JP7429622B2 - Optical glass manufacturing method - Google Patents

Description

The present invention relates to a method for manufacturing optical glass.

In recent years, the digitalization and high definition of devices that use optical systems have progressed rapidly, and various optical devices such as photographic devices such as digital cameras and video cameras, and image reproduction (projection) devices such as projectors and projection televisions, etc. In the field of optical systems, there is an increasing demand to reduce the number of optical elements such as lenses and prisms used in optical systems, and to reduce the weight and size of the entire optical system.

Platinum, which is often used in crucibles in the production of optical glass, has a high melting point of over 1,700°C and is suitable for melting glass, but on the other hand, it easily reacts with oxygen and deteriorates, so oxidized platinum and platinum ions are used in glass production. It melts inside. The platinum that dissolves into the glass absorbs visible light, resulting in coloring of the final product, optical glass.

Furthermore, it is desired that the final optical glass product contains fewer bubbles. For example, if a lens is made of optical glass that has bubbles mixed in, the bubbles will be reflected in the projected image, and the image will be distorted due to the effects of light scattered by the bubbles.

The Japan Optical Glass Industry Association standard JOGIS 12-2012 "Method for Measuring Bubbles in Optical Glass" is used as an indicator of how many bubbles are contained in optical glass.
According to the Japan Optical Glass Industry Association standard JOGIS 12-2012 "Method for measuring bubbles in optical glass," bubbles that exist in optical glass and have a diameter of 30 μm or more are considered bubbles.

However, even if there are many microscopic bubbles with a diameter of less than 30 μm, which do not pose a problem in terms of standards, the internal quality may deteriorate, and they may affect the final product as much as or more than bubbles with a diameter of 30 μm or more. be.
On the other hand, in order to reduce platinum-derived coloring of optical glass and reduce bubbles in the glass, the following methods have been proposed.

Japanese Patent Application Publication No. 2019-019050 Japanese Patent Application Publication No. 2016-074558

Patent Document 1 has discovered that glass with reduced platinum-derived coloration can be obtained by increasing the water content in the melting process.
Patent Document 2 has discovered that glass with a high defoaming effect can be obtained by using a sulfur component as an oxidizing agent when melting glass.

When melting optical glass, the optimal method for suppressing platinum-derived coloring of the glass and generation of bubbles in the glass varies depending on the amount of glass melted, the raw materials used, production equipment, melting conditions, etc. Those skilled in the art are required to be able to select various methods as appropriate.
Furthermore, no conventional invention has found a method for reducing fine bubbles that do not pose a problem in terms of standards.

The present invention was made in view of the above-mentioned circumstances, and its purpose is to prevent the formation of fine bubbles while suppressing the coloring of the glass due to platinum that oxidizes and dissolves into the glass during the melting process. The objective is to obtain a reduced optical glass.

As a result of extensive testing and research to solve the above problems, the present inventor has developed a process for melting glass by adding a reducing agent and chlorine to a raw material containing ₃ B ₂ O components and ₃ La ₂ O components. We have discovered a method for producing optical glass that suppresses the formation of fine bubbles while suppressing the coloring of the glass due to platinum oxidized and dissolved into the glass.

Specifically, the present invention provides the following.

(1) A method for producing optical glass by melting glass raw materials,
The glass raw material is mass % in terms of oxide,
La ₂ O ₃ components 30.0 to 65.0%,
3.0 to 25.0% of B ₂ O ₃ components,
Contains
A method for producing optical glass, characterized by adding a reducing agent and chlorine.

(2) The glass raw material is mass% in terms of oxide,
_SiO2 component is 20.0% or less,
Containing at least one or more of ₂ TiO components, ₅ Nb ₂ O components, and ₃ WO components,
The method for producing optical glass according to (1).

(3) characterized by adding 0.01% or more of chlorine;
The method for producing optical glass according to (1) or (2).

(4) The optical glass has a platinum content of 8 ppm or less,
The method for producing optical glass according to (1) to (3).

The present invention has been made in view of the above-mentioned problems, and its purpose is to add a reducing agent and chlorine to a raw material containing _three La ₂ O components and _three B ₂ O components, thereby producing glass. An object of the present invention is to provide a method for producing optical glass that suppresses the formation of fine bubbles while suppressing the coloring of the glass due to platinum oxidized and dissolved into the glass during the process of melting the glass.

