JP4817610B2 - LAMINATED PIEZOELECTRIC ELEMENT, ITS MANUFACTURING METHOD, AND INJECTION DEVICE USING THE SAME - Google Patents

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 one using a laminated piezoelectric element is laminated piezoelectric actuator is known formed by laminating piezoelectric body and the internal electrodes alternately. Multilayer piezoelectric actuator is fired simultaneously types are classified into two types of stack type formed by alternately laminating piezoelectric ceramic and internal electrode plates, lower voltage, when considered from the viewpoint of production cost, thin Therefore, a co-fired multilayer piezoelectric actuator is showing an advantage.

Figure 5 shows part of a cross section of a conventional multilayer piezoelectric element, but the piezoelectric member 51 and the internal electrodes 52 are alternately laminated, the inner electrode 52 on the entire principal surface of the piezoelectric member 51 It is not formed but has a so-called partial electrode structure. By laminating the internal electrodes 52 of this partial electrode structure alternately left and right, the internal electrodes 52 are alternately connected to the external electrodes 54 formed on the side surfaces of the multilayer electronic component every other layer. When used as a laminated piezoelectric actuator, lead wires (not shown) are further connected and fixed to the external electrodes 54 by solder.

Such multilayer piezoelectric element is to print the internal electrode paste for forming the internal electrode 52 in the ceramic green sheet which becomes a piezoelectric member 51 in a pattern so that a predetermined electrode structure, the internal electrode paste is coated green to prepare a laminate molded body obtained sheet by stacking a plurality, which was calcined, by baking a conductive paste for forming the external electrodes 54 on the sides, have been created, Ltd. (see Patent Document 1).

Such multi-layer piezoelectric element is generally a piezoelectric layer 63 and the piezoelectric member 51 and the internal electrodes 52 are laminated alternately is formed, the protective layer 62 is laminated on both main surfaces of the upper and lower in the stacking direction Has been. Such multi-layer piezoelectric element is a plain what the protective layer 62 does not contain an electrode 61, the difference in shrinkage during firing between the protective layer 62 and the piezoelectric layer 63 occurs, or stress is generated, In order to prevent the occurrence of cracks, an electrode 61 similar to the piezoelectric layer 63 is laminated on the protective layer 62 to prevent cracks that occur after firing (see Patent Document 2) .
As the internal electrode 52, an alloy of silver and palladium is used. Further, in order to simultaneously fire the piezoelectric body 51 and the internal electrode 52 , the metal composition of the internal electrode 52 is 70% by mass of silver and 30% by mass of palladium. % and to have (see Patent Document 3).
JP-A-61-133715 Japanese Patent Laid-Open No. 9-270540 Japanese Utility Model Publication No. 1-130568

  However, unlike a conventional multilayer electronic component (for example, a multilayer ceramic capacitor), the multilayer piezoelectric actuator has a feature that the ceramic of the piezoelectric body 51 is deformed with energization. That is, the number of times of driving and the number of times of the ceramic deformation of the piezoelectric body 51 are the same. In recent years, it has been desired to apply a higher electric field and continuously drive for a long time in order to ensure a large amount of displacement under a large pressure with a small stacked piezoelectric actuator.

  However, in the improvement of Patent Document 2, when a high voltage is applied and continuous driving is performed for a long time, cracks occur at the interface between the electrode 61 and the piezoelectric layer 63 forming the protective layer 12, and the function as an actuator is achieved. There was a problem in durability.

  Therefore, an object of the present invention is to provide a laminated piezoelectric element and a jetting device that are excellent in durability even when a piezoelectric actuator is continuously driven for a long time under high voltage and high pressure.

In view of the above problems, the present onset Ming has a laminated body formed by alternately stacking at least one piezoelectric element and a plurality of internal electrodes, made of a piezoelectric material on both end surfaces in the stacking direction of the laminate protection In a method of manufacturing a laminated piezoelectric element , comprising a pair of external electrodes, each having a layer, and having a pair of external electrodes alternately connected to every other layer on a side surface of the multilayer body, and applying an electric field to the external electrodes Forming metal layers on both end faces of the columnar laminate having the protective layer , sintering the columnar laminate and dispersing the metal of the metal layer in the protective layer, and then removing the metal layer It is characterized by including .

Moreover, the manufacturing method of the multilayer piezoelectric element of the present invention is characterized in that, in the above configuration, the thickness of the metal layer is 5 mm or less .

The multilayer piezoelectric element of the present invention is manufactured using the above manufacturing method.

