JPH1048602A - Liquid crystal display device and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a intra-surface response type liquid crystal display device which is drivable with a low voltage and is free from after-images. SOLUTION: A cell is formed by subjecting the surfaces of both of a substrate 1a and counter substrate 1b having comb-shaped pixel electrodes 2 and counter electrodes 3 to surface treatments for parallel orienting liquid crystal molecules to form oriented films 7 and sticking the two substrates to each other. A liquid mixture of photoreactive monomers which are monomers contg. unsatd. bonds and liquid crystals 4 having positive dielectric anisotropy is injected into this cell and thereafter, the cell is sealed. The liquid crystal cell is then subjected to photoirradiation for a specified period of time, by which the photoreactive monomers are polymerized to high-molecular polymers 5 existing like meshes in the liquid crystals 4. Since the netlike shape of the high polymers is formed in the liquid crystals 4, liquid crystal orientation is maintained to some extent and the occurrence/loss of disclination lines by voltage impression/non-impression are suppressed and good display characteristics are obtd. Since the liquid crystals 4 having the positive dielectric anisotropy are usable, the low-voltage driving is possible.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an in-plane response type liquid crystal display device and a method of manufacturing the same, and more particularly to an improvement in display characteristics thereof.

[0002]

2. Description of the Related Art Liquid crystal display devices are widely used as display devices for watches, calculators, etc. because of their features such as thinness, light weight, and low power consumption. Especially thin film transistor (TF
TN-type liquid crystal display devices that perform active driving by T) or the like are being replaced by CRTs, which are the most common conventional display devices, in display devices such as word processors and personal computers, televisions, and the like. But this T
The N-type liquid crystal display device generally has a problem that the viewing angle is narrow, and when viewed from an oblique direction, the contrast is reduced and the gradation is inverted. In particular, in recent years, the size of liquid crystal display devices has been increased, and there is a difference in display even when viewing the upper, lower, left and right ends of the display surface from the same observation point.

The display principle of the TN type liquid crystal display device will be described below. In the normally white mode, the polarizing plate is installed in crossed Nicols. When no voltage is applied, the liquid crystal molecules are twisted by 90 ° between the upper and lower substrates, and light is transmitted due to the optical rotation caused by the twist. On the other hand, when a voltage is applied, the liquid crystal molecules rise, the optical rotation action disappears, and the light is blocked. In a TN-type liquid crystal display device, it is considered that display quality degradation when observed from an oblique direction is caused by anisotropy in a rising direction of liquid crystal molecules. That is, when viewing the liquid crystal molecules rising from one direction from various directions, the optical contribution thereof changes, so that it is considered that a display change with respect to the viewing angle occurs, which can be said to be an essential problem of the TN type liquid crystal display device. In order to solve this problem, recently, an in-plane response type liquid crystal display device has been proposed. This in-plane response type liquid crystal display device forms two interdigital electrodes (interdigital electrodes) on the same substrate, applies a voltage between the electrodes, generates an electric field parallel to the substrate surface, and generates liquid crystal molecules. Is to respond. Generally, the liquid crystal material has a negative dielectric anisotropy (n-type).
Is used.

[0004]

