Patent ID: 7354984

Claim:
A method for drying a nonionic alkylene oxide polymer water-soluble resin, which comprises putting a nonionic alkylene oxide polymer water-soluble resin into a container, degassing the container to a vacuum degree of at most 150 mmHg inside the container, and, with the vacuum degree in the container kept as such, introducing a dry gas having a dew point not higher than the dew point DP calculated according to the following formula (1), into the container at an introduction rate not lower than the introduction rate V calculated according to the following formula (2): DP (Â° C.)=âˆ’21.6 log 10 Vacâ€ƒâ€ƒ(1), V (L/min)=0.5Ã—[Vac/(273 +T )]Ã— V 0 (2), wherein Vac, T and V 0 have the following meanings: Vac indicates the vacuum degree (mm Hg), T indicates the temperature inside the container (Â° C.), V 0 indicates the volume of the container (L), wherein the alkylene oxide polymer water-soluble resin to be dried is powder or pellets of the resin and wherein the resin contains at least 50% by weight of alkylene oxide structure units, the alkylene oxide structure units contain at least 60% by weight of ethylene oxide structure units, and the resin has a melting point of not higher than 90Â° C., a glass transition point of from âˆ’100 to âˆ’30Â° C., a crystallization temperature of not higher than 50Â° C. and a weight-average molecular weight of from 20,000 to 500,000.