Patent GB-1398409-A (GB)
Title: Method of making a composite sheet of thermoplastic synthetic resin material having voids in its interior
IPC: H05B3/14
Filed: 1972-06-08
Abstract: 1398409 Synthetic resin laminates NISSEKI PLASTIC CHEMICAL CO Ltd 8 June 1972 [10 June 1971 2 March 1972 4 April 1972 11 April 1972 (2)] 26894/72 Headings B5N and B5A A method of making a composite sheet of thermoplastic synthetic resin material, e.g. polyethylene, polypropylene, polystyrene or polyvinylchloride, the composite sheet having voids in its interior, comprises the steps of bonding a first layer to an intermediate layer, bonding a second layer to the intermediate layer, feeding the bonded layers into a compressing and temperature regulating device which compresses the bonded layers in a direction substantially perpendicular to the plane of the bonded layers and which cools the second layer and heats the first layer so that the temperature of the first layer is higher than the temperature of the second layer at the exit of the compressing and temperature regulating device, and feeding the bonded layers into a compressing and cooling device which compresses and cools the bonded layers to form the composite sheet, wherein the intermediate layers have open cells therein which open cells form closed cells when the intermediate layer and one of the first and second layers are bonded together. In the embodiment shown in Figs. 1 and 2, a first layer and an intermediate layer formed with open cells and bonded together to form a bonded sheet 1 are bonded by rollers 3 and 4 with a second layer 2 in molten sheet form supplied by an extruder. The resultant composite sheet 8 is fed into a compressing and regulating device 5 adapted to control the surface temperature t 1  of the second layer independantly of the surface temperature t 2  of the first layer, the composite sheet 8 being subjected to cooling of the surface of the second layer and heating of the surface of the first layer on the device. The thus treated composite sheet is then fed to the compressing and cooling device 7 where it is cooled on both surfaces. A preheater 9 may be used to heat the composite sheet 1 prior to bonding as may an auxiliary heater 6. The device 5 comprises a pair of rubber belts 12 for conveying and compressing the composite, the upper span of upper belt 12 being cooled by cold water in container 11 and the lower span of lower belt 12 being heated by water in container 10. The device 7 comprises a similar pair of rubber belts 12 both of which are cooled by cold water in containers 11. The intermediate layer having cells may be formed by the apparatus shown in Figs. 4 and 5 which comprises an endless embossing belt 51 of heatresistant material, e.g. synthetic rubber, nylon or polytetrafluoroethylene provided with a multiplicity of perforations 52 and driven by a driving pulley 53. In operation, a sotened or molten sheet 54 of the resin is supplied to the upper surface of the upper run of the belt 51 and fed to a position above vacuum chamber 55, portions of the sheet being drawn downwards by the vacuum to form a multiplicity of projections of the sheet 54 protruding into the perforations of the belt 51. An endless belt 56 driven by pulley 57 and running in synchronism and in contact with the lower surface of the belt 51 forms the bottoms of the perforations 52, the belt 56 being formed from a material having a multiplicity of openings or perforations therethrough for applying vacuum to the sheet 54 through the belt 51, the surface of the belt 56 which may be a metallic screen or a sheet or fabric of synthetic resin being optionally covered with a release material A protective belt 56, e.g. of wire gauze or perforated steel sheet may be provided to minimize friction. A means 58 having projections thereon may be provided to detach the product from the belt. In a preferred embodiment, the cells of the product are connected by ducts.