JP3290731B2 - Liquid crystal display device - Google Patents

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 have great advantages of thinness, light weight, and low power consumption, and are therefore frequently used as display elements of OA equipment such as liquid crystal televisions, Japanese word processors, and desktop personal computers. In particular, the twisted nematic (TN) type liquid crystal display system, in which the alignment state of liquid crystal molecules is twisted by about 90 °, uses a cathode ray tube (CR) by incorporating an active switching element such as a TFT.
T) A super twist nematic (STN) type liquid crystal display system in which liquid crystal molecules are twisted at an angle of 90 ° or more can provide high display multiplex driving.

A conventional TN type liquid crystal display device has:
The alignment layer for controlling the twist angle and the tilt angle of the liquid crystal composition is provided on the surface of the transparent substrate on which the driving and pixel electrodes are arranged, and the alignment layer of the opposing substrate has a narrow space. A liquid crystal cell is formed so as to face the liquid crystal cell, a liquid crystal composition is sandwiched between the liquid crystal cells, and two orthogonal polarizing plates are disposed on the outermost layer.

Among the constituent members of such a liquid crystal display element, an alignment layer is obtained by subjecting an insulating film surface to various alignment treatments for the purpose of aligning liquid crystal molecules in a certain direction on a surface in contact with a liquid crystal composition. is there. A rubbing method has been conventionally used as an alignment treatment, and a polyimide film is mainly used as an 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 a rubbing process is performed on the polyimide film, the director direction and pretilt direction of the liquid crystal molecules are necessarily 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 viewing angle dependency such that a display color and a contrast ratio change depending on a viewing direction because a liquid crystal molecule has a twisted structure in a liquid crystal cell and its rise has directionality. There are difficulties. For this reason, many methods have been proposed for compensating the pretilt direction by the alignment treatment and improving the visual characteristics.

For example, a method of changing the pretilt angle of liquid crystal molecules by dividing a region in a pixel (Japanese Patent Application Laid-Open No. 62-159119) and a method of changing an alignment processing direction in a region in a pixel (Japanese Patent Application Laid-Open No. 63-106624) Publication).

[0006]

However, in order to perform an alignment treatment for compensating the visual sense in the liquid crystal element using a polyimide film or the like, it is necessary to increase the number of steps in the manufacturing process, increase the processing accuracy, and align the counter substrate. Many problems arise, such as improvement in accuracy. For example, when forming an alignment state having a plurality of pretilt or tilt-up directions to reduce the visual dependency peculiar to a liquid crystal display element by setting the liquid crystal alignment in a fine pixel to two or more states, A rubbing process must be performed a plurality of times on a fine polyimide film or the like on the pixel surface for each pretilt or tilt-up direction. Further, a similar rubbing process is performed on the counter substrate a plurality of times, and high-precision processing and substrate alignment are required so that each fine pixel surface and alignment processing region do not shift.

Furthermore, when a polyimide alignment film that has been widely used in the past is used, the pretilt angle difference between adjacent alignment processing regions is required to be at least 2 degrees, which limits the usable polyimide alignment film material. There is a problem with being done.

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

The present invention has been made to address such a problem, and it is possible to control the pretilt direction of an adjacent alignment region regardless of the pretilt angle of an alignment film used in a multiple alignment process in a fine pixel region. It is another object of the present invention to provide a liquid crystal display device having a wide viewing angle characteristic by preventing alignment defects and display defects due to misalignment between upper and lower substrates.

[0010]

The liquid crystal display device of the present invention comprises a pair of substrates each having an alignment layer on the surface, at least one of which is transparent, and the pair of substrates facing each other. arrangement, and the liquid crystal composition disposed in the gap, one of the alignment layer to regulate the director and the pretilt direction of the liquid crystal composition, the other of the alignment layer is restricted only director, before Symbol director and Purechi
Alignment layer for regulating the belt direction, and having a plurality of alignment treatment region that different orientation states.

In the liquid crystal display device of the present invention, one surface of the alignment layer in contact with the liquid crystal composition is subjected to a rubbing treatment for aligning the liquid crystal molecules in a certain direction and causing a pretilt or tilt up in a certain direction. ing. Still another 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 the non-uniform 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 non-uniform pretilt alignment processing film is determined by the alignment processing state of the alignment film on the counter substrate surface. In other words, on the non-uniform pretilt alignment treatment film, in consideration of the alignment and the alignment state in which the director direction of the liquid crystal molecules is constant in the adjacent fine alignment region and the pretilt or tilt-up directions are opposite to each other, the nonuniform pretilt is considered. Rubbing is performed in a specific direction for each fine pixel area of the alignment film on the counter substrate side with respect to the alignment film, and the alignment and alignment determined by this alignment process are reflected in the pretilt or tilt-up direction on the non-uniform pretilt alignment film. I do.
Accordingly, the fine alignment processing region is formed uniformly over the entire surface of the pixel without accurately aligning the divided alignment processing regions on the upper and lower substrates, and a self-pretilt and self-alignment alignment film can be easily obtained.

