JPH06329425A - Production of silica glass - Google Patents

Abstract

PURPOSE:To provide a method for producing silica glass in which the occurrence of cracking in a process for drying a get is suppressed. CONSTITUTION:A partial polycondensate of an alkoxysilane containing an acidic component in an amount of >=1X10<-4>mol based on 100g partial polycondensate of the alkoxysilane is used as the partial polycondensate of the alkoxysilane in a method for producing silica glass by hydrolyzing the partial polycondensate of the alkoxysilane in the presence of a solvent, an organic polymeric compound and a basic catalyst, providing a sol, gelatinizing the resultant sol, drying the gelatinized sol, affording a dried gel, burning the gel and providing the glass.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing silica glass used for optics, semiconductors, electronics industry, physics and chemistry and the like.

[0002]

2. Description of the Related Art Silica glass is an important material indispensable for semiconductor manufacturing because it is excellent in heat resistance, corrosion resistance and optical characteristics. Furthermore, it is a photomask substrate for manufacturing optical fibers, ICs, and TFT substrates. It is used for such purposes, and its uses are expanding more and more.

Attention has been paid to the sol-gel method which enables low-priced synthesis of high-purity silica glass. The outline is briefly described. To the alkoxysilane represented by the general formula Si (OR) ₄ (R: alkyl group), water (pH may be adjusted with alkali or acid) is added and hydrolyzed to give a silica hydrosol (referred to as a sol in the present invention). ). At this time,
A suitable solvent is generally added so that the alkoxysilane and water are uniform. This sol is allowed to stand and is allowed to gel by heating. Then, the liquid phase (alcohol produced by hydrolysis of alkoxysilane, added solvent, water, etc.) in the gel is evaporated and dried to obtain a silica dry gel (in the present invention, a dry gel). Silica glass is obtained by firing this dry gel in an appropriate atmosphere.

A problem in the above-mentioned method for producing silica glass by the sol-gel method is cracking during gel drying process. As a method for preventing this cracking, a partial polycondensate of alkoxysilane is used as a raw material for alkoxysilane (Japanese Patent Laid-Open No. 61-270225), and choline is used as a catalyst for the hydrolysis of alkoxysilane (Japanese Patent Laid-Open No. 2006-270225). No. 62-165128), an organic polymer compound is added at the time of sol preparation (JP-A-62-2651).
30), the polycondensate composition of the partial polycondensate of alkoxysilane is optimized (JP-A-3-247515), and a solvent having a higher boiling point than water and a small surface tension is used as a solvent (special feature). Methods such as Kaihei 2-14835) have been proposed.

[0005]

However, even when these proposed methods are used, cracks often occur in the process of drying the gel when the size of the dried gel becomes large, and the yield increases as the size of the dried gel becomes larger. Drops sharply. The present invention provides a method for producing silica glass that suppresses the occurrence of cracks in the dry gel.

[0006]

According to the present invention, a partial polycondensate of an alkoxysilane is hydrolyzed to a sol in the presence of a solvent, an organic polymer compound and a base catalyst, and further gelled.
Partial polycondensation product of alkoxysilane is a partial polycondensation product of alkoxysilane in the method for producing silica glass, which is dried to form a dry gel and then baked to form glass. 1 x 10 for 100g
It is characterized by containing ^-4 mol or more.

The present inventor uses a partial polycondensate of an alkoxysilane as a raw material, and hydrolyzes it in the presence of an organic polymer compound using a base as a catalyst to produce a sol, gelling and drying it to obtain a dry gel. As a result of investigating the cause of defective cracking of the dried gel in the process, the concentration of the salt produced by the reaction between the acid component contained in the partial polycondensation product of the alkoxysilane and the base added as a hydrolysis catalyst is It was found that there is a close relationship with the occurrence of cracks in the process.

