JPH09281495A - Liquid crystal display panel and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the failure of oriented films by rubbing treatment, etc., by smoothing the surfaces of these oriented films. SOLUTION: This process comprises forming transparent electrodes 6, 7 on the opposite sides of substrates 4, 5, forming the oriented films 8, 9 subjected to the orientation treatments covering these electrodes and sealing a liquid crystal material 11 between the substrates. The liquid crystal display panel is produced by using the process for production having a stage for smoothing the ruggedness existing on the oriented films at this time. As a result, the failure of the oriented films 8, 9, the remaining of splinters and the flawing by the splinters are lessened.

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 panel used for color televisions, computer terminals, etc., and a method for manufacturing the same. More specifically, the present invention relates to a liquid crystal display panel that operates in a super twisted nematic (hereinafter referred to as STN) mode and a manufacturing method thereof.

[0002]

2. Description of the Related Art Currently, liquid crystal display panels are used in many fields such as car navigation systems, computer terminals, color televisions, etc., because they are characterized by low voltage, low power consumption and thin and light weight. The driving method of the liquid crystal display panel is roughly classified into an active matrix method and a simple matrix method.

The active matrix system uses one pixel for each pixel.
Each of them has a panel structure in which a switching element such as a thin film transistor (TFT) is attached, and shows high-speed response, high contrast, and excellent display characteristics, and is often used in color televisions and the like that require high image quality. However, since the panel structure is complicated, there is a problem that the manufacturing cost is high.

On the other hand, the simple matrix system has a display characteristic that is inferior to that of the active matrix system, but is characterized by a simple panel structure and low manufacturing cost. However, in recent years, high-speed response represented by multiple simultaneous selection method,
By introducing a driving method that achieves high contrast, improving the characteristics of liquid crystal materials, and optimizing cell parameters, we have achieved display characteristics that are cheaper than the active matrix method and that can support moving images. Against this background, there is an increasing demand for higher image quality in the simple matrix method.

STN driven by this simple matrix method
FIG. 4 is a schematic diagram of the configuration of the liquid crystal display panel using the mode.
Shown in The liquid crystal cell 1 is sandwiched by a pair of upper and lower polarizing plates 2 ′ and 3 ′. On the inner surface of the upper substrate 4, I
A transparent electrode 6 made of TO or the like is formed by patterning, and an alignment film 8 is applied to the surface thereof. Alignment film 8
Is subjected to an alignment treatment for aligning liquid crystal molecules in a specific direction by rubbing treatment or the like. Similarly, the transparent electrode 7 is also patterned on the inner surface of the lower substrate 5, and the alignment film 9 is applied to the surface of the transparent electrode 7 to perform the alignment treatment. The upper and lower substrates 4 and 5 are opposed to each other via a spacer 10, and the liquid crystal material 1 that operates in the STN mode between the substrates.
1 is enclosed. An optically active agent is mixed in the liquid crystal material 11 and twist-aligned at a twist angle of about 200 degrees (hereinafter referred to as a twist angle).

A general STN liquid crystal display panel has a cell gap of about 6 μm and a response time (sum of ON time and OFF time) of 200 to 300 msec. It is difficult to display a moving image with this response time. Therefore, as cell parameter optimization, a narrow cell gap or the like has been attempted for the purpose of high-speed response, and a wide twist angle has been attempted for the purpose of high contrast.

[0007]

In the liquid crystal display panel of FIG. 4 described above, the alignment films 8 and 9 formed on the transparent electrodes 6 and 7 are affected by the shape of the underlying transparent electrode, and are actually It is not flat but has an uneven shape like the alignment film 9.
When the rubbing treatment is applied to this alignment film, the edge portion of the convex portion of the alignment film may be damaged. As a result, the alignment of liquid crystal molecules in the vicinity of the damaged portion is disturbed, which causes a display defect. The fragments themselves cause display defects as dust, and damage the alignment film surface to cause display defects.

By the way, in the STN liquid crystal display panel, the cell gap variation, the elastic energy of the liquid crystal material, the energy balance such as the binding energy of the liquid crystal-alignment film interface, etc. may affect the alignment defect. Therefore, it is necessary to design a panel with a margin for alignment stability. Usually, this margin is defined by an allowable range (hereinafter referred to as d / p margin) of the ratio d / p between the cell gap d and the twist pitch p of the liquid crystal material. The lower limit is defined by the minimum d / p at which under-twist does not occur, and the upper limit is defined by the maximum d / p at which no stripe domain occurs.

