JP2011241103A - Method for producing optical glass, optical element and optical instrument - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing an optical glass which provides a hardly colored glass particularly containing NbOthat is a transition metal oxide.SOLUTION: The method for producing an optical glass containing NbOas an essential component uses a melting vessel 11 in which a glass raw material S is melted, a refining vessel 12 which communicates with the melting vessel 11 and in which glass is refined, and an agitation vessel 13 which communicates with the refining vessel 12 and in which glass is agitated, and comprises: a step (melting step) of melting the glass raw material S in the melting vessel 11; a step (refining step) of refining the molten glass raw material S in the refining vessel 12; a step (agitation step) of agitating the resulting refined molten glass G in the agitation vessel 13; a step (outflow step) of discharging the agitated molten glass G; and a step (molding step) of molding the discharged glass.

Description

  The present invention relates to a method for producing optical glass, an optical element, and an optical element.

  In recent years, optical devices that use optical lenses have been rapidly improved in functionality, and accordingly, there is an increasing demand for higher accuracy for optical lenses. The market demand for higher accuracy specifically includes high homogeneity inside the glass, extremely high transmittance, and constant optical properties such as refractive index and Abbe number. Various methods are known to achieve this.

  As such a method, a method is known in which a part of molten glass transferred from a clarification tank for refining molten glass to a stirring tank for stirring molten glass is branched and refluxed to a clarification tank (see Patent Document 1). In addition, it is known that a circulating mixing cylinder is provided inside the stirring tank and the molten glass is refluxed inside the stirring tank (see Patent Document 2). In addition, it is known that a melting tank, a clarification tank, and a stirring tank are made of platinum and the outer surface thereof is covered with a refractory (see Patent Document 2).

JP-A-10-287429 JP 10-338528 A JP 2008-201617 A

However, in the methods described in Patent Document 1 to Patent Document 3, when a raw material containing an Nb ₂ O ₅ component having an action of enhancing dispersion is used, the formed glass is colored, so that light transmission is achieved. An optical glass with a high rate cannot be obtained.

The present invention has been made in view of the above circumstances, contain Nb ₂ O ₅ component is particularly transition metals, and coloring which can obtain a low glass, to provide a method for producing an optical glass For the purpose.

As a result of intensive studies and research to solve the above problems, the inventors of the present invention have a glass raw material containing an Nb ₂ O ₅ component, and are provided with a melting tank, a clarification tank, and a stirring tank, By using an apparatus in which a clarification tank is connected and a clarification tank and a stirring tank are connected, it has been found that the transmittance of glass to visible light can be increased while having high dispersion, and the present invention has been completed. It was. Specifically, the present invention provides the following.

(1) A method for producing optical glass containing an Nb ₂ O ₅ component as an essential component, a melting tank for melting a glass raw material, a clarification tank communicating with the melting tank and clarifying the glass, and the clarification A step of melting the glass raw material in the melting tank (melting step), a step of clarifying the molten glass raw material in the clarification tank (clarification step), and a stirring tank that is communicated with the tank and stirs the glass. A production method comprising a step of stirring molten glass in the stirring tank (stirring step), a step of discharging the stirred molten glass (outflow step), and a step of forming the outflowed glass (molding step).

  (2) The manufacturing method according to (1), wherein at least a part of a portion in contact with glass in the melting tank, the clarification tank, and the stirring tank is made of quartz.

  (3) The manufacturing method according to (1) or (2), wherein at least a part of a portion in contact with glass in the melting tank and clarification tank is made of quartz, and a part in contact with the glass in the stirring tank is made of platinum. .

  (4) The production method according to (2) or (3), further comprising a step of bubbling an oxidizing gas in the molten glass.

  (5) From (1) to (1), further comprising a step of composing at least a part of a portion in contact with glass in the melting tank, clarification tank, and stirring tank with platinum, and bubbling a non-oxidizing gas in the molten glass. 3) The production method according to any one of the above.

  (6) The manufacturing method according to any one of (1) to (5), wherein a material containing antimony and / or tin is used as the glass raw material.

  (7) An optical element comprising a glass molded body produced by the production method according to any one of (1) to (6) and having a platinum content of 50 ppm or less on an oxide basis.

  (8) An optical apparatus using the optical element according to (7).

According to the present invention, by using a melting tank, a clarification tank communicated with the melting tank, and a stirring tank communicated with the clarification tank, and containing the Nb ₂ O ₅ component in the optical glass, It is possible to provide an optical glass manufacturing method capable of obtaining a glass that has a refractive index and high dispersion and that has reduced coloration particularly after heat treatment.

It is sectional drawing which shows a preferable example of the glass melting apparatus used by embodiment of this invention.

The method for producing an optical glass of the present invention is a method for producing an optical glass containing an Nb ₂ O ₅ component as an essential component, a melting tank for melting a glass raw material, and a glass tank that is communicated with the melting tank and clarifies the glass. And a step of melting the glass raw material in the melting tank (melting step), and a step of clarifying the molten glass raw material in the clarification tank. (Clarification step), a step of stirring the clarified molten glass in the stirring tank (stirring step), a step of discharging the stirred molten glass (outflow step), and a step of forming the outflowed glass (forming step). The refractive index and dispersion are increased by the Nb ₂ O ₅ component, and the molten glass is melted, clarified, and stirred in separate tanks, so that it is made of a material suitable for the temperature and oxygen concentration of the molten glass in each step. It is possible to use a melting tank, a clarification tank, and a stirring tank. That is, reduction of Nb ₂ O ₅ due to excessive heating of the molten glass G can be reduced while reducing elution of the components of the glass melting apparatus 1 into the molten glass G having a high oxygen concentration. Accordingly, it is possible to obtain an optical glass that has high dispersion and little coloration.

  Hereinafter, embodiments of the method for producing an optical glass of the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and appropriate modifications are made within the scope of the object of the present invention. Can be implemented. In addition, although description may be abbreviate | omitted suitably about the location where description overlaps, the meaning of invention is not limited.

[Glass raw material]
First, the glass raw material used with the manufacturing method of this invention is demonstrated. Glass raw material used in the present invention contain Nb ₂ O ₅ as an essential component, is and appropriately selected from a glass capable of forming raw material. Among these, it is preferable to use glass raw materials as described below.

  Hereafter, the composition range of each component which comprises the glass raw material used by this invention is described below. In the present specification, unless otherwise specified, the content of each component is expressed as mass% (mass% based on oxide) with respect to the total mass of the glass raw material having an oxide conversion composition. Here, the “oxide equivalent composition” means that when the oxide, composite salt, metal fluoride, etc. used as a glass raw material in the present invention are all decomposed and changed into an oxide when melted, the generated oxidation It is the composition which described each component contained in a glass raw material by making the total mass of a thing into 100 mass%.

<About essential and optional components>
Glass material used in the present invention contains _Nb 2 _{O 5} component. By melting the raw glass containing Nb ₂ O ₅ component in a glass melting apparatus having a melting tank, a clarification tank connected to the melting tank, and a stirring tank connected to the clarification tank, By melting, clarifying, and stirring the glass in a tank made of a material suitable for temperature, oxygen concentration, etc., the dissolution of the melting equipment (especially noble metals such as Pt) is reduced while the reduction of the Nb ₂ O ₅ component is reduced. Therefore, the coloring of the glass can be reduced. Therefore, the content of the Nb ₂ O ₅ component with respect to the total mass of the glass raw material having an oxide conversion composition is preferably 10.0%, more preferably 20.0%, and most preferably 30.0%. On the other hand, by setting the content of the Nb ₂ O ₅ component to 60.0% or less, the stability of the glass can be increased and the devitrification resistance can be increased. Therefore, the content of the Nb ₂ O ₅ component is preferably 60.0%, more preferably 58.0%, and most preferably 56.0% with respect to the total mass of the glass raw material having an oxide equivalent composition. Nb ₂ O ₅ component can contain the glass raw material by using, for example, _Nb 2 _{O 5} or the like.

