Electrically conductive polydiorganosiloxanes

Claim 1

An electrically conductive composition having improved electrical life when subjected to high voltage electrical impulses consisting essentially of a curable vinyldiorganosiloxy endblocked polydiorganosiloxane, the organic radicals being selected from the group consisting of methyl, ethyl, phenyl, and 3,3,3-trifluoropropyl radicals, there being from 0 to 50 inclusive percent 3,3,3-trifluoropropyl radicals and from 0 to 50 inclusive percent phenyl radicals, all percentages of radicals being based on the total number of organic radicals in the polydiorganosiloxane, greater than 15 percent by weight, based on the weight of the composition, of carbonaceous particles of less than 20 micrometers average diameter, a crosslinking agent consisting of a polyorganohydrogensiloxane having an average of at least 2.1 silicon-bonded hydrogen atoms per molecule, said molecules consisting essentially of units selected from the group consisting of H(CH 3 )SiO units; R 2 SiO units; H(CH 3 ) 2 SiO 1/2 units, R 3 SiO 1/2 units, and SiO 2 units, R being selected from the group consisting of alkyl radicals having from 1 to 6 carbon atoms inclusive, phenyl radicals, and 3,3,3-trifluoropropyl radicals, the amount of polyorganohydrogensiloxane being sufficient to provide from 1.2 to 3 inclusive silicon-bonded hydrogen atoms for every silicon-bonded vinyl group in the composition, a platinum-containing catalyst, soluble in the polydiorganosiloxane, and present in an amount sufficient to provide at least 1 part by weight of platinum for every one million parts by weight of the polydiorganosiloxane, an amount of a platinum catalyst inhibitor sufficient to give the desired shelf life, and optionally a phenyl-containing polysiloxane, the composition further restricted in that there must be present greater than 2 percent by weight of phenyl radicals based on the weight of the cured composition, said phenyl radical being present in either the vinyldiorganosiloxy endblocked polydiorganosiloxane, the crosslinking agent, or phenyl-containing polysiloxane separately or in combination.