JPH09138410A - Forming method of oriented film for liquid crystal display element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a forming method of an oriented film for a liquid crystal display element so that an oriented film having uniform film thickness can be formed by arranging injection holes in such a manner that one line of injection holes is dislocated by a half pitch of nozzles from the adjacent line of injection holes. SOLUTION: The ink jet nozzle 2 used is an area-type one to inject a soln. to form an oriented film. The diameter of the injection hole 4 is, for example, 50μm and the pitch (p) of injection holes 4 in one line is, for example, 100μm. One line of injection holes is arranged as dislocated by a half pitch (p/2) to the adjacent line. By this method, a problem of irregular thickness due to variation in overlap amt. of liquid drops is prevented compared to a conventional method in which a line-type ink jet nozzle is used and a coating liquid is applied by controlling the relative velocity between an ink jet nozzle and a substrate or the timing of coating.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for forming an alignment film of a liquid crystal display device.

[0002]

2. Description of the Related Art In recent years, liquid crystal display elements, which have the great advantages of thinness, light weight, and low power consumption, have been actively used as display devices for personal OA equipment such as Japanese word processors and desktop personal computers. Most of liquid crystal display elements (hereinafter, also referred to as LCDs) use twisted nematic liquid crystal, and the display method can be roughly classified into two methods of an optical rotation mode and a birefringence mode.

The LCD of the optical rotation mode is, for example, a twisted nematic (TN) type liquid crystal having a molecular arrangement twisted by 90 degrees, and in principle, displays in black and white, and exhibits a high contrast ratio and a good gradation display property. In addition, since the response speed is fast (several tens of milliseconds), it is a liquid crystal television with a clock, a calculator, a simple matrix drive, an active matrix drive equipped with a switching element for each pixel, and a full-color display combined with a color filter. Etc. (TFT (Thin F
ilm Transistor-LCD and MIM (Metal Insulator)
Metal) -LCD).

On the other hand, a birefringence mode display type LCD
Is a super-twist (ST) type liquid crystal having a molecular arrangement twisted by 90 degrees or more, and has abrupt electro-optical characteristics. Therefore, each pixel does not have a switching element (thin film transistor or diode) and has a simple matrix shape. Even with this electrode structure, a large capacity display can be easily obtained by time-division driving.
In order to uniformly display these liquid crystal display elements, it is necessary to uniformly align liquid crystal molecules on the entire surface of the substrate.

The liquid crystal display element is a device for sandwiching a liquid crystal composition between electrodes of two substrates and applying a voltage from the electrodes of the two substrates to the liquid crystal composition for display. At times, in order to perform uniform display, it is necessary to give a pretilt angle (angle between the molecular axis of the liquid crystal molecule and the surface of the alignment film) to the liquid crystal molecule in advance. Thus, the alignment film also plays an important role in giving a pretilt angle.

Conventionally, the alignment film of these liquid crystal display elements is formed by forming a thin film of an organic polymer compound such as polyimide by offset printing on a substrate on which electrodes and the like are formed, and then lightly rubbing with a cloth or the like. It is generally performed by doing (rubbing process).

A method for forming an alignment film by offset printing is, as shown in FIG.
An alignment film material, for example, polyimide is dropped onto the nozzle 2 through the nozzle 50, and the doctor roller 51 is pressed against the anilox roller 52 to stretch the dropped polyimide so that the thickness of the polyimide becomes uniform. Then, this uniformly stretched polyimide film is transferred onto the printing plate 54 provided on the plate cylinder 53, and the polyimide film transferred onto the printing plate 54 is further transferred onto the surface of the substrate 60, The alignment film 62 is formed.

Further, a method of forming an alignment film by directly spraying a high molecular compound such as polyimide on the surface of a substrate on which electrodes and the like are formed has been considered (Japanese Patent Laid-Open No. 54-21862). (See Japanese Laid-Open Patent Publication No. 63-106727).

[0009]

In the method of forming an alignment film by offset printing, the alignment film is formed by transferring the film of the alignment film material flattened on the printing plate 54 to the substrate surface. Thickness uniformity is good. However, there is a problem that the use efficiency of the alignment film material is low because it is necessary to apply the alignment film material to the doctor roller 51 and the anix roller 52.

On the other hand, the method of forming the alignment film by spraying the alignment film material on the substrate surface has good use efficiency of the alignment film material, but there is no step of flattening on the indirect member like offset printing. However, it is difficult to obtain a uniform film thickness distribution.

