Chemically strengthened optical glass

Abstract

Provided is a high-hardness chemically strengthened optical glass in which crack resistance is enhanced while the refractive index and Abbe number required in the conventional optical glass are maintained.　A chemically strengthened optical glass characterized by having a compressive stress layer on the surface thereof and by containing, in terms of oxide-equivalent mass%, 2.0-20.0% of a SiO2 component, 5.0-35.0% of a B2O3 component, 20.0-60.0% of a La2O3 component, 2.0-25.0% of a TiO2 component, 2.0-15.0% of a Nb2O5 component, and more than 0% to 10.0% of a Li2O component, and in that Hv change rate [(Hvafter – Hvbefore) / Hvbefore] × 100 ≥ 3.0%.

Description

Technical Field

[0001] The present invention relates to a chemically strengthened optical glass having a compressive stress layer on its surface.

Background Art

[0002] In recent years, wearable terminals used in AR (virtual reality) and VR (virtual reality) such as projector glasses, glasses-type displays, goggle-type displays, virtual reality display devices, augmented reality display devices, and virtual image display devices, and in-vehicle cameras have attracted attention.

[0003] Since such wearable terminals and in-vehicle cameras are assumed to be used in a harsh external environment, while maintaining the high refractive index, Abbe number, and transmittance required for conventional optical glasses, impact resistance, wind pressure resistance, scratch resistance, etc. (hereinafter referred to as "crack resistance") are improved. There is a demand for high-hardness optical glass. There is also a requirement for miniaturization.

[0004] Patent Document 1 discloses a high refractive index and high dispersion glass having a refractive index (nd) of 1.64 to 1.83 and an Abbe number (νd) of 36 to 56, which addresses the digitalization and high definition of optical devices. However, it is not assumed to be used in a harsh external environment, and there is no disclosure of high-hardness optical glass with crack resistance as an issue. In addition, at the time of filing Patent Document 1 and the like, modern cutting-edge technologies such as VR and AR were not generally popularized. Furthermore, since the spread of in-vehicle cameras, which are the main players in "peripheral recognition sensors" for automotive autonomous driving and safety assurance, has increased rapidly in recent years, high-hardness optical glass with improved crack resistance was not assumed at the time of filing Patent Document 1.

[0005] Furthermore, in the case of high-strength optical glass, since it is possible to make the glass used for the optical lens thinner, the optical lens can be thinned and miniaturized.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] Therefore, an object of the present invention is to obtain a high-hardness optical glass having improved crack resistance while maintaining the refractive index and Abbe number required for conventional optical glasses.

Means for Solving the Problems

[0008] As a result of intensive test research to solve the above problems, the present inventor has found a glass composition and formulation suitable for obtaining a high-hardness optical glass having a high Vickers hardness (Hv) with a compressive stress layer on the surface by chemically strengthening the optical glass, and has completed the present invention. Specifically, the present invention provides the following.

[0009] (1) Having a compressive stress layer on the surface, In terms of mass% in terms of oxides, The SiO2 component is 2.0 to 20.0%, The B2O3 component is 5.0 to 35.0%, The La2O3 component is 20.0 to 60.0%, The TiO2 component is 2.0 to 25.0%, The Nb2O5 component is 2.0 to 15.0%, Containing more than 0% to 10.0% of the Li2O component, Hv change rate [(Hv after -Hv before ) / Hv before ×100≧3.0%, which is a chemically strengthened optical glass.

[0010] (2)The chemically strengthened optical glass according to (1), further containing 0 to 15.0% of the Y2O3 component and 0 to 15.0% of the ZrO2 component.

[0011] ​ (3) The chemically strengthened optical glass according to (1) or (2), characterized in that the value of the mass ratio CaO / Li2O is 2.0 or less.

[0012] (4) The chemically strengthened optical glass according to any one of (1) to (3), characterized in that the value of the mass ratio Ln2O3 / Li2O is 2.0 to 200.0.

[0013] (5) The chemically strengthened optical glass according to any one of (1) to (4), characterized in that the value of the mass ratio TiO2 / Li2O is 0.2 to 40.

[0014] (6) The chemically strengthened optical glass according to any one of (1) to (5), characterized in that the refractive index (nd) is 1.75 to 2.05 and the Abbe number (νd) is 20.0 to 45.0.

