JP2009116167A - Manufacturing method of liquid crystal display element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve display quality of a liquid crystal display device.
[Solution]
A step of forming an electrode pattern on each surface of a pair of substrates, a step of forming an alignment film on the electrode pattern, a step of rubbing the alignment film, and a step of irradiating plasma on the alignment film subjected to the rubbing treatment And a step of forming a liquid crystal cell by sandwiching a liquid crystal between a pair of substrates on which an alignment film irradiated with plasma is formed.
[Selection] Figure 2

Description

  The present invention relates to a method for manufacturing a liquid crystal display element (LCD).

  In manufacturing the LCD, a rubbing process is performed after forming an alignment film above the substrate. Japanese Patent Application Laid-Open No. 2005-234254 proposes a rubbing treatment method with few alignment defects.

JP 2005-234254 A

  In the LCD manufacturing process, if the cleaning after the rubbing is insufficient, the rubbing cloth dust and the fine dust adhered by static electricity due to the rubbing remain on the surface of the alignment film and become cells, and display defects due to visual recognition of the dust itself, Or a display defect occurs due to disorder of liquid crystal alignment in the vicinity of dust.

  In a simple matrix type LCD, only a surface treatment to the extent that an air blow is performed after the rubbing treatment is performed, and the superposition is often performed without performing cleaning or the like. Since strong static electricity is generated after rubbing, it was not possible to completely remove fine dust by air blow.

  An object of the present invention is to provide a liquid crystal display element with improved display quality.

  According to one aspect of the present invention, a step of forming an electrode pattern on each surface of a pair of substrates, a step of forming an alignment film on the electrode pattern, a step of rubbing the alignment film, A method for manufacturing a liquid crystal display element, comprising: irradiating plasma on the alignment film subjected to rubbing treatment; and forming a liquid crystal cell by sandwiching liquid crystal between a pair of substrates on which the alignment film irradiated with the plasma is formed. Is provided.

  According to the present invention, a liquid crystal display element with improved display quality can be provided.

  With reference to FIG. 1, the outline of the manufacturing method of the liquid crystal display element produced by an Example is demonstrated. FIG. 1 is a schematic cross-sectional view of a liquid crystal display element.

  A transparent indium tin oxide (ITO) film is formed on the surface of each of the two glass substrates 1A and 1B by CVD, vapor deposition, sputtering, etc., and a desired ITO electrode pattern 2 and external extraction wiring 2l are formed by photolithography. Form. As a glass substrate, blue plate glass having a plate thickness of 0.7 mm and a substrate size of 150 mm × 300 mm was used and washed using a washing machine. Here, brush cleaning using an alkaline detergent, brush cleaning with pure water, draining with an air knife, IR (infrared) and UV (ultraviolet) cleaning were performed. The thickness of ITO is 800 mm.

  An insulating film 4 is formed on the glass substrates 1A and 1B with the ITO electrode pattern 2 by flexographic printing. The insulating film 4 is not essential, but may be formed to prevent a short circuit between the upper and lower substrates. As a method for forming the insulating film, a method such as vapor deposition or sputtering may be performed using a metal mask in addition to flexographic printing.

  Next, an alignment film 5 having substantially the same pattern as that of the insulating film 4 is formed on the insulating film 4 by flexographic printing or the like. Next, a rubbing process is performed. The rubbing is a process in which a cylindrical roll wound with a cloth is rotated at high speed and rubbed on the alignment film 5.

  After the alignment film 5 is formed, surface treatment is performed by irradiating atmospheric pressure plasma. The detailed steps of alignment film formation and surface treatment will be described in the examples for each type of LCD.

  The sealing material 6 is screen-printed in a predetermined pattern. A dispenser may be used for forming the sealing material 6 instead of screen printing. A thermosetting ES-7500 (manufactured by Mitsui Chemicals) is used as the sealing material, but a photo-curing material or a combined light / heat sealing material may be used. The sealing material 6 contains several percent of glass fibers having a diameter of 6 μm.

  The conductive material 7 is printed at a predetermined position. Here, the seal material ES-7500 containing a few percent of styrene balls plated with 6.5 μm Au is screen-printed at a predetermined position as the conductive material 7.

  The sealing material pattern 6 and the conductive material pattern 7 are formed only on the upper substrate 1B, and a gap control material is sprayed on the lower substrate 1A by a dry spraying method. A 6 μm plastic ball is used as the gap control material.

  The two substrates 1A and 1B are stacked into cells at predetermined positions so that the alignment film 5 is on the inside, and the sealing material 6 is cured by heat treatment in a pressed state.

  Next, the glass substrate is scratched with a scriber device, and is divided into a predetermined size and shape by breaking to create empty cells.

