Optical glass, preforms and optical components

Abstract

This invention provides an optical glass, which is a high refractive index (nd) glass, and has a low specific gravity relative to its refractive index, high resistance to devitrification, and is inexpensive. The optical glass of this invention has SiO2, B2O3, La2O3, and TiO2 as essential components, and contains, by mass percent (based on oxides), more than 0% to 15.0% of SiO2, more than 0% to 15.0% of B2O3, 20.0% to 40.0% of La2O3, and 20.0% to 40.0% of TiO2, and the sum of the contents of RO components (where R is one or more selected from the group consisting of Mg, Ca, Sr, Ba, and Zn) is more than 0% to 18.0%.

Description

[Technical Field]

[0001] This invention relates to an optical glass, a preform, and an optical element. [Previous Technology]

[0002] Optical glass and optical elements can be used for applications such as combining lenses from different optical zones to improve the optical characteristics of cameras or imaging devices, or mounting them in optical machines to realize various optical designs. In particular, making optical glass and optical elements lighter will lead to the miniaturization or weight reduction of the optical machine body or module. For example, for cameras with zoom or autofocus functions, making the optical elements lighter allows for smoother power transmission between the actuator and the lens, thereby improving performance.

[0003] On the other hand, as high-refractive-index glasses, La-based glasses as described in Patent Document 1, P-Nb-based glasses as described in Patent Document 2, and Bi-based glasses as described in Patent Document 3 are known. [Prior Art Documents] [Patent Documents]

[0004] [Patent Document 1] CN102745894. [Patent Document 2] Japanese Patent No. 4262256. [Patent Document 3] Japanese Unexamined Patent Publication No. 2020-19710. [Summary of the Invention]

[0005] [The problem the invention aims to solve]

[0006] In the manufacture of glass, there is a tendency that the more the content of components that increase the refractive index is increased, the greater the specific gravity becomes. The glasses disclosed in Patent Documents 1 and 2 contain more rare earth elements or Bi2O3, which are high-specific-gravity components, and therefore have a high specific gravity relative to their refractive index. It cannot be said that the optical glass is sufficiently lightweight.

[0007] In order to reduce the material cost of optical glass, it is desirable that the raw material cost of optical glass be as cheap as possible. However, the glass described in Patent Document 3 contains a large amount of Nb2O5, which is an expensive raw material, so it is difficult to say that it fully meets this requirement.

[0008] This invention was made in view of the above-mentioned problems. The object of this invention is to obtain an optical glass that has a low specific gravity relative to its refractive index, high resistance to devitrification, and is inexpensive. [Means for solving the problem]

[0009] In order to solve the above-mentioned problems, the inventors of this case have repeatedly conducted in-depth experimental research and found that by using SiO2, B2O3, La2O3, TiO2 and RO components in combination and adjusting the mass ratio, optical glass with low specific gravity relative to refractive index, high resistance to devitrification, and low cost can be obtained, thus completing the present invention. Specifically, the present invention provides the following embodiments.

[0010] (1) An optical glass having SiO2, B2O3, La2O3 and TiO2 as essential components, containing more than 0% to 15.0% of SiO2, more than 0% to 15.0% of B2O3, 20.0% to 40.0% of La2O3 and 20.0% to 40.0% of TiO2 by mass% based on oxides, and the sum of the contents of RO (where R is one or more selected from the group consisting of Mg, Ca, Sr, Ba and Zn) is more than 0% to 18.0%, the mass ratio of SiO2 / (SiO2+B2O3) is more than 0.40, and the mass ratio of (La2O3+TiO2) / (SiO2+B2O3) is more than 3.3 to 7.5.

[0011] (2) The optical glass described in (1) has a refractive index (nd) of 1.95000 to 2.15000 and an Abbe number (νd) of 20.00 to 30.00. When the specific gravity is set as d and the refractive index is nd, it satisfies the relationship d≦7.494×nd-10.361.

[0012] (3) The optical glass described in (1) or (2) wherein the mass ratio of SiO2 / (SiO2+B2O3) is 0.40 or more and the mass ratio of (La2O3+TiO2) / (SiO2+B2O3) is 3.3 or more to 7.5 or less.

[0013] (4) The optical glass described in any one of (1) to (3) wherein, by mass%, the Ta2O5 content is 2.0% or less and the mass ratio of Y2O3 / La2O3 is 0.40 or less.

[0014] An optical element blank is made of optical glass as described in any one of (1) to (4).

[0015] An optical element comprising optical glass as described in any one of (1) to (4).

