BIAXIALLY ORIENTED POLYESTER FILM

摘要

PROBLEM TO BE SOLVED: To provide a biaxially oriented polyester film having excellent windability and useful as a substrate film of a magnetic recording medium having excellent electromagnetic characteristics and less dropout with a slight track shift when used as the magnetic recording medium, especially a magnetic linear digital recording medium. SOLUTION: This biaxially oriented polyester film is characterized as follows. The height of protrusions formed on the film surface caused by lubricant particles contained in the film is >=0.2μm and the number of coarse protrusions having >=10μm diameter in bottom parts of the protrusions is 10-300 based on 100 cm<2> . The center surface average roughness WRa on the film surface is 4-12 nm. The Young's modulus is 6.5-12 GPa in the longitudinal direction of the film and 5-8 GPa in the transverse direction of the film.