Patent Publication Number: US-2023134046-A1

Title: Inkjet head

Description:
This application claims priority to Korean Patent Application No. 10-2021-0146702, filed on Oct. 29, 2021, and all the benefits accruing therefrom under 35 U.S.C. § 119, the content of which in its entirety is herein incorporated by reference. 
     BACKGROUND 
     (a) Technical Field 
     The present disclosure relates to an inkjet head. 
     (b) Description of the Related Art 
     An inkjet device includes an inkjet head having a nozzle for ejecting ink. The inkjet head may eject ink from a plurality of nozzle holes formed in a nozzle surface. The inkjet head may form wires of a display panel, a color filter, or various thin films such as spacers by ejecting a conductive material, a color filter material, a curable material, or an insulating material as ink onto a substrate. 
     The ink may contain particles for each of the materials described above together with a solvent. 
     SUMMARY 
     Particles in ink have a relatively large specific gravity and settle easily in an inkjet head. 
     Embodiments have been made in an effort to prevent defects such as spots of an image by preventing functional deviation of a thin film of a display panel printed using an inkjet head by preventing a concentration of ejected ink from being changed depending on a position of a nozzle due to non-uniform settling and dispersion of ink particles in the inkjet head. 
     In addition, the embodiments have been made in an effort to reduce an ink material cost by preventing wastage of an ink material by preventing unnecessary operations such as ink purge to control concentration dispersion of ink ejected from the nozzle of the inkjet head. 
     An embodiment of the present invention provides an inkjet head including: a head body having a storage chamber capable of storing ink; a first inlet pipe and a second inlet pipe connected to the head body and which extend in first different directions and inject the ink in the first different directions; a first outlet pipe and a second outlet pipe connected to the head body and which extend in second different directions and ejecting the ink in the second different directions; and a nozzle plate positioned under the head body and which includes a plurality of nozzles. 
     The first inlet pipe and the second inlet pipe may be positioned at a first end of the head body, and the first outlet pipe and the second outlet pipe may be positioned at a second end of the head body facing the first edge. 
     The first inlet pipe and the first outlet pipe may extend in a first direction, and the second inlet pipe and the second outlet pipe may extend in a second direction that is perpendicular to the first direction. 
     The inkjet head may further include a first filter and a second filter positioned within the storage chamber and which extend in third different directions. 
     The first filter may extend parallel to the nozzle plate, and may overlap the first inlet pipe and the first outlet pipe in a plan view, and the second filter may be positioned inside the second inlet pipe, and may overlap the second inlet pipe in a direction in which the second inlet pipe extends. 
     The first filter may be positioned below the first inlet pipe and the first outlet pipe and above the second inlet pipe and the second outlet pipe. 
     The inkjet head may further include a third filter positioned in the storage chamber and spaced apart from an inner surface of the head body. 
     The third filter may be connected to the first filter and the second filter, and the third filter may be extended in a direction in which the second filter is extended. 
     The inkjet head may further include a cover plate positioned within the storage chamber and between the first filter and the nozzle plate, and the cover plate may be positioned below the second inlet pipe and overlaps the nozzles on the plan view. 
     The cover plate may include a pair of edge portions adjacent to opposite edges of an inner surface of the head body in the second direction, and a central portion positioned between the pair of edge portions and connected to the pair of edge portions, and a width of the central portion in a third direction may be smaller than a width of the edge portions in the third direction. 
     The edge portions may be in contact with the inner surface of the head body, and the central portion may be spaced apart from the inner surface of the head body. 
     The cover plate may define one or more holes therein. 
     The holes may not overlap the nozzles in the plan view. 
     The cover plate may have a mesh or net shape. 
     The inkjet head may further include: a first flow controller positioned on a lower, inner surface of the head body and which does not overlap the nozzles in the plan view, and the first flow controller may be positioned between a side, inner surface of the body and an outer nozzle row among a plurality of nozzle rows in which the nozzles are arranged, and the first flow controller may extend along the outer nozzle row. 
     The inkjet head may further include a second flow controller positioned on the lower, inner surface of the head body and which does not overlap the nozzles in the plan view, and the second flow controller may be positioned between two adjacent inner nozzle rows positioned inside among the nozzle rows, and the second flow controller may extend along the inner nozzle rows. 
