JP2007193180A - Method for spraying spacer to transparent substrate of liquid crystal display cell, device, and liquid crystal display cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the occurrence of a streak-like dark stripe by the fluctuation of the gap amount in the cell gap of a liquid crystal display cell. <P>SOLUTION: Droplets of spacer ink are dropped on the surface of a substrate 1 at a predetermined interval by operating an ink jet means 23 while the substrate 1 is transported by a transport table 20 in the X direction, and by jetting spacer ink from each nozzle 30 constituting each ink jet head 26. When medium spacer beads whose particle diameter is the standard diameter of 4 μm are used, large spacer beads of 4.2 μm in particle diameter and small spacer beads of 3.8 μm in particle diameter are mixed at the predetermined ratio. The cell gap G is formed with the fluctuation range of ±0.2 μm of 4 μm as a base for the height of each spacer 4 in the X direction which is the horizontal scan direction. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  In order to form a cell gap serving as a liquid crystal sealing space between two transparent substrates that are superposed on each other, the present invention provides a method and apparatus for dispersing spacers on a transparent substrate surface of a liquid crystal display cell by an inkjet method, and The present invention relates to a liquid crystal display cell in which a transparent substrate on which spacers are dispersed is bonded to the other transparent substrate and liquid crystal is sealed between the transparent substrates.

  As a liquid crystal display device, for example, a color TFT liquid crystal display cell is composed of a TFT substrate made of a transparent substrate such as glass and a color filter substrate, which are in close contact with each other. Instead, it is joined through a minute gap called a so-called cell gap, and liquid crystal is sealed in this cell gap. A cell gap, which is a minute gap in which liquid crystal is enclosed, is secured by a spacer made of an aggregate of a plurality of spacer beads. The spacer is composed of agglomerates of spacer beads composed of spherical fine particles having a particle diameter of 3 to 5 μm, and either a TFT substrate or a color filter substrate, for example, a color filter substrate is used as a substrate to be processed, and a large number of spacers are formed on the surface. It will be distributed.

  Spacer beads as a component of the spacer are opaque particles. Therefore, if the spacer beads are located in the pixel region, the image quality of the display image is deteriorated when configured as a liquid crystal display device. Therefore, in order to prevent this image quality deterioration, the spacer is limited to the black matrix region. Placed in. For this purpose, a spacer ink made of a suspension in which spacer beads are uniformly dispersed in a solvent is used, and this spacer ink is landed on the black matrix region. As this spacer ink supply method, for example, as disclosed in Patent Document 1, a method of ejecting by ink jet has been conventionally known. In the ink jet system, a droplet of spacer ink is ejected from a micro nozzle of the ink jet head toward a substrate to be processed by using an ink jet means including an ink jet head provided with a minute nozzle, and is attached to the substrate to be processed. Is.

  After droplets of spacer ink ejected from each nozzle of the ink jet head land on a predetermined position of the substrate to be processed, the solvent evaporates, and spacer beads remain on the substrate to be processed after drying. . One droplet ejected from the ejection port includes a plurality of, specifically 5 to 8 spacer beads. While the solvent is volatilized, these spacer beads are in close contact with each other. The aggregate of the spacer beads is a spacer, and the spacer is dispersed almost uniformly on the entire surface of the substrate to be processed.

The ink jet head of the ink jet means faces the dispersion surface of the spacers on the substrate to be processed, but the substrate to be processed is disposed horizontally, and the ink jet head is disposed at an upper position separated from the substrate to be processed by a predetermined distance. And while conveying a to-be-processed substrate, the droplet of spacer ink is intermittently ejected over the predetermined width from the some nozzle which comprises an inkjet head toward a to-be-processed substrate. Further, when the width dimension of the substrate to be processed is large, the ink jet means is configured to shift in a direction orthogonal to the conveyance direction of the substrate to be processed. Accordingly, the spacer ink droplets are supplied to the entire surface of the substrate to be processed by ejecting the spacer ink droplets while reciprocating the substrate to be processed and shifting the ink jet means in the direction orthogonal thereto. Accordingly, the transport direction of the substrate to be processed is the main scanning direction when the spacer ink is ejected, and the direction orthogonal to the main scanning direction is the sub-scanning direction.
JP 2003-251243 A

