Patent Publication Number: US-10328696-B2

Title: Liquid ejection head

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present disclosure relates to a liquid ejection head. 
     Description of the Related Art 
     A known example of the configuration of a piezoelectric liquid ejection head is such that a plate-like piezoelectric actuator is joined to a substrate (a cavity plate) in which a plurality of pressure chambers and ejection ports are formed (Japanese Patent Laid-Open No. 2001-162796 and No. 2001-260349). A piezoelectric actuator having a structure in which piezoelectric layers are laminated is joined to a substrate so as to cover the openings of pressure chambers provided in the substrate. A plurality of ejection ports communicating with the individual pressure chambers are open from a surface of the substrate different from a surface to which the piezoelectric actuator is joined. In this configuration, one wall of each pressure chamber is constituted by the piezoelectric actuator. The capacity of the pressure chambers is reduced by piezoelectric deformation of the piezoelectric actuator, thereby causing the liquid in the pressure chambers to be ejected from the ejection ports to the outside. 
     In the configuration disclosed in Japanese Patent Laid-Open No. 2001-162796, the pressure chambers are open from one surface of the substrate, to which the plate-like piezoelectric actuator is joined so as to cover the openings of the pressure chambers. The substrate has a multilayer structure in which a plurality of plate members (plates) are laminated. Of these plates, a base plate has through holes serving as pressure chambers, and the piezoelectric actuator is joined to one surface of the base plate. A spacer plate is joined to a surface of the base plate opposite to the surface to which the piezoelectric actuator is joined. Two manifold plates each have a through hole that constitutes a common liquid chamber and are joined to a surface of the spacer plate opposite to a surface joined to the base plate. An ejection port plate (an ejection-port formed member) is joined to the manifold plates to cover the through hole and has ejection ports. Each plate has channels connecting the common liquid chamber and the pressure chambers, channels connecting the pressure chambers to the ejection ports, and channels connecting a liquid supply source (not shown) to the common liquid chamber. In this configuration, liquid flows among the plates. In other words, the liquid from the liquid supply source is stored in the common liquid chamber, from which the liquid is supplied to the pressure chambers through the channels. When the piezoelectric actuator is deformed, so that the capacities of the pressure chambers are reduced, the liquid in the pressure chambers is ejected from the ejection ports through the channels. 
     The substrate with a structure disclosed in Japanese Patent Laid-Open No. 2001-162796 has a plurality of recesses on a first surface of the plate-like ejection-port formed member and has a plurality of ejection ports that are open from a second surface of the election-port formed member so as to communicate with the recesses. The plate-like piezoelectric actuator is joined to the first surface of the ejection-port formed member to close the recesses to form the pressure chambers. The pressure chambers and the election ports are arranged in a plurality of arrays. Adjacent pressure chambers are partitioned by a thin partition wall in the arrangement direction. 
     In the configuration disclosed in Japanese Patent Laid-Open No. 2001-20349, the piezoelectric actuator constitutes one wall of each pressure chamber, and the common liquid chamber is disposed at a position opposing the piezoelectric actuator with one plate (wall) interposed therebetween. With this configuration, when the piezoelectric actuator is deformed so as to protrude toward the inside of the pressure chambers, pressure due to the deformation can push a wall (referred to as “opposing wall”) at a position opposing the piezoelectric actuator to deform the wall. In particular, the common liquid chamber is positioned on the back of the opposing wall as viewed from the pressure chambers, so that the opposing wall is not firmly supported, being easily deformed by the pressure generated by the piezoelectric actuator. The deformation of the opposing wall can decrease the amount of reduction in the capacities of the pressure chambers, possibly not providing sufficient pressure to satisfactorily eject the liquid. In other words, part of energy generated by the piezoelectric actuator is used for deformation of the opposing wall rather than liquid ejection, resulting in poor energy efficiency. In addition, the deformation of the opposing wall also causes pressure to the liquid in the common liquid chamber, which applies pressure to the liquid in the other pressure chambers via the liquid in the common liquid chamber, possibly causing crosstalk. 
