Nippon Ester Co., Ltd.

Ichiro Fukami

Hideo Kawamura

Shuhei Wada

Fusayuki Yoshikawa

In a process for continuously producing polyester which comprises continuously polymerizing bis-.beta.-hydroxyethyl terephthalate and/or a lower polymer thereof using a plurality of vacuum polymerization reactors equipped with a stirrer disposed in series, the improvement which comprises automatically and continuously measuring stirring power or stirring axis reaction force of at least the final polymerization reactor among the polymerization reactors from which a polymer having a limiting viscosity (.eta.) of 0.25 or more is removed, and controlling the vacuum in the polymerization reactors based on changes in the stirring power or reaction force so that the stirring power or reaction force is kept at a prescribed level, by which the degree of polymerization of the polymer removed from the polymerization reactors is controlled. A process for producing a polyester spun fiber is also disclosed.

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Okazaki, Japan

Ichiro Fukami