Patent Publication Number: US-2005128251-A1

Title: Ink-jet printhead

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to an ink-jet printhead. More particularly, the present invention relates to an ink-jet printhead in which bubbles are generated by a liquid plasma discharge to eject ink.  
      2. Description of the Related Art  
      Generally, ink-jet printheads are devices for printing a predetermined image, color or black and white, by ejecting a small volume droplet of printing ink at a desired position on a recording sheet. Ink-jet printheads are generally categorized into two types depending on which ink ejection mechanism is used. A first type is a thermally driven ink-jet printhead, in which a heat source is employed to form and expand bubbles in ink causing ink droplets to be ejected. A second type is a piezoelectrically driven ink-jet printhead, in which a piezoelectric material is deformed to exert pressure on ink causing ink droplets to be ejected.  
       FIG. 1A  illustrates an exploded perspective view of a configuration of a thermally driven ink-jet printhead.  FIG. 1B  illustrates a cross-sectional view for explaining a process of ejecting an ink droplet in the thermally driven ink-jet printhead of  FIG. 1A .  
      Referring to  FIGS. 1A and 1B , the conventional thermally driven ink-jet printhead includes a substrate  10 , a barrier  14  installed on the substrate  10  to define an ink chamber  26  and an ink channel  24 , a heater  12  installed on the bottom of the ink chamber  26 , and a nozzle plate  18 , in which a nozzle  16  for ejecting an ink droplet  29 ′ is formed. In operation, when a pulse current is applied to the heater  12  and heat is generated by the heater  12 , ink  29  in the ink chamber  26  is boiled to generate a bubble  28 . The generated bubble  28  continuously expands, thereby exerting pressure on the ink  29  in the ink chamber  26  to eject the ink droplet  29 ′ out of the printhead via the nozzle  16 . Subsequently, ink  29  from a manifold  22  is supplied to the ink chamber  26  via the ink channel  24 , thereby again filling the ink chamber  26  with ink  29 .  
      However, in a thermally driven ink-jet printhead, a cavitation pressure generated when bubbles disappear is concentrated in a central portion of the heater  12 , thereby deteriorating the heater  12 .  
       FIG. 2  illustrates a cross-sectional view of another conventional ink-jet printhead, which attempts to solve a defect of a thermally driven printhead as described above.  
      Referring to  FIG. 2 , when a laser beam L generated from a laser light source  30  is irradiated onto predetermined color inks  32 Y,  32 M, and  32 C filling ink containers  37 Y,  37 M, and  37 C, respectively, light energy is transformed into sound energy, thereby generating bubbles in the inks  32 Y,  32 M, and  32 C. Ink droplets are then ejected onto a sheet of paper  50  by the bubbles generated as described above and a required image is formed.  
      However, in the ink-jet printhead as described above, since a laser light source required to generate a high-energy laser beam is expensive and an optical configuration is complicated, it is difficult to miniaturize and integrate the ink-jet printhead.  
       FIG. 3  illustrates a cross-sectional view of still another conventional ink-jet printhead.  
      Referring to  FIG. 3 , an ink chamber  53  is filled with ink  51  including an electrolyte, and a pair of electrodes  52   a  and  52   b  is formed on a bottom surface of the ink chamber  53 . When an electrolysis signal is applied from a signal generator  57  to the pair of electrodes  52   a  and  52   b , ink electrolysis is performed around the electrodes  52   a  and  52   b  and gas bubbles  55   a  and  55   b  are generated and expanded. Subsequently, ink  51  in the ink chamber  53  is ejected in droplets  56  through a nozzle  54 .  
      The ink-jet printhead as described above is advantageous in that it uses a small driving voltage, but is disadvantageous in that ink ejectivity is small, harmful gas may be generated, ink must have a high conductivity, and voltage switching for gas extinction is required.  
     SUMMARY OF THE INVENTION  
      The present invention is therefore directed to an ink-jet printhead, which substantially overcomes one or more of the problems due to the limitations and disadvantages of the related art.  
      It is a feature of an embodiment of the present invention to provide an ink-jet printhead in which bubbles are generated by a liquid plasma discharge to eject ink, thereby printing images with high integration and high resolution.  
      It is another feature of an embodiment of the present invention to provide an ink-jet printhead having a simplified configuration and an increased lifetime.  
      It is still another feature of an embodiment of the present invention to provide an ink-jet printhead having a large ink ejectivity and avoids generating a harmful gas.  
      It is yet another feature of an embodiment of the present invention to provide an ink-jet printhead that has no restrictions on properties such as photosensitivity and conductivity with relation to an ink that may be used.  
      At least one of the above and other features and advantages of the present invention may be realized by providing an ink-jet printhead including an ink flow path having a nozzle for ejecting ink, at least one pair of electrodes provided in the ink flow path, each of the at least one pair of electrodes being separated from each other, and a voltage application unit for applying a voltage between the at least one pair of electrodes to generate a plasma discharge caused by liquid ionization between the pair of electrodes to generate a bubble for ejecting the ink.  
