JPH0717388B2 - 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 a heavy material that is indispensable for semiconductor manufacturing because it has excellent heat resistance, corrosion resistance, and optical properties. Furthermore, optical glass, photomask substrates for IC manufacturing, TFT substrates, 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 requires a high temperature of 2,000 ° C or higher in the manufacturing process, which consumes a large amount of energy, requires a material that can withstand such a high temperature during manufacturing, and is economical because it is difficult to obtain a high-purity product. There are some problems in terms of quality.

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

Silicon alkoxides represented by the general formula Si (OR) ₄ (R: alkyl group) (including polycondensates thereof in the present invention), for example, (RO) ₃ Si · {OSi (OR) ₂ } _n・ OSi (OR) ₃ , (n
= 0 to 8, R: alkyl group), water (pH may be adjusted with alkali or acid) is added and hydrolyzed to give a silica hydrosol (in the present invention, referred to as 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. Then, the gel is evaporated to dryness 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 remains an unsolved problem 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 that does not cause cracks or breaks.

(Means for Solving the Problems) In the present invention, in the method for producing silica glass by the sol-gel method, the viscosity of a 2% (wt%) aqueous solution at 20 ° C. is 100 to 10,000 centipoise at the time of sol preparation. Hydroxyalkyl cellulose 0.1 to 100 parts by weight of silicon alkoxide
It is characterized by adding 5.0 weights.

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 with water or a mixed solution of water and alcohol to generate a silica sol, hydroxyalkyl cellulose is previously added and uniformly dissolved in water, alcohol, or a mixed solution of water and alcohol.

The molecular weight of hydroxyalkyl cellulose added is 2%
An aqueous solution having a viscosity at 20 ° C. of 100 to 10,000 centipoise, preferably 5,000 to 8,000 centipoise, most preferably 1,000 to 6,000 centipoise can be used, and these may be used alone or as a mixture.

Hydroxyalkyl cellulose of 2% aqueous solution
If the viscosity at 20 ° C is less than 100 centipoise, it is necessary to add a considerable amount to the system in order to obtain an effective effect, and cracks and fractures may occur in the subsequent gel vitrification process of gel. It will be easier. On the other hand, when the viscosity of a 2% aqueous solution at 20 ° C. exceeds 10,000 centipoise, it becomes extremely difficult to obtain a uniform gel because of the remarkable gelation-promoting effect. The high molecular weight hydroxyalkyl cellulose deposited therein decomposes and burns during the subsequent firing process, resulting in large voids in the gel, which tend to remain as defects in the glass.

As the hydroxyalkyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxybutyl cellulose and the like can be used.

The amount of hydroxyalkyl cellulose added should be selected according to the molecular weight of the hydroxyalkyl cellulose. In the case of hydroxyalkyl cellulose having a relatively low molecular weight, addition of less than 0.1 parts by weight to 100 parts by weight of silicon alcotyside has almost no effect. On the other hand, in the case of a relatively high molecular weight hydroxyalkyl cellulose, if it is added in an amount of more than 5.0 parts by weight with respect to 100 parts by weight of silicon alkoxide, it will be extremely difficult to obtain a uniform gel due to the remarkable gelation promoting effect.

The catalyst added with water is not particularly limited, such as base and acid,
Bases give preferable results in terms of gelation time and ease of sintering of the obtained dry gel. The alcohol added with water is not particularly limited, but it is preferable to use methyl alcohol, ethyl alcohol, 1-propyl alcohol, 2-propyl alcohol, etc. from the viewpoint of solubility in both water and alkoxide.

Silica glass is prepared 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, and then drying at a temperature above room temperature for several weeks to give a dry gel. Method, for example, 1000 to 14 in air
It is obtained by heating to 00 ° C. and sintering.

(Action) The cause of the addition effect of hydroxyalkyl cellulose is unknown, 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 formation of gel in the gel during the drying process It is thought that this contributed to the relaxation of the generated stress and made the gel larger.

Example 1 3 mol of methyl alcohol, 3 mol of water and 0.0005 mol of choline were mixed, and 7.6 g of hydroxypropyl cellulose (viscosity of a 2% aqueous solution at 20 ° C. was 400 centipoise) was added and dissolved. . The obtained solution was slowly added to 1 mol of silicomethoxide (Si (OCH ₃ ) ₄ ) and further thoroughly mixed to obtain a silica sol. This was put in a Teflon-coated glass dish with a diameter of 150 mm, sealed with aluminum foil, and gelled at room temperature. After that, a hole was opened in the lid, and the gel was dried in a thermostat of 50 ° C. for 2 weeks, then transferred to a thermostat of 120 ° C. and dried for 1 day to obtain a dry gel having a diameter of about 120 mm. The dry gel thus obtained has a bulk density of about 0.6 g / cm ^3.
There were no cracks or breaks.

When the obtained gel was heated and sintered in air to 1300 ° 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 2.3 g of hydroxypropyl cellulose having a viscosity of 4000 centipoise at 20 ° C. in a 2% aqueous solution was mixed with 3 mol of methyl alcohol, 3 mol of water and 0.0005 mol 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 3 1.2 g of hydroxybutyl cellulose having a viscosity of 14000 centipoise at 20 ° C. in a 2% aqueous solution was mixed with 3 mol of methyl alcohol, 3 mol of water and 0.0005 mol 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.

(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. The size is basically not limited, and the shape can be any of plate, rod, and tube.

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 (1)

[Claims] 1. A silicon alkoxide is hydrolyzed to give a silica sol, which is gelled and dried to give a dry gel.
Then, in the method of producing the silica glass to be sintered, the silicon alkoxide is hydrolyzed to form silica sol.
% Aqueous solution having a viscosity of 100 to 10,000 centipoise at 20 ° C. is added in an amount of 0.1 to 5.0 parts by weight with respect to 100 parts by weight of silicon alkoxide.