JPS61251509A - Production of spherical silica powder - Google Patents

Abstract

PURPOSE:A slurry of silica powder in water or an organic solvent is spray-dried and roasted to give spherical silica particles which are added to rubber or resins to increase abrasion resistance and friction without any adverse effect on toughness. CONSTITUTION:Silica powder is dispersed in water or an organic solvent, and spray-dried. The powder is roasted at 800-1,200 deg.C. The silica powder to be roasted has preferably more than 30m<2>/g of specific surface area. The organic solvent used is, e.g., an alcohol or ketone boiling at an appropriate temperature. The concentration of the slurry is about 5-30wt% as a silica powder.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention uses rubber,
The present invention relates to a method for producing spherical silica powder that is suitable as an additive that is added to resins and the like and does not adversely affect toughness.

<Prior art and problems> Used. Generally, such additives have a specific surface area of 30 tr? /I or more fine powder is used.

However, when imparting properties such as high abrasion properties, that is, large frictional force in addition to wear resistance, the particle size is rather coarse, and the average particle size is 1. Silica powder of θ to 100μ is used. Next, the shape of the silica is preferably spherical.

This is because spherical particles are more easily contained in the resin, and the content can be increased. In particular, L is added to epoxy resin.
When used as a sealant for SI, it is necessary that the silica content is large and the purity of the silica is high. Furthermore, the silica powder is also required to be free of pores. If pores exist, the gas in the pores may have an adverse effect on the resin and the like.

Generally, there are two ways to obtain silica powder: one is to crush natural silica stone, and the other is to artificially synthesize silica powder. However, in the method of obtaining silica powder by crushing natural silica stone, it is difficult to make the particle size uniform, and the shape is irregular.
The purity of iO is also low. On the other hand, methods for artificially synthesizing silica powder include (1) a method using a precipitate produced by the neutralization reaction of a silicate and an acid, (n) a method of reacting silicon tetrachloride with water vapor in the gas phase, etc. There is. However, although the silica powder obtained by such a synthesis method is a highly pure powder, the specific surface area is Δ9. The particle size is too fine to be added to improve toughness and friction.

For this reason, conventionally, fine silica powder obtained by the above synthesis method was fired at a high temperature of 1000° C. or higher.

A predetermined silica powder is obtained by crushing a molten silica lump or the like to a required particle size. However, since the silica powder obtained by this method is pulverized to make the particle size uniform, its shape is irregular and the particle size distribution is wide. If silica powder is added to rubber or resin for this purpose, there is a problem in that it has a significant adverse effect on toughness.

<Structure of the Invention> In the present invention, fine silica powder is dispersed in a solvent and spray-dried to agglomerate individual silica powders to a suitable particle size, and then baked at a predetermined temperature to form spherical particles with a suitable particle size. By using silica, the problems of the prior art described above are solved. That is, according to one invention.

After dispersing the silica powder in water or organic solvent.

A method for producing spherical silica is provided, which comprises spray-drying this slurry and firing it at a temperature ranging from SOO to 1200°C.

In the present invention, silica powder is first dispersed in water or an organic solvent. As this dispersion medium, in addition to water, organic solvents such as alcohols and ketones having a suitable boiling point can be used. Further, a small amount of soluble resin that decomposes and evaporates at low temperatures may be added to these dispersion media. This resin serves as a binder and has the effect of shortening the firing time. The dispersion means is not particularly limited. For example, the silica powder may be gradually added as it is to the dispersion medium being stirred.

Note that a highly concentrated slurry can be obtained in a short time by using a ball mill, sand glider, or the like.

The silica powder used as a raw material preferably has a specific surface area of 30.9 or more. If the particle size is coarser than this, it becomes difficult to disperse in the dispersion medium.

Although the concentration of the slurry is not particularly limited, it is preferable that the silica powder be 5 to 30% by weight based on the dispersion medium.

Since the concentration of the slurry affects the granulated powder and ultimately the powder particle size after firing, it may be determined depending on the particle size of the powder to be obtained. Note that if the concentration is too high, the viscosity will become too high and spraying will not be possible. On the other hand, if the concentration is too low, it is necessary to use a large amount of slurry, resulting in poor production efficiency.

This slurry is then spray dried. The spray dryer used may be of any type, such as a two-fluid nozzle type or a centrifugal spray type. The above slurry is agglomerated into particles of appropriate size and granulated by being sprayed.

The spray-dried powder is collected using a cyclone or the like.

Then it is fired. The firing temperature is SOO to 1200°C. If the temperature is lower than 800° C., the sintering rate within the granulated particles is low, so no matter how long the firing is performed, only powder with residual pores is obtained. On the other hand, if the firing temperature exceeds 1200° C., the granulated powder starts to be fired together, resulting in the powder becoming coarser than necessary and the particle size becoming non-uniform. Although the firing time varies depending on the particle size of the raw silica powder and the firing temperature, it is usually possible to obtain spherical silica powder without voids by firing for about 3 to 20 hours.

<Effects of the Invention> The silica powder produced by the method of the present invention has an average particle size of 1.
It has a thickness of 0 to 100μ and is suitable as an additive added to rubbers, resins, etc. to improve wear resistance and friction properties. Furthermore, the silica powder obtained by the present invention has a spherical shape.
Rubber because the particle size is uniform.

Even when added to the resin, it does not have any adverse effect on the toughness. That is, since the particles of the silica powder of the present invention have a uniform spherical shape, when it is dispersed in a resin or the like, it becomes uniformly dispersed. Therefore, compared to irregularly shaped silica, when the same amount is added to resin, there is less decrease in toughness, and compared to conventional irregularly shaped silica, a larger amount of silica can be added, improving the wear resistance and high friction properties of resin etc. You can improve even further.

<Example> 50 g of silica powder shown in Table 1 was dispersed in a dispersion medium to prepare a slurry of a predetermined concentration. Next, approximately 5 cc of this slurry was passed through a two-fluid nozzle with a diameter of 0.41111 mm.
It was sprayed at a speed of /min. At the same time, air having an inlet temperature of 200° C. was introduced into the spray drying line machine at a rate of 0.5 m/min to evaporate the dispersion medium of the sprayed aggregated particles to form granulated powder. This granulated powder was collected with a cyclone, and then fired under the atmosphere, temperature, and time shown in the table.

Table 1 summarizes the specific surface area of the silica powder used as a raw material, the type of dispersion medium, the dispersion concentration, the firing time, and the properties of the obtained silica powder.

As is clear from Table 1, all of the silica powders obtained by the method of the present invention have an average particle size of 8 to 46μ and a specific surface area of 0.35 to 0.09g. It can be seen that it has a suitable particle size. Furthermore, the shapes of the silica powders are all spherical or approximately spherical, and the particle size distribution is uniform, so that the toughness of rubber and resin is not adversely affected.

<Comparative Example> Silica powder having a specific surface area shown in Table 2 was used and fired at a predetermined temperature and time shown in Table 2. The properties of the obtained silica powder are summarized in Table 2.

As is clear from Table 2, the raw material silica powder is 3.2
In the case of a silica powder having a specific surface area of 5 d/I, a large number of pores are present in the obtained silica powder. Also, the firing temperature is 12509C, 7
Even at 50° C., pores were clearly observed, and some of the pores were irregular in shape.

Claims (2)

[Claims] (1) After dispersing silica powder in water or organic solvent,
A method for producing spherical silica powder, which comprises spray drying this slurry and firing at a temperature range of 800 to 1200°C. (2) The manufacturing method according to claim 1, wherein the silica powder dispersed in water or an organic solvent has a specific surface area of 30 m
＾2/g or more method.