Optical Glass and Optical Elements

Abstract

To provide optical glass excellent in homogeneity with a small specific gravity, while having high refractive index high dispersion characteristic; and to provide an optical element comprising optical glass.SOLUTION: In optical glass, in terms of mass%, the content of SiO2 is 20-51%, the content of TiO2 is 20-40%, the content of Na2O is 5-28%, and the content of BaO is below 2.0%. In the optical glass, preferably, the refractive index nd is 1.67-1.77 and the Abbe number νd is 26-33, more preferably, the specific gravity is 3.40 or less.SELECTED DRAWING: None

Description

[Technical field]

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

[0002] Optical glass, which has both a high refractive index and high dispersion characteristics (low Abbe number), is in high demand as a material for optical elements such as various lenses. For example, by combining it with a high refractive index, low dispersion lens, a compact, highly functional optical system for correcting chromatic aberration can be constructed. Furthermore, by making the optically functional surface of a high refractive index, high dispersion lens aspheric, various optical systems can be made even more highly functional and compact.

[0003] High refractive index, high dispersion optical glass is known in which components such as Nb2O5 and TiO2 that impart high refractive index and high dispersion properties are added to SiO2, a glass network forming component. Patent documents 1 to 3 describe such high refractive index, high dispersion optical glass. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2005-097036 A [Patent Document 2] Special Publication No. 2016-521237 [Patent Document 3] JP 2018-168011 A Summary of the Invention [Problem to be solved by the invention]

[0005] When the optical glass is SiO2-Nb2O5-TiO2-based and contains a large amount of alkali metal components, as in the optical glasses disclosed in Patent Documents 1 and 2, the bricks (refractory material) constituting the melting tank may be corroded by the molten glass during melting. As a result, foreign matter originating from the refractory material may get mixed into the glass and contaminate the glass. Another problem occurs in that the life of the melting tank is shortened.

[0006] Foreign matter in glass scatters light and reduces the quality of the optical glass. In addition, when the glass is heated, softened, and molded, the foreign matter can become the starting point for crystal precipitation, making the glass more susceptible to devitrification.

[0007] In addition, SiO2-Nb2O5-TiO2-based high refractive index, high dispersion glasses contain a relatively large amount of Nb2O5, which causes a problem of high specific gravity. In the optical glass disclosed in Patent Document 3, the Nb2O5 content is reduced, but the BaO content is high, so the specific gravity cannot be reduced sufficiently.

[0008] SUMMARY OF THE PRESENT EMBODIMENTS The present invention has an object to solve the above problems and to provide an optical glass that has a high refractive index and high dispersion characteristics, while also having a small specific gravity and good homogeneity, and an optical element made of said optical glass. [Means for solving the problem]

[0009] (1) Expressed in mass percent, SiO2 content is 20-51%, TiO2 content is 20-40%, Na2O content is 5-28%, BaO content is less than 2.0%; The total content of Li2O, Na2O, K2O and Cs2O (R2O) is 8-28%, The mass ratio of the SiO2 content to the total content of SiO2, B2O3 and P2O5 (SiO2+B2O3+P2O5) [SiO2 / (SiO2+B2O3+P2O5)] is 0.90 or more; The mass ratio of SiO2 to R2O [SiO2 / R2O] is 1.5 to 3.2. The mass ratio of the total content of SiO2 and R2O (SiO2+R2O) to the total content of TiO2 and Nb2O5 (TiO2+Nb2O5) [(SiO2+R2O) / (TiO2+Nb2O5)] is 2.6 or less, The mass ratio of the TiO2 content to the total content of TiO2, Nb2O5 and ZrO2 (TiO2+Nb2O5+ZrO2) [TiO2 / (TiO2+Nb2O5+ZrO2)] is 0.90 or more, The mass ratio of the total content of CaO and BaO (CaO+BaO) to the total content of MgO, CaO, SrO and BaO (R´O) [(CaO+BaO) / R´O] is 0.90 or more; The mass ratio of the total content of Na2O and K2O to R2O [(Na2O+K2O) / R2O] is 0.98 or more, The mass ratio of the content of BaO to the total content of Na2O, K2O and CaO [BaO / (Na2O+K2O+CaO)] is 0.15 or less; The mass ratio of the BaO content to the total content of TiO2 and Nb2O5 [BaO / (TiO2+Nb2O5)] is 0.12 or less; Optical glass.

[0010] (2) The optical glass according to (1), which has a refractive index nd of 1.67 to 1.77 and an Abbe number vd of 26 to 33.

[0011] (3) The optical glass according to (1) or (2), which has a specific gravity of 3.40 or less.

[0012] (4) An optical element made of the optical glass according to any one of (1) to (3) above. Effect of the Invention

[0013] According to one aspect of the present invention, it is possible to provide an optical glass that has a high refractive index and high dispersion characteristics, while having a relatively small specific gravity and good homogeneity. Also, according to another aspect of the present invention, it is possible to provide an optical element made of the optical glass. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] In the present invention and this specification, the glass composition of optical glass is expressed on an oxide basis unless otherwise specified. Here, "glass composition on an oxide basis" refers to a glass composition obtained by converting the glass raw materials into oxides that exist in the optical glass after all of them are decomposed during melting, and each glass component is conventionally expressed as SiO2, TiO2, etc. The content and total content of glass components are on a mass basis unless otherwise specified, and "%" means "mass%".

