PURPOSE: To provide a polyester film excellent in running performance, running durability against repeated use, winding characteristics like a pancake and slitting characteristics and useful as a base film for a magnetic recording medium satisfying even the requirement of high image quality.
CONSTITUTION: This polyester film contains spherical silica particles having 0.1-2.0μm volume average particle diameter and a relative standard deviation of >0.5 in polyester and simultaneously satisfies inequalities ΔN(1,413-8,327×F, 20<ΔN<80 and F<0.1800, wherein ΔN=(NMD-NTD)×1,000 and F=(NMD+ NTD)/2-nz (where NMD is the refractive index of the film in the longitudinal direction, NTD is the refractive rndex of the film in the width direction and nz is the refractive index of the film in the thickness direction).
ODAJIMA AKIO
KIDA KATSUMI
