JPH07159774A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To attain brightness, achromaticity and sufficient contrast in the case of using as a transmission type provided with backlight low in light emitting luminance or in the case of using as a reflection type provided with a reflection plate. CONSTITUTION:The angle of twist orientation of a liquid crystal is controlled to 230-260 deg., the product DELTAn.d of refraction index anisotropy DELTAn of the liquid crystal and the thickness (d) of a liquid crystal layer 14 is controlled to 0.82-0.88mum and the phase difference of a phase different plate 12 is controlled to 0.54-0.6mum. And the angle between the lagging axis direction of the phase different plate 12 and the orientation direction of liquid crystal molecule in the boundary between a transparent substrate 13 in the side where the phase different plate 12 is arranged and the liquid crystal layer 14 is controlled to 75-105 deg. to use in normally white mode.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device.

[0002]

2. Description of the Related Art In recent years, liquid crystal twist angles have been increased from 180 ° to 270.
A super-twisted nematic (STN) that uses a birefringence mode by increasing the angle to ° facilitates increasing the capacity of a liquid crystal display device with a simple matrix, resulting in 640 × 400
Although a display with about pixels can be sufficiently made, there is a problem that the display is colored due to wavelength dispersion due to the use of the birefringence effect.

As one of the methods of eliminating the coloring of the display, a method of canceling the optical wavelength dispersion by using an optical compensation layer has been devised. A liquid crystal cell twisted in the opposite direction with almost the same Δn · d is used as the optical compensation layer (for example, Technical Report of the Institute of Television Engineers, Vol. 11, No. 27, 79).
Page) and one or more retardation plates.

From the viewpoint of reduction in thickness and weight and reduction in cost, a method using a retardation plate is currently the mainstream. Transparent, normally black (type that is dark when no voltage is applied and bright when voltage is applied) S using a backlight
In the case of TN, practically achromatic and sufficient contrast can be obtained by using two retardation plates (for example, Television Engineering Society technical report Vol. 13, No. 53, p. 31).

[0005]

However, in normally black, the pixels are dark, so that the brightness E is low.
There is a problem that the brightness of white display is low when an L backlight is used or when a reflective plate is used as a reflection type. Moreover, in order to reduce the cost, the phase difference plate is 1
In the case of the optical compensation structure using one sheet, the coloring is not completely eliminated and the contrast is lowered. In addition, when normally white is used, it is difficult to optimize the voltage application, and thus there is a problem that it is difficult to eliminate coloring in black display.

An object of the present invention is to provide a liquid crystal which is bright and achromatic and has a sufficient contrast when used as a transmissive type equipped with a backlight having a low emission brightness or when used as a reflective type equipped with a reflector. It is to provide a display element.

[0007]

A liquid crystal display element according to claim 1, wherein a nematic liquid crystal is sealed between a pair of transparent substrates having transparent electrodes inside and arranged substantially in parallel,
The liquid crystal cell includes one retardation plate disposed on one outer side and a pair of polarizing plates disposed on both outer sides with the liquid crystal cell and the retardation plate sandwiched therebetween, and the liquid crystal twist alignment angle is set to 230 °.
The refractive index anisotropy Δn of the liquid crystal and the thickness d of the liquid crystal are set to 260 °.
The product Δn · d is 0.82 μm to 0.88 μm, and the phase difference of the retardation plate is 0.54 μm to 0.62 μm.

According to another aspect of the liquid crystal display device of the present invention, a liquid crystal cell in which a nematic liquid crystal is sealed between a pair of transparent substrates which have transparent electrodes inside and are arranged substantially parallel to each other, and is arranged outside one of the liquid crystal cells. A single retardation plate and a pair of polarizing plates arranged on both outer sides with the liquid crystal cell and the retardation plate interposed therebetween,
The angle formed by the direction of the slow axis of the retardation plate and the orientation direction of the liquid crystal molecules at the interface between the transparent substrate on the side where the retardation plate is arranged and the liquid crystal is 75 ° to 105 °.

A liquid crystal display device according to a third aspect is the first aspect.
Alternatively, in the liquid crystal display element described in 2, the reflection plate is arranged outside one of the pair of polarizing plates. The liquid crystal display element according to claim 4 is the liquid crystal display element according to claim 1, 2 or 3, which is bright when no voltage is applied,
It is a normally white type that darkens when a voltage is applied.

