JP3909275B2 - Multilayer piezoelectric element and injection device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a multilayer piezoelectric element and an injection device, for example, a multilayer piezoelectric element and an injection device used for a precision positioning device such as a fuel injection device for an automobile and an optical device, a driving element for vibration prevention, and the like. .
[0002]
[Prior art]
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.
[0003]
FIG. 4 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. The internal electrode 52 is formed so that one end thereof is alternately covered with the insulator 61 on the left and right sides, and the strip-like external electrode 70 is electrically connected to the internal electrode 52 every two layers on the left and right. On the strip-shaped external electrode 70, a lead wire 76 is further fixed with solder 77.
[0004]
By the way, in recent years, in order to ensure a large amount of displacement under a large pressure with a small piezoelectric actuator, a higher electric field is applied to continuously drive for a long time.
[0005]
[Problems to be solved by the invention]
However, in the above-described piezoelectric actuator, when continuously driven for a long time under a high electric field and high pressure, peeling occurs between the internal electrode 52 formed between the piezoelectric bodies 51 and the external electrode 70 for the positive electrode and the negative electrode. There is a problem that the voltage is not supplied to some of the piezoelectric bodies 51 and the displacement characteristics change during driving.
[0006]
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.
[0007]
[Means for Solving the Problems]
The multilayer piezoelectric element of the present invention includes a pair of columnar laminates formed by alternately laminating piezoelectric bodies and internal electrodes, and a pair of the internal electrodes connected alternately every other layer. A plurality of external electrodes, and a protruding conductive terminal protruding from a side surface of the columnar stacked body is provided at every other end of the internal electrode, and the protruding conductive terminal with joining external electrode to become the tip from the plate-like conductive member, it is provided a conductive auxiliary member made of a conductive adhesive buried conductive mesh member to the external electrode, and the main component of glass glass region, characterized in that there I covering the side surface of the columnar laminate following the side surface and the side surface of the root portion of the protruding conductive terminals.
[0008]
In the multi-layer piezoelectric element of the present invention, a protruding conductive terminal protruding from the side surface of the columnar stacked body is provided at every other end of the internal electrode, and a plate-shaped conductive member is formed at the tip of the protruding conductive terminal. Since the external electrodes are joined, when the actuator is driven in the stacking direction, the protruding conductive terminals are deformed to absorb the stress generated by the expansion and contraction of the actuator . Thereby , even when it is made to operate continuously for a long time under a high electric field and high pressure, disconnection between the external electrode and the internal electrode can be suppressed, and the durability can be greatly improved.
[0009]
Further, in the present invention, since the conductive auxiliary member made of the conductive adhesive in which the conductive mesh-like member is embedded is provided on the outer surface of the plate-like conductive member, the actuator is driven at a high speed by supplying a large current. Even in the case of making it, a large current can be passed through the conductive auxiliary member . Thereby, it can prevent that an external electrode raise | generates local heat_generation | fever and is disconnected, and durability can be improved significantly. Furthermore, since a conductive mesh-like member is embedded in the conductive adhesive, it is possible to prevent a problem that a crack occurs in the conductive adhesive due to expansion and contraction of the actuator.
[0010]
Furthermore, according to the present invention, the glass region mainly composed of glass, since there I covering the side surface of the columnar laminate following the side surface and the side surface of the root portion of the protruding conductive terminals, the glass area projection The conductive terminal can be held. Thereby, the intensity | strength of a protruding conductive terminal can be improved.
In addition, when the glass region in the present invention is gradually decreasing as the thickness in the direction perpendicular to the side surface of the columnar laminate is separated from the protruding conductive terminal, the surface of the glass region becomes a gently inclined surface, It is possible to prevent stress from being concentrated on a part of the glass region.
[0011]
Moreover, the multilayer piezoelectric element of the present invention is characterized in that a concave groove is formed between the protruding conductive terminals on the side surface of the columnar multilayer body so that the end of the internal electrode is exposed. In such a multilayer piezoelectric element, the generated stress can be reduced compared to a so-called partial electrode structure multilayer piezoelectric element, and the thickness of the end portion of the internal electrode connected to the external electrode via the protruding conductive terminal is columnar. Since it can be effectively made thicker than the thickness of the internal electrode inside the laminate, it is possible to prevent the problem of contact failure between the internal electrode and the external electrode.
