JPH10123509A - Reflection liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve brightness on a display surface by providing an isotropic diffusion layer on an opposite 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 opposite to each other. The isotropic diffusion layer 5 is provided on the bottom 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 isotropic diffusion layer 5, and passes 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 As shown in FIG. 7, a conventional reflection type liquid crystal display device has a pair of glass substrates 51, 52 provided with transparent electrode layers 53, 54 on the respective inner surfaces thereof. 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 was 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 layer of a dielectric anisotropic liquid crystal containing a dichroic dye is disposed between a pair of transparent substrates facing each other, and incident light is incident on a facing surface of one of the substrates. While providing an isotropic diffusion layer, an electrode layer and a liquid crystal alignment film are sequentially stacked on the diffusion layer, and an electrode layer and a liquid crystal alignment film are sequentially stacked on the opposite surface of the other substrate. And a reflection type liquid crystal display device provided with a reflector 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 a diffusion layer, a liquid crystal layer and the other substrate to reach a reflector having an uneven surface, and is reflected by the uneven surface. Then, light is emitted from the pair of substrates, the liquid crystal layer, and the diffusion layer. The light emission direction is a direction having a predetermined angle from the vertical direction with respect to the diffusion layer. Since the liquid crystal display device of the present invention does not have a polarizing plate in this light path, in the liquid crystal display device of the present invention, light transmittance increases, and light emitted from the display surface side looks bright, that is, the display surface becomes bright.

[0006] The isotropic diffusion layer of the incident light is for diffusing the incident light of all azimuth angles forward, respectively.
Those having a half width of 5 degrees or more and 10 degrees or less are preferable. If the half-value width is less than 5 degrees, the forward diffusion of the incident light into the isotropic diffusion layer becomes insufficient, and the width of the diffusion angle of the light passing through the liquid crystal layer becomes narrow, so that the viewing angle can be visually observed as a good display. When the half-width exceeds 10 degrees, the ratio of incident light that is back-scattered on the surface of the isotropic diffusion layer increases, so that the transmittance of the liquid crystal layer for incident light decreases, which contributes to display. Since the amount of light decreases, the contrast decreases. Therefore, the above-mentioned range is desirable for the half width. In particular, an isotropic diffusion layer having a half width of 7 degrees or more and 8 degrees or less is more preferable because the viewing angle can be widened and the contrast can be increased.

[0007] The pair of electrode layers is transparent and differs depending on the type of liquid crystal display device. For example, in a reflection type liquid crystal display device of a TFT type, an electrode layer provided on a diffusion layer serves as a common electrode, and an electrode layer on the opposite side corresponds to a layer including 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.

[0008] The reflector having the uneven surface is for increasing the viewing angle by diffusing and reflecting the 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 the 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 coincide with each other, and the light vibration direction When it is perpendicular to the parallel component of, it does not absorb light.

[0010] In the liquid crystal display device of the present invention, a λλ 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 again passes through the 板 λ plate, the vibration direction is rotated by 90 degrees and the light vibrates in a direction parallel to the major axis direction of the dichroic dye molecules. This is because the dichroic dye absorbs light when passing through the liquid crystal layer.

[0011]

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 isotropic diffusion layer 5 is provided on the lower surface of the upper glass substrate 1, and a transparent common electrode layer 6 is laminated on the lower surface of the diffusion layer 5, and an alignment film 7 made of polyimide is laminated on the lower surface of the electrode. An electrode layer 8 composed of a large number of transparent pixel electrodes is formed on the lower glass substrate 2, and an alignment film 9 composed 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.

