Optical glass and optical element

Abstract

To provide an optical glass having a desired optical constant, a low temperature coefficient of a relative refractive index (dn / dT) due to a temperature change, and a large average linear thermal expansion coefficient, and an optical element that comprises the optical glass.SOLUTION: An optical glass has a refractive index nd of 1.63-1.80 and an Abbe number νd of 22-34. An Nb2O5 content is 25-55 mass%. A WO3 content is less than 30 mass%. A total content of TiO2, Nb2O5, WO3, Bi2O3 and Ta2O5 [TiO2+Nb2O5+WO3+Bi2O3+Ta2O5] is 36-60 mass%. A mass ratio of a total content of TiO2, Nb2O5, WO3, Bi2O3 and Ta2O5 to a total content of P2O5, B2O3, SiO2, Al2O3, Li2O, Na2O, K2O and Cs2O [(TiO2+Nb2O5+WO3+Bi2O3+Ta2O5) / (P2O5+B2O3+SiO2+Al2O3+Li2O+Na2O+K2O+Cs2O)] is 1.10 or less. A mass ratio of a content of TiO2 to a total content of P2O5 and B2O3 [TiO2 / (P2O5+B2O3)] is 0.50 or less. The optical glass satisfies (A) or (B).SELECTED DRAWING: None

Description

[Technical field]

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

[0002] Optical elements incorporated in in-vehicle optical devices and in optical devices that generate heat, such as projectors, copy machines, laser printers, and broadcasting equipment, are used in environments with large temperature changes. If optical characteristics such as the refractive index change due to temperature changes, this affects the imaging characteristics of the optical system.

[0003] Here, it is known that the effect on the imaging characteristics of the optical system can be reduced by combining an optical element whose temperature coefficient of relative refractive index (dn / dT) is negative with an optical element whose temperature coefficient is positive.

[0004] The temperature coefficient of relative refractive index (dn / dT) represents the change in refractive index with respect to temperature change. For optical elements whose refractive index decreases as the temperature increases, the temperature coefficient of relative refractive index is negative. Conversely, for optical elements whose refractive index increases as the temperature increases, the temperature coefficient of relative refractive index is positive.

[0005] In addition, if the glass melting temperature and forming temperature are high, not only is productivity poor, but glass melting equipment (e.g., crucibles, molten glass stirring equipment, etc.) in the melting process is corroded, and this is also economical. Therefore, there is a demand for glass with a low liquidus temperature LT, that is, a low glass melting temperature and forming temperature.

[0006] Patent Document 1 discloses an optical glass having a negative temperature coefficient of relative refractive index (dn / dT). However, it was found that the glass of Patent Document 1 has a high liquidus temperature LT and is inferior in productivity and economy.

[0007] In addition, the average linear thermal expansion coefficient of the optical element is important in optical design. When combining a low refractive index, low dispersion glass material with a high refractive index, high dispersion glass material, the smaller the difference in the average linear thermal expansion coefficient of the glass materials, the better the bonding. For example, a low refractive index, low dispersion glass material containing fluorine usually has a large average linear thermal expansion coefficient. Therefore, the high refractive index, high dispersion glass material to be combined with it is also required to have a high average linear thermal expansion coefficient. The optical glass disclosed in Patent Document 2 has a high refractive index, but low dispersion and a small average linear thermal expansion coefficient. Therefore, there is a demand for an optical glass that is high refractive index, high dispersion, and has a large average linear thermal expansion coefficient. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2019-1697 A [Patent Document 2] JP 2007-106611 A Summary of the Invention [Problem to be solved by the invention]

[0009] Therefore, an object of the present invention is to provide an optical glass having desired optical constants, a low temperature coefficient of relative refractive index (dn / dT) due to temperature change, and a large average linear thermal expansion coefficient, as well as an optical element made of said optical glass. [Means for solving the problem]

[0010] The gist of the present invention is as follows. (1) The refractive index nd is 1.63 to 1.80, The Abbe number νd is 22 to 34; The content of Nb2O5 is 25 to 55 mass%; The WO3 content is less than 30% by mass, The total content of TiO2, Nb2O5, WO3, Bi2O3 and Ta2O5 [TiO2+Nb2O5+WO3+Bi2O3+Ta2O5] is 36 to 60 mass%; the mass ratio of the total content of TiO2, Nb2O5, WO3, Bi2O3 and Ta2O5 to the total content of P2O5, B2O3, SiO2, Al2O3, Li2O, Na2O, K2O and Cs2O [(TiO2+Nb2O5+WO3+Bi2O3+Ta2O5) / (P2O5+B2O3+SiO2+Al2O3+Li2O+Na2O+K2O+Cs2O)] is 1.10 or less; The mass ratio of the TiO2 content to the total content of P2O5 and B2O3 [TiO2 / (P2O5+B2O3)] is 0.50 or less, Optical glass that satisfies the following (A) or (B). (A) The P2O5 content is 20 to 36 mass%; the mass ratio of the total content of P2O5, B2O3 and SiO2 to the total content of Li2O, Na2O, K2O and Cs2O [(P2O5+B2O3+SiO2) / (Li2O+Na2O+K2O+Cs2O)] is 1.50 or less; The mass ratio of the B2O3 content to the P2O5 content [B2O3 / P2O5] is 0.05 to 0.39; The total content of MgO, CaO, SrO and BaO [MgO+CaO+SrO+BaO] is 8.0 mass% or less. (B) the P2O5 content is 25 to 38 mass%; The content of Al2O3 is less than 5% by mass, the mass ratio of the total content of P2O5, B2O3 and SiO2 to the total content of Li2O, Na2O, K2O and Cs2O [(P2O5+B2O3+SiO2) / (Li2O+Na2O+K2O+Cs2O)] is 1.80 or less; The total content of MgO, CaO, SrO and BaO [MgO+CaO+SrO+BaO] is 7.0% by mass or less, The mass ratio of the content of TiO2 to the total content of TiO2, Nb2O5, WO3, Bi2O3 and Ta2O5 [TiO2 / (TiO2+Nb2O5+WO3+Bi2O3+Ta2O5)] is 0.25 or more.

[0011] (2) The optical glass according to (1), in which the mass ratio of the total content of P2O5, B2O3, and SiO2 to the total content of Li2O, Na2O, K2O, and Cs2O [(P2O5+B2O3+SiO2) / (Li2O+Na2O+K2O+Cs2O)] is 1.00 or more.

[0012] (3) The optical glass according to (1) or (2), in which the mass ratio of the total content of TiO2, Nb2O5, WO3, Bi2O3 and Ta2O5 to the total content of P2O5, B2O3, SiO2, Al2O3, Li2O, Na2O, K2O and Cs2O [(TiO2+Nb2O5+WO3+Bi2O3+Ta2O5) / (P2O5+B2O3+SiO2+Al2O3+Li2O+Na2O+K2O+Cs2O)] is 0.50 or more.

[0013] (4) The average linear thermal expansion coefficient α at 100 to 300 °C is 100 × 10 -7 ~200×10 -7 ℃ -1 The optical glass according to any one of (1) to (3),

[0014] (5) The temperature coefficient of the relative refractive index dn / dT at the wavelength of the He-Ne laser (633 nm) is -0.1 × 10 in the range of 20 to 40 °C. -6 ~-13.0×10 -6 ℃ -1 5. The optical glass according to claim 1, wherein

[0015] (6) An optical element made of the optical glass according to any one of (1) to (5) above. Effect of the Invention

[0016] According to the present invention, it is possible to provide an optical glass having desired optical constants, a low temperature coefficient of relative refractive index (dn / dT) due to temperature change, and a large average linear thermal expansion coefficient, as well as an optical element made of said optical glass. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] 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%".