The partial polycondensation product of an alkoxysilane is obtained by hydrolyzing and polycondensing an alkoxysilane monomer in the presence of a suitable solvent with water in an amount less than that required to completely hydrolyze the alkoxy group. It is synthesized by removing the solvent and water. During this hydrolysis, an acid is added as a catalyst. Most of this acid is removed in the solvent removal step, but some remains in the final product.

When a sol is prepared by using a partial polycondensate of alkoxysilane as a raw material and a base catalyst, a salt is formed in the sol by the reaction between the acid component remaining in the partial polycondensate of alkoxysilane and a base. However, this salt amount changes depending on the fluctuation of the acid component concentration in the partial polycondensate of the alkoxysilane.

[0010] As a result of further study focusing on the concentration of the salt formed in the sol in the process of preparing the sol, the partial polycondensation product of alkoxysilane was obtained in the presence of a solvent, an organic polymer compound and a base catalyst. Partial polycondensation of alkoxysilane as a partial polycondensation product of alkoxysilane in the process for producing silica glass by hydrolyzing into a sol, gelling the sol, drying into a dry gel, and firing into glass Thing 100
It was confirmed that by using the one containing 1 × 10 ⁻⁴ mol or more of the acid component with respect to g, the cracking of the gel during the drying process was largely suppressed.

The acid component remaining in the partial polycondensate of the alkoxysilane is measured by titration with an appropriate base (for example, choline in methanol), and its existing form (whether in the free acid state or not) is used. It does not matter whether it is in the form of a compound with silicon, etc.), and it is important that it reacts with a base added in the sol preparation process to form a salt.

When the acid component is less than 1 × 10 ^-4 mol per 100 g of the partial polycondensate of alkoxysilane, the gel has a high bulk density, and many cracks and cracks are generated during the drying process. There is no particular upper limit on the concentration of the acid component in the partial polycondensate of the alkoxysilane, but as the acid concentration increases, gelation of the sol occurs in a short time and the workability decreases. When a partial polycondensate of an alkoxysilane is stored for a long period of time, the concentration of the acid component in the partial polycondensate of the alkoxysilane is reduced because the humidity stability and the moisture content in the atmosphere deteriorate and the gelation occurs. Is 20 per 100 g of alkoxysilane partial polycondensate
It is preferably × 10 ^-4 mol or less. The residual acid component concentration is 2 × 10 with respect to 100 g of the partial polycondensate of alkoxysilane.
^-4 to 10 x 10 ^-4 mol is particularly preferred.

As the alkoxy group of the partial polycondensate of alkoxysilane, a methoxy group is preferable from the viewpoints of ease of hydrolysis when using a base catalyst, cost, and the like. That is, polymethoxysiloxane is preferable as the partial polycondensate of the alkoxysilane.

As the solvent, methanol, ethanol,
At least one of alcohols such as n-propanol and iso-propanol can be used, and N, N
At least one solvent having a high boiling point and a low surface tension such as dimethylacetamide, N, N-dimethylformamide, methoxyethanol, ethoxyethanol, and tetrahydrofurfuryl alcohol may be added.

As the organic polymer compound, at least one of polyvinyl acetate, polyethylene glycol and its derivatives, hydroxypropyl cellulose and the like can be used, and polyvinyl acetate is particularly preferable.

As the base catalyst, ammonium hydroxide,
At least one of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, choline and the like can be used, but choline is particularly preferable. The amount of the base catalyst added is not particularly limited, but of the added base catalyst, the concentration of the portion (effective base catalyst) not consumed for salt formation by the reaction with the acid component in the partial polycondensation product of alkoxysilane As a partial polycondensate of alkoxysilane 1
It is preferably 1 to 7 × 10 ⁻⁴ mol per 00 g.

As described above, a partial polycondensate of alkoxysilane is hydrolyzed in the presence of an organic polymer compound using a base as a catalyst to form a sol, and the sol is gelated and dried to prepare a dry gel. Silica glass is manufactured by heating this dried gel in a known method, for example, in air and then in helium at a temperature of 1200 to 1400 ° C. and sintering.

