JP2005039199A - Unit type laminated piezoelectric element and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a unit type laminated piezoelectric element having piezoelectric units laminated and bonded with an adhesive agent and a small displacement loss, and its manufacturing method. <P>SOLUTION: A plurality of piezoelectric units 2 that are formed by alternately laminating a piezoelectric layer 21 and inner electrode layers 211 and 212 are laminated and bonded by using an adhesive agent 11. The adhesive agent 11 bonding the piezoelectric units 2 exist in the outer periphery region on the adhesive face 25, and does not exist in the internal region including the centroidal position G of the adhesive face 25. Moreover, a method of manufacturing a unit type laminated piezoelectric element 1 is: manufacturing a piezoelectric unit 2; manufacturing a laminate in which a plurality of piezoelectric units 2 are laminated; applying the adhesive agent 11 to the boundary of lamination of the piezoelectric units 2 exposed onto the side of the laminate; and introducing the adhesive agent 11 between each of the piezoelectric units 2 in such a manner that the adhesive agent 11 exists in the outer periphery region on the adhesive face 25 of the piezoelectric unit 2 for integration. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a unit type laminated piezoelectric element that can be used as a drive source for an injector for fuel injection of an internal combustion engine and a method for manufacturing the same.

  As a drive source of a fuel injection injector for a vehicle engine or the like, a unit type stacked piezoelectric element in which a desired number of piezoelectric units in which piezoelectric layers and internal electrode layers are alternately stacked may be used. . The unit type laminated piezoelectric element has a low operating stress and can obtain a high displacement, and therefore is suitable for an injector drive source.

However, there is a problem that a large displacement loss occurs in the unit type laminated piezoelectric element having the conventional configuration.
That is, in the unit type laminated piezoelectric element, each piezoelectric unit is laminated and bonded using an adhesive, and this adhesive causes a displacement loss.
More specifically, both end surfaces in the stacking direction of the piezoelectric unit face the piezoelectric units adjacent to each other. Accordingly, the end surfaces in the stacking direction of the piezoelectric units become adhesive surfaces and face the adhesive surfaces of other piezoelectric units.
When laminating and bonding piezoelectric units, apply adhesive to one or both of the bonding surfaces, stack the piezoelectric units, apply a load from both end surfaces in the stacking direction of the stacked piezoelectric units using clamps, etc. Are laminated and integrated.
By receiving a load from the stacking direction by a clamp or the like, the adhesive spreads over the entire bonding surface. Even if the piezoelectric units are stacked without covering the entire surface of the adhesive surface with an adhesive, the result is often a state where the entire surface is not applied with adhesive.

By the way, a partial electrode configuration type and a full-surface electrode configuration type are known as laminated piezoelectric elements. In both types, the vicinity of the center of the bonding surface serves as a drive unit in which the piezoelectric layer expands when a voltage is applied from the internal electrode layer to the piezoelectric layer. And when the said adhesive agent exists in the adhesive surface concerning a drive part, the adhesive agent which does not expand | extend at the time of electricity supply will absorb the expansion | extension of a piezoelectric layer, and will cause a displacement loss.
If the actual displacement is smaller than the amount of displacement predicted from the results of considering the material for forming the piezoelectric layer, the applied voltage, the thickness of the piezoelectric layer and the number of piezoelectric layers constituting the multilayer piezoelectric element, etc. This difference is called displacement loss.

In order to reduce the displacement loss, it is desirable that no adhesive is present between the piezoelectric units. As a method of stacking piezoelectric units that do not use an adhesive, a method of stacking piezoelectric units and fixing them from the outside is known.
However, the method of fixing from the outside is very difficult to prevent the displacement of the piezoelectric unit, and it is preferable to directly laminate and bond the piezoelectric unit with an adhesive from the viewpoint of manufacturing efficiency for quickly stacking and bonding the piezoelectric unit. .

JP 05-218519 A

  The present invention has been made in view of such conventional problems, and is intended to provide a unit-type laminated piezoelectric element having a small displacement loss and a method for manufacturing the same, by laminating and bonding piezoelectric units with an adhesive. is there.

A first aspect of the present invention is a unit-type laminated piezoelectric element formed by laminating and bonding a plurality of piezoelectric units formed by alternately laminating piezoelectric layers and internal electrode layers using an adhesive.
The unit type laminated piezoelectric material, wherein the adhesive for bonding the piezoelectric units is present in an outer peripheral region on the bonding surface of the piezoelectric units, and is not present in an inner region including the gravity center position G of the bonding surface. It exists in an element (Claim 1).

The unit type laminated piezoelectric element according to the first aspect of the present invention provides an adhesive only in the outer peripheral area, leaving the center of gravity of the adhesive surface and its periphery when the piezoelectric unit is adhesively laminated using an adhesive. It has a bonded configuration.
By the way, a partial electrode configuration type and a full-surface electrode configuration type are known as laminated piezoelectric elements. In both types, the vicinity of the center of the bonding surface serves as a drive unit in which the piezoelectric layer expands when a voltage is applied from the internal electrode layer to the piezoelectric layer. And when the said adhesive agent exists in the adhesion surface concerning a drive part, the adhesive agent which does not expand | extend at the time of electricity supply will absorb the expansion | extension of a piezoelectric layer, and will cause a displacement loss.

In the configuration according to the first aspect of the present invention, the adhesive existing in the drive unit is reduced as compared with the prior art, and therefore the displacement loss of the unit type laminated piezoelectric element can be reduced.
Moreover, since only the outer peripheral region is laminated and bonded with an adhesive, positional displacement of the piezoelectric unit is difficult to occur.
This positional deviation mainly occurs in the direction orthogonal to the direction in which the piezoelectric units are stacked. This is a so-called stacking misalignment.

