Storage stable heat curable organosiloxane compositions containing microencapsulated platinum-containing catalysts

Claim 1

In an improved one-part, storage stable, heat curable organosiloxane composition comprising (A) a curable polyorganosiloxane containing at least two ethylenically unsaturated hydrocarbon radicals per molecule; (B) an organohydrogensiloxane containing at least two silicon bonded hydrogen atoms per molecule in an amount sufficient to achieve curing of said polyorganosiloxane (A), where the sum of the average number of ethylenically unsaturated hydrocarbon radicals per molecule of (A) and the average number of silicon bonded hydrogen atoms per molecule of said organohydrogensiloxane (B) is greater than 4, and (C) an amount of a platinum-containing hydrosilation catalyst sufficient to promote curing of said composition at a temperature of at least 70° C. and above, the improvement comprising the presence of said platinum-containing catalyst in the form of microcapsules that in turn, comprise said catalyst as finely divided particles or droplets that are completely enveloped within a thermoplastic organic polymer where the average diameter of said microcapsules is less than 500 microns, and said thermoplastic organic polymer constitutes at least 50 percent of the weight of said microcapsules.