Patent Publication Number: US-10328702-B2

Title: Nozzle plate, liquid ejection head using same, and recording device

Description:
TECHNICAL FIELD 
     The present disclosure relates to a nozzle plate, a liquid ejection head using the same, and a recording device. 
     BACKGROUND ART 
     Known in the art is a method for preparing a nozzle plate used in a liquid ejection head, including exposing a resin reacting with respect to light to prepare a matrix corresponding to a shape of a nozzle, forming a metal plating layer on the periphery of the matrix, and peeling off the metal plating layer (for example see Patent Literature 1). 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: Japanese Patent Publication No. 2006-175678A 
     SUMMARY OF INVENTION 
     A nozzle plate of the present disclosure includes a first surface, a second surface on the opposite side to the first surface, and a plurality of through holes which penetrate through the plate from the first surface to the second surface and become nozzles. Each of the through holes includes, on at least the first surface side forming the side where the liquid is ejected, an inversely tapered part having a cross-sectional area becoming larger toward the first surface. The first surface includes a first region and a second region which is not superimposed on the first region. A first through hole of one the through holes is arranged in the first region. A second through hole of one the through holes is arranged in the second region. When defining the width of the inversely tapered part when viewed from the first surface side as “T”, the width T of the inversely tapered part in the first through hole is larger than the width T of the inversely tapered part in the second through hole. A thickness of the nozzle plate in the first region is thinner than a thickness of the nozzle plate in the second region. 
     Further, a liquid ejection head of the present disclosure includes the nozzle plate, a plurality of pressurizing chambers which are individually linked with the plurality of through holes, and a plurality of pressurizing parts for applying pressure to the plurality of pressurizing chambers. 
     Further, a recording device of the present disclosure includes the liquid ejection head, a conveying part for conveying a recording medium with respect to the liquid ejection head, and a control part which controls the liquid ejection head. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1A  is a side view of a recording device including a liquid ejection head according to an embodiment of the present disclosure, and  FIG. 1B  is a plan view. 
         FIG. 2  A plan view of a head body forming part of the liquid ejection head in  FIGS. 1A and 1B . 
         FIG. 3  An enlarged view of a region surrounded by a one-dot chain line in  FIG. 2  and a plan view after omitting part of the channels for explanatory purposes. 
         FIG. 4  An enlarged view of a region surrounded by a one-dot chain line in  FIG. 2  and a plan view after omitting part of the channels for explanatory purposes. 
         FIG. 5A  is a vertical cross-sectional view along the V-V line in  FIG. 3 , and  FIG. 5B  is an enlarged vertical cross-sectional view of a nozzle  8  in  FIG. 5A . 
         FIG. 6  is a plan view of the head body, and  FIG. 6B  is an enlarged plan view when viewing a nozzle from an ejection hole side. 
         FIGS. 7A to 7E  are schematic cross-sectional views of steps in one method of production for manufacturing a nozzle plate according to an embodiment of the present disclosure, and  FIGS. 7F to 7J  are schematic cross-sectional views of steps in another method of production for manufacturing a nozzle plate according to an embodiment of the present disclosure. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
       FIG. 1A  is a schematic side view of a recording device including liquid ejection heads  2  according to an embodiment of the present disclosure as constituted by a color inkjet printer  1  (below, sometimes simply referred to as a “printer”), and  FIG. 1B  is a schematic plan view. The printer  1  conveys a recording medium of the printing paper P from guide rollers  82 A to conveying rollers  82 B to thereby make the printing paper P move relative to the liquid ejection heads  2 . A control part  88  controls the liquid ejection heads  2  based on image or text data to make them eject liquid toward the printing paper P and shoot droplets onto the printing paper P to thereby perform recording such as printing on the printing paper P. 
     In the present embodiment, the liquid ejection heads  2  are fixed with respect to the printer  1 , so the printer  1  becomes a so-called line printer. As another embodiment of the recording device of the present invention, there can be mentioned a so-called serial printer which alternately performs an operation of moving the liquid ejection heads  2  to reciprocate or the like in a direction crossing the conveying direction of the printing paper P, for example, a substantially perpendicular direction, and conveyance of the printing paper P. 
     To the printer  1 , a plate-shaped head mounting frame  70  (below, sometimes simply referred to as a “frame”) is fixed so that it becomes substantially parallel to the printing paper P. The frame  70  is provided with not shown  20  holes. Twenty liquid ejection heads  2  are mounted in the hole portions. The portions of the liquid ejection heads  2  which eject the liquid face the printing paper P. A distance between the liquid ejection heads  2  and the printing paper P is set to for example about 0.5 to 20 mm. Five liquid ejection heads  2  configure one head group  72 . The printer  1  has four head groups  72 . 
     A liquid ejection head  2  has a long shaped elongated in a direction from the front to the inside in  FIG. 1A  and in the up-down direction in  FIG. 1B . This long direction will be sometimes called as the “longitudinal direction”. In one head group  72 , three liquid ejection heads  2  are aligned in a direction crossing the conveying direction of the printing paper P, for example, a substantially perpendicular direction. The other two liquid ejection heads  2  are aligned at positions offset along the conveying direction so that each is arranged between two among the three liquid ejection heads  2 . The liquid ejection heads  2  are arranged so that ranges which can be printed by the liquid ejection heads  2  are connected in the width direction of the printing paper P (in the direction crossing the conveying direction of the printing paper P) or the ends overlap each other, therefore printing without a gap becomes possible in the width direction of the recording medium P. 
     The four head groups  72  are arranged along the conveying direction of the printing paper P. To each liquid ejection head  2 , a liquid, for example, ink, is supplied from a not shown liquid tank. To the liquid ejection heads  2  belonging to one head group  72 , ink of the same color is supplied. Inks of four colors can be printed by the four head groups  72 . The colors of inks ejected from the head groups  72  are for example magenta (M), yellow (Y), cyan (C), and black (K). If printing such inks is carried out by controlling by the control part  88 , color images can be printed. 
     The number of liquid ejection heads  2  mounted in the printer  1  may be one as well so far as printing is carried out for a range which can be printed by one liquid ejection head  2  in a single color. The number of liquid ejection heads  2  included in the head group  72  or the number of head groups  72  can be suitably changed according to the target of printing or printing conditions. For example, the number of head groups  72  may be increased as well in order to perform printing by further multiple colors. Further, if a plurality of head groups  72  for printing in the same color are arranged and printing is alternately carried out in the conveying direction, the conveying speed can be made faster even if liquid ejection heads  2  having the same performances are used. Due to this, the printing area per time can be made larger. Further, it is also possible to raise the resolution in the width direction of the printing paper P by preparing a plurality of head groups  2  for printing in the same color and arranging them offset in a direction crossing the conveying direction. 
     Further, other than printing colored inks, a coating agent or other liquid may be printed as well in order to treat the surface of the printing paper P. 
     The printer  1  performs printing on the recording medium of the printing paper P. The printing paper P is wound around the paper feed roller  80 A. After passing between the two guide rollers  82 A, it passes under the liquid ejection heads  2  mounted in the frame  70 . After that, it passes between the two conveying rollers  82 B and is finally collected by the collection roller  80 B. When printing, by rotation of the conveying rollers  82 B, the printing paper P is conveyed at a constant speed, and printing is carried out by the liquid ejection heads  2 . The collection roller  80 B takes up the printing paper P fed out from the conveying rollers  82 B. The conveying speed is set to for example 75 m/min. Each roller may be controlled by the control part  88  or may be operated manually by a person. 
     The recording medium may be a roll of fabric or the like other than printing paper P. Further, the printer  1 , in place of directly conveying the printing paper P, may directly convey a conveyor belt and carry the recording medium on the conveyor belt to convey it. When performing this, a sheet, cut fabric, wood, tile, etc. can be used as the recording medium. Further, a liquid containing conductive particles may be ejected from the liquid ejection heads  2  to print a wiring pattern etc. of an electronic apparatus as well. Furthermore, predetermined amounts of liquid chemical agents or liquids containing chemical agents may be ejected from the liquid ejection heads  2  toward a reaction vessel or the like to cause a reaction etc. and thereby prepare pharmaceutical products. 
