JPH0822750B2 - Silica glass manufacturing method - Google Patents

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, and the like.

(Conventional technology) Silica glass is an important material indispensable for semiconductor manufacturing because it has excellent heat resistance, corrosion resistance, and optical properties. In addition, optical glass, photomask substrate for IC manufacturing, TFT substrate, etc. Are being used for, and their applications are expanding.

Conventional methods for producing silica glass include a method in which natural quartz is melted by an electric furnace or an oxyhydrogen flame, or a method in which silicon tetrachloride is oxidized at a high temperature in an oxyhydrogen flame or a plasma flame and melted. Also consumes a large amount of energy because it requires a high temperature of 2,000 ° C or higher in the manufacturing process, requires materials that can withstand such high temperatures during manufacturing, and is economical because it is difficult to obtain high-purity materials. ， I have some quality problems.

On the other hand, in recent years, a method called a sol-gel method for synthesizing silica glass at a low temperature has attracted attention. The outline is briefly described.

Silicon alkoxide represented by the general formula Si (OR) ₄ (R: alkyl group) (in the present invention,
(Including its polycondensate), eg (RO) ₃ Si ・ {OSi (OR)
₂ } _n · OSi (OR) ₃ , (n = 0 to 8, R: alkyl group) is added with water (pH may be adjusted with alkali or acid) and hydrolyzed to obtain a silica hydrosol (the present invention). In that is called silica sol). At this time, an appropriate alcohol is generally added as a solvent so that the silicon alkoxide and the water become a uniform system. This silica sol is allowed to gel by standing, heating, addition of a gelling agent, and the like. Thereafter, the gel is evaporated and dried to obtain a silica dry gel. Silica glass is obtained by sintering this dry gel in an appropriate atmosphere.

(Problems to be Solved by the Invention) However, there are still unsolved problems in the production of silica glass by the sol-gel method. In particular, cracks and cracks are likely to occur in the gel during the process of drying the gel, which makes it difficult to manufacture a monolithic large dry gel without cracks and cracks with high yield.

The present invention provides a method for producing silica glass without cracks or cracks.

(Means for Solving Problems) The present invention relates to a method for producing silica glass by a sol-gel method, in which a polyalkylene glycol ether such as a polyethylene glycol ether having a molecular weight of 100 to 10,000 is used as a silicon alkoxide during sol preparation. It is characterized in that 0.1 to 20 parts by weight is added to 100 parts by weight.

In the present invention, the alkyl group of the silicon alkoxide is not particularly limited, but it is preferable to use a silicon alkoxide having a methyl group, an ethyl group, a propyl group or a butyl group in view of ease of hydrolysis and gelation time. Is preferred. When hydrolyzing a silicon alkoxide by adding water or a mixed solution of water and alcohol to form a silica sol, add polyalkylene glycol ether to water, alcohol, or a mixed solution of water and alcohol in advance and uniformly dissolve them. .

The molecular weight (weight average molecular weight) of the polyalkylene glycol ether to be added is 100 to 10,000, preferably 1,000 to
8,000, most preferably 300 to 6,000, can be used and these can be used alone or as a mixture. If the molecular weight of the polyalkylene glycol ether is less than 100, it is necessary to add a considerable amount to the system in order to obtain an effective effect, and cracks and cracks will occur in the subsequent gel vitrification step of the gel. It will be easier. On the other hand, if the molecular weight exceeds 10,000,
Due to the remarkable gelation-promoting effect, it is very difficult to obtain a uniform gel. The amount of polyalkylene glycol ether added should be selected according to the molecular weight of the polyalkylene glycol ether. In the case of a relatively low molecular weight polyalkylene glycol ether, addition of less than 0.1 part by weight to 100 parts by weight of silicon alkoxide has almost no effect. On the other hand, in the case of a relatively high molecular weight polyalkylene glycol methyl ether, addition of more than 20 parts by weight to 100 parts by weight of a polycondensation product of a silicon alkoxide causes a remarkable gelation-promoting effect, and it is extremely difficult to obtain a uniform gel. Becomes difficult.

Polyalkylene glycol ether (mono ether,
Polyether glycol methyl ether, polyethylene glycol ethyl ether, polyethylene glycol propyl ether, polyethylene glycol butyl ether, polypropylene glycol methyl ether, polypropylene glycol ethyl ether, polypropylene glycol propyl ether, polypropylene glycol butyl ether, polybutylene glycol methyl ether, polybutylene Glycol ethyl ether, polybutylene glycol propyl ether, polybutylene glycol butyl ether, etc. can be used.

