| abstract |
A biaxially oriented polyethylene 2,6-naphthalate film having superior physical properties in the machine direction such as tensile strength and Young''s modulus, particularly useful as a base of magnetic recording tape, is prepared by stretching an undrawn film of polyethylene 2,6-naphthalate consisting essentially of ethylene 2,6-naphthalate units and having an intrinsic viscosity of at least 0.35, first in the machine direction to 3.5-5 times the original length at a temperature ranging from 10*C. above the second order transition temperature of said polyethylene 2,6-naphthalate to 170*C., and then in the transverse direction at a draw ratio 50-90 percent of that of the machine direction stretching at a temperature ranging from 3*C. above said second order transition temperature to 160*C. and satisfying the following relationship |