      The ink may be one of a dielectric liquid and a conductive liquid.  
      A gap between the at least one pair of electrodes may be approximately 1 μm to approximately 10 μm.  
      One of a direct current pulse voltage and an alternating current pulse voltage may be applied between the at least one pair of electrodes. The voltage applied between the at least one pair of electrodes may be greater than approximately 1 MV/m. The voltage may be applied between the at least one pair of electrodes for a time of approximately 0.1 to approximately 10 μs.  
      The ink flow path may include an ink chamber to be supplied with ink to be ejected through the nozzle and an ink channel to supply ink to the ink chamber. The at least one pair of electrodes may be provided in the ink chamber. The at least one pair of electrodes may be provided on a bottom surface of the ink chamber. Alternatively, the at least one pair of electrodes may be provided in the ink channel. As a further alternative, the at least one pair of electrodes may be provided in the ink chamber and the ink channel.  
      The at least one pair of electrodes may be a plurality of pairs of electrodes. The ink flow path may include an ink chamber to be supplied with ink to be ejected through the nozzle and a plurality of ink channels to supply ink to the ink chamber, wherein one pair of the plurality of pairs of electrodes is provided in each of the plurality of ink channels. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above and other features and advantages of the present invention will become more apparent to those of ordinary skill in the art by describing in detail exemplary embodiments thereof with reference to the attached drawings in which:  
       FIG. 1A  illustrates an exploded perspective view of a conventional thermally driven ink-jet printhead;  
       FIG. 1B  illustrates a cross-sectional view for explaining a process of ejecting an ink droplet from the conventional thermally driven ink-jet printhead of  FIG. 1A ;  
       FIG. 2  illustrates a cross-sectional view of another conventional ink-jet printhead;  
       FIG. 3  illustrates a cross-sectional view of still another conventional ink-jet printhead;  
       FIG. 4  illustrates a cross-sectional view of an ink-jet printhead according to an embodiment of the present invention;  
       FIG. 5  illustrates a top view of an interior of the ink-jet printhead of  FIG. 4 ;  
       FIGS. 6A through 6C  illustrate stages in a droplet ejection process of the ink-jet printhead according to an embodiment of the present invention; and  
       FIGS. 7 through 9  illustrate various modifications of the ink-jet printhead according to an embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Korean Patent Application No. 2003-91871, filed on Dec. 16, 2003, in the Korean Intellectual Property Office, and entitled: “Ink-jet Printhead,” is incorporated by reference herein in its entirety.  
      The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. The invention may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the figures, the dimensions of layers and regions are exaggerated for clarity of illustration. It will also be understood that when a layer is referred to as being “on” another layer or substrate, it can be directly on the other layer or substrate, or intervening layers may also be present. Like reference numerals refer to like elements throughout.  
       FIGS. 4 and 5  illustrate a cross-sectional view and a top view, respectively, of an ink-jet printhead according to an embodiment of the present invention.  
      Referring to  FIGS. 4 and 5 , the ink-jet printhead according to an embodiment of the present invention includes an ink flow path having a nozzle  106  through which ink  100  is ejected out of the printhead, a pair of electrodes  107   a  and  107   b  provided in the ink flow path, and a voltage application unit  110  for applying a voltage between the pair of electrodes  107   a  and  107   b.    
      The ink flow path may include an ink chamber  102  and an ink channel  104 . The ink chamber  102  is a space that is filled with ink  100  to be ejected through the nozzle  106 . The ink channel  104  is a passage through which ink  100  is supplied to the ink chamber  102 . The ink channel  104  is connected to an ink tank (not shown), in which ink  100  is stored. The ink  100  may be a dielectric liquid or a conductive liquid.  
      The pair of electrodes  107   a  and  107   b  may be provided on a bottom surface of the ink chamber  102  to be separated from each other. A gap between the electrodes  107   a  and  107   b  may be approximately 1 μm to approximately 10 μm. Alternatively, two or more pairs of electrodes may be provided in the ink chamber  102 .  
      In operation, the voltage application unit  110  applies a voltage to generate a plasma discharge caused by liquid ionization between the pair of electrodes  107   a  and  107   b . The voltage applied between the electrodes  107   a  and  107   b  may be a direct current pulse voltage or an alternating current pulse voltage. A bubble  120  is then generated and expanded in the ink  100  around the electrodes  107   a  and  107   b  by the liquid plasma discharge. Ink  100  in the ink chamber  102  is then ejected out of the printhead through the nozzle  106  due to expansion of the bubble  120 . An ejection speed of an ink droplet can be approximately 1 to 50 m/s.  
