Liquid crystal display devices are presently widely used as display devices which can realize thin structure/light weight. The display characteristics of liquid crystal display devices are known to be substantially influenced by the alignment of liquid crystal, the pretilt angle of liquid crystal, the stability of the pretilt angle, electrical characteristics, etc. In order to improve the display characteristics of such liquid crystal display devices, not only the liquid crystal material to be used but also the liquid crystal alignment film which uniformly aligns the liquid crystal becomes important. If the liquid crystal alignment film has low liquid crystal alignment properties, image failure may occur, and if the alignment controlling power of liquid crystal is low, the liquid crystal which has been continuously driven will not recover to the initial state, thus causing persistence of the displayed image. Further, the liquid crystal alignment film also has an influence over the voltage retention characteristics and the charge accumulation characteristics when the liquid crystal is driven. If the voltage retention is low, the contrast on the displayed image may decrease, and if accumulation of the charge against a DC voltage is significant, persistence of the displayed image may occur. Further, a rubbing treatment is presently commonly carried out for formation of a liquid crystal alignment film. If the rubbing resistance of the liquid crystal alignment film is low, the film may be separated or the film surface may be scraped away by rubbing, which may cause display failure.
In order to solve such problems as peeling of the film by rubbing, the liquid crystal alignment properties and the voltage retention characteristics, a liquid crystal alignment film comprising a mixture of a polyamic acid having an alkylene structure at the diamine moiety and a polyamic acid having an aliphatic structure at the tetracarboxylic acid moiety has been proposed (e.g. JP-A-11-264984, JP-A-11-335461). However, characteristics required for a liquid crystal alignment film become strict along with an improvement in performance of liquid crystal display devices, and it becomes difficult to satisfy all the required characteristics only with conventional technique.