A spun polyester fiber, a drawn polyester yarn, and methods for making
them. Polyethylene terephthalate yarn is prepared by extruding a molten
melt-spinnable polyethylene terephthalate having an intrinsic viscosity
of at least about 0.8 through a shaped extrusion orifice having a
plurality of openings to form a molten spun yarn; solidifying gradually
said molten spun yarn by passing said molten spun yarn through a
solidification zone which comprises (i) a retarded cooling zone and (ii)
a cooling zone adjacent said retarded cooling zone where, in said cooling
zone, said yarn is rapidly cooled and solidified in a gaseous atmosphere;
withdrawing at sufficient speed said solidified yarn from said
solidification zone to form a crystalline partially oriented yarn; and
hot drawing said crystalline partially oriented yarn at a total draw
ratio between about 1.5/1 and about 2.5/1 to produce a drawn yarn having
an effective crosslink density (N) between about 10.times.10.sup.21 and
about 20.times.10.sup.21 crosslinks per cubic centimeter. The yarns and
fibers so prepared may be used to make treated tire cord having high
tenacity in combination with improved dimensional stability.