Process and composition for the manufacture of products from silicone rubber

Claim 1

A process for the manufacture of a molded silicone rubber product comprising the steps of: (a) forming a substantially uniform mixture comprising room temperature vulcanizing or heat curing silicone rubber components and a liquid phase including an organic peroxide cross-linking agent encapsulated within an encapsulating material to form microcapsules, the microcapsules being impervious to the cross-linking agent and having a wall thickness and a rupture strength designed to withstand external agitation, but to rupture when the internal vapor pressure reaches a rupture point; (b) maintaining substantially all of said cross-linking agent in the microcapsules isolated from said silicone rubber components until the temperature and pressure are such that the cross-linking agent is released from the microcapsules; (c) performing a molding cycle having a first and second portion, (i) the first portion being a flowing step comprising flowing the mixture to fill a mold cavity with the mixture prior to any significant cross-linking agent induced cross-linking, (ii) the second portion being a cross-linking step comprising raising the temperature of the mixture within the mold cavity to raise the vapor pressure within the microcapsules to the rupture point to cause the microcapsules to rupture, and to release the organic peroxide cross-linking agent, substantially all cross-linking occurring during the second portion of the molding cycle; and (d) removing the cured mixture from the mold cavity to provide the silicone rubber product.