JP7045777B2 - Transducer and power generation system using it - Google Patents

Description

The present invention relates to a transducer provided with a flexible piezoelectric element and a power generation system using the transducer as a power generation device.

Piezoelectric materials generate an electric charge when pressure is applied to cause strain. Utilizing the characteristics of this piezoelectric material, a power generation system has been developed that converts vibration energy such as environmental vibration into electrical energy to generate electricity. For example, Patent Document 1 describes a power generation system in which a piezoelectric element is installed on a road surface and a person or a vehicle passes over the piezoelectric element to generate electricity. In this type of power generation system, it is necessary to install the piezoelectric element in a wide range, and it is required that the amount of power generation is large. Further, the piezoelectric element needs to be durable against repeated deformation, and the influence from the environment such as moisture and dust must be eliminated as much as possible.

Known examples of the piezoelectric material include ceramics such as lead zirconate titanate (PZT), polymers such as polyvinylidene fluoride (PVDF) and polylactic acid, and composites in which piezoelectric particles are filled in a polymer matrix. .. Of these, it is not easy to increase the area by using ceramics. If a polymer is used, it is easy to increase the area, but there is a problem that the amount of power generation is small. In particular, in the case of resin, since it lacks flexibility, it is difficult to install it on a curved surface or the like, and there is a problem in durability.

As a technique for increasing the amount of power generation in a piezoelectric element using a polymer material, for example, Patent Document 2 uses a power generation body in which an electlet dielectric and an electrode are partially bonded to form a gap between them. In addition, a laminated power generation body in which a plurality of the power generation bodies are laminated and a support member is interposed between the power generation bodies is described. In the laminated power generator described in Patent Document 2, power is generated by electrostatic induction according to the change in the distance of the gap formed between the electret dielectric and the electrode, and the external force is easily transmitted by the support member. As a result, the change in the distance of the gap is increased.

Patent Document 3 describes a power generation device including a resin film having a plurality of pores, a power generation element having a pair of electrodes arranged on both sides thereof, and an elastic body laminated on the power generation element. .. In the power generation device described in Patent Document 3, a plurality of pores are provided in the resin film, and the resin film is pressed by an elastic body having irregularities to increase the amount of deformation of the pores and improve the piezoelectricity. There is.

In Patent Document 4, a piezoelectric film and an elastically deformable flat plate-shaped base material are alternately used as constituent members of a mobile power generation device that generates power based on the relative flow of an external fluid when the moving body moves. The power generation units stacked in the above are described. In the power generation unit described in Patent Document 4, the piezoelectric film is deformed by the deformation of the base material. Further, FIG. 7 of Patent Document 4 describes a form in which the surface of the power generation unit is covered with a resin covering material.

Japanese Unexamined Patent Publication No. 2006-197704 Japanese Unexamined Patent Publication No. 2014-121201 Japanese Unexamined Patent Publication No. 2014-207391 International Publication No. 2015/06847

As described above, the piezoelectric element requires durability as well as a large amount of power generation. As a method for imparting durability to the piezoelectric element and eliminating the influence from the environment, as described in FIG. 7 of Patent Document 4, a method of covering the piezoelectric element with a covering material can be considered. However, when the covering material is made of resin, the flexibility is poor, which hinders the deformation of the piezoelectric element. Therefore, even if the amount of power generation can be increased by making the piezoelectric element easily deformed, the effect is diminished by the presence of the covering material, and the effect of increasing the amount of power generation cannot be exerted. As described above, it has been difficult to achieve both an increase in power generation and an improvement in durability in the piezoelectric element.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a transducer having a large amount of generated charge and excellent durability by using a flexible piezoelectric element. Another object of the present invention is to provide a power generation system having a large amount of power generation and excellent durability by using the transducer.

(1) In order to solve the above problems, the transducer of the present invention includes a piezoelectric layer containing an elastomer and piezoelectric particles, an electrode layer arranged so as to sandwich the piezoelectric layer, and an elastic body layer arranged at least on the outermost layer. A piezoelectric element having a And it is characterized in that a cushioning portion containing at least one of solids having a smaller elastic coefficient than the elastic body layer is partitioned.

(2) In order to solve the above problems, the power generation system of the present invention is characterized by comprising the transducer of the present invention and an electric circuit for extracting electric energy from the transducer.

(1) According to the transducer of the present invention, the matrix (base material) of the piezoelectric layer constituting the piezoelectric element is an elastomer, and the elastic body layer is arranged on the outermost layer of the piezoelectric element. Since the piezoelectric element is flexible and can be manufactured by an extrusion method or a coating method, it is easy to increase the area. Further, if a relatively flexible material is used for the exterior material, it can be arranged in a place having a complicated shape such as a curved surface. An elastic body layer is arranged at least on the outermost layer of the piezoelectric element. That is, the elastic layer is arranged outside the stacking direction of the piezoelectric layer and the electrode layer. When a force is applied to the piezoelectric element in the stacking direction (thickness direction) of the piezoelectric layer and the electrode layer (when the piezoelectric element is compressed), the elastic body layer expands in the plane direction, and a shearing force is applied to the piezoelectric layer. It works. As a result, a tensile force in the surface direction is applied to the piezoelectric layer in addition to the pressing force in the thickness direction, and the strain of the piezoelectric layer increases. As a result, the amount of charge generated in the piezoelectric layer increases, and the sensitivity (S / N ratio (Signal-Noise Ratio)) and the amount of power generation in the piezoelectric element are improved.

In the transducer of the present invention, a cushioning portion is partitioned between the exterior material and the piezoelectric element. The shock absorber contains at least one of a gas, a non-volatile liquid, and a solid having a modulus of elasticity smaller than that of the elastic layer. The cushioning portion is arranged in a direction in which the piezoelectric element expands when pressed in the thickness direction. FIG. 1 shows a schematic cross-sectional view of an example of the transducer of the present invention. FIG. 1A shows the state before compression, and FIG. 1B shows the state after compression.

As shown in FIG. 1A, the transducer 10 includes a piezoelectric element 20 and an exterior material 30. The exterior material 30 is made of an elastomer and has a bag shape. The piezoelectric element 20 is housed inside the exterior material 30. A buffer portion 31 is arranged between the piezoelectric element 20 and the exterior material 30. The buffer portion 3 is arranged so as to surround the side surface of the piezoelectric element 20, in other words, the outer circumference. Air is housed in the shock absorber 31. The piezoelectric element 20 has a piezoelectric layer 21, a pair of electrode layers 22a and 22b, and a pair of elastic body layers 23a and 23b. The piezoelectric layer 21 contains an elastomer and piezoelectric particles. The pair of electrode layers 22a and 22b are arranged one by one on both sides in the thickness direction with the piezoelectric layer 21 interposed therebetween. The elastic body layer 23a is arranged on the upper surface (outside) of the electrode layer 22a. The elastic body layer 23b is arranged on the lower surface (outside) of the electrode layer 22b.

As shown by the white arrows in FIG. 1 (b), when a load is applied from above the transducer 10, the exterior material 30 is deformed so as to be recessed downward, and the elastic body layer 23a of the piezoelectric element 20 is also pressed against the surface. Stretch in the direction. Along with this, the piezoelectric layer 21 and the electrode layers 22a and 22b also extend in the plane direction. Since there is a buffer portion 31 in which air is housed in the direction in which the piezoelectric element 20 extends, that is, on the outer peripheral side, even if the piezoelectric element 20 bulges in the outer peripheral direction, its deformation is not easily regulated by the exterior material 30.

As described above, the presence of the cushioning portion between the exterior material and the piezoelectric element makes it difficult for the exterior material to hinder the stretch deformation of the piezoelectric element even when the exterior material has poor flexibility. Therefore, according to the transducer of the present invention, it is possible to realize both the effect of increasing the amount of electric charge generated by the elastic layer and the effect of improving durability by the exterior material.

