JPS6280622A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To obtain a good image of high contrast and wide visual field angle even in the higher time division driving system by specifying the twist angle of liquid crystal molecules and the angle of a director direction. CONSTITUTION:A twist angle alpha of liquid crystal molecules should be >200 deg. and <=360 deg., preferably, >=240 deg. and <=300 deg., more preferably, 720 deg.. If the twist angle alpha is >360 deg., the change of the intensity of a transmitting light for an impressed voltage is gentle and the response characteristic is insufficient; and if the twist angle alpha is <200 deg., the malfunction of turn-on/off for time division driving is apt to occur. The angle (pretilt angle) between surfaces of substrates 1 and 2 and the director direction of liquid crystal molecules brought into contact with surfaces is <=5 deg.. The pretilt angle is controlled by shapes and electrostatic properties of surfaces of oriented layers formed on substrates 1 and 2, the structure of liquid crystal molecules, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a liquid crystal display device, and particularly to a twisted nematic type (hereinafter referred to as rTN type) liquid crystal display device having excellent time division characteristics.

[Conventional technology]

TN type liquid crystal display devices have low power consumption,
It is currently widely used because it has advantages such as low manufacturing cost, light weight, and can be made into a W-shape.

A TN type liquid crystal display device is constructed by sealing a nematic liquid crystal with positive or negative dielectric anisotropy between two electrode plates, and usually the liquid crystal molecules are continuously twisted into a 90” spiral. It is said to be in a state of

However, this type with a twist angle of 90° (hereinafter referred to as "90°
In liquid crystal display devices (referred to as "twisted type"), the intensity of transmitted light (or reflected light) changes slowly in response to changes in applied voltage. The ratio of the selected point voltage to the highest non-selected point voltage) becomes small, so the contrast is low and it is difficult to obtain clear images.
It also has the problem of a narrow viewing angle. For example, A
In a 4-size liquid crystal display device, it is said that a duty ratio of 1/200 or more is desirable for practical use.・The contrast ratio (
The brightness ratio (brightness ratio when selected and when not selected) is as low as about 3.

As a technique for solving the problems of such a 90° twist type liquid crystal display device, Japanese Patent Application Laid-Open No. 107020/1983 discloses a method in which the twist angle of liquid crystal molecules is 180° to 360°.
, and the optical axis of the liquid crystal molecules aligned to at least one electrode substrate is 1[the inclination angle with respect to the polar substrate is 5°
A larger liquid crystal display is disclosed. According to this liquid crystal display device, it is said that it is possible to realize a high contrast ratio of 18.6 when driven at a duty ratio of 1/100, for example.

However, this liquid crystal display device has a problem in that it is not easy to manufacture. That is, in manufacturing this liquid crystal display device, in order to set the director direction of liquid crystal molecules aligned on at least one electrode substrate to be larger than 5°, the alignment plate has an angle of 5° or more, preferably 20° or more. It is necessary to form unevenness (hereinafter referred to as "pretilt"), and for this purpose, an oblique vapor deposition method is usually used.

However, in this method, the allowable range of the optimal thinning angle is extremely narrow, so when the area of the substrate is large, the deposition angle will differ partially, making it difficult to form a pretilt of the same 4KG over the entire area of the substrate. In particular, in manufacturing large-area liquid crystal display devices, there are problems in terms of yield during mass production, number of steps, manufacturing cost, etc.

[Problem that the invention seeks to solve]

The present invention solves the problems of the prior art described above, (1)
In a 90° twist type liquid crystal display device, when the time division order is increased during time division driving, the operating margin becomes smaller, the contrast becomes low (and it is difficult to obtain clear images); Kaisho 60-1070
In the liquid crystal display device disclosed in Publication No. 20, it is disadvantageous in terms of yield, number of steps, manufacturing cost, etc. during mass production, especially when manufacturing a large-area liquid crystal display device. It is an object of the present invention to provide a liquid crystal display device that can obtain good images with high contrast and a wide viewing angle even in a high-order time division driving method, and can be manufactured at low cost.