     The first flow controller and the second flow controller may have a pointed top, and a height of the second flow controller may be greater than a height of the first flow controller. 
     An embodiment of the present invention provides an inkjet head including: a head body having a storage chamber capable of storing ink; a first inlet pipe and a second inlet pipe connected to the head body; a first outlet pipe and a second outlet pipe connected to the head body; a nozzle plate positioned under the head body and which includes a plurality of nozzles; and a first filter and a second filter positioned within the storage chamber and which extend in different directions, where the first filter extends parallel to the nozzle plate and overlaps the first inlet pipe in a plan view, the second filter is positioned inside the second inlet pipe, and overlaps the second inlet pipe in a direction in which the second inlet pipe extends, and the ink includes at least one of quantum dots or scatterers. 
     An embodiment of the present invention provides an inkjet head including: a head body having a storage chamber capable of storing ink; one or more inlet pipes and one or more outlet pipes connected to the head body; a nozzle plate positioned under the head body and which includes a plurality of nozzles; a filter positioned in the storage chamber and which overlaps the inlet pipe; and a cover plate positioned within the storage chamber and between the filter and the nozzle plate, where the cover plate overlaps the nozzles in a plan view, and the cover plate defines one or more holes therein. 
     An embodiment of the present invention provides an inkjet head including: a head body having a storage chamber capable of storing ink; one or more inlet pipes and one or more outlet pipes connected to the head body; a nozzle plate positioned under the head body and which includes a plurality of nozzles; and a first flow controller and a second flow controller positioned on a lower, inner surface of the head body and which does not overlap the nozzles in a plan view, where the first flow controller is positioned between a side, inner surface of the body and an outer nozzle row among a plurality of nozzle rows in which the nozzles are arranged, the first flow controller extends along the outer nozzle row, the second flow controller is positioned between two adjacent inner nozzle rows positioned inside among the nozzle rows, and the second flow controller extends along the inner nozzle rows. 
     The first flow controller and the second flow controller may have a pointed top, and a height of the second flow controller may be greater than a height of the first flow controller. 
     According to the embodiments, it is possible to effectively prevent defects such as spots of an image by preventing functional deviation of a thin film of a display panel printed using an inkjet head by preventing a concentration of ejected ink from being changed depending on a position of a nozzle due to non-uniform sedimentation and dispersion of ink particles in the inkjet head. 
     In addition, according to the embodiments, it is possible to reduce an ink material cost by preventing wastage of an ink material by preventing unnecessary operations such as ink purge to control concentration dispersion of ink ejected from the nozzle of the inkjet head. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    and  FIG.  2    each illustrate a top plan view of an inkjet head according to an embodiment, 
         FIG.  3    illustrates a cross-sectional view of the inkjet head illustrated in  FIG.  1    taken along line A 1 -A 2 , 
         FIG.  4    illustrates a cross-sectional view of the inkjet head illustrated in  FIG.  1    taken along line B 1 -B 2 , 
         FIG.  5    illustrates a top plan view of an ink head according to another embodiment, 
         FIG.  6    illustrates a cross-sectional view of the inkjet head illustrated in  FIG.  5    taken along line A 3 -A 4 , 
         FIG.  7    illustrates a cross-sectional view of the inkjet head illustrated in  FIG.  5    taken along line B 3 -B 4 , 
         FIG.  8    illustrates a top plan view of an ink head according to still another embodiment, 
         FIG.  9    illustrates a cross-sectional view of the inkjet head illustrated in  FIG.  8    taken along line A 5 -A 6 , 
         FIG.  10    illustrates a cross-sectional view of the inkjet head illustrated in  FIG.  8    taken along line B 5 -B 6 , 
         FIG.  11    illustrates a top plan view of an ink head according to yet another embodiment, 
         FIG.  12    illustrates a cross-sectional view of the inkjet head illustrated in  FIG.  11    taken along line A 7 -A 8 , and 
         FIG.  13    illustrates a cross-sectional view of the inkjet head illustrated in  FIG.  11    taken along line B 7 -B 8 . 
     
    
    
     DETAILED DESCRIPTION 
     The present invention will be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. 
     To clearly describe the present invention, parts that are irrelevant to the description are omitted, and like numerals refer to like or similar constituent elements throughout the specification. 
