Polypropylene base porous film and production process for the same

Abstract

Provided is a porous film which is excellent in a water vapor transmission rate, a tear strength and a weatherability. This porous film can be produced by melt-extruding, for example, by a T-die method, a composition comprising 100 parts by weight of a resin blend (1) comprising 100 parts by weight of {circle around (1)} an ethylene-propylene copolymer, 3 to 40 parts by weight of {circle around (2)} a low density polyethylene and 3 to 40 parts by weight of {circle around (3)} an ethylene-vinyl acetate copolymer and 100 to 200 parts by weight of calcium carbonate (2), or a composition comprising 100 parts by weight of the above resin blend (1), 100 to 200 parts by weight of calcium carbonate (2), 0.5 to 20 parts by weight of titanium dioxide (3) coated on a surface thereof with silica and/or alumina, 0.2 to 10 parts by weight of a hindered amine light stabilizer (4) having a molecular weight of 1500 to 4500 and 0.03 to 3 parts by weight of an ethyl ester phosphorus acid or biphenylene phosphonites antioxidant (5), receiving the extruded matter at a draft ratio of 2 to 30 and a non-stretched film-forming speed of 20 m/minute or more, cooling it by an air chamber method or an air knife method and then stretching it in a monoaxial or biaxial direction by at least 1.3 time in terms of an area magnification.

Dependencies are inferred from the claim text.