JPS62265130A - Production of silica glass - Google Patents

Abstract

PURPOSE:To easily produce the title large-sized silica glass without cracks, etc., by hydrolyzing silicon alkoxide or its polycondensation product by adding an org. binder to form a silica sol, gelating the sol, and drying and sintering the gel. CONSTITUTION:Silicon alkoxide shown by the general formula, Si(OR)4, (where R is an alkyl group) and/or its polycondensation product are hydrolyzed by adding water or an alcohol and an alcohol-soluble org. binder, and a silica sol is obtained. The silica sol is allowed to stand and gelated, and the gel is then dried to obtain a dry gel. The control of the hydrolysis rate and drying conditions is facilitated by the org. binder, the uniformity of the formed gel is improved, the strength of the gel is increased, and the cracking and crazing of the dry gel are prevented. The dry gel is sintered, and large-sized silica glass without cracks, etc., is easily obtained.

Description

[Detailed description of the invention] (Industrial application field) The present invention is applicable to optics, semiconductor industry, and electronic industry.

This article relates to a method for manufacturing silica glass that is free from cracks and breaks and is used for physical and chemical purposes.

(Prior art) Silica glass has good heat resistance, corrosion resistance, and optical properties, so it has recently become an important material indispensable for semiconductor manufacturing, and is also used as a photomask substrate for optical fiber and IC manufacturing. It is used for TF'T substrates and its applications are expanding more and more.

Conventional methods for manufacturing silica glass include melting natural quartz in an electric furnace or oxyhydrogen flame, or oxidizing and melting silicon tetrachloride at high temperature in an oxyhydrogen flame or plasma flame, but neither method can produce it. The process requires high temperatures of 2,000'C or more, consuming a large amount of energy, and materials that can withstand such high temperatures are required during manufacturing.

In addition, it has several problems in terms of economy and quality, such as the difficulty in obtaining high-purity products.

On the other hand, in recent years, a method of synthesizing silica glass at low temperature called the sol-gel method has been attracting attention.

The outline will be briefly described below.

Silicon alkoxides and/or polycondensates thereof represented by the general formula Si(OR)4 (where R represents an alkyl group) (for example, (ROhSi.(O8i(ORh).03)
i(OR)3. n=o~8.几 is an alkyl group), add water (a catalyst such as alkali or acid may be added),
It is hydrolyzed to produce silica hydrosil (hereinafter referred to as silica sol). At this time, an appropriate solvent (for example, alcohol) may be added so that the silicon alkoxide and water form a uniform system. This silica sol is allowed to stand still and is gelled by heating and adding a gelling agent.

Further, the gel is evaporated to dryness to obtain a dry gel.

Silica glass is obtained by sintering this dried gel in a suitable atmosphere.

(Problems to be Solved by the Invention) However, there are still unresolved problems in the production of silica glass by the sol-gel method. In particular, during the process of drying the gel, cracks and fractures are likely to occur in the gel, making it difficult to produce a monolithic large-sized dry gel without cracks and fractures with a good yield.

Cracks and splits during the gelation and drying shrinkage processes are largely due to the internal structure of the gel and the drying conditions.

There are two methods for hydrolyzing and gelling silicon alkoxide: one method uses a base such as ammonia as a catalyst, and the other method uses an acid such as hydrochloric acid as a catalyst.

When ammonia is used as a catalyst, the polycondensation rate is significantly faster than the hydrolysis rate, and the resulting dry gel has a coarse structure with large particles, and the bonding force between the two particles is weak, resulting in dry gels with a diameter of 2 cm or more. It is difficult to obtain gel.

On the other hand, when an acid is used as a catalyst, the rate of hydrolysis is faster.

Grain growth is difficult to occur because the polycondensation rate is very slow.

Therefore, a gel with strong binding strength can be obtained, but cracking when an acid catalyst is used is thought to be caused by the drying conditions. In addition, in the case of an acid catalyst, it takes about 30 minutes to gel at room temperature. Therefore, it is necessary to increase the gelling temperature in order to shorten the gelling time. However, 50-70
One that is gelled at ℃ has the disadvantage that it tends to contain air bubbles.

