New Japan Chemical Co., Ltd.

Koichi Ogino

Kiyoshi Sadamitsu

Naoki Ikeda

Kenichiro Nagata

Manabu Hoki

Disclosed is a successively biaxially stretched film obtained by successive biaxial stretching method comprising extruding a melt of a &#x3b2;-crystal nucleating agent-containing polypropylene-based resin composition from a T-die, cooling the extruded resin on a chill roll, and stretching the resulting web sheet longitudinally and then transversely, wherein the longitudinally stretched sheet is made to have a degree of &#x3b2;-crystal orientation of less than 0.3 by the following method (I) and/or (II), optionally subjected to annealing treatment, and transversely stretched: method (I): melting the polypropylene-based resin composition containing needle crystals of a specific &#x3b2;-crystal nucleating agent at a temperature not lower than m.p. of the polypropylene-based resin and lower than dissolution temperature of the &#x3b2;-crystal nucleating agent in the polypropylene-based resin melt, and extruding the melt from the T-die at the same temperature, method (II): adjusting neck-in ratio during longitudinal stretching to 25 to 55%. The porous polypropylene film has good breakage resistance during manufacture, excellent thickness uniformity, high porosity and air-permeability, and is useful for battery separators.

Successively biaxial-oriented porous polypropylene film and process for production thereof

Disclosed is a successively biaxially stretched film obtained by successive biaxial stretching method comprising extruding a melt of a &#x3b2;-crystal nucleating agent-containing polypropylene-based resin composition from a T-die, cooling the extruded resin on a chill roll, and stretching the resulting web sheet longitudinally and then transversely, wherein the longitudinally stretched sheet is made to have a degree of &#x3b2;-crystal orientation of less than 0.3 by the following method (I) and/or (II), optionally subjected to annealing treatment, and transversely stretched: The porous polypropylene film has good breakage resistance during manufacture, excellent thickness uniformity, high porosity and air-permeability, and is useful for battery separators.

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Takatsuki, Japan

Koichi Ogino