JPH07218915A - Liquid crystal display panel and manufacture thereof - Google Patents

Abstract

PURPOSE:To enable low voltage driving without damaging display quality by providing an area with a large pretilt angle outside a display area to form a liquid crystal display panel. CONSTITUTION:An upside glass substrate 5 and a downside glass substrate 6 are faced each other with a gap between and sealed by a seal agent 8 excepting for a liquid crystal injection port 7 but a display area 9 is not spread over the full area of the sealed area due to the seal agent 8 but a little margin (external part of the display area) exists on the up, down, left and right sides. Then, a high pretilt angle area 10 is prepared at one side (a lengthwise terminal part in this case) and after aneal processing is finished by injecting liquid crystal, a direction to twist the liquid crystal is arranged to the display area 9 by starting gradual cooling from this area 10. Further, the high pretilt angle area 10 is provided by adopting either of a method for changing the kind of an oriented film or a method for changing rubbing conditions.

Description

Detailed Description of the Invention

[0001]

The present invention has good display quality and
The present invention relates to a method for manufacturing a liquid crystal display panel that can be driven at a low voltage.

Liquid crystal display panels are classified into a simple matrix type and an active matrix type, which are properly used depending on the application. The active matrix type has a thin film transistor (abbreviated as TFT) in each pixel. , When a particular pixel is selected, its TFT is turned on and the others are turned off. Therefore, even if the number of scanning lines is large, crosstalk (Cross
s-talk) can be suppressed and a high contrast ratio can be obtained, which is suitable for large area display.

Here, as a liquid crystal used for display, a nematic liquid crystal is used, and a TN display using a twisted nematic effect is mainly used.

[0004]

2. Description of the Related Art A liquid crystal display panel adopting a TN display system is
An alignment film is formed on each of a first glass substrate on which a large number of pixels and bus lines are patterned and a pattern on a second glass substrate including a common electrode made of ITO (a solid solution of indium oxide and tin oxide). After film formation and orientation treatment, the first and second substrates are made to face each other with a gap of several μm, TN crystal is enclosed in this gap, and the vibration direction of the transmitted light is orthogonal. As described above, the liquid crystal display panel is formed by disposing the polarizing plates adjacent to the outer sides of the first and second glass substrates.

Here, a liquid crystal display panel adopting the TN display system, in particular, a liquid crystal display panel adopting the active matrix system can obtain display characteristics comparable to that of a CRT (cathode ray tube), and therefore, it is a display element for a portable television, a personal computer or the like. It is also used in portable devices such as notebook personal computers due to its low power consumption, but at that time, the drive voltage is set to reduce the power consumption as much as possible and extend the battery usage time. Is required to be further reduced.

Here, as a method of lowering the driving voltage, the dielectric anisotropy or elastic modulus of the liquid crystal material is changed. The amount of chiral liquid crystal added to the nematic liquid crystal is reduced to increase the chiral pitch of the liquid crystal, and the twisting of the liquid crystal molecules when a voltage is applied is easily released. Although methods such as the above have been considered, and methods up to the present have been mainly researched, there is a limit to the reduction in voltage by this method.

In the method (1), since the force that defines the twisting direction of the liquid crystal molecules is reduced, a region (reverse twisting region) in which the liquid crystal molecule is twisted in the direction opposite to the predetermined twisting direction is generated, resulting in display unevenness. There is a problem called.

[0008]

The demand for liquid crystal display panels for portable devices such as portable televisions and notebook type personal computers is increasing, so that the drive voltage of the display panel is further increased in order to extend the operating time by the battery. Need to be lowered. Therefore, the practical application of a new method for achieving this is an issue.

[0009]

The above problems are solved by providing a region having a large pretilt angle outside the display region forming the liquid crystal display panel, injecting the liquid crystal into the liquid crystal display panel, and at a temperature higher than the transition point of the liquid crystal. This can be solved by forming a liquid crystal display panel, which is characterized by cooling from a region having a large pretilt angle outside the display region after performing the annealing process.

[0010]

The present invention is intended to put the above method, which is considered as a low voltage driving method for a liquid crystal display panel, into practical use.