According to the method for producing optical glass of the present invention, it contains 30.0 to 65.0% of _{the 3} components of La ₂ O and 3.0 to 25.0% of the ₃ components of B ₂ O in terms of mass % in terms of oxides. By adding a reducing agent and chlorine to the glass raw materials, we have created an optical system that suppresses the coloring of the glass due to platinum that oxidizes and dissolves into the glass during the melting process, and also suppresses the formation of microscopic bubbles. You can get glass.

EMBODIMENT OF THE INVENTION Hereinafter, the embodiment of the optical glass and the manufacturing method of the optical glass of this invention is described in detail. The present invention is not limited to the following embodiments, and can be implemented with appropriate modifications within the scope of the purpose of the present invention. Note that the description may be omitted as appropriate for parts where the description overlaps, but this does not limit the gist of the invention.

[Glass component]
In this specification, unless otherwise specified, the content of each component is expressed in mass % based on the total mass of the composition in terms of oxides. Here, the "composition equivalent to oxide" refers to the composition when it is assumed that the oxides, composite salts, metal fluorides, etc. used as raw materials for the glass components of the present invention are all decomposed and converted into oxides when melted. The composition shows each component contained in the glass, with the total mass of the produced oxides being 100% by mass.

The La ₂ O ₃ component is a component that increases the refractive index of the glass and improves the chemical durability of the glass, and is an essential component in the glass of the present invention. In particular, by setting the content of the La ₂ O ₃ component to 65.0% or less, the Abbe number can be increased while improving the devitrification resistance of the glass. Therefore, the upper limit of the content of the La ₂ O ₃ components relative to the total mass of the glass in terms of oxide composition is preferably 65.0% or less, more preferably 62.0% or less, and most preferably 59.0% or less. Upper limit. On the other hand, the lower limit of the content of the _three La ₂ O components relative to the total mass of the glass in terms of oxide composition is preferably 30.0% or more, more preferably 35.0% or more, and most preferably 40.0% or more. .

The B ₂ O ₃ component is a component that enhances devitrification resistance by promoting the formation of a stable glass, and is an essential component in the glass of the present invention. In particular, by setting the content of the B ₂ O ₃ components to 25.0% or less, a decrease in the refractive index due to the B ₂ O ₃ components can be suppressed, making it easier to obtain a high refractive index. Therefore, the upper limit of the content of the _three B ₂ O components relative to the total mass of the glass in terms of oxide composition is preferably 25.0% or less, more preferably 20.0% or less, and even more preferably 15.0% or less. . On the other hand, the lower limit of the content of the _three B ₂ O components relative to the total mass of the glass in terms of oxide composition is preferably 3.0% or more, more preferably 4.0% or more, and most preferably 5.0% or more. .

The Nb ₂ O ₅ component is a component that increases the refractive index and Abbe number of the glass when it is contained in an amount exceeding 0%.On the other hand, by reducing the content of the Nb ₂ O ₅ component to 15.0% or less, the glass It is possible to improve the stability and devitrification resistance. Therefore, the upper limit of the content of the _five Nb ₂ O components relative to the total mass of the glass in terms of oxide composition is preferably 15.0% or less, more preferably 13.0% or less, and most preferably 11.0% or less. .

When the _SiO2 component is contained in an amount exceeding 0%, it is a component that increases the transmittance of short-wavelength visible light by reducing the coloring of the glass, and also increases the devitrification resistance of the glass by promoting stable glass formation. and is an optional component in the glass of the present invention. In particular, by setting the content of the SiO ₂ component to 20.0% or less, a decrease in the refractive index due to the SiO ₂ component can be suppressed, making it easier to obtain a high refractive index. Therefore, the content of the _two SiO components relative to the total mass of the glass in terms of oxide composition is preferably 20.0% or less, more preferably 15.0% or less, more preferably 12.0% or less, and most preferably 9.0% or less. The upper limit is 0% or less. On the other hand, the lower limit of the content of the two SiO ₂ components relative to the total mass of the glass in terms of oxide composition is preferably more than 0%, more preferably 1.0% or more, and most preferably 2.0% or more.

The TiO ₂ component is a component that increases the refractive index of the glass and the chemical durability of the glass when it is contained in an amount exceeding 0%, and is an optional component of the glass of the present invention. In particular, by including _two components of TiO, a high refractive index can be obtained. On the other hand, by controlling the content of the two TiO ₂ components to 25.0% or less, devitrification due to excessive content can be suppressed, and deterioration of transmittance can be suppressed. The lower limit of the content of the _two TiO components relative to the total mass of the glass in terms of oxide composition is preferably more than 0%, more preferably 3.0% or more, and most preferably 6.0% or more. On the other hand, the upper limit of the content of the _two TiO components relative to the total mass of the glass in terms of oxide composition is preferably 25.0% or less, more preferably 20.0% or less, and most preferably 15.0% or less.

