JPH0695120A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To provide the high-reliability large-screen liquid crystal display device which has a wide angle of view and high contrast and is thin and light by simple cell production process. CONSTITUTION:This liquid crystal display device is constituted by disposing a first substrate 5 having plural pixel electrodes 2 on one main surface and a second substrate 6 having a counter preferably 7 on one main surface in such a manner that the main surfaces on one side thereof face each other and clamping a liquid crystal layer 14 consisting of a liquid crystal compsn. having negative dielectric anisotropy therebetween. The liquid crystal display device consists of means for segmenting and forming the surfaces of the respective pixel electrodes 2 to plural region surfaces A, B varying in hardness and oriented films subjected to a rubbing orientation treatment to induce the liquid crystal molecules of the liquid crystal layers formed on these plural region surfaces to perpendicular alignment to vary the tilt directions of the liquid crystal compsn. when electric fields are impressed between the region surfaces varying in the hardness.

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,
In particular, the present invention relates to a field effect birefringence control type liquid crystal display device.

[0002]

2. Description of the Related Art A liquid crystal display device that is generally used at present has a problem that the viewing angle is narrow. A method of arranging the film is being studied.

In a field effect birefringence control type liquid crystal display device using a vertical alignment film, optimization of Δnd and arrangement of an optical compensation film (for example, S. Yamauchi et al., SID8
9, Digest, p.378 (1989) and JFClerc, JAPAN DISPLA
Y'89, p.188 (1989)) and two-layer cell structure (eg H. Seki e
The improvement of the viewing angle has been reported by IDRC DIGEST, p.188 (1991)). In all of these, the problem was how to reduce the viewing angle dependence of retardation and expand the viewing angle by using an oriented cell with uniform surface. On the other hand, recently, it was reported that the viewing angle was improved by positively forming regions with different vertical alignments in the panel and making the tilt direction of the liquid crystal composition when applying an electric field different within one pixel. Has been done. For example, the multi-domain method announced by Stanley Electronics (JFClerc, ； SID'91 Digest, p.7
58 (1991) and T. Yamamoto et al., SID'91 Digest, p.76.
2 (1991)). This is a method of processing the pixel electrode into a special shape and using the tilt of the electric field between the upper and lower electrodes to control the tilt direction during ON in one pixel, or a method of finely moving in different directions within one pixel. This is a method of improving the viewing angle by making the tilt direction of the liquid crystal composition when an electric field is applied to be different within one pixel by creating a surface shape that is tilted to the right. However, these methods are not easy to manufacture in that the electrodes have a special shape and the orientation surface is partially inclined.

Further, in the TN type general LCD, it is disclosed in
63-106624, JP 64-88520, JP 1-24
Divide each picture element into multiple areas, such as the 5223 publication,
A method of aligning each region and a method of forming a multi-domain by making rubbing directions different have been proposed, but both are not easy in manufacturing because it is necessary to perform rubbing alignment treatment a plurality of times for each minute pixel.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the problem of viewing angle as described above and provide a wide viewing angle, high contrast large screen liquid crystal display device by a simple method.

[0006]

According to the present invention, a first substrate having a plurality of pixel electrodes on one main surface and a second substrate having a counter electrode on one main surface are arranged so that the one main surfaces face each other. In a liquid crystal display device in which a liquid crystal layer made of a liquid crystal composition having a negative dielectric anisotropy is sandwiched therebetween, each pixel electrode is divided into a plurality of region surfaces having different hardness, A vertical alignment film that is formed on the area surface and is subjected to rubbing alignment treatment to tilt-align the liquid crystal molecules of the liquid crystal layer, and the tilt directions of the liquid crystal composition when an electric field is applied are made different in the area surfaces having different hardness. A characteristic liquid crystal display device is obtained.

Further, it is possible to dispose and form a base film having different hardness on each of the plurality of region surfaces, or to configure one of the plurality of regions by the pixel electrode surface itself.

Further, the base film in a plurality of regions can be selected based on the pencil hardness of 2H.

[0009]

In order to expand the viewing angle, it is useful to reduce the retardation change of the liquid crystal panel with respect to the viewing angle. In a field effect birefringence control type liquid crystal display device using a vertical alignment film, a voltage is applied to tilt the liquid crystal to change the retardation of the cell for display. Therefore, the retardation of the cell when a voltage is applied greatly depends on the tilt direction. From this, it can be seen that the tilt direction may be set to various directions within one pixel for expanding the viewing angle. However, tilting in a disorderly direction results in display failure. Therefore, it is necessary to control the tilt direction so that it has order within one pixel. In order to control the tilt direction and obtain high contrast, it is useful to have a certain small pretilt angle.