However, even if d / p is within the d / p margin, if a damaged portion, a scratch, or dust exists on the alignment film, the defective alignment is likely to occur with the damaged portion as a nucleus. Further, widening the twist angle and narrowing the cell gap used as a means for achieving high-speed response and high contrast of the liquid crystal display panel tend to narrow the d / p margin, which further increases the frequency of alignment defects.

[0010]

In order to solve the above-mentioned problems, a liquid crystal display panel according to the present invention comprises a transparent electrode and an alignment film which covers the transparent electrode and is subjected to an alignment treatment, on the opposite sides of the pair of substrates. A liquid crystal display panel in which a liquid crystal material is sealed between the liquid crystal display panels, characterized in that the unevenness present on the alignment film that causes the alignment failure is smoothed.

The method of manufacturing a liquid crystal display panel according to the present invention is characterized by including a step of smoothing the irregularities existing on the alignment film. Further, the step of smoothing the concavities and convexities present on the alignment film is characterized in that etching is carried out by setting conditions excessively higher than the optimum conditions for etching in the process of forming the transparent electrode by etching.

Further, the step of smoothing the concavities and convexities present on the alignment film is characterized in that in the step of forming the transparent electrode by etching, etching is further performed after the transparent electrode is formed. By taking these measures, the alignment film is not damaged by the rubbing treatment. Alignment disorder and display defects in the vicinity of the damaged portion, display defects due to fragments, and display defects due to scratches on the alignment film caused by the fragments are eliminated, and the yield of the liquid crystal display panel is improved. Also, by smoothing the irregularities on the alignment film, damage to the alignment film, debris, and the reduction of scratches due to debris,
Alignment defects such as stripe domain and under twist are less likely to occur.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION

(Embodiment 1) The present invention will be specifically described with reference to FIG. FIG. 1 is a schematic view of an STN liquid crystal display panel of the present invention. The liquid crystal cell 1 is sandwiched by polarizing plates 2 and 3 which are integrated with a retardation plate for compensating the coloring characteristic of STN. Transparent electrodes 6 and 7 made of ITO are formed on the inner surfaces of the upper substrate 4 and the lower substrate 5 by patterning. Alignment films 8 and 9 are applied to the surface and subjected to an alignment treatment by a rubbing treatment. The upper and lower substrates 4 and 5 on which the ITO transparent electrode and the alignment film are laminated are opposed to each other with a spacer 10 interposed therebetween.

Here, the ITO transparent electrodes 6, 7 are the substrate 4,
A thin film was formed on 5 by a sputtering method or a vapor deposition method, and then wet etching was performed to form row electrodes and column electrodes for liquid crystal display patterning. The resistance value of ITO can be freely adjusted by the film thickness, and here the film thickness is 1500Å and 15Ω
The sheet resistance was / □. In the pattern formation of the ITO transparent electrode, the transparent electrode having a gentle electrode edge portion like 7 was formed by performing etching by setting the temperature, the time, and the like in excess of the optimum conditions of the wet etching.

Alignment films 8 and 9 containing polyimide as a main component were applied onto the transparent electrodes 6 and 7, and after alignment treatment by rubbing treatment, the alignment film surface was observed with an optical microscope. No damage to the alignment film, which is considered to be the cause, or scratches on the alignment film due to debris generated by the damage was confirmed. Next, the cross section of the substrate-transparent electrode-alignment film was observed by a scanning electron microscope. FIG. 2 shows a schematic cross-sectional view of the substrate-transparent electrode-alignment film produced by the present invention, and FIG. 5 shows a schematic cross-sectional view of the substrate-transparent electrode-alignment film produced by the conventional method. From FIGS. 2 and 5, it can be seen that the surface of the alignment film in the present invention is smoothed under the influence of the gentle shape of the edge portion of the transparent electrode as compared with the conventional case. Further, the damage of the alignment film caused by the rubbing treatment which is present in the conventional case does not exist on the surface of the alignment film in the case of the present invention, and therefore, the fragments of the alignment film were not observed.

