JPH10142604A - Liquid crystal display element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To completely delete a disclination line in a liquid crystal element. SOLUTION: In each of four corners of a resist wall, a notch structure formed into a rectangle, a wedge shape, a rod shape, or a semi-elliptic shape is formed, for example. Then, in the four corners of the resist wall, distortion is reduced and generation of a disclination line can be prevented. In addition, a disclination line is formed in each side, while intermissions are formed in the four corners. Under this condition, a monomer in the system is cured by ultraviolet rays by means of impression of voltage, the disclination line is deformed so as to be shortened when voltage is impressed, and in concrete, the disclination line is extinguished. Under this condition, the orienting condition is fixed, so that a liquid crystal element in which no disclination line is generated can be provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a liquid crystal display device used for various display devices such as a word processor and a personal computer.

[0002]

2. Description of the Related Art Conventionally, a liquid crystal display device having a structure in which a liquid crystal layer is provided between a pair of substrates is known. When a TN mode liquid crystal layer is used, the viewing angle characteristics are as shown in FIGS. 2 (b-1) to 2 (b-3). That is, when the voltage is applied as shown in FIG. 2B-2 or FIG. 2B-3 with respect to the voltage non-applied state shown in FIG. A, as shown
The transmittance of light from both directions B is different, resulting in poor viewing angle characteristics.

In order to improve the viewing angle characteristics of a liquid crystal display device, it is necessary to improve the alignment state of the liquid crystal and to align the liquid crystal molecules in at least two directions in the pixel. FIG. 2A-1 shows the liquid crystal display element 1
In the figure, a polymer medium 7 is provided between a pair of substrates 1 and 2 so as to surround a liquid crystal region 8, and a display medium is provided. The liquid crystal region 8 is provided for each pixel, and has a disclination line 6 perpendicular to the substrates 1 and 2 substantially at the center. The orientation direction of the liquid crystal molecules is on both sides of the disclination line 6. Is different. That is, the liquid crystal molecules are oriented in two or more directions.

FIGS. 2 (a-1) to 2 (a-3) show viewing angle characteristics in that case, and FIG. 2 (a-1) shows a state where no voltage is applied, and FIGS. a-3) is a voltage applied state. In such an alignment state, the apparent light transmittance of the liquid crystal molecules when viewed from both directions A and B is averaged in the halftone state of FIG. 2A-2. Therefore, A, B
The transmittance of light from both directions is equal, and the viewing angle characteristics are as shown in FIG.
It is improved compared to the TN mode shown in (b-1) to (b-3).

[0005] The following are known as specific examples of the technique for aligning liquid crystal molecules in at least two directions in a pixel, that is, in a wide viewing angle mode.

As a liquid crystal display element having a polymer wall in the liquid crystal display element, not requiring a polarizing plate, and requiring no alignment treatment, the birefringence of the liquid crystal is used to change the transparent or opaque state electrically. A control method has been proposed.

This liquid crystal display element basically displays the transparent state when the ordinary light refractive index of the liquid crystal molecules and the refractive index of the polymer wall are made to match and the orientation of the liquid crystal molecules is aligned by applying a voltage. When no voltage is applied, the light scattering state due to the disorder of the alignment of the liquid crystal molecules is displayed.

[0008] As a proposed technique, a mixture of a light or thermosetting resin and a liquid crystal is injected between a pair of substrates, and then the resin is cured by applying light or heat to the liquid crystal. A method of forming a liquid crystal region in the form of droplets in a polymer wall made of a resin by precipitation is known (Japanese Patent Application Laid-Open No. Sho.
No. 1-502128).

Further, for such a liquid crystal display device,
2. Description of the Related Art Wide viewing angle mode liquid crystal display elements in which polarizing plates orthogonal to each other (crossed Nicols state) are combined are known (JP-A-4-338923 and JP-A-4-212928).
Since these liquid crystal display elements use depolarization due to the scattering phenomenon, their light transmittance is lower than that of a liquid crystal display element provided with two polarizing plates in parallel (parallel Nicol state). On the other hand, it does not exceed 50% in principle. Therefore, the display becomes dark.

