JP5359129B2 - Piezoelectric actuator, liquid discharge head, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problems that charges are concentrated on the common electrode layer of a piezoelectric element member for taking out a common electrode to the outside, heat is generated and stable ink droplet discharge characteristics can not be obtained. <P>SOLUTION: On a base member 13, at least three piezoelectric element members 12 for which a plurality of piezoelectric element columns 12a and 12b are arrayed are lined and arrayed in the array direction of the piezoelectric element columns. The common electrode layer 23 of each piezoelectric element member 12 and the base member 13 are electrically conducted, and the common electrode layer 23 of the piezoelectric element member 122 at the center is taken out to the outside from the common electrode layer 23A for outside takeout of the common electrode layer 23 of the piezoelectric element member 121 positioned at the end in the array direction. The average resistance value of a conductive layer 41A between the part 23a of the common electrode layer 23 of the piezoelectric element member 121 positioned at the end and the base member 13 is made lower than the average resistance value of a conductive layer 41B between the part 23a of the common electrode layer 23 of the piezoelectric element member 122 at the center and the base member 13. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a piezoelectric actuator, a liquid discharge head, and an image forming apparatus.

  In general, a printer, a fax machine, a copier, a plotter, or an image forming apparatus that combines a plurality of these functions includes, for example, a recording head composed of a liquid ejection head that ejects ink droplets, It is also referred to as “paper”, but the material is not limited, and a recording medium, recording medium, transfer material, recording paper, etc. are also used synonymously.) Some perform formation (recording, printing, printing, and printing are also used synonymously).

  The “image forming apparatus” means an apparatus that forms an image by discharging liquid onto a medium such as paper, thread, fiber, fabric, leather, metal, plastic, glass, wood, ceramics, etc. “Formation” not only applies an image having a meaning such as a character or a figure to a medium, but also applies an image having no meaning such as a pattern to the medium (a liquid discharge device that simply discharges droplets). Means). Further, “ink” is not limited to ink in a narrow sense, and is not particularly limited as long as it becomes liquid when ejected, and includes, for example, a DNA sample, a resist, a pattern material, and the like. .

  For example, as an ink jet head as a liquid discharge head, a displacement in the d33 or d31 direction of a piezoelectric element as an electromechanical conversion element as a pressure generating means for generating pressure to pressurize ink that is liquid in the liquid chamber is used. A so-called piezoelectric type is known in which an elastically deformable diaphragm that forms a wall surface is deformed and droplets are ejected by changing the volume / pressure in the liquid chamber.

  As an inkjet head using such a laminated piezoelectric element, conventionally, as described in Patent Document 1, piezoelectric layers and internal electrodes are alternately laminated, and individual external electrodes and common sides are formed on both end faces. A plurality of piezoelectric element columns are formed by forming grooves on the laminated piezoelectric element member on which external electrodes are formed, leaving a part of the plurality of piezoelectric element columns as a plurality of driving parts and non-driving parts at both ends. It is known that the common electrode is taken out from the non-driving portions at both ends of the piezoelectric element columns in the arrangement direction.

  Further, as described in Patent Document 2, as a line-type inkjet head, a plurality of nozzle openings are arranged on a single continuous nozzle plate, and the piezoelectric element processes a plurality of bulk piezoelectric bodies. As a structure for taking out the common electrode of the plurality of piezoelectric bodies to the outside, the structure in which the conductive portion of the piezoelectric body is conducted with respect to the conductive base to make contact with the outside is arranged. Are known.

Japanese Patent No. 3114771 JP 2006-175845 A

  However, when a long piezoelectric actuator or a liquid discharge head is configured by arranging a plurality of piezoelectric element members, the piezoelectric element member is used as a drive unit up to the piezoelectric element column at the end. Cannot be taken out to the outside by using the non-driving part.

  Therefore, the common electrode is once connected to the base member from the surface of the piezoelectric element member that is bonded to the base member, and then connected to the piezoelectric element member located at the end, and the non-driving portion of the piezoelectric element member at the end (non-driving piezoelectric element column) It is possible to take out the structure from the above.

  At this time, there is no problem when the number of piezoelectric element members arranged is small, but when the number of piezoelectric element members is large, or the number of piezoelectric element members arranged is small, the length of one piezoelectric element member is very large. When the current flowing through the common electrode increases, such as when it is long, it cannot be used as it is. That is, as the flowing current becomes enormous, heat is generated locally and a characteristic defect is caused. Further, as the resistance value increases, a resistance difference occurs between the piezoelectric element member near the center in the arrangement direction and the piezoelectric element member near the end in the arrangement direction, causing a problem that the drive timing of the actuator is shifted.

  Further, in the configuration of the liquid discharge head in which the piezoelectric actuator and the vibration plate formed of a conductive member such as a metal material are combined, when a voltage is applied to the piezoelectric element member, the vibration plate formed of the conductive member is charged. Occurs and a minute current flows. The minute current flows through the ink to the liquid sensing metal part, and the metal forming the diaphragm flows out. As a result, the diaphragm is melted and pinholes are generated. There is a problem that ink leaks from the generated pinhole and causes electrical destruction. For this reason, the diaphragm and the common electrode must be electrically connected in order to have the same potential as the common electrode of the piezoelectric element. However, if an attempt is made to pull out to the same surface on which the individual electrode is formed, an FPC or the like The joining area with the external substrate (external signal transmission means) and the area where the common electrode and the diaphragm are joined must coexist, and the piezoelectric element must be lengthened (enlarged) to secure the area. There is a problem of not becoming.

  The present invention has been made in view of the above problems, and an object of the present invention is to reduce the heat generated when a plurality of piezoelectric element members are arranged so that the length can be increased.

In order to solve the above problems, the piezoelectric actuator according to the present invention is:
On the base member, at least three piezoelectric element members in which a plurality of piezoelectric element columns are arranged are arranged side by side in the arrangement direction of the piezoelectric element columns,
The common electrode layer of each piezoelectric element member and the base member are electrically connected,
Common electrodes of the other piezoelectric element member located in the middle in the array direction from the common electrode layer in a portion of the piezoelectric element member located at an end in the arrangement direction is taken to the outside,
An average resistance value between the common electrode layer of the some piezoelectric element members and the base member is compared with an average resistance value between the common electrode layer of the other piezoelectric element members and the base member. rather than low-Te,
Each piezoelectric element member is fixed to the base member via a conductive adhesive,
The average density of the conductive particles contained in the conductive adhesive that fixes the part of the piezoelectric element members is greater than the average density of the conductive particles contained in the conductive adhesive that fixes the other piezoelectric element members. A high density configuration was used.