Advantages of the Invention

[0015] According to the present invention, it is possible to provide a chemically strengthened optical glass having a high hardness with improved crack resistance while maintaining a high refractive index and Abbe number, and having a compressive stress layer.

Embodiments for Carrying Out the Invention

[0016] The composition ranges of the respective components constituting the chemically strengthened optical glass of the present invention are described below. In this specification, the content of each component is expressed as mass% with respect to the total mass of the oxide-converted composition, unless otherwise specified. Here, the "oxide-converted composition" is a composition in which, assuming that oxides, double salts, metal fluorides, etc. used as raw materials for the glass constituent components of the present invention are all decomposed into oxides during melting, the total mass number of the generated oxides is 100 mass%, and each component contained in the glass is expressed.

[0017] [Glass Components] The chemically strengthened optical glass of the present invention has a compressive stress layer on its surface and contains, in terms of mass% in terms of oxide, 2.0 to 20.0% of SiO2 component, 5.0 to 35.0% of B2O3 component, 20.0 to 60.0% of La2O3 component, 2.0 to 25.0% of TiO2 component, 2.0 to 15.0% of Nb2O5 component, and more than 0% to 10.0% of Li2O component, and the Hv change rate [(Hv after -Hv before ) / Hv before ×100≧3.0%, which is characterized by this.

[0018] [Regarding essential components and optional components] The SiO2 component is a component that forms the network structure of the glass, is a component that reduces devitrification (generation of crystalline substances), which is not preferable as optical glass, and is an essential component of the chemically strengthened optical glass of the present invention. In particular, by setting the content of the SiO2 component to 2.0% or more, a stable optical glass can be produced. Therefore, the content of the SiO2 component is preferably 2.0% or more, more preferably 2.5% or more, more preferably 3.0% or more, more preferably 3.5% or more, more preferably 4.0% or more, and still more preferably 4.5% or more as the lower limit. On the other hand, by setting the content of the SiO2 component to 20.0% or less, an excessive increase in viscosity and deterioration of meltability can be suppressed, and a decrease in refractive index can be suppressed. Therefore, the content of the SiO2 component is preferably 20.0% or less, more preferably 15.0% or less, more preferably 12.0% or less, and still more preferably 10.0% or less as the upper limit.

[0019] The B2O3 component is a component that forms the network structure of the glass, is a component that reduces devitrification (generation of crystalline substances), which is not preferable as optical glass, and is an essential component of the chemically strengthened optical glass of the present invention. In particular, by setting the content of the B2O3 component to 5.0% or more, the formation of stable glass can be promoted and the devitrification resistance can be enhanced. Therefore, the content of the B2O3 component is preferably 5.0% or more, more preferably 8.0% or more, and still more preferably 10.0% or more as the lower limit. On the other hand, by setting the content of the B2O3 component to 35.0% or less, a decrease in the refractive index can be suppressed. Therefore, the content of the B2O3 component preferably has an upper limit of 35.0% or less, more preferably 33.0% or less, and even more preferably 30.0% or less.

[0020] The La2O3 component is a component that can improve the refractive index and is an essential component of the chemically strengthened optical glass of the present invention. In particular, by setting the content of the La2O3 component to 20.0% or more, the refractive index of the desired glass can be achieved. Therefore, the content of the La2O3 component preferably has a lower limit of 20.0% or more, more preferably 25.0% or more, and even more preferably 30.0% or more. On the other hand, by setting the content of the La2O3 component to 60.0% or less, deterioration of devitrification due to excessive addition can be reduced. Therefore, the content of the La2O3 component preferably has an upper limit of 60.0% or less, more preferably 55.0% or less, and even more preferably 53.0% or less.

[0021] The TiO2 component is a component that increases the refractive index and enhances chemical durability (acid resistance), and is an essential component of the chemically strengthened optical glass of the present invention. In particular, by setting the content of the TiO2 component to 2.0% or more, the refractive index, Abbe number, etc. of the desired glass can be achieved. Therefore, the content of the TiO2 component preferably has a lower limit of 2.0% or more, more preferably 2.5% or more, and even more preferably 3.0% or more. On the other hand, by setting the content of the TiO2 component to 25.0% or less, a decrease in the transmittance of the glass to visible light (especially light with a wavelength of 500 nm or less) can be suppressed. Therefore, the content of the TiO2 component preferably has an upper limit of 25.0% or less, more preferably 23.0% or less, even more preferably 20.0% or less, and even more preferably 18.0% or less.