As a method of improving the viewing angle characteristics of a liquid crystal display element using a non-scattering type polarizing plate, a mixture of liquid crystal and a photocurable resin is injected between a pair of substrates, and the mixture is irradiated with light to form a phase. A method for producing a display medium in which a liquid crystal region and a polymer wall are combined by separation has been disclosed (Japanese Patent Laid-Open No. 5-2 / 1993).
No. 7242).

In the case of this method, the orientation of the liquid crystal region (domain) is disturbed by the generated polymer wall to be in a random state, and the rising directions of the liquid crystal molecules in the individual domains when voltage is applied are different. Since the apparent transmittance as viewed from the direction becomes equal, that is, Δn · d is averaged, the viewing angle characteristics in the halftone state are improved.

A pixel division method is known (Japanese Patent Laid-Open No.
-210099). This method is a method of dividing one pixel into two or more, and inevitably generates a line (disclination line) in which the alignment state changes in the central portion of the pixel, thereby lowering the contrast.

As a technique for preventing the above-mentioned disclination line from being generated in a pixel, there has been proposed a method of obtaining a liquid crystal display element in which each pixel is oriented axially symmetrically and has excellent viewing angle characteristics (JP-A-7-120728). issue). As an example of a method of manufacturing this liquid crystal display element, a resist wall is arranged around a pixel as shown in FIG. 3A, and a liquid crystal phase and a uniform phase are formed by the resist wall as shown in FIG. 3B. (Isotropic phase)
A method has been proposed in which a liquid crystal phase is grown as shown in FIG. 3D by applying voltage to make the axis symmetric as shown in FIG. 3C.

[0014]

However, even in the case of the method shown in FIG. 3 described above, a disclination line is generated around the pixel, and the disclination line cannot be completely erased. It is observed as part roughness. Therefore, the results still required improvement.

SUMMARY OF THE INVENTION The present invention has been made to solve such problems of the prior art, and has as its object to provide a liquid crystal display element capable of completely eliminating the disclination line.

[0016]

A liquid crystal display device according to the present invention is a liquid crystal display device having a region in which each pixel is axially symmetric with respect to at least one axis. Surrounding the oriented region, a concave concave resist wall whose four corners protrude outside the pixel is provided,
Thereby, the above object is achieved.

In the liquid crystal display device of the present invention, it is preferable that the resist wall is formed so that its four corners are formed with a curve of 10 μmR or less.

The operation of the present invention will be described below.

In order to completely erase the disclination line, the structure of the resist wall was studied diligently.
As a result, the present invention has been achieved. The details will be described below.

When patterning a resist material using a photomask, it is known that the corners become round under exposure conditions, development conditions, and the like. In such a situation, when the photomask is oriented in an axisymmetric manner, even if the photomask is at a right angle, FIG.
As shown in (a), the resist wall is curved. Then
The orientation of the liquid crystal molecules is distorted from the entire circumference of the resist wall.
As shown in (b), when a voltage is applied, the disclination line remains in a circle without being cut at four corners.

On the other hand, when the four corners of the resist wall are almost perpendicular as shown in FIG.
At the center of the resist wall, the orientation changes greatly and the distortion increases, but at the four corners of the resist wall, the orientation direction of the liquid crystal molecules on the upper and lower substrates and the surface of the resist wall are in the same direction. As a result, as shown in FIG. 5B, distortion is reduced at the four corners of the resist wall, and the occurrence of disclination lines can be prevented. Further, a disclination line is formed on each side, and the four corners are interrupted.

In such a state, if the monomer present in the system is cured by ultraviolet light while applying a voltage, the disclination line is deformed and shortened when the voltage is applied, and specifically, disappears. Since the alignment state is fixed, a liquid crystal display element in which no disclination lines occur after irradiation with ultraviolet rays can be obtained.

