JPH06214234A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To prevent the orientation defect and display defect by mis-alignment between upper and lower substrates and to expand a visual field characteristic by forming oriented layers in such a manner that one thereof regulates the director and pretilt directions of liquid crystal molecules and the other thereof regulates only the director. CONSTITUTION:The boundary of a substrate 1 in contact with a liquid crystal compsn. has finely divided director orientation directions and finely divided pretilt directions 6 and 7 determined by finely divided rubbing directions 4, 5. The boundary of a counter substrate 2 in contact with a liquid crystal compsn. is determined only in the uniform director orientation direction by a microgroove orientation treated film 3 of the fine ruggedness structure. The pretilt or tilt up directions 8 and 9 on the microgroove boundary on the non- uniform pretilt orientation treated film are inevitably determined if a TN liquid crystal mode of a left hand twist is used. Then, the orientation dividing treatment on the surface of the counter substrate 2 is automatically generated simply by dividing only the surface oriented film of the substrate 1 and subjecting the film to a polyimide rubbing treatment.

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 elements are widely used as display elements for OA 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.

A 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.

Of the constituent members of such a liquid crystal display element, the alignment layer is one in which various kinds of alignment treatment are applied to the surface of the insulating film for the purpose of aligning liquid crystal molecules in a certain direction on the surface in contact with the liquid crystal composition. is there. A rubbing method has been conventionally used as the alignment treatment, and a polyimide film is mainly used as the alignment layer material. The rubbing method is a means for inducing liquid crystal molecule alignment ability on the film surface by rubbing (rubbing) the film surface in a certain direction using a fibrous substance such as cotton or cloth. When the rubbing process is performed on the polyimide film, the director direction and the pretilt direction of the liquid crystal molecules are inevitably determined by the rubbing direction. The director direction and pretilt direction of the liquid crystal molecules are important factors that determine the visual direction and visual characteristics of the liquid crystal display device. In general, a conventional TN type liquid crystal display element has a structure in which liquid crystal molecules are twisted in a liquid crystal cell and has a rising direction, so that the display color and the contrast ratio change depending on the viewing direction, which is called viewing angle dependence. There are difficulties. Therefore, many methods have been proposed to improve the visual characteristics by compensating the pretilt direction by the alignment treatment.

For example, a method of dividing a region in a pixel to change the pretilt angle of liquid crystal molecules (Japanese Patent Laid-Open No. 62-159119) and a method of changing the orientation processing direction in the region in the pixel (Japanese Patent Laid-Open No. 63-106624). Issue gazette) etc.

[0006]

However, in order to perform the alignment treatment for compensating the vision in the liquid crystal element by using the polyimide film or the like, the number of steps in the manufacturing process is increased, the processing accuracy is increased, and the alignment of the counter substrate is performed. There are many problems such as improvement in accuracy. For example, when forming an array state having a plurality of pretilt or tilt-up directions that reduces the visual dependence peculiar to a liquid crystal display element by setting the liquid crystal arrays in fine pixels to two or more states, A polyimide film on a fine pixel surface or the like must be rubbed a plurality of times for each pretilt or tilt-up direction. Further, a similar rubbing treatment is performed on the counter substrate as well, so that highly precise processing and substrate alignment are required so that each fine pixel surface and the alignment treatment region are not displaced.

Furthermore, when a polyimide alignment film which has been widely used in the past is used, the pretilt angle difference between adjacent alignment treatment regions is required to be at least 2 degrees or more, so that usable polyimide alignment film materials are limited. There is a problem that it will be done.

The misalignment of the upper and lower substrates causes a combination different from the predetermined alignment direction and arrangement direction even if it is fine, and, for example, in a TN type liquid crystal display element, the misalignment of the upper and lower substrates induces a reverse twist alignment state. However, there is a problem that display characteristics are extremely deteriorated.

The present invention has been made to solve such a problem, and it is possible to control the pretilt direction of the adjacent alignment regions regardless of the pretilt angle of the alignment film used in the multiple alignment treatment process in the fine pixel region. And to prevent alignment defects and display defects due to misalignment of the upper and lower substrates, and to provide a liquid crystal display device having a wide viewing angle characteristic.