[0015] The content of the glass component can be quantified by known methods, such as inductively coupled plasma atomic emission spectrometry (ICP-AES), inductively coupled plasma mass spectrometry (ICP-MS), etc. In this specification and the present invention, the content of a component being 0% means that the component is substantially not contained, and it is acceptable for the component to be contained at an unavoidable impurity level.

[0016] Hereinafter, one embodiment of the present invention will be described.

[0017] The optical glass according to this embodiment contains SiO2, TiO2, and Na2O as essential components.

[0018] In the optical glass according to this embodiment, the SiO2 content is 20 to 51%. The lower limit of the SiO2 content is preferably 25%, more preferably 30%, and even more preferably 33%. From the viewpoint of maintaining the refractive index, the upper limit of the SiO2 content is preferably 50%, more preferably 49%, and even more preferably 48%.

[0019] SiO2 is a glass network forming component. If the SiO2 content is less than 20%, the thermal stability of the glass decreases and the liquidus temperature increases. In addition, the viscosity of the glass decreases when melted, making it more susceptible to corrosion of the bricks (refractories) that make up the melting tank. If the SiO2 content is more than 51%, the refractive index nd decreases, making it difficult to produce glass with the required optical properties. By keeping the SiO2 content within the above range, it is possible to maintain thermal stability and suppress corrosion of refractories.

[0020] In the optical glass according to this embodiment, the content of TiO2 is 20 to 40%. TiO2 is a component that imparts high refractive index and high dispersion characteristics. Nb2O5 and ZrO2 also impart high refractive index and high dispersion characteristics, but TiO2 is less likely to increase the specific gravity of the glass compared to Nb2O5 and ZrO2. If the content of TiO2 is more than 40%, the dispersion becomes too high, the thermal stability of the glass decreases, and the coloring of the glass becomes strong. On the other hand, if the content of TiO2 is less than 20%, it becomes difficult to obtain a desired refractive index.

[0021] Therefore, from the viewpoint of obtaining a desired refractive index, the lower limit of the TiO2 content is preferably 22%, more preferably 24%, and even more preferably 25%. From the viewpoint of maintaining thermal stability, suppressing coloration, and achieving a desired dispersion, the upper limit of the TiO2 content is preferably 38%, more preferably 36%, and even more preferably 35%. By setting the TiO2 content within the above range, it is possible to maintain the thermal stability of the glass while suppressing an increase in specific gravity, and to achieve the desired optical properties.

[0022] In the optical glass according to this embodiment, the Na2O content is 5 to 28%. Na2O improves the meltability of glass and has the function of adjusting the viscosity of the molten glass. If the Na2O content is less than 5%, the viscosity adjustment function becomes insufficient. On the other hand, if the Na2O content is more than 28%, the refractive index decreases and the viscosity of the molten glass decreases, causing significant corrosion of the refractory material by the molten glass.

[0023] Therefore, from the viewpoints of improving the meltability and optimizing the viscosity of the molten glass, the lower limit of the Na2O content is preferably 8%, and more preferably 10%, 12%, and 13%, in that order. On the other hand, from the viewpoints of suppressing corrosion of the refractory material during glass melting and achieving a desired refractive index, the upper limit of the Na2O content is preferably 25%, and more preferably 23%, 21%, 19%, and 17%, in that order.

[0024] In the optical glass according to this embodiment, the content of BaO is less than 2.0%. BaO is a component that increases the specific gravity. Therefore, the upper limit of the content of BaO is preferably 1.5%, more preferably 1.0%, and even more preferably 0.5%. The lower limit of the content of BaO is preferably 0%. The content of BaO may be 0%. By setting the content of BaO within the above range, an increase in the specific gravity can be suppressed.

[0025] In the optical glass according to this embodiment, the total content of Li2O, Na2O, K2O, and Cs2O (hereinafter sometimes referred to as "R2O") is 8 to 28%. Li2O, Na2O, K2O, and Cs2O are components that act to improve the meltability of glass. If R2O is less than 8%, the meltability decreases, raw materials are more likely to remain unmelted, and the viscosity of the molten glass becomes too high, reducing the fluidity of the molten glass and decreasing the amount of glass produced per unit time. On the other hand, if R2O is more than 28%, the viscosity of the molten glass decreases, and a melting tank made of a refractory material such as bricks is more likely to be corroded by the molten glass.

[0026] Therefore, the lower limit of R2O is preferably 9%, and more preferably 10%, 12%, and 13% in that order. From the viewpoint of suppressing corrosion of the refractory, the upper limit of R2O is preferably 26%, more preferably 24%, and still more preferably 22%. By keeping R2O within the above range, meltability and glass productivity can be maintained.

[0027] In the optical glass according to this embodiment, the mass ratio of the content of SiO2 to the total content of SiO2, B2O3 and P2O5 (SiO2+B2O3+P2O5) [SiO2 / (SiO2+B2O3+P2O5)] is 0.90 or more. In the optical glass according to this embodiment, the network forming component is mainly SiO2, and the content of SiO2 is remarkably higher than the contents of B2O3 and P2O5, which can be network forming components other than SiO2.

[0028] Therefore, the preferred lower limit of the mass ratio [SiO2 / (SiO2+B2O3+P2O5)] is 0.95, and the more preferred lower limit is 0.98. The preferred upper limit of the mass ratio is 1. The mass ratio may be 1. By setting the mass ratio within the above range, the desired properties can be obtained.