Implementation Method

[0017] The optical glass of the present invention contains: more than 0% to 15.0% of SiO2, more than 0% to 15.0% of B2O3, 20.0% to 40.0% of La2O3, 20.0% to 40.0% of TiO2, and the sum of the contents of RO (where R is one or more selected from the group consisting of Mg, Ca, Sr, Ba, and Zn) is more than 0% to 18.0%, the mass ratio of SiO2 / (SiO2 + B2O3) is 0.40 or more, and the mass ratio of (La2O3 + TiO2) / (SiO2 + B2O3) is 3.3 or more to 7.5 or less. According to the present invention, when SiO2, B2O3, La2O3, TiO2, and RO are used together and the mass ratios are adjusted, a glass with a low specific gravity relative to the refractive index and low cost can be obtained.

[0018] Hereinafter, embodiments of the optical glass of the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and appropriate modifications can be made to implement it within the scope of the purpose of the present invention. Furthermore, descriptions that are repeated may sometimes be omitted, but this does not limit the scope of the invention.

[0019] [Glass Composition] The composition range of each component constituting the optical glass of the present invention is described below. In this specification, unless otherwise specified, the content of each component is expressed as a percentage of mass relative to the total mass of the glass, which is entirely composed of oxides. Here, "oxide-converted composition" refers to the composition of each component contained in the glass, assuming that the oxides, complex salts, and metal fluorides used as raw materials constituting the glass of the present invention are completely decomposed and converted into oxides upon melting, with the total mass of the generated oxides set at 100% by mass.

[0020] [Regarding essential and optional components] SiO2 is an essential component that can increase the viscosity of molten glass, reduce glass coloration, and improve devitrification resistance. Therefore, the content of SiO2 is preferably more than 0%, more preferably 1.0% or more, more preferably 2.0% or more, more preferably 3.0% or more, more preferably 4.0% or more, and more preferably 5.0% or more. On the other hand, by setting the content of SiO2 to 15.0% or less, the decrease in refractive index can be suppressed, and the specific gravity can be reduced. Therefore, the content of SiO2 is preferably 15.0% or less, more preferably 13.0% or less, more preferably 11.0% or less, more preferably 9.0% or less, more preferably 7.0% or less, and more preferably 6.0% or less. SiO2, K2SiF6, Na2SiF6, etc., can be used as raw materials for SiO2.

[0021] The B2O3 component is an essential component of the glass-forming oxide in the optical glass of the present invention, which contains a relatively large amount of rare earth oxides. In particular, by containing more than 0% B2O3, the devitrification resistance of the glass can be improved and the specific gravity can be reduced. Therefore, the content of B2O3 is preferably more than 0%, more preferably 1.0% or more, more preferably 2.0% or more, and more preferably 3.0% or more. On the other hand, by setting the content of B2O3 to 15.0% or less, the decrease in refractive index and the increase in Abbe number can be suppressed, and the deterioration of chemical durability can be suppressed. Therefore, the content of B2O3 is preferably 15.0% or less, more preferably 13.0% or less, more preferably 12.0% or less, more preferably 10.0% or less, more preferably 8.0% or less, and more preferably 6.0% or less. B2O3 can be made from raw materials such as H3BO3, Na2B4O7, Na2B4O7•10H2O, and BPO4.

[0022] La2O3 is an essential component for increasing the refractive index and is also a component that does not easily color the glass. Therefore, the content of La2O3 is preferably 20.0% or more, more preferably 23.0% or more, even more preferably 25.0% or more, even more preferably more than 27.0%, and even more preferably 29.0% or more. On the other hand, by setting the content of La2O3 to 40.0% or less, the stability of the glass can be improved and devitrification reduced, and the increase in specific gravity can be suppressed. Therefore, the content of La2O3 is preferably 40.0% or less, more preferably 38.0% or less, even more preferably 36.0% or less, and even more preferably 34.0% or less. La2O3, La(NO3)3•XH2O (X is any integer) or the like can be used as raw materials.

[0023] TiO2 is an essential component that can increase refractive index, reduce specific gravity, and improve devitrification resistance. Therefore, the content of TiO2 is preferably 20.0% or more, more preferably 22.0% or more, further preferably 24.0% or more, further preferably 26.0% or more, and further preferably 28.0% or more. On the other hand, by setting the content of TiO2 to 40.0% or less, devitrification caused by excessive TiO2 can be suppressed. Therefore, the content of TiO2 is preferably 40.0% or less, more preferably 38.0% or less, further preferably 36.0% or less, further preferably 34.0% or less, further preferably 32.0% or less, and further preferably less than 30.0%. TiO2 can be made from TiO2 or the like.

