Patent Publication Number: US-11660865-B2

Title: Print head unit and inkjet printer including the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority to and the benefit of Korean Patent Application No. 10-2020-0125226 filed in the Korean Intellectual Property Office on Sep. 25, 2020, the entire content of which is incorporated herein by reference. 
     BACKGROUND 
     1. Field 
     Aspects of some embodiments of the present invention relate to a print head unit and an inkjet printer including the same. 
     2. Description of the Related Art 
     As interests in information displays and demands on using portable information media increase, researches and commercialization on display devices are actively performed. 
     The above information disclosed in this Background section is only for enhancement of understanding of the background and therefore the information discussed in this Background section does not necessarily constitute prior art. 
     SUMMARY 
     Aspects of some embodiments of the present invention include a print head unit capable of uniformly supplying light-emitting elements to a substrate, and an inkjet printer including the same. 
     An inkjet printer according to some embodiments of the present invention includes a substrate on a stage; a print head unit positioned above the stage and configured to discharge an ink to the substrate; and an ink supply unit configured to supply the ink to the print head unit, wherein the print head unit includes: a manifold configured to guide movement of the ink in a first direction therein; a head block under the manifold and including a plurality of channels connected to the manifold and piezoelectric elements adjacent to the channels to discharge the ink through the channels; a nozzle unit under the head block and including nozzles corresponding to the channels; a dispersion plate between the manifold and the head block and configured to disperse the ink in a second direction intersecting the first direction to supply the ink to the head block; and resistance plates between the dispersion plate and the head block, formed parallel substantially to the second direction, and configured to prevent the ink from flowing in the first direction. 
     According to some embodiments, the ink may include a solid dispersed in a solvent, and the solid may be at least one selected from light-emitting elements, quantum dots, and color filter materials, each of which has a diameter or a length ranging from a nanoscale to a microscale. 
     According to some embodiments, a first surface of the dispersion plate adjacent to the manifold may be inclined along the second direction, and the ink supplied to the dispersion plate may be supplied between the dispersion plate and the head block along the first surface. 
     According to some embodiments, a second surface of the dispersion plate adjacent to the head block may include a central portion and a peripheral portion positioned in the second direction with respect to the central portion, the central portion may be higher than the peripheral portion with respect to an upper surface of the head block, and the resistance plates may be at the central portion. 
     According to some embodiments, the resistance plates may be arranged at an equal interval along the first direction. 
     According to some embodiments, a length of the dispersion plate in the first direction may be greater than a length of the head block in the first direction, and the dispersion plate may cover the head block in the first direction. 
     According to some embodiments, some of the resistance plates may be adjacent to both sides of the dispersion plate in the first direction. 
     According to some embodiments, a distance between the resistance plates in an area adjacent to a side of the dispersion plate in the first direction may be different from a distance between the resistance plates in an area adjacent to a central portion of a planar area of the dispersion plate. 
     According to some embodiments, the resistance plates may be integrally formed with the dispersion plate. 
     According to some embodiments, the resistance plates may be formed by bending from a mother substrate parallel to a lower surface of the dispersion plate, and the mother substrate may be coupled to the dispersion plate. 
     According to some embodiments, the print head unit may further include a filter between the manifold and the dispersion plate. 
     A print head unit according to some embodiments of the present invention includes a manifold configured to guide movement of an ink in a first direction therein; a head block under the manifold and including a plurality of channels connected to the manifold and piezoelectric elements adjacent to the channels to discharge the ink through the channels; a nozzle unit under the head block and including nozzles corresponding to the channels; a dispersion plate between the manifold and the head block and configured to disperse the ink in a second direction intersecting the first direction to supply the ink to the head block; and resistance plates between the dispersion plate and the head block, formed parallel substantially to the second direction, and configured to prevent the ink from flowing in the first direction. 
     According to some embodiments, a first surface of the dispersion plate adjacent to the manifold may be inclined along the second direction, and the ink supplied to the dispersion plate may be supplied between the dispersion plate and the head block along the first surface 
     According to some embodiments, a second surface of the dispersion plate adjacent to the head block may include a central portion and a peripheral portion positioned in the second direction with respect to the central portion, the central portion may be higher than the peripheral portion with respect to an upper surface of the head block, and the resistance plates may be at the central portion. 
     According to some embodiments, the resistance plates may be arranged at an equal interval along the first direction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic perspective view illustrating an inkjet printer according to some embodiments. 
         FIG.  2    is a cross-sectional view illustrating a substrate used in the inkjet printer of  FIG.  1    according to some embodiments. 
         FIG.  3    is a cross-sectional view illustrating an example of a print head unit included in the inkjet printer of  FIG.  1    according to some embodiments. 
         FIG.  4    is a schematic perspective view illustrating the print head unit of  FIG.  3    according to some embodiments. 
         FIG.  5    is a perspective view illustrating an example of resistance plates included in the print head unit of  FIG.  4    according to some embodiments. 
