JP2006272702A - Liquid ejection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid ejection device hardly undergoing deterioration in displacement characteristics irrespective of repeated displacement and high in displacement stability for a long time. <P>SOLUTION: The liquid ejection device includes (1) a flow channel member equipped with a liquid compression chamber filled with liquid and a liquid ejection port in communication with the liquid compression chamber, and (2) a piezoelectric actuator wherein a piezoelectric element holding a piezoelectric ceramic layer between a pair of electrode layers is provided on a diaphragm comprising the piezoelectric ceramic layer, the pair of electrode layers are applied with electric field to deform the piezoelectric element to deform the whole piezoelectric element including a part of the diaphragm, wherein the capacity of the liquid compression chamber is increased/decreased by the deformation of the piezoelectric actuator to eject the liquid in the liquid compression chamber as liquid droplets through the liquid ejection port. The flow channel member comprises a conductive material, and when voltage is applied between the flow channel member and the electrode layer, at least a part of the diaphragm is polarized in a direction opposite to the polarization direction of the piezoelectric ceramic layer. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a liquid ejecting apparatus, and more particularly to a liquid ejecting apparatus that can be suitably used for a recording apparatus such as an ink jet printer or an ink jet plotter, a liquid supply apparatus, and a liquid ejecting apparatus.

  In recent years, liquid ejection devices that eject minute droplets from liquid ejection ports are not only printers for consumers such as inkjet printers and inkjet plotters, but also the formation of electronic circuits and the manufacture of color filters for liquid crystal displays, It is also beginning to be used in industrial applications such as the manufacture of organic EL displays.

  Such a liquid ejection device moves in the main operation direction, and intermittently ejects liquid droplets from the liquid ejection port of the liquid ejection device while moving the recording paper, the diaphragm, etc. in the sub-scanning direction intersecting the main scanning direction. Recording is performed by discharging. The term “recording” as used herein refers to printing characters or images on the surface of recording paper in the case of a printer. In industrial applications, an insulating layer or dielectric layer is formed on the surface of a diaphragm or the like. Electronic circuits, color filters for liquid crystal displays, light emitting cells for organic EL displays, and the like can be formed.

  In these applications, liquid discharge ports are arranged at high density in order to repeatedly discharge a specific amount of droplets to each region divided into a large number of minute regions at high speeds and accurately. It has become.

  The liquid discharge port that discharges the liquid droplets communicates with the liquid pressurizing chamber, and the liquid droplets can be discharged from the liquid discharge port by applying pressure to the liquid filled in the liquid pressurizing chamber. Examples of such a pressurizing method include a piezoelectric method, a heating method, and an electrostatic method.

  The piezoelectric method is to pressurize the liquid by increasing / decreasing the volume of the liquid pressurizing chamber by deformation of the piezoelectric actuator, and there are few restrictions on the type of liquid in industrial applications where organic solvents or acidic or alkaline liquids are used, In addition, a piezoelectric method having excellent durability has attracted attention.

  A print head used in an inkjet recording apparatus using a piezoelectric method has a structure in which a piezoelectric actuator 51 is provided on a flow path member 53 as shown in, for example, FIG. 1). In the piezoelectric flow path member 53, a plurality of liquid pressurizing chambers 53 a are partitioned by partition walls 53 b, and the liquid pressurizing chambers 53 a are arranged side by side so as to contact the piezoelectric actuator 51.

  The piezoelectric actuator 51 is formed by providing a piezoelectric ceramic layer 55 on a diaphragm 52 having a common electrode 54 formed on the surface thereof, and providing a drive electrode 56 on the piezoelectric ceramic layer 55. In other words, the displacement formed by the drive electrode 56, the opposed portion 54a of the common electrode 54 facing the drive electrode 56, and the sandwiching region 55a of the piezoelectric ceramic layer 55 sandwiched between the drive electrode 56 and the opposed portion 54a. A plurality of elements 57 are arranged on the diaphragm 52.

  In recent years, the displacement element has been made thinner, and the displacement element has been increasingly applied with a voltage higher than the coercive electric field of the piezoelectric body.

