JP5215743B2 - Optical glass manufacturing method, precision press molding preform manufacturing method, and optical element manufacturing method - Google Patents

Description

  The present invention relates to a method for producing optical glass, a method for producing a precision press-molding preform, and a method for producing an optical element.

  Fluorine-containing glass such as fluorophosphate glass is very useful as low-dispersion glass. For example, fluorine-containing glass into which copper ions or the like are introduced is widely used as near-infrared absorbing glass.

As a method for producing optical glass made of the above fluorine-containing glass, a method of clarifying and homogenizing a glass obtained by heating and melting a raw material in a molten state (hereinafter referred to as a melting method) is known.
In the above melting method, the melting of the glass raw material and the clarification and homogenization of the glass are usually carried out in a platinum or platinum alloy crucible having erosion resistance so that impurities are not melted into the molten glass in an extremely high temperature state. Is called.

However, since fluorine-containing glass, especially fluorophosphate glass, has extremely strong erodibility, even if a crucible made of platinum or a platinum alloy is used, the crucible is eroded and its constituent components are taken into the glass. Platinum or a platinum alloy mixed in the glass precipitates as a foreign substance, and becomes a light scattering source, thereby reducing the quality of the optical glass (see, for example, Patent Document 1).
JP 2002-128528 A (fourth line from the lower right column of the second page to two lines from the upper left column of the third page)

  Under such circumstances, the present invention provides an optical glass that can reduce contamination of platinum or platinum alloy foreign matter into glass when an optical glass made of fluorine-containing glass is produced by a melting method. It is an object of the present invention to provide a method and a method for producing a precision press-molding preform and an optical element from optical glass produced by the method.

In order to reduce the mixing of platinum or platinum alloy foreign matter into the glass, the present inventor obtained the following knowledge as a result of repeated studies.
(A) Fluorine-containing glass such as fluorophosphate glass has a very small amount of platinum or platinum alloy that is taken in from a crucible and precipitates as a foreign substance, despite the extremely small amount of platinum in the glass compared to glass that originally does not contain fluorine. Because there are many, the melting ability of platinum or platinum alloy is very small.
(B) Most of the platinum or platinum alloy in the glass is taken in from the crucible when the raw material is vitrified.

  Based on these findings, the present inventors have further studied, and as a result, when using a container made of gold or gold alloy, which is a material other than platinum or platinum alloy, when the raw material is vitrified, platinum or platinum in the glass is used. The inventors have found that alloy contamination can be reduced and the amount of precipitation as foreign matter can be reduced, and the present invention has been completed.

That is, the present invention
(1) A method for producing optical glass comprising fluorine-containing glass,
A glass raw material is melted in a container made of gold or a gold alloy, and then melted in a container made of platinum or a platinum alloy.
(2) The method for producing an optical glass according to the above (1), wherein the fluorine-containing glass is at least one selected from fluorophosphate glass, fluoroborate glass, fluorosilicate glass, fluoroborosilicate glass, and fluoroborosilicate glass,
(3) The method for producing optical glass according to (1) or (2) above, wherein the gold or gold alloy container is a container made of pure gold or a gold-based alloy,
(4) Any of the above (1) to (3), wherein the container made of platinum or platinum alloy is a container made of platinum or an alloy of platinum and at least one metal selected from zirconia, gold, iridium, and rhodium. A method for producing the optical glass according to
(5) A method for producing a precision press-molding preform, wherein the optical glass obtained by the method according to any one of (1) to (4) is molded in a molten state,
(6) A method for producing an optical element characterized by precision press-molding the preform for precision press-molding obtained by the method described in (5) above, and (7) (1) to (4) above The present invention provides a method for producing an optical element, comprising a step of grinding and polishing a glass molded body made of an optical glass obtained by any one of the methods.

  According to the present invention, when an optical glass made of fluorine-containing glass is produced by a melting method, the raw material is vitrified using a container made of gold or a gold alloy, thereby reducing contamination of foreign matter into the glass. And a method for producing a precision press-molding preform and an optical element from the optical glass produced by the method.

[Method for producing optical glass]
First, the manufacturing method of the optical glass of this invention is demonstrated.
The method for producing optical glass of the present invention is a method for producing optical glass made of fluorine-containing glass, wherein a glass raw material is melted in a gold or gold alloy container and then melted in platinum or a platinum alloy container. It is characterized by that.

  In the method of the present invention, since the most characteristic point is the optical glass manufacturing process, this point will be described first, and then the glass raw material and the resulting glass will be described.

  The container made of gold or gold alloy for melting the glass raw material is preferably a container made of one or more selected from gold-based alloys such as pure gold, gold platinum, and zirconia reinforced gold. The container shape is not particularly limited, but is preferably a cylindrical shape.

