JPH10142638A - Liquid crystal display panel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize an uniformed orientation by providing a liquid crystal transferred from spray orientation to π-twist orientation or bend orientation, and a nuclear generating means for promoting the transfer from spray orientation to π-twist orientation or bend orientation. SOLUTION: A polyimide orienting film 15 is formed on surfaces of glass substrates 1, 20 with ITO 51, the substrates 1, 20 are rubbed in the same direction, and stuck together so that a liquid crystal is spray oriented through spacer beads 11. In the spacer dispersion for gap formation, silica beads 12 are mixed with the spacer beads 11 and dispersed as spherical grains which are nucleus generating means. When a voltage is applied between the substrates 1, 20, the distortion of spray orientation is increased to generate normal domain nucleuses having bend orientation or π-twist orientation are generated during the spray orientation, and the transfer to stable bend orientation or π-twist orientation is caused. The normal domain nucleuses having bend orientation or π-twist orientation are generated and grown in large quantities and extended to the whole area.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an OCB type liquid crystal display panel using nematic liquid crystal and having excellent viewing angle characteristics.

[0002]

2. Description of the Related Art A display panel (display element) using a nematic liquid crystal has several modes depending on the orientation of liquid crystal molecules. The most popular is the twisted nematic (T
N) mode, and homeotropic (vertical)
There are birefringence mode and guest-host mode of orientation or homogeneous (horizontal) orientation. Especially in TN mode,
It is the mainstream in an active matrix liquid crystal display panel in which an active element is provided for each pixel electrode on one substrate.

The TN liquid crystal is a state in which a liquid crystal having a positive dielectric anisotropy is sandwiched between substrates with electrodes subjected to horizontal alignment processing and twisted by 90 degrees to make a stable state. Is rotated by 90 degrees, and when the transmission axes of the polarizer and the analyzer arranged with the liquid crystal layer interposed therebetween are orthogonal to each other, white display is performed (normally white mode). When the liquid crystal molecules rise by application of a voltage, the incident polarized light travels through the liquid crystal layer as it is, so that it is absorbed by the analyzer and black display is performed.

[0004] The horizontal alignment process is usually achieved by rubbing polyimide, and at this time, a pretilt of the liquid crystal of about several degrees occurs corresponding to the rubbing direction. T
The twist direction of the N liquid crystal is basically determined by the pretilt directions of the upper and lower substrates. That is, the twisting direction is determined by aligning the liquid crystal layer without causing splay distortion. Furthermore, in order to prevent reverse twist orientation and to make the twist direction uniform, the twist direction is determined by adding a small amount of chiral substance (optically active substance) to the liquid crystal, matching the pretilt direction on the upper and lower substrates. I have. The liquid crystal is aligned with a substantially uniform pretilt from near the interface of one substrate to near the interface of the opposite substrate. When a voltage is applied between the upper and lower substrates,
First, the liquid crystal molecules at the center of the liquid crystal layer rise in the pretilt direction given initially, and the entire liquid crystal layer follows the rise.

Therefore, the direction in which the liquid crystal rises is the same in the entire panel, and the manner in which the refractive index of the liquid crystal layer changes according to the direction in which the panel is viewed. Therefore, the light transmittance greatly changes depending on the viewing angle direction. For this reason, a significant reduction in contrast, color change, gradation inversion, and the like occur depending on the viewing angle direction, and there is a serious problem in viewing angle characteristics. In particular, in the normally white mode, the viewing angle characteristics are greatly different between the case of observing from the rising direction of the liquid crystal molecules at the center of the liquid crystal layer (viewing angle direction) and the case of observing from the opposite direction (the opposite viewing angle direction). The gradation inversion phenomenon is severe on the side of the viewing angle from the front, and the contrast is significantly reduced on the side of the opposite viewing angle, and whitening occurs. Normally, the viewing angle direction is set in the vertical direction, so that in the TN mode, the viewing angle characteristics are asymmetric in the vertical direction.

Many methods have been proposed to improve the viewing angle characteristics of the TN mode. For example, "S
ID 94 DIGEST, 927 ", OCB (Optically Compensated) for obtaining a wide viewing angle by aligning a liquid crystal with a bend and combining it with an optical phase compensation film.
Birefringence) system. The OCB method has a feature that the response speed is much faster than the TN method, and is a very attractive method.

