WO2023248696A1

WO2023248696A1 - Piezoelectric film, piezoelectric element, electroacoustic transducer, and method for manufacturing piezoelectric film

Info

Publication number: WO2023248696A1
Application number: PCT/JP2023/019320
Authority: WO
Inventors: 哲三好
Original assignee: 富士フイルム株式会社
Priority date: 2022-06-24
Filing date: 2023-05-24
Publication date: 2023-12-28

Abstract

The present invention provides: a piezoelectric film that, in a piezoelectric element having a protrusion for connecting to an external power source, can suppress noise generated by vibrations in the protrusion and also suppresses peeling when the piezoelectric film is used by being attached to a diaphragm; and a related piezoelectric element, electroacoustic transducer, and method for manufacturing a piezoelectric film. The piezoelectric film has a piezoelectric layer comprising a polymer composite piezoelectric material containing piezoelectric particles in a matrix containing a polymer material, and an electrode layer provided on both sides of the piezoelectric layer, the piezoelectric layer having unpolarized regions that are not polarized in some portions.

Description

Piezoelectric film, piezoelectric element, electroacoustic transducer, and method for manufacturing piezoelectric film

The present invention relates to a piezoelectric film, a piezoelectric element, an electroacoustic transducer, and a method for manufacturing a piezoelectric film.

Piezoelectric elements are used for a variety of purposes as so-called exciters, which vibrate and produce sound by attaching them in contact with various objects. For example, by attaching an exciter to an image display panel, screen, etc., and causing these to vibrate, it is possible to produce sound instead of a speaker.

It has been proposed to use a piezoelectric film in which a piezoelectric layer is sandwiched between an electrode layer and a protective layer as a piezoelectric element. It has also been proposed to laminate multiple layers of piezoelectric films and use them as piezoelectric elements.

For example, Patent Document 1 discloses a polymer composite piezoelectric material having piezoelectric particles dispersed in a matrix containing a polymer material, and an electrode layer formed on both surfaces of the polymer composite piezoelectric material. A piezoelectric product whose loss tangent at a frequency of 1 kHz, determined by physical viscoelasticity measurement, has a maximum value of 0.1 or more in a temperature range exceeding 50°C and 150°C or less, and whose value at 50°C is 0.08 or more. Film is listed. Further, Patent Document 1 describes a piezoelectric element in which a piezoelectric film is folded back one or more times and multiple layers of piezoelectric films are laminated.

International Publication No. 2020/196850

A piezoelectric element made by folding a piezoelectric film is used as an exciter that generates sound from the diaphragm by attaching it to a diaphragm and causing the diaphragm to vibrate. In order to connect an external power source to the electrode layer of such a piezoelectric element, a protrusion that protrudes in the plane direction from the laminated portion of the piezoelectric film is provided, and the external power source is connected to the electrode layer at this protrusion. That is what is being considered. When voltage is applied from the connection between the electrode layer provided on the protruding part and an external power supply to drive the piezoelectric element, the protruding part generates significant heat, and in the worst case, there is a risk of thermal runaway and the inability to continuously drive the piezoelectric element. be. In order to suppress such heat generation, it is preferable that the area of the protrusion is wide.

However, according to studies conducted by the present inventors, it has been found that when the piezoelectric element has a protrusion, vibrations also occur in the protrusion, resulting in the generation of unnecessary sound (noise).

Furthermore, when a piezoelectric film or piezoelectric element is attached to a diaphragm to form an electroacoustic transducer, there is a problem in that the diaphragm and the piezoelectric film or piezoelectric element separate from each other due to the vibration of the piezoelectric film or piezoelectric element. I understand.

An object of the present invention is to solve the problems of the prior art, and to suppress the generation of noise caused by vibration in the protrusion in a piezoelectric element having a protrusion for connection to an external power source. It is an object of the present invention to provide a piezoelectric film, a piezoelectric element, an electroacoustic transducer, and a method for manufacturing a piezoelectric film, which can be used by attaching the piezoelectric film to a diaphragm and which can suppress peeling when used.

In order to solve the above-mentioned problems, the present invention has the following configuration.
[1] A piezoelectric film having a piezoelectric layer made of a polymer composite piezoelectric material containing piezoelectric particles in a matrix containing a polymer material, and electrode layers provided on both sides of the piezoelectric layer,
A piezoelectric film in which a piezoelectric layer partially has an unpolarized region.
[2] The piezoelectric film according to [1], wherein the piezoelectric layer has a polarized region polarized in the thickness direction and an unpolarized region in the region sandwiched between the pair of electrode layers constituting the electrode pair. .
[3] The piezoelectric film according to [1], wherein the unpolarized region is present at the outer edge of the piezoelectric film.
[4] A piezoelectric element formed by laminating multiple layers of piezoelectric films by folding back the piezoelectric film according to any one of [1] to [3] one or more times,
In plan view, the piezoelectric film has a laminated part where two or more layers overlap and a protrusion part that protrudes from the laminated part,
The protruding portion has a connecting portion for connecting the electrode layer and an external power source,
A piezoelectric element in which unpolarized regions are present in the protrusions.
[5] An electroacoustic transducer comprising the piezoelectric film according to any one of [1] to [3] attached to a diaphragm.
[6] An electroacoustic transducer comprising the piezoelectric element according to [4] attached to a diaphragm.
[7] The electroacoustic transducer according to [5], wherein the electrode layer of the piezoelectric film and the diaphragm are not electrically connected.
[8] The electroacoustic transducer according to [6], wherein the electrode layer of the piezoelectric film and the diaphragm are not electrically connected.
[9] A method for producing a piezoelectric film, comprising: a piezoelectric layer made of a polymer composite piezoelectric material containing piezoelectric particles in a matrix containing a polymer material; and electrode layers provided on both sides of the piezoelectric layer. ,
a piezoelectric layer forming step of forming an unpolarized piezoelectric layer on the main surface of one electrode layer;
After the piezoelectric layer forming step, a polarization treatment step of polarizing a part of the piezoelectric layer;
After the polarization treatment step, an electrode lamination step of laminating the other electrode layer on the main surface of the piezoelectric layer,
In the polarization process, an electrode member is placed facing the main surface of the piezoelectric layer on the opposite side from one electrode layer, and after one electrode layer is connected to the ground, a DC voltage is applied between the electrode member and the electrode member. The polarization process is performed by applying
A method for manufacturing a piezoelectric film, in which a polarized region and an unpolarized region are formed in a piezoelectric layer by regulating the region to be polarized.
[10] The polarization treatment is a corona poling treatment,
The method for producing a piezoelectric film according to [9], wherein the electrode member is a wire-shaped corona electrode.
[11] In the polarization treatment step, the region to be polarized is regulated by making the length of the region of the wire-shaped corona electrode where corona discharge occurs shorter than the width of the piezoelectric layer, as described in [10]. A method for manufacturing a piezoelectric film.
[12] In the polarization process, an insulator or a conductor connected to the ground is placed on a part of the main surface of the piezoelectric layer opposite to one of the electrode layers to control the area to be polarized. The method for producing a piezoelectric film according to [9].

According to the present invention, in a piezoelectric element having a protruding part for connecting to an external power source, it is possible to suppress noise generation due to vibration in the protruding part, and also to prevent peeling when used by pasting it on a diaphragm. A piezoelectric film, a piezoelectric element, an electroacoustic transducer, and a method for manufacturing a piezoelectric film can be provided.

FIG. 1 is a perspective view schematically showing an example of a piezoelectric element of the present invention having a piezoelectric film of the present invention. FIG. 2 is a side view of the piezoelectric element shown in FIG. 1. FIG. FIG. 2 is a perspective view showing a state before the piezoelectric film shown in FIG. 1 is folded back. 4 is a diagram for explaining polarized regions and unpolarized regions of the piezoelectric film shown in FIG. 3. FIG. 2 is a diagram schematically showing an example of an electroacoustic transducer of the present invention having the piezoelectric element shown in FIG. 1. FIG. It is a perspective view which shows typically another example of the piezoelectric film of this invention. 8 is a diagram schematically showing an example of the electroacoustic transducer of the present invention having the piezoelectric film shown in FIG. 7. FIG. FIG. 2 is a conceptual diagram for explaining an example of a method for manufacturing a piezoelectric film. FIG. 2 is a conceptual diagram for explaining an example of a method for manufacturing a piezoelectric film. FIG. 2 is a conceptual diagram for explaining an example of a method for manufacturing a piezoelectric film. FIG. 3 is a conceptual diagram for explaining an example of a polarization treatment process. FIG. 7 is a conceptual diagram for explaining another example of the polarization treatment process. FIG. 2 is a conceptual diagram for explaining an example of a method for manufacturing a piezoelectric film. FIG. 2 is a diagram schematically showing an example of a conventional piezoelectric element. 1 is a diagram schematically showing an example of a conventional electroacoustic transducer having a piezoelectric film.

Hereinafter, the piezoelectric film, piezoelectric element, electroacoustic transducer, and method for manufacturing the piezoelectric film of the present invention will be described in detail based on preferred embodiments shown in the accompanying drawings.

Although the description of the constituent elements described below may be made based on typical embodiments of the present invention, the present invention is not limited to such embodiments.
Note that in this specification, a numerical range expressed using "~" means a range that includes the numerical values written before and after "~" as the lower limit and upper limit.

[Piezoelectric film and piezoelectric element]
The piezoelectric film of the present invention is
A piezoelectric film having a piezoelectric layer made of a polymer composite piezoelectric material containing piezoelectric particles in a matrix containing a polymer material, and electrode layers provided on both sides of the piezoelectric layer,
The piezoelectric film is a piezoelectric film in which the piezoelectric layer partially has an unpolarized region.