It is known that when the minute tilt direction is different in one pixel, the change in retardation in the viewing angle direction is smaller than that in the case where the entire surface is uniformly tilted in one direction, so that the viewing angle is widened. ing.

The inventors have found in many experiments that the hardness of the underlayer of the vertical alignment layer has a great influence on the formation of the fine pretilt angle vertical alignment layer. Usually, FIG. 2 (a)
The vertical alignment layer 4a having a small pretilt angle as shown in FIG.
Can be obtained by applying a long-chain alkylsilane compound, a monobasic chromium complex or the like on the glass substrate 5 as an alignment layer via the undercoat film 3a, and then performing a rubbing treatment.
At this time, if the hardness of the base film 3a of the vertical alignment layer 4a is harder than the pencil hardness 2H, the liquid crystal molecules 14a tilt in the rubbing direction as shown in FIG. 2A. On the other hand, as shown in FIG. 2B, the hardness of the base film 3b is not more than the pencil hardness 2H, for example, 1
When a soft film of H is used, the liquid crystal molecules 14a are tilted in the direction opposite to the rubbing direction when the rubbing alignment treatment is performed on the vertical alignment layer 4b.

This is because when the base is hard, the alignment film on the surface is aligned in a direction slightly tilted in the rubbing direction by rubbing, and as a result, the liquid crystal molecules are slightly tilted in the rubbing direction as shown in FIG. 2A. Conceivable. On the other hand, when the base is soft, the rubbing alignment treatment deforms the base film itself on which the alignment film is formed, as shown in FIG. 2B, and the wrinkles appear to be wrinkled. It is considered that the vertical alignment layer is oriented in the direction opposite to the rubbing direction, and the liquid crystal molecules are slightly tilted in the direction opposite to the rubbing direction due to the influence of the alignment film. Here, when the pretilt angle is small, there is a problem in that disclination is severely generated in the boundaries where the tilt directions are different and the appearance is deteriorated. However, this can be solved by sufficiently increasing the pretilt angle in each area or forming a black matrix or an auxiliary capacitance element in the disclination generating portion to make it invisible.

That is, as shown in FIG. 1, the surface area of the transparent pixel electrode 2 made of, for example, ITO formed on the substrate 5 is divided into a plurality of areas having different hardnesses, for example, two areas based on the pencil 2H, and these areas have a predetermined hardness. When the underlying films 3a and 3b are formed and the common vertical alignment layer 4 is deposited thereon, and the alignment layer is rubbed in the direction of the arrow, the liquid crystal molecules 14a are formed on the underlying films when the voltage is applied for the above-mentioned reason. It will tilt in different directions on 3a and 3b. Therefore, if the films 3a and 3b having the same hardness are arranged to face each other as the underlying films of the vertical alignment layer 11 on the counter substrate 6, liquid crystal layers having tilts in different directions in two regions on each pixel electrode. Will be obtained.

As described above, according to the present invention, the undercoating films having different hardness are formed in one pixel, the vertical alignment process is performed thereafter, and the rubbing alignment process is performed only once for each substrate. Can be tilted in the direction, and the viewing angle dependence of retardation during voltage application is reduced,
This makes it possible to obtain a wide viewing angle.

[0015]

EXAMPLES Examples of the present invention will be described below.

[Embodiment 1] FIG. 3 is a schematic plan view of a liquid crystal display device according to an embodiment of the present invention, and FIG. 4 is a schematic sectional view of a liquid crystal display device according to an embodiment of the present invention.

A TFT array substrate 5 in which a TFT (thin film transistor) element 1 using amorphous silicon and a pixel electrode 2 are arranged on the surface of one main surface is manufactured by a thin film technique. Next, only in the half surface area of the pixel electrode 2, Si
Solution ZQ-2 containing O ₂ and ZrO ₂ as main components to form a film
(Catalyst Kasei Kogyo Co., Ltd.) was applied in a stripe shape by a printing method and baked in air at 180 ° C. for 30 minutes to form an insulating base film 3 having a pencil hardness of 1H in about 500 angstrom sections. In the remaining area, the electrode surface itself was left exposed. Then, octadecyltriethoxysilane (ODS) was applied on the entire surface by a dipping method, and then dried in a nitrogen atmosphere at 150 ° C. for 30 minutes to form a vertical alignment film. After that, rubbing treatment was performed as shown by an arrow 12 in the figure to form the alignment film 4.

