Optical glass and optical element

Abstract

To provide an optical glass and an optical element having a reduced reduction color.SOLUTION: There is provided an optical glass which contains 1 to 45 mass% of B2O3 and 10 to 60 mass% of La2O3, contains at least one oxide selected from the group consisting of TiO2, Nb2O5, WO3 and Bi2O3 and has a value of βOH represented by the following expression (2) of 0.1 to 2.0 mm-1: βOH=-[ln(B / A)] / t...(2).SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to optical glass and optical elements.

Background Art

[0002] In recent years, with the high functionality and miniaturization of devices such as imaging optical systems and projection optical systems, the demand for optical glass with a high refractive index as a material for effective optical elements has been increasing.

[0003] Optical glass with a high refractive index as described in Patent Document 1 usually contains a large amount of high refractive index components such as Ti, Nb, W, and Bi as glass components. These components are easily reduced during the melting process of the glass, and the reduced components absorb light on the short wavelength side of the visible light region, causing the glass to be colored (hereinafter sometimes referred to as "reduction color").

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In view of such a situation, the present invention aims to provide optical glass and optical elements with reduced reduction color.

Means for Solving the Problems

[0006] The gist of the present invention is as follows. 〔1〕B 2 O 3 is contained in an amount of 1 to 45% by mass, and La 2 O 3 is contained in an amount of 10 to 60% by mass, and TiO 2 , Nb 2 O 5 , WO3 and Bi 2 O 3 At least one oxide selected from the group consisting of The value of βOH shown in the following formula (2) is 0.1 to 2.0 mm -1 That is, optical glass. βOH=-[ln(B / A)] / t …(2) (In formula (2), t represents the thickness (mm) of the glass used in measuring the external transmittance, A represents the external transmittance (%) at a wavelength of 2500 nm when light is incident on the glass parallel to the thickness direction, and B represents the external transmittance (%) at a wavelength of 2900 nm when light is incident on the glass parallel to the thickness direction. In addition, ln is the natural logarithm.)

[0007] [2] SiO 2 The optical glass according to [1], comprising 0.1 to 25 mass % of

[0008] [3] SiO 2 0.5 to 15 mass% of B 2 O 3 1 to 30 mass% of La 2 O 3 The optical glass according to [1], comprising 20 to 60 mass % of

[0009] [4] In mass %, B 2 O 3 The content of SiO 2 The content of [1] to [3] is greater than that of The optical glass according to any one of the above.

[0010] [5] B 2 O 3 and La 2 O 3 TiO relative to the total content 2 Mass ratio of the content [TiO 2 / (B 2 O 3 +La 2 O 3 The optical glass according to any one of [1] to [4], wherein the refractive index (R) is 0.030 or more.

[0011] 〔6〕The Abbe number νd is 20 to 45, and the refractive index nd is 1.75 to 2.50, the optical glass according to any one of 〔1〕 to 〔5〕.

[0012] 〔7〕An optical element made of the optical glass according to any one of 〔1〕 to 〔6〕 above.

Advantages of the Invention

[0013] According to the present invention, an optical glass and an optical element with reduced reduction color can be provided.

Embodiments for Carrying Out the Invention

[0014] Hereinafter, one aspect 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 when melted, and the notation of each glass component follows the convention, such as SiO 2 , TiO 2 and so on. The content and total content of the 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, for example, methods such as inductively coupled plasma atomic emission spectrometry (ICP-AES) and inductively coupled plasma mass spectrometry (ICP-MS). 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 properties related to dispersion and is represented by the following formula (1). 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)

[0018] The optical glass according to the embodiment of the present invention B 2 O 3 contains 1 to 45% by mass, and La 2 O 3 contains 10 to 60% by mass, TiO 2 , Nb 2 O 5 , WO 3 and Bi 2 O 3 and contains at least one oxide selected from the group consisting of the value of βOH shown in the following formula (2) is 0.1 to 2.0 mm -1 is. βOH=-[ln(B / A)] / t …(2) 〔In 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, ln is the natural logarithm.〕

[0019] Hereinafter, the optical glass according to this embodiment (hereinafter, may be simply described as "glass") will be described in detail.

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

[0021] B 2 O 3 is a glass network - forming component, which has the function of maintaining low dispersibility and improving the thermal stability of the glass. On the other hand, B 2 O 3 If the content is high, there is a possibility that the volatilization amount of the glass components increases during glass melting. Also, the devitrification resistance tends to decrease. Therefore, the content of B 2 O 3 is preferably within the above range.

[0022] The glass according to this embodiment contains La 2 O 3 in an amount of 10 - 60%. The lower limit of the content of La 2 O 3 is preferably 20%, more preferably 22%, 24%, 27%, and 30% in that order. Also, the upper limit of the content of La 2 O 3 is preferably 57%, more preferably 55% and 53% in that order.

[0023] La 2 O 3 has the function of increasing the refractive index nd. It also has the function of enhancing chemical durability. On the other hand, when the content of La 2 O 3 increases, the specific gravity increases and the thermal stability of the glass decreases. Therefore, it is preferable that the content of La 2 O 3 is within the above range.

[0024] The glass according to this embodiment contains at least one oxide selected from the group consisting of TiO 2 , Nb 2 O 5 , WO 3 and Bi 2 O 3 . TiO 2 , Nb 2 O 5 , WO3 and Bi 2 O 3 All of them are 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 further preferably 0.25 mm -1 , 0.3 mm -1 , 0.35 mm -1 in this order. Also, the upper limit of the value of βOH is preferably 1.8 mm -1 and further 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 incident on 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] βOH represented by the above formula (2) means the absorbance due to the hydroxyl group. Therefore, by evaluating βOH, the content of water (and / or hydroxide ions, hereinafter simply referred to as "water") in the glass can be evaluated. That is, a glass with a high βOH means that the water content in the glass is high.

[0029] By increasing the water content in the glass and increasing the value of βOH, the reduction color can be reduced and the annealing treatment time can be shortened. Also, a defoaming and clarification effect can be obtained. On the other hand, if the value of βOH is too high, the amount of volatiles from the molten glass tends to increase. Therefore, it is preferable to set the value of βOH within the above range.