[Means for solving problems]

In a liquid crystal display device in which a liquid crystal composition is disposed between a pair of substrates each having a polarizing element, the above-mentioned problem is solved by (a) the twist angle of the liquid crystal molecules in the liquid crystal composition disposed between the pair of substrates; The size is thicker than 200°3
(b) angles formed by each surface of the pair of substrates and the director direction of the liquid crystal molecules in contact with the surfaces are both 5° or less.

An overview of the present invention will be explained with reference to FIG.

FIG. 1 is an explanatory diagram showing an exploded view of the main parts of a liquid crystal display device. In FIG. 1, ■ and 2 are substrates, 9 and l
O represents a polarizing element, and C represents a liquid crystal layer.

In the present invention, "ζ" represents the magnitude of the twist angle α of the liquid crystal molecules, which is greater than 200° and less than 360°, preferably 240°.
In the present invention, if the torsion angle α is larger than 360°, the intensity change of the transmitted light with respect to the applied voltage will be gradual, resulting in insufficient response characteristics, and If the angle α is smaller than 200°, the intensity change of the transmitted light differs when the applied voltage increases and decreases (hysteresis phenomenon), which tends to cause on/off malfunctions during time-division driving.

The twist angle α is the direction of the alignment process for defining the alignment direction of liquid crystal molecules in the substrates l and 2, and the liquid crystal layer C.
It can be defined by the type and size of the nematic liquid crystal that constitutes the liquid crystal or the optically active substance added thereto.

Further, in the present invention, the angle between the surfaces of substrates l and 2 and the director direction (direction of the optical axis (long axis) of the liquid crystal molecules) of the liquid crystal molecules in contact with the surfaces (hereinafter referred to as "pretilt angle") is 5. ° or less.

The pretilt angle of the liquid crystal molecules can be determined by the shape and electrostatic properties of the surfaces of the alignment layers formed on the substrates 1 and 2, the structure of the liquid crystal molecules, and the like. The method for forming the alignment layers of substrates 1 and 2 is not particularly limited, but may include rubbing with an imide-based, amide-based, polyvinyl alcohol-based, phenoxy-based polymeric substance such as sebum cotton to form grooves in a certain direction on the surface of the substrate. It can be easily formed using a rubbing method, etc.

When the alignment layer is formed by a rubbing process, the pretilt angle of the liquid crystal molecules can be controlled by the rubbing conditions (pressure during rubbing, number of times of rubbing, etc.) or heat treatment after the rubbing process.

In the present invention, the polarization axis direction of at least one of the polarizing element 9 and IO is 20° or more and 70° in the twist direction of the liquid crystal molecules with respect to the director direction of the liquid crystal molecules in contact with the surface of the substrate on the polarizing element side. Below, preferably 85°
It is preferable to have the deviation angles β and γ of 95° or less. If the deviation angles β and γ are out of the above range, the intensity of the transmitted light changes slowly with respect to the applied voltage, resulting in insufficient response characteristics.

In the present invention, the liquid crystal composition constituting the liquid crystal layer C includes nematic liquid crystals such as cyclohexylcarboxylic acid ester compounds, biphenyl compounds, phenylcyclohexane compounds, pyrimidine compounds, azo-azoxy compounds, benzoate ester compounds, etc. consisting of a mixture of The liquid crystal composition may contain a smeffic liquid crystal component, a cholesterinic liquid crystal component, etc., if necessary.

As the optically active substance, use is made of nematic liquid crystals, which are generally called chiral nematic ink liquid crystals, such as ester-based, biphenyl-based, phenylcyclohexane-based, or azo-based liquid crystals, which have an optically active group represented by the following general formula as a terminal group. I can do Koki.

(R+, Rx, Rs: an alkyl group or a hydrogen atom, and R, R1, and R1 are different from each other) As specific examples of the optically active substance, compounds having the structures shown below can be used, for example.

