Patent Publication Number: US-10759175-B2

Title: Liquid discharge head, head module, liquid discharge device, and liquid discharge apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This patent application is based on and claims priority pursuant to 35 U.S.C. § 119(a) to Japanese Patent Application No. 2018-037327, filed on Mar. 2, 2018, and Japanese Patent Application No. 2018-245490, filed on Dec. 27, 2018, in the Japan Patent Office, the entire disclosure of each of which is hereby incorporated by reference herein. 
     BACKGROUND 
     Technical Field 
     Aspects of the present disclosure relate to a liquid discharge head, a head module, a liquid cartridge, a liquid discharge device, and a liquid discharge apparatus. 
     Related Art 
     As an image forming apparatus to form image on a recording medium such as a sheet of paper, an inkjet recording apparatus is known that includes an inkjet head mounted on a carriage. The inkjet recording apparatus discharges ink droplets from the inkjet head onto the recording medium while reciprocally moving the carriage in a main scanning direction to form a desired image pattern on the recording medium. 
     An inkjet head in such an inkjet recording apparatus includes a plurality of pressure chambers and nozzles, a common chamber, a piezoelectric device including a piezoelectric element and a heater, and a drive integrated circuit (IC) to drive the inkjet head. The piezoelectric device is disposed adjacent to the pressure chamber. 
     When ink is supplied from the ink tank to the common chamber, some air in the common chamber may remain in the common chamber as air bubbles. When the air bubbles remained in the common chamber, the air bubbles may be guided to the nozzles when the inkjet head discharges ink droplets from the nozzles. Thus, discharge failure of the ink droplets may occur that causes defects in image quality. 
     SUMMARY 
     In an aspect of this disclosure, an improved liquid discharge head includes a plurality of nozzles to discharge a liquid, a plurality of pressure chambers communicating with the plurality of nozzles, respectively, a plurality of individual supply channels communicating with the plurality of pressure chambers, respectively, a plurality of common-supply branch channels each having a side face and a bottom face and communicating with two or more of the plurality of individual supply channels, respectively, and a common-supply main channel communicating with the plurality of common-supply branch channels. The plurality of common-supply branch channels includes a curved portion on a corner between the side face and the bottom face of each of the plurality of common-supply branch channels along a direction of liquid flow in the plurality of common-supply branch channels. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The aforementioned and other aspects, features, and advantages of the present disclosure will be better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
         FIG. 1  is a cross-sectional view of an example of a liquid discharge head according to embodiments of the present disclosure in a transverse direction of a liquid chamber; 
         FIG. 2  is a cross-sectional view of the example of the liquid discharge head according to embodiments in a longitudinal direction of the liquid chamber; 
         FIG. 3  is a perspective view of the example of a support substrate of the liquid discharge head according to embodiments; 
         FIG. 4  is an outer perspective view of the liquid discharge head according to another example according to embodiments of the present disclosure; 
         FIG. 5  is an exploded perspective view of another example of the liquid discharge head of  FIG. 4 ; 
         FIG. 6  is a cross-sectional perspective view of another example of the liquid discharge head of  FIG. 4 ; 
         FIG. 7  is an exploded perspective view of another example of the liquid discharge head without a frame of  FIG. 4 ; 
         FIG. 8  is a cross-sectional perspective view of another example of channels; 
         FIG. 9  is an enlarged cross-sectional perspective view of another example of the channels; 
         FIG. 10  is a plan view of another example of the channels; 
         FIG. 11  is an enlarged schematic perspective view of an example of a curved portion formed in another example of the channels in the head; 
         FIG. 12  is a schematic cross-sectional view of the example of the curved portion in the channels of the head; 
         FIG. 13  is a schematic plan view of the example of the curved portion in the channels of the head; 
         FIG. 14  is a schematic cross-sectional view of another example (first variation) of channels with a curved portion; 
         FIG. 15  is a schematic cross-sectional view of still another example (second variation) of channels with a curved portion; 
         FIG. 16  is a schematic cross-sectional view of still another example (third variation) of channels with a curved portion; 
         FIG. 17  is a schematic plan view of still another example (fourth variation) of channels with a curved portion; 
         FIG. 18  is an exploded perspective view of a head module according to embodiments; 
         FIG. 19  is an exploded perspective view of the head module viewed from a nozzle surface of the head module; 
         FIG. 20  is a perspective view of an example of an inkjet recording apparatus according to embodiments; 
         FIG. 21  is a side view of the example of the ink jet recording apparatus according to embodiments; 
         FIG. 22  is a plan view of an example of a main part of a liquid discharge apparatus including a liquid discharge head according to embodiments; 
         FIG. 23  is a side view of the example of the main part of the liquid discharge apparatus including the liquid discharge head according to embodiments; 
         FIG. 24  is a plan view of an example of a liquid discharge device according to another embodiment of the present disclosure; and 
         FIG. 25  is a front view of another example of a liquid discharge device according to another embodiment of the present disclosure. 
     
    
    
     The accompanying drawings are intended to depict embodiments of the present disclosure and should not be interpreted to limit the scope thereof. The accompanying drawings are not to be considered as drawn to scale unless explicitly noted. 
     DETAILED DESCRIPTION 
     In describing embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this patent specification is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that have the same function, operate in an analogous manner, and achieve similar results. 
     Although the embodiments are described with technical limitations with reference to the attached drawings, such description is not intended to limit the scope of the disclosure and all the components or elements described in the embodiments of this disclosure are not necessarily indispensable. As used herein, 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 cross-sectional view of an example of a liquid discharge head according to the present disclosure in a transverse direction of a pressure chamber. 
       FIG. 2  is a cross-sectional view of an example of the liquid discharge head according to the present disclosure in a longitudinal direction of the pressure chamber. 
       FIG. 3  is an external perspective view of an example of a support substrate of the liquid discharge head. 