An object of the present invention is to provide a method for producing silica glass that eliminates the above-mentioned drawbacks.

(Means for Solving the Problems) The present invention involves hydrolyzing a silicon alkoxide and/or its polycondensate represented by the general formula Si (OR) 4 (where Rd represents an alkyl group) to form a silica sol. In the method for producing silica glass which involves gelling, drying and sintering, item # relates to a method for producing silica glass in which an alcohol-soluble organic binder is added during hydrolysis.

In the present invention, there are no particular limitations on the alkyl group of the silicon alkoxide and/or its polycondensate. When water and alcohol are added to silicon alkoxide and/or its polycondensate and hydrolyzed to produce silica sol, an alcohol-soluble organic binder is added in advance to the water or alcohol. Examples of organic binders include acrylic acid polymer, isocyanate, ethylene oxide polymer, and hydroxyl ethyl cellulose.

Polyethylene glycol, polyvinyl alcohol.

Examples include methylcellulose and wax, and these organic binders may be used alone or in combination. The concentration of the organic binder relative to the silicon alkoxide and/or its polycondensate is appropriately adjusted depending on the type of silicon alkoxide and/or its polycondensate used, the rate of hydrolysis, etc. The alcohol used is not limited as long as it can dissolve both the silicon alkoxide and/or its polycondensate and the organic binder.

One or more types of alcohol may be used.

The medium is not particularly limited, such as bases and acids, but bases are preferred from the viewpoint of gelation time.

Silica glass is obtained by transferring the silica sol produced as described above to a container such as a petri dish, keeping it at room temperature to 70°C to gel it, and then drying it at a temperature above room temperature to form a dry gel.
Further, it can be obtained by sintering using a known method.

(Function) The organic binder moderately controls the rate of hydrolysis of silicon alkoxide and/or its polycondensate, while improving the uniformity of the gel produced.

Improves the strength of the gel and prevents it from cracking and splitting. Furthermore, the addition of an organic binder makes it easier to control the drying conditions of the gel.

(Example) The present invention will be explained with reference to two examples.

Example 1 1 mol of silicon tetramethoxide (S i (0CR
3) To 4), 3 moles of methyl alcohol was added and mixed well. 0.01 mol/l of ammonia water was added to this solution and thoroughly mixed to obtain a silica sol. This was placed in a Teflon-coated glass petri dish with a diameter of 90 m, sealed, and gelatinized at room temperature.

After that, a hole was made in the lid, and it was dried for 7 days in a constant temperature bath at 50℃, and then transferred to a constant temperature bath at 120℃ and dried for 1 day.
70 dry gels were obtained. The bulk density of the dry gel thus obtained was 0.74 g/cm''.

There were no cracks or breaks at all.

When this dried gel was heated and sintered to 1,250°C, a transparent silica glass having a diameter of 45 plates and a thickness of 511 inches without any cracks or breaks was obtained. Analysis of this silica glass revealed that its properties matched those of commercially available silica glass.

Example 2 The concentration of polyethylene glycol in Example 1 was changed to 10
A dry gel was obtained in the same manner as in Example 1 except that the weight was increased. The dried gel obtained had no cracks or breaks.

Example 3 A dry gel was obtained by performing the same operation as in Example 1 except for the following. The dried gel obtained had no cracks or breaks.

Example 4 Example 1 except that the same polyvinyl alcohol as in Example 3 was used as the organic binder and the concentration was 10% by weight.
A dry gel was obtained in the same manner as above. The dried gel obtained had no cracks or breaks.

It can be easily manufactured by the method. There are basically no restrictions on its size, and it can be manufactured in any shape such as a plate, rod, or tube.

Further, due to the invention, silica glass can be manufactured at a lower cost than before, so its application can be expanded not only to fields such as photomask substrates for IC manufacturing, which have been conventionally used, but also to substrates for liquid crystal displays, etc. −＼”・

Claims (1)

[Claims] 1. Production of silica glass by hydrolyzing silicon alkoxide and/or its polycondensate represented by the general formula Si(OR)_4 (where R represents an alkyl group) to obtain silica sol, then gelling, drying and sintering A method for producing silica glass, characterized in that an alcohol-soluble organic binder is added during the hydrolysis.