| 摘要 |
A biaxially oriented film of a polyethylene-2,6-naphthalenedicarboxylate, which (1) has a Young's modulus of at least 600 kg/mm2 in the transverse direction and a Young's modulus of at least 500 kg/mm2 in the longitudinal direction, the Young's modulus in the transverse direction being greater than the Young's modulus in the longitudinal direction, (2) satisfies the following relationships between an elongation ST (%) in the transverse direction per kg/mm2 of a load at 120 DEG C. and the Young's modulus YT (kg/mm2) in the transverse direction, -0.001YT+0.89<ST<-0.001YT+1.57 when YT is at least 1,200 kg/mm2, and -0.31<ST<0.37 when YT is greater than 1,200 kg/mm2, and (3) has a heat shrinkage percentage of 0.1% or less in the longitudinal direction when heat-treated under no load at 70 DEG C. for 1 hour. This film is almost free from a dimensional change in the transverse direction and is excellent in lubricity and durability and is useful as a base film for a magnetic recording medium capable of high-density recording for a long time.
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