CN113135653B

CN113135653B - Optical glass and optical element

Info

Publication number: CN113135653B
Application number: CN202011144491.9A
Authority: CN
Inventors: 三上修平
Original assignee: Hoya Corp
Current assignee: Hoya Corp
Priority date: 2017-07-20
Filing date: 2018-07-04
Publication date: 2022-11-01
Anticipated expiration: 2038-07-04
Also published as: JP7228023B2; CN113135653A; JP2019123667A; JP2022027829A; WO2019017205A1; JP2024051037A; JP7445037B2; JP6989559B2; JP2023053164A

Abstract

The invention provides an optical glass and an optical element. The optical glass of the present invention contains 3 to 45 mass% of B₂O₃20 to 60 mass% of La₂O₃Comprising a compound selected from TiO₂、Nb₂O₅、WO₃And Bi₂O₃At least 1 oxide of (1), the value of beta OH represented by the following formula (2) being 0.1 to 2.0mm^‑1。βOH＝‑[ln(B/A)]/t···(2)。

Description

Optical glass and optical element

The application is a divisional application of an invention patent application with the application number of 201880002819.8, the application date of the original application is 7, month and 4 days in 2018, and the invention name is 'optical glass and optical element'.

Technical Field

The present invention relates to an optical glass and an optical element.

Background

In recent years, with the increase in performance and the reduction in size of apparatuses such as an imaging optical system and a projection optical system, there has been an increasing demand for optical glass having a high refractive index as an effective optical element material.

The high-refractive-index optical glass described in patent document 1 generally contains a large amount of high-refractive-index components such as Ti, nb, W, bi, and the like as glass components. These components are easily reduced during the melting of the glass, and the reduced components absorb light on the short wavelength side of the visible light range, thereby causing coloring (hereinafter, sometimes referred to as "reduced color") of the glass.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open No. 2007-112697.

Disclosure of Invention

Problems to be solved by the invention

The present invention has been made in view of such circumstances, and an object thereof is to provide an optical glass and an optical element in which a reduction color is reduced.

Means for solving the problems

The gist of the present invention is as follows.

[1]An optical glass comprising 1 to 45 mass% of B₂O₃10 to 60 mass% of La₂O₃，

Comprising a compound selected from TiO₂、Nb₂O₅、WO₃And Bi₂O₃At least 1 oxide of (a) or (b),

the value of beta OH represented by the following formula (2) is 0.1 to 2.0mm^-1。

βOH＝-[ln(B/A)]/t…(2)

In the 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 2500nm when the glass is incident in parallel with the thickness direction thereof, and B represents the external transmittance (%) at a wavelength of 2900nm when the glass is incident in parallel with the thickness direction thereof. In addition, ln is a natural logarithm. ]

[2]According to [1]The optical glass contains 0.1 to 25 mass% of SiO₂。

[3]According to [1]The optical glass contains 0.5 to 15 mass% of SiO₂1 to 30 mass% of B₂O₃20 to 60 mass% of La₂O₃。

[4]According to [1]～[3]The optical glass according to any one of the above items, wherein B is represented by mass%₂O₃In an amount greater than SiO₂The content of (a).

[5]According to [1]～[4]The optical glass according to any of the above, wherein TiO₂Content of (A) and (B)₂O₃And La₂O₃In total content of [ TiO ]₂/(B₂O₃+La₂O₃)]Is 0.030 or more.

[6] The optical glass according to any one of [1] to [5], wherein the Abbe's number vd is from 20 to 45 and the refractive index nd is from 1.75 to 2.50.

[7] An optical element comprising the optical glass according to any one of the above [1] to [6 ].

Effects of the invention

According to the present invention, optical glass and an optical element in which a reduction color is reduced can be provided.

Detailed Description

One embodiment of the present invention will be described below. In the present invention and the present specification, the glass composition is expressed on an oxide basis unless otherwise specified. The "oxide-based glass composition" herein refers to a glass composition obtained by converting all glass raw materials decomposed during melting into substances present in the glass in the form of oxides, and the symbols of the respective glass components are conventionally described as SiO₂、TiO₂And the like. Unless otherwise specified, the content and total content of the glass components are based on mass, "%" means "% by mass" and "ppm" means "ppm by mass".

The content of the glass component can be quantified by a known method such as inductively coupled plasma emission spectroscopy (ICP-AES), inductively coupled plasma mass spectrometry (ICP-MS), or the like. In addition, in the present specification and the present invention, a content of 0% of a constituent means that the constituent is substantially not contained, and the constituent is allowed to be contained at an inevitable impurity level.

In the present specification, unless otherwise specified, the refractive index is a refractive index nd at d-line (wavelength 587.56 nm) of helium.

The abbe number ν d is used as a value representing a property related to chromatic dispersion, and is represented by the following formula (1). Here, nF is the refractive index at the F line (wavelength 486.13) of blue hydrogen, and nC is the refractive index at the C line (wavelength 656.27 nm) of red hydrogen.

νd＝(nd-1)/(nF-nC)…(1)

In the optical glass of the embodiment of the present invention,

containing 1 to 45 mass% of B₂O₃10 to 60 mass% of La₂O₃，

βOH＝-[ln(B/A)]/t…(2)

Hereinafter, the optical glass (hereinafter, may be abbreviated as "glass") of the present embodiment will be described in detail.

The glass of the present embodiment contains 1 to 45% of B₂O₃。B₂O₃The lower limit of the content of (b) is preferably 2%, and more preferably 3%, 4%, and 6% in this order. In addition, B₂O₃The upper limit of the content of (b) is preferably 30%, and more preferably 25%, 20%, and 15% in this order.

B₂O₃Is a network-forming component of glass, and has the effects of maintaining low dispersion and improving the thermal stability of glass. On the other hand, when B₂O₃When the content (b) is large, the amount of volatilization of glass components during glass melting may increase. In addition, the devitrification resistance tends to be lowered. Thus, B₂O₃The content of (b) is preferably in the above range.

The glass of the present embodiment contains 10 to 60% of La₂O₃。La₂O₃The lower limit of the content of (b) is preferably 20%, and more preferably 22%, 24%, 27%, and 30% in this order. Further, la₂O₃The upper limit of the content of (b) is preferably 57%, and more preferably 55% and 53% in this order.

La₂O₃Has the function of improving the refractive index nd. In addition, it has an effect of improving chemical durability. On the other hand, when La₂O₃When the content of (A) is increased, the specific gravity increases, and further, the glass hasThe thermal stability is reduced. Thus, la₂O₃The content of (b) is preferably in the above range.

The glass of the present embodiment comprises a material selected from the group consisting of TiO₂、Nb₂O₅、WO₃And Bi₂O₃At least 1 oxide of (a). TiO 2₂、Nb₂O₅、WO₃And Bi₂O₃All components contribute to increasing the refractive index, and by including these components, an optical glass having a high refractive index can be obtained.

