JPH07104287A - Reflective liquid crystal display - Google Patents

Abstract

(57) [Summary] [Structure] The liquid crystal 3 is sandwiched between the two substrates 1 and 2 on which the electrodes 4 and 5 and the alignment films 6 and 7 are formed, and the reflection plate 8 is arranged outside the one substrate 1. In the reflection type liquid crystal display device, a light scattering layer 9 composed of a polymer dispersion type liquid crystal layer is provided on a substrate 2 opposite to the substrate 1 on which the reflection plate 8 is arranged,
A quarter wave plate 10 was provided between the reflection plate 8 and the substrate 1. [Effects] A reflective liquid crystal display device using a nematic liquid crystal with a low driving voltage can be formed, and an electrode formed on a light scattering layer is flattened so that the liquid crystal layer has a uniform thickness and is transparent. The reflection type liquid crystal display device has a small rate distribution and high visibility.

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, and more particularly to a reflective liquid crystal display device by active driving.

[0002]

2. Description of the Related Art A conventional reflective liquid crystal display device is shown in FIG. In FIG. 2, 1 and 2 are substrates made of glass or the like, 3 is liquid crystal, 4 and 5 are electrodes for applying a voltage to the liquid crystal 3, and 6 and 7 are for orienting the liquid crystal 3 in a predetermined direction when no voltage is applied. Alignment film, 8 is substrate 2
It is a reflector for reflecting the light incident from the side.

In this reflection type liquid crystal display device, a cholesteric liquid crystal containing a dye is used as the liquid crystal 3, and when no voltage is applied, it is homogenously or homeotropically arranged by the regulating force of the alignment films 6 and 7, and the substrate 2 side. The light incident from is absorbed by the dye of the liquid crystal 3 to display black.

When a voltage is applied to the electrodes 4 and 5, the liquid crystal 3 is oriented, for example, perpendicularly to the substrates 1 and 2 due to its dielectric anisotropy, and the light incident from the substrate 2 side receives the liquid crystal 3.
To be displayed in white.

In this reflection type liquid crystal display device, since it is difficult to see that the reflection plate 8 is a flat plate having a mirror surface, irregularities are usually formed on the reflection surface of the reflection plate 8 to have an effect of scattering light. That is, since the light scattering effect of the liquid crystal 3 itself is small, if there is no light scattering mechanism, the light goes straight only to the side opposite to the incident light, and for example, even if an image is viewed from above, it cannot be actually seen.

However, if unevenness is formed on the reflection plate 8, the reflection on the reflection plate 8 becomes irregular reflection. Therefore, there is a problem that it cannot be applied to a reflective liquid crystal display device of a nematic liquid crystal using a quarter wavelength plate in which the polarization of incident light must be maintained. Further, when the cholesteric liquid crystal is used, the ON / OFF response characteristic is worse than when the nematic liquid crystal is used, which causes a problem that the driving voltage is significantly increased.

In order to solve such a problem, as shown in FIG. 3, for example, the inner surface of the substrate 2 on the light incident side is roughened so as to have a light scattering effect and the reflection of the reflection plate 8 is also increased. The surface is made to be a mirror surface, and a quarter is provided between the reflection plate 8 and the substrate 1.
It is possible to arrange a wave plate 9 and use a nematic liquid crystal as the liquid crystal 3. However, even if the inner surface of the substrate 2 on the light incident side is roughened, a sufficient light scattering effect cannot be obtained, and the incident side is not formed. When the inner surface of the substrate 2 is roughened, the surface of the electrode 5 formed thereon also becomes roughened, the thickness of the liquid crystal 3 becomes uneven, and the partial transmittance of the display screen becomes uneven. There was a problem of becoming.

[0008]

The reflective liquid crystal display device according to the present invention has been considered in view of such problems, and is characterized in that an electrode and an alignment film are formed. In a reflection type liquid crystal display device in which a liquid crystal is sandwiched between two substrates and a reflection plate is arranged on the outside of one substrate, a polymer dispersion type liquid crystal layer is formed on the substrate opposite to the substrate on which the reflection plate is arranged. A light scattering layer is provided, and a quarter wavelength plate is provided between the reflection plate and the substrate.

[0009]

As described above, when the light scattering layer is provided on the substrate on the side opposite to the substrate on which the reflector is arranged, a reflection type liquid crystal display device using a nematic liquid crystal with a low driving voltage can be constructed and When the light-scattering layer is composed of a polymer-dispersed liquid crystal layer, the electrodes formed on the light-scattering layer are flattened, and the liquid crystal layer has a uniform thickness and a small transmittance distribution, which improves visibility. It becomes a high reflection type liquid crystal display device.

[0010]

Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. FIG. 1 is a sectional view showing an embodiment of a reflective liquid crystal display device according to the present invention. Reference numerals 1 and 2 are substrates made of a translucent member such as glass, 3 is a liquid crystal, 4 and 5 are liquid crystals.
Electrodes for applying a voltage to the substrate, 6 and 7 an alignment film for orienting the liquid crystal 3 in a predetermined direction when no voltage is applied, 8 a reflecting plate for reflecting light incident from the substrate 2 side, and 9 a substrate A light scattering layer 10 formed of a polymer dispersion type liquid crystal layer or the like formed on the second side is a quarter wavelength plate disposed between the substrate 1 and the reflection plate 8.

