Microporous Thermoplastic Sheets

摘要

Thermoplastic polymeric sheets are rendered microporous and remain substantially flat by contacting the sheet with a first fluid composition that contains or more solvents for the polymeric sheet to render the sheet microporous and then contacting the microporous sheet with a second fluid composition that is substantially free of solvents for the polymer and that contains a non-solvent that is miscible with the one or more solvents of the first composition. Contacting the microporous sheet with the second fluid composition preferably occurs prior to substantial evaporation of the first fluid compositions, or solvents thereof, from the microporous sheet.