[0029] In the optical glass according to this embodiment, the mass ratio [SiO2 / R2O] of the content of SiO2 to the total content R2O of Li2O, Na2O, K2O, and Cs2O is 1.5 to 3.2. If this mass ratio is less than 1.5, the refractory material is significantly corroded by the molten glass, and particulate refractory material from the corroded wall of the melting tank is likely to enter the molten glass and contaminate the glass, or the life of the melting tank is likely to be shortened. On the other hand, if this mass ratio is greater than 3.2, problems such as reduced meltability, more likely to remain raw materials, and an excessively high viscosity of the molten glass, which is likely to reduce the amount of glass produced per unit time, are likely to occur.

[0030] Therefore, the lower limit of the mass ratio [SiO2 / R2O] is preferably 1.7, and more preferably 1.9, 2.1, and 2.3 in that order. The upper limit of the mass ratio is preferably 3.1, and more preferably 3.0. By setting the mass ratio within the above range, corrosion of the refractory material by the molten glass can be suppressed, and a decrease in meltability can be suppressed.

[0031] In the optical glass according to this embodiment, the mass ratio [(SiO2+R2O) / (TiO2+Nb2O5)] of the total content of SiO2 and R2O (SiO2+R2O) to the total content of TiO2 and Nb2O5 (TiO2+Nb2O5) is 2.6 or less. Among the glass components, TiO2 and Nb2O5 have a strong effect of increasing the refractive index, while SiO2 and alkali metal oxides have a weaker effect of increasing the refractive index than TiO2 and Nb2O5.

[0032] Therefore, the preferred upper limit of the mass ratio [(SiO2+R2O) / (TiO2+Nb2O5)] is 2.5, more preferably 2.3, and even more preferably 2.1. The preferred lower limit of the mass ratio is 1.4, more preferably 1.5, and even more preferably 1.6. By setting the mass ratio within the above range, a glass with a high refractive index can be obtained.

[0033] In the optical glass according to this embodiment, the mass ratio [TiO2 / (TiO2+Nb2O5+ZrO2)] of the content of TiO2 to the total content (TiO2+Nb2O5+ZrO2) of TiO2, Nb2O5, and ZrO2 is 0.90 or more. The preferred lower limit of this mass ratio is 0.95, and the more preferred lower limit is 0.98. The preferred upper limit of this mass ratio is 1. This mass ratio may be 1. Among TiO2, Nb2O5, and ZrO2, which have a strong effect of increasing the refractive index, TiO2 is the component that is relatively difficult to increase the specific gravity. By setting this mass ratio in the above range, it is possible to obtain a desired refractive index while suppressing an increase in the specific gravity.

[0034] In the optical glass according to this embodiment, the mass ratio [(CaO+BaO) / R'O] of the total content (CaO+BaO) of CaO and BaO to the total content (R'O) of MgO, CaO, SrO and BaO is 0.90 or more. The preferred lower limit of this mass ratio is 0.95, and more preferably 0.98. The preferred upper limit of this mass ratio is 1. This mass ratio may be 1. Among alkaline earth metal oxides, CaO and BaO are components that have a strong effect of maintaining the thermal stability of the glass when introduced in appropriate amounts. By setting this mass ratio in the above range, the thermal stability of the glass can be maintained. In addition, in the optical glass according to this embodiment, by setting the above mass ratio in the above range while reducing the content of BaO, an increase in specific gravity can be suppressed.

[0035] In the optical glass according to this embodiment, the mass ratio of the total content of Na2O and K2O to R2O [(Na2O+K2O) / R2O] is 0.98 or more. The preferred lower limit of the mass ratio is 0.99. The preferred upper limit of the mass ratio is 1. The mass ratio may be 1. Among the alkali metal oxides, Li2O has a relatively strong effect of corroding refractories, and Cs2O is more likely to increase the specific gravity than other alkali metal oxides. Among the alkali metal oxides, Na2O and K2O are excellent in maintaining the thermal stability of the glass. Therefore, by setting the mass ratio in the above range, it is possible to suppress the corrosion of the refractory and the increase in specific gravity, and to maintain the thermal stability of the glass.

[0036] In the optical glass according to this embodiment, the mass ratio of the content of BaO to the total content of Na2O, K2O, and CaO [BaO / (Na2O+K2O+CaO)] is 0.15 or less. The preferred upper limit of this mass ratio is 0.12, and more preferably 0.10. The preferred lower limit of this mass ratio is 0. This mass ratio may be 0. Na2O, K2O, and CaO have the function of improving the meltability of the glass. In addition, BaO is a component that increases the specific gravity. Therefore, by setting this mass ratio in the above range, the meltability can be improved and the increase in specific gravity can be suppressed.

[0037] In the optical glass according to this embodiment, the mass ratio of the content of BaO to the total content of TiO2 and Nb2O5 [BaO / (TiO2+Nb2O5)] is 0.12 or less. The preferred upper limit of this mass ratio is 0.10, and the more preferred upper limit is 0.08. The preferred lower limit of this mass ratio is 0. This mass ratio may be 0. TiO2 and Nb2O5 are components that impart high refractive index and high dispersion characteristics. Also, BaO is a component that increases the specific gravity. Therefore, by setting this mass ratio in the above range, it is possible to suppress an increase in specific gravity while maintaining the desired high refractive index and high dispersion characteristics.

