JP2009076760A - Laminated piezoelectric element and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laminated piezoelectric element, capable of preventing failures such as deterioration of insulation and short-circuit, due to the migration of electrode material via a slit groove portion. <P>SOLUTION: The laminated piezoelectric element 1 includes a ceramic laminate 15 provided, by alternately laminating piezoelectric ceramic layers 11 and internal electrode layers 13 and 14, and side electrodes 17 and 18. The internal electrodes 13 and 14 include internal electrode portions 131 and 141 and alternate portions 132 and 142. The ceramic laminate 15 includes the slit groove portion 12 circularly formed over the entire circumference of outer peripheral surface 150 of the ceramic laminate 15. When a groove width of an opening portion of the slit groove portion 12 is W1 and a groove width of a position of 30 μm outward from the tip of the slit groove portion 12 is W2, the relation W2/W1=0.05-0.8 is satisfied. In the slit groove portion 12, an insulating resin 19 is so arranged as to shield between the side electrodes 17 and 18 which are in a communicating state via the slit groove portions 12. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a multilayer piezoelectric element applied to, for example, a piezoelectric actuator and a manufacturing method thereof.

Conventionally, a multilayer piezoelectric element has been used in a piezoelectric actuator that is a drive source of an injector for fuel injection in an automobile.
A laminated piezoelectric element is formed by bonding a pair of external electrodes that are electrically connected alternately to internal electrodes to a ceramic laminate in which piezoelectric ceramics and internal electrodes are alternately stacked, for example. And it is comprised so that a displacement may arise in a piezoelectric ceramic by applying a voltage with respect to an internal electrode layer.

The multilayer piezoelectric element is used over a long period under severe conditions. Therefore, for example, in order to improve the electrical insulation on the outer peripheral surface of the ceramic laminate, a ceramic laminate having a holding portion with a part of the end portion of the internal electrode inward is widely used.
However, in the ceramic laminate having the above structure, when the holding portion is provided, a portion that is displaced when a voltage is applied and a portion that is not displaced (piezoelectric inactive portion) are generated. Therefore, stress concentration occurs at the boundary, and there is a possibility that cracks or the like occur.

  Therefore, in order to reduce displacement restraint due to the piezoelectric inactive portion and avoid cracks due to stress concentration, for example, in Patent Document 1, a slit is formed on the outer peripheral surface of the ceramic laminate, and the Young in the slit is more young than the piezoelectric ceramic. A multilayer piezoelectric element provided with a low-rate filler has been proposed. Moreover, in patent document 2, the recessed part (slit) which exposed the edge part of the internal electrode was formed in the side surface in which the side electrode was provided in the ceramic laminated body, and the internal electrode with a different polarity exposed to the side electrode and the recessed part is insulated. In order to achieve this, a multilayer piezoelectric element in which an insulating filler is filled in the recess has been proposed.

JP-A-4-133482 JP 2004-297041 A

  However, when the laminated piezoelectric element is used as a piezoelectric actuator of a fuel injection injector, it is exposed to a high temperature and high humidity environment for a long time. For this reason, if the insulating filler (insulating resin, etc.) is insufficiently filled in the slit, migration of the electrode material may occur through the slit, which may cause problems such as a decrease in insulation and a short circuit. .

  The present invention has been made in view of such conventional problems, and a multilayer piezoelectric element capable of preventing problems such as a decrease in insulation and a short circuit due to migration of an electrode material through a slit groove portion and the same A manufacturing method is to be provided.

According to a first aspect of the present invention, there is provided a ceramic laminate formed by alternately laminating a plurality of piezoelectric ceramic layers and a plurality of internal electrode layers, and a pair provided on a pair of side surfaces formed on the outer peripheral surface of the ceramic laminate. In the laminated piezoelectric element having the side electrode of
The internal electrode layer has a conductive internal electrode portion, and a holding portion in which an outer peripheral end portion of the internal electrode portion is kept at a predetermined distance inward from an outer peripheral surface of the ceramic laminate, In the internal electrode portion, alternately connected to any one of the side electrodes,
The ceramic laminate has a slit-shaped slit groove that is recessed inward from the outer peripheral surface of the ceramic laminate at a predetermined depth,
The slit groove portion is formed in an annular shape over the entire outer peripheral surface of the ceramic laminate so that the internal electrode portion is not exposed on the inner wall surface, and is directed inward from the outer peripheral surface of the ceramic laminate. When the groove width of the opening of the slit groove portion is W1, and the groove width at a position of 30 μm outward from the tip of the slit groove portion is W2, W2 / W1 = 0. Satisfies the relationship of .05 to 0.8,
In the slit groove part, an insulating resin having an electrical insulating property is disposed so as to cut off the pair of side electrodes that are in communication with each other through the slit groove part. It exists in a piezoelectric element (Claim 1).

  In the multilayer piezoelectric element of the present invention, the ceramic multilayer body has a slit-shaped slit groove that is recessed inward from the outer peripheral surface of the ceramic multilayer body at a predetermined depth. The slit groove portion is formed in an annular shape over the entire outer peripheral surface of the ceramic laminate so that the internal electrode portion is not exposed on the inner wall surface. And in the said slit groove part, the insulating resin which has electrical insulation is arrange | positioned so that between the said pair of side surface electrode which is in a communication state via this slit groove part may be interrupted | blocked.

That is, the pair of side surface electrodes are exposed in the slit groove portion, and the exposed side surface electrodes are in communication with each other via the slit groove portion. And this communication state is interrupted | blocked by the said insulating resin arrange | positioned in the said slit groove part.
Therefore, the insulating resin provided in the slit groove prevents the material (electrode material) constituting the side electrode from moving through the slit groove and reaching the other side electrode. it can. That is, the migration of the electrode material between the side electrodes can be blocked, and the occurrence of problems such as a decrease in insulation and a short circuit can be prevented. Thereby, sufficient insulation can be ensured, and durability and reliability can be improved.

