JPH01119523A - Production of silica glass - Google Patents

Abstract

PURPOSE:To easily obtain large-sized silica glass free from cracks and crazes when silica glass is produced by a sol-gel process by adding specific amount of polyalkylene glycol at the time of preparation of sol. CONSTITUTION:Silicon alkoxide is hydrolyzed to prepare silica sol, this silica sol is converted into gel, this gel is dried and the resulting dry gel is sintered to produce silica glass. In the stage for preparing the silica sol by hydrolysis, polyalkylene glycol having 100-60,000mol.wt. is added by 0.1-20pts.wt. per 100pts.wt. silicon alkoxide.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention produces silica glass used for optics, semiconductor industry, electronic industry, physics and chemistry, etc.

(Prior technology) Silica glass has excellent heat resistance, corrosion resistance, and optical properties, so it is an important material indispensable for semiconductor manufacturing, and is also used in optical fibers, photomask substrates for IC manufacturing, TPT substrates, etc. It has been used for many years, and its applications are being expanded 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. The manufacturing process requires a high temperature of 2,000°C or higher, which consumes a large amount of energy, and materials that can withstand such high temperatures are required during manufacturing, and it is difficult to obtain high-purity materials, making it economical. 5) There are some problems in terms of quality.

In contrast, a method for synthesizing silica glass at low temperatures called the sol-gel method has recently attracted attention, and a brief overview thereof will be given below.

Silicon alkoxide (including its polycondensate in the present invention) represented by the general formula S l (OR) a (R: alkyl group) 1 For example, (RO)ss i・(O3
1(OR)z) ,・os 1(OR)*, (n=
o~8. R: Alkyl group) to water (alkali or acid)
1 (which may be adjusted) and hydrolyzed to produce silica hydrosil (referred to as silica sol in the present invention).
At this time, an appropriate alcohol is generally added as a solvent so that the silicon alkoxide and water form a homogeneous system. This silica sol is gelled by standing still, increasing the temperature, adding a gelling agent, etc. Thereafter, the gel is evaporated to dryness to obtain a dry silica 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 cracks are likely to occur in the gel, making it difficult to produce a monolithic large-sized dried gel without cracks or cracks with a good yield.

The present invention provides a method for manufacturing silica glass that does not cause cracks or cracks.

(Means for Solving the Problems) The present invention provides a method for producing silica glass using the sol-gel method, in which polyalkylene glycol such as polyethylene glycol with a molecular weight ranging from 100 to 60,000 is converted into silicon alkoxide during sol preparation. 0.1 per 100 parts by weight
It is characterized by adding up to 20 parts by weight.

In the present invention, there are no particular restrictions on the alkyl group of silicon alkoxide, but from the viewpoint of ease of hydrolysis and gelation time, silicon alkoxide having a methyl group, ethyl group, propyl group, or butyl group is used. is preferred. When adding water or a mixed solution of water and alcohol to silicon alkoxide and hydrolyzing it to generate silica sol, add polyalkylene glycol such as polyethylene glycol to the water, alcohol, or mixed solution of water and alcohol in advance and dissolve it uniformly. The molecular weight (weight average molecular weight) of the polyalkylene glycol to be added is from 100 to 60,000°, preferably from 1,500 to
50,000. Most preferably 10.000-40.0
Polyalkylene glycols with a molecular weight of 100 can be used, and these can be used alone or as a mixture.
less than.

In order to obtain an effective effect, it is necessary to add a considerable amount to the system, which tends to cause cracks and fractures in the subsequent gel sintering and vitrification process.

On the other hand, when the molecular weight of 9 exceeds 60,000, it becomes extremely difficult to obtain a uniform gel due to the significant gelation promoting effect. The amount of polyalkylene glycol added should be selected depending on the molecular weight of the polyalkylene glycol.

In the case of relatively low molecular weight polyalkylene glycol, adding less than 0.1 part by weight to 21,100 parts by weight of Silicon Alfti will have little effect. In this case, if more than 20 parts by weight is added to 100 parts by weight of the silicon alkoxide condensation product, it becomes extremely difficult to obtain a uniform gel due to the significant effect of promoting gelation. As polyalkylene glycol.

