JP2635313B2 - Method for producing silica glass - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing crack-free and crack-free silica glass used for optics, semiconductor industry, electronics industry, physics and chemistry, and the like.

(Prior art) Silica glass is recently an important material for semiconductor manufacturing due to its excellent heat resistance, corrosion resistance and optical properties. In addition, optical fibers, photomask substrates for IC manufacturing, TFT substrates, etc. And its applications are expanding.

Conventional methods for producing silica glass include a method in which natural quartz is melted in an electric furnace or an oxyhydrogen flame, and a method in which silicon tetrachloride is oxidized at a high temperature in an oxyhydrogen flame or a plasma flame to melt. The process requires a high temperature of 2,000 ° C or higher, which consumes a large amount of energy, requires materials that can withstand such a high temperature during manufacturing, and is economically and quality-friendly because it is difficult to obtain high-purity products. Has several problems.

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

A silicon alkoxide represented by the general formula Si (OR) ₄ (where R represents an alkyl group) and / or a polycondensate thereof (for example, (RO) ₃ Si · (OSi (OR) ₂ ) _n · OSi (OR) ₃ , n
= 0 to 8, R is an alkyl group), and water (a catalyst such as an alkali or an acid may be added) is added thereto to hydrolyze to obtain a silica hydrosol (hereinafter, silica sol). At this time, an appropriate solvent (for example, alcohol) may be added so that the silicon alkoxide and water become a uniform system. This silica sol is allowed to stand and gelled by adding a heating gelling agent. Further, the gel is dried by evaporation. This dried gel is sintered in an appropriate atmosphere to obtain silica glass.

(Problems to be Solved by the Invention) However, the production of silica glass by the sol-gel method still has unsolved problems. In particular, cracks and cracks are easily generated in the gel during the drying process, and it is difficult to produce a large monolithic dry gel without cracks and cracks with good yield.

Cracks and cracks in the process of gelation and drying shrinkage largely depend on the internal structure of the gel and the drying conditions. There are a method of using a base such as ammonia as a catalyst and a method of using an acid such as hydrochloric acid as a catalyst for hydrolyzing a silicon alkoxide to form a gel.

When ammonia is used as a catalyst, the rate of polycondensation is much faster than the rate of hydrolysis. It is difficult to obtain a gel.

On the other hand, when an acid is used as a catalyst, the rate of hydrolysis is high and the rate of polycondensation is very low, so that grain growth is unlikely to occur. Therefore, a gel with a strong binding force can be obtained, but cracking when an acid catalyst is used is considered to be due to drying conditions. In the case of an acid catalyst, it takes a considerable time to gel at room temperature.
Therefore, it is necessary to increase the gelation temperature in order to shorten the gelation time. However, those gelled at 50 to 70 ° C. have a disadvantage that they tend to contain air bubbles.

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

(Means for Solving the Problems) The present invention hydrolyzes a silicon alkoxide represented by the general formula Si (OR) ₄ (where R represents an alkyl group) and / or a polycondensate thereof into a silica sol, The present invention also relates to a method for producing silica glass which is then gelled, dried and sintered, and relates to a method for producing silica glass wherein an alcohol-soluble organic binder is added during the hydrolysis.

In the present invention, there is no particular limitation 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 to hydrolyze to form a silica sol, an alcohol-soluble organic binder is added to the water or alcohol in advance. Examples of the organic binder include acrylic acid polymer, isocyanate, ethylene oxide polymer, hydroxyl ethyl cellulose, polyethylene glycol, polyvinyl alcohol, methyl cellulose, wax, and the like. These organic binders may be used alone or in combination. The concentration of the organic binder with respect to the silicon alkoxide and / or the polycondensate thereof is appropriately adjusted depending on the type of the silicon alkoxide and / or the polycondensate used, the rate of hydrolysis, and the like. The alcohol used is not limited as long as it dissolves both the silicon alkoxide and / or its polycondensate and the organic binder. One or more alcohols may be used.

