JPH05303099A - Liquid crystal display panel and liquid crystal display device - Google Patents

Abstract

PURPOSE:To eliminate the nonuniform brightness unequalness within a screen by making the visual angle characteristics with the vertical direction of a liquid crystal display panel symmetrical. CONSTITUTION:Two sheets of substrates 1A, 1B subjected to orientation treatments of different pretilt angles are stuck to each other while a desired spacing is maintained therebetween in such a manner that the orientation treatment directions thereof are in the same direction and that the surfaces formed with oriented films 3A, 3B face each other. A nematic liquid crystal 7 is encapsulated into this spacing. As a result, the liquid crystal display panel to be subjected to light modulation by the double refraction effect of an electric field control is eventually provided with the nearly symmetrical visual angle characteristic with the vertical direction of the panel by the spray oriented constitution and, therefore, the generation of the nonuniform brightness unequalness within the screen is obviated and the image display having the high image quality is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display panel and a liquid crystal display device for displaying an image, and more particularly to a liquid crystal display panel and a liquid crystal display device having high display quality.

[0002]

2. Description of the Related Art In order to obtain an image with a particularly high display quality among liquid crystal display devices, active matrix drive type display devices using thin film transistors as switching elements have been actively developed in recent years. This is because a high contrast ratio can be obtained regardless of the number of scanning electrodes and a clear image can be obtained even in a large-capacity display with high resolution, as compared with a simple matrix driving method without a switching element.

A liquid crystal display mode widely used in such an active matrix type liquid crystal display device is a TN (Twisted Nematic) type NW (Normally Wh).
ite) mode. The TN method has 90 liquid crystal molecules between the substrates.
A liquid crystal display panel having a twisted structure is sandwiched between two polarizing plates. The polarization axes of the two polarizing plates are orthogonal to each other, and the one polarizing plate is bonded so that the polarization axis is parallel or perpendicular to the long axis direction of the liquid crystal molecules in contact with one substrate. The mode is the NW mode. In the TN mode NW mode, white display is performed at no voltage applied or at a low voltage near a certain threshold voltage, and black display is performed at a higher voltage.

The display image is obtained as described above because when a voltage is applied to the liquid crystal display panel, the liquid crystal molecules try to align in the direction of the electric field while unwinding the twisted structure, and the liquid crystal molecules pass through the liquid crystal display panel depending on the alignment state of the molecules. This is because the polarization characteristics of the incoming light change and the light transmittance is modulated. By the way, even in the state of the same molecular arrangement, the polarization characteristics of light change depending on the incident direction of the light incident on the liquid crystal display panel, so that the light transmittance differs depending on the incident direction. Therefore, the characteristics of the liquid crystal display panel have viewing angle dependence. This viewing angle dependency has the following features. First, in the NW mode, it is remarkable in the vicinity of black display in which liquid crystal molecules stand up with respect to the substrate by applying a voltage. The viewing angle dependency at that time has characteristics that include the long axis of the liquid crystal molecules near the center of the liquid crystal layer and that is substantially symmetrical with respect to a plane perpendicular to the substrate, and that the light beam having a traveling direction in this plane is directed to the substrate. Since the transmittance significantly changes depending on the incident angle, the viewing angle characteristics change greatly in this direction.

FIG. 10 shows the rubbing treatment direction in the conventional liquid crystal display panel. Generally, the rubbing treatment is performed on the front substrate 21 in the direction of arrow 23 and on the opposite substrate 22 in the direction of arrow 24 with respect to the screen. As a result, the major axis directions of the liquid crystal molecules near the center of the liquid crystal layer are aligned in a plane perpendicular to the substrates 21 and 22, so that the direction in which the viewing angle characteristics change greatly is the vertical direction 25 of the screen, and Is symmetric.

[0006]

However, the above-mentioned conventional TN type liquid crystal display panel in the NW mode has the following problems.