As described above, in a conventional in-plane response type liquid crystal display device, an n-type nematic liquid crystal having a small absolute value of dielectric anisotropy is generally used. There was a problem of getting high. FIG. 3 is a partial cross-sectional view showing a liquid crystal alignment state when a positive dielectric anisotropy (p-type) nematic liquid crystal is used in a conventional in-plane response type liquid crystal display device. In the drawing, 2 is a comb-shaped pixel electrode, 3 is a comb-shaped counter electrode, and 1a is 2
A substrate having two comb-shaped electrodes, 1b is a counter substrate, 4 is a liquid crystal having a positive dielectric anisotropy, 6 is a disclination line, and 7 is an alignment film. As shown in FIG. 3, when a p-type nematic liquid crystal 4 is used in a conventional liquid crystal display device, when a voltage is applied between the comb-shaped pixel electrode 2 and the counter electrode 3, electric lines of force rise between the electrodes. Causes distortion,
Since the liquid crystal molecules 4 attempt to align along the direction of the electric field,
In the vicinity of the center between the electrodes, domains in different alignment states are adjacent to each other, and as a result, a disclination line 6 is generated. Since the occurrence / disappearance of the disclination line 6 involves hysteresis, there is a problem that an afterimage is generated and display quality is reduced. FIG. 4 is a diagram showing a voltage-transmittance curve for explaining the concept of hysteresis. In the figure, ΔT indicates a hysteresis width. If there is a hysteresis, even if the same voltage is applied to the liquid crystal, the transmittance will be different between the step-up process and the step-down process, and when performing display using such a liquid crystal display device, an afterimage appears,
There is a problem that the display quality is extremely reduced.

The present invention has been made to solve the above problems, and provides an in-plane response type liquid crystal display device which can be driven at a low voltage, has no afterimages, and has excellent display characteristics. The purpose is to do.

[0006]

A liquid crystal display device according to the present invention comprises a substrate having a plurality of electrodes arranged in parallel with each other, and a liquid crystal arranged between the substrate and the counter substrate with an alignment film interposed therebetween. A liquid crystal display device provided with a voltage between electrodes to generate an electric field in a substantially horizontal direction on a substrate surface to make liquid crystal respond in-plane, wherein the liquid crystal contains a polymer. Further, the electrodes are such that another comb-shaped electrode is arranged between the electrodes of the comb-shaped electrode. Further, the liquid crystal has a positive dielectric anisotropy. A step of bonding a substrate having a plurality of electrodes arranged in parallel with each other and a substrate facing the substrate after performing a surface treatment for aligning the liquid crystal; and The manufacturing method includes a step of forming a liquid crystal cell by injecting a mixture of monomers and a step of irradiating the liquid crystal cell with light for a certain time to polymerize a photoreactive monomer.

Further, as the mixture of the liquid crystal and the photoreactive monomer, a liquid that exhibits a liquid crystal phase is used. Further, at least one or more acrylic monomers are used as the photoreactive monomer. Further, as a liquid mixture of the liquid crystal and the photoreactive monomer, a mixture containing an acrylic monomer in a weight ratio of 1 wt% or more and 10 wt% or less is used.
Light irradiation is performed in a state where a voltage is applied between the comb-shaped electrodes.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 FIG. FIG. 1 is a partial sectional view showing an in-plane response type liquid crystal display device according to Embodiment 1 of the present invention. In the figure, 1a is a substrate having two comb-shaped electrodes (interdigital electrodes), 1b is a counter substrate, 2 is a comb-shaped pixel electrode, 3 is a comb-shaped counter electrode, and 4 is a positive dielectric anisotropic electrode. A liquid crystal having a property, 7 is an alignment film, 55 is a high molecular polymer present in a network in the liquid crystal 4, and a photoreactive monomer (monomer) is polymerized by light irradiation. In the present embodiment, a voltage is applied between the comb-shaped pixel electrode 2 and the counter electrode 3 arranged on the substrate 1a, an electric field is generated in a substantially horizontal direction on the substrate surface, and the liquid crystal molecules 4 are driven in-plane. In the liquid crystal display device, a photoreactive monomer is mixed into the liquid crystal 4 and polymerized by light irradiation to obtain a high molecular polymer.

