JPH06214235A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To improve the visual sense characteristic of the device and to obtain good display characteristics by having a region where a part of a liquid crystal compsn. in one pixel region of a substrate orients perpendicularly. CONSTITUTION:Transparent electrodes 5 are formed on a transparent substrate 4 and a part of a horizontally oriented film 2 which is applied over the entire surface of the pixels and is subjected to an orientation treatment, such as rubbing, is subjected to a perpendicular orientation treatment, by which the perpendicularly oriented film 3 is formed. Liquid crystal molecules 1 are held in a perpendicularly oriented state at all times in the region of this perpendicularly oriented film 3 regardless of the presence or absence of voltage impression. A rise in a specified direction by elasticity with respect to the liquid crystal molecules in the horizontal orientation direction is observed with the liquid crystal molecules in the proximate part of this perpendicularly oriented region in the form of the molecules being dragged by the molecules of the perpendicularly oriented region. This rise in the specified direction is settable as the rise direction at the time of the voltage impression. Then, the regions varying in visual field angles are provided within one pixel by dividing the rise direction of the liquid crystal molecules 1 in plural directions. As a result, the visual field at the time of macroscopically viewing the screen is corrected and the wide visual field angle 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, and more particularly to a liquid crystal display device having improved viewing angle characteristics.

[0002]

2. Description of the Related Art In recent years, liquid crystal display devices have been widely used as display devices for office automation equipment such as liquid crystal televisions, Japanese word processors and desktop personal computers because they have the great advantages of thinness, light weight and low power consumption. In particular, the twisted nematic (TN) liquid crystal display system in which the alignment state of liquid crystal molecules is twisted by about 90 ° is obtained by incorporating an active switch element such as a TFT into a cathode ray tube (CR).
T) It is possible to have the same display characteristics, and the super twist nematic (STN) type liquid crystal display system in which the alignment state of liquid crystal molecules is twisted by 90 ° or more enables high-duty multiplex drive.

The conventional TN type liquid crystal display device is
A transparent substrate on which driving electrodes, pixel electrodes, etc. are provided with an alignment layer for controlling the twist angle and the tilt angle of the liquid crystal composition, and the alignment layer on the counter substrate are arranged with a narrow space. The structure is such that they face each other to form a liquid crystal cell, the liquid crystal composition is sandwiched between them, and two orthogonal polarizing plates are arranged in the outermost layer.

However, the conventional TN type liquid crystal display system has a structure in which liquid crystal molecules are twisted in a liquid crystal cell.
Since the rise is directional, there is a drawback in that the display color and the contrast ratio change depending on the viewing direction, which has a viewing angle dependency. Therefore, the liquid crystal display device has not yet completely exceeded the display performance of a cathode ray tube (CRT).

For this reason, many methods have been proposed for improving the viewing angle characteristics of TN type liquid crystal display elements. For example, a method of disposing an optical anisotropic element having an optical axis substantially parallel to the substrate surface of the liquid crystal cell between the polarizing plate and the liquid crystal cell, and dividing the screen into a plurality of display patterns. A method of changing the orientation treatment for each display pattern (Japanese Patent Laid-Open No. 57-18673)
No. 5), a method of changing the pretilt angle of liquid crystal molecules by dividing an area in a pixel (Japanese Patent Laid-Open No. 62-159119), and a method of changing the orientation processing direction in the area in the pixel (Japanese Patent Laid-Open No. 6-159119).
3-106624), a method of arranging a capacitive element in a part of the pixel to change the electric field (USP 4840460) and the like.

[0006]

However, even in an example in which an optical anisotropic element having an optical axis substantially parallel to the substrate surface of a liquid crystal cell is arranged, it is necessary to improve the vertical viewing angle when trying to improve the left and right viewing angle characteristics. It is difficult to improve the overall viewing angle characteristics in a well-balanced manner due to the drawback that the characteristics deteriorate. That is, there is a problem in that the display pattern looks inverted depending on the specific direction and angle at which the liquid crystal display element is viewed, or the display pattern cannot be seen at all.

Further, in the method of dividing the area in the pixel to change the pretilt angle of the liquid crystal molecules and the method of changing the alignment treatment direction of the alignment film, disclination occurs at the boundary where the pretilt angle and the alignment treatment direction change. However, there is a drawback that the display characteristics are deteriorated. In a high-definition liquid crystal display device, a method of dividing an area within a pixel is a very difficult technique because it is essential to divide an extremely fine pixel area into smaller pieces and perform strict alignment processing within the area. There is a problem that the method has not been established yet.

Further, it is difficult to improve the viewing angle characteristics in the front, rear, left and right directions by changing the orientation treatment for each display pattern or changing the electric field by disposing a capacitive element.

As described above, in the TN type liquid crystal display device, it is difficult to deal with this problem because the rising of the liquid crystal molecules is directional.

