JPH08172227A - Laminated piezoelectric actuator and manufacture thereof - Google Patents

Abstract

PURPOSE: To improve the migration resistance, conductivity and adhesive properties by forming an external electrode by containing a specific quantity of Pd or Ni flake and thermosetting resin. CONSTITUTION: Inner electrodes 12a, 12b by Ni plating are formed on a piezoelectric magnetic board 11, 150 layers are adhesively laminated by using epoxy resin adhesive, and insulating plates 16 are adhesively laminated on both the ends. The side is divided into right and left halves, and insulating films 13 made of epoxy resin having the length of the half of the side are alternately formed at the right and left sides of the parts exposed with the electrodes 12a, 12b. The right and left halves of the laminated surface are coated with conductive paste containing 80wt.% (70 to 90wt.%) of Pd or Ni flake and epoxy resin to form external electrodes 14. The flake has high migration resistance, an adhesive strength of 100kg/cm<2> or more, electric resistivity of 0.10/cm<2> , thereby improving the migration resistance, the conductivity and the adhesive properties.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laminated piezoelectric actuator and a method of manufacturing the laminated piezoelectric actuator, and more particularly to a laminated piezoelectric actuator excellent in weather resistance and used as a precision positioning mechanism in a precision machine tool, a recording head, or the like. The manufacturing method is related.

[0002]

2. Description of the Related Art Conventionally, when a stress is applied, an electric field proportional to the stress is generated, and conversely, when an electric field is applied and polarized, a strain proportional to the electric field is generated, or a mechanical stress is generated, which is a so-called piezoelectric effect. Piezoelectric materials are used in various applications such as vibrators, filters, and actuators by utilizing their characteristics. Among them, a laminated piezoelectric actuator, which is one type of actuator that utilizes mechanical strain in proportion to an applied electric field, has a large displacement amount, and the displacement amount can be freely selected by the number of laminated piezoelectric bodies. Since it has excellent characteristics such as excellent load bearing characteristics, it is often used as a precision positioning mechanism in precision machine tools, precision magnetic disks, recording / reproducing heads, linear step motors and the like.

FIG. 3 is a perspective view showing an example of a laminated piezoelectric material conventionally used in a laminated piezoelectric actuator. In FIG. 3, reference numeral 11 denotes a piezoelectric ceramic substrate. Internal electrodes 12a and 12b made of a metal plating layer are formed on the laminated surface of the piezoelectric ceramic substrate 11 that has been polarized.
Piezoelectric ceramic substrates 11 are adhered and laminated with an adhesive made of resin so that the polarization directions thereof are opposed to each other. The end portions of the internal electrodes 12a and 12b are semi-cylindrical insulating members 23 on alternate two side surfaces of the laminated piezoelectric body 20a.
And the strip-shaped external electrodes 24 are alternately insulated by the
Of the piezoelectric ceramic substrate 11 are connected to each other, and the internal electrodes 12a formed on the laminated surfaces facing each other in the polarization direction of the piezoelectric ceramic substrate 11 and the internal electrodes 12b formed on the other laminated surfaces are connected to each other. The lead terminals 15 lead out to the outside.

The laminated piezoelectric body 20a having the above structure is
A resin or the like is applied to the surface to impart weather resistance, or it is enclosed in an airtight container and used as a laminated piezoelectric actuator.

Further, as a type different from the above-mentioned laminated piezoelectric actuator, there is also one having a pair of external electrodes 24 formed in parallel with one side surface of the laminated piezoelectric body 20b as shown in FIG. In this case, the end portions of the internal electrodes 12a and 12b exposed on the side surface are alternately insulated from the left and right halves of the side surface by the insulating coating 13 having a length half the width of the side surface, and the strip-shaped outer portion is formed from above. The electrode 24 is formed,
The internal electrodes 12a formed on the laminated surfaces of the piezoelectric ceramic substrate 11 whose polarization directions face each other are connected to each other, and the internal electrodes 12b formed on the other laminated surfaces are connected to each other.

