| 摘要 |
PROBLEM TO BE SOLVED: To provide a polyolefin microporous film excellent in balance of porosity, air permeability, a piercing strength and heat shrinkage. SOLUTION: The method for producing the polyolefin microporous film includes a process to prepare a gel-like molded product by melting and kneading the polyolefin with a liquid solvent, extruding the molten and kneaded product from a die, simultaneously and biaxially drawing (primary drawing) in the machine and vertical directions, subsequently drawing (secondary drawing) at a higher temperature than that of the simultaneous biaxial drawing to increase anisotropy against the primary drawing. The redrawing is carried out to satisfy both relations: 0<λ<SB>1t</SB>/λ<SB>2m</SB>≤10, whereinλ<SB>1t</SB>denotes a draw ratio of the biaxial drawing in the vertical direction andλ<SB>2m</SB>denotes a draw ratio of the redrawing in the machine direction, and 0<λ<SB>1m</SB>/λ<SB>2t</SB>≤10, whereinλ<SB>1m</SB>denotes a draw ratio of the biaxial drawing in the machine direction andλ<SB>2t</SB>denotes a draw ratio of the redrawing in the vertical direction. COPYRIGHT: (C)2004,JPO |