  The piezoelectric actuator according to the present invention is
  On the base member, at least three piezoelectric element members in which a plurality of piezoelectric element columns are arranged are arranged side by side in the arrangement direction of the piezoelectric element columns,
  The common electrode layer of each piezoelectric element member and the base member are electrically connected,
  The common electrode of another piezoelectric element member positioned in the middle in the arrangement direction is taken out from the common electrode layer of a part of the piezoelectric element members located at the end in the arrangement direction,
  An average resistance value between the common electrode layer of the some piezoelectric element members and the base member is compared with an average resistance value between the common electrode layer of the other piezoelectric element members and the base member. Each piezoelectric element member is fixed to the base member via a conductive adhesive,
  The composition of the conductive particles contained in the conductive adhesive that fixes the part of the piezoelectric element members is higher in conductivity than the composition of the conductive particles contained in the conductive adhesive that fixes the other piezoelectric element members. Is composition
The configuration.

  The liquid discharge head according to the present invention is configured to include the piezoelectric actuator according to the present invention.

  The image forming apparatus according to the present invention is configured to include the liquid discharge head according to the present invention.

According to the liquid ejection head of the present invention, even if the current concentrated on the piezoelectric element member at the end increases, heat generation and the like are reduced, and the length can be further increased.

  According to the liquid ejection head according to the present invention, since the piezoelectric actuator according to the present invention is provided, there is little deterioration of the droplet ejection characteristics due to heat generation, and stable droplet ejection can be performed.

  According to the image forming apparatus of the present invention, since the liquid ejection head according to the present invention is mounted, stable image formation can be performed.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. An ink jet head as a liquid discharge head according to the present invention will be described with reference to FIGS. 1 is an exploded perspective view of the head, FIG. 2 is a sectional explanatory view along a direction (liquid chamber longitudinal direction) orthogonal to the nozzle arrangement direction of the head, and FIG. 3 is a nozzle arrangement direction (liquid chamber) of the head. It is some cross-sectional explanatory drawing along a transversal direction.

  This inkjet head includes a flow path substrate (liquid chamber substrate) 1 formed of a SUS substrate, a nozzle plate 2 bonded to the upper surface of the flow path substrate 1, and a vibration plate member 3 bonded to the lower surface of the flow path substrate 1. And a plurality of nozzles 5 for ejecting ink droplets to communicate with each of the pressurized liquid chambers 6, and each fluid resistance portion 7 that also serves as a supply path for supplying the liquid ink to each of the pressurized liquid chambers 6. Forming.

  Here, the flow path substrate 1 is formed by opening the pressurizing liquid chambers 6, the fluid resistance portions 7, and the like by subjecting the SUS substrate to mechanical processing such as etching or punching using an acidic etchant. Yes. The pressurized liquid chambers 6 are arranged at a pitch corresponding to, for example, 150 dpi.

  The nozzle plate 2 forms a nozzle 5 having a diameter of 10 to 30 μm, for example, corresponding to each pressurized liquid chamber 6 and is bonded to the flow path substrate 1 with an adhesive. The nozzle plate 2 may be made of a metal such as stainless steel or nickel, a resin such as a polyimide resin film, silicon, or a combination thereof. Further, a water repellent film is formed on the nozzle surface (surface in the ejection direction: ejection surface) by a known method such as a plating film or a water repellent coating in order to ensure water repellency with ink.

  The diaphragm member 3 is made of a metal plate made of nickel, for example. And in diaphragm area 3A which forms the wall surface of pressurizing fluid room 6 of diaphragm member 3, it formed in diaphragm 3B which is the thinnest part about 3-10 micrometers in thickness, and the central part of this diaphragm 3B. It has island-shaped convex portions 3C. Further, a beam 3D is provided between the island-shaped convex portions 3C of the diaphragm member 3 so as to correspond to the liquid chamber interval wall 6a, and a beam 3E is provided around the diaphragm member 3.

  A piezoelectric actuator 10 according to the present invention that deforms and displaces the diaphragm region 3A is disposed outside the diaphragm region 3A of the diaphragm member 3 (on the side opposite to the pressurized liquid chamber 6). The piezoelectric actuator 10 includes three or more (three examples here) piezoelectric element members 12 in which a plurality of piezoelectric element columns 12 a and 12 b are formed on a conductive base member 13. The piezoelectric element members 12 are arranged side by side in a column arrangement direction (hereinafter, simply referred to as “array direction”), and two rows of piezoelectric element members 12 are arranged (not limited to three rows per row).

  The piezoelectric element member 12 is formed by forming a plurality of piezoelectric element columns 12 a and 12 b by providing a groove 30 that is not divided by groove processing (slit processing) while being bonded and fixed to the base member 13. The piezoelectric element columns 12a and 12b are the same, but the piezoelectric element column 12a is a driving piezoelectric element column (driving unit) to which a driving waveform is applied, and the piezoelectric element column 12b is a supporting column piezoelectric element column (non-driving) to which a driving waveform is not applied. Drive unit).

  The piezoelectric element member 12 includes zirconate titanate (PZT) 21 having a thickness of 10 to 50 μm / layer and internal electrodes 22 and 22 made of silver / palladium (AgPd) having a thickness of several μm / layer. The electrodes are alternately stacked, and the internal electrodes 22 and 22 are alternately drawn out to the end face and connected to the common electrode layer 23 and the individual electrode layer 24 which are external electrodes (end face electrodes). By making the piezoelectric element member 12 a laminated type having a thickness of 10 to 50 μm / layer, low voltage driving is possible. For example, in order to obtain an electric field strength of 1000 V / mm of the piezoelectric element, a pulse voltage of 10 to 50 V is applied. Good. The piezoelectric element (synonymous with electromechanical conversion element) is not limited to PZT.

  Here, the driving piezoelectric element column 12a of the piezoelectric element member 12 is adhesively bonded to the island-shaped convex portion 32 of the vibration plate region 3a of the vibration plate member 3 corresponding to the pressurized liquid chamber 6, respectively. 12b is bonded to the beam 3D of the diaphragm member 3 with an adhesive. By applying a drive waveform to the drive piezoelectric element column 12a, the drive piezoelectric element column 12a expands and contracts, the diaphragm portion 3B of the diaphragm member 3 bends, and the internal volume / volume of the liquid chamber 6 changes.

