Optical glass and optical elements

Abstract

To provide optical glass and optical elements with reduced reducing color. [Solution] A solution containing 1 to 45% by mass of B2O3, 10 to 60% by mass of La2O3, and at least one oxide selected from the group consisting of TiO2, Nb2O5, WO3, and Bi2O3, wherein the βOH value shown in the following formula (2) is 0.1 to 2.0 mm -1 This is optical glass. βOH = -[ln(B / A)] / t …(2)

Description

[Technical Field]

[0001] This invention relates to optical glass and optical elements. [Background technology]

[0002] In recent years, with the increasing sophistication and miniaturization of imaging and projection optical systems, the demand for high-refractive-index optical glass as an effective material for optical elements has been growing.

[0003] High refractive index optical glass, such as that described in Patent Document 1, typically contains large amounts of high refractive index components such as Ti, Nb, W, and Bi as glass components. These components are easily reduced during the glass melting process, and the reduced components absorb light on the short wavelength side of the visible light range, causing discoloration of the glass (hereinafter sometimes referred to as "reduction color"). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2007-112697 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] This invention has been made in view of the above circumstances and aims to provide optical glass and optical elements with reduced reducing color. [Means for solving the problem]

[0006] The gist of this invention is as follows: [1] Contains 1 to 45% by mass of B2O3 and 10 to 60% by mass of La2O3, It comprises at least one oxide selected from the group consisting of TiO2, Nb2O5, WO3, and Bi2O3. The βOH value shown in formula (2) below is 0.1 to 2.0 mm. -1Optical glass. βOH = -[ln(B / A)] / t …(2) [In equation (2), t represents the thickness (mm) of the glass used for measuring the external transmittance, A represents the external transmittance (%) at a wavelength of 2500 nm when light is incident on the glass parallel to its thickness direction, and B represents the external transmittance (%) at a wavelength of 2900 nm when light is incident on the glass parallel to its thickness direction. Also, ln is the natural logarithm.]

[0007] [2] The optical glass described in [1], containing 0.1 to 25% by mass of SiO2.

[0008] [3] The optical glass described in [1], containing 0.5 to 15 mass% of SiO2, 1 to 30 mass% of B2O3, and 20 to 60 mass% of La2O3.

[0009] [4] Expressed in mass %, the B2O3 content is greater than the SiO2 content of [1] to [3] Optical glass as described in one of the following.

[0010] [5] An optical glass according to any of [1] to [4], wherein the mass ratio of the TiO2 content to the total content of B2O3 and La2O3 [TiO2 / (B2O3+La2O3)] is 0.030 or higher.

[0011] [6] The Abbe number νd is between 20 and 45. An optical glass as described in any of [1] to [5], having a refractive index nd of 1.75 to 2.50.

[0012] [7] An optical element made of optical glass as described in any of [1] to [6] above. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide optical glass and optical elements with reduced reducing color. [Modes for carrying out the invention]

[0014] Hereinafter, one embodiment of the present invention will be described. In the present invention and this specification, the glass composition is expressed on an oxide basis unless otherwise specified. Here, the "glass composition on an oxide basis" refers to a glass composition obtained by converting all glass raw materials into oxides existing in the glass by decomposition during melting, and the notation of each glass component follows the convention, such as SiO2, TiO2, etc. The content and total content of glass components are on a mass basis unless otherwise specified, "% " means "mass% ", and "ppm" means "mass ppm".

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

[0016] 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).

[0017] The Abbe number νd is used as a value representing the property related to dispersion and is represented by the following formula (1). Here, nF is the refractive index at the F - line of blue hydrogen (wavelength 486.13 nm), and nC is the refractive index at the C - line of red hydrogen (656.27 nm). νd=(nd - 1) / (nF - nC) ···(1)

[0018] The optical glass according to an embodiment of the present invention contains 1 - 45 mass% of B2O3 and 10 - 60 mass% of La2O3, contains at least one oxide selected from the group consisting of TiO2, Nb2O5, WO3, and Bi2O3, and the value of βOH shown in the following formula (2) is 0.1 - 2.0 mm -1 is as follows. βOH=-[ln(B / A)] / t …(2) [In equation (2), t represents the thickness (mm) of the glass used for measuring the external transmittance, A represents the external transmittance (%) at a wavelength of 2500 nm when light is incident on the glass parallel to its thickness direction, and B represents the external transmittance (%) at a wavelength of 2900 nm when light is incident on the glass parallel to its thickness direction. Also, ln is the natural logarithm.]

[0019] The optical glass according to this embodiment (hereinafter sometimes simply referred to as "glass") will be described in detail below.

[0020] The glass according to this embodiment contains 1 to 45% B2O3. The lower limit of the B2O3 content is preferably 2%, and more preferably in the order of 3%, 4%, and 6%. The upper limit of the B2O3 content is preferably 30%, and more preferably in the order of 25%, 20%, and 15%.

[0021] B2O3 is a network-forming component in glass, and it plays a role in maintaining low dispersibility and improving the thermal stability of the glass. On the other hand, if the B2O3 content is high, the amount of volatilization of glass components may increase during glass melting. Also, the devitrification resistance tends to decrease. For this reason, it is preferable that the B2O3 content be within the above range.

[0022] The glass according to this embodiment contains 10 to 60% La2O3. The lower limit of the La2O3 content is preferably 20%, and more preferably 22%, 24%, 27%, and 30% in that order. The upper limit of the La2O3 content is preferably 57%, and more preferably 55% and 53% in that order.

[0023] La2O3 has the effect of increasing the refractive index nd. It also has the effect of improving chemical durability. On the other hand, if the La2O3 content is high, the specific gravity increases and the thermal stability of the glass decreases. For this reason, it is preferable to keep the La2O3 content within the above range.

[0024] The glass according to this embodiment contains at least one oxide selected from the group consisting of TiO2, Nb2O5, WO3, and Bi2O3. TiO2, Nb2O5, WO3, and Bi2O3 are all components that contribute to increasing the refractive index. By including these components, an optical glass with a high refractive index can be obtained.

[0025] In the glass according to this embodiment, the value of βOH shown in the following formula (2) is 0.1 to 2.0 mm -1 is. The lower limit of the value of βOH is preferably 0.2 mm -1 and more preferably 0.25 mm -1 , 0.3 mm -1 , 0.35 mm -1 in this order. Further, the upper limit of the value of βOH is preferably 1.8 mm -1 and more preferably 1.6 mm -1 , 1.5 mm -1 , 1.4 mm -1 , 1.2 mm -1 in this order. βOH = -[ln(B / A)] / t …(2)

[0026] Here, in the above formula (2), t represents the thickness (mm) of the glass used for measuring the external transmittance, A represents the external transmittance (%) at a wavelength of 2500 nm when light is incident on the glass parallel to its thickness direction, and B represents the external transmittance (%) at a wavelength of 2900 nm when light is incident on the glass parallel to its thickness direction. Also, in the above formula (2), ln is the natural logarithm. The unit of βOH is mm -1 is.

