JP2609139B2 - Laminated retarder - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises a laminate of birefringent films, and can easily control the wavelength characteristic of birefringence, and is suitable for preventing coloration of a birefringent liquid crystal display. The present invention relates to a multilayered phase difference plate.

BACKGROUND OF THE INVENTION The use of a high-contrast liquid crystal display utilizing the birefringence of an STN (Super Twisted Nematic) liquid crystal has increased the size of a screen in a personal computer, a wad processor, and the like. Such displays are STN
With elliptically polarized light based on the birefringence of liquid crystal, the display via a polarizing plate is generally colored in a greenish or yellowish system. Therefore, means for compensating for the phase difference due to the birefringence of the STN liquid crystal and returning the elliptically polarized light to the linearly polarized light to cancel the coloring are taken. As a means therefor, a method using a retardation plate made of a birefringent film has been proposed. This method is called the FTN method, etc., and enables a monochrome display using a single-layer cell, and superimposes a separate liquid crystal cell on the D-ST.
The bulky and heavy weight problems of the N method are solved.

In order to cancel the coloring of the display by the above-mentioned FTN method and realize a good black-and-white display, it is required that the compensation by the retardation plate, including the birefringence depending on the wavelength, be highly matched.

Conventional technology and problems Conventionally, as a retardation plate composed of a birefringent film,
A monolayer film of a uniaxially or biaxially stretched plastic film has been known.

However, it has been difficult to obtain a retardation plate having a necessary birefringence wavelength characteristic as a single-layer birefringent film. In particular, it was very difficult to mass-produce as a large area product. That is, the birefringence of the birefringent film changes depending on the stretching conditions. Further, the same stretching conditions vary depending on the film material. Further, the birefringence varies depending on the wavelength of light even for the same birefringent film. Therefore, when a wavelength-dependent retardation to be compensated is determined in advance as in the above-described STN liquid crystal cell, to obtain a single-layer film-based retardation plate that performs compensation highly consistent with this, it is necessary to use a film. It is necessary to control the thickness and stretching conditions with high precision while maintaining good transparency, and there is a problem that processing is difficult and yield and mass productivity are poor. In addition, in order to obtain a single-layer film that compensates for a predetermined retardation, there is a problem that it is necessary to know in advance the change characteristics of the birefringence based on the film material and its stretching conditions. . Therefore, without such knowledge, the production of a necessary retardation plate requires enormous trial and error, and in such a case, there is no guarantee that the required retardation plate can be obtained.

Means for Solving the Problems The present invention obtains a new finding that the wavelength characteristics of the birefringence can be controlled by laminating two or more birefringent films having different characteristics. It has overcome the challenges.

That is, the present invention comprises a laminate of two or more of birefringent films made of a transparent stretched plastic film in a combination having different wavelength dependences of retardation due to birefringence, and two types of birefringence. In the case of a laminate of functional films, the maximum direction of their in-plane refractive indices is in a non-orthogonal relationship in a combination of those having different signs of orientation birefringence,
Another object of the present invention is to provide a laminated retardation plate characterized in that the orientation birefringence has the same sign.

Action Combination with different wavelength dependence of phase difference due to birefringence 2
By forming a retardation plate by laminating at least two or more kinds of transparent birefringent films, the wavelength characteristics of the birefringence in each birefringent film can be superimposed or adjusted, and can be controlled. The control can be performed by changing the combination of the birefringent films, changing the intersection angle of the optical axes in the laminated film, and the like. As a result, a retardation plate having a required birefringence wavelength characteristic can be easily formed using a birefringent film having known properties.

EXAMPLES The laminated retardation film of the present invention is obtained by laminating two or more birefringent films. As the birefringent film, a transparent stretched plastic film stretched uniaxially or biaxially is used. Lamination is performed in a combination in which the wavelength dependence of the phase difference due to birefringence is different. By laminating two or more types of birefringent films having different birefringence wavelength characteristics, the overall birefringence wavelength characteristics can be adjusted. FIG. 1 shows a configuration example of the laminated retardation plate. 1 and 3
Are birefringent films having different wavelength dependences of retardation due to birefringence, and 2 is a transparent adhesive layer.

There is no particular limitation on the transparent stretched plastic film forming the birefringent film. Any known transparent stretched plastic film having birefringence can be used.

