JPH09152609A - Liquid crystal display device - Google Patents

Abstract

(57) Abstract: To improve the response speed of a display device having a wide viewing angle characteristic and to increase the temporal stability of an axisymmetric arrangement for each picture element. A liquid crystal display element having a liquid crystal cell (15) in which liquid crystal molecules are axially symmetrically arranged in each picture element (32) along an axis perpendicular to the surfaces of the substrates (20, 21). The thickness d of the liquid crystal layer sandwiched between is 0.5
A liquid crystal display device having a size of from μm to 4.0 μm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device that improves the viewing angle characteristics that are currently a problem in TN mode liquid crystal display devices. Liquid crystal display devices are used in portable display devices such as personal computers and word processors because of their low power consumption characteristics. Increasing the number of lines and screen size of these devices are being enthusiastically studied. In this case, the selection time per line or pixel is shortened, and an element capable of operating at high speed is required as a liquid crystal element. INDUSTRIAL APPLICABILITY The present invention can be used in the fields of high-definition and large-sized LCDs by utilizing the characteristics of high speed and wide viewing angle.

[0002]

2. Description of the Related Art A conventional wide viewing angle technique will be described below.
In order to improve the alignment state of the liquid crystal and the viewing angle characteristics of the liquid crystal display element, it is necessary to align the liquid crystal molecules in at least two directions within the picture element.

Referring to FIGS. 6A to 6F, a liquid crystal cell in which liquid crystal molecules are aligned in at least two directions and a TN
Compare with the liquid crystal cell of the mode. 6 (a) to 6 (c)
In the liquid crystal cell in which the liquid crystal layer 8 is covered with the polymer wall 7 and is oriented in two or more directions as shown in FIG.
6 (b) when a voltage is applied to the liquid crystal layer in accordance with FIG.
In the intermediate state shown in, the liquid crystal molecules 9 rise in different directions in one picture element. This orientation averages the apparent light transmittance of the liquid crystal molecules when viewed from both the A and B directions. As a result, the transmittances of light from both A and B directions become equal, and the viewing angle characteristics are shown in FIG.
It is improved as compared with the TN mode of (e).

The following is a specific example of the wide viewing angle mode.

As a liquid crystal cell having a polymer wall which does not require a polarizing plate and does not require an alignment treatment, the birefringence of the liquid crystal is utilized to electrically control the transparent or cloudy state. A method has been proposed. This method basically matches the ordinary refractive index of the liquid crystal molecules with the refractive index of the support medium, and when a voltage is applied to align the liquid crystals,
The transparent state is displayed, and the light scattering state due to the disorder of the alignment of the liquid crystal molecules is displayed when no voltage is applied.

As a proposed method, a method of mixing liquid crystal and a light or thermosetting resin and then curing the resin to deposit the liquid crystal to form liquid crystal droplets in the resin is known. It is disclosed in JP-A-61-502128. Further, a wide viewing angle mode display element in which a liquid crystal display element and polarizing plates which are orthogonal to each other are combined is disclosed in Japanese Patent Application Laid-Open No. Hei 4 (1999) -1999.
No. 338923 and Japanese Patent Laid-Open No. 4-212928.

As a method for improving the viewing angle characteristics of a liquid crystal cell using a non-scattering type polarizing plate, Japanese Patent Laid-Open No. 27242/1993 discloses a liquid crystal and a polymer material by phase separation from a mixture of liquid crystal and a photocurable resin. A method of making the composite material is disclosed. In this method, the produced polymer material disturbs the alignment state of the liquid crystal domain, resulting in a random state.
As a result, the rising directions of the liquid crystal molecules are different in each domain when a voltage is applied, the values of Δn × d are averaged, and the apparent transmittance seen from each direction becomes equal. Therefore, this method improves the viewing angle characteristics in the halftone state.

