JP6075777B2 - Piezoelectric actuator substrate, liquid ejection head using the same, and recording apparatus - Google Patents

Description

  The present invention relates to a piezoelectric actuator substrate, a liquid discharge head using the same, and a recording apparatus.

  In recent years, printing apparatuses using inkjet recording methods such as inkjet printers and inkjet plotters are not only printers for general consumers, but also, for example, formation of electronic circuits, manufacture of color filters for liquid crystal displays, manufacture of organic EL displays It is also widely used for industrial applications.

  In such an ink jet printing apparatus, a liquid discharge head for discharging liquid is mounted as a print head. This type of print head includes a heater as a pressurizing unit in an ink flow path filled with ink, heats and boiles the ink with the heater, pressurizes the ink with bubbles generated in the ink flow path, A thermal head system that ejects ink as droplets from the ink ejection holes, and a part of the wall of the ink channel filled with ink is bent and displaced by a displacement element, and the ink in the ink channel is mechanically pressurized, and the ink A piezoelectric method for discharging liquid droplets from discharge holes is generally known.

  In addition, in such a liquid discharge head, a serial type that performs recording while moving the liquid discharge head in a direction (main scanning direction) orthogonal to the conveyance direction (sub-scanning direction) of the recording medium, and main scanning from the recording medium There is a line type in which recording is performed on a recording medium conveyed in the sub-scanning direction with a liquid discharge head that is long in the direction fixed. The line type has the advantage that high-speed recording is possible because there is no need to move the liquid discharge head as in the serial type.

  In order to print droplets at a high density in any of the serial type and line type liquid discharge heads, the density of the discharge holes for discharging the droplets formed in the liquid discharge head is increased. There is a need.

  Therefore, a piezoelectric actuator substrate having a fluid discharge head, a flow path member having discharge holes connecting the manifold and the manifold via a plurality of pressurization chambers, and a plurality of displacement elements provided so as to cover the pressurization chambers, respectively. Is known (see, for example, Patent Document 1). This piezoelectric actuator substrate is a laminate of a piezoelectric ceramic layer and a ceramic diaphragm, and the displacement element includes a common electrode exposed to the end surface inside the piezoelectric actuator substrate and a plurality of electrodes on the surface of the piezoelectric actuator substrate. It consists of individual electrodes and a piezoelectric ceramic layer between them. A plurality of displacement elements are arranged at the center of the piezoelectric actuator substrate.

JP 2003-305852 A

In the piezoelectric actuator substrate described in Patent Document 1, the displacement element is driven by applying a voltage between the common electrode and the individual electrode. However, there is a problem that the common electrode exposed on the end face of the piezoelectric actuator substrate comes into contact with the surrounding conductive portion and short-circuits, thereby affecting the driving of the displacement element. For example, the end face of the piezoelectric actuator substrate may be deformed or the end face may be electrically connected to a metal flow path member or the like by attaching conductive particles of a common electrode or other conductive members to the end face. It happens when it ends.

  Accordingly, an object of the present invention is to provide a piezoelectric actuator substrate that is not easily short-circuited with the outside, a liquid discharge head using the same, and a recording apparatus.

  The piezoelectric actuator substrate of the present invention is a piezoelectric actuator substrate in which a ceramic diaphragm, an internal electrode, a piezoelectric ceramic layer, and a plurality of individual electrodes are laminated in this order. Includes a common electrode positioned at the center of the piezoelectric actuator substrate and disposed so as to overlap the plurality of individual electrodes, and a peripheral electrode disposed at a peripheral portion of the piezoelectric actuator substrate, The peripheral electrode reaches the end on the end face side of the piezoelectric actuator substrate in the peripheral portion over substantially the entire outer periphery of the piezoelectric actuator substrate, and the common electrode and the peripheral electrode are electrically separated. It is characterized by being.

  The liquid discharge head of the present invention includes the piezoelectric actuator substrate and a flow path member that is laminated on the piezoelectric actuator substrate and has discharge holes for discharging liquid.

  The recording apparatus of the present invention includes the liquid discharge head, a transport unit that transports a recording medium to the liquid discharge head, and a control unit that controls the piezoelectric actuator substrate.

  According to the piezoelectric actuator substrate of the present invention, since the peripheral electrode reaching the end face of the piezoelectric actuator substrate is electrically separated from the common electrode, the peripheral region is electrically connected to other conductive parts. Even if it has been, the influence on the driving of the displacement element can be reduced.

1 is a schematic configuration diagram of a printer that is a recording apparatus according to an embodiment of the present invention. FIG. 2 is a plan view of a flow path member and a piezoelectric actuator substrate that constitute the liquid ejection head of FIG. 1. FIG. 3 is an enlarged view of a region surrounded by an alternate long and short dash line in FIG. FIG. 3 is an enlarged view of a region surrounded by an alternate long and short dash line in FIG. (A) It is a fragmentary top view of the piezoelectric actuator board | substrate which concerns on one Embodiment of this invention, (b) is a perspective view of the same part as (a). It is a longitudinal cross-sectional view along the VV line of FIG.

  FIG. 1 is a schematic configuration diagram of a color ink jet printer which is a recording apparatus including a liquid discharge head according to an embodiment of the present invention. This color inkjet printer 1 (hereinafter referred to as printer 1) has four liquid ejection heads 2. These liquid discharge heads 2 are arranged along the conveyance direction of the printing paper P and are fixed to the printer 1. The liquid discharge head 2 has an elongated shape in a direction from the front to the back in FIG. This long direction is sometimes called the longitudinal direction.