  Further, an FPC cable 15 as an external signal transmission means (connection means) for giving a drive waveform to each piezoelectric element column 12a is connected to one end face of the piezoelectric element member 12. The FPC cable 15 includes a plurality of driver ICs 16 for applying drive waveforms (electric signals) for driving each channel (corresponding to each pressurized liquid chamber 6). As described above, by mounting a plurality of driver ICs 16 on the FPC cable 15, it is possible to set an electrical signal for each driver IC 16 and easily correct variations in the displacement characteristics of each drive channel of the drive piezoelectric element column 12a. Will be able to.

  Further, a frame member 17 surrounding the periphery of the piezoelectric actuator 10 is joined to the beam 3E around the diaphragm member 3 with an adhesive. The frame member 17 is provided with a common liquid chamber 18 for supplying ink from the outside to the pressurized liquid chamber 6 so as to be disposed on the opposite side across the driver IC 16 and at least the base member 13. Yes. The common liquid chamber 18 communicates with the fluid resistance portion 7 and the pressurized liquid chamber 6 through the through hole 8 of the diaphragm member 3.

  In the ink jet head configured as described above, for example, the drive piezoelectric element column 12a contracts by lowering the voltage applied to the drive piezoelectric element column 12a of the piezoelectric element member 12 from the reference potential, and the diaphragm region 3A of the diaphragm member 3 is contracted. Is lowered and the volume of the pressurized liquid chamber 6 expands, so that the ink flows into the pressurized liquid chamber 6 and then the voltage applied to the driving piezoelectric element column 12a is increased so that the driving piezoelectric element column 12a is stacked in the stacking direction. And the diaphragm region 3A is deformed in the direction of the nozzle 5 to contract the volume / volume of the pressurized liquid chamber 6, whereby the ink in the pressurized liquid chamber 6 is pressurized and ink droplets are ejected from the nozzle 5. Discharged.

  Then, by returning the voltage applied to the driving piezoelectric element column 12a to the reference potential, the diaphragm region 3A is restored to the initial position, and the pressurized liquid chamber 6 expands to generate a negative pressure. Ink is filled into the pressurized liquid chamber 6 from the chamber 18. Therefore, after the vibration of the meniscus surface of the nozzle 4 is attenuated and stabilized, the operation proceeds to the next droplet discharge.

  Note that the driving method of the head is not limited to the above example (drawing-pushing), and striking or pushing can be performed depending on the direction of the drive waveform.

  Next, the piezoelectric actuator according to the first embodiment of the present invention in the liquid discharge head configured as described above will be described with reference to FIG. 4 is an explanatory side sectional view taken along line AA of FIG. 2 for explaining the actuator, FIGS. 5 and 6 are explanatory views for explaining an internal electrode pattern of the piezoelectric element member, and FIGS. FIG. 9 is an explanatory view for explaining the formation process of the piezoelectric element member, and FIG. 10 is a perspective explanatory view of FIG.

  Here, among the three piezoelectric element members 12 arranged on the base member 13, the piezoelectric element member 12 located at the end in the arrangement direction is referred to as “piezoelectric element member 121”, and other than the piezoelectric element member 121 located at the end. The piezoelectric element member 12 is referred to as a “piezoelectric element member 122” located in the center in the arrangement direction.

  First, the piezoelectric element member 121 located at the end will be described with reference to FIGS. 5, 7, and 8. The piezoelectric element member 121 is formed by alternately laminating piezoelectric layers (piezoelectric material layers) 21 and internal electrodes 22A and internal electrodes 22B having a pattern shape as shown in FIGS. In other words, the internal electrodes 22A and 22B including the region portions (connection portions) 22Aa and 22Ba connected to both end surfaces are used for the piezoelectric element member 121 located at the end.

  In this case, in the piezoelectric element member 121 located at the end, the end surface in the longitudinal direction (arrangement direction) on the side where the connecting portions 22Aa and 22Ba of the internal electrodes 22A and 22B are provided is short as shown in FIG. The internal electrodes 22A and 22B are drawn out to both end faces in the hand direction. On the other hand, as shown in FIG. 8A, the longitudinal end surface of the piezoelectric element member 121 located at the end where the region portions 22Aa and 22Ba of the internal electrodes 22A and 22B are not provided is the internal electrode 22A. , 22B are pulled out to the end faces that are alternately different in the short direction (direction orthogonal to the arrangement direction).

  Accordingly, as shown in FIGS. 7B and 8B, the both ends of the short side direction and the bottom surface are formed by sputtering so that external electrodes are not formed on both end surfaces of the piezoelectric element member 121 in the longitudinal direction. A metal film 71 is formed. As a material for forming the metal film 71, Ag, Au, Cu, or the like is preferably used. In this example, Au is formed to a thickness of 0.4 μm by sputtering.

  Then, as shown in FIGS. 7 (c) and 8 (c), an end portion which becomes the outer side in the short direction of the base member 13 at the time of joining is cut off obliquely on the bottom surface side which becomes the joining surface with the base member 13. By forming the processed surface 28, the individual electrode layer 24 and the common electrode layer 23 made of the metal film 71 are formed. Accordingly, the common electrode layer 23 is formed in a state having a portion 23 a that goes around to the bottom surface of the piezoelectric element member 121. Further, at the end portion of the piezoelectric element member 121, the external electrode common electrode layer 23A that is electrically connected to the common electrode layer 23 by the internal electrodes 22Aa and 22Ba is formed on the end surface on the individual electrode 24 side. The piezoelectric element column 12b on which the external extraction common electrode layer 23A is formed is referred to as a “non-driving portion 26”.

  Next, the piezoelectric element member 122 located at the center will be described with reference to FIGS. The piezoelectric element member 122 is formed by alternately laminating internal electrodes 22C and internal electrodes 22D having a pattern shape as shown in FIGS. 6 (a) and 6 (b). As a result, the both end surfaces in the longitudinal direction of the piezoelectric element member 122 are in a state in which the internal electrodes 22C and 22D are alternately drawn out to the different end surfaces in the short direction as shown in FIG.

  Therefore, as shown in FIG. 9B, similarly to the piezoelectric element member 121, both end faces and bottom faces in the short direction are used by sputtering so that external electrodes are not formed on both end faces in the longitudinal direction of the piezoelectric element member 122. A metal film 71 is formed on the substrate. Then, as shown in FIG. 9 (c), a processed surface 28 is formed by obliquely notching the end portion that becomes the outer side in the short direction of the base member 13 at the time of joining on the bottom surface side that becomes the joining surface with the base member 13. Thus, the individual electrode layer 24 and the common electrode layer 23 made of the metal film 71 are formed. Accordingly, the common electrode layer 23 is formed in a state having a portion 23 a that goes around to the bottom surfaces of the piezoelectric element members 121 and 122.

