Patent GB-989091-A (GB)
Title: Improvements in or relating to reinforced plastic materials
IPC: B29C41/50
Filed: 1960-03-14
Abstract: 989,091. Bonded fibre fabrics. A. SHAW. June 13, 1961 [March 14, 1960], No. 8971/60. Heading D1R. [Also in Divisions B2 and B5] A method of making material comprising reinforcing members or particles (e.g. in the form of fibres or powder) distributed and embedded in and bonded together by synthetic resin or other plastic material comprises depositing the constituents of the material on to a mould or former by subjecting the oonstituents to a high electric potential relative to the mould or former so that electric forces of mutual repulsion act between the particles of plastic and electric forces of mutual repulsion act between the reinforcing members or particles and electric forces of attraction act between the constituents and the mould or former. As shown, containment vessel 11 comprises two atomizers 15 and 16 for injecting liquid synthetic resin material; an electrode 26 in the form of an electrostatic shield; two sets 14 and 20 of electrodes, each set comprising conducting wires which are mutually parallel and perpendicular to the wires in the other set; a mould 13 on which the material is to be deposited; two electrodes 34 (and for magnets) constituting control plates; an inlet 33 for the reinforcing material; and an outlet connected to exhaust pump 35. Liquid resin containing an accelerator is supplied from tank 17 to atomiser 15 and liquid resin containing a catalyst is supplied from tank 18 to atomizer 16. The atomizers and electrode 26 are maintained (by means not shown) at a high negative electric potential (of order of 100, 000 volts) with respect to electrodes 14 and 20. Chopped glass fibres are fed from hopper 28 to conveyer belt 29 and thence to shoot 31 surrounding the neck of which is a source 33 of alpha-particles which irradiates the glass fibres as they pass it so that they carry positive electric charges. Shoot 31 comprises means (not shown in detail) for providing a substantially gas tight entry to vessel 11 and for admitting a controlled stream of gas of low molecular weight to carry the glass fibres in it. From shoot 31 the fibres are conveyed by the gas through Venturi-tube 33 into vessel 11. The negatively charged drops of resin move under the electric field towards mould 13, and are attracted towards the oppositely charged fibres so that each fibre becomes thoroughly coated with resin and acquires a residual negative charge, and is then accelerated by the electrostatic field towards mould 13 which it strikes with a high velocity. As the resin is deposited on the mould the catalyst and accelerator become mixed causing the resin to set to form a reinforced material of high density and free from voids. In operation the potential is first applied only to electrodes 14 whereby the fibres impacting on the mould tend to align themselves parallel to each other in a direction transverse to that of the electric field. After forming a layer in this manner the potential is then applied only to electrodes 20 and a successive layer is formed wherein the fibres are aligned in a direction substantially at right angles to those in the previous layer. By this procedure better bonding and compacting of the fibres is achieved. Alternating potential may be applied to one or both electrodes 14, 20. Instead of chopped glass fibres, glass powder or asbestos particles may be used. Instead of using electrodes as 14 and 20, electrical connection may be made directly to mould 13 if it is of conducting material; or if it is of non-conducting or poorly conducting material conducting wires may be embedded in the mould to provide electrodes. The mould may be moved relatively to the stream of material reaching it. As shown it may be rotated about an axis to form a cylindrical article. Potentials may be applied to plates 34 to control the field so as to deposit material selectively upon one or more parts of the mould. Selective deposition may also be obtained by use of only certain of the wires in electrodes 14 and 20. The reinforcing particles may be given a charge similar in sign and magnitude to that on the resin particles. Composite structures of sandwich form comprising outer layers of material as described above with an inner layer of foamed plastic may be made by first casting the foamed plastic inner layer to shape in a separate mould and then casting the outer layers on to its surfaces by the above described method so as to become bonded thereto, or by first depositing an outer layer of material by the above described method, then depositing thereon a layer of beads of foamed plastic (such as polystyrene) by suitable means and then depositing, on the foamed layer, the second outer layer by the above described method.