JPH07277743A - Production of synthetic silica glass - Google Patents

Abstract

PURPOSE:To produce synthetic silica glass excellent in optical properties and applicable as, e.g. optics such as lens, prism, a beam splitter, a spectroscope and a mirror, a substrate for photomask or a TFT base plate for liquid crystal display according to the sol-gel method. CONSTITUTION:This is a method for production of synthetic silica glass by preparing a wet gel from a silica sol mixture solution composed of tetramethoxysilane or tetraethoxysilane and a silica sol solution containing silica fine particles according to the sol-gel method, drying it and heat-treating it. In this method, formation of the wet gel is carried out by blending one or more kinds of alcohols represented by ROH (provided that R is a 3 to 8C alkyl group) in the silica sol mixture solution before gelling so that the wet gel may contain the alcohols in an amount of 0.5 to 10wt.% in total and the resultant wet get is dried and heat treated to obtain synthetic silica glass. According to this method, the get can be effectively prevented from cracking during the drying process by a function of the alcohols contained in the gel and the objective synthetic silica glass free from an air bubble and excellent in optical properties can be produced in a high yield.

Description

Detailed Description of the Invention

[0001]

INDUSTRIAL APPLICABILITY The present invention can be applied to various optical components such as lenses, prisms, beam splitters, spectroscopes, mirrors, optical parts, photomask substrates, TFT substrates for liquid crystal displays, etc. The present invention relates to a method for producing synthetic quartz glass by the sol-gel method.

[0002]

2. Description of the Related Art The sol-gel method is known as one of the methods for producing synthetic quartz glass. For example, JP-A-60
In JP-A-215532, a mixed solution of silica sol and silicon alkoxide is gelled under an acidic catalyst to prepare a wet gel, the wet gel is dried to obtain a dry gel, and the dry gel is fired to form a transparent quartz glass body. A method of manufacturing is disclosed.

In the conventional sol-gel method, gel is cracked in the wet gel drying step, and large silica glass,
In particular, it has been extremely difficult to manufacture quartz glass having a large thickness with a high yield. The first reason that the wet gel breaks in the drying step is the stress due to the capillary force of the solution component in the pores of the porous gel. In other words, in the process of evaporating the solution of the gel, the solutions in the pores of different diameters in the gel have different capillary forces, which causes the gel to be unevenly stressed, resulting in cracking of the gel. It happens. As a method of preventing the cracking of the gel, for example, there is a method of adding ethylene glycol or glycerin having a low surface tension to the raw material to prepare a gel and reducing the stress due to the capillary force of the solution (Japanese Patent Laid-Open No. 2-14).
1432, JP-A-2-141433). However, in this method, it is necessary to add a large amount of ethylene glycol or glycerin in order to reduce the surface tension of the solution, and these high-viscosity high-boiling compounds are not completely removed even when the gel is heated at high temperature. In some cases, it may cause bubbles in the synthesized quartz glass, or the residual carbon may deteriorate the optical quality of the quartz glass.

[0004]

The object of the present invention is to provide a sol-
It is an object of the present invention to provide a method for producing synthetic quartz glass by the gel method, which prevents gel breakage in the drying step and does not deteriorate the optical quality of the synthesized quartz glass.

[0005]

According to the present invention, a wet gel is obtained by a sol-gel method from a silica sol mixed solution composed of tetramethoxysilane or tetraethoxysilane and a silica sol solution containing silica fine particles and dried. In the method of producing synthetic quartz glass by heat treatment, at least one kind of alcohol represented by ROH (R is a C _{3 to} C ₈ alkyl group) in the wet gel is 0.5 to 10 weight in total. %, So that the alcohol is present in the silica sol mixed solution before gelation so that the synthetic quartz glass is produced.