Further, the piezoelectric element of the present invention is a piezoelectric element formed by laminating a plurality of layers of piezoelectric films by folding the piezoelectric film one or more times,
In plan view, the piezoelectric film has a laminated part where two or more layers overlap and a protrusion part that protrudes from the laminated part,
The protruding portion has a connecting portion for connecting the electrode layer and an external power source,
It is a piezoelectric element in which unpolarized regions are present in the protrusions.

FIG. 1 is a perspective view schematically showing an example of a piezoelectric element of the present invention having a piezoelectric film of the present invention. FIG. 2 shows a side view of the piezoelectric element of FIG. 1. FIG. 3 shows a perspective view of the piezoelectric film of the piezoelectric element of FIG. 1 before it is folded back. Note that the plan view is a view seen from the lamination direction in which a plurality of piezoelectric films 10 are laminated.

The piezoelectric element 50 shown in FIGS. 1 and 2 is made by laminating three layers of piezoelectric films 10a by folding back one rectangular piezoelectric film 10a twice in one direction. That is, this piezoelectric element 50 is a laminated piezoelectric element in which three layers of piezoelectric films 10a are laminated.
Although omitted in FIG. 1 to simplify the drawing and clearly show the structure of the piezoelectric element 50, the piezoelectric film 10a has electrode layers on both sides of the piezoelectric layer 20, and covers both electrode layers. It has a protective layer. Further, in FIG. 3, illustration of the protective layer is omitted.
Furthermore, in the following description, the direction in which the piezoelectric film 10a is folded back (the left-right direction in FIG. 1) is referred to as the folding direction.

As shown in FIG. 8, which will be described later, the piezoelectric film 10a includes a piezoelectric layer 20 made of a polymer composite piezoelectric material containing piezoelectric particles 36 in a matrix 34 containing a polymer material, and a piezoelectric layer 20 provided on both sides of the piezoelectric layer 20. (the first electrode layer 24 and the second electrode layer 26). Moreover, the piezoelectric film 10a has a protective layer (first protective layer 28 and second protective layer 30) provided on each electrode layer.

The piezoelectric layer 20 is polarized in the thickness direction. When a voltage is applied to the electrode layers (electrode pair) that sandwich the piezoelectric layer 20, the piezoelectric particles 36 in the piezoelectric layer 20 expand and contract in the polarization direction according to the applied voltage. As a result, the piezoelectric film 10a (piezoelectric layer 20) contracts in the thickness direction. At the same time, the piezoelectric film 10a also expands and contracts in the plane direction due to the Poisson ratio. Thereby, the piezoelectric film 10a can exhibit piezoelectric performance.
Each component of the piezoelectric film will be detailed later.

By folding back the piezoelectric film 10a having such piezoelectric performance, the piezoelectric element 50 can be formed by laminating a plurality of layers of piezoelectric films.
In the example shown in FIGS. 1 and 2, the piezoelectric element 50 has a laminated part 11a in which three layers of piezoelectric films 10a overlap in plan view, and a protrusion part 11b that protrudes outward in the plane direction from the laminated part 11a. That is, in the piezoelectric element 50, when one piezoelectric film 10a is folded twice, the two layers from the bottom side in FIG. 1 have approximately the same length in the folding direction, and the top surface By making the length of the piezoelectric film 10a serving as the side layer longer than the piezoelectric film 10a of the other layer so that one end in the folding direction does not overlap with the piezoelectric film 10a of the other layer, the protruding portion 11b is It was established.

In the example shown in FIG. 1, the piezoelectric element 50 is made by folding back the piezoelectric film 10a twice and laminating three layers of piezoelectric films 10a, but the piezoelectric element is not limited to this. It may be one in which piezoelectric films are laminated, or one in which four or more layers of piezoelectric films are laminated.

Adjacent layers of the piezoelectric film 10a in the laminated portion 11a are adhered to each other by an adhesive layer 14.
As the adhesive layer 14 for adhering piezoelectric films to each other, various known adhesive layers can be used as long as they can adhere adjacent piezoelectric films 10 to each other. As the adhesive layer 14, the same material as the adhesive layer for pasting the diaphragm and the piezoelectric element, which will be described later, can be used.

In the present invention, the laminated portion 11a is a region where two or more layers of piezoelectric films overlap when viewed in plan, that is, when the piezoelectric element is viewed from above (or from below) in FIG. That is, as shown in FIGS. 1 and 2, a region where three layers of the piezoelectric film 10a overlap is the laminated portion 11a.

On the other hand, the protruding portion 11b is a region that protrudes from the laminated portion 11a in the surface direction, and is a region that does not overlap with other layers in plan view. In the example shown in FIGS. 1 and 2, the right end of the uppermost layer in the figures is the protrusion 11b.

As shown in FIG. 1, the protrusion 11b includes a conductive wire 40 and a conductive wire 42 for connecting the first electrode layer 24 and the second electrode layer 26 (hereinafter also collectively referred to as electrode layers) and an external electrode. is formed. As shown in FIG. 2, when the piezoelectric film 10a has a protective layer (the first protective layer 28 and the second protective layer 30), the protective layer (the first protective layer 28 and the second protective layer 30) in the region of the protrusion 11b is A through hole is formed in the layer 30) to expose the electrode layer, and a connecting portion is provided to be electrically connected to the conductive wire 40 and the conductive wire 42, respectively. There are no restrictions on the method for forming the through holes, and depending on the material for forming the protective layer, known methods such as laser processing, dissolution and removal using a solvent, and mechanical processing such as mechanical polishing may be used. .

The connecting portion is connected to a conductive wire filled with a known conductive material such as a conductive metal paste such as a silver paste, a conductive carbon paste, or a conductive nano ink and connected to an external power source.
Note that there is no restriction on the method of connecting the electrode layer and the conductive wire in the protruding portion 11b, and various known methods can be used.

The piezoelectric element 50 of the present invention is driven by applying a voltage to the electrode layer using an external power source via the connection part provided on the protrusion 11b. When the piezoelectric element 50 is driven, the piezoelectric element 50 expands and contracts in the plane direction, bends the diaphragm to which the piezoelectric element 50 is attached, and as a result vibrates the diaphragm to generate sound. The diaphragm vibrates according to the magnitude of the driving voltage applied to the piezoelectric element 50, and generates sound according to the driving voltage applied to the piezoelectric element 50.
That is, the piezoelectric element 50 can be used as an exciter.

Here, as described above, in the conventional piezoelectric element 250 (see FIG. 14), when a voltage is applied from the connection between the electrode layer provided on the protrusion 211b and the external power source in order to drive the piezoelectric element 250, the protrusion It has been found that vibration also occurs in the portion 211b, causing a problem that unnecessary sound (noise) is generated.

In contrast, in the piezoelectric element 50 of the present invention, the piezoelectric layer 20 of the protrusion 11b has an unpolarized region 20b. In the example shown in FIGS. 1 and 2, the piezoelectric element 50 has an unpolarized region 20b in which the entire piezoelectric layer 20 of the protrusion 11b is not polarized. Further, the entire area of the piezoelectric layer 20 of the laminated portion 11a other than the protruding portion 11b is a polarized region 20a polarized in the thickness direction.

Therefore, in the state before folding the piezoelectric film 10a of the piezoelectric element 50, in other words, in the state in which the folded piezoelectric film 10a is unfolded, the piezoelectric film 10a is partially attached to the piezoelectric layer 20, as shown in FIG. It has an unpolarized region 20b that is not polarized, and the other region (the region that becomes the laminated portion 11a) is a polarized region 20a that is polarized in the thickness direction. In other words, in the piezoelectric film 10a, the area of the piezoelectric layer 20 that becomes the protruding part 11b when folded back is the unpolarized area 20b, and the other area (the area that becomes the laminated part 11a) is polarized in the thickness direction. This is the polarized region 20a.
FIG. 4 shows a perspective view of the piezoelectric film 10a with the second electrode layer 26 omitted for explanation. As shown in FIG. 4, the piezoelectric film 10a has a rectangular shape and has an unpolarized region 20b in a region of a predetermined width along one edge. That is, the unpolarized region 20b exists at the outer edge of the piezoelectric film 10a.

Further, as shown in FIG. 3, in the piezoelectric film 10a, the piezoelectric layer 20 is polarized in the thickness direction in the region sandwiched between the pair of electrodes (the first electrode layer 24 and the second electrode layer 26). It has a polarized region 20a and an unpolarized region 20b. That is, the electrode layer sandwiching the polarized region 20a and the electrode layer sandwiching the unpolarized region 20b are integral. Therefore, even if the piezoelectric film 10a is folded back to form the piezoelectric element 50 and the unpolarized region 20b is present in the protrusion 11b, by providing the protrusion 11b with a connecting part for connecting to an external power source, the laminated part 11a and A voltage can be appropriately applied to the polarized region 20a.

As described above, the piezoelectric layer 20 (piezoelectric film 10a) is polarized in the thickness direction, thereby exhibiting piezoelectric performance that expands and contracts in accordance with the applied voltage. Therefore, when a voltage is applied to the electrode layer (electrode pair) of the laminated portion 11a in which the piezoelectric layer 20 is polarized through the connection portion of the protruding portion 11b, the piezoelectric element 50 exhibits piezoelectric performance. Stretch and contract in the plane direction. On the other hand, the unpolarized region 20b in which the piezoelectric layer 20 is not polarized does not expand or contract even when a voltage is applied to the electrode layer of the protrusion 11b. Therefore, vibration does not occur in the protruding portion 11b, and generation of unnecessary sound (noise) can be suppressed.