[0018] 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.

[0019] In this specification, the thermal stability and devitrification resistance of glass both refer to the resistance to crystal precipitation in glass. In particular, the thermal stability refers to the resistance to crystal precipitation when molten glass solidifies, and the devitrification resistance refers to the resistance to crystal precipitation when solidified glass is reheated, such as during reheat pressing.

[0020] In this specification, unless otherwise specified, the refractive index refers to the refractive index nd at the d line of helium (wavelength 587.56 nm).

[0021] The Abbe number νd is used as a value representing the properties related to dispersion, and is expressed by the following formula: Here, nF is the refractive index at the F line (wavelength 486.13 nm) of blue hydrogen, and nC is the refractive index at the C line (656.27 nm) of red hydrogen. νd=(nd-1) / nF-nC (1)

[0022] The optical glass according to this embodiment will now be described in detail. In this embodiment, the optical glass is The refractive index nd is 1.63 to 1.80, The Abbe number νd is 22 to 34; The content of Nb2O5 is 25 to 55 mass%; The WO3 content is less than 30% by mass, The total content of TiO2, Nb2O5, WO3, Bi2O3 and Ta2O5 [TiO2+Nb2O5+WO3+Bi2O3+Ta2O5] is 36 to 60 mass%; the mass ratio of the total content of TiO2, Nb2O5, WO3, Bi2O3 and Ta2O5 to the total content of P2O5, B2O3, SiO2, Al2O3, Li2O, Na2O, K2O and Cs2O [(TiO2+Nb2O5+WO3+Bi2O3+Ta2O5) / (P2O5+B2O3+SiO2+Al2O3+Li2O+Na2O+K2O+Cs2O)] is 1.10 or less; The mass ratio of the TiO2 content to the total content of P2O5 and B2O3 [TiO2 / (P2O5+B2O3)] is 0.50 or less, Satisfy either (A) or (B) below. (A) The P2O5 content is 20 to 36 mass%; the mass ratio of the total content of P2O5, B2O3 and SiO2 to the total content of Li2O, Na2O, K2O and Cs2O [(P2O5+B2O3+SiO2) / (Li2O+Na2O+K2O+Cs2O)] is 1.50 or less; The mass ratio of the B2O3 content to the P2O5 content [B2O3 / P2O5] is 0.05 to 0.39; The total content of MgO, CaO, SrO and BaO [MgO+CaO+SrO+BaO] is 8.0 mass% or less. (B) the P2O5 content is 25 to 38 mass%; The content of Al2O3 is less than 5% by mass, the mass ratio of the total content of P2O5, B2O3 and SiO2 to the total content of Li2O, Na2O, K2O and Cs2O [(P2O5+B2O3+SiO2) / (Li2O+Na2O+K2O+Cs2O)] is 1.80 or less; The total content of MgO, CaO, SrO and BaO [MgO+CaO+SrO+BaO] is 7.0% by mass or less, The mass ratio of the content of TiO2 to the total content of TiO2, Nb2O5, WO3, Bi2O3 and Ta2O5 [TiO2 / (TiO2+Nb2O5+WO3+Bi2O3+Ta2O5)] is 0.25 or more.

[0023] Hereinafter, unless otherwise specified, the optical glass according to this embodiment means the optical glass according to this embodiment that satisfies the above (A) and the optical glass according to this embodiment that satisfies the above (B).

[0024] In the optical glass according to this embodiment, the refractive index nd is 1.63 to 1.80. The lower limit of the refractive index nd may be 1.65, 1.67, or 1.69, and the upper limit of the refractive index nd may be 1.79, 1.78, or 1.77.

[0025] The refractive index nd can be adjusted to a desired value by appropriately adjusting the content of each glass component. Components that act to relatively increase the refractive index nd (high refractive index components) include Nb2O5, TiO2, WO3, Bi2O3, Ta2O5, ZrO2, La2O3, etc. On the other hand, components that act to relatively decrease the refractive index nd (low refractive index components) include P2O5, SiO2, B2O3, Li2O, Na2O, K2O, etc. Therefore, for example, the refractive index nd can be increased by increasing the mass ratio of the total content of TiO2, Nb2O5, WO3, Bi2O3 and Ta2O5 to the total content of P2O5, B2O3, SiO2, Al2O3, Li2O, Na2O, K2O and Cs2O [(TiO2+Nb2O5+WO3+Bi2O3+Ta2O5) / (P2O5+B2O3+SiO2+Al2O3+Li2O+Na2O+K2O+Cs2O)], and the refractive index nd can be decreased by decreasing this mass ratio.

[0026] In the optical glass according to this embodiment, the Abbe number vd is 22 to 34. The lower limit of the Abbe number vd may be 22.5, 23, or 23.5, and the upper limit of the Abbe number vd may be 32, 30, or 28.

[0027] The Abbe number νd can be adjusted to a desired value by appropriately adjusting the content of each glass component. Components that relatively lower the Abbe number νd, i.e., high dispersion components, are Nb2O5, TiO2, WO3, Bi2O3, Ta2O5, ZrO2, etc. On the other hand, components that relatively increase the Abbe number νd, i.e., low dispersion components, are P2O5, SiO2, B2O3, Li2O, Na2O, K2O, La2O3, BaO, CaO, SrO, etc.

[0028] In the optical glass according to this embodiment, the Nb2O5 content is 25 to 55%. The lower limit of the Nb2O5 content is preferably 27%, and more preferably 29%, 31%, and 33% in that order. The upper limit of the Nb2O5 content is preferably 53%, and more preferably 51%, 49%, and 47% in that order.

[0029] Nb2O5 is a component that contributes to high refractive index and high dispersion. Therefore, by setting the content of Nb2O5 within the above range, an optical glass having the desired optical constants can be obtained. On the other hand, if the content of Nb2O5 is too high, the coloring of the glass may be intensified.

[0030] In the optical glass according to this embodiment, the content of WO3 is less than 30%. The upper limit of the content of WO3 is preferably 20%, and more preferably 15%, 10%, and 5% in that order. The lower the content of WO3, the more preferable, and the lower limit is preferably 0%. The content of WO3 may be 0%.

[0031] By setting the content of WO3 within the above range, it is possible to increase the transmittance, suppress an increase in the specific gravity of the glass, and reduce the temperature coefficient of the relative refractive index (dn / dT).

[0032] In the optical glass according to this embodiment, the total content of TiO2, Nb2O5, WO3, Bi2O3 and Ta2O5 [TiO2+Nb2O5+WO3+Bi2O3+Ta2O5] is 36 to 60%. The lower limit of the total content is preferably 38%, more preferably 40%, 41%, and 42% in that order. The upper limit of the total content is preferably 58%, more preferably 56%, 54%, and 52% in that order.

[0033] TiO2, Nb2O5, WO3, Bi2O3 and Ta2O5 are components that contribute to high dispersion of glass. Therefore, by setting the total content [TiO2+Nb2O5+WO3+Bi2O3+Ta2O5] within the above range, optical glass with desired optical constants can be obtained. In addition, the thermal stability of the glass can be improved. On the other hand, if the total content is too high, optical glass with desired optical constants may not be obtained, and the thermal stability of the glass may decrease, causing the coloring of the glass to intensify.

