OPTICAL FILM AND ITS PRODUCING METHOD

PROBLEM TO BE SOLVED: To provide an optical film and its producing method which can improve the quality of the optical film by prescribing frequency and depth (intensity) of recessed shaped longitudinal streaks appearing after being stretched and can largely upgrade the quality of a display device without allowing streak-like contrasting to appear on a display device regarding the optical film as a various kinds of function films such as a protective film, a phase difference film and an antireflective film used for a liquid crystal display device or the like. SOLUTION: The optical film is taken up through the step of stretching an unstretched film in the range of 1.3 times or more and 5.0 times or less to the film width direction (lateral direction) by a melt casting film forming method. The number of recessed shaped longitudinal streaks extending to the film lengthwise direction (longitudinal direction) of depth of 100 nm or more and 500 nm or less contained every 10 cm of the film width direction is one or less. COPYRIGHT: (C)2009,JPO&INPIT