     Further, since sizes and thicknesses of constituent members shown in the accompanying drawings are arbitrarily given for better understanding and ease of description, the present invention is not limited to the illustrated sizes and thicknesses. In the drawings, the thicknesses of layers, films, panels, regions, etc., are exaggerated for clarity. In the drawings, for better understanding and ease of description, the thicknesses of some layers and areas are exaggerated. 
     It will be understood that when an element such as a layer, film, region, or substrate is referred to as being “on” another element, it can be directly on the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” another element, there are no intervening elements present. Further, in the specification, the word “on” or “above” means positioned on or below the object portion, and does not necessarily mean positioned on the upper side of the object portion based on a gravitational direction. 
     It will be understood that, although the terms “first,” “second,” “third” etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, “a first element,” “component,” “region,” “layer” or “section” discussed below could be termed a second element, component, region, layer or section without departing from the teachings herein. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used herein, “a”, “an,” “the,” and “at least one” do not denote a limitation of quantity, and are intended to include both the singular and plural, unless the context clearly indicates otherwise. For example, “an element” has the same meaning as “at least one element,” unless the context clearly indicates otherwise. “At least one” is not to be construed as limiting “a” or “an.” “Or” means “and/or.” As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. It will be further understood that the terms “comprises” and/or “comprising,” or “includes” and/or “including” when used in this specification, specify the presence of stated features, regions, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components, and/or groups thereof. 
     Furthermore, relative terms, such as “lower” or “bottom” and “upper” or “top,” may be used herein to describe one element&#39;s relationship to another element as illustrated in the Figures. It will be understood that relative terms are intended to encompass different orientations of the device in addition to the orientation depicted in the Figures. For example, if the device in one of the figures is turned over, elements described as being on the “lower” side of other elements would then be oriented on “upper” sides of the other elements. The term “lower,” can therefore, encompasses both an orientation of “lower” and “upper,” depending on the particular orientation of the figure. Similarly, if the device in one of the figures is turned over, elements described as “below” or “beneath” other elements would then be oriented “above” the other elements. The terms “below” or “beneath” can, therefore, encompass both an orientation of above and below. 
     In addition, unless explicitly described to the contrary, the word “comprise” and variations such as “comprises” or “comprising” will be understood to imply the inclusion of stated elements but not the exclusion of any other elements. 
     Further, in the specification, the phrase “in a plan view” means when an object portion is viewed from above (i.e., view in a z direction), and the phrase “in a cross-sectional view” means when a cross-section taken by vertically cutting an object portion is viewed from the side. 
     An inkjet head according to an embodiment will be described with reference to  FIG.  1    to  FIG.  4   . 
       FIG.  1    and  FIG.  2    each illustrate a top plan view of an inkjet head according to an embodiment,  FIG.  3    illustrates a cross-sectional view of the inkjet head illustrated in  FIG.  1    taken along line A 1 -A 2 , and  FIG.  4    illustrates a cross-sectional view of the inkjet head illustrated in  FIG.  1    taken along line B 1 -B 2 . 
     An inkjet head  1000  according to an embodiment includes a head body  800 , a plurality of inlet pipes  310   p  and  330   p,  a plurality of outlet pipes  320   p  and  340   p,  a nozzle plate  100 , a first filter  410 , a second filter  420 , and a cover plate  500 . 
     The head body  800  has a storage chamber  810  capable of storing ink. The head body  800  has an inner surface  801 . 
     The ink to be stored in the storage chamber  810  may vary depending on purpose of an inkjet device including an inkjet head. For example, the ink may include a conductive material, a color filter material, a curable material, an insulating material, an emission layer material, or a color conversion layer material, and various films such as wires of a display panel, color filters, spacers, and emission layers may be formed by ejecting ink onto substrate. 
     The emission layer material or the color conversion layer material included in the ink may include, e.g., a semiconductor nano-crystal, and the semiconductor nanocrystal may include at least one of a phosphor, a quantum dot, or a scatterer. The quantum dot may have a core-shell structure including a core including semiconductor nanocrystals and a shell surrounding the core. 
     The ink contains particles for each of the materials described above together with a solvent. 
     The inlet pipes may include a first inlet tube  310   p  and a second inlet pipe  330   p  each having inlets for injecting ink in different directions, and the outlet pipes may include a first outlet pipe  320   p  and a second outlet pipe  340   p  having outlets for ejecting ink in different directions. 