  The piezoelectric element members 121 and 122 configured in this manner are bonded and fixed to the base member 13 formed of a metal material (for example, SUS304) that is a conductive member with a conductive adhesive. The resin component of the conductive adhesive is preferably a two-component curable epoxy that cures at room temperature. The conductive adhesive contained Ag as conductive particles, and the particle size distribution of Ag used was 3 μm at the center. The resin component is not limited to epoxy, and urethane, acrylic, silicone, and the like can also be used.

  As a result, the piezoelectric element member 121 located at the end is bonded and fixed in a state of being electrically connected to the base member 13 via the conductive layer 41A formed of the conductive adhesive, and the piezoelectric element member 122 is electrically conductive adhesive. The base member 13 is bonded and fixed to the base member 13 through the conductive layer 41B formed in the above.

  Here, as the conductive adhesive for fixing the piezoelectric element member 121 to the base member 13, a resin component to Ag ratio of 1: 2 was used. In addition, a conductive adhesive that fixes the piezoelectric element member 122 to the base member 13 was used with a resin component to Ag ratio of 1: 1. That is, each of the piezoelectric element members 121 and 122 is fixed to the base member 13 via a conductive adhesive, and the average of conductive particles contained in the conductive adhesive that fixes the piezoelectric element member 121 that takes out the common electrode to the outside. The density is configured to be higher than the average density of the conductive particles contained in the conductive adhesive that fixes the other piezoelectric element member 122.

  As a result, the average resistance value of the conductive layer 41A electrically connecting the common electrode layer 23 of the piezoelectric element member 121 and the base member 13 electrically connects the common electrode layer 23 of the piezoelectric element member 122 and the base member 13 to each other. Therefore, the average resistance value of the conductive layer 41B to be connected is lower (lower resistance). That is, by making the ratio composition between the resin component of the conductive adhesive and Ag as described above, the average resistance value of the common electrode layer 23 and the base member 13 of the piezoelectric element member 121 located at the end is the central portion. The piezoelectric element member 122 and the base member 13 which are located in the base member 13 are electrically connected in a state where the resistance value is lower than the average resistance value.

  After the piezoelectric element members 121 and 122 are joined and fixed to the base member 13 in this way, as shown in FIG. 10, the common electrode layer (common-side external electrode) 23 is provided on both end surfaces of the piezoelectric element members 121 and 122 in the short direction. And the individual electrode layer (individual side external electrode) 24 and the external extraction common electrode 23A are provided with slit processing (groove processing) to form the grooves 30, so that a plurality of piezoelectric element columns 12a and 12b are formed. It is formed. In the groove processing at this time, the slits (grooves) 30 are not formed up to the base member 13 with respect to the piezoelectric element members 121 and 122, and the bridge portion 27 having a predetermined width D in the depth direction is left at the bottom. . Accordingly, one piezoelectric element member 12 is a member integrally including a plurality of piezoelectric element columns 12a and 12b. The gap (gap) 31 between the piezoelectric element members 12 (121, 122) is the same as the width L1 of the groove 31.

  In this case, the piezoelectric element column located on the longitudinal end side of the base member 13 of the piezoelectric element member 121 becomes the non-driving portion 26 as described above. Since the region portions 22Aa and 22Ba of the internal electrodes 22A and 22B are provided corresponding to the non-driving portion 26, the metal film 71 on the individual electrode side end face of the non-driving portion 26 is the common electrode layer 23A for external extraction. It becomes.

  The path of charge movement of the piezoelectric element member configured as described above will be described with reference also to FIG. 10. When a voltage is applied to the common electrode layer 23 of the piezoelectric element member 122, the charge is shared by the piezoelectric element member 122. It moves from the electrode layer 23 to the base member 13 through the conductive layer 41B (path 51). Then, the charge that has moved in the base member 13 (path 52) travels along the conductive layer 41A of the piezoelectric element member 121 to the common electrode layer 23 (path 53). Some of the charges also move between the piezoelectric element columns through the conductive layer 41A. Next, the electric charge that has moved in the common electrode layer 23 of the piezoelectric element member 121 (path 54) moves in the internal electrode layers 22A and 22B in the non-driving unit 26 (path 55), and is extracted to the outside of the non-driving unit 26. A path to move to the common electrode layer 23A is taken.

  By connecting the common electrode line of the FPC cable 15 to the external lead common electrode layer 23A of the non-driving portion 26 of the piezoelectric element member 121, the common electrode layer 23 of the piezoelectric element member 122 is formed on one end surface of the piezoelectric element member 121. Can be taken out. That is, here, the common electrode layer 23 of the central piezoelectric element member 122 that is the other piezoelectric element member 12 from the common electrode layer 23 (23A) of the piezoelectric element member 121 located at the end that is a part of the piezoelectric element members 12 is used. Is taken out to the outside.

  Since the path as described above is taken, charges from the piezoelectric element member 122 located at the center are concentrated on the piezoelectric element member 121 located at the end.

  Therefore, the average resistance value of the conductive layer 41A made of a conductive adhesive that joins the piezoelectric element member 121 and the base member 13 is set to be the conductive value that joins the piezoelectric element member 122 and the base member 13 at the center. Since the resistance value is lower than the average resistance value of the conductive layer 41B made of the adhesive, heat generation due to charge concentration can be reduced.

  As described above, the piezoelectric actuator of the liquid discharge head has an average resistance value between the common electrode layer and the base member of a part of the piezoelectric element member that takes out the common electrode to the outside. Since the resistance is lower than the average resistance value between the common electrode layer of the other piezoelectric element member from which the common electrode is taken out via the member and the base member, the piezoelectric element member at the end Even if the concentrated current increases, heat generation and the like are reduced, and the length can be further increased.

  And the liquid discharge head provided with this piezoelectric actuator has little deterioration of the droplet discharge characteristic due to heat generation, and can perform stable droplet discharge.

  Note that there may be a plurality of piezoelectric element members for taking out the common electrode to the outside. For example, piezoelectric element members at both ends in the arrangement direction may be used. Further, the number of piezoelectric element members at the center is not limited to one.

Next, a piezoelectric actuator according to a second embodiment of the present invention will be described with reference to FIG. FIG. 11 is an explanatory perspective view of a main part of the piezoelectric actuator according to the embodiment.
Also here, a conductive adhesive is used to fix the piezoelectric element members 121 and 122 and the base member 13, and conductive layers 41C and 41D are formed between the piezoelectric element members 121 and 122 and the base member 13, respectively. Yes. The resin component of the conductive adhesive is preferably a two-component curable epoxy that cures at room temperature.

