Molding compounds having low durometer and high tear strength
AssigneeGeneral Electric Company
InventorRobert A. Smith
Life of this patent
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Abstract
Silicone mold compositions are provided which exhibit low durometer and high tear strength properties and comprise a main filler of precipitated silica and a reinforcing co-filler selected from acicular CaSiO.sub.3 fillers, fumed aluminum oxide fillers, and spherical ceramic fillers. The co-fillers have large surface areas and small particle sizes. The co-fillers are used with alkoxy silane cross-linking agents of the formula (RO).sub.4 Si, particularly n-propylsilicate. Two-part silicone cure systems are provided which enable the rapid achievement of full die B tear strengths without the need for prolonged aging of these materials.
Claims21
A curable silicone composition comprising from about 40 to about 80% by weight based on the entire silicone composition of a polymer system having a viscosity of between about 30,000 and 50,000 cps at 25.degree. C. comprising:
- up to 50% by weight of the polymer system of Component (A), an organopolysiloxane fluid substantially free of silanol and having a viscosity of from about 20 to about 1,000 cps at 25.degree. C. and up to 100% by weight of the polymer system of Component (B), a silanol chain-stopped organopolysiloxane, substantially free of silanol-on-chain and vinyl-on-chain, having a viscosity of from about 20,000 to about 150,000 cps at 25.degree. C.;
- up to about 30% by weight based on the entire silicone composition of Component (C), a finely divided precipitated silica filler;
- between about 0.1 and about 15% by weight based on the entire silicone composition of an alkoxy silane crosslinker;
- between about 0.05 and about 25% by weight based on the entire silicone composition of at least one finely divided reinforcing co-filler selected from the group consisting of acicular CaSiO.sub.3 fillers, spherical ceramic fillers, and fumed metal oxide fillers;
- and
- a catalytic amount of an addition catalyst.
A two-part room temperature vulcanizable silicone compound comprising from about 40 to about 80% by weight based on the entire silicone composition of a polymer system comprising:
- up to 50% by weight of the polymer system of Component (A), an organopolysiloxane fluid substantially free of silanol and having a viscosity of from about 20 to about 1,000 cps at 25.degree. C. and up to 100% by weight of the polymer system of Component (B), a silanol chain-stopped organopolysiloxane, substantially free of silanol-on-chain and vinyl-on-chain, having a viscosity of from about 20,000 to about 150,000 cps at 25.degree. C.;
- up to about 30% by weight based on the entire silicone composition of Component (C), a finely divided precipitated silica filler;
- between about 0.1 and about 15% by weight based on the entire silicone composition of an alkoxy silane crosslinker;
- between 0.05 and about 25% by weight based on the entire silicone composition of at least one finely divided reinforcing co-filler selected from the group consisting of acicular CaSiO.sub.3 fillers, spherical ceramic fillers, and fumed metal oxide fillers;
- and
- a catalytic amount of an additional catalyst,
- wherein Components (A) and (B) are in one part of the two-part system and the crosslinker and catalyst are in the other part of said two-part system.
Dependencies are inferred from the claim text.