     Furthermore, in the case where adjacent pressure chambers are partitioned by a thin partition wall, as disclosed in Japanese Patent Laid-Open No. 2001-260349, the pressure due to the deformation of the piezoelectric actuator can deform the thin partition wall, causing pressure to be applied also to the liquid in the adjacent pressure chamber. The generation of crosstalk causes part of the energy generated by the piezoelectric actuator to be used for deformation of the partition wall, resulting in poor energy efficiency. Furthermore, when the Liquid in the adjacent pressure chamber vibrates and is thereafter ejected from the adjacent pressure chamber, the vibrating liquid cannot exhibit desired behavior, which may decrease the accuracy of liquid ejection. Furthermore, in some cases, the liquid may be ejected or dropped from the ejection ports even though a piezoelectric actuator at a position facing the adjacent pressure chamber is not operated. Increasing the thickness of a partition wall between adjacent pressure chambers to prevent crosstalk increases the size of the entire liquid ejection head, which is undesirable because it hinders high density. 
     SUMMARY OF THE INVENTION 
     The present disclosure provides a liquid ejection head capable of high-accuracy liquid ejection with high energy efficiency. 
     A liquid ejection head according to an aspect of the present disclosure includes a plurality of ejection ports, a plurality of pressure chambers each communicating with each of the ejection ports, a piezoelectric actuator constituting part of walls of the pressure chambers, and a common liquid chamber containing liquid to be supplied to the pressure chambers. The pressure chambers and the common liquid chamber are opposed with an opposing wall interposed therebetween. The opposing wall faces the wall of the pressure chambers constituted by the piezoelectric actuator. A reinforcing portion that supports the opposing wall is provided in the common liquid chamber. 
     Further features of the present disclosure will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded perspective view of a liquid ejection head according to a first embodiment of the present disclosure. 
         FIG. 2  is an exploded perspective view of a substrate and a piezoelectric actuator of the liquid ejection head in  FIG. 1 . 
         FIG. 3  is an exploded perspective view of the substrate of the liquid ejection head in  FIG. 1 . 
         FIG. 4  is a partly cut-away exploded perspective view of the substrate illustrating a relevant part in  FIG. 3  in enlarged view. 
         FIG. 5  is a cross-sectional view of the liquid ejection head in  FIG. 1 . 
         FIG. 6  is an exploded perspective view of the piezoelectric actuator of the liquid ejection head in  FIG. 1 . 
         FIG. 7  is a partly cut-away exploded perspective view of a substrate of a liquid ejection head according to a second embodiment of the present disclosure. 
         FIG. 8  is a cross-sectional view of the liquid ejection head according to the second embodiment. 
         FIG. 9  is a partly cut-away exploded perspective view of a substrate of a liquid ejection head according to a third embodiment of the present disclosure. 
         FIG. 10  is a cross-sectional view of the liquid ejection head according to the third embodiment. 
         FIG. 11  is a partly cut-away exploded perspective view of a substrate of a liquid ejection head according to a fourth embodiment of the present disclosure. 
         FIG. 12  is a cross-sectional view of the liquid ejection head according to the fourth embodiment. 
         FIG. 13  is a partly cut-away exploded perspective view of a substrate of a liquid ejection head according to a fifth embodiment of the present disclosure. 
         FIG. 14  is a cross-sectional view of the liquid ejection head according to the fifth embodiment. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Embodiments of the present disclosure will be described with reference to the drawings. 
     Basic Structure of Liquid Ejection Head 
       FIG. 1  illustrates the basic structure of a liquid ejection head according to a first embodiment of the present disclosure. This liquid ejection head has a configuration in which a piezoelectric actuator  20  is joined to a substrate (a cavity unit)  10 . Furthermore, an electrical wiring member (flexible flat cable)  40  for connection with an external device is overlaid and joined to the piezoelectric actuator  20 . Ejection ports are open in the lowermost surface of the substrate  10  in  FIG. 1 , from which liquid (for example, liquid ink) is elected. 
     Substrate 
     As illustrated in  FIGS. 2 to 5 , the substrate  10  of the present embodiment has a structure in which five thin plate members (plates) of an ejection-port formed member (an ejection port plate, or a first plate)  11 , two manifold plates  12   a  (a third plate) and  12   b  (a fourth plate), a spacer plate  13 , and a base plate  14  (a second plate) are laminated. In one example, the ejection-port formed member  11  is made of synthetic resin, and the other plates  12   a ,  12   b ,  13 , and  14  are made of a 42% nickel alloy steel plate with a thickness of about 50 μm to 250 μm (a longitudinal elasticity modulus of 147 GPa). The ejection-port formed member  11  has many minute-diameter ejection ports  15  for ejecting ink at minute intervals. The ejection ports  15  are disposed in two rows in a staggered arrangement along the long sides (a first direction) of the ejection-port formed member  11 . 