Generally, silver paste, silver palladium paste, etc. are often used for the external electrodes 24 of the above-mentioned laminated piezoelectric actuator. The conductive paste containing these metal materials has good compatibility with the ceramic surface and is a good material for exhibiting electrical performance.

However, these materials have a problem in that, when the laminated piezoelectric actuator is actually used for a long time, particularly when it is used under high humidity, migration is likely to occur, which causes a failure or the like.

On the other hand, when a material such as platinum or gold is used as the external electrode 24, there is no problem of migration as described above, but by simply applying a paste containing a metal such as silver or silver-palladium as in the prior art. It has been considered difficult to form the external electrode 24 having excellent conductivity.

That is, generally, when the platinum or the like is used for an electrode, the resin contained in the conductor paste is heated to about 700 ° C. after applying the conductor paste containing the platinum or gold. And the like are decomposed and eliminated, and the metal is baked on the surface of the ceramic to form an electrode. However, in the case of the laminated piezoelectric actuator, a resin is used for laminating and adhering the piezoelectric ceramic substrate 11, and since the performance of the piezoelectric body is deteriorated by the heating, heating to such a high temperature is required. I can't.

Therefore, conventionally, when platinum or gold is used as the external electrode 24, a method of forming the external electrode 24 by a thin film forming method such as vapor deposition has been used.

[0011]

However, in the method of forming the external electrode 24 by the thin film method, it is necessary to mount the laminated piezoelectric bodies 20a and 20b inside a vacuum container or the like and perform the vapor deposition, Therefore, there is a problem that equipment for the production is required, the work for vapor deposition is troublesome, and the manufacturing cost becomes high.

[0012] Therefore, the present inventor has used 70 flake of Au.
We proposed a method of forming an external electrode of a laminated piezoelectric actuator by applying a conductive paste containing 90 to 90 wt% of a thermosetting resin and curing it at a low temperature of 150 ° C. or lower (Japanese Patent Application No. 5-181790). issue).

The laminated piezoelectric actuator manufactured by the above method has the effect of being excellent in various characteristics such as migration resistance and durability, but has some drawbacks in terms of economy. That is, the conductive paste containing gold flakes used in the laminated piezoelectric actuator has a small effect on the unit price of the laminated piezoelectric actuator because the amount thereof is small, but expensive gold flakes are still used. However, this is a factor of price increase, and there has been a demand for an even cheaper conductive paste.

The present invention has been made in view of the above problems, and is a multilayer piezoelectric actuator in which an external electrode is formed at a lower cost, which is excellent in migration resistance, conductivity, adhesiveness with a laminated piezoelectric material, and the like. It is an object of the present invention to provide a method for manufacturing the above-mentioned laminated piezoelectric actuator in which the performance of the piezoelectric actuator is not deteriorated even by heat treatment when forming the electrodes.

[0015]

In order to achieve the above object, in a laminated piezoelectric actuator according to the present invention, an external electrode is composed of 70 to 90 wt% of Pd or Ni flakes and a thermosetting resin. It is characterized by being present.

In the method of manufacturing the laminated piezoelectric actuator according to the present invention, the flakes 70 to 9 of Pd or Ni are used.
It is characterized in that a conductive paste containing 0 wt% and a thermosetting resin is applied and cured at a temperature of 150 ° C. or less to form an external electrode.

First, the laminated piezoelectric actuator according to the present invention will be described. In the laminated piezoelectric actuator according to the present invention, the piezoelectric ceramic substrate is, for example, a piezoelectric ceramic substrate in which internal electrodes made of metal flakes such as Ni are uniformly formed on the laminated surface by a plating method, and the thickness thereof is 1
PZT-based piezoelectric ceramics having a size of about 00 to 300 μm are used, and about 50 to 400 of the piezoelectric ceramic substrates having an adhesive such as an epoxy resin applied to the laminated surface are adhered and laminated. Further, the exposed portion of the internal electrodes on the side surface of this laminate is divided into a left half and a right half, and insulating films having a length half the width of the side surface are alternately formed on the left and right sides, Strip-shaped external electrodes are formed on the left and right halves of the laminated surface, and the internal electrodes are formed on the laminated surfaces where the polarization directions of the piezoelectric ceramic substrate face each other, and formed on the other laminated surfaces. The internal electrodes are selectively connected to each other. A lead terminal is connected to the external electrode. The insulating coating is made of, for example, an epoxy resin or an acrylic resin and has a thickness of 10 to 50 μm.
m. Instead of the insulating coating, the insulating member 23 described in the section “Prior Art” may be used.