The catalyst to be added together with water is not particularly limited, such as a base and an acid, but a base gives a preferable result in view of gelation time and ease of sintering of the obtained dry gel. The alcohol added with water is not particularly limited, but water,
In terms of solubility in both alkoxides, methyl alcohol, ethyl alcohol, 1-propyl alcohol, 2
-It is preferable to use propyl alcohol or the like.

Silica glass is prepared by transferring the silica sol prepared as described above into a container such as a petri dish, keeping it at room temperature to 70 ° C to gel, and then drying at a temperature above room temperature for several weeks to give a dry gel. Method, for example, 1,000 in air
It is obtained by heating to 1,400 ° C. and sintering.

(Action) The cause of the addition effect of the polyalkylene glycol ether is not known in detail, but the control of the formation of silica fine particles in the sol, the bonding between these silica fine particles in the gel, and the drying process in the gel It is thought that this contributed to the relaxation of the stress generated in the gel and enabled the gel to become larger.

Example 1 54 g of water, 96 g of methyl alcohol and 0.06 g of choline were mixed,
Polyethylene glycol methyl ether (molecular weight
350) was added and dissolved. 152 g of the obtained solution
Was slowly added to the silicomethoxide (Si (OCH ₃ ) ₄ ) and mixed well to obtain silica sol.
The sample was placed in a Teflon-coated glass petri dish, sealed with aluminum foil, and gelled at room temperature. Then, make a hole in the lid and dry it in a constant temperature bath at 50 ° C for 2 weeks.
It was transferred to a constant temperature bath at ℃ and dried for 1 day to obtain a dry gel having a diameter of about 110 mm. The bulk density of the dried gel thus obtained is about
It was 0.7 g / cm ³ , and there were no cracks or breaks.

When the obtained gel was heated and sintered in air to 1,300 ° C, a transparent silica glass with a diameter of about 80 mm and a thickness of 5 mm without cracks or cracks was obtained. As a result of the analysis, this silica glass was in agreement with the silica glass.

Example 2 Polyethylene glycol methyl ether 1 having a molecular weight of 750
5.2 g was mixed and dissolved with 54 g water, 96 g methyl alcohol, 0.06 g choline. Then, the same drying as in Example 1 was performed to obtain a dried gel. The dried gel obtained was free of cracks and splits.

Example 3 11.4 g of polyethylene glycol methyl ether having a molecular weight of 2,000 was mixed and dissolved with 54 g of water, 96 g of methyl alcohol and 0.06 g of choline. Then, the same operation as in Example 1 was performed to obtain a dry gel. The dried gel obtained was free of cracks and splits.

Example 4 7.6 g of polyethylene glycol methyl ether having a molecular weight of 5,000 was mixed and dissolved with 54 g of water, 96 g of methyl alcohol and 0.06 g of choline. Then, the same operation as in Example 1 was performed to obtain a dry gel. The dried gel obtained was free of cracks and splits.

Example 5 1.52 g of polyethylene glycol methyl ether having a molecular weight of 5,000 was mixed and dissolved with 54 g of water, 96 g of methyl alcohol and 0.06 g of choline. Hereinafter, the same operation as in Example 1 was performed to obtain a dry gel. The dried gel obtained had no cracks or splits.

(Effects of the Invention) According to the present invention, it is possible to easily manufacture a large-sized silica glass having no cracks or cracks by the Zolgel method. There is basically no restriction on the size, and the shape is plate, bar,
It can be manufactured in any shape such as tubular.

Further, according to the present invention, silica glass can be manufactured at a lower cost than before, so that the application can be expanded not only to the fields of photomask base materials for IC manufacture which have been conventionally used but also to liquid crystal display base materials and the like.

Claims (2)

[Claims] (1) hydrolyzing a silicon alkoxide into a silica sol, gelling this, and drying to form a dry gel;
Next, in the method for producing silica glass to be sintered, at the stage of hydrolyzing silicon alkoxide to form silica sol, 0.1 to 20 parts by weight of polyalkylene glycol ether having a molecular weight of 100 to 10,000 is added to 100 parts by weight of silicon alkoxide. A method for producing silica glass, which comprises: 2. The method for producing silica glass according to claim 1, wherein the polyalkylene glycol ether is polyethylene glycol methyl ether.