The silica sol solution containing fine silica particles used in the present invention is a dispersion of fine silica particles in an aqueous solvent. Examples of the fine silica particles include water,
Particle diameter of 0.1-0.5 μm synthesized by adding tetramethoxysilane or tetraethoxysilane to a mixed solution of ammonia and methanol or ethanol
Preferred are spherical silica fine particles.
The silica fine particles thus obtained are in the state of silica sol dispersed in a solvent containing water, and contain methanol or ethanol used in the synthesis of silica fine particles, or methanol or ethanol produced by hydrolysis of tetramethoxysilane or tetraethoxysilane. Has been. The concentration of the methanol or ethanol in the silica sol is preferably 10% by weight or less, more preferably 1% by weight or less by evaporating the solvent of the silica sol solution or adding water. Is adjusted to 20 to 40% by weight. Methanol and ethanol have low boiling points, so even if they are taken into the gel, they are mostly evaporated and removed in the gel drying process. However, when the concentration of methanol or ethanol in the silica sol solution exceeds 10% by weight, the synthetic quartz glass is used. Carbon is likely to remain inside, which may cause deterioration of optical characteristics.

There is no particular limitation on the method of mixing the silica sol solution and tetramethoxysilane or tetraethoxysilane, but preferably they are mixed as follows. First, the pH of the silica sol solution is adjusted to about 2 with an acidic aqueous solution under stirring conditions.
Adjust to. Then, tetramethoxysilane or tetraethoxysilane is added to 0.1 mol of silica fine particles in the silica sol solution in an amount of 0.1 to 1.0 mol to prepare a silica sol mixed solution, and the added tetramethoxysilane or tetraethoxysilane is added. Hydrolyze. afterwards,
Adjust the pH to 4-5 with a basic aqueous solution under stirring conditions,
The hydrolyzed tetramethoxysilane or tetraethoxysilane is dehydrated and polycondensed to initiate gelation.

When the polymerization proceeds, gelation occurs after several hours, but ROH such as propanol, butanol, pentanol, hexanol, heptanol, and octanol is added to the silica sol mixed solution before gelation (where R is C _{3 to} C ₈ ). At least one kind of alcohol represented by (alkyl group) is added to the total weight of the silica sol mixed solution before gelling, and in the above case, to the total weight of the silica sol mixed solution after addition of the basic aqueous solution. It is present in an amount to add up to 0.5-10% by weight. These alcohols may be added before gelation, and may be added before or after forming the silica sol mixed solution. For example, a method of adding to the silica sol solution before adding the acidic aqueous solution,
There are a method of adding after adjusting H, a method of adding after adding tetramethoxysilane or tetraethoxysilane, a method of adding to tetramethoxysilane or tetraethoxysilane, a method of adding after adding a basic aqueous solution, and the like. Further, the alcohol represented by ROH is not limited to a linear alcohol, but a branched alcohol.
The type may be one type or two or more types.

When the silica sol mixed solution after addition of the basic aqueous solution is poured into a suitable container and kept at room temperature, the entire silica sol mixed solution containing alcohol and the like gels in several hours to obtain a wet gel containing alcohol. . By allowing the alcohol having 3 to 8 carbon atoms to exist in the wet gel in this manner, gel cracking easily occurs.
In the drying step in the temperature range of 0 to 200 ° C., the evaporation of the solution component from the gel can be continuously controlled to prevent the evaporation from occurring at a certain temperature at a time, and to prevent the gel from cracking. In particular, the boiling points are different, preferably 50
When two or more kinds of alcohols having a carbon number of 3 to 8 and having a temperature of not less than 0 ° C. are selected and allowed to exist in the gel, cracking of the gel can be more effectively prevented. The boiling point of the added alcohol is 20
When the temperature exceeds 0 ° C. or the amount of added alcohol exceeds 10% by weight, compounds other than alcohol, particularly compounds containing elements other than C, H, O and Si, cyclic compounds or unsaturated compounds When it is present in the wet gel, carbon and a different element remain in the synthesized quartz glass, which causes deterioration of optical characteristics. If the amount of alcohol added is less than 0.5% by weight, the gel cracking cannot be effectively prevented.