In the second invention, a plurality of piezoelectric units formed by alternately laminating piezoelectric layers and internal electrode layers are bonded using an adhesive, and the adhesive for bonding the piezoelectric units is In manufacturing a unit type laminated piezoelectric element that exists in the outer peripheral region of the bonding surface of the piezoelectric unit and does not exist in the inner region including the gravity center position G of the bonding surface,
A piezoelectric unit is produced by alternately laminating the piezoelectric layers and the internal electrode layers,
A laminate in which a plurality of the above piezoelectric units are laminated is produced,
By applying an adhesive to the stack boundary of the piezoelectric units exposed on the side surfaces of the laminate, the adhesive is introduced between the piezoelectric units so that the adhesive exists in the outer peripheral area of the adhesive surface of each piezoelectric unit. And a unit type laminated piezoelectric element manufacturing method characterized in that they are integrated (claim 10).

According to a second aspect of the present invention, when a unit-type laminated piezoelectric element is manufactured, a laminated body is produced by laminating piezoelectric units without previously applying an adhesive to the adhesive surface, and then exposed on the side surface of the laminated body. An adhesive is applied to the boundary between the stacked piezoelectric units. Then, this adhesive is introduced by soaking in the piezoelectric units from the above-mentioned lamination boundary, and the adhesive is applied to the outer peripheral region of the adhesive surface.
According to this method, the adhesive can be easily applied to the outer peripheral region of the bonding surface.
Displacement loss of the unit type laminated piezoelectric element can be reduced by providing an adhesive only in the outer peripheral region and bonding the piezoelectric unit. Further, by performing the laminating and bonding with the adhesive even in only the outer peripheral region, the positional deviation of the piezoelectric unit is hardly generated, and the piezoelectric unit can be easily laminated, so that the manufacturing efficiency is improved.
The adhesive is preferably applied over the entire circumference of the stacking boundary of the piezoelectric units, but it is also possible to apply only a portion of the entire circumference.

  As described above, according to the present invention, it is possible to provide a unit-type laminated piezoelectric element having a small displacement loss and a method for manufacturing the same while laminating and bonding piezoelectric units with an adhesive.

In general, the multilayer piezoelectric element has a cross-sectional shape of the piezoelectric layer and a cross-sectional shape of the internal electrode layer that are substantially the same, and the internal electrode layer is exposed on the side surface. There are partial electrode types in which the cross-sectional shape of the layers is small, and only some of the internal electrode layers are exposed on the side surfaces, but the first and second inventions can be applied to both types. In addition, the said cross-sectional shape is a cross-sectional shape at the time of cut | disconnecting in the direction substantially orthogonal to the lamination direction.
In the first and second inventions, a piezoelectric layer having a cross-sectional shape that is formed by chamfering a corner such as a square, a rectangle, a square, a barrel, a square or a rectangle can be used.
The shape of the internal electrode layer is not particularly limited, and the first and second inventions can be applied.

Moreover, in the unit type laminated piezoelectric element, when a voltage is applied from the internal electrode layer, the drive unit expands,
If the straight line passing through the center of gravity G on the bonding surface is X, the length of the internal region along the straight line X is L, and the length of the drive unit along the straight line X on the bonding surface is L0. It is preferable that / 4 ≦ L (claim 5).
Further, it is more preferable that L0 / 2 ≦ L, where L is the length of the internal region along the straight line X and L0 is the length of the drive unit along the straight line X on the bonding surface. ).

Here, an arbitrary straight line X passing through the center of gravity position G on the bonding surface is assumed. By establishing the above relationship with respect to any of the straight lines X, the effects of the present invention can be obtained with certainty, and a unit type laminated piezoelectric element with a small displacement loss can be obtained.
If L0 / 4> L, the displacement loss may increase.

Moreover, it is preferable that the outer peripheral area | region which provides an adhesive agent in the said adhesive surface corresponds with the place which does not become a drive part in a unit type laminated piezoelectric element.
As a result, it is possible to obtain a unit-type laminated piezoelectric element in which no adhesive is present in the drive unit, and the displacement loss can be extremely reduced.
When the unit type laminated piezoelectric element is a full surface electrode type, the area occupied by the drive unit is equal to the adhesive surface.

Moreover, in the unit type laminated piezoelectric element, when a voltage is applied from the internal electrode layer, the drive unit expands,
It is preferable that S0 / 16 ≦ S, where S is the area of the internal region and S0 is the area of the drive unit on the bonding surface.
More preferably, S0 / 4 ≦ S, where S is the area of the internal region and S0 is the area of the drive portion on the bonding surface.
Thereby, the effect of the present invention can be obtained with certainty, and a unit type multilayer piezoelectric element with a small displacement loss can be obtained.
If S0 / 16> S, the displacement loss may increase.

  In addition, L0, L, S0, and S are the adhesion surfaces obtained by observing, with an electron microscope, the unit-type laminated piezoelectric element cut and exposed so as to be orthogonal to the lamination direction, or by peeling the piezoelectric unit. Can be measured by observing it with an electron microscope.

In addition, as the adhesive, epoxy type, polyimide type, etc. can be used. In order to follow the displacement without generating a crack with respect to the displacement due to driving of the piezoelectric element, silicone having a particularly low elastic modulus is used. It is preferable to use an adhesive composed of at least one of a system and a urethane system.
Furthermore, since the silicone-based adhesive is excellent in heat resistance, it is possible to obtain a unit type laminated piezoelectric element suitable for an injector application of a vehicle engine (diesel or the like) as shown in the first embodiment.

In the method for manufacturing a unit type laminated piezoelectric element according to the second invention, an adhesive is applied to the lamination boundary of the piezoelectric unit exposed on the side surface, and the adhesive is soaked between the piezoelectric units from the lamination boundary. The adhesive is applied to the outer peripheral area of the adhesive surface, but the adhesive can be naturally absorbed.
That is, the adhesion surface of the piezoelectric unit is generally an uneven surface when enlarged and observed with an electron microscope or the like (see FIG. 11 described later).
For this reason, there is a minute space formed by meshing the concave and convex surfaces at the lamination boundary where the adhesive surface of the piezoelectric unit abuts. Therefore, the adhesive applied to the side surface of the laminate naturally penetrates between the piezoelectric units through capillary action.

