JP2005150548A - Laminated piezoelectric element and spraying device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laminated piezoelectric element in which, since a desired displacement does not change effectively even by continuously driving, an apparatus doe not incorrectly operate and which has excellent durability, and to provide a spraying device using the same. <P>SOLUTION: The laminated piezoelectric element includes a laminate obtained by alternately laminating at least one piezoelectric element and a plurality of internal electrodes, and a pair of external electrodes in which the internal electrodes are alternately connected at every other layer to the side face of the laminate, and drives by applying an electric field to the external electrode. The change rate of the element size before and after the continuous drive falls within 1%. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a laminated piezoelectric element and an injection device, for example, a fuel injection device for an automobile engine, a liquid injection device such as an inkjet, a drive element mounted on a precision positioning device such as an optical device, a vibration prevention device, and the like, and a combustion Sensor elements mounted on pressure sensors, knock sensors, acceleration sensors, load sensors, ultrasonic sensors, pressure sensitive sensors, yaw rate sensors, etc., and circuit elements mounted on piezoelectric gyros, piezoelectric switches, piezoelectric transformers, piezoelectric breakers, etc. The present invention relates to a stacked piezoelectric element and a jetting device used.

  Conventionally, as a multilayer piezoelectric element, a multilayer piezoelectric actuator in which piezoelectric bodies and electrodes are alternately stacked is known. Multi-layer piezoelectric actuators are classified into two types: simultaneous firing type and stack type in which piezoelectric ceramics and internal electrode plates are stacked alternately. Considering low voltage and low manufacturing cost, simultaneous firing type The multilayer piezoelectric actuator is advantageous for thinning and is advantageous for durability.

  FIG. 1 shows a conventional multilayer piezoelectric element, in which piezoelectric bodies 11 and internal electrodes 12 are alternately stacked. However, the internal electrodes 12 are not formed on the entire main surface of the piezoelectric body 11 and are so-called. It has a partial electrode structure. By laminating the internal electrodes 12 of this partial electrode structure alternately on the left and right, the internal electrodes 12 can be alternately connected to the external electrodes 15 formed on the side surface of the multilayer electronic component. By printing an internal electrode paste on a ceramic green sheet in a pattern that has a predetermined electrode structure, producing a laminated molded body obtained by laminating a plurality of green sheets coated with this internal electrode paste, and firing this The laminated body was produced (for example, refer patent document 1).

  In such a laminated piezoelectric element, piezoelectric bodies 11 and internal electrodes 12 are alternately laminated to form a columnar laminated body 13, and inactive layers 14 are laminated on both end faces in the laminating direction. The internal electrode 12 is formed so that one end thereof is electrically connected to the external electrode 15 alternately on the left and right sides. When used as a multilayer piezoelectric actuator, lead wires are further connected and fixed to the external electrodes 15 by soldering.

  Further, as the internal electrode, an alloy of silver and palladium is used. Further, in order to simultaneously fire the piezoelectric body and the internal electrode, the metal composition of the internal electrode is 70% by weight of silver and 30% by weight of palladium. (For example, see Patent Document 2).

  As described above, the internal electrode made of a metal composition containing a silver-palladium alloy containing palladium is used instead of the internal electrode made of a metal composition containing only silver. This is because when a potential difference is applied between the electrodes, a so-called silver migration phenomenon occurs in which silver in the electrode moves along the element surface from the positive electrode to the negative electrode of the pair of electrodes. This phenomenon occurred remarkably in a high temperature and high humidity atmosphere.

In recent years, a piezoelectric actuator is installed in an injection device, and in order to ensure a large amount of displacement under a large pressure, a higher electric field is applied and driven continuously for a long time.
JP-A-61-133715 Japanese Utility Model Publication No. 1-130568

  However, the piezoelectric body has a characteristic that the amount of displacement changes depending on the environmental temperature to be used. Therefore, there is a problem that the volume of the internal electrode is increased by increasing the element temperature and the amount of displacement of the piezoelectric actuator is changed. It was. In addition, a change in the displacement amount during driving causes a load fluctuation with respect to the power source for voltage control, which causes a problem of placing a burden on the power source. Furthermore, when the rate of change of the displacement amount is large, not only the displacement amount itself deteriorates but also there is a problem that when the device temperature rise exceeds the heat dissipation amount, a thermal runaway phenomenon occurs and the device is destroyed.

  In addition, when a high electric field is applied to the piezoelectric actuator, the joint between the internal electrode and the external electrode generates significant local heat due to a narrow path of electrical conduction, thereby reducing the expansion and contraction of the piezoelectric actuator. Long-term continuous drive of the injection device using the air has become difficult.

  Further, in order to suppress the above-described increase in element temperature, an internal electrode having a small specific resistance has been demanded. However, the specific resistance value of the silver-palladium alloy is significantly higher than the specific resistance of silver or palladium alone, depending on the composition ratio. In the composition of the silver-palladium alloy with 70 wt% silver and 30 wt% palladium, palladium There was a problem that the resistance was 1.5 times that of a single substance. Moreover, when the sintered density of the internal electrode is lowered, the resistance is further increased.

  It is an object of the present invention to provide a multilayer piezoelectric element and a jetting device that are excellent in durability and do not change in displacement even when a piezoelectric actuator is continuously driven for a long time under high voltage and high pressure. And

  The multilayer piezoelectric element of the present invention has a multilayer body in which at least one piezoelectric body and a plurality of internal electrodes are alternately stacked, and the internal electrodes are alternately connected to the side surface of the multilayer body every other layer. In the laminated piezoelectric element that includes the pair of external electrodes and is driven by applying an electric field to the external electrodes, the change rate of the element dimensions before and after continuous driving is within 1%.

