摘要 |
PROBLEM TO BE SOLVED: To provide a method for manufacturing a polyvinyl acetal resin in the shape of minute powdery particles that has excellent transparency and solvent solubility, and that has little impurities derived from the acid catalyst and its neutralizer, without requiring cooling of the reaction system to <=0 deg.C in the condensation reaction of a polyvinyl alcohol with a low degree of polymerization and an aldehyde. SOLUTION: A polyvinyl alcohol and an aldehyde is subjected to condensation reaction in a water phase in the presence of an acid catalyst to form a polyvinyl acetal resin. First, a part of the total amount of the aldehyde to be added is added to 70-85 wt.% of the total polyvinyl alcohol to be added so as to carry out condensation reaction at <=20 deg.C. Then, the temperature of the reaction system is lowered. While deposition of polyvinyl acetal as a reaction product has not occurred the residual 30-15 wt.% of the polyvinyl alcohol was added in two or more portions, and then the residual amount of the aldehyde is added to the reaction system to continue the reaction.
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