In the glass of the present embodiment, the value of β OH represented by the following formula (2) is 0.1 to 2.0mm^-1. The lower limit of the value of. Beta.OH is preferably 0.2mm^-1And still more preferably 0.25mm in this order^-1、0.3mm^-1、0.35mm^-1. Further, the upper limit of the value of β OH is preferably 1.8mm^-1And still more preferably 1.6mm in this order^-1、1.5mm^-1、1.4mm^-1、1.2mm^-1。

βOH＝-[ln(B/A)]/t…(2)

In the 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 2500nm when the glass is incident in parallel with the thickness direction thereof, and B represents the external transmittance (%) at a wavelength of 2900nm when the glass is incident in parallel with the thickness direction thereof. In the formula (2), ln is a natural logarithm. Beta OH in mm^-1。

The "external transmittance" is a ratio (Iout/Iin) of an intensity Iout of transmitted light transmitted through the glass to an intensity Iin of incident light entering the glass, that is, a transmittance taking into consideration surface reflection of the glass surface, and can be obtained by measuring a transmission spectrum using a spectrophotometer.

The β OH represented by the above formula (2) means the absorbance by a hydroxyl group. Therefore, by evaluating β OH, 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 β OH means that the water content in the glass is high.

By increasing the content of water in the glass and increasing the value of beta OH, the reduction color can be reduced and the annealing treatment time can be shortened. In addition, defoaming and clarifying effects can be obtained. On the other hand, when the value of β OH is too high, the amount of volatile matter from the molten glass tends to increase. Therefore, the value of β OH is preferably in the above range.

The method for increasing the β OH of the glass is not particularly limited, and examples thereof include: in the melting step, an operation of increasing the amount of water in the molten glass is performed. Examples of the operation of increasing the amount of water in the molten glass include: a treatment of adding water vapor in a molten atmosphere, a treatment of bubbling a gas containing water vapor in the melt, and the like.

(glass component)

The glass components other than the above in the present embodiment will be described in detail below.

In the glass of the present embodiment, siO₂The lower limit of the content of (b) is preferably 0.1%, and more preferably 0.5%, 1%, 1.5%, 2%, and 3% in this order. Furthermore, siO₂The upper limit of the content of (b) is preferably 25%, and more preferably 15%, 10%, 8%, and 7% in this order.

SiO₂Is a network forming component of glass, and has the function of improving the thermal stability, chemical durability and weather resistance of the glass. On the other hand, when SiO₂When the content of (2) is large, the devitrification resistance of the glass may be lowered. Thus, siO₂The content of (b) is preferably in the above range.

In the glass of the present embodiment, P₂O₅The content of (b) 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 this order. P₂O₅The content of (b) may be 0%.

P₂O₅Is a component that lowers the refractive index nd and also lowers the thermal stability of the glass. Thus, P₂O₅The content of (b) is preferably in the above range.

In the glass of the present embodiment, al₂O₃The content of (A) is preferably 5% or less, and more preferably 4% or less in this orderLower, less than 3%, less than 2%, less than 1%. Al (Al)₂O₃The content of (b) may be 0%.

Al₂O₃The glass component is a glass component having an effect 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 Al is₂O₃When the content (c) is large, the devitrification resistance of the glass is lowered. In addition, problems such as an increase in glass transition temperature Tg and a decrease in thermal stability tend to occur. Thus, al₂O₃The content of (b) is preferably in the above range.

In the glass of the present embodiment, siO₂And B₂O₃Total content of [ SiO ]₂+B₂O₃]The lower limit of (b) is preferably 2%, and more preferably 4%, 6%, 8%, and 10% in this order. Further, the total content [ SiO ]₂+B₂O₃]The upper limit of (b) is preferably 35%, and more preferably 30%, 26%, 24%, and 22% in this order.

SiO₂And B₂O₃Is a network-forming component of glass, and is a component for improving the thermal stability and devitrification resistance of glass. Thus, siO₂And B₂O₃Total content of [ SiO ]₂+B₂O₃]The above range is preferred.

In the glass of the present embodiment, B is preferably represented by mass%₂O₃Content of [ B ]₂O₃]Greater than SiO₂Content of [ SiO ]₂]([B₂O₃]>[SiO₂]). More preferably B₂O₃In an amount greater than SiO₂1.3 times of ([ B ])₂O₃]>[SiO₂]×1.3)。

By making B₂O₃In an amount greater than SiO₂Thereby enabling an increase in Abbe number.

In the glass of the present embodiment, the upper limit of the content of ZnO is preferably 30%, and more preferably 25%, 20%, 15%, 10%, 7%, and 5% in this order. The content of ZnO is preferably more than 0%, and the lower limit thereof is more preferably 0.1%, and still more preferably 0.3%, 0.5%, and 1% in this order.

ZnO is a glass component having an effect of improving the thermal stability of glass and improving the meltability and chemical durability of glass. On the other hand, when the content of ZnO is too large, the specific gravity increases. Therefore, the content of ZnO is preferably in the above range.

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

BaO is a glass component effective for maintaining a high refractive index, and also has an effect of improving thermal stability and resistance to devitrification of the glass. On the other hand, when the content is increased, the specific gravity increases and the devitrification resistance decreases. Therefore, the content of BaO is preferably in the above range.

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

In the glass of the present embodiment, the upper limit of the content of CaO is preferably 10%, and more preferably 8%, 6%, 4%, and 2% in this order. The lower limit of the CaO content is preferably 0%.

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

MgO, caO and SrO are glass components having an effect of improving the thermal stability and devitrification resistance of the glass. On the other hand, when the content of these glass components becomes large, the specific gravity increases, the high dispersion property is impaired, and further, the thermal stability and devitrification resistance of the glass are lowered. Therefore, the respective contents of these glass components are preferably within the above ranges.

In the glass of the present embodiment, gd₂O₃The upper limit of the content of (b) is preferably 35%, and more preferably 30%, 25%, 20%, 17%, and 12% in this order. In addition, gd₂O₃The lower limit of the content of (B) is preferably 0%, and further in orderPreferably 1%, 3%, 4%, 5%.

In the glass of the present embodiment, Y₂O₃The upper limit of the content of (b) is preferably 25%, and more preferably 20%, 15%, 10%, 7%, and 5% in this order. Furthermore, Y₂O₃The lower limit of the content of (b) is preferably 0%, and more preferably 1%, 2%, and 3% in this order.

Gd₂O₃And Y₂O₃All contribute to improvement in weather resistance and increase in refractive index. On the other hand, when the content becomes too large, the thermal stability of the glass is lowered, and the glass becomes susceptible to devitrification in production. Therefore, the respective contents of these glass components are preferably within the above ranges.

In the glass of the present embodiment, Y₂O₃The upper limit of the content of (b) is preferably 5%, and more preferably 4%, 3%, 2%, and 1% in this order. In addition, yb₂O₃The lower limit of the content of (b) is preferably 0%.

Yb₂O₃The component contributes to improvement of weather resistance and increase of refractive index. On the other hand, yb₂O₃And La₂O₃、Gd₂O₃、Y₂O₃This is because the specific gravity of the glass is increased because of its large molecular weight. When the specific gravity of the glass increases, the mass of the optical element increases. For example, when a lens having a large mass is incorporated in a camera lens of an auto focus type, power required for driving the lens at the time of auto focus increases, and the consumption of a battery becomes severe. Therefore, it is desired to reduce Yb₂O₃The content (c) of (a) inhibits an increase in the specific gravity of the glass.

In the glass of the present embodiment, zrO₂The upper limit of the content of (b) is preferably 18%, and more preferably 15%, 12%, 10%, 8%, and 7% in this order. Further, zrO₂The lower limit of the content of (b) is preferably 0%, and more preferably 1%, 2%, and 3% in this order.

