JPH05102548A - Piezoelectric device - Google Patents

Abstract

PURPOSE:To obtain piezoelectric devices which are excellent in solder-based lead connection performance without damaging their flexibility by installing a spray-coated electrode on one side of a polymer piezoelectric film or a sheet. CONSTITUTION:There is provided a spray coated electrode 2 on one side of a polymer piezoelectric film 1. Copper, aluminum and zinc are cited for the material of the spray coated electrode 2. Especially, zinc or zinc alloy with copper or the like is favorably used since they can be sprayed at a relatively low temperature and provided an excellent electrode film in terms of soldering properties. The thickness of the spray coated electrode 2 can be selected within the scope in which excellent soldering properties can be provided without damaging the flexibility of piezoelectric devices. Generally, the thickness ranges from 10 to 100mum. Especially, it is more favorable to set the thickness which ranges from 20 to 50mu. It is also acceptable to adopt the structure where a metal foil electrode 5 is pasted on the side opposite to the side on which the spray coated electrode 2 of the piezoelectric film 1 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-based piezoelectric element having a spray-coated electrode.

[0002]

2. Description of the Related Art Polymer piezoelectric materials such as a polarized vinylidene fluoride resin (hereinafter, typically referred to as PVDF) are (1) more flexible and thinner than ceramic piezoelectric materials. It is easy to increase the area, 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 the same or less, but the permittivity ε is small. a, d _h / hydrostatic voltage output coefficient determined by epsilon (g _h constant) is extremely large, and the thus sensitivity characteristics are excellent; (3) low density, due to low elasticity, acoustic impedance (sound velocity × density), It has characteristics such that it is close to the values of water and living organisms, therefore there is little reflection between water and living organisms and the element, and efficient energy transmission is possible. Taking advantage of such characteristics, the polymer piezoelectric material is generally used as an electro-mechanical (acoustic) conversion element such as a speaker, a microphone, an ultrasonic probe, a hydrophone, a seismograph, a strain gauge, a sphygmomanometer, and a bimorph fan. As a pyroelectric conversion element, application to a wide range of applications has been proposed or put into practical use.

When a film-shaped or sheet-shaped polymer piezoelectric material (hereinafter, generically referred to as "polymer piezoelectric material 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. 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 adopt a complicated electrode terminal fixing structure for inputting and outputting an electric signal for 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.

Based on the above-mentioned circumstances, in the conventional polymer piezoelectric element, the vapor deposition electrode is adopted even if a complicated terminal structure is adopted when importance is attached to flexibility, while it is possible when the lead wire connection is required. Metal foil electrodes have been adopted even at the expense of flexibility.

[0007] A main object of the present invention is to provide a polymer-based piezoelectric element having an electrode structure which is excellent in lead wire connectivity by solder without essentially impairing flexibility.

[0008]

As a result of continuing the research for the above-mentioned purpose, the present inventors have surprisingly found that the formation of an electrode by thermal spraying, which has not been conventionally considered for application to a polymer piezoelectric element having poor heat resistance. However, they have reached the present invention by finding that not only can this be achieved by setting appropriate conditions, but rather that the piezoelectric characteristics of the polymer piezoelectric element be enhanced, that is, a polymer piezoelectric element with improved sensitivity can be provided.

That is, the flexible piezoelectric element of the present invention is characterized in that at least one surface of a polymer piezoelectric film is provided with a thermal spray coating electrode.

The thermal spray coating is generally a method for forming a metallic coating by spraying a molten metallic material toward a counter substrate and solidifying it on the surface. Generally, it is almost used for surface treatment of polymer films. Absent. Furthermore, in addition to the low heat resistance inherent in the material, it is possible to perform thermal spray coating with improved piezoelectric properties in polymer piezoelectric films that have undergone polarization treatment in order to exhibit excellent piezoelectric properties. It was quite surprising to the inventors.