Here, in the example shown in FIG. 1 etc., the entire area of the piezoelectric layer 20 of the protrusion 11b is configured as the unpolarized region 20b, but the present invention is not limited to this, and at least one portion of the piezoelectric layer 20 of the protrusion 11b is It suffices if the portion is the unpolarized region 20b. From the viewpoint of suppressing unnecessary sound (noise) caused by the protrusion 11b, it is preferable that the entire area of the piezoelectric layer 20 of the protrusion 11b is the unpolarized region 20b.

In addition, in the example shown in FIG. 1, etc., the entire region other than the protruding portion 11b of the piezoelectric layer 20 (the region that becomes the laminated portion 11a) is configured to be the polarized region 20a, but the structure is not limited to this, and the laminated An unpolarized region 20b may be included in a part of the region that becomes part 11a. From the viewpoint of appropriately driving the piezoelectric element 50 and obtaining high piezoelectric performance, it is preferable that the entire region that becomes the laminated portion 11a is the polarized region 20a.

Here, the polarized region and the unpolarized region can be measured as follows.

A ferroelectric material such as PZT is used as the piezoelectric particles in a piezoelectric film that uses a polymer composite piezoelectric material formed by dispersing piezoelectric particles in a matrix containing a polymer material as a piezoelectric layer. The crystal structure of this ferroelectric material is divided into many domains with different directions of spontaneous polarization, and in this state, the spontaneous polarization of each domain and the resulting piezoelectric effect cancel each other out. No piezoelectricity is observed as a whole.

Therefore, in such piezoelectric films, it is possible to align the direction of spontaneous polarization in each domain by applying electrical polarization processing such as poling to the piezoelectric layer and applying an external electric field of a certain value or more. It is being said. The polarized piezoelectric particles exhibit a piezoelectric effect in response to an external electric field. Thereby, the piezoelectric film expands and contracts in the plane direction in response to the applied voltage, and vibrates in a direction perpendicular to the plane, thereby converting vibration (sound) and electrical signals.

Generally, X-ray diffraction (XRD) is used to analyze the crystal structure of such piezoelectric layers (piezoelectric particles), and XRD is used to examine how atoms are arranged inside the crystal. This makes it possible to distinguish between polarized regions and unpolarized regions.

Specifically, when the polymer composite piezoelectric material that is the piezoelectric layer 20 is evaluated by X-ray diffraction method (XRD), the (002) plane peak intensity (c domain) derived from the piezoelectric particles and the (200 ) If the ratio α to the plane peak intensity (a domain) is 1 or more, it is regarded as a polarized region, and if it is less than 1, it is regarded as an unpolarized region. The X-ray irradiation area in this XRD evaluation was 1 cm square, and the evaluation was performed two-dimensionally with a 1 mm interval in the X and Y directions within the plane of the piezoelectric layer, and the polarized and unpolarized regions were measured. can do.

Here, the (002) plane peak intensity is the tetragonal peak around 43.5° in the XRD pattern obtained by XRD analysis (θ-2θ method), and the (200) plane peak intensity is the In the XRD pattern obtained by analysis, this is a tetragonal peak around 45°. The (002) plane peak intensity corresponds to the proportion of domains (c domains) whose polarization axis is perpendicular to the X-ray diffraction plane (in-plane direction of the piezoelectric film), and the (200) plane peak intensity is It corresponds to the proportion of domains (a-domains) whose polarization axes are parallel to the X-ray diffraction plane. Originally, polarization processing of a piezoelectric body is an act of inverting the polarization of the c domain (180° domain switching), but this 180° domain switching itself cannot be determined by XRD analysis. However, with 180° domain switching (disappearance of the 180° domain wall), the 90° domain wall, which was previously clamped to the 180° domain wall, can now move easily and A so-called 90° domain motion (a-domain⇔c-domain) occurs in response to the stimulus. In other words, if the ratio of the c-domain is high after polarization treatment by XRD, the 180° domain wall has disappeared, that is, the polarization inversion of the c-domain has progressed sufficiently, and high piezoelectricity can be obtained.
XRD analysis can be performed using an X-ray diffraction device (X'Pert PRO manufactured by PANalytical) or the like.

Such a piezoelectric element 50 is attached to a diaphragm and used as an electroacoustic transducer.
FIG. 5 schematically shows an example of an electroacoustic transducer having the piezoelectric element 50 described above.
The electroacoustic transducer 100a shown in FIG. 5 includes a piezoelectric element 50 and a diaphragm 102. The piezoelectric element 50 has the same configuration as the example shown in FIG. 1 and the like. The piezoelectric element 50 and the diaphragm 102 are attached to each other with an adhesive layer (not shown).

In such an electroacoustic transducer 100a, by applying a driving voltage to the piezoelectric film 10a of the piezoelectric element 50, the piezoelectric film 10a expands and contracts in the plane direction, and due to the expansion and contraction of the piezoelectric film 10a, the piezoelectric element 50 expands and contracts.
The expansion and contraction of the piezoelectric element 50 in the plane direction causes the diaphragm 102 to bend, 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 10a, and generates sound according to the driving voltage applied to the piezoelectric film 10a.

The diaphragm 102 preferably has flexibility. In addition, in the present invention, having flexibility is synonymous with having flexibility in a general interpretation, and indicates that it is possible to bend and bend. , indicating that it can be bent and stretched without breaking or damage.

The diaphragm 102 is not particularly limited as long as it is preferably flexible, and various sheet-like materials (plate-like materials, films) 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 made of polyethylene naphthalate (PEN), triacetyl cellulose (TAC), cyclic olefin resins, etc., foamed polystyrene, foamed plastics made of foamed styrene, foamed polyethylene, etc., and corrugated paperboard on one or both sides. Examples include various corrugated cardboard materials made by gluing paperboard.

In the electroacoustic transducer 100a, the diaphragm 102 may be an organic electroluminescence (OLED) display, a liquid crystal display, or a microLED (Light Emitting Diode) display, as long as it has flexibility. , and display devices such as inorganic electroluminescent displays can also be suitably used.

In addition, in the electroacoustic transducer 100a, it is preferable that the electrode layer of the piezoelectric element 50 (piezoelectric film 10a) and the diaphragm 102 are not electrically connected.
If the electrode layer of the piezoelectric element 50 and the diaphragm 102 are electrically connected, troubles such as short circuits may occur. Therefore, by configuring the electrode layer of the piezoelectric element 50 and the diaphragm 102 to be not electrically connected, the risk of occurrence of failure can be reduced.

The adhesive layer has fluidity when it is pasted and then becomes solid.Even a layer made of adhesive is a gel-like (rubber-like) soft solid when it is pasted and remains in a gel-like state after that. It may be a layer made of an adhesive that does not change, or a layer made of a material that has characteristics of both an adhesive and a pressure-sensitive 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 be directly transmitted to the diaphragm 102. If a viscous substance that dampens vibration exists between the diaphragm 102 and the piezoelectric element 50, the efficiency of transmitting the energy of the expansion and contraction of the piezoelectric element 50 to the diaphragm 102 will decrease, resulting in electroacoustic conversion. As a result, the driving efficiency of the device 100 decreases.
Considering this point, the adhesive layer that adheres the diaphragm and the piezoelectric element (piezoelectric film) to the diaphragm and the piezoelectric element (piezoelectric film) is an adhesive layer that is made of an adhesive that provides a solid and harder adhesive layer than an adhesive layer that is made of an adhesive. Preferably, it is a layer of agent. More preferable adhesive layers include, specifically, adhesive layers made of thermoplastic adhesives such as polyester adhesives and styrene-butadiene rubber (SBR) adhesives.
Adhesion, unlike adhesion, is useful when a high bonding temperature is required. In addition, thermoplastic adhesives are suitable because they have "relatively low temperature, short time, and strong adhesion."

There is no limit to the thickness of the adhesive layer, and a thickness that provides sufficient adhesive strength (adhesive strength, adhesive strength) may be appropriately set depending on the material of the adhesive layer.
Here, in the electroacoustic transducer 100, the thinner the adhesive layer is, the higher the transmission effect of the elastic energy (vibration energy) of the piezoelectric element 50 to the diaphragm 102 can be, and the higher the energy efficiency can be. Further, if the adhesive layer is thick and rigid, expansion and contraction of the piezoelectric element 50 may be restricted.
Considering this point, it is preferable that the adhesive layer be thinner. Specifically, the thickness of the adhesive layer after attachment is preferably 0.1 to 50 μm, more preferably 0.1 to 30 μm, even more preferably 0.1 to 10 μm.

Note that in the electroacoustic transducer 100, the adhesive layer is provided as a preferred embodiment and is not an essential component.
Therefore, the electroacoustic transducer 100 may not have an adhesive layer, 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 piezoelectric element 50 has a rectangular shape 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 center may be connected with bolts. The electroacoustic transducer may be configured by fastening with a member such as a nut.

However, in this case, when a driving voltage is applied from the power source, the piezoelectric element 50 expands and contracts independently with respect to the diaphragm 102, and in some cases, only the piezoelectric element 50 is bent, causing the piezoelectric element 50 to expansion and contraction is not transmitted to the diaphragm 102. In this way, when the piezoelectric element 50 expands and contracts independently with respect to the diaphragm 102, the vibration efficiency of the diaphragm 102 caused by the piezoelectric element 50 decreases. There is a possibility that the diaphragm 102 cannot be vibrated sufficiently.
Taking this point into consideration, it is preferable that the diaphragm 102 and the piezoelectric element 50 be attached using an adhesive layer.