In the OCB method, it is necessary to initially align the liquid crystal in a splay state, and to apply an electric field to the liquid crystal during use to cause an alignment transition to a bend alignment (or π twist alignment). In other words, when the liquid crystal rises by applying a voltage, the distortion of the splay alignment increases,
A transition to a stable bend or π-twist orientation occurs. By observing this state, it can be seen that a nucleus of a desired normal domain having a bend or π twist orientation in the splay orientation is generated and grown.

[0008]

However, according to the experiments of the present inventors, it is not easy to cause the transition from the splay orientation to the bend orientation or the π twist orientation, and a considerably high voltage of 10 V or more is required. I need. It is generally difficult to apply such a high voltage because of the restriction of the driving voltage.

Further, the nucleation density of the bend-oriented or π-twist-oriented domains generated by the application of an electric field is extremely low, and it takes a considerable time for the domains to spread over the entire region. Further, it is very difficult to cause a transition in all the pixels, and some pixels are left without any transition. If there is a pixel that does not undergo the alignment transition and remains in the splay alignment, the pixel is recognized as a display defect, and the display quality as a display is greatly reduced.

In order to realize uniform alignment without alignment defects, the invention of new means is required. Therefore, an object of the present invention is to change the splay alignment to the bend alignment or π
An object of the present invention is to provide a liquid crystal display panel capable of efficiently performing transition to twist alignment and achieving uniform alignment without alignment defects.

[0011]

According to a first aspect of the present invention, there is provided a liquid crystal display panel comprising: a pair of substrates having electrodes; and a voltage interposed between the pair of substrates. The liquid crystal device includes a liquid crystal that transitions to a twist alignment or a bend alignment, and a nucleus generating unit that promotes the transition from the spray alignment to the π twist alignment or the bend alignment.

According to the liquid crystal display panel of the first aspect,
When a voltage is applied between the electrodes, the distortion of the splay alignment increases, a nucleus of a normal domain having a bend orientation or a π twist orientation is generated in the sprain orientation, and a transition to a stable bend orientation or a π twist orientation occurs. . At this time,
Many nuclei of normal domains having bend orientation or π twist orientation are generated and grown by the nucleus generating means, and the domains are spread over the entire region in a short time. As described above, the nucleus generating means increases the nucleus generation density of the alignment domain, efficiently performs the transition, and enables uniform alignment without any alignment defects. Therefore, a high-quality OCB liquid crystal display panel can be obtained.

According to a second aspect of the present invention, in the liquid crystal display panel according to the first aspect, the nucleation means orients the liquid crystal at a central portion between the pair of substrates substantially perpendicularly to the substrate surface. According to the liquid crystal display panel of the second aspect, in addition to the effect of the first aspect, the liquid crystal in the central portion between the substrates has a hybrid alignment, and the alignment state near the bend alignment or the π twist alignment generated by the application of the electric field is initially set. By applying an electric field between the substrates, the hybrid orientation portion is further stabilized, and serves as a nucleus for generation of a bend orientation or π twist orientation domain, and the orientation of this portion spreads around. . Therefore, the whole orientation transition is performed more efficiently.

According to a third aspect of the present invention, in the liquid crystal display panel according to the second aspect, the nucleus generating means is a particle having a thickness smaller than a gap between the pair of substrates and a surface of which has a property of vertically aligning the liquid crystal. It exists between a pair of substrates. According to the liquid crystal display panel of the third aspect, in addition to the effect of the second aspect, the liquid crystal display panel can be easily dispersed throughout the liquid crystal.
Uniform orientation is easily obtained.

According to a fourth aspect of the present invention, in the liquid crystal display panel according to the second aspect, the nucleation means has a spherical particle having a particle diameter smaller than a gap between the pair of substrates and a surface of which has a property of vertically aligning the liquid crystal. And exists between the pair of substrates. According to the liquid crystal display panel of the fourth aspect, in addition to the effect of the second aspect, the controllability of the particle diameter is excellent.

According to a fifth aspect of the present invention, in the liquid crystal display panel according to the second aspect, the nucleation means is a convex portion having a thickness smaller than a gap between the pair of substrates and a surface of which has a property of vertically aligning the liquid crystal. , Formed on a substrate.
According to the liquid crystal display panel of the fifth aspect, in addition to the effect of the second aspect, the size of the convex portion can be easily controlled.

According to a sixth aspect of the present invention, in the liquid crystal display panel according to the second aspect, a pretilt angle of the liquid crystal near the interface between the pair of substrates is at least 3 ° or more. According to the liquid crystal display panel of the sixth aspect, in addition to the effect of the second aspect, the growth rate of the domain of the bend alignment or the π twist alignment can be increased, and the electric field strength for maintaining the alignment can be reduced. . That is, the energy difference from the splay alignment can be increased to facilitate the growth of the bend alignment or π twist alignment domain.

