Patent ID: 8580909

Claim:
Process for producing a chemically crosslinked polyurethane film, comprising the steps of A) chemically reacting a mixture comprising two or more polyols with one or more polyisocyanates, at least one of the polyols or at least one of the polyisocyanates comprising molecules having a functionality of three or more, the ratio of the total number of isocyanate groups to the total number of hydroxyl groups being less than 1.0, to give a hydroxyl-functionalized, meltable reaction product, in the form of a hydroxyl-functionalized polyurethane hotmelt prepolymer, B) introducing the hydroxyl-functionalized polyurethane hotmelt prepolymer and one or more polyisocyanates into a continuously operating mixing assembly wherein a chemical reaction takes place between the hydroxyl-functionalized polyurethane hotmelt prepolymer and the polyisocyanates in the melt, C) coating the melt emerging from the mixing assembly onto an incoming web-form material or between two incoming web-form materials, in the course of which the reaction between the hydroxyl-functionalized polyurethane hotmelt prepolymer and the polyisocyanates started in step B) continues to form a chemically crosslinked nonmeltable polyurethane film.