[0027] Note that the "external transmittance" is the ratio (Iout / Iin) of the intensity Iout of the transmitted light that has passed through the glass to the intensity Iin of the incident light that enters the glass, that is, the transmittance considering the surface reflection on the surface of the glass. The transmittance can be obtained by measuring the transmission spectrum using a spectrophotometer.

[0028] The βOH represented by formula (2) above represents the absorbance due to the hydroxyl group. Therefore, by evaluating βOH, the water (and / or hydroxide ions, hereinafter simply referred to as "water") content in the glass can be evaluated. In other words, a high βOH level in glass indicates a high water content.

[0029] Increasing the water content in the glass and thereby raising the βOH value reduces the reduction color and shortens the annealing time. Furthermore, degassing and clarification effects are achieved. On the other hand, if the βOH value is too high, the amount of volatile matter from the molten glass tends to increase. Therefore, it is preferable to keep the βOH value within the above range.

[0030] There are no particular limitations on the methods for increasing the βOH content of glass, but one example is to increase the water content in the molten glass during the melting process. Examples of operations to increase the water content in the molten glass include adding water vapor to the molten atmosphere or bubbling a water vapor-containing gas into the molten material.

[0031] (Glass component) Other glass components in this embodiment will be described in detail below.

[0032] In the glass according to this embodiment, the lower limit of the SiO2 content is preferably 0.1%, and more preferably in the order of 0.5%, 1%, 1.5%, 2%, and 3%. The upper limit of the SiO2 content is preferably 25%, and more preferably in the order of 15%, 10%, 8%, and 7%.

[0033] SiO2 is a network-forming component in glass and improves the thermal stability, chemical durability, and weather resistance of the glass. On the other hand, a high SiO2 content may reduce the devitrification resistance of the glass. Therefore, it is preferable to keep the SiO2 content within the above range.

[0034] In the glass according to this embodiment, the P2O5 content is preferably less than 7%, and more preferably 5% or less, 4% or less, 3% or less, 2% or less, and 1% or less, in that order. The P2O5 content may also be 0%.

[0035] P2O5 is a component that lowers the refractive index nd and also reduces the thermal stability of the glass. Therefore, it is preferable to keep the P2O5 content within the above range.

[0036] In the glass according to this embodiment, the Al2O3 content is preferably 5% or less, and more preferably 4% or less, 3% or less, 2% or less, and 1% or less, in that order. The Al2O3 content may be 0%.

[0037] Al2O3 is a glass component that improves the chemical durability and weather resistance of glass, and can be considered a network-forming component. On the other hand, if the Al2O3 content is high, 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 tend to occur. For this reason, it is preferable that the Al2O3 content be within the above range.

[0038] In the glass according to this embodiment, the lower limit of the total content of SiO2 and B2O3 [SiO2+B2O3] is preferably 2%, and more preferably in the order of 4%, 6%, 8%, and 10%. The upper limit of the total content [SiO2+B2O3] is preferably 35%. Furthermore, the percentages are more preferable in the order of 30%, 26%, 24%, and 22%.

[0039] SiO2 and B2O3 are network-forming components of glass and improve its thermal stability and devitrification resistance. Therefore, the total content of SiO2 and B2O3 [SiO2 + B2O3] is preferably within the above range.

[0040] Furthermore, in the glass according to this embodiment, preferably, the B2O3 content [B2O3] is greater than the SiO2 content [SiO2] in mass percent ([B2O3]>[SiO2]). More preferably, the B2O3 content is greater than 1.3 times the SiO2 content ([B2O3]>[SiO2]×1.3). By increasing the B2O3 content to a level greater than the SiO2 content, the Abbe number can be increased.

[0041] In the glass according to this embodiment, the upper limit of the ZnO content is preferably 30%, and more preferably in the order of 25%, 20%, 15%, 10%, 7%, and 5%. Furthermore, the ZnO content is preferably greater than 0%, and the lower limit is more preferably 0.1%, and more preferably in the order of 0.3%, 0.5%, and 1%.

[0042] ZnO is a glass component that improves the thermal stability of glass, as well as its meltability and chemical durability. On the other hand, if the ZnO content is too high, the specific gravity increases. Therefore, it is preferable that the ZnO content be within the above range.

[0043] In the glass according to this embodiment, the upper limit of the BaO content is preferably 20%, and more preferably in the order of 19%, 18%, 17%, and 16%. The lower limit of the BaO content is preferably 0%, and more preferably in the order of 2%, 5%, and 10%.

[0044] BaO is an effective glass component for maintaining a high refractive index and also improves the thermal stability and devitrification resistance of the glass. On the other hand, if the BaO content increases, the specific gravity increases and the devitrification resistance decreases. Therefore, it is preferable that the BaO content be within the above range.

[0045] In the glass according to this embodiment, the upper limit of the MgO content is preferably 5%, and more preferably in the order of 4%, 3%, 2%, and 1%. The lower limit of the MgO content is preferably 0%.

[0046] In the glass according to this embodiment, the upper limit of the CaO content is preferably 10%, and more preferably 8%, 6%, 4%, and 2%, in that order. The lower limit of the CaO content is preferably 0%.

[0047] In the glass according to this embodiment, the upper limit of the SrO content is preferably 7%, and more preferably in the order of 5%, 4%, 3%, and 1%. The lower limit of the SrO content is preferably 0%.

[0048] MgO, CaO, and SrO are all glass components that improve the thermal stability and devitrification resistance of glass. On the other hand, if the content of these glass components increases, the specific gravity increases, impairing high dispersibility, and the thermal stability and devitrification resistance of the glass decrease. Therefore, it is preferable that the content of each of these glass components be within the above range.

[0049] In the glass according to this embodiment, the upper limit of the Gd2O3 content is preferably 35%, and more preferably in the order of 30%, 25%, 20%, 17%, and 12%. The lower limit of the Gd2O3 content is preferably 0%, and more preferably in the order of 1%, 3%, 4%, and 5%.

[0050] In the glass according to this embodiment, the upper limit of the Y2O3 content is preferably 25%, and more preferably in the order of 20%, 15%, 10%, 7%, and 5%. The lower limit of the Y2O3 content is preferably 0%, and more preferably in the order of 1%, 2%, and 3%.

[0051] Gd2O3 and Y2O3 are both components that contribute to improving the weather resistance and increasing the refractive index of glass. On the other hand, if the content is too high, the thermal stability of the glass decreases, and the glass becomes more prone to devitrification during manufacturing. Therefore, it is preferable that the content of each of these glass components is within the above range.

[0052] In the glass according to this embodiment, the upper limit of the Yb2O3 content is preferably 5%, and more preferably in the order of 4%, 3%, 2%, and 1%. The lower limit of the Yb2O3 content is preferably 0%.

[0053] Yb2O3 is a component that contributes to improved weather resistance and higher refractive index. On the other hand, because Yb2O3 has a larger molecular weight than La2O3, Gd2O3, and Y2O3, it increases the specific gravity of the glass. When the specific gravity of the glass increases, the mass of the optical element increases. For example, if a lens with a large mass is incorporated into an autofocus imaging lens, the power required to drive the lens during autofocus increases, leading to rapid battery drain. Therefore, it is desirable to reduce the Yb2O3 content to suppress the increase in the specific gravity of the glass.