  The glass raw material is melted and vitrified in the container (hereinafter, this melting process is appropriately referred to as rough melt). 700-1000 degreeC is preferable and the heating temperature at the time of rough melt has more preferable 800-900 degreeC. The heating time is preferably 30 to 240 minutes, more preferably 60 to 180 minutes. The atmosphere during rough melting is preferably a dry atmosphere, and examples thereof include dry air and dry nitrogen. Even if the atmosphere during melting is an oxidizing atmosphere, by using a container made of gold or a gold alloy, the container does not deteriorate due to oxidation during rough melting. However, in order to prevent substitution of oxygen in the atmosphere with fluorine in the glass, it is effective to perform rough melting in a non-oxidizing atmosphere.

  The glass raw material is melted until the raw material is vitrified. Further, the glass may be homogenized by continuing heating. However, in order to promote the refining action in a platinum or platinum alloy container, which will be described later, the heat treatment should be terminated when the raw material is vitrified. Is preferred.

If you melting a glass raw material by melting method, usually, in addition to container made of platinum or platinum alloy, although the SiO ₂ has a container for the main component is used, the present inventors have studied, the SiO ₂ primary The container as a constituent component was eroded violently by fluorine-containing glass such as fluorophosphate glass, and it was found that it cannot be used. On the other hand, when a glass raw material is melted using a gold or gold alloy container, it is possible to prevent platinum or a platinum alloy from being mixed into the glass while preventing the container from being eroded by the glass. As a result, the present invention has been completed.

  In the method of the present invention, glass obtained by rough melting a raw material in a gold or gold alloy container is melted in a platinum or platinum alloy container, and the glass is clarified.

  Examples of the gold or gold alloy constituting the container include pure gold and gold-based alloys such as gold / platinum alloys and gold / zirconia alloys (also called reinforced gold). Examples of platinum or a platinum alloy constituting the container include platinum, a platinum / zirconia alloy, a platinum / gold alloy, a platinum / iridium alloy, and a platinum / rhodium alloy.

The temperature during melting is preferably from 700 to 1000 ° C, more preferably from 800 to 900 ° C. High-temperature glass tends to react with moisture in the atmosphere, and this reaction lowers the quality of the glass. Therefore, the atmosphere during melting is preferably a dry atmosphere. The moisture content in the dry atmosphere is preferably equivalent to a dew point of −30 ° C. or lower, and examples of the gas include inert gases such as nitrogen and argon.
Moreover, it is preferable to homogenize the glass by performing a stirring process together with the melting process.

  In the above melting operation, by connecting a gold or gold alloy container and a platinum or platinum alloy container with a pipe, the glass produced in the gold or gold alloy container is placed in a platinum or platinum alloy container. The glass body obtained by once cooling and solidifying the glass produced in a gold or gold alloy container is heated again in the platinum or platinum alloy container. It may be melted.

  In the method of the present invention, rough melting is performed in the gold or gold alloy container, and subsequent glass melting treatment (clarification process) is performed in a platinum or platinum alloy container. It is ideal to continue the glass melting treatment (clarification treatment) in a gold or gold alloy container. However, since gold or gold alloy has lower strength and melting point than platinum or platinum alloy, it is 1000 ° C or higher. It is unsuitable to form a melting furnace that requires a clarification process at a high temperature. For this reason, in the method of the present invention, the container made of gold or gold alloy only needs a simple shape and is used only for the rough melt process having a relatively low melting temperature, and the subsequent melting process (clarification process) is made of platinum. Alternatively, by using a platinum alloy container, the mixture of platinum or platinum alloy into the glass is minimized.

Next, the glass raw material used and the optical glass obtained will be described.
Examples of the raw material for the fluorine-containing glass include phosphates and fluorides corresponding to the respective glass components such as Ba (PO ₃ ) ₂ , AlF ₃ , MgF ₂ , CaF ₂ , and SrF ₂ .

  Examples of the optical glass composed of the obtained fluorine-containing glass include those composed of one or more selected from fluorophosphate glass, fluoroborate glass, fluorosilicate glass, fluoroborosilicate glass, fluoroborosilicate glass, and the like. The method can be suitably used particularly in the case of producing optical glass made of fluorophosphate glass.

As a preferred embodiment of the optical glass made of fluorophosphate glass, P ⁵⁺ 3-50%, Al ³⁺ 0.1-40%, Mg ²⁺ 0-20%, Ca ²⁺ 0-25%, Sr ^{2+ in} terms of cation%. 0-30%, Ba2 ⁺ 0-30%, Li ⁺ 0-30%, Na ⁺ 0-10%, K ⁺ 0-10%, Y3 ⁺ 0-10%, La3 ⁺ 0-5%, Gd3 ⁺ 0 Mention may be made of optical glasses containing ~ 5%.

