JPH11174451A - Liquid crystal display - Google Patents

Abstract

(57) [Summary] [PROBLEMS] A liquid crystal display device having high contrast and high display quality by preventing the generation of a domain region due to a horizontal electric field of an adjacent picture element as a liquid crystal display panel becomes smaller and higher definition. I will provide a. A liquid crystal display device in which a liquid crystal layer made of a liquid crystal material having a negative dielectric anisotropy is enclosed is provided.
A vertical alignment film is formed on the electrodes formed on a single substrate, and an alignment process is performed so that each of the vertical alignment films deviates from the anti-parallel alignment direction.

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 using a liquid crystal having a negative dielectric anisotropy.

[0002]

2. Description of the Related Art Conventionally, a liquid crystal display device of an ECB mode (DAP) or a TN mode using a liquid crystal having a negative dielectric anisotropy has been known. A panel having a vertical alignment film formed by rubbing (rubbing the alignment direction in the opposite direction) was formed on the panel.
By sandwiching between two polarizing plates set in different directions, the liquid crystal molecules are oriented almost perpendicular to the substrate when no voltage is applied, thereby eliminating the birefringence generated by the liquid crystal and displaying black. In the case of the ECB mode, birefringence is generated by applying a voltage and tilting the liquid crystal molecules in a direction in which the liquid crystal molecules are rubbed in parallel to the substrate, thereby obtaining a high contrast as a white display. Has become. In the case of the TN mode, a high contrast can be obtained as a white display by applying a voltage and tilting the liquid crystal molecules while twisting the liquid crystal molecules in parallel with the substrate, thereby utilizing the optical rotatory power. It has become.

There are a DAP panel and a TN mode by the ECB mode using a liquid crystal having a negative dielectric anisotropy based on such a principle. Among them, in recent years, in particular, they are used for a projection apparatus or a direct-view type small display panel. In addition, the development of the above-described ECB mode display panel for obtaining a high-definition, high-contrast, high-quality display panel has been progressing.

[0004]

However, when driving a liquid crystal display panel in such a high-definition ECB mode, there is a problem that high-speed driving by field inversion is difficult in principle because of the small size and high definition. is there.
Therefore, in order to perform high-speed driving, it is necessary to perform 1h inversion driving. However, when performing 1h inversion driving, an electric field having an opposite phase is applied between adjacent picture elements. As a result, as shown in FIG. 10A, the horizontal electric field 19 that has not been generated at the time of the field inversion becomes, as shown in FIG.
This occurs during 1h inversion driving, and the way the liquid crystal molecules fall when the electric field is ON (in the case of normally black) is not uniform. (In the figure, reference numeral 18 indicates the direction of the electric field.)
There is a problem that domains appear as shown in (b) in the display, and the display quality is degraded due to a decrease in luminance during white display.

[0005] Further, in the liquid crystal display panel, the smaller the pixel size and the higher the definition, the narrower the pixel pitch becomes. As a result, the distance between the picture elements becomes smaller. The domain due to the influence is largely generated near the center of the picture element portion. As a result, in a small and high-definition liquid crystal display panel, the brightness is extremely reduced, and the contrast and the display quality are reduced, thereby greatly hindering the miniaturization and high definition of the liquid crystal display panel.

[0006] As a method for preventing the deterioration of the display quality in the ECB mode using a liquid crystal having a negative dielectric anisotropy, there are the following methods.
For example, as disclosed in Japanese Patent Application Laid-Open No. Hei 4-223433, the contrast is lowered by rubbing the liquid crystal molecules in an oblique direction (anti-parallel direction) with respect to each side of the rectangular pixel electrode. There are known ways to prevent this.

However, in the above-described method, the inclination direction of the liquid crystal molecules is made uniform in the portion where the flatness is deteriorated near the boundary between the picture element electrode and the picture element interval of the liquid crystal display panel (when no electric field is applied). Although this is an effective technique, it is difficult to suppress the influence of the domain due to the lateral electric field, and in the above-mentioned publication, adjacent pixels are reduced by reducing the pitch between picture elements in order to increase the definition of the liquid crystal display panel. It has been difficult to suppress the generation of domains due to the horizontal electric field of the picture element.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and has been developed to reduce the size of a liquid crystal display panel and increase the definition of a liquid crystal display panel. It is an object of the present invention to provide a liquid crystal display device with high contrast and high display quality by preventing such problems.

