satisfies the above range, it becomes easier to maintain good reheat press moldability and good thermal stability of the glass while maintaining the desired Abbe number and refractive index.

[0474] <Light transmittance of glass> The light transmittance of the optical glass according to the fourth embodiment can be evaluated by the coloring degrees λ80, λ70 and λ5. The spectral transmittance of a glass sample with a thickness of 10.0 mm ± 0.1 mm is measured in the wavelength range of 200 to 700 nm, and the wavelength at which the external transmittance is 80% is defined as λ80, the wavelength at which the external transmittance is 70% is defined as λ70, and the wavelength at which the external transmittance is 5% is defined as λ5.

[0475] The λ80 of the optical glass according to the first embodiment is preferably 700 nm or less, more preferably 650 nm or less, and even more preferably 600 nm or less. λ70 is preferably 600 nm or less, more preferably 550 nm or less, and even more preferably 500 nm or less. λ5 is preferably 500 nm or less, more preferably 450 nm or less, and even more preferably 400 nm or less.

[0476] (Optical glass manufacturing) The optical glass according to the fourth embodiment may be produced by blending glass raw materials to obtain the above-described predetermined composition, and then using the blended glass raw materials in accordance with a known glass manufacturing method. For example, a plurality of compounds may be blended and thoroughly mixed to form batch raw materials, which are then placed in a quartz crucible or platinum crucible for rough melting. The molten material obtained by rough melting is then rapidly cooled and pulverized to produce cullet. The cullet is then placed in a platinum crucible, heated, and remelted to produce a glass melt, which is then refined and homogenized, and then formed and slowly cooled to obtain the optical glass. Known methods may be used to form and slowly cool the glass melt.

[0477] The compounds used when preparing the batch raw materials are not particularly limited as long as they can introduce desired glass components into the glass to achieve desired contents. Examples of such compounds include oxides, carbonates, nitrates, hydroxides, and fluorides.

[0478] (Manufacturing of optical elements, etc.) To produce an optical element using the optical glass according to the fourth embodiment, a known method may be applied. For example, in the production of the optical glass, molten glass is poured into a mold and formed into a plate to produce a glass material made of the optical glass according to the present invention. The obtained glass material is cut, ground, and polished as appropriate to produce cut pieces of a size and shape suitable for press molding. The cut pieces are heated and softened, and press-molded (reheat pressed) using a known method to produce an optical element blank that approximates the shape of the optical element. The optical element blank is annealed, and then ground and polished using a known method to produce an optical element.

[0479] The optically functional surface of the fabricated optical element may be coated with an anti-reflection film, a total reflection film, or the like depending on the intended use.

[0480] According to one aspect of the present invention, an optical element made of the above optical glass can be provided. Examples of optical elements include lenses such as flat lenses, spherical lenses, and aspherical lenses, as well as prisms, diffraction gratings, and light guide plates. Examples of lens shapes include biconvex lenses, plano-convex lenses, biconcave lenses, plano-concave lenses, convex meniscus lenses, and concave meniscus lenses. Examples of uses for light guide plates include display devices such as augmented reality (AR) display type eyeglasses and mixed reality (MR) display type eyeglasses. Such light guide plates are plate-shaped glass attached to the frame of eyeglasses and made of the above optical glass. If necessary, a diffraction grating may be formed on the surface of the light guide plate to change the direction of propagation of light propagating through the light guide plate by repeated total reflection. The diffraction grating can be formed by a known method. When an eyeglass device having the above light guide plate is worn, light propagating through the light guide plate enters the pupil, thereby exhibiting augmented reality (AR) display or mixed reality (MR) display functions. Such eyeglass-type devices are disclosed, for example, in JP-A-2017-534352. The light guide plate can be produced by a known method. The optical element can be manufactured by a method including a step of processing a glass molded body made of the optical glass. Examples of processing include cutting, milling, rough grinding, fine grinding, and polishing. By using the glass described above during such processing, breakage can be reduced, enabling a stable supply of high-quality optical elements.

[0481] (Image display device) The image display device according to the fourth embodiment can be similar to that of the first embodiment. [Example]

[0482] The present invention will be described in more detail below with reference to examples, although the present invention is not limited to the embodiments shown in the examples.