[0024] The mass sum of the RO component (where R is one or more selected from the group consisting of Ca, Sr, Ba, and Zn) is preferably more than 0% to less than 18.0%. In particular, by setting this mass sum to more than 0%, the melt flowability during glass production can be improved, and the resistance to devitrification can be enhanced. Therefore, this mass sum is preferably more than 0%, more preferably 1.5% or more, more preferably 2.0% or more, more preferably 3.5% or more, more preferably 5.0% or more, and more preferably 6.0% or more. On the other hand, by setting this mass sum to less than 18.0%, the decrease in refractive index can be suppressed. Therefore, this mass sum is preferably less than 18.0%, more preferably less than 16.0%, more preferably less than 14.0%, and more preferably less than 12.0%.

[0025] The mass ratio of SiO2 / (SiO2 + B2O3) is preferably 0.40 or higher. In particular, by setting this mass ratio to 0.40 or higher, the viscosity of the molten glass can be increased, and the resistance to devitrification can be improved. Therefore, this mass ratio is preferably 0.40 or higher, more preferably 0.45 or higher, and even more preferably 0.50 or higher, and even more preferably 0.55 or higher. On the other hand, by setting this mass ratio to 1.0 or lower, the meltability during glass production can be improved, and the resistance to devitrification can be improved. Therefore, this mass ratio is preferably 1.0 or lower, more preferably 0.80 or lower, even more preferably 0.75 or lower, even more preferably 0.70 or lower, and even more preferably 0.65 or lower.

[0026] The mass ratio (La2O3 + TiO2) / (SiO2 + B2O3) is preferably 3.3 or more to 7.5 or less. In particular, by setting this mass ratio to 3.3 or more, a glass with a low specific gravity relative to its refractive index can be obtained. Therefore, this mass ratio is preferably 3.3 or more, more preferably 3.5 or more, and even more preferably 4.0 or more. On the other hand, by setting this mass ratio to 7.5 or less, devitrification resistance can be improved. Therefore, this mass ratio is preferably 7.5 or less, more preferably 7.0 or less, and even more preferably 6.5 or less.

[0027] The mass ratio of Y₂O₃ / La₂O₃ is preferably 0.40 or less. In particular, by setting this mass ratio to be greater than 0, glass with a low specific gravity relative to its refractive index can be obtained. Therefore, this mass ratio is preferably greater than 0, more preferably 0.10 or more, and even more preferably 0.12 or more, and even more preferably 0.14 or more. On the other hand, by setting this mass ratio to be 0.40 or less, devitrification resistance can be improved. Therefore, this mass ratio is preferably 0.40 or less, more preferably 0.38 or less, and even more preferably 0.36 or less.

[0028] The Nb2O5 component, when present in amounts exceeding 0%, can increase the refractive index of the glass and improve its resistance to devitrification by lowering the liquidus temperature of the glass. Therefore, the content of the Nb2O5 component is preferably 0% or more, more preferably 1.0% or more, more preferably 3.0% or more, more preferably 6.0% or more, and more preferably 8.0% or more. On the other hand, by setting the content of the Nb2O5 component to 18.0% or less, the material cost of the glass can be suppressed, and the reduction of the Abbe number can be suppressed. In addition, devitrification caused by excessive Nb2O5 component can be reduced, and the reduction of the transmittance of the glass to visible light (especially wavelengths below 500 nm) can be suppressed. Therefore, the content of the Nb2O5 component is preferably 18.0% or less, more preferably 15.0% or less, more preferably 13.0% or less, and more preferably 10.0% or less.

[0029] The Y2O3 content is any component that can maintain a high refractive index and a high Abbe number while suppressing the material cost of the glass and reducing its specific gravity, even when it is more than 0%. Therefore, the Y2O3 content is preferably 0% or more, more preferably 1.0% or more, more preferably 2.0% or more, and more preferably 4.0% or more. On the other hand, by setting the Y2O3 content to 10.0% or less, the decrease in the refractive index of the glass can be suppressed, and the stability of the glass can be improved. In addition, the deterioration of the solubility of the glass raw materials can be suppressed. Therefore, the Y2O3 content is preferably 15.0% or less, more preferably 12.0% or less, more preferably 9.0% or less, and more preferably 7.0% or less.

[0030] ZrO2 content, when present in amounts exceeding 0%, can improve the refractive index and Abbe number of glass, and can also enhance devitrification resistance. Therefore, the ZrO2 content is preferably exceeding 0%, more preferably 1.0% or more, further preferably exceeding 3.5%, further preferably exceeding 5.0%, and further preferably exceeding 6.5%. On the other hand, by setting the ZrO2 content to 15.0% or less, devitrification caused by excessive ZrO2 content can be reduced. Therefore, the ZrO2 content is preferably 15.0% or less, more preferably less than 12.0%, further preferably less than 10.0%, and further preferably less than 8.0%.