ZrO₂The glass component is a component contributing to increase in refractive index and has an effect of improving thermal stability and resistance to devitrification of the glass. On the other hand, when ZrO₂When the content of (b) is too large, thermal stability tends to be lowered. Thus, zrO₂The content of (b) is preferably in the above range.

In the glass of the present embodiment, tiO₂The content of (b) is preferably more than 0%, and the lower limit thereof is more preferably 0.1%, and still more preferably 1%, 3%, 4%, and 5% in this order. Furthermore, tiO₂The upper limit of the content of (b) is preferably 30%, and more preferably 25%, 23%, 21%, and 20% in this order.

TiO₂The component contributes to an increase in refractive index, and also plays a role in improving chemical durability. On the other hand, when TiO₂When the content of (b) is too large, the devitrification resistance of the glass may be lowered. Thus, tiO₂The content of (b) is preferably in the above range.

In the glass of the present embodiment, nb₂O₅The lower limit of the content of (b) is preferably 0.1%, and more preferably 1%, 3%, 4%, and 5% in this order. Further, nb₂O₅The upper limit of the content of (b) is preferably 35%, and more preferably 30%, 25%, 20%, 16%, 15%, 14%, 12% in this order.

Nb₂O₅The glass composition has a component contributing to increase in refractive index, and also has an effect of improving thermal stability and chemical durability of the glass. On the other hand, when Nb₂O₅When the content of (b) is too large, the thermal stability of the glass may be lowered, and further, the coloring of the glass tends to be enhanced. Thus, nb₂O₅The content of (b) is preferably in the above range.

In the glass of the present embodiment, nb₂O₅And TiO₂Total content of [ Nb ]₂O₅+TiO₂]The lower limit of (b) is preferably 13%, and more preferably 13.5%, 14%, 14.5%, 15% in this order. Further, the total content [ Nb ]₂O₅+TiO₂]The upper limit of (b) is preferably 40%, and more preferably 35%, 32%, 31%, and 30% in this order.

Nb₂O₅And TiO₂The component contributes to increase in refractive index. On the other hand, when Nb₂O₅In an amount ofIn many cases, the thermal stability and devitrification resistance of the glass are lowered. Thus, nb₂O₅And TiO 2₂The total content of (b) is preferably in the above range.

In the glass of the present embodiment, WO₃The upper limit of the content of (b) is preferably 25%, and more preferably 20%, 15%, 10%, and 5% in this order. WO₃The lower limit of the content of (b) is preferably 0%.

WO₃Has the effect of lowering the glass transition temperature Tg. On the other hand, when WO₃When the content of (b) is too large, the coloring of the glass increases and the specific gravity increases. Thus, WO₃The content of (b) is preferably in the above range.

In this embodiment, bi₂O₃The upper limit of the content of (b) is preferably 20%, and more preferably 15%, 10%, 5%, and 3% in this order. In addition, bi₂O₃The lower limit of the content of (b) is preferably 0%.

Bi₂O₃Has the function of improving the thermal stability of the glass by proper content. On the other hand, when Bi is increased₂O₃When the amount of (b) is (c), the coloring of the glass increases and the specific gravity increases. Thus, bi₂O₃The content of (b) is preferably in the above range.

In the glass of the present embodiment, nb₂O₅、TiO₂、WO₃And Bi₂O₃Total content of [ Nb ]₂O₅+TiO₂+WO₃+Bi₂O₃]The upper limit of (b) is preferably 40%, and more preferably 37%, 35%, 33%, and 32% in this order. Further, the total content [ Nb ]₂O₅+TiO₂+WO₃+Bi₂O₃]The lower limit of (b) is preferably 1.0%, and more preferably 1.5%, 5%, 10%, 13%, 13.5%, 14%, 14.5%, 15% in this order.

TiO₂、WO₃And Bi₂O₃And Nb₂O₅Also, the component contributes to increasing the refractive index. Therefore, the total content [ Nb ]₂O₅+TiO₂+WO₃+Bi₂O₃]Preferably the above rangeAnd (5) enclosing.

Among the glasses of the present embodiment, tiO is preferable₂Content of (A) and (B)₂O₃And La₂O₃In total content of [ TiO ]₂/(B₂O₃+La₂O₃)]The lower limit is preferably 0.030, and more 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. Further, mass ratio [ TiO ]₂/(B₂O₃+La₂O₃)]The upper limit of (d) is preferably 1.5, and more preferably 1.0, 0.8, and 0.6 in this order.

At Nb₂O₅、TiO₂、WO₃And Bi₂O₃Wherein the component having the largest increasing effect of the refractive index nd per unit content expressed by mass% is TiO₂. Furthermore, tiO₂Can be easily reduced during the melting process when TiO is used₂When reduced, the transmittance in the visible short-wavelength region tends to decrease significantly. On the other hand, in the glass of the present embodiment, B is a main component₂O₃And La₂O₃Such a problem due to reduction does not occur. Therefore, tiO in which the transmittance in the visible short wavelength region is greatly reduced is preferable₂B in an amount not causing such a problem₂O₃And La₂O₃Is large in total content, i.e., mass ratio [ TiO ]₂/(B₂O₃+La₂O₃)]Is small.

In the glass of the present embodiment, tiO₂Content of (2) and Nb₂O₅、TiO₂、WO₃And Bi₂O₃Mass ratio of the total content of [ TiO ]₂/(Nb₂O₅+TiO₂+WO₃+Bi₂O₃)]The lower limit of (b) is preferably 0.05, and more preferably 0.25, 0.30, 0.40, and 0.45 in this order. In addition, mass ratio [ TiO ]₂/(Nb₂O₅+TiO₂+WO₃+Bi₂O₃)]Preferably has an upper limit of1.00, and further 0.90, 0.80, and 0.75 can be set.

As mentioned above, tiO₂Is easily reduced in the melting process when TiO is used₂When reduced, the transmittance in the visible short-wavelength region tends to decrease significantly. In the present embodiment, even in Nb₂O₅、TiO₂、WO₃And Bi₂O₃TiO which is particularly likely to cause coloring among components contributing to increase in refractive index₂Is large, i.e. mass ratio [ TiO ]₂/(Nb₂O₅+TiO₂+WO₃+Bi₂O₃)]In the case where the amount is within the above range, the increase in coloration can be suppressed by introducing a gas into the atmosphere in the melting step and bubbling the gas into the melt.

In the glass of the present embodiment, ta₂O₅The upper limit of the content of (b) is preferably 25%, and more preferably 20%, 16%, 12%, 8%, 4% in this order. Further, ta₂O₅The lower limit of the content of (b) is preferably 0%.

Ta₂O₅The glass composition also has an effect of improving the thermal stability of the glass, which contributes to an increase in refractive index. On the other hand, when Ta₂O₅When the content (b) is increased, the thermal stability of the glass is lowered, and the glass raw material is likely to be melted and left when the glass is melted. Thus, ta₂O₅The content of (b) is preferably in the above range.

In the glass of the present embodiment, li₂The upper limit of the content of O is preferably 10%, and more preferably 7%, 5%, 4%, 3%, 2%, 1% in this order. Li₂The lower limit of the content of O is preferably 0%.