The Al ₂ O ₃ component is a component that, when contained in an amount exceeding 0%, improves the chemical durability of the glass and increases the viscosity when the glass is melted, and is an optional component in the glass of the present invention. In particular, by controlling the content of the _three Al ₂ O components to 10.0% or less, it is possible to increase the meltability of the glass and weaken the tendency of the glass to devitrify. Therefore, the upper limit of the content of the _three Al ₂ O components relative to the total mass of the glass in terms of oxide composition is preferably 10.0% or less, more preferably 5.0% or less, and most preferably 3.0% or less. .

The Y ₂ O ₃ component is a component that increases the refractive index of the glass and increases the Abbe number when it is contained in an amount exceeding 0%, and is an optional component in the glass of the present invention. In particular, by controlling the content of the _three Y ₂ O components to 15.0% or less, it is possible to obtain a desired optical number while increasing the devitrification resistance of the glass. Therefore, the upper limit of the content of the _three Y ₂ O components relative to the total mass of the glass in terms of oxide composition is preferably 15.0% or less, more preferably 12.0% or less, and most preferably 11.0% or less. . On the other hand, the lower limit of the content of the _three Y ₂ O components relative to the total mass of the glass in terms of oxide composition is preferably more than 0%, more preferably 3.0% or more, and most preferably 5.0% or more.

The Gd ₂ O ₃ component is a component that increases the refractive index of the glass and increases the Abbe number when it is contained in an amount exceeding 0%, and is an optional component in the glass of the present invention. In particular, by controlling the content of the Gd ₂ O ₃ component to 20.0% or less, it is possible to obtain a desired optical number while increasing the devitrification resistance of the glass. Therefore, the content of the Gd ₂ O ₃ components relative to the total mass of the glass in terms of oxide composition is preferably 20.0% or less, more preferably 15.0% or less, more preferably 10.0% or less, and more preferably The upper limit is 5.0% or less, most preferably 3.0% or less.

When the _ZrO2 component is contained in an amount exceeding 0%, it is a component that reduces the coloring of the glass and increases the transmittance of short wavelength visible light, and also promotes stable glass formation and increases the devitrification resistance of the glass. , is an optional component in the glass of the present invention. On the other hand, by controlling the content of the ZrO ₂ components to 15.0% or less, devitrification due to excessive content of the ZrO ₂ components can be reduced. Therefore, the upper limit of the content of the _two ZrO components relative to the total mass of the glass in terms of oxide composition is preferably 15.0% or less, more preferably 12.0% or less, and most preferably 9.0% or less. do. On the other hand, the lower limit of the content of the _two ZrO components relative to the total mass of the glass in terms of oxide composition is preferably more than 0%, more preferably 1.0% or more, and most preferably 3.0% or more.

The WO ₃ component is a component that increases the refractive index of the glass when it is contained in an amount exceeding 0%, and is an optional component in the glass of the present invention. In particular, by controlling the content of the _three WO components to 15.0% or less, it is possible to improve the devitrification resistance of the glass and to suppress a decrease in the transmittance of the glass to short-wavelength visible light. Therefore, the upper limit of the content of the _three WO components relative to the total mass of the glass in terms of oxide composition is preferably 15.0% or less, more preferably 10.0% or less, and most preferably 5.0% or less.

The ZnO component is a component that lowers the liquidus temperature of the glass and increases the devitrification resistance of the glass when it is contained in an amount of more than 0%, and is an optional component in the glass of the present invention. In particular, by controlling the content of the ZnO component to 15.0% or less, it is possible to easily obtain a high refractive index and low dispersion. Therefore, the upper limit of the content of the ZnO component with respect to the total mass of the glass in terms of oxide composition is preferably 15.0% or less, more preferably 12.0% or less, and most preferably 9.0% or less.