     The liquid discharge head  1   a  includes a piezoelectric device  12  to generate energy to discharge the liquid and a diaphragm  13  on an actuator substrate  201  in which a pressure-chamber partition wall  14  and a pressure chamber  15  are formed. 
     Hereinafter, “the liquid discharge head” is simply referred to as “head”. The pressure chamber  15  is partitioned by the pressure-chamber partition wall  14 . 
     The piezoelectric device  12  is sandwiched between a common electrode  121  and an individual electrode  122 , and a wiring layer is laminated on each electrode layers to apply voltage on the piezoelectric device  12 . A pressure chamber  15  is formed by the actuator substrate  201  and a nozzle substrate  203 . The actuator substrate  201 , and the support substrate  202  and the nozzle substrate  203  are bonded to form the head  1   a . Silicon is used as a base material of the actuator substrate  201  and the support substrate  202 . The actuator substrate  201  includes a common chamber  18  and a branch chamber  66 . The actuator substrate  201  and the support substrate  202  made of silicon have sufficient rigidity. Further, it becomes easier to process the common chamber  18  and the branch chamber  66  in the actuator substrate  201  and the support substrate  202 . 
     The head  1   a  configured as described above fills each pressure chambers  15  with a liquid, for example, a recording liquid (ink). The head  1   a  applies a pulse voltage of 20 V, for example, generated by an oscillation circuit, to the piezoelectric device  12  via an individual electrode  122  corresponding to the nozzle  16  from which the liquid is to be discharged, through a lead wire  42  and a connection hole formed in an interlayer insulating film  45  based on image data sent from a controller when each of the pressure chambers  15  is filled with the liquid. 
     Application of the pulse voltage makes the piezoelectric device  12  contract in a direction parallel to the diaphragm  13  due to an electrostrictive effect, and the diaphragm  13  bends toward the pressure chamber  15 . Thus, the pressure in the pressure chamber  15  rises sharply, and the recording liquid is discharged from the nozzle  16  communicating with the pressure chamber  15 . 
     After the application of the pulse voltage, the shrunk piezoelectric device  12  returns to an original position, and the bent (deflected) diaphragm  13  returns to an original position. Thus, a pressure inside the pressure chamber  15  becomes negative compared to the common chamber  18  (see  FIG. 2 ), and the liquid (ink) supplied from the outside via the branch chamber  66  is supplied to the pressure chamber  15  via a fluid restrictor  17  from a common-supply channel  19  and the common chamber  18 . Repeating the above-described processes, the head  1   a  can continuously discharge the liquid and form an image on a recording medium (sheet) arranged opposite to the head  1   a.    
     A method of manufacturing the head  1   a  according to the present disclosure is described below. The head  1   a  is manufactured according to the following processes (1) to (10). 
     (1) The diaphragm  13  is film-formed on a silicon single-crystal substrate having a plane orientation (100) as the actuator substrate  201 . For example, the silicon single crystal substrate having a plate thickness of 400 μm may be used as the actuator substrate  201 . The diaphragm  13  may be a single layer or a laminated film as long as the diaphragm  13  has a function as a diaphragm and is consistent with the subsequent manufacturing process. 
     For example, as a material of the diaphragm  13 , a silicon oxide film, a polysilicon film, an amorphous silicon film, or a silicon nitride film is used. The silicon oxide film, the polysilicon film, the amorphous silicon film, or the silicon nitride film is laminated to be film-formed by a Low-Pressure Chemical Vapor Deposition (LP-CVD) method to obtain desired rigidity. 
     Considering the consistency of manufacturing process, the rigidity of the diaphragm  13 , and the stress applied on the diaphragm  13  as a whole, number of layers of lamination is preferably about three to seven layers. The uppermost layer of the diaphragm  13  is a silicon oxide film formed by the LP-CVD method to ensure adhesion with the common electrode  121  formed after the diaphragm  13 . Then, a layer of the common electrode  121  made of TiO 2  and Pt is film-formed by a sputtering method to have thicknesses of 10 nm and 160 nm, respectively. 
     (2) Next, a film made of lead zirconate titanate (PZT) is film-formed for a plurality of times on the common electrode  121  as the piezoelectric device  12  by a spin coat method, for example, and the film is deposited until the film has a thickness of 2 μm. Next, the individual electrodes  122  made of strontium oxide (SRO) and Pt are film-formed by the sputtering method to have thicknesses of 40 nm and 100 nm, respectively. 
     The method of forming the piezoelectric device  12  is not limited to the spin coating method. For example, a sputtering method, an ion plating method, an aerosol method, a sol-gel method, an inkjet method, or the like can be used. Then, the piezoelectric device  12  and the individual electrode  122  are formed by the photolithography-etching method at positions corresponding to the pressure chambers  15  to be formed later. Further, the piezoelectric device  12  is formed at a position corresponding to a bonding portion  48  (see  FIG. 1 ). 
     (3) Next, an interlayer insulating film  45  is formed in order to insulate the common electrode  121  and the piezoelectric device  12  from the lead wire  42  to be formed later. Here, the interlayer insulating film  45  is formed by depositing an SiO 2  film to 1000 nm, for example, by a plasma Chemical Vapor Deposition (CVD) method. The interlayer insulating film  45  may be a film other than the SiO 2  film by the plasma CVD method as long as the film has an insulating property without affecting the piezoelectric device  12  and an electrode material. 
     Next, connection holes for connecting the individual electrode  122  and the lead wire  42  are formed by the photolithography-etching method. When the common electrode  121  is connected to the lead wire  42 , a connection hole is similarly formed. 
     (4) Next, a film made of TiN/Al, for example, is film-formed to 30 nm and 3 μm, respectively, as a lead wire  42  by the sputtering method. The film made of TiN is used as a barrier layer to prevent alloying of Pt, which is a material of the individual electrode  122  or the common electrode  121  with Al, which is a material of the lead wire  42 . 
