METHOD FOR PRODUCING AROMATIC POLYIMIDE FILM WHEREIN LINEAR EXPANSION COEFFICIENT IN TRANSVERSE DIRECTION IS LOWER THAN LINEAR EXPANSION COEFFICIENT IN MACHINE DIRECTION

摘要

Disclosed is a commercially easily practicable method for producing an aromatic polyimide film wherein the linear expansion coefficient in the transverse direction (TD) is lower than the linear expansion coefficient in the machine direction (MD). A self-supporting aromatic polyimide precursor film used in the production of the aromatic polyimide film is so adjusted as to have a solvent content within the range of 25-45% by mass and an imidization ratio within the range of 5-40%.  While heating the self-supporting aromatic polyimide precursor film, stretching of the precursor film in the transverse direction is started at a temperature within the range of 80-240°C, and the stretched self-supporting aromatic polyimide precursor film is converted into a self-supporting aromatic polyimide film at a temperature within the range of 350-580°C.