JP3873094B2 - Piezoelectric element - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a laminated piezoelectric element used as an actuator such as a liquid ejection head for ejecting liquid droplets such as an inkjet head.
[0002]
[Prior art]
A droplet ejection head, for example, the inkjet head 15 shown in FIG. 1 is formed of a nozzle 1, a liquid chamber 2, a liquid supply channel 3, and a vibration film 21, and one end of the piezoelectric element 4 is fixed to the vibration film 21. The other end of the piezoelectric element 4 is fixed to the base 20. The piezoelectric element 4 is provided with electrodes 5 and 6, and electric wirings 7 and 8 for passing a current to the electrodes 5 and 6 are attached. The piezoelectric element 4 is fixed to the base 20 via an adhesive 9. By applying a current to the electrical wirings 7 and 8 and applying a voltage, electric charges are accumulated in the piezoelectric element 4 to cause deformation, and after this power storage, the vibrating membrane 21 is pushed in the A direction by discharging. A droplet 22 in the chamber 2 is ejected from the nozzle 1. As described above, a droplet ejection head (for example, an ink jet head) using the piezoelectric element 4 can eject a predetermined amount of liquid according to the deformation amount of the piezoelectric element 4, so that it can be applied to an image creating apparatus such as a printer. Used.
[0003]
By the way, with the recent development of technology, downsizing of printers and the like is unavoidable. In addition, in a liquid ejection head using a piezoelectric element, it is desired that droplet formation efficiency and flying force are large. However, since the piezoelectric element has a very small unit length and expansion / contraction rate per unit voltage, it is necessary to apply a high voltage in order to obtain the flying force of the liquid required for liquid ejection, and the drive circuit and electrical insulation. There is a problem that countermeasures become complicated.
[0004]
In order to solve such problems, there has been proposed a piezoelectric element for a liquid ejection head in which electrodes and piezoelectric materials are alternately laminated in a sandwich shape as disclosed in JP-A-63-295269. According to this piezoelectric element, since the distance between the electrodes can be reduced, there is an effect that the voltage of the drive signal can be lowered.
[0005]
By the way, the liquid ejection head is formed so that one end of the piezoelectric element is fixed to the base, the other end is fixed to the vibration film, and the vibration film is pushed by deformation by an applied voltage. It is necessary not to be deformed when applied. In other words, the fixed side needs to be prevented from being deformed even when an electric charge is applied.
[0006]
However, the multilayer piezoelectric element described in Japanese Patent Application Laid-Open No. 63-295269 has a problem that the fixed portion is deformed. Furthermore, it is difficult to reduce the size of such a laminated piezoelectric element, and there is a problem that its application is limited.
[0007]
On the other hand, a piezoelectric element in which piezoelectric materials are alternately stacked and a dummy electrode that is not subjected to a voltage is provided in a part of the electrode structure is described in Japanese Patent Laid-Open No. 4-235041. It is described that the piezoelectric element produced by this method has warpage and undulation in the length direction and width direction within 10 microns.
[0008]
However, since the piezoelectric element obtained by this method is deformed at the fixed portion when charged, the accuracy of the inkjet head is not necessarily good. Further, since the piezoelectric material layer is laminated on the conductive material layer, and the dummy electrode and the conductive material layer are provided on the piezoelectric material, it is not always possible to say that the piezoelectric element is downsized.
[0009]
[Problems to be solved by the invention]
Accordingly, there is a need for a piezoelectric element that is miniaturized without causing deformation at the fixed portion when charged.
[0010]
[Means for Solving the Problems]
As a result of intensive studies to solve the above problems, the inventors of the present invention have provided an insulating layer at both ends instead of providing a dummy conductive layer to which no voltage is applied in the laminated piezoelectric element, and the voltage is applied between the piezoelectric element layers. It is found that a part that is charged and deformed is generated only in the part applied to the base, and that the part fixed to the base and the part fixed to the vibration film can be prevented from being deformed when a voltage is applied. Completed the invention.
