JP2002040438A - Liquid crystal display device and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device in which display failure such as image persistence phenomenon and white (black) dots is prevented. SOLUTION: In the liquid crystal display device having color layers (3, 4, 5) formed on one substrate, alignment films (11, 13) consisting of polyimide and formed on the color layers (3, 4, 5), the other substrate opposing to the face of the first substrate where the alignment films (11, 13) are formed, and a liquid crystal layer (10) disposed in the gap between the first substrate and the other substrate, the imidization degree of the alignment films (11, 13) differs along the thickness direction.

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 having a colored layer and a method of manufacturing the same.

[0002]

2. Description of the Related Art A liquid crystal display device comprises two electrode substrates each having an alignment film, with the alignment films facing each other, and a liquid crystal layer sandwiched between the two substrates.
The two electrode substrates are bonded together by a sealing material and a sealing material arranged in a peripheral region. In order to maintain a distance between the two substrates, a granular spacer or a photo-spray is dispersed. Spacer pillars made of resin formed by lithography are arranged.

When a liquid crystal display device displays a color image,
In many cases, red (R), green (G),
A colored layer made of blue (B) is provided.

[0004]

However, in the above-mentioned liquid crystal display device, display unevenness such as burn-in may occur. In addition, white (black) spots sometimes occurred due to moisture.

[0005] The present invention has been made under such circumstances,
An object of the present invention is to provide a liquid crystal display device in which display defects such as burn-in and white (black) spots are prevented.

Another object of the present invention is to provide a burn-in or white (black) image.
An object of the present invention is to provide a method for manufacturing a liquid crystal display device in which display defects such as blurs are prevented.

[0007]

In order to solve the above-mentioned problems, the present invention provides a colored layer formed on one substrate, an alignment film made of polyimide formed on the colored layer,
A liquid crystal display device comprising: the other substrate disposed so as to face a surface of the one substrate on which the alignment film is formed; and a liquid crystal layer disposed in a gap between the one substrate and the other substrate. The present invention also provides a liquid crystal display device, wherein the imidation ratio of the alignment film differs in the thickness direction.

The present invention also relates to a method of manufacturing a liquid crystal display device as described above, wherein the alignment film material is heat-treated by increasing the temperature stepwise to form an alignment film. Provide a way.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS According to the study of the present inventors, display unevenness such as image sticking is caused by the fact that a specific component in a colored layer remains unreacted or an impurity contained in a colored layer is removed.
As a result of being eluted in the liquid crystal layer, it was found to be generated. Therefore, it is possible to suppress the occurrence of display unevenness unless the substances causing these factors are eluted in the liquid crystal layer.

[0010] On the other hand, white spots or black spots are defects caused by invasion from the outside or hydrolysis of the alignment film by water contained in the liquid crystal. This defect can be suppressed by preventing the alignment film from being hydrolyzed by moisture.

The present inventors have found that such display unevenness is closely related to the imidization ratio of the polyimide alignment film. Here, FIG. 1 shows the results obtained by examining the imidation ratio of the polyimide alignment film and the degree of occurrence of image sticking and white (black) spots.

The imidation ratio of the polyimide alignment film is:
NMR method, that is, H-NMR with d-DMSO solution
Is measured, and the aromatic proton and COOH calculated from the ratio of the aromatic proton to the residual COOH proton and the theoretical structure are used.
It was calculated from the ratio with proton.

From FIG. 1, it can be seen from FIG. 1 that when the imidation ratio of the polyimide alignment film is low, seizure hardly occurs and white (black) smears easily occur, whereas when the imidization ratio is high, white (black) smears occur. It can be seen that it is difficult to cause seizure. In other words, when the defective causative substance is caused by the coloring layer material or the like, a lower imidization rate is more effective, and when the defective causative substance is caused by moisture or the like, a higher imidization rate is more effective. It can be said that there is.

Therefore, the present inventors examined the degree of occurrence of defects by changing the imidation ratio of the polyimide constituting the alignment film in the thickness direction of the alignment film. Specifically, the imidization ratio was high on the alignment film surface and low on the bottom. As a result, generation of both image sticking and white (black) spots could be suppressed. The present invention has been made based on such findings.

