GB711166A - Process and apparatus for the manufacture of staple fibres of polyamides - Google Patents

Abstract

<PICT:0711166/IV (a)/1> A band of continuous filaments of a polyamide composed predominantly of e - amino-caproic acid residues (but still containing water-soluble monomeric or low molecular weight polymeric compounds as impurities) is continuously stretched to a multiple of its original length, washed under tension with hot water and, if desired, treated with a greasing agent, then dried to a moisture content of less than 10 per cent. while maintaining the tension then mechanically crimped at a raised temperature, and cut into staple fibres which are then opened up by means of a stream of air. If desired, the staple fibres may be treated with a greasing agent while being opened up by the stream of air. The stretching mechanism may comprise two roller assemblies rotatable at different speeds. The washing may take place in a vat provided with rotatable cylindrical feed members or in a channel provided with feed rollers. Drying may be effected by passing the band of filaments over a heated drum. The crimping apparatus may comprise a pair of intake rollers, a heated compression chamber into which the band is fed by the rollers, a pressure flap controlled by a weight, and a discharge channel. The polyamide may contain 5-15 per cent. of water-soluble monomers or low polymers, particularly caprolactam, or it may be one in which the water-soluble components have been reduced to below 5 per cent. by evaporation under vacuum during a continuous polymerization process, or by subjecting the polyamide to an extraction treatment before supplying it to the melt-spinning apparatus. If desired, the band of filaments may be obtained directly from melt-spinning apparatus. Stretching may be effected in the cold or at elevated temperature, e.g. 140-185 DEG C. Boiling water may be used for the washing step. The hot or boiling water may contain wetting or dispersing agents. Following this treatment, the tensioned band of filaments may be passed through liquids containing greasing agents, tanning agents, or dyestuffs. If desired, toothed wheels may be used for the crimping. The process is preferably carried out as a continuous operation from the stretching to the formation of the staple fibres, but if desired the crimping and cutting may be effected separately from the stretching, washing, and drying. Between the compression crimping apparatus and the cutting device there may be interposed a creel brake, clock spring brake, claw brake, or other braking device which acts by changing the direction of travel of the band. Such a device straightens out loops which may form when the band leaves the crimping device. The compression chamber may be heated by a steam-jacket, by an electric resistance heater or by a high frequency electric heater. As shown, filaments from rolls 1 are formed into a band 2 and stretched between roller assemblies 3, 4, the temperature being regulated by heater 5. The band 2 travels round drums 7 in a washing vat 6, the various turns being kept apart with the aid of comb 8. The band then passes through a trough 10, where it is treated with a greasing liquid, and on to a drying drum 11. After leaving the drum 11, the band 2 is gripped by intake rollers 14 of the crimping apparatus 15. In compression chamber 17 which is heated by the device 16, the band is pressed against the flap 19 which is provided with a weight 18. As the pressure of the compressed band increases, the flap 19 is lifted so as to permit the band to enter the discharge channel 20. The band is then drawn via the creel brake 21 into the staple cutting machine 22. The cut fibres 23 are carried along by a strong air current 24, opened up, and conveyed into storage bin 25. If the crimping channel of the crimping apparatus is made sufficiently long, e.g. 600 mm., the friction set up in the compression chamber may produce sufficient compression of the band to impart the desired crimping even when the flap is in the open position.