WO2023181699A1

WO2023181699A1 - Electroacoustic transducer

Info

Publication number: WO2023181699A1
Application number: PCT/JP2023/004729
Authority: WO
Inventors: 崇裕岩本
Original assignee: 富士フイルム株式会社
Priority date: 2022-03-24
Filing date: 2023-02-13
Publication date: 2023-09-28

Abstract

Provided is an electroacoustic transducer that can obtain a high sound pressure when the electroacoustic transducer is configured by affixing a piezoelectric element to a diaphragm.　This electroacoustic transducer comprises: a diaphragm that has a flexibility; and a piezoelectric element that is affixed to the diaphragm via an adhesive layer and that has a flexibility. When the spring constant of the deflection of the diaphragm is K1 (N/mm), the Young's modulus of the adhesive layer is E2 (N/mm2) and the thickness is ｈ2 (mm), |50 * K1 − E2 * ｈ2| ≤ 2.5 is satisfied.

Description

electroacoustic transducer

The present invention relates to an electroacoustic transducer.

Piezoelectric elements can be used as diaphragms to vibrate the diaphragm and produce sound by attaching it to the diaphragm in contact with the diaphragm. It's being used. 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.

For example, Patent Document 1 discloses an electroacoustic transducer including an exciter on one main surface of a diaphragm, in which the loss tangent at a frequency of 1 Hz measured by dynamic viscoelasticity of the exciter is determined at a temperature of 0 to 50°C. The maximum value is within the range, the maximum value is 0.08 or more, and the product of the exciter thickness and the storage modulus at a frequency of 1 Hz and 25°C measured by dynamic viscoelasticity is the same as that of the diaphragm. Electroacoustic transducers are described that have a thickness that is less than or equal to three times the product of Young's modulus.

International Publication No. 2020/179353

According to studies by the present inventors, it has been found that when a piezoelectric element is attached to a diaphragm to form an electroacoustic transducer, sufficient sound pressure may not be obtained. The inventor further investigated this point and found that the obtained sound pressure changes depending on the relationship between the hardness of the adhesive layer that adheres the piezoelectric element and the diaphragm and the hardness of the diaphragm. As described in Patent Document 1, the relationship between the hardness of the diaphragm and the piezoelectric element has been studied, but the relationship between the hardness of the adhesive layer and the hardness of the diaphragm has not been sufficiently studied. It wasn't.

An object of the present invention is to solve the problems of the prior art, and to provide an electroacoustic transducer that can obtain high sound pressure in which a piezoelectric element is attached to a diaphragm. It is about providing.

In order to solve the above-mentioned problems, the present invention has the following configuration.
[1] An electroacoustic transducer including a flexible diaphragm and a flexible piezoelectric element attached to the diaphragm via an adhesive layer,
When the spring constant of the deflection of the diaphragm is K ₁ (N/mm), the Young's modulus of the adhesive layer is E ₂ (N/mm ² ), and the thickness is h ₂ (mm), |50×K ₁ An electroacoustic transducer that satisfies -E ₂ ×h ₂ |≦2.5.
[2] The electroacoustic transducer according to [1], wherein a spring constant K ₁ of the deflection of the diaphragm is lower than 0.1 N/m.
[3] The piezoelectric element includes 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. , [1] or [2].
[4] The electroacoustic transducer according to [3], wherein the piezoelectric element is formed by laminating multiple layers of piezoelectric films.

According to the present invention, it is possible to provide an electroacoustic transducer in which a piezoelectric element is attached to a diaphragm, which can obtain high sound pressure.

FIG. 1 is a diagram schematically showing an example of an electroacoustic transducer of the present invention. FIG. 2 is a partially enlarged view of the electroacoustic transducer shown in FIG. 1. FIG. It is a figure which shows typically another example of the piezoelectric element used for the electroacoustic transducer of this invention. FIG. 2 is a diagram schematically showing an example of a piezoelectric film included in the electroacoustic transducer of the present invention. 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. It is a graph showing the relationship between the difference and the average sound pressure.

Hereinafter, the electroacoustic transducer 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.