  Further, as shown in FIG. 3B, a plurality of drive electrodes 56 are arranged on the surface of the piezoelectric ceramic layer 55 to form a plurality of displacement elements 57. Usually, the drive electrodes 56 are formed so as to form a matrix arrangement. The piezoelectric actuator 51 is disposed on the flow path member 53 so that the drive electrode 56 is positioned immediately above the liquid pressurizing chamber 53a.

  In such a print head, a voltage is applied between the common electrode 54 and the predetermined drive electrode 56 to displace the sandwiching region 55a of the piezoelectric ceramic layer 55 immediately below the drive electrode 56, whereby the displacement region 57a corresponds. It is deformed so as to be convex in the direction of the liquid pressurizing chamber 53a, pressurizing the ink in the liquid pressurizing chamber 53a, and ejecting liquid droplets from the liquid ejection port 58 opened on the bottom surface of the flow path member 53. it can.

  When such a piezoelectric actuator 51 is used, the piezoelectric ceramic layer 55 is subjected to polarization treatment to increase the amount of displacement and enhance the droplet discharge performance. For example, it is disclosed that a voltage is applied to the common electrode 54 and the drive electrode 56 to polarize a portion of the piezoelectric ceramic layer 55 sandwiched between these electrodes in a specific direction (see, for example, Patent Document 2). .

  However, since the polarization of the piezoelectric ceramic layer 55 gradually deteriorates with the passage of time, there has been a problem that the displacement characteristics are gradually lowered and, as a result, the droplet ejection characteristics are also lowered.

Therefore, especially when a voltage higher than the coercive electric field is applied to the deterioration over time of the piezoelectric actuator 51, the piezoelectric body is uniformly repolarized regardless of the difference in its driving history, and its displacement performance It has been proposed to recover sufficiently and evenly (see, for example, Patent Document 3).
JP 2003-165214 A JP 2001-105592 A JP 2002-355967 A

  However, although the piezoelectric actuator described in Patent Document 1 can recover the displacement characteristics by repolarizing a piezoelectric ceramic layer whose characteristics have been degraded repeatedly by repolarization, repolarization is necessary again when repeated displacement occurs, and the liquid ejection device There has been a problem that the repolarization process must be performed with frequent stoppage.

  Accordingly, an object of the present invention is to provide a liquid ejection apparatus that is less likely to deteriorate in displacement characteristics even when repeatedly displaced and has high long-term displacement stability.

The liquid ejection device of the present invention is
(1) a flow path member including a liquid pressurizing chamber filled with a liquid and a liquid discharge port communicating with the liquid pressurizing chamber;
(2) A piezoelectric element formed by sandwiching a piezoelectric ceramic layer between a pair of electrode layers is provided on a diaphragm made of a piezoelectric ceramic layer, and an electric field is applied to the pair of electrode layers to A piezoelectric actuator that deforms the entire piezoelectric element including a part of the diaphragm by deforming;
A liquid ejection device that ejects the liquid in the liquid pressurization chamber as droplets through the liquid ejection port by increasing or decreasing the volume of the liquid pressurization chamber by deformation of the piezoelectric actuator,
The flow path member is made of a conductive material, and by applying a voltage between the flow path member and the electrode layer, at least a part of the diaphragm is placed in a direction opposite to the polarization direction of the piezoelectric ceramic layer. It is characterized by being polarized.

  In particular, it is preferable that a plurality of the displacement elements are provided in a matrix on the diaphragm.

  The thickness of the diaphragm is preferably 5 to 50 μm.

  Furthermore, it is preferable to provide a control means for performing polarization of the diaphragm.

  Further, it is preferable that the liquid pressurizing chamber is filled with a conductive liquid, and the liquid filled in the liquid pressurizing chamber is used as one electrode for polarization of the diaphragm.

  According to the present invention, even if a piezoelectric body is used for the diaphragm, if the piezoelectric body is polarized in the opposite direction to the piezoelectric ceramic layer constituting the displacement element, the compliance of the piezoelectric body can be increased and the durability can be improved. As a result, a liquid ejecting apparatus that can be stably driven for a long period of time is realized by using a piezoelectric actuator whose displacement characteristics are unlikely to deteriorate even when repeatedly displaced.