[0022] The Nb2O5 component is a component that increases the refractive index and stabilizes the glass, and is an essential component of the chemically strengthened optical glass of the present invention. In particular, by setting the content of the Nb2O5 component to 2.0% or more, the devitrification resistance can be enhanced. Therefore, the content of the Nb2O5 component preferably has a lower limit of 2.0% or more, more preferably 2.5% or more, still more preferably 3.0% or more, and even more preferably 3.5% or more. On the other hand, by setting the content of the Nb2O5 component to 15.0% or less, devitrification due to excessive content can be reduced. Therefore, the content of the Nb2O5 component preferably has an upper limit of 15.0% or less, more preferably 13.0% or less, and even more preferably 11.0% or less.

[0023] When the Li2O component is contained in an amount exceeding 0%, it is a component that improves the meltability of the glass and is also a component used for ion exchange in chemical strengthening as described later, and is an essential component in the chemically strengthened optical glass of the present invention. In particular, by setting the content of the Li2O component to exceed 0%, an exchange reaction between the sodium component (sodium ion) with a large ionic radius in the molten salt and the lithium component (lithium ion) with a small ionic radius in the substrate proceeds, and as a result, a compressive stress is formed on the substrate surface. Therefore, the content of the Li2O component preferably has a lower limit of more than 0%, more preferably 0.1% or more, and even more preferably 0.2% or more. On the other hand, by setting the content of the Li2O component to 10.0% or less, a decrease in the refractive index can be suppressed, and an increase in devitrification due to excessive content can be suppressed. Therefore, the content of the Li2O component preferably has an upper limit of 10.0% or less, more preferably 8.0% or less, still more preferably 6.0% or less, and even more preferably 4.1% or less.

[0024] When the Y2O3 component is contained in an amount exceeding 0%, it is a component that can improve the refractive index, and is an optional component in the chemically strengthened optical glass of the present invention. Therefore, the content of the Y2O3 component is preferably more than 0%, more preferably 1.0% or more, still more preferably 2.0% or more, still more preferably 2.5% or more, and even more preferably 3.0% or more as the lower limit. On the other hand, by setting the content of the Y2O3 component to 15.0% or less, devitrification due to excessive content can be reduced. Therefore, the content of the Y2O3 component is preferably 15.0% or less, more preferably 13.0% or less, still more preferably 11.0% or less as the upper limit.

[0025] When the ZrO2 component contains more than 0%, it is a component that increases the refractive index of the glass and is an optional component in the chemically strengthened optical glass of the present invention. Therefore, the content of the ZrO2 component is preferably more than 0%, more preferably 1.0% or more, still more preferably 2.0% or more, still more preferably 2.5% or more, and even more preferably 3.0% or more as the lower limit. On the other hand, by setting the content of the ZrO2 component to 15.0% or less, devitrification due to excessive content of the ZrO2 component can be reduced. Therefore, the content of the ZrO2 component is preferably 15.0% or less, more preferably 13.0% or less, still more preferably 10.0% or less, still more preferably 8.0% or less, and even more preferably 7.0% or less as the upper limit.

[0026] When the Na2O component contains more than 0%, it is a component that adjusts the refractive index and Abbe number while adjusting the meltability of the glass, and in chemical strengthening, it is a component that can improve the surface compressive stress. Therefore, the content of the Na2O component is preferably more than 0%, more preferably 0.05% or more as the lower limit. On the other hand, by setting the content of the Na2O component to 10.0% or less, it is difficult to lower the refractive index of the glass and devitrification of the glass can be reduced. Therefore, the content of the Na2O component is preferably 10.0% or less, more preferably 5.0% or less, still more preferably 3.0% or less as the upper limit.

[0027] When the K2O component contains more than 0%, it is a component that adjusts the refractive index and Abbe number while adjusting the fusibility of the glass, and in chemical strengthening, it is an optional component that can improve the surface compressive stress. Therefore, the content of the K2O component is preferably more than 0%, more preferably 0.1% or more, still more preferably 0.3% or more, and even more preferably 0.4% or more as the lower limit. On the other hand, by setting the content of the K2O component to 5.0% or less, it is difficult to lower the refractive index of the glass and devitrification of the glass can be reduced. Therefore, the content of the K2O component is preferably 5.0% or less, more preferably 4.0% or less, still more preferably 3.0% or less, and even more preferably 2.0% or less as the upper limit.

