JPS5981623A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To obtain a liquid crystal display device capable of being enhanced in brightness and contrast even through low voltage drive by rendering the direction of incident light rectangular to that of the absorption axis of a dichroic dye, when this axis direction is parallel to one of substrate surfaces. CONSTITUTION:A transparent electrode 11 made of In2O3, SnO2, or their mixture, and an orienting film 12 are formed on a transparent substrate 10 made of glass or plastics. A transparent electrode 14 and an orienting film 13 are formed on the other transparent substrate 15, and a reflective plate 16 is formed on the reverse side of the substrate 15. 18 is a liquid crystal layer incorporating a dichroic dye, and 17 is a sealant. The orienting films 12, 13 is formed on the substrates 10, 15 are rubbed in the directions from (a) to (c) on the substrate 10 and reversely from (c) to (a) on the substrate 15. As a result, the liquid crystal molecules 19 incline by about 2-4 deg. on the interface between the liquid crystal layers and the orienting films 12, 13 of both substrates 10, 15, but the molecules 19 are aligned in the rubbing direction almost in parallel to both substrate, 10, 15.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a liquid crystal display device, and particularly to a guest-host type liquid crystal display device 4 in which a dichroic dye is mixed.

[Prior art]

Cholesteric phase change liquid crystal, nematic 1
Guest-host liquid crystal (f
'i, color display is possible and viewing angle dependence is small.

FIG. 1 shows a cross-sectional view of a conventional liquid crystal display element in which a dichroic dye is added to a nematic liquid crystal. Transparent electrodes 3 are formed on transparent substrates 2 and 6, and further alignment and film 4 are formed. In addition, both transparent substrates have a spacer 5 of 8 to 10 μm.
They face each other with a gap of m8 degrees, and a liquid crystal 8 is sealed between them.

In the case of a reflective liquid crystal display device, the reflective plate 7 is attached to the transparent substrate 6, and the polarizing plate 1 can be attached to the other transparent substrate I.

When the above-mentioned liquid crystal display element is illuminated with the light source 9 as shown in FIG. 2 and the relationship between the driving voltage and the brightness B of the reflected light is determined, the result will be as shown in FIG. 3, for example.

In the conventional display method, the brightness J3 changes slowly with respect to the drive voltage, and the contrast ratio cannot be increased unless the drive voltage is increased, making it particularly difficult to apply to devices that perform gradation display.

[Purpose of the invention]

An object of the present invention is to provide a display device that can increase brightness and contrast even when driven at low pressure by optimizing the illumination conditions of a liquid crystal display element.

[Summary of the invention]

The present invention has experimentally confirmed that the optical properties of guest-host type liquid crystal display devices significantly depend on the illumination direction. The brightness and contrast of the display element are improved by making light incident in the direction of the absorption axis and approximately in the same direction.

A second feature of the present invention is that the inclined surface of the reflecting plate is substantially parallel to the absorption axis direction of the dichroic dye.

[Embodiments of the invention]

Hereinafter, the present invention will be specifically explained based on Examples.

FIG. 4 shows a cross-sectional view of a liquid crystal display element according to an embodiment of the present invention. Glass, glass, etc. CD Hide EIIJ substrate 10 with In, 0. , SnO2, or a mixture thereof, a transparent electrode 11 and an alignment film 12 are formed. A transparent electrode 14 and an alignment film 13 are formed on one transparent substrate 15, and a reflecting plate 16 is provided on the opposite side of the substrate. 18 is a liquid crystal layer mixed with dichroic dye;
17 is a sealant.

At this time, the side of the transparent substrate 10 is set as the light incident side.
The thickness of the liquid crystal layer 18 is approximately 8 μm.

FIG. 5 shows the rubbing direction of the alignment films formed on the transparent substrates 10 and 15. For the transparent substrate 10, from a to C.
On the other hand, the transparent substrate 15 is rubbed in the direction C to a.

As a result, the alignment state of the liquid crystal molecules is schematically shown in FIG. 6. At the interface between the alignment film of the side substrate and the liquid crystal layer, the liquid crystal molecules 19 are tilted by about 2 to 4 degrees, but the substrate 10.15
are arranged in the rubbing direction substantially parallel to the . The liquid crystal used here includes Merck's ZL11132. In addition, the alignment film is an organic sieve with good insulation properties! It can be obtained by applying the proboscis with a spinner, etc.

