JP3159757B2 - Liquid crystal display - Google Patents

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.

[0002]

2. Description of the Related Art A liquid crystal display device comprises a liquid crystal panel in which liquid crystal is inserted between a pair of opposed transparent substrates. A common electrode, an alignment film, and the like are provided on the inner surface of one glass substrate, and a pixel electrode, an alignment film, and the like are provided on the inner surface of the other substrate. Recently, active matrix circuits are often formed together with pixel electrodes on the latter substrate. Further, a polarizing plate is provided outside each of these substrates. Usually, these polarizing plates are arranged so that transmission axes of polarized light are orthogonal to each other.

[0003] Twisted nematic liquid crystals are often used in liquid crystal display panels. The liquid crystal molecules pretilt and twist according to the alignment films of both substrates. In other words, the major axis direction of the molecules of the liquid crystal extends in parallel with the orientation direction of the alignment film of the substrates, and the orientation directions of the alignment films of the two substrates are substantially perpendicular to each other. As it twists in a spiral. It is also known that liquid crystal molecules pretilt according to the orientation direction.

The alignment of the liquid crystal is achieved by rubbing the alignment film in a predetermined direction, and the rubbing direction matches the alignment direction of the liquid crystal. The orientation of the liquid crystal is
For example, it can be controlled by forming the alignment film by oblique evaporation. When no voltage is applied to the liquid crystal, the molecules of the liquid crystal maintain the initial twist and pretilt, and the incident light travels while rotating along the twist of the liquid crystal and exits from the liquid crystal cell. At this time, a white display is obtained. When a voltage is applied, the liquid crystal rises, the birefringence effect of the liquid crystal is weakened, and the above-described swirling effect of light is weakened, so that incident light is less likely to pass through the liquid crystal cell, and a black display can be obtained. In this way, an image having a bright and dark contrast as a whole is formed while controlling the voltage applied to the liquid crystal.

When a voltage is applied to the liquid crystal, the molecules of the liquid crystal rise in a direction having a pretilt. actually,
When a voltage is applied, not all molecules of the liquid crystal rise in the same manner, but molecules of the liquid crystal located near the alignment film of the substrate rise only slightly due to the regulation of the alignment film. The rising liquid crystal molecules rise the largest. Therefore, the formation of a black display when a voltage is applied mainly depends on the behavior of the molecules of the liquid crystal positioned at the intermediate portion between the two substrates.

The liquid crystal molecules have a long rod shape,
The birefringence effect differs between the case where light shines from the long axis direction and the case where light shines from the short axis direction. When a voltage is applied, the molecules of the liquid crystal do not rise until they become perpendicular to the surface of the substrate, but rise to a certain angle with respect to the surface of the substrate. Therefore, when the liquid crystal molecules rise to a certain angle with respect to the surface of the substrate due to the application of the voltage, the viewer relatively changes the major axis direction of the liquid crystal molecules depending on the positional relationship between the screen and the viewer. However, the degree of black display obtained due to the difference in light transmittance differs. Therefore, depending on the position of the viewer, the contrast between light and dark in the image is reduced. This is generally recognized as a viewing angle characteristic of a liquid crystal display device.

In order to solve such a problem, Japanese Patent Application Laid-Open No. 54-5754 discloses a method in which two liquid crystal alignment sections having different twist directions of liquid crystal molecules are formed in each small unit area of liquid crystal. Has been proposed. Also, JP-A-63
Japanese Patent No. 106624 proposes forming two liquid crystal alignment sections having different alignment directions of liquid crystal molecules in one pixel. According to these proposals, the overall visual characteristics can be improved by mixing a liquid crystal alignment section having a certain viewing angle characteristic with another liquid crystal alignment section having a different viewing angle characteristic.

