GB1030187A - Layflat tubular film manufacture - Google Patents

Abstract

1,030,187. Plastics layflat tubular film. CANADIAN INDUSTRIES Ltd. March 3, 1965 [March 5, 1964], No. 9093/65. Heading B5B. In producing plastics layflat tubular film of predetermined width by continuously extruding a melt of the plastics material through an annular die to form seamless tubing, withdrawing and flattening the set tubing at a predetermined distance from the point of extrusion, and maintaining a bubble of a gaseous medium in the section of the tubing extending between the points of extrusion and flattening such that the tubing is inflated while it is in the formative plastic state, the width of the flattened tubing is continuously controlled by passing the flattened tubing past a detecting means comprising a metered gas tube in contact with, and extending transversely and beyond each side of, the tubing, the gas tube being provided on the surface contacting the tubing with gas escaping means located on each side of the tubing and extending at least partially across the tubing at its predetermined width on each side. Any change in the width of the tubing while in contact with the gas escaping means results in a change of the effective area of the gas escaping means and hence in a variation of the gas pressure inside the metered gas tube, this variation being used to control compensating readjustment of the shape of the bubble in the tubing. The tubing may be cooled from its formative plastic state to the set condition by directing a controlled volume of a stream of a gaseous cooling medium to impinge externally and circumferentially on the tubing and/or by introducing a flowing gaseous medium into the tubing to both inflate and cool the tubing; the shape of the bubble may be readjusted by varying either the rate of supply of the external cooling gaseous medium or the volume of the gaseous medium introduced into the tubing, the latter alternative being preferred. The metered gas tube detecting means is preferably located close to the flattening point of the inflated tubing, i.e. as close as possible to the flattening or squeeze rolls. The gas tube may be extendable to allow production of film of any desired predetermined width. The gas escaping means may be, for example, slits or series of holes, from which issues any suitable inert gas, for example air. The detecting means may be coupled to a signalling device to indicate that manual compensating readjustment is necessary; however, such readjustment is preferably made by coupling the detecting means to automatic adjusting means, for example an electropneumatic relay system, an apparatus for which is fully described and illustrated, and its use exemplified in the production of a layflat tubular film of polythene.