PURPOSE: To obtain a polyester film for a magnetic recording medium having superior electromagnetic transducing characteristics and traveling performance by adding a prescribed finely powered titanic acid compound to a specified polyester.
CONSTITUTION: A film is formed by chiefly using a composition prepd. by adding 0.05W20wt% finely powdered MTiO3 of 0.03W2.5μm average particle size to polyester consisting essentially of structural units represented by the formula. In the compound, M is at least one kind of group IIA element. The film has ≥350kg/mm2 Young's modulus in the longitudinal direction and 0.5W10% coefft. of thermal shrinkage at 150°C. In case where M is Sr, Ca or Mg, the electromagnetic transducing characteristics are further improved. In case where the melt viscosity of the film is 500W8,000P, especially 1,000W7,000P, the traveling performance is further improved. In case where the film has 35W70, especially 40W60 grain size and 0.935W0.975 refractive index in the thickness direction, the electromagnetic transducing characteristics are further improved.
OKASAKA HIDESADA
YOSHII TOSHIYA
