JPH05335642A - Piezoelectric element and its manufacture - Google Patents

Abstract

PURPOSE:To improve electrode release strength and obtain a piezoelectric element with improved characteristics under usage conditions where a greater stress is applied without deteriorating piezoelectric characteristics by treating the surface of a polymer-piezoelectric body film and then laminating and contact-bonding a porous sheet-shaped electrode on the surface. CONSTITUTION:In a piezoelectric element 10a, a mesh-shaped porous sheet- shaped electrode 2 is buried to both surface layers of a polymer piezoelectric body film 1 and a lead or a terminal is connected to one part of it. The porous sheet-shaped electrode is formed in plane weave and diagonal weave by an arbitrary conductive material with a proper rigidity such as carbon fiber in addition to a metal material such as copper, stainless steel, and platinum. For manufacturing the piezoelectric element 10a, the surface of the polymer piezoelectric film 1 is treated by a solvent medium. a porous sheet-shaped electrode is contacted, and then both are contact-bonded. Then, the surface covering layer of the porous sheet-shaped electrode 2 is partially eliminated using a solvent medium and a lead wire or a terminal connection part is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polymer piezoelectric element having a porous sheet electrode.

[0002]

2. Description of the Related Art Polymer piezoelectric materials such as a polarized vinylidene fluoride resin (hereinafter typically referred to as PVDF) have a large flexibility (1) and a thin film as compared with ceramic piezoelectric materials. It is easy to increase the size, increase the area, and increase the length, and it is possible to make any shape and form; (2) The hydrostatic piezoelectric strain constant d _h is equal to or less than that,
The dielectric constant epsilon is low, hydrostatic voltage output coefficient determined by d _h / ε (g _h constant) is extremely large, and the thus sensitivity characteristics are excellent; (3) low density, due to low elasticity, acoustic impedance ( Sound velocity x density) is close to that of water and living organisms,
Therefore, there is little reflection between water and a living body and the element, and efficient energy transmission is possible. Taking advantage of such characteristics, the polymer piezoelectric material is generally used in electro-mechanical (acoustic) conversion elements such as speakers, microphones, ultrasonic probes, hydrophones, seismographs, strain gauges, blood pressure monitors, and bimorph fans. As a pyroelectric conversion element, application to a wide range of applications has been proposed or put into practical use.

When a film- or sheet-shaped polymer piezoelectric material subjected to polarization treatment (hereinafter, generically referred to as "polymer piezoelectric film") is formed into an element, electrodes are usually provided on both surfaces thereof. At this time, the electrode is generally a vapor-deposited electrode of copper, aluminum or the like, considering that the heat resistance of the polymer piezoelectric body including the piezoelectric characteristics imparted by orientation-polarization and the like is around 100 ° C. Alternatively, foil electrodes of these metals attached with an adhesive are used. Further, the present inventors have also proposed a thermal spraying electrode in which a metal having a relatively low melting point such as zinc is thermally sprayed to form a layer on the surface (Japanese Patent Application No. 356668 of 1991). However, each of these electrodes has problems as described below.

[0004]

First, the vapor deposition electrode is generally provided with a thin electrode thickness of about 0.02 to 0.1 μm and, in addition, the adhesive strength with the polymer piezoelectric material is not sufficient and the vapor deposition electrode does not adhere to the electrode. It is very difficult to connect the lead wires by soldering. Therefore, it is necessary to employ a complicated electrode terminal structure for inputting an electric signal in the polymer piezoelectric element provided with the vapor deposition electrode.

On the other hand, the metal foil electrode is generally 6 to 1
A metal foil with a thickness of about 00 μm is coated with polyester resin,
5-40μ made of urethane resin, epoxy resin, etc.
It is attached to a polymer piezoelectric film via an adhesive layer of about m, and is formed as an electrode capable of connecting lead wires by soldering. However, this metal foil electrode has a drawback that it impairs an important advantage of flexibility of the polymer piezoelectric element, particularly when it is provided on both surfaces of the polymer piezoelectric film. In addition, depending on the state of use, especially on the surface exposed to the outside air, the adhesive may deteriorate and the durability of the piezoelectric element may become a problem. Further, due to the existence of the adhesive layer which is a non-piezoelectric material, the hydrostatic piezoelectric strain constant d _h may be lowered in some cases.