         FIG.  6    is a view for describing a function of the resistance plates of  FIG.  5    according to some embodiments. 
         FIG.  7    is a view illustrating a comparative example of light-emitting elements supplied through the inkjet printer of  FIG.  1    and aligned on a substrate. 
         FIG.  8    is a view illustrating an example of light-emitting elements supplied through the inkjet printer of  FIG.  1    and aligned on a substrate according to some embodiments. 
         FIG.  9    is a view for describing a process of manufacturing the resistance plates of  FIG.  5    according to some embodiments. 
         FIG.  10    is a perspective view illustrating resistance plates included in the print head unit of  FIG.  4    according to some embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     While aspects of some embodiments of the present invention are open to various modifications and alternative embodiments, aspects of some embodiments thereof will be described and illustrated by way of example in the accompanying drawings. However, it should be understood that there is no intention to limit the present invention to the particular example embodiments disclosed, and, on the contrary, embodiments according to the present invention include all modifications, equivalents, and alternatives falling within the spirit and scope of embodiments according to the present invention. 
     Like numbers refer to like elements throughout the drawings. In the accompanying drawings, the sizes of structures may be exaggerated for clarity. Although the terms “first”, “second”, etc. are used herein to describe various elements, these elements should not be limited by these terms. The terms are used only for the purpose of distinguishing one element from another. For example, without departing from the scope of the present invention, a first element could be termed a second element, and similarly a second element could be also termed a first element. A single form of expression is meant to include multiple elements unless otherwise stated. 
     It will be understood that the terms “comprises” and/or “comprising,” or “includes” and/or “including,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, components, and/or combinations thereof but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or combinations thereof. In addition, when a layer, a film, an area, or a plate is referred to as being “on” or “under” another layer, another film, another area, or another plate, it can be “directly” or “indirectly” on the other layer, film, area, plate, or one or more intervening layers may also be present. Further, in the present invention, when a part of a layer, a film, an area, a plate, and the like is formed on another part, a direction, in which the part is formed, is not limited only to an up direction, and includes a lateral direction or a down direction. On the contrary, it will be understood that when an element such as a layer, film, area, or plate is referred to as being “beneath” another element, it can be directly beneath the other element or intervening elements may also be present. 
     In the present application, when it is described that an element (such as a first element) is “operatively or communicatively coupled with/to” or “connected” to another element (such as a second element), the element can be directly connected to the other element or can be connected to the other element through another element (e.g., a third element). On the contrary, when it is described that an element (e.g., a first element) is “directly connected” or “directly coupled” to another element (e.g., a second element), it means that there is no intermediate element (e.g., a third element) between the element and the other element. 
     Hereinafter, aspects of some embodiments of the present invention will be described in more detail with reference to the accompanying drawings. In the following description, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. 
       FIG.  1    is a schematic perspective view illustrating an inkjet printer according to some embodiments. 
     Referring to  FIG.  1   , an inkjet printer  1  (or printing device) includes a stage  10  and a print head unit  20 . In addition, the inkjet printer  1  may further include a moving unit  30 . 
     The stage  10  may support the substrate  100 . The stage  10  may be made of a rigid material, but the material of the stage  10  is not limited thereto. The stage  10  may have a rectangular parallelepiped shape, but the shape of the stage  10  is not limited thereto. 
     According to some embodiments, the stage  10  may be configured to move the substrate  100  using a rail or the like. 
     A substrate  100  may be located on the stage  10 . The substrate  100  is a substrate constituting a display panel that displays images. For example, the substrate  100  may include a base substrate, a thin film transistor, an insulating layer, and the like. The substrate  100  will be described in more detail below with reference to  FIG.  2   . 
     The print head unit  20  is located above the stage  10  and may discharge (or spray) an ink on the substrate  100 . 
     The moving unit  30  may be coupled to the print head unit  20  and may move the print head unit  20 . According to some embodiments, the moving unit  30  may include a support part  31  for supporting the print head unit  20 , a guide part  32  coupled to the support part  31  to guide the movement of the print head unit  20 , and a coupling part  33  coupled to the print head unit  20  and movable along the guide part. According to some embodiments, the inkjet printer  1  may further include an ink supply unit (for example, an ink tank  40  illustrated in  FIG.  3   ) that supplies an ink to the print head unit  20  and may further include a control unit that controls the operation of the moving unit  30  (and the stage  10 , ink supply unit, and the like). 
       FIG.  2    is a cross-sectional view illustrating a substrate used in the inkjet printer of  FIG.  1   . In  FIG.  2   , the substrate  100  is briefly illustrated in relation to an ink INK supplied from the inkjet printer  1 . For example, a substrate  100  is briefly illustrated based on one pixel of a display panel. 
     The substrate  100  may include a base substrate SUB, first and second bank patterns PW 1  and PW 2 , first and second electrodes ETL 1  and ETL 2 , a first insulating layer INS 1 , and a bank BNK. 
