Liquid ejection head

Abstract

To enable downsizing and suppress reduction of a displacement amount of a piezoelectric element.SOLUTION: A piezoelectric actuator 12 laminated on an upper surface of a flow channel unit formed with a pressure chamber 22 is provided with a piezoelectric element 12X for applying pressure to ink in the pressure chamber 22 in a part partially superposed on the pressure chamber 22 in relation to a vertical direction. The piezoelectric element 12X has a common electrode arranged between a piezoelectric layer 12b and the flow channel unit and kept at a ground potential, and an individual electrode 12d arranged on an upper surface of the piezoelectric layer 12b and selectively applied with a ground potential and a drive potential. The pressure chamber 22 and the individual electrode 12d each have a shape long in a scan direction, and when the width (length along a short direction) of the pressure chamber 22 is α, and the width (length along a short direction) of the individual electrode 12d is β, satisfy the relational expression of 0.5107α+18.476<β<0.7326α+54.409.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a liquid ejection head that ejects liquid from a nozzle. [Background technology]

[0002] Patent Document 1 discloses an inkjet head (liquid ejection head) including a flow path unit and a piezoelectric actuator. The flow path unit has flow paths formed therein, each including a plurality of nozzles and a plurality of pressure chambers that communicate with the nozzles. The piezoelectric actuator is stacked on the flow path unit so as to cover the plurality of pressure chambers. The piezoelectric actuator includes a plurality of piezoelectric sheets stacked on top of each other, a first constant potential electrode and a second constant potential electrode (constant potential electrodes) that are provided in common to the plurality of pressure chambers, and individual electrodes (drive electrodes) that are provided individually for the plurality of pressure chambers and overlap with the corresponding pressure chambers in the stacking direction of the flow path unit and the piezoelectric actuator.

[0003] The portions of the piezoelectric actuator that overlap with each of the multiple pressure chambers in the stacking direction (piezoelectric elements) are deformed in the stacking direction by generating a potential difference between two electrodes (a constant potential electrode and a drive electrode) that are arranged on either side of the piezoelectric sheet in the stacking direction, thereby changing the pressure of the ink in the pressure chambers and causing ink to be ejected from the nozzles that communicate with the pressure chambers. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 4831186 Summary of the Invention [Problem to be solved by the invention]

[0005] In the liquid ejection head described above, the area of ​​the drive electrodes needs to be reduced in order to miniaturize the device. However, reducing the area of ​​the drive electrodes reduces the amount of displacement of the piezoelectric element in the piezoelectric actuator. This reduces the amount of displacement of the piezoelectric element, which causes problems such as a decrease in the ejection speed and amount of ink ejected from the nozzle.

[0006] An object of the present invention is to provide a liquid ejection head that can be made smaller and that can suppress a decrease in the amount of displacement of a piezoelectric element. [Means for solving the problem]

[0007] The liquid ejection head of the present invention comprises: a flow path unit in which a flow path including a nozzle and a pressure chamber communicating with the nozzle is formed; and a piezoelectric actuator stacked on the flow path unit, the piezoelectric actuator having a piezoelectric element that applies pressure to liquid in the pressure chamber at a portion that overlaps with the pressure chamber in a stacking direction of the flow path unit and the piezoelectric actuator, the piezoelectric element comprising: a piezoelectric layer; a constant potential electrode that is arranged between the piezoelectric layer and the flow path unit; and a piezoelectric element that is arranged on a surface of the piezoelectric layer opposite to the constant potential electrode side. and a drive electrode to which a first potential and a second potential higher than the first potential are selectively applied, and the constant potential electrode is maintained at a third potential that is equal to or higher than the first potential and equal to or lower than the second potential, and both the pressure chamber and the drive electrode have a shape that is long in one direction perpendicular to the stacking direction, and when the length of the pressure chamber along a short side direction perpendicular to both the stacking direction and the one direction is α and the length of the drive electrode along the short side direction is β, the relational expression 0.5107α+18.476<β<0.7326α+54.409 is satisfied.

