Improvements in or relating to the production of composite crimped artificial fibres

Abstract

Abstract <PICT:0760179/IV(a)/1> <PICT:0760179/IV(a)/2> Crimped artificial fibres are produced by spinning from a mixture comprising solutions of different fibre-forming thermoplastic materials which solutions have been combined in laminated form so that the thickness of the layers are no greater than the diameter of the spinneret holes, the resultant filaments being stretched and then heated in a relaxed state until they crimp. The different solutions to be combined may contain cellulose esters, ethers or mixed ester-ethers, polymeric vinyl resins such as vinyl acetate or chloride, acrylic acid and methacrylic acid compounds, vinylidene compounds, polyethylene, and conjoint polymers thereof. Particularly suitable are polymers of acrylonitrile, its derivatives and copolymers. Preferred spinning solutions are firstly an aqueous nitric acid solution containing at least 50 per cent by weight of polyacrylonitrile the balance being polyacrylamide, and secondly a solution having the same components in different proportions. The different proportions may be obtained by allowing a nitric acid solution of polyacrylonitrile to ripen at a slightly elevated temperature for different periods to produce different degrees of saponification of the nitrile to amide groups. The mixing of the two solutions in laminar form is effected in the device shown in Fig. 2. The two solutions enter passages 13 and 14 which terminate in passages of flattened cross-section 16, 15 which unite to a single passage 17, also of flattened cross-section, the laminated filament emerging through circular passage 18. The general layout, Fig. 1, includes tanks 1, 2 for the two solutions, metering pump 3 for feeding solution from tank 1, mixing device 4 (as shown in Fig. 2), filter 5 and a series of metering pumps 6, 7, 8 ... each leading to a spinneret 10 and take-up device 12. The quantity of solution fed from tank 2 to the mixing device 4 is determined by the total consumption of pumps 6, 7, 8 ... less the quantity drawn from tank 1 by pump 3. The filter 5 may have an acid-resistant wire mesh with openings of 0.04 mm. and a polyvinyl chloride filter with openings of 0.02 mm. The two solutions are combined in the device 4 into layers of 0.15 mm. thickness. It is stated that notwithstanding the passage of the laminated mixture through the filter 5 and metering pumps 6, 7, 8 ... the mixture retains sufficient of its laminated structure to cause crimping of the fibres on subsequent heating, whereas if the two solutions are intimately mixed in a stirrer, no crimping results. In an example, a first solution of 90 parts of polyacrylonitrile (average mol. weight 65,000) and 1 part of urea are dissolved in 910 parts of 59 per cent nitric acid, the solution being filtered and degassed, and a second solution of 90 parts of a conjoint polymer of 60 parts acrylonitrile and 40 parts acrylamide (average mol. weight 65,000) similarly dissolved, are passed through the apparatus shown in Figs. 1 and 2, the solutions being combined in layers of 0.15 mm. and spun through a spinneret having 10 holes of 0.2 mm. diameter into a spinning bath of 20-30 per cent nitric acid at 10-20 DEG C. at a rate of 70 gms./hr., the pumps being so adjusted that the two solutions are delivered in equal proportions. The filaments are drawn off at 4 metres/min. and subsequently washed free from acid, dried, and stretched 9-fold at 160 DEG C. Crimping is effected by heating the filaments in boiling water, or by a smooth heating plate at 140-180 DEG C., or in a current of hot gases. U.S.A. Specification 2,439,815 is referred to.

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