According to a seventh aspect of the present invention, in the liquid crystal display panel according to the second aspect, the alignment treatment of the liquid crystal is performed by rubbing. According to the liquid crystal display panel of the seventh aspect, the same effect as that of the second aspect is obtained. An eighth aspect of the present invention is the liquid crystal display panel according to the second aspect, wherein the pair of substrates has an alignment film, and the alignment film is formed of a material containing polyimide or polyamic acid.

According to the liquid crystal display panel of the eighth aspect,
In addition to the effect of claim 2, the alignment stability is excellent. According to a ninth aspect of the present invention, in the liquid crystal display panel according to the second aspect, the electrodes are formed for each pixel, and an active element for forming an active matrix panel is provided for each pixel.

According to the liquid crystal display panel of the ninth aspect,
This has the same effect as the second aspect. A liquid crystal display panel according to a tenth aspect is the liquid crystal display panel according to the ninth aspect, wherein at least one or more nucleus generating units are provided for all the pixels.
According to the liquid crystal display panel of the tenth aspect, in addition to the effect of the ninth aspect, in all the pixels of the active matrix liquid crystal display panel, the transition from the splay alignment to the bend alignment or the π twist alignment is caused to occur, and the alignment is performed. Display defects due to defects can be eliminated.

According to the eleventh aspect of the present invention, in the liquid crystal display panel according to the ninth aspect, a vertical electric field directed between a pair of substrates that is equal to or higher than a threshold electric field at which a domain of the generated bend alignment or π twist alignment can grow is formed between pixels. It is provided with a generating means. According to the liquid crystal display panel of the eleventh aspect, in addition to the effect of the ninth aspect, the alignment transition of all the pixels can be performed even when the nucleus generating means does not exist in all the pixels.

According to a twelfth aspect of the present invention, there is provided a liquid crystal display panel according to the first aspect, further comprising means for applying a large electric field to the liquid crystal display panel, which is larger than a driving electric field applied in a normal display state. According to the liquid crystal display panel of the twelfth aspect, in addition to the effect of the first aspect, the alignment transition can be more reliably caused.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A liquid crystal display panel according to a first embodiment of the present invention will be described with reference to FIGS. FIG.
FIG. 1A is a schematic sectional view of a liquid crystal display panel according to a first embodiment of the present invention. This liquid crystal display panel was manufactured as follows. Glass substrates 1 and 2 with ITO 51
A polyimide alignment film 15 is formed on the surface of the substrate 0, and the substrates 1 and 20 are rubbed (parallel rubbed) in the same direction, and are bonded via spacer beads 11 having a diameter of 6 μm so that the liquid crystal is spray-aligned. Was. At the time of dispersing the spacers for forming the gap, the beads were mixed with spacer beads 11 having a diameter of 6 μm, and silica beads 12 having a diameter of 3 μm were dispersed as spherical particles as nucleation means. The dispersion density of the silica beads 12 was about 200 beads / mm ² . The surface of the silica beads 12 is treated with a silane coupling agent having a hydrophobic group so that the liquid crystal is vertically aligned on the surface.

FIG. 1 (b) is an enlarged view of FIG. 1 (a), schematically showing the alignment state of the liquid crystal molecules 13 near the silica beads 12. The refractive index anisotropy Δn = 0.134 and the dielectric anisotropy Δε = 9.5 without adding a chiral agent.
Of the liquid crystal 14 was annealed at a temperature higher than the isotropic phase transition temperature of the liquid crystal 14 for 1 hour, and then cooled to room temperature. In this state, the liquid crystal was in a splay alignment state.

In order to examine the pretilt angle of the liquid crystal 14, a pretilt evaluation cell having the same orientation treatment was prepared. From the measurement results, the pretilt angle obtained by the combination of the alignment film 15 and the liquid crystal 14 used here was about 5 °.
It turned out to be. When a voltage of 5 V was applied between the pixel electrode and the common electrode of this liquid crystal display panel, the initial splay alignment region was shifted to π twist alignment within several seconds.

