JP2000171769A - Substrate cleaning tank - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a liquid crystal panel uniform in display by removing foreign matters stuck at the time of rubbing without needing special facilities and without increasing man-hours by using ionized water produced by electrolysis of water for cleaning a substrate. SOLUTION: This substrate cleaning tank has a pH-of-water adjusting means for adjusting the pH of water by electrolyzing water, and the adjusting means adjusts the pH of water to 6.6 to 6 for obtaining acid ionized water with a low surface tension. A polyimid oriented film oriented by rubbing is washed in the obtained acid ionized water, so that a difference in solubility constant between the polyimid oriented film and the acid ionized water can be reduced. This method permits to remove foreign matters sticking on the surface by making use of the low surface tension without making any change in the rubbed oriented film surface, and is also effective to remove a processing agent easy to be transferred from a rayon cloth. Thus, an excellent yield without defect of display and evenness of display are realized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for cleaning a substrate of a liquid crystal panel, and more particularly to a substrate cleaning tank for a substrate having a rubbed alignment film.

[0002]

2. Description of the Related Art In recent years, liquid crystal display panels utilizing electro-optical characteristics of liquid crystal have been actively applied to office automation equipment due to their large screens and large capacities. At present, as a mode of operation of a liquid crystal display panel that is generally put into practical use, a twisted nematic (TN) type in which liquid crystal molecules exhibit an alignment state of 90 ° twisting between two glass substrates, twisted from 180 ° to 270 °. There is a super twisted nematic (STN) type exhibiting an alignment state. The TN type is mainly used for an active matrix type liquid crystal display panel.
The types are used for simple matrix type liquid crystal panels.

TN used for an active matrix type liquid crystal display panel or a small size liquid crystal display panel
In the case of the mold, at the glass substrate interface, the liquid crystal molecules have a certain pretilt angle θp with respect to the glass substrate in one direction,
It is uniformly oriented and twisted 90 ° between the upper and lower glass substrates. For the 90 ° twisted alignment, generally, an alignment film consisting of a polyimide thin film formed on a glass substrate should be rubbed in one direction using rayon cloth, etc., and arranged so that the direction is orthogonal between the upper and lower substrates. Is obtained by

FIG. 2 is a sectional view showing the basic structure of a liquid crystal display panel. In FIG. 2, 1 is an upper glass substrate, 2 is a segment electrode, 3 is a lower glass substrate, 4 is a common electrode, 5 and 6 are alignment films, 7 is a chiral nematic liquid crystal layer,
8 is a spacer, 9 is a sealing material, and 10 is a polarizing plate.

In the liquid crystal display panel having the above-described structure, the liquid crystal molecules between the upper glass substrate 1 and the lower glass substrate 3 have a 90 ° angle.
A twisted nematic (TN) liquid crystal display panel is referred to as a twisted nematic (TN) liquid crystal display panel, and a super twisted nematic (STN) liquid crystal display panel is referred to as a twisted nematic (TN) liquid crystal display panel. In any of the liquid crystal display panels, the liquid crystal molecules are oriented in a certain direction in the upper and lower substrate surfaces while maintaining a state of being raised with a tilt (pretilt angle θp) of several degrees with respect to the substrate.

FIG. 3 is a conceptual diagram showing the alignment state of the liquid crystal molecules. As shown in FIG. 3, the pretilt angle θp of the liquid crystal molecules 13 at the interface of the substrate 11 is determined by the substrate including the electrodes. An alignment film 12 is formed at an interface between 11 and liquid crystal molecules 13. A commonly used orientation method is, as described above,
First, an alignment film 12 made of a polyimide material or the like is formed on the substrate 11 and its surface is rubbed in a certain direction. The pretilt angle θp differs depending on how the alignment film 12 is rubbed.

[0007]

As described above, FIG.
In order to control the orientation of the liquid crystal molecules 13 uniformly over the entire surface of the substrate 11, it is necessary to perform uniform rubbing over the entire surface. In order to obtain a uniform rubbing state, the orientation generally tends to be excessive. As a result, a large number of foreign substances 14 such as shavings of the alignment film 12 are generated and adhere to the alignment film 12, the rayon cloth used for rubbing comes off, and this also adheres to the surface. May be transferred to the alignment film surface.

