WO2023166892A1

WO2023166892A1 - Electroacoustic transducer

Info

Publication number: WO2023166892A1
Application number: PCT/JP2023/002784
Authority: WO
Inventors: 裕介香川
Original assignee: 富士フイルム株式会社
Priority date: 2022-03-03
Filing date: 2023-01-30
Publication date: 2023-09-07

Abstract

Provided is an electroacoustic transducer formed by sticking a piezoelectric element to a vibration plate, wherein even when the vibration plate is flexible, it is possible to obtain a high sound pressure. This electroacoustic transducer, which has a vibration plate and a piezoelectric element stuck to the vibration plate, includes a high-stiffness layer disposed between the vibration plate and the piezoelectric element, wherein when K₁ is the bending stiffness of the vibration plate, K₂ is the bending stiffness of the piezoelectric element, and K₃ is the bending stiffness of the high-stiffness layer, K₁<K₂<10xK₃ is satisfied.

Description

Electroacoustic transducer

The present invention relates to electroacoustic transducers.

A piezoelectric element can be used as a so-called exciter (exciter), in which various articles (diaphragms) are attached in contact with an article (diaphragm) to vibrate the article (diaphragm) and produce sound. It's being used. For example, by attaching an exciter to an image display panel, a screen, or the like and vibrating them, sound can be produced instead of a speaker.

For example, in Patent Document 1, a plurality of piezoelectric films in which a piezoelectric layer is sandwiched between two thin film electrodes are laminated, and the piezoelectric films are polarized in the thickness direction and are adjacent to each other. A laminated piezoelectric element in which the polarization direction of the piezoelectric film is opposite is described, and this laminated piezoelectric element is adhered to a diaphragm to form an electroacoustic transducer.

WO2020/095812

According to the study of the present inventor, it was found that when a piezoelectric element is attached to a diaphragm to form an electroacoustic transducer, a high sound pressure cannot be obtained if the diaphragm is too soft. The present inventor believes that if the diaphragm is too soft, the expansion and contraction in the plane direction caused by the vibration of the piezoelectric element is absorbed by expansion and contraction in the plane direction. It was thought that high sound pressure could not be obtained because it was not converted to expansion and contraction of the

SUMMARY OF THE INVENTION An object of the present invention is to solve the problems of the prior art. An object of the present invention is to provide an electroacoustic transducer capable of obtaining

In order to solve the problems described above, the present invention has the following configurations.
[1] An electroacoustic transducer having a diaphragm and a piezoelectric element attached to the diaphragm,
having a high-rigidity layer disposed between the diaphragm and the piezoelectric element,
An electroacoustic transducer that satisfies _K1 < _K2 <10× _K3 , where K1 is the bending rigidity of _the diaphragm, _K2 is the bending rigidity of the piezoelectric element, and _K3 is the bending rigidity of the high-rigidity layer.
[2] The electroacoustic transducer according to [1], wherein the high-rigidity layer has a flexural rigidity _K3 of 0.03 N· ^m2 or less.
[3] The electroacoustic transducer according to [1] or [2], wherein the bending stiffness K ₁ of the diaphragm is 0.02 N·m ² or less.
[4] The electroacoustic transducer according to any one of [1] to [3], wherein the area of the high-rigidity layer in plan view is smaller than the area of the diaphragm.
[5] Any one of [1] to [4], wherein the piezoelectric element includes a piezoelectric film having a piezoelectric layer, electrode layers provided on both sides of the piezoelectric layer, and protective layers provided on the electrode layers. Electroacoustic transducer according to any one of the above.
[6] The electroacoustic transducer according to [5], wherein the piezoelectric element is formed by laminating a plurality of piezoelectric films.
[7] The electroacoustic transducer according to [5] or [6], wherein the piezoelectric layer is composed of a polymeric composite piezoelectric body containing piezoelectric particles in a matrix containing a polymeric material.

According to the present invention, it is possible to provide an electroacoustic transducer in which a piezoelectric element is attached to a diaphragm, and which is capable of obtaining high sound pressure even when the diaphragm is soft. .

It is a figure which shows typically an example of the electroacoustic transducer of this invention. FIG. 2 is a partially enlarged view of the electroacoustic transducer shown in FIG. 1; It is a figure for demonstrating the effect|action of the electroacoustic transducer of this invention. FIG. 4 is a diagram schematically showing another example of a piezoelectric element used in the electroacoustic transducer of the present invention; FIG. 4 is a diagram schematically showing an example of a piezoelectric film included in the electroacoustic transducer of the present invention; It is a conceptual diagram for explaining an example of a method of manufacturing a piezoelectric film. It is a conceptual diagram for explaining an example of a method of manufacturing a piezoelectric film. It is a conceptual diagram for explaining an example of a method of manufacturing a piezoelectric film. It is a figure for demonstrating the conventional electroacoustic transducer.

Hereinafter, the electroacoustic transducer of the present invention will be described in detail based on preferred embodiments shown in the accompanying drawings.

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

[Electroacoustic transducer]
The electroacoustic transducer of the present invention is
An electroacoustic transducer having a diaphragm and a piezoelectric element attached to the diaphragm,
having a high-rigidity layer disposed between the diaphragm and the piezoelectric element,
An electroacoustic transducer that satisfies _K1 < _K2 <10× _{K3, where K1 is the flexural rigidity of the diaphragm, K2 is the flexural rigidity of the piezoelectric element, and K3} _is _the _flexural rigidity of the high-rigidity layer. be.

FIG. 1 shows a diagram schematically showing an example of the electroacoustic transducer of the present invention. FIG. 2 shows a partially enlarged view of the electroacoustic transducer of FIG.

The electroacoustic transducer 100 shown in FIG. 1 has a piezoelectric element 50 , a diaphragm 102 , and a high-rigidity layer 104 arranged between the piezoelectric element 50 and the diaphragm 102 . As shown in FIG. 2, the piezoelectric element 50 and the high-rigidity layer 104 are adhered with the adhesion layer 16 . Also, the high-rigidity layer 104 and the diaphragm 102 are adhered by the adhesion layer 16 .