[0031] The Gd₂O₃, Yb₂O₃, and Lu₂O₃ components, when present in amounts exceeding 0%, are any components that can improve the refractive index and Abbe number of the glass. However, the raw materials for Gd₂O₃, Yb₂O₃, and Lu₂O₃ are expensive. Higher contents of these components increase production costs and the glass's density. Therefore, the contents of Gd₂O₃, Yb₂O₃, and Lu₂O₃ are preferably 10.0% or less, more preferably 8.0% or less, further preferably 7.0% or less, and further preferably 4.0% or less, respectively. Especially from the viewpoint of reducing material costs, it is best to have none of these components present.

[0032] Ta2O5 is any component that can increase the refractive index of glass and improve its resistance to devitrification when its content exceeds 0%. However, the raw material price of Ta2O5 is high, and a higher Ta2O5 content increases production costs. Furthermore, by setting the Ta2O5 content to 10.0% or less, the melting temperature of the raw material decreases, reducing the energy required for melting and thus lowering the manufacturing cost of optical glass. Therefore, the Ta2O5 content is preferably 10.0% or less, more preferably 5.0% or less, further preferably 3.0% or less, and even more preferably 2.0% or less. Especially from the perspective of reducing material costs, it is best to have no Ta2O5 content.

[0033] When the WO3 content exceeds 0%, it can reduce the coloration of the glass caused by other high-refractive-index components, increase the refractive index, reduce the glass transition point, and improve the resistance to devitrification. Therefore, the WO3 content is preferably 0% or more, more preferably 0.3% or more, and even more preferably 0.5% or more. On the other hand, by setting the WO3 content to 10.0% or less, the material cost of the glass can be suppressed, the reduction of the Abbe number can be suppressed, and the specific gravity can be reduced. In addition, the visible light transmittance can be increased by reducing the coloration of the glass caused by the WO3 content. Therefore, the WO3 content 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.

[0034] When the ZnO content exceeds 0%, it can improve the stability of the glass and reduce the amount of coloring components. Additionally, it can reduce the glass transfer point and improve chemical durability. Therefore, the ZnO content is preferably 0% or more, more preferably 0.3% or more, more preferably 0.5% or more, and more preferably 1.0% or more. On the other hand, by setting the ZnO content to 15.0% or less, the decrease in the refractive index of the glass can be suppressed, and devitrification caused by excessive reduction in viscosity can be reduced. Therefore, the ZnO content is preferably 15.0% or less, more preferably 12.0% or less, more preferably 10.0% or less, more preferably 8.0% or less, more preferably 6.0% or less, and more preferably 3.0% or less.

[0035] The MgO, CaO, SrO, and BaO components are any components that can adjust the refractive index, melt flow properties, or devitrification resistance of the glass when their content exceeds 0%. Therefore, the content of MgO, CaO, SrO, and BaO components is preferably 0% or more, more preferably 3.0% or more, further preferably 5.0% or more, and further preferably 7.0% or more. On the other hand, by setting the content of MgO, CaO, SrO, and BaO components to 18.0% or less, the decrease in refractive index can be suppressed, and devitrification caused by excessive content of these components can be reduced. Therefore, the content of MgO, CaO, SrO, and BaO components is preferably 18.0% or less, more preferably 16.0% or less, further preferably 14.0% or less, and further preferably 12.0% or less.

[0036] When the content of Li2O, Na2O, and K2O exceeds 0%, the meltability of the glass can be improved, and the arbitrary composition of the glass transfer point can be reduced. On the other hand, by setting the content of Li2O, Na2O, and K2O to 10.0% or less, the refractive index of the glass is less likely to decrease, and the devitrification of the glass can be reduced. Therefore, the content of Li2O, Na2O, and K2O is preferably 10.0% or less, more preferably 5.0% or less, more preferably 3.0% or less, and more preferably 1.0% or less, respectively.

[0037] The P2O5 component, when present in amounts exceeding 0%, functions as a glass-forming component, capable of lowering the liquidus temperature of the glass and improving its resistance to devitrification. Furthermore, by setting the P2O5 content to 10.0% or less, the reduction in the chemical durability of the glass, particularly its water resistance, can be suppressed. Therefore, the P2O5 content is preferably 10.0% or less, more preferably 5.0% or less, further preferably 3.0% or less, and even more preferably 1.0% or less.

[0038] GeO2 content, when present in amounts exceeding 0%, can increase the refractive index of glass and improve its resistance to devitrification. However, the raw material price of GeO2 is high, and a higher GeO2 content increases production costs. Therefore, the GeO2 content is preferably 10.0% or less, more preferably 5.0% or less, further preferably 3.0% or less, and even more preferably 1.0% or less. In particular, from the viewpoint of reducing material costs, it is also possible to omit the GeO2 content.

