JP2023070535A - Liquid crystal display device - Google Patents

Abstract

To provide a multi-domain vertically aligned liquid crystal element with which the specific resistance of a liquid crystal is stabilized and damage due to static electricity is reduced by adding a charging removal function agent to the liquid crystal.SOLUTION: A multi-domain vertically aligned liquid crystal display device comprises: first and second substrates which are arranged facing each other and have light transmissivity; first and second transparent electrodes having a prescribed pattern which are formed on the facing surfaces of the first and second substrates, the first and second transparent electrodes having a plurality of slits formed by removing the electrodes in a shape of substantially a rectangle, with the slits in one substrate and the slits in the other substrate arranged alternately along a direction that is orthogonal to the longitudinal direction of the slits; first and second vertical alignment films which are formed covering the first and second transparent electrodes; and a liquid crystal layer that fills a space between the first and second vertical alignment films, the liquid crystal layer formed including a nonionic substance, and added with a charge removal function agent which has a functionality to reduce damage due to electrostatic discharge.SELECTED DRAWING: Figure 1

Description

The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device having a vertically aligned liquid crystal cell.

As a liquid crystal display device capable of achieving high contrast, there is a vertically aligned liquid crystal display device in which liquid crystal molecules arranged between opposing substrates are aligned in a direction perpendicular to the substrate surfaces. A voltage is applied between the counter electrodes formed on the counter substrate, and the liquid crystal molecules are tilted to perform display. In order to define the direction in which the liquid crystal molecules fall, a method of forming an alignment film on the electrode surface and performing rubbing to give a pretilt is widely used. In this case, the tilting direction is usually one direction.

In order to obtain a wide viewing angle region, it is desirable to have a multi-domain with two or more tilt directions. As a method of forming a multi-domain, there is a method of forming slits in electrodes. When one electrode provided with a slit and the other electrode without a slit face each other, the electric lines of force generated from the position corresponding to the center of the slit of the other electrode are directed to the electrode ends on both sides of the slit of the one electrode. head to the department. Gradient electric fields tilted in different directions are formed across the slit.

FIG. 7 shows a configuration in which slits 108 and 118 are alternately arranged in transparent electrodes 104 and 114 formed on opposing surfaces of opposing transparent substrates 103 and 113 arranged in parallel, with their in-plane positions shifted by half a pitch. indicates The electric lines of force 120 directed from the ends of the electrode 104 on both sides of the slit 108 to the opposing electrode 114 form a symmetrically inclined oblique electric field. The direction in which the liquid crystal molecules fall when a voltage is applied is reversed. In this manner, two alignment domains in which the alignment directions of liquid crystal molecules are different can be formed (see, for example, Patent Document 1).

Forming a slit in the electrode electrically separates the electrode regions on both sides of the slit. Increasing the length of the slit can also increase the difference in electrical properties with position along the slit. In order to form an electrode with uniform properties, the length of the slit is limited, the electrode portions on both sides are electrically connected at both ends of the slit, and a large number of slits are distributed within the electrode plane, It is desirable to have uniform properties in

8A and 8B are a plan view and a cross-sectional view of a multi-domain vertical alignment liquid crystal display device using oblique electric field alignment control. FIG. 8A is a superimposed plan view showing the distribution of slits (apertures) in the opposing substrate projected onto the same plane, and FIG. 8B is a cross-sectional view schematically showing the lamination structure of the liquid crystal display device.

In FIG. 8A, the slits 108 of the upper electrode and the slits 118 of the lower electrode have the same pitch in the vertical direction and the same pitch in the horizontal direction in the plane of the substrate, and are shifted by half a pitch in the vertical direction and the horizontal direction between the substrates. are placed. The vertical position passing through both the slit 108 of the upper electrode and the slit 118 of the lower electrode has a structure similar to that of FIG. A multi-domain will arise that is a slight modification of the two domains of 7.

In the laminated structure of the liquid crystal display device shown in FIG. 8B, the transparent electrode 104 on the lower surface of the upper substrate 103 has a slit opening 108, and an insulating film 105 and a vertical alignment film 106 are formed thereon. A transparent electrode 114 on the upper surface of a lower substrate 113 facing the upper substrate 103 has a slit opening 118, and an insulating film 115 and a vertical alignment film 116 are formed thereon.

