JPH10123510A - Reflection liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve brightness on a display surface by providing an anisotropic diffusion plate on an outer surface of one side substrate of a pair of transparent substrates opposite to each other and providing a reflection plate turning its rugged surface to the substrate side outward the other side substrate. SOLUTION: A dielectric anisotropic liquid crystal layer 3 containing a two color property dystuff molecule 4 is arranged between a pair of glass substrates 1, 2 inner surfaces. The anisotropic diffusion plate 5 is provided on the outer surface of the upward glass substrate 1. A 1/4λ plate 10 is provided on the bottom surface of the downward glass substrate 2, and a rugged reflection plate 11 is provided on its bottom surface. Incident light from the display surface side of the upward substrate 1 is diffused when it passes through the anisotropic diffusion plate 5 to pass through a common electrode layer 6, an oriented film 7 and the liquid crystal layer 3. Then, the incident light passes through the oriented film 9, an electrode layer 8, the substrate 2 and the 1/4λ plate 10 to arrive at the rugged reflection plate 11. Then, the light reflects according to the rugged shape of the rugged surface 12 of the rugged reflection plate 11. These reflected light emit from the display surface side of the upward substrate 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflection type liquid crystal display device having improved display surface brightness.

[0002]

2. Description of the Related Art In a conventional reflection type liquid crystal display device, as shown in FIG. 5, transparent electrode layers 53 and 54 are provided on the inner surfaces of a pair of glass substrates 51 and 52, respectively. 55 and 56 are provided, a chiral nematic liquid crystal layer 57 is provided between the pair of substrates, and polarizing plates 58 and 59 are provided outside the pair of substrates 51 and 52, respectively.
Was provided. Further, on the outside of one of the polarizing plates 59, an uneven reflecting plate 60 is provided with the uneven surface facing the polarizing plate 59 side.

[0003]

In such a conventional reflection type liquid crystal display device, more than 60% of the light incident on the polarizing plate 58 side of the liquid crystal display device is more than 60% due to the use of two polarizing plates. It was cut in the device. Therefore, only 40% of the incident light is used for screen display, and there is a problem that the display surface of the reflective liquid crystal display device is dark when viewed with the naked eye. An object of the present invention is to provide a reflective liquid crystal display device that is bright when viewed from the display surface side of the liquid crystal display device.

[0004]

According to the present invention, a dielectric anisotropic liquid crystal layer containing a dichroic dye is disposed between a pair of opposing transparent substrates, and incident light is incident on one of the substrates. An anisotropic diffusion plate is provided, and an electrode layer and an alignment film of liquid crystal are sequentially stacked on the inner surface of the one substrate, and an electrode layer and an alignment film of a liquid layer are sequentially stacked on the inner surface of the other substrate. In addition, the present invention is a reflection type liquid crystal display device comprising a reflection plate having an uneven surface facing the substrate outside the other substrate.

In such a reflection type liquid crystal display device, light incident on one substrate on the display surface side passes through an anisotropic diffusion plate, a liquid crystal layer and the other substrate to reach a reflection plate having an uneven surface. The light is reflected by the surface and emitted from the pair of substrates, the liquid crystal layer, and the anisotropic diffusion plate. The light emission direction is a direction having a predetermined angle from a vertical direction with respect to the anisotropic diffusion plate. In this light path, since the liquid crystal display device of the present invention has no polarizing plate, the light transmittance is increased, and light emitted from the display surface side looks bright. That is, the display surface becomes bright.

[0006] The anisotropic diffusion plate is a transparent diffusion plate having a characteristic that the transmitted light can be freely changed into straight light and scattering depending on the angle of the incident light. For example, when the diffuser is viewed from the side opposite to the side of the incident light to the anisotropic diffuser, the range of 20 degrees to 70 degrees is opaque in one direction in front and the other range is transparent. Can be used. In such an anisotropic diffusion plate, when light from a predetermined direction enters the reflective liquid crystal display device, it is diffused forward and guided into the liquid crystal display device. The pair of electrode layers is transparent and differs depending on the type of the liquid crystal display device. For example, in a reflection type liquid crystal display device of a TFT type, an electrode layer laminated on a substrate provided with an anisotropic diffusion plate serves as a common electrode, and an electrode layer on the opposite side corresponds to a layer composed of a large number of pixel electrodes. As the alignment film, a commonly used transparent alignment film can be used. For example, an alignment film made of polyimide can be used.

