| 摘要 |
PROBLEM TO BE SOLVED: To produce a film that has a high tensile modulus in the longitudinal direction and a low heat shrinkage in the same direction by constituting a main component of the film of homopolypropylene having a meso pentad percentage in a specified range. SOLUTION: The film is a reinforced, biaxially oriented polypropylene film that comprises as a main component homopolypropylene having a meso pentad of 98-99.5% and that has a refractive index in the longitudinal direction in a range of 1.512-1.530. The film has preferably a tensile modulus in the longitudinal direction of not less than 3 GPa, a heat shrinkage at 120 deg.C in the longitudinal direction of not more than 3% and a plane orientation coefficient of 0.0135-0.0155. A polypropylene resin having a predetermined meso pentad percentage is extruded at a temperature of 230-290 deg.C, cooled and hardened to produce a unstretched film. The unstretched film is heated to a temperature of 115-150 deg.C and stretched at a temperature of 145-163 deg.C simultaneously at a stretch ratio of 7-12 times in the longitudinal direction and at a stretch ratio of 3-6 times in the width direction. The stretched film is further stretched at a stretch ratio of 1.2-2.4 times in the longitudinal direction and then heat treated at a temperature of 150-165 deg.C to produce a reinforced, biaxially oriented polypropylene film.
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