JP4690031B2 - Spacer forming method and apparatus - Google Patents

Description

  The present invention relates to a spacer forming method and apparatus for keeping a liquid crystal sealing gap between a pair of substrates used in a liquid crystal panel constant, and more particularly, to a spacer forming position on a substrate of ink in which the spacer is dispersed in a solvent. The present invention relates to a spacer forming method and apparatus using an ink jet method (droplet discharge method) of dropping on a substrate.

  The response characteristics, contrast, and viewing angle required for the liquid crystal panel largely depend on the thickness of the liquid crystal layer. For this reason, the thickness of the liquid crystal layer is controlled to be constant by interposing a spacer between the pair of substrates in which the liquid crystal is sealed. As a method for forming the spacer, a method of forming a columnar shape on one substrate, a method of spraying ball-shaped spacers, and the like are known.

  The method for forming the spacers in a columnar shape requires steps such as film formation and etching by photolithography, which requires many steps and is costly and troublesome. In addition, as a method of spraying the ball-shaped spacer on the substrate, there are a wet spraying method of spraying and a dry spraying method of spraying the powdered spacer directly on the substrate with an air flow such as compressed dry nitrogen, In either case, spacers are scattered in the pixel region, and luminance reduction or luminance unevenness may occur, the spacer distribution on the substrate may become non-uniform, and the inter-substrate gap may become non-uniform.

In view of this, a technique has been proposed in which spacers are simply formed locally on the black matrix, which is a non-pixel region of the color filter, by an inkjet method (see, for example, Patent Document 1). In this method, a spacer-containing ink in which ball-shaped spacers are dispersed in a solvent is dropped from a nozzle onto the black matrix, and the solvent is evaporated to leave the spacer on the black matrix.
JP-A-11-24083

  In spacer formation by the ink jet method, if the concentration of the spacer in the ink is low, one spacer is not included per drop, or the number necessary for ensuring a stable gap is not included. Increasing the spacer concentration can increase the number of spacers contained in one droplet, but as the spacer concentration is increased, the variation in the discharge speed increases. In general, the ink jet method ejects ink droplets while moving the line head in a certain scanning direction with respect to the substrate. In this case, the relative position between the head and the substrate is displaced before it reaches the substrate after being ejected, and there is a problem that the accuracy of the reaching position on the substrate is deteriorated. When the positional accuracy of the ink is deteriorated, there is a possibility that the spacer included in the ink protrudes from the pixel region.

  In addition, by using a low spacer density ink having excellent ejection speed stability, a plurality of droplets are dropped onto one spacer forming position and stacked, so that even if the spacer density is lowered, the required number of inks are provided at one spacer forming position. Although it is possible to form a spacer, if a plurality of ink drops are applied at each spacer forming position, the time required for the spacer forming process becomes longer depending on the number of drops, and the current liquid crystal panel manufacturing apparatus There is a problem that it cannot meet the required high-speed tact.

  The present invention has been made in view of the above-mentioned problems, and the object of the present invention is to provide a spacer concentration at one spacer forming position in order to ensure the accuracy of the spacer forming position and to secure the required number of spacers per one spacer forming position. It is an object of the present invention to provide a spacer forming method and apparatus capable of shortening the time required for dropping a plurality of ink droplets with reduced ink.

The present invention employs the following configuration in order to solve the above problems.
That is, the spacer forming method of the present invention increases the discharge speed of ink droplets discharged later by increasing the discharge pressure of ink droplets discharged later than the discharge pressure of ink droplets discharged earlier. Multiple ink droplets are ejected from the ejection port of the inkjet head so as to be faster, and before the ink droplet ejected earlier reaches the spacer formation position, the ink droplet ejected later is ejected first. The plurality of ink droplets ejected from the ejection port are integrally dropped onto the spacer forming position by causing the ink droplets to catch up during the flight.

Further, the spacer forming apparatus of the present invention has a pressure chamber that takes in the spacer-containing ink and discharges it as droplets due to a pressure change that occurs inside, and is a spacer discharge head that can move relative to the substrate;
At each spacer formation position, a plurality of droplets are ejected by applying pressure to the spacer-containing ink in the pressure chamber a plurality of times, and among the plurality of droplets, the droplets ejected later are ejected first. And a drive unit that controls the number of spacers in the landing droplets by applying pressure to the spacer-containing ink a plurality of times so as to catch up with the droplets and fly together.