Recently, the present inventors have made the liquid crystal molecules in an axially symmetrical orientation state (such as a spiral shape) in the pixel region by performing light control using a photomask or the like during photopolymerization. By controlling the liquid crystal molecules with a voltage, the spiral alignment of the liquid crystal molecules operates so as to change to a homeotropic state, and a liquid crystal display element with significantly improved viewing angle characteristics is disclosed in Japanese Patent Laid-Open No. 7-120728. Disclosure.

Further, the inventors of the present invention have disclosed a liquid crystal display element in a wide viewing angle display mode, which is a crystalline polymer and which utilizes an axially symmetric alignment control force having a spherulite structure on the substrate surface. It is disclosed in Japanese Patent No. 308496.

Further, Japanese Patent Laid-Open No. 6-194655 discloses a method in which an alignment film is applied on a substrate and alignment treatment such as rubbing is not performed, and liquid crystal molecules are aligned in random directions.

A method in which picture elements are divided into a plurality of regions and liquid crystal molecules are arranged so that their respective alignment states mutually compensate for the viewing angle characteristics of the respective regions is disclosed in JP-A-57-186.
No. 735 is disclosed.

[0012]

The liquid crystal display element for wide viewing angle display described above is based on the TN mode, is manufactured with a liquid crystal cell thickness of 4.5 to 6 μm, and has a response speed of about 40 ms. (Τ _d + τ _r ). Therefore,
There is a problem in response speed for high definition LCDs.

In the method for forming the axially symmetric alignment from the liquid crystal and the photocurable resin as described above, in the state before the curing reaction of the photocurable resin for stabilizing the axially symmetric alignment,
The time-dependent change of the axisymmetric orientation (change from the axisymmetric orientation to another orientation state with time) occurs. Therefore, when industrially producing an axially symmetric orientation, it is not possible to set a time between the axially symmetric orientation operation and the orientation stabilization treatment by the curing reaction, which imposes restrictions on the manufacturing apparatus.

Further, in the method of forming the axially symmetric orientation by the orientation treatment on the substrate, even in the storage state at room temperature,
The axisymmetric orientation changes to another orientation state. That is, the stability of axial symmetry is poor.

In view of the above problems, the present inventors have diligently studied the liquid crystal cell structure, the response speed, and the stability of the axisymmetric alignment. It is an object of the present invention to provide a wide viewing angle mode liquid crystal display device having a fast response and a stable axially symmetric orientation.

[0016]

A liquid crystal display element of the present invention is a liquid crystal display element including a liquid crystal cell having a pair of translucent substrates and a liquid crystal layer sandwiched between the pair of translucent substrates. The pair of translucent substrates have translucent electrodes on the side facing the liquid crystal layer, and the liquid crystal cell has a plurality of pictures arranged in a matrix in the plane direction of the translucent substrate. The liquid crystal cell has an aligning means, and the aligning means arranges liquid crystal molecules of the liquid crystal layer in each of the plurality of picture elements in the transparent substrate. The liquid crystal layer has an axially symmetric orientation centered on an axis perpendicular to the surface of the liquid crystal and has a thickness of 0.5 μm or more and 4.0 or more.
The liquid crystal display device is in the range of μm or less, and the above object is achieved thereby. .

In one embodiment, Δn × d (Δn is a birefringence index of liquid crystal molecules, d of the liquid crystal layer in the plurality of picture elements.
Is the thickness of the liquid crystal layer) is 300 nm or more and 650 nm
It is as follows.

In another embodiment, a twist angle of liquid crystal molecules in the liquid crystal layers in the plurality of picture elements from one of the pair of transparent substrates to the other is 45 ° or more and 150 °.
It is in the following range.

In still another embodiment, the liquid crystal material of the liquid crystal layer contains at least a Cl-based liquid crystal compound. In yet another embodiment, the alignment means is an alignment wall formed between the plurality of picture elements.

In still another embodiment, a polymer wall is further formed between the plurality of picture elements.

In still another embodiment, the alignment means is an alignment film formed on the pair of translucent electrodes and having axially symmetrical fine grooves.

In still another embodiment, the alignment wall has a vertical alignment property.

The operation will be described below.

