JPH08313938A - Liquid crystal display device - Google Patents

Abstract

PURPOSE: To decrease the reflectance when a black color is displayed and to obtain high contrast by increasing the absorption efficiency of dyes mixed in a guest-host type liquid crystal. CONSTITUTION: Pixel electrodes 3, 4 and common electrodes 5, 6 are formed on the upper and lower electrode substrates 1, 2 in such a manner that each pixel electrode faces the common electrode. White display is obtd. by producing an electric field in the vertical direction, while black display is obtd. by producing an electric field in the horizontal direction. Thereby, reflectance for light is decreased when a black state is displayed and a display of high contrast is obtd.

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 used in personal computers, portable information equipments and various other electronic equipments.

[0002]

2. Description of the Related Art As a so-called panel type display device, various display principles are known. In particular, liquid crystal display devices utilizing the electro-optical characteristics of liquid crystals have been widely used as thin and lightweight display means in recent years.

In general, a liquid crystal display device sandwiches a liquid crystal in which molecules are oriented in a predetermined direction between a pair of substrates in which a large number of electrodes are arranged, and an electric field is applied between the electrodes to direct the orientation of the molecules. Instead, it transmits and blocks light to display an image.

In the liquid crystal display device of the above type, an alignment film is provided on the electrodes, and the alignment film defines the alignment direction of liquid crystal molecules.

On the other hand, in a so-called polymer dispersion type liquid crystal display device in which a guest-host type liquid crystal substance mixed with a dye is dispersed in a polymer, an image is displayed without the above-mentioned alignment film.

The prior art relating to this type of polymer-dispersed liquid crystal display device is disclosed in, for example, Tokushusho Sho-6.
It is disclosed in Japanese Patent Laid-Open No. 2-502780.

[0007]

In the above-mentioned conventional polymer dispersion type liquid crystal display device, since the molecular alignment of the liquid crystal is random in the state where no electric field is applied, the reflectance of the dye is high at the time of black display, Light absorption was not efficient, and there was a limit to the improvement of contrast.

It is an object of the present invention to provide a liquid crystal display device which solves the above-mentioned problems of the prior art and reduces the reflectance of black display to improve the contrast ratio.

[0009]

In order to achieve the above object, the first invention according to claim 1 encloses a guest-host type liquid crystal between a pair of substrates each having an electrode on the opposite surface. In a liquid crystal display device, a pixel electrode and a common electrode are alternately arranged on each of the pair of substrates, and a pixel electrode formed on one of the pair of substrates and a common electrode formed on the other substrate. It is formed at positions facing each other through the liquid crystal, and the direction of the electric field formed between the pixel electrode and the common electrode formed on the pair of substrates is controlled to change the molecular alignment direction of the liquid crystal. Characterize.

A second invention according to claim 2 has one common electrode over the entire inner surface of one of the pair of substrates,
Individual electrodes and the other common electrode are alternately arranged on the inner surface of the other substrate, and a guest-host type liquid crystal is sealed between both substrates, and one common electrode formed on one of the pair of substrates and the other common electrode. It is characterized in that the direction of the electric field formed between the pixel electrode and the common electrode formed on the substrate is controlled to change the molecular orientation direction of the liquid crystal.

Further, a third invention according to claim 3 is
In the first and second inventions, the direction of the electric field is controlled to be a direction perpendicular to the pair of substrate surfaces. Further, a fourth invention according to claim 4 is the above-mentioned first invention.
The direction of the electric field in the second invention is controlled to the pair of substrate surfaces and the direction perpendicular to the substrate surfaces.

Further, a fifth invention according to claim 5 is
At least one of the pair of substrates in the first, second, third, or fourth invention is provided with an active element arranged for each pixel.

Further, a sixth invention according to claim 6 is
The invention is characterized in that a reflector is provided on either the outside or the inside of one of the pair of substrates in the first, second, third, fourth, or fifth invention.

And, a seventh invention according to claim 7 is
A reflecting plate is provided outside one of the pair of substrates in the first, second, third, fourth, or fifth invention, and a retardation plate is provided between the reflecting plate and the substrate. And

The retardation plate in the seventh invention is a quarter-wave plate, and instead of the reflection plate in the sixth and seventh inventions, the substrate surface may be mirror-polished. .