Moreover, the multilayer piezoelectric element of the present invention is characterized in that, in the above configuration, the melting point of the metal is 1.6 times or less with respect to the firing temperature of the multilayer body .

Further, in the above structure, the metal is at least one of Ag, Pd, Cu, Ca, Na, Pb, and Ni .

In the above structure, the dispersion of the metal and wherein 0.001 to 1.0% by mass Rukoto respect to the protective layer.

Further, in the above structure, the thickness of the protective layer is characterized 0.1~2.0mm der Rukoto.

Moreover, the said structure WHEREIN: The said metal contains the metal which comprises the said internal electrode, It is characterized by the above-mentioned .

Further, in the above structure, the internal electrode contains Ag and Pd .

In the above configuration, when the content of Ag in the internal electrode is M1 (mass%) and the content of Pd is M2 (mass%), 85 ≦ M1 <100, 0 <M2 ≦ 15, M1 + M2 = and features that you satisfy the 100.

  The injection device of the present invention includes a storage container having an injection hole, and a valve which is stored in the storage container and ejects liquid from the injection hole by driving the laminated piezoelectric element. And

  As described above, according to the multilayer piezoelectric element of the present invention, by dispersing the metal in the protective layer, the stress at the time of firing shrinkage generated between the protective layer and the piezoelectric layer can be relaxed and made uniform. Therefore, durability can be improved even in continuous use at a high voltage for a long time, and a laminated piezoelectric element having excellent durability can be provided.

  In addition, when the melting point of the metal is 1.6 times or less than the firing temperature of the laminate, it is possible to enhance the effect of diffusing the metal into the protective layer 12.

  Further, when the metal is at least one of Ag, Pd, Cu, Ca, Na, Pb, and Ni, the diffusion efficiency of the metal into the protective layer 12 is enhanced, and at the same time, It is possible to make the metal dispersion uniform.

  In addition, when the metal dispersion amount is 0.001 to 1.0% by mass with respect to the protective layer, the protective layer 12 can be fired without firing the insulating layer without damaging the insulating property of the protective layer 12. Thus, the difference in firing shrinkage between the piezoelectric layer 11 and the piezoelectric layer 11 can be reduced, and the laminated piezoelectric element 10 with little residual stress after firing can be obtained.

  Further, when the thickness of the protective layer is 0.1 to 2.0 mm, the metal is uniformly dispersed in the protective layer 12 and can withstand stress due to vibration during continuous driving of the multilayer piezoelectric element 10. It becomes possible.

  Further, when the internal electrode contains Ag and Pd, and the content of Ag in the internal electrode is M1 (mass%) and the content of Pd is M2 (mass%), 85 ≦ M1 <100 , 0 <M2 ≦ 15 and M1 + M2 = 100, the specific resistance of the internal electrode 2 can be reduced and the heat generation of the internal electrode 2 can be suppressed, so that the durability of the multilayer piezoelectric element 10 during continuous driving can be reduced. Improve sexiness. In addition, migration of Ag in the internal electrode 2 to the piezoelectric body 1 can be suppressed, and higher durability can be obtained.

  1A and 1B show an embodiment of a laminated piezoelectric element of the present invention, in which FIG. 1A is a perspective view and FIG. 1B is a cross-sectional view showing a laminated state of a piezoelectric layer, an internal electrode layer, and a protective layer.

  As shown in FIG. 1, the multilayer piezoelectric element 10 of the present invention has end portions where the internal electrodes 2 are exposed on a pair of opposing side surfaces of a piezoelectric layer 11 formed by alternately laminating piezoelectric bodies 1 and internal electrodes 2. A pair of external electrodes 4 that are electrically conductive every other layer are joined. Further, a protective layer 12 in which the piezoelectric body 1 is laminated is laminated above and below the piezoelectric layer 11. Here, when the multilayer piezoelectric element 10 of the present invention is used as a multilayer piezoelectric actuator, the lead wire 6 is connected and fixed to the external electrode 4 by soldering, and the lead wire 6 is connected to the external voltage supply unit. Good.

Since the internal electrode 2 is made of a metal material such as silver - palladium, it has a function of applying a predetermined voltage to each piezoelectric body 1 through the internal electrode 2 to cause the piezoelectric body 1 to be displaced by the inverse piezoelectric effect. On the other hand, since the protective layer 12 is a layer of a plurality of piezoelectric bodies 1 on which the internal electrode 2 is not disposed, no displacement occurs even when a voltage is applied.