[0012]
In the multilayer piezoelectric element of the present invention, it is desirable that the main component of the internal electrode, the protruding conductive terminal and the external electrode is silver. According to such a configuration, the main components of the internal electrode, the protruding conductive terminal, and the external electrode are made of the same silver, so that the protruding conductive terminal and the external electrode are connected, and the protruding conductive terminal and the external electrode are externally connected. Silver interdiffuses between the electrodes, thereby strengthening the bonding strength between them, and the external electrode and the internal electrode are disconnected even when the actuator is driven under a high electric field. Therefore, the durability can be greatly improved. Further, by using silver having a low Young's modulus as the main component of the protruding conductive terminals and the external electrode, the stress generated when the actuator is driven can be sufficiently absorbed, and disconnection between the external electrode and the internal electrode can be suppressed.
[0013]
Furthermore, in the multilayer piezoelectric element of the present invention, the conductive adhesive is made of a conductive material and a resin having an imide bond. According to such a configuration, an actuator excellent in durability at high temperatures can be obtained by using a matrix resin as a resin having an imide bond such as polyimide or polyamideimide, which is particularly excellent in heat resistance among the resins. .
[0014]
In the multilayer piezoelectric element of the present invention, the conductive material of the conductive adhesive is non-spherical silver powder. According to such a configuration, the silver powder has a small volume resistivity and excellent oxidation resistance, and further, by making the particle shape of the silver powder a non-spherical shape such as a needle shape or a flake shape, The entanglement between the conductive material particles becomes larger than the case, and as a result, the shear strength of the conductive adhesive can be greatly improved, and the specific resistance can also be lowered.
[0015]
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.
[0016]
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.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
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. 4C is a perspective view showing a part of FIG. 2A in an enlarged manner, and FIG.
[0018]
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. Protruding conductive terminals 5 that can be deformed in the expansion and contraction direction of the laminated piezoelectric element are provided at the ends of the internal electrodes 2 that are covered with the insulator 3 every other layer and are not covered with the insulator 3, The external electrode 4 made of a plate-like conductive member is joined to the tip of the conductive terminal 5.
[0019]
A conductive auxiliary member 7 is provided outside the external electrode 4, and the conductive auxiliary member 7 is configured by embedding a conductive mesh member 7 b in a conductive adhesive 7 a. A lead wire 6 is connected and fixed to each conductive auxiliary member 7.
[0020]
The piezoelectric body 1 is made of, for example, lead 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.
[0021]
The thickness of the piezoelectric body 1, that is, the distance between the internal electrodes 2 is preferably 50 to 250 μm. In order to obtain a larger displacement amount by applying a voltage to the stacked piezoelectric actuator, a method of increasing the number of stacked layers is used. However, when the number of stacked layers is increased, the piezoelectric body 1 is too thick. This is because the actuator cannot be reduced in size and height, and on the other hand, if the thickness of the piezoelectric body 1 is too thin, dielectric breakdown tends to occur.
[0022]
An internal electrode 2 is arranged between the piezoelectric bodies 1. The internal electrode 2 is formed of a metal material (silver main component) such as silver-palladium, and applies a predetermined voltage to each piezoelectric body 1. Thus, the piezoelectric body 1 is caused to cause displacement due to the reverse piezoelectric effect.
[0023]
Further, on the side surface of the columnar stacked body 1a between the protruding conductive terminals 5, a groove 11 having a depth of 50 to 500 μm and a width of 30 to 200 μm in the stacking direction is formed so that the end of the internal electrode 2 is exposed. The insulator 11 is formed by filling the concave groove 11 with glass, epoxy resin, polyimide resin, polyamideimide resin, silicone rubber, or the like. The insulator 3 is preferably made of a material having a low elastic modulus, specifically silicone rubber, which follows the deformation of the columnar laminate 1a in order to strengthen the bonding with the columnar laminate 1a. is there.
