GB1287261A - Improvements in tubular envelopes of extrudable synthetic plastics material - Google Patents

Abstract

1287261 Extruded tubular envelopes GENERAL INDUSTRIAL PLASTICS Ltd 17 Oct 1969 [30 July 1968] 36321/68 Heading B5B [Also in Division B8] A method of making a tubular envelope of extrudable synthetic plastics material comprises extruding the material in a plastic condition into the form of a tubular film, flattening part of the tube during the setting of the material so as to form a longitudinal crease in the wall of the tube inflating the flattened part of the tube and then flattening the inflated tube along an axial plane lying at an angle preferably less than 90 degrees, to the axial plane passing through said crease, so as to form a tubular envelope with a crease extending along the face thereof. In the preferred embodiment the whole of the tube is flattened to produce two creases. The process may be effected by the apparatus in Fig. 1, in which the tubular plastics film 11 is extruded from an extrusion die 10, flattened by pinch rolls 12 to form crease edges 20, the film is optionally cooled in a cooling bath 16 (for thermoplastic materials), then inflated by an air bubble trapped by the pinch rolls 17 and 18, the vertical planes of the axes transverse to the film of the pinch rolls 17 and 18 being at an angle, so that the former edges of the film become longitudinal creases in the final flatten film 21. The longitudinal creases are preferably not superimposed. Alternatively the pinch rolls 17 and 18 may be omitted and the film inflated by a trapped air bubble, passed back through the pinch rolls 12, the twist to form a crease in the film being imparted between the first and second pass through the nip rolls 12 for example by an operator at the start of a run. All pinch rolls may be water cooled. Air cooling may be substituted for the cooling bath 16. The film so produced which is preferably of a thermoplastic for example polyvinyl chloride or polyethylene may be cut into lengths and the envelopes so formed used in packaging, when the longitudinal creases facilitate opening of the envelopes, which when made from a thermoplastic, may after insertion of the merchandise be heat-sealed.