GB868377A - Improvements in or relating to organo-siloxane compositions - Google Patents

Abstract

In curing a silicone rubber-forming composition in two stages, a composition comprising a mixture of a siloxane convertible to the solid, elastic state, one or more fillers and 2 vulcanizing agents having a difference of at least 20 DEG C. between the temperatures at which free radical reactions between themselves and the siloxane are initiated, is partially cured throughout its volume by raising the whole composition to a temperature sufficiently high to activate the vulcanizing agent with the lower reaction temperature, stored in the semi-cured state, and finally completely cured by heating at a temperature sufficiently high to activate the second vulcanizing agent. Specified components of the composition are:-siloxanes-having a viscosity of at least 1000cs. at 25 DEG C. and a R/Si ratio of 1,9 to 2,01 : 1, wherein R is an alkyl, alkenyl, cycloaliphatic, aryl, polyfluoro-aliphatic or a halogenated alkyl or aryl radical; fillers-clay, diatomaceous earth, crushed quartz, silica (fume, aerogel and xerogel), barium zirconate, TiO2, ZnO, Fe2O3, ZrO, C black, glass flock, asbestos, cork, wood flour and organic fibrous materials; vulcanizing agents-(110 DEG -130 DEG C.) benzoyl- and 2 : 4-dichlorobenzoyl-peroxides; (about 150 DEG C.) di-t-butyl- and dicumyl-peroxides and t-butyl perbenzoate. The peroxides may be used as dispersions in dimethylpolysiloxane oils. Examples are given. Uses: for making sheet material and for coating base material for making insulating tapes. Specifications 685,664, 715,181 and 792,041 are referred to.