[0483] It should be noted that Example 1 corresponds to the first embodiment, Example 2 corresponds to the second embodiment, Example 3 corresponds to the third embodiment, and Example 4 corresponds to the fourth embodiment.

[0484] Example 1 (Example 1-1) Glass samples having the glass compositions shown in Tables 1-1(1), 1-1(2), 1-1(3), and 1-1(4) were prepared by the following procedure, and various evaluations were performed.

[0485] [Optical glass manufacturing] First, oxides, hydroxides, carbonates, and nitrates corresponding to the constituent components of the glass were prepared as raw materials. These raw materials were weighed and mixed thoroughly so that the resulting optical glass had the glass composition shown in Tables 1-1(1), 1-1(2), 1-1(3), and 1-1(4). The resulting raw materials (batch raw materials) were placed in a platinum crucible and heated at 1350°C to 1400°C for 2 hours to form a molten glass. The mixture was stirred to homogenize and refined, and then the molten glass was cast into a mold preheated to an appropriate temperature. The cast glass was heat-treated at around the glass transition temperature (Tg) for 30 minutes and then allowed to cool to room temperature in a furnace to obtain a glass sample.

[0486] [Confirmation of glass composition] The content of each glass component in the obtained glass samples was measured using inductively coupled plasma atomic emission spectroscopy (ICP-AES), and it was confirmed that the compositions were as shown in Tables 1-1(1), 1-1(2), 1-1(3), and 1-1(4).

[0487] [Optical property measurement] The resulting glass samples were further annealed at temperatures near the glass transition temperature (Tg) for approximately 30 minutes to approximately 2 hours, and then cooled to room temperature in a furnace at a rate of -30°C / hour to obtain annealed samples. The refractive indices (nd, ng, nF, and nC), Abbe number (νd), specific gravity, glass transition temperature (Tg), λ80, λ70, and λ5 of the resulting annealed samples were measured. The results are shown in Tables 1-2(1), 1-2(2), 1-2(3), and 1-2(4).

[0488] (i) Refractive indexes nd, ng, nF, nC and Abbe number νd The refractive indices nd, ng, nF, and nC of the annealed sample were measured by the refractive index measurement method of JIS standard JIS B 7071-1, and the Abbe number vd was calculated according to the following formula. νd=(nd-1) / (nF-nC)

[0489] (ii) Specific gravity The specific gravity was measured by the Archimedes method.

[0490] (iii) Glass transition temperature Tg The glass transition temperature Tg was measured using a differential scanning calorimeter (DSC3300SA) manufactured by NETZSCH JAPAN at a temperature rise rate of 10°C / min.

[0491] (iv) λ80, λ70, and λ5 The spectral transmittance of an annealed sample with a thickness of 10.0 mm ± 0.1 mm was measured in the wavelength range of 200 to 700 nm. The wavelength at which the external transmittance was 80% was defined as λ80, the wavelength at which the external transmittance was 70%, and the wavelength at which the external transmittance was 5% was defined as λ5.

[0492] [Table 1-1(1)]

[0493] [Table 1-1(2)]

[0494] [Table 1-1(3)]

[0495] [Table 1-1(4)]

[0496] [Table 1-2(1)]

[0497] [Table 1-2(2)]

[0498] [Table 1-2(3)]

[0499] [Table 1-2(4)]

[0500] (Example 1-2) The optical glasses (Nos. 1-1 to 1-105) prepared in Example 1-1 were compared with the optical glasses disclosed in the examples of Patent Documents 1 to 4. The optical glasses of Example 1-1 and the optical glasses disclosed in the examples of Patent Documents 1 to 4 were plotted on a graph with the refractive index nd on the vertical axis and the specific gravity on the horizontal axis. The results are shown in Figure 1.

[0501] As shown in FIG. 1, the optical glass of Example 1-1 and the optical glasses disclosed in the examples of Patent Documents 1 to 4 are distinguished from each other by the line nd=0.2×specific gravity+1.18.

