JP2022052419A - Production method of transparent glass - Google Patents

Abstract

To provide a production method of transparent quartz glass capable of preventing bubbles from remaining, when using granulated silica powder obtained by granulating silica fine powder which may generate bubbles upon melting.SOLUTION: A production method of transparent glass includes a mixing step for mixing silica powder having a mean particle size of 100 μm or more with granulated silica powder having a mean particle size of 100 μm or more obtained by granulating silica fine powder having a mean particle size of 50 μm or less, and a melting step for melting the mixed silica powder at 1,700°C or higher.SELECTED DRAWING: None

Description

The present invention relates to a method for producing transparent glass using granulated silica powder.

In recent years, with the increasing integration of semiconductors, various glass jigs and crucibles used in the optical fiber and semiconductor industries have been subject to extremely strict control regarding the purity of their constituent glass materials. Conventionally, as a method for producing high-purity glass products applied to these applications, alkoxysilane is used as a starting material, which is hydrolyzed to obtain silica gel powder by a process called a sol-gel method, and then this is performed. There is known a method of producing a desired quartz glass product of interest by firing the silica gel into a quartz glass powder and then melt-vitrifying the silica gel.

However, in quartz glass products that require transparency, bubbles are often generated in the quartz glass during molten vitrification, and the bubbles generated inside the quartz glass product remain, so that the transparency of the quartz glass is lost. That is, there was a problem that transparent glass could not be obtained. The term "transparent glass" as used herein means glass in which visible light is not scattered on the surface or inside of an object and visible light is not absorbed by the substances constituting the object, and the other side through the glass can be seen without dullness.

Therefore, as a method for making quartz glass transparent, synthetic silica fine powder described in Patent Documents 1 and 2 is once formed into a molded body by means such as casting molding and dry press molding, and 1700 is used in a reduced pressure atmosphere. A method of obtaining transparent quartz glass by heating and melting to a temperature of ° C. or higher, or filling a heat-resistant container with a synthetic silica powder having a relatively coarse particle size, which is described in Patent Document 3, without forming the glass, and in a reduced pressure atmosphere as it is. There is a manufacturing method in which transparent quartz glass is obtained by heating and melting with.

Further, the spherical granules obtained by granulating silica fine powder described in Patent Document 4 are used to improve the filling property of the powder, and the powder is melted under reduced pressure with a load applied, and further hot hydrostatic press. A method for producing transparent quartz glass to be treated has been conventionally known.

Japanese Unexamined Patent Publication No. 1-275438 Japanese Unexamined Patent Publication No. 1-270530 Japanese Unexamined Patent Publication No. 2-014840 Japanese Unexamined Patent Publication No. 9-295825

However, a manufacturing method in which silica fine powder is formed into a molded product and then heated and melted in a reduced pressure atmosphere, and a relatively coarse silica powder is filled in a heat-resistant container without being molded and then heated and melted in a reduced pressure atmosphere as it is. In the manufacturing method, large bubbles of 1 mm or more may remain. Therefore, a process of melting the spherical granules obtained by granulating silica fine powder under reduced pressure under reduced pressure and further performing a hot hydrostatic pressure press treatment is required after the melting, and one or more steps before and after the melting. This is a manufacturing method that requires additional labor and know-how because it is necessary to add.

The present invention provides a method for producing transparent quartz glass, which can prevent bubbles from remaining when quartz glass is produced using granulated silica powder obtained by granulating silica fine powder that can generate bubbles when melted. The task is to do.

As a result of diligent studies to solve these problems, the present inventors have made the granulated silica powder produced by granulating silica fine particles coexist with the silica powder having a relatively large particle size. By melting the glass, it was found that transparent glass in which the generation of air bubbles is suppressed can be produced.