     The base substrate SUB may include a transparent insulating material to transmit light. The base substrate SUB may be a rigid substrate or a flexible substrate. The rigid substrate may be, for example, one of a glass substrate, a quartz substrate, a glass ceramic substrate, and a crystalline glass substrate. The flexible substrate may be one of a film substrate and a plastic substrate which include a polymer organic material. 
     According to some embodiments, the base substrate SUB may include a pixel circuit layer PCL, or the pixel circuit layer PCL may be located on the base substrate SUB. 
     The pixel circuit layer PCL may include a plurality of insulating layers, and semiconductor patterns and conductive patterns which are located between the plurality of insulating layers. Here, the semiconductor pattern and the conductive pattern may constitute a transistor, a capacitor, and lines connected thereto. The transistors, the capacitors, and the lines may constitute a pixel circuit that allows light-emitting elements LD to be described below to emit light. That is, transistors and the like may be located on the base substrate SUB as a pixel circuit for allowing the light-emitting elements LD to emit light. 
     First and second bank patterns PW 1  and PW 2  may be located on the base substrate SUB (or pixel circuit layer PCL) and may be spaced apart from each other. 
     The first and second bank patterns PW 1  and PW 2  may be positioned in an emission area EMA. In order to guide light emitted from the aligned light-emitting elements LD to an upward direction of the substrate  100 , the first and second bank patterns PW 1  and PW 2  operate as support members which support the first and second electrodes ETL 1  and ETL 2  so as to change surface profiles (or cross-sectional shapes) of the first and second electrodes ELT 1  and ETL 2 . That is, the first and second bank patterns PW 1  and PW 2  may change the surface profile of the first and second electrodes ELT 1  and ETL 2 . 
     The first and second bank patterns PW 1  and PW 2  may be inorganic insulating films including an inorganic material or organic insulating films including an organic material. According to some embodiments, the first and second bank patterns PW 1  and PW 2  may include a single organic insulating film and/or a single inorganic insulating film, but embodiments according to the present invention are not limited thereto. According to some embodiments, the first and second bank patterns PW 1  and PW 2  may be provided in the form of a multi-film in which at least one organic insulating film and at least one inorganic insulating film are stacked. However, the material of the first and second bank patterns PW 1  and PW 2  is not limited to the above-described example embodiments, and according to some embodiments, the first and second bank patterns PW 1  and PW 2  may include a conductive material. 
     Each of the first and second bank patterns PW 1  and PW 2  may have a trapezoidal cross section of which a width is gradually decreased toward an upper portion thereof, but embodiments according to the present invention are not limited thereto. According to some embodiments, each of the first and second bank patterns PW 1  and PW 2  may include a curved surface with a cross section having a semi-ellipse shape, or a semi-circle shape (or hemispherical shape) of which a width is gradually decreased upward from one surface of the substrate SUB. 
     The first and second electrodes ETL 1  and ETL 2  may be located on the first and second bank patterns PW 1  and PW 2 . 
     Each of the first and second electrodes ETL 1  and ETL 2  may be made of a material having certain reflectance in order to allow light emitted from the light-emitting elements LD to travel in an image display direction of a display device. Each of the first and second electrodes ETL 1  and ETL 2  may be made of a conductive material having certain reflectance. According to some embodiments, each of the first and second electrodes ETL 1  and ETL 2  may include an opaque metal, and the opaque metal may include, for example, a metal such as silver (Ag), magnesium (Mg), aluminum (Al), platinum (Pt), palladium (Pd), gold (Au), nickel (Ni), neodymium (Nd), iridium (Ir), chromium (Cr), titanium (Ti), or an alloy thereof. According to some embodiments, each of the first and second electrodes ETL 1  and ETL 2  may include a transparent conductive material, and the transparent conductive material may include a conductive oxide such as indium tin oxide (ITO), indium zinc oxide (IZO), zinc oxide (ZnO), indium gallium zinc oxide (IGZO), or indium tin zinc oxide (ITZO), or a conductive polymer such as poly(3,4-ethylenedioxythiophene) (PEDOT). When each of the first and second electrodes ETL 1  and ETL 2  includes a transparent conductive material, a separate conductive layer made of an opaque metal may be added to reflect light emitted from the light-emitting elements LD in the image display direction of the display device. 
     Each of the first and second electrodes ETL 1  and ETL 2  may be provided and/or formed as a single-film, but embodiments according to the present invention are not limited thereto. According to some embodiments, each of the first and second electrodes ETL 1  and ETL 2  may be provided and/or formed as a multi-film in which at least two or more materials of metals, alloys, conductive oxides, and conductive polymers are stacked. As an example, each of the first and second electrodes EL 1  and EL 2  may be formed as a multi-film in which ITO, silver (Ag), and ITO are sequentially stacked. 
     A first insulating layer INS 1  may be located between the first electrode EL 1  and the second electrode EL 2 . 
