| 摘要 |
PROBLEM TO BE SOLVED: To obtain a polyester film having high strengths and excellent hot dimensional stability by blending a non-liquid crystal polyester with a copolyester having mesogenic groups in the main chain on condition that the copolyester used has a specified glass transition temperature. SOLUTION: The glass transition temperature of the copolyester used should be 75-110 deg.C. It is desirable that the copolyester polyester is one comprising structural units of formulae I, II, III, and IV. In formula II, R1 is formula V, formula VI, or the like. Although the copolymerization ratio is arbitrary, it is most desirably such that the structural units of formula I account for 40-85 mol% of the total structural units of formula I and formula II when the structural units are ones of formula I, III, and IV. It is desirable that the copolymerization amount of the mesogenic groups in the main chain of the copolyester is 5-95 mol%, the ratio of the melt viscosity of the non-liquid crystal polyester to that of the copolymer polyester is 5 or above, and the copolymer polyester content is 0.1-20 wt.%.
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