JP5315260B2 - Manufacturing method of liquid crystal display device - Google Patents

Description

  The present invention relates to a method for manufacturing a liquid crystal display device. In particular, the present invention relates to a method for applying an alignment film provided on a substrate constituting a liquid crystal panel.

  In the liquid crystal panel, an alignment film is provided in the display area of each transparent substrate in order to control the alignment of liquid crystal molecules enclosed between a pair of transparent substrates. In order to uniformly align liquid crystal molecules over the entire display area, it is necessary to make the film thickness of the alignment film uniform. Conventionally, a polyimide-based material has been used as a material for the alignment film. Usually, after applying a solution of polyamic acid, the alignment film is formed by baking at a predetermined temperature and imidization.

  The alignment film material is generally printed and applied onto a transparent substrate using a flexographic printing machine. The flexographic printing plate is made of a photo-curable resin and can form an arbitrary printing pattern. The surface of the flexographic printing plate is provided with a concavo-convex shape having a predetermined density and roughness so as to hold an alignment film material such as a polyamic acid solution. In order to produce the concavo-convex shape, techniques such as chemical etching and photolithography are used. Further, the alignment film material applied on the transparent substrate by the flexographic printing plate maintains the uneven shape of the plate even on the transparent substrate. Therefore, by applying predetermined heat, the viscosity of the alignment film material is lowered and the solvent contained in the alignment film material is removed. Thereby, the alignment film material is flattened. This process is called temporary drying, and a hot plate or the like is used for heating. Then, by baking at a higher temperature, the alignment film material is imidized to form the alignment film.

  Since the liquid crystal panel has extremely abrupt threshold characteristics, the threshold voltage changes due to a slight difference in the thickness of the alignment film. When this change occurs partially, it appears as display unevenness. Accordingly, in such an alignment film printing process, the printed film thickness and the film thickness uniformity are important. Conventionally, in order to apply an alignment film to a desired film thickness, in flexographic printing, adjustment of the solution concentration, printing pressure, printing speed, unevenness density and unevenness of a printing plate, etc. has been made as appropriate.

  However, even when the adjustment as described above is performed, a difference in the drying speed due to the difference in the thickness of the alignment film has occurred in the central portion and the peripheral portion of the display area. Due to this difference in drying speed, the surface shape of the alignment film partially differs, and there is a problem that display unevenness occurs. Furthermore, as the alignment film becomes thinner, unevenness due to the difference in drying speed has become more prominent.

  Further, in a general manufacturing method, a plurality of liquid crystal display panels are manufactured at once using a large substrate. Therefore, a plurality of liquid crystal display panels are laid out on a large substrate. Also in the alignment film printing process, printing is performed on a large-sized substrate, and an alignment material is provided so as to correspond to the display area of each liquid crystal panel. As described above, in a configuration in which a plurality of display areas corresponding to individual liquid crystal panels are arranged on a large substrate, not only the film thickness is uniform in each display area, but also the film thickness between the display areas is increased. It needs to be uniform. However, as the printing range is increased, the risk of film thickness variation increases.

  As a method of manufacturing a liquid crystal display device that solves such problems, the coating layer is repeatedly applied by repeating the alignment film application and pre-baking a plurality of times so that the layer thickness after application of the alignment film material is 20 nm or less. A method of forming an alignment film having a required film thickness is known (for example, see Patent Document 1). By using such a method, even if unevenness occurs in one application, it is averaged, and the layer thickness per one time is sufficiently thin, so that the solvent is easily removed in pre-baking and leaves a trace on the alignment film surface. As a result, the orientation state does not change.

JP 2002-31800 A

  However, in the manufacturing method described in Patent Document 1, there is a problem that the cost increases because the overcoating is performed by repeating the alignment film coating and the pre-baking a plurality of times. In addition, when forming a thin film of several tens of millimeters, it is difficult to apply repeatedly, and there is a problem that this method cannot be applied.

  In view of the above, an object of the present invention is to provide an inexpensive manufacturing method capable of more uniformly printing the film thickness of the central portion and the peripheral portion of the display area in order to reduce drying unevenness of the alignment film.

  In order to solve the above problems, the present invention has the following manufacturing method. That is, the present invention is a method of manufacturing a liquid crystal display device in which a plurality of liquid crystal panels are collectively manufactured using a large transparent substrate on which a plurality of liquid crystal panels are laid out. A large-sized liquid crystal cell, a large-sized liquid crystal cell is formed by attaching a large-sized transparent substrate and a large-sized counter substrate to each other with a large-sized transparent substrate facing the large-sized transparent substrate and providing a certain gap through a sealing material. A step of separating the liquid crystal cell and a step of sealing the liquid crystal in the gap, and in the printing process, a flexo having a concavo-convex pattern provided in a strip shape over a plurality of display areas corresponding to a plurality of liquid crystal panels. The alignment film was printed by the printing plate.