[0024]
The protruding conductive terminals 5 and the insulators 3 are alternately formed on the internal electrodes 2 exposed on the side surfaces of the columnar laminated body 1a on which the external electrodes 4 are formed.
[0025]
That is, the end portions of the internal electrodes 2 are alternately insulated by the insulators 3 filled in the concave grooves 11, and the other uninsulated end portions of the internal electrodes 2 are connected to the protruding conductive terminals 5. It is joined to the external electrode 4 made of a plate-like conductive member.
[0026]
External electrodes 4 each made of a plate-like conductive member are connected and fixed to the internal electrodes 2 via projecting conductive terminals 5 on the opposite side surfaces of the columnar laminate 1a, and are laminated on the external electrodes 4. The internal electrodes 2 are electrically connected every other layer. The external electrode 4 made of this plate-like conductive member serves to commonly supply a voltage necessary for displacing the piezoelectric body 1 by the inverse piezoelectric effect to each connected internal electrode 2.
[0027]
In the present invention, since the external electrode 4 made of a plate-like conductive member is connected to the internal electrode 2 via the protruding conductive terminal 5 in this way, the actuator is driven continuously for a long time under a high electric field and high pressure. Even in this case, the projecting conductive terminal 5 can absorb the stress generated by the expansion and contraction of the actuator, and the disconnection between the external electrode 4 and the internal electrode 2 can be suppressed, and an actuator having excellent durability can be provided. .
[0028]
As shown in FIG. 1C, the thickness B in the same direction as the stacking direction of the projecting conductive terminals 5 lowers the resistance of the connecting portion between the external electrode 4 and the internal electrode 2 and drives the actuator. From the viewpoint of sufficiently absorbing the generated stress, it is desirable that the thickness be 1 μm or more and 1/2 or less of the thickness of the piezoelectric body 1. In particular, the thickness B is desirably 5 to 25 μm.
[0029]
The protrusion height h of the protruding conductive terminal 5 is desirably 1/20 or more of the thickness of the piezoelectric body 1 from the viewpoint of sufficiently absorbing the stress generated by the expansion and contraction of the actuator. In particular, the protrusion height h is desirably 15 to 50 μm.
[0030]
Further, the thickness t of the external electrode 4 made of a plate-like conductive member follows the expansion and contraction of the actuator, and between the external electrode 4 and the protruding conductive terminal 5 or between the protruding conductive terminal 5 and the internal electrode 2. From the viewpoint of not causing disconnection, it is desirable that the thickness is 50 μm or less.
[0031]
Furthermore, the lead wire 6 is connected and fixed to the conductive auxiliary member 7 with solder. The lead wire 6 serves to connect the conductive auxiliary member 7 and the external electrode 4 to an external voltage supply unit.
[0032]
The internal electrode 2 is made of a metal or alloy containing silver as a main component, such as silver, a silver-palladium alloy, or a silver-platinum alloy. The main component of the protruding conductive terminals 5 and the external electrodes 4 is preferably silver. This is because the inner electrode 2, the protruding conductive terminal 5, and the outer electrode 4 are made of the same silver as the main component so that the protruding conductive terminal 5 and the protruding electrode 5 This is because silver interdiffuses between the external electrodes 4, thereby strengthening the bonding strength between them. Also, the protruding conductive terminals 5 and the external electrodes 4 are preferably made of 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.
[0033]
Further, since the conductive auxiliary member 7 made of the conductive adhesive 7a in which the conductive mesh member 7b is embedded is formed outside the external electrode 4, a large current is supplied to the actuator to drive at high speed. Even in this case, a large current can be passed through the conductive auxiliary member 7, the external electrode 4 can be prevented from being disconnected due to local heat generation, and the durability can be greatly improved. Furthermore, since the conductive mesh-like member 7b is embedded in the conductive adhesive 7a, it is possible to prevent a problem that a crack occurs in the conductive adhesive 7a due to expansion and contraction of the actuator. As the mesh member 7b, there are a member in which a metal wire is knitted, a member in which a large number of holes are formed in a metal plate, and the like. By making the mesh shape, the expansion and contraction deformation of the external electrode 7 can be improved.
