JP2799005B2 - Manufacturing method of liquid crystal display device - Google Patents

Description

The present invention relates to a method for manufacturing a liquid crystal display device. More specifically, it relates to the improvement.

(B) Conventional technology Conventionally, as a method of forming an alignment film relating to the unidirectional horizontal alignment method of liquid crystal molecules, a spinner method in which an alignment film is formed on a substrate by using centrifugal force, a method in which a substrate is placed in an alignment film solution. There are known a dipping method in which an alignment film is formed by dipping, an offset printing method in which an alignment film solution is transferred onto a substrate by a printing machine to form an alignment film, and the like.

In addition, as a method of aligning the alignment film, a rubbing method in which a substrate on which an alignment film of silicon oxide or polyimide is formed is rubbed in one direction using a brushed or planted cloth, and silicon oxide is vacuum-deposited on the substrate obliquely In general, an oblique deposition method or the like for growing in a specific direction is used.

In addition to the above, Lang using a polymer compound
There are known alignment methods such as a method of forming an alignment film by pulling up a muir-blodgett (LB) film and rubbing the formed alignment film, and applying a magnetic field to the alignment film formed by pulling up the LB film.

(C) Problems to be Solved by the Invention However, it is difficult to reduce the thickness of the alignment film to 500 ° or less by the spinner method, the dipping method, or the offset printing method, which is the above-described method for forming the alignment film. As the film thickness increases, the insulating property increases, and a voltage drop occurs, and the voltage applied to the liquid crystal decreases.

Further, it is difficult to make the film thickness uniform by the above-described method for forming an alignment film. When the film thickness is non-uniform as described above, a voltage difference occurs in the same substrate when an electric field is applied, which causes display unevenness.

On the other hand, in the alignment treatment of the alignment film described above, in the rubbing method, in the case of a large-area, high-definition substrate, unevenness of the rubbing pressure due to unevenness on the substrate is likely to occur. Above, due to the thickness of the gate electrode, the source electrode, the non-linear element, etc., a step is formed with respect to the plane of the substrate, and the rubbing strength in the shadow of the step becomes weak. In addition, uneven rubbing pressure also occurs due to the difference in the thickness of the substrate. These pressure irregularities adversely affect the display as the alignment irregularities of the liquid crystal molecules.
Further, in the rubbing method, the cloth fiber and the impurities contained in the cloth adhere to the alignment film due to contact with the cloth, thereby changing the characteristics. Therefore, cleaning after the alignment treatment is indispensable, and a large amount of a cleaning solvent is required. . Furthermore, in a liquid crystal display element having a non-linear element array such as a TFT and a MIM, static electricity is generated due to friction at the time of rubbing, and the semiconductor switching element may be destroyed.

On the other hand, the oblique deposition method has a problem that the growth direction of the attached silicon oxide crystal spreads in a fan shape, and flakes are generated to cause uneven alignment.

Furthermore, a method of depositing a plurality of monomolecular layers (LB films) of a polymer compound on a substrate and aligning the liquid crystal molecules in parallel with the pulling direction of the substrate does not provide a sufficient alignment regulating force, and also increases the pretilt angle. You can't get it. In the above method of rubbing an alignment film composed of an accumulated LB film, the LB film is extremely thin and has weak adhesion to a substrate, so that the film may be broken by fiber contact during rubbing. Further, a method of applying a magnetic field to an alignment film formed from the LB film as a cumulative film does not provide a sufficient alignment force as a liquid crystal display device.

The present invention has been made in view of such a situation, and an object of the present invention is to provide a method of manufacturing a liquid crystal display device capable of forming an alignment film having a uniform thickness, no contamination, and no accumulation of static electricity and the like.

(D) Means for Solving the Problems According to the present invention, a pair of substrates on which an alignment film for aligning liquid crystal in a predetermined direction is formed, with the alignment film-forming surface facing the pair, In the method for manufacturing a liquid crystal display device, wherein a predetermined voltage can be applied between the substrates, the alignment film is formed by laminating at least one monomolecular layer of a polymer compound on the substrate. Is formed, and the accumulated film is polymerized as necessary.At least a part of the resulting accumulated film is accelerated and electrically neutralized to contain ionic particles containing neutral atoms. And a method for manufacturing a liquid crystal display device, wherein the liquid crystal display device is formed by performing an alignment treatment by irradiating light from above.