If these deposits are present, the liquid crystal molecules 13 in the vicinity of the foreign matter 14 cause the alignment disorder 15, and display defects in the state of the liquid crystal panel appear. To remove deposits,
It is necessary to clean the surface of the alignment film 12 after rubbing. Conventionally, as a cleaning method, isopropyl alcohol was used, or water containing a detergent was used.
Isopropyl alcohol is a flammable hazard and requires special equipment for handling. In addition, detergent mixed water tends to leave detergent after washing.To prevent this, careful cleaning with pure water after washing is required, which increases man-hours and requires special equipment for treating the washed waste liquid. Was needed.

In view of the above, the present invention is intended to clean a substrate having a rubbed alignment film, remove foreign substances adhering at the time of rubbing, and improve the display of the display without increasing special facilities and man-hours. An object of the present invention is to provide a substrate cleaning tank capable of obtaining a uniform liquid crystal panel.

[0010]

Means for Solving the Problems In order to solve the above problems, the substrate cleaning tank of the present invention has a water pH adjusting means for adjusting the pH value of water by electrolyzing water, and has a low surface tension. In order to obtain acidic ionic water, the pH of water
The H value is adjusted from 6.6 to 6, the polyimide alignment film that has been subjected to alignment treatment by rubbing with acidic ion water is washed, and the polyimide alignment film and the acidic ion water are washed so as to reduce the difference in solubility constant between them. I did it.

In the substrate cleaning method of the present invention, not pure neutral water but ion water produced by electrolyzing water is used for cleaning the substrate. In particular, in order to clean the alignment film before and after rubbing, it is preferable to use acidic ions which do not change the film quality of the alignment film and have a low surface tension. At the time of cleaning, it is also effective to raise the temperature or use ultrasonic waves in combination in order to increase the cleaning power.

That is, in addition to being able to remove foreign substances adhering to the rubbed surface by making use of a low surface tension without changing the surface of the rubbed alignment film, it is also effective for removing a processing agent which is easily transferred from rayon cloth. is there. Therefore,
A liquid crystal panel manufactured using a substrate washed with ion water has no display defects, and can have excellent yield and uniform display.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Prior to describing an embodiment of the present invention, a comparative example will be described with reference to the sectional view of the basic structure of the liquid crystal display panel shown in FIG.

(Comparative Example) Upper glass substrate 1 having indium tin oxide (ITO) having a sheet resistance of 30 Ω / □
Is patterned by photolithography to obtain a striped segment electrode 2 having a pitch of 500 μm and a width of 400 μm. The common electrode 4 having the same shape in the form of a stripe is formed on the lower glass substrate 3 by using a similar technique. The segment electrode 2 and the common electrode 4 are arranged so as to be orthogonal to each other.

On the segment electrode 2 and the common electrode 4, an alignment film 5 having a thickness of 50 nm is formed by spin coating.
Form 6 was formed and cured at 240 ° C. for 2 hours. As an alignment film material, polyimide SE-4110 (manufactured by Nissan Chemical Industries, Ltd.) was used. The upper and lower glass substrates 1 and 3 on which the alignment films 5 and 6 are thus formed are oriented by using a rayon cloth so that the liquid crystal twist between the upper and lower glass substrates 1 and 3 becomes 240 °. Was rubbed. It was confirmed that a large amount of shavings of the alignment films adhered to the surfaces of the alignment films 5 and 6 after rubbing near the ends of the electrodes 2 and 4. Further, the rubbed upper and lower glass substrates 1 and 3 were bonded to each other to produce a liquid crystal panel as shown in FIG. A nematic liquid crystal material (ZLI-1840 manufactured by Merck) to which a thermosetting epoxy resin and a spacer 8 having a diameter of 7 μm (trade name: Micropearl manufactured by Sekisui Fine) are added as a sealing material 9 and a rotatory substance is added by a vacuum injection method. To form a chiral nematic liquid crystal layer 7. When the polarizing plates 10 were arranged vertically so as to sandwich the manufactured liquid crystal panel, and displayed by multiplex driving of 1/300 duty, not only luminance unevenness was observed in the portion where a large number of shavings were adhered, but also The luminance unevenness was large as a whole.

