JP6166118B2 - 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 inside the piezoelectric actuator substrate, a plurality of individual electrodes on the surface of the piezoelectric actuator substrate, and a gap therebetween. It consists of a piezoelectric ceramic layer. A plurality of displacement elements are arranged at the center of the piezoelectric actuator substrate.

JP 2003-305852 A

The crystal grain size in the piezoelectric ceramic layer of the piezoelectric actuator substrate as described in Patent Document 1 is considered to be designed mainly to increase the characteristics of the displacement element, for example, the displacement amount and durability. . Patent Document 1 does not describe changing the size of crystal grains in the piezoelectric ceramic layer. In the piezoelectric actuator substrate of Patent Document 1,
The crystal grain size is considered to be substantially constant regardless of the position in the piezoelectric ceramic layer.

  Further, when the piezoelectric actuator substrate is destroyed by an external force, the peripheral portion of the piezoelectric actuator substrate is often the starting point, but the crystal grain size of the peripheral portion is comparable to the crystal grain size of the displacement element portion. And the mechanical strength of the peripheral part was low, and there was a problem that the piezoelectric actuator substrate was easily broken.

  Accordingly, an object of the present invention is to provide a piezoelectric actuator substrate that is difficult to be destroyed, a liquid discharge head using the same, and a recording apparatus.

  The piezoelectric actuator substrate of the present invention is a piezoelectric actuator substrate including a piezoelectric ceramic layer and a plurality of pairs of electrodes arranged so as to sandwich the piezoelectric ceramic layer. A central region in which a plurality of displacement elements including the piezoelectric ceramic layer and the pair of electrodes arranged so as to sandwich the piezoelectric ceramic layer are disposed, and a peripheral region in which the displacement elements are not disposed The average crystal grain size of the piezoelectric ceramic layer in the peripheral region is smaller than the average crystal grain size of the piezoelectric ceramic layer in the central region.

  The liquid discharge head of the present invention includes the piezoelectric actuator substrate and a flow path member that is bonded to 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, the mechanical strength can be increased in the peripheral region because the crystal grain size is smaller than the crystal grain size in the central region.

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. It is a partial top view of the piezoelectric actuator board | substrate which concerns on one Embodiment of this invention. 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. 5 is a partial plan view of the piezoelectric actuator substrate 21 and shows about half of the piezoelectric actuator substrate 21. The other half is substantially symmetric with the structure shown in FIG. In FIG. 5 as well, the common electrode surface electrode 37 and the through hole 38 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 overlapping piezoelectric actuator unit 21, the droplets ejected 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 10 to 90 μm, and the total thickness of the piezoelectric actuator substrate 21 is 20 to 100 μm. The thickness of the piezoelectric ceramic layer 21a is, for example, 22 μm, and the thickness of the piezoelectric ceramic layer 21b is, for example, 18 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 includes a common electrode 34 that is an internal electrode made of a metal material such as an Ag-Pd system, an individual electrode 35 that is made of a metal material such as an Au system, an Ag system that is formed on the individual electrode 25, and the like. The connection land 36 is made of a metal material. 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. The thickness of the individual electrode 35 when forming the Au-based conductor is 0.3 to 1 μm, and the thickness of the individual electrode 35 when forming the Ag-based conductor 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 the 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 common electrodes 34 are alternately arranged. May be.

The piezoelectric actuator substrate 21 is provided with a plurality of displacement elements 50 each including the individual electrode 35, the common electrode 34, and the portion of the piezoelectric ceramic layer 21 b sandwiched between them. When viewed in plan, the displacement element 50 is arranged in the central region 21-1 of the piezoelectric Akucheeta substrate 21, the peripheral region 21 2 of the piezoelectric Akucheeta substrate 21 not disposed. Boundary line E in FIG. 5 indicates the boundary between the central region 21-1 and the peripheral region 21 2. The central region 21-1 is a region that includes all the displacement elements 50 and has a small area (in 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.

In the central region 21-1, the grain size of the crystal grains of the piezoelectric ceramic layer 21b is set to a state in which the variation in grain size due to the part is small at least in the plane direction, and the average crystal grain size is substantially constant regardless of the part. Is done. This is to prevent the displacement characteristics of the displacement element 50 from varying depending on the position of the displacement element 50 in the piezoelectric actuator substrate 21. Further, the average crystal grain size in the central region 21-1 is basically designed to enhance the characteristics of the displacement element 50. For example, the amount of displacement is increased, the decrease in the amount of displacement when driving is repeated is reduced, or destruction due to a short circuit or the like is unlikely to occur. The specific suitable particle size varies depending on the composition, but in the PZT-based composition, for example, the average crystal particle size is preferably 3.5 to 4.5 μm. The average crystal grain size can be measured by an intercept method or the like. In the intercept method, for example, the surface of the piezoelectric ceramic layer 21b is scanned with a scanning electron microscope (SEM).
Using an image taken with an electron microscope or the like, measurement is performed with a measurement length including 100 or more crystal particles, and 1.5 × L / n (n: number of crystal particles per length L, L: measurement length) )).