Moreover, it is preferable that the glass raw material used by this invention contains antimony and / or tin. As a result, even if the oxygen component is removed more than necessary by clarification and stirring of the molten glass and an oxygen deficient state occurs in the molten glass, it is easily supplemented by oxygen atoms released from antimony and / or tin. More specifically, reduction of a transition metal component such as Nb ₂ O ₅ component in the molten glass, which can be caused by unnecessary removal of the oxygen component, is difficult to occur due to this oxygen atom. That is, it is possible to reduce the coloring of the glass by increasing the transmittance of the glass with respect to visible light on the short wavelength side, which tends to decrease due to the reduction of the transition metal component. In addition, especially when heat-treating glass, the inclusion of a small amount of antimony and / or tin promotes the oxidation of transition metal components such as Nb ₂ O ₅ component contained in the glass in a reduced state. Therefore, the glass can be dedistorted, and coloring can be reduced by increasing the transparency of the glass especially for visible light on the short wavelength side. Therefore, the mass sum of one or more selected from the group consisting of the Sb ₂ O ₃ component and the SnO ₂ component with respect to the total mass of the glass raw material having an oxide equivalent composition is preferably more than 0%, more preferably 0.00. The lower limit is 01%, and most preferably 0.02%.

Of these, the content of the Sb ₂ O ₃ component is preferably 1.0% or less. Thereby, since dissolution of the melting equipment (especially noble metals such as Pt) due to oxygen released from the Sb ₂ O ₃ component is reduced, it is possible to reduce the coloration of the glass caused by the dissolution of the melting equipment. Therefore, the content of the Sb ₂ O ₃ component with respect to the total mass of the glass raw material having an oxide conversion composition is preferably 1.0%, more preferably 0.5%, and most preferably from the viewpoint of reducing dissolution of the melting equipment. Has an upper limit of 0.3%. Sb ₂ O ₃ component is, for example, _{Sb 2 O 3, Sb 2 O} 5, Na may be contained in the glass raw material with _{2 H 2 Sb 2 O 7 ·} 5H 2 O and the like.

On the other hand, the content of the SnO ₂ component is preferably 0.5% or less. Thereby, since dissolution of the melting equipment (especially noble metals such as Pt) due to oxygen released from the SnO ₂ component is reduced, the coloration of the glass caused by the dissolution of the melting equipment can be reduced. Therefore, the content of the SnO ₂ component with respect to the total mass of the glass raw material having an oxide conversion composition is preferably 0.5%, more preferably 0.3%, and most preferably from the viewpoint of reducing dissolution of the melting equipment. The upper limit is 0.1%. SnO ₂ component, for example _SnO, can be contained in the glass raw material with SnO 2, SnO ₃ and the like.

Also, one or more mass sum is selected from the group consisting of _Sb 2 _{O 3} component and SnO ₂ component with respect to the total mass of the glass raw material of the oxide equivalent composition, preferably 1.0%, more preferably 0.5 %, Most preferably 0.3%.

The P ₂ O ₅ component is a glass forming component, a component that lowers the melting temperature of the glass, and is an optional component in the glass raw material. In particular, by reducing the content of the P ₂ O ₅ component to 40.0% or less, a decrease in the refractive index of the glass can be reduced. Therefore, the content of the P ₂ O ₅ component is preferably 40.0%, more preferably 35.0%, and most preferably 30.0% with respect to the total mass of the glass raw material having an oxide equivalent composition. Although P ₂ O ₅ component is possible to obtain a glass having the desired properties without containing, by setting the content of P ₂ O ₅ component to 10.0%, the glass in the visible light While improving the transmittance | permeability with respect to glass, stability of glass can be improved and devitrification resistance can be improved. Moreover, since the melting temperature of glass becomes low, reduction of the Nb ₂ O ₅ component due to evaporation of the oxygen component can be reduced. Therefore, the content of the P ₂ O ₅ component with respect to the total mass of the glass raw material having an oxide conversion composition is preferably 10.0%, more preferably 15.0%, and most preferably 20.0%. The P ₂ O ₅ component can be contained in the glass raw material using, for example, Al (PO ₃ ) ₃ , Ca (PO ₃ ) ₂ , Ba (PO ₃ ) ₂ , BPO ₄ , H ₃ PO _{4 and the} like.

The TiO ₂ component and the WO ₃ component are components that increase the refractive index and dispersion of the glass, and are optional components in the glass raw material. In particular, by setting the content of the TiO ₂ component and / or the WO ₃ component to a predetermined value or less, the stability of the glass can be enhanced and the devitrification resistance can be enhanced. Therefore, the content of the TiO ₂ component is preferably 30.0%, more preferably 28.0%, and most preferably 25.0% with respect to the total mass of the glass raw material having an oxide equivalent composition. . The content of the WO ₃ component is preferably 20.0%, more preferably 15.0%, and most preferably 10.0%. In addition, there is no technical disadvantage even if neither TiO ₂ component nor WO ₃ component is contained, but by making TiO ₂ component 0.1% or more, or WO ₃ component 0.1% or more, Desired high refractive index and high dispersion can be easily obtained. Therefore, the content of the TiO ₂ component is preferably 0.1%, more preferably 1.0%, and most preferably 2.0% with respect to the total mass of the glass raw material having an oxide equivalent composition. . The content of the WO ₃ component is preferably 0.1%, more preferably 1.0%, and most preferably 2.0%. The TiO ₂ component and the WO ₃ component can be contained in the glass raw material using, for example, TiO ₂ , WO ₃ or the like.

The Li ₂ O component, the Na ₂ O component, and the K ₂ O component are components that lower the glass transition point (Tg) and increase devitrification resistance during glass formation, and are optional components in the glass raw material. is there. In particular, by setting the content of one or more of the Li ₂ O component, Na ₂ O component and K ₂ O component to a predetermined value or less, a desired high refractive index can be easily obtained, and the stability of the glass can be improved. The occurrence of devitrification and the like can be reduced by increasing it. Therefore, the content of the Li ₂ O component is preferably 20.0%, more preferably 18.0%, and most preferably 15.0% with respect to the total mass of the glass raw material having an oxide equivalent composition. To do. The content of the Na ₂ O component is preferably 35.0%, more preferably 30.0%, and most preferably 25.0%. Further, the content of the K ₂ O component is preferably 20.0%, more preferably 15.0%, and most preferably 10.0%. Li ₂ O component, Na ₂ O component and K ₂ O component are, for example, Li ₂ CO ₃ , LiNO ₃ , LiF, Na ₂ CO ₃ , NaNO ₃ , NaF, Na ₂ SiF ₆ , K ₂ CO ₃ , KNO ₃ , _KF, can be contained in the glass raw material with KHF _2, K ₂ SiF ₆ and the like.

Furthermore, in this glass raw material, the mass sum of the content of the Rn ₂ O component (wherein Rn is one or more selected from the group consisting of Li, Na, and K) is 35.0% or less. preferable. In particular, when the mass sum of the contents of the Rn ₂ O component is 35.0% or less, a decrease in the refractive index of the glass can be suppressed, so that a desired high refractive index can be easily obtained. Moreover, since the stability of the glass is enhanced, the occurrence of devitrification or the like to the glass can be reduced. Therefore, the mass sum of the content of the Rn ₂ O component with respect to the total mass of the glass raw material having an oxide conversion composition is preferably 35.0%, more preferably 30.0%, and most preferably 25.0%. To do. An optical glass having desired characteristics can be obtained without containing any Rn ₂ O component. However, when the mass sum of the content of the Rn ₂ O component is 0.1% or more, glass can be obtained. While achieving high dispersion, the glass transition point (Tg) can be lowered and the water resistance of the glass can be increased. Moreover, since the liquidus temperature of glass becomes low, the devitrification resistance of glass can be improved more. Therefore, the mass sum of the content of the Rn ₂ O component with respect to the total mass of the glass raw material having an oxide conversion composition is preferably 0.1%, more preferably 3.0%, and most preferably 5.0%. To do.

