JPH03209440A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To facilitate an orientation treatment and to improve orientation stability by orienting liquid crystal molecules in such a manner that the molecules attain the twist orientation of a specific angle range in a thickness direction when a voltage is impressed thereto. CONSTITUTION:A perpendicular orienting agent of a silane system is applied on one of glass substrates 11, 21 having transparent electrodes 12, 22 and is dried. The other substrate is subjected to the similar treatment. The two substrates 11, 21 are stuck to each other via a spacer in such a manner that the oriented film surfaces face each other and the rubbing directions intersect orthogonally with each other. A liquid crystal compsn. mixture composed of a liquid crystal compsn. having negative dielectric constant anisotropy and cholesteric liquid crystal is injected into the gap between the two substrates to produce the liquid crystal cell. The cell is so constituted that the liquid crystal molecules attain the twist orientation of the >=1 deg. and <100 deg. angle range. The productivity and orientation stability are improved in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to improvements in liquid crystal display devices, particularly DAP type liquid crystal display devices.
The present invention relates to an AP type liquid crystal display element.

[Conventional technology]

As liquid crystal display elements, TN type liquid crystal display elements, STN type liquid crystal display elements, and DAP type liquid crystal display elements are conventionally known.

Among the two types, TN type liquid crystal display elements have a black and white display and have a simple structure, so they are widely used mainly in the display parts of watches and calculators, but because of their poor voltage transmittance characteristics, The drawback is that it cannot be used for large capacity displays without switching elements such as thin film transistors.

Further, the STN type liquid crystal display element has excellent steepness of voltage transmittance characteristics and is capable of displaying a large capacity.

On the other hand, there is a problem that the display is colored. For this reason, a method of displaying black and white using a compensating plate has been developed, but this method requires a complicated structure and high cost, and also requires high accuracy in cell thickness, resulting in poor productivity.

On the other hand, + D A P (Deformation
n' ofVertically Aligned
Phase) type liquid crystal display elements are a display method that has been known for a long time.They have excellent steep voltage transmittance characteristics and are capable of large-capacity display.Moreover, they can display black and white or, depending on the cell condition settings, can display color filters. It has the feature that multicolor display is possible without using .

The following is the first part about the structure and principle of the DAP type liquid crystal display element.
This will be explained with reference to the figures.

FIG. 1 is a sectional view showing an example of the basic configuration of a DAP type liquid crystal display element.
A liquid crystal layer 3 made of a liquid crystal composition having negative dielectric constant anisotropy is formed between a pair of transparent substrates 11.21 such as glass or plastic having a substrate 11.21, and its outer periphery is sealed 14.21.
24 to form a liquid crystal cell of a DAP type liquid crystal display element. A liquid crystal is placed on the side of the substrate 11.21 and the transparent electrode 12.22 of this cell that are in contact with the liquid crystal.
Alignment film 15.25 for alignment perpendicular to 21
is formed.

Further, a pair of polarizing plates 16 and 26 are provided on the outside of the cell, and the cell and the pair of polarizing plates constitute a DAP type liquid crystal display element.

In a DAP type liquid crystal display element having such a configuration, when no voltage is applied, the liquid crystal is aligned perpendicularly to the substrate 11.21, and at this time, birefringence due to the liquid crystal does not occur, and the upper and lower polarizing plates 16.26 When the polarization axes are orthogonal, a black display is obtained. Also, when a voltage is applied between the upper and lower transparent electrodes,
The liquid crystal molecules are tilted with respect to the substrate 11.21 as shown in Figure 2(b), and when the direction of the tilt is other than parallel or perpendicular to the transmission or absorption axis of the polarizing plate, birefringence occurs and light is emitted. To Penetrate.

The spectrum of this transmitted light corresponds to retardation, and by adjusting the thickness of the liquid crystal layer 3, the birefringence of the liquid crystal, and the applied voltage, it is possible to display white or colored.

[Problem to be solved by the invention]

By the way, the above-mentioned DAP type liquid crystal display element is capable of large-capacity display, and also has the feature of being able to display black and white or, depending on cell condition settings, multicolor display without using a color filter. However, the drawback is that it is difficult to control the alignment of liquid crystals.

