Hydraulic silicone crumb with improved heat stability

Claim 1

A silicone crumb comprising the cured product obtained by curing a mixture of (A) a vinyl-containing polyorganosiloxane consisting essentially of units selected from the group consisting of diorganosiloxane units, monoorganosilsesquioxane units, triorganosiloxy units, and mixtures thereof in which the organic radicals are monovalent hydrocarbon radicals or monovalent halogenated hydrocarbon radicals, in the polyorganosiloxane the organic radicals being such that at least 0.1 weight percent of them are vinyl radicals, (B) a silicon-bonded hydrogen containing polysiloxane in which there is at least 0.5 weight percent silicon-bonded hydrogen atoms, the valences of the silicon atoms not being satisfied by divalent oxygen atoms or silicon-bonded hydrogen atoms are satisfied by monovalent hydrocarbon radicals or monovalent halogenated hydrocarbon radicals, (C) a platinum catalyst for the hydrosilation reaction of (A) and (B), (D) from 0.1 to 2 weight percent of a heat stability additive based on the total weight of the composition, wherein the heat stability additive is selected from the group consisting of the product obtained by mixing (1) a hydrocarbon endblocked polymethylsiloxane fluid having an average of from 1.9 to 3.0 methyl groups per silicon atom, and (2) an organometallic compound in sufficient amount to provide from more than 0.1 to 10.0 parts by weight of the metal per 100 parts by weight of the mixture of (1) plus (2), said organometallic compound being selected from the group consisting of organotitanium, organozirconium, and organohafnium compounds wherein each organic group consists of carbon, oxygen, and hydrogen atoms and which is bonded to the metal by at least one metal-oxygen-carbon linkage, and heating the mixture of (1) and (2) in an inert atmosphere to decompose the organometallic compound, and a mixture of (3) a hydrocarbon endblocked polymethylsiloxane fluid having an average of from approximately 1.9 to less than 3.0 methyl groups per silicon and (4) a siloxymetal compound in sufficient amount to provide more than 0.1 part by weight of the metal per 100 parts by weight of the mixture of (3) plus (4), said siloxy-metal compound being an organosilicon compound having at least one silicon-oxygen-titanium bond, one silicon-oxygen-zirconium bond, or one silicon-oxygen-hafnium bond, the cured product being in a fine particulate form which exhibits an extrusion rate of at least 50 grams per minute through an orifice of 0.5 inch diameter under a pressure of 345 kilopascals and compression points of less than 1035 kilopascals for the first two compressions.