Unitika Ltd.

Shouji Miyazaki

Shigemitsu Murase

Masaru Sugawa

Kouji Kakumoto

Mikio Ide

Melt-spun polyester fibers are taken up in the absence of heat at a speed of 5,000 to 6,000 m/min under conditions that satisfy the following relations (IX) and (X), subsequently heat-treating the fibers for a period of from 0.01 to 0.05 seconds with a heating roller while the length of the melt-spun fibers is held constant with no drawing step being provided between the taking up and heat treatment steps, and finally winding up the heated fibers

Process for producing polyester fibers

A polyester fiber and process embodiments for the production thereof are described, wherein the polyester fiber is produced by high-speed spinning and is characterized by a filament fineness of from 1 to 3 d, a strength of at least 4.0 g/d, an elongation of up to 40%, a crystallinity (X.rho.) of from 40 to 55%, a birefringence of from 140.times.10.sup.-3 to 165.times.10.sup.-3, an orientation function of from 0.36 to 0.45 in the amorphous portion, and a thermal shrinking stress that satisfies the relations

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Kyoto, Japan

Shouji Miyazaki