Production of low shrink polyester fiber

A melt-spinning process for production of a low shrinkage polyester yarn having uniform properties of breaking strength in grams per denier of at least 7.0, and a residual thermal shrinkage measured in an oven at 350.degree. F. for 1 minute of 0.8 to -0.7 percent, which comprises:

• supplying a melt of high molecular weight, linear polyester polymer at a temperature below the spinning temperature and at a high pressure to a spinning unit comprising a spinning pump, a spinneret, and a spinning filter disposed between said pump and said spinneret;
• passing said melt by means of said spinning pump through said spinning filter prior to said melt passing through said spinneret whereby the temperature of the melt is increased to about 305.degree. to 310.degree. C.;
• extruding the melt at a rate of 50 to 90 pounds per hour downwardly through a spinneret having a plurality of extrusion orifices to form filaments;
• advancing the extruded filaments downwardly through a substantially stationary column of air having a temperature of 100.degree. to 330.degree. C. and a height of from 1 to 1.5 feet immediately below the spinneret, the average distance between adjacent filaments immediately below the spinneret being 0.28 to 0.4 inch;
• subsequently advancing the filaments downwardly through a quenching zone wherein they are in contact with a cross flow of cooling air introduced into the path of the filaments at a temperature not above 35.degree. C., said air contacting the filaments at a volumetric rate of 100 to 800 cubic feet of air per pound of filaments entering the quenching zone, whereby the temperature of the filaments is reduced to not over 55.degree. C.;
• lubricating the cooled filaments at a temperature of 40.degree. to 60.degree. C. by surface contact with a roll surface at a contact angle of about 10.degree. to 12.degree., said roll having a surface of 140 to 160 RMS;
• passing the lubricated filaments over a forwardly roll system maintained at a temperature of less than 50.degree. C.;
• heating the filaments substantially immediately above their second order transition temperature;
• drawing the filaments substantially instantly by passing said filaments over a draw roll system maintained at a temperature of between about 130.degree. and about 190.degree. C.;
• heat treating the drawn filaments by passing said filaments for 144-192 milliseconds over a heated roll system maintained at a temperature in the range of about 246.degree. to about 249.degree. C., said filaments being maintained at a tension in grams of between about 0.045 and about 0.075 gram per denier;
• and winding up said filaments.