As described above, the above-mentioned method has a problem that there is a trade-off relationship between the use efficiency of the alignment film material and the uniformity of the film thickness.

In order to solve this problem, it has been considered to form an alignment film by using a line type ink jet nozzle 12 as shown in FIG. The line-type inkjet nozzle 12 is an inkjet nozzle in which the ink ejection holes 14 are arranged in one row, and a solution of an alignment film material injected from the supply port 13 (hereinafter, also referred to as an alignment film solution) is an injection command signal. Based on the above, the spray coating is performed on the substrate 40 while moving relative to the substrate 40.

In the method of forming an alignment film using this line type ink jet nozzle, the use efficiency of the alignment film material is high, but the droplets of the alignment film solution are always moving relative to the substrate 40. Since the ink is ejected more, there is a problem that a film thickness difference occurs between the landing points of the droplets when the relative movement speed of the inkjet nozzle 12 deviates from a specified value or when the ejection timing deviates. For example, when the moving speed of the substrate 40 with respect to the inkjet nozzle 12 is slower than a specified value,
As shown in (a), the overlap amount of the applied droplets 35 becomes large, and the film thickness of the alignment film becomes larger than a desired value. Further, the area where the alignment film is applied is not in a desired shape, and there is a possibility that the printing position accuracy is deteriorated and an alignment failure area is generated. On the other hand, the inkjet nozzle 12
When the moving speed of the substrate 40 with respect to is faster than the specified value,
As shown in FIG. 7B, the overlap amount of the applied droplets 35 becomes small (droplets are separated from each other in some cases), and the thickness of the alignment film becomes small. Further, as in the case where the speed of the substrate 40 with respect to the inkjet nozzle 12 is small, the print area also has a different shape from the desired shape, and the display defect such as the above-described alignment defect may occur.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a method for forming an alignment film of a liquid crystal display device, which can form an alignment film having a uniform film thickness distribution.

[0015]

A first aspect of the method for forming an alignment film of a liquid crystal display device according to the present invention has a plurality of ejection holes arranged in each row at a predetermined pitch, and the ejection holes of any row are provided. Includes spraying the alignment film solution onto the substrate by using an area type ink jet nozzle arranged so as to be displaced by half the pitch with respect to the arrangement of the ejection holes in adjacent rows. To do.

A second aspect of the method for forming an alignment film of a liquid crystal display device according to the present invention uses a line type ink jet nozzle having a plurality of ejection holes arranged in a line at a predetermined pitch. The next injection of the alignment film solution is performed at a position shifted from the previous injection position by a half of the pitch in a direction substantially orthogonal to the traveling direction of the substrate.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION A first embodiment of a method for forming an alignment film of a liquid crystal display device according to the present invention will be described with reference to FIG. FIG. 1 is a configuration diagram of an inkjet nozzle 2 used in the alignment film forming method of the present embodiment. The inkjet nozzle 2 is an area type inkjet nozzle, and for example, 2500 × 2500 ejection holes 4 for ejecting the alignment film solution are provided on the surface facing the substrate (not shown) (see FIG. 1B). The diameter of the ejection hole 4 is, for example, 50 μ
m, and the pitch p of the ejection holes 4 in each row is 100 μ, for example.
m. Then, the ejection holes 4 in any row have a half pitch (= p / 2) with respect to the arrangement of the ejection holes 4 in the row adjacent to the above row.
They are arranged with a shift (see FIG. 1 (b)).

The alignment film solution is sent from the outside to the ink jet nozzle 2 through the supply port 3, and the ink jet nozzle 2 is operated based on the jet command signal to jet the alignment film solution from the jet holes 4. The inkjet nozzle 2 is configured to be able to independently control the ejection from each ejection hole 4.

An alignment film is formed by using the above-mentioned ink jet nozzle 2 as follows. Since the inkjet nozzle 2 used in this embodiment has a size that covers the entire alignment film forming region of the substrate, after the substrate is placed facing the inkjet nozzle 2, the inkjet nozzle 2 is replaced with the inkjet nozzle 2 as shown in FIG. Spray coating is performed without moving any of the substrates 40. At this time, the alignment film solution is not ejected from the ejection holes protruding from the alignment film formation region. The alignment film solution used is an alignment film material such as AL-1051.
It is a 2.0% by weight solution of (trade name). After spraying the alignment film solution onto the substrate 40, the substrate 40 is heated at 100 ° C. for 15
By drying for 2 seconds and heating and baking at 180 ° C. for 30 minutes, the solvent (eg, γ-butyl lactone) in the applied alignment film solution is removed to form an alignment film.