In the above optical glass, anionic component F ^- and ^{O 2-} allocations, F ^- and ^{O 2-} F to the total amount of ^- the molar ratio ^F of the content of - ^/ (F - ^{+ O 2-)} is 0.25 A range of 0.95 is preferred. By setting the amount of the anion component as described above, low dispersion characteristics can be imparted to the glass.

  According to the optical glass, it is possible to realize optical characteristics having a refractive index value nd of 1.40000 to 1.60000 and an Abbe number (νd) of 67 or more. The upper limit of the Abbe number (νd) is not particularly limited, but it is preferable to set the Abbe number (νd) to 100 or less from the viewpoint of stably producing the glass.

In the optical glass, those containing two or more of Ca ²⁺ , Sr ²⁺ and Ba ²⁺ as the divalent cation component (R ²⁺ ) are preferable.

The optical glass preferably has a total content of 1 cation% or more of Mg ²⁺ , Ca ²⁺ , Sr ²⁺ and Ba ²⁺ which are divalent cation components (R ²⁺ ), Mg ²⁺ , Ca ²⁺ , Sr. More preferably, the contents of ²⁺ and Ba ²⁺ are each 1 cation% or more.

  Hereinafter, the composition of the optical glass will be described in detail. The ratio of each cation component is expressed in% cation based on the molar ratio, and the ratio of each anion component is also expressed in% anion based on the molar ratio. To do.

P ⁵⁺ is an important cation component as a glass network former. If it is less than 5%, the stability of the glass is lowered, and if it exceeds 50%, P ⁵⁺ needs to be introduced as an oxide raw material, so the oxygen ratio increases. Does not meet the target optical characteristics. Therefore, the amount is 5% to 50%, more preferably 5% to 40%, and particularly preferably 5% to 35%. When introducing P ^5+, the use of PCl 5 is not appropriate because it erodes platinum and is highly volatile and hinders stable production, and is preferably introduced as a phosphate.

Al ³⁺ is a component that improves the stability of fluorophosphate glass. If it is less than 0.1%, the stability decreases, and if it exceeds 40%, the glass transition temperature (Tg) and the liquidus temperature (LT) increase greatly. As a result, the molding temperature rises and striae due to surface volatilization during molding occurs strongly, making it impossible to obtain a homogeneous glass molded body, particularly a press molding preform. Therefore, the amount is 0.1% to 40%, more preferably 5% to 40%, and particularly preferably 10% to 35%.

Introduction of Mg ²⁺ , Ca ²⁺ , Sr ²⁺ , and Ba ²⁺ , which are divalent cation components (R ²⁺ ), contributes to improvement of the stability of the glass. However, since the stability as glass decreases due to excessive introduction, it is preferable to set Mg ²⁺ , Ca ²⁺ , Sr ²⁺ , and Ba ²⁺ in the following ranges.

First, the preferable content of Mg ²⁺ is 0 to 20%, more preferably 1 to 20%, still more preferably 5 to 15%, and particularly preferably 5 to 10%. The preferable content of Ca ²⁺ is 0 to 25%, more preferably 1 to 25%, still more preferably 5 to 20%, and particularly preferably 5 to 16%. The preferable content of Sr ²⁺ is 0 to 30%, more preferably 1 to 30%, still more preferably 5 to 25%, and particularly preferably 10 to 20%. The preferable content of Ba ²⁺ is 0 to 30%, more preferably 1 to 30%, still more preferably 1 to 25%, still more preferably 5 to 25%, and particularly preferably 8 to 25%.

It is preferable to introduce two or more of Mg ²⁺ , Ca ²⁺ , Sr ²⁺ and Ba ²⁺ , rather than introducing each singly, and more than two of Ca ²⁺ , Sr ²⁺ and Ba ²⁺ are introduced. preferable. In order to further enhance the effect of introducing the divalent cation component (R ²⁺ ), the total content of Mg ²⁺ , Ca ²⁺ , Sr ²⁺ and Ba ²⁺ is preferably 1 cation% or more. Moreover, when it introduces exceeding each upper limit, stability will fall rapidly. Ca ²⁺ and Sr ²⁺ can be introduced in a relatively large amount, but Mg ²⁺ and Ba ²⁺ particularly lower the stability. However, since Ba ²⁺ is a component capable of realizing a high refractive index while maintaining low dispersion, it is preferably introduced in a large amount within a range not impairing stability.