[0008] From another perspective, a liquid ejection head of the present invention comprises: a flow path unit in which a flow path including a nozzle and a pressure chamber communicating with the nozzle is formed; and a piezoelectric actuator laminated on the flow path unit, the piezoelectric actuator having a piezoelectric element that applies pressure to liquid in the pressure chamber at a portion that overlaps with the pressure chamber in a lamination direction of the flow path unit and the piezoelectric actuator, the piezoelectric element being disposed between a piezoelectric layer, the piezoelectric layer and the flow path unit, and selectively applying a first potential and a second potential higher than the first potential. and a constant potential electrode arranged on the surface of the piezoelectric layer opposite to the drive electrode side, the constant potential electrode being maintained at a third potential that is equal to or higher than the first potential and equal to or lower than the second potential, the pressure chamber and the drive electrode both have a shape that is long in one direction perpendicular to the stacking direction, and when the length of the pressure chamber along a short side direction perpendicular to both the stacking direction and the one direction is α and the length of the drive electrode along the short side direction is β, the relationship of 0.5107α+18.476<β<0.7326α+54.409 is satisfied. [Effects of the Invention]

[0009] As a result of various experiments and extensive research, the inventors of the present invention have found that the displacement of the piezoelectric element varies depending on the width of the pressure chamber (length along the short side) and the width of the drive electrode (length along the short side). With the liquid ejection head of the present invention, as is clear from the simulation results described below, the width of the pressure chamber and the width of the drive electrode have a relationship that allows for a sufficient increase in the displacement of the piezoelectric element. Therefore, the width of the drive electrode can be set to a size that allows for a sufficient increase in the displacement of the piezoelectric element without being too small or too large relative to the width of the pressure chamber. This allows for a reduction in the area of ​​the drive electrode, thereby enabling the device to be miniaturized and preventing a decrease in the displacement of the piezoelectric element. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a plan view of a printer equipped with an inkjet head according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a plan view of the inkjet head shown in FIG. [Figure 3] FIG. 3 is an enlarged view of the area indicated by A in FIG. [Figure 4] FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. [Figure 5] FIG. 4 is a cross-sectional view taken along line VV in FIG. [Figure 6] 10 is a graph showing the results of a simulation of the amount of displacement (displacement volume) of a piezoelectric element when the width of an individual electrode is changed. [Figure 7] 10 is a graph showing the relationship between the width of the pressure chamber and the width of the individual electrode at which the displacement of the piezoelectric element is at its maximum, and the relationship between the width of the pressure chamber and the width of the individual electrode at which the displacement of the piezoelectric element is 90%. [Figure 8] FIG. 5 is a cross-sectional view corresponding to FIG. 4, showing an inkjet head according to a second embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] First Embodiment A first preferred embodiment of the present invention will now be described with reference to FIG.

[0012] (Overall printer configuration) As shown in FIG. 1, the printer 100 according to this embodiment includes an inkjet head 1 (the “liquid ejection head” of the present invention), a carriage 2, guide rails 3a and 3b, a platen 4, conveying rollers 5a and 5b, an ink tank 6, and a control unit 7.

[0013] The carriage 2 is supported by two guide rails 3a and 3b that extend in the horizontal scanning direction (left-right direction in FIG. 1), and moves along the guide rails 3a and 3b in the scanning direction. The inkjet head 1 is mounted on the carriage 2 and moves together with the carriage 2 in the scanning direction. In the following description, the right side of FIG. 1 in the scanning direction will be referred to as "one side," and the left side of FIG. 1 will be referred to as "the other side." Furthermore, the direction perpendicular to the scanning direction in FIG. 1 (the direction from top to bottom in FIG. 1) will be referred to as the transport direction, and the direction perpendicular to the paper surface will be referred to as the up-down direction.

[0014] Ink of four colors, black, yellow, cyan, and magenta, is supplied to the inkjet head 1 through pipes (not shown) from ink tanks 6. The inkjet head 1 ejects ink from a plurality of nozzles 21 that open to a nozzle surface 11y (see FIG. 4) that is the lower surface of the inkjet head 1.

[0015] The multiple nozzles 21 form nozzle rows 21a along the transport direction. The inkjet head 1 has four nozzle rows 21a aligned in the scanning direction. Black, yellow, cyan, and magenta inks are ejected from the multiple nozzles 21 in order, starting with the nozzle row 21a located on the rightmost side in the scanning direction in FIG. 1. The configuration of the inkjet head 1 will be described in detail later.

