JP2007012867A - Actuator and discharge device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric actuator and discharge device assuring excellent drive durability by mitigating deterioration in displacement due to repetitive drive. <P>SOLUTION: The piezoelectric actuator 1 displaces a displacement element 6 by laminating a common electrode 3, a piezoelectric ceramic layer 4, and a drive electrode 5 in this sequence on a piezoelectric vibrating plate 2; allocating a plurality of drive electrodes 5 on the surface of the piezoelectric ceramic layer 4; forming a plurality of displacement elements 6 each of which is formed by holding the piezoelectric ceramic layer 4 with the drive electrode 5 and common electrode 3; and by applying a drive voltage across the common electrode 3 and drive electrode 5. In the piezoelectric actuator and the discharge device comprising the same actuator, the elastic compliance S<SB>1</SB>of the piezoelectric vibrating plate 2 is larger than an elastic compliance S<SB>2</SB>of the piezoelectric ceramics layer 4. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a piezoelectric actuator and a discharge device, and more specifically, for example, a fuel injection injector, an inkjet printer, or a piezoelectric resonator, an oscillator, an ultrasonic motor, an ultrasonic vibrator, a filter or an acceleration sensor, a knocking sensor, and an AE. More particularly, the present invention relates to a piezoelectric actuator and a discharge device that are suitably used as a print head using spreading vibration, stretching vibration, and thickness vibration.

Conventionally, products using piezoelectric ceramics include, for example, piezoelectric actuators, filters, piezoelectric resonators (including oscillators), ultrasonic vibrators, ultrasonic motors, piezoelectric sensors, and the like. Among these, the piezoelectric actuator has a very high response speed to the electric signal of the order of 10 ⁻⁶ seconds. Therefore, the piezoelectric actuator for positioning the XY stage of the semiconductor manufacturing apparatus or the print head of the ink jet printer using the piezoelectric method is used. It is applied to piezoelectric actuators used in In particular, due to the recent increase in speed and price of color printers, there is an increasing demand for use in piezoelectric actuators for ink ejection such as inkjet printers.

  For example, as shown in FIG. 3, a print head used in an inkjet printer using a piezoelectric method includes a plurality of ink flow paths 101 arranged in parallel, and a flow path member 103 in which a partition wall 102 is formed as a wall partitioning each ink flow path 101. The piezoelectric actuator 104 is provided on the top (see Patent Document 1).

  In the piezoelectric actuator 104, a piezoelectric ceramic layer 106 and a drive electrode 107 are laminated in this order on a piezoelectric diaphragm 105 having a common electrode 110 provided on the upper surface, and a plurality of drive electrodes 107 are arranged on the surface of the piezoelectric ceramic layer 106. Thus, a plurality of displacement elements 108 are formed. The piezoelectric actuator 104 is mounted on the flow path member 103 so that the positions of the ink flow path 101 and the drive electrode 107 are aligned.

  The print head as described above applies the voltage between the common electrode 110 and the predetermined drive electrode 107 to displace the piezoelectric ceramic layer 106 immediately below the drive electrode 107, thereby causing the ink in the ink flow path 101 to flow. The ink is ejected from an ink ejection port 109 opened on the bottom surface of the flow path member 103 under pressure.

By the way, the piezoelectric actuator 104 has a configuration in which a piezoelectric active part (displacement element 108) and a piezoelectric inactive part (part excluding the displacement element 108) are provided on the same plane (piezoelectric diaphragm 105). In order to drive such a piezoelectric actuator 104 with a high displacement, it is necessary to apply a high driving voltage exceeding the coercive electric field of piezoelectric ceramics and to accompany non-linear displacement associated with 90 ° domain inversion.
However, there is a problem in that the amount of displacement is reduced if driving is continued for a long time with a high driving voltage exceeding the coercive electric field of piezoelectric ceramics.

  As a method for solving the above problem, Patent Document 2 describes that La is substituted for a part of Pb site of lead zirconate titanate (PZT), and at least one of Nb, Ta, and Sb is substituted for Ti · Zr site. A piezoelectric ceramic composition is described in which PZT is softened by replacement to increase the amount of displacement, and chromium oxide is added to improve durability.

However, even if the piezoelectric ceramic composition described in this document is used, in the case of a piezoelectric actuator having a configuration in which the piezoelectric active portion and the piezoelectric inactive portion are provided on the same plane, the piezoelectric actuator is repeatedly driven. Then, the displacement may be deteriorated.
Japanese Patent Laid-Open No. 11-31321 Japanese Patent Laid-Open No. 10-7460

  An object of the present invention is to provide a piezoelectric actuator and a discharge device that suppress displacement deterioration due to repeated driving and have excellent driving durability.

