POLYESTER FILM AND MAGNETIC RECORDING MEDIUM.

摘要

Polyester film for use as a base for magnetic recording medium is prepd. from a polyester obtd. using a germanium cpd. as polymerisation catalyst, and has Young's modulus in the longitudinal direction (Emd) at least 350 kg/square mm; Young"s modulus in the transverse direction (Etd) at least 350 kg/mm2; Emd.Etd at least 250,000 square kg/mm; refractive index (nzd) across the thickness of the film at least 1.480 and not more than 1.492. The max. surface roughness (Rt) on at least one side surface is no more than 100 nm. The film may be a laminate of two films both satisfying the above criteria, in which case one film may contain fine particles and pref. has Rt no less than 30 nm.