| 摘要 |
Textile yarns capable of bulking are made by melt-spinning orientable linear condensation polyesters by a process wherein at least two groups of filaments having substantially different deniers are spun simultaneously with substantial attenuation of the extruded filaments and under conditions producing no, or only low, crystallinity in the as-spun filaments, the groups of filaments being collected as a single yarn. Preferably the polyester is such that at least 75% of the recurring units are ethylene terephthalate units, but in the preparation of such polyesters minor proportions of glycols other than ethylene glycol, e.g. diethylene glycol, butylene glycol, decamethylene glycol and 1,4-hydroxymethylcyclohexane, or of dicarboxylic acids (or ester-forming derivatives thereof) other than terephthalic acid, e.g. adipic acid, dimethyl sebacate and sodium 3,5-dicarbomethoxybenzene sulphonate, may be used. Spinning may be into air or an aqueous medium, and the difference in denier may be produced by extruding the polyester at different rates of flow, e.g. through orifices of different sizes or by applying different pressures to different orifices, or both. A divided pack, to the sections of which polymer is fed at different rates, may be used. The filaments may be of non-round crosssection, e.g. cruciform, asterisk, Y, ribbon, zig-zag or keyhole, and where the denier of the filaments of the finest group does not exceed 8, the filaments of another group may be of a denier at least 25% greater than that of the finest filaments. The filaments may be oriented either by the use of spinning speeds of 3000-5200 yards per min., or by subsequently cold- or hot-drawing the extruded filaments up to five times their original length. The filaments show a differential shrinkage when the yarn is subjected to subsequent heat-treatment; filaments showing differential extension, or mixed shrinkage and extension, on subsequent heat-treatment of the yarn may be made if the oriented filaments are subjected to a preliminary heat-treatment which reduces the total shrinkage of the yarn. Thus the oriented filaments may be heated for a time and under conditions such that the smallest denier filaments shrink by at least 20%, without producing the maximum level of crystallinity obtainable at the specific temperature in the medium in which the filaments are heated. In both types of yarn the bulk may be developed by finally heating the yarn to 70-220 DEG C., if desired in the presence of water, and preferably while the yarn is substantially free from tension. Provided that the oriented yarn, after preliminary heat-treatment if this has been effected, is not subjected to ambient temperatures of about 70 DEG C. or more, the bulking stage may be deferred until the yarn has been incorporated in a woven or knitted fabric. Specification 712,950 is referred to. |
