Optical glass and optical element

Abstract

The invention provides optical glass and an optical element, wherein the specific gravity is reduced and the raw material cost is reduced while the high refractive index is maintained. Optical glass having 5% by mass or more of SiO2, 15% by mass or less of B2O3, 1-15% by mass of [Li2O + Na2O + K2O], 0.5 or less of [Li2O / (Li2O + Na2O + K2O)], 0.5 or less of [(Li2O + Na2O + K2O) / (MgO + CaO + SrO + BaO)], 15% by mass or more of TiO2, 1-30% by mass of Nb2O5, 1.0 or less of [SiO2 / TiO2], 0.7 or less of [BaO / (MgO + CaO + SrO + BaO)], 30% by mass or more of [TiO2 + Nb2O5 + Y2O3 + ZrO2 + La2O3 + G.

Description

Technical Field

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

[0002] In recent years, with the development of AR (augmented reality), MR (mixed reality), and VR (virtual reality) technologies, goggle-type or glasses-type display devices have been developed as AR devices, MR devices, and VR devices. For example, goggle-type display devices require lenses with a high refractive index and low specific gravity, and the demand for glass that can be used for such lenses is gradually increasing. However, in order to achieve the characteristics of high refractive index and low specific gravity, glass components such as Nb and Li that have high raw material costs are currently used for glasses that can be used for such lenses. Therefore, the increase in raw material costs has become a problem.

[0003] Patent Document 1 discloses a high-refractive-index optical glass. However, the optical glass of Patent Document 1 has a high specific gravity relative to its refractive index and contains a large amount of glass components such as Nb and Li, which are high in raw material cost, in order to be used as a lens for AR devices and the like.

[0004] Therefore, there is a need for an optical glass that can reduce specific gravity and raw material costs while maintaining a high refractive index.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent document 1: International Publication No. 2021 / 171950. Summary of the Invention

[0008] Problems to be solved by the invention

[0009] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an optical glass and an optical element having a reduced specific gravity and a reduced raw material cost while maintaining a high refractive index.

[0010] Solutions for solving problems

[0011] The gist of the present invention is as follows.

[0012] (1) An optical glass, wherein:

[0013] The content of SiO2 is 5% by mass or more,

[0014] The content of B2O3 is 15% by mass or less,

[0015] The total content of Li2O, Na2O and K2O [Li2O+Na2O+K2O] is 1 to 15% by mass.

[0016] The mass ratio of the content of Li2O to the total content of Li2O, Na2O and K2O [Li2O / (Li2O+Na2O+K2O)] is 0.5 or less,

[0017] The mass ratio of the content of K2O to the total content of Li2O, Na2O and K2O [K2O / (Li2O+Na2O+K2O)] is 0.5 or less,

[0018] The mass ratio of the total content of Li2O, Na2O and K2O to the total content of MgO, CaO, SrO and BaO [(Li2O+Na2O+K2O) / (MgO+CaO+SrO+BaO)] is 0.6 or less,

[0019] The content of TiO2 is 15% by mass or more,

[0020] The content of Nb2O5 is 1 to 30% by mass.

[0021] The mass ratio of the SiO2 content to the TiO2 content [SiO2 / TiO2] is 1.0 or less,

[0022] The total content of MgO, CaO, SrO and BaO [MgO+CaO+SrO+BaO] is 5% by mass or more,

[0023] The mass ratio of the BaO content to the total content of MgO, CaO, SrO and BaO [BaO / (MgO+CaO+SrO+BaO)] is 0.7 or less,

[0024] The total content of TiO2 and Nb2O5 [TiO2 + Nb2O5] is 30% by mass or more,

[0025] The mass ratio of the TiO2 content to the total content of TiO2, Nb2O5, Y2O3, ZrO2, La2O3, Gd2O3, Ta2O5, WO3, Yb2O3 and Bi2O3 [TiO2 / (TiO2+Nb2O5+Y2O3+ZrO2+La2O3+Gd2O3+Ta2O5+WO3+Yb2O3+Bi2O3)] is greater than 0.6.

[0026] (2) An optical element composed of the optical glass described in (1) above.

[0027] (3) A light guide plate made of the optical glass described in (1) above.

[0028] Effects of the Invention

[0029] According to the present invention, it is possible to provide an optical glass and an optical element having a reduced specific gravity and a reduced raw material cost while maintaining a high refractive index. DETAILED DESCRIPTION

[0030] Unless otherwise noted, glass compositions in this invention and throughout this specification are expressed on an oxide basis. "Glass composition on an oxide basis" refers to the glass composition obtained by completely decomposing the glass raw materials during melting and converting them into substances present as oxides in the glass. The designations of individual glass components follow common practice, such as SiO₂ and TiO₂. Unless otherwise noted, the content and total content of glass components are by mass, and "%" means "mass %."

[0031] The content of glass components can be quantified by known methods, such as inductively coupled plasma atomic emission spectrometry (ICP-AES) and inductively coupled plasma mass spectrometry (ICP-MS). In this specification and the present invention, a 0% content of a component means that the component is substantially absent, but the presence of the component as an unavoidable impurity level is permitted.

[0032] In this specification, the terms "thermal stability" and "reheat stability" of glass refer to the difficulty of crystallization in the glass. Specifically, thermal stability refers to the difficulty of crystallization when molten glass hardens, while reheat stability refers to the difficulty of crystallization when hardened glass is reheated, such as during a reheat press.

[0033] Unless otherwise specified, the refractive index is the refractive index nd at the d-line of helium (wavelength 587.56 nm).

[0034] The Abbe number vd is used as a value to represent the properties related to dispersion and is expressed by the following formula. F is the refractive index at the F line of blue hydrogen (wavelength 486.13nm), n C It is the refractive index at the C line of red hydrogen (656.27nm).

[0035] vd=(nd-1) / (n F -n C )

[0036] Hereinafter, one embodiment of the present invention will be described.

[0037] In the optical glass according to this embodiment, the SiO2 content is 5% or more. The lower limit of the SiO2 content is preferably 5.0%, and more preferably 6.0%, 8.0%, 10.0%, 12.0%, 14.0%, 16.0%, 17.0%, 18.0%, 19.0%, and 20.0%. In addition, the upper limit of the SiO2 content is preferably 30.0%, and more preferably 29.0%, 28.0%, 27.0%, 26.0%, 25.0%, and 24.0%.