[0010]

A liquid crystal display device of the present invention comprises a pair of substrates, each of which has an alignment layer on its surface, at least one of which is transparent, and the alignment layers are opposed to each other at a narrow interval. The liquid crystal composition is sandwiched between a pair of substrates, one of the alignment layers regulates the director and pretilt direction of liquid crystal molecules of the liquid crystal composition, and the other one regulates only the director. .

In the liquid crystal display device of the present invention, one surface of the alignment layer which is in contact with the liquid crystal composition is subjected to a rubbing treatment for aligning liquid crystal molecules in a certain direction and pretilting or tilting up in a certain direction. ing. Further, the other surface is subjected to a rubbing treatment for arranging only the directors of the liquid crystal molecules in a certain direction, and the pretilt or tilt-up direction of the liquid crystal molecules is not determined on this nonuniform pretilt alignment treatment film. Here, that the pretilt or tilt-up direction is not determined means that the pretilt or tilt-up direction on the nonuniform pretilt alignment treatment film is determined by the alignment treatment state of the alignment film on the surface of the counter substrate. In other words, on the non-uniform pretilt alignment treatment film, when the director directions of the liquid crystal molecules in the adjacent fine alignment regions are constant, the pretilt or tilt-up directions are opposite to each other. Rubbing is performed in a specific direction for each fine pixel area of the alignment film on the opposite substrate side with respect to the alignment film, and the orientation and alignment state determined by this alignment process is reflected in the pretilt or tilt-up direction on the non-uniform pretilt alignment film. To do.
Therefore, the fine alignment treatment region is uniformly formed over the entire surface of the pixel without accurately aligning the divided alignment treatment regions on the upper and lower substrates, and the self-pretilt and self-alignment alignment film can be easily obtained.

Next, a specific example of the pixel portion of the above-mentioned liquid crystal display element will be described with reference to FIGS. 1 and 2. 1 and 2 are perspective views showing an example of finely divided alignment and alignment regions in a liquid crystal display device of the present invention. As a nonuniform pretilt alignment treatment film, FIG. 1 is a microgroove alignment treatment film, and FIG. 2 is a pretilt alignment treatment film. This is an example of using a polymer alignment treatment film that does not contribute to the tilt-up direction.

In FIG. 1, the interface of the substrate 1 in contact with the liquid crystal composition is covered with a polyimide film, and the fine division director alignment direction and the fine division pretilt directions 6 and 7 determined by the fine division rubbing directions 4 and 5 are defined. To have. At the interface of the counter substrate 2 in contact with the liquid crystal composition, only the uniform director alignment direction is determined by the microgroove alignment treatment film 3 having a fine concavo-convex structure. Here, when the left-twisted TN liquid crystal mode is used, the pretilt or tilt-up direction 8 on the microgroove interface on the nonuniform pretilt alignment treatment film and the chiral agent contained in the liquid crystal composition and the energy stable state of the liquid crystal alignment are used. 9 is inevitably decided. Therefore, the opposing substrate 2 can be formed by dividing only the surface alignment film of the substrate 1 and subjecting it to a polyimide rubbing treatment without going through the conventional difficult process of assembling the upper and lower substrates with high precision.
The orientation division processing on the surface automatically occurs.

In FIG. 2, as in FIG. 1, the interface of the substrate 10 in contact with the liquid crystal composition is covered with a polyimide film and has a director alignment direction and pretilt directions 15 and 16 determined by rubbing directions 12 and 13. . On the other hand, the surface of the counter substrate 11 that is in contact with the liquid crystal composition is covered with a polystyrene material, and is uniformly aligned only in the rubbing direction 14. Here, the polystyrene-based alignment film has a characteristic that the treatment in the rubbing direction 14 aligns liquid crystal molecules in a direction rotated by 90 degrees with respect to the rubbing direction 14, that is, in a direction perpendicular to the rubbing direction 14, and does not contribute to the pretilt or tilt-up direction at all. . Therefore, FIG.
As in the case of, the pre-tilt or tilt-up direction of the liquid crystal molecules on the polystyrene-based alignment film is inevitably determined to be the 17 and 18 directions only by the alignment treatment of the counter substrate 11, and the alignment division regions are automatically set. Occurs. Also in this case, the difficult process of assembling the upper and lower substrates with high precision can be omitted.