     As illustrated in  FIGS. 3 to 5 , the two manifold plates  12   a  and  12   b  are provided with common liquid chambers  23  extending substantially along the long sides of the manifold plates  12   a  and  12   b . The common liquid chambers  23  are positioned so as to sandwich the rows of the ejection ports  15 , described above, from both sides in the short side direction. The upper manifold plate  12   a  has recesses  23   a  that are open from the lower surface, and the lower manifold plate  12   b  has recesses  23   b  that are open from the upper surface. The manifold plates  12   a  and  12   b  are laminated so that the openings of the recesses  23   a  and  23   b  face each other to constitute the common liquid chambers  23 . The common liquid chambers  23  are connected to a plurality of pressure chambers  16  via through holes  18 , described later. Protrusions  12   d  are respectively provided in the recesses  23   a  and  23   b . An end of each protrusion  12   d  in the recess  23   a  and an end of each protrusion  12   d  in the recess  23   b  come into contact and join together to constitute a reinforcing portion  1  (the protrusion  12   d ). 
     As illustrated in  FIGS. 3 and 4 , the plurality of pressure chambers  16  are provided in the base plate  14  in two rows in a staggered arrangement along the long sides (in the first direction, described above) of the base plate  14 . Each pressure chamber  16  is formed in an elongated shape so that its longitudinal direction is orthogonal to the longitudinal direction of the base plate  14 . A first end  16   a  of each pressure chamber  16  is positioned substantially at the center of the base plate  14  in the short side direction. The first ends  16   a  are disposed in a staggered arrangement like minute-diameter through holes  17  in the spacer plate  13  and the two manifold plates  12   a  and  12   b . The first ends  16   a  communicate with the staggered ejection ports  15  of the ejection-port formed member  11  through the through holes  17  serving as liquid channels. A second end  16   b  of each pressure chamber  16  is formed as a recess that is open downwards, as illustrated in  FIG. 4 . The second ends  16   b  communicate with the common liquid chambers  23  of the manifold plates  12   a  and  12   b  via through holes  18  provided on the right and left sides of the spacer plate  13 . Supply holes  19   a  (see  FIG. 3 ) provided at one end of the uppermost base plate  14  of the substrate  10  communicate with the common liquid chambers  23  via through holes  19   b  of the spacer plate  13  and through holes  19   c  of the upper manifold plate  12   a . The supply holes  19   a  are provided with a filter  29  for removing dust in liquid supplied from an liquid tank (not shown) disposed above. The pressure chambers  16  are disposed such that their longitudinal direction are orthogonal to the longitudinal direction of the common liquid chamber  23 . 
     As described above, the substrate  10  of the present embodiment is configured such that liquid flows from the supply holes  19   a  provided at one end of the base plate  14  through the through holes  19   b  and  19   c  into the common liquid chambers  23 . The liquid in the common liquid chambers  23  is distributed into the pressure chambers  16  through the through holes  18 , and thereafter flows from the pressure chambers  16  through the through holes  17  to reach the election ports  15  corresponding to the pressure chambers  16  (see  FIGS. 3 to 5 ). The uppermost base plate  14  of the substrate  10  has groove-like recesses constituting the pressure chambers  16 , and the recesses are open upward, as described above. The piezoelectric actuator  20  is laminated on the base plate  14 , so that the openings of the recesses are closed by the piezoelectric actuator  20  to constitute the pressure chambers  16 . 
