Optical film manufacturing method, optical film manufacturing apparatus and optical film

#This application is based on Japanese Patent Application No. 2005-304567 filed on Oct. 19, 2005, in Japanese Patent Office, the entire content of which is hereby incorporated by reference.

#The present invention relates to an optical film manufacturing method and an optical film manufacturing method for manufacturing an optical film used in various forms of display apparatuses such as a liquid crystal display apparatus (LCD) or organic electroluminescent display, particularly to an optical film having a birefringence and used for a polarizing plate protecting film used in these display apparatuses and a retardation film.

#Generally, a liquid crystal display apparatus is basically arranged in such a way that a polarizing plate is provided on both sides of the liquid crystal cell. The polarizing plate permits the passage of only the light on the plane of polarization in a predetermined direction. It plays a major role in the liquid crystal display apparatus in the sense of making visible a change in the light distribution of the liquid crystal due to an electric field. The performances of the liquid crystal display apparatus greatly depends on the performance of the polarizing plate.

#FIG. 1 is a partially enlarged perspective view representing the first embodiment of the film drying zone of the solution-casting film-forming apparatus for embodying the optical film manufacturing method of the present invention;

#FIG. 2 is a partially enlarged front view in FIG. 1;

#FIG. 3 is a partially enlarged front view representing a variation of the dry air spraying header in the film drying zone of FIG. 1;

#The following describes the best form of embodiment of the present invention without the present invention being restricted thereto:

#In the method of manufacturing an optical film of the present invention, a dope in which a thermoplastic resin film material is dissolved in a solvent is cast onto a support member from a casting die, and the solvent is evaporated on the support member so that a web is formed. After that, the web is separated, and is conveyed by a conveyance roll. Then the web is dried in a drying zone, whereby an optical film is produced. Even if there is unevenness in characteristic in connection to the web (such as a fine variation in film thickness and unevenness along a lateral direction of a film producing apparatus) in a drying zone, this method corrects the unevenness (the lack of uniformity).

#According to the present invention, in a solution-casting film-forming method, lack of uniformity in characteristic in connection to a web such as a thickness, a conveyance tension and a retardation value along the lateral direction of the film during a film production are measured on on-line basis, and the temperature, velocity or volume of the drying air along the lateral direction of the film in a drying process are adjusted so as to reduce the aforementioned lack of uniformity. This procedure ensures high-precision uniformity in the optical value required of an optical film.