In the printer 1, a paper feed unit 114, a transport unit 120, and a paper receiver 116 are sequentially provided along the transport path of the printing paper P. In addition, the printer 1 is provided with a control unit 100 for controlling the operation of each unit of the printer 1 such as the liquid discharge head 2 and the paper feeding unit 114.

  The paper supply unit 114 includes a paper storage case 115 that can store a plurality of printing papers P, and a paper supply roller 145. The paper feed roller 145 can send out the uppermost print paper P among the print papers P stacked and stored in the paper storage case 115 one by one.

  Between the paper feed unit 114 and the transport unit 120, two pairs of feed rollers 118a and 118b and 119a and 119b are arranged along the transport path of the printing paper P. The printing paper P sent out from the paper supply unit 114 is guided by these feed rollers and further sent out to the transport unit 120.

  The transport unit 120 includes an endless transport belt 111 and two belt rollers 106 and 107. The conveyor belt 111 is wound around belt rollers 106 and 107. The conveyor belt 111 is adjusted to such a length that it is stretched with a predetermined tension when it is wound around two belt rollers. Thus, the conveyor belt 111 is stretched without slack along two parallel planes each including a common tangent line of the two belt rollers. Of these two planes, the plane closer to the liquid ejection head 2 is a transport surface 127 that transports the printing paper P.

  As shown in FIG. 1, a conveyance motor 174 is connected to the belt roller 106. The transport motor 174 can rotate the belt roller 106 in the direction of arrow A. The belt roller 107 can rotate in conjunction with the transport belt 111. Therefore, the conveyance belt 111 moves along the direction of arrow A by driving the conveyance motor 174 and rotating the belt roller 106.

  In the vicinity of the belt roller 107, a nip roller 138 and a nip receiving roller 139 are arranged so as to sandwich the conveyance belt 111. The nip roller 138 is urged downward by a spring (not shown). A nip receiving roller 139 below the nip roller 138 receives the nip roller 138 biased downward via the conveying belt 111. The two nip rollers are rotatably installed and rotate in conjunction with the conveyance belt 111.

  The printing paper P sent out from the paper supply unit 114 to the transport unit 120 is sandwiched between the nip roller 138 and the transport belt 111. As a result, the printing paper P is pressed against the transport surface 127 of the transport belt 111 and is fixed on the transport surface 127. The printing paper P is transported in the direction in which the liquid ejection head 2 is installed according to the rotation of the transport belt 111. The outer peripheral surface 113 of the conveyor belt 111 may be treated with adhesive silicon rubber. Thereby, the printing paper P can be securely fixed to the transport surface 127.

  The four liquid discharge heads 2 are arranged close to each other along the conveyance direction by the conveyance belt 111. Each liquid discharge head 2 has a head body 13 at the lower end. A large number of ejection holes 8 for ejecting liquid are provided on the lower surface of the head body 13.

Liquid droplets (ink) of the same color are ejected from the ejection holes 8 provided in one liquid ejection head 2. Each liquid discharge head 2 is supplied with liquid from an external liquid tank (not shown). The ejection holes 8 of each liquid ejection head 2 are arranged at equal intervals in one direction (a direction parallel to the printing paper P and perpendicular to the conveyance direction of the printing paper P and the longitudinal direction of the liquid ejection head 2). Printing can be performed without gaps in one direction. The colors of the liquid ejected from each liquid ejection head 2 are magenta (M), yellow (Y), cyan (C), and black (K), respectively. Each liquid ejection head 2 is disposed with a slight gap between the lower surface of the head body 13 and the transport surface 127 of the transport belt 111.

  The printing paper P transported by the transport belt 111 passes through the gap between the liquid ejection head 2 and the transport belt 111. At that time, droplets are ejected from the head main body 13 constituting the liquid ejection head 2 toward the upper surface of the printing paper P. As a result, a color image based on the image data stored by the control unit 100 is formed on the upper surface of the printing paper P.

  A separation plate 140 and two pairs of feed rollers 121a and 121b and 122a and 122b are arranged between the transport unit 120 and the paper receiver 116. The printing paper P on which the color image is printed is conveyed to the peeling plate 140 by the conveying belt 111. At this time, the printing paper P is peeled from the transport surface 127 by the right end of the peeling plate 140. Then, the printing paper P is sent out to the paper receiving unit 116 by the feed rollers 121a to 122b. In this way, the printed printing paper P is sequentially sent to the paper receiving unit 116 and stacked on the paper receiving unit 116.

  Note that a paper surface sensor 133 is installed between the liquid ejection head 2 and the nip roller 138 that are the most upstream in the transport direction of the printing paper P. The paper surface sensor 133 includes a light emitting element and a light receiving element, and can detect the leading end position of the printing paper P on the transport path. The detection result by the paper surface sensor 133 is sent to the control unit 100. The control unit 100 can control the liquid ejection head 2, the conveyance motor 174, and the like so that the conveyance of the printing paper P and the printing of the image are synchronized based on the detection result sent from the paper surface sensor 133.

  Next, the head main body 13 constituting the liquid discharge head of the present invention will be described. FIG. 2 is a top view showing the head main body 13 shown in FIG. FIG. 3 is an enlarged plan view of a region surrounded by a one-dot chain line in FIG. 2 and is a part of the head main body 13. In FIG. 3, for the sake of explanation, some of the flow paths are omitted. FIG. 4 is an enlarged plan view at the same position as FIG. 3, and a part of the flow path different from FIG. 3 is omitted. 3 and 4, in order to make the drawings easy to understand, the pressurizing chamber 10 (pressurizing chamber group 9), the squeezing chamber 12, the discharge hole 8, and the like that are to be drawn by broken lines below the piezoelectric actuator substrate 21 are illustrated. It is drawn with a solid line. FIG. 5A is a partial plan view of the piezoelectric actuator substrate 21, and about 1/3 of the piezoelectric actuator substrate 21 is shown. About 1/3 on the opposite side (not shown) has a structure that is substantially symmetrical to the structure shown in FIG. 5, and about 1/3 in the center has the same structure as the lower side of FIG. in the process of. FIG. 5B is a perspective view of the same portion as FIG. 5A, showing the pattern of the internal electrode 34 through, and the individual electrodes 35 and the like on the surface are omitted. In FIG. 5B, the region where the internal electrode 34 exists is shown by shading so that it can be easily understood. Similarly, in FIGS. 5A and 5B, the common electrode surface electrode 37, the through hole 38, and the internal electrode 34 are drawn with solid lines. 6 is a longitudinal sectional view taken along line VV in FIG.