Observation of the state of the alignment transition when a voltage is applied under a polarizing microscope shows that the surface of the liquid crystal has a 3 μm
An extremely large number of π-twisted nuclei were effectively generated and grown from the portion of the silica beads 12 having a diameter, which was observed. FIG. 2 schematically shows a liquid crystal alignment state of the liquid crystal display panel of the present invention when no voltage is applied. The orientation of the liquid crystal molecules 13 in the pair of upper and lower substrates 1 and 20 is substantially parallel to the substrates 1 and 20 as shown in FIG. 2A, and the pretilt near the substrate interface is provided so that the liquid crystal is spray-aligned. You. When an electric field is applied between the substrates 1 and 20 of the liquid crystal display panel in such an alignment state, FIG.
As shown in FIG. 2B, the liquid crystal rises, the splay distortion becomes extremely large, and the transition to the bend alignment or π twist alignment shown in FIG. 2C occurs. When the liquid crystal molecules 13 rise considerably, the bend alignment and the π twist alignment are optically very close to each other, and can be regarded as substantially equivalent. Therefore, it does not matter whether the transition is to the bend orientation or the π twist orientation. According to the experimental results of the present inventors, it is considered that the transition to the π twist orientation often occurs in practice.

According to the first embodiment, the electrodes 1 and
When a voltage is applied between the two, the distortion of the splay alignment increases, a nucleus of a normal domain having a bend orientation or a π twist orientation is generated in the sprain orientation, and a transition to a stable bend orientation or a π twist orientation occurs. . At this time,
Many nuclei of normal domains having a bend orientation or a π twist orientation are generated and grown by the silica beads 12 of the nucleus generating means, and the domains are spread over the entire region in a short time. As described above, the nucleation density of the orientation domain is increased by the silica beads 12 of the nucleation means, and the transition is performed efficiently,
Uniform alignment without alignment defects can be achieved as a whole. Therefore, a high-quality OCB liquid crystal display panel can be obtained.

Further, the nucleus generating means makes the pair of substrates 1 and 2
The liquid crystal in the central portion between 0 and 0 is oriented substantially perpendicular to the substrate surface, so that the liquid crystal in the central portion between the substrates 1 and 20 has a hybrid orientation, and is in an alignment state close to bend alignment or π twist alignment generated by application of an electric field. By applying an electric field between the substrates 1 and 20, the hybrid alignment portion is further stabilized and becomes a nucleus of generation of a bend alignment or a π twist alignment domain. Spread around. Therefore, the whole orientation transition is performed more efficiently.

Further, the silica beads 12 as nucleation means are particles having a particle diameter smaller than the gap between the pair of substrates 1 and 20 and having a surface whose liquid crystal molecules 13 of the liquid crystal 14 are vertically aligned. Since it exists between the pair of substrates, it is easy to be dispersed throughout the liquid crystal 14, uniform alignment is easily obtained, and since the particles are spherical, the controllability of the particle diameter is excellent.

A comparative example of the first embodiment will be described below.
That is, a voltage of 5 V was applied to a liquid crystal display cell formed in exactly the same manner as in the first embodiment except that the silica beads 12 having a diameter of 3 μm whose surface was vertically aligned were not dispersed. The transition from the spray TN orientation to the π twist orientation occurred, but the transition took several tens of seconds. In addition, when observing the state of orientation transition under voltage application under a polarizing microscope, it was found that nucleation of the transition occurred only from a small portion of the spacer beads, and the nucleation efficiency was extremely poor.

The voltage-transmittance characteristic of a liquid crystal display panel using bend alignment or π twist alignment is not good in steepness and is not suitable for time-division driving. However, an active matrix in which an active element is provided for each pixel is provided. It is preferable to use it as a panel. Further, in the first embodiment, spherical beads are used as particles having a thickness smaller than the gap between the pair of substrates 1 and 20 and the surface of which has the property of vertically aligning the liquid crystal 14. Non-spherical particles such as cubic and rectangular particles can also be used as long as the particles have a thickness equal to or less than the gap and do not cause a gap defect. However, spherical beads are particularly preferable because they are unlikely to cause gap defects and have excellent dispersibility.

The thickness (particle size) of the particles is
The gap may be equal to or smaller than the cell gap, that is, the cell gap. However, in order to enhance the effect of promoting the orientation transition, the gap is preferably set to about half of the cell gap. As the alignment film material used in the first embodiment of the present invention, polyimide or polyamic acid having excellent stability is particularly preferable, but the material of the alignment film 15 is not limited to these. The alignment treatment is generally performed by a rubbing treatment, but is not limited to the rubbing treatment method, and can be performed by an oblique evaporation method, polarized UV light irradiation, or the like.

