WO2023042542A1

WO2023042542A1 - Piezoelectric element and electroacoustic transducer

Info

Publication number: WO2023042542A1
Application number: PCT/JP2022/028181
Authority: WO
Inventors: 裕介香川; 栄貴小沢
Original assignee: 富士フイルム株式会社
Priority date: 2021-09-16
Filing date: 2022-07-20
Publication date: 2023-03-23
Also published as: TW202313325A

Abstract

Provided are: a piezoelectric element having a piezoelectric film, wherein heat generation can be suppressed without lowering output even when the piezoelectric element is driven at a high voltage and/or a high current; and an electroacoustic transducer. The piezoelectric element comprises: a piezoelectric film having a piezoelectric layer, an electrode layer provided on both surfaces of the piezoelectric layer, and a protective layer provided on the electrode layer; and a heat conductive member bonded to at least one protective layer side via an adhesive layer, wherein a laminate composed of the heat conductive member and the adhesive layer has a heat conductivity of 0.3 W/mK or more in the thickness direction, and the adhesive layer includes a resin having a glass transition temperature of 0 °C or less.

Description

Piezoelectric elements and electroacoustic transducers

The present invention relates to piezoelectric elements and electroacoustic transducers.

Piezoelectric elements are used for various purposes as so-called exciters, which vibrate and produce sound by attaching them to various items. For example, by attaching an exciter to an image display panel, a screen, or the like and vibrating them, sound can be produced instead of a speaker.

As a piezoelectric element, it has been proposed to use a piezoelectric film in which a piezoelectric layer is sandwiched between electrode layers and protective layers. It is also proposed to laminate a plurality of piezoelectric films and use them as a piezoelectric element.
For example, in Patent Document 1, a plurality of piezoelectric films in which a piezoelectric layer is sandwiched between two thin film electrodes are laminated, and the piezoelectric films are polarized in the thickness direction and are adjacent to each other. Laminated piezoelectric elements are described in which the polarization directions of the piezoelectric films are opposite.

WO2020/095812

A piezoelectric film in which a piezoelectric layer is sandwiched between electrode layers and protective layers generates heat when driven at high voltage and/or high current, and in the worst case, it may not be possible to continuously drive it. As means for suppressing heat generation, it is conceivable to reduce the size of the piezoelectric film, lower the drive voltage, or reduce the number of layers in the case of a structure in which piezoelectric films are laminated to reduce the capacitance. , the sound pressure (output) decreases at the same time.

SUMMARY OF THE INVENTION An object of the present invention is to solve the problems of the prior art. A piezoelectric element having a piezoelectric film generates heat without lowering its output even when driven at high voltage and/or high current. An object of the present invention is to provide a piezoelectric element and an electroacoustic transducer that can be suppressed.

In order to solve the problems described above, the present invention has the following configurations.
[1] A piezoelectric film having a piezoelectric layer, electrode layers provided on both sides of the piezoelectric layer, and protective layers provided on the electrode layers;
a heat conductive member attached to at least one protective layer side via an adhesive layer,
The thermal conductivity in the thickness direction of the laminate of the thermally conductive member and the adhesive layer is 0.3 W/mK or more,
The adhesive layer is a piezoelectric element containing a resin having a glass transition temperature of 0° C. or less.
[2] The piezoelectric element according to [1], wherein the adhesive layer contains an acrylic resin.
[3] The piezoelectric element according to [1] or [2], wherein the area of the portion where the heat conducting member and the piezoelectric film are adhered is 10% or more of the area of the outermost surface of the piezoelectric film.
[4] The piezoelectric element according to any one of [1] to [3], wherein a plurality of heat-conducting members are affixed in a plane direction of the piezoelectric film with a space therebetween.
[5] The piezoelectric element according to any one of [1] to [4], wherein the thermally conductive member is a laminate of an inorganic material and a resin film.
[6] The piezoelectric element according to any one of [1] to [5], which has a plurality of piezoelectric films.
[7] One layer of the laminated piezoelectric films has an overhanging portion that overhangs the other piezoelectric films in the plane direction,
The piezoelectric element according to [6], wherein the heat-conducting member is attached to the projecting portion.
[8] The piezoelectric element according to any one of [1] to [7], wherein the piezoelectric layer is a polymeric composite piezoelectric body containing piezoelectric particles in a matrix containing a polymeric material.
[9] An electroacoustic transducer comprising the piezoelectric element according to any one of [1] to [8] attached to a diaphragm.
[10] The electroacoustic transducer according to [9], wherein the heat-conducting member is in contact with the diaphragm.
[11] A heat-conducting member is provided on a part of the surface of the piezoelectric element that is attached to the diaphragm,
The electroacoustic transducer according to [9] or [10], which has an adhesive layer for attaching the piezoelectric element and the diaphragm in a region other than the surface to which the heat conducting member is attached.

According to the present invention, it is possible to provide a piezoelectric element having a piezoelectric film and an electroacoustic transducer capable of suppressing heat generation without reducing output even when driven at high voltage and/or high current.

1 is a diagram schematically showing an electroacoustic transducer of the present invention having an example of a piezoelectric element of the present invention; FIG. FIG. 4 is a diagram schematically showing an electroacoustic transducer of the invention having another example of the piezoelectric element of the invention; FIG. 4 is a diagram schematically showing an electroacoustic transducer of the invention having another example of the piezoelectric element of the invention; FIG. 4 is a diagram schematically showing an electroacoustic transducer of the invention having another example of the piezoelectric element of the invention; FIG. 4 is a diagram schematically showing another example of the piezoelectric film included in the piezoelectric element of the present invention; 1 is a cross-sectional view conceptually showing an example of a piezoelectric film included in a piezoelectric element of the present invention; FIG. It is a conceptual diagram for explaining an example of a method of manufacturing a piezoelectric film. It is a conceptual diagram for explaining an example of a method of manufacturing a piezoelectric film. It is a conceptual diagram for explaining an example of a method of manufacturing a piezoelectric film. 1 is a side view conceptually showing a cutting device used in Examples. FIG.

The piezoelectric element and electroacoustic transducer of the present invention will be described in detail below based on preferred embodiments shown in the accompanying drawings.

The description of the constituent elements described below may be made based on representative embodiments of the present invention, but the present invention is not limited to such embodiments.
In this specification, a numerical range represented by "-" means a range including the numerical values before and after "-" as lower and upper limits.

[Piezoelectric element and electroacoustic transducer]
The piezoelectric element of the present invention is
A piezoelectric film having a piezoelectric layer, electrode layers provided on both sides of the piezoelectric layer, and protective layers provided on the electrode layers;
a heat conductive member attached to at least one protective layer side via an adhesive layer,
The thermal conductivity in the thickness direction of the laminate of the thermally conductive member and the adhesive layer is 0.3 W/mK or more,
The adhesive layer is a piezoelectric element containing a resin having a glass transition temperature of 0° C. or lower.

Further, the electroacoustic transducer of the present invention is
It is an electroacoustic transducer in which the piezoelectric element is attached to a diaphragm.

FIG. 1 shows a diagram schematically showing the electroacoustic transducer of the present invention having an example of the piezoelectric element of the present invention.

An electroacoustic transducer 100a shown in FIG. 1 has a piezoelectric element 50a, a diaphragm 102, and an adhesive layer 104 for bonding the piezoelectric element 50a to the diaphragm 102. As shown in FIG.
The piezoelectric element 50 a has three piezoelectric films 10 , a thermally conductive member 52 , and an adhesive layer 54 for adhering the thermally conductive member 52 and the piezoelectric film 10 .

The piezoelectric element 50a is formed by stacking three piezoelectric films 10, and a thermally conductive member 52 is adhered to one outermost surface side via an adhesive layer 54. A vibrating plate 102 is attached via an adhesive layer 104 to the outermost surface of the piezoelectric element 50a on the side opposite to the heat conducting member 52 . Moreover, in the example shown in FIG. 1, as a preferred mode, the heat conducting member 52 has a larger size in the surface direction than the piezoelectric film 10, covers the piezoelectric film 10, and contacts the diaphragm 102 at its end.

The piezoelectric film 10 has a piezoelectric layer, electrode layers provided on both sides of the piezoelectric layer, and protective layers provided on the electrode layers. Therefore, the heat conducting member 52 and the diaphragm 102 are attached to the protective layer of the piezoelectric film 10 respectively. The piezoelectric film 10 will be detailed later.
Although illustration is omitted, adjacent piezoelectric films 10 are attached to each other by an adhesive layer. A power supply for applying a driving voltage is connected to each piezoelectric film 10 .

In such an electroacoustic transducer 100a, when a drive voltage is applied to the piezoelectric film 10 of the piezoelectric element 50a, the piezoelectric film 10 expands and contracts in the plane direction. stretches to
Due to the expansion and contraction of the piezoelectric element 50a in the plane direction, the diaphragm 102 bends, and as a result, the diaphragm 102 vibrates in the thickness direction. Due to this vibration in the thickness direction, the diaphragm 102 generates sound. The diaphragm 102 vibrates according to the magnitude of the driving voltage applied to the piezoelectric film 10 and generates sound according to the driving voltage applied to the piezoelectric film 10 .
That is, this electroacoustic transducer 100a can be used as a speaker using the piezoelectric element 50 as an exciter.

Although the piezoelectric element 50a shown in FIG. 1 is obtained by laminating three layers of the piezoelectric film 10, the present invention is not limited to this. That is, the piezoelectric element may have one layer (one sheet) of the piezoelectric film 10, or may have a plurality of laminated layers. When a plurality of piezoelectric films 10 are laminated, the number of laminated piezoelectric films 10 may be two, or four or more. In this regard, the same applies to the piezoelectric elements shown in FIGS. 2 to 4, which will be described later.