As the external electrode, a hardened body containing 70 to 90 wt% of Pd or Ni flakes and a thermosetting resin is used.

The thermosetting resin in the cured product is a cross-linked epoxy resin obtained by mixing a polymer such as bisphenol and epichlorohydrin with a curing agent such as an aliphatic or aromatic amine, polyamide or acid anhydride. , Or a urethane resin containing a curing agent such as a polyol or an amine,
Furthermore, silicone resin, vinyl copolymer, cyanoacrylate, etc. are mentioned, and the content thereof is usually 10 to 30 w.
t% is preferred.

The flakes of Pd or Ni used in the present invention are thin plate-like bodies having an average particle size of several μm or less and a thickness of several μm or less, and their wide surfaces have an island shape.
It is desirable that the flakes of Pd or Ni be uniformly dispersed in the resin.

In order to impart weather resistance to the laminated piezoelectric actuator of the present invention, a resin or the like is usually applied to the surface of the laminated body of piezoelectric substrates having the above-mentioned structure, or the laminated body of the piezoelectric substrates is hermetically sealed. It is configured by being enclosed in a container.

Next, a method of manufacturing the laminated piezoelectric actuator according to the present invention will be described.

In the method of manufacturing a laminated piezoelectric actuator according to the present invention, an adhesive is applied to the laminated surface of the piezoelectric ceramic substrate on which the internal electrodes are formed, and the piezoelectric ceramic substrate is bonded and laminated. Next, in the left and right portions of the laminated body where the internal electrodes are exposed, insulating coatings are alternately formed in halves to insulate the internal electrodes, and strip-shaped external electrodes are formed on the insulating coatings.

Since the step of forming the external electrode is a step close to the final step of assembling the laminated piezoelectric actuator, the laminated piezoelectric body manufactured in the steps so far is not destroyed or damaged. There is a need. In the present invention, a conductive paste containing 70 to 90 wt% of Pd or Ni flakes, a thermosetting resin, a curing agent having a particle size of 20 μm or less, which is mixed if necessary, and a volatile solvent for viscosity adjustment. And is subjected to a curing treatment at a temperature of 150 ° C. or lower for 1 to 5 hours to form an external electrode. The temperature during the curing treatment is more preferably 80 to 150 ° C. Pd mentioned above
Alternatively, in order to prepare a conductive paste containing Ni flakes and a thermosetting resin, a device for uniform dispersion and mixing such as a mixer and a roller mill is used to sufficiently stir and disperse and mix. Then, a known method that is usually performed, for example, by coating a resin or the like on the surface of the laminated body of the piezoelectric substrate, or by enclosing the laminated body of the piezoelectric substrate in an airtight container, the manufacture of the laminated piezoelectric actuator Complete.

In the above-mentioned laminated piezoelectric actuator,
The one in which one pair of external electrodes is formed on one side surface of the laminated piezoelectric body has been described. For example, one external electrode is provided on each of the two side surfaces of the laminated piezoelectric body as in the laminated piezoelectric actuator described in FIG. What is formed may be used.

[0026]

The Pd or Ni flakes used for the external electrode in the present invention have high migration resistance, and their migration characteristics are almost the same as those of platinum flakes. Therefore, according to the laminated piezoelectric actuator of the present invention, the external electrode containing the flakes of Pd or Ni and having excellent migration resistance is formed.

Next, the adhesiveness and conductivity of the formed external electrodes with the laminated piezoelectric material will be described.