In the glass of the present embodiment, na₂The upper limit of the content of O is preferably 10%, and more preferably 7%, 5%, 4%, 2%, and 1% in this order. Na (Na)₂The lower limit of the content of O is preferably 0%.

In the glass of the present embodiment, K₂The upper limit of the content of O is preferably 10%, and more preferably 7%, 5%, 4%, 2%, and 1% in this order. K₂Lower content of OThe limit is preferably 0%.

Li₂O、Na₂O and K₂All of O has the effect of lowering the liquidus temperature and improving the thermal stability of the glass, but when the content of these elements is increased, the chemical durability and weather resistance are reduced. Thus, li₂O、Na₂O and K₂The respective contents of O are preferably within the above ranges.

In the glass of the present embodiment, cs₂The upper limit of the content of O is preferably 5%, and more preferably 4%, 3%, 2%, and 1% in this order. Cs₂The lower limit of the content of O is preferably 0%.

Cs₂O has an effect of improving the thermal stability of the glass, but when the content of these is increased, the chemical durability and weather resistance are reduced. Thus, cs₂The respective contents of O are preferably in the above ranges.

In the glass of the present embodiment, li₂O、Na₂O、K₂O and Cs₂Total content of O [ Li₂O+Na₂O+K₂O+Cs₂O]The upper limit of (b) is preferably 15%, and more preferably 10%, 7%, 5%, 3%, 1% in this order. Further, total content [ Li ]₂O+Na₂O+K₂O+Cs₂O]The lower limit of (B) is preferably 0%.

By total content [ Li₂O+Na₂O+K₂O+Cs₂O]The lower limit of (b) satisfies the above, and the meltability and thermal stability of the glass can be improved, and the liquidus temperature can be lowered. Further, by the total content [ Li₂O+Na₂O+K₂O+Cs₂O]The upper limit of (b) satisfies the above, and thus a decrease in resistance to devitrification can be suppressed.

In the glass of the present embodiment, sc₂O₃The content of (b) is preferably 2% or less. Further, sc₂O₃The lower limit of the content of (b) is preferably 0%.

In the glass of the present embodiment, hfO₂The upper limit of the content of (b) is preferably 2% or less, and more preferably 1%, 0.5%, and 0.1% in this order. Further, hfO₂The lower limit of the content of (b) is preferably 0%.

Sc₂O₃、HfO₂Has an effect of improving the high dispersion of glass, but is an expensive component. Thus, sc₂O₃、HfO₂The respective contents of (a) are preferably within the above ranges.

In the glass of the present embodiment, lu₂O₃The content of (b) is preferably 2% or less. Furthermore, lu₂O₃The lower limit of the content of (b) is preferably 0%.

Lu₂O₃The glass composition has an effect of improving the high dispersion property of glass, but is a glass component that increases the specific gravity of glass due to its large molecular weight. Thus, lu₂O₃The content of (b) is preferably in the above range.

In the glass of the present embodiment, geO₂The content of (b) is preferably 2% or less. Furthermore, geO₂The lower limit of the content of (b) is preferably 0%.

GeO₂The glass composition has an effect of improving the high dispersion property of the glass, but is particularly expensive among glass compositions generally used. Therefore, geO is a useful material for reducing the production cost of glass₂The content of (b) is preferably in the above range.

The glass of the present embodiment preferably consists essentially of the above-described components, i.e., B as an essential component₂O₃And La₂O₃SiO as an optional component₂、P₂O₅、Al₂O₃、ZnO、BaO、MgO、CaO、SrO、Gd₂O₃、Y₂O₃、Yb₂O₃、ZrO₂、TiO₂、Nb₂O₅、WO₃、Bi₂O₃、Ta₂O₅、Li₂O、Na₂O、K₂O、Cs₂O、Sc₂O₃、HfO₂、Lu₂O₃And GeO₂In the above-described configuration, the total content of the glass components is preferably greater than 95%, more preferably greater than 98%, still more preferably greater than 99%, and still more preferably greater than 99.5%.

In the present embodiment, as more preferable embodiments, there are mentioned:

containing 1 to 45% of B₂O₃10 to 60 percent of La₂O₃More than 0% of TiO₂And more than 0% of ZnO, wherein the ZnO is a zinc oxide,

TiO₂content of (2) and Nb₂O₅、TiO₂、WO₃And Bi₂O₃Mass ratio of the total content of [ TiO ]₂/(Nb₂O₅+TiO₂+WO₃+Bi₂O₃)]The content of the organic acid is more than 0.4,

the value of beta OH represented by the following formula (2) is 0.1 to 2.0mm^-1The optical glass of (1).

βOH＝-[ln(B/A)]/t…(2)

In the formula (2), t represents the thickness (mm) of the glass for measuring the external transmittance, a represents the external transmittance (%) at a wavelength of 2500nm when the glass is incident in parallel with the thickness direction thereof, and B represents the external transmittance (%) at a wavelength of 2900nm when the glass is incident in parallel with the thickness direction thereof. In addition, ln is a natural logarithm. ]

In the above-mentioned more preferable embodiment, B₂O₃、La₂O₃、TiO₂And content and mass ratio of ZnO [ TiO ]₂/(Nb₂O₅+TiO₂+WO₃+Bi₂O₃)]And β OH, the more preferred numerical ranges described above can be applied. The above-described preferable numerical range can be appropriately applied to the content and the mass ratio of other glass components.

In the glass of the present embodiment, the content of platinum Pt is preferably less than 10ppm, and more preferably 8ppm or less, 7ppm or less, and 5ppm or less in this order. The lower limit of the content of Pt is not particularly limited, and about 0.001ppm is inevitably contained.

By setting the content of Pt in the above range, coloration of the glass by Pt can be reduced, and the transmittance can be improved.

In the glass of the present embodiment, the glass raw material is melted in a non-oxidizing atmosphere in the manufacturing process thereof. Examples of the non-oxidizing atmosphere includeFor example: inert gases such as nitrogen, carbon dioxide, argon and helium, and water vapor. Generally, oxygen in a melting atmosphere reacts with platinum, which is a material of a melting vessel (crucible or the like), to produce platinum dioxide and platinum ions (Pt)⁴⁺) Which dissolves into the molten glass, thereby producing coloration. In the present embodiment, by reducing the oxygen partial pressure in the melting atmosphere, oxidation of platinum can be suppressed, and the amount of Pt dissolved in the molten glass can be reduced. As a result, coloring from Pt can be reduced.

< composition of other ingredients >

Pb, as, cd, tl, be, se are toxic. Therefore, it is preferable that the optical glass of the present embodiment does not contain these elements as glass components.

U, th and Ra are radioactive elements. Therefore, the optical glass of the present embodiment preferably does not contain these elements as glass components.

V, cr, mn, fe, co, ni, cu, pr, nd, pm, sm, eu, tb, dy, ho, er, tm, ce increase the coloration of the glass and can become a fluorescence generating source. Therefore, it is preferable that the optical glass of the present embodiment does not contain these elements as glass components.

Sulfate is an oxidizing agent that can be optionally added to function as a clarifying agent. The sulphate is decomposed by heating to form a clear gas SO₂And O₂. The sulfate is not particularly limited, and examples thereof include zinc sulfate and zirconium sulfate.