[0034] In the optical glass according to this embodiment, the mass ratio of the total content of TiO2, Nb2O5, WO3, Bi2O3 and Ta2O5 to the total content of P2O5, B2O3, SiO2, Al2O3, Li2O, Na2O, K2O and Cs2O [(TiO2+Nb2O5+WO3+Bi2O3+Ta2O5) / (P2O5+B2O3+SiO2+Al2O3+Li2O+Na2O+K2O+Cs2O)] is 1.10 or less. The upper limit of the mass ratio is preferably 1.07, and more preferably 1.04, 1.02, and 1.00 in that order. The lower limit of the mass ratio is more preferably 0.50, and more preferably 0.55, 0.60, and 0.65 in that order.

[0035] By setting the mass ratio [(TiO2+Nb2O5+WO3+Bi2O3+Ta2O5) / (P2O5+B2O3+SiO2+Al2O3+Li2O+Na2O+K2O+Cs2O)] within the above range, an optical glass having desired optical constants can be obtained.

[0036] In the optical glass according to this embodiment, the mass ratio of the content of TiO2 to the total content of P2O5 and B2O3 [TiO2 / (P2O5+B2O3)] is 0.50 or less.

[0037] By setting the mass ratio [TiO2 / (P2O5+B2O3)] within the above range, an optical glass having desired optical constants and high thermal stability can be obtained.

[0038] As described above, the optical glass according to this embodiment satisfies either (A) or (B). First, (A) will be described in detail.

[0039] The optical glass according to this embodiment is (A) The P2O5 content is 20 to 36 mass%; the mass ratio of the total content of P2O5, B2O3 and SiO2 to the total content of Li2O, Na2O, K2O and Cs2O [(P2O5+B2O3+SiO2) / (Li2O+Na2O+K2O+Cs2O)] is 1.50 or less; The mass ratio of the B2O3 content to the P2O5 content [B2O3 / P2O5] is 0.05 to 0.39; The total content of MgO, CaO, SrO and BaO [MgO + CaO + SrO + BaO] is 8.0 mass% or less; The requirements for the above can be met.

[0040] In the optical glass according to this embodiment that satisfies the above (A), the P2O5 content is 20 to 36%. The lower limit of the P2O5 content is preferably 21%, and more preferably 22%, 23%, and 24% in that order. The upper limit of the P2O5 content is preferably 35%, and more preferably 34%, 33%, and 32% in that order.

[0041] P2O5 is a glass network-forming component and is an essential component for containing a large amount of highly dispersible components in the glass. By setting the content of P2O5 within the above range, an optical glass having high thermal stability and desired optical constants can be obtained.

[0042] In the optical glass according to this embodiment that satisfies the above (A), the mass ratio of the total content of P2O5, B2O3 and SiO2 to the total content of Li2O, Na2O, K2O and Cs2O [(P2O5+B2O3+SiO2) / (Li2O+Na2O+K2O+Cs2O)] is 1.50 or less. The upper limit of this mass ratio is preferably 1.47, and more preferably 1.44, 1.42, and 1.40 in that order. The lower limit of this mass ratio is preferably 1.00, and more preferably 1.05, 1.08, and 1.10 in that order.

[0043] By setting the mass ratio [(P2O5+B2O3+SiO2) / (Li2O+Na2O+K2O+Cs2O)] in the above range, it is possible to obtain an optical glass that has high thermal stability, a low temperature coefficient of the relative refractive index (dn / dT), and a large average linear thermal expansion coefficient.

[0044] In the optical glass according to this embodiment that satisfies the above (A), the mass ratio of the B2O3 content to the P2O5 content [B2O3 / P2O5] is 0.05 to 0.39. The lower limit of this mass ratio is preferably 0.06, and more preferably 0.07, 0.08, and 0.09, in that order. The upper limit of this mass ratio is more preferably 0.36, and more preferably 0.33, 0.31, and 0.29, in that order.

[0045] By setting the mass ratio [B2O3 / P2O5] within the above range, it is possible to obtain an optical glass that has a low temperature coefficient of relative refractive index (dn / dT), a large average linear thermal expansion coefficient, high resistance to devitrification, and a low liquidus temperature LT.

[0046] In the optical glass according to the present embodiment that satisfies the above (A), the total content of MgO, CaO, SrO and BaO [MgO+CaO+SrO+BaO] is 8.0% or less. The upper limit of the total content is preferably 6%, and more preferably 5%, 4%, and 3%, in that order. The lower limit of the total content is preferably 0%.

[0047] By setting the total content [MgO+CaO+SrO+BaO] within the above range, high dispersion can be promoted.

[0048] In the optical glass according to this embodiment that satisfies the above (A), the mass ratio of the content of TiO2 to the total content of P2O5 and B2O3 [TiO2 / (P2O5+B2O3)] is 0.50 or less. The upper limit of this mass ratio is preferably 0.47, and more preferably 0.44, 0.42, and 0.40 in that order. The lower limit of this mass ratio is more preferably 0.00, and more preferably 0.03, 0.06, 0.08, and 0.10 in that order.

[0049] By setting the mass ratio [TiO2 / (P2O5+B2O3)] within the above range, an optical glass having desired optical constants and high thermal stability can be obtained.

[0050] Non-limiting examples of the contents and ratios of glass components in the optical glass according to this embodiment that satisfies the above (A) are given below.

[0051] In the optical glass according to this embodiment that satisfies the above (A), the upper limit of the B2O3 content is preferably 10%, more preferably 8%, 7%, and 6%, in that order. The lower limit of the B2O3 content is preferably 1%, more preferably 1.5%, 1.8%, and 2.0%, in that order.

[0052] B2O3 is a glass network forming component and has the function of improving the thermal stability of glass. On the other hand, if the content of B2O3 is high, the devitrification resistance tends to decrease. Therefore, the content of B2O3 is preferably within the above range.

[0053] In the optical glass according to this embodiment which satisfies the above (A), the Al2O3 content is preferably 3% or less, more preferably 2% or less, and even more preferably 1% or less. The Al2O3 content may be 0%.

[0054] Al2O3 is a glass component that has the function of improving the chemical durability and weather resistance of glass, and can be considered as a network forming component. On the other hand, if the content of Al2O3 increases, the devitrification resistance of the glass decreases. In addition, problems such as an increase in the glass transition temperature Tg and a decrease in thermal stability are likely to occur. From the viewpoint of avoiding such problems, it is preferable that the upper limit of the content of Al2O3 is within the above range.

[0055] In the optical glass according to this embodiment that satisfies the above (A), the lower limit of the mass ratio of the content of TiO2 to the total content of TiO2, Nb2O5, WO3, Bi2O3 and Ta2O5 [TiO2 / (TiO2+Nb2O5+WO3+Bi2O3+Ta2O5)] is preferably 0, more preferably 0.02, 0.04, 0.06 in that order. The upper limit of the mass ratio is preferably 0.50, more preferably 0.45, 0.40, 0.35 in that order.

[0056] Among the components that increase the refractive index, TiO2 is a component that has a particularly large effect of increasing the refractive index. Therefore, from the viewpoint of obtaining the desired optical constants, it is preferable that the mass ratio [TiO2 / (TiO2+Nb2O5+WO3+Bi2O3+Ta2O5)] is in the above range.

[0057] In the optical glass according to this embodiment that satisfies the above (A), the lower limit of the TiO2 content is preferably 0%, and more preferably 1%, 2%, 3%, and 4%, in that order. The TiO2 content may be 0%. The upper limit of the TiO2 content is preferably 15%. , and 13%, 11%, and 10% are more preferable in that order.

[0058] TiO2 contributes greatly to high dispersion. On the other hand, TiO2 tends to increase the coloring of the glass and may deteriorate the meltability. Therefore, the content of TiO2 is preferably within the above range.

