Easily demouldable and non blocking polyurethane elastomers, process for their production and their use.

摘要

1. A nonblocking, thermoplastic polyurethane elastomer which is readily removable from the mold, contains a mixture of thermoplastic polyrethanes containing different amounts of urethane groups and has been prepared by reacting (a) organic diisocyanates, (b) polylhydroxy compounds having molecular weights of from 500 to 8,000 and (c) diols having molecular weights of from 60 to 400 in a ratio such that the number of equivalents of NCO groups of the diisocyanates (a) to the number of equivalents of the sum of the hydroxyl groups of components (b) and (c) is from 1:0.85 to 1:1.2, wherein the mixture essentially consists of A) from 50 to 99.5 parts by weight of a thermoplastic polyurethane elastomer A containing from 10 to 50 % by weight of urethane groups and having a melt flow index of from 0.1 to 100 at 190 degrees C and B) from 0.5 to 50 parts by weight of a thermoplastic polyurethane elastomer which contains free isocyanate groups and from 20 to 60 % by weight of urethane groups and has a melt flow index of 10 to 1,000 at 190 degrees C, and in the preparation of which only from 50 to 90 mol % of the diisocyanates (a) have been converted, with the proviso that the content of urethane groups in the polyurethane elastomer B is never less than 10 % by weight higher than the content of urethane groups is A and the melt flow index of the polyurethane elastomer B at the melting point is equal to or greater than than of A.