On the other hand, an ITO film is formed on the entire surface of the counter substrate 6 as the transparent counter electrode 7, and the solution ZQ-2 is formed in a stripe shape so as to face the ZQ-2 base film 3 on the TFT array substrate 5. After coating and baking to form an insulating base film 8 having a pencil hardness of 1H of about 500 angstroms, ODS was applied and dried to form a vertical alignment film. Then, the surface was subjected to a rubbing treatment as indicated by an arrow 13 in the figure to form an alignment film 11. Then, an epoxy resin adhesive containing 6 μm glass fiber is printed around the substrates 5 and 6 so that the alignment films 4 and 11 on one main surface of each substrate 5 and 6 face each other.
Moreover, the underlying films 3 and 8 of ZQ-2 were aligned so as to face each other. The substrates were heated to cure the adhesive and the substrates 5 and 6 were bonded together. As a liquid crystal composition, EN-18 (manufactured by Chisso Corporation) was used for the liquid crystal layer 14 sandwiched between these substrates. In a region A where the base films 3 and 8 having a pencil hardness of 1H face each other and a region B where an electrode surface having a hardness of 2H or more directly faces each other, the tilt direction of the liquid crystal molecules 14a when the driving voltage is applied to the pixel electrodes 5 and 6 is Is different.

When the active matrix liquid crystal display element thus produced was sandwiched between a pair of polarizing plates and was driven and lit in a normally black mode, a wide viewing angle was obtained and a contrast ratio of 150: 1 was obtained. A uniform and good display was obtained over the entire screen.

[Comparative Example 1] In Example 1, when neither the TFT array substrate nor the counter substrate was provided with a ZQ-2 film having a pencil hardness of 1H, similarly, ODS was used as a vertical aligning agent, and after rubbing after forming a vertical aligning layer. By doing so, a liquid crystal display device was prepared and lighting was evaluated. As a result, the contrast ratio was as high as about 150: 1, but the viewing angle was narrow.

[Comparative Example 2] In Example 1, after forming the entire ZQ-2 film on both the TFT array substrate and the counter substrate, ODS was similarly used as the vertical aligning agent, and the vertical aligning layer was formed and rubbed to form a liquid crystal. When a display element was prepared and lighting was evaluated, the contrast ratio was as high as about 150: 1, but the viewing angle was narrow.

[Embodiment 2] FIG. 5 shows a schematic sectional view of a liquid crystal display device according to another embodiment of the present invention, and FIG. 6 shows a schematic sectional view of the entire device.

A TFT array substrate 5 in which a TFT (thin film transistor) element 1 using amorphous silicon and a pixel electrode 2 are arranged on the surface of one main surface is prepared by a thin film technique. A solution NHC (Nissan Chemical Co., Ltd.) in which a film containing SiO ₂ as a main component is first formed only on the half surface of the pixel electrode 2.
Was applied in a stripe shape by a printing method and baked in air at 350 ° C. for 30 minutes to form an insulating base film 20 having a pencil hardness of 8H. After that, a solution Z containing SiO ₂ and ZrO ₂ as the main components to form a film is formed on the region where NHC is not formed.
Q-2 (manufactured by Catalysts & Chemicals Industry Co., Ltd.) is applied by a printing method and baked in air at 180 ° C. for 30 minutes to give a pencil hardness of 1H.
The insulative base film 21 was formed in a thickness of about 500 Å so as to have the same height as the base film 20. After that, a monobasic chromium complex FC-805 (manufactured by Sumitomo 3M Limited) was applied to the entire surface by a dipping method, and then 150 in a nitrogen atmosphere.
A vertical alignment layer was formed by drying at 30 ° C. for 30 minutes. Then, rubbing treatment was performed to form the alignment film 4.