Further, the liquid crystal of each of the above inventions can control absorption and transmission of light, and the distance between the pixel electrode and the common electrode formed on the same substrate in the fifth invention is between a pair of substrates. And the display signal input to the electrode of one of the substrates is an inverted signal of the display signal input to the electrode of the other substrate.

[0017]

With the above-described structure of the present invention, the absorption efficiency of the dye in the liquid crystal display device of the type that displays by absorbing and transmitting light by the dye added to the liquid crystal is improved, and the reflectance for black display (at the time of absorption) is improved. High contrast is reduced.

That is, in the structure of the first aspect of the invention, in a liquid crystal display device in which a guest-host type liquid crystal is enclosed between a pair of substrates each having an electrode on the opposite surface, the pixel electrodes formed on the pair of substrates are common. By controlling the direction of the electric field formed between the electrode and the electrode, the molecular orientation direction of the liquid crystal is changed, the absorption efficiency of the dye is improved, and black display (during absorption)
The reflectance is reduced and a high contrast is obtained.

In the structure of the second invention, the direction of the electric field formed between one common electrode formed on one of the pair of substrates and the pixel electrode and the common electrode formed on the other substrate is controlled. By doing so, the molecular orientation direction of the liquid crystal is changed, the light absorption efficiency of the dye is improved, the reflectance of black display (at the time of light absorption) is reduced, and high contrast is obtained.

Furthermore, in the structure of the third invention, the molecular alignment direction of the liquid crystal is changed by controlling the direction of the electric field in the first and second inventions to be a direction perpendicular to the pair of substrate surfaces. The absorption efficiency of the dye is improved, the reflectance of black display (when absorbing light) is reduced, and high contrast is obtained.

Further, in the structure of the fourth invention, the molecules of the liquid crystal are controlled by controlling the direction of the electric field in the first and second inventions to the pair of substrate surfaces and a direction perpendicular to the substrate surfaces. The orientation direction changes, the light absorption efficiency of the dye is improved, the reflectance of black display (at the time of light absorption) is reduced, and high contrast is obtained.

Further, in the structure of the fifth invention, the active element arranged for each pixel is provided on at least one of the pair of substrates in the first, second, third, or fourth invention. A so-called active matrix type liquid crystal display device is configured, and high contrast liquid crystal display can be performed.

Further, in the structure of the sixth invention, a reflector is provided on either the outside or the inside of the pair of substrates in the first, second, third, fourth or fifth invention. As a result, a bright display can be obtained by increasing the efficiency of incident light.

In the structure of the seventh invention, a reflector is provided outside one of the pair of substrates in the first, second, third, fourth or fifth invention, and the reflector plate and By providing the phase difference plate between the substrates, the light absorption effect is increased, and a display with higher contrast can be obtained.

[0025]

Embodiments of the liquid crystal display device according to the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a cross-sectional view of an essential part for explaining the structure of a first embodiment of a liquid crystal display device according to the present invention, in which 1 is an upper electrode substrate, 2 is a lower electrode substrate, 3 is an upper pixel electrode, 4 Is a lower pixel electrode, 5 is an upper common electrode, 6 is a lower common electrode, 7
Is a polymer-dispersed guest-host liquid crystal, 8 is a dye, and 9 is a reflector.

In the figure, the upper electrode substrate 1 corresponds to one of a pair of substrates, and is made of glass or a plastic plate and a plastic film, and the lower electrode substrate 2 also corresponds to the other of the pair of substrates. It consists of a plastic plate.

The upper pixel electrode 3 and the upper common electrode 5 are arranged adjacent to each other on the upper electrode substrate 1, and the lower pixel electrode 4 and the lower common electrode 6 are adjacent to each other on the lower electrode substrate 2. It is arranged to fit.

A position where the upper pixel electrode 3 of the upper electrode substrate 1 and the lower common electrode 6 of the lower electrode substrate 2 face each other, and the lower pixel electrode 4 of the lower electrode substrate 2 and the upper common electrode 5 of the upper electrode substrate 1 face each other. The guest-host liquid crystal 7 mixed with the dye 8 is sandwiched between the two electrode substrates 1 and 2. Further, a reflection plate 9 is installed on the back surface of the electrode substrate 2.

In the liquid crystal display device having the above-described structure, signals having opposite polarities are applied between the lower pixel electrode 4 and the upper common electrode 5 to form an electric field in a direction perpendicular to both substrate surfaces. The molecules are oriented vertically and transmit light to give a white display.

