JPH0720472A - Production of liquid crystal display device - Google Patents

Abstract

PURPOSE:To provide the process for production of the liquid crystal display device capable of uniformalizing the film thickness of oriented films formed of prescribed printing patterns from the circumferential end to the central part. CONSTITUTION:The printing patterns 14 are formed on the surface of a letterpress printing plate 13 of a photosetting resin plate consisting of polyurethane. The printing patterns 14 are segmented to the central part 15 and the circumferential end part 16 and are formed to rugged shapes. The parts formed to the rugged shapes are formed with many cylindrical projecting parts of a circular surface shape. The frequencies of ruggedness are set at the frequencies larger than the frequencies of the ruggedness in the central part 15 and the amt. of the oriented film liquid holding in the circumferential ends 16 is decreased, by which the amt. of the oriented film liquid after printing is uniformalized. The same drying speed is maintained at the circumferntial end part 16 and the central part and the compsn. of the oriented films does not change any more. The oriented films which are uniform and are free from unequalness are thus obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a liquid crystal display device which forms an alignment film for a pair of electrode substrates.

[0002]

2. Description of the Related Art Generally, a liquid crystal display device has a twisted nematic (TN) type and a dynamic scattering (D) type depending on an operation mode.
S) type, guest host (GH) type, ST type and SBE
There are many types such as (Supertwisted Birefringence Effect) type. At present, most liquid crystal display devices have field effect type TN type, ST type or SB type.
Type E is used. Further, as an example of a liquid crystal display device using such an operation mode, for example, Japanese Patent Laid-Open No. Sho 60
An SBE type liquid crystal display device described in Japanese Patent Laid-Open No. 107020/1998 is known.

The structure of the liquid crystal display device described in Japanese Patent Laid-Open No. 60-107020 is usually such that two transparent substrates having transparent electrodes formed on one side thereof are opposed to each other with a space therebetween, and the periphery of these transparent substrates is surrounded. Is sealed to form a cell, and nematic liquid crystal is injected into the cell. The distance between these transparent substrates is about 4 to 12 μm, and as the nematic liquid crystal, cyclohexane-based, ester-based, biphenyl-based, pyrimidine-based liquid crystal, etc. are used.

Further, a chiral agent is added to the nematic liquid crystal, and the molecular axis of the liquid crystal molecule is 180 ° to 360 °,
It is preferably twisted between the transparent substrates at an angle of 270 °. Further, the liquid crystal molecules have a so-called pretilt whose molecular axis is larger than 5 ° with respect to the substrate plane due to the function of the alignment layer formed on each transparent substrate.

In the method of manufacturing such a liquid crystal display device, in the method of manufacturing the so-called alignment film forming the alignment layer, the material liquid of the alignment film is generally applied by printing by a relief printing method. In this case, the alignment film material is polyimide (PI) or polyvinyl alcohol (PV
A) is used. Furthermore, a photocurable resin is used for the relief printing plate, and an arbitrary printing pattern can be formed. And, in order to hold the polyimide liquid or the polyvinyl alcohol liquid on the surface of this relief printing plate,
An unevenness treatment with a predetermined roughness is applied. Examples of the uneven treatment include etching the surface with a chemical agent and forming an uneven pattern of an arbitrary pattern with a photomask.

Further, the alignment film liquid transferred onto the glass substrate by the relief printing plate has an island shape on the glass substrate due to the unevenness. Then, in order to level the alignment film liquid in such a state uniformly, it is necessary to reduce the viscosity of the alignment film liquid by applying heat and to evaporate the solvent contained in the alignment film liquid to perform the leveling. is there. This step is called temporary drying, and a solvent such as a hot plate is used for solvent evaporation. Then, after the preliminary drying, in order to completely polymerize the alignment film material, the alignment film is further baked at a high temperature to form an alignment film.

By the way, since such a liquid crystal display device has extremely rapid threshold characteristics, the alignment film is required to have extremely high uniformity. That is, even a slight change in the orientation film, for example, a slight change in the thickness of the orientation film or the composition of the orientation film causes a change in the threshold voltage and the lighting state. Here, if the threshold voltage partially changes, that part of the liquid crystal display device becomes uneven, and the stability of display quality is impaired. On the other hand, recently, a liquid crystal display device which performs gradation display has also appeared, and the uniformity of the alignment film becomes a further problem.

However, as described above, when the alignment film is printed by a relief printing plate having a uniform or the same unevenness on the surface, the film thickness at the peripheral edge of the print pattern is the film thickness at the center of the print pattern. It tends to be thicker. This difference in film thickness is because the escape of the alignment film liquid is different between the peripheral edge portion and the central portion of the print pattern. That is, the coating is uniformly applied in the central portion, but the alignment film liquid does not escape at the peripheral end portions, and the coating amount is larger than that in the central portion. As a result, the film thickness of the alignment film after provisional drying becomes thicker at the peripheral edges.