The liquid crystal display element according to the present invention is a liquid crystal display element having wide viewing angle characteristics in which liquid crystal molecules are arranged in the picture element in axial symmetry with respect to an axis perpendicular to the substrate surface. Since it is thin, the response speed is fast, and the arrangement of the axisymmetric liquid crystal molecules is stable against changes over time.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be shown below, but the present invention is not limited thereto.

(Embodiments 1 to 4 and Comparative Examples 1 to 1)
3) As shown in FIG. 1, ITO layer (mixture of indium oxide and tin oxide, thickness 150 nm (1500
Two 1.1 mm-thick glass substrates 20 and 21 each having a transparent common electrode 18 and a transparent pixel electrode 22 made of Å)) are used. The pixel electrodes 22 are arranged in a matrix on the substrate 21. The translucent electrodes 18 and 22 are electrically connected to a drive circuit outside the substrate, and a known drive circuit can be used as the drive circuit. A TFT that electrically connects the translucent electrode and a drive circuit outside the substrate is provided on one translucent substrate. TFT
(Not shown) OMR-83 (made by Tokyo Ohka Co., Ltd.) on the substrate 21
An alignment wall 24 having the structure shown in FIGS. 1A and 1B was produced using a resist. At this time, the alignment wall 24
If the height is higher than 2/3 of the distance between the substrates (thickness of the liquid crystal layer), the gap between the upper and lower substrates is filled, and it becomes difficult to inject the mixture of the liquid crystal and the photocurable resin. Therefore, the height of the alignment wall 24 was set to be ⅔ or less of the thickness of the liquid crystal layer of each example. The orientation wall 24 is formed between the portions 32 corresponding to the picture elements on the substrate. The alignment wall 24 preferably has a property of vertically aligning liquid crystal molecules on the surface of the wall (vertical alignment property). By using the produced two substrates and keeping the distance between the glass substrates 20 and 21 by a spacer (not shown) of X μm,
A cell 15 having different substrate-to-substrate distances was constructed.

[0027]

[Table 1]

The liquid crystal material used is ZLI-4792 (manufactured by Merck: Δn = 0.094) or E8 (manufactured by Merck: Δn = 0.247). Furthermore, the chiral agent S-811 (was added to the liquid crystal material so that the twist angle of the liquid crystal molecules was 90 ° (d / p (ratio of the thickness d of the liquid crystal layer to the pitch) was 0.25) in each cell. (Manufactured by Merck) was added for adjustment. If the twist angle of the liquid crystal molecules between the substrates is about 45 ° or less, or about 150 ° or more, the light transmittance is significantly reduced. Therefore, the twist angle range is about 45 ° or more and about 150 ° or less. It may be less than °. The maximum value of the transmittance is obtained when the twist angle is about 90 °.

Next, R-684 (manufactured by Nippon Kayaku Co., Ltd.) 0.2
0 g, p-phenylstyrene 0.20 g, compound A 0.10 g represented by the following chemical formula 1,

[0030]

Embedded image

4.5 g of liquid crystal material, and photoinitiator Irg
After 0.025 g of a mixture of uagure 651 (manufactured by Ciba-Geigy Co., Ltd.) was uniformly mixed, corresponding materials were capillary-injected into the cell 15 as shown in Table 1. After that, the temperature was once raised to obtain a uniform phase, and the temperature was lowered so that the liquid crystal region became one with respect to the picture element 32. And then,
A voltage was applied between the translucent electrodes to establish an axially symmetric orientation state.
The axisymmetric orientation ratio (probability of axisymmetric orientation in all picture elements) in this state was observed with a polarizing microscope. The results are shown in Table 2 (in Table 2, ◯ indicates an axially symmetrical orientation rate of 95% or more, Δ indicates 80 to 95%, and x indicates 0 to 80%).
In Comparative Example 1, the distance between the substrates 20 and 21 was too short to inject the mixture of the liquid crystal and the photocurable resin, and the liquid crystal display element could not be manufactured.