Note that oblique evaporation of StO2 is used as a means for distributing the liquid crystal molecules in a four-sphere arrangement δ as shown in FIG. Approximately 1 to 4 wt % of a black pigment or the like is added to the liquid crystal described above. As a result, the dye molecules receive the normal forces of the liquid crystal molecules and are aligned in substantially the same direction as the liquid crystal molecules. As shown in FIG. 7(a), the dye used in this example has the largest absorption when the light vibrating in the long axis direction of the dye molecule 20 is incident;
When an element vibrating in the short axis direction shown in Figure 7Cb) is incident, the absorption is the smallest, and the long axis direction of the dye molecule and the minor absorption direction coincide.

When Mr. Kienma measured the optical characteristics of the liquid crystal display element shown in FIG. 6 under the conditions shown in FIG. 8, he obtained the results described below.

Note that a reflective plate 16 was attached to the transparent substrate 15, and linear surface light, which was deflected by a light source 21 and a polarizing plate 22, was projected onto the element from an oblique (angle θ) direction with respect to the substrate 10.

Here, the transmission axis of the polarizing plate 22 is rubbed almost parallel to the rubbing direction. The angle ψ between the incident direction of light and the direction of absorption axis (rubbing direction) of the dichroic dye when no driving voltage is applied is the a-side tone O shown in Figure 5, and is taken in the clockwise direction. Ta.

The measurement point 100 of the reflected light (observer's position) is 1 (I
] Direction perpendicular to the substrate, where the distortion of the J strip is the least and the specular reflection of the incident light is also minimal.

FIG. 9 is a plot of the relationship between the drive voltage Vrms and the brightness of reflected light around θ-30°. Also,
FIG. 10 is a plot of the relationship between contrast ratio CR, brightness BR, and angle ψ. Figure 10(a) is θ-10°, Figure 10(b)
shows the case where θ3 is 80°, and FIG. 10(C) shows the case where θ=30°.

where: e) -17 Trust ratio is the ratio of brightness at V=3vrms and V=0.

As a result, if ψ=90° or 270°, the brightness is
It is clear that saturation occurs at a low voltage around 3 Vrms, and the contrast ratio becomes maximum around ψ=90° or 270°.

Next, examples of the reflector will be described. Assuming that the aforementioned θ and ψ are constant, in order to make the liquid crystal display element brighter, it is necessary to increase the amount of light reflected in the vertical direction of the element.

FIG. 11 is a plan view of the reflector 16, and the X-Y cross-sectional view is as shown in FIG. , most of the light incident from the θ direction of the perpendicular to the base is reflected in the perpendicular direction. It is assumed that θ is approximately 11 equal to θ explained in FIG.

When the reflection characteristics of the reflector plate 1G described above are measured by the method shown in FIG. 13, they are shown in FIG.
The reflected light is also greatest at °.

FIG. 15 shows a combination of transparent substrates 10 and 15 and a reflecting plate 16 of a liquid crystal display element. This is done so that the inclined surface of the reflection plate and the absorption axis direction of the dichroic dye when the full drive voltage is not applied are approximately parallel to each other. At this time, if ψ=90° or ψ=270°,
The reflected light becomes the largest, and the brightness of the liquid crystal display element becomes the maximum.

FIG. 16 shows a specific example of a reflective guest-host liquid crystal display device based on the above-mentioned knowledge.

The observer 23 views the substrate from a direction substantially perpendicular to the substrate. Furthermore, the angle θ is set to a value that allows the specular reflection component of the transparent substrate 10 to be almost ignored, but is preferably around θ-10 to 40°.

The inclined surface of the reflection plate 16 is parallel to the absorption axis direction (rubbing direction) of the dichroic dye when no driving IE pressure is applied.

Fig. 16(a) &J2, a light source 21 and a polarizing plate 22 are installed in the ψ=90° direction, and Fig. 16(b) r
Two light sources and two polarizing plates are installed in the i, ψ=270° direction.

In FIG. 16(C), the display surface is illuminated from two directions in order to reduce variations in brightness. The light source 24 and the polarizing plate 25 are in the ψ=90° direction, and the light source 21 is in the ψ=270° direction.
and polarizing plate 22'f: installed.

