JP2005072325A - Laminated piezoelectric device and injection equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laminated piezoelectric device which hardly suffers from disconnection between an external electrode and an internal electrode and is superior in durability even if it is operated in a high electrical field under a high pressure for a long term and an injection equipment. <P>SOLUTION: The laminated piezoelectric device is provided with a laminated body 1a that a plurality of piezoelectric bodies 1 and a plurality of internal electrodes 2 are alternately laminated, and a pair of external electrodes 4 on the side of the laminated body 1a wherein the internal electrodes 2 are alternately connected with every layer therebetween. The external electrode 4 contains a conductive material and a glass, and it is made of porous conductor forming a three-dimensional mesh structure. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a laminated piezoelectric element and an injection device, for example, a laminated structure such as a piezoelectric transformer, a precision positioning device such as an automobile fuel injection device and an optical device, a laminated piezoelectric actuator used for a vibration preventing drive element, and the like. The present invention relates to a type piezoelectric element and an injection device.

  Conventionally, as a multilayer piezoelectric element, a multilayer piezoelectric actuator in which piezoelectric bodies and internal electrodes are alternately stacked is known. Multilayer piezoelectric actuators are classified into two types: the simultaneous firing type and the stack type in which piezoelectric ceramics and internal electrode plates are alternately laminated. Since the multilayer piezoelectric actuator of the type is advantageous for thinning, its superiority is being shown.

  FIG. 6 shows a conventional laminated piezoelectric actuator. In this actuator, piezoelectric bodies 51 and internal electrodes 52 are alternately laminated to form a columnar laminated body 53, which is inactive on both end faces in the laminating direction. Layer 55 is laminated. One end portion of the internal electrode 52 is alternately exposed on the side surface of the columnar stacked body 53, and the external electrode 70 is formed on the side surface of the columnar stacked body 53 where the end portion of the internal electrode 52 is exposed. ing. The other end of the internal electrode 52 is covered with an insulator 61 and insulated from the external electrode 70.

Conventionally, an external electrode is formed by applying a conductive paste made of organic components of 71 to 95% by mass of silver and 5 to 29% by mass of the glass powder, and the rest is baked at 500 to 1000 ° C. (For example, refer to Patent Document 1).
JP 2000-40635

  However, in the conventional multilayer piezoelectric actuator, when driven continuously for a long time under a high electric field and high pressure, the external electrode 70 may not be able to follow the expansion and contraction of the multilayer body 53 or may be disconnected, or the external electrode 70 and the internal electrode 52 may be disconnected. There is a problem that a contact failure occurs between them, and voltage is not supplied to some of the piezoelectric bodies 51, and the displacement characteristics change during driving.

  That is, in recent years, in order to ensure a large amount of displacement under a large pressure with a small multilayer piezoelectric actuator, a higher electric field is applied and driven continuously for a long period of time. The external electrode 70 is not flexible simply by applying and baking on the side surface of the columnar laminate 53, and cannot follow expansion and contraction in the stacking direction of the columnar laminate 53, and the connection between the internal electrode 52 and the external electrode 70 is released. There is a problem that peeling occurs or a crack occurs in the external electrode 70 and the wire is disconnected, so that voltage is not supplied to some of the piezoelectric bodies 51 and the displacement characteristics change during driving.

  The present invention provides a multilayer piezoelectric element and an injection device that are excellent in durability without disconnecting the external electrode and the internal electrode even when continuously driven for a long time under a high electric field and high pressure. Objective.

  The multilayer piezoelectric element of the present invention is provided on a side surface of a multilayer body in which a plurality of piezoelectric bodies and a plurality of internal electrodes are alternately stacked, and the internal electrodes are alternately connected every other layer. A laminated piezoelectric element comprising a pair of external electrodes, wherein the external electrodes are made of a porous conductor containing a conductive material and glass and having a three-dimensional network structure.

  In such a laminated piezoelectric element, the external electrode contains a conductive material and glass and is made of a porous conductor having a three-dimensional network structure. For example, the actuator body that is a laminated body expands and contracts in the laminating direction when driven. Even in this case, since the external electrode is flexible, the external electrode can follow the expansion and contraction of the laminate, and problems such as disconnection of the external electrode and defective contact between the external electrode and the internal electrode can be prevented.