The MgO component, CaO component, SrO component, and BaO component are components that increase the devitrification resistance of the glass by lowering the liquidus temperature of the glass, and are optional components in the glass raw material. In particular, by making the content of one or more of MgO component, CaO component, SrO component and BaO component below a predetermined level, desired high refractive index and high dispersion can be easily obtained, devitrification resistance and chemical durability. The decline in sex can be suppressed. Therefore, the content of the MgO component is preferably 5.0%, more preferably 4.0%, and most preferably 3.0% with respect to the total mass of the glass raw material having an oxide equivalent composition. The content of the CaO component is preferably 10.0%, more preferably 8.0%, and most preferably 5.0%. Further, the content of the SrO component is preferably 10.0%, more preferably 8.0%, and most preferably 5.0%. The content of the BaO component is preferably 30.0%, more preferably 28.0%, and most preferably 25.0%. Examples of the MgO component, CaO component, SrO component, and BaO component include MgCO ₃ , MgF ₂ , CaCO ₃ , CaF ₂ , Sr (NO ₃ ) ₂ , SrF ₂ , BaCO ₃ , Ba (NO ₃ ) ₂ , BaF _2, etc. It can be used and contained in the glass raw material.

  The glass raw material preferably has a mass sum of the content of the RO component (wherein R is one or more selected from the group consisting of Mg, Ca, Sr, and Ba) of 30.0% or less. Thereby, since the fall of the refractive index and dispersion | distribution by RO component is suppressed, it can make it easy to obtain desired high refractive index and high dispersion | distribution. Therefore, the mass sum of the content of the RO component with respect to the total mass of the glass raw material having an oxide equivalent composition is preferably 30.0%, more preferably 25.0%, and most preferably 20.0%. An optical glass having desired characteristics can be obtained without containing any RO component, but the liquid phase temperature of the glass is lowered by containing at least one of the RO components in an amount of 0.1% or more. Therefore, the devitrification resistance of the glass can be further increased. Therefore, in this case, the mass sum of the RO component content with respect to the total mass of the glass raw material having an oxide conversion composition is preferably 0.1%, more preferably 0.5%, and most preferably 1.0%. And

The La ₂ O ₃ component, the Gd ₂ O ₃ component, and the Y ₂ O ₃ component are components that increase the refractive index of the glass and improve the chemical durability of the glass, and are optional components in the glass raw material. In particular, by increasing the content of the Ln ₂ O ₃ component (wherein Ln is one or more selected from the group consisting of Y, La and Gd) to a predetermined level or less, the Abbe number is increased by the Ln ₂ O ₃ component Therefore, desired high dispersion can be easily obtained. Further, when the content of Ln ₂ O ₃ component to a predetermined or less, the liquidus temperature of the glass is lowered, it is possible to increase the light transmittance to increase the devitrification resistance of the glass. Therefore, the content of each of the Ln ₂ O ₃ components with respect to the total mass of the glass raw material having an oxide conversion composition is preferably 10.0%, more preferably 8.0%, and most preferably 5.0%. To do. Further, the total content of the Ln ₂ O ₃ components with respect to the total mass of the glass raw material having an oxide conversion composition is preferably 20.0%, more preferably 18.0%, and most preferably 15.0%. To do. The Ln ₂ O ₃ component uses, for example, Y ₂ O ₃ , YF ₃ , La ₂ O ₃ , La (NO ₃ ) ₃ .XH ₂ O (X is an arbitrary integer), Gd ₂ O ₃ , GdF _{3 and the} like. Can be contained in glass raw materials.

The SiO ₂ component and the B ₂ O ₃ component are components that reduce coloration and increase the transmittance for visible light having a short wavelength, and lower the liquidus temperature of the glass to increase the devitrification resistance of the glass. It is an optional component in the raw material. In particular, by making the content of the SiO ₂ component and / or B ₂ O ₃ component 10.0% or less, a decrease in the refractive index due to the SiO ₂ component and / or B ₂ O ₃ component can be suppressed. A high refractive index can be easily obtained. Accordingly, the content of the SiO ₂ component and / or the B ₂ O ₃ component with respect to the total mass of the glass raw material having an oxide equivalent composition is preferably 10.0%, more preferably 8.0%, and even more preferably 5.0. % Is the upper limit, most preferably less than 2.0%. Examples of the SiO ₂ component and the B ₂ O ₃ component include SiO ₂ , K ₂ SiF ₆ , Na ₂ SiF ₆ , H ₃ BO ₃ , Na ₂ B ₄ O ₇ , Na ₂ B ₄ O ₇ · 10H ₂ O, and BPO _4. Etc. can be contained in the glass raw material.

The GeO ₂ component is a component that increases the refractive index of the glass and lowers the liquidus temperature of the glass to increase the devitrification resistance of the glass, and is an optional component in the glass raw material. In particular, the material cost of glass can be reduced by setting the content of the GeO ₂ component to 10.0% or less. Therefore, the content of the GeO ₂ component with respect to the total mass of the glass raw material having an oxide conversion composition is preferably 10.0%, more preferably 8.0%, and most preferably 5.0%. GeO ₂ component can contain the glass raw material by using, for example, GeO ₂ or the like.

Bi ₂ O ₃ component, increasing the refractive index of the glass, or to enhance the dispersion of the glass, which is an optional component in the glass material. In particular, by setting the content of the Bi ₂ O ₃ component to 20.0% or less, the liquidus temperature of the glass can be lowered to suppress the loss of devitrification resistance. Can be suppressed. Therefore, the content of the Bi ₂ O ₃ component with respect to the total mass of the glass raw material having an oxide conversion composition is preferably 20.0%, more preferably 15.0%, and even more preferably less than 10.0%. And most preferably less than 5.0%.

The ZrO ₂ component is a component that increases the transmittance for visible light and increases the devitrification resistance of the glass to increase the devitrification resistance of the glass, and is an optional component in the glass raw material. In particular, by making the content of the ZrO ₂ component 10.0% or less, a decrease in the refractive index due to the ZrO ₂ component can be suppressed, so that a desired high refractive index can be easily obtained. Therefore, the content of the ZrO ₂ component with respect to the total mass of the glass raw material having an oxide equivalent composition is preferably 10.0%, more preferably 8.0%, and most preferably 5.0%. ZrO ₂ component can contain in the glass raw material by using, for example, a _ZrO 2, ZrF _4, and the like.

A ZnO component is a component which raises the devitrification resistance of glass by lowering | hanging the liquidus temperature of glass, and is an arbitrary component in a glass raw material. In particular, the desired high refractive index and high dispersion can be easily obtained by setting the content of the ZnO component to 10.0% or less. Accordingly, the content of the ZnO component with respect to the total mass of the glass raw material having an oxide equivalent composition is preferably 10.0%, more preferably 8.0%, and most preferably 5.0%. ZnO components are, for example ZnO, can be contained in the glass raw material with ZnF ₂ and the like.

The Al ₂ O ₃ component is a component that improves the chemical durability of the glass and increases the viscosity when the glass is melted, and is an optional component in the glass raw material. In particular, by setting the content of the Al ₂ O ₃ component to 10.0% or less, the devitrification tendency of the glass can be weakened while improving the meltability of the glass. Therefore, the upper limit of the content of the Al ₂ O ₃ component with respect to the total mass of the glass raw material having an oxide equivalent composition is preferably 10.0%, more preferably 8.0%, and most preferably 5.0%. The Al ₂ O ₃ component can be contained in the glass raw material using, for example, Al ₂ O ₃ , Al (OH) ₃ , AlF ₃ or the like as the raw material.

Ta ₂ O ₅ component is a component that raises the refractive index of the glass, which is an optional component in the glass material. In particular, by making the content of the Ta ₂ O ₅ component 10.0% or less, it is possible to make the glass difficult to devitrify. Therefore, the content of the Ta ₂ O ₅ component with respect to the total mass of the glass raw material having an oxide equivalent composition is preferably 10.0%, more preferably 8.0%, and most preferably 4.0%. The Ta ₂ O ₅ component can be contained in the glass raw material using, for example, Ta ₂ O ₅ as a raw material.

<About ingredients that should not be included>
Other components can be added to the glass raw material as needed within a range that does not impair the properties of the glass. However, the transition metal components such as V, Cr, Mn, Fe, Co, Ni, Cu, Ag and Mo, excluding the above-mentioned components, are more likely to cause glass coloring than Nb, Ti and W, for example. Because of its strong nature, the effects relating to the light transmittance of the present invention can be easily reduced. Therefore, it is preferable to reduce the content of these transition metal components, and it is more preferable that they are not substantially contained.

