JPS6259516A - Production of silica - Google Patents

Abstract

PURPOSE:In producing silica by calcining bulky silica obtained by sol-gel method, to smoothly and easily produce silica while preventing volume expansion and foaming in the calcining process, by treating the bulky silica with water before the calcining process is carried out. CONSTITUTION:Bulky silica, for example, is obtained by neutralizing an aqueous solution of sodium silicate with an acid such as hydrochloric acid, etc., gelatinizing the prepared silica sol, filtering and drying, is dried preferably at about 60-300 deg.C and dried to >=about 80wt% silica content. The bulky silica is treated with water in such a way that it is in an immersed state completely in water usually at room temperature. The water treated bulky silica is ground and calcined at about 500-1,300 deg.C for 1-8hr to produce high-purity silica having high silica bulk specific gravity. The bulky silica causes no foaming, no scattering, no adhesion to the wall of a calcining container and no damage of the calcining container by the calcination.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing silica, and particularly to a method for producing silica.
The present invention relates to a method for producing silica from bulk silica produced by a gel method.

[Prior art] In recent years, synthetic silica has come to be used as a filler for resin compositions for encapsulating electronic components, as a raw material for multi-component optical fibers, fine ceramics, optical glass, quartz for the electronic industry, etc. There is a demand for high bulk specific gravity and high purity.

In particular, silica for encapsulation, which is used as a filler in resin compositions for encapsulating electronic components, has a higher purity as the degree of integration increases, such as in LSIs and VLSIs, which causes soft errors. It is required that the content of elements and compounds such as uranium and thorium, which are α-ray decay substances, be as low as possible, and that the specific surface area be small.

Conventionally, as a method for producing this type of synthetic silica, for example, an aqueous sodium silicate solution is neutralized with an acid such as hydrochloric acid, the obtained silica sol is gelled, and the obtained bulk silica is dried at a temperature of 500 to 1300°C. A method of producing silica by sintering at 500 to 1300 °C, and a method of producing silica by hydrolyzing tetraalkoxysilane under acidic conditions, gelling the obtained silica sol, drying the obtained bulk silica, and then sintering it at 500 to 1300 °C to produce silica. (Japanese Unexamined Patent Publication No. 182.237/1989)
A method called the so-called sol-gel method has been proposed.

[Problems to be Solved by the Invention] However, in this conventional sol-gel method, when the generated silica sol is gelled, it becomes lumpy silica, but this lumpy silica is heated at 500 to 1300°C in the sintering process.
When heated, volumetric expansion and foaming occur, and during this foaming, silica scatters, and silica adheres to the walls of the sintered container, making it difficult to use the container repeatedly.
In some cases, the sintered container may be damaged.

Means for solving the L problem The present invention 1.! was devised in view of this point of view,
This is a method for producing silica in which water treatment is performed prior to the sintering process when bulk silica obtained by the sol-gel method is sintered to produce τ silica.

The bulk silica used in the present invention may be produced by any method, for example, by neutralizing an aqueous solution of lium silicate with an acid such as hydrochloric acid, Those obtained by gelation, filtration, and drying, and those obtained by hydrolyzing tetraalco-1.disilanes such as tetramethoxysilane and tetra-1.l-xysilane in the presence of oxalic acid or diaphragm acid. A product obtained by gelling a silica sol, filtering it, and drying it can be used.

For example, when drying this bulk silica under atmospheric pressure, the temperature is usually 60 to 300°C, preferably 100 to 200°C.
Dehydrate and dry at ℃ to reduce the silica content to 80% by weight or more.
The content is preferably 90% by weight or more. Regarding the drying temperature, if it is lower than 60°C, there is a problem that the dehydration and drying speed becomes extremely slow. Furthermore, although there is no particular problem if the dehydration/drying temperature is made higher than 300° C., the process economy becomes worse. Generally speaking, regarding the degree of drying, it is necessary that the silica content be 80% by weight or more, and 80% by weight or more.
If it is less than 0% by weight, problems such as volumetric expansion, foaming, and adhesion to the vessel wall may occur.