Next, a specific example in the pixel portion of the above-described liquid crystal display device will be described with reference to FIGS. 1 and 2 are perspective views showing an example of a finely divided alignment and alignment region in the liquid crystal display device of the present invention. FIG. 1 shows a micro-groove alignment processing film as a non-uniform pretilt alignment processing film, and FIG. This is an example in which a polymer alignment treatment film that does not contribute to the tilt-up direction is used.

In FIG. 1, the interface of the substrate 1 in contact with the liquid crystal composition is covered with a polyimide film, and the finely divided director orientation direction and the finely divided pretilt directions 6 and 7 determined by the finely divided rubbing directions 4 and 5 are defined. Have. The interface of the opposing substrate 2 in contact with the liquid crystal composition has only a uniform director alignment direction determined by the microgroove alignment processing film 3 having a fine uneven structure. Here, when the left-twisted TN liquid crystal mode is used, the pre-tilt or tilt-up direction 8 and the tilt-up direction 8 on the microgroove interface on the non-uniform pretilt alignment treatment film are increased due to the energy stability of the liquid crystal composition and the chiral agent contained in the liquid crystal composition. 9 is inevitably determined. Therefore, only the surface alignment film of the substrate 1 is divided and subjected to the polyimide rubbing process without going through the conventional complicated process of assembling the upper and lower substrates with high accuracy.
The orientation division processing on the surface automatically occurs.

In FIG. 2, the interface in contact with the liquid crystal composition of the substrate 10 is covered with a polyimide film as in FIG. 1, 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 opposing substrate 11 that is in contact with the liquid crystal composition is covered with a polystyrene-based material, and is subjected to uniform alignment only in the direction indicated by the rubbing direction 14. Here, the polystyrene-based alignment film has the property of aligning the liquid crystal molecules in a direction rotated by 90 degrees with respect to the rubbing direction 14, that is, a direction perpendicular to the rubbing direction 14 by the treatment in the rubbing direction 14, and has no characteristic in the pretilt or tilt-up direction. . Therefore, FIG.
As in the case of (1), the pretilt or tilt-up direction of the liquid crystal molecules on the polystyrene-based alignment film is inevitably determined in the 17 and 18 directions only by the alignment processing of the counter substrate 11, and the alignment division region is automatically determined. Occurs. Also in this case, a difficult process of assembling the upper and lower substrates with high accuracy can be omitted.

In the non-uniform pretilt alignment film according to the present invention, only the director direction is determined, and an organic polymer material or an inorganic material which does not contribute to the pretilt or tilt-up direction is rubbed. Can be used. Examples of the organic polymer material include polystyrene, poly-4-vinylpyridine, and a polyimide polymer. In addition, microgrooves formed on a substrate using an inorganic substance and an organic substance can also be used effectively.

The director, pretilt or tilt-up direction is controlled by an alignment film formed of a heterocyclic polymer such as polyimide, polyamideimide, polybenzimidazole, polybenzimidazopyrololone, polyquinoxaline, polybenthiazole and polybenzoxazole. 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 liquid crystals, alkenyl Nematic liquid crystal materials such as cyclohexylbenzonitrile are exemplified. Generally, these compounds are used as a mixture, and a chiral agent or the like is further added.

The liquid crystal display element of the present invention comprises a pair of substrates each having at least one electrode formed by a simple matrix, an active matrix driving method or the like, and the above-mentioned alignment film formed on the electrodes. After the alignment films are arranged facing each other and the periphery thereof is sealed, a liquid crystal composition is injected to form a liquid crystal cell, and an exterior assembly is formed. In particular, in the present invention, better display is possible by employing the active matrix driving method.

[0019]

By using a divided alignment film surface and a non-uniform pretilt alignment film, the display characteristics can be easily and little changed even with little change in the conventional manufacturing process and little occurrence of divided regions. A good liquid crystal display element can be obtained.

[0020]

Embodiments of the present invention will be described below in detail. Example 1 to Example 6 A transparent electrode was formed on a transparent substrate, and a polyimide alignment film forming solution was applied thereon, followed by post-baking and completely cured 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) The thing of 5 degrees (Example 6) was used. A rubbing process was performed in a predetermined direction by separating a rubbed region and a non-processed region using a mask for dividing the polyimide alignment film layer into predetermined fine pixel regions. Next, the divided masks were exchanged, and rubbing was performed in a direction in which the rubbing direction was different from the previous direction by 180 °, so that the pretilt directions of the regions adjacent to each other were set to be symmetric with respect to the boundary surface between the adjacent alignment regions.