In the piezoelectric element 50a shown in FIG. 1, as a preferred embodiment, the polarization directions of adjacent piezoelectric films 10 are opposite to each other. Therefore, in adjacent piezoelectric films 10, the first electrode layers 14 face each other and the second electrode layers 16 face each other. Therefore, the power supply, whether it is an AC power supply or a DC power supply, always supplies power of the same polarity to the facing electrodes. Therefore, in the piezoelectric element 50a, even if the electrodes of the piezoelectric films 10 adjacent to each other come into contact with each other, there is no risk of short-circuiting.

In the piezoelectric element 50a, the polarization direction of the piezoelectric film 10 can be detected with a d33 meter or the like. Alternatively, the polarization direction of the piezoelectric film 10 may be known from the polarization processing conditions described later.

Here, in the piezoelectric element 50a of the present invention, the thermal conductivity in the thickness direction of the laminate of the heat conducting member 52 and the adhesive layer 54 is 0.3 W/mK or more, and the adhesive layer 54 has a glass transition temperature of contains resins below 0°C.

As mentioned above, the piezoelectric film sandwiching the piezoelectric layer between the electrode layer and the protective layer generates heat when driven at high voltage and/or high current. have a nature. As means for suppressing heat generation, it is conceivable to reduce the size of the piezoelectric film, lower the drive voltage, or reduce the number of layers in the case of a structure in which piezoelectric films are laminated to reduce the capacitance. , the sound pressure decreases at the same time.

On the other hand, in the piezoelectric element 50a of the present invention, the heat conductive member 52 is laminated on the piezoelectric film 10, so that the heat generated by the piezoelectric film 10 is transferred to the heat conductive member 52 and radiated, so that the piezoelectric film It is possible to suppress the temperature of 10 from rising. Here, the piezoelectric film 10 and the heat-conducting member 52 need to be adhered with an adhesive layer or the like. Therefore, in the present invention, by setting the thermal conductivity in the thickness direction of the laminate of the heat-conducting member 52 and the adhesive layer 54 to 0.3 W/mK or more, the heat generated by the piezoelectric film 10 is transferred to the heat-conducting member 52 . heat can be transferred to and dissipated.

Here, since a material such as a metal with high thermal conductivity used as a material of the thermally conductive member 52 generally has a high Young's modulus, when the thermally conductive member 52 is adhered to the piezoelectric film 10, the piezoelectric film 10 is There is a risk that the vibration of the piezoelectric film 10 will be hindered due to restraint. That is, the output is lowered, and for example, the sound pressure when using the electroacoustic transducer as a speaker is lowered. On the other hand, in the present invention, the adhesive layer 54 contains a resin having a glass transition temperature of 0° C. or less, so that the adhesive layer becomes flexible at the general operating temperature of the piezoelectric element 50a. , the vibration of the piezoelectric film 10 can be suppressed from being hindered by the heat conducting member 52 . As a result, it is possible to suppress a decrease in output such as sound pressure.

From the viewpoint of heat dissipation, the thermal conductivity in the thickness direction of the laminate of the thermally conductive member and the adhesive layer is preferably 0.5 W/mK or more.

A method for measuring the thermal conductivity in the thickness direction of the laminate of the thermally conductive member and the adhesive layer is as follows.
Thermal conductivity (W/(mK)) can be determined as thermal diffusivity (m ² /s) x specific heat (J/(gK)) x density (g/cm ³ ). Perform the following measurements using

<Thermal conductivity>
The thermal diffusivity of the thermally conductive member removed from the piezoelectric element is measured. For the measurement, ai-phase 1u manufactured by iPhase can be used. At this time, the holding load is 50 g.

<Specific heat>
A few mg of the heat-conducting member can be cut out and specific heat can be measured using DSC Q2000 manufactured by TA Instruments. The measurement pan is aluminum, the standard sample is sapphire, and the heating rate is 1°C/min.

<Density>
A pycnometer ULTRAPYC 1200e manufactured by Qauntachrome instruments can be used to measure the density of the heat conductive member.

In addition, from the viewpoint of suppressing a decrease in output, the adhesive layer preferably contains a resin with a glass transition temperature of 0°C or lower, and more preferably contains a resin with a glass transition temperature of -20°C or lower.

The method for measuring the glass transition temperature of the resin contained in the adhesive layer is as follows.
Using a DMA (dynamic viscoelasticity measuring device, such as Seiko Instruments DMS6100), the loss coefficient Tan δ at each temperature is obtained at a measurement temperature range of -50 to 120 ° C and a measurement frequency of 2 Hz, and the temperature at which Tan δ peaks. Define Tg. The measurement is repeated three times and the average is taken as the final Tg. A rotational rheometer or the like can also be used for the measurement.

Here, in the example shown in FIG. 1, as a preferred mode, the heat conducting member 52 has a size larger than that of the piezoelectric film 10 in the surface direction, covers the piezoelectric film 10, and is in contact with the diaphragm 102 at its end. It has a configuration, but is not limited to this. The heat-conducting member 52 may be laminated on the piezoelectric film 10 so that the size in the surface direction is equal to or smaller than the size of the piezoelectric film 10 . Since the heat conducting member 52 is in contact with the diaphragm 102 , the piezoelectric film 10 generates heat, and the heat transferred to the heat conducting member 52 can be transferred to the diaphragm 102 and radiated over a wider area. temperature rise can be more suitably suppressed.

In the example shown in FIG. 1, the heat conducting member 52 and the diaphragm 102 are configured to be in direct contact with each other, but the present invention is not limited to this. may The adhesive layer for adhering the thermally conductive member 52 and the vibration plate 102 is not particularly limited, but it is preferable to use the same adhesive layer as the adhesive layer 54 for adhering the piezoelectric element 50a and the thermally conductive member 52 .

In the example shown in FIG. 1, the piezoelectric element 50a is attached to the diaphragm 102 via the adhesive layer 104. However, the present invention is not limited to this. It may be configured to be connected to the diaphragm 102 . Also, the heat conducting member 52 may be connected to a sheet-like object covering the piezoelectric element 50a. Alternatively, the piezoelectric element 50a may be attached to the diaphragm 102 via the adhesive layer 104, and the piezoelectric element 50a may be covered with a sheet-like material.

Also, in the example shown in FIG. 1, the heat conducting member 52 is configured to be adhered to one of the outermost surfaces of the laminated piezoelectric films 10, but is not limited to this. From the viewpoint of heat dissipation, it is preferable that the ratio of the area to which the thermally conductive member 52 is adhered to the total area of the outermost surface of the piezoelectric film 10 is large. On the other hand, from the viewpoint of suppressing the vibration of the piezoelectric film 10 from being hindered by the heat conducting member 52, it is preferable that the ratio of the area to which the heat conducting member 52 is adhered to the total area of the outermost surface of the piezoelectric film 10 is small. . From these points of view, the area of the portion where the heat conducting member 52 and the piezoelectric film 10 are adhered is preferably 10% or more of the area of the outermost surface of the piezoelectric film, and is preferably 20% or more and 50% or less. is more preferable, and 30% or more and 40% or less is even more preferable. Since the piezoelectric film 10 is very thin, the area of the portion where the heat conducting member 52 and the piezoelectric film 10 are attached to the total area of both main surfaces of the piezoelectric film 10 should be within the above range.

Also, in the example shown in FIG. 1, the configuration is such that one thermally conductive member 52 is provided, but the configuration is not limited to this. A configuration in which a plurality of thermally conductive members are affixed in a spaced-apart manner in the plane direction of the piezoelectric film may be employed.
FIG. 2 is a diagram schematically showing an electroacoustic transducer of the invention having another example of the piezoelectric element of the invention.

An electroacoustic transducer 100b shown in FIG. 2 has a piezoelectric element 50b, a diaphragm 102, and an adhesive layer 104 for attaching the piezoelectric element 50b to the diaphragm 102. As shown in FIG.
The piezoelectric element 50b has three piezoelectric films 10, three thermally conductive members 52a to 52c, and an adhesive layer 54 for adhering the thermally conductive members 52a to 52c and the piezoelectric film 10 together.

The piezoelectric element 50b is formed by stacking three piezoelectric films 10, and is attached to the diaphragm 102 via an adhesive layer 104 on one outermost surface side. Heat conducting members 52a to 52c are adhered via an adhesive layer 54 to the outermost surface of the piezoelectric element 50b opposite to the vibration plate 102. As shown in FIG. Specifically, the example shown in FIG. 2 has three thermally conductive members 52a to 52c, and the three thermally conductive members 52a to 52c are spaced apart by a predetermined distance in the planar direction of the main surface of the piezoelectric film 10. are placed. Moreover, as a preferred embodiment, each of the

heat conducting members

52a and 52c is in contact with the diaphragm 102 at its end. That is, the heat conducting member 52a is arranged so that one end is in contact with the diaphragm 102 and the other end is adhered to the end of the outermost surface of the piezoelectric element 50b on the side opposite to the diaphragm 102. It is One end of the heat conducting member 52c is the outermost surface of the piezoelectric element 50b on the side opposite to the vibration plate 102 and the end opposite to the end to which the heat conducting member 52a is adhered. , and the other end is in contact with the diaphragm 102 . Moreover, the thermally conductive member 52b is attached between the thermally conductive member 52a and the thermally conductive member 52c on the outermost surface of the piezoelectric element 50b on the side opposite to the vibration plate 102 . In other words, in the piezoelectric element 50 b , the thermally conductive member is divided into a plurality of pieces and adhered to the piezoelectric film 10 .

In this way, by adopting a structure in which a plurality of thermally conductive members are adhered to each other in the plane direction of the piezoelectric film, the area where the thermally conductive members are adhered is increased to suppress temperature rise. , the vibration of the piezoelectric film 10 can be more suitably suppressed from being hindered by the heat-conducting member.

In the example shown in FIG. 2, the configuration is such that the three heat conduction members are spaced apart, but the present invention is not limited to this. A configuration in which two or more thermally conductive members are spaced apart from each other may also be used. The smaller the size of one thermally conductive member, the less likely it is that the vibration of the piezoelectric film will be disturbed.

