Patent GB-1143682-A (GB)
IPC: B29C65/48
Filed: 1965-12-29
Abstract: 1,143,682. Films; laminates; webs &c. DIAPORIT S.A. 29 Dec., 1965 [4 Jan., 1965], No. 55061/65. Headings B5A, B5B and B5N. [Also in Divisions B1 and C3] A process for the production of coherent, porous webs from particulate synthetic thermoplastic material comprises spreading the particulate material into a layer, heating the particles in the layer to a temperature below the softening point of the material to suppress their rebound elasticity, exposing the heated particles to radiation in the wavelength range from 0À6 x 10<SP>-4</SP> to 3 x 10<SP>-2</SP> cms which penetrates the particles without warming up their mass to bond contiguous particles together over the touching parts of their surface areas, thereby forming a coherent web retaining pores in the web between the particles, and cooling the porous web with or without further processing of the web prior to and/or following the cooling step. Preferably, the rebound elasticity of the particles is suppressed by subjecting them to radiant heat in the wavelength range between 1 x 10<SP>-1</SP> cms. and the wavelength of the radiation in the subsequent irradiation step, and the heated particles are preferably exposed to radiation in the wavelength range from 7,500 to 32,000 Angstrom units. One or more additional layers of particulate fitted thermoplastic material may be deposited on the first layer, each additional layer being treated and bonded to the preceding layer in the same way as the particles of the first layer are bonded inter se. One or more insertions in the form of filaments or strips may be introduced into the layer, or, when more than one layer is present, between the layers. The formed web may be subjected to a shaping processing stage for imparting a desired surface to the sheet or for imparting a different shape to a part or a whole of the sheet. Thus the sheet may be formed into a tube in the shaping process stage by curling its edges over and continuously welding the seam between the edges. Such a process may be followed by processing the formed porous web to reduce or eliminate its porosity. If desired, the starting synthetic thermoplastic material may contain finely divided cork, wood, corundum or rubber or other non-thermoplastics material in uniform distribution through it, and the plastics material may, if desired, be continuously applied to a backing material, immediately after it having been produced, e.g. a wall lining material or a floor covering. The plastics web may be provided underneath with a web of different material or interposed between two other webs. Adhesives may be used to bond the webs together. Suitable webs of foreign material may be films of polyvinyl chloride, woven webs made of natural or synthetic fibres, including glass and webs of cellular material with open or closed pores. The webs of foreign material may be introduced in a production line if desired, in front of the first irradiation zone. The particles of which the coherent porous web sheet are formed are suitably all of substantially the same order of magnitude within the range of 25 to 800 microns. In apparatus as shown, granular or pulverulent thermoplastic material is fed from hopper 5 via spreader means 6 on to the upper run 1A of endless band 1. Suitably the layer of granular material is 50 cms. wide and 3 mms. deep, and of uniform thickness. Rollers 8 serve to impart precise dimensions to the deposited plastics layer 7 and possibly to condense the layer to a given extent. The layer is next exposed to the action of thermal radiation generated at heating station 9, the heating elements suitably being electric radiators, emitting radiation in the desired wavelength to suppress the rebound elasticity of the material. The layer 7 is next subjected to any desired local forming effects, e.g. by the impression of profiles or patterns, at belt 10A which has a surface bearing raised embossments. The layer is next heated by radiators 12, and thereafter forms a coherent layer which may be smoothed by roller pair 13, and by providing the upper or both of these rollers with appropriate profiles, one or more denser zones of any desired width may thus be rolled into the still formable layer to create longitudinal or transverse grooves on the layer, in which the porosity of the layer is reduced. The layer is next cooled by blowers 14, or alternatively by means of a bath of quenching liquid. Stripping apron 15 lifts the band 7 off the conveyer band 1, and suitable cutting devices, e.g. in the form of circular knives, permit the band behind the cooling zone 14 to be divided into longitudinal strips, each strip being separately wound or taken to different machines for further processing. Processing may consist in the production of tubes by curling over the strip edges in the manner described in welding the resultant longitudinal seam. Such tubes are useful as drainpipes. This method is illustrated in Fig. 2. The return run 1B of conveyer band 1 travels across means 16 for cleaning the band and removing residues of plastic material, e.g. revolving brush 16 and compressed air nozzles or water jets (not shown) for washing the band. Another possibility for further processing the band behind the second irradiation stage consists in making individual, particularly narrow longitudinal zones of the plastics band completely impervious, so that the resultant product has a strip filtering effect, permitting several media to be independently filtered through the same band of material. Fractional filtrations can likewise be performed in this way by inserting the filter band into a suitable casing divided into several compartments. The impermeable zones are produced by sufficiently condensing the material to destroy all the cavities between the individual particles in the zones of compression. The particles are compressed until they form a solid integral whole, by the use of pressure rollers or cylinders acting upon the plastics band from above and below. A plastics band with impermeable longitudinal zones which need not be wider than a pencil line is useful for the production of permeable pipes. The finished pipes will then have walls divided along their length into a plurality of separate permeable strips. Transverse divisions by the provision of impermeable zones may likewise be created, e.g. by means of rollers extending across the band above and below the same and formed between recessed portions with axially extending bands which will then press transverse compressed zones into the band of material. A second feed hopper and spreader bar may be provided for depositing a second layer of the same or different width of material on the first layer, suitably between the two stations 12 and 13. The second layer may be a material of the same or different kind and the particle size may be different from that used for forming the first layer. For treating the second layer a corresponding sequence of treatment stations must be associated with the conveyer band. The incorporation in or application to the plastics band of extraneous components is likewise effected at a suitable point, most conveniently between stages 9 and 12 in Fig. 1. Glass filaments, rubber threads, steel or copper wires may thus be introduced in order to impart special proparties to the final product. Alternatively, the product may be provided with the abovementioned additional layers of other materials during its actual production, either at a point which intervenes between the above-mentioned treatment stages or at a point which follows the stages of the forming process as such. Other processing stages should likewise preferably be arranged directly to follow the last described stage of the process, such additional stages comprising bending, pressing, drawing, stamping and/or cutting operations. Fig. 2 shows the division of a finished plastics band into three component strips of which the two outer strips are continuously shaped into tubes of different diameters, whereas the centre strip remains a band-shaped final product. The division of the band is effected by means of circular knives, the divided strip at the back being elevated to a higher level and the strip at the front to a lower working level.