[0059] In the optical glass according to this embodiment which satisfies the above (A), the lower limit of the total content of TiO2, Nb2O5, WO3 and Bi2O3 [TiO2+Nb2O5+WO3+Bi2O3] is preferably 36%, more preferably 38%, 40%, 41%, and 42% in that order. The upper limit of the total content [TiO2+Nb2O5+WO3+Bi2O3] is preferably 58%, more preferably 56%, 54%, and 52% in that order.

[0060] TiO2, Nb2O5, WO3 and Bi2O3 contribute to high dispersion of glass, and also improve the thermal stability of glass by adding appropriate amounts. On the other hand, they are also components that increase the coloring of glass. Therefore, it is preferable that the total content [TiO2 + Nb2O5 + WO3 + Bi2O3] is within the above range.

[0061] In the optical glass according to the present embodiment which satisfies the above condition (A), the lower limit of the Na2O content is preferably 6%, more preferably 8%, 9%, and 10%, in that order. The upper limit of the Na2O content is preferably 30%, more preferably 28%, 26%, and 25%, in that order.

[0062] Na2O is a component that contributes to lowering the specific gravity of glass, improves the meltability of glass, and increases the average linear thermal expansion coefficient. On the other hand, if the Na2O content is high, the devitrification resistance decreases. Therefore, the Na2O content is preferably within the above range.

[0063] In the optical glass according to the present embodiment which satisfies the above (A), the upper limit of the total content of Li2O, Na2O and K2O [Li2O+Na2O+K2O] is preferably 35%, more preferably 33%, 31%, and 30% in that order, and the lower limit of the total content is preferably 10%, more preferably 14%, 17%, and 18% in that order.

[0064] Li2O, Na2O and K2O all have the function of improving the thermal stability of glass. However, if their contents are too high, chemical durability and weather resistance may decrease. Therefore, it is preferable that the total content of Li2O, Na2O and K2O [Li2O + Na2O + K2O] is within the above range.

[0065] Next, (B) will be explained in detail.

[0066] The optical glass according to this embodiment is (B) the P2O5 content is 25 to 38 mass%; The content of Al2O3 is less than 5% by mass, the mass ratio of the total content of P2O5, B2O3 and SiO2 to the total content of Li2O, Na2O, K2O and Cs2O [(P2O5+B2O3+SiO2) / (Li2O+Na2O+K2O+Cs2O)] is 1.80 or less; The total content of MgO, CaO, SrO and BaO [MgO+CaO+SrO+BaO] is 7.0% by mass or less, The mass ratio of the content of TiO2 to the total content of TiO2, Nb2O5, WO3, Bi2O3 and Ta2O5 [TiO2 / (TiO2+Nb2O5+WO3+Bi2O3+Ta2O5)] is 0.25 or more; The requirements for the above can be met.

[0067] In the optical glass according to this embodiment that satisfies the above (B), the P2O5 content is 25 to 38%. The lower limit of the P2O5 content is preferably 26%, and more preferably 27%, 28%, 29%, and 30%, in that order. The upper limit of the P2O5 content is preferably 37%.

[0068] P2O5 is a glass network-forming component and is an essential component for containing a large amount of highly dispersible components in the glass. By setting the content of P2O5 within the above range, an optical glass having high thermal stability and desired optical constants can be obtained.

[0069] In the optical glass according to this embodiment that satisfies the above (B), the Al2O3 content is less than 5%. The Al2O3 content is preferably 3% or less, more preferably 2% or less, and even more preferably 1% or less. The Al2O3 content may be 0%.

[0070] Al2O3 is a glass component that has the function of improving the chemical durability and weather resistance of glass, and can be considered as a network forming component. On the other hand, if the content of Al2O3 increases, the devitrification resistance of the glass decreases. In addition, problems such as an increase in the glass transition temperature Tg and a decrease in thermal stability are likely to occur. From the viewpoint of avoiding such problems, it is preferable that the upper limit of the content of Al2O3 is within the above range.

[0071] In the optical glass according to this embodiment that satisfies the above (B), the mass ratio of the total content of P2O5, B2O3 and SiO2 to the total content of Li2O, Na2O, K2O and Cs2O [(P2O5+B2O3+SiO2) / (Li2O+Na2O+K2O+Cs2O)] is 1.80 or less. The upper limit of this mass ratio is preferably 1.78, more preferably 1.76 and 1.74 in that order. The lower limit of this mass ratio is preferably 1.00, more preferably 1.05, 1.08 and 1.10 in that order.

[0072] By setting the mass ratio [(P2O5+B2O3+SiO2) / (Li2O+Na2O+K2O+Cs2O)] in the above range, it is possible to obtain an optical glass that has high thermal stability, a low temperature coefficient of the relative refractive index (dn / dT), and a large average linear thermal expansion coefficient.

[0073] In the optical glass according to this embodiment that satisfies the above (B), the total content of MgO, CaO, SrO and BaO [MgO+CaO+SrO+BaO] is 7.0% or less. The upper limit of the total content is preferably 6%, and more preferably 5%, 4%, and 3%, in that order. The lower limit of the total content is preferably 0%.

[0074] By setting the total content [MgO+CaO+SrO+BaO] within the above range, high dispersion can be promoted.

[0075] In the optical glass according to this embodiment that satisfies the above (B), the mass ratio of the content of TiO2 to the total content of TiO2, Nb2O5, WO3, Bi2O3 and Ta2O5 [TiO2 / (TiO2+Nb2O5+WO3+Bi2O3+Ta2O5)] is 0.25 or more. The lower limit of this mass ratio is preferably 0.26, and more preferably 0.27, 0.28, and 0.29 in that order. The upper limit of this mass ratio is preferably 0.50, and more preferably 0.45, 0.40, and 0.35 in that order.

[0076] Among the components that increase the refractive index, TiO2 is a component that has a particularly large effect of increasing the refractive index. Therefore, from the viewpoint of obtaining the desired optical constants, it is preferable that the mass ratio [TiO2 / (TiO2+Nb2O5+WO3+Bi2O3+Ta2O5)] is in the above range.

[0077] In the optical glass according to this embodiment that satisfies the above (B), the mass ratio of the content of TiO2 to the total content of P2O5 and B2O3 [TiO2 / (P2O5+B2O3)] is 0.50 or less. The upper limit of this mass ratio is preferably 0.47, and more preferably 0.46 and 0.45 in that order. The lower limit of this mass ratio is preferably 0.00, and more preferably 0.20, 0.25, 0.30, and 0.35 in that order.

[0078] By setting the mass ratio [TiO2 / (P2O5+B2O3)] within the above range, an optical glass having desired optical constants and high thermal stability can be obtained.

[0079] Non-limiting examples of the contents and ratios of glass components in the optical glass according to this embodiment that satisfies the above (B) are given below.

[0080] In the optical glass according to this embodiment which satisfies the above (B), the lower limit of the mass ratio of the B2O3 content to the P2O5 content [B2O3 / P2O5] is preferably 0. The mass ratio may be 0. The upper limit of the mass ratio is more preferably 0.36, and further more preferably 0.33, 0.31, and 0.29, in that order.

[0081] By setting the mass ratio [B2O3 / P2O5] within the above range, it is possible to obtain an optical glass that has a low temperature coefficient of relative refractive index (dn / dT), a large average linear thermal expansion coefficient, high resistance to devitrification, and a low liquidus temperature LT.

[0082] In the optical glass according to this embodiment that satisfies the above (B), the upper limit of the B2O3 content is preferably 10%, and more preferably 8%, 7%, and 6%, in that order. The lower limit of the B2O3 content is preferably 0%. The B2O3 content may be 0%.

[0083] B2O3 is a glass network forming component and has the function of improving the thermal stability of glass. On the other hand, if the content of B2O3 is high, the devitrification resistance tends to decrease. Therefore, the content of B2O3 is preferably within the above range.

