METHOD FOR MANUFACTURING A POROUS MEMBRANE

A porous membrane that simultaneously achieves excellent electric performance and excellent mechanical strength, and has skin layers on the opposite sides thereof, the skin layers having same pore characteristics, and a method for manufacturing the same are provided. A porous membrane contains a polyethylene resin having a weight-average molecular weight of no less than 300,000 and less than 500,000, micro pores are oriented in a multilayered structure, pores of sizes that are relatively larger than those of pores in each of skin layers on the opposite sides are distributed in a core layer and skin layers on the opposite sides have same pore characteristics. A porous membrane manufacturing method includes: a process of obtaining a mixture of a liquid-type paraffin wax and a solid-type paraffin wax; a process of adding the wax mixture into a polyethylene resin; and a process of immersing the resulting resin mixture into an organic solvent to extract the wax mixture.