The MgO component is an optional component that lowers the liquidus temperature of the glass and increases the devitrification resistance of the glass when it is contained in an amount exceeding 0%, and is a component that makes it difficult to reduce the transmittance of visible light. It is an optional component in the glass of the invention. In particular, by controlling the content of the MgO component to 10.0% or less, it is possible to easily obtain a high refractive index and low dispersion. Therefore, the upper limit of the content of the MgO component relative to the total mass of the glass in terms of oxide composition is preferably 10.0% or less, more preferably 5.0% or less, and most preferably 3.0% or less.

The CaO component is a component that lowers the liquidus temperature of the glass and increases the devitrification resistance of the glass when it is contained in an amount of more than 0%, and is an optional component in the glass of the present invention. In particular, by setting the content of CaO component to 20.0% or less, it is possible to easily obtain a high refractive index and low dispersion, and it is possible to suppress a decrease in the devitrification resistance and chemical durability of the glass. can. Therefore, the upper limit of the content of the CaO component with respect to the total mass of the glass in terms of oxide composition is preferably 20.0% or less, more preferably 15.0% or less, and most preferably 10.0% or less.

The SrO component is a component that lowers the liquidus temperature of the glass and increases the devitrification resistance of the glass when it is contained in an amount exceeding 0%, and is an optional component in the glass of the present invention. In particular, by controlling the content of the SrO component to 10.0% or less, it is possible to easily obtain a high refractive index and low dispersion, and it is possible to suppress a decrease in the devitrification resistance and chemical durability of the glass. can. Therefore, the upper limit of the content of the SrO component relative to the total mass of the glass in terms of oxide composition is preferably 10.0% or less, more preferably 5.0% or less, and most preferably 3.0% or less.

The BaO component is a component that increases the refractive index of the glass and increases the devitrification resistance of the glass when it is contained in an amount of more than 0%, and is a component that makes it difficult to reduce the transmittance of visible light. It is an optional component in glass. In particular, by controlling the content of the BaO component to 20.0% or less, it is possible to easily obtain a high refractive index and low dispersion, and it is possible to suppress a decrease in devitrification resistance and chemical durability. Therefore, the upper limit of the content of the BaO component with respect to the total mass of the glass in terms of oxide composition is preferably 20.0% or less, more preferably 15.0% or less, and most preferably 10.0% or less.

The Li ₂ O component is a component that lowers the melting temperature of the glass when contained in an amount exceeding 0%, and is an optional component in the glass of the present invention. In particular, by controlling the content of the Li ₂ O component to 10.0% or less, a high refractive index can be easily obtained, and the stability of the glass can be increased to reduce the occurrence of devitrification and the like. Therefore, the upper limit of the content of the Li ₂ O component with respect to the total mass of the glass in terms of oxide composition is preferably 10.0% or less, more preferably 5.0% or less, and most preferably 3.0% or less.

The Na ₂ O component is a component that lowers the melting temperature of the glass when it is contained in an amount exceeding 0%, and is an optional component in the glass of the present invention. In particular, by controlling the content of the Na ₂ O component to 10.0% or less, it is possible to easily obtain a high refractive index, and also to improve the stability of the glass and reduce the occurrence of devitrification and the like. Therefore, the upper limit of the content of the Na ₂ O component relative to the total mass of the glass in terms of oxide composition is preferably 10.0% or less, more preferably 5.0% or less, and most preferably 3.0% or less.

The K ₂ O component is a component that lowers the melting temperature of the glass when it is contained in an amount exceeding 0%, and is an optional component in the glass of the present invention. In particular, by controlling the content of the K ₂ O component to 10.0% or less, it is possible to easily obtain a high refractive index, and also to improve the stability of the glass and reduce the occurrence of devitrification and the like. Therefore, the upper limit of the content of the K ₂ O component based on the total mass of the glass in terms of oxide composition is preferably 10.0% or less, more preferably 5.0% or less, and even more preferably 3.0% or less.

The Ta ₂ O ₅ component is a component that, when contained in an amount exceeding 0%, can increase the refractive index of the glass and improve the devitrification resistance. The upper limit of the content of the _five Ta ₂ O components is preferably 5.0% or less, more preferably 3.0% or less, more preferably 1.0% or less, and even more preferably 0.5% or less.

The P ₂ O ₅ component is a component that lowers the liquidus temperature of the glass and improves the devitrification resistance when it is contained in an amount exceeding 0%. The upper limit of the content of the P ₂ O ₅ component is preferably 5.0% or less, more preferably 3.0% or less, more preferably 1.0% or less, and still more preferably 0.5% or less.