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

The two substrates subjected to the above-described alignment treatment were arranged so that the alignment films faced each other, and a nematic liquid crystal composition was sandwiched therebetween to produce a liquid crystal cell having an electrode spacing of 6 μm. At this time, there was almost no need for fine adjustment for arranging the pixel regions subjected to the fine division alignment processing 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 the display state were evaluated. Table 1 shows the results. In the comparative example, the same method as that of Example 1 was adopted except that the substrates in which the tilt angle of the polyimide alignment film was changed from 0 ° to 5 ° corresponding to Example 1 to Example 6 were arranged so as to face each other. 9 is an evaluation result of the liquid crystal display element manufactured in the above.

Examples 7 to 12 A transparent electrode was formed on a transparent substrate, and a polyimide alignment film forming solution was applied thereon, followed by post-baking to completely cure the film, thereby obtaining an alignment film having a thickness of 700 angstroms. The tilt angles of the polyimide alignment film are 0 ° (Example 7), 1 ° (Example 8), 2 ° (Example 9), 3 ° (Example 10), 4 °
(Example 11) and those of 5 ° (Example 12) were used.
A rubbing process was performed in a predetermined direction by separating a rubbed region and a non-processed region using a mask for dividing the polyimide alignment film layer into predetermined fine pixel regions. Next, the divided masks were exchanged, and rubbing was performed in a direction in which the rubbing direction was different from the previous direction by 180 °, so that the pretilt directions of the regions adjacent to each other were set to be symmetric with respect to the boundary surface between 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, followed by post-baking to completely cure the resultant, thereby obtaining an alignment film having a thickness of 700 Å. . This alignment film was uniformly rubbed on the entire surface of the substrate so as to match the rubbing direction of the above-mentioned polyimide alignment film. At this time, if the rubbing direction is parallel to the rubbing direction of the polyimide alignment film, it is not necessary to particularly consider the direction of the processing.

The two substrates subjected to the above-mentioned alignment treatment were arranged so that the alignment films faced each other, and a nematic liquid crystal composition was sandwiched therebetween to produce a liquid crystal cell having an electrode spacing of 6 μm. Poly-4-
Since the liquid crystal molecules are arranged on the vinylpyridine film with the director direction aligned in the direction perpendicular to the rubbing direction, this liquid crystal cell forms a TN structure. In addition, since the pretilt or tilt-up direction is determined by the rubbing direction of the opposing substrate surface, fine division alignment is automatically performed even on a poly-4-vinylpyridine film uniformly rubbed. An area is formed. Therefore, there was almost no need for fine adjustment for arranging the pixel regions subjected to the fine division alignment process to face each other without error. Finally, an exterior assembly was formed to obtain a liquid crystal display device.

The alignment state and the display state were evaluated using these liquid crystal display elements. Table 1 shows the results. In the comparative example, the same method as in Example 7 was adopted except that the substrates in which the tilt angle of the polyimide alignment film was changed from 0 ° to 5 ° corresponding to Example 7 to Example 12 were arranged so as to face each other. 9 is an evaluation result of the liquid crystal display element manufactured in the above.

As shown in Table 1, the liquid crystal display devices of Examples 1 to 12 had a polyimide alignment film having a pretilt angle of 0.
Also in the case of °, a very good display state was obtained by accurately reflecting the orientation and the arrangement state determined by the rubbing direction. In addition, by performing the fine division alignment treatment only on one of the pair of substrates facing each other, a uniform and fine division alignment and alignment state can be obtained. 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 regulates only the director. Almost any alignment layer that can align liquid crystal molecules by rubbing treatment can be used and has a very wide application range.

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

[Brief description of the drawings]

FIG. 1 is a perspective view showing an example of a finely divided alignment and alignment region 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 a finely divided alignment and alignment region 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 ... fine division rubbing direction, 6, 7, 15, 16 ... fine division pretilt Direction, 8, 9, 17, 18 ... tilt-up direction, 14 ... rubbing direction.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) G02F 1/1337 505

Claims (3)

(57) [Claims] 1. A liquid crystal composition comprising: a pair of substrates each having an alignment layer on the surface, at least one of which is transparent; and the pair of substrates arranged with the respective alignment layers facing each other; If, comprising a, one of the alignment layer regulates the director and the pretilt direction of the liquid crystal composition, the orientation layer and the other of the alignment layer is restricted only director, regulating the pre-Symbol director and pretilt directions
But the liquid crystal display element characterized by having a plurality of alignment treatment areas with different orientation states. 2. The liquid crystal display device according to claim 1, wherein
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 device according to claim 1, wherein
A liquid crystal display device, wherein the alignment layer that regulates only the director is a polymer alignment treatment film.