[0009]

In order to achieve the above object, a liquid crystal display device according to a first aspect of the present invention has at least two substrates on which electrodes are formed, which are arranged to face each other. In a liquid crystal display device in which a liquid crystal layer made of a liquid crystal material having a negative dielectric anisotropy is sealed between both substrates, a liquid crystal as the liquid crystal material is provided on electrodes formed on the two substrates. An alignment film for vertically aligning molecules with respect to the substrate is formed, and each alignment film formed on both substrates is subjected to an alignment process so as to deviate from the anti-parallel alignment direction. Thus, the above object is achieved.

At this time, each of the alignment films formed on the two substrates has been subjected to an alignment treatment so that each of the alignment films is shifted from the antiparallel alignment direction by a range of 5 ° to 20 °. Is preferred.

Further, in the liquid crystal display device according to a second aspect of the present invention, at least two substrates on which electrodes are formed are arranged to face each other, and a negative dielectric anisotropy is provided between the two substrates. In a liquid crystal display device in which a liquid crystal layer made of a liquid crystal material is sealed, electrodes formed on the two substrates are provided with:
An alignment film for vertically aligning the liquid crystal molecules as the liquid crystal material with respect to the substrate is formed, and each of the alignment films formed on the both substrates has an antiparallel alignment direction. , And a chiral agent is added to the liquid crystal material, thereby achieving the object described above.

Preferably, a chiral agent is added to the liquid crystal material so that the liquid crystal material is twisted between 5 ° and 20 ° between the two substrates.

Preferably, the orientation film at this time is made of a material containing at least one of polyimide, polyamic acid and silicon oxide.

According to the present invention as described above, in a liquid crystal display device using a liquid crystal having a negative dielectric anisotropy, a domain due to a horizontal electric field caused by a pixel interval that becomes narrower as the size and the definition are increased. Generation of regions can be suppressed, luminance and contrast can be improved, and display quality can be significantly improved.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 shows Embodiment 1 of the present invention.
FIG. 3 is a cross-sectional view illustrating a configuration of a liquid crystal display device in FIG. As shown in the figure, rectangular transparent electrodes 3 and 4 made of ITO or the like are formed on the inner surfaces of two substrates 1 and 2 made of glass or the like which are arranged to face each other. The electrodes 3 and 4 are formed in directions orthogonal to each other. The upper layer of the transparent electrodes 3 and 4 thus formed is provided with a rubbed vertical alignment film 5,
6 are formed.

These two substrates 1 and 2 are
And the gap between the two substrates 1 and 2 is maintained at a constant thickness by a spacer 7, and is made of a nematic liquid crystal having a negative dielectric anisotropy. It is formed with a liquid crystal layer 8 interposed.

The liquid crystal display device according to the first embodiment is completed by sandwiching the liquid crystal display device manufactured in this manner between two polarizing plates 9 and 10 having different polarization axes by 90 degrees.

Next, a method of manufacturing the liquid crystal display device according to the first embodiment will be described.

The liquid crystal display device according to the first embodiment includes:
As shown in FIG. 1, two substrates 1 and 2 are arranged to face each other. The thickness of the two substrates 1 and 2 is 1 mm.
Was formed on the substrates 1 and 2 with a thickness of 100 nm on the substrates 1 and 2 by sputtering.

On the transparent electrodes 3 and 4, JALS204 (polyimide-based alignment film: Nippon Gosei) is used as alignment films 5 and 6, which are alignment films in which liquid crystal molecules have vertical alignment with respect to substrates 1 and 2. Rubber Co., Ltd.) was formed by a printing method so as to have a film thickness of 100 nm, and was baked at about 180 ° C. Thereafter, by using a rubbing method, the direction of the orientation direction 12 applied to the substrate 1 and the direction of the orientation direction 13 applied to the substrate 2 as shown in FIG. Is the opposite direction) from 0 ° to 4 °
(0 °). In this case, the intersection angle between the arrows 12 and 13 corresponds to the shifted angle.

