GB1106254A - Improvements in and relating to the production of nets from thermoplastic sheets or films - Google Patents

Abstract

A method of forming a non-woven openwork net from a thermoplastic material comprises extruding the thermoplastic material to produce a flat film having integral loops at its longitudinal edges, embossing the flat film with a desired pattern of embossments, engaging the embossed, flat film adjacent the integral loops in two divergent guides, each guide comprising two members spaced apart by a distance slightly greater than the thickness of the embossed film, drawing the film along so that it is stressed longitudinally by draw rollers and so that the integral loops, cooperating with the divergent guides, cause simultaneous transverse stressing of the film and thus net formation, the loops being maintained in an expanded state during the transverse stressing. Thermoplastic materials specified include polymers of olefins and copolymers thereof, ethylene and propylene polymers being preferred, especially high density polyethylene, which may be stressed at temperatures from room temperature to 100 DEG C. The apparatus of Application No. 22812/64 may be utilised, and the loops may be held in their expanded state by means selected from the group consisting of a cord, roll, hollow tube, liquid, grease and compressed gas maintained within the loops (so as to form edge beads) during the transverse of the film. Non-woven nets may be made from films so produced. Solid fillers, as in application No. 22812/64 may be utilised to fill the edge beads, e.g. polytetrafluoroethylene cords, and if a cutting operation is not to be performed these solid or "free-floating" fillers are introduced into the integral loops at the beginning of the stretching operation. They are introduced into the first part of the film as it is extruded and brought to the divergent guides upon which the transverse stretching is carried out. Alternatively, mandrils anchored at the die, around which the molten material is extruded to form the loops may be extended into said loops to constitute the fillers for the transverse stretching zone. Alternatively the mandrils may have extensions of the desired length attached to them. In either case, means may be provided for supplying air at low pressure into the interior of the loops, just after the loops have been formed, so as to hold them open while they are setting after extrusion. When the net has been formed the loops may be cut from the longitudinal edges before the net is collected on a roller.