| 摘要 |
PROBLEM TO BE SOLVED: To uniformly introduce a sulfonic group by causing water to adhere to a sheet and subsequently contacting this sheet with sulfuric anhydride gas. SOLUTION: A sheet is imparted with 50-200 mass % of water and is brought into contact with sulfuric anhydride gas diluted with nitrogen gas or a rare gas such as, helium or the like to a concentration of 10-80 mass % and subsequently heated to 80-120 deg.C for not more than 120 min to effect sulfonation. Then, the sheet is washed with sulfuric acid of a low concentration to remove by-products and further washed with water to give a sheet having introduced thereinto a sulfonic group. As a resin to form the sheet is employed a polyolefin, a polyester, a polyamide, a fluororesin or the like. The sheet can be in the form of a film, a porous membrane, a woven fabric, a knit, a nonwoven fabric or the like. As a separator for a cell is employed a fiber sheet comprising a nonwoven fabric and a microporous film and excellent in maintenance of an electrolyte, and as the resin for forming the sheet is desirably employed a polyolefinic resin or the like excellent in resistance to alkalis and to acids.
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