The head body 13 includes a flat plate-like channel member 4 and a piezoelectric actuator substrate 21 that is bonded and laminated on the channel member 4. The piezoelectric actuator substrate 21 has a trapezoidal shape, and is disposed on the upper surface of the flow path member 4 so that a pair of parallel opposing sides of the trapezoid is parallel to the longitudinal direction of the flow path member 4. In addition, two piezoelectric actuator substrates 21 are arranged on the flow path member 4 as a whole in a zigzag manner, two along each of the two virtual straight lines parallel to the longitudinal direction of the flow path member 4. Yes. The oblique sides of the piezoelectric actuator substrates 21 adjacent to each other on the flow path member 4 partially overlap in the short direction of the flow path member 4. In the area printed by driving the piezoelectric actuator substrate 21 in the overlapping portion, the droplets discharged by the two piezoelectric actuator substrates 21 are mixed and landed.

  A manifold 5 that is a part of the liquid flow path is formed inside the flow path member 4. The manifold 5 has an elongated shape extending along the longitudinal direction of the flow path member 4, and an opening 5 b of the manifold 5 is formed on the upper surface of the flow path member 4. A total of ten openings 5 b are formed along each of two straight lines (imaginary lines) parallel to the longitudinal direction of the flow path member 4. The opening 5b is formed at a position that avoids a region where the four piezoelectric actuator substrates 21 are disposed. The manifold 5 is supplied with liquid from a liquid tank (not shown) through the opening 5b.

  The manifold 5 formed in the flow path member 4 is branched into a plurality of branches (the manifold 5 at the branched portion may be referred to as a sub-manifold 5a). The manifold 5 connected to the opening 5 b extends along the oblique side of the piezoelectric actuator substrate 21 and is disposed so as to intersect with the longitudinal direction of the flow path member 4. In the region sandwiched between the two piezoelectric actuator substrates 21, one manifold 5 is shared by the adjacent piezoelectric actuator substrates 21, and the sub-manifold 5 a is branched from both sides of the manifold 5. These sub-manifolds 5 a extend in the longitudinal direction of the head main body 13 adjacent to each other in regions facing the piezoelectric actuator substrates 21 inside the flow path member 4.

  The flow path member 4 has four pressure chamber groups 9 in which a plurality of pressure chambers 10 are formed in a matrix (that is, two-dimensionally and regularly). The pressurizing chamber 10 is a hollow region having a substantially rhombic planar shape with rounded corners. The pressurizing chamber 10 is formed so as to open on the upper surface of the flow path member 4. These pressurizing chambers 10 are arranged over almost the entire surface of the upper surface of the flow path member 4 facing the piezoelectric actuator substrate 21. Accordingly, each pressurizing chamber group 9 formed by these pressurizing chambers 10 occupies a region having substantially the same shape as the piezoelectric actuator substrate 21. Further, the opening of each pressurizing chamber 10 is closed by adhering the piezoelectric actuator substrate 21 to the upper surface of the flow path member 4.

  In the present embodiment, as shown in FIG. 3, the manifold 5 branches into four rows of E1-E4 sub-manifolds 5a arranged in parallel with each other in the short direction of the flow path member 4, and each sub-manifold The pressurizing chambers 10 connected to 5a constitute a row of the pressurizing chambers 10 arranged in the longitudinal direction of the flow path member 4 at equal intervals, and the four rows are arranged in parallel to each other in the lateral direction. Two rows of the pressure chambers 10 connected to the sub-manifold 5a are arranged on both sides of the sub-manifold 5a.

  As a whole, the pressurizing chambers 10 connected from the manifold 5 constitute rows of the pressurizing chambers 10 arranged in the longitudinal direction of the flow path member 4 at equal intervals, and the rows are arranged in 16 rows parallel to each other in the short side direction. ing. The number of pressurizing chambers 10 included in each pressurizing chamber row is arranged so as to gradually decrease from the long side toward the short side corresponding to the outer shape of the displacement element 50 that is an actuator. . The discharge holes 8 are also arranged in the same manner. As a result, it is possible to form an image with a resolution of 600 dpi in the longitudinal direction as a whole.

That is, when the discharge holes 8 are projected so as to be orthogonal to a virtual straight line parallel to the longitudinal direction of the flow path member 4, each sub-manifold 5a is connected to the range R of the virtual straight line shown in FIG. One discharge hole 8, that is, a total of 16 discharge holes 8, is equally spaced at 600 dpi. Moreover, the individual flow paths 32 are connected to the sub manifolds 5a at intervals corresponding to 150 dpi on average. This is because when the discharge holes 8 for 600 dpi are divided and connected to the four sub-manifolds 5a, the individual flow paths 32 connected to the sub-manifolds 5a are not always connected at equal intervals. In other words, the individual flow paths 32 are formed at intervals of an average of 170 μm (25.4 mm / 150 = 169 μm intervals if 150 dpi) in the main scanning direction.