The present invention has been made in order to solve the above problems, and an object thereof is to provide a liquid crystal display device having a wide viewing angle characteristic.

[0011]

In the liquid crystal display device of the present invention, a pair of substrates, each of which has an alignment layer on its surface and at least one of which is transparent, are arranged with the alignment layers facing each other with a narrow space. The liquid crystal composition is sandwiched between the pair of substrates, and one pixel region of the substrate has a region in which a part of the liquid crystal composition is vertically aligned.

The region where a part of the liquid crystal composition according to the present invention is vertically aligned can be obtained by subjecting a part of the alignment layer to a vertical alignment treatment. FIG. 1 shows an example of a cross-sectional structure of the liquid crystal display device of the present invention. In FIG. 1, a transparent alignment electrode 5 is formed on a transparent substrate 4, and a part of a horizontal alignment film 2 applied to the entire surface of a pixel and subjected to an alignment process such as rubbing is subjected to a vertical alignment process to form a vertical alignment film 3. To do. In the region of the vertical alignment film 3, the liquid crystal molecules 1 are always in the vertical alignment state regardless of whether or not a voltage is applied. The liquid crystal molecules in the vicinity of the vertical alignment region rise in a certain direction due to the elasticity of the liquid crystal molecules with respect to the liquid crystal molecules in the horizontal alignment region while being dragged by the molecules in the vertical alignment region. The rising in this fixed direction can be set as the rising direction when a voltage is applied. Therefore, the rising direction of the liquid crystal molecule can be divided into a plurality of directions, and regions with different viewing angles can be provided in one pixel. As a result, when viewing the screen macroscopically, the field of view is corrected and a wide viewing angle can be realized. further,
Since the rise in the initial state of the liquid crystal molecules is different between the periphery of the vertical alignment region of the liquid crystal molecules and the distant portion, the voltage threshold is different, which is advantageous in driving.

It is preferable that the vertical alignment processing region is located at a position where one pixel can be uniformly divided. Since the areas of regions having different viewing angles can be made the same within one pixel by dividing the regions evenly, it is possible to maximize the effect of canceling the goodness of the viewing angle.

When a pixel is divided into two regions having different viewing angles, it is preferable that the vertical alignment processing region is a line having a predetermined width that linearly divides the pixel. This allows the liquid crystal molecules to rise better in a certain direction. Further, the width of the vertical alignment treatment region is preferably narrow in order to increase the aperture ratio, but if it is too narrow, a sufficient vertical alignment treatment region cannot be secured, so that it is preferably in the range of 2 μm to 50 μm. The vertical alignment processing region may be formed in a circular shape, for example, at the center of one pixel.

The vertical alignment treatment may be performed on either one of the two substrates facing each other or both of them, but preferably, the same treatment is performed on the surfaces of both substrates to make the facing portions vertical alignment and horizontal alignment. .

As the alignment film that can be used in the present invention, an alignment film that can reduce the pretilt angle is desirable, and an alignment film that does not cause the pretilt angle is more preferable. This is because the rising direction of the liquid crystal molecules is determined by the pretilt angle itself of the alignment film capable of increasing the pretilt angle.

Specific examples of the horizontal alignment film include polyalkylenes such as polyethylene, polyisobutene and polybutadiene, polyacrylates such as polyacrylate, polymethylmethacrylate, polycyanoacrylate and polyacrylonitrile, polyvinyl alcohol, polyvinyl acetate and polyvinyl. Polyvinyls such as butyral, polyvinyl chloride, polyvinylpyridinium,
Polyimide, polyamideimide, polybenzimidazole, polybenzimidazopyrrolone, polyquinoxaline,
Heterocyclic polymers such as polybenzthiazole and polybenzoxazole, methylcellulose, cellulose acetate, cellulose triacetate and mixed acetate, cellulose derivatives such as nitrocellulose, poly-
(Glycidopropyltrimethoxysilane), polyhexamethylsiloxane, polyester silicone, polymethylphenylsiloxane, polymethylparadimethylsiloxane, polysilanes such as polymethylsiloxane, polytetrafluoroethylene, polyfluoropropyl Co tetrafluoroethylene FEP, Fluorine-based polymers such as polyvinylidene fluoride, polyperfluoro1.3-dimethylcyclohexane, polyperfluorocyclohexene, polyperfluorodimethylcyclobutane, polyacetylene Co perfluoro1.3-dimethylcyclohexane, silicone rubber, polystyrene, polypara. Xylylene, polyethylene terephthalate, polyurethane, polyamide, polysulfone, polyether, polynaphthalene, polycyanoacetylene , Polyaniline, urea-formaldehyde resin, epoxy resin, phenolic resin, casein, ionomer, coumarone-indene resin, etc. polymer film or organic silane applied and then subjected to orientation treatment such as rubbing, SiO from 60 ° Examples thereof include oblique vapor deposition films and the like.