That is, the gist of the present invention is as follows.
[1] A mixing step of mixing a silica powder having an average particle size of 100 μm or more and a granulated silica powder having an average particle size of 100 μm or more produced by granulating silica fine powder having an average particle size of 50 μm or less. A method for producing transparent glass, which comprises a melting step of melting the mixed silica powder at 1700 ° C. or higher.
[2] The method for producing transparent glass according to [1], wherein the silica fine powder having an average particle size of 50 μm or less has an iron content of 1 ppm or less.
[3] The method according to [1] or [2], wherein the mixing ratio of the silica powder having an average particle size of 100 μm or more and the granulated silica powder is 1: 6 or more and 6: 1 or less in terms of weight ratio. How to make transparent glass.
[4] The granulated silica powder is prepared by mixing silica fine particles having an average particle size of 50 μm or less, a dispersion medium, and a binder to prepare a slurry having a silica fine particle content of 50% by mass or less, and preparing the prepared slurry. The method for producing transparent glass according to any one of [1] to [3], which is obtained by spray-drying and granulating.
[5] The method for producing transparent glass according to [4], wherein the spray drying temperature is 100 ° C. or higher and 350 ° C. or lower.
[6] The method for producing transparent glass according to [4] or [5], wherein the dispersion medium is water having an iron content of 1 ppm or less.
[7] The method for producing transparent glass according to any one of [4] to [6], wherein the binder is a hydrophilic organic binder.

INDUSTRIAL APPLICABILITY According to the present invention, transparent glass in which the generation of bubbles is suppressed can be manufactured without requiring a step of removing bubbles.

The present invention will be described in detail below, but the present invention is not limited to the following embodiments, and can be variously modified and carried out within the scope of the gist thereof. In addition, when the expression "-" is used in this specification, it shall be used as an expression including numerical values or physical property values before and after the expression.

In one embodiment of the present invention, a silica powder having an average particle size of 100 μm or more and a granulated silica powder having an average particle size of 100 μm or more made by granulating silica fine powder having an average particle size of 50 μm or less are mixed. A method for producing transparent glass, comprising a mixing step and a melting step of melting the mixed silica powder at 1700 ° C. or higher.
Conventionally, a method for manufacturing transparent glass that is heated and melted after using silica fine powder as a raw material, or transparent glass that is filled in a heat-resistant container as it is without molding silica powder having a relatively coarse particle size and then heated and melted. In the above manufacturing method, large bubbles of 1 mm or more may remain. Therefore, a process for removing air bubbles was required. According to the present embodiment, it is possible to provide transparent glass in which the generation of bubbles is suppressed without such treatment, and the production efficiency can be improved.

The mixing step is a step of mixing a silica powder having an average particle size of 100 μm or more and a granulated silica powder having an average particle size of 100 μm or more produced by granulating silica fine powder having an average particle size of 50 μm or less. ..
The mixing ratio of the silica powder having an average particle size of 100 μm or more and the granulated silica powder having an average particle size of 100 μm or more is not particularly limited, and is usually 1: 6 or more and 6: 1 or less in terms of weight ratio, preferably. It is 1: 3 or more and 3: 1 or less. Increasing the proportion of granulated powder improves the fluidity and makes it easier to handle. On the other hand, by reducing the proportion of granulated powder to prevent the generation of bubbles, transparent glass with less bubbles can be easily obtained. Can be done.
The silica powder having an average particle size of 100 μm or more is not particularly limited, and may be a natural silica powder or a synthetic silica powder. Further, the shape thereof is not particularly limited, and is generally a crushed shape, but the shape is not limited to this, and spherical particles having improved circularity may be used. When purity is important, synthetic silica powder is more preferable because a high-purity product can be easily obtained.

The silica powder can be obtained by, for example, a so-called sol-gel method using alkoxysilane as a raw material. Hydrolysis of alkoxysilane by the sol-gel method is carried out by reacting alkoxysilane with water according to a well-known method. As the alkoxysilane, a tetrafunctional, lower alkoxysilane having 1 to 4 carbon atoms such as tetramethoxysilane and tetraethoxysilane or an oligomer thereof is preferable because hydrolysis is rapidly performed.