The GeO ₂ component is a component that can increase the refractive index of the glass and improve the devitrification resistance when it is contained in an amount exceeding 0%. The upper limit of the content of the _two GeO components is preferably 5.0% or less, more preferably 3.0% or less, more preferably 1.0% or less, and still more preferably 0.5% or less.

The Ga ₂ O ₃ component is a component that can improve the chemical durability of glass and improve the devitrification resistance of molten glass when it is contained in an amount exceeding 0%. The upper limit of the content of the _three Ga ₂ O components is 5.0% or less, more preferably 3.0% or less, more preferably 1.0% or less, and even more preferably 0.5% or less.

The Bi ₂ O ₃ component is a component that can increase the refractive index and lower the glass transition point when contained in an amount exceeding 0%. The upper limit of the content of the _three Bi ₂ O components is preferably 5.0% or less, more preferably 3.0% or less, more preferably 1.0% or less, and even more preferably 0.5% or less.

The TeO ₂ component is a component that can increase the refractive index and lower the glass transition point when contained in an amount exceeding 0%. The upper limit of the content of the _two TeO components is preferably 5.0% or less, more preferably 3.0% or less, more preferably 1.0% or less, and even more preferably 0.5% or less.

The SnO ₂ component is a component that, when contained in an amount exceeding 0%, reduces oxidation of the molten glass to clarify it, and increases the visible light transmittance of the glass. The upper limit of the content of the _two SnO components is preferably 5.0% or less, more preferably 3.0% or less, more preferably 1.0% or less, and still more preferably 0.5% or less.

The F component is a component that can improve the meltability of glass when contained in an amount exceeding 0%, but on the other hand, when the content is too large, devitrification due to volatilization of the F component is caused. The upper limit of the content of the F component is preferably 5.0% or less, more preferably 3.0% or less, more preferably 1.0% or less, and still more preferably 0.5% or less.

The Sb ₂ O ₃ component is a component capable of defoaming the molten glass when it is contained in an amount exceeding 0%.
On the other hand, if the content of the _three Sb ₂ O components is too large, the transmittance in the short wavelength region of the visible light region will deteriorate. Therefore, the upper limit of the content of the _three Sb ₂ O components is preferably 1.0% or less, more preferably 0.5% or less, and even more preferably 0.3% or less.

The sum of the contents (sum of mass) of the _three Ln ₂ O components (in the formula, Ln is one or more selected from the group consisting of La, Y, Gd, and Yb) is 30.0% or more and 65.0%. The devitrification resistance can be improved in the following cases.
Therefore, the sum of the _three Ln ₂ O components is preferably 30.0% or more, more preferably 32.0% or more, more preferably 35.0% or more, more preferably 38.0% or more, and even more preferably 42.0% or more. The lower limit is .0% or more, more preferably 45.0% or more, even more preferably 47.5% or more.
On the other hand, the upper limit of the sum of the contents (sum of mass) of the _three Ln ₂ O components is preferably 65.0% or less, more preferably 62.0% or less, and even more preferably 60.0% or less.

The total content of SiO ₂ components, B ₂ O ₃ components, and Al ₂ O ₃ components, the mass sum SiO ₂ +B ₂ O ₃ +Al ₂ O ₃ , is set to 8.0% or more and 28.0% or less. , can increase the stability of the glass.
Therefore, the mass sum SiO ₂ +B ₂ O ₃ +Al ₂ O ₃ is preferably 8.0% or more, more preferably 9.0% or more, more preferably 10.0% or more, and even more preferably 11.5% or more. The lower limit is more preferably 13.0% or more.
On the other hand, the upper limit of the mass sum SiO ₂ +B ₂ O ₃ +Al ₂ O ₃ is preferably 28.0% or less, more preferably 26.0% or less, even more preferably 24.0% or less.

_The mass ratio _{Ln 2 O 3 / (SiO 2 + B 2 O 3} + _{Al 2} By setting O ₃ ) to 6.0 or less, devitrification resistance can be improved.
Therefore, the mass ratio Ln ₂ O ₃ /(SiO ₂ +B ₂ O ₃ +Al ₂ O ₃ ) is preferably 6.0 or less, more preferably 5.5 or less, still more preferably 5.0 or less, even more preferably 4 The upper limit is .5 or less.