  As a result of intensive studies to solve the above-mentioned problems, the present inventor has obtained the following knowledge. That is, it is known that when a high driving voltage exceeding the coercive electric field is applied to the piezoelectric ceramic, a linear displacement mainly accompanying 180 ° domain inversion and a nonlinear displacement accompanying 90 ° domain inversion occur. In the non-linear displacement accompanying 90 ° domain inversion, in addition to the poor responsiveness to the voltage, the piezoelectric actuator having the configuration in which the piezoelectric active portion and the piezoelectric inactive portion are provided on the same plane as described above is applied to the piezoelectric actuator. When a high drive voltage exceeding the coercive electric field of ceramics is applied, the piezoelectric vibration of the piezoelectric active part is constrained by the inactive part around the piezoelectric active part, and further, an inactive layer (piezoelectric vibration plate) immediately below the piezoelectric active part is applied. As a result, the responsiveness to voltage is significantly reduced. Then, due to this decrease in responsiveness, charge accumulation occurs due to continuous voltage application, and as a result, the crystal orientation of the piezoelectric active portion of the piezoelectric ceramic does not return and the amount of displacement gradually decreases. We found a new durability deterioration mechanism.

Further, when a voltage is applied to the piezoelectric active part in the thickness direction, the piezoelectric active part contracts in the surface direction and vibrates to extend in the thickness direction. At this time, vibration is constrained by the portion facing the piezoelectric active portion of the piezoelectric diaphragm and the inactive portion around the piezoelectric active portion in the same plane. This is because the vibration constraint is a 90 ° domain motion (lattice changes from the horizontal direction to the vertical direction) motion, and dulls the motion of electric charges (responsiveness to an electric field). In order to improve the movement of electric charges (responsiveness to an electric field), it has been found that the restraining force needs to be small, and if the diaphragm itself is soft (elastic compliance S _{1 of the} diaphragm), the restraining force becomes small.

  Therefore, by setting the elastic compliance between the piezoelectric diaphragm and the piezoelectric ceramic layer to a predetermined relationship, it was possible to suppress displacement deterioration due to repeated driving, and to improve the driving durability of the piezoelectric actuator.

That is, the piezoelectric actuator and the discharge device of the present invention have the following configurations.
(1) A common electrode, a piezoelectric ceramic layer, and a drive electrode are laminated in this order on the piezoelectric diaphragm, and a plurality of the drive electrodes are arranged on the surface of the piezoelectric ceramic layer, and the drive electrode and the common electrode A piezoelectric actuator in which a plurality of displacement elements configured by sandwiching a piezoelectric ceramic layer are formed and a displacement voltage is displaced by applying a drive voltage between the common electrode and the drive electrode, and the elasticity of the piezoelectric diaphragm A piezoelectric actuator characterized in that compliance S ₁ is larger than elastic compliance S ₂ of the piezoelectric ceramic layer.
(2) The piezoelectric actuator according to (1), wherein a ratio S ₁ / S ₂ of the elastic compliance S ₁ of the piezoelectric diaphragm to the elastic compliance S ₂ of the piezoelectric ceramic layer is 1.03 or more.
(3) elastic compliance S ₁ of the piezoelectric vibrating plate is from 1.35 to 1.51, elastic compliance S ₂ of the piezoelectric ceramic layer is 1.31 to 1.47 above (1) or (2) according Piezoelectric actuator.
(4) The piezoelectric actuator according to any one of (1) to (3), wherein the piezoelectric diaphragm has a porosity of 2 to 9% and the piezoelectric ceramic layer has a porosity of 2% or less.
(5) When the lattice constant ratio of the piezoelectric diaphragm is c ₁ / a ₁ and the lattice constant ratio of the piezoelectric ceramic layer is c ₂ / a ₂ , c ₂ / a ₂ is 1.010 to 1.016. The piezoelectric actuator according to any one of (1) to (4), which is greater than a value of c ₁ / a ₁ .
(6) The piezoelectric actuator according to any one of (1) to (5), wherein the displacement element is displaced with a driving voltage of 1.0 to 1.5 times the coercive electric field of the displacement element.
(7) The piezoelectric actuator according to any one of (1) to (6) is mounted on a flow path member having a pressure generation chamber, a liquid flow path, and a liquid discharge port. Discharge device.
(8) The ejection device according to (7), which is used for a print head.