[0038] Non-limiting examples of the contents and ratios of glass components other than those described above in the optical glass according to this embodiment are given below.

[0039] In the optical glass according to this embodiment, the mass ratio of the total content of CaO and TiO2 to the content of SiO2 [(CaO+TiO2) / SiO2] is preferably 1.10, more preferably 1.08, and even more preferably 1.07. The preferred lower limit of this mass ratio is 0.90, more preferably 0.92, and even more preferably 0.93. From the viewpoint of obtaining a glass with good thermal stability, it is preferable that this mass ratio is within the above range.

[0040] In the optical glass according to this embodiment, the upper limit of the total content (R'O) of MgO, CaO, SrO and BaO is preferably 20%, more preferably 16%, 14% and 12%, in that order. The lower limit of R'O is preferably 2%, more preferably 4%, 5% and 6%, in that order. From the viewpoints of improving meltability and suppressing a decrease in thermal stability, it is preferable that R'O is within the above range.

[0041] In the optical glass according to this embodiment, the upper limit of the mass ratio of the BaO content to the CaO content [BaO / CaO] is preferably 0.30, and more preferably 0.28 and 0.26 in that order. The lower limit of this mass ratio is preferably 0. This mass ratio may be 0. From the viewpoint of suppressing an increase in specific gravity, it is preferable that this mass ratio is within the above range.

[0042] Like Na2O, K2O improves the meltability of glass and adjusts the viscosity of molten glass to an appropriate range. If an excessive amount of K2O is introduced, the refractive index may decrease and the corrosiveness of the molten glass may increase. The preferred upper limit of the K2O content is 7%, more preferably 6%, and even more preferably 5%. The preferred lower limit of the K2O content is 0%. The K2O content expressed in mass% is preferably less than the Na2O content.

[0043] Li2O is a component that improves the melting property of glass. However, Li2O corrodes refractories more easily than other alkali metal oxides. Therefore, the preferred range of the Li2O content is 0 to 3%, more preferably 0 to 2%, and even more preferably 0 to 1%. The Li2O content may be 0%.

[0044] Compared with other alkali metal oxides, Cs2O can easily increase the specific gravity. In addition, Cs2O is a component with high raw material costs. Therefore, the preferred range of the Cs2O content is 0 to 5%, more preferably 0 to 3%, and even more preferably 0 to 1%. The Cs2O content may be 0%.

[0045] CaO has the function of improving the thermal stability and meltability of the glass, and the function of adjusting the Abbe number. If CaO is excessive, the thermal stability of the glass may decrease, and the refractive index may decrease. The upper limit of the CaO content is preferably 15%, more preferably 13%, and even more preferably 12%. The lower limit of the CaO content is preferably 3%, more preferably 5%, and even more preferably 6%.

[0046] MgO and SrO, together with CaO and BaO, have the function of improving meltability, but if the content of any of the components becomes excessive, the thermal stability of the glass may decrease. The preferred range of the MgO content is 0 to 10%, more preferably 0 to 5%, and even more preferably 0 to 3%. The MgO content may be 0%. The preferred range of the SrO content is 0 to 10%, more preferably 0 to 5%, and even more preferably 0 to 3%. The SrO content may be 0%.

[0047] From the viewpoint of obtaining the above-mentioned properties and characteristics, the total content of SiO2, TiO2, Na2O, K2O, CaO and BaO is preferably 96% or more, more preferably 99% or more, and even more preferably 99.5% or more.

[0048] In the optical glass according to this embodiment, the upper limit of the P2O5 content is preferably 10%, and more preferably 8%, 5%, and 3%, in that order. The lower limit of the P2O5 content is preferably 0%. The P2O5 content may be 0%. In order to obtain an optical glass having a high refractive index and a reduced specific gravity, it is preferable that the P2O5 content be within the above range.

[0049] In the optical glass according to this embodiment, the upper limit of the B2O3 content is preferably 10%, and more preferably 8%, 5%, and 3%, in that order. The lower limit of the B2O3 content is preferably 0%. The B2O3 content may be 0%. B2O3 has the effect of improving the thermal stability of the glass, but if the B2O3 content is too high, the refractive index may decrease. Therefore, it is preferable that the B2O3 content be within the above range.

[0050] In the optical glass according to this embodiment, the upper limit of the Al2O3 content is preferably 10%, and more preferably 8%, 5%, 3%, 1%, and 0.5% in that order. The lower limit of the Al2O3 content is preferably 0%. The Al2O3 content may be 0%. Although Al2O3 has the function of increasing chemical durability, if the Al2O3 content is too high, the melting property of the glass may deteriorate. Therefore, it is preferable that the Al2O3 content is within the above range.

[0051] In the optical glass according to this embodiment, the upper limit of the ZrO2 content is preferably 10%, and more preferably 8%, 5%, 3%, 1%, and 0.5% in that order. The lower limit of the ZrO2 content is preferably 0%. The ZrO2 content may be 0%. ZrO2 is a component that contributes to a high refractive index. On the other hand, if the ZrO2 content is too high, the thermal stability may decrease and the specific gravity may increase. Therefore, the ZrO2 content is preferably within the above range.

[0052] In the optical glass according to this embodiment, the upper limit of the Nb2O5 content is preferably 10%, and more preferably 8%, 5%, and 3%, in that order. The lower limit of the Nb2O5 content is preferably 0%. The Nb2O5 content may be 0%.

