JPH0561048A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To prevent the generation of domains and to enhance a display grade. CONSTITUTION:The materials of an oriented film 23 formed on an active matrix substrate 20 and an oriented film 13 formed on a counter substrate 10 are varied the material and the pretilt angles determined by the respective oriented films 23, 13 are varied with both substrates 20, 10. Only the active matrix substrate 20 side has the high pretilt angle if, for example, the oriented film 23 on the active matrix substrate 20 side is formed of the material to provide >=7 deg. pretilt angle and the oriented film 13 on the counter substrate 10 on the opposite side is formed of the material to provide <=5 deg. pretilt angle and, therefore, the liquid crystal molecules are hardly brought into reverse tilt arrangement and the domains are hardly generated.

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 used in office automation equipment and video equipment.

[0002]

2. Description of the Related Art As the liquid crystal display device, a liquid crystal display device having a structure shown in FIG. 3 has been conventionally known. This display device includes an active matrix substrate 1 and the substrate 1.
A pixel electrode 4 formed on the active matrix substrate 1, and a counter electrode 5 formed on the counter substrate 2. The counter substrate 2 includes a counter substrate 2 and a liquid crystal layer 3 sandwiched between the substrates 1 and 2. A voltage is applied between the two to change the dielectric anisotropy of the liquid crystal layer 3 to perform display. In order to align the liquid crystal molecules of the liquid crystal layer 3 uniformly, the alignment films 6 and 7 are formed on the inner surfaces of the substrates 1 and 2 which are in contact with the liquid crystal layer 3.
The alignment films 6 and 7 impart the pretilt angle θ shown in FIG. 4 to the liquid crystal layer 3. When the dielectric anisotropy is reversed positively or negatively, the directions of the molecular axes of the liquid crystal molecules 3a are opposite when the voltage is applied and when the voltage is not applied, but the liquid crystal molecules are the same. Change the orientation state to.

[0003]

By the way, in the case of the above-mentioned conventional liquid crystal display device, the alignment films 6 and 7 are usually formed by applying an insulating film such as polyimide or polyamide-imide, and applying the insulating film to a cloth or the like. Oriented by rubbing with. The polyimide-based alignment film is fired at a temperature of 200 ° C. or lower from the viewpoint of heat resistance of the color filter.

However, the pretilt angle of the alignment film thus produced is often as small as several degrees. When the pretilt angle is small, it is advantageous in terms of viewing angle characteristics, but when lighting is performed at a high temperature, the alignment direction of the liquid crystal is difficult to stabilize, and the alignment direction of the liquid crystal is likely to partly collapse. In particular, when the film thickness difference between the thin film transistor element and the color filter is large, as in a color liquid crystal display device provided with a thin film transistor, the reverse tilt arrangement as shown in FIG. There is a problem that a domain is generated, which may locally transmit light and impair the display quality.

The present invention is intended to solve the problems of the prior art, and an object thereof is to provide a liquid crystal display device of high display quality which prevents the occurrence of domains.

[0006]

In a liquid crystal display device of the present invention, a liquid crystal layer is interposed between a pair of substrates arranged to face each other, and a pretilt liquid crystal layer is formed on the inner surfaces of both substrates in contact with the liquid crystal layer. In a liquid crystal display device in which an alignment film that imparts a corner is formed, the materials and the pretilt angles of the alignment films on the two substrates are different, and thereby the above object is achieved.

[0007]

In the present invention, the materials of the alignment films formed on both substrates are made different, and the pretilt angles determined by each alignment film are made different for both substrates. For example, if the orientation film on the substrate side on which the pixel electrodes and the like are formed is made of a material having a pretilt angle of 7 ° or more, and the orientation film on the opposite side substrate is made of a material having a pretilt angle of 5 ° or less, Since only the substrate side on which the element electrodes and the like are formed has a high pretilt angle, the liquid crystal molecules are unlikely to be in the reverse tilt arrangement and domains are less likely to occur.

[0008]

EXAMPLES Examples of the present invention will be described below.

FIG. 1 is a sectional view showing the liquid crystal display device of this embodiment. This liquid crystal display device includes an active matrix substrate 20 and a counter substrate 10 arranged to face the substrate 20.
And a liquid crystal layer 31 enclosed between both substrates 20 and 10.