  That is, in the conventional piezoelectric actuator, since the electrode layer gradually contracts due to creep at the boundary of the deformation region of the displacement element, the compressive stress acting on the piezoelectric element gradually increases and deteriorates the displacement characteristics. However, there was a phenomenon that the displacement performance was not fully recovered. Therefore, if the piezoelectric body used for the diaphragm is polarized in the opposite direction to the piezoelectric ceramic layer that constitutes the displacement element, the compliance of the piezoelectric body can be increased, the creep deformation of the electrode layer can be suppressed, and the characteristics of the piezoelectric actuator can be suppressed. Deterioration can be prevented.

  The case where the liquid ejection apparatus of the present invention is applied to an inkjet head will be described as an example.

  FIG. 1 is an explanatory diagram in which a part of circuit control is added to a schematic cross-sectional view of an ink jet head using a liquid ejection apparatus of the present invention.

  According to FIG. 1, the piezoelectric actuator 1 used for the liquid ejection apparatus of the present invention has a structure provided on the flow path member 3 (see, for example, Patent Document 1). In the piezoelectric flow path member 3, a plurality of liquid pressurizing chambers 3 a are partitioned by partition walls 3 b, and the liquid pressurizing chambers 3 a are arranged side by side so as to contact the piezoelectric actuator 1.

  The piezoelectric actuator 1 includes a piezoelectric ceramic layer 5 provided on a diaphragm 2 having a common electrode 4 formed on a surface thereof, and a drive electrode 6 provided on the piezoelectric ceramic layer 5. In other words, if the displacement element 7 is defined as having a piezoelectric ceramic layer sandwiched between a pair of electrode layers, the piezoelectric actuator 1 has a facing portion facing the driving electrode 6 and the driving electrode 6 of the common electrode 4. A plurality of displacement elements 7 formed by the drive electrode 6 and the sandwiching region of the piezoelectric ceramic layer 5 sandwiched between the opposing portions are disposed on the diaphragm 2.

  As shown in FIG. 1B, a plurality of drive electrodes 6 are arranged on the surface of the piezoelectric ceramic layer 5 to form a plurality of displacement elements 7. Usually, the drive electrodes 6 are formed in a matrix arrangement. The piezoelectric actuator 1 is disposed on the flow path member 3 so that the drive electrode 6 is positioned immediately above the liquid pressurizing chamber 3a. With such a configuration, the liquid discharge ports 8 can be formed with high density, and when used as an inkjet head, higher-definition printing can be performed.

  In such a print head, the common electrode 5 and the drive electrode 6 are each connected to a drive circuit 9, and the drive circuit 9 is connected to control means (not shown). Then, by applying a voltage between the common electrode 4 and the predetermined drive electrode 6 to displace the sandwiching region 5a of the piezoelectric ceramic layer 5 directly below the drive electrode 6, the liquid pressurizing chamber 3a corresponding to the displacement region 7a. The liquid in the liquid pressurizing chamber is changed as a droplet from the liquid discharge port 8 opened at the bottom surface of the flow path member 3 by increasing or decreasing the volume in the liquid pressurizing chamber 3a. It can be discharged.

  According to the present invention, the diaphragm is made of a so-called piezoelectric material exhibiting piezoelectricity, for example, lead zirconate titanate (PZT) and PZT with oxides such as lanthanum, barium, niobium, zinc, nickel, and manganese. A PZT-based piezoelectric material such as PLZT to which one or more kinds are added can be mentioned. Moreover, the material which has lead magnesium niobate (PMN), lead nickel niobate (PNN), lead zinc niobate, lead manganese niobate, lead antimony stannate, lead titanate, barium titanate etc. can be illustrated. .

  Such a diaphragm can be fired simultaneously with the piezoelectric element formed thereon. For example, a conductive paste serving as the common electrode 23 is printed on the surface of the piezoelectric green sheet, and another piezoelectric ceramic green sheet is laminated thereon so as to cover the common electrode, and the obtained laminate is fired and sintered. Form the body. Thereafter, the drive electrode 6 can be produced by applying a conductive paste to the surface of the sintered body and performing a heat treatment.

