| 摘要 |
PURPOSE:To increase the hydrophilicity of a microporous sheet without any additive, by saponifying the microporous sheet based on cellulose acetate to a specified degree of acetylation. CONSTITUTION:A cellulose acetate solution is formed by dissolving a cellulose diacetate/cellulose triacetate mixture of a degree of acetylation of about 55-59% in a solvent mixture comprising a good solvent therefor, a poor solvent therefor and/or a nonsolvent therefor. This solution is cast on a support and dried to form a film of cellulose acetate. This film is peeled from the support to obtain a microporous sheet. This sheet is saponified with a dilute solution of an alkali to a degree of acetylation >=40%. It is required that when crystallization treatment is performed after saponification, the average degree of saponification after saponification is at least about 48%. An alkali solution (e.g., a solution of NaOH or KOH) of a concentration of 0.5-3wt% is desirable as the saponifying solution.
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