[0038] SiO2 is a network-forming component in glass, improving its thermal stability, chemical durability, and weather resistance, as well as increasing the viscosity of molten glass. Too little SiO2 can reduce the glass's resistance to devitrification. Too much SiO2 can lower the refractive index nd.

[0039] In the optical glass according to this embodiment, the B2O3 content is 15% or less. The upper limit of the B2O3 content is preferably 15.0%, and more preferably 13.0%, 10.0%, 9.0%, 8.0%, 7.0%, 6.0%, and 5.0%. The lower limit of the B2O3 content is preferably 0.0%, and more preferably 1.0%, 2.0%, and 3.0%.

[0040] B2O3 improves the thermal stability of glass and increases its solubility. Furthermore, among the network-forming components of glass, B2O3 has a relatively high refractive index and can reduce specific gravity. By adjusting the B2O3 content within the above range, the solubility of the glass can be improved, and an optical glass with a high refractive index and a low specific gravity can be obtained. On the other hand, if the B2O3 content is too low, there is a risk of compromising the high refractive index and increasing the specific gravity. Furthermore, if the B2O3 content is too high, there is a risk of increasing the volatilization of glass components during glass melting.

[0041] In the optical glass according to this embodiment, the total content of Li₂O, Na₂O, and K₂O (Li₂O + Na₂O + K₂O) is 1 to 15%. The lower limit of this total content is preferably 1.0%, with 2.0%, 3.0%, and 4.0% being more preferred in that order. Furthermore, the upper limit of this total content is preferably 10%, with 9.0%, 8.0%, and 7.0% being more preferred in that order.

[0042] By keeping the total content [Li2O+Na2O+K2O] within the above range, the viscosity of the glass can be appropriately maintained, thereby improving the productivity of the glass. In addition, it is possible to suppress the light absorption caused by the reducing components generated by Ti and Nb, thereby promoting the elimination of electronic defects in the glass by lowering the melting temperature and slow cooling, thereby improving the internal transmittance at 460nm. On the other hand, when the total content is too low, the solubility of the glass raw materials deteriorates, and it is necessary to set a high melting temperature for the raw materials. When the total content is too high, the viscosity of the glass will decrease, and the thermal stability will also decrease, which may lead to a risk of worsening productivity. In addition, the resistivity of the molten glass will decrease, and the heating efficiency when the molten glass is electrically heated will decrease. As a result, there is a risk of reducing the solubility of the glass and worsening productivity.

[0043] In the optical glass according to this embodiment, the mass ratio of the Li₂O content to the total content of Li₂O, Na₂O, and KO [Li₂O / (Li₂O+Na₂O+KO)] is 0.5 or less. The upper limit of this mass ratio is preferably 0.50, with 0.40, 0.30, 0.20, and 0.10 being more preferred. Furthermore, the lower limit of this mass ratio is preferably 0.00, with 0.01 and 0.02 being more preferred. By setting this mass ratio within the above range, an optical glass having a high refractive index, a low specific gravity, and reduced raw material costs can be obtained.

[0044] In the optical glass according to this embodiment, the mass ratio of the KO content to the total content of LiO, NaO, and KO [KO / (LiO + NaO + KO)] is 0.5 or less. The upper limit of this mass ratio is preferably 0.40, with 0.35 and 0.30 being more preferred. Furthermore, the lower limit of this mass ratio is preferably 0.00, with 0.05, 0.10, and 0.15 being more preferred. By setting this mass ratio within this range, an optical glass having a high refractive index and a low specific gravity can be obtained.

[0045] In the optical glass according to this embodiment, the mass ratio of the total content of Li2O, Na2O, and KO to the total content of MgO, CaO, SrO, and BaO [(Li2O + Na2O + KO) / (MgO + CaO + SrO + BaO)] is 0.6 or less. The upper limit of this mass ratio is preferably 0.50, and more preferably 0.45, 0.40, 0.35, and 0.30, respectively. The lower limit of this mass ratio is preferably 0.05, and more preferably 0.10, 0.15, and 0.20, respectively.

[0046] By adjusting the mass ratio [(Li₂O + Na₂O + KO) / (MgO + CaO + SrO + BaO)] within the above range, optical glass with a reduced specific gravity can be obtained. Furthermore, the reduced color of the glass can be suppressed, improving the internal transmittance. On the other hand, if this mass ratio is too low, there is a risk of deteriorating the meltability of the glass. Furthermore, if this mass ratio is too high, there is a risk of volatilizing the glass components more easily during melting, reducing the viscosity of the molten glass, and lowering its thermal stability.

[0047] In the optical glass according to this embodiment, the TiO2 content is 15% or more. The lower limit of the TiO2 content is preferably 20.0%, and more preferably 22.0%, 24.0%, 26.0%, and 28.0%. Furthermore, the upper limit of the TiO2 content is preferably 60.0%, and more preferably 55.0%, 50.0%, 45.0%, 40.0%, 38.0%, and 36.0%.

[0048] By controlling the TiO2 content within the above range, an optical glass with a high refractive index and low specific gravity can be obtained. On the other hand, if the TiO2 content is too low, there is a risk of lowering the refractive index and increasing the specific gravity. Furthermore, if the TiO2 content is too high, there is a risk of reducing the internal transmittance of the glass in the visible light region, particularly in the short wavelength region, and also reducing the resistance to devitrification.

[0049] In the optical glass according to this embodiment, the Nb2O5 content is 1 to 30%. The lower limit of the Nb2O5 content is preferably 1.0%, and more preferably 1.5%, 2.0%, 2.5%, and 3.0%. The upper limit of the Nb2O5 content is preferably 20.0%, and more preferably 18.0%, 16.0%, 14.0%, 12.0%, and 10.0%.

[0050] By controlling the Nb2O5 content within the above range, an optical glass having a high refractive index, reduced raw material costs, and improved thermal stability can be obtained. On the other hand, if the Nb2O5 content is too low, there is a risk of lowering the refractive index. If the Nb2O5 content is too high, there is a risk of reducing devitrification resistance.

[0051] In the optical glass according to this embodiment, the mass ratio of the SiO2 content to the TiO2 content [SiO2 / TiO2] is 1.0 or less. The upper limit of this mass ratio is preferably 0.80, and more preferably 0.75, 0.70, 0.65, or 0.60. The lower limit of this mass ratio is preferably 0.20, and more preferably 0.25, 0.30, 0.35, or 0.40.