     Further, a position sensor, speed sensor, temperature sensor, and the like may be attached to the printer  1 , and the control part  88  may control the portions in the printer  1  in accordance with the states of the portions in the printer  1  seen from the information from the sensors. For example, when the temperature of the liquid ejection heads  2  or temperature of the liquid in the liquid tank, the pressure applied by the liquid in the liquid tank to the liquid ejection heads  2 , and so on exert an influence upon the ejection amount, ejection speed, and other ejection characteristics of the ejected liquid, a driving signal for ejecting the liquid may be changed in accordance with that information as well. 
     Next, a liquid ejection head  2  according to an embodiment of the present disclosure will be explained.  FIG. 2  is a plan view showing a head body  13  forming a principal part of a liquid ejection head  2  shown in  FIGS. 1A and 1B .  FIG. 3  is an enlarged plan view of a region surrounded by a one-dot chain line in  FIG. 2  and a view showing a portion of the head body  13 .  FIG. 4  is an enlarged view of the same position as  FIG. 3 .  FIG. 3  and  FIG. 4  are drawn while omitting part of the channels for facilitating understanding of the drawings. Further, in  FIG. 3  and  FIG. 4 , for facilitating understanding of the drawings, the pressurizing chambers  10 , apertures  12 , nozzles  8 , etc. which are located below piezoelectric actuator substrates  21  and so should be drawn by broken lines are drawn by solid lines.  FIG. 5A  is a vertical cross-sectional view along the V-V line in  FIG. 3 , while  FIG. 5B  is an enlarged vertical cross-sectional view of a nozzle  8 .  FIG. 6A  is a plan view of the head body  13 , and  FIG. 6B  is an enlarged plan view when viewing the nozzle  8  located at the position of B in  FIG. 6A  from the ejection hole  8   d  side. 
     The head body  13  has a plate-shaped channel member  4  and piezoelectric actuator substrates  21  on the channel member  4 . The channel member  4  is made by stacking a nozzle plate  31  having nozzles  8  and a channel member body formed by stacking plates  22  to  30 . The piezoelectric actuator substrates  21  have trapezoidal shapes and are arranged on the upper surface of the channel member  4  so that pairs of parallel facing sides of the trapezoids become parallel to the longitudinal direction of the channel member  4 . Further, along each of two virtual straight lines which are parallel to the longitudinal direction of the channel member  4 , two each piezoelectric actuator substrates  21  are arranged, that is, a total of four are arranged on the channel member  4  in a zigzag manner as a whole. Slanted sides of the piezoelectric actuator substrates  21  which are adjacent to each other on the channel member  4  partially overlap in the traverse direction of the channel member  4 . In a region printed by driving the piezoelectric actuator substrates  21  in these overlapped portions, the droplets ejected by the two piezoelectric actuator substrates  21  are shot while mixed. 
     Inside the channel member  4 , manifolds  5  are formed as parts of the liquid channel. The manifolds  5  have elongated shapes extending along the longitudinal direction of the channel member  4 . Openings  5   b  of the manifolds  5  are formed in the upper surface of the channel member  4 . There are  10  openings  5   b . Five each are formed along the two straight lines which are parallel to the longitudinal direction of the channel member  4 . The openings  5   b  are formed at positions avoiding the region in which the four piezoelectric actuator substrates  21  are arranged. Into the manifolds  5 , liquid is supplied through the openings  5   b  from a not shown liquid tank. 
     Each manifold  5  formed in the channel member  4  is branched into a plurality of parts (a branched part of a manifold  5  will be sometimes referred to as a “sub-manifold  5   a ”). The manifold  5  linked with an opening  5   b  extends so as to be run along a slanted side of a piezoelectric actuator substrate  21  and is arranged so as to cross the longitudinal direction of the channel member  4 . In a region sandwiched between two piezoelectric actuator substrates  21 , one manifold  5  is shared by adjoining piezoelectric actuator substrates  21 . Sub-manifolds  5   a  are branched from the two sides of the manifold  5 . These sub-manifolds  5   a  extend in the longitudinal direction of the head body  13  so that they are adjacent to each other in regions facing the piezoelectric actuator substrates  21  inside the channel member  4 . 
     The channel member  4  has four pressurizing chamber groups  9  in which pluralities of pressurizing chambers  10  are formed in matrices (that is two-dimensionally and regularly). A pressurizing chamber  10  is a hollow region having a substantially diamond shaped planar shape having rounded corner portions. The pressurizing chamber  10  is formed so as to open in the upper surface of the channel member  4 . These pressurizing chambers  10  are arranged over substantially the entire surfaces of the regions facing the piezoelectric actuator substrates  21  at the upper surface of the channel member  4 . Accordingly, each pressurizing chamber group  9  formed by these pressurizing chambers  10  occupies a region having substantially the same size and shape as those of a piezoelectric actuator substrate  21 . Further, the opening of each pressurizing chamber  10  is closed by bonding the piezoelectric actuator substrate  21  to the upper surface of the channel member  4 . 
     In the present embodiment, as shown in  FIG. 3 , each manifold  5  is branched into four lines of E 1  to E 4  sub-manifolds  5   a  arranged in the transverse direction of the channel member  4  parallel to each other. The pressurizing chambers  10  linked with each sub-manifold  5   a  configure a column of the pressurizing chambers  10  arranged at equal intervals in the longitudinal direction of the channel member  4 . Four of those columns are arranged in the transverse direction in parallel to each other. On the two sides of each sub-manifold  5   a , two columns each of pressurizing chambers  10  linked with the sub-manifold  5   a  are arranged. 
     Overall, the pressurizing chambers  10  connected from a manifold  5  configure columns of pressurizing chambers  10  which are arranged at equal intervals in the longitudinal direction of the channel member  4 . Sixteen of those columns are arranged in the transverse direction in parallel to each other. The pressurizing chambers  10  included in the columns of pressurizing chambers are arranged so that their numbers gradually decrease from the long side of the actuator formed by a displacement element  50  toward the short side corresponding to the outer shape. 
     The nozzles  8  are arranged at substantially equal intervals of about 42 μm (interval of 25.4 mm/150=42 μm in a case of 600 dpi) in the resolution direction of the head body  13 , that is, the longitudinal direction. Due to this, the head body  13  can form an image with a resolution of 600 dpi in the longitudinal direction. In the part where the trapezoid-shaped piezoelectric actuator substrates  21  overlap, the nozzles  8  located below the two piezoelectric actuator substrates  21  are arranged so as to complement each other. Due to this, the nozzles  8  are arranged in the longitudinal direction of the head body  13  at intervals corresponding to 600 dpi. 
     Further, at each sub-manifold  5   a , individual channels  32  are connected at intervals corresponding to 150 dpi on an average. This means that, when designing 600 dpi worth of nozzles  8  linked divided among four sub-manifolds  5   a , since the individual channels  32  to be linked with each sub-manifold  5   a  are not always linked at equal intervals, the individual channels  32  are formed in directions of extension of the manifold  5   a , that is, in a main scanning direction at intervals not more than 170 μm on average (intervals of 25.4 mm/150=169 μm in a case of 150 dpi). 
     At positions facing the pressurizing chambers  10  in the upper surfaces of the piezoelectric actuator substrates  21 , later explained individual electrodes  35  are formed. The individual electrodes  35  are one size smaller than the pressurizing chambers  10  but have substantially the same shapes as those of the pressurizing chambers  10  and are arranged so as to fit into the regions facing the pressurizing chambers  10  in the upper surfaces of the piezoelectric actuator substrates  21 . 
     In the ejection hole surface  31   a  at the bottom of the channel member  4 , a large number of ejection holes  8   d  open as openings on the lower sides of the nozzles  8 . The nozzles  8  are arranged at positions avoiding the regions facing the sub-manifolds  5   a  arranged on the lower surface side of the channel member  4 . Further, the nozzles  8  are arranged in the regions facing the piezoelectric actuator substrates  21  on the lower surface side of the channel member  4 . An ejection hole group of the ejection holes  8  occupies a region having substantially the same size and shape as a piezoelectric actuator substrate  21 . The droplets can be ejected from the ejection holes  8   d  by displacing the corresponding displacement element  50  of the piezoelectric actuator substrate  21 . Further, the nozzles  8  in each ejection hole group are arranged at equal intervals along a plurality of straight lines parallel to the longitudinal direction of the channel member  4 . 