     Alloyed Pt changes volume and generates stress to cause peeling of the film. Pt is alloyed when Pt is contact directly with Al at a bottom of the contact hole and is alloyed during a thermal history of a later manufacturing process. Further, the lead wire  42  is also formed in a portion to become the bonding portion  48  to be bonded with the support substrate  202  later. 
     (5) Next, as the passivation film  150 , a silicon nitride film is formed to a thickness of 1000 nm, for example, by the plasma CVD method. 
     (6) Then, an opening is formed in the lead wire pad  41 , an actuator  160 , and the common-supply channel  19  of the lead wire  42  by the lithography-etching method. 
     (7) Next, the diaphragm  13  at a portion to be the common-supply channel  19  and the common chamber  18  is removed by the lithography-etching method. 
     (8) Next, a concave portion  67  is formed at a position corresponding to the actuator  160  by the lithography-etching method to form a main chamber  68  and a branch chamber  66 . Further, a curved portion  70  is formed on a corner between a side wall (side face) and a bottom wall (bottom face) of the branch chamber  66  in the support substrate  202 . 
     At this time, the support substrate  202  made of Si is processed by dry etching. Controlling conditions of the dry etching enables control of the degree of roundness (radius) of a curved portion  70  in a vicinity of a partition wall. Then, the support substrate  202  and the actuator substrate  201  are bonded together with the adhesive  49  via the bonding portion  48 . 
     At this time, the adhesive  49  is coated to a thickness of about 1 μm on the support substrate  202  by a general thin-film transfer device. Then, the actuator substrate  201  is polished by a known technique to have a desired thickness (for example, a thickness of 80 μm) to form the pressure chamber  15 , the common chamber  18 , and the fluid restrictor  17 . Alternatively, the actuator substrate  201  may be etched, for example, instead of polished. 
     (9) Next, the partition wall of the head  1   a  other than the partition walls of the pressure chamber  15 , the common chamber  18 , and the fluid restrictor  17  is covered with a resist by the lithography-etching method. Then, anisotropic wet etching is performed with an alkaline solution (potassium hydroxide (KOH) solution or Tetramethylammonium hydroxide (TMAH) solution) to form the pressure chamber  15 , the common chamber  18 , and the fluid restrictor  17 . Further, the dry etching using an Inductively Coupled Plasma (ICP) etcher may be used to form the pressure chamber  15 , the common chamber  18 , and the fluid restrictor  17  other than the anisotropic wet etching using an alkaline solution. 
     (10) Next, the head  1   a  is manufactured by bonding the nozzle substrate  203  to the actuator substrate  201 . The nozzle substrate  203  includes the nozzles  16  opened at positions corresponding to the pressure chambers  15  formed separately with the nozzles  16 . 
     The head  1   a  manufactured through the above-described processes (1) to (10) including the curved portion  70  formed on the corner between the side face and the bottom face of the branch chamber  66  has enhanced bubble discharging property and can prevent discharge failure or decrease in the discharge speed. Thus, the above-described manufacturing process can increase manufacturing yield of the head  1   a  that can stably discharge the liquid. 
     As described-above, the head  1   a  includes the common chamber  18  to supply the liquid and the support substrate  202  includes the branch chambers  66  communicating with the nozzles  16  and the common chamber  18 . The curved portion  70  is formed at the corner between the side face and the bottom face of the branch chamber  66  as illustrated in  FIG. 2 . Thus, the head  1   a  according to the present disclosure has as enhanced bubble discharging property and can prevent discharge failure or decrease in the discharge speed. 
     Next, another example of a head  1  according to the present disclosure is described with reference to  FIGS. 4 to 10 . 
       FIG. 4  is an outer perspective view of the head  1 . 
       FIG. 5  is an exploded perspective view of the head  1 . 
       FIG. 6  is a cross-sectional view of the head  1 . 
       FIG. 7  is an exploded perspective view of the head  1  excluding a frame. 
       FIG. 8  is a cross-sectional perspective view of channels and chambers of the head  1 . 
       FIG. 9  is an enlarged cross-sectional perspective view of the channels and chambers of the head  1 . 
       FIG. 10  is a plan view of the channels and chambers of the head  1 . 
     In  FIGS. 4 to 10 , the head  1  before the curved portion  70  is formed is illustrated. 
     The head  1  includes a nozzle plate  10 , a channel plate (individual channel member  20 ), a diaphragm  30 , a common channel member  50 , a damper  60 , a frame  80 , and a substrate (flexible wiring substrate  101 ) mounting a drive circuit  102 . 
     The nozzle plate  10  includes a plurality of nozzles  11  to discharge liquid. As illustrated in  FIG. 10 , the plurality of nozzles  11  are arranged two-dimensionally in a matrix and are arranged side by side in three directions of a first direction F, a second direction S and a third direction T. 
     The individual channel member  20  includes a plurality of pressure chambers  21  (individual chambers) respectively communicating with the plurality of nozzles  11 , a plurality of individual supply channels  22  respectively communicating with the plurality of pressure chambers  21 , and a plurality of individual collection channels  23  respectively communicating with the plurality of pressure chambers  21 . A combination of one pressure chamber  21 , one individual supply channel  22  communicating with one pressure chamber  21 , and one individual collection channel  23  communicating with one pressure chamber  21  is collectively referred to as an individual channel  25 . 
     The diaphragm  30  forms a diaphragm  31  serving as a deformable wall face of the pressure chamber  21 , and the piezoelectric element  40  is formed on the diaphragm  31  to form a single body. Further, as illustrated in  FIGS. 8 and 9 , a supply opening  32  communicating with the individual supply channel  22  and a collection opening  33  communicating with the individual collection channel  23  are formed on the diaphragm  30 . The piezoelectric element  40  is pressure generator to deform the diaphragm  31  to pressurize the liquid in the pressure chamber  21 . 
     Note that the individual channel member  20  and the diaphragm  30  are not limited to separate members, and thus, for example, the same member, such as a Silicon on Insulator (SOI) substrate, may be used to form the individual channel member  20  and the diaphragm  30  as a single body. That is, an SOI substrate sequentially film-formed in an order of a silicon oxide film, a silicon layer, and a silicon oxide film on a silicon substrate is used for forming the individual channel member  20  and the diaphragm  30 . 