Li ⁺ is a component that lowers the glass transition temperature (Tg) without impairing the stability. However, if it exceeds 30%, the durability of the glass is impaired and at the same time the workability is lowered. Therefore, the amount is 0-30%. A preferable range is 0 to 25%, and a more preferable range is 0 to 20%.

However, when it is desired to lower the glass transition temperature particularly for precision press molding applications, the amount of Li ⁺ is preferably 2 to 30%, more preferably 5 to 25%, and more preferably 5 to 20%. More preferably.

Na ⁺ and K ⁺ have the effect of lowering the glass transition temperature (Tg), respectively, like Li ⁺ , but at the same time, the thermal expansion coefficient tends to be larger than that of Li ⁺ . Moreover, since NaF and KF have a very high solubility in water as compared with LiF, the water resistance is also deteriorated. Therefore, the amounts of Na ⁺ and K ⁺ are 0 to 10%, respectively. A preferable range for both Na ⁺ and K ⁺ is 0 to 5%, and it is more preferable not to introduce them.

Y ³⁺ , La ³⁺ and Gd ³⁺ have the effect of improving the stability and durability of the glass and increasing the refractive index. However, if it exceeds 5%, the stability deteriorates and the glass transition temperature (Tg) is large. In order to increase, the amount is set to 0 to 5%. A preferable range is 0 to 3%.

From the viewpoint of stably producing high-quality optical glass, the total amount of P ⁵⁺ , Al ³⁺ , Mg ²⁺ , Ca ²⁺ , Sr ²⁺ , Ba ²⁺ , Li ⁺ and Y ³⁺ , La ³⁺ , Gd ³⁺ is used as a cation. % Is preferably over 95%, more preferably over 98%, further preferably over 99%, and even more preferably 100%.

  The optical glass can contain a lanthanoid such as Ti, Zr and Zn in addition to the cation component described above, and a cation component such as B within a range not impairing the object of the present invention.

Ratio of anionic components, while realizing the desired optical properties, in order to obtain an optical glass having excellent stability, F ^- and O ^2-F to the total amount of ^- the molar ratio of the content of F ^- / ( F ⁻ + O ²⁻ ) is set to 0.25 to 0.95.

  As the optical glass made of fluoroborate glass, the optical glass made of fluorosilicate glass, the optical glass made of fluoroborosilicate glass, and the optical glass made of fluoroborosilicate glass, conventionally known ones can be appropriately selected and used.

  Each of the above optical glasses is an excellent glass both as a glass for producing an optical element by precision press molding and as a glass for producing an optical element by grinding and polishing.

[Precision press molding preform manufacturing method]
Next, a method for manufacturing a precision press-molding preform will be described.
The method for producing a precision press-molding preform of the present invention is characterized in that the optical glass obtained by the method for producing optical glass of the present invention is molded in a molten state.

  Here, the precision press-molding preform means that a glass having a weight equal to the weight of the press-molded product is previously molded into a shape suitable for precision press-molding.

Fluorine-containing glass such as fluorophosphate glass has properties that it has a higher degree of wear and a higher thermal expansion coefficient than other general optical glasses. Such a property is not preferable for polishing. When the degree of wear is large, processing accuracy is lowered, and scratches during polishing are likely to remain on the glass surface. In addition, polishing is performed while the cutting fluid is applied to the glass. However, if the cutting fluid is applied to the glass whose temperature has been increased by polishing, or if glass having polishing flaws is introduced into the cleaning fluid whose temperature has been increased during ultrasonic cleaning, the temperature of the glass changes greatly. In the case of fluorophosphate glass that is exposed to heat and has a large thermal expansion coefficient, the glass is easily damaged by thermal shock. Therefore, it is desirable to manufacture a precision press-molding preform by a method that does not depend on polishing. From such a viewpoint, in the method of the present invention, optical glass is molded in a molten state to produce a precision press-molding preform. In this case, by making the entire surface of the preform a surface formed by solidifying the glass in the molten state, the preform is washed or prevented from being damaged when heated prior to precision press molding. Can be reduced.

  In the method for producing a precision press-molding preform of the present invention, a preferred first aspect (hereinafter referred to as preform production method I) is to let molten glass flow out of a pipe, to separate the molten glass lump, and to cool the glass. In this process, it is formed into a preform.

  The molten glass is continuously discharged at a constant flow rate from a platinum or platinum alloy pipe heated to a predetermined temperature. A molten glass lump having a weight equivalent to one preform is separated from the molten glass that has flowed out. When separating the molten glass lump, it is desirable to avoid the use of a cutting blade so as not to leave a cut mark. For example, the molten glass is dropped from the outlet of the pipe, or the molten glass flow tip flowing out is supported by the support. It is preferable to use a method in which the molten glass lump is separated from the front end of the molten glass flow by using the surface tension of the molten glass by suddenly dropping the support at a timing at which the molten glass lump of the target weight can be separated.