[0034]
Furthermore, the amount of the conductive material dispersed in the conductive adhesive 7a constituting the conductive auxiliary member 7 can sufficiently reduce the specific resistance of the conductive adhesive 7a and maintain high adhesive strength. 15-80 volume% is desirable. That is, by setting the content of the conductive material to 15 to 80% by volume, the contact between the conductive material particles becomes easy, so that the specific resistance of the conductive adhesive 7a can be reduced, and the conductive material becomes conductive when a large current is passed. Local heat generation at the adhesive 7a portion can be prevented, and since the content of the matrix resin component responsible for adhesion is appropriate, high adhesive strength can be maintained, and peeling of the conductive adhesive 7a during driving can be prevented.
[0035]
Further, the resin used as the matrix of the conductive adhesive 7a is caused by the difference in thermal expansion between the conductive adhesive 7a and the external electrode 4 having a different thermal expansion and the mesh member 7b embedded in the conductive adhesive 7a. It is possible to absorb the generated stress and the stress generated by the expansion and contraction of the actuator, and prevent the problem that the conductive adhesive 7a is peeled off during driving or the conductive adhesive 7a is cracked. It is desirable that the elastic modulus is 20 GPa or less and the elongation is 10% or more.
[0036]
Furthermore, the void ratio of the conductive adhesive 7a is preferably 5% or more from the viewpoint of easily absorbing the stress generated by the expansion and contraction of the actuator. In addition, the 5% weight reduction temperature of the matrix resin of the conductive adhesive 7a is desirably 250 ° C. or higher from the viewpoint that a strong adhesive force can be maintained even when used at a high temperature.
[0037]
Here, a method for measuring the 5% weight reduction temperature of the resin will be briefly described. First, when the form before use is a varnish-like resin, the evaporation of the solvent and the curing of the resin are completed in advance. In general, thermogravimetric analysis (TG) is used to measure the 5% weight loss temperature. That is, the temperature of the resin as a sample is increased at a constant temperature increase rate (1 to 10 ° C./min) in the atmosphere, and the weight at that time is sequentially measured. The temperature at which 5% of the initial weight is reduced is the 5% weight reduction temperature of the resin. By using a resin having a measured 5% weight loss temperature of 250 ° C. or higher as the matrix of the conductive adhesive 7a, the conductive auxiliary member 7 having excellent durability at high temperatures can be formed.
[0038]
Furthermore, it is desirable that the matrix resin of the conductive adhesive 7a is a resin having an imide bond such as polyimide or polyamideimide that is particularly excellent in heat resistance among the resins. Thereby, an actuator excellent in durability at high temperatures can be obtained.
[0039]
In addition, the matrix resin of the conductive adhesive 7a is thermoplastic because it relieves the stress caused by the difference in thermal expansion between the columnar laminate 1a and the external electrode 4 under the condition of a heat cycle between low temperature and high temperature. It is desirable that Furthermore, considering the environment when used for a fuel injection valve for automobiles, etc., where the temperature environment is severe, the glass transition temperature of the matrix resin of the conductive adhesive 7a is 180 in order to prevent a decrease in strength at high temperatures. It is desirable that the temperature be higher than or equal to ° C. This is because the use of a resin at a temperature higher than its glass transition temperature generally causes a decrease in adhesive strength.
[0040]
The conductive material constituting the conductive adhesive 7a is preferably silver powder because it has a small volume resistivity and excellent oxidation resistance. Furthermore, the shape of the conductive material powder is such as increasing the entanglement of the conductive material particles, thereby greatly improving the shear strength of the conductive adhesive 7a and reducing the specific resistance. The non-spherical shape is desirable.
[0041]
Next, the manufacturing method of 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 bonded to the piezoelectric body 1 by a tape molding method such as a known doctor blade method or calendar roll method. A ceramic green sheet is produced.
[0042]
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. Here, as the silver-palladium powder, an alloy powder of 70% silver and 30% palladium was used.
[0043]
Then, a green sheet having a conductive paste printed on the upper surface is laminated, the binder is debindered at a predetermined temperature, and then fired at 900 to 1200 ° C.
