. . "In cases where organic solvents are used and are required to be removed after the completion of the reaction, for example, spray dryer, drum dryer, thin-layer evaorator, etc. can be employed for removal of them or the solvents such as n-hexane, which do not dissolve the blocked organic polyisocyanates, can be added to allow the blocked organic polyisocyanates to precipitate, followed by filtering" . .