The content of sulfate is expressed as an added proportion. That is, the content of sulfate when the total content of all glass components excluding sulfate is defined as 100 mass% is preferably less than 1 mass%, more preferably less than 0.5 mass%, and still more preferably less than 0.3 mass%. The content of sulfate may be 0 mass%.

Sb(Sb₂O₃) And is an element that can be added arbitrarily and functions as a clarifying agent. However, sb (Sb)₂O₃) The oxidation property is strong, and when the amount of addition is large, oxidation of platinum from the platinum crucible may be promoted. In addition, sb (Sb) contained in the glass at the time of precision press molding₂O₃) Pressing intoSince the molding surface of the mold is oxidized, the molding surface may be significantly deteriorated to make precision press molding impossible when precision press molding is repeated. As a result, the surface quality of the molded optical element is degraded. Therefore, the glass of the present embodiment preferably does not contain Sb (Sb)₂O₃)。

The glass of the present embodiment is preferably composed of substantially the above glass components, but may contain other components within a range not to impair the action and effect of the present invention. In the present invention, the inclusion of inevitable impurities is not excluded.

(glass characteristics)

< refractive index nd >

In the glass of the present embodiment, the refractive index nd is preferably 1.75 or more, and may be 1.77 or more, or 1.80 or more. The refractive index nd is preferably 2.50 or less, and may be 2.20 or less and 2.10 or less. The refractive index nd can be increased by Nb₂O₅、TiO₂、WO₃And Bi₂O₃Total content of [ Nb ]₂O₅+TiO₂+WO₃+Bi₂O₃]Thereby improving, in addition, by increasing SiO₂The content of (c) is decreased.

< Abbe number ν d >

In the glass of the present embodiment, the abbe number ν d is 20 or more. The abbe number ν d may be in the range of 20 to 45, or 21 to 45. Abbe number vd can be increased by adding La₂O₃Can be increased by increasing B₂O₃And the content of (c) is decreased.

< light transmittance of glass >

The optical glass of the present embodiment can be evaluated for light transmittance by a coloring degree λ 70.

The spectral transmittance was measured in the wavelength range of 200 to 700nm for a glass sample having a thickness of 10.0 mm. + -. 0.1mm, and the wavelength at which the external transmittance becomes 70% was defined as λ 70.

The optical glass of the present embodiment has a λ 70 of preferably 480nm or less, more preferably 470nm or less, still more preferably 450nm or less, and particularly preferably 440nm or less. λ 70 can be reduced by reducing the platinum Pt content.

Further, λ 70 of the optical glass of 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, and 175 in this order.

In addition, b is TiO₂Content of (A) and (B)₂O₃And La₂O₃In total content of [ TiO ]₂/(B₂O₃+La₂O₃)]。

When mass ratio [ TiO ]₂/(B₂O₃+La₂O₃)]When the transmittance in the visible short wavelength region increases, the transmittance decreases, and the coloring degree λ 70 increases. In the optical glass of the present embodiment, the reduction color is reduced, and λ 70 can be suppressed to the range represented by the above formula (3).

<T450>

The optical glass of the present embodiment can be evaluated for light transmittance by T450.

In the present embodiment, T450 is the external transmittance at a wavelength of 450nm in terms of a thickness of 10.0 mm. "external transmittance" means a transmittance that is obtained by perpendicularly entering a glass sample processed to have mutually parallel optically polished planes in one optically polished plane, and taking into consideration the ratio (Iout/Iin) of the intensity Iout of transmitted light transmitted through the glass to the intensity Iin of the incident light, that is, the surface reflection of the surface of the glass. The transmittance can be obtained by measuring the transmission spectrum using a spectrophotometer.

The thickness of the glass used for the measurement may be 10.0mm, and when the thickness is not 10.0mm, the transmittance may be converted to 10.0mm by a known method.

The T450 of the optical glass of the present embodiment is preferably 65% or more, more preferably 70% or more, and further preferably 75% or more. T450 can be increased by reducing the reducing color of the glass.

<T400>

The optical glass of the present embodiment can be evaluated for light transmittance by T400.

An external transmittance T400 at a wavelength of 400nm was measured with a spectrophotometer on a glass sample having a thickness of 10.0 mm. + -. 0.1 mm. The transmittance can be converted to a transmittance at a thickness of 10.0mm by a known method. The larger the value of T400, the more excellent the transmittance, and the lower the coloring of the glass.

The T400 of the optical glass of the present embodiment is preferably 50% or more, more preferably 60% or more, and further preferably 70% or more. T400 can be increased by reducing the reducing color of the glass.

<τ400>

The optical glass of the present embodiment can be evaluated for optical transparency by τ 400.

An internal transmittance T400 at a wavelength of 400nm was measured with a spectrophotometer on a glass sample having a thickness of 10.0 mm. + -. 0.1 mm. The transmittance at a thickness of 10.0mm can be converted by a known method. The larger the value of τ 400, the more excellent the transmittance, the more the coloration of the glass is reduced.

The τ 400 of the optical glass of the present embodiment is preferably 50% or more, more preferably 60% or more, and further preferably 70% or more. τ 400 can be increased by reducing the reducing color of the glass.

< specific gravity of glass >

In the glass of the present embodiment, the specific gravity is preferably 7 or less, and more preferably 6.5 or less and 6 or less in this order. The specific gravity is preferably 2.5 or more, and more preferably 3 or more and 3.5 or more in this order. If the specific gravity of the glass can be reduced, the weight of the lens can be reduced. As a result, power consumption for autofocus driving of the camera lens having the lens mounted thereon can be reduced. On the other hand, when the specific gravity is excessively reduced, the thermal stability is lowered.

< glass transition temperature Tg >

The glass transition temperature Tg of the optical glass of the present embodiment is preferably 800 ℃ or lower, and more preferably 770 ℃ or lower and 750 ℃ or lower in this order. The glass transition temperature Tg is preferably 300 ℃ or higher, and more preferably 350 ℃ or higher and 400 ℃ or higher in this order. GlassThe glass transition temperature Tg can be increased by increasing Li₂O、Na₂O and K₂Total content of O [ Li₂O+Na₂O+K₂O]And thus is reduced.

By making the upper limit of the glass transition temperature Tg satisfy the above range, it is possible to suppress an increase in the forming temperature and annealing temperature of the glass, and to reduce thermal damage to the press-forming equipment and annealing equipment. Further, when the lower limit of the glass transition temperature Tg satisfies the above range, the thermal stability of the glass can be easily maintained while maintaining a desired abbe number and refractive index.

(quality of optical glass)

In general, as a defect of the optical glass, bubbles, dross (foreign matter), and striae are included.

The evaluation of these defects can be performed by determining how many defects are contained per unit amount of glass. The ratio of the light transmittance inhibition varies depending on the amount of bubbles and dross per unit cross-sectional area of the glass.

However, in the case where the unit of evaluation defect (evaluation unit) is extremely small, when an area where bubbles and dross are not present is selected, there is no optical defect in this range. However, optical glass, which is a commonly used industrial product, is required to have not only homogeneity in a very small range such as 1mm × 1mm, but also homogeneity of glass having a cross-sectional area of, for example, about 100mm × 100mm or a volume equal to or larger than a predetermined value.

Further, not only the evaluation unit but also the production unit of the optical glass should be discussed.