[0028] When the MgO component, CaO component, SrO component, and BaO component contain more than 0%, they are components that increase the refractive index of the glass and are optional components in the chemically strengthened optical glass of the present invention. Therefore, the content of the MgO component, CaO component, SrO component, and BaO component is preferably more than 0% respectively, more preferably 0.1% or more, still more preferably 0.5% or more, and even more preferably 1.0% or more as the lower limit. On the other hand, by setting the content of the MgO component, CaO component, SrO component, and BaO component to 10.0% or less respectively, a decrease in hardness due to the salt bath during chemical strengthening can be suppressed. Therefore, the content of the MgO component, CaO component, SrO component, and BaO component is preferably 10.0% or less respectively, more preferably 8.0% or less, and even more preferably 5.0% or less as the upper limit.

[0029] When the ZnO component contains more than 0%, it is a component that increases the refractive index of the glass and is an optional component in the chemically strengthened optical glass of the present invention. Therefore, the content of the ZnO component is preferably more than 0%, more preferably 0.5% or more, and even more preferably 1.0% or more as the lower limit. On the other hand, by setting the content of the ZnO component to 10.0% or less, a decrease in hardness due to the salt bath during chemical strengthening can be suppressed. Therefore, the content of the ZnO component is preferably 10.0% or less, more preferably 8.0% or less, and even more preferably 6.0% or less as the upper limit.

[0030] When the Al2O3 component is contained in an amount exceeding 0%, it is an effective component for enhancing the chemical durability of the glass and improving the devitrification resistance of the molten glass, and is an optional component in the chemically strengthened optical glass of the present invention. Therefore, the content of the Al2O3 component is preferably more than 0%, more preferably 0.5% or more, and even more preferably 1.0% or more as the lower limit. On the other hand, by setting the content of the Al2O3 component to 5.0% or less, devitrification due to excessive content can be reduced. Therefore, the content of the Al2O3 component is preferably 5.0% or less, more preferably 4.0% or less, more preferably 3.0% or less, and even more preferably 2.0% or less as the upper limit.

[0031] The WO3 component is an optional component that can increase the refractive index, lower the Abbe number, and improve the meltability of the glass raw material. Therefore, the content of the WO3 component is preferably more than 0%, more preferably 0.5% or more as the lower limit. On the other hand, by setting the content of the WO3 component to 10.0% or less, it is difficult to increase the partial dispersion ratio of the glass, and the coloring of the glass can be reduced and the internal transmittance can be increased. Therefore, the content of the WO3 component is preferably 10.0% or less, more preferably 5.0% or less, more preferably 3.0% or less as the upper limit.

[0032] When the Sb2O3 component is contained in an amount exceeding 0%, it is an optional component that can defoam the molten glass. Therefore, the content of the Sb2O3 component may preferably be more than 0%, more preferably 0.03% or more, and even more preferably 0.05% or more as the lower limit. On the other hand, by setting the content of the Sb2O3 component to less than 1.0%, a decrease in transmittance in the short wavelength region of the visible light region, solarization of the glass, and a decrease in internal quality can be suppressed. Therefore, the content of the Sb2O3 component is preferably less than 1.0%, more preferably 0.5% or less, and even more preferably 0.3% or less.

[0033] When the sum of the contents of the RO component (wherein R is one or more selected from the group consisting of Mg, Ca, Sr, and Ba) exceeds 0%, the low-temperature fusibility can be improved. Therefore, the sum of the contents of the RO component is preferably more than 0%, more preferably 0.1% or more, and even more preferably 0.3% or more as the lower limit. On the other hand, since the sum of the contents of the RO component can suppress the decrease in devitrification resistance due to excessive content and suppress the decrease in hardness due to the salt bath during chemical strengthening, it is preferably 20.0% or less. Therefore, the sum of the contents of the RO component is preferably 20.0% or less, more preferably 15.0% or less, even more preferably 10.0% or less, still more preferably 8.0% or less, and even more preferably 5.0% or less as the upper limit.

[0034] The Gd2O3 component and the Yb2O3 component are optional components that can increase the refractive index and decrease the partial dispersion ratio by containing at least one of the components in an amount exceeding 0%. Therefore, the content of each of the Gd2O3 component and the Yb2O3 component is preferably more than 0%, more preferably 1.0% or more as the lower limit. On the other hand, if the Gd2O3 component and the Yb2O3 component are contained in a large amount, the liquidus temperature will decrease and the glass will devitrify. In particular, by setting the content of each of the Gd2O3 component and the Yb2O3 component to 15.0% or less, devitrification can be reduced and coloring can be reduced. Therefore, the content of each of the Gd2O3 component and the Yb2O3 component is preferably 15.0% or less, more preferably 10.0% or less, even more preferably 8.0% or less, still more preferably 5.0% or less, and most preferably 3.0% or less as the upper limit.

