KR101048704B1 - Cleaning method of substrate for liquid crystal display device - Google Patents

Abstract

The present invention relates to a method of cleaning a substrate for a liquid crystal display device, the method comprising: cleaning the substrate for the liquid crystal display device on which the alignment layer is formed by using a cleaning liquid composition containing an organic solvent; and drying the washed substrate. As,

According to the present invention, foreign substances such as photodegradation products formed on the substrate are completely removed so that no afterimage occurs.

washing

Description

Method of washing an substrate for liquid crystal display device

1A and 1B are exploded perspective views of a general liquid crystal display device.

2 is a schematic diagram of a cleaning process of a substrate for a liquid crystal display device according to the present invention.

3A is a C-V curve of a substrate for a liquid crystal display device cleaned according to a conventional method.

3B is a C-V curve of the substrate for a liquid crystal display device cleaned according to the present invention.

The present invention relates to a method for cleaning a substrate for a liquid crystal display device, and more particularly, to a method for cleaning a substrate after forming an alignment film for the initial alignment of the liquid crystal.

Among the ultra-thin flat panel displays, where the display screen is only a few centimeters (cm) thick, the liquid crystal display has a low operating voltage, so it has low power consumption and can be used as a portable device. The applications range from spacecraft to aircrafts.

A liquid crystal display device generally includes a color filter substrate on which a color filter layer is formed, a thin film transistor substrate facing the color filter substrate and on which a thin film transistor is formed, and a liquid crystal layer formed between the two substrates.

In such a liquid crystal display device, the alignment of the liquid crystal layer is changed by applying a voltage, and thus the light transmittance is adjusted to reproduce an image. Accordingly, an electrode is formed on the thin film transistor substrate and / or the color filter substrate for voltage application. A pixel electrode is disposed on the thin film transistor substrate and a common electrode is disposed on the color filter substrate to form a vertical electric field between the two substrates. In some cases, the pixel electrode and the common electrode are arranged in parallel on the thin film transistor substrate to form a horizontal electric field.

1A is an exploded perspective view of the liquid crystal display device in the former case, and FIG. 1B is an exploded perspective view of the liquid crystal display device in the latter case.

According to the liquid crystal display of FIG. 1A, the thin film transistor substrate 10 has a gate line 12 and a data line 14 intersected with each other, and a thin film transistor T is formed at an intersection thereof. The pixel electrode 16 is formed in connection with (T). In addition, a light shielding layer 22 is formed on the color filter substrate 20 to prevent leakage of light, and R, G, and B color filter layers 24 are formed between the light shielding layers 22. The common electrode 25 is formed. In this case, a vertical electric field is formed between the pixel electrode 16 formed on the thin film transistor substrate 10 and the common electrode 25 formed on the color filter substrate 20, thereby adjusting the alignment direction of the liquid crystal.

According to the liquid crystal display device of FIG. 1B, the thin film transistor substrate 10 has a gate line 12 and a data line 14 intersected with each other, and a thin film transistor T is formed at an intersection thereof. The pixel electrode 16 is formed in connection with the thin film transistor T. In addition, the common electrode 18 is formed to be arranged in parallel with the pixel electrode 16. A light shielding layer for preventing light leakage is formed on the color filter substrate 20, and color filter layers R, G, and B are formed therebetween. In this case, a horizontal electric field is formed between the pixel electrode 16 and the common electrode 18 formed on the thin film transistor substrate 10, thereby adjusting the alignment direction of the liquid crystal.

Both substrates 10 and 20 of the above structure are joined to form one liquid crystal panel, and a liquid crystal layer is formed between both substrates 10 and 20. At this time, if the liquid crystal layer is arbitrarily arranged between both substrates 10 and 20, it is difficult to obtain a consistent molecular arrangement of the liquid crystal layer, so that the initial orientation of the liquid crystal on the thin film transistor substrate 10 and / or the color filter substrate 20. An alignment film (not shown) for forming is formed.

The alignment film is mainly formed by the rubbing orientation method.

In the rubbing orientation method, an organic polymer such as polyimide is applied onto a substrate in a thin film form, and then the side chains of the organic polymer are aligned in a predetermined direction by rotating a rubbing roll wound with a rubbing cloth to rub the organic polymer. It is a way. The liquid crystal is aligned in the direction in which the side chains of the organic polymer are aligned, and therefore, the moving direction of the rubbing roll becomes the alignment direction of the liquid crystal.