[0054] In the glass according to this embodiment, the upper limit of the ZrO2 content is preferably 18%, and more preferably in the order of 15%, 12%, 10%, 8%, and 7%. The lower limit of the ZrO2 content is preferably 0%, and more preferably in the order of 1%, 2%, and 3%.

[0055] ZrO2 is a component that contributes to a high refractive index and is a glass component that improves the thermal stability and devitrification resistance of glass. On the other hand, if the ZrO2 content is too high, the thermal stability tends to decrease. Therefore, it is preferable that the ZrO2 content be within the above range.

[0056] In the glass according to this embodiment, the TiO2 content is preferably greater than 0%, more preferably 0.1%, and more preferably 1%, 3%, 4%, and 5% in that order. The upper limit of the TiO2 content is preferably 30%, and more preferably 25%. The percentages are most preferred in the order of %, 23%, 21%, and 20%.

[0057] TiO2 is a component that contributes to a high refractive index and also improves chemical durability. On the other hand, if the TiO2 content is too high, the resistance to devitrification may decrease. Therefore, it is preferable to keep the TiO2 content within the above range.

[0058] In the glass according to this embodiment, the lower limit of the Nb2O5 content is preferably 0.1%, and more preferably in the order of 1%, 3%, 4%, and 5%. The upper limit of the Nb2O5 content is preferably 35%, and more preferably in the order of 30%, 25%, 20%, 16%, 15%, 14%, and 12%.

[0059] Nb2O5 is a component that contributes to a high refractive index and also improves the thermal stability and chemical durability of the glass. On the other hand, if the Nb2O5 content is too high, the thermal stability of the glass may decrease, and the glass tends to become more discolored. Therefore, it is preferable to keep the Nb2O5 content within the above range.

[0060] In the glass according to this embodiment, the lower limit of the total content of Nb2O5 and TiO2 [Nb2O5+TiO2] is preferably 13%, and more preferably in the order of 13.5%, 14%, 14.5%, and 15%. The upper limit of the total content [Nb2O5+TiO2] is preferably 40%, and more preferably in the order of 35%, 32%, 31%, and 30%.

[0061] Nb2O5 and TiO2 are components that contribute to a high refractive index. On the other hand, if the Nb2O5 content is too high, the thermal stability and devitrification resistance of the glass will decrease. Therefore, it is preferable that the total content of Nb2O5 and TiO2 be within the above range.

[0062] In the glass according to this embodiment, the upper limit of the WO3 content is preferably 25%, and more preferably 20%, 15%, 10%, and 5%, in that order. The lower limit of the WO3 content is preferably 0%.

[0063] WO3 has the effect of lowering the glass transition temperature (Tg). On the other hand, if the WO3 content becomes too high, the discoloration of the glass increases, and the specific gravity also increases. Therefore, it is preferable that the WO3 content be within the above range.

[0064] In this embodiment, the upper limit of the Bi2O3 content is preferably 20%, and more preferably 15%, 10%, 5%, and 3%, in that order. The lower limit of the Bi2O3 content is preferably 0%.

[0065] Bi2O3 improves the thermal stability of glass when included in an appropriate amount. On the other hand, increasing the Bi2O3 content increases the coloration of the glass and also increases its specific gravity. Therefore, it is preferable that the Bi2O3 content be within the above range.

[0066] In the glass according to this embodiment, the upper limit of the total content of Nb2O5, TiO2, WO3, and Bi2O3 [Nb2O5+TiO2+WO3+Bi2O3] is preferably 40%, and more preferably in the order of 37%, 35%, 33%, and 32%. The lower limit of the total content [Nb2O5+TiO2+WO3+Bi2O3] is preferably 1.0%, and more preferably in the order of 1.5%, 5%, 10%, 13%, 13.5%, 14%, 14.5%, and 15%.

[0067] TiO2, WO3, and Bi2O3, along with Nb2O5, are components that contribute to a high refractive index. Therefore, the total content [Nb2O5 + TiO2 + WO3 + Bi2O3] is preferably within the above range.

[0068] In the glass according to this embodiment, the mass ratio of TiO2 content to the total content of B2O3 and La2O3 [TiO2 / (B2O3+La2O3)] is preferably small, with a lower limit of preferably 0.030, and further preferably decreasing in the order of 0.035, 0.040, 0.045, 0.050, 0.055, 0.060, 0.065, 0.070, 0.075, 0.080, 0.085, 0.090, 0.095, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, and 0.50. The upper limit of the mass ratio [TiO2 / (B2O3+La2O3)] is preferably 1.5, and further preferably in the order of 1.0, 0.8, and 0.6.

[0069] Of Nb2O5, TiO2, WO3, and Bi2O3, TiO2 has the greatest effect in increasing the refractive index (nd) per unit content in mass percent. Furthermore, TiO2 is easily reduced during the glass melting process, and when TiO2 is reduced, the transmittance in the visible short wavelength range increases significantly. It is prone to decrease. On the other hand, B2O3 and La2O3, which are the main components in the glass according to this embodiment, do not cause such reduction problems. Therefore, compared to the TiO2 content which significantly reduces transmittance in the visible short wavelength range, B2O3 does not cause such problems. A large total content of TiO2 and La2O3 is preferable, meaning a small mass ratio [TiO2 / (B2O3+La2O3)] is desirable.

[0070] In the glass according to this embodiment, the lower limit of the mass ratio of TiO2 content to the total content of Nb2O5, TiO2, WO3, and Bi2O3 [TiO2 / (Nb2O5+TiO2+WO3+Bi2O3)] is preferably 0.05, and more preferably 0.25, 0.30, 0.40, and 0.45 in that order. The upper limit of the mass ratio [TiO2 / (Nb2O5+TiO2+WO3+Bi2O3)] is preferably 1.00, and can also be 0.90, 0.80, or 0.75.

[0071] As described above, TiO2 is easily reduced during the glass melting process, and when TiO2 is reduced, the transmittance in the visible short wavelength range tends to decrease significantly. In this embodiment, even when the content of TiO2, which is particularly prone to causing discoloration among the components that contribute to increasing the refractive index, such as Nb2O5, TiO2, WO3, and Bi2O3, is high, i.e., when the mass ratio [TiO2 / (Nb2O5+TiO2+WO3+Bi2O3)] is within the above range, the increase in discoloration can be suppressed by introducing gas into the atmosphere or bubbling gas into the molten material during the melting process.

[0072] In the glass according to this embodiment, the upper limit of the Ta2O5 content is preferably 25%, and more preferably in the order of 20%, 16%, 12%, 8%, and 4%. The lower limit of the Ta2O5 content is preferably 0%.