[0052] By adjusting the mass ratio [SiO2 / TiO2] within the above range, an optical glass having a high refractive index and a low specific gravity can be obtained. In addition, the thermal stability of the glass can be improved, thereby increasing the solubility of the glass.

[0053] In the optical glass according to this embodiment, the total content of MgO, CaO, SrO, and BaO (MgO + CaO + SrO + BaO) is 5% or greater. The lower limit of this total content is preferably 15.0%, with 16.0%, 17.0%, and 18.0% being more preferred in that order. Furthermore, the upper limit of this total content is preferably 40.0%, with 38.0%, 36.0%, 34.0%, 32.0%, and 30.0% being more preferred in that order.

[0054] By keeping the combined content of [MgO + CaO + SrO + BaO] within the above range, the solubility of the glass can be improved, and the thermal stability of the glass can be enhanced. On the other hand, if the combined content is too low, there is a risk of deteriorating the solubility of the glass and increasing the erosion of refractory bricks during glass melting. Furthermore, if the combined content is too high, there is a risk of failing to achieve the desired optical properties and reducing thermal stability.

[0055] In the optical glass according to this embodiment, the mass ratio of the BaO content to the total content of MgO, CaO, SrO, and BaO [BaO / (MgO+CaO+SrO+BaO)] is 0.7 or less. The upper limit of this mass ratio is preferably 0.65, with 0.60, 0.55, 0.50, 0.40, 0.30, and 0.25 being more preferred. The lower limit of this mass ratio is preferably 0.01, with 0.05, 0.10, and 0.15 being more preferred.

[0056] By setting the mass ratio [BaO / (MgO+CaO+SrO+BaO)] within the above range, an optical glass with a low specific gravity and high dispersibility can be obtained. If the mass ratio is too high, there is a risk of increasing the specific gravity, decreasing thermal stability, and reducing devitrification resistance.

[0057] In the optical glass according to this embodiment, the combined content of TiO2 and Nb2O5 (TiO2 + Nb2O5) is 30% or greater. The lower limit of this combined content is preferably 30.0%, with 31.0%, 32.0%, 33.0%, 34.0%, and 35.0% being more preferred. Furthermore, the upper limit of this combined content is preferably 60.0%, with 55.0%, 50.0%, and 45.0% being more preferred.

[0058] TiO2 and Nb2O5 are both components that contribute to increasing the refractive index. Therefore, by adjusting the total content [TiO2 + Nb2O5] within the above range, an optical glass with a high refractive index and a low specific gravity can be obtained.

[0059] In the optical glass according to the present embodiment, the mass ratio of the content of TiO2 to the total content of TiO2, Nb2O5, Y2O3, ZrO2, La2O3, Gd2O3, Ta2O5, WO3, Yb2O3, and Bi2O3 is [TiO2 / (TiO2+Nb2O5+Y2O3+ZrO2+La2O3+Gd2O3+Ta2O5+WO3+Yb2O3+Bi2O3)]

[0060] The lower limit of the mass ratio is preferably 0.65, and more preferably 0.66, 0.67, and 0.68. In addition, the upper limit of the mass ratio is preferably 0.95, and more preferably 0.90, 0.88, 0.86, 0.84, and 0.82.

[0061] By adjusting the mass ratio [TiO2 / (TiO2+Nb2O5+Y2O3+ZrO2+La2O3+Gd2O3+Ta2O5+WO3+Yb2O3+Bi2O3)] within the above range, an optical glass having a high refractive index and a further reduced specific gravity can be obtained.

[0062] The following non-limiting examples are given regarding the contents and ratios of glass components other than those described above in the optical glass according to the present embodiment.

[0063] In the optical glass according to the present embodiment, the lower limit of the mass ratio of TiO2 to Nb2O5 [TiO2 / Nb2O5] is preferably 1.5, and more preferably 1.6, 1.7, 1.8, 1.9, and 2.0, respectively. Furthermore, the upper limit of this mass ratio is preferably 20.0, and more preferably 19.0, 18.0, 17.0, 16.0, and 15.0, respectively.

[0064] To achieve optical glass with a high refractive index, a further reduced specific gravity, and lower raw material costs, it is preferable to keep the mass ratio [TiO2 / Nb2O5] within the above range. On the other hand, if this mass ratio is too low, there is a risk of increasing the liquidus temperature, deteriorating solubility, and increasing erosion of refractory bricks during glass melting. This, in turn, risks increasing manufacturing costs. Furthermore, if this mass ratio is too high, there is a risk of reducing the glass's resistance to devitrification and its transmittance.

[0065] In the optical glass according to the present embodiment, the upper limit of the mass ratio of the Nb2O5 content to the total content of TiO2, Nb2O5, Y2O3, ZrO2, La2O3, Gd2O3, Ta2O5, WO3, Yb2O3, and Bi2O3 [Nb2O5 / (TiO2+Nb2O5+Y2O3+ZrO2+La2O3+Gd2O3+Ta2O5+WO3+Yb2O3+Bi2O3)] is preferably 0.30, with 0.25 and 0.20 being more preferred in that order. Furthermore, the lower limit of this mass ratio is preferably 0.01, with 0.02, 0.03, 0.04, and 0.05 being more preferred in that order.

[0066] From the perspective of obtaining optical glass with a high refractive index, further reduced specific gravity and reduced raw material costs, it is preferred to keep the mass ratio [Nb2O5 / (TiO2+Nb2O5+Y2O3+ZrO2+La2O3+Gd2O3+Ta2O5+WO3+Yb2O3+Bi2O3)] within the above range.

[0067] In the optical glass according to the present embodiment, the mass ratio of the total content of TiO2, Nb2O5, Y2O3, ZrO2, La2O3, Gd2O3, Ta2O5, WO3, Yb2O3, and Bi2O3 to the total content of MgO, CaO, SrO, and BaO [(TiO2 + Nb2O5 + Y2O3 + ZrO2 + La2O3 + Gd2O3 + Ta2O5 + WO3 + Yb2O3 + Bi2O3) / (MgO + CaO + SrO + BaO)] is preferably 1.0, with 1.1, 1.2, 1.3, and 1.4 being more preferred in that order. Furthermore, the upper limit of this mass ratio is preferably 3.0, with 2.9, 2.8, 2.7, and 2.6 being more preferred in that order.