[0016] The platen 4 is disposed opposite the nozzle surface 11y (see FIG. 4), which is the underside of the inkjet head 1, and extends in the scanning direction over the entire length of the recording paper P. The platen 4 supports the recording paper P from below. The transport rollers 5a, 5b are disposed upstream and downstream of the carriage 2 in the transport direction, respectively, and transport the recording paper P in the transport direction.

[0017] The control unit 7 includes a ROM (Read Only Memory), a RAM (Random Access Memory), an ASIC (Application Specific Integrated Circuit) including various control circuits, and the like. The control unit 7 is electrically connected to a motor (not shown) for moving the carriage 2, a motor (not shown) for rotating the transport rollers 5a and 5b, a driver IC 71 (see FIG. 4) described below, and the like. The ASIC of the control unit 7 executes various processes related to the operation of the printer 100, such as printing onto the recording paper P. For example, in the printing process, the ASIC alternates between an ink ejection operation in which ink is ejected while the inkjet head 1 is moved in the scanning direction together with the carriage 2, and a transport operation in which the transport rollers 5a and 5b transport the recording paper P a predetermined distance in the transport direction.

[0018] (inkjet head 1) Next, the detailed configuration of the inkjet head 1 will be described with further reference to Figures 2 to 5. As shown in Figure 2, the inkjet head 1 has a rectangular shape that is elongated in the transport direction when viewed from above. The inkjet head 1 includes a flow path unit 11, a piezoelectric actuator 12, and the like.

[0019] (flow path unit 11) 4 and 5, the flow path unit 11 is composed of four plates 11a to 11d that are stacked in the vertical direction and bonded to one another. The plates 11a to 11d are lined up in this order from top to bottom. A plurality of individual flow paths 20 and a manifold 30 are formed within the flow path unit 11. Through holes that form these individual flow paths 20 and manifold 30 are formed in each of the plates 11a to 11d.

[0020] As shown in FIG. 2, the flow path unit 11 is formed with four manifolds 30, each extending along the transport direction and spaced apart from one another in the scanning direction. The four manifolds 30 correspond to black, yellow, cyan, and magenta inks, respectively. The manifolds 30 communicate with the ink tanks 6 via supply ports 30a provided at the upstream ends in the transport direction. The supply ports 30a open to the top surface 11x of the flow path unit 11. As shown in FIG. 4, the manifolds 30 are formed as through-holes formed in the plate 11c.

[0021] As shown in Fig. 4, each of the individual flow paths 20 has a nozzle 21. Each manifold 30 is provided in common to the individual flow paths 20 corresponding to the nozzles 21 that make up one nozzle row 21a. Ink in the ink tank 6 is fed into the manifold 30 from a supply port 30a. The ink fed into the manifold 30 moves within the manifold 30 from the upstream side to the downstream side in the transport direction, while being supplied to each individual flow path 20 and ejected from the nozzle 21.

[0022] 4, each individual flow path 20 includes a nozzle 21, a pressure chamber 22, a connecting flow path 23, and a communication hole 24. As shown in Fig. 2, a nozzle row 21a constituted by the nozzles 21 of the multiple individual flow paths 20 provided for each manifold 30 is located on the other side of the manifold 30 in the scanning direction.

[0023] As shown in FIG. 4, the nozzles 21 are formed as through-holes formed in the plate 11d and open to a nozzle surface 11y, which is the lower surface of the flow path unit 11. The pressure chambers 22 are formed as through-holes formed in the plate 11a and open to an upper surface 11x of the flow path unit 11. As shown in FIG. 3, the pressure chambers 22 have a generally rectangular shape that is elongated in the scanning direction when viewed from above. That is, the multiple pressure chambers 22 belonging to one nozzle row 21a are aligned along the short side direction (transport direction). As shown in FIG. 4, a connection flow path 23 is connected to the other end of the pressure chamber 22 in the scanning direction, and the pressure chamber 22 communicates with the nozzles 21 via the connection flow path 23. Furthermore, a communication hole 24 is connected to one end of the pressure chamber 22 in the scanning direction, and the pressure chamber 22 communicates with the manifold 30 via the communication hole 24.