[0039] The Al2O3 and Ga2O3 components, when present in amounts exceeding 0%, are any components that can improve the chemical durability and devitrification resistance of the glass. On the other hand, by setting the content of each of the Al2O3 and Ga2O3 components to 10.0% or less, devitrification caused by excessive content can be suppressed. Therefore, the content of the Al2O3 and Ga2O3 components is preferably 10.0% or less, more preferably 5.0% or less, further preferably 3.0% or less, and further preferably 1.0% or less, respectively.

[0040] When the Bi2O3 content exceeds 0%, it can increase the refractive index and reduce the glass transition point. On the other hand, by setting the Bi2O3 content to 10.0% or less, the increase in specific gravity can be suppressed. Therefore, the Bi2O3 content is preferably 10.0% or less, more preferably 5.0% or less, further preferably 3.0% or less, and further preferably 1.0% or less. In particular, from the viewpoint of reducing specific gravity, it is also possible to omit the Bi2O3 content.

[0041] When the TeO2 content exceeds 0%, it can increase the refractive index and reduce the arbitrary composition of the glass transition point. On the other hand, TeO2 has the following problem: when the glass raw material is melted using a platinum crucible or a molten pool in contact with the molten glass is made of platinum, it may alloy with platinum. Therefore, the content of TeO2 is preferably 10.0% or less, more preferably 5.0% or less, more preferably 3.0% or less, and more preferably 1.0% or less.

[0042] The SnO2 component, when present in amounts exceeding 0%, reduces the oxidation of molten glass, thereby clarifying it and improving the visible light transmittance of the glass. On the other hand, by setting the SnO2 content to 3.0% or less, the coloring and devitrification of the glass caused by the reduction of molten glass can be reduced. Furthermore, the alloying between the SnO2 component and the melting equipment (especially precious metals such as Pt) can be reduced, thus extending the lifespan of the melting equipment. Therefore, the SnO2 content is preferably 3.0% or less, more preferably 2.0% or less, and even more preferably 1.0% or less.

[0043] The Sb2O3 component is any component capable of defoaming molten glass when it is present in amounts exceeding 0%. On the other hand, if the amount of Sb2O3 is too high, the transmittance in the short wavelength region of the visible light region will decrease. Therefore, the content of the Sb2O3 component is preferably 1.0% or less, more preferably 0.5% or less, and even more preferably 0.3% or less.

[0044] Furthermore, the component used to clarify and defoam the glass is not limited to the Sb2O3 component mentioned above, but may be a clarifying agent, defoamer or a combination of these components known in the glass manufacturing industry.

[0045] The F component, when present in amounts exceeding 0%, can increase the Abbe number of the glass, decrease the glass transition point, and improve devitrification resistance. However, if the content of the F component, i.e., the total amount of fluorides formed by replacing one or more of the oxides of the aforementioned metallic elements (calculated as F), exceeds 10.0%, the volatilization of the F component increases, making it difficult to obtain stable optical constants and homogeneous glass. Therefore, the content of the F component is preferably 10.0% or less, more preferably 5.0% or less, further preferably 3.0% or less, and further preferably 1.0% or less.

[0046] [Regarding components that should not be contained] Next, the components that should not be contained in the optical glass of the present invention and components that are not suitable to be contained will be explained.

[0047] Other components may be added as needed without compromising the properties of the glass of this invention. Among them, transition metal components such as V, Cr, Mn, Fe, Co, Ni, Cu, Ag and Mo, other than Ti, Zr, Nb, W, La, Gd, Y, Yb and Lu, have the following properties: even when each component is contained alone or in combination in small amounts, the glass is still colored and absorbs specific wavelengths in the visible light region. Therefore, it is preferable that they are not substantially contained, especially in optical glass that uses wavelengths in the visible light region.

[0048] In addition, lead compounds such as PbO and arsenic compounds such as As2O3 are components with high environmental impact, so it is ideal to have them practically absent, that is, to have them completely except for unavoidable contamination.

[0049] Furthermore, in recent years, the use of various components such as Th, Cd, Tl, Os, Be, and Se has tended to be controlled as hazardous chemicals. This means that not only the glass manufacturing process, but also the processing steps and the disposal of finished products require environmental countermeasures. Therefore, when environmental impact is a concern, it is preferable to have these components substantially absent.

[0050] [Manufacturing Method] The optical glass of the present invention is manufactured, for example, in the following manner. That is, the above-mentioned raw materials are uniformly mixed in such a way that each component is within a predetermined content range, the mixture is put into a platinum crucible, and melted in an electric furnace at a temperature range of 1100°C to 1500°C for 2 to 5 hours, depending on the melting difficulty of the glass raw materials, and stirred and homogenized. Then, after cooling to an appropriate temperature, it is cast into a mold and slowly cooled, thereby manufacturing the optical glass of the present invention.