  In addition, the multilayer piezoelectric element of the present invention includes a multilayer body in which at least one piezoelectric body and a plurality of internal electrodes are alternately stacked, and the internal electrodes are alternately disposed on the side surfaces of the multilayer body. In a laminated piezoelectric element that includes a pair of connected external electrodes and is driven by applying an electric field to the external electrodes, the rate of change in thickness dimension of the internal electrodes before and after continuous driving is within 5%. And

  In the multilayer piezoelectric element of the present invention, the metal composition in the internal electrode is mainly composed of a Group VIII metal and / or a Group Ib metal.

  In the multilayer piezoelectric element of the present invention, when the content of the group VIII metal in the internal electrode is M1 (wt%) and the content of the group Ib metal is M2 (wt%), 0 <M1 ≦ 15 85 ≦ M2 <100 and M1 + M2 = 100 are satisfied.

  In the multilayer piezoelectric element of the present invention, the group VIII metal is at least one of Ni, Pt, Pd, Rh, Ir, Ru, and Os, and the group Ib metal is at least of Cu, Ag, and Au. It is one or more types.

  In the multilayer piezoelectric element of the present invention, the group VIII metal is at least one of Pt and Pd, and the group Ib metal is at least one of Ag and Au.

  In the multilayer piezoelectric element of the present invention, the group VIII metal is Ni and the group Ib metal is Cu.

  The multilayer piezoelectric element of the present invention is characterized in that an inorganic composition is added to the internal electrode together with a metal composition.

The multilayer piezoelectric element of the present invention is characterized in that the inorganic composition is mainly composed of a perovskite oxide made of PbZrO ₃ —PbTiO ₃ .

  In the multilayer piezoelectric element of the present invention, the piezoelectric body contains a perovskite oxide as a main component.

In the multilayer piezoelectric element of the present invention, the piezoelectric body is mainly composed of a perovskite oxide made of PbZrO ₃ —PbTiO ₃ .

  In the multilayer piezoelectric element of the present invention, the firing temperature of the multilayer body is 900 ° C. or higher and 1000 ° C. or lower.

  The multilayer piezoelectric element of the present invention is characterized in that the compositional deviation in the internal electrode is 5% or less before and after firing.

  In the multilayer piezoelectric element of the present invention, the internal electrodes whose ends are exposed on the side surfaces of the multilayer body and the internal electrodes whose ends are not exposed are alternately configured, and the ends are exposed. A groove is formed in the piezoelectric body portion between the internal electrode and the external electrode that is not, and the groove is filled with an insulator having a Young's modulus lower than that of the piezoelectric body.

  An injection device according to the present invention includes a storage container having an injection hole, the multilayer piezoelectric element according to any one of claims 1 to 16 stored in the storage container, and driving of the multilayer piezoelectric element. And a valve for ejecting liquid from the ejection hole.

  As described above, according to the multilayer piezoelectric element of the present invention, it has a columnar laminated body in which at least one piezoelectric body and a plurality of internal electrodes are alternately laminated, and the internal electrode is disposed on a side surface of the columnar laminated body. Has a pair of external electrodes alternately connected in every other layer, and in a laminated piezoelectric element that is driven by applying an electric field to the external electrodes, the rate of change in element dimensions before and after continuous driving should be within 1% Thus, even if the multilayer piezoelectric element is continuously driven, the displacement amount does not change effectively, so that the malfunction of the apparatus is eliminated, and furthermore, excellent durability without thermal runaway can be achieved.

  In the multilayer piezoelectric element of the present invention, the rate of change in the thickness dimension of the internal electrode before and after continuous driving is within 5%, so that the displacement amount is effective even when the multilayer piezoelectric element is continuously driven. Since it does not change, there is no malfunction of the device, and it can have excellent durability without thermal runaway.

  Furthermore, since the metal composition in the internal electrode is mainly composed of a Group VIII metal and / or a Group Ib metal, the internal electrode can be formed with a metal composition having high heat resistance. Simultaneous firing with the body becomes possible.

  Further, when the content of the group VIII metal in the internal electrode is M1 (wt%) and the content of the group Ib metal is M2 (wt%), 0 <M1 ≦ 15, 85 ≦ M2 <100, M1 + M2 = By satisfying 100, the specific resistance of the internal electrode can be reduced, so that heat generation of the internal electrode portion can be suppressed even when the multilayer piezoelectric element is continuously driven for a long time. In addition, since the temperature rise of the multilayer piezoelectric element can be suppressed, the element displacement can be stabilized.

  Furthermore, the group VIII metal is at least one or more of Ni, Pt, Pd, Rh, Ir, Ru, and Os, and the group Ib metal is at least one or more of Cu, Ag, and Au. As an internal electrode raw material, either an alloy raw material or a mixed powder raw material can be used.

  Furthermore, when the Group VIII metal is at least one of Pt and Pd and the Group Ib metal is at least one of Ag and Au, the internal electrode excellent in heat resistance and oxidation resistance can be obtained. Can be formed.

  Further, since the Group VIII metal is Ni and the Group Ib metal is Cu, stress generated by displacement during driving can be relieved, and the internal electrode excellent in heat resistance and thermal conductivity is formed. it can.

  Further, by adding an inorganic composition together with the metal composition to the internal electrode, the adhesion strength at the interface between the internal electrode and the piezoelectric body is increased, so that peeling at the interface between the internal electrode and the piezoelectric body is suppressed. can do.