     The first insulating layer INS 1  may include an inorganic insulating film made of an inorganic material or an organic insulating film made of an organic material. As an example, the first insulating layer INS 1  may include at least one selected from metal oxides such as silicon nitride (SiN x ), silicon oxide (SiO x ), silicon oxynitride (SiO x N y ), and aluminum oxide (AlO x ), but embodiments according to the present invention are not limited thereto. According to some embodiments, the first insulating layer INS 1  may be formed as an organic insulating film that may enable planarizing support surfaces of the light-emitting elements LD. 
     The bank BNK may be a structure defining (or partitioning) the emission area (this is, an area of each of the pixels provided on the display panel) and may be, for example, a pixel defining film. The bank BNK may include at least one light-blocking material and/or reflective material to prevent light leakage defects in which light (or light) leaks between the emission area EMA and other emission areas. 
     The ink INK may be supplied to the emission area EMA of the above-described substrate  100  using the inkjet printer  1  (see  FIG.  1   ). The ink INK may be a mixture including a fluid solvent SLV and the plurality of light-emitting elements LD included (or dispersed) in the solvent SLV. 
     The light-emitting element LD may have a shape extending in one direction. When it is assumed that an extending direction of the light-emitting element LD is a length direction, the light-emitting element LD may have one end portion (or lower end portion) and the other end portion (or upper end portion) in the extending direction. The light-emitting element LD may include semiconductor layers located at both end portions thereof and an active layer located between the semiconductor layers in the length direction. The active layer may emit light having a wavelength of 400 nm to 900 nm. 
     The light-emitting element LD may be provided in various shapes. As an example, the light-emitting element LD may have a rod-like shape or a bar-like shape which is long in a length direction thereof (i.e., has an aspect ratio greater than one). The light-emitting element LD may include, for example, a light-emitting diode (LED) manufactured in a very small size to such an extent as to have a diameter and/or a length ranging from a nanoscale to a microscale. 
     For example, the diameter of the light-emitting element LD may be in a range of about 0.5 μm to about 500 μm, and the length thereof may be in a range of about 1 μm to about 10 μm. However, the diameter and length of the light-emitting element LD are not limited thereto, and the size of the light-emitting element LD may be changed to meet the requirements (or design conditions) of a lighting device or a self-luminous display device to which the light-emitting element LD is applied. 
     After the light-emitting elements LD are supplied to the emission area EMA, an alignment signal may be applied to the first and second electrodes ETL 1  and ETL 2  to form an electric field between the first electrode ELT 1  and the second electrode ETL 2 , thereby aligning the light-emitting elements between the first electrode ELT 1  and the second electrode ETL 2  due to the electric field. The solvent SLV may be volatilized or removed through other methods after the light-emitting elements LD are aligned, thereby finally aligning the light-emitting elements on the substrate  100 . 
     Meanwhile, in  FIG.  2   , it has been described that the inkjet printer  1  (see  FIG.  1   ) supplies the ink INK to the substrate  100  and the ink INK includes light-emitting elements LD, but the ink INK is not limited thereto. For example, instead of the light-emitting elements LD, the ink INK may include a light conversion material (for example, a quantum dot) that converts a wavelength of light emitted from the light-emitting elements LD into a specific wavelength and re-emits the light or a color filter material that blocks or transmits only a specific wavelength of light emitted from the light-emitting elements LD. The light conversion material (for example, the quantum dot) and the color filter material may have a diameter and/or length ranging from a nanoscale to a microscale similar to the light-emitting element LD. That is, the ink INK may include a nanoscale or microscale solid in the solvent SLV. 
       FIG.  3    is a cross-sectional view illustrating an example of a print head unit included in the inkjet printer of  FIG.  1   .  FIG.  4    is a schematic perspective view illustrating the print head unit of  FIG.  3   .  FIG.  4    schematically illustrates a print head unit  20  based on a filter  23 , a dispersion plate  24 , and a head block  26  provided in a main body  21  of the print head unit  20 .  FIG.  5    is a perspective view illustrating an example of resistance plates included in the print head unit of  FIG.  4   . For convenience of description, resistance plates  25  are illustrated in  FIG.  5    based on a state in which the dispersion plate  24  of  FIG.  4    is turned over by an angle of 180°. 
     Referring to  FIGS.  1  to  3   , the print head unit  20  may be connected to an ink tank  40  (or ink storage unit) through first and second transmission pipes  41  and  42 . The ink tank  40  may store an ink INK and may supply the ink INK to the print head unit  20  through the first transmission pipe  41  (and an inlet). The remaining ink INK after being discharged from the print head unit  20  may be supplied or returned to the ink tank  40  from the print head unit  20  through the second transmission pipe  42  (and an outlet). That is, the ink INK may pass through the first transmission pipe  41 , and a portion may be discharged from the print head unit  20 , and a portion may be recycled back into the ink tank  40  through the second transmission pipe  42 . 
     Each of the first and second transmission pipes  41  and  42  may be formed of a flexible hose, but embodiments according to the present invention are not limited thereto. The first and second transmission pipes  41  and  42  may be provided to have various configurations within a range capable of stably moving the ink INK. 
