| abstract |
The purpose of the present invention is to provide a porous film which not only exhibits excellent mechanical strength and thermal properties, but is also unlikely to wrinkle as a result of changes over time, despite being thin, and is appropriate for use as a battery separator which contributes to production-property improvements. A porous film having a polyethylene-based resin as the principal component thereof, the porous film being characterized in that the thickness thereof is in the range of 1-10μm, the shrinkage thereof in the widthwise direction at 40°C over 24 hours is 0-0.8%, the piercing strength thereof is 100-500gf, the elasticity thereof in the widthwise direction is in the range of 700-2000 MPa, the elasticity thereof in the lengthwise direction is in the range of 500-1800 MPa, and the lengthwise-direction-elasticity/widthwise-direction-elasticity ratio is 0.3-1.0. |