  The multilayer piezoelectric element of the present invention is characterized in that the external electrode is partially bonded to the side surface of the multilayer body. In such a multilayer piezoelectric element, the external electrode is partially bonded to the side surface of the multilayer body, so that the stress generated with respect to the expansion and contraction of the multilayer body can be absorbed more flexibly than the case where the entire surface is bonded. .

  Furthermore, the multilayer piezoelectric element of the present invention is characterized in that the external electrode is diffusion bonded to the end portion of the internal electrode exposed on the side surface of the multilayer body. In such a laminated piezoelectric element, the conductive material constituting the external electrode and the internal electrode can be firmly bonded by diffusion bonding, thereby causing local heat generation or sparking at the connection portion between the internal electrode and the external electrode during driving. Occurrence can be prevented.

  In the multilayer piezoelectric element of the present invention, it is desirable that a neck portion is formed at the end portion of the internal electrode, and this neck portion is embedded in the external electrode. In such a multilayer piezoelectric element, the internal electrode end exposed on the side surface of the multilayer body is connected to the external electrode through the neck portion, and even when a large current is passed through the multilayer piezoelectric element to drive it at high speed, And local heat generation at the joint of the external electrode can be prevented.

  Furthermore, the multilayer piezoelectric element of the present invention is characterized in that the conductive material of the external electrode is mainly composed of silver. In such a multilayer piezoelectric element, the stress generated by the expansion and contraction of the multilayer body can be flexibly absorbed by using silver having a low Young's modulus as the conductive material forming the external electrode. In addition, by using silver as the conductive material constituting the external electrode, diffusion bonding with a silver-palladium alloy generally used as a conductive material for the internal electrode is facilitated, and the external electrode and the internal electrode are more firmly connected. Can be connected.

  In the multilayer piezoelectric element of the present invention, the external electrode has a porosity of 30 to 70% by volume. By setting the porosity of the external electrode to 30 to 70% by volume, the stress generated by the expansion and contraction of the laminate can be sufficiently absorbed.

  Furthermore, the laminated piezoelectric element of the present invention is characterized in that the softening point of the glass constituting the external electrode is not more than the melting point of the conductive material constituting the external electrode. In such a multilayer piezoelectric element, the baking temperature of the external electrode can be set to a temperature not higher than the melting point of the conductive material and not lower than the softening point of the glass component, and the aggregation of the conductive material can be prevented. Bonding strength can be obtained.

  Moreover, the multilayer piezoelectric element of the present invention is characterized in that the glass constituting the external electrode is amorphous. By making the glass component amorphous, the Young's modulus is lower than that of crystalline, so that cracks in the external electrode can be suppressed.

  The multilayer piezoelectric element of the present invention is characterized in that the thickness of the external electrode is smaller than the thickness of the piezoelectric body constituting the multilayer body. By making the thickness of the external electrode thinner than the thickness of the piezoelectric body, the hardness of the external electrode is reduced, the load at the contact between the external electrode and the internal electrode can be reduced when the laminate expands and contracts, and the contact failure can be suppressed.

  Further, in the multilayer piezoelectric element of the present invention, it is desirable that the baking temperature (° C.) of the external electrode is 4/5 or less of the firing temperature (° C.) of the multilayer body. When the baking temperature of the external electrode is 4/5 or less of the firing temperature of the columnar laminate, the amount of diffusion of the glass component constituting the external electrode into the laminate can be made appropriate, and the bonding strength between the laminate and the external electrode is reduced. Can be prevented.

  In the multilayer piezoelectric element of the present invention, the concave groove formed on the side surface of the multilayer body is filled with an insulator having a Young's modulus lower than that of the piezoelectric body, and the internal electrode and the external electrode are insulated every other layer. It is characterized by. By forming a groove on the side of the laminate and filling the groove with an insulator, insulation between the internal electrode and the external electrode can be secured, and the Young's modulus is lower in the groove than the piezoelectric body. Since the insulator is filled, the insulator in the concave groove is deformed following the deformation of the laminated body, and the generation of cracks and the like in the vicinity of the concave groove can be prevented, and the generated stress can be reduced.

  The multilayer piezoelectric element of the present invention is characterized in that the metal component contained in the internal electrode contains Ag as a main component and contains one or more of Pd and Pt group metals in an amount of 15 atomic% or less. By making the content of the Pd and Pt group metals contained in the internal electrode 15 atomic% or less, the compositional difference between the internal electrode and the external electrode can be reduced, so that the mutual diffusion of metal between the internal electrode and the external electrode This improves the reliability of bonding between the internal electrode and the external electrode, and improves the durability.