     Operation and Configuration of Liquid Ejection 
     In the liquid ejection head of the present embodiment, the pressure chambers  16  of the substrate  10  are closed by the piezoelectric actuator  20 . In other words, part of the walls of each pressure chamber  16  is constituted by the piezoelectric actuator  20 . Accordingly, when electric power is appropriately supplied from an electrode (to be described later) to the piezoelectric actuator  20 , the piezoelectric actuator  20  is deformed in a protruding shape toward the inside of the pressure chamber  16 , that is, so as to reduce the capacity of the pressure chamber  16 . This causes pressure to be applied to the liquid in the pressure chamber  16 , and the liquid is ejected to the outside through the through hole  17  from the ejection port  15 . When the piezoelectric actuator  20  is deformed toward the inside of the pressure chambers  16  to reduce the capacity in this manner, the pressure is also applied through the liquid to the other walls of the pressure chamber  16  other than the wall constituted by the piezoelectric actuator  20 . In particular, a pressure in a direction perpendicular to a wall at a position facing the piezoelectric actuator  20  (part of the spacer plate  13 , referred to as “opposing wall  13   a ”) is applied to the opposing wall  13   a . If the opposing wall  13   a  is deformed by the pressure, the amount of reduction in the capacity of the pressure chamber  16  is decreased, resulting in poor energy efficiency, and in some cases, the capacity is not reduced enough to eject the liquid from the ejection port  15 . In addition, the deformation of the opposing wall  13   a  can draw the base plate  14  constituting the side walls of the pressure chamber  16  to deform the base plate  14 . In particular, deformation of a thin partition wall positioned between adjacent pressure chambers  16  out of the side walls of the pressure chambers  16  that the base plate  14  constitutes can cause so-called crosstalk in which the liquid in pressure chambers  16  that do not eject liquid is also influenced by the vibration and so on. The deformation of the opposing wall  13   a  of the pressure chamber  16  is likely to occur due to the fact that the pressure chamber  16  and the common liquid chamber  23  are opposed to each other with the opposing wall  13   a  interposed therebetween, that is, the fact that the common liquid chamber  23  is positioned on the back of the opposing wall  13   a  as viewed from the inside of the pressure chamber  16 , so that a firmly supporting member is not present. The deformation of the opposing wall  13   a  can cause the pressure to be applied also to the liquid in the common liquid chamber  23  and also to the liquid in other pressure chambers  16  via the liquid in the common liquid chamber  23 , possibly causing crosstalk. 
     For that reason, the present disclosure is configured such that deformation of the opposing wall  13   a  hardly occurs by disposing the reinforcing portion  1  constituted by the protrusion  12  in the common liquid chamber  23 , and supporting the opposing wall  13   a  from the back with the reinforcing portion  1 . Specifically, the common liquid chamber  23  of the present embodiment is formed of two manifold plates  12   a  and  12   b  laminated each other. The manifold plates  12   a  and  12   b  are overlapped with one another so that the recess  23   a  that is open from one surface of the manifold plate  12   a  and the recess  23   b  that is open from one surface of the manifold plate  12   b  face each other. The recesses  23   a  and  23   b  face each other to form the common liquid chamber  23 . The protrusion  12   d  protruding toward the opposite manifold plate  12   a  or  12   b  is provided in each of the recesses  23   a  and  23   b . When the manifold plates  12   a  and  12   b  are laminated, the ends of the protrusions  12   d  are brought into contact with each other to constitute the columnar reinforcing portion  1  standing in the common liquid chamber  23 . 
     With this configuration, even if pressure is applied to the opposing wall  13   a  via the liquid when the piezoelectric actuator  20  constituting one wall of the pressure chamber  16  is deformed, the opposing wall  13   a  is hardly deformed. This is because the reinforcing portion  1  in the common liquid chamber  23  positioned on the back of the opposing wall  13   a  as viewed from the pressure chamber  16  supports the opposing wall  13   a . Since the opposing wall  13   a  is hardly deformed, almost all of the energy generated by the piezoelectric actuator  20  is used to reduce the capacity of the pressure chamber  16 , which is energy efficient, allowing the liquid in the pressure chamber  16  to be satisfactorily ejected from the ejection ports  15  to the outside. Furthermore, in the present embodiment, the common liquid chamber  23  is constituted by providing the bottomed recesses  23   a  and  23   b  in the manifold plates  12   a  and  12   b  rather than by providing through holes in the manifold plates  12   a  and  12   b . In other words, the common liquid chamber  23  is not positioned on the back of the opposing wall  13   a  as viewed from the pressure chamber  16  but is positioned with part (a thin portion) of the manifold plate  12   a  interposed therebetween. Accordingly, part (the thin portion) of the manifold plate  12   a  also supports the opposing wall  13   a  of the pressure chamber  16 , contributing to suppression of deformation. 
