Self-crimping filaments
1,094,933. Producing self-crimping polypropylene filaments. IMPERIAL CHEMICAL INDUSTRIES Ltd. April 4, 1966 [April 20, 1965], No. 16543/65. Heading B5B. Self-crimping composite polypropylene filaments are produced by conjugate melt spinning of two propylene polymers having the same intrinsic viscosity, but different molecular weight distributions, and subsequently drawing and/or relaxing the tension in the filaments. The " dispersion coefficient " of at least one component must be at least 6À5 and the dispersion coefficients of the polymers may differ by at least 0À5. The component polymers may have a viscosity of at least 1À0. The unrelaxed spun filaments may be drawn 2-4 times their original length and the drawing may be effected by means of a snubbing surface heated to not over 100 C. The drawn filaments may be heat treated on the draw roll which is maintained at a temperature of up to 100 C. The crimped filaments may be stabilized by heat treatment at 100.. 140 C. The " dispersion coefficient ", which is an expression of the molecular weight distribution of a propylene polymer is defined as the ratio of the weight average molecular weight to the number average molecular weight of the polymer, these values being determined by light scattering and membrane osmometry techniques described in detail in the Specification. The intrinsic viscosities of the polymer are measured in decalin solution at 135 C., the units of intrinsic viscosity being decilitres/gram.