  In addition, lead compounds such as PbO and components of Th, Cd, Tl, Os, Be, and Se tend to be refrained from being used as harmful chemical substances in recent years. In addition, measures for environmental measures are required until disposal after commercialization. Therefore, when importance is placed on the environmental impact, it is preferable not to substantially contain them except for inevitable mixing. As a result, the optical glass is substantially free of substances that pollute the environment. Therefore, the optical glass can be manufactured, processed, and discarded without taking special environmental measures.

[Production of optical glass]
In the production method of the present invention, an optical glass is produced by performing a melting step, a clarification step, a stirring step, an outflow step, and a forming step on the glass raw material.

<Glass melting device>
In these melting step, clarification step, stirring step and outflow step, for example, a glass melting apparatus 1 including a melting tank 11, a clarification tank 12, and a stirring tank 13 as shown in FIG. 1 is used. In FIG. 1, the melting tank 11 and the clarification tank 12 are communicated by a communication pipe 16, and the clarification tank 12 and the stirring tank 13 are communicated by a communication pipe 17. Here, the melting tank 11 performs a melting process for melting the glass raw material S, the clarification tank 12 performs a clarification process for clarifying the glass, and the stirring tank 13 performs a stirring process for stirring the glass. Thereby, since the molten glass G flows in order of the melting tank 11, the clarification tank 12, and the stirring tank 13, the melting tank 11, the clarification comprised with the material suitable for the temperature, oxygen concentration, etc. of the molten glass G in each process. A tank 12 and a stirring tank 13 can be used. That is, reduction of Nb ₂ O ₅ due to excessive heating of the molten glass G can be reduced while reducing elution of the components of the glass melting apparatus 1 into the molten glass G having a high oxygen concentration. Accordingly, it is possible to obtain an optical glass that has high dispersion and little coloration.

  Specifically, the melting tank 11, the clarification tank 12, and the stirring tank 13 are made of quartz, platinum, and a platinum alloy with at least a part of the portion (the vessel walls 111, 121, 131) in contact with the raw glass S and / or the molten glass G. It is preferable to comprise at least one selected from the group consisting of Thereby, the melting tank 11, the clarification tank 12, and the stirring tank 13 can endure the heat of the molten glass G.

  Here, with respect to at least one of the melting tank 11, the clarification tank 12, and the stirring tank 13, it is preferable that at least a part of a portion where the raw glass S and / or the molten glass G is in contact is made of quartz. Thereby, since reaction with the molten glass G before oxygen concentration is reduced by clarification and stirring among at least one of the melting tank 11, the clarification tank 12, and the stirring tank 13 is reduced, the glass to the molten glass G is reduced. Elution of the components of the melting apparatus 1 can be reduced, and optical glass with less coloring can be formed.

In particular, at least a part of the portion (the vessel walls 111 and 121) of the melting tank 11 and the clarification tank 12 in contact with the raw glass S and / or the molten glass G is made of quartz, while the raw glass S in the stirring tank 13. And / or at least a part of the part (container wall 131) in contact with the molten glass G is preferably composed of platinum or a platinum alloy. Thereby, while the elution to the molten glass G of the component contained in the melting tank 11 and the clarification tank 12 in which the molten glass G with a particularly high oxygen concentration is stored is reduced, the stirring tank 13 is free of platinum or a platinum alloy. By increasing the thermal conductivity of the container wall 131 by electrons, even if bubbles are included in the molten glass G, the thermal uniformity of the molten glass G is increased. Therefore, the elution of the components of the glass melting apparatus 1 into the molten glass G and the coloring of the optical glass through the reduction of Nb ₂ O ₅ due to local excessive heating of the molten glass G can be reduced.

The supply of the glass raw material S to the melting tank 11, the supply of the molten glass G from the melting tank 11 to the clarification tank 12, and the supply of the molten glass G from the clarification tank 12 to the stirring tank 13 are preferably performed continuously. . Thereby, since the temperature of the molten glass G stored in the tank to which the glass raw material S or the molten glass G is supplied is less likely to fluctuate, excess gas components contained in the molten glass G due to local cooling of the molten glass G And the coloring of the optical glass due to the reduction of Nb ₂ O ₅ by local excessive heating of the molten glass G can be reduced. On the other hand, the supply of the glass raw material S to the melting tank 11, the supply of the molten glass G from the melting tank 11 to the clarification tank 12, and the supply of the molten glass G from the clarification tank 12 to the stirring tank 13 are performed intermittently. It is also preferable. As a result, a time during which the molten glass G and the glass raw material S containing a large amount of excess gas components are not supplied is generated, so that the excess glass components contained in the molten glass G are sufficiently discharged. It can be sent to a tank made of a different material in the next process.

<Bubbling>
The production method of the present invention preferably includes a step of bubbling gas in the molten glass G. Thereby, the discharge of the oxygen component contained in the molten glass G is promoted, and the concentration of the oxygen component is appropriately adjusted in a short time, so that the transition metal component such as the Nb ₂ O ₅ component contained in the molten glass G Since reduction and elution of components (particularly noble metals such as Pt) contained in the glass melting apparatus 1 into the molten glass G can be reduced, an optical glass with little coloring can be obtained.

  Bubbling is preferably performed before the molten glass G is stored in the tank provided with the outflow means 14 or before the molten glass G flows out of the outflow means 14, more specifically, When the molten glass G is stored in the melting tank 11 and / or the clarification tank 12, it is preferable to carry out the melting process and / or the clarification process. As a result, the gas supplied to the molten glass G can be easily discharged between the bubbling tank and the stirring tank 13, so that it is difficult for bubbles to flow out from the outflow means 14, and bubbles are formed in the optical glass. Can be reduced.

  Here, the gas to be bubbled is appropriately selected from gases that hardly dissolve in the molten glass G and have little unnecessary reaction with the molten glass G.

Among them, it is preferable to use an oxidizing gas as a gas to be bubbled. Accordingly, since the transition metal component of the Nb ₂ O ₅ component or the like contained in a reduced state in the molten glass G is oxidized, it can reduce the coloration of the optical glass by reduction of the transition metal component. Examples of the oxidizing gas include oxygen (O ₂ ), ozone (O ₃ ), or a mixed gas of one or more of these gases, and it is particularly preferable to use oxygen. In particular, the use of oxygen makes it difficult for the gas to be bubbled to react with components other than the transition metal contained in the molten glass G, so that an optical glass having desired characteristics can be easily obtained.

  In the case of using an oxidizing gas, the melting tank 11 and / or the clarification tank 12 for bubbling are made of quartz at least part of the portion (the vessel walls 111 and 121) in contact with the raw glass S and / or the molten glass G. It is preferable. Thereby, since the elution of the components contained in the melting tank 11 and / or the fining tank 12 due to the molten glass G being combined with the oxidizing gas is reduced, the coloring of the optical glass due to these components can be reduced.

On the other hand, it is also preferable to use a non-oxidizing gas as a gas to be bubbled. As a result, the discharge of the oxygen component contained in the molten glass G is promoted, and the component (particularly a noble metal such as Pt) contained in the glass melting apparatus caused by the excess oxygen component contained in the molten glass G leads to the molten glass G. By reducing the elution of the optical glass, the coloring of the optical glass can be reduced. Non-oxidizing gases include, for example, helium (He), neon (Ne), argon (Ar), krypton (Kr) or xenon (Xe), inert gas such as nitrogen (N ₂ ), carbon monoxide (CO) or hydrogen (H ₂₎ a reducing gas such as, or is one or more mixed gas of these gases and the like, it is preferable to use particularly inert gases. Thereby, since the chemical reaction between the gas supplied to the molten glass G and the molten glass G is suppressed, it becomes difficult for the gas to be taken into the molten glass G. Less susceptible to adverse effects.

  A reducing gas may be used as the gas supplied to the molten glass G. When the oxygen component taken in from the molten glass G reacts with the reducing gas, the oxygen partial pressure of the gas after taking in the oxygen component is reduced. Therefore, the non-oxidizing gas after taking in the oxygen component can further easily take in the oxygen component.