[0030] The method for increasing the βOH of the glass is not particularly limited, and examples include performing an operation to increase the water content in the molten glass in the melting process. Examples of the operation for increasing the water content in the molten glass include a treatment of adding water vapor to the melting atmosphere and a treatment of bubbling a gas containing water vapor into the melt.

[0031] (Glass components) The glass components other than the above in this embodiment will be described in detail below.

[0032] In the glass according to this embodiment, the content of SiO 2 has a lower limit that is preferably 0.1%, more preferably 0.5%, 1%, 1.5%, 2%, 3% in this order. Also, the content of SiO 2 has an upper limit that is preferably 25%, more preferably 15%, 10%, 8%, 7% in this order.

[0033] SiO 2 is a network-forming component of the glass and has the function of improving the thermal stability, chemical durability, and weather resistance of the glass. On the other hand, if the content of SiO 2 is large, the devitrification resistance of the glass may decrease. Therefore, it is preferable to set the content of SiO 2 within the above range.

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

[0035] P 2 O 5 is a component that reduces the refractive index nd and is also a component that reduces the thermal stability of the glass. Therefore, it is preferable that the content of P 2 O 5 is within the above range.

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

[0037] Al 2 O 3 is a glass component that has the function of improving the chemical durability and weather resistance of the glass and can be considered as a network-forming component. On the other hand, when the content of Al 2 O 3 increases, the devitrification resistance of the glass decreases. Also, problems such as an increase in the glass transition temperature Tg and a decrease in thermal stability are likely to occur. Therefore, it is preferable that the content of Al 2 O 3 is within the above range.

[0038] In the glass according to this embodiment, the lower limit of the total content [SiO 2 and B 2 O 3 [SiO 2 +B 2 O 3 is preferably 2%, more preferably 4%, 6%, 8%, 10% in this order. Also, the total content [SiO2 +B 2 O 3 The upper limit of [] is preferably 35%, more preferably 30%, 26%, 24%, 22% in that order.

[0039] SiO 2 and B 2 O 3 are glass network - forming components and components that improve the thermal stability and devitrification resistance of the glass. Therefore, the total content of SiO 2 and B 2 O 3 [SiO 2 +B 2 O 3 is preferably within the above range.

[0040] Also, in the glass according to this embodiment, in terms of mass%, preferably the content of B 2 O 3 [B 2 O 3 is greater than the content of SiO 2 [SiO 2 ([B 2 O 3 > [SiO 2 ). More preferably, the content of B 2 O 3 is greater than 1.3 times the content of SiO 2 ([B 2 O 3 > [SiO 2 ×1.3). B 2 O 3 By making the content of B 2 greater than the content of SiO

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

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

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

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

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

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

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

[0048] MgO, CaO, and SrO are all glass components that function to improve the thermal stability and devitrification resistance of glass. On the other hand, when the content of these glass components increases, the specific gravity increases, the high dispersibility is impaired, and the thermal stability and devitrification resistance of the glass decrease. Therefore, the content of each of these glass components is preferably within the above range.

[0049] In the glass according to this embodiment, Gd 2 O 3 The upper limit of the content is preferably 35%, more preferably 30%, 25%, 20%, 17%, 12% in that order. Also, Gd 2 O 3 The lower limit of the content is preferably 0%, more preferably 1%, 3%, 4%, 5% in that order.

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

[0051] Gd 2 O 3 and Y 2 O 3 Both contribute to improving the weather resistance of the glass and increasing the refractive index. On the other hand, if the content becomes too high, the thermal stability of the glass decreases, and the glass is likely to devitrify during manufacturing. Therefore, the content of each of these glass components is preferably within the above range.

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

[0053] Yb 2 O 3 is a component that contributes to improving weather resistance and increasing the refractive index. On the other hand, Yb 2 O 3 compared with La 2 O 3 Gd 2 O 3 Y 2 O 3 has a larger molecular weight, so 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, when a lens with a large mass is incorporated into an autofocus imaging lens, the power required for driving the lens during autofocus increases, and the battery consumption becomes severe. Therefore, it is desirable to reduce the content of Yb 2 O 3 to suppress the increase in the specific gravity of the glass.

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

[0055] ZrO 2 is a component that contributes to increasing the refractive index and is a glass component that has the function of improving the thermal stability and devitrification resistance of the glass. On the other hand, when the content of ZrO 2 is too high, the thermal stability tends to decrease. Therefore, the content of ZrO 2 is preferably within the above range.

[0056] In the glass according to this embodiment, the content of TiO 2 is preferably more than 0%, and its lower limit is more preferably 0.1%, further preferably 1%, 3%, 4%, 5% in this order. Also, the upper limit of the content of TiO 2 is preferably 30%, more preferably 25 %, 23%, 21%, 20% in this order.

[0057] TiO 2 is a component that contributes to increasing the refractive index and also functions to improve chemical durability. On the other hand, when the content of TiO 2 is too high, there is a risk of a decrease in devitrification resistance. Therefore, it is preferable that the content of TiO 2 is within the above range.

[0058] In the glass according to this embodiment, the lower limit of the content of Nb 2 O 5 is preferably 0.1%, and more preferably 1%, 3%, 4%, 5% in this order. Also, the upper limit of the content of Nb 2 O 5 is preferably 35%, and more preferably 30%, 25%, 20%, 16%, 15%, 14%, 12% in this order.

[0059] Nb 2 O 5 is a component that contributes to increasing the refractive index and also has the function of improving the thermal stability and chemical durability of the glass. On the other hand, when the content of Nb 2 O 5 is too high, there is a risk of a decrease in the thermal stability of the glass, and there is also a tendency for the coloring of the glass to intensify. Therefore, it is preferable that the content of Nb 2 O 5 is within the above range.

[0060] In the glass according to this embodiment, the lower limit of the total content of Nb 2 O 5 and TiO 2 [Nb 2 O 5 +TiO 2 is preferably 13%, and more preferably 13.5%, 14%, 14.5%, 15% in this order. Also, the upper limit of the total content [Nb 2 O 5 +TiO 2 is preferably 40%, and more preferably 35%, 32%, 31%, 30% in this order.

