Heat curing organopolysiloxane composition

Claim 1

Heat-curing organopolysiloxane composition consisting essentially of (A) 100 parts by weight of organopolysiloxane gum with the general formula ##STR2## in which R 1 and R 2 are selected from the group consisting of monovalent hydrocarbon groups excluding alkenyl groups, and cyanoalkyl groups, and n is equal to or greater than 3,000, (B) 50 to 150 parts by weight of organopolysiloxane gum with the general formula R.sup.3.sub.3 SiO[R.sup.4.sub.2 SiO].sub.m SiR.sup.3.sub.3 in which R 3 is selected from the group consisting of monovalent hydrocarbon group, cyanoalkyl group, and the hydroxyl group; R 4 is selected from the group consisting of monovalent hydrocarbon group, and cyanoalkyl group, of which 0.1 to 0.2 percent of the radicals attached to the silicon atoms are alkenyl group; and m is equal to or greater than 3,000. (C) 0.5 to 10 parts by weight of organohydrogenpolysiloxane having at least 2 silicon-bonded hydrogen atoms in each molecule, having a viscosity ranging from 10 to 1000 centipoise at 25° C. surface area of at least 250 m 2 /g, at the rate of 20 to 50 parts by weight per 100 parts by weight of the total quantity of components (A) plus (B), (E) 0.1 to 5 parts by weight of organoperoxide, and (F) 1 to 50 parts by weight of organopolysiloxane oil with the general formula (CH.sub.3).sub.2 R.sup.5 Si[R.sup.6.sub.2 SiO].sub.p SiR.sup.5 (CH.sub.3).sub.2 in which R 5 is a hydroxyl group or methyl group; R 6 is a monovalent hydrocarbon group, of which 10 to 75 percent of the radicals attached to the silicon atoms are alkenyl group; and p is 5 to 100.