Waterproof breathable polyurethane membranes and porous substrates protected therewith

Claim 1

A coating system for laminating fabrics and for rendering the resulting laminate waterproof and water vapor transmissible, which system comprises: (1) a basecoat chain extended polyurethane prepolymer solute composition dissolved in a fugitive compatible solvent therefor, said solute being a block copolymer reaction product of: (a) a polyisocyanate; (b) a polyalkylene ether glycol wherein the number of carbon atoms of the alkylene radical thereof is 2; and (c) an isocyanate reactive hydroxyl group-containing polydimethylsiloxane having a functionality of at least 2, said basecoat composition being adapted to be coated onto the surface of a fabric layer; and (2) an adhesive chain extended polyurethane prepolymer solute composition dissolved in a fugitive compatible solvent therefor, said solute being the reaction product of (a) a polyisocyanate and (b) a polyalkylene ether glycol wherein the number of carbon atoms of the alkylene radical thereof is at least 3, said adhesive composition being adapted to be coated onto the surface of said basecoat composition coated onto the surface of said fabric layer and to adhesively receive thereon a second fabric layer applied thereto under sufficient pressure as to effectuate at least partial intermingling of said basecoat and adhesive coatings, the concentrations of said polyalkylene ether glycol of (1)(b) and (2)(b) of said basecoat and adhesive compositions being sufficient to provide an intermingled chain extended prepolymer matrix between said fabric layers wherein the mole ratio of (1)(b) to (2)(b) is within the range of from 1.5:0.5 and 0.5:1.5 and the concentration of said polydimethylsiloxane of (1)(c) of said basecoat composition being sufficient to provide within said matrix a mole ratio of said polydimethylsiloxane to the total of said polyalkylene ether glycols of (1)(b) and (2)(b) of from 0.1:1 to 0.3:1.