[Electroacoustic transducer]
The electroacoustic transducer of the present invention includes:
An electroacoustic transducer comprising a flexible diaphragm and a flexible piezoelectric element attached to the diaphragm via an adhesive layer,
When the spring constant of the deflection of the diaphragm is K ₁ (N/mm), the Young's modulus of the adhesive layer is E ₂ (N/mm ² ), and the thickness is h ₂ (mm), |50×K ₁ It is an electroacoustic transducer that satisfies -E ₂ ×h ₂ |≦2.5.

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

The electroacoustic transducer 100 shown in FIG. 1 includes a piezoelectric element 50, a diaphragm 102, and an adhesive layer 104 disposed between the piezoelectric element 50 and the diaphragm 102. The piezoelectric element 50 and the diaphragm 102 are adhered to each other with an adhesive layer 104.

The diaphragm 102 is flexible. 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) and cyclic olefin resins, foamed polystyrene, foamed plastics made of foamed styrene and foamed polyethylene, etc., veneer boards, cork boards, leather such as cowhide, Carbon sheets, various paperboards such as Japanese paper, various corrugated cardboard materials made by pasting other paperboards on one or both sides of corrugated paperboard, various metals such as stainless steel, aluminum, copper and nickel, and various alloys. Examples include thin film metals. Further, the diaphragm 102 may be made of a composite material in which film-like materials made of these materials are bonded together.

In addition, as long as the diaphragm 102 has flexibility, an organic electroluminescent (OLED (Organic Light Emitting Diode)) display, a liquid crystal display, a micro LED (Light Emitting Diode) display, and an inorganic electroluminescent display may be used. Display devices such as displays, projector screens, and the like can also be suitably used.

The piezoelectric element 50 is used as a so-called exciter that exhibits piezoelectricity in response to an applied voltage and causes the diaphragm 102 to vibrate.

In the example shown in FIG. 2, the piezoelectric element 50 is made by laminating three layers of piezoelectric films 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 a protection layer provided on the electrode layer. (first protective layer 28 and second protective layer 30). Note that in FIG. 2, illustration of the protective layer is omitted in order to clearly show the configuration of the piezoelectric element 50. The piezoelectric film 10 will be described in detail later.

As shown in FIG. 2, 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. The piezoelectric element 50 (piezoelectric film 10) is driven as a piezoelectric body by applying a voltage to the first electrode layer 24 and the second electrode layer 26, so that the piezoelectric layer 20 expands and contracts. When the piezoelectric element 50 is driven, the piezoelectric element 50 expands and contracts in the plane direction, bends the diaphragm 102 to which the piezoelectric element 50 is attached, and as a result vibrates the diaphragm 102 in the thickness direction to produce sound. generate. The diaphragm 102 vibrates according to the magnitude of the driving voltage applied to the piezoelectric element 50, and the electroacoustic transducer 100 generates sound according to the applied driving 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.

The adhesion layer 104 is for adhering the diaphragm 102 and the piezoelectric element 50.

As mentioned above, according to the inventor's study, when a piezoelectric element is attached to a diaphragm to form an electroacoustic transducer, the gain is determined by the relationship between the hardness of the adhesive layer and the hardness of the diaphragm. It was found that the sound pressure generated changes. In other words, it has been found that unless the hardness of the adhesive layer is set appropriately relative to the hardness of the diaphragm, there is a problem in that the resulting sound pressure decreases.

On the other hand, in the electroacoustic transducer of the present invention, the spring constant of the deflection of the diaphragm 102 is K ₁ (N/mm), the Young's modulus of the adhesive layer 104 is E ₂ (N/mm ² ), and the thickness is When h ₂ (mm) is expressed as h 2 (mm), |50×K ₁ −E ₂ ×h ₂ |≦2.5 is satisfied.

The electroacoustic transducer of the present invention has a value obtained by multiplying the deflection spring constant K ₁ (N/mm) of the diaphragm 102 by 50, the Young's modulus E ₂ (N/mm ² ) of the adhesive layer 104, and the thickness h ₂ (mm), that is, the absolute value of the difference (hereinafter also referred to as difference D) from the spring constant K ₂ (=E ₂ ×h ₂ ) of the adhesive layer 104, shall be 2.5 or less. Therefore, the obtained sound pressure can be improved.