  In the multilayer piezoelectric element 10 of the present invention, as a result of intensive studies by the present inventors, the metal 14 is dispersed in the protective layer 12 as shown in FIG. Thus, the difference in firing shrinkage between the protective layer 12 and the piezoelectric layer 11 can be alleviated, and a laminated piezoelectric element with very little residual stress can be obtained. In addition, since the dispersed metal 14 promotes sintering when the laminated body 10a is fired and a dense laminated body 10a is obtained, it can withstand stress caused by vibration during continuous driving of the laminated piezoelectric element 10. Since it became possible, the durability was improved, and it was found that it was highly reliable even after long-term use. The dispersion means that the metal element diffuses from the surface of the protective layer 12 to the inside of the protective layer 12, and the dispersion of the metal 14 can be specified by an analysis method such as an EPMA (Electron Probe Micro Analysis) method. Specifically, when an arbitrary cross section of the protective layer is analyzed by EPMA, the distribution state of the metal can be confirmed.

  Furthermore, it is desirable that the melting point of the metal 14 dispersed in the protective layer 12 is 1.6 times or less with respect to the firing temperature of the multilayer piezoelectric element. This is because the metal 14 having a melting point higher than the above melting point has a poor metal diffusion efficiency in the protective layer 12. When two or more kinds of metals 14 are added or when an alloy composed of two or more kinds is added, the melting point of each metal needs to be 1.6 times or less than the firing temperature of the multilayer piezoelectric element. There is. However, it goes without saying that the metal that does not contribute to the dispersion in the protective layer 12 does not have to be below the melting point described above.

  The metal 14 dispersed in the protective layer 12 is preferably at least one of Ag, Pd, Cu, Ca, Na, Pb, and Ni. This is because these metals 14 have a melting point near or lower than the firing temperature of the laminated body 10a, so that the diffusion into the protective layer 12 is activated during the firing of the laminated body 10a. Promotes uniform dispersion of metal 14.

  On the other hand, the amount of the metal 14 dispersed in the protective layer 12 is preferably 0.001 to 1.0% by mass with respect to the protective layer 12. This is because when 0.001% by mass or less, the shrinkage difference and shrinkage profile during firing of the protective layer 12 and the piezoelectric layer 11 are different, and a large distortion occurs between the two. In the worst case, delamination occurs after firing. Or delamination is likely to occur after prolonged use. Moreover, when the metal 14 to disperse is larger than 1.0 mass%, the insulation of the protective layer 12 will deteriorate and the function as a protective layer will be impaired. Further, in order to further reduce the residual stress after firing of the protective layer 12 and to eliminate defects after firing of the multilayer piezoelectric element, the content of the metal 14 with respect to the protective layer 12 is set to 0.05% by mass to 1%. More preferably, the content is 0.0% by mass. In order to obtain high reliability against stress due to vibration during continuous driving of the multilayer piezoelectric element, the content of the metal 12 is more preferably 0.1% by mass to 1.0% by mass. . The measurement of the content of the metal 14 with respect to the protective layer 12 can be quantified by ICP (Inductively Coupled Plasma Atomic) emission analysis.

  Furthermore, the thickness of the protective layer 12 is preferably 0.1 mm to 2.0 mm. This is because the protective layer 12 is thin when the thickness is 0.1 mm or less, and thus the protective layer 12 may be broken due to stress caused by vibration generated during continuous driving of the multilayer piezoelectric element 10. On the other hand, if it is thicker than 2.0 mm, it is difficult to disperse the metal 14 in the protective layer 12. Here, if the degree of dispersion of the metal 14 in the protective layer 12 is poor, there is a difference in the amount of shrinkage and the shrinkage profile between the portion where the metal is dispersed and the portion where the metal is less dispersed. Large distortion occurs during shrinkage, delamination occurs after firing, and delamination tends to occur after prolonged use. In addition, although the protective layer 12 is distribute | arranged to the both end surfaces in the lamination direction of the laminated body 10a, the thickness of the protective layer 12 is the thickness of the protective layer 12 distribute | arranged to either one of the said both end surfaces. Is shown.

  Further, it is desirable that the metal 14 dispersed in the protective layer 12 has a metal composition constituting the internal electrode 2. This is because when a material other than the metal constituting the internal electrode 2 is used, the firing shrinkage profiles of the protective layer 12 and the piezoelectric layer 13 including the internal electrode 2 are different at the time of firing the laminated body 10a. Because there are cases.