FIG. 2 is a characteristic diagram showing the relationship between the heat treatment time and the imidization ratio at various heat treatment temperatures of polyimide. From FIG. 2, it can be seen that the higher the heat treatment temperature is, the higher the imidization ratio is obtained. At any heat treatment temperature, the imidation ratio is saturated in a short time of about 15 minutes, so that the imidation ratio is 15 minutes. It can be seen that the imidization ratio corresponding to the heat treatment temperature can be obtained by the above heat treatment time.

Thus, the present inventors can gradually increase the imidation ratio near the surface by increasing the heat treatment temperature stepwise, while increasing the heat treatment time near the bottom for a long time. If not, the temperature does not reach the heat treatment temperature, so that it has been found that the imidization ratio can be kept low.

As described above, by gradually increasing the heat treatment temperature, the imidization ratio of the polyimide constituting the alignment film can be made lower on the substrate side, higher on the liquid crystal layer side, and different in the thickness direction. As described above, according to the present invention, since the imidation ratio of the polyimide constituting the alignment film is different in the thickness direction, both display defects such as image sticking and white (black) spots are effectively prevented. It is possible.

Hereinafter, embodiments of the present invention will be described. FIG. 3 is a sectional view schematically showing a liquid crystal display device according to one embodiment of the present invention. In the liquid crystal display device shown in FIG. 3, an array substrate (color filter substrate) 2 and a counter substrate 9 are arranged to face each other. Are held, and the liquid crystal layer 10 is sandwiched.

The array substrate 2 and the counter substrate 9 are adhered to each other by a seal 8 arranged so as to surround the outer periphery of the substrate except for a liquid crystal injection port (not shown), and a sealing material (not shown) is provided at the liquid crystal injection port. Is applied. As a sealing material, a thermosetting epoxy adhesive was used.

The opposing substrate 9 is constituted by sequentially providing a transparent electrode 12 made of ITO and an alignment film 13 on a transparent substrate. On the array substrate 2, signal lines and scanning lines are arranged so as to intersect with each other.
Are formed, and a pixel electrode 6 connected to this switching element is arranged. The green colored layer (G) 4 and the blue colored layer (B) cover the switching element 1.
5. Red colored layers (R) 3 are arranged in a stripe shape.

The pixel electrode 6 is disposed on the colored layers 3, 4, and 5, and is connected to a switching element via through holes (not shown) formed in the colored layers 3, 4, and 5. ing. Further, an alignment film 11 is disposed on the entire surface of the substrate so as to cover the pixel electrode 6 and the coloring layers 3, 4, and 5.

Next, the manufacturing process of the liquid crystal display device shown in FIG. 2 described above will be described. First, a manufacturing process of the array substrate 2 will be described. In the same manner as in a normal process, film formation and patterning are repeated on a glass substrate to form a switching element 1 composed of a thin film transistor and an electrode wiring.

Next, as a red coloring material, an ultraviolet curable acrylic resin resist in which a red pigment is dispersed is applied by a spinner to the entire surface of the substrate on which the switching elements 1 and the electrode wirings are formed.

Next, light having a wavelength of 365 nm is irradiated at a dose of 100 mJ / cm ² through a photomask that irradiates light to a portion where a red coloring layer is to be formed.
Develop with a 1% aqueous solution of KOH for 10 seconds to form a red colored layer 3 on that portion. Similarly, a green coloring layer 4 and a blue coloring layer 5 are formed.

After that, an ITO film as a pixel electrode 6 is
A film was formed to a thickness of 00 ° by a sputtering method and patterned by a photolithography method. Then, S as an alignment film material
E-7492 (trade name: manufactured by Nissan Chemical Co., Ltd.) is applied to the entire surface to a thickness of 500 °, and is applied at 150 ° C. for 20 minutes for 180 minutes.
After firing at 10 ° C. for 10 minutes and at 220 ° C. for 5 minutes, rubbing treatment was performed to form an alignment film 11.