  According to the present invention, it is important to polarize at least a part of the diaphragm in a direction opposite to the polarization direction of the piezoelectric ceramic layer by applying a voltage between the flow path member and the electrode layer. It is.

  In conventional piezoelectric actuators, the electrode layer gradually shrinks due to creep at the boundary of the deformation region of the displacement element, so that the compressive stress acting on the piezoelectric element gradually increases and degrades the displacement characteristics. There has been a phenomenon that has not fully recovered.

  Therefore, if the piezoelectric body used for the diaphragm is polarized in the direction opposite to the piezoelectric ceramic layer constituting the displacement element, the compliance of the piezoelectric body can be increased and the creep deformation of the electrode layer can be suppressed.

  Then, creep occurs in the electrode between the active layer and the non-active layer elastically, or in the piezoelectric ceramic of the non-active layer, the strain in the tensile direction is fixed by the rotation of the domain in the crystal, and the active layer is compressed. Therefore, it is possible to suppress the deterioration of the characteristics due to the action, and to realize a stable piezoelectric actuator that can be driven for a long time.

  Further, by applying a voltage between the flow path member and the electrode layer, it is possible to easily polarize the diaphragm without providing any electrode.

  In particular, it is preferable to fill the liquid pressurizing chamber with a conductive liquid and use the liquid filled in the liquid pressurizing chamber as one electrode for polarization of the diaphragm. Thereby, the polarization of the whole diaphragm can be performed more uniformly, and it becomes easy to suppress the occurrence of variations in displacement of the displacement elements and variations in characteristics.

  Furthermore, it is preferable that the liquid ejection apparatus includes a control unit for polarizing the diaphragm. Specifically, a conducting wire for polarization is formed at one end of the common electrode and the flow path member configured on the diaphragm, and a polarization control circuit is provided. Thereby, it is possible to polarize only the diaphragm in the reverse direction independently of the voltage application between the active layer and the common electrode.

  The displacement elements 7 are preferably provided in a matrix. In particular, by arranging them at a high density, droplets of a desired size can be ejected into a desired space at a desired timing. Printing with high image quality can be performed.

  The thickness of the diaphragm is preferably 5 to 50 μm, particularly 10 to 40 μm, and more preferably 15 to 30 μm. By setting the thickness of the diaphragm to 5 to 50 μm, a high electric field can be applied between the pair of electrodes at a low voltage, and the piezoelectric actuator can be flexed efficiently.

  The flow path member 3 may be made of metal, ceramic, or resin. However, the flow path member 3 only needs to have conductivity and be able to polarize the diaphragm. For example, in the case of metal, a thin plate having grooves and holes is laminated on the surface and inside, and a liquid channel, a liquid pressurizing chamber, and a liquid discharge port are provided inside.

  More specifically, the metal channel member 3 forms a liquid pressurizing chamber 3a and a liquid discharge port 8 by etching a metal thin plate formed to a predetermined thickness by a piezoelectric method or the like. Examples of the metal material forming the flow path member 3 include an Fe—Cr alloy, an Fe—Ni alloy, a WC—TiC alloy, and the like. It is preferable to use a Ni-based alloy.

  As a material constituting the piezoelectric ceramic layer 4, lead zirconate titanate (PZT), or one in which one or more oxides of lanthanum, barium, niobium, zinc, nickel, manganese, etc. are added to the PZT, For example, a PZT piezoelectric material such as PLZT can be exemplified.

  Also illustrated are piezoelectric ceramics mainly composed of lead magnesium niobate (PMN), lead nickel niobate (PNN), lead zinc niobate, lead manganese niobate, lead antimony stannate, lead titanate, barium titanate, etc. it can.

  Examples of the common electrode 5 include single metals such as Ag, Pd, Pt, Rh, Au, and Ni, or alloys containing these metals. In particular, Ag-Pd alloys are inexpensive and have high conductivity. Is preferred. The common electrode 5 can be obtained by preparing a conductive paste containing the above metal or alloy powder, applying it to the surface of the piezoelectric ceramic green sheet, and simultaneously firing the laminated body.

