Patent ID: 7235203
Filing Date: 2007-06-26
Classification: B29C,B29K,C08J,H01M,Y02E,Y10T

Abstract:
1. A process for producing 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 thickness uniformity of 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 and 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 1/2 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 a cross sectional image 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 1/2 to 1/20, said process comprising a sequential biaxial stretching step which comprises extruding a melt of a polypropylene-based resin composition containing a β-crystal nucleating agent from a T-die, cooling the extrudate on a chill roll, and stretching the thus obtained β-crystal nucleating agent-containing polypropylene unstretched web sheet first longitudinally and then transversely, characterized in that the degree of orientation of β-crystals calculated from a pole figure of the crystal lattice (300) plane of the β-crystals determined by X-ray diffraction of the sheet obtained after longitudinal stretching is adjusted to less than 0.30 by carrying out the following method (I) and/or method (II): method (I): melting a polypropylene-based resin composition consisting essentially of (i) the polypropylene-based resin, (ii) needle crystals of at least one amide compound as the β-crystal nucleating agent, and if desired (iii) at least one polyolefin modifier at a temperature (T (1) at least one member selected from the group consisting of N,N′-diphenylhexanediamide, N,N′-dicyclohexylterephthalamide and N,N′-dicyclohexyl-2,6-naphthalenedicarboxamide, (2) at least one member selected from the group consisting of N,N′-dicyclohexanecarbonyl-p-phenylenediamine, N,N′-dibenzoyl-1,5-diaminonaphthalene, N,N′-dibenzoyl-1,4-diaminocyclohexane and N,N′-dicyclohexanecarbonyl-1,4-diaminocyclohexane, (3) at least one member selected from the group consisting of N-cyclohexyl-4-(N-cyclohexanecarbonylamino)benzamide and N-phenyl-5-(N-benzoylamino)pentaneamide, or (4) a mixture of two or more members of the above amide compounds of (1) to (3)), method (II): adjusting the neck-in ratio during longitudinal stretching to at least 25% and not more than 55%.