Patent ID: 8114478

Claim:
A method of preparing a dual-sided membrane sheet comprising the steps of: a) forming a microporous polymer sheet having a length, width and thickness and wherein the sheet comprises: two opposing outer surfaces extending along the length of the sheet and defining the thickness of the sheet, two opposing edges extending along the length of the sheet and defining the width of the sheet, an edge section extending inward from each edge along the length of the sheet wherein the edge sections border a bulk section located therebetween, and wherein the thickness of edge sections is at least 10% greater than the thickness of the bulk section, and a plurality of capillary channels extending in a direction along the length and through the bulk section of the sheet; and b) forming a semi-permeable discriminating layer upon at least a portion of the opposing outer surfaces of the sheet; and wherein the sheet is advanced along a production pathway during at least a portion of: step a), step b), or while transferring the sheet from step a) to step b) by engaging the sheet along one or more of the edge sections.