A liquid crystal layer 107 is injected into the space between the upper and lower substrates to form a liquid crystal cell 121 . Outside the upper and lower substrates, polarizing plates 101 and 111 arranged in, for example, a crossed Nicol arrangement are arranged via viewing angle compensating plates 102 and 112 to provide a normally black display. Note that the insulating films 105 and 115 arranged between the transparent electrode and the alignment film may be omitted.

As shown in FIG. 8A, the upper and lower slit openings 108 and 118 are aligned in the major axis (horizontal) direction and the minor axis (vertical) direction, respectively, and the positions in the upper and lower substrates are shifted from each other by half a pitch. Therefore, the lateral position of the connecting portion of the upper slit opening 108 corresponds to the lateral position of the central portion of the lower slit opening 118 . It is said that when the frequency of the drive waveform is low, display unevenness (dark area) occurs and display quality deteriorates (see, for example, Patent Document 2).

If the liquid crystal layer has a very high resistance, static electricity builds up, which can be harmful when discharged. There have been proposals to incorporate additives into liquid crystals to reduce the hazards of electrostatic discharge.

Chinese Patent No. 104774622 (Patent Literature 3) discloses an example of using a chemical substance containing a crown ether compound as a material imparting an antistatic function. Mitsubishi Chemical Corporation has developed crown ethers, azacrowns, silacrowns, and linear polyethers, which are nonionic anti-static additives, as additives that significantly lower the resistivity of liquid crystal compositions. have been reported (Patent Documents 4 to 7).
These nonionic substances that have the function of reducing the specific resistance of liquid crystals and reducing the damage caused by electrostatic discharge are called charge removal functional agents.

JP 2004-252298 A JP 2016-148870 A China Patent No. 104774622 JP-A-02-311594 JP-A-04-072384 JP-A-04-072385 JP-A-04-180993

Kazuo Koyama, Masashi Akahane, "Evaluation of anchoring strength of nematic liquid crystals from saturation field", Proceedings of the 15th Liquid Crystal Symposium, 2B21, P222-223 Yasuo Togo, Masashi Akahane, "Evaluation of pretilt angle and anchoring strength of nematic LCD by CV measurement", Proceedings of the 22nd Liquid Crystal Symposium, 2A16, P165-166

Realization of a multi-domain vertical alignment liquid crystal display device that can reduce the damage caused by electrostatic discharge is desired.

It is an object of the present invention to provide a multi-domain vertically aligned liquid crystal device to which an antistatic agent is added, which stabilizes the resistivity of the liquid crystal and reduces damage caused by static electricity.

First and second substrates arranged to face each other and having translucency;
First and second transparent electrodes having a predetermined pattern formed on the opposing surfaces of the first and second substrates, and having a plurality of slits formed by removing the electrodes in a substantially rectangular shape. first and second transparent electrodes in which slits on one substrate and slits on the other substrate are alternately arranged along a direction orthogonal to the longitudinal direction of the slits;
first and second vertical alignment films formed to cover the first and second transparent electrodes;
A liquid crystal layer filling the space between the first and second vertical alignment films, the liquid crystal layer containing a non-ionic material and added with an antistatic agent having a function of reducing damage caused by electrostatic discharge. a liquid crystal layer;
There is provided a multi-domain vertically aligned liquid crystal display comprising:

A multi-domain is formed by alternately arranged slits on the opposing substrate. By adding an antistatic agent to the liquid crystal, the harm caused by electrostatic discharge can be reduced.

1 is a cross-sectional view showing the structure of a liquid crystal display device according to an embodiment; FIG. 4 is a table showing the results of experiments conducted in an atmosphere of 25° C. for samples 1 to 4; 4 is a table showing the results of experiments conducted in an atmosphere of 80° C. for samples 1 to 4; 10 is a table showing experimental results of samples 5 and 6 in an atmosphere of 25° C.; 10 is a table showing experimental results of samples 5 and 6 in an atmosphere of 80° C.; 6A and 6B are graphs showing CV measurement plots for Samples 1-4 and Samples 3-6 with straight lines indicating anchoring strength. FIG. 4 is a cross-sectional view showing a gradient electric field due to alternate slits formed in opposing electrodes in previous research. 8A and 8B are a plan view and a cross-sectional view of a multi-domain vertically aligned liquid crystal display device using oblique electric field alignment control, which was studied in previous research.