[0502] That is, the optical glass of the present invention is clearly distinguishable from the optical glasses disclosed in the examples of Patent Documents 1 to 4 by the line nd=0.2×specific gravity+1.18, and it has been found to have the remarkable effect of having a smaller ratio for the same refractive index nd.

[0503] (Examples 1-3) Lens blanks were prepared by a known method using each of the optical glasses prepared in Example 1-1, and the lens blanks were processed by a known method such as polishing to prepare various lenses. The optical lenses produced include various lenses such as a flat lens, a biconvex lens, a biconcave lens, a plano-convex lens, a plano-concave lens, a concave meniscus lens, and a convex meniscus lens. By combining various lenses with lenses made of other types of optical glass, it was possible to effectively correct secondary chromatic aberration.

[0504] Furthermore, because the glass has a low specific gravity, each lens is lighter than lenses with equivalent optical properties and size, making them suitable for use in goggle-type or eyeglass-type AR or MR display devices. Similarly, prisms were fabricated using the various optical glasses fabricated in Example 1-1.

[0505] (Examples 1-4) Each optical glass prepared in Example 1-1 was processed into a rectangular thin plate having a length of 50 mm, a width of 20 mm, and a thickness of 1.0 mm to obtain a light guide plate. This light guide plate was incorporated into a head-mounted display 1 shown in FIG.

[0506] When the images from the head-mounted display obtained in this way were evaluated at the eyepoint, high-brightness, high-contrast images could be observed over a wide viewing angle.

[0507] Example 2 Example 2-1 Glass samples having the glass compositions shown in Tables 2-1(1), 2-1(2), 2-1(3), 2-1(4), 2-2(1), 2-2(2), 2-2(3), and 2-2(4) were prepared by the following procedure, and various evaluations were performed.

[0508] [Optical glass manufacturing] First, oxides, hydroxides, carbonates, and nitrates corresponding to the glass constituents were prepared as raw materials. These raw materials were weighed and mixed so that the resulting optical glass had the glass composition shown in Tables 2-1(1), 2-1(2), 2-1(3), 2-1(4), 2-2(1), 2-2(2), 2-2(3), and 2-2(4). The raw materials were then thoroughly mixed. The resulting raw material mixture (batch raw material) was placed in a platinum crucible and heated at 1350°C to 1400°C for 2 hours to form a molten glass. The mixture was stirred to homogenize and refined, and the molten glass was then cast into a mold preheated to an appropriate temperature. The cast glass was then heat-treated for 30 minutes at a temperature near the glass transition temperature (Tg) and allowed to cool to room temperature in a furnace to obtain a glass sample.

[0509] [Confirmation of glass composition] The content of each glass component in the obtained glass samples was measured using inductively coupled plasma atomic emission spectroscopy (ICP-AES), and it was confirmed that the compositions were as shown in Tables 2-1(1), 2-1(2), 2-1(3), 2-1(4), 2-2(1), 2-2(2), 2-2(3), and 2-2(4).

[0510] [Optical property measurement] The resulting glass samples were further annealed at temperatures near the glass transition temperature (Tg) for approximately 30 minutes to approximately 2 hours, and then cooled to room temperature in a furnace at a rate of -30°C / hour to obtain annealed samples. The refractive indices (nd, ng, nF, and nC), Abbe number (νd), specific gravity, glass transition temperature (Tg), λ80, λ70, and λ5 of the resulting annealed samples were measured. The results are shown in Tables 2-3(1), 2-3(2), 2-3(3), and 2-3(4).

[0511] (i) Refractive indexes nd, ng, nF, nC and Abbe number νd The refractive indices nd, ng, nF, and nC of the annealed sample were measured by the refractive index measurement method of JIS standard JIS B 7071-1, and the Abbe number vd was calculated according to the following formula. νd=(nd-1) / (nF-nC)

[0512] (ii) Specific gravity The specific gravity was measured by the Archimedes method.

[0513] (iii) Glass transition temperature Tg The glass transition temperature Tg was measured using a differential scanning calorimeter (DSC3300SA) manufactured by NETZSCH JAPAN at a temperature rise rate of 10°C / min.