The diaphragm 102 has flexibility as a preferred embodiment. In the present invention, having flexibility is synonymous with having flexibility in general interpretation, and indicates that it is possible to bend and bend, specifically , indicating that it can be bent and stretched without fracture and damage.

Diaphragm 102 is not limited as long as it preferably has flexibility, and various sheet-like materials (plate-like material, film) can be used.
Examples include polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS), polycarbonate (PC), polyphenylene sulfite (PPS), polymethyl methacrylate (PMMA), polyetherimide (PEI), polyimide (PI), Resin films made of polyethylene naphthalate (PEN), triacetyl cellulose (TAC), cyclic olefin resins, etc., expanded polystyrene, expanded plastics made of expanded styrene, expanded polyethylene, etc., plywood, cork board, leather such as cowhide, Examples include various types of paperboard such as carbon sheets and Japanese paper, and various types of corrugated board made by pasting another paperboard onto one or both sides of corrugated paperboard.

In addition, as long as it has flexibility, the diaphragm 102 may be an organic electroluminescence (OLED (Organic Light Emitting Diode)) display, a liquid crystal display, a micro LED (Light Emitting Diode) display, or an inorganic electroluminescence display. A display device such as a display, a projector screen, and the like are also suitable for use.

The high-rigidity layer 104 is arranged between the vibration plate 102 and the piezoelectric element 50 .
Here, if the bending rigidity of the diaphragm 102 is _K1 , the bending rigidity of the piezoelectric element 50 is _K2 , and the bending rigidity of the high-rigid layer 104 is _K3 , then _K1 < _K2 <. It has a high rigidity that satisfies 10×K ₃ .

The high-rigidity layer 104 is not particularly limited as long as it satisfies the flexural rigidity relationship K ₁ <K ₂ <10×K ₃ , 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), polyphenylene sulfide (PPS), polyetheretherketone (PEEK), cyclic olefin resins, etc., as well as aluminum, stainless steel, copper, nickel, titanium, and a metal sheet made of platinum or the like.

The piezoelectric element 50 is used as a so-called exciter (exciton) that exhibits piezoelectricity according to the applied voltage and vibrates the diaphragm 102 .

In the example shown in FIG. 2, the piezoelectric element 50 is obtained by laminating three layers of the piezoelectric film 10 by folding one long rectangular piezoelectric film 10 twice in one direction. The piezoelectric film 10 includes a piezoelectric layer 20, a first electrode layer 24 and a second electrode layer 26 (hereinafter collectively referred to as electrode layers) provided on both sides of the piezoelectric layer 20, and protective layers provided on the electrode layers. layers (first protective layer 28 and second protective layer 30). In FIG. 2, illustration of the protective layer is omitted in order to clearly show the configuration of the piezoelectric element 50. As shown in FIG. The piezoelectric film 10 will be detailed later.

As shown in FIG. 1, a power source is connected to the first electrode layer 24 and the second electrode layer 26 of the piezoelectric film 10 that constitute the piezoelectric element 50 . When a voltage is applied to the first electrode layer 24 and the second electrode layer 26 , the piezoelectric element 50 (piezoelectric film 10 ) expands and contracts the piezoelectric layer 20 to drive the piezoelectric element 50 (piezoelectric film 10 ) as a piezoelectric body. When the piezoelectric element 50 is driven, the piezoelectric element 50 expands and contracts in the plane direction, bending the diaphragm 102 to which the piezoelectric element 50 is adhered, and as a result vibrating the diaphragm 102 in the thickness direction to produce sound. generate. The diaphragm 102 vibrates according to the magnitude of the drive voltage applied to the piezoelectric element 50, and the electroacoustic transducer 100 generates sound according to the applied drive voltage.
That is, the electroacoustic transducer 100 has a configuration in which the piezoelectric element 50 (laminated piezoelectric film 10) is used as an exciter.

Here, as described above, it has been found that when a piezoelectric element is attached to a diaphragm to form an electroacoustic transducer, a high sound pressure cannot be obtained if the diaphragm is too soft. When the diaphragm is too soft, that is, when the bending stiffness _K1 of the diaphragm is smaller than the bending stiffness _K2 of the piezoelectric element, the piezoelectric element 50 is driven as shown in FIG. Since the diaphragm 102 expands and contracts in the plane direction and absorbs the expansion and contraction in the plane direction caused by It was thought that high sound pressure could not be obtained because it was not converted to

On the other hand, the electroacoustic transducer 100 of the present invention has the high-rigidity layer 104 between the diaphragm 102 and the piezoelectric element 50, the bending rigidity of the diaphragm 102 is _K1 , and the bending rigidity of the piezoelectric element 50 is Assuming that the rigidity is _K2 and the bending rigidity of the high-rigidity layer 104 is _K3 , _K1 < _K2 <10× _K3 is satisfied. If the high-rigidity layer 104 having a high bending rigidity that satisfies this relational expression is provided between the diaphragm 102 and the piezoelectric element 50, the piezoelectric element 50 expands and contracts in the plane direction by the high-rigidity layer 104, as shown in FIG. is regulated, the expansion and contraction of the piezoelectric element 50 in the planar direction is converted into expansion and contraction in the vertical direction. Accordingly, when the piezoelectric element 50 is driven, the piezoelectric element 50 vibrates in the vertical direction, and the vibration plate 102 can vibrate in the vertical direction. By vibrating the diaphragm 102 in the vertical direction, the air can be greatly vibrated, so that a high sound pressure can be obtained.

Here, the flexural rigidity K of each component is the product of Young's modulus E and area moment of inertia I.
Young's modulus E may be measured by a known method. As an example, a test piece can be cut out from each component and a tensile test can be performed using this test piece to measure the Young's modulus of each component. Since the piezoelectric element 50 has frequency dependence, dynamic viscoelasticity measurement was performed, and the storage elastic modulus at 1 kHz was defined as Young's modulus. The dynamic viscoelasticity measurement is as described later.

Further, the moment of inertia I of each component may be calculated from the shape (width and thickness) of each component. If the cross section is rectangular, it can be obtained from the width b and the thickness h by I=(b×h ³ )/12. In addition, when the shape in plan view is rectangular, the length of the long side is defined as the width b.

