NOVELTY - A polyimide film is manufactured from a copolymer of an aromatic di-anhydride and an aromatic diamine, and has an average coefficient of linear thermal expansion of less than or equal to 35 ppm/ degrees C, when measured at 50-250 degrees C for a film thickness of 50-100 mu m according to a TMA method, with a yellowing index of less than or equal to 15.    USE - As polyimide film in a substrate for a display; in an alignment layer; in a protective film (claimed); for LCDs; in various fields including semiconductor insulating films, TFT-LCD insulating films, passivation films, liquid crystal alignment layers, optical communication materials, protective films for solar cells and flexible display substrates; in various fields of application including advanced heat resistant materials such as automobile materials, aircraft materials and spacecraft materials and electronic materials such as insulation coating agents, insulating films and electrode protective films of TFT-LCD; for display materials such as optical fibers and transparent electrode films; and as substrate for color filter.    ADVANTAGE - The film has an average coefficient of linear thermal expansion of less than or equal to 35 ppm/ degrees C, when measured at 50-250 degrees C for a film thickness of 50-100 mu m according to a TMA method, with a yellowing index of less than or equal to 15. The film has an average transmittance of greater than or equal to 85% at 380-780 nm, when measured using a UV spectrophotometer for the film thickness of 50-100 mu m; has a transmittance of greater than or equal to 88% at 550 nm and a transmittance of greater than or equal to 70% at 440 nm, when measured using a UV spectrophotometer for the film thickness of 50-100 mu m; has a 50% cut-off wavelength of less than or equal to 400 nm, when measured using UV spectrophotometer; and has color coordinates in which L is greater than or equal to 90, a is less than or equal to 5 and b is less than or equal to 5, when measured using a UV spectrophotometer for the film thickness of 50-100 mu m. The film is colorless and transparent; and has superior mechanical properties and high thermal stability.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for preparation of the film involving polymerizing the diamine and the dianhydride in presence of a first solvent, thus obtaining a polyamic acid solution; imidizing the polyamic acid solution; adding the imidized solution to a second solvent; performing filtration and drying, thus obtaining a solid polyimide resin; and dissolving the solid polyimide resin in the first solvent, thus preparing a polyimide solution, which is then subjected to a film forming process.