The piezoelectric actuator substrate 21 may be broken, for example, cracked due to an external force during the manufacturing process or use. At that time, the end portion of the piezoelectric actuator substrate 21 often serves as a starting point of destruction. In particular, after the flow path member 4 is laminated, an end portion that receives stress due to a difference in thermal expansion coefficient becomes a starting point of destruction. The average grain size that is designed to improve the characteristics of the displacement element 50, the mechanical strength of the peripheral region 21 2 is lowered, since the piezoelectric actuator substrate 21 is hardly broken, the peripheral area 21-2 Is made smaller than the average crystal grain size of the central region 21-1, and the mechanical strength of the peripheral region 21-2 is increased. For this reason, the peripheral region 21-2 is a region that surrounds the central region 21-1 and includes the outer peripheral end of the piezoelectric actuator substrate 21. Such a configuration is particularly useful for the piezoelectric actuator substrate 21 having a thickness of 100 μm that is easily broken by an external force.

  For example, in the PZT-based composition described above, it is preferable that the average crystal grain size of the peripheral region 21-2 be 2.5 to 3.5 μm. Thereby, the ring bending strength in the peripheral region 21-2 can be increased to 53 MPa with respect to the ring bending strength 48MPa in the central region 21-1, and the piezoelectric actuator substrate 21 may be broken from the end portion. Can be lowered. The peripheral region 21-2 may not necessarily have a large overall particle size. Of the peripheral region 21-2, the average crystal grain size in the range of about 100 μm from the end of the piezoelectric actuator substrate 21 only needs to be smaller than the average makeup particle size of the central region 21-1, and is 0.55 to 0.85 times. Preferably, it is 0.65 to 0.75 times.

  The peripheral region 21-2 has a width of about 0.5 to 2 mm from the end of the piezoelectric actuator substrate 21. The average crystal grain size at the end of the piezoelectric actuator substrate 21 in the peripheral region 21-2 is made smaller than the average crystal grain size in the central region 21-1, as described above. The average crystal grain size of the peripheral region 21-2 on the central region 21-1 side may be made smaller than the average crystal grain size of the central region 21-1 as in the end side, or the central region 21. As large as the average crystal grain size of -1.

  Further, in the piezoelectric actuator substrate 21, electrical connection with the outside is performed by the individual electrode 35 (more precisely, the connection electrode 35 b) and the common electrode surface electrode 37. A part of the common electrode 37 enters the through hole 38 penetrating the piezoelectric ceramic layer 21 b to form a through electrode, and a surface electrode (through electrode) 37 for the common electrode is formed below the through hole 38. The common electrode 34 is electrically connected. The diameter of the through hole 38 is about 50 to 200 μm.

  By disposing the through electrode in the through hole 38 in the peripheral region 21-2, the strength of the piezoelectric ceramic layer 21 b to which the through electrode is bonded is increased and the bonding strength of the through electrode is increased. Even if stress is applied to the electrode surface electrode 37, the connection is not easily broken. By disposing the common electrode surface electrode 37 in the peripheral region 21-2, the bonding strength of the common electrode surface electrode 37 can be increased in the same manner. In this case, the average crystal grain size of the portion where the through electrode or the common electrode surface electrode 37 is disposed in the peripheral region 21-2 is made smaller than the average crystal grain size of the central region 21-1.

  In other words, the above-described configuration includes a plurality of individual electrodes 35 in which a plurality of pairs of electrodes constituting the displacement element 50 are disposed on one main surface of the piezoelectric ceramic layer 21b, and the piezoelectric ceramic layer 21b. Is formed of a common electrode 34 disposed to face the plurality of individual electrodes 35, and penetrates the piezoelectric ceramic layer 21 b in the peripheral region 21-2. 34 is provided with a through electrode and a common electrode surface electrode 37 which are electrically connected to the electrode 34.

  As shown in FIG. 6, the common electrode 34 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 34 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. As a result, 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 34, 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.

  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 to the piezoelectric ceramic layer 21b in the polarization direction by setting the individual electrode 35 to a potential different from that of the common electrode 34, the 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, since 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 34, it 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 34 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 an actual driving procedure in the present embodiment, the individual electrode 35 is set to a potential higher than the common electrode 34 (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 34 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 composed 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. . In a part of the green sheet, a hole to be a through hole 38 is formed by punching or laser. In addition, an electrode paste to be the common electrode 34 is formed on a part of the green sheet by printing or the like.

  Next, each green sheet is laminated to produce a laminate, and pressure adhesion is performed. At this time, the thickness of the green sheet is adjusted so that the position of the common electrode 34 in the stacking direction is close to the main surface on the side where the individual electrode 35 is arranged when the piezoelectric actuator substrate 21 is formed. For example, the thickness of the fired piezoelectric ceramic layer 21a is 22 μm, and the thickness of the piezoelectric ceramic layer 21b is 18 μm. Thereby, the position in the stacking direction of the common electrode 34 is disposed closer to the main surface on the side where the individual electrode 35 is disposed than the center of the stacking thickness.