On the other hand, signals of opposite polarities are applied between the lower pixel electrode 4 and the lower common electrode 6, or signals of opposite polarities are simultaneously applied between the upper pixel electrode 3 and the upper common electrode 6. By forming an electric field parallel to the surfaces of the substrates, the liquid crystal molecules are aligned in the direction parallel to the surfaces of both substrates, and the light is absorbed by the dye 8 to display black.

According to this embodiment, the light absorption effect of the dye is enhanced, and a liquid crystal display device capable of high-contrast display can be obtained.

FIG. 2 is a sectional view of an essential part for explaining the structure of the second embodiment of the liquid crystal display device according to the present invention, in which 10 is a retardation plate consisting of a quarter-wave plate, and the same reference numerals as those in FIG. Corresponds to the same part.

In the figure, the upper electrode substrate 1 corresponds to one of the pair of substrates, is made of a glass or plastic plate, and the lower electrode substrate also corresponds to the other of the pair of substrates.
Made of glass or plastic plate.

The upper pixel electrode 3 and the upper common electrode 5 are arranged adjacent to each other on the upper electrode substrate 1, and the lower pixel electrode 4 and the lower common electrode 6 are adjacent to each other on the lower electrode substrate 2. It is arranged to fit.

The upper pixel electrode 3 of the upper electrode substrate 1 and the lower common electrode 6 of the lower electrode substrate 2, and the lower pixel electrode 4 of the lower electrode substrate 2 and the upper common electrode 5 of the upper electrode substrate 1 face each other. The guest-host liquid crystal 7 mixed with the dye 8 is sandwiched between the two electrode substrates 1 and 2.

On the back surface of the lower electrode substrate 2, the phase difference plate 1 is provided.
The reflection plate 9 is installed via 0.

With this structure, the polarization direction of the light when the electric field is formed in the direction parallel to the surface of the electrode substrate is rotated by the retardation plate 10, so that the light absorption at the time of black display is improved and the contrast is further enhanced. Can be displayed.

FIG. 3 is a cross-sectional view of an essential part for explaining the constitution of the third embodiment of the liquid crystal display device according to the present invention.

In the figure, the upper electrode substrate 1 corresponds to one of the pair of substrates, is made of a glass or plastic plate, and the lower electrode substrate also corresponds to the other of the pair of substrates.
Made of glass or plastic plate.

The upper pixel electrode 3 and the upper common electrode 5 are arranged on the upper electrode substrate 1 so as to be adjacent to each other, and the lower pixel electrode 4 is arranged on the lower electrode substrate 2 via a reflector 9 made of an insulating material. The lower common electrode 6 is arranged so as to be adjacent to each other.

The upper pixel electrode 3 of the upper electrode substrate 1 and the lower common electrode 6 of the lower electrode substrate 2, and the lower pixel electrode 4 of the lower electrode substrate 2 and the upper common electrode 5 of the upper electrode substrate 1 face each other. The guest-host liquid crystal 7 mixed with the dye 8 is sandwiched between the two electrode substrates 1 and 2.

With this structure, since the reflection plate 9 is installed on the inner surface of the lower electrode substrate, a liquid crystal display device having a high reflection efficiency of incident light and capable of high contrast display can be obtained.

Although the reflector 9 in the present embodiment is an insulator, it is made of a conductive material and the lower pixel electrode 4 and the lower common electrode 6 are formed via an insulating layer. You may

FIG. 4 is a cross-sectional view of an essential part for explaining the constitution of the fourth embodiment of the liquid crystal display device according to the present invention.

In the figure, the upper electrode substrate 1 corresponds to one of the pair of substrates, is made of a glass or plastic plate, and the lower electrode substrate also corresponds to the other of the pair of substrates.
Made of glass or plastic plate.

The upper pixel electrode 3 and the upper common electrode 5 are arranged on the upper electrode substrate 1 so as to be adjacent to each other. On the lower electrode substrate 2, the lower pixel electrode 4 is formed below the reflector 9 made of an insulating material. And the lower common electrode 6 is arranged adjacent to each other.

The upper pixel electrode 3 of the upper electrode substrate 1 and the lower common electrode 6 of the lower electrode substrate 2, and the lower pixel electrode 4 of the lower electrode substrate 2 and the upper common electrode 5 of the upper electrode substrate 1 face each other. The guest-host liquid crystal 7 mixed with the dye 8 is sandwiched between the two electrode substrates 1 and 2.

