JPH01119526A - 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 polyethylene imine 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, polyethylene imine having 100-200,000mol.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 art) Silica glass has excellent heat resistance, corrosion resistance, and optical properties, so it is an important material indispensable for semiconductor manufacturing. It is used for boards, etc., 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. 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.

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 alkoxide (including its polycondensate in the present invention) represented by the general formula S i (OR) a (R: alkyl group) 1 For example, (RO)3St・(O
S i (OR)z)-・03i(OR)s, (n
=o~B, R: alkyl group) is added with water (pH may be adjusted with an alkali or acid) 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 any cracks or cracks with a good yield.

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

(Means for Solving the Problems) The present invention provides a method for producing silica glass using a sol-gel method, in which polyethyleneimine having a molecular weight in the range of 100 to 200,000 is mixed with silicon alkoxide 10
It is characterized by adding 0.1 to 20 parts by weight relative to 0 parts by weight.

In the present invention, there are no particular restrictions on the alkyl group of the silicon alkoxide, but from the viewpoint of ease of hydrolysis and gelation time, silicon alkoxides having a methyl group, ethyl group, propyl group, or butyl group are used. It is preferable. When adding water or a mixed solution of water and alcohol to silicon alkoxide and hydrolyzing it to produce silica sol, polyethyleneimine yjci is added in advance to water, alcohol, or a mixed solution of water and alcohol to uniformly dissolve it.

Molecular weight of polyethyleneimine to be added (weight average molecular weight)
can be used in the range of 100 to 200,000, and these may be used alone or as a mixture. In order to obtain an effective effect, the molecular weight of polyethyleneimine is less than 100.

It is necessary to add a considerable amount to the system, and cranks and cracks are likely to occur during the subsequent gel sintering and vitrification process. On the other hand, if the molecular weight exceeds 200,000, it becomes extremely difficult to obtain a uniform gel due to the significant gelation promoting effect. The amount of polyethyleneimine added should be selected depending on the molecular weight of the polyethyleneimine. In the case of relatively low molecular weight polyethyleneimine, adding less than 0.1 part by weight to 100 parts by weight of silicon alkoxide will hardly have any effect. On the other hand, in the case of relatively high molecular weight polyethyleneimine, if it is added in excess of 20 parts by weight to 100 parts by weight of the silicon alkoxide condensate, it has a significant gelation promoting effect, making it extremely difficult to obtain a uniform gel. Become. The catalyst to be added together with water is not particularly limited, such as a base or an acid, but a base gives preferable results in terms of gelation time and ease of sintering the resulting dry gel. There are no particular restrictions on the alcohol added with water, but water.

From the point of view of solubility for both alkoxides.

Preferably, methyl alcohol, ethyl alcohol, 1-propyl alcohol, 2-propyl alcohol, etc. are 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 9, for example 1,000-1.
It is obtained by raising the temperature to 400°C and sintering it.

(Effect) Although the details of the cause of the effect of adding polyethyleneimine are unknown, it is due to the control of the formation of silica particles in the sol, the bonding between these silica particles in the gel, and the generation of silica particles in the gel during the drying process. It is thought that this contributed to the relaxation of the stress caused by the gel, making it possible to increase the size of the gel.

Example l Water 54g, methyl alcohol 96g, choline 0.06g
and polyethyleneimine (average molecular weight 50
1,000 to 60,000) was added and dissolved. The resulting solution was mixed with 152 g of silicomethoxide (
It was slowly added to St (OCL) 4) and mixed thoroughly to obtain 2 silica sol. This was placed in a Teflon-coated glass Petri dish with a diameter of 1501 mm, sealed with aluminum foil, and gelatinized at room temperature. After that, a hole was made in the lid, and it was dried for 2 weeks in a constant temperature oven at 50℃, and then heated to 120℃.
The mixture was transferred to a constant temperature bath at 0.degree. C. and dried for one day to obtain a dried gel having a diameter of about 1101 mm. The bulk density of the dry gel thus obtained was about 0.7 g/-, and there were no cracks or cracks.

When the obtained gel was heated and sintered in air to 1,300'C, a transparent silica glass having a diameter of about 80 mm and a thickness of 5 fflII+ without any cracks or breaks was obtained. As a result of analysis, this silica glass matched that of the silica glass.

Example 2 7.6 g of polyethyleneimine with an average molecular weight of 150.000 to 60.000 was mixed and dissolved with 54 g of water, 96 g of methyl alcohol, and 0.06 g 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 breaks.

Example 3 7.6 g of polyethyleneimine of 10,000 molecules @ 5
It was mixed and dissolved with 4g of water, 96g of methyl alcohol, and 0.06g of choline. Thereafter, the same operation as in Example 1 was performed to obtain a dry gel. The resulting dry gel contains
There were no cracks or cracks at all.

Example 4 15.2 g of polyethyleneimine with molecular weight s, ooo was
It was mixed and dissolved with 4g of water, 96g of methyl alcohol, and 0.06° 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 22.8 g of polyethyleneimine with a molecular weight of 2.000,
54g water, 96g methyl alcohol, 0.06g
was mixed and dissolved with choline. below.

A dry gel was obtained by performing the same operation as in Example 1. Obtained. There were no cracks or breaks in the dried gel.

(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 manufactured 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. A method for producing silica glass, which comprises adding 0.1 to 20 parts by weight of polyethyleneimine having a molecular weight of 100 to 200,000 to 100 parts by weight of silicon alkoxide in the step of preparing a silica sol.