Extrudable silicone elastomer compositions

Claim 1

An elastomeric organopolysiloxane obtained by curing an extrudable, curable composition consisting essentially of (1) 100 parts by weight of a liquid triorganosiloxy endblocked polydiorganosiloxane exhibiting a viscosity of from 5,000 to 200,000 centipoises at 25° C., wherein the triorganosiloxy groups are vinyldimethylsiloxy or vinylmethylphenylsiloxy and at least 95% of the diorganosiloxane groups are dimethylsiloxane; (2) from 20 to 60 parts by weight of finely divided amorphous silica particles having a surface area greater than 100 square meters per gram, wherein at least a portion of the silicon atoms on the surface of the particles are bonded to trimethylsiloxy groups and vinyl-containing siloxy groups selected from the group consisting of (a) CH 2 ═CH(CH 3 ) 2 SiO[(CH 3 ) 2 SiO-- x (b) CH 2 ═CH(CH 3 ) (C 6 H 5 )SiO[(CH 3 ) 2 SiO-- x where the average value of x is from 0 to 20, and (c) organosiloxy groups consisting essentially of repeating units of the general formulae ##STR4## the total number of repeating units in each organosiloxy group being from 2 to about 20, and the molar ratio of dimethylsiloxy units to methylvinylsiloxy units having an average value of from 1:1 to 5:1, the relative concentrations of trimethylsiloxy and vinyl-containing siloxy groups being sufficient to provide (1) from 0.01 to 0.5 percent of vinyl groups, based on the weight of silica, and (2) from 1 to 100 moles of trimethylsiloxy groups for each mole of vinyl-containing siloxy groups; (3) from 10 to 50 parts of a organopolysiloxane resin consisting essentially of (d) R 2 1 (CH 2 ═CH--SiO 0 .5 units, (e) R 3 2 SiO 0 .5 units and (f) SiO 4/2 units wherein the molar ratio of the combination of (d) and (e) units to (f) units is from 0.6 to 1.1, and the concentration of (d) units is from 0.2 to 8% based on the weight of said organopolysiloxane resin, and R 1 and R 2 are alkyl containing from 1 to 4 carbon atoms or phenyl, with the proviso that at least 95% of the R 1 and R 2 groups are methyl; (4) a liquid organohydrogensiloxane in an amount sufficient to provide from 1 to 3 silicon-bonded hydrogen atoms per vinyl group present in components (1), (2) and (3) combined, said organohydrogensiloxane having an average of at least three silicon-bonded hydrogen atoms per molecule and consisting essentially of units selected from the group consisting of methylhydrogensiloxy, dimethylsiloxy, dimethylhydrogensiloxy, trimethylsiloxy and SiO 4/2 units; and (5) a platinum-containing catalyst in sufficient amount to provide at least 0.1 part by weight of platinum per million parts by weight of said triorganosiloxy endblocked polydiorganosiloxane.