With this structure, since the reflecting plate 9 is installed on the entire surface of the lower electrode substrate 2, light absorption at the lower electrode is reduced, the reflection efficiency of incident light is further increased, and a higher contrast display is achieved. A possible liquid crystal display device can be obtained.

Although the reflector 9 in this embodiment is an insulator, it is made of a conductive material, and an insulating layer is provided between the lower pixel electrode 4, the lower common electrode 6 and the reflector 9. You may form through.

FIG. 5 is a plan view of an essential part for explaining an example of the electrode substrate of the liquid crystal display device according to the present invention, in which 11 is a signal electrode, 12 is a scanning electrode, 13 is a pixel electrode, 14 is a common electrode, and 15 is a common electrode. It is an active element.

The pixel electrode 13 corresponds to the upper pixel electrode 3 or the lower pixel electrode 4 in each of the above embodiments, and the common electrode 14 is the upper common electrode 5 or the lower common electrode 6 similarly.
Corresponding to.

In the figure, the signal electrode 11 and the scanning electrode 1
2 are arranged in a grid pattern, and the active elements 15 are arranged at the intersections of these.

The pixel electrode 13 and the common electrode 14 are formed in a comb-teeth shape and are connected to the active element 15, and the comb-teeth are arranged adjacent to each other.

The total number of comb teeth of the pixel electrode 13 and the common electrode 14 is set to an even number, and the gap between the comb teeth of the pixel electrode 13 and the common electrode 14 is made symmetrical with respect to the pixel pitch, thereby making the same. It is possible to form a liquid crystal element with the electrode substrate. FIG. 6 is a block diagram illustrating a configuration example of a drive circuit of a liquid crystal display device according to the present invention. 161 is an upper substrate signal side drive circuit, 162 is a lower substrate signal side drive circuit, 17 is a scanning side drive circuit, and 18 Is a display signal, 19 is a signal side synchronization signal, 20 is a scanning side synchronization signal, 2
Reference numeral 1 is a display signal inverting circuit, 22 is an upper common power source, 23 is a lower common power source, and the same reference numerals as those in the above embodiment correspond to the same portions.

In the figure, the upper electrode substrate 1 is driven by the upper substrate signal side drive circuit 161, the scanning side drive circuit 17 and the upper side common power supply 22. Similarly, the lower electrode substrate 2
Is driven by the lower substrate signal side drive circuit 162, the scanning side drive circuit 17, and the lower common power supply 23.

The signals given to the upper substrate signal side drive circuit 161 and the lower substrate signal side drive circuit 162 are the display signal inversion circuit 21.
Therefore, the display signal 18 and the signal-side synchronization signal 19 which are the same signal are input, respectively, and the common power supplies 22 and 23 apply voltages of opposite polarities.

This drive circuit drives the liquid crystal display device of each of the above-described embodiments, and has the effect of the present invention.

FIG. 7 is a cross-sectional view of an essential part for explaining the structure of the fifth embodiment of the liquid crystal display device according to the present invention. 1 is an upper electrode substrate, 2 is a lower electrode substrate, 3 is an upper pixel electrode, 4 Is a lower pixel electrode, 5 is an upper common electrode, 6 is a lower common electrode, 7
Is a polymer-dispersed guest-host liquid crystal, 8 is a dye, and 9 is a reflector.

In the figure, the upper electrode substrate 1 corresponds to one of the pair of substrates, is made of a glass or plastic plate, and the lower electrode substrate also corresponds to the other of the pair of substrates.
Made of glass or plastic plate.

The upper common electrode 5 is formed on the entire surface of the upper electrode substrate 1, and the lower pixel electrode 4 and the lower common electrode 6 are arranged adjacent to each other on the lower electrode substrate 2. A guest-host liquid crystal 7 containing a dye 8 is sandwiched between the upper electrode substrate 1 and the lower electrode substrate 2. A reflector 9 is installed on the back surface of the electrode substrate 2.

In the liquid crystal display device configured as described above, when signals of opposite polarities are applied between the lower pixel electrode 4 and the upper common electrode 5 to form an electric field in a direction perpendicular to both substrate surfaces, the liquid crystal is formed. The molecules are oriented vertically and transmit light to give a white display.