[0053] Nb2O5 is a component that contributes to increasing the refractive index and improves glass stability. On the other hand, if the content of Nb2O5 is too high, the specific gravity may increase and the thermal stability may decrease. Therefore, it is preferable that the content of Nb2O5 is within the above range.

[0054] In the optical glass according to this embodiment, the upper limit of the WO3 content is preferably 10%, and more preferably 8%, 5%, and 3% in that order. The lower limit of the WO3 content is preferably 0%. The WO3 content may be 0%.

[0055] WO3 is a component that contributes to increasing the refractive index. On the other hand, if the content of WO3 is too high, the thermal stability may decrease, the specific gravity may increase, and the coloring of the glass may increase, causing the transmittance to decrease. Therefore, it is preferable that the content of WO3 is within the above range.

[0056] In the optical glass according to this embodiment, the upper limit of the Bi2O3 content is preferably 10%, and more preferably 8%, 5%, and 3%, in that order. The lower limit of the Bi2O3 content is preferably 0%. The Bi2O3 content may be 0%.

[0057] When an appropriate amount of Bi2O3 is contained, it has the function of improving the thermal stability of the glass. It is also a component that contributes to increasing the refractive index. On the other hand, if the content of Bi2O3 is too high, the specific gravity increases. Furthermore, the coloring of the glass increases. Therefore, it is preferable that the content of Bi2O3 is within the above range.

[0058] In the optical glass according to this embodiment, the upper limit of the ZnO content is preferably 10%, and more preferably 8%, 5%, and 3%, in that order. The lower limit of the ZnO content is preferably 0%. The ZnO content may be 0%.

[0059] ZnO is a glass component that improves the thermal stability of glass. However, if the content of ZnO is too high, the specific gravity increases. Therefore, from the viewpoint of improving the thermal stability of glass and maintaining the desired optical properties, the content of ZnO is preferably within the above range.

[0060] In the optical glass according to this embodiment, the upper limit of the Ta2O5 content is preferably 10%, and more preferably 8%, 5%, and 3%, in that order. The lower limit of the Ta2O5 content is preferably 0%. The Ta2O5 content may be 0%.

[0061] Ta2O5 is a component that contributes to a high refractive index. It is also a glass component that has the function of improving the thermal stability of glass. On the other hand, if the content of Ta2O5 is large, the thermal stability of the glass decreases, and when the glass is melted, the glass raw material is likely to remain unmelted. In addition, the specific gravity increases. Therefore, it is preferable that the content of Ta2O5 is within the above range.

[0062] In the optical glass according to this embodiment, the upper limit of the La2O3 content is preferably 10%, and more preferably 8%, 5%, and 3%, in that order. The lower limit of the La2O3 content is preferably 0%. The La2O3 content may be 0%.

[0063] La2O3 is a component that contributes to increasing the refractive index. On the other hand, if the content of La2O3 increases, the specific gravity increases and the thermal stability of the glass decreases. Therefore, from the viewpoint of suppressing the increase in specific gravity and the decrease in the thermal stability of the glass, it is preferable that the content of La2O3 is within the above range.

[0064] In the optical glass according to this embodiment, the upper limit of the Y2O3 content is preferably 10%, and more preferably 8%, 5%, and 3%, in that order. The lower limit of the Y2O3 content is preferably 0%. The Y2O3 content may be 0%.

[0065] Y2O3 is a component that contributes to increasing the refractive index. On the other hand, if the content of Y2O3 is too high, the thermal stability of the glass decreases, and the glass becomes more likely to devitrify during production. Therefore, from the viewpoint of suppressing the decrease in the thermal stability of the glass, it is preferable that the content of Y2O3 is within the above range.

[0066] In the optical glass according to this embodiment, the Sc2O3 content is preferably 2% or less. The lower limit of the Sc2O3 content is preferably 0%. The Sc2O3 content may be 0%.

[0067] In the optical glass according to this embodiment, the content of HfO2 is preferably 2% or less. The lower limit of the content of HfO2 is preferably 0%. The content of HfO2 may be 0%.

[0068] Sc2O3 and HfO2 have the effect of increasing the dispersibility of the glass, but are expensive components, so the contents of Sc2O3 and HfO2 are preferably within the above ranges.

[0069] In the optical glass according to this embodiment, the content of Lu2O3 is preferably 2% or less. The lower limit of the content of Lu2O3 is preferably 0%. The content of Lu2O3 may be 0%.

[0070] Lu2O3 has the function of increasing the dispersibility of the glass, but because it has a large molecular weight, it is also a glass component that increases the specific gravity of the glass, so the content of Lu2O3 is preferably within the above range.

[0071] In the optical glass according to this embodiment, the GeO2 content is preferably 2% or less. The lower limit of the GeO2 content is preferably 0%. The GeO2 content may be 0%.

[0072] GeO2 has the function of increasing the high dispersibility of the glass, but is an extremely expensive component among commonly used glass components, and therefore, from the viewpoint of reducing the manufacturing cost of the glass, it is preferable that the content of GeO2 is within the above range.

[0073] In the optical glass according to this embodiment, the upper limit of the Gd2O3 content is preferably 3.0%, more preferably 2.0%. The lower limit of the Gd2O3 content is preferably 0%. The Gd2O3 content may be 0%.