[0032]

[Table 2]

From Table 2, the stability of the photocurable resin for fixing the axially symmetrical alignment before the curing reaction varies depending on the thickness of the cell 15, and the thickness of the liquid crystal layer is about 4 μm or less. It was found that the axially symmetric orientation was stabilized. If the distance between the glass substrates 20 and 21 is small, it becomes difficult to inject the mixture of the liquid crystal material and the photo-curable resin. Therefore, in order to obtain the desired stability of the axisymmetric alignment, the thickness of the liquid crystal layer should be adjusted. It may be set to about 0.5 μm or more and about 4 μm or less.

The liquid crystal cell 15 was irradiated for 30 minutes at a position of 3 mW / cm ² (365 nm) under a high pressure mercury lamp in order to fix the axially symmetrical alignment state. After that, the resin was cured by continuously irradiating ultraviolet rays for 20 minutes.

Observation of the produced cell with a polarization microscope revealed that in the liquid crystal cells of Embodiments 1 to 4 and Comparative Example 2,
As shown in FIG. 2, a polymer wall 25 was further formed on the alignment wall 24. Further, the liquid crystal region 32 is formed by being framed by the resist pattern on which the alignment wall 24 is formed, and the alignment of the liquid crystal molecules is located at the center of each pixel and is perpendicular to the central axis perpendicular to the substrate surface. It was observed that they were in a symmetrical orientation. According to this observation, each picture element region has a pair of extinction regions 23 facing each other with the central axis interposed therebetween.

Polarizing plates (not shown) were attached to both substrates of the prepared cell so that the polarization axes thereof were orthogonal to each other to complete the cell. From the viewpoint of viewing angle characteristics, the polarization axis of the polarizing plate is preferably parallel to the vertical and horizontal directions (x and y directions) of the cell as shown in FIG.

Next, the response speed of the prepared cell was measured. Table 3 shows the results. In Table 3, τ _d
And τ _r are the response speeds of the liquid crystal layer when a voltage is applied and when the applied voltage is erased, respectively.

[0038]

[Table 3]

From Table 3, it was found that the response speed of liquid crystal molecules was increased by reducing the thickness of the liquid crystal layer.
The liquid crystal cell 15 of the fourth embodiment having a liquid crystal layer thickness of about 4 μm has a response time of about 38 μs, and is suitable for application to a high-definition display device. From these results, it can be seen that by setting the thickness of the liquid crystal layer in the range of about 0.5 μm or more and about 4 μm or less, a liquid crystal cell that realizes a high response speed can be manufactured.

The viewing angle characteristics of the liquid crystal display element of Embodiment 4 are shown in FIG. The coordinates, Ψ and θ in FIG. 3 (a) were determined as shown in FIG. 3 (b). FIG.
The closed curve shown in (a) is an isocontrast line indicating CR = 10, and the inside of the isocontrast line shown is:
Higher contrast than outside. As is clear from FIG. 3A, excellent display characteristics were obtained in which the reduction in contrast was small over a wide range. The liquid crystal display elements of the other embodiments also had substantially the same viewing angle characteristics.

As can be understood through these embodiments and comparative examples, the liquid crystal display element (wide viewing angle display mode) in which the axially symmetric alignment is performed has a liquid crystal layer thickness of about 0.5 μm or more and about 4 μm.
By setting it within the range of m or less, the axially symmetric orientation can be stably produced, and the time constraint can be reduced between the axially symmetric orientation operation and the orientation stabilization treatment by the curing reaction. In addition, by setting the thickness of the liquid crystal layer within the range of about 0.5 μm or more and about 4 μm or less, the response speed can be increased, and a liquid crystal cell suitable for application to a high-definition display device can be manufactured. . Further, when the material of the alignment wall 24 has the vertical alignment property, the axially symmetric alignment can be more stably maintained until the axially symmetric alignment of the liquid crystal molecules is fixed.