     The channel member  4  included in the head body  13  has a multilayer structure formed by stacking a plurality of plates. These plates, from the upper surface of the channel member  4 , include a cavity plate  22 , base plate  23 , aperture plate  24 , supply plates  25  and  26 , manifold plates  27 ,  28 , and  29 , cover plate  30 , and nozzle plate  31 . These plates are formed with large numbers of holes. The plates are stacked while positioning them so that these holes communicate with each other and form the individual channels  32  and sub-manifolds  5   a . The head body  13 , as shown in  FIGS. 5A and 5B , is configured so that the portions configuring the individual channels  32  are arranged at different positions so as to be close to each other, for example the pressurizing chambers  10  are arranged at the upper surface of the channel member  4 , the sub-manifolds  5   a  are arranged at the lower surface side at the inside, and the ejection holes  8   d  are arranged at the bottom surface and so that the sub-manifolds  5   a  and the ejection holes  8   d  are linked through the pressurizing chambers  10 . 
     The holes formed in the plates will be explained. These holes include the following: First, there are the pressurizing chambers  10  formed in the cavity plate  22 . Second, there are the communication holes which form channels connected from ends of the pressurizing chambers  10  to the sub-manifolds  5   a . The communication holes are formed in each of the plates from the base plate  23  (in more detail, the entrances of the pressurizing chambers  10 ) up to the supply plate  25  (in more detail, the exits of the sub-manifolds  5   a ). Note that, the communication holes include the apertures  12  formed in the aperture plate  24  and the individual supply channels  6  formed in the supply plates  25  and  26 . 
     Third, there are the communication holes which form channels connected from the other ends of the pressurizing chambers  10  to the ejection holes  8   d . These communication holes will be called “descenders” (partial channels) in the following description. The descenders are formed in each of the plates from the base plate  23  (in more detail, the exits of the pressurizing chambers  10 ) up to the nozzle plate  31  (in more detail, the ejection holes  8   d ). The ejection hole  8   d  sides of the descenders are particularly small in cross-sectional areas and form the nozzles  8  at the nozzle plate  31 . Details of the shapes of the nozzles  8  will be explained later. 
     Fourth, there are the communication holes which form the sub-manifolds  5   a . These communication holes are formed in the manifold plates  27  to  30 . 
     Such communication holes are linked with each other and configure the individual channels  32  from the inflowing ports of the liquid from the sub-manifolds  5   a  (the exits of the sub-manifolds  5   a ) up to the ejection holes  8   d . The liquid supplied to the sub-manifolds  5   a  is ejected from the ejection holes  8   d  by the following route. First, the liquid runs from the sub-manifold  5   a  toward the upward direction through the individual supply channels  6  and reaches first end parts of the apertures  12 . Next, it advances horizontally along the directions of extension of the apertures  12  and reaches the other end parts of the apertures  12 . From there, it proceeds in the upward direction and reaches first end parts of the pressurizing chambers  10 . Further, it advances horizontally along the directions of extension of the pressurizing chambers  10  and reaches the other end parts of the pressurizing chambers  10 . From there, it mainly goes downward while moving in the horizontal direction little by little and advances to the ejection holes  8   d  opened in the bottom surface. 
     Each piezoelectric actuator substrate  21 , as shown in  FIGS. 5A and 5B , has a multilayer structure comprised of two piezoelectric ceramic layers  21   a  and  21   b . Each of these piezoelectric ceramic layers  21   a  and  21   b  has a thickness of about 20 μm. The thickness of the part of the piezoelectric actuator substrate  21  displacing, that is, the displacement element  50 , is about 40 μm. By being not more than 100 μm, the amount of displacement can be made large. Both of the piezoelectric ceramic layers  21   a  and  21   b  extend across a plurality of pressurizing chambers  10  (see  FIG. 3 ). These piezoelectric ceramic layers  21   a  and  21   b  are made of a lead zirconate titanate (PZT)-based ceramic material having ferroelectricity. 
     Each piezoelectric actuator substrate  21  has a common electrode  34  made of Ag—Pd or another metal material and individual electrodes  35  made of Au or another metal material. The individual electrodes  35  are arranged on the upper surface of the piezoelectric actuator substrate  21  at positions facing the pressurizing chambers  10  as explained above. One end of each individual electrode  35  is configured by an individual electrode body  35   a  facing a pressurizing chamber  10  and an lead out electrode  35   b  which is led out to the outside of the region facing the pressurizing chamber  10 . 
     The piezoelectric ceramic layers  21   a  and  21   b  and common electrode  34  have substantially the same shapes. Therefore, if preparing these by simultaneous firing, the warping can be kept small. A piezoelectric actuator substrate  21  of 100 μm or less easily warps in the firing process. The amount becomes large as well. Further, if warping occurs, when stacking the substrate on the channel member  4 , the parts are joined by causing that warped part to deform, therefore the deformation at that time influents fluctuation of the characteristics of the displacement element  50  and consequently leads to variation of the liquid ejection characteristics. Therefore, the warping is desirably a small one of at most the same extent as the thickness of the piezoelectric actuator substrate  21 . Further, in order to reduce warping due to a difference of behavior in shrinking during firing between a location where there is an internal electrode and a location where there isn&#39;t, the internal electrode of the common electrode  34  is formed flat without projecting patterns at the inside. Note that, here, “the substantially the same shapes” means that the difference in the dimensions at the peripheries is not more than 1% of the widths of those portions. The peripheries of the piezoelectric ceramic layers  21   a  and  21   b  are basically formed by cutting the layers before firing in a state where they are superimposed on each other, therefore their positions become the same within a range of processing accuracy. The common electrode  34  is also resistant against warping if formed by cutting it at the same time as the piezoelectric ceramic layers  21   a  and  21   b  after solid printing. However, by printing it by patterns with similar shapes to the piezoelectric ceramic layers  21   a  and  21   b  but a bit smaller, the common electrode  34  is no longer exposed at the side surfaces of the piezoelectric actuator  21 , therefore the electrical reliability becomes higher. 
     Details will be explained later, but the individual electrodes  35  are supplied with driving signals (drive voltages) from the control part  88  through an FPC (flexible printed circuit) as external wiring. The driving signals are supplied by a constant period synchronous with the conveying speed of the printing paper P. The common electrode  34  is formed over substantially the entire surface in the surface direction in the region between the piezoelectric ceramic layer  21   a  and the piezoelectric ceramic layer  21   b . That is, the common electrode  34  extends so as to cover all pressurizing chambers  10  in the regions facing the piezoelectric actuator substrates  21 . The thickness of the common electrode  34  is about 2 μm. The common electrode  34  is grounded in a not shown region and is held at the ground potential. In the present embodiment, a surface electrode (not shown) different from the individual electrodes  35  is formed on the piezoelectric ceramic layer  21   b  at a position avoiding the group of electrodes configured by the individual electrodes  35 . The surface electrode is electrically connected to the common electrode  34  through a through-hole formed inside the piezoelectric ceramic layer  21   b  and is connected to external wiring in the same way as the large number of individual electrodes  35 . 
     Note that, as will be explained later, predetermined driving signals are selectively supplied to the individual electrodes  35 . Due to this, pressure is applied to the liquid in the pressurizing chambers  10  corresponding to the individual electrodes  35 . Due to this, through the individual channels  32 , droplets are ejected from the corresponding ejection holes  8 . That is, the portions facing the pressurizing chambers  10  in the piezoelectric actuator substrates  21  correspond to the individual displacement elements  50  (actuators) corresponding to the pressurizing chambers  10  and ejection holes  8 . That is, in the stacked body configured by the two piezoelectric ceramic layers, a displacement element  50  having the structure as shown in  FIG. 5  as a unit structure is assembled for each pressurizing chamber  10  by portions of vibration plate  21   a , common electrode  34 , piezoelectric ceramic layer  21   b , and individual electrodes  35  right above the pressurizing chamber  10 . The piezoelectric actuator substrates  21  include pluralities of displacement elements  50 . Note that, in the present embodiment, the amount of the liquid which is ejected from an ejection hole  8  by one ejection operation is about 5 to 7 μL (picoliters). 
