1. Field of the Invention
The present invention relates to an ink-jet printhead. More particularly, the present invention relates to a method of forming a hydrophobic coating layer on a surface of a nozzle plate for an ink-jet printhead.
2. Description of the Related Art
Generally, an ink-jet printhead is a device that ejects small volume ink droplets at desired positions on a recording medium to print a desired color image. Ink-jet printheads are generally categorized into two types depending on which ink ejection mechanism is used. A first type is a thermal ink-jet printhead, in which ink is heated to form ink bubbles and the expansive force of the bubbles causes ink droplets to be ejected. A second type is a piezoelectric ink-jet printhead, in which a piezoelectric crystal is deformed to exert pressure on ink causing ink droplets to be ejected.
FIG. 1 illustrates a cross-sectional view of a conventional piezoelectric ink-jet printhead.
Referring to FIG. 1, a flow path plate 10 having ink flow paths including a manifold 13, a plurality of restrictors 12, and a plurality of pressurizing chambers 11 is formed. A nozzle plate 20 having a plurality of nozzles 22 at positions corresponding to the respective pressurizing chambers 11 is formed on a lower side of the flow path plate 10. In FIG. 1, only an exemplary one of each of the plurality of pressurizing chambers 11, restrictors 12, and nozzles 22, is shown. A piezoelectric actuator 40 is disposed on an upper side of the flow path plate 10. The manifold 13 is a common passage through which ink from an ink reservoir (not shown) is introduced into each of the plurality of pressurizing chambers 11. Each of the plurality of restrictors 12 is an individual passage through which ink from the manifold 13 is introduced into a respective pressurizing chamber 11. Each of the plurality of pressurizing chambers 11 is filled with ink to be ejected and collectively may be arranged at one or both sides of the manifold 13. Volumes of each of the plurality of pressurizing chambers 11 change according to the driving of the piezoelectric actuator 40, thereby generating a change of pressure to perform ink ejection or introduction. To generate this change in pressure, an upper wall of each pressurizing chamber 11 of the flow path plate 10 serves as a vibrating plate 14 that can be deformed by the piezoelectric actuator 40.
The piezoelectric actuator 40 includes a lower electrode 41, a piezoelectric layer 42, and an upper electrode 43, which are sequentially stacked on the flow path plate 10. A silicon oxide layer 31 is formed as an insulating film between the lower electrode 41 and the flow path plate 10. The lower electrode 41 is formed on the entire surface of the silicon oxide layer 31 and serves as a common electrode. The piezoelectric layer 42 is formed on the lower electrode 41 in a position corresponding to an upper side of each of pressurizing chamber 11. The upper electrode 43 is formed on the piezoelectric layer 42 and serves as a driving electrode for applying a voltage to the piezoelectric layer 42.
In an ink-jet printhead of the above-described construction, a water-repellent surface treatment for the nozzle plate 20 directly affects ink ejection performance, such as directionality and ejection speed of ink droplets to be ejected through the nozzles 22. More specifically, to enhance ink ejection performance, inner surfaces of the nozzles 22 must be hydrophilic and an outer surface of the nozzle plate 20, outside of the nozzles 22, must be water-repellent, i.e., hydrophobic.
In view of these requirements, it is common to form a hydrophobic coating layer on a surface of a nozzle plate. Various methods of forming such a hydrophobic coating layer are known. There are largely two types of conventional hydrophobic coating layer formation methods. A first type uses a coating solution for selective coating a surface of a specific material. A second type uses a nonselective coating solution.
FIG. 2 illustrates a conventional ink-jet printhead having a sulfur compound layer as a hydrophobic coating layer on a surface of a nozzle plate.
Referring to FIG. 2, initially, a metal layer 52 is formed on a surface of a nozzle plate 51 through which a nozzle 55 is bored. A sulfur compound layer 53 is then formed on a surface of the metal layer 52 by coating the metal layer 52 with a sulfur compound. After this coating, the sulfur compound should be coated only on the surface of the metal layer 52.
According to this conventional method, however, the metal layer 52 may also be formed on an inner surface of the nozzle 55, in addition to the outer surface of the nozzle plate 51. Further, when a large number of nozzles are used, the metal layer 52 may be non-uniformly formed at different areas of the nozzle plate 51 and different portions of the nozzle 55. In this case, the sulfur compound layer 53 is also formed on an inner surface of the nozzle 55 or is not uniformly formed. Resultantly, when the sulfur compound layer 53, which is a hydrophobic coating layer, is formed poorly, a periphery of the nozzle 55 may be easily contaminated by ink and ink droplet ejection performance may deteriorate due to low ejection speed or non-uniform ejection direction.
FIG. 3 illustrates a conventional ink-jet printhead having a fluorine resin-containing water-repellent layer on a surface of a nozzle plate.
Referring to FIG. 3, a water-repellent layer 90 is formed on a surface of a nozzle plate 70. The water-repellent layer 90 is composed of a nickel base 96, fluorine resin particles 94, and a hard material 98. A fluorine resin layer 92 is formed on a surface of the water-repellent layer 90. To form such a water-repellent layer 90, initially, a polymer resin 74 is filled in a nozzle 72. The water-repellent layer 90 is then formed on the surface of the nozzle plate 70 and the polymer resin 74 is removed. Accordingly, the water-repellent layer 90 is formed only on the surface of the nozzle plate 70.
However, this conventional method involves a cumbersome process to remove the polymer resin 74 filled in the nozzle 72.
Another conventional method discloses a method of forming a water-repellent layer on a surface of a nozzle plate while a gas is injected through a nozzle to prevent a water-repellent coating from forming on an inner surface of the nozzle. However, this method requires a complicated apparatus and a difficult process, which renders industrial application difficult.