However, since the rubbing orientation method is performed by friction between the rubbing cloth and the substrate, dust may be generated, and static electricity may be formed, and particles may adhere to the substrate. Therefore, after performing the rubbing orientation method, a cleaning process for removing foreign matter such as dust and particles formed on the substrate is performed. The cleaning process of the substrate performed after the rubbing orientation is mainly performed using deionized water (DI water).

On the other hand, since the rubbing orientation method is performed by the physical contact between the rubbing roll and the substrate, there is a high possibility of problems of light leakage as follows.

First, a problem of light leakage may occur when the arrangement of the rubbing cloth is disturbed.

Since a structure such as a thin film transistor, a color filter layer, and an electrode layer is formed on the substrate (see FIGS. 1A and 1B), a portion of the rubbing cloth wound on the rubbing roll when the rubbing roll rotates on the structure formed on the substrate is formed. The array may be disturbed. As such, when the rubbing cloth is disturbed, the region rubbed by the disturbed rubbing cloth is not aligned with the side chain of the organic polymer, resulting in uneven alignment of the liquid crystal in the area, resulting in light leakage.

Second, when the rubbing cloth does not come into contact with the substrate, light leakage may occur.

Electrode layers such as pixel electrodes and common electrodes are formed on the substrate (see FIGS. 1A and 1B). Thus, due to the step of the electrode layer, a region in which the rubbing cloth cannot come into contact with the substrate is generated. In this case, the alignment of the liquid crystal is not achieved in the region, resulting in light leakage.

As such, the rubbing orientation method has a problem in that light leakage occurs due to physical contact between the rubbing roll and the substrate. Therefore, in recent years, in order to solve such a problem of the rubbing orientation method, the manufacturing method of the alignment film which does not require a physical contact is studied variously.                         

Especially, the photo-alignment method which manufactures an oriented film by irradiating UV to a polymer film was proposed. In order for the alignment of the liquid crystal to occur, the alignment layer must have structural anisotropy, which can be obtained by anisotropically reacting the polymer film with UV.

Photo-alignment method can be divided into photo-decomposition, photo-isomerization, photo-dimerization, etc. according to the kind of reaction to the UV of the alignment material used.

Taking the photolysis reaction as an example, irradiation with polarized UV light on the polymer alignment material decomposes the bonds of the side chains located in the polarization direction so that only the side chains in the direction perpendicular to the polarization direction remain, so that the liquid crystal can be oriented in that direction. will be.

However, in the case of using a photoalignment method such as a photolysis reaction, since the bonds of the side chains of the polymer alignment material are decomposed, a problem such as an afterimage may occur when the decomposed side chain material is not removed. Therefore, it is necessary to perform a cleaning process for removing the decomposed side chain material, but the conventional decommissioning process using pure water is not complete removal of the decomposed side chain material. Therefore, there is a need for a new method for cleaning a substrate on which an alignment film is formed by a photoalignment method.

SUMMARY OF THE INVENTION The present invention has been made to meet the above requirements, and an object of the present invention is to provide a method for cleaning a substrate on which an alignment film is formed by a photoalignment method.

Another object of the present invention is to provide a method for cleaning a substrate on which an alignment layer is formed by applying a rubbing alignment method and a photoalignment method together.

Although the optical alignment method can solve the problems related to the rubbing alignment method, there is a fatal defect with low anchoring energy. More specifically, in the rubbing orientation method, since the side chains of the organic polymer are aligned in a predetermined direction as described above, not only the orientation of the liquid crystal is controlled by the chemical interaction between the side chains and the liquid crystal, Since rubbing generates regular grooves on the surface of the substrate, the alignment of the liquid crystals is also controlled by the mechanical interaction between the grooves and the liquid crystals. On the other hand, in the photoalignment method, no groove is formed on the surface of the substrate, and the alignment of the liquid crystal is controlled only by the chemical interaction between the polymer film and the liquid crystal by the photoreaction. Therefore, the photo-alignment method has a lower anchoring energy than the rubbing alignment method and causes a problem of afterimage occurrence.