  Individual electrodes 35 or dummy individual electrodes 45 to be described later are formed on the upper surface of the piezoelectric actuator substrate 21 at positions facing the respective pressure chambers 10 and dummy pressure chambers to be described later. That is, the individual electrodes 35 and the upper surface of the piezoelectric actuator substrate 21 are formed in the first direction and in a direction different from the first direction. The individual electrode 35 and the dummy individual electrode 45 are slightly smaller than the pressurizing chamber 10 and have a shape substantially similar to the pressurizing chamber 10, and are in a region facing the pressurizing chamber 10 on the upper surface of the piezoelectric actuator substrate 21. Arranged to fit.

  A large number of discharge holes 8 are formed in the liquid discharge surface on the lower surface of the flow path member 4. These discharge holes 8 are arranged at positions avoiding the area facing the sub-manifold 5a arranged on the lower surface side of the flow path member 4. Further, these discharge holes 8 are arranged in a region facing the piezoelectric actuator substrate 21 on the lower surface side of the flow path member 4. These discharge hole groups 7 occupy regions having substantially the same shape as the piezoelectric actuator substrate 21, and droplets can be discharged from the discharge holes 8 by displacing the corresponding displacement elements 50 of the piezoelectric actuator substrate 21. The arrangement of the discharge holes 8 will be described in detail later. The discharge holes 8 in each region are arranged at equal intervals along a plurality of straight lines parallel to the longitudinal direction of the flow path member 4.

  The above flow paths are flow paths that are directly related to the discharge of liquid droplets, but the flow path member 4 is provided with a dummy pressurizing chamber that is omitted in the drawing. The dummy pressurizing chambers are formed in a line around the trapezoidal region where the pressurizing chamber 10 is provided. Due to the dummy pressurizing chamber, the rigidity of the flow path member 4 around the pressurizing chamber 10 that is the outermost of the pressurizing chambers 10 is close to the state of the other pressurizing chambers 10, so that the liquid ejection characteristics Variation can be reduced. The shape of the dummy pressurizing chamber is the same as that of the pressurizing chamber, but it is not connected to other flow paths. The dummy pressurizing chambers are arranged so as to extend the matrix-like arrangement of the pressurizing chambers 10.

  The flow path member 4 included in the head body 13 has a stacked structure in which a plurality of plates are stacked. These plates are a cavity plate 22, a base plate 23, an aperture (squeezing) plate 24, supply plates 25 and 26, manifold plates 27, 28 and 29, a cover plate 30 and a nozzle plate 31 in order from the upper surface of the flow path member 4. is there. A number of holes are formed in these plates. Each plate is aligned and laminated so that these holes communicate with each other to form the individual flow path 32 and the sub-manifold 5a. As shown in FIG. 6, the head main body 13 has the pressurizing chamber 10 on the upper surface of the flow path member 4, the sub-manifold 5 a on the inner lower surface side, and the discharge holes 8 on the lower surface, and the individual flow paths 32. Are arranged close to each other at different positions, and the sub-manifold 5 a and the discharge hole 8 are connected via the pressurizing chamber 10.

  The holes formed in each plate will be described. These holes include the following. First, the pressurizing chamber 10 formed in the cavity plate 22. Secondly, there is a communication hole that constitutes a flow path that connects from one end of the pressurizing chamber 10 to the sub-manifold 5a. This communication hole is formed in each plate from the base plate 23 (specifically, the inlet of the pressurizing chamber 10) to the supply plate 25 (specifically, the outlet of the sub-manifold 5a). The communication hole includes the aperture 12 formed in the aperture plate 24 and the individual supply flow path 6 formed in the supply plates 25 and 26.

Third, there is a communication hole that constitutes a flow path that communicates from the other end of the pressurizing chamber 10 to the discharge hole 8. This communication hole is referred to as a descender (partial flow path) in the following description. The descender is formed on each plate from the base plate 23 (specifically, the outlet of the pressurizing chamber 10) to the nozzle plate 31 (specifically, the discharge hole 8). Fourthly, there is a communication hole constituting the sub-manifold 5a. The communication holes are formed in the manifold plates 27 to 29.

  Such communication holes are connected to each other to form an individual flow path 32 extending from the liquid inflow port (the outlet of the submanifold 5a) from the submanifold 5a to the discharge hole 8. The liquid supplied to the sub-manifold 5a is discharged from the discharge hole 8 through the following path. First, from the sub-manifold 5a, it passes through the individual supply flow path 6 and reaches one end of the aperture 12. Next, it proceeds horizontally along the extending direction of the aperture 12 and reaches the other end of the aperture 12. From there, it reaches one end of the pressurizing chamber 10 upward. Furthermore, it progresses horizontally along the extending direction of the pressurizing chamber 10 and reaches the other end of the pressurizing chamber 10. While moving little by little in the horizontal direction from there, it proceeds mainly downward and proceeds to the discharge hole 8 opened in the lower surface.

  As shown in FIG. 6, the piezoelectric actuator substrate 21 has a laminated structure including two piezoelectric ceramic layers 21a and 21b. The piezoelectric ceramic layers 21a and 21b are each about 20 μm. The piezoelectric actuator substrate 21 is laminated on the planar surface of the flow path member 4 where the pressurizing chamber 10 is open, and the piezoelectric ceramic layers 21 a and 21 b straddle the plurality of pressurizing chambers 10. (See FIG. 3). These piezoelectric ceramic layers 21a and 21b are made of ferroelectric lead zirconate titanate (PZT), potassium sodium niobate, bismuth sodium titanate, and other ceramic materials.

