Patent ID: 7682689
Filing Date: 2010-03-23
Classification: B29C,B29K,C08J,H01M,Y02E,Y10T

Abstract:
1. A successively biaxially stretched, β-crystal nucleating agent-containing polypropylene porous film, comprising a polypropylene-based resin and a β-crystal nucleating agent, the film having a film thickness uniformity is 0.1 or less, and the film exhibiting the following pore structures (a) and (b) when observed in cross section in the longitudinal and transverse directions of the film under an electron microscope: (a) in the cross section in the transverse direction: more lamella cross sections are present than in the image of the cross section in the longitudinal direction; there are numerous pores between these lamella cross sections; the maximum pore size in the thickness direction of the pores is 0.1 to 5 μm; the maximum pore size in the transverse direction is 1 to 50 μm; and the ratio of the maximum pore size in the thickness direction/the maximum pore size in the transverse direction is from ½ to 1/20; (b) in the cross section in the longitudinal direction: there are no lamella cross sections or fewer lamella cross sections than in the image of the cross section in the transverse direction; there are numerous pores; the maximum pore size in the thickness direction of the pores is 0.1 to 5 μm; the maximum pore size in the longitudinal direction is 1 to 50 μm; and the ratio of the maximum pore size in the thickness direction/the maximum pore size in the longitudinal direction is from ½ to 1/20; wherein the longitudinally stretched film is made to have a degree of β-crystal orientation of less than 0.3.