On the other hand, the sprayed electrode is preferable in terms of adhesion to the polymer piezoelectric material, lead wire connectivity by soldering, and flexibility of the obtained piezoelectric element.
Due to the heat resistance of the polymer piezoelectric material, only a low melting point metal can be easily formed by thermal spraying, and the problem is that the electrode material used is limited.

All of the above conventional electrodes are formed on the entire surface of the polymer piezoelectric material. Therefore, in the conventional piezoelectric element, it is necessary to cover the entire piezoelectric body or store the piezoelectric body in a sealed case for the purpose of electrical insulation or protection of the electrode from the surrounding environment in actual use. It was

The main object of the present invention is to provide a piezoelectric element having an electrode structure integrally formed with a polymer piezoelectric material, which does not substantially impair the excellent flexibility of the polymer piezoelectric material. ..

[0009]

Means for Solving the Problems As a result of research for the above-mentioned purpose, the present inventors found that an element in which a porous sheet-like electrode is embedded in the surface layer of a polymer piezoelectric film and integrally formed is The present invention has been completed by discovering that, despite the structure, it exhibits the same level of piezoelectric characteristics as an element obtained by adhesively fixing a foil electrode, is excellent in electrode peeling strength, and has a relatively small decrease in flexibility. Further, such a structure in which the porous sheet-shaped electrode is embedded in the surface layer of the polymer piezoelectric film is effectively formed by treating the surface of the polymer piezoelectric film with a good solvent and then pressure-bonding the porous sheet-shaped electrode. It was also found to be done.

That is, the piezoelectric element of the present invention is characterized in that a porous sheet-shaped electrode is embedded in a polymer piezoelectric material. The mesh electrode is a preferred embodiment of the porous sheet electrode.

Further, the method for producing a piezoelectric element of the present invention is characterized in that the surface of the polymer piezoelectric film or sheet is treated with a solvent, and then a porous sheet-shaped electrode is laminated on the treated surface and pressure-bonded. To do.

[0012]

The piezoelectric element of the present invention employs a structure in which a porous sheet-like electrode is used and the electrode is embedded inside and / or on the surface of the polymer piezoelectric material. Therefore, a part of the polymer piezoelectric material penetrates into the through hole of the electrode, and a piezoelectric element having excellent electrode peeling strength is formed in which the electrode and the piezoelectric body are integrated. In addition, the excellent flexibility of the porous sheet-like electrode provides an element with a relatively small reduction in flexibility in forming the element.

[0013]

DETAILED DESCRIPTION OF THE INVENTION As the polymer piezoelectric material used in the present invention, vinylidene cyanide-vinyl acetate copolymer having a relatively high heat resistance is preferably used, and vinylidene fluoride having excellent piezoelectric characteristics is used. -Based resin piezoelectric materials are preferable, and among them, β-type crystallization under ordinary crystallization conditions is more preferable than vinylidene fluoride (VDF) homopolymer, which requires uniaxial stretching for β-type crystallization suitable for developing piezoelectricity. Possible VDF-based copolymers (eg, predominant amount of VDF and inferior amount of vinyl fluoride (VF) trifluoroethylene (TrF
E) or a copolymer with tetrafluoroethylene (TFE)) is preferred, and moreover a predominant amount (particularly 70 to 80 mol%) of VDF and a subordinate amount (particularly 30 to 20 mol%) of T.
A copolymer with rFE is most preferably used. These polymer piezoelectric materials are formed by film formation by melt extrusion,
If necessary, uniaxial stretching or heat treatment at a softening temperature or lower and polarization treatment by applying an electric field at a softening temperature or lower are applied to obtain a polymer piezoelectric film.

FIG. 1 is a plan view of a preferred embodiment of the piezoelectric element of the present invention, and FIG. 2 is a sectional view taken along the line II--II in FIG. With reference to FIGS. 1 and 2, in this piezoelectric element 10a, a mesh-shaped porous sheet-shaped electrode 2 is embedded in the surface layers of both surfaces of a polymer piezoelectric film 1 as described above, and a part thereof is lead. It has a structure of a wire or a terminal connecting portion 3.