Furthermore, since the piezoelectric body is mainly composed of a perovskite oxide made of PbZrO ₃ —PbTiO ₃ , the piezoelectric body and the internal electrode can be fired at the same time. The specific resistance of the internal electrode can be reduced.

  Furthermore, since the compositional deviation in the internal electrode is 5% or less before and after firing, the internal electrode can be configured to follow expansion and contraction due to the driving of the multilayer piezoelectric element. Can be suppressed.

  1A and 1B show an embodiment of a laminated piezoelectric element according to the present invention. FIG. 1A is a perspective view, and FIG. 1B is a perspective development view showing a laminated state of a piezoelectric layer and an internal electrode layer.

  As shown in FIG. 1, the multilayer piezoelectric element of the present invention includes a pair of opposing side surfaces of a laminate 13 in which piezoelectric bodies 11 and internal electrodes 12 are alternately laminated, and an end portion where the internal electrodes 12 are exposed. The external electrodes 15 that are electrically conductive are joined every other layer. In addition, an inactive layer 14 formed of the piezoelectric body 11 is stacked on both ends of the stacked body 13 in the stacking direction. Here, when the multilayer piezoelectric element of the present invention is used as a multilayer piezoelectric actuator, a lead wire may be connected and fixed to the external electrode 15 with solder, and the lead wire may be connected to an external voltage supply unit.

  An internal electrode 12 is arranged between the piezoelectric bodies 11. Since the internal electrode 12 is formed of a metal material such as silver-palladium, a predetermined voltage is applied to each piezoelectric body 11 through the internal electrode 12. The piezoelectric body 11 has a function of causing displacement due to the reverse piezoelectric effect.

  On the other hand, since the inert layer 14 is a layer of a plurality of piezoelectric bodies 11 in which the internal electrode 12 is not disposed, no displacement occurs even when a voltage is applied.

  In the multilayer piezoelectric element of the present invention, the element dimension change rate before and after continuous driving of the multilayer piezoelectric element is within 1%. This is because when the change rate of the element size before and after continuous driving of the multilayer piezoelectric element exceeds 1%, the change in the displacement amount of the multilayer piezoelectric element increases and the multilayer piezoelectric element is destroyed due to thermal runaway. is there.

Here, the change rate of the element dimension before and after continuous driving is the dimension in the stacking direction of the stacked piezoelectric element after an arbitrary AC voltage is applied to the stacked piezoelectric element and continuously driven about 1 × 10 ⁹ times. 3 shows the ratio of change with respect to the dimensions of the multilayer piezoelectric element before continuous driving.

  In the multilayer piezoelectric element of the present invention, the rate of change in the thickness dimension of the internal electrode 12 before and after continuous driving of the multilayer piezoelectric element is within 5%. This is because if the rate of change of the thickness dimension of the internal electrode 12 before and after continuous driving of the multilayer piezoelectric element exceeds 5%, the degradation of the multilayer piezoelectric element indicated by the rate of change of the displacement amount of the multilayer piezoelectric element increases. This is because the durability of the multilayer piezoelectric element is significantly reduced.

Here, the rate of change in the thickness dimension of the internal electrodes before and after continuous driving is the direction in which the stacked piezoelectric elements are laminated after an arbitrary AC voltage is applied to the stacked piezoelectric elements and continuously driven about 1 × 10 ⁹ times. The ratio of the thickness dimension of the internal electrode in FIG. 5 shows the change in the thickness dimension of the internal electrode before continuous driving. The thickness dimension of the internal electrodes is determined so that the internal electrodes 12 (two locations) in contact with the inactive layer 14 and the stacking direction of the stacked piezoelectric elements are stacked when five or more internal electrodes 12 are arranged in the stacked piezoelectric element. Internal electrode 12 (one place) located in the middle, and any internal electrode 12 (two places) arranged between the internal electrode 12 located in the middle and the internal electrode 12 in contact with the inert layer 14 The thickness dimension was measured by SEM, and the average value was taken. Moreover, when the internal electrodes 12 arranged in the multilayer piezoelectric element were less than 5, the thickness dimensions of all the internal electrodes 12 were measured, and the average value was taken as the thickness dimension of the internal electrodes.

  In the multilayer piezoelectric element of the present invention as described above, it is necessary to prevent volume expansion due to oxidation of the internal electrode 12 in order to control the change rate of the element dimension before and after continuous driving and the thickness dimension of the internal electrode 12. . Here, in order to suppress the volume expansion, the following may be performed.

  Up to now, as means for suppressing changes in the element dimensions before and after continuous driving and the thickness dimension of the internal electrode, there are a method of keeping the element temperature constant during continuous driving and a method of finely controlling the driving voltage according to the element temperature. Has been used. Specifically, a heat sink that actively dissipates heat was attached to control the driving voltage while monitoring the element temperature, or to control the temperature around the element.

  On the other hand, in the present invention, the element temperature during continuous driving is controlled by suppressing the heat generation of the element itself generated by driving. In order to control the element temperature, it is necessary to reduce the dielectric loss (tan δ) of the piezoelectric body 11 or the element resistance.

In order to reduce the dielectric loss (tan δ) of the piezoelectric body 11, when the piezoelectric body 11 is formed with a perovskite oxide such as PbZrO ₃ —PbTiO ₃ as a main component, the laminate 13 is fired in an oxygen-excess atmosphere. In addition, there is a method of slowing the rate of temperature decrease from the maximum firing temperature in the treatment after firing the laminate 13. Specifically, the temperature lowering rate may be 600 ° C./hour or less, preferably 300 ° C./hour or less. Further, the value of dielectric loss (tan δ) may be less than 1.5%, preferably 0.5% or less.

