GB609167A - Manufacture of artificial fibres - Google Patents

Abstract

Synthetic fibres are formed from fusible fibre-forming organic polymers by a process comprising the rapid heating of the polymer under non-oxidizing conditions to a highly fluid state, forming a film from the polymer while it is still fluid, directing upon the said film a stream of inert elastic fluid in such a way as to cause portions of the film to be drawn off, the pressure and temperature of said inert fluid being regulated so as to cause the formation of either continuous fibres, staple fibres or mixtures of beads and fibres. Suitable polymeric materials are polystyrene, polyethylene, vinyls acrylate, acrylonitrile polymers and copolymers, alkyd resins, polyamides, natural or synthetic rubber. The inert elastic fluid is preferably super - heated steam. Suitable <PICT:0609167/IV(a)/1> apparatus for carrying out the invention is shown in the drawings. The polymer is heated in a vessel 5 which is provided with a heating jacket 6 and fitted with a combined agitator and screw means 7 which pumps the molten polymer to a constant delivery gear pump 13 which is also enclosed in a heating jacket 14. The gear pump 13 delivers the molten polymer to a metal fibre-forming nozzle assembly 17 which is connected in its turn to a steam line 18. The pressure of the steam is regulated by a valve 19 capable of maintaining a constant desired pressure. The assembly 17 is surrounded at about its middle point by an electric induction heater 20, a second induction heater 21 being placed close to the exit end of the nozzle assembly. The steam or other vapour leaves the assembly by a nozzle tip 22 and strikes a rotating drum 23 having a foraminated collecting surface 24 such as cotton cloth. This drum is mounted within a partly enclosed chamber 25 from which the expanded steam and atmospheric gases are removed by a vent 27. The nozzle assembly (Fig. 2) comprises a cylindrical metal member 30 internally positioned within a tubular metal casing 45. Extending through the member 30 are eight circumferentially arranged longitudinal passageways 31 which taper together toward the nozzle tip. A very slightly tapered metal rod 34 is positioned within each passageway by pins 36 to form an annular clearing space 35. The polymer inlet pipe 29 leads through the bushing 32 to a manifold space 33 communicating with the passageways. An annular depression in the other end of the member 30 forms a second manifold space 37 from which bores 38 converge into a common orifice 40 within the nozzle 22. Steam from the inlet pipe 18 passes along a central passageway 41 by means of inlets 43 and also along an annular passageway 42. The inlets 43 are so placed that they do not communicate with the polymer passageways 31. Steam passing along 42 enters an auxiliary nozzle chamber 46 formed by the nozzle cap 47 being threaded into the casing 45, the said chamber being so positioned as to have its orifice concentrically superimposed on the nozzle tip 22. Thus, an annular jet space 48 is provided which will blow into fibres any accumulation of molten polymer at the external end of the nozzle. The nozzle may be heated by means other than induction heaters. A film of polymer almost at its decomposition temperature flows along the central orifice 40, being propelled in the direction of the tip 22 by frictional contact with the steam passing along the central passageway 41. When steam at low velocity (such as a few hundred feet per minute) is employed, and at a temperature substantially the same as that of the polymer, the fibres are floated out into the atmosphere as continuous filaments having little or no molecular orientation. With steam velocities approaching the order (theoretical) of 20,000 to 80,000 feet per minute and at a temperature substantially the same as that of the polymer fibres of random staple lengths, considerably oriented and crimped are produced. Toward the higher limit of steam velocity the length of the fibres is decreased and the orientation lessened. At steam temperatures lower than that of the polymer atomization occurs, so that the proportion of beads to fibres can be controlled by varying the temperature. Beads in small proportion are an advantage when a felted mass is required. The fibres and bats formed can be employed as textile fibres or as heat insulators or moulding materials. In an example, polystyrene of average molecular weight 50,000 is heated to 200-260 DEG C. in a closed container and pumped into a fibre-forming nozzle. The nozzle tip temperature determined by a pyrometer was 380 DEG C. Steam at 100 lbs. per square inch pressure is super-heated to 315-400 DEG C. and fed into the steam passages of the nozzle assembly. The polystyrene leaves the nozzle at 370 DEG C. in the form of a tow or stream of kinky oriented staple fibres of average diameter 4 microns and of length 4 to 10 inches. With polymers of higher molecular weight, higher nozzle tip temperatures are required, and conversely the lower the average molecular weight the lower the nozzle tip temperature. Polymers contaminated with plasticisers or monomers may be utilized owing to the immediate vaporization of these materials on reaching the common orifice 40.