GB969110A - Improvements in the manufacture of polyamide yarns - Google Patents

Abstract

Crimped, elastic, or voluminous stable yarns are made by melt-spinning yarns containing composite filaments of polyamides of uniform composition, in which the double refractions of their components in the unstretched state differ by at least 0.002, stretching them at a temperature of at least 60 DEG C., and subsequently relaxing the tension on the yarns. Polyamides of uniform composition are defined as being of uniform chemical composition but differing in their double refraction in the unstretched composite filament. The polyamides of uniform composition may differ in their reduced viscosities by at least 0.06. Reduced viscosity is defined as ln c rel/C where c rel. is the relative viscosity of a solution of concentration C, said concentration being 0.2 gms. of polyamide per 100 ccs. of solution, measured at 20 DEG C., in 94% by weight sulphuric acid. The necessary double refraction difference may be produced not only by a difference in the solution viscosities of the polyamides, as defined above, but by a difference in melt viscosities of the components at the moment the filaments are formed, e.g. by differential temperature adjustments in the area of the spinneret, or by the use of different melting conditions on two p polyamides of uniform compositions and of the same viscosity, i.e. identical polyamides. Yarns consisting wholly of composite filaments so made may be heat set while substantially free from tension after having undergone spontaneous crimping. Such yarns are characterized by their high elasticity, expressed by a take-up value of at least 40 and a half-value decrimping force of at least 1.0 mg. per denier. For definitions of these terms, see Specification. Such composite filaments, on being relaxed, develop a three-dimensional crimp and sometimes double spiralling. Yarns containing both composite and unitary filaments consisting of one of the two components of the composite filaments are relaxed and then stabilized by twisting, e.g. to 50-200 or more, turns per metre, and/or heat-setting under tension. The more composite filaments the yarn contains the more voluminous it is, but the take-up value is rapidly increased, i.e. the final product tends to be crimped, which is undesirable in a voluminous yarn since it can only be stabilized by sacrificing its voluminosity. Hence yarns containing both composite and unitary filaments are preferred for the production of materials which are not required to have much elasticity but a large yarn volume, especially yarns containing 30-70% composite filaments. Either or both components may contain matting agents, pigments, stabilizers or plasticizers. The ratio of unitary to composite filaments can be varied. Specified materials include all fibre-forming polyamides having melting points over 60 DEG C., e.g. polycaprolactam (nylon 6), polyhexamethylene adipamide (nylon 66), polyhexamethylene sebacamide (nylon 610) and polyaminoundecanoic acid (nylon 11). Specification 930,629 is referred to.