Next, this laminate is placed on a ceramic firing jig mainly composed of zirconia or the like with the main surface on the side where the individual electrodes 35 are formed facing upward, and is, for example, 1050 in a high concentration oxygen atmosphere. Simultaneous firing at 0 ° C. produces a piezoelectric actuator body. In firing, the common electrode 34 mainly composed of gold, silver, copper or the like is sintered at a lower temperature than the piezoelectric ceramic layers 21a and 21b. After the common electrode 34 is sintered to form a substantially integrated structure, the piezoelectric ceramic layers 21a and 21b are fired and contracted at a higher temperature. At this time, since the position of the common electrode 34 in the stacking direction is located above the center, the firing shrinkage of the stack is restricted above the center, and the end of the piezoelectric actuator element body is lowered downward. It deforms as follows. Since the firing proceeds in this state, the temperature rise is slow in the vicinity of the end portion in contact with the firing jig having a large heat capacity compared to the central portion of the piezoelectric actuator element body, and the sintering is difficult to proceed. Thereby, compared with the center area | region 21-1, the crystal grain diameter becomes small in the peripheral area | region 21-2. When the thickness of the piezoelectric actuator substrate 21 is increased, the influence that the lower surface of the piezoelectric actuator substrate 21 is in contact with the firing jig extends to the upper surface of the piezoelectric actuator substrate 21 (the surface on which the individual electrode 35 is disposed). In order to facilitate, the thickness of the piezoelectric actuator substrate 21 is preferably 100 μm or less.

  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. At the time of printing, a part of the Ag paste enters the through hole 38, and the electrode surface electrode 37 is electrically connected to the common electrode 34 through the part that has entered the through hole 38 by firing. When firing, the Ag paste is separately fired from the green sheet laminate, and the piezoelectric actuator substrate 21 is deformed so that the end portion is raised upward by firing shrinkage of the Ag paste. By doing so, the downward deformation at the time of firing the laminate and the upward deformation at the time of firing the Ag paste are offset, and the final warpage of the piezoelectric actuator substrate 21 can be reduced.

  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 the piezoelectric actuator substrate) 21-2 ... Peripheral region (of the piezoelectric actuator substrate) 22 to 31 ... Plate 32 ... Individual flow path 34 ... Common electrodes (internal electrodes)
34a: Thick part of the common electrode (thickness around the through hole) 35 ... Individual electrode 35a ... Individual electrode body 35b ... Connection electrode 36 ... Connection land 37 ... Common Surface electrode for electrode 38... Through hole 45... Dummy individual electrode 46... Dummy connection land 50.
E ... Boundary line (between the central region and the peripheral region of the piezoelectric actuator substrate)

Claims (6)

A piezoelectric actuator substrate comprising a piezoelectric ceramic layer and a plurality of pairs of electrodes arranged so as to sandwich the piezoelectric ceramic layer,
The piezoelectric actuator substrate has a plurality of displacement elements composed of a pair of electrodes of the plurality of pairs of electrodes and a portion sandwiched between the pair of electrodes in the piezoelectric ceramic layer,
When viewed in plan,
Wherein the piezoelectric actuator substrate, and one central region where the displacement element has a plurality arranged, and one of the peripheral regions arranged and the displacement element is not disposed to surround the central region is present,
The piezoelectric actuator substrate, wherein an average crystal grain size of the piezoelectric ceramic layer in the peripheral region is smaller than an average crystal grain size of the piezoelectric ceramic layer in the central region. Before Symbol pairs of electrodes, wherein the plurality of individual electrodes disposed on one main surface of the piezoelectric ceramic layer, on the other main surface of the piezoelectric ceramic layer, arranged so as to face the plurality of individual electrodes The common electrode, and
2. The piezoelectric actuator substrate according to claim 1, further comprising a through electrode that penetrates the piezoelectric ceramic layer and is electrically connected to the common electrode in the peripheral region.   The piezoelectric actuator substrate according to claim 1 or 2, wherein the piezoelectric actuator substrate has a thickness of 100 µm or less. On the main surface of the piezoelectric ceramic layer on the common electrode side, another piezoelectric ceramic layer is laminated to form a piezoelectric ceramic laminate,
The piezoelectric ceramic laminate is fired at the same time, and the common electrode is arranged in a stacking direction of the piezoelectric ceramic laminate from a main surface opposite to one main surface on which the plurality of individual electrodes are arranged. , Arranged near the one main surface,
3. The piezoelectric actuator substrate according to claim 2, wherein the plurality of individual electrodes are fired and baked separately from the piezoelectric ceramic laminate. 5. A liquid discharge head comprising: the piezoelectric actuator substrate according to claim 1; and a flow path member that is bonded to 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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