[0044]
Thereafter, as shown in FIG. 2A, the concave grooves 11 are formed on every other side surface of the columnar laminated body 1a by a dicing apparatus or the like.
[0045]
Next, as shown in FIG. 2 (b), 50 to 80% by volume of silver powder having a particle size of 0.1 to 10 μm is formed on the side surface of the columnar laminate 1 a between the concave grooves 11, and the balance is 0. A silver glass conductive paste 21 prepared by adding a binder to a mixture of 20 to 50% by volume of glass powder having a softening point of 1 to 10 μm and containing silicon as a main component and having a softening point of 600 to 950 ° C. is applied and dried. Thereafter, as shown in FIG. 2 (c), heat treatment is performed at 700 to 950 ° C. with a load applied to the silver glass conductive paste 21 so as to press the plate-like conductive member serving as the external electrode 4. The glass in the silver glass conductive paste 21 is melted, and silver components present in the melted glass gather at the end of the internal electrode 2, and as shown in FIG. 2 (d), from the side surface of the columnar laminate 1 a. A protruding conductive terminal 5 that protrudes can be formed, and the tip of the protruding conductive terminal 5 can be connected to the external electrode 4. During the heat treatment, the silver component in the silver glass conductive paste 21 diffuses into the end 2a of the internal electrode 2, and as shown in FIG. 1 (d), the thickness of the end 2a of the internal electrode 2 is the center of the columnar laminate 1a. It becomes thicker than the thickness of the internal electrode 2 of a part. Thereby, the joint strength of the protruding conductive terminal 5 with respect to the end 2a of the internal electrode 2 can be improved.
[0046]
That is, by dispersing the glass component in the paste, the glass is softened during the above-described heat treatment, and in this state, silver that does not easily diffuse into the piezoelectric body 1 diffuses and gathers at the end of the internal electrode 2. A protruding conductive terminal 5 as shown in FIG. 2D can be formed. That is, the internal electrode 2, the silver glass conductive paste 21 and the silver component in the plate-like conductive member are diffused to each other and between the internal electrode 2 and the protruding conductive terminal 5 and between the protruding conductive terminal 5 and the plate-like conductive material. The members are firmly joined. Further, in the vicinity of the base of the protruding conductive terminal 5, the glass in the silver glass conductive paste 21 gathers to form a raised portion 5 a to hold the protruding conductive terminal 5.
[0047]
This protruding conductive terminal 5 is formed on a part of the side surface of the columnar laminate 1a, is formed in a rail shape, and its length is substantially the same as the width of the external electrode 4 made of a plate-like conductive member. Yes. The length of the protruding conductive terminal 5 may be shorter than the width of the external electrode 4.
[0048]
The silver component in the silver glass conductive paste 21 is 50 to 80% by volume, and the remaining glass powder is 20 to 50% by volume. Becomes an appropriate amount, and the protruding height h of the formed projecting conductive terminal 5 can be increased, and the glass component which is the remaining solid content in the silver glass conductive paste 21 becomes an appropriate amount. The glass component that melts at the time of baking 21 is also an appropriate amount, the silver component easily gathers at the end of the internal electrode 2, and the protruding height h of the protruding conductive terminal 5 can be increased.
[0049]
The load applied during the formation of the above-mentioned protruding conductive terminal 5 and the heat treatment for bonding the protruding conductive terminal 5 and the external electrode 4 is preferably 2 to 500 kPa in terms of pressure. By setting this range, it is possible to sufficiently perform diffusion bonding between the protruding conductive terminal 5 and the plate-like conductive member 4a, increase the strength of the bonded portion, and the pressure becomes appropriate. The deformation of the conductive electrode 5 can be prevented.
[0050]
Note that the silver glass conductive paste 21 is applied and dried in advance on the portion of the plate-like conductive member corresponding to the space between the concave grooves 11 of the columnar laminate 1a, and this plate-like conductive member is pressed against the columnar laminate 1a. You may heat-process in the state which added the load. Moreover, the silver glass conductive paste 21 is applied and dried on the entire surface of the plate-like conductive member, and this plate-like conductive member is pressed against the surface where the internal electrode 2 of the columnar laminate 1a is exposed on the conductive paste application surface side. Even if the heat treatment is performed, the protruding conductive terminals 5 are formed, and the tip portions thereof can be connected to the external electrodes 4. In this case, the process can be further shortened.