[0011]
The present invention is a piezoelectric element in which piezoelectric materials and conductive materials are alternately laminated, wherein one end of the piezoelectric material is provided with a layer of conductive material, and the other end is provided with a layer of insulating material. The present invention relates to a piezoelectric element configured such that a layer of a conductive material and a layer of an insulating material are alternately stacked via a piezoelectric material.
[0012]
In a more preferred embodiment, the insulating material and the piezoelectric material are both ceramics.
[0013]
In a preferred embodiment, the insulating material is a material harder than the piezoelectric material.
[0014]
The present invention further relates to a liquid ejection head in which any one of the piezoelectric elements is incorporated in a liquid ejection head.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
In the piezoelectric element of the present invention, as shown in FIG. 2 (7), a conductive material layer 11 is provided at one end of the piezoelectric material 10, and an insulating material layer 12 is provided at the other end. 11 and insulating material layers 12 are alternately stacked via the piezoelectric material 10.
[0016]
As the piezoelectric material, ceramics, plastics (for example, thermosetting resin) and the like are preferably used. Of these, ceramics is preferably used. Preferred ceramics include lead zirconate titanate composite perovskite ceramics, structural ceramics MoSiO ₂ -Mo ₂ B ₂ , heat-resistant ceramics, dielectric ceramics, but lead zirconate titanate composite perovskite ceramics, derivative ceramics Is more preferable in terms of elasticity and the like.
[0017]
The conductive material is not particularly limited, but metals such as Ag, Pd, Pt, Au, and W are preferable, and Ag and Pd are more preferable.
[0018]
As the insulating material, an insulating material that is the same as the piezoelectric material or higher in hardness than the piezoelectric material is preferably used. Examples thereof include lead zirconate titanate composite perovskite ceramics, structural ceramics MoSiO ₂ —Mo ₂ B ₂ , heat resistant ceramics, dielectric ceramics, and the like.
[0019]
The insulating material is preferably a material harder than the piezoelectric material in order to prevent deformation of the fixed portion when the piezoelectric element is applied. The piezoelectric material and the insulating material may be the same material or different materials. In the case of different materials, the insulating material is preferably a harder material than the piezoelectric material. As such a combination, the piezoelectric material is a dielectric ceramic, and the insulating material is a lead zirconate titanate-based composite perovskite ceramic, structural ceramics MoSiO ₂ —Mo ₂ B ₂ , or heat resistant ceramics.
[0020]
Hereinafter, the manufacture of the piezoelectric element of the present invention will be described with reference to FIG. As shown in FIG. 2 (1), a first piezoelectric material 10a (for example, lead zirconate titanate-based composite novelpskite ceramics) prepared in a green sheet shape or a paste shape is placed on a surface plate, In addition, as the first conductive material 11a, for example, a conductive paste such as Ag or Pd is printed on the right side of the first piezoelectric material 10a as shown in FIG. .
[0021]
Next, as shown in FIG. 2 (2), the first insulating material 12a (for example, lead zirconate titanate-based composite perovskite ceramic) is formed to have substantially the same thickness as the first conductive material 11a. For example, printing is performed on the left side of the first piezoelectric material 10a by a thick film printing method, a silk printing method, or the like so as not to overlap the first conductive material 11a.
[0022]
Thereafter, as shown in FIG. 2 (3), the second piezoelectric material 10b is disposed on the layer of the first insulating material 12a and the layer of the first conductive material 11a obtained in FIG. 2 (2).
[0023]
Next, as shown in FIG. 2 (4), the second conductive material 11b is arranged on the left side of the second piezoelectric material 10b in the same manner as the first conductive material 11a. The second insulating material 12b is disposed on the right side in the same manner as the first insulating material 12a. In other words, the conductive material and the insulating material are arranged so as to have the opposite positional relationship to that shown in FIG.