The transducer of the present invention is suitable as a power generation device because the amount of power generated by the piezoelectric element is large. Moreover, since the sensitivity of the piezoelectric element is high, it is easy to detect a small load. Therefore, the transducer of the present invention is used not only as a power generating device but also as a biological information sensor for measuring pulse rate and respiratory rate by arranging it directly on the skin of the human body or indirectly through clothes. Can be done.

(2) The power generation system of the present invention includes the above-mentioned transducer of the present invention. Therefore, the amount of power generation is large and the durability is excellent. In addition, the transducer can be installed in a large area over a wide area. Therefore, the power generation system of the present invention is suitable for a system that is embedded in a road, a bridge, a railroad rail, or the like and generates power by pressing from a moving body passing therethrough.

FIG. 1A is a schematic cross-sectional view of an example of the transducer of the present invention, FIG. 1A shows a state before compression, and FIG. 1B shows a state after compression. It is a schematic diagram of the power generation system of 1st Embodiment. It is a cross-sectional view in the thickness direction of a transducer constituting the power generation system. It is a circuit diagram of the power generation system. It is a transmission top view of the transducer of the second embodiment. It is a transmission top view of the transducer of the third embodiment. It is a transmission top view of the transducer of the 4th embodiment. It is sectional drawing in the radial direction of the transducer of the 5th Embodiment.

Hereinafter, embodiments of the transducer and power generation system of the present invention will be described.

(1) First Embodiment First, the configuration of the transducer and the power generation system of the first embodiment will be described. FIG. 2 shows a schematic diagram of the power generation system of the first embodiment. FIG. 3 shows a cross-sectional view in the thickness direction of the transducers constituting the power generation system. FIG. 4 shows a circuit diagram of the power generation system. In FIG. 2, the transducer is shown in the top view and is shown through the exterior material for convenience of explanation.

<Power generation system>
As shown in FIG. 2, the power generation system 1 includes a transducer 10 and an electric circuit 40. The transducer 10 is electrically connected to the electric circuit 40 via the wiring 41. As shown in FIG. 4 surrounded by an alternate long and short dash line, the electric circuit 40 includes a rectifier circuit 42, a capacitor 43, a switch 44, and a load 45. The rectifier circuit 42 converts the AC voltage output from the transducer 10 into a DC voltage. The capacitor 43 stores rectified power. The electric power stored in the capacitor 43 is supplied to the load 45 via the switch 44. In this way, the electric circuit 40 extracts electric energy from the transducer 10.

<Transducer>
As shown in FIG. 2 for a top view of transmission and FIG. 3 for a cross-sectional view in the thickness direction, the transducer 10 includes a piezoelectric element 20 and an exterior material 30. The piezoelectric element 20 has a rectangular sheet shape (shown by solid line hatching in FIG. 2), and has five units 24 and six elastic body layers 230. The unit 24 and the elastic layer 230 are alternately arranged in the thickness direction (vertical direction).

Each of the five units 24 has a piezoelectric layer and a pair of electrode layers arranged so as to sandwich the piezoelectric layer (electrode layer / piezoelectric layer / electrode layer, not shown). The piezoelectric layer contains an elastomer and piezoelectric particles. The pair of electrode layers contains an elastomer and a conductive material. The pair of electrode layers are arranged one by one on both sides in the thickness direction (vertical direction) of the piezoelectric layer. That is, the piezoelectric element 20 has five piezoelectric layers, and the piezoelectric layers are laminated via an electrode layer. Wiring 41 is connected to each of the electrode layers. The electrode layer and the electric circuit 40 are electrically connected by a wiring 41.

The six elastic layers 230 are all made of thermoplastic elastomer and have an elastic modulus of 19 MPa. The six elastic body layers 230 are arranged between the upper surface of the uppermost unit 24 and the lower surface of the lowermost unit 24 (that is, the outermost layer of the piezoelectric element 20) and between adjacent units 24.

The exterior material 30 is composed of an upper sheet and a lower sheet, and has a bag shape due to the peripheral portions of both sheets being bonded to each other (indicated by dotted hatching in FIG. 2). Both the upper sheet and the lower sheet are made of an elastomer having excellent durability and moisture resistance. The piezoelectric element 20 is housed inside the exterior material 30. An insertion hole for taking out the wiring 41 connected to the transducer 10 is formed in a part of the peripheral portion of the exterior material 30.

A buffer portion 31 is arranged between the piezoelectric element 20 and the exterior material 30. The cushioning portion 31 is arranged so as to surround the side surface of the piezoelectric element 20 in the thickness direction, in other words, the outer periphery of the piezoelectric element 20. Air is housed in the shock absorber 31. That is, there is a gap between the outer circumference of the piezoelectric element 20 and the exterior material 30. The upper and lower surfaces of the piezoelectric element 20 are in contact with the exterior material 30, but are not adhered to each other.

<Action effect>
Next, the operation and effect of the transducer and the power generation system of the first embodiment will be described. When a load is applied from above the transducer 10, the elastic layer 230 of the piezoelectric element 20 is pressed and stretches in the plane direction. Then, the unit 24 also extends in the plane direction so as to be pulled by the elastic body layer 230. At this time, since the tensile force in the plane direction is applied to the piezoelectric layer constituting the unit 24 in addition to the pressing force, the strain of the piezoelectric layer becomes large. Here, on the outer peripheral side of the elastic body layer 230 and the unit 24 (piezoelectric element 20), there is a buffer portion 31 (gap) in which air is housed. Further, the upper and lower surfaces of the piezoelectric element 20 are not adhered to the exterior material 30. Therefore, even if the piezoelectric element 20 bulges in the outer peripheral direction, its deformation is not easily regulated by the exterior material 30. Therefore, the piezoelectric element 20 can generate a large amount of electric charge. Further, the piezoelectric element 20 has five units 24. Therefore, the amount of charge generated is larger than that when the unit 24 is used alone (see FIG. 1 above). Further, the exterior material 30 is made of an elastomer having excellent durability and moisture resistance. Therefore, in the transducer 10, the effect of increasing the amount of electric charge generated by the elastic body layer 230 and the effect of improving durability by the exterior material 30 are compatible. Further, since the transducer 10 is mainly composed of an elastomer material, it is easy to increase the area and it is easy to arrange it in a place having a complicated shape such as a curved surface.

(2) Second Embodiment The transducer and power generation system of this embodiment differs from that of the first embodiment only in the shape and arrangement of the piezoelectric elements constituting the transducer. Therefore, the differences will be mainly described here. FIG. 5 shows a top view of the transmission of the transducer of the present embodiment. FIG. 5 corresponds to the transducer shown in FIG. 2 above. In FIG. 5, the members corresponding to FIG. 2 are indicated by the same reference numerals.

As shown in FIG. 5, the transducer 10 includes five piezoelectric elements 20 and an exterior material 30. Each of the five piezoelectric elements 20 has a band shape (indicated by solid line hatching in FIG. 5). The five piezoelectric elements 20 are arranged in parallel with each other at predetermined intervals in the lateral direction. The outer periphery of each piezoelectric element 20 is surrounded by an exterior material 30 with a cushioning portion 31 interposed therebetween. That is, the exterior material 30 is attached not only to the peripheral portion but also between the adjacent piezoelectric elements 20 (indicated by dotted line hatching in FIG. 5). The cushioning portion 31 is arranged between the piezoelectric element 20 and the exterior material 30, that is, so as to surround the outer periphery of the piezoelectric element 20. Air is housed in the shock absorber 31. The configuration of each piezoelectric element 20 is the same as the configuration of the piezoelectric element 20 of the first embodiment (see FIG. 3 above).