The slit groove portion has a groove width that gradually decreases inward from the outer peripheral surface of the ceramic laminate, and the groove width of the opening of the slit groove portion is W1, and the slit groove portion is outward from the tip of the slit groove portion. When the groove width at 30 μm is W2, the relationship of W2 / W1 = 0.05 to 0.8 is satisfied.
By making the slit groove part into the above shape, the insulating resin easily flows into the slit groove part by capillary action. Therefore, the insulating resin can be easily disposed in the slit groove.

  As described above, according to the present invention, it is possible to prevent a problem such as a decrease in insulation and a short circuit due to the migration of the electrode material through the slit groove, and to easily dispose the insulating resin in the slit groove. It is possible to provide a multilayer piezoelectric element that can be used.

According to a second aspect of the present invention, in the method for manufacturing the multilayer piezoelectric element of the first aspect,
In disposing the insulating resin in the slit groove, an application step of applying the insulating resin to the opening of the slit groove on the outer peripheral surface of the ceramic laminate,
An operation step of operating the multi-layer piezoelectric element to infiltrate the insulating resin into the slit groove and disposing the insulating resin in a desired region within the slit groove;
And a curing step of curing the insulating resin. A method of manufacturing a multilayer piezoelectric element according to claim 10.

  In the production method of the present invention, when the insulating resin is disposed in the slit groove portion, the coating step, the disposing step, and the curing step are performed as described above. In the arrangement step, the laminated piezoelectric element is operated to infiltrate the insulating resin into the slit groove and arrange the insulating resin in a desired region in the slit groove. Therefore, the insulating resin can be easily infiltrated into the slit groove due to the pumping effect by operating the multilayer piezoelectric element. Thereby, the said insulating resin can be arrange | positioned easily and reliably in the desired area | region in the said slit groove part.

  In the first invention, the internal electrode layer includes an internal electrode portion having conductivity, and an electrode in which an outer peripheral end portion of the internal electrode portion is kept at a predetermined distance inward from an outer peripheral surface of the ceramic laminate. And having a recording part. By providing the holding portion, the internal electrode layer can realize reliable insulation on one side surface (side surface on the holding portion side) of the ceramic laminate.

In addition, the slit groove portion is a portion in the ceramic laminate, in which the crystal particles constituting the piezoelectric ceramic layer are separated in the stacking direction, and the shape can be changed more easily than the piezoelectric ceramic layer.
Moreover, although the said slit groove part can be provided in various positions, for example, it is preferable to provide two or more with a fixed space | interval in the lamination direction of the said ceramic laminated body. Thereby, the stress accumulated in the stacking direction of the ceramic laminate can be effectively relaxed.
The elastic modulus of the insulating resin disposed in the slit groove is preferably smaller than the elastic modulus of the piezoelectric ceramic layer. Thereby, the stress relaxation effect by the said slit groove part can fully be exhibited.

Further, when the ceramic laminate is seen through the ceramic laminate in the laminating direction, only the piezoelectric active region which is a region where all the internal electrode portions are polymerized and at least a part of the internal electrode portions are polymerized. Or it has a piezoelectric inactive area | region which is an area | region which does not superpose at all, and it is preferable that the said slit groove part is formed in the said piezoelectric inactive area | region.
Here, the piezoelectric inactive region is a portion where piezoelectric displacement does not occur and is not driven. Therefore, stress (strain) is likely to be concentrated in the piezoelectric inactive region according to the piezoelectric displacement. Therefore, the stress applied to the piezoelectric inactive region can be effectively relieved by forming the slit groove in the piezoelectric inactive region.

The piezoelectric inactive region is preferably a region including the entire outer peripheral surface of the ceramic laminate in consideration of insulation and durability against moisture and the like.
That is, the slit groove portion is formed in an annular shape over the entire outer peripheral surface of the ceramic laminate. Therefore, the stress relaxation effect by the said slit groove part can be exhibited notably.

  When the ratio (W2 / W1) between the groove width W1 of the opening of the slit groove and the groove width W2 at a position of 30 μm outward from the tip of the slit groove is less than 0.05, the slit groove Since the particles of the material constituting the piezoelectric ceramic layer separated in the stacking direction on the inner wall surface of the inner wall are partially columnar and there is a region to be bonded, the flow of the insulating resin into the slit groove may be deteriorated There is. On the other hand, if it exceeds 0.8, the width difference between the opening and the tip of the slit groove becomes small, so that the capillary phenomenon hardly occurs, and the flow of the insulating resin into the slit groove becomes worse. There is a fear.

In addition, it is preferable that the insulating resin includes at least a region facing the side electrode in the slit groove and is disposed in a region wider than the side electrode.
In this case, the side electrode exposed in the slit groove can be covered with the insulating resin. Therefore, migration of the electrode material between the side electrodes can be reliably blocked.
In the case where the internal electrode portion is exposed on the outer peripheral surface other than the pair of side surfaces of the ceramic laminate, the piezoelectric ceramic is also provided between the exposed internal electrode portion and the side electrode. Migration of the electrode material occurs through the surface of the layer and the slit groove. Migration of the electrode material in such a path can also be reliably blocked. The electrode material in this case includes not only the material constituting the side electrode but also the material constituting the internal electrode portion.

Moreover, it is preferable that the said insulating resin is arrange | positioned at the area | region of the width direction both ends of the said pair of side surface of the said ceramic laminated body in the said slit groove part at least.
In this case, similarly to the above, migration of the electrode material between the side electrodes and between the internal electrode portions exposed on the outer peripheral surface of the ceramic laminate and the side electrodes can be reliably prevented.

Further, it is preferable that the insulating resin is filled in all regions in the slit groove portion.
In this case, similarly to the above, migration of the electrode material between the side electrodes and between the internal electrode portions exposed on the outer peripheral surface of the ceramic laminate and the side electrodes can be further prevented.
Further, since the insulating resin is filled in the slit groove portion, it is possible to prevent the particles constituting the piezoelectric ceramic layer and the side electrode from falling off in the slit groove portion.