[0007] The reflector having an uneven surface is for increasing the viewing angle by diffusing and reflecting light incident from the substrate on the display surface side and passing through the diffusion layer and the liquid crystal layer. A reflecting plate having a surface roughness Ra (μm) of 0.20 or more and 0.32 or less is desirable in the apparatus of the present invention. If it is less than 0.20, the effect of diffusing light incident on the reflector is small. On the other hand, if it exceeds 0.32, the polarization shift generated when reflecting light incident on the reflector becomes large,
The black display becomes thin and the contrast becomes small. Particularly desirable is 0.26 or more and 0.28 or less. In this range, the diffusion effect of light incident on the reflector having the uneven surface is increased, and the polarization shift is also reduced.
The contrast also increases.

As a liquid crystal having a dichroic dye, a liquid crystal having positive and negative dielectric anisotropy can be used. For example, when a liquid crystal having a negative dielectric anisotropy is used, when an electric field is applied to the liquid crystal layer, each liquid crystal molecule is oriented in a substrate surface direction, that is, in a lying state, and the electric field is not applied to the liquid crystal layer. Sometimes, it is in a state in which it faces in a direction crossing a pair of substrates, that is, in a standing state. When an electric field is applied to the liquid crystal layer, the dichroic dyes are arranged in the same direction as the liquid crystal molecules, so that the direction of vibration of the incident light is parallel to the major axis of the dichroic dye molecules. It is absorbed by sex dyes and displays black. On the other hand, when no electric field is applied to the liquid crystal layer, the dichroic dye stands in a direction crossing the pair of substrates, so that the vibration direction of the incident light is orthogonal to the major axis direction of the dichroic dye molecules and does not absorb light. For,
The display becomes bright white. The dichroic dye is preferably a black dichroic dye that absorbs all wavelengths of visible light. For example, a dichroic dye in the case of using a liquid crystal having a negative dielectric anisotropy absorbs light when the major axis direction of the dye molecule and the parallel component of the light vibration direction match, and the light vibrates. When it is perpendicular to the parallel component of the direction, it does not absorb light.

In the liquid crystal display device of the present invention, a 1 / 4.lambda. Plate may be provided between the substrate and the reflector having the uneven surface. The ４λ plate is provided because, when an electric field is applied to the liquid crystal layer, of the light incident from the display surface side, the light that has passed through the liquid crystal layer without being absorbed by the dichroic dye is reflected by the uneven reflection plate. When returning, these lights are made to be able to be absorbed by the dichroic dye. That is, when the return light reflected by the reflection plate is transmitted again through the ４λ plate, the vibration direction is rotated by 90 degrees, and the light is oscillated in a direction parallel to the major axis direction of the dichroic dye. Is absorbed by the dichroic dye when passing through the liquid crystal layer.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings, taking a TFT type reflection type liquid crystal display device as an example. In FIG. 1, reference numerals 1 and 2 denote a pair of glass substrates, 3 denotes a layer of a negative dielectric anisotropic liquid crystal, 3a denotes liquid crystal molecules,
Is a dichroic dye molecule in the liquid crystal layer 3. An anisotropic diffusion plate 5 is provided on the outer surface of the upper glass substrate 1, while a transparent common electrode layer 6 is formed on the inner surface of the glass substrate 1, and an alignment film 7 made of polyimide is laminated on the lower surface of the electrode. ing. A large number of transparent pixel electrodes 8 are formed on the lower glass substrate 2, and an alignment film 9 made of polyimide is further formed thereon. A ４λ wavelength plate 10 is provided on the lower surface of the lower glass substrate 2, and a reflecting plate 11 having an uneven surface is provided on the lower surface of the ４λ wavelength plate 10.

The liquid crystal molecules 3a and the dichroic dye molecules 4
Is a state where the electrodes 6 and 8 are not applied and stands as shown in FIG. 1, and when these electrodes 6 and 8 are applied, the apparatus is in a lying state as shown in FIG.

As the anisotropic diffusion plate 5, Lumisty (trade name, manufactured by Sumitomo Chemical Co., Ltd.) was used. This is a film-shaped diffusion plate, and a layer having a different refractive index is about 3 μm in the film.
In particular, in the present embodiment, a range of 20-70 degrees is opaque in one direction in front of the diffuser when viewed from the side opposite to the side of light incident on the anisotropic diffuser. Those whose other areas appeared transparent were used.

The reflection plate 11 has an uneven surface 12 formed on the entire surface as shown in FIG. The surface roughness of the uneven surface 12 is
0.28 μm. The uneven surface 12 is formed in a pattern shape that reflects and diffuses light.