A description will be given of a method and an operation of the liquid crystal display device according to the present embodiment. Substrate 1a having comb-shaped pixel electrode 2 and counter electrode 3 and counter substrate 1
A surface treatment is performed on both surfaces of b to align the liquid crystal molecules in parallel to form an alignment film 7. Two substrates are bonded together to form a cell. After injecting a liquid mixture of the photoreactive monomer, which is a monomer containing an unsaturated bond, and the liquid crystal 4 into this cell,
Seal. Next, by irradiating the liquid crystal cell with light for a certain period of time, the photoreactive monomer is polymerized to become a polymer 55 existing in a network in the liquid crystal 4, and a desired liquid crystal display device is obtained. In the liquid crystal display device thus formed, since a polymer network structure is formed in the liquid crystal 4, the liquid crystal alignment during light irradiation, that is, when no voltage is applied is maintained to some extent. This suppresses the occurrence / disappearance of disclination lines, thereby maintaining good display characteristics.

[0010] By using a liquid crystal phase as a liquid mixture of the liquid crystal 4 and the photoreactive monomer, better display characteristics can be maintained. Further, by using at least one kind of acrylic monomer as the photoreactive monomer, the liquid crystal alignment maintaining property of the polymer 55 by irradiation with light is improved. Further, in the liquid mixture of the liquid crystal 4 and the photoreactive monomer, the weight ratio of the acrylic monomer is 1
By setting the content to not less than 10% by weight, good liquid crystal alignment retention characteristics can be obtained.

In the present embodiment, the pixel electrode 2 and the counter electrode 3 for generating a horizontal electric field are comb-shaped and are arranged on the same plane. However, they need not be on the same plane. A structure in which different layers are formed with an insulating film interposed therebetween may be used. Further, the electrode structure may be any shape as long as a horizontal electric field can be applied to the liquid crystal 4, and is not limited to a comb shape.

As described above, according to the present embodiment, since the liquid crystal 4 includes the high polymer 55 forming a network structure, the liquid crystal 4 having a positive dielectric anisotropy is conventionally used. The occurrence / disappearance of the disclination line at the time of voltage application / non-application, which has been a problem, is suppressed, the afterimage phenomenon is eliminated, and a liquid crystal display device with good display characteristics can be obtained.

Embodiment 2 FIG. FIG. 2 is a partial cross-sectional view showing an in-plane response type liquid crystal display device according to Embodiment 2 of the present invention. 2A shows a state in which a voltage is applied between the comb-shaped pixel electrode 2 and the counter electrode 3, and FIG. 2B shows a state in which no voltage is applied. In the figure, 5 indicates a photoreactive monomer which is a monomer containing an unsaturated bond, and 6 indicates a disclination line. In the drawings, the same or corresponding parts have the same reference characters allotted, and description thereof will be omitted.

The liquid crystal display device according to the present embodiment is manufactured by the same method as in the first embodiment. However,
In this embodiment, the liquid crystal cell into which the liquid mixture of the liquid crystal 4 and the photoreactive monomer 5 has been injected is irradiated with light for a certain period of time while a voltage is applied. When a voltage is applied, the lines of electric force are distorted between the pixel electrode 2 and the counter electrode 3 in a mountain-like manner, and the liquid crystal 4 having positive dielectric anisotropy tends to be arranged along the direction of the electric field. In the vicinity of the center, domains having different liquid crystal orientations are adjacent to each other, and as a result, a disclination line 6 is generated. In a state where this voltage is applied, the liquid mixture of the liquid crystal 4 and the photoreactive monomer 5 is irradiated with light, for example, ultraviolet light to polymerize the photoreactive monomer 5, and as shown in FIG. High molecular polymer 5
By setting 5, the disclination line 6 is generated even when no voltage is applied. In the conventional in-plane response type liquid crystal display device, since the occurrence / disappearance of the disclination 6 involves hysteresis, there is a problem that an afterimage is generated and display quality is deteriorated. Since the generation / disappearance of the disclination line 6 due to the application / non-application of the image is eliminated, the occurrence of an afterimage when displaying a moving image is suppressed, and the display quality is improved.