     When viewing a piezoelectric actuator substrate  21  on a plane, the individual electrode bodies  35   a  are arranged so as to be superimposed on the pressurizing chambers  10 . The part of the piezoelectric ceramic layer  21   b  positioned at the center of a pressurizing chamber  10  and sandwiched between an individual electrode  35  and the common electrode  34  is polarized in the stacking direction of the piezoelectric actuator substrate  21 . The orientation of polarization may be upward or downward. By giving a driving signal corresponding to that direction, driving can be carried out. 
     As shown in  FIG. 5 , the common electrode  34  and the individual electrodes  35  are arranged so as to sandwich only the piezoelectric ceramic layer  21   b  at the uppermost layer. A region in the piezoelectric ceramic layer  21   b  which is sandwiched between an individual electrode  35  and the common electrode  34  is called an “active portion”. Polarization is applied in the thickness direction to the piezoelectric ceramic in that portion. In a piezoelectric actuator substrate  21  in the present embodiment, only the piezoelectric ceramic layer  21   b  at the uppermost layer includes active portions. The piezoelectric ceramic  21   a  does not include active portions and acts as a vibration plate. This piezoelectric actuator substrate  21  has a so-called unimorph type configuration. 
     In an actual driving procedure in the present embodiment, the individual electrodes  35  are rendered a potential higher than the common electrode  34  (below, referred to as a “high potential”) in advance. Whenever there is an ejection request, the individual electrodes  35  are once rendered the same potential as that of the common electrode  34  (below, referred to as a “low potential”), then are again rendered the high potential at a predetermined timing. Due to this, at the timing when the individual electrodes  35  become the low potential, the piezoelectric ceramic layers  21   a  and  21   b  return to their original shapes, therefore the capacities of the pressurizing chambers  10  increase compared with the initial state (state where the potentials of the electrodes are different). At this time, negative pressures are given to the interiors of the pressurizing chambers  10 , and liquid is sucked into the pressurizing chambers  10  from the manifold  5  sides. After that, at the timing when the individual electrodes  35  are rendered the high potential again, the piezoelectric ceramic layers  21   a  and  21   b  deform so as to protrude to the pressurizing chamber  10  sides, and the capacities of the pressurizing chambers  10  are reduced. By this, the pressures in the pressurizing chambers  10  become positive pressures, the pressures to the liquid rise, and droplets are ejected. That is, in order to eject droplets, driving signals including pulses based on the high potential are supplied to the individual electrodes  35 . This pulse width is ideally the AL (acoustic length) duration of propagation of a pressure wave from the manifolds  5  to the ejection holes  8   d  in the pressurizing chambers  10 . According to this, when the internal portions of the pressurizing chambers  10  invert from the negative pressure state to the positive pressure state, pressures of the two are combined, and the droplets can be ejected under a stronger pressure. 
     As explained above, each nozzle  8  is a through hole formed in the nozzle plate  31 . Further, the nozzles  8  are arranged in the same regions as the four trapezoidal-shaped pressurizing chamber groups  9  shown in  FIG. 2 . The nozzles  8  in the head body  13  are arranged in the nozzle arrangement region  7  formed by combining trapezoidal shapes (see  FIG. 6A ). The nozzle arrangement region  7  has unevenness due to the combination of trapezoids but is roughly a rectangular region which is long in the longitudinal direction of the head body  13  as a whole. 
     A “center part  7   a ” of the nozzle arrangement region  7  means a region which is positioned at the center and has a length of ⅕ of the whole when equally dividing the nozzle arrangement region  7  into five sections in the longitudinal direction. Further, the “end parts  7   b ” of the nozzle arrangement region  7  mean the two regions positioned on the ends each having a length of ⅕ of the whole when equally dividing the nozzle arrangement region  7  into five sections in the longitudinal direction. The end part  7   b  positioned on the left side will be sometimes referred to as the “first end part  7   ba ”, while the end part positioned on the right side will be sometimes referred to as the “second end part  7   bb ”. Note that, in this embodiment, the center part  7   a  and end parts  7   b  in the longitudinal direction of the nozzle arrangement region  7  are explained, but the center part and end parts in another direction may be rendered the state similar to this explanation as well. 
     The thickness of the nozzle plate  31 , that is, the length of each nozzle  8 , is for example 20 to 100 μm. In order to make the fluid resistance of the nozzle  8  low, the thickness of the nozzle plate  31  is desirably as thin as possible. However, if it is too thin, handling in manufacturing becomes difficult. Therefore, the thickness is set at the optimum value as a thickness where both can be achieved. The shape of the cross-section of the nozzle  8  is preferably circular, however, it may also be elliptical, triangular, square, or another rotary symmetrical shape. The shape of the portion in the nozzle  8  which has the smallest cross-sectional area is for example a circle having a diameter of 10 to 60 μm. The diameter of the portion having the smallest cross-sectional area is the control factor for setting the ejection amount and is set in accordance with the desired ejection amount. 
     One opening of each nozzle  8  is an ejection hole  8   d  which opens to the outside of the channel member  4  and is an opening at the side where the liquid is ejected. Further, the other opening of the nozzle  8  is an internal opening  8   c  which opens toward the inside of the channel member  4  and is an opening at the side where the liquid is supplied. 
     This means the following when viewing the nozzle plate  31  alone. One surface of the nozzle plate  31  forms a first surface  31   a  which forms a surface on the side from which the liquid flies out, that is, the ejection hole surface  31   a , while the surface on the opposite side to the first surface  31   a  forms a second surface  31   b . The through holes which form the nozzle  8  penetrate from the first surface  31   a  to the second surface  31   b . The openings of the through holes in the first surface (ejection hole surface)  31   a  side form the ejection holes  8   d , while the openings of the through holes in the second surface  31   b  side form the internal openings  8   c.    
     Each nozzle  8 , on the ejection hole  8   d  side, includes the inversely tapered part  8   b  in which the cross-sectional area of the opening becomes larger toward the ejection hole  8   d . The inversely tapered part  8   b , when viewed from the ejection hole  8   d  side, that is, from the ejection hole surface  31   a  side, looks like a ring-shaped region on the periphery of a circular portion penetrating through the nozzle plate  31 . The width of this ring-shaped region in the case where it is viewed from the ejection hole  8   d  side will be defined as the width T of the inversely tapered part  8   b  (this will be sometimes simply be referred to as the “width T”). The width T will be explained by using  FIG. 6B .  FIG. 6B  is a plan view when viewing the nozzle  8  from the ejection hole  8   d  side. The inversely tapered part  8   b  appears like it is ring shaped. L 1  is a virtual straight line along the longitudinal direction of the liquid ejection head  2 . The widths of the facing portions in the inversely tapered part  8   b  along L 1  are T 1   a  [μm] and T 1   b  [μm]. L 2  is the direction in which the liquid ejection head  2  and the recording medium are relatively conveyed at the time of printing. The widths of the facing portions along L 2  in the inversely tapered part  8   b  are T 2   a  [μm] and T 2   b  [μm]. 
     The width T will be explained another way using  FIG. 5B . The nearest point A is the narrowest part of the nozzle  8 . The length from the outside of the diameter D at the nearest point A up to the edge of the opening of the ejection hole  8   d , that is, the boundary between the nozzle  8  and the ejection hole surface  31   a , along the ejection hole surface  31   a , is the width T. In  FIG. 5B , the widths T at two facing locations are shown as T 2   a  [μm] and T 2   b  [μm]. 