     The ink tank  40  and the first and second transmission pipes  41  and  42  may collectively constitute or be referred to as an ink supply unit, although according to some embodiments the ink supply unit may include additional components without departing from the spirit and scope of embodiments according to the present disclosure. 
     The print head unit  20  may include the main body  21  having an empty space therein, a manifold  22  formed or provided in the main body  21 , the filter  23 , the dispersion plate  24 , the resistance plates  25  (or flow resistance plates), the head block  26 , and a nozzle unit  27 . 
     The manifold  22  may have a space formed in a first direction DR 1 , may be connected to the first and second transmission pipes  41  and  42 , and may guide the movement of the ink INK in the first direction DR 1  therein. In addition, the manifold  22  may supply the ink INK in a third direction DR 3  (that is, a downward direction in which the filter  23  or the like is positioned). 
     The filter  23  may be located under the manifold  22  (that is, in the third direction DR 3  with respect to the manifold  22 ) and may filter foreign substances contained in the ink INK. The filter  23  may prevent nozzles NZL of the nozzle unit  27  from being clogged by the foreign substances contained in the ink INK. For example, the filter  23  may be a mesh plate including a plurality of fine openings. 
     The dispersion plate  24  may be positioned under the filter  23  (that is, in the third direction DR 3  with respect to the filter  23 ) and may disperse the ink INK in a second direction DR 2  intersecting the first direction DR 1  to supply the ink INK to the head block  26 . In addition, the dispersion plate  24  may be spaced apart from the head block  26  by a distance (e.g., a set or predetermined distance) GAP, and the ink INK dispersed and introduced through a relatively narrow gap between the dispersion plate  24  and the head block  26  may apply uniform pressure to an upper surface of the head block  26 . That is, the dispersion plate  24  can equalize the supply pressure of the ink INK. For example, the distance (e.g., the set or predetermined distance) GAP may be about 150 μm but is not limited thereto. 
     For reference, when the print head unit  20  does not include the dispersion plate  24 , the ink INK supplied to the head block  26  from the manifold  22  through the filter  23  may apply greater pressure to a specific portion of the head block  26  (for example, a portion adjacent to the second transmission pipe  42 ) in a direction (that is, the first direction DR 1 ) in which the ink INK is moved in the manifold  22 , thereby causing a deviation in discharge amount of the ink INK (or ink discharge amount) discharged from the head block  26 . In order to prevent or reduce variations in discharge amounts of the ink INK, the dispersion plate  24  may supply the ink INK to the head block  26  by dispersing the ink INKL in the second direction intersecting the movement direction (that is, the first direction DR 1 ) in which the ink INK flows in the manifold  22 . 
     According to some embodiments, a first surface SF_U (that is, an upper surface) of the dispersion plate  24  may be inclined in the second direction DR 2  with respect to on one surface of the filter  23  (or, upper surface of the head block  26 ). In this case, the ink INK supplied through the filter  23  may be supplied between the dispersion plate  24  and the head block  26  along the first surface SF_U of the dispersion plate  24 . 
     As illustrated in  FIG.  4   , the first surface SF_U of the dispersion plate  24  may have a shape inclined from a center portion thereof in the second direction DR 2  and a direction opposite to the second direction DR 2 . The ink INK may be moved in an ink movement direction DR_INK (or ink supply direction) illustrated in  FIG.  4    along the shape of the first surface SF_U of the dispersion plate  24  and may be introduced onto an upper surface of the head block  26  through the gap between the dispersion plate  24  and the head block  26 . 
     According to some embodiments, a second surface SF_L of the dispersion plate  24  may include a central portion and a peripheral portion positioned in the second direction DR 2  with respect to the central portion, and the central portion may be higher that the peripheral portion with respect to the upper surface of the head block  26 . 
     As illustrated in  FIG.  5   , the second surface SF_L of the dispersion plate  24  has a shape of which a central portion is recessed, and the central portion of the second surface SF_L may have a step difference SD from a peripheral portion of the second surface SF_L. For example, the step difference SD may be about 800 μm but is not limited thereto. 
     The resistance plates  25  may be located under the dispersion plate  24 , and each of the resistance plates  25  may be formed substantially parallel to the second direction DR 2 . The resistance plates  25  may prevent the ink INK from flowing in the first direction DR 1  under the dispersion plate  24  (that is, the first direction DR 1  substantially perpendicular to the second direction DR 2  in which the ink INK is supplied from the dispersion plate  24 ). The resistance plates  25  may be made of a rigid material. 
     As illustrated in  FIG.  5   , the resistance plates  25  may be located at the central portion of the second surface SF_L of the dispersion plate  24 . Each of the resistance plates  25  may have a height (that is, a height in the third direction DR 3 ) corresponding to the step difference SD between the central portion and the peripheral portion of the dispersion plate  24  and may have a shape extends in the second direction DR 2 . According to the arrangement of the resistance plates  25 , the flow resistances of the ink INK in the second direction DR 2  equal to an ink movement direction DR_INK are the same, and the flow resistance of the ink INK in the first direction DR 1  substantially perpendicular to the ink movement direction DR_INK may be increased. That is, it may be difficult for the ink INK to move in the first direction DR 1  due to the resistance plates  25 . 