A second embodiment of the present invention will be described with reference to FIG. FIG. 3 is a sectional view schematically showing a liquid crystal alignment state of a liquid crystal display panel according to a second embodiment of the present invention. The liquid crystal display panel was manufactured as follows. ITO5
A polyimide alignment film 15 is formed on the surfaces of the glass substrates 1 and 20 with 1, and the substrates 1 and 20 are rubbed (parallel rubbed) in the same direction to form spacer beads (not shown) having a diameter of 6 μm. , So that the liquid crystal molecules 13 were splay-aligned. In the second embodiment, the convex portion 41 having a vertically oriented surface is formed as follows. An acrylic film having a property of vertically aligning the liquid crystal molecules 13 is formed on the polyimide alignment film 15 to a thickness of about 3 μm.
It was formed in a square shape of 0 μm. On the surface of this portion, the liquid crystal molecules 13 are vertically aligned. Such regions were formed at a density of 9 pieces / mm ² .

A nematic liquid crystal having a refractive index anisotropy Δn = 0.134 and a dielectric anisotropy Δε = 9.5 to which no chiral agent is added is injected between the substrates 1 and 20 and the liquid crystal 14 isotropically. After annealing for 1 hour at a temperature equal to or higher than the phase transition temperature, it was cooled to room temperature. In this state, the liquid crystal 14 was in the splay alignment state. In order to check the pretilt of the liquid crystal 14, a pretilt evaluation cell having the same orientation treatment was prepared. From the measurement results, the alignment film 1 used here was used.
The pretilt angle obtained by the combination of 5 and liquid crystal is about 5 °
It turned out to be.

When a voltage of 5 V was applied between the pixel electrode and the common electrode of the liquid crystal display panel, the initial splay alignment region was shifted to π twist alignment within several seconds. When observing the state of the orientation transition at the time of applying a voltage under a polarizing microscope, a process in which nuclei are effectively generated and grown from the vertically oriented convex portions 41 was observed. The thickness of the protrusion 41 may be equal to or less than the gap between the substrates 1 and 20, but is preferably about half the cell gap in order to enhance the effect of promoting the orientation transition.

A third embodiment of the present invention will be described with reference to FIGS. 4 and 5 show a third embodiment of the present invention.
It is a top view and a sectional view of one pixel of a liquid crystal display panel of an embodiment. The actual panel is 64 cm long with a diagonal of 26 cm.
It is composed of 0 (× RGB trio) × 480 horizontal pixels. FIG. 5 is a sectional view of the dashed-dotted line portion 22 in FIG. On the lower substrate 1, a pixel electrode 2 of ITO and a thin film transistor 3 as an active element for driving the pixel electrode 2 are formed. On the upper substrate 20, a black matrix light shielding layer 4 made of chromium, a color filter 5, and a common electrode 7 of ITO are formed. The light shielding layer 4 covers all except the opening. On each of the electrodes 2 and 7, an alignment film 15 made of soluble polyimide was applied. The alignment treatment was performed by rubbing. As for the rubbing directions of the substrates 1 and 20, the rubbing direction of the lower substrate 1 is indicated by a dotted arrow A, and the rubbing direction of the upper substrate 20 is indicated by a solid arrow B.

The beads 31 having a diameter of 4 μm were dispersed by mixing with a spherical spacer having a diameter of 8 μm. The dispersion density of the 8 μm beads and the 4 μm beads is about 200 beads / m2, respectively.
m ² and about 400 pieces / mm ² . 4 μm beads 31
Is treated with a silane coupling agent having a hydrophobic group so that the liquid crystal is vertically aligned on the surface. With this dispersion density, the calculation was such that an average of 10 or more 4 μm beads existed for each pixel of each of RGB, and the existence of 4 μm beads could be confirmed in almost all pixels. 4 and 5, the spacer beads having a diameter of 8 μm are omitted.

A nematic liquid crystal having a refractive index anisotropy Δn = 0.134 and a dielectric anisotropy Δε = 9.5 to which no chiral agent is added is injected, and the temperature is higher than the isotropic phase transition temperature of the liquid crystal 14. And then cooled to room temperature. In this state, the liquid crystal was in a splay alignment state.
In order to check the pretilt of the liquid crystal 14, a pretilt evaluation cell having the same alignment treatment was prepared. From the measurement results, it was found that the pretilt angle obtained with the combination of the alignment film 15 and the liquid crystal 14 used here was about 5 °.