[0074] Gd2O3 is a component that contributes to a high refractive index. On the other hand, if the content of Gd2O3 is too high, the thermal stability of the glass decreases. In addition, if the content of Gd2O3 is too high, the specific gravity of the glass increases, which is not preferable. Therefore, from the viewpoint of suppressing the increase in specific gravity while maintaining good thermal stability of the glass, it is preferable that the content of Gd2O3 is within the above range.

[0075] In the optical glass according to this embodiment, the content of Yb2O3 is preferably 2% or less. The lower limit of the content of Yb2O3 is preferably 0%. The content of Yb2O3 may be 0%.

[0076] Yb2O3 is a component that increases the specific gravity of glass. If the content of Yb2O3 is too high, the thermal stability of the glass decreases. From the viewpoint of preventing the decrease in the thermal stability of the glass and suppressing the increase in the specific gravity, it is preferable that the content of Yb2O3 is within the above range.

[0077] The optical glass according to this embodiment is preferably composed mainly of the above-mentioned glass components, namely, SiO2, TiO2, and Na2O as essential components and BaO, K2O, Li2O, Cs2O, CaO, MgO, SrO, P2O5, B2O3, Al2O3, ZrO2, Nb2O5, WO3, Bi2O3, ZnO, Ta2O5, La2O3, Y2O3, Sc2O3, HfO2, Lu2O3, GeO2, Gd2O3, and Yb2O3 as optional components, and the total content of the above-mentioned glass components is preferably 95% or more, more preferably 98% or more, even more preferably 99% or more, and even more preferably 99.5% or more.

[0078] The optical glass according to this embodiment is preferably composed essentially of the above glass components, but may contain other components as long as they do not impair the effects of the present invention. Furthermore, the present invention does not exclude the inclusion of unavoidable impurities.

[0079] (Other Ingredients) In addition to the above components, the optical glass according to this embodiment may contain small amounts of Sb2O3, CeO2, etc., as fining agents. In this specification, the content of the fining agents is expressed as an exclusive percentage, and is not included in the total content of all glass components expressed on an oxide basis. Therefore, when the total content of all glass components other than the fining agents is taken as 100 mass%, the total amount of the fining agents is preferably 1 mass% or less, and more preferably 0.5 mass% or less, or 0.1 mass% or less. The content of the fining agents may be 0 mass%.

[0080] Pb, Cd, As, Th, etc. are components that pose a concern for their environmental impact. Therefore, the content of each of PbO, CdO, and ThO2 is preferably 0 to 0.1%, more preferably 0 to 0.05%, and even more preferably 0 to 0.01%, and it is particularly preferable that PbO, CdO, and ThO2 are substantially not contained.

[0081] The content of As2O3 is preferably 0 to 0.1%, more preferably 0 to 0.05%, and even more preferably 0 to 0.01%, and it is particularly preferable that As2O3 is substantially not contained.

[0082] Furthermore, the optical glass according to this embodiment has a high transmittance over a wide range of the visible region. To make the most of these features, it is preferable that the glass does not contain any coloring elements. Examples of coloring elements include Cu, Co, Ni, Fe, Cr, Eu, Nd, and Er. Each element is preferably contained in an amount of less than 100 ppm by mass, more preferably 0 to 80 ppm by mass, and even more preferably 0 to 50 ppm by mass or less, and particularly preferably is not contained substantially.

[0083] In addition, Ga, Te, Tb, etc. are components that do not need to be incorporated and are expensive components, so the content range of Ga2O3, TeO2, and TbO2 expressed in mass% is preferably 0 to 0.1%, more preferably 0 to 0.05%, even more preferably 0 to 0.01%, still more preferably 0 to 0.005%, even more preferably 0 to 0.001%, and particularly preferably not substantially contained.

[0084] (Glass properties) [Abbe number νd, refractive index nd] In the optical glass according to this embodiment, from the viewpoint of correcting chromatic aberration in combination with a lens made of glass having other optical properties, the Abbe number vd is preferably equal to or greater than 26, more preferably equal to or greater than 26.5, and even more preferably equal to or greater than 27. A preferred upper limit to the Abbe number vd is 33, a more preferred upper limit is 32.5, and an even more preferred upper limit is 32.

[0085] Optical glass with a high refractive index nd is desirable because it allows the absolute value of the curvature of the optically functional surface of the lens to be reduced (the curve of the optically functional surface of the lens to be made gentler) while maintaining the same light-collecting power. In the optical glass according to this embodiment, the lower limit of the refractive index nd is preferably 1.67, more preferably 1.675, and even more preferably 1.68.

[0086] On the other hand, if the refractive index is made too high, the relative ratio of the high refractive index component increases, and the specific gravity of the glass increases. From the viewpoint of suppressing the increase in specific gravity, the upper limit of the refractive index nd in the optical glass according to this embodiment is preferably 1.77, more preferably 1.765, and even more preferably 1.76.

[0087] [Transmittance] The optical glass according to this embodiment can be an optical glass with extremely little coloring. Such an optical glass is suitable as a material for imaging optical elements such as camera lenses and projection optical elements such as projectors.

[0088] Generally, the coloring degree of optical glass is expressed by λ80, λ70, λ5, etc. For a glass sample with a thickness of 10.0 mm ± 0.1 mm, the spectral transmittance is measured in the wavelength range of 200 to 700 nm, and the wavelength at which the external transmittance is 80% is λ80, the wavelength at which the external transmittance is 70%, and the wavelength at which the external transmittance is 5% is λ5. The optical glass according to this embodiment has a preferred λ80 of 480 nm or less, a preferred λ70 of 440 nm or less, and a preferred λ5 of 380 nm or less.

