Abstract:
There is provided an inkjet print head. The inkjet print head includes a pressure chamber storing ink drawn from a reservoir in order to be ejected through a nozzle, a restrictor provided as a path between the reservoir and the pressure chamber, and a stepped part provided inside the pressure chamber and creating variations in ink flow inside the pressure chamber.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the priority of Korean Patent Application No. 10-2009-0103711 filed on Oct. 29, 2009, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to an inkjet print head, and more particularly, to an inkjet print head allowing for variations in the size and speed of ink droplets ejected therefrom even in the case that the inkjet print head is the same size as another inkjet print head by constructing a pressure chamber having a stepped structure in which pressure variations occur due to the driving force of a piezoelectric element. 
         [0004]    2. Description of the Related Art 
         [0005]    In general, an inkjet print head converts electrical signals into physical impulses so that ink droplets are ejected through a small nozzle. 
         [0006]    An inkjet print head may be divided into two types according to actuator driving methods, a piezoelectric-type inkjet print head using a driving force caused by the transformation of piezoelectric materials and a bubble jet-type inkjet print head allowing ink to be ejected by bubbles generated in ink using heating elements. 
         [0007]    In recent years, a piezoelectric inkjet head has been used in industrial inkjet printers. For example, it is used to directly form a circuit pattern by spraying ink prepared by melting metals such as gold or silver onto a printed circuit board (PCB). A piezoelectric inkjet head is also used for creating industrial graphics, or for the manufacturing of a liquid crystal display (LCD), an organic light emitting diode (OLED), and a solar cell. 
         [0008]    Inside an inkjet print head of an industrial inkjet printer, there are provided an inlet through which ink is drawn from a cartridge, a reservoir storing the ink being drawn, and a pressure chamber transferring the driving force of an actuator so as to move the ink stored in the reservoir toward a nozzle. 
         [0009]    With the recent expansion of industrial inkjet printer applications, the size and speed of ink droplets have been needed to be controlled, and thus further research has been required. 
         [0010]    A pressure chamber according to the related art has the same height at a portion connected with a restrictor and at a portion connected with a nozzle. That is, the pressure chamber has a regular parallelepiped structure in which the upper and lower surfaces thereof have a uniform distance therebetween. 
         [0011]    By causing the distance between the upper and lower surfaces of a pressure chamber to be uniform, if inkjet print heads have the same size, ink droplets of consistent size and speed are the result. Therefore, there is a need for the development of an inkjet print head having a difference in the size and speed of ink droplets to match desired inkjet applications, even in the case that the inkjet print head is the same size as another inkjet print head. 
       SUMMARY OF THE INVENTION 
       [0012]    An aspect of the present invention provides an inkjet print head allowing for variations in the size and speed of ink droplets ejected therefrom even in the case that the inkjet print head is the same size as another inkjet print head by constructing a pressure chamber having a stepped structure in which pressure variations occur due to the driving force of a piezoelectric element. 
         [0013]    According to an aspect of the present invention, there is provided an inkjet print head including: a pressure chamber storing ink drawn from a reservoir in order to be ejected through a nozzle; a restrictor provided as a path between the reservoir and the pressure chamber; and a stepped part provided inside the pressure chamber and creating variations in ink flow inside the pressure chamber. 
         [0014]    The stepped part may have a stepped upper surface having increased height in a direction toward the restrictor inside the pressure chamber. 
         [0015]    The stepped part may have a multiple stepped structure and allow for gradually increased height in the direction toward the restrictor. 
         [0016]    The stepped part may have a stepped upper surface having increased height in a direction toward the nozzle inside the pressure chamber. 
         [0017]    The stepped part may have a multiple stepped structure and allow for gradually increased height in the direction toward the nozzle. 
         [0018]    The stepped part may have a stepped upper surface having increased height in a direction toward both the restrictor and the nozzle inside the pressure chamber. 