(Embodiments 5 and 6 and Comparative Example 4) As shown in FIG. 4, an ITO layer (a mixture of indium oxide and tin oxide, 150 nm (1500 Å)) is formed on a transparent common electrode 18 and a transparent layer. Two 1.1 mm thick translucent glass substrates 20 and 21 each having a pixel electrode 22 are used. The pixel electrodes 22 are arranged in a matrix on the substrate 21. This transparent electrode 18
And 22 are electrically connected to a drive circuit outside the substrate. A known drive circuit can be used as the drive circuit. A TFT (not shown) that electrically connects the translucent pixel electrode 22 and a drive circuit outside the substrate is provided on the translucent substrate 21. Then, the light-transmissive electrodes 18 and 22 on each light-transmissive substrate are coated with photosensitive polyimides 36 and 38 by spin coating. Then, by photolithography, a polyimide alignment film 40 having concentric narrow grooves 42 as shown in FIG. 5A was prepared for each picture element. Further, this narrow groove may be a radial narrow groove 43 as shown in FIG. A cell (15 ′) having a different inter-substrate distance was produced by inserting a Y μm spacer (not shown) between the translucent substrates thus produced and keeping the distance between the glass substrates 20 and 21. In this cell, a liquid crystal material ZLI-4792 (manufactured by Merck & Co .: chiral agent S-811 so that the twist angle between the substrates was 90 °) was obtained.
Adjusted). When the twist angle of the liquid crystal molecules between the substrates is about 45 ° or less, or about 150 °
In the above cases, the light transmittance is significantly reduced, so the twist angle range may be about 45 ° or more and about 150 ° or less. In addition, the maximum value of the transmittance is about 90 for the twist angle.
Obtained when the angle is set to °. The cell was once heated above the isotropic temperature of the liquid crystal material and then gradually cooled. The liquid crystal molecules in the liquid crystal cell are formed on the transparent substrate by the narrow groove 42.
Was oriented in the direction of, and was in an axially symmetric orientation state. Further, a polarizing plate (not shown) was attached in the same manner as in Embodiments 1 to 4 to manufacture a liquid crystal display element. Table 4 shows the spacer diameter, Δn × d, display characteristics, and changes with time of high temperature storage of the fabricated cells.

[0043]

[Table 4]

As described above, by setting the thickness of the liquid crystal layer to about 4 μm or less, it was possible to manufacture a liquid crystal display device which operates at high speed and has excellent stability as in the first to fourth embodiments. . If the distance between the glass substrates 20 and 21 is small, it becomes difficult to inject the mixture of the liquid crystal material and the photo-curable resin. Therefore, the thickness of the liquid crystal layer is about 0.5 μm or more and about 4 μm.
You can set it as follows.

In the first to sixth embodiments described above, in order to obtain a bright display in all directions, Δn × d (Δ
It is desirable that the range of the value of n is the birefringence of the liquid crystal molecules and the value of d is the thickness of the liquid crystal layer is set in the range of about 300 nm to about 650 nm.

Further, the liquid crystal material is preferably a liquid crystal compound containing Cl (chlorine). The Cl-based liquid crystal material has a larger Δn (birefringence) than other liquid crystal materials, and even if the thickness of the liquid crystal layer is reduced, the desired retardation (value of Δn × d)
Is obtained. As such a liquid crystal material, for example, TL202 (Δn = 0.1851) can be used.

The liquid crystal cells shown in the first to sixth embodiments are simple matrix drive, a-Si TFT, p-Si.
It can be driven by a driving method such as active driving using active elements such as TFT and MIM, and is not particularly limited in the present invention. The driving method can be selected according to the characteristics of the liquid crystal display element used in the present system.

Further, as the substrate material, transparent solid glass, polymer film or the like can be used.

As the plastic substrate, a material which does not absorb visible light is preferable, and PET, acrylic polymer, styrene, polycarbonate, etc. can be used. Further, two kinds of these substrates may be combined to form a cell on a different kind of substrate, and two kinds of substrates having different thicknesses may be used in combination regardless of the same kind and different kind.

Further, in the case of a plastic substrate, a liquid crystal display device in which a polarizing plate is integrated can be manufactured by making the substrate itself have a polarizing ability.

