JPH0348140B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a method for producing quartz glass by a sol-gel method.

[Prior art]

Quartz glass is used in crucibles and boards during the IC manufacturing process.
It began to be used in diffusion furnaces, etc., and its usefulness was recognized, and with the development of products with fewer hydroxyl groups and better optical uniformity, it was used for various optical applications. In particular, silica glass fibers for optical communications have been attracting attention recently.

As described above, quartz glass is used in various fields, and the scope of its use is expanding. However, the manufacturing cost of quartz glass is high, and the high price has become a problem. The sol-gel method is recognized as a method for manufacturing inexpensive, high-quality quartz glass.

As a method to obtain large-sized quartz glass with good yield using the sol-gel method, fine powdered silica is added to a sol prepared by hydrolyzing alkyl silicate.
One method is to adjust the pH to 3 to 6, then dry and sinter at 50 to 90°C. This solution simultaneously solved the problem of cracks during dry gel production and the problems of cracks and cracks during sintering, making it possible to manufacture fairly large quartz glass (4 inch diameter or more) at low cost.

Methods for producing high-quality quartz glass that does not contain crystals, bubbles, or impurities include a method that effectively disperses fine powder silica using harmonic vibration, and a method that uses centrifugation to remove lumps that remain due to insufficient dispersion. Several methods have been proposed and have shown some success. However, a small amount of irregularly shaped foreign matter (several μm to 50 μm) is present, and it has not been possible to produce completely homogeneous quartz glass.

Irregularly shaped foreign particles include dust mixed in during the manufacturing process and commercially available fine powder silica (e.g. Cab-o-
sil (manufactured by Cabot), Aerosil (manufactured by Degussa),
Fransil (manufactured by F-ransil), DC Silica (Daw
The cause is thought to be coarse particles (which do not pass through a 45 μm filter) contained in the product (manufactured by Corning Inc.). High-quality quartz glass cannot be manufactured unless these foreign substances already present in the sol are separated and a homogeneous sol is prepared. As it currently stands, it cannot be used in optical systems, etc., so its range of applications is extremely limited.

〔the purpose〕

The present invention solves these problems,
The object of the present invention is to provide a method for producing completely homogeneous high-quality quartz glass by pressure filtration using a polypropylene filter.

〔overview〕

The method for producing quartz glass of the present invention is a method for producing quartz glass by a sol-gel method using at least an alkyl silicate and finely powdered silica as raw materials. After applying ultrasonic waves to this sol solution, the sol solution is centrifuged and filtered under pressure using a polypropylene filter with a diameter of 50 μm or less.

Furthermore, the functions of the above-mentioned constituent elements of the present invention will be explained below.

First, the effect of applying ultrasonic waves to the mixed sol solution is to reduce the particle size in the sol and lower the clay content, thereby facilitating the next step of centrifugation and filter filtration.

Next, centrifugation removes foreign particles as small as a few μm.
It works to remove foreign substances in a wide range, including large particles of about 100μm or more, and at least 100μm.
Since the larger lumps can be reliably removed, it facilitates filtration with a 50 μm filter in the next step.

In addition, centrifugation has the effect of lowering the viscosity in the same way as the application of ultrasonic waves, and has the effect of further reducing the viscosity of the sol applied with the previous ultrasonic wave, thereby facilitating filter filtration in the next step.

Next, when using a polypropylene filter, since polypropylene is hydrophobic, the -OH
Since the group and glass have extremely good affinity, it is difficult for a hydrolyzate of an alkyl silicate or a mixture of a hydrolyzate of an alkyl silicate and fine powder silica to adhere to and grow on the glass as a nucleus and cause clogging. By applying pressure, even if a cartridge type filter with a large area is used, a large amount of filter processing can be performed efficiently.
Also, 50μm filter filtration is at least 50μm.
It is possible to completely remove foreign substances that can be easily recognized by the naked eye, and filtration using a filter with a coarser roughness has little filtration effect.

Furthermore, following 50μm filter filtration,
It is possible to effectively obtain a sol with uniform particle size without causing clogging even when filtered with a particle diameter of 10 μm or less.

〔Example〕

Hereinafter, the present invention will be described in detail based on examples.

Example 1 Ethyl silicate 4.4 and 0.05N hydrochloric acid aqueous solution
3.6 was stirred vigorously to obtain a colorless and transparent homogeneous solution. There is fine powdered silica (Aerosil OX-50) 1.5
Kg was gradually added and stirred thoroughly. sol at 20℃
When irradiated with 28KHz ultrasonic waves for 2 hours while maintaining the temperature at Furthermore
A centrifugal force of 1500G was applied for 10 minutes to sediment the insufficiently dispersed large particles.