     The first inlet pipe  310   p  has a first inlet  310  through which ink may be injected. The first inlet pipe  310   p  may be positioned at a side (e.g., top side of the head body  800 ) facing the nozzle plate  100 , and may be positioned at an end (e.g., left end) of the head body  800 . The first inlet  310  and the first inlet pipe  310   p  may extend in a z direction, but the present invention is not limited thereto. The first inlet  310  is connected to the storage chamber  810 . 
     The first outlet pipe  320   p  has a first outlet  320  through which ink may be ejected. The first outlet pipe  320   p  may be positioned at a side (e.g., top side of the head body  800 ) facing the nozzle plate  100 , and may be positioned at an end (e.g., right end) opposite to the end (e.g., left end) where the first inlet pipe  310   p  is positioned among ends of the head body  800 . The first outlet  320  and the first outlet pipe  320   p  may extend in the z direction, but the present invention is not limited thereto. The first outlet  320  is connected to the storage chamber  810 . 
     The second inlet pipe  330   p  has a second inlet  330  through which ink may be injected. The second inlet pipe  330   p  may be positioned at the end (e.g., left end) of the head body  800  in which the first inlet pipe  310   p  is positioned. The second inlet  330  and the second inlet pipe  330   p  may extend in a y-direction perpendicular to the z-direction, but the present invention is not limited thereto. The second inlet  330  is connected to the storage chamber  810 . 
     The second outlet pipe  340   p  has a second outlet  340  through which ink may be ejected. The second outlet pipe  340   p  may be positioned at an end (e.g., right end) of the head body  800  where the first outlet pipe  320   p  is positioned, and may be positioned to face the second inlet pipe  330   p.  The second outlet  340  and the second outlet pipe  340   p  may extend in they direction, but the present invention is not limited thereto. The second outlet  340  is connected to the storage chamber  810 . 
     The first inlet pipe  310   p  and the second inlet pipe  330   p  are positioned at a first end (e.g., left end) of the head body  800 , and the first outlet pipe  320   p  and the second outlet pipe  340   p  may be positioned at a second end (e.g., right end) of the head body  800  facing the first end. 
     The nozzle plate  100  is positioned under the head body  800 , and includes (in other words, “defines”) a plurality of nozzles  110  that are holes through which ink  10  can be ejected downward. 
     The nozzles  110  may be arranged to form a plurality of nozzle rows  115   a,    115   b,    115   c,  and  115   d  on an xy plane (i.e., plane defined by x direction and y direction). As used herein, the “nozzle row” means a row of nozzles. The nozzle rows  115   a,    115   b,    115   c,  and  115   d  each may extend in the y direction. Referring to FIG. 1  and  FIG.  2   , an example in which the nozzles  110  are arranged to form four nozzle rows  115   a,    115   b,    115   c,  and  115   d  is illustrated, but the number of nozzle rows according to the invention is not limited thereto. 
     A piezoelectric element  200  may be positioned on the nozzle plate  100  and between the adjacent nozzles  110 . When a driving signal is applied to the piezoelectric element  200 , the nozzle  110  may be contracted or expanded to easily eject ink by deformation of the piezoelectric element  200 . 
     The first inlet pipe  310   p,  the first outlet pipe  320   p,  the second inlet pipe  330   p,  the second outlet pipe  340   p,  and the nozzle plate  100  may be formed in or connected to the head body  800  to form the inkjet head  1000  in a bonded form. 
     The nozzle plate  100  is positioned at a bottom of the head body  800 , and the first inlet pipe  310   p,  the first outlet pipe  320   p,  the second inlet pipe  330   p,  and the second outlet pipe  340   p  are positioned above the nozzle plate  100 . The second inlet pipe  330   p  and the second outlet pipe  340   p  may be positioned below the first inlet pipe  310   p  and the first outlet pipe  320   p,  respectively. Herein, up and down directions are based on the z direction, and are the same hereafter. 
     The first filter  410  is positioned in the storage chamber  810 , may extend parallel to the xy plane, and may be parallel to the nozzle plate  100 . Referring to  FIG.  1    and  FIG.  3   , the first filter  410  may overlap most of an interior space of the head body  800  in a top plan view. In this case, as illustrated in  FIG.  1    and  FIG.  3   , an edge of the first filter  410  may be in contact with an inner surface  801  of the head body  800 . 