When a voltage of 5 V was applied between the pixel electrode 2 and the common electrode 7 of the liquid crystal display panel, the splay alignment region, which had originally existed, changed to the π twist alignment or the bend alignment. The distinction between the π twist orientation and the bend orientation could not be clarified. When observing the state of the orientation transition at the time of applying a voltage under a polarizing microscope, a process in which nuclei having a π twist orientation were effectively generated from the 4 μm beads 31 and grown were observed. When the alignment state was examined after applying a voltage of 5 V for 1 minute, almost no alignment defects were found, and π twist alignment or bend alignment was obtained in almost all pixels. When approximately 1000 pixels were randomly sampled and examined, 0.7% of the pixels had alignment defects in which splay alignment remained. In these pixels, it was presumed that the alignment transition did not occur because there was no 4 μm beads 31 whose surface was vertically oriented.

A comparative example 2 of the third embodiment will be described below. That is, a liquid crystal display panel was manufactured in the same manner as in the third embodiment except that 4 μm beads having a vertically oriented surface were not dispersed. The liquid crystal alignment state after annealing was splay alignment, as in the first embodiment. When a voltage of 5 V was applied between the pixel electrode 2 and the common electrode 7 of this liquid crystal display panel, and one minute later, the alignment state was examined. As a result, a large number of spray TN alignment regions remained. When about 1000 pixels were randomly sampled and examined, 54% of the pixels had alignment defects.

A fourth embodiment of the present invention will be described with reference to FIGS. 6 and 7 show a fourth embodiment of the present invention.
It is a top view and a sectional view of one pixel of a liquid crystal display panel of an embodiment. The actual panel is 64 cm long with a diagonal of 26 cm.
It is composed of 0 (× RGB trio) × 480 horizontal pixels. FIG. 7 is a sectional view of the dashed-dotted line portion 23 in FIG. On the lower substrate 1, a pixel electrode 2 of ITO and a thin film transistor 3 for driving the pixel electrode 2 are formed. Upper substrate 2
0, a black matrix light-shielding layer 4 made of chromium
And a color filter 5 and a common electrode 7 of ITO. The light shielding layer 4 covers all except the opening. On the alignment film 15 of the lower substrate 1, a projection 32 having a square planar shape with a vertical orientation of 3 μm and a side length of 10 μm is formed.

The alignment film 15 was formed of a soluble polyimide, and the alignment was performed by rubbing. As for the rubbing directions of the substrates 1 and 20, the rubbing direction of the lower substrate 1 is indicated by a dotted arrow A, and the rubbing direction of the upper substrate 20 is indicated by a solid arrow B. An empty cell having a cell thickness of about 7 microns was assembled by spraying a spherical spacer having a diameter of 7 microns. Then, the refractive index anisotropy Δn = without adding the chiral agent
A fluorine-based nematic liquid crystal having 0.134 and dielectric anisotropy Δε = 9.5 was injected, annealed at a temperature higher than the isotropic phase transition temperature of the liquid crystal 14 for 1 hour, and then cooled to room temperature. In this state, the liquid crystal 14 was in the splay alignment state.

In order to check the pretilt of the liquid crystal 14, a pretilt evaluation cell having the same orientation treatment was prepared. From the measurement results, it was found that the pretilt angle obtained by combining the alignment film and the liquid crystal used here was about 5 °. When a voltage of 5 V was applied between the pixel electrode 2 and the common electrode 7 of the liquid crystal display panel, the initially existing splay alignment region was changed to π twist alignment or bend alignment. The distinction between the π twist orientation and the bend orientation could not be clarified.

When observing the state of the orientation transition when a voltage is applied under a polarizing microscope, it can be seen that the π effectively disappears from the vertically oriented convex portions 32.
The process of generating and growing twist-oriented nuclei was observed. In addition, when the alignment state was examined after applying a voltage of 5 V for 1 minute, there was no alignment defect, and π
Twisted or bend orientation was obtained. In the fourth embodiment, the vertically oriented convex portions 32 are formed on the pixel electrodes 2 of the lower substrate 1, but may be formed on the common electrode 7 of the upper substrate 20 or on both substrates 1 and 20. Similar effects can be obtained.

A fifth embodiment of the present invention will be described with reference to FIGS. 8 and 9 show a fifth embodiment of the present invention.
It is a top view and a sectional view of one pixel of a liquid crystal display panel of an embodiment. The actual panel is 64 cm long with a diagonal of 26 cm.
It is composed of 0 (× RGB trio) × 480 horizontal pixels. FIG. 9 is a sectional view of the dashed-dotted line portion 24 in FIG. In the fifth embodiment, an ITO pixel electrode 2 is formed on a transparent dielectric film 16 formed on a wiring. The pixel electrode 2 is formed on the source wiring so as to overlap with the source wiring. Otherwise, the configuration is exactly the same as that of the third embodiment except that the surface has a vertical orientation of 4 mm.
μm beads 33 are dispersed.