         [0019]    The stepped part may have a multiple stepped structure and allow for gradually increased height in the direction toward both the restrictor and the nozzle. 
         [0020]    The stepped part may have a stepped upper surface having reduced height in a direction toward both the restrictor and the nozzle inside the pressure chamber. 
         [0021]    The stepped part may have a multiple stepped structure and allow for gradually reduced height in the direction toward both the restrictor and the nozzle. 
         [0022]    The stepped part may have a micro-pillar provided thereon. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    The above and other aspects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
           [0024]      FIG. 1  is an exploded perspective view schematically illustrating an inkjet print head according to an exemplary embodiment of the present invention; 
           [0025]      FIG. 2  is a cross-sectional view illustrating an inkjet print head according to an exemplary embodiment of the present invention; 
           [0026]      FIG. 3  is a cross-sectional view illustrating an inkjet print head according to another exemplary embodiment of the present invention; 
           [0027]      FIG. 4  is a cross-sectional view illustrating an inkjet print head according to another exemplary embodiment of the present invention; 
           [0028]      FIG. 5  is a cross-sectional view illustrating an inkjet print head according to another exemplary embodiment of the present invention; 
           [0029]      FIG. 6  is a cross-sectional view illustrating an inkjet print head according to another exemplary embodiment of the present invention; 
           [0030]      FIG. 7  is a cross-sectional view illustrating an inkjet print head according to another exemplary embodiment of the present invention; and 
           [0031]      FIG. 8  is a schematic perspective view illustrating micro-pillars arranged in an inkjet print head according to an exemplary embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0032]    Exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. The invention may, however, be embodied in many different forms and should not be construed as being 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. 
         [0033]    Throughout the drawings, the same reference numerals will be used to refer to the same or like parts. 
         [0034]      FIG. 1  is an exploded perspective view schematically illustrating an inkjet print head according to an exemplary embodiment of the present invention.  FIG. 2  is a cross-sectional view illustrating an inkjet print head according to an exemplary embodiment of the present invention. 
         [0035]    Referring to  FIGS. 1 and 2 , an inkjet print head  200  according to an exemplary embodiment of the invention may include a pressure chamber  224 , a restrictor  246 , and a stepped part  241 . 
         [0036]    The inkjet print head  200  is a structure manufactured by stacking silicon or glass substrate plates. Holes or grooves are formed in the substrate plates by micro electro mechanical systems (MEMS) processing and those substrate plates are stacked, and thus the pressure chamber  224 , the restrictor  246 , and the stepped part  241  are formed. 
         [0037]    The inkjet print head  200  according to this embodiment may be formed by stacking lower, intermediate, and upper substrates  260 ,  240  and  220 . 
         [0038]    A silicon plate of the inkjet print head  200  may have a double layer structure. Also, more substrates may be stacked to form an inkjet print head. 
         [0039]    The upper substrate  220  may have an inlet  222  and the pressure chamber  224  formed therein. The inlet  222  allows ink to be drawn into the inkjet print head  200 , and the pressure chamber  224  allows ink to be supplied with a driving force for ejection. On the top of the pressure chamber  224 , a piezoelectric element  250  may be provided to have a membrane  225  disposed therebetween. The piezoelectric element  250  supplies the pressure chamber  224  with the driving force for ink ejection. 
         [0040]    The piezoelectric element  250  may allow ink ejection to be made by transforming the membrane  225  that is the upper surface of the pressure chamber  224 . A piezoelectric element may convert electrical energy into mechanical energy or vice versa, and its representative material is Pb (Zr, Ti) O 3 . Also, for the ink ejection, a bubble jet or thermal jet method, besides a piezoelectric method using the piezoelectric element  250 , may be used. 
         [0041]    The lower substrate  260  may have a nozzle  262  formed therein. The intermediate substrate  240  may have a damper  244  and a reservoir  242  formed therein. The reservoir  242  stores ink inside the inkjet print head  200 . Also, the intermediate substrate  240  may have the restrictor  246  formed therein in order to prevent the ink of the pressure chamber  224  from flowing backward into the reservoir  242 . 
