Method of manufacturing of birefringent film and application of the film

Abstract

The present invention provides a method of manufacturing a birefringent film capable of manufacturing a birefringent film with a high production efficiency, while omitting the bowing phenomenon when manufacturing the birefringent film by stretching a polymer film in the widthwise direction, thereby limiting unevenness in birefringence, retardation and orientation angle and hence producing excellent optical characteristics, as well as achieving successive lamination when laminating with a polarizing film. The method of manufacturing the birefringent film including a step of stretching the polymer film, includes stretching the polymer film in the widthwise direction while at the same time shrinking the same in the lengthwise direction so as to satisfy the relational expression: (1 / STD)1 / 2<=SMD<1, in which the length in the widthwise direction and the length in the lengthwise direction, of the polymer film before being stretched are respectively designated as 1, and STD represents a change ratio of the length in the widthwise direction of the polymer film due to stretching and SMD represents a change ratio of the length in the lengthwise direction of the polymer film due to shrinking, and make the stretched polymer film have an Nz coefficient of 0.9-1.1.

Description

technical field [0001] The present invention relates to a method for producing a birefringent film, an optical film using the birefringent film, and various image display devices. Background technique [0002] In various image display devices such as liquid crystal display devices, a birefringent film is generally used for the purpose of improving display characteristics, for example, eliminating coloring or widening a viewing angle. [0003] Such a birefringent film is generally produced by uniaxially stretching or biaxially stretching a polymer film to adjust its birefringence or retardation. [0004] When such a birefringent film is used together with a polarizing film in a liquid crystal display device, the two films need to be arranged so that the slow axis of the birefringent film is substantially perpendicular to the absorption axis of the polarizing film. In addition, generally, the slow axis of the birefringent film coincides with the stretching direction thereof, ...

AI Technical Summary

Problems solved by technology

However, in such a method, after laminating a polymer film on a base material, the film is stretched by expanding together with the base material, and the film is shrunk to perform relaxation by returning the base material to its original width. However, it is difficult to effectively produce an industrially stable and uniform birefringent film due to problems such as a small relaxation effect through the polymer film

Also, attempts have been made to reduce the bending phenomenon by cooling after stretching, but the above phenomenon cannot be completely avoided (for example, Non-Patent Document 1)

[0011] As another method, a method of thermally shrinking the base material of the laminated polymer film by relaxing the base material of the laminated polymer film between the clips of the tenter stretching machine is also disclosed (for example, Patent Document 1), but the above-mentioned base material is limited to those having Heat-shrinkable substrates, especially when the thickness of the substrate is too thick, also have problems such as wrinkles when relaxed, and deviations such as birefringence on the polymer film.

In addition, methods for setting stretching conditions, such as a method of setting the width of a stretched film to the square root of the stretching ratio (for example, Patent Document 2), and adjusting the width of shrinkage associated with longitudinal stretching are also disclosed. prescribed method (for example, Patent Document 3), a method of performing thermal relaxation after stretching (for example, Patent Document 4), etc., but they all have the problem of being difficult to produce with high productivity

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