  Furthermore, the multilayer piezoelectric element of the present invention is characterized in that a conductive auxiliary member made of a conductive adhesive in which a metal mesh or a mesh-like metal plate is embedded is provided on the outer surface of the external electrode. . Thereby, even when a large current is input to the laminated body and driven at a high speed, the large current can flow through the conductive auxiliary member, so that the external electrode can be prevented from being disconnected due to local heat generation, Durability can be greatly improved.

  Moreover, since the metal mesh or the mesh-like metal plate is embedded in the conductive adhesive, it is possible to prevent the problem that the conductive adhesive cracks due to the expansion and contraction of the laminate.

  In addition, the multilayer piezoelectric element of the present invention is characterized in that the conductive adhesive is made of a polyimide resin in which conductive particles are dispersed. By using a highly heat-resistant polyimide resin as the matrix component of the conductive adhesive, the conductive adhesive can maintain high adhesive strength even when used at high temperatures.

  Furthermore, the conductive particles of the conductive adhesive are silver powder. By using silver powder having a low specific resistance as the conductive particles, the resistance value of the conductive adhesive can be lowered, and local heat generation can be prevented even when driven by flowing a large current. Further, the conductive particles may be non-spherical particles such as flakes and needles because the entanglement between the conductive particles can be strengthened and the strength of the conductive adhesive can be further increased. desirable.

  In addition, the injection device of the present invention includes 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. It comprises.

  In such an injection device, as described above, the disconnection between the external electrode and the internal electrode can be suppressed in the multilayer piezoelectric element itself, and the durability can be greatly improved. Therefore, the durability of the injection device can also be improved.

  According to the multilayer piezoelectric element of the present invention, since the external electrode is formed of a porous conductor having a three-dimensional network structure containing a conductive material and glass, the external electrode generates stress caused by expansion and contraction of the multilayer piezoelectric element. Since it can absorb sufficiently, it is possible to suppress disconnection of external electrode and internal electrode even when operated continuously at high speed under high electric field and high pressure for a long time. An element can be provided.

  1A and 1B show an embodiment of a multilayer piezoelectric element comprising a multilayer piezoelectric actuator according to the present invention. FIG. 1A is a perspective view, and FIG. 1B is a longitudinal section along the line AA 'in FIG. FIG.

  As shown in FIG. 1, the multilayer piezoelectric actuator has an end portion of the internal electrode 2 on the side surface of a quadrangular columnar stacked body 1a in which a plurality of piezoelectric bodies 1 and a plurality of internal electrodes 2 are alternately stacked. A porous conductor that is covered with an insulator 3 every other layer and is made of a conductive material and glass mainly composed of silver and has a three-dimensional network structure at the end of the internal electrode 2 that is not covered with the insulator 3 The external electrodes 4 are joined and lead wires 6 are connected and fixed to the external electrodes 4. Reference numeral 9 denotes an inactive layer.

The piezoelectric body 1 is made of, for example, a lead ceramic zirconate titanate Pb (Zr, Ti) O ₃ (hereinafter abbreviated as PZT) or a piezoelectric ceramic material mainly composed of barium titanate BaTiO ₃ . The piezoelectric ceramics are those piezoelectric strain constant d ₃₃ indicating the piezoelectric characteristic is high is preferable.

  The thickness of the piezoelectric body 1, that is, the distance between the internal electrodes 2 is preferably 50 to 250 μm. As a result, the multilayer piezoelectric actuator can reduce the size and height of the actuator and prevent dielectric breakdown of the piezoelectric body 1 even if the number of layers is increased in order to obtain a larger displacement by applying a voltage. it can.

  An internal electrode 2 is disposed between the piezoelectric bodies 1, and the internal electrode 2 is formed of a metal material such as silver-palladium, and a predetermined voltage is applied to each piezoelectric body 1. It acts to cause displacement due to the reverse piezoelectric effect.

  Further, a groove having a depth of 30 to 500 μm and a width in the stacking direction of 30 to 200 μm is formed on the side surface of the columnar laminated body 1 a, and glass having a lower Young's modulus than the piezoelectric body 1 is formed in the groove, An insulator 3 is formed by filling an epoxy resin, a polyimide resin, a polyamideimide resin, a silicone rubber, or the like. The insulator 3 is preferably made of a material having a low elastic modulus that follows the displacement of the columnar laminate 1a, particularly silicone rubber, in order to strengthen the bonding with the columnar laminate 1a.