Moreover, it is preferable that the depth of the said slit groove part is 0.4-0.8 mm (Claim 5).
When the depth of the slit groove is less than 0.4 mm, the stress generated at the tip of the slit groove may exceed the material strength of the multilayer piezoelectric element when the multilayer piezoelectric element is operated. . As a result, a crack is generated from the tip of the slit groove, and there is a high possibility that the insulation is lowered by moisture entering the crack. On the other hand, when the thickness exceeds 0.8 mm, the load generated when the multilayer piezoelectric element is operated is lowered, and the function as an actuator may be lowered.

Moreover, it is preferable that the said slit groove part is formed using the burning-out material burnt down by degreasing | defatting or baking or both the processes (Claim 6).
In this case, in the degreasing and / or baking processes, the burnout material can be burned down to easily form the slit groove.
Further, since the inner wall surface of the slit groove portion becomes a free-fired surface and irregularities in units of microns are formed, a capillary phenomenon easily occurs, and the insulating resin easily flows into the slit groove portion. Further, since the inner wall surface of the slit groove portion is a free-fired surface that is not subjected to machining or the like, it is possible to prevent the particles constituting the piezoelectric ceramic layer from falling off in the slit groove portion.

Note that the degreasing and firing processes here are performed when the ceramic laminate is manufactured in the process of manufacturing the multilayer piezoelectric element. That is, degreasing treatment before firing of the ceramic laminate and firing treatment of the ceramic laminate.
Further, the burned-out material is disposed in advance in the portion where the slit groove portion of the ceramic laminate is to be formed before the degreasing and firing treatments.

In addition, as the burnout material, for example, carbonized organic particles obtained by carbonizing powdery carbon particles, resin particles, powdery organic particles, or the like can be used.
When carbon particles are used as the burned-out material, the slit groove can be formed with good shape accuracy by taking advantage of the characteristics of the carbon particles that the shape change due to heat is small. Moreover, when an acrylic resin is used, it has the characteristic that the influence on degreasing and baking is small.

On the other hand, when the carbonized organic particles are used as the burnout material, the cost for forming the slit groove can be suppressed.
Here, the carbonized organic particles refer to particles that have been carbonized to some extent by removing a part of the water contained in the organic particles to form fine particles with good fluidity and dispersibility.
As the organic particles, for example, particles obtained by pulverizing soybeans and corn, particles obtained by pulverizing a resin material, and the like can be used.

The insulating resin preferably contains any one of urethane, silicone, fluorosilicone, and silicone-modified epoxy as a main component.
In this case, the elastic modulus of the insulating resin is much smaller than the elastic modulus of the multilayer piezoelectric element, and the deformation of the slit groove part due to the operation of the multilayer piezoelectric element is hindered by the insulating resin. Therefore, it is possible to suppress the occurrence of excessive stress in the slit groove portion. In addition, since the thermal stress of the insulating resin itself is reduced, the stress associated with the difference in thermal expansion between the multilayer piezoelectric element and the insulating resin can be reduced.

The insulating resin preferably contains silicone as a main component, and further contains platinum or an organic peroxide or both as a curing agent.
In this case, the curing reaction of the insulating resin can be favorably progressed by the action of platinum as the curing agent and / or the organic peroxide.
In particular, the insulating resin containing an organic peroxide as a curing agent is resistant to catalyst poisons, and can be reliably cured even in dirty application sites that normally cause curing inhibition. In addition, fine grooves such as the slit grooves are difficult to clean inside, and thus the above-described effects can be exhibited particularly effectively.

The multilayer piezoelectric element is preferably used for a piezoelectric actuator for an injector that is a drive source of the injector.
The injector is used under severe conditions of high temperature and high humidity. Therefore, by using the above excellent multilayer piezoelectric element as an actuator, durability and reliability can be improved, and the performance of the entire injector can be improved.

In the second aspect of the invention, it is preferable that in the curing step, the insulating resin is cured while operating the multi-layer piezoelectric element.
In this case, the insulating resin can be easily infiltrated into the slit groove due to the pumping effect by the operation of the multilayer piezoelectric element while the curing reaction of the insulating resin proceeds.

Further, it is preferable that the insulating resin is degassed after the coating step.
In this case, it is possible to reduce gaps and biting air (voids) in the insulating resin. Therefore, the insulating resin can be more easily infiltrated into the slit groove.
In addition, after the said application | coating process includes the said arrangement | positioning process, the said hardening process, before and after those processes.

Moreover, in the said hardening process, it is preferable to harden this insulating resin, vacuum-defoaming the said insulating resin (Claim 13).
In this case, in the curing step, the insulating resin can be cured in a state in which the gaps in the insulating resin and the biting air (voids) are reduced.

Example 1
A laminated piezoelectric element according to an embodiment of the present invention will be described with reference to the drawings.
As shown in FIGS. 1 and 2, the multilayer piezoelectric element 1 of this example includes a ceramic laminate 15 in which a plurality of piezoelectric ceramic layers 11 and a plurality of internal electrode layers 13 and 14 are alternately laminated, and the ceramics. It has a pair of side electrodes 17 and 18 formed on side surfaces 151 and 152 formed on the outer peripheral surface 150 of the laminate 15.

  The internal electrode layers 13, 14 include conductive internal electrode portions 131, 141, and outer portions 132, 142 whose outer peripheral end portions refrain from the outer peripheral surface 150 of the ceramic laminate 15 at a predetermined holding distance. The internal electrode layers 13 and 14 are electrically connected to alternately different side electrodes 17 and 18.

The ceramic laminate 15 has a slit-like slit groove 12 that is recessed inward from the outer peripheral surface 150 at a predetermined depth.
The slit groove portion 12 is formed in the circumferential direction over the entire outer peripheral surface 150 of the ceramic laminate 15 so that the internal electrode portions 131 and 141 are not exposed on the inner wall surface 123 thereof. A plurality of slit grooves 12 are formed at a constant interval in the stacking direction of the ceramic laminate 15. The interval D between the slit groove portions 12 is 0.88 mm.