When a non-oxidizing gas is used, at least one of the melting tank 11, the clarification tank 12, and the stirring tank 13 is at least one of the portions (the vessel walls 111, 121, 131) with which the raw glass S and / or the molten glass G are in contact. The part is preferably composed of platinum or a platinum alloy. Thereby, while elution of the components contained in the melting tank 11, the clarification tank 12 and / or the stirring tank 13 is reduced, the thermal conductivity of the vessel walls 111, 121, 131 is increased, so that bubbles are formed in the molten glass G. Even if it is contained, the soaking property of the molten glass G is enhanced. Therefore, the elution of the components of the glass melting apparatus 1 into the molten glass G and the coloring of the optical glass due to the reduction of Nb ₂ O ₅ by local excessive heating of the molten glass G can be reduced.

  The gas supply means for bubbling is not particularly limited as long as the gas can be supplied into the molten glass G. In the present embodiment, the gas supply that opens in the molten glass G of the melting tank 11 and / or the clarification tank 12 is provided. The gas supply device 2 includes pipes 21 and 22, gas supply valves 23 and 24 provided in the gas supply pipes 21 and 22, and a gas supply source 25 provided in the gas supply valves 23 and 24. Gas is supplied from the openings of the gas supply pipes 21 and 22 while the timing and supply speed of supplying the gas from the gas supply source 25 are adjusted by the gas supply valves 23 and 24. Therefore, bubbling suitable for the amount of the molten glass G stored in the melting tank 11 and / or the clarification tank 12 and the length of time for which the molten glass G is stored in the melting tank 11 and / or the clarification tank 12 is performed. Can do.

  Here, it is preferable that the gas supply pipes 21 and 22 are formed of quartz, platinum, or a platinum alloy at least at a portion in contact with the molten glass G. Thereby, since the gas supply pipes 21 and 22 can endure the heat of the molten glass G and the reaction between the gas supply pipes 21 and 22 and the molten glass G is reduced, the bubbling to the molten glass G can be performed reliably. Thus, an optical glass having desired characteristics can be formed. In particular, when the portion in contact with the molten glass G is formed of platinum or a platinum alloy, it is preferable that at least a part of the gas supply pipes 21 and 22 extend upward from the openings 211 and 221. As a result, the portion of the molten glass G in contact with the gas supply pipes 21 and 22 is easily removed of excess oxygen components by the bubbles supplied from the openings 211 and 221, so that the platinum components from the gas supply pipes 21 and 22 are removed. Elution can also be reduced, and the life of the gas supply pipes 21 and 22 can be extended.

<Melting process>
In the melting step, the glass raw material S supplied to the melting tank 11 is melted to form a molten glass G. Here, the method of forming the molten glass G is appropriately selected depending on the properties of the glass raw material S.

  For example, it is preferable to melt a batch made of glass raw material S that has not been vitrified by a single heating operation and to perform vitrification of glass raw material S and formation of molten glass G at the same time. Thereby, the molten glass G is formed with a small heating time, and the contact time between the glass raw material S and the melting tank 11 is reduced. Therefore, the components contained in the melting tank 11 (especially noble metals such as Pt) into the glass. Coloring due to elution can be reduced.

On the other hand, among the glass raw materials S, a cullet obtained by cooling at least a part by melting one or more kinds containing Nb ₂ O ₅ component, which is said to be difficult to melt and vitrify, is made into other glass raw materials and others. It is also preferable to mix and melt the cullet. Thereby, melting and vitrification are facilitated by being divided into a plurality of times, and the generation rate of bubbles from the glass raw material S and the molten glass G is reduced, so that the soaking properties of the glass raw material S and the molten glass G are reduced. Therefore, an optical glass having a more uniform composition and characteristics can be obtained.

The melting temperature at which the glass raw material S is melted in the melting step is appropriately selected from temperatures at which the glass raw material S can be melted and vitrified after cooling. More specifically, the melting temperature is preferably 1000 ° C. or higher, more preferably 1030 ° C. or higher, and most preferably 1050 ° C. or higher. Thereby, since the glass raw material S becomes easy to be melt | dissolved and it becomes difficult to produce undissolved residue, a homogeneous optical glass can be obtained after the stirring process mentioned later. On the other hand, the melting temperature is preferably less than 1300 ° C, more preferably less than 1250 ° C, and most preferably less than 1240 ° C. By setting the melting temperature to a predetermined temperature or less, excessive evaporation of the oxygen component from the molten glass G is reduced, so that coloring of the optical glass due to reduction of the Nb ₂ O ₅ component can be reduced.

  The “melting temperature” in the present specification refers to the average of the temperature of the glass raw material S in the upper part of the melting tank 11 and the temperature of the glass raw material S in the lower part of the melting tank 11. Here, the temperature of the glass raw material S in the upper part and the lower part of the melting tank 11 can be calculated | required using the thermocouple which is not shown in the inside of the melting tank 11, and the wall surface. Moreover, you may obtain | require the temperature of the glass raw material S in the upper part of the melting tank 11 using a radiation thermometer.

  The melting time for melting the glass material S in the melting step is appropriately selected from the time during which the glass material S can be melted and the elution of components from the melting tank 11 can be reduced. More specifically, the melting time of the glass raw material S is preferably 0.01 hours or more, more preferably 0.1 hours or more, and most preferably 0.2 hours or more. Thereby, since the undissolved residue of the glass raw material S does not easily occur in the molten glass G, a homogeneous optical glass can be obtained. On the other hand, the melting time is preferably 10 hours or less, more preferably 8 hours or less, and most preferably 7 hours or less. Thereby, since the molten glass G which has been vitrified to some extent is sent to the clarification tank 12, the proportion of the unreacted glass raw material S stored in the melting tank 11 is increased, and the vitrification of the glass raw material S is facilitated. it can. In particular, when the melting tank 11 is made of platinum or a platinum alloy, the contact time between the molten glass G and the melting tank 11 is reduced. Glass can be easily obtained.

The “melting time” in the specification of the present application indicates an average time during which the glass raw material S stays in the melting tank 11. For example, when the supply and discharge rates of the glass raw material S are constant, the supply of the glass raw material S to the melting tank 11 is started (when the glass raw material S is heated to the melting temperature after the glass raw material S is supplied, it is supplied. The time from the time when the temperature of the glass raw material S reaches the above melting temperature) to the time when the discharge of the glass raw material S from the melting tank 11 is started (or the time when the glass raw material S shifts to the clarification step described later) is Δt _ab [h ] When the supply of the glass raw material S to the melting tank 11 is completed (when the glass raw material S is heated to the melting temperature after the supply of the glass raw material S, the temperature of the supplied glass raw material S reaches the melting temperature described above. When the time from the point of time) to the point of time when the discharge of the glass raw material S from the melting tank 11 is completed (or the point of time when the clarification process is described later) is Δt _cd [h], the melting time Δt ₁ [h] is ,below (1) obtained from the.

<Clarification process>
In the clarification process, the glass raw material S melted in the melting process is retained in the clarification tank 12 for a predetermined time to be clarified. As a result, the vitrification of the glass raw material S is further promoted, and excess gas components (for example, oxygen atoms and hydrogen atoms) generated by vitrification become bubbles and are easily discharged from the clarification tank 12. Therefore, devitrification of the glass can be reduced, and elution of components (particularly noble metals such as Pt) contained in the glass melting apparatus 1 into the glass can be reduced. Therefore, it is possible to make it difficult to reduce the light transmittance of visible light of the optical glass. The “molten glass” in the present specification includes not only the molten glass material S after vitrification but also the molten glass material S before vitrification.

The clarification temperature at which the molten glass G is clarified in the clarification step is appropriately selected from temperatures at which vitrification can proceed, but is preferably a temperature higher than the melting temperature. More specifically, the fining temperature in the fining step is preferably 1020 ° C. or higher, more preferably 1050 ° C. or higher, and most preferably 1080 ° C. or higher. Thereby, while the efficiency of vitrification of the glass raw material S is enhanced, the viscosity of the molten glass G becomes small, and bubbles containing a non-oxidizing gas and an excess gas component easily float the molten glass G. An optical glass with less devitrification and bubbles can be easily obtained. Moreover, since the oxygen concentration in the molten glass G can be reduced, also when the stirring tank 13 is comprised with platinum or a platinum alloy, the elution to the molten glass G of the component contained in the stirring tank 13 can be reduced. On the other hand, the fining temperature is preferably less than 1300 ° C, more preferably less than 1250 ° C, and most preferably less than 1240 ° C. By setting the fining temperature to a predetermined temperature or less, excessive evaporation of the oxygen component from the molten glass G is reduced, so that coloring of the optical glass due to reduction of the Nb ₂ O ₅ component can be reduced.

