Semi-conductive silicone elastomers

Claim 2

In a composition vulcanizable to an electrically conductive silicone elastomer, said composition comprising: i. a vinylorganopolysiloxane gum; ii. an organohydrogenpolysiloxane; iii. an electically conductive carbon black filler in an amount capable of rendering the cured composition electrically conductive; and iv. a small, effective amount, sufficient to cure the composition with steam or under compression molding conditions, of a peroxide catalyst which is not normally capable of curing the composition on exposure to hot air, the improvement which comprises including in said composition v. a catalyst comprising platinum or a platinum compound in a small amount, at least effective to render the composition vulcanizable upon exposure to hot air but less than an amount which will cause any substantial cross-linking of the composition within 24 hours at a temperature of about 23° C.

Claim 3

A composition as defined in claim 1 wherein said organohydrogenpolysiloxane (ii) comprises from about 0.1 to about 1.0 parts by weight, said filler (iii) comprises from about 20 to about 50 parts by weight, said peroxide catalyst (iv) comprises from about 0.2 to about 2.0 parts by weight, and said catalyst comprising platinum or a platinum compound (v) comprises from about 0.0001 to about 0.005 parts by weight per 100 parts by weight of said gum (i).

Claim 4

A composition as defined in claim 1 wherein the vinylorganopolysiloxane gum (i) is of the formula ##STR2## where R and R' may be the same or different and are monovalent hydrocarbon groups free of aliphatic unsaturation, with at least 50 mole percent of R' being methyl and where n has a value sufficient to provide a gum-like consistency at room temperature.

Claim 5

A composition as defined in claim 1 wherein the organohydrogenpolysiloxane (ii) is comprised of structural units of the formula R.sub.a Hb Si O (4-a-b/2) wherein R is a monovalent hydrocarbon free of aliphatic unsaturation, a is from about 0.5 to 2, inclusive, b is from about 0.05 to 2, inclusive, and the sum of a and b is from about 1 to 3, inclusive.

Claim 6

A composition as defined in claim 1 wherein said vinylorganopolysiloxane gum is a methylvinylpolysiloxane gum.

Claim 7

A composition as defined in claim 5 wherein said methylvinylpolysiloxane gum is a dimethylvinyl chain-stopped dimethylpolysiloxane gum.

Claim 8

A composition as defined in claim 1 wherein said carbon black filler (iii) is an acetylene black.

Claim 9

A composition as defined in claim 1 wherein said peroxide is dicumyl peroxide, di-t-butyl peroxide or a mixture thereof.

Claim 10

A composition as defined in claim 1 wherein said catalyst (v) comprises finely divided elemental platinum, chloroplatinic acid, a platinum hydrocarbon complex, a platinum alcoholate, a platinum chloride-olefin complex or a mixture of any of the foregoing.

Claim 11

A composition as defined in claim 1 which, after vulcanization, exhibits a volume resistivity of less than 10,000 ohm-cm., a Shore A hardness of at least 50, a tensile strength of greater than 450 pounds per square inch and an elongation of greater than 100 percent at break.

Claim 12

In a process for preparing an electrically conductive vulcanized silicone elastomer comprising: A. forming a composition of: i. a vinylorganopolysiloxane gum; ii. an organohydrogenpolysiloxane; iii. an electrically conductive carbon black filler in an amount capable of rendering the cured composition electrically conductive; and iv. a small, effective amount, sufficient to cure the composition with steam or under compression molding conditions, of a peroxide catalyst which is not normally capable of curing the composition on exposure to hot air, and B. heating the composition under vulcanizing conditions until it is substantially cured, the improvement which comprises adding to said composition before vulcanization (v) a catalyst comprising platinum or a platinum compound in a small amount, at least sufficient to render the composition vulcanizable upon exposure to hot air but less than an amount which will cause any substantial cross-linking of the composition within 24 hours at a temperature of about 23° C., shaping to form, and thereafter heating the composition in hot air until it has been substantially completely vulcanized.

Claim 13

In a process for preparing an electrically conductive vulcanized silicone elastomer comprising: A. forming a composition of: i. a vinylorganopolysiloxane gum; ii. an organohydrogenpolysiloxane; iii. an electrically conductive carbon black filler in an amount capable of rendering the cured composition electrically conductive; and iv. a small, effective amount, sufficient to cure the composition with steam or under compression molding conditions, of a peroxide catalyst which is not normally capable of curing the composition on exposure to hot air, and B. heating the composition under vulcanizing conditions until it is substantially cured, the improvement which comprises adding to said composition before vulcanization (v) a catalyst comprising platinum or a platinum compound in a small amount, at least sufficient to render the composition vulcanizable upon exposure to hot air but less than an amount which will cause any substantial cross-linking of the composition within 24 hours at a temperature of about 23° C., shaping to form, and thereafter heating the composition in hot air until it has been substantially completely vulcanized.

Claim 14

A process as defined in claim 11 wherein said organohydrogenpolysiloxane (ii) comprises from about 0.1 to about 1.0 parts by weight, said filler (iii) comprises from about 20 to about 50 parts by weight, said peroxide catalyst (iv) comprises from about 0.2 to about 2.0 parts by weight, and said catalyst comprising platinum or a platinum compound (v) comprises from about 0.0001 to about 0.005 parts by weight per 100 parts by weight of said gum (i).

Claim 15

A process as defined in claim 11 wherein the vinylorganopolysiloxane gum (i) is of the formula ##STR3## wherein R and R' may be the same or different and are monovalent hydrocarbon groups free of aliphatic unsaturation, with at least 50 mole percent of R' being methyl and where n has a value sufficient to provide a gum like consistency at room temperature.

Claim 16

A process as defined in claim 11 wherein the organohydrogenpolysiloxane (ii) is comprised of structural units of the formula R.sub.a H.sub.b Si O (4-a-b/2) wherein R is a monovalent hydrocarbon free of aliphatic unsaturation, a is from about 0.5 to 2, inclusive, b is from about 0.05 to 2, inclusive, and the sum of a and b is from about 1 to 3, inclusive.

Claim 17

A process as defined in claim 11 wherein said vinylorganopolysiloxane gum is a methylvinylpolysiloxane gum.

Claim 18

A process as defined in claim 15 wherein said methylvinylpolysiloxane gum is a dimethylvinyl chain-stopped dimethylpolysiloxane gum.

Claim 19

A process as defined in claim 11 wherein said carbon black filler (iii) is an acetylene black.

Claim 20

A process as defined in claim 11 wherein said peroxide is dicumyl peroxide, di-t-butyl peroxide or a mixture thereof.

Claim 21

A process as defined in claim 11 wherein said catalyst (v) comprises finely divided elemental platinum, chloroplatinic acid, a platinum hydrocarbon complex, a platinum alcoholate, a platinum chloride-olefin complex or a mixture thereof.

Claim 22

A process as defined in claim 11 in which said composition, after vulcanization, exhibits a volume resistivity of less than 10,000 ohm-cm., a Shore A hardness of at least 50, a tensile strength of greater than 450 pounds per square inch and an elongation of greater than 100 percent at break.

Claim 23

A process as defined in claim 11 wherein vulcanization is effected by heating said composition in air at a temperature of from about 400° to about 750° F. for from about 2 to about 15 minutes.