[0068] From the perspective of obtaining optical glass with a high refractive index, further reduced specific gravity and reduced raw material costs, it is preferred to keep the mass ratio [(TiO2+Nb2O5+Y2O3+ZrO2+La2O3+Gd2O3+Ta2O5+WO3+Yb2O3+Bi2O3) / (MgO+CaO+SrO+BaO)] within the above range.

[0069] As 2 O 3 and PbO are both toxic. Therefore, in the optical glass according to the present embodiment, the content of each of As 2 O 3 and PbO is preferably 0%, and preferably, substantially no As 2 O 3 and PbO are contained.

[0070] In the optical glass according to this embodiment, the upper limit of the P2O5 content is preferably 5.0%, and more preferably 4.0%, 3.0%, 2.0%, 1.0%, and 0.6%. Furthermore, the lower the P2O5 content, the better, and the lower limit is preferably 0.0%. The P2O5 content may also be 0.0%.

[0071] From the viewpoint of suppressing devitrification of the glass and erosion of refractory bricks during melting of the glass, the P2O5 content is preferably within the above range.

[0072] In the optical glass according to this embodiment, the lower limit of the Al2O3 content is preferably 0.00%, and more preferably 0.01%, 0.02%, and 0.03%. The upper limit of the Al2O3 content is preferably 5.0%, and more preferably 4.0%, 3.0%, 2.0%, 1.0%, and 0.5%. The Al2O3 content may be 0.00%.

[0073] Al2O3 is a component that reduces the effect of lowering specific gravity and has the effect of lowering the refractive index. From the perspective of obtaining glass with a high refractive index and low specific gravity, the lower the Al2O3 content, the better. Excessive Al2O3 content can reduce the glass's resistance to devitrification, increase its glass transition temperature (Tg), and reduce its thermal stability.

[0074] In the optical glass according to the present embodiment, the upper limit of the ZrO2 content is preferably 0.01%, and more preferably 0.05%, 0.10%, 0.30%, and 0.50%. In addition, the upper limit of the ZrO2 content is preferably 20.0%, and more preferably 15.0%, 12.0%, and 10.0%.

[0075] If the ZrO2 content is too low, there is a risk of increased erosion of refractory bricks. If the ZrO2 content is too high, there is a risk of deteriorating the meltability of the glass. From the perspective of suppressing erosion of refractory bricks and obtaining optical glass with a high refractive index, and from the perspective of maintaining the meltability and thermal stability of the glass, the ZrO2 content is preferably within the above range.

[0076] In the optical glass according to this embodiment, the upper limit of the WO3 content is 10.0%, and more preferably 5.0%, 3.0%, 2.0%, 1.0%, and 0.5% in that order. The lower limit of the WO3 content is preferably 0.0%. The WO3 content may be 0.0%.

[0077] The WO3 content is preferably within the above range to achieve an optical glass with reduced specific gravity and UV transmittance. On the other hand, excessive WO3 content can reduce internal transmittance and increase specific gravity. Furthermore, there is a risk of reduced transmittance in the visible light region, particularly in the short-wavelength region, and destabilizing the glass.

[0078] In the optical glass according to this embodiment, the upper limit of the Bi2O3 content is 5.0%, and more preferably 3.0%, 2.0%, 1.0%, and 0.5% in that order. The lower limit of the Bi2O3 content is preferably 0.0%. The Bi2O3 content may be 0.0%.

[0079] The Bi2O3 content is preferably within the above range to achieve optical glass with reduced specific gravity and UV transmittance. However, excessive Bi2O3 content increases the specific gravity and risks reducing internal transmittance, not only in the short-wavelength region, but also in the short-wavelength region. Furthermore, there is a risk of increased platinum corrosion and increased glass staining.

[0080] In the optical glass according to this embodiment, the upper limit of the Li2O content is preferably 5.0%, and more preferably 4.0%, 3.0%, and 2.0%. The lower the Li2O content, the better. The lower limit is preferably 1.0%, and more preferably 0.5%, 0.1%, and 0.0%, whichever is lower. The Li2O content may be 0.0%.

[0081] The Li2O content is preferably within the above range to achieve optical glass with a high refractive index, low specific gravity, and reduced raw material costs. Li2O also improves the meltability of the glass, reduces the resistivity of the molten glass, and suppresses reduction coloring that can occur during melting. On the other hand, excessive Li2O content can reduce chemical durability, weather resistance, and stability during reheating.

[0082] In the optical glass according to this embodiment, the upper limit of the Na2O content is preferably 15.0%, more preferably 12.0%, 10.0%, and 8.0%, respectively. The lower limit of the Na2O content is preferably 0.50%, more preferably 1.0%, 1.5%, and 2.0%, respectively.

[0083] From the perspective of obtaining optical glass with a reduced specific gravity, the Na2O content is preferably within the above range. Furthermore, Na2O improves the meltability of glass and reduces the specific resistivity of molten glass. On the other hand, too little Na2O may reduce the solubility of the glass. Too much Na2O may reduce the refractive index.

[0084] In the optical glass according to this embodiment, the upper limit of the K₂O content is preferably 10.0%, with 8.0%, 6.0%, 5.0%, and 4.0% being more preferred in this order. The lower the K₂O content, the more preferred it is. The lower limit is preferably 1.0%, with 0.50%, 0.30%, 0.10%, 0.05%, and 0.01% being more preferred, whichever is lower. The K₂O content may be 0.0%.

[0085] From the viewpoint of improving the meltability of the glass, it is preferable to set the content of K2O to the above range. On the other hand, if the content of K2O is too high, there is a risk of significantly lowering the refractive index.

[0086] In the optical glass according to this embodiment, the upper limit of the Cs2O content is preferably 15.0%, and more preferably 10.0%, 5.0%, 4.0%, 3.0%, 2.0%, and 1.0%. The lower limit of the Cs2O content is preferably 0.0%. The Cs2O content may also be 0.0%.

[0087] Cs2O has the effect of improving the meltability of glass and improving thermal stability. On the other hand, when the content of Cs2O is too high, there is a risk of significantly lowering the refractive index and deteriorating the chemical durability of the glass.

[0088] In the optical glass according to this embodiment, the upper limit of the MgO content is preferably 10.0%, and more preferably 8.0%, 6.0%, 4.0%, and 2.0%. Furthermore, the lower the MgO content, the better, and the lower limit is preferably 0.0%. The MgO content may also be 0.0%.