The wet gel contains methanol or ethanol having boiling points of about 65 ° C. and about 78 ° C., which are produced by the hydrolysis of tetramethoxysilane or tetraethoxysilane, respectively, which has 3 to 3 carbon atoms added.
Although it has the effect of preventing the gel from breaking with the alcohol of No. 8, methanol or ethanol alone cannot prevent the gel from breaking. In addition, instead of tetramethoxysilane or tetraethoxysilane added to the silica sol solution, a silicon alkoxide having a C ₃ or more alkoxy group such as tetrapropoxysilane, tetrabutoxysilane, or tetrapentoxysilane may be used to synthesize the gel. Although the synthesized wet gel can contain an alcohol having an alkyl group of C ₃ or more such as propanol, butanol, and pentanol,
It is difficult to completely hydrolyze these silicon alkoxides, and the unhydrolyzed alkoxy groups cause bubbles in the quartz glass and deteriorate the optical properties of the quartz glass due to residual carbon. Therefore, the RO
The alcohol represented by H must be added as an alcohol having 3 to 8 carbon atoms.

The wet gel is dried by heating in a dryer in the air or under reduced pressure for 300 hours or longer, preferably for 400 hours or longer to 200 ° C. in stages to dry. In order to prevent the gel from cracking more effectively, it is preferable to perform so-called gel aging by treating the gel at 50 to 100 ° C. in a closed container before starting the drying of the gel. Also,
A container that can control the evaporation amount of the solution from the gel in order to prevent the gel from cracking more effectively in the gel drying process,
For example, it is preferable to put the gel in a closed container having a small hole in the lid and dry it.

The gel which has been subjected to the drying step is treated with about 18
Transparent quartz glass can be obtained by heating to 00 ° C., sintering and vitrification. In order to efficiently remove carbon coming from alcohol, for example from 200 ° C to 1200
A method of heating up to 1800C in an oxygen atmosphere and heating up to 1800C in an inert gas atmosphere can be mentioned. According to such a method, it is possible to prevent cracking of the gel, and it is possible to produce a synthetic quartz glass having no bubbles and excellent optical characteristics with a high yield.

[0013]

The presence total from 0.5 to 10 wt% of at least one or more alcohols [acting] ROH in the gel (R is an alkyl group of C ₃ -C ₈₎ represented by the easy cracking of the gel occurs It is considered that in the drying step in the temperature range of 50 to 200 ° C., evaporation of the solution component from the gel can be prevented from occurring at one time, and cracking of the gel can be prevented.

[0014]

EXAMPLES The present invention will be specifically described below based on Examples and Comparative Examples. Example 1 1 mol of tetramethoxysilane was added dropwise to 1 liter of the methanol solution in a solution containing 8 mol of water and 1 mol of ammonia in 1 liter of a methanol solution under stirring conditions to contain fine silica particles. A silica sol solution was synthesized.
The solvent in the silica sol solution was evaporated and water was added to obtain a silica sol solution having a silica fine particle content adjusted to 30% by weight. The concentration of methanol in this silica sol solution was about 1% by weight. 4500g of this silica sol solution
Under stirring conditions, 100 g of 1-propanol, 1-pentanol and 1-octanol were added. Next, after adding an aqueous hydrochloric acid solution to adjust the pH to 2.0, about 1500 g of tetramethoxysilane is added under stirring conditions,
A silica sol mixed solution was prepared. The added tetramethoxysilane was hydrolyzed under acidic conditions in the presence of water. Then, an aqueous ammonia solution was added to the silica sol mixed solution to adjust the pH to 4.8, and then the mixture was quickly poured into a sealable cylindrical container and allowed to stand, and then gelled in about 2 hours. It contained about 4.5% by weight in total,
A wet gel having a diameter of about 200 mm and a height of about 200 mm was obtained. A total of 20 wet gels were produced. When the wet gel in the closed container was kept at room temperature for 2 days and then heated to 70 ° C. and left for 4 days, water was released from the gel by dehydration polycondensation of the gel. After throwing this water out of the container,
Instead of the lid of the closed container, a lid with small holes was placed, and the gel was dried in a dryer at 70 ° C. for 340 hours. Then, the gel was taken out of the container and heated in the air from 70 ° C. to 200 ° C. over 70 hours to dry the gel.