Next, another example of the piezoelectric film of the present invention will be described using FIG. 6.
The piezoelectric film 10b shown in FIG. 6 is a single rectangular piezoelectric film. In FIG. 6, illustration of the protective layer is omitted in order to simplify the drawing and clearly show the configuration of the piezoelectric element 50. The piezoelectric film 10b shown in FIG. 6 has the same configuration as the piezoelectric film 10a shown in FIG. 3, except that the arrangement of the unpolarized regions 20b in the piezoelectric layer 20 is different.

In the piezoelectric film 10b shown in FIG. 6, two regions of a predetermined width along the opposing edges (left and right edges in the figure) of the piezoelectric layer 20 are unpolarized regions 20b, and the other regions are unpolarized regions 20b. The region , that is, the center region in the left-right direction in the figure is a polarized region 20a polarized in the thickness direction. That is, the unpolarized region 20b exists at the outer edge of the piezoelectric film 10b.

As shown in FIG. 7, such a piezoelectric film 10b can be attached to a diaphragm 102 and used as an electroacoustic transducer 100b.

As mentioned above, when a conventional piezoelectric film is attached to a diaphragm to form an electroacoustic transducer, there is a problem in that the vibration of the piezoelectric film causes the bond between the diaphragm and the piezoelectric film to peel off. I understand. In the case of a conventional configuration in which the piezoelectric layer is polarized over the entire area of the piezoelectric film 210, as in the electroacoustic transducer 200b shown in FIG. 15, as shown by the arrow in FIG. Expands and contracts (vibrates). In the case of such a configuration, stress is concentrated at the end of the bonding surface between the piezoelectric film 210 and the diaphragm 202, and peeling occurs from the end and progresses inward.

In contrast, the electroacoustic transducer 100b having the piezoelectric film 10b of the present invention has an unpolarized region 20b at the outer edge of the piezoelectric film 10b. Therefore, as shown by arrows in FIG. 7, the piezoelectric film 10b expands and contracts (vibrates) in the center region of the piezoelectric film 10b, but does not expand and contract (vibrates) in the regions at both ends. Therefore, it is possible to reduce the stress concentrated at the end of the bonding surface between the piezoelectric film 10b and the diaphragm 102, and it is possible to suppress the occurrence of peeling from the end.

In addition, from the viewpoint of suppressing peeling between the piezoelectric film and the diaphragm, the width of the unpolarized region in the piezoelectric film (width in the direction perpendicular to the nearby edges) is preferably 1 mm or more, more preferably 3 mm or more, and 10 mm or more. The above is more preferable. On the other hand, if the unpolarized area is too large, the output of the piezoelectric film will decrease, and the sound pressure of the electroacoustic transducer will decrease. Therefore, the width of the unpolarized region in the piezoelectric film is preferably 10% or less of the width of the piezoelectric film, more preferably 5% or less, and even more preferably 3% or less.

Further, in the example shown in FIG. 6, the piezoelectric film 10b has two unpolarized regions 20b along two opposing edges among the four edges in a plan view, but the present invention is not limited to this. For example, the configuration may include the unpolarized region 20b along one or three edges, or the unpolarized region 20b may be provided along the four edges, that is, over the entire outer edge of the piezoelectric film 10b. may have.

Alternatively, in the example shown in FIG. 6, the configuration is such that the unpolarized region 20b is provided in the entire area along the edge of the piezoelectric film 10b, but the structure is not limited to this, and a part of the area along the edge of the piezoelectric film 10b is used. It is also possible to have an unpolarized region 20b in the region. For example, the piezoelectric film 10b may have an unpolarized region 20b at at least one of its four corners in a plan view.

Further, in the example shown in FIG. 7, the single-layer piezoelectric film 10b is attached to the diaphragm 102, but the present invention is not limited to this. For example, in a piezoelectric element 50 in which a piezoelectric film 10a is folded multiple times and multiple layers of piezoelectric films are laminated as shown in FIG. A configuration including a polarized region 20b may also be used. Specifically, in FIG. 5, the piezoelectric element 50 has an unpolarized region 20b of a predetermined width along the right edge of the piezoelectric film 10a on the diaphragm 102 side (lower side in the figure). By doing so, stress concentration can be prevented from occurring at the end portions of the bonding surfaces between the piezoelectric element 50 and the diaphragm 102, and peeling from the end portions can be suppressed.

Note that also in the electroacoustic transducer 100b, it is preferable that the electrode layer of the piezoelectric film 10b and the diaphragm 102 are not electrically connected.

Furthermore, in the example shown in FIG. 7, the piezoelectric film 10b has an unpolarized region 20b at the outer edge thereof, but the present invention is not limited thereto. For example, in a piezoelectric element 50 formed by folding a piezoelectric film 10a as shown in FIG. An unpolarized region 20b may be provided in a region along the right edge in the figure of the adhesion surface. In this case, before the piezoelectric film 10a of the piezoelectric element 50 is folded back, the unpolarized region 20b is formed in a region other than the outer edge of the piezoelectric film 10a.

Hereinafter, the constituent elements of the piezoelectric film of the present invention will be explained. In the following description, the piezoelectric films 10a to 10b are also collectively referred to as the piezoelectric film 10 unless it is necessary to distinguish them.

FIG. 8 shows a part of the piezoelectric film 10 in an enlarged manner.
The piezoelectric film 10 shown in FIG. A second protective layer 30 laminated on the surface opposite to the body layer 20 , a first electrode layer 24 laminated on the other surface of the piezoelectric layer 20 , and a layer opposite to the piezoelectric layer 20 of the first electrode layer 24 A first protective layer 28 is laminated on the side surface. That is, the piezoelectric film 10 has a structure in which the piezoelectric layer 20 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, the piezoelectric layer 20 is a polymer composite piezoelectric material containing piezoelectric particles 36 in a matrix 34 containing a polymer material, as conceptually shown in FIG.

As the material for the matrix 34 (matrix and binder) of the polymer composite piezoelectric material constituting the piezoelectric layer 20, it is preferable to use a polymer material that has viscoelasticity at room temperature. Note that in this specification, "normal temperature" refers to a temperature range of about 0 to 50°C.

Here, the polymer composite piezoelectric material (piezoelectric layer 20) preferably satisfies the following requirements.
(i) Flexibility For example, when holding a newspaper or magazine in a loosely bent state like a document for portable use, it is constantly subjected to 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 will be generated, and cracks will occur at the interface between the polymer matrix and the piezoelectric particles, which may eventually lead to destruction. Therefore, a polymer composite piezoelectric material is required to have appropriate softness. Moreover, if strain energy can be diffused to the outside as heat, stress can be alleviated. Therefore, the loss tangent of the polymer composite piezoelectric material is required to be appropriately large.

To summarize the above, a flexible polymer composite piezoelectric material used as an exciter is required to behave hard against vibrations of 20 Hz to 20 kHz, and to behave softly against vibrations of several Hz or less. Further, the loss tangent of the polymer composite piezoelectric material is required to be appropriately large for vibrations of all frequencies below 20 kHz.
Furthermore, it is preferable that the spring constant can be easily adjusted by laminating layers 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 increases or the frequency decreases, large-scale molecular motion causes a decrease (relaxation) in the storage modulus (Young's modulus) or a maximum in the loss modulus (absorption). It is observed as Among these, the relaxation caused by micro-Brownian motion of molecular chains in the amorphous region is called principal dispersion, and a very large relaxation phenomenon is observed. The temperature at which this main dispersion occurs is the glass transition point (Tg), and the viscoelastic relaxation mechanism appears most prominently.
In the polymer composite piezoelectric material (piezoelectric layer 20), by using a polymer material whose glass transition point is at room temperature, in other words, a polymer material that has viscoelasticity at room temperature, for the matrix, it can withstand vibrations of 20Hz to 20kHz. This results in a polymer composite piezoelectric material that is hard and behaves softly when subjected to slow vibrations of several Hz or less. In particular, in order to suitably exhibit this behavior, it is preferable to use a polymer material whose glass transition point at a frequency of 1 Hz is at room temperature, that is, 0 to 50° C., for the matrix of the polymer composite piezoelectric material.

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

Further, the polymer material having viscoelasticity at room temperature preferably has a storage modulus (E') at a frequency of 1 Hz measured by dynamic viscoelasticity measurement of 100 MPa or more at 0°C and 10 MPa or less at 50°C.
As a result, the bending moment that occurs when the polymer composite piezoelectric material is slowly bent by an external force can be reduced, and at the same time, it can behave stiffly 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.
However, on the other hand, in consideration of securing good moisture resistance, etc., it is also suitable for the polymer material to have a dielectric constant of 10 or less at 25°C.

Examples of polymeric materials that have viscoelasticity at room temperature that meet these conditions include cyanoethylated polyvinyl alcohol (cyanoethylated PVA), polyvinyl acetate, polyvinylidene chloride core acrylonitrile, polystyrene-vinyl polyisoprene block copolymer, and polyvinyl methyl. Examples include ketones and polybutyl methacrylate. Furthermore, commercially available products such as Hybler 5127 (manufactured by Kuraray Co., Ltd.) can also be suitably used as these polymeric materials. Among these, 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 polymeric material having viscoelasticity at room temperature, it is preferable to use a polymeric material having a cyanoethyl group, and it is particularly preferable to use cyanoethylated PVA. That is, in the present invention, it is preferable for the piezoelectric layer 20 to use a polymeric material having a cyanoethyl group as the matrix 34, and it is particularly preferable to use cyanoethylated PVA.
In the following explanation, the above-mentioned polymeric materials represented by cyanoethylated PVA are also collectively referred to as "polymeric materials having viscoelasticity at room temperature."