     According to some embodiments, the resistance plates  25  may be arranged to be spaced apart from each other in the first direction DR 1  at the same first distance D 1  (or separation distance). However, the arrangement of the resistance plates  25  is not limited thereto. For example, an interval between the resistance plates  25  at an end of the dispersion plate  24  (that is, an end in the first direction DR 1 ) may be smaller than an interval between the resistance plates  25  at an area center of the dispersion plate  24  (that is, an area center in a plan view). Regarding the flow of the ink INK to be described with reference to  FIG.  7   , the resistance plates  25  may be relatively densely arranged at the end of the dispersion plate  24  (that is, the end in the first direction DR 1 ). 
     According to some embodiments, the resistance plates  25  may be integrally formed with the dispersion plate  24 . However, the resistance plates  25  are not limited thereto, and the resistance plates  25  may be manufactured separately from the dispersion plate  24  and may be coupled to the dispersion plate  24 . This will be described in more detail below with reference to  FIG.  9   . 
     Meanwhile, in  FIG.  5   , the resistance plates  25  are illustrated as being located in a direction perpendicular to the first direction DR 1  (that is, a moving direction of the ink INK in the manifold  22  illustrated in  FIG.  4   ), but the resistance plates  25  are not limited thereto. For example, at least some of the resistance plates  25  may be located in a diagonal direction intersecting each of the first direction DR 1  and the second direction DR 2 . That is, the resistance plates  25  may be arranged in various directions intersecting the first direction DR 1  within a range capable of uniformly maintaining a density of the light-emitting elements LD (or solid material) in the ink INK by reducing the flow of the ink INK in the first direction DR 1  under the dispersion plate  24 . 
     Referring again to  FIGS.  3  and  4   , the head block  26  may be positioned under the dispersion plate  24  (that is, in the third direction DR 3  with respect to the dispersion plate  24 ). 
     The head block  26  may include a plurality of channels CH (or chambers) and piezoelectric elements PZ. 
     The channels CH may be connected to and communicate with the manifold  22  via the filter  23  and the dispersion plate  24 . As illustrated in  FIG.  4   , the channels CH may be arranged in a matrix structure in the first direction DR 1  and the second direction DR 2 . 
     The piezoelectric elements PZ may be located adjacent to the channels CH, and may discharge the ink INK through the channels CH. As illustrated in  FIG.  3   , the piezoelectric elements PZ may be arranged to correspond to the channels CH, may contract and expand in response to a signal provided from the outside (for example, a control unit), and may press the corresponding channels CH to discharge a specific amount of ink INK. 
     The nozzle unit  27  may include the nozzles NZL which are located under the head block  26  (that is, in the third direction DR 3  with respect to the head block  26 ) and are positioned to correspond to the channels CH of the head block  26 , respectively. 
     The ink INK discharged through one of the nozzles NZL of the nozzle unit  27  via one of the channels CH of the head block  26  may be supplied to the emission area EMA described with reference to  FIG.  2    (that is, one of pixels included in a display panel). That is, the ink INK may be supplied to the emission areas EMA of a substrate  100  through the nozzles NZL of the nozzle unit  27 . 
     Meanwhile, the planar size of the head block  26  may be the same as or different from the planar size of the dispersion plate  24 . For example, as illustrated in  FIG.  6   , a length of the dispersion plate  24  in the first direction DR 1  may be greater than a length of the head block  26  in the first direction DR 1 , and the head block  26  can be covered with the dispersion plate  24 . In this case, the ink INK can be dispersed more widely through the dispersion plate  24  and supplied to the head block  26 . 
     As described with reference to  FIGS.  3  to  5   , the print head unit  20  may include the dispersion plate  24  and the resistance plates  25  located between the manifold  22  and the head block  26 . Thus, the ink INK moved in the first direction DR 1  from the manifold  22  may be dispersed in the second direction DR 2  through the dispersion plate  24  to be supplied to the upper surface of the head block  26 . In addition, the ink INK may be prevented from flowing from the upper surface of the head block  26  in the first direction DR 1  through the resistance plates  25 . Therefore, solids (for example, the light-emitting elements LD) in the ink INK may be prevented from being concentrated in a specific area, and the ink INK having a uniform concentration (for example, the ink INK including a uniform number of light-emitting elements LD) may be discharged to the substrate  100  through the channels CH of the head block  26  and the nozzles NZL of the nozzle unit  27 . 