This penetration can be controlled by changing the viscosity of the adhesive or by applying an appropriate amount of pressure from both end faces in the stacking direction when the piezoelectric units are stacked, so only the outer peripheral area of the bonding surface The unit type laminated piezoelectric element can be easily manufactured so that the adhesive is present.
Furthermore, after the piezoelectric units are stacked and the adhesive is applied to the side surface, the piezoelectric unit is integrated by curing the adhesive. However, the viscosity of the adhesive may be reduced by heating during curing. In this case, the adhesive enters between the piezoelectric units even during curing.

Moreover, when apply | coating an adhesive agent to a laminated body, it is preferable to carry out in a pressure-reduced environment.
As described above, there is a minute space at the layer boundary where the adhesive surface of the piezoelectric unit abuts. Therefore, when working in a reduced pressure environment, the air contained in the minute space is easily discharged outside the piezoelectric unit. Is smoothly implemented.

Further, by chamfering the corners facing the bonding surface of the piezoelectric unit in advance (see FIG. 14), it is possible to easily introduce the adhesive into the stack boundary.
In addition, the piezoelectric unit is preferably laminated after being subjected to polarization treatment, and an adhesive is applied to the lamination boundary (see FIG. 12).

By applying the polarization treatment, the drive unit extends in the stacking direction, so that the cross-sectional shape of the piezoelectric unit is deformed, and the stack boundary of the piezoelectric unit in the stack is opened (see FIG. 13). Accordingly, it is possible to easily introduce the adhesive into the lamination boundary.
In addition, after the adhesive is applied to the stack boundary of the stacked body, it may wait until the adhesive is introduced between the piezoelectric units, or may be heated before the introduction is completed. The adhesive can also move until it is heated to cure the adhesive.

In the first and second inventions, it is of course possible to use a dedicated adhesive for bonding the piezoelectric unit as the adhesive, but an external electrode material or a molding material is applied as the adhesive. It is preferable. This can streamline the manufacturing process.
That is, in the first invention, an external electrode material that is electrically connected to the internal electrode layer is disposed on a side surface of the multilayer body formed by stacking the piezoelectric units, and A molding material covering the side surface is provided, and the adhesive is preferably made of the external electrode material and / or the molding material.
As shown in the examples to be described later, side electrode materials made of baked silver or the like are provided in advance on the side surfaces of each piezoelectric unit, and then, after the piezoelectric units are laminated, these are arranged on the plurality of side electrode materials. The external electrode material can be applied so as to be connected.

The external electrode material is preferably formed by applying an external electrode material having a viscosity of 0.1 to 200 Pa · S containing a conductive material and a thermosetting resin, followed by heat curing. .
The molding material is preferably formed by applying a molding material containing a thermosetting resin and having a viscosity of 0.1 to 100 Pa · S, followed by heat curing.

  In the second invention as well, after the laminate is manufactured using the external electrode material electrically connected to the internal electrode layer and / or the molding material covering the side surface of the laminate as the adhesive. The external electrode material and the molding material are applied to the side surface of the laminate, and the external electrode material and / or the molding material are soaked between the piezoelectric units, and then the external electrode material and the molding material Is preferably cured by heating (claim 11).

And it is preferable that the said external electrode material is heat-cured, after apply | coating the external electrode material with a viscosity of 0.1-200 Pa * S containing a conductive material and a thermosetting resin (Claim 12).
The mold material is preferably heat-cured after applying a mold material having a viscosity of 0.1 to 100 Pa · S containing a thermosetting resin.

  Here, when using the said external electrode material as an adhesive agent, it is preferable that the viscosity of the external electrode material in the apply | coated state is 0.1-200 Pa * S as mentioned above. Here, when the viscosity of the external electrode material is less than 0.1 Pa · S, there is a problem that the viscosity is too low, causing problems such as dripping at the time of application, and manufacturing workability is lowered. Therefore, 10 Pa · S or more is more preferable. On the other hand, when it exceeds 200 Pa · S, there is a problem that the degree of penetration between the piezoelectric units becomes low. For this reason, 100 Pa · S or less is more preferable.

In addition, as said electrically-conductive material contained in the said external electrode material to apply | coat, a silver filler can be used, for example.
Further, as the thermosetting resin to be contained in the external electrode material, it is preferable to use a resin having a time (gelation time) of 10 seconds to 20 minutes until heating to start thickening due to curing. If the gelation time is too short, there is a problem that penetration between the piezoelectric units is not sufficiently performed. Therefore, more preferably 20 seconds or more. On the other hand, when it exceeds 20 minutes, there exists a problem that a hardening state will become difficult to stabilize.

Moreover, it is preferable to add a low molecular weight polymer or a solvent in the range of 1-10 wt% to the said external electrode material to apply | coat.
Here, when the thermosetting resin is an epoxy, the low molecular weight polymer refers to a reactive diluent. Specifically, for example, n-butyl glycidyl ether, allyl glycidyl ether, 2-ethylhexyl glycidyl ether, ethylene Examples include glycol diglycidyl ether.

  When the thermosetting resin is silicone, the low-molecular polymer refers to a low-molecular siloxane, specifically, for example, diorganosiloxane. Examples of the solvent include alcohols such as ethylene glycol, propylene glycol, benzyl alcohol, and diethylene glycol, or ethers such as anisole, methyl carbitol, and ethyl carbitol, other butyl cellosolves, butyl carbitol acetate, butyl carbitol, and the like. There is.

  Since these have high polarity, they can easily penetrate between the piezoelectric units. Here, when the amount of addition is less than 1 wt%, there is a problem that curing due to addition is not often made. On the other hand, when it exceeds 10 wt%, there is a problem that it may cause voids during heating.

