Silicon pressure sensitive adhesive compositions

Claim 1

A silicone pressure sensitive adhesive composition comprising: (A) 30 to 70 parts by weight of a polydiorganosiloxane having the general formula R.sup.1 R.sub.2 SiO(R.sub.2 SiO).sub.n SiR.sub.2 R.sup.1 wherein each R denotes a monovalent hydrocarbon radical, each R 1 denotes an alkenyl radical and the subscript n is a number having an average value of greater zero; (B) 30 to 70 parts by weight of an organopolysiloxane consisting essentially of R 3 SiO 1/2 siloxane units and (R 2 O) a SiO.sub.(4-a)/2 siloxane units in a molar ratio of from 0.6:1 to 0.9:1, wherein R is as noted for component (A) above, the methyl radical comprises at least 50 mol percent of all R radicals, R 2 denotes H or R, and the subscript a has a value of from 0 to 0.3; the total of (A) and (B) being 100 parts by weight; (C) 1 to 25 parts by weight of an organopolysiloxane consisting essentially of R 3 SiO 1/2 siloxane units and (R 2 O) a SiO.sub.(4-a)/2 siloxane units in a molar ratio of from 1:1 to 1.7:1, wherein R, R 2 and the subscript a are as noted for component (B) above, the methyl radical comprises at least 50 mol percent of all R radicals, R 2 denotes H or R, and the subscript a has a value of from 0 to 0.3; and an effective amount of a curing agent for the composition, said curing agent comprising (D) an organohydrogenpolysiloxane having an average of at least 2 silicon-bonded hydrogen atoms in each molecule in an amount sufficient to provide from 1 to 40 silicon-bonded hydrogen atoms per alkenyl radical in component (A). (E) a platinum-containing catalyst for the addition reaction of alkenyl radicals with silicon-bonded hydrogen atoms, in an amount sufficient to provide from 0.1 to 1000 parts by weight of platinum for every one million parts by weight of the combined quantity of components (A) through (C), and (F) at least one addition-reaction inhibitor in an amount sufficient to retard the curing reaction at room temperature.