[0024] The connection flow path 23 connects the nozzle 21 and the pressure chamber 22 to each other. The connection flow path 23 is configured by a through hole formed in each of the plates 11b and 11c. The communication hole 24 connects the manifold 30 and the pressure chamber 22 to each other. The communication hole 24 is configured by a through hole formed in the plate 11b.

[0025] Ink supplied from the manifold 30 to the individual flow paths 20 flows through the communication holes 24 into the pressure chambers 22, moves approximately horizontally within the pressure chambers 22, and then flows into the connecting flow paths 23. The ink that has flowed into the connecting flow paths 23 moves downward and is ejected from the nozzles 21.

[0026] (Piezoelectric Actuator 12) The piezoelectric actuator 12 is laminated on the upper surface 11x of the flow path unit 11. As shown in Figures 4 and 5, the piezoelectric actuator 12 includes a vibration plate 12a, a piezoelectric layer 12b, a common electrode 12c, and a plurality of individual electrodes 12d.

[0027] The diaphragm 12a is disposed on the upper surface 11x of the flow path unit 11 so as to span the plurality of pressure chambers 22. In this embodiment, the diaphragm 12a is made of a piezoelectric material containing lead zirconate titanate as a main component, for example. The diaphragm 12a may also be made of a material other than a piezoelectric material, such as a metal material such as stainless steel or a synthetic resin material.

[0028] The piezoelectric layer 12b is laminated on the surface (upper surface) of the vibration plate 12a opposite to the flow path unit 11 side. The piezoelectric layer 12b corresponds to the "piezoelectric layer" of the present invention. The piezoelectric layer 12b is arranged so as to straddle the multiple pressure chambers 22. The piezoelectric layer 12b is made of a piezoelectric material whose main component is, for example, lead zirconate titanate.

[0029] The common electrode 12c is disposed on the surface (lower surface) of the piezoelectric layer 12b facing the flow channel unit 11. In other words, the common electrode 12c is disposed between the vibration plate 12a and the piezoelectric layer 12b. The common electrode 12c is disposed so as to straddle the plurality of pressure chambers 22. The plurality of individual electrodes 12d are disposed on the surface (upper surface) of the piezoelectric layer 12b opposite the common electrode 12c side. The plurality of individual electrodes 12d are individually provided for the plurality of pressure chambers 22. As shown in FIG. 3, the individual electrodes 12d have a rectangular shape that is elongated in the scanning direction when viewed from above. The center of the individual electrode 12d in the short side direction (transport direction) coincides with the center of the pressure chamber 22 in the short side direction (transport direction). The individual electrodes 12d vertically overlap the corresponding pressure chambers 22 except for one end on one side in the scanning direction.

[0030] The common electrode 12c and the individual electrodes 12d are electrically connected to a driver IC 71. The driver IC 71 maintains the potential of the common electrode 12c at ground potential (0V: "third potential" of the present invention). The driver IC 71 also selectively applies either ground potential (0V: "first potential" of the present invention) or a predetermined drive potential higher than ground potential (e.g., 20V: "second potential" of the present invention) to each of the individual electrodes 12d. Specifically, the driver IC 71 generates a drive signal based on a control signal from the control unit 7 and supplies the drive signal to the individual electrode 12d. This causes the potential of the individual electrode 12d to change between ground potential and the drive potential. In other words, the common electrode 12c corresponds to a "constant potential electrode" of the present invention, and the individual electrode 12d corresponds to a "drive electrode" of the present invention.

[0031] The portions of the piezoelectric layer 12b sandwiched between the common electrode 12c and each individual electrode 12d are polarized downward. In the piezoelectric actuator 12, the portions of the vibration plate 12a, the piezoelectric layer 12b, and the common electrode 12c that overlap each pressure chamber 22 in the vertical direction, and the portions formed by the individual electrodes 12d, respectively, form piezoelectric elements 12X that apply pressure to the ink in the pressure chambers 22. In other words, the piezoelectric elements 12X are provided individually for each of the multiple pressure chambers 22.

[0032] When the potential of the individual electrode 12d of each piezoelectric element 12X of the piezoelectric actuator 12 is switched from the ground potential to the drive potential, the potential difference between the individual electrode 12d and the common electrode 12c generates an electric field in the portion of the piezoelectric layer 12b sandwiched between these electrodes, which faces downward in the same direction as the polarization. This electric field causes the portion of the piezoelectric layer 12b to contract horizontally, deforming the piezoelectric element 12X so that it becomes convex toward the pressure chamber 22.