  The piezoelectric actuator substrate 21 is made of a metal material such as an Ag-Pd material, an internal electrode 34, an individual electrode 35 made of a metal material such as Au, and a metal material such as an Ag material formed on the individual electrode 25. The connecting land 36 is provided. The internal electrode 34 includes a common electrode 34a and a peripheral electrode 34b. These will be described in detail later. Only the individual electrode 35 may be formed of an Ag-based metal material. As described above, the individual electrode 35 is disposed on the upper surface of the piezoelectric actuator substrate 21 at a position facing the pressurizing chamber 10 and the dummy pressurizing chamber, and the individual electrode main body 35a to the pressurizing chamber 10 is not provided. And a connection electrode 35b drawn to a position. When the individual electrode 35 is formed of an Au-based conductor, the thickness is 0.3 to 1 μm, and when the individual electrode 35 is formed of an Ag-based conductor, the thickness is 1 to 3 μm. A connection land 36 is formed on the connection electrode 35b. The connection land 36 is made of, for example, silver containing glass frit, and has a convex shape with a thickness of about 5 to 15 μm. Further, connection bumps are further formed on the connection lands 36 as necessary, and are electrically joined to electrodes provided on an FPC (Flexible Printed Circuit) (not shown). Although details will be described later, a drive signal (drive voltage) is supplied to the individual electrode 35 from the control unit 100 through the FPC. The drive signal is supplied in a constant cycle in synchronization with the conveyance speed of the print medium P.

  The above is a structure in the case where the piezoelectric actuator substrate 21 has two piezoelectric ceramic layers, but three or more piezoelectric ceramic layers are laminated so that the individual electrodes 35 and the internal electrodes 34 are alternately arranged. May be.

  As shown in FIG. 6, the common electrode 34a and the individual electrode 35 are disposed so as to sandwich only the uppermost piezoelectric ceramic layer 21b. A region sandwiched between the individual electrode 35 and the common electrode 34a in the piezoelectric ceramic layer 21b is called an active portion, and the piezoelectric ceramic in that portion is polarized in the thickness direction. In the piezoelectric actuator substrate 21 of the present embodiment, only the uppermost piezoelectric ceramic layer 21b includes an active portion, and the piezoelectric ceramic 21a does not include an active portion and functions as a diaphragm. The piezoelectric actuator substrate 21 has a so-called unimorph type configuration.

As will be described later, when a predetermined drive signal is selectively supplied to the individual electrode 35, pressure is applied to the liquid in the pressurizing chamber 10 corresponding to the individual electrode 35. by this,
Droplets are discharged from the corresponding discharge holes 8 through the individual flow paths 32. That is, the portion of the piezoelectric actuator substrate 21 that faces each pressure chamber 10 corresponds to an individual displacement element 50 (actuator) corresponding to each pressure chamber 10 and the discharge hole 8. That is, in the laminate composed of two piezoelectric ceramic layers, the displacement element 50 having a unit structure as shown in FIG. 6 is positioned immediately above the pressurizing chamber 10 for each pressurizing chamber 10. The diaphragm 21a, the common electrode 34a, the piezoelectric ceramic layer 21b, and the individual electrode 35 are formed. The piezoelectric actuator substrate 21 includes a plurality of displacement elements 50. In the present embodiment, the amount of liquid discharged from the discharge hole 8 by one discharge operation is about 5 to 7 pL (picoliter).

  A large number of individual electrodes 35 are individually electrically connected to the actuator control means via contacts and wirings on the FPC so that potentials can be individually controlled.

  On the piezoelectric actuator substrate 21, a plurality of displacement elements 50 including individual electrodes 35, a common electrode 34 a, and a portion of the piezoelectric ceramic layer 21 b sandwiched between them are arranged. When viewed in plan, the displacement element 50 is disposed in the central region 21-1 of the piezoelectric actuator substrate 21 and is not disposed in the outer peripheral region. The central region 21-1 is a region that includes all the displacement elements 50 and has a small area (with a convex polygon). Note that the dummy individual electrodes 45 on the rows A, B, and C shown in FIG. 5 are dummy, and these do not constitute the displacement element 50. Some of the dummy individual electrodes 45 have shapes different from those of the individual electrodes 35 in order to cover the ends of the piezoelectric actuator substrate 21 and to form the common electrode surface electrode 37 and the like. The dummy individual electrode 45 is not connected to electrical wiring for driving from the outside. Furthermore, while the piezoelectric ceramic layer 21b directly below the individual electrode 35 is polarized, the piezoelectric ceramic layer 21b directly below the dummy individual electrode 45 is not polarized.

  The internal electrode 34 is located at the central portion of the piezoelectric actuator substrate 21 and is disposed so as to overlap the plurality of individual electrodes 35, and the peripheral electrode 34 b disposed at the peripheral portion of the piezoelectric actuator substrate 21. Is included. The peripheral electrode 34 b reaches the end on the end face side of the piezoelectric actuator substrate 21 in the peripheral portion of the piezoelectric actuator substrate 21 over almost the entire outer periphery of the piezoelectric actuator substrate 21. The common electrode 34a and the peripheral electrode 34b are electrically separated. That is, the common electrode 34a and the peripheral electrode 34b are not connected by a conductor pattern. As a result, even if the peripheral electrode 34b, which is the internal electrode 34 exposed on the end face of the piezoelectric actuator substrate 21, may be connected to another conductive part, the driving of the displacement element 50 is affected. Things are almost gone.