Polyethylene glycol, polymethylene glycol, polypropylene glycol, polybutylene glycol, etc. can be used. The catalyst to be added together with water is not particularly limited, such as bases and acids.

From the viewpoint of gelation time and ease of sintering of the resulting dry gel, a base gives more preferable results. There are no particular restrictions on the alcohol added together with water, but from the viewpoint of solubility in both water and alkoxide, methyl alcohol, ethyl alcohol, 1-propyl alcohol, 2-propyl alcohol,
- Preferably, propyl alcohol or the like is used.

Silica glass is obtained by transferring the silica sol prepared 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 for several weeks to form a dry gel.

Further known methods 1, for example 1,000-1.
It is obtained by raising the temperature to 400°C and sintering it.

(Effect) The details of the effects of adding polyalkylene glycol are unknown, but they include control of the formation of silica particles in the sol, bonding between these silica particles in the gel, and formation of silica particles in the gel during the drying process. It is thought that this contributed to alleviation of the stress generated and made it possible to increase the size of the gel.

Example 1 54 g of water, 96 g of methyl alcohol, 0.06 g of choline
and polyethylene glycol (molecular weight 50
．． 000) was added and dissolved. The obtained solution was slowly added to 152 g of silicomethoxide (Si (OCH Ri a") and mixed thoroughly to obtain a silica sol. This was placed in a Teflon-coated glass petri dish with a diameter of 150 mm. , sealed with aluminum foil and gelatinized at room temperature.Then, a hole was made in the lid and dried in a constant temperature bath at 50℃ for two weeks, then transferred to a constant temperature bath at 120℃ and dried for one day. A dry gel of 110 m- was obtained.The bulk density of the dry gel thus obtained was approximately 0.7 g/
AJ, and there were no cranks or cracks at all.

When the obtained gel was heated and sintered in air to 300° C., a transparent silica glass having a diameter of about 80+U+ and a thickness of 5III11 without cracks or cracks was obtained. As a result of analysis, this silica glass matched that of the silica glass.

Example 2 7.6 g of 120,000 molecule polyethylene glycol
, 54 g of water, and 96 g of methyl alcohol.

It was mixed and dissolved with 0.06g of choline. Thereafter, drying was carried out in the same manner as in Example 1 to obtain a dried gel. The dried gel obtained had no cracks or cracks.

Example 3 12.2 g of polyethylene glycol with a molecular weight of 8.000
54g of water, 96g of methyl alcohol.

It was mixed and dissolved with 0' and 06 g of choline. Thereafter, the same operation as in Example 1 was performed to obtain a dry gel. The dried gel obtained had no cracks or cracks.

Example 4 15.2 g of polyethylene glycol with molecular weight t, ooo
54g of water, 96g of methyl alcohol.

It was mixed and dissolved with 0.06g of choline. Thereafter, the same operation as in Example 1 was performed to obtain a dry gel. The dried gel obtained had no cracks or cracks.

Example 5 30.4 g of polyethylene glycol with molecular weight t, ooo
, 54 g of water, and 96 g of methyl alcohol.

It was mixed and dissolved with 0.06g of choline. Thereafter, the same operation as in Example 1 was performed to obtain a dry gel. Obtained. Dry Kel has no cracks or cracks.
There wasn't any.

(Effects of the Invention) According to the present invention, large-sized silica glass without cranks or cracks can be easily produced by the Solcale method. There are basically no restrictions on its size, and it can be manufactured in any shape such as a plate, rod, or tube.

Furthermore, according to the present invention, silica glass can be produced at a lower cost than before, so it can be applied 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)

[Scope of Claims] 1. In a method for producing silica glass in which silicon alkoxide is hydrolyzed to form silica sol, this is gelled, dried to form a dry gel, and then sintered, silicon alkoxide is hydrolyzed. In the step of making a silica sol, polyalkylene glycol with a molecular weight of 100 to 60,000 is
0.1 to 20 per 100 parts by weight of silicon alkoxide
A method for producing silica glass characterized by weight addition. 2. The method for producing silica glass according to claim 1, wherein the polyalkylene glycol is polyethylene glycol.