In other words, in order to obtain a homogeneous display in a DAP type liquid crystal display element, it is necessary to control the direction in which the liquid crystal tilts when a voltage is applied. 2 (a), θ from the vertical direction. It is necessary to control the tilted orientation, but this tilt angle θ. If the voltage is small, the direction in which the liquid crystal tilts when a voltage is applied is not uniform, causing display unevenness due to an alignment defect called reverse tilt, resulting in a problem that the contrast is reduced. Also, the tilt angle θ. If you increase , the above orientation defect will not occur, but the viewing angle will become narrower,
The steepness of the voltage transmittance characteristic deteriorates, resulting in a decrease in contrast during simple matrix driving, and display performance is impaired.

Furthermore, conventional DAP type liquid crystal display elements have drawbacks in terms of manufacturing.

That is, the tilt angle θ is conventionally considered preferable.

is from 1° to 3°. Methods for controlling this orientation include applying a vertical alignment agent such as an alkoxysilane having a long-chain alkyl group onto the substrate and then lapping it; Methods are known in which the substrate is evaporated diagonally and subjected to horizontal alignment treatment, and then the surface is treated with a vertical alignment agent, but the tilt angle of the liquid crystal obtained by these methods has poor reproducibility. However, there was a problem in that the yield was likely to decrease.

The present invention has been made in view of the above circumstances, and has no alignment defects, a wide viewing angle, no alignment defects even at small tilt angles, high contrast, and easy alignment processing, which improves productivity. It is an object of the present invention to provide a DAP type liquid crystal display element having high alignment stability and high time division drive characteristics.

[Means for Solving the Problems] In order to achieve the above object, a liquid crystal display element according to the present invention comprises two substrates subjected to vertical alignment treatment, a nematic liquid crystal sealed in the substrates, and an optically active substance. It is composed of a liquid crystal composition having negative dielectric anisotropy and a pair of polarizing plates, and when a voltage is applied, the liquid crystal molecules tilt in the thickness direction by 1° or more.
It is characterized in that it is configured to have a twisted orientation in the 00° non-grooved angle range.

[For production]

Here, the basic configuration of the device is the same as that shown in FIG. 1, but in the device of the present invention, the liquid crystal molecules take a twisted orientation in an angle range of 1° or more and less than 100° when a voltage is applied. It is configured as follows.

Such orientation can be achieved by using a liquid crystal composition, for example, a mixed composition of a nematic liquid crystal and an optically active substance with a negative dielectric anisotropy, specifically a nematic liquid crystal with a negative dielectric anisotropy and a small amount. A composition such as a mixed composition of a cholesteric liquid crystal, or a mixed composition of a nematic liquid crystal with negative dielectric anisotropy and a small amount of a non-liquid crystal optically active substance is used, and the liquid crystal is placed on a substrate in a specific direction. This is achieved by applying a process to orient the substrate by tilting it by a minute angle.

Here, when the above liquid crystal composition is used, a twisted structure is induced in the liquid crystal by the optically active substance, but the induced natural pitch (pitch without alignment regulation) Po and the thickness d of the liquid crystal layer 3 are There are favorable conditions for this relationship. This relationship is expressed as d/P, and it is preferable that 0.005≦d/Pゎ≦0.5.

However, the more preferable range depends on the twist angle. For example, if the twist angle when voltage is applied is 90°, d
/Po is preferably from 0.15 to 0.5. In a range of d/Po that satisfies such conditions, orientation defects due to reverse tilt during voltage application can be extremely effectively reduced or eliminated.

Note that if the twist angle during voltage application is smaller than 1°, tilt disclination occurs and display quality deteriorates.

Further, if the twist angle during voltage application is larger than 100°, the steepness of the voltage transmittance characteristic deteriorates, and the contrast decreases during high time division.

Further, the amount of the optically active substance added is determined by the thickness d of the liquid crystal layer 3.
Since it depends on the type of nematic liquid crystal and the type of optically active substance, it is generally in the range of 0.01% to 10%, although it cannot be said in general terms.

Next, as the orientation treatment, a slightly inclined vertical orientation treatment is preferably performed.

As alignment agents, alkoxysilanes having long-chain alkyl groups, alkoxytitanium, alkoxyzirconium, organometallic compounds such as chromium complexes of long-chain alkyl carboxylic acids or fluorine-substituted alkyl carboxylic acids, fluorine-substituted polyalkylene resins, etc. are generally used for vertical alignment. Materials used for processing can be used. The alignment film formed from the above material is preferably subjected to a rubbing treatment in one direction. Further, an oblique vapor deposition method of Si◯ can also be adopted. The preferred tilt angle obtained by this alignment treatment is in the range of 0.1° to 5°, and more preferably,
It ranges from 0.1° to 36°.

