JPH02130522A - Phase plate having lamination structure and liquid crystal display element using same - Google Patents

Abstract

PURPOSE:To obtain uniform refractive index anisotropy to large area by constituting the phase plate by laminating drawn plastic films which have refractive index anisotropy in a film surface so that a main optical axis having a large refractive index between two optical main axis directions in each film surface is mutually parallel. CONSTITUTION:The phase plate 1 is constituted by laminating the drawn plastic films 1a-1c which have small retardation. Then, those films 1a-1c are laminated so that the main axis X(X1, X2, X3) in the direction where the refractive index is large between the optical main axes (X1, X2, X3) and Y(Y1, Y2, Y3) (where nX is the X-directional refractive index and nY is the Y-directional refractive index and nX is larger than nY. Thermoplastic high polymer films of polycarbon ate, polystyrene, etc., in addition to polyvinyl alcohol and cellulose triacetate are usable as films 1a-1c. Further, the films may be made of a mixture of them. Consequently, the refractive index anisotropy is uniformed to large area.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention relates to a phase plate having a laminated structure.
onplate) and a liquid crystal display element using the same.

[Conventional technology]

This type of phase plate has the function of converting linearly polarized light into circularly polarized light or elliptically polarized light, vice versa, converting circularly polarized light or elliptically polarized light into linearly polarized light, or rotating the plane of polarization. Therefore, in liquid crystal display elements, a phase plate is used for color compensation or viewing angle compensation by applying the above principle.

This phase plate is STN (supertwisted n
(ematic) mode and ECB (electrica) mode.
lly controlled birefringe
It is mainly used in birefringence modes such as TN (twisted nematic) mode, which compensates for interference colors caused by birefringence and makes the display black and white.
Even when used in mode, slight coloring can be eliminated (Japanese Utility Model Publication No. 62-94316).

FIG. 2 is a sectional view showing the structure of a liquid crystal display element using a phase plate for color compensation. In the figure, 11 is a light-transmitting first substrate, 21 is a light-transmitting second substrate, and each of the substrates 11 and 21 is an alignment film 12, 2 that has been subjected to alignment treatment.
2 and transparent electrodes 13, 23, both substrates 11 and 21 are arranged facing each other and separated from each other, and a liquid crystal is sealed between them to form a liquid crystal layer 14, thereby forming a liquid crystal cell A. Reference numeral 15 indicates a peripheral sealant, and this liquid crystal cell A is attached to the first polarizer 1.
6 and the second polarizer 26, and a phase plate 17 is disposed between the second substrate 21 and the second polarizer 2G to form a liquid crystal display element.

In the above configuration, the light that passes through the first polarizer 16 and enters the liquid crystal cell A as linearly polarized light becomes elliptically polarized light in the liquid crystal layer 14 due to the optical anisotropy of the liquid crystal. It acts to return polarized light to linear polarization again. A white or black background is obtained by a second polarizer z6 placed parallel or perpendicular to the polarization direction of this linearly polarized light.

The phase plate 17 conventionally used is a polymer film such as polyvinyl alcohol or triacetyl cellulose that is stretched and oriented to have optical anisotropy within the film plane, and if necessary, glass, It has a sandwich structure with isotropic plastic. In the phase plate 17, among the optical principal axes of the phase plate 17, the one (X) having the largest in-plane refractive index in that direction is the transmission axis (P2) or absorption axis of the second polarizing plate 26. Arranged in an angular relationship other than parallel or perpendicular (
In Figure 3, α≠0,90°).

Next, we will discuss the case where a phase plate is used for viewing angle compensation.Liquid crystal display elements generally produce color changes depending on the viewing angle. This is because the effective refractive index anisotropy of the liquid crystal changes because the optical path becomes oblique, and the optical path length changes. This is particularly noticeable in the above-mentioned birefringence mode. Such viewing angle dependence can also be reduced by using a phase plate as shown in FIG. In this case, the basic element configuration is the same as in Figure 2, but the axis X of the phase plate is arranged parallel to or perpendicular to the transmission axis or absorption axis of the second polarizing plate (as shown in Figure 3). α
= 0″ or 90″).

[Problem to be solved by the invention]

The following characteristics are required for a phase plate for a liquid crystal display element.

■It is easy to expand the area.

■It must be low cost.

■Refractive index anisotropy must be uniform over a large area.

■Appropriate refractive index anisotropy can be obtained.

Items (1) and (2) above can be achieved relatively easily by using a stretched plastic film. (3) is relatively easy when the refractive index anisotropy is small (less than 0°3 IJs in terms of retardation), but if it is larger than that, it is difficult to stretch uniformly over a large area, and an area of about 10a1 to 30cd is It is a limit, and ■ will not be satisfied. Since phase plates for liquid crystal display elements, such as color compensation plates, are selected from those with retardation in the range of about 0.3 ps to 1.2 IJs, it is difficult to increase the area using conventional methods.

The present invention does not have the above-mentioned drawbacks, that is, the above-mentioned
The object of the present invention is to provide a phase plate that satisfies the characteristics of ~■ and a high-quality liquid crystal display element using the same.

[Means to solve the problem]

In order to achieve the above object, 1 according to the present invention, a plurality of stretched plastic films having refractive index anisotropy within the film plane are arranged such that the refractive index is larger among the two optical principal axis directions within the film plane. There is provided a phase plate characterized by having a structure in which the main axes of the directions are laminated so that they are parallel to each other.