(Embodiment) The upper and lower glass substrates 1 and 3 equivalent to the comparative example were washed with acidic ion water. The ion water used was produced in the electrolysis water tank shown in FIG. That is,
A divided tank with a porous membrane 16 to partition the water tank
A cathode 19 and an anode 20 are arranged in each of 17 and B tank 18. When an electric field is applied between the cathode 19 and the anode 20 in this state, the cathode 19
In the A tank 17 having the above, the hydrogen ions collected near the cathode are converted into hydrogen gas (H2) and released out of the tank.
Produces alkaline ionized water 21. On the other hand, in the B tank 18 including the anode 20, oxygen gas (O2) is generated and released from near the anode,
The acidic ion water 22 is formed in the B tank 18.

The pH value of the water can be adjusted by the duration of the electrolysis. In the present embodiment, acidic ion water 22 having a pH value of 6 was used. After heating the substrate cleaning tank filled with the acidic ionized water 22 to 60 ° C., the rubbed substrate equivalent to that of the comparative example was immersed and left gently for 15 minutes. Dry the removed substrate,
When the surface was observed, there was no shavings that had adhered before cleaning. In addition, a liquid crystal panel was prepared using the cleaned substrate in the same manner as in the comparative example, and the polarizing plates were vertically arranged.
When 10 was arranged and the display was performed by the multiplex drive of 1/300 duty, a uniform display with almost no luminance unevenness was obtained.

The above embodiment has been described using a so-called super twisted nematic (STN) mode in which liquid crystal molecules are largely twisted up and down. However, the substrate cleaning tank of the present invention uses only an STN mode liquid crystal display panel. It is also effective in twisted nematic (TN) mode twisted 90 ° up and down, and can be used for cleaning a so-called active matrix type liquid crystal display panel in which a thin film active element is formed on a substrate. . As described above, the difference between the solubility constants of the polyimide alignment film and the acidic ionic water is reduced, and the H value of the acidic ionic water is adjusted for cleaning. Etc. could be removed more by washing. Table 1 shows data indicating the relationship between the pH value of acidic ionized water and the contact angle of the polyimide alignment film. The wettability between the acidic ionized water and the polyimide alignment film can be quantitatively measured by the contact angle of the surface tension related to the wettability. If the contact angle is small, the difference in the solubility constant between the polyimide alignment film and the acidic ionic water is also small.

[0019]

[Table 1]

In the embodiment, the pH value of the cleaning solution is
Although the pH value of 6 was used, the optimum pH value also depends on the type of the alignment film, and also depends on the water temperature and the immersion time. However, when polyimide as a condensation polymer is used as the alignment film, it is not preferable to be alkaline from the viewpoint of film quality deterioration due to hydrolysis. Further, if the pH is too close to neutral, the washing ability is reduced, so the pH value is preferably 6.6 or less. Also,
To shorten the cleaning time, it is also effective to raise the water temperature or to apply ultrasonic waves.

[0021]

As described above, by cleaning the rubbed substrate using the substrate cleaning bath of the present invention, foreign substances adhering during rubbing are removed, and a liquid crystal panel having a uniform display can be provided. It becomes possible. Further, since the cleaning liquid does not contain a chemical, the treatment of the used cleaning liquid is easy, and the cleaning liquid has great industrial value in that it does not pollute the environment.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing a method for producing ionized water by electrolysis according to the present invention.

FIG. 2 is a sectional view showing a basic configuration of a liquid crystal display panel to be cleaned in the present invention.

FIG. 3 is a conceptual diagram showing an alignment state of liquid crystal molecules in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Upper glass substrate 2 Segment electrode 3 Lower glass substrate 4 Common electrode 5, 6, 12 Alignment film 7 Chiral nematic liquid crystal layer 8 Spacer 9 Sealing material 10 Polarizing plate 11 Substrate 13 Liquid crystal molecule 14 Foreign material 15 Alignment disorder 16 Porous film 17 A tank 18 B tank 19 Cathode 20 Anode 21 Alkaline ionized water 22 Acidic ionized water

Claims (1)

[Claims] 1. A water pH adjusting means for adjusting the pH value of water by electrolyzing water, wherein the water pH adjusting means adjusts the pH value of the water to 6 to obtain acidic ion water having a low surface tension. Cleaning the polyimide alignment film that has been subjected to alignment treatment by rubbing with the acidic ionized water, adjusting the solubility to a difference in solubility constant between the polyimide alignment film and the acidic ionized water. A substrate cleaning tank characterized by the above-mentioned.