[0051]
Thereafter, as shown in FIG. 2 (e), on the outside of the external electrode 4, 15-80% by volume of non-spherical silver powder such as needles or flakes as a conductive material, and the balance as a matrix with an elastic modulus of 20 GPa. Below, 20% to 85% by volume of a thermoplastic resin having an imide bond with an elongation of 10% or more, a 5% weight loss temperature of 250 ° C. or more, a glass transition temperature of 180 ° C. or more, and a conductivity mixed with a solvent. After applying an adhesive paste and embedding a conductive mesh member 7b in the conductive adhesive 7a, the conductive adhesive 7a is heated and cured at 150 to 300 ° C. to form the conductive auxiliary member 7. .
[0052]
The reason why the content of the conductive material in the conductive adhesive 7a is 15 to 80% by volume is within this range, since the contact between the conductive material particles is good, and the specific resistance of the conductive adhesive 7a is small. In addition, it is possible to prevent local heat generation in the conductive adhesive 7a portion when a large current is passed, and the content of the matrix resin component responsible for adhesion is appropriate, so that high adhesive strength can be maintained, and conductivity during driving can be maintained. Peeling of the adhesive 7a can be prevented.
[0053]
Further, by setting the elastic modulus of the matrix resin to 20 GPa or less and the elongation to 10% or more, a plate-like conductive member having a thermal expansion different from that of the conductive adhesive 7a and a mesh shape embedded in the conductive adhesive 7a. The stress generated by the difference in thermal expansion from the member 7b and the stress generated by the expansion and contraction of the actuator can be absorbed, and the conductive adhesive 7a is peeled off during driving or cracks are generated in the conductive adhesive 7a. Can be prevented from occurring.
[0054]
Furthermore, in the present invention, it is desirable that the 5% weight reduction temperature of the matrix resin constituting the conductive adhesive 7a is 250 ° C. or higher. It is possible to maintain a strong adhesive force when used at a high temperature by using a resin having high heat resistance with a 5% weight loss temperature of 250 ° C. or higher as a matrix resin. Even when continuously driving at high speed with an applied electric field, an actuator having high durability can be provided without the conductive adhesive 7a being peeled off.
[0055]
In the present invention, the matrix resin constituting the conductive adhesive 7a is desirably a resin having an imide bond. This makes it possible to obtain an actuator excellent in durability at high temperatures by making the matrix resin a resin having an imide bond such as polyimide or polyamideimide, which is particularly excellent in heat resistance among the resins.
[0056]
Furthermore, in the present invention, it is desirable that the matrix resin constituting the conductive adhesive 7a exhibits thermoplasticity and has a glass transition temperature of 180 ° C. or higher. This is because the resin used as the matrix is a thermoplastic resin, so that the thermal expansion of the columnar laminate 1a and the external electrode 4 is possible not only for continuous use at high temperatures but also for heat cycle conditions between low and high temperatures. This is because stress resulting from the difference can be absorbed and high strength can be maintained.
[0057]
In addition, regarding the glass transition point of the matrix resin, in general, when the resin is used at a temperature higher than the glass transition point of the resin, the strength of the resin is significantly reduced. Considering the environment, it is desirable that the temperature be 180 ° C. or higher.
[0058]
Moreover, it is desirable that the void ratio of the conductive adhesive 7a constituting the conductive auxiliary member 7 is 5% or more. This is to make it easier to absorb the stress caused by the expansion and contraction of the actuator by setting the void ratio in the conductive adhesive 7a to 5% or more.
[0059]
Note that the void ratio of the conductive adhesive 7a depends on the viscosity of the paste before the heat curing of the conductive adhesive 7a, the amount of the solvent contained in the paste, and the heating temperature during the heat curing of the conductive adhesive 7a. Can be changed by profile.
[0060]
Thereafter, the groove 3 is filled with the insulator 3 and the lead wire 6 is connected to complete the multilayer piezoelectric element of the present invention.
[0061]
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.