From the viewpoint of improving sound pressure, the bending stiffness K ₃ of the high-rigidity layer 104 preferably satisfies 9×K ₃ >K ₂ , more preferably satisfies 8×K ₃ >K ₂ , and more preferably satisfies 7×K ₃ > It is even more preferable to satisfy _K2 .

Further, from the viewpoint of preventing the high-rigidity layer 104 from interfering with the vibration of the piezoelectric element 50, the bending rigidity _K3 of the high-rigidity layer 104 is preferably 0.03 N·m ² or less, more preferably 0.025 N·m ² or less. is more preferable, and 0.02 N·m ² or less is even more preferable. On the other hand, from the viewpoint of improving the sound pressure, the bending stiffness _K3 of the high-rigidity layer 104 is preferably 0.005 N·m ² or more, more preferably 0.01 N·m ² or more.

The flexural rigidity K ₃ of the high-rigidity layer 104 can be adjusted by appropriately setting the material, thickness, and width of the high-rigidity layer 104 .

Further, in the present invention, the bending rigidity K ₁ of the diaphragm 102 is smaller than the bending rigidity K ₃ of the high-rigidity layer 104 . Therefore, the bending stiffness K ₁ of the diaphragm 102 is, for example, 0.02 N·m ² or less.

It is preferable that the area of the high-rigidity layer 104 is smaller than the area of the diaphragm 102 when viewed from above, that is, when viewed from a direction perpendicular to the main surface of the diaphragm 102 . This can increase the amplitude when the vibration plate 102 is expanded and contracted by the piezoelectric element 50 through the high-rigidity layer 104, and the sound pressure can be improved.

Also, the area of the high-rigidity layer 104 in plan view is preferably 0.5 times or more that of the piezoelectric element 50, and more preferably substantially the same. If the area of the high-rigidity layer 104 is smaller than 0.5 times the area of the piezoelectric element 50, the expansion and contraction of the area of the piezoelectric element 50 that is not bonded to the high-rigidity layer 104 is not transmitted to the diaphragm 102 and is useless. Become. On the other hand, since the area of the high-rigidity layer 104 is 0.5 times or more, preferably equal to or more than the area of the piezoelectric element, the expansion and contraction of the piezoelectric element 50 in the plane direction is efficiently converted into expansion and contraction in the vertical direction. be able to.

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

In addition, in the example shown in FIG. 1, the piezoelectric element 50 has a piezoelectric film laminated in multiple layers by folding the long piezoelectric film 10 one or more times, but it is not limited to this. As shown in FIG. 4, the piezoelectric element may have a configuration in which a plurality of sheet-shaped (cut-sheet-shaped) piezoelectric films 10 are laminated.

In the piezoelectric element shown in FIG. 4, three piezoelectric films 10 are laminated with adhesive layers 19 interposed therebetween. Each of the three piezoelectric films is connected to a power supply.

In the piezoelectric element shown in FIG. 4, as a preferred mode, the piezoelectric film 10 is polarized in the thickness direction, and the polarization directions of adjacent piezoelectric films 10 are opposite to each other. Therefore, in adjacent piezoelectric films 10, the first electrode layers 24 face each other and the second electrode layers 26 face each other. Therefore, the power supply, whether it is an AC power supply or a DC power supply, always supplies power of the same polarity to the facing electrodes. Therefore, in the piezoelectric element shown in FIG. 4, even if the electrodes of the adjacent piezoelectric films 10 come into contact with each other, there is no risk of short-circuiting.

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

A piezoelectric element in which long piezoelectric films are folded and laminated has the following advantages.
That is, when a plurality of cut sheet-like piezoelectric films 10 are laminated, the first electrode layer 24 and the second electrode layer 26 must be connected to the drive power source for each piezoelectric film. On the other hand, in the structure in which the long piezoelectric film 10 is folded and laminated, the laminated body can be configured with only one long piezoelectric film 10 . In addition, in the configuration in which the long piezoelectric film 10 is folded and laminated, only one power source is required for applying the driving voltage, and the electrodes from the piezoelectric film 10 need only be drawn out at one point.
Furthermore, in the structure in which the long piezoelectric films 10 are folded and laminated, the polarization directions of adjacent piezoelectric films are inevitably opposite to each other.

The constituent elements of the electroacoustic transducer of the present invention will be described below.

FIG. 5 shows an enlarged view of a portion of the piezoelectric film 10. As shown in FIG.
The piezoelectric film 10 shown in FIG. 5 includes a piezoelectric layer 20 that is a sheet-like material having piezoelectric properties, a first electrode layer 24 that is laminated on one surface of the piezoelectric layer 20 , and piezoelectric layers of the first electrode layer 24 . A first protective layer 28 laminated on the surface opposite to the body layer 20, a second electrode layer 26 laminated on the other surface of the piezoelectric layer 20, and the second electrode layer 26 opposite to the piezoelectric layer 20. and a second protective layer 30 laminated on the side surface. That is, the piezoelectric film 10 has a configuration 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, various known piezoelectric layers can be used as the piezoelectric layer 20 .
In the present invention, as conceptually shown in FIG. 5, the piezoelectric layer 20 is preferably a polymeric composite piezoelectric body containing piezoelectric particles 36 in a matrix 34 containing a polymeric material.

As the material of the polymer composite piezoelectric matrix 34 (matrix and binder) that constitutes the piezoelectric layer 20, it is preferable to use a polymer material that has viscoelasticity at room temperature. In this specification, "ordinary temperature" refers to a temperature range of about 0 to 50.degree.

Here, the polymer composite piezoelectric body (piezoelectric layer 20) preferably satisfies the following requirements.
(i) Flexibility For example, when gripping a loosely bent state like a document like a newspaper or magazine for portable use, it is constantly subjected to a relatively slow and large bending deformation of several Hz or less from the outside. become. At this time, if the polymer composite piezoelectric material is hard, a correspondingly large bending stress is generated, and cracks occur at the interface between the polymer matrix and the piezoelectric particles, which may eventually lead to destruction. Therefore, the polymer composite piezoelectric body is required to have appropriate softness. Moreover, stress can be relieved if strain energy can be diffused to the outside as heat. Therefore, it is required that the loss tangent of the polymer composite piezoelectric material is appropriately large.