  In the present invention, in order to stabilize the discharge speed per droplet of the spacer-containing ink and increase the accuracy of the spacer formation position, a plurality of ink drops are applied to one spacer formation position even if the spacer concentration is lowered. The required number of spacers can be reliably formed at one spacer forming position. Further, the plurality of ink drops are successively increased in the discharge speed of the ink to be discharged later, and the ink droplets discharged earlier are caught up before reaching the substrate to be combined during the flight. Therefore, the time required for dropping all the droplets (a plurality of droplets) required at one spacer forming position can be shortened as compared with the case where each droplet is landed on the substrate in order and stacked.

  In order to suppress and stabilize the variation in the ejection speed, the spacer concentration in the ink is preferably 2.5% by weight or less.

  According to the present invention, a plurality of ink droplets are ejected from the ejection port of the inkjet head so that the later the ink droplets ejected, the faster the ejection speed. Before reaching the position, the ink droplets ejected later are allowed to catch up with the previously ejected ink droplets during the flight, and a plurality of ink droplets ejected from the ejection port are integrated to form a spacer. As a result, the time required for dropping all the droplets (plural drops) required at one spacer forming position can be shortened. As a result, the spacer forming process for the entire substrate and further the liquid crystal panel manufacturing The time required for the process can be shortened.

  Hereinafter, specific embodiments to which the present invention is applied will be described in detail with reference to the drawings. In addition, this invention is not limited to the following embodiment, A various deformation | transformation is possible based on the technical idea of this invention.

  The liquid crystal panel is configured by sealing liquid crystal in a gap of about several μm formed between a pair of substrates. One of the pair of substrates is configured by forming a polarizing plate, a color filter, a counter electrode, an alignment film, and the like on a glass substrate. The other is formed by forming a polarizing plate, a pixel electrode, a driving transistor, an alignment film, and the like on a glass substrate.

  Both substrates are bonded together with the alignment films facing each other. A sealing material for integrally bonding the two substrates is applied to one substrate, and a spacer is formed on the other substrate to which the sealing material is not applied.

  Usually, the spacer is formed on a color filter side substrate having a color filter. As shown in FIG. 5, the color filter includes a grid-like black matrix 1 and red pixels R, green pixels G, and blue pixels B formed in the respective grid eyes. The black matrix 1 is a non-pixel region that surrounds each pixel of RGB so as to be blackened and always blocks light from the backlight regardless of the on / off of the voltage applied to the liquid crystal cell.

  The spacer-containing ink is dropped onto the dropping region 2 (indicated by a circle in the figure) located at the intersection of the grid-like black matrix 1 by an ink jet method. The spacer-containing ink is not directly dropped on the black matrix 1, but the position (overlapping position) corresponding to the black matrix intersection in the portion (alignment film) where the substrate on which the spacer is formed faces the other substrate. It is dripped.

  The spacer is dispersed in a solvent such as water or alcohol. The spacer is a spherical plastic, glass, silica or the like having a diameter (for example, 4 to 5 μm) corresponding to a gap (liquid crystal sealing gap) between both substrates.

  As shown in FIG. 1, the spacer-containing ink uses a spacer discharge head (inkjet head) 4 having a plurality of pressure chambers 5 and discharge ports 6 corresponding thereto, as shown in FIG. It is dripped in area 2). In this embodiment, for each spacer formation position, a plurality of droplets d (in the case of 2 drops and 3 drops in FIG. 1) from the discharge port 6 positioned facing the spacer formation position. Example) is continuously ejected, and the ejected plural droplets d are combined into one during the flight before reaching the spacer forming position on the substrate 3, and the combined droplet D forms the spacer. It is made to drip at the position. The solvent in the droplet D dropped at the spacer forming position is naturally evaporated or heated and evaporated, and the spacer remains at the spacer forming position.

  The piezoelectric member provided corresponding to each pressure chamber 5 is displaced, and each liquid chamber d is discharged from the discharge port 6 by deformation of each pressure chamber 5 due to the displacement of the piezoelectric member. FIG. 2A shows an example of a voltage waveform applied to the piezoelectric member from the driving unit when two droplets d are continuously ejected. First, when a voltage of −V is applied to the piezoelectric member for a time T1, the pressure chamber 5 is deformed so as to expand its volume. Due to the expansion of the volume, the pressure in the pressure chamber 5 is reduced, and ink is taken into each pressure chamber 5 from the common ink chamber communicating with each pressure chamber 5. Subsequently, when a voltage of + V is applied to the piezoelectric member for a time T2, the pressure chamber 5 is deformed so as to reduce the volume. By reducing the volume, the pressure in the pressure chamber 5 increases, and the first ink droplet d is ejected from the ejection port 6. Then, after the time T3, the same operation as described above is repeated, and the second droplet d is ejected. Time T4 is a time interval until the ink dropping to the next spacer formation position is started.

