Patent GB-1434946-A (GB)
Title: Process for obtaining fibrid materials
IPC: D01D5/40
Filed: 1973-04-13
Abstract: 1434946 Fibrids ANIC SpA 13 April 1973 [26 May 1972 1 Aug 1972] 18059/73 Heading B5B [Also in Division D1] Fibrous products are made in fibrid form, by passing a liquid phase fibre-forming material through a first zone in which it leaves continuously in filamentary form and from the first zone to a collecting zone which the fibreforming material either reaches in substantially solid form, or at which the said material solidifies or undergoes completion of solidification, and, before the fibre-forming material reaches the collecting zone, subjecting it to the action of at least one moving fluid medium having a flow velocity component in the direction of travel of said material sufficient to draw said material and a turbulence sufficient to disintegrate said material into fibrid form. The liquid phase fibre-forming material may be a polymer solution or melt and the fluid medium a coagulant therefor, e.g. a liquid non-solvent, or may be a gas, e.g. carbon dioxide, air or nitrogen at an elevated temperature sufficient to evaporate any polymer solvent. Polymer melt used may contain a diluent, e.g. a blowing agent and the fluid medium may be at a temperature sufficiently low to solidify the melt. In a preferred method, continuous filamentary lengths of the fibre-forming material are produced as the said material leaves the first zone, and a fluid medium is directed through a passage surrounding and including said first zone in the same direction as the fibre forming material and having a Reynold's number such that its flow has a turbulence sufficient to disintegrate the continuous filamentary lengths as they are drawn thereby away from the first zone. Thus in Fig. 1, polymer solution in feed tank 1 is spun through spinneret 2 into the tapered pipe 4 to which fluid is supplied at 5, the fluid undergoing an increase in velocity where the pipe narrows. Thermostatic jackets 3 and 6 surrounding tank 1 and pipe 4 enable desired operating temperatures to be maintained. In Fig. 2, pressure vessel 7 is fitted with a stirrer 8 and thermostatic jacket 9. Polymer leaving the vessel is extruded from spinneret 10 and duets 11 and 11a provide a flow of gas around the polymer, the gas travelling through passage 11 providing turbulence so as to disintegrate the polymer fibres into fibrids which are collected on endless belt 12. By using a short distance between the spinneret and the support, the polymer fibrids coalesce together to yield a polymer fibre or sheet in which fibrid structures are apparent; using greater spinneret and support distances, fibrids 2 to 5 mm. in length are obtained which become entwined so as to constitute a short fibre structure similar to paper. In examples fibrids are made using the apparatus of Fig. 1 by spinning (i) a solution of polyethylene in decalin into methanol; (ii) a solution of polyvinyl chloride in tetrahydrofuran into water; (iii) a solution of polystyrene in tetrahydrofuran into water; (iv) a solution of polyvinyl chloride, polyethylene, polypropylene and polystyrene in 1,2,4-trichlorobenzene into methanol; (v) a solution of polyethene and polystyrene in n-heptane into gaseous nitrogen; (vi) using the apparatus of Fig. 2, fibrids are made by spinning a solution of polyethylene in n-heptane into gaseous nitrogen. The fibrids become joined together on the support to form either a film structure when the belt is close to the spinneret, or a mat structure similar to paper if the belt is further away. A non-woven fabric structure is obtained by reducing the gas pressure so as to reduce the defence of fibrillation, and using a continuous belt a substantial distance from the spinneret. In each case the mechanical properties of the structure obtained are improved by subjecting them to calendering at elevated temperatures.