JPH0829933B2 - Method for producing spherical silica - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for obtaining spherical silica particles having a narrow particle size distribution and good dispersion as a larger particle size. The silica particles obtained by the present invention are used as a ceramic raw material and a filler in various fields.

(Prior art and its problems) It is conventionally known that silica particles having a narrow particle size distribution and good dispersion can be obtained by hydrolyzing and polymerizing alkoxide of silicon in the presence of a basic catalyst. (W.
Stober, Journal of Colloid and Interfase Science 2
6,62 (1968)).

It has also been proposed to combine this hydrolysis / polymerization method with a particle growth method to obtain larger particles. (Proceedings of the Annual Meeting of the Ceramic Society of 1986, P.245-246) However, it has been suggested that precipitation of new crystals can be avoided after a certain number of repetitions of this growth reaction. It is not possible to prevent the precipitation of a new crystal in the growth reaction in stages, and it becomes a seed crystal in the growth reaction after the next time, so after all, after repeating the growth reaction many times, it is divided into about 3 points. Larger particles having different particle size distributions and uniform particle diameters have the drawback that they have not yet been successful.

(Means for Solving Problems) The inventors of the present invention have conducted extensive studies in view of the above problems, and as a result, in such a hydrolysis / particle growth method, hydrolysis / polymerization reaction is performed under specific conditions. If it is maintained and the alkoxide is repeatedly supplied by a specific method, spherical silica particles can be prevented from precipitating new seed crystals even in the initial stage of the growth reaction while maintaining monodispersion, and a substantially uniform and large size can be obtained. They have found that they can be grown as particles and have reached the present invention.

An object of the present invention is to obtain a silica particle having a relatively large particle size and a narrow particle size distribution by repeating the particle growth reaction a number of times in a specific alkoxide and solvent system.

Therefore, the object of the present invention is to subject tetraalkoxysilane and water to stirring in the presence of a basic catalyst in a reaction solvent to carry out hydrolysis / polymerization reaction of tetraalkoxysilane to produce silica particles. Then, a tetraalkoxysilane is added to a reaction solution containing the silica particles as a seed crystal, and the growth reaction is repeated. (A) The growth reaction is performed by seeding the silica particles obtained in the previous reaction. (B) 1 to 20 mol of water, 0.1 to 10 mol of basic catalyst, and 0.01 to 1 of tetraalkoxysilane are added to the reaction liquid 1 in the first seed crystal silica formation reaction in each growth reaction. (C) Addition of tetraalkoxysilane in each growth reaction can be easily achieved by adding the total amount at once while stirring the content to be added.

 Hereinafter, the present invention will be described in detail.

Typical examples of the tetraalkoxysilane used in the present invention include methoxide, ethoxide, isopropoxide, butoxide and the like. The solvent used may be methanol, ethanol, isopropanol, butanol or the like, and the combination of the alkoxysilane and the solvent can be arbitrarily selected. As the catalyst for hydrolysis / polymerization, basic catalysts such as ammonia / amine and caustic can be used, but ammonia is usually most commonly used.

First, in the method of the present invention, water and a basic catalyst are respectively dissolved in a solvent, and alkoxysilane is added to the solution to carry out a hydrolysis / polymerization reaction to obtain silica particles to be seed crystals. At this time, 1 to 20 mol of water in the reaction system and 0.
It is necessary to use an amount corresponding to each concentration range of 1 to 10 mol / tetraalkoxysilane and 0.01 to 1 mol /.
The reaction is carried out in a constant temperature bath under stirring while maintaining the temperature at -20 to 40 ° C, but it is important to add all of the tetraalkoxysilane to the solvent in which water and the catalyst are dissolved at a time. Within a few minutes, monodispersed and spherical silica particles are formed and the reaction solution becomes cloudy, and the solution temperature rises due to the hydrolysis / polymerization exothermic reaction, but further stirring is continued in a thermostatic bath to sufficiently hydrolyze the solution. Polymerize. Next, in the growth reaction of the present invention, the hydrolyzate of the alkoxysilane in the presence of a basic catalyst causes the particles to grow by depositing on the surface of the seed crystal. It is important that no new nuclei are generated by the addition. As a seed crystal for that purpose, generally seed crystals may be generated as described above, but more preferable seed crystal conditions are that the number of seed crystals per unit volume of the reaction solution is 10 ¹¹ / cm ³ or more and the seed crystal surface area is 10 ³ cm ²
/ cm ³ or more. Next, in the method of the present invention, the reaction solution adjusted according to the above-mentioned requirements is used as a primary reaction solution, and a tetrahydrate having a predetermined temperature of 0.01 to 1 mol / per unit volume of the primary reaction solution (hereinafter the same) is added thereto. Alkoxysilane was added all at once while stirring the content to be added (the first time means the above-mentioned first reaction liquid), and the hydrolysis / polymerization reaction was carried out, resulting in uniform growth in a monodispersed state. Spherical silica particles are obtained. Further, by using this as a secondary reaction liquid and repeating the same operation in the following, the growth of spherical silica particles can be continued while maintaining the monodispersion.

As described above, in the present invention, the unit operation of the hydrolysis / polymerization reaction of the tetraalkoxysilane is sequentially repeated, but the hydrolysis / polymerization reaction of the tetraalkoxysilane is twice equivalent to the tetraalkoxysilane as shown by the following formula. Water is consumed and the water concentration in the reaction system changes.