In the present embodiment, a plurality of piezoelectric elements 20 are arranged in the exterior material 30. As a result, the degree of freedom in shape is improved, and for example, it is possible to generate power only in a place where power is desired to be generated, or to thin out piezoelectric elements according to the application to improve flexibility. Further, when the transducer 10 of the present embodiment is used as a sensor, it becomes easy to identify the place where the load is applied.

(3) Third Embodiment The transducer and power generation system of the present embodiment differs from that of the second embodiment only in the length of a part of the piezoelectric element constituting the transducer. Therefore, the differences will be mainly described here. FIG. 6 shows a top view of the transmission of the transducer of the present embodiment. FIG. 6 corresponds to FIG. 5 above. In FIG. 6, the members corresponding to those in FIG. 5 are indicated by the same reference numerals.

As shown in FIG. 6, the transducer 10 includes five piezoelectric elements 20 and an exterior material 30. Each of the five piezoelectric elements 20 has a band shape and differs only in length (indicated by solid line hatching in FIG. 5). That is, the three piezoelectric elements 20 on the left side when viewed from above are shorter than the two piezoelectric elements 20 on the right side. The five piezoelectric elements 20 are arranged in parallel with each other at predetermined intervals in the lateral direction. The outer periphery of each piezoelectric element 20 is surrounded by an exterior material 30 with a cushioning portion 31 interposed therebetween.

(4) Fourth Embodiment The transducer and power generation system of the present embodiment and that of the second embodiment differ only in the number and arrangement of piezoelectric elements constituting the transducer. Therefore, the differences will be mainly described here. FIG. 7 shows a top view of the transmission of the transducer of the present embodiment. FIG. 7 corresponds to FIG. 5 above. In FIG. 7, the members corresponding to FIG. 5 are indicated by the same reference numerals.

As shown in FIG. 7, the transducer 10 includes ten piezoelectric elements 200 to 209 and an exterior material 30. Each of the ten piezoelectric elements 200 to 209 has a band shape (indicated by solid line hatching in FIG. 7). The ten piezoelectric elements 200 to 209 are arranged in two upper and lower layers, five each. The five upper piezoelectric elements 200 to 204 extend in the front-rear direction, and are arranged in parallel with each other at predetermined intervals in the left-right direction. The lower five piezoelectric elements 205 to 209 extend in the left-right direction, and are arranged in parallel with each other at predetermined intervals in the front-rear direction. When viewed from above, the upper five piezoelectric elements 200 to 204 and the lower five piezoelectric elements 205 to 209 are arranged in a grid pattern. The electrode layer in the piezoelectric elements 200 to 209 and the electric circuit 40 are electrically connected by wirings 410 and 411.

The exterior material 30 is partially attached not only to the peripheral portion but also to a section where the piezoelectric elements 200 to 209 are not arranged (indicated by dotted line hatching in FIG. 7). The cushioning portion 31 is arranged between the piezoelectric elements 200 to 209 and the exterior material 30. Air is housed in the shock absorber 31. The configurations of the individual piezoelectric elements 200 to 209 are the same as the configurations of the piezoelectric elements 20 of the first embodiment (see FIG. 3 above).

In the present embodiment, a plurality of piezoelectric elements 20 are arranged in two stages in the exterior material 30. As a result, the amount of power generation becomes larger. In addition, it is possible to generate electricity only in the place where it is desired to generate electricity, or to thin out the piezoelectric elements according to the application to improve the flexibility. Further, when the transducer 10 of the present embodiment is used as a sensor, the detection area can be enlarged in addition to facilitating the identification of the place where the load is applied.

(5) Fifth Embodiment The transducer and power generation system of the present embodiment and those of the first embodiment differ only in the usage mode of the transducer. Therefore, the differences will be mainly described here. FIG. 8 shows a radial cross-sectional view of the transducer of the present embodiment. In FIG. 8, the members corresponding to those in FIG. 2 above are designated by the same reference numerals.

As shown in FIG. 8, the transducer 10 is a sheet-shaped transducer 10 of the first embodiment wound with one end inside and toward the other end. Looking at the radial cross section of the transducer 10, the piezoelectric element 20 has a spiral shape in which six layers are laminated in the radial direction. According to the present embodiment, it is possible to realize a form in which a large number of piezoelectric elements 20 are laminated by simply manufacturing the transducer 10 in a sheet shape as in the first embodiment and winding the transducer 10. Therefore, when a load is applied from the radial direction of the transducer 10, a larger amount of power generation can be obtained. Further, according to the present embodiment, it can be applied to a place where it is difficult to arrange a sheet-shaped transducer.

(6) Other Embodiments The transducer and power generation system of the present invention are not limited to the above embodiments, and various modifications and improvements that can be made by those skilled in the art are made without departing from the gist of the present invention. It can be carried out in the form.

For example, in the above embodiment, the power generation system is configured from one transducer and the electric circuit, but a plurality of transducers stacked or the like may be connected to the electric circuit to form the power generation system. In the above embodiment, the transducer is used as a power generation device, but the transducer of the present invention may be used as a sensor. When used as a sensor, it has a high S / N ratio, so it is easy to detect a small load. The components of the transducer of the present invention will be described in detail below.

<Piezoelectric element>
The piezoelectric element has a piezoelectric layer containing an elastomer and piezoelectric particles, an electrode layer arranged so as to sandwich the piezoelectric layer, and an elastic body layer arranged at least in the outermost layer. The number of piezoelectric layers may be one layer or two or more layers. From the viewpoint of increasing the amount of power generation, it is desirable to stack a plurality of, for example, several tens to several hundreds of piezoelectric layers via the electrode layer. The elastic layer may be arranged at least in the outermost layer. However, as shown in the above embodiment, when a plurality of piezoelectric layers are laminated via the electrode layer, they may be arranged between adjacent electrode layers in the middle of the laminated body. That is, the elastic layer may be arranged between the units composed of the piezoelectric layer and the electrode layer sandwiching the piezoelectric layer. In this case, the amount of power generation can be increased. In the fifth embodiment, the embodiment in which one piezoelectric element is wound together with the exterior material is shown, but only the piezoelectric element may be wound and accommodated in the tubular exterior material.

[Piezoelectric layer]
As the elastomer constituting the piezoelectric layer, one or more selected from crosslinked rubber and thermoplastic elastomer may be used. As flexible elastomers with relatively low elasticity, urethane rubber, silicone rubber, nitrile rubber (NBR), hydride nitrile rubber (H-NBR), acrylic rubber, natural rubber, isoprene rubber, ethylene-propylene-diene rubber (EPDM) , Ethylene-vinyl acetate copolymer, ethylene-vinyl acetate-acrylic acid ester copolymer, butyl rubber, styrene-butadiene rubber, fluororubber, epichlorohydrin rubber, chloroprene rubber, chlorinated polyethylene, chlorosulfonated polyethylene and the like. Further, an elastomer modified by introducing a functional group or the like may be used. Examples of the modified elastomer include carboxyl group-modified nitrile rubber (X-NBR) and carboxyl group-modified hydrogenated nitrile rubber (XH-NBR).

The amount of electric charge (C) generated when a load is applied to the piezoelectric layer is represented by the following equation (a) by the piezoelectric strain constant (C / N) of the piezoelectric layer and the applied load (N).
Amount of generated charge = Piezoelectric strain constant x Load ... (a)
Piezoelectric particles are particles of a compound having piezoelectricity. As a compound having piezoelectricity, a strong dielectric having a perovskite-type crystal structure is known. For example, barium titanate, strontium titanate, potassium niobate, sodium niobate, lithium niobate, potassium niobate sodium niobate are known. , Potassium niobate lithium sodium niobate, lead zirconate titanate (PZT), barium titanate strontium (BST), bismas lanthanum titanate (BLT), bismus strontium tantalate (SBT) and the like. As the piezoelectric particles, one or more of these may be used.

