Dimethyl 2,6-naphthalenedicarboxylate and dimethyl sebacate were dispersed in ethylene glycol and an addition product of two ethylene oxides tobisphenol A (BPA•2EO). Then, 0.029 part of manganese acetate tetrahydrate, 0.028 parts of antimony trioxide and 0.1% of spherical silica particles having a mean particle size of 0.3 μm were added to 100 parts of the total of dimethyl 2,6-naphthalenedicarboxylate and dimethyl sebacate, and heated with stirring to conduct the reaction. The temperature was elevated to 235° C. while removing methanol produced as a by-product. After the by-production of methanol was completed, 0.03 part of trimethyl phosphate was added thereto. Then, the pressure was reduced to 0.3 Torr while elevating the temperature to 285° C. to conduct the polymerization by changing the reaction time. Dyes described in JP-A-7-168309, compounds I-6 and I-24, were each further added to the solid matter in an amount of 54 ppm. The copolymerization composition ratios of sebacic acid (SA) and BPA•2EO and the intrinsic viscosities of polyesters thus obtained are shown in Table II-1.