On the other hand, signals of opposite polarities are applied between the lower pixel electrode 4 and the lower common electrode 6 to form an electric field parallel to the substrate surfaces, so that the liquid crystal molecules are aligned in a direction parallel to both substrate surfaces. The light is oriented, and the light is absorbed by the dye 8 to give a black display.

Also in this embodiment, the light absorption effect of the dye is enhanced, and a liquid crystal display device capable of high-contrast display can be obtained.

The reflector 9 in this embodiment may be constructed as shown in FIG. 3 or FIG. 4, or the retardation plate shown in FIG. 2 may be installed.

[0066]

As described above, according to the present invention,
In a liquid crystal display device that uses a liquid crystal mixed with a dye to display by absorbing and transmitting light by the dye, the reflectance at the time of black display is significantly reduced, and the contrast ratio is improved. The image display of can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view of an essential part for explaining the configuration of a first embodiment of a liquid crystal display device according to the present invention.

FIG. 2 is a cross-sectional view of essential parts for explaining the configuration of a second embodiment of the liquid crystal display device according to the present invention.

FIG. 3 is a cross-sectional view of essential parts for explaining the configuration of a third embodiment of the liquid crystal display device according to the present invention.

FIG. 4 is a cross-sectional view of essential parts for explaining the configuration of a fourth embodiment of the liquid crystal display device according to the present invention.

FIG. 5 is a plan view of relevant parts for explaining an example of the electrode substrate of the liquid crystal display device according to the present invention.

FIG. 6 is a block diagram illustrating a configuration example of a drive circuit of a liquid crystal display device according to the present invention.

FIG. 7 is a cross-sectional view of essential parts for explaining the configuration of a fifth embodiment of the liquid crystal display device according to the present invention.

[Explanation of symbols]

 1 Upper Electrode Substrate 2 Lower Electrode Substrate 3 Upper Pixel Electrode 4 Lower Pixel Electrode 5 Upper Common Electrode 6 Lower Common Electrode 7 Polymer Dispersed Guest Host Liquid Crystal 8 Dye 9 Reflector 10 Phase Difference Plate 11 Signal Electrode 12 Scanning Electrode 13 Pixel electrode 14 Common electrode 15 Active element 161 Upper substrate signal side driving circuit 162 Lower substrate signal side driving circuit 17 Scan side driving circuit 18 Display signal 19 Signal side synchronizing signal 20 Scan side synchronizing signal 21 Display signal inverting circuit 22 Upper common power supply 23 Lower common power supply.

Claims (7)

[Claims] 1. A liquid crystal display device in which a guest-host type liquid crystal is sealed between a pair of substrates each having an electrode on its opposite surface, wherein a pixel electrode and a common electrode are alternately arranged on each of the pair of substrates, A pixel electrode formed on one of the pair of substrates and a common electrode formed on the other substrate are formed at positions facing each other through the liquid crystal, and the pixel electrode formed on the pair of substrates A liquid crystal display device, wherein a direction of an electric field formed between the liquid crystal display device and a common electrode is controlled to change a molecular alignment direction of the liquid crystal. 2. A guest-host type liquid crystal having a common electrode on the entire inner surface of one of a pair of substrates, the individual electrodes and the other common electrode being alternately arranged on the inner surface of the other substrate, between the substrates. The liquid crystal molecules are aligned by controlling the direction of an electric field formed between one common electrode formed on one of the pair of substrates and the pixel electrode and the common electrode formed on the other substrate. A liquid crystal display device characterized by changing directions. 3. The liquid crystal display device according to claim 1, wherein the direction of the electric field is controlled in a direction perpendicular to the pair of substrate surfaces. 4. The liquid crystal display device according to claim 1, wherein the direction of the electric field is controlled to be the pair of substrate surfaces and a direction perpendicular to the substrate surfaces. 5. The liquid crystal display device according to claim 1, wherein at least one of the pair of substrates is provided with an active element arranged for each pixel. 6. A liquid crystal display device according to any one of claims 1, 2, 3, 4 or 5, wherein a reflector is provided on either the outside or the inside of the pair of substrates. 7. A reflector according to claim 1, 2, 3, 4, or 5, wherein a reflection plate is provided outside one of the pair of substrates, and a retardation plate is provided between the reflection plate and the substrate. Characteristic liquid crystal display device.