The particle size of the piezoelectric particles is not particularly limited. For example, when a plurality of types of piezoelectric particle powders having different average particle diameters are used, it is possible to mix the large particle size piezoelectric particles and the small particle size piezoelectric particles in the elastomer. In this case, the piezoelectric particles having a small particle size enter between the piezoelectric particles having a large particle size, and the pressure is easily transmitted to the piezoelectric particles. As a result, the piezoelectric strain constant of the piezoelectric layer becomes large, and the amount of generated charge can be increased.

The blending amount of the piezoelectric particles may be determined in consideration of the flexibility of the piezoelectric layer and the piezoelectric element, and the piezoelectric performance of the piezoelectric layer. When the blending amount of the piezoelectric particles is large, the piezoelectric performance of the piezoelectric layer is improved, but the flexibility is decreased. Therefore, it is desirable to adjust the blending amount of the piezoelectric particles so as to achieve the desired flexibility in the combination of the elastomer and the piezoelectric particles to be used.

In addition to the elastomer and the piezoelectric particles, the piezoelectric layer may contain reinforcing particles having a smaller relative permittivity than the piezoelectric particles. The relative permittivity of the reinforcing particles is preferably 100 or less, more preferably 30 or less, provided that it is smaller than the relative permittivity of the piezoelectric particles.

In the structure in which the piezoelectric particles having a large relative permittivity are connected, the external force is easily transmitted to the piezoelectric particles, so that the improvement of the piezoelectric strain constant of the above-mentioned formula (a) can be expected. However, when the piezoelectric particles having a large relative dielectric constant are connected, the dielectric constant of the piezoelectric layer as a whole increases. On the other hand, when the piezoelectric layer contains both the piezoelectric particles and the reinforcing particles, the connection between the piezoelectric particles having a large relative permittivity is divided by the intervention of the reinforcing particles having a smaller relative permittivity. This makes it possible to suppress an increase in the dielectric constant of the piezoelectric layer as a whole. On the other hand, since the connected structure of the particles is maintained by the reinforcing particles and the piezoelectric particles, the piezoelectric strain constant can be maintained. That is, when the piezoelectric layer contains reinforcing particles, the dielectric constant of the entire piezoelectric layer can be made smaller than when only the piezoelectric particles are contained while maintaining the piezoelectric strain constant. Therefore, a large amount of generated charge can be obtained by the above-mentioned formula (a).

As the reinforcing particles, particles having a large electric resistance are desirable. When the electric resistance of the reinforcing particles is large, the dielectric breakdown strength of the piezoelectric layer becomes large. As a result, in the polarization treatment of the piezoelectric layer described later, a high electric field can be applied to shorten the treatment time. In addition, the number of piezoelectric elements destroyed during the polarization process can be reduced, which improves productivity.

Further, it is desirable that the reinforcing particles are chemically bonded to the elastomer. In this case, since a network of reinforcing particles is formed in the elastomer, impurity ions ionized by cross-linking agents, additives, moisture in the air, and the like become difficult to move, and the electrical resistance of the piezoelectric layer increases. The chemical bond between the reinforcing particles and the elastomer can be realized, for example, by surface-treating the reinforcing particles. As a surface treatment method, a surface treatment agent having a functional group capable of reacting with the elastomer polymer is previously reacted with the reinforcing particles, and the reinforcing particles are mixed with the elastomer polymer, or the surface of the reinforcing particles is acid or alkaline. Alternatively, a method of dissolving in subcritical water to generate a hydroxyl group and then mixing with an elastomer polymer having a functional group capable of reacting with the hydroxyl group can be mentioned. When the reinforcing particles are chemically bonded to the elastomer, the reinforcing particles are less likely to be displaced even after repeated expansion and contraction. In addition, since the reinforcing particles are not easily peeled off from the elastomer, fluctuations in physical properties and output from the initial values are reduced. Therefore, the output is stable and the sag resistance of the piezoelectric layer is improved. Further, since the breaking elongation of the piezoelectric layer becomes large, it is possible to suppress the deterioration of the piezoelectric performance due to local fracture or the like at the time of stretching. As a result, high piezoelectric performance can be maintained even in the stretched state.

The type of reinforcing particles is not particularly limited. For example, oxides such as titanium dioxide, silica and barium titanate, and particles such as rubber and resin can be used. However, when relatively soft particles such as rubber particles are included, the applied load may be attenuated by the resin particles and may not be easily transmitted to the piezoelectric particles. From the viewpoint of facilitating the transmission of force to the piezoelectric particles, increasing the piezoelectric strain constant of the piezoelectric layer in the above-mentioned formula (a), and increasing the amount of generated charge, the reinforcing particles have a higher elastic modulus than the elastomer of the matrix. It is better to use particles with a large charge. For example, metal oxide particles such as titanium dioxide are suitable because they have a small relative permittivity and a large effect of improving dielectric breakdown resistance. As a method for producing metal oxide particles, the sol-gel method is suitable because particles having low crystallinity and a low relative permittivity can be obtained.

The piezoelectric layer is produced by curing a composition obtained by adding a powder of piezoelectric particles, a cross-linking agent, or the like to an elastomer polymer under predetermined conditions. After that, the piezoelectric layer is subjected to a polarization treatment. That is, a voltage is applied to the piezoelectric layer to align the polarization directions of the piezoelectric particles in a predetermined direction.

[Electrode layer]
The electrode layer may be arranged so as to face the polarization direction of the piezoelectric particles. The electrode layer may be formed on the entire surface of the piezoelectric layer, or may be formed only on a part of the surface. It is desirable that the electrode layer is deformable following the piezoelectric layer. The flexible electrode layer can be formed from, for example, a conductive material in which a conductive material is mixed with a binder, conductive fibers, or the like. As the binder, it is desirable to use one or more selected from elastomers, that is, crosslinked rubbers and thermoplastic elastomers. Examples of elastomers having a relatively small elastic modulus, flexibility, and good adhesiveness to a piezoelectric layer include acrylic rubber, silicone rubber, urethane rubber, urea rubber, fluororubber, and H-NBR. Further, an elastomer modified by introducing a functional group or the like, such as an epoxy group-modified acrylic rubber or a carboxyl group-modified hydrogenated nitrile rubber, may be used.

The type of conductive material is not particularly limited. For example, metal particles made of silver, gold, copper, nickel, rhodium, palladium, chromium, titanium, platinum, iron, and alloys thereof, metal oxide particles made of zinc oxide, titanium oxide, etc., titanium carbonate, etc. It may be appropriately selected from conductive carbon materials such as metal carbide particles, metal nanowires composed of silver, gold, copper, platinum, and nickel, carbon black, carbon nanotubes, graphite, thin layer graphite, and graphene. Further, particles coated with a metal such as silver-coated copper particles may be used. As the conductive material, one of these can be used alone or in combination of two or more.

The blending amount of the conductive material may be appropriately determined so that the electrode layer can achieve a desired volume resistivity. When the blending amount of the conductive material is large, the volume resistivity of the electrode layer can be reduced, but the flexibility is lowered. The electrode layer may contain a cross-linking agent, a cross-linking accelerator, a dispersant, a reinforcing material, a plasticizer, an antiaging agent, a coloring agent and the like as other components.

For example, when an elastomer is used as a binder, a conductive paint is prepared by adding a conductive material and, if necessary, an additive to a polymer solution in which the polymer of the elastomer is dissolved in a solvent, stirring and mixing. Can be done. The electrode layer may be formed by directly applying the prepared conductive coating material to one surface of the piezoelectric layer. Alternatively, a conductive paint may be applied to the releasable film to form an electrode layer, and the formed electrode layer may be transferred to one surface of the piezoelectric layer.

