Biaxially oriented poly-p-phenylene sulfide films

A heat set biaxially oriented poly-p-phenylene sulfide film comprising predominantly a plurality of recurring units of the formula ##STR12## said film having a melt viscosity of about 100 to 600,000 poise at 300.degree. C. and at a shear rate of 200 sec.sup.-1, produced by biaxially stretching to an extent of an area ratio of about 3 to 25, followed by heat-setting at a temperature between about 180.degree. C. and the melting point.

A heat set biaxially oriented poly-p-phenylene sulfide film comprising predominantly a plurality of recurring units of the formula ##STR13## produced by a process which comprises (a) casting amorphous poly-p-phenylene sulfide film, (b) stretching said amorphous film within the range of about 2.0 to 5.0 times at a temperature between about 80.degree.-120.degree. C., so that the film birefringence in the stretching direction is between 0.05 to 0.30, thereafter (c) stretching said film in a direction transverse to that of step (b) within a range of about 1.5 to 5.0 times at a temperature between about 80.degree.-150.degree. C., thereby producing a biaxially stretched film, and (d) heat-setting said biaxially oriented film at a temperature between about 180.degree. C. and the melting point.

A heat set biaxially oriented poly-p-phenylene sulfide film wherein the degree of planar orientation of the film measured by the X-ray pole figure method is more than about 0.50.

A heat set biaxially oriented film comprising poly-p-phenylene sulfide and additive and/or filler wherein said poly-p-phenylene sulfide is composed of predominantly a plurality of recurring units of the formula ##STR14## said film having a specific gravity greater than about 1.330 and lower than about 1.400, a melting viscosity of about 100 to 600,000 poise at 300.degree. C. and at a shear rate of 200.sup.-1.

Electric insulation material comprising a heat set biaxially oriented film consisting essentially of a high molecular weight poly-p-phenylene sulfide comprising predominantly a plurality of recurring units of the formula ##STR15## said film having a dielectric strength of greater than about 100 kV/mm and a tensile strength of greater than about 5 kg/mm.sup.2 at least in one direction.

Magnetic recording medium comprising a heat set biaxially oriented film consisting essentially of a high molecular weight poly-p-phenylene sulfide comprising predominantly a plurality of recurring units of the formula ##STR16## said film having a tensile modulus of greater than about 250 kg/mm.sup.2 and a thermal linear expansion coefficient of about 2.0.times.10.sup.-4 to 2.0.times.10.sup.-4 mm/mm/.degree.C. within a temperature range between 20.degree.-150.degree. C. at least in one direction.

A capacitor comprising a heat set biaxially oriented film consisting essentially of a high molecular weight poly-p-phenylene sulfide comprising predominatly a plurality of recurring units of the formula ##STR17## said film having an electrical dissipation factor of less than about 1.0% for 10.sup.3 Hz from room temperature up to 150.degree. C.

A printed circuit board comprising a heat set biaxially oriented film consisting essentially of a high molecular weight poly-p-phenylene sulfide comprising predominantly a plurality of recurring units of the formula ##STR18## said film having a thermal dimensional shrinkage of less than about 5% at 250.degree. C. after 30 seconds exposure, and a folding endurance under a weight of 2.5 kg/mm.sup.2 in excess of about 500 times at least in one direction.