In FIG. 1, an epoxy resin is used as a thermosetting resin, a curing agent having a particle size of several μm, an alcohol solvent, and Pd or Ni flakes are mixed at various ratios to form a conductive paste ( Adhesive) was prepared and Pd or N in the conductive paste when the external electrode was formed using this
5 is a graph showing the relationship between the adhesive strength and the electrical resistivity with respect to the content of flakes of i. In this case, the curing temperature is 1
The curing time is 50 ° C. and 1 hour. For comparison, the relationship between the content of flakes and the electrical resistivity when gold flakes are used is also shown. The adhesive strength was the same regardless of which metal was used, so only one example is shown.

As is clear from FIG. 1, Pd or Ni
The content of flakes of 70 wt% or more of the whole, 90w
In the case of t% or less, an external electrode having an adhesive strength of 100 kg / cm ² or more and an electric resistivity of 0.1 Ω / cm ² or less is formed.

The following are specific characteristics required for the external electrodes of the laminated piezoelectric ceramic substrate. That is, first, in order for the laminated piezoelectric actuator to operate smoothly without causing a voltage drop or the like, the electrical resistivity needs to be about 0.1 Ω / cm ² or less, and the external electrode peels off during operation. Adhesive strength is 100kg /
It is necessary to have about cm ² or more. In the present invention, Pd or N, which can have a large contact area with each other in the conductive paste and has excellent conductivity when the conductive paste is formed.
Since the flakes of i are used and the content of the flakes of Pd or Ni in the conductive paste containing the thermosetting resin is in the range of 70 to 90 wt%, the characteristic value required for the external electrode described above. Are satisfied.

As described above, according to the laminated piezoelectric actuator of the present invention, the flakes 70 to 9 of Pd or Ni are formed.
Since the external electrode is constituted by including 0 wt% and a thermosetting resin, it has an external electrode excellent in migration resistance, conductivity, adhesion to a laminated piezoelectric material, etc. and is inexpensive and excellent in durability. It becomes a laminated piezoelectric actuator.

According to the method of manufacturing the laminated piezoelectric actuator of the present invention, the flakes 7 of Pd or Ni are used.
Since a conductive paste containing 0 to 90 wt% and a thermosetting resin is applied and cured at a temperature of 150 ° C. or less to form an external electrode, the performance of the piezoelectric actuator deteriorates due to the heat treatment when forming the external electrode. Without doing so, the external electrode excellent in migration resistance, conductivity, adhesion to the laminated piezoelectric material, etc. is formed at low cost, and the laminated piezoelectric actuator excellent in durability is manufactured.

[0033]

EXAMPLES AND COMPARATIVE EXAMPLES Examples of a laminated piezoelectric actuator and a method of manufacturing the same according to the present invention will be described below with reference to the drawings.

FIG. 2 is a perspective view schematically showing a laminated piezoelectric material constituting the laminated piezoelectric actuator according to the embodiment.

The laminated piezoelectric material 10 is exactly the same as the conventional one shown in FIG. 4 except for the external electrodes 14,
Here, the structure thereof will not be particularly described, and the manufacturing process thereof will be described below.

First, the piezoelectric ceramic substrate 11 used in this embodiment has a thickness of 110 μm and has Ni-plated internal electrodes 12a and 12b. 150 pieces of this piezoelectric ceramic substrate 11 were adhered and laminated using an epoxy resin as an adhesive agent, and insulating plates 16 having a thickness of 2 mm were further adhered to both ends thereof to produce a laminated body. The produced laminate had a length of 5.2 mm, a width of 4.5 mm, and a height of 21 mm.

Next, the side surface of this laminated body is divided into a left half and a right half, and an insulating film made of an epoxy resin or the like having a length half the width of the side surface is formed in the portion where the internal electrodes 12a and 12b are exposed. 13 were formed alternately on the left and right.