     The silicon substrate in the SOI substrate forms the individual channel member  20 , and the silicon oxide film, the silicon layer, and the silicon oxide film in the SOI substrate form the diaphragm  31 . In the above-described configuration, the layer structure of the silicon oxide film, the silicon layer, and the silicon oxide film in the SOI substrate becomes the diaphragm  30 . As described above, the diaphragm  30  includes a member made of the material that is film-formed on a surface of the individual channel member  20 . 
     The common channel member  50  includes a plurality of common-supply branch channels  52  communicating with two or more individual supply channels  22  and a plurality of common-collection branch channels  53  communicating with two or more individual collection channels  23 . The plurality of common-supply branch channels  52  and the plurality of common-collection branch channels  53  are alternately arranged adjacent to each other in the second direction S of the nozzles  11 . 
     As illustrated in  FIG. 9 , the common channel member  50  includes a through-hole serving as a supply port  54  that connects the supply opening  32  of the individual supply channel  22  and the common-supply branch channel  52  and a through-hole serving as a collection port  55  that connects the collection opening  33  of the individual collection channel  23  and the common-collection branch channel  53 . 
     Further, as illustrated in  FIG. 6 , the common channel member  50  includes one or more common-supply main channel  56  communicating with the plurality of common-supply branch channels  52  and one or more common-collection main channel  57  communicating with the plurality of common-collection branch channels  53 . 
     The damper  60  includes a supply-side damper  62  that faces (opposes) the supply port  54  of the common-supply branch channel  52  and a collection-side damper  63  that faces (opposes) the collection port  55  of the common-collection branch channel  53 . 
     As illustrated in  FIG. 9 , the common-supply branch channel  52  and the common-collection branch channel  53  are formed by sealing grooves with the supply-side damper  62  or the collection-side damper  63  of the damper  60 . The grooves are alternately arranged in the common channel member  50  in which both of the common-supply branch channel  52  and the common-collection branch channel  53  are formed. As a material of the damper  60 , it is preferable to use a metal thin film or an inorganic thin film resistant to an organic solvent. A thickness of the damper  60  of the supply-side damper  62  and the collection-side damper  63  is preferably 10 μm or less. 
     As illustrated in  FIG. 12 , a protective film  84  (also referred to as a liquid contacting film) is formed on the inner wall surfaces (including the side face and the bottom face) of the common-supply branch channel  52  and the common-collection branch channel  53  and the inner wall surfaces (including the side face and the bottom face) of the common-supply main channel  56  and the common-collection main channel  57 . The protective film  84  protects the inner wall surfaces from the liquid (ink, for example) flow in the channels in the head  1   a.    
     For example, a silicon oxide film is formed on the inner wall surface of the common-supply branch channel  52  and the common-collection branch channel  53 , and the inner wall surface of the common-supply main channel  56  and the common-collection main channel  57 . 
     The common channel member  50  is made of a silicon (Si) substrate as a base material, and the silicon oxide film is formed by heat processing the Si substrate. The common channel member  50  includes the common-supply branch channels  52  and the common-supply main channel  56 , and the common-collection branch channels  53  and the common-collection main channel  57 . A tantalum silicon oxide film to protect a surface of the Si substrate from the ink is formed on the silicon oxide film. 
     The frame  80  includes a supply port  81  and a collection port  82  formed on a top surface of the frame  80 . The supply port  81  supplies the liquid supplied from outside of the head  1  to the common-supply main channel  56 . The collection port  82  discharges the liquid from the common-collection main channel  57  to outside of the head  1 . 
     Next, the present embodiment including the curved portion  70  in the above-described head  1   a  is described below. 
       FIG. 11  is a schematic perspective view of an example of the curved portion  70  formed in the channels in the head  1   a  described with reference to  FIGS. 4 to 10 . 
       FIG. 12  is a schematic cross-sectional view of an example of the curved portion  70  formed in the channels in the head  1   a.    
       FIG. 13  is a schematic plan view of an example of the curved portion  70  formed in the channels in the head  1   a.    
     The curved portion  70  is formed at each corner between the side face and the bottom face of the common-supply branch channel  52  and at each corner between the side face and the bottom face of the common-collection branch channel  53 . Thus, each of the plurality of common-supply branch channels  52  including a curved portion  70  on a corner between a side face and a bottom face of each of the plurality of common-supply branch channels  52  along a direction of liquid flow in the plurality of common-supply branch channels  52 . 
     “Each corner” is also referred to as “each part between the side face and the bottom face”. The curved portion  70  is formed to include the protective film  84  when the protective film  84  is formed on the inner wall surface of the channels as the channels illustrated in  FIG. 12 . Thus, the protective film  84  covers the curved portion  70  of each channel such as the common-supply branch channel  52  and the common-collection branch channel  53 . 
     Here, “each part” is, for example, a corner formed by two surfaces. Alternatively, “each part” may be, for example, a part at which two surfaces intersects. Thus, the curved portion  70  is formed in “each part” between the side face and the bottom face of the common-supply branch channel  52  so that “each part” at which the side face and the bottom face intersects has a curved surface. Further, the corner having an acute angle formed between the side face and the bottom face disappears. 
     The curved portion  70  is formed at the corner between the side face and the bottom face along a direction of liquid flow (indicated by arrow A or B in  FIG. 11 ) of the common-supply branch channel  52  and the common-collection branch channel  53 . As illustrated in  FIG. 13 , the curved portion  70  is also formed at the corner between the side face and the bottom face along a direction of liquid flow (indicated by arrow C or D in  FIG. 13 ) of the common-supply main channel  56  and the common-collection main channel  57 . 
     Other variations of the channels of the head  1   a  including the curved portion  70  illustrated in  FIGS. 11 to 13  are described below with reference to  FIGS. 14 to 17 . One or more of the following variations may be combined with each other. 