  In order to reduce the element resistance, it is preferable to use a material having a small specific resistance value for the internal electrode 12 and to have a dense structure in which a path for electrical conduction is ensured.

  Furthermore, since it is desirable that the temperature characteristic of the displacement amount of the constituent material of the piezoelectric body 11 is constant regardless of the operating temperature, a piezoelectric material having a small displacement amount with respect to a change in element temperature during continuous driving is preferable.

  Further, in order to efficiently release the heat inside the element to the outside of the element, it is preferable that the internal electrode 12 through which heat is transmitted has a composition having excellent heat conduction characteristics.

  Furthermore, it is desirable that the metal composition in the internal electrode 12 is mainly composed of a Group VIII metal and / or a Group Ib metal. This is because the above-described metal composition has high heat resistance, so that the piezoelectric body 11 and the internal electrode 12 having a high firing temperature can be fired simultaneously.

  Further, when the metal composition in the internal electrode 12 has a group VIII metal content of M1 (wt%) and a group Ib metal content of M2 (wt%), 0 <M1 ≦ 15, 85 ≦ M2 < It is preferable that the main component is a metal composition satisfying 100 and M1 + M2 = 100. This is because when the Group VIII metal exceeds 15% by weight, the specific resistance of the internal electrode 12 increases, and the internal electrode 12 may generate heat when the stacked piezoelectric element is continuously driven. Further, in order to suppress migration of the group Ib metal in the internal electrode 2 to the piezoelectric body 11, the group VIII metal is preferably made 0.001 wt% or more and 15 wt% or less. Further, from the viewpoint of improving the durability of the multilayer piezoelectric element, it is preferably 0.1% by weight or more and 10% by weight or less. Moreover, when it is excellent in heat conduction and higher durability is required, 0.5 wt% or more and 9.5 wt% or less are more preferable. Further, when higher durability is required, the content is more preferably 2% by weight or more and 8% by weight or less.

  Here, when the group Ib metal content is less than 85% by weight, the specific resistance of the internal electrode 12 increases, and the internal electrode 12 may generate heat when the stacked piezoelectric element is continuously driven. In order to suppress migration of the group Ib metal in the internal metal 12 to the piezoelectric body 11, the group Ib metal is preferably 85 wt% or more and 99.999 wt% or less. Moreover, 90 weight% or more and 99.9 weight% or less are preferable at the point of improving the durability of a laminated piezoelectric element. Moreover, when higher durability is required, 90.5 weight% or more and 99.5 weight% or less are more preferable. Moreover, when higher durability is calculated | required, 92 to 98 weight% is further more preferable.

  The Group VIII metal and the Group Ib metal indicating the weight percentage of the metal component in the internal electrode 12 can be specified by an analysis method such as an EPMA (Electron Probe Micro Analysis) method.

  Furthermore, the metal component in the internal electrode 12 of the present invention is such that the group VIII metal is at least one of Ni, Pt, Pd, Rh, Ir, Ru, and Os, and the group Ib metal is Cu, Ag, or Au. Of these, at least one is preferable. This is because the metal composition has excellent mass productivity in recent alloy powder synthesis techniques.

  Furthermore, it is preferable that the metal component in the internal electrode 12 is a group VIII metal of at least one of Pt and Pd and a group Ib metal of at least one of Ag and Au. Thereby, there is a possibility that the internal electrode 12 having excellent heat resistance and small specific resistance can be formed.

  Further, the metal component in the internal electrode 12 is preferably such that the Group VIII metal is Ni and the Group Ib metal is Cu. Thereby, the internal electrode 12 excellent in heat resistance and thermal conductivity may be formed.

Furthermore, it is preferable to add an inorganic composition to the internal electrode 12 together with the metal composition. Accordingly, there is a possibility that the internal electrode 12 and the piezoelectric body 11 can be firmly bonded, and it is preferable that the inorganic composition contains a perovskite oxide composed of PbZrO ₃ —PbTiO ₃ as a main component.

Furthermore, it is preferable that the piezoelectric body 11 has a perovskite oxide as a main component. This is because, for example, when formed of a perovskite type piezoelectric ceramic material typified by barium titanate (BaTiO ₃ ) or the like, the piezoelectric strain constant d ₃₃ indicating the piezoelectric characteristics is high, so that the amount of displacement can be increased. Further, the piezoelectric body 11 and the internal electrode 12 can be fired simultaneously. The piezoelectric body 11 described above preferably contains a perovskite oxide composed of PbZrO ₃ —PbTiO ₃ having a relatively high piezoelectric strain constant d ₃₃ as a main component.

  Furthermore, it is preferable that a calcination temperature is 900 degreeC or more and 1000 degrees C or less. This is because when the firing temperature is 900 ° C. or lower, the firing temperature is low, so firing is insufficient, and it becomes difficult to manufacture the dense piezoelectric body 11. Further, if the firing temperature exceeds 1000 ° C., the stress due to the difference between the shrinkage of the internal electrode 12 and the shrinkage of the piezoelectric body 11 during firing becomes large, and cracks may occur during continuous driving of the multilayer piezoelectric element. Because there is.

  Further, the compositional deviation in the internal electrode 12 is preferably 5% or less before and after firing. This is because when the compositional deviation in the internal electrode 12 exceeds 5% before and after firing, the metal material in the internal electrode 12 is more migrated to the piezoelectric body 11, and the expansion and contraction due to the driving of the multilayer piezoelectric element is prevented. The internal electrode 12 may not be able to follow.