Embodiment 1 FIG. Hereinafter, a method of manufacturing an in-plane response type liquid crystal display device which is Embodiment 1 of the present invention and evaluation results of display characteristics will be described. The structure of the liquid crystal display device of the present embodiment is the same as that of the first embodiment, and is between the substrate 1a on which the comb-shaped pixel electrode 2 and the counter electrode 3 are formed as shown in FIG. The liquid crystal 4 and the polymer 55 having a positive dielectric anisotropy are arranged on the substrate.
The width and interval of the pixel electrode 2 and the counter electrode 3 are both 10
μm, and chromium was used as an electrode material. The surfaces of both substrates 1a and 1b were subjected to a surface treatment for aligning the liquid crystal 4 in parallel, and were bonded together so that the cell gap was 4 μm.

As a liquid crystal material, a liquid crystal E8 manufactured by Merck Co., Ltd. was used, to which 2,2-dimethoxy-2 as a polymerization initiator was added.
When 20% by weight of a photoreactive monomer 2-ethylhexyl acrylate containing 5% by weight of -phenylacetophenone was mixed, an isotropic liquid state was obtained. After injecting the liquid between the substrates, the liquid was irradiated with ultraviolet light having an illuminance of 50 mW / cm2 for 4 hours.
When irradiated for 0 seconds, phase separation occurs and the liquid crystal phase is formed again.
Created the desired cell. When a moving image was displayed on the liquid crystal display device described above, good display characteristics with no afterimage were exhibited.

Embodiment 2 FIG. The structure of the liquid crystal display according to the second embodiment of the present invention is the same as that of the first embodiment, and the description is omitted. As a liquid crystal material, a liquid crystal E8 manufactured by Merck was used, and 2,2-dimethoxy-2-, a polymerization initiator, was added thereto.
Photoreactive monomer mixture containing 15% by weight of phenylacetophenone (2-ethylhexyl acrylate / 1,6
-Hexyl diacrylate = 7/3) was mixed at 4 wt% to show a liquid crystal phase. After injecting the liquid between the substrates, the liquid was irradiated with ultraviolet light having an illuminance of 50 mW / cm2 for 60 seconds,
Created the desired cell. When a moving image was displayed on the liquid crystal display device described above, good display characteristics with no afterimage were exhibited.

Embodiment 3 FIG. The structure of the liquid crystal display according to the third embodiment of the present invention is the same as that of the first embodiment, and the description is omitted. As a liquid crystal material, a liquid crystal E8 manufactured by Merck was used, and 2,2-dimethoxy-2-, a polymerization initiator, was added thereto.
A photoreactive monomer mixture containing 5% by weight of phenylacetophenone (2-ethylhexyl acrylate / 1,6-
(Hexyl diacrylate = 7/3) was mixed at 4 wt%. After injecting this liquid between the substrates, the illuminance 50 mW / cm 2
Was irradiated for 60 seconds to form a target cell. When a moving image was displayed on the liquid crystal display device described above, good display characteristics with no afterimage were exhibited.

Embodiment 4 FIG. The structure of the liquid crystal display according to the fourth embodiment of the present invention is the same as that of the first embodiment, and the description is omitted. As a liquid crystal material, a liquid crystal E8 manufactured by Merck was used, and 2,2-dimethoxy-2-, a polymerization initiator, was added thereto.
A photoreactive monomer mixture containing 5% by weight of phenylacetophenone (2-ethylhexyl acrylate / 1,6-
Hexyl diacrylate = 7/3) was mixed at 1 wt%. After injecting this liquid between the substrates, the illuminance 50 mW / cm 2
Was irradiated for 60 seconds to form a target cell. When a moving image was displayed on the liquid crystal display device described above, good display characteristics with no afterimage were exhibited.