[0035] The P2O5 component is an optional component that can enhance the stability of the glass. Therefore, the content of the P2O5 component is preferably more than 0%, more preferably 0.5% or more as the lower limit. On the other hand, by setting the content of the P2O5 component to 5.0% or less, an increase in the partial dispersion ratio due to an excessive content of the P2O5 component can be reduced. Therefore, the content of the P2O5 component is preferably 5.0% or less, more preferably 3.0% or less, and even more preferably 1.0% or less as the upper limit.

[0036] The Ta2O5 component is an optional component that can increase the refractive index, decrease the Abbe number and the partial dispersion ratio, and enhance the devitrification resistance. In particular, by setting the content of the Ta2O5 component to 10.0% or less, the amount of the Ta2O5 component, which is a rare mineral resource, is reduced, and the glass is more easily melted at a lower temperature, so the production cost of the glass can be reduced. Also, this can reduce the devitrification of the glass due to an excessive content of the Ta2O5 component. Therefore, the content of the Ta2O5 component is preferably 10.0% or less, more preferably 5.0% or less, even more preferably 3.0% or less, and even more preferably 1.0% or less as the upper limit. In particular, from the viewpoint of reducing the material cost of the glass, the Ta2O5 component may not be contained.

[0037] The GeO2 component is an optional component that can increase the refractive index and reduce devitrification. By setting the content of the GeO2 component to 10.0% or less, the amount of the expensive GeO2 component used is reduced, so the material cost of the glass can be reduced. Therefore, the content of the GeO2 component is preferably 10.0% or less, more preferably 5.0% or less, even more preferably 3.0% or less, and even more preferably 1.0% or less as the upper limit.

[0038] The Ga2O3 component is an optional component that can increase the refractive index and improve the devitrification resistance. On the other hand, by setting the content of the Ga2O3 component to 10.0% or less, devitrification due to an excessive content of the Ga2O3 component can be reduced. Therefore, the content of the Ga2O3 component is preferably 10.0% or less, more preferably 5.0% or less, still more preferably 3.0% or less, and even more preferably 1.0% or less as the upper limit.

[0039] The Bi2O3 component is an optional component that can increase the refractive index and lower the Abbe number, and can also lower the glass transition point. By setting the content of the Bi2O3 component to 10.0% or less, it is difficult to increase the partial dispersion ratio, and the coloring of the glass can be reduced and the internal transmittance can be increased. Therefore, the content of the Bi2O3 component is preferably 10.0% or less, more preferably 5.0% or less, more preferably 3.0% or less, and even more preferably 1.0% or less as the upper limit.

[0040] The TeO2 component is an optional component that can increase the refractive index, lower the partial dispersion ratio, and lower the glass transition point. By setting the content of the TeO2 component to 10.0% or less, the coloring of the glass can be reduced and the internal transmittance can be increased. Also, by reducing the use of the expensive TeO2 component, glass with a lower material cost can be obtained. Therefore, the content of the TeO2 component is preferably 10.0% or less, more preferably 5.0% or less, more preferably 3.0% or less, and even more preferably 1.0% or less as the upper limit. In particular, from the perspective of reducing the material cost of the glass, the TeO2 component may not be contained.

[0041] The SnO2 component is an optional component that can clarify (defoam) the molten glass and increase the visible light transmittance of the glass. By setting the content of the SnO2 component to 1.0% or less, it is possible to make it difficult for the coloring of the glass due to the reduction of the molten glass and the devitrification of the glass to occur. Also, since the alloying of the SnO2 component and the melting equipment (especially noble metals such as Pt) is reduced, the long life of the melting equipment can be achieved. Therefore, the content of the SnO2 component is preferably 1.0% or less, more preferably 0.5% or less, and still more preferably 0.1% or less as the upper limit.

