1. Field of the Invention
The present invention relates to an inkjet recording head that adopts an inkjet recording method for performing recording on a recording medium by discharging ink toward the recording medium.
2. Description of the Related Art
Today, an inkjet recording method can record high definition images at high speed, and perform recording on a recording medium which is not subjected to special treatment. Accordingly, the inkjet recording method is widely used. Various discharge methods are used in an inkjet recording head for realizing the inkjet recording method. For example, a method for discharging ink by applying energy obtained by heating and bubbling the ink, and a method for utilizing piezoelectric elements are typical methods. In the inkjet recording head that adopts these methods, even higher definition and higher quality images have been demanded in recent years. Therefore, the inkjet recording head is required to discharge smaller ink droplets to meet the demand.
However, if a diameter of a discharge port is decreased to discharge the smaller ink droplets, a flow resistance of the discharge port is increased. Therefore, discharge efficiency may be deteriorated. In order to reduce the flow resistance of the discharge port for solving this problem, it is effective in reducing a thickness of an orifice plate.
Reduction of the thickness of the orifice plate is effective in reducing the flow resistance, but is disadvantageous for its strength. In particular, when a material of the orifice plate is resin, the orifice plate itself may be swollen by ink liquid, and may be eventually deformed. Therefore, it is concerned about influence on discharge of the ink droplets.
To solve this problem, it is effective to provide a rib in an orifice plate, as discussed in Japanese Patent Application Laid-Open No. 10-146976. This is because strength against deformation of the orifice plate is improved by providing the rib. As the rib provided in the orifice plate, a configuration for providing the rib with a length longer than a width of an ink flow path near a communication portion between an ink supply port and the ink flow path is known, as discussed in Japanese Patent Application Laid-Open No. 2000-158657. A single continuous rib or a plurality of discontinuous ribs is provided on the ink supply ports along an array direction of electrothermal conversion elements required for discharging the ink.
If an orifice plate is extremely thin, as described above, a structure in which a single continuous rib is provided on the ink supply ports is effective for improving strength of the orifice plate against the deformation, as discussed in Japanese Patent Application Laid-Open No. 2000-158657 . FIG. 11 illustrates a configuration of a conventional inkjet recording head in which a single continuous rib is provided on ink supply ports.
In an inkjet recording head 100 illustrated in FIG. 11, an ink supply port 41 serving as a through-port is formed on a substrate 11, and a rib 61 is provided on a back surface of an orifice plate 71 located on the ink supply port 41. At both sides of the ink supply port 41, discharge energy generating elements 31 for generating discharge energy required for discharging the ink are arranged. Between the discharge energy generating elements 31, coating resin layers 21 serving as ink flow path walls for forming the ink flow paths as nozzles are provided. On the coating resin layer 2, the orifice plate 71 including discharge ports 81 is provided. In the inkjet recording head 100, when a width W of the rib 61 is about 20 to 30 μm, an opening width T of the ink supply port 41 is, normally, 100 to 200 μm, which is enough wider compared with the width W. Therefore, conventionally, even if the opening width T of the ink supply port 41 or a position of the rib 61 with respect to the ink supply port 41 varies by the order of several tens pm during manufacturing, there is little influence on an ink supply.
However, in the above-described inkjet recording head, recently, there is a demand for reduction in size of the substrate for purpose of reduction in cost. Since it is effective in reducing the size of the ink supply port to reduce the cost, there is another demand for making an opening width of the ink supply port smaller than conventional one. When a rib is provided on an ink supply port with a small opening width and if a position of the rib in the orifice plate is displaced from a design position with respect to the ink supply port, an opening area of the ink supply port may become very small. Since flow resistance of the ink increases as the opening area decreases, there is a concern that refilling speed (charging speed of ink to the orifice plate) becomes slower.
Thus, if a plurality of discontinuous ribs is used on the ink supply ports, as discussed in Japanese Patent Application Laid-Open No. 2000-158657, a clearance is created between the ribs, and decrease in the refilling speed can be suppressed compared with the single continuous rib. However, since the ribs are discontinuous, there arises a problem that strength of the orifice plate is deteriorated compared with a conventional continuous structure.