     The width T of the inversely tapered part  8   b  in one nozzle  8  is the average of the widths T of different parts of the inversely tapered part  8   b  in that nozzle  8  and can be measured by for example calculating a mean value of T 1   a , T 1   b , T 2   a , and T 2   b . In one nozzle  8 , if the variation of the widths of the inversely tapered part  8   b  due to the location is small, one portion may be measured and that value may be defined as the width T of that nozzle  8 . Further, the surface area of the inversely tapered part  8   b  when viewed from the ejection hole  8   d  side may be divided by the length of the outer circumference of the ejection hole  8   b  to calculate the width T of the nozzle  8  as well. 
     If the width T becomes large, the liquid builds up from the ejection hole surface  31   a , therefore when the liquid flies off from the ejection hole surface  31   a , the force pulling the liquid back into the nozzle  8  becomes large. That is, if the width T becomes large, the speed of flight of the liquid falls. Further, if the width T becomes large, part of the liquid does not fly off, but is pulled back into the nozzle  8 , therefore the amount of the ejected liquid becomes small. These actions may be due to the surface tension of the liquid. 
     Further, when the length of a nozzle  8  becomes longer, the fluid resistance of the nozzle  8  becomes larger, therefore the speed of flight of the liquid falls. The length of a nozzle  8  is the thickness of the nozzle plate  31 , therefore the speed of flight of the liquid which is ejected from a nozzle  8  located in a thick portion of the nozzle plate  31  becomes lower. 
     The width T and the thickness of the nozzle plate  31  are desirably constant in the nozzle plate  31 . However, as will be explained later, due to conditions in the manufacturing processes, they are sometimes tend to vary with certain distributions in the nozzle plate  31 . Therefore, it may be considered to reduce the variation of speed of flight by controlling the distributions in the nozzle plate  31  to cancel out their influences with each other. 
     The first surface of the nozzle plate  31  comprised of the ejection hole surface  31   a  is provided with a first region and a second region which is not superimposed on the first region. In the embodiment explained above, for example, the center part  7   a  can be provided as the first region, and the end parts  7   b  can be provided as second regions. Conversely, the center part  7   a  can be provided as the second region, and the end parts  7   b  can be provided as first regions. Further, a region which is different from the center part  7   a  and end parts  7   b  can be provided as the first region or second region as well. 
     A nozzle (through hole)  8  arranged in the first region will be defined as a “first nozzle” (first through hole), and a nozzle (through hole)  8  arranged in the second region will be defined as a “second nozzle” (second through hole). The width T of the first nozzle is made larger than the width T of the second nozzle, and the thickness of the nozzle plate  31  in the first region becomes thinner than the thickness of the nozzle plate  31  in the second region. By doing this, the influence by the width T and the influence by the thickness of the nozzle plate  31  are cancelled out, therefore it is possible to reduce the difference between the speed of flight of the droplets ejected from the first nozzle in the first region and the speed of flight of the droplets ejected from the second nozzle in the second region. 
     The number of nozzles  8  included in each region only has to be one or more. There are no restrictions on the breadth and arrangement of each region. It is unnecessary that the widths T of all nozzles  8  in the first region are larger than the widths T of all nozzles  8  in the second region. The average of the widths T of the nozzles  8  in the first region only has to be larger than the average width T of the nozzles  8  in the second region. The average in each region may be obtained by measuring all nozzles  8  and calculating the average of the results if there are five or less. If there are more than five, the average may be obtained by measuring the nozzle  8  near the center of the region and, based on that center, the four nozzles  8  which are most distant from that center in the four directions each different by 90 degrees and calculating the average of the results. Note that, in a case where four nozzles  8  corresponding to such conditions do not exist, and only three or two exist, the corresponding three or two may be calculated. The thickness of the nozzle plate  31  may be measured so as to include the nozzles  8  measured in its width T. 
     Even if the difference of speed of flight is reduced by cancellation, the ranges of changes of the width T and the thickness of the nozzle plate  31  are desirably small in the nozzle plate  31 . There is a case where the width T and the thickness of the nozzle plate  31  change by certain trends in the nozzle plate  31  related to the manufacturing conditions. In such case, those tendencies are controlled and the ranges of changes are made small. Specifically, in a predetermined direction of the nozzle plate  31 , a second region, first region, and second region are arranged in that order or a first region, second region, and first region are arranged in that order. When a second region, first region, and second region are arranged in that order, concerning the width T, a region having a narrow width T, a region having a broad width T, and a region having a narrow width T are arranged. Concerning the thickness, a thin region, a thick region, and a thin region are arranged. By setting the manufacturing conditions so that such trends are caused, the ranges of changes in the width T and the thickness of the nozzle plate  31  can be made smaller. 
     The changes of the width T and the thickness of the nozzle plate  31  become large in the direction where the spread of the nozzle arrangement region  7  is large. That is, when the nozzle arrangement region  7  is long in one direction, the changes become large in the longitudinal direction. Therefore, desirably a second region, first region, and second region are arranged in that order in the longitudinal direction or a first region, second region, and first region are arranged in that order. Further, in order to make the difference of speed of flight in the entire area of the nozzle plate  31  small, preferably the center part  7   a  of the nozzle plate  31  is set to become the first region and the end parts  7   b  on the two ends to become the second regions or the center part  7   a  is set to become the second region and the end parts  7   b  on the two ends are set to become the first regions. 
     Next, the case where the center part  7   a  of the nozzle plate  31  is the first region and the end parts on the two ends are the second regions will be further explained. Also in an inverse case, the relationships between the width T and the thickness of the nozzle plate  31  and the speed of flight become the same as that in the following explanation. 
     The center part  7   a  of the nozzle plate  31  being the first region and the end parts  7   b  on the two ends being second regions means that the width T is broad in the center part  7   a  and is narrow at the end parts  7   b  on the two ends. In the method of production of the nozzle plate  31  which will be explained later, the width T sometimes exhibits such a trend. Therefore, by making the thickness of the nozzle plate  31  thin at the center part  7   a , but thick at the two end parts, the influence due to the tendency of the width T can be cancelled out. 
     For example, assume that, at the second regions of the end parts on the two sides of the nozzle plate  31 , the thickness of the nozzle plate  31  is 40 μm, the width T is 1 μm, and the speed of flight is 7 m/s. At the first region of the center part  7   a  of the nozzle plate  31 , if the width T is 2.6 μm, the speed of flight falls by about 0.7 m/s due to the influence of that. Further, if the thickness of the center part  7   a  of the nozzle plate  31  is made 35 μm, the speed of flight rises by about 0.7 m/s due to the influence of that. Accordingly, those influences are cancelled out by each other, so the speed of flight at the center part  7   a  can be controlled to about 7 m/s. 
     In order to reduce the variation in the speed of flight, desirably a difference between the width T at the first end part  7   ba , defined as the width TE 1 , and the width T at the second end part  7   bb , defined as the width TE 2 , is small. The degree of influence upon the speed of flight is considered to be not the value of difference itself, but the ratio of difference relative to TE 1  and TE 2 . Therefore, when evaluating (absolute value in difference between TE 1  and TE 2 )/(mean value of TE 1  and TE 2 ), that value is preferably ⅕ or less, further preferably 1/10, particularly preferably 1/20. Note that, the width TE 1  of the first end part  7   ba  and the width TE 2  of the second end part  7   bb  may be measured in the same way as the widths T of the first region and the second region. 
     In the case explained above, if the average of the end parts on the two sides is 1 μm, while the width TE 1  of the first end part  7   ba  is 0.6 μm and the width TE 2  of the second end part  7   bb  is 1.4 μm, (TE 2 −TE 1 )/[(TE 1 +TE 2 )/2] becomes equal to 0.2, that is, ⅕. That is, the difference between the width TE 1  and the width TE 2  is preferably made this or lower. 
     In order to make the variation of speed of flight small, desirably the difference between a thickness DE 1  of the nozzle plate  31  at the first end part  7   ba  and a thickness DE 2  at the second end part  7   bb  is small. The degree of influence upon the speed of flight is considered to be not the value of the difference itself, but the ratio of difference relative to DE 1  and DE 2 . Therefore, when evaluating (absolute value in difference between DE 1  and DE 2 )/(mean value of DE 1  and DE 2 ), that value is preferably 1/20 or less, further preferably 1/40, and particularly preferably 1/80. Here, the reason why this numerical value has become smaller than the numerical value for the width T is that the thickness of the nozzle plate  31  exerts a larger influence upon the speed of flight than the width T. Note that, the thickness DE 1  of the first end part  7   ba  and the thickness DE 2  of the second end part  7   bb  may be measured in the same way as the thicknesses in the first region and second region. 
