Patent GB-1333833-A (GB)
Title: Method of and an apparatus for extruding a foamed sheet of  thermoplastic resin
IPC: B29C44/00
Filed: 1971-04-19
Abstract: 1333833 Foamed thermoplastic resin sheets ASAHI-DOW Ltd 19 April 1971 [3 April 1970 10 April 1970 1 Sept 1970] 25734/71 Heading C3C [Also in Division B5] The widthwise expansion and consequent longitudinal corrugation of a thick extruded flat thermoplastic sheet issuing from a die and including a foamable thermoplastic resin, is restricted by cooling of the die surfaces defining the exterior surfaces of the sheet, and by directing cooling air against the exterior surfaces of the extruded sheet and towards the die to ensure  solidification of the exterior sheet surfaces issuing therefrom, the sheet being drawn away from the die by thickness determining means when continued cooling of the sheet is effected. The die extrusion passage also tapers towards the outlet which has no land portion defined between parallel surfaces, or a land portion of a length not greater than seven times the depth thereof. The surfaces of the sheet, if of the foamable resin, may be drawn from the die by the thickness determining means, e.g. a cooled plurality of opposed roll pairs, or endless belts, or rolls and moving moulds to produce a fibrillated surface resembling wood grain, for which extrusion temperatures are specified, and the effect may be enhanced by sanding or painting. In the described embodiment, a foamable resin is extruded from a flat sheet orifice 16 to which it is supplied, via a breaker plate 5, a manifold passage including a choke 10 which is adjustable transversely by alternate "push" and "pull" bolts 12, 13 and the tapering die passage 15 cooled by fluid passages 17, 171. The air cooling the sheet surfaces is directed towards the orifice 16 from openings 20, 20<SP>1</SP> of distributing pipes 19, 19<SP>1</SP> extending across the die width. The sheet is drawn from the die by pre-pressing rolls 22, 22<SP>1</SP>, followed by further adjustably spaced apart pressing rolls 23, 23<SP>1</SP>, when further cooling is effected by natural air cooling, or by the rolls through which either cooling medium, e.g. water, is fed, or the lower rolls whereof rotate through a water bath. Further cooling is effected by natural air cooling on roller conveyers 25, prior to cutting by means 26, 26<SP>1</SP>. Examples are specified in which: (1) and (2), polystyrene containing n-pentane and talc is extruded and passes through sequential roll pairs to produce a 20 mm. sheet of 0À4 gr./c.c. mean density; (3), acrylonitrile, butadiene, styrene copolymer,containing azodicarbonamide and talc was extruded by similar apparatus to produce a 10 mm. thick sheet of 0À6 gr./c.c. mean density; (4), a multi-layer sheet was produced comprising respective unfoamed outer layers of high impact polystyrene (1À0 mm. thick) and of 50% mixture of high impact and general purpose polystyrene (0À2 mm.), and an inner expanded layer of general purpose polystyrene containing n-pentane and talc (4À8 mm.) to produce a sheet of mean density 0À3 gr./c.c. The foamed resin may also comprise an acrylonitrile styrene copolymer, polyethylene, polypropylene, ethylene vinyl acetate copolymer, vinyl chloride polymer, or polymethylmethacrylate, used individually or mixed.