  Moreover, when using the said mold material as an adhesive agent, it is preferable that the viscosity of the mold material in the apply | coated state is 0.1-100 Pa * S. Here, when the viscosity of the molding material is less than 0.1 Pa · S, there is a problem that the viscosity is too low, causing problems such as dripping at the time of application, and manufacturing workability is lowered. Therefore, 5 Pa · S or more is more preferable. On the other hand, when it exceeds 100 Pa · S, there is a problem that the degree of penetration between the piezoelectric units becomes low. Therefore, more preferably, it is 30 Pa · S or less.

  Further, as the thermosetting resin to be contained in the molding material, it is preferable to use a resin having a time (gelation time) of 10 seconds to 20 minutes until heating to start thickening due to curing. If the gelation time is too short, there is a problem that penetration between the piezoelectric units is not sufficiently performed. Therefore, more preferably 20 seconds or more. On the other hand, when it exceeds 20 minutes, there exists a problem that a hardening state will become difficult to stabilize.

  Moreover, it is preferable to add a low molecular weight polymer or a solvent in the range of 1-10 wt% to the said mold material to apply | coat. In this case, the same low molecular polymer or solvent as described above can be applied.

  Moreover, when apply | coating the said adhesive agent with respect to the said lamination | stacking boundary, it is preferable to give a compressive load to the said laminated body from the lamination direction (Claim 14). As a result, the adhesive can be soaked in a state where the piezoelectric units are sufficiently in close contact with each other, so that soaking of the adhesive into the position of the center of gravity of the adhesive surface can be prevented relatively easily.

  Further, it is preferable that the compressive load is continuously applied after the adhesive is applied to the lamination boundary until the adhesive is cured. Thereby, the adhesion effect by an adhesive agent can be heightened.

  Next, in the injector configured to open and close the valve body by using the displacement of the piezoelectric actuator to perform fuel injection control, the piezoelectric actuator is composed of the unit type stacked piezoelectric element of the first invention. There is an injector characterized in that (claim 16).

  The injector uses a piezoelectric actuator composed of the above excellent unit type laminated piezoelectric element. As described above, this piezoelectric actuator has excellent driving characteristics with little displacement loss. Therefore, even an injector equipped with this piezoelectric actuator can exhibit very excellent driving characteristics.

Embodiments of the present invention will be described below with reference to the drawings.
(Example 1)
As shown in FIGS. 1 to 3, the unit-type stacked piezoelectric element 1 according to this example uses an adhesive 11 for a piezoelectric unit 2 in which piezoelectric layers 21 and internal electrode layers 211 and 212 are alternately stacked. A plurality of layers are bonded together.
The adhesive 11 that bonds the piezoelectric units 2 exists in the outer peripheral region 251 of the bonding surface 25 of the piezoelectric unit 2 and does not exist in the inner region 252 including the center of gravity position G of the bonding surface 25.

Details will be described below.
The unit type laminated piezoelectric element 1 according to this example is used as an injector drive source for fuel injection in a diesel engine. The fuel injection pressure is as high as 200 MPa.

  As shown in FIG. 1, the unit type laminated piezoelectric element 1 according to this example is formed of epoxy on the side surfaces 291 and 292 of the laminate in which the piezoelectric units 2 are laminated via the side electrode material 151 made of a mixture of glass and silver. An external electrode material 152 made of a mixture of a resin and a silver filler is joined so as to be electrically connected to the internal electrode layers 211 and 212, and further, a molding material so as to cover the entire outer peripheral surface of the laminate in which the piezoelectric units 2 are laminated. 153 is provided.

As shown in FIG. 1 and FIG. 2, the square piezoelectric layer 21 constituting the piezoelectric unit 2 of this example is provided with an internal electrode layer 212 so that the electrode non-forming portion 210 is located on the right side of the drawing, and on the left side of the drawing. In some cases, the internal electrode layer 211 is provided so that the electrode non-forming portion 210 is positioned, and these are alternately laminated.
Therefore, in the piezoelectric unit 2 of this example, by applying a voltage so that the internal electrode layers 211 and 212 are at different potentials, the two internal electrode layers 211 and 212 as shown in FIG. The sandwiched drive unit 221 extends. The non-driving part 220 sandwiched between the electrode non-forming parts 210 does not expand even when energized.

As shown in FIG. 1, the piezoelectric units 2 are stacked with the adhesive surfaces 25 facing each other. However, as shown in FIG. 3, the outer peripheral region 251 of the adhesive surface 25 has the adhesive 11 and includes the center of gravity G. The inner peripheral region 252 is free of the adhesive 11.
Further, in FIG. 1 according to this example, the adhesive surface 25 of the piezoelectric unit 2 is described so as not to come into contact in order to clearly describe how the adhesive enters, but actually, the adhesive surface 25 as shown in FIG. Since it has an uneven surface, the protrusions may fit into the recesses, or the protrusions may come into contact with each other. In addition, a minute space may be partially formed.

Then, as shown in FIG. 4, a straight line X passing through the center of gravity position G on the bonding surface 25 is considered. The length of the internal region 252 along the straight line X is L, and the length of the drive unit 221 along the straight line X is L0. For any of the straight lines X, L0 / 4 ≦ L is established in the unit type laminated piezoelectric element 1 according to this example.
As shown in FIG. 5, there may be a case where a plurality of independent internal regions 252 are provided.

The unit type laminated piezoelectric element 1 according to this example adheres only to the outer peripheral region 251 while leaving the barycentric position G of the bonding surface 25 and its periphery when the piezoelectric unit 2 is bonded and laminated using the adhesive 11. The agent 11 is provided and adhered.
In the configuration according to this example, the adhesive present in the drive unit 221 is reduced as compared with the prior art, and accordingly, the displacement loss of the unit type multilayer piezoelectric element 1 can be reduced.
In addition, although only the outer peripheral region 251 is laminated and bonded with the adhesive 11, it is difficult for the piezoelectric unit 2 to be misaligned.
As described above, according to this example, it is possible to obtain a unit-type laminated piezoelectric element having a small displacement loss while laminating and bonding piezoelectric units with an adhesive.