  As the conductive adhesive for fixing the piezoelectric element member 121 located at the end to the base member 13 to form the conductive layer 41C, a conductive adhesive containing both Ni particles and Ag particles is used. The particle size distributions of Ni particles and Ag particles were those having a center of 3 μm. The composition ratio of Ni particles and Ag particles was 1: 1 by weight. The ratio of the resin component to the conductive particles (Ni, Ag) was 1: 1. As the conductive particles, other particles such as Au, Cu, or a resin surface layer coated with a metal such as Au may be used. Ag and Au are noble metals and are expensive, but have the effect of reducing resistance, such as good conductivity and not being oxidized.

  On the other hand, as the conductive adhesive for forming the conductive layer 41D by fixing the piezoelectric element member 122 located at the center to the base member 13, a conductive adhesive containing only Ni particles as the conductive particles was used. The ratio of the resin component to the conductive particles (Ni) was 1: 1.

  By adopting such a metal particle (conductive particle) configuration, the conductive adhesive used for joining the piezoelectric element member 122 in the central portion uses relatively inexpensive particles, and the piezoelectric element member 121 in the central portion of the end is used. Although the conductive adhesive used for joining is expensive, it can form a conductive layer having a low resistance value.

  The base member 13 is made of a conductive material such as SUS material. The SUS material is preferable because it has a high Young's modulus and conductivity, but an oxide film can easily be formed on the surface as a passive film, which may impair the conductivity.

  Therefore, here, the Au film 42 having good ohmic properties with the conductive particles in the conductive adhesive is formed on the surface of the base member 13. As a forming method, first, the organic material on the surface of the base member 13 of SUS316 is removed by plasma treatment. Thereafter, an Au film 452 having a thickness of 1 μm is formed on the surface to which the piezoelectric element member is bonded using Au as a target in the sputtering apparatus. Au can be suitably used because it does not form an oxide film by bonding with oxygen and has a stable contact resistance when brought into contact with conductive particles. In addition, the same effect can be obtained with other metals such as Al, Cu, and Ni. The base member 13 and the piezoelectric element members 121 and 122 thus obtained have good ohmic properties with the conductive adhesive, and can further reduce resistance.

Next, a piezoelectric actuator according to a third embodiment of the present invention will be described with reference to FIGS. FIG. 12 is an explanatory perspective view of a main part of the piezoelectric actuator according to the embodiment, and FIGS. 13 and 15 are explanatory views for explaining a formation process of the piezoelectric element member.
First, the base member 13 to which the piezoelectric element member 12 is bonded is formed by forming Au serving as the first conductive layer 83 with a thickness of 0.4 μm on the ceramic substrate 131 that is an insulating member by sputtering, and then the second member. The solder to be the conductive layer 84 is similarly formed by sputtering to a thickness of 3 μm, and the conductive layers 83 and 84 of Au and solder are uniformly formed over the entire surface to which the piezoelectric element member 12 is bonded. Yes.

  Next, as shown in FIG. 13A and FIG. 14A, the piezoelectric element member 121 located at the end has a piezoelectric layer (piezoelectric material layer) and a piezoelectric layer (piezoelectric material layer) as described in the first embodiment. A member obtained by alternately laminating internal electrodes 22A and internal electrodes 22B having a pattern shape as shown in FIGS. 5A and 5B is formed, as shown in FIGS. 13B and 14B. Then, a metal film 81 is formed using a sputtering method. Here, Cu is used as the metal film 81 to have a thickness of 10 μm. In addition, as a material of the metal film 81, another metal may be sufficient and Al, Ni, etc. may be sufficient.

  Further, a metal film 82 is formed on the metal film 81 of the piezoelectric element member 121. Here, the metal film 82 is made of Au with a thickness of 0.4 μm using the sputtering method in the same manner as the metal film 81. Then, as shown in FIGS. 13C and 14C, a processed surface 28 is formed so that the metal films 81 and 82 are formed into the common electrode layer 23, the external electrode common electrode layer 23A, and the individual electrode layer 24. To separate.

  Further, as shown in FIG. 15A, the piezoelectric element member 122 in the central portion is similar to the piezoelectric layer (piezoelectric material layer) shown in FIG. 6A and FIG. A member in which internal electrodes 22C and internal electrodes 22D having a pattern shape as shown in FIG. 15B are alternately laminated is formed, and only the metal film 82 is formed as shown in FIG. Here, the metal film 82 is made of Au with a thickness of 0.4 μm using the sputtering method in the same manner as the metal film 81. Then, as shown in FIG. 15C, the processed surface 28 is formed to separate the metal film 82 into the common electrode layer 23 and the individual electrode layer 24.

  As a result, the piezoelectric element member 121 is formed with the external electrode layer 23 of 10.4 μm in total of the metal layer 81 (Cu layer) and the metal layer 82 (Au layer), and the piezoelectric element member 122 has the metal layer The external electrode layer 23 having a thickness of 0.4 μm is formed by one layer 82 (Au layer).

  Here, after the piezoelectric element members 121 and 122 are positioned and arranged with high accuracy on the base member 13 described above, heat at 250 ° C. is applied to solder the base member 13 and the piezoelectric element members 121 and 122 to each other. .

  The state of charge movement in the piezoelectric actuator configured as described above will be described. When a voltage is applied to the piezoelectric element member 122, the charge generated in the metal layer 82 as the common electrode layer 23 of the piezoelectric element member 122 becomes piezoelectric. It moves through the metal layer 82 of the element member 122 to the conductive layers 83 and 84 of the base member 13 (path 91). The electric charges move in the conductive layers 83 and 84 (path 92), a part moves to the metal layers 81 and 82 as the common electrode layer 23 of the piezoelectric element member 121 (path 93), and a part in the path 92 Moving. The electric charge passing through the path 93 passes through the metal layers 81 and 82 as the common electrode layer 23 formed on the piezoelectric element member 121 (path 94), and further moves through the internal electrodes 22Aa and 22Ba (path 95) to the outside. It moves to the common electrode layer 23A for extraction (comprising the metal layers 81 and 82).

  By connecting the common electrode line of the FPC cable 15 to the external electrode common electrode layer 23A of the non-driving portion 26 of the piezoelectric element member 121, another piezoelectric element member 122 is connected to one end surface of the piezoelectric element member 121 located at the end. The common electrode layer 23 can be taken out to the outside.

  In this configuration, since the conductive layers 83 and 84 formed on the base member 13 are thin and have a high resistance value, if the charge flowing into the piezoelectric element member 121 located at the end increases, a malfunction occurs due to local heat generation or the like. It will be.