  Here, the deviation of the composition in the internal electrode 12 indicates the rate of change in which the composition of the internal electrode 12 changes as the elements constituting the internal electrode 12 evaporate or diffuse into the piezoelectric body 11 by firing.

  In addition, the internal electrodes 12 whose end portions are exposed on the side surfaces of the multilayer piezoelectric element of the present invention and the internal electrodes 12 whose end portions are not exposed are alternately configured, and the internal electrodes 12 whose end portions are not exposed and A groove is formed in the piezoelectric portion between the external electrodes 15, and an insulator having a Young's modulus lower than that of the piezoelectric body 12 is preferably formed in the groove. As a result, in such a multilayer piezoelectric element, stress generated by displacement during driving can be relieved, so that heat generation of the internal electrode 12 can be suppressed even when continuously driven.

  Next, a method for producing the multilayer piezoelectric element of the present invention will be described.

The multilayer piezoelectric element of the present invention includes a calcined powder of a perovskite oxide piezoelectric ceramic made of PbZrO ₃ —PbTiO ₃ or the like, a binder made of an organic polymer such as acrylic or butyral, and DBP (phthalate). A ceramic green sheet that forms a slurry by mixing with a plasticizer such as dioctyl acid) or DOP (dibutyl phthalate), and then forming the slurry by a tape molding method such as a known doctor blade method or calendar roll method. Is made.

  Next, a conductive paste is prepared by adding and mixing a binder, a plasticizer, and the like to the metal powder constituting the internal electrode such as silver-palladium, and this is applied to the upper surface of each green sheet by 1-40 μm by screen printing or the like. Print on thickness.

  Then, a plurality of green sheets with conductive paste printed on the upper surface are laminated, the binder is debindered at a predetermined temperature, and then fired at 900 to 1200 ° C., whereby the laminate 13 is produced. Preferably, as described above, firing is performed in the range of 900 to 1000 ° C.

  In addition, the laminated body 13 is not limited to what is produced by the said manufacturing method, If what can produce the laminated body 13 which laminates | stacks alternately the several piezoelectric body 11 and the some internal electrode 12 will be what? It may be formed by any manufacturing method.

  Thereafter, the internal electrodes 12 whose ends are exposed and the internal electrodes 12 whose ends are not exposed are alternately formed on the side surfaces of the multilayer piezoelectric element, and the internal electrodes 12 and the external electrodes 15 whose ends are not exposed are formed alternately. A groove is formed in the piezoelectric portion, and an insulator such as resin or rubber having a Young's modulus lower than that of the piezoelectric body 11 is formed in the groove. Here, the groove is formed on the side surface of the laminate 13 by an internal dicing device or the like.

  The external electrode 15 is preferably made of silver having a low Young's modulus or an alloy containing silver as a main component because the conductive material constituting the external electrode 15 sufficiently absorbs stress generated by expansion and contraction of the actuator.

A binder is added to the glass powder to produce a silver glass conductive paste, which is formed into a sheet and dried (the solvent is scattered), and the raw density of the sheet is controlled to 6 to 9 g / cm ^3. The sheet is transferred to the external electrode forming surface of the columnar laminate 13, and is at a temperature higher than the softening point of the glass, at a temperature not higher than the melting point of silver (965 ° C.), and not higher than 4/5 of the firing temperature (° C.). By baking at a temperature, the binder component in the sheet prepared using the silver glass conductive paste is scattered and lost, and the external electrode 15 made of a porous conductor having a three-dimensional network structure can be formed.

  The baking temperature of the silver glass conductive paste effectively forms a neck portion, diffuses and joins silver in the silver glass conductive paste and the internal electrode 12, and effectively creates voids in the external electrode 15. The temperature is preferably 550 to 700 ° C. from the viewpoint that the external electrode 15 and the side surface of the columnar laminate 13 are partially joined. The softening point of the glass component in the silver glass conductive paste is preferably 500 to 700 ° C.

  When the baking temperature is higher than 700 ° C., the sintering of the silver powder of the silver glass conductive paste proceeds too much, so that a porous conductor having an effective three-dimensional network structure cannot be formed, and the external electrode 15 May become too dense, and as a result, the Young's modulus of the external electrode 15 may become too high to absorb the stress during driving sufficiently and the external electrode 15 may be disconnected. Preferably, baking should be performed at a temperature within 1.2 times the softening point of the glass.

  On the other hand, when the baking temperature is lower than 550 ° C., since the diffusion bonding is not sufficiently performed between the end portion of the internal electrode 12 and the external electrode 15, the neck portion is not formed, and the internal electrode 12 and the external electrode are not driven. There is a possibility of causing a spark between the electrodes 15.

  Note that the thickness of the silver glass conductive paste sheet is preferably thinner than the thickness of the piezoelectric body 11. More preferably, it is 50 μm or less from the viewpoint of following the expansion and contraction of the actuator.

  Next, the laminated body 13 on which the external electrode 15 is formed is immersed in a silicone rubber solution, and the silicone rubber solution is vacuum degassed to fill the groove of the laminated body 13 with silicone rubber. The laminated body 13 is pulled up, and the side surface of the laminated body 13 is coated with silicone rubber. Thereafter, the silicone rubber coated inside the grooves and coated on the side surfaces of the columnar laminate 13 is cured to complete the multilayer piezoelectric element of the present invention.