The catalyst is not particularly limited, such as a base and an acid. However, a base is preferred from the viewpoint of gelation time.

Silica glass is formed as described above, and the silica sol is transferred to a container such as a shearing container, gelled at room temperature to 70 ° C, and then dried at room temperature or higher to form a dry gel.
Further, it is obtained by sintering by a known method.

(Action) The organic binder controls the hydrolysis rate of silicon alkoxide and / or its polycondensate moderately,
It improves the uniformity of the generated gel, improves the strength of the gel, and prevents cracking and cracking of the gel. The addition of the organic binder makes it easier to control the drying conditions of the gel.

(Examples) The present invention will be described with reference to examples.

Example 1 1 mol of silicon tetramethoxide (Si (OCH ₃ ) ₄ )
Then, 3 mol of methyl alcohol was added and mixed well.
5% by weight of polyethylene glycol (a reagent manufactured by Wako Pure Chemical Industries, polymerization degree: 20,000
0) was added, and the dissolved solution was added in an amount of 2.5 mol and further mixed well to obtain a silica sol. This was placed in a glass scaffold coated with 90 mm diameter Teflon, sealed, and gelled at room temperature. Thereafter, a hole was formed in the lid, and the lid was dried in a thermostat at 50 ° C. for 7 days, then transferred to a thermostat at 120 ° C. and dried for 1 day to obtain a dried gel having a diameter of 67 mm. The bulk density of the dried gel thus obtained was 0.74 g / cm ³ , and there was no crack or crack.

The dried gel was heated and sintered to 1,250 ° C.
A transparent silica glass of 5 mm × 5 mm thickness without cracks or cracks was obtained. Analysis of this silica glass revealed that its properties were consistent with those of a commercially available silica glass.

Example 2 The concentration of polyethylene glycol in Example 1 was adjusted to 10
A dry gel was obtained by performing the same operation as in the example except that the amount was changed to% by weight. The resulting dried gel was completely free of cracks and cracks.

Example 3 Using polyvinyl alcohol (a reagent manufactured by Komune Chemical Co., Ltd., degree of polymerization: 2,000) as an organic binder, the concentration was 5% by weight.
A dried gel was obtained by performing the same operation as in Example 1 except that the above conditions were satisfied. The resulting dried gel was completely free of cracks and cracks.

Example 4 Example 1 was repeated except that the same polyvinyl alcohol as in Example 3 was used as the organic binder and the concentration was 10% by weight.
The same operation as described above was performed to obtain a dried gel. The resulting dried gel was completely free of cracks and cracks.

(Effect of the Invention) According to the present invention, large-sized silica glass free from cracks and cracks can be easily produced by a sol-gel method. The size is basically not limited, and it can be manufactured in any shape such as plate, rod, and tube.

In addition, since silica glass can be manufactured at a lower cost according to the present invention, it can be applied not only to photomask base materials for IC manufacturing which have been conventionally used, but also to liquid crystal display base materials.

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Takao Nakata 4-3-1-1, Higashicho, Hitachi City, Ibaraki Pref. Hitachi Chemical Co., Ltd. Ibaraki Research Laboratories (56) References JP-A-60-108325 (JP, A) JP-A-57-190645 (JP, A) JP-A-60-141627 (JP, A) JP-A-59-102833 (JP, A) JP-A-59-107938 (JP, A) JP-A-59-156935 (JP, A) JP, A)

Claims (1)

(57) [Claims] 1. A method for producing a silica sol by hydrolyzing a silicon alkoxide represented by the general formula Si (OR) ₄ (where R represents an alkyl group) and / or a polycondensate thereof, and then gelating the silica sol in a container. A method for producing silica glass to be dried and sintered, wherein the hydrolysis is carried out in the presence of a base catalyst, and wherein an alcohol-soluble organic binder is added during the hydrolysis. Law.