  The separated molten glass lump is formed into a desired shape in the process of cooling the glass on the recess of the preform mold. At that time, in order to prevent wrinkles on the preform surface or breakage in the glass cooling process called can cracking, it is preferable to mold the glass lump in a state of being lifted by applying upward wind pressure to the glass block. In that case, it is preferable to spray the gas on the surface of the glass lump to promote the cooling of the surface from the viewpoint of reducing and preventing the occurrence of striae.

  After the temperature of the glass is lowered to a temperature range that does not deform even when an external force is applied to the preform, the preform is taken out from the preform mold and gradually cooled.

  In order to reduce the volatilization of the glass component from the glass surface, it is preferable to perform glass outflow and preform molding in a dry atmosphere (dry nitrogen atmosphere, dry air atmosphere, dry mixed gas atmosphere of nitrogen and oxygen, etc.). .

  In the method for producing a press-molding preform of the present invention, a preferred second aspect (referred to as preform production method II) is to form a glass molded body by molding molten glass, and machine the glass molded body. A preform made of optical glass is produced.

  As a preferred embodiment of the preform production method II, first, molten glass is continuously discharged from the pipe and poured into a mold disposed below the pipe. As the mold, a flat bottom and a side wall that surrounds the bottom from three sides and one side of which is open are used. The side walls that sandwich the opening side and bottom from both sides face each other in parallel, and the mold is placed, fixed, and poured into the mold so that the center of the bottom is positioned vertically below the pipe and the bottom is horizontal. The molten glass is spread so as to have a uniform thickness in the region surrounded by the side walls, and after cooling, the glass is drawn out horizontally from the opening on the side surface of the mold at a constant speed. The drawn glass molded body is sent into an annealing furnace and annealed. In this way, a plate-like glass molded body having a certain width and thickness and having reduced and suppressed surface striae is obtained.

  Next, the plate-like glass molded body is cut or cleaved and divided into a plurality of glass pieces called cut pieces, and these glass pieces are ground and polished to finish a preform for press molding with a target weight.

  As another method, a mold having a cylindrical through-hole is disposed and fixed vertically below the pipe so that the central axis of the through-hole faces the vertical direction. At this time, it is preferable to arrange | position a casting_mold | template so that the central axis of a through-hole may be located in the vertically downward direction of a pipe. Then, molten glass is poured from the pipe into the mold through-hole at a constant flow rate to fill the glass in the through-hole, and the solidified glass is drawn vertically downward from the lower end opening of the through-hole at a constant speed, gradually cooled, A cylindrical rod-shaped glass molded body is obtained. After annealing the glass molded body thus obtained, a plurality of glass pieces are obtained by cutting or cleaving from a direction perpendicular to the central axis of the cylindrical bar. Next, the glass piece is ground and polished to finish a preform for press molding with a desired weight. Also in these methods, it is preferable to perform the outflow and shaping of the molten glass in a dry atmosphere as described above. Furthermore, also in these methods, it is effective to reduce and prevent striae by accelerating cooling by blowing a gas onto the glass surface during molding.

  Both preform production methods I and II can produce a high-quality and highly accurate preform, which is suitable as a method for producing a preform for precision press molding.

[Method of manufacturing optical element]
Next, the manufacturing method of the optical element of this invention is demonstrated.
The first aspect of the optical element manufacturing method of the present invention (hereinafter referred to as optical element manufacturing method I) is to perform precision press molding of the preform obtained by the precision press molding preform manufacturing method of the present invention. Features.

  The precision press molding is also called mold optics molding, and is a well-known method in the technical field. According to precision press molding, an optical functional surface can be formed by press molding by precisely transferring the molding surface of a press mold to glass, and machining such as grinding and polishing is performed to finish the optical functional surface. There is no need to add.

  Therefore, the optical element manufacturing method I of the present invention is suitable for the production of optical elements such as lenses, lens arrays, diffraction gratings, and prisms, and is particularly suitable as a method for producing aspherical lenses with high productivity. Yes.

  According to the optical element manufacturing method I of the present invention, since the glass transition temperature (Tg) constituting the preform is low, the press molding temperature can be lowered, and the molding surface of the press mold is damaged. Can be reduced and the life of the mold can be extended. Further, since the glass constituting the preform has high stability, devitrification of the glass can be effectively prevented even in the reheating and pressing steps. Furthermore, a series of steps for obtaining a final product from glass melting can be performed with high productivity.

