New Japan Chemical Co., Ltd.

Kenichiro Nagata

Kiyoshi Sadamitsu

Naoki Ikeda

Manabu Hoki

Koichi Ogino

Toshiaki Kobayashi

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.

Disclosed is a porous film made of a resin composition containing (I) (i) a propylene-ethylene copolymer or (ii) a polypropylene-based resin mixture containing a propylene-ethylene copolymer, each having an ethylene content of 3.0 to 7.0 wt. % and an MFR measured at 230&#xb0; C. of 2.0 to 4.0 g/10 min and (II) a &#x3b2;-crystal nucleating agent; the film having a porosity of 20 to 80%, a Gurley air permeability of 5,000 sec/100 cc or lower as measured according to JIS P-8117, a water vapor permeability of 2,000 g/m&#xb7;24 h or higher as measured according to JIS Z-0208 and a water pressure resistance of 75 kPa or higher as measured according to JIS L-1092 using an aqueous surfactant solution; a process for producing the same; and an absorbent article employing the porous film as a backsheet.

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Kyoto, Japan

Kenichiro Nagata