  Furthermore, when the Ag content in the internal electrode 2 is M1 (mass%) and the Pd content is M2 (mass%), 85 ≦ M1 <100, 0 <M2 ≦ 15, and M1 + M2 = 100 are satisfied. A metal composition is preferred. This is because when Pd exceeds 15% by mass, the specific resistance of the internal electrode 2 increases, and the internal electrode 2 may generate heat when the multilayer piezoelectric element is continuously driven. Moreover, in order to suppress migration of Ag in the internal electrode 2 to the piezoelectric body 1, it is preferable that Pd be 0.001 mass% or more and 15 mass% or less. Further, in terms of improving the durability of the multilayer piezoelectric element 10, the content is preferably 0.1% by mass or more and 10% by mass or less. Moreover, when it is excellent in heat conduction and needs higher durability, 0.5 mass% or more and 9.5 mass% or less are more preferable. In addition, when higher durability is required, it is more preferably 2% by mass or more and 8% by mass or less.

  Here, when Ag is less than 85% by mass, the specific resistance of the internal electrode 2 increases, and the internal electrode 2 may generate heat when the multilayer piezoelectric element 10 is continuously driven. Further, in order to suppress migration of Ag in the internal metal 2 to the piezoelectric body 1, Ag is preferably set to 85 mass% or more and 99.999 mass% or less. Moreover, 90 mass% or more and 99.9 mass% or less are preferable at the point of improving the durability of the laminated piezoelectric element 10. Moreover, when higher durability is required, 90.5 mass% or more and 99.5 mass% or less are more preferable. Moreover, when higher durability is calculated | required, 92 to 98 mass% is further more preferable.

  Furthermore, it is preferable that a calcination temperature is 900 degreeC or more and 1200 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 1. Further, if the firing temperature exceeds 1200 ° C., the stress due to the difference between the shrinkage of the internal electrode 2 and the shrinkage of the piezoelectric body 1 during firing becomes large, and cracks may occur during continuous driving of the multilayer piezoelectric element 10. Because there is.

  Further, the internal electrode 2 whose end is exposed on the side surface of the multilayer piezoelectric element 10 of the present invention and the internal electrode 2 whose end is not exposed are alternately configured, and the internal electrode 2 where the end is not exposed. A groove 3 is formed in a portion of the piezoelectric body 1 between the outer electrode 4 and the external electrode 4, and an insulator having a Young's modulus lower than that of the piezoelectric body 1 is preferably formed in the groove. Thereby, in such a multilayer piezoelectric element 10, stress generated by displacement during driving can be relieved, so that heat generation of the internal electrode 2 can be suppressed even when continuously driven.

  The external electrode 4 is preferably made of a porous conductor having a three-dimensional network structure. If the external electrode 4 is not composed of a porous conductor having a three-dimensional network structure, the external electrode 4 does not have flexibility and cannot follow the expansion and contraction of the laminated piezoelectric actuator. A contact failure between the external electrode 4 and the internal electrode 2 may occur. 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. For this reason, voids exist in a state of being connected to some extent without completing the sintering, suggesting a state in which the conductive material powder and the glass powder constituting the external electrode 4 are three-dimensionally connected and joined.

  Alternatively, the porosity in the external electrode 4 is desirably 30 to 70% by volume. Here, the porosity is the ratio of the voids 4 a in the external electrode 4. This is because if the porosity in the external electrode 4 is smaller than 30% by volume, the external electrode 4 cannot withstand the stress generated by the expansion and contraction of the multilayer piezoelectric actuator, and the external electrode 4 may be disconnected. In addition, when the porosity in the external electrode 4 exceeds 70% by volume, the resistance value of the external electrode 4 increases, and thus when the large current is passed, the external electrode 4 may cause local heat generation and break. There is.

  Furthermore, it is desirable that a glass rich layer is formed on the surface layer portion of the external electrode 4 on the piezoelectric body 1 side. This is because, if the glass-rich layer is not present, it is difficult to bond the glass component in the external electrode 4, so that there is a possibility that the external electrode 4 cannot easily be firmly bonded to the piezoelectric body 1.

  In addition, the softening point (° C.) of the glass constituting the external electrode 4 is desirably 4/5 or less of the melting point (° C.) of the conductive material constituting the internal electrode 2. When the softening point of the glass constituting the external electrode 4 exceeds 4/5 of the melting point of the conductive material constituting the internal electrode 2, the softening point of the glass constituting the external electrode 4 and the internal electrode 2 are constituted. Since the melting point of the conductive material becomes the same temperature, the temperature at which the external electrode 4 is baked inevitably approaches the melting point constituting the internal electrode 2, so that the internal electrode 2 and the external electrode 4 are baked when the external electrode 4 is baked. The conductive material aggregates to prevent diffusion bonding, and the baking temperature cannot be set to a temperature sufficient to soften the glass component of the external electrode 4, so that sufficient bonding strength with the softened glass cannot be obtained. There is a case.