FIG. 1 is a schematic cross-sectional view showing the configuration of a liquid crystal display device for segment display, which was used as an experimental object. A first substrate S1 and a second substrate S2 formed of a transparent substrate such as a glass substrate or a plastic substrate are arranged to face each other. A first electrode 1 made of a transparent electrode layer such as indium tin oxide (ITO) and having a substantially rectangular slit opening 5 is formed on the facing surface of the first substrate S1. A vertical alignment film 2 made of polyimide is formed. A second electrode 11 made of a transparent electrode layer and having a substantially rectangular slit opening 15 is also formed on the facing surface of the second substrate S2, and a polyimide vertical alignment film 12 is formed on the electrode surface. ing.

The slit openings 5 and 15 are distributed, for example, in the pattern shown in FIG. 8A on the substrate. The distance between the first electrode 1 and the second electrode 11 including the alignment films 2 and 12 is, for example, about 3.8 μm.

A space sandwiched between the vertical alignment films 2 and 12 is filled with a liquid crystal layer 50 . The pretilt angle of the liquid crystal molecules on the alignment films 2 and 12 is approximately 90 degrees. In the liquid crystal cell space, spacers made of plastic particles or the like are distributed and arranged to maintain the thickness of the liquid crystal cell space. The periphery of the liquid crystal cell space is sealed with a sealing material such as epoxy resin. A nematic liquid crystal material having a negative dielectric anisotropy Δε (Δε<0) is injected into the liquid crystal cell space to form the liquid crystal layer 50 .

Outside the counter substrates S1 and S2, polarizing plates P1 and P2 in, for example, a crossed Nicol arrangement are arranged via retardation plates PS1 and PS2. The combination of the polarizing plates P1 and P2 in the crossed Nicols arrangement and the vertically aligned liquid crystal layer provides a high light shielding rate and facilitates realization of a high contrast.

An antistatic agent is added to the liquid crystal layer 50 . The charge removal functional agent is a non-ionic substance such as a crown ether compound, which forms a conductive compound when it absorbs moisture, bonds to the surface of the alignment film, and is attached to at least one surface of the alignment films 2 and 12. Gives conductivity to the part. These conductive films have the function of lowering the effective resistivity of the liquid crystal layer 50, which is a high resistance material.

The antistatic agent in the liquid crystal absorbs moisture on the alignment film, provides conductivity, and exhibits excellent static resistance. The specific resistance of the liquid crystal material to be used can be increased as compared with the case of using an ionic conductive substance. The voltage holding ratio can be increased, and display quality such as contrast can be improved.

It is desirable that the concentration of the charge removing agent in the liquid crystal be such that it can reduce the damage caused by the discharge of static electricity. If the concentration of the charge removing agent is too high, display unevenness including a dark region that flows during the liquid crystal display is caused in a low frequency region. Therefore, it is desirable that the concentration of the charge removing agent in the liquid crystal be such that it can prevent damage caused by static discharge and does not cause display unevenness. However, the effect of the antistatic agent also changes depending on the combination with the alignment film. Therefore, a plurality of samples were prepared by changing the combination of the concentration of the charge removing agent and the orientation film.

FIG. 2 is a table showing experimental results of samples 1 to 4 at a temperature of 25.degree. U-60* was used as an antistatic agent. In the table, the antistatic agent is written as dopant. Samples 1, 2, and 3 were obtained by changing the concentration of the charge removal agent to 50 ppm and changing the orientation film material to A, B, and C. Sample 4 does not contain any antistatic agent (concentration of 0 ppm). The experiment was conducted by changing the frequency to 60, 90, 120, 150, 200, 300, 500 and 1000 (Hz). When there was display unevenness that could be visually observed, it was evaluated as x, and when there was no display unevenness when visually observed, it was evaluated as ○. Sample 1 and sample 2 were all x. Samples 3 and 4 were all ◯. However, since Sample 4 does not contain an antistatic agent, countermeasures against display unevenness caused by static electricity remain a problem.

FIG. 3 is a table showing experimental results of samples 1 to 4 at a temperature of 80.degree. In addition to sample 1 and sample 2, sample 3 was also x. Sample 4 was evaluated as ◯, but since it does not contain an antistatic agent, a countermeasure is required. Therefore, Sample 5, in which the concentration of the charge removal agent was lowered to 5 ppm, and Sample 6, in which the concentration was lowered to 2.5 ppm, were prepared.