[0089] [Glass transition temperature Tg] The glass transition temperature Tg of the optical glass according to this embodiment is preferably 640°C or lower. If the glass transition temperature is low, the heating temperature can be lowered when the glass is reheated and softened for press molding. As a result, it becomes easier to suppress fusion between the glass and the press mold. In addition, since the heating temperature can be lowered, the thermal wear of the glass heating device, the press mold, etc. can also be reduced. Furthermore, since the annealing temperature of the glass can also be lowered, the life of the annealing furnace can be extended. The glass transition temperature is more preferably 635°C or lower, and even more preferably 630°C or lower.

[0090] [specific gravity] The specific gravity of the optical glass according to this embodiment is preferably 3.40 or less, more preferably 3.20 or less, even more preferably 3.10 or less, and particularly preferably 3.00 or less.

[0091] [Application] A preferred embodiment of the optical glass according to this embodiment is an optical glass for optical lenses or an optical glass for prisms.

[0092] [Manufacturing method] The optical glass according to this embodiment can be obtained, for example, by blending, melting, and shaping glass raw materials so as to obtain the required characteristics. As the glass raw materials, for example, oxides, carbonates, nitrates, sulfates, etc. can be used. As the method of melting and shaping the glass, known methods can be used.

[0093] [Glass material for press molding, its manufacturing method, and manufacturing method of glass molded body] According to one aspect of the present invention, it is possible to provide a glass material for press molding made of the optical glass according to the present embodiment, a glass molded body made of the optical glass according to the present embodiment, and methods for manufacturing the same. Press molding of glass materials for press molding can be carried out by pressing the glass material for press molding in a heated and softened state with a press mold. Both heating and press molding can be carried out in the atmosphere. By uniformly applying a powdered mold release agent such as boron nitride to the surface of the glass material for press molding and then heating and press molding, it is possible to reliably prevent the glass from fusing with the mold and also to smoothly stretch the glass along the molding surface of the press mold. By annealing after press molding to reduce distortion inside the glass, a homogeneous optical element blank can be obtained.

[0094] Examples of glass materials for press molding include preforms for precision press molding, glass materials for press molding optical element blanks (glass gobs for press molding), and the like, and include glass chunks having a mass equivalent to the mass of the desired press molded product.

[0095] Glass materials for press molding are also called preforms, and include not only those used for press molding as they are, but also those used for press molding after being subjected to mechanical processing such as cutting, grinding, and polishing. Cutting methods include a method in which a groove is formed in the portion of the surface of the glass plate to be cut by a method called scribing, and local pressure is applied to the groove portion from the back side of the surface on which the groove is formed, thereby breaking the glass plate at the groove portion, and a method in which the glass plate is cut by a cutting blade. Grinding methods include spherical processing and smoothing processing using a curve generator. Polishing methods include polishing using abrasive grains such as cerium oxide and zirconium oxide.

[0096] [Optical element blank and its manufacturing method] According to one aspect of the present invention, an optical element blank made of the optical glass according to this embodiment can be provided. The optical element blank is a glass molded body having a shape similar to that of the optical element to be manufactured. The optical element blank can be produced by a method of molding glass into a shape that includes a processing allowance to be removed when processing into the shape of the optical element to be manufactured, or the like. For example, the optical element blank can be produced by a method of heating and softening a glass material for press molding and press molding it (reheat press method), a method of supplying a molten glass lump to a press mold by a known method and press molding it (direct press method), or the like.

[0097] [Optical elements and their manufacturing methods] According to one aspect of the present invention, an optical element made of the optical glass according to this embodiment can be provided. Examples of the type of optical element include lenses such as spherical lenses and aspherical lenses, prisms, and diffraction gratings. Examples of the lens shape include biconvex lenses, plano-convex lenses, biconcave lenses, plano-concave lenses, convex meniscus lenses, and concave meniscus lenses. The optical element can be manufactured by a method including a process of processing a glass molded body made of the optical glass according to this embodiment. Examples of the processing include cutting, machining, rough grinding, fine grinding, and polishing. When such processing is performed, the use of the above glass can reduce breakage, and high-quality optical elements can be stably supplied. EXAMPLES

[0098] The present invention will be described in more detail below with reference to examples, although the present invention is not limited to the embodiments shown in the examples.

[0099] Example 1 To obtain the glass compositions shown in Tables 1(1) to 1(3), the corresponding oxides and the like were used as raw materials for introducing the respective components, and the raw materials were weighed and thoroughly mixed to obtain blended raw materials.

[0100] The raw materials were placed in a platinum crucible and heated to melt. After melting, the molten glass was poured into a mold and allowed to cool to near the glass transition temperature, and then immediately placed in an annealing furnace and annealed at near the glass transition temperature for about 1 hour. After that, the glass was allowed to cool to room temperature in the furnace, and optical glasses having the compositions shown in Tables 1(1) to (3) were obtained.

[0101] When the obtained optical glass was observed under magnification with an optical microscope, no crystal precipitation, foreign matter such as platinum particles originating from the platinum crucible, bubbles, or striae were observed.

[0102] The properties of the optical glass thus obtained were measured by the methods described below, and the results are shown in Table 2.