  If the common electrode 34a is simply not exposed to the outside, the common electrode 34a may be formed in a pattern smaller than the piezoelectric actuator substrate 21, for example, a pattern having the same shape as the central region 21-1 so as to overlap the individual electrode 35. Although it is only good, if it does so, the curvature and deformation | transformation of the peripheral part of the piezoelectric actuator board | substrate 21 will become large. Specifically, since the firing shrinkage rate in the planar direction of the piezoelectric actuator substrate 21 is different between the portion where the internal electrode 34 (common electrode 34a) is present and the portion where the internal electrode 34 (common electrode 34a) is not present, the piezoelectric actuator substrate 21 is warped due to the difference. The peripheral edge is deformed. If such a piezoelectric actuator substrate 21 is laminated on the flow path member 4, the variation in the displacement amount of the displacement element 50 near the peripheral portion may increase, and if the warp or deformation is large, the piezoelectric actuator substrate 21 will crack. Or the pressure chamber 10 cannot be covered, and the liquid ejection head 2 cannot be manufactured.

On the other hand, it can be considered that the common electrode 34 a has a slightly smaller pattern than the piezoelectric actuator substrate 21. However, if the size difference is small, the common electrode 34a may be exposed to the outside at the end face of the piezoelectric actuator substrate due to manufacturing variations. If the size difference is increased to some extent in consideration of manufacturing variations, the possibility of exposure can be reduced. However, due to manufacturing variations, etc. Variations in width occur. Originally, the peripheral portion is a portion where warpage or deformation is likely to occur during firing, and therefore variation in warpage or deformation increases if the width of the portion without the internal electrode 34 (common electrode 34a) varies. More precisely, the absolute values of warpage and deformation amount in each piezoelectric actuator substrate 21 are relatively small. However, when a large number of piezoelectric actuator substrates 21 are manufactured, warpage or deformation between a plurality of piezoelectric actuator substrates 21 is not possible. The difference in deformation becomes large.

  In summary, if the size of the common electrode 34a is made significantly smaller than that of the piezoelectric actuator substrate 21, the absolute value of the warp and deformation amount of the piezoelectric actuator substrate 21 will increase, and slightly smaller than the piezoelectric actuator substrate 21. If it is reduced, the common electrode 34a may be exposed, and the difference in warpage and deformation amount among the plurality of piezoelectric actuator substrates 21 will increase.

  Therefore, as described above, the peripheral electrode 34b is disposed around the common electrode 34a, and the peripheral electrode 34b extends to the end on the end face side of the piezoelectric actuator substrate 21 in the peripheral portion in almost the entire outer periphery of the piezoelectric actuator substrate 21. Arrange to reach.

  Here, the fact that almost the entire outer periphery reaches the end on the end face side of the piezoelectric actuator substrate 21 in the peripheral portion means that the peripheral electrode 34b is in the piezoelectric actuator in the peripheral portion in 90% or more of the outer peripheral length. It means that the end of the substrate 21 has been reached. This proportion is further preferably 95%, in particular 100%. By doing in this way, the curvature and deformation | transformation of a peripheral part can be made small. The peripheral electrode 34b reaching the end on the end surface side of the piezoelectric actuator substrate 21 in the peripheral portion is exposed to the outside at the end surface. However, it does not necessarily reach the end face completely, and the peripheral electrode 34b is affected by the difference in contraction behavior between the piezoelectric ceramic layers 21a, 21b and the peripheral electrode 34b and the thermal expansion coefficient difference in the firing process. It may be in a state of entering the inside of about several μm from the end face. Here, including such a state, the peripheral electrode 34b is exposed to the outside at the end face.

  The separation distance between the common electrode 34a and the peripheral electrode 34b is preferably 50 μm or more, and more preferably 100 μm or more, so that short-circuiting due to foreign matter, printing pattern bleeding, or misalignment is unlikely to occur. Further, when the separation distance is increased, deformation due to the absence of the internal electrode 34 in the portion is increased. Therefore, the separation distance is preferably 2000 μm or less, more preferably 1000 μm or less, and particularly preferably 500 μm or less. It is preferable to make the separation distance substantially constant in the piezoelectric actuator substrate 21 because there is no portion where the amount of deformation caused by the absence of the internal electrode 34 is increased. Specifically, the ratio of the minimum separation distance to the maximum separation distance is 50% or more, and further 80% or more.

Further, since the common electrode 34a and the peripheral electrode 34b are separated from each other, the thickness of the piezoelectric actuator substrate 21 at that portion is thinner than the portion where the common electrode 34a and the peripheral electrode 34b are present. As a result, recesses are formed on both surfaces of the piezoelectric actuator substrate 21 so as to surround the central region 21-1. Since the concave portion on the piezoelectric ceramic layer 21a side is a portion where the adhesive is accumulated when bonding with the flow path member 4, the piezoelectric actuator substrate 21 is hardly peeled off from the end surface. Further, it is possible to prevent the adhesive from protruding from the piezoelectric actuator substrate 21 to the outside. Further, the adhesion between the piezoelectric actuator substrate 21 and the flow path member 4 may be performed only in the central region 21-1 on the inner side surrounded by the recesses. If it does so, since it will become difficult to affect the adhesion | attachment in the center area | region 21-1, the influence by the curvature | sledge of a peripheral part and a deformation | transformation site | part will become difficult, and stable adhesion | attachment can be performed.