According to the present invention, in the piezoelectric actuator having the piezoelectric active portion and the piezoelectric inactive portion provided on the same plane, the elastic compliance S ₁ of the piezoelectric diaphragm is larger than the elastic compliance S ₂ of the piezoelectric ceramic layer. Therefore, the restraint of the piezoelectric vibration of the piezoelectric active portion described above can be reduced, the response of 90 ° domain inversion by voltage application can be improved, and charge accumulation by continuous voltage application can be suppressed. Displacement deterioration is suppressed, and there is an effect that a discharge device suitable for a piezoelectric actuator and a print head excellent in driving durability and long-term reliability can be obtained. In addition, since the 90 ° domain inversion amount that contributes to the displacement can be increased, a large displacement amount can be exhibited even if the drive voltage is set small as described in (6) above. Further, if the diaphragm is made highly elastic, an effect that the diaphragm is easily bent can be obtained.

  According to the above description (4), since the porosity of the piezoelectric diaphragm is 3 to 8%, the piezoelectric vibration restraint of the piezoelectric active portion is reduced, and the piezoelectric diaphragm functions as a sufficient elastic body and as a piezoelectric diaphragm. The strength of the can be ensured. Further, by setting the porosity of the piezoelectric ceramic layer to 2% or less, the piezoelectric constant of the piezoelectric material for obtaining a large amount of displacement can be maintained. Moreover, substantially the same piezoelectric material composition can be used for the piezoelectric diaphragm and the piezoelectric ceramic layer. According to the above description (5), it is possible to use substantially the same piezoelectric material composition, and for example, by changing the composition ratio of Zr and Ti, the lattice constant ratio can be set in the above range. The responsiveness of domain inversion can be improved easily.

<Piezoelectric actuator>
Hereinafter, an embodiment of a piezoelectric actuator of the present invention will be described in detail with reference to the drawings. FIG. 1 is an enlarged schematic cross-sectional view showing the piezoelectric actuator of the present embodiment. As shown in the figure, the piezoelectric actuator 1 of the present embodiment includes a piezoelectric diaphragm 2, a common electrode 3, a piezoelectric ceramic layer 4 and a drive electrode 5. On the piezoelectric diaphragm 2, the common electrode 3, The piezoelectric ceramic layer 4 and the drive electrode 5 are laminated in this order.

  The common electrode 3 and the drive electrode 5 constitute an electrode of the piezoelectric actuator 1, and a plurality of drive electrodes 5 are formed on the surface of the piezoelectric ceramic layer 4 in an independent state. As a result, a plurality of displacement elements 6 configured by sandwiching the piezoelectric ceramic layer 4 between the common electrode 3 and the drive electrode 5 are arranged on the piezoelectric diaphragm 2.

  In the piezoelectric actuator 1 as described above, the piezoelectric active portion (displacement element 6) and the piezoelectric inactive portion (the common electrode 3 and the piezoelectric ceramic layer 4 that do not constitute the displacement element 6) are in the same plane (piezoelectric diaphragm 2). Disposed by connecting a lead wire to the drive electrode 5, electrically connecting the lead wire to an external power source, and applying a drive voltage between the common electrode 3 and the drive electrode 5. Element 6 is displaced.

  The height of the piezoelectric actuator 1 is not particularly limited, but is preferably 100 μm or less. By using such a thin layer, a large displacement can be obtained, and high-efficiency driving can be realized at a low voltage. In particular, it is preferably 80 μm or less, more preferably 65 μm or less, and even more preferably 50 μm or less in that the characteristics as the piezoelectric actuator 1 can be sufficiently exhibited. On the other hand, the lower limit of the height is 3 μm, preferably 5 μm, more preferably 10 μm, and even more preferably 20 μm in order to have sufficient mechanical strength and prevent breakage during handling and operation. The height of the piezoelectric diaphragm 2 and the piezoelectric ceramic layer 4 is about 5 to 50 μm, preferably about 10 to 30 μm.

  The piezoelectric diaphragm 2 may be any material as long as it has a high insulating property, but is preferably composed of a piezoelectric ceramic layer made of piezoelectric ceramic, and more preferably a piezoelectric ceramic having a piezoelectric active portion and an inactive portion. It is preferable that the main component is substantially the same as that of the layer 4. The main component preferably contains Pb, Zr, or Ti in order to obtain a high displacement.

  The piezoelectric ceramic in the present invention means a ceramic exhibiting piezoelectricity, for example, Bi layered compound, tungsten bronze structure material, perovskite structure compound of alkali Nb acid compound, lead zirconate titanate (PZT) or titanium containing Pb. Perovskite structure compounds containing lead acid can be exemplified, but among these, lead zirconate titanate (PZT) and lead titanate containing Pb enhance wettability with the electrode and increase adhesion strength with the electrode. Is preferred.