  Further, as shown in FIG. 3, the slit groove portion 12 has a groove width that gradually decreases inward from the outer peripheral surface 150 of the ceramic laminate 15. When the groove width of the opening 121 of the slit groove 12 is W1, and the groove width at a position of 30 μm outward from the tip 122 of the slit groove 12 is W2, the relationship of W2 / W1 = 0.05 to 0.8 is established. Satisfies. In this example, W1 = 7 μm and W2 = 3 μm. Moreover, the depth D of the slit groove part 12 is 0.6 mm.

  As shown in FIG. 4, an insulating resin 19 having electrical insulation is disposed in the slit groove portion 12 so as to cut off the side electrodes 17 and 18 that are in communication with each other via the slit groove portion 12. ing. In this example, the insulating resin 19 includes regions facing the side electrodes 17 and 18 in the slit groove portion 12 on the side surfaces 151 and 152 of the ceramic laminate 15 and wider than the side electrodes 17 and 18. It is arranged. That is, the insulating resin 19 is disposed so as to cover the side electrodes 17 and 18 exposed in the slit groove 12.

Next, a method for manufacturing the multilayer piezoelectric element of this example will be described with reference to the drawings.
In this example, a green sheet manufacturing process, an electrode printing process, a burned-slit printing process, a crimping process, a laminate cutting process, a firing process, and a process of disposing an insulating resin (application process / arrangement process / curing process) are performed. Thus, a laminated piezoelectric element is manufactured.
Hereinafter, a manufacturing method is demonstrated for every process.

<Green sheet production process>
First, a ceramic raw material powder such as lead zirconate titanate (PZT) serving as a piezoelectric material was prepared. Specifically, Pb ₃ O ₄ , SrCO ₃ , ZrO ₂ , TiO ₂ , Y ₂ O ₃ and Nb ₂ O ₅ are prepared as starting materials, and these starting materials are used as the target composition PbZrO ₃ —PbTiO ₃ —Pb ( Y _1/2 Nb _1/2 ) O ₃ was weighed in a stoichiometric ratio, wet mixed, and calcined at a temperature of 850 ° C. for 5 hours. Next, the calcined powder was wet pulverized by a pearl mill. This calcined powder pulverized product (particle size (D ₅₀ value): 0.7 ± 0.05 μm) is dried, and then a solvent, a binder, a plasticizer, a dispersant, etc. are added and mixed by a ball mill, and the resulting slurry Was degassed and the viscosity was adjusted while stirring with a stirrer in a vacuum apparatus.

And the said slurry was apply | coated on the carrier film with the doctor blade method, and the 80-micrometer-thick green sheet | seat was shape | molded. The green sheet was cut into a predetermined size to produce a wide green sheet 110 (FIGS. 5 to 7).
In addition to the doctor blade method used in this example, an extrusion molding method and various other methods can be employed as the green sheet molding method.

<Electrode printing process>
Next, as shown in FIGS. 5 and 6, electrode materials 130 and 140 that serve as internal electrode layers are printed on the green sheet 110, and two types of sheets, a first electrode print sheet 31 and a second electrode print sheet 32, are printed. Formed.
Below, formation of the electrode printing sheets 31 and 32 is further demonstrated.

In forming the first electrode print sheet 31, as shown in FIG. 5, the electrode material 130 is printed on the print area 41 on the green sheet 110 in a portion that will eventually become the internal electrode layer 13, and the first electrode print sheet 31 is printed. A sheet 31 was formed.
Further, in forming the second electrode print sheet 32, as in the first electrode print sheet, as shown in FIG. 6, the electrode material 140 is applied to the portion to be the internal electrode layer 14 in the print region 41 on the green sheet 110. Printed. Thereby, the 2nd electrode printing sheet 32 was formed.

In the first electrode print sheet 31 and the second electrode print sheet 32, the electrode materials 130 and 140 formed on the green sheet 110 are exposed on different side surfaces.
In this example, paste-like Ag / Pd alloys were used as the electrode materials 130 and 140. In addition to the above, simple substances such as Ag, Pd, Cu, and Ni, and alloys such as Cu / Ni can be used.

<Burned slit printing process>
Moreover, in this example, since the slit groove part 12 (refer FIGS. 1-4) is provided in the side surface of the ceramic laminated body 15 of the multilayer piezoelectric element 1 to be manufactured, as shown in FIG. The burned-out slit printing process to form was performed.

As shown in the figure, in the printing region 41 on the green sheet 110, a burned-out slit layer 120 made of a burned-out material burned out by baking was printed on a portion that finally becomes the slit groove portion 12. Thereby, the burned-out slit printing sheet 33 was formed.
At this time, as shown in FIG. 8, the burned slit layer 120 after printing is formed on the burned slit layer 120 so that (W2 / W1) becomes a predetermined ratio when the burned slit layer 120 is finally burned to form the slit groove portion 12. Leveling was performed so that the end surface on the inner peripheral side had a gentle ridgeline shape.

  In this example, as the burnt-out material constituting the burnt-out slit layer 120, a material made of carbon particles that is small in thermal deformation and can maintain high shape accuracy of the groove formed by the firing process is used. In addition to carbon particles, carbonized powdery carbonized organic particles can also be used. The carbonized organic particles can be obtained by carbonizing powdery organic particles, or by pulverizing the carbonized organic material. Furthermore, as the organic substance, a polymer material such as an acrylic resin, and grains such as corn, soybean, and wheat flour can be used. In this case, the manufacturing cost can be suppressed. Further, the slit can be formed by machining after firing the piezoelectric element.

  In the electrode printing process and the burnout slit printing process, as shown in FIGS. 5 to 7, the electrode material 130, 140, and the burnout are formed by leaving a gap 42 so as to avoid a portion to be cut in the subsequent laminate cutting process. The slit layer 120 is printed. That is, printing is performed by providing a gap 42 between adjacent print areas 41 on the green sheet 110.

<Crimping process>
Next, as shown in FIG. 9, the formed first electrode print sheet 31, second electrode print sheet 32, and burnt-slit print sheet 33 were laminated in a predetermined order with the printing regions 41 aligned in the lamination direction. At this time, the 1st electrode printing sheet 31 and the 2nd electrode printing sheet 32 were laminated | stacked alternately, and the burning-out slit printing sheet 33 was inserted and laminated | stacked in the position which wants to form the slit groove part 12. FIG.