As the spacer 10, a plastic spacer having a particle size of 6.2 μm was used, and a cell having a cell gap d of the liquid crystal material 11 of about 6.0 μm was produced. By enclosing the STN liquid crystal material 11 in the cell manufactured in this way,
A liquid crystal display panel as shown in FIG. 1 was produced. This liquid crystal material 11 is a nematic liquid crystal material (RD
P-50664) with an optically active agent (S-81 manufactured by Merck & Co., Inc.
0.95% by weight of 1) is mixed and twisted at a twist angle of 240 °. Twisting pitch of liquid crystal material p = 1
The thickness was 1.5 μm, and was adjusted to be substantially in the center of the d / p margin confirmed by the preliminary investigation.

When the display characteristics of this liquid crystal display panel were evaluated, there were no display defects caused by scratches on the surface of the alignment film when no voltage was applied, and display defects such as point defects caused by damage to the alignment film or fragments thereof. Was not found. next,
When the voltage was gradually applied to the liquid crystal display panel while observing the alignment state of the liquid crystal material with an optical microscope, paying particular attention to the edge portion of the ITO transparent electrode, alignment defects such as stripe domains and undertwist did not occur. (Example 2) Another example will be specifically described. A schematic view of the STN liquid crystal display panel of the present invention is shown in FIG. The liquid crystal cell 1 is sandwiched by polarizing plates 2 and 3 which are integrated with a retardation plate for compensating the coloring characteristic of STN. Transparent electrodes 6 and 7 made of ITO are formed on the inner surfaces of the upper substrate 4 and the lower substrate 5 by patterning. Alignment films 8 and 9 are applied to the surface and subjected to an alignment treatment by a rubbing treatment. The upper and lower substrates 4 and 5 on which the ITO transparent electrode and the alignment film are laminated are opposed to each other with a spacer 10 interposed therebetween.

Here, the ITO transparent electrodes 6 and 7 are formed on the substrate 4 and
A thin film was formed on 5 by a sputtering method or a vapor deposition method, and then wet etching was performed to form row electrodes and column electrodes for liquid crystal display patterning. The resistance value of ITO can be freely adjusted by the film thickness, and here the film thickness is 1000Å and 20Ω.
The sheet resistance was / □. After the wet etching in the pattern formation of the ITO transparent electrode, the resist on the produced electrode pattern is removed, and the wet etching is further performed for a short time to form a transparent electrode having a gentle electrode edge portion and an electrode surface as in 7 did.

Alignment films 8 and 9 containing polyimide as a main component were applied on the transparent electrodes 6 and 7, and after alignment treatment by rubbing treatment, the alignment film surface was observed with an optical microscope. Similarly to the above, no damage to the alignment film, which is considered to be caused by the rubbing treatment, or scratches on the alignment film due to debris caused by the damage was confirmed. Next, the cross section of the substrate-transparent electrode-alignment film was observed by a scanning electron microscope. Also in this case, it was confirmed that the surface of the alignment film was smoothed under the influence of the gentle shape of the entire ITO as in Example 1. In addition, damage to the alignment film and fragments of the alignment film due to the rubbing treatment were not observed.

For the spacer 10, a plastic spacer having a particle size of 4.2 μm is used for the purpose of speeding up the response of the liquid crystal display panel, and a cell having a cell gap d of the liquid crystal material 11 of about 4.0 μm and having a narrow cell gap is used. It was made. The STN liquid crystal material 11 was enclosed in the cell manufactured as described above to manufacture a liquid crystal display panel as shown in FIG. The liquid crystal material 11 is obtained by mixing a nematic liquid crystal material (ES-4414XX manufactured by Chisso Petrochemical Co., Ltd.) with an optical activator (CM33 manufactured by Chisso Petrochemical Co., Ltd.) in an amount of 1.38% by weight and twisted at a twist angle of 250 °. The twist pitch p of the liquid crystal material was p = 7.85 μm, and the twist was adjusted to be substantially in the center of the d / p margin confirmed by the preliminary investigation.

When the display characteristics of this liquid crystal display panel were evaluated, there were no display defects caused by scratches on the surface of the alignment film when no voltage was applied, and display defects such as point defects caused by damage to the alignment film or fragments thereof. Was not found. next,
When the voltage was gradually applied to the liquid crystal display panel while observing the alignment state of the liquid crystal material with an optical microscope, paying particular attention to the edge portion of the ITO transparent electrode, alignment defects such as stripe domains and undertwist did not occur.