[0033] Furthermore, when the potential of the individual electrode 12d is switched from the drive potential to ground, the individual electrode 12d and the common electrode 12c become the same potential, and the piezoelectric element 12X returns to the state before the deformation. Then, when the potential of the individual electrode 12d is switched between ground and the drive potential, the deformation of the piezoelectric element 12X changes the volume of the pressure chamber 22, applying pressure to the ink in the pressure chamber 22, and ink is ejected from the nozzle 21 communicating with the pressure chamber 22.

[0034] Here, as shown in FIG. 3 , the width of the pressure chamber 22 is width α, and the width of the individual electrode 12d is width β. The width of the pressure chamber 22 is the length along the short side of the pressure chamber 22. As described above, the pressure chamber 22 has a substantially rectangular shape that is elongated in the scanning direction when viewed from above. Therefore, the distance between a pair of parallel long sides of the pressure chamber 22 that extend along the scanning direction is the width of the pressure chamber 22. Furthermore, the width of the individual electrode 12d is the length along the short side of the individual electrode 12d. As described above, the individual electrode 12d has a rectangular shape that is elongated in the scanning direction when viewed from above. Therefore, the distance between a pair of parallel long sides of the individual electrode 12d that extend along the scanning direction is the width of the individual electrode 12d. In this embodiment, the width α of the pressure chamber 22 and the width β of the individual electrode 12d have the relationship shown in Equation 1, which will be described later.

[0035] The inventors of the present application found that the displacement amount D of the piezoelectric element 12X changes depending on the width α of the pressure chamber 22 and the width β of the individual electrode 12d. Then, through simulation, the inventors found a correlation between the displacement amount D of the piezoelectric element 12X and the width β of the individual electrode 12d. FIG. 6 shows the simulation results of the displacement amount D (displacement volume) of the piezoelectric element 12X when the width β of the individual electrode 12d is changed. The width β of the individual electrode 12d is set to be less than the width α of the pressure chamber 22. The width α of the pressure chamber 22 is 300 μm, the length of the pressure chamber 22 (length along the scanning direction) is 800 μm, the thickness of the vibration plate 12a is 11 μm, the thickness of the piezoelectric layer 12b is 18 μm, and the drive potential is 20 V.

[0036] 6, the displacement D of the piezoelectric element 12X is greatest when the width β of the individual electrode 12d is 230 μm. The displacement D of the piezoelectric element 12X decreases as the width β of the individual electrode 12d becomes smaller than 230 μm. The displacement D of the piezoelectric element 12X also decreases as the width β of the individual electrode 12d becomes larger than 230 μm. In other words, the displacement D of the piezoelectric element 12X decreases not only when the width β of the individual electrode 12d is too small relative to the width α of the pressure chamber 22, but also when the width β of the individual electrode 12d is too large.

[0037] Furthermore, the inventors of the present application changed the set values ​​of the width α of the pressure chamber 22, the length of the pressure chamber 22 (length along the scanning direction), the thickness of the vibration plate 12a, and the thickness of the piezoelectric layer 12b, and calculated the width β (optimum width) of the individual electrode 12d at which the displacement D of the piezoelectric element 12X is maximized. As a result, it was found that the optimum width of the individual electrode 12d is independent of the length of the pressure chamber 22 (length along the scanning direction), the thickness of the vibration plate 12a, and the thickness of the piezoelectric layer 12b, but is correlated with the width α of the pressure chamber 22. The width α of the pressure chamber 22 was changed within a range of 250 μm or more and 450 μm or less.

[0038] 7, the simulation results of the width α of the pressure chamber 22 and the optimum width of the individual electrode 12d are shown by black circles. As shown by the solid line in FIG. β=0.6217α+36.443 (Formula 1) In this case, the width α of the pressure chamber 22 and the width β of the individual electrode 12d have a relationship that maximizes the displacement amount D of the piezoelectric element 12X. As described above, the width α of the pressure chamber 22 and the width β of the individual electrode 12d in this embodiment satisfy the relationship of Equation 1 above.

