Method of making a foundation polydiorganosiloxane-silica mixture using a hydrolyzable polydiorganosiloxane surface modifying agent, the resulting mixture and a room temperature curing sealant made from the foundation mixture

摘要

A process of making a polydiorganosiloxane-silica foundation mixture from a free-flowing, powdered, surface-modified, reinforcing silica- polydiorganosiloxane concentrate used to make, for example, RTV silicone sealant compositions which have non-sag properties. The foundation mixtures are made by combining, mixing, and heating a reinforcing silica filler and a surface modifying agent to a temperature of 90 C. to 180 C. using 0.1 to 0.5 parts by weight of the surface modifying agent 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 concentrate. The foundation mixture is obtained by massing the concentrate and adding more polydiorganosiloxane to obtain a mixture which has from 8 to 20 weight percent silica filler. RTV silicone sealant compositions can be obtain in 10 to 15 minutes from the start of making the surface modified silica filler to the complete sealant composition.