  In addition, the unit type laminated piezoelectric element 1 described in this example has a square piezoelectric layer 2, but has a barrel shape as shown in FIGS. 6A and 6B, or FIG. It can also be constituted of a substantially octagonal type piezoelectric layer 21 with square corners cut as shown in FIG. Further, in this example, the piezoelectric unit having a partial electrode configuration has been described, but a full-surface electrode configuration may be used.

(Example 2)
In this example, the performance of the unit type laminated piezoelectric element having the configuration according to Example 1 was evaluated together with a comparative sample.
That is, unit type laminated piezoelectric elements according to samples 1 to 3 are prepared.
As shown in FIG. 8, in the bonding surface 25 according to this example, the adhesive is provided in the outer peripheral region 251, and the inner peripheral region 252 including the gravity center position G has no adhesive. Moreover, the shape of the outer peripheral area | region 251 of this example is a square shape.
The length of the internal region along the straight line X passing through the center of gravity position G on the bonding surface 25 is L, and the length of the drive unit along the straight line X on the bonding surface 25 is L0. Here, the straight line X is drawn so as to pass through the center of the opposite sides of the square piezoelectric layer.

Sample 1 has an epoxy adhesive, and has a drive portion length L0. The length L of the inner region from the center of gravity position G toward the end of the piezoelectric layer on the right side of the drawing is 0.3L0. The length L of the inner region toward the end of the piezoelectric layer is 0.35L0.
In sample 2, the adhesive is epoxy, the length L of the inner region from the center of gravity position G toward the end of the piezoelectric layer on the right side of the drawing is 0.15L0, and from the center of gravity position G to the end of the piezoelectric layer on the left side of the drawing. The length L of the inner region toward it is 0.2L0.
Unlike the sample 2, the sample 3 uses a silicone system as an adhesive, and the length of the inner region is the same as that of the sample 2.

As a reference sample, a laminated piezoelectric element constituted by laminating a piezoelectric layer and an internal electrode layer without using an adhesive was prepared. The amount of displacement was measured when a voltage of 150 V was applied to the reference sample with a preload of 500 N in the stacking direction.
The difference between the amount of displacement applied to the reference sample and the amount of displacement when samples 1 to 3 were displaced under the same conditions was defined as “displacement loss”.
Further, the insulation reliability was evaluated by an endurance test in which voltage was applied to the unit type laminated piezoelectric element according to Samples 1 to 3 and repeated expansion and contraction.

As a result, the displacement loss was 0.1 μm or less for Sample 1, and 0.2 μm for Examples 2 and 3. The insulation reliability was 1000 hours for sample 1, 1500 hours for sample 2, and 2000 hours for sample 3.
As described above, it has been found that by providing an adhesive in the outer peripheral region satisfying L0 / 4 ≦ L, a unit-type laminated piezoelectric element having a smaller displacement loss can be obtained.
Further, from the measurement of insulation reliability, the insulation reliability is improved by changing the adhesive to low stress, that is, by changing the epoxy system of sample 2 to the silicone system of sample 3, and the unit type laminated piezoelectric element It has been found that the lifetime of

In addition, for the unit type laminated piezoelectric element having the configuration according to the sample 1, the length L of the internal region was appropriately changed, the displacement loss was measured for each element, and the result was shown in the diagram according to FIG. .
As a result, it was found that L0 / 2 ≦ L is effective in reducing the displacement loss.

Further, for the unit type laminated piezoelectric element having the configuration according to the sample 1, the area S of the internal region was appropriately changed, the displacement loss was measured for each element, and the result is shown in the diagram of FIG.
Thus, it was found that S0 / 4 ≦ S is effective in reducing the displacement loss.

(Example 3)
A method of manufacturing the unit type laminated piezoelectric element according to Example 1 will be described with reference to FIGS.
A powder of PZT (lead zirconate titanate) is prepared. This powder is crushed and added with other additives and binders to form a slurry. A green sheet is produced from the slurry using doctor blade molding or the like.
Moreover, an additive and a binder are added to Ag and Pd powder to form a paste, thereby producing a conductive paste for the internal electrode layer.

Next, the sheet is punched into a predetermined size to obtain a section. The conductive paste is printed on this section. By stacking 20 printed sections, and then pressing from at least one of the end faces on both sides in the stacking direction, the sections are crimped, and then cut to a predetermined size, so that the internal electrode layer is similar to the piezoelectric unit. A pressure-bonded body in which every other printed part was exposed on one side surface was manufactured and fired. Thereafter, a conductive paste containing a glass material and silver was applied to the side surface of the crimped body and fired.
As a result, the piezoelectric unit 2 was obtained in which the internal electrode layers 211 and 212 became conductive with the side electrode material 151 made of a mixture of glass and silver on every other side 291 and 292.

Thereafter, a desired number of the piezoelectric units 2 are stacked as shown in FIG. 12A and 12B show a state in which two piezoelectric units 2 are stacked for easy viewing. The actual embodiment 1 is a unit-type laminated piezoelectric element 1 in which 23 piezoelectric units 2 are laminated. According to the method of this example, unit-type lamination in which about 2 to 40 piezoelectric units 2 are laminated. Type piezoelectric element 1 can be manufactured.
Next, in the laminated body 200 in which the piezoelectric units 2 are laminated, as shown in FIGS. 11B and 12A, the adhesive 11 is applied to the laminated boundary 250 of the piezoelectric unit 2 exposed on the side surface of the laminated body 200. Apply.
Thereby, as shown in FIG. 12B, the adhesive 11 is naturally introduced and enters the outer peripheral region of the bonding surface 25 of the piezoelectric unit 2.