[0039] Furthermore, the width α of the pressure chamber 22 was changed to calculate the width β (allowable width) of the individual electrode 12d at which the displacement D of the piezoelectric element 12X was 90% of the maximum value. In Fig. 7, the simulation results for the width α of the pressure chamber 22 and the allowable width of the individual electrode 12d (longer than the optimum width) are indicated by black squares, and the simulation results for the width α of the pressure chamber 22 and the allowable width of the individual electrode 12d (shorter than the optimum width) are indicated by black triangles.

[0040] As shown by the dashed-dotted line in Fig. 7, when β = 0.7326α + 54.409, the width α of the pressure chamber 22 and the width β (optimum width or greater) of the individual electrode 12d have a relationship that allows the displacement D of the piezoelectric element 12X to be 90% of the maximum value. Also, as shown by the two-dotted line in Fig. 7, when β = 0.5107α + 18.476, the width α of the pressure chamber 22 and the width β (optimum width or less) of the individual electrode 12d have a relationship that allows the displacement D of the piezoelectric element 12X to be 90% of the maximum value.

[0041] From the above, when the width α of the pressure chamber 22 and the width β of the individual electrode 12d satisfy the relationship of the following formula 2, the displacement amount D of the piezoelectric element 12X can be made sufficiently large. 0.5107α+18.476<β<0.7326α+54.409 (Formula 2)

[0042] Each of the multiple pressure chambers 22 and the individual electrode 12d of the multiple piezoelectric elements 12X provided for that pressure chamber 22 satisfy the relationship of the above-mentioned formula 1. That is, in FIG. 5, the width of the individual electrode 12d of the piezoelectric element 12X provided in the pressure chamber 22 located on the left side and having a width α1 is width β1. Also, the width of the individual electrode 12d of the piezoelectric element 12X provided in the pressure chamber 22 located on the right side and having a width α2 is width β2. In this case, the width α1 of the left pressure chamber 22 and the width β1 of the individual electrode 12d satisfy the relationship of the above-mentioned formula 1. Also, the width α2 of the right pressure chamber 22 and the width β2 of the individual electrode 12d satisfy the relationship of the above-mentioned formula 1.

[0043] (Features of the first embodiment) As described above, the inkjet head 1 of this embodiment includes a flow path unit 11 in which flow paths including nozzles 21 and pressure chambers 22 communicating with the nozzles 21 are formed, and a piezoelectric actuator 12 stacked on the upper surface 11x of the flow path unit 11, the piezoelectric actuator 12 having a piezoelectric element 12X provided in a portion that overlaps with the pressure chamber 22 in the vertical direction, for applying pressure to ink in the pressure chamber 22. The piezoelectric element 12X includes a vibration plate 12a, a piezoelectric layer 12b stacked on the upper surface of the vibration plate 12a, a common electrode 12c that is disposed between the vibration plate 12a and the piezoelectric layer 12b and is maintained at ground potential, and an individual electrode 12d that is disposed on the upper surface of the piezoelectric layer 12b and is selectively applied with ground potential or a drive potential. Both the pressure chamber 22 and the individual electrode 12d have a shape that is elongated in the scanning direction, and when the width of the pressure chamber 22 (length along the transport direction) is α and the width of the individual electrode 12d (length along the transport direction) is β, β=0.6217α+36.443 (Formula 1) The following relation is satisfied.

[0044] The inventors of the present application have found that the displacement D of the piezoelectric element 12X varies depending on the width α of the pressure chamber 22 and the width β of the individual electrode 12d. As is clear from the above simulation results, in the inkjet head 1 of this embodiment, the width α of the pressure chamber 22 and the width β of the individual electrode 12d have a relationship that maximizes the displacement D of the piezoelectric element 12X. Therefore, the width β of the individual electrode 12d can be set to a size that maximizes the displacement D of the piezoelectric element 12X without being too small or too large relative to the width α of the pressure chamber 22. Therefore, the area of ​​the individual electrode 12d can be reduced to miniaturize the device and prevent a decrease in the displacement of the piezoelectric element 12X.

[0045] Furthermore, in the inkjet head 1 of the above-described embodiment, the common electrode 12c is maintained at 0 V. Therefore, voltage control is easy.