  Furthermore, it is desirable that the glass constituting the external electrode 4 be amorphous. This is because, in crystalline glass, the external electrode 4 cannot absorb the stress generated by the expansion and contraction of the laminated piezoelectric actuator, so that cracks and the like may occur.

  Furthermore, it is desirable that the thickness of the external electrode 4 is thinner than the thickness of the piezoelectric body 1. This is because when the thickness of the external electrode 4 is larger than the thickness of the piezoelectric body 1, the strength of the external electrode 4 increases, so that when the laminated body 10 expands and contracts, the load on the joint between the external electrode 4 and the internal electrode 2 is increased. May increase and contact failure may occur.

  Further, as shown in FIG. 2, it is desirable to provide a conductive auxiliary member 7 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 4. If the conductive auxiliary member 7 is not provided on the outer surface of the external electrode 4, the external electrode 4 cannot withstand the large current and is locally heated when driven by flowing a large current through the multilayer piezoelectric element 10. there's a possibility that.

  Further, if a mesh or a mesh-like metal plate is not used on the outer surface of the external electrode 4, the stress due to expansion and contraction of the multilayer piezoelectric element 10 directly acts on the external electrode 4, so that the external electrode 4 is laminated due to fatigue during driving. There is a possibility that peeling from the side surface of the piezoelectric element 10 becomes easy.

  Furthermore, it is desirable that the conductive adhesive is made of a polyimide resin in which conductive particles are dispersed. This is because the conductive adhesive has a high adhesive strength by using a polyimide resin having a relatively high heat resistance even when the laminated piezoelectric element 10 is driven at a high temperature by using the polyimide resin. Easy to maintain.

  Furthermore, it is desirable that the conductive particles are silver powder. This makes it easy to suppress local heat generation in the conductive adhesive by using silver powder having a relatively low resistance value for the conductive particles.

  Next, the manufacturing method of the multilayer piezoelectric element 10 of the present invention will be described.

The multilayer piezoelectric element 10 according to 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 DOP ( A slurry formed by mixing with a plasticizer such as dioctyl phthalate) or DBP (dibutyl phthalate) and having the above-mentioned range of impurities is prepared, and the slurry is formed into a tape by a well-known doctor blade method, calendar roll method or the like Thus, a ceramic green sheet to be the piezoelectric body 1 is produced.

  Next, this green sheet is cut into an arbitrary size and fixed to a frame.

  Next, a binder, a plasticizer, and the like are added to and mixed with the metal powder constituting the silver-palladium internal electrode 2 to prepare a conductive paste, and this is applied to the upper surface of each green sheet by screen printing or the like. A green sheet for the piezoelectric layer 11 is prepared by printing to a thickness.

Next, a green sheet for the protective layer 12 is prepared.

Then, the green sheet for the piezoelectric layer 11 and the green sheet for the protective layer 12 on which the conductive paste is printed on the upper surface are formed so that the protective layer 12 has a thickness of 0.1 to 2.0 mm above and below the piezoelectric layer 11. A plurality of layers are laminated, and pressure is applied at the same time so that they are closely attached. In this way, the green sheet is fixed to the frame, and the protective layer 12 and the piezoelectric layer 11 are simultaneously adhered.

  Thereafter, the green sheet is cut into an appropriate size, and as shown in FIG. 3, a conductive paste (for example, Ag, Pd, Cu, etc.) having a metal component on both end faces of the laminate 10a provided with the protective layer 12 is provided. The metal layer 8 is printed using Ca, Na, Ni, Pb or the like. Thereafter, after debinding at a predetermined temperature, firing is performed at 900 to 1200 ° C., and after firing, the metal layer 8 is removed by a surface grinder or the like, whereby the laminate 10a is manufactured.

  Here, it is desirable that the thickness of the metal layer 8 is 5 mm or less. This is because if the thickness of the metal layer 8 exceeds 5 mm, the metal layer 8 may be cracked due to the difference in firing shrinkage between the metal layer 8 and the protective layer 12 when the laminate 10a is fired.