This is because, as shown in FIG. 12, the bonding surface 25 of the piezoelectric unit 2 is not a perfect plane, but is an uneven surface formed with a large number of minute protrusions and recesses. This is because the space 259 exists and the adhesive 11 naturally permeates from the capillary phenomenon with respect to the minute space 259.
Thereafter, the laminate 200 is heated and cured from both ends in the laminating direction to integrate the piezoelectric unit 2, and finally, the external electrode material 152 made of an epoxy resin and a silver filler is attached to the side electrode material 151. Screen printing is performed on the side electrode material 151, and after the external electrode plate 154 is assembled, the external electrode material 151 is cured by heating. Finally, the molding material 153 was applied by a dispensing method and heated and cured to obtain a unit type laminated piezoelectric element 1.

In the unit type laminated piezoelectric element 1 manufactured by the method according to this example, the adhesive 11 can be easily applied to the outer peripheral region 251 of the bonding surface 25.
By disposing the adhesive 11 only in the outer peripheral region 251 and bonding the piezoelectric unit 2, the displacement loss of the unit type stacked piezoelectric element can be reduced. In addition, even if only the outer peripheral region 251 is laminated, the bonding of the piezoelectric unit 2 is less likely to occur and the piezoelectric unit 2 can be easily laminated, so that the manufacturing efficiency is improved.

  As described above, according to this example, it is possible to provide a method for manufacturing a unit-type laminated piezoelectric element having a small displacement loss while laminating and bonding piezoelectric units with an adhesive.

(Example 4)
In this example, the point that the piezoelectric unit 2 is subjected to the polarization process in the middle of the manufacturing method according to the example 3 will be described.
That is, the negative electrode and the positive electrode are brought into contact with the pair of side electrode materials 151 in the piezoelectric unit 2, and a direct current is applied to apply a different potential to the piezoelectric layer 21 from the stacking direction. Before flowing the DC current, as shown in FIG. 13A, both end faces in the stacking direction (which become adhesive surfaces when stacked) were substantially parallel and flat. As shown in FIG. 13B, the drive unit 221 protrudes in the stacking direction, and the cross section becomes a drum shape.

Accordingly, when the piezoelectric units 2 subjected to polarization treatment are stacked, as shown in FIG. 14B, an opening 261 having a wedge-shaped cross section is formed at the stack boundary 250, and the adhesive is applied to the opening 261. By applying, the adhesive penetrates between the piezoelectric units more easily. For reference, FIG. 14A shows a state in which the piezoelectric units 2 before the polarization treatment are stacked.
Other details are the same as those of the third embodiment, and have the same effects.

(Example 5)
In this example, the point formed by rounding the corners of the piezoelectric unit 2 during the manufacturing method according to the third embodiment will be described.
As shown in FIG. 15, it is possible to easily introduce the adhesive to the lamination boundary by chamfering the corners facing the bonding surface 25 of the piezoelectric unit 2 in advance.
That is, as shown in FIG. 15, an opening 266 having a wedge-shaped cross section is formed at the lamination boundary 250, and the adhesive 11 is more easily applied between the piezoelectric units 2 by applying the adhesive 11 to the opening 266. It penetrates.
Other details are the same as those of the third embodiment, and have the same effects.

(Example 6)
This example shows an example in which a unit type laminated piezoelectric element is produced using an external electrode material and a molding material as the adhesive, with reference to FIGS.
First, similarly to Example 3, a powder of PZT (lead zirconate titanate) is prepared. This powder is crushed and added with other additives and binders to form a slurry. A green sheet is produced from the slurry using doctor blade molding or the like.
Moreover, an additive and a binder are added to Ag and Pd powder to form a paste, thereby producing a conductive paste for the internal electrode layer.

Next, the sheet is punched into a predetermined size to obtain a section. The conductive paste is printed on this section. By stacking 20 printed sections, and then pressing from at least one of the end faces on both sides in the stacking direction, the sections are crimped, and then cut to a predetermined size, so that the internal electrode layer is similar to the piezoelectric unit. A pressure-bonded body in which every other printed part was exposed on one side surface was manufactured and fired. Thereafter, a conductive paste containing a glass material and silver was applied to the side surface of the crimped body and fired.
As a result, as shown in FIG. 16A, the piezoelectric layers 21 and the internal electrode layers 211 and 212 are alternately laminated, and the internal electrode layers 211 and 212 are alternately mixed with glass and silver on the side surfaces 291 and 292. Thus, the piezoelectric unit 2 that can be conducted by the side electrode material 151 is obtained.

Thereafter, as shown in FIG. 16A, a desired number of the piezoelectric units 2 are stacked and clamped with a predetermined pressure F. 16 (a) to 16 (c) and FIGS. 17 (a) and 17 (b) are exaggerated between the bonding surfaces 25 of the two piezoelectric units 2 for easy viewing. There is a part.
Next, in the laminated body 200 in which the piezoelectric units 2 are laminated, as shown in FIG. 16B, along the plurality of side electrode materials 151 arranged in a straight line of the piezoelectric unit 2 exposed on the side surface of the laminated body 200. The external electrode material 152 is applied so as to cover them.

In this example, the external electrode material 152 contains a silver filler as a conductive material, an epoxy resin as a thermosetting resin, and ethylene glycol diglycidyl ether as a reactive diluent, with a viscosity of 30 Pa · S, gel An external electrode material having a conversion time of 10 minutes was employed.
As shown in FIG. 16C, the external electrode material 152 is naturally introduced into and enters the outer peripheral region of the bonding surface 25 of the piezoelectric unit 2, and also functions as the adhesive. In this state, the plurality of piezoelectric units 2 are integrated by heating and curing the external electrode material 152.
In this example, the side electrode material 151 is provided with a margin on the side surface of the piezoelectric unit 2 so as not to reach both ends in the stacking direction. Therefore, since the side electrode material 151 does not exist in the immediate vicinity of the bonding surface of the piezoelectric unit 2, the penetration of the external electrode material 152 into the bonding surface is favorably performed.

