| 摘要 |
PROBLEM TO BE SOLVED: To obtain the subject undrawn yarn having a birefringence, a boiling water shrinkage, etc., falling within respectively specific ranges and useful as a yarn for supplying a spontaneously stretchable yarn to give a woven or knit fabric having light-weight, high bulkiness, excellent springiness and resilience and exhibiting the feeling of worsted yarn fabric. SOLUTION: This highly oriented undrawn polyester yarn has a birefingence of 45×10<-3> to 75×10<-3> , a C% value of <=4%, a boiling water shrinkage of 40-70% and a variation of the boiling water shrinkage of <=6%. This undrawn yarn can be produced by setting the L/D ratio to 2,900<=V<=3,200, 1.0<=L/D<=2.5, 0.22<=X/V<=0.31 and 750<=X<=900 wherein V is the spinning speed, L is the length of the nozzle and D is the diameter of the nozzle.
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