Book -OCII□-CIl-C,l+.

C11° In the present invention, the thickness d of the liquid crystal layer C is preferably 20 μm or less, particularly 10 μm or less, and the ratio d/ It is preferable that p is in the range of 0.5 to 1.2. If the value of this ratio d/p is out of the above range, the spontaneous twisting of the liquid crystal molecules, the thickness d of the liquid crystal JlJC and the twist angle α
This may result in misalignment of liquid crystal molecules that causes unevenness or spots in images.

Further, in the present invention, the refractive index anisotropy Δn of the liquid crystal layer C
The product Δn-d of 17sd of the liquid crystal IC is 0.4-0.6 or 0.7-0.
It is preferable that it is 1.2.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 2 is an explanatory sectional view showing an embodiment of the present invention.

In the liquid crystal display device shown in FIG. 2, two substrates 1 and 2 are arranged facing each other with a distance between them, and the substrate
The substrate 2 is constructed by forming an electrode N4 and an alignment layer 6 on the inner surface of the support plate 11, and the substrate 2 is constructed by forming an electrode layer 5 and an orientation layer N7 on the inner surface of the support plate 21.

Further, the space between both substrates 1 and 2 is sealed by a sealing portion 3, thereby forming a cell. Inside the cell, spacers 8 are arranged in a distributed manner and a liquid crystal composition is filled, forming a liquid crystal layer C. Further, in FIG. 0, a front polarizing element 9 and a rear polarizing element 10 are formed on the outer surfaces of the substrates 1 and 2, respectively, and 13 is a reflecting plate formed on the outer surface of the rear polarizing element 10. be. Note that the reflective plate 13 may not be used in a transmissive type liquid crystal display device.

The materials constituting the support plates 11 and 21 include glasses such as soda glass, borosilicate glass, and quartz;
Plastics such as axially oriented polyethylene telescrate, polyether sulfone, and polyvinyl alcohol, and metals such as aluminum and stainless steel can be used.

The electrode layers 4 and 5 have a support plate 11 with a thickness of 1.1 mm.
and a thickness 10 spaced apart parallel to the surfaces of 21
For example, ITO (tin and indium oxide)
Transparent electrodes E and Eo constitute one electrode layer 4, and transparent electrode E° constitute the other electrode layer 5, which are arranged at right angles to each other. For example, 0.31 and 0.3I
A matrix-type display electrode structure consisting of III and 11 pixels is constructed.

The orientations N6 and 7 are formed by rubbing the surface of a coating film made of j7500 polyetheramide n1L-1100J (manufactured by Hitachi Chemical Co., Ltd., Ltd.) with rayon suede.

The liquid crystal composition constituting the liquid crystal layer C is a nematic liquid crystal "rZLI-2293" (manufactured by Merck & Co., Ltd.) containing an optically active substance r.
2% by weight of S-811J (manufactured by Merck & Co., Ltd.) was added.

Note that the substrates 1 and 2 may further include a dielectric layer, an alkali ion migration prevention layer, an antireflection layer, a polarizing layer,
A reflective layer etc. can be provided.

The front polarizing element 9 is composed of rF-1205DUJ (Nitto Denko's type), and its polarization axis direction is 30 degrees in the twist direction of the liquid crystal molecules with respect to the director direction of the liquid crystal molecules in contact with the surface of the alignment layer 6. are arranged so as to have a deviation angle β of . Similarly, the rear polarizing element 10 and the reflecting plate 13 are
The polarization axis direction is arranged at a deviation angle T of 30° from the director direction of the liquid crystal molecules in contact with the surface of the alignment layer 6 with respect to the twist direction of the liquid crystal molecules.

Note that the spacer 8 is made of glass fiber rELC.
-O3-060SSSJ (manufactured by Asahi Fiberglass) and Structbond rXN-5A-CJ (manufactured by Mitsui Toatsu Chemicals) were used as the sealing material constituting the seal portion 3.