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 softly against vibrations of several Hz or less. Also, the loss tangent of the polymer composite piezoelectric body is required to be moderately large with respect to vibrations of all frequencies of 20 kHz or less.
Furthermore, it is preferable that the spring constant can be easily adjusted by laminating according to the rigidity (hardness, stiffness, spring constant) of the mating material (diaphragm) to which the adhesive layer 16 is attached. The thinner it is, the more energy efficient it can be.

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

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

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

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

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

As the polymer material having viscoelasticity at room temperature, it is preferable to use a polymer material having a cyanoethyl group, and it is particularly preferable to use cyanoethylated PVA. That is, in the present invention, the piezoelectric layer 20 preferably uses a polymer material having a cyanoethyl group as the matrix 34, and particularly preferably uses cyanoethylated PVA.
In the following description, the above-mentioned polymeric materials represented by cyanoethylated PVA are collectively referred to as "polymeric materials having viscoelasticity at room temperature".

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

The matrix 34 using such a polymeric material having viscoelasticity at room temperature may use a plurality of polymeric materials together, if necessary.
That is, in addition to viscoelastic materials 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, cyanoethylhydroxysaccharose, cyanoethylhydroxycellulose, cyanoethylhydroxypullulan, cyanoethylmethacrylate, cyanoethylacrylate, cyanoethyl Cyano groups such as hydroxyethylcellulose, cyanoethylamylose, cyanoethylhydroxypropylcellulose, cyanoethyldihydroxypropylcellulose, cyanoethylhydroxypropylamylose, cyanoethylpolyacrylamide, cyanoethylpolyacrylate, cyanoethylpullulan, cyanoethylpolyhydroxymethylene, cyanoethylglycidolpullulan, cyanoethylsaccharose and cyanoethylsorbitol. Alternatively, polymers having cyanoethyl groups, and synthetic rubbers such as nitrile rubber and chloroprene rubber are exemplified.
Among them, polymer materials having cyanoethyl groups are preferably used.
Moreover, in the matrix 34 of the piezoelectric layer 20, these dielectric polymer materials are not limited to one type, and a plurality of types may be added.

In addition to the dielectric polymer material, the matrix 34 also contains thermoplastic resins such as vinyl chloride resin, polyethylene, polystyrene, methacrylic resin, polybutene, and isobutylene for the purpose of adjusting the glass transition point Tg, and Thermosetting resins such as phenolic resins, urea resins, melamine resins, alkyd resins, and mica may be added.
Furthermore, a tackifier such as rosin ester, rosin, terpene, terpene phenol, and petroleum resin may be added for the purpose of improving adhesiveness.

When adding a material other than a polymer material having viscoelasticity, such as cyanoethylated PVA, to the matrix 34 of the piezoelectric layer 20, the addition amount is not particularly limited, but the ratio of the material to the matrix 34 is 30% by mass or less. is preferable.
As a result, the characteristics of the polymer material to be added can be expressed without impairing the viscoelastic relaxation mechanism in the matrix 34, so that the dielectric constant can be increased, the heat resistance can be improved, and the adhesion between the piezoelectric particles 36 and the electrode layer can be improved. favorable results can be obtained in terms of

The piezoelectric layer 20 is a layer made of a polymeric composite piezoelectric material containing piezoelectric particles 36 in such a matrix 34 . Piezoelectric particles 36 are dispersed in the 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 ceramic particles constituting the piezoelectric particles 36 include lead zirconate titanate (PZT), lead zirconate lanthanate titanate (PLZT), barium titanate (BaTiO ₃ ), zinc oxide (ZnO), and A solid solution (BFBT) of barium titanate and bismuth ferrite (BiFe ₃ ) is exemplified.

The particle size of the piezoelectric particles 36 is not limited, and may be appropriately selected according to the size of the piezoelectric film 10, the application of the piezoelectric element 50, and the like. The particle size of the piezoelectric particles 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 achieve both high piezoelectric characteristics and flexibility.

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 dispersed irregularly in the matrix 34. may have been

In the piezoelectric film 10, the quantitative ratio of the matrix 34 and the piezoelectric particles 36 in the piezoelectric layer 20 is not limited. It may be appropriately set according to the properties required for the piezoelectric film 10 .
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 more preferably 50% to 80%.
By setting the amount ratio between the matrix 34 and the piezoelectric particles 36 within the above range, favorable results can be obtained in terms of achieving both high piezoelectric characteristics and flexibility.

In the piezoelectric film 10 , the thickness of the piezoelectric layer 20 is not particularly limited, and may be appropriately determined according to the application of the piezoelectric film 10 , the number of layers of the piezoelectric film in the piezoelectric element 50 , the properties required of the piezoelectric film 10 , and the like. , should be set.
The thicker the piezoelectric layer 20 is, the more advantageous it is in terms of rigidity such as stiffness of the so-called sheet-like material, but the voltage (potential difference) required to expand and contract the piezoelectric film 10 by the same amount is increased.
The thickness of the piezoelectric layer 20 is preferably 10 to 300 μm, more preferably 20 to 200 μm, 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.

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

In the present invention, the piezoelectric layer 20 is a polymeric composite piezoelectric body containing piezoelectric particles 36 in a matrix 34 made of a polymeric material having viscoelasticity at room temperature, such as cyanoethylated PVA, as described above. No restrictions.
That is, in the piezoelectric film 10 of the present invention, various known piezoelectric layers can be used for the piezoelectric layer.

As an example, a high-performance dielectric material containing similar piezoelectric particles 36 in a matrix containing a dielectric polymer material such as the polyvinylidene fluoride, vinylidene fluoride-tetrafluoroethylene copolymer, and vinylidene fluoride-trifluoroethylene copolymer described above may be used. Molecular composite piezoelectric material, piezoelectric layer made of polyvinylidene fluoride, piezoelectric layer made of fluorine resin other than polyvinylidene fluoride, piezoelectric layer made by laminating a film made of poly-L-lactic acid and a film made of poly-D-lactic acid, etc. is also available.
However, as described above, it is hard against vibrations of 20 Hz to 20 kHz, and can behave softly against slow vibrations of several Hz or less, and has excellent acoustic characteristics and excellent flexibility. Therefore, a polymeric composite piezoelectric body containing piezoelectric particles 36 in a matrix 34 made of a polymeric material having viscoelasticity at room temperature, such as the cyanoethylated PVA described above, is preferably used.