As the non-uniform pretilt alignment film according to the present invention, only the alignment in the director direction is determined, and the organic polymer material or the inorganic material that does not contribute to the determination of the pretilt or tilt up direction is rubbed. Can be used. Examples of organic polymer materials include polystyrene, poly-4-vinyl pyridine, and polyimide polymers. Further, microgrooves formed on a substrate using an inorganic substance and an organic substance can also be effectively used.

As the director, the alignment film for controlling the pretilt or tilt-up direction, a heterocyclic polymer such as polyimide, polyamideimide, polybenzimidazole, polybenzimidazopyrrolone, polyquinoxaline, polybenzthiazole, polybenzoxazole or the like is used. Can be mentioned.

The liquid crystal composition that can be used in the liquid crystal display device of the present invention is a nematic liquid crystal substance 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, alkenyl Examples are nematic liquid crystal substances such as cyclohexylbenzonitriles. Generally, these compounds are used as a mixture, and a chiral agent or the like is further added.

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 the 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.

[0019]

By using the divided alignment treatment film surface and the non-uniform pretilt alignment treatment film, the display characteristics can be easily changed without causing a large change in the conventional manufacturing process and almost no fine displacement of the divided region occurs. A good liquid crystal display device can be obtained.

[0020]

EXAMPLES Examples of the present invention will be described in detail below. Examples 1 to 6 A transparent electrode was formed on a transparent substrate, a polyimide alignment film forming solution was applied on the transparent electrode, and post baking was performed to completely cure the transparent electrode to obtain an alignment film having a thickness of 700 angstroms. The tilt angle of the polyimide alignment film is 0 ° (Example 1), 1 ° (Example 2), 2 ° (Example 3), 3 ° (Example 4), 4 °.
(Example 5) and 5 ° (Example 6) were used. A rubbing process was performed in a predetermined direction by dividing the rubbing-processed region and the non-processed region with a mask that divides the polyimide alignment film layer into predetermined fine pixel regions. Next, the divided masks were replaced with each other, and rubbing treatment was performed in a direction in which the rubbing direction was different from the previous direction by 180 °, and the pretilt directions of the regions adjacent to each other were set to be symmetrical with respect to the boundary surface of the adjacent alignment regions.

On the other hand, a transparent electrode is formed on a transparent substrate serving as a counter substrate, and a photosensitive polyimide alignment film forming solution is applied to the entire surface of the substrate and post-baked to completely cure the film to a thickness of 7
An alignment film of 00 angstrom was obtained. The surface of this alignment film layer was exposed using a parallel exposure machine PLA-105 (trade name of Nikon Corporation) through an exposure mask having slits having a periodic pattern shape. At this time, the line and space in the exposure mask was set to 1 μm width. Subsequently, development and rinsing treatment were performed to remove unnecessary polyimide, and then annealing was performed at a temperature of 230 ° C. to form a periodic concave-convex pattern having a rectangular cross section on the substrate. This periodic pattern serves as a non-uniform pretilt alignment treatment film for controlling the direction of the liquid crystal molecule director on the counter substrate surface.

A liquid crystal cell having an electrode interval of 6 μm was prepared by arranging the two substrates subjected to the above-mentioned alignment treatment so that the alignment films face each other and sandwiching the nematic liquid crystal composition. At this time, there was almost no need for fine adjustment for arranging the pixel regions that have been subjected to the fine division orientation processing so as to face each other without error. Finally, an exterior assembly was formed to obtain a liquid crystal display device.

The alignment state and display state were evaluated using these liquid crystal display elements. The results are shown in Table 1. In the comparative example, the same method as in Example 1 was adopted except that the tilt angle of the polyimide alignment film was changed from 0 ° to 5 ° corresponding to Examples 1 to 6 and the substrates were arranged so as to face each other. It is an evaluation result of the liquid crystal display element produced in.

Examples 7 to 12 A transparent electrode was formed on a transparent substrate, a polyimide alignment film forming solution was applied on the transparent electrode, and post baking was performed to completely cure the transparent electrode, thereby obtaining an alignment film having a thickness of 700 angstroms. The tilt angle of the polyimide alignment film is 0 ° (Example 7), 1 ° (Example 8), 2 ° (Example 9), 3 ° (Example 10), 4 °.
(Example 11) and 5 ° (Example 12) were used.
A rubbing process was performed in a predetermined direction by dividing the rubbing-processed region and the non-processed region with a mask that divides the polyimide alignment film layer into predetermined fine pixel regions. Next, the divided masks were replaced with each other, and rubbing treatment was performed in a direction in which the rubbing direction was different from the previous direction by 180 °, and the pretilt directions of the regions adjacent to each other were set to be symmetrical with respect to the boundary surface of the adjacent alignment regions.

