JPH11302011A5 - - Google Patents

Description

[Name of invention] Manufacturing method of expanded silica particles

[0001]
[Technical Field to which the Invention Belongs]
The present invention relates to amorphous, non-porous silica fine particles that are suitable for use as fillers in resins, paints, cosmetics, films, etc., and have a solubility in cell-simulating fluids as high as that of silica gel.
The invention also relates to a method for producing the expanded silica particles obtained in this context.

[0035]
More specifically, an aqueous solution of alkali silicate and an aqueous solution of mineral acid are introduced into a vessel equipped with an outlet through separate inlets and instantaneously mixed uniformly, adjusting the pH to 7 to 9 to produce a silica sol having an _SiO2 concentration of 130 g/ L or more and a pH of 7 to 9. The resulting silica sol is then immediately released from the outlet into a gaseous medium such as air, where it is allowed to float in a parabolic arc and gel in mid-air. An aging tank filled with water is placed at the drop point, and the sol is dropped into the tank and allowed to age for several minutes to several tens of minutes.

[0036]
Acid is added to the aging tank to lower the pH and stop the aging. After thorough washing with water, solid-liquid separation is performed to obtain spherical silica hydrogel. The silica hydrogel is further thoroughly dried at a temperature of about 50 to 180°C using a dryer or the like to obtain spherical silica gel particles with a particle size of 2 to 4 mm, as shown in Examples 3 and 4 below . Irregularly shaped crushed products can be easily obtained by crushing the spherical particles in the same manner as above.

[0059]
When such a pulverization step is performed, it is not necessary to pulverize the silica into fine particles before calcination. As shown in Example 5 below, for example, when silica gel having a particle diameter of several mm is calcined, a foam- like calcined product, i.e., foamed silica gel , is obtained. That is, the silica gel expands and foams upon calcination to obtain spherical foamed silica particles. By pulverizing this foam, the amorphous and non-porous silica microparticles of the present invention can be produced. Although the foamed silica particles may be pulverized in this manner to impart high amorphousness by applying a mechanochemical action as described below, they are useful in themselves as foamed particles.

[0087]
Example 3
A sodium silicate aqueous solution ( _SiO2 / _Na2O molar ratio = 3, _SiO2 concentration 20 wt%) was introduced into a container equipped with an outlet at a flow rate of 2000 mL /min, and a 20 wt% sulfuric acid aqueous solution was introduced at a flow rate of 1100 mL /min through separate inlets. The mixture was instantly mixed uniformly and adjusted to a pH of 7-9 to form a sol. The mixture was immediately ejected into the air through the outlet and gelled in mid-air while tracing a parabolic arc. An aging tank filled with room-temperature water was placed at the point of impact, and the resulting gel was collected and aged for 30 minutes. Sulfuric acid was then added to lower the pH and terminate the aging. After thorough water washing, the mixture was dried to obtain spherical silica gel with a particle diameter of 2-4 mm. This spherical silica gel could be crushed to a few micrometers as described below to form amorphous silica gel particles, or it could be calcined to form expanded spherical silica particles as described in Example 5 below.

[0102]
Example 5
100 g of silica gel with a particle diameter of 2 to 4 mm obtained in Example 3 was placed in a crucible and baked in an electric furnace at 1050°C for 0.5 hours to obtain spherical silica particles that had been foamed and expanded to a particle diameter of 4 to 10 mm , i.e., foamed silica particles .

[0119]
[Effects of the Invention]
As described above, according to the present invention, silica fine particles are provided which are amorphous and non-porous, yet have a high dissolution rate in a cell-simulating fluid comparable to that of silica gel.
Furthermore, according to the present invention, there are provided spherical expanded silica particles which are useful in themselves and which are obtained in the process of producing the amorphous, non-porous silica fine particles.

Claims (5)

A method for producing expanded silica particles, comprising the steps of: introducing an aqueous solution of alkali silicate and an aqueous solution of mineral acid into a container equipped with an outlet through separate inlets, instantly mixing them uniformly, adjusting the pH to 7 to 9, and producing a silica sol; discharging the resulting silica sol from the outlet into a gaseous medium and gelling it in air; aging the gel in an aging tank filled with water to produce a silica hydrogel, which is then subjected to solid/liquid separation and dried to produce spherical silica gel particles; and calcining the obtained spherical silica gel particles to cause them to foam and expand. 2. The method for producing expanded silica particles according to claim 1, wherein spherical silica gel particles having a particle diameter of 2 to 4 mm are fired to expand and foam the particles to a particle diameter of 4 to 10 mm. The silica sol produced is SiO ₂ 3. The method for producing expanded silica particles according to claim 1, wherein the concentration is 130 g/L or more. 4. The method for producing expanded silica particles according to claim 1, wherein the silica hydrogel is dried at a temperature of 50 to 180°C. 5. The method for producing expanded silica particles according to claim 1, wherein the spherical silica gel particles are baked at a temperature of 900 to 1100[deg.] C. for 0.2 to 1 hour to be foamed and expanded.