[0010]

According to the structure of the present invention, the twist orientation angle of the liquid crystal is set to 230 ° to 260 °, and the refractive index anisotropy Δn of the liquid crystal is set.
The product Δn · d of the liquid crystal thickness d and the liquid crystal thickness d is 0.82 μm to 0.88 μm, and the retardation of the retardation plate is 0.54 μm to 0.62 μm, or the slow axis direction of the retardation plate, The transparent substrate on the side where the retardation plate is placed and the alignment direction of the liquid crystal molecules at the interface of the liquid crystal have an angle of 75 ° to 105 °, which is used as a transmission type equipped with a backlight with low emission brightness. In some cases, when it is used as a reflection type having a reflection plate, the normally white color can enhance the brightness of white display, and a bright, achromatic color and sufficient contrast can be obtained. In this case, black display at the time of voltage application becomes a problem, but particularly in the case of the optical compensation configuration with one retardation plate, the magnitude of the retardation or the direction of the slow axis of the retardation plate is specified. As a result, when used as a transmissive type or a reflective type, practically sufficiently achromatic black display can be obtained.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. 1 is a sectional view of a liquid crystal display device according to a first embodiment of the present invention. In FIG. 1, 11 is an upper polarizing plate, 12 is a retardation plate, 13 is an upper transparent substrate, 14 is a liquid crystal layer, 15 is a lower transparent substrate, and 16 is a reflective polarizing plate. FIG. 2 is a configuration diagram of the liquid crystal display element shown in FIG. 1 in the main axial direction. In FIG. 2, 21 is the absorption axis of the upper polarizing plate 11, 22 is the slow axis of the retardation plate 12, 23 is the alignment direction of liquid crystal molecules at the interface between the upper transparent substrate 13 and the liquid crystal layer 14,
4 is the alignment direction of the liquid crystal molecules at the interface between the lower transparent substrate 15 and the liquid crystal layer 14, 25 is the absorption axis direction of the reflective polarizing plate 16, and 26 is
Is the angle formed by the slow axis 22 of the retardation plate and the alignment direction 23 of the liquid crystal molecules at the interface between the upper transparent substrate and the liquid crystal layer, and 27 is the twist angle of the liquid crystal.

In this embodiment, as the liquid crystal layer 14, a twist angle 27 is set to 240 ° by using ZLI-2293 manufactured by Merck & Co., which is mixed with a chiral material having a right-handed optical rotatory power. Here, the refractive index anisotropy Δn and the thickness d of the liquid crystal layer 14
The product of Δn and d is 0.82, 0.84, 0.86, 0.88 μm 4
In the two cases, the phase difference of the phase difference plate 12 is 0.54 μm
FIG. 3 shows the contrast plotted by optimizing the compensation structure in a normally white range between 0.62 μm. The upper limit of the phase difference of the phase difference plate 12 in manufacturing is
At present, the maximum is about 0.65 μm.

It can be seen from FIG. 3 that the structure in which a practically sufficient contrast is obtained is within this range. In all the configurations here, the slow axis 2 of the retardation plate is used.
The angle 26 formed by 2 and the alignment direction 23 of the liquid crystal molecules at the interface between the upper transparent substrate and the liquid crystal layer is in the range of 75 ° to 105 °, and in the vicinity of the black display where maximum contrast is obtained,
Practically achromatic.

FIG. 4 is a sectional view of a liquid crystal display element according to the second embodiment of the present invention. In FIG. 4, 41 is an upper polarizing plate, 42 is a retardation plate, 43 is an upper transparent substrate, 44 is a liquid crystal layer, 45 is a lower transparent substrate, and 46 is a lower polarizing plate. FIG. 5 is a configuration diagram in the main axial direction of the liquid crystal display element shown in FIG. Reference numeral 51 is the absorption axis of the upper polarizing plate 41, 52 is the slow axis of the retardation plate 42, 53 is the alignment direction of liquid crystal molecules at the interface between the upper transparent substrate 43 and the liquid crystal layer 44, and 54 is the lower transparent substrate 45.
The alignment direction of liquid crystal molecules at the interface between the liquid crystal layer 44 and the liquid crystal layer 44, 55 is the absorption axis direction of the lower polarizing plate 46, and 56 is the slow axis 5 of the retardation plate.
2 is an angle formed by the alignment direction 53 of liquid crystal molecules at the interface between the upper transparent substrate and the liquid crystal layer, and 57 is a twist angle of the liquid crystal.

In this embodiment, as in the first embodiment, the liquid crystal layer 44 is made of ZLI-2293 manufactured by Merck & Co., which is mixed with a chiral material having a right-handed optical rotatory power, and has a twist angle of 5.
7 is 240 °. Also in this embodiment, the first
The difference from the example is that the product Δn · d of the refractive index anisotropy Δn and the thickness d of the liquid crystal layer 44 is fixed to 0.84 μm, and the transmission type using an EL backlight is normally white. This is the point of comparing normally black. FIG. 6 is a diagram showing the relationship between the phase difference of the phase difference plate 42 and the relative brightness of white display in normally white and normally black in the second embodiment. Looking at FIG. 6, the relative brightness is slightly lowered in the normally black. However, it is practically usable.