     The storage chamber  810  may be divided into an upper area and a lower area with respect to the first filter  410  as a boundary. 
     The first filter  410  may be positioned below the first inlet pipe  310   p  and the first outlet pipe  320   p  and above the second inlet pipe  330   p  and the second outlet pipe  340   p.  The first filter  410  may overlap the first inlet pipe  310   p  and the first outlet pipe  320   p  in a top plan view. 
     The first filter  410  may block impurities other than particles  11  of an ink material injected from the first inlet  310 , and then may pass the ink to a lower side of the first filter  410 . To this end, the first filter  410  may have a hole sized enough to pass the particles  11  of the ink material and to block impurities larger than the particles  11 . 
     The ink that is injected as indicated by a straight arrow pointing down in the z direction in  FIG.  3    and  FIG.  4    may move downward through the first filter  410  after impurities are removed, and the impurities may move along the straight arrow in the y direction on the first filter  410  in  FIG.  3    along the first filter  410  and may again be externally ejected through the first outlet  320  as indicated by a straight arrow pointing upward in the z direction. 
     The first filter  410  may be omitted in a certain embodiment. 
     The second filter  420  is positioned in the storage chamber  810 , and may extend parallel to the xz plane (See  FIG.  3   ). The second filter  420  is positioned inside the second inlet  330 , and may be positioned at a boundary between the second inlet  330  and the storage chamber  810 . That is, the second filter  420  may overlap the second inlet  330  and the second inlet pipe  330   p  on the xz plane (i.e., a view in y direction). 
     The second filter  420  may block injection of impurities other than the particles  11  of the ink material injected from the second inlet  330 , and then may send the ink to the storage chamber  810 . To this end, the second filter  420  may have a hole sized enough to pass the particles  11  of the ink material and to block impurities larger than the particles  11 . 
     The second filter  420  may have a same material and structure as those of the first filter  410 . The second filter  420  may be connected to or separated from the first filter  410 . 
     The ink that is injected as indicated by a straight arrow in the y-direction in the second inlet  330  in  FIG.  3    may be injected to the storage chamber  810  after impurities are removed through the second filter  420 . 
     The cover plate  500  is positioned in the storage chamber  810 , and may extend parallel to the xy plane. The cover plate  500  may be positioned between the first filter  410  and the nozzle plate  100 , and positioned below the second inlet  330 . 
     Referring to  FIG.  1    to  FIG.  4   , the cover plate  500  may overlap the nozzles  110  on the xy plane (i.e., in a top plan view). 
     The cover plate  500  may block the particles  11  of the ink material injected to the storage chamber  810  from settling directly toward the nozzle  110 . 
     The cover plate  500  may have a continuous plane. The cover plate  500  may include opposite edge portions  501  and a central portion  502  therebetween on the xy plane (i.e., in the plan view). The central portion  502  may be connected to the pair of edge portions  501 , and may be integrally formed (i.e., monolithic) with the edge portions  501 . 
     The opposite edge portions  501  may be positioned in regions adjacent to left and right ends of the inner surface  801  of the head body  800  in which the first inlet  310 , the second inlet  330 , the first outlet  320 , and the second outlet  340  are positioned. The edge portions  501  may overlap the first inlet  310  or the first inlet pipe  310   p,  and the first outlet  320  and the first outlet pipe  320   p  on the xy plane (i.e., in the plan view). 
     The edge portions  501  may serve to block the ink, which is injected to or ejected from the storage chamber  810  through the first inlet  310 , the second inlet  330 , the first outlet  320 , or the second outlet  340 , from not-circulating and settling directly into the nozzle  110 . 
     Edges of the edge portions  501  may be in contact with the inner surface  801  of the head body  800 . 
     An x-directional width of the central portion  502  is smaller than an x-directional width of each of the edge portions  501 . As illustrated in  FIG.  1   ,  FIG.  2   , and  FIG.  3   , the central portion  502  is spaced apart from an inner wall of the head body  800 , and thus ink may flow toward the nozzle plate  100  through a space between the central portion  502  and the head body  800 . 