  That is, it is a crystal containing Pb as an A site constituent element and Zr and / or Ti as a B site constituent element. In particular, a lead zirconate titanate-based compound has a higher d constant. This is preferable for obtaining a stable piezoelectric sintered body.

The piezoelectric ceramic preferably contains at least one of Sr, Ba, Ni, Sb, Nb, Zn, Yb, and Te. Thereby, a more stable piezoelectric sintered body (piezoelectric actuator 1) can be obtained. For example, Pb (Zn _1/3 Sb _2/3 ) O ₃ and Pb (Ni _1/2 Te _1/2 ) are used as subcomponents. The thing formed by solid solution of O ₃ can be exemplified.

  In particular, it is desirable to further contain an alkaline earth element as the A site constituent element. As the alkaline earth element, Ba and Sr are particularly preferable in that a high displacement can be obtained, and it is particularly preferable that Ba is contained in 0.02 to 0.08 mol and Sr is contained in 0.02 to 0.12 mol. High and effective in obtaining large displacement.

As the piezoelectric ceramics as described above, for _{example, Pb 1-xy Sr x Ba} y (Zn 1/3 Sb 2/3) a (Ni 1/2 Te 1/2) b Zr 1-abc Ti c O 3 + αwt % Pb _1/2 NbO ₃ (0 ≦ x ≦ 0.14, 0 ≦ y ≦ 0.14, 0.05 ≦ a ≦ 0.1, 0.002 ≦ b ≦ 0.01, 0.44 ≦ c ≦ 0.50, α = 0.1 to 1.0).

The elastic compliance S ₁ of the piezoelectric diaphragm 2 according to the present invention is larger than the elastic compliance S ₂ of the piezoelectric ceramic layer 4. As a result, even in the case of a piezoelectric actuator having a configuration in which the piezoelectric active portion and the piezoelectric inactive portion are provided on the same plane, the restraint of piezoelectric vibration of the piezoelectric active portion is reduced, and the response of 90 ° domain inversion by voltage application is reduced. Thus, accumulation of charges due to continuous voltage application is suppressed, and displacement deterioration due to repeated driving is suppressed. Specifically, for example, the ratio S ₁ / S ₂ of the elastic compliance S ₁ of the piezoelectric diaphragm ₂ to the elastic compliance S ₂ of the piezoelectric ceramic layer 4 is 1.03 or more, preferably 1.03 to 1.10, more preferably. Is preferably 1.10 to 1.16.

The elastic compliance S ₁ of the piezoelectric diaphragm 2 is 1.40 to 1.51, preferably 1.35 to 1.40, and the elastic compliance S ₂ of the piezoelectric ceramic layer 4 is 1.38 to 1.47. Preferably, it is 1.31 to 1.38, and the elastic compliances S ₁ and S ₂ may be in the above relationship within these ranges. The elastic compliance in the present invention means the softness of the piezoelectric ceramic, and is a value calculated from the resonance frequency measured by the impedance gain phase analyzer and the density obtained from the volume and weight of the piezoelectric ceramic. .

The piezoelectric actuator 1 according to the present invention in which the elastic compliances S ₁ and S ₂ have a predetermined relationship can increase the 90 ° domain inversion amount that contributes to the displacement. Therefore, even if the drive voltage is set small, the large displacement The amount can be indicated. Specifically, for example, the displacement element 6 applied to the piezoelectric actuator 1 has a predetermined driving voltage of 1.0 to 1.5 times, preferably 1.0 to 1.2 times the coercive electric field of the displacement element 6. It can be displaced by the amount of displacement.

Here, in the case where the main components of the piezoelectric diaphragm 2 and the piezoelectric ceramic layer 4 are made of substantially the same material, in order to make the elastic compliance S ₁ of the piezoelectric diaphragm ₂ larger than the elastic compliance S ₂ of the piezoelectric ceramic layer 4, For example, the porosity of the piezoelectric diaphragm 2 and the piezoelectric ceramic layer 4 may be set to a predetermined value.

Specifically, the porosity of the piezoelectric diaphragm 2 is 2 to 9%, preferably 3 to 8%, and the porosity of the piezoelectric ceramic layer 4 is 2% or less. Thereby, even when the main components of the piezoelectric diaphragm 2 and the piezoelectric ceramic layer 4 are made of substantially the same material, the elastic compliances S ₁ and S ₂ can be in the above relationship. In addition, the ratio S ₁ / S ₂ can be easily set to 1.03 or more, the piezoelectric vibration restraint of the piezoelectric active portion can be reduced, and the piezoelectric diaphragm 2 functioning as a sufficient elastic body can be obtained. . The reason why the upper limit value of the porosity of the piezoelectric diaphragm 2 is 9% is to ensure bending strength as the diaphragm.