Also, the distance between the heat-conducting members is not particularly limited, but is preferably 0.1 mm to 5 mm, more preferably 0.5 mm to 2 mm. As described above, the larger the ratio of the area of the portion where the heat conducting member 52 and the piezoelectric film 10 are adhered to the area of the outermost surface of the piezoelectric film, the higher the heat dissipation, and the smaller the ratio, the more inhibited the vibration. From these points of view, the distance between the heat-conducting members may be appropriately adjusted so that the area ratio of the portion where the heat-conducting member 52 and the piezoelectric film 10 are adhered is within a suitable range.

Also, in the example shown in FIG. 2, the adhesive layer 54 is divided according to the heat conducting members 52a to 52c. However, it is not limited to this, and the adhesive layer 54 may be a single layer that adheres a plurality of heat conducting members to the piezoelectric film 10 .

Further, in the case where the piezoelectric element has a plurality of piezoelectric films, one layer of the laminated piezoelectric films has a projecting portion that projects in the plane direction more than the other piezoelectric films, and the heat conducting member It is good also as a structure stuck on an overhang part.
FIG. 3 shows a diagram schematically showing the electroacoustic transducer of the present invention having another example of the piezoelectric element of the present invention.

An electroacoustic transducer 100c shown in FIG. 3 has a piezoelectric element 50c, a diaphragm 102, and an adhesive layer 104 for attaching the piezoelectric element 50c to the diaphragm 102. As shown in FIG.
The piezoelectric element 50 c has three piezoelectric films 10 , a thermally conductive member 52 , and an adhesive layer 54 for adhering the thermally conductive member 52 and the piezoelectric film 10 .

As shown in FIG. 3, among the three piezoelectric films 10 in the piezoelectric element 50c, the piezoelectric film 10 arranged at the farthest position from the vibration plate 102 has a larger planar dimension than the other piezoelectric films 10. It has a projecting portion 11 that is large and projects in the surface direction. The heat-conducting member 52 is adhered to the surface of the projecting portion 11 facing the diaphragm 102 via an adhesive layer 54 . Also, the end of the heat conducting member 52 on the side opposite to the piezoelectric film 10 is in contact with the diaphragm 102 .

Thus, in the configuration in which the piezoelectric element has a plurality of piezoelectric films, the thickness of the piezoelectric element can be reduced by providing a projecting portion on one piezoelectric film and adhering the thermally conductive member to the projecting portion. can be thinned.

The area of the projecting portion 11 when viewed from the direction perpendicular to the main surface of the piezoelectric film 10 is preferably 10% to 100%, more preferably 20% to 70%, of the area of the laminated portion of the piezoelectric film 10. preferable.

In addition, in the example shown in FIG. 1, the piezoelectric element has a heat-conducting member on the side opposite to the side attached to the diaphragm, but the present invention is not limited to this. For example, a heat conductive member is provided on a part of the surface of the piezoelectric element to be adhered to the diaphragm, and an adhesive layer that adheres the piezoelectric element and the diaphragm to a region other than the surface to which the heat conductive member is adhered. It is good also as a structure which has.
FIG. 4 shows a diagram schematically showing the electroacoustic transducer of the present invention having another example of the piezoelectric element of the present invention.

An electroacoustic transducer 100d shown in FIG. 4 has a piezoelectric element 50d, a diaphragm 102, and an adhesive layer 104 for bonding the piezoelectric element 50c to the diaphragm 102. As shown in FIG.
The piezoelectric element 50d has three piezoelectric films 10, a heat conducting member 52d, and an adhesive layer 54d for adhering the heat conducting member 52d and the piezoelectric film 10 together.

As shown in FIG. 4, the heat-conducting member 52d is attached to the end of the surface (attachment surface) of the laminated piezoelectric film 10 on the diaphragm 102 side via the adhesive layer 54d. In the illustrated example, the heat-conducting member 52d is a frame-shaped member whose outer circumference has substantially the same size and shape as the piezoelectric film 10 . The adhesive layer 54d is also formed in a frame shape corresponding to the heat conducting member 52d. The surface of the heat conducting member 52 d opposite to the piezoelectric film 10 is in contact with the diaphragm 102 .

A bonding layer 104 for bonding the piezoelectric element 50d and the vibration plate 102 is filled in the space surrounded by the frame-shaped heat-conducting member 52d. That is, the heat conducting member 52d and the adhesive layer 104 are arranged at substantially the same position in the thickness direction.

Thus, the heat conducting member 52d is provided at the end of the adhered surface of the piezoelectric element 50d to the diaphragm 102, and the piezoelectric element 50d and the diaphragm 102 are adhered inside the heat conducting member 52d. By forming the adhesive layer 104, the heat conducting member 52d and the adhesive layer 104 are arranged at substantially the same position in the thickness direction, so the thickness of the electroacoustic transducer 100d can be reduced.

The area of the heat conducting member 52d when viewed from the direction perpendicular to the main surface of the piezoelectric film 10 is preferably 20% to 50%, more preferably 30% to 40%, of the area of the piezoelectric film 10. preferable.

In addition, in the example shown in FIG. 4, the heat-conducting member 52d is a frame-shaped member, and is arranged over the entire edge (peripheral portion) of the adhered surface of the piezoelectric film 10. However, the present invention is limited to this. It is sufficient that the heat-conducting member is disposed on a portion of the adhered surface of the piezoelectric film 10 .

In addition, in the example shown in FIG. 1 and the like, the piezoelectric element has a configuration in which a plurality of piezoelectric films are laminated. By folding the long piezoelectric film 10L one or more times, the piezoelectric film may be laminated in multiple layers.

The configuration in which the long piezoelectric film 10L is folded and laminated has the following advantages.
That is, when a plurality of cut sheet-shaped piezoelectric films 10 are laminated, the first electrode layer 14 and the second electrode layer 16 must be connected to the drive power source for each piezoelectric film. On the other hand, in the configuration in which the long piezoelectric film 10L is folded and laminated, the laminated body can be configured with only one long piezoelectric film 10L. In addition, in the configuration in which the long piezoelectric film 10L is folded and laminated, only one power source is required for applying the drive voltage, and the electrodes from the piezoelectric film 10L need only be drawn out at one point.
Furthermore, in the structure in which the long piezoelectric films 10L are folded and laminated, the polarization directions of adjacent piezoelectric films are inevitably opposite to each other.

The constituent elements of the piezoelectric element and electroacoustic transducer of the present invention will be described below. In the following description, the piezoelectric elements 50a to 50d are collectively referred to as the piezoelectric element 50 when there is no need to distinguish them. Similarly, electroacoustic transducers 100a-100d are also referred to as electroacoustic transducer 100. FIG. Also, the

heat conducting members

52, 52a to 52d are collectively referred to as the heat conducting member 52.

FIG. 6 shows an enlarged view of a part of the piezoelectric film 10. As shown in FIG.
Piezoelectric film 10 shown in FIG. A second protective layer 20 laminated on the surface opposite to the body layer 12, a first electrode layer 14 laminated on the other surface of the piezoelectric layer 12, and the first electrode layer 14 opposite to the piezoelectric layer 12. and a first protective layer 18 laminated on the side surface. That is, the piezoelectric film 10 has a configuration in which the piezoelectric layer 12 is sandwiched between electrode layers, and a protective layer is laminated on the surface of the electrode layer that is not in contact with the piezoelectric layer.

In the present invention, various known piezoelectric layers can be used for the piezoelectric layer 12 .
In the present invention, the piezoelectric layer 12 is preferably a polymeric composite piezoelectric body containing piezoelectric particles 26 in a matrix 24 containing a polymeric material, as conceptually shown in FIG.

As the material of the polymer composite piezoelectric matrix 24 (matrix and binder) that constitutes the piezoelectric layer 12, it is preferable to use a polymer material that has viscoelasticity at room temperature. In this specification, "ordinary temperature" refers to a temperature range of about 0 to 50.degree.

Here, the polymer composite piezoelectric body (piezoelectric layer 12) preferably satisfies the following requirements.
(i) Flexibility For example, when gripping a loosely bent state like a document like a newspaper or magazine for portable use, it is constantly subjected to a relatively slow and large bending deformation of several Hz or less from the outside. become. At this time, if the polymer composite piezoelectric material is hard, a correspondingly large bending stress is generated, and cracks occur at the interface between the polymer matrix and the piezoelectric particles, which may eventually lead to destruction. Therefore, the polymer composite piezoelectric body is required to have appropriate softness. Moreover, stress can be relieved if strain energy can be diffused to the outside as heat. Therefore, it is required that the loss tangent of the polymer composite piezoelectric material is appropriately large.

In summary, the flexible polymer composite piezoelectric material used as an exciter is required to behave hard against vibrations of 20 Hz to 20 kHz and softly against vibrations of several Hz or less. Also, the loss tangent of the polymer composite piezoelectric body is required to be moderately large with respect to vibrations of all frequencies of 20 kHz or less.
Furthermore, it is preferable that the spring constant can be easily adjusted by laminating according to the rigidity (hardness, stiffness, spring constant) of the mating material (diaphragm) to which the adhesive layer 104 is attached. The thinner it is, the more energy efficient it can be.

In general, polymer solids have a viscoelastic relaxation mechanism, and as the temperature rises or the frequency decreases, large-scale molecular motion causes a decrease (relaxation) in the storage elastic modulus (Young's modulus) or a maximum loss elastic modulus (absorption). is observed as Among them, the relaxation caused by the micro-Brownian motion of the molecular chains in the amorphous region is called principal dispersion, and a very large relaxation phenomenon is observed. The temperature at which this primary dispersion occurs is the glass transition point (Tg), and the viscoelastic relaxation mechanism appears most prominently.
In the polymer composite piezoelectric body (piezoelectric layer 12), by using a polymer material having a glass transition point at room temperature, in other words, a polymer material having viscoelasticity at room temperature as a matrix, it is possible to suppress vibrations of 20 Hz to 20 kHz. This realizes a polymer composite piezoelectric material that is hard at first and behaves softly with respect to slow vibrations of several Hz or less. In particular, it is preferable to use a polymer material having a glass transition point at room temperature, ie, 0 to 50° C. at a frequency of 1 Hz, for the matrix of the polymer composite piezoelectric material, because this behavior is favorably expressed.