[0024]
Then, as shown in FIG. 2 (5), the third piezoelectric material 10c is arranged on the layer of the second conductive material 11b and the second insulating material 12b obtained in FIG. 2 (4). As shown in (6), the third insulating material 12c and the third conductive material 11c are arranged on the third piezoelectric material 10c in the same manner as in FIG. 2 (2). Four piezoelectric materials 10d are arranged.
[0025]
In this way, by stacking the conductive material 11 and the insulating material 12 so as to be alternately stacked via the piezoelectric material 10, the stacked piezoelectric element shown in FIG. 2 (7) is obtained.
[0026]
FIG. 3 shows an example in which gold electrodes 5 and 6 are formed by sputtering or plating for the purpose of flowing a current from the outside to a conductive material (that is, an electrode) alternately incorporated in the obtained piezoelectric element 4. The shape as an element is completed. By the way, as shown in FIG. 3, the piezoelectric element 4 of the present invention has regions X in which the insulating material 12 and the conductive material 11 are alternately arranged via the piezoelectric material 10, and the conductive material 11 and the piezoelectric material 10 are alternately arranged. There are three regions, namely, a region Y disposed in a region Z, and a region Z in which the insulating material 12 and the conductive material 11 are alternately disposed via the piezoelectric material 10. Since the same material is laminated in the region X and the region Z, the mechanical properties (hardness, elastic modulus, etc.) are almost the same, but the region Y is formed of a piezoelectric material and a conductive material. Therefore, the hardness is not high as compared with the regions X and Z. When the lead zirconate titanate composite perovskite ceramic is used for the piezoelectric material, it is Hv 400-600.
[0027]
The rigidity of the portion of the region Y that creates the displacement is almost the same as before, or is soft, but if the hardness of the region X and the region Z that directly presses the vibrating membrane is higher than the hardness of the region Y, the liquid chamber 2 in FIG. The force applied to the liquid will increase. That is, by increasing the hardness of the portion (region X or region Z) fixed to the base and the vibration film, the force generated by the deformation of the piezoelectric element can be sufficiently transmitted to the liquid.
[0028]
For example, by using dielectric ceramics as the piezoelectric material and using structural ceramics and heat-resistant ceramics (Hv 2000 to 3400) having higher hardness than the dielectric ceramics as the insulating material 12, the hardness of the region X or the region Z is substantially reduced. Can be high. In particular, when dielectric ceramics are used as the piezoelectric material and structural ceramics are used as the insulating material, these materials are compatible, so that they can be melted by firing and bonded more firmly. Accordingly, a piezoelectric element which is flat and has a hard end and strong is produced.
[0029]
In this way, by configuring the both ends of the piezoelectric element to be hard, it becomes possible to eject a liquid with higher viscosity.
[0030]
FIG. 3B is a schematic diagram showing the hardness of each of the regions X, Y, and Z of the piezoelectric element thus formed, and shows that the hardness of the region X and the region Z is higher than the hardness of the region Y. ing. With this configuration, there is also an effect that the movement of the piezoelectric element region Y deformed with a specific natural vibration is amplified when a voltage is applied.
[0031]
FIG. 4 is a diagram illustrating a case where the insulating material 12 is not stacked. Since the conductive material 11 is not laminated in the region L and the region N shown in FIG. 4B, the thickness is insufficient as compared with the region M, and as shown in FIG. The portion is thick and the regions L and N on both sides are thin. In the process of creating a piezoelectric element by heating, pressurizing and firing such a laminate, the pressure is not evenly applied to the laminate, the strength of the piezoelectric element itself is reduced, and peeling of the layer occurs. It causes a fatal defect as an element. In addition, since deformation occurs in the outer portions of the region L and the region N, twisting, warping, and the like occur.
[0032]
FIG. 5 is a schematic diagram showing one method of manufacturing a piezoelectric element. By arranging the conductive material and the insulating material on the piezoelectric material as shown in FIG. Can be formed. A large number of such patterns can be created on a plane, a large print mask pattern can be created, and a large number of piezoelectric elements can be created at one time. When performing such a cut, it is possible to cut accurately by printing or cutting the cut mark on the surface in advance.