  Here, the concentration of the spacer beads in the spacer ink is strictly controlled, and the particle size is controlled so that the particle size of the spacer beads dispersed in the spacer ink is as uniform as possible. In a commonly used spacer ink, the dispersion of the particle diameter of the dispersed spacer beads is suppressed to ± 0.05 μm or less. In addition, since the ink jet head can easily control ejection from the nozzles and can impart directivity to the ejected droplets, the droplets of the spacer ink are accurately landed at predetermined positions in the black matrix region. To be able to. As a result, the spacers can be uniformly dispersed at predetermined positions on the entire surface of the substrate to be processed, and when the other transparent substrate is bonded, a uniform cell gap can be formed therebetween.

  Here, the two transparent substrates bonded to each other are made of thin plates, and a pressing force is applied during the bonding. Therefore, the transparent substrate is bent when a pressing force is applied at the time of bonding. As a result, the opposing surfaces of both transparent substrates come into close contact with the spacer, and the cell gap is stably maintained. In this way, when the two substrates are bonded, the substrate to be processed is rectangular, and particularly when the liquid crystal display cell is large in size, the thin and light stripes are streaked toward the main scanning direction of the ink jet means. Many stripes may be formed. The generation of the streaky shading pattern in the bonded substrate is caused by a minute variation in the gap amount in the cell gap.

  The cell gap basically depends on the particle size of the spacer beads. Therefore, the cell gap does not vary greatly, but the error range of the particle size of the spacer beads is about ± 0.05 μm. Thus, the fluctuation range of the gap amount is larger than 0.1 μm and may be about 0.3 μm or more. In addition, in the main scanning direction, fluctuations that repeat regularly to some extent are shown for each traveling width of the inkjet head having a plurality of nozzles. When configured as a liquid crystal display device, even if thin streaky shading due to fluctuations in the gap amount as described above occurs on the display surface, when a liquid crystal display cell is configured, an image displayed on the display is not displayed. Although not particularly reduced, it is not only preferable in terms of appearance, but in order to display a higher quality image, it is desirable to suppress variation in the gap amount as small as possible.

  As described above, since the spacer ink is sprayed while the inkjet head and the substrate to be processed are moved relative to each other, the inkjet head and the substrate to be processed are brought into a non-contact state, and even during the relative movement between the inkjet head and the substrate to be processed. In order to prevent the head from coming into contact with the substrate to be processed, it is necessary to provide a certain distance between the inkjet head and the substrate to be processed. The spacer ink is a suspension of spacer beads. From the viewpoint of preventing clogging, the diameter of the minute nozzles of the inkjet head is set to a minimum of about 20 μm. Therefore, the spacer ink ejected from the nozzles has a certain extent until it reaches the substrate to be processed as droplets. In the liquid crystal display cell, the black matrix region formed on the substrate has a very thin band shape with a width dimension of about 10 to 30 μm. In addition, the inkjet head needs to be spaced about 1 mm from the substrate to be processed. When the nozzle diameter of the inkjet head is set to a minimum of 20 μm, the size of the droplet when landing on the substrate to be processed is large. The thickness is 40 μm or more. That is, the size of the droplet upon landing is slightly larger than the width dimension of the black matrix region.

  There is no problem if it is ejected from each nozzle constituting the inkjet head under strictly the same conditions, but if the ejection direction of the liquid droplet deviates from the normal direction, especially if it is deviated randomly in the nozzle alignment direction, The intervals between the landing positions of the liquid droplets are not uniform. In addition, even if it is a TFT substrate or a color filter substrate, there are minute irregularities on the surface of the substrate to be processed, so that depending on the landing position, some spacer beads fall into the depressions, contributing to the cell gap of each spacer. There will be variations in the number of spacer beads.

  For the above reasons, the gap amount of the cell gap varies. Therefore, fluctuations in the gap amount can be suppressed by accurately controlling the landing position of the droplet or by reducing the droplet when landing. However, if the inkjet head is extremely close to the substrate to be processed, there is a high possibility of contact during movement, and there is a limit to reducing the nozzle diameter from the viewpoint of preventing clogging of the spacer ink. . For this reason, in practice, it is impossible to prevent fluctuations in the gap amount of the cell gap described above.