      Generally, in order to generate a liquid plasma discharge, when the liquid is pure water, a voltage of greater than approximately 100 MV/m is required, however, when the liquid is a conductive liquid, a voltage of greater than approximately 1 MV/m is required. In addition, the size of a voltage required to generate a liquid plasma discharge is determined according to a shape of the electrodes, an electric conductivity of the ink, a distance between the electrodes, temperature, and pressure.  
       FIGS. 6A through 6C  illustrate stages in a droplet ejection process of the ink-jet printhead according to an embodiment of the present invention.  
      Referring to  FIGS. 6A through 6C , an ink ejection process of the ink-jet printhead according to an embodiment of the present invention will be described.  
      First, referring to  FIG. 6A , in a state in which a voltage is not applied between the pair of electrodes  107   a  and  107   b , ink  100  in the ink chamber  102  fills an entrance of the nozzle  106  by a capillary force to form a meniscus. A gap between the electrodes  107   a  and  107   b  may be approximately 1 μm to approximately 10 μm. A direct current pulse voltage or an alternating current pulse voltage is then applied between the electrodes  107   a  and  107   b  by the voltage application unit  110 . A voltage of greater than approximately 1 MV/m may be applied for approximately 0.1 to approximately 10 μs. When a predetermined voltage is applied between the electrodes  107   a  and  107   b , ink  100  around the electrodes  107   a  and  107   b  is ionized. Resultantly, current flows between the electrodes  107   a  and  107   b  via the ionized ink  100 , thereby inducing a plasma discharge.  
      Referring to  FIG. 6B , bubble  120  is generated and expanded between the electrodes  107   a  and  107   b  by the plasma discharge. Thus, ink  100  in the ink chamber  102  is forced through the nozzle  106 .  
      Referring to  FIG. 6C , the applied voltage is interrupted when the bubble  120  has maximally expanded. When the applied voltage is interrupted, the bubble  120  contracts gradually until it dissipates, and the ink  100  forced through the nozzle  106  is ejected out of the printhead in an ink droplet  100 ′. An ejection speed and an ejection volume of the ink droplet  100 ′ may be controlled by the voltage applied between the electrodes  107   a  and  107   b  and a pulse period thereof. Subsequently, the ink chamber  102  is refilled with ink  100 , the printhead is returned to an initial state, and the above process is repeated.  
       FIGS. 7 through 9  illustrate various modifications of the ink-jet printhead according to an embodiment of the present invention. Only differences from the above mentioned embodiment will be described.  
      Referring to  FIG. 7 , an ink flow path may include an ink chamber  202  and an ink channel  204 . Each of a pair of electrodes  207   a  and  207   b  is provided in a single body on a bottom of the ink chamber  202  and on interior walls of the ink channel  204  connected to the ink chamber  202 . When a predetermined voltage to generate a liquid plasma discharge is applied between the electrodes  207   a  and  207   b , a bubble  220  is generated and expanded, and ink in the ink chamber  202  is ejected out of the printhead through a nozzle  206  due to expansion of the bubble  220 .  
      Referring to  FIG. 8 , a pair of electrodes  307   a  and  307   b  may be provided on interior walls of an ink channel  304  connected to an ink chamber  302 . In operation, a bubble  320  is generated and expanded between the electrodes  307   a  and  307   b  by a liquid plasma discharge.  
      Referring to  FIG. 9 , an ink flow path may include an ink chamber  402  and a plurality of ink channels  403 ,  404 , and  405 . Multiple pairs of electrodes ( 406   a  and  406   b ), ( 407   a  and  407   b ), and ( 408   a  and  408   b ) may be respectively provided on interior walls of the ink channels  403 ,  404 , and  405  connected to the ink chamber  402 . In operation, when a predetermined voltage to generate a liquid plasma discharge is applied between the multiple pairs of electrodes ( 406   a  and  406   b ), ( 407   a  and  407   b ), and ( 408   a  and  408   b ), respective bubbles  419 ,  420 , and  421  are generated and expanded, and ink in the ink chamber  402  is ejected through a nozzle  406  due to expansion of the bubbles  419 ,  420 , and  421 .  
      As described above, an ink-jet printhead according to an embodiment of the present invention may have one or more of the following advantages.  
      First, since ink is ejected by bubbles generated by a liquid plasma discharge, an ink-jet printhead may have a simplified configuration that does not require a heater or a piezoelectric element.  
      Second, since a defect generated by deterioration of a heater in a conventional printhead is prevented, a lifetime of a printhead can be increased.  
      Third, since bubbles generated by a liquid plasma discharge are used to eject ink, the ejectivity of ink may be very large and generation of a harmful gas may be prevented.  
      Fourth, there is no restriction on properties such as photosensitivity and conductivity with relation to ink that may be used.  
      Exemplary embodiments of the present invention have been disclosed herein and, although specific terms are employed, they are used and are to be interpreted in a generic and descriptive sense only and not for purpose of limitation. Accordingly, it will be understood by those of ordinary skill in the art that various changes in form and details may be made without departing from the spirit and scope of the present invention as set forth in the following claims.