         [0042]    The piezoelectric element  250  may be formed to have electrodes on the top and bottom of a piezoelectric material layer that is transformed by current supply. Those upper and lower electrodes may be connected with a flexible printed circuit board in order to apply voltage thereto. 
         [0043]    The nozzle  262  may eject the ink stored in the pressure chamber  224  in the form of droplets by the driving force of the piezoelectric element  250 . Here, the nozzle  262  decides the size and direction of the droplets. 
         [0044]    The intermediate substrate  240  may have the stepped part  241  formed therein. The stepped part  241  may allow the upper and lower surfaces of the pressure chamber  224 , which are formed by bonding the intermediate and upper substrates  240  and  220 , to have different depths therebetween. 
         [0045]    Referring to  FIG. 2 , the stepped part  241  has a stepped upper surface  2412  formed to have increased height in a direction toward the restrictor  246 . That is, the depth of the pressure chamber  224  increases in a direction toward the nozzle  262 . Such a structure is defined as a diffusion-type pressure chamber. 
         [0046]    As a result of a simulation of the volume and ejection speed of ink droplets from an inkjet print head including such a diffusion-type pressure chamber, the volume of ink droplets was 0.92 pL and the ejection speed was 1.59 m/s. 
         [0047]    In a simulation of the volume and ejection speed of ink droplets from an inkjet print head including a conventional flat-type pressure chamber and having the same size as the inkjet print head including the diffusion-type pressure chamber, the volume of ink droplets was 1.28 pL and the ejection speed was 2.78 m/s. 
         [0048]    That is, the inkjet print head including the diffusion-type pressure chamber reduces the volume and ejection speed of ink droplets. 
         [0049]    The stepped part  241  inside the diffusion-type pressure chamber allows the depth of the pressure chamber  224  to be increased before ink is drawn into the nozzle  262 , thereby acting as a kind of damper. 
         [0050]      FIG. 3  is a cross-sectional view of an inkjet print head according to another exemplary embodiment of the present invention. 
         [0051]    Referring to  FIG. 3 , in an inkjet print head according to this embodiment, in contrast to the inkjet print head according to the aforementioned embodiment, a stepped part  243  has a stepped upper surface  2432  formed to have increased height in a direction toward the nozzle  262 . That is, the depth of the pressure chamber  224  decreases in a direction toward the nozzle  262 . Such a structure is defined as a convergence-type pressure chamber. 
         [0052]    As a result of a simulation of the volume and ejection speed of ink droplets from an inkjet print head including such a convergence-type pressure chamber, the volume of ink droplets was 1.13 pL and the ejection speed was 2.20 m/s. 
         [0053]    In a simulation of the volume and ejection speed of ink droplets from an inkjet print head including a conventional flat-type pressure chamber and having the same size as the inkjet print head including the convergence-type pressure chamber, the volume of ink droplets was 1.28 pL and the ejection speed was 2.78 m/s. 
         [0054]    That is, the inkjet print head including the convergence-type pressure chamber reduces the volume and ejection speed of ink droplets. 
         [0055]    The convergence-type pressure chamber allows ink to flow smoothly toward a nozzle outlet direction and prevents ink from flowing backward into the restrictor  246  after being ejected therefrom. 
         [0056]      FIG. 4  is a cross-sectional view of an inkjet print head according to another exemplary embodiment of the present invention.  FIG. 5  is a cross-sectional view of an inkjet print head according to another exemplary embodiment of the present invention. 
         [0057]    Referring to  FIG. 4 , a stepped part  245  has a multiple stepped structure gradually increasing the height of the stepped part  245  in a direction toward the restrictor  246  and gradually increasing the depth of the pressure chamber  224  in a direction toward the nozzle  262 , thereby forming a diffusion-type pressure chamber. 
