Polyolefin-based porous film and method for producing the same
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United States of America Patent
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Jun 5, 2018
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app pub date -
Oct 7, 2015
filing date -
Dec 28, 2010
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Abstract
A method for producing a polyolefin-based porous film includes an (A) step: a raw fabric forming step for forming a non-porous raw fabric from a polyolefin-based resin composition, a (B) step: an MD cold stretching step for cold stretching the non-porous raw fabric obtained in the (A) step at a temperature of −20° C. to (Tm−30)° C. (Tm is a melting point (° C.) of the non-porous raw fabric) in an extruding direction (MD) of the raw fabric to make the raw fabric porous; a (D) step: a TD cold stretching step for cold stretching a film processed in the (B) step in a direction (TD) perpendicular to the MD, and an (H) step: a thermal fixing step, in the above order. A thermal fixing temperature T2 (° C.) in the (H) step satisfies expressions (1) and (2) below; T2>T1 (1), (Tm−3)≥T2≥(Tm−40) (2) (in the expressions, T1 represents a stretching temperature (° C.) in the (D) step, and Tm represents the melting point (° C.) of the non-porous raw fabric). A polyolefin-based porous film made of a polyolefin-based resin composition has a pore surface area of 35.0 to 42.0 m2/g and birefringence of 2.0×10−2 to 4.0×10−2.
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