  In order to set the porosity of the piezoelectric diaphragm 2 to 2 to 9%, when the primary raw material mixed powder of the piezoelectric ceramic is calcined and synthesized, the firing temperature is about 94 to 97% or more (vs. firing temperature ratio 0.94 to The calcining synthesis may be performed at a temperature of 0.97 or more. In order to reduce the porosity of the piezoelectric ceramic layer 4 to 2% or less, the firing temperature is about 85 to 93% (vs. firing temperature ratio of 0.85 to 0). .93) may be carried out at a temperature of .93). Thus, by changing the calcining synthesis temperature, the sinterability can be changed, and as a result, the porosity can be easily changed. The setting of the calcining temperature in the present invention is not limited to this, and can naturally be changed depending on the composition of the piezoelectric ceramic, the raw material particle size, and the like.

  The porosity is a value obtained by cutting the piezoelectric diaphragm 2 and the piezoelectric ceramic layer 4, applying a mirror finish to the cross section, and calculating the pore area by image processing from a cross-sectional mirror image with a magnification of 2000 times.

Further, in the case where the main components of the piezoelectric diaphragm 2 and the piezoelectric ceramic layer 4 are made of substantially the same material, in order to make the elastic compliances S ₁ and S ₂ have the predetermined relationship, instead of the above-described porosity, For example, the lattice constant ratio between the piezoelectric diaphragm 2 and the piezoelectric ceramic layer 4 may be set to a predetermined value and relationship.

Specifically, the lattice constant ratio c ₂ / a ₂ of the piezoelectric ceramic layer 4 is 1.010 to 1.016, and is larger than the value of the lattice constant ratio c ₁ / a ₁ of the piezoelectric diaphragm 2. preferable. By setting each lattice constant ratio to such a value and relationship, the elastic compliances S ₁ and S ₂ can be set to the above relationship. When the same piezoelectric material composition is used, the lattice constant ratio is simply set to the lattice constant ratio by changing the ratio of Zr and Ti in the lead zirconate titanate (PZT) composition, for example. And can be obtained by selecting a composition ratio corresponding to each piezoelectric ceramic layer.

Here, the value of the lattice constant ratio c ₁ / a ₁ of the piezoelectric diaphragm 2 is 1.008 to 1.013, preferably 1.008 to 1.010. The lattice constant ratios c ₁ / a ₁ and c ₂ / a ₂ indicate the a-axis orientation from the peak chart obtained from the XRD (X-ray diffraction method) measurement of each of the piezoelectric diaphragm 2 and the piezoelectric ceramic layer 4. The (200) orientation plane spacing [d (200)] and the (002) orientation plane spacing [d (002)] indicating c-axis orientation are derived and the ratio [d (002)] / [d (200)].

  The common electrode 3 is not particularly limited as long as it has conductivity, and for example, Au, Ag, Pd, Pt, Cu, Al, Rh, Ni alone or at least one of these as a main component. An alloy such as an Ag—Pd alloy can be exemplified. Further, the height of the common electrode 3 needs to be conductive and not to prevent displacement, and is generally about 0.5 to 5 μm, preferably 1 to 3 μm.

  The driving electrode 5 is not particularly limited as long as it has conductivity, and the same one as exemplified for the common electrode 3 can be used. The height of the drive electrode 5 needs to be conductive and not to prevent displacement, for example, about 0.1 to 2 μm, preferably 0.1 to 1.0 μm, and more preferably 0.1. It should be 1 to 0.5 μm.

<Method for manufacturing piezoelectric actuator>
Next, the manufacturing method of the piezoelectric actuator of this invention is demonstrated.
(First step)
First, as a raw material, for example _{Pb 1-xy Sr x Ba y} (Zn 1/3 Sb 2/3) a (Ni 1/2 Te 1/2) b Zr 1-abc Ti c O 3 + αwt% Pb 1/2 NbO ₃ (0 ≦ x ≦ 0.14, 0 ≦ y ≦ 0.14, 0.05 ≦ a ≦ 0.1, 0.002 ≦ b ≦ 0.01, 0.44 ≦ c ≦ 0.50, α = 0.1-1.0) The primary raw material is weighed so as to have the composition shown, and mixed and ground by a ball mill to prepare a primary raw material mixed powder. Here, the average particle diameter is preferably 1 μm or less, more preferably 0.7 μm or less, in order to more uniformly mix the primary raw materials.