  Further, in the printing process, the alignment film is printed excluding the regions corresponding to the electrode terminals of the plurality of liquid crystal panels. Furthermore, slits for stress distribution may be provided in the uneven pattern provided in the strip shape of the flexographic printing plate. This slit is desirably formed with a width of 0.05 mm or more.

  In addition, the alignment film may be printed on the counter substrate by a flexographic printing plate having a concavo-convex pattern provided in a strip shape across a plurality of display areas corresponding to a plurality of liquid crystal panels.

  According to the present invention, it is possible to reduce the difference in the drying speed of the alignment film that occurs between the central portion and the peripheral portion of the display area, and it is possible to avoid a decrease in display quality such as unevenness.

It is a schematic diagram which shows the cross-sectional structure of the liquid crystal panel manufactured using the manufacturing method of this invention. It is a top view of the flexographic printing plate used with the manufacturing method of this invention. It is the schematic plan view which showed a mode that the alignment film was printed on the transparent substrate. It is a top view of the flexographic printing plate used with the manufacturing method of this invention.

  A method for manufacturing the liquid crystal display device of the present invention will be described below. In the manufacturing method of the present invention, a plurality of liquid crystal panels are manufactured at once using a large transparent substrate on which a plurality of liquid crystal panels are laid out. That is, an electrode pattern is formed on a large transparent substrate so as to correspond to each liquid crystal panel. Next, an alignment film is provided on the large transparent substrate by printing. At this time, the alignment film is printed using a flexographic printing plate having a concavo-convex pattern provided in a strip shape over a plurality of display areas corresponding to a plurality of liquid crystal panels. Next, the large-sized transparent substrate is opposed to the large-sized transparent substrate, and the large-sized liquid crystal cell is formed by bonding with a certain gap through a sealing material. Thereafter, the individual liquid crystal cells are separated from the large liquid crystal cell. Then, liquid crystal is sealed in the gap between the substrates. The liquid crystal may be enclosed when assembling a large format liquid crystal cell, or may be enclosed before being separated into individual liquid crystal cells.

  According to the present invention, an alignment film printed on a large transparent substrate is printed by a flexographic printing plate having a concavo-convex pattern provided in a strip shape over a plurality of display areas. Thereby, the outer peripheral part of the alignment film in each cell is reduced from the conventional four sides to two sides, and the difference in the drying speed of the alignment film generated in the central part and the peripheral part of the display area can be reduced. For this reason, it is possible to avoid deterioration in display quality such as unevenness. Hereinafter, it demonstrates in detail using an Example.

  FIG. 1 is a schematic cross-sectional view of a liquid crystal panel 1 manufactured by the manufacturing method of this embodiment. The pair of transparent substrates 2 face each other with a certain gap, and liquid crystal is sealed in the gap. A transparent electrode 3 is provided on the inner surface of each substrate. The transparent electrode 3 is formed in a desired pattern by photolithography. The transparent electrode 3 is formed of a transparent conductive film called ITO in which indium (In) containing tin (Sn) as an impurity is oxidized, and a desired resistance value can be set. Since ITO is a low-resistance semiconductor material, its resistance value is 10Ω / □ to 100Ω / □, which is the most general-purpose level. Usually, ITO is formed by a vacuum film forming method called a sputtering method or a vapor deposition method. The pair of transparent substrates 2 on which the transparent electrodes 3 are formed face each other with the alignment film 6 interposed therebetween. For the alignment film 6, polyimide, PVA, organosilane, or the like is used, and a rubbing process is performed to control the alignment of liquid crystal molecules. Both substrates may use alignment films of the same material or different materials. Further, an undercoat layer 4 or the like may be provided on the base of the alignment film 6 to smooth the surface, or to prevent a short circuit due to foreign matter. In this embodiment, the planarizing layer 5 is provided on the upper substrate and the overcoat layer 4 is provided on the lower substrate. However, the present invention is not limited to this configuration. For example, the structure upside down from FIG. 1 may be used, or the same layer may be provided on both substrates. Moreover, the structure which does not provide the planarization layer 5 or the overcoat layer 4 in one or any board | substrate may be sufficient. Thereafter, the pair of transparent substrates 2 are fixed by the sealant 9 after the spacers 7 are dispersedly arranged on the display surface so that the transparent electrodes 3 face each other. In general, a large number of such structural units are arranged in a matrix on the surface of the transparent substrate 2. Thereafter, each display surface arranged on a large substrate is separated, and liquid crystal is injected into the gap between the substrates. A UV curable resin is applied to the liquid crystal injection port and sealed by UV irradiation. Next, a polarizing plate (not shown) is disposed on the upper and lower surfaces, and a lighting device is combined to obtain a liquid crystal display device. In the reflective liquid crystal display device, a reflecting plate is arranged instead of the lighting device, and in the semi-transmissive liquid crystal display device, a semi-transmissive reflecting plate and the lighting device are arranged.