[0089] From the perspective of improving the stability of the glass and reducing the coloring of the glass, it is preferable to set the MgO content within the above range. On the other hand, if the MgO content is too high, there is a risk that a high refractive index and a low specific gravity cannot be achieved at the same time.

[0090] In the optical glass according to the present embodiment, the upper limit of the CaO content is preferably 20.0%, and more preferably 18.0%, 16.0%, 14.0%, 12.0%, and 10.0%. In addition, the lower limit of the CaO content is preferably 1.0%, and more preferably 2.0%, 3.0%, and 4.0%.

[0091] From the viewpoint of obtaining an optical glass having a high refractive index, a low specific gravity, and improved meltability, it is preferred that the CaO content be within the above range. On the other hand, if the CaO content is too low, there is a risk of not being able to achieve both a high refractive index and a low specific gravity. In addition, if the CaO content is too high, there is a risk of reducing the thermal stability of the glass and reducing the anti-devitrification property.

[0092] In the optical glass according to this embodiment, the upper limit of the SrO content is preferably 20.0%, and more preferably 19.0%, 18.0%, 17.0%, 16.0%, and 15.0%. In addition, the lower limit of the SrO content is preferably 1.0%, and more preferably 1.5%, 2.0%, and 2.3%.

[0093] From the viewpoint of improving meltability, the SrO content is preferably within the above range. On the other hand, if the SrO content is too high, there is a risk of increasing the specific gravity, failing to maintain high dispersibility, reducing the thermal stability of the glass, and reducing the devitrification resistance.

[0094] In the optical glass according to this embodiment, the upper limit of the BaO content is preferably 25.0%, and more preferably 24.0%, 23.0%, 22.0%, 21.0%, and 20.0%. In addition, the lower limit of the BaO content is preferably 0.50%, and more preferably 0.70%, 1.0%, 1.20%, and 1.50%.

[0095] From the perspective of improving meltability, it is preferred that the BaO content be within the above range. On the other hand, if the BaO content is too low, there is a risk of reducing the stability of the glass. In addition, if the BaO content is too high, there is a risk of significantly increasing the specific gravity, making it impossible to maintain high dispersibility, reducing the thermal stability of the glass, and reducing the anti-devitrification property.

[0096] In the optical glass according to this embodiment, the upper limit of the ZnO content is preferably 10.0%, and more preferably 8.0%, 6.0%, 4.0%, and 2.0%. Furthermore, the lower the ZnO content, the better, and the lower limit is preferably 0.0%. The ZnO content may also be 0.0%.

[0097] From the viewpoint of lowering the glass transition temperature Tg, the ZnO content is preferably within the above range. On the other hand, if the ZnO content is too high, not only the specific gravity increases, but also the stability of the glass may be impaired.

[0098] In the optical glass according to this embodiment, the upper limit of the La2O3 content is preferably 10.0%, and more preferably 5.0%, 4.0%, 3.0%, 2.0%, and 1.0%. In addition, the lower limit of the La2O3 content is preferably 0.0%. The La2O3 content may also be 0.0%.

[0099] From the perspective of obtaining an optical glass with a high refractive index without deteriorating the internal transmittance of the glass, the La2O3 content is preferably within the above range. On the other hand, when the La2O3 content is too low, there is a tendency to lower the refractive index. Furthermore, when the La2O3 content is too high, there is a risk of increasing the specific gravity and reducing the thermal stability of the glass.

[0100] In the optical glass according to this embodiment, the upper limit of the Gd2O3 content is preferably 10.0%, and more preferably 5.0%, 4.0%, 3.0%, 2.0%, and 1.0%. Furthermore, the lower the Gd2O3 content, the better, and the lower limit is preferably 0.0%. The Gd2O3 content may also be 0.0%.

[0101] From the perspective of obtaining an optical glass with a high refractive index without deteriorating the internal transmittance of the glass, the Gd2O3 content is preferably within the above range. On the other hand, excessive Gd2O3 content may reduce the thermal stability of the glass and increase the specific gravity, thereby increasing manufacturing costs.

[0102] In the optical glass according to this embodiment, the upper limit of the Y2O3 content is preferably 10.0%, and more preferably 8.0%, 5.0%, 3.0%, 2.0%, and 1.5%, in that order. Furthermore, the lower limit of the Y2O3 content is preferably 0.0%.

[0103] By introducing Y2O3 within the above range to replace, for example, ZrO2 or Nb2O5, an optical glass with a high refractive index and low specific gravity can be obtained without deteriorating the internal transmittance of the glass. On the other hand, if the Y2O3 content is too low, the refractive index tends to decrease. Furthermore, if the Y2O3 content is too high, there is a risk of reducing the thermal stability of the glass and lowering its resistance to devitrification.

[0104] In the optical glass according to the present embodiment, the upper limit of the GeO2 content is preferably 10.0%, and more preferably 6.0%, 4.0%, 3.0%, 2.0%, and 1.0% in that order. Furthermore, the lower the GeO2 content, the more preferable it is, and the lower limit is preferably 0.0%.

[0105] GeO 2 is an expensive glass component, and when the GeO 2 content is too high, there is a risk of increasing the manufacturing cost.

[0106] In the optical glass according to this embodiment, the upper limit of the Ta2O5 content is preferably 5%, more preferably 3%, 2%, and 1%, respectively. The lower limit of the Ta2O5 content is preferably 0%, and the Ta2O5 content may be 0.0%.

[0107] Ta2O5 is a glass component that increases the refractive index without degrading the internal transmittance of the glass. However, Ta2O5 is an expensive glass component, and excessive Ta2O5 content can increase raw material costs and specific gravity. Therefore, the Ta2O5 content is preferably within the above range.

[0108] In the optical glass according to this embodiment, the content of Sc2O3 is preferably 2% or less. The lower limit of the content of Sc2O3 is preferably 0%.

[0109] In the optical glass according to this embodiment, the content of HfO 2 is preferably 2% or less. In addition, the lower limit of the content of HfO 2 is preferably 0%.

[0110] Sc2O3 and HfO2 are expensive components that have the effect of increasing the refractive index. Therefore, it is preferred that the content of each of Sc2O3 and HfO2 be within the above range.

[0111] In the optical glass according to this embodiment, the content of Lu 2 O 3 is preferably 2% or less. The lower limit of the content of Lu 2 O 3 is preferably 0%.

[0112] Lu2O3 has the function of adjusting the refractive index of glass, but due to its large molecular weight, it is a glass component that increases the specific gravity of glass. Therefore, the content of Lu2O3 is preferably within the above range.

