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

摘要

An aromatic polyimide film having a TD linear expansion coefficient lower than that MD linear expansion coefficient is produced by an industrially advantageous process which is performed under such conditions that a self-supporting aromatic polyimide precursor film having a solvent content 25-45 wt % and an imidation ratio 5-40% is prepared and stretched in the transverse direction under heating initially at 80-240° C. and the stretched self-supporting aromatic polyimide precursor film is subsequently converted to a self-supporting aromatic polyimide film by heating the precursor film at 350-580° C.