In the NW mode, when a voltage is applied and the liquid crystal molecules rise completely vertically to the substrate surface, the liquid crystal molecules become true black when viewed from the direction perpendicular to the substrate. This is a liquid crystal molecule
This is because when the major axis direction of the molecule is parallel to the traveling direction of light, no optical phase difference occurs and the light passes through the liquid crystal layer without changing the polarization component. However, in reality, even when a considerable voltage is applied, the liquid crystal molecules near the substrate interface have a strong interaction with the substrate and are hard to rise. Further, since the liquid crystal molecules in the central portion of the liquid crystal layer do not rise completely, the optical phase difference does not disappear with respect to the light traveling in the direction perpendicular to the substrate, and true black is not obtained.

On the other hand, in such a state of the molecular alignment, the light having a traveling direction substantially equal to the major axis direction of the liquid crystal molecules at the center of the liquid crystal layer has an optical phase difference more than the light traveling in the direction perpendicular to the substrate. Less. Therefore, it is possible to obtain a display with a good contrast ratio in which black sinks when the light is incident (hereinafter referred to as an incident angle in the viewing angle direction) at an angle of up or down with respect to the substrate by several degrees. However, black does not suddenly sink in light that is incident from an angle that is symmetrical with respect to the incident angle in the viewing angle direction and the substrate normal line (hereinafter referred to as an incident angle in the reverse viewing angle direction). Therefore, in the actual liquid crystal display panel, the viewing angle characteristic is remarkably asymmetrical with respect to the vertical direction of the screen centering on the substrate normal, as shown in the viewing angle characteristic diagram of the conventional liquid crystal display panel shown in FIG.

In the case of a direct-view large-screen liquid crystal display device using a liquid crystal display panel having such an asymmetry, uneven display with different brightness is produced above and below the liquid crystal display panel,
If the viewing angle of the liquid crystal display panel is changed in the vertical direction even a little, the display brightness of each part of the liquid crystal display panel changes abruptly, and the display becomes very difficult to see.

Further, when the liquid crystal display panel having such an asymmetry is used in a projection type image system requiring a high contrast ratio, the following problems occur.

First, in the case of the projection type, in order to make the image bright, it is desirable that the F number of the projection lens is made small and light is made incident on the lens at a wide angle. This means that light is taken into the liquid crystal display panel at a wide incident angle. Therefore, since light having an incident angle in the reverse viewing angle direction is also incident, the brightness of black display is raised and an image with a low contrast ratio is obtained. Further, it is necessary to collect the light from a light source by a condenser lens or the like in order to take the light into the liquid crystal display panel as much as possible.
Further, a metal halide lamp or the like is used as the light source, but it is difficult to form a parallel light flux because such an actual light source is not a point light source. Due to the limitations of these optical systems,
In an actual system, the incident angle of the light beam and the incident angle distribution (how wide angle the light is captured) are slightly different in each part in the screen of the liquid crystal display panel. As a result, when the viewing angle characteristics of the liquid crystal display panel are asymmetric, the viewing angle dependence of the liquid crystal display panel is different in all parts of the screen, and the transmittance of the liquid crystal display panel changes, causing uneven brightness unevenness in the screen. become.

The present invention is to solve the above-mentioned conventional problems. The liquid crystal display panel having a simple structure instead of the TN mode and utilizing the electric field control birefringence effect makes the viewing angle characteristics in the vertical direction symmetrical, and It is an object of the present invention to provide a liquid crystal display panel that can realize a display without uneven brightness unevenness.

Further, according to the present invention, the viewing angle characteristics with respect to the vertical direction of the liquid crystal display panel are made symmetrical without inclining the main axis of the light incident on the liquid crystal display panel from the substrate normal direction, and there is no uneven brightness in the screen. An object of the present invention is to provide a liquid crystal display device that can realize high-quality image display with a high contrast ratio.

[0014]

In order to achieve this object, the liquid crystal display panel of the present invention is configured so that two substrates subjected to alignment treatment with different pretilt angles have the same alignment treatment direction. It has a structure in which it is pasted and nematic liquid crystal is sealed in the gap.