Note that these polymeric materials having viscoelasticity at room temperature may be used alone or in combination (mixture) of multiple types.

The matrix 34 using such a polymeric material having viscoelasticity at room temperature may be made of a plurality of polymeric materials in combination, if necessary.
That is, in addition to the viscoelastic material such as cyanoethylated PVA, other dielectric polymeric materials may be added to the matrix 34 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, cyanoethylhydroxysucrose, cyanoethylhydroxycellulose, cyanoethylhydroxypullulan, cyanoethyl methacrylate, cyanoethyl acrylate, cyanoethyl Cyano groups such as hydroxyethyl cellulose, cyanoethyl amylose, cyanoethyl hydroxypropyl cellulose, cyanoethyl dihydroxypropyl cellulose, cyanoethyl hydroxypropyl amylose, cyanoethyl polyacrylamide, cyanoethyl polyacrylate, cyanoethyl pullulan, cyanoethyl polyhydroxymethylene, cyanoethyl glycidol pullulan, cyanoethyl saccharose and cyanoethyl sorbitol Examples include polymers having a cyanoethyl group, and synthetic rubbers such as nitrile rubber and chloroprene rubber.
Among them, polymeric materials having cyanoethyl groups are preferably used.
Further, in the matrix 34 of the piezoelectric layer 20, the number of these dielectric polymer materials is not limited to one type, and a plurality of types may be added.

In addition to the dielectric polymer material, the matrix 34 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 phenol resins, urea resins, melamine resins, alkyd resins, and mica may also be added.
Furthermore, for the purpose of improving tackiness, tackifiers such as rosin ester, rosin, terpene, terpene phenol, and petroleum resin may be added.

In the matrix 34 of the piezoelectric layer 20, when adding a material other than a viscoelastic polymeric material such as cyanoethylated PVA, there is no particular limitation on the amount added, but the proportion in the matrix 34 is 30% by mass or less. It is preferable that
This allows the properties of the added polymer material to be expressed without impairing the viscoelastic relaxation mechanism in the matrix 34, resulting in higher dielectric constant, improved heat resistance, improved adhesion between the piezoelectric particles 36 and the electrode layer, etc. Favorable results can be obtained in this respect.

The piezoelectric layer 20 is a layer made of a polymer composite piezoelectric material that includes such a matrix 34 and piezoelectric particles 36 . Piezoelectric particles 36 are dispersed in matrix 34 . Preferably, the piezoelectric particles 36 are uniformly (substantially uniformly) dispersed in the matrix 34.
The piezoelectric particles 36 are made of ceramic particles having a perovskite or wurtzite crystal structure.
Examples of the ceramic particles constituting the piezoelectric particles 36 include lead zirconate titanate (PZT), lead lanthanate zirconate titanate (PLZT), barium titanate (BaTiO ₃ ), zinc oxide (ZnO), and A solid solution (BFBT) of barium titanate and bismuth ferrite (BiFe ₃ ) is exemplified.

There is no limit to the particle size of the piezoelectric particles 36, and it may be selected as appropriate depending on the size of the piezoelectric film 10, the use of the piezoelectric element 50, and the like. The particle size of the piezoelectric particles 36 is preferably 1 to 10 μm.
By setting the particle size of the piezoelectric particles 36 within this range, favorable results can be obtained in that the piezoelectric film 10 can have both high piezoelectric properties and flexibility.

Note that the piezoelectric particles 36 in the piezoelectric layer 20 may be uniformly and regularly dispersed in the matrix 34, or if they are uniformly dispersed, they may be irregularly dispersed in the matrix 34. may have been done.

In the piezoelectric film 10, the ratio of the matrix 34 to the piezoelectric particles 36 in the piezoelectric layer 20 is not limited, and depends on the size and thickness of the piezoelectric film 10 in the plane direction, the use of the piezoelectric element 50, and It may be set as appropriate depending on the characteristics etc. required of the piezoelectric element 50.
The volume fraction of the piezoelectric particles 36 in the piezoelectric layer 20 is preferably 30 to 80%, more preferably 50% or more, and therefore even more preferably 50 to 80%.
By setting the quantity ratio of the matrix 34 to the piezoelectric particles 36 within the above range, favorable results can be obtained in terms of achieving both high piezoelectric properties and flexibility.

In the piezoelectric film 10, the thickness of the piezoelectric layer 20 is not particularly limited, and may be determined as appropriate depending on the use of the piezoelectric element 50, the number of laminated piezoelectric films in the piezoelectric element 50, the characteristics required of the piezoelectric film 10, etc. , just set it.
The thicker the piezoelectric layer 20 is, the more advantageous it is in terms of rigidity such as the 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 increases.
The thickness of the piezoelectric layer 20 is preferably 10 to 300 μm, more preferably 20 to 200 μm, and even more preferably 30 to 150 μm.
By setting the thickness of the piezoelectric layer 20 within the above range, favorable results can be obtained in terms of ensuring both rigidity and appropriate flexibility.

Furthermore, the piezoelectric layer 20 is preferably polarized (poled) in the thickness direction.

As shown in FIG. 8, the piezoelectric film 10 has a second electrode layer 26 on one side of the piezoelectric layer 20, a second protective layer 30 thereon, and a second electrode layer 26 on one side of the piezoelectric layer 20. It has a structure in which it has a first electrode layer 24 on its surface and a first protective layer 28 thereon. Here, the first electrode layer 24 and the second electrode layer 26 form an electrode pair.

That is, in the piezoelectric film 10, both surfaces of the piezoelectric layer 20 are sandwiched between an electrode pair, that is, a second electrode layer 26 and a first electrode layer 24, and this laminate is sandwiched between a second protective layer 30 and a first protective layer 28. It has a structure in which it is sandwiched between.
In this way, in the piezoelectric film 10, the region sandwiched between the second electrode layer 26 and the first electrode layer 24 expands and contracts depending on the applied voltage.
Note that the second electrode layer 26 and the second protective layer 30, as well as the first electrode layer 24 and the first protective layer 28 are added for convenience in order to explain the piezoelectric film 10. Therefore, the first and second aspects of the present invention have no technical meaning and are unrelated to actual usage conditions.

In the present invention, the piezoelectric film 10 includes, in addition to these layers, an adhesive layer for pasting the electrode layer and the piezoelectric layer 20, and a pasting layer for pasting the electrode layer and the protective layer. It may have an attached layer.
The adhesive may be an adhesive or a pressure-sensitive adhesive. Further, as the adhesive, a polymeric material obtained by removing the piezoelectric particles 36 from the piezoelectric layer 20, that is, the same material as the matrix 34, can also be suitably used. Note that the adhesive layer may be provided on both the first electrode layer 24 side and the second electrode layer 26 side, or may be provided only on one of the first electrode layer 24 side and the second electrode layer 26 side. good.

In the piezoelectric film 10, the first protective layer 28 and the second protective layer 30 cover the first electrode layer 24 and the second electrode layer 26, and also serve to impart appropriate rigidity and mechanical strength to the piezoelectric layer 20. is in charge of That is, in the piezoelectric film 10, the piezoelectric layer 20 consisting of the matrix 34 and the piezoelectric particles 36 exhibits excellent flexibility against slow bending deformation, but depending on the application, it may have low rigidity. or mechanical strength may be insufficient. The piezoelectric film 10 is provided with a first protective layer 28 and a second protective layer 30 to compensate for this.
The first protective layer 28 and the second protective layer 30 have the same structure, except for the arrangement position. Therefore, in the following description, when there is no need to distinguish between the first protective layer 28 and the second protective layer 30, both members are collectively referred to as protective layers.

The protective layer is not limited and various sheet-like materials can be used, and various resin films are suitably exemplified as an example.
Among them, polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS), polycarbonate (PC), polyphenylene sulfite (PPS), and polymethyl methacrylate (PMMA) are used because of their excellent mechanical properties and heat resistance. ), polyetherimide (PEI), polyimide (PI), polyethylene naphthalate (PEN), triacetyl cellulose (TAC), cyclic olefin resin, and the like are suitably used.

There is also no limit to the thickness of the protective layer. Moreover, the thicknesses of the first protective layer 28 and the second protective layer 30 are basically the same, but may be different.
Here, if the rigidity of the protective layer is too high, it not only restricts the expansion and contraction of the piezoelectric layer 20 but also impairs its flexibility. Therefore, the thinner the protective layer is, the more advantageous it is, except when mechanical strength and good handling properties as a sheet-like product are required.

In the piezoelectric film 10, if the thickness of the protective layer is at most twice the thickness of the piezoelectric layer 20, favorable results can be obtained in terms of ensuring both rigidity and appropriate flexibility. .
For example, when the piezoelectric layer 20 has a thickness of 50 μm and the protective layer is made of PET, the thickness of the protective layer is preferably 100 μm or less, more preferably 50 μm or less, and even more preferably 25 μm or less.

In the piezoelectric film 10, a second electrode layer 26 is provided between the piezoelectric layer 20 and the second protective layer 30, and a first electrode layer 24 is provided between the piezoelectric layer 20 and the first protective layer 28. It is formed. The first electrode layer 24 and the second electrode layer 26 are provided to apply a voltage to the piezoelectric layer 20 (piezoelectric film 10).

The first electrode layer 24 and the second electrode layer 26 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 24 and the second electrode layer 26, both members are collectively referred to as electrode layers.

In the present invention, there are no restrictions on the material for forming the electrode layer, 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, Further, indium tin oxide and the like are exemplified. Alternatively, conductive polymers such as PEDOT/PPS (polyethylenedioxythiophene-polystyrene sulfonic acid) are also exemplified. Among them, copper, aluminum, gold, silver, platinum, and indium tin oxide are preferably exemplified as the electrode layer. Among these, copper is more preferable from the viewpoints of conductivity, cost, flexibility, and the like.