  Therefore, here, the common electrode layer 23 of the piezoelectric element member 121 located at the end is formed of two layers of the metal layers 81 and 82, and the common electrode layer of the central piezoelectric element member 121 is increased by increasing the thickness thereof. Since the resistance value is lower than that of the electrode layer 83, 84 of the base member 13 (path 92), most of the electric charge flowing to the metal layers 81, 82 serving as the common electrode layer 23 is led to heat generation or abruptness. An increase in resistance can be prevented.

  The common electrode layer of the piezoelectric element member 121 located at the end has a two-layer structure of metal layers 81 and 82, and the common electrode layer of the central piezoelectric element member 122 has a one-layer structure of the metal layer 81. The conductive layer interposed between a part of the piezoelectric element members 121 and the base member 13 from which the common electrode is taken out and the conductive layer interposed between the other piezoelectric element members 122 and the base member 13 have different layer structures. However, with the same layer structure, the thickness of the common electrode layer of the piezoelectric element member located at the end is made thicker than the thickness of the common electrode layer of the central piezoelectric element member to reduce the resistance. You can also. In this case, the film thickness can be changed by changing the target of the sputtering apparatus or changing the processing time without changing the chamber.

  As described above, the conductive layer is interposed between each piezoelectric element member and the base member, and the conductive layer interposed between a part of the piezoelectric element members and the base member for taking out the common electrode to the outside, and the other piezoelectric elements. The conductive layer interposed between the member and the base member has a different layer structure or thickness so that the resistance value between some of the piezoelectric element members and the base member that take out the common electrode to the outside can be changed. The resistance value between the piezoelectric element member and the base member can be easily lowered.

  Next, a piezoelectric actuator according to a fourth embodiment of the present invention will be described with reference to FIGS. 16 is an explanatory side sectional view similar to that along the line AA in FIG. 2 for explaining the actuator, FIG. 17 is an explanatory view seen from the direction of arrow B in FIG. 16, and FIG. FIG. 19 and FIG. 20 are explanatory views for explaining the formation process of the piezoelectric element member.

  As described in the first embodiment, the piezoelectric element member 121 located at the end includes the piezoelectric layer (piezoelectric material layer) 21 and the above-described FIG. 5 as shown in FIGS. 19 (a) and 20 (a). The internal electrodes 22A and the internal electrodes 22B having the pattern shapes as shown in (a) and (b) are alternately stacked, and as shown in FIGS. 19 (b) and 20 (b), the piezoelectric element member 121 is formed. A metal film 71 is formed on the both end surfaces and the bottom surface in the short direction by sputtering so that external electrodes are not formed on both end surfaces in the longitudinal direction.

  Further, as shown in FIGS. 19C and 20C, a metal film 72 is formed by sputtering on one end surface of the piezoelectric element member 121 in the arrangement direction where there is no adjacent piezoelectric element column. The metal film 72 is preferably thick, and here, Al is formed to a thickness of 4 μm. In addition to Al, the metal film 72 may be a conductive metal such as Cu, Au, Ag, or Ni, or may be a low melting point alloy such as solder.

  Then, as shown in FIGS. 19 (d) and 20 (d), the end portion that becomes the outer side in the short direction of the base member 13 is cut obliquely on the bottom surface side that becomes the bonding surface with the base member 13. By forming the processed surface 28, the individual electrode layer 24 and the common electrode layer 23 made of the metal film 71 are formed. Accordingly, the common electrode layer 23 is formed in a state having a portion 23 a that goes around to the bottom surface of the piezoelectric element member 121. Further, at the end portion of the piezoelectric element member 121, the external electrode common electrode layer 23A that is electrically connected to the common electrode layer 23 by the internal electrodes 22Aa and 22Ba is formed on the end surface on the individual electrode 24 side. Further, a bridged common electrode layer 23 </ b> B that connects the common electrode layer 23 and the external extraction common electrode layer 23 </ b> A outside the piezoelectric element member 121 is formed of the metal film 72.

  Since the piezoelectric element member 122 located at the center is the same as that of the first embodiment, description thereof is omitted.

  These piezoelectric element members 121 and 122 are bonded and fixed on the base member 13 with the conductive adhesive 41 in a predetermined positional relationship, and groove processing is performed in the same manner as in the first embodiment described above to form a plurality of piezoelectric element columns. 12a and 12b are formed. The piezoelectric element members 121 and 122 may be fixed by other than the conductive adhesive, and may be conductive, for example, metal fusion bonding.

  Further, the base member 13 is preferably conductive, and stainless steel, iron, copper, aluminum, and the like are preferable. Alternatively, as described above, a conductive film may be formed on the surface of a nonconductive material such as ceramic.

  With this configuration, the piezoelectric element member 121 positioned at the end where the common electrode is externally extracted has the common electrode layer 23 connected to the external electrode common electrode layer 23A via the connection regions 22Aa and 22Ba of the internal electrodes 22A and 22B. In addition, it is electrically connected to the external extraction common electrode layer 23A via the cross-linked common electrode layer 23B.

  As described above, the common electrode of the piezoelectric element member positioned at the center in the arrangement direction is taken out from the common electrode of the piezoelectric element member positioned at the end in the arrangement direction, and the piezoelectric element adjacent to the piezoelectric element member positioned at the end is extracted. Even if the current concentrated on the piezoelectric element member located at the end where the common electrode is taken out increases, heat is generated even if the conductive layer that becomes the common electrode is formed on the end face in the arrangement direction without the element pillars Etc. can be reduced and the length can be further increased.

  Thereby, even if electric charges concentrate on the common electrode layer 23 of the piezoelectric element member 121 that takes out the common electrode from the common electrode layer 23 of the other piezoelectric element member 122 to the outside, heat generation can be suppressed.

Next, a piezoelectric actuator according to a fifth embodiment of the present invention will be described with reference to FIG. FIG. 21 is an explanatory side view of the main part of the actuator.
Here, in the same configuration as the piezoelectric actuator according to the fourth embodiment, the bridging common electrode layer 23B of the piezoelectric element member 121 and the diaphragm member 3 formed of a metal material are electrically connected by the conductive member 89. ing. As a result, the common electrode layer 23 and the diaphragm member 3 are at the same potential, and the charge generated in the diaphragm member 3 can be released through the common electrode layer 23, and the pin due to the elution of the diaphragm member 3 into the ink. The generation of holes can be prevented.

  In this case, the FPC 15A connected to the piezoelectric element member 121 is provided with the common electrode line 101 connected to the external extraction common electrode 23A and the individual electrode line 102 connected to the driving piezoelectric element column 12a, respectively, and the piezoelectric element member 122. The FPC 15B connected to is provided with an individual electrode line 102 connected to the driving piezoelectric element column 12a. The configurations of the FPCs 15A and 15B are the same as those of the fifth embodiment, although the description of the first to fourth embodiments is omitted.