  The thickness of the common electrode 5 is preferably 0.5 to 8 [mu] m, particularly 0.7 to 4 [mu] m, and more preferably 0.9 to 3 [mu] m, in order to ensure sufficient conductivity and not disturb the deformation of the piezoelectric actuator 1.

  As the metal forming the drive electrode 6, the same metal or alloy as that of the common electrode 5 can be used. However, it is preferable to use Au in consideration of electric resistance and corrosion resistance. The thickness of the drive electrode is preferably 0.5 to 5 μm, and more preferably 0.5 to 2 μm.

  The drive electrode 6 is made of a conductive paste containing a metal powder such as Au, and is formed on the surface of the laminated sintered body of the diaphragm 2, the common electrode 5 and the piezoelectric ceramic layer 4 by a printing method such as a screen printing method. This pattern can be printed and formed (for example, FIG. 1B). Also, a plating resist layer having an opening of a predetermined shape is formed on the surface of the piezoelectric ceramic layer 4 using a photolithographic method or the like, and after the plating of the metal, the resist layer is removed to form a predetermined shape. It is also possible to do.

  The total thickness of the piezoelectric actuator 1 is preferably 100 μm or less, particularly 80 μm or less, more preferably 65 μm or less, and more preferably 50 μm or less in order to be deformed satisfactorily when a drive voltage is applied from the drive circuit 9. Further, considering sufficient mechanical strength and prevention of breakage during handling and operation, it is preferably 10 μm or more, particularly 20 μm or more.

  When the piezoelectric characteristic of the piezoelectric actuator 1 is deteriorated and the polarization process for reproducing the piezoelectric ceramic layer 2 is performed, the piezoelectric ceramic layer 2 is polarized in order to efficiently polarize the piezoelectric ceramic layer 2 at a low voltage. The thickness of is preferably 50 μm or less, particularly 30 μm or less, and more preferably 20 μm or less. Moreover, in order to provide sufficient mechanical strength and to effectively prevent breakage during handling and operation, the thickness is desirably 5 μm or more.

  In order to improve the corrosion resistance to acid, alkali solution, corrosive water-based ink, etc., the piezoelectric actuator 1 has a surface of the diaphragm 2 constituting the wall surface of the liquid pressure chamber 3a made of a ceramic layer having corrosion resistance. It is desirable to coat.

  The piezoelectric actuator 1 and the flow path member 3 can be joined together by, for example, bonding via an adhesive layer (not shown). Examples of the adhesive include conventionally known various adhesives, but considering the heat resistance of the inkjet head and the improvement of resistance to ink, an epoxy adhesive having a thermosetting temperature of 100 to 250 ° C., It is preferable to use a thermosetting adhesive such as phenol resin or polyphenylene ether resin. The ink jet head is manufactured by laminating the piezoelectric actuator 1 and the flow path member 3 through these adhesive layers and heating them to the thermosetting temperature of the adhesive.

  At the time of recording, the control unit controls the drive circuit 9 based on the recording information such as characters and images transmitted from the host computer, and the drive circuit 9 causes the common electrode 5 and the arbitrary drive electrode 6 to be connected. In the meantime, a drive voltage having a predetermined pulse waveform is applied. Then, the region of the piezoelectric actuator 1 to which the drive voltage is applied operates, and ink droplets are ejected from the liquid ejection port 8 communicating with the liquid pressurizing chamber 3a corresponding to the region to perform recording.

  FIG. 2 shows another structure of the piezoelectric actuator used in the liquid ejection apparatus of the present invention. According to FIG. 2A, the diaphragm 12 is composed of a first piezoelectric ceramic layer 12a, a second piezoelectric ceramic layer 12b, and an internal electrode layer 12c formed so as to be sandwiched therebetween. A common electrode 15, a piezoelectric ceramic layer 14, and a plurality of drive electrodes 16 are formed on the diaphragm 12 in this order. Although not shown, the common electrode 15, the internal electrode 12c, and the drive electrode 16 are each connected to a drive circuit (not shown).