  As a press mold used for precision press molding, known molds such as silicon carbide, zirconia, alumina and other heat-resistant ceramic molds provided with a release film can be used. A silicon press mold is preferable, and a carbon-containing film or the like can be used as the release film. In view of durability and cost, a carbon film is particularly preferable.

  In precision press molding, it is desirable that the molding atmosphere be a non-oxidizing gas in order to keep the molding surface of the press mold in a good state. The non-oxidizing gas is preferably nitrogen or a mixed gas of nitrogen and hydrogen.

  As a preferable aspect in the manufacturing method I of the optical element of the present invention, the following two modes of manufacturing methods Ia and Ib of the optical element can be shown.

(Optical element manufacturing method Ia)
In the optical element manufacturing method Ia, a preform is introduced into a press mold, heated together, and precision press-molded.

In this optical element manufacturing method Ia, the temperature of the press mold and the preform is heated to a temperature at which the glass constituting the preform exhibits a viscosity of 10 ⁶ to 10 ¹² dPa · s. It is preferable to perform molding.

The glass is preferably cooled to a temperature showing a viscosity of 10 ¹² dPa · s or more, more preferably 10 ¹⁴ dPa · s or more, and even more preferably 10 ¹⁶ dPa · s or more. It is desirable to remove from the mold.

  Under the above conditions, the shape of the molding surface of the press mold can be accurately transferred with glass, and the precision press molded product can be taken out without being deformed.

(Optical Element Manufacturing Method Ib)
In the optical element production method Ib, a separately heated preform is introduced into a preheated press mold and precision press molding is performed.

  According to this optical element manufacturing method Ib, since the preform is heated in advance before being introduced into the press mold, an optical element having good surface accuracy without surface defects is manufactured while shortening the cycle time. can do.

  The preheating temperature of the press mold is preferably set lower than the preheating temperature of the preform. Thus, by lowering the preheating temperature of the press mold, it is possible to reduce the wear of the press mold.

In the optical element production method Ib, it is preferable that the glass constituting the preform is preheated to a temperature exhibiting a viscosity of 10 ⁹ dPa · s or less, more preferably about 10 ⁹ dPa · s.

The preform is preferably preheated while floating, more preferably preheated to a temperature at which the glass constituting the preform exhibits a viscosity of 10 ^5.5 to 10 ⁹ dPa · s ^. It is more preferable to preheat to a temperature showing a viscosity of ⁵ dPa · s or more and less than 10 ⁹ dPa · s.

Moreover, it is preferable to start cooling the glass simultaneously with the start of pressing or in the middle of pressing.
The temperature of the press mold is adjusted to a temperature lower than the preheating temperature of the preform, and the temperature at which the glass exhibits a viscosity of 10 ⁹ to 10 ¹² dPa · s may be used as a guide.

In this method, it is preferable that after the press molding, the glass is cooled to a viscosity of 10 ¹² dPa · s or more and then released.

  The precision press-molded optical element is taken out from the press mold and gradually cooled as necessary. When the molded product is an optical element such as a lens, an optical thin film may be coated on the surface as necessary.

  The second aspect of the optical element manufacturing method of the present invention (hereinafter referred to as optical element manufacturing method II) is a step of grinding and polishing a glass molded body made of optical glass obtained by the optical glass manufacturing method of the present invention. It is characterized by including.

  Specific examples of the optical element production method II include, for example, a method of manufacturing an optical element by flowing molten glass to form a glass molded body, annealing, and then performing machining such as cutting, grinding, and polishing. It is done. For example, an optical element such as various lenses can be manufactured by slicing the cylindrical rod-shaped glass molded body described above from a direction perpendicular to the cylinder axis, and grinding and polishing the obtained cylindrical glass. .

  An antireflection film or a near infrared light reflection film may be appropriately formed on the surface of these optical elements.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited at all by these examples.

Example 1 (Example of optical glass production)
As raw materials for glass, phosphates and fluorides corresponding to the respective glass components are used. The raw materials were weighed so as to be a glass having a composition of 1 to 14, and mixed sufficiently.
The blended raw material was put in a pure gold crucible, melted for 1 hour with stirring at 850 ° C., then rapidly cooled and ground to obtain a rough melt cullet. In this melting process, dry air was continuously supplied into a pure gold crucible to keep the atmosphere dry. Here, dry nitrogen may be used instead of dry air.
Next, 10 kg of this rough melt cullet was put into a platinum crucible sealed with a lid, heated to 900 ° C., stirred and melted. Next, a sufficient amount of dry gas was introduced into the platinum crucible and the molten glass was clarified at 1100 ° C. for 2 hours while maintaining a dry atmosphere. Examples of the dry gas include an inert gas such as nitrogen, a mixed gas of an inert gas and oxygen, oxygen, and the like.
After clarification, the temperature of the glass was lowered to 850 ° C., which was lower than the temperature at the time of clarification, and then the molten glass was poured out from a pipe connected to the bottom of the crucible, cast into a mold, and formed into a sheet glass.
The gas introduced into the pure gold crucible and the platinum crucible was cleaned through a filter and then discharged to the outside.

