Process for the production of radiation-crosslinked thermoplastic polyurethanes

Claim 1

A process for the production of polyurethanes suitable for thermoplastic processing comprising mixing I. at least 75% by weight of preformed thermoplastic polyurethane elastomers, or of a blend of (A) substantially bifunctional, compound essentially containing two Zerewitinoff-active hydrogen atoms per molecule and having a molecular weight of from 400 to 20,000, (B) substantially bifunctional chain-extending agents selected from the group consisting of diols and diamines, having a molecular weight of from 32 to 399 and (C) organic diisocyanates, wherein the molar ratio of the sum of (A) and (B) to the diisocyanates (C) is from 0.9 to 1.1, and optionally (D) which is at least one member selected from the group consisting of stabilizers, lubricants and other known additives and excluding peroxides and polymerization initiators which decompose into radicals under the effect of actinic light, with II. (E) from 4 to 24% by weight of at least one monomeric acrylate and/or methacrylate compound which is characterized in that it is predominantly free of hydroxyl groups and predominantly nonincorporable and is derived from the corresponding acid and an aliphatic, cycloaliphatic or araliphatic monoalcohol containing at least six carbon atoms in the alcohol residue as crosslinking agent, and III. (F) from 0.01 to 3% by weight of a polymerization inhibitor and/or an antioxidant by adding said II and III to said I before complete formation of the highly polymeric polyurethane or to the melt of preformed polyurethane elastomer at a temperature below 230° C. and cooling the mixture to a temperature below 130° C. in less than 5 minutes in continuous extruders and optionally granulating the resulting mixture.