Further, in the second liquid crystal display panel of the present invention, the two substrates that have been subjected to the alignment treatment with the same pretilt angle of 45 ° or more from the substrate surface have the same alignment treatment direction. It has a structure in which it is pasted and nematic liquid crystal is sealed in the gap.

[0016]

With this configuration, the light having both incident angles in the vertical direction is affected by the liquid crystal molecules oriented in the viewing angle direction and the liquid crystal molecules oriented in the reverse viewing angle direction in the process of passing through the liquid crystal layer. Become almost equal in the vertical direction,
Therefore, the viewing angle characteristics of the liquid crystal display panel with respect to the vertical direction can be made substantially symmetrical, and a good image display can be obtained without causing uneven brightness unevenness in the screen. Furthermore, by compensating the birefringence remaining in the liquid crystal display panel with the optical retardation plate, it is possible to obtain a high-quality image display with a high contrast ratio. ,

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A liquid crystal display panel and a liquid crystal display device according to a first embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing the arrangement of liquid crystal molecules in a liquid crystal display panel according to the first embodiment of the present invention.
Such a liquid crystal display panel is manufactured as follows. First, a polyimide alignment film 3 is formed on a glass substrate (hereinafter referred to as a row electrode substrate) 1A on which a transparent row electrode 2A is formed.
A (for example, JALS-199 manufactured by Japan Synthetic Rubber Co., Ltd.) is formed by offset printing. Next transparent column electrode 2B
Another substrate (hereinafter, referred to as a column electrode substrate) 1B on which is formed
A polyimide alignment film 3B (for example, JALS-194 manufactured by Japan Synthetic Rubber Co., Ltd.) is formed on the top by offset printing. The two substrates are heated at 190 ° C. for 1 hour to evaporate the solvent and cure the alignment film on the substrates.

Next, using a rayon cloth, the row electrode substrate 1
A, 8A and 8B on the alignment films 3A and 3B on the column electrode substrate 1B
The rubbing process is performed in such a direction. This row electrode substrate 1
A and the column electrode substrate 1B are bonded so as to face each other so that the electrode sides face each other. Liquid crystal material ZLI-4792 manufactured by Merck & Co. was injected into such a panel to obtain a liquid crystal display panel. Note that reference numerals 4 and 5 indicate the pretilt angle, and reference numeral 6 indicates the inclination of the liquid crystal molecules 7 in the middle portion of the liquid crystal layer.

In order to know the pretilt angle caused by rubbing in the case of using the above alignment film material and liquid crystal material, measurement by the crystal rotation method was performed. For the measurement, two transparent substrates coated with the same alignment film and subjected to a rubbing treatment were attached to each other with a cell thickness of 20 μm so as to have a homogeneous alignment, and a measurement cell into which a liquid crystal material was injected was used. As a result of the measurement, it was found that the panel using JALS-199 had a pretilt angle 4 of about 3 °, and the panel using JALS-194 had a pretilt angle 5 of about 4 °.
It was found that the orientation of the liquid crystal display panel in this example had a configuration as shown in FIG.

The first polarizing plate whose polarization axis is set so as to form an angle of 45 ° with the rubbing direction is provided on one surface on the outside of the liquid crystal display panel produced as described above, and the other surface is provided on the other surface. The second polarizing plate was provided so that the polarizing axis was orthogonal to the polarizing axis of the first polarizing plate. A voltage was applied to the liquid crystal display panel configured as described above, and the viewing angle dependence of the vertical transmittance of the panel was measured. As a result, the characteristics shown in FIG. 2 were obtained, and with respect to the substrate normal line of the liquid crystal display panel. Although there is a tendency for black to sink in the direction of the lower viewing angle, we were able to obtain almost symmetrical characteristics in the vertical direction.