By setting the mass sum TiO ₂ +Nb ₂ O ₅ +WO ₃ , which is the total content of ₂ TiO components, ₅ Nb ₂ O components, and ₃ WO components, to 5.0% or more and 35.0% or less, the refractive index ( It is possible to reduce the reduced color derived from the high refractive index component while increasing n _d ).
Therefore, the mass sum TiO ₂ +Nb ₂ O ₅ +WO ₃ is preferably 5.0% or more, more preferably 7.0% or more, more preferably 12.0% or more, more preferably 15.5% or more, and The lower limit is preferably 20.0% or more.
On the other hand, the upper limit of the mass sum TiO ₂ +Nb ₂ O ₅ +WO ₃ is preferably 35.0% or less, more preferably 30.0% or less, and still more preferably 27.0% or less.

In the present invention, the total content of the following components is preferably 95.0% or more, 97.0% or more, and 98.0% or more in this order.
La ₂ O ₃ components, Y ₂ O ₃ components, Gd ₂ O ₃ components, Yb ₂ O ₃ components, SiO ₂ components, B ₂ O ₃ components, Al ₂ O ₃ components, TiO ₂ components, Nb ₂ O ₅ components, WO ₃ components, Bi ₂ O ₃ components, ZnO component, ZrO ₂ components, MgO component, CaO component, SrO component, BaO component, Li ₂ O component, Na ₂ O component, K ₂ O component, Ta ₂ O ₅ components.

<About ingredients that should not be included>
Next, components that should not be included in the optical glass of the present invention and components that are not preferably included will be explained.

Other components may be added as necessary within a range that does not impair the properties of the glass of the present invention. However, each transition metal component such as Nd, V, Cr, Mn, Fe, Co, Ni, Cu, Ag, and Mo, excluding Ti, Zr, Nb, W, La, Gd, Y, Yb, and Lu, is Even if a small amount of these substances is contained singly or in combination, the glass will be colored and have the property of absorbing specific wavelengths in the visible range. is preferred.

Further, since lead compounds such as PbO and arsenic compounds such as As ₂ O ₃ are components with a high environmental load, it is desirable that they are substantially not contained, that is, not contained at all except for unavoidable contamination.

Furthermore, the use of Th, Cd, Tl, Os, Be, and Se as harmful chemical substances has tended to be avoided in recent years, and they are used not only in the glass manufacturing process but also in the processing process and disposal after product production. Environmental measures are required throughout. Therefore, when placing importance on the environmental impact, it is preferable not to substantially contain these.

The optical glass of the present invention is characterized by adding a reducing agent. By adding a reducing agent, platinum incorporation into the glass can be suppressed and transmittance can be improved. The upper limit of the content of the reducing agent is preferably 3.0% or less, more preferably 2.0% or less, still more preferably 1.0% or less, and most preferably 0.8% or less. On the other hand, the content of the reducing agent is preferably 0.01% or more, more preferably 0.05% or more, more preferably 0.1% or more, even more preferably 0.2% or more, and most preferably The lower limit is 0.3% or more. Examples of the reducing agent include single elements such as carbon and S, organic compounds such as sucrose, and raw materials that generate reducing gas upon thermal decomposition such as ammonium sulfate.

The optical glass of the present invention is characterized by adding chlorine. In optical glasses that often use platinum crucibles, chlorine reacts with platinum to form platinum chloride, which is a component that actually increases the amount of platinum.
In the present invention, by adding chlorine together with a reducing agent, it is possible to suppress the generation of fine bubbles while suppressing the contamination of platinum. The content of chlorine is preferably 2.0% or less, more preferably 1.0% or less, still more preferably 0.5% or less, still more preferably 0.4% or less, and most preferably 0.3%. The upper limit is % or less. On the other hand, the content of chlorine is preferably 0.01% or more, more preferably 0.03% or more, more preferably 0.05% or more, more preferably 0.08% or more, and most preferably 0. .1% or more is the lower limit. By adjusting the chlorine content, fine bubbles can be reduced without affecting the optical properties or transmittance _λ70 . Chlorine is not particularly limited, but examples include chloride raw materials and chloride gas.

[Production method]
The optical glass of the present invention is produced, for example, as follows. That is, the above-mentioned raw materials are uniformly mixed so that each component is within a predetermined content range, the prepared mixture is put into a platinum crucible, and a known glass material is mixed according to the difficulty of melting the glass raw materials and the melting scale. What is necessary is just to produce it according to a manufacturing method. The timing of adding the reducing agent and chlorine includes a method of adding them as raw materials, and a method of creating a reducing atmosphere or chlorine bubbling during the melting process of glass raw materials.