[0061] Nb 2 O 5 and TiO 2 are components that contribute to increasing the refractive index. On the other hand, when the content of Nb 2 O 5 is too high, the thermal stability and devitrification resistance of the glass decrease. Therefore, the total content of Nb 2 O 5 and TiO 2 is preferably within the above range.

[0062] In the glass according to this embodiment, the upper limit of the content of WO 3 is preferably 25%, more preferably 20%, 15%, 10%, and 5% in this order. The lower limit of the content of WO 3 is preferably 0%.

[0063] WO 3 has the function of lowering the glass transition temperature Tg. On the other hand, when the content of WO 3 becomes too high, the coloring of the glass increases and the specific gravity also increases. Therefore, the content of WO 3 is preferably within the above range.

[0064] In this embodiment, the upper limit of the content of Bi 2 O 3 is preferably 20%, more preferably 15%, 10%, 5%, and 3% in this order. Also, the lower limit of the content of Bi 2 O 3 is preferably 0%.

[0065] Bi 2 O 3 has the function of improving the thermal stability of the glass by containing an appropriate amount. On the other hand, increasing the content of Bi 2 O 3 increases the coloring of the glass and also increases the specific gravity. Therefore, the content of Bi 2 O 3 is preferably within the above range.

[0066] In the glass according to this embodiment, Nb2 O 5 、 TiO 2 、 WO 3 and Bi 2 O 3 The upper limit of the total content [Nb 2 O 5 + TiO 2 + WO 3 + Bi 2 O 3 is preferably 40%, more preferably 37%, 35%, 33%, 32% in that order. Also, the lower limit of the total content [Nb 2 O 5 + TiO 2 + WO 3 + Bi 2 O 3 is preferably 1.0%, more preferably 1.5%, 5%, 10%, 13%, 13.5%, 14%, 14.5%, 15% in that order.

[0067] TiO 2 、 WO 3 and Bi 2 O 3 are components that contribute to increasing the refractive index together with Nb 2 O 5 . Therefore, it is preferable that the total content [Nb 2 O 5 + TiO 2 + WO 3 + Bi 2 O 3 is within the above range.

[0068] In the glass according to this embodiment, the mass ratio of the content of TiO 2 O 3 to the total content of B 2 O 3 and La 2 O 2 / (B 2 O 3 + La 2 O 3)] is preferably small, and the lower limit is preferably 0.030, and further preferably 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, 0.50 in this order. Also, the upper limit of the mass ratio [TiO 2 / (B 2 O 3 +La 2 O 3 )] is preferably 1.5, and further preferably 1.0, 0.8, 0.6 in this order.

[0069] Nb 2 O 5 、TiO 2 、WO 3 およびBi 2 O 3 Among them, the component with the largest refractive index nd increasing effect per unit content in mass% representation is TiO 2 . Also, TiO 2 is easily reduced during the glass melting process. When TiO 2 is reduced, the transmittance in the visible short wavelength region is likely to decrease significantly . On the other hand, in the glass according to this embodiment, B 2 O 3 and La 2 O 3 do not cause such problems due to reduction. Therefore, with respect to the content of TiO 2 that significantly reduces the transmittance in the visible short wavelength region, the total content of B 2 O 3 and La 2 O 3 is large, that is, the mass ratio [TiO 2 / (B 2 O 3 +La 2 O 3 )] is preferably small.

[0070] In the glass according to this embodiment, Nb2 O 5 , TiO 2 , WO 3 and Bi 2 O 3 The mass ratio of the content of TiO 2 to the total content of [TiO 2 / (Nb 2 O 5 +TiO 2 +WO 3 +Bi 2 O 3 )] has a lower limit that is preferably 0.05, and more preferably 0.25, 0.30, 0.40, 0.45 in this order. Also, the upper limit of the mass ratio [TiO 2 / (Nb 2 O 5 +TiO 2 +WO 3 +Bi 2 O 3 )] can be preferably 1.00, and more preferably 0.90, 0.80, 0.75.

[0071] As described above, TiO 2 is easily reduced during the glass melting process. When TiO 2 is reduced, the transmittance in the short wavelength region of the visible light is likely to decrease significantly. In this embodiment, among the components contributing to the increase in refractive index such as Nb 2 O 5 , TiO 2 , WO 3 and Bi 2 O 3 , especially TiO 2 which is likely to cause coloring has a large content, that is, even when the mass ratio [TiO 2 / (Nb 2 O 5 +TiO 2 +WO 3 +Bi 2 O 3 )] is within the above range, the increase in coloring can be suppressed by introducing gas into the atmosphere or bubbling gas into the melt during the melting process.

[0072] In the glass according to this embodiment, Ta 2 O5 The upper limit of the content is preferably 25%, more preferably 20%, 16%, 12%, 8%, and 4% in this order. Also, Ta 2 O 5 The lower limit of the content is preferably 0%.

[0073] Ta 2 O 5 is a component that contributes to increasing the refractive index and also has the function of improving the thermal stability of the glass. On the other hand, when the content of Ta 2 O 5 increases, the thermal stability of the glass decreases, and when melting the glass, the remaining unmelted glass raw materials are likely to occur. Therefore, the content of Ta 2 O 5 is preferably within the above range.

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

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

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

[0077] Li 2 O, Na 2 O and K 2 O all have the function of lowering the liquidus temperature and improving the thermal stability of the glass, but when the content of these increases, the chemical durability and weather resistance decrease. Therefore, Li2 O, Na 2 O and K 2 The content of each of O is preferably within the above range respectively.

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

[0079] Cs 2 CsO has the function of improving the thermal stability of the glass, but when these contents increase, the chemical durability and weather resistance decrease. Therefore, 2 the content of each of CsO is preferably within the above range.

