Cellulose ester film, process for producing cellulose ester film, optical film, polarizing plate and liquid crystal display unit

Abstract

The invention provides a cellulose ester film that excels in uniformity of retardation as an optical property, especially uniformity of retardation in the direction of film width, and further contrast; a process for producing such a cellulose ester film; and making use of the film, an optical film, polarizing plate and liquid crystal display unit. There is provided a process characterized by subjecting, to melting film formation, a solid cellulose ester having been suspension washed with a poor organic solvent to cellulose ester in the presence of an antioxidant so that the content of free acids in the cellulose ester is 50 ppm or less.

Description

technical field [0001] The present invention relates to cellulose ester film, the manufacture method of cellulose ester film, optical film, polarizer and liquid crystal display device, more specifically, the present invention relates to cellulose ester film, the manufacture method of cellulose ester film, described fiber The retardation uniformity as the optical characteristic of the plain ester film, especially the retardation uniformity in the film width direction is favorable, and contrast is also favorable. Background technique [0002] Liquid crystal display devices (LCD) can be directly connected to IC circuits at low voltage and low power consumption, and can be particularly thinned. Therefore, they are widely used in word processors, personal computers, televisions, monitors, and portable information terminals. and other display devices. The basic structure of such an LCD is, for example, to arrange polarizing plates on both sides of a liquid crystal cell. [0003]...

AI Technical Summary

Problems solved by technology

[0007] In short, the current situation of cellulose ester films for optics is that there are manufacturing burdens and equipment burdens due to the use of solvents in the manufacturing process, and the optical properties and mechanical properties are not sufficient.

[0008] In terms of methods for removing impurities contained in cellulose esters, the following method has been disclosed: a method of washing powdery cellulose esters with water or a poor solvent (see, for example, Patent Document 6), but the current situation is that the impurities cannot be sufficiently removed. Acetic acid removes impurities, but its concentration is still 200ppm. Films using these cellulose esters have insufficient optical and mechanical properties. The current problem is that impurities must be removed.

[0009] In recent years, attempts to melt film-form cellulose ester films have been used for silver halide photography (see, for example, Patent Document 7) or polarizer protective films (see, for example, Patent Document 8), but there is a problem that fibers Vegetarian ester is a polymer with very high viscosity when melted, and its glass transition temperature is also high. Therefore, even if the cellulose ester is melted, extruded from the die, and then cast on a cooling drum or a cooling belt, It is still difficult to level, but it solidifies in a short time after extrusion, so the haze, bright spot foreign matter, etc. Uniformity, etc., are lower than solution cast film

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