     First Variation 
       FIG. 14  is a schematic cross-sectional view of another example (first variation) of a channel portion provided with the curved portion. The bottom face of the common-supply branch channel  52  and the common-collection branch channel  53  is rougher than the side face of the common-supply branch channel  52  and the common-collection branch channel  53 , respectively, as illustrated by a rough surface  83  in  FIG. 14 . Thus, the bottom face of one of the plurality of common-supply branch channels  52  is rougher than the side face of the one of the plurality of common-supply branch channels  52 . 
     Thus, the protective film  84  can be further contact closely (adhere) to the bottom faces of the common-supply branch channel  52  and the common-collection branch channel  53 . In  FIG. 14 , the protective film  84  illustrated in  FIG. 12  is omitted to illustrate a roughness of the surface of the bottom face of each channel. Thus, an adhesion of the protective film  84  to the bottom face of each channel is improved. Thus, it is possible to prevent deformation of a shape of the curved portion  70  due to peeling of the protective film  84  from the bottom face or the like. 
     Second Variation 
       FIG. 15  is a schematic cross-sectional view of still another example (second variation) of the channels including the curved portion  70 . The damper  60  constitutes an upper face of the common-supply branch channel  52  and the common-collection branch channel  53  opposite (facing) the bottom face of the common-supply branch channel  52  and the common-collection branch channel  53 . The damper  60  is bonded to the common channel member  50  with an adhesive  85 . 
     A recess  87  (step) is formed at an edge of an opening of each of the common-supply branch channel  52  and the common-collection branch channel  53 . The edge of the opening opposes (faces) to the damper  60  and is adjacent to the adhesive  85 . Thus, the adhesive  85  at time of bonding the damper  60  flows into the recess  87 . The recess  87  prevents the adhesive  85  from flowing onto the bottom face of the common-supply branch channel  52  and the common-collection branch channel  53 . Thus, the recess  87  can prevent deformation of the curved portion  70  due to the adhesive  85  flowing into the curved portion  70 . 
     Third Variation 
       FIG. 16  is a schematic cross-sectional view of still another example (third variation) of a channel portion provided with the curved portion. 
     In  FIG. 16 , a peripheral edge of the supply port  54  and a peripheral edge of the collection port  55  is raised to form a protrusion  89  having a sharply pointed tip. The protrusion  89  is formed on raised portions of the supply port  54  and the collection port  55 . The supply port  54  is formed in the bottom face of the common-supply branch channel  52 , and the collection port  55  is formed in the bottom face of the common-collection branch channel  53 . The protrusion  89  surrounds each of the peripheral edge of the supply port  54  and the collection port  55 . 
     Thus, bubbles in the common-supply branch channel  52  and the common-collection branch channel  53  contact the protrusion  89 , whereby the bubble is divided into smaller bubbles, and the common-supply branch channel  52  and the common-collection branch channel  53 . Bubbles are likely to be discharged from the inside of  53 . 
     In  FIG. 16 , the protective film  84  illustrated in  FIG. 12  is omitted to illustrate the protrusion  89  formed on the peripheral edge of the supply port  54  and the collection port  55 . 
     Fourth Variation 
       FIG. 17  is a schematic plan view of another example (fourth variation) of a channel portion provided with the curved portion. 
     The supply port  54  formed in the bottom face of the common-supply branch channel  52  and the collection port  55  formed in the bottom face of the common-collection branch channel  53  are disposed in a region where the curved portion  70  is not formed. 
     Thus, the supply port  54  is formed in the bottom face of the common-supply branch channel  52  and is not formed in a region where the curved portion  70  is formed. 
     Thus, lengths of the through-holes of all the supply ports  54  formed in one common-supply branch channel  52  become identical. Thus, a fluid resistance of each supply ports  54  due to the lengths becomes constant. Similarly, the lengths of the through-holes of all the collection ports  55  formed in the common-collection branch channel  53  become identical, and a fluid resistance of each collection ports  55  due to the lengths becomes constant. 
     Head Module 
     Next, an example of a head module according to the present disclosure is described with reference to  FIGS. 18 and 19 . 
       FIG. 18  is an exploded perspective view of the head module  100 . 
       FIG. 19  is an exploded perspective view of the head module  100  viewed from the nozzle surface side of the head module  100 . 
     The head module  100  includes a plurality of heads  1  configured to discharge a liquid, a base  103  that holds the plurality of heads  1 , and a cover  113  serving as a nozzle cover of the plurality of heads  1 . Further, the head module  100  includes a heat radiator  104 , a manifold  105  forming the channels to supply the liquid to the plurality of heads  1 , a printed circuit board  106  (PCB) connected to the flexible wiring substrate  101 , the drive circuit  102 , and a module case  107 . 
     Liquid Cartridge and Liquid Discharge Apparatus 
     An embodiment of a liquid cartridge and a liquid discharge apparatus mounting the liquid cartridge according to the present embodiment is described with reference to  FIGS. 20 and 21 . Following describes an ink cartridge and an inkjet recording apparatus using ink as a liquid cartridge and a liquid discharge apparatus. 
       FIG. 20  is a schematic perspective view of an inkjet recording apparatus according to the present embodiment. 
       FIG. 21  is a cross-sectional side view of the inkjet recording apparatus of  FIG. 20 . 
     The inkjet recording apparatus  90  includes a carriage  98  movable in a main scanning direction inside an apparatus body  181 , and a printing mechanism  91  including the heads  1  mounted on the carriage  98  and ink cartridges  99  that supplies ink to the heads  1 . The heads  1  may be the head  1   a  illustrated in  FIGS. 1 through 17  or the head  1  illustrated in  FIGS. 18 and 19 . The main scanning direction is indicated by arrow “MSD” in  FIG. 20 . 