As shown in FIG. 5, the piezoelectric film 10 has a first electrode layer 24 on one surface of the piezoelectric layer 20, and a first protective layer 28 thereon. , a second electrode layer 26 is provided on the surface, and a second protective layer 30 is provided 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 electrode pairs, that is, the first electrode layer 24 and the second electrode layer 26 , and this laminate is formed into the first protective layer 28 and the second protective layer 30 . It has a configuration sandwiched between.
Thus, in the piezoelectric film 10, the region sandwiched between the first electrode layer 24 and the second electrode layer 26 expands and contracts according to the applied voltage.
Note that the first electrode layer 24 and the first protective layer 28, and the second electrode layer 26 and the second protective layer 30 are attached for the sake of explanation of the piezoelectric film 10. As shown in FIG. Therefore, the first and second aspects of the present invention have no technical significance and are irrelevant to the actual usage conditions.

In the present invention, the piezoelectric film 10 includes, in addition to these layers, an adhesive layer for attaching the electrode layer and the piezoelectric layer 20 and an adhesive layer for attaching the electrode layer and the protective layer. It may have a layer.
The adhesive may be an adhesive or an adhesive. Also, the same material as the matrix 34, that is, the polymer material obtained by removing the piezoelectric particles 36 from the piezoelectric layer 20, can be preferably used as the adhesive. 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 on only 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 provide the piezoelectric layer 20 with appropriate rigidity and mechanical strength. is responsible for That is, in the piezoelectric film 10, the piezoelectric layer 20 made up of the matrix 34 and the piezoelectric particles 36 exhibits excellent flexibility against slow bending deformation, but depending on the application, the rigidity may increase. and mechanical strength may be insufficient. The piezoelectric film 10 is provided with a first protective layer 28 and a second protective layer 30 to compensate.
The first protective layer 28 and the second protective layer 30 have the same configuration, except for the arrangement position. Therefore, in the following description, when there is no need to distinguish between the first protective layer 28 and the second protective layer 30, both members are collectively referred to as protective layers.

Various sheet materials can be used for the first protective layer 28 and the second protective layer 30 without limitation, and various resin films are preferably exemplified as examples.
Among them, polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS), polycarbonate (PC), polyphenylene sulfite (PPS), polymethyl methacrylate (PMMA), due to their excellent mechanical properties and heat resistance. ), polyetherimide (PEI), polyimide (PI), polyethylene naphthalate (PEN), triacetyl cellulose (TAC), cyclic olefin resins, and the like are preferably used.

The thicknesses of the first protective layer 28 and the second protective layer 30 are also not limited. Also, the thicknesses of the first protective layer 328 and the second protective layer 30 are basically the same, but may be different.
Here, if the rigidity of the first protective layer 28 and the second protective layer 30 is too high, not only will the expansion and contraction of the piezoelectric layer 20 be restricted, but also the flexibility will be impaired. Therefore, the thinner the first protective layer 28 and the second protective layer 30, the better, except for cases where mechanical strength and good handling properties as a sheet-like article are required.

In the piezoelectric film 10, if the thickness of the first protective layer 28 and the second protective layer 30 is not more than twice the thickness of the piezoelectric layer 20, it is possible to ensure both rigidity and appropriate flexibility. favorable results can be obtained.
For example, when the thickness of the piezoelectric layer 20 is 50 μm and the first protective layer 28 and the second protective layer 30 are made of PET, the thicknesses of the first protective layer 28 and the second protective layer 30 are preferably 100 μm or less. 50 μm or less is more preferable, and 25 μm or less is even more preferable.

In the piezoelectric film 10, a first electrode layer 24 is provided between the piezoelectric layer 20 and the first protective layer 28, and a second electrode layer 26 is provided between the piezoelectric layer 20 and the second protective layer 30. It is formed. The first electrode layer 24 and the second electrode layer 26 are provided for applying 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, the materials for forming the first electrode layer 24 and the second electrode layer 26 are not limited, and various conductors can be used. Specifically, metals such as carbon, palladium, iron, tin, aluminum, nickel, platinum, gold, silver, copper, titanium, chromium and molybdenum, alloys thereof, laminates and composites of these metals and alloys, Also, indium tin oxide and the like are exemplified. Alternatively, conductive polymers such as PEDOT/PPS (polyethylenedioxythiophene-polystyrenesulfonic acid) are also exemplified. Among them, copper, aluminum, gold, silver, platinum, and indium tin oxide are preferably exemplified as the first electrode layer 24 and the second electrode layer 26 . Among them, copper is more preferable from the viewpoint of conductivity, cost, flexibility, and the like.

In addition, the method of forming the first electrode layer 24 and the second electrode layer 26 is not limited, and may be a vapor phase deposition method (vacuum film formation method) such as vacuum deposition or sputtering, a film formation by plating, or the formation of the above materials. A variety of known methods are available, such as affixing the foils.

Among them, a thin film of copper, aluminum, or the like formed by vacuum deposition is particularly preferably used as the first electrode layer 24 and the second electrode layer 26 because the flexibility of the piezoelectric film 10 can be ensured. be. Among them, a copper thin film formed by vacuum deposition is particularly preferably used.

The thicknesses of the first electrode layer 24 and the second electrode layer 26 are not limited. Also, the thicknesses of the first electrode layer 24 and the second electrode layer 26 are basically the same, but may be different.
Here, as with the first protective layer 28 and the second protective layer 30 described above, if the rigidity of the first electrode layer 24 and the second electrode layer 26 is too high, not only will the expansion and contraction of the piezoelectric layer 20 be restricted, Flexibility is also impaired. Therefore, the thinner the first electrode layer 24 and the second electrode layer 26, the better, as long as the electrical resistance does not become too high.