4 and 5 are tables showing experimental results for samples 5 and 6 at ambient temperatures of 25° C. and 80° C., respectively. In sample 5, the concentration of the antistatic agent was 5 ppm, and C was used as the alignment film material. Sample 6 has an antistatic agent concentration of 2.5 ppm and an alignment film material of C. Experimental results of samples 3 and 4 are also shown for comparison. Samples 5 and 6 had experimental results of ◯ at all frequencies. If antistatic measures are taken by doping an antistatic agent (dopant concentration > 0), it is considered that a satisfactory result without display unevenness can be obtained in a region where the dopant concentration is 5 ppm or less.

It is known that the capacitance C is a function of the applied voltage V and the anchoring strength AΘ (see Non-Patent Document 1 and Non-Patent Document 2). The anchoring strength AΘ can be read from the CV measurement plots shown in FIGS. 6A and 6B. A graph is used in which the reciprocal of the applied voltage V is plotted on the horizontal axis and the capacitance C is plotted on the vertical axis. The capacitance was normalized by the initial value C0.

FIG. 6A shows CV measurement plots of Samples 1 to 4 in a 25° C. atmosphere. The plots of samples 1 to 4 are actual measurements of the capacitance value Cp at f=1 kHz in RpCp (parallel equivalent circuit) mode using an LCR meter. Here, Rp is the equivalent parallel resistance in RpCp mode, and Cp is the equivalent parallel capacitance component in RpCp mode. Also, the anchoring strength AΘ is a simulation value obtained using, for example, LCD-master (manufactured by Shintech). From the CV characteristic plots, it can be seen that samples 1 to 4 have different anchoring strengths. The anchoring strength AΘ is indicated by a solid line and a dashed line. The solid line and broken line of the anchoring strength AΘ are simulation values obtained along the plots of samples 3 and 4 in which there was no display unevenness in FIG. In other words, the solid line of the anchoring strength AΘ is calculated along the plot of sample 3, and the broken line is calculated along the plot of sample 4. From this result, it can be inferred that the anchoring strength within the range of the solid line and the broken line of the anchoring strength AΘ is the range of the anchoring strength in which display unevenness does not occur. Therefore, it was found that display unevenness does not occur at 25° C. if the anchoring strength AΘ is in the range of 10.0×10̂-5 to 14.0×10̂-5 (J/m2).

FIG. 6B shows the CV measurement plots of Samples 5 and 6 in an atmosphere of 25° C. together with the CV measurement plots of Samples 3 and 4. As shown in FIG. The anchoring strength AΘ is indicated by a solid line, a one-dot dashed line, and a dashed line. Here, the one-dot dashed line of the anchoring strength AΘ is a newly calculated line along the plots of Samples 4 to 6 in addition to the solid and dashed lines in FIG. 6A.

From the plot of the CV characteristics, the anchoring strength of sample 3 and the anchoring strengths of samples 4 to 6 diverge. Sample 3 causes display unevenness at an ambient temperature of 80° C., as shown in FIGS. Therefore, it was found that display unevenness does not occur even at 80° C. if the anchoring strength AΘ is in the range of 12.0×10∧-5 to 14.0×10∧-5 (J/m2).

Although the present invention has been described along with the embodiments, these are not restrictive. For example, it will be apparent to those skilled in the art that various modifications, improvements, combinations, etc. are possible.

Claims (4)

First and second substrates arranged to face each other and having translucency;
First and second transparent electrodes having a predetermined pattern formed on the opposing surfaces of the first and second substrates, and having a plurality of slits formed by removing the electrodes in a substantially rectangular shape. first and second transparent electrodes in which slits on one substrate and slits on the other substrate are alternately arranged along a direction orthogonal to the longitudinal direction of the slits;
first and second vertical alignment films formed to cover the first and second transparent electrodes;
A liquid crystal layer filling the space between the first and second vertical alignment films, the liquid crystal layer containing a non-ionic material and added with an antistatic agent having a function of reducing damage caused by electrostatic discharge. a liquid crystal layer;
A multi-domain vertically aligned liquid crystal display device comprising: 2. The multi-domain vertical alignment liquid crystal display device according to claim 1, wherein the concentration of the charge removing functional agent contained in the liquid crystal layer is positive (>0) and 5 ppm or less. The anchoring strength of the liquid crystal layer at 25° C. is
10.0x10∧-5 to 14.0x10∧-5 (J/m2)
3. The multi-domain vertical alignment liquid crystal display device according to claim 1, wherein the range is . The anchoring strength of the liquid crystal layer at 80° C. is
12.0x10∧-5 to 14.0x10∧-5 (J/m2)
3. The multi-domain vertical alignment liquid crystal display device according to claim 1, wherein the range is .

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