Here, in consideration of variations in the panel manufacturing process during mass production, the twist pitch p of the liquid crystal material is adjusted so as to be at both ends of the d / p margin, and the liquid crystal material is sealed to form a liquid crystal display panel. It was made. Specifically, the same liquid crystal material ES-4414XX as described above is used, and the pitch p = 8.5 μm in the vicinity of the under twist and the pitch p = in the vicinity of the stripe domain by adjusting the addition amount of the optically active agent CM33.
The pitch p was adjusted to 7.3 μm. These liquid crystal materials were enclosed in a cell manufactured according to the present invention and a cell manufactured by a conventional method to manufacture a liquid crystal display panel. The cell gaps d are both equal and 4.0 μm.

Observation of these liquid crystal display panels without applying a voltage revealed that in the conventional panel in which a liquid crystal material with a pitch of p = 8.5 μm was enclosed, alignment defects (undertwist) centered on the edge of the transparent electrode were observed. Was confirmed. When the voltage was gradually applied, the pitch p =
In a conventional panel in which a liquid crystal material of 7.3 μm was sealed, alignment failure (stripe domain) was confirmed around the transparent electrode edge portion and the gap between the electrodes.

From these results, it can be seen that the liquid crystal display panel of the present invention is less likely to cause alignment defects such as stripe domains and undertwist as compared with the conventional liquid crystal display panel.

[0025]

As described above, the liquid crystal display panel manufactured by the manufacturing method of the present invention has the following effects as compared with the conventional liquid crystal display panel. (1) Since the surface of the alignment film is smoothed, the alignment film is not damaged by the rubbing treatment.

(2) Since the alignment film is not damaged due to (1), the alignment film fragments will not damage the alignment film surface due to the damage, and the fragments will not remain as dust on the alignment film surface. (3) From (1) and (2), there are no display defects such as point defects due to damages to the alignment film, scratches on the alignment film surface, dust from alignment film fragments, and the like.

(4) Even if the cell gap or the like varies in the panel manufacturing process during mass production, the alignment film surface is smoothed, and alignment film damage, alignment film surface scratches, alignment film fragment dust, etc. Since they do not exist, alignment domains such as stripe domains and under twist are less likely to occur with these as cores.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a liquid crystal display panel showing a first embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view of a substrate-transparent electrode-alignment film produced according to Example 1 of the present invention.

FIG. 3 is a schematic view of a liquid crystal display panel showing Embodiment 2 of the present invention.

FIG. 4 is a schematic view of a conventional STN liquid crystal display panel.

FIG. 5 is a schematic cross-sectional view of a substrate-transparent electrode-alignment film produced by a conventional method.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Liquid crystal cell 2, 3 Polarizing plate integrated with a retardation plate for color compensation 2 ', 3'Polarizing plate 4, 5 Substrate 6, 7 Transparent electrode 8, 9 Alignment film 10 Spacer 11 Liquid crystal material 21 Transparent electrode 22 Alignment film 23 Alignment film breakage 23 'Alignment film fragment

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Shigeru Senbonmatsu 1-8 Nakase, Mihama-ku, Chiba, Chiba Seiko Electronics Co., Ltd. (72) Hiroyuki Fujita 1-8, Nakase, Mihama-ku, Chiba, Chiba Prefecture In Seiko Electronics Co., Ltd. (72) Inventor Shuhei Yamamoto 1-8 Nakase, Nakase, Mihama-ku, Chiba, Chiba In Seiko Electronics Co., Ltd.

Claims (4)

[Claims] 1. A liquid crystal display panel having a transparent electrode and an alignment film covering the transparent electrode and subjected to an alignment treatment inside the pair of substrates, wherein a liquid crystal material is sealed between the substrates, and the unevenness present on the alignment film is formed. A liquid crystal display panel characterized by smoothing. 2. A method for manufacturing a liquid crystal display panel, comprising a pair of substrates, a transparent electrode and an alignment film covering the transparent electrode and subjected to an alignment treatment, wherein a liquid crystal material is sealed between the substrates. A method for manufacturing a liquid crystal display panel, comprising a step of smoothing existing unevenness. 3. The step of smoothing unevenness existing on the alignment film is performed by setting conditions excessively higher than optimum conditions for etching in the process of forming the transparent electrode by etching. The method for manufacturing a liquid crystal display panel according to claim 2. 4. The liquid crystal display panel according to claim 2, wherein the step of smoothing the irregularities existing on the alignment film is further performed after the transparent electrode is formed in the step of forming the transparent electrode by etching. Manufacturing method.