     Furthermore, in the present embodiment, the opposing wall  13   a  of the pressure chamber  16  is hardly deformed, so that there is little possibility of occurrence of crosstalk via the liquid in the common liquid chamber  23 . Furthermore, there is little possibility of occurrence of crosstalk due to deformation of the base plate  14  constituting the side wall of the pressure chamber  16  drawn by the opposing wall  13   a . Considering an effect on preventing deformation of the opposing wall  13   a , the reinforcing portion  1  is increased in size, but excessive resistance to the flow of the liquid in the common liquid chamber  23  is undesirable. For that reason, the reinforcing portion  1  preferably have, in plan view, substantially a length of half the length of the pressure chamber  16  in the longitudinal direction of the pressure chamber  16 , more preferably at least half, and a length equal to the length of the pressure chamber  16  in the crosswise direction of the pressure chamber  16 . Deformation of the opposing wall  13   a  at a position close to the ejection port  15  particularly has a great influence on the performance of liquid ejection. Accordingly, the reinforcing portion  1  may be disposed at a position nearer to the ejection port  15  than the center of the pressure chamber  16 . More specifically, the center of gravity of the reinforcing portion  1  is nearer to the ejection port  15  than the center of gravity of the pressure chamber  16 . 
     Piezoelectric Actuator 
     The piezoelectric actuator  20  of the present embodiment described above will be described. The piezoelectric actuator  20  has a configuration in which a plurality of piezoelectric layers and electrode layers are alternately laminated. The piezoelectric layers are each formed of a piezoelectric sheet  21  made of piezoelectric ceramic with a thickness of about 30 μm. As illustrated in  FIG. 6 , the piezoelectric actuator  20  has a structure in which the plurality of piezoelectric sheets  21  are layered, on the uppermost surface of which a top sheet  22  is laminated. Each electrode layer is formed on the upper surface (a wide surface) of each piezoelectric sheet  21  as an electrode pattern made of metal film, as will be described below. Of the plurality of piezoelectric sheets  21 , a plurality of piezoelectric sheets  21  adjacent to the substrate  10  (on the lower side) constitute an active layer including an active portion that can be expanded and contracted in correspondence with the pressure chambers  16 . The plurality of piezoelectric sheets  21  on the upper side may constitute a constraint layer including a constraint portion that constrains upward expansion and contraction of the active portion. In the active layer, the electrode layers each sandwiched between the piezoelectric layers, that is, individual electrodes  24  provided in correspondence with the pressure chambers  16  to selectively apply a voltage and a common electrode  25  having a wide shape extending across the plurality of pressure chambers  16  and having a common polarity, are alternately formed in the laminating direction. Specifically, the individual electrodes  24  are formed on the upper surface of each even-numbered piezoelectric sheet  21  counted from the lowermost piezoelectric sheet  21 , and the common electrode  25  is formed on the upper surface of each odd-numbered piezoelectric sheet  2  counted from the lowermost piezoelectric sheet  21 . Extending portions  25   a  extending across substantially the entire length of the vicinity of the short sides of the piezoelectric sheet  21  having the common electrode  25  are formed on both ends on the long sides of the piezoelectric sheet  21  and are connected to the common electrode  25 . On each piezoelectric sheet  21  on which the common electrode  25  is formed, dummy individual electrodes  26  are formed at the same positions in plan view (vertically overlapping positions) as the positions of the individual electrodes  24  on the upper surface of the vicinity of the ends of the long sides where the common electrode  25  is not formed. The dummy individual electrodes  26  are substantially equal in width to the individual electrodes  24  and shorter in length than the individual electrodes  24 . Dummy common electrodes  27  are formed at positions on the upper surface of each piezoelectric sheet  21  on which the individual electrodes  24  are formed, the positions corresponding to the extending portions  25   a  (vertically overlapping positions, in the vicinity of both ends of the long sides of the piezoelectric sheet  21 ). The individual electrodes  24 , the common electrodes  25 , the dummy individual electrodes  26 , and the dummy common electrodes  27  are formed at predetermined portions in predetermined patterns by screen printing an electrically conductive paste made of an alloy of silver and palladium. Surface electrodes  30  and  31  are formed by printing on the upper surface of the top sheet  22 , on which an electrical wiring member  40  are placed and joined, and various kinds of wiring pattern (not shown) of the electrical wiring member  40  are electrically connected to the surface electrodes  30  and  31 . 