For example, FIG. 6 shows an example in which two liquid crystal alignment sections A and B having different alignment states are formed in one pixel. In FIG. 6, the left figure shows the alignment directions of the two liquid crystal alignment sections A and B by arrows, and the middle figure shows the arrangement of the liquid crystal molecules 20c when the display screen is viewed from the front. The figure shows the arrangement of the liquid crystal molecules 20c as viewed from the side of the display screen. FIG. 6 is a diagram when a voltage is applied to the twisted nematic liquid crystal. At this time, the molecules 20c of the liquid crystal in the liquid crystal alignment section A are in a plane perpendicular to the display screen, and the lower end is inclined toward the back of the display screen. Further, the molecules 20C of the liquid crystal in the liquid crystal alignment section B are in a plane perpendicular to the display screen, and the upper end is inclined toward the back of the display screen.

FIG. 7 shows the voltage-transmittance characteristics of the liquid crystal alignment section A, and the dashed line C is the characteristic when viewed from the front, and the dashed lines L and U are when viewed from obliquely downward and obliquely upward at an angle of 40 degrees. 5 is a voltage / transmittance curve of the sample. As shown by the broken lines L and U, the liquid crystal display device has a viewing angle characteristic depending on the viewing position. Therefore, the solid line I shows the characteristic obtained by adding the characteristics of the broken line L and the broken line U and dividing by two. The characteristics of the solid line I are close to those of the one-dot chain line C, and there are no extremely high transmittance portions and extremely low transmittance portions, so that the viewing angle characteristics are improved.

[0010]

Therefore, as shown in FIG. 6, a liquid crystal alignment section B having characteristics complementary to the liquid crystal alignment section A is provided, and the liquid crystal alignment section A and the liquid crystal alignment section B are combined. It can be seen that if one unit is used, an averaged characteristic I can be obtained. In FIG. 6, the direction of orientation of one substrate is indicated by an arrow 22a, and the direction of orientation of the substrate facing it is indicated by an arrow 26a. In order to realize the liquid crystal alignment sections A and B having different alignment states as described above, one substrate is subjected to alignment processing twice in different alignment directions 22a, and the other substrate is similarly subjected to twice alignment processing in different alignment directions 26a. It was necessary to perform an orientation treatment.

In order to perform an alignment process on a substrate in a different alignment direction 22a, it is necessary to perform rubbing or the like using a mask or the like having a minute opening, and such a troublesome rubbing process is performed for each substrate. Need to be performed twice. Therefore, there is a problem that the number of steps is considerably increased in manufacturing such an alignment division type liquid crystal display device. SUMMARY OF THE INVENTION It is an object of the present invention to provide a liquid crystal display device that can easily perform an alignment process in a device having liquid crystal alignment sections having different alignment states in a plurality of minute unit regions.

[0012]

A liquid crystal display device according to the present invention comprises a liquid crystal 20 inserted between first and second opposing substrates 18 and 16, and an alignment state within a plurality of minute unit areas. In the liquid crystal display device having the first and second liquid crystal alignment sections A and B different from each other, the alignment directions of the first and second liquid crystal alignment sections on the first substrate are different, and the first and second liquid crystal alignment sections are different. 2 in the liquid crystal orientation section of the pretilt of the liquid crystal molecules in the vicinity of said second substrate is rather smaller than the pretilt of the liquid crystal molecules in the vicinity of the first substrate, the first
2 for the different liquid crystal alignment sections.
In a certain direction .

[0013]

In the above structure, the alignment processing of the second substrate can be performed more easily than the alignment processing of the first substrate.
Alignment processing can be facilitated.

[0014]

FIG. 3 to FIG. 7 explain first and second liquid crystal alignment sections which are the premise of the present invention. FIG.
Is a liquid crystal panel 10 of the liquid crystal display device according to the embodiment of the present invention.
FIG. 3 is a diagram showing polarizing plates 12 and 14. LCD panel 1
0 denotes a liquid crystal 2 between a pair of transparent glass substrates 16 and 18.
0 is enclosed. Light from a light source (not shown) enters the liquid crystal panel 10 from the direction of the arrow L, and the viewer E views the liquid crystal panel 10 from a direction opposite to the incident direction.
In the following description, the substrate 16 on the light incident side is referred to as a lower substrate, and the substrate 18 on the viewer side is referred to as an upper substrate.

