Method of manufacturing polyvinyl alcohol films oriented in two orthogonal directions

摘要

A PVA film successively oriented in two orthogonal directions is prepared by firstly elongating the film in the longitudinal direction by more than 200% while maintaining the water content (Z x 100)% at a value of from 10 to 35% and the temperature in a range of from (1.50/Z +20) DEG C to 75 DEG C. The film is then preheated while maintaining its water content at least 7%, and then elongated laterally by more than 200% at a temperature of from 45 DEG to 110 DEG C. Then the film is heat treated at a temperature of 110 DEG to 210 DEG C while permitting the film to shrink by less than 15% in the lateral direction. Finally, the film is cooled to room temperature under tension.