[0080] In the glass according to this embodiment, Li 2 O, Na 2 O, K 2 O and Cs 2 The total content of O [Li 2 O + Na 2 O + K 2 O + Cs 2 O] has an upper limit that is preferably 15%, more preferably 10%, 7%, 5%, 3%, 1% in this order. Also, the lower limit of the total content [Li 2 O + Na 2 O + K 2 O + Cs 2 O] is preferably 0%.

[0081] The lower limit of the total content [Li 2 O + Na 2 O + K 2 O + Cs 2 O] satisfying the above can improve the meltability and thermal stability of the glass and can lower the liquidus temperature. Also, the upper limit of the total content [Li 2 O + Na 2 O + K 2 O + Cs 2 O] satisfying the above can suppress the decrease in devitrification resistance.

[0082] In the glass according to this embodiment, Sc 2 O 3 content is preferably 2% or less. Also, the lower limit of the Sc 2 O 3 content is preferably 0%.

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

[0084] Sc 2 O 3 , HfO 2 has the function of enhancing the high dispersibility of the glass, but is an expensive component. Therefore, the content of each of Sc 2 O 3 , HfO 2 is preferably within the above range.

[0085] In the glass according to this embodiment, the content of Lu 2 O 3 is preferably 2% or less. Also, the lower limit of the Lu 2 O 3 content is preferably 0%.

[0086] Lu 2 O 3 has the function of enhancing the high dispersibility of the glass, but since its molecular weight is large, it is also a glass component that increases the specific gravity of the glass. Therefore, the content of Lu 2 O 3 is preferably within the above range.

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

[0088] GeO 2has the function of enhancing the high dispersibility of glass, but among the commonly used glass components, it is a particularly expensive component. Therefore, from the perspective of reducing the manufacturing cost of glass, the content of GeO 2 is preferably within the above range.

[0089] The glass according to this embodiment mainly consists of the above-mentioned components, that is, B as an essential component 2 O 3 and La 2 O 3 , SiO as an optional component 2 , P 2 O 5 , Al 2 O 3 , ZnO, BaO, MgO, CaO, SrO, Gd 2 O 3 , Y 2 O 3 , Yb 2 O 3 , ZrO 2 , TiO 2 , Nb 2 O 5 , WO 3 , Bi 2 O 3 , Ta 2 O 5 , Li 2 O, Na 2 , K 2 , Cs 2 , Sc 2 O 3 , HfO 2 , Lu 2 O 3 and GeO 2 is preferably composed of, 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 most preferably more than 99.5%.

[0090] In this embodiment, as a more preferred aspect, B 2 O 3 is 1 to 45%, La 2 O 3is 10 to 60%, TiO 2 is more than 0%, ZnO is more than 0%, and Nb 2 O 5 , TiO 2 , WO 3 and Bi 2 O 3 The mass ratio of the content of TiO 2 to the total content of [TiO 2 / (Nb 2 O 5 +TiO 2 +WO 3 +Bi 2 O 3 )] is 0.4 or more, and the value of βOH shown in the following formula (2) is 0.1 to 2.0 mm -1 . Examples thereof include optical glass. βOH = -[ln(B / A)] / t …(2) [In 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, ln is the natural logarithm.]

[0091] In the above more preferred embodiment, the contents of B 2 O 3 , La 2 O 3 , TiO 2 and ZnO, the mass ratio [TiO / (Nb 2 O 2 +TiO 5 +WO 2 +Bi 3 O 2 + 3 )], and the value of βOH The more preferred numerical ranges described above can be applied. Also, for the contents and mass ratios of other glass components, the preferred numerical ranges described above can be appropriately applied.

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

[0093] By setting the Pt content within the above range, the coloring of the glass caused by Pt can be reduced and the transmittance can be improved.

[0094] In the manufacturing process of the glass according to this embodiment, the glass raw material is melted in a non-oxidizing atmosphere. Examples of the non-oxidizing atmosphere include inert gases such as nitrogen, carbon dioxide, argon, and helium, and water vapor. Usually, oxygen in the melting atmosphere reacts with platinum, which is a material such as a melting container (crucible, etc.), to generate platinum dioxide or platinum ions (Pt 4+ ) and coloring occurs when it dissolves in the molten glass. In this embodiment, by reducing the oxygen partial pressure in the melting atmosphere, the oxidation of platinum can be suppressed and the amount of Pt dissolved in the molten glass can be reduced. As a result, the coloring derived from Pt can be reduced.

[0095] <Other component compositions> Pb, As, Cd, Tl, Be, and Se all have toxicity. 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 coloring of the glass and become a source of fluorescence. Therefore, it is preferable that the optical glass of this embodiment does not contain these elements as glass components.

[0098] Sulfate is an optionally addable oxidizing agent that functions as a fining agent. Sulfate is decomposed by heat to produce fining gases SO 2 and O 2 . As the sulfate, although not particularly limited, examples include zinc sulfate, zirconium sulfate, etc.

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

[0100] Sb(Sb 2 O 3 ) is also an optionally addable element that functions as a fining agent. However, Sb(Sb 2 O 3 ) has strong oxidizing properties, and if the addition amount is increased, there is a risk of promoting the oxidation of platinum derived from the platinum crucible. Also, during precision press molding, Sb(Sb 2 O 3 ) contained in the glass oxidizes the molding surface of the press molding die. As a result, during repeated precision press molding, the molding surface deteriorates significantly, and there is a risk that precision press molding cannot be performed. Consequently, the surface quality of the molded optical element deteriorates. Therefore, the glass according to the present embodiment preferably does not contain Sb(Sb 2 O 3 ).

[0101] Note that the glass according to the present embodiment is preferably basically composed of the above glass components, but it is also possible to contain other components within a range that does not prevent the operational effects of the present invention. Also, in the present invention, the inclusion of inevitable impurities is not excluded.

[0102] (Glass properties) <Refractive index nd> In the glass according to this embodiment, the refractive index nd is preferably 1.75 or more, and may further be 1.77 or more, 1.80 or more. Also, the refractive index nd is preferably 2.50 or less, and may further be 2.20 or less, 2.10 or less. The refractive index nd is 2 O 5 , TiO 2 , WO 3 and Bi 2 O 3 The total content of [Nb 2 O 5 +TiO 2 +WO 3 +Bi 2 O 3 can be increased, and can be reduced by increasing the content of SiO 2 .

