Flexible magnetic recording media having a polyester-polyurethane binder and chromium dioxide pigment

Claim 1

A flexible magnetic recording media, comprising; a flexible substrate, and a ferromagnetic chromium dioxide pigment-loaded-binder adhesively coating said substrate; the improvement comprising said binder being a thermoplastic polyurethane formed as a reaction product of: (A) a hydroxyl-terminated polyester which itself is a reaction product of a difunctional alcohol (diol) having hydrolytic stability, and a dicarboxylic acid selected from the group consisting of adipic acid, azelaic acid and 1,12-dodecanedioic acid, or mixtures thereof, said polyester having a hydroxyl number of about 50 to 250; (B) a chain extender comprising a primary or a secondary alcohol selected from the group consisting of 1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol and 2,5-hexanediol, the resultant hydroxyl number of said polyester and chain extender being about 130 to 300; and (C) an aromatic diisocyanate; wherein the relative proportions of (A), (B) and (C) are selected to produce a pigment-loaded polyurethane having a hard segment content in the range of about 37 to 40 percent by weight, and a soft segment molecular weight (M n ) in the range of about 500 to 1500, wherein the pigment loading is in the range 80 to 88% by weight.