FIG. 4 shows a dried state of the applied alignment film liquid. As shown, for example, the alignment film liquid 11 applied in a square shape starts to dry from the peripheral end and is shown by hatching. The dry part gradually expands toward the central part. In this case, if the coating amount at the peripheral edge portion is large, a difference occurs in the drying speed between the peripheral edge portion and the central portion, resulting in nonuniform film composition and difference in dielectric constant. As a result, in the liquid crystal display device, the threshold voltage and the lighting state change, and partial unevenness occurs.

[0010]

When the alignment film liquid is printed and applied on the glass substrate by the relief printing plate as described above, the alignment film liquid transferred in a predetermined print pattern on the glass substrate is Since the coating amount at the peripheral edge portion is larger than that at the central portion, it is difficult to form an alignment film having a uniform film thickness, and the film composition becomes non-uniform and the dielectric constant is different. As a result, there is a problem that becomes a cause of impairing the stability of display quality.

An object of the present invention is to provide a method for manufacturing a liquid crystal display device, which can make the film thickness of an alignment film formed in a predetermined printing pattern uniform from the peripheral edge part to the central part.

[0012]

A method of manufacturing a liquid crystal display device according to claim 1, wherein a liquid crystal layer is held between a pair of opposing electrode substrates via an alignment film, The alignment film includes a first region having irregularities formed at a first frequency, and a second region formed around the first region at a second frequency higher than the first frequency. The print area is used to print.

A method of manufacturing a liquid crystal display device according to a second aspect is the method of manufacturing a liquid crystal display device according to the first aspect,
The first frequency is ½ or less of the second frequency.

A method of manufacturing a liquid crystal display device according to a third aspect is the method of manufacturing a liquid crystal display device according to the first or second aspect, wherein the print area has a first frequency and a second frequency that are continuous. It is changing.

[0015]

In the method of manufacturing a liquid crystal display device according to claim 1, the irregularity frequency at the peripheral edge portion of the printing region for printing the alignment film liquid is set to be higher than the irregularity frequency at the central portion, and the alignment retained at the peripheral edge portion is performed. By reducing the amount of membrane fluid,
The amount of the alignment film liquid after printing can be made uniform, the drying speed is the same in the surrounding area and in the central part, the composition change of the alignment film does not occur, and a uniform and uniform alignment film can be formed. Can be displayed.

A method of manufacturing a liquid crystal display device according to a second aspect is the method of manufacturing a liquid crystal display device according to the first aspect,
Since the first frequency is ½ or less of the second frequency, the amount of the alignment film liquid retained at the peripheral edge portion can be surely reduced, and therefore the amount of the alignment film liquid can be made uniform throughout.

According to a third aspect of the present invention, there is provided a method of manufacturing a liquid crystal display device according to the first or second aspect, wherein the printing area has a first frequency and a second frequency which are continuously changed. Since the amount of the alignment film liquid retained at the peripheral edge portion can be continuously reduced, there is no sacrifice between the first frequency and the second frequency, and the amount of the alignment film liquid can be made uniform throughout.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, 13 is a relief printing plate, and this relief printing plate 13 uses a photo-curing resin plate made of polyurethane, for example, and a printing area having a predetermined shape, that is, a printing pattern 14 is formed on the surface thereof. Has been done. The print pattern 14 includes a central portion 15 that is a first area and a peripheral end portion 16 that is a second area and is located around the central portion 15.
Are divided into a central part 15 and a peripheral end part 16
In order to hold the alignment film liquid to be printed, it is formed in an uneven shape. 2 and 3 are enlarged views of the portion formed in the uneven shape, and cylindrical protrusions 17 having a circular surface shape are formed in a large number at a predetermined frequency, that is, roughness in these portions. Has been formed. Although PI, PVA and the like can be used as the material of the alignment film, PI is particularly preferable and the viscosity is optimally 35 to 60 cp, preferably 40 cp to 50 cp, and can be changed by the resin concentration.

Here, the irregularity frequency of the central portion 15 is referred to as a first frequency, and the irregularity frequency of the peripheral end portion 16 is referred to as a second frequency. Then, the first frequency is set to a value smaller than the second frequency, for example, the central portion 15 is set to a first frequency of 250 lines / inch and the peripheral end portion 16 is set to a second frequency of 400 lines / inch. Is set to.

By thus setting the unevenness frequency at the central portion 15 and the peripheral edge portion 16 of the printing pattern 14 so that the amount of the alignment film liquid retained on the relief printing plate 13 is at the central portion.
There are fewer peripheral edges 16 than 15 and the central part
Since a relief portion for the alignment film liquid is formed at the boundary between the peripheral edge portion 15 and the peripheral edge portion 15, the amount of the alignment film liquid printed and coated on the substrate (not shown) by the relief printing plate 13 is uniform over the entire printing coating surface. Become.

The arranging direction of the cylindrical convex portions 17 is, for example, a direction inclined by 27 ° with respect to the horizontal, as shown in FIG. This inclination angle changes according to the surface shape of the color spreading plate or the color spreading roller of the printing press. Also, the cylindrical protrusion
The area ratio of 17 is, for example, 35%, but the area ratio of this cylindrical convex portion 17 and the number of lines may be changed according to the desired film thickness.