     The inkjet recording apparatus  90  further includes a sheet feeding cassette  93  (sheet tray) to stack a large number of sheets  92  as recording media. The sheet feeding cassette  93  is attached to a lower portion of the apparatus body  181  in such a manner that the sheet feeding cassette  93  can be inserted into and removed from a front side of the apparatus body  181 . 
     Further, the inkjet recording apparatus  90  includes a manual feed tray  94  to manually feed the sheets  92 . Further, the sheets  92  fed from the sheet feeding cassette  93  or the manual feed tray  94  is taken into the apparatus body  181 . After required image is recorded on the sheets  92  by the printing mechanism  91 , the sheets  92  on which the image is recorded is ejected to a sheet ejection tray  95  mounted on a rear side of the inkjet recording apparatus  90 . 
     The printing mechanism  91  holds the carriage  98  with a main guide rod  96  and a sub-guide rod  97  so that the carriage  98  is slidable in the main scanning direction MSD. The main guide rod  96  and the sub-guide rod  97  are guides laterally bridged between left and right side plates. The carriage  98  mounts the heads  1  that discharge droplets of yellow (Y), cyan (C), magenta (M), and black (K) inks, respectively. 
     The heads  1  each include nozzle arrays including nozzles  11  arranged in a direction intersecting the main scanning direction MSD. For example, the nozzles  11  are arranged in the second direction S illustrated in  FIG. 10  that is the direction intersecting the main scanning direction MSD. The heads  1  are mounted on the carriage  98  so that the heads  1  discharge the ink downward. Further, the carriage  98  detachably mounts the ink cartridges  99  that supplies ink of the respective colors (Y, C, M, K) to the heads  1 . 
     Each of the ink cartridges  99  has an atmosphere communication port, a supply port, and a porous body. The atmosphere communication port is disposed at an upper portion of the ink cartridge  99  to communicate with the atmosphere. The supply port is disposed at a lower portion of the ink cartridge  99  to supply ink to the heads  1 . The porous body is disposed inside the ink cartridge  99  to be filled with ink. Ink to be supplied to the heads  1  is kept at a slight negative pressure by capillary force of the porous body. In the present embodiment, four heads  1  discharges colors of yellow (Y), cyan (C), magenta (M), and black (K), respectively. However, a single head  1  having nozzles  11  to discharge ink droplets of four colors of yellow (Y), cyan (C), magenta (M), and black (K) may be used. 
     Here, the carriage  98  is slidably fitted to the main guide rod  96  on a rear side of the apparatus body  181  (downstream side in a sheet conveyance direction indicated by arrow SCD in  FIGS. 20 and 21 ) and is slidably fitted to the sub-guide rod  97  on a front side of the apparatus body  181  (upstream side in the sheet conveyance direction SCD). 
     A timing belt  194  is stretched between a driving pulley  192  and a driven pulley  193  rotationally driven by the main scanning motor  191  to move and scan the carriage  98  in the main scanning direction MSD. The timing belt  194  is secured to the carriage  98 . The carriage  98  is reciprocally moved by forward and reverse rotations of the main scanning motor  191 . 
     The inkjet recording apparatus  90  further includes a sheet feed roller  195 , a friction pad  196 , a guide  197 , conveyance rollers  198  and  199 , and leading end roller  110 . The sheet feed roller  195  and the friction pad  196  separate the sheet  92  and feed the sheet  92  set in the sheet feeding cassette  93  to the printing mechanism  91 . The guide  197  guides the sheet  92 . The conveyance rollers  198  and  199  reverses and conveys the sheet  92  to the printing mechanism  91 . The conveyance roller  199  is pressed against a circumferential surface of the conveyance roller  198 . The leading end roller  110  regulates a feeding angle of the sheet  92  from the conveyance roller  198 . The conveyance roller  198  is rotationally driven via a gear train by a sub-scanning motor  200 . 
     A print receiver  111  as a sheet guide is provided to guide the sheet  92  fed from the conveyance roller  198  below the heads  1  in accordance with the movement range of the carriage  98  in the main scanning direction MSD. The inkjet recording apparatus  90  includes a conveyance roller  112  and a spur roller  118  on the downstream side of the print receiver  109  in the sheet conveyance direction SCD. The conveyance roller  112  and the spur roller  118  are driven to rotate to feed the sheet  92  in the sheet conveyance direction SCD (sheet ejection direction) toward the sheet ejection tray  95 . The inkjet recording apparatus  90  further includes a sheet ejection roller  114  and a spur roller  115  to feed the sheet  92  to the sheet ejection tray  95  and guides  116  and  119  constituting a sheet ejection passage. 
     In recording, the inkjet recording apparatus  90  drives the heads  1  in response to image signals while moving the carriage  98 , discharges ink to the stopped sheet  92  to record one line of a desired image on the sheet  92 , feeds the sheet  92  in a predetermined amount, and then records a next line on the sheet  92 . When the inkjet recording apparatus  90  receives a signal indicating an end of recording operation or a signal indicating that a rear end of the sheet  92  has reached a recording area, the inkjet recording apparatus  90  terminates a recording operation and ejects the sheet  92 . 
     A maintenance unit  117  to recover the heads  1  from discharge failure is disposed at a position out of the recording area on a right end side in the moving direction (main scanning direction MSD) of the carriage  98  (see  FIG. 20 ). The maintenance unit  117  has a cap, a suction unit, and a cleaner such as a wiper. While waiting for printing, the carriage  98  moves to the maintenance unit  117 . 
     The maintenance unit  117  caps the head  1  with the cap to keep the nozzles  11  in a wet state to prevent occurrence of discharge failure due to ink drying. Further, because the inkjet recording apparatus  90  discharges ink irrelevant to printing during recording or the like, the viscosity of ink in all the nozzles  11  is kept constant. Thus, the inkjet recording apparatus  90  can stably discharge the liquid. 