  The “clarification temperature” in the present specification refers to the average of the temperature of the molten glass G in the upper part of the clarification tank 12 and the temperature of the molten glass G in the lower part of the clarification tank 12. Here, the temperature of the molten glass G in the upper part and the lower part of the clarification tank 12 can be determined using a thermocouple (not shown) provided in the clarification tank 12 or on the wall surface. Moreover, you may obtain | require the temperature of the molten glass G in the upper part of the clarification tank 12 using a radiation thermometer.

The clarification time during which the molten glass G is retained in the clarification step is preferably 0.01 hours or more, more preferably 0.2 hours or more, and most preferably 0.3 hours or more. Thereby, since vitrification of molten glass G and discharge of bubbles containing a non-oxidizing gas and an excess gas component are advanced, an optical glass with less devitrification and bubbles can be obtained. On the other hand, the clarification time is preferably 10 hours or less, more preferably 8 hours or less, and most preferably 5 hours or less. Thereby, since excessive evaporation of the oxygen component from the molten glass G is reduced, coloring of the optical glass due to reduction of the Nb ₂ O ₅ component can be reduced. In particular, when the clarification tank 12 is made of platinum or a platinum alloy, the contact time between the molten glass G and the clarification tank 12 is reduced. Glass can be easily obtained.

In addition, “clarification time” in the specification of the present application indicates an average time during which the molten glass G stays in the clarification tank 12. For example, when the supply speed of the glass raw material S and the discharge speed of the molten glass G are constant, from the time of starting the supply of the glass raw material S to the clarification tank 12 (or the time of shifting from the melting process to the clarification process). Δt _ab ′ [h] is the time until the start of discharge of the molten glass G from the clarification tank 12 (or the time of transition to the stirring step described later), and the supply of the glass raw material S to the melting tank 11 is completed. Δt _cd ′ is the time from the time point (or the time point when the melting process is shifted to the clarification process) to the time point when the discharge of the molten glass G from the clarification tank 12 is completed (or the time point when the process moves to the stirring process described later). when the [h], fining time Delta] t ₂ [h] is determined from the following equation (2).

<Stirring step>
In the stirring step, the clarified molten glass G is stirred in the stirring tank 13. Since excess gas components are taken into the non-oxidizing gas bubbles remaining in the molten glass G and the bubbles remaining in the molten glass G are easily discharged to the outside of the agitation tank 13, it is possible to obtain an optical glass with few bubbles. it can. At the same time, since the uniformity of the composition of the molten glass G is enhanced, fluctuations in the characteristics of the optical glass to be formed can be reduced.

  The stirring means 4 for stirring the molten glass G in the stirring step is appropriately selected depending on the viscosity of the molten glass G, the shape of the stirring tank 13, and the like. Here, in the stirring means 4, the stirring blade 41 is provided in the vicinity of the bottom surface and / or the wall surface of the stirring tank 13, and the stirring blade 41 runs along the bottom surface and / or the wall surface of the stirring tank 13 with the rotating shaft 43 as an axis. It is preferable to rotate. Thereby, the flow of the molten glass G is formed along the bottom surface and the wall surface of the agitation tank 13, so that the bubbles are efficiently removed from the bottom surface and the wall surface of the agitation tank 13 in which bubbles are easily formed. In particular, the stirring blade 41 of the stirring means 4 is preferably provided along the bottom surface of the stirring tank 13. Thereby, also when discharging all the molten glass G from the stirring tank 13, since the molten glass G is stirred until immediately before the stirring tank 13 is emptied, bubbles are formed from the start to the end of the outflow process. Can be reduced.

  Of the stirring means 4, the material of the portion that contacts the molten glass G, such as the stirring blade 41 and the rotating shaft 43, is appropriately selected from materials that have low reactivity with the molten glass G and can withstand the temperature of the stirring process. Selected. More specifically, one or more selected from the group consisting of quartz, platinum and platinum alloys can be mentioned, and among these, platinum and / or platinum alloys are preferable. In particular, by using platinum and / or a platinum alloy, the toughness of the stirring blade 41 and the rotating shaft 43 is enhanced, so that the breakage of the stirring blade 41 and the rotating shaft 43 when the molten glass G is stirred can be reduced. It is possible to extend the service life.

The stirring temperature at which the molten glass G is stirred in the stirring step is preferably a refrigeration temperature or lower. More specifically, the highest temperature among the stirring temperatures in the stirring step is preferably less than 1300 ° C, more preferably less than 1250 ° C, and most preferably less than 1240 ° C. Thereby, while the bubbles containing the non-oxidizing gas remaining in the molten glass G are removed, it is difficult for the oxygen component contained in the molten glass G to evaporate more than necessary. Therefore, optical glass with little coloring can be obtained by reducing the reduction of the Nb ₂ O ₅ component while reducing the elution of the components contained in the stirring tank 13 and the stirring means 4 into the molten glass G. On the other hand, the lowest temperature among the stirring temperatures is preferably 1000 ° C. or higher, more preferably 1050 ° C. or higher, and most preferably 1100 ° C. or higher. Thereby, since the viscosity of the molten glass G does not become too high, the load applied to the stirring means 4 is reduced while bubbles are easily removed. Therefore, the stirring step can be performed efficiently and the life of the stirring means 4 can be extended.

  In addition, since this stirring temperature should just exist in the temperature range which can discharge | emit the bubble contained in the molten glass G, it does not necessarily need to be constant temperature over the predetermined time which performs a stirring process. At this time, the highest temperature among the stirring temperatures is preferably a temperature equal to or lower than the clarification temperature from the viewpoint of reducing unnecessary evaporation of the oxygen component contained in the molten glass G, but temporarily discharges bubbles. In order to promote, the temperature may be higher than the fining temperature.

  Moreover, it is preferable to use the average temperature in the several location of the molten glass G which retains in the stirring tank 13 in the stirring process as "stirring temperature" in this specification. More specifically, it is preferable to use the average of the temperature of the molten glass G in the upper part of the stirring tank 13 and the temperature of the molten glass G in the lower part of the stirring tank 13. Accordingly, even when a temperature gradient is generated inside the molten glass G, coloring of the molten glass G can be easily suppressed, and thus an optical glass having a high visible light transmittance can be easily obtained. . Here, the temperature of the molten glass G in the upper part and the lower part of the stirring tank 13 can be obtained using a thermocouple (not shown) provided in the stirring tank 13 or on the wall surface. Moreover, you may obtain | require the temperature of the molten glass G in the upper part of the stirring tank 13 using a radiation thermometer.

  The stirring time for stirring the molten glass G in the stirring tank 13 is preferably 0.01 hours or more, more preferably 0.2 hours or more, and most preferably 0.3 hours or more. Thereby, since the air bubbles contained in the molten glass G are easily removed, the air bubbles can be hardly left in the optical glass. On the other hand, the stirring time is preferably 10 hours or less, more preferably 8 hours or less, and most preferably 5 hours or less. As a result, reduction of the transition metal component due to evaporation of the oxygen component contained in the molten glass G is reduced. In particular, when the stirring vessel 13 is made of platinum or a platinum alloy, the molten glass of the component contained in the stirring vessel 3 Elution to G is also reduced. Therefore, it is possible to easily obtain an optical glass that has both the small number of bubbles and the high light transmittance.

In addition, “stirring time” in the present specification refers to an average time during which the molten glass G is stirred by the stirring means 4. For example, when the supply speed of the molten glass G to the stirring tank 13 and the discharge speed from the stirring tank 13 are equal and constant and the stirring of the molten glass G is always performed in the stirring tank 13, the molten glass G is stored in the stirring tank 13. When the volume of the molten glass G is V [m ³ ] and the supply rate and discharge rate of the molten glass G supplied to and discharged from the stirring tank 13 is v [m ³ / h], the stirring time Δt ₃ [h] Is generally obtained from the following equation (3).
Δt ₃ = V / v (3)
In addition, when the molten glass G does not flow into the stirring tank 13 and is not discharged from the stirring tank 13 during the stirring process, the stirring of the molten glass G by the stirring means 4 is started. T _S , and when the stirring time of the molten glass G by the stirring means 4 is t _G , the stirring time Δt ₃ [h] is obtained from the following equation (4).
Δt ₃ = t _G −t _S (4)

<Outflow process>
In the outflow process, the stirred molten glass G is caused to flow out of the stirring tank. Thereby, since the flow of the molten glass G is formed, the optical glass having a high visible light transmittance can be continuously and / or intermittently formed into a desired shape.