By means having a configuration in which the pixel electrode 2 and the source line overlap each other, the horizontal electric field generated between the source line and the pixel electrode 2 is weakened, and the vertical electric field in the direction in which the liquid crystal molecules are made to rise is generated. Alternatively, it can be made larger than the threshold electric field at which a domain having a π twist orientation can grow. When a voltage of 5 V was applied between the pixel electrode 2 and the common electrode 7 of the liquid crystal display panel, the initially existing splay alignment region was changed to π twist alignment or bend alignment. The distinction between the π twist orientation and the bend orientation could not be clarified.

When observing the state of the orientation transition when a voltage was applied under a polarizing microscope, it was observed that nuclei having a π twist orientation were effectively generated from the 4 μm beads 33 and grown. When the alignment state was examined after applying a voltage of 5 V for 1 minute, no alignment defect was found, and π twist alignment or bend alignment was obtained in all the pixels. In the fifth embodiment, a bend alignment or a π twist alignment was obtained even in a pixel in which the 4 μm beads 33 having a vertically oriented surface did not exist. This is because in the fifth embodiment, the domain can grow to the next pixel beyond the wiring.

When a voltage of 20 V was initially applied to the liquid crystal display panel of the fifth embodiment for 1 second, alignment transition of all pixels could be confirmed. As described above, it has been demonstrated that when a driving voltage (approximately 5 V) applied to a liquid crystal in a normal display state, that is, a voltage (electric field) larger than an electric field, is applied, alignment transition can be reliably performed in a short time. . Note that the bend orientation or the π twist orientation returns to the splay orientation again at an electric field intensity below a certain threshold,
It is needless to say that it is preferable that a constant electric field for maintaining the orientation is always applied during the display.

The larger the pretilt angle, the higher the growth rate of the bend or π twist orientation domain, and the smaller the electric field strength for maintaining the orientation. As a result of the study, it was found that the pretilt angle of the liquid crystal was preferably 3 ° or more. In particular, it is preferable to set 3 ° or more in all the regions. Further, in the present invention, it is preferable that at least one or more nucleus generating means is provided for every pixel.

The liquid crystal material used in the present invention is:
The material is not limited to a fluorine-based material, and any material having a positive dielectric anisotropy, such as a cyano-based liquid crystal, can be used. However, for an active matrix type liquid crystal display panel, it is particularly preferable to use a liquid crystal composition containing a fluorine-based material having a high voltage holding ratio and excellent reliability as a main component.

[0051]

According to the liquid crystal display panel of the first aspect, when a voltage is applied between the electrodes, the distortion of the splay alignment increases, and the nucleus of the normal domain having a bend alignment or a π twist alignment in the sprain alignment. Occurs, and a transition to stable bend orientation or π twist orientation occurs. At this time, many nuclei of normal domains having bend orientation or π twist orientation are generated and grown by the nucleus generating means, and the domains are spread over the entire region in a short time. As described above, the nucleus generating means increases the nucleus generation density of the alignment domain, efficiently performs the transition, and enables uniform alignment without any alignment defects. Therefore, a high-quality OCB liquid crystal display panel can be obtained.

According to the liquid crystal display panel of the second aspect,
In addition to the effect of the first aspect, the liquid crystal in the central portion between the substrates has a hybrid orientation, and the liquid crystal has an alignment state close to bend alignment or π twist alignment generated by application of an electric field from an initial stage. By applying
The hybrid orientation portion is further stabilized, and serves as a nucleus for generation of a bend orientation or π twist orientation domain, and the orientation of this portion spreads around. Therefore, the whole orientation transition is performed more efficiently.

According to the liquid crystal display panel of the third aspect,
In addition to the effect of the second aspect, it is easy to disperse the entire liquid crystal and uniform alignment is easily obtained. According to the liquid crystal display panel of the fourth aspect, in addition to the effect of the second aspect, the controllability of the particle diameter is excellent. According to the liquid crystal display panel of the fifth aspect, in addition to the effect of the second aspect, the size of the convex portion can be easily controlled.

According to the liquid crystal display panel of the sixth aspect,
In addition to the effect of the second aspect, the growth rate of the domain of the bend orientation or the π twist orientation can be increased, and the electric field strength for maintaining the orientation can be decreased.
That is, the energy difference from the splay alignment can be increased to facilitate the growth of the bend alignment or π twist alignment domain.

