| 摘要 |
PROBLEM TO BE SOLVED: To provide a porous film capable of being processed into a thin film, having a high strength and excellent SD characteristics, capable of being rapidly occluded at low temperature, and capable of maintaining the shape at high temperature by forming the porous film having one or more layers containing a mixture of at least three kinds of polyolefin resins having different melt indexes, respectively. SOLUTION: This porous film is obtained by dry-blending three kinds of HDPE having melt indexes(MI) of 0.03, 0.5 and 9.5, respectively, by use of a mixer so as to form a composition comprising 30 wt.% of the polymer having a MI of 0.03, 60 wt.% of the polymer having a MI of 0.5 and 10 wt.% of the polymer having a MI of 9.5, melt-extruding the blend by use of a monolayer screw extruder under a condition comprising a resin temperature of 250 deg.C to form a 37 μm thickness transparent film, thermally treating the film at a temperature of 130 deg.C for a time of 24 h in a drying oven, subjecting the film to a 130% stretching treatment at 120 deg.C and thermally setting the stretched film at 120 deg.C. The obtained white porous film has a thickness of 25 μm and a Gurley value of 550 sec/100 cc. |
