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AssigneeNew Japan Chemical Co., Ltd.
InventorsKiyoshi Sadamitsu, Naoki Ikeda, Manabu Hoki, Kenichiro Nagata, Koichi Ogino
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Disclosed is a successively biaxially stretched film obtained by successive biaxial stretching method comprising extruding a melt of a β-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 β-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 β-crystal nucleating agent at a temperature not lower than m.p. of the polypropylene-based resin and lower than dissolution temperature of the β-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.
A successively biaxially stretched, β-crystal nucleating agent-containing polypropylene porous film, comprising a polypropylene-based resin and a β-crystal nucleating agent, the film having a film thickness uniformity is 0.1 or less, and the film exhibiting the following pore structures (a) and (b) when observed in cross section in the longitudinal and transverse directions of the film under an electron microscope:
A battery separator comprising a successively biaxially stretched, β-crystal nucleating agent-containing polypropylene porous film,
Dependencies are inferred from the claim text.