Therefore, the present inventors have studied a method of simultaneously applying the rubbing orientation method and the photoalignment method as a solution to solve the problems of the rubbing orientation method and the photoalignment method. That is, in the rubbing orientation method, when the arrangement of the rubbing cloth is disturbed or when the rubbing cloth does not come into contact with the substrate, the alignment material applied to the substrate in the region cannot be aligned in a certain alignment direction. By arranging the alignment materials that cannot be aligned by the optical alignment method using the optical alignment method, the problems of the conventional rubbing alignment method and the optical alignment method can be solved simultaneously.

Even when the rubbing orientation method and the photoalignment method are applied together, since a decomposition product of the polymer alignment material is formed as a contaminant on the substrate, a new method for cleaning the substrate on which such contaminants are formed is required. Another object of the present invention is to provide a method of cleaning a substrate on which an alignment layer is formed by applying a rubbing alignment method and a photo alignment method together.

The present invention, in order to achieve the above object, the step of performing a cleaning using a cleaning liquid composition containing an organic solvent on the substrate for the liquid crystal display device with an alignment film formed; And it provides a method for cleaning a substrate for a liquid crystal display device comprising the step of drying the cleaned substrate.

When the alignment film is formed by the photo-alignment method, the inventors have found that the decomposition products of the polymer alignment film by light irradiation are not completely removed as pure water used in the prior art. When applying the present invention was found that the decomposition products of the polymer alignment film is almost completely removed.

Here, the washing step may be a shower step using a cleaning liquid composition containing an organic solvent.

In addition, the cleaning process may be performed by a shower step using a cleaning liquid composition containing an organic solvent, and a cavitation jet jet process using a cleaning liquid composition containing an organic solvent.

In addition, the cleaning process may be made of a shower process using a cleaning liquid composition containing an organic solvent, and a mega-sonic cleaning process.

The cleaning process may include a shower process using a cleaning liquid composition containing an organic solvent, a cavitation-jet process using a cleaning liquid composition containing an organic solvent, and a mega-sonic cleaning process. .

In addition, the drying process may be made of a spin drying process and an oven process.

In addition, a brush cleaning process of the lower surface of the substrate may be added before the cleaning process.

The cleaning liquid composition may be composed of an organic solvent or a mixed solvent of an organic solvent and pure water. In the case of a mixed solvent, the organic solvent and the pure water are preferably in a ratio of 99: 1 to 1:99.

The organic solvent is preferably isopropyl alcohol (IPA) or ammonia water, but is not limited thereto, such as methanol, ethanol, 2-propanol, n-butanol, 2-methyl-1-propanol, ethyl glycol, propyl glycol, Butyl glycol, ethyl diglycol, butyl diglycol, n-pentane, acetone, ethyl acetate, methyl ethyl ketone, n-heptane, toluene, methyl isobutyl ketone, isobutyl acetate, n-butyl acetate, sec-butyl alcohol, 2 A solvent selected from the group consisting of -ethoxyethanol, methyl n-amyl ketone, 2-ethoxy ethyl acetate, n-dikene, 2-butoxy ethanol, isophorone can be used.

The alignment layer may be formed by a photoalignment method, or may be formed by a combination of a rubbing alignment method and a photoalignment method.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

2 is a schematic view of a cleaning process of a substrate for a liquid crystal display device according to a preferred embodiment of the present invention.

As can be seen in Figure 2, the substrate cleaning process is largely composed of a wet process and a drying process.

The wet process may include a brush cleaning process, a shower process, a cavitation-jet process, and a mega-sonic process.

The wet process is based on the shower process, and the cavitation jet process and / or megasonic process may be additionally added when the shower process does not completely remove the polymer decomposition products or other foreign matter. The brush cleaning process is not a process of removing a polymer alignment film decomposition product formed on an upper surface of the substrate, but a process for removing dust or other foreign substances generated on the lower surface of the substrate, and may be applied as necessary. Hereinafter, each process is demonstrated.

