Heat-resistant polyorganosiloxane composition

Claim 1

A heat-resistant polyorganosiloxane composition comprising (A) a polyorganosiloxane having a viscosity at 25° C. of at least 0.1 Pa.s and having an average unit formula R.sub.a R'SiO.sub.(4-a-b)/2 wherein R is vinyl group or allyl group; R' is a group selected from the group consisting of lower alkyl group, phenyl, and 3,3,3-trifluoropropyl; a is a number such that at least two R are present in each molecule; and a+b has an average value of from 1.8 to 2.3, (B) a hydrogenpolyorganosiloxane with a viscosity at 25° C. of from 0.001 to 100 Pa.s and having an average unit formula R".sub.c H.sub.d SiO.sub.(4-c-d)/2 wherein R" is a lower alkyl group of phenyl; d is a number such that at least two hydrogen atoms are present in each molecule; and c+d has an average value of from 1.8 to 3, the proportions of polyorganosiloxane (A) and hydrogenpolyorganosiloxane (B) are such that the number of --SiH in (B) is from 1.2 to 7.0 times the number of R in (A). (C) 0 to 20 weight percent of a siloxane copolymer formed from dimethylvinylsiloxy units, trimethylsiloxy units, and SiO 2 units, based on the total weight of (A) and (B), (D) a platinum-containing catalyst in an amount to give from 1.0 to 1,000 ppm as platinum metal based on the total weight of (A), (B), and (C), (E) 1 to 30 weight percent of carbon black based on the total weight of (A), (B), and (C), and (F) 0.01 to 1.0 weight percent of acetylacetone salt of a metal based on the total weight of (A), (B), and (C).