  Specifically, in this example, the burnout slit printing sheet 33 is laminated every 11 layers of the laminated structure of the first electrode printing sheet 31 and the second electrode printing sheet 32, and the first electrode printing sheet 31 and the second electrode are laminated. A total of 59 print sheets 32 were stacked, and green sheets on which no electrode material and burned-out layer were printed were stacked on both ends in the stacking direction. And the 1st electrode printing sheet 31 and the 2nd electrode printing sheet 32 were laminated | stacked so that the electrode material 130 and the electrode material 140 might be exposed to the opposing end surface of a printing area | region alternately.

The sheets laminated in this way were heated at a temperature of 100 ° C. and pressed at 50 MPa in the laminating direction to produce a pre-laminated body 100.
In FIG. 9, the preliminary laminated body 100 is shown in a form in which the actual number of laminated layers is omitted for convenience of drawing.

<Laminate cutting process>
Next, as shown in FIGS. 10 to 12, the formed preliminary laminate 100 was cut in the stacking direction along the cutting position 43 to form the intermediate laminate 10.
The preliminary laminated body 100 may be cut for each intermediate laminated body 10 or may be cut including a plurality of intermediate laminated bodies 10. In this example, each of the intermediate laminates 10 was cut and cut so that the electrode materials 130 and 140 and the burned slit layer 120 were exposed on the side surfaces of the intermediate laminate 10.
In FIGS. 11 and 12, the preliminary laminated body 100 and the intermediate laminated body 10 are shown in a form in which the actual number of laminated layers is omitted for convenience of drawing.

<Baking process>
Next, 90% or more of the binder resin contained in the green sheet 110 of the intermediate laminate 10 was removed by heating (degreasing). Heating was performed by gradually raising the temperature to 500 ° C. over 80 hours and holding for 5 hours.
Next, the degreased intermediate laminate 10 was fired. Firing was performed by gradually raising the temperature to 1050 ° C. over 12 hours, holding for 2 hours, and then gradually cooling.

In this manner, as shown in FIGS. 1 and 2, the ceramic laminate 15 having the slit-like slit groove portion 12 formed by burning out the burned slit layer 120 is produced. The slit groove 12 is provided with a slit-like space over the entire outer peripheral surface 150 of the ceramic laminate 15.
Further, as shown in the figure, the produced ceramic laminate 15 includes piezoelectric ceramic layers 10 formed by sintering green sheets 110 and internal electrode layers 13 and 14 formed by electrode materials 130 and 140 alternately. Laminated.

Next, after firing, the four corners of the ceramic laminate 15 were chamfered to form chamfered surfaces 161-164. Thereby, the radial direction cross section of the ceramic laminated body 15 becomes octagonal shape.
Then, the entire surface was polished to produce a ceramic laminate 15 having a length of 6 mm, a width of 6 mm, and a height of 4.8 mm, and side electrodes 17 and 18 were baked on the side surfaces 151 and 152 of the ceramic laminate 15. At this time, the internal electrode layers 13 and 14 are electrically connected to the side electrodes 17 and 18 of the different side surfaces 151 and 152, respectively.
Thereafter, lead wires or mesh electrode plates were connected to the side electrodes 17 and 18 with a conductive resin or solder (not shown).
Thereby, the multilayer piezoelectric element 1 before the insulating resin 19 was provided was produced.

Furthermore, in this example, as shown in FIG. 4, by performing a process of disposing the insulating resin 19 (application process / arrangement process / curing process), a desired inside of the slit groove 12 of the multilayer piezoelectric element 1 is obtained. An insulating resin 19 is disposed in the region.
This will be described below.

<Application process>
In this example, first, the insulating resin 19 was applied to the opening 121 of the slit groove 12 in the outer peripheral surface 150 of the ceramic laminate 15 with a dispenser or the like.

<Installation process>
Next, the multilayer piezoelectric element 1 was operated at a predetermined voltage. As a result, expansion and contraction in the stacking direction is performed, and as shown in FIG. 13, the slit groove portion 12 opens by about 0.5 μm in the stacking direction when dotted (dotted line portion). By repeating this expansion and contraction, the volume in the slit groove 12 was increased and decreased, and the insulating resin 19 was infiltrated into the slit groove 12 by the pumping effect. Then, an insulating resin 19 is disposed in a desired region in the slit groove 12. In this arrangement step, the insulating resin 19 was vacuum degassed.

<Curing process>
Next, the disposed insulating resin 19 was cured by heating. In this curing step, the multilayer piezoelectric element 1 was operated while continuing from the placement step.

  In this example, a thermosetting silicone resin was used as the insulating resin 19. In addition to the above, a highly heat-resistant urethane resin, fluorosilicone resin, or the like can be used.

As described above, the multilayer piezoelectric element 1 was manufactured as shown in FIGS.
In FIG. 1 and FIG. 2, the ceramic laminate 15 is shown in a form in which the actual number of layers is omitted for the convenience of drawing.

Next, functions and effects of the multilayer piezoelectric element 1 of this example will be described.
In the multilayer piezoelectric element 1 of the present example, the ceramic multilayer body 15 has a slit-shaped slit groove portion 12 that is recessed inward from the outer peripheral surface 150 of the ceramic multilayer body 15 at a predetermined depth. The slit groove portion 12 is formed in an annular shape over the entire outer peripheral surface 15 of the ceramic laminate 15 so that the internal electrode portions 131 and 141 are not exposed on the inner wall surface 123 thereof. In the slit groove 12, an insulating resin 19 having electrical insulation is disposed so as to block between the pair of side surface electrodes 17 and 18 that are in communication with each other via the slit groove 12.

