GB1093217A - Process and apparatus for the preparation of thermoplastic film - Google Patents

Abstract

1,093,217. Films. DOW CHEMICAL CO. March 22, 1965 [April 8, 1964], No. 12080/65. Heading B5B. A roll of thermoplastic resinous film of substantially uniform diameter is made by inflating a flattened tubular film, heating the inflated film to a temperature sufficient to remove wrinkles, collapsing the film, and winding it into a roll while causing the film issuing from any given point of the film supply means to describe a generally helical pattern on the inflated portion of the tube. The helical traverse of the film may be provided by causing the supply means for the flattened film and the collapsing means to rotate, relative to each other, about an axis colinear with the axis of the inflated tube. Alternate right and left hand helical traverse may be provided. In one embodiment (Fig. 1), a deflated tubular film 13 from supply roll 11 is fed between guide-plates 30, 31, inflated by insertion of an air-hose between the film layers and then sealing the puncture, passed through ovens 35, 36, collapsed by converging rolls 47 and wound up at 58. The roll support assembly 20 is carried by platform 19, which is supported on bearings 22, and is rotatable by means of gear-box 25 and motor 26. In operation, the relative rotation between the nip rolls 14, 15 and the nip rolls 53, 54 is maintained at a rate sufficient to cause a lengthwise line drawn upon the flattened film prior to entering nip rolls 14, 15 to cyclically deviate through at least 360 degrees or integral multiples thereof at the collapsing rolls, thereby obtaining complete randomization of any irregularities in the film. Fig. 2 shows the randomizing action when film from a supply roll 60 is passed, after inflation through an annular oven 64 and is collapsed by wind-up rolls 65 which are rotating relative to the supply roll. In further embodiment, the film wind-up station may be made to rotate or oscillate while the film supply means and the oven are fixed relative to each other. The film supply means may be an extrusion die instead of a wound roll, in which case, to avoid incomplete randomization caused by twisting of the melt at the die, the extruded film bubble is first collapsed and then re-inflated. The process is applicable to tubular films of polystyrene, polyvinyl toluene, polyolefins, polymers and copolymers of vinyl chloride, vinyl acetate and vinylidene chloride, and copolymers of vinylidene chloride and acrylonitrile. Examples describe the processing of polypropylene films.