Furthermore, there are no restrictions on the method of forming the electrode layer, including vapor deposition methods (vacuum film formation methods) such as vacuum evaporation and sputtering, film formation by plating, and methods of pasting foil made of the above materials. Various known methods are available.

Among these, thin films made of copper, aluminum, or the like formed by vacuum deposition are particularly preferably used as the electrode layer because the flexibility of the piezoelectric film 10 can be ensured. Among these, a copper thin film formed by vacuum evaporation is particularly preferably used.

There is no limit to the thickness of the electrode layer. Further, the thicknesses of the first electrode layer 24 and the second electrode layer 26 are basically the same, but may be different.
Here, similarly to the above-mentioned protective layer, if the rigidity of the electrode layer is too high, it not only restricts the expansion and contraction of the piezoelectric layer 20 but also impairs its flexibility. Therefore, it is advantageous for the electrode layer to be thinner, as long as the electrical resistance does not become too high.

In the piezoelectric film 10, it is preferable that the product of the thickness of the electrode layer and the Young's modulus be less than the product of the thickness of the protective layer and the Young's modulus, since flexibility will not be significantly impaired.
For example, in the case of a combination in which the protective layer is made of PET (Young's modulus: approximately 6.2 GPa) and the electrode layer is made of copper (Young's modulus: approximately 130 GPa), and the thickness of the protective layer is 25 μm, the thickness of the electrode layer is The thickness is preferably 1.2 μm or less, more preferably 0.3 μm or less, and particularly preferably 0.1 μm or less.

As described above, the piezoelectric film 10 has a piezoelectric layer 20 formed by dispersing piezoelectric particles 36 in a matrix 34 containing a polymeric material, sandwiched between the first electrode layer 24 and the second electrode layer 26, and further includes: This laminate has a structure in which a first protective layer 28 and a second protective layer 30 are sandwiched between them.
In such a piezoelectric film 10, it is preferable that the maximum value of the loss tangent (Tan δ) at a frequency of 1 Hz as measured by dynamic viscoelasticity exists at room temperature, and it is preferable that 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, so that the polymer matrix and piezoelectric particles are This can prevent cracks from forming at the interface.

The piezoelectric film 10 preferably has a storage 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 also applies to the piezoelectric layer 20.
This allows the piezoelectric film 10 to have a large frequency dispersion in storage modulus (E') at room temperature. That is, it is hard against vibrations of 20 Hz to 20 kHz, and can behave soft against vibrations of several Hz or less.

Furthermore, the piezoelectric film 10 has a product of thickness and storage modulus (E') at a frequency of 1 Hz measured 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 also applies to the piezoelectric layer 20.
Thereby, the piezoelectric film 10 can have appropriate rigidity and mechanical strength without impairing its 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. Regarding this condition, the piezoelectric layer 20 is also the same.
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 f ₀ changes due to a change in the curvature of the speaker can also be reduced.

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

In the piezoelectric element 50, a power source (external power source) is connected to the first electrode layer 24 and the second electrode layer 26 of the piezoelectric film 10, which applies a driving voltage to expand and contract the piezoelectric film 10, that is, supplies driving power.
The power source is not limited and may be either a direct current power source or an alternating current power source. Furthermore, the drive voltage may be appropriately set to a drive voltage that can appropriately drive the piezoelectric film 10, depending on the thickness and forming material of the piezoelectric layer 20 of the piezoelectric film 10.

As described above, in the case of a piezoelectric element in which piezoelectric films are folded and laminated, electrodes are drawn out from the first electrode layer 24 and the second electrode layer 26 at the protrusion 11b. There is no limit to the method of drawing out the electrodes from the first electrode layer 24 and the second electrode layer 26, and various known methods can be used.
As an example, a method of connecting a conductive material such as copper foil to the first electrode layer 24 and the second electrode layer 26 and drawing out the electrodes to the outside, and a method of penetrating the first protective layer 28 and the second protective layer 30 with a laser or the like are available. Examples include a method of forming a hole, filling the through hole with a conductive material, and drawing out an electrode to the outside.
Examples of suitable electrode extraction methods include the method described in JP-A No. 2014-209724 and the method described in JP-A No. 2016-015354.

[Method for manufacturing piezoelectric film]
The method for manufacturing a piezoelectric film of the present invention includes:
A method for producing a piezoelectric film having a piezoelectric layer made of a polymer composite piezoelectric material containing piezoelectric particles in a matrix containing a polymeric material, and electrode layers provided on both sides of the piezoelectric layer, the method comprising:
a piezoelectric layer forming step of forming an unpolarized piezoelectric layer on the main surface of one electrode layer;
After the piezoelectric layer forming step, a polarization treatment step of polarizing a part of the piezoelectric layer;
After the polarization treatment step, an electrode lamination step of laminating the other electrode layer on the main surface of the piezoelectric layer,
In the polarization process, an electrode member is placed facing the main surface of the piezoelectric layer on the opposite side from one electrode layer, and after one electrode layer is connected to the ground, a DC voltage is applied between the electrode member and the electrode member. The polarization process is performed by applying
This is a method of manufacturing a piezoelectric film in which a polarized region and an unpolarized region are formed in a piezoelectric layer by regulating the region to be polarized.
Moreover, as a preferable embodiment, in the piezoelectric film manufacturing method of the present invention, the polarization treatment is a corona poling treatment, and the electrode member is a wire-shaped corona electrode.

An example of a method for manufacturing the piezoelectric film 10 will be described below with reference to FIGS. 9 to 13.

First, a sheet-like material 12a shown in FIG. 9 in which the first electrode layer 24 is formed on the surface of the first protective layer 28 is prepared. Furthermore, a sheet-like material 12c, conceptually shown in FIG. 13, in which a second electrode layer 26 is formed on the surface of a second protective layer 30 is prepared.

The sheet-like material 12a may be produced by forming a copper thin film or the like as the first electrode layer 24 on the surface of the first protective layer 28 by vacuum evaporation, sputtering, plating, or the like. Similarly, the sheet-like material 12c may be produced by forming a copper thin film or the like as the second electrode layer 26 on the surface of the second protective layer 30 by vacuum evaporation, sputtering, plating, or the like.
Alternatively, a commercially available sheet material in which a copper thin film or the like is formed on a protective layer may be used as the sheet material 12a and/or the sheet material 12c.
The sheet-like material 12a and the sheet-like material 12c may be the same or different.

Note that if the protective layer is very thin and has poor handling properties, a protective layer with a separator (temporary support) may be used as necessary. Note that as the separator, PET or the like having a thickness of 25 to 100 μm can be used. The separator may be removed after thermocompression bonding of the electrode layer and the protective layer.

Next, as shown in FIG. 10, a paint (coating composition) that will become the piezoelectric layer 20 is applied onto the first electrode layer 24 of the sheet-like material 12a, and then cured to form the piezoelectric layer 20 ( piezoelectric layer formation process). In this way, a piezoelectric laminate 12b in which the sheet-like material 12a and the piezoelectric layer 20 are laminated is manufactured. The piezoelectric layer 20 formed in the piezoelectric layer forming step is in an unpolarized state.

Various methods can be used to form the piezoelectric layer 20 depending on the material used to form the piezoelectric layer 20.
As an example, first, a polymer material such as the above-mentioned cyanoethylated PVA is dissolved in an organic solvent, and then piezoelectric particles 36 such as PZT particles are added and stirred to prepare a paint.
There are no restrictions on the organic solvent, and various organic solvents such as dimethylformamide (DMF), methyl ethyl ketone (MEK), and cyclohexanone can be used.
After preparing the sheet-like material 12a and preparing the paint, the paint is cast (coated) on the sheet-like material 12a, and the organic solvent is evaporated and dried. Thereby, as shown in FIG. 10, a piezoelectric laminate 12b having the first electrode layer 24 on the first protective layer 28 and the piezoelectric layer 20 laminated on the first electrode layer 24 was manufactured. do.

There are no restrictions on the coating method, and all known methods (coating devices) such as a bar coater, slide coater, and doctor knife can be used.
Alternatively, if the polymeric material can be heated and melted, the polymeric material is heated and melted, the piezoelectric particles 36 are added thereto to produce a melted material, and the sheet shown in FIG. 9 is formed by extrusion molding or the like. A piezoelectric laminate 12b as shown in FIG. 10 may be produced by extruding it in a sheet form onto the shaped object 12a and cooling it.

Note that, as described above, in the piezoelectric layer 20, the matrix 34 may contain a polymeric piezoelectric material such as PVDF in addition to the polymeric material having viscoelasticity at room temperature.
When adding these polymer piezoelectric materials to the matrix 34, the polymer piezoelectric materials to be added to the paint may be dissolved. Alternatively, the polymeric piezoelectric material to be added may be added to a polymeric material that is heated and melted and has viscoelasticity at room temperature, and then heated and melted.

Once the piezoelectric layer 20 is formed, calendaring may be performed if necessary. Calendar processing 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 using a heated press, a heated roller, etc. to flatten the surface.

Next, polarization treatment (poling) is performed on the piezoelectric layer 20 of the piezoelectric laminate 12b (polarization treatment step). Although the polarization treatment of the piezoelectric layer 20 may be performed before the calender treatment, it is preferably performed after the calender treatment.
There are no restrictions on the method for polarizing the piezoelectric layer 20, and any known method can be used. Examples include electric field poling, corona poling, and the like, in which a DC electric field is directly applied to the object to be polarized.
Furthermore, in the piezoelectric film 10 of the present invention, the polarization treatment is performed not in the plane direction of the piezoelectric layer 20 but in the thickness direction.

