The present invention relates to a droplet ejection apparatus.
Typically, a display such as a liquid crystal display or an electroluminescence display includes a substrate that displays an image. The substrate has an identification code (for example, a two-dimensional code) representing product information including the name of the manufacturer and the product number, for purposes of quality control and production control. The identification code includes a plurality of dots formed by, for example, colored thin films or recesses. The dots are arranged to form a predetermined pattern so that the identification code can be identified in accordance with the arrangement pattern of the dots.
As a method for forming one such identification code, JP-A-11-77340 discloses a laser sputtering method and JP-A-2003-127537 discloses a waterjet method. In the laser sputtering method, dots are formed by films provided through sputtering by radiating laser beams onto a metal foil. In the waterjet method, dots are marked on a substrate by ejecting water containing abrasive onto the substrate.
However, in the laser sputtering method, the interval between the metal foil and the substrate must be adjusted to several or several tens of micrometers in order to form each dot in a desired size. The substrate and the metal foil thus must have extremely flat surfaces and adjustment of the interval between the substrate and the metal foil must be carried out with accuracy on the order of micrometer. This limits application of the method to a restricted range of substrates, and use of the method is limited. In the waterjet method, the substrate may be contaminated by water, dust, and the abrasive that are splashed onto the substrate when the dots are marked on the substrate.
In order to solve these problems, an inkjet method has been focused on as an alternative method for forming the identification code. In the inkjet method, dots are formed on a substrate by ejecting droplets of liquid containing metal particles from an ejection head onto the substrate through nozzles. The droplets are then dried to mark the dots on the substrate. The method thus can be applied to a relatively wide range of substrates. Further, the method prevents contamination of the substrate caused by formation of the identification code.
JP-A-8-174860, JP-A-9-290514, JP-A-2001-225479, and JP-A-2002-36583 and Japanese Patent Re-publication No. WO2000/03877 each describes a droplet ejection apparatus used for the inkjet method. The droplet ejection apparatus has a valve mechanism arranged between an ink tank that retains ink and a droplet ejection head. The valve mechanism selectively opens and closes in correspondence with the difference between the pressure of the ink in the ink tank and the pressure of the ink in the droplet ejection head. Specifically, the valve mechanism opens in correspondence with negative pressure caused by consumption of the ink by the droplet ejection head, supplying the ink to the droplet ejection head under stable pressure. The droplet ejection apparatus thus avoids leakage of the ink. Further, the size and the receiving position of each of the droplets are stabilized, improving position accuracy for forming the dots.
To manufacture the aforementioned types of displays, a plurality of identification codes are formed on a single mother substrate so as to enhance productivity for forming the displays. The portions corresponding to the substrates each of which corresponds to one of the identification codes are then cut out from the mother substrate. In this manner, the multiple substrates are obtained from the single mother substrate. In other words, to perform the inkjet method, identification code areas are defined at separate positions on the mother substrate. The droplet ejection head thus operates only when the droplet ejection head is arranged above any one of the code areas. As a result, most of the time necessary for forming the multiple identification codes is consumed by movement of the droplet ejection head from one identification code area to another.
Accordingly, to improve productivity for forming the identification codes by the inkjet method, it is desired that the droplet ejection head is mounted in a multi-joint robot so that the droplet ejection head is transported in two-dimensional direction at high speed.
Japanese Patent Re-publication No. WO2000/03877 describes a structure including a coil spring and a movable film. The coil spring constantly urges the movable film to elastically contact a valve seat. The coil spring receives rocking of the ink caused by movement of the droplet ejection head, stabilizing the pressure in the droplet ejection head. In other words, the coil spring receives the force generated by interaction between acceleration of the droplet ejection head in the two-dimensional direction and the mass of the ink.
However, the structure described by Japanese Patent Re-publication No. WO2000/03877 does not address to the force produced by interaction between the acceleration of the droplet ejection head and the mass of the valve body of the valve mechanism. Thus, if the mass of the valve body or the acceleration of the droplet ejection head is excessively great, the valve body may receive the force acting in the direction of the acceleration of the droplet ejection head, leading to erroneous operation of the valve mechanism.
Further, if the droplet ejection head is arranged in the multi-joint robot, a liquid supply tube connecting the liquid tank to the droplet ejection head may interfere with an arm of the robot. In this case, stable supply of the liquid is hampered.
Therefore, in the droplet ejection apparatus having the droplet ejection head installed in the multi-joint robot, stable droplet ejection by the droplet ejection head is difficult to ensure.