In the liquid crystal display device with the above configuration, the thickness d of the liquid crystal layer C is 6.3 μm, the twist angle α of the liquid crystal molecules is 270° counterclockwise (clockwise) from the front, and the thickness d of the liquid crystal layer C is pinched. The ratio d/p with p was 0.75.

This liquid crystal display device was operated by a time division drive method at a duty ratio of 1/100, and its contrast ratio and viewing angle were determined. Note that the viewing angle is as shown in Figure 3.
With the normal direction of the substrate 1.2 as the Z axis, the X axis (same as the rubbing direction of the alignment layer 6 on the substrate l) and the Y axis are determined,
The angle between the observation direction and the Z axis is θ, and the angle between the observation direction and the X axis is Φ.

As a result, the contrast ratio in the visible light region of wavelengths 400 to 700 nm, that is, selective! The ratio of the brightness of the reflected light in the non-selected state (dark) to the brightness of the reflected light in the non-selected state (bright) was as good as 1:4 or more, and a clear image with excellent contrast was obtained.

Furthermore, the viewing angle for images with a contrast ratio of 1:3 or higher was as wide as 0°<θ<50° and 10°<Φ<80°.

Next, for comparison, the content of the optically active substance was set at 0.25%, and the ratio between IIs d and pinch p of the liquid crystal layer C was d/p.
A liquid crystal display device was constructed in the same manner as in the above embodiment, except that the angle of twist α of the liquid crystal molecules was 0.2 and the twist angle α of the liquid crystal molecules was 90°.

When the contrast ratio and viewing angle of this liquid crystal display device were determined using the method described above, the contrast ratio was 1.
:2.1, which did not reach 1:3, and was confirmed to be insufficient for practical use.

〔Effect of the invention〕

According to the present invention, it is possible to provide a liquid crystal display device that can obtain good images with high contrast and a wide viewing angle even in a high-order time-division driving method, and can be manufactured at low cost. .

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing an overview of the present invention, FIG. 2 is an explanatory sectional view showing an embodiment of the invention, and FIG. 3 is an explanatory diagram for specifying the viewing angle. 1.2...Substrate 11.21...Support plate 3
... Seal part 4.5 ... Electrode layer 6.7.
...Alignment layer C...Liquid crystal layer 9...Front polarizing element 10...Backward polarizing element 13...Reflector plate Ashi 2 diagram procedural amendment (voluntary) Patented on November 22, 1985 Director General Michibe Uga1, Indication of the case, Patent Application No. 221341 of 19852, Name of the invention, Liquid crystal display device3, Person making the amendment Relationship to the case Patent applicant address: 1 Nishi-Shinjuku, Shinjuku-ku, Tokyo No. 26-2 Name (127) Konishi Roku Photo Industry Co., Ltd. 4, Column 6 of detailed explanation of the invention in the agent's specification, Contents of amendment (1) From r360' in page 6, line 5 of the specification If it's big,
``is smaller than r200','' is corrected. (2) If it is smaller than 1-200° in the 6th shell, 7th line,
If it is larger than 1-360°,” correct it. (3) 1-1 in the 7th true, 20th line, preferably 85° or more and 950° or less” is deleted. (4) 11th line 4th line 1-Nenatake liquid crystal”
"Nematic liquid crystal" is corrected. (5) "Orientation layer 6" in the 16th back row 8th row is "orientation layer 7"
I am corrected.

Claims (1)

[Scope of Claims] 1) A liquid crystal display device comprising a liquid crystal composition disposed between a pair of substrates each having a polarizing element, wherein: (a) liquid crystal molecules in the liquid crystal composition disposed between the pair of substrates; The size of the torsion angle is greater than 200°3
(b) An angle between each surface of the pair of substrates and a director direction of liquid crystal molecules in contact with the surfaces is both 5° or less.