JP2001021924A - Liquid crystal display device and production thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve contrast by holding a liquid crystal layer containing a dichroic dye between substrates, on which electrodes are formed and adding a gelling agent to the liquid crystal layer. SOLUTION: This device consists of substrates 1, 2 on which first and second electrodes 3, 4 facing each other are formed, respectively, and a liquid crystal layer containing a dichroic dye 8 held between the substrates, and a gelling agent 11 is added to the liquid crystal layer. Preferably, the gelling agent 11 has characteristic groups expressed by the formula. In the formula, A is a divalent functional group. The proportion of the gelling agent 11 added is preferably <=1 mol%. Since the gelling agent 11 forms an intermolecular hydrogen bond to gel, it generates hydrogen bonds which are weak bonds with the liquid crystal molecules and therefore, its restraint on the liquid crystal 7 is low and does not inhibit the response of the liquid crystal 7 to the electric field though the viscosity of the liquid crystal increases. Moreover, by gelling, random alignment of the liquid crystal 7 and the dye 8 is suppressed to increase the apparent order parameter and the interaction between the liquid crystal 7 and the dye 8 and to make the contrast improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an element used for a display device using a liquid crystal and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, in a liquid crystal element, electrodes are formed on opposing substrates, and a voltage is applied to a liquid crystal held between them, thereby changing the alignment state and changing the light transmission state. It is a thing using. Therefore, controlling the alignment of the liquid crystal is indispensable for improving the display performance, and the improvement of the order parameter of the liquid crystal, the development of the alignment film, and the research on the alignment method have been actively conducted. In addition, since bright display can be realized by effectively using light, improvements in polarizing plates and development of optical components such as reflectors and scattering plates have been conducted.

[0003] Above all, a guest-host (G) using a dichroic dye capable of eliminating a polarizing plate or forming a single sheet.
The H) type liquid crystal display device is considered to be effective as a reflection type display mode because light can be effectively used.

FIG. 4 is a sectional view of a guest-host liquid crystal element. A first substrate 1 on which a first electrode 3 is formed, and a second electrode 4
The second substrates 2 on which are formed are opposed to each other, and alignment films 5 and 6 subjected to a parallel alignment process are provided on the respective substrates. Liquid crystal 7 and black dichroic dye 8 between first substrate 1 and second substrate 2
To form a liquid crystal display element. When no voltage is applied, the liquid crystal 7 and the dichroic dye 8 are in a homogeneous alignment.
Since the dye is twisted by 0 degrees, the light absorption axis of the dye absorbs light in any direction and becomes a dark state. When a voltage is applied, the dichroic dye 9 rises and changes its direction following the movement of the liquid crystal molecules 10 due to the application of the voltage, becomes perpendicular to the substrate, and the light absorption of the dye is reduced, resulting in a bright state. However, if the order parameter of the liquid crystal is not too high, the orientation direction varies, and the orientation of the dichroic dye following the movement of the liquid crystal also varies. For this reason, when no voltage is applied, the black in the dark state does not sink due to the disturbance of the alignment due to the disorder of the alignment, or when the voltage is applied, the direction and angle at which the liquid crystal rises with respect to the substrate vary, and the absorption of the dichroic dye is not uniform. There is a problem that the white of the state becomes dark and the contrast becomes low as a whole.

[0005]

As described above, the conventional GH type liquid crystal display device using a dichroic dye is effective as a bright display mode, but has a low contrast because the order parameter of the liquid crystal is low. There is a problem.

An object of the present invention is to provide a liquid crystal display device having a high contrast by improving the order parameter of the liquid crystal in consideration of such a problem of the display device.

[0007]

According to the present invention, in order to achieve the above object, there is provided a substrate on which opposed first and second electrodes are formed, and a liquid crystal layer containing a dichroic dye held between the substrates. , A gelling agent was added to the liquid crystal layer.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The liquid crystal display device of the present invention is a guest-host type liquid crystal display device using a dye as a guest and a liquid crystal as a host. The liquid crystal layer as a host is represented by a general formula (Formula 2). It is characterized by containing a gelling agent. In the general formula (Chemical Formula 2), A is a divalent functional group.

[0009]

Embedded image

In particular, when the liquid crystal molecules have a structure having a benzene ring, the orientation ability of the liquid crystal layer is remarkably improved by mixing the compound represented by the general formula (Formula 2). The alignment ability is also improved for molecules.

In addition, since the gelling agent represented by the general formula (Formula 2) forms an intermolecular hydrogen bond and gels, it also forms a weak bond called a hydrogen bond with liquid crystal molecules. As a result, the liquid crystal is less restricted and the viscosity is increased, but does not hinder the response of the liquid crystal to the electric field. Furthermore, by gelation,
The liquid crystal and the dye can be prevented from being randomly oriented, the apparent order parameter can be improved, the interaction between the liquid crystal and the dye can be increased, and the contrast can be improved.