By classifying the silica powder into a silica powder having an average particle size of 100 μm or more using a sieve or the like, a silica powder having an average particle size of 100 μm or more can be obtained. The upper limit of the average particle size is not particularly limited, but is usually 200 μm or less, preferably 150 μm or less.
In the present specification, the average particle size of the silica powder before granulation means the median diameter (D50) measured by the laser diffraction type particle size distribution measuring device SALD-2300 (manufactured by Shimadzu Corporation).

The granulated silica powder is produced by granulating silica fine powder having an average particle size of 50 μm or less. The silica fine powder having an average particle size of 50 μm or less, which is a raw material of the granulated silica powder, preferably has an iron content of 1 ppm or less from the viewpoint of making the glass transparent.
The analysis of metal impurities such as iron can be performed by ICP-MS, fluorescent X-ray analysis, or the like.

The granulation method is not particularly limited, and examples thereof include a method in which raw material silica fine powder is slurried, a binder is added, and spray granulation is performed. The dispersion medium for slurry formation is usually water, but the dispersion medium is not limited to this as long as it can be used as a dispersion medium for granulation. The dispersion medium preferably has an iron content of 1 ppm or less.
The average particle size of the granulated silica powder may be measured using a particle image analyzer because it can be measured without damaging the granulated state.

The binder is not particularly limited, and an organic binder, an inorganic binder, or the like can be used, and a hydrophilic organic binder is preferable, and examples thereof include an acrylic polymer and polyvinylpyrrolidone. When the binder is used, it is usually used at a ratio of 3 parts by mass or more to 10 parts by mass with respect to 100 parts by mass of the raw material silica. By using the binder, the strength of the granulated silica powder is increased and the remaining amount of the silica fine powder is reduced, so that the granulated silica powder can be recovered in a yield of 80% by mass or more. ..

The spraying may be a known spray (sprayer) and is not particularly limited. The granulated silica powder may be dried, or a spray drying device such as a spray dryer that performs spray drying at one time may be used. When a spray drying device is used, the spray drying temperature is preferably 100 ° C. or higher and 350 ° C. or lower, more preferably 150 ° C. or higher, and even more preferably 200 ° C. or lower.

A preferable method for producing the granulated silica powder is to mix silica fine particles having an average particle size of 50 μm or less, a dispersion medium, and a binder to prepare a slurry having a silica fine particle content of 50% by mass or less, preferably 40% by mass or less. Then, the prepared slurry is spray-dried and granulated. The silica fine particles in the slurry are usually 10% by mass or more, preferably 30% by mass or more.

The granulated silica powder is usually calcined at 1000 ° C. or higher and 1300 ° C. or lower. The firing temperature is preferably 1100 ° C. or higher and 1250 ° C. or lower, and the firing time is usually 30 hours or longer and 60 hours or lower. The atmosphere at the time of firing is not particularly limited, but it is preferable to create a dry air atmosphere. The dry air preferably has a dew point of −40 ° C. or lower.

By classifying the granulated silica powder into a granulated silica powder having an average particle size of 100 μm or more using a sieve or the like, it is possible to obtain a granulated silica powder having an average particle size of 100 μm or more. The upper limit of the average particle size is not particularly limited, but is usually 200 μm or less, preferably 150 μm or less.

The mixed silica powder mixed in the mixing step preferably has an iron content of 10 ppm or less, more preferably 1 ppm or less, still more preferably 0.01 ppm or more, and particularly preferably 0.001 ppm or less. When the iron content of the silica powder is within the above range, when the silica powder is melted and vitrified, the glass tends to become transparent without crystallizing, and the glass is less likely to break.