The volume resistivity of the electrode layer is preferably 100 Ω · cm or less in both the natural state and the stretched state up to the stretched state of 10% in the uniaxial direction. It is more preferable that it is 10 Ω · cm or less. This is because if the electric resistance of the electrode layer is large, or if the electric resistance is increased due to stretching, the electromotive voltage generated in the piezoelectric layer drops in the electrode layer, and the output voltage becomes small. The natural state means a state in which no load is applied and the state is not deformed (no load state). The state of being stretched by 10% in the uniaxial direction means a state in which the length in the uniaxial direction is 1.1 times the natural state. In the present invention, the volume resistivity of the electrode is measured in both the natural state and the state extended by 10% in the uniaxial direction, and if the volume resistivity is 100 Ω · cm or less, “natural state and then uniaxial direction”. It is judged that the condition that the volume resistivity in the stretched state up to the stretched state of 10% is 100 Ω · cm or less ”is satisfied. Needless to say, the piezoelectric element in the present invention can be extended not only in the uniaxial direction but also in the biaxial direction, the diameter expansion direction, and the like.

From the viewpoint of making the piezoelectric element flexible, the breaking elongation of the unit (electrode layer / piezoelectric layer / electrode layer) composed of the piezoelectric layer and the pair of electrode layers arranged sandwiching the piezoelectric layer is 10% or more. Is desirable. It is more preferable that it is 30% or more. In the present specification, the elongation at break is a value of elongation at cutting measured by a tensile test specified in JIS K6251: 2010 regardless of the form such as a single layer or a unit. The tensile test shall be performed using a dumbbell-shaped No. 5 test piece at a tensile speed of 100 mm / min.

[Elastic body layer]
The elastic layer may be arranged so as to cover, for example, the outermost electrode layer. When the elastic layer is arranged, the elastic layer extends in the plane direction, so that a shearing force can be applied to the piezoelectric layer. As a result, a tensile force in the surface direction is applied to the piezoelectric layer in addition to the pressing force in the stacking direction, and the strain in the surface direction of the piezoelectric layer increases. As the distortion in the plane direction of the piezoelectric layer increases, the amount of charge generated increases. As a result, the sensitivity of the piezoelectric element is improved and the amount of power generation is increased.

The effect of increasing the amount of generated charge by the elastic body layer is more remarkable as the elastic modulus in the extension direction of the elastic body layer is smaller. For example, the elastic modulus of the elastic layer is preferably 50 MPa or less. Further, in order to prevent the elastic body layer from breaking and the piezoelectric element from breaking during stretching, it is desirable that the breaking elongation of the elastic body layer is larger than the breaking elongation of the piezoelectric layer. In the present specification, the elastic modulus is a value calculated from a stress-elongation curve obtained by a tensile test specified in JIS K7127: 1999. The tensile test shall be performed using a test piece of test piece type 2 at a tensile speed of 100 mm / min.

The elastic layer is preferably made of an elastomer. That is, for the elastic layer, one or more selected from crosslinked rubber and thermoplastic elastomer may be used. Elastomers with relatively low elasticity, flexibility, and good adhesion to the electrode layer include natural rubber, isoprene rubber, butyl rubber, acrylic rubber, silicone rubber, urethane rubber, urea rubber, fluororubber, NBR, thermoplastic polyurethane, and heat. Examples include plastic polyester. Among them, thermoplastic polyurethane enables strong adhesion to the electrode layer and the piezoelectric layer by temporarily melting it by applying heat. By firmly adhering the elastic layer, it is possible to reduce the decrease in sensitivity when the elastic layer is repeatedly strained and stretched.

The Poisson's ratio of the elastomer is approximately 0.5. Therefore, in the elastic layer made of elastomer, the force applied in the thickness direction acts as it is as the force in the surface direction. Therefore, the larger the thickness of the elastic layer, the greater the effect of increasing the strain of the piezoelectric layer and the greater the effect of increasing the amount of generated charge. On the other hand, when the thickness of the elastic layer becomes large, the piezoelectric element becomes thick, so that the amount of power generation per unit volume may become small. Therefore, the thickness per layer of the elastic layer may be, for example, 5 μm or more and 1000 μm or less.

<Exterior material>
The characteristics required for the exterior material that houses the piezoelectric element include durability against repeated loads, water resistance, moisture resistance, flame retardancy, and the like, and differ depending on the application of the transducer. Therefore, the material of the exterior material may be appropriately determined according to the application of the transducer.

For example, in a form of being embedded in a road or used on a road, water resistance, moisture resistance, ozone resistance, etc. are required in addition to durability. In this case, as the material of the exterior material, butyl rubber, silicone rubber, NBR, H-NBR, acrylic rubber, natural rubber, isoprene rubber, EPDM and the like are suitable. Butyl rubber includes regular butyl rubber, chlorinated butyl rubber, brominated butyl rubber and the like. These types may be used alone or in combination of two or more. Further, in order to suppress the permeation of water, a low moisture permeable material such as talc, clay, montmorillonite, or synthetic smectite may be blended. The addition of a filler such as a low moisture permeable material may be appropriately adjusted depending on the location where the transducer is placed. For example, when it is embedded in a road, its water resistance, moisture resistance, and ozone resistance do not have to be so high as compared with the case where it is placed on the road. On the other hand, if it is placed under a hard object such as concrete, it is difficult for a force to be applied to the piezoelectric element, so it is necessary to increase the sensitivity. In this case, it is necessary to take measures such as reducing the amount of filler that improves durability and increasing flexibility. When it is placed on the road, the conditions such as water and ozone become stricter than giving priority to sensitivity because it is close to the load source, so it is advisable to make a formulation that enhances durability against these.

Depending on the material of the exterior material, a part or all of the surface (the surface extending in the extension direction) of the piezoelectric element may be adhered to the exterior material. However, in order to prevent the deformation of the piezoelectric element from being hindered as much as possible, it is desirable that the surface of the piezoelectric element and the exterior material are not adhered to each other. The exterior material may be one that seals the inside, or may have a communication hole through which the contents of the cushioning portion can move between the inside and the outside. Further, a bag portion that can temporarily accommodate the contents of the cushioning portion may be provided outside the exterior material.

<Cushioning unit>
A cushioning section is partitioned between the exterior material in the direction in which the piezoelectric element is stretched by pressing and the piezoelectric element, which houses at least one of a gas, a non-volatile liquid, and a solid having a modulus of elasticity smaller than that of the elastic layer. To. Examples of the gas include air and inert gases such as nitrogen and argon. Examples of the non-volatile liquid include process oils and ionic liquids. Examples of the solid include an elastomer and a foam having an elastic modulus smaller than that of the elastic layer.

Next, the present invention will be described in more detail with reference to examples. A piezoelectric layer, an electrode layer, an elastic layer, and an exterior material were manufactured, and a transducer was manufactured by appropriately combining these, and its sensitivity, amount of generated charge, and durability were evaluated.

<Manufacturing of piezoelectric layer>
[Piezoelectric layer 1]
First, 100 parts by mass of a carboxyl group-modified hydrogenated nitrile rubber polymer (“Tervan (registered trademark) XT8889” manufactured by LANXESS) as an elastomer was dissolved in acetylacetone to prepare a polymer solution. Next, in the prepared polymer solution, a powder of sodium niobate ((K _0.5 Na _0.5 Nb _1.0 ) O ₃ ) as piezoelectric particles (d50% particle diameter (median diameter): 3 μm) 385. A part by mass was added and kneaded. Subsequently, the kneaded product was repeatedly passed through three rolls five times to obtain a slurry. Then, 5 parts by mass of tetrakis (2-ethylhexyloxy) titanium as a cross-linking agent was added to the obtained slurry and kneaded with an air stirrer, and then the slurry was applied onto the substrate by the bar coat method. This was heated at 150 ° C. for 1 hour to produce a piezoelectric layer 1 having a thickness of 0.06 mm (60 μm). The content of the piezoelectric particles in the piezoelectric layer 1 is 42% by volume when the elastomer is 100% by volume. The breaking elongation of the piezoelectric layer 1 was 320%.