On the other hand, as the transparent electrode 7 on the counter substrate 6, I
A TO film is formed on the entire surface, and NHC liquid and ZQ-2 are formed on the TO film so as to face the base films 20 and 21 of the TFT array substrate 5.
After forming the underlying films 22 and 23 by sequentially printing the liquid, TF
Like the T array substrate 5, FC-805 was applied over the entire surface and dried in a nitrogen atmosphere at 150 ° C. for 30 minutes to form a vertical alignment layer, and then the surface was rubbed to form an alignment film 11. Then, as shown in FIG. 6, the alignment film 1 on the substrate 6 is formed.
An epoxy adhesive containing a glass fiber having a diameter of 5 μm as a peripheral sealing agent 9 was printed along the periphery of 1 except for an injection port (not shown). Next, resin balls having a particle size of 5 μm were dispersed as spacers 10 on the surface of the substrate 5. The TFT array substrate 5 and the counter substrate 6 are made to have a B region harder than 2H by making the underlying films 20 and 22 having a pencil hardness of 8H face each other, and the underlying films 21 and 23 having a pencil hardness of 1H are made to face each other and are softer than 2H. A liquid crystal cell was prepared by aligning it so that it would be the A region and adhering it at an interval of 5 μm.
A liquid crystal layer 14 was formed by using -18 (manufactured by Chisso Corporation) to inject through the inlet. The rubbing direction is indicated by arrows 12 and 13. This liquid crystal display element was sandwiched between a pair of polarizing plates 25 and 26 to form a liquid crystal display device.

When the device was driven and evaluated in a normally black mode, the contrast ratio was about 150: 1.
The display was wide, the viewing angle was wide, and there was no display defect, and a uniform and good display was obtained.

[Comparative Example 3] In Example 2, after the NHC having a hardness of 8H was formed on the entire surface of both the TFT array substrate and the counter substrate, FC-805 was similarly used as a vertical aligning agent and a film was rubbed to form a liquid crystal. When a display element was prepared and lighting was evaluated, the contrast was high at about 150: 1, but the viewing angle was narrow.

[0027]

According to the present invention, it is possible to provide a highly reliable large-screen liquid crystal display device having a wide viewing angle, a high contrast, a thin shape and a light weight by a simple cell manufacturing process. Further, the present invention is not limited to the materials, conditions and rubbing directions described in the embodiments, and similar effects can be obtained by placing other materials, other conditions and other rubbing directions. Further, the shape of the plurality of regions formed for each pixel electrode and the number of regions can be arbitrarily selected. Further, although the normally black mode active matrix driving method is used in the present embodiment, the same effect can be obtained by the normally white mode or simple matrix driving method.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing an outline of a liquid crystal display device of the present invention.

2 (a) and 2 (b) are views for explaining the operation of the present invention.

FIG. 3 is a schematic plan view of an embodiment of the liquid crystal display device of the present invention.

FIG. 4 is a schematic cross-sectional view of an embodiment of the liquid crystal display device of the present invention.

FIG. 5 is a schematic cross-sectional view of another embodiment of the liquid crystal display device of the present invention.

FIG. 6 is a schematic cross-sectional view of another embodiment of the liquid crystal display device of the present invention.

[Explanation of symbols]

 2 ... Pixel electrodes 3, 8 ... Insulating base film 4, 11 ... Alignment film 5 ... TFT array substrate 6 ... Counter substrate 7 ... Counter electrode 14 ... Liquid crystal layer 14a ... Liquid crystal molecules A, B ... Region

Continuation of the front page (72) Noriko Ogoshi Inventor, Toshiba Electronics Engineering Co., Ltd. 7-1, Nisshin-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa

Claims (3)

[Claims] 1. A first substrate having a plurality of pixel electrodes on one main surface and a second substrate having a counter electrode on one main surface are arranged so that the one main surface faces each other, and between these substrates. In a liquid crystal display device sandwiching a liquid crystal layer made of a liquid crystal composition having a negative dielectric anisotropy, means for partitioning and forming each pixel electrode into a plurality of area faces having different hardness, A vertical alignment film that is formed and is subjected to rubbing alignment treatment to tilt-align the liquid crystal molecules of the liquid crystal layer, and the tilt directions of the liquid crystal composition when applying an electric field are made different in the region surfaces having different hardnesses. Liquid crystal display device. 2. The liquid crystal display device according to claim 1, wherein one of the plurality of region surfaces is the pixel electrode surface itself. 3. The liquid crystal display device according to claim 1, wherein one of the plurality of region surfaces is formed of a soft underlayer having a pencil hardness of 2H or less.