PURPOSE: To obtain a biaxially oriented polyester film having high modulus and excellent dimensional stability, by blending two polyesters and molding the blend into a film having a specified coefficient of face orientation and a specified crystalline size.
CONSTITUTION: The titled film is obtd. from a blend of a polyester (A) composed of units of formulas I and II and a polyester (B) having a flow temp. of 200W350°C and liquid crystal forming properties. The film is a biaxially oriented polyester film wherein the blending ratio of the polyester (B) is 1W15wt%, one face of the crystal of the polyester (A) is face-oriented in the film face, a coefficient of orientation of the crystal face is 0.75W0.95 and crystalline size in the direction of the crystal face is 40W75. In the formula, n is 2,4 or 6 ; R is 2,6-naphthalene, a group of formula I or II. A polymer contg. structural units of formulas V and VI is particularly preferred as the polyester A.
HOTTA KUNIHIRO
MINAMI TOMOYUKI
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