  FIG. 2 is a plan view schematically showing the flexographic printing plate 10 used in this embodiment. The flexographic printing plate 10 has a concavo-convex pattern 11 formed in a band shape in the plane. FIG. 2 schematically shows the actual arrangement of the display area 12. Here, the concavo-convex pattern 11 is formed in a strip shape so as to cover the display area of the liquid crystal panel arranged in the column direction. As described above, the concave / convex pattern 11 on the surface of the flexographic printing plate 10 does not correspond to each display area 12 but is formed over a plurality of display areas 12. By using the flexographic printing plate 10 to print the alignment film 6, the difference in the drying speed of the alignment film 6 that occurs between the central portion and the peripheral portion of the display area 12 can be reduced. It becomes possible to avoid deterioration in quality. By using such a flexographic printing plate 10, printing with less in-plane drying unevenness can be performed even with the alignment film 6 thinned to several tens of millimeters. The flexographic printing plate 10 is used for printing an alignment film 6 provided on one or both of a pair of opposing transparent substrates 2.

  FIG. 3 is a schematic plan view showing a state in which the alignment film 6 is printed on the transparent substrate 2. As shown in the figure, the alignment film 6 is printed so as to continuously cover the display area 12 of the liquid crystal panel arranged in the column direction. In the figure, the display area 12 corresponds to the inside of the broken line, and the alignment film 6 is provided in the display area 12. At this time, the alignment film 6 is not printed on the electrode terminal portion 13 of the liquid crystal panel. By doing in this way, the connectivity at the time of connecting FPC and TAB later can be improved.

  Further, the planarizing layer 5 and the overcoat layer 6 can be printed using such a flexographic printing plate 10.

  FIG. 4 is a plan view schematically showing the flexographic printing plate 20 used in this embodiment. The flexographic printing plate 20 of the second embodiment is different from the flexographic printing plate 10 of the first embodiment shown in FIG. 2 in that slits 14 are provided in the strip-shaped uneven pattern 11. In addition, since the manufacturing method of the liquid crystal display device using the flexographic printing plate 20 is the same as that of Example 1, the overlapping description is abbreviate | omitted. The slit 14 is provided for the purpose of giving relief of stress applied to the flexographic printing plate 20 during printing. In particular, when the printing area is large, there is a possibility that the stress during printing generated between the flexographic printing plate 20 and the transparent substrate 2 is concentrated on a part of the flexographic printing plate 20 and distortion occurs. This distortion may cause local printing unevenness. Therefore, by providing the slits 14 in the belt-shaped uneven pattern 11 and releasing the stress applied to the flexographic printing plate 20 during printing, printing unevenness can be prevented more reliably.

  In this embodiment, as shown in FIG. 4, one slit 14 is provided in each strip-shaped uneven pattern 11, but the present invention is not limited to this design. That is, a plurality of slits 14 may be provided in each strip-shaped uneven pattern 11, or a different number of slits 14 may be provided for each strip-shaped uneven pattern 11. The slit 14 is preferably provided with a width of 0.05 mm or more. When the width of the slit 14 is 0.05 mm or less, it is difficult to completely release the stress during printing, and as a result, local unevenness occurs.

  It is possible to reduce the unevenness of drying of the alignment film and to more uniformly print the film thickness of the central portion and the peripheral portion of the display area at a low cost, and thus can be applied to a liquid crystal display device with good display quality.

DESCRIPTION OF SYMBOLS 1 Liquid crystal panel 2 Transparent substrate 3 Transparent electrode 4 Overcoat layer 5 Flattening layer 6 Orientation film 7 Spacer 8 Liquid crystal layer 9 Sealing material 10, 20 Flexographic printing plate 11 Concavity and convexity pattern 12 Display area 13 Electrode terminal part 14 Slit

Claims (4)

In a manufacturing method of a liquid crystal display device that uses a large transparent substrate on which a plurality of liquid crystal panels are laid out to collectively produce a plurality of liquid crystal panels,
A printing process for providing an alignment film on a large transparent substrate;
Forming a large-sized liquid crystal cell by facing the large-sized transparent substrate to the large-sized transparent substrate, providing a certain gap via a sealing material, and bonding the large-sized transparent substrate and the large-sized counter substrate;
Separating the individual liquid crystal cells from the large format liquid crystal cells;
Enclosing a liquid crystal in the gap,
In the printing step, the alignment film is printed by a flexographic printing plate having a concavo-convex pattern provided in a strip shape over a plurality of display areas corresponding to the plurality of liquid crystal panels ,
The method of manufacturing a liquid crystal display device, wherein the flexographic printing plate is provided with slits for stress distribution in the concavo-convex pattern provided in the belt shape.   2. The method of manufacturing a liquid crystal display device according to claim 1, wherein in the printing step, the alignment film is printed excluding a region corresponding to an electrode terminal of the plurality of liquid crystal panels. 3. The method of manufacturing a liquid crystal display device according to claim 1, wherein the slit for stress dispersion is formed with a width of 0.05 mm or more. Wherein the counter substrate also Claim 1-3, characterized in that the orientation film by flexographic printing plate having a concavo-convex pattern provided on the strip over a plurality of display areas corresponding to the plurality of liquid crystal panels are printed The manufacturing method of the liquid crystal display device as described in any one of these.

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