The melting step is a step of melting the mixed silica powder at 1700 ° C. or higher to make transparent glass.
The glass is usually melted by a vacuum melting method, an oxyhydrogen melting method, or the like, but is not particularly limited. Melting may be performed at 1700 ° C. or higher. For example, in the case of the vacuum melting method, the silica powder mixed in the graphite crucible is weighed, and the graphite crucible whose surface is flattened by tapping is placed in a vacuum heating furnace at 1780 ° C. for 1 hour. An example is a method of heating, then cooling, and vitrifying.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the description of the following examples as long as it does not deviate from the gist thereof.

[Example 1]
Silica fine powder with an average particle size of 5 μm measured with a laser diffraction type particle size distribution measuring device SALD-2300 (manufactured by Shimadzu Corporation), ultrapure water, and Oricox KC-115VP (5 wt% with respect to the silica fine powder). (Made by Kyoeisha Chemical Co., Ltd.) was mixed to prepare a slurry having a silica fine powder concentration of 33 wt%. The slurry was granulated into silica powder having an average particle size of 150 μm using a spray dryer facility. This particle size was measured using a particle image analyzer "Moforogi G3" (Malvern Panalytical).

45 g of the mixed silica powder obtained by mixing the granulated silica powder and the silica powder having an average particle size of 150 μm at a mass ratio of 1: 1 was weighed into a graphite rubbing pot having a capacity of 50 cc, and the surface was flattened by tapping. .. Then, this graphite crucible was heated in a vacuum heating furnace at 1780 ° C. for 1 hour and then cooled to obtain a cylindrical silica molten glass ingot. The bubbles in the obtained ingot were observed using a loupe, and the number of bubbles having a diameter of 0.5 mm or less formed in the transparent glass layer in a bubble-free state was counted. No bubbles with a diameter of more than 0.5 mm were generated, and the cells were transparent.

[Example 2]
A mixed silica powder obtained by mixing the granulated silica powder produced in Example 1 and a silica powder having an average particle size of 150 μm at a mass ratio of 5: 1 is melted by the same method as in Example 1, and columnar silica is formed. A fused glass ingot was obtained. When bubbles were confirmed by the same method as in Example 1, no bubbles having a diameter of more than 0.5 mm were observed and the bubbles were transparent.

[Comparative Example 1]
Only the granulated silica powder produced in Example 1 was melted by the same method as in Example 1 to obtain a cylindrical silica molten glass ingot. When bubbles were confirmed by the same method as in Example 1, bubbles of 0.5 mm or more were gathered in the central part of the glass ingot innumerably, and the central part was white and the other side of the glass could not be seen at all.

Since the transparent glass obtained by the manufacturing method of the present embodiment can suppress the generation of bubbles, it can be used as a material for various glass products such as semiconductor jigs and silica glass crucibles, which are applications for which bubble-free is required.

Claims (7)

A mixing step of mixing a silica powder having an average particle size of 100 μm or more and a granulated silica powder having an average particle size of 100 μm or more produced by granulating silica fine powder having an average particle size of 50 μm or less, and the above-mentioned mixing. A method for producing transparent glass, which comprises a melting step of melting silica powder at 1700 ° C. or higher. The method for producing transparent glass according to claim 1, wherein the silica fine powder having an average particle size of 50 μm or less has an iron content of 1 ppm or less. The transparent glass according to claim 1 or 2, wherein the mixing ratio of the silica powder having an average particle size of 100 μm or more and the granulated silica powder is 1: 6 or more and 6: 1 or less in terms of weight ratio. Production method. The granulated silica powder is a mixture of silica fine particles having an average particle size of 50 μm or less, a dispersion medium, and a binder to prepare a slurry having a silica fine particle content of 50% by mass or less, and the prepared slurry is spray-dried. The method for producing transparent glass according to any one of claims 1 to 3, which is obtained by granulation. The method for producing transparent glass according to claim 4, wherein the spray drying temperature is 100 ° C. or higher and 350 ° C. or lower. The method for producing transparent glass according to claim 4 or 5, wherein the dispersion medium is water having an iron content of 1 ppm or less. The method for producing transparent glass according to any one of claims 4 to 6, wherein the binder is a hydrophilic organic binder.