[0113] In the optical glass according to this embodiment, the Yb2O3 content is preferably 2% or less, more preferably 1% or less, and even more preferably 0.5% or less. Furthermore, the lower limit of the Yb2O3 content is preferably 0%. The Yb2O3 content may also be 0.0%.

[0114] While Yb2O3 has the effect of adjusting the refractive index of glass, its high molecular weight increases the specific gravity of the glass. When the specific gravity of glass increases, the weight of the optical element increases. Therefore, it is desirable to reduce the Yb2O3 content to suppress the increase in the specific gravity of the glass.

[0115] Furthermore, when the Yb2O3 content is too high, the thermal stability of the glass decreases. Furthermore, absorption occurs in the infrared region. From the perspective of preventing a decrease in the glass's devitrification resistance and suppressing an increase in specific gravity, the Yb2O3 content is preferably within the above range.

[0116] Preferably, the optical glass involved in this embodiment is mainly composed of the above-mentioned components, that is, SiO2, TiO2 and Nb2O5 as essential components, and B2O3, P2O5, Al2O3, ZrO2, WO3, Bi2O3, Li2O, Na2O, K2O, Cs2O, MgO, CaO, SrO, BaO, ZnO, La2O3, Gd2O3, Y2O3, GeO2, Ta2O5, Sc2O3, HfO2, Lu2O3 and Yb2O3 as arbitrary components, and the total content of the above-mentioned glass components is preferably 95% or more, more preferably 98% or more, further preferably 99% or more, and further preferably 99.5% or more.

[0117] In addition, although it is preferred that the optical glass involved in this embodiment is basically composed of the above-mentioned glass components, it can also contain other components within the range that does not affect the effects of the present invention. In addition, in the present invention, the inclusion of inevitable impurities is not excluded.

[0118] (Other ingredients)

[0119] Cd, Tl, Be, and Se are all toxic. Therefore, it is preferable that the optical glass according to this embodiment does not contain these elements as glass components.

[0120] U, Th, and Ra are all radioactive elements. Therefore, it is preferable that the optical glass according to this embodiment does not contain these elements as glass components.

[0121] V, Cr, Mn, Fe, Co, Ni, Cu, Pr, Nd, Pm, Sm, Eu, Tb, Dy, Ho, Er, and Tm can increase the coloration of glass and turn it into a fluorescent light source. Therefore, although the optical glass of this embodiment can contain trace amounts of these elements within a range that does not impair the functions of the optical glass, it is preferably substantially free of these elements as glass components.

[0122] Sb2O3 and CeO2 are elements that can be added arbitrarily, acting as fining agents. Sb2O3 is the most effective fining agent. CeO2 has a lesser fining effect than Sb2O3. Adding large amounts of CeO2 can increase the coloring of the glass.

[0123] The Sb2O3 content is expressed as an external ratio. That is, when the total content of all glass components other than Sb2O3 and CeO2 is set to 100% by mass, the Sb2O3 content is preferably 1.0% by mass or less, and more preferably 0.4% by mass or less, 0.2% by mass or less, 0.1% by mass or less, 0.05% by mass or less, 0.03% by mass or less, 0.02% by mass or less, and 0.01% by mass or less, in that order. The Sb2O3 content may also be 0%.

[0124] The CeO2 content is also expressed as an external ratio. That is, when the total content of all glass components other than CeO2 and Sb2O3 is taken as 100% by mass, the CeO2 content is preferably within a range of 2% by mass or less, more preferably 1% by mass or less, even more preferably 0.5% by mass or less, and even more preferably 0.1% by mass or less. The CeO2 content may also be 0%. By adjusting the CeO2 content within the above range, the clarity of the glass can be improved.

[0125] (Glass properties)

[0126] <Refractive Index nd>

[0127] In the optical glass of this embodiment, the upper limit of the refractive index nd can be 2.00, and further can be 1.99, 1.98, 1.97, 1.96, or 1.95. In addition, the lower limit of the refractive index nd can be 1.82, and further can be 1.83, 1.84, or 1.85. The refractive index can be controlled by adjusting the content of TiO2, Nb2O5, ZrO2, Y2O3, etc., which are glass components that contribute to increasing the refractive index, or by adjusting the content of low-refractive-index components such as SiO2, Al2O3, and B2O3, or by introducing modifying components such as CaO.

[0128] <Abbe number vd>

[0129] In the optical glass of this embodiment, the upper limit of the Abbe number vd can be 30.0, and can also be 29.0, 28.0, 27.0, 26.0, 25.0, or 24.0. Furthermore, the lower limit of the Abbe number vd can be 15.0, and can also be 16.0, 17.0, 18.0, 19.0, 20.0, 21.0, or 22.0. By adjusting the Abbe number vd within the above range, a glass with desired dispersibility can be obtained. The Abbe number vd can be controlled by adjusting the content of TiO2, Nb2O5, WO3, ZrO2, and Bi2O3, which are glass components that contribute to improved dispersion.

[0130] <Specific Gravity of Glass>

[0131] The optical glass involved in this embodiment is a high-refractive-index glass with a low specific gravity. If the specific gravity of the glass can be reduced, the weight of the lens can be reduced. On the other hand, when the specific gravity is too low, thermal stability is reduced.

[0132] Therefore, in the optical glass according to this embodiment, the upper limit of the specific gravity is preferably 7.0, more preferably 6.0, 5.0, 4.5, and 4.0 in that order. The lower limit of the specific gravity is preferably 2.5, more preferably 2.8, 3.0, and 3.2 in that order.

[0133] The specific gravity is determined by the atomic weight of the structural components contained in the glass and the volume occupied by these atoms. For example, when an oxide containing an element from the sixth period or an element with an atomic number greater than 57 is introduced, there is a tendency for the specific gravity to increase. However, if the volume occupied by the element is also large, the increase in specific gravity can be suppressed. However, when the volume occupied by an element is too large, the refractive index decreases. In addition, the volume occupied by an element is not fixed and may vary slightly due to the presence of other glass components. The specific gravity value can be controlled by adjusting the total content and ratio of each component in this way. In addition, the volume occupied by each element may also vary slightly due to the slow cooling conditions of the glass.