In either embodiment, the directions of the polarization axes of the 1114 light plates 22 and 25 are adjusted so that the light directed to the observer 23 is minimized when no driving voltage is applied.

FIG. 17 shows a specific example of a liquid crystal display device according to the present invention. Here, the illumination method for liquid crystal display elements will be described as the first method.
．． An explanation will be given by taking FIG. 1(C) as an example.

The external light blocking wall 34 prevents light other than light sources 35 and 36 such as tungsten lamps from entering the liquid crystal display element 37 . A structure that prevents the light from the leakage light blocking walls 38 and 39 from passing through parts other than the polarizing plates 40 and 41, and effectively utilizes the light from the light sources by providing a reflective wall on the inner surface. shall be. Further, the light sources 35 and 36 are installed at ψ-90° and 2700°, and at θ˜30°.

Here, ψ and θ are determined by the position of the measurement point on the substrate, but in this embodiment, the measurement point is approximately at the center of the display section. Depending on the type and distance of the light source, ψ may be different in a part of the substrate, but in that case, ψ in the main part of the display section may be taken into consideration. Note that the observer 43 of the liquid crystal display element visually observes the liquid crystal display element 37 through the viewing window 42 .

In this embodiment, since ψ=90° and 270°, the optical display device is bright and has good contrast.

Furthermore, since the light is incident from opposite directions, there is little variation in the brightness of the display surface.

FIG. 18 shows another embodiment.

By arranging the condensing lenses 42 and 43 in front of the light sources 35 and 36, the light from the light sources can be efficiently irradiated onto the liquid crystal display confectionery 37, allowing a bright display.

In the past, light passed through the polarizing plate twice, once when it was incident and once when it was reflected, but in Embodiment C shown in Figures 17 and 18, the light passes through the polarizing plate only when it is incident. There is less attenuation of light due to passing through a polarizing plate than with conventional methods, and sufficient brightness can be obtained.

FIG. 19 shows a structural diagram of a liquid crystal display element that can obtain effects similar to those of the above-described embodiment.

That is, the reflective substrate is made up of the substrate 27, the reflective electrode 26, and the alignment film 13. In this case, the reflective electrode 26 is an electrode opposite to the transparent electrode 11, and the brightness of the reflected light changes depending on the difference in electric potential between the two electrodes.

Note that the substrate 27 may be either a transparent substrate or an opaque substrate.

Further, as another implementation array of liquid crystal display elements, a known active matrix configuration as shown in FIG. 20 may be used. That is, the horizontal scanning circuit 28 and the vertical scanning circuit 29
A switching transistor 30 and a storage capacitor 31 are formed on an all-single-crystal silicon substrate, and the substrate and a transparent substrate having a transparent electrode 33 are made to face each other to form a liquid crystal pixel 32 to display an image.

Note that the horizontal scanning circuit 28, the vertical scanning circuit 29, and the switching transistor 30 can also be configured with a known TF'T.

Further, the present invention can also be applied to known liquid crystals such as constellic-nematic phase change liquid crystals and smectic liquid crystals in which dichroic dyes are mixed.

In the embodiments of the present invention described above, explanation has been given by taking as an example a negative type liquid crystal display confectionery in which the alignment film on the surface of the substrate is subjected to parallel alignment treatment, but the invention is not limited to this. The present invention can also be applied to so-called positive type liquid crystal display confectionery in which the liquid crystal molecules and dichroic dye molecules are vertically aligned and become substantially flat with respect to the substrate when a voltage is applied.

Furthermore, the dichroic dye is not limited to the positive type, in which the long axis direction of the fx molecule and the absorption axis direction are aligned, as in this example, but also the dichroic dye, in which the short axis direction and the absorption axis direction of the dye molecule are aligned. It is also possible to use a negative type. In other words, regardless of the type of liquid crystal or dichroic dye, when the absorption axis direction of the dichroic dye is approximately parallel to the substrate, the absorption axis direction of the dichroic dye, the incident direction of light, and the reflection It is sufficient to consider the slope of the plate.

Further, in this practical example, the polarizing plates 40 and 41 are attached to the light sources 35 and 36, but the present invention can also be applied even if they are attached directly to the substrate as in the conventional example.