According to the liquid crystal display panel of the seventh aspect,
This has the same effect as the second aspect. According to the liquid crystal display panel of the eighth aspect, in addition to the effect of the second aspect, the alignment stability is excellent. According to the liquid crystal display panel of the ninth aspect, the same effect as that of the second aspect is obtained. According to the liquid crystal display panel of the tenth aspect, in addition to the effect of the ninth aspect, in all the pixels of the active matrix liquid crystal display panel, the transition from the splay alignment to the bend alignment or the π twist alignment is caused to occur, and the alignment is performed. Display defects due to defects can be eliminated.

According to the liquid crystal display panel of the eleventh aspect, in addition to the effect of the ninth aspect, even if the nucleus generating means does not exist in all the pixels, the alignment transition of all the pixels can be performed. According to the liquid crystal display panel of the twelfth aspect, in addition to the effect of the first aspect, the alignment transition can be more reliably caused.

[Brief description of the drawings]

1A and 1B show a liquid crystal display panel according to a first embodiment of the present invention, wherein FIG. 1A is a schematic cross-sectional view thereof, and FIG. 1B is a cross-sectional view schematically showing a liquid crystal alignment state of the liquid crystal display panel. .

FIG. 2 is a schematic diagram showing a transition from a splay alignment to a bend alignment based on the first embodiment.

FIG. 3 is a cross-sectional view schematically illustrating a liquid crystal alignment state of a liquid crystal display panel according to a second embodiment.

FIG. 4 is a partially enlarged plan view of a liquid crystal display panel according to a third embodiment.

FIG. 5 is a cross-sectional view taken along an alternate long and short dash line 22 in FIG.

FIG. 6 is a partially enlarged plan view of a liquid crystal display panel according to a fourth embodiment.

FIG. 7 is a cross-sectional view taken along a dashed line 23 in FIG.

FIG. 8 is a partially enlarged plan view of a liquid crystal display panel according to a fifth embodiment.

FIG. 9 is a cross-sectional view taken along a dashed line 24 in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Lower substrate 2 Pixel electrode 3 Thin film transistor 5 Color filter 7 Common electrode 12 Beads with nucleus generating means whose surface is vertically aligned 13 Liquid crystal molecules 14 Liquid crystal 15 Alignment film 20 Upper substrate 31 Beads whose surface is vertically aligned 32 Surface is vertical Orientation convexity 33 Surface-beads with vertical orientation 41 Surface with vertical orientational protrusions

Claims (12)

[Claims] 1. A pair of substrates having electrodes, a liquid crystal interposed between the pair of substrates and transitioning from a splay alignment to a π twist alignment or a bend alignment by applying a voltage between the electrodes; A liquid crystal display panel having nucleation means for promoting a transition from orientation to π twist orientation or bend orientation. 2. The liquid crystal display panel according to claim 1, wherein the nucleus generating means aligns the liquid crystal at the center between the pair of substrates substantially perpendicularly to the substrate surface. 3. The nucleus generating means is a particle having a thickness smaller than a gap between a pair of substrates and a surface of which has a property of vertically aligning liquid crystal, and is present between the pair of substrates. Liquid crystal display panel as described. 4. The nucleus generating means is a spherical particle having a particle diameter smaller than a gap between a pair of substrates and a surface of which has a property of vertically aligning liquid crystal, and is present between the pair of substrates. The liquid crystal display panel according to claim 2. 5. The liquid crystal according to claim 2, wherein the nucleation means is a convex portion having a thickness smaller than a gap between the pair of substrates and a surface having a property of vertically aligning the liquid crystal, and formed on the substrate. Display panel. 6. The liquid crystal display panel according to claim 2, wherein a pretilt angle of the liquid crystal near an interface between the pair of substrates is at least 3 °. 7. The liquid crystal display panel according to claim 2, wherein the alignment treatment of the liquid crystal is performed by rubbing. 8. The liquid crystal display panel according to claim 2, wherein the pair of substrates has an alignment film, and the alignment film is formed of a material containing polyimide or polyamic acid. 9. The liquid crystal display panel according to claim 2, wherein the electrode is formed for each pixel, and an active element for forming an active matrix panel is provided for each pixel. 10. At least one pixel corresponding to all pixels
10. The liquid crystal display panel according to claim 9, further comprising nucleation means at more than three places. 11. A device according to claim 9, further comprising means for generating a vertical electric field between the pixels in a direction opposite to a pair of substrates, which is equal to or larger than a threshold electric field at which a domain of the generated bend orientation or π twist orientation can grow. Liquid crystal display panel. 12. The liquid crystal display panel according to claim 1, further comprising means for applying a large electric field to the electrodes, which is higher than a driving electric field applied to the liquid crystal in a normal display state.