  The present invention has been made in view of the above points, and an object of the present invention is to suppress the generation of streak gray stripes due to the gap amount variation in the cell gap of the liquid crystal display cell.

  In order to achieve the above-described object, a method of dispersing the spacers for forming a cell gap on the surface of the transparent substrate constituting the liquid crystal cell of the present invention in such a manner that a predetermined pitch is provided in the width direction of the transparent substrate. Ink jet heads having a plurality of nozzles are arranged opposite to each other, and a plurality of types of spacer beads having different particle diameters are used as solvents while the transparent substrate, the ink jet head, and the nozzles are relatively moved in the crossing direction of the nozzles. It is characterized in that the droplets of spacer ink uniformly dispersed on the surface of the transparent substrate are sprayed from the respective ejection ports of the inkjet nozzle.

  In addition, in the present invention, the configuration of the spacer spraying device that disperses the spacers for forming the cell gap on the surface of the transparent substrate constituting the liquid crystal cell is obtained by uniformly dispersing a plurality of types of spacer beads having different particle diameters in the solvent. Ink supply means for supplying spacer ink and a plurality of nozzles at predetermined pitch intervals in the width direction of the transparent substrate in order to spread the spacer ink supplied from the ink supply means on the surface of the transparent substrate. The present invention is characterized in that it includes a provided inkjet head, and a drive unit that relatively moves the transparent substrate and the inkjet head at least in a direction intersecting the nozzle arrangement direction.

  Further, the liquid crystal display cell according to the present invention has a transparent substrate in which a spacer in which a plurality of types of spacer beads having different particle sizes are aggregated is dispersed on the surface of the black matrix, and a cell gap is formed on the transparent substrate by the spacer. The other transparent substrate is bonded as formed, and liquid crystal is sealed in this cell gap.

  It is practically impossible to make all the ejection conditions of the spacer ink by the plurality of nozzles constituting the ink jet head the same. If the particle size of the spacer beads contained in the spacer ink is made uniform, the height of the spacer becomes substantially constant in the main scanning direction. On the other hand, since spacer ink is ejected from nozzles having different ejection conditions, the number of spacer beads contributing to the spacer spacing and the cell gap differs in the sub-scanning direction. That is, if the spacer beads have a constant particle size, gaps that are uniform in the main scanning direction and fluctuate in the sub-scanning direction are formed. This is the cause of streaky shading. Therefore, if the gap variation in the sub-scanning direction cannot be prevented, if the gap in the main scanning direction is also made nonuniform, streaky shading is not generated.

  Since the gap fluctuation width in the main scanning direction is the gap fluctuation width in the sub-scanning direction, specifically, the gap fluctuation width is 0.3 μm or more, it should be equal to or less than this fluctuation width. For example, when configured as a liquid crystal display cell, the image quality is not substantially affected. In the present invention, when referring to a plurality of types of spacer beads having different particle diameters, the particle diameter can be changed continuously, but can also be changed in stages. Moreover, when changing in steps, it may be two steps, and can also be changed in three steps. The gap amount is usually 3 to 5 μm. For example, when the gap amount is based on 4 μm, a spacer bead having a particle diameter of 4.2 μm and a spacer bead of 3.8 μm are mixed, or 4.2 μm, It is also possible to mix three types of spacer beads of 4.0 μm and 3.8 μm. The amount of the intermediate medium size spacer beads can be the same as the total amount of the spacer beads of large and small particle sizes, and the large, medium, and small spacer beads are distributed almost evenly. You can also.