  Then, a lead wire is connected to the external electrode 15, a direct current voltage of 0.1 to 3 kV / mm is applied to the pair of external electrodes 15 via the lead wire, and the laminate 13 is subjected to polarization treatment. When a multilayer piezoelectric actuator using the multilayer piezoelectric element is completed, a lead wire is connected to an external voltage supply unit, and a voltage is applied to the internal electrode 12 via the lead wire and the external electrode 15, each piezoelectric The body 11 is largely displaced by the inverse piezoelectric effect, and thereby functions as an automobile fuel injection valve that injects and supplies fuel to the engine, for example.

  Furthermore, a conductive auxiliary member made of a conductive adhesive in which a metal mesh or a mesh-like metal plate is embedded on the outer surface of the external electrode 15 may be formed. In this case, even when a large current is input to the actuator by providing a conductive auxiliary member on the outer surface of the external electrode 15 and the actuator is driven at a high speed, a large current can flow through the conductive auxiliary member. For the reason that the current flowing through 15 can be reduced, the external electrode 15 can be prevented from causing local heat generation and disconnection, and the durability can be greatly improved. Furthermore, since a metal mesh or a mesh-like metal plate is embedded in the conductive adhesive, it is possible to prevent the conductive adhesive from cracking.

  The metal mesh is a braided metal wire, and the mesh metal plate is a mesh formed by forming holes in a metal plate.

  Furthermore, the conductive adhesive constituting the conductive auxiliary member is preferably made of a polyimide resin in which silver powder is dispersed. That is, by dispersing silver powder having a low specific resistance in a polyimide resin having high heat resistance, a conductive auxiliary member having a low resistance value and maintaining a high adhesive strength can be formed even when used at high temperatures. . More preferably, the conductive particles are non-spherical particles such as flakes or needles. This is because by making the shape of the conductive particles non-spherical particles such as flakes and needles, the entanglement between the conductive particles can be strengthened, and the shear strength of the conductive adhesive can be further increased. This is because it can be increased.

  The multilayer piezoelectric element of the present invention is not limited to these, and various modifications can be made without departing from the gist of the present invention.

  Moreover, although the example which formed the external electrode 15 in the side surface which the laminated body 13 opposes above was demonstrated, in this invention, you may form a pair of external electrode in the side surface provided adjacently, for example.

  FIG. 2 shows an injection device according to the present invention. An injection hole 33 is provided at one end of the storage container 31, and a needle valve 35 that can open and close the injection hole 33 is stored in the storage container 31. Has been.

  A fuel passage 37 is provided in the injection hole 33 so as to be able to communicate. The fuel passage 37 is connected to an external fuel supply source, and fuel is always supplied to the fuel passage 37 at a constant high pressure. Therefore, when the needle valve 35 opens the injection hole 33, the fuel supplied to the fuel passage 37 is formed to be injected into a fuel chamber (not shown) of the internal combustion engine at a constant high pressure.

  Further, the upper end portion of the needle valve 35 has a large diameter, and serves as a piston 41 slidable with a cylinder 39 formed in the storage container 31. In the storage container 31, the piezoelectric actuator 43 described above is stored.

  In such an injection device, when the piezoelectric actuator 43 is extended by applying a voltage, the piston 41 is pressed, the needle valve 35 closes the injection hole 33, and the supply of fuel is stopped. When the application of voltage is stopped, the piezoelectric actuator 43 contracts, the disc spring 45 pushes back the piston 41, and the injection hole 33 communicates with the fuel passage 37 so that fuel is injected.

  Further, the present invention relates to a multilayer piezoelectric element and an injection device, but is not limited to the above-described embodiments. For example, a fuel injection device for an automobile engine, a liquid injection device such as an inkjet, an optical device, etc. Drive elements mounted on positioning devices, vibration prevention devices, etc., or sensor elements mounted on combustion pressure sensors, knock sensors, acceleration sensors, load sensors, ultrasonic sensors, pressure sensors, yaw rate sensors, etc., and piezoelectric gyros Needless to say, the present invention can be applied to elements other than circuit elements mounted on piezoelectric switches, piezoelectric transformers, piezoelectric breakers, etc., as long as the elements use piezoelectric characteristics.

  A multilayer piezoelectric actuator comprising the multilayer piezoelectric element of the present invention was produced as follows.

First, a slurry in which a calcined powder of a piezoelectric ceramic mainly composed of lead zirconate titanate (PbZrO ₃ -PbTiO ₃ ), a binder, and a plasticizer is mixed, and the piezoelectric body 11 having a thickness of 150 μm is formed by a doctor blade method. A ceramic green sheet was prepared.

  On one side of this ceramic green sheet, 300 sheets of a conductive paste in which a binder is added to a silver-palladium alloy formed at an arbitrary composition ratio are laminated by a screen printing method to a thickness of 3 μm, and 1000 ° C. Baked in.

  Next, a groove having a depth of 50 μm and a width of 50 μm was formed at every other end portion of the internal electrode on the side surface of the multilayer body by a dicing apparatus.

Next, a mixture of 90% by volume of flaky silver powder having an average particle diameter of 2 μm and 10% by volume of amorphous glass powder having a remaining softening point of 640 ° C. mainly composed of silicon having an average particle diameter of 2 μm. In addition, 8 parts by mass of the binder was added to 100 parts by mass of the total weight of the silver powder and the glass powder, and mixed sufficiently to prepare a silver glass conductive paste. The silver glass conductive paste thus produced was formed on a release film by screen printing, dried and then peeled off from the release film to obtain a sheet of silver glass conductive paste. The raw density of this sheet was measured by the Archimedes method and found to be 6.5 g / cm ³ .