  Thereafter, the internal electrodes 2 whose ends are exposed and the internal electrodes 2 whose ends are not exposed are alternately formed on the side surface of the laminated body 10a, and the piezoelectric material between the internal electrodes 2 and the external electrodes 4 whose ends are not exposed is formed. A groove 3 is formed in the body 1, and an insulator such as resin or rubber having a Young's modulus lower than that of the piezoelectric body 1 is formed in the groove 3. Here, the groove 3 is an internal dicing device or the like, and the conductive material constituting the external electrode 4 on the side surface of the piezoelectric layer 11 sufficiently absorbs the stress generated by the expansion and contraction of the laminated piezoelectric element 10, so that the Young's modulus is low. Silver or an alloy containing silver as a main component is desirable.

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 piezoelectric layer 11, and is a temperature higher than the softening point of the glass, 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, the binder component in the sheet produced using the silver glass conductive paste is scattered and disappeared, and the external electrode 4 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 between the particles, diffuses and joins the silver in the silver glass conductive paste and the internal electrode 2, and the voids in the external electrode 4 550-700 ° C. is desirable from the viewpoint that the external electrode 4 and the side surface of the columnar piezoelectric layer 11 are partially bonded. 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 between the particles is not formed, and the internal electrode is driven during driving. There is a possibility of causing a spark between the external electrode 4 and the external electrode 4.

  Note that the thickness of the silver glass conductive paste sheet is preferably thinner 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.

  Next, the piezoelectric layer 11 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 3 of the piezoelectric layer 11 with silicone rubber, and then the silicone rubber solution Then, the piezoelectric layer 11 is pulled up, and the side surface of the piezoelectric layer 11 is coated with silicone rubber. Thereafter, the silicone rubber coated inside the groove 3 and coated on the side surface of the piezoelectric layer 11 is cured, thereby completing the multilayer piezoelectric element 10 of the present invention.

  Then, by connecting the lead wire 6 to the external electrode 4 and applying a direct current voltage of 0.1 to 3 kV / mm to the pair of external electrodes 4 through the lead wire 6 to polarize the piezoelectric layer 11, A multilayer piezoelectric actuator using the multilayer piezoelectric element 10 of the present invention is completed, and the lead wire 6 is connected to an external voltage supply unit so that a voltage can be applied to the internal electrode 2 via the lead wire and the external electrode 4. For example, each piezoelectric body 1 is greatly displaced by the inverse piezoelectric effect, and thereby functions as an automobile fuel injection valve for injecting and supplying fuel to the engine, for example.

  Further, a conductive auxiliary member 7 made of a conductive adhesive in which a metal mesh or a mesh-like metal plate is embedded may be formed on the outer surface of the external electrode 4. 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 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 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 can be further increased. This is because it can be increased.

  The multilayer piezoelectric element 10 and the manufacturing method thereof according to the present invention are not limited to these, and various modifications can be made without departing from the gist of the present invention. For example, when the metal 14 is dispersed in the protective layer, the metal layer 8 is printed on both end faces of the laminated body 10a in which the protective layer 12 is disposed, and the metal 14 is dispersed in the protective layer 12 by firing. The metal 14 may be added in advance to the green sheet for forming the protective layer 12. Further, when the metal 14 having a relatively low melting point compared to the firing temperature of the laminated body 10a is dispersed, for example, the laminated body 10a is arranged in a crucible, and the metal 14 is provided in the vicinity thereof and fired simultaneously. The metal vapor scattered from the metal 14 may be deposited on the protective layer 14 and dispersed.

  Moreover, although the example which formed the external electrode 4 in the side surface which the piezoelectric layer 11 opposes above was demonstrated, in this invention, you may form a pair of external electrode 4 in the side surface provided, for example.

  FIG. 4 shows an injection device of 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.

  In addition, the injection device of the present invention is not limited to the above-described embodiments. For example, the injection device is mounted on a fuel injection device for an automobile engine, a liquid injection device such as an ink jet, a precision positioning device such as an optical device, a vibration prevention device, or the like. Drive element or sensor element mounted on combustion pressure sensor, knock sensor, acceleration sensor, load sensor, ultrasonic sensor, pressure sensor, yaw rate sensor, etc., and piezoelectric gyro, piezoelectric switch, piezoelectric transformer, piezoelectric breaker Needless to say, even if the circuit element is other than the circuit element mounted on the device, it can be implemented as long as the element uses piezoelectric characteristics.

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

First, a slurry is prepared by mixing a calcined powder of a piezoelectric ceramic mainly composed of lead zirconate titanate (PbZrO ₃ —PbTiO ₃ ), a binder, and a plasticizer. A ceramic green sheet was prepared.