[0134] <Glass transition temperature Tg>

[0135] In the optical glass according to this embodiment, the upper limit of the glass transition temperature (Tg) is not particularly limited. However, considering productivity factors such as the time required for slow cooling, it is preferably 850°C, with 800°C, 750°C, and 700°C being more preferred in that order. Furthermore, the lower limit of the glass transition temperature (Tg) is not particularly limited. However, from the perspective of ensuring that the optical glass has appropriate heat resistance, it is preferably 100°C, with 200°C, 300°C, 400°C, and 500°C being more preferred in that order. The glass transition temperature (Tg) can be controlled by adjusting the amount of network-forming components in the glass and the ratio of the components.

[0136] By satisfying the above upper limit of the glass transition temperature Tg, increases in the molding temperature and annealing temperature during reheating and pressing of the glass can be suppressed, and thermal damage to reheating press molding equipment and annealing equipment can be reduced.

[0137] By satisfying the above lower limit of the glass transition temperature Tg, it is possible to maintain a desired Abbe number and refractive index, and to easily maintain good reheating press moldability and thermal stability of the glass.

[0138] <Glass Coloring>

[0139] In the optical glass of this embodiment, light transmittance is evaluated using the tinting degrees λ80, λ70, and λ5. Spectral transmittance is measured for a glass sample with a thickness of 10.0 mm ± 0.1 mm within a wavelength range of 200 to 700 nm, with the wavelength at which external transmittance reaches 80% being λ80, the wavelength at which external transmittance reaches 70% being λ70, and the wavelength at which external transmittance reaches 5% being λ5. The upper limit of λ80 for the optical glass of this embodiment is preferably 690 nm, with 685 nm and 680 nm being possible. The upper limit of λ70 is preferably 680 nm, with 670 nm and 660 nm being possible. The upper limit of λ5 is preferably 400 nm, with 395 nm and 390 nm being possible.

[0140] (Manufacturing of optical glass)

[0141] The optical glass involved in this embodiment can be manufactured by mixing glass raw materials in a manner that forms the above-mentioned specified composition and using the mixed glass raw materials according to a known glass manufacturing method. For example, a plurality of compounds are mixed and fully mixed to form a batch of raw materials. The batch of raw materials is placed in a crucible composed of refractory bricks and heated to form molten glass. Then, after clarification and homogenization, the molten glass is shaped and slowly cooled to obtain the optical glass. The clarification and homogenization process can be appropriately melted in a platinum crucible. When melting in a platinum crucible, in order to suppress oxidation of the platinum, it can also be melted in a non-oxidizing environment, such as a nitrogen environment or a water vapor environment. The molding and slow cooling of the molten glass can be performed using known methods. In addition, cullet obtained by rapidly cooling the molten glass after coarse melting in refractory bricks, quartz crucibles, etc. can also be used as a raw material in the glass raw materials.

[0142] In addition, as long as the desired glass components in the glass can be introduced in the desired content, there is no particular limitation on the compounds used when mixing the batch raw materials, but examples of such compounds include oxides, carbonates, nitrates, hydroxides, hydrates, fluorides, chlorides, etc.

[0143] (Manufacturing of optical components, etc.)

[0144] Optical elements produced using the optical glass according to the embodiments of the present invention can be produced using known methods. For example, in the production of the optical glass described above, molten glass is poured into a mold and formed into a plate to produce a glass blank comprising the optical glass according to the present invention. The resulting glass blank is then appropriately cut, ground, and polished to produce slices of a size and shape suitable for press molding. The slices are heated and softened, and then press molded (reheated and pressed) using known methods to produce a semi-finished optical element having a shape similar to that of the optical element. The semi-finished optical element is annealed, ground, and polished using known methods to produce the optical element.

[0145] The optical functional surface of the manufactured optical element may be coated with an antireflection film, a total reflection film, or the like, depending on the intended use.

[0146] According to one embodiment of the present invention, an optical element composed of the above-mentioned optical glass can be provided. Examples of optical element types include plane lenses, spherical lenses, aspherical lenses, prisms, diffraction gratings, light guide plates, and the like. Examples of lens shapes include biconvex lenses, plano-convex lenses, biconcave lenses, plano-concave lenses, convex meniscus lenses, and concave meniscus lenses.

[0147] Optical elements can be manufactured by a method comprising processing a glass molded body composed of the above-mentioned optical glass. Examples of processing include cutting, chipping, rough grinding, fine grinding, and polishing. By using the above-mentioned glass, breakage can be reduced, and high-quality optical elements can be stably provided.

[0148] The light guide plate can be made using the above-mentioned optical glass by a known method. As the use of the light guide plate, display devices such as glasses-type devices of augmented reality (AR) display type, mixed reality (MR) display type or virtual reality (VR) display type can be exemplified. Such a light guide plate is a plate-shaped glass mounted on the frame of the glasses-type device, and is composed of the above-mentioned optical glass. If necessary, a diffraction grating can also be formed on the surface of the light guide plate, and the diffraction grating is used to change the direction of travel of light that is propagated by repeated total reflection inside the light guide plate. The diffraction grating can be formed by a known method. When a glasses-type device having the above-mentioned light guide plate is worn, the light propagating inside the light guide plate enters the pupil, thereby exhibiting the functions of augmented reality (AR) display, mixed reality (MR) display or virtual reality (VR) display. For example, Japanese Patent Publication No. 2017-534352 discloses such a glasses-type device.

[0149] Optical components, particularly lenses and light guide plates, can be made less susceptible to breakage by chemically strengthening the glass during the manufacturing process. Chemical strengthening can be performed using a known method.

[0150] [Example]

[0151] Hereinafter, the present invention will be described in further detail with reference to Examples. However, the present invention is not limited to the embodiments shown in the Examples.

[0152] (Example 1)

[0153] Glass samples having the glass compositions shown in Tables 1(1) to (4), 2(1) to (4), and 3(1) to (4) were prepared in the following order and various evaluations were performed. No. 64 is a comparative example.

[0154] [Production of optical glass]

[0155] Prepare oxides, hydroxides, carbonates, and nitrates corresponding to the structural components of the glass as raw materials. Weigh and blend the raw materials so that the optical glass obtained has the glass composition shown in Table 1 (1) to (4). The raw materials are thoroughly mixed. The blended raw materials (batch raw materials) obtained in this manner are placed in a crucible made of refractory oxide and heated at 1150°C to 1450°C for 1 hour to form molten glass. After being transferred to a platinum crucible, the molten glass is stirred to make it uniform and clarified. The molten glass is then poured into a mold preheated to an appropriate temperature. Alternatively, the pre-blended raw materials are placed in a platinum crucible, heated for 2 hours, and then poured into a mold using the same procedure. The poured glass is heat treated at a temperature near the glass transition temperature Tg or about 10 to 100°C lower than Tg for 30 minutes, and then allowed to cool to room temperature in a furnace to obtain a glass sample.