The potassium niobate sodium powder used was produced by the following steps.
(1) First mixing step As a raw material, powders of K ₂ CO ₃ , Na ₂ CO ₃ , and Nb ₂ O ₅ were used. These powders were weighed based _on the composition of the desired sintered body (K _0.5 Na _0.5 Nb _1.0 ) O3 and then wet mixed in anhydrous acetone for 16 hours. The resulting mixed powder was evaporated and then dried in an oven to volatilize acetone.
(2) Temporary firing step The mixed powder after volatilizing acetone was put into an alumina crucible, and the crucible was put into a slightly larger crucible. The inner crucible was placed face down to cover the mixed powder. This double crucible was placed in an electric furnace and calcined at 910 ° C. for 10 hours.
(3) Second Mixing Step The obtained calcined product was pulverized in a mortar to form a powder, and then this powder was wet-mixed in anhydrous acetone for 16 hours. The resulting mixed powder was evaporated and then dried in an oven to volatilize acetone.
(4) Main firing step Put the mixed powder after volatilizing acetone into a double crucible in the same manner as in (2), and bake at 150 ° C for 1 hour, 550 ° C for 3 hours, and 1098 ° C for 2 hours. went.
(5) Crushing Step The obtained fired product was crushed into single particles by a ball mill.
(6) Classification step The obtained powder is mixed with methyl ethyl ketone, classified by a centrifuge (“CR22G” manufactured by Hitachi Koki Co., Ltd.), separated by decantation, dried, and niobate acid. A single powder of sodium potassium was obtained.

[Piezoelectric layer 2]
The piezoelectric layer 2 was manufactured in the same manner as the piezoelectric layer 1 except that the blending amount of the piezoelectric particles with respect to the elastomer was changed to 840 parts by mass. The content of the piezoelectric particles in the piezoelectric layer 2 is 67.7% by volume when the elastomer is 100% by volume. The breaking elongation of the piezoelectric layer 2 was 5%.

<Manufacturing of electrode layer>
[Electrode layer 1]
First, three types of monomers, ethyl acrylate (EA), acrylonitrile (AN), and allyl glycidyl ether (AGE), were suspended and polymerized to produce a glycidyl ether group-modified acrylic rubber polymer as an elastomer. The mixing ratio of the monomers was 96% by mass for EA, 2% by mass for AN, and 2% by mass for AGE. Next, 68 parts by mass of the glycidyl ether-based modified acrylic rubber polymer was dissolved in butyl cellosolobacetate, and 35 parts by mass of the conductive material, 25 parts by mass of the dispersant, 6 parts by mass of the cross-linking agent, and cross-linking promotion were added to the polymer solution. A liquid composition was prepared by adding 1 part by mass of the agent (details of the raw materials such as the conductive material will be described later). Subsequently, the liquid composition was pulverized by a wet jet mill (“NanoVeta (registered trademark)” manufactured by Yoshida Kikai Kogyo Co., Ltd.). The crushing treatment was performed 6 times in total by the pass operation (6 pass treatment). The first pass was performed with a straight nozzle (nozzle diameter 170 μm) and a processing pressure of 90 MPa, and the second and subsequent passes were performed with a cross type nozzle (nozzle diameter 170 μm) and a processing pressure of 130 MPa. The liquid composition after the pulverization treatment was applied on a film made of polyethylene terephthalate (PET) which had been mold-released by a bar coating method. This was heated at 150 ° C. for 2 hours to produce an electrode layer 1 having a thickness of 0.015 mm (15 μm). The breaking elongation of the electrode layer 1 was 320%, the volume resistivity in the natural state was 0.05 Ω · cm, and the volume resistivity in the 10% stretched state was 0.1 Ω · cm. The volume resistivity of the electrode layer 1 in the natural state and the 10% stretched state was measured by a resistivity meter (“Loresta (registered trademark) GP” manufactured by Mitsubishi Chemical Analytech Co., Ltd.) (hereinafter, the same applies to the electrode layer 2). ).

Details of the raw materials used to prepare the liquid composition are as follows.
Conductive material: Thin-layer graphite, "iGurafen-α" manufactured by Aitec Inc.
Dispersant: High molecular weight polyesteric acid amidoamine salt, Kusumoto Kasei Co., Ltd. "Disparon (registered trademark) DA7301".
Cross-linking agent: amino group-terminated butadiene-acrylonitrile copolymer, CVC Thermoset Specialties Ltd. "ATBN 1300 x 16".
Crosslink promoter: Zinc complex, KING INDUSTRIES, INC "XK-614".

[Electrode layer 2]
A conductive silver paste (“DW250-H-5” manufactured by Toyobo Co., Ltd.) was applied onto a release-treated PET film by a bar coating method. This was heated at 150 ° C. for 1 hour to produce an electrode layer 2 having a thickness of 0.015 mm (15 μm). The breaking elongation of the electrode layer 2 was 4%, the volume resistivity in the natural state was 0.0002Ω · cm, and the volume resistivity in the 10% stretching state could not be measured due to breaking.

<Elastic body layer>
[Elastic body layer 1]
A thermoplastic polyether polyurethane sheet (“ESMER (registered trademark) URS” manufactured by Nihon Matai Co., Ltd., thickness 0.25 mm) was used as the elastic layer 1. The elastic layer 1 had a breaking elongation of 600% and an elastic modulus of 23 MPa.

[Elastic body layer 2]
A thermoplastic polyester elastomer (“Hytrel (registered trademark) 3046” manufactured by Toray DuPont Co., Ltd.) was formed into a sheet having a thickness of 0.18 mm (180 μm) to form an elastic layer 2. The elongation at break of the elastic layer 2 was 550%, and the elastic modulus was 19 MPa.

[Elastic body layer 3]
A thermoplastic polyester elastomer (“Hytrel 4047” manufactured by Toray DuPont Co., Ltd.) was formed into a sheet having a thickness of 0.18 mm (180 μm) to form an elastic layer 3. The elongation at break of the elastic layer 3 was 500%, and the elastic modulus was 46 MPa.

[Elastic body layer 4]
A polyester film (“Diafoil (registered trademark)” manufactured by Mitsubishi Chemical Corporation, thickness 0.1 mm (100 μm)) was used as the elastic layer 4. The elongation at break of the elastic layer 4 was 90%, and the elastic modulus was 1500 MPa.

<Exterior material>
First, 90 parts by mass of chlorinated butyl rubber (“HT1066” manufactured by JSR Corporation), 10 parts by mass of regular butyl rubber (“JSR butyl 365” manufactured by JSR Corporation), and a polyacrylic acid salt powder of a water-absorbent polymer ((() "Aqualic (registered trademark) CS-S6" manufactured by Nippon Catalyst Corporation, 150 parts by mass of average particle size (15 μm), 5 parts by mass of zinc oxide as a cross-linking aid, and "Tacky Roll" manufactured by Taoka Chemical Industry Co., Ltd. (Registered trademark) 201 ”) 10 parts by mass and 200 parts by mass of talc (“Microace (registered trademark) K-1 ”manufactured by Nippon Tarku Co., Ltd.”) were kneaded with a roll to prepare a master batch. Next, the masterbatch was dissolved in toluene to prepare a paint. Then, the prepared paint was applied to the substrate, the coating film was dried, and then heated at 150 ° C. for 20 minutes to cure. The obtained sheet was used as an exterior material. The elastic modulus of the obtained sheet was 60 MPa, and the elongation at break was 60%.

