| 摘要 |
<p>A process is disclosed of making a polydiorganosiloxane-silica universal mixture from a free-flowing, powdered, surface-modified, reinforcing silica-polydiorganosiloxane composition used to make, for example, RTV silicone sealant compositions which are non-sag. These mixtures are made by combining, mixing and heating a reinforcing silica filler and a diol surface modifying agent at 20 DEG C. to 180 DEG C. using 0.05 to 0.5 part by weight of the diol per one part by weight of the silica. Polydiorganosiloxane is added gradually to the resulting fluidized filler over a time period of less than 10 minutes to obtain the free flowing powdered reinforcing silica-polydiorganosiloxane. The foundation mixture is obtained by massing the above composition and adding more polydiorganosiloxane to obtain a mixture which has from 5 to 20 weight percent of silica filler. The product mixtures have a plateau stress of greater than 700 dynes/cm<2> and a shear-thinned viscosity of no more than 1,000 Pa.s at a shear stress of 50,000 dynes/cm<2>. RTV silicone sealant compositions are obtained in 10 to 15 minutes from the start of making the surface modified silica filler to the final sealant composition.</p> |