[0084] In the optical glass according to this embodiment that satisfies the above (B), the lower limit of the TiO2 content is preferably 0%, and more preferably 1%, 2%, 3%, 4%, 6%, 8%, 10%, and 12%, in that order. The TiO2 content may be 0%. The upper limit of the TiO2 content is preferably 15%.

[0085] TiO2 contributes greatly to high dispersion. On the other hand, TiO2 tends to increase the coloring of the glass and may deteriorate the meltability. Therefore, the content of TiO2 is preferably within the above range.

[0086] In the optical glass according to this embodiment which satisfies the above (B), the lower limit of the total content of TiO2, Nb2O5, WO3 and Bi2O3 [TiO2+Nb2O5+WO3+Bi2O3] is preferably 36%, more preferably 38%, 40%, 41%, 42% in that order. The upper limit of the total content [TiO2+Nb2O5+WO3+Bi2O3] is preferably 58%, more preferably 56%, 54%, 52%, 50%, 48%, 46% in that order.

[0087] TiO2, Nb2O5, WO3 and Bi2O3 contribute to high dispersion of glass, and also improve the thermal stability of glass by adding appropriate amounts. On the other hand, they are also components that increase the coloring of glass. Therefore, it is preferable that the total content [TiO2 + Nb2O5 + WO3 + Bi2O3] is within the above range.

[0088] In the optical glass according to the present embodiment which satisfies the above condition (B), the lower limit of the Na2O content is preferably 6%, more preferably 8%, 9%, and 10%, in that order. The upper limit of the Na2O content is preferably 30%, more preferably 28%, 26%, 25%, 22%, 20%, 18%, and 17%, in that order.

[0089] Na2O is a component that contributes to lowering the specific gravity of glass, improves the meltability of glass, and increases the average linear thermal expansion coefficient. On the other hand, if the Na2O content is high, the devitrification resistance decreases. Therefore, the Na2O content is preferably within the above range.

[0090] In the optical glass according to this embodiment which satisfies the above (B), the upper limit of the total content of Li2O, Na2O and K2O [Li2O+Na2O+K2O] is preferably 35%, more preferably 33%, 31%, 30%, 28%, 27%, 26%, 25% in that order. The lower limit of the total content is preferably 10%, more preferably 14%, 17%, 18%, 20% in that order.

[0091] Li2O, Na2O and K2O all have the function of improving the thermal stability of glass. However, if their contents are too high, chemical durability and weather resistance may decrease. Therefore, it is preferable that the total content of Li2O, Na2O and K2O [Li2O + Na2O + K2O] is within the above range.

[0092] In the optical glass according to this embodiment which satisfies the above (B), the Nb2O5 content is 25 to 55%. The lower limit of the Nb2O5 content is preferably 27%, and more preferably 29%. The upper limit of the Nb2O5 content is preferably 53%, and more preferably 51%, 49%, 47%, 40%, 35%, and 33%, in that order.

[0093] Nb2O5 is a component that contributes to high refractive index and high dispersion. Therefore, by setting the content of Nb2O5 within the above range, an optical glass having the desired optical constants can be obtained. On the other hand, if the content of Nb2O5 is too high, the coloring of the glass may be intensified.

[0094] Next, the characteristics of the optical glass according to this embodiment will be described.

[0095] In the optical glass according to this embodiment, the lower limit of the average linear thermal expansion coefficient α at 100 to 300° C. is preferably 100×10 -7 ℃ -1 and even 105×10 -7 ℃ -1 , 110×10 -7 ℃ -1 , 115×10 -7 ℃ -1 , 120×10 -7 ℃ -1 The upper limit of the average linear thermal expansion coefficient α is more preferably 200×10 -7 ℃ -1 and even 190×10 -7 ℃ -1 , 180×10 -7 ℃ -1 , 170×10 -7 ℃ -1 , 160×10-7 ℃ -1 The order of preference is:

[0096] By setting the average linear expansion coefficient α at 100 to 300° C. within the above range, it is possible to suppress the change in refractive index accompanying the thermal expansion of the glass, that is, the increase in the temperature coefficient of the relative refractive index dn / dT.

[0097] The average linear expansion coefficient α is measured based on the JOGIS08-2003 standard. The sample is a round bar with a length of 20 mm ± 0.5 mm and a diameter of 5 mm ± 0.5 mm, and is heated at a constant rate of 4°C per minute while a load of 98 mN is applied to the sample, and the temperature and sample elongation are measured. In this specification, the average linear expansion coefficient α is defined as [°C -1 ], but the unit is [K -1 ], the value of the average linear expansion coefficient α is the same.

[0098] In the optical glass according to this embodiment, the temperature coefficient dn / dT of the relative refractive index at the wavelength (633 nm) of a He-Ne laser is in the range of 20 to 40° C., and is preferably −1.0×10 -6 ~-10.0×10 -6 ℃ -1 and even -1.5×10 -6 ~-9.0×10 -6 ℃ -1 , -2.0×10 -6 ~-8.0×10 -6 ℃ -1 , -2.5×10 -6 ~-7.0×10 -6 ℃ -1 , -3.0×10 -6 ~-6.5×10 -6 ℃ -1 The order of preference is:

[0099] By setting dn / dT in the above range and combining it with an optical element with a positive dn / dT, the fluctuation in refractive index is small even in an environment where the temperature of the optical element fluctuates greatly, and the desired optical characteristics can be exhibited with high precision over a wider temperature range.

[0100] The temperature coefficient of the relative refractive index dn / dT is measured based on the interferometric method of JOGIS18-2008. In this specification, the temperature coefficient dn / dT is defined as [℃ -1 ], but the unit is [K -1 ], the value of the temperature coefficient dn / dT is the same.

[0101] (Glass component) 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.

[0102] In the optical glass according to this embodiment, the upper limit of the SiO2 content is preferably 5%, and more preferably 3%, 2%, and 1% in that order. The SiO2 content may be 0%.

[0103] In addition, a quartz glass melting device such as a quartz glass crucible may be used to melt glass. In this case, a small amount of SiO2 is dissolved from the melting device into the glass melt, so even if the glass raw material does not contain SiO2, the produced glass contains a small amount of SiO2. The amount of SiO2 mixed into the glass from the quartz glass melting device depends on the melting conditions, but is, for example, about 0.5 to 1 mass% of the total content of all glass components. The content ratio of glass components other than SiO2 remains constant, and the amount of SiO2 increases by about 0.5 to 1 mass%. The above amount increases or decreases depending on the melting conditions. Since the optical properties such as the refractive index and Abbe number change depending on the content of SiO2, the content of glass components other than SiO2 is finely adjusted to obtain optical glass with desired optical properties.

[0104] SiO2 is a glass network forming component, and has the functions of improving the thermal stability, chemical durability, and weather resistance of glass, increasing the viscosity of molten glass, and making it easier to mold the molten glass. On the other hand, if the SiO2 content is high, the devitrification resistance of glass tends to decrease. Therefore, it is preferable that the upper limit of the SiO2 content is within the above range.

[0105] In this embodiment, the upper limit of the Bi2O3 content is preferably 15%, and more preferably 10%, 7%, 5%, and 3% in that order. The lower limit of the Bi2O3 content is preferably 0%.

[0106] When an appropriate amount of Bi2O3 is contained, it has the function of improving the thermal stability of the glass. On the other hand, if the content of Bi2O3 is increased, the coloring of the glass increases. Therefore, it is preferable that the content of Bi2O3 is within the above range.