  External electrodes 4 are joined to opposing side surfaces of the columnar laminate 1a, and the laminated internal electrodes 2 are electrically connected to the external electrodes 4 every other layer. The external electrode 4 serves to commonly supply a voltage necessary for displacing the piezoelectric body 1 to each connected internal electrode 2 by the inverse piezoelectric effect.

  Furthermore, a lead wire 6 is connected and fixed to the external electrode 4 with solder. The lead wire 6 serves to connect the external electrode 4 to an external voltage supply unit.

  In the present invention, the external electrode 4 includes a conductive material and glass, and is composed of a porous conductor having a three-dimensional network structure as shown in FIG. Here, the three-dimensional network structure does not mean a state in which a so-called spherical void exists in the external electrode 4, but the conductive material powder and the glass powder constituting the external electrode 4 are baked at a relatively low temperature. Therefore, the void exists in a state where the sintering is not completed and the voids are connected to some extent, and the conductive material powder and the glass powder constituting the external electrode 4 are three-dimensionally connected and joined. 2A is an enlarged cross-sectional view of a part of FIG. 1B, and FIG. 2B is an enlarged cross-sectional view of FIG.

  The external electrode 4 is composed of 80 to 97% by volume of a conductive material and 3 to 20% by volume of glass, and a small amount of glass is dispersed in the conductive material. It is desirable to contain 5 to 15% by volume of glass. The external electrode 4 is partially joined to the side surface of the columnar laminate 1a. That is, the end portion of the internal electrode 2 exposed on the side surface of the columnar laminated body 1a is diffusion bonded, and the side surface of the piezoelectric body 1 of the columnar laminated body 1a is partially bonded. That is, a mixture of a conductive material and glass is partially bonded to the side surface of the piezoelectric body 1, and a gap 4 a is formed between the side surface of the piezoelectric body 1 and the external electrode 4. Also, a large number of voids 4a are formed in the external electrode 4 so that the external electrode 4 is made of a porous conductor. The shape of the gap 4a is a complicated shape in which the shape before baking of the conductive material and the glass remains relatively as it is.

  In the present invention, the outer electrode 4 made of a conductive material and glass and made of a porous conductor having a three-dimensional network structure is diffusion bonded to the inner electrode 2 and partially bonded to the columnar laminate 1a. Therefore, even when the actuator is continuously driven for a long time under a high electric field and high pressure, a spark is caused between the external electrode 4 and the internal electrode 2, or the external electrode 4 is peeled off from the columnar laminate 1a. Or the problem of disconnection can be prevented. In the present invention, the external electrode 4 can be made entirely porous by baking a conductive material made of glass and a conductive material forming the external electrode 4 at a relatively low temperature, and the columnar laminate 1a. Can be partially joined to the side of

  The conductive material constituting the external electrode 4 is preferably silver having a low Young's modulus or an alloy containing silver as a main component from the viewpoint of sufficiently absorbing the stress generated by the expansion and contraction of the actuator.

  In the present invention, as shown in FIG. 2B, the neck 4b is formed at the end of the internal electrode 2 connected to the external electrode 4, and the internal electrode 2 and the external electrode 4 are firmly connected. Has been realized. The neck portion 4b is formed by diffusion bonding of the conductive material in the external electrode 4 and the electrode material of the internal electrode 2.

  Furthermore, in the present invention, the porosity in the external electrode 4, that is, the ratio of the void 4 a in the external electrode 4 is 30 to 70% by volume. Thereby, the stress which arises by expansion / contraction of an actuator can be received flexibly. That is, when the porosity in the external electrode 4 is smaller than 30% by volume, the external electrode 4 may not withstand the stress generated by the expansion and contraction of the actuator, and the external electrode 4 may be disconnected. On the other hand, when the porosity in the external electrode 4 is greater than 70% by volume, the resistance value of the external electrode 4 increases, and when a large current is passed, the external electrode 4 generates local heat and is disconnected. There is a possibility.