<Manufacturing of transducers>
A laminated body was manufactured by appropriately combining the manufactured piezoelectric layer, electrode layer, and elastic body layer, and the laminated body was housed in an exterior material to manufacture a transducer. The laminate was manufactured as follows. First, the electrode layers were arranged on two surfaces (upper surface and lower surface) in the thickness direction of the piezoelectric layer, and the piezoelectric layer and the electrode layer were pressure-bonded using a laminator (“LPD3223” manufactured by Fujipla Co., Ltd.). Next, the elastic layer is laminated on the upper electrode layer or both the upper and lower electrode layers, and the surface of the elastic layer is ironed to soften the elastic layer, whereby the elastic layer is fused to the electrode layer. I let you. In the former case, the structure of the laminated body is "elastic body layer / unit (electrode layer / piezoelectric layer / electrode layer)" (hereinafter referred to as "first laminated body"), and in the latter case, the structure of the laminated body. Is an "elastic body layer / unit (electrode layer / piezoelectric layer / electrode layer) / elastic body layer" (hereinafter referred to as "second laminated body"). Each of the laminated bodies has a square thin plate shape having a length of 30 mm and a width of 30 mm. A DC power supply was connected to the electrode layer of the laminated body, and an electric field of 20 V / μm was applied to the piezoelectric layer for 5 minutes to perform the polarization treatment. Then, it was held at 120 ° C. for 30 minutes for aging treatment.

[Example 1]
A transducer was manufactured by combining a first laminated body and a second laminated body using the piezoelectric layer 1, the electrode layer 1, and the elastic body layer 1. First, four first laminated bodies were stacked, and then one second laminated body was stacked to manufacture a piezoelectric element composed of a total of five laminated bodies. The structure of the manufactured piezoelectric element (layered structure of each layer) is the same as that of the transducer of the first embodiment (see FIG. 3 above).

A square exterior material sheet having a length of 40 mm and a width of 40 mm was arranged on two surfaces (upper surface and lower surface) in the thickness direction of the piezoelectric element so that the centers of the respective surfaces coincided with each other. Then, the peripheral edge portion from 1 mm to 2 mm from the outer peripheral surface of the exterior material sheet was welded with the techno impulse clip sealer Z1. In this way, in the diameter-expanding direction of the piezoelectric element, a frame-shaped cushioning portion having a width of 4 mm is partitioned between the piezoelectric element and the exterior material sheet. Air is contained in the shock absorber. The manufactured transducer is referred to as the transducer of the first embodiment.

[Example 2]
The piezoelectric element was configured only from the second laminated body (elastic body layer 1 / electrode layer 1 / piezoelectric layer 1 / electrode layer 1 / elastic body layer 1) using the piezoelectric layer 1, the electrode layer 1, and the elastic body layer 1. Except for the points, the transducer was manufactured in the same manner as in Example 1. The manufactured transducer is referred to as a transducer of the second embodiment.

[Example 3]
The transducer was manufactured in the same manner as in Example 1 except that the cushioning portion contained an elastic body instead of air. As the elastic body, a silicone rubber sheet (“KE1950-10” manufactured by Shin-Etsu Chemical Co., Ltd., elastic modulus 0.4 MPa) was used. The method of accommodating the elastic body in the shock absorber is as follows. First, a square-shaped silicone rubber sheet having a length of 35 mm and a width of 35 mm was prepared, and the central portion thereof was hollowed out into a square shape having a length of 30 mm and a width of 30 mm. Next, the piezoelectric element was placed in the hollowed out portion of the silicone rubber sheet so that the outer periphery of the piezoelectric element was surrounded by the silicone rubber. In this state, one square-shaped exterior material sheet having a length of 40 mm and a width of 40 mm was placed on each of the two surfaces of the piezoelectric element in the thickness direction so that the centers of the surfaces coincided with each other. Then, the peripheral edge portion from 4 mm to 5 mm from the outer peripheral surface of the exterior material sheet was welded with the techno impulse clip sealer Z1. In this way, in the diameter-expanding direction of the piezoelectric element, a frame-shaped cushioning portion having a width of 5 mm in which silicone rubber is housed is partitioned between the piezoelectric element and the exterior material sheet. The manufactured transducer is referred to as a transducer of Example 3.

[Example 4]
A transducer was manufactured in the same manner as in Example 1 except that the elastic body layer of the piezoelectric element was changed to the elastic body layer 2. The manufactured transducer is referred to as a transducer of Example 4.

[Example 5]
A transducer was manufactured in the same manner as in Example 1 except that the elastic body layer of the piezoelectric element was changed to the elastic body layer 3. The manufactured transducer will be referred to as the transducer of Example 5.

[Example 6]
The transducer was manufactured in the same manner as in Example 1 except that the entire two surfaces (upper surface and lower surface) in the thickness direction of the piezoelectric element were adhered to the exterior material. First, a square adhesive sheet ("Elfan (registered trademark) UH370" manufactured by Nihon Matai Co., Ltd.) having a length of 30 mm and a width of 30 mm is applied to a square exterior material sheet having a length of 40 mm and a width of 40 mm. They were pasted together so that the centers would match. Next, the laminated sheets were arranged one by one on two surfaces in the thickness direction of the piezoelectric element so that the centers of the respective surfaces coincided with each other. Then, by heating the surface of the laminated sheet corresponding to the portion of the adhesive sheet with an iron, the piezoelectric element and the exterior material were adhered to each other via the adhesive sheet. Then, the peripheral edge portion from 1 mm to 2 mm from the outer peripheral surface of the exterior material sheet was welded with the techno impulse clip sealer Z1. In this way, in the diameter-expanding direction of the piezoelectric element, a frame-shaped cushioning portion having a width of 4 mm is partitioned between the piezoelectric element and the exterior material sheet. Air is contained in the shock absorber. The manufactured transducer is referred to as a transducer of Example 6.

[Example 7]
The transducer was manufactured in the same manner as in Example 6 except that the size of the adhesive sheet was changed to 5 mm in length and 5 mm in width. The manufactured transducer will be referred to as the transducer of Example 7. In the transducer of the seventh embodiment, a part (5 mm square) of two surfaces (upper surface and lower surface) of the piezoelectric element in the thickness direction are adhered to the exterior material.

[Comparative Example 1]
The transducer was manufactured in the same manner as in Example 6 except that the size of the adhesive sheet was changed to 40 mm in length and 40 mm in width, which are the same as the size of the exterior material. The manufactured transducer is referred to as a transducer of Comparative Example 1. In the transducer of Comparative Example 1, the entire two surfaces (upper surface and lower surface) of the piezoelectric element in the thickness direction are adhered to the exterior material. Further, since the peripheral edge of the exterior material that is not laminated with the piezoelectric element is also adhered via the adhesive sheet, the cushioning portion is partitioned between the piezoelectric element and the exterior material sheet in the diameter expansion direction of the piezoelectric element. Not.

[Comparative Example 2]
The transducer was manufactured in the same manner as in Example 3 except that the type of the elastic body was changed to a polyester film (“Diafoil (registered trademark)” manufactured by Mitsubishi Chemical Corporation, elastic modulus of 1500 MPa). The manufactured transducer is referred to as a transducer of Comparative Example 2.

[Comparative Example 3]
The transducer was manufactured in the same manner as in Example 1 except that no exterior material was used. The manufactured transducer is referred to as a transducer of Comparative Example 3. The transducer of Comparative Example 3 is composed only of a piezoelectric element composed of a total of five laminated bodies.

[Reference Example 1]
A transducer was manufactured in the same manner as in Example 1 except that the piezoelectric layer and the electrode layer of the piezoelectric element were changed to the piezoelectric layer 2 and the electrode layer 2. The manufactured transducer is referred to as the transducer of Reference Example 1.

