Cast film cooling method

Abstract

An improved air cooling method for the production of cast film is shown. The device is intended to increase production rates for film without reducing the level of film gauge control. The devices utilizes a soft box for the bulk of the cooling and a directional source of pressurized air to deflect exhaust air from the soft box from striking the web curtain between the die and chill roll.

We claim:  
     
         1 . A method for producing thermoplastic film by the technique in which a melt curtain is extruded from a slot die onto a chilled casting roll, the improvement comprising discharging a diffuse stream of cooling air onto a substantial portion of the surface of a thermoplastic web on a cooled casting roll and deflecting said diffuse stream of cooling air by discharging a linear source of pressurized towards said diffuse stream, whereby said linear source of pressurized air discharge diverts said diffuse air discharge from said thermoplastic web after said web is discharged from said slot die but prior to the time at which said web strikes said chilled casting roll.  
     
     
         2 . A cooling device according to  claim 1  wherein said air discharged from said linear source is directed towards the web at an angle of approximately 30 degrees from the tangent to the cooling roll at the point at which said air discharged from said linear source strikes said cooling roll.  
     
     
         3 . An improved cooling device according to  claim 2  wherein said diffuse stream of cooling air is cooled to a temperature below ambient temperature.