     When the discharge failure occurs, the nozzles  11  of the heads  1  are sealed with the cap, and ink and bubbles in the nozzles  11  are suctioned out by the suction unit through a tube. The cleaner (wiper) removes ink and dusts adhered to a nozzle face, in which nozzles  11  are formed, of the head  1 , thus recovering the head  1  from the discharge failure. The suctioned ink is drained to a waste ink container disposed on a lower portion of the apparatus body  181 , absorbed into an ink absorber in the waste ink container, and held in the ink absorber. 
     As described above, the inkjet recording apparatus  90  according to the present embodiment mounts the heads  1  or  1   a  as described above. Thus, the inkjet recording apparatus  90  can have stable ink discharge characteristics and improve image quality. 
     Although the above-described embodiments describe the head  1  used to the inkjet recording apparatus  90 , the head  1  may be used to a device that discharges liquid other than ink, for example, a liquid resist for patterning. 
     Thus, the head  1  according to the present disclosure has as enhanced bubble discharging property and can prevent discharge failure or decrease in the discharge speed. As described above, the ink cartridge  99  and inkjet recording apparatus  90  including the head  1  according to the present embodiment can stably obtain high-quality image. 
     Liquid Discharge Head and Liquid Discharge Apparatus 
     Next, embodiments of the head and the liquid discharge apparatus including the head according to the present embodiment are described below with reference to  FIGS. 22 to 23 . 
       FIG. 22  is a plan view of an example of a liquid discharge apparatus including the head according to the present embodiment.  FIG. 23  is a side view of an example of a main part of the liquid discharge apparatus of  FIG. 22 . 
     The liquid discharge apparatus  1000  according to the present embodiment is a serial-type apparatus in which a main scan moving unit  493  reciprocally moves a carriage  403  in a main scanning direction indicated by arrow MSD in  FIG. 22 . The main scan moving unit  493  includes a guide  401 , a main scanning motor  405 , and a timing belt  408 , for example. The guide  401  is bridged between a left side plate  491 A and a right side plate  491 B that movably holds the carriage  403 . The main scanning motor  405  reciprocally moves the carriage  403  in the main scanning direction MSD via the timing belt  408  bridged between a driving pulley  406  and a driven pulley  407 . 
     The carriage  403  mounts a liquid discharge device  440 . The head  1  according to the present embodiment and a head tank  441  forms the liquid discharge device  440  as a single unit. The head  1  or  1   a  as illustrated in  FIGS. 1 through 21  may be used as the head  1  in  FIGS. 22 and 23 . The head  1  of the liquid discharge device  440  discharges liquid of each color, for example, yellow (Y), cyan (C), magenta (M), and black (K). 
     The head  1  includes nozzle arrays each including a plurality of nozzles  11  arrayed in row in a sheet conveyance direction SCD in  FIG. 28 , perpendicular to the main scanning direction MSD. The head  1  is mounted to the carriage  403  so that the liquid droplets are discharged downward. 
     The liquid stored in the liquid cartridges  450  is supplied to the head tank  441  by a supply unit  494  that supplies the liquid stored outside the head  1  to the head  1 . 
     The supply unit  494  includes a cartridge holder  451  which is a filling section to mount the liquid cartridges  450 , a tube  456 , a liquid feed unit  452  including a liquid feed pump, and the like. The liquid cartridges  450  are detachably attached to the cartridge holder  451 . The liquid is supplied to the head tank  441  by the liquid feed unit  452  via the tube  456  from the liquid cartridges  450 . 
     The liquid discharge apparatus  1000  in the present embodiment includes a conveyance unit  495  to convey the sheet  410  as a recording medium. The conveyance unit  495  includes a conveyance belt  412  as a conveyance unit and a sub-scanning motor  416  to drive the conveyance belt  412 . 
     The conveyance belt  412  attracts the sheet  410  and conveys the sheet  410  at a position facing the head  1 . The conveyance belt  412  is an endless belt and is stretched between a conveyance roller  413  and a tension roller  414 . The adsorption of the sheet  410  by the conveyance belt  412  can be performed by electrostatic adsorption, air adsorption, or the like. 
     The conveyance roller  413  is driven and rotated by the sub-scanning motor  416  via a timing belt  417  and a timing pulley  418 , so that the conveyance belt  412  circulates in the sheet conveyance direction SCD. 
     At one side in the main scanning direction MSD of the carriage  403 , a maintenance unit  420  to maintain and recover the head  1  in good condition is disposed on a lateral side of the conveyance belt  412 . The maintenance unit  420  is composed of, for example, a cap  421  for capping the nozzle surface (the surface on which the nozzles  11  are formed) of the head  1 , a wiper  422  for wiping the nozzle surface, and the like. 
     The main scan moving unit  493 , the supply unit  494 , the maintenance unit  420 , and the conveyance unit  495  are mounted to a housing that includes the left side plate  491 A, the right side plate  491 B, and a rear side plate  491 C. 
     In the liquid discharge apparatus  1000  thus configured, the sheet  410  is conveyed on and attracted to the conveyance belt  412  and is conveyed in the sheet conveyance direction SCD by the cyclic rotation of the conveyance belt  412 . 
     The head  1  is driven in response to image signals while the carriage  403  moves in the main scanning direction MSD, to discharge liquid to the sheet  410  stopped, thus forming an image on the sheet  410 . 
     As described above, the liquid discharge apparatus  1000  includes the head  1  according to the present embodiment, thus allowing stable formation of high quality images. 
     Next, another embodiment of the liquid discharge device according to the present disclosure is described below with reference to  FIG. 24 . 
       FIG. 24  is a plan view of an example of the liquid discharge device  440  according to the present embodiment. The liquid discharge device  440  includes a housing, the main scan moving unit  493 , the carriage  403 , and the head  1  among components of the liquid discharge apparatus  1000  as illustrated in  FIG. 23 . The left side plate  491 A, the right side plate  491 B, and the rear side plate  491 C forms the housing. Note that, in the liquid discharge device  440 , at least one of the maintenance unit  420  and the supply unit  494  may be mounted on, for example, the right side plate  491 B. 