[0018]

In the present invention, the concentration of the acid component in the partial polycondensate of the alkoxysilane is set to 1 × 10 ^-4 mol or more per 100 g of the partial polycondensate of the alkoxysilane so that the gel cracks during the drying process. Although the details of the cause that can largely prevent this are unknown, it is presumed as follows. In a sol in which an organic polymer compound coexists,
When silica particles produced by hydrolysis and polycondensation of alkoxysilane interact with organic polymer compounds (hydrogen bonds, etc.), resulting in low bulk density of the gel that prevents cracking during the drying process. Conceivable. It is speculated that the surface potentials of the silica particles and the organic polymer compound influence this interaction. The trace amount of salt produced by the reaction between the acid component in the partial polycondensate of the alkoxysilane and the added base catalyst causes a decrease in the surface potential of the silica particles and the organic polymer compound, and as a result, The interaction with the organic polymer compound is strengthened, the interaction between the silica-organic polymer compound composites is strengthened, the bulk density of the gel is promoted, and the occurrence of cracks during the drying process is suppressed. Presumed to be.

As described above, in the present invention, a partial polycondensate of an alkoxysilane is hydrolyzed in the presence of a solvent, an organic polymer compound and a base catalyst to give a sol, and the sol is gelated and dried to give a dry gel. In the method for producing silica glass that is calcined into glass, pay attention to the residual acid component in the partial polycondensate of alkoxysilane, and adjust the concentration of the acid component to 1 × per 100 g of partial polycondensate of alkoxysilane. 10 ^-4
When the amount is more than the molar amount, it becomes possible to control the generation of cracks during the drying process.

[0020]

【Example】

Examples 1-3, Comparative Examples 1-2 Tetramethoxysilane in methanol as a solvent, nitric acid as a catalyst to partially hydrolyze and polycondense with water, and by changing the conditions of the step of removing the solvent, a methanol solution of choline. The concentration of the residual acid component measured by titration with 1 to 10 g of tetramethoxysilane partial polycondensate (polymethoxysiloxane) is 1 × 10 ⁻⁶ mol (Comparative Example 1) 5 × 10 ⁻⁵ mol (Comparative Example) 2) 1 × 10 ⁻⁴ mol (Example 1) 2 × 10 ⁻⁴ mol (Example 2) 6 × 10 ⁻⁴ mol (Example 3) to prepare polymethoxysiloxane. 2000 g of each polymethoxysiloxane, 1800 g of methanol, 50 g of polyvinyl acetate (average molecular weight 1500) (solid content)
Was added and mixed. A choline methanol solution (1M) was added to this mixed solution at a concentration of 3 × per 100 g of polymethoxysiloxane rather than the concentration of residual acid in the polymethoxysiloxane.
It was added in an excess of 10 ^-4 mol. Then, the temperature of the mixed solution was maintained at 15 ° C., 800 g of water was added dropwise with stirring, and after completion of the addition, the mixture was further mixed for 1 hour to obtain a sol.
The salt concentration in each of these sols was 1 × 10 ⁻⁶ mol (Comparative Example 1), 5 with respect to 100 g of polymethoxysiloxane, respectively.
× 10 ⁻⁵ mol (Comparative Example 2), 1 × 10 ⁻⁴ mol (Example 1), 2 × 10 ⁻⁴ mol (Example 2), 6 × 10 ⁻⁴ mol (Example 3) and residual acid The concentration of base (choline) not consumed in the neutralization reaction with (concentration of effective base) is 3 × 10 ⁻⁴ mol per 100 g of polymethoxysiloxane.
The obtained sol was poured into a Teflon-coated stainless steel container (260 mm square) at a rate of 1000 g, and the opening was sealed with a polyvinyl chloride film and further sealed with an aluminum foil. The container containing the sol is heated to 40 ° C. to gel the sol, then the aluminum foil is removed, and then 30 ° C. and then 60 ° C.
Then, the temperature was raised to 120 ° C. to remove the solvent in the gel to obtain a dry gel. Table 1 shows the state of cracks in the dried gel produced using each polymethoxysilane raw material. As is clear from Table 1, the salt concentration in the sol was 10% by weight of polymethoxysiloxane 10.
When it is 1 × 10 ⁻⁴ mol or more per 0 g, a crack-free dry gel can be produced with a high yield.