In the piezoelectric film 10, if the product of the thickness of the first electrode layer 24 and the second electrode layer 26 and the Young's modulus is less than the product of the thickness of the first protective layer 28 and the second protective layer 30 and the Young's modulus , is preferred because it does not significantly impair flexibility.
For example, the first protective layer 28 and the second protective layer 30 are made of PET (Young's modulus: about 6.2 GPa), and the first electrode layer 24 and the second electrode layer 26 are made of copper (Young's modulus: about 130 GPa). In this case, if the thickness of the first protective layer 28 and the second protective layer 30 is 25 μm, the thickness of the first electrode layer 24 and the second electrode layer 26 is preferably 1.2 μm or less, more preferably 0.3 μm or less. , it is preferably 0.1 μm or less.

As described above, in the piezoelectric film 10, the piezoelectric layer 20 formed by dispersing the piezoelectric particles 36 in the matrix 34 containing a polymer material is sandwiched between the first electrode layer 24 and the second electrode layer 26, and further, This laminate has a structure in which a first protective layer 28 and a second protective layer 30 are sandwiched.
In such a piezoelectric film 10, the maximum value of the loss tangent (Tan δ) at a frequency of 1 Hz by dynamic viscoelasticity measurement preferably exists at room temperature, and the maximum value of 0.1 or more exists at room temperature. more preferred.
As a result, even if the piezoelectric film 10 is subjected to a relatively slow and large bending deformation of several Hz or less from the outside, the strain energy can be effectively diffused to the outside as heat. It is possible to prevent cracks from occurring at the interface of

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

In addition, the piezoelectric film 10 has a product of thickness and storage elastic modulus (E′) at a frequency of 1 Hz determined by dynamic viscoelasticity measurement of 1.0×10 ⁵ to 2.0×10 ⁶ N/m at 0° C. , 1.0×10 ⁵ to 1.0×10 ⁶ N/m at 50°C. Note that this condition applies to the piezoelectric layer 20 as well.
As a result, the piezoelectric film 10 can have appropriate rigidity and mechanical strength within a range that does not impair flexibility and acoustic properties.

Furthermore, the piezoelectric film 10 preferably has a loss tangent (Tan δ) of 0.05 or more at 25° C. and a frequency of 1 kHz in a master curve obtained from dynamic viscoelasticity measurement. This condition applies to the piezoelectric layer 20 as well.
As a result, the frequency characteristics of the speaker using the piezoelectric film 10 are smoothed, and the amount of change in sound quality when the lowest resonance frequency _f0 changes as the curvature of the speaker changes can be reduced.

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

In the piezoelectric element 50 , a power source is connected to the first electrode layer 24 and the second electrode layer 26 of each piezoelectric film 10 to apply a drive voltage for expanding and contracting the piezoelectric film 10 , that is, to supply drive power.
There are no restrictions on the power source, and it may be a DC power source or an AC power source. Also, the driving voltage may be appropriately set according to the thickness of the piezoelectric layer 20 of the piezoelectric film 10, the forming material, and the like, so that the piezoelectric film 10 can be properly driven.

There are no restrictions on the method of extracting electrodes from the first electrode layer 24 and the second electrode layer 26, and various known methods can be used.
Examples include a method of connecting a conductor such as a copper foil to the first electrode layer 24 and the second electrode layer 26 to lead the electrodes to the outside, and a method of penetrating the first protective layer 28 and the second protective layer 30 by a laser or the like. Examples include a method of forming a hole, filling the through hole with a conductive material, and leading an electrode to the outside.
Examples of suitable methods for extracting electrodes include the method described in Japanese Patent Application Laid-Open No. 2014-209724 and the method described in Japanese Patent Application Laid-Open No. 2016-015354.

In the case where the piezoelectric element has a structure in which piezoelectric films are folded and laminated as shown in FIG. It is preferable that a connecting portion for connecting the first electrode layer 24 and the second electrode layer 26 to the power source be formed on the projecting portion. The method of connecting the electrode layer and the wiring in the protruding portion is not limited, and various known methods can be used.

As the adhesive layer 16 , various known layers can be used as long as they can adhere the vibration plate 102 and the high-rigidity layer 104 and the piezoelectric element 50 and the high-rigidity layer 104 together.
Therefore, the adhesive layer 16 has fluidity at the time of bonding and then becomes a solid. Even a layer made of an adhesive, which is a gel-like (rubber-like) soft solid at the time of bonding, remains gel-like after that. It may be a layer made of an adhesive that does not change its shape, or a layer made of a material that has the characteristics of both an adhesive and an adhesive. Also, the adhesive (adhesive) may be any of a moisture-curable adhesive, a thermoplastic adhesive, and a thermosetting adhesive. Moreover, you may use a double-sided tape as an adhesion layer.

The thickness of the adhesive layer 16 is not limited, and the thickness that provides sufficient adhesive strength (adhesive strength, cohesive strength) may be appropriately set according to the material of the adhesive layer 16 .
Here, in the electroacoustic transducer 100, the thinner the adhesive layer 16, the higher the effect of transmitting the stretching energy (vibrational energy) of the piezoelectric element 50 to the diaphragm 102, and the energy efficiency can be increased. Also, if the adhesive layer 16 is thick and rigid, it may restrict expansion and contraction of the piezoelectric element 50 .
Considering this point, the adhesive layer 16 is preferably thinner. Specifically, the thickness of the adhesive layer 16 is preferably 0.1 to 50 μm, more preferably 0.1 to 30 μm, even more preferably 0.1 to 10 μm after being attached.

In addition, in the electroacoustic transducer 100, the adhesion layer 16 is provided as a preferable aspect, and is not an essential component.
Therefore, the electroacoustic transducer 100 does not have the adhesive layer 16, and the vibration plate 102, the high-rigidity layer 104 and the piezoelectric element 50 are fixed using known crimping means, fastening means, fixing means, and the like. may For example, when the shape of the piezoelectric element 50 is rectangular in plan view, the four corners may be fastened with members such as bolts and nuts to form an electroacoustic transducer, or the four corners and the central portion may be bolted together. The electroacoustic transducer may be configured by fastening with a member such as a nut.