  The common electrode 34 a is disposed so as to overlap with the individual electrode main body 35 a that is displaced to pressurize the pressurizing chamber 10. Thereby, each displacement element 50 is displaced by the piezoelectric deformation of the piezoelectric ceramic layer 21b immediately below the individual electrode main body 35a. By the way, a part of the connection electrode 35b for supplying a voltage to the individual electrode 35a located on the outermost side of the central region 21-1 is directed to the outside of the central region 21-1. The piezoelectric ceramic layer 21b immediately below the connection electrode 35b is piezoelectrically deformed by applying a voltage. This deformation not only contributes to pressurization of the pressurizing chamber 10, but also inhibits pressurization or crosstalk. It affects the surrounding displacement element 50. Therefore, originally, it is preferable that the piezoelectric ceramic layer 21b immediately below the connection electrode 35b is not piezoelectrically deformed, but the displacement element 50 further in the center of the central region 21-1 is displaced while being affected by this piezoelectric deformation. On the other hand, if the displacement element 50 located on the outermost side of the central region 21-1 is not affected by the piezoelectric deformation, there is a difference in displacement amount between the displacement elements 50. End up. In this case, the above-described difference can be reduced by arranging the common electrode 34a so as to overlap not only all the individual electrode bodies 35a but also all the connection electrodes 35b.

  Since the common electrode 34 a is the internal electrode 34, it is preferable to provide a through electrode 38 that penetrates the piezoelectric ceramic layer 21 b in order to be electrically connected to the outside on the surface of the piezoelectric actuator substrate 21. If the through electrode 38 is disposed in the central region 21-1, the area where the displacement element 50 can be disposed is reduced and the structure is different from the surroundings, which may affect the displacement characteristics. Therefore, the through electrode 38 may be disposed at a position close to the outside of the central region 21-1, and the through electrode 38 and the common electrode 34a may be electrically connected. The common electrode 34a may be provided with a protrusion 34aa protruding from the central region 21-1, so that the protrusion 34aa and the through electrode 38 overlap each other.

  Also, a second through electrode (not shown) is provided in the piezoelectric ceramic layer 21b at a position overlapping the peripheral electrode 34b so that it can be confirmed whether the peripheral electrode 34b and the common electrode 34a are short-circuited for some reason. Also good.

  An example of a driving method at the time of liquid ejection of the piezoelectric actuator substrate 21 in the present embodiment will be described with respect to a driving voltage (drive signal) supplied to the individual electrode 35. When an electric field is applied in the polarization direction to the piezoelectric ceramic layer 21b by setting the individual electrode 35 to a potential different from that of the common electrode 34a, a portion to which the electric field is applied functions as an active portion that is distorted by the piezoelectric effect. At this time, the piezoelectric ceramic layer 21b expands or contracts in the thickness direction, that is, the stacking direction, and tends to contract or extend in the direction perpendicular to the stacking direction, that is, the surface direction, due to the piezoelectric lateral effect. On the other hand, the remaining piezoelectric ceramic layer 21a is an inactive layer that does not have a region sandwiched between the individual electrode 35 and the common electrode 34a, and therefore does not spontaneously deform. That is, the piezoelectric actuator substrate 21 has the piezoelectric ceramic layer 21b on the upper side (that is, the side away from the pressurizing chamber 10) as a layer including the active portion and the lower side (that is, the side close to the pressurizing chamber 10). This piezoceramic layer 21a is a so-called unimorph type structure having an inactive layer.

  In this configuration, when the individual electrode 35 is set to a predetermined positive or negative potential with respect to the common electrode 34a by the actuator controller so that the electric field and the polarization are in the same direction, a portion sandwiched between the electrodes of the piezoelectric ceramic layer 21b. (Active part) contracts in the surface direction. On the other hand, the piezoelectric ceramic layer 21a, which is an inactive layer, is not affected by an electric field, so that it does not spontaneously shrink and tries to restrict deformation of the active portion. As a result, there is a difference in strain in the polarization direction between the piezoelectric ceramic layer 21b and the piezoelectric ceramic layer 21a, and the piezoelectric ceramic layer 21b is deformed so as to protrude toward the pressurizing chamber 10 (unimorph deformation).

In the actual driving procedure in the present embodiment, the individual electrode 35 is set to a potential higher than the common electrode 34a (hereinafter referred to as a high potential) in advance, and the individual electrode 35 is temporarily set to the same potential as the common electrode 34a every time there is a discharge request. (Hereinafter referred to as a low potential), and then set to a high potential again at a predetermined timing. As a result, the piezoelectric ceramic layers 21a and 21b return to their original shapes at the timing when the individual electrodes 35 become low potential, and the volume of the pressurizing chamber 10 increases compared to the initial state (the state where the potentials of both electrodes are different). To do. At this time, a negative pressure is applied to the pressurizing chamber 10 and the liquid is sucked into the pressurizing chamber 10 from the manifold 5 side. Thereafter, at the timing when the individual electrode 35 is set to a high potential again, the piezoelectric ceramic layers 21a and 21b are deformed so as to protrude toward the pressurizing chamber 10, and the pressure in the pressurizing chamber 10 is reduced due to the volume reduction of the pressurizing chamber 10. The pressure becomes positive and the pressure on the liquid rises, and droplets are ejected. That is, a drive signal including a pulse based on a high potential is supplied to the individual electrode 35 in order to eject a droplet. This pulse width is ideally AL (Acoustic Length), which is the length of time during which the pressure wave propagates from the manifold 5 to the discharge hole 8 in the pressurizing chamber 10. According to this, when the inside of the pressurizing chamber 10 is reversed from the negative pressure state to the positive pressure state, both pressures are combined, and the liquid droplets can be discharged at a stronger pressure.

  The liquid discharge head 2 as described above is manufactured as follows, for example. A tape made of a piezoelectric ceramic powder and an organic composition is formed by a general tape forming method such as a roll coater method or a slit coater method, and a plurality of green sheets that become piezoelectric ceramic layers 21a and 21b after firing are produced. . A part of the green sheet is punched or lasered to form a through hole. Further, an electrode paste to be the internal electrode 34 is formed on a part of the green sheet by printing or the like. The internal electrode 34 is printed in a pattern divided into a common electrode 34 a and a peripheral electrode 34.