  300 sheets of conductive paste prepared by adding a binder to a silver-palladium alloy formed at an arbitrary composition ratio on one side of this ceramic green sheet by a screen printing method are prepared for a laminate. did. Separately from this, green sheets having a thickness of 100 μm that can be the protective layer 12 are produced by the above-described method, and these are laminated in order so that 5 to 20 protective layers, 300 laminates, and 5 to 20 protective layers are formed. And pressed.

  Next, a conductive paste in which a binder is added to Pd, Ni, Cu, Ag, Na, Pb, W, or Mo, or a conductive paste in which a binder is added to a silver-palladium alloy, and a laminated body 10 a having a protective layer 12. The metal layer 8 was formed by screen printing with a thickness of 5 μm on both end faces of the protective layer 12, that is, the end face of the protective layer 12. Thereafter, after firing at 1000 ° C. for a certain time, the metal layer 8 was removed by a surface grinder or the like.

  Then, a groove 3 having a depth of 50 μm and a width of 50 μm was formed at every other end of the internal electrode on the side surface of the laminate by a dicing apparatus, and the groove 3 was filled with silicone rubber and cured.

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 mass 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. When the raw density of this sheet was measured by Archimedes method, it was 6.5 g / cm ³ And the sheet of silver glass paste was transferred to the external electrode surface of the laminate and baked at 650 ° C. for 30 minutes, 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 measured using an image analysis device for a cross-sectional photograph of the external electrode. In addition, K ₂ CO ₃ or Na ₂ CO ₃ powder was added to the raw materials of the piezoelectric body 1, the internal electrode 2 and the external electrode 4. The alkali metal contained in the obtained piezoelectric body, internal electrode, and external electrode of the sintered body was detected using ICP analysis.

Further, as a comparative example, a laminated piezoelectric element in which a protective layer was provided with an electrode that did not pass through an external electrode as shown in FIG. Here, the piezoelectric body of the multilayer piezoelectric element has the same composition as that of the present invention described above, and the electrode disposed on the internal electrode and the protective layer has a silver / palladium ratio of 95: 5 . . Then, after laminating 10 protective layers, 300 laminates, and 10 protective layers in this order, external electrodes, lead wires, etc. were provided in the same manner as in the present invention to produce a laminated piezoelectric material (Table Sample number 1 of 1).

  After that, the lead wire 6 is connected to the external electrode 4, and a 3 kV / mm direct current electric field is applied to the positive and negative external electrodes 4 through the lead wire 15 for 15 minutes to perform polarization treatment, as shown in FIG. A multilayer piezoelectric actuator using the multilayer piezoelectric element was produced.

  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, a drive test was performed by applying an AC voltage of 0 to +170 V at a frequency of 150 Hz to the multilayer piezoelectric element at room temperature.

Then, this multilayer piezoelectric element was subjected to a continuous driving test up to 1 × 10 ⁹ times of driving, and the number of defectives was expressed as a defective rate. Moreover, about the metal 14 disperse | distributed to the protective layer 12, it analyzed by EPMA and the presence or absence of dispersion | distribution of a metal in three places in arbitrary cross sections of the protective layer 12. FIG. On the other hand, the content of the metal 14 in the protective layer 12 was determined by taking out samples at arbitrary three locations in the protective layer 12 and performing ICP emission analysis on each sample to obtain an average value of the calculated contents. The results are as shown in Table 1. Note that the ratio of the melting point of the dispersed metal to the firing temperature shown in Table 1 indicates the ratio of the melting point of the dispersed metal to the firing temperature of the laminate 10a.

  From Table 1, the laminated piezoelectric actuator of Sample No. 1, which is a comparative example, was provided with an electrode on the protective layer, so that the electrodes in the protective layer and the piezoelectric layer were subjected to stress caused by vibration of the laminated piezoelectric element during the continuous driving test. Cracks were generated at the interface, and the defect rate increased.

  On the other hand, in the laminated piezoelectric actuators of sample numbers 2 to 21 which are the examples of the present invention, the metal is dispersed in the protective layer 12, so that during firing shrinkage that occurs between the protective layer 12 and the piezoelectric layer 13. In addition to relieving and equalizing the stress, cracks and the like in the protective layer 12 could be suppressed even during continuous use at a high voltage for a long time, and the defect rate decreased because of excellent durability.

  In Sample Nos. 2 and 3, since the melting point of the metal constituting the electrode layer 8 was significantly higher than the firing temperature of the laminate 10a, the metal 14 was difficult to disperse in the protective layer 12 and the effects described above were difficult to achieve. .

