The method of the invention for controlling oil-absorbing properties of the silicone rubber powder will be further described in more detail with reference to application examples. In the following examples, all values of viscosities correspond to viscosities at 25° C. The oil-absorbing properties of the silicone rubber powders were measured by the method described below.
[Oil-Absorbing Properties]
[0022]
Change of oil-absorbing properties of the silicone rubber powders with time was evaluated in terms of the maximum amount of the absorbed oil. More specifically, by using an instrument for measuring absorbed amounts (Model. S-410 produced by Asahisouken Co., Ltd.), 10 g of the silicone rubber powder stored under predetermined conditions were gradually added under stirring conditions to a decamethylcyclopentasiloxane, and then the maximum amount of oil (g/10 g) absorbed by the silicone rubber powder was determined as the amount of the added decamethylcyclopentasiloxane that corresponded to the maximum stirring torque of the mixture.
Reference Example 1
[0023]
A liquid silicone rubber composition was prepared by uniformly mixing the following components at −10° C.: 96 parts by mass of a dimethylpolysiloxane capped at both molecular terminals with dimethylvinylsiloxy groups and having a viscosity of 400 mPa·s (the content of vinyl groups=0.5 mass %); 4.5 parts by mass of a methylhydrogenpolysiloxane capped at both molecular terminals with trimethylsiloxy groups and having a viscosity of 20 mPa·s (the content of silicon-bonded hydrogen atoms=1.5 mass %); 49.5 parts by mass of a dimethylpolysiloxane capped at both molecular terminals with trimethylsiloxy groups and having a viscosity of 100 mPa·s; and an isopropanol solution of a chloroplatinic acid (the content of metallic platinum in terms of mass units was 50 ppm per mass of the composition). The obtained liquid silicone rubber composition was quickly mixed at 25° C. with 300 parts by mass of a 1.5 mass % aqueous solution prepared from pure water and polyoxyethylene (9 mole added) lauryl ether. Following this, the obtained mixture was passed through a homogenizer at a rate of 300 kgf/cm2, whereby a uniform aqueous dispersion of a liquid silicone rubber composition was obtained. The dispersion was cured by being held at quiescence for 24 hours at 35° C. to produce an aqueous slurry of a silicone rubber powder. The slurry was dried in a hot-air-flow dryer, water was removed, and a silicone rubber powder was obtained. All particles of the powder were spherical and had an average diameter of 6 μm.