JPH04125521A - Production of liquid crystal display device - Google Patents

Abstract

PURPOSE:To obtain the orientation slightly inclined in a specified direction from a perpendicular direction uniformly over the entire surface of a large screen with high productivity by applying polyamic acid solns. on respective substrates, then subjecting the coatings to imidization treatments dividedly to two stages and executing rubbing operations during this time. CONSTITUTION:The raw materials (polyamic acid solns.) of the oriented films 15A, 15B of polyimide exhibiting perpendicular orientation are applied on the glass substrates 11A, 11B formed with patterned transparent electrodes 13A, 13B and are dried. The imidization rate of the thin films of the polyamic acid formed in such a manner is thereafter increased by the 1st imidization (imidization I). These oriented films are then subjected to the rubbing operations. The imidization rate of the oriented films is again increased by the 2nd imidization II after the rubbing operations to complete the formation of the oriented films. The imidization treatments I, II for improving such imidization rate are generally executed by heating. The pretilt angle decreased by the rubbing operations is restored by the 2nd imidization and the high pretilt angle (>88 deg.), namely, the angle of inclination of liquid crystal molecules is decreased.

Description

[Detailed Description of the Invention] [Summary] Regarding a method for manufacturing a liquid crystal display device, a rubbing method, which is usually used for horizontally aligned alignment films, is applied to a vertically aligned polyimide alignment film, and the rubbing method is applied to a vertically aligned polyimide alignment film. The aim is to uniformly and highly productively achieve an orientation slightly tilted in a certain direction (88°, pretilt angle < 90°) across a large screen, and each has a predetermined pattern of transparent electrodes and vertical alignment. When manufacturing a liquid crystal display device in which a liquid crystal is sandwiched between two substrates, at least one of which is transparent, having a polyimide alignment film, after applying a polyamic acid solution, which is a precursor of the polyimide alignment film, to each substrate, The imidization process is performed in at least two stages, and the rubbing operation is performed between the first imidization process and the second imidization process.

: Industrial application field] The present invention relates to a method for manufacturing a liquid crystal display device.

In recent years, display devices in which liquid crystal molecules are aligned in the homeotropic direction (vertical direction) have been attracting attention as a simple matrix method capable of increasing capacity. The orientation of the liquid crystal molecules required for this display method is not completely perpendicular to the substrate, but rather an orientation that is very close to perpendicular, yet slightly tilted in a certain direction from the perpendicular direction. There is a need.

Incidentally, the tilted arrangement is used for the purpose of lowering the threshold voltage at which liquid crystal molecules begin to tilt when responding to an electric field in a liquid crystal display device, and for the purpose of uniformly aligning the directions in which the liquid crystal molecules tilt to prevent reverse tilt.

[Conventional technology]

Conventionally, in order to obtain such an orientation slightly tilted from the vertical direction to a certain direction, SiO was deposited on the substrate in an oblique direction.
A method that has been widely used is to create a large number of small inclined planes that are slightly inclined with respect to the substrate surface, and then apply a vertical alignment agent to the inclined planes to achieve vertical alignment (for example, Matsumoto et al. , co-authored with Tsunoda: Latest Technology of Liquid Crystals (Kogyo Kenkyukai, 1983)
) p. 161-162).

In addition, in the case of a liquid crystal display device such as the TN9STN system in which liquid crystal molecules are aligned in a substantially horizontal direction, a thin film of an organic polymer material such as polyimide is formed on a substrate as an alignment film, and the surface is rubbed with a cloth or the like. By using this method, liquid crystal molecules are aligned in a predetermined direction. This method has high productivity and is currently used in mass production.

[Problem to be solved by the invention]

With the SiO oblique evaporation method, which has traditionally been used as a method to slightly tilt liquid crystal molecules in a certain direction from the vertical direction, it is extremely difficult to form a minute inclined surface uniformly over the entire large screen. However, there are limits to increasing the size. Furthermore, even in the case of small screens, there is a problem in that the productivity is extremely low because vapor deposition involves vacuum operation.

