POLYVINYL ALCOHOL POWDER OF EXCELLENT SOLUBILITY

摘要

PROBLEM TO BE SOLVED: To obtain a polyvinyl alcohol polymer which can be dissolved with a small change in torque without being brought into a state of unwetted agglomerates, leaves a small amount of insolubles, and has excellent water solubility by selecting a polyvinyl alcohol(PVA) powder containing a specified proportion of particles having a specified particle diameter. SOLUTION: The PVA powder contains at least 20 wt.% particles having a particle diameter of 500-1,000μm. The particle diameter is one represented by the value in the state in which the content of volatiles (including water) in the PVA is at most 10 wt.%. The PVA used is exemplified by a partial or full saponificate of polyvinyl acetate and a saponificate of a copolymer as well. It is desirably one having a degree of saponification of at least 90 mol% and an average degree of polymerization of 300-3,000. It is obtained by mechanically grinding coarse PVA particles and suitably blending classified fractions to obtain a portion having an adjusted particle diameter. The adjustment of the particle diameter desirably consists of classifying the mechanically ground particles and blending fractions in a suitable ratio.