Toyo Boseki Kabushiki Kaisha

Yuziro Matsuyama

Katsuaki Kuze

Osamu Makimura

Hiroshi Hashimoto

Takeshi Ohta

Ryuichi Murashige

Yoshio Yamaoka

A polyester having an initial accumulation electric charge of not less than 2.9 .mu.c/mm.sup.2 when determined in a melt state according to the method as hereinabove defined and a heat resistance of not more than 0.210 when determined according to the method as hereinabove defined, which comprises at least one magnesium compound and at least one phosphorus compound solubilized therein in amounts as satisfying the following formulas:

Polyester composition

A process for production of a polyester comprising units of ethylene terephthalate as the major repeating units by supplying terephthalic acid and ethylene glycol continuously or intermittently to bis(beta-hydroxyethyl) terephthalate or its oligomer so as to carry out esterification under a pressure of not more than about 1.0 kg/cm.sup.2, followed by polycondensation, which is characterized in that at least one magnesium compound is incorporated into the reaction system in an amount of about 30 to 400 ppm in terms of Mg to the polyester when the esterification rate in the step of esterification reaches about 20-80% and at least one phosphorus compound is incorporated into the reaction system in an amount as satisfying the following equation (I) at the stage after the esterification rate reaches not less than about 91% and before the termination of the initial condensation in the step of esterification:

Process for production of polyester

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Shiga, Japan

Yuziro Matsuyama