BIAXIALLY ORIENTED MULTILAYER FILM

摘要

Disclosed is a biaxially oriented multilayer polyester film which has dimensional stability against environmental changes such as temperature change or humidity change, while exhibiting low elongation when a load is applied thereto under high temperature conditions. The biaxially oriented multilayer film is obtained by laminating a film layer (A) which is composed of an aromatic polyester (A) and a film layer (B) which is composed of an aromatic polyester (B). This biaxially oriented multilayer film is characterized in that the ratio of 6,6'-(alkylenedioxy)di-2-naphthoic acid content represented by formula (I) in the total acid content is less than 5% by mole in the aromatic polyester (A), while the ratio is not less than 5% by mole but less than 80% by mole in the aromatic polyester (B). The biaxially oriented multilayer film is also characterized in that the tan d peak on the high temperature side as determined by viscoelasticity in the film-forming direction is not less than 135°C. (In the structural formula (I), R represents an alkylene group having 1-10 carbon atoms.)