Various known materials can be used as the polymer material having viscoelasticity at room temperature. Preferably, a polymer material having a maximum value of 0.5 or more in loss tangent Tan δ at a frequency of 1 Hz in a dynamic viscoelasticity test at normal temperature, ie, 0 to 50° C., is used.
As a result, when the polymer composite piezoelectric body is slowly bent by an external force, the stress concentration at the interface between the polymer matrix and the piezoelectric particles at the maximum bending moment is relaxed, and high flexibility can be expected.

The polymer material having viscoelasticity at room temperature preferably has a storage elastic modulus (E') at a frequency of 1 Hz measured by dynamic viscoelasticity of 100 MPa or more at 0°C and 10 MPa or less at 50°C.
As a result, the bending moment generated when the polymeric composite piezoelectric body is slowly bent by an external force can be reduced, and at the same time, it can behave rigidly against acoustic vibrations of 20 Hz to 20 kHz.

Further, it is more preferable that the polymer material having viscoelasticity at room temperature has a dielectric constant of 10 or more at 25°C. As a result, when a voltage is applied to the polymer composite piezoelectric material, a higher electric field is applied to the piezoelectric particles in the matrix, so a large amount of deformation can be expected.
On the other hand, however, in consideration of ensuring good moisture resistance and the like, it is also suitable for the polymer material to have a dielectric constant of 10 or less at 25°C.

Examples of polymeric materials having viscoelasticity at room temperature that meet these conditions include cyanoethylated polyvinyl alcohol (cyanoethylated PVA), polyvinyl acetate, polyvinylidene chloride core acrylonitrile, polystyrene-vinylpolyisoprene block copolymer, and polyvinylmethyl. Examples include ketones and polybutyl methacrylate. Commercially available products such as Hybler 5127 (manufactured by Kuraray Co., Ltd.) can also be suitably used as these polymer materials. Among them, as the polymer material, it is preferable to use a material having a cyanoethyl group, and it is particularly preferable to use cyanoethylated PVA.

As the polymer material having viscoelasticity at room temperature, it is preferable to use a polymer material having a cyanoethyl group, and it is particularly preferable to use cyanoethylated PVA. That is, in the present invention, the piezoelectric layer 12 preferably uses a polymer material having a cyanoethyl group as the matrix 24, and particularly preferably uses cyanoethylated PVA.
In the following description, the above-mentioned polymeric materials represented by cyanoethylated PVA are collectively referred to as "polymeric materials having viscoelasticity at room temperature".

These polymer materials having viscoelasticity at room temperature may be used alone or in combination (mixed).

The matrix 24 using such a polymer material having viscoelasticity at room temperature may use a plurality of polymer materials together, if necessary.
That is, in addition to viscoelastic materials such as cyanoethylated PVA, other dielectric polymer materials may be added to the matrix 24 as necessary for the purpose of adjusting dielectric properties and mechanical properties.

Examples of dielectric polymer materials that can be added include polyvinylidene fluoride, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, and polyvinylidene fluoride-trifluoroethylene copolymer. and fluorine-based polymers such as polyvinylidene fluoride-tetrafluoroethylene copolymer, vinylidene cyanide-vinyl acetate copolymer, cyanoethylcellulose, cyanoethylhydroxysaccharose, cyanoethylhydroxycellulose, cyanoethylhydroxypullulan, cyanoethylmethacrylate, cyanoethylacrylate, cyanoethyl Cyano groups such as hydroxyethylcellulose, cyanoethylamylose, cyanoethylhydroxypropylcellulose, cyanoethyldihydroxypropylcellulose, cyanoethylhydroxypropylamylose, cyanoethylpolyacrylamide, cyanoethylpolyacrylate, cyanoethylpullulan, cyanoethylpolyhydroxymethylene, cyanoethylglycidolpullulan, cyanoethylsaccharose and cyanoethylsorbitol. Alternatively, polymers having cyanoethyl groups, and synthetic rubbers such as nitrile rubber and chloroprene rubber are exemplified.
Among them, polymer materials having cyanoethyl groups are preferably used.
Moreover, in the matrix 24 of the piezoelectric layer 12, these dielectric polymer materials are not limited to one type, and a plurality of types may be added.

In addition to the dielectric polymer material, the matrix 24 also includes thermoplastic resins such as vinyl chloride resin, polyethylene, polystyrene, methacrylic resin, polybutene, and isobutylene for the purpose of adjusting the glass transition point Tg, and Thermosetting resins such as phenolic resins, urea resins, melamine resins, alkyd resins, and mica may be added.
Furthermore, a tackifier such as rosin ester, rosin, terpene, terpene phenol, and petroleum resin may be added for the purpose of improving adhesiveness.

When adding a material other than a polymer material having viscoelasticity, such as cyanoethylated PVA, to the matrix 24 of the piezoelectric layer 12, the addition amount is not particularly limited, but the ratio of the material to the matrix 24 is 30% by mass or less. is preferable.
As a result, the characteristics of the polymer material to be added can be expressed without impairing the viscoelastic relaxation mechanism in the matrix 24, so that the dielectric constant can be increased, the heat resistance can be improved, and the adhesion between the piezoelectric particles 26 and the electrode layer can be improved. favorable results can be obtained in terms of

The piezoelectric layer 12 is a layer made of a polymeric composite piezoelectric material containing piezoelectric particles 26 in such a matrix 24 . Piezoelectric particles 26 are dispersed in the matrix 24 . Preferably, the piezoelectric particles 26 are uniformly (substantially uniformly) dispersed in the matrix 24 .
The piezoelectric particles 26 are made of ceramic particles having a perovskite or wurtzite crystal structure.
Examples of ceramic particles forming the piezoelectric particles 26 include lead zirconate titanate (PZT), lead zirconate lanthanate titanate (PLZT), barium titanate (BaTiO ₃ ), zinc oxide (ZnO), and A solid solution (BFBT) of barium titanate and bismuth ferrite (BiFe ₃ ) is exemplified.

The particle size of the piezoelectric particles 26 is not limited, and may be appropriately selected according to the size of the piezoelectric film 10, the application of the piezoelectric element 50, and the like. The particle size of the piezoelectric particles 26 is preferably 1 to 10 μm.
By setting the particle size of the piezoelectric particles 26 within this range, favorable results can be obtained in that the piezoelectric film 10 can achieve both high piezoelectric characteristics and flexibility.

The piezoelectric particles 26 in the piezoelectric layer 12 may be uniformly and regularly dispersed in the matrix 24, or if they are uniformly dispersed, they will be dispersed irregularly in the matrix 24. may have been

In the piezoelectric film 10, the quantitative ratio of the matrix 24 and the piezoelectric particles 26 in the piezoelectric layer 12 is not limited, and the size and thickness of the piezoelectric film 10 in the plane direction, the application of the piezoelectric element 50, and It may be appropriately set according to the characteristics required for the piezoelectric element 50 .
The volume fraction of the piezoelectric particles 26 in the piezoelectric layer 12 is preferably 30% to 80%, more preferably 50% or more, and therefore more preferably 50% to 80%.
By setting the amount ratio between the matrix 24 and the piezoelectric particles 26 within the above range, favorable results can be obtained in terms of achieving both high piezoelectric characteristics and flexibility.

In the piezoelectric film 10 , the thickness of the piezoelectric layer 12 is not particularly limited, and may be appropriately determined according to the application of the piezoelectric element 50 , the number of layers of the piezoelectric film in the piezoelectric element 50 , the properties required of the piezoelectric film 10 , and the like. , should be set.
The thicker the piezoelectric layer 12 is, the more advantageous it is in terms of rigidity such as stiffness of the so-called sheet-like material, but the voltage (potential difference) required to expand and contract the piezoelectric film 10 by the same amount is increased.
The thickness of the piezoelectric layer 12 is preferably 10-300 μm, more preferably 20-200 μm, and even more preferably 30-150 μm.
By setting the thickness of the piezoelectric layer 12 within the above range, favorable results can be obtained in terms of ensuring both rigidity and appropriate flexibility.

Also, the piezoelectric layer 12 is preferably polarized (poled) in the thickness direction.

In the present invention, the piezoelectric layer 12 is a polymeric composite piezoelectric body containing piezoelectric particles 26 in a matrix 24 made of a polymeric material having viscoelasticity at room temperature, such as cyanoethylated PVA, as described above. No restrictions.
That is, in the piezoelectric film 10 of the present invention, various known piezoelectric layers can be used as the piezoelectric layer.

As an example, a high-performance dielectric material containing similar piezoelectric particles 26 in a matrix containing a dielectric polymer material such as the polyvinylidene fluoride, vinylidene fluoride-tetrafluoroethylene copolymer, and vinylidene fluoride-trifluoroethylene copolymer described above may be used. Molecular composite piezoelectric material, piezoelectric layer made of polyvinylidene fluoride, piezoelectric layer made of fluorine resin other than polyvinylidene fluoride, piezoelectric layer made by laminating a film made of poly-L-lactic acid and a film made of poly-D-lactic acid, etc. is also available.
However, as described above, it is hard against vibrations of 20 Hz to 20 kHz, and can behave softly against slow vibrations of several Hz or less, and has excellent acoustic characteristics and excellent flexibility. Therefore, a polymer composite piezoelectric body containing piezoelectric particles 26 in a matrix 24 made of a polymer material having viscoelasticity at room temperature, such as the cyanoethylated PVA described above, is preferably used.

As shown in FIG. 6, the piezoelectric film 10 has a second electrode layer 16 on one surface of the piezoelectric layer 12, and a second protective layer 20 thereon. has a first electrode layer 14 on the surface thereof, and a first protective layer 18 thereon. Here, the first electrode layer 14 and the second electrode layer 16 form an electrode pair.