When a light beam was incident on each of the obtained optical glasses and the optical path of the light beam in the glass was observed from the side, no light scattering due to platinum foreign matter was observed. Further, when the inside of the glass was enlarged and observed with an optical microscope, no platinum foreign matter was observed.
In addition, the obtained optical glass No. About 1-14, the refractive index (nd), Abbe number ((nu) d), and glass transition temperature (Tg) were measured as follows. The measurement results are shown in Tables 1-3.

(1) Refractive index (nd) and Abbe number (νd)
It measured about the optical glass obtained by making slow cooling temperature-fall rate -30 degreeC / hour.
(2) Glass transition temperature (Tg)
The glass transition temperature (Tg) was measured using a thermomechanical analyzer manufactured by Rigaku Corporation with a heating rate of 4 ° C./min.

Comparative Example 1 (Optical glass production comparative example)
No. shown in Tables 1 to 3 The raw materials corresponding to each component were weighed and mixed well so as to obtain a glass having a composition of 1 to 14.
Each of the above prepared raw materials was put into a platinum crucible sealed with a lid and heated at 1200 ° C. for 1 hour with stirring to melt the raw materials. Subsequently, the molten glass was clarified over 1 hour at 900 ° C. with stirring while introducing a sufficient drying gas into the platinum crucible and maintaining a dry atmosphere.
After clarification, the temperature of the glass was lowered to 850 ° C., which is lower than the temperature at the time of clarification, and then the molten glass was poured out from the pipe connected to the bottom of the crucible, cast into a mold, and formed into a glass block.
The gas introduced into the platinum crucible was cleaned through a filter and then discharged to the outside.
When light was incident on each optical glass obtained and the optical path of the light in the glass was observed from the side, the optical path was clearly observed by light scattering by the platinum foreign matter, and many platinum foreign matters were mixed in the glass block. It was confirmed that

Example 2 (Preform production example)
Each molten glass composed of the optical glass Nos. 1 to 14 obtained in Example 1 is constant from a platinum alloy pipe whose temperature is adjusted to a temperature range in which stable outflow is possible without devitrification of the glass. The molten glass lump with the weight of the target preform was separated by a method of dropping the support and dropping the glass lump after supporting the molten glass flow tip using a drop or a support. . Next, each molten glass lump obtained was received in a receiving mold having a gas outlet at the bottom, and gas was blown out from the gas outlet to form the glass lump. Preforms for precision press molding consisting of 1 to 14 were produced. The shape of the preform was made spherical or flat spherical by adjusting and setting the separation interval of the molten glass. The weights of the obtained preforms precisely matched the set values, and all of the preforms were smooth and the surfaces were formed by solidification of the molten glass.

  Next, when the inside of the preform was observed, no contamination of platinum foreign matter was observed, and no striae were observed. FIG. 2 shows a photograph taken by arbitrarily selecting one of the obtained preforms.

  Separately, the surface of a glass piece obtained by casting molten glass into a mold, blowing a dry gas onto the glass surface to form a glass plate or cylindrical rod while promoting cooling, annealing, and then cutting the glass. Were ground and polished to obtain a preform having a smooth entire surface. In this case as well, no striae was found on the surface of the plate-like glass or cylindrical bar formed by casting the molten glass obtained by atmosphere substitution.

Comparative Example 2 (Preform production example)
Each preform was produced in the same manner as in Example 2 except that the optical glass obtained in Comparative Example 1 was used.
Next, when the inside of the preform was observed, it was found that platinum foreign matter was mixed inside. One arbitrarily selected from the obtained preforms is shown, and the photograph taken is shown in FIG. 3 (indicated by white dots inside (center part) of the circular preform shown in FIG. Platinum foreign matter).