  Here, the outflow means 14 that causes the molten glass G to flow out in the outflow process is an outflow pipe extending from the stirring tank 13 as shown in FIG. 1, for example.

  The outflow temperature at which the molten glass G flows out in the outflow step is preferably lower than the fining temperature and the stirring temperature. More specifically, the outflow temperature in the outflow step is preferably less than 1200 ° C, more preferably less than 1180 ° C, and most preferably less than 1150 ° C. Thereby, since reduction | restoration of the transition metal component by evaporation of the oxygen component contained in the molten glass G and the elution to the molten glass G of the component contained in the outflow means 14 are suppressed, coloring of optical glass can be reduced. On the other hand, this outflow temperature is preferably 1020 ° C or higher, more preferably 1050 ° C or higher, and most preferably 1060 ° C or higher. Thereby, desired fluidity | liquidity is ensured in a fluid glass and the flow volume of the molten glass G becomes substantially constant, Therefore The clogging of the molten glass G in an outflow means and the shaping | molding defect of optical glass can be reduced.

  The “outflow temperature” in the present specification refers to the temperature of the molten glass G in the outflow means 14. Here, the temperature of the molten glass G in the outflow means 14 can be obtained using a thermocouple (not shown) provided on the wall surface of the outflow means 14 or a radiation thermometer.

<Molding process>
In the forming step, the molten glass G supplied at a predetermined flow rate is formed by the forming means 5. Thereby, since the molten glass G is formed into a predetermined shape by the forming means 5 and loses its fluidity, evaporation of gas components from the molten glass G and reduction of Nb ₂ O ₅ are stopped. Can be obtained.

  Here, it is preferable that the shaping | molding temperature which shape | molds the molten glass G at a shaping | molding process is a temperature below a clarification temperature and stirring temperature similarly to the above-mentioned outflow temperature. More specifically, it is preferably less than 1200 ° C, more preferably less than 1150 ° C, and most preferably 1100 ° C or less. As a result, reduction of the transition metal component due to evaporation of the oxygen component contained in the molten glass G is suppressed, and rapid temperature fluctuations when the molten glass G and the forming means 5 come into contact are reduced. And an optical glass with few cracks can be obtained. On the other hand, the outflow temperature is preferably 900 ° C. or higher, more preferably 1000 ° C. or higher, and most preferably 1050 ° C. or higher. Thereby, since the desired fluidity | liquidity is ensured to fluid glass, the shaping | molding defect of optical glass can be reduced.

  The “molding temperature” in the present specification refers to the temperature of the molding means 5 when the molten glass G contacts the molding means 5 such as a mold. Here, the temperature at which the molten glass G contacts the forming means 5 can be obtained using a radiation thermometer.

In the manufacturing method of this invention, it is preferable to heat-process with respect to the glass shape | molded by the formation process. Thereby, even if the reduced Nb ₂ O ₅ component is contained in the molded glass, the Nb ₂ O ₅ component can be oxidized to reduce the coloring of the glass. Here, in the glass formed in the present invention, the platinum component such as Pt contained in the glass melting device 1 is reduced by the glass melting device 1 described above, so that it is difficult to remove even by heat treatment. Has been reduced.

[Optical glass]
The optical glass produced according to the present invention needs to have a high refractive index (n _d ) and a high dispersion. In particular, the refractive index ( _nd ) of the optical glass is preferably 1.75, more preferably 1.80, most preferably 1.84, preferably 2.30, more preferably 2.20, most preferably 1.84. The upper limit is preferably 2.10. Further, the Abbe number (ν _d ) of the optical glass is preferably 29, more preferably 27, still more preferably 25, and most preferably 19. As a result, the degree of freedom in optical design is increased, and a large amount of light refraction can be obtained even if the device is made thinner. In particular, since the method of the present invention contains the Nb ₂ O ₅ component, the Abbe number (νd) is less than 19, more specifically less than 18.5, and more specifically less than 18. It is also useful when producing the optical glass. In addition, the lower limit of the Abbe number (ν _d ) of the optical glass is not particularly limited and is appropriately determined according to the technical level. The Abbe number (ν _d ) of the optical glass obtained by the present invention is approximately It is often 10 or more, specifically 12 or more, and more specifically 15 or more.

  Moreover, the optical glass produced by the present invention is less colored. In particular, the optical glass produced according to the present invention has a spectroscopic analysis of light having a wavelength of 420 nm with a sample having a thickness of 10 mm after a reheating test in which the temperature is raised to a reheating temperature of (Tg-100) ° C. or higher and (Tg + 100) ° C. or lower. The transmittance is preferably 20% or more, more preferably 25% or more, and most preferably 30% or less. Thereby, the transparency with respect to the visible light of glass is improved, and coloring is reduced. That is, an optical element such as a lens having desired optical characteristics can be produced from this optical glass. The lower limit of the spectral transmittance of the optical glass with respect to the light having a wavelength of 420 nm is not particularly limited, and is appropriately determined according to the technical level. In many cases, the lower limit of the rate is approximately 85% or less, specifically 80% or less, and more specifically 78% or less.

  Here, the optical glass produced according to the present invention may be heated to the above-described reheating temperature simultaneously with, for example, precision annealing or press molding. This allows the transition metal component contained in the glass to be oxidized when the glass is heat-treated while being molded into the desired shape or enhanced resistance to mechanical impacts. An optical glass having a high spectral transmittance can be obtained. In addition, the use of the optical glass produced by this invention is not limited to the use which requires temperature rising to reheating temperature.

  Moreover, it is preferable that the optical glass produced by this invention has a low glass transition point (Tg). In particular, the optical glass produced according to the present invention preferably has a glass transition point (Tg) of 700 ° C. or lower. Thereby, since glass softens at lower temperature, glass can be press-molded at lower temperature. In addition, it is possible to extend the life of the mold by reducing oxidation of the mold used for press molding. Therefore, the upper limit of the glass transition point (Tg) of the optical glass produced according to the present invention is preferably 700 ° C., more preferably 680 ° C., and most preferably 670 ° C. The lower limit of the glass transition point (Tg) of the optical glass produced according to the present invention is not particularly limited, but is generally 100 ° C. or higher, specifically 150 ° C. or higher, and more specifically 200 ° C. or higher. Many.

[Production of optical elements]
The optical glass produced according to the present invention can produce various optical elements and optical elements such as lenses and prisms useful for optical design. These optical elements are preferably used for optical devices such as cameras and projectors. As a result, the absorption of light by the optical element is reduced and the light transmittance is increased, so that high-definition and high-precision imaging characteristics and projection characteristics can be realized.

  In particular, an optical element made of a molded product of optical glass produced in the present invention has a platinum content of 50 ppm or less based on oxides. As a result, the discoloration of the glass, which was difficult to remove even when heated, has been reduced, so that the optical element can be used in a visible region such as a camera or projector while increasing the degree of freedom regarding the optical element manufacturing process. It can be preferably used for the purpose of transmitting the light. Here, the content of platinum contained in the optical element on the oxide basis is preferably 10 ppm, more preferably 5 ppm, and most preferably 3 ppm.

Table 1 shows the composition of the glass raw material used for the production of the optical glass, the type of gas used for bubbling, the gas supply speed and the gas supply position, and the melting process, clarification process, stirring process, outflow process, and molding process. Temperature and time are shown. Also shown in Table 1 are the refractive index (n _d ), Abbe number (ν _d ), glass transition point (Tg), and spectral transmittance for light having a wavelength of 420 nm after the reheating test. . The following examples are merely for illustrative purposes and are not limited to these examples.

  In Examples (No. 1 to No. 2) and Comparative Examples (No. 1) of the present invention, oxides, hydroxides, carbonates, nitrates, fluorides, and water corresponding to the raw materials of the respective components are used. High-purity raw materials used for ordinary optical glasses such as oxides and metaphosphoric acid compounds were selected. These were weighed in the proportions of the examples and comparative examples shown in Table 1, all the raw materials were uniformly mixed, and after melting at the melting temperature shown in Table 1 for 0.5 to 30 hours, they were cooled. A cullet (raw glass) in which a part of the glass raw material S was vitrified was produced.