[0073] Ta2O5 is a component that contributes to a high refractive index and also improves the thermal stability of the glass. On the other hand, if the Ta2O5 content is high, the thermal stability of the glass decreases, and unmelted glass raw materials are more likely to occur when the glass is melted. Therefore, it is preferable that the Ta2O5 content be within the above range.

[0074] In the glass according to this embodiment, the upper limit of the Li2O content is preferably 10%, and more preferably in the order of 7%, 5%, 4%, 3%, 2%, and 1%. The lower limit of the Li2O content is preferably 0%.

[0075] In the glass according to this embodiment, the upper limit of the Na2O content is preferably 10%, and more preferably in the order of 7%, 5%, 4%, 2%, and 1%. The lower limit of the Na2O content is preferably 0%.

[0076] In the glass according to this embodiment, the upper limit of the K2O content is preferably 10%, and more preferably in the order of 7%, 5%, 4%, 2%, and 1%. The lower limit of the K2O content is preferably 0%.

[0077] Li2O, Na2O, and K2O all have the effect of lowering the liquidus temperature and improving the thermal stability of the glass, but if their content increases, chemical durability and weather resistance will decrease. For this reason, it is preferable that the content of Li2O, Na2O, and K2O be within the above ranges.

[0078] In the glass according to this embodiment, the upper limit of the Cs2O content is preferably 5%, and more preferably in the order of 4%, 3%, 2%, and 1%. The lower limit of the Cs2O content is preferably 0%.

[0079] While Cs2O improves the thermal stability of glass, its high content reduces chemical durability and weather resistance. Therefore, the Cs2O content is preferably within the specified range.

[0080] In the glass according to this embodiment, the upper limit of the total content of Li2O, Na2O, K2O, and Cs2O [Li2O+Na2O+K2O+Cs2O] is preferably 15%, and more preferably in the order of 10%, 7%, 5%, 3%, and 1%. The lower limit of the total content [Li2O+Na2O+K2O+Cs2O] is preferably 0%.

[0081] By ensuring that the lower limit of the total content [Li2O+Na2O+K2O+Cs2O] satisfies the above requirements, the fusion properties and thermal stability of the glass can be improved, and the liquidus temperature can be lowered. Furthermore, by ensuring that the upper limit of the total content [Li2O+Na2O+K2O+Cs2O] satisfies the above requirements, the decrease in devitrification resistance can be suppressed.

[0082] In the glass according to this embodiment, the Sc2O3 content is preferably 2% or less. Furthermore, the lower limit of the Sc2O3 content is preferably 0%.

[0083] In the glass according to this embodiment, the upper limit of the HfO2 content is preferably 2% or less, and more preferably in the order of 1%, 0.5%, and 0.1%. The lower limit of the HfO2 content is preferably 0%.

[0084] Sc2O3 and HfO2 enhance the dispersibility of glass, but they are expensive components. Therefore, it is preferable that the respective contents of Sc2O3 and HfO2 are within the above ranges.

[0085] In the glass according to this embodiment, the Lu2O3 content is preferably 2% or less. Furthermore, the lower limit of the Lu2O3 content is preferably 0%.

[0086] Lu2O3 enhances the dispersibility of glass, but due to its large molecular weight, it also increases the specific gravity of the glass. Therefore, the Lu2O3 content is preferably within the above range.

[0087] In the glass according to this embodiment, the GeO2 content is preferably 2% or less. Furthermore, the lower limit of the GeO2 content is preferably 0%.

[0088] GeO2 enhances the high dispersion properties of glass, but it is by far the most expensive component among commonly used glass components. Therefore, from the viewpoint of reducing the cost of glass manufacturing, it is preferable that the GeO2 content be within the above range.

[0089] The glass according to this embodiment is preferably composed mainly of the above-mentioned components, namely B2O3 and La2O3 as essential components, and SiO2, P2O5, Al2O3, ZnO, BaO, MgO, CaO, SrO, Gd2O3, Y2O3, Yb2O3, ZrO2, TiO2, Nb2O5, WO3, Bi2O3, Ta2O5, Li2O, Na2O, K2O, Cs2O, Sc2O3, HfO2, Lu2O3, and GeO2 as optional components, and the total content of the above-mentioned glass components is preferably more than 95%, more preferably more than 98%, even more preferably more than 99%, and even more preferably more than 99.5%.

[0090] In this embodiment, a more preferred embodiment is, It contains 1-45% B2O3, 10-60% La2O3, more than 0% TiO2, and more than 0% ZnO. Quality of TiO2 content relative to the total content of Nb2O5, TiO2, WO3, and Bi2O3 The quantity ratio [TiO2 / (Nb2O5+TiO2+WO3+Bi2O3)] is 0.4 or higher, The βOH value shown in formula (2) below is 0.1 to 2.0 mm. -1 Optical glass is one example. βOH = -[ln(B / A)] / t …(2) [In equation (2), t represents the thickness (mm) of the glass used for measuring the external transmittance, A represents the external transmittance (%) at a wavelength of 2500 nm when light is incident on the glass parallel to its thickness direction, and B represents the external transmittance (%) at a wavelength of 2900 nm when light is incident on the glass parallel to its thickness direction. Also, ln is the natural logarithm.]

[0091] The content of B2O3, La2O3, TiO2, and ZnO in the above more preferred embodiment. The quantity, mass ratio [TiO2 / (Nb2O5+TiO2+WO3+Bi2O3)], and the value of βOH Therefore, the aforementioned preferred numerical range can be applied. Furthermore, the aforementioned preferred numerical range can also be appropriately applied to the content and mass ratio of other glass components.

[0092] In the glass according to this embodiment, the platinum Pt content is preferably less than 10 ppm, and more preferably 8 ppm or less, 7 ppm or less, and 5 ppm or less, in that order. The lower limit of the Pt content is not particularly limited, but it will inevitably contain about 0.001 ppm.

[0093] By setting the Pt content within the above range, it is possible to reduce the discoloration of the glass caused by Pt and improve its transmittance.

[0094] In this embodiment, the glass is manufactured by melting the glass raw materials in a non-oxidizing atmosphere. Examples of a non-oxidizing atmosphere include inert gases such as nitrogen, carbon dioxide, argon, and helium, as well as water vapor. Typically, oxygen in the melting atmosphere reacts with platinum, which is a material of the melting vessel (crucible, etc.), to form platinum dioxide and platinum ions (Pt 4+ Discoloration occurs when oxidative stress is generated and dissolves into the molten glass. In this embodiment, by reducing the partial pressure of oxygen in the molten atmosphere, the oxidation of platinum can be suppressed, and the amount of Pt dissolved into the molten glass can be reduced. As a result, discoloration caused by Pt can be reduced.

[0095] <Other component composition> Pb, As, Cd, Tl, Be, and Se are all toxic. Therefore, it is preferable that the optical glass of this embodiment does not contain these elements as glass components.

[0096] U, Th, and Ra are all radioactive elements. Therefore, it is preferable that the optical glass of this embodiment does not contain these elements as glass components.