If the spring constant K ₂ of the adhesive layer 104 is too large with respect to the spring constant K ₁ of the deflection of the diaphragm 102 and the difference D exceeds 2.5, the adhesive layer 104 may cause the diaphragm 102 to bend. It is considered that sufficient sound pressure cannot be obtained because the diaphragm 102 is restrained and becomes difficult to vibrate. On the other hand, if the spring constant K ₂ of the adhesive layer 104 is too small with respect to the spring constant K ₁ of the deflection of the diaphragm 102 and the difference D exceeds 2.5, the expansion and contraction of the piezoelectric element 50 may be It is considered that sufficient sound pressure cannot be obtained because the adhering layer 104 absorbs the sound and it becomes difficult to transmit it to the diaphragm 102. On the other hand, by setting the difference D to 2.5 or less, the adhesive layer 104 can hardly restrain the diaphragm 102 and the diaphragm 102 can easily vibrate. It is considered that a high sound pressure can be obtained because the expansion and contraction are more easily transmitted to the diaphragm 102 via the adhesive layer 104.

From the viewpoint of improving sound pressure, the difference D is preferably 2 or less, more preferably 1.5 or less, and most preferably 0.

Note that the spring constant K ₁ of the deflection of the diaphragm 102 can be measured as follows.
A sample with a length of 30 mm and a width of 10 mm is cut out from the diaphragm 102, and its viscoelasticity is examined in the viscoelasticity measurement mode of a dynamic viscoelasticity measuring device (DMA) in the temperature range of 0°C to 100°C, and when converted into frequency. The storage modulus at 1 kHz and 25° C. is taken as the value of Young's modulus E ₁ of the diaphragm. As the DMA, a dynamic viscoelasticity measuring device DMS6100 manufactured by SII Nanotechnology Co., Ltd. (SII Nanotechnology Co., Ltd.) or the like can be used.
The measurement conditions were a temperature increase rate of 2° C./min (in a nitrogen atmosphere). The measurement frequencies were 0.1 Hz, 0.2 Hz, 0.5 Hz, 1 Hz, 2 Hz, 5 Hz, 10 Hz and 20 Hz. The measurement mode was tensile measurement. Furthermore, the distance between the chucks was 20 mm.

Thereafter, the spring constant K ₁ of the deflection of the diaphragm 102 is calculated from the following equation.
K ₁ = W/δ (N/mm) = 48 x E ₁ x b x h ₁ ³ / (12 x L ³ )
Here, W: Load (N), δ: Deflection (mm), E ₁ : Young's modulus (N/mm ² ), b: Width of the diaphragm (mm), h ₁ : Thickness of the diaphragm (mm) , L: length (mm) of the diaphragm.

Further, the Young's modulus E ₂ of the adhesive layer 104 can be measured as follows.
After peeling off the piezoelectric element 50 and the diaphragm 102, the adhesive layer 104 is peeled off, and in the same way as the diaphragm 102, the viscoelasticity is examined in the temperature range of 0°C to 100°C in the viscoelastic measurement mode of the DMA, and the frequency The converted value of Young's modulus E ₂ at 1 kHz and 25° C. is calculated.

Further, the thickness h ₂ of the adhesive layer 104 is measured by peeling off the piezoelectric element 50 and the diaphragm 102, and then peeling off the adhesive layer 104.

The thickness of the adhesive layer 104 is not limited as long as the difference D satisfies 2.5 or less, and sufficient adhesive force (adhesive force, adhesive force) can be obtained depending on the material of the adhesive layer 104. The thickness may be set appropriately.
Specifically, the thickness of the adhesive layer 104 after attachment is preferably 0.1 μm to 50 μm, more preferably 0.1 μm to 30 μm, and even more preferably 0.1 μm to 10 μm.

Various known adhesive layers can be used as the adhesive layer 104 as long as it can adhere the diaphragm 102 and the piezoelectric element 50 and satisfies the difference D of 2.5 or less.
Therefore, even though the adhesive layer 104 is a layer made of an adhesive that has fluidity when pasted together and then becomes solid, it remains a gel-like (rubber-like) soft solid when pasted together, and it remains a gel-like (rubber-like) solid when pasted together. It may be a layer made of an adhesive whose shape does not change, or a layer made of a material that has characteristics of both an adhesive and a pressure-sensitive adhesive. Further, the adhesive (pressure-sensitive adhesive) may be any of a moisture-curable adhesive, a thermoplastic adhesive, and a thermosetting adhesive. Further, as the adhesive layer 104, double-sided tape, adhesive sheet, etc. may be used.

