GB794725A - A method and apparatus for producing webs or sheets of fibrous material - Google Patents

Abstract

<PICT:0794725/IV (a)/1> A sheet-like body of randomly - arranged fibres is made from a fibre-forming liquid containing a thermoplastic or elastomeric material by discharging a non-converging, high-velocity stream of gas, e.g. from a nozzle 6, and expelling a jet of the fibre-forming liquid, e.g. from nozzle 4, at a relatively low velocity into the high-velocity gas stream, the direction of expulsion being coincident with the direction of gas flow. The high-velocity gas stream attenuates the liquid and breaks it into discontinuous lengths which set, at least partly, to form fibres which are collected on a porous rotating drum or form, or an endless moving screen 8. Deposition of the fibres may be assisted by a suction box 10, or by inducing an electrostatic charge on the extruded liquid and the resulting fibres, e.g. by earthing the nozzles 4 and 6 and surrounding them by a coaxial open-ended cylinder maintained at a high potential. The endless travelling receiving screen is also maintained at a high potential or backed by a plate maintained at high potential. Air from a blower may be introduced through duct 7A into chamber 1 surrounding the nozzles to provide a secondary air stream of lower velocity. Further blowers may introduce further air streams at a point above the nozzles. In an alternative form the nozzles are directed downwardly and a secondary air stream travels upwardly in chamber 1. Adhesion of fibres to the walls of chamber 1 may be reduced by providing a deflector 11 or the top part of the chamber wall may consist of a travelling endless band which carries the deposited fibres up to the receiving screen. A number of nozzle assemblies 4, 6 may be accommodated in a single chamber. The fibres may be tacky and adhere to one another as they are deposited or they may be made tacky by heat or a solvent after formation of the sheet. The sheet may be calendered or locally consolidated. Sheets formed in different chambers, or in different zones of the same chamber may be laminated between pressure rollers. A single web may be folded upon itself or cut into pieces which are superposed, the layers becoming bonded to form a unitary structure. Preformed, non-adhesive fibres or particles may be introduced into one or more of the air or gas streams, which may be heated. The deposited fibres may not adhere, the resulting sheet being used as a source of fibres, which may be cut to form flock. The fibre-forming liquid may be a melt or solution, e.g. a solution of a vulcanizable natural rubber composition in benzene or solvent naphtha containing a small quantity of ethyl alcohol or in a petroleum hydrocarbon solvent, a neoprene composition dissolved in benzene, plasticised cellulose acetate in acetone-ethyl alcohol, ethyl cellulose in toluene-ethyl alcohol, a vinyl chloride-acetate copolymer in tetrahydrofuran and, if desired, methyl-isobutyl ketone, a vinyl chloride-acrylonitrile copolymer in a mixture of dimethylformamide and acetone, polyacrylonitrile in dimethylformamide, or polystyrene in toluene. A surface-active agent may be added, e.g. a 2-alkyl substituted imidazoline may be added to a solution of a vinyl chloride-acrylonitrile copolymer in a mixture of dimethylformamide and acetone. Other fibre-forming substances specified are butadiene - styrene, butadiene - acrylonitrile, and isoprene - isobutylene copolymers, organic polysulphides, cellulose acetate-butyrate, hydroxyethyl cellulose (water-soluble), polymethyl or polyethyl acrylate, polyesters, nylon, which may be alcohol-soluble, thermosetting resins which can exist in a thermoplastic state, e.g. urea-, thio-urea-, or melamine-formaldehyde, alkyd resins, or silicones. Gas-forming materials such as ammonium carbonate, sodium bicarbonate, or diazoaminobenzene may be added to the elastomeric material. The gas streams may comprise a chemically reactive gas, steam, nitrogen, or carbon dioxide. The particles or fibres which may be added to the gas streams may be talc, wood flour, ground cork, leather dust, starch, rayon staple fibres, cotton, kapok, asbestos. The products are suitable for use as filters, or heat or sound insulation, e.g. for aircraft or arctic clothing. Specification 577,534, [Group VIII], is referred to.