Curable fluorinated silicone elastomer

Claim 2

A curable fluorinated silicone elastomeric composition comprising (a) 100 parts by weight of polydiorganosiloxane gum having from 45 to 50 percent of the organic radicals being 2-(perfluoroalkyl)ethyl radicals in which the perfluoroalkyl radical has from 1 to 4 inclusive carbon atoms, from 50 to 55 percent of the organic radicals being selected from the group consisting of monovalent hydrocarbon radicals having from 1 to 6 carbon atoms, from 0.1 to 1 percent of the monovalent hydrocarbon radicals having aliphatic unsaturation, (b) from 20 to 65 parts by weight of reinforcing silica filler having a surface area of at least 150 m 2 /g, said silica being treated with anticrepe-hardening agent, (d) means for curing, and characterized in that it includes (c) from 0.8 to 5 parts by weight, based on 100 parts by weight of (a) plus (b), of polytetrafluoroethylene powder.

Claim 3

The composition of claim 1 in which (d) is from 0.1 to 3.0 parts by weight, based on the weight of (a) plus (b), of an organic peroxide vulcanizing agent.

Claim 4

The composition of claim 2 in which the polydiorganosiloxane gum is a hydroxyl endblocked gum having a Williams plasticity number of greater than 250, the 2-(perfluoroalkyl)ethyl radicals are 3,3,3-trifluoropropyl radicals, the polytetrafluoroethylene powder is present in an amount of from 1 to 3 parts by weight, and the peroxide is present in an amount of from 0.2 to 1 part by weight.

Claim 5

The composition of claim 3 in which the silica filler is present in an amount of from 45 to 60 parts.

Claim 6

The composition of claim 4 in which there is also present organosilicon compound in an amount sufficient to yield from 0.075 to 0.60 part by weight vinyl radical based on 100 parts by weight of (a).

Claim 7

The composition of claim 1 in which an acid acceptor selected from the group consisting of magnesium oxide, magnesium hydroxide, calcium oxide, and calcium hydroxide is present in an amount of less than 10 parts by weight based on 100 parts by weight of (a) plus (b).

Claim 8

The composition of claim 6 in which the polydiorganosiloxane gum is a hydroxyl endblocked gum having a Williams plasticity number of greater than 250, the 2-(perfluoroalkyl)ethyl radicals are 3,3,3-trifluoropropyl radicals, from 0.5 to 1.0 of the monovalent hydrocarbon radicals are vinyl radicals; the reinforcing silica is present in an amount of from 45 to 60 parts by weight, the reinforcing silica being treated in situ by including from 5 to 65 parts by weight of organosilicon compound, the organosilicon compound being hydroxyl endblocked polydiorganosiloxane fluid having a viscosity below 1 Pa.s at 25°C, containing 3,3,3-trifluoropropyl radicals and vinyl radicals, the vinyl radicals being present in an amount of from 0.075 to 0.60 part by weight; the polytetrafluoroethylene powder is present in an amount of from 1 to 3 parts by weight; the acid acceptor is present in an amount of from 1 to 5 parts by weight; and an organic peroxide vulcanizing agent is present in an amount from 0.2 to 1 part by weight, both acid acceptor and vulcanizing agent based upon 100 parts by weight of (a) plus (b).

Claim 11

A method of producing an improved fluorinated silicone elastomer characterized by (a) mixing the composition of claim 1 (b) forming to the desired configuration, and (c) vulcanizing; to yield a cured fluorinated silicone elastomer having improved retention of physical properties after exposure to hot fuel, hot petroleum oil and hot air.