The two substrates 1, 2 thus produced
On top, spacers 7 were sprayed so that the substrate spacing was 6 μm. Then, the substrates 1 and 2 are wound leftward 0 ° to 40 ° and rightward wound 0 ° to 4 ° with respect to the rubbing direction of the substrate 1.
It was arranged so as to be 0 °, and was bonded with a seal resin 11 which is a thermosetting adhesive. Then, between the substrates 1 and 2, MLC-2012 (manufactured by Merck) 8 which is a liquid crystal having a negative dielectric anisotropy is injected and sealed by a vacuum injection method. A liquid crystal display device was created.

As shown in FIG. 2, polarizing plates 9 and 10 are arranged in crossed Nicols on the upper and lower surfaces of the liquid crystal display panel manufactured in this manner, and the phase is reversed every one line in pseudo 1h inversion driving. Maximum luminance characteristics of each panel when a rectangular wave (60 Hz) is applied (the maximum luminance in anti-parallel orientation is 10
6 is shown in FIG. 6, and the maximum contrast value of each panel (when the maximum contrast in anti-parallel alignment is 100) is shown in FIG. As shown in FIG. 6 and FIG.
It can be seen that when shifted by 20 °, both the brightness and the contrast are higher than in the anti-parallel alignment.

The orientation states of the anti-parallel alignment panel, the panel with a left-handed winding exceeding 20 ° and the panel with a right-handed winding exceeding 20 ° when an electric field was applied were observed with a microscope.
Although a domain region as shown in FIG. 5B was observed,
As shown in FIG. 5 (a), almost no domain region was observed in the panel bonded so as to have a left-handed winding of 5 ° to 20 ° and a right-handed winding of 5 ° to 20 °.

As described above, in the liquid crystal display device in which the vertical alignment film is formed, the upper and lower substrates are each subjected to the alignment treatment so as to be shifted from the anti-parallel alignment direction by 5 ° to 20 °, so that the horizontal electric field is generated. Thus, the liquid crystal display device according to the first embodiment configured as described above can improve the luminance and the contrast, and can greatly improve the display quality. Became possible.

(Embodiment 2) FIG. 3 shows Embodiment 1 of the present invention.
FIG. 3 is a cross-sectional view illustrating a configuration of a liquid crystal display device in FIG. As shown in the figure, rectangular transparent electrodes 3 and 4 made of ITO or the like are formed on the inner surfaces of two substrates 1 and 2 made of glass or the like which are arranged to face each other. The electrodes 3 and 4 are formed in directions orthogonal to each other. The upper layer of the transparent electrodes 3 and 4 thus formed is provided with a rubbed vertical alignment film 5,
6 are formed.

These two substrates 1 and 2 are
And the gap between the two substrates 1 and 2 is maintained at a constant thickness by a spacer 7, and is made of a nematic liquid crystal having a negative dielectric anisotropy. It is formed with a liquid crystal layer 8 interposed.

The liquid crystal display device according to the first embodiment is completed by sandwiching the liquid crystal display element manufactured as described above between two polarizing plates 9 and 10 whose polarization axes are different from each other by 90 degrees.

Next, a method of manufacturing the liquid crystal display device according to the first embodiment will be described.

The liquid crystal display device according to the first embodiment is
As shown in FIG. 3, two substrates 1 and 2 are arranged to face each other. The thickness of the two substrates 1 and 2 is 1 mm.
Was formed on the substrates 1 and 2 with a thickness of 100 nm on the substrates 1 and 2 by sputtering.

On the transparent electrodes 3 and 4, JALS204 (polyimide-based alignment film: Nippon Gosei) is an alignment film having liquid crystal molecules having vertical alignment with respect to the substrates 1 and 2 as alignment films 5 and 6. Rubber Co., Ltd.) was formed by a printing method so as to have a film thickness of 100 nm, and was baked at about 180 ° C. Thereafter, using a rubbing method, the direction of the alignment processing direction 14 applied to the substrate 1 and the direction of the alignment processing direction 15 applied to the substrate 2 as shown in FIG. Was subjected to an orientation treatment so as to be able to be bonded in the opposite direction))).