     Upper and lower edges of the central portion  502  in  FIG.  2    may be spaced apart from the inner surface  801  of the head body  800 . 
     Without the second inlet  330  and the second outlet  340 , a circulating amount of the ink positioned under the first filter  410  may be reduced in the storage chamber  810 , and thus settling of ink particles may easily occur, and it is easy to cause a deviation in concentration of ink particles depending on a position of the nozzle  110 . Then, defects such as spots due to functional deviation of the thin film of the display panel formed using the inkjet head  1000  may occur. 
     However, according to the present embodiment, it is possible to improve circulation of ink in the storage chamber  810  by adding the second inlet  330  and the second outlet  340  in addition to the first inlet  310  and the first outlet  320 . Thus, it is possible to prevent non-uniform dispersion in the concentration of ink particles due to particles settling in the space between the cover plate  500  and the head body  800 . Resultantly, it is possible to effectively prevent non-uniformity of the concentration of the ink ejected depending on the position of the nozzle  110  by non-uniform settling and dispersion of the particles of the ink in the storage chamber  810 , and defects such as image spots may be reduced by preventing functional deviation of the thin film of the display panel formed by using the inkjet head  1000  according to the invention. In addition, there is no need to perform operations such as ink purge for controlling the concentration distribution of the particles  11  of the ink  10 , thereby preventing wastage of the ink material and reducing the ink material cost. 
     In addition, according to an embodiment, it is possible to prevent the particles of the ink injected, from directly descending to the nozzle  110  by the cover plate  500 . 
     The cover plate  500  may include a metal, but the present invention is not limited thereto. 
     According to another exemplary embodiment, the cover plate  500  may be omitted. 
     The second filter  420  between the second inlet  330  and the storage chamber  810  may reduce imbalance in purification of ink in the space between the first filter  410  and the nozzle plate  100  while blocking impurities in the ink. 
     Since the second inlet  330  is positioned on the cover plate  500 , it is possible to prevent ink vortex flow directly above the nozzle plate  100  and to prevent sedimentation of particles on the cover plate  500 . 
     An inkjet head according to another embodiment will be described with reference to  FIG.  5    to  FIG.  7   . 
       FIG.  5    illustrates a top plan view of an ink head according to another embodiment,  FIG.  6    illustrates a cross-sectional view of the inkjet head illustrated in  FIG.  5    taken along line A 3 -A 4 , and  FIG.  7    illustrates a cross-sectional view of the inkjet head illustrated in  FIG.  5    taken along line B 3 -B 4 . 
     An inkjet head  1001  according to the present embodiment is mostly the same as the inkjet head  1000  according to the embodiment illustrated in  FIG.  1    to  FIG.  4    described above, but may further include a first flow controller  610  and a second flow controller  620 , which are positioned in the storage chamber  810  and are formed on a bottom surface of the head body  800  (See  FIG.  7   ). In  FIG.  5   , the line A 3 -A 4  is divided into two lines inside the head body  800 : an upper line passing through the second flow controller  620 , and a lower line passing through the nozzles  110 . 
     The first flow controller  610  and the second flow controller  620  do not overlap the nozzles  110  on the xy plane (i.e., in the top plan view). 
     The first flow controllers  610  may be positioned outside the nozzle rows  115   a  and  115   d  at opposite edges among the nozzle rows  115   a,    115   b,    115   c,  and  115   d,  i.e., between the outer nozzle row  115   a  and the upper inner surface  801  of the head body  800  and between the outer nozzle row  115   d  and the lower inner surface  801  in  FIG.  5   . 
     The first flow controllers  610  each may be elongated in a direction in which the nozzle rows  115   a  and  115   d  extend, i.e., in the y-direction, and are adjacent to each of the nozzle rows  115   a  and  115   d  along the nozzle rows  115   a  and  115   d.    
     A cross-sectional structure of the first flow controller  610  viewed on the xz plane (i.e., view in the y direction in  FIG.  7   ) may have a substantially triangular shape with a pointed top, but the present invention is not limited thereto. 