  Thus, when the diaphragm 12 is composed of two piezoelectric ceramic layers and a conductive member is inserted between them, the second piezoelectric ceramic layer 12b is preferably polarized. At that time, by using the drive circuit 9 between the internal electrode 12c and the metal flow path member 3 to polarize the second piezoelectric ceramic layer 12a, the piezoelectric material has little deterioration in displacement characteristics even when repeatedly displaced. An actuator and a liquid ejection apparatus using the actuator and having high long-term displacement stability can be provided.

  In any method, when driving the piezoelectric actuator 11, it is preferable to short-circuit the common electrode 15 and the internal electrode 12c in the drive circuit so that both are at the ground potential. The common electrode 15, the internal electrode 12c, and the drive electrode 16 are each connected to a drive circuit (not shown). Accordingly, it is possible to prevent a potential difference from being generated between the electrodes 12a and 12c that sandwich the diaphragm 12 due to the piezoelectric effect as the diaphragm 12 is deformed, and an unnecessary influence on the deformation of the piezoelectric actuator 11.

  The liquid ejection device of the present invention can always maintain the displacement state of the piezoelectric actuator in a good state without reducing the operation rate of the piezoelectric ink jet head. Therefore, for example, in a recording apparatus for industrial use, an electronic circuit, a color filter for a liquid crystal display, a light emitting cell for an organic EL display, etc., can be accurately formed in a desired shape without reducing productivity. it can. In addition, in a small printer for consumer use, it is possible to continue recording characters and images without increasing the standby time and reducing the operation speed other than the normal standby time.

  The liquid discharge apparatus shown in FIG. 1 was manufactured.

  First, an acrylic resin emulsion, pure water, and a nylon ball with an average particle size of 10 mm are added to a piezoelectric ceramic powder mainly composed of lead zirconate titanate having a particle size of 0.5 to 3.0 μm. After mixing for 30 hours by a ball mill, a green sheet having a thickness of 35 to 37 μm to be the piezoelectric ceramic layer 4 and the vibration plate 2 was formed on a PET film having a thickness of 30 μm by using the obtained slurry.

  Next, the obtained green sheet is cut into 50 × 50 mm together with the PET film and classified into a set of two sheets, and then a metal that becomes the common electrode 12c is formed on substantially the entire surface of one of the two sheets. The paste was printed by a screen printing method, and without printing the metal paste on the remaining one green sheet, each green sheet and the metal paste was dried at 50 ° C. for 20 minutes using an explosion-proof dryer.

  The metal paste used was a mixture of silver powder and palladium powder having an average particle diameter of 2 to 4 μm in a ratio of 7 to 3.

  And after aligning the position of the other one green sheet on the printed surface of the above metal paste, it is thermocompression bonded by holding for 60 seconds while applying a pressure of 5 MPa at a temperature of 60 ° C. A laminate of sheets was formed. After that, a metal paste is filled in a pre-formed through hole, degreased by heating at 100 ° C. to 300 ° C. at a heating rate of 8 ° C. per hour for 25 hours, cooled to room temperature, and further a firing furnace And firing at a peak temperature of 1100 ° C. for 2 hours to obtain a laminated piezoelectric ceramic plate in which the diaphragm 2 and the piezoelectric ceramic layer 4 each have a thickness of 20 μm.

  Next, the driving electrode 6 is printed on the surface of the laminated piezoelectric ceramic plate with a metal paste, and is baked by passing through a continuous furnace having a peak temperature of 800 ° C. in 30 minutes, and then the outer edge is cut with a dicing saw. Were aligned to 33 mm × 12 mm.

  After that, the surface on which the drive electrode 6 is formed is placed facing the base, and the end surface is masked and put into a sputtering apparatus, and Pd, Cu and Au are sequentially formed on the surface of the piezoelectric ceramic 4, The lower surface electrode 5 having a total thickness of about 1 μm was formed to produce the piezoelectric actuator 1 of the present invention.

  The piezoelectric actuator 1 is formed with 90 drive electrodes 25 per row at a pitch of 254 μm in two rows parallel to the longitudinal direction.