     In the case explained above, if the average of the two end parts was 40 μm, while the thickness DE 1  of the first end part  7   ba  is 43.5 μm, and the thickness DE 2  of the second end part  7   bb  is 36.5 μm, (DE 2 −DE 1 )/[(DE 1 +DE 2 )/2] becomes equal to about 0.043. That is, the difference between the thickness DE 1  and the thickness DE 2  is preferably made this extent or lower. 
     Preferably the influence due to the width T and the influence due to the thickness of the nozzle plate  31  are cancelled out also between the first end part  7   ba  and the second end part  7   bb . That is, when the width TE 2  of the second end part  7   bb  is larger than the width TE 1  of the first end part  7   ba , the thickness DE 1  of the nozzle plate  31  at the first end part  7   ba  is preferably thinner than the thickness DE 2  of the nozzle plate  31  at the second end part  7   bb . Conversely, when the width TE 2  of the second end part  7   bb  is smaller than the width TE 1  of the first end part  7   ba , the thickness DE 1  of the nozzle plate  31  at the first end part  7   ba  is preferably thicker than the thickness DE 2  of the nozzle plate  31  at the second end part  7   bb.    
     The width T of an inversely tapered part  8   b  is preferably 4 μm or less. The length of the inversely tapered part  8   b , i.e., by another expression, the depth of the inversely tapered part  8   b , is preferably 10 μm or less, more preferably 5 μm or less. The longer the length of the inversely tapered part  8   b , the easier the variation in the meniscus position at the time of ejection and the easier the variation in the ejection direction. Therefore, the length of the inversely tapered part  8   b  is preferably short. 
     Each nozzle  8  includes at the internal opening  8   c  side the tapered part  8   a  in which the cross-sectional area of the opening becomes larger toward the internal opening  8   c . The internal opening  8   c  of the tapered part  8   a  is inclined by an angle θ relative to the direction perpendicular to the nozzle plate  31 . θ is preferably 10 to 30 degrees. The inclination of the tapered part  8   a  is substantially constant over at least a half of the length of the tapered part  8   a  on the internal opening  8   c  side. The inclination gradually becomes gentler the further to the ejection hole  8   d  side from the portion having substantially a constant inclination resulting in linkage with the inversely tapered part  8   b  at the portion having the smallest cross-sectional area. The boundary between the tapered part  8   a  and the inversely tapered part  8   b  does not include any edge where the angle suddenly changes. The angle smoothly changes from the tapered part  8   a  to the inversely tapered part  8   b.    
     Here, consider the shape of the inner surface of a nozzle  8  positioned in a certain direction distant from the center axis of the nozzle  8 . At the internal opening  8   c  side, the distance from the center axis is long. The distance from the center becomes shorter from the internal opening  8   c  toward the ejection hole  8   d . The distance becomes the shortest at a certain location. This location is the boundary between the tapered part  8   a  and the inversely tapered part  8   b  and is called the “nearest point A”. The nozzle  8  ideally has the shape of a rotating body with respect to the center axis. Preferably the depth of the nearest point A, that is, the distance from the ejection hole  8   a , does not change for each angle seen from the center axis. In actuality, however, a certain extent of variation occurs on manufacture. If the nearest point A is the edge part where the angle drastically changes and there is a large variation in the position in the depth direction of the nearest point A among each angle from the center axis, the variation in the ejection direction also becomes large. For this reason, preferably there is no edge part and the angle smoothly changes from the tapered part  8   a  to the inversely tapered part  8   b.    
     Further, the surface roughness of the inner surface of a nozzle  8  is smaller in the inversely tapered part  8   b  than the tapered part  8   a . Due to this, it is possible to suppress variation in the ejection direction due to the influence of unevenness at the inversely tapered part  8   b  side. This is believed to be because if the surface roughness of the inversely tapered part  8   b  is large, separation of the tail from the inversely tapered part  8   b  becomes delayed and therefore the influence of the difference of the width of the inversely tapered part  8   b  becomes larger or the position at which the tail finally separates varies due to the influence of the surface roughness, but due to the above, such effects become harder to occur. The surface roughness of the inner surface of the nozzle  8  can be measured by cutting the nozzle  8  in the vertical direction. The surface roughness of the tapered part  8   a  is controlled to for example Rmax0.13 to 0.25 μm, while the surface roughness of the inversely tapered part  8   b  is controlled to for example Rmax0.10 to 0.15 μm. If the surface roughness of the inversely tapered part  8   b  is smaller by 0.02 μm or more than the surface roughness of the tapered part  8   a , it is possible to suppress the variation of ejection direction more, so this is preferable. 
     Next, two methods of production for manufacturing a nozzle plate  31  provided with such nozzles  8  will be explained. First, a method of production using a negative type photoresist on which exposed portions are cured will be explained, then a method of production using a positive type photoresist from which exposed portions are dissolved will be explained. 
       FIGS. 7A to 7E  are vertical cross-sectional views of steps of the method of production of a nozzle plate  31  using a negative type photoresist. First, an electroforming substrate  102  made of stainless steel or another metal is prepared. In the electroforming substrate  102 , the surface on the side where the nozzle plate  31  is to be formed by plating in a later explained step is preferably polished to Rmax100 nm or less. As shown in  FIG. 7A , a negative type photoresist film  104  is formed on the side of the polished surface of the electroforming substrate  102 . The photoresist film  104  is formed by coating a liquid photoresist by spin coating or another technique or by hot press bonding a dry film type resist. 
     A photo mask  106  formed with a mask pattern so that nozzles  8  can be formed with desired dimensions and arrangement is prepared. As shown in  FIG. 7B , the photoresist film  104  is exposed through the photo mask  106 . As the light source, use may be made of g-rays of a high pressure mercury lamp (wavelength: 436 nm), i-rays of a high pressure mercury lamp (wavelength: 365 nm), a KrF excimer laser (wavelength: 248 nm), ArF excimer laser (wavelength: 193 nm), or the like. 
     The photomask  106  allows light to pass through only the portions corresponding to the nozzles  8 . The parts of the photoresist film  104  under the opening portions are cured since the light strikes it (below, the parts which are cured will be sometimes referred to as the “cured parts”). The light passing through the photomask  106  spreads outward from the opening portions due to the phenomenon of light diffraction. In the vicinities of the boundaries of the opening portions, the light becomes weaker by the amount of the diffraction light which spreads outward, therefore the amount of sensitization of the photoresist film  104  falls. Basically, the larger the distance from the photomask  106 , the greater the influence by this. That is, the further from the photomask  106 , gradually the narrower the range of the cured parts. Due to this, the cured parts become shapes forming the tapered parts  8   a.    
     However, the photoresist film  104  at the portion immediately above the electroforming substrate  102  is also exposed by the light which is reflected at the interface between the electroforming substrate  102  and the photoresist film  104 . For this reason, in the vicinity of this interface, the dimensions of the cured parts become larger. The reflected light is diffused and attenuates inside the photoresist film  104 . Therefore, the further from the interface, gradually the smaller the sizes of the cured parts. 
     The effect of reflected light occurs in the range from the interface between the electroforming substrate  102  and the photoresist film  104  to about 1 to 10 μm. By doing this, the cured parts become shapes forming the inversely tapered parts  8   b  in the vicinity of the interface. At a place which is further distant from the interface, the influence of the reflection light becomes smaller and the influence of the diffraction light explained above becomes larger, therefore the cured parts become shapes forming tapered parts  8   a  which become larger the further from the interface. Further, by doing this, it is possible to form cured parts which become shapes gradually changing in angle from the inversely tapered parts  8   b  to the tapered parts  8   a . In the method of production of the positive type, the angles from the inversely tapered parts  8   b  to the tapered parts  8   a  change more smoothly and gradually to link the parts, therefore preparation of a nozzle plate  31  by a positive type photoresist film  104  is more preferred than that by a negative type. 