The two substrates 1, 2 thus produced
On top, spacers 7 were sprayed so that the substrate spacing was 6 μm. Then, the substrates 1 and 2 were arranged so as to be in an anti-parallel orientation, and bonded together with a seal resin 11 which is a thermosetting adhesive. Then, MLC-2012 (manufactured by Merck), which is a liquid crystal having a negative dielectric anisotropy.
In FIG. 8, a left-handed chiral additive S-811 (manufactured by Merck) and a right-handed chiral additive R-811 (manufactured by Merck) are added by an amount of twisting (twisting) of 0 ° to 40 ° between the upper and lower substrates of the panel. The materials thus obtained were blended, injected between the substrates 1 and 2 by a vacuum injection method, and sealed to form a liquid crystal display device according to the first embodiment.

As shown in FIG. 4, the polarizing plates 9 and 10 are arranged in a crossed Nicols on the upper and lower surfaces of the liquid crystal display panel manufactured in this manner, and the opposite phases are obtained for each line in the pseudo 1h inversion driving. Maximum luminance characteristics of each panel when a square wave (60 Hz) is applied (the maximum luminance without adding a chiral agent is 100
8), and FIG. 9 shows the maximum contrast value of each panel (when the maximum contrast when no chiral agent is added is 100). As shown in FIGS. 8 and 9, the anti-parallel orientation panel is placed at 5 ° between the upper and lower substrates.
It can be seen that when the chiral additive is added to the liquid crystal such that the liquid crystal is twisted by 20 °, both the brightness and the contrast are higher than in the anti-parallel alignment.

When the electric field was applied to the anti-parallel alignment panel (panel without chiral), the panel exceeding the left twist of 20 °, and the panel exceeding the right twist of 20 °, the alignment state was observed with a microscope. Although the domain region shown in Fig. 5 was observed,
In the panel in which the chiral additive was added to the liquid crystal so that the angle was 0 ° and the right twist was 5 ° to 20 °, almost no domain region was observed as shown in FIG.

As described above, in the liquid crystal display device in which the vertical alignment film is formed, the chiral additive is added to the liquid crystal so that the anti-parallel alignment panel is twisted by 5 ° to 20 ° between the upper and lower substrates. In addition, it is possible to suppress the generation of domains due to the horizontal electric field.
The contrast can be improved, and the display quality can be greatly improved.

One of the transparent electrodes formed on the substrate of the liquid crystal display element according to the first and second embodiments of the present invention may be a reflective electrode. In this way, the same tests as those of the first and second embodiments were performed, but almost the same results as those of the transmission type liquid crystal display element described above were obtained.

Further, the alignment film having vertical alignment formed on the substrate of the liquid crystal display element according to Embodiments 1 and 2 of the present invention is changed from a polyimide type (JALS204: manufactured by Nippon Synthetic Rubber Co., Ltd.) to a polyamic acid type (JALS204). (JALS955: manufactured by Japan Synthetic Rubber Co., Ltd.).
Further, it is also possible to form an alignment film by an oblique evaporation method using silicon oxide (SiO), and a test similar to the above-described first and second embodiments was performed using such a liquid crystal display element. As a result, almost the same results as those of the above-described liquid crystal display device could be obtained.

[0038]

As described above, according to the present invention,
In a liquid crystal display device using a liquid crystal having a negative dielectric anisotropy, it is possible to suppress the generation of a domain region due to a lateral electric field due to a pixel interval that becomes narrower as the size and the definition become higher, and the brightness and contrast become higher. , And the display quality can be greatly improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration of a liquid crystal display device according to Embodiment 1 of the present invention.

FIG. 2 is a perspective view illustrating a relationship between a polarization axis and a rubbing direction of the liquid crystal display device according to the first embodiment of the present invention.

FIG. 3 is a cross-sectional view illustrating a configuration of a liquid crystal display device according to a second embodiment of the present invention.

FIG. 4 is a perspective view showing a relationship between a polarization axis and a rubbing direction of a liquid crystal display device according to a second embodiment of the present invention.