     All of piezoelectric sheets  21  of the piezoelectric actuator  20  other than the lowermost piezoelectric sheet  21  have through holes  32  for connecting the surface electrodes  30 , the individual electrodes  24  and the dummy individual electrodes  26  at corresponding positions in plan view together. Likewise, a through hole  33  for connecting at least one surface electrode  31  and the extending portion  25   a  of the common electrode  25  and the dummy common electrode  27  at a corresponding position in plan view is provided. In the illustrated embodiment, the through hole  33  is formed in the surface electrodes  31  at the four corners of the uppermost piezoelectric sheet  21  and the extending portion  25   a  of the common electrode  25  and the dummy common electrode  27  at a corresponding position in plan view. The interior of the through holes  32  is filled with an electrically conductive material to electrically connect the individual electrodes  24  of the individual layers and the surface electrodes  30  at corresponding positions in plan view. Likewise, the interior of the through holes  33  is filled with an electrically conductive material to electrically connect the extending portions  25   a  of the individual layers and the surface electrode  31  at the corresponding position in plan view. In an actual manufacturing process, the through holes  32  and  33  are formed in a ceramic green sheet constituting each piezoelectric sheet  21 , and an electrically conductive paste made of an alloy of silver and palladium is applied to the green sheet by screen printing or the like to form electrode patterns. At that time, the electrically conductive material forming the electrode patterns enters the interior of the through holes  32  and  33  and fills them. This allows the upper and lower surfaces of the piezoelectric sheets  21  to be electrically conducted through the through holes  32  and  33 . The piezoelectric sheets  21  are laminated so that the electrode patterns or the dummy electrodes of the lower layers and the through holes  32  and  33  of the upper layers are aligned and are pressed in the laminating direction to form a single unit, and it is burned as is well known to form the piezoelectric actuator  20 . 
     As described above, the through holes  32  and  33  of the piezoelectric layers sandwiched between the individual electrodes  24  and the common electrode  25  are filled with an electrically conductive material. As is well known, when the common electrodes  25  are grounded, and a positive high voltage for polarization is applied to all of the individual electrodes  24 , an area of each piezoelectric sheet  21  between the electrodes is polarized in a direction from the individual electrodes  24  to the common electrode  25  to form an active portion. In other words, the second piezoelectric sheet  21  counted from the bottom to the uppermost piezoelectric sheet  21  constitute the active layer. When a driving positive low voltage is selectively applied to the individual electrodes  24  with the common electrodes  25  grounded, the active portion is extended due to a piezoelectric longitudinal effect. Thus, distortion in the laminating direction occurs in the piezoelectric layers sandwiched between the individual electrodes  24  and each common electrode  25 . The amount of displacement due to the distortion increases toward the interior of the pressure chamber  16  corresponding to each individual electrode  24 , which reduces the capacity of the pressure chamber  16 , so that the liquid in the pressure chamber  16  is ejected as droplets from the ejection port  15  to the outside. The thus-ejected droplets are attached to a desired position of a printing medium (not shown) to perform desired recording (image formation or printing). 
     First Embodiment 
     More concrete embodiments of the present disclosure will be described. In the following description, only the characteristics of the embodiments will be described, and description of configurations similar to those already described will be omitted. 
     In a first embodiment of the present disclosure, as illustrated in  FIGS. 3 to 5 , the upper manifold plate  12   a  has recesses  23   a  that are open only downward, and the lower manifold plate  12   b  has the recesses  23   b  that are open only upward. The manifold plates  12   a  and  12   b  are laminated so that the recesses  23   a  and  23   b  face each other to form the common liquid chamber  23 . The common liquid chamber  23  (recesses  23   a  and  23   b ) is provided with the reinforcing portions  1  therein at positions of the manifold plates  12   a  and  12   b  where the through holes  18  are not closed and which overlap with the pressure chambers  16  in the laminating direction. The reinforcing portions  1  are structures that suppress deformation of the opposing wall  13   a  to allow liquid ejection with high energy efficiency and that contribute to suppress the occurrence of crosstalk. In the present embodiment, the reinforcing portions  1  are provided in each of the recesses  23   a  and  23   b , and the protrusions  12   d  that are joined together to constitute each reinforcing portion  1  have the same shape. 