The porous sheet electrode of the present invention is, for example,
In addition to metal materials such as copper, stainless steel, aluminum, steel, tin, zinc, gold, silver, titanium, and platinum, it is possible to use any conductive material having appropriate rigidity such as carbon fiber.

In order to form the mesh-like porous sheet-shaped electrode 2, in addition to the plain weave as shown, an arbitrary weave such as twill weave, tatami twill weave, flat tatami twill weave, twill weave can be adopted. , Its name is 40 mesh (for example, opening 350
μm, wire woven wire mesh of 290 μm) to 1000 mesh (for example, filtration particle size of about 25 μm, wire diameter 80 (length) /
55 (horizontal) μm, 120 mesh in the longitudinal direction is a twill weave wire mesh, especially 60 mesh (for example, opening 240 μm,
A plain weave wire mesh having a wire diameter of 180 μm) to 635 mesh (for example, a twill weave wire mesh having an opening of 20 μm and a wire diameter of 20 μm) is preferably used. Therefore, the through holes (opening or the number of filtering particles) of the mesh-shaped porous sheet electrode 2 are 20 to 350 μm, and the wire diameter is 20 to 300 μm.
The range is appropriate. It is particularly preferable that the wire mesh is made of high strength metal such as stainless steel or titanium. With a wire mesh of more than 1000 mesh, the through holes are too small and the electrode peeling strength tends to decrease as described below. Conversely, in the case of a wire mesh of less than 40 mesh, one of the main parameters showing piezoelectric characteristics, The hydraulic piezoelectric strain constant d _h becomes smaller. However, even in this case, the d _h constant becomes smaller, but the dielectric constant ε also decreases, so that the hydrostatic piezoelectric output coefficient (g _h constant) expressed by the ratio of the d _h constant and the dielectric constant ε as described later. Are maintained at the same level.

FIG. 3 is a plan view of another preferred embodiment of the piezoelectric element of the present invention, and FIG. 4 is a sectional view taken along the line IV-IV in FIG. This piezoelectric element 10b
Is a perforated sheet-shaped electrode 12 in the form of a perforated plate in which a large number of through holes 12a are provided in the surface layers of both sides of the polymer piezoelectric film 1.
It has a structure in which is embedded. Instead of the mesh-shaped porous sheet-shaped electrode 2, a porous plate-shaped electrode 12 provided with through holes 12a
1 has a structure essentially similar to that of the piezoelectric element 10a shown in FIGS.

The porous plate electrode 12 and the mesh electrode 2 can be made of the same material. Through hole 1
The hole diameter of 2a and the distance between the through holes can be set according to the openings and the wire diameters of the mesh electrode 2, respectively. However, the distance between the through holes can be set more freely. In addition, the mesh-like porous sheet electrode 2
In the case of, the perforated plate electrode 12
(Thus, the aperture ratio of the through hole 12a) is preferably set in the range of 10 to 70%, particularly 20 to 60%. When the aperture ratio is less than 10%, the electrode peeling strength decreases, and when it exceeds 70%, the _dh constant decreases.

The thickness of the porous sheet-shaped electrode of the present invention (corresponding to the wire diameter in the plain-woven or twilled mesh-shaped electrode 2) is 10 to 800 μm, and particularly 20 to 300 μm.
The range of m is preferable. The thickness of the electrode is 10μ
If it is less than m, the rigidity of the obtained piezoelectric element is not sufficient, and wrinkles are liable to occur when the piezoelectric element is laminated on a polymer piezoelectric film swollen with a good solvent and pressure-bonded thereto. Conversely, 800 μm
If it exceeds, it becomes difficult to embed the porous sheet-like electrode in the polymer piezoelectric film 1 to an extent sufficient to give an appropriate electrode peeling strength.