  Next, the primary raw material mixed powder prepared above is calcined at a predetermined calcining temperature and then pulverized with a ball mill to prepare a plurality of predetermined calcined powders. The average particle size of the calcined powder is 1 μm or less, more preferably the average particle size is 0.7 μm or less, like the primary raw material mixed powder.

  Here, as described above, a plurality of predetermined calcined powders can be obtained from the primary raw material mixed powder by changing the calcining temperature. Further, a plurality of primary raw material mixed powders whose compositions are changed by adjusting a, b, and c in the above formula are prepared, and the plurality of primary raw material mixed powders are calcined and synthesized at a predetermined calcining temperature, respectively. A plurality of calcined powders may be prepared by pulverizing with a ball mill.

(Second step)
Each calcined powder prepared above and an organic binder component are mixed to prepare a sheet forming slurry. Next, the required number of tape-like green sheets are prepared by a general sheet forming method such as a roll coater method, a slit coater method, or a doctor blade method, using this forming slurry. The green sheet is divided into a green sheet that can be a piezoelectric ceramic layer and a green sheet that can be a piezoelectric diaphragm.

(Third step)
Next, a common electrode paste containing the electrode material exemplified for the common electrode is prepared. This common electrode paste contains components such as an organic material such as ethyl cellulose in addition to electrode materials (Au, Ag, etc.). Then, a common electrode paste is printed by a method such as screen printing on one surface of the green sheet produced as described above to become a piezoelectric diaphragm by firing.

(Fourth process)
The green sheets produced in the second step and the third step are laminated and brought into close contact to produce a laminate. In addition, as a method of performing adhesion, there are a method using an adhesion liquid containing an adhesive component, a method of adhering the organic binder component in the green sheet by adhesion, a method of adhering only by pressure, and the like. It can be illustrated.

(Fifth step)
After the laminated body obtained in the fourth step is pressurized at a pressure of 10 to 50 MPa, it is cut into a desired shape. This is debindered at about 400 ° C., and then fired at 900 to 1100 ° C. in a (high concentration) oxygen atmosphere to obtain a piezoelectric actuator body.

(Sixth step)
A drive electrode pattern is printed on the surface of the piezoelectric actuator main body obtained in the fifth step by a method such as screen printing, and a baking process is performed at 500 to 800 ° C, preferably 650 to 800 ° C. It is formed. Then, the piezoelectric ceramic layer is obtained by polarizing the piezoelectric ceramic layer.

<Discharge device / printing head>
The piezoelectric actuator of the present invention is excellent in driving durability and has a plurality of displacement elements on one substrate (vibrating plate). Therefore, the piezoelectric actuator includes a pressure generating chamber, a liquid flow path, and a liquid discharge port. It can use suitably for the discharge apparatus attached on the flow-path member which has an exit. Examples of such a discharge device include a print head used in a recording device using an inkjet method. Hereinafter, an embodiment of a print head including the piezoelectric actuator of the present invention will be described.

  FIG. 2A is a schematic cross-sectional view showing the print head of this embodiment, and FIG. 2B is a plan view thereof. In FIGS. 2A and 2B, the same or equivalent parts as those in FIG. 1 described above are denoted by the same reference numerals and description thereof is omitted.

  As shown in FIGS. 2A and 2B, the ink jet print head 20 includes a plurality of ink pressurization chambers 13a arranged in parallel, and a flow in which a partition wall 13b is formed as a wall partitioning each ink pressurization chamber 13a. The piezoelectric actuator 1 described above is joined on the path member 13.

  The flow path member 13 is obtained by a rolling method or the like, and the ink discharge hole 18 and the ink pressurizing chamber 13a are provided by being processed into a predetermined shape by etching. The flow path member 13 is preferably formed of at least one selected from the group consisting of Fe—Cr, Fe—Ni, and WC—TiC, and is made of a material particularly excellent in corrosion resistance to ink. Desirably, the Fe-Cr system is more preferable.

  The flow path member 13 and the piezoelectric actuator 1 are joined using an adhesive or the like so that the piezoelectric diaphragm 2 is in contact with the space of the ink flow path 13a. More specifically, each drive electrode of the displacement element 6 is connected. 5 and each ink flow path 13a are joined so as to correspond to each other.

  That is, in the inkjet print head 20, the common electrode 3, the piezoelectric ceramic layer 4 and the drive electrode 5 are laminated in this order on the piezoelectric diaphragm 2, and the piezoelectric actuator 1 is placed directly above the ink flow path 13a. Is adhered to the flow path member 13 so as to be disposed.