[0097] V, Cr, Mn, Fe, Co, Ni, Cu, Pr, Nd, Pm, Sm, Eu, Tb, Dy, Ho, Er, Tm, and Ce can increase the coloration of glass and become sources of fluorescence. Therefore, it is preferable that the optical glass of this embodiment does not contain these elements as glass components.

[0098] Sulfates are optional oxidizing agents that function as clarifying agents. Sulfates decompose upon heat to produce clarifying gases SO2 and O2. Examples of sulfates include zinc sulfate and zirconium sulfate, although these are not particularly limited.

[0099] The sulfate content shall be expressed as an external percentage. That is, the sulfate content, when the total content of all glass components other than sulfate is taken as 100% by mass, is preferably in the range of less than 1% by mass, more preferably less than 0.5% by mass, and even more preferably less than 0.3% by mass. The sulfate content may also be 0% by mass.

[0100] Sb(Sb2O3) is an optional element that can be added and function as a clarifying agent. However, Sb(Sb2O3) is highly oxidizing, and increasing the amount added may accelerate the oxidation of platinum derived from the platinum crucible. Furthermore, during precision press forming, the Sb(Sb2O3) contained in the glass oxidizes the molding surface of the press forming die, and as precision press forming is repeated, the molding surface may deteriorate significantly, potentially making precision press forming impossible. As a result, the surface quality of the formed optical element deteriorates. Therefore, the glass according to this embodiment preferably does not contain Sb(Sb2O3).

[0101] While the glass according to this embodiment is preferably composed of the above-mentioned glass components, it may also contain other components as long as they do not hinder the effects of the present invention. Furthermore, the present invention does not exclude the inclusion of unavoidable impurities.

[0102] (Glass properties) <refractive index nd> In the glass according to this embodiment, the refractive index nd is preferably 1.75 or higher, and may be 1.77 or higher, or 1.80 or higher. Furthermore, the refractive index nd is preferably 2.50 or lower, and may be 2.20 or lower, or 2.10 or lower. The refractive index nd can be increased by increasing the total content of Nb2O5, TiO2, WO3, and Bi2O3 [Nb2O5+TiO2+WO3+Bi2O3], and can be decreased by increasing the SiO2 content.

[0103] <Abbe number νd> In the glass according to this embodiment, the Abbe number νd is 20 or greater. The Abbe number νd may be in the range of 20 to 45, or 21 to 45. The Abbe number νd can be increased by increasing the La2O3 content and decreased by increasing the B2O3 content.

[0104] <Light transmittance of glass> The light transmittance of the optical glass according to this embodiment can be evaluated by the degree of coloration λ70. For a glass sample with a thickness of 10.0 mm ± 0.1 mm, the spectral transmittance is measured in the wavelength range of 200 to 700 nm, and the wavelength at which the external transmittance is 70% is defined as λ70.

[0105] The λ70 of the optical glass according to this embodiment is preferably 480 nm or less, more preferably 470 nm or less, even more preferably 450 nm or less, and particularly preferably 440 nm or less. λ70 can be reduced by reducing the platinum Pt content.

[0106] Furthermore, the λ70 of the optical glass according to this embodiment preferably satisfies the following formula (3). λ70 ≤ a × b + 373 ···(3) In formula (3), a is preferably 200, and more preferably in the order of 195, 190, 185, 180, and 175. Furthermore, b is the mass ratio of the TiO2 content to the total content of B2O3 and La2O3 [TiO2 / (B2O3+La2O3)].

[0107] As the mass ratio [TiO2 / (B2O3+La2O3)] increases, the transmittance in the visible short-wavelength region decreases, and the degree of coloration λ70 increases. In the optical glass according to this embodiment, the reduction color is reduced, and λ70 can be kept within the range shown by the above formula (3).

[0108] <t450> The light transmittance of the optical glass according to this embodiment can be evaluated using T450. In this embodiment, T450 is the external transmittance at a wavelength of 450 nm when converted to a thickness of 10.0 mm. "External transmittance" is the ratio (Iout / Iin) of the intensity of transmitted light that has passed through the glass to the intensity of incident light Iin incident perpendicular to one of the optically polished planes of a glass sample processed to have parallel and optically polished planes. In other words, it is the transmittance that also takes into account surface reflection at the surface of the glass. The transmittance is obtained by measuring the transmission spectrum using a spectrophotometer. The glass thickness used for measurement may be 10.0 mm, but if the thickness is not 10.0 mm, it may be converted to the transmittance at a thickness of 10.0 mm using a well-known method.

[0109] The T450 of the optical glass according to this embodiment is preferably 65% ​​or more, more preferably 70% or more, and even more preferably 75% or more. T450 can be increased by reducing the reducing color of the glass.

[0110] <t400> The light transmittance of the optical glass according to this embodiment can also be evaluated using T400. For a glass sample with a thickness of 10.0 mm ± 0.1 mm, the external transmittance T400 at a wavelength of 400 nm is measured using a spectrophotometer. This value may also be converted to the transmittance at a thickness of 10.0 mm using a well-known method. A higher T400 value indicates better transmittance and reduced glass discoloration.

[0111] The T400 of the optical glass according to this embodiment is preferably 50% or more, more preferably 60% or more, and even more preferably 70% or more. T400 can be increased by reducing the reduction color of the glass.

[0112] <τ400> The light transmittance of the optical glass according to this embodiment can also be evaluated by τ400. For a glass sample with a thickness of 10.0 mm ± 0.1 mm, the internal transmittance τ400 at a wavelength of 400 nm is measured using a spectrophotometer. This value may be converted to the transmittance at a thickness of 10.0 mm using a well-known method. A larger τ400 value indicates better transmittance and reduced glass discoloration.

[0113] The τ400 of the optical glass according to this embodiment is preferably 50% or more, more preferably 60% or more, and even more preferably 70% or more. τ400 can be increased by reducing the reduction color of the glass.

[0114] <Specific gravity of glass> In the optical glass according to this embodiment, the specific gravity is preferably 7 or less, and more preferably 6.5 or less, followed by 6 or less. Furthermore, the specific gravity is preferably 2.5 or more, and more preferably 3 or more, followed by 3.5 or more. Reducing the specific gravity of the glass reduces the weight of the lens. As a result, the power consumption of the autofocus drive of the camera lens on which the lens is mounted can be reduced. On the other hand, reducing the specific gravity too much leads to a decrease in thermal stability.

[0115] <Glass transition temperature Tg> The glass transition temperature Tg of the optical glass according to this embodiment is preferably 800°C or lower, and more preferably 770°C or lower, followed by 750°C or lower. Furthermore, the glass transition temperature Tg is preferably 300°C or higher, and more preferably 350°C or higher, followed by 400°C or higher. The glass transition temperature Tg can be reduced by increasing the total content of Li2O, Na2O, and K2O [Li2O + Na2O + K2O].

[0116] By ensuring that the upper limit of the glass transition temperature (Tg) satisfies the above range, the rise in the glass molding temperature and annealing temperature can be suppressed, thereby reducing thermal damage to the press molding equipment and annealing equipment. Furthermore, by ensuring that the lower limit of the glass transition temperature (Tg) satisfies the above range, it becomes easier to maintain good thermal stability of the glass while maintaining the desired Abbe number and refractive index.