[0062]
In the multilayer piezoelectric element configured as described above, since the external electrode 4 made of a plate-like conductive member is connected to the internal electrode 2 via the protruding conductive terminals 5, the actuator can be operated continuously under a high electric field. Even when driven, the projecting conductive terminal 5 is deformed and the projecting conductive terminal 5 can sufficiently absorb the stress generated during driving, so that a spark is generated between the external electrode 4 and the internal electrode 2. Further, since the conductive auxiliary member 7 made of the conductive adhesive 7a in which the conductive mesh member 7b is embedded is provided on the outside of the external electrode 4, a large current is supplied to the actuator. In the case of driving at a high speed, a large current can be passed through the conductive auxiliary member 7, so that the problem that the external electrode 4 is disconnected due to local heat generation can be prevented, and a highly reliable actuating device can be obtained. It is possible to provide a mediator.
[0063]
In the above example, the example in which the external electrode 4 is formed on the opposing side surface of the columnar laminate 1a has been described. However, in the present invention, for example, a pair of external electrodes 4 may be formed on the adjacent side surfaces.
[0064]
FIG. 3 shows an injection device 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.
[0065]
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.
[0066]
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.
[0067]
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.
[0068]
【Example】
First, a columnar laminate was produced. The piezoelectric body was formed of PZT with a thickness of 150 μm, the internal electrode was formed with a silver-palladium alloy of 70% silver and 30% palladium with a thickness of 3 μm, and the number of stacked piezoelectric bodies and internal electrodes was 300 layers.
[0069]
Next, a concave groove having a depth of 150 μm and a width of 75 μm was formed on the side surface of the columnar laminate including the ends of every other internal electrode exposed on the external electrode formation surface of the columnar laminate. Thereafter, from the volume of the silver powder having an average particle diameter of 5 μm on the side surface of the columnar laminated body between the concave grooves, the balance is from 40 volume% of the glass powder having an average particle diameter of 5 μm and a softening point mainly composed of silicon of 750 ° C. A silver glass conductive paste prepared by adding a binder to the resulting mixture was applied and dried.
[0070]
Furthermore, heat treatment is performed at 900 ° C. in a state where a plate-like conductive member made of silver having a thickness of 25 μm is pressed at 30 kPa on the silver glass conductive paste, thereby forming projecting conductive terminals protruding from the columnar laminate, The tip of the protruding conductive terminal was connected to the plate-shaped conductive member.
[0071]
Thereafter, on the outside of the plate-like conductive member, 50 vol% of flaky silver powder having an average particle diameter of 5 μm as a conductive material, the balance being a matrix with an elastic modulus of 10 GPa, an elongation of 30%, and a 5% weight loss temperature Is applied with a conductive adhesive paste in which 50% by volume of a thermoplastic polyimide resin having a glass transition temperature of 200 ° C. or higher and a solvent is mixed, and the conductive adhesive paste is made into a mesh having a thickness of 50 μm made of nickel. After embedding the member, the conductive adhesive was heated and cured at 220 ° C. to form a conductive auxiliary member.
[0072]
Thereafter, silicone rubber is filled in the concave groove as an insulator, lead wires are connected to the conductive auxiliary member, and a 3 kV / mm DC electric field is applied to the external electrodes of the positive and negative electrodes through the lead wires for 15 minutes for polarization. The laminated piezoelectric actuator as shown in FIG.
[0073]
Note that silver and palladium were dispersed in the protruding conductive terminals. At this time, the average height of the protruding conductive terminals was 20 μm, and the void ratio of the conductive adhesive was 10%.
[0074]
As a result of applying a DC voltage of 150 V to the obtained multilayer piezoelectric actuator, a displacement of 40 μm was obtained in the stacking direction. Furthermore, as a result of applying a driving test by applying an AC voltage of 0 to +150 V at a frequency of 120 Hz to this actuator at a room temperature, a displacement of 40 μm was obtained when driving up to 1 × 10 ⁹ cycles, and abnormalities in the external electrodes were observed. I couldn't see it.