[0156] [Confirmation of glass composition]

[0157] The content of each glass component of the obtained glass sample was measured using inductively coupled plasma atomic emission spectrometry (ICP-AES), and it was confirmed that it matched the compositions shown in Table 1 (1) to (4).

[0158] [Measurement of optical properties]

[0159] The obtained glass sample was further annealed at about 30 minutes to about 2 hours near the glass transition temperature Tg, and then cooled to room temperature in a furnace at a cooling rate of -30°C / hour to obtain an annealed sample. The refractive indices nd, ng, and n of the obtained annealed sample were measured. F and n C , Abbe number vd, specific gravity, glass transition temperature Tg, and coloring degrees λ80, λ70, and λ5. The results are shown in Tables 4(1) to (4).

[0160] (i) Refractive index nd, ng, n F 、n C and the Abbe number vd

[0161] The refractive indexes nd, ng, and n were measured using the refractive index measurement method of JIS B 7071-1. F 、n C , calculate the Abbe number vd according to the following formula.

[0162] vd=(nd-1) / (n F -n C )

[0163] (ii) Specific gravity

[0164] Specific gravity was measured using the Archimedes method.

[0165] (iii) Glass transition temperature Tg

[0166] The glass transition temperature Tg was measured using a differential scanning calorimeter (DSC3300SA) manufactured by NETZSCH Japan Co., Ltd. at a heating rate of 10° C. / min.

[0167] (iv) Coloring degrees λ80, λ70, λ5

[0168] The above sample was processed to a thickness of 10 mm and to have parallel, optically polished flat surfaces. Spectral transmittance was measured over the wavelength range of 280 nm to 700 nm. The intensity of light incident perpendicularly on one optically polished surface was defined as intensity A, and the intensity of light emitted from the other surface was defined as intensity B. The spectral transmittance B / A was calculated. The wavelength at which the spectral transmittance was 80% was defined as λ80, the wavelength at which the spectral transmittance was 70% was defined as λ70, and the wavelength at which the spectral transmittance was 5% was defined as λ5. The spectral transmittance also includes light reflection losses at the sample surface.

[0169]

Table 1(1)

[0170]

[0171]

Table 1(2)

[0172]

[0173]

Table 1(3)

[0174]

[0175]

Table 1(4)

[0176]

[0177]

Table 2(1)

[0178]

[0179]

Table 2(2)

[0180]

[0181]

Table 2(3)

[0182]

[0183]

Table 2(4)

[0184]

[0185]

Table 3(1)

[0186]

[0187]

Table 3(2)

[0188]

[0189]

Table 3(3)

[0190]

[0191]

Table 3(4)

[0192]

[0193]

Table 4(1)

[0194]

[0195]

Table 4(2)

[0196]

[0197]

Table 4(3)

[0198]

[0199]

Table 4(4)

[0200]

[0201] (Example 2)

[0202] Using each optical glass produced in Example 1, a lens semi-finished product was produced by a known method, and the lens semi-finished product was processed by a known method such as polishing to produce various lenses.

[0203] The optical lenses produced include various lenses, such as plane lenses, biconvex lenses, biconcave lenses, plano-convex lenses, plano-concave lenses, concave meniscus lenses, and convex meniscus lenses. Semi-finished lenses can also be made by cutting optical glass without heating and softening it. Prisms can also be made using the optical glasses produced in Example 1 using known methods.

[0204] Furthermore, each optical glass produced in Example 1 was used to produce a light guide plate for an augmented reality display device such as a wearable display by a known method.

[0205] The light guide plate produced is lighter than light guide plates with the same optical properties and size due to the low specific gravity of glass, and is suitable as a light guide plate for augmented reality display devices such as wearable displays.

[0206] The embodiments disclosed herein are illustrative in all respects and are not restrictive. The scope of the present invention is indicated by the scope of the claims, not by the foregoing description, and is intended to include all modifications within the meaning and scope equivalent to the scope of the claims.

[0207] For example, the optical glass according to one embodiment of the present invention can be produced by adjusting the composition described in the specification with respect to the glass composition exemplified above.

[0208] Furthermore, it is of course possible to arbitrarily combine two or more items described as examples or preferred ranges in the specification.

Claims

1. An optical glass, wherein: The content of SiO2 is 5% by mass or more, The content of B2O3 is 15% by mass or less, The total content of Li2O, Na2O and K2O [Li2O+Na2O+K2O] is 1 to 15% by mass. The mass ratio of the content of Li2O to the total content of Li2O, Na2O and K2O [Li2O / (Li2O+Na2O+K2O)] is 0.5 or less, The mass ratio of the content of K2O to the total content of Li2O, Na2O and K2O [K2O / (Li2O+Na2O+K2O)] is 0.5 or less, The mass ratio of the total content of Li2O, Na2O and K2O to the total content of MgO, CaO, SrO and BaO [(Li2O+Na2O+K2O) / (MgO+CaO+SrO+BaO)] is 0.6 or less, The content of TiO2 is 15% by mass or more, The content of Nb2O5 is 1 to 30% by mass. The mass ratio of the SiO2 content to the TiO2 content [SiO2 / TiO2] is 1.0 or less, The total content of MgO, CaO, SrO and BaO [MgO+CaO+SrO+BaO] is 5% by mass or more, and the mass ratio of the BaO content to the total content of MgO, CaO, SrO and BaO [BaO / (MgO+CaO+SrO+BaO)] is 0.7 or less, The total content of TiO2 and Nb2O5 [TiO2 + Nb2O5] is 30% by mass or more, The mass ratio of the TiO2 content to the total content of TiO2, Nb2O5, Y2O3, ZrO2, La2O3, Gd2O3, Ta2O5, WO3, Yb2O3 and Bi2O3 [TiO2 / (TiO2+Nb2O5+Y2O3+ZrO2+La2O3+Gd2O3+Ta2O5+WO3+Yb2O3+Bi2O3)] is greater than 0.

6.

2. An optical element composed of the optical glass according to claim 1.

3. A light guide plate composed of the optical glass according to claim 1.

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