As described above, by using the present invention, cells can be manufactured without defective alignment even at a very small tilt angle, so the range of use of the alignment agent can be greatly expanded. Also,
When a cell is manufactured with a small pretilt angle, the viewing angle can be increased, and the display quality is also extremely excellent. Note that the present invention does not limit the method of alignment treatment.

Now, the pretilt direction of liquid crystal molecules on the substrate surface is determined by the rubbing direction in the rubbing method, and by the vapor deposition direction in the oblique evaporation method.

As shown in FIG. 3, in the present invention, the liquid crystal takes a twisted orientation with a tilt angle when a voltage is applied, but at this time, it is not preferable for the liquid crystal to take a spray orientation.
The reverse tilt suppressing effect will be reduced. Therefore, in the present invention.

Preferably, the direction of this pretilt is controlled. Therefore, the angle α formed by the pretilt directions of the upper and lower substrates defined in FIG.
, the natural torsion angle determined by (=d/P0X360°
) and within 1° to 100°, preferably within twice the natural twist angle.

It is preferable that the transmission axes of the polarizing plates 16 and 26 arranged above and below form an angle of about 30° to 60° with the pretilt direction of liquid crystal molecules on the adjacent substrates.

〔Example〕

Hereinafter, specific examples of the present invention will be described.

The basic structure of the liquid crystal display element is the same as that shown in FIG.

Example 1 Glass substrate 11.21 having transparent electrodes 12 and 22 made of I To (Indium Tin Oxide)
A silane-based vertical alignment agent (for example, 0DS manufactured by Chisso Co., Ltd.)
-E) is applied, dried at 120°C, and then rubbed in one direction with a cotton cloth. Then, the same process is applied to the other substrate, and the open substrates II and 21 are bonded together via a spacer so that the alignment film surfaces face each other and the rubbing directions are perpendicular to each other. Then, a mixed liquid crystal composition of a liquid crystal composition EN37 manufactured by Chisso Corporation, which has negative dielectric constant anisotropy, and 8811 manufactured by Merck Co., Ltd., which is a cholesteric liquid crystal, was injected into the gap between the open substrates to produce a liquid crystal cell.

The pitch of the liquid crystal used here was 30 μm, and the liquid crystal layer 3
The thickness d is 7.5 μm. Further, the pretilt angle was 0.2'.

Next, a pair of neutral gray linear polarizing plates 16° 26 are placed above and below the liquid crystal cell fabricated as described above so that their polarization axes are perpendicular to each other and form an angle of 45° with the rubbing direction. A liquid crystal display element was formed.

The liquid crystal display element shown in Example 1 was black when no voltage was applied, and became colorless when a voltage of 2.8 V was applied. Furthermore, no alignment defects such as tilt disclination were observed, and an extremely uniform display was obtained. Further, the steepness expressed as the ratio of the voltage at which the transmittance changes by 10% and the voltage at which the transmittance changes by 50% was 1.13, and it was confirmed that the device had excellent time-division drive characteristics.

Example 2 Glass substrates 11 and 2 subjected to the same orientation treatment as in Example 1
1 were pasted together via a spacer so that the alignment film surfaces faced each other and the rubbing direction formed an angle of 45°. A liquid crystal cell was prepared by injecting a mixed liquid crystal composition of liquid crystal composition EN37 and cholesteric liquid crystal 5811 manufactured by Merck & Co., Ltd.

Note that the pitch of the liquid crystal used here was 70 μm, and the thickness d of the liquid crystal layer 3 was 7.5 μm.

Next, a pair of neutral gray linear polarizing plates 15° and 26 are placed above and below the liquid crystal cell fabricated as described above so that the polarization axis forms a 45° angle with the rubbing direction to form a liquid crystal display element. Formed.

The liquid crystal display element shown in Example 2 was black when no voltage was applied, and became colorless when a voltage of 2.8 V was applied. Furthermore, no alignment defects such as tilt disclination were observed, and an extremely uniform display was obtained. In addition, the steepness was 1.12, and it was confirmed that it had excellent time-division drive characteristics.

Next, as a comparative example, a liquid crystal display element having the configuration shown below was manufactured and compared.