The embedding of the porous sheet-shaped electrodes 2, 12 into the polymer piezoelectric film laminate should be performed to such an extent that the anchor effect is exhibited and the required electrode peeling strength is obtained, and usually, At least 30%, especially at least 50% of the thickness should be embedded in the surface layer of the polymeric piezoelectric film 1. FIG. 5 is a plan view of still another preferred embodiment of the piezoelectric element of the present invention, and FIG. 6 is a side view thereof. In this piezoelectric element 10c, twill-woven mesh-shaped electrodes 22 are provided on both surface layers of the polymer piezoelectric film 1 at 50% of the thickness.
It has a structure embedded up to. Even with such partial embedding, the electrode peeling strength is significantly improved by the anchor effect of the polymer piezoelectric material that partially penetrates the through holes of the porous sheet electrode. It is also possible to embed 100% of the thickness, that is, to completely embed it. At this time, the electrodes are covered with the resin of the polymer piezoelectric material. In that case,
It is advisable to lightly wipe a part of the resin coating layer on the surface with a solvent to expose the electrodes, and then connect the lead wires or terminals to the element. Further, in the present invention, the “surface layer of the polymer piezoelectric film” refers to a region from the surface to a depth comparable to the thickness of the porous sheet electrode.

The polymer piezoelectric film 1 has a thickness of 50 to 20.
It is preferable to have a thickness of about 00 μm, particularly 200 to 1000 μm. When the thickness of the film is less than 50 μm, it is difficult to embed the porous sheet electrode, and problems such as film deformation and variation in piezoelectric characteristics occur. On the other hand, when the thickness exceeds 2000 μm, the flexibility of the film is impaired, and a high voltage is required for polarization, which causes edge discharge and makes polarization extremely difficult. According to the invention,
When the porous sheet-shaped electrode is embedded in the surface layer of the polymer piezoelectric film, the distance between the electrodes of the element is narrowed by the depth of the embedding. Therefore, the thickness of the polymer piezoelectric film 1 is preferably selected from the above range in consideration of the thickness of the porous sheet electrode to be used and the embedding depth.

In the above, the preferred three modes of the piezoelectric element of the present invention have been described with reference to FIGS. However, various modifications of the above embodiment are possible within the scope of the present invention. For example, the porous sheet electrodes 2, 12
Need only be embedded on at least one surface of the polymer piezoelectric film 1, and the electrodes on the other surface should be conventional vapor-deposited electrodes,
It may be a metal foil electrode or a sprayed electrode. In addition to the mesh-shaped electrode 2 or the perforated plate-shaped electrode 12 having a through hole as shown in the above examples, the porous sheet-shaped electrode has holes or voids communicating with the front and back surfaces of a non-woven fabric, felt or the like. It is possible to use a sheet-shaped conductor that can be impregnated with a polymer piezoelectric resin swollen or dissolved by a solvent or thermally dissolved.

Further, as shown in FIG. 7 corresponding to FIG. 2, the piezoelectric element has two porous sheet-shaped electrodes 32 similar to the porous sheet-shaped electrode 2 as an intermediate electrode so as to be embedded in each one surface. It is also possible to form a piezoelectric element 10d having a laminated structure as a whole by sandwiching and sandwiching the polymer piezoelectric film 1. As described above, the porous sheet electrode of the present invention can be embedded not only in the surface layer of the polymer piezoelectric material but also in the inside thereof. In this piezoelectric element 10d, the intermediate electrode is arranged so as to project from the polymer piezoelectric film 1 on one of the four sides, and the projecting portion serves as the lead wire or the terminal connecting portion 3.

Next, the method of the present invention for manufacturing the above-described piezoelectric element will be described. First, the surface of the polymer piezoelectric film 1 on which the porous sheet electrode is to be embedded is treated with a solvent. As the solvent at this time, a good solvent for the polymer piezoelectric material constituting the polymer piezoelectric film 1 is preferably used, but it is sufficient if it has a solvent ability to swell even if the polymer piezoelectric material cannot be dissolved. Examples of such a solvent include ketone solvents such as acetone and methyl ethyl ketone; tetrahydrofuran, NN dimethylacetamide, dimethylformamide, and the like. For the solvent treatment, a solvent is applied to the surface of the polymer piezoelectric film by a method such as coating, spraying or dipping, and the solvent and the film are heated at room temperature to 90 ° C. for 2 seconds to, for example.
It is enough to leave them in contact for about 1 hour. The processing conditions such as temperature and time may differ depending on the composition of the polymer piezoelectric material, the type of solvent, the shape and thickness of the electrode. Since the electrode peeling strength increases as the temperature in the subsequent crimping step increases, for this purpose, a solvent having a weak dissolving power is used in the solvent treatment step, and a high temperature within the heat resistant temperature range of the piezoelectric body is used. Is also preferable.