[0514] (iv) λ80, λ70, and λ5 The spectral transmittance of an annealed sample with a thickness of 10.0 mm ± 0.1 mm was measured in the wavelength range of 200 to 700 nm. The wavelength at which the external transmittance was 80% was defined as λ80, the wavelength at which the external transmittance was 70%, and the wavelength at which the external transmittance was 5% was defined as λ5.

[0515] [Table 2-1(1)]

[0516] [Table 2-1(2)]

[0517] [Table 2-1(3)]

[0518] [Table 2-1(4)]

[0519] [Table 2-2(1)]

[0520] [Table 2-2(2)]

[0521] [Table 2-2(3)]

[0522] [Table 2-2(4)]

[0523] [Table 2-3(1)]

[0524] [Table 2-3(2)]

[0525] [Table 2-3(3)]

[0526] [Table 2-3(4)]

[0527] (Example 2-2) Lens blanks were prepared by known methods using the optical glasses prepared in Example 2-1, and the lens blanks were processed by known methods such as polishing to prepare various lenses. The optical lenses produced include various lenses such as a flat lens, a biconvex lens, a biconcave lens, a plano-convex lens, a plano-concave lens, a concave meniscus lens, and a convex meniscus lens. By combining various lenses with lenses made of other types of optical glass, it was possible to effectively correct secondary chromatic aberration.

[0528] Furthermore, because the glass has a low specific gravity, each lens is lighter than lenses with equivalent optical properties and size, making them suitable for use in goggle-type or eyeglass-type AR or MR display devices. Similarly, prisms were fabricated using the various optical glasses fabricated in Example 2-1.

[0529] (Example 2-3) Each optical glass prepared in Example 2-1 was processed into a rectangular thin plate measuring 50 mm in length, 20 mm in width, and 1.0 mm in thickness to obtain a light guide plate. This light guide plate was incorporated into a head-mounted display 1 shown in FIG.

[0530] When the images from the head-mounted display obtained in this way were evaluated at the eyepoint, high-brightness, high-contrast images could be observed over a wide viewing angle.

[0531] Example 3 (Example 3-1) Glass samples having the glass compositions shown in Tables 3-1(1), 3-1(2), 3-1(3), and 3-1(4) were prepared by the following procedure, and various evaluations were performed.

[0532] [Optical glass manufacturing] First, oxides, hydroxides, carbonates, and nitrates corresponding to the constituent components of the glass were prepared as raw materials. These raw materials were weighed and mixed so that the resulting optical glass had the composition shown in Tables 3-1(1), 3-1(2), 3-1(3), and 3-1(4). The raw materials were then thoroughly mixed. The resulting blended raw materials (batch raw materials) were placed in a platinum crucible and heated at 1350°C to 1400°C for two hours to form a molten glass. The mixture was stirred to homogenize and refined, and the molten glass was then cast into a mold preheated to an appropriate temperature. The cast glass was then heat-treated for 30 minutes at a temperature near the glass transition temperature (Tg), and then allowed to cool to room temperature in a furnace to obtain a glass sample.

[0533] [Confirmation of glass composition] The content of each glass component in the obtained glass samples was measured using inductively coupled plasma atomic emission spectroscopy (ICP-AES), and it was confirmed that the compositions were as shown in Tables 3-1(1), 3-1(2), 3-1(3), and 3-1(4).

[0534] [Optical property measurement] The resulting glass samples were further annealed at temperatures near the glass transition temperature (Tg) for approximately 30 minutes to approximately 2 hours, and then cooled to room temperature in a furnace at a rate of -30°C / hour to obtain annealed samples. The refractive indices (nd, ng, nF, and nC), Abbe number (νd), specific gravity, glass transition temperature (Tg), λ80, λ70, and λ5 of the resulting annealed samples were measured. The results are shown in Tables 3-2(1), 3-2(2), 3-2(3), and 3-2(4).

[0535] (i) Refractive indexes nd, ng, nF, nC and Abbe number νd The refractive indices nd, ng, nF, and nC of the annealed sample were measured by the refractive index measurement method of JIS standard JIS B 7071-1, and the Abbe number vd was calculated according to the following formula. νd=(nd-1) / (nF-nC)

[0536] (ii) Specific gravity The specific gravity was measured by the Archimedes method.