  Spacers can be uniformly distributed over the entire surface of the transparent substrate by the ink jet method, and when configured as a liquid crystal display cell, the gap amount in the cell gap is varied in a controlled state, and the variation in the gap amount is also changed. Rather than having regularity in the main scanning direction and the sub-scanning direction, random fluctuations can be generated, thereby suppressing the occurrence of streaky gray stripes in the liquid crystal display cell.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. First, in FIG. 1, reference numeral 1 denotes a substrate, and this substrate 1 is a transparent substrate made of glass or the like, specifically, for example, a TFT substrate. Switching elements made of thin film transistors are formed in a matrix on the substrate 1, and the color filters are bonded in an aligned state. In the figure, reference numeral 2 denotes a pixel area constituting pixels of each color of RGB, and the pixel area 2 is partitioned by a black matrix area 3. When the spacers 4 are uniformly dispersed in the black matrix region 3 and the TFT substrate and the color filter are joined by the spacers 4, a gap called a cell gap is formed between the two substrates. Thus, a liquid crystal display cell is formed by sealing liquid crystal in the gap between the two substrates formed by the spacer 4.

  Here, as shown in FIG. 2, the spacer 4 is an aggregate of a plurality of spacer beads 4a, and one spacer 4 includes approximately 5 to 8 spacer beads 4a. The spacer 4 is obtained by aggregating the spacer beads 4a by adhering droplets of spacer ink made of a suspension in which the spacer beads 4a are uniformly dispersed in a predetermined solvent to the substrate 1 and volatilizing the solvent. It is. In other words, as shown by the phantom line in the figure, when the spacer ink is landed, it becomes a droplet having a predetermined spread, but when the solvent volatilizes, the spacer beads 4a are aggregated. Aggregates of spacer beads 4 a included in the droplets are spacers 4.

  FIG. 3 shows a system configuration for spreading the spacers 4 on the substrate 1. In the figure, 10 is a work carry-in part, and 11 is a work carry-out part. The substrate 1 to be processed is carried in from the work carry-in unit 10. Then, the substrate 1 carried in in this way is transported to the ink dropping stage 13 through a pretreatment stage 12 for performing processing such as surface modification as required. In the ink dropping stage 13, spacer ink is dispersed on the surface of the substrate 1.

  After the spacer ink has landed on the surface of the substrate 1, the substrate 1 moves to the first heat treatment stage 14, volatilizes the ink component from the spacer ink, and then the substrate 1 is baked in the second heat treatment stage 15. As a result, the spacer beads are fixed to the surface of the substrate 1. Here, the reason why the substrate 1 is heat-treated in two stages is to remove the ink components by quickly drying the spacer ink dropped from the inkjet means 23 in the first stage. When the substrate 1 is rapidly heated to a high temperature, the individual spacer beads 4a in the spacer ink do not aggregate and are dried in the disjointed positions. Although the substrate 1 can be naturally dried, it is efficiently dried by heating at a low temperature in the first heat treatment stage 14. Further, in the second stage, the substrate 1 is baked by heating at a high temperature, and the spacer 4 having dried ink is fixed to the substrate 1. When the spacer ink is naturally dried, heating is performed in one stage.

  As shown in FIG. 4, the substrate 1 is placed on a transfer table 20 and fixedly held on the transfer table 20 by means such as vacuum suction. The conveying table 20 is conveyed by the ball screw feeding means 21 along the X-axis guide 22 in the X direction (main scanning direction) in the figure. During this time, spacer ink is intermittently dropped onto the surface of the substrate 1. For this purpose, an ink jet means 23 is disposed on the ink dropping stage 13, and this ink jet means 23 is attached to a Y-axis guide 24 having a gate shape so as to straddle the transport table 20. The guide 24 is provided with a moving table 25 on which the ink jet means 23 is installed. The moving table 25 is movable in the Y direction (sub-scanning direction) orthogonal to the conveying direction of the conveying table 20. The inkjet unit 23 includes an inkjet head 26 and an ink bottle 27 as an ink supply unit. The inkjet head 26 and the ink bottle 27 are moved in the Y direction along the Y-axis guide 24 by the moving base 25. Become. Accordingly, the transport table 20 and the movable table 25 and their drive mechanisms constitute drive means for driving the substrate 1 and the inkjet head 26. The drive may be provided on either the substrate 1 side or the inkjet head 26 side.

