Heat-curable silicone elastomer composition

A heat-curable silicone elastomer composition comprising:

• (A) a thermoplastic resin with a melting or softening point of 40.degree. to 150.degree. C. containing a platinum catalyst and a hydrosilylation reaction retarding agent and being in the form of fine-grained powder or particles having a particle size of 0.1 .mu.m to 1 mm, in which both the platinum catalyst and the reaction retarding agent are associated with the thermoplastic resin, the amount of the platinum catalyst contained in the thermoplastic resin being not more than 50 parts by weight per 100 parts by weight of the thermoplastic resin, and the amount of the hydrosilylation reaction retarding agent contained in the thermoplastic resin being not more than 100 moles per mole of the platinum atoms contained in the platinum catalyst,
• (B) an organopolysiloxane having at least two unsaturated aliphatic hydrocarbon groups bonded to silicone atoms in its molecule, and
• (C) an organohydrogenpolysiloxane having at least two silicon-bonded hydrogen atoms in its molecule;
• the amount of the component (A) in the composition being such that the amount of the platinum contained in the composition is 1 to 1000 ppm based on the amount of the component (B), and
• the amount of the component (C) in the composition being such that the molar ratio of the silicon-bonded hydrogen atoms in the component (C) to the silicon-bonded unsaturated aliphatic hydrocarbon groups in the component (B) is from 1/10 to 12/1.