This application claims priority from Japanese Patent Application No. 2017-197405 filed on Oct. 11, 2017. The entire contents of the priority application are incorporated herein by reference.
The technology described herein relates to a method of producing a liquid crystal panel.
An example of the method of cleaning a glass substrate for a liquid crystal panel is described in Japanese Unexamined Patent Application Publication No. 11-176794. In such a cleaning method, a glass substrate for a liquid crystal panel is cleaned by wet cleaning using a cleaning liquid. The cleaning improves film-formation acceptability of the glass substrate.
The wet cleaning has a low ability to remove foreign substances and provides low wettability to the cleaned surface of the substrate. To solve the problems, a treatment agent is added to the cleaning liquid to make the contact angle of the substrate smaller or a silane coupling agent is used to improve the adhesion of the film to the surface of the substrate. This improves the film formation acceptability of the substrate. However, the employment of such agents increases the ion density of the surface of the substrate in some cases due to the effect (elution) of the added agents. In such a case, a liquid-crystals holding rate may be lowered, leading to a decrease in reliability (specifically described, the substrate may have unevenness and stains when subjected to a long-term aging test or stored for a long-time period).
The technology described herein was made in view of the above-described circumstance and an object thereof is to provide a method of producing a liquid crystal panel in which film-formation acceptability of a glass substrate is improved.
To solve the above-described problem, a method of producing a liquid crystal panel according to the technology described herein includes a first dry-cleaning process of dry cleaning a glass substrate for a liquid crystal panel, a wet-cleaning process of wet cleaning the glass substrate after the first dry cleaning process, and a second dry-cleaning process of dry cleaning the glass substrate after the wet-cleaning process.
The dry cleaning (first dry-cleaning process) makes the contact angle of the glass substrate smaller, allowing the cleaning liquid to spread over the glass substrate during the wet cleaning. This allows the wet cleaning to more reliably remove foreign substances. Furthermore, during formation of a film on the glass substrate after the second dry-cleaning process, the smaller contact angle of the glass substrate allows the solution containing a film forming material to spread over the glass substrate, i.e., the substrate has higher film-formation acceptability. After the dry cleaning, the contact angle of the glass substrate increases with time. If the method does not include the second dry-cleaning process, after the first dry-cleaning process, the contact angle of the glass substrate increases by a value corresponding to the duration of the wet-cleaning process. This lowers the film-formation acceptability. In the above-described method, the additional dry cleaning (second dry-cleaning process) after the wet-cleaning process allows the glass substrate to move on to the next process while keeping the low contact angle.
The technology described herein improves the film-formation acceptability of the glass substrate.
One embodiment according to the technology described herein will be described with reference to
As illustrated in
As illustrated in
The array substrate 30 includes a glass substrate having various films formed by photolithography on its inner surface. The array substrate 30 mainly includes TFTs, pixel electrodes, and common electrodes facing the pixel electrodes (all not illustrated). A driver 17 configured to drive the liquid crystal panel 111s disposed on an end of the array substrate 30. Alignment films 22, 22 are disposed on surfaces of the CF substrate 21 and the array substrate 30 adjacent to the liquid crystal layer 23. Specifically described, the alignment film 22 on the CF substrate 21 is disposed on the surface of the glass substrate included in the CF substrate 21 (for example, on the surface of the overcoat film) and the alignment film 22 on the array substrate 30 is disposed on the surface of the glass substrate included in the array substrate 30 (for example, on the surfaces of the common electrodes). However, the arrangement of the alignment films 22 is not limited to the above. Examples of the material of the overcoat film include, but are not limited to, polyimide, an acrylic resin, and an epoxy resin. The overcoat film may be an inorganic protective film, such as a nitride film and an oxide film. Examples of the material of the common electrode include, but are not limited to, a transparent electrode material, such as indium tin oxide (ITO) and indium zinc oxide (IZO).