[0033]
Further, the piezoelectric element of the present invention can be arranged so as to have a layer structure as shown in FIG. In this case, the portion having high hardness is only on one side, but such a specification may be used.
[0034]
The piezoelectric element of the present invention is manufactured from a piezoelectric material and a dielectric material. An example in which a piezoelectric element is formed using dielectric ceramics as a piezoelectric material and structural ceramics as an insulating material will be described. First, dielectric ceramics and a binder (for example, polyvinyl alcohol: PVA) are mixed, dehydrated, dried, and temporarily fired. The preliminary firing is preferably performed at 700 ° C. to 800 ° C. so that the crystal structure of the ceramic is in a stage before the perovskite structure. After firing, it is pulverized, further dehydrated and dried, and a binder (PVA) is added to form a sheet. The thickness of the sheet is preferably 1.2 to 1.3 times that after the main firing. After forming the sheet, the shape is adjusted by punching and the internal electrodes are silk-printed.
[0035]
In the same manner as the piezoelectric material using structural ceramics as the insulating material, the sheet is formed and shaped by punching or the like. The internal electrode is not printed.
[0036]
A piezoelectric material and an insulating material are laminated as shown in FIG. 2 and fired at 1100 ° C. to 1500 ° C. After firing, it is processed and shaped to produce a piezoelectric element.
[0037]
A liquid ejection head or the like in which the piezoelectric element of the present invention is used often has a fine head pitch, and the piezoelectric element as an actuator is often used with a fine cut. In the conventional piezoelectric element, since the conductive material to be an electrode exists in each layer, the end portion of the electrode is peeled off at the conductive material portion at the time of this cutting, and the end portion of the piezoelectric element may be chipped. Many of them had a great influence on the head yield. In the present invention, since the conductive material and the insulating material are alternately provided, the electrode layer can be almost halved compared to the conventional one, and the hardness of the end of the piezoelectric element can be increased, so that peeling occurs at the time of cutting. Therefore, the yield of cutting the piezoelectric element can be improved.
[0038]
When one end of the obtained piezoelectric element is bonded and fixed to the base, and the other end is bonded and fixed to the vibration film and disposed in correspondence with the nozzle opening, a droplet ejection head is obtained.
[0039]
[Action]
In the piezoelectric element of the present invention, the conductive material layer and the insulating material layer are provided on the piezoelectric material, and the conductive material and the insulating material are alternately laminated via the piezoelectric material. Not only the thickness is reduced (that is, the size is reduced), but the deformed portion of the intermediate region is configured to be the same as or more flexible than the conventional one, and is fixed to the electrode and / or diaphragm Since the (end portion of the piezoelectric element) can be made harder than the conventional one, the deformation of the piezoelectric element in the fixed portion is suppressed, and the accuracy of transmitting the pressure due to the deformation to the diaphragm is increased.
[0040]
When one end of the piezoelectric element of the present invention is bonded and fixed to the base and the other end is bonded and fixed to the vibration film and disposed in correspondence with the nozzle opening, a droplet ejection head can be obtained. By using the piezoelectric element of the present invention, there is provided a droplet ejection head that is highly accurate in transmitting deformation and is miniaturized. It can be used as a small droplet ejection head for ejecting highly viscous droplets.
[0041]
【Example】
Piezoelectric elements were made using dielectric ceramics as the piezoelectric material and structural ceramics as the insulating material. First, dielectric ceramics and a binder (PVA) were mixed, dehydrated and dried, and calcined at 750 ° C. After firing, it was pulverized, further dehydrated and dried, and a binder (PVA) was added to form a sheet. After forming the sheet, the shape was adjusted by punching, and the internal electrode was silk-printed.
[0042]
On the other hand, structural ceramics were used as the insulating material, and in the same manner as the piezoelectric material, a sheet was formed and formed by punching. The obtained piezoelectric material and insulating material were laminated as shown in FIG. 2 and fired at 1300 ° C. After firing, it was processed and shaped to obtain a piezoelectric element as shown in FIG.