     Second Embodiment 
     In a second embodiment of the present disclosure, as illustrated in  FIGS. 7 and 8 , the protrusions  12   d  in the recess  23   b  of the lower manifold plate  12   b  each have a groove  12   c  extending in the longitudinal direction of the common liquid chamber  23 . In this configuration, the groove  12   c  provided in each protrusion  12   d  serves as a passage of the liquid, which allows the entire common liquid chamber  23  to be smoothly filled with the liquid, which produces a small pressure loss in the common liquid chamber  23 , leading to good liquid supply performance. The groove  12   c  may be disposed in each protrusion  12   d  in the recess  23   a  of the upper manifold plate  12   a . To further reduce the pressure loss, the groove  12   c  may be disposed in the protrusions  12   d  of both of the recesses  23   a  and  23   b . In other words, the present embodiment has the groove  12   c  in one or both of the protrusions  12   d  in the recesses  23   a  and  23   b.    
     Third Embodiment 
     In a third embodiment of the present disclosure, as illustrated in  FIGS. 9 and 10 , the protrusion  12   d  in the recess  23   b  of the lower manifold plate  12   b  is smaller in planar shape than the protrusion  12   d  in the recess  23   a  of the upper manifold plate  12   a . In this configuration, the upper protrusion  12   d  and the lower protrusion  12   d  whose ends are in contact with each other to form a step portion  12   e . The step portion  12   e  serves as a passage of the liquid, which allows the entire common liquid chamber  23  to be smoothly filled with the liquid, which produces a small pressure loss in the common liquid chamber  23 , leading to good liquid supply performance. This configuration also facilitates bonding of the manifold plates  12   a  and  12   b  including the recesses  23   a  and  23   b  together. Alternatively, the step portion may be formed by a structure in which the protrusion  12   d  in the recess  23   b  of the lower manifold plate  12   b  is larger in plan view than the protrusion  12   d  in the recess  23   a  of the manifold plate  12   a . In other words, in the present embodiment, one of the protrusions  12   d  in the recesses  23   a  and  23   b  is smaller in planar shape than the other, and the step portion  12   e  is formed by both of the protrusions  12   d.    
     Fourth Embodiment 
     In a fourth embodiment of the present disclosure, as illustrated in  FIGS. 11 and 12 , the shape of the reinforcing portion  1  is the same as that in the first embodiment, but part of the recess  23   a  of the upper manifold plate  12   a  is a slit-like opening  23   c  passing through the manifold plate  12   a . The opening  23   c  has such a shape that the through holes  18  illustrated in  FIG. 7  are substantially widened and extend in the longitudinal direction of the common liquid chamber  23 . The opposing wall  13   a  constitutes part of the walls of the common liquid chamber  23  at the position of the opening. This configuration increases the capacity of the common liquid chamber  23 , which reduces pressure loss, enhancing the liquid supply performance. 
     Fifth Embodiment 
     In a fifth embodiment of the present disclosure, as illustrated in  FIGS. 13 and 14 , only one manifold plate  12  is disposed between the spacer plate  13  and the ejection port plate  11 . The manifold plate  12  has recesses  23   d  that are open from the upper surface. The recesses  23   d  are covered by the spacer plate  13  (the opposing wall  13   a ) to form the common liquid chamber  23 . Each recess  23   d  is provided with protruding reinforcing portions  1  protruding toward the spacer plate  13 . An end of each reinforcing portion  1  is in contact with the opposing wall  13   a  and joined thereto. The manifold plate  12  of the present embodiment has a thickness substantially twice the thickness of each of the manifold plates  12   a  and  12   b  of the first embodiment. The common liquid chamber  23  of the present embodiment has a capacity equal to or larger than of the capacity of the common liquid chamber  23  of the first embodiment. In this configuration, the spacer plate  13  directly faces the common liquid chamber  23 , and part (the thin-wall portion) of the manifold plate  12  is not interposed between the spacer plate  13  and the common liquid chamber  23  unlike the first embodiment. This increases the capacity of the common liquid chamber  23  and reduces pressure loss, thereby increasing the liquid supply performance. Since only one manifold plate  12  is used, the number of components is decreased, thereby reducing the cost. 
     The liquid ejection head according to an embodiment of the present disclosure allows high-accuracy liquid ejection with high energy efficiency. 
     While the present disclosure has been described with reference to exemplary embodiments, it is to be understood that the disclosure is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2016-173601 filed Sep. 6, 2016, which is hereby incorporated by reference herein in its entirety.