On the inner surface of the lower substrate 16, a common electrode 2 of ITO is provided.
1 and an alignment film 22 are provided, and a pixel electrode 24 and an alignment film 26 are provided on the inner surface of the upper substrate 18. Further, FIG.
Shows a storage capacitor electrode 28 provided between the upper substrate 18 and the pixel electrode 24 via an insulating layer. FIG.
Shows the arrangement of the pixel electrodes 24 and the active matrix circuit provided on the upper substrate 18. The active matrix circuit includes a data bus line 30 and a gate bus line 32 extending vertically and horizontally in a matrix, and the pixel electrode 24 is connected to the data bus line 30 and the gate bus line 32 via a thin film transistor (TFT) 34. 5 shows an equivalent circuit in which the storage capacitor electrode 28 is provided in parallel with the liquid crystal 20.

Referring to FIGS. 3 and 4, the twisted nematic liquid crystal 20 twists and pretilts according to the alignment direction 22a of the lower substrate 16 and the alignment direction 26a of the upper substrate. The orientation direction 22a and the orientation direction 26a are provided in directions perpendicular to each other. FIG. 4 shows a liquid crystal 20 in a minute area.
Are twisted counterclockwise as indicated by the arrow T. Here, 20L indicates liquid crystal molecules located near the lower alignment film 22, and 20C indicates the lower alignment film 2
2U indicate liquid crystal molecules located in an intermediate portion between the upper alignment film 26 and 20U.

When a voltage is applied to the liquid crystal 20, it can be said that the transmittance of the liquid crystal cell is determined by the molecules 20C of the liquid crystal located at an intermediate portion between the lower alignment film 22 and the upper alignment film 26.
As described above, the intermediate molecules 20 of the liquid crystal in the liquid crystal alignment section A are used.
C is in a plane perpendicular to the display screen, and its lower end is inclined toward the back of the display screen. The intermediate molecules 20C of the liquid crystal in the liquid crystal alignment section B are inclined in reverse. Therefore, when the liquid crystal alignment section A and the liquid crystal alignment section B are combined, a characteristic that is not affected by the viewing angle is obtained as shown by the solid line I in FIG. Conventionally, in order to obtain such characteristics, the lower substrate 16 has different orientation directions 2.
It is necessary to perform the alignment process twice in 2a, and to perform the alignment process twice in different orientation directions 26a on the upper substrate 18 as well.

FIG. 1 is a diagram illustrating the principle of the present invention. FIG. 1 shows a liquid crystal alignment section A and a liquid crystal alignment section B.
The directions of the liquid crystal molecules in the vicinity of the upper substrate 18 are opposite in the liquid crystal alignment section A and the liquid crystal alignment section B, but are pretilt at the angle α. The liquid crystal molecules in the vicinity of the lower substrate 16 are pretilted at an angle β in a certain direction. The angle α is larger than the angle β. Therefore, the alignment process of the alignment film 22 of the lower substrate 16 can be performed more easily than the conventional case where the alignment process is performed twice in different alignment directions 22a.

When the alignment direction of the lower substrate 16 is fixed as described above, in FIG. 1, for example, the molecules of the liquid crystal in the liquid crystal alignment section B are oriented rightward in the vicinity of the upper substrate 18, whereas the liquid crystal molecules in the liquid crystal alignment section B are oriented upward. In the vicinity of the substrate 16, the liquid crystal molecules are oriented downward to the right. When a voltage is applied to the liquid crystal 20 in such a state, there is a possibility that the rising direction of the liquid crystal molecules between the upper substrate 18 and the lower substrate 16 of the liquid crystal alignment section B may not be constant.

However, in the present invention, since the angle α is larger than the angle β, the behavior of the molecules of the liquid crystal greatly depends on the orientation having the large pretilt angle α. As a result, when a voltage is applied to the liquid crystal 20, the rising direction of the liquid crystal molecules between the upper substrate 18 and the lower substrate 16 of the liquid crystal alignment section B becomes constant. In the illustrated example, there is no problem with the liquid crystal alignment section A.