In the active matrix substrate 20, a metal wiring 25 including a plurality of gate bus wirings and a plurality of source bus wirings is formed on a substrate 21 made of glass or the like so as to form a lattice pattern. The pixel electrodes 22 and thin film transistors (not shown) are formed in a matrix in a region surrounded by 25. Furthermore, a protective insulating film 26 and an alignment film 23 are formed in this order thereover.

On the other hand, the counter substrate 10 is a light-shielding mask 1 made of metal or the like on a substrate 11 also made of glass or the like.
4, the color filter 15, the overcoat film 16, the counter electrode 12, and the alignment film 13 are formed in this order.

Alignment films 23 and 13 are provided between the active matrix substrate 20 and the counter substrate 10 having such a structure.
The liquid crystal layer 31 is disposed so as to be sandwiched between. The alignment film 23 on the active matrix substrate 20 side is formed of STN (Super Twisted NeW) having a pretilt angle of 7 ° or more.
matic) material, and is formed by firing at a temperature of 200 ° or more. Specifically, it was formed by applying a resin such as Sun Ever manufactured by Nissan Chemical Co., Ltd. and baking it at a temperature of 250 ° C. The firing temperature is set to 200 ° C. or higher because the manufacturing constraint temperature on the active matrix substrate 20 side is higher than that on the counter substrate 10 side having the color filter 15.

The alignment film 13 on the opposite substrate 10 side is formed of a material having a pretilt angle of 5 ° or less. Concrete formation is a normal TN (Twisted Nematic)
Type alignment film liquid, such as Nitto Denko or Hitachi Chemical's polyimide insulating varnish, is coated by printing, etc.
Firing was performed at a temperature of 80 ° C. for 1 to 3 hours. In the case of this alignment film 13, the firing temperature was set to 200 ° C. or lower in view of the heat resistance of the color filter 15.

Therefore, when the two alignment films 23 and 13 made of different materials are rubbed with a cloth or the like to perform the alignment treatment, and the liquid crystal layer 31 is sandwiched between the alignment films 23 and 13, the liquid crystal layer is formed. In No. 31, the pretilt angle is different between the active matrix substrate 20 side and the counter substrate 10 side. More specifically, the pretilt angle of 7 ° or more on the side of the active matrix substrate 20 is larger than the pretilt angle of 5 ° or less on the side of the counter substrate 10 side. As described above, when the pretilt angle is high only on the active matrix substrate 20 side, as shown in the arrangement state of the liquid crystal molecules 31a when a voltage is applied in FIG.
In 1a, the reverse tilt sequence is less likely to occur, and the domain is less likely to occur.

In the above embodiment, the pretilt angle on the side of the counter substrate 10 is set to 5 ° or less and the pretilt angle on the side of the active matrix substrate 20 is set to 7 ° or more. This is because there are restrictions in terms of use and there are very few materials that can give a high pretilt angle at temperatures of 200 ° C or less. If such regulatory conditions can be eliminated, two pretilt angles can be set in different angle ranges. Other angle ranges may be used.

[0016]

According to the present invention, it is possible to prevent the reverse tilt alignment from occurring in the liquid crystal molecules and suppress the generation of domains, so that it is possible to improve the display quality.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a liquid crystal display device of this embodiment.

FIG. 2 is a schematic view showing an arrangement state of liquid crystal molecules when a voltage is applied to the liquid crystal display device of FIG.

FIG. 3 is a cross-sectional view showing a conventional liquid crystal display device.

FIG. 4 is a schematic diagram showing an arrangement state of liquid crystal molecules when a voltage is applied in the case where both of the conventional two have a small pretilt angle.

[Explanation of symbols]

 10 Counter substrate 13 Alignment film 20 Active matrix substrate 23 Alignment film 31 Liquid crystal layer

Continued Front Page (72) Inventor Katsumi Irie 22-22 Nagaike-cho, Abeno-ku, Osaka

Claims (1)

[Claims] 1. A liquid crystal display in which a liquid crystal layer is interposed between a pair of substrates arranged to face each other, and an alignment film for giving a pretilt angle to the liquid crystal layer is formed on the inner surfaces of both substrates in contact with the liquid crystal layer. A liquid crystal display device, wherein the materials and the pretilt angles of the alignment films on the both substrates are different.