Next, the porous sheet electrode is brought into contact with the surface of the polymer piezoelectric film 1 which has been subjected to the solvent treatment, and the both are pressure-bonded. It is also preferable that the contact surface of the porous sheet-like electrode with the polymer piezoelectric film 1 be subjected in advance to a surface treatment for improving the adhesiveness with the polymer piezoelectric material, a coating for protecting the electrode, or the like. An example of such pretreatment may be coating with a resin having the same quality as or compatibility with the polymer piezoelectric material.

After completion of the solvent treatment step, it is preferable to immediately proceed to the next pressure bonding step. It is also preferable to wipe or drop the surface liquid of the polymer piezoelectric film between both steps.

The higher the temperature in the crimping process, the higher the electrode peeling.
This is preferable in this respect because it increases the peel strength, but it is generally
Above the temperature, within the heat resistant temperature range of the piezoelectric material
It is 50 to 90 ° C. On the other hand, the pressure for crimping is 1 kg / c
m²Or 700kg / c where the piezoelectric polymer is plastically deformed
m²Up to about 5kg / cm for practical use²~ 100 kg
/ Cm²Is preferred. Also, the crimping time is 10
It is about one second to one hour.

In the case of obtaining a piezoelectric element having a porous sheet electrode 32 sandwiched between films 1 as an intermediate electrode as shown in FIG. 7, generation of voids in the vicinity of the intermediate electrode 32 is suppressed and good piezoelectricity is obtained. In order to obtain the characteristics and the strong electrode peeling strength, it is necessary to appropriately determine the pressure bonding condition and the solvent treatment condition in which the solvent-treated surface layer resin of the piezoelectric substance flows into the pores of the electrode and the solvent escapes. In particular, when the vertical or horizontal dimension is small, it is easy to find such a condition. Pressing with a roller is also one of the preferable methods.

The polarization treatment of the polymer piezoelectric film can be performed after the electrodes are formed, but the method of forming the electrodes on the polarization-treated piezoelectric film can be more preferably adopted.

As another method for producing the piezoelectric element of the present invention, while holding the porous sheet-like electrode in the mold using a jig, the piezoelectric resin melted by heat or the piezoelectric material dissolved in a solvent is used. It is also possible to adopt a method of pouring body resin and casting. However, in this case, the polarization treatment of the polymer piezoelectric material is performed after the electrode formation.

Obtained piezoelectric elements 10a, 10b, 10d
In, the lead wire or the terminal connecting portion 3 is formed by partially removing the surface coating layer of the porous sheet-shaped electrode 2, 12 or 32 with a solvent.

The thus-obtained piezoelectric element of the present invention maintains impact resistance and flexibility that ceramic piezoelectric elements do not have, while exhibiting improved electrode peel strength as compared with conventional polymer piezoelectric elements. Have. Therefore, it can be used for the same purpose as the conventional polymer piezoelectric element, and has an excellent suitability for use under a condition where a larger stress is applied.

[0033]

EXAMPLES The present invention will be described in more detail below with reference to examples and comparative examples. The following characteristics were evaluated for the piezoelectric elements produced in these examples.

The piezoelectric properties: was determined by measuring the hydrostatic piezoelectric constant (d _h constant) in the following manner. The sample is immersed in silicon oil placed in a pressure resistant container, and the charge amount Q (Coulomb (C)) of the sample is measured while applying a pressure P (Newton (N) / m ² ) from a nitrogen gas source to the container. The resulting increased amount dQ of the charge with respect to the pressure increase dP in the vicinity gauge pressure 2 kg / cm ^2, was calculated by the following _{equation: d h = (dQ / dP} ) / A unit is C / N. Where A is the electrode area (m ² )
Is.