  On the other hand, a liquid pressurizing chamber 3a having a length of 2 mm and a width of 0.18 mm is formed on a stainless steel foil having a thickness of 100 μm by a punching process using a die press method, and a flow path communicating with the liquid pressurizing chamber 3a. And the flow path member 3 was formed by bonding together the 100-micrometer-thick and 40-micrometer-thick stainless steel foil which formed the liquid discharge port 8 by the punching process which used the etching and the die press, respectively, through the adhesive agent.

  Next, the piezoelectric actuator 1 and the diaphragm 2 are joined together with an adhesive, and on the surface of the piezoelectric actuator 1, the drive electrodes 6 and the electrode material filled in the through holes from the common electrode 4 are exposed. Were joined to the drive circuit 9 via a flex circuit to obtain an ink jet head. Note that the lower surface electrode 3 b is electrically connected to the diaphragm 1, and both are used connected to the ground potential of the drive circuit 9.

  Here, a plurality of ink jet heads are produced, and signals are continuously applied from the drive circuit 9 to the drive electrodes 6, and vertical vibrations due to bending are applied to the drive electrodes 6 from the surface of the piezoelectric actuator 1. Observation was made with a laser Doppler vibration system, and the displacement of the piezoelectric actuator 1 was measured.

  In the long-term durability test, continuous application was performed at a driving frequency of 25 kHz and a driving frequency of 10 kHz.

  And every 100 million times of continuous drive, when the common electrode 5 and the lower surface electrode 21 are interrupted and a voltage of −25 V is applied to the diaphragm 2 and the polarization process is performed, and when the polarization process is not performed Displacement was measured at both, and the change in displacement after 10 billion drive cycles was compared.

  By applying the reverse polarization process to the diaphragm 2 according to the present invention, it was possible to suppress the deterioration of the average displacement to 5% or less with respect to the drive count of 10 billion times. On the other hand, when the reverse polarization treatment was not performed, the average displacement was -30%.

1 shows a structure of a liquid ejection apparatus according to the present invention, where (a) is a schematic explanatory view, and (b) is a plan view. It is a schematic sectional drawing which shows the structure of the piezoelectric actuator used for the liquid discharge apparatus of this invention. The structure of the conventional liquid discharge apparatus is shown, (a) is a schematic explanatory drawing, (b) is a top view.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 11 ... Piezoelectric actuator 2, 12 ... Diaphragm 3 ... Flow path member 3a ... Liquid pressurization chamber 3b ... Partition 4, 14, ... Common electrode 5, 15 ... Piezoelectric ceramic layers 6, 16 ... drive electrodes 7, 17 ... displacement element 7a ... displacement region 8 ... liquid discharge port 9 ... drive circuit 12a ... first piezoelectric ceramic layer 12b ..Second piezoelectric ceramic layer 12c ... internal electrode layer

Claims (5)

(1) a flow path member including a liquid pressurizing chamber filled with a liquid and a liquid discharge port communicating with the liquid pressurizing chamber;
(2) A piezoelectric element formed by sandwiching a piezoelectric ceramic layer between a pair of electrode layers is provided on a diaphragm made of a piezoelectric ceramic layer, and an electric field is applied to the pair of electrode layers to A piezoelectric actuator that deforms the entire piezoelectric element including a part of the diaphragm by deforming;
A liquid ejecting apparatus for ejecting the liquid in the liquid pressurizing chamber as droplets through the liquid ejecting port by increasing or decreasing the volume of the liquid pressurizing chamber by deformation of the piezoelectric actuator,
The flow path member is made of a conductive material, and by applying a voltage between the flow path member and the electrode layer, at least a part of the diaphragm is placed in a direction opposite to the polarization direction of the piezoelectric ceramic layer. A liquid ejection apparatus characterized by being polarized. The liquid projecting apparatus according to claim 1, wherein a plurality of the displacement elements are provided in a matrix on the diaphragm. The liquid projecting apparatus according to claim 1, wherein the diaphragm has a thickness of 5 to 50 μm. The liquid projecting apparatus according to claim 1, further comprising a control unit configured to perform polarization of the diaphragm. 5. The liquid pressurizing chamber is filled with a conductive liquid, and the liquid filled in the liquid pressurizing chamber is used as one electrode for polarization of the diaphragm. The liquid discharge apparatus according to any one of the above.

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