| 摘要 |
PURPOSE: To obtain the subject film consisting of a polyester with specific chemical structure, excellent in thin film formability and durability at high humidity because of its low humidity expansion coefficient and hygroscopicity and excellent mechanical properties, thus useful for e.g. electrolytic capacitor separators, microfilters. CONSTITUTION: This film has structure of the formula (R1 , R2 and R3 are each a divalent hydrocarbon-based group such as 1,4-phenylene or ethylene; X, Y and Z are such as to satisfy the relationship: 0.01<=X<=0.9 in terms of molar fraction, assuming that Y=Z and (X+Y)=1), pref. having the following characteristics: porosity: >=20%; having fine pores communicating with both the surfaces; and humidity expansion coefficient: 50×10<-6> cm/cm/%RH uniaxially and/or biaxially.
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