That is, in the piezoelectric film 10, both surfaces of the piezoelectric layer 12 are sandwiched between electrode pairs, that is, the second electrode layer 16 and the first electrode layer 14, and this laminate is formed into the second protective layer 20 and the first protective layer 18. It has a configuration sandwiched between.
Thus, in the piezoelectric film 10, the region sandwiched between the second electrode layer 16 and the first electrode layer 14 expands and contracts according to the applied voltage.
The second electrode layer 16 and the second protective layer 20 as well as the first electrode layer 14 and the first protective layer 18 are attached for the sake of convenience in describing the piezoelectric film 10 . Therefore, the first and second aspects of the present invention have no technical significance and are irrelevant to the actual usage conditions.

In the present invention, the piezoelectric film 10 includes, in addition to these layers, an adhesive layer for attaching the electrode layer and the piezoelectric layer 12 and an adhesive layer for attaching the electrode layer and the protective layer. It may have a layer.
The adhesive may be an adhesive or an adhesive. Also, the same material as the matrix 24, that is, the polymer material obtained by removing the piezoelectric particles 26 from the piezoelectric layer 12, can be suitably used as the adhesive. The adhesive layer may be provided on both the first electrode layer 14 side and the second electrode layer 16 side, or may be provided on only one of the first electrode layer 14 side and the second electrode layer 16 side. good.

In the piezoelectric film 10, the second protective layer 20 and the first protective layer 18 cover the first electrode layer 14 and the second electrode layer 16, and provide the piezoelectric layer 12 with appropriate rigidity and mechanical strength. is responsible for That is, in the piezoelectric film 10, the piezoelectric layer 12 made up of the matrix 24 and the piezoelectric particles 26 exhibits excellent flexibility against slow bending deformation, but depending on the application, the rigidity may increase. and mechanical strength may be insufficient. The piezoelectric film 10 is provided with a second protective layer 20 and a first protective layer 18 to compensate.
The first protective layer 18 and the second protective layer 20 have the same configuration, except for the arrangement position. Therefore, in the following description, when there is no need to distinguish between the first protective layer 18 and the second protective layer 20, both members are collectively referred to as protective layers.

Various sheet materials can be used for the second protective layer 20 and the first protective layer 18 without limitation, and various resin films are preferably exemplified as examples.
Among them, polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS), polycarbonate (PC), polyphenylene sulfite (PPS), polymethyl methacrylate (PMMA), due to their excellent mechanical properties and heat resistance. ), polyetherimide (PEI), polyimide (PI), polyethylene naphthalate (PEN), triacetyl cellulose (TAC), cyclic olefin resins, and the like are preferably used.

The thicknesses of the second protective layer 20 and the first protective layer 18 are also not limited. Also, the thicknesses of the second protective layer 20 and the first protective layer 18 are basically the same, but may be different.
Here, if the rigidity of the second protective layer 20 and the first protective layer 18 is too high, not only will the expansion and contraction of the piezoelectric layer 12 be constrained, but also the flexibility will be impaired. Therefore, the thinner the second protective layer 20 and the first protective layer 18, the better, except for the case where mechanical strength and good handling property as a sheet-like article are required.

In the piezoelectric film 10, if the thickness of the second protective layer 20 and the first protective layer 18 is not more than twice the thickness of the piezoelectric layer 12, it is possible to ensure both rigidity and appropriate flexibility. favorable results can be obtained.
For example, when the thickness of the piezoelectric layer 12 is 50 μm and the second protective layer 20 and the first protective layer 18 are made of PET, the thickness of the second protective layer 20 and the first protective layer 18 is preferably 100 μm or less. 50 μm or less is more preferable, and 25 μm or less is even more preferable.

In the piezoelectric film 10, the second electrode layer 16 is provided between the piezoelectric layer 12 and the second protective layer 20, and the first electrode layer 14 is provided between the piezoelectric layer 12 and the first protective layer 18. It is formed. The second electrode layer 16 and the first electrode layer 14 are provided for applying voltage to the piezoelectric layer 12 (piezoelectric film 10).

The first electrode layer 14 and the second electrode layer 16 are basically the same except for their positions. Therefore, in the following description, when there is no need to distinguish between the first electrode layer 14 and the second electrode layer 16, both members are collectively referred to as electrode layers.

In the present invention, the materials for forming the second electrode layer 16 and the first electrode layer 14 are not limited, and various conductors can be used. Specifically, metals such as carbon, palladium, iron, tin, aluminum, nickel, platinum, gold, silver, copper, titanium, chromium and molybdenum, alloys thereof, laminates and composites of these metals and alloys, Also, indium tin oxide and the like are exemplified. Alternatively, conductive polymers such as PEDOT/PPS (polyethylenedioxythiophene-polystyrenesulfonic acid) are also exemplified. Among them, copper, aluminum, gold, silver, platinum, and indium tin oxide are preferably exemplified as the second electrode layer 16 and the first electrode layer 14 . Among them, copper is more preferable from the viewpoint of conductivity, cost, flexibility, and the like.

In addition, the method of forming the second electrode layer 16 and the first electrode layer 14 is not limited, and may be a vapor phase deposition method (vacuum film formation method) such as vacuum deposition or sputtering, a film formation by plating, or the formation of the above materials. A variety of known methods are available, such as affixing the foils.

In particular, thin films of copper, aluminum, etc., formed by vacuum deposition are preferably used as the second electrode layer 16 and the first electrode layer 14 because the flexibility of the piezoelectric film 10 can be ensured. be. Among them, a copper thin film formed by vacuum deposition is particularly preferably used.

The thicknesses of the second electrode layer 16 and the first electrode layer 14 are not limited. Moreover, although the thicknesses of the second electrode layer 16 and the first electrode layer 14 are basically the same, they may be different.
Here, similarly to the second protective layer 20 and the first protective layer 18 described above, if the rigidity of the second electrode layer 16 and the first electrode layer 14 is too high, not only will the expansion and contraction of the piezoelectric layer 12 be restricted, Flexibility is also impaired. Therefore, the thinner the second electrode layer 16 and the first electrode layer 14, the better, as long as the electrical resistance does not become too high.

In the piezoelectric film 10, if the product of the thickness of the second electrode layer 16 and the first electrode layer 14 and the Young's modulus is less than the product of the thickness of the second protective layer 20 and the first protective layer 18 and the Young's modulus , is preferred because it does not significantly impair flexibility.
For example, the second protective layer 20 and the first protective layer 18 are made of PET (Young's modulus: about 6.2 GPa), and the second electrode layer 16 and the first electrode layer 14 are made of copper (Young's modulus: about 130 GPa). In this case, if the thickness of the second protective layer 20 and the first protective layer 18 is 25 μm, the thickness of the second electrode layer 16 and the first electrode layer 14 is preferably 1.2 μm or less, more preferably 0.3 μm or less. , it is preferably 0.1 μm or less.

As described above, in the piezoelectric film 10, the piezoelectric layer 12, which is formed by dispersing the piezoelectric particles 26 in the matrix 24 containing a polymer material, is sandwiched between the second electrode layer 16 and the first electrode layer 14, and further, This laminate has a structure in which the second protective layer 20 and the first protective layer 18 are sandwiched.
In such a piezoelectric film 10, the maximum value of the loss tangent (Tan δ) at a frequency of 1 Hz by dynamic viscoelasticity measurement preferably exists at room temperature, and the maximum value of 0.1 or more exists at room temperature. more preferred.
As a result, even if the piezoelectric film 10 is subjected to a relatively slow and large bending deformation of several Hz or less from the outside, the strain energy can be effectively diffused to the outside as heat. It is possible to prevent cracks from occurring at the interface of

The piezoelectric film 10 preferably has a storage elastic modulus (E') at a frequency of 1 Hz measured by dynamic viscoelasticity measurement of 10 to 30 GPa at 0°C and 1 to 10 GPa at 50°C. Note that this condition applies to the piezoelectric layer 12 as well.
Accordingly, the piezoelectric film 10 can have a large frequency dispersion in the storage elastic modulus (E') at room temperature. That is, it can act hard against vibrations of 20 Hz to 20 kHz and soft against vibrations of several Hz or less.

In addition, the piezoelectric film 10 has a product of thickness and storage elastic modulus (E′) at a frequency of 1 Hz determined by dynamic viscoelasticity measurement of 1.0×10 ⁵ to 2.0×10 ⁶ N/m at 0° C. , 1.0×10 ⁵ to 1.0×10 ⁶ N/m at 50°C. Note that this condition applies to the piezoelectric layer 12 as well.
As a result, the piezoelectric film 10 can have appropriate rigidity and mechanical strength within a range that does not impair flexibility and acoustic properties.

Furthermore, the piezoelectric film 10 preferably has a loss tangent (Tan δ) of 0.05 or more at 25° C. and a frequency of 1 kHz in a master curve obtained from dynamic viscoelasticity measurement. This condition applies to the piezoelectric layer 12 as well.
As a result, the frequency characteristics of the speaker using the piezoelectric film 10 are smoothed, and the amount of change in sound quality when the lowest resonance frequency _f0 changes as the curvature of the speaker changes can be reduced.

In the present invention, the storage elastic modulus (Young's modulus) and loss tangent of the piezoelectric film 10, piezoelectric layer 12, etc. may be measured by known methods. As an example, the dynamic viscoelasticity measuring device DMS6100 manufactured by SII Nanotechnology Co., Ltd. (manufactured by SII Nanotechnology Co., Ltd.) may be used for measurement.
As an example of the measurement conditions, the measurement frequency is 0.1 Hz to 20 Hz (0.1 Hz, 0.2 Hz, 0.5 Hz, 1 Hz, 2 Hz, 5 Hz, 10 Hz and 20 Hz), and the measurement temperature is -50 to 150 ° C. , a heating rate of 2° C./min (in a nitrogen atmosphere), a sample size of 40 mm×10 mm (including the clamping area), and a distance between chucks of 20 mm.