In the case of producing 1ml of glass and in the case of producing 1000kg of glass, the degree of difficulty of production was judged to be cloudiness even if the required homogeneity was the same. That is, even when the same raw material is melted and vitrified, the required amount of heat varies depending on the amount of glass, and for example, under the conditions of a melting temperature of 1250 ℃ and a melting time of 2 hours, a melt (molten glass) free from bubbles and dross can be produced when 1ml of glass is produced, whereas the raw material cannot be sufficiently melted when 1000kg of glass is produced.

Depending on the amount of glass, not only the conditions required for vitrification but also the temperature and time required for deaeration (fining) need to be changed. When the amount of glass is increased, the amount of heat required for vitrification increases, and the melting time and the fining time also become longer. As a result, the amount of platinum Pt constituting the crucible eluted into the molten glass increased.

That is, when producing optical glass as an industrial product, it is necessary to set the glass capacity to be equal to or more than a predetermined value, and melting and refining conditions and the amount of Pt mixed into glass from a production apparatus (such as a crucible) also vary as compared with experiments and small-scale glass production.

For streaks, the degree of homogeneity is a more important property. Since the "streak" is a drawback originally in the discussion of the optical homogeneity (spatial refractive index distribution) of a predetermined volume, the evaluation unit is naturally required to be equal to or more than a predetermined level. The uniformity of the refractive index was different between the case of producing 1000ml of glass and the case of producing 10ml of glass 100 times.

In general, when manufacturing optical glass, glass having excellent homogeneity can be obtained when 1000ml of glass melt is manufactured at a time.

As described above, the optical glass handled as an industrial product is discussed in the case of manufacturing a capacity equal to or greater than a predetermined value, and the discussion of the difficulty in producing high-quality optical glass in this range is inseparable from the discussion of the characteristics and quality of the optical glass according to the manufacturing method thereof.

The techniques discussed for glass melting on a very small scale (e.g., small scale experimentation) are not directly applicable to glass melting at the industrial product level. Furthermore, when the glass production scale is different, the characteristics and quality of the glasses produced by the respective methods cannot be compared in a lump.

In the present embodiment, in order to distinguish the characteristics and quality of glass at the experimental level from those at the industrial level, the concept of the degree of homogeneity of glass is introduced. The degree of homogeneity of the glass can be evaluated by the refractive index distribution.

< refractive index Profile >

The refractive index distribution of the optical glass of the present 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. Refractive index distribution the continuous body having a glass volume of 100ml or more was measured. The glass capacity of the sample used for refractive index measurement was set to 1ml or more.

The volume of the glass can be calculated, for example, by measuring the mass of the glass and calculating the volume from the measurement result and the specific gravity.

Specifically, 100ml or more of glass a was prepared, and the refractive index at 2 positions a and B completely opposed to a was measured.

If there is a portion having a known refractive index, the portion is set as a, and the refractive index of a portion B farthest from a is measured. A total of 2 or more glass sheets were taken from the glass a, and the refractive index was measured.

In the present embodiment, the refractive index distribution is evaluated using the refractive index nd, but the evaluation may be performed using refractive indices at other wavelengths as appropriate.

(production of optical glass)

The optical glass according to the embodiment of the present invention may be produced by mixing glass raw materials so as to have the above-described predetermined composition, and using the mixed glass raw materials according to a known glass production method. For example, a plurality of compounds are blended and mixed thoroughly to prepare a batch, and the batch is put into a platinum crucible and subjected to a rough melting (melting step).

In the melting step of the glass of the present embodiment, a reducing agent may be added to the glass raw material. The reducing agent is not particularly limited, and examples thereof include: al, si, ti, W, H₂CO, C and the like exhibit reducing properties. More specifically, examples of the substance exhibiting reducibility include a carbon compound and activated carbon C. By adding a reducing agent to the glass raw material, highly reactive oxygen generated when the glass raw material is vitrified reacts with the reducing agent, and oxidation reaction of platinum from the platinum crucible can be suppressed. It is provided withAs a result, the Pt content in the glass can be reduced.

The melting atmosphere in the melting step of the glass of the present embodiment is preferably a non-oxidizing atmosphere. By performing the melting step in a non-oxidizing atmosphere, the partial pressure of oxygen in the melting atmosphere can be reduced, oxidation of platinum in the platinum crucible can be suppressed, and the amount of Pt dissolved in the molten glass can be reduced.

The non-oxidizing atmosphere is not particularly limited, and examples thereof include: inert gas atmosphere such as nitrogen, carbon dioxide, argon, helium, and the like, and atmosphere of water vapor is added. In order to increase the β OH of the finally obtained glass, an atmosphere in which water vapor is added is preferable.

By adding water vapor to the molten atmosphere, the value of β OH of the finally obtained optical glass can be increased, pt or the like can be effectively prevented from being dissolved in the glass, and dissolved gas sufficient for improving the defoaming property and the fining property can be supplied to the glass.

The method for adding water vapor to the molten atmosphere is not particularly limited, and examples thereof include: a method in which a connecting tube is inserted into the crucible from an opening portion provided in the melting apparatus, and water vapor is supplied to a space in the crucible through the connecting tube as needed.

In the melting step, bubbling may be accompanied in order to stir the melt. Bubbling during melting can be continued after the compounded material is melted. By stirring the melt in the melting step, only the glass component is oxidized, and the oxidation of platinum from the platinum crucible is suppressed. This is because the glass component tends to be more easily oxidized than platinum. As a result, the reduction reaction of the glass component is suppressed to reduce the reduction color, and the dissolution of platinum into the molten material is suppressed to reduce the coloration derived from platinum.

The gas used for bubbling is not particularly limited, and a known gas can be used. Examples thereof include: inert gases such as nitrogen, carbon dioxide, argon, helium, air, and these gases containing water vapor.

By using a gas containing water vapor as the gas for bubbling, the value of β OH of the optical glass finally obtained can be increased, platinum is effectively prevented from dissolving in the glass, and a dissolved gas sufficient for improving the defoaming property and the fining property can be supplied to the glass.

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, further preferably 30% by volume or more, further preferably 40% by volume or more, further preferably 50% by volume or more, further preferably 60% by volume or more, further preferably 70% by volume or more, particularly preferably 80% by volume or more, and further particularly preferably 90% by volume or more. The higher the water vapor content is, the more preferable, and particularly, the above range is set, whereby the value of β OH of the finally obtained optical glass can be increased.

The melt obtained by the rough melting is quenched and pulverized to produce cullet. Further, the cullet was put into a platinum crucible, heated and remelted (remelt) to prepare a molten glass, and the molten glass was further clarified and homogenized, then molded, and slowly cooled to obtain an optical glass. The molten glass can be formed and slowly cooled by a known method.

Further, if a desired glass component can be introduced into the glass in a desired content, the compound used in the preparation of the batch is not particularly limited, and examples of such a compound include: oxides, carbonates, nitrates, hydroxides, fluorides, etc.

(production of optical element, etc.)

In order to manufacture an optical element using the optical glass of the embodiment of the present invention, a known method can be applied. For example, the above molten glass is poured into a mold and molded into a plate shape to produce a glass preform made of the optical glass of the present invention. The obtained glass blank is cut, ground and polished as appropriate to produce a cut sheet having a size and shape suitable for press molding.