At this time, the imidation ratio of the alignment film is 99% or more from 50 ° to the film surface and 80% from 200 ° to 250 °.
%, And 400% to 60% at 60%. Next, as a method for manufacturing the counter substrate 9, an ITO film was formed as a transparent electrode on a glass substrate to a thickness of 1500 ° by a sputtering method.
After an alignment film material was similarly formed thereon, a rubbing treatment was performed to form an alignment film 13.

Thereafter, a seal 8 is printed on the periphery of the array substrate 2 except for the liquid crystal injection port, and an electrode transfer material for applying a voltage from the array substrate 2 to the counter substrate 9 is provided around the seal 8. Formed on top.

Next, the array substrate 2 and the counter substrate 9 are arranged so that the respective alignment films face each other and the rubbing direction of each alignment film is 90 degrees, and the seal 8 is cured by heating. , Stuck together.

Next, the liquid crystal composition 10 was injected from the injection port by a usual method, and then the injection port was sealed with an ultraviolet curable resin to complete a liquid crystal display device.

The liquid crystal display device thus manufactured was subjected to a continuous lighting test under a condition of high temperature and high humidity (50 ° C., 80%) for 1000 hours, but there was no display unevenness and good display quality. Was able to be secured.

In the above-described example, granular spacers are scattered on the substrates as spacers for keeping a constant distance between the two substrates. However, a resin layer is applied on the substrates in a predetermined thickness. Alternatively, one obtained by patterning into a predetermined shape can be used as a spacer. In this case, as the resin layer, a method in which the above-described colored layers are stacked and formed, or a transparent or black material can be used separately from the colored layers. These can be formed by using a photosensitive material or, in the case of a non-photosensitive material, etching by using a photosensitive resist as a mask.

[0032]

As described above in detail, according to the present invention, the elution of impurities from the inside of the alignment film to the liquid crystal layer is suppressed by varying the imidation ratio of the alignment film in the thickness direction. In addition, since hydrolysis of the alignment film due to moisture in the liquid crystal layer can be suppressed, burn-in or white (black) occurs.
It is possible to effectively prevent display unevenness such as blemishes.

[Brief description of the drawings]

FIG. 1 is a characteristic diagram showing the dependence of a defect on the imidation rate.

FIG. 2 is a characteristic diagram showing a relationship between a heat treatment time and an imidization ratio of polyimide at various heat treatment temperatures.

FIG. 3 is a longitudinal sectional view showing a liquid crystal display device according to one embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Switching element, 2 ... Array substrate, 3 ... Color layer (red), 4 ... Color layer (green), 5 ... Color layer (blue), 6 ... Pixel electrode 7 ... Spacer, 8 ... Seal, 9 ... Counter substrate , 10: liquid crystal composition, 11, 13: alignment film. 12 ... transparent electrode,

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Takeshi Yamamoto 1-9-2, Hara-cho, Fukaya-shi, Saitama F-term inside the Toshiba Fukaya Plant (reference) 2H090 HB08Y LA04 LA15 MA06 MB01 MB13 2H091 FA02Y GA06 GA13 LA15 LA16

Claims (5)

[Claims] A color layer formed on one of the substrates; an alignment film made of polyimide formed on the color layer; and a facing surface of the one substrate on which the alignment film is formed. A liquid crystal display device having a liquid crystal layer disposed in a gap between the one substrate and the other substrate, wherein the imidation ratio of the alignment film is different in a thickness direction. Liquid crystal display device. 2. The method according to claim 1, wherein the imidization ratio is higher on the liquid crystal layer side.
The liquid crystal display device according to claim 1, wherein the liquid crystal display device has a lower color layer side. 3. The liquid crystal display device according to claim 1, wherein the difference between the highest part and the lowest part of the imidization ratio is 20 to 80%. 4. The method for manufacturing a liquid crystal display device according to claim 1, wherein the alignment film material is heat-treated by increasing the temperature stepwise to form an alignment film. Method. 5. The method according to claim 4, wherein the temperature is increased stepwise within a range of 150 ° C. to 300 ° C.