Therefore, in order to obtain a liquid crystal display device in which no disclination lines are generated, in order to make the four corners of the resist wall close to a right angle, when forming the resist wall using a photomask, the resist to be formed is formed. The resist wall is formed such that the shape of the wall is concave so that the four corners protrude outside the pixel.

[0024]

Embodiments of the present invention will be described below.

According to the present invention, when a resist wall is formed using a photomask, the resist wall is formed as a photomask having four corners concavely protruding outside the pixels. Then, the four corners of the resist wall after formation are in a state close to a right angle or in a concave shape protruding outside the pixel, and as a result, as described in the operation section, a liquid crystal display element in which no disclination line is generated at all Can be obtained.

The shapes of the four corners of the resist wall, which are essential parts of the present invention, will be described in detail below.

The R at the corner of the resist wall after formation is preferably 10 μmR or less. The reason is that if it is larger than 10 μm, the distortion at the four corners does not disappear, the disclination line becomes a continuous body (circle) when a voltage is applied, and the disclination line cannot be erased.

The same result as above can be obtained even if there are concave portions at the four corners of the resist wall.

Examples of the concave portions provided at the four corners of the resist wall include a rectangle, a wedge, and the like as shown in FIGS.
Notch structures such as pile type and semi-elliptical shape are applicable. However, the cut structure shown in FIG. 1 is only an example, and other shapes may be used without any particular limitation.

The depth of the cut is preferably 3 μm or more and 10 μm or less, which can be easily formed by photolithography. If the thickness is smaller than 3 μm, the cut portion may be buried due to the accuracy of resist formation.
If the size is larger, the shape surrounding the pixel becomes complicated, and the newly formed corner may undesirably impair the axisymmetric alignment when the axisymmetric liquid crystal droplet grows.

The driving method for driving the liquid crystal display element of the present invention includes simple matrix driving, a-Si (amorphous silicon), TFT (thin film transistor), p-S
A driving method such as active driving using a switching element such as i (polysilicon) -TFT or MIM can be used, and there is no particular limitation. However, it is preferable to select from the above driving methods according to the characteristics of the present liquid crystal display element.

The materials of the substrate constituting the liquid crystal display device of the present invention are as follows. As the substrate material, a transparent solid glass, a polymer film, or the like can be used. As the plastic substrate, a material that does not absorb visible light is preferable, and PET, an acrylic polymer, styrene, polycarbonate, or the like can be used. Further, two types of these substrates may be combined to produce a liquid crystal display device using different types of substrates, or two types of substrates having the same thickness but different thicknesses may be used in combination. In the case of a plastic substrate, a liquid crystal display device in which a polarizing plate is integrated can be manufactured by giving the substrate itself a polarizing ability.

Hereinafter, embodiments of the present invention will be described more specifically. However, the present invention is not limited to this.

(Embodiment 1) The liquid crystal display device of Embodiment 1 was manufactured as follows.

As one of the two substrates for forming the liquid crystal display element, a color filter substrate having a thickness of 1.1 mm and having a transparent electrode made of ITO (a mixture of indium oxide and tin oxide) having a thickness of 1500 angstroms was used. In the color filter substrate, a portion corresponding to the seal portion and the pixel region is covered with a black matrix (BM).

As one substrate, a TFT substrate is used.
On this TFT substrate, beads having a diameter of 4 μm (Micropearl: manufactured by Sekisui Chemical Co., Ltd.) were sprayed, and the OMR-83 was placed thereon.
A resist (manufactured by Tokyo Ohkasha Co., Ltd.) was applied, and a resist wall having a rectangular cut structure at four corners shown in FIG. 4A was formed by photolithography. The resist wall had a pattern that also existed in an intermediate region between the display region and the sealing material.

Next, the sealing material was screen-printed with a sealing plate, and the color filter and the TFT substrate were bonded.

Next, the following mixture was injected into the prepared cell. The mixture was prepared by adding 0.20 g of R-684, 0.20 g of p-phenylstyrene, and 0.1 A of the following compound A.
0g and a liquid crystal material ZLI-4792 (Merck: $ n
= 0.094: so that the chiral pitch becomes 90 °,
It was adjusted in S-811. ) Is uniformly mixed with 4.5 g of a photopolymerization initiator (Irugacure 651) and 0.025 g of a photopolymerization initiator (Irugacure 651).

