| 摘要 |
PROBLEM TO BE SOLVED: To provide a stretched laminated porous polyolefin film having uniform micropores, proper in pore closing temp. by heat, high in closed pore keeping upper limit temp., wide in a closed pore keeping temp. region, excellent in air permeability and having a proper heat shrinkage factor. SOLUTION: A high m.p. polyolefin film and a low m.p. polyolefin film different in m.p. by 20 deg.C or higher are prepared and the high m.p. polyolefin film is heat-treated at temp. lower than its m.p. by 35-55 deg.C while the low m.p. polyolefin film is heat-treated at a temp. lower than its m.p. by 30-55 deg.C and both polyolefin films are bonded within a temp. range from the m.p. of the low m.p. polyolefin film to temp. higher than the m.p. by 10 deg.C under pressure to obtain a laminated film consisting of three or more layers of the high and low m.p. polyolefin films. This laminated film is stretched by 5-200% within a temp. range from -20 deg.C to 50 deg.C and subsequently stretched by 100-400% at 70-130 deg.C to be perforated and subsequently thermally fixed. |