  In the present invention, the softening point of the glass component constituting the external electrode 4 is not higher than the melting point of the conductive material constituting the external electrode 4. This is because the baking temperature of the external electrode 4 can be made lower than the melting point of the conductive material and higher than the softening point of the glass component. As a result, baking can be performed at a temperature not lower than the softening point of the glass component and not higher than the melting point of the conductive material, so that aggregation of the conductive material can be prevented, a porous body can be formed, and baking can be performed with sufficient bonding strength. it can.

  In the present invention, the glass component constituting the external electrode 4 is amorphous. As a result, the external electrode 4 can absorb the stress generated by the expansion and contraction of the actuator, and the occurrence of cracks and the like can be prevented.

  In the present invention, it is desirable that the thickness of the external electrode 4 be thinner than the thickness of the piezoelectric body 1 constituting the columnar laminated body 1a. As a result, the external electrode 4 has an appropriate strength in the stacking direction of the columnar laminate 1a, and when the actuator expands and contracts, it is possible to prevent an increase in load at the contact point between the external electrode 4 and the internal electrode 2, thereby preventing a contact failure Can be prevented.

  A method for producing the multilayer piezoelectric element of the present invention will be described. First, the columnar laminate 1a is produced. A columnar laminate 1a formed by alternately laminating a plurality of piezoelectric bodies 1 and a plurality of internal electrodes 2 includes a calcined powder of piezoelectric ceramics such as PZT and a binder made of an organic polymer such as acrylic or butyral. , DBP (diethyl phthalate), DOP (dibutyl phthalate) and the like are mixed with a plasticizer to produce a slurry, and the slurry is formed into a piezoelectric material 1 by a tape molding method such as a known doctor blade method or calendar roll method. A ceramic green sheet is produced.

  Next, a conductive paste is prepared by adding a binder, a plasticizer, and the like to silver-palladium powder, and this is printed on the upper surface of each green sheet to a thickness of 1 to 40 μm by screen printing or the like.

  Then, a plurality of green sheets each having a 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., thereby producing the columnar laminate 1a. .

  The columnar laminate 1a is not limited to the one produced by the above-described manufacturing method, and any method can be used as long as the columnar laminate 1a formed by alternately laminating a plurality of piezoelectric bodies and a plurality of internal electrodes can be produced. It may be formed by any manufacturing method.

  Thereafter, as shown in FIG. 3A, grooves are formed on every other side of the columnar laminate 1a by a dicing apparatus or the like.

Further, 80 to 97% by volume of silver powder having a particle size of 0.1 to 10 μm, 3 to 20 volume of glass powder having a remaining particle size of 0.1 to 10 μm and a softening point of 450 to 800 ° C. mainly composed of silicon. %, A binder is added 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 21 is controlled to 6 to 9 g / cm ³ . Then, as shown in FIG. 3B, the sheet 21 is transferred to the external electrode forming surface of the columnar laminate 1a having grooves, and is heated to a temperature higher than the softening point of the glass and the melting point of silver (965). In the sheet 21 produced using the silver glass conductive paste, as shown in FIG. 3 (c), by baking at a temperature of 4/5 or less of the firing temperature (° C.). The binder component is scattered and disappears, and the three-dimensional network structure It is possible to form the external electrode 4 formed of a porous conductive material that forms the.

In particular, in order to form the external electrode 4 having a three-dimensional network structure, it is important to control the raw density of the sheet 21 to 6 to 9 g / cm ³ . The raw density of the sheet 21 can be measured by the Archimedes method. In particular, in order to set the porosity of the external electrode 4 to 30 to 70%, it is desirable to set the green density to 6.2 to 7.0 g / cm ³ .

  When this silver glass conductive paste is baked, voids 4a are formed in the external electrode 4, and silver in the silver glass conductive paste is diffusion-bonded to the silver-palladium alloy in the internal electrode 2 to form a neck portion. 4b is formed, and the external electrode 4 is partially bonded to the side surface of the laminate. In the neck portion 4b, Pd diffuses from the internal electrode 2 to form a silver-palladium alloy.

  The baking temperature of the silver glass conductive paste effectively forms the neck portion 4b, diffuses and joins the silver in the silver glass conductive paste and the internal electrode 2, and makes the void in the external electrode 4 effective. 550 to 700 ° C. is desirable in that the external electrode 4 and the side surface of the columnar laminate 1a 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 so much that a porous conductor having an effective three-dimensional network structure cannot be formed, and the external electrode 4 Becomes too dense, and as a result, the Young's modulus of the external electrode 4 becomes too high to absorb the stress during driving sufficiently, and the external electrode 4 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 2 and the external electrode 4, the neck portion 4 b is not formed and There is a possibility of causing a spark between the external electrodes 4.

