Patent ID: 6218479
Filing Date: 2001-04-17
Classification: C08G,C08L

Abstract:
A thermoplastic molding composition having a Shore A hardness, as determined according to DIN 53 505, of 65 to 85, and a low shrinkage, as determined according to DIN 16 770 (Part 3), of lower than 2.5% consisting of a blend ofA) 5 to 54 parts by weight of a first thermoplastic polyurethane produced from an organic diisocyanate, a substantially linear polyester polyol and/or polyether polyol having a number average molecular weight of 500 to 5000 and a chain extending diol having a molecular weight of 60 to 400, said first thermoplastic polyurethane having a Shore A hardness of 60 to 75, andB) 95 to 46 parts by weight of second thermoplastic polyurethane prepared by a continuous process comprisinga) mixing under high shear an organic diisocyanate with at least one substantially linear polyol having a number average molecular weight of 500 to 5000 selected from the group consisting of polyether polyol and polyester polyol, at a NCO/OH ratio of 2.0:1 to 5.0:1, to form a first mixture, andb) enabling the components of said first mixture to react in a reactor at a temperature greater than 120.degree. C., up to a conversion greater than 90% with respect to said polyol, to form an isocyanate-terminated prepolymer, andc) mixing said prepolymer with additional organic diisocyanate to attain an NCO/OH ratio of 2.05:1 to 6.0:1 to form a second mixture, andd) cooling said second mixture to a temperature lower than 190.degree. C., ande) mixing said second mixture continuously with at least one chain extending diol having a molecular weight of 60 to 400, for at most 5 seconds, to obtain a third mixture, andf) enabling the components of said third mixture to react continuously in an extruder to form said second thermoplastic polyurethane,said second thermoplastic polyurethane characterized in having an NCO:OH ratio of 0.9:1 to 1.1:1 and a Shore A hardness of 76 to 90, said composition characterized in that it is readily de-moldable and in that it exhibits low molding shrinkage in the absence of plasticizer.