[Reference Example 2]
A transducer was manufactured in the same manner as in Example 1 except that the elastic body layer of the piezoelectric element was changed to the elastic body layer 4. The manufactured transducer is referred to as a transducer of Reference Example 2.

<Transducer evaluation>
Table 1 shows the configuration and evaluation results of the manufactured transducers. In Table 1, the methods for evaluating the breaking elongation of the unit, the volume resistivity of the electrode layer, the amount of generated charge, the sensitivity, and the durability are as follows.

[Breaking elongation of the unit]
The breaking elongation of the unit consisting of the piezoelectric layer and the pair of electrode layers arranged sandwiching the piezoelectric layer is measured by the above-mentioned method, and if the breaking elongation is 10% or more, it is good (indicated by ○ in Table 1), 10%. If it was less than, it was evaluated as defective (indicated by x in Table 1).

[Volume resistivity of electrode layer]
It is good when both the volume resistivity of the electrode layer in the natural state and the volume resistivity in the 10% stretched state are 100 Ω · cm or less (indicated by ○ in Table 1), and one of them is 100 Ω · cm. If it exceeds or cannot be measured, it is evaluated as defective (indicated by x in Table 1).

[Amount of generated charge]
The transducer was installed in a fatigue endurance tester (“MMT-101N” manufactured by Shimadzu Corporation), and a sine wave (frequency 1 Hz) with a compressive load of 6 N was applied with a cylindrical jig having a diameter of 10 mm. The amount of electric charge generated at that time was measured using a charge amplifier (“NEXUS Charge Amplifier type 2692” manufactured by Brüel & Kjer) and an oscilloscope (“DLM2022” manufactured by Yokogawa Electric Corporation).

[sensitivity]
The transducer was installed in a fatigue endurance tester (same as above), and sine waves (frequency 1 Hz) with compressive loads of 2N, 4N, and 6N were applied in order with a cylindrical jig having a diameter of 10 mm. The amount of charge generated at that time was measured using a charge amplifier (same as above) and an oscilloscope (same as above). Then, the amount of generated charge measured for each compressive load was divided by the added stress, and the average value was calculated to obtain the sensitivity of the transducer.

[durability]
The transducer was allowed to stand in an environment with a temperature of 60 ° C. and a humidity of 90% for 3000 hours. Then, the transducer was installed in the fatigue endurance tester (same as above), and after applying a sine wave (frequency 10 Hz) with a compressive load of 10 N 100,000 times with a cylindrical jig with a diameter of 10 mm, constant displacement vibration 5 in the tensile direction. % Sine wave (frequency 10 Hz) was applied 10,000 times. Then, the sensitivity and the amount of generated charge were measured by the method described above. Durability is good when both the sensitivity and the amount of generated charge are 80% or more of the values before the fatigue durability test (indicated by a circle in Table 1), and durability is less than 80%. It was evaluated as defective (indicated by x in Table 1).

As shown in Table 1, according to the transducers of Examples 1 to 7 having a buffering portion, the amount of generated charge was as large as ^10-9 C and the sensitivity was also good. Since the amount of generated charge is large, it can be seen that the amount of power generation is large. In addition, the durability after repeated displacement was also at a satisfactory level. On the other hand, according to the transducer of Comparative Example 1 having no buffering portion, the amount of generated charge was as small as ^10-10 C, and the sensitivity was also significantly reduced. Further, also in the transducer of Comparative Example 2 in which a solid (polyester film) having an elastic modulus larger than that of the elastic body layer was arranged in the cushioning portion, the amount of generated charge was small and the sensitivity was low. Further, according to the transducer of Comparative Example 3 having no exterior material, the amount of generated charge was large and the sensitivity was good, but the durability was deteriorated. In the transducer of Reference Example 1, since the piezoelectric layer and the electrode layer had poor flexibility, the volume resistivity of the electrode layer and the breaking elongation of the unit were both poor. Therefore, the amount of generated charge was large and the sensitivity was at a satisfactory level, but the durability was deteriorated. Further, since the transducer of Reference Example 2 uses a polyester film having a very large elastic modulus for the elastic body layer, the effect of increasing the strain of the piezoelectric layer by the elastic body layer is not exhibited, and a desired amount of generated charge and sensitivity can be obtained. There wasn't.

Since the transducer of the present invention has a large amount of power generation and is excellent in durability, it is useful for a power generation device that is embedded in a road and generates power by vibration from a person or a car. Further, the transducer of the present invention is suitable as a biometric information sensor for measuring a respiratory state and a heart rate because it has high sensitivity and can detect a small load. In addition, it is suitable as a pressure sensor for robots (including industrial and communication), medical, nursing care, health, sports equipment, automobiles, and the like.

1: Power generation system, 10: Transducer, 20, 200 to 209: Piezoelectric element, 21: Piezoelectric layer, 22a, 22b: Electrode layer, 23a, 23b, 230: Elastic body layer, 24: Unit (electrode layer / piezoelectric layer / Electrode layer), 30: Exterior material, 31: Buffer, 40: Electric circuit, 41, 410, 411: Wiring, 42: Rectifier circuit, 43: Condenser, 44: Switch, 45: Load.

Claims (16)

A piezoelectric element having a piezoelectric layer containing an elastomer and piezoelectric particles, an electrode layer arranged across the piezoelectric layer, and an elastic body layer arranged at least in the outermost layer in the stacking direction.
An exterior material that houses the piezoelectric element and has an elastomer.
The two elastic body layers of the outermost layer of the piezoelectric element are covered with the exterior material.
A buffer in which at least one of a gas, a non-volatile liquid, and a solid having a modulus of elasticity smaller than that of the elastic layer is accommodated between the exterior material and the piezoelectric element in the direction in which the piezoelectric element is stretched by pressing. The part is divided ,
A transducer characterized in that the surface of the piezoelectric element is not adhered to the exterior material when the surface extending in the extension direction of the outermost layer of the piezoelectric element is used as a surface . The transducer according to claim 1, wherein the buffer contains a gas. The transducer according to claim 1 or 2, wherein the piezoelectric element has a plurality of the piezoelectric layers, and the piezoelectric layers are laminated via the electrode layer. The transducer according to claim 3, wherein the elastic layer is interposed between adjacent electrode layers. The transducer according to any one of claims 1 to 4, wherein the elastic modulus of the elastic body layer is 50 MPa or less. The transducer according to any one of claims 1 to 5, wherein the unit comprising the piezoelectric layer and the pair of electrode layers arranged so as to sandwich the piezoelectric layer has a breaking elongation of 10% or more. The transducer according to any one of claims 1 to 6, wherein the volume resistivity of the electrode layer in the natural state and in the stretched state from the stretched state to 10% in the uniaxial direction is 100 Ω · cm or less. The transducer according to any one of claims 1 to 7 , wherein the exterior material has a bag shape. The piezoelectric element is formed by winding a sheet-shaped piezoelectric element.
The transducer according to any one of claims 1 to 8 , wherein the piezoelectric element has a spiral cross section in the stacking direction. The transducer according to claim 9 , wherein the exterior material is wound together with the piezoelectric element. The transducer according to any one of claims 1 to 10 , wherein the exterior material has butyl rubber. The transducer according to any one of claims 1 to 11 , wherein the exterior material has one or more selected from talc, clay, montmorillonite, and synthetic smectite. The transducer according to any one of claims 1 to 12 , wherein the exterior material has a water-absorbent polymer. The transducer according to any one of claims 1 to 13 , which is used as a power generation device. The transducer according to claim 14 ,
An electric circuit for extracting electric energy from the transducer and
Power generation system equipped with. The power generation system according to claim 15 , which has a plurality of the transducers.

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