  In Sample No. 17, since the dispersion amount of the metal 14 exceeded 1.0 mass% with respect to the protective layer 12, the insulating property of the protective layer 12 was deteriorated to cause dielectric breakdown, and the defect rate was slightly increased. .

  On the other hand, in the sample numbers 4-16 and 18-21, since the dispersion amount of the metal 14 was 0.001-1.0 mass% with respect to the protective layer 12, it was easy to show the effect mentioned above. In particular, sample numbers 11 to 13, 16 in which the dispersion amount is 0.1% by mass and the metal 14 is composed of silver and palladium, that is, the metal 8 contains the metal constituting the internal electrode 2. , And 18 to 21, since the insulating property of the protective layer 12 was maintained and the diffusion of the metal 14 into the protective layer 12 was easy, cracks in the protective layer 12 and the like even in continuous use at a high voltage for a long time Since the durability was excellent and the durability was excellent, the defect rate was remarkably lowered.

The laminated piezoelectric element of this invention is shown, (a) is a perspective view, (b) is a side view which shows the lamination | stacking state of a piezoelectric layer, an internal electrode layer, and a protective layer. 2A and 2B show a laminated piezoelectric element in which a conductive auxiliary member is formed on the outer surface of an external electrode, where FIG. 1A is a perspective view and FIG. 1B is a cross-sectional view. It is a side view which shows the lamination | stacking state of the electrode layer and protective layer in 1 process which shows the manufacturing method of the lamination type piezoelectric element of this invention. It is explanatory drawing which shows the injection apparatus of this invention. The partial expanded side view of the conventional lamination type piezoelectric element is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Piezoelectric body 2 ... Internal electrode 3 ... Groove 4 ... External electrode 6 ... Lead wire 7 ... Conductive auxiliary member 8 ... Electrode layer 10 ... Multilayer piezoelectric Body element 10a ... Laminated body 11 ... Piezoelectric layer 12 ... Protective layer 14 ... Metal 31 ... Storage container 33 ... Injection hole 35 ... Valve 43 ... Piezoelectric actuator 51 ..Piezoelectric body 52 ... Internal electrode 54 ... External electrode 61 ... Electrode 62 ... Protective layer 63 ... Piezoelectric layer

Claims (11)

It has a laminate formed by alternately laminating at least one piezoelectric body and a plurality of internal electrodes, and a protective layer made of a piezoelectric material is disposed on both end faces of the laminate in the laminating direction, and on the side surface of the laminate In the manufacturing method of a laminated piezoelectric element , which includes a pair of external electrodes in which the internal electrodes are alternately connected every other layer, and is driven by applying an electric field to the external electrodes , both ends of the columnar laminated body having the protective layer A multilayer piezoelectric element comprising a step of forming a metal layer on a surface, sintering the columnar laminate, dispersing the metal of the metal layer in the protective layer, and then removing the metal layer Manufacturing method . The method for manufacturing a multilayer piezoelectric element according to claim 1, wherein the metal layer has a thickness of 5 mm or less. A multilayer piezoelectric element manufactured by using the manufacturing method according to claim 1. 4. The multilayer piezoelectric element according to claim 3, wherein the melting point of the metal is 1.6 times or less than the firing temperature of the multilayer body. Wherein the metal is Ag, Pd, Cu, Ca, Na, Pb, multi-layer piezoelectric element according to claim 3 or 4, characterized in that at least one or more of and Ni. The multi-layer piezoelectric element according to any one of claims 3 to 5, wherein the dispersion amount of the metal is 0.001 to 1.0 wt% relative to the protective layer. The multi-layer piezoelectric element according to any one of claims 3 to 6 the thickness of the protective layer is characterized by a 0.1 to 2.0 mm. The multi-layer piezoelectric element according to any one of claims 3 to 7, characterized in that it contains a metal said metal constituting the internal electrode. The multi-layer piezoelectric element according to any one of claims 3 to 8 wherein the inner electrode is characterized by containing Ag and Pd. When the Ag content in the internal electrode is M1 (mass%) and the Pd content is M2 (mass%), 85 ≦ M1 <100, 0 <M2 ≦ 15, and M1 + M2 = 100 are satisfied. The multilayer piezoelectric element according to claim 9, wherein A container having an injection hole, a valve for ejecting the laminated piezoelectric element according to any one of claims 3 to 10 stored in the container, the liquid from the ejection hole by a drive of the laminated piezoelectric element An injection device comprising:

Images