  As shown in FIG. 5, the ink jet head 26 constituting the ink jet means 23 is composed of a large number of minute nozzles 30 arranged at a predetermined pitch interval, and a constant amount of spacer ink is intermittently supplied from each nozzle 30. It can be sprayed on. The ejection of the spacer ink is individually controlled for each nozzle 30 to eject the spacer ink. As shown in FIG. 6, the inkjet head 26 includes a chamber piece 31 communicating with the nozzle 30, and the chamber piece 31 is connected to an ink supply path from the ink bottle 27.

  An actuator 32 made of a piezoelectric element is mounted on the chamber piece 31. When a voltage is applied to the actuator 32, the actuator 32 is deformed and the chamber piece 31 expands as shown by a one-dot chain line in FIG. It will be. As a result, the spacer ink is sucked into the chamber piece 31 from the ink bottle 27 side. Next, when the voltage application to the actuator 32 is cut off, the original state is restored. At this time, the volume of the chamber piece 31 is reduced, and spacer ink corresponding to the volume reduction is ejected from the nozzle 30.

  A plurality of inkjet heads 26 are preferably mounted on the inkjet means 23, and each of these inkjet heads 26 is disposed at predetermined intervals. Accordingly, when the ink jet means 23 is moved in one direction in the X direction, the spacer ink is intermittently dropped onto the surface of the substrate 1 in a band-shaped range corresponding to the width of each ink jet head 26. After the ink jet unit 23 moves from the start point position to the end point position in the X direction, it is shifted in the Y direction by the width of the ink jet head 26 and moved in the opposite direction in the X direction. Spacer ink is dripped so as to fill the portion. It is more desirable to arrange the plurality of inkjet heads 26 arranged in such a manner as to be inclined at a predetermined angle with respect to the Y direction. If comprised in this way, the pitch space | interval of spacer ink can be changed by changing this inclination angle.

  By configuring as described above, while the substrate 1 is transported in the X direction by the transport table 20, the ink jet unit 23 is operated to eject the spacer ink from each nozzle 30 constituting each ink jet head 26. Then, spacer ink droplets are dropped on the surface of the substrate 1 at predetermined intervals. When the substrate 1 reaches the moving end in the X direction, the inkjet means 23 is shifted in the Y direction to move the substrate 1 back in the X direction, and the dropping of the spacer ink is continued during this time. As a result, the spacer ink is uniformly dropped on the entire surface of the substrate 1, and then the substrate 1 is heated and dried, whereby the solvent in the spacer ink is volatilized. At this volatilization, the spacer 4 in which the spacer beads 4 a aggregate is formed on the substrate 1. Remain.

  In this state, on the surface of the substrate 1 on which the spacer 4 is formed, as shown in FIG. 7, the other substrate 5 (if the substrate 1 is a TFT substrate, the other substrate is a color filter substrate). Be joined. As a result, the bonded substrate 6 is formed. A cell gap G formed by the spacer 4 is interposed between the substrates 1 and 5 constituting the bonded substrate 6, and liquid crystal is sealed in the cell gap G. Is done. This cell gap G is an interval substantially corresponding to the diameter of the spacer beads 4 a constituting the spacer 4. In FIG. 7, reference numeral 7 denotes a sealing material for defining and forming a liquid crystal sealing space.

  Now, the particle size of the spacer beads 4a dispersed in the spacer ink is 4 μm, the error range is ± 0.05 μm or less, and the spacers 4 are dispersed on each black matrix region 3 on the substrate 1 by the above-described method. Then, the other substrate 5 is joined to the substrate 1, and the width of the cell gap G is larger than the variation in the error range of the particle diameter in the spacer beads 4a, specifically 0.2 μm or more. Depending on the case, a fluctuation range of around 0.4 μm may occur. However, even if the gap amount fluctuates to such a level, the image quality of the displayed image is not significantly reduced when configured as a liquid crystal display cell.

  In consideration of the above points, in the present invention, the spacer beads 4a dispersed in the spacer ink are mixed with those having different particle diameters. For example, when the target gap amount of the cell gap is 4 μm, when using intermediate spacer beads having a particle diameter of 4 μm, which is the reference diameter, a large spacer beads having a particle diameter of 4.2 μm and a particle diameter of 3. Mix 8 μm small diameter spacer beads. For the mixing ratio of the spacer beads, the amount of the intermediate diameter spacer beads is equal to the total amount of the large diameter and small diameter spacer beads, or the amount of each of the intermediate diameter, large diameter and small diameter spacer beads. Are equal.