Furthermore, TN and STN, which align liquid crystal molecules almost horizontally,
If the rubbing method used in this method is directly applied to a polyimide alignment film with vertical alignment, it is possible to tilt the liquid crystal molecules in the rubbing direction, but the tilt from the vertical becomes large (it is difficult to The problem arises that the pretilt angle, which is the angle formed by the substrate and the liquid crystal molecules, becomes too small (pretilt angle <85°).

The present invention uses a rubbing method, which is normally used for horizontally aligned alignment films, on a vertically aligned polyimide alignment film, and furthermore, the alignment is slightly tilted in a certain direction from the vertical direction (
The purpose is to achieve a uniform tilt angle of 88° (pretilt angle of 90°) over the entire large screen with high productivity.

[Means to solve the problem]

In order to achieve the above object, according to the present invention, a liquid crystal is sandwiched between two substrates, at least one of which is transparent, each having a predetermined pattern of transparent electrodes and a polyimide alignment film with vertical alignment. When manufacturing a liquid crystal display device, after coating a polyamic acid solution, which is a precursor of a polyimide alignment film, on each substrate, it is imidized in at least two stages. A method for manufacturing a liquid crystal display device is provided, which comprises performing a rubbing operation between the second imidization treatment.

When heating the substrate for imidization of the alignment film, is the heating temperature the same for imidization treatment before and after rubbing, or is the heating temperature for the first imidization treatment higher than that for the second imidization treatment? lower than that of

FIG. 1 shows the manufacturing process of the present invention.

A raw material (polyamic acid solution) for a polyimide alignment film exhibiting vertical alignment is applied onto a glass substrate on which a patterned transparent electrode is formed and dried. Thereafter, the imidization rate of the thin film of polyamic acid thus formed is increased by the first imidization (imidization ①). Next, a rubbing operation is performed on the second alignment film. After the rubbing loss, the imidization rate of the alignment film is increased again by the second imidization, and the formation of the alignment film is completed. The imidization treatment 1=Il of t for improving the imidization rate is generally performed by heating.

In this way, two identical substrates having the formed alignment films are made to face each other at a predetermined distance with a spacer interposed therebetween, and are bonded together using a sealing material to form a panel.

After a liquid crystal material is injected into this panel (between both layers), the injection port is sealed, and polarizing means are provided on both sides of this panel to form a liquid crystal display device.

In the present invention, when forming an alignment film exhibiting an orientation (slightly tilted in a certain direction from the vertical direction), as described above, the operation of advancing the imidization of the alignment film of polyamitsutaic acid, which is the alignment film material, is carried out in two steps ( The process is divided into imidization (1) and imidization (2), and a rubbing operation is performed between the two imidization treatment stages.

By doing this, the pretilt angle reduced by the rubbing operation is recovered by the second imidization, and the pretilt angle (>88°), that is, the tilt angle of the liquid crystal molecules can be reduced.

That is, as shown in FIG. 2, the pretilt angle is restored due to the change in imidization rate of the alignment film due to imidization (2). It is clear from Figure 2 that the pretilt angle, which was once reduced by the rubbing operation, is recovered by the imprint H, and the pretilt angle becomes high.
) pretilt angle (pretilt angle>88°) is obtained.

Embodiment 2 FIG. 3 shows the basic structure of a liquid crystal display device manufactured according to an embodiment of the present invention. This liquid crystal display device consists of a pair of identical glass substrates 11A and IIB, and transparent electrodes 13A and 1 of a predetermined pattern are formed on one side of each of the substrates facing each other.
3B, and overlapping alignment films 15A and 15B are formed thereon, respectively. A nematic liquid crystal 10 is filled between both vertical alignment films 15, A, and 15B, and linear polarizing plates 19 are arranged perpendicularly to each other on both sides of the cell. Complete by attaching 19B to.