As the adhesive layer 104, for example, an adhesive sheet: NCF-D692 (manufactured by Lintec Corporation), a film hot melt adhesive: Elfan UH203, Elfan NT120 (manufactured by Nippon Matai Corporation), etc. can be used.

The value obtained by multiplying the spring constant K ₁ (N/mm) of the deflection of the diaphragm 102 by 50 times the Young's modulus E ₂ (N/mm ² ) and the thickness h ₂ (mm) of the adhesive layer 104 (the adhesive The difference D from the spring constant K ₂ ) of the adhesive layer 104 is determined by the material of the diaphragm 102 (Young's modulus E ₁ ), the width b, the thickness h ₁ , the length L, and the material of the adhesive layer 104 (Young's modulus E ₂ ), the thickness _h2, etc. may be appropriately adjusted to 2.5 or less.

Here, from the viewpoint of flexibility of the electroacoustic transducer 100, the spring constant K ₁ of the deflection of the diaphragm 102 is preferably lower than 0.1 N/m, more preferably 0.05 N/m or less, More preferably, it is .01 N/m or less.

Here, although the piezoelectric element 50 shown in FIGS. 1 and 2 is made by folding and laminating three layers of piezoelectric films 10, the present invention is not limited to this. That is, the piezoelectric element may have one layer (one sheet) of the piezoelectric film 10, or may have a plurality of layers laminated. When a plurality of piezoelectric films 10 are laminated, the number of piezoelectric films 10 laminated may be two or four or more. Regarding this point, the piezoelectric element shown in FIG. 3, which will be described later, is also similar.

Further, 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 the piezoelectric element 50 is not limited to this. As shown in FIG. 3, the piezoelectric element may have a structure in which a plurality of sheet-like (cut sheet-like) piezoelectric films 10 are laminated.

In the piezoelectric element shown in FIG. 3, three piezoelectric films 10 are laminated with an adhesive layer 19 in between. Each of the three piezoelectric films is connected to a power source.

In a preferred embodiment of the piezoelectric element shown in FIG. 3, 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 the adjacent piezoelectric films 10, the first electrode layers 24 and the second electrode layers 26 face each other. Therefore, whether the power source is an AC power source or a DC power source, power of the same polarity is always supplied to the facing electrodes. Therefore, in the piezoelectric element shown in FIG. 3, even if the electrodes of adjacent piezoelectric films 10 come into contact with each other, there is no risk of short-circuiting.

Note that the polarization direction of the piezoelectric film 10 may be detected using a d33 meter or the like. Alternatively, the polarization direction of the piezoelectric film 10 may be determined from the polarization processing conditions described below.

Further, in the example shown in FIG. 3, the polarization directions of the adjacent piezoelectric films 10 are opposite to each other, but the polarization directions of the adjacent piezoelectric films 10 may be the same.

A piezoelectric element made by folding and laminating long piezoelectric films has the following advantages.
That is, when a plurality of cut sheet-shaped piezoelectric films 10 are laminated, it is necessary to connect the first electrode layer 24 and the second electrode layer 26 for each piezoelectric film to a driving power source. On the other hand, in a structure in which long piezoelectric films 10 are folded and laminated, the laminate can be constructed from only one long piezoelectric film 10. Further, in the structure in which long piezoelectric films 10 are folded and laminated, only one power source is required for applying the driving voltage, and furthermore, the electrodes need only be drawn out from the piezoelectric film 10 at one location.
Furthermore, in the structure in which long piezoelectric films 10 are folded and laminated, the polarization directions of adjacent piezoelectric films are necessarily opposite to each other.

Hereinafter, the piezoelectric film used in the piezoelectric element of the electroacoustic transducer of the present invention will be explained.