The cut pieces are heated and softened, and press-molded (secondary hot-pressing) by a known method to produce an optical element blank having a shape similar to that of the optical element. The optical element blank can be annealed, polished and polished by a known method to produce an optical element.

The optical element can also be produced by roughly polishing (barrel polishing) the cut pieces, equalizing the weight of the pieces and easily adhering a release agent to the surfaces, press-molding the reheated and softened glass into a shape close to the desired shape of the optical element, and finally grinding and polishing the glass.

Alternatively, the optical element can be manufactured by separating a predetermined weight of molten glass from the mold, directly press-molding the separated glass, and finally grinding and polishing the separated glass.

The optically functional surface of the optical element thus produced may be coated with an antireflection film, a total reflection film, or the like depending on the purpose of use.

Examples

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

Glass samples having glass compositions shown in table 1 were produced in the following order and subjected to various evaluations.

[ production 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 raw materials were weighed and blended so that the glass compositions of the obtained optical glasses became the respective compositions shown in table 1, and the raw materials were sufficiently mixed. The prepared raw material (batch) thus obtained is put into a platinum crucible, heated at 1250 to 1400 ℃ for 2 hours to be melted to obtain molten glass (melting step), and stirred at 1300 to 1400 ℃ for 1 to 2 hours for homogenization and clarification (homogenization/clarification step). The molten glass is cast into a mold preheated to an appropriate temperature. The cast glass was heat-treated at a temperature 100 ℃ lower than the glass transition temperature Tg for 30 minutes, and left to cool to room temperature in a furnace, thereby obtaining a glass sample.

The following operations are performed in the melting step and the homogenization/clarification step.

A platinum tube was inserted into a platinum crucible disposed in the furnace from outside the melting furnace, and water vapor was supplied to the space in the platinum crucible through the platinum tube. The flow rate of the supplied water vapor was set to 25cc/min.

Further, nitrogen was supplied to the space in the platinum crucible through the platinum tube, and the molten material was bubbled with steam from a tube provided at the lower portion of the crucible. The flow rates of nitrogen and water vapor to be supplied were 30L/min for nitrogen and 0.1cc/min for water vapor.

Further, the presence or absence of the additive, the conditions of the melting step and the homogenization/clarification step were changed as shown in tables 2 to 4 to prepare glass samples. Specifically, the following is described.

Example 1-B

A glass sample was obtained in the same manner as in example 1-a, except that the prepared raw material corresponding to No.1 shown in table 1 was charged into a platinum crucible together with the additive materials shown in table 2, heated and melted under the conditions of condition 1-1 to condition 1-9 shown in table 2 to prepare a molten glass (melting step), stirred for homogenization, and clarified (homogenizing and clarifying step).

(example 1-C)

A glass sample was obtained in the same manner as in example 1-a, except that the prepared raw material corresponding to No.2 shown in table 1 was charged into a platinum crucible together with the additive materials shown in table 3, heated and melted under the conditions of condition 2-1 to condition 2-4 shown in table 3 to prepare a molten glass (melting step), stirred for homogenization, and clarified (homogenizing/clarifying step).

Example 1-D

A glass sample was obtained in the same manner as in example 1-a, except that the prepared raw material corresponding to No.4 shown in table 1 was charged into a platinum crucible together with the additive materials shown in table 4, heated and melted under the conditions of conditions 4-1 to 4-5 shown in table 4 to prepare a molten glass (melting step), stirred for homogenization, and clarified (homogenizing and clarifying step).

[ confirmation of glass composition ]

The contents of the respective glass components in the obtained glass samples were measured by inductively coupled plasma emission spectrometry (ICP-AES) to confirm that the compositions were as shown in table 1.

[ measurement of amount of Pt in glass ]

The content of platinum Pt in the glass was quantified by inductively coupled plasma mass spectrometry (ICP-MS). The quantitative results are shown in tables 1 to 4.

[ confirmation of defoaming/clarifying Effect ]

The number of bubbles observed in the glass was counted for the obtained glass sample, and the number of bubbles (residual bubbles) contained per unit mass (kg) was calculated. The calculation results are shown in tables 2 to 4.

[ measurement of optical Properties ]

The resulting glass samples were tested for β OH, λ 70, T400 and T450. Further, the obtained glass sample was annealed at 710 ℃ for 72 hours, then cooled to room temperature at a cooling rate of-30 ℃/hour in a furnace to prepare an annealed sample, and the refractive indices nd, ng, nF and nC, abbe numbers ν d, λ 70 and T400 were measured.

Refractive indices nd, ng, nF, nC and Abbe number vd

The refractive indices nd, ng, nF and nC of the above annealed samples were measured by a refractive index measuring method according to JIS B7071-1, and Abbe number ν d was calculated based on formula (1). The results are shown in Table 1.

νd＝(nd-1)/(nF-nC)···(1)

(ii)βOH

The above glass sample was processed into a plate-like glass sample having a thickness of 1mm and having planes parallel to each other and optically polished. Light was incident on the polished surface of the plate-like glass sample from the vertical direction, and the external transmittance a at the wavelength of 2500nm and the external transmittance B at the wavelength of 2900nm were measured with a spectrophotometer, and β OH was calculated from the following formula (2). The results are shown in tables 1 to 4.

βOH＝-[ln(B/A)]/t···(2)

In the above formula (2), ln is a natural logarithm, and the thickness t corresponds to the interval of the 2 planes. The external transmittance also includes reflection loss at the surface of the glass sample, and is a ratio of the intensity of transmitted light to the intensity of incident light entering the glass sample (transmitted light intensity/incident light intensity).

(iii)λ70

A glass sample obtained in example 1-A was processed in a manner such that it had a thickness of 10mm and had planes parallel to each other and optically polished, and the spectral transmittance in a wavelength region from 280nm to 700nm was measured. The spectral transmittance B/a was calculated by setting the intensity of light that was incident perpendicularly on one optically polished plane as intensity a and the intensity of light that was emitted from the other plane as intensity B. The wavelength at which the spectral transmittance became 70% was defined as λ 70. The spectral transmittance also includes reflection loss of light at the sample surface. The results are shown in Table 1.

The glass samples obtained in examples 1-B to 1-D were measured for λ 70 before annealing (before heat treatment) and after annealing (after heat treatment) in the same manner as described above. Tables 2 to 4 show λ 70 before annealing (before heat treatment) and after annealing (after heat treatment).

(iv)T400

The T400 of the glass sample obtained in example 1-B was measured before the annealing treatment (before the heat treatment) and after the annealing treatment (after the heat treatment). Specifically, a glass sample or an annealed sample was processed in a manner of having a thickness of 10mm, having planes parallel to each other and optically polished, and the spectral transmittance at a wavelength of 400nm was measured. In addition, the spectral transmittance also includes reflection loss of light at the sample surface.

In table 2, T400 before annealing treatment (before heat treatment) and after annealing treatment (after heat treatment) are shown.

(v)T450

A sample of the glass obtained in example 1-A was processed in a manner such that it had a thickness of 10mm and planes parallel to each other and optically polished, and the spectral transmittance at a wavelength of 450nm was measured. In addition, the spectral transmittance also includes reflection loss of light at the sample surface. The results are shown in Table 1.

[ Table 1]

[ Table 2]

[ Table 3]

[ Table 4]

From the results shown in table 1, it was found that optical glass having a high spectral transmittance at a wavelength of 450nm and little coloration was obtained as a result of increasing the value of β OH by introducing water vapor into the molten glass and bubbling the same through the molten glass.