The particle size of the produced silica decreases as the content of silica and force increases by 1% during the dehydration and drying stage of the bulk silica, and by adjusting this silica content, the particle size of the produced silica can be adjusted. for example,
When the silica content is 80 to 85% by weight, the particle size of the generated silica is about 2 to 6H, and when the silica content is 95% by weight or more, the particle size of the generated silica is about 2s1.
It becomes below.

In the present invention, the bulk silica is treated with water before being sintered.

The drainage used for this water treatment may be as long as it is added to the bulk silica so that the bulk silica is completely immersed in the water. requires mixing to ensure good contact with water.

Therefore, if a small amount of water is used, the problem arises that the bulk silica is only partially immersed and cannot be crushed effectively unless mixed.

Also, what should be done during this water treatment? Although smallpox is usually carried out at room temperature, since heat is generated by water treatment, the temperature after water treatment is higher than the temperature before water treatment.

The massive silica thus treated with water and crushed is then sintered in a sintering step.

This sintering step can be carried out in the same manner as conventionally known methods, and is usually carried out at a sintering temperature of 500 to 1300°C, preferably 800 to 1200°C, for usually 1 to 8 hours, preferably 3 to 6 hours. It will be done. Even if the sintering time is made longer than 8 hours, there is no significant change in the physical properties and properties of the product.

The silica produced by the method of the present invention can be used for various purposes in the same way as silica produced by the conventional so-called sol-gel method.

[Example 1] Hereinafter, the method of the present invention will be specifically explained based on Examples and Comparative Examples.

Example 100 parts by weight of tetramethoxysilane, 16.7 parts by weight of methanol and 23 parts by weight of water were placed in a stainless steel reaction vessel equipped with a stirring device.
．． Charge the 3-layer chamber, and while stirring, blow purified carbon dioxide gas through a 0.2μ membrane filter at a rate that keeps the inside of the reaction vessel saturated with carbon dioxide gas until the reaction system becomes transparent. The tetramethoxysilane is hydrolyzed to form a silica sol, which is then gelled and dried at 150°C for 24 hours to form a bulk silica 45.9
1 part of weight/j was obtained. The silica content of this bulk silica is 8
It was 5% by weight.

Next, 50 fflω parts of water was added to this bulk silica to crush it, and it was left as it was at room temperature for 1 hour, and after filtration, the
It was dried at 0°C for 5 hours to give a silica content of 95% by weight, and then sintered at 1100±50°C for 3 hours. The yield No. 6 of the obtained silica was 38.2 parts (yield 98% based on tetramethoxysilane), and the particle size was 3-5.
txm, and the specific surface area was 2/g.

In this example, no foaming phenomenon or adhesion to the container was observed during the sintering process, and the sintering process could proceed smoothly.

Example 2 Silica was produced in the same manner as in Example 1, except that the bulk silica was dried at 200° C. for 24 hours and the silica content was 95%. The yield of the obtained silica was 38.4 times (yield 98.5% based on 1-xysilane), the particle size was 2 mm or less, and the specific surface area was 2ffl/g. 'C-There was.

In this example as well, no foaming phenomenon or adhesion to the container was observed during the sintering process, and the sintering process could proceed smoothly.

Comparative Example Bulk silica with a silica content of 85% by weight was prepared in the same manner as in the above example, and after further drying without water treatment to a silica content of 95% by weight, it was sintered in the same manner as in the example. produced silica.

In this comparative example, foaming phenomenon and adhesion to the container occurred during the sintering process, and the product could not be taken out.

[Effects of the Invention] According to the method of the present invention, when silica is produced by sintering lumped silica using the sol-gel method, foaming and scattering of silica, and The sintering process can be carried out smoothly without silica adhering to the walls, which prevents repeated use, or even damaging the sintering container. Manufacturing of silica becomes easier.

Claims (1)

[Claims] (1) A method for producing silica, which comprises carrying out water treatment prior to the sintering process when producing silica by sintering bulk silica obtained by a sol-gel method.