Here, in the manufacturing method of the present invention, the polarization treatment step includes arranging a corona electrode facing the main surface of the piezoelectric layer 20 on the opposite side to one electrode layer (first electrode layer 24), After connecting one electrode layer (first electrode layer) to ground, polarization treatment is performed by applying a voltage between one electrode layer (first electrode layer) and the corona electrode to generate corona discharge. This is a corona poling process, and by regulating the area to be polarized, a polarized area and an unpolarized area are formed in the piezoelectric layer 20.
As a result, it is possible to produce a piezoelectric film in which the piezoelectric layer has an unpolarized region in which the piezoelectric layer is not polarized.

As a method of regulating the region to be polarized, for example, the length of the region where corona discharge occurs of a wire-shaped corona electrode is made shorter than the width of the piezoelectric layer, thereby regulating the region to be polarized. Polarization is performed by arranging an insulator or a conductor connected to ground on a part of the main surface of the piezoelectric layer opposite to one electrode layer (first electrode layer). Examples include methods of regulating areas.

FIG. 11 is a diagram for explaining a method of regulating the region to be polarized by making the length of the region of the corona electrode where corona discharge occurs shorter than the width of the piezoelectric layer.
As shown in FIG. 11, a wire-shaped corona electrode 60 faces the surface (top surface) of the piezoelectric layer 20 of the piezoelectric laminate 12b opposite to the first electrode layer 24 and is movable along this surface. Place. The distance between the piezoelectric layer 20 and the corona electrode 60 is, for example, about 1 mm. This corona electrode 60 and the first electrode layer 24 are connected to a DC power source, and a DC voltage of several kV, for example, 6 kV is applied between the first electrode layer 24 and the corona electrode 60 from the DC power source to discharge the corona. cause Further, the corona electrode 60 is moved (scanned) along the upper surface of the piezoelectric layer 20 while maintaining the interval to polarize the piezoelectric layer 20. Thereby, the piezoelectric layer 20 is polarized in the thickness direction.

At that time, as shown in FIG. 11, a part of the wire-shaped corona electrode 60 is covered with a first covering member 62 made of an insulator such as alumina, so that the wire-shaped corona electrode 60 faces the area covered with the first covering member 62. Corona discharge is not generated in the region of the piezoelectric layer 20, and polarization treatment is prevented. That is, in the example shown in FIG. 11, by covering a part of the wire-shaped corona electrode 60 with the first covering member 62, the length of the region of the corona electrode 60 where corona discharge occurs is made smaller than the width of the piezoelectric layer 20. It's also shorter. Thereby, unpolarized regions 20b and polarized regions 20a can be formed in the piezoelectric layer 20.

The position, length, etc. of the first covering member 62 may be appropriately set according to the region of the piezoelectric layer 20 in which the unpolarized region 20b is formed.
Further, as the material of the first covering member 62, alumina, zirconia, etc. can be used.

In the example shown in FIG. 11, a part of the corona electrode 60 is covered with the first covering member 62 to form the unpolarized region 20b in the piezoelectric layer 20, but the present invention is not limited to this.
For example, the length of the corona electrode 60 itself may be made shorter than the width of the piezoelectric layer 20 (width in the longitudinal direction of the wire-shaped corona electrode), and the corona electrode may be placed in a region of the piezoelectric layer 20 that does not face the corona electrode 60. The unpolarized region 20b may be formed without causing discharge. Alternatively, a portion of the corona electrode 60 may be made of tungsten wire to make corona discharge less likely to occur and form the unpolarized region 20b.

FIG. 12 shows a method of regulating the area to be polarized by placing an insulator or a conductor connected to ground on a part of the main surface of the piezoelectric layer opposite to one electrode layer. It is a figure for explaining.
As shown in FIG. 12, a wire-shaped corona electrode 60 faces the surface (top surface) of the piezoelectric layer 20 of the piezoelectric laminate 12b opposite to the first electrode layer 24 and is movable along this surface. Place. The distance between the piezoelectric layer 20 and the corona electrode 60 is, for example, about 1 mm. This corona electrode 60 and the first electrode layer 24 are connected to a DC power source, and a DC voltage of several kV, for example, 6 kV is applied between the first electrode layer 24 and the corona electrode 60 from the DC power source to discharge the corona. cause Further, the corona electrode 60 is moved (scanned) along the upper surface of the piezoelectric layer 20 while maintaining the interval to polarize the piezoelectric layer 20. Thereby, the piezoelectric layer 20 is polarized in the thickness direction.

At this time, as shown in FIG. 12, a part of the upper surface of the piezoelectric layer 20 is covered with an insulating or conductive second covering member 64 connected to the ground. Corona discharge is not generated in the region, or the region exposed to corona discharge is regulated to prevent it from being polarized. Thereby, unpolarized regions 20b and polarized regions 20a can be formed in the piezoelectric layer 20.

The position, length, etc. of the second covering member 64 may be appropriately set according to the area in the piezoelectric layer 20 where the unpolarized area 20b is formed.

As the insulating second covering member 64, alumina, a rubber sheet, etc. can be used.
Further, as the conductive second covering member 64, a copper foil sheet or the like can be used. Note that when using the conductive second covering member 64, the second covering member 64 is connected to ground.

After the polarization treatment step, as shown in FIG. Stack toward 20.
Furthermore, this laminate is thermocompressed using a hot press device, a heating roller, etc., with the first protective layer 28 and the second protective layer 30 sandwiched therebetween, thereby forming the piezoelectric laminate 12b and the sheet-like material 12c. 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 12b and the sheet-like material 12c together using an adhesive, and preferably further press-bonding them.

Note that this piezoelectric film 10 may be manufactured using a cut sheet-like sheet material 12a, a sheet-like material 12c, etc., or may be manufactured using a roll-to-roll method. Good too.

The produced piezoelectric film may be cut into desired shapes according to various uses.
The polarized region of the piezoelectric film 10 produced in this way is polarized not in the plane direction but in the thickness direction, and great piezoelectric properties can be obtained even without stretching treatment after polarization treatment. Therefore, the polarized region of the piezoelectric film 10 has no in-plane anisotropy in its piezoelectric properties, and when a driving voltage is applied, it expands and contracts isotropically in all directions in the plane.

Here, as described above, the piezoelectric layer 20 includes piezoelectric particles 36 in the matrix 34. Further, a second electrode layer 26 and a first electrode layer 24 are provided so as to sandwich the piezoelectric layer 20 in the thickness direction.
When a voltage is applied to the second electrode layer 26 and the first electrode layer 24 of the piezoelectric film 10 having such a piezoelectric layer 20, in the polarization region 20a, the piezoelectric particles 36 move in the polarization direction according to the applied voltage. Expand and contract. As a result, the piezoelectric film 10 (polarized region 20a of the piezoelectric layer 20) contracts in the thickness direction. At the same time, the piezoelectric film 10 also expands and contracts in the in-plane direction due to the Poisson ratio. This expansion/contraction is approximately 0.01 to 0.1%.

As mentioned above, the thickness of the piezoelectric layer 20 is preferably about 10 to 300 μm. Therefore, the expansion and contraction in the thickness direction is very small, about 0.3 μm at most.
On the other hand, the piezoelectric film 10, that is, the piezoelectric layer 20 (polarized region 20a) 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 a maximum of about 0.2 mm by applying a voltage.

The diaphragm 102 is attached to the piezoelectric film 10 with an adhesive layer. Therefore, the diaphragm 102 is bent by the expansion and contraction of the piezoelectric film 10, 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.

Furthermore, 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 bend, which may suppress the vibration of the diaphragm 102 during driving. On the other hand, when the mass of the piezoelectric film 10 is small, the resonance frequency becomes high, and vibration of the diaphragm 102 at low frequencies may be suppressed. Considering these points, it is preferable that the mass of the piezoelectric film 10 is appropriately adjusted according to the spring constant of the diaphragm 102.

Although the piezoelectric element of the present invention has been described in detail above, the present invention is not limited to the above-mentioned examples, and it goes without saying that various improvements and changes may be made without departing from the gist of the present invention. It is.

Hereinafter, the present invention will be explained in more detail by giving specific examples of the present invention. It should be noted that the present invention is not limited to this example, and the materials, usage amounts, ratios, processing contents, processing procedures, etc. shown in the following examples may be changed as appropriate without departing from the spirit of the present invention. can.

[Example 1]
<Preparation of piezoelectric film>
A piezoelectric film was produced by the method shown in FIGS. 9 to 13 described above.
First, cyanoethylated PVA (CR-V, manufactured by Shin-Etsu Chemical Co., Ltd.) was dissolved in dimethylformamide (DMF) at the composition ratio shown below. Thereafter, PZT particles as piezoelectric particles were added to this solution in the composition ratio shown below, 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 commercially available PZT raw material powder at 1000 to 1200° C., and then crushing and classifying it to an average particle size of 5 μm.

On the other hand, a sheet-like product was prepared by vacuum-depositing a 0.3 μm thick copper thin film onto a 4 μm thick PET film. That is, in this example, the first electrode layer and the second electrode layer are copper vapor deposited thin films with a thickness of 0.3 μm, and the first protective layer and the second protective layer are PET films with a thickness of 4 μm.
The previously prepared paint for forming the piezoelectric layer was applied onto the first electrode layer (copper deposited thin film) of the sheet using a slide coater. The coating material was applied so that the thickness of the coating film after drying was 50 μm.
Next, the sheet material coated with the paint was heated and dried on a hot plate at 120° C. to evaporate the DMF. As a result, a piezoelectric laminate having a first electrode layer made of copper on a first protective layer made of PET, and a piezoelectric layer (polymer composite piezoelectric layer) with a thickness of 50 μm on top of the first electrode layer was produced. did. The produced piezoelectric laminate was cut into a size of 170 mm x 200 mm.