It is desirable that the thickness of the silver glass conductive paste sheet 21 is smaller than the thickness of the piezoelectric body 1. More preferably, it is 50 μm or less from the viewpoint of following the expansion and contraction of the actuator.

  The reason why the silver powder in the silver glass conductive paste 21 is 80 to 97 vol% and the remaining glass powder is 3 to 20 vol% is that when the silver powder is less than 80 vol%, the glass component is relatively small. When the baking is performed, the void 4a cannot be effectively formed in the external electrode 4 and the external electrode 4 cannot be partially bonded to the side surface of the columnar laminate 1a. Is more than 97% by volume, the glass component is relatively reduced, the bonding strength between the external electrode 4 and the columnar laminate 1a is weakened, and the external electrode 4 is peeled off from the columnar laminate 1a while driving the actuator. This is because there is a risk of losing.

  The glass components constituting the external electrode 4 are silica glass, soda lime glass, lead alkali silicate glass, aluminoborosilicate glass, borosilicate glass, aluminosilicate glass, borate glass, phosphoric acid. Salt glass or the like is used.

For example, as borosilicate glass, alkaline earth such as SiO ₂ 40 to 70 mass%, B ₂ O ₃ 2 to 30 mass%, Al ₂ O ₃ 0 to 20 mass%, MgO, CaO, SrO, BaO. What contains 0-10 mass% of alkali metal oxides in a total amount, and 0-10 mass% of alkali metal oxides can be used. Further, the borosilicate glass may be a glass containing 5 to 30% by mass of ZnO. ZnO has the effect of lowering the working temperature of borosilicate glass.

As the phosphate _glass, P ₂ O 5 40 to 80 _{wt%, Al} 2 O 3 0 to 30 _{wt%, B} 2 O 3 0 to 30 wt%, ZnO0～30 mass% alkaline earth metal oxide Glass containing 0 to 30% by mass of the product and 0 to 10% by mass of the alkali metal oxide can be used.

As the lead glass, PbO30～80 _wt%, SiO 2 0 to 40 _{wt%, Bi} 2 O 3 0 to 30 _{wt%, Al} 2 O 3 0 to 20 wt%, ZnO0～30 wt%, an alkaline earth Glasses containing 0 to 30% by mass of metal oxide and 0 to 10% by mass of alkali metal oxide can be used.

  Next, the columnar laminated body 1a on which the external electrode 4 is formed is immersed in a silicone rubber solution, and the silicone rubber solution is vacuum degassed to fill the groove of the columnar laminated body 1a with silicone rubber. The columnar laminate 1a is pulled up from the solution, and the side surface of the columnar laminate 1a is coated with silicone rubber. Thereafter, the silicone rubber filled in the groove and coated on the side surface of the columnar laminate 1a is cured.

  Thereafter, the lead wire 6 is connected to the external electrode 4 to complete the multilayer piezoelectric element of the present invention.

  Then, by applying a direct current voltage of 0.1 to 3 kV / mm to the pair of external electrodes 4 via the lead wires 6 to polarize the columnar laminated body 1a, a laminated piezoelectric actuator as a product is completed, When the lead wire 6 is connected to an external voltage supply unit and a voltage is applied to the internal electrode 2 via the lead wire 6 and the external electrode 4, each piezoelectric body 1 is greatly displaced by the reverse piezoelectric effect, and for example, It functions as an automobile fuel injection valve that supplies fuel to the engine.

  The multilayer piezoelectric element configured as described above has a columnar laminated body in which the external electrode 4 is made of a porous conductor containing a conductive material mainly composed of silver and glass and having a three-dimensional network structure. Since it is connected to the side surface 1a, even when the actuator is continuously driven under a high electric field, the external electrode 4 can sufficiently absorb the stress generated during driving, so that the spark between the external electrode 4 and the internal electrode 2 can be obtained. Can be prevented, and the external electrode 4 can be prevented from being broken, and a highly reliable actuator can be provided.