However, in this case, the piezoelectric element 50 expands and contracts independently of the diaphragm 102 when a drive voltage is applied from the power supply. is not transmitted to the diaphragm 102. In this way, when the piezoelectric element 50 expands and contracts independently of the diaphragm 102, the efficiency of vibration of the diaphragm 102 by the piezoelectric element 50 decreases. There is a possibility that the diaphragm 102 cannot be sufficiently vibrated.
Considering this point, it is preferable that the diaphragm 102, the high-rigidity layer 104 and the piezoelectric element 50 are adhered with the adhesion layer 16 as shown in FIG.

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

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

Here, the piezoelectric element 50 is adhered to the high-rigidity layer 104 as described above. Therefore, expansion and contraction of the piezoelectric element 50 (piezoelectric film 10) in the plane direction is restrained and converted into expansion and contraction in the thickness direction (vertical direction).

The vibration plate 102 is adhered to the piezoelectric element 50 by the adhesion layer 16 via the high-rigidity layer 104 . Therefore, the vertical expansion and contraction of the piezoelectric element 50 bends the diaphragm 102, and as a result, the diaphragm 102 vibrates in the thickness direction.
Due to this vibration in the thickness direction, the diaphragm 102 generates sound. That is, the diaphragm 102 vibrates according to the magnitude of the voltage (driving voltage) applied to the piezoelectric film 10 and generates sound according to the driving voltage applied to the piezoelectric film 10 .

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

Further, as shown in FIGS. 1 and 4, in the case of a piezoelectric element having a configuration in which a plurality of piezoelectric films are laminated, the piezoelectric films are attached to each other by an adhesive layer 19 .
As the adhesive layer 19 for attaching the piezoelectric films to each other, various known layers can be used as long as the adjacent piezoelectric films 10 can be attached. A material similar to that of the adhesive layer 16 can be used.

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

First, a sheet-like object 11a having a first protective layer 28 and a first electrode layer 24 formed thereon as shown in FIG. 6 is prepared. Further, a sheet-like object 11c conceptually shown in FIG. 8 is prepared in which the second electrode layer 26 is formed on the surface of the second protective layer 30 .

The sheet 11a 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 deposition, sputtering, plating, or the like. Similarly, the sheet 11c 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 deposition, sputtering, plating, or the like.
Alternatively, a commercially available sheet having a copper thin film or the like formed on a protective layer may be used as the sheet 11a and/or the sheet 11c.
The sheet-like material 11a and the sheet-like material 11c may be the same or different.

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

Next, as shown in FIG. 7, a paint (coating composition) that will form the piezoelectric layer 20 is applied on the first electrode layer 24 of the sheet 11a, and then cured to form the piezoelectric layer 20. As a result, a laminated body 11b in which the sheet-like material 11a and the piezoelectric layer 20 are laminated is produced.

Various methods can be used for forming the piezoelectric layer 20 depending on the material forming the piezoelectric layer 20 .
As an example, first, a polymer material such as cyanoethylated PVA is dissolved in an organic solvent, and piezoelectric particles 36 such as PZT particles are added and stirred to prepare a coating material.
Organic solvents are not limited, and various organic solvents such as dimethylformamide (DMF), methyl ethyl ketone (MEK), and cyclohexanone can be used.
After the sheet-like material 11a is prepared and the paint is prepared, the paint is cast (applied) on the sheet-like material 11a and dried by evaporating the organic solvent. As a result, as shown in FIG. 7, a laminated body 11b having the first electrode layer 24 on the first protective layer 28 and the piezoelectric layer 20 laminated on the first electrode layer 24 is produced. .

There are no restrictions on the method of casting the coating material, and known methods (coating equipment) such as bar coaters, slide coaters and doctor knives can all be used.
Alternatively, if the polymer material is heat-meltable, the polymer material is heat-melted and the piezoelectric particles 36 are added to prepare a melt, which is then extruded into a sheet shown in FIG. A laminate 11b as shown in FIG. 7 may be produced by extruding a sheet onto the shaped object 11a and cooling it.

As described above, in the piezoelectric layer 20, the matrix 34 may be added with a polymeric piezoelectric material such as PVDF (PolyVinylidene DiFluoride) other than the polymeric material having viscoelasticity at room temperature.
When these polymeric piezoelectric materials are added to the matrix 34, the polymeric piezoelectric materials to be added to the paint may be dissolved. Alternatively, the polymer piezoelectric material to be added may be added to a polymer material that has been melted by heating and has viscoelasticity at room temperature, and then melted by heating.

After the piezoelectric layer 20 is formed, it may be calendered, if desired. Calendering may be performed once or multiple times.
As is well known, calendering is a process in which a surface to be treated is heated and pressed by a hot press, hot rollers, or the like to flatten the surface.

Next, the piezoelectric layer 20 of the laminate 11b having the first electrode layer 24 on the first protective layer 28 and the piezoelectric layer 20 formed on the first electrode layer 24 is subjected to polarization treatment (poling). )I do. The polarization treatment of the piezoelectric layer 20 may be performed before calendering, but is preferably performed after calendering.
The method of polarization treatment of the piezoelectric layer 20 is not limited, and known methods can be used. For example, electric field poling, in which a DC electric field is directly applied to an object to be polarized, is exemplified. When electric field poling is performed, the second electrode layer 26 may be formed before the polarization treatment, and the electric field poling treatment may be performed using the first electrode layer 24 and the second electrode layer 26. .
Moreover, in the piezoelectric film 10 of the present invention, the polarization treatment is preferably performed in the thickness direction of the piezoelectric layer 20, not in the plane direction.

Next, as shown in FIG. 8, the previously prepared sheet-like material 11c is laminated on the piezoelectric layer 20 side of the laminated body 11b subjected to the polarization treatment, with the second electrode layer 26 facing the piezoelectric layer 20. .
Furthermore, this laminate is thermocompression bonded using a hot press device, a heating roller, or the like while sandwiching the first protective layer 28 and the second protective layer 30, thereby joining the laminate 11b and the sheet-like material 11c. By bonding, the piezoelectric film 10 as shown in FIG. 5 is produced.
Alternatively, the piezoelectric film 10 may be produced by bonding the laminated body 11b and the sheet-like material 11c together using an adhesive and preferably further pressing them together.