As a comparative example, as shown in FIG. 3, the row electrode substrate 1A and the column electrode substrate 1B have the same alignment film (for example, JA).
LS-194 alignment film) 3B is formed by printing, and then processed by rubbing so that both substrates have the same pretilt angle 5, and both substrates take the rubbing direction like 8A, 8B on the electrode side. Were opposed to each other and bonded, and liquid crystal was injected. When a sticking voltage was applied to both sides of this liquid crystal display panel in the same direction as that of the liquid crystal display panel in the first embodiment, two kinds of alignment regions appeared irregularly, and one alignment region had an upper surface. The liquid crystal display panel has a non-uniform viewing angle and a downward viewing angle in the other alignment region, making it difficult to see.

The reason why such a phenomenon appears is as follows. A liquid crystal display panel as a comparative example has both substrates 1A,
Since the pretilt angles 5 of the liquid crystal molecules 7 of 1B are equal, as shown in FIG. 3, the liquid crystal molecules 7 at the center of the liquid crystal layer have no inclination,
The major axis is arranged parallel to the substrate surface. In this case, when a voltage is applied between the substrates, the liquid crystal molecules 7 in the central part of the liquid crystal layer form an angle 10 with respect to the substrate normal in the vertical direction of the screen as shown in FIG.
The energy at the time of elastic deformation is the same regardless of whether A (+ θm) or 10B (-θm) is tilted and rises. Therefore, the viewing angle characteristics of the liquid crystal display panel in this case are such that black rises slightly above the direction perpendicular to the substrate when it rises at an angle of 10A, and black appears slightly below when it rises at an angle of 10B. It has a characteristic of sinking. Therefore, in such an orientation, it is possible to
Two orientations will occur irregularly.

On the other hand, in the liquid crystal display panel of the first embodiment, as shown in FIG. 1, since the pretilt angles 4 and 5 of the liquid crystal molecules 7 at the interfaces of the respective substrates are different, the liquid crystal molecules 7 at the center of the liquid crystal layer are formed. Does not always deform in a certain direction and two orientation regions do not appear, and a uniform orientation can be maintained.

Next, a second embodiment of the present invention will be described with reference to the drawings. FIG. 5 is a sectional view showing the arrangement of liquid crystal molecules in the liquid crystal display panel according to the second embodiment of the present invention. Such a liquid crystal display panel is manufactured as follows. First, an alignment film (for example, JALS-199 alignment film) 3C is formed on a glass substrate 1A on which a transparent electrode 2A is formed.
Are formed by offset printing. Next, an active matrix array substrate 1 in which pixel electrodes are arranged in a matrix and thin film transistor elements are connected to each pixel electrode.
The same alignment film as that on the glass substrate 1A (JALS-199)
Alignment film) 3C is formed by offset printing. Both substrates are heated at 190 ° C. for 1 hour to cure the alignment film.
A vertical aligning agent (for example, ODS-E manufactured by Chisso Co.) was added to the surface of the both substrates, on which the alignment films were formed, with 0.8% ethanol.
Spin-coat the diluted solution to 2500 rpm and
Heat-dry at 30 ° C. for 30 minutes.

Next, rayon cloth is used for the glass substrate 1A and the active matrix array substrate 1B in the directions 8A and 8B.
Then, the rubbing treatment was performed with the same strength so that the pretilts of both substrates became equal. The two substrates are laminated so that the electrodes are opposed to each other, and the liquid crystal material ZLI manufactured by Merck is used.
-4792 was injected.

The pretilt angle 11 caused by the above-mentioned alignment treatment and rubbing in the case of using the liquid crystal material was found to be 50 ° by measurement by the crystal rotation method using a homogeneous cell.

The first polarizing plate whose polarization axis is set so as to form an angle of 45 ° with the rubbing direction is provided on one surface on the outside of the liquid crystal display panel prepared as described above, and the other surface is provided on the other surface. A second polarizing plate was provided so that the polarization axis was orthogonal to the polarization axis of the first polarizing plate, and a liquid crystal display panel was obtained. When a voltage was applied to this liquid crystal display panel and the viewing angle dependency on the transmittance in the vertical direction of the liquid crystal display panel was measured, it showed the characteristics shown in FIG. 6 and was completely symmetrical with respect to the substrate normal line of the liquid crystal display panel. It was possible to obtain various characteristics. Also the first
Compared with the example, the transmittance for light in the normal direction to the substrate was low and the contrast ratio was about 100, which was relatively high.

