PREPARATION OF THERMOPLASTIC FILM

摘要

PURPOSE:To uniformize physical properties in a lateral direction and to also enhance a thermal dimensional stability by setting a film to be heat-treated having specific characteristic in its end part and/or the end part thereof to a specific heat treatment condition. CONSTITUTION:A film to be heat-treated is constituted so as to satisfy TC-TE >=30( deg.C) [wherein TE( deg.C) is the max. temp. of the heat-shrinkage stress of the end part of the film in the longitudinal direction and TC( deg.C) is the max. temp. of the heat-shrinkage stress of the central part of the film in the longitudinal direction] and heat-treated. A film constituted so as to satisfy FE/FC >=2 [wherein FE(kg/mm<2>) is the stretching tension of a polymer (E) constituting the end part of the film in the longitudinal direction and FE(kg/mm<2>) is the stretching tension of a polymer (C) constituting the central part of the film] is heat treated. The polymers (C), (E) are separately supplied to two extruders to be melted therein and extruded from a cap 3 through respective pipings 1, 2 and cooled and solidified on a casting drum 4 to obtain a composition film 7.