Further, according to the present invention, there is provided a liquid crystal cell composed of a pair of opposing light-transmitting substrates and a liquid crystal layer sandwiched between the light-transmitting substrates, and a pair of polarized light arranged so as to sandwich the liquid crystal cell. a plurality of stretched plastic films having refractive index anisotropy in the plane of the film, which are generally skewed on at least one side between the pair of light-transmitting substrates and the polarizer adjacent thereto;
It is characterized by being composed of a phase plate whose main component is a structure laminated so that the principal axes in the direction of the larger refractive index among the two optical principal axes in the film plane are parallel to each other. A liquid crystal display element is provided.

[Effect]

In the present invention, by laminating plastic films with small retardation to provide the retardation of the phase plate, appropriate refractive index anisotropy can be uniformly obtained over a large area.

Therefore, it is possible to increase the display area.

〔Example〕

The present invention will be explained in more detail below with reference to Examples.

FIG. 1 is a perspective view showing the structure of a phase plate 1 according to an embodiment of the present invention. As shown in FIG.
It is constructed by laminating e. These stretched plastic films 1a, lb, and lc have in-plane optical principal axes X (Xx-L, Xs), Y (Y□, Y,, Y,) (
When the refractive index in the X direction is nz g and the refractive index in the Y direction is n, nx>ny. ], the main axes X (Xx-LtXi) in the direction in which the refractive index increases are parallel to each other.

Plastic films LA, LB, and LC include polyvinyl alcohol and cellulose triacetate, which are commonly used as phase plates, as well as polycarbonate, polystyrene, polyester, polyether sulfone, polysulfone, polyether ether ketone, polypropylene, polyethylene, and polyphenylene ether. , polyacrylic ester, polymethacrylic ester, and other thermoplastic polymer films. It may also be composed of a mixture of these.

Each of the plastic films LA, LB, and LC may be simply laminated, but in order to reduce the interface with air and improve transmittance, it is preferable that the plastic films are fixed with an adhesive or an adhesive. Other isotropic film layers can also be provided between or on the outside for purposes such as protection. Further, although the phase plate 1 having a three-layer structure is illustrated in this embodiment, the present invention is not limited to this, and may have a laminated structure with an arbitrary number of layers.

According to the phase plate of the present invention, the retardation Rx of each plastic film = (nxi - nyi) d l
(However, "xi" Yi is the refractive index of the i-th plastic film in the X-axis direction and Y-axis direction, and di is the thickness of the i-th plastic film.) By setting the phase plate (laminate) to a small value, Retardation R (=ΣRi)
Since i=1, the stretching conditions are relaxed and the width is 30 cm x 30 cm.
Uniform refractive index anisotropy can be obtained over a large area of about +m.

For example, when polyvinyl alcohol is used, R = R
, =R, =R, =0.221 By preparing and laminating each stretched film, R = 0.884. is S
A phase plate suitable for converting TN mode into black and white can be uniformly manufactured.

In order to apply the phase plate 1 described above to a liquid crystal display element, the phase plate 1 is provided in place of the phase plate 17 in FIG.
The other configurations may be the same.A liquid crystal display element using the phase plate as a color compensation plate or a viewing angle compensation plate has uniform color compensation or viewing angle compensation over a large area as described above, so that the display is uniform and the display quality is excellent.

〔Effect of the invention〕

As explained in detail above, according to the present invention, a plurality of stretched plastic films having refractive index anisotropy in the film plane are arranged in the direction in which the refractive index is larger among the two optical principal axis directions in the film plane. Since the phase plate is constructed by stacking the layers so that the principal axes in a certain direction are parallel to each other, uniform refractive index anisotropy can be obtained over a large area. A liquid crystal display element to which this phase plate is applied has uniform color compensation or viewing angle compensation over a large area, making it possible to provide a uniform and high-quality display over a large area.

[Brief explanation of the drawing]

Fig. 1 is a perspective view showing an example of the structure of a phase plate according to the present invention, Fig. 2 is a sectional view showing an example of the structure of a liquid crystal display element using the phase plate, and Fig. 3 shows the optical principal axis (X) of the phase plate. FIG. 2 is an explanatory diagram of the angular relationship between the polarizer and the transmission axis (P2) of the polarizer. 1... Phase plate, la, lb, lc... plastic film 11.21... substrate, 12, 22... alignment film, 13.23... transparent type pole, 14... liquid crystal layer , 15... Periphery sealant, 16.26... Polarizer, 17... Phase plate.

Claims (2)

[Claims] (1) A plurality of stretched plastic films having refractive index anisotropy within the film plane are arranged so that the principal axes in the direction with the highest refractive index among the two optical principal axis directions within the film plane are parallel to each other. A phase plate characterized by having a laminated structure. (2) a liquid crystal cell composed of a pair of opposing light-transmitting substrates and a liquid crystal layer sandwiched between the light-transmitting substrates; a pair of polarizers disposed to sandwich the liquid crystal cell; A plurality of stretched plastic films, which are provided at least on one side between a transparent substrate and a polarizer adjacent thereto and have refractive index anisotropy in the film plane, are arranged in two optical principal axes directions in the film plane. 1. A liquid crystal display element comprising a phase plate whose main component is a structure laminated so that the principal axes in the direction in which the refractive index is high are parallel to each other.