  The nanometer-sized metal particle-containing liquid crystal 3 is injected into the empty cell by an injection method utilizing capillary action, and then the injection port is sealed with an end seal material. Thereafter, the glass substrate is chamfered and cleaned to form the liquid crystal display element 101.

  Hereinafter, an embodiment will be described for each type of LCD.

Example 1
Example 1 is directed to the manufacture of twisted nematic (TN) -LCDs. As the alignment film, a low pretilt angle horizontal alignment film material for TN (manufactured by Nissan Chemical Co., Ltd., SE-410) is used. This alignment film is printed on the substrate and then subjected to main baking (180 ° C. to 250 ° C., 1 hour to 2 hours). Here, heat treatment is performed at 180 ° C. for 1.5 hours.

  Rubbing is performed as an alignment treatment. The rubbing is performed so that the liquid crystal layer is twisted 90 degrees on the substrate surface.

  After rubbing, surface treatment with atmospheric pressure plasma (AP) is performed.

  Please refer to FIG. FIG. 2 is a schematic diagram of alignment film processing using atmospheric pressure plasma AP. As shown in the drawing, the substrate 1 on which the electrode 2 and the alignment film 5 are formed is conveyed in the direction of the arrow, and the atmospheric pressure plasma AP is irradiated from above to the alignment film 5. The atmospheric pressure plasma AP is generated by supplying a plasma generating gas from the gas supply source GS between the plasma electrodes 9 and applying an AC voltage from the power source PS between the electrodes. The generated plasma is irradiated onto the substrate from the nozzle 10. The plasma conditions are a power of 4.5 kW, a nitrogen gas flow rate of 300 l / min, and a dry air flow rate of 300 ml / min. The distance between the nozzle head and the alignment film surface is 3 mm.

  Here, two types of conveyance speeds of 3 m / min and 1 m / min are used, the former being weak AP processing conditions and the latter being strong AP processing conditions. The width of the nozzle is about 150 mm. Air blow is performed after AP treatment.

  Thereafter, a main seal pattern is formed on the substrate by screen printing or a dispenser, and a gap control agent is sprayed. Then, the two substrates are bonded to form an empty cell. A liquid crystal for STN (Δn = 0.093) manufactured by Dainippon Ink & Chemicals, Inc. is injected into the void portion of the empty cell by a vacuum injection method (method using a capillary phenomenon) to complete a TN-LCD.

  Note that the liquid crystal cell may be formed by an ODF (drop injection) method in which a sealing material is applied to one substrate to form a frame, a liquid crystal is dropped on the frame, and then the other substrate is bonded.

  Three types of liquid crystal display elements of no AP treatment, weak AP treatment, and strong AP treatment were produced by the above method, and their pretilt angles were measured at a plurality of points. The crystal rotation method was used for the measurement, and light was applied to six minute areas (0.5 mmΦ).

  With reference to FIG. 3, the effect of the AP processing will be examined. FIG. 3 is a table of pretilt angles of the respective elements. As shown in the figure, when AP processing is not performed (only air blow), the pretilt angles of the six areas are 1.4276 ° to 1.9795 °. The difference between the maximum value and the minimum value is 0.5519 °. In addition, minute dust of about 0.1 mm to 0.3 mm was observed in the cell.

  On the other hand, looking at the pretilt angle of the cell subjected to AP processing, the pretilt angle is lower than that of the untreated cell, and the difference between the maximum value and the minimum value is small. In the case of weak AP processing, the pretilt angles at 6 points are 0.93979 ° to 1.0317 °, and the difference between the maximum value and the minimum value is 0.09191 °. In the case of strong AP processing, the pretilt angles at six points are 0.64694 ° to 0.75657 °, and the difference between the maximum value and the minimum value is 0.10963 °.

  In general, the lower the pretilt angle, the higher the contrast of the multiplex-driven TN-LCD, and therefore it can be said that AP processing is preferable. Since the width of the variation in the pretilt angle is also small, the display uniformity will be high. In addition, when the AP treatment was performed, the fine dust seen when untreated was not observed. It is considered that minute dust adheres to the alignment film due to static electricity. When AP treatment is performed, static electricity is removed (the effect of removing static electricity has been confirmed), and it is considered that fine dust is no longer attached.

  It is known that the atmospheric pressure plasma AP has a function of decomposing organic substances. Therefore, among the alignment films, side chains, main chains (organic bonds), etc., which have a larger rise or rise in an abnormal direction, are decomposed, and as a result, an alignment film having a low pre-tilt angle with little variation is decomposed. It is thought that it is obtained. A low pretilt angle can be realized by weakening rubbing or the like. However, in that case, it is not realistic because a place where the pretilt angle becomes 0 ° occurs. Therefore, it is effective to perform AP processing as in the embodiment.