The obtained highly homogeneous sol (hereinafter referred to as sol A) was sent to a filter (polypropylene cartridge type filter (manufactured by Toyo Kagaku Sangyo Co., Ltd.)) with a pore size of 50 μm using an air pump, and the sol was 0.3 μm in diameter.
Filtration was carried out at a pressure of Kg/cm ² . 8 sol is 2
I was able to process it in minutes.

After adjusting the pH of the collected sol to 4.2, an amount of the sol to a depth of 1 cm was transferred to a polypropylene container (width 20 cm x 20 cm x height 10 cm) and dried at 60°C for 7 days. A dry gel with a diameter of 14 cm and a thickness of 0.7 cm was obtained, and when heated to 1300 °C at a heating rate of 180 °C/hr, quartz glass with a diameter of 10 cm and a thickness of 0.5 cm was produced.

Although the quartz glass contained some irregularly shaped foreign matter of several tens of micrometers, it was superior in quality to the quartz glass produced by directly gelling Sol A.

Example 2 Sol A was passed through the same filter with a pore size of 50 μm as used in Example 1, and then passed through a polypropylene cartridge type filter (manufactured by Toyo Kagaku Sangyo Co., Ltd.) with a pore size of 10 μm. 3
Applying a pressure of Kg/cm ² , 8 sols could be processed in 3 minutes.

When the recovered sol was made into quartz glass by the same operation as in Example 1, it was found to have a fairly high degree of homogeneity, with only a few irregularly shaped foreign particles of 10 to 20 μm present per 1 mm ² .

Example 3 Sol A was passed through the same filter with a pore size of 50 μm as used in Example 1, and then passed through the same filter with a pore size of 10 μm as used in Example 2 three times.

When the recovered sol was made into quartz glass by the same operation as in Example 1, there was no irregularly shaped foreign matter of 10 μm or more, and the quality was extremely high.

Example 4 Sol A was passed through a filter with the same pore size of 50 μm as used in Example 1 and 10 μm as used in Example 2, and then the pore size of a polypropylene cartridge type filter (manufactured by Toyo Kagaku Sangyo Co., Ltd.) was passed through.
Passed through a 5 μm filter. By applying a pressure of 0.5 kg/cm ² , 8 sols could be processed in 3 minutes.

When the recovered sol was made into quartz glass by the same operation as in Example 1, there was no irregularly shaped foreign matter of 10 μm or more, and the quality was extremely high.

Example 5 Sol A was passed through polypropylene filters with pore diameters of 50 μm and 10 μm, and then further passed through a polypropylene filter with pore diameter of 1 μm. 0.5
Applying a pressure of Kg/cm ² , 8 sols could be processed in 5 minutes.

When the recovered sol was made into quartz glass by the same operation as in Example 1, it was completely homogeneous and of extremely high quality.

Comparative Example 1 When Sol A was made into quartz glass by the same operation as in Example 1 without passing it through a filter, it was found that the silica glass had a thickness of several tens of μm.
Irregularly shaped foreign objects were scattered, and string-like objects that were thought to have been mixed in from the outside were also observed.

Comparative Example 2 When sol No. 8 was filtered in the same manner as in Example 1, only the filter was replaced with glass filter #2, sol No. 5 could be filtered, but no more could be filtered.

It was after 25 minutes that the filter became clogged and could no longer be filtered.

〔effect〕

As described above, according to the present invention, in a method for producing quartz glass by a sol-gel method using at least an alkyl silicate and finely powdered silica as raw materials, a sol solution in which finely powdered silica is added and stirred to a hydrolyzed solution of an alkylsilicate. By applying ultrasonic waves to the sol, centrifuging the sol, and performing pressure filtration using a polypropylene filter with a diameter of 50 μm or less, it is possible to remove amorphous foreign substances with a size of several tens of μm or less. Even if a large amount of filtration is performed, clogging will hardly occur, so there is no need to change the filter midway through the process.
It is possible to efficiently filter continuously for a long time.
As a result, optically completely homogeneous, high-quality quartz glass can be easily produced in large quantities.

The ability to process large quantities of filters has opened up endless possibilities for applications such as quartz substrates for photomasks, quartz glass fibers for optical communications, and various optical cells.

Claims (1)

[Claims] 1. In a method for producing quartz glass by the sol-gel method using at least alkyl silicate and fine powder silica as raw materials, fine powder silica is added and stirred to a hydrolyzed solution of alkyl silicate to form a sol solution, and the sol solution is subjected to ultrasonic waves. After applying the voltage, the sol solution is centrifuged and made of polypropylene.
A method for producing quartz glass characterized by performing pressure filtration using a filter of 50 μm or less.