[0103] <Abbe number νd> In the glass according to this embodiment, the Abbe number νd is 20 or more. 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 content of La 2 O 3 , and can be reduced by increasing the content of B 2 O 3 .

[0104] <Light transmittance of glass> The light transmittance of the optical glass according to this embodiment can be evaluated by the coloring degree 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 becomes 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, still more preferably 450 nm or less, and particularly preferably 440 nm or less. λ70 can be reduced by reducing the platinum Pt content.

[0106] In addition, λ70 of the optical glass according to the present embodiment preferably satisfies the following formula (3). λ70 ≦ a × b + 373 ···(3) In formula (3), a is preferably 200, and more preferably 195, 190, 185, 180, 175 in this order. In addition, b is the mass ratio [TiO 2 O 3 and La 2 O 3 of the content of TiO 2 with respect to the total content of 2 B 2 O 3 and La 2 O 3 )].

[0107] As the mass ratio [TiO 2 / (B 2 O 3 + La 2 O 3 )] increases, the transmittance in the visible short wavelength region decreases, and the coloring degree λ70 increases. In the optical glass according to the present embodiment, the reduced color is reduced, and λ70 can be suppressed 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 by T450. In this embodiment, T450 is the external transmittance at a wavelength of 450 nm when converted to a thickness of 10.0 mm. The "external transmittance" refers to 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 is incident perpendicularly to one of the optically polished planes of a glass sample processed to have mutually parallel and optically polished planes, that is, the transmittance considering the surface reflection on the surface of the glass. The transmittance can be obtained by measuring the transmittance spectrum using a spectrophotometer. Note that the thickness of the glass during 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 by 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 reduction color of the glass.

[0110] <t400> The light transmittance of the optical glass according to this embodiment can also be evaluated by 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 with a spectrophotometer. It may be converted to the transmittance at a thickness of 10.0 mm by a well-known method. The larger the value of T400, the better the transmittance, which means that the coloring of the glass is reduced.

[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 with a spectrophotometer. It may be converted to the transmittance at a thickness of 10.0 mm by a well-known method. The larger the value of τ400, the better the transmittance, which means that the coloring of the glass is reduced.

[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, 6 or less in that order. Also, the specific gravity is preferably 2.5 or more, and more preferably 3 or more, 3.5 or more in that order. If the specific gravity of the glass can be reduced, the weight of the lens can be decreased. As a result, the power consumption of the autofocus drive of the camera lens equipped with the lens can be reduced. On the other hand, if the specific gravity is reduced too much, the thermal stability will decrease.

[0115] <Glass transition temperature Tg> The glass transition temperature Tg of the optical glass according to this embodiment is preferably 800 °C or lower, more preferably 770 °C or lower, and still more preferably 750 °C or lower in this order. Further, the glass transition temperature Tg is preferably 300 °C or higher, more preferably 350 °C or higher, and still more preferably 400 °C or higher in this order. The glass transition temperature Tg can be reduced by increasing the total content of Li 2 O, Na 2 O and K 2 O [Li 2 O + Na 2 O + K 2 O].

[0116] By satisfying the upper limit of the glass transition temperature Tg within the above range, an increase in the molding temperature and annealing temperature of the glass can be suppressed, and thermal damage to the press molding equipment and annealing equipment can be reduced. Further, by satisfying the lower limit of the glass transition temperature Tg within the above range, it becomes easier to maintain good thermal stability of the glass while maintaining a desired Abbe number and refractive index.

[0117] (Quality of optical glass) Generally, the defects of optical glass include bubbles, foreign substances (bumps), and veining. The evaluation of these defects is performed by measuring the amount of defects contained in the glass per unit amount. The ratio of inhibiting light transmittance changes according to the abundance of bubbles and bumps per unit cross-sectional area of the glass.

[0118] However, when the unit for evaluating defects (evaluation unit) is extremely small, if a region where there are no bubbles or bumps is selected, it means that there are no optical defects in that range. However, for optical glass as an industrially produced product generally used, the homogeneity is not in a minute range such as 1 mm × 1 mm, but the homogeneity of glass having a cross-sectional area of about 100 mm × 100 mm or a volume of a certain amount or more is required.

[0119] And not only the evaluation unit but also the production unit of the optical glass should be discussed. Even if the required homogeneity is the same when producing 1 ml of glass and when producing 1000 kg of glass, there is a huge difference in the difficulty of manufacturing. That is, even when melting and vitrifying the same raw materials, the amount of heat required varies according to the amount of glass. For example, even under the conditions of a melting temperature of 1250 °C and a melting time of 2 hours, when producing 1 ml of glass, a melt (molten glass) without bubbles or lumps can be produced, whereas when producing 1000 kg of glass, the raw materials cannot even be melted.

[0120] Not only do the conditions required for vitrification change according to the amount of glass, but the temperature and time required for defoaming (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 constituting the crucible eluted into the molten glass increases.

[0121] That is, when producing optical glass, which is an industrial product, it is necessary to make the glass volume above a certain level. Compared with experiments and small-scale glass production, the melting and clarification conditions and the amount of Pt mixed into the glass from the production equipment (such as crucibles) also change.

[0122] Regarding vein patterns, homogeneity is an even more important characteristic. Originally, the defect of "vein pattern" is a defect discussing 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 is different between the case of producing a 1000 ml glass melt at once and the case of producing 10 ml of glass melt 100 times. Generally, when producing optical glass, it is possible to obtain glass with excellent homogeneity by producing a 1000 ml glass melt at once.

[0123] As described above, optical glass treated as an industrial product is discussed for the case of producing a volume above a certain level, and the difficulty of producing high-quality optical glass within this range and the characteristics and quality of the optical glass according to its manufacturing method are discussed inseparably.

[0124] The technology discussed for glass melting on a very small scale (e.g., small-scale experiments) is not directly applicable to glass melting at the industrial product level. And when the scale of glass production is different, it is not possible to uniformly compare the characteristics and quality of the glass produced by each method.