Si (OR) ₄ + 2H ₂ O → SiO ₂ + 4ROH Therefore, in order to maintain the above-mentioned conditions, water is appropriately added to compensate for the decrease in water. By this, the catalyst and water concentration for the initial tetraalkoxysilane were controlled within the above-mentioned optimum range, and the initial total number of seed crystals, the condition of the total surface area, and the condition of the temporary total addition of tetraalkoxysilane were added, and the new particles continued to exist. A repeating operation is ensured in which only seed crystals grow uniformly without being generated. Similarly, from the above viewpoint, the alkoxysilane concentration condition for the repeated growth reaction is defined based on the volume of the first reaction liquid as described above. In addition, in the method of the present invention, the addition of the alkoxysilane is performed by temporarily adding the entire amount in any of the reactions, and the end of each reaction can be confirmed, for example, by the temperature transition in the reaction system after the addition of the alkoxysilane. .

The number of repetitions of the growth reaction in the method of the present invention can be freely selected according to the desired particle diameter of any desired silica particles, and particles having a desired size can be obtained.

The size of silica particles that can be expected to be specifically used as a raw material for products and the like varies from about 0.1 μm to 1.0 μm or more. Therefore, the number of repetitions of the growth reaction in the method of the present invention also depends on the starting alkoxysilane. Although it depends on the type of the present invention, it can be obtained from one repetition to several tens of times, and it is expected that a wide variety of demands will come out in the future technical development. It seems that the application and range of application will be further expanded.

(Examples) Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples.

Example 1 313.8 g of distilled and purified methanol, 23.8 g of distilled water and 28%
The reaction solution prepared by dissolving and mixing 60.8 g of ammonia water was placed in a flask and thereafter kept in a constant temperature bath at 20 ° C. while stirring at 500 rpm. Next, distillatively refined tetramethoxysilane 7.6g at 20 ℃
Then, the whole amount was added at once to the reaction solution kept at 20 ° C. After about 15 seconds, the reaction liquid became cloudy, and at the same time, the temperature of the reaction liquid rose to 22 ° C. In the reaction solution, one minute after the addition of tetramethoxysilane, the average particle size = 0.20 μm,
There were uniform spherical particles with a geometric standard deviation of 1.05, and the particle size did not change thereafter. That is, the hydrolysis / polymerization reaction of tetramethoxysilane was completed in about 1 minute. The reaction solution temperature dropped to 20 ° C 5 minutes after the addition of tetramethoxysilane.
The first reaction solution was obtained by adding 1.8 g of a considerable amount of water consumed by the hydrolysis / polymerization of the above.

Next, while stirring the primary reaction solution, 7.6 g of tetramethoxysilane adjusted to 20 ° C. was added all at once, and after 5 minutes, the temperature of the reaction solution reached 20 ° C. 1.8 g of distilled water was added to make a second reaction solution. By repeating this step as a unit operation for 40 times with respect to the first reaction liquid, uniform spherical silica having an average particle diameter of 0.70 μm and a geometric standard deviation of 1.04 was obtained. An electron micrograph of the obtained spherical silica is shown in FIG. 1 as a particle structure. B) is a magnification of 5,000 times,
B) is a magnification of 10,000 times. The grain growth process at this time is shown in FIG. FIG. 2 also shows the particle size calculation value obtained by assuming that all the tetramethoxysilane added by repeating the above unit operation is deposited as silica on various crystal surfaces evenly. The measured value and the calculated value of the particle size by SEM) were in good agreement. From this, it can be seen that the seed crystal in the primary reaction liquid did not generate a new seed crystal even if the unit operation was repeated, and uniformly grew while maintaining the monodispersion.

Comparative Example 1 313.8 g of distilled and purified methanol, 23.8 g of distilled water and 28%
The reaction solution prepared by dissolving and mixing 60.8 g of ammonia water was placed in a flask and thereafter kept in a 20 ° C. thermostat while stirring at 500 rpm. Next, distillatively refined tetramethoxysilane 7.6g at 20 ℃
After adjusting to 2, the reaction solution kept at 20 ° C. was added dropwise at a constant rate and the whole amount was added in 5 minutes. 0.05 μm in the reaction solution
There were very widely distributed particles including the following fine particles, and uniform spherical particles were not produced as in the example.

Comparative Example 2 After obtaining a primary reaction solution under the same conditions as in Example, 7.6 g of tetramethoxysilane adjusted to 20 ° C. was added dropwise to the primary reaction solution at a constant rate and the whole amount was added in 5 minutes. In addition to the grown seed crystal particles, fine particles of 0.1 μm or less were newly formed in the reaction solution, and the seed crystal did not grow uniformly while maintaining monodispersion as in the example.

(Effect of the Invention) According to the present invention, silica particles having a relatively large particle size and a very uniform particle size can be obtained.

[Brief description of drawings]

FIG. 1 shows the particle structure of the spherical silica obtained in Example 1, and FIG. 2 is the number of repetitions of the particle growth reaction at this time-average particle diameter curve.

Claims (1)

[Claims] 1. Tetraalkoxysilane and water are stirred in a reaction solvent in the presence of a basic catalyst to hydrolyze and polymerize tetraalkoxysilane to produce silica particles, and then the silica particles are produced. The method comprises repeating the growth reaction by adding tetraalkoxysilane to a reaction liquid containing particles as seed crystals. (A) The growth reaction is repeated by using the silica particles obtained in the previous reaction as seed crystals, b) In each of the growth reactions, 1 to 20 mol of water, 0.1 to 10 mol of the basic catalyst, and 0.01 to 1 of tetraalkoxysilane relative to the reaction liquid 1 in the first seed crystal silica formation reaction
(C) Tetraalkoxysilane is added in each growth reaction in a range corresponding to the molar amount, and the total amount of tetraalkoxysilane is added all at once with stirring of the content to be added.