Method for making skinned polyurethane composites

A method for forming a skinned composite comprising forming a layer of a polyurethane-forming reaction mixture against a plasticized thermoplastic skin layer that contains 25 to 45% by weight of plasticizer, based on the combined weight of plasticizer and thermoplastic skin layer, and then curing the reaction mixture to form a polyurethane layer adhering to the skin, wherein the polyurethane-forming reaction mixture comprises

• a) one or more polyols;
• b) one or more organic polyisocyanates;
• c) at least one blowing agent selected from water or a mixture of water and a hydrocarbon, hydrofluorocarbon, fluorocarbon, fluorochlorocarbon, hydrofluorochlorocarbon or dialkyl ether physical blowing agent in an amount sufficient to provide a foam density of 80 to 500 kg/m3;
• d) at least one catalyst for the reaction of isocyanate groups towards hydroxyl groups;
• wherein component a) includes at least one polyester polyol, and/or component b) includes at least one isocyanate-terminated prepolymer which is a reaction product of a polyester polyol with an excess of one or more polyisocyanates, and further wherein the at least one polyester polyol in component a) and/or provided in the preparation of the at least one isocyanate-terminated prepolymer included within component b) constitutes from 0.5 to 7% of the combined weight of components a) and b);
• and further wherein the polyurethane-forming reaction mixture contains from 0.02 to 0.3% by weight of a Bronsted acid having a molecular weight of up to about 400 selected from one or more of formic acid, acetic acid, an alkanoic acid having three to eight carbon atoms, sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, benzene sulfonic acid and an alkyl benzene sulfonic acid in which the alkyl group contains 1 to 20 carbon atoms, based on the combined weight of the a) one or more polyols and the Bronsted acid.