[0117] (Quality of optical glass) Generally, drawbacks of optical glass include bubbles, imperfections (foreign matter), and striations. These defects are evaluated by measuring the amount of defects contained in a unit quantity of glass. The degree to which light transmission is inhibited changes depending on the amount of bubbles and imperfections present per unit cross-sectional area of ​​the glass.

[0118] However, if the unit for evaluating defects (evaluation unit) is extremely small, selecting an area where no bubbles or imperfections exist will result in the absence of optical defects within that range. However, optical glass used as an industrial product generally requires homogeneity not in minute areas such as 1 mm x 1 mm, but rather in glass with a cross-sectional area of, for example, 100 mm x 100 mm or a certain volume or larger.

[0119] Furthermore, not only the evaluation unit, but also the production unit of optical glass should be discussed. Even if the required homogeneity is the same, there is a vast difference in the difficulty of manufacturing 1 ml of glass compared to 1,000 kg of glass. In other words, even when melting and vitrifying the same raw materials, the amount of heat required changes depending on the amount of glass. For example, even under conditions of a melting temperature of 1250°C and a melting time of 2 hours, it is possible to produce a molten glass (molten glass) without bubbles or lumps when producing 1 ml of glass, whereas when producing 1,000 kg of glass, it is difficult to even melt the raw materials.

[0120] Depending on the amount of glass, not only do the conditions required for vitrification change, but the temperature and time required for degassing (clarification) also need to be changed. Increasing the amount of glass increases the amount of heat required for vitrification, and the melting time and clarification time also become longer. As a result, the amount of platinum (Pt) that makes up the crucible leaches into the molten glass increases.

[0121] In other words, when producing optical glass, which is an industrial product, it is necessary to have a certain minimum glass volume. Compared to experiments or small-scale glass production, the melting and clarification conditions, as well as the amount of Pt mixed into the glass from the production equipment (crucible, etc.), will also change.

[0122] Regarding striations, homogeneity is an even more important characteristic. The drawback of "striations" itself is that it deals with the optical homogeneity (refractive index distribution in space) of a certain volume, so naturally the evaluation unit needs to be above a certain level. Even when producing the same 1000 ml of glass, the uniformity of the refractive index will differ between producing 1000 ml of molten glass at once and producing 10 ml of molten glass 100 times. Generally, when manufacturing optical glass, producing 1000 ml of molten glass in one go results in glass with superior homogeneity.

[0123] As described above, discussions regarding optical glass as an industrial product focus on the production of quantities exceeding a certain volume. The difficulty of producing high-quality optical glass within this range, and the characteristics and quality of the optical glass depending on the manufacturing method, are discussed inseparably.

[0124] The techniques discussed for glass melting on a very small scale (e.g., small-scale experiments) cannot be directly applied to glass melting at the industrial product level. Furthermore, when the scale of glass production differs, it is not possible to uniformly compare the properties and quality of glass produced by each method.

[0125] In this embodiment, the concept of glass homogeneity is introduced to distinguish between the properties and quality of experimental-level glass and those of industrial-level glass. Glass homogeneity can be evaluated by its refractive index distribution.

[0126] <Refractive index distribution> The refractive index distribution of the optical glass according to this embodiment is preferably within 0.00050, more preferably within 0.00030, more preferably within 0.00010, more preferably within 0.00007, and more preferably within 0.00005. The refractive index distribution is measured for a continuum having a glass volume of 100 ml or more. The glass volume of the sample used for refractive index measurement is 1 ml or more. The volume of glass can be calculated, for example, by measuring its mass and combining that with its specific gravity.

[0127] Specifically, prepare a glass (a) of 100 ml or more, and measure the refractive index at two points: an arbitrary point A and a point B opposite to A. Furthermore, if there is a known refractive index in one part of the glass, designate that part as A, and measure the refractive index of part B, which is furthest from A. Obtain a total of two or more glass fragments from glass a and measure their refractive indices. In this embodiment, the refractive index distribution was evaluated using the refractive index nd, but the evaluation may be performed using the refractive index at other wavelengths as appropriate.

[0128] (Manufacturing of optical glass) The glass according to the embodiment of the present invention can be produced by blending glass raw materials to achieve the above-described predetermined composition, and then using the blended glass raw materials according to a known glass manufacturing method. For example, several types of compounds may be blended and thoroughly mixed to form a batch raw material, and the batch raw material may be placed in a platinum crucible and roughly melted (melting step).

[0129] In the glass melting process according to this embodiment, a reducing agent can be added to the glass raw material. The reducing agent is not particularly limited, but examples include substances that exhibit reducing properties such as Al, Si, Ti, W, H2, CO, and C. More specifically, carbon compounds and activated carbon C can be given as examples of substances that exhibit reducing properties. By adding a reducing agent to the glass raw material, the highly reactive oxygen generated during the vitrification of the glass raw material reacts with the reducing agent, suppressing the oxidation reaction of platinum derived from the platinum crucible. As a result, the Pt content in the glass can be reduced.

[0130] In the glass melting process according to this embodiment, the melting atmosphere is preferably a non-oxidizing atmosphere. By performing the melting process in a non-oxidizing atmosphere, the partial pressure of oxygen in the melting atmosphere is reduced, the oxidation of platinum derived from the platinum crucible is suppressed, and the amount of Pt dissolved in the molten glass can be reduced.

[0131] The non-oxidizing atmosphere is not particularly limited, but examples include inert gas atmospheres such as nitrogen, carbon dioxide, argon, and helium, or water vapor addition atmospheres. A water vapor addition atmosphere is preferred in order to increase the βOH content of the final glass.

[0132] By adding water vapor to the molten atmosphere, the βOH value of the final optical glass can be increased, the dissolution of Pt and other materials into the glass can be effectively prevented, and sufficient dissolved gas can be supplied to the glass to improve degassing and clarification properties.

[0133] The method of adding steam to the molten atmosphere is not particularly limited, but one example is to insert a connecting pipe into the crucible through an opening in the melting apparatus and supply steam to the space inside the crucible through this pipe as needed.

[0134] In the melting process, bubbling may be used to agitate the molten material. Bubbling during melting may also be continued after the compounding materials have melted. By agitating the molten material in the melting process, the oxidation of the glass component progresses while the oxidation of platinum derived from the platinum crucible is suppressed. This is because the glass component tends to oxidize more easily than platinum. As a result, the reduction reaction of the glass component is suppressed, reducing the reduction color, and the dissolution of platinum into the molten material is suppressed, reducing the coloration derived from platinum.

[0135] The gas used for bubbling is not necessarily limited, and any known gas can be used. Examples include inert gases such as nitrogen, carbon dioxide, argon, and helium, as well as air and water vapor.

[0136] By using a gas containing water vapor as the bubbling gas, the βOH value of the final optical glass can be increased, effectively preventing platinum from dissolving into the glass, and supplying the glass with enough dissolved gas to improve degassing and clarification properties.