     Here, since the surface on the side where the photoresist film  104  is to be formed is polished as explained above, the light reflected at the electroforming substrate  102  is substantially uniformly reflected at the side corresponding to the ejection holes  8   d  of the nozzles  8 . Due to this, variation in the shapes of the cured parts of the photoresist film  104  corresponding to the inversely tapered parts  8   b  of the nozzles  8  according to position becomes smaller. If the polishing is insufficient and therefore there is unevenness or there are parts having a low reflectivity, the difference of intensity of the reflected light becomes large depending to the positions in the nozzle  8 . If there are parts having weak reflection light, curing does not advance at those parts, therefore the inversely tapered parts  8   b  become smaller and also the widths of the inversely tapered parts  8   a  become smaller. Conversely, if there are parts having strong reflection light, curing advances at those parts, therefore the inversely tapered parts  8   a  become larger and also the widths of the inversely tapered parts  8   a  become larger. If there are such parts, the difference in the width of the inversely tapered part  8   a  between the parts of the inner surface of the nozzle facing each other becomes larger. If that difference becomes 1.5 μm or more, a drop in precision occurs in the ejection direction. 
     Next, the uncured photoresist film  104  is removed by a development solution. Due to this, the cured parts of the photoresist film  104  which form the shapes of the nozzles  8  are left by patterning as shown in  FIG. 7C . 
     In the above explanation, the explanation was given as if the cured parts and the uncured parts were clearly different. In actuality, however, the state between the cured parts and the uncured parts continuously varies. If development is strongly carried out on a part having a low degree of curing, the photoresist film  104  does not remain, but the photoresist film  104  remains if weak development is carried out. That is, even if the degrees of curing due to exposure are the same, according to whether the development is strong or weak, a difference arises in the shapes of the cured parts which remain. The parts of the photoresist film  104  which correspond to the inversely tapered parts  8   b  as explained above are not parts which are directly cured, therefore are easily influenced by development. 
     The development is for example carried out as follows. The electroforming substrate  102  is made to rotate at 100 rpm while the development solution is supplied. Further, the photoresist film  104  is held for 50 seconds in a state immersed in the development solution for still development, then the development solution is discharged. Such a process is repeated several times. The region corresponding to the nozzle plate  31  is a rectangular region which is long in one direction. At the time of making the electroforming substrate  102  rotate while the development solution is being supplied, a difference arises in the speed of flow of the development solution in the long rectangular region. If the speed of flow of the development solution is fast, the development becomes strong, so it becomes harder to make the photoresist film  104  remain. As a result, the inversely tapered parts  8   b  become smaller. 
     Generally speaking, in the rectangular region corresponding to the nozzle plate  31 , desirably the difference of intensity of development is small. However, as explained above, in this case, a desired difference is given to the shapes of the inversely tapered parts  8   b  so that the influence of the thickness of the nozzle plate  31  is cancelled out. Note that, conversely, the difference of the intensity of the development which remains even if the conditions are adjusted may also be cancelled out by adjusting the thickness of the nozzle plate  31 . The adjustment of development is for example carried out as follows. 
     In order to reduce the difference of development between the end parts  7   b  on the two sides in the rectangular region corresponding to the nozzle plate  31 , the rectangular region may be arranged at a position which is symmetrical with respect to rotation. Due to this, the intensity of development becomes substantially symmetrical in the longitudinal direction in the rectangular region corresponding to the nozzle plate  31 . More specifically, the rectangular region corresponding to the nozzle plate  31  is arranged so that the virtual straight line passing through the center of rotation and the virtual straight line along the longitudinal direction of the rectangular region corresponding to the nozzle plate  31  are substantially perpendicular to each other in the vicinity of the center of the rectangular region corresponding to the nozzle plate  31 . When arranged in this way, between the first end part  7   ba  and the second end part  7   bb , the speeds of flow of the development solutions when supplying the development solutions can be made substantially the same, therefore the intensities in development can also be made substantially the same. Note that, in the above case, at the center part  7   a , compared with the first end part  7   ba  and the second end part  7   bb , the speed of the development solution becomes slow, therefore the development becomes weak, and the inversely tapered part  8   b  is apt to become large. 
     In order to make the difference in the intensity of development between the end parts  7   b  on the two sides and the center part  7   a  small, the influence of the rotation may be made relatively small. For example, by making the rotation speed slower or making the time of the still development longer, the influence of the development at the time of rotation may be made relatively small. Conversely, in order to make the difference in the intensity of development between the end parts  7   b  on the two sides and the center part  7   a  larger, the rotation speed may be made faster or the time of the still development may be made shorter. 
     Note that, in order to make the inversely tapered part  8   b  in the center part  7   a  smaller, after performing the development as explained above, the region corresponding to the nozzle plate  31  may be divided and additional development may be performed only for the center part  7   a.    
     As explained above, even if the arrangement of the rectangular region corresponding to the nozzle plate  31  is made symmetric, there sometimes arises a very small difference in the intensity of development between the first end part  7   ba  and the second end part  7   bb . This is considered to be due to the influence by the rotation direction, position of supply of the development solution, the amount of supply of the development solution, etc. When this influence is large, adjustment is carried out as follows to make the difference between the width TE 1  and the width TE 2  small. 
     When processing under the same conditions, the trends in intensity of development become almost the same, therefore adjustment is carried out so that those trends are cancelled out. For example, if the development becomes stronger in the first end part  7   ba  than that in the second end part  7   bb , the arrangement of the rectangular region corresponding to the nozzle plate  31  may be offset a little from the position where it is symmetrical about rotation to thereby control the distance from the center of the rotation up to the second end part  7   bb  to become a bit longer than the distance from the center of the rotation to the first end part  7   ba . When doing this, the speed of the development solution passing through the second end part  7   bb  becomes faster, therefore the intensity of development can be strengthened. 
     After development in the development solution, according to need, a rinse is carried out by superpure water or the like so as to prevent unwanted parts from remaining. 
     The nozzle plate  31  is prepared by forming a plating film  31  on the electroforming substrate  102  on which the patterned photoresist film  104  was formed prepared as described above. The electroforming substrate  102  is dipped in a plating solution containing Ni, Cu, Cr, Ag, W, Pt, Pd, Rd, or the like and supplying electricity whereby, as shown in  FIG. 7D , the plating film  31  is formed on the surface of the electroforming substrate  102  on which the photoresist film  104  was arranged. The plating film  31  for example contains Ni as its principal ingredient. The formation of the plating film  31  is stopped by time management or the like before it reaches the height of the photoresist film  104  resulting in the nozzle plate  31  of a predetermined thickness. 
     At the time of formation of the plating film  31 , it is possible to arrange a shield plate restricting the movement of ions so as to adjust the distribution of thickness of the plating film  31 . The plating solution is placed in a plating tank which is larger than the plating film  31  which forms the nozzle plate  31 . That is, the route of flow of ions becomes broader than the region in which the plating film  31  is formed. Under such conditions, compared with the center part  7   a  of the plating film  31 , the outer circumferential portion of the plating film  31  becomes faster in growth. As a result, in the outer circumferential portion of the nozzle plate  31 , the thickness becomes greater compared with the center part  7   a . By suitably arranging the shield plate, this tendency can be weakened. Conversely, when increasing the number of shield plates arranged at the outer circumferential portion of the plating film  31  and narrowing the route of flow of ions compared with the center part  7   a , the thickness of the outer circumferential portion of the nozzle plate  31  can be made smaller compared with the center part  7   a . Even if the shield plate is arranged symmetrical relative to the nozzle plate  31 , the thickness of the nozzle plate  31  sometimes becomes asymmetrical. This is considered to be derived from the influences by the position of the nozzle plate  31  in the plating tank and so on. Where the difference in the thickness between the first end part  7   ba  and the second end part  7   bb  is large, by arranging the shield plate considering that difference, the difference in thickness between the first end part  7   ba  and the second end part  7   bb  can be made small. 
     Next, the photoresist film  104  inside the nozzles  8  is removed by using an organic solvent or the like. Further, the nozzle plate  31  is peeled off from the electroforming substrate  102 . 
