Patent GB-799609-A (GB)
Title: Fibrous elastomeric products and a method for their production
IPC: D01D5/247
Filed: 1955-11-24
Abstract: 799,609. Rubber threads. AMERICAN VISCOSE CORPORATION. Nov. 24, 1955 [Dec. 23, 1954], No. 33707/55. Class 70. [Also in Group VIII] Fibrous products are prepared by extruding a liquid containing natural or synthetic rubber and a blowing agent into a high velocity gas stream to form a multiplicity of solid fibres which are heated to a temperature below that at which the blowing agent is activated, for a sufficient period of time to cure partially the skins of the fibres, and then heating the fibres to a higher temperature to activate the blowing agent and render the fibres hollow. The fibres may be cured by maintaining them at the higher temperature for a sufficient period or by heating them to a still higher temperature. The blowing agent may comprise diazoaminobenzene, dinitroso pentamethylene, tetramine, ammonium carbonate, or sodium bicarbonate. The liquid to be extruded may comprise a solution of natural or synthetic rubber containing, in addition to the blowing agent, vulcanizing ingredients, fillers, e.g., carbon black, clay, whiting, and French chalk, abrasives, e.g., emery, carborundum and silica, a dye or pigment, or a plasticizer, e.g., paraffin wax or stearic acid. The additives may be mixed with the natural or synthetic rubber on a mill 1, and the mix added in a tank 2 to a solvent supplied from a tank 3. The liquid mix is then passed to a storage tank 4 from which it is fed by a pump 5 through a filter 6 to extruding nozzles 7 in towers 8. A stream of primary gas is passed over each of the nozzles 7, by means of a blower 10 and conduits 9, so that the sprayed liquid is attenuated and forms discontinuous fibres. A blower 11 supplies secondary gas streams to the towers. The fibres are collected on endless conveyer screens 12 and the vaporized solvent and gases supplied to the towers are removed through suction chests 13. The fibrous webs are then pressed together by rolls 14 and passed through a chamber 15 where their outer surfaces receive a coating of a detackifier, e.g., talc. The laminated web is then heated (a) in a chamber 17 to 90‹C. to vulcanize the outer skin of the fibres, (b) in a chamber 18 to 110‹C. to activate the blowing agent and to render the fibres hollow, and (c) in a chamber 19 to 125‹C. to vulcanize the natural or synthetic rubber. The vulcanized sheet is then trimmed by a device 21, dusted with talc in a chamber 22, and wound on a roll 23. The heat treating chambers may be replaced by a single chamber divided into three sections, or into two sections when the partial vulcanization and the activation of the blowing agent are combined. The fibres produced are of varying lengths and of diameters varying throughout their lengths. Fig. 2 illustrates the form of the voids 16 in a fibre. Thick laminated sheets may be formed by adhering together two layers of the laminated sheet produced in the apparatus described, or by adhering such sheet to a web of another material. A mat of loose fibres which are not bonded together may be obtained by collecting the fibres at a greater distance from the nozzles than in the apparatus described, and incorporating a detackifier, e.g., talc, in the liquid extruded and in the primary and secondary gas streams. Products containing fibres of two or more different elastomers or elastomeric compositions may be formed by supplying liquids containing different elastomers or compositions to different extruding nozzles 7, a plurality of which are provided in each chamber 8. Coloured products may be obtained by extruding liquids containing different colouring agents through different nozzles. Alternatively the liquid extruded through some of the nozzles may not contain a blowing agent so that products are formed having both solid and hollow fibres. A fibrous layer may be adhered to certain areas only of the surface of a second layer of the same or a different elastomer. In an alternative apparatus the extrusion nozzles are mounted at the top of each tower and direct the extruded liquid in a direction opposite to the flow of secondary gas. Composite sheets may be produced by introducing non-adhesive particles or fibres into either the primary or secondary gas stream. In a further apparatus an electric heating coil is provided for heating the secondary gas stream, and additional blowers introduce a tertiary gas stream into the towers in the vicinity of the zones at which the fibres are formed. In a further modified apparatus the fibres are deposited on a shaped collecting surface, e.g., ring-shaped member which is rotated. In an example the liquid extruded comprised a solution in naphtha or petroleum containing 40 per cent by weight of a mixture of 100 parts by weight of smoked sheet, 60 parts whiting, 40 parts clay, 3À7 parts urea as blowing agent, and vulcanizing ingredients. Specification 794,725 [Group VIII] is referred to.