Polyurethane urea elastic yarn having excellent uniformity and thermosetting property

Abstract

The present invention provides a polyurethane urea elastic yarn and, more particularly, to a polyurethane urea elastic yarn having excellent uniformity and thermosetting property that is prepared by (1) preparing a prepolymer using a mixture containing 2 to 25 mol. % of 2,4′-diphenylmethane diisocyanate with respect to the total weight of the diisocyanate; (2) adding a chain extender to the prepolymer; and (3) preparing a polyurethane urea polymer having a solid content of at least 40 mol. % in the final polymer, stirring the polyurethane urea polymer to obtain a polyurethane urea spinning solution, and then aging and spinning the polyurethane urea spinning solution. The polyurethane urea elastic yarn prepared by the above method displays excellent uniformity and thermosetting properties, and union/knitted yarn using this elastic yarn displays no deterioration in uniformity, thus securing good fabric quality, and also enables thermosetting at low temperature, thus preventing thermal embrittlement of the relative yarn, and resulting in excellent yellowing and touch of the union/knitted yarn.

What is claimed is: 
     
         1 . A polyurethane urea elastic yarn having a cross section ratio of 1.20 or less and a HSE value of 50% or greater according to the following measurement methods:
 (1) Cross section ratio measurement method: measured by cutting the polyurethane urea elastic yarn vertically to a lengthwise direction, measuring width W and length H of the cross section and calculating the ratio, wherein as the cross section ratio approaches 1.0, the cross section of the elastic yarn is closer to a circle with higher uniformity,   wherein the cross section ratio=W/H,   wherein W is the length of the longest straight line crossing the cross section of the yarn; and H is the length of the shortest straight line intersecting perpendicular to the longest straight line W crossing the cross section of the yarn,   
       
         
           
           
               
               
           
         
         (2) HSE measurement method: measured by elongating an initial yarn L0 exposed to atmosphere by 100% (L1), performing a dry heat treatment on the yarn at 170° C. for one minute, cooling down the yarn to the room temperature, measuring the length of the yarn (L2), performing a wet heat treatment on dry heat treated yarn at 100° C. for 30 minutes while the yarn is loose, drying the yarn at room temperature, and then measuring the length of the yarn (L3), wherein
   HSE (%)={( L 3− L 0)/( L 1− L 0)}×100.
 
 
       
     
     
         2 . The polyurethane urea elastic yarn as claimed in  claim 1 , wherein in the manufacture of the polyurethane urea elastic yarn, 2,4′-diphenyl methane diisocyanate is used at an amount of 2 to 25 mol. % with respect to the total weight of diisocyanate. 
     
     
         3 . The polyurethane urea elastic yarn as claimed in  claim 1 , wherein in the manufacture of the polyurethane urea elastic yarn, solid content of the polymer right before passing through a spinning nozzle is at least 40 wt. %. 
     
     
         4 . The polyurethane urea elastic yarn as claimed in  claim 1 , wherein in the manufacture of the polyurethane urea elastic yarn, NCO % during a first polymerization of polyol and diisocyanate is in the range of 1.7 to 4.1%.