That is, conventionally, the amount of the chiral liquid crystal added to the nematic liquid crystal is reduced to facilitate the twisting of the liquid crystal when a voltage is applied, thereby lowering the driving voltage. There is a problem that a twist area is generated and display unevenness occurs, and it has not been practically applicable. However, the present invention suppresses the occurrence of the reverse twist area by providing an area having a large pretilt angle outside the display area.

That is, it has been known that increasing the pretilt angle of the alignment film from the prior art increases the force that determines the twisting direction of the liquid crystal molecules and suppresses the occurrence of the reverse twist region. There is a problem that the viewing angle characteristics of the liquid crystal display panel are deteriorated when the value is increased.

FIG. 2 is a T-V (transmittance-applied voltage) characteristic diagram for explaining this, and the T-V characteristic 1 viewed from the front is shown.
Compared to the viewing angle, the twist direction of the twisted nematic liquid crystal is 30
T when the pretilt angle of the liquid crystal is 2 °.
Compared to −V characteristic 2, TV with pretilt angle of 12 °
Characteristic 3 is far inferior, and the brightness inversion is severe. Therefore, the pretilt angle cannot be increased in the display area.

Therefore, according to the present invention, the pretilt angle in the display area is the same as the conventional one, a high pretilt angle area is provided outside the display area, and the twisting direction of the liquid crystal in this area is first fixed, and the twisting direction is set in this twisting direction. Following this, the liquid crystal in the display area is also twisted uniformly.The method is to inject the liquid crystal into the liquid crystal display panel and seal it, and then to use a high pretilt angle when cooling from the temperature above the transition temperature of the nematic liquid crystal. This is to gradually cool from the region so that the twist directions are aligned.

FIG. 3 is a plan view of a liquid crystal display panel, in which an upper glass substrate 5 and a lower glass substrate 6 are opposed to each other with a gap of several μm therebetween, and a sealant 8 except for a liquid crystal injection port 7. The display area 9 is provided in the center, but the display area 9 does not cover the entire area sealed by the sealant 8 but has some room in the vertical and horizontal directions. (Outside the display area) exists. Therefore, according to the present invention, a high pretilt angle region 10 is formed on this one side (the end portion in the longitudinal direction in this figure), and after the liquid crystal is injected and the annealing treatment is finished, the liquid crystal is gradually cooled from this region 10. The twisting direction of is aligned with the display area 9.

According to experiments, the high pretilt angle region 10
It was found that when the display area 9 having a low pretilt angle and the display area 9 having a low pretilt angle are too close to each other, the display area 9 close to the high pretilt angle area 10 also has a large pretilt angle and deteriorates the viewing angle characteristics.

Next, a high pretilt angle region is provided in the display panel.
As a method for producing 10, the method can be realized by either changing the type of the alignment film or changing the rubbing conditions.

Further, the chiral pitch of the chiral liquid crystal added for twisting the nematic liquid crystal in a predetermined direction generally becomes longer as the temperature rises, but for the purpose of the present invention to regulate the twisting direction, it follows the temperature rise. It is advantageous to use a material having a short chiral pitch.

[0019]

【Example】

Example 1: (Example of forming a high pretilt angle region by changing rubbing conditions) Two glass substrates having a thickness of 1.1 mm were used and the number of pixels as shown in FIG. A 10.4 inch active matrix type liquid crystal display panel was formed. Here, the high pretilt angle region 10 is formed with a width of 3 mm at a position 2 mm away from the display region 9.

Here, the alignment film is formed by using polyimide having a thickness of about 1000Å, and the number of times of rubbing with respect to this alignment film is set to 10 in the display region 9 to realize a pretilt angle of 2 °. , As for the high pretilt angle area 10 twice
A pre-tilt angle of 12 ° has been realized. The high pretilt angle region 10 was covered with a resist when the display region 9 was rubbed.

Next, the liquid crystal display panel filled with the liquid crystal is annealed at a temperature 10 ° C. higher than the transition temperature of the liquid crystal for 10 minutes, and then air is uniformly sprayed when the liquid crystal display panel is pulled out from the constant temperature bath. It was pulled out while gradually cooling from a certain direction of the high pretilt angle region.