[Table 1] ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ Comparative example or salt in polymethoxy sol Effective base Dry gel retention is an example. Siloxane concentration Concentration (no cracking / total number) Residual acid concentration ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ ━━━━━━ Comparative Example 1 1 × 10 ^-6 1 × 10 ^-6 3 × 10 ^-4 0 (0/4) ───────────────────── ──────────────── Comparative example ^{2 5 × 10 -5 5 × 10} -5 3 × 10 -4 0 (0/4) ────────── ────────────────────────── Example 1 1 × 10 ⁻⁴ 1 × 10 ⁻⁴ 3 × 10 ⁻⁴ 0.75 (3/4) ──────────────────────────────────── Example 2 2 × 10 ⁻⁴ 2 × 10 ⁻⁴ 3 × 10 ^-4 1 (4/4) ───────────────────────────────────── Example 3 6 × 10 ^-4 6 × 10 ^-4 3 × 10 ^-4 1 (4/4) ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ ━━━━━━ Each concentration unit: mol / 100g polymethoxysiloxane

[0021]

EFFECTS OF THE INVENTION According to the present invention, silica glass without cracks or cracks can be stably produced by the sol-gel method, and the cost reduction of silica glass, which is an advantage of the sol-gel method, can be effectively realized. Various quartz glass substrates used for semiconductor or liquid crystal production can be supplied at low cost. Further, the size and shape of the glass that can be produced are basically not limited, and not only plate materials but also rods and tubes can be produced, and application to a jig for semiconductor production is also possible.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshikatsu Shimazaki 48, Wadai, Tsukuba City, Ibaraki Pref., Tsukuba Research Laboratory, Hitachi Chemical Co., Ltd. (72) Inventor, Hiroki Terasaki 48, Wadai, Tsukuba, Ibaraki Hitachi Chemical Incorporated company Tsukuba Development Laboratory (72) Inventor Hidekuni Banno 48 Wadai, Tsukuba City, Ibaraki Prefecture Hitachi Chemical Co., Ltd.Inside Tsukuba Development Laboratory, Inc. (72) Inventor Hiroshi Honda, 48 Daiwa Station, Tsukuba City, Ibaraki Prefecture Incorporated company Tsukuba R & D Laboratory (72) Inventor Nobuaki Takane 48 Wadai, Tsukuba, Ibaraki Prefecture Hitachi Chemical Co., Ltd. In Tsukuba R & D Laboratory (72) Inventor Yoshiro Ota 3-22, Shiohama, Kawasaki-ku, Kawasaki-shi, Kanagawa No. 9 Tama Chemical Industry Co., Ltd. Kawasaki Laboratory (72) Inventor Fujio Takeda 4491 Sakura, Hamaoka-cho, Ogasa-gun, Shizuoka Prefecture Tama Chemical Industry Formula company Hamaoka in the factory

Claims (1)

[Claims] 1. A partial polycondensate of an alkoxysilane is hydrolyzed in the presence of a solvent, an organic polymer compound and a base catalyst to give a sol, which is further gelled, dried to give a dry gel, and fired to give a glass. In the method for producing silica glass according to claim 1, the alkoxysilane partial polycondensate contains an acid component in the alkoxysilane partial polycondensate of 1 × 10 ⁻⁴ mol or more per 100 g of the alkoxysilane partial polycondensate. A method for producing silica glass, characterized in that