     In the peeled off nozzle plate  31 , as shown in  FIG. 7E , nozzles  8  having tapered parts  8   a  on the upper side in the drawing and inversely tapered parts  8   b  on the lower side in the drawing are formed. According to need, the surface on the ejection hole  8   d  side of the nozzle plate  31  may be formed with a water repellent (ink repellent) film or the like by a fluororesin, carbon, or the like. 
     Note that, before performing exposure, heating may be carried out in advance to promote the curing reaction. The heating step can be easily controlled if using an oven, hotplate, etc. Further, due to this heating step, in the photoresist film  104 , the curing reaction on the electroforming substrate  102  side is promoted more, therefore the surface roughness of the side surfaces of the photoresist film  104  after development becomes smaller on the side close to the electroforming substrate  102  than the side far from the electroforming substrate  102 . The surface roughness of the side surfaces of the photoresist film  104  after the development is transferred to the nozzles  8  and becomes the surface roughness of the inner surfaces of the nozzles  8 . For this reason, if prepared as described above, the surface roughness of the inversely tapered parts  8   b  can be made smaller than the surface roughness of the tapered parts  8   a . The surface roughness of the inversely tapered parts  8   b , which exert a great influence upon the ejection characteristics, becomes smaller, so the variation in the ejection characteristics can be reduced. 
       FIGS. 7F to 7J  are vertical cross-sectional views of steps of the method of production of a nozzle plate  31  using a positive type photoresist. 
     In  FIG. 7F , a positive type photoresist film  204  is formed on one surface of an electroforming substrate  202 . As the electroforming substrate  202 , one substantially the same as the one used in the negative type explained above may be used. However, the surface on the photoresist film  204  side does not always have to be polished. This is because in this manufacturing process, the interface side between the electroforming substrate  202  and the photoresist film  204  becomes the internal opening  8   c  sides of the nozzles  8 . Therefore, even if the precision of formation on the internal opening  8   c  sides varies due to the influence of the light reflected at the interface between the electroforming substrate  202  and the photoresist film  204 , the influence exerted upon the ejection characteristics is lower compared with the case where the shapes on the ejection hole  8   d  sides vary. However, by performing polishing, the precision of formation of the internal opening  8   c  sides can be made higher and the variation in the ejection characteristics can be reduced, therefore preferably polishing is carried out. The positive type photoresist film  204  can be formed by the same technique as that for the negative type photoresist film  104 . 
     In  FIG. 7G , the photomask  206  is designed to block light only at the portions corresponding to the nozzles  8  in the photomask  206 . The parts of the photoresist film  204  under the other portions where the light is passed are dissolved and removed. In the same way as the previous manufacturing process of the nozzle plate  31  using the negative type photoresist, the light passed through the photomask  206  spreads inwardly from the light shielding portions due to the phenomenon of light diffraction. In the vicinities of the boundaries of the light shielding portions, the light becomes weaker by the amount of the diffraction light which spreads toward the inside, therefore the amount of sensitization of the photoresist film  204  is lowered. Basically, the larger the distance from the photomask  206 , the larger the influence by this. That is, the further from the photomask  206 , gradually the narrower the range of dissolution and removal. Due to this, as shown in  FIG. 7H , the shapes for forming the tapered parts  8   a  are formed. 
     In  FIG. 7I , the plating film  31  is formed in the same way as the manufacturing process using the negative type photoresist. Although the explanation was omitted in the negative type production method, in the vicinity of the photoresist film  204 , the speed of formation of the plating film  31  becomes slower than that at its periphery. For this reason, even if the plating film  31  is formed for the same time, in the vicinity of the photoresist film  204 , the plating film  31  becomes thinner. Therefore, curved parts  31   c  in which the thickness of the plating film  31  becoming gradually thinner toward the photoresist film  204  are formed. 
     In the negative type process, the upper surface of the plating film  31  in  FIG. 7I  becomes the ejection hole surface  31   a . That is, the inversely tapered part  8   b  is formed predicated on the curved portion  31   c . The curved portion  31   c  exhibits an inversely tapered shape where the cross-sectional area being larger toward the ejection hole surface  31   b . However, by just managing the process conditions of the plating film  31 , it is difficult to form the curved portion  31   c  with such a high precision that the width T in the curved portion  31   c  is contained within the desired dimensional range. 
     Therefore, after the residue of the photoresist film  204  is removed and the nozzle plate  31  is peeled off from the electroforming substrate  202 , the nozzle plate  31  is polished from the curved part  31   b  side, that is, the ejection hole  8   b  side. This polishing can be carried out by lapping, buffing, chemical polishing, electrolytic polishing, or other various techniques. By adjusting the amount of polishing according to the location of the nozzle plate  31 , the widths T of the curved portion  31   c  can be adjusted. The curved portion  31   c  which remains after polishing becomes the inversely tapered parts  8   b.    
     In the nozzle plate  31  processed in this way, as shown in  FIG. 7J , the nozzles  8  each having the tapered part  8   a  on the lower side in the drawing and having the inversely tapered part  8   b  on the upper side in the drawing are formed. Then, by adjusting the polishing amount according to the location in the nozzle plate  31 , the widths T of the inversely tapered parts  8   b  can be made different in magnitude in the nozzle plate  31 . 
     Note that, the curved portion  31   c  is formed in the two positive type and negative type manufacturing processes. In the negative type process, the curved portion  31   c  is positioned on the ejection hole  8   d  side, therefore the influence due to the variation in the shape of the curved portion  31   c  exerted upon ejection is large. For this reason, the width T of the inversely tapered part  31   b  is adjusted by performing polishing as explained above. In the positive type, the curved portion  31   c  is positioned on the internal opening  8   c  side, so the influence exerted upon the ejection is small compared with the negative type, therefore the shape of the curved portion  31   c  which varied may be left as it is as well. Further, the shape may be adjusted by polishing in the same way as that in the negative type or the curved portion  31   c  may be removed by polishing. 
     REFERENCE SIGNS LIST 
     
         
           1  . . . printer, 
           2  . . . liquid ejection head, 
           4  . . . channel member 
           5  . . . manifold
         5   a  . . . sub-manifold     5   b  . . . opening of manifold   
     
           6  . . . individual supply channel 
           7  . . . nozzle arrangement region
         7   a  . . . center part (of nozzle arrangement region)     7   b  . . . end part (of nozzle arrangement region)     7   ba  . . . first end part (of nozzle arrangement region)     7   bb  . . . second end part (of nozzle arrangement region)   
     
           8  . . . nozzle, through hole
         8   a  . . . tapered part     8   b  . . . inversely tapered part     8   c  . . . internal opening     8   d  . . . ejection hole   
     
           9  . . . pressurizing chamber group 
           10  . . . pressurizing chamber 
           11   a ,  11   b ,  11   c ,  11   d  . . . columns of pressurizing chambers 
           12  . . . aperture 
           13  . . . head body 
           15   a ,  15   b ,  15   c ,  15   d  . . . columns of ejection holes 
           21  . . . piezoelectric actuator substrate
         21   a  . . . piezoelectric ceramic layer (ceramic vibration plate)     21   b  . . . piezoelectric ceramic layer   
     
           22  to  30  . . . plates 
           31  . . . plate (nozzle plate), plating film
         31   a  . . . ejection hole surface, first surface     31   b  . . . second surface     31   c  . . . curved part   
     
           32  . . . individual channel 
           34  . . . common electrode 
           35  . . . individual electrode
         35   a  . . . individual electrode body     35   b  . . . extraction electrode   
     
           36  . . . connection electrode 
           50  . . . displacement element 
           70  . . . head mounting frame 
           72  . . . head group 
           80 A . . . paper feed roller 
           80 B . . . collection roller 
           82 A . . . guide roller 
           82 B . . . conveying roller 
           88  . . . control part 
           102 ,  202  . . . electroforming substrates 
           104 ,  204  . . . photoresist films 
           106 ,  206  . . . photomasks 
         A . . . nearest point 
         P . . . printing paper 
         T, T 1   a , T 1   b , T 2   a , T 2   b  . . . widths of inversely tapered part