| abstract |
(57) [Problem] To provide a porous film having a film thickness and a porosity at a level equal to or higher than that of a conventional product, and also having excellent electrolyte retention ability. SOLUTION: In the composite porous film, a porous layer having a smaller pore diameter than the porous layer is laminated on both sides of a porous layer made of a polyolefin resin. The polyolefin-based resin includes polyethylene, polypropylene and the like. This composite porous film is made of nickel- It can be used as a separator for alkaline secondary batteries such as cadmium batteries, nickel-zinc batteries and nickel-hydrogen batteries. |