Process for spinning naphthalate polyester fibers

Claim 1

A process for producing a naphthalate polyester filament, fiber or yarn having a diffraction intensity ratio (R) between a Bragg reflection angle 2θ = 18.7° and 2θ = 15.6° , as determined by the X-ray diffraction method, being in the range of more than 1.73 and up to 5.00, which comprises melt-spinning a naphthalate polyester containing at least 85 mol % of ethylene-2,6-naphthalate units and having an intrinsic viscosity of 0.45 to 1.0, using a spinning nozzle having a cross sectional area of 0.049 to 3.14 mm 2 per hole at a spinning temperature expressed by the following equation: 28.6 [η] + 301.4 ≧ T ≧ 35.7 [η] + 279.3 wherein T is the spinning temperature in ° C. and [η] is the intrinsic viscosity of the polyester, said spinning being at a draft ratio of 50-20,000 and the draft ratio satisfying the following equation: -7.43 × 10.sup.-.sup.5 W + 2.37 ≦log D ≧2.27 √A + 1.98 wherein W is the take-up speed in meters per minute, D is the draft ratio, and A is the cross-sectional area in square millimeter per hole of the spinning nozzle, and then cooling the extruded filaments, and taking up the extruded filaments by Godet rollers at a speed of 3,000 to 8,000 meters per minute.