An electrode 4 made of a transparent conductive film such as ITO and an alignment film 6 made of a polyimide resin are formed on the substrate 1. In addition, below the substrate 1, 1
A quarter-wave plate 10 and a reflector 9 which is vapor-deposited on aluminum and has a mirror surface are provided. The reflector 9 reflects light incident from the substrate 2 side, not diffusely reflecting it, but reflecting it. The liquid crystal 3 is sandwiched between the substrate 1 and the substrate 2. The liquid crystal 3 is composed of, for example, a guest-host liquid crystal in which a dichroic dye is mixed, the dichroic dye is composed of, for example, an azo-based and anthraquinone-based liquid crystal, and the host liquid crystal is composed of, for example, a nematic liquid crystal. .

The substrate 2 is provided with a light scattering layer 9 composed of a polymer dispersion type liquid crystal layer or the like. The light-scattering layer 9 is made of, for example, a mixture of a liquid crystal and a polymer composed of a monomer such as 2-ethylhexyl acrylate and an oligomer such as urethane acrylate, and a liquid crystal on the substrate 2.
By forming it to 10 μm and exposing it to UV light to cure only the polymer, a large number of liquid crystal droplets with a particle size of 1 to several μm are dispersed in the polymer, or the liquid crystal is sponge-like polymer. Are formed to be dispersed. As a result, since a large number of liquid crystals are dispersed in the polymer, the light scattering layer 9 has the property of scattering light. Since this liquid crystal is required to enhance the light scattering effect, it is desirable to use a cyano liquid crystal or the like having high refractive index anisotropy, but a fluorine liquid crystal or the like may be used. If this light-scattering layer 9 is formed on the substrate 1 side, the resolution of the image will be reduced and high-density pixel display will be difficult. Therefore, it is important to provide the light scattering layer 9 on the substrate 2 side.

On the light scattering layer 9, a smoothing film 11 made of, for example, PVA is applied and cured. On this smooth film 11, for example, ITO or the like is deposited by a sputtering method to form the electrode 5. That is, the liquid crystal in the light scattering layer 9 does not need to be driven, and merely serves as a scatterer. In addition, an alignment film 7 for aligning the liquid crystal 3 in a predetermined direction when no voltage is applied is formed on the electrode 5. The alignment film 7 is made of, for example, a polyimide resin.

As another method of forming the scattering portion, a transparent film such as polyethylene terephthalate is sandwiched between substrates with a mixture of polymer and liquid crystal having a thickness of 1 to 10 μm,
It is also possible to form a confusion body in which liquid crystal droplets are dispersed by exposing with UV light.

Next, the operation of the reflective liquid crystal display device according to the present invention will be described. Light incident from the substrate 2 side is scattered by the light scattering layer 9 and enters the guest-host liquid crystal 3. In the guest-host liquid crystal 3, polarized light parallel to the guest molecules is absorbed. Next, since the reflection plate 8 is a mirror surface, the polarized light is retained, and since the polarized light is twisted by 90 degrees by the quarter-wave plate 10, the polarized light perpendicular to the guest molecule which is not absorbed in the outward path is reflected in the guest molecule in the return path. The light is absorbed in parallel with, resulting in a black display.

In a state where the guest molecule is in a standing state, light is not absorbed by the guest molecule in either the outward path or the return path, and thus white display is performed. Even when the light is emitted from the substrate 2 on the return path, the light is scattered by the light scattering layer 9, so that it is easily visually recognized by the observer, and thus the display is easy to see.

[0017]

As described above, according to the liquid crystal display device of the present invention, the light scattering layer made of the polymer dispersion type liquid crystal layer is provided on the side of the substrate opposite to the substrate on which the reflection plate is arranged, and Since the quarter-wave plate is provided between the reflection plate and the substrate, a reflection type liquid crystal display device using a nematic liquid crystal with a low driving voltage can be constructed and is formed on the light scattering layer. The electrodes are flat, the thickness of the liquid crystal layer is uniform, the distribution of the transmittance is small, and the visibility is high.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a reflective liquid crystal display device according to the present invention.

FIG. 2 is a diagram showing a conventional reflective liquid crystal display device.

FIG. 3 is a diagram showing another conventional reflective liquid crystal display device.

[Explanation of symbols]

1, 2 ... Substrate, 3 ... Liquid crystal, 4, 5 electrodes, 6, 7
... Alignment film, 8 ... Reflector, 9 ... Light scattering layer,
10 ... Quarter wave plate

Claims (1)

[Claims] 1. A reflective liquid crystal display device in which a liquid crystal is sandwiched between two substrates on which an electrode and an alignment film are formed, and a reflector is arranged outside one of the substrates, wherein the substrate on which the reflector is arranged is A light-scattering layer composed of a polymer-dispersed liquid crystal layer is provided on the opposite substrate, and 1 / is provided between the reflector and the substrate.
A reflection type liquid crystal display device comprising a four-wave plate.