Polypropylene base porous film and production process for the same

Abstract

Provided is a porous film which is excellent in a tear strength and has a low heat shrinkage. Such film is produced by subjecting to heat treatment on specific conditions, a porous film comprising a resin composition comprising: (a) a polypropylene base resin blend comprising 100 parts by weight of an ethylene-propylene block copolymer having a maximum peak temperature (Tm) of 140° C.≦Tm≦165° C. which is given by differential scanning calorimetry (DSC), 3 to 40 parts by weight of low density polyethylene and 3 to 40 parts by weight of an ethylene-vinyl acetate copolymer, (b) calcium carbonate, (c) titanium oxide coated on a surface thereof with silica and/or alumina, (d) a hindered amine light stabilizer having a molecular weight of 1500 to 4500, (e) an ethyl ester phosphorous acid or biphenylene phosphonite antioxidant, and (f) a hindered phenol antioxidant, wherein the above resin composition comprises 100 to 200 parts by weight of (b), 0.5 to 20 parts by weight of (c), 0.2 to 10 parts by weight of (d), 0.03 to 3 parts by weight of (e) and 0.05 to 3 parts by weight of (f) each per 100 parts by weight of (a). A laminate sheet comprising this polypropylene base porous film and a polyolefin base nonwoven fabric is excellent in a moisture permeability, a weatherability and a heat resistance.

Dependencies are inferred from the claim text.