  Furthermore, in the present embodiment, the pressure in the pressure chamber 5 at the time of discharge gradually increases as the time after the first droplet d is discharged, so that the discharge speed of each droplet d discharged from the discharge port 6 is increased. Increasingly. In other words, the droplet d that is discharged later has a higher discharge speed, so that the droplet d that has been discharged earlier can reach the substrate 3 before the droplet d that has been discharged earlier. The liquid droplet d discharged on the surface catches up and merges in the middle (during flight). The combined droplets D land on the substrate 3. As a result, the time required for dropping all the droplets can be shortened as compared with the method in which a plurality of droplets d are landed on the substrate 3 one by one. As a result, the entire time of the spacer forming process can be shortened.

  As described above, as a first method for gradually increasing the pressure in the pressure chamber 5 at the time of ejection, pulse voltages + V and −V (applied from the drive unit to the piezoelectric member in order to eject each droplet d. There is a method in which the size of FIG.

  As a second method, the amplitude of the pressure vibration in the pressure chamber 5 is gradually increased by adjusting the times T1, T2, and T3 shown in FIG. Thus, the pressure at the time of discharge may be gradually increased. For example, during time T 1 and T 2, the pressure wave generated in the pressure chamber 5 propagates from one end of the pressure chamber 5 (end on the common ink chamber side) to the other end of the pressure chamber 5 (end on the ejection port 6 side). By setting the time, the amplitude of the pressure vibration in the pressure chamber 5 can be gradually increased.

  2C shows a voltage waveform applied to the piezoelectric member when the number of droplets ejected continuously is three, and FIG. 2E shows a voltage waveform applied when there are four droplets. For the ejection of 5 droplets or more, the pulse is repeated according to the number of ejected droplets. The applied voltage waveform is not limited to a rectangular pulse, and may be a rectangular pulse having a slope as shown in FIGS. Further, it may be a triangular pulse, a trigonometric pulse waveform, or a combination thereof.

  Next, the result of evaluating the variation in the discharge speed with various spacer concentrations will be described. A spacer discharge head (inkjet head) having an average discharge droplet capacity of 15 pl was used, and a spacer having a diameter of 4 μm was used. As a result, when the spacer concentration was higher than 2.5% by weight, the variation in the discharge speed reached 20%. Therefore, the spacer concentration is preferably 2.5% by weight or less. Furthermore, the spacer concentration is set to 2.0% by weight or less to suppress the variation in the discharge speed to 10% or less, and the spacer concentration is set to 1.5% by weight or less in order to suppress the variation in the discharge speed to 5% or less. It was experimentally obtained.

  Table 1 shows the number of droplets d discharged and the average per discharge when a plurality of droplets are discharged by the above-described second method using an ink with a spacer concentration of 1.0% by weight. The relationship between the droplet volume, the average discharge speed, and the average number of spacers formed at the landing position of the combined droplet D is shown.

  Further, based on this Table 1, FIG. 3 is a graph showing the relationship between the number of discharges, the average discharge speed, and the number of average spacers to be landed, and FIG. 4 is a graph showing the number of discharges and the average droplet capacity per discharge. The relationship with the average number of spacers is shown in the graph.

  The average discharge speed and the average droplet capacity tend to increase gradually when the number of discharges is from 1 to 3, but stabilizes almost constant when the number of discharges is 3 or more. That is, in the discharge of 3 drops or more at a spacer concentration of 1.0% by weight, it is possible to suppress variations in the discharge speed and drop volume of each drop. As a result, the displacement of the landing positions can be suppressed when discharging the spacer-containing ink to a plurality of spacer formation positions one after another while the position of the spacer discharge head and the substrate is relatively changed. Can improve the accuracy. Further, since the number of spacers formed at the landing position is proportional to the number of ejections, the number of spacers formed at one place can be easily controlled by controlling the number of ejections.