As the polymer piezoelectric material used in the present invention, a vinylidene cyanide-vinyl acetate copolymer having a relatively high heat resistance is preferably used, and a vinylidene fluoride resin piezoelectric material having excellent piezoelectric characteristics is also used. In particular, compared to vinylidene fluoride (VDF) homopolymer that requires uniaxial stretching for β-type crystallization suitable for exhibiting piezoelectricity, VD capable of β-type crystallization under normal crystallization conditions.
F-based copolymer (for example, a copolymer of a predominant amount of VDF and a subordinate amount of vinyl fluoride (VF) trifluoroethylene (TrFE) or tetrafluoroethylene (TFE))
Further, a copolymer of a predominant amount (particularly 70 to 80 mol%) of VDF and a subordinate amount (particularly 30 to 20 mol%) of TrFE is most preferably used.

After being formed into a film by melt extrusion or the like, these polymer piezoelectric materials are subjected to polarization treatment by uniaxial stretching or heat treatment at a softening temperature or lower, and application of an electric field at a softening temperature or lower, if necessary. Before thermal spray coating, the polymer piezoelectric film used in the present invention preferably has a thickness of about 200 to 2000 μm, particularly 300 to 1000 μm. If the thickness of the film is less than 200 μm, the heat resistance during thermal spraying is poor, and problems such as film deformation and variations 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.

In its most basic form, the flexible piezoelectric element of the present invention has, as shown in FIG. 1, a spray-coated electrode 2 on one surface of a polymer piezoelectric film 1 as described above. It is also preferable to preliminarily roughen the surface of the polymer piezoelectric film 1 covered with the electrodes 2 or both surfaces of the film 1 if necessary.

Examples of the material of the sprayed electrode 2 include copper, aluminum, zinc and the like. Among them, zinc which can be sprayed at a relatively low temperature and which gives an electrode film excellent in solderability, or An alloy of zinc and copper is preferably used. The thickness of the spray-coated electrode 2 can be selected within a range that provides good solderability and does not impair the flexibility of the piezoelectric element, but is generally set in the range of 10 to 100 μm, particularly preferably 20 to 50 μm.

The thermal spraying method used for forming the electrode 2 needs to be one that does not excessively heat the polymer piezoelectric film 1 so that the piezoelectric characteristics of the polymer piezoelectric film 1 are not essentially impaired. Arc spraying or gas spraying (plasma spraying) can be used. In particular, the wire arc spraying is a preferred embodiment because the thermal load on the polymer piezoelectric film 1 is smaller than that of other spraying methods, and even in that case, the thermal spraying process does not force the piezoelectric film 1 to be cooled. It is preferable to place it on a rotating body and control the heat load.

As shown in FIG. 1, the flexible piezoelectric element of the present invention, when used as the piezoelectric element, faces the surface of the polymer piezoelectric film 1 opposite to the surface on which the thermal spray coating electrode 2 is provided. It has an electrode 3. The counter electrode 3 may be a spray-coated electrode similar to the spray-coated electrode 2, or may be a vapor-deposited electrode of copper, aluminum, or the like when lead wire connectivity by soldering is not so required.

As a preferred form of the flexible piezoelectric element of the present invention, as shown in FIG. 2, an adhesive layer 4 is provided on the surface of the polymer piezoelectric film 1 opposite to the surface on which the thermal spray coating electrode 2 is formed. A structure in which the metal foil electrode 5 is attached can also be adopted. The adhesive layer 4 can also be formed by a conductive adhesive in which conductive particles are dispersed, but an epoxy resin, a urethane resin, a polyester resin, a butadiene resin, a propylene resin having more excellent adhesive strength. It is preferable to form a layer having a thickness of about 5 to 40 μm with an adhesive such as an acrylic resin.

The metal foil electrode 5 has a thickness of 6 to 200 μm, more preferably 20 to 120 μm, and particularly 20 to 8 of a metal having good conductivity such as copper, aluminum, tin, zinc, gold, silver and platinum.
A foil of 0 μm is preferably used.

