| 摘要 |
PURPOSE:To obtain a microporous film having suitable pore sizes and a sharp pore size distribution by extruding and cooling a specific polyolefin soln. to give a get-like compsn. and stretching, drying, and again stretching the compsn. CONSTITUTION:A soln. is obtd. by dissolving, in 50-90wt.% solvent, 10-50wt.% poly olefin which contains at least 1wt.% component with a mol.wt. of 7X10<5> or higher and has a ratio of wt. average mol.wt. to number average mol.wt. of 10-300. The soln. is heated to 140-250 deg.C, extruded through a die, and cooled to give a gel-like compsn. The compsn. is stretched 2-10 times at least monoaxially at a temp. between the crystal dispersion temp. and the temp. 10 deg.C higher than the m.p. of the polyolefin, heated to remove the residual solvent, and stretched again 1.1-5 times at least monoaxially at a temp. at least 10 deg.C lower than the m.p., giving a microporous polyolefin film having a void content of 35-95%, a mean size of interconnecting pore of 0.05-0.2mum, a breaking strength of 0.2kg/15mm-width or higher, and a pore size distribution (a ratio of max. pore size to mean interconnecting pore size) of 1.5 or lower. |
