GB1235121A - Producing yarn-like materials by fibrillation - Google Patents

Abstract

1,235,121. Producing yarn-like products by fibrillation. IMPERIAL CHEMICAL INDUSTRIES Ltd. 8 Jan., 1969 [25 Jan., 1968], No. 4003/68. Heading B5B. Bulky yarn-like materials are produced by forming a synthetic organic thermoplastic polymeric substance into at least one ribbon or tape, longitudinally orienting the ribbon or tape, mechanically crimping the oriented ribbon or tape, heat treating the crimped ribbon or tape to set the crimp and fibrillating the crimped ribbon or tape. The products obtained comprise a bundle of fibrils having a sinusoidal or sawtooth crimp joined together in a random network. The term "ribbon" is defined as an elongated structure wider than it is thick which is produced by extrusion of the molten polymer or a solution thereof through a die having one or more extrusion slots, solidifying the ribbon and winding up or forwarding the ribbon to the next step at a linear speed preferably somewhat in excess of the linear extrusion rate. The term "tape" is defined as an elongated structure of ribbon form which in this case is produced by melt extruding or casting the polymer to form a film which is longitudinally slit before or after orientation into a number of narrower widths. The ribbons and tapes usually have a rectangular crosssection, but may consist of thick and thin longitudinal ribs alternating transversely across the width, having been produced by extrusion through a die comprising a straight row of circular holes joined by narrow slots. The orientation of the ribbon or tape is preferably effected while it is in a heated but not thermoplastic state. The process of the invention is preferably carried out in a continuous manner, but may be carried out in two or more stages, the ribbon or tape being collected in a temporary package between one stage and the next. The mechanical crimping of the ribbon or tape may be effected by passing the oriented ribbon or tape through a stuffer box or gear crimper of known form which produce crimp of a sinusoidal or sawtooth form or by passage over a narrow heated edge which produces a helical crimp. Two or more ribbons or tapes may be simultaneously passed through the stuffer box or gear crimper in superimposed relationship. The crimp inserted is set by a heat treatment at a temperature below the softening point of the ribbon or tape and, preferably, at a temperature at which crystallization occurs at a fairly rapid rate. This heat treatment may conveniently be carried out by passing steam or hot air through the downstream part of the stuffer box or by heating the ribbon or tape prior to crimping or by heating one or both of the gear crimping wheels. Alternatively the crimped material may be heat treated in a relaxed condition by passing it through a hot air oven on a slowly moving foraminous conveyer. It is desirable to allow the crimped heat set material to cool before the fibrillating step. The thermoplastic substances used may be polyamides, polyesters, polyolefines, vinylidene chloride copolymers, polystyrene, polyacrylonitrile or acrylonitrile copolymers. An additional bulking effect may be produced by using conjugate ribbons or tapes composed of layers of polymeric substances possessing different shrinkage properties either on release of drawing tension or in a relaxed heat treatment. The fibrillation of the crimped ribbon or tape may be effected by high-speed twisting or false-twisting, but it is preferred to use a jet of a turbulent fluid, preferably gaseous, such as air or steam to effect fibrillation as this may allow both a heat treatment and a relaxation to be effected in the same piece of apparatus. Stress points, lines or areas may be introduced into the ribbon or tape prior to fibrillation, preferably prior to crimping and more preferably prior to orientation. Such prestressing of the ribbon or tape may be introduced by, for example, passing the undrawn ribbon or tape (or film from which the tape is cut) through embossed nip rolls prior to orientation. Alternatively a freshly extruded film may be cast on to an engraved or patterned roller in place of the smooth roller usually used.