[0051] [Physical Properties] The optical glass of the present invention preferably has a high refractive index and a high Abbe number (low dispersion). In particular, the lower limit of the refractive index (nd) of the optical glass of the present invention is preferably 1.95000, more preferably 2.00000, and even more preferably 2.05000. The upper limit of the refractive index (nd) is preferably 2.15000, more preferably 2.13000, and even more preferably 2.11000. In addition, the lower limit of the Abbe number (νd) of the optical glass of the present invention is preferably 20.00, more preferably 20.50, and even more preferably 21.00, and the upper limit is preferably 30.00, more preferably 29.00, and even more preferably 28.00.

[0052] Here, the relationship between the refractive index (nd) and specific gravity (d) of the optical glass of the present invention satisfies the formula (d ≤ 7.494 × nd - 10.361). Previously, only expensive glass with a refractive index (nd) of 2.00 or higher and a low specific gravity was known. In contrast, in the present invention, by satisfying the above-mentioned relationship and thereby having a smaller specific gravity (d) relative to the refractive index (nd), it is possible to contribute to the weight reduction of optical components or optical machines. More specifically, the relationship between the refractive index (nd) and specific gravity (d) of the optical glass of the present invention preferably satisfies the formula (d ≤ 7.494 × nd - 10.361), more preferably satisfies the formula (d ≤ 7.494 × nd - 10.561), and even more preferably satisfies the formula (d ≤ 7.494 × nd - 10.761). On the other hand, if the specific gravity (d) is too small relative to the refractive index (nd), the devitrification increases, making it difficult to obtain stable glass. Therefore, the relationship between the refractive index (nd) and the specific gravity (d) is preferably one that satisfies the formula (d≦7.494×nd-11.161), more preferably one that satisfies the formula (d≦7.494×nd-11.061), and even more preferably one that satisfies the formula (d≦7.494×nd-10.961).

[0053] From the viewpoint of contributing to the weight reduction of optical components or optical machines, the upper limit of the specific gravity of the optical glass of the present invention is preferably 5.50, more preferably 5.30, and even more preferably 5.20. On the other hand, the specific gravity of the optical glass of the present invention is preferably about 4.30 or more, more specifically 4.50 or more, and even more specifically 4.70 or more. The specific gravity of the optical glass of the present invention is measured based on the Japan Optical Glass Manufacturers Association standard JOGIS05-1975 "Method for Determining the Specific Gravity of Optical Glass".

[0054] The optical glass of the present invention preferably has high resistance to devitrification, and more specifically, has a low liquidus temperature. That is, the upper limit of the liquidus temperature of the optical glass of the present invention is preferably 1350°C, more preferably 1320°C, further preferably 1300°C, and even more preferably 1250°C. This reduces crystallization of the glass even when the molten glass flows out at a lower temperature, thus reducing devitrification during glass formation from the molten state and minimizing the impact on the optical properties of optical components using the glass. Furthermore, since glass can still be formed even when the melting temperature is lowered, the manufacturing cost of the glass can be reduced by suppressing the energy consumed during glass formation. On the other hand, the lower limit of the liquidus temperature of the optical glass of the present invention is not particularly limited, but the liquidus temperature of the glass obtained by the present invention is generally about 800°C or higher, specifically 850°C or higher, and more specifically 900°C or higher. Furthermore, the "liquid phase temperature" referred to in this instruction manual means the following temperature: 5cc of glass shavings are added to a 50ml platinum crucible and completely melted at 1400℃. The temperature is then lowered to a predetermined temperature and maintained for 1 hour. After cooling outside the furnace, the glass surface and any crystallization are immediately observed. The lowest temperature at which no crystallization is visible is the temperature between 1350℃ and 800℃, expressed in 10℃ increments.

[0055] [Preforms and Optical Elements] Glass molded bodies can be manufactured from optical glass using methods such as grinding, hot pressing, or precision pressing. That is, glass molded bodies can be manufactured by machining optical glass, such as grinding and polishing; or by manufacturing a preform for molding from optical glass, then hot pressing the preform followed by grinding to manufacture a glass molded body; or by precision pressing a preform manufactured through grinding or a preform formed by known floating-point forming methods to manufacture a glass molded body. Furthermore, the methods for manufacturing glass molded bodies are not limited to these methods.

