BIAXIALLY ORIENTED POLYESTER FILM FOR MAGNETIC RECORDING MEDIUM

摘要

PROBLEM TO BE SOLVED: To prepare a biaxially oriented polyester film for a magnetic recording medium excellent in winding properties, abrasion resistance and traveling durability and especially useful as a base film of a magnetic recording medium for a high speed duplicator. SOLUTION: This biaxially oriented polyester film for a magnetic recording medium includes 0.001-0.03wt.% cross-linked polymer particles A having 0.8-1.6μm average particle diameter (dA), 0.1-0.8wt.% inert particles B having 0.4-0.8μm average particle diameter (dB) and 0.05-1.0wt.% inert inorganic particles C having 0.01-0.3μm average particle diameter (dC) and >=7 Mohs' hardness. Further, the ratio of the average particle diameters of the cross-linked polymer particles A to the inert inorganic particles B (dA/dB) satisfies the following relation of formula (1) and the ratio of the three-dimensional roughness SRz averaging the values at ten points on the film surface to the average three-dimensional roughness SRa at the central surface (SRz/SRa) satisfies the following relation of formula (2): (1) 1.5<=dA/dB<=3; (2) SRz/SRa>=20.