On the other hand, hydrostatic piezoelectric output coefficient (g _h constant)
Is a multi-frequency LCR meter manufactured by YHP Co., Ltd.
It was calculated by the formula g _h = d _h / ε. The unit is volts (V) × m / N.

Flexibility: The sample is supported by two fulcrums with an interval of 4 cm, and a load value per 1 cm width required to bend the sample by applying a load W at a speed of 5 mm / min at the center of the fulcrum for 2 mm is obtained. And the flexural load (g / cm).

Electrode peeling strength: An epoxy adhesive (Araldite AW106 (resin): HV) on a copper foil having a thickness of 35 μm
953U (curing agent) = 1: 1, Nippon Ciba Geigy Co., Ltd. was applied, and the surface coating resin layer was lightly wiped with acetone to be bonded to the electrode forming surface of the piezoelectric element, and 9
It was pressed at 0 ° C. and a pressure of 100 kgf / cm ² for 20 minutes. Subsequently, JIS C-64 was applied to this laminated sample.
In accordance with No. 81, a 90 ° peel test was performed at a speed of 50 mm / min. The electrode peeling strength is the degree of inconvenience such as cracking or peeling of the electrode that occurs around the solder when connecting the lead wire to the electrode by soldering or when handling the element thereafter, that is, connecting the lead wire by soldering. It is empirically known to show a good correlation with sex.

In the test of flexibility and electrode peeling strength,
STROGRA manufactured by Toyo Seiki Co., Ltd. as a testing machine
PH-R2 was used.

Example 1 A piezoelectric element having the structure shown in FIGS. 1 and 2 was formed as follows.

First, a VDF / TrFE (75/25 molar ratio) copolymer (manufactured by Kureha Chemical Industry Co., Ltd.) was used at a die temperature of 2
The sheet was extruded at 65 ° C., heat-treated at 125 ° C. for 13 hours, and then kept at 138 ° C. under an electric field of 60 V / μm for 5 hours.
The polarization treatment was performed for a total of 1 hour including the minute and the raising / lowering time to obtain a polymer piezoelectric film 1 having a thickness of 500 μm. The flexibility (deflection load) of this film was 47 g / cm.

The polymer piezoelectric film was dipped in acetone at 30 ° C. for 30 seconds, and then both surfaces thereof were held by a 500 mesh (twill weave, opening 26 μm, wire diameter 25 μm) stainless steel (SUS316) wire mesh. Was pressure-bonded under the conditions of a temperature of 90 ° C., a pressure of 50 kg / cm ² , and a time of 2 minutes to obtain a piezoelectric element having the structure shown in FIG.

Example 2 In Example 1, the 500 mesh wire mesh was replaced with VDF.
A piezoelectric element was obtained in the same manner as above, except that a resin-coated wire net was used after being dipped in a 7.5% concentration THF solution of a / TrFE (75/25 molar ratio) copolymer.

Comparative Example 1 An alumina-based abrasive having a grain size of # 220 was applied to both sides of the polymer piezoelectric film obtained in Example 1 with an air pressure of 4.0 kg /.
After sandblasting under conditions of cm ² and distance of 15 cm, an SBR adhesive (“4693 Scotch Grip” manufactured by Sumitomo 3M Limited, 10-20% concentration in the solvent 1,2-dichloroethane) was used. After being applied on both sides and held by the wire net of Example 1, pressure was applied under the conditions of preheating: 90 ° C. for 4 minutes and pressure: 90 ° C. for 4 minutes at −150 kg / cm ² to obtain a piezoelectric element.

Comparative Example 2 In the same manner as in Comparative Example 1, a 35 μm-thick copper foil was attached to both surfaces of a polymer piezoelectric film roughened and coated with an adhesive to obtain a piezoelectric element.