[0043]
The hardness of the obtained piezoelectric element was measured using a micro Vickers hardness meter. Stacked and compounded elements cannot be measured directly with a micro Vickers hardness tester. Therefore, first, a calibration curve was created by determining the laser displacement of a ceramic having a known Hv value of a micro Vickers hardness meter by measuring the speed of the waveform. Next, the speed per hour of the waveform at the measurement site of the obtained piezoelectric element was measured and converted to the value of a micro Vickers hardness meter. The Hv value at the center (Y part in FIG. 3) of the obtained piezoelectric element was 640, but the Hv values at both ends (X part and Z part in FIG. 3) were 2400 and 2500, respectively. . That is, as shown in FIG. 3B, a piezoelectric element is obtained in which both ends are very hard and hardly change, but the hardness of the central portion (Y portion in FIG. 3) is lower than both ends and only the central portion can be changed. It was.
[0044]
In the obtained piezoelectric element, the portion corresponding to the X portion in FIG. 3 was 2 mm, the portion corresponding to the Y portion was 3.5 mm, and the portion corresponding to the Z portion was 1.5 mm. Although the displacement amount of the Y part was 1 μm, the displacements of the X part and the Z part were not measured.
[0045]
【The invention's effect】
The piezoelectric element of the present invention is configured such that the conductive material layer and the insulating material layer are alternately arranged via the piezoelectric material. By using a material having high hardness as the insulating material, both ends of the piezoelectric element are configured to be harder than the central portion, and the piezoelectric element is reduced in size. When a voltage is applied, the central portion (capacitor portion) is deformed, but both ends are not easily deformed, so that the pressure due to the deformation is transmitted with high accuracy. Even highly viscous liquids can be injected.
[0046]
In addition, since the manufacturing is relatively simple, a large number of mask patterns can be used to reduce the manufacturing cost. In addition, the conductive material portion is less likely to be peeled or chipped during manufacturing, greatly increasing production efficiency. To do.
[0047]
Furthermore, the piezoelectric element of the present invention increases the transmission speed of force when used as an actuator by using ceramic instead of the dummy electrode of the piezoelectric element described in Japanese Patent Laid-Open No. 4-250441. Can be used as the PZT material itself, so that thermal distortion during firing of the piezoelectric element can be eliminated. In addition, the possibility of peeling of the internal electrode is reduced even after several hundred million uses, and the life is long and the reliability is improved.
[0048]
Since the piezoelectric element of the present invention can be applied not only to a droplet ejection head (for example, an ink jet head) but also to those using any piezoelectric element, an industrial effect is great.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a structure of a liquid ejection head.
FIG. 2 is a cross-sectional view showing a manufacturing process of the piezoelectric element of the present invention.
FIG. 3 is a schematic diagram showing the cross section of the piezoelectric element of the present invention and the hardness of each region.
FIG. 4 is a cross-sectional view of a piezoelectric element when an insulating material is not used.
FIG. 5 is a schematic view when a large number of piezoelectric elements of the present invention are simultaneously formed.
FIG. 6 is another embodiment of the piezoelectric element of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Nozzle 2 Liquid chamber 3 Liquid supply path 4 Piezoelectric element 5, 6 Electrode 7, 8 Electrical wiring 9 Adhesive 10 Piezoelectric material 11 Conductive material 12 Insulating material 20 Base 21 Vibrating film 22 Droplet

Claims (3)

A piezoelectric material and a conductive material is a piezoelectric element that are alternately stacked, at one end of the piezoelectric material layer of conductive material, the other end is provided with a layer of insulating material, the insulating material is the A piezoelectric element which is a material harder than a piezoelectric material and is configured such that the conductive material layer and the insulating material layer are alternately stacked via the piezoelectric material.   The piezoelectric element according to claim 1, wherein both the insulating material and the piezoelectric material are ceramics. Liquid injection head in which the piezoelectric element described incorporated into the liquid injection head according to claim 1 or 2.

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