  Next, in this example, as shown in FIG. 17A, the molding material 153 was applied by a dispensing method so as to cover almost the entire side surface of the laminate 200. As the mold material 153 of this example, a mold material containing polyorganosiloxane as a thermosetting resin and diorganosiloxane, having a viscosity of 15 Pa · S and a gel time of 5 minutes was employed.

  As shown in FIG. 17B, the molding material 153 is naturally introduced into the outer peripheral region of the bonding surface 25 of the piezoelectric unit 2, enters, and also functions as the adhesive. In this state, the plurality of piezoelectric units 2 are integrated more firmly by heating and curing the molding material 153.

In this example, both the external electrode material 152 and the mold material 153 function as the adhesive, but only one of them can be used as the adhesive. In this example, the side electrode material 151 is provided in advance on the side surface of each piezoelectric unit 2. However, when the external electrode material 152 and the internal electrode layers 211 and 212 can be sufficiently electrically connected. Further, the arrangement of the side electrode material 151 can be omitted.
The adhesive component may be only part of the external electrode material composition or the mold material composition. For example, the conductive material of the external electrode material may not be in the bonded portion, and only the cured component of the low molecular weight polymer in the resin component may be present in the bonded portion.

Here, with reference to FIG. 18 to FIG. 20, a description will be given of how the external electrode material 152 penetrates into the adhesive surface when the external electrode material 152 is used as an adhesive.
The example shown in FIG. 18 is an example in which the central portion in the width direction of the external electrode material 152 has penetrated most toward the center. The example shown in FIG. 19 is an example infiltrated substantially uniformly corresponding to the presence of the external electrode material 152. FIG. 20 shows an example in which not only the side surface on which the external electrode material 152 is applied but also the entire outer peripheral portion.
The difference between these forms can be controlled by adjusting the viscosity and gelation time of the external electrode material 152 and the shape or surface property of the bonding surface of each piezoelectric unit 2.

Next, in the case of FIG. 18 and FIG. 20 described above, a description will be given of how to penetrate the adhesive surface when the molding material 153 is used as an adhesive.
FIG. 21 shows an example in which partial bonding by the external electrode material 152 is performed as shown in FIG. 18 and the molding material 153 is infiltrated around a portion where the external electrode material 152 does not exist.
FIG. 22 shows an example in which the entire outer periphery is bonded by the external electrode material 152 as shown in FIG. 20 and the molding material 153 is soaked in almost the entire periphery overcoming the presence of the external electrode material 152. Indicates.

23 and 24 show an example in which only the molding material 153 permeates almost the entire periphery without penetration of the external electrode material 152 into the bonding surface, and only the molding material 1 is used as an adhesive.
In addition, there are various forms of the penetration into the adhesive surface.

(Example 7)
In this example, the unit type laminated piezoelectric element 1 of Example 1 is used as a piezoelectric actuator of an injector 6.
The injector 6 of this example is applied to a common rail injection system of a diesel engine as shown in FIG.
As shown in the figure, the injector 6 includes an upper housing 62 in which the unit type laminated piezoelectric element 1 serving as a drive unit is accommodated, and a lower portion fixed to the lower end thereof and in which an injection nozzle portion 64 is formed. A housing 63 is provided.

The upper housing 62 is substantially cylindrical, and the unit type 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 the fuel tank (not shown).
The drain passage 624 passes through a gap 60 between the vertical hole 621 and the drive unit (piezoelectric element) 1, and further, three ways described later by a passage (not shown) that extends downward in the upper and lower housings 62 and 63 from the gap 60. The valve 651 communicates.

  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 unit laminated piezoelectric element 1 shown in the first embodiment is used as a drive source in the injector 6 having the above-described configuration. As described above, this unit-type laminated piezoelectric element 1 has very little displacement loss and excellent operation performance. Therefore, it is possible to improve the performance and reliability of the injector 6 as a whole.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory diagram showing an overall configuration of a unit-type laminated piezoelectric element in Example 1. FIG. 3 is an explanatory diagram illustrating a piezoelectric layer, an internal electrode layer, and a driving unit in Example 1. Explanatory drawing which shows the outer peripheral area | region and inner peripheral area | region in an adhesive surface in Example 1. FIG. FIG. 3 is an explanatory diagram of the length of the drive unit and the length of the internal region on the bonding surface in the first embodiment. FIG. 3 is an explanatory diagram illustrating an outer peripheral region and two inner peripheral regions on the bonding surface in the first embodiment. FIG. 3 is an explanatory diagram of a barrel-type piezoelectric layer and internal electrode layers in Example 1. FIG. 3 is an explanatory diagram of an octagonal piezoelectric layer and internal electrode layers in Example 1. FIG. 6 is an explanatory diagram of the length of the drive unit and the length of the internal region on the bonding surface in the second embodiment. FIG. 9 is a diagram illustrating a relationship between the length of the internal region and the displacement loss in the second embodiment. FIG. 9 is a diagram showing the relationship between the area of the internal region and the displacement loss in Example 2. Explanatory drawing which shows applying the adhesive agent by laminating | stacking the piezoelectric unit in Example 3. FIG. Sectional explanatory drawing which shows laminating | stacking the piezoelectric unit in Example 3, and apply | coating an adhesive agent. Explanatory drawing of the piezoelectric unit in Example 4 before and behind the polarization process. Explanatory drawing about the state which laminated | stacked the piezoelectric unit before and after the polarization process in Example 4, respectively. FIG. 10 is an explanatory diagram of a piezoelectric unit with rounded corners in Example 5. In Example 6, (a) explanatory view showing a state in which the piezoelectric units are laminated, (b) explanatory view showing a state immediately after the external electrode material is applied to the side surface of the laminated body, (c) the external electrode material is a piezoelectric unit Explanatory drawing which shows the state soaked in between the joint surfaces. In Example 6, (a) Explanatory drawing which shows the state immediately after apply | coating a molding material to the side surface of a laminated body, (b) Explanatory drawing which shows the state which the molding material penetrate | infiltrated between the joint surfaces of the piezoelectric unit. Explanatory drawing which shows an example of the penetration form of the external electrode material in Example 6. FIG. Explanatory drawing which shows an example of the penetration form of the external electrode material in Example 6. FIG. Explanatory drawing which shows an example of the penetration form of the external electrode material in Example 6. FIG. Explanatory drawing which shows an example of the penetration | infiltration form of an external electrode material and a mold material in Example 6. FIG. Explanatory drawing which shows an example of the penetration | infiltration form of an external electrode material and a mold material in Example 6. FIG. Explanatory drawing which shows an example of the penetration form of the external electrode material in Example 6. FIG. Explanatory drawing which shows an example of the penetration form of the external electrode material in Example 6. FIG. Explanatory drawing which shows the structure of the injector in Example 7. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Unit type laminated piezoelectric element 11 Adhesive 2 Piezoelectric unit 21 Piezoelectric layer 211 Internal electrode layer 152 External electrode material 153 Mold material 6 Injector