[0056] In this way, the optical glass of the present invention is useful for various optical components and optical designs. It is particularly preferred that a preform is formed from the optical glass of the present invention, and that this preform is then used for hot pressing or precision pressing to manufacture optical components such as lenses or prisms. This allows for the formation of preforms with large diameters, thus enabling high-precision imaging and projection characteristics with high precision when used in optical machines such as cameras or projectors, even with the pursuit of large-scale optical components. [Example]

[0057] The composition of the embodiments (No. 1 to No. 15) and comparative examples (No. A) of the present invention, as well as the results of their refractive index (nd), Abbe number (νd), liquidus temperature and specific gravity, are shown in Tables 1 and 2. Furthermore, the following embodiments are for illustrative purposes only and are not limited to these embodiments.

[0058] The glass in the embodiments and comparative examples of the present invention is made by means of the following method: high-purity raw materials used in conventional optical glass, such as corresponding oxides, hydroxides, carbonates, nitrates, fluorides, metaphosphates, etc., are selected as raw materials for each component. They are weighed and mixed uniformly in a manner that makes up the composition ratio of each embodiment shown in the table. The mixture is then placed in a platinum crucible and melted in an electric furnace at a temperature range of 1100°C to 1500°C for 2 to 5 hours, depending on the melting difficulty of the glass raw materials. After stirring and homogenizing, the mixture is cast into a mold or the like and then slowly cooled.

[0059] The refractive index (nd) and Abbe number (νd) of the glass in the embodiment are expressed as measured values ​​for d-rays (587.56 nm) from a helium lamp. The Abbe number (νd) is calculated using the aforementioned refractive index for d-rays, the refractive index (nF) for F-rays (486.13 nm) from a hydrogen lamp, and the refractive index (nC) for C-rays (656.27 nm), according to the formula Abbe number (νd) = [(nd - 1) / (nF - nC)]. Furthermore, the relationship (d ≤ 7.494 × nd - 10.361) is calculated using the measured value of nd.

[0060] The specific gravity d of the glass in the examples and comparative examples was measured based on the Japanese Optical Glass Manufacturers Association standard JOGIS05-1975 "Method for Determination of Specific Gravity of Optical Glass".

[0061] The liquidus temperature of the glass in the examples and comparative examples was determined as follows: 5cc of glass shavings were added to a 50ml platinum crucible and completely melted at 1400°C. The temperature was then lowered to any temperature set in increments of 10°C within the range of 1350°C to 800°C and maintained for 1 hour. After being removed from the furnace and cooled, the glass surface and whether crystals were visible were immediately observed. The lowest temperature at which crystals were not visible was the lowest temperature at which crystals were not observed.

[0062] [Table 1] No. 1 2 3 4 5 6 7 8 SiO2 5.21 4.87 5.03 5.20 7.07 10.07 7.07 5.21 B2O3 3.92 3.93 4.06 4.19 9.35 6.35 10.35 3.92 Al2O3 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 P2O5 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Y2O3 4.93 0.44 5.22 5.38 0.20 0.20 0.20 4.93 La2O3 30.78 29.84 32.65 33.72 33.39 33.39 33.39 30.55 Gd2O3 0.00 9.37 0.00 0.00 0.00 0.00 0.00 0.00 TiO2 28.60 27.13 28.42 28.94 25.19 25.19 25.19 35.03 ZrO2 6.74 7.06 6.69 7.53 7.51 7.51 7.51 3.54 Nb2O5 8.24 7.93 8.19 8.45 9.18 9.18 9.18 5.24 WO3 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Bi2O3 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 MgO 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 ZnO 0.58 0.00 0.00 0.00 1.39 1.39 0.39 0.58 High 0.00 0.00 0.00 0.00 6.71 6.72 6.72 0.00 SrO 0.00 0.00 0.00 6.59 0.00 0.00 0.00 0.00 Bag 11:00 9.43 9.74 0.00 0.00 0.00 0.00 11:00 Li2O 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Na2O 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 K2O 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Sb2O3 0.00 0.00 0.00 0.00 0.01 0.00 0.00 0.00 total 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 nd 2.09697 2.10191 2.09637 2.10277 2.01196 2.01305 2.00745 2.10809 vd 22.20 22.40 22.37 22.26 24.00 24.30 24.30 22.10 proportion 4.85 5.04 4.85 4.76 4.36 4.38 4.34 4.73 7.494×nd-10.361 5.35 5.39 5.35 5.40 4.72 4.72 4.68 5.44 Liquid phase temperature 1190 1210 1190 1210 1100 1100 1200 1210 RO 11.58 9.43 9.74 6.59 8.10 8.11 7.11 11.58 Ln2O3 35.71 39.65 37.87 39.10 33.59 33.59 33.59 35.48 RO / Ln2O3 0.32 0.24 0.26 0.17 0.24 0.24 0.21 0.33 Si / (Si+B) 0.57 0.55 0.55 0.55 0.43 0.61 0.41 0.57 (La+Ti) / (Si+B) 6.51 6.47 6.72 6.67 3.57 3.57 3.36 7.19 Y / La 0.16 0.01 0.16 0.16 0.01 0.01 0.01 0.16