  Next, the sheet of silver glass paste was transferred to the surface of the external electrode 15 of the laminate 13 and baked at 650 ° C. for 30 minutes to form the external electrode 15 made of a porous conductor having a three-dimensional network structure. The porosity of the external electrode 15 at this time was 40% when a cross-sectional photograph of the external electrode 15 was measured using an image analyzer.

  Thereafter, a lead wire is connected to the external electrode 15, a 3 kV / mm direct current electric field is applied to the positive and negative external electrodes 15 through the lead wire for 15 minutes, and polarization is performed. As shown in FIG. A multilayer piezoelectric actuator using a piezoelectric element was produced.

  (Example 1) In addition to the above manufacturing method, in the multilayer piezoelectric actuator of the present invention manufactured by controlling the resistance value of the element resistance and the dielectric loss (tan δ) of the piezoelectric body 11, the multilayer piezoelectric actuator is continuously driven. We measured the element dimensions and the rate of change in element temperature before and after, and verified the relationship between them and the element displacement after continuous driving of the multilayer piezoelectric actuator.

  In addition, as a comparative example, a sample was manufactured in which the change rate of the element dimension before and after continuous driving of the multilayer piezoelectric actuator exceeded 1%.

When a DC voltage of 170 V was applied to the multilayer piezoelectric actuator obtained as described above, a displacement of 45 μm in the stacking direction was obtained in all multilayer piezoelectric actuators. Further, a test was performed in which the multilayer piezoelectric actuator was continuously driven up to 1 × 10 ⁹ times by applying an AC voltage of 0 to +170 V at a frequency of 150 Hz at room temperature. The results are as shown in Table 1.

  From Table 1, Sample No. 8, which is a comparative example, has an element dimension change rate before and after continuous driving exceeding 1%, so that the amount of element displacement after continuous driving is remarkably reduced. Further, the internal electrode 12 and the external electrode Since high-temperature local heat was generated at the junction with No. 15, the laminated piezoelectric actuator was destroyed due to thermal runaway.

In contrast, Sample Nos. 1 to 7, which are examples of the present invention, were stacked piezoelectric actuators formed within a range where the element dimension change rate before and after continuous driving was within 1%, so 1 × 10 ⁹ times. Even if it is continuously driven, the element displacement after continuous driving does not drop significantly, it has the effective displacement required as a multilayer piezoelectric actuator, and it has excellent durability without thermal runaway or malfunction A multilayer piezoelectric actuator having the characteristics was successfully fabricated.

(Example 2) In addition to the above manufacturing method, in the multilayer piezoelectric actuator of the present invention manufactured by controlling the resistance value of the element resistance and the dielectric loss (tan δ) of the piezoelectric body 11, the multilayer piezoelectric actuator is continuously driven. Later, the rate of change of the thickness dimension of the internal electrode 12 and the rate of change of the element temperature were measured, and the relationship between these and the degree of deterioration indicated by the rate of change of the displacement amount before and after continuous driving of the multilayer piezoelectric actuator was verified.

  Here, the degree of deterioration is measured by measuring the element displacement after driving the multilayer piezoelectric actuator an arbitrary number of times (the element displacement after continuous driving), and the element displacement before the continuous driving (in the initial state). The amount of change with respect to the amount of displacement of the element after continuous driving is shown with respect to the amount of displacement. Thereby, it is possible to confirm the deterioration caused by continuously driving the laminated piezoelectric actuator a predetermined number of times.

  Further, as a comparative example, a sample was manufactured in which the rate of change in the thickness dimension of the internal electrode 12 before and after continuous driving of the multilayer piezoelectric actuator was in the range exceeding 5%.

When a DC voltage of 170 V was applied to the multilayer piezoelectric actuator obtained as described above, a displacement of 45 μm in the stacking direction was obtained in all multilayer piezoelectric actuators. Furthermore, a driving test was performed in which the multilayer piezoelectric actuator was continuously driven up to 1 × 10 ⁹ times by applying an AC voltage of 0 to +170 V at a frequency of 150 Hz at room temperature. The results are as shown in Table 2.

  From Table 2, in Sample Nos. 8 and 9, which are comparative examples, since the rate of change in the thickness dimension of the internal electrode 12 before and after continuous driving exceeded 5%, the element displacement after continuous driving was significantly reduced. The degree of deterioration increased. In Sample No. 9, oxidative expansion was promoted by the significant heat generation of the internal electrode 12, and the multilayer piezoelectric actuator was destroyed due to thermal runaway.

In contrast, Sample Nos. 1 to 7, which are examples of the present invention, are multilayer piezoelectric actuators in which the rate of change in the thickness dimension of the internal electrode 12 before and after continuous driving was within 5%. × 10 Even after ⁹ times of continuous driving, the element displacement after continuous driving is not significantly reduced, it has the effective amount of displacement required as a multilayer piezoelectric actuator, and there is no thermal runaway or malfunction. A laminated piezoelectric actuator having excellent durability that does not occur can be produced.

  (Example 3) In the above-described manufacturing method, in the multilayer piezoelectric actuator having the internal electrode 12 formed with various electrode material compositions, the maximum rate of change of the element displacement amount during continuous driving of the multilayer piezoelectric actuator was measured. The relationship between the electrode material composition of the electrode 12 and the degree of deterioration due to continuous driving of the multilayer piezoelectric actuator was verified.

