Fine-denier polyester fiber

PURPOSE: Title deeply dyeable fiber that consists of ethylene terephthalate units and has specified filament denier, thermal stress maximum on temperatur-rising, crystal size and crystal angle. CONSTITUTION: A polyester containing ethylene terephthalate as the major structural unit is subjected to high-speed spinning so that the optical birefringence Δ n becomes higher than 25×10 -3 and to subsequent drawing at a temperature ranging from 80°C lower than the filament melting point to 5°C lower than the fusing point. The resultant fiber has a filament denier of less than 1, preferably less than 0.7 denier, the maximum heat stress on temperature-rising of less than 0.32, preferably less than 0.3g/d, crystal size of larger than 30, preferably 35Å, which is calculated by wide-angle X-ray diffraction and a crystal orientation angle of less than 10.5, preferably 10°. COPYRIGHT: (C)1981,JPO&Japio