Asahi Kasei Kogyo Kabushiki Kaisha

Satoshi Iijima

Kenji Takasa

This 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.

Biaxially oriented polyoxymethylene film

There is disclosed a biaxially oriented film formed of film forming composition comprising a polyoxymethylene polymer in which the major constituent of the main chains of said polymer each of consists substantially of repeating units of oxymethylene group --CH.sub.2 --O--, said film being characterized in that, when said film is remelted at a temperature above the melting point of said film and the resulting melt is recrystallized isothermally at 140.degree. C. into a solid in film form, the number of polyoxymethylene spherulites in the crystal structure at the surface of the resulting film would be at least 50 per 0.1 mm.sup.2 area of the resulting film surface, as measured with a polarizing microscope through cross-polarizers, and a process for manufacturing the same.

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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Kamakura, Japan

Satoshi Iijima