Optical compensation film, and polarizing plate and liquid crystal display employing the same

Abstract

The present invention provides an optical compensation film, which has excellent visibility such as light leakage, uneven color tone and front contrast, and can simultaneously realize retardation and wavelength dispersion. The optical compensation film is characterized by containing a cellulose ester, the following polymer (a), and the following compound (b). (a) A polymer produced by copolymerizing an ethylenically unsaturated monomer having in its molecule a partial structure represented by Formula (1) with at least one ethylenically unsaturated monomer. (b) An esterified compound produced by esterifying all or a part of OH groups in a compound (A) having one furanose structure or one pyranose structure, or an esterified compound produced by esterifying all of or a part of OH groups in a compound (B) containing nor less than 2 and not more than 12 structures of at least one of a furanose structure or a pyranose structure.

Description

[0001]This is a U.S. National Phase Application under 35 U.S.C. 371 of International Application PCT / TP2008 / 069447, filed on Oct. 27, 2008.[0002]This application claims the priority of Japanese application No. 2007-287153, filed Nov. 5, 2007, the entire content of which is hereby incorporated by reference.TECHNICAL HELD[0003]The present invention relates to an optical compensation film used for a liquid crystal display, in particular, relates in detail to an optical compensation film which is excellent in visibility (light leakage, color tone unevenness, front contrast), and compatible to both retardation and wavelength dispersion characteristic.TECHNICAL BACKGROUND[0004]A cellulose ester film, a polycarbonate film, a poly cyclic olefin film, and so on are widely used as an optical film for liquid crystal displays.[0005]Since the transparency of a cellulose ester film is optically high and also its birefringence is low, it has been mainly used as a protective film (hereinafter; refe...

AI Technical Summary

Benefits of technology

[0021]An optical compensation film having excellent visibility such as light leakage, color tone unevenness, front contrast and having compatibility of retardation and wave length dispersion properties can be provided by this invention.BEST EMBODIMENT TO PRACTICE THE INVENTION

[0022]The best embodiment to practice the invention is described in detail, however this invention is not restricted thereto.

[0023]The liquid crystal display elements generally have viewing angle characteristics, and there is problem of lowering contrast when observed remote angle from normal angle. It is known that it is effective to provide an optical compensation film (a phase difference film) between the crystal cell and a polarizer to dissolve this problem. It is preferable in general the retardation within a plane (Ro) in the range of 20 to 200 nm, and the retardation in the thickness direction (Rt) in the range of 70 to 400 nm.

[0024]The optical compensation film of this invention is characterized by comprising Polymer (a) manufactured by copolymerizing an ethylenically unsaturated monomer having a partial structure represented by Formula (1) in its molecule with at least one ethylenically unsaturated monomer, and esterified Compound (b) in which all or a part of OH groups in Compound (A) having one furanose or pyranose structure are esterified, or an esterified compound in which all or a part of OH groups in Compound (B), in which 2 to 12 of at least one type of furanose or pyranose structure are bonded, are esterified.

[0025]Further improvement of visibility such as front contrast is expected according to generalization of large format liquid crystal display recently. The inventors studied the above mentioned problem and found that improvement of visibility (light leakage color tone unevenness, front contrast) in addition to compatibility of retardation control and wave length dispersion property are attained by employing Polymer (a) obtained by copolymerizing ethylenically unsaturated monomer having a partial structure represented by Formula (1) in its molecule with at least one ethylenically unsaturated monomer, and accomplished this invention.

Problems solved by technology

However, even if such a technology is used, as an optical compensation film which serves as a polarizing plate protective film, it has an insufficient pasting ability with polyvinyl alcohol being a polarization film, and a polarizing plate protective film consisting of a cellulose ester film has been recognized to be an indispensable optical film in a liquid crystal display even now.

Basically, since cellulose ester film has the circumstances where it has been used as polarizing plate protective film due to its low birefringence characteristic, it may be not easy to provide the function.

In order to acquire a desired retardation value, a technique to add a compound having a retardation increasing effect to a cellulose ester film and to further stretch the film is proposed (Patent Documents 1 and 2), but there are problems that the wavelength dispersion characteristic does no stabilize over time and the permeability of the film is deteriorated by the stretching.

If the wavelength dispersion characteristic is insufficient, phenomena such as light leakage from a polarizing plate (especially light leakage with an elapse of time), uneven color tone of an image on a liquid crystal display and front contrast deterioration occur.

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