| 摘要 |
PURPOSE:To improve the state of the surface, and to obtain excellent dimensional stability by controlling the temperature of a heating roll while loading static charges, which use a central section as a starting point on viewing in the travelling direction of a film, being retarded successively and reaching both end sections, to the film. CONSTITUTION:When a polyester film is longitudinal relaxation-treated by passing the film through a heating roll and a cooling roll, the temperature T of the heating roll is controlled so as to satisfy Tg<=T<=Tg+90 deg. (where Tg represents the secondary transition temperature of polyester). The film 1 is made to travel, and passed through the heating roll 2. An electrostatic electrode 4 is connected to a high voltage generator 3, and static charges are loaded to the film 1. The film after passage through the heating roll is passed through the cooling roll so as to be relaxed by 0.050-3.0% in the longitudinal direction, and the speed of heat shrinkage in the longitudinal direction of the film in an atmosphere at 70 deg.C in brought to 0.02% or less per hr. |