Further, in order to obtain a relief printing plate 13 having such a cylindrical convex portion 17 and in which a central portion 15 and a peripheral end portion 16 are formed with printing patterns 14 having different concave and convex frequencies, a printing pattern can be obtained. When forming 14, the photomask is generally used for patterning. That is, if the shape of the cylindrical convex portion 17 is formed when the mask pattern is formed, it can be easily obtained.

Next, the process of forming the alignment film will be described.

First, an electrode substrate on which an alignment film is formed, that is, a glass substrate having a transparent conductive electrode made of, for example, ITO (indium tin oxide) formed on one main surface is rubbed and washed with, for example, an alkaline detergent. Then, after rinsing with pure water, draining is performed with, for example, an air knife.
Then, for example, infrared rays are used to evaporate water, and further, for example, ultraviolet rays are used to decompose organic substances.

Next, the letterpress printing plate 13 is used to print the alignment film. That is, the liquid, which is the alignment film material, is transferred and printed on the glass substrate by a relief printing machine equipped with this relief printing plate 13.

Immediately after printing the liquid of the alignment film material,
The printed substrate is heated by, for example, a hot plate at about 60 ° C. for about 1 minute, and is temporarily dried as described above. After this temporary drying, this substrate is baked in a clean oven at about 260 ° C. to obtain an alignment film.

Here, when printing the liquid of the alignment film material, as described above, the printing is performed by the relief printing plate 13 in which the uneven frequency of the central portion 15 and the peripheral edge portion 16 of the printing pattern 14 is changed. The amount of the alignment film liquid printed and applied on top is uniform over the entire printing and application surface. Therefore, in the case of temporary drying, when the drying progresses from the peripheral edge portion toward the central portion as shown in FIG. 4, there is no difference in the drying speed between the peripheral edge portion and the central portion as in the conventional case. . Therefore, an alignment film having a uniform film thickness can be obtained, and the film composition does not become non-uniform and the dielectric constant does not differ, and the threshold voltage and the lighting state of the liquid crystal display device become constant.

In the above embodiment, the thickness of the alignment film after firing is 600 angstroms, the in-plane variation and the film thickness difference between the peripheral edge portion and the central portion are ± 50 angstroms or less, which is good without unevenness. A liquid crystal display device having excellent display quality could be obtained.

In the above embodiment, the central portion of the printing area
The first frequency at 15 was 250 lines / inch and the second frequency at the peripheral edge 16 was 400 lines / inch,
The present invention is not limited to this, and the first frequency may be set to ½ or less of the second frequency. Moreover, you may form so that a 1st frequency and a 2nd frequency may change continuously. Even in this case, the amount of the alignment film liquid applied by printing is uniform over the entire surface of the printed portion, and a uniform film thickness is obtained to obtain an alignment film having no uneven film composition and no difference in dielectric constant. be able to.

[0031]

According to the method of manufacturing a liquid crystal display device of the first aspect, the irregularity frequency at the peripheral edge portion of the printing region for printing the alignment film liquid is set to be higher than the irregularity frequency at the central portion, and the peripheral edge portion is By reducing the amount of alignment film liquid retained, the amount of alignment film liquid after printing can be made uniform, the drying speed is the same in the surrounding area and the central part, and composition change of the alignment film does not occur. A uniform and uniform alignment film can be formed, and good display can be achieved.

According to the method of manufacturing the liquid crystal display device of claim 2, in addition to the method of manufacturing the liquid crystal display device of claim 1, the first frequency is 1/2 or less of the second frequency. Since the amount of the alignment film liquid held at the peripheral edge portion can be surely reduced, the amount of the alignment film liquid can be made uniform throughout.

According to the method of manufacturing a liquid crystal display device described in claim 3, in addition to the method of manufacturing a liquid crystal display device according to claim 1 or 2, the print area has a first frequency and a second frequency. Since it continuously changes, the amount of the alignment film liquid retained at the peripheral edge can be continuously reduced, so that there is no Sakai between the first frequency and the second frequency, and the amount of the alignment film liquid can be reduced. Can be made uniform throughout.

[Brief description of drawings]

FIG. 1 is a plan view of a relief printing plate used in an example of a method for manufacturing a liquid crystal display device of the present invention.

FIG. 2 is an enlarged perspective view showing an uneven portion of the relief printing plate shown in FIG. 1 above.

3 is a sectional view of the cylindrical convex portion shown in FIG. 2 above.

FIG. 4 is a process diagram showing a drying process of the alignment film liquid printed on the above.

[Explanation of symbols]

 14 Print pattern as print area 15 Central part as first area 16 Peripheral edge as second area

Claims (3)

[Claims] 1. A method of manufacturing a liquid crystal display device comprising a liquid crystal layer held between a pair of opposing electrode substrates via an alignment film, wherein the alignment film has irregularities formed at a first frequency. Manufacturing of a liquid crystal display device, characterized in that printing is performed by a printing region having a first region and a second region formed around the first region with a second frequency higher than the first frequency. Method. 2. The method of manufacturing a liquid crystal display device according to claim 1, wherein the first frequency is ½ or less of the second frequency. 3. The method of manufacturing a liquid crystal display device according to claim 1, wherein the print area has a first frequency and a second frequency which are continuously changed.