In the piezoelectric element 50 , a power source is connected to the second electrode layer 16 and the first electrode layer 14 of each piezoelectric film 10 to apply a drive voltage for expanding and contracting the piezoelectric film 10 , that is, to supply drive power.
There are no restrictions on the power source, and it may be a DC power source or an AC power source. Also, the driving voltage may be appropriately set according to the thickness of the piezoelectric layer 12 of the piezoelectric film 10, the material used for forming the piezoelectric film 10, and the like, so that the piezoelectric film 10 can be properly driven.

There are no restrictions on the method of extracting electrodes from the second electrode layer 16 and the first electrode layer 14, and various known methods can be used.
As an example, a method of connecting a conductor such as a copper foil to the second electrode layer 16 and the first electrode layer 14 to lead the electrodes to the outside, and a method of penetrating the second protective layer 20 and the first protective layer 18 by a laser or the like. Examples include a method of forming a hole, filling the through hole with a conductive material, and leading an electrode to the outside.
Examples of suitable methods for extracting electrodes include the method described in Japanese Patent Application Laid-Open No. 2014-209724 and the method described in Japanese Patent Application Laid-Open No. 2016-015354.

The heat-conducting member 52 is a member that conducts and radiates heat generated by the piezoelectric film 10 .
As the heat-conducting member 52, a member containing a metal material such as stainless steel, a copper alloy, and aluminum, graphite, and an inorganic material with high thermal conductivity such as ceramic is used.

In addition, in order to provide insulation, the thermally conductive member 52 may have a structure in which a resin film such as PET, polyester, or polypropylene is laminated on the layer made of the above inorganic material. In this case, the heat conducting member 52 may have a structure in which a resin film is laminated on one surface of a metal foil, or may have a structure in which resin films are laminated on both surfaces of the metal foil.

The thickness of the heat-conducting member 52 is preferably thinner from the standpoint of preventing the vibration of the piezoelectric film from being hindered. Moreover, the thinner one is preferable also from a heat dissipation viewpoint. From these points of view, the thickness of the heat conducting member 52 is preferably 0.1 μm to 1000 μm, more preferably 1 μm to 100 μm, even more preferably 1 μm to 50 μm.

The adhesive layer 54 adheres the protective layer of the piezoelectric film 10 and the heat conducting member 52 together. Accordingly, the adhesive layer 54 is made of an adhesive material that allows the protective layer of the piezoelectric film 10 and the thermally conductive member 52 to be adhered together.
Here, as described above, the adhesive layer 54 contains a resin having a glass transition temperature of 0° C. or lower. By including a resin with a glass transition temperature of 0° C. or lower, the adhesive layer 54 becomes a gel-like (rubber-like) soft state at 0° C. or higher, preventing the heat-conducting member 52 from binding the piezoelectric film 10 . It is possible to prevent the expansion and contraction of the piezoelectric film 10 from being inhibited.

Examples of adhesive resins with a glass transition temperature of 0°C or lower include acrylic resins such as ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, and isononyl acrylate, silicone, and urethane rubber. be done.

Here, in the present invention, the thermal conductivity in the thickness direction of the laminate of the thermally conductive member 52 and the adhesive layer 54 is 0.3 W/mK or more. In order to ensure such thermal conductivity, the adhesive layer 54 may contain a filler made of a material with high thermal conductivity such as metal.

The thickness of the adhesive layer 54 is preferably thicker from the viewpoint of preventing vibration of the piezoelectric film, but is preferably thinner from the viewpoint of heat dissipation. From these points of view, the thickness of the adhesive layer 54 is preferably 1 μm to 500 μm, more preferably 5 μm to 300 μm, even more preferably 10 μm to 200 μm.

In the electroacoustic transducer 100 having the piezoelectric element 50 described above, the diaphragm 102 preferably has flexibility. In the present invention, having flexibility is synonymous with having flexibility in general interpretation, and indicates that it is possible to bend and bend, specifically , indicating that it can be bent and stretched without fracture and damage.
Diaphragm 102 is not limited as long as it preferably has flexibility, and various sheet-like materials (plate-like material, film) can be used.
Examples include polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS), polycarbonate (PC), polyphenylene sulfite (PPS), polymethyl methacrylate (PMMA), polyetherimide (PEI), polyimide (PI), Resin films composed of polyethylene naphthalate (PEN), triacetyl cellulose (TAC), cyclic olefin resins, etc.; expanded polystyrene, expanded plastics composed of expanded styrene, expanded polyethylene, etc.; Examples include various corrugated cardboard materials made by pasting paperboards of the above.
In the electroacoustic transducer 100, the diaphragm 102 may be an organic electroluminescence (OLED (Organic Light Emitting Diode)) display, a liquid crystal display, or a micro LED (Light Emitting Diode) display as long as it has flexibility. , and display devices such as inorganic electroluminescence displays can also be suitably used.

In the electroacoustic transducer 100 , the diaphragm 102 and the piezoelectric element 50 are adhered by the adhesion layer 104 .

Various known layers can be used for the adhesive layer 104 as long as the diaphragm 102 and the piezoelectric element 50 can be adhered.
Therefore, the adhesive layer 104 has fluidity at the time of bonding and then becomes a solid. Even a layer made of an adhesive, which is a gel-like (rubber-like) soft solid at the time of bonding, remains gel-like after that. It may be a layer made of an adhesive that does not change its shape, or a layer made of a material that has the characteristics of both an adhesive and an adhesive.

Here, in the electroacoustic transducer 100, by expanding and contracting the piezoelectric element 50, the diaphragm 102 is bent and vibrated to generate sound. Therefore, in the electroacoustic transducer 100 , it is preferable that the expansion and contraction of the piezoelectric element 50 is directly transmitted to the diaphragm 102 . If a substance having a viscosity that reduces vibration is present between the diaphragm 102 and the piezoelectric element 50, the efficiency of transmission of the expansion and contraction energy of the piezoelectric element 50 to the diaphragm 102 is lowered, resulting in electroacoustic conversion. The driving efficiency of the device 100 is lowered.
Considering this point, the sticking layer 104 is preferably an adhesive layer made of an adhesive that provides a solid and hard sticking layer 104 rather than a sticky layer made of an adhesive. As a more preferable adhesive layer 104, specifically, an adhesive layer made of a thermoplastic type adhesive such as a polyester adhesive and a styrene-butadiene rubber (SBR) adhesive is exemplified.
Adhesion, unlike sticking, is useful in seeking high adhesion temperatures. Further, a thermoplastic type adhesive is suitable because it has "relatively low temperature, short time, and strong adhesion".

The thickness of the adhesive layer 104 is not limited, and the thickness that provides sufficient adhesive strength (adhesive strength, cohesive strength) may be appropriately set according to the material of the adhesive layer 104 .
Here, in the electroacoustic transducer 100, the thinner the adhesive layer 104, the higher the effect of transmitting the stretching energy (vibrational energy) of the piezoelectric element 50 to the diaphragm 102, and the higher the energy efficiency. Also, if the adhesive layer 104 is thick and rigid, it may restrict expansion and contraction of the piezoelectric element 50 .
Considering this point, the adhesive layer 104 is preferably thinner. Specifically, the thickness of the adhesive layer 104 is preferably 0.1 to 50 μm, more preferably 0.1 to 30 μm, and even more preferably 0.1 to 10 μm after being attached.

Note that in the electroacoustic transducer 100, the adhesive layer 104 is provided as a preferred embodiment and is not an essential component.
Therefore, the electroacoustic transducer 100 does not have the adhesive layer 104, and the diaphragm 102 and the piezoelectric element 50 may be fixed using known crimping means, fastening means, fixing means, or the like. For example, when the shape of the piezoelectric element 50 is rectangular in plan view, the four corners may be fastened with members such as bolts and nuts to form an electroacoustic transducer, or the four corners and the central portion may be bolted together. The electroacoustic transducer may be configured by fastening with a member such as a nut.

However, in this case, the piezoelectric element 50 expands and contracts independently of the diaphragm 102 when a drive voltage is applied from the power supply. is not transmitted to the diaphragm 102. In this way, when the piezoelectric element 50 expands and contracts independently of the diaphragm 102, the efficiency of vibration of the diaphragm 102 by the piezoelectric element 50 decreases. There is a possibility that the diaphragm 102 cannot be sufficiently vibrated.
Considering this point, it is preferable that the vibration plate 102 and the piezoelectric element 50 are adhered with an adhesion layer 104 as shown in FIG.

Here, as described above, the piezoelectric layer 12 contains the piezoelectric particles 26 in the matrix 24 . A second electrode layer 16 and a first electrode layer 14 are provided so as to sandwich the piezoelectric layer 12 in the thickness direction.
When a voltage is applied to the second electrode layer 16 and the first electrode layer 14 of the piezoelectric film 10 having such a piezoelectric layer 12, the piezoelectric particles 26 expand and contract in the polarization direction according to the applied voltage. As a result, the piezoelectric film 10 (piezoelectric layer 12) shrinks in the thickness direction. At the same time, due to the Poisson's ratio, the piezoelectric film 10 also expands and contracts in the in-plane direction. This expansion and contraction is about 0.01 to 0.1%.

As described above, the thickness of the piezoelectric layer 12 is preferably about 10-300 μm. Therefore, the expansion and contraction in the thickness direction is as small as about 0.3 μm at maximum.
In contrast, the piezoelectric film 10, that is, the piezoelectric layer 12, has a size much larger than its thickness in the plane direction. Therefore, for example, if the length of the piezoelectric film 10 is 20 cm, the piezoelectric film 10 expands and contracts by about 0.2 mm at maximum due to voltage application.

The diaphragm 102 is attached to the piezoelectric film 10 with an adhesive layer 104 . Therefore, the expansion and contraction of the piezoelectric film 10 bends the diaphragm 102, and as a result, the diaphragm 102 vibrates in the thickness direction.
Due to this vibration in the thickness direction, the diaphragm 102 generates sound. That is, the diaphragm 102 vibrates according to the magnitude of the voltage (driving voltage) applied to the piezoelectric film 10 and generates sound according to the driving voltage applied to the piezoelectric film 10 .