  A head-integrated ink cartridge can also be configured by integrating an ink tank that supplies ink to a liquid discharge head including the piezoelectric actuator according to the present invention.

Next, an example of an image forming apparatus including the liquid ejection head according to the present invention will be described with reference to FIGS. Note that FIG. 22 is a schematic configuration diagram for explaining the overall configuration of the mechanism unit of the apparatus, and FIG. 23 is a plan view for explaining a main part of the mechanism unit.
This image forming apparatus is a serial type image forming apparatus, and a carriage 233 is slidably held in the main scanning direction by main and sub guide rods 231 and 232 which are guide members horizontally mounted on the left and right side plates 201A and 201B. The main scanning motor that does not perform moving scanning in the direction indicated by the arrow (carriage main scanning direction) via the timing belt.

  The carriage 233 has recording heads 234a and 234b (which are composed of liquid ejection heads according to the present invention for ejecting ink droplets of each color of yellow (Y), cyan (C), magenta (M), and black (K). When not distinguished, it is referred to as “recording head 234”). A nozzle row composed of a plurality of nozzles is arranged in the sub-scanning direction orthogonal to the main scanning direction, and is mounted with the ink droplet ejection direction facing downward.

  Each of the recording heads 234 has two nozzle rows. One nozzle row of the recording head 234a has black (K) droplets, the other nozzle row has cyan (C) droplets, and the recording head 234b has one nozzle row. One nozzle row ejects magenta (M) droplets, and the other nozzle row ejects yellow (Y) droplets.

  The carriage 233 is equipped with head tanks 235a and 235b (referred to as “head tank 235” when not distinguished) for supplying ink of each color corresponding to the nozzle rows of the recording head 234. The sub tank 235 is supplementarily supplied with ink of each color from the ink cartridge 210 of each color via the supply tube 36 of each color.

  On the other hand, as a paper feed unit for feeding the paper 242 loaded on the paper stacking unit (pressure plate) 241 of the paper feed tray 202, a half-moon roller (feed) that feeds the paper 242 from the paper stacking unit 241 one by one. A separation pad 244 made of a material having a large coefficient of friction is provided opposite to the sheet roller 243 and the sheet feeding roller 243, and the separation pad 244 is urged toward the sheet feeding roller 243 side.

  In order to feed the sheet 242 fed from the sheet feeding unit to the lower side of the recording head 234, a guide member 245 for guiding the sheet 242, a counter roller 246, a conveyance guide member 247, and a tip pressure roller. And a conveying belt 251 which is a conveying means for electrostatically attracting the fed paper 242 and conveying it at a position facing the recording head 234.

  The conveyor belt 251 is an endless belt, and is configured to wrap around the conveyor roller 252 and the tension roller 253 so as to circulate in the belt conveyance direction (sub-scanning direction). In addition, a charging roller 256 that is a charging unit for charging the surface of the transport belt 251 is provided. The charging roller 256 is disposed so as to come into contact with the surface layer of the conveyor belt 251 and to rotate following the rotation of the conveyor belt 251. The transport belt 251 rotates in the belt transport direction when the transport roller 252 is rotationally driven through timing by a sub-scanning motor (not shown).

  Further, as a paper discharge unit for discharging the paper 242 recorded by the recording head 234, a separation claw 261 for separating the paper 242 from the transport belt 251, a paper discharge roller 262, and a paper discharge roller 263 are provided. A paper discharge tray 203 is provided below the paper discharge roller 262.

  A duplex unit 271 is detachably mounted on the back surface of the apparatus body 1. The duplex unit 271 takes in the paper 242 returned by the reverse rotation of the transport belt 251, reverses it, and feeds it again between the counter roller 246 and the transport belt 251. The upper surface of the duplex unit 271 is a manual feed tray 272.

  Further, a maintenance / recovery mechanism 281 that is a head maintenance / recovery device according to the present invention includes a recovery means for maintaining and recovering the nozzle state of the recording head 234 in the non-printing area on one side of the carriage 233 in the scanning direction. Is arranged. The maintenance / recovery mechanism 281 includes cap members (hereinafter referred to as “caps”) 282a and 282b (hereinafter referred to as “caps 282” when not distinguished) for capping each nozzle surface of the recording head 234, and nozzle surfaces. A wiper blade 283 that is a blade member for wiping the ink, and an empty discharge receiver 284 that receives liquid droplets for discharging the liquid droplets that do not contribute to recording in order to discharge the thickened recording liquid. ing.

  In addition, in the non-printing area on the other side in the scanning direction of the carriage 233, the liquid that receives liquid droplets when performing idle ejection that ejects liquid droplets that do not contribute to recording in order to discharge the recording liquid thickened during recording or the like. An ink recovery unit (empty discharge receiver) 288 that is a recovery container is disposed, and the ink recovery unit 288 includes an opening 289 along the nozzle row direction of the recording head 234 and the like.

  In this image forming apparatus configured as described above, the sheets 242 are separated and fed one by one from the sheet feeding tray 202, and the sheet 242 fed substantially vertically upward is guided by the guide 245, and is conveyed to the conveyor belt 251 and the counter. It is sandwiched between the rollers 246 and conveyed, and further, the leading end is guided by the conveying guide 237 and pressed against the conveying belt 251 by the leading end pressing roller 249, and the conveying direction is changed by approximately 90 °.

  At this time, a positive output and a negative output are alternately applied to the charging roller 256, that is, an alternating voltage is applied, and a charging voltage pattern in which the conveying belt 251 alternates, that is, in the sub-scanning direction that is the circumferential direction. , Plus and minus are alternately charged in a band shape with a predetermined width. When the sheet 242 is fed onto the conveyance belt 251 charged alternately with plus and minus, the sheet 242 is attracted to the conveyance belt 251, and the sheet 242 is conveyed in the sub scanning direction by the circumferential movement of the conveyance belt 251.

  Therefore, by driving the recording head 234 according to the image signal while moving the carriage 233, ink droplets are ejected onto the stopped paper 242 to record one line, and after the paper 242 is conveyed by a predetermined amount, Record the next line. Upon receiving a recording end signal or a signal that the trailing edge of the paper 242 has reached the recording area, the recording operation is finished and the paper 242 is discharged onto the paper discharge tray 203.

  Since this image forming apparatus is equipped with the liquid ejection head according to the present invention, the ink droplet ejection characteristics can be stabilized and a high-quality image can be formed.