     Next, another embodiment of the liquid discharge device  440  according to the present disclosure is described below with reference to  FIG. 25 . 
       FIG. 25  is a plan view of another example of the liquid discharge device  440  according to the present embodiment. The liquid discharge device  440  includes the head  1  to which a channel part  444  is mounted, and tubes  456  connected to the channel part  444 . Further, the channel part  444  is disposed inside a cover  442 . Instead of the channel part  444 , the liquid discharge device  440  may include the head tank  441  as illustrated in  FIG. 23 . A connector  443  electrically connected with the head  1  is provided on an upper part of the channel part  444 . 
     The liquid discharge apparatus  1000  according to the present embodiment includes the head  1  or the liquid discharge device  440  and drives the head  1  to discharge the liquid. The liquid discharge apparatus may be, for example, an apparatus capable of discharging liquid to a material to which liquid can adhere or an apparatus to discharge liquid toward gas or into liquid. 
     The liquid discharge apparatus may include devices to feed, convey, and eject the material on which liquid can adhere. The liquid discharge apparatus may further include a pretreatment apparatus to coat a treatment liquid onto the material, and a post-treatment apparatus to coat a treatment liquid onto the material, onto which the liquid has been discharged. 
     The “liquid discharge apparatus” may be, for example, an apparatus to form an image on a sheet by discharging ink, or a three-dimensional fabrication apparatus to discharge a fabrication liquid to a powder layer in which powder material is formed in layers to form a three-dimensional fabrication object. 
     Further, the liquid discharge apparatus is not limited to one in which significant images such as letters and graphics are visualized by the ejected liquid. For example, the liquid discharge apparatus may be an apparatus to form meaningless images, such as meaningless patterns, or fabricate three-dimensional images. 
     The above-described term “material on which liquid can be adhered” represents a material on which liquid is at least temporarily adhered, a material on which liquid is adhered and fixed, or a material into which liquid is adhered to permeate. 
     Examples of the “material on which liquid can be adhered” include recording media, such as paper sheet, recording paper, recording sheet of paper, film, and cloth, electronic component, such as electronic substrate and piezoelectric element, and media, such as powder layer, organ model, and testing cell. The “material on which liquid can be adhered” includes any material on which liquid is adhered, unless particularly limited. 
     Examples of the “material on which liquid can be adhered” include any materials on which liquid can be adhered even temporarily, such as paper, thread, fiber, fabric, leather, metal, plastic, glass, wood, ceramic, construction materials (e.g., wall paper or floor material), and cloth textile. 
     Examples of the “liquid” are, e.g., ink, treatment liquid, DNA sample, resist, pattern material, binder, fabrication liquid, or solution and dispersion liquid including amino acid, protein, or calcium. 
     The “liquid discharge apparatus” may be an apparatus to relatively move the head and a material on which liquid can be adhered. However, the liquid discharge apparatus is not limited to such an apparatus. For example, the liquid discharge apparatus may be a serial head apparatus that moves the head or a line head apparatus that does not move the head. 
     Examples of the “liquid discharge apparatus” further include a treatment liquid coating apparatus to discharge a treatment liquid to a sheet to coat the treatment liquid on a sheet surface to reform the sheet surface and an injection granulation apparatus in which a composition liquid including raw materials dispersed in a solution is discharged through nozzles to granulate fine particles of the raw materials. 
     The “liquid discharge device” is an assembly of parts relating to liquid discharge. The term “liquid discharge device” represents a structure including the head and a functional part(s) or mechanism combined to the head to form a single unit. For example, the “liquid discharge device” includes a combination of the head with at least one of a head tank, a carriage, a supply unit, a maintenance unit, and a main scan moving unit. 
     Examples of the “single unit” include a combination in which the head and one or more functional parts and devices are secured to each other through, e.g., fastening, bonding, or engaging, and a combination in which one of the head and the functional parts and devices is movably held by another. The head may be detachably attached to the functional part(s) or device(s) each other. 
     The liquid discharge device may be, for example, formed by the head and the head tank as a single head, such as the liquid discharge device  440  illustrated in  FIG. 23 . Alternatively, the head and the head tank coupled (connected) with a tube or the like may form the liquid discharge device as a single unit. A unit including a filter may be added at a position between the head tank and the head of the liquid discharge device. 
     The head and the carriage may form the “liquid discharge device” as a single unit. 
     In still another example, the liquid discharge device includes the head movably held by a guide that forms part of a main scan moving unit, so that the head and the main scan moving unit form a single unit. The head, the carriage, and the main scan moving unit may form the liquid discharge device as a single unit. 
     In still another example, the cap that forms part of the maintenance unit may be secured to the carriage mounting the head so that the head, the carriage, and the maintenance unit form a single unit as the liquid discharge device. 
     Further, a tube may be coupled to the head to which either the head tank or a channel member is attached, so that the head and the supply unit form a single liquid discharge device. 
     The main scan moving unit may be a guide only. The supply device may include only a tube(s) or a loading unit. 
     The pressure generator used in the head is not limited to a particular-type of pressure generator. The pressure generator is not limited to the piezoelectric actuator (or a laminated piezoelectric element) described in the above-described embodiments, and may be, for example, a thermal actuator that employs an electrothermal transducer element, such as a thermal resistor, or an electrostatic actuator including a diaphragm and opposed electrodes. 
     The terms “image formation”, “recording”, “printing”, “image printing”, and “fabricating” used herein may be used synonymously with each other. 
     The above-described embodiments are illustrative and do not limit the present disclosure. Thus, numerous additional modifications and variations are possible in light of the above teachings. For example, elements and/or features of different illustrative embodiments may be combined with each other and/or substituted for each other within the scope of the present disclosure. 
     Numerous additional modifications and variations are possible in light of the above teachings. Such modifications and variations are not to be regarded as a departure from the scope of the present disclosure and appended claims, and all such modifications are intended to be included within the scope of the present disclosure and appended claims.