In the method of manufacturing a liquid crystal display element according to the present invention, there is provided a step of fixing a substrate having an alignment-treated first electrode and a similar second substrate while maintaining a predetermined interval therebetween. And enclosing a mixture containing at least dichroic dye molecules, liquid crystal molecules, and a gelling agent in the gap.

As the orientation treatment of the substrate, a polyimide resin for parallel orientation or vertical orientation was applied and baked. Here, as a method for forming the alignment film, in addition to the above, lecithin or a silane-based surfactant is applied by a printing method, a dip method, a spray method, or the like, or a method of vaporizing the silane-based surfactant. Can be Further, when the surface of the vertical alignment film or the horizontal alignment film is rubbed, the alignment direction of the liquid crystal can be regulated. Recently, a technique has been developed in which molecules of an alignment film are controlled in a deflection direction by irradiating polarized light of ultraviolet light to regulate the alignment direction of a liquid crystal, and this method can also be used. By controlling the molecular structures of the alignment film and the gelling agent, the gelling agent can be aligned just by coating the alignment film, and the liquid crystal and the dye can be aligned in that direction.

The first substrate and the second substrate which have been subjected to the above-mentioned alignment treatment are opposed to each other and bonded together via a spacer. Resin balls of a fixed size were used as spacers. Alternatively, a photoresist having a constant thickness can be formed by applying a photoresist on the first substrate and developing the photoresist by applying ultraviolet rays only to the spacer portion.

As a method of enclosing a mixture containing dichroic dye molecules, liquid crystal molecules, and a gelling agent in the gap between the first substrate and the second substrate by the spacer, there are capillary injection and vacuum injection. Further, since the viscosity is increased to some extent by the gelling agent, a liquid crystal layer can be formed on the first substrate by spin coating or printing, and the second substrate can be stacked. This can reduce the time-consuming step of implantation.

The mixing of the dichroic dye molecules and the gelling agent into the liquid crystal molecules was carried out by heating the liquid crystal above the phase transition temperature. Furthermore, it was possible to dissolve uniformly in a short time by applying vibration such as applying ultrasonic waves or stirring. Similarly, the chiral agent is mixed with the liquid crystal molecules to the left or
An orientation state twisted to the right can be realized.

As described above, the liquid crystal display device according to the present embodiment can be manufactured. Hereinafter, the present invention will be described in more detail with reference to specific examples, but it goes without saying that the present invention is not limited to the following examples.

Example 1 FIG. 1 shows a schematic configuration of a cross section of a liquid crystal display element according to an embodiment of the present invention. First electrode 3
And the second substrate 4 on which the second electrode 4 is formed.
The substrates 2 were opposed to each other, and alignment films 5 and 6 subjected to a parallel alignment process were provided on the respective substrates. A liquid crystal display element is formed by including a liquid crystal 7, a black dichroic dye 8, a chiral agent and a gelling agent 11 (G1) between the first substrate 1 and the second substrate 2. Note that (G1) is represented by the following general formula (Formula 3). The distance between the substrates was 5 microns.

[0019]

Embedded image

A polyimide resin for parallel alignment was applied as the alignment films 5 and 6 on the surfaces of the first electrode 3 and the second electrode 4 and fired. By rubbing the alignment films 5 and 6, the alignment direction on the second substrate 2 was twisted by 180 degrees with the alignment direction on the opposing first substrate 1 and bonded via a spacer.

A nematic liquid crystal (Np) 7, a black dichroic dye (p-type) 8, a chiral agent and a gelling agent 11 (0.5% mol) are formed between the cells formed by the two substrates 1 and 2. ) Is mixed and injected, resulting in a 180-degree twisted orientation in the cell. When light is incident, the orientation direction of the dichroic dye 8 is twisted by 180 degrees, so that light in any direction is absorbed and becomes dark. When a voltage is applied, the liquid crystal rises and the dye is in the same alignment state, so that light absorption is lost and the liquid crystal enters a bright state.

A cell b (cell a mixed with the gelling agent 11 is referred to as a) was prepared without mixing the gelling agent 11 under the same other conditions, and the transmission was measured in the same manner.
As shown in FIG. 2, the transmittance of the dark state was lower in the case of “a”, and the transmittance in the bright state was increased, so that the contrast was improved.

FIG. 3 shows the results of measuring the contrast of the liquid crystal cell at an imprint voltage of 5 V while changing the amount of the gelling agent to 10 mol%. Up to 0.5 mol%, the improvement in contrast is proportional to the addition amount, and up to 1 mol%, while slightly increasing, and if over 1 mol%, the contrast decreases and the threshold voltage increases. Therefore, in order to improve the contrast, the amount of the gelling agent is preferably set to 2.5 mol% or less. When the amount of the gelling agent exceeds 1 mol%, the contrast starts to decrease. Therefore, the appropriate amount of the gelling agent to improve the contrast is 1 mol% or less. Further, in order to improve the contrast and obtain a particularly good contrast, the amount of the gelling agent added should be between 0.5 mol% and 1 mol%, between 1 mol% and 1.5 mol%, especially 1 mol%. % Is preferable.