In the production process of the liquid crystal panel 11, the surface of the glass substrate is cleaned before the alignment film is formed on the glass substrate.
In the treatment tank 41, discharge lamps 47 configured to emit excimer UV to the glass substrate 31 are disposed. This enables the glass substrate 31 to be dry cleaned with excimer UV in the treatment tank 41. In the treatment tank 42, the glass substrate 31 is wet cleaned. In the treatment tank 42, cleaning liquid dispensers 48 and an air knife 49 are disposed. The cleaning liquid dispensers 48 are configured to eject a cleaning liquid onto the glass substrate 31. The air knife 49 is configured to spray highly-pressurized air (compressed air) to the surface of the glass substrate 31 to blow the cleaning liquid away. The cleaning liquid dispensers 48 may be any one of a line shower, a cavitation jet nozzle, a megasonic device-attached water jet nozzle, and any combination thereof, for example. Examples of the cleaning liquid include, but are not limited to, pure water and ultra-pure water. The cleaning liquid may be an alkali chemical.
In the treatment tank 43, IR heaters 50 are disposed to dry the glass substrate 31. In the treatment tank 44, discharge lamps 47 configured to emit excimer UV to the glass substrate 31 are disposed. This enables the glass substrate 31 to be dry cleaned with excimer UV in the treatment tank 44. The dry cleaning is not limited to the dry-cleaning method using excimer UV and may be one using atmospheric-pressure plasma. The dry cleaning using atmospheric-pressure plasma Is more preferable than the dry cleaning using excimer UV, because the dry cleaning using atmospheric-pressure plasma is less likely to damage the glass substrate 31 (the overcoat film, for example). The alignment film applicator 45 is configured to form alignment films by an inkjet method, for example. The alignment film applicator 45 is configured to continuously eject liquid droplets for forming an alignment film onto the glass substrate 31 while moving over the glass substrate 31.
Next, a method of producing the liquid crystal panel 11 Is described. The method of producing the liquid crystal panel 11 includes a structure formation process (photolithography process), a cleaning process, an alignment film formation process, a substrate bonding process, and a polarizing plate attachment process. In the structure formation process, various metal films or insulating films are formed on the inner surfaces of glass substrates, which constitute the CF substrate 21 and the array substrate 30, by photolithography to form various structures. In the cleaning process, the inner surfaces of the CF substrate 21 and the array substrate 30 (surfaces of the glass substrates 31), which are adjacent to the liquid crystal layer, are cleaned. In the alignment film formation process, alignment films are formed on the inner surfaces of the CF substrate 21 and the array substrate 30, which are adjacent to the liquid crystal layer. In the substrate bonding process, the CF substrate 21 and the array substrate 30 are bonded together with the liquid crystal layer 23 therebetween. In the polarizing plate attachment process, polarizing plates are attached to the outer surfaces of the CF substrate 21 and the array substrate 30. In the following description, the cleaning process and the alignment film formation process are described in detail.
A method of cleaning the glass substrate 31 (a glass substrate for a liquid crystal panel) in the cleaning process of the embodiment includes a first dry-cleaning process of dry cleaning the glass substrate 31, a wet-cleaning process of wet cleaning the glass substrate 31 after the first dry-cleaning process, and a second dry-cleaning process of dry cleaning the glass substrate 31 after the wet-cleaning process.
(First Dry-Cleaning Process)
In the first dry-cleaning process, the discharge lamps 47 emit excimer UV to the glass substrate 31 transported by the rollers 46 to the treatment tank 41 in
(Wet-Cleaning Process)
In the wet-cleaning process, the glass substrate 31 transported by the rollers 46 to the treatment tank 42 is wet cleaned. Specifically described, line shower cleaning, cavitation jet cleaning, and megasonic cleaning are sequentially performed, for example, by using the cleaning liquid dispensers 48.
(Drying Process)
After the wet-cleaning process, a drying process is performed in the treatment tank 43 by using the IR heater 50.