[0107] In the optical glass according to this embodiment, the upper limit of the Ta2O5 content is preferably 10%, and more preferably 7%, 5%, and 3%, in that order. The lower limit of the Ta2O5 content is preferably 0%. The Ta2O5 content may be 0%.

[0108] Ta2O5 is a glass component that improves the thermal stability and devitrification resistance of glass. On the other hand, Ta2O5 increases the refractive index and makes the glass highly dispersible. In addition, when the content of Ta2O5 increases, the thermal stability of the glass decreases, and when the glass is melted, the glass raw material is likely to remain unmelted. Therefore, the content of Ta2O5 is preferably within the above range. Furthermore, Ta2O5 is an extremely expensive component compared to other glass components, and when the content of Ta2O5 increases, the production cost of the glass increases. Furthermore, since Ta2O5 has a larger molecular weight than other glass components, it increases the specific gravity of the glass, and as a result, increases the weight of the optical element.

[0109] In the optical glass according to this embodiment, the upper limit of the Li2O content is preferably 5%, and more preferably 3%, 2%, and 1% in that order. The lower limit of the Li2O content is preferably 0%. The Li2O content may be 0%.

[0110] Li2O is a component that contributes to lowering the specific gravity of glass, improves the meltability of glass, and increases the average linear thermal expansion coefficient. On the other hand, if the content of Li2O increases, the devitrification resistance decreases. Therefore, the content of Li2O is preferably within the above range.

[0111] In the optical glass according to this embodiment, the lower limit of the K2O content is preferably 1%, more preferably 2%, 3%, and 4%, in that order, and the upper limit of the K2O content is preferably 13%, more preferably 12%, 11%, and 10%, in that order.

[0112] K2O is a component that contributes to lowering the specific gravity of glass and improves the thermal stability of glass. It also increases the average linear thermal expansion coefficient. On the other hand, if the content of K2O increases, the thermal stability decreases and striae tend to occur during vitrification. Therefore, the content of K2O is preferably within the above range.

[0113] In the optical glass according to this embodiment, the upper limit of the Cs2O content is preferably 5%, and more preferably 3%, 2%, and 1% in that order. The lower limit of the Cs2O content is preferably 0%. The Cs2O content may be 0%.

[0114] Although Cs2O has the function of improving the melting property of glass, if the content is too high, the thermal stability and refractive index nd of the glass decrease, and the volatilization of glass components during melting increases, making it impossible to obtain the desired glass. Therefore, the content of Cs2O is preferably within the above range.

[0115] In the optical glass according to this embodiment, the content of MgO is preferably 5% or less, more preferably 3% or less, and further more preferably 1% or less. The lower limit of the content of MgO is preferably 0%. The content of MgO may be 0%.

[0116] In the optical glass according to this embodiment, the CaO content is preferably 5% or less, more preferably 3% or less, and even more preferably 1% or less. The lower limit of the CaO content is preferably 0%. The CaO content may be 0%.

[0117] In the optical glass according to this embodiment, the SrO content is preferably 6% or less, more preferably 5% or less, 3% or less, and further more preferably 1% or less. The lower limit of the SrO content is preferably 0%.

[0118] In the optical glass according to this embodiment, the BaO content is preferably 8% or less, more preferably 5% or less, 3% or less, and 1% or less in that order. The lower limit of the BaO content is preferably 0%.

[0119] MgO, CaO, SrO, and BaO are glass components that improve the thermal stability and devitrification resistance of glass. However, if the content of these glass components is high, the high dispersibility is impaired and the thermal stability and devitrification resistance of glass are reduced. Therefore, it is preferable that the content of each of these glass components is within the above-mentioned range.

[0120] In the optical glass according to this embodiment, the upper limit of the ZnO content is preferably 10%, and more preferably 6%, 4%, and 3% in that order. The lower the ZnO content, the more preferable it is, and the lower limit is preferably 0%. The ZnO content may be 0%.

[0121] ZnO is a glass component that improves the thermal stability of glass. However, if the ZnO content is too high, the specific gravity of the glass increases. Also, the temperature coefficient of the relative refractive index (dn / dT) increases. Therefore, the ZnO content is preferably within the above range.

[0122] In the optical glass according to this embodiment, the ZrO2 content is preferably 5% or less, more preferably 3% or less, and even more preferably 1% or less. The lower limit of the ZrO2 content is preferably 0%.

[0123] ZrO2 is a glass component that improves the thermal stability and devitrification resistance of glass. However, if the content of ZrO2 is too high, the thermal stability tends to decrease. Therefore, the content of ZrO2 is preferably within the above range.

[0124] In the optical glass according to this embodiment, the upper limit of the Sc2O3 content is preferably 2%, and the lower limit of the Sc2O3 content is preferably 0%.

[0125] In the optical glass according to this embodiment, the upper limit of the HfO2 content is preferably 2%. The lower limit of the HfO2 content is preferably 0%.

[0126] Both Sc2O3 and HfO2 have the function of increasing the refractive index nd and are expensive components, so the respective contents of Sc2O3 and HfO2 are preferably within the above ranges.

[0127] In the optical glass according to this embodiment, the upper limit of the Lu2O3 content is preferably 2%, and the lower limit of the Lu2O3 content is preferably 0%.

[0128] Lu2O3 has the function of increasing the refractive index nd. In addition, since it has a large molecular weight, it is also a glass component that increases the specific gravity of the glass. Therefore, the content of Lu2O3 is preferably within the above range.

[0129] In the optical glass according to this embodiment, the upper limit of the GeO2 content is preferably 2%. Also, the lower limit of the GeO2 content is preferably 0%.

[0130] GeO2 has the function of increasing the refractive index nd, and is an extremely expensive component among commonly used glass components. Therefore, from the viewpoint of reducing the manufacturing cost of the glass, the content of GeO2 is preferably in the above range.

[0131] In the optical glass according to this embodiment, the upper limit of the La2O3 content is preferably 2%. The lower limit of the La2O3 content is preferably 0%. The La2O3 content may be 0%.

[0132] High La2O3 content reduces the thermal stability and devitrification resistance of the glass, Therefore, from the viewpoint of suppressing deterioration in thermal stability and resistance to devitrification, the content of La2O3 is preferably within the above range.

[0133] In the optical glass according to this embodiment, the upper limit of the Gd2O3 content is preferably 2%, and the lower limit of the Gd2O3 content is preferably 0%.

[0134] If the content of Gd2O3 is too high, the thermal stability and devitrification resistance of the glass are reduced, and the glass is easily devitrified during production. 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 the thermal stability and devitrification resistance of the glass in a good condition, the content of Gd2O3 is preferably within the above range.

[0135] In the optical glass according to this embodiment, the upper limit of the Y2O3 content is preferably 2%. The lower limit of the Y2O3 content is preferably 0%. The Y2O3 content may be 0%.

[0136] If the content of Y2O3 is too high, the thermal stability and resistance to devitrification of the glass decrease. Therefore, from the viewpoint of suppressing the decrease in the thermal stability and resistance to devitrification, the content of Y2O3 is preferably within the above range.

[0137] In the optical glass according to this embodiment, the upper limit of the Yb2O3 content is preferably 2%, and the lower limit of the Yb2O3 content is preferably 0%.

[0138] Yb2O3 has a larger molecular weight than La2O3, Gd2O3, and Y2O3, and therefore increases the specific gravity of the glass. When the specific gravity of the glass increases, the mass of the optical element increases. For example, when a lens with a large mass is incorporated into an autofocus imaging lens, the power required to drive the lens during autofocus increases, causing rapid battery consumption. Therefore, it is desirable to reduce the Yb2O3 content and suppress the increase in the specific gravity of the glass.

