Magnetisches Aufzeichnungsmittel und Polyesterfilm dafür

摘要

A biaxially oriented polyester film for magnetic recording media which has (1) a Young's modulus in a machine direction of 5.0 GPa or less and a Young's modulus in a direction perpendicular to the machine direction of 8.0 GPa or more, (2) a surface roughness on one side of 0.3 to 1.5 nm when measured for a measurement area of 246.6 x 187.5 mu m and 0.1 to 3.0 nm when measured for a measurement area of 2.5 x 1.9 mm and a surface roughness on the other side of 0.6 to 2.5 nm when measured for a measurement area of 246.6 x 187.5 mu m and 0.1 to 5.0 nm when measured for a measurement area of 2.5 x 1.9 mm, and (3) a heat shrinkage factor in a machine direction when heated at 105 DEG C for 30 minutes of 0 to 1.5 % and when heated at 150 DEG C for 30 minutes of 2.0 to 5.0 % and a heat shrinkage factor in a direction perpendicular to the machine direction when heated at 105 DEG C for 30 minutes of 0.5 to 3.0 % and when heated at 150 DEG C for 30 minutes of 6.0 to 11.0 %.