| 摘要 |
PROBLEM TO BE SOLVED: To obtain a porous film having a high porosity, a small maximum pore diameter, and a narrow pore diameter distribution by dissolving under heating an ultrahigh-molecular-weight polyolefin resin in a mixed solvent comprising a good solvent and a poor solvent, kneading the solution at a specified temperature, cooling the solution to the solidifying point or below to form a gel-like sheet, rolling the sheet at a specified temperature, biaxially orienting the rolled sheet, and desolventing the oriented sheet. SOLUTION: Five to fifty wt.% ultrahigh-molecular-weight polyolefin resin having a weight-average molecular weight of 5×105 to 20×106 is dissolved under heating in a mixed solvent comprising 55-95 wt.% good solvent such as decane and 5-45 wt.% poor solvent such as tetraethylene glycol dimethyl ether and kneaded at 115-185 deg.C. Next, the mixture is molded into a gel-like sheet by cooling to the solidification temperature of the solvent. The sheet is crystallized, and then biaxially oriented at an areal draw ratio of 4-400 at a temperature in the range of (M+5) to (M-30) deg.C, and the oriented film is desolvented to obtain a film having a porosity of 50-80%, a maximum pore diameter of 0.030-0.045μm, a pore diameter distribution of 1.5-2.5 and a thickness of 1-60μm. |