  Furthermore, in the present invention, as shown in FIG. 4, a conductive auxiliary member 7 made of a conductive adhesive 7 a in which a metal mesh or a mesh-like metal plate 7 b is embedded is formed on the outer surface of the external electrode 4. Also good. In this case, by providing a conductive auxiliary member 7 on the outer surface of the external electrode 4, a large current can be supplied to the conductive auxiliary member 7 even when a large current is input to the actuator and driven at high speed. Because the current flowing through the external electrode 4 can be reduced, it is possible to prevent the external electrode 4 from causing local heat generation and disconnection, and the durability can be greatly improved. Furthermore, since the metal mesh or the mesh-like metal plate 7b is embedded in the conductive adhesive 7a, it is possible to prevent the conductive adhesive 7a from cracking.

  In FIGS. 2A and 4C, the thickness of the external electrode is made larger than the thickness of the piezoelectric body for convenience.

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

  In the present invention, it is preferable that the metal component contained in the internal electrode 2 contains Ag as a main component and contains one or more of Pd and Pt group metals in an amount of 15 atomic% or less. By setting the content of the Pd and Pt group metals contained in the internal electrode 2 to 15 atomic% or less, the compositional difference between the internal electrode 2 and the external electrode 4 can be reduced. The interdiffusion of the metal becomes good, the reliability of the joint between the internal electrode 2 and the external electrode 4 can be improved, and the durability can be improved. Moreover, the internal electrode 2 can be improved in bonding force of the internal electrode 2 in the columnar laminate 1a by appropriately containing a powder having substantially the same composition as that of the columnar laminate 1a.

  Further, the conductive adhesive 7a constituting the conductive auxiliary member 7 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 a high heat resistance, the conductive auxiliary member 7 having a low resistance value and a high adhesive strength can be formed even when used at a high temperature. it can. More preferably, the conductive particles are non-spherical particles such as flakes or needles. This is because the entanglement between the conductive particles can be strengthened by making the shape of the conductive particles non-spherical particles such as flakes and needles, and the shear strength of the conductive adhesive 7a can be increased. It is because it can raise more.

  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 4 in the side surface which the columnar laminated body 1a opposes was demonstrated in the said example, in this invention, you may form a pair of external electrode in the side surface provided adjacently, for example.

  FIG. 5 shows an injection apparatus according to the present invention. In the figure, reference numeral 31 denotes a storage container. 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.

  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.

Example First, a columnar laminate was produced. The piezoelectric body was formed of PZT having a thickness of 150 μm, the internal electrode was formed of a 3 μm-thick silver-palladium alloy (containing 10 atomic% Pd), and the number of stacked layers of the piezoelectric body and the internal electrode was 300 layers. The firing temperature was 1000 ° C.

  Thereafter, as shown in FIG. 3A, grooves having a depth of 50 μm and a width of 50 μm were formed at every other end of the internal electrode on the side surface of the columnar laminate 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 well 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, as shown in FIG. 3 (b), the sheet of silver glass paste is transferred to the external electrode surface of the columnar laminate, and baked at 650 ° C. for 30 minutes. As shown in FIG. 3 (c), An external electrode made of a porous conductor having a three-dimensional network structure was formed. The porosity of the external electrode at this time was 40% when a cross-sectional photograph of the external electrode was measured using an image analyzer. Further, when measured with an analytical electron microscope (EPMA), silver in the silver glass conductive paste and silver-palladium alloy in the internal electrode diffused and joined to each other, and the palladium from the internal electrode was joined to the joint with the internal electrode. The neck part which diffused was formed. Furthermore, when measured with a cross-sectional photograph of the external electrode, the joint between the external electrode and the side surface of the columnar laminate was about 50%.

  Thereafter, a lead wire is connected to the external electrode, a 3 kV / mm DC electric field is applied to the positive and negative external electrodes via the lead wire for 15 minutes to perform polarization treatment, and the laminated piezoelectric actuator as shown in FIG. Was made.

As a result of applying a DC voltage of 170 V to the obtained multilayer piezoelectric actuator, a displacement of 45 μm was obtained in the stacking direction. Furthermore, as a result of applying a driving test by applying an AC voltage of 0 to +170 V to this actuator at a frequency of 150 Hz at a room temperature, a displacement of 45 μm was obtained when driving up to 2 × 10 ⁸ cycles, and abnormalities in the external electrodes were observed. I couldn't see it. In addition, a laminated piezoelectric actuator was fabricated and evaluated in the same manner as described above except that the raw density of the silver glass conductive paste was changed to form external electrodes having a porosity of 30% by volume and 70% by volume. As a result, when it was driven up to 2 × 10 ⁸ cycles, a displacement of 45 μm was obtained, and no abnormality of the external electrode was observed.