[0039]

Embedded image

Next, the temperature was once increased to make the phase uniform, and then the temperature was decreased so that one liquid crystal region existed for each pixel.

Next, a voltage was applied between the transparent electrodes of both substrates to bring about an axially symmetric alignment state. Subsequently, in this state, a voltage is applied to fix the alignment state, for example, after UV irradiation, 2 times.
Irradiation was carried out at a light intensity of 3 mW / cm ² under a high-pressure mercury lamp (wavelength: 365 nm) for 40 minutes while applying a voltage for 2 minutes after the start.

Observation of the liquid crystal display device produced as described above with a polarizing microscope reveals that a liquid crystal region is formed according to the pattern of the resist wall and is in an axially symmetric alignment state about the central axis. Was observed. Further, when a voltage was applied to the liquid crystal display element, no generation of disclination lines was observed. For example, in 400 pixels, there was no pixel in which a disclination line occurred.

Next, polarizing plates were stuck on both sides of the manufactured liquid crystal display device such that the polarizing axes were orthogonal to each other. At this time, it is preferable from the viewpoint of viewing angle characteristics that the polarizing axis of the polarizing plate be attached in the vertical and horizontal directions of the liquid crystal display element. In the liquid crystal display element thus manufactured, uniform display was obtained even when the viewing angle direction was changed in the display area.

As described above, by using the resist walls having the recesses at the four corners, a uniform axially symmetric alignment state in which no disclination line occurs can be achieved, and a uniform display region can be manufactured.

(Embodiments 2 and 3, Comparative Examples 1 and 2) In Embodiments 2 and 3, instead of the notch structure of Embodiment 1,
An axially symmetric orientation was prepared in the same manner as in Embodiment 1 using a cut structure in which R at the four corners had the values shown in the table below, and evaluation was performed at 400 pixels. Comparative Examples 1 and 2 also used the notch structure in which the Rs at the four corners were the values shown in the table below.
In the same manner as in the above, an axially symmetric orientation was prepared and evaluated at 400 pixels.

As a result, as shown in the following table, Embodiment 2
In No. 3, the disclination line completely disappeared, whereas in Comparative Examples 1 and 2, a circular disclination line was observed in a considerable number of pixels.

[0047]

[Table 1]

[0048]

As described above in detail, in the case of the present invention, by providing concave cut structures at the four corners of the resist wall, an axisymmetric liquid crystal display element in which no disclination lines are generated is formed. It becomes possible.

[Brief description of the drawings]

FIG. 1 is a plan view showing a typical example of a structure in which cuts (concave depressions) are formed at four corners of a resist wall, which is a main part of the present invention.

FIG. 2 is a diagram illustrating a principle of improving a viewing angle characteristic of a liquid crystal display element described in the related art.

FIG. 3 is a process diagram for explaining a concept in a case where a liquid crystal phase and an isotropic phase are separated by a resist wall to form an axially symmetric orientation in the related art.

FIG. 4 is a view for explaining a state of alignment of liquid crystal molecules and a state of occurrence of a disclination line when a corner (R) of a resist wall is a curve in the related art.

FIG. 5 is a diagram for explaining a state of alignment of liquid crystal molecules and a state of occurrence of a disclination line when a corner of a resist wall targeted by the present invention is a right angle.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, 2 Substrate 6 Disclination line 7 Polymer wall 8 Liquid crystal area 10 Liquid crystal display element

Claims (2)

[Claims] 1. A liquid crystal display device having a region in which each pixel is oriented axially symmetrically with respect to at least one axis, wherein four corners surround a region oriented axially symmetrically on a substrate. A liquid crystal display device having a concavely concave resist wall protruding outward. 2. The resist wall has four corners of 10 μm.
2. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is formed as a curve not more than R.