Next, a display method of the liquid crystal display device will be described. As shown in FIG. 3, incident light R from the display surface side of the upper substrate 1 is applied to the anisotropic diffusion plate 5 from the viewpoint opposite to the incident light side with respect to the anisotropic diffusion plate 5. The light enters at an angle of 30 degrees in one direction from the front and diffuses as r10, r20, and r30 when passing through the diffusion plate 5, and the common electrode layer 6, the alignment film 7, and the liquid crystal layer 3 of FIG. Pass through. Then, the light passes through the alignment film 9, the electrode layer 8, the substrate 2 and the １ ／ λ plate 10 shown in FIG. Then, according to the uneven shape of the uneven surface 12 of the uneven reflection plate 11, r10 is changed to, for example, r11, r12, r13,
r20 is, for example, r21 and r22, and r30 is, for example, r3
1, reflected in the direction of r32. When these reflected lights exit from the display surface side of the substrate 1 above, they enter the observer's eyes on the display surface side.

In FIG. 4, which is a graph in which the horizontal axis represents the contrast, which is the value obtained by dividing the white reflectance (%) by the black reflectance (%), and the black circle represents the white reflectance (%). In this embodiment, the contrast is 5 and the white reflectance is 30.
In contrast to 0%, the white reflectivity is significantly increased and the brightness is improved as compared with the contrast of 5 and the white reflectivity of 40% in the commercially available conventional example of FIG. ing.

[0016] The white reflectance and the black reflectance are as follows:
Using a liquid crystal panel evaluation device (LCD 5000 manufactured by Otsuka Electronics Co., Ltd.), an incident angle of 30 was applied to a white plate (a plate having an MgO standard white surface).
Using the output of the reflected light at a reflection angle of 15 degrees when illuminated in degrees as a reference, the output of the reflected light measured under the same irradiation conditions using a liquid crystal panel, that is, a liquid crystal display, instead of the white plate, is used as the reference. It is the value divided by the output and expressed as a percentage (%). In particular, the white reflectance indicates the value of the percentage on the white display surface of the liquid crystal display device of the present embodiment, while the black reflectance indicates the percentage on the black display surface of the liquid crystal display device of the present embodiment.

[0017]

According to the present invention, there is provided a reflection type liquid crystal display device having a layer of a dielectric anisotropic liquid crystal containing a dichroic dye, wherein an anisotropic diffusion plate and a reflection plate having an uneven surface are provided. In addition, a brighter display surface can be provided as compared with a reflection type liquid crystal display device having a conventional polarizing plate.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing one embodiment of a reflection type liquid crystal display device according to the present invention.

FIG. 2 is a development view of the reflective liquid crystal display device shown in FIG.

FIG. 3 is a schematic diagram showing states of light input and output in the reflective liquid crystal display device shown in FIG.

FIG. 4 is a diagram showing a relationship between contrast and white reflectance in the reflective liquid crystal display device shown in FIG.

FIG. 5 is a cross-sectional view showing a conventional reflective liquid crystal display device.

[Description of Signs] 1, 2 Glass substrate 3 Negative dielectric anisotropic liquid crystal layer 3a Liquid crystal molecules 4 Dichroic dye molecules 5 Anisotropic diffusion plate 6, 8 Electrode layer 7, 9 Alignment film 10 1 / 4λ plate 11 Uneven reflector

Claims (4)

[Claims] 1. A layer of a dielectric anisotropic liquid crystal containing a dichroic dye is provided between inner surfaces of a pair of transparent substrates facing each other, and an anisotropic diffusion plate for incident light is provided on an outer surface of one of the substrates. With
An electrode layer and an alignment film of liquid crystal are sequentially stacked on the inner surface of the one substrate, and an electrode layer and an alignment film of a liquid layer are sequentially stacked on the inner surface of the other substrate. A reflection type liquid crystal display device comprising a reflection plate having an uneven surface facing the substrate. 2. The uneven reflection plate has a surface roughness of 0.20.
2. The reflective liquid crystal display device according to claim 1, wherein the reflective liquid crystal display device has a thickness of not less than μm and not more than 0.32 μm. 3. The reflective liquid crystal display device according to claim 1, wherein the dichroic dye is a black dichroic dye that absorbs all wavelengths of visible light. 4. The method according to claim 1, further comprising the step of:
2. The reflection type liquid crystal display device according to claim 1, further comprising a / 4λ plate.