Patent GB-1087410-A (GB)
Title: Apparatus and process for producing and electrostatically charging fibrous webs
Inventor: HOLLBERG HERBERT JOHN
IPC: D01D5/04
Filed: 1966-05-13
Abstract: 1,087,410. Electrostatically charging flashspun fibrous webs. E. I. DU PONT DE NEMOURS & CO. May 13, 1966, No. 21352/66. Heading B5B. [Also in Divisions D1 and H1] As depicted in Fig. 1, an apparatus for forming a non-woven fibrous web by " flashspinning " ("flash-spinning " is described in Specification 891,943), opening it by mechanical means, electrostatically charging it and forwarding it for deposition on a moving surface, comprises a pressure reduction orifice 3 in a spinneret 1 through which orifice a solution 2 of synthetic fibre-forming organic polymer in a volatile solvent or liquefied vapour at an elevated temperature and pressure flows into a chamber 4 at a lower pressure and is then extruded through a flash-spinning orifice 5 into a web-forming chamber 6 at or near atmospheric pressure to form a multifibrous strand 7 consisting of a large number of interconnecting random length fibres each having the form of a very thin narrow ribbon. The strand or " plexifilament " and the vaporized solvent impinge upon a baffle 8 which may be stationary, or, as depicted in Fig. 1, mounted on shaft 10 which is oscillatably mounted in bearing 11 and is powered to oscillate by means not shown. The strand is thereby spread out into a web sheet form 7. The spreading of the strand may also be effected by means of a shroud surrounding the spinneret orifice and extending outwards from the spinneret face. The shroud may be used with or without the baffle 8. A target plate 13 (Figs. 1 and 5) and an ion gun 14 (Figs. 1 and 2) are disposed on opposite sides of the path of advance of the web 7 downstream from the spinneret and the mechanical strand opening and web forming baffle 8. Target plate 13 is so disposed that the blast of vaporized solvent originating at the spinneret orifice 5 and the air flow pattern in chamber 6 carry the web 7 along its charging surface. Target plate 13 is connected to earth by wire 15 and microammeter 16. As depicted in Fig. 2, a preferred ion gun comprises individual resistors 28 housed in a compartment 26<SP>1</SP> and connected individually by means of insulated leads 32 to needles 25 protruding from one face of a housing 24. The resistors 28 are connected in parallel to high voltage terminal connections 33. After passing through the charging zone, the electrostatically charged web 7 is deposited upon a collecting surface, which may be the peripheral surface of a rotating drum, or, as depicted in Fig. 1, the upper run 9 of an endless travelling belt driven by rolls 36. The belt is given an opposite electric charge by power, source 37 to that imposed on the web 7 in the charging zone, whereby the web 7 is attracted to surface 9 as a sheet 38 which is carried out of chamber 6 through port 39. The sheet 38 is lightly compacted by the roll 44 and collected on wind-up roll 42. Flexible seals 40 at ports 39 and 41 assist retention of vapour within chamber 6, the upper portion of which may communicate with a solvent recovery unit 43. In the example, strands are flash spun from 13% solutions of polyethylene in " Freon " 11 (trichlorofluoromethane) at 186 C. and 950- 985 p.s.i.g. pressure and treated as described to form sheets weighing 2.5 to 2.7 oz. per sq. yd.