FIG. 4 shows a part of the piezoelectric film 10 in an enlarged manner.
The piezoelectric film 10 shown in FIG. A first protective layer 28 that is laminated on the surface opposite to the body layer 20, a second electrode layer 26 that is laminated on the other surface of the piezoelectric layer 20, and a layer that is opposite to the piezoelectric layer 20 of the second electrode layer 26. A second protective layer 30 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, various known piezoelectric layers can be used as the piezoelectric layer 20.
In the present invention, the piezoelectric layer 20 is preferably a polymeric composite piezoelectric material containing piezoelectric particles 36 in a matrix 34 containing a polymeric 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 An example is a solid solution of barium titanate and bismuth ferrite (BiFe ₃ ) (BFBT).

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, there is no limit to the ratio of the matrix 34 to the piezoelectric particles 36 in the piezoelectric layer 20, and it is subject to the size and thickness of the piezoelectric film 10 in the plane direction, the use of the piezoelectric film 10, and It may be set as appropriate depending on the characteristics required of 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 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 film 10, 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.

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

As an example, a matrix containing a dielectric polymer material such as polyvinylidene fluoride, vinylidene fluoride-tetrafluoroethylene copolymer, and vinylidene fluoride-trifluoroethylene copolymer described above, and a matrix containing similar piezoelectric particles 36 may be used. Molecular composite piezoelectric materials, piezoelectric layers made of polyvinylidene fluoride, piezoelectric layers made of fluororesin other than polyvinylidene fluoride, piezoelectric layers laminated with films made of poly-L-lactic acid and films made of poly-D-lactic acid, etc. is also available.
However, as mentioned above, it is hard against vibrations of 20 Hz to 20 kHz, can behave softly against slow vibrations of several Hz or less, provides excellent acoustic characteristics, and has excellent flexibility. A polymer composite piezoelectric material including piezoelectric particles 36 is suitably used in the matrix 34 made of a polymeric material having viscoelasticity at room temperature, such as the above-mentioned cyanoethylated PVA.

As shown in FIG. 4, the piezoelectric film 10 has a first electrode layer 24 on one side of the piezoelectric layer 20, a first protective layer 28 thereon, and a first electrode layer 24 on one side of the piezoelectric layer 20. It has a structure in which it has a second electrode layer 26 on its surface and a second protective layer 30 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 first electrode layer 24 and a second electrode layer 26, and this laminate is sandwiched between a first protective layer 28 and a second protective layer 30. It has a structure in which it is sandwiched between.
In this way, in the piezoelectric film 10, the region sandwiched between the first electrode layer 24 and the second electrode layer 26 expands and contracts depending on the applied voltage.
Note that the first electrode layer 24 and the first protective layer 28, as well as the second electrode layer 26 and the second protective layer 30 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.

There are no restrictions on the first protective layer 28 and the second protective layer 30, 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 first protective layer 28 and the second protective layer 30. Further, 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, it is advantageous for the first protective layer 28 and the second protective layer 30 to be thinner, unless mechanical strength or good handling properties as a sheet-like material are required.

In the piezoelectric film 10, if the thickness of the first protective layer 28 and the second protective layer 30 is twice or less the thickness of the piezoelectric layer 20, it is possible to achieve both rigidity and appropriate flexibility. Favorable results can be obtained in this respect.
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 thickness of the first protective layer 28 and the second protective layer 30 is preferably 100 μm or less, The thickness is more preferably 50 μm or less, and even more preferably 25 μm or less.

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 to apply 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 materials for forming the first electrode layer 24 and the second electrode layer 26, 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 first electrode layer 24 and the second electrode layer 26. Among these, copper is more preferable from the viewpoints of conductivity, cost, flexibility, and the like.

Furthermore, there is no restriction on the method of forming the first electrode layer 24 and the second electrode layer 26, and they may be formed using a vapor deposition method (vacuum film forming method) such as vacuum evaporation and sputtering, plating, or using the above-mentioned materials. Various known methods can be used, such as a method of pasting a foil that has been prepared.

Among these, thin films of copper, aluminum, etc. formed by vacuum deposition are particularly preferably used as the first electrode layer 24 and the second electrode layer 26 because they can ensure the flexibility of the piezoelectric film 10. Ru. Among these, a copper thin film formed by vacuum evaporation is particularly preferably used.