The shower process is a process of shower cleaning a substrate on which an alignment layer is formed of a cleaning liquid composition including an organic solvent as a basic process of a wet process. The cleaning liquid composition may be made of an organic solvent alone, or may be made of a mixed solvent of an organic solvent and pure water. In the case of a mixed solvent, the organic solvent and the pure water are preferably in a ratio of 99: 1 to 1:99. The organic solvent is preferably isopropyl alcohol (IPA) or ammonia water, but is not limited thereto, such as methanol, ethanol, 2-propanol, n-butanol, 2-methyl-1-propanol, ethyl glycol, propyl glycol, Butyl glycol, ethyl diglycol, butyl diglycol, n-pentane, acetone, ethyl acetate, methyl ethyl ketone, n-heptane, toluene, methyl isobutyl ketone, isobutyl acetate, n-butyl acetate, sec-butyl alcohol, 2 A solvent selected from the group consisting of -ethoxyethanol, methyl n-amyl ketone, 2-ethoxy ethyl acetate, n-dikene, 2-butoxy ethanol, isophorone can be used.

The cavitation-jet process is a process of cleaning a substrate with a solvent dispersed at high pressure by filling a tank with a solvent and then applying pressure with a piston, and it is possible to remove fine foreign matters as compared with the shower process. The solvent used in the cavitation jet process is preferably a cleaning liquid containing an organic solvent used in the shower process.

The megasonic process is a process of removing particulates on a substrate by vibrating MHz in a flowing solvent. More specifically, the substrate and the particulates on the substrate are slipped due to the difference in natural frequencies in the solvent. The solvent penetrates and the fine particles are removed from the substrate. Pure water may be used as the solvent.

The cavitation-jet process and the megasonic process may be selected and applied only as needed, and both may be applied. If both are applied, the application order is not particularly limited, and the cavitation jet process may be applied first, or the megasonic process may be applied first.

The brush cleaning process is a process of removing foreign matters of relatively large particles by rotating the brush while spraying a solvent required for cleaning, the cleaning liquid composition comprising an organic solvent used in the shower process may be applied as the solvent, May be applied.

Through the wet process, the polymer decomposition products on the substrate may be completely removed, and in consideration of the removal efficiency, it is preferable to increase the time of the wet process, but the productivity should be considered, so the wet process time is preferably about 1 minute to 20 minutes.

After the wet process is completed, a drying process of drying the cleaning liquid composition is performed.

The drying process may include a spin drying process and an oven process.

The spin drying step is a step of rotating the substrate at a high speed of about 2200 to 2500 rpm to remove the cleaning liquid remaining on the substrate by the wet process from the substrate by centrifugal force.

The oven process is a process for completely removing the cleaning liquid by applying heat to the spin-dried substrate, performing a second oven process in the range of about 70 to 90 ℃ and a second oven process at about 120 to 140 ℃ Process is preferred. The oven process temperature is selected in consideration of the boiling point of the cleaning liquid applied in the wet process.

Each process described above can be carried out through process equipment known in the art.

On the other hand, the liquid crystal display element substrate applied to the cleaning process is a substrate having an alignment film formed on the surface thereof, and the alignment film is formed by a photo alignment method or a combination of a rubbing alignment method and a photo alignment method.

Hereinafter, the alignment film formed by the combination of the rubbing orientation method and the photoalignment method will be described.

The photo-alignment method has a problem in that anchoring energy is lower than the rubbing alignment method and afterimage occurs due to the technology up to now, and the rubbing alignment method is mainly applied in major production lines. However, since the rubbing orientation method is also difficult to overcome the problem of light leakage when the substrate size increases, the inventors devised a method of combining the rubbing orientation method and the photoalignment method.

That is, in the rubbing orientation method, when the arrangement of the rubbing cloth is disturbed or when the rubbing cloth does not come into contact with the substrate, the alignment material applied to the substrate in the region cannot be aligned in a certain orientation direction. It is designed to align the alignment material that is not aligned by the optical alignment method.

In this case, when the photoalignment method is applied, the UV irradiation process may be performed on the entire surface of the substrate on which the alignment material is applied, or may be performed only on the step generation region on the substrate on which the alignment material is applied. That is, when the rubbing cloth does not come into contact with the substrate, a step may be formed in the substrate, and thus, UV may be irradiated only in the step forming area. You can also investigate.

In the case of irradiating the polarized UV to only the step forming region, the step forming region differs depending on whether the substrate is a thin film transistor substrate or a color filter substrate, and the same substrate is used in whether the liquid crystal display device is in TN mode or IPS. It also differs depending on whether the mode is used.

In addition, the rubbing process and the UV irradiation process may be performed at the same time, the rubbing process may be performed before the UV irradiation process, UV irradiation process may be performed before the rubbing process.