Note that 17 is a spacer that also serves as a sole material for separating both substrates 11A, 11B by a predetermined distance.

Transparent electrodes 13A, 13B are formed on glass substrates 11A, 11B by sputtering and patterned. After that, a vertically aligned polyimide material (Nichikagaku: R
'W-722) is applied on one side of the substrate. Then, the solvent was dried at 80°C and heated at 170°C for 10 minutes (
Imidization I). Next, a rubbing operation (liquid crystal molecules become more inclined in the rubbing direction) is performed using a special cloth according to a well-known method, followed by heating at 170°C for 60 minutes (
Imidization ■). Vertical alignment film 15 formed in this manner. A pair of glass substrates having A-15B are made to face each other with a spacer 17 in between and bonded together to form a panel, and after injecting the liquid crystal material 10, the injection port is sealed. Two polarizing plates 19A and 19B are attached to both outer surfaces of this panel so that the rubbing direction of the alignment film and the polarization direction of the polarizing plate form an angle of 45° to form a liquid crystal display device.

Figure 2 shows the experimental results, showing the first imidization.
Although a pretilt angle (substantially vertical) of approximately 90° is obtained by this, the pretilt angle decreases to nearly 80′ due to the rubbing process. As mentioned above, rubbing (although productivity is high, there is a problem that the pretilt angle decreases. Therefore, according to the present invention, by performing the second imidization (heating), the pretilt angle is approximately 89°. recover to.

It should be noted that the heating temperature for the first imidization 1 and the second concave imidization (■) may be the same, but it has been confirmed that it is more effective if the heating temperature is higher for the second time. It was done.

Further, according to the present invention, the imidization treatment may be divided into two or more times depending on the number of times of rubbing, and in any case, the imidization treatment (heating) may be performed again after the rubbing treatment. Imidization treatment is generally performed by heating, but is not limited to this).

C. Effects of the Invention] As explained above, according to the present invention, a liquid crystal display device in which liquid crystal molecules are aligned in the homeotropic direction, is slightly tilted in a certain direction from the vertical direction (tilt angle 2). ° or less) Very high) Pretilt angle (88°Pretilt angle <
90°) can be achieved evenly and with high productivity over a large screen by highly productive rubbing.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the manufacturing process of the liquid crystal display device of the present invention, and FIG. 2 is a graph of experimental results showing that the pretilt angle is recovered by changing the imidization rate of the alignment film during the second imidization. , FIG. 3 is a cross-sectional view showing an example of a liquid crystal display device obtained by Kokito. 10... Nematic liquid crystal layer, 11A, 11B... Glass substrate, 13A, 13B... Transparent electrode, 15A45B... Vertical alignment polyimide alignment film. Fig. Imidization rate-pretilt angle characteristic diagram Fig. 2 Basic configuration of a liquid crystal display device Fig. 3 10...? Matic liquid crystal layer +1A, I old...Glass substrate 13A, +38...Transparent electrode 15A, 158...Vertical alignment polyimide alignment film

Claims (1)

[Claims] 1. Transparent electrodes each having a predetermined pattern (13A, 13
B) and a polyimide alignment film with vertical alignment (15A,
15B), in which a liquid crystal (10) is sandwiched between two substrates (11A, 11B) at least one of which is transparent, a polyamic acid which is a precursor of a polyimide alignment film is placed on each substrate. A liquid crystal display device characterized in that after applying an acid solution, it is imidized in at least two stages, and a rubbing operation is performed between the first imidization treatment and the second imidization treatment. manufacturing method. 2. The manufacturing method according to claim 1, wherein when heating the substrate for imidization of the alignment film, the heating temperature is the same in the two stages of imidization treatment before and after rubbing. 3. Claim 1, wherein when heating the substrate for imidization of the alignment film, the heating temperature during imidization treatment before rubbing is lower than the heating temperature during imidization treatment after rubbing.
The manufacturing method described in.