The reason why the flexible piezoelectric element having the structure shown in FIG. 2 is preferably used is that when the metal foil electrode 5 as described above is used, it is preferable to solder the both sides together with the spray-coated electrode 2 provided on the opposite surface. Secure lead wire connectivity,
This is because when the metal foil electrode 5 is attached to one surface of the polymer piezoelectric film, the flexibility is remarkably less deteriorated than when it is attached to both surfaces.

According to another preferred embodiment of the present invention, a laminated piezoelectric element as shown in FIG. 3 is formed as a bimorph diaphragm. In this laminated piezoelectric element, a pair of polymer piezoelectric films 1 each having a thermally sprayed coating electrode 2 formed on one surface thereof on both sides of a metal foil electrode 5 forming a central layer with an adhesive layer 4 interposed therebetween are provided. They are attached so that they are on the outer sides of each other. When only one layer of the metal foil electrode 5 is used as described in the example of FIG. 2,
While the decrease in flexibility due to this can be tolerated, the spray-coated electrodes 2 provided on both sides ensure good lead wire connectivity by soldering. Further, the structure of FIG. 3 is vertically symmetrical with the metal foil electrode 5 whose flexibility is located at the center as a neutral axis, and has an advantage that vibration characteristics are also symmetrical. When obtaining the structure of FIG. 3, it is of course possible to first attach the polymer piezoelectric film 1 on both surfaces of the metal foil electrode 5, and then form the thermal spray coating electrodes 2 on both surfaces by thermal spraying.

In the laminated piezoelectric element shown in FIG. 3, the polarization directions p of the upper and lower polymer piezoelectric films 1 are set to the same direction as shown, and a voltage is applied from the AC power source 6,
Repeats an action similar to the fan movement of a fan. This laminated piezoelectric element is suitable as a bimorph diaphragm because it has appropriate flexibility and the thermal spray coating electrode 2 is firmly coated on the piezoelectric film 1.

[0022]

EXAMPLES Examples of preparation and evaluation of the piezoelectric element of the present invention will be shown below. The following characteristics were evaluated for the piezoelectric elements produced in the following examples.

Piezoelectric property: Hydrostatic pressure piezoelectric strain constant (d _h constant) was measured by the following method. 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. Then, the increase amount dQ of the charge with respect to the pressure increase dP near the gauge pressure of 2 kg / cm ² was obtained and calculated by the following formula.

D _h = (dQ / dP) / A The unit is C / N. Where A is the electrode area (m ² )
Is.

Flexibility: Samples are spaced 4c apart as shown in FIG.
It is supported by two fulcrums of m and 1 cm required to bend the sample by 2 mm by applying a load W at a speed of 5 mm / min at the center of the fulcrum.
The load value per width was determined and used as 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
953 U (curing agent) = 1: 1, Nippon Ciba Geigy Co., Ltd. was applied, and it was attached to the electrode forming surface of the piezoelectric element, and pressed at 90 ° C. under a pressure of 100 kgf / cm ² for 20 minutes. Subsequently, JIS C was applied to this laminated sample.
A 90-degree peel test was performed at a speed of 50 mm / min according to -6481. Note that this electrode peel strength is the degree of inconvenience such as cracking or peeling of the electrode around the solder when connecting the lead wire to the electrode by soldering or when handling the element thereafter, that is, lead wire connection 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 FIG. 2 was formed as follows.

First, a VDF / TrFE (75/25 molar ratio) copolymer (manufactured by Kureha Chemical Industry) was used at a die temperature of 265 ° C.
Sheet extruded, and after heat treatment at 125 ℃ for 13 hours,
Under an electric field of 5 MV / m, a holding time of 5 minutes at 123 ° C. and a polarization process of 1 hour including the elevating time were performed, and a thickness of 500
A polymer piezoelectric film 1 having a thickness of μm was obtained.