[0046] Furthermore, in the inkjet head 1 of the above-described embodiment, the pressure chambers 22 and the individual electrodes 12d are both rectangular in shape when viewed from above. When the pressure chambers 22 and the individual electrodes 12d are rectangular, the displacement D of the piezoelectric elements 12X is larger than when, for example, the pressure chambers 22 and the individual electrodes 12d have a different shape (for example, a diamond shape) and have the same longitudinal and lateral lengths as the rectangular pressure chambers 22 and the individual electrodes 12d.

[0047] Additionally, in the inkjet head 1 of the above-described embodiment, each of the multiple pressure chambers 22 and the individual electrode 12d of the multiple piezoelectric elements 12X that is provided for that pressure chamber 22 satisfy the relationship of the above-described formula 1. Therefore, the width β of the individual electrode 12d of the piezoelectric element 12X that corresponds to each pressure chamber 22 can be suitably set according to the width α of each pressure chamber 22.

[0048] Second Embodiment Next, an inkjet head 101 according to a second embodiment of the present invention will be described with reference to Fig. 8. The inkjet head 101 of this embodiment differs from the first embodiment in the configuration of the piezoelectric actuator 112 (piezoelectric element 112X). Hereinafter, configurations common to the first embodiment will be assigned the same reference numerals and descriptions thereof will be omitted as appropriate.

[0049] In the piezoelectric element 12X of the first embodiment, the common electrode 12c is disposed between the vibration plate 12a and the piezoelectric layer 12b, and the individual electrode 12d is disposed on the upper surface of the piezoelectric layer 12b. On the other hand, in the piezoelectric element 112X of the present embodiment, the common electrode 12c is disposed on the upper surface of the piezoelectric layer 12b, and the individual electrode 12d is disposed between the vibration plate 12a and the piezoelectric layer 12b.

[0050] In this embodiment, the portions of the piezoelectric layer 12b sandwiched between the common electrode 12c and each individual electrode 12d are polarized upward. Therefore, in each piezoelectric element 112X of the piezoelectric actuator 112, when the potential of the individual electrode 12d is switched from ground potential to the drive potential, an electric field is generated in the portion of the piezoelectric layer 12b sandwiched between these electrodes, in the same upward direction as the polarization direction, due to the potential difference between the individual electrode 12d and the common electrode 12c maintained at ground potential. This electric field causes the above-mentioned portion of the piezoelectric layer 12b to contract horizontally, deforming the piezoelectric element 112X so as to convex toward the pressure chamber 22.

[0051] (Features of the second embodiment) In the inkjet head 101 of this embodiment, as in the first embodiment, the area of ​​the individual electrodes 12d can be reduced to make the device smaller, and the decrease in the displacement amount D of the piezoelectric element 112X can be suppressed.

[0052] Although the embodiments of the present invention have been described above with reference to the drawings, the specific configurations should not be considered to be limited to these embodiments. The scope of the present invention is defined by the claims rather than the above description of the embodiments, and further includes all modifications within the meaning and scope of the claims.

[0053] In the above embodiment, the description has been given of a case where the width α of the pressure chamber 22 and the width β of the individual electrode 12d satisfy the relationship of the above-mentioned formula 1, and have a relationship that can maximize the displacement amount D of the piezoelectric element 12X, but this is not limiting. In other words, it is sufficient that the width α of the pressure chamber 22 and the width β of the individual electrode 12d satisfy the relationship of the above-mentioned formula 2, and can make the displacement amount D of the piezoelectric element 12X 90% or more of the maximum value.

[0054] Furthermore, in the above-described embodiment, the common electrode 12c is maintained at ground potential, and the individual electrodes 12d are selectively applied with either ground potential or a predetermined drive potential higher than ground potential. However, this is not limiting. When the lower of the two potentials selectively applied to the individual electrodes 12d is designated as a first potential and the higher potential is designated as a second potential, the common electrode 12c may be maintained at a third potential that is equal to or greater than the first potential and equal to or less than the second potential. For example, the common electrode 12c may be maintained at a third potential of 10 V, and either a first potential of 0 V or a second potential of 20 V may be selectively applied to the individual electrodes 12d.