When a DC voltage of 170 V was applied to the multilayer piezoelectric actuator obtained as described above, a displacement of 45 μm in the stacking direction was obtained in all multilayer piezoelectric actuators. Furthermore, a driving test was performed in which the multilayer piezoelectric actuator was continuously driven up to 1 × 10 ⁹ times by applying an AC voltage of 0 to +170 V at a frequency of 150 Hz at room temperature. The results are as shown in Table 3.

  From Table 3, in Sample No. 1, since the internal electrode 12 was made of 100% silver, silver migration occurred and the laminated piezoelectric actuator was damaged, so that continuous driving became difficult.

  Sample Nos. 18 and 19 have a group VIII metal content of more than 15% by weight and a group lb metal content of less than 85% by weight in the metal composition in the internal electrode 12. Since the deterioration is increased by continuous driving, the durability of the multilayer piezoelectric actuator is lowered.

  In contrast, in Sample Nos. 2 to 15, when the metal composition in the internal electrode 12 is M1 (wt%) of the Group VIII metal content and M2 (wt%) of the Group Ib metal content is 0 <M1 ≦ 15, 85 ≦ M2 <100, and a metal composition satisfying M1 + M2 = 100 is used as a main component, so that the specific resistance of the internal electrode 12 can be reduced and the heat generated in the internal electrode 12 can be suppressed even when continuously driven. As a result, a multilayer actuator with a stable element displacement after a predetermined continuous drive could be produced.

  Further, since the sample numbers 15 to 17 are mainly composed of a metal composition in which the Group VIII metal in the internal electrode 12 is Ni or the Group Ib metal is Cu, the specific resistance of the internal electrode 12 can be reduced, and even when continuously driven. Since heat generation generated in the internal electrode 12 could be suppressed, a multilayer actuator with stable element displacement after a predetermined continuous drive could be manufactured.

  It should be noted that the present invention is not limited to the above-described embodiments, and various modifications may be made without departing from the scope of the present invention.

1A and 1B show a laminated piezoelectric element of the present invention, in which FIG. 1A is a perspective view, and FIG. 1B is a perspective developed view showing a laminated state of a piezoelectric layer and an internal electrode layer. It is a side view which shows the injection apparatus of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Piezoelectric body 12 ... Internal electrode 13 ... Laminated body 14 ... Inactive layer 15 ... External electrode 31 ... Storage container 33 ... Injection hole 35 ... Valve 43 ..Piezoelectric actuator

Claims (15)

It has a laminate formed by alternately laminating at least one piezoelectric body and a plurality of internal electrodes, and has a pair of external electrodes in which the internal electrodes are alternately connected to every other side surface of the laminate, A multilayer piezoelectric element driven by applying an electric field to the external electrode, wherein a change rate of an element dimension before and after continuous driving is within 1%. It has a laminate formed by alternately laminating at least one piezoelectric body and a plurality of internal electrodes, and has a pair of external electrodes in which the internal electrodes are alternately connected to every other side surface of the laminate, A multilayer piezoelectric element driven by applying an electric field to the external electrode, wherein the rate of change in thickness dimension of the internal electrode before and after continuous driving is within 5%. 3. The multilayer piezoelectric element according to claim 1, wherein the metal composition in the internal electrode contains a Group VIII metal and / or a Group Ib metal as a main component. When the content of the Group VIII metal in the internal electrode is M1 (wt%) and the content of the Group Ib metal is M2 (wt%), 0 <M1 ≦ 15, 85 ≦ M2 <100, M1 + M2 = 100 The multilayer piezoelectric element according to claim 3, wherein the multilayer piezoelectric element is satisfied. The group VIII metal is at least one of Ni, Pt, Pd, Rh, Ir, Ru, and Os, and the group Ib metal is at least one of Cu, Ag, and Au. Item 5. The multilayer piezoelectric element according to any one of Items 3 to 4. 6. The stacked type according to claim 3, wherein the Group VIII metal is at least one of Pt and Pd, and the Group Ib metal is at least one of Ag and Au. Piezoelectric element. 6. The multilayer piezoelectric element according to claim 3, wherein the Group VIII metal is Ni and the Group lb metal is Cu. The multilayer piezoelectric element according to claim 1, wherein an inorganic composition is added to the internal electrode together with the metal composition. 9. The multilayer piezoelectric element according to claim 8, wherein the inorganic composition contains a perovskite oxide composed of PbZrO ₃ —PbTiO ₃ as a main component. The multilayer piezoelectric element according to claim 1, wherein the piezoelectric body contains a perovskite oxide as a main component. The multilayer piezoelectric element according to claim 10, wherein the piezoelectric body contains a perovskite oxide composed of PbZrO ₃ —PbTiO ₃ as a main component. The multilayer piezoelectric element according to claim 1, wherein a firing temperature of the multilayer body is 900 ° C. or higher and 1000 ° C. or lower. The multilayer piezoelectric element according to claim 1, wherein the compositional deviation in the internal electrode is 5% or less before and after firing. The internal electrodes whose end portions are exposed on the side surfaces of the laminate and the internal electrodes whose end portions are not exposed are alternately configured, and the internal electrodes between which the end portions are not exposed and the external electrodes are formed. 14. The multilayer piezoelectric element according to claim 1, wherein a groove is formed in the piezoelectric body portion, and the groove is filled with an insulator having a Young's modulus lower than that of the piezoelectric body. . A storage container having an injection hole, the stacked piezoelectric element stored in the storage container, and a valve that ejects liquid from the injection hole by driving the stacked piezoelectric element. An injection device comprising:

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