FIG. 2 shows an alignment film 2 of the liquid crystal display of FIG.
It is a figure which shows the rubbing process for production | generation of 2 and 26.
(A) shows the alignment processing of the upper substrate 18, and (B) shows the alignment processing of the lower substrate. In (A), first, the first rubbing is performed on the alignment film 26 of the upper substrate 18 using a rubbing roller 53 around which a rubbing material such as a fiber is wound, and then the rubbing roller 53 is moved in the reverse direction by using a mask 54. The second rubbing is performed while proceeding to step, and finally the mask 54 is removed. Then, the portion processed by the first rubbing and covered with the mask 54 becomes, for example, the liquid crystal alignment section A, and the portion processed by the second rubbing becomes the liquid crystal alignment section B.

In (B), damping vibration rubbing was performed on the alignment film 22 of the lower substrate 16 using a rubbing roller 53.
In other words, the orientation film 2 is
2 and the amount of pressing the rubbing roller 53 against the alignment film 22 was gradually reduced. As a result, the pretilt angle α with respect to the lower substrate 16 is set to 0.5 degrees or less.
The pretilt angle α with respect to the upper substrate 18 was 1.1 degrees. In order to make the angle α larger than the angle β, various processes can be performed. For example, the alignment materials of the upper alignment film 26 and the lower alignment film 22 can be changed. For example, JALS-21 made by Japan Synthetic Rubber
9 and AL 1054 can be used respectively.
It is also possible to change rubbing conditions.

The liquid crystal alignment section A and the liquid crystal alignment section B have different viewing angle characteristics, and in order to form a uniform image without the difference being recognized by a viewer, the area of these liquid crystal alignment sections is limited to some extent. It is desirable to be small. Preferably, one unit region forming the pair of liquid crystal alignment sections A and B is formed so as to coincide with one pixel region surrounded by the data bus line 30 and the gate bus line 32. When a color filter is provided on the lower substrate 16 for color display, one pixel region is a region for each of R, G, and B of the color filter. However, one unit area may be an integral multiple (up to about three times) of one pixel area or a reciprocal multiple of an integer of one pixel area. Further, the liquid crystal alignment sections A and B can be arranged in a matrix or staggered pattern, or can be formed to extend in a stripe shape.

[0024]

[0025]

Although all the embodiments of the present invention have been described with the configuration in which the polarizing plates are orthogonal to each other, the configuration in which the polarizing plates are parallel can also improve the viewing angle characteristics.

[0027]

As described above, according to the present invention,
The alignment process can be easily performed in the alignment division panel, and a liquid crystal display device having excellent viewing angle characteristics and contrast can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing the principle of the present invention and a first embodiment.

2A and 2B are diagrams illustrating a rubbing process, in which FIG. 2A illustrates rubbing of an upper substrate, and FIG. 2B illustrates rubbing of a lower substrate.

FIG. 3 is a schematic sectional view of a liquid crystal display device.

FIG. 4 is a perspective view illustrating the behavior of a twisted nematic liquid crystal.

FIG. 5 is a diagram showing an active matrix circuit.

FIG. 6 is a diagram showing two conventional liquid crystal alignment sections.

[7] Ru FIG der showing the viewing angle characteristic of the liquid crystal display device.

[Explanation of symbols]

 16, 18: substrate 20: liquid crystal 21, 24: electrode 22, 26: alignment film

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Yoshiro Koike 1015 Kamikodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Prefecture Inside Fujitsu Limited (56) References JP-A-58-173720 (JP, A) JP-A-63-106624 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G02F 1/1337

Claims (2)

(57) [Claims] 1. A liquid crystal display device in which liquid crystal is inserted between first and second opposing substrates and has first and second liquid crystal alignment sections having different alignment states in a plurality of minute unit regions. In the above, the alignment directions of the first and second liquid crystal alignment sections in the first substrate are different, and the pretilt of liquid crystal molecules near the second substrate in the first and second liquid crystal alignment sections. There rather smaller than the pre-tilt of the liquid crystal molecules in the vicinity of the first substrate, the alignment process of the second substrate, wherein the different liquid crystal alignment division
A liquid crystal display device, wherein the liquid crystal display device is oriented in a certain direction with respect to 2. The liquid crystal display device according to claim 1, wherein alignment films of different materials are provided on the first and second substrates.