  Next, after laminating each green sheet, it is pressurized and brought into close contact to produce a laminated body. The laminated body is cut into the shape of the piezoelectric actuator substrate 21 to produce a laminated body. At this time, the conductor pattern to be the peripheral electrode 34a is exposed on the end face of the multilayer body, and the conductor pattern to be the common electrode 34a is not exposed. When cutting, a part of the conductor pattern that becomes the peripheral electrode 34a may be rubbed and adhere to the end faces of the piezoelectric ceramic layers 21a and 21b. Further, the adhering material may cause a short circuit between the flow path member 4 and the peripheral conductor 34b later, but the peripheral conductor 34b and the common electrode 34a are not electrically connected to each other even if such a situation occurs. The driving of the displacement element 50 is hardly affected. Next, this laminated body is fired in a high-concentration oxygen atmosphere to produce a piezoelectric actuator element body.

  Thereafter, the individual electrodes 35 and the common electrode surface electrode 37 are printed on the surface of the piezoelectric actuator element body using Ag paste, and then fired at a temperature lower than the firing temperature of the piezoelectric actuator element body, for example, 650 ° C. During printing, a part of the Ag paste enters the through hole. Then, by firing, the electrode surface electrode 37 is electrically connected to the common electrode 34a through a portion that has entered the through hole and becomes the through electrode 38.

  Next, the flow path member 4 is produced by laminating plates 22 to 31 obtained by a rolling method or the like via an adhesive layer. Holes to be the manifold 5, the individual supply flow path 6, the pressurizing chamber 10, the descender, and the like are processed in the plates 22 to 31 into a predetermined shape by etching.

  These plates 22 to 31 are preferably formed of at least one metal selected from the group consisting of Fe—Cr, Fe—Ni, and WC—TiC, particularly when ink is used as a liquid. Since it is desired to be made of a material having excellent corrosion resistance against ink, Fe-Cr is more preferable.

The piezoelectric actuator substrate 21 and the flow path member 4 can be laminated and bonded through, for example, an adhesive layer. As the adhesive layer, a known material can be used, but in order not to affect the piezoelectric actuator substrate 21 and the flow path member 4, an epoxy resin, phenol resin, polyphenylene having a thermosetting temperature of 100 to 150 ° C. It is preferable to use at least one thermosetting resin adhesive selected from the group of ether resins. By heating to the thermosetting temperature using such an adhesive layer, the piezoelectric actuator substrate 21 and the flow path member 4 can be heat-bonded.

DESCRIPTION OF SYMBOLS 1 ... Printer 2 ... Liquid discharge head 4 ... Flow path member 5 ... Manifold 5a ... Sub manifold 5b ... Manifold opening 6 ... Individual supply flow path 8 ... Discharge Hole 9 ... Pressurizing chamber group 10 ... Pressurizing chamber 11a, b, c, d ... Pressurizing chamber row 12 ... Squeezing 13 ... Liquid discharge head body 15a, b, c, d ... Discharge hole array 21 ... Piezoelectric actuator substrate 21a ... Piezoelectric ceramic layer (ceramic diaphragm)
21b ... Piezoelectric ceramic layer 21-1 ... Central region (of piezoelectric actuator substrate) 22-31 ... Plate 32 ... Individual flow path 34 ... Internal electrode 34a ... Common electrode 34aa ... -Protruding part 34b ... Peripheral electrode 35 ... Individual electrode 35a ... Individual electrode body 35b ... Connection electrode 36 ... Connection land 37 ... Surface electrode for common electrode 38 ... Through electrode 45 ... Dummy individual electrode 46 ... Dummy connection land 50 ... Pressure part (displacement element)

Claims (6)

A piezoelectric actuator substrate in which a ceramic diaphragm, an internal electrode, a piezoelectric ceramic layer, and a plurality of individual electrodes are laminated in this order,
When viewed in plan,
The internal electrode includes a common electrode that is located at the center of the piezoelectric actuator substrate and is disposed so as to overlap the plurality of individual electrodes, and a peripheral electrode that is disposed at a peripheral portion of the piezoelectric actuator substrate. And
The peripheral electrode reaches the end on the end face side of the piezoelectric actuator substrate in the peripheral portion in substantially the entire outer periphery of the piezoelectric actuator substrate,
The piezoelectric actuator substrate, wherein the common electrode and the peripheral electrode are electrically separated. The individual electrode includes an individual electrode body and a connection electrode drawn from the individual electrode body;
2. The piezoelectric actuator substrate according to claim 1, wherein the common electrode is disposed at a position overlapping all the individual electrode bodies and all the connection electrodes when viewed in a plan view.   When seen in a plan view, the common electrode has a protruding portion protruding outward from a central region where the plurality of individual electrodes are arranged, and the piezoelectric ceramic layer is located at a position overlapping the protruding portion of the piezoelectric ceramic layer. 3. The piezoelectric actuator substrate according to claim 1, wherein a through electrode penetrating the layer and electrically connected to the protruding portion is disposed.   A second through electrode that penetrates the piezoelectric ceramic layer and is electrically connected to the peripheral electrode is disposed at a position overlapping the peripheral electrode of the piezoelectric ceramic layer when seen in a plan view. The piezoelectric actuator substrate according to any one of claims 1 to 3.   A liquid discharge head comprising: the piezoelectric actuator substrate according to claim 1; and a flow path member that is laminated on the piezoelectric actuator substrate and has a discharge hole for discharging a liquid.   6. A recording apparatus comprising: the liquid discharge head according to claim 5; a transport unit that transports a recording medium to the liquid discharge head; and a control unit that controls the piezoelectric actuator substrate.

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