Further, by adjusting the mass of the piezoelectric film 10 according to the spring constant of the diaphragm 102, the sound pressure level can be improved. If the mass of the piezoelectric film 10 is large, the diaphragm 102 will be bent, which may suppress vibration of the diaphragm 102 during driving. On the other hand, if the mass of the piezoelectric film 10 is small, the resonance frequency will be high, possibly suppressing the vibration of the diaphragm 102 at low frequencies. Considering these points, it is preferable to appropriately adjust the mass of the piezoelectric film 10 according to the spring constant of the diaphragm 102 .

Although not shown in the drawings, when a piezoelectric element has a plurality of piezoelectric films, the piezoelectric films are attached to each other by an adhesive layer.
As the adhesive layer for attaching the piezoelectric films to each other, as long as the adjacent piezoelectric films 10 can be attached, various known adhesive layers can be used. Materials similar to the deposition layer 104 can be used.

An example of a method for manufacturing the piezoelectric film 10 will be described below with reference to FIGS. 7 to 10. FIG.

First, a sheet-like object 42 having the second electrode layer 16 formed on the surface of the second protective layer 20 shown in FIG. 7 is prepared. Further, a sheet 40 having the first electrode layer 14 formed on the surface of the first protective layer 18 conceptually shown in FIG. 9 is prepared.

The sheet 42 may be produced by forming a copper thin film or the like as the second electrode layer 16 on the surface of the second protective layer 20 by vacuum deposition, sputtering, plating, or the like. Similarly, the sheet 40 may be produced by forming a copper thin film or the like as the first electrode layer 14 on the surface of the first protective layer 18 by vacuum deposition, sputtering, plating, or the like.
Alternatively, a commercially available sheet having a copper thin film or the like formed on a protective layer may be used as the sheet 42 and/or the sheet 40 .
The sheet-like material 42 and the sheet-like material 40 may be the same or different.

In addition, when the protective layer is very thin and the handling property is poor, a protective layer with a separator (temporary support) may be used as necessary. As the separator, PET or the like having a thickness of 25 to 100 μm can be used. The separator may be removed after the electrode layer and protective layer are thermocompression bonded.

Next, as shown in FIG. 8 , a paint (coating composition) that will form the piezoelectric layer 12 is applied onto the second electrode layer 16 of the sheet 42 and cured to form the piezoelectric layer 12 . As a result, a piezoelectric laminate 46 in which the sheet-like material 42 and the piezoelectric layer 12 are laminated is produced.

Various methods can be used to form the piezoelectric layer 12 depending on the material forming the piezoelectric layer 12 .
As an example, first, the polymer material such as cyanoethylated PVA described above is dissolved in an organic solvent, and then piezoelectric particles 26 such as PZT particles are added and stirred to prepare a paint.
Organic solvents are not limited, and various organic solvents such as dimethylformamide (DMF), methyl ethyl ketone (MEK), and cyclohexanone can be used.
After the sheet 42 is prepared and the paint is prepared, the paint is cast (applied) onto the sheet 42 and dried by evaporating the organic solvent. As a result, as shown in FIG. 8, a piezoelectric laminate 46 having the second electrode layer 16 on the second protective layer 20 and the piezoelectric layer 12 laminated on the second electrode layer 16 is produced. do.

There are no restrictions on the method of casting the coating material, and known methods (coating equipment) such as bar coaters, slide coaters and doctor knives can all be used.
Alternatively, if the polymer material is heat-meltable, the polymer material is heat-melted and the piezoelectric particles 26 are added to prepare a melt, which is then extruded or otherwise molded into the sheet shown in FIG. A piezoelectric laminate 46 such as that shown in FIG.

As described above, in the piezoelectric layer 12, the matrix 24 may be added with a polymeric piezoelectric material such as PVDF, in addition to the polymeric material having viscoelasticity at room temperature.
When these polymeric piezoelectric materials are added to the matrix 24, the polymeric piezoelectric materials to be added to the paint may be dissolved. Alternatively, the polymer piezoelectric material to be added may be added to a polymer material that has been melted by heating and has viscoelasticity at room temperature, and then melted by heating.

After the piezoelectric layer 12 is formed, it may be calendered, if desired. Calendering may be performed once or multiple times.
As is well known, calendering is a process in which a surface to be treated is heated and pressed by a hot press, hot rollers, or the like to flatten the surface.

Next, the piezoelectric layer 12 of the piezoelectric laminate 46 having the second electrode layer 16 on the second protective layer 20 and the piezoelectric layer 12 formed on the second electrode layer 16 is subjected to a polarization treatment ( polling). The polarization treatment of the piezoelectric layer 12 may be performed before calendering, but is preferably performed after calendering.
The method of polarization treatment of the piezoelectric layer 12 is not limited, and known methods can be used. For example, electric field poling, in which a DC electric field is directly applied to an object to be polarized, is exemplified. When electric field poling is performed, the first electrode layer 14 may be formed before the polarization treatment, and the electric field poling treatment may be performed using the first electrode layer 14 and the second electrode layer 16. .
Moreover, in the piezoelectric film 10 of the present invention, it is preferable that the polarization treatment is performed not in the surface direction of the piezoelectric layer 12 but in the thickness direction.

Next, as shown in FIG. 9, the previously prepared sheet 40 is laminated on the piezoelectric layer 12 side of the piezoelectric laminate 46 that has been subjected to the polarization treatment, with the first electrode layer 14 facing the piezoelectric layer 12 . do.
Furthermore, this laminated body is thermocompression bonded using a hot press device, a heating roller, etc., with the first protective layer 18 and the second protective layer 20 sandwiched between them, to form the piezoelectric laminated body 46 and the sheet-like material 40. are bonded together to produce a piezoelectric film 10 as shown in FIG.
Alternatively, the piezoelectric film 10 may be produced by bonding the piezoelectric laminate 46 and the sheet-like material 40 together using an adhesive and preferably further pressing them together.

The piezoelectric film 10 may be manufactured using the cut sheet-like sheet 42 and the sheet 40, or may be manufactured using roll to roll. good too.

The produced piezoelectric film may be cut into a desired shape according to various uses.
The piezoelectric film 10 produced in this manner is polarized in the thickness direction rather than in the plane direction, and excellent piezoelectric properties can be obtained without stretching after the polarization treatment. Therefore, the piezoelectric film 10 has no in-plane anisotropy in piezoelectric properties, and expands and contracts isotropically in all directions in the plane direction when a driving voltage is applied.

Although the piezoelectric element of the present invention has been described in detail above, the present invention is not limited to the above examples, and various improvements and modifications may be made without departing from the gist of the present invention. is.

Hereinafter, the present invention will be described in more detail by giving specific examples of the present invention. The present invention is not limited to this example, and the materials, amounts used, proportions, processing details, processing procedures, etc. shown in the following examples can be changed as appropriate without departing from the gist of the present invention. can.

[Preparation of piezoelectric film]
A piezoelectric film as shown in FIG. 6 was produced by the method shown in FIGS. 7 to 10 described above.
First, cyanoethylated PVA (CR-V, manufactured by Shin-Etsu Chemical Co., Ltd.) was dissolved in dimethylformamide (DMF) at the following compositional ratio. After that, PZT particles as piezoelectric particles were added to this solution at the following composition ratio, and the mixture was stirred with a propeller mixer (rotation speed: 2000 rpm) to prepare a paint for forming a piezoelectric layer.
・PZT particles・・・・・・・・・・300 parts by mass ・Cyanoethylated PVA・・・・・・・・30 parts by mass ・DMF・・・・・・・・・・・・70 parts by mass The PZT particles used were obtained by sintering a commercially available PZT raw material powder at 1000 to 1200° C. and then pulverizing and classifying the sintered particles to an average particle size of 5 μm.

On the other hand, a sheet-like material was prepared by vacuum-depositing a copper thin film with a thickness of 0.3 μm on a PET film with a thickness of 4 μm. That is, in this example, the first electrode layer and the second electrode layer are 0.3 μm thick copper-deposited thin films, and the first protective layer and the second protective layer are 4 μm thick PET films.
Using a slide coater, the previously prepared paint for forming the piezoelectric layer was applied onto the second electrode layer (copper-deposited thin film) of the sheet-like material. In addition, the paint was applied so that the thickness of the coating film after drying was 50 μm.
Next, the sheet-like material coated with the paint was dried by heating on a hot plate at 120° C. to evaporate the DMF. As a result, a piezoelectric laminate having a second electrode layer made of copper on a second protective layer made of PET and a piezoelectric layer (polymer composite piezoelectric layer) having a thickness of 50 μm thereon is produced. bottom.

The produced piezoelectric layer was subjected to polarization treatment in the thickness direction.

A sheet-like material obtained by vapor-depositing the same thin film on a PET film was laminated on the piezoelectric laminate that had been subjected to the polarization treatment, with the first electrode layer (copper thin film side) facing the piezoelectric layer.
Next, the laminate of the piezoelectric laminate and the sheet-like material is thermocompression bonded at a temperature of 120° C. using a laminator device, so that the piezoelectric layer and the first electrode layer are adhered and adhered. A piezoelectric film as shown in 10 was produced.

Next, this piezoelectric film was cut into a rectangle with a planar shape of 20 cm x 5 cm.

[Example 1]
Five piezoelectric films cut out were laminated via an adhesive layer (acrylic adhesive). Next, a heat conductive tape (9876-10 manufactured by 3M Co., Ltd.) cut into a rectangle of 20 cm×5 cm was adhered to one outermost surface of the laminated piezoelectric film to fabricate a piezoelectric element. This heat conductive tape has a metal foil coated with a polymer film and an acrylic adhesive layer. That is, this thermally conductive tape is a laminate of a thermally conductive member and an adhesive layer, and has a structure in which the thermally conductive member is a laminate of a metal foil and a resin film.
The thermal conductivity in the thickness direction of this thermal conductive tape (laminate of thermal conductive member and adhesive layer) is 0.8 W/mK.