Further, instead of using a horizontal alignment film, fine grooves (grooves) formed on a substrate by using an inorganic material and an organic material can also be used as an effective horizontal alignment means.

Examples of the vertical alignment film include organic silanes having a large number of carbon atoms as an amphipathic interfacial agent. Specifically, octadecylethoxysilane, lecithin, hexadecylamine, mistyric acid complex, represented by the following formula 4 Examples thereof include graded amine compounds.

[0020]

[Chemical 1]

[Chemical 2] Further, a glass surface or the like etched with an acid is also effective as a vertical alignment surface.

A method of alignment treatment in which a horizontal alignment region is provided in one pixel region of a substrate and at least a part thereof is used as a vertical alignment region is the above-described vertical alignment film with respect to an alignment surface subjected to horizontal alignment treatment. A method of partially applying a vertical alignment treatment agent, or as shown in FIG. 2, a vertical alignment treatment is performed on a transparent substrate 4 to form a vertical alignment film 3, and then the horizontal alignment film 2 is patterned on the substrate to perform the alignment treatment. And the like.

The boundary between the vertical alignment region and the horizontal alignment region does not need to be clearly divided, and preferably gradually changes from the vertical alignment region to the horizontal alignment region. As a result, the pretilt angle of the liquid crystal molecules has a change region of 0 ° to 90 ° with respect to the substrate surface. The liquid crystal composition that can be used in the liquid crystal display device of the present invention is a nematic liquid crystal material exhibiting a nematic phase. For example, cyanobiphenyls,
Cyanophenyl esters, benzoic acid esters, cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexanes, cyano-substituted phenylpyrimidines, alkoxy-substituted phenylpyrimidines, phenyldioxane, tolan-based liquid crystals, alkenylcyclohexylbenzonitriles, etc. An example is a nematic liquid crystal substance. Generally, these compounds are used as a mixture, and a chiral agent or the like is further added. Among such liquid crystal compositions, the bending elastic constant K ₃₃ is 1.5 × 10 ^-11 N
As described above, more preferably a liquid crystal composition of 1.8 × 10 ⁻¹¹ N or more is suitable for the liquid crystal display device of the present invention. Bending elastic constant
When K ₃₃ is 1.5 × 10 ⁻¹¹ N or more, the liquid crystal molecules can be more easily aligned in the change from the vertical alignment region to the horizontal alignment region.

The liquid crystal display device of the present invention comprises a pair of substrates, at least one of which is transparent, and on which electrodes are formed according to a simple matrix or active matrix driving method and the above-mentioned alignment film is formed on the electrodes. After the alignment films are arranged to face each other and the periphery is sealed, a liquid crystal composition is injected to prepare a liquid crystal cell, and an exterior assembly is formed. Particularly, in the present invention, by adopting the active matrix driving method, it is possible to perform better display. In this case, the vertical alignment region leads to a decrease in aperture ratio, so it is desirable to form the vertical alignment region in the wiring portion such as the auxiliary capacitance region.

[0024]

EXAMPLES Examples of the present invention will be described in detail below. Example 1 A transparent electrode was formed on two transparent substrates, and a silane treatment agent for horizontal alignment KBM-630 (trade name of Shin-Etsu Silicone Co., Ltd.) was applied and post-baked to fix the substrates on the substrates. After rubbing the alignment film for horizontal alignment, octadecylethoxysilane, a vertical alignment agent diluted with alcohol, was applied to the stripes in the center of the pixel and post-baked to fix the alignment film on the horizontal alignment film. Two substrates with this orientation were placed so that the vertical alignment processing areas faced each other, and a nematic liquid crystal composition was sandwiched between them to form a liquid crystal cell with an electrode spacing of 6 μm, and an exterior assembly was formed to obtain a liquid crystal display device. It was

The isocontrast characteristics of this liquid crystal display device were investigated. The result is shown in FIG. The characteristics of the same liquid crystal display device as in Example 1 were shown as a comparative example except that the vertical alignment agent octadecylethoxysilane was not applied to the stripes in the center of the pixel. As shown in FIG. 3, the liquid crystal display device of Example 1 exhibited good equal contrast characteristics and a wide viewing angle.