That is, the pair of side electrodes 17 and 18 are exposed in the slit groove 12, and the exposed side electrodes 17 and 18 are in communication with each other via the slit groove 12. This communication state is blocked by an insulating resin 19 disposed in the slit groove 12.
Therefore, as shown in FIG. 14, the material (electrode material) constituting the side electrodes 17 and 18 moves through the slit groove portion 12 and reaches the other side electrodes 17 and 18 (migration in the path K1). This can be prevented by the insulating resin 19 (see FIG. 4) disposed in the groove 12. That is, the migration of the electrode material between the side surface electrodes 17 and 18 (path K1) can be blocked, and the occurrence of problems such as a decrease in insulation and a short circuit can be prevented. Thereby, sufficient insulation can be ensured, and durability and reliability can be improved. FIG. 14 shows the migration path of the electrode material.

Further, the slit groove 12 has a groove width that gradually decreases inward from the outer peripheral surface 150 of the ceramic laminate 15, the groove width of the opening 121 of the slit groove 12 is W 1, and the tip 122 of the slit groove 12. When the groove width at a position of 30 μm outward is W2, the relationship of W2 / W1 = 0.05 to 0.8 is satisfied.
By making the slit groove part 12 into the above-mentioned shape, the insulating resin 19 can easily flow into the slit groove part 12. Therefore, the insulating resin 19 can be easily disposed in the slit groove portion 12.

  Further, in this example, the insulating resin 19 includes a region facing the side electrodes 17 and 18 in the slit groove 12 and is disposed in a region wider than the side electrodes 17 and 18. Therefore, the side electrodes 17 and 18 exposed in the slit groove 12 can be covered with the insulating resin 19. Thereby, migration of the electrode material between the side electrodes 17 and 18 (path | route K1) can be interrupted | blocked reliably.

  Further, the ceramic laminate 15 of this example has a configuration in which only the internal electrode portion 141 is exposed on the outer peripheral surface 150 other than the side surfaces 151 and 152. Therefore, as shown in FIG. 14, migration of the electrode material occurs between the exposed internal electrode portion 141 and the side electrode 17 via the surface of the piezoelectric ceramic layer 11 and the slit groove portion 12 (migration in the path K2). However, in this example, the migration of the electrode material in such a path can also be reliably blocked by the insulating resin 19 (see FIG. 4) disposed in the slit groove portion 12. The electrode material in this case includes not only the material constituting the side electrode 17 but also the material constituting the internal electrode portion 141.

  In the manufacturing method of this example, when the insulating resin 19 is disposed in the slit groove portion 12, an application process, an arrangement process, and a curing process are performed. In the disposing step, the multilayer piezoelectric element 1 is operated to infiltrate the insulating resin 19 into the slit groove 12 and dispose the insulating resin 19 in a desired region in the slit groove 12. Therefore, the insulating resin 19 can be easily infiltrated into the slit groove portion 12 by the pumping effect obtained by operating the multilayer piezoelectric element 1. Thereby, the insulating resin 19 can be easily and reliably disposed in a desired region in the slit groove portion 12.

  In this example, the insulating resin 19 is degassed after the coating process, that is, in the disposing process. Therefore, the clearance in the insulating resin 19 and the biting air (void) can be reduced. Thereby, the insulating resin 19 can be more easily infiltrated into the slit groove portion 12.

  In the curing step, the insulating resin 19 is cured while operating the multilayer piezoelectric element 1. Therefore, the insulating resin 19 can be easily infiltrated into the slit groove portion 12 by the pumping effect caused by the operation of the multilayer piezoelectric element 1 while the curing reaction of the insulating resin 19 proceeds.

  Thus, the multilayer piezoelectric element 1 of the present example can prevent problems such as a decrease in insulation and a short circuit due to migration of the electrode material through the slit groove 12. The insulating resin 19 can be easily disposed in the slit groove portion 12.

Further, in this example, the slit groove portion 12 is a portion in the ceramic laminate 15 in which the crystal particles constituting the piezoelectric ceramic layer 11 are separated in the lamination direction, and the shape can be changed more easily than the piezoelectric ceramic layer 11. The stress accumulated in the stacking direction of the ceramic laminate 15 can be effectively relaxed.
Moreover, although the slit groove part 12 was provided with two or more with the fixed space | interval in the lamination direction of the ceramic laminated body 15, it can also be provided in various positions other than this.

Moreover, although the internal electrode parts 131 and 141 and the slit groove part 12 were formed in the pattern of the combination shown in FIG. 15, it is not limited to this pattern.
Further, as shown in FIGS. 2 and 16, when the ceramic laminate 15 is seen through in the laminating direction, the piezoelectric active region 158, which is a region where all the internal electrode portions 131 and 141 are superposed, and at least a part of the interior thereof. It has a piezoelectric inactive region 159 that is a region where only the electrode portions 131 and 141 are polymerized or not polymerized at all.

As shown in FIG. 2, the slit groove portion 12 is formed in the piezoelectric inactive region 159. Therefore, the stress applied to the piezoelectric inactive region 159 can be effectively relieved by the slit groove portion 12.
Further, as shown in FIGS. 2 and 16, the piezoelectric inactive region 159 is a region including the entire outer peripheral surface 150 of the ceramic laminate 15. Since the slit groove 12 is also formed in an annular shape over the entire outer peripheral surface 150 of the ceramic laminate 15, the stress relaxation effect by the slit groove 12 can be remarkably exhibited.

(Example 2)
In this example, the arrangement position of the insulating resin 19 in the slit groove 12 is changed.
In this example, as shown in FIG. 17, the insulating resin 19 is disposed in a region near both ends in the width direction of the pair of side surfaces 151 and 152 of the ceramic laminate 15 in the slit groove 12. In this example, the insulating resin 19 is filled from the opening 121 to the tip 122 of the slit groove 12 in four regions facing the chamfered surfaces 161 to 164 in the slit groove 12.
Other configurations are the same as those in the first embodiment.

In this case, migration of the electrode material between the side electrodes 17 and 18 (path K1) and between the internal electrode portion 141 exposed on the outer peripheral surface 150 of the ceramic laminate 15 and the side electrode 17 (path K2) is ensured. Can be prevented.
The other functions and effects are the same as those of the first embodiment.

  Further, in this example, the insulating resin 19 is disposed in the four regions facing the chamfered surfaces 161 to 164 in the slit groove portion 12, but as shown in FIG. 18, in addition to this, the region facing the side electrodes 17, 18 In this case, the insulating resin 19 may be disposed. Also in this case, the same effect as described above can be obtained.

