POROUS POLYPROPYLENE RESIN FILM, SEPARATOR FOR USE IN A BATTERY, AND BATTERY

As a porous film in which the air-permeability at the time of elongation of the porous film was adjusted, whereby, when used as a battery separator, the holes of a separator in an electrode/separator wound body have been controlled, a polypropylene series resin porous film is proposed, in which, for a porous film having a polypropylene series resin as the main component, regarding air-permeability (Pa) prior to elongation and air-permeability (Pa') at 5% elongation, (1) Pa'is 1,000 seconds/100 ml or less and (2) Pa'/Pa is 1.5 or less.