  Among these, in Examples (No. 1 to No. 2) of the present invention, a melting tank made of quartz, a clarification tank made of platinum communicated with the melting tank through a communication pipe, and a communication pipe connected to the clarification tank. A glass melting apparatus provided with a stirring tank made of platinum in communication was used. Then, the raw glass was continuously supplied to the melting tank of the glass melting apparatus at a supply rate of 1.5 to 3.0 L / min. Here, in the melting tank, while melting the raw glass at the melting temperature and melting time shown in Table 1 to form the molten glass, the molten glass is made into a clarification tank at the same speed as the supply speed of the raw glass to the melting tank. Supplied. Moreover, in the clarification tank, molten glass was supplied to the stirring tank at the same speed as the supply speed of the molten glass to the clarification tank, while leaving the molten glass at the clarification temperature and clarification time shown in Table 1. Moreover, in the stirring tank, the stirring blade made of platinum provided along the bottom surface of the stirring tank is used at the stirring temperature and stirring time described in Table 1, and the stirring blade is rotated along the bottom surface of the stirring tank. The molten glass was stirred. At the same time, the molten glass is supplied to the outflow means at the same rate as the molten glass is supplied to the stirring tank, the temperature of the molten glass is adjusted to the outflow temperature shown in Table 1, and the outflow means provided on the bottom surface of the stirring tank ( The molten glass was caused to flow out from the outflow pipe), and the molten glass adjusted to the molding temperature shown in Table 1 was supplied to the mold and cast, and these were gradually cooled to produce glass.

  On the other hand, in the comparative example (No. 1), a melting tank made of platinum, a clarification tank made of platinum communicated with the melting tank by a communication pipe, and a stirring tank made of platinum communicated with the clarification tank by a communication pipe And the glass was produced in the procedure similar to an Example (No.1-No.2) using the glass melting apparatus provided with these.

  At this time, in an Example (No.1-No.2) and a comparative example (No.1), among the melting tank (melting tank 11 of FIG. 1) and the clarification tank (clarification tank 12 of FIG. 1) of raw material glass. The gas described in Table 1 and the oxygen partial pressure gas were continuously supplied to the tank described in Table 1 at the supply rate described in Table 1 as necessary.

The refractive index of the glass obtained in Example (No.1~No.2) and Comparative Example (No.1) _{(n d)} and Abbe number (ν _d), the Japanese Optical Glass Industrial Standard JOGIS01-2003 Measured based on. The glass used in this measurement was annealed under a slow cooling furnace with a slow cooling rate of −25 ° C./hr.

  Moreover, the glass transition point (Tg) of the glass obtained by an Example (No.1-No.2) and a comparative example (No.1) was calculated | required by measuring using a horizontal type | mold expansion measuring device. Here, the sample used for the measurement was φ4.5 mm and a length of 5 mm, and the heating rate was 4 ° C./min.

  Moreover, the content of the Pt component of the glass obtained in the examples (No. 1 to No. 2) and the comparative example (No. 1) is obtained by converting the glass obtained by the examples and comparative examples into a powder form, and performing acid treatment. About the solution obtained by doing, it measured using the ICP emission-analysis apparatus (Seiko Instruments Co., Ltd. product Vista-PRO).

  Moreover, about the transmittance | permeability of the glass obtained by an Example (No.1-No.2) and a comparative example (No.1), it measured according to Japan Optical Glass Industry Association standard JOGIS02. Specifically, the face-to-face parallel polished product having a thickness of 10 ± 0.1 mm was measured in accordance with JISZ8722 to measure the spectral transmittance with respect to light having a wavelength of 420 nm, and the presence / absence and degree of coloring of the glass were determined from the transmittance value. . In this example, the transmittance of the glass was measured after a reheating test assuming precision annealing and press molding. Here, the glass reheating test was carried out by placing a prismatic glass sample of 15 mm × 15 mm × 30 mm prepared from the glass obtained in the examples and comparative examples on a refractory and placing it in an electric furnace for 150 minutes at room temperature. The temperature was raised to 20 ° C. higher than the glass transition point (Tg) of the glass sample, and the temperature was kept for 30 minutes. The glass after the reheating test was cooled to room temperature and taken out of the furnace, and then the two opposing surfaces were polished to a thickness of 10 mm ± 0.1 mm, and the spectral transmittance was measured by the same method as described above. .

  As shown in Table 1, each of the optical glasses obtained in the examples of the present invention had a spectral transmittance of 20% or more, more specifically 55% or more, for light having a wavelength of 420 nm after the reheating test. It was. On the other hand, the glass obtained in the comparative example had a spectral transmittance of less than 40% for light having a wavelength of 420 nm after the reheating test. For this reason, it became clear that the optical glass obtained by the Example of this invention has high spectral transmittance with respect to visible light compared with the glass obtained by a comparative example, especially after reheating, and is hard to color.

The optical glasses obtained in the examples of the present invention all have a refractive index (n _d ) of 1.80 or more, more specifically 1.84 or more, and this refractive index (n _d ) is 2. It was 20 or less, more specifically 1.95 or less, and was within the desired range.

The optical glasses obtained in the examples of the present invention all have an Abbe number (ν _d ) of 10 or more, more specifically 17.3 or more, and the Abbe number (ν _d ) of 29 or less. Specifically, it was 24.0 or less, which was within a desired range.

  Further, the optical glasses obtained in the examples of the present invention all had a platinum content of 50 ppm or less, more specifically 3.0 ppm or less, and were within a desired range.

  Further, the optical glasses of the examples of the present invention all had a glass transition point (Tg) of 700 ° C. or less, more specifically 660 ° C. or less, and were within a desired range.

Therefore, the optical glass obtained in the example of the present invention has a high dispersion (low Abbe number ν _d ) while the refractive index (n _d ) is within a desired range, and is particularly colored after heat treatment. Has been reduced, and it has become clear that press molding is easy to perform.

  Although the present invention has been described in detail 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.

DESCRIPTION OF SYMBOLS 1 Glass melting apparatus 11 Melting tank 12 Clarification tank 13 Stirring tank 111, 121, 131 Instrument wall 14 Outflow means 16, 17 Communication pipe 2 Gas supply apparatus 21, 22 Gas supply pipe 211, 221 Opening 23, 24 Gas supply valve 25 Gas Supply source 3 Raw material supply means 31 Raw material storage tank 32 Raw material supply valve 33 Raw material supply pipe 4 Stirring means 41 Stirring blade 5 Molding means

Claims (8)

A method for producing an optical glass containing an Nb ₂ O ₅ component as an essential component,
Using a melting tank that melts the glass raw material, a clarification tank that communicates with the melting tank and clarifies the glass, and a stirring tank that communicates with the clarification tank and stirs the glass.
A step of melting the glass raw material in the melting tank (melting step), a step of clarifying the molten glass raw material in the clarification tank (clarification step), a step of stirring the clarified molten glass in the stirring tank (stirring step), and stirring. The manufacturing method which has the process (outflow process) which flows out the molten glass which flowed, and the process (molding process) which shape | molds the outflowed glass.   The manufacturing method of Claim 1 which comprises at least one part of the part which glass contacts in the said melting tank, a clarification tank, and a stirring tank.   The manufacturing method of Claim 1 or 2 which comprises at least one part of the part which glass contacts in the said melting tank and clarification tank with quartz, and comprises the part which glass contacts in the said stirring tank.   The production method according to claim 2 or 3, further comprising a step of bubbling an oxidizing gas in the molten glass. In the melting tank, the clarification tank, and the stirring tank, at least part of the portion in contact with the glass is composed of platinum,
The method according to any one of claims 1 to 3, further comprising a step of bubbling a non-oxidizing gas in the molten glass.   The manufacturing method according to any one of claims 1 to 5, wherein a material containing antimony and / or tin is used as the glass raw material.   An optical element comprising a glass molded body produced by the production method according to claim 1 and having a platinum content of 50 ppm or less based on oxides.   An optical apparatus using the optical element according to claim 7.

Images