GB1370355A - Plastic materials - Google Patents

Abstract

1370355 Extruding laminar plastics LEESONA CORP 8 Sept 1971 [9 Sept 1970] 41948/71 Heading B5A At least two different thermoplastics from different heated screw extrusion sources are combined in layers I, B, Fig. 5, parallel to the sides of the rectangular, e.g. square passage, of a die adapter, from which the layers are delivered to the outlet slot of a flat film die to be extruded as a laminate in which each layer, Fig. 6, is of substantially uniform thickness across the full width of the extrusion, compared to the variation experienced at the edges, Fig. 8 (not shown), when the layers are combined in a circular passage. The extruded film is drawn from the die by a vertical three roll stack. The layers of the extrusion may comprise low or medium and high density polyethylene, e.g. for shrink film; a blend of low density polyethylene and ethylene vinyl acetate, and medium density polyethylene; high density polyethylene, and ethylene vinyl acetate; medium density polyethylene, polypropylene, and high density polyethylene; low density polyethylene, and polyvinyl chloride; an ionomeric polymer, and nylon. The film may comprise three layers either each of a different thermoplastics, or the outer layers being of the same thermoplastics. In the Fig. 4 embodiment, different thermoplastics respectively supplied to the inlets 46, 54 of the adapter are delivered to the rectangular outlet passage 48 thereof on either side of a plate 62 extending across and parallel to the passage walls. In the Fig. 9 embodiment, a pair of the plates 124, 126 extend across the rectangular passage 128, with one thermoplastics being delivered between the plates, and two further different thermoplastics being delivered each from the exterior of-one of the plates. In the Figs. 11 and 12 embodiment (not shown), a pair of the plates (150, 152) is also provided, with one thermoplastics being delivered from between the plates and another thermoplastics being delivered from the exterior of both plates. The relative thickness of each layer of the extruded laminate may be varied by adjustment of the plate, by the speed of the extruders supplying the thermoplastics, or by valving means.