In the present embodiment, the reason why the alignment failure did not occur unlike the liquid crystal display panel described in the comparative example shown in FIG. 3 was that the pretilt angles 11 of both substrates were the same, for the following reason.

In this embodiment, the pretilt angle of the substrate interface is 11
Therefore, as shown in FIG. 5, the alignment energy of the liquid crystal molecules 7 in the central portion of the liquid crystal layer is more stable when the liquid crystal molecules 7 rise vertically from the surface of the substrate than before the voltage is applied. Such a molecular arrangement has a pretilt angle of 11 at the substrate interface.
It has been found from a preliminary study using liquid crystal display panels with different pretilt angles that the occurrence of the angle is higher than about 45 °. As described above, when the liquid crystal molecules 7 in the central portion of the liquid crystal layer have already risen vertically, the molecular deformation when a voltage is applied can occur only in the case shown in FIG. 7, and therefore uniform alignment is obtained. ..

Next, a liquid crystal display panel according to the third embodiment of the present invention will be described. As the panel, the same panel as in the first embodiment shown in FIG. 1 is used. When a voltage of 6 V was applied to the liquid crystal display panel shown in FIG. 1 and the contrast ratio to light in the normal direction to the substrate at that time was measured, it was about 50. This is because at a voltage of 6 V, the liquid crystal molecules near the substrate interface of the liquid crystal display panel do not rise much, and therefore, the polarization is changed due to the influence of the birefringence of the liquid crystal in the vicinity, and black does not sink completely. At this time,
The optical phase difference remaining on the liquid crystal display panel was measured by an ellipsometer to be about 24 nm.

In this embodiment, in order to improve the contrast ratio, an optical retardation plate for canceling the optical retardation remaining in the liquid crystal display panel is installed. As the optical retardation plate, one having a substrate material of polyvinyl alcohol and having a retardation of about 25 nm by uniaxial stretching was used. As shown in FIG. 8, the rubbing direction 15 of the liquid crystal display panel 14 and the slow axis 17 of the optical retardation plate 16 were stacked so as to be orthogonal to each other. On one outer surface of the liquid crystal display panel, the polarization axis 1 is formed so as to form an angle of 45 ° with the rubbing direction.
The first polarizing plate 12 with 3A set was provided, and the second polarizing plate 18 was provided on the other surface so that the polarization axis 13B was orthogonal to the polarization axis 13A of the first polarizing plate.

A voltage was applied to the liquid crystal display panel 14 to measure the viewing angle dependence of the transmittance in the vertical direction of the panel. As a result, it was possible to obtain characteristics that were substantially symmetric with respect to the substrate normal line of the liquid crystal display panel. It was Further, the contrast ratio was as high as about 300 as compared with the first embodiment shown in FIG.

Next, a fourth embodiment of the present invention will be described with reference to FIG.
Will be described with reference to. As the panel, the same panel as in the second embodiment shown in FIG. 5 is used. The contrast ratio of the liquid crystal display panel 19 at an applied voltage of 6 V is
As described in the second embodiment, it is about 100. The contrast ratio is higher than that of the liquid crystal display panel of the first embodiment because the liquid crystal molecules near the substrate interface have a higher pretilt, so that the liquid crystal display panel of the second embodiment is more likely to stand up, and thus the remaining optical phase difference. Is relatively small. When this optical phase difference was measured by an ellipsometer, it was about 17n.
It was m.

In this embodiment, in order to further improve the contrast ratio, the optical retardation plate 20 for canceling the optical retardation remaining in the liquid crystal display panel is installed. As the optical retardation plate 20, a material having a retardation of about 17 nm by uniaxial stretching using polyvinyl alcohol as a substrate material was used.
Then, the polarizing plates 12 and 1 are arranged so as to have a configuration as shown in FIG.
8. The liquid crystal display panel 19 and the optical retardation plate 20 were bonded together.