On the other hand, a transparent electrode was formed on a transparent substrate serving as a counter substrate, and a poly-4-vinylpyridine solution was applied to the entire surface of the substrate and then post-baked to completely cure it to obtain an alignment film having a film thickness of 700 angstrom. . This alignment film was uniformly rubbed on the entire surface of the substrate so as to match the rubbing direction of the polyimide alignment film described above. At this time, if the rubbing treatment direction is parallel to the rubbing direction of the polyimide alignment film, the direction of the treatment progress does not have to be particularly considered.

Two substrates subjected to the above-mentioned alignment treatment were placed so that the alignment films face each other, and a nematic liquid crystal composition was sandwiched between them to prepare a liquid crystal cell with an electrode interval of 6 μm. Poly-4-
Since liquid crystal molecules are aligned on the vinyl pyridine film in a direction perpendicular to the rubbing direction, the liquid crystal cell forms a TN structure. Further, since the pretilt or tilt-up direction is determined by the rubbing treatment direction of the opposing substrate surface, even finely divided alignment is automatically performed on the poly-4-vinylpyridine film uniformly rubbed on the entire surface. A region is formed. Therefore, there is almost no need for fine adjustment for arranging the pixel regions that have been subjected to the fine division alignment processing so as to face each other without error. Finally, an exterior assembly was formed to obtain a liquid crystal display device.

Using these liquid crystal display elements, the alignment state and display state were evaluated. The results are shown in Table 1. In the comparative example, the same method as in Example 7 was adopted except that the tilt angle of the polyimide alignment film was changed from 0 ° to 5 ° corresponding to Examples 7 to 12 and the substrates were arranged so as to face each other. It is an evaluation result of the liquid crystal display element produced in.

As shown in Table 1, in the liquid crystal display elements shown in Examples 1 to 12, the pretilt angle of the polyimide alignment film was 0.
Even in the case of °, a very good display state was obtained by accurately reflecting the orientation and arrangement state determined by the rubbing treatment direction. In addition, uniform fine division alignment and alignment can be obtained only by performing fine division alignment treatment on either one of a pair of opposing substrates, and thus alignment due to misalignment of upper and lower substrates, alignment defects and display defects are reduced. It was

[0029]

[Table 1]

[0030]

As described above, in the liquid crystal display device of the present invention, one of the alignment layers regulates the director and pretilt direction of the liquid crystal molecules of the liquid crystal composition, and the other one regulates only the director. As long as the alignment layer is capable of aligning the liquid crystal molecules by the rubbing treatment, it can be almost used and the application range is extremely wide.

Further, since only one of the surfaces of the alignment layer is finely divided and aligned to automatically form the finely divided alignment and alignment state, defects due to alignment defects are reduced and visual characteristics are improved. It Further, the manufacturing process is also simplified.

[Brief description of drawings]

FIG. 1 is a perspective view showing an example of finely divided alignment and array regions in a liquid crystal display device of the present invention using a microgroove alignment treatment film.

FIG. 2 is a perspective view showing an example of finely divided alignment and alignment regions in a liquid crystal display device of the present invention using a polymer alignment treatment film.

[Explanation of symbols]

1, 2, 10, 11 ... Substrate, 3 ... Microgroove alignment treatment film, 4, 5, 12, 13 ... Micro-divided rubbing direction, 6, 7, 15, 16 ... Micro-divided pretilt Direction, 8, 9, 17, 18 ... Tilt up direction, 14 ... Rubbing direction.

Claims (3)

[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. A liquid crystal display device, wherein one of the alignment layers regulates a director and a pretilt direction of liquid crystal molecules of the liquid crystal composition, and the other one regulates only a director. 2. The liquid crystal display device according to claim 1,
A liquid crystal display device, wherein the alignment layer that regulates only the director is a microgroove alignment treatment film. 3. The liquid crystal display element according to claim 1,
A liquid crystal display device, wherein the alignment layer that regulates only the director is a polymer alignment treatment film.