In the method of the present invention, a substrate commonly used in the art can be used as it is, and a transparent glass substrate is preferable. An electrode corresponding to a predetermined display pattern is formed on the substrate.

In the method of the present invention, an alignment film is formed on the substrate. The alignment film is composed of a monomolecular layer of a polymer compound (hereinafter referred to as an LB film). The polymer compound may be any one that forms an LB film and is commonly used in the art.For example, it is obtained from a polyamic acid and a long chain alkylamine compound having hydrophobicity. Is preferred. The accumulation film is obtained by depositing a plurality of the LB films. The LB film can be formed by an LB film forming apparatus known in the art. When an LB film is formed by the above apparatus, film forming conditions are selected from the relationship between the area of the film spread on the water surface and the surface pressure. For example, the surface pressure is 4
The range of 3535 mN / m is preferred. That is, if it is less than 4 mN / m, a gap is generated between molecules, and if it is more than 35 mN / m, the film may be broken, which is not preferable. When the film is used as a liquid crystal alignment film, the film is formed by a method of pulling up the substrate perpendicularly to the water surface within the range of the liquid film. In this way, an LB film is obtained on the substrate. By accumulating and depositing such a lifting operation several times, a predetermined accumulated film is obtained. However,
In the formation of the cumulative film, it is necessary to dry the first LB film after the formation.

In the method of the present invention, the alignment film comprising the above-obtained cumulative film is subjected to polymerization, if necessary. That is, when the cumulative film obtained above is partially obtained from a precursor before polymerization, it is necessary to complete the polymerization. For example, when the monomolecular layer has a polyamic acid derivative as a constitutional unit, it is necessary to polymerize it into an imide compound.

In the method of the present invention, the accumulative film obtained above is irradiated with accelerated particles on at least a part of its surface. This irradiation is performed from a specific direction. The above-mentioned specific direction is preferably an oblique direction parallel to the pulling-up direction at the time of the film formation from the viewpoint of uniformity of orientation. Specifically, reference is made to the description of the embodiment described later.
The accelerated particles may be charged particles or electrically neutral particles. The charged particles include ions. A device known in the art is used for the irradiation of the particles. When ions are used as the accelerated particles in the present invention, an ion beam irradiation device can be used. Further, when the cumulative film in the above ion irradiation is an insulating film such as polyimide,
It is a preferred embodiment of the present invention to electrically neutralize the charge due to ion irradiation. For this specific example, reference is made to the description of the embodiment described later.

(E) Function According to the present invention, an alignment film composed of a thin and uniform cumulative film is formed on a substrate. An alignment treatment is performed without contaminating the surface of the alignment film by a non-contact method of irradiating the alignment film with particles accelerated from a specific direction.

Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited thereto.

(F) Examples Sanever 11 which is a commercially available polyamic acid for liquid crystal alignment
0 (trade name; manufactured by Nissan Chemical Industries, Ltd.) is diluted to 1 mmol / per polyamic acid repeating unit using a mixed solvent of N-methylpyrrolidone and benzene (1: 1). An N, N-dimethyl-n-hexadecylamine solution of the same concentration and the same solvent is added so as to be twice equivalent to the repeating unit of the polyamic acid to prepare a polyamic acid alkylamine salt solution.

Using this solution, an LB film of a polyamic acid alkylamine salt solution was formed on the substrate by using an LB film having the structure shown in FIG. In the figure, 1 is a water tank, 2
Is a partition plate, 3 is a substrate, 4 is a lifting machine, 5 is a Wilhelmi plate, 6 is a film pressure gauge, 7 is ion-exchanged water, and 8 is LB.
The film 9 is an LB film adhered on the substrate.