[0125] In this embodiment, in order to distinguish between the characteristics and quality of glass at the experimental level and those of glass at the industrial level, the concept of glass homogeneity is introduced. The homogeneity of glass can be evaluated by the 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, still more preferably within 0.00010, even more preferably within 0.00007, and even more preferably within 0.00005. The refractive index distribution is measured for a continuous body having a glass volume of 100 ml or more. Also, the glass volume of the sample used for refractive index measurement is 1 ml or more. Note that the volume of the glass can be calculated, for example, by measuring the mass of the glass and using the measurement result and the specific gravity.

[0127] Specifically, prepare 100 ml or more of glass a, and measure the refractive indices at two locations: an arbitrary location A and a location B that is antipodal to A. Also, if there is a site where the refractive index is known, use that site as A and measure the refractive index at site B that is farthest from A. Obtain a total of two or more glass pieces from glass a and perform refractive index measurement. In this embodiment, the evaluation of the refractive index distribution was performed using the refractive index nd, but the evaluation may be performed using the refractive index at other wavelengths as appropriate.

[0128] (Manufacture of optical glass) The glass according to the embodiment of the present invention may be prepared by formulating glass raw materials so as to have the above-mentioned predetermined composition, and then producing the formulated glass raw materials according to a known glass manufacturing method. For example, a plurality of compounds are formulated and thoroughly mixed to obtain a batch raw material, and the batch raw material is put into a platinum crucible and roughly melted (melting step).

[0129] In the melting step of the glass according to the present embodiment, a reducing agent can be added to the glass raw materials. The reducing agent is not particularly limited, and examples thereof include substances showing reducibility such as Al, Si, Ti, W, H 2 , CO, C and the like. More specifically, examples of the substance showing reducibility can include carbon compounds and activated carbon C. By adding a reducing agent to the glass raw materials, oxygen with high reaction activity generated during the vitrification of the glass raw materials reacts with the reducing agent, and the oxidation reaction of platinum derived from the platinum crucible is suppressed. As a result, the Pt content in the glass can be reduced.

[0130] The melting atmosphere in the melting step of the glass according to the present embodiment is preferably a non-oxidizing atmosphere. By performing the melting step in a non-oxidizing atmosphere, the oxygen partial pressure 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, and examples thereof include an inert gas atmosphere such as nitrogen, carbon dioxide, argon, helium, and a steam-added atmosphere. In order to increase the βOH of the finally obtained glass, a steam-added atmosphere is preferable.

[0132] By adding steam to the melting atmosphere, the value of βOH of the finally obtained optical glass can be increased, the dissolution of Pt and the like into the glass can be effectively prevented, and sufficient dissolved gas for improving the defoaming property and clarity can be supplied to the glass.

[0133] The method of adding water vapor to the melting atmosphere is not particularly limited. For example, a connection pipe is inserted into the crucible from an opening provided in the melting apparatus, and water vapor is supplied into the space in the crucible through this pipe as needed.

[0134] In the melting process, for the purpose of stirring the melt, bubbling can also be involved. The bubbling during melting may continue even after melting the formulated materials. By stirring the melt in the melting process, while the oxidation of the glass components progresses, the oxidation of platinum derived from the platinum crucible is suppressed. This is because the glass components tend to be more easily oxidized than platinum. As a result, the reduction reaction of the glass components is suppressed and the reduction color is reduced, and at the same time, the dissolution of platinum into the melt is suppressed and the coloring derived from platinum is also reduced.

[0135] The gas used for bubbling is not necessarily limited, and known gases can be used. For example, inert gases such as nitrogen, carbon dioxide, argon, helium, air, and these gases containing water vapor can be mentioned.

[0136] By using a gas containing water vapor as the gas used for bubbling, the value of βOH of the finally obtained optical glass can be increased, the dissolution of platinum into the glass can be effectively prevented, and a sufficient amount of dissolved gas for improving the defoaming property and clarity can be supplied to the glass.

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

[0138] The melt obtained by rough melting is rapidly cooled and pulverized to produce cullets. Further, the cullets are placed in a platinum crucible, heated, and remelted to form molten glass. After clarification and homogenization, the molten glass is formed and slowly cooled to obtain optical glass. Known methods may be applied for the forming and slow cooling of the molten glass.

[0139] In addition, if a desired glass component can be introduced into the glass so as to have a desired content, the compounds used when preparing the batch raw materials are not particularly limited. Examples of such compounds include oxides, carbonates, nitrates, hydroxides, fluorides, and the like.

[0140] (Manufacture of optical elements, etc.) To manufacture an optical element using the optical glass according to an embodiment of the present invention, a known method may be applied. For example, the above-mentioned molten glass is poured into a mold to be formed into a plate shape, and a glass material made of the optical glass according to the present invention is manufactured. The obtained glass material is appropriately cut, ground, and polished to produce a cut piece having a size and shape suitable for press forming.

[0141] The cut piece is heated and softened, and press formed (hot press) by a known method to produce an optical element blank approximating the shape of the optical element. The optical element blank is annealed, and can be ground and polished by a known method to manufacture an optical element.

[0142] The cut piece may be roughly polished (barrel polishing) to equalize the weight and make it easier to adhere a release agent to the surface, reheated, and the softened glass is press formed into a shape approximating the shape of 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 on a forming die and directly press formed, and finally ground and polished to manufacture the optical element.

[0144] An antireflection film, a total reflection film, etc. may be coated on the optical functional surface of the manufactured optical element according to the purpose of use.

Example

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

[0146] Glass samples having the glass compositions shown in Table 1 were prepared by the following procedure and various evaluations were performed.

[0147] [Manufacture of Optical Glass] (Example 1-A) First, oxides, hydroxides, carbonates, and nitrates corresponding to the constituent components of the glass were prepared as raw materials, and the above raw materials were weighed and formulated so that the glass composition of the obtained optical glass would be each composition shown in Table 1, and the raw materials were sufficiently mixed. The thus-obtained formulated raw materials (batch raw materials) were put into a platinum crucible and heated at 1250°C to 1400°C for 2 hours to be melted into molten glass (melting process), stirred at 1300 to 1400°C for 1 to 2 hours for homogenization, and clarified (homogenization and clarification process). The molten glass was cast into a mold preheated to an appropriate temperature. The cast 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] In the melting process and the homogenization and clarification process, the following operations were performed.