[0139] Moreover, if the content of Yb2O3 is too high, the thermal stability and devitrification resistance of the glass are reduced. From the viewpoint of preventing a decrease in the thermal stability of the glass and suppressing an increase in the specific gravity, the content of Yb2O3 is preferably within the above range.

[0140] The optical glass according to this embodiment which satisfies the above condition (A) is preferably composed mainly of the above-mentioned glass components, namely, P2O5, Nb2O5, and B2O3 as essential components and WO3, SiO2, Al2O3, TiO2, Bi2O3, Ta2O5, Li2O, Na2O, K2O, Cs2O, MgO, CaO, SrO, BaO, ZnO, ZrO2, Sc2O3, HfO2, Lu2O3, GeO2, La2O3, Gd2O3, Y2O3, 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.

[0141] The optical glass according to this embodiment which satisfies the above condition (B) is preferably composed mainly of the above-mentioned glass components, namely, P2O5 and Nb2O5 as essential components and B2O3, WO3, SiO2, Al2O3, TiO2, Bi2O3, Ta2O5, Li2O, Na2O, K2O, Cs2O, MgO, CaO, SrO, BaO, ZnO, ZrO2, Sc2O3, HfO2, Lu2O3, GeO2, La2O3, Gd2O3, Y2O3, 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.

[0142] In the optical glass according to this embodiment, the upper limit of the TeO2 content is preferably 2%, and the lower limit of the TeO2 content is preferably 0%.

[0143] Since TeO2 is toxic, it is preferable to reduce the content of TeO2, and therefore the content of TeO2 is preferably within the above range.

[0144] 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.

[0145] <Other ingredient composition> Pb, As, Cd, Tl, Be, and Se are all toxic, so it is preferable that the optical glass according to this embodiment does not contain these elements as glass components.

[0146] U, Th, and Ra are all radioactive elements, and therefore it is preferable that the optical glass according to this embodiment does not contain these elements as glass components.

[0147] V, Cr, Mn, Fe, Co, Ni, Cu, Pr, Nd, Pm, Sm, Eu, Tb, Dy, Ho, Er, and Tm increase the coloring of the glass and can be sources of fluorescence, so it is preferable that the optical glass according to this embodiment does not contain these elements as glass components.

[0148] Sb (Sb2O3) and Ce (CeO2) are optional elements that function as fining agents. Of these, Sb (Sb2O3) is a fining agent with a large fining effect. However, Sb (Sb2O3) is highly oxidizing, and if the amount of Sb (Sb2O3) added is increased, the coloring of the glass increases due to light absorption by Sb ions, which is undesirable. In addition, when melting glass, if Sb is present in the molten material, the dissolution of platinum, which constitutes the glass melting crucible, into the molten material is promoted, and the platinum concentration in the glass increases. If platinum exists as an ion in the glass, the coloring of the glass increases due to light absorption. In addition, if platinum exists as a solid in the glass, it becomes a source of light scattering, degrading the quality of the glass. Ce (CeO2) has a smaller fining effect than Sb (Sb2O3). Adding a large amount of Ce (CeO2) will intensify the coloring of the glass. Therefore, when adding a fining agent, it is preferable to add Sb (Sb2O3) while paying attention to the amount added.

[0149] The content of Sb2O3 is expressed as an exclusive percentage. That is, when the total content of all glass components other than Sb2O3 and CeO2 is taken as 100 mass%, the content of Sb2O3 is preferably less than 1 mass%, more preferably less than 0.1 mass%. Furthermore, less than 0.05 mass%, less than 0.03 mass%, and less than 0.02 mass% are more preferable in that order. The content of Sb2O3 may be 0 mass%.

[0150] The CeO2 content is also expressed as an exclusive ratio. That is, when the total content of all glass components other than CeO2 and Sb2O3 is taken as 100 mass%, the CeO2 content is preferably less than 2 mass%, more preferably less than 1 mass%, further preferably less than 0.5 mass%, and even more preferably less than 0.1 mass%. The CeO2 content may be 0 mass%. By setting the CeO2 content in the above range, the clarity of the glass can be improved.

[0151] (Glass properties) <Glass transition temperature Tg> The glass transition temperature Tg of the optical glass according to this embodiment is preferably 570° C. or less, more preferably 560° C. or less, 550° C. or less, 540° C. or less, and 530° C. or less in that order.

[0152] By setting the upper limit of the glass transition temperature Tg within the above range, it is possible to suppress increases in the molding temperature and annealing temperature of the glass, thereby reducing thermal damage to press molding equipment and annealing equipment. Also, by setting the lower limit of the glass transition temperature Tg within the above range, it becomes easier to maintain the thermal stability of the glass well while maintaining the desired Abbe number and refractive index.

[0153] <Specific gravity of glass> In the optical glass according to this embodiment, the specific gravity is preferably 3.60 or less, and more preferably 3.50 or less, and then 3.40 or less. If the specific gravity of the glass can be reduced, the weight of the lens can be reduced. As a result, the power consumption of the autofocus drive of the camera lens in which the lens is mounted can be reduced.

[0154] <Light transmittance of glass> The light transmittance of the optical glass according to this embodiment can be evaluated by the coloring degree λ5. The spectral transmittance of a glass sample having a thickness of 10.0 mm±0.1 mm is measured in the wavelength range of 200 to 700 nm, and the wavelength at which the external transmittance becomes 5% is defined as λ5.

[0155] The λ5 of the optical glass according to this embodiment is preferably 400 nm or less, more preferably 380 nm or less, and further preferably 370 nm or less.

[0156] By using optical glass in which λ5 is shortened, it is possible to provide an optical element that enables suitable color reproduction.

[0157] (Optical glass manufacturing) The optical glass according to the embodiment of the present invention may be produced by blending glass raw materials to obtain the above-mentioned predetermined composition, and using the blended glass raw materials according to a known glass manufacturing method. For example, a plurality of compounds may be blended and thoroughly mixed to obtain a batch raw material, and the batch raw material may be placed in a quartz crucible or a platinum crucible to be roughly melted (rough melt). The molten material obtained by the rough melting is quenched and crushed to produce cullet. The cullet is then placed in a platinum crucible, heated and remelted (remelt) to obtain a molten glass, which is then clarified and homogenized, molded, and slowly cooled to obtain an optical glass. A known method may be applied to the molding and slow cooling of the molten glass.

[0158] In addition, as long as a desired glass component can be introduced into the glass in a desired content, the compound used when preparing the batch raw materials is not particularly limited. Examples of such compounds include oxides, carbonates, nitrates, hydroxides, fluorides, etc.

[0159] (Manufacturing of optical elements, etc.) To manufacture an optical element using the optical glass according to the embodiment of the present invention, a known method may be applied. For example, glass raw materials are melted to form molten glass, and the molten glass is poured into a mold and molded into a plate shape to manufacture a glass material made of the optical glass according to the present invention. The obtained glass material is appropriately cut, ground, and polished to manufacture cut pieces of a size and shape suitable for press molding. The cut pieces are heated and softened, and press molded (reheat pressed) by a known method to manufacture an optical element blank that is similar to the shape of the optical element. The optical element blank is annealed, and then ground and polished by a known method to manufacture an optical element.

[0160] The optically functional surface of the prepared optical element may be coated with an anti-reflection film, a total reflection film, or the like depending on the intended use.

[0161] Examples of optical elements include various lenses such as spherical lenses, prisms, and diffraction gratings.

[0162] The present invention will be described below with reference to examples, but the present invention is not limited to the following examples.