After one surface of the polymer piezoelectric film 1 was roughened, it was attached to a copper foil having a thickness of 35 μm via a polyester adhesive layer 4 having a thickness of 20 μm.

Then, the other surface of the polymer piezoelectric film 1 thus adhered is sandblasted with an alumina-based abrasive having a grain size of # 60 to roughen the surface, and then an electric wire spraying machine (Kato Metallikon Co., Ltd.) is used. Made, DK type metal sprayer E
Type) to spray a zinc sprayed electrode 2 having a thickness of about 40 μm by performing spraying under the conditions of an air pressure of 5 kg / cm ² and a voltage of 15 V to obtain a piezoelectric element.

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

Zinc sprayed electrodes 2 were formed on both sides of the same polymer piezoelectric film 1 as in Example 1 by the same method as in Example 1 to obtain a piezoelectric element.

A 90-degree peel test was conducted on this piezoelectric element, and the peel strength of the electrode was found to be 1.08 kg / c.
It was m.

Comparative Example 1 A piezoelectric element was obtained by forming a 0.03 μm thick aluminum vapor-deposited film on each side of the polymer piezoelectric film 1 formed in Example 1. When a 90-degree peel test was performed on this piezoelectric element, the peel strength of the electrode was 0.0.
It was 3 kg / cm and could be easily peeled off.

Comparative Example 2 A piezoelectric element was obtained by sticking a copper foil having a thickness of 35 μm on both sides of the polymer piezoelectric film 1 formed in Example 1 via a polyester adhesive layer having a thickness of 20 μm.

Comparative Example 3 Instead of the aluminum used in Comparative Example 1, copper was used as the vapor-deposited metal to obtain a piezoelectric element.

A soldering test was conducted on each electrode of the piezoelectric element obtained in each of the above-mentioned examples. As a result, the zinc-sprayed electrodes and the copper foil electrodes of Examples 1 and 2 and Comparative Example 2 had good solder lead wire connectivity. However, the copper vapor-deposited electrode of Comparative Example 3 was found to be peeled from the solder peripheral portion or cracked when the lead wire was soldered.

Next, the piezoelectric characteristics (d _h constant) and the flexibility (deflection load) of each piezoelectric element were measured, and the results shown in the following table were obtained.

[0040]

[0041]

As described above, according to the present invention, by providing the thermal spray coating electrode on at least one surface of the polymer piezoelectric film, the piezoelectric characteristics (high sensitivity) superior to the element provided with the conventional vapor deposition electrode can be obtained. In addition, a piezoelectric element having excellent strength and flexibility for connecting lead wires by soldering can be obtained.

[Brief description of drawings]

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

FIG. 2 is a schematic cross-sectional view of another embodiment of the piezoelectric element of the present invention.

FIG. 3 is a schematic cross-sectional view showing another embodiment of the piezoelectric element of the present invention together with the connection state thereof.

FIG. 4 is an explanatory diagram of a method for measuring flexibility of a piezoelectric element in Examples and Comparative Examples.

[Explanation of symbols]

 1: Polymer piezoelectric film 2: Thermal spray coating electrode 3: Counter electrode 4: Adhesive layer 5: Metal foil electrode

Claims (4)

[Claims] 1. A flexible piezoelectric element comprising a polymer piezoelectric film or sheet provided with a spray-coated electrode on at least one surface thereof. 2. The device according to claim 1, wherein the spray-coated electrode is made of zinc. 3. The element according to claim 1, wherein a metal foil electrode is attached to a surface of the polymer piezoelectric film or sheet opposite to the surface provided with the sprayed coating electrode. 4. The two flexible piezoelectric elements having the same or different structure according to any one of claims 1 to 3 are laminated and adhered to each other so that the surface having the spray-coated electrodes is on the outside. Multilayer piezoelectric element.