[0537] (iii) Glass transition temperature Tg The glass transition temperature Tg was measured using a differential scanning calorimeter (DSC3300SA) manufactured by NETZSCH JAPAN at a temperature rise rate of 10°C / min.

[0538] (iv) λ80, λ70, and λ5 The spectral transmittance of an annealed sample with a thickness of 10.0 mm ± 0.1 mm was measured in the wavelength range of 200 to 700 nm. The wavelength at which the external transmittance was 80% was defined as λ80, the wavelength at which the external transmittance was 70%, and the wavelength at which the external transmittance was 5% was defined as λ5.

[0539] [Table 3-1(1)]

[0540] [Table 3-1(2)]

[0541] [Table 3-1(3)]

[0542] [Table 3-1(4)]

[0543] [Table 3-2(1)]

[0544] [Table 3-2(2)]

[0545] [Table 3-2(3)]

[0546] [Table 3-2(4)]

[0547] (Example 3-2) Lens blanks were prepared by a known method using each of the optical glasses prepared in Example 3-1, and the lens blanks were processed by a known method such as polishing to prepare various lenses. The optical lenses produced include various lenses such as a flat lens, a biconvex lens, a biconcave lens, a plano-convex lens, a plano-concave lens, a concave meniscus lens, and a convex meniscus lens. By combining various lenses with lenses made of other types of optical glass, it was possible to effectively correct secondary chromatic aberration.

[0548] Furthermore, because the glass has a low specific gravity, each lens is lighter than lenses with equivalent optical properties and size, making them suitable for use in goggle-type or eyeglass-type AR or MR display devices. Similarly, prisms were fabricated using the various optical glasses fabricated in Example 3-1.

[0549] (Example 3-3) Each optical glass prepared in Example 3-1 was processed into a rectangular thin plate measuring 50 mm in length, 20 mm in width, and 1.0 mm in thickness to obtain a light guide plate. This light guide plate was incorporated into a head-mounted display 1 shown in FIG.

[0550] When the images from the head-mounted display obtained in this way were evaluated at the eyepoint, high-brightness, high-contrast images could be observed over a wide viewing angle.

[0551] Example 4 Example 4-1 Glass samples having the glass compositions shown in Tables 4-1(1), 4-1(2), 4-1(3), 4-1(4), 4-2(1), 4-2(2), 4-2(3), and 4-2(4) were prepared by the following procedure, and various evaluations were performed.

[0552] [Optical glass manufacturing] First, oxides, hydroxides, carbonates, and nitrates corresponding to the glass constituents were prepared as raw materials. These raw materials were weighed and mixed so that the resulting optical glass had the glass composition shown in Tables 4-1(1), 4-1(2), 4-1(3), 4-1(4), 4-2(1), 4-2(2), 4-2(3), and 4-2(4). The raw materials were then thoroughly mixed. The resulting raw material mixture (batch raw material) was placed in a platinum crucible and heated at 1350°C to 1400°C for 2 hours to form a molten glass. The mixture was stirred to homogenize and refined, and the molten glass was then cast into a mold preheated to an appropriate temperature. The cast glass was then heat-treated near the glass transition temperature (Tg) for 30 minutes and allowed to cool to room temperature in a furnace to obtain a glass sample.

[0553] [Confirmation of glass composition] The content of each glass component in the obtained glass samples was measured using inductively coupled plasma atomic emission spectroscopy (ICP-AES), and it was confirmed that the compositions were as shown in Tables 4-1(1), 4-1(2), 4-1(3), 4-1(4), 4-2(1), 4-2(2), 4-2(3), and 4-2(4).

[0554] [Optical property measurement] The resulting glass samples were further annealed at temperatures near the glass transition temperature (Tg) for approximately 30 minutes to approximately 2 hours, and then cooled to room temperature in a furnace at a rate of -30°C / hour to obtain annealed samples. The refractive indices (nd, ng, nF, and nC), Abbe number (νd), specific gravity, glass transition temperature (Tg), λ80, λ70, and λ5 of the resulting annealed samples were measured. The results are shown in Tables 4-3(1), 4-3(2), 4-3(3), and 4-3(4).