When a voltage was applied to this liquid crystal display panel and the viewing angle dependency on the transmittance in the vertical direction of the panel was measured, it was possible to obtain characteristics which were completely symmetrical with respect to the substrate normal line of the liquid crystal display panel. .. In addition, the contrast ratio was 400, which was extremely high as compared with the second embodiment. Furthermore, when this liquid crystal display panel was incorporated into a projector and an image was projected on the screen, a high contrast and uniform and excellent display could be obtained.

[0036]

As described above, according to the present invention, the liquid crystal molecules in the thickness direction of the liquid crystal layer are arranged substantially symmetrical with respect to the vertical direction of the liquid crystal display panel, and the viewing angle characteristics of the liquid crystal display panel in the vertical direction are improved. Since they can be made almost symmetrical, it is possible to obtain a high-quality image display in which uneven brightness unevenness does not occur in the screen.

[Brief description of drawings]

FIG. 1 is a structural cross-sectional view showing the alignment of liquid crystal molecules of a liquid crystal display panel according to a first embodiment of the present invention.

FIG. 2 is a diagram showing the viewing angle dependence of the transmittance in the vertical direction of the liquid crystal display panel.

FIG. 3 is a structural cross-sectional view showing the alignment of liquid crystal molecules of a liquid crystal display panel manufactured as a comparative example.

FIG. 4 is a structural cross-sectional view showing the alignment of liquid crystal molecules when a voltage is applied to the liquid crystal display panel.

FIG. 5 is a structural cross-sectional view showing the orientation of liquid crystal molecules of a liquid crystal display panel according to a second embodiment of the present invention.

FIG. 6 is a diagram showing viewing angle dependence of transmittance in the vertical direction of the liquid crystal display panel.

FIG. 7 is a structural cross-sectional view showing the alignment of liquid crystal molecules when a voltage is applied to the liquid crystal display panel.

FIG. 8 is a configuration diagram of a liquid crystal display panel in a third embodiment of the present invention.

FIG. 9 is a configuration diagram of a liquid crystal display panel in a fourth embodiment of the present invention.

FIG. 10 is a diagram showing a rubbing processing direction in a conventional liquid crystal display panel.

FIG. 11 is a view angle characteristic diagram of a conventional liquid crystal display panel.

[Explanation of symbols]

 1A glass substrate (substrate) 1B glass substrate (substrate) 3A alignment film 3B alignment film 4 pretilt angle 5 pretilt angle 7 liquid crystal molecules

Claims (6)

[Claims] 1. Two substrates, which have been subjected to orientation treatments with different pretilt angles, are laminated with the orientation treatment directions being the same direction and the orientation faces facing each other while maintaining a desired gap, A liquid crystal display panel in which nematic liquid crystal is sealed in the gap. 2. Two substrates, which have been subjected to an alignment treatment with the same pretilt angle of 45 ° or more from the substrate surface, have the same alignment treatment direction and the oriented faces face each other. A liquid crystal display panel in which a nematic liquid crystal is sealed in the gap and bonded together. 3. A liquid crystal display according to claim 1, wherein the pixel electrodes are formed in a matrix on one of the substrates, and one or more thin film transistor elements are connected to each of the pixel electrodes. panel. 4. The liquid crystal display panel according to claim 1, a voltage applying means for controlling the optical anisotropy of the liquid crystal display panel, and an optical phase plate for canceling the optical anisotropy at a predetermined voltage. Liquid crystal display device equipped. 5. The liquid crystal display panel according to claim 2, a voltage applying means for controlling the optical anisotropy of the liquid crystal display panel, and an optical phase plate for canceling the optical anisotropy at a predetermined voltage. Liquid crystal display device equipped. 6. The pixel electrodes are formed in a matrix on one substrate of the liquid crystal display panel, and one or more thin film transistor elements are connected to each of the pixel electrodes. The liquid crystal display device according to claim 4.