Further, although the present invention is not limited to the observation direction of the viewer, it is preferable to observe from a direction substantially perpendicular to the substrate, as in this embodiment, because the distortion of the screen is minimized.

Furthermore, the first invention is not limited to the presence or absence of a reflective plate, and can also be applied to a transmissive liquid crystal display device.

〔Effect of the invention〕

According to the present invention, by setting a specific relationship between the light irradiation direction and the direction of the dichroic dye's absorption axis, it is possible to obtain a bright display device with high contrast even when driven at a low voltage.

Furthermore, by setting a specific relationship between the inclined surface of the reflector and the direction of the absorption axis of the dichroic dye, an even brighter display device can be obtained.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of a conventional liquid crystal display element, Figure 2 is a diagram showing the illumination method of a conventional liquid crystal display element, and Figure 3 is a diagram showing the electricity of the liquid crystal.
4 is a cross-sectional view of an embodiment of the liquid crystal display element according to the present invention, FIG. 5 is a diagram showing the rubbing direction of the liquid crystal alignment film, FIG. 6 is a diagram of the arrangement state of liquid crystal molecules, and FIG. The figure is a diagram explaining the absorption characteristics of dyes, Figure 8 is a perspective view showing the illumination conditions of a liquid crystal display element, Figure 9 is a diagram of drive voltage vs. brightness characteristics, Figure 10 is a diagram of contrast characteristics versus angle ψ, FIG. 11 is a plan view of a reflector used in an embodiment of the present invention; FIG. 12 is a sectional view of FIG. 11; FIG. 13 is a perspective view showing illumination conditions of the reflector of FIG. 14 is an optical characteristic diagram of the reflector shown in FIG. 11, FIG. 15C is a three-dimensional developed view of an embodiment of the present invention, and FIG. 16 is a perspective view showing the method of illuminating a liquid crystal display element according to the present invention. 17 and 18 are block diagrams of a specific device of the present invention, and FIGS. 19 and 20 are diagrams showing other embodiments of the liquid crystal display element used in the present invention. 2,6,10.15...transparent substrate, 3,11.14.
...Transparent electrode, 4,12.13...Alignment film, 7,16
...Reflector, 9,21,24,35.36...Light source,], 22,25,40.41...Polarizing plate, 42°43...Condensing lens, 34... External light blocking wall, 38° 39... Leakage light blocking wall, 37... Liquid crystal display element. Fig. 1 'l Fig. 2 Bath 3z No. + Fig. forward entrance S port n ↓ Fig. 9 - Drive voltage vrmi Fig. 10 (0L) y(n 10th port (-e-) Army 10 Fig. (C) 117B Trial 120 Ant' 14-121 1) ('/=27F) % 15 Figure 16 Figure 19

Claims (1)

[Scope of Claims] (1) A liquid crystal display element in which liquid crystal mixed with a dichroic dye is held between one substrate and the other substrate, each having electrodes on opposing surfaces; On the other hand, in a liquid crystal display device equipped with an illumination means that allows light to enter obliquely, the direction of the absorption axis of the dichroic dye is the surface of one of the substrates. !
are parallel to each other, the incident direction of the light is substantially perpendicular to the absorption axis direction of the dichroic dye. 2. A liquid crystal display element in which liquid crystal mixed with a dichroic dye is held between one substrate and the other substrate, each having electrodes on opposing surfaces, and a reflective plate adjacent to the other substrate; In the liquid crystal display device comprising an illumination means for diagonally incident light onto the one substrate, when the absorption axis direction of the dichroic dye is substantially parallel to the surface of the one substrate, A liquid crystal characterized in that the incident direction of the light is substantially perpendicular to the absorption axis direction of the dichroic dye, and the inclined surface of the reflecting plate is substantially parallel to the absorption axis direction of the dichroic dye. Display device. 3. A liquid crystal display device according to claim 1 or 2, wherein the light is linearly polarized light. 4. A liquid crystal display device according to claim 3, wherein the illumination means includes a polarizing plate. 5. A liquid crystal display device according to claim 1 or 2, wherein the illumination means receives light from a plurality of directions. 6. A liquid crystal display device according to claim 1 or 2, characterized in that the display is viewed from a direction perpendicular to the one substrate.