Next, the surface of the produced piezoelectric element opposite to the heat-conducting member was attached to a diaphragm to produce an electroacoustic transducer. As the diaphragm, a plate-shaped member having a size of 500 mm×450 mm, a thickness of 0.8 mm, and a material of aluminum was used. An acrylic pressure-sensitive adhesive was used as a bonding layer for bonding the piezoelectric element and the diaphragm. Note that the heat conducting member and the diaphragm are not in direct contact.

[Example 2]
A piezoelectric element was produced in the same manner as in Example 1 except that a heat conductive tape (9876B-08 manufactured by 3M) was used instead of the heat conductive tape (9876-10 manufactured by 3M), and an electroacoustic transducer was manufactured. made. This heat conductive tape has a metal foil coated with a polymer film and an acrylic adhesive layer. That is, this thermally conductive tape is a laminate of a thermally conductive member and an adhesive layer, and has a structure in which the thermally conductive member is a laminate of a metal foil and a resin film. The thermal conductivity in the thickness direction of this thermal conductive tape (laminate of thermal conductive member and adhesive layer) is 1.4 W/mK.

[Example 3]
A piezoelectric element was produced in the same manner as in Example 1 except that a thermal conductive tape (TR-5310EX manufactured by Nitto Denko Corporation) was used instead of the thermal conductive tape (9876-10 manufactured by 3M), and electroacoustic conversion was performed. I made a vessel. This heat conductive tape has a polyester film and an acrylic adhesive layer. The thermal conductivity in the thickness direction of this thermal conductive tape (laminate of thermal conductive member and adhesive layer) is 0.4 W/mK.

[Example 4]
The same as in Example 1, except that a heat conductive tape was cut into a rectangular shape of 20 cm x 10 cm, adhered to one of the outermost surfaces of the laminated piezoelectric films, and both ends of the heat conductive tape were placed in contact with the diaphragm. Then, a piezoelectric element was produced, and an electroacoustic transducer was produced.

[Example 5]
Two 20 cm x 5 cm rectangles of heat conductive tape were cut out and attached to one of the outermost surfaces of the laminated piezoelectric film with a gap of 5 mm, and the end of each heat conductive tape was placed in contact with the diaphragm. A piezoelectric element was produced in the same manner as in Example 1 except for the above, and an electroacoustic transducer was produced. The ratio of the area of the portion to which the heat conductive tape is attached is 45% of the area of the outermost surface of the piezoelectric film (90% of the area of one surface).

[Example 6]
A heat-conducting tape was cut into a 5 cm x 5 cm rectangle, and was attached to one of the outermost surfaces of the laminated piezoelectric film so that the area of the attached portion was 5% of the area of the outermost surface of the piezoelectric film. A piezoelectric element and an electroacoustic transducer were fabricated in the same manner as in Example 1, except that the ends of the conductive tape were placed in contact with the diaphragm.

[Comparative Example 1]
A piezoelectric element was produced in the same manner as in Example 1, except that the heat conductive tape was not adhered, and an electroacoustic transducer was produced.

[Comparative Example 2]
A piezoelectric element was produced in the same manner as in Example 1 except that Kapton tape (registered trademark) manufactured by DuPont Toray Co., Ltd. was used instead of the thermal conductive tape (9876-10 manufactured by 3M), and an electroacoustic transducer was obtained. was made.
The thermal conductivity in the thickness direction of this Kapton tape is 0.16 W/mK.

[Comparative Example 3]
A piezoelectric element was fabricated in the same manner as in Example 1, except that a heat-conducting member composed of a PET film and a copper foil, which did not have an adhesive layer, was attached to the piezoelectric film using Aron Alpha (registered trademark) manufactured by Toagosei Co., Ltd. was produced, and an electroacoustic transducer was produced.
Aron alpha has a glass transition temperature of 50° C. or higher.

[evaluation]
The sound pressure and the temperature reached were evaluated for the fabricated electroacoustic transducers of Examples and Comparative Examples.

<Sound pressure>
The diaphragm was erected by supporting the short sides of the diaphragm. On the diaphragm side, a microphone was installed at a position of 1 m in the normal direction (perpendicular to the PET film) from the center of the piezoelectric element, the piezoelectric element was driven, and the sound pressure at a frequency of 1 kHz was measured.
The input signal to the piezoelectric element was a 20-20 kHz sweep sine wave (50 Vrms).

<Achievement temperature>
The produced electroacoustic transducer was connected to a continuous driving test (50 Vrms), and the temperature reached by the piezoelectric element after continuous driving for 30 minutes was measured by thermography (U5855A manufactured by Keysight Technologies). The ambient temperature for measurement was 23°C. An SN2 signal was used as an input signal. The SN2 signal is a noise signal standard defined by JEITA, and is a noise signal obtained by cutting high frequency components and low frequency components of a white noise signal. The frequency of the applied voltage was in the range of 20 Hz to 20 kHz. Also, the temperature of the piezoelectric element was measured at an arbitrary position where the highest temperature was reached.
Table 1 shows the results. In Table 1, the item "Attached area" indicates the ratio of the area of the portion to which the thermal conductive tape (thermal conductive member) is attached to the area of the outermost surface of the laminated piezoelectric film. Further, the item of continuity is an item representing whether the heat conducting member is composed of one sheet or divided into two or more pieces.

From Table 1, it can be seen that the examples of the present invention have a high sound pressure and a low ultimate temperature. Since Comparative Example 1 does not have a heat-conducting member, it can be seen that the temperature reached is high. It can be seen that in Comparative Example 2, the temperature reached is high because the thermal conductivity in the thickness direction of the laminate of the thermally conductive member and the adhesive layer is low. In Comparative Example 3, since the glass transition temperature of the adhesive layer is high, the vibration of the piezoelectric film is inhibited and the sound pressure is lowered.

Moreover, from the comparison of Examples 1 to 3, it is found that the thermal conductivity in the thickness direction of the laminate of the thermally conductive member and the adhesive layer is preferably high.
Also, from the comparison between Example 1 and Example 4, it can be seen that it is preferable that the heat-conducting member and the diaphragm are in contact with each other.
Moreover, from the comparison between Example 4 and Example 5, it can be seen that by dividing the heat conducting member into a plurality of pieces, it is possible to more preferably reduce the inhibition of the vibration of the piezoelectric film, which is preferable.
From the above, the effect of the present invention is clear.

The piezoelectric element of the present invention can be used, for example, in various sensors such as sound wave sensors, ultrasonic sensors, pressure sensors, tactile sensors, strain sensors and vibration sensors (especially for infrastructure inspection such as crack detection and manufacturing site inspection such as foreign matter contamination detection). useful), acoustic devices such as microphones, pickups, speakers and exciters (specific applications include noise cancellers (used in cars, trains, airplanes, robots, etc.), artificial vocal cords, buzzers for preventing insects and vermin from entering , furniture, wallpaper, photographs, helmets, goggles, headrests, signage, robots, etc.), automobiles, smartphones, smart watches, haptics used for games, etc. Ultrasonic probes and hydrophones Acoustic transducers, actuators used for water drop adhesion prevention, transport, agitation, dispersion, polishing, etc., dampers used in containers, vehicles, buildings, sports equipment such as skis and rackets, and roads, floors, mattresses, and chairs , shoes, tires, wheels, and personal computer keyboards.

Reference Signs List

10, 10L piezoelectric film 11 projecting portion 14 first electrode layer 16 second electrode layer 18 first protective layer 20 second protective layer 24 matrix 26 piezoelectric particles 40 sheet 42 sheet 46

piezoelectric laminate

50a, 50b, 50c,

50d Piezoelectric element

52, 52a, 52b, 52c, 52d

Heat conduction member

54,

54d Adhesive layer

100a, 100b, 100c, 100d Electroacoustic transducer 102 Diaphragm 104 Adhesion layer

Claims

A piezoelectric film having a piezoelectric layer, electrode layers provided on both sides of the piezoelectric layer, and protective layers provided on the electrode layers;
a heat-conducting member attached to at least one of the protective layers via an adhesive layer;
The thermal conductivity in the thickness direction of the laminate of the thermally conductive member and the adhesive layer is 0.3 W/mK or more,
The piezoelectric element, wherein the adhesive layer contains a resin having a glass transition temperature of 0° C. or lower.
The piezoelectric element according to claim 1, wherein the adhesive layer contains an acrylic resin.
The piezoelectric element according to claim 1, wherein the area of the portion where the thermally conductive member and the piezoelectric film are attached is 10% or more of the area of the outermost surface of the piezoelectric film.
2. The piezoelectric element according to claim 1, wherein a plurality of said thermally conductive members are affixed with a space therebetween in the surface direction of said piezoelectric film.
The piezoelectric element according to claim 1, wherein the thermally conductive member is a laminate of an inorganic material and a resin film.
The piezoelectric element according to claim 1, comprising a plurality of layers of the piezoelectric film.
one layer of the laminated piezoelectric films has an overhanging portion that overhangs the other piezoelectric films in a plane direction;
7. The piezoelectric element according to claim 6, wherein said thermally conductive member is attached to said projecting portion.
The piezoelectric element according to claim 1, wherein the piezoelectric layer is a polymeric composite piezoelectric body containing piezoelectric particles in a matrix containing a polymeric material.
An electroacoustic transducer in which the piezoelectric element according to any one of claims 1 to 8 is attached to a diaphragm.
The electroacoustic transducer according to claim 9, wherein said heat conducting member is in contact with said diaphragm.
The thermally conductive member is provided on a part of the bonding surface of the piezoelectric element to the vibration plate,
10. The electroacoustic transducer according to claim 9, further comprising an adhesion layer for adhering said piezoelectric element and said diaphragm in a region other than the surface to which said heat conducting member is adhered.