[0063] [Table 2] No. 9 10 11 12 13 14 15 A SiO2 4.72 5.13 5.79 5.06 5.01 4.97 4.39 8.16 B2O3 6.48 4.13 3.92 4.08 4.04 4.00 4.51 5.06 Al2O3 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 P2O5 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Y2O3 0.51 9.92 3.93 7.00 5.20 2.75 0.44 0.00 La2O3 39.74 26.59 25.77 30.30 32.50 35.70 32.94 47.85 Gd2O3 7.06 0.00 0.00 0.00 0.00 0.00 6.04 0.00 TiO2 20.29 28.54 28.50 28.18 28.29 27.67 27.20 12.18 ZrO2 6.28 7.33 6.74 7.34 6.66 7.20 7.08 5.63 Nb2O5 8.62 8.34 8.24 8.23 8.15 8.08 7.95 12.15 WO3 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Bi2O3 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 MgO 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 ZnO 1.20 0.00 0.00 0.00 0.44 0.00 0.00 6.20 CaO 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 SrO 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 BaO 5.00 9.92 17.01 9.80 9.70 9.62 9.46 2.55 Li2O 0.10 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Na2O 0.00 0.00 0.10 0.00 0.00 0.00 0.00 0.00 K2O 0.00 0.10 0.00 0.00 0.00 0.00 0.00 0.00 Sb2O3 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.20 total 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 nd 2.05657 2.09385 2.07348 2.09982 2.09883 2.10049 2.09908 2.02030 vd 24.03 22.34 22.34 22.35 22.37 22.42 22.44 29.00 proportion 5.05 4.74 4.80 4.81 4.85 4.92 4.95 5.11 7.494×nd-10.361 5.05 5.33 5.18 5.38 5.37 5.38 5.37 4.78 Liquid phase temperature 1200 1230 1190 1210 1180 1210 1210 - RO 6.20 9.92 17.01 9.80 10.14 9.62 9.46 8.75 Ln2O3 47.31 36.52 29.70 37.30 37.70 38.45 39.41 47.85 RO / Ln2O3 0.13 0.27 0.57 0.26 0.27 0.25 0.24 0.18 Si / (Si+B) 0.42 0.55 0.60 0.55 0.55 0.55 0.49 0.62 (La+Ti) / (Si+B) 5.36 5.96 5.59 6.40 6.72 7.06 6.76 4.54 Y / La 0.01 0.37 0.15 0.23 0.16 0.08 0.01 0.00

[0064] According to the above embodiments, it can be seen that the present invention is a high refractive index (nd) glass, and has a small specific gravity relative to the refractive index and high resistance to devitrification. [Simplified Explanation of the Diagram]

[0016] [Figure 1] is a graph showing the relationship between the refractive index (nd) and specific gravity (d) of the glass in the embodiment of this case.

Claims

1. An optical glass comprising SiO2, B2O3, La2O3, and TiO2 as essential components; and containing, by mass% based on oxides: 4.0% to 15.0% SiO2; 0% to 15.0% B2O3; 20.0% to 40.0% La2O3; 25.19% to 40.0% TiO2; and a total content of RO components of 2.0% to 14.0%, wherein R is one or more selected from the group consisting of Mg, Ca, Sr, Ba, and Zn; and a ZnO content of 0.3% to 12.0%.

2. The optical glass described in claim 1 has a refractive index (nd) of 1.95000 to 2.15000 and an Abbe number (νd) of 20.00 to 30.00, and satisfies the relationship d ≤ 7.494 × nd - 10.361 when the specific gravity is set as d and the refractive index is set as nd.

3. The optical glass described in claim 1 or 2, wherein the mass ratio of SiO2 / (SiO2+B2O3) is 0.40 or more; and the mass ratio of (La2O3+TiO2) / (SiO2+B2O3) is 3.3 or more to 7.5 or less.

4. The optical glass described in claim 1 or 2, wherein the Ta2O5 content is 2.0% or less and the mass ratio of Y2O3 / La2O3 is 0.40 or less.

5. The optical glass described in claim 3, wherein the Ta2O5 content is 2.0% or less and the mass ratio of Y2O3 / La2O3 is 0.40 or less.

6. An optical element blank comprising optical glass as described in any one of claims 1 to 5.

7. An optical element comprising optical glass as described in any one of claims 1 to 5.

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