The LB film 8 of the polyamic acid alkylamine salt solution is heated to 20 ° C.
The LB film 8 spreads on the ion-exchanged water 7, which is spread on the surface of the ion-exchanged water 7, and the pressure is applied by the partition plate 2 provided in the water tank 1. And the correlation between the pressure and the surface pressure (π) were examined. The result is shown in FIG. From the figure, it was found that a good π-A curve was obtained, and a liquid film was obtained when the surface pressure was in the range of 4 to 20 mN / m. The area occupied by the polymer per repeating unit is
It was 1.1nm ^2. Further, it was found that when the surface pressure exceeded 35 mN / m, the film was broken, and when the surface pressure was less than 4 mN / m, the gap between the molecules was as small as possible, which was unfavorable for film formation. When used as a liquid crystal alignment film, the solid film in the range of 20 to 35 mN / m in the π-A curve of FIG.
The molecules are densely packed in the LB film, and it is difficult to cause alignment parallel to the pulling direction when pulling up the substrate, and the alignment regulating force of the liquid crystal molecules is reduced. Therefore, the conditions for forming the LB film are preferably such that the LB film is formed in the range of the liquid film. In this case, the substrate was pulled up perpendicular to the water surface while maintaining the surface pressure of 15 mN / m to obtain the LB film. This process was repeated five times to form a five-layered cumulative film on the substrate (however, after the initial LB film formation, the film was left to dry for 30 minutes after the film formation was completed to enhance the adhesion between the substrate and the LB film). This work was not performed from the second time onward.)

Substrate as a display electrode on a transparent glass substrate
What partially formed ITO (indium-tin oxide) was used. Further, the lifting speed of the substrate was set to 10 mm / min.
It should be noted that there was no significant change in the film thickness or orientation of the formed film even when the lifting speed was increased to 10 cm / min. However, 5mm / mi
At a pulling speed of n or less, the alignment regulating force at the time of pulling was extremely weak.

Next, the substrate on which the cumulative film was formed was treated with acetic anhydride-pyridine-
After immersion in a mixed solution of benzene (1: 1: 3) at 20 ° C. for 12 hours to desorb long-chain alkyl groups and complete imidization, the mixture was left under a vacuum of 1 × 10 ⁻³ Torr for 12 hours. The imidization accelerator was removed. The thickness of the polyimide thus obtained is 20
Å was extremely thin and uniform.

Next, on the substrate on which the polyimide alignment film was formed in the above process, the substrate was irradiated with accelerated particles from an oblique direction using an ion beam irradiation apparatus having the structure shown in FIG. In the figure, 11 is an AC power supply, 12 is a plasma generator,
13 is an acceleration electrode, 14 is an extraction electrode, 15 is a ground electrode, 16
Is a bell jar, 17 is a substrate fixing device, 18 is a substrate, 19 is a mask, 20 is a neutralizing filament, 21 is a gas flow control device,
Reference numeral 22 denotes a gas cylinder for introduction, 23 denotes a cock, and 24 denotes a vacuum pump.

The substrate 18 was mounted on a substrate fixing device 17 and fixed at an appropriate angle with respect to the irradiation direction of the accelerated particles. After the inside of the bell jar 16 is reached to a degree of vacuum of 1 to 2 × 10 ⁻⁵ Torr using the vacuum pump 24, argon, krypton, xenon,
A gas such as oxygen is passed through the gas flow control device 21 through a bell jar.
The gas introduced by the plasma generator 12 is introduced into the plasma generator 16 at a pressure of 1 to 10 × 10 ⁻⁴ Torr,
A voltage of about 100 to 500 V was applied to the accelerating electrode 13 to give kinetic energy to the generated ions and irradiate the alignment film. At this time, the orientation uniformity of the light irradiated from the oblique direction parallel to the oblique direction parallel to the pulling direction of the substrate during the LB film formation is better Showed good results. In addition, since an insulating film such as polyimide is charged by ion irradiation, the neutralizing filament 20 emits thermoelectrons to neutralize the ions.

Using the substrate thus formed, a TN cell having a cell thickness of 5 μm as shown in FIG. 4 was produced. In the figure, 31 and 32 are glass substrates, 33 and 34 are transparent electrodes,
35 and 36 are alignment films, 37 and 38 are sealing resins, 39 and 40 are spacers, and 41 is liquid crystal.

Various properties of the liquid crystal cell obtained above are shown in the following [Table 1]. Here, argon is used as a gas to be introduced, irradiation angle and irradiation time are used as parameters of irradiation conditions,
As evaluation items, alignment uniformity, pretilt angle, voltage holding ratio, and memory voltage when a DC voltage was applied were shown. The orientation uniformity was defined by the area where uniform horizontal orientation was obtained. (In this table, ◎ indicates perfect uniform orientation, and the area in which the orientation is ○ or Δ will be reduced.
Indicates that it is not oriented).

