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Abstract

The present invention provides a biaxially oriented film of a polyoxymethylene polymer having the main part of each of the main chains thereof substantially composed of repeating units of the oxymethylene group, --CH.sub.2 --O--, which biaxially oriented polyoxymethylene polymer film is characterized by the fact that the crystallinity thereof measured by the density method is in the range of 75 to 95% and the degree of crystal orientation measured by the X-ray diffraction method in the two directions of end and edge are each in the range of 80 to 98%. This film possesses a high modulus of elasticity, outstanding dimensional stability, and low equilibrium water absorption ratio and, therefore, it is particularly suitable as a base film of a magnetic recording medium. This film is produced by accurately controlling the orientation conditions and other processing conditions.

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First Claim