[0137] The water vapor content in such a water vapor-containing gas is preferably 10% by volume or more, more preferably 20% by volume or more, even more preferably 30% by volume or more, even more preferably 40% by volume or more, even more preferably 50% by volume or more, even more preferably 60% by volume or more, still more preferably 70% by volume or more, particularly preferably 80% by volume or more, and even more preferably 90% by volume or more. A higher water vapor content is preferable, and by setting it within the above range in particular, the βOH value of the final optical glass can be increased.

[0138] The molten material obtained by rough melting is rapidly cooled and pulverized to produce cullet. The cullet is then heated in a platinum crucible and remelted to produce molten glass. After further clarification and homogenization, the molten glass is shaped and slowly cooled to obtain optical glass. Known methods can be applied to shape and slowly cool the molten glass.

[0139] Furthermore, the compounds used when preparing the batch raw materials are not particularly limited, as long as the desired glass components can be introduced into the glass in the desired amounts. Examples of such compounds include oxides, carbonates, nitrates, hydroxides, and fluorides.

[0140] (Manufacturing of optical elements, etc.) To manufacture an optical element using the optical glass according to the embodiment of the present invention, known methods can be applied. For example, the molten glass described above can be poured into a mold and formed into a plate to produce a glass material made of the optical glass according to the present invention. The obtained glass material can be cut, ground, and polished as appropriate to produce cut pieces of a size and shape suitable for press molding.

[0141] The cut pieces are heated and softened, then press-formed (reheat press) using a known method to produce an optical element blank that approximates the shape of the optical element. The optical element blank is then annealed. Optical elements can be fabricated by grinding and polishing using known methods.

[0142] The cut pieces can also be roughly polished (barrel polished) to equalize their weight and make it easier for a release agent to adhere to the surface, then reheated to soften the glass, which is then press-formed into a shape similar to the desired optical element, and finally ground and polished to manufacture the optical element.

[0143] Alternatively, a predetermined weight of molten glass may be separated onto a mold and directly press-formed, and finally ground and polished to manufacture the optical element.

[0144] Depending on the intended use, the optical functional surface of the fabricated optical element may be coated with an anti-reflective coating, a total reflection coating, or the like. [Examples]

[0145] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to the embodiments shown in the examples.

[0146] Glass samples with the glass compositions shown in Table 1 were prepared using the following procedure and evaluated in various ways.

[0147] [Manufacturing of optical glass] (Example 1-A) First, oxides, hydroxides, carbonates, and nitrates corresponding to the constituent components of glass were prepared as raw materials. These raw materials were weighed and blended so that the glass composition of the resulting optical glass would be as shown in Table 1, and the raw materials were thoroughly mixed. The resulting blended raw materials (batch raw materials) were placed in a platinum crucible and heated at 1250°C to 1400°C for 2 hours to melt them into molten glass (melting process). The mixture was then stirred at 1300°C to 1400°C for 1 to 2 hours to homogenize and clarify it (homogenization and clarification process). The molten glass was poured into a mold preheated to an appropriate temperature. The poured glass was heat-treated at a temperature 100°C lower than the glass transition temperature (Tg) for 30 minutes, and then allowed to cool to room temperature in the furnace to obtain a glass sample.

[0148] The following operations were performed in the melting process and the homogenization / clarification process.

[0149] A platinum pipe was inserted from outside the melting furnace into a platinum crucible placed inside the furnace, and steam was supplied to the space inside the platinum crucible through this platinum pipe. The flow rate of the supplied steam was set to 25 cc / min.

[0150] Furthermore, nitrogen was supplied to the space inside the platinum crucible through the platinum pipe mentioned above, and water vapor was bubbled into the molten material from a pipe installed at the bottom of the crucible. The flow rates of the supplied nitrogen and water vapor were 30 L / min for nitrogen and 0.1 cc / min for water vapor.

[0151] Furthermore, glass samples were prepared by changing the presence or absence of additives, and the conditions in the melting process and homogenization / clarification process, as shown in Tables 2-4. Specifically, the changes were as follows:

[0152] (Example 1-B) The raw materials corresponding to No. 1 listed in Table 1 were placed in a platinum crucible along with the additives shown in Table 2. The mixture was heated and melted under conditions 1-1 to 1-9 shown in Table 2 to obtain molten glass (melting process), then stirred to homogenize and clarified (homogenization and clarification process). Glass samples were obtained in the same manner as in Example 1-A.

[0153] (Example 1-C) The raw materials corresponding to No. 2 listed in Table 1 were placed in a platinum crucible along with the additives shown in Table 3. The mixture was heated and melted under conditions 2-1 to 2-4 shown in Table 3 to obtain molten glass (melting process), then stirred to homogenize and clarified (homogenization and clarification process). Glass samples were obtained in the same manner as in Example 1-A.

[0154] (Example 1-D) The raw materials corresponding to No. 4 listed in Table 1 were placed in a platinum crucible along with the additives shown in Table 4. The mixture was heated and melted under the conditions 4-1 to 4-5 shown in Table 4 to obtain molten glass (melting process), then stirred to homogenize and clarified (homogenization and clarification process). Glass samples were obtained in the same manner as in Example 1-A.

[0155] [Confirmation of glass component composition] The obtained glass samples were analyzed using inductively coupled plasma atomic emission spectroscopy (ICP-AES) to measure the content of each glass component, and it was confirmed that the compositions were as shown in Table 1.

[0156] [Measurement of Pt content in glass] The platinum (Pt) content in the glass was quantified by inductively coupled plasma mass spectrometry (ICP-MS). The quantification results are shown in Tables 1-4.

[0157] [Confirmation of defoaming and clarification effects] For the obtained glass samples, the number of bubbles observed inside the glass was counted, and the number of bubbles (residual bubbles) per unit mass (kg) was calculated. The calculation results are shown in Tables 2 to 4.

[0158] [Measurement of optical properties] The obtained glass samples were subjected to measurements of βOH, λ70, T400, and T450. Furthermore, the obtained glass samples were annealed at 710°C for 72 hours. Annealed samples were prepared by cooling them to room temperature in a furnace at a rate of -30°C / hour, and the refractive indices nd, ng, nF, and nC, Abbe number νd, λ70, and T400 were measured.

[0159] (i) Refractive index nd, ng, nF, nC and Abbe number νd For the above annealed samples, the refractive indices nd, ng, nF, and nC were measured according to the refractive index measurement method of JIS standard JIS B 7071-1, and the Abbe number νd was calculated based on equation (1). The results are shown in Table 1. νd=(nd-1) / (nF-nC) ···(1)

[0160] (ii)βOH The above glass sample was processed into a plate-shaped glass sample with a thickness of 1 mm and having parallel, optically polished surfaces. Light was incident on the polished surface of this plate-shaped glass sample from a direction perpendicular to it, and the external transmittance A at a wavelength of 2500 nm and the external transmittance B at a wavelength of 2900 nm were measured using a spectrophotometer, respectively, and βOH was calculated using the following formula (2). The results are shown in Tables 1 to 4. βOH = -[ln(B / A)] / t ···(2)

[0161] In equation (2) above, ln is the natural logarithm, and the thickness t corresponds to the distance between the two planes. Furthermore, the external transmittance includes reflection loss at the surface of the glass sample and is the ratio of the intensity of transmitted light to the intensity of incident light entering the glass sample (transmitted light intensity / incident light intensity).