Example 2 A transparent electrode was formed on two transparent substrates, and octadecylethoxysilane, a vertical alignment agent diluted with alcohol, was applied to the entire surface of the substrate and post-baked to fix it on the substrate. A low tilt angle polyimide alignment film forming solution was applied on this, and post-baking was performed to completely cure it to obtain an alignment film having a film thickness of 1000 Å. Next, the polyimide alignment film was patterned into a linear stripe of 5 μm at the pixel center using a resist, and the polyimide alignment film was patterned. Then, the polyimide alignment film was horizontally aligned, and the etched part was defined as a vertical alignment region. Two substrates with this orientation were placed so that the vertical alignment processing areas faced each other, and a nematic liquid crystal composition was sandwiched between them to form a liquid crystal cell with an electrode spacing of 6 μm, and an exterior assembly was formed to obtain a liquid crystal display device. It was

This liquid crystal display device showed a good alignment state in the initial state, and was able to be divided into two regions having different rising directions of liquid crystal molecules by writing by applying a voltage, and a wide viewing angle could be secured.

Example 3 A transparent electrode was formed on two transparent substrates, and a low-tilt-angle polyimide alignment film forming solution was applied to the entire surface of the substrate, followed by post-baking to completely cure the alignment film having a thickness of 1000 angstroms. Obtained. The alignment film was rubbed for horizontal alignment and then octadecylethoxysilane, a vertical alignment agent diluted with alcohol, was applied to the stripes in the center of the pixel and post-baked to fix it on the polyimide alignment film. The two substrates with this alignment are placed so that the vertical alignment treatment areas face each other, and the nematic liquid crystal composition is sandwiched between the electrodes.
A 6 μm liquid crystal cell was prepared and an exterior assembly was formed to obtain a liquid crystal display device.

This liquid crystal display device showed a good alignment state in the initial state, and was able to be divided into two regions having different rising directions of liquid crystal molecules by writing by applying a voltage, and a wide viewing angle could be secured.

Example 4 A transparent electrode was formed on two transparent substrates, and a photosensitive polyimide alignment film forming solution was applied to the entire surface of the substrate and post-baked to completely cure it to obtain an alignment film having a thickness of 1000 angstroms. . After that, patterning was performed with a line and space having a width of 1 μm to form a horizontal alignment film. A vertical aligning agent octadecylethoxysilane diluted with alcohol was applied to the horizontal alignment film on the stripes in the center of the pixel and post-baked to fix it on the polyimide alignment film. Two substrates with this orientation were placed so that the vertical alignment processing areas faced each other, and a nematic liquid crystal composition was sandwiched between them to form a liquid crystal cell with an electrode spacing of 6 μm, and an exterior assembly was formed to obtain a liquid crystal display device. It was

This liquid crystal display device showed a good alignment state in the initial state, and was able to be divided into two regions having different rising directions of liquid crystal molecules by writing by applying a voltage, and a wide viewing angle could be secured.

Example 5 A transparent electrode was formed on two transparent substrates, and octadecylethoxysilane, a vertical alignment agent diluted with alcohol, was applied to the entire surface of the substrate and post-baked to fix it on the substrate. A photosensitive polyimide alignment film forming solution was applied on the entire surface of the substrate and post-baked to completely cure it to obtain an alignment film having a thickness of 5000 Å. Furthermore, a line and space with a width of 1 μm was patterned at a depth of 3000 Å, and the center of the pixel was completely etched into a linear line of 5 μm so that only that part of the line had a vertically aligned substrate surface. Two substrates with this orientation were placed so that the vertical alignment treatment areas faced each other, and a nematic liquid crystal composition was sandwiched between them to form a liquid crystal cell with an electrode spacing of 6 μm, and an exterior assembly was formed to obtain a liquid crystal display device. It was

This liquid crystal display device showed a good alignment state in the initial state, and was able to be divided into two regions having different rising directions of liquid crystal molecules by writing by applying a voltage, and a wide viewing angle could be secured.

[0034]

As described above, since the liquid crystal display device of the present invention has a region where at least a part of the liquid crystal composition in one pixel region of the substrate is vertically aligned, the one pixel region is viewed. It can be divided and displayed in different areas. As a result, the visual characteristics of the liquid crystal display device are improved, and good display characteristics can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a cross-sectional configuration of a liquid crystal display device of the present invention.

FIG. 2 is a diagram showing an example of a method for forming an alignment film of a liquid crystal display device of the present invention.

FIG. 3 is a diagram showing isocontrast characteristics of the liquid crystal display device of Example 1. The broken line shows a comparative example.

[Explanation of symbols]

1 ... Liquid crystal molecules, 2 ... Horizontal alignment film, 3 ... Vertical alignment film, 4 ... Transparent substrate, 5 ... Transparent electrode.

Claims (2)

[Claims] 1. A pair of substrates, each of which has an alignment layer on its surface, at least one of which is transparent, is made to face the alignment layers with a narrow space, and the liquid crystal composition is sandwiched between the pair of substrates. And a non-vertical alignment region centered on a vertically aligned region existing in a part of the liquid crystal composition in one pixel region of the substrate. 2. The liquid crystal display device according to claim 1,
A liquid crystal display device, wherein the one pixel region is divided into a plurality of alignment regions having a rising direction determined by the vertically aligned liquid crystal composition.