[0103] (i) Refractive index nd, ng, nF, nC and Abbe number νd The refractive indexes nd, ng, nF, and nC of the glass obtained by cooling at a cooling rate of -30°C / hour were measured according to the refractive index measurement method of the Japan Optical Glass Industry Association standard, and the Abbe number vd was calculated according to formula (1). νd=(nd-1) / (nF-nC) (1)

[0104] (ii) Transmittance (λ80, λ70, and λ5) The spectral transmittance of a sample with a thickness of 10.0 mm ± 0.1 mm was measured in the wavelength range of 200 to 700 nm. The wavelength at which the external transmittance was 80% was defined as λ80, the wavelength at which the external transmittance was 70% was defined as λ70, and the wavelength at which the external transmittance was 5% was defined as λ5.

[0105] (iii) Glass transition temperature Tg The measurements were carried out using a differential scanning calorimeter (DSC3300) manufactured by NETZSCH at a heating rate of 10° C. / min.

[0106] (iv) Specific gravity Measurement was performed by Archimedes method.

[0107] [Table 1(1)]

[0108] [Table 1(2)]

[0109] [Table 1(3)]

[0110] [Table 2]

[0111] Example 2 A glass melting furnace equipped with a refractory melting vat, a platinum alloy refining vat, and a working vat (stirring vat) was used, and batch raw materials prepared to obtain each of the optical glasses produced in Example 1 were charged into the melting vat to melt the glasses.

[0112] The batch raw materials were melted in the melting vat to become molten glass. The glass passed through pipes connecting the melting vat to the fining vat and then to the working vat, and was refined and homogenized as it flowed from the melting vat to the fining vat and then from the fining vat to the working vat. The glass was then poured into the molding mold through an outflow pipe attached to the bottom of the working vat.

[0113] The glass was molded in a mold and annealed to obtain optical glass. When the obtained optical glass was observed, no unmelted raw materials, no refractory material contamination, and no crystal precipitation were found.

[0114] In this manner, the optical glasses obtained in Example 1 were produced using a continuous glass melting furnace. The glass melting furnace has a known structure.

[0115] Example 3 Lens blanks were prepared by a known method using each of the optical glasses prepared in Example 2, and the lens blanks were processed by a known method such as polishing to prepare various lenses.

[0116] The optical lenses produced include various lenses such as a biconvex lens, a biconcave lens, a plano-convex lens, a plano-concave lens, a concave meniscus lens, and a convex meniscus lens.

[0117] Because the glass has a low specific gravity, each lens is lighter than lenses having the same optical properties and size, and is suitable for use in various imaging devices, especially autofocus imaging devices because of its energy saving potential. In the same manner, prisms were made using the various optical glasses made in Example 2.

[0118] The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims.

[0119] For example, by adjusting the composition as described in the specification to the glass compositions exemplified above, an optical glass according to one aspect of the present invention can be produced. Furthermore, it is of course possible to arbitrarily combine two or more of the items described in the specification as examples or preferred ranges.

Claims

1. In mass %, SiO 2 The content is 20-51%, TiO 2 The content is 20-40%, Na 2 O content: 5-28% The content of BaO is less than 2.0%; Li 2 O, Na 2 O.K. 2 O and Cs 2 The total content of O (R 2 O) 8-28%, SiO 2 , B 2 O 3 and P 2 O 5 The total content (SiO 2 +B 2 O 3 +P 2 O 5 ) to SiO 2 Mass ratio of the content [SiO 2 / (SiO 2 +B 2 O 3 +P 2 O 5 ) is 0.90 or more, R 2 SiO to O 2 Mass ratio of the content [SiO 2 / R 2 O] is 1.5 to 3.2, TiO 2 and Nb 2 O 5 The total content (TiO 2 +Nb 2 O 5 ) to SiO 2 Content and R 2 Total of O(SiO 2 +R 2 O) mass ratio [(SiO 2 +R 2 O) / (TiO 2 +Nb 2 O 5 ) is 2.6 or less, TiO 2 , Nb 2 O 5 and ZrO 2 The total content (TiO 2 +Nb 2 O 5 + ZrO 2 ) TiO 2 The mass ratio of the content [TiO 2 / (TiO 2 +Nb 2 O 5 + ZrO 2 ) is 0.90 or more, a mass ratio [(CaO+BaO) / R'O] of the total content of CaO and BaO (CaO+BaO) to the total content of MgO, CaO, SrO and BaO (R'O) is 0.90 or more; R 2 Na to O 2 O and K 2 Mass ratio of the total content of O [(Na 2 O+K 2 O) / R 2 O] is 0.98 or more, Na 2 O.K. 2 The mass ratio of the BaO content to the total content of O and CaO [BaO / (Na 2 O+K 2 O + CaO)] is 0.15 or less, TiO 2 and Nb 2 O 5 The mass ratio of the BaO content to the total content [BaO / (TiO 2 +Nb 2 O 5 ) is 0.12 or less, a mass ratio of the total content of CaO and TiO 2 to the content of SiO 2 [(CaO+TiO 2 ) / SiO 2 ] of 0.90 to 1.10; Optical glass.

2. 2. The optical glass according to claim 1, which has a refractive index nd of 1.67 to 1.77 and an Abbe number vd of 26 to 33.

3. 3. The optical glass according to claim 1, which has a specific gravity of 3.40 or less.

4. An optical element comprising the optical glass according to any one of claims 1 to 3.

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