The alignment layer may be any material that can be applied at the same time the rubbing alignment method and the photo-alignment method, but is preferably polyimide, polyamic acid, polyvinylcinnamate, polyazobenzene ( polyazobenzene, Polyethyleneimine, Polyvinyl alcohol, Polyamide, Polyethylene, Polystylene, Polyphenylenephthalamide, Polyester, Polyurethane (Polyurethane), and polymer materials selected from polymethyl methacrylate are used.

Figure 3a shows the C-V curve of the substrate cleaned according to the conventional method, Figure 3b shows the C-V curve of the substrate cleaned according to the present invention.

FIG. 3A illustrates a change in capacitance according to voltage application after performing a shower process using only pure water in an IPS mode thin film transistor substrate having an alignment layer formed by a rubbing orientation method and a photoalignment method using pure water.

FIG. 3b shows a change in capacitance according to voltage application after performing a shower process with isopropyl alcohol (IPA) and pure water 1: 1 in an IPS mode thin film transistor substrate having an alignment layer formed by a rubbing orientation method and a photoalignment method. It is measured.

3A and 3B, R-DC values were determined by taking average values of left and right values of the portion with the largest amount of hysteresis (ie, R-DC = (x + y) / 2). In the case of FIG. 3A, the R-DC value is 130 mV, while in the case of FIG. 3B, the R-DC value is 50 mV.

That is, in the case of Figure 3a it can be seen that the afterimage shows a large bar hysteresis amount is very large, Figure 3b can be seen that the bar image after the hysteresis amount is very small. From such a result, it can be seen that the substrate cleaned using an organic solvent such as IPA is much more effective in cleaning than the substrate cleaned with pure water as in the prior art, and thus no afterimage occurs.

In the liquid crystal display device cleaned according to the present invention, foreign substances such as photodegradation products formed on the substrate are completely removed so that no afterimage occurs.

Claims (16)

Cleaning the substrate for the liquid crystal display element on which the alignment film is formed by using a cleaning liquid composition containing an organic solvent; And A step of drying the cleaned substrate; The organic solvent is isopropyl alcohol (IPA) or ammonia water, methanol, ethanol, 2-propanol, n-butanol, 2-methyl-1-propanol, ethyl glycol, propyl glycol, butyl glycol, ethyl diglycol, butyl diglycol , n-pentane, acetone, ethyl acetate, methyl ethyl ketone, n-heptane, toluene, methyl isobutyl ketone, isobutyl acetate, n-butyl acetate, sec-butyl alcohol, 2-ethoxyethanol, methyl n-amyl ketone , 2-ethoxy ethyl acetate, n-dikene, 2-butoxy ethanol, isophorene; And the alignment layer is formed by performing a photo alignment method after a rubbing alignment method. The method of claim 1, And said cleaning step comprises a shower step using a cleaning liquid composition containing an organic solvent. The method of claim 1, The cleaning step is a shower step using a cleaning liquid composition containing an organic solvent; And A method of cleaning a substrate for a liquid crystal display device, comprising a cavitation jet process or a mega-sonic process using a cleaning liquid composition containing an organic solvent. The method of claim 1, The cleaning step is a shower step using a cleaning liquid composition containing an organic solvent; Cavitation jet process using a cleaning liquid composition containing an organic solvent; And A method of cleaning a substrate for a liquid crystal display device, characterized by comprising a mega-sonic process. The method of claim 1, wherein the drying process comprises a spin drying process and an oven process. The method of claim 1, further comprising a brush cleaning process on a lower surface of the substrate before the cleaning process. The cleaning method of any one of claims 1 to 6, wherein the cleaning liquid composition comprises only an organic solvent. The cleaning method of any one of claims 1 to 6, wherein the cleaning liquid composition comprises an organic solvent and a pure water in a ratio of 99: 1 to 1:99. delete delete delete delete delete delete delete The method according to any one of claims 1 to 6, The alignment layer may be made of polyimide, polyamic acid, polyvinylcinnamate, polyazobenzene, polyethyleneimine, polyvinyl alcohol, polyamide. , Selected from the group consisting of polyethylene, polystylene, polyphenylenephthalamide, polyester, polyurethane, and polymethyl methacrylate The cleaning method of the board | substrate for liquid crystal display elements characterized by the above-mentioned.

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