[0042] The Rn2O component (wherein Rn is one or more selected from the group consisting of Li, Na, and K) can improve the meltability of the glass when the sum (mass sum) of the contents is more than 0%. Therefore, the sum of the Rn2O components is preferably more than 0%, more preferably 0.1% or more, still more preferably 0.3% or more, and even more preferably 0.5% or more as the lower limit. On the other hand, by setting the sum (mass sum) of the contents of the Rn2O component to 20.0% or less, a decrease in refractive index can be suppressed, and devitrification due to excessive content can be reduced. Therefore, the upper limit is preferably 20.0% or less, more preferably 15.0% or less, still more preferably 10.0% or less, and even more preferably 8.0% or less.

[0043] The Ln2O3 component (wherein Ln is one or more selected from the group consisting of La, Y, Gd, and Yb) can easily obtain a high refractive index when the sum (mass sum) of the contents is 20.0% or more. Therefore, the sum of the Ln2O3 components is preferably 20.0% or more, more preferably 30.0% or more, and still more preferably 40.0% or more as the lower limit. On the other hand, by setting the sum (mass sum) of the contents of the Ln2O3 component to 70.0% or less, devitrification due to excessive content can be reduced. Therefore, the upper limit is preferably 70.0% or less, more preferably 68.0% or less, still more preferably 65.0% or less, and even more preferably 60.0% or less.

[0044] By setting the mass ratio CaO / Li2O to 2.0 or less, a decrease in hardness due to the salt bath during chemical strengthening can be suppressed. Therefore, the mass ratio CaO / Li2O preferably has an upper limit of 2.0 or less, more preferably 1.8 or less, still more preferably 1.5 or less, and even more preferably 1.2 or less. In particular, from the viewpoint of chemical strengthening, since it is possible to prevent roughening of the surface by the salt bath, it is desirable to set the mass ratio CaO / Li2O to 0.

[0045] When the mass ratio of Ln2O3 / Li2O is 2.0 or more, it is easier to obtain a high refractive index. Therefore, the mass ratio of Ln2O3 / Li2O preferably has a lower limit of 2.0 or more, more preferably 10.0 or more. On the other hand, by setting the mass ratio of Ln2O3 / Li2O to 200 or less, it is possible to prevent the deterioration of devitrification due to the excessive addition of components. Therefore, the mass ratio of Ln2O3 / Li2O preferably has an upper limit of 200 or less, more preferably 195 or less, and even more preferably 190 or less. In particular, from the viewpoint of chemical strengthening, since the increase in hardness due to chemical strengthening is likely to occur, it is desirable that the mass ratio of Ln2O3 / Li2O be less than 189.

[0046] When the mass ratio of TiO2 / Li2O is 0.2 or more, it is easier to obtain a desired refractive index and Abbe number. Therefore, the mass ratio of TiO2 / Li2O preferably has a lower limit of more preferably 0.2 or more, more preferably 0.5 or more, and even more preferably 1.0% or more. On the other hand, by setting the mass ratio of TiO2 / Li2O to 40 or less, it is possible to prevent the deterioration of devitrification due to the excessive addition of components. Therefore, the mass ratio of TiO2 / Li2O preferably has an upper limit of 40 or less, more preferably 35 or less, and even more preferably 33 or less. In particular, from the viewpoint of chemical strengthening, since the increase in hardness due to chemical strengthening is likely to occur, it is desirable that the mass ratio of TiO2 / Li2O be 30 or less.

[0047] [Manufacturing method] The chemically strengthened optical glass of the present invention is produced, for example, as follows. That is, raw materials such as oxides, carbonates, nitrates, and hydroxides are uniformly mixed so that each component is within a predetermined content range, and the prepared mixture is put into a platinum crucible and melted in an electric furnace at a temperature range of 1200 to 1500 ° C for 1 to 4 hours according to the melting difficulty of the glass composition. After stirring and homogenizing, it is cooled to an appropriate temperature and then cast into a mold and slowly cooled, and then chemically strengthened.

[0048] [Chemical strengthening] The chemical strengthening method for glass is a method for strengthening the surface of glass, which is also called the chemical strengthening method, the chemical strengthening method, or the ion exchange strengthening method. In the chemically strengthened optical glass according to the present invention, the surface of the glass is strengthened by performing an ion exchange treatment on the surface of the glass to form a surface layer (compressive stress layer) in which compressive stress remains. Ion exchange generally involves, at a temperature below the glass transition point, replacing alkali metal ions with a small ionic radius (typically, lithium ions, sodium ions) on the glass surface with alkali ions with a larger ionic radius (typically, sodium ions or potassium ions for lithium ions, and potassium ions for sodium ions) by ion exchange. As a result, compressive stress remains on the surface of the glass, and the strength of the glass is improved.