[0163] (Example) [Preparation of glass samples] Compound raw materials corresponding to each component, i.e., raw materials such as phosphates, carbonates, and oxides, were weighed and thoroughly mixed to prepare blended raw materials so as to obtain glass having the compositions of Samples No. 1 to 52 shown in Tables 1 to 6. The blended raw materials were placed in a platinum crucible, heated to 900 to 1350°C in an air atmosphere to melt, and homogenized and clarified by stirring to obtain molten glass. The molten glass was cast into a mold to be shaped, and slowly cooled to obtain a block-shaped glass sample. Alternatively, the raw materials may be charged into a quartz glass crucible, melted, transferred to a platinum crucible, and further heated to melt, homogenized by stirring, and the molten glass obtained by clarification may be poured into a mold and shaped, followed by slow cooling.

[0164] [Glass sample evaluation] The glass composition, specific gravity, refractive index nd, Abbe number νd, λ5, glass transition temperature Tg, temperature coefficient of relative refractive index dn / dT, and average linear expansion coefficient α of the obtained glass samples were measured by the methods described below. The results are shown in Tables 1, 2, and 4.

[0165] [1] Glass composition The content of each glass component in the obtained glass sample was measured by inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0166] [2] Specific gravity Measurements were made based on the Japan Optical Glass Industry Association standard JOGIS-05.

[0167] [3] Refractive index nd and Abbe number νd Measurements were made based on the Japan Optical Glass Industry Association standard JOGIS-01.

[0168] [4] λ5 A glass sample was processed to have a thickness of 10 mm and parallel optically polished flat surfaces, and the spectral transmittance was measured in the wavelength range from 280 nm to 700 nm. The intensity of the light beam perpendicularly incident on one of the optically polished flat surfaces was defined as intensity A, and the intensity of the light beam emerging from the other flat surface was defined as intensity B, and the spectral transmittance B / A was calculated. The wavelength at which the spectral transmittance was 5% was defined as λ5. Note that the spectral transmittance also includes the reflection loss of the light beam on the sample surface.

[0169] [5] Glass transition temperature Tg The glass transition temperature Tg was measured using a differential scanning calorimeter (DSC3300SA) manufactured by NETZSCH JAPAN at a heating rate of 10° C. / min.

[0170] [6] Measurement of the temperature coefficient of relative refractive index dn / dT The obtained glass samples were measured based on the interference method of JOGIS18-2008. A He-Ne laser with a wavelength of 633 nm was used as the light source, and measurements were made continuously in the temperature range of -70 to 150°C. Among the measurement results, the dn / dT values ​​in the range of 20°C to 40°C are shown in Tables 1, 2, and 4.

[0171] [7] Measurement of average linear expansion coefficient α The average linear expansion coefficient α from 100 to 300°C was measured in accordance with the provisions of JOGIS08-2003. The specimen was a round bar with a length of 20 mm ±0.5 mm and a diameter of 5 mm ±0.5 mm, and was heated at a constant rate of 4°C per minute while a load of 98 mN was applied to the specimen, and the temperature and specimen elongation were measured.

[0172] [Table 1]

[0173] [Table 2]

[0174] [Table 3]

[0175] [Table 4]

[0176] [Table 5]

[0177] [Table 6]

[0178] Example 2 The glass sample obtained in Example 1 was cut and ground to prepare cut pieces. The cut pieces were press molded by a reheat press to prepare optical element blanks. The optical element blanks were precisely annealed to precisely adjust the refractive index to a required refractive index, and then ground and polished by a known method to obtain various lenses such as biconvex lenses, biconcave lenses, planoconvex lenses, planoconcave lenses, concave meniscus lenses, and convex meniscus lenses.

[0179] 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.

[0180] 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. The refractive index nd is 1.63 to 1.77, the Abbe number νd is 22 to 34, Nb 2 O 5 The content of which is 25 to 35% by mass, WO 3 content is less than 30% by mass, TiO 2 The content thereof is 8 to 14.24% by mass, and Li 2 The content of O is 0.89 mass% or less, the content of Na2O is 17 mass% or less, TiO 2 、 Nb 2 O 5 、 WO 3 、 Bi 2 O 3 and Ta 2 O 5 The total content of [TiO 2 + Nb 2 O 5 + WO 3 + Bi 2 O 3 + Ta 2 O 5 is 36 to 60% by mass, P 2 O 5 , B 2 O 3 , SiO 2 , Al 2 O 3 , Li 2 O, Na 2 O, K 2 O and Cs 2 The mass ratio of TiO 2 , Nb 2 O 5 , WO 3 , Bi 2 O 3 and Ta 2 O 5 to the total content of P 2 , Nb 2 O 5 , WO 3 , Bi 2 O 3 , Ta 2 O 5 [(TiO 2 + Nb 5 O 2 + WO 3 + Bi 2 O 2 + Ta 3 O 2 + P 2 O 2 + B 2 O)] is 1.10 or less, P 2 O 5 and B 2 O 3 The mass ratio [TiO 2 / (P 2 O 2 + B 5 O 2 )] of the content of TiO 3 to the total content of is 0.50 or less, and the optical glass satisfies the following (B). (B) P 2 O 5 The content of which is 27 to 38% by mass, Al 2 O 3 The content of which is less than 5% by mass, Li 2 O, Na 2 O, K 2 O and Cs 2 P with respect to the total content of O 2 O 5 , B 2 O 3 and SiO 2 The mass ratio of the total content [(P 2 O 5 + B 2 O 3 + SiO 2 ) / (Li 2 O + Na 2 O + K 2 O + Cs 2 O)] is 1.80 or less, The total content of MgO, CaO, SrO, and BaO [MgO + CaO + SrO + BaO] is 7.0 mass% or less. TiO 2 , Nb 2 O 5 , W.O. 3 , Bi 2 O 3 and Ta 2 O 5 TiO relative to the total content 2 The mass ratio of the content [TiO 2 / (TiO 2 +Nb 2 O 5 +W.O. 3 +Bi 2 O 3 +Ta 2 O 5 ) is 0.25 or more.

2. Li 2 O, Na 2 O, K 2 O and Cs 2 P with respect to the total content of O 2 O 5 , B 2 O 3 and SiO 2 The mass ratio of the total content [(P 2 O 5 + B 2 O 3 + SiO 2 ) / (Li 2 O + Na 2 O + K 2 O + Cs 2 O)] is 1.00 or more. The optical glass according to claim 1.

3. P 2 O 5 , B 2 O 3 , SiO 2 , Al 2 O 3 , Li 2 O, Na 2 O, K 2 O and Cs 2 The mass ratio of TiO 2 , Nb 2 O 5 , WO 3 , Bi 2 O 3 and Ta 2 O 5 to the total content of [TiO 2 , Nb 2 O 5 , WO 3 , Bi 2 O 3 , Ta 2 O 5 ) / (P 2 O 5 , B 2 O 3 , SiO 2 , Al 2 O 3 , Li 2 O, Na 2 O, K 2 O, Cs 2 O)] is 0.50 or more, the optical glass according to claim 1 or 2.

4. The average linear thermal expansion coefficient α at 100 to 300 °C is 100×10 -7 to 200×10 -7 °C -1 The optical glass according to any one of claims 1 to 3, wherein the optical glass has such a coefficient.

5. The temperature coefficient dn / dT of the relative refractive index at the wavelength of the He-Ne laser (633 nm) is -0.1×10 -6 to -13.0×10 -6 °C -1 The optical glass according to any one of claims 1 to 4, wherein the optical glass has the temperature coefficient dn / dT of the relative refractive index at the wavelength of the He-Ne laser (633 nm) in the range of 20 to 40°C.

6. An optical element made of the optical glass according to any one of Claims 1 to 5.