[0555] (i) Refractive indexes nd, ng, nF, nC and Abbe number νd The refractive indices nd, ng, nF, and nC of the annealed sample were measured by the refractive index measurement method of JIS standard JIS B 7071-1, and the Abbe number vd was calculated according to the following formula. νd=(nd-1) / (nF-nC)

[0556] (ii) Specific gravity The specific gravity was measured by the Archimedes method.

[0557] (iii) Glass transition temperature Tg The glass transition temperature Tg was measured using a differential scanning calorimeter (DSC3300SA) manufactured by NETZSCH JAPAN at a temperature rise rate of 10°C / min.

[0558] (iv) λ80, λ70, and λ5 The spectral transmittance of an annealed sample with a thickness of 10.0 mm ± 0.1 mm was measured in the wavelength range of 200 to 700 nm. The wavelength at which the external transmittance was 80% was defined as λ80, the wavelength at which the external transmittance was 70%, and the wavelength at which the external transmittance was 5% was defined as λ5.

[0559] [Table 4-1(1)]

[0560] [Table 4-1(2)]

[0561] [Table 4-1(3)]

[0562] [Table 4-1(4)]

[0563] [Table 4-2(1)]

[0564] [Table 4-2(2)]

[0565] [Table 4-2(3)]

[0566] [Table 4-2(4)]

[0567] [Table 4-3(1)]

[0568] [Table 4-3(2)]

[0569] [Table 4-3(3)]

[0570] [Table 4-3(4)]

[0571] (Example 4-2) The optical glasses (Nos. 4-1 to 4-97) prepared in Example 4-1 were compared with the optical glasses disclosed in the examples of Patent Documents 1 to 4. First, the optical glasses of Example 4-1 and the optical glasses disclosed in the examples of Patent Documents 1 to 4 were plotted on a graph with the mass ratio [LiO / {100-(SiO+B+P+GeO)}] on the vertical axis and the mass ratio [TiO / (TiO+Nb+WO+ZrO+SrO+BaO+ZnO+La+Gd+Y+Ta+Bi+Bi)] on the horizontal axis. The results are shown in Figure 4.

[0572] Next, the ratio of refractive index nd to specific gravity [refractive index nd / specific gravity] is plotted on the vertical axis, and the mass ratio [TiO2 / (TiO2+Nb2O5+WO3+ZrO2+SrO+BaO+ZnO+La2O3+ The optical glasses of Example 4-1 (Nos. 4-1 to 4-97) and the optical glasses disclosed in the examples of Patent Documents 1 to 4 were plotted on a graph with the horizontal axis being the refractive index (Gd2O3+Y2O3+Ta2O5+Bi2O3). The vertical axis is the ratio [refractive index nd / specific gravity], and the larger this value, the higher the refractive index and the lower the specific gravity. The results are shown in Figure 5.

[0573] As shown in FIG. 4, the optical glass of Example 4-1 and the optical glasses disclosed in the examples of Patent Documents 1 to 4 are distinguished by the boundary between the line on the horizontal axis where the mass ratio [TiO2 / (TiO2+Nb2O5+WO3+ZrO2+SrO+BaO+ZnO+La2O3+Gd2O3+Y2O3+Ta2O5+Bi2O3)] is 0.40 and the line on the vertical axis where the mass ratio [Li2O / {100-(SiO2+B2O3+P2O5+GeO2)}] is 0.02.

[0574] Furthermore, as shown in FIG. 5, the optical glass of Example 4-1 exhibits a higher value for the ratio [refractive index nd / specific gravity] on the vertical axis than the optical glasses disclosed in the examples of Patent Documents 1-4.

[0575] That is, the optical glass of Example 4-1 is clearly distinguishable based on its composition from the optical glasses disclosed in the examples of Patent Documents 1 to 4, and it was found to have the remarkable effect of having a large ratio [refractive index nd / specific gravity].

[0576] (Example 4-3) Lens blanks were prepared by a known method using each of the optical glasses prepared in Example 4-1, and the lens blanks were processed by a known method such as polishing to prepare various lenses. The optical lenses produced include various lenses such as a flat lens, a biconvex lens, a biconcave lens, a plano-convex lens, a plano-concave lens, a concave meniscus lens, and a convex meniscus lens. By combining various lenses with lenses made of other types of optical glass, it was possible to effectively correct secondary chromatic aberration.

