POLYURETHANE PRODUCIBLE IN ABSENCE OF SOLVENT, AND ITS USE AS BINDER FOR MAGNETIC RECORDING MEDIUM

摘要

PROBLEM TO BE SOLVED: To obtain a thermoplastic polyurethane containing no isocyanate group, useful as a binder having improved dispersion characteristics for a mag netic recording medium having excellent magnetic characteristics, by subjecting a specific constituent component to melt polymerization and specifying a molecu lar weight, etc. SOLUTION: Constituent components comprising (A) a 1 mol of a polyol having 400-4,000 molecular weigh, (B) 0.3-9 mol of a mixture of (i) optionally a 2-18C diol and (ii) 0.03-0.4 mol of a diol containing one or more acidic groups, (C) 0-1 mol of a 3-18C polyol containing three or more OH groups, (D) 1.25-13 mols of a 6-30C diisocyanate and (E) 0-1 mol of a 2-16C primary or secondary amino-alcohol are subjected to melt polymerization so as to make the molar ratio of OH group and NH group in the components A, B, C and E to NCO group in the component D of 0.98-1.4 to give the objective polyurethane containing an acidic group, soluble in tetrahydrofuran and having 15,000-70,000 molecular weight.