Embodiment 5 FIG. The structure of the liquid crystal display according to the fifth embodiment of the present invention is the same as that of the first embodiment, and the description is omitted. As a liquid crystal material, a liquid crystal E8 manufactured by Merck was used, and 2,2-dimethoxy-2-, a polymerization initiator, was added thereto.
A photoreactive monomer mixture containing 5% by weight of phenylacetophenone (2-ethylhexyl acrylate / 1,6-
(Hexyl diacrylate = 7/3) was mixed at 4 wt%. After injecting the liquid between the substrates, the cell was irradiated with ultraviolet light having an illuminance of 50 mW / cm 2 for 60 seconds while applying a voltage of 6 V, thereby forming a target cell. When a moving image was displayed on the liquid crystal display device described above, good display characteristics with no afterimage were exhibited.

[0021]

As described above, according to the present invention, since the polymer is formed so as to form a network structure in the liquid crystal, the occurrence of disclination lines when voltage is applied / not applied is reduced. Loss can be suppressed, there is no afterimage,
A liquid crystal display device having good display characteristics can be obtained.

Further, since a P-type liquid crystal having a large absolute value of dielectric anisotropy can be used, a liquid crystal display device which can be driven at a low voltage can be obtained.

[Brief description of the drawings]

FIG. 1 is a partial sectional view showing an in-plane response type liquid crystal display device according to a first embodiment of the present invention.

FIG. 2 is a partial cross-sectional view showing a case where light irradiation is performed while applying a voltage to a liquid crystal display device according to a second embodiment of the present invention.

FIG. 3 is a partial cross-sectional view showing an alignment state when a liquid crystal having a positive dielectric anisotropy is used in a conventional in-plane response type liquid crystal display device.

FIG. 4 is a voltage-transmittance curve diagram for explaining the concept of hysteresis.

[Explanation of symbols]

1a a substrate having two comb-shaped electrodes, 1b a counter substrate,
2 pixel electrode, 3 counter electrode, 4 liquid crystal having positive dielectric anisotropy, 5 photoreactive monomer, 6 disclination line, 7 alignment film 55 polymer.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shin Tabata 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Mitsui Electric Co., Ltd. (72) Inventor Masaya Mizunuma 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Rishi Electric Co., Ltd. (72) Inventor Yasuhiro Morii 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Sanbishi Electric Co., Ltd. (72) Inventor Masayuki Fujii 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Mitsui Electric Inside the corporation

Claims (8)

[Claims] A substrate having a plurality of electrodes arranged in parallel with each other, a liquid crystal arranged between the substrate and the counter substrate via an alignment film, and applying a voltage between the plurality of electrodes; What is claimed is: 1. A liquid crystal display device that generates an electric field in a substantially horizontal direction on a substrate surface and makes the liquid crystal respond in-plane, wherein the liquid crystal contains a polymer. 2. The electrode according to claim 1, wherein another comb-shaped electrode is arranged between each of the comb-shaped electrodes.
The liquid crystal display device as described in the above. 3. The liquid crystal display device according to claim 1, wherein the liquid crystal has a positive dielectric anisotropy. 4. A step of bonding a substrate having a plurality of electrodes arranged in parallel with each other and a substrate facing the substrate after performing a surface treatment for aligning liquid crystal,
Inject a mixture of liquid crystal and photoreactive monomer between the substrates,
A method for manufacturing a liquid crystal display device, comprising: a step of forming a liquid crystal cell; and a step of irradiating the liquid crystal cell with light for a predetermined time to polymerize the photoreactive monomer. 5. A liquid mixture of a liquid crystal and a photoreactive monomer,
5. The method according to claim 4, wherein a liquid crystal phase is used. 6. The method according to claim 4, wherein at least one kind of acrylic monomer is used as the photoreactive monomer. 7. A liquid mixture of a liquid crystal and a photoreactive monomer,
7. The method for manufacturing a liquid crystal display device according to claim 6, wherein an acrylic monomer containing a weight ratio of 1 wt% or more and 10 wt% or less is used. 8. The method for manufacturing a liquid crystal display device according to claim 4, wherein the light irradiation is performed while a voltage is applied between the electrodes.