  As described above, the ink bottle 27 is filled with the spacer ink in which a plurality of types of spacer beads having different particle diameters are dispersed, and this spacer ink is ejected from the nozzle 30 provided in the inkjet head 26. Then, on the substrate 1, the spacer beads 4 a constituting the spacer 4 when the solvent is volatilized are fluctuated depending on the location even though they are the same nozzle 30.

  That is, in FIG. 8, when spacer beads 4a having different sizes are 4aM for intermediate diameter spacer beads, 4aL for large diameter spacer beads, and 4aS for small diameter spacer beads, each spacer 4 positioned on the substrate 1 is used. The spacer beads constituting the are irregular within a controlled range and have no regularity. In this way, by changing the particle size of the spacer beads, in the X direction which is the main scanning direction, the height of each spacer 4 becomes 4 μm as a reference, and the fluctuation range becomes ± 0.2 μm. The gap amount varies irregularly also in the Y direction, which is the sub-scanning direction, due to the difference in the spacer ink ejection conditions of each nozzle 30. The gap amount is approximately ± 0. 2 μm. As a result, compared to the case where uniform spacer beads are used, the spacers formed by the droplets ejected from the nozzle 30 under the same conditions have different sizes depending on the location, and minute irregularities are generated in the X direction. become. Therefore, when the bonded substrate 6 is used, a minute height difference is generated in the X direction and the Y direction, and the generation of streak gray stripes can be suppressed.

It is structure explanatory drawing of the board | substrate with which a spacer is spread | dispersed. It is an enlarged view of the spacer obtained when a solvent is volatilized from spacer ink. It is explanatory drawing which shows the whole structure of the mechanism which spreads and fixes the spacer bead to a board | substrate. It is an external view which shows the structure of an ink dripping stage. It is a structure explanatory view showing the tip part of an ink jet head. It is explanatory drawing of the operation | movement which ejects the spacer ink from the micro nozzle which comprises an inkjet head. It is sectional drawing which shows the state which joined two transparent substrates. It is sectional drawing which shows an example of arrangement | positioning of the spacer in the X direction of a board | substrate.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,5 Substrate 2 Pixel region 3 Black matrix region 4 Spacer 4a Spacer bead 4aM Intermediate diameter spacer bead 4aL Large diameter spacer bead 4aS Small diameter spacer bead 6 Bonded substrate 20 Transport table 23 Inkjet means 26 Inkjet head 30 Small nozzle 31 Chamber piece 32 Actuator

Claims (3)

It is a method of dispersing so as to disperse spacers for forming a cell gap on the surface of a transparent substrate constituting a liquid crystal cell,
While disposing an inkjet head having a plurality of nozzles at predetermined pitch intervals in the width direction of the transparent substrate, and relatively moving the transparent substrate and the inkjet head in the crossing direction of the nozzle alignment direction, A droplet of spacer ink in which a plurality of types of spacer beads having different particle diameters are uniformly dispersed in a solvent is sprayed from each ejection port of an inkjet nozzle onto the surface of the transparent substrate. Spacer spraying method. A spacer spraying device for spraying so as to disperse spacers for forming a cell gap on the surface of a transparent substrate constituting a liquid crystal cell,
An ink supply means for supplying spacer ink in which a plurality of types of spacer beads having different particle diameters are uniformly dispersed in a solvent;
An inkjet head provided with a plurality of nozzles at predetermined pitch intervals in the width direction of the transparent substrate in order to disperse the spacer ink supplied from the ink supply means on the surface of the transparent substrate;
A spacer spraying device comprising: a drive unit that relatively moves the transparent substrate and the inkjet head at least in the direction intersecting the nozzle arrangement direction. A transparent substrate in which a spacer in which a plurality of types of spacer beads having different particle diameters are aggregated is dispersed on the surface of the black matrix, and the other transparent substrate is formed so that a cell gap is formed on the transparent substrate by the spacer. A liquid crystal display cell that is joined and liquid crystal is sealed in the cell gap.

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