Then, in an oxygen stream up to 900 ° C., about 3
The components that remained in the gel such as alcohol and water were removed by heating stepwise over 80 hours. Further, from 900 ° C. to 1100 ° C., it is heated under a reduced pressure of 1 × 10 ⁻² Torr or less for about 3 hours, and then gradually heated to 1800 ° C. for 2 hours, with a diameter of 120 mm and a height of 120 mm. A transparent synthetic quartz glass was prepared. Table 1 shows the number of gels with cracks in each step of drying the gel up to 70 ° C, drying up to 200 ° C, heating up to 900 ° C, and heating up to 1800 ° C to vitrify. Indicated. The obtained quartz glass was optically polished and the number of bubbles in the glass was observed with a stereomicroscope.
It was shown to.

Example 2 To 4500 g of the silica sol solution of Example 1 was added under stirring conditions.
650 g of 1-propanol was added. Then, gelation was performed in the same manner as in Example 1 to give 1-propanol approximately 9.
A wet gel containing 2% by weight and having a diameter of about 200 mm and a height of about 200 mm was obtained. A total of 20 wet gels were produced. After the gel was dried, the same procedure as in Example 1 was performed. As in Example 1, the number of cracked gels in each step and the observation results of bubbles in glass are shown in Table 1.

Example 3 4500 g of the silica sol solution of Example 1 was added under stirring conditions.
300 g of 1-octanol was added. Then, gelation was performed in the same manner as in Example 1, and 1-octanol was added to about 4.
A wet gel containing 5% by weight and having a diameter of about 200 mm and a height of about 200 mm was obtained. A total of 20 wet gels were produced. After the gel was dried, the same procedure as in Example 1 was performed. As in Example 1, the number of cracked gels in each step and the observation results of bubbles in glass are shown in Table 1.

Comparative Example 1 To 4500 g of the silica sol solution of Example 1 was added an aqueous hydrochloric acid solution to adjust the pH to 2.0, and then about 1500 g of tetramethoxysilane was added under stirring conditions to prepare a silica sol mixed solution. Aqueous ammonia solution was added to the silica sol mixed solution to adjust the pH to 4.8, and then it was quickly cast into a sealable cylindrical container and allowed to stand, and then gelled in about 2 hours.
A wet gel having a diameter of about 200 mm and a height of about 200 mm was obtained. A total of 20 wet gels were produced. After the gel was dried, the same procedure as in Example 1 was performed. As in Example 1, the number of cracked gels in each step and the observation results of bubbles in glass are shown in Table 1.

Comparative Example 2 4500 g of the silica sol solution of Example 1 was added under stirring conditions.
300 g of 1-dodecanol was added. This was gelled in the same manner as in Example 1, and 1-dodecanol was added to about 4.
A wet gel containing 5% by weight and having a diameter of about 200 mm and a height of about 200 mm was obtained. A total of 20 wet gels were produced. After the gel was dried, the same procedure as in Example 1 was performed. As in Example 1, the number of cracked gels in each step and the observation results of bubbles in glass are shown in Table 1.

[0020]

[Table 1]

[0021]

INDUSTRIAL APPLICABILITY In the production of quartz glass by the sol-gel method, a lens, a prism, a beam splitter, which effectively prevents breakage of gel and has excellent optical characteristics without bubbles,
It is possible to manufacture a synthetic quartz glass applicable to a spectroscope, an optical component such as a mirror, a photomask substrate, a liquid crystal display TFT substrate, and the like, particularly a large quartz glass with a high yield.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hatsushi Inoue 2-18-17 Shimogusa, Suginami-ku, Tokyo (72) Inventor Hidetaka Katayama 701 Shinroji, Kokuraminami-ku, Kitakyushu-shi, Fukuoka (72) Inventor Tetsuhiko Takeuchi Nagano 3-3-5 Yamato, Suwa-shi, Japan Seiko Epson Corporation

Claims (1)

[Claims] 1. A synthetic silica glass is obtained by a wet gel obtained by a sol-gel method from a silica sol mixed solution composed of tetramethoxysilane or tetraethoxysilane and a silica sol solution containing silica fine particles, which is dried and heat-treated. a process for preparing, ROH in the wet gel (wherein, R represents an alkyl group of C ₃ -C ₈₎ as the alcohol represented by the presence of 0.5 to 10 wt%, prior to gelling the silica sol mixture A method for producing synthetic quartz glass, characterized in that at least one kind of the alcohol is present in a solution.