(Example 2) A cell was prepared in which G2 represented by the following general formula (Formula 4) was added instead of G1 used in Example 1.

[0025]

Embedded image

During the addition, the mixture was heated to the phase transition temperature of the liquid crystal. When the amount of G2 added was examined, the same contrast improvement as when 0.5% by mole of G1 was added at an amount of 0.1% by mole was obtained.

This is presumably because G2 has a higher gelling ability than G1, so that the order parameter of the liquid crystal can be increased with a small amount (1/5). Further, the gelling agent also binds to the dye molecules, and by strengthening the mutual alignment relationship between the liquid crystal molecules and the dye molecules, the dichroic ratio is consequently increased, which is considered to contribute to the contrast and improvement.

It has also been found that the addition of G2 makes the alignment of liquid crystal molecules and dye molecules uniform, and that these molecules are connected by hydrogen bonds, so that they move at high speed when a voltage is applied.

(Embodiment 3) In the embodiment 3, the homogeneous alignment is performed, but the homeotropic alignment can be achieved by using a vertical alignment film for the substrate. By making the liquid crystal an n-type nematic liquid crystal, when no voltage is applied, the liquid crystal and the dye are arranged perpendicularly to the substrate, transmit light, and enter a bright state. When a voltage is applied, the liquid crystal is arranged in parallel to the substrate, and if there is a chiral agent, the liquid crystal will be in a twisted state. The pigments are arranged in line with that, absorbing light and becoming dark. Also in this case, when the gelling agents (G1 and G2) were added, the transmittance in the bright state was increased and the contrast was improved.

[0030]

According to the present invention, there is provided a liquid crystal display device comprising a substrate on which opposed first and second electrodes are formed and a liquid crystal layer containing a dichroic dye held between the substrates. The agent was added. The liquid crystal molecules and the dye were bound by the gel by adding the gelling agent, and the apparent order parameter was improved, whereby the contrast could be improved. In addition, due to the loose bond with the gelling agent, the alignment of the liquid crystal and the dye could be effectively improved without a large increase in the threshold voltage. Thereby, a display device with high contrast can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of a cross section of a liquid crystal display element.

FIG. 2 is a diagram showing changes in applied voltage and transmittance.

FIG. 3 is a diagram showing a relationship between an additive concentration and a contrast.

FIG. 4 is a diagram showing a schematic configuration of a cross section of a liquid crystal display element.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st board | substrate 2 2nd board | substrate 3 1st electrode 4 2nd electrode 5 Parallel alignment film 6 Parallel alignment film 7 Liquid crystal 8 Dichroic dye 9 Dichroic dye 10 Liquid crystal 11 Gelling agent

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G02F 1/1339 500 G02F 1/1339 500 5G435 G09F 9/00 343 G09F 9/00 343D 9/35 303 9 / 35 303 385 385 F-term (reference) 2H088 FA02 GA11 GA13 HA03 KA30 LA09 2H089 LA07 MA03X NA14 NA17 QA15 RA06 SA17 TA04 2H090 HB08Y HB12Y HC05 HC06 HC07 HC13 KA06 LA02 MA01 MA02 MB01 4H027 BE07 CA03 A04 A07 A07 A03 A03 A02 A07 A03 A04 A07 A03 A03 A04 A07 A03 A02 A FB01 JA01 5G435 AA02 BB12 BB16 CC12 HH20 KK05

Claims (7)

[Claims] 1. A liquid crystal display device comprising a substrate on which opposed first and second electrodes are formed and a liquid crystal layer containing a dichroic dye held between the substrates, wherein a gelling agent is added to the liquid crystal layer. A liquid crystal display device characterized in that: 2. The liquid crystal display device according to claim 1, wherein the gelling agent has the following characteristic group. Embedded image 3. The liquid crystal display device according to claim 1, wherein the amount of the gelling agent is 1 mol% or less. 4. A step of fixing a substrate having a first electrode which has been subjected to an alignment treatment and a similar second substrate so as to face each other with a predetermined distance therebetween, and fix at least dichroic dye molecules in the gap. A method for manufacturing a liquid crystal display device, comprising at least a step of enclosing a mixture containing liquid crystal molecules and a gelling agent. 5. A mixture comprising at least a dichroic dye molecule, a liquid crystal molecule and a gelling agent. 6. A liquid crystal display device comprising a liquid crystal layer having a gelling agent. 7. A liquid crystal display device comprising a liquid crystal layer having a dichroic dye and a gelling agent.