       FIG.  6    is a view for describing a function of the resistance plates of  FIG.  5   . A print head unit according to a comparative example may not include the resistance plates  25 , and in this case, the flow of the ink INK supplied to the upper surface of the head block  26  is illustrated in  FIG.  6   .  FIG.  7    is a view illustrating a comparative example of light-emitting elements supplied through the inkjet printer of  FIG.  1    and aligned on a substrate.  FIG.  8    is a view illustrating an example of light-emitting elements supplied through the inkjet printer of  FIG.  1    and aligned on a substrate. 
     First, referring to  FIGS.  3  to  6   , the ink INK dispersed in the second direction DR 2  through the dispersion plate  24  may be supplied to the upper surface of the head block  26  in the ink movement direction DR_INK. 
     The ink INK supplied to an area adjacent to an end (or both sides) of the head block  26  in the first direction DR 1  (and a direction opposite to the first direction DR 1 ) may be moved toward a center of an planar area of the head block  26 . The end of the head block  26  in the first direction DR 1  may be closed, and the inks INK moved from an upper side and a lower side of the head block  26  in the second direction DR 2  may meet each other at a central portion of the head block  26  (that is, in an area between the upper side and the lower side of the head block  26 ), and thus, a flow of the ink INK may occur in the first direction DR 1 . 
     The flow of the ink INK may generate a vortex in an area adjacent to the end of the head block  26  in the first direction DR 1 . As illustrated in  FIG.  6   , due to a combination of the flow of the ink INK in a direction opposite to the first direction DR 1  in a first area A 1  and the flow of the ink INK in the first direction DR 1  (and a direction opposite direction to the second direction DR 2 ) in a second area A 2  and a third area A 3 , the ink INK may rotate and move in the first to third areas A 1  to A 3 . 
     As described with reference to  FIG.  2   , the ink INK includes the solvent SLV and the solids (for example, the light-emitting elements LD) contained in the solvent SLV. Due to the flow (or vortex) of the ink INK in the first direction DR 1 , the solvent SLV may easily move in the first direction DR 1 , but the solids may not relatively easily move in the first direction DR 1 . Due to a difference in moving characteristic between the solvent SLV and the solids, the concentration of the ink INK in areas in which a vortex occurs (for example, in the first area A 1  and the third area A 3 ) may be lower than the concentration of the ink INK in an area in which a vortex does not occur (or at a portion corresponding to a rotation axis of a vortex, for example, a central portion of the second area A 2 ). That is, the concentration of the ink may be non-uniform INK on the upper surface of the head block  26 . 
     Referring to  FIGS.  1  and  4  to  7   ,  FIG.  7    illustrates the concentration of the ink INK (for example, the number of the blight-emitting elements LD) supplied to the substrate  100  at a time through a print head unit not provided with the resistance plates  25 . 
     As illustrated in  FIG.  7   , the number of the light-emitting elements LD supplied to the first area A 1  and the third area A 3  is 50 or less, which is smaller than 55 that is an average number of the light-emitting elements LD supplied to other areas (for example, the second area A 2 ). Such a non-uniform distribution of the light-emitting elements LD may cause a luminance deviation of a display device including the substrate  100  and degrade image quality. For example, in the first area A 1  and the third area A 3  in which the number of the light-emitting elements LD is relatively small (thus, luminance is relatively low), a spot may be visible to a user. 
     Meanwhile, the number of the light-emitting elements LD supplied to a fourth area A 4  positioned in a direction opposite to the first direction DR 1  may also be 50 or less. 
     Meanwhile, the print head unit  20  according to some embodiments of the present invention may include the resistance plates  25  described with reference to  FIG.  5    and may prevent the flow of the ink INK in the first direction DR 1  between the dispersion plate  24  and the head block  26  through the resistance plates  25 . Accordingly, it is possible to prevent the flow of the ink INK and the non-uniformity in the concentration of the ink INK caused by the flow in the first to third areas A 1  to A 3  (see  FIG.  6   ). 
     Referring to  FIGS.  1  and  4  to  8   ,  FIG.  8    illustrates the concentration of the ink INK (for example, the number of the blight-emitting elements LD) supplied to the substrate  100  at a time through the print head unit  20  according to some embodiments of the present invention (that is, the print heat unit  29  provided with the resistance plates  25 ). 
     As illustrated in  FIG.  8   , the numbers of light-emitting elements LD supplied to the first to third areas A 1  to A 3  may be similar and may also similar to the number of the light-emitting elements LD supplied to other areas. That is, the relatively uniform distribution of the light-emitting elements LD may alleviate a luminance deviation of a display device including the substrate  100  and may alleviate or prevent a degradation of image quality. 
     As described with reference to  FIGS.  6  to  8   , the resistance plates  25  may prevent the ink INK from flowing in the first direction DR 1  between the dispersion plate  24  and the head block  26 , may make the concentration of the ink INK uniform on the upper surface of the head block  26 , thereby making the concentration of the ink INK discharged through the print head unit  20  uniform. 
       FIG.  9    is a view for describing a process of manufacturing the resistance plates of  FIG.  5   . 