[0162] (iii)λ70 The glass sample obtained in Example 1-A was processed to have a thickness of 10 mm and parallel, optically polished planes, and its spectral transmittance was measured in the wavelength range from 280 nm to 700 nm. The intensity of light rays incident perpendicularly to one of the optically polished planes was defined as intensity A, and the intensity of light rays emitted from the other plane was defined as intensity B, and the spectral transmittance B / A was calculated. The wavelength at which the spectral transmittance was 70% was defined as λ70. Note that the spectral transmittance includes the reflection loss of light rays at the sample surface. The results are shown in Table 1.

[0163] For the glass samples obtained in Examples 1-B to 1-D, λ70 was measured before annealing (before heat treatment) and after annealing (after heat treatment) in the same manner as described above. Tables 2 to 4 show the λ70 before annealing (before heat treatment) and after annealing (after heat treatment).

[0164] (iv)T400 For the glass samples obtained in Example 1-B, the T400 was measured before annealing (before heat treatment) and after annealing (after heat treatment). Specifically, the glass samples or annealed samples were processed to have a thickness of 10 mm and parallel, optically polished surfaces, and the spectral transmittance at a wavelength of 400 nm was measured. Note that the spectral transmittance includes the reflection loss of light rays at the sample surface. Table 2 shows the T400 before annealing (before heat treatment) and after annealing (after heat treatment).

[0165] (v)T450 The glass sample obtained in Example 1-A was processed to have a thickness of 10 mm and parallel, optically polished surfaces, and its spectral transmittance at a wavelength of 450 nm was measured. Note that the spectral transmittance includes the reflection loss of light rays at the sample surface. The results are shown in Table 1.

[0166] [Table 1]

[0167] [Table 2]

[0168] [Table 3]

[0169] [Table 4]

[0170] As shown in Table 1, by introducing water vapor into the molten atmosphere or bubbling water vapor into the molten glass to increase the βOH value, we were able to obtain optical glass with less coloration and high transmittance at a wavelength of 450 nm.

[0171] The results in Tables 2-4 show that by increasing the βOH value of the glass, optical glass with less coloration and high transmittance in the visible range can be obtained without prolonged heat treatment in an oxidizing atmosphere after glass molding.

[0172] (Example 2) A 15mm × 175mm × 1500mm glass block was prepared from glass having the composition of No. 1 shown in Table 1 and manufactured according to condition 1-1 in Table 2. This block was then cut into five equal parts, yielding five 15mm × 175mm × 300mm glass blocks. Five refractive index measurement samples 1-5 were prepared using each of the five divided glass blocks, and the refractive index nd of each sample was measured. Using the refractive index nd of sample 1, which was located at one of the two ends before cutting, as a reference, the refractive index distributions of samples 2-5 were as follows.

[0173] The difference between the refractive index nd of sample 2, taken from a part adjacent to sample 1, and the refractive index nd of sample 1 was +0.00001. The difference between the refractive index nd of sample 3, taken from the central part, and the refractive index nd of sample 1 was +0.00002. The difference between the refractive index of sample 4, taken from a part adjacent to sample 3, and the refractive index of sample 1 was 0.00000. The difference between the refractive index of sample 5, taken from the opposite end of sample 1 (one of the two ends before cutting), and the refractive index of sample 1 was -0.00003. As described above, the refractive index distribution at the five locations was 0.00005.

[0174] When the refractive index distribution was measured in the same way for glass having the composition of No. 1 shown in Table 1 and prepared according to conditions 1-2 to 1-9 in Table 2, the refractive index distribution at five locations was within 0.00005.

[0175] Furthermore, when the refractive index distribution was measured in the same manner for glasses having each of the compositions No. 2 to 17 shown in Table 1 and prepared under the conditions of Example 1-A, the refractive index distribution at five points was within 0.00005.

[0176] (Example 3) Using the optical glass prepared in Examples 1-A to 1-D, lens blanks were fabricated by known methods, and various lenses were produced by processing the lens blanks by known methods such as polishing. The optical lenses fabricated include various types such as biconvex lenses, biconcave lenses, plano-convex lenses, plano-concave lenses, concave meniscus lenses, and convex meniscus lenses. By combining various lenses with lenses made of other types of optical glass, secondary chromatic aberration could be effectively corrected.

[0177] Furthermore, because the glass has a low specific gravity, each lens is lighter than lenses with equivalent optical properties and size, making them suitable for various imaging devices, especially autofocus imaging devices, due to their energy-saving properties. Similarly, prisms were fabricated using the various optical glasses produced in Examples 1-A to 1-D.

[0178] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims rather than by the foregoing description, and all modifications within the meaning and scope equivalent to the claims are intended to be included.

[0179] For example, by performing the compositional adjustments described in the specification on the glass compositions exemplified above, an optical glass according to one aspect of the present invention can be produced. Furthermore, it is certainly possible to arbitrarily combine two or more items described as examples or preferred scopes in the specification.

Claims

1. B 2 O 3 1 to 45% by mass, La 2 O 3 It contains 10 to 60% by mass of TiO 2 , Nb 2 O 5 , WO 3 and Bi 2 O 3 comprises at least one oxide selected from the group consisting of The βOH value shown in formula (2) below is 0.1 to 2.0 mm. -1 Optical glass. βOH=-[ln(B / A)] / t...(2) [In equation (2), t represents the thickness (mm) of the glass used for measuring the external transmittance, A represents the external transmittance (%) at a wavelength of 2500 nm when light is incident on the glass parallel to its thickness direction, and B represents the external transmittance (%) at a wavelength of 2900 nm when light is incident on the glass parallel to its thickness direction. Also, ln is the natural logarithm.]

2. SiO 2 The optical glass according to claim 1, comprising 0.1 to 25% by mass of the following.

3. SiO 2 0.5 to 15% by mass, B 2 O 3 1 to 30% by mass, La 2 O 3 The optical glass according to claim 1, comprising 20 to 60% by mass of the above.

4. Expressed in mass percentage, B 2 O 3 The content of SiO 2 The optical glass according to any one of claims 1 to 3, having a content greater than that of [the specified value].

5. B 2 O 3 and La 2 O 3 TiO 2 Mass ratio of the content [TiO 2 / (B 2 O 3 +La 2 O 3 The optical glass according to any one of claims 1 to 4, wherein the ratio of ) is 0.030 or greater.

6. The Abbe number νd is between 20 and 45. The optical glass according to any one of claims 1 to 5, wherein the refractive index nd is 1.75 to 2.

50.

7. An optical element made of optical glass according to any one of claims 1 to 6.

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