The piezoelectric film 10 may be manufactured using the cut-sheet-shaped sheet-like material 11a and the sheet-like material 11c, etc., or may be manufactured using a roll-to-roll process. good too.

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

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

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

[Example 1]
[Preparation of piezoelectric film]
A piezoelectric film as shown in FIG. 5 was produced by the method shown in FIGS. 6 to 8 described above.
First, cyanoethylated PVA (CR-V, manufactured by Shin-Etsu Chemical Co., Ltd.) was dissolved in dimethylformamide (DMF) at the following compositional ratio. After that, PZT particles as piezoelectric particles were added to this solution at the following composition ratio, and the mixture was stirred with a propeller mixer (rotation speed: 2000 rpm) to prepare a paint for forming a piezoelectric layer.
・PZT particles・・・・・・・・・・300 parts by mass ・Cyanoethylated PVA・・・・・・・・30 parts by mass ・DMF・・・・・・・・・・・・70 parts by mass The PZT particles used were obtained by sintering a commercially available PZT raw material powder at 1000 to 1200° C. and then pulverizing and classifying the sintered particles to an average particle size of 5 μm.

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

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

A sheet-like material obtained by vapor-depositing the same thin film on a PET film was laminated on the polarized piezoelectric laminate 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, thereby adhering and bonding the piezoelectric layer and the second electrode layer. A piezoelectric film as shown in No. 5 was produced.

<Production of piezoelectric element>
The piezoelectric film was cut into a rectangle having a planar shape of 200 mm×270 mm. A piezoelectric element was fabricated by laminating five layers of piezoelectric films by folding the cut piezoelectric film four times in the longitudinal direction. The planar shape of the laminated portion was 200 mm×50 mm. An adhesive layer (acrylic pressure-sensitive adhesive) was used to adhere between the laminated piezoelectric films. An electrode lead-out portion was formed in a region protruding from the laminated portion. The thickness of the entire piezoelectric element was 400 μm.

<Fabrication of Electroacoustic Transducer>
A high-rigidity layer was adhered to the laminated portion of the manufactured piezoelectric element. The high-rigidity layer was made of SUS304, 80 μm thick, and 200 mm×50 mm in size. Next, the surface of the high-rigidity layer opposite to the piezoelectric element was adhered to the diaphragm. A PET plate having a thickness of 0.2 mm and a length of 450 mm and a width of 500 mm was used as the diaphragm. The lateral direction of the diaphragm and the longitudinal direction of the piezoelectric element were matched, and the center of the laminated part of the piezoelectric element was aligned with the center of the diaphragm and adhered. The piezoelectric element and the high-rigidity layer, and the high-rigidity layer and the vibration plate were adhered with an adhesion layer (acrylic adhesive).

The Young's modulus of the piezoelectric element, the high-rigidity layer, and the diaphragm were measured by the method described above, the geometrical moment of inertia was calculated, and the flexural rigidity of each member was determined.
The piezoelectric element had a Young's modulus of 10 GPa, a geometrical moment of inertia of 1.1 E ⁻¹² , and a flexural rigidity K ₂ of 1.1 E ⁻² .
The high-rigidity layer had a Young's modulus of 193 GPa, a geometrical moment of inertia of 8.5 E ⁻¹⁵ , and a flexural rigidity K ₃ of 1.6 E ⁻³ .
The diaphragm had a Young's modulus of 4 GPa, a geometrical moment of inertia of 1.1 E ⁻¹² , and a flexural rigidity K ₁ of 4.5 E ⁻³ .

[Comparative Example 1]
An electroacoustic transducer was produced in the same manner as in Example 1, except that the highly rigid layer was not provided.

[evaluation]
Sound pressure was evaluated for the fabricated electroacoustic transducers of Examples and Comparative Examples.

<Sound pressure>
A sine wave with a frequency of 2 kHz and an applied voltage of 50 Vrms was input to the piezoelectric element while the short side of the diaphragm was supported, and the sound pressure was measured with a microphone placed at a distance of 1 m from the center of the diaphragm. This measurement was repeated 5 times, and the average of the data of 3 points excluding the maximum and minimum was used as the representative value.
Table 1 shows the results.

From Table 1, it can be seen that the sound pressure of the example of the present invention is higher than that of the comparative example.
From the above, the effect of the present invention is clear.

REFERENCE SIGNS LIST 10

piezoelectric film

11a, 11c sheet 11b laminate 16, 19 adhesive layer 20 piezoelectric layer 24 first electrode layer 26 second electrode layer 28 first protective layer 30 second protective layer 34 matrix 36 piezoelectric particles 50 piezoelectric Element 58 Core rod 100 Electroacoustic transducer 102 Diaphragm 104 High rigidity layer

Claims

An electroacoustic transducer having a diaphragm and a piezoelectric element attached to the diaphragm,
Having a high-rigidity layer disposed between the diaphragm and the piezoelectric element,
Let K1 be the flexural rigidity of the diaphragm, K2 be the flexural rigidity of the piezoelectric element, and K3 be the flexural rigidity of the high- rigidity layer. converter.
The electroacoustic transducer according to claim 1, wherein the bending stiffness K3 of the high stiffness layer is 0.03 N·m2 or less .
3. The electroacoustic transducer according to claim 1 , wherein said diaphragm has a flexural rigidity K1 of 0.02 N.m2 or less.
The electroacoustic transducer according to claim 1 or 2, wherein the area of the high-rigidity layer in plan view is smaller than the area of the diaphragm.
3. The electric device according to claim 1, wherein the piezoelectric element includes a piezoelectric film having a piezoelectric layer, electrode layers provided on both sides of the piezoelectric layer, and protective layers provided on the electrode layers. acoustic transducer.
The electroacoustic transducer according to claim 5, wherein the piezoelectric element is formed by laminating a plurality of layers of the piezoelectric film.
6. The electroacoustic transducer according to claim 5, wherein the piezoelectric layer is composed of a polymeric composite piezoelectric body containing piezoelectric particles in a matrix containing a polymeric material.