The produced piezoelectric layer was polarized in the thickness direction by corona poling using a wire-shaped corona electrode.
At that time, a 20 mm wide region along one of the 200 mm long edges of the top surface of the piezoelectric layer was covered with an insulating second covering member (material: nitrile rubber) to perform polarization treatment. As a result, a piezoelectric layer having polarized regions and unpolarized regions was formed. Note that a rubber magnet may be used as the second covering member. This is an extrusion molded product made by mixing a magnetic material with a mainly rubber-based (nitrile rubber/acrylic rubber) binder, and since it has magnetic force, it is easy to place the sample on a stage, such as when performing polarization treatment on a metal stage. This is suitable because it can be fixed.

On top of the polarized piezoelectric laminate, a sheet-like material in which the same thin film was deposited on a PET film was laminated with the second 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 second electrode layer are adhered and bonded to form a piezoelectric layer. A film was produced.

The produced piezoelectric film was folded twice in the direction of the 170 mm side, and the piezoelectric films were laminated with an adhesive layer (acrylic adhesive) to form a laminated part with a length of 200 mm and a width of 50 mm, and a laminated part with a length of 200 mm and a width of 20 mm. A piezoelectric element having a protrusion was fabricated. When folded back, the unpolarized region became a protrusion.

[Comparative example 1]
A piezoelectric film was produced to produce a piezoelectric element in the same manner as in Example 1, except that when performing the corona poling treatment, the entire surface of the piezoelectric layer was polarized without covering it with the second covering member.

[evaluation]
<Sound quality>
The produced piezoelectric elements of Examples and Comparative Examples were adhered to a diaphragm to produce electroacoustic transducers. As the diaphragm, a plate-like member having a size of 500 mm x 450 mm, a thickness of 0.8 mm, and made of aluminum (A5052) was used. The transverse direction of the diaphragm and the longitudinal direction of the piezoelectric element were aligned, and the piezoelectric element was attached with the center of the laminated portion of the piezoelectric element aligned with the center of the diaphragm. An acrylic adhesive was used as the adhesive layer that adheres the piezoelectric element and the diaphragm.

A music signal was input to the piezoelectric element via an amplifier using a commercially available CD sound source, and a sensory evaluation was performed at a location 1 meter in front of the diaphragm to evaluate the sound quality on a 10-point scale. Table 1 shows the average scores of a total of 20 testers.
The results are shown in Table 1.

From Table 1, it can be seen that the sound quality of the examples of the present invention is improved compared to the comparative examples. This is because there is less noise. In the example, by making the protrusion into an unpolarized region, the protrusion does not vibrate arbitrarily, and noise components are reduced, resulting in improved sound quality.

[Example 2]
The size was 50 mm x 200 mm, and when performing corona poling treatment, a 3 mm wide insulating second covering member (material: nitrile rubber) was placed along each of the four edges of the top surface of the piezoelectric layer. A piezoelectric film was produced in the same manner as in Example 1 except that the polarization treatment was performed.

[Comparative example 2]
A piezoelectric film was produced in the same manner as in Example 2, except that when performing the corona poling treatment, the upper surface of the piezoelectric layer was not covered with the second covering member and the entire surface was subjected to the polarization treatment.

[evaluation]
<Sound quality, appearance abnormality (peeling)>
The produced piezoelectric films of Examples and Comparative Examples were adhered to a diaphragm to produce electroacoustic transducers. As the diaphragm, a plate-like member having a size of 500 mm x 450 mm, a thickness of 0.8 mm, and made of aluminum (A5052) was used. The lateral direction of the diaphragm and the longitudinal direction of the piezoelectric film were aligned, and the piezoelectric film was attached with the center of the diaphragm aligned with the center of the diaphragm. A hot melt adhesive sheet (Cranbetter, manufactured by Kurabo Industries, Ltd.) was used as the adhesive layer for adhering the piezoelectric film and the diaphragm. The thickness of the adhesive layer was 30 μm.

A pink noise signal was input to the piezoelectric film via an amplifier using a noise signal generator, and the piezoelectric film was driven continuously for 10,000 hours to examine changes in sound pressure and appearance abnormalities before and after the test.
The results are shown in Table 2.

From Table 2, it can be seen that the sound pressure of the examples of the present invention is not lower than that of the comparative examples, and there is no abnormality in appearance. That is, it can be seen that in the examples of the present invention, the piezoelectric film, which is difficult to peel off, is difficult to peel off from the diaphragm, compared to the comparative examples.
In Comparative Example 1, peeling occurred at the outer peripheral edge of the bonding surface between the piezoelectric film and the diaphragm. Further, in Comparative Example 1, it is considered that the sound pressure decreased due to this peeling.
From the above, the effects of the present invention are clear.

The piezoelectric film and piezoelectric element of the present invention can be used, for example, in the manufacture of various sensors such as sonic sensors, ultrasonic sensors, pressure sensors, tactile sensors, strain sensors, and vibration sensors (particularly for infrastructure inspections such as crack detection and foreign object detection). (Useful for on-site inspections), acoustic devices such as microphones, pickups, speakers, and exciters (Specific applications include noise cancellers (used in cars, trains, airplanes, robots, etc.), artificial vocal cords, and pest/vermin intrusion. Examples include protective buzzers, furniture, wallpaper, photographs, helmets, goggles, headrests, signage, robots, etc.), haptics, ultrasonic probes, and hydrophones used in automobiles, smartphones, smart watches, games, etc. ultrasonic transducers such as, actuators used for water droplet prevention, transportation, stirring, dispersion, polishing, etc., vibration dampers used for containers, vehicles, buildings, sports equipment such as skis and rackets, and roads, floors, etc. It can be suitably used as a vibration power generation device for use in mattresses, chairs, shoes, tires, wheels, computer keyboards, and the like.

10a, 10b piezoelectric film 11a laminated portion

11b protruding portion

12a, 12c sheet-like material 12b piezoelectric laminate 14 adhesive layer 20 piezoelectric layer 20a polarized region 20b unpolarized region 24 first electrode layer 26 second electrode layer 28 first protective layer 30 second protective layer 34 matrix 36

piezoelectric particles

40, 42 conducting wire 50 piezoelectric element 60 corona electrode 62 first covering member 64

second covering member

100a, 100b electroacoustic transducer 102 diaphragm

Claims

A piezoelectric film having a piezoelectric layer made of a polymer composite piezoelectric material containing piezoelectric particles in a matrix containing a polymer material, and electrode layers provided on both sides of the piezoelectric layer,
A piezoelectric film, wherein the piezoelectric layer has an unpolarized region in which the piezoelectric layer is not polarized.
The piezoelectric film according to claim 1, wherein the piezoelectric layer has a polarized region polarized in the thickness direction and the unpolarized region in a region sandwiched between the pair of electrode layers constituting an electrode pair. .
The piezoelectric film according to claim 1, wherein the unpolarized region is present at an outer edge of the piezoelectric film.
A piezoelectric element formed by laminating a plurality of piezoelectric films by folding the piezoelectric film according to any one of claims 1 to 3 one or more times,
In a plan view, the piezoelectric film has a laminated part in which two or more layers overlap, and a protrusion part that protrudes from the laminated part,
The protruding portion has a connecting portion for connecting the electrode layer and an external power source,
A piezoelectric element, wherein the unpolarized region is present in the protrusion.
An electroacoustic transducer comprising the piezoelectric film according to any one of claims 1 to 3 attached to a diaphragm.
An electroacoustic transducer comprising the piezoelectric element according to claim 4 attached to a diaphragm.
The electroacoustic transducer according to claim 5, wherein the electrode layer of the piezoelectric film and the diaphragm are not electrically connected.
The electroacoustic transducer according to claim 6, wherein the electrode layer of the piezoelectric film and the diaphragm are not electrically connected.
A method for producing a piezoelectric film comprising: a piezoelectric layer made of a polymer composite piezoelectric material containing piezoelectric particles in a matrix containing a polymer material; and electrode layers provided on both sides of the piezoelectric layer.
a piezoelectric layer forming step of forming the unpolarized piezoelectric layer on the main surface of one of the electrode layers;
After the piezoelectric layer forming step, a polarization treatment step of polarizing a part of the piezoelectric layer;
After the polarization treatment step, an electrode lamination step of laminating the other electrode layer on the main surface of the piezoelectric layer,
In the polarization treatment step, after arranging an electrode member facing the main surface of the piezoelectric layer opposite to the one electrode layer and connecting the one electrode layer to ground, The polarization process is performed by applying a DC voltage between the
A method for manufacturing a piezoelectric film, wherein a polarized region and an unpolarized region are formed in the piezoelectric layer by regulating the region to be polarized.
The polarization treatment is a corona poling treatment,
The method for manufacturing a piezoelectric film according to claim 9, wherein the electrode member is a wire-shaped corona electrode.
10. In the polarization treatment step, the region to be polarized is regulated by making the length of the region of the wire-shaped corona electrode where the corona discharge occurs shorter than the width of the piezoelectric layer. A method for producing a piezoelectric film as described in .
In the polarization treatment step, an insulator or a conductor connected to earth is placed on a part of the main surface of the piezoelectric layer opposite to the one electrode layer, so that the region to be polarized is The method for manufacturing a piezoelectric film according to claim 9, wherein the method regulates the following.