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

[0150] In addition, nitrogen was supplied into the space in the platinum crucible through the above platinum pipe, and steam was bubbled into the melt from a pipe installed at the lower part of the crucible. The flow rates of the supplied nitrogen and steam were set to 30 L / min for nitrogen and 0.1 cc / min for steam.

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

[0152] (Example 1-B) The compounding raw materials corresponding to No. 1 described in Table 1 were put into a platinum crucible together with the additives shown in Table 2, heated and melted under the respective conditions of Conditions 1-1 to 1-9 shown in Table 2 to obtain molten glass (melting process), stirred to achieve homogenization, and clarified (homogenization and clarification process). Otherwise, glass samples were obtained in the same manner as in Example 1-A.

[0153] (Example 1-C) The compounding raw materials corresponding to No. 2 described in Table 1 were put into a platinum crucible together with the additives shown in Table 3, heated and melted under the respective conditions of Conditions 2-1 to 2-4 shown in Table 3 to obtain molten glass (melting process), stirred to achieve homogenization, and clarified (homogenization and clarification process). Otherwise, glass samples were obtained in the same manner as in Example 1-A.

[0154] (Example 1-D) The compounding raw materials corresponding to No. 4 described in Table 1 were put into a platinum crucible together with the additives shown in Table 4, heated and melted under the respective conditions of Conditions 4-1 to 4-5 shown in Table 4 to obtain molten glass (melting process), stirred to achieve homogenization, and clarified (homogenization and clarification process). Otherwise, glass samples were obtained in the same manner as in Example 1-A.

[0155] [Confirmation of Glass Component Composition] For the obtained glass samples, the content of each glass component was measured by inductively coupled plasma atomic emission spectrometry (ICP-AES), and it was confirmed that it was as shown in each composition in Table 1.

[0156] [Measurement of Pt Content in Glass] The content of platinum Pt in the glass was quantified by inductively coupled plasma mass spectrometry (ICP-MS). The quantification results are shown in Tables 1 to 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) contained per unit mass (kg) was calculated. The calculation results are shown in Tables 2 to 4.

[0158] [Measurement of Optical Properties] For the obtained glass samples, βOH, λ70, T400, and T450 were measured. Further, after annealing the obtained glass samples at 710 °C for 72 hours, they were cooled in the furnace at a temperature reduction rate of -30 °C / hour to room temperature to prepare annealed samples, and the refractive indices nd, ng, nF, and nC, Abbe number νd, λ70, and T400 were measured.

[0159] (i) Refractive indices nd, ng, nF, nC, and Abbe number νd For the above annealed samples, the refractive indices nd, ng, nF, and nC were measured by 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 samples were processed into plate-shaped glass samples having a thickness of 1 mm and planes that are parallel to each other and optically polished. Light was incident on the polished surface of this plate-shaped glass sample from a direction perpendicular thereto, and the external transmittance A at a wavelength of 2500 nm and the external transmittance B at a wavelength of 2900 nm were each measured using a spectrophotometer, and βOH was calculated by the following Equation (2). The results are shown in Tables 1 to 4. βOH = -[ln(B / A)] / t ···(2)

[0161] In the above Equation (2), ln is the natural logarithm, and the thickness t corresponds to the distance between the two planes. Further, the external transmittance includes the 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 (transmitted light intensity / incident light intensity) incident on the glass sample.

[0162] (iii) λ70 The glass sample obtained in Example 1-A was processed to have a thickness of 10 mm and flat surfaces that were parallel to each other and optically polished, and the spectral transmittance in the wavelength range from 280 nm to 700 nm was measured. The intensity of the light ray incident perpendicularly to one of the optically polished flat surfaces was defined as intensity A, and the intensity of the light ray exiting 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 becomes 70% was designated as λ70. Note that the spectral transmittance includes the reflection loss of the light ray 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 before annealing treatment (before heat treatment) and after annealing treatment (after heat treatment) was measured in the same manner as above. Tables 2 to 4 show λ70 before annealing treatment (before heat treatment) and after annealing treatment (after heat treatment).

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

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

[0166]

Table 1

[0167]

Table 2

[0168]

Table 3

[0169]

Table 4

[0170] From the results of Table 1, by introducing water vapor into the melting atmosphere or bubbling water vapor into the molten glass to increase the value of βOH, an optical glass with less coloring and a high transmittance at a wavelength of 450 nm was obtained.

[0171] From the results of Tables 2 to 4, it was found that by increasing the value of βOH of the glass, an optical glass with less coloring and a high transmittance in the visible region can be obtained without performing heat treatment in an oxidizing atmosphere for a long time after glass forming.

[0172] (Example 2) A glass block of 15 mm × 175 mm × 1500 mm made of glass having the composition of No. 1 shown in Table 1 and prepared under the condition 1-1 of Table 2 was fabricated, cut into five equal parts, and five glass blocks of 15 mm × 175 mm × 300 mm were obtained. Five refractive index measurement samples 1 to 5 were fabricated using each of the five equally divided glass blocks, and the refractive index nd of each sample was measured. Based on the refractive index nd of sample 1 located at one of the two ends before cutting, the refractive index distributions of samples 2 to 5 were as follows.

[0173] The difference between the refractive index nd of sample 2 collected from the 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 collected from the central part and the refractive index nd of sample 1 was +0.00002. The difference between the refractive index of sample 4 collected from the part adjacent to sample 3 and the refractive index of sample 1 was 0.00000. The difference between the refractive index of sample 5 collected from the end of the opposite pole of sample 1 among the two ends before cutting and the refractive index of sample 1 was -0.00003. As described above, the refractive index distributions at five locations were 0.00005.

[0174] For the glass having the composition of No. 1 shown in Table 1 and prepared under the conditions of Conditions 1-2 to 1-9 in Table 2, the refractive index distribution was measured in the same manner, and the refractive index distributions at five locations were within 0.00005.