(Example 3)
In this example, the arrangement position of the insulating resin 19 in the slit groove 12 is changed.
In this example, as shown in FIGS. 19A and 19B, the insulating resin 19 is filled in all regions in the slit groove portion 12. In this example, the insulating resin 19 is filled from the opening 121 to the tip 122 of the slit groove 12 in all regions in the slit groove 12.
Other configurations are the same as those in the first embodiment.

In this case, the migration of the electrode material between the side electrodes 17 and 18 (path K1) and between the internal electrode portion 141 exposed on the outer peripheral surface 150 of the ceramic laminate 15 and the side electrode 17 (path K2) is further increased. Can be prevented.
In addition, since the slit groove 12 is filled with the insulating resin 19, the particles constituting the piezoelectric ceramic layer 11 and the side electrodes 17 and 18 in the slit groove 12 can be prevented from falling off.
The other functions and effects are the same as those of the first embodiment.

Example 4
In this example, the filling property of the insulating resin and the durability of the multilayer piezoelectric element are evaluated.
First, the filling property of the insulating resin was evaluated.
In this example, as shown in FIG. 3, the ratio (W2 / W1) = 0.43 of the groove width W1 of the opening of the slit groove and the groove width W2 at a position of 30 μm outward from the tip of the slit groove. A certain laminated piezoelectric element (samples E11 and E12) was prepared, and a laminated piezoelectric element (sample C11) in which (W2 / W1) = 0.98 was prepared as a comparative product.

Next, an insulating resin was applied to the opening of the slit groove with a dispenser or the like on the multilayer piezoelectric element of each sample. And about the sample E12, insulating resin was infiltrated in the slit groove part, operating a laminated piezoelectric element with a predetermined voltage.
Subsequently, the cross section was cut in the lamination direction of the ceramic laminate, and the degree of filling of the insulating resin into the slit groove was visually confirmed.

  The results are shown in Table 1. As shown in the table, in the sample C11 which is a comparative product, an unwet portion at the tip 122 of the slit groove 12 was confirmed. On the other hand, the samples E11 and E12 which are the products of the present invention were firmly filled from the opening 121 to the tip 122. As a result, it was found that the multilayer piezoelectric element of the present invention was excellent in the filling property of the insulating resin.

Next, the durability of the multilayer piezoelectric element was evaluated.
In this example, the laminated piezoelectric element (Sample E21) of Example 1 and the laminated piezoelectric element (Sample E22) of Example 3 were prepared, and a laminated product in which no insulating resin was disposed in the slit groove as a comparative product. Type piezoelectric element (sample C21) was prepared.

  Next, an electric field of 2.6 kV / mm was applied to the laminated piezoelectric element of each sample under the condition of 85 ° C./90% RH. Next, each sample was connected in series to a resistor R having a known resistance value to construct a circuit. And the voltage (leakage current value) concerning resistance R was read with the digital meter, applying an electric field to each sample. The case where the calculated insulation resistance of the element (sample) was less than 10 MΩ was regarded as the life of the element, and the time at that time was measured.

  The results are shown in Table 2. As shown in the table, the sample C21, which is a comparative product, did not reach a lifetime of 500 hours. On the other hand, samples E21 and E22, which are products of the present invention, have a lifetime exceeding 1000 hours. Thereby, it was found that the multilayer piezoelectric element of the present invention was excellent in durability and reliability.

(Example 5)
In this example, the multilayer piezoelectric element 1 of Examples 1 to 3 is used as an injector 6.
As shown in FIG. 20, the injector 6 of this example is applied to a common rail injection system of a diesel engine.
As shown in the figure, the injector 6 has an upper housing 62 in which the multilayer piezoelectric element 1 as a drive unit is accommodated, and a lower housing 63 that is fixed to the lower end and in which an injection nozzle portion 64 is formed. is doing.

The upper housing 62 is substantially cylindrical, and the laminated piezoelectric element 1 is inserted and fixed in a vertical hole 621 that is eccentric with respect to the central axis.
A high-pressure fuel passage 622 is provided in parallel to the side of the vertical hole 621, and an upper end portion thereof communicates with an external common rail (not shown) through a fuel introduction pipe 623 protruding to the upper side of the upper housing 62. .

A fuel lead-out pipe 625 communicating with the drain passage 624 protrudes from the upper portion of the upper housing 62, and the fuel flowing out from the fuel lead-out pipe 625 is returned to a fuel tank (not shown).
The drain passage 624 passes through a gap 60 between the vertical hole 621 and the piezoelectric actuator 1 serving as a drive unit, and further, a three-way valve, which will be described later, by a passage (not shown) extending downward from the gap 60 in the upper and lower housings 62 and 63. It communicates with 651.

  The injection nozzle section 64 has a nozzle needle 641 that slides in the vertical direction in the piston body 631, and an injection hole 643 that is opened and closed by the nozzle needle 641 and injects high-pressure fuel supplied from a fuel reservoir 642 into each cylinder of the engine. I have. The fuel reservoir 642 is provided around the middle portion of the nozzle needle 641, and the lower end portion of the high-pressure fuel passage 622 is opened here. The nozzle needle 641 receives the fuel pressure in the valve opening direction from the fuel reservoir 642 and receives the fuel pressure in the valve closing direction from the back pressure chamber 644 provided facing the upper end surface, and the pressure in the back pressure chamber 644 is reduced. When lowered, the nozzle needle 641 is lifted, the nozzle hole 643 is opened, and fuel is injected.

  The pressure in the back pressure chamber 644 is increased or decreased by the three-way valve 651. The three-way valve 651 is configured to selectively communicate with the back pressure chamber 644 and the high pressure fuel passage 622 or the drain passage 624. Here, a ball-shaped valve body that opens and closes a port communicating with the high-pressure fuel passage 622 or the drain passage 624 is provided. The valve body is driven by the drive unit 1 through a large-diameter piston 652, a hydraulic chamber 653, and a small-diameter piston 654 disposed below the valve body.