[0055] Furthermore, in the above-described embodiment, the pressure chambers 22 and the individual electrodes 12d are both rectangular in shape when viewed from above, but this is not limiting. The pressure chambers 22 and the individual electrodes 12d may have shapes that are long in the same direction, and may be elliptical or diamond-shaped, for example. Furthermore, the pressure chambers 22 and the individual electrodes 12d do not need to have the same shape; for example, one may be rectangular and the other elliptical.

[0056] In the above embodiment, the flow path unit 11 has a plurality of pressure chambers 22 arranged along its short side, but the present invention is not limited to this. It is sufficient that the flow path unit 11 is provided with at least one pressure chamber 22.

[0057] The recording format of the printer 100 is not limited to the serial type, but may be a line type in which ink is ejected from nozzles of a head that is long in the width direction of the recording paper P and is fixed in position.

[0058] The liquid ejected from the nozzles 21 is not limited to ink, but may be any liquid (for example, a treatment liquid that aggregates or precipitates components in the ink). Furthermore, the object onto which the liquid is ejected is not limited to the recording paper P, but may also be, for example, a cloth, a substrate, etc. [Explanation of symbols]

[0059] 1. Inkjet head (liquid ejection head) 11 Flow path unit 12 Piezoelectric Actuator 12b Piezoelectric layer (piezoelectric layer) 12c Common electrode (constant potential electrode) 12d Individual electrode (drive electrode) 12x Piezoelectric Elements 21 nozzles 22 Pressure Chamber

Claims

1. a flow path unit in which a flow path including a nozzle and a pressure chamber communicating with the nozzle is formed; a piezoelectric actuator stacked on the flow path unit, the piezoelectric actuator having a piezoelectric element that applies pressure to liquid in the pressure chamber at a portion that overlaps with the pressure chamber in a stacking direction of the flow path unit and the piezoelectric actuator, The piezoelectric element is a piezoelectric layer; a constant potential electrode disposed between the piezoelectric layer and the flow path unit; a drive electrode disposed on a surface of the piezoelectric layer opposite to the constant potential electrode, the drive electrode being selectively applied with a first potential or a second potential higher than the first potential; the constant potential electrode is maintained at a third potential that is equal to or higher than the first potential and equal to or lower than the second potential; each of the pressure chambers and the drive electrodes has a shape that is elongated in one direction perpendicular to the stacking direction; When the length of the pressure chamber along the short side direction perpendicular to both the stacking direction and the one direction is α [μm], and the length of the drive electrode along the short side direction is β [μm], β＝０．６２１７α＋３６．４４３ A liquid ejection head characterized by satisfying the following relational expression.

2. a flow path unit in which a flow path including a nozzle and a pressure chamber communicating with the nozzle is formed; a piezoelectric actuator stacked on the flow path unit, the piezoelectric actuator having a piezoelectric element that applies pressure to liquid in the pressure chamber at a portion that overlaps with the pressure chamber in a stacking direction of the flow path unit and the piezoelectric actuator, The piezoelectric element is a piezoelectric layer; a driving electrode disposed between the piezoelectric layer and the flow path unit, the driving electrode being selectively applied with a first potential or a second potential higher than the first potential; a constant potential electrode disposed on a surface of the piezoelectric layer opposite to the driving electrode side, the constant potential electrode is maintained at a third potential that is equal to or higher than the first potential and equal to or lower than the second potential; each of the pressure chambers and the drive electrodes has a shape that is elongated in one direction perpendicular to the stacking direction; When the length of the pressure chamber along the short side direction perpendicular to both the stacking direction and the one direction is α [μm], and the length of the drive electrode along the short side direction is β [μm], β＝０．６２１７α＋３６．４４３ A liquid ejection head characterized by satisfying the relationship:

3. 3. The liquid ejection head according to claim 1, wherein the third potential is 0V.

4. 4. The liquid ejection head according to claim 1, wherein the pressure chamber and the drive electrode each have a rectangular shape when viewed from the stacking direction.

5. In the flow path unit, the pressure chambers are arranged in the short-side direction, the piezoelectric actuator has a plurality of the piezoelectric elements provided individually for the plurality of pressure chambers, Each of the plurality of pressure chambers and the drive electrode provided for the pressure chamber among the plurality of piezoelectric elements, β＝０．６２１７α＋３６．４４３ 5. The liquid ejection head according to claim 1, wherein the following relationship is satisfied:

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