Comparative Example A laminated piezoelectric material having the same structure as in the example except that the silver glass conductive paste was applied to the side surface of the columnar laminate and dried (green density 9.1 g / cm ³ ), and the baking temperature was changed to 820 ° C. An actuator was produced. At this time, the external electrode did not have a three-dimensional network structure, was almost a bulk body, had a porosity of 10%, had a spherical void, and was bonded to the entire side surface of the columnar laminate.

As in the example, the obtained laminated piezoelectric actuator was subjected to a driving test by applying an AC voltage of 0 to +170 V at a frequency of 150 Hz at room temperature. As a result, the external electrode was disconnected in 5 × 10 ⁶ cycles, A spark has occurred.

The laminated piezoelectric element of this invention is shown, (a) is a perspective view, (b) is a longitudinal cross-sectional view along the A-A 'line of (a). (A) And (b) is sectional drawing which expands and shows a part of FIG.1 (b), (c) is sectional drawing. It is explanatory drawing for demonstrating the manufacturing method of the lamination type piezoelectric element of this invention. 1 shows a laminated piezoelectric element in which a conductive auxiliary member is formed on the outer surface of an external electrode, wherein (a) is a perspective view, (b) is a cross-sectional view taken along line AA ′ of (a), and (c) is (b). It is sectional drawing which expands and shows a part of). It is explanatory drawing which shows the injection apparatus of this invention. It is a longitudinal cross-sectional view of a conventional multilayer piezoelectric actuator.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Piezoelectric body 1a ... Columnar laminated body 2 ... Internal electrode 3 ... Insulator 4 ... External electrode 4a ... Air gap 4b ... Neck part 7 ... Conductive auxiliary member 31 ... Storage container 33 ... Injection hole 35 ... Valve 43 ... Piezoelectric actuator

Claims (14)

A laminated body formed by alternately laminating a plurality of piezoelectric bodies and a plurality of internal electrodes, and a pair of external electrodes provided on the side surface of the laminated body, wherein the internal electrodes are alternately connected every other layer. A laminated piezoelectric element, wherein the external electrode is made of a porous conductor containing a conductive material and glass and having a three-dimensional network structure. 2. The multilayer piezoelectric element according to claim 1, wherein the external electrode is partially bonded to the side surface of the multilayer body. The multilayer piezoelectric element according to claim 1 or 2, wherein the external electrode is diffusion-bonded to an end portion of the internal electrode exposed on the side surface of the multilayer body. 4. The multilayer piezoelectric element according to claim 1, wherein the conductive material of the external electrode is mainly composed of silver. The multilayer piezoelectric element according to claim 1, wherein the porosity of the external electrode is 30 to 70% by volume. The laminated piezoelectric element according to any one of claims 1 to 5, wherein the softening point of the glass constituting the external electrode is not higher than the melting point of the conductive material constituting the external electrode. The laminated piezoelectric element according to claim 1, wherein the glass constituting the external electrode is amorphous. The multilayer piezoelectric element according to any one of claims 1 to 7, wherein the thickness of the external electrode is thinner than the thickness of the piezoelectric body constituting the multilayer body. 9. An insulating material having a Young's modulus lower than that of a piezoelectric body is filled in a concave groove formed on a side surface of the laminated body, and the internal electrode and the external electrode are insulated every other layer. The multilayer piezoelectric element according to any one of the above. The multilayer piezoelectric element according to any one of claims 1 to 9, wherein the metal component of the internal electrode contains Ag as a main component and contains at least one of Pd and Pt group metals in an amount of 15 atomic% or less. . The conductive auxiliary member made of a conductive adhesive in which a metal mesh or a mesh-like metal plate is embedded is provided on the outer surface of the external electrode. Multilayer piezoelectric element. The multilayer piezoelectric element according to claim 11, wherein the conductive adhesive is made of a polyimide resin in which conductive particles are dispersed. The multilayer piezoelectric element according to claim 12, wherein the conductive particles are silver powder. A storage container having an injection hole, the stacked piezoelectric element according to any one of claims 1 to 13 stored in the storage container, and a liquid is ejected from the injection hole by driving the stacked piezoelectric element. An injection device comprising a valve.

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