  In this example, the multilayer piezoelectric element 1 of the first to third embodiments is used as a drive source in the injector 6 having the above-described configuration. As described above, the multilayer piezoelectric element 1 has excellent durability and reliability. Therefore, the performance of the injector 6 as a whole can be improved.

FIG. 3 is an explanatory diagram showing a structure of a multilayer piezoelectric element in Example 1. FIG. 3 is a cross-sectional view of a multilayer piezoelectric element in Example 1. FIG. 3 is an explanatory diagram illustrating a cross-sectional structure of a slit groove portion in the first embodiment. Sectional drawing which shows the AA cross section of FIG. Explanatory drawing which shows the process of forming the 1st electrode printing sheet in Example 1. FIG. Explanatory drawing which shows the process of forming the 2nd electrode printing sheet in Example 1. FIG. Explanatory drawing which shows the process of forming a burning-out slit printing sheet in Example 1. FIG. Sectional drawing which shows the BB cross section of FIG. Explanatory drawing which shows the process of laminating | stacking the electrode printing sheet and the burning-slit printing sheet in Example 1. FIG. FIG. 3 is a top view of a pre-laminated body in Example 1. Sectional drawing of the preliminary | backup laminated body in Example 1. FIG. FIG. 3 is an explanatory diagram showing a cross-sectional structure of an intermediate laminate in Example 1. FIG. 3 is an explanatory diagram illustrating a cross-sectional structure of a slit groove portion when the multilayer piezoelectric element is extended by an operation of the multilayer piezoelectric element in the first embodiment. FIG. 3 is an explanatory diagram illustrating a migration path through a slit groove in the first embodiment. FIG. 3 is a development explanatory view of a ceramic laminate showing a formation pattern of internal electrode portions and slit groove portions in Example 1. FIG. 3 is an explanatory diagram showing the arrangement position of the internal electrode portion when the ceramic laminated body is seen through in the lamination direction in Example 1. Sectional drawing of the slit groove part which shows the arrangement | positioning position of insulating resin in Example 2. FIG. Sectional drawing of the slit groove part which shows the arrangement | positioning position of insulating resin in Example 2. FIG. Sectional drawing of the slit groove part which shows the arrangement | positioning position of insulating resin in Example 3. FIG. Explanatory drawing which shows the structure of the injector in Example 5. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Laminated-type piezoelectric element 11 Piezoelectric ceramic layer 12 Slit groove part 13, 14 Internal electrode layer 131, 141 Internal electrode part 132, 142 Retaining part 15 Ceramic laminated body 150 Outer peripheral surface 17, 18 Side electrode 19 Insulating resin

Claims (13)

It has a ceramic laminate formed by alternately laminating a plurality of piezoelectric ceramic layers and a plurality of internal electrode layers, and a pair of side electrodes provided respectively on a pair of side surfaces formed on the outer peripheral surface of the ceramic laminate. In laminated piezoelectric elements,
The internal electrode layer has a conductive internal electrode portion, and a holding portion in which an outer peripheral end portion of the internal electrode portion is kept at a predetermined distance inward from an outer peripheral surface of the ceramic laminate, In the internal electrode portion, alternately connected to any one of the side electrodes,
The ceramic laminate has a slit-shaped slit groove that is recessed inward from the outer peripheral surface of the ceramic laminate at a predetermined depth,
The slit groove portion is formed in an annular shape over the entire outer peripheral surface of the ceramic laminate so that the internal electrode portion is not exposed on the inner wall surface, and is directed inward from the outer peripheral surface of the ceramic laminate. When the groove width of the opening of the slit groove portion is W1, and the groove width at a position of 30 μm outward from the tip of the slit groove portion is W2, W2 / W1 = 0. Satisfies the relationship of .05 to 0.8,
In the slit groove part, an insulating resin having an electrical insulating property is disposed so as to cut off the pair of side electrodes that are in communication with each other through the slit groove part. Piezoelectric element.   2. The laminated piezoelectric material according to claim 1, wherein the insulating resin includes at least a region facing the side electrode in the slit groove and is disposed in a region wider than the side electrode. element.   2. The multilayer piezoelectric element according to claim 1, wherein the insulating resin is disposed at least in a region near both ends in the width direction of the pair of side surfaces of the ceramic laminate in the slit groove.   The multilayer piezoelectric element according to claim 1, wherein the insulating resin is filled in all regions in the slit groove portion.   5. The multilayer piezoelectric element according to claim 1, wherein the slit groove has a depth of 0.4 to 0.8 mm.   The multilayer piezoelectric element according to any one of claims 1 to 5, wherein the slit groove portion is formed using a burnt-out material that is burned down by degreasing and / or baking or both treatments.   7. The multilayer piezoelectric element according to claim 1, wherein the insulating resin contains any one of urethane, silicone, fluorosilicone, and silicone-modified epoxy as a main component.   8. The multilayer piezoelectric element according to claim 7, wherein the insulating resin contains silicone as a main component, and further contains platinum, an organic peroxide, or both as a curing agent.   9. The multilayer piezoelectric element according to claim 1, wherein the multilayer piezoelectric element is used for a piezoelectric actuator for an injector that is a drive source of the injector. In the method for manufacturing the multilayer piezoelectric element according to any one of claims 1 to 9,
In disposing the insulating resin in the slit groove, an application step of applying the insulating resin to the opening of the slit groove on the outer peripheral surface of the ceramic laminate,
An operation step of operating the multi-layer piezoelectric element to infiltrate the insulating resin into the slit groove and disposing the insulating resin in a desired region within the slit groove;
A method for producing a laminated piezoelectric element, comprising: a curing step for curing the insulating resin.   11. The method of manufacturing a multilayer piezoelectric element according to claim 10, wherein in the curing step, the insulating resin is cured while operating the multilayer piezoelectric element.   12. The method for manufacturing a multilayer piezoelectric element according to claim 10, wherein the insulating resin is vacuum degassed after the coating step.   13. The method for manufacturing a multilayer piezoelectric element according to claim 12, wherein in the curing step, the insulating resin is cured while vacuum degassing the insulating resin.

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