Next, in the left half and right half of the laminated surface,
An external electrode 14 is formed by applying a conductive paste containing 80% wt of Pd or Ni flakes and an epoxy resin, and the internal electrode is formed on the laminated surface of the piezoelectric ceramic substrate 11 in which the polarization directions face each other. 12a and the internal electrodes 12b formed on the other laminated surfaces were selectively connected. After that, it is dried at 150 ° C. for 1 hour to perform a curing treatment, and epoxy resin is also applied to the lead terminal joint portion of the external electrode 14 to attach the lead terminal 15, and the curing treatment is also performed at 150 ° C. for 1 hour. Then, the laminated piezoelectric material 10 was manufactured. Finally, the side surface of the laminated piezoelectric body 10 was mainly coated with resin to complete the laminated piezoelectric actuator.

Next, the basic electrical performance of the laminated piezoelectric actuator manufactured by the above method was measured for 10 samples.

As a comparative example, the basic electric performance was similarly measured for a conventional laminated piezoelectric actuator coated with a silver paste as an external electrode. The results are shown in Table 1 below. In Table 1 below, Example 1 is the case where the Pd paste is used, and Example 2 is the case where the Ni paste is used.

[0041]

[Table 1]

As is clear from the results shown in Table 1 above,
In the laminated piezoelectric actuator according to the example, the basic electric performance was comparable to that of the conventional laminated piezoelectric actuator in which the external electrode was formed of silver. The electric resistivity of the conductor portion is Pd = 0.08.
4 (Ω / cm ² ), Ni = 0.098 (Ω / cm ² ), and it was confirmed that the electrode characteristics were sufficiently satisfied.

Next, as the most important durability test, a test in which a rated voltage is continuously applied in an environment of a temperature of 40 ° C. and a relative humidity of 90% is performed, and the test is broken by 2000 hours. I checked what I did.

As a result, in the laminated piezoelectric actuator according to the example, only one out of the 20 tested samples (10 coated with Pd paste and 10 coated with Ni paste) was used. In contrast to the destruction, all of the 25 tested multilayer piezoelectric actuators were destroyed, which proves that the multilayer piezoelectric actuator of the example has extremely excellent durability.

[0045]

As described above in detail, in the laminated piezoelectric actuator according to the present invention, the external electrode is composed of 70 to 90 wt% of Pd or Ni flakes and the thermosetting resin. It is possible to provide an inexpensive and durable laminated piezoelectric actuator having an external electrode that is excellent in migration resistance, conductivity, adhesion to a laminated piezoelectric material, and the like.

Further, in the method for manufacturing the laminated piezoelectric actuator according to the present invention, a conductive paste containing 70 to 90 wt% of Pd or Ni flakes and a thermosetting resin is applied, and the temperature is set to 150 ° C. or lower. Since the external electrode is formed by curing with, the performance of the piezoelectric actuator is not deteriorated by the heat treatment when forming the external electrode, and it is excellent in migration resistance, conductivity, adhesiveness with the laminated piezoelectric material at low cost. It is also possible to form external electrodes, and thus it is possible to manufacture the laminated piezoelectric actuator having excellent durability.

[Brief description of drawings]

FIG. 1 is an adhesive strength and electrical resistivity with respect to a content of Pd or Ni flakes with respect to a laminated piezoelectric material when an external electrode is formed using a conductive paste containing Pd or Ni flakes and an epoxy resin. It is a graph showing the relationship of. As a comparative example, the case where a conductive paste using gold flakes is used is also shown.

FIG. 2 is a perspective view schematically showing a laminated piezoelectric body used in the laminated piezoelectric actuator according to the embodiment.

FIG. 3 is a perspective view showing an example of a laminated piezoelectric material conventionally used in a laminated piezoelectric actuator.

FIG. 4 is a perspective view showing another example of a laminated piezoelectric body conventionally used in a laminated piezoelectric actuator.

[Explanation of symbols]

 14 External electrode

Claims (2)

[Claims] 1. Pd or Ni flakes 70-90 wt.
% And a thermosetting resin are included in the external electrodes, a laminated piezoelectric actuator. 2. Pd or Ni flakes 70-90 wt.
%, And a conductive paste containing a thermosetting resin is applied, and 1
The method for manufacturing a laminated piezoelectric actuator according to claim 1, wherein the external electrode is formed by curing at a temperature of 50 ° C. or less.