PROCESS FOR PREPARING A MICROPOROUS FILM

摘要

1452977 Stretching semi-permeable films CELANESE CORP 29 May 1974 [30 May 1973] 23744/74 Heading B5B Open celled microporous polymer films are made by cold stretching a non-porous crystalline film at a temperature between - 20‹ and 20‹ C. below the crystalline melting point and sequentially hot stretching the film in a plurality of discrete steps at a temperature between 20‹ below and 5‹ C. below the crystalline melting point. The total stretch ratio is preferably between 10 and 300% and the hot stretch step comprises 2-30 discrete steps. Specified polymers are polyolefins, polyacetal, polyamide, polyester, polyalkylenic sulphide or polyarylene oxide and the stretching is preferably carried out first at 25-120‹ C. (cold stretching) and then at 120-150‹ C. (hot stretching).