Process for preparing universal polydiorganosiloxane-silica mixtures using hydrolyzable polydiorganosiloxane surface modifiers, mixtures obtained therefrom and room temperature curable sealants prepared therefrom

摘要

The present invention relates to a process for preparing a polydiorganosiloxane-silica mixture from, for example, surface modified soft reinforced silica-polydiorganosiloxane powders used to prepare unsagging RTV silicone sealant compositions. These mixtures are prepared by combining reinforcing silica filler and surface modifier at 90 to 180 ° C. using 0.1 to 0.5 parts by weight of surface modifier per 1 part by weight of silica, mixing and heating. The polydiorganosiloxane is slowly added to the fluidized filler obtained over a time period of less than 10 minutes to obtain a soft, reinforced silica-polydiorganosiloxane powder. The final mixture is obtained by agglomerating the concentrate and adding polydiorganosiloxane to obtain a mixture containing 3 to 20% by weight silica filler. The RTV silicone sealant composition is obtained within 10-15 minutes from the initiation of the method.