The isotropic diffusion layer 5 is manufactured as shown in FIG. That is, as shown in FIG. 2A, in the tank 12, fine particles 13 made of polystyrene having a diameter of 3 μm and a diameter of 4 μm are mixed at an equal weight of 35% by weight with respect to the acrylic resin 14, and are uniformly dispersed. Then, as shown in FIG. 2B, this dispersion is applied onto the glass substrate 1 to form an acrylic resin film 15 having a thickness of 10 μm. Then, as shown in FIG. 2C, an overcoat layer 16 is formed on the acrylic resin film 15 by spin coating, and the overcoat layer 16 is formed to a thickness of 8 μm as shown in FIG. 2D. The surface is polished to form a diffusion layer 5 having a half width of about 7 degrees. Further, as shown in FIG.
The transparent electrode layer 6 is formed on the isotropic diffusion layer 5 by TO.

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. 4, the incident light R from the display surface side of the upper substrate 1 enters the isotropic diffusion layer 5 at an angle of 30 degrees with respect to the vertical direction, and the isotropic diffusion layer 5 When passing through, it diffuses like, for example, r10, r20, r30 and passes through the common electrode layer 6, the alignment film 7, and the liquid crystal layer 3 in FIG. 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.

FIG. 5 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 in FIG. Has a contrast of 4 and a white reflectance of 120%, whereas the commercially available conventional example shown in FIG.
Compared to contrast 5 and white reflectance 40%,
It turned out that the whole reflectance was raised significantly and the brightness was improved. The white reflectance and the black reflectance were measured using a liquid crystal panel evaluation device (LCD 500 manufactured by Otsuka Electronics Co., Ltd.).
0), a liquid crystal panel, that is, a liquid crystal display, is used instead of the white plate based on the output of the reflected light at a reflection angle of 15 degrees when a white plate (a plate having an MgO standard white surface) is irradiated at an incident angle of 30 degrees. It is a value expressed as a percentage (%) by dividing the output of the reflected light measured under the same irradiation conditions using the apparatus by the reference output. In particular, the white reflectance indicates the value of the percentage on the white display surface of the liquid crystal display device of the embodiment, while the black reflectance indicates the value of the percentage on the black display surface of the liquid crystal display device of the embodiment.

FIG. 6 shows the relationship between the reflection angle obtained by changing the reflection angle of 15 degrees on the horizontal axis and the white reflectance (%) depending on these reflection angles on the vertical axis. As shown by a black circle and a black square in the conventional example in FIG. 7, in the reflection angle region excluding the reflection angle of 23 to 34 degrees, which is hardly visible due to regular reflection, the present embodiment is significantly whiter than the conventional example. It has been found that the reflectance is greatly improved and the display screen can be displayed brightly.

[0018]

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 isotropic diffusion layer 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 view showing a manufacturing process of a diffusion layer in the reflection type liquid crystal display device shown in FIG.

FIG. 3 is a development view of the reflective liquid crystal display device shown in FIG.

FIG. 4 is a schematic diagram showing states of light input and output in the reflection type liquid crystal display device shown in FIG.

FIG. 5 is a diagram showing a relationship between contrast and white reflectance in the reflective liquid crystal display device shown in FIG.

FIG. 6 is a diagram showing a relationship between a reflection angle and a reflection angle-dependent white reflectance in the reflection type liquid crystal display device shown in FIG.

FIG. 7 is a sectional view showing a conventional reflective liquid crystal display device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, 2 Glass substrate 3 Negative dielectric anisotropic liquid crystal layer 3a Liquid crystal molecule 4 Dichroic dye molecule 5 Isotropic diffusion layer 6, 8 Electrode layer 7, 9 Alignment film 10 1/4 λ plate 11 Uneven reflection plate

Claims (4)

[Claims] 1. A layer of a dielectric anisotropic liquid crystal containing a dichroic dye is provided between a pair of opposing transparent substrates, and an isotropic diffusion layer of incident light is provided on the opposing surface of one of the substrates. In addition, an electrode layer and a liquid crystal alignment film are sequentially stacked on the diffusion layer, and an electrode layer and a liquid crystal alignment film are sequentially stacked on the opposing surface of the other substrate. A reflection type liquid crystal display device comprising a reflection plate having an uneven surface facing the substrate side. 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.