The pretilt angle is required to be at least 0.5 ° or more, and if it is too small, disclination occurs because the liquid crystal molecules do not rise in one direction when voltage is applied.

The voltage holding ratio is related to the display contrast at the time-division driving, and the larger the value, the greater the contrast. However, a value of about 95% provides a sufficiently practical contrast.

The memory voltage at the time of applying a DC voltage is an index mainly for display quality in an active matrix type liquid crystal display device having a non-linear element array, and the flicker phenomenon when an asymmetric waveform voltage is applied to liquid crystal molecules is applied. The lower the value, the higher the display quality. This value has a correlation with the film thickness of the alignment film, and the smaller the film thickness, the smaller the value. Here is a rectangular wave of ± 3V30Hz
An applied voltage for eliminating flicker after applying a DC voltage of 2 V for 30 minutes was defined. This value is obtained by forming an alignment film on a polyimide by spinner method, dipping method, offset printing method, etc., and performing alignment treatment by rubbing method.
0.8 V, about 2 V when silicon oxide is rubbed, and about 2 V when silicon oxide is obliquely deposited.

As shown in the above [Table 1], an LB film of a polyamic acid alkylamine salt solution was deposited on the substrate of the above example,
A polyimide film is formed by imidation, and the particles further accelerated are 40 to 80 with respect to the normal direction of the substrate.
By using the alignment method in which the liquid crystal molecules are horizontally aligned in one direction by irradiating in the range of ゜, a liquid crystal element having extremely high display quality can be obtained in both the simple matrix type and the active matrix type.

When the liquid crystal molecular alignment method of the present invention was applied to an active matrix type liquid crystal display device having a TFT,
No change in TFT characteristics before and after irradiation, no disconnection or short circuit of the bus line, and no alignment unevenness due to steps were observed.

(G) Effects of the Invention According to the present invention, it is possible to form an alignment film having a uniform thickness, no contamination, and no accumulation of static electricity and the like, without being affected by the thickness and unevenness of the surface of the substrate. A stable liquid crystal display device can be obtained. In either case of a simple matrix type or an active matrix type, a liquid crystal display device having extremely high display quality can be obtained.

[Brief description of the drawings]

FIG. 1 is an explanatory view of the structure of an LB film forming apparatus used for forming an alignment film in one example of the method of the present invention, and FIG. 2 is a graph showing the relationship between the area of the film developed on the water surface and the surface pressure in the apparatus of FIG. FIG. 3 is a graph showing the relationship, FIG. 3 is an explanatory view of a configuration of an ion beam irradiation apparatus used for forming an alignment film in an example of the method of the present invention, and FIG. 4 is an explanatory view of an example of a liquid crystal cell obtained by the method of the present invention. FIG. 1 ... water tank, 2 ... partition plate, 3,18 ... substrate, 4 ... pulling machine, 5 ... Wilhelmi plate, 6 ... membrane pressure gauge, 8,9 ... LB film, 11 ... AC Power supply, 12 Plasma generator, 13 Accelerating electrode, 17 Substrate fixing device, 19 Mask, 20 Neutralizing filament, 21 Gas flow controller, 24 Vacuum pump, 31 32, glass substrate, 33, 34 transparent electrode, 35, 36 alignment film, 37, 38 sealing resin, 39, 40 spacer, 41 liquid crystal.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-1-161314 (JP, A) JP-A-64-77022 (JP, A) JP-A-59-182969 (JP, A) JP-A-63-163 318059 (JP, A)

Claims (1)

(57) [Claims] 1. A pair of substrates on which an alignment film for aligning a liquid crystal in a predetermined direction is disposed, with the alignment film forming surfaces facing each other,
In the method of manufacturing a liquid crystal display device, wherein a liquid crystal is interposed therebetween and a predetermined voltage can be applied between the substrates, the alignment film is formed by laminating one or more monomolecular layers of a polymer compound on the substrate. After forming a cumulative film and polymerizing the cumulative film as needed, at least a portion of the resulting cumulative film is accelerated and electrically neutralized with ionic particles containing neutral atoms containing neutral atoms. A method for manufacturing a liquid crystal display device, wherein the liquid crystal display device is formed by performing an alignment treatment by irradiating from an oblique direction.