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

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

[0177] In addition, since the glass has a low specific gravity, each lens has a smaller weight than lenses having the same optical characteristics and size, and is particularly suitable for autofocus type imaging devices for reasons such as energy saving. Similarly, prisms were prepared using the various optical glasses prepared in Examples 1-A to 1-D.

[0178] The embodiments disclosed this time should be considered illustrative in all respects and not restrictive. The scope of the present invention is shown not by the above description but by the claims, and it is intended that all modifications within the meaning and scope equivalent to the claims be included.

[0179] For example, by performing the composition adjustment described in the specification on the glass composition exemplified above, an optical glass according to one aspect of the present invention can be produced. Moreover, it is of course possible to arbitrarily combine two or more of the matters exemplified or described as preferred ranges in the specification.

Claims

1. B 2 O 3 3 to 45 mass% of La 2 O 3 Contains 20 to 60 mass% TiO 2 , Nb 2 O 5 , W.O. 3 and Bi 2 O 3 At least one oxide selected from the group consisting of TiO 2 The content is 4% by mass or more, P 2 O 5 The content is 2% by mass or less, The value of βOH shown in the following formula (2) is 0.1 to 2.0 mm -1 That is, optical glass. βOH=-[ln(B / A)] / t...(2) (In formula (2), t represents the thickness (mm) of the glass used in measuring the external transmittance, A represents the external transmittance (%) at a wavelength of 2500 nm when light is incident on the glass parallel to the thickness direction, and B represents the external transmittance (%) at a wavelength of 2900 nm when light is incident on the glass parallel to the thickness direction. In addition, ln is the natural logarithm.)

2. B 2 O 3 3 to 45 mass% of La 2 O 3 Contains 20 to 60 mass% TiO 2 , Nb 2 O 5 , W.O. 3 and Bi 2 O 3 At least one oxide selected from the group consisting of TiO 2 and Nb 2 O 5 The total content is 11.3 mass% or more, P 2 O 5 The content is 2% by mass or less, The value of βOH shown in the following formula (2) is 0.1 to 2.0 mm -1 That is, optical glass. βOH=-[ln(B / A)] / t...(2) (In formula (2), t represents the thickness (mm) of the glass used in measuring the external transmittance, A represents the external transmittance (%) at a wavelength of 2500 nm when light is incident on the glass parallel to the thickness direction, and B represents the external transmittance (%) at a wavelength of 2900 nm when light is incident on the glass parallel to the thickness direction. In addition, ln is the natural logarithm.)

3. B 2 O 3 3 to 45 mass% of La 2 O 3 Contains 20 to 60 mass% TiO 2 , Nb 2 O 5 , W.O. 3 and Bi 2 O 3 At least one oxide selected from the group consisting of Nb 2 O 5 , TiO 2 , W.O. 3 and Bi 2 O 3 TiO relative to the total content 2 The mass ratio of the content [TiO 2 / (Nb 2 O 5 + TiO 2 +W.O. 3 +Bi 2 O 3 ) is 0.45 or more, P 2 O 5 The content is 2% by mass or less, The value of βOH shown in the following formula (2) is 0.1 to 2.0 mm -1 That is, optical glass. βOH=-[ln(B / A)] / t...(2) (In formula (2), t represents the thickness (mm) of the glass used in measuring the external transmittance, A represents the external transmittance (%) at a wavelength of 2500 nm when light is incident on the glass parallel to the thickness direction, and B represents the external transmittance (%) at a wavelength of 2900 nm when light is incident on the glass parallel to the thickness direction. In addition, ln is the natural logarithm.)

4. SiO 2 The optical glass according to any one of claims 1 to 3, comprising 0.1 to 25 mass % of

5. SiO 2 0.5 to 15 mass% of B 2 O 3 3 to 30 mass% of La 2 O 3 The optical glass according to any one of claims 1 to 3, comprising 20 to 60 mass % of

6. In mass %, B 2 O 3 The content of SiO 2 The optical glass according to any one of claims 1 to 5, wherein the content of

7. B 2 O 3 and La 2 O 3 TiO relative to the total content 2 The mass ratio of the content [TiO 2 / (B 2 O 3 +La 2 O 3 7. The optical glass according to claim 1, wherein the refractive index is 0.090 or greater.

8. The Abbe number νd is 20 to 37.37; 8. The optical glass according to claim 1, having a refractive index nd of 1.90043 to 2.

50.

9. Nb 2 O 5 and TiO 2 The optical glass according to any one of claims 1 to 8, wherein the total content of is 13 mass % or more.

10. Nb 2 O 5 and TiO 2 The optical glass according to any one of claims 1 to 9, wherein the total content of is 40 mass % or less.

11. Nb 2 O 5 , TiO 2 , W.O. 3 and Bi 2 O 3 The optical glass according to any one of claims 1 to 10, wherein the total content of is 40 mass % or less.

12. Nb 2 O 5 , TiO 2 , W.O. 3 and Bi 2 O 3 The optical glass according to any one of claims 1 to 11, wherein the total content of is 1.0 mass % or more.

13. B 2 O 3 , La 2 O 3 , SiO 2 , P 2 O 5 , Al 2 O 3 , ZnO, BaO, MgO, CaO, SrO, Gd 2 O 3 , Y 2 O 3 , Yb 2 O 3 , ZrO 2 , TiO 2 , Nb 2 O 5 , W.O. 3 , Bi 2 O 3 , Ta 2 O 5 , Li 2 O, Na 2 O.K. 2 O, Cs 2 O, Sc 2 O 3 , HfO 2 , Lu 2 O 3 and GeO 2 The optical glass according to any one of claims 1 to 12, wherein the total content of is more than 95 mass %.

14. 14. The optical glass according to claim 1, wherein the platinum (Pt) content is less than 10 ppm by mass.

15. 15. The optical glass according to claim 1, which has a volume of 100 ml or more and a refractive index distribution of 0.00050 or less.

16. An optical element comprising the optical glass according to any one of claims 1 to 15.

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