     The second flow controllers  620  may be positioned between two inner nozzle rows  115   b  and  115   c  among the nozzle rows  115   a,    115   b,    115   c,  and  115   d.  Particularly, the second flow controller  620  may be positioned in a center of the bottom surface of the head body  800 , and may be positioned between two adjacent nozzle rows  115   b  and  115   c.  One or more second flow controllers  620  may be positioned between the two adjacent nozzle rows  115   b  and  115   c.    FIG.  5    and  FIG.  7    each illustrate an example in which two second flow controllers  620  are positioned between two adjacent nozzle rows  115   b  and  115   c  in the center, but a number of second flow controllers  620  according to the invention is not limited thereto. 
     The second flow controllers  620  each may be elongated in a direction in which the nozzle rows  115   b  and  115   c  extend, i.e., in the y-direction, and are adjacent to each of the nozzle rows  115   b  and  115   c  along the nozzle rows  115   b  and  115   c.    
     A cross-section structure of the second flow controller  620  viewed on the xz plane (i.e., view in the y direction in  FIG.  7   ) may have a substantially triangular shape with a pointed top, but the present invention is not limited thereto. 
     A z-directional height of the second flow controller  620  in the z direction may be greater than a z-directional height of the first flow controller  610 . A cross-sectional size of the second flow controller  620  shown in  FIG.  7    may be larger than a cross-sectional size of the first flow controller  610 . 
     The first flow controller  610  may prevent the ink  10  injected in a direction of the straight arrows in  FIG.  7    from settling around the cover plate  500  and being directly ejected to the outer nozzle rows  115   a  and  115   d.  The second flow controller  620  that is larger than the first flow controller  610  may induce sedimentation of the particles  11  by blocking a flow of the particle  11  around the inner nozzle rows  115   b  and  115   c  as indicated by the curved line arrows in  FIG.  7   . Accordingly, it is possible to improve relatively lower concentration of the particles  11  of the ink  10  in a central region of the nozzle plate  100  than the concentration of the particles  11  in an edge region of the nozzle plate  100  close to the space between the cover plate  500  and the left and right sides of the head body  800 . Thus, the concentration of the particles  11  of the ink  10  passing through the nozzles  110  of the nozzle plate  100  may be made more uniform. 
     An inkjet head according to still another embodiment will be described with reference to  FIG.  8    to  FIG.  10   . 
       FIG.  8    illustrates a top plan view of an ink head according to still another embodiment,  FIG.  9    illustrates a cross-sectional view of the inkjet head illustrated in FIG.  8  taken along line A 5 -A 6 , and  FIG.  10    illustrates a cross-sectional view of the inkjet head illustrated in  FIG.  8    taken along line B 5 -B 6 . 
     The inkjet head  1002  according to the present embodiment is mostly the same as the inkjet head  1000  or the inkjet head  1001  described above, but may include a cover plate  510  instead of the cover plate  500 . 
     The cover plate  510  may include (i.e., define) at least one hole  52  therein. The hole  52  may not overlap the nozzles  110  on the xy plane (i.e., in the plan view). Since the hole  52  does not overlap the nozzles  110 , particles  11  of ink  10  descending through the hole  52  may be prevented from settling directly into the nozzles  110 . 
     The at least one hole  52  may divide a central portion  502  into two or more regions.  FIG.  8    illustrates an example in which one hole  52  divides the central portion  502  into two regions. 
     The particles  11  of the ink  10  may descend toward the nozzle plate  100  also through the hole  52  in the center of the cover plate  510  in addition to the space between the cover plate  510  and the left and right sides of the head body  800  as indicated by the curved arrows in  FIG.  10   , and thus it is possible to relatively improve a lower concentration of the particles  11  of the ink  10  in a central region of the nozzle plate  100  than the concentration of the particles  11  in an edge region of the nozzle plate  100  close to the space between the cover plate  510  and the left and right sides of the head body  800 . Thus, the concentration of the particles  11  of the ink  10  passing through the nozzles  110  of the nozzle plate  100  may be made more uniform. 
     Referring to  FIG.  9    and  FIG.  10   , the cover plate  510  may have a mesh or net shape. Accordingly, the cover plate  510  may include a plurality of holes  51 . Each of the holes  51  is smaller than the hole  52  dividing the central portion  502  of the cover plate  510 . The hole  51  may be larger than or equal to a size of the particles  11  of the ink. Accordingly, circulation of the particles  11  of the ink  10  by the cover plate  510  may be further improved. 
     In addition, the characteristics of the cover plate  500  of the above-described embodiment may be equally applied to the cover plate  510  according to the present embodiment. 