From the results of tables 2 to 4, it is understood that by increasing the value of β OH of the glass, optical glass with less coloration and high transmittance in the visible region is obtained without performing a long-term heat treatment in an oxidizing atmosphere after glass molding.

(example 2)

A glass block of 15 mm. Times.175 mm. Times.1500 mm, which was formed of a glass having a composition of No.1 shown in Table 1 and produced under condition 1-1 of Table 2, was produced, and cut into 5 equal parts to obtain 5 glass blocks of 15 mm. Times.175 mm. Times.300 mm. 5 samples 1 to 5 for refractive index measurement were prepared from each glass block divided into 5 parts, and the refractive index nd of each sample was measured. The refractive index distributions of samples 2 to 5 based on the refractive index of sample 1 at one of the 2 ends before cutting are as follows.

The difference between the refractive index nd of the sample 2 collected from the portion adjacent to the sample 1 and the refractive index nd of the sample 1 was +0.00001, the difference between the refractive index nd of the sample 3 collected from the central portion and the refractive index nd of the sample 1 was +0.00002, the difference between the refractive index nd of the sample 4 collected from the portion adjacent to the sample 3 and the refractive index nd of the sample 1 was 0.00000, and the difference between the refractive index nd of the sample 5 collected from the end portion diametrically opposed to the sample 1 among the 2 end portions before cutting and the refractive index nd of the sample 1 was-0.00003.

As described above, the refractive index distribution at 5 is 0.00005.

The refractive index distribution of glasses having the composition of No.1 shown in Table 1 and produced under the conditions 1-2 to 1-9 of Table 2 was measured in the same manner, and as a result, the refractive index distribution in 5 places was within 0.00005.

Further, the refractive index distribution of the glass having each composition of Nos. 2 to 17 shown in Table 1 and produced under the conditions of example 1-A was measured by the same method, and as a result, the refractive index distribution in 5 places was within 0.00005.

(example 3)

Using the optical glasses produced in examples 1-a to 1-D, lens blanks were produced by a known method, and the lens blanks were processed by a known method such as polishing to produce various lenses.

The optical lenses produced are various lenses such as a biconvex lens, a biconcave lens, a plano-convex lens, a plano-concave lens, a concave meniscus lens, and a convex meniscus lens.

The various lenses can be combined with lenses made of other types of optical glass, thereby correcting secondary chromatic aberration favorably.

Further, since glass has a low specific gravity, it is lighter than a lens having optical characteristics and a size equivalent to those of each lens, and is suitable for various image pickup devices, particularly for an automatic focusing type image pickup device for energy saving reasons and the like. In the same manner, prisms were produced using the various optical glasses produced in examples 1-A to 1-D.

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

For example, the optical glass according to one embodiment of the present invention can be produced by adjusting the composition of the glass composition of the above example as described in the specification.

It is to be understood that 2 or more items described as examples or preferable ranges in the specification can be arbitrarily combined.

Claims

1. An optical glass comprising 3 to 45 mass% of B₂O₃20 to 60 mass% of La₂O₃，

P₂O₅the content of (B) is 2% by mass or less,

the refractive index nd is 1.83481 or more,

the value of beta OH represented by the following formula (2) is 0.1 to 2.0mm^-1，

βOH＝-[ln(B/A)]/t　···(2)

In the formula (2), t represents the thickness of the glass used for measuring the external transmittance, A represents the external transmittance expressed by% at a wavelength of 2500nm when the glass is incident in parallel with the thickness direction thereof, B represents the external transmittance expressed by% at a wavelength of 2900nm when the glass is incident in parallel with the thickness direction thereof, the thickness is in mm, ln is a natural logarithm,

λ 70 satisfies the following formula (3):

λ70≤a×b+373　···(3)

in the formula (3), a is 175, b is TiO₂Content of (A) and B₂O₃And La₂O₃TiO in the mass ratio of the total content of₂/(B₂O₃+La₂O₃)。

2. The optical glass according to claim 1, wherein SiO is contained in an amount of 0.1 to 25 mass%₂。

3. The optical glass according to claim 1, wherein SiO is contained in an amount of 0.5 to 15 mass%₂And 3 to 30 mass% of B₂O₃20 to 60 mass% of La₂O₃。

4. The optical glass according to any one of claims 1 to 3, wherein B represents B in mass%₂O₃In an amount greater than SiO₂The content of (a).

5. The optical glass according to any one of claims 1 to 3, wherein TiO₂Content of (A) and (B)₂O₃And La₂O₃In the total content of (A) to (B) TiO₂/(B₂O₃+La₂O₃) Is 0.030 or more.

6. The optical glass according to any one of claims 1 to 3, wherein Abbe's number ν d is 20 to 45, and refractive index nd is 1.83481 to 2.50.

7. The optical glass according to any one of claims 1 to 3, wherein Nb₂O₅And TiO 2₂The total content of (B) is 13 mass% or more.

8. The optical glass according to any one of claims 1 to 3, wherein Nb₂O₅And TiO₂The total content of (B) is 40 mass% or less.

9. The optical glass according to any one of claims 1 to 3, wherein Nb₂O₅、TiO₂、WO₃And Bi₂O₃The total content of (B) is 40 mass% or less.

10. The optical glass according to any one of claims 1 to 3, wherein Nb₂O₅、TiO₂、WO₃And Bi₂O₃The total content of (B) is 1.0% by mass or more.

11. The optical glass according to any one of claims 1 to 3, wherein B is₂O₃、La₂O₃、SiO₂、P₂O₅、Al₂O₃、ZnO、BaO、MgO、CaO、SrO、Gd₂O₃、Y₂O₃、Yb₂O₃、ZrO₂、TiO₂、Nb₂O₅、WO₃、Bi₂O₃、Ta₂O₅、Li₂O、Na₂O、K₂O、Cs₂O、Sc₂O₃、HfO₂、Lu₂O₃And GeO₂The total content of (B) is more than 95% by mass.

12. An optical glass comprising 3 to 45 mass% of B₂O₃20 to 60 mass% of La₂O₃TiO of more than 0 mass%₂And more than 0 mass% of ZnO,

TiO₂content of (2) and Nb₂O₅、TiO₂、WO₃And Bi₂O₃In the total content of (A) to (B) TiO₂/(Nb₂O₅+TiO₂+WO₃+Bi₂O₃) The content of the organic acid is more than 0.4,

P₂O₅the content of (B) is 2 mass% or less,

the refractive index nd is 1.83481 or more,

βOH＝-[ln(B/A)]/t　···(2)

λ 70 satisfies the following formula (3):

λ70≤a×b+373　···(3)

in the formula (3), a is 175, b is TiO₂Content of (A) and (B)₂O₃And La₂O₃Mass of the total content ofTiO 2₂/(B₂O₃+La₂O₃)。

13. The optical glass according to any one of claims 1 to 3 and 12, wherein the content of platinum Pt is less than 10 mass ppm.

14. The optical glass according to any one of claims 1 to 3 and 12, wherein the volume is 100ml or more and the refractive index distribution is 0.00050 or less.

15. The optical glass according to any one of claims 1 to 3 and 12, wherein the refractive index nd is 1.85135 or more.

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