Biaxially oriented unidirectionally long polyethylene-2, 6-naphthalenedicarboxylate film

A biaxially oriented, unidirectionally long polyethylene- 2,6-naphthalenedicarboxylate film useful as a substrate for a magnetic recording video tape, said film having a first surface and a second surface, wherein the film has the following characteristic properties:

• (A) the Young's Modulus in the longitudinal direction and the Young's modulus in the transverse direction are each at least 600 kg/mm.sup.2, and the Young's modulus in the longitudinal direction is greater than the Young's modulus in the transverse direction,
• (B) the heat shrinkage factor in the transverse direction when the film has been treated under no load at 105.degree. C. for 30 minutes is at least 1%,
• (C) the surface roughness, Ra, of the first surface of the film is up to 5 nm, said first surface being a surface to be coated with a metal layer by vapor deposition and,
• (D) the heat shrinkage factor in the longitudinal direction when the film has been treated under no load at 105.degree. C. for 30 minutes is up to 1%.