FIG. 5A is a view of a liquid crystal display panel according to an embodiment of the present invention observed by a microscope on an alignment state when an electric field is applied, and FIG. 5B is a view of a conventional liquid crystal display panel. It is the drawing which observed the orientation state at the time of electric field application with a microscope.

FIG. 6 is a cross-Nicol arrangement of polarizing plates on the upper and lower surfaces of the liquid crystal display panel according to Embodiment 1 of the present invention;
It is the figure which showed the maximum luminance characteristic of each panel at the time of applying a rectangular wave of an opposite phase for every line in the pseudo 1h inversion drive.

FIG. 7 is a cross-Nicol arrangement of polarizing plates on the upper and lower surfaces of the liquid crystal display panel according to Embodiment 1 of the present invention;
It is the figure which showed the maximum contrast value of each panel at the time of applying a rectangular wave of an opposite phase for every line in the pseudo 1h inversion drive.

FIG. 8 is a cross-Nicol layout of polarizing plates on the upper and lower surfaces of a liquid crystal display panel according to Embodiment 2 of the present invention;
It is the figure which showed the maximum luminance characteristic of each panel at the time of applying a rectangular wave of an opposite phase for every line in the pseudo 1h inversion drive.

FIG. 9 is a cross-Nicol layout of polarizing plates on the upper and lower surfaces of a liquid crystal display panel according to Embodiment 2 of the present invention;
It is the figure which showed the maximum contrast value of each panel at the time of applying a rectangular wave of an opposite phase for every line in the pseudo 1h inversion drive.

FIG. 10A is a principle diagram of a lateral electric field generated in an adjacent picture element at the time of pseudo field inversion, and FIG. 10B is a lateral electric field generated at an adjacent picture element at the time of 1h inversion. FIG.

[Explanation of symbols]

 Reference Signs List 1 (upper) substrate 2 (lower) substrate 3 (upper) electrode 4 (lower) electrode 5 (upper) vertical alignment film 6 (lower) vertical alignment film 7 spacer 8 liquid crystal layer 9 (upper) polarizing plate 10 ( (Lower) polarizing plate 11 Seal resin 12 (Upper) rubbing direction 13 (Lower) rubbing direction 14 (Upper) rubbing direction 15 (Lower) rubbing direction 16 (Upper) polarization axis 17 (Lower) polarization axis 18 Electric field direction 19 Transverse electric field

Claims (5)

[Claims] 1. A liquid crystal display in which at least two substrates having electrodes formed thereon are opposed to each other, and a liquid crystal layer made of a liquid crystal material having a negative dielectric anisotropy is sealed between the two substrates. In the apparatus, on the electrodes formed on the two substrates, alignment films for vertically aligning the liquid crystal molecules as the liquid crystal material with respect to the substrates are respectively formed, and the alignment films are formed on both the substrates. A liquid crystal display device, wherein each of the alignment films is subjected to an alignment process so as to deviate from the anti-parallel alignment direction. 2. An alignment process is performed on each of the alignment films formed on the two substrates so that each of the alignment films is shifted from the anti-parallel alignment direction to a range of 5 ° or more and 20 ° or less. The liquid crystal display device according to claim 1, wherein: 3. A liquid crystal display in which at least two substrates on which electrodes are formed are arranged to face each other, and a liquid crystal layer made of a liquid crystal material having a negative dielectric anisotropy is sealed between the two substrates. In the apparatus, on the electrodes formed on the two substrates, alignment films for vertically aligning the liquid crystal molecules as the liquid crystal material with respect to the substrates are respectively formed, and the alignment films are formed on both the substrates. A liquid crystal display device, wherein each of the alignment films is subjected to an alignment treatment so as to have an antiparallel alignment direction, and a chiral agent is added to the liquid crystal material. 4. The liquid crystal material according to claim 2, wherein the liquid crystal material is
The liquid crystal display device according to claim 3, wherein a chiral agent is added so as to twist the substrate between 5 ° and 20 °. 5. The liquid crystal display device according to claim 1, wherein the alignment film is made of a material containing at least one of polyimide, polyamic acid, and silicon oxide.