[0577] Furthermore, because the glass has a low specific gravity, each lens is lighter than lenses with equivalent optical properties and size, making them suitable for use in goggle-type or eyeglass-type AR or MR display devices. Similarly, prisms were fabricated using the various optical glasses fabricated in Example 4-1.

[0578] (Example 4-4) Each optical glass prepared in Example 4-1 was processed into a rectangular thin plate measuring 50 mm in length, 20 mm in width, and 1.0 mm in thickness to obtain a light guide plate. This light guide plate was incorporated into a head-mounted display 1 shown in FIG.

[0579] When the images from the head-mounted display obtained in this way were evaluated at the eyepoint, high-brightness, high-contrast images could be observed over a wide viewing angle.

[0580] Comparative Example Glass samples having the glass compositions shown in Table 5(1) were prepared by the following procedure and various evaluations were carried out. Note that Comparative Examples 1 to 7 each have the same composition as the glass disclosed in the following document. Comparative example 1: Physics and Chemistry of Glasses, vol.12, p.93, 1971 Comparative example 2: J. Non-Crystalline Solids, vol.107, p.244, 1989 Comparative example 3: J. American Ceramic Soc., vol.73, p.2743, 1990 Comparative example 4: Applied Optics, vol.29, p.3126, 1990 Comparative example 5: Applied Optics, vol.29, p.3126, 1990 Comparative Example 6: JP 2003-252646 Comparative example 7: J. American Ceramic Soc., vol.94, p.2086, 2011

[0581] [Optical glass manufacturing] First, oxides, hydroxides, carbonates, and nitrates corresponding to the constituent components of the glass were prepared as raw materials. These raw materials were weighed and mixed thoroughly so that the resulting optical glass would have the composition shown in Table 5(1). The resulting blended raw materials (batch raw materials) were placed in a platinum crucible and heated at 1350°C to 1400°C for two hours to form a molten glass. The mixture was stirred to homogenize and refined, and the molten glass was then cast into a mold preheated to an appropriate temperature. The cast glass was then heat-treated for 30 minutes at a temperature near the glass transition temperature Tg and allowed to cool to room temperature in a furnace, yielding a glass sample.

[0582] [Confirmation of glass composition] The content of each glass component in the obtained glass sample was measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES), and it was confirmed that each composition was as shown in Table 5(1).

[0583] [Optical property measurement] The obtained glass sample was further annealed at a temperature near the glass transition temperature Tg for about 30 minutes to about 2 hours, and then cooled to room temperature in a furnace at a rate of -30°C / hour to obtain an annealed sample. The refractive index nd and specific gravity of the obtained annealed sample were measured. The results are shown in Table 5(2).

[0584] (i) Refractive index nd The refractive index nd of the annealed sample was measured by the refractive index measurement method of JIS standard JIS B 7071-1.

[0585] (ii) Specific gravity The specific gravity was measured by the Archimedes method.

[0586] [Glass Observation] The obtained glass samples were observed. In Comparative Examples 1 to 7, all were partially or completely devitrified, and no glass suitable for use as optical glass was obtained. Photographs of the glass samples obtained in Comparative Examples 1, 2, and 4 to 7 are shown in Figures 6 to 11, respectively.

[0587] [Table 5(1)]

[0588] [Table 5(2)]

[0589] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims.

[0590] For example, by adjusting the composition as described in the specification for the glass compositions exemplified above, an optical glass according to one aspect of the present invention can be produced. Furthermore, it is of course possible to arbitrarily combine two or more of the items described in the specification as examples or preferred ranges.