As described above, according to the above embodiment, the twist orientation angle of the liquid crystal is 230 ° to 260 °, and the product Δn · d of the refractive index anisotropy Δn of the liquid crystal and the thickness d of the liquid crystal is 0.82. μm
~ 0.88μm, the phase difference between the phase difference plate 12, 42 is 0.54μ
By setting m to 0.62 μm, the slow axis of the retardation plate 2
The angles 26, 56 formed by the liquid crystal molecules 2, 52 and the alignment directions 23, 53 of the liquid crystal molecules at the interface between the upper transparent substrate and the liquid crystal layer are 75 ° to 105 °.
It is within the range of °. With this configuration, when it is used as a transmissive type having a low-emission luminance backlight or when it is used as a reflective type having a reflector, it is possible to increase the luminance of white display by using normally white. It is bright, achromatic and has sufficient contrast. in this case,
Black display at the time of voltage application becomes a problem, but in the case of the optical compensation configuration with one retardation plate 12, 42 as in the above embodiment, the magnitude of the retardation, or the retardation plates 12, 42. By specifying the direction of the slow axis of, it is possible to obtain sufficiently achromatic black display in practical use when used as a transmission type or a reflection type.

Further, the twist orientation angle of the liquid crystal is 230 °.
˜260 °, product Δn · d of refractive index anisotropy Δn of liquid crystal and thickness d of liquid crystal is 0.82 μm to 0.88 μm, retardation plates 12, 42
Even if the phase difference of 0.54 μm to 0.62 μm is not satisfied, the slow axes 22 and 52 of the retardation plate and the alignment directions 23 and 53 of the liquid crystal molecules at the interface between the upper transparent substrate and the liquid crystal layer are formed. If the angles 26 and 56 are within the range of 75 ° to 105 °, some effects can be obtained.

The phase difference plate 12 in the above embodiment,
As 42, polycarbonate, polyvinyl alcohol, or poly (fucca vinylidene) is used.

[0019]

As described above, in the liquid crystal display device of the present invention, the twist orientation angle of the liquid crystal is set to 230 ° to 260 °,
The product of refractive index anisotropy Δn of liquid crystal and thickness d of liquid crystal Δn · d
Is 0.82 μm to 0.88 μm, and the phase difference of the retardation plate is 0.54 μm.
m to 0.62 μm, or the angle between the slow axis direction of the retardation plate and the alignment direction of the liquid crystal molecules at the interface between the transparent substrate on which the retardation plate is arranged and the liquid crystal is 75 °. ~ 105
By setting to °, by using a normally white when used as a transmissive type equipped with a backlight with low emission brightness, or when used as a reflective type equipped with a reflector,
The brightness of white display can be increased, and bright and achromatic colors provide sufficient contrast. In this case, black display at the time of voltage application becomes a problem, but particularly in the case of the optical compensation configuration with one retardation plate, the magnitude of the retardation or the direction of the slow axis of the retardation plate is specified. As a result, when used as a transmissive type or a reflective type, practically sufficiently achromatic black display can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view of a liquid crystal display device according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram in the main axial direction of the liquid crystal display element according to the first embodiment of the present invention.

FIG. 3 is a diagram showing the relationship between the phase difference of the phase difference plate and the contrast of the liquid crystal display element according to the first embodiment of the present invention.

FIG. 4 is a sectional view of a liquid crystal display element according to a second embodiment of the present invention.

FIG. 5 is a configuration diagram of a liquid crystal display element according to a second embodiment of the present invention in the main axial direction.

FIG. 6 is a diagram showing the relationship between the phase difference of the retardation plate and the relative luminance of the liquid crystal display element according to the second embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 11 upper polarizing plate 12 retardation plate 13 upper transparent substrate 14 liquid crystal layer 15 lower transparent substrate 16 reflective polarizing plate 41 upper polarizing plate 42 retardation plate 43 upper transparent substrate 44 liquid crystal layer 45 lower transparent substrate 46 lower polarizing plate

Claims (4)

[Claims] 1. A liquid crystal cell in which a nematic liquid crystal is sealed between a pair of transparent substrates which have transparent electrodes inside and are arranged substantially in parallel, and one retardation plate which is arranged outside one of the liquid crystal cells. The liquid crystal cell and a pair of polarizing plates disposed on both outer sides of the retardation plate are provided, and the twist orientation angle of the liquid crystal is 230 ° to 260 °.
A liquid crystal display device in which the product Δn · d of the refractive index anisotropy Δn of the liquid crystal and the thickness d of the liquid crystal is 0.82 μm to 0.88 μm, and the retardation of the retardation plate is 0.54 μm to 0.62 μm. 2. A liquid crystal cell in which a nematic liquid crystal is sealed between a pair of transparent substrates which have transparent electrodes inside and are arranged substantially parallel to each other, and one retardation plate which is arranged outside one of the liquid crystal cells. The liquid crystal cell and a pair of polarizing plates arranged on both outer sides with the retardation plate interposed therebetween, the direction of the slow axis of the retardation plate, the transparent substrate on the side where the retardation plate is disposed, and A liquid crystal display device in which the angle formed by the alignment direction of liquid crystal molecules at the liquid crystal interface is 75 ° to 105 °. 3. The liquid crystal display element according to claim 1, wherein a reflection plate is arranged outside one of the pair of polarizing plates. 4. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is of a normally white type which is bright when no voltage is applied and dark when a voltage is applied.