JPH0336762B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The present invention relates to a method for producing spherical silica powder, which is suitable as an additive that is added to rubbers, resins, etc. to improve wear resistance and friction properties, and does not adversely affect toughness. <Prior art and problems> It is known that adding silica powder to rubber, resin, etc. greatly improves wear resistance, and it is widely used. Generally, as such additives, fine powder having a specific surface area of 30 m ² /g or more is used. However, when imparting properties such as high abrasion properties, that is, large frictional force in addition to wear resistance, silica powder having a relatively coarse particle size and an average particle size of 1.0 to 100 μm is used. Next, the shape of the silica is preferably spherical. This is because the spherical shape is easier to contain in the resin,
This is because the content can be increased. In particular, when it is incorporated into an epoxy resin and used as a sealant for LSI, 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, silica powder can be obtained by two methods: pulverizing natural silica stone and artificially synthesizing silica powder. However, in the method of obtaining silica powder by crushing natural silica stone, it is difficult to make the particle size uniform, the shape is irregular, and the purity of SiO is low. On the other hand, methods for artificially synthesizing silica powder include () a method using a precipitate produced by the neutralization reaction of a silicate and an acid, () 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 highly pure, the specific surface area is only 30 m ² /
The particle size is too fine to be added to improve toughness and friction properties. For this reason, in the past, fine silica powder obtained by the above synthesis method was calcined at a high temperature of 1000°C or higher, or a predetermined silica powder was obtained by pulverizing a molten silica lump to the required particle size. ing. However, the silica powder obtained by this method has an irregular shape and a wide particle size distribution because it is pulverized to make the particle size uniform. Therefore, there is a problem in that when this silica powder is added to rubber or resin, it has a significant adverse effect on toughness. <Structure of the Invention> The present invention involves dispersing fine silica powder in a solvent and spray-drying it to agglomerate each silica powder to an appropriate particle size, and then firing this at a predetermined temperature to produce spherical silica particles with a suitable particle size. By doing so, the problems of the prior art described above are solved. That is, according to the present invention, after dispersing silica powder in water or an organic solvent, this slurry is spray-dried and heated at 800 to 1200°C.
Provided is a method for producing spherical silica characterized by firing at a temperature range of . In the present invention, silica powder is first dispersed in water or an organic solvent. As the dispersion medium, in addition to water, organic solvents having an appropriate boiling point such as alcohols and ketones 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 if a ball mill, sand glider, etc. are used, a highly concentrated slurry can be obtained in a short time. The silica powder used as a raw material has a specific surface area of 30m ² /
g or more is preferable. 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, etc.
Then it is fired. The firing temperature is 800-1200℃.
If the temperature is lower than 800°C, the sintering rate within the granulated particles will be low, so no matter how long the firing is performed, only powder with residual pores will be obtained. On the other hand, the firing temperature is 1200℃
If the temperature exceeds this value, calcination of the granulated powders will begin to occur, 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 silica powder used as the raw material 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 1.0 to 100μ, and is suitable as an additive added to rubber, resin, etc. to improve wear resistance and friction properties. . Furthermore, since the silica powder obtained in the present invention is spherical and has a uniform particle size, it will not adversely affect the toughness even when added to rubber or resin. That is, since the particles of the silica powder of the present invention have a uniform spherical shape, when dispersed in a resin or the like, the particles become uniformly dispersed. Therefore, compared to irregularly shaped silica, when the same amount is added to resin, there is less decrease in toughness, and since a larger amount of silica can be added compared to conventional irregularly shaped silica, it improves the wear resistance and high friction properties of resin etc. can be further improved. <Example> 50 g of silica powder shown in Table 1 was dispersed in a dispersion medium to prepare a slurry of a predetermined concentration. This slurry was then sprayed at a rate of about 5 c.c./min through a two-fluid nozzle with a 0.4 mm diameter hole. At the same time, air having an inlet temperature of 200° C. was introduced into the spray dryer at a rate of 0.5 m ³ /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. 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 are summarized in Table 1. 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 8.
46μ and a specific surface area of 0.35 to 0.09 m ³ /g, which indicates that it has a particle size suitable for improving friction properties. Furthermore, the shape of this silica powder is spherical or approximately spherical, the particle size distribution is uniform, and 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, when the raw material silica powder has a specific surface area of 3.25 m ² /g, a large number of pores are present in the obtained silica powder. Also, the firing temperature
Voids were clearly observed in the samples heated to 1250℃ and 750℃.
Moreover, the shape of some of them is undefined.

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Claims (1)

[Claims] 1. A method for producing spherical silica powder, which comprises dispersing silica powder in water or an organic solvent, spray-drying the slurry, and firing the slurry at a temperature in the range of 800 to 1200°C. 2. The manufacturing method set forth in claim 1, comprising:
A method in which the specific surface area of silica powder dispersed in water or an organic solvent is 30 m ² /g or more.