| 摘要 |
PROBLEM TO BE SOLVED: To obtain a polyester which is used for melt spinning, has excellent fiber formability and excellent productivity and can give partially oriented undrawn fibers having excellent drawability, process passableness and draw fiber physical properties, by copolymerizing trimellitic acid, trimesic acid or one of their derivatives so as to satisfy specific conditions. SOLUTION: This polyester copolymerized with trimellitic acid, trimesic acid or one of their derivatives so as to satisfy the conditions of the inequalities: 0.08<=c<=0.28, and 1.48<=c+2×(IV)<=1.60 [c(mol.%) is the copolymerization amount of the trimelliic acid, the trimesic acid or one of their derivatives; IV (dVg) is the intrinsic viscosity of the polyester]. The main repeating units preferably comprise ethylene terephthalate units. The polyester is preferably melt-spun at a taking speed of 3,000 to 5,000 m/min to obtain the polyester partially oriented undrawn fiber preferably having a birefringence of 0.020 to 0.060.
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