The combination and the number of laminated layers of birefringent films having different wavelength dependences of the phase difference due to birefringence can be appropriately determined according to the wavelength characteristics of the required birefringence, or the phase difference to be compensated. A laminate using two or three or more birefringent films can be used. In that case, 3
In the case of a laminate using two or more types of birefringent films, the type of combination and the lamination relationship based on the maximum direction of the in-plane refractive index can be arbitrarily determined. On the other hand, in the case of a laminate of two types of birefringent films, the combination of those having the same positive or negative orientation birefringence depending on whether the maximum direction of the in-plane refractive index appears in the stretching direction or appears perpendicular to the stretching direction. The lamination relationship based on the maximum direction (stretching direction) of the in-plane refractive index can be arbitrarily determined. However, in the case of a combination of those having different orientation birefringence, that is, a combination of one having a positive and negative orientation birefringence, The layers are in a stacked state having a parallel function or an intersecting relationship other than orthogonal, in which the maximum directions of the in-plane refractive indices are non-orthogonal. The smaller the number of layers, the more advantageous it is in terms of the transparency of the formed laminated retardation plate. Lamination may be performed partially on the base birefringent film as required. The partial lamination may be performed by an appropriate method such as a method of previously arranging and bonding a suitable continuous medium such as an isotropic film and laminating the same on a base film. An adhesive or a pressure-sensitive adhesive is usually used for laminating the birefringent films. Those having good transparency such as an acrylic adhesive or a pressure-sensitive adhesive are preferably used. A birefringent film which does not require a drying treatment at a high temperature and does not change the birefringence characteristics of the birefringent film is preferably used. From the viewpoint of not requiring a drying treatment, a material which can be coated without a solvent by a suitable coating machine such as a squeeze coater can be preferably used. From the viewpoint of preventing deterioration of the birefringent film, a method of transferring an adhesive layer provided on a separator can be preferably applied.

The retardation of the formed laminated retardation plate depends on the used birefringent film, its thickness, the wavelength of incident light, and the like.

FIG. 2 illustrates the wavelength dependence of the phase difference. The laminated retardation plate used was a stretched polycarbonate film having a birefringence of 0.003 and a thickness of 100 μm with respect to light having a wavelength of 633 nm and a stretched cellulose acetate film having a birefringence of 0.001 and a thickness of 150 μm. They are laminated so that the crossing angle of the in-plane refractive index (the maximum direction of the in-plane refractive index based on the stretching process) is 0 degree or 90 degrees. Curve I is the case where the intersection angle is 0 degree, and curve II is the same.
90 degrees. Even the same combination of birefringent films has different characteristics due to differences in the crossing angles of the optical axes. Curve I approximately corresponds to the sum of the retardation of each birefringent film. Curve II substantially corresponds to the case where the retardation due to the stretched cellulose acetate film is reduced by the retardation due to the stretched polycarbonate film. When the crossing angle of the optical axis is between 0 and 90 degrees, there is a phase difference between the curves I and II. In addition, the curve PC is a stretched polycarbonate film,
Curve Cel shows the wavelength dependence when each stretched cellulose acetate film is used alone.

The laminated retardation plate of the present invention can be preferably used for forming an FTN black-and-white display excellent in contrast by canceling coloring due to retardation in a display using a birefringent liquid crystal cell such as an STN liquid crystal cell.

FIG. 3 shows a configuration example of an FTN type display.
Reference numerals 4 and 7 denote polarizing plates, 5 denotes a laminated retardation plate, 6 denotes a display panel comprising a birefringent liquid crystal cell, and the polarizing plate 4 side is the viewing side. Incidentally, 51 is an adhesive layer.

Effects of the Invention According to the laminated retardation film of the present invention, it is possible to provide a birefringence index or a wavelength characteristic of retardation that cannot be realized by a single-layer birefringent film. In addition, a birefringent film or a retardation having different wavelength characteristics can be provided by using a birefringent film having known characteristics, and a wide range of film materials can be selected when obtaining necessary characteristics. Furthermore, the manufacture of large-area objects and the like is easy. As a result, it is possible to easily obtain a retardation plate having necessary wavelength characteristics in terms of birefringence or retardation and excellent in transparency with easy processing and small labor.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a configuration example of a laminated retardation plate, FIG. 2 is a graph showing the wavelength dependence of a phase difference in the embodiment, and FIG. 3 is a cross-sectional view showing a configuration example of an FTN type display. is there. 1,3: birefringent film 2: adhesive layer 4, 7: polarizing plate 5: laminated retardation plate 6: display panel Curve I: when the optical axis crosses at 0 degree Curve II: when the optical axis crosses the angle At 90 degrees PC: For stretched polycarbonate film Cel: For stretched cellulose acetate film

Claims (2)

(57) [Claims] 1. A birefringent film comprising a transparent stretched plastic film and two or more birefringent films laminated in a combination having different wavelength dependences of retardation due to birefringence, and two types of birefringent films. In the case of a film laminate,
A laminated retardation plate comprising a combination of different orientation birefringences in which the maximum directions of the in-plane refractive indices are non-orthogonal or a combination of orientation birefringences having the same sign. 2. The laminated retardation film according to claim 1, wherein the laminated retardation film is formed so as to compensate for the retardation in the birefringent liquid crystal cell.