  In the above embodiment, the image forming apparatus having a printer configuration is described. However, the present invention is not limited to this, and the present invention can be applied to an image forming apparatus such as a printer / fax / copier multifunction machine. Further, the present invention can be similarly applied to a line type liquid discharge head and a line type image forming apparatus. Furthermore, the present invention can be applied to a liquid discharge head or an image forming apparatus that discharges a DNA sample, a resist, a pattern material, or the like.

FIG. 3 is an exploded perspective view of a liquid discharge head according to the present invention. It is sectional explanatory drawing which follows the direction (liquid chamber longitudinal direction) orthogonal to the nozzle arrangement direction of the head. It is a partial cross-sectional explanatory drawing along the nozzle arrangement direction (liquid chamber short direction) of the head. It is principal part side sectional explanatory drawing in alignment with the AA of FIG. 2 with which it uses for description of the piezoelectric actuator which concerns on 1st Embodiment of this invention. It is explanatory drawing with which it uses for description of the internal electrode pattern of some piezoelectric element members. It is explanatory drawing with which it uses for description of the internal electrode pattern of another piezoelectric element member. It is an end surface explanatory drawing of the piezoelectric element member seen from the arrow B direction of FIG. 4 used for description of the formation process of a part of piezoelectric element members. FIG. 5 is also an end face explanatory view of the piezoelectric element member as seen from the direction of arrow C in FIG. 4. It is an end surface explanatory drawing of the piezoelectric element member seen from the arrow D direction of FIG. 4 used for description of the formation process of another piezoelectric element member. FIG. 5 is a perspective explanatory view of FIG. 4. It is principal part perspective explanatory drawing of the piezoelectric actuator which concerns on 2nd Embodiment of this invention. It is principal part perspective explanatory drawing of the piezoelectric actuator which concerns on 3rd Embodiment of this invention. It is an end surface explanatory drawing of the piezoelectric element member similar to seeing from the arrow B direction of FIG. FIG. 5 is also an end face explanatory view of a piezoelectric element member similar to that seen from the direction of arrow C in FIG. 4. It is an end surface explanatory drawing of the piezoelectric element member similar to seeing from the arrow D direction of FIG. 4 with which it uses for description of the formation process of another piezoelectric element member. It is principal part side sectional explanatory drawing along the AA line of FIG. 2 with which it uses for description of the piezoelectric actuator which concerns on 4th Embodiment of this invention. It is explanatory drawing seen from the arrow B direction of FIG. It is explanatory drawing seen from the arrow D direction of FIG. It is end surface explanatory drawing seen from the arrow B direction of FIG. 16 with which it uses for description of the formation process of one part piezoelectric element member. It is the end surface explanatory drawing similarly seen from the arrow C direction of FIG. It is principal part side explanatory drawing of the piezoelectric actuator which concerns on 5th Embodiment of this invention. 1 is a schematic configuration diagram illustrating an overall configuration of a mechanism unit illustrating an example of an image forming apparatus including a liquid ejection head according to the present invention. It is a principal part top explanatory drawing of a mechanism part similarly.

Explanation of symbols

1 ... channel substrate
2 ... Nozzle plate
3 ... Diaphragm
5 ... Nozzle
DESCRIPTION OF SYMBOLS 6 ... Pressurized liquid chamber 10 ... Piezoelectric actuator 12 ... Laminated piezoelectric element member 12a ... Drive piezoelectric element column 12b ... Supporting piezoelectric element column 13 ... Base member 23 ... Common electrode layer 23A ... Common electrode layer for external extraction 23B ... Common cross-linking Electrode layer 24 ... Individual electrode layer 41 ... Conductive adhesive 41A, 41B, 41C, 41D ... Conductive layer 81, 82 ... Metal layer 121 ... Piezoelectric element member at end 122 ... Central piezoelectric element member 234 ... Recording head ( Liquid discharge head)

Claims (8)

On the base member, at least three piezoelectric element members in which a plurality of piezoelectric element columns are arranged are arranged side by side in the arrangement direction of the piezoelectric element columns,
The common electrode layer of each piezoelectric element member and the base member are electrically connected,
Common electrodes of the other piezoelectric element member located in the middle in the array direction from the common electrode layer in a portion of the piezoelectric element member located at an end in the arrangement direction is taken to the outside,
An average resistance value between the common electrode layer of the some piezoelectric element members and the base member is compared with an average resistance value between the common electrode layer of the other piezoelectric element members and the base member. rather than low-Te,
Each piezoelectric element member is fixed to the base member via a conductive adhesive,
The average density of the conductive particles contained in the conductive adhesive that fixes the part of the piezoelectric element members is greater than the average density of the conductive particles contained in the conductive adhesive that fixes the other piezoelectric element members. A piezoelectric actuator characterized by high density .   On the base member, at least three piezoelectric element members in which a plurality of piezoelectric element columns are arranged are arranged side by side in the arrangement direction of the piezoelectric element columns,
  The common electrode layer of each piezoelectric element member and the base member are electrically connected,
  The common electrode of another piezoelectric element member positioned in the middle in the arrangement direction is taken out from the common electrode layer of a part of the piezoelectric element members located at the end in the arrangement direction,
  An average resistance value between the common electrode layer of the some piezoelectric element members and the base member is compared with an average resistance value between the common electrode layer of the other piezoelectric element members and the base member. Each piezoelectric element member is fixed to the base member via a conductive adhesive,
  The composition of the conductive particles contained in the conductive adhesive that fixes the part of the piezoelectric element members is higher in conductivity than the composition of the conductive particles contained in the conductive adhesive that fixes the other piezoelectric element members. Is composition
A piezoelectric actuator characterized by that.   3. The piezoelectric actuator according to claim 1, wherein the base member is a member having conductivity or a member having a conductive film formed on an insulating member. Conductive layer is interposed between the base member and the piezoelectric element member, a conductive layer interposed between said part of the piezoelectric element member and the base member, the other piezoelectric element member and said base member the piezoelectric actuator according to any one of claims 1 to 3 as compared with the conductive layers interposed, multi layer structure or thickness, wherein the thick between. The piezoelectric actuator according to claim 4 , wherein a conductive layer interposed between the piezoelectric element member and the base member is a part of the common electrode layer. A liquid discharge head comprising the piezoelectric actuator according to any one of claims 1 to 5 . The liquid ejection head according to claim 6 , wherein the common electrode layer of the piezoelectric actuator is electrically connected to a vibration plate that is vibrated by the piezoelectric actuator. An image forming apparatus comprising the liquid discharge head according to claim 7 .

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