[0075]
Further, as a result of a drive test by applying an AC voltage of 0 to +150 V at 150 ° C. at a frequency of 120 Hz to the laminated piezoelectric actuator manufactured in the same manner as described above, when driving up to 1 × 10 ⁹ cycles, the external No abnormality of the electrode was observed.
[0076]
Furthermore, a driving test in which an AC voltage of 0 to +150 V is applied at a frequency of 120 Hz at a frequency of 120 × 5 × 10 ⁷ cycles to a laminated piezoelectric actuator manufactured in the same manner as described above, and 0 to +150 V at 150 ° C. A drive test in which 5 × 10 ⁷ cycles of AC voltage was applied at a frequency of 120 Hz was alternately repeated 20 times in total, and when driving was performed up to a total of 1 × 10 ⁹ cycles, no abnormality was found in the external electrodes.
[0077]
On the other hand, as a comparative example, one end portion of the internal electrode is alternately covered with an insulator made of glass, and the above-described silver glass conductive paste is applied thereon and heat-treated at 700 ° C. When the actuator shown in FIG. 4 that is electrically connected to the internal electrode every other layer on the left and right sides was manufactured and tested in the same manner as described above, sparks were generated in the external electrode in 1 × 10 ⁵ cycles in the driving test.
[0078]
【The invention's effect】
According to the multilayer piezoelectric element of the present invention, the protruding conductive terminals protruding from the side surfaces of the columnar stacked body are provided at every other end of the internal electrode, and the plate-shaped conductive member is provided at the tip of the protruding conductive terminal. A conductive auxiliary member made of a conductive adhesive in which a conductive mesh-like member is embedded in the external electrode, and a glass region mainly composed of glass has the protruding shape the because there I covering the side surface of the columnar laminate following the side surface and the side surface of the root portion of the conductive terminal, it is possible to provide a multilayer piezoelectric element having high reliability.
[Brief description of the drawings]
1A and 1B show a multilayer piezoelectric element of the present invention, in which FIG. 1A is a perspective view, FIG. 1B is a longitudinal sectional view taken along line AA ′ in FIG. 1A, and FIG. The perspective view which expands and shows a part of (b), (d) is sectional drawing which expands and shows a part of (b).
FIG. 2 is a process diagram showing a method for producing a multilayer piezoelectric element of the present invention.
FIG. 3 is an explanatory view showing an injection device of the present invention.
FIG. 4 is a longitudinal sectional view of a conventional multilayer piezoelectric actuator.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Piezoelectric body 1a ... Columnar laminated body 2 ... Internal electrode 4 ... External electrode 5 ... Protruding conductive terminal 7 ... Conductive auxiliary member 7a ... Conductive adhesive 7b ... Mesh-like member 11 ... Concave groove 31 ... Storage container 33 ... Injection hole 35 ... Valve 43 ... Piezoelectric actuator

Claims (4)

A columnar laminated body formed by alternately laminating piezoelectric bodies and internal electrodes, and a pair of external electrodes provided on the side surfaces of the columnar laminated body and having the internal electrodes alternately connected every other layer. A laminated piezoelectric element,
Providing a protruding conductive terminal protruding from the side surface of the columnar laminated body at every other end of the internal electrode, and joining an external electrode made of a plate-like conductive member to the tip of the protruding conductive terminal; A conductive auxiliary member made of a conductive adhesive in which a conductive mesh member is embedded in the external electrode is provided,
Glass region mainly composed of glass, laminated piezoelectric elements, characterized in that there I covering the side surface of the columnar laminate following the side surface and the side surface of the root portion of the protruding conductive terminals.   2. The multilayer piezoelectric element according to claim 1, wherein a thickness of the glass region in a direction perpendicular to a side surface of the columnar laminated body gradually decreases as the distance from the protruding conductive terminal is increased.   3. The multilayer piezoelectric element according to claim 1, wherein a concave groove in which an end of the internal electrode is exposed is formed between the projecting conductive terminals on the side surface of the columnar laminate.   A storage container having an injection hole, the multilayer piezoelectric element according to any one of claims 1 to 3 accommodated in the storage container, and a valve for ejecting liquid from the injection hole by driving the multilayer piezoelectric element An injection device comprising:

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