Comparative Example 3 An electro-spraying thermal spraying machine (Kato Metallikon Co., Ltd.) was applied to both surfaces of a polymer piezoelectric film roughened in the same manner as in Comparative Example 1.
Made, DK type metal sprayer E type), air pressure 5Kg
/ Cm ² and voltage 15V, thermal spraying is performed and thickness is about 40
A μm zinc sprayed electrode was formed to obtain a piezoelectric element.

The results of the above-described characteristic evaluations of the various piezoelectric elements obtained above are summarized in Table 1 below.

[0047]

[Table 1]

Example 3 A piezoelectric element was obtained in the same manner as in Example 1 except that the pressure bonding temperature was changed to room temperature, 50 ° C. and 70 ° C.

The measured values of the electrode peeling strength and d _h of the obtained piezoelectric element are shown together with the results of Example 1 in FIGS. 8 and 9 and in Table 3 below.

Example 4 As shown in Table 2 below, a wire mesh of 40 mesh to 800 mesh (the 500 mesh wire mesh used in Example 1 is also described) is used, and the pressure bonding temperature is 50 ° C. A piezoelectric element was obtained in the same manner as in Example 1.

[0051]

[Table 2] 1) The number of horizontal line meshes. The number of vertical line meshes is 80
2) Shown as the number of filtered particles; 3) Horizontal line diameter / vertical line diameter.

The measured values of the electrode peeling strength and d _h of the obtained piezoelectric element are summarized in FIGS. 10 and 11 and Table 3 below.

[0053]

[Table 3] 1) The mesh wire mesh was too hard to peel at 90 °.

[0054]

As is apparent from the results of the above-mentioned Examples and Comparative Examples, according to the present invention, by embedding a porous sheet-like electrode in a polymer piezoelectric material, the flexibility and the like of a conventional polymer piezoelectric element can be obtained. There is provided a piezoelectric element in which the mechanical strength typified by the electrode peeling strength is remarkably improved and an effective manufacturing method thereof, while maintaining the advantages of 1. Therefore, it is possible to obtain a piezoelectric element which is not only provided as it is for the use of the conventional polymer piezoelectric element but also has excellent suitability under a use condition in which severe stress is applied.

[Brief description of drawings]

FIG. 1 is a plan view of an embodiment of a piezoelectric element of the present invention.

2 is a cross-sectional view taken along line II-II in FIG.

FIG. 3 is a plan view of another embodiment of the piezoelectric element of the present invention.

4 is a cross-sectional view taken along line IV-IV in FIG.

FIG. 5 is a plan view of yet another embodiment of the piezoelectric element of the present invention.

FIG. 6 is a side view of FIG.

FIG. 7 is a cross-sectional view of an example of a piezoelectric element having a multi-layered structure according to the present invention.

FIG. 8 is a graph of experimental data showing the pressure-bonding temperature dependence of the electrode peeling strength of the piezoelectric element of the present invention.

FIG. 9 is a graph of experimental data showing the pressure-bonding temperature dependence of the d _h constant of the piezoelectric element of the present invention.

FIG. 10 is a graph of experimental data showing the dependence of the electrode peel strength of the piezoelectric element of the present invention on the wire mesh opening.

FIG. 11 is a graph of experimental data showing the dependence of d _h constant of the piezoelectric element of the present invention on the wire mesh opening.

[Explanation of symbols]

 1: Polymer piezoelectric film 2, 22, 32: Mesh-like porous sheet-like electrode 3: Lead wire or terminal connecting portion 10a, 10b, 10c, 10d: Piezoelectric element of the present invention 12: Porous sheet-like electrode with perforations 12a: through hole

Claims (4)

[Claims] 1. A piezoelectric element in which a porous sheet-shaped electrode is embedded in a polymer piezoelectric material. 2. The porous sheet electrode is provided on at least one surface of a polymer piezoelectric film or sheet,
The piezoelectric element according to claim 1, wherein the piezoelectric element is embedded in the surface layer. 3. The piezoelectric element according to claim 1, wherein the porous sheet electrode is a mesh electrode. 4. A method for manufacturing a piezoelectric element, which comprises treating the surface of a polymer piezoelectric film or sheet with a solvent, and then laminating and adhering a porous sheet-like electrode on the treated surface.