There is no limit to the thickness of the first electrode layer 24 and the second electrode layer 26. 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 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, it not only restricts the expansion and contraction of the piezoelectric layer 20, but also Flexibility is also impaired. Therefore, it is advantageous for the first electrode layer 24 and the second electrode layer 26 to be thinner, 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 Young's modulus is less than the product of the thickness of the first protective layer 28 and the second protective layer 30 and Young's modulus, then , is suitable because it does not significantly impair flexibility.
For example, a combination in which 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) is used. 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. Among them, it is 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 is connected to the first electrode layer 24 and the second electrode layer 26 of each 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.

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.

In addition, when the piezoelectric element has a configuration 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 a power source be formed in the protruding portion. Note that there is no restriction on the method of connecting the electrode layer and the wiring in the protrusion, and various known methods can be used.

Here, as described above, the piezoelectric layer 20 includes piezoelectric particles 36 in the matrix 34. Further, 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) contracts in the thickness direction. At the same time, the piezoelectric film 10 also expands and contracts in the in-plane direction due to Poisson's 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, 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 in the plane direction by applying a voltage.

The diaphragm 102 is attached to the piezoelectric film 10 (piezoelectric element 50) 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, the sound pressure level can be improved by adjusting the mass of the piezoelectric film 10 (piezoelectric element 50) according to the spring constant of the diaphragm 102. If the mass of the piezoelectric element 50 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 element 50 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 element 50 is appropriately adjusted according to the spring constant of the diaphragm 102.

Further, as shown in FIGS. 2 and 3, when the piezoelectric element 50 has a structure in which a plurality of piezoelectric films 10 are laminated, the piezoelectric films 10 are adhered to each other by an adhesive layer 19.
As the adhesion layer 19 for adhering the piezoelectric films 10 to each other, various known ones can be used as long as they are capable of adhering adjacent piezoelectric films 10 to each other. The same material as the adhesive layer 104 to be adhered can be used.

Hereinafter, an example of a method for manufacturing the piezoelectric film 10 will be described with reference to FIGS. 5 to 7.

First, a sheet-like material 11a shown in FIG. 5 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 11c, conceptually shown in FIG. 7, in which a second electrode layer 26 is formed on the surface of a second protective layer 30 is prepared.

The sheet-like material 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 evaporation, sputtering, plating, or the like. Similarly, the sheet-like material 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 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 11a and/or the sheet material 11c.
The sheet-like material 11a and the sheet-like material 11c 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. 6, a paint (coating composition) that will become the piezoelectric layer 20 is applied onto the first electrode layer 24 of the sheet-like material 11a, and then cured to form the piezoelectric layer 20. As a result, a laminate 11b in which the sheet-like material 11a and the piezoelectric layer 20 are laminated is produced.

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 the sheet-like material 11a is prepared and the paint is prepared, the paint is cast (coated) on the sheet-like material 11a, and the organic solvent is evaporated and dried. As a result, as shown in FIG. 6, a laminate 11b having the first electrode layer 24 on the first protective layer 28 and the piezoelectric layer 20 stacked on the first electrode layer 24 is produced. .

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. 5 is formed by extrusion molding or the like. A laminate 11b as shown in FIG. 6 may be produced by extruding it into a sheet shape onto the shaped material 11a 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 (Polyvinylidene DiFluoride) in addition to the polymeric material that has 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, 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. 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. For example, electric field poling is exemplified, in which a DC electric field is directly applied to an object to be polarized. Note that when performing electric field poling, 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. .
Furthermore, in the piezoelectric film 10 of the present invention, it is preferable that the polarization treatment is performed not in the plane direction of the piezoelectric layer 20 but in the thickness direction.

Next, as shown in FIG. 7, the previously prepared sheet material 11c is laminated on the piezoelectric layer 20 side of the polarized stack 11b with the second electrode layer 26 facing the piezoelectric layer 20. .
Further, this laminate is thermocompressed using a hot press device, a heated roller, etc., with the first protective layer 28 and the second protective layer 30 sandwiched therebetween, thereby bonding the laminate 11b and the sheet-like material 11c. The piezoelectric film 10 as shown in FIG. 4 is produced by bonding them together.
Alternatively, the piezoelectric film 10 may be produced by bonding the laminate 11b and the sheet-like material 11c together using an adhesive, and preferably further press-bonding them. As the adhesive at this time, the same material as the matrix of the piezoelectric layer 20 can be used.