[0051]

In the liquid crystal display element of the present invention, the liquid crystal molecules are oriented in axial symmetry, which allows wide viewing angle display, and further by reducing the thickness of the liquid crystal layer,
It has the effects of increasing the response speed and improving the stability of the axisymmetric orientation.

Further, by forming an alignment wall having a vertical alignment property between the picture elements of the liquid crystal cell, the axially symmetric arrangement of the liquid crystal molecules is stable even before the polymer wall made of the curable polymer is cured. And held.

Further, the value of Δn × d is set to 300 nm or more and 65
By setting the thickness to 0 nm or less, a display device having high contrast in all directions can be obtained.

Furthermore, by using a compound containing Cl (chlorine) as the liquid crystal material, Δn of the liquid crystal layer becomes large, and even if the liquid crystal layer is made thin, a liquid crystal display device having high contrast in all directions can be obtained.

[Brief description of the drawings]

FIG. 1A is a cross-sectional view of a cell manufactured in any of Embodiments 1 to 4. (B) is a plan view of the alignment wall in the cell of (a).

2A and 2B are diagrams showing an alignment state of the display element shown in Embodiment Mode 1 observed with a polarization microscope.

FIG. 3A is an iso-contrast diagram showing the viewing angle characteristics of the display device shown in the fourth embodiment. (B)
It is a schematic diagram showing the coordinate in (a).

FIG. 4 is a cross-sectional view of the cells manufactured in the fifth and sixth embodiments.

5 (a) and (b) show Embodiments 5 and 6; FIG.
It is a figure which shows the fine groove pattern for every picture element on the board | substrate produced by.

FIG. 6 is a principle diagram of improving the viewing angle characteristics. (A)-(c) is sectional drawing of the conventional wide viewing angle display device. (D)-(f)
FIG. 4 is a cross-sectional view of a conventional TN mode display device.

[Explanation of symbols]

 18 translucent common electrode 20, 21 translucent substrate 22 translucent pixel electrode 24 alignment wall 25 polymer wall 32 pixel region 40 alignment film 42 concentric circular grooves 43 radial thin grooves

Claims (8)

[Claims] 1. A liquid crystal display device comprising a liquid crystal cell having a pair of translucent substrates and a liquid crystal layer sandwiched between the pair of translucent substrates, wherein the pair of translucent substrates are A transparent electrode is provided on the side facing the liquid crystal layer, and the liquid crystal cell has a plurality of picture elements arranged in a matrix in the plane direction of the transparent substrate. Orienting means is provided, and the orienting means comprises
Within each picture element of the plurality of picture elements, the liquid crystal molecules of the liquid crystal layer are oriented in axial symmetry about an axis perpendicular to the surface of the transparent substrate, and the thickness of the liquid crystal layer is 0. A liquid crystal display device in the range of 5 μm or more and 4.0 μm or less. 2. Δn × of the liquid crystal layer in the plurality of picture elements
d (Δn is the birefringence of liquid crystal molecules, d is the thickness of the liquid crystal layer)
The value of is 300 nm or more and 650 nm or less.
3. The liquid crystal display device according to item 1. 3. The twist angle of the liquid crystal molecules in the liquid crystal layers in the plurality of picture elements from one of the pair of translucent substrates to the other is in the range of 45 ° to 150 °. Item 3. The liquid crystal display device according to item 1 or 2. 4. The liquid crystal material of the liquid crystal layer contains at least C
The liquid crystal display device according to claim 1, which contains an l-based liquid crystal compound. 5. The liquid crystal display element according to claim 1, wherein the alignment means is an alignment wall formed between the plurality of picture elements. 6. The liquid crystal display device according to claim 5, wherein a polymer wall is further formed between the plurality of picture elements. 7. The liquid crystal display device according to claim 1, wherein the alignment means is an alignment film formed on the pair of translucent electrodes and having axially symmetrical fine grooves. 8. The liquid crystal display device according to claim 5, wherein the alignment wall has a vertical alignment property.