(Second Dry-Cleaning Process)
In the second dry-cleaning process, the discharge lamps 47 emit excimer UV to the glass substrate 31 transported by the rollers 46 to the treatment tank 44.
(Alignment Film formation Process)
In the alignment film formation process, the alignment film applicator 45 (nozzle head) ejects a solution, which includes an alignment film material (polyimide, for example), in a form, of liquid droplets onto the surface of the cleaned glass substrate 31 (ink-jet method). The droplets on the glass substrate 31 spread to be united together and become a film. Then, the film is subjected to drying treatment (preliminary baking and main baking) and alignment treatment using a rubbing technique to form the alignment film 22. In an example illustrated in
Next, effects of the embodiment are described. In this embodiment, the contact angle of the glass substrate 31 is made smaller (wettability is made higher) by the dry cleaning (first dry-cleaning process), allowing the cleaning liquid to spread over the glass substrate 31 in the wet cleaning. This enables foreign substances to be more reliably removed in the wet cleaning. Furthermore, the smaller contact angle of the glass substrate 31 allows the solution containing a film forming material to spread over the glass substrate during formation of a film on the glass substrate 31 after the second dry-cleaning process, improving film-formation acceptability. Specifically described, the solution constituting the alignment film 22 is able to spread over the glass substrate 31, and thus formability of the alignment film 22 is improved.
Furthermore, the dry cleaning using excimer UV decomposes the contaminant such as an organic substance on the surface of the glass substrate 31, and the decomposed materials are oxidized and removed by active oxygen generated by application of the excimer UV. The dry cleaning may use atmospheric-pressure plasma. In such a case, the contaminant such as an organic substance on the surface of the glass substrate 31 is removed by the use of the atmospheric-pressure plasma.
The third row from the left (wet-cleaning process and drying process) in
Referring to foreign substance removal rates of the
comparative examples 1 to 3, the foreign substance removal rate is higher in the comparative example 3, in which the dry cleaning was performed for 20 seconds before the wet-cleaning process, than in the comparative example 2, in which the duration of the wet cleaning was longer than that in the comparative example 1 by 70 seconds. Furthermore, comparison between the comparative example 3 and the example reveals that the substrate contact angles after the cleaning were made smaller by the second dry-cleaning process. Furthermore, as indicated in
Next, with respect to the glass substrate 31,
For example, in the comparative example 3 in
As indicated in
Furthermore, the inventor of the present, application found that, when the substrate contact angle is smaller than 7°, the liquid crystal display device 10 is able to have a display quality that does not allow the brightness defect, in the alignment film caused by the pinhole to be recognized, if including an ND filter, and when the substrate contact angle is smaller than 5°, the liquid crystal display device 10 is able to have a display quality that does not allow the brightness defect in the alignment film caused by the pinhole to be recognized, without an ND film, at a higher brightness. As can be seen from
The technology described herein is not limited to the embodiments described above and illustrated by the drawings. For example, the following embodiments will be included in the technical scope.
(1) In the above embodiment, the alignment film formation process is performed after the second dry-cleaning process. However, the technology described herein is not limited to this example. A film formation process other than the alignment film formation process may be performed after the second dry-cleaning process.
(2) The wet cleaning and the dry cleaning are not limited to those described in the above embodiment.
(3) In the above embodiment, the dry cleaning using excimer UV is performed in the first dry-cleaning process and the second dry-cleaning process. However, the technology described herein is not limited to this example. For example, the dry cleaning using excimer UV may be performed in the first dry-cleaning process (in the treatment tank 41) and the dry cleaning using atmospheric-pressure plasma may be performed in the second dry-cleaning process (in the treatment tank 44), and vice versa. Alternatively, the dry cleaning using atmospheric-pressure plasma may be performed in the first and second dry-cleaning process.
Number | Date | Country | Kind |
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2017-197405 | Oct 2017 | JP | national |