[Physical properties]
The optical glass of the present invention preferably has a refractive index (n _d ) of 1.75000 or more. The lower limit of the refractive index (n _d ) of the glass of the present invention is preferably 1.75000 or more, more preferably 1.80000 or more, still more preferably 1.85000 or more. The upper limit of this refractive index (n _d ) is preferably 2.10000 or less, more preferably 2.07000 or less, still more preferably 2.05000 or less. Further, the lower limit of the Abbe number (v _d ) of the glass of the present invention is preferably 20.00 or more, more preferably 23.00 or more, and still more preferably 25.00 or more. The upper limit of this Abbe number (v _d ) is preferably 45.00 or less, more preferably 40.00 or less, and even more preferably 37.00 or less.

It is preferable that the optical glass of the present invention has a high visible light transmittance, particularly a high transmittance of light on the short wavelength side of visible light, and thereby has little coloring.
The shortest wavelength (λ ₇₀ ) at which a 10 mm thick sample of the glass of the present invention exhibits spectral transmittance is preferably 470 nm or less, more preferably 450 nm or less, still more preferably 430 nm or less, and even more preferably 420 nm or less. shall be.

It is preferable that the optical glass of the present invention has a small amount of platinum and therefore has little coloring.
In particular, the upper limit of the amount of platinum in the optical glass of the present invention is preferably 8 ppm or less, more preferably 7 ppm or less, and still more preferably 6 ppm or less. This suppresses coloring due to platinum and increases the transparency of the glass to visible light, so that this optical glass can be preferably used for optical elements such as lenses that transmit light.

The optical glass of the present invention is characterized by having few microbubbles. In the present invention, fine bubbles refer to bubbles less than 30 μm in diameter.
In particular, the number of fine bubbles in the optical glass of the present invention is preferably 53.5 or less, more preferably 45.0 or less, even more preferably 35.0 or less, and even more preferably 25.0 or less. . The number of fine bubbles is calculated using a glass measuring 1.4 cm long x 2.4 cm wide x 1.0 cm thick. This makes it possible to suppress deterioration of internal quality, so that this optical glass can be preferably used for optical elements that transmit light, such as lenses.

[Preform and optical element]
A glass molded body can be produced from the produced optical glass using, for example, a polishing method or a mold press forming method such as reheat press molding or precision press molding. That is, mechanical processing such as grinding and polishing is performed on optical glass to produce a glass molded body, or a preform for mold press molding is produced from optical glass, and this preform is subjected to reheat press molding. After that, a glass molded body is produced by polishing, or a glass molded body is produced by performing precision press molding on a preform produced by polishing, or a preform molded by known levitation molding, etc. can be created. Note that the means for producing the glass molded body are not limited to these means.

Thus, the optical glass of the present invention is useful for various optical elements and optical designs. Among these, it is particularly preferable to form a preform from the optical glass of the present invention and perform reheat press molding, precision press molding, etc. using this preform to produce optical elements such as lenses and prisms. This makes it possible to form preforms with large diameters, so even though the optical elements are larger, they still have high-definition and high-precision imaging and projection characteristics when used in optical equipment such as cameras and projectors. can be realized.

Compositions of Examples and Comparative Examples of glasses of the present invention, refractive index (n _d ), Abbe number (ν _d ), and wavelengths (λ ₇₀ , λ As a result of ₅ ), the amount of platinum (ppm) in the glass and the measured values of bubbles (bubbles) in the glass are shown in the table. The following examples are for illustrative purposes only and are not intended to be limiting.

The glasses of Examples and Comparative Examples of the present invention are both used in ordinary optical glasses containing corresponding oxides, hydroxides, carbonates, nitrates, fluorides, metaphosphoric acid compounds, etc. as raw materials for each component. High-purity raw materials, reducing agents, and chloride raw materials were selected, weighed so as to have the composition, reducing agent, and chlorine proportions of each example shown in the table, mixed uniformly, and then placed in a platinum crucible. Depending on the difficulty of melting the glass raw material, it was melted in an electric furnace at a temperature range of 1100 to 1500°C for 30 minutes to 2 hours, stirred to homogenize, poured into a mold, etc., and slowly cooled.

In the Examples and Comparative Examples of the glasses of the present invention, reducing agents, chlorine, and sulfuric acid were added in the amounts shown in the table. Here, sulfuric acid plays the role of a defoaming agent.