         [0058]    Also, referring to  FIG. 5 , a stepped part  247  has a multiple stepped structure gradually increasing the height of the stepped part  247  in a direction toward the nozzle  262  and gradually reducing the depth of the pressure chamber  224  in a direction toward the nozzle  262 , thereby forming a convergence-type pressure chamber. 
         [0059]    As shown in  FIGS. 4 and 5 , the diffusion-type and convergence-type pressure chambers having a multiple stepped structure may allow the flowing of ink to be smoothly adjusted, and also allow the volume and ejection speed of ink droplets to be adjusted. 
         [0060]      FIG. 6  is a cross-sectional view of an inkjet print head according to another exemplary embodiment of the present invention.  FIG. 7  is a cross-sectional view of an inkjet print head according to another exemplary embodiment of the present invention. 
         [0061]    Referring to  FIG. 6 , a stepped part  249   a  may have stepped upper surfaces  2492  formed to have increased height in a direction toward both the restrictor  246  and the nozzle  262  inside the pressure chamber  224 . 
         [0062]    Also, the stepped part  249   a  has a multiple stepped structure and allows the height of the stepped part  249   a  to be gradually increased in a direction toward both the restrictor  246  and the nozzle  262 , whereby an inkjet print head has a structure in which the depth of the pressure chamber  224  gradually decreases in a direction toward both the restrictor  246  and the nozzle  262 . 
         [0063]    Referring to  FIG. 7 , a stepped part  249   b  may have stepped upper surfaces  2494  formed to have reduced height in a direction toward both the restrictor  246  and the nozzle  262  inside the pressure chamber  224 . 
         [0064]    Also, the stepped part  249   b  has a multiple stepped structure and allows the height of the stepped part  249   b  to be gradually reduced in a direction toward both the restrictor  246  and the nozzle  262 , whereby an inkjet print head has a structure in which the depth of the pressure chamber  224  gradually increases in a direction toward both the restrictor  246  and the nozzle  262 . 
         [0065]    By properly combining the principles of the diffusion-type and convergence-type pressure chambers, the volume, speed and flow rate of ink droplets may be improved. 
         [0066]      FIG. 8  is a schematic perspective view illustrating micro-pillars arranged in an inkjet print head according to an exemplary embodiment of the present invention. 
         [0067]    Referring to  FIG. 8 , micro-pillars  248  may be formed on a stepped part  241  inside the pressure chamber  224 . 
         [0068]    The micro-pillars  248  attenuate sound waves generated in the pressure chamber  224  by the driving force of the piezoelectric element  250  and generate flow resistance to ink flowing backward into the restrictor  246  after ink is ejected from the pressure chamber  224 . 
         [0069]    That is, the micro-pillars  248  may supplement the flow resistance to ink of the convergence-type pressure chamber flowing backwards and complement the flow resistance to ink of the diffusion-type pressure chamber flowing backwards. 
         [0070]    The inkjet print head according to exemplary embodiments of the present invention has an effect to enable variations in the size and speed of ink droplets by allowing for variations in the distance between the upper and lower surfaces of a pressure chamber even in the case that the inkjet print head is the same size as another inkjet print head. 
         [0071]    Also, an inkjet print head having desired size and speed of ink droplets in inkjet applications may be selected by allowing the size and speed of ink droplets to be different. 
         [0072]    As set forth above, according to exemplary embodiments of the invention, an inkjet print head achieves variations in the size and speed of ink droplets by constructing a pressure chamber in a manner that the distances between the upper and lower surfaces of the pressure chamber differ even in the case that the inkjet print head has the same size as another inkjet print head. 
         [0073]    Also, the variations in the size and speed of ink droplets may allow for selections of an inkjet print head having desired size and speed of ink droplets in inkjet applications. 
         [0074]    While the present invention has been shown and described in connection with the exemplary embodiments, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the spirit and scope of the invention as defined by the appended claims.