  When a voltage is applied between the common electrode 3 and the predetermined drive electrode 5 by an external drive circuit, the piezoelectric ceramic layer 4 immediately below the drive electrode 5 to which the voltage is applied is displaced, and the ink pressurizing chamber The ink in 13 a is pressurized, and ink droplets are ejected from the ink ejection holes 18.

  By using the piezoelectric actuator that is the laminated piezoelectric body of the present invention as the actuator of such a print head 20, a print head can be realized using an inexpensive IC. Since this print head is excellent in displacement characteristics, a feature of high-speed and high-precision ejection is obtained, and as a result, a print head suitable for high-speed printing can be provided. In addition, by mounting the print head of the present invention on a printer, for example, a printer having an ink tank that supplies ink to the print head and a recording paper transport mechanism for printing on recording paper has been conventionally used. Compared with this, it is possible to easily achieve high-speed and high-precision printing.

In the embodiment described above, the porosity and the lattice constant ratio are applied separately, and the elastic compliance S ₁ of the piezoelectric diaphragm ₂ is larger than the elastic compliance S ₂ of the piezoelectric ceramic layer 4. However, the present invention is not limited to this, and the elastic compliances S ₁ and S ₂ may be in a predetermined relationship by combining the porosity and the lattice constant ratio.

  Further, in the case where the main components of the piezoelectric diaphragm 2 and the piezoelectric ceramic layer 4 are made of substantially the same material, the case where the porosity and the lattice constant ratio have predetermined values and relationships has been described. Even when the main components of the ceramic layer 4 are different, the porosity and the lattice constant ratio may be set to the above-described predetermined values and relationships without particular limitation.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further in detail, this invention is not limited to a following example.

[Example]
<Creation of piezoelectric actuator>
First, piezoelectric ceramic powder (primary raw material mixed powder) containing lead zirconate titanate (PZT) with a raw material composition shown in Table 1 and having a purity of 99% or more was prepared as a raw material. And the prepared ceramic powder was calcined and synthesized at the calcining temperature shown in Table 1 to prepare each calcined powder.

  Using each of the calcined powders prepared above, green sheets (for piezoelectric ceramic layers and piezoelectric diaphragms) were produced. That is, to each calcined powder, polybutyl methacrylate as an aqueous binder, polycarboxylic acid ammonium salt as a dispersant, isopropyl alcohol and pure water as a solvent are added and mixed, and this slurry is applied onto a carrier film by a doctor blade method. Each green sheet was prepared in a sheet shape having a thickness of 30 μm by coating (Nos. A to I in Table 1).

  Next, the green sheets prepared above were used in combinations shown in Table 2. That is, the common electrode paste was printed at a thickness of 4 μm on the surface of the green sheet for the piezoelectric diaphragm to form the common electrode. Further, the piezoelectric ceramic layer green sheet was laminated on the piezoelectric diaphragm green sheet with the surface on which the common electrode was printed facing upward, and was pressed to obtain a laminate.

After degreasing the laminate, the laminate was sintered in an atmosphere of 980 ° C. and oxygen 99% or more for 4 hours to produce a piezoelectric actuator body. Next, a drive electrode was formed on one side of the surface of the actuator body. The drive electrode applied Au paste by screen printing. This was formed by baking at 600 to 800 ° C. in the air. Finally, lead wires were connected to the drive electrodes with solder to produce piezoelectric actuators that are piezoelectric elements having a shape as shown in FIG. 1 (Sample Nos. 1 to 27 in Table 2). In Table 2, “S ₁ / S ₂ ” indicates the ratio S ₁ / S ₂ of the elastic compliance S ₁ of the piezoelectric diaphragm to the elastic compliance S ₂ of the piezoelectric ceramic layer.

No. in Table 1 The lattice constant ratio c / a, porosity and elastic compliance of the sintered bodies A to I were measured by the following methods. The measurement results are shown in Table 1.
(Lattice constant ratio c / a)
The lattice constant ratio c / a indicates the (200) orientation spacing [d (200)] indicating the a-axis orientation from the peak chart obtained from the XRD (X-ray diffraction method) measurement and the c-axis orientation ( 002) The interplanar spacing [d (002)] of the orientation plane was derived and obtained from the ratio [d (002)] / [d (200)].

(Porosity)
The porosity is obtained by cutting each sintered body, mirror-treating the cross section thereof, and indicating the pore area obtained by image processing from a cross-sectional mirror image with a magnification of 2000 times as a percentage of the visual field area.

