| 摘要 |
PURPOSE:To obtain a film which is used as the magnetic tape base and the like and has a uniform thickness by a method wherein thermoplastic resin is extruded in the form of a film from a die slit, cooled and set on a rotary cooling drum controlled at a constant speed and film tension is kept constant when it is taken up from the drum. CONSTITUTION:Thermoplastic resin such as polyethylene, polypropylene, etc. is heated, fused and extruded in the form of a film from a die slit, cooled and set on a rotary cooling drum controlled at a constant speed in which the instantaneous rotation fluctuation ratio given by the no load formula is within the accuracy of + or -1%. In addition, in order to keep constant the tension of the film taken up from the cooling drum, the film is extended through two or more rolls and at least one dancer roll. Accordingly, the film with uniform thickness is obtained by the effect of film thickness fluctuation control added to that of constant speed control of the cooling drum. |
