ES363814A1 - Variable denier yarn - Google Patents

Abstract

Each filament of bulky continuous multifilament textured polyester yarns (or staple fibres obtained therefrom), particularly polyethylene terephthalate yarns, comprises at least three types of zones of different mean diameter, the finest zones having the highest crystallinity and the greatest molecular orientation, the thickest zones having the lowest crystallinity and the least molecular orientation, and the intermediate zones (whose mean diameter is between the mean diameters of the finest and the thickest zones) having a crystallinity and a molecular orientation between those of the finest and the thickest zones. Each filament furthermore possesses transverse grooves of attenuated relief at least in the thickest zones and has a non-spiral three-dimensional crimp. The thickest parts of the filaments may be unoriented and relatively non-crystalline. The thinnest parts of the filaments may have a crystallinity index between 30% and 60% and an angle of molecular orientation less than 40 degrees, and the thickest parts may have a crystallinity index less than 30%, and an angle of molecular orientation of about 90 degrees. The yarns of the invention may be produced by partially stretching an undrawn multifilament yarn of synthetic thermoplastic material in at least two stages, of which the first is carried out while the yarn is in contact with a crackpromoting agent, the degree of stretch in the first stage being greater than in the second, and subsequently heat treating the stretched yarn in a relaxed state. The crack-promoting agent may be of any known type, such as a monohydric alcohol, a glycol, dimethylformamide, kerosene, perchlorethylene, a polyoxyethylenic liquid, or pyridine. In an example, a 30-filament polyethylene terephthalate yarn is stretched at a stretch ratio of 2À1 while passing through a bath of 25% aqueous ethanol at 35 C. The yarn is then stretched at a stretch ratio of 1À2 in air between the first set of stretching rolls and a second set of stretching rolls, and thereafter heat-treated in the relaxed state while immersed in water the initial temperature of which is gradually raised to 100 C. The yarn is then dried under tension with free access of air, and finally heated for 5 minutes in an oven at 180 C. The heat treatment in the relaxed state can be carried out in a continuous manner immediately after the stretching stages or as an independent operation on the yarn or on a fabric, e.g. a woven fabric, made therefrom, and may for example be combined with a dyeing treatment of the woven fabric yarn according to the invention has high dimensional stability and high apparent volume. The yarns can be converted into knitted fabrics.