As described above, in the forming method of the first embodiment, the ejection holes 4 of an arbitrary row are adjacent to the ejection holes 4 of an adjacent row.
Since it is performed using the area type ink jet nozzles that are displaced by a half pitch with respect to the arrangement, the relative speed between the ink jet nozzles and the substrate and the timing of coating are controlled using the line type ink jet nozzle as in the past. However, unevenness in film thickness due to variations in the overlapping amount of droplets does not occur as compared with the case of coating.

The area type ink jet nozzle 2
Is smaller than the alignment film formation region, for example, the number of ejection holes 4 is 500 × 500, and the diameter of ejection holes 4 is 50.
When the pitch p is 100 μm and the ejection holes 4 have a pitch p of 100 μm, the inkjet nozzle 2 is relatively moved a plurality of times with respect to the substrate as shown in FIG. It will be. Also in this case, an alignment film having a uniform film thickness distribution can be formed as in the case of the forming method according to the first embodiment.

Further, in the forming method of the first embodiment, the ejection holes 4 in any row are adjacent to the ejection holes 4 in any row.
The area type ink jet nozzles 2 are arranged so as to be displaced by a half pitch (p / 2) with respect to the arrangement of FIG.
Even if an area type ink jet nozzle in which the ejection holes 4 are arranged in a matrix as shown in FIG. 4 is used, an alignment film having a more uniform film thickness distribution than in the conventional case can be formed.

Next, a second embodiment of the method for forming an alignment film of a liquid crystal display device according to the present invention will be described with reference to FIG.
The forming method of this embodiment uses a line type ink jet nozzle 12 as shown in FIG.
The next jetting position of the inkjet nozzle 12 is shifted from the previous jetting position by a half of the arrangement pitch p of the jet holes 14 in a direction substantially orthogonal to the traveling direction of the substrate (not shown), and the next jetting next time. The spray coating is performed by moving the position in the opposite direction by a half pitch from the next spray position. Therefore, the movement of the inkjet nozzle 12 proceeds in a zigzag manner as shown in FIG. in this case,
By appropriately selecting the relative speed between the substrate and the inkjet nozzle 12, it is possible to obtain the same effect as that of the first embodiment.

[0024]

As described above, according to the present invention, an alignment film having a uniform film thickness distribution can be formed.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an inkjet nozzle used in a first embodiment of a method for forming an alignment film of a liquid crystal display element according to the present invention.

FIG. 2 is an explanatory diagram illustrating a forming method according to the first embodiment.

FIG. 3 is an explanatory diagram illustrating a modified example of the forming method according to the first embodiment.

FIG. 4 is a schematic diagram of an arrangement of ejection holes of an inkjet nozzle used in another modification of the forming method according to the first embodiment.

FIG. 5 is an explanatory diagram illustrating a second embodiment of a method for forming an alignment film of a liquid crystal display element according to the present invention.

FIG. 6 is an explanatory view illustrating a conventional alignment film forming method.

FIG. 7 is an explanatory view illustrating a problem of a conventional alignment film forming method.

FIG. 8 is an explanatory diagram illustrating formation of an alignment film by an offset printing method.

[Explanation of symbols]

 2 Area type inkjet nozzle 3 Alignment film solution supply port 4, 14 Jet hole 12 Line type inkjet nozzle 35 Alignment film solution 40 Substrate

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Muneharu Akiyoshi 8 Shinsugita-cho, Isogo-ku, Yokohama-shi, Kanagawa, Ltd., Toshiba Corporation Yokohama Works (72) Inventor Akiko Kamino, Shinsita-cho, Isogo-ku, Yokohama, Kanagawa Address Stock Company Toshiba Yokohama Office

Claims (2)

[Claims] 1. A plurality of ejection holes are arranged in each row at a predetermined pitch, and the ejection holes of any row are arranged so as to be offset from the arrangement of the ejection holes of an adjacent row by half the pitch. A method for forming an alignment film for a liquid crystal display device, comprising a step of spraying and applying an alignment film solution onto a substrate using an area type inkjet nozzle. 2. A line type ink jet nozzle having a plurality of ejection holes arranged in a line at a predetermined pitch is used.
The liquid crystal display device characterized in that the next jetting of the alignment film solution from this ink jet nozzle is carried out at a position shifted by half the pitch in a direction substantially orthogonal to the traveling direction of the substrate from the previous jetting position. Alignment film forming method.