     Referring to  FIGS.  5  and  9   , areas of a mother substrate PLT (for example, a metal plate) corresponding to the resistance plates  25  may be cut (or punched), and corresponding areas may be bent or curved, thereby forming the resistance plates  25 . Thereafter, the mother substrate PLT may be bent based on a first virtual line L_B 1  and a second virtual line L_B 2  so that the mother substrate PLT may have the same or similar shape as the second surface SF_L of the dispersion plate  24 . The mother substrate PLT on which the resistance plates  25  are formed may be coupled to the second surface SF_L of the dispersion plate  24  through an interference fit method or a separate coupling member. 
     As described with reference to  FIG.  9   , the resistance plates  25  can be easily manufactured through punching and bending processes for the mother substrate. 
       FIG.  10    is a perspective view illustrating another example of resistance plates included in the print head unit of  FIG.  4   .  FIG.  10    illustrates a view corresponding to  FIG.  5   . 
     Referring to  FIGS.  5  and  10   , the resistance plates  25  illustrated in  FIG.  5    are uniformly spaced apart from each other, but resistance plates  25 _ 1  illustrated in  FIG.  10    are arranged non-uniformly. 
     According to some embodiments, some of the resistance plates  25 _ 1  may be located adjacent to an end (or both sides) of a dispersion plate  24  in a first direction DR 1  (and in a direction opposite to the first direction DR 1 ). 
     As described with reference to  FIG.  6   , the flow of an ink INK in the first direction DR 1  between the dispersion plate  24  and a head block  26  may start in an area adjacent to the end (or both sides) of the dispersion plate  24  in the first direction DR 1  (and a direction opposite to the first direction DR 1 ), and the flow of the ink INK in the first direction DR 1  may be greatest in a corresponding area. 
     Accordingly, in order to prevent the flow of ink INK in the first direction DR 1  in an area adjacent to the end (or both sides) of the dispersion plate  24  in the first direction DR 1  (and the direction opposite to the first direction DR 1 ), the resistance plate  25 _ 1  may be located adjacent to the end (or both sides) of the dispersion plate  24  in the first direction DR 1  (and the direction opposite to the first direction DR 1 ). According to some embodiments, the resistance plate  25 _ 1  may be located only in an area adjacent to the end (or both sides) of the dispersion plate  24  in the first direction DR 1  (and the direction opposite to the first direction DR 1 ). 
     According to some embodiments, a distance between the resistance plates  25 _ 1  in the area adjacent to the end (or both sides) of the dispersion plate  24  in the first direction DR 1  (and the direction opposite to the first direction DR 1 ) may be different from a distance between the resistance plates  25 _ 1  in an area adjacent to a center of a planar area of the dispersion plate  24 . 
     As illustrated in  FIG.  10   , in the area adjacent to the end (or both sides) of the dispersion plate  24  in the first direction DR 1  (and the direction opposite to the first direction DR 1 , the resistance plate  25 _ 1  may be spaced apart from each other by a second distance D 2 , and in the area adjacent to the center of the planar area of the dispersion plate  24 , the resistance plates  25 _ 1  may be spaced apart from each other by a third distance D 3 . Here, the third distance D 3  may be greater than the second distance D 2 . 
     As described with reference to  FIG.  6   , the first to third areas A 1  to A 2  adjacent to the end (or both sides) of the dispersion plate  24  in the first direction DR 1  (and the direction opposite to the first direction DR 1 ), the flow of the ink INK in the first direction DR 1  may be great. Accordingly, in consideration of the fact that the flow of the ink INK in the first direction DR 1  is different for each area, in the area adjacent to the end (or both sides) of the dispersion plate  24  in the first direction DR 1  (and the direction opposite to the first direction DR 1 ), the resistance plates  25 _ 1  may be separated by a relatively small second distance D 2 , and in the area adjacent to the center of the planar area of the dispersion plate  24 , the resistance plates  25 _ 1  may be separated by a relatively large third distance D 3 . 
     As described with reference to  FIG.  10   , the resistance plates  25 _ 1  may be separated by a non-uniform distance. 
     In a print head unit and an inkjet printer including the same according to some embodiments of the present invention, a dispersion plate and resistance plates are located between a manifold and a head block. An ink moved in a first direction from the manifold may be dispersed in the second direction through the dispersion plate to be supplied to an upper surface of the head block, and the ink may be prevented from flowing in the first direction from the upper surface of the head block through the resistance plates. Accordingly, the concentration of solids (for example, light-emitting elements) in the ink may be prevented from becoming non-uniform due to the flow of the ink in the first direction, and the light-emitting elements may be uniformly supplied from the print head unit to a substrate. 
     The effects and characteristics of some embodiments of the present invention are not limited by the above-described contents, and more various effects are included in the present specification. 
     Although aspects of some embodiments of the present invention have been described, it is understood that the present invention should not be limited to these example embodiments but various changes and modifications can be made by one ordinary skilled in the art within the spirit and scope of the invention as hereinafter claimed. 
     Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification, but should be defined by the claims and their equivalents.