Claims

1. SiO 2 -TiO 2 -Nb 2 O 5 is a glass containing SiO 2 The content of is 10% by mass or more, TiO 2 The content of is 10% by mass or more, Nb 2 O 5 The content is 35% by mass or less, Na 2 O.K. 2 O, and Cs 2 Total content of O [Na 2 O+K 2 O+Cs 2 O] is 11.0 mass% or less, TiO 2 and Nb 2 O 5 The total content [TiO 2 +Nb 2 O 5 ] is 20% by mass or more, La 2 O 3 , Gd 2 O 3 , and Y 2 O 3 The total content [La 2 O 3 +Gd 2 O 3 +Y 2 O 3 ] is 10% by mass or less, The refractive index nd is 1.86 to 2.15, The specific gravity is 4.2 or less, An optical glass having a specific gravity and a refractive index nd that satisfy the following formula (1): nd≧0.2×specific gravity+1.18…(1)

2. SiO 2 The content is 10 to 50 mass %, TiO 2 The content is 20 to 50 mass %, The content of BaO is 0 to 10 mass %, Nb 2 O 5 The content is 1 to 50 mass %, P 2 O 5 The content of is 10% by mass or less, Li 2 O, Na 2 O.K. 2 O, and Cs 2 The total content of O [Li 2 O + Na 2 O+K 2 O+Cs 2 O] is 0.1 to 20 mass %, La 2 O 3 , Gd 2 O 3 , and Y 2 O 3 The total content [La 2 O 3 +Gd 2 O 3 +Y 2 O 3 ] is 0 to 10 mass %, TiO 2 and Nb 2 O 5 The total content [TiO 2 +Nb 2 O 5 ] is 45 to 65 mass %, TiO 2 and TiO 2 and Nb 2 O 5 The mass ratio of the total content of [TiO 2 / (TiO 2 +Nb 2 O 5 ) )] is 0.45 or more, Li 2 O content and Li 2 O, Na 2 O.K. 2 O, and Cs 2 The mass ratio of the total content of Li 2 O / (Li 2 O + Na 2 O+K 2 O+Cs 2 O)] is 0.1 to 1; the Abbe number νd is 25 or less; An optical glass having a refractive index nd of 1.86 or more.

3. SiO 2 The content is 10 to 50 mass %, TiO 2 The content is 20 to 50 mass %, Nb 2 O 5 The content is 1 to 35 mass %, P 2 O 5 The content of is 10% by mass or less, Na 2 The O content is 0 to 8 mass %, TiO 2 and Nb 2 O 5 The total content [TiO 2 +Nb 2 O 5 ] is 40 to 80 mass %; TiO 2 and TiO 2 and Nb 2 O 5 The mass ratio of the total content of [TiO 2 / (TiO 2 +Nb 2 O 5 ) )] is 0.3 or more, The content of BaO is less than 16.0% by mass, The refractive index nd is 1.88 or more, An optical glass having a ratio of refractive index nd to specific gravity [refractive index nd / specific gravity] of 0.50 or more.

4. P 2 O 5 The content of is 10% by mass or less, SiO 2 The content of is 10% by mass or more, Nb 2 O 5 The content is 10 to 35 mass %, TiO 2 The content of is 20% by mass or more, The content of BaO is 10% by mass or less, Li 2 The content of O and SiO 2 , B 2 O 3 , P 2 O 5 , and GeO 2 The mass ratio of the total content of glass components other than [Li 2 O / {100-(SiO 2 +B 2 O 3 +P 2 O 5 +GeO 2 )}] is 0.02 or more, TiO 2 and the content of TiO 2 , Nb 2 O 5 , W.O. 3 , ZrO 2 , SrO, BaO, ZnO, La 2 O 3 , Gd 2 O 3 , Y 2 O 3 , Ta 2 O 5 , and Bi 2 O 3 The mass ratio of the total content of [TiO 2 / (TiO 2 +Nb 2 O 5 +WO 3 + ZrO 2 +SrO+BaO+ZnO+La 2 O 3 +Gd 2 O 3 +Y 2 O 3 +Ta 2 O 5 +Bi 2 O 3 ) )] is 0.40 or more, An optical glass having a refractive index nd of 1.86 or more.

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

6. A light guide plate made of the optical glass according to any one of claims 1 to 4.

7. The light guide plate according to claim 6 , which has a diffraction grating on its surface.

8. 5. An image display device comprising an image display element and a light guide plate for guiding light emitted from said image display element, wherein said light guide plate is made of the optical glass according to any one of claims 1 to 4.

Images