  In Example 1, the contrast ratio of the 1/8 Duty drive TN-LCD could be increased to 1.5 times by changing the pretilt angle from an average of 1.6 ° to 0.8 °.

(Example 2)
The second embodiment is directed to the manufacture of a super twist nematic STN-LCD. The type and size of the glass substrate and the cleaning method are the same as in Example 1. After the glass substrate is washed, an ITO film is formed, and then the alignment film is flexographically printed. Here, a high pretilt angle horizontal alignment film material (manufactured by Nissan Chemical Industries) for STN is used as the alignment film. This alignment film is finally baked (180 ° C. to 250 ° C., 1 to 2 hours). Here, heat treatment is performed at 200 degrees for 1.5 hours.

  Next, rubbing is performed as an alignment film treatment. The rubbing is performed so that the liquid crystal layer is twisted 180 °.

  AP processing is performed after rubbing. The AP processing method is the same as that shown in FIG. The plasma conditions are a power of 3.0 kW, a nitrogen gas flow rate of 300 l / min, a dry air flow rate of 300 ml / min, a distance between the nozzle head and the substrate of 3 mm, and a transfer speed of 3 m / min.

  Thereafter, a liquid crystal display element is completed in the same manner as in Example 1. However, the liquid crystal to be injected is STN liquid crystal (Δn = 0.165) manufactured by Dainippon Ink and Chemicals, Inc. The polarizing plate is arranged so as to be normally black.

  A sample of STN-LCD was prepared by the above method. For comparison, only a quarter (area ratio) region of one liquid crystal cell was subjected to AP treatment, and the remaining 3/4 region was not treated. After the treatment, the entire surface was blown with air.

  FIG. 4 is a plan view of a sample display unit. The left 1/4 area (referred to as the left area) is the area where AP processing has been performed, and the right 3/4 area (referred to as the right area) is the area where AP processing has not been performed. A voltage that kept black display, that is, a voltage slightly lower than the threshold voltage, was applied to the sample. As shown in the figure, the left region remains black, but white point-like display defects (referred to as white point defects) are observed in the right region.

  The white spot defect is not seen when no voltage is applied, but is seen only when a voltage in the vicinity of the threshold is applied. Therefore, it is considered that the white spot defect is caused by a variation in the local pretilt angle of the alignment film. After that, a plurality of samples were produced, but no white spot defect was confirmed in the area subjected to AP treatment. This is presumably because, for the same reason as in Example 1, the variation in the pretilt angle of the alignment film was reduced and the amount of fine dust was reduced.

  Although the sample according to Example 2 could not measure the pretilt angle, there was almost no difference in the voltage-transmittance characteristics of the LCD with and without the AP process, so the pretilt angle itself was different between the AP process area and the unprocessed area. It is considered to be the same level.

  By performing AP treatment after the alignment film is rubbed as in the above embodiment, display defects can be reduced and display quality can be improved.

  Although the present invention has been described with reference to the embodiments, the present invention is not limited thereto. For example, in the case of a liquid crystal display device using an alignment film, the effect of AP treatment can be expected (at least for removal of minute dust). Applicable LCD types include D (Dual) STN-LCD, F (Film) STN-LCD, VA (Vertical Alignment) -LCD, and the like. In addition, display uniformity can be expected to improve in TFT-LCDs using IPS (in-plane switching), multi-domain VA, TN mode, and the like.

  It will be apparent to those skilled in the art that other various modifications, improvements, combinations, and the like can be made.

FIG. 1 is a schematic cross-sectional view of a liquid crystal display element. FIG. 2 is a schematic diagram of alignment film processing using atmospheric pressure plasma AP. FIG. 3 is a table of pretilt angles of the respective elements. FIG. 4 is a plan view of a sample display unit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 1A, 1B (Transparent) board | substrate 2, 2l Electrode 3 Liquid crystal 4 Insulating film 5 Orientation film 6 Sealing material 7 Conductive material 8 Polarizing plate 9 Plasma generator 10 Nozzle 101 Liquid crystal display element AP Atmospheric pressure plasma

Claims (3)

Forming an electrode pattern on each surface of a pair of substrates;
Forming an alignment film on the electrode pattern;
Rubbing the alignment film; and
Irradiating the rubbing-treated alignment film with plasma;
Forming a liquid crystal cell by sandwiching liquid crystal between a pair of substrates on which an alignment film irradiated with the plasma is formed.   The method of manufacturing a liquid crystal display element according to claim 1, wherein the plasma irradiation is performed while conveying the substrate on which the alignment film is formed or moving the plasma head.   The method for manufacturing a liquid crystal display element according to claim 1, wherein the plasma is atmospheric pressure plasma.

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