  In addition, the number of ejections may be 8 or more. However, if the number of ejections is increased too much, for example, when a standard inkjet head with a ejection droplet capacity of 10 pl is used as a spacer ejection head, There is a possibility that the total volume of the landed droplets reaches 80 pl and protrudes greatly from the spacer formation region. In this case, the spacer may reach the pixel region, and the solvent may adversely affect the alignment characteristics depending on the type of the alignment film serving as a base. For this reason, the total droplet volume to be landed must be suppressed to 75 pl or less. Further, if the total droplet volume to be landed is less than 15 pl, the number of spacers included in the droplet volume decreases, and it becomes difficult to secure 2 to 8 spacers that are normally required in one spacer formation region. From the above, the optimum range varies somewhat depending on the design of the target liquid crystal display element, but the total droplet volume landed at one spacer forming position needs to be controlled in the range of 15 to 75 pl.

  As described above, according to the present embodiment, by suppressing the spacer concentration to a predetermined concentration or less, it is possible to suppress variations in the discharge speed and the amount of discharged droplets of each droplet discharged from each of the plurality of discharge ports. Since the spacer-containing ink can be stably ejected from the beginning of ejection, the accuracy of the spacer formation position can be increased, and as a result, the yield of liquid crystal panel manufacturing can be improved. Even if the spacer concentration is lowered, a plurality of ink drops are applied to one spacer forming position, so that the necessary number of spacers can be reliably formed at one spacer forming position. Further, the plurality of ink drops are successively increased in the discharge speed of the ink to be discharged later, and the ink droplets discharged earlier are caught up before reaching the substrate to be combined during the flight. Therefore, the time required for dropping all the droplets (a plurality of droplets) required at one spacer forming position can be shortened as compared with the case where each droplet is landed on the substrate in order and stacked. As a result, it is possible to shorten the time required for the spacer forming step for the entire substrate and further for the liquid crystal panel manufacturing step.

  Note that it is not necessary to form spacers at all intersections of the black matrix 1 as long as a uniform and stable inter-substrate gap can be maintained in the substrate surface direction. Further, the required number of spacers in the entire substrate varies depending on the size of the substrate plane dimension. Alternatively, the ink may be dropped on a line-shaped portion other than the intersecting portion of the black matrix 1 to form a spacer in that portion.

In the embodiment of the present invention, it is a diagram showing that a plurality of droplets of spacer-containing ink are continuously ejected from each ejection port of the spacer ejection head, are combined into one, and land on a substrate. In embodiment of this invention, it is a wave form diagram of the voltage applied to the drive part which produces a pressure change in a pressure chamber. In the embodiment of the present invention, it is a graph showing the relationship between the number of ejected spacer-containing ink, the average ejection speed, and the average number of spacers. In the embodiment of the present invention, it is a graph showing the relationship between the number of ejected spacer-containing ink, the average droplet capacity per ejection, and the average number of spacers. It is a top view which shows the dripping area | region of the spacer containing ink on a black matrix.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Black matrix, 2 ... Dripping area | region of the spacer containing ink, 4 ... Spacer discharge head, 5 ... Pressure chamber, 6 ... Discharge port.

Claims (3)

A spacer-containing ink in which granular spacers for keeping a liquid crystal sealing gap formed between a pair of substrates are dispersed in a solvent is opposed to a spacer formation position on one of the pair of substrates. In the spacer forming method of discharging from the discharge port of the spacer discharge head positioned and dropping to the spacer forming position,
By increasing the ejection pressure of the ink droplets ejected after the ejection pressure of the ink droplets ejected earlier, multiple ink droplets are arranged so that the ejection speed becomes faster for the ink droplets ejected later. Before the ink droplet ejected from the ejection port reaches the spacer formation position, the ink droplet ejected later is allowed to catch up with the previously ejected ink droplet during the flight. A method of forming a spacer, wherein a plurality of ink droplets discharged from the discharge port are integrally dropped onto the spacer forming position.   2. The spacer forming method according to claim 1, wherein the concentration of the spacer in the ink is 2.5% by weight or less. A spacer-containing ink in which granular spacers for maintaining a liquid crystal sealing gap formed between a pair of substrates are dispersed in a solvent is dropped onto a spacer forming position on one of the pair of substrates. A spacer forming device,
A spacer discharge head that has a pressure chamber that takes in the spacer-containing ink and discharges it as droplets due to a pressure change generated inside, and is movable relative to the substrate;
For each spacer forming position, a plurality of droplets are ejected by applying pressure to the spacer-containing ink in the pressure chamber a plurality of times, and the droplets ejected later among the plurality of droplets are ejected first. A drive unit for controlling the number of spacers in the landing droplets by applying pressure to the spacer-containing ink a plurality of times so as to catch up with the formed droplets during flight and to be integrated;
A spacer forming apparatus comprising:

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