Comparative Example 1 A silane-based vertical alignment agent 0DS-E manufactured by Chisso Corporation was applied to one of the glass substrates 11 and 21 having transparent electrodes 12 and 22 made of IT○ (Indiusa Tin Oxide), and after drying at 120°C, Rub in one direction with cotton cloth. Then, the same process is applied to the other substrate, and the open substrates 11 and 21 are bonded together via a spacer so that the alignment film surfaces face each other and the rubbing directions are antiparallel. Then, a liquid crystal composition EN37 manufactured by Chisso Corporation having negative dielectric constant anisotropy was injected into the gap between the open substrates to produce a liquid crystal cell. The thickness d of the liquid crystal layer 3 of this liquid crystal cell is 7.5
It is μm.

A pair of neutral gray linear polarizing plates 16 and 26 are arranged above and below the liquid crystal cell thus fabricated so that their polarization axes are perpendicular to each other and form an angle of 45° with the rubbing direction to produce a liquid crystal display. An element was formed.

This liquid crystal teaching element is black when no voltage is applied;
．． It becomes colorless when a voltage of 8V is applied.

Many alignment defects such as tilt disclination occurred, resulting in extremely non-uniform display.

Comparative Example 2 Glass substrate 11.21 having transparent electrodes 12 and 22 made of ITO (Indium Tin Oxide)
On one of the substrates, SiO was diagonally evaporated from a direction of 60° from the normal line of the substrate to a thickness of about 300 mm, and then a silane-based vertical alignment agent 0DS-E manufactured by Chisso Corporation was applied and dried at 120°C. . Next, the other substrate is subjected to the same process, and both substrates 1, 1, and 21 are bonded together via a spacer so that the alignment film surfaces face each other and the vapor deposition directions are antiparallel. Then, a liquid crystal composition EN37 manufactured by Chisso Corporation having negative dielectric constant anisotropy was injected into the gap between the open substrates to produce a liquid crystal cell. The thickness d of the liquid crystal layer 3 of this liquid crystal cell is 7.5 μm
It is. Further, the pretilt angle was 2°.

A pair of linear polarizing plates 16 and 26 of neutral gray are arranged above and below the liquid crystal cell thus prepared so that their polarization axes are perpendicular to each other and form an angle of 45° with the vapor deposition direction to form a liquid crystal display element. was formed.

This liquid crystal teaching element is black when no voltage is applied;
．． It becomes colorless by applying a voltage of 8 cm. Further, although a uniform display was obtained without occurrence of tilt disclination, the viewing angle was narrower than that of the liquid crystal display elements of Examples 1 and 2.

〔Effect of the invention〕

As explained above, the present invention adds an optically active substance to the liquid crystal composition of a DAP type liquid crystal display element to give the liquid crystal molecules a slight twisted structure when a voltage is applied, thereby eliminating alignment defects (reverse tilt). This effectively suppresses the occurrence of such defects, and as a result, a liquid crystal display element with uniform display without alignment defects can be obtained.

Furthermore, according to the present invention, since alignment defects do not occur even at a small pretilt angle, a liquid crystal display element with high contrast and a wide viewing angle can be obtained. Furthermore, since alignment treatment is easy, productivity is high and a liquid crystal display element with excellent alignment stability can be easily provided.

Furthermore, in the liquid crystal display element according to the present invention, voltage transmittance characteristics of 1. Since it has excellent ul property, it also has high time-division writing characteristics.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing an example of the basic configuration of a DAP type liquid crystal display element, FIG. 2 is an explanatory diagram of the alignment direction of liquid crystal molecules in the DAP type liquid crystal display element, and FIG. 3 is a liquid crystal display of the liquid crystal display element according to the present invention. FIG. 4, which is an explanatory diagram of the orientation direction of molecules, is a projection diagram of the liquid crystal molecules on the substrate onto the substrate surface. 3...Liquid crystal layer, 11.2]...Substrate, 12.
22...Transparent electrode, 14.24...Outer seal, 15.25...Alignment film, 16.26...Polarizing plate. Agent Toru Kabayama (and 1 other person) θn Fig. 1° upper base q・1 1 --- Lower 8 board 1) 1 Arrow ερi crest or arc [with] upper surface

Claims (1)

[Claims] It consists of two substrates subjected to vertical alignment treatment, a liquid crystal composition with negative dielectric anisotropy made of nematic liquid crystal and an optically active substance sealed in the substrates, and a pair of polarizing plates. When applied, liquid crystal molecules move at least 1° in the thickness direction10
1. A liquid crystal display element configured to have a twisted orientation in an angular range of less than 0°.