Example 3 (Example of optical element production)
Each preform made of optical glass Nos. 1 to 14 obtained in Example 2 was precision press-molded using a press apparatus shown in FIG. 1 to obtain an aspheric lens. Specifically, after the preform 4 is placed between the lower mold 2 and the upper mold 1 of the press mold composed of the upper mold 1, the lower mold 2 and the body mold 3, the inside of the quartz tube 11 is placed in a nitrogen atmosphere and the heater 12 Was energized to heat the inside of the quartz tube 11. The temperature inside the press mold is set to a temperature at which the glass to be molded exhibits a viscosity of 10 ⁸ to 10 ¹⁰ dPa · s, and while maintaining the same temperature, the push bar 13 is lowered and the upper mold 1 is pressed to form. The preform set in the mold was pressed. The press pressure was 8 MPa, and the press time was 30 seconds. After pressing, the pressure of the press is released, and the glass molded product that has been press-molded is kept in contact with the lower mold 2 and the upper mold 1 until the viscosity of the glass reaches 10 ¹² dPa · s or more. Then, the glass molded product is taken out of the mold and rapidly cooled to room temperature. An aspheric lens consisting of 1 to 14 was obtained. All of the obtained aspherical lenses had extremely high surface accuracy.
In FIG. 1, reference numeral 9 is a support rod, reference numeral 10 is a lower mold, a barrel holder, and reference numeral 14 is a thermocouple.
An aspherical lens obtained by precision press molding was provided with an antireflection film as required.

Example 4 (Example of optical element production)
Each preform made of optical glass Nos. 1 to 14 obtained in Practical Example 2 was precision press-molded by a method different from Example 3. In this method, first, the preform was preheated to a temperature at which the viscosity of the glass constituting the preform was 10 ⁸ dPa · s while the preform floated. On the other hand, a press mold having an upper mold, a lower mold, and a body mold is heated to a temperature at which the glass constituting the preform exhibits a viscosity of 10 ⁹ to 10 ¹² dPa · s, and the preheated preform is pressed. It was introduced into the mold cavity and precision press-molded at 10 MPa.
When the pressing of the glass and the press mold was started and the viscosity of the formed glass was cooled to 10 ¹² dPa · s or more, the molded product was released from the mold, and the optical glass no. An aspheric lens consisting of 1 to 14 was obtained. All of the obtained aspherical lenses had extremely high surface accuracy.
An aspherical lens obtained by precision press molding was provided with an antireflection film as required. In this way, a glass optical element with high internal quality could be obtained with high productivity and high accuracy.

Example 5 (Production Example of Optical Element)
Each molten glass made of optical glass Nos. 1 to 14 obtained in Practical Example 1 was continuously poured from a pipe into a mold, formed into a sheet glass in a dry nitrogen atmosphere, and slowly cooled. Next, when the inside of the glass was observed, no striae was observed.
This plate glass was cut, ground and polished to produce a spherical lens.
Next, the plate glass was cut, ground, and polished to obtain a material for press molding, and this material was heated, softened, and press molded to produce an optical element blank. These blanks were gradually cooled and then ground and polished to obtain optical glass Nos. A spherical lens consisting of 1 to 14 was obtained.
An antireflection film or a near infrared light reflection film may be appropriately formed on the surface of these spherical lenses.

  According to the present invention, when an optical glass made of fluorine-containing glass is produced by a melting method, a method for producing an optical glass capable of reducing contamination of foreign matter in the glass, and an optical glass produced by the method. A method for producing a precision press-molding preform and an optical element, respectively, can be provided.

It is the schematic of the precision press molding apparatus used in the Example of this invention. 2 is an enlarged photograph of a precision press-molding preform obtained in an example of the present invention. 3 is an enlarged photograph of a precision press-molding preform obtained in a comparative example of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Upper type | mold 2 ... Lower type | mold 3 ... Body type | mold 4 ... Preform 9 ... Support rod 10 ... Lower type | mold, barrel type | mold holder 11 ... Quartz tube 12 ... Heater 13 ... Push rod 14 ... Thermocouple

Claims (7)

A method for producing optical glass comprising fluorine-containing glass,
An optical glass manufacturing method comprising melting a glass raw material in a container made of gold or a gold alloy and then melting it in a container made of platinum or a platinum alloy.   The method for producing an optical glass according to claim 1, wherein the fluorine-containing glass is at least one selected from fluorophosphate glass, fluoroborate glass, fluorosilicate glass, fluoroborosilicate glass, and fluoroborosilicate glass.     The method for producing optical glass according to claim 1 or 2, wherein the container made of gold or a gold alloy is a container made of pure gold or a gold-based alloy.   4. The optical device according to claim 1, wherein the container made of platinum or a platinum alloy is a container made of platinum or an alloy of platinum and at least one metal selected from zirconia, gold, iridium, and rhodium. Glass manufacturing method.   A method for producing a precision press-molding preform, wherein the optical glass obtained by the method according to claim 1 is molded in a molten state.   A method for producing an optical element, comprising: precision press-molding a precision press-molding preform obtained by the method according to claim 5.   A method for producing an optical element, comprising a step of grinding and polishing a glass molded body made of the optical glass obtained by the method according to claim 1.