Magnetic recording medium having segmented copolyester binder

Claim 1

Magnetic recording medium comprising a nonmagnetizable backing member bearing a coating of magnetizable particles in a binder, which binder consists essentially of a thermoplastic segmented copolyester consisting essentially of about 25 to 75 percent by weight of amorphous ester units and 75 to 25 percent by weight of crystallizable ester units joined through ester linkages, the crystallizable ester units being of the formula ##STR5## and the amorphous ester units being of the formula ##STR6## wherein R 1 is primarily tetramethylene, phenylene and/or naphthalene, R 2 consists of divalent radicals remaining after removal of the hydroxyl groups of one or more saturated aliphatic diols containing 2-12 carbon atoms, R 3 is R 1 or R 5 where R 5 consists of divalent radicals remaining after removal of the carboxyl groups of saturated aliphatic dimer acids and contains 22-50 carbon atoms, and R 4 is R 2 or R 6 where R 6 consists of divalent radicals remaining after removal of the terminal hydroxyl groups of long chain aliphatic diols having average molecular weights of 200-4000, at least one of R 3 and R 4 in each amorphous ester unit is R 5 or R 6 , and where R 1 is essentially entirely aromatic, the copolyester contains at least 50 percent by weight of amorphous ester units, and said copolyester has a DTA melting temperature of from about 65° to 150° C., an inherent viscosity of at least 0.5 dl/g at 25° C., as measured in 0.3 g/dl solution in chloroform at 25° C., and a Tg less than 0° C.