     An inkjet head according to yet another embodiment will be described with reference to  FIG.  11    to  FIG.  13   . 
       FIG.  11    illustrates a top plan view of an ink head according to yet another embodiment,  FIG.  12    illustrates a cross-sectional view of the inkjet head illustrated in  FIG.  11    taken along line A 7 -A 8 , and  FIG.  13    illustrates a cross-sectional view of the inkjet head illustrated in  FIG.  11    taken along line B 7 -B 8 . 
     The inkjet head  1003  according to the present embodiment is mostly the same as the inkjet head  1000 , the inkjet head  1001 , and the inkjet head  1002  described above, but may further include a third filter  430  and a fourth filter  440 . 
     In  FIG.  11   , the line A 7 -A 8  do not pass through the third filter  430  or the fourth filter  440 , but for convenience of understanding, the fourth filter  440  is illustrated in  FIG.  12   . 
     The third filter  430  and the fourth filter  440  may be positioned in the storage chamber  810 , and each of them may extend parallel to the yz plane. The third filter  430  and the fourth filter  440  are positioned close to the opposite edges (i.e., left and right inner surfaces in  FIG.  13   ) of the head body  800 , respectively, and are spaced apart from the inner surface  801  of the head body  800  by an interval GP that is greater than 0. The third filter  430  and the fourth filter  440  may face each other with the cover plate  510  therebetween. 
     Referring to  FIG.  12    and  FIG.  13   , the third filter  430  and the fourth filter  440  may be parallel to the yz plane. That is, the third filter  430  and the fourth filter  440  may extend from an upper region to a lower region of the cover plate  510  and extend in the y direction in which the first filter  410  extends. 
     Unlike in the above-described embodiment, referring to  FIG.  11   , upper and lower ends of the first filter  410  may be spaced apart from the inner surface  801  of the head body  800 . Such a distance may be equal to the interval GP. 
     The third filter  430  and the fourth filter  440  may be connected to at least one of the first filter  410  or the second filter  420 . In addition, the third filter  430  and the fourth filter  440  may be connected to the first filter  410  and the second filter  420  to form one overturned lid, and may overlap and cover the nozzles  110  at the bottom. The first filter  410 , the second filter  420 , the third filter  430 , and the fourth filter  440  connected to each other may form a cuboid shape with an open bottom, but the shape formed by the filters together is not limited thereto, and other shapes such as a dome may be formed in another embodiment. 
     The third filter  430  and the fourth filter  440  may have the same material and function as those of the first filter  410  or the second filter  420 . That is, the third filter  430  and the fourth filter  440  may pass the ink  10  toward the nozzle  110  after blocking impurities other than the particles  11  of the material of the ink  10  injected therein. To this end, the third filter  430  and the fourth filter  440  may have (i.e., define the hole therein) a hole sufficiently sized to pass the particles  11  of the ink material and to block impurities larger than the particles  11 . 
     The ink that is injected as indicated by a straight arrow in  FIG.  12    and  FIG.  13    may move toward the nozzle  110  through the first filter  410 , the second filter  420 , the third filter  430 , and the fourth filter  440  after the impurities are removed. 
     According to the present embodiment, the ink moves toward the nozzle plate  100  through the interval GP in the storage chamber  810  and passes through the third filter  430  and the fourth filter  440 , and thus circulation of the ink  10  in the storage chamber  810  may be further improved by reducing the number of particles of which circulation is stagnant after passing through the first filter  410 . 
     While this invention has been described in connection with what is presently considered to be practical embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. 
     DESCRIPTION OF SYMBOLS 
       10 : ink 
       11 : particle 
       100 : nozzle plate 
       110 : nozzle 
       115   a,    115   b,    115   c,    115   d:  row of nozzles 
       200 : piezoelectric element 
       310 ,  330 : inlet 
       310   p,    330   p:  inlet pipe 
       320 ,  340 : outlet 
       320   p,    340   p:  outlet pipe 
       410 ,  420 ,  430 ,  440 : filter 
       500 ,  510 : cover plate 
       610 ,  620 : flow controller 
       800 : head body 
       801 : inner side surface 
       810 : storage chamber 
       1000 ,  1001 ,  1002 ,  1003 : inkjet head