[0049] The chemical strengthening method can be implemented, for example, in the following steps. The glass base material is brought into contact with or immersed in a molten salt containing potassium or sodium, such as potassium nitrate (KNO3), sodium nitrate (NaNO3), or a mixed salt or composite salt thereof. This treatment of bringing into contact with or immersing in the molten salt (chemical strengthening treatment) may be performed in one step or two steps.

[0050] For example, in the case of a two-step chemical strengthening treatment, first, it is brought into contact with or immersed in a sodium salt or a mixed salt of potassium and sodium heated at 370°C to 550°C for 1 to 1440 minutes, preferably 90 to 800 minutes. Subsequently, second, it is brought into contact with or immersed in a potassium salt or a mixed salt of potassium and sodium heated at 350°C to 550°C for 1 to 1440 minutes, preferably 60 to 800 minutes. In the case of a one-step chemical strengthening treatment, it is brought into contact with or immersed in a salt containing potassium or sodium, or a mixed salt thereof, heated at 370°C to 550°C for 1 to 1440 minutes, preferably 60 to 800 minutes.

[0051] Regarding the heat strengthening method, there is no particular limitation. For example, after heating the glass base material to 300°C to 600°C, rapid cooling such as water cooling and / or air cooling is performed. By the temperature difference between the surface and the inside of the glass substrate, a compressive stress layer can be formed. In addition, by combining with the above chemical treatment method, the compressive stress layer can also be formed more effectively.

[0052] Regarding the ion implantation method, there is no particular limitation. For example, any ions are collided with the surface of the glass base material at an acceleration energy and acceleration voltage such that the surface of the base material is not damaged, thereby implanting the ions into the surface of the base material. Thereafter, if necessary, heat treatment is performed to form a compressive stress layer on the surface in the same manner as other methods.

[0053] [Refractive Index and Abbe Number] The chemically strengthened optical glass of the present invention preferably has a high refractive index. In particular, the refractive index (nd) of the chemically strengthened optical glass of the present invention is preferably 1.75 or more, more preferably 1.78 or more, and still more preferably 1.79 or more as the lower limit. On the other hand, the upper limit of this refractive index is preferably 2.05 or less, more preferably 2.00 or less, more preferably 1.95 or less, and more preferably 1.90 or less as the upper limit. In addition, the Abbe number (νd) of the chemically strengthened optical glass of the present invention is preferably 20.0 or more, more preferably 22.0 or more, and still more preferably 25.0 or more as the lower limit. On the other hand, the upper limit of this Abbe number is preferably 45.0 or less, more preferably 40.0 or less, and still more preferably 39.0 or less as the upper limit.

[0054] [Specific Gravity] From the viewpoint of contributing to the weight reduction of optical elements and optical devices, the specific gravity of the chemically strengthened optical glass of the present invention is preferably 5.00 or less, more preferably 4.85 or less, more preferably 4.50 or less, and still more preferably 4.30 or less as the upper limit. On the other hand, the specific gravity of the optical glass of the present invention is generally 2.00 or more, more specifically 2.50 or more, and still more specifically 3.00 or more in many cases.

[0055] [Vickers hardness] The hardness of the chemically strengthened optical glass of the present invention is confirmed by Vickers hardness (Hv). Since Vickers hardness is known to correlate with scratch resistance, the scratch resistance of the present invention is expressed by Vickers hardness (Hv). That is, a chemically strengthened optical glass with improved crack resistance can be provided by setting the Hv change rate represented by the following formula to 3.0% or more. Hv change rate [(Hv after -Hv before ) / Hv before ×100 In the above formula, Hv after represents the Vickers hardness of the chemically strengthened optical glass, and Hv before represents the Vickers hardness of the optical glass before chemical strengthening. The chemically strengthened optical glass of the present invention may have an Hv change rate represented by the following formula of 3.0% or more, preferably 3.5% or more, more preferably 4.0% or more, more preferably 5.0% or more, more preferably 5.5% or more, more preferably 6.0% or more, more preferably 6.5% or more, and even more preferably 7.0% or more, thereby showing better crack resistance compared to the optical glass before chemical strengthening.