In this way, by changing the addition amount of the chiral liquid crystal to the nematic liquid crystal and changing the chiral pitch at room temperature to 100 to 400 μm to make a liquid crystal display panel, the chiral pitch and the occurrence of defective pixels in 500 pixels are generated. The relationship between the number and the voltage (V _sat ) at which a contrast of 100 is obtained in a normally white display was investigated. The chiral liquid crystal used is a normal type in which the pitch becomes longer as the temperature rises.

FIG. 1 shows the relationship between the chiral pitch and the number of defective pixels. That is, the chiral pitch is changed by changing the addition amount of the chiral liquid crystal to the nematic liquid crystal in the conventional structure having only the display region having the pretilt angle of 2 ° in the display panel and the embodiment 1 having the high pretilt angle region according to the present invention. When changing from 100 to 400 μm and comparing, the conventional configuration shows the tendency of the solid line 12,
To achieve uniform orientation and reduce the number of defects to 0 ~ 100 μ
While the chiral pitch of m or less is required, Example 1 shown by the broken line 13 of the white circle shows that the pitch can be increased to about 200 μm.

Further, the voltage (V _sat ) at which the contrast 100 is obtained in the normally white display is 3.5 V in the conventional configuration (chiral pitch 100 μm), whereas it is 3.
It was found that it could be reduced to 2 V (chiral pitch 200 μm). Example 2: (Example of forming high pretilt angle region by changing alignment film) A liquid crystal display panel is formed in the same manner as in Example 1 except that the high pretilt angle region is formed by using a polyimide having a different modification degree. did.

The rubbing condition is that the pushing amount is 0.3 m.
m, the number of rubbing times is 5, so that the pretilt angle in the display area is 3 ° and the pretilt angle in the high pretilt angle area is
It became 13 °. Then, as in Example 1, the amount of chiral liquid crystal added to the nematic liquid crystal was changed to change the chiral pitch to 100 to 400 μm, and the relationship with the number of defects generated was examined. The results are the same as in Example 1, and no occurrence of the reverse twist region was observed up to the chiral pitch of 200 μm.
We were able to achieve _sat = 3.2 V. Example 3: (Example of forming high pretilt angle region by changing chiral liquid crystal and rubbing condition) Example 1 except that a chiral liquid crystal added to nematic liquid crystal whose chiral pitch becomes shorter as temperature rises. A liquid crystal display panel was formed in the same manner as in. Then, the chiral pitch was changed to 100 to 400 μm at room temperature, and the relationship between the chiral pitch and the number of defective pixels in 500 pixels and the voltage (V _sat ) at which a contrast of 100 was obtained in normally white display were investigated. It was Here, the chiral pitch at the transition temperature of liquid crystals with a chiral pitch of 300 μm at room temperature (75 ° C for this material) is as short as ~ 130 μm.

The dashed-dotted line 14 in FIG. 1 shows the result of Example 3. V _sat = 3.0 V could be realized without the occurrence of the reverse twist region up to the chiral pitch of 300 μm.

[0027]

According to the present invention, it is possible to drive at a low voltage without impairing the display quality by implementing the present invention, and it is possible to expand the applications of the liquid crystal display panel.

[Brief description of drawings]

FIG. 1 is a relationship diagram between a chiral pitch and the number of defective pixels in a liquid crystal display panel.

FIG. 2 is a TV characteristic diagram showing a viewing angle characteristic of a pretilt angle.

FIG. 3 is a plan view of a liquid crystal display panel.

[Explanation of symbols]

 5,6 Glass substrate 9 Display area 10 High pretilt angle area

Claims (4)

[Claims] 1. A liquid crystal display panel adopting a TN display system, wherein a region having a larger pretilt angle than an inner side is provided outside one side of a display region forming the liquid crystal display panel. 2. Injecting liquid crystal into the liquid crystal display panel according to claim 1, performing annealing treatment at a temperature equal to or higher than the transition point of the liquid crystal, and then cooling from a region having a large pretilt angle outside the display region. A method for manufacturing a liquid crystal display panel, comprising: 3. The method of manufacturing a liquid crystal panel according to claim 2, wherein the formation of the region having a large pretilt angle is caused by changing a rubbing condition of the alignment film or a kind of the alignment film. 4. The method for manufacturing a liquid crystal panel according to claim 2, wherein a liquid crystal of a type in which the chiral pitch becomes shorter as the temperature rises is used as the chiral liquid crystal forming the TN liquid crystal.