(Elastic compliance)
For the elastic compliance, each layer of the produced laminated sintered body was peeled off from the common electrode (internal electrode) utilizing electrolysis in water and the piezoelectric ceramic layer, and the elastic compliance of each layer was measured. After forming Au deposition on the front and back surfaces of the peeled piezoelectric ceramic layer to about 100 nm, the outer side was processed to 2.5 mm × 10 mm to prepare a test piece. The measurement was performed by measuring the resonance frequency measured from the impedance gain phase analyzer 4194a manufactured by Agilent Technologies, and the density calculated from the volume and weight, and calculating from the following formula (I).

<Evaluation of piezoelectric actuator>
About the piezoelectric actuator obtained above (sample No. 1-27 of Table 2), displacement deterioration was evaluated. The evaluation method is shown below, and the results are shown in Table 2.
(Evaluation method for displacement degradation)
The piezoelectric actuator obtained above was processed into a size of 8 mm × 8 mm, and adhered to a metal substrate having an outer shape of 10 mm × 10 mm with holes of 1 mm × 1 mm, to obtain a sample for displacement measurement. Further, polarization was performed by applying a DC voltage of 3 kv / mm for 5 minutes in the thickness direction between the common electrode and the drive electrode. Next, a voltage of 2 kV / mm is applied to displace the displacement element for 50 hours, and the initial displacement (after 0 minutes) and the displacement after 50 hours are expressed by the formula: [1- (displacement / initial displacement after 50 hours)] It applied to * 100 and the displacement deterioration rate (%) was computed. The displacement was measured with a Doppler displacement meter.

  As is apparent from Table 2, the sample Nos. Within the scope of the present invention. 1, 6, 7, 11-13, 16-19, 21-27 had a displacement deterioration rate after 5 hours endurance of 5% or less. From this, it can be seen that the displacement deterioration due to repeated driving is suppressed, and a piezoelectric actuator excellent in driving durability is obtained. On the other hand, the sample outside the range of the present invention has a higher displacement deterioration rate than the sample within the range of the present invention. 5, 15 and 20 show that the deterioration rate exceeds 10%, indicating a large deterioration.

1 is an enlarged schematic cross-sectional view showing a piezoelectric actuator according to an embodiment of the present invention. (A) is a schematic sectional drawing which shows the printing head for inkjet concerning one Embodiment of this invention, (b) is the top view. It is a schematic sectional drawing which shows the conventional print head for inkjet.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Piezoelectric actuator 2 Piezoelectric diaphragm 3 Common electrode 4 Piezoelectric ceramic layer 5 Drive electrode 6 Displacement element 13 Flow path member 13a Ink pressurizing chamber 13b Partition 18 Ink ejection hole 20 Print head

Claims (8)

A common electrode, a piezoelectric ceramic layer, and a drive electrode are laminated in this order on the piezoelectric diaphragm, and a plurality of the drive electrodes are arranged on the surface of the piezoelectric ceramic layer, and the piezoelectric ceramic layer is composed of the drive electrode and the common electrode. A piezoelectric actuator that forms a plurality of displacement elements that are sandwiched between, and displaces the displacement element by applying a drive voltage between the common electrode and the drive electrode,
A piezoelectric actuator wherein the elastic compliance S ₁ of the piezoelectric vibrating plate, and wherein the greater than the elastic compliance S ₂ of the piezoelectric ceramic layer. _2. The piezoelectric actuator according to claim _{1, wherein} a ratio S ₁ / S ₂ of elastic compliance S ₁ of the piezoelectric diaphragm to elastic compliance S ₂ of the piezoelectric ceramic layer is 1.03 or more. Elastic compliance S ₁ of the piezoelectric vibrating plate is from 1.35 to 1.51, according to claim 1 or 2 piezoelectric actuator according elastic compliance S ₂ of the piezoelectric ceramic layer is from 1.31 to 1.47.   The piezoelectric actuator according to any one of claims 1 to 3, wherein the piezoelectric diaphragm has a porosity of 2 to 9%, and the piezoelectric ceramic layer has a porosity of 2% or less. When the lattice constant ratio of the piezoelectric diaphragm is c ₁ / a ₁ and the lattice constant ratio of the piezoelectric ceramic layer is c ₂ / a ₂ , c ₂ / a ₂ is 1.010 to 1.016, and The piezoelectric actuator according to claim 1, wherein the piezoelectric actuator is larger than a value of c ₁ / a ₁ .   6. The piezoelectric actuator according to claim 1, wherein the displacement element is displaced with a driving voltage of 1.0 to 1.5 times the coercive electric field of the piezoelectric ceramic layer.   A discharge device comprising the piezoelectric actuator according to claim 1 mounted on a flow path member having a pressure generating chamber, a liquid flow path, and a liquid discharge port. The discharge device according to claim 7 used for a print head.

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