Examples

[0056] In the following examples, the present invention is shown in detail for illustrative purposes. However, it should be noted that these examples are for illustrative purposes only, and many modifications will be made by those skilled in the art without departing from the spirit and scope of the present invention.

[0057] As Examples (No. 1 to No. 25) and Comparative Example 1, glasses of various compositions as listed in Tables 1 to 4 were prepared. In each case, high-purity raw materials such as the corresponding oxides, hydroxides, carbonates, nitrates, fluorides, metaphosphate compounds, etc. were selected as raw materials for each component, weighed and mixed so as to be in the ratio of the composition of each Example shown in Tables 1 to 4, and then put into a platinum crucible. Depending on the melting difficulty of the glass composition, it was melted in an electric furnace at a temperature range of 1200 to 1400 °C for 1 to 4 hours, stirred and homogenized, then cooled to an appropriate temperature and cast into a mold or the like, and slowly cooled to obtain the product. For each of these glasses, the refractive index (nd) and Abbe number (νd) measured are shown in Tables 1 to 4.

[0058] The refractive index (nd) and Abbe number (νd) of the glass were shown as the measured values for the d-line (587.56 nm) of a helium lamp in accordance with the V-block method specified in JIS B 7071-2:2018. Also, the Abbe number (νd) was calculated from the formula Abbe number (νd)=[(nd - 1) / (n F ) - n C )] using the values of the refractive index for the F-line (486.13 nm) of a hydrogen lamp (n F ) and the refractive index for the C-line (656.27 nm) of a hydrogen lamp (n C ). Here, the refractive index (nd) and Abbe number (νd) were determined by measuring the glass obtained with a slow cooling rate of -25 °C / hr.

[0059] Thereafter, they were immersed in potassium nitrate (KNO3) (K bath) or sodium nitrate (NaNO3) (Na bath) at the temperatures and times listed in Tables 1 to 4. Also, the results of calculating the Hv change rate for each of these glasses are shown in Tables 1 to 4.

[0060] The specific gravity ρ of the glasses of the Examples and Comparative Example was measured based on the Japan Optical Glass Industry Association Standard JIS Z8807:2012 "Method for Measuring the Specific Gravity of Optical Glass".

[0061] The Vickers hardness of the glass was determined by dividing the load when a diamond square pyramid indenter with an angle of 136° was pressed into the test surface at a load of 980.7 mN for 10 seconds to create an indentation, by the surface area (mm 2 ) calculated from the diagonal length of the indentation depression. The measurement was performed using a micro Vickers hardness tester HMV-G21D manufactured by Shimadzu Corporation.

[0062]

Table 1

[0063]

Table 2

[0064]

Table 3

[0065]

Table 4

[0066] The chemically strengthened optical glass of the examples of the present invention showed a high refractive index while showing a Hv change rate [(Hv after -Hv before ) / Hv before ×100 ≧ 3.0%.

Claims

1. having a compressive stress layer on the surface, in terms of mass% in terms of oxide, SiO ２ component is 2.0 to 20.0%, B ２ O ３ The content is 5.0 to 23.75%, La ２ O ３ The content of the component is 36.43 to 60.0%, TiO ２ The content of the component is 2.0 to 25.0%, Nb ２ O ５ The content of the component is 2.0 to 15.0%, Li ２ contains more than 0% to 10.0% of the O component, the content of the CaO component is 5.0% or less, Hv change rate [(Hv ａｆｔｅｒ - Hv ｂｅｆｏｒｅ ) / Hv ｂｅｆｏｒｅ × 100 ≥ 3.0% is a characteristic of chemically strengthened optical glass.

2. Y ２ O ３ The content of the component is 0 to 15.0%, ZrO ２ The chemically strengthened optical glass according to claim 1, further containing 0 to 15.0% of the ２ component.

3. Mass ratio CaO / Li ２ The chemically strengthened optical glass according to claim 1 or 2, characterized in that the value of O is 2.0 or less.

4. Mass ratio of Ln ２ O ３ / Li ２ The chemically strengthened optical glass according to any one of claims 1 to 3, characterized in that the value of O / LiO is from 2.0 to 200.

0.

5. Mass ratio of TiO ２ / Li ２ The chemically strengthened optical glass according to any one of claims 1 to 4, characterized in that the value of O is 0.2 to 40.

6. The chemically strengthened optical glass according to any one of Claims 1 to 5, characterized in that the refractive index (nd) is 1.75 to 2.05 and the Abbe number (νd) is 20.0 to 45.0.

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