The refractive index (n _d ) of the glasses of Examples and Comparative Examples was shown as a value measured against the d-line (587.56 nm) of a helium lamp in accordance with the V block method specified in JIS B 7071-2:2018. . In addition, the Abbe number (ν _d ) is the refractive index of the above d-line, the refractive index (n _F ) for the F-line (486.13 nm) of the hydrogen lamp, and the refractive index (n _C ) for the C-line (656.27 nm). It was calculated from the formula of Abbe number (ν _d )=[( _nd −1)/(n _F −n _C )] using the value of . Then, from the values of the determined refractive index (n _d ) and Abbe number (ν _d ), the intercept b in the relational expression _nd = −a×ν _d +b when the slope a is 0.01 was determined.

The transmittance of the glasses of Examples and Comparative Examples was measured according to the Japan Optical Glass Industry Association standard JOGIS02-2003. In the present invention, the presence or absence and degree of coloring of the glass was determined by measuring the transmittance of the glass. Specifically, according to JIS Z8722, the spectral transmittance of 200 to 800 nm was measured for a parallel-polished product with a thickness of 10 ± 0.1 mm, and the light transmittance (spectral transmittance), λ ₇₀ (when transmittance was 70%) was measured. wavelength) was determined.

The amount of platinum (ppm) in the glasses of Examples and Comparative Examples was measured using an ICP-MS (inductively coupled plasma mass spectrometer).

The measurement of bubbles in the glass in Examples and Comparative Examples was performed based on the Japan Optical Glass Industry Association standard JOGIS 12-2012 "Method for measuring bubbles in optical glass."

The number of fine bubbles in the glass of Examples and Comparative Examples was determined using a stereomicroscope SZ61 manufactured by Olympus Corporation using a glass sample measuring 1.4 cm long x 2.4 cm wide x 1.0 cm thick. I did the calculations.
A glass sample in which the number of fine bubbles with a diameter of less than 30 μm is 53.5 or less is marked as “○”, and a glass sample in which the number of fine bubbles exceeds 53.5 is marked as “×”.

All of the glasses of the present invention in Examples of the present invention had a λ ₇₀ (wavelength at 70% transmittance) of 450 nm or less. More specifically, all of the glasses of the present invention in Examples of the present invention had a λ ₇₀ (wavelength at 70% transmittance) of 420 nm or less. On the other hand, the glass of Comparative Example B containing only chlorine had a λ ₇₀ greater than 450 nm. Therefore, it became clear that the optical glass of the example of the present invention was less likely to be colored than the glass of the comparative example.

The optical glasses of Examples of the present invention all had a platinum content of 8 ppm or less. On the other hand, the glass of Comparative Example B containing only chlorine had a platinum content exceeding 8 ppm. Therefore, it became clear that the glasses of Examples of the present invention contained less platinum than the glasses of Comparative Examples.

The optical glasses of the examples of the present invention all have a bubble evaluation of grade 1, but the optical glasses of the examples of the present invention have fewer fine bubbles than the glasses of the comparative examples, so they have good internal quality. It became clear that.

Therefore, by adding a reducing agent and chlorine to the optical glass of the embodiment of the present invention, the coloring of the glass due to platinum oxidized and dissolved into the glass during the process of melting the glass can be suppressed, and fine bubbles can be suppressed. It was revealed that the occurrence of was suppressed.

Although the present invention has been described in detail above for the purpose of illustration, this embodiment is only for the purpose of illustration, and many modifications can be made by those skilled in the art without departing from the spirit and scope of the present invention. will be understood.

Claims (4)

A method for producing optical glass by melting glass raw materials, the method comprising:
The glass raw material is mass % in terms of oxide,
La ₂ O ₃ component 30.0 to 65.0%,
B ₂ O ₃ component 3.0 to 15.0 %
Contains
Contains at least one of TiO ₂ component, Nb ₂ O ₅ component, and WO ₃ component, and the mass sum TiO ₂ +Nb ₂ O ₅ +WO ₃ is 15.5% or more and 35.0% or less,
A method for producing optical glass, characterized by adding a reducing agent and chlorine. The glass raw material is mass % in terms of oxide,
The SiO ₂ component is 20.0% or less,
The method for manufacturing optical glass according to claim 1. characterized in that the chlorine is added in an amount of 0.01% or more,
The method for manufacturing optical glass according to claim 1 or 2. The optical glass has a platinum content of 8 ppm or less,
A method for producing optical glass according to claims 1 to 3.