Optical film, method for producing the same and polarizing plate using the same

Abstract

A method for producing an optical film comprising the steps of: (i) melt casting a cellulose ester resin or a cycloolefin resin by extruding melt of the cellulose ester resin or the cycloolefin resin from a die onto a roll-shaped cooling drum; (ii) cooling and solidifying the extruded melt to form a film; (iii) stretching the film in a lateral direction of the film; and (iv) winding the film in a roll, wherein the cooling drum has plural regions divided predeterminedly in an axis direction of the cooling drum, a temperature of each region being independently controlled.

Description

[0001] This application is based on Japanese Patent Application No. 2005-092168 filed on Mar. 28, 2005 in Japanese Patent Office, the entire content of which is hereby incorporated by reference. FIELD OF THE INVENTION [0002] The present invention relates to an optical film which can be applied for various kinds of functional film such as a polarizing plate protective film, a retardation film and a viewing angle extending film used for a liquid crystal displaying (LCD), an antireflection film for a plasma display, as well as a functional film for an organic EL display, and also relates to a method for producing such an optical film and to a polarizing plate using the optical film. BACKGROUND OF THE INVENTION [0003] Liquid crystal display has been widely applied as a monitor since it is space saving as well as energy saving compared to the conventional CRT display. Moreover, liquid crystal display is also becoming popular as a TV. Various kinds of optical films such as a polarization ...

AI Technical Summary

Problems solved by technology

However, the method has a problem such as that the large equipment is necessary for drying the solvent.

This method has an advantage that the equipment can be made relatively compact because the drying of solvent is not necessary, while having a disadvantage in that the obtained film is not fully satisfactory in the uniformity in the film thickness and in the retardation values.

However, a problem is posed that, when the films (unstretched films) obtained by the methods described in Patent Documents 1 and 2 are each stretched in the lateral direction and when the film is observed under crossed nicols condition, the darkness of the observing field is not uniform and unevenness of the darkness is observed.

Moreover, a problem is posed on such the methods that the thickness distribution in the lateral direction of the stretched film cannot be controlled because the thickness profile of the film in the lateral direction is decided by the distance between the cooling roller and the endless belt or the space between the cooling drums.

A problem is also posed that the darkness of the observing field is not uniform and unevenness of the darkness is observed when the film (unstretched film) obtained by the method described in Patent Document 3 is stretched in the lateral direction and observed under crossed nicols condition.

Moreover, the thickness profile of the film cannot be freely controlled by the method since the resin film is in contact with the drum at a temperature near the glass transition point (Tg) of the resin.

Regarding the method described in Patent document 4, a problem is posed that, when the distance between the cooling drum and the die is increased, undulation appears on the surface of the film in molten state, whereby flatness of the film deccreses.

The methods described in Patent Documents 5 and 6 are each the method for controlling the stretching conditions and the thickness, however, the control of the retardation of the film in the lateral direction has not been fully easy.

The method described in Patent Document 7 is a method to reduce the optical distortion at the central portion of the film while the film is formed by passing through two cooling rollers, however, it has not been fully easy to improve the uniformity in thickness or in retardation of the film.

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