| 摘要 |
PROBLEM TO BE SOLVED: To obtain a porous body having improved strengths by using a synthetic resin prepared by introducing urethane bonds into part of a polyvinyl acetal polymer. SOLUTION: A polyvinyl acetal resin polymer containing polyvinyl acetal, polyvinyl alcohol, and polyvinyl acetate and represented by the formula is dissolved in e.g. ethyl alcohol to form a solution of a concentration of 3-30 wt.%, and e.g. n-hexane in an amount corresponding to 10-40 wt.% of the polymer is added to the solution to solubilize the polyvinyl acetal resin polymer. Next, 0.1-1 wt.%, based on the total weight, isocyanate compound such as diphenylmethane diisocyanate is added to the mixture under agitation, and the resultant mixture is applied to the surface of a thermoplastic resin film and dried at 50-80 deg.C to obtain a porous film having a thickness of 10-50μm. The opening rate of the porous body is 10-85 %, and the thickness of the resin fiber is 2-10μm. In the formula, R is H or a 1-4C alkyl; X (wt.%) is 70-85; Y (wt.%) is 10-25; and Z (wt.%) is 0.5-10.
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