Claims (16)

In a unit-type laminated piezoelectric element formed by laminating and bonding a plurality of piezoelectric units formed by alternately laminating piezoelectric layers and internal electrode layers using an adhesive,
The unit type laminated piezoelectric material, wherein the adhesive for bonding the piezoelectric units is present in an outer peripheral region on the bonding surface of the piezoelectric units, and is not present in an inner region including the gravity center position G of the bonding surface. element. 2. The mold according to claim 1, wherein an external electrode material electrically connected to the internal electrode layer is disposed on a side surface of the multilayer body formed by laminating the piezoelectric units, and the side surface of the multilayer body is covered. Material is arranged,
The unit type laminated piezoelectric element, wherein the adhesive comprises the external electrode material and / or the molding material.   3. The external electrode material according to claim 2, wherein the external electrode material is formed by applying an external electrode material having a viscosity of 0.1 to 200 Pa · S containing a conductive material and a thermosetting resin, followed by heat curing. Unit-type stacked piezoelectric element.   4. The unit type laminate according to claim 2, wherein the mold material is formed by applying a mold material having a viscosity of 0.1 to 100 Pa · S containing a thermosetting resin and then heat-curing the mold material. Type piezoelectric element. The unit type laminated piezoelectric element according to claim 1, wherein when a voltage is applied from the internal electrode layer, the driving unit expands.
If the straight line passing through the center of gravity G on the bonding surface is X, the length of the internal region along the straight line X is L, and the length of the drive unit along the straight line X on the bonding surface is L0. / 4 ≦ L, a unit-type laminated piezoelectric element,   The length of the inner region along the straight line X is L, and the length of the drive unit along the straight line X on the bonding surface is L0. Unit-type stacked piezoelectric element. The unit type laminated piezoelectric element according to claim 1, wherein when a voltage is applied from the internal electrode layer, the driving unit expands.
S0 / 16 ≦ S, where S is the area of the inner region and S0 is the area of the driving portion on the bonding surface.   8. The unit-type laminated piezoelectric element according to claim 7, wherein S0 / 4 ≦ S, where S is the area of the internal region and S0 is the area of the driving portion on the bonding surface.   9. The unit type laminated piezoelectric element according to claim 1, wherein the adhesive is made of at least one of a silicone type and a urethane type. A plurality of piezoelectric units formed by alternately laminating piezoelectric layers and internal electrode layers are bonded using an adhesive, and the adhesive for bonding the piezoelectric units is an outer peripheral region on the bonding surface of the piezoelectric unit. In manufacturing a unit type laminated piezoelectric element that does not exist in the inner region including the center of gravity position G of the bonding surface,
A piezoelectric unit is produced by alternately laminating the piezoelectric layers and the internal electrode layers,
A laminate in which a plurality of the above piezoelectric units are laminated is produced,
By applying an adhesive to the stack boundary of the piezoelectric units exposed on the side surfaces of the laminate, the adhesive is introduced between the piezoelectric units so that the adhesive exists in the outer peripheral area of the adhesive surface of each piezoelectric unit. And a united laminated piezoelectric element manufacturing method, characterized by being integrated.   In Claim 10, after producing the said laminated body using the external electrode material electrically connected to the said internal electrode layer or / and the molding material which covers the side surface of the said laminated body as said adhesive agent, this laminated body A method for producing a unit type laminated piezoelectric element, wherein the external electrode material and the molding material are applied to the side surfaces of the piezoelectric material, and the external electrode material or / and the molding material are soaked between the piezoelectric units. .   12. The unit type laminated piezoelectric material according to claim 11, wherein the external electrode material is cured by heating after applying an external electrode material having a viscosity of 0.1 to 200 Pa · S containing a conductive material and a thermosetting resin. Manufacturing method of body element.   The unit type multilayer piezoelectric element according to claim 11 or 12, wherein the molding material is heat-cured after applying a molding material having a viscosity of 0.1 to 100 Pa · S containing a thermosetting resin. Production method.   The unit according to any one of claims 10 to 13, wherein when the adhesive is applied to the stack boundary, a compressive load is applied to the stack from the stack direction. Method for manufacturing a multilayer piezoelectric element.   15. The method of manufacturing a unit type laminated piezoelectric element according to claim 14, wherein the compressive load is continuously applied after the adhesive is applied to the lamination boundary until the adhesive is cured. . In an injector configured to open and close the valve body using the displacement of the piezoelectric actuator and perform fuel injection control,
The injector according to any one of claims 1 to 9, wherein the piezoelectric actuator comprises the unit type laminated piezoelectric element according to any one of claims 1 to 9.

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