Note that this piezoelectric film 10 may be manufactured using a cut sheet-like sheet material 11a, a sheet-like material 11c, 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 piezoelectric film 10 produced in this manner is polarized not in the plane direction but in the thickness direction, and has great piezoelectric properties even without stretching after polarization. Therefore, 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.

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

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 as shown in FIG. 4 was produced by the method shown in FIGS. 5 to 7 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 laminate was produced that had 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 thereon. .

The produced piezoelectric layer was polarized in the thickness direction.

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 to adhere and bond the piezoelectric layer and the second electrode layer. A piezoelectric film as shown in 4 was produced.

<Production of piezoelectric element>
The piezoelectric film was cut into a rectangle with a planar shape of 170 mm x 150 mm. The cut piezoelectric film was folded back four times in the longitudinal direction (in the direction of the 170 mm side) to produce a piezoelectric element in which five layers of piezoelectric films were laminated. The planar shape of the laminated portion is 30 mm x 150 mm. The piezoelectric films to be laminated were attached with an adhesive layer (acrylic adhesive). An electrode extension portion was formed in a region protruding from the laminated portion.

<Production of electroacoustic transducer>
The produced piezoelectric element was attached to a diaphragm. As the diaphragm, a PET board with a thickness of 0.3 mm, a width of 400 mm and a length of 500 mm was used. The longitudinal direction of the diaphragm was aligned with the longitudinal direction of the piezoelectric element, and the piezoelectric element was attached so that the center of the laminated portion of the piezoelectric element was aligned with the center of the diaphragm. The piezoelectric element and the diaphragm were attached using an adhesive sheet: NCF-D692 (manufactured by Lintec Corporation, thickness 50 μm).

The Young's modulus E ₁ of the diaphragm was measured using the dynamic viscoelasticity measuring device DMS6100 manufactured by SII Nanotechnology Co., Ltd. (manufactured by SII Nanotechnology Co., Ltd.) using the method described above, and found to be 2.1 GPa. The spring constant K ₁ of the deflection of the diaphragm 102 was calculated from the Young's modulus E ₁ of the diaphragm, width b = 450 mm, length L = 500 mm, and thickness h ₁ = 0.3 mm. The spring constant of deflection K ₁ was 0.0007 N/mm.

Further, the Young's modulus E ₂ of the adhesive layer was measured by DMA using the above-mentioned method after peeling off the piezoelectric element and the diaphragm, and found to be 1.0E+05 Pa. Further, the thickness h ₂ of the adhesive layer was measured by the method described above and was found to be 50 μm.

The _value ⁽ spring _constant _K The difference D from ₂ ) was 0.03.

[Examples 2 to 8, Comparative Examples 1 to 12]
Electrical conduction was carried out in the same manner as in Example 1, except that the material of the diaphragm (Young's modulus E ₁ ), the thickness h ₁ , the type of adhesive layer (Young's modulus E ₂ ), and the thickness h ₂ were changed as shown in Table 1. We created an acoustic transducer.
In Table 1, in the adhesive layer type column, D692 represents the adhesive sheet NCF-D692 manufactured by Lintec Co., Ltd., and UH203 represents the film-like hot melt adhesive: Elfan UH203 manufactured by Nippon Matai Co., Ltd. (thickness: 50 μm), NT120 represents Elfan NT120 (thickness: 50 μm), a film-like hot melt adhesive manufactured by Nippon Matai Co., Ltd., and Lio Elm represents Lio Elm TSU41SI-25DL (thickness: 25 μm) manufactured by Toyochem Co., Ltd. , No. 5603 is double-sided tape No. manufactured by Nitto Denko Corporation. 5603.

[evaluation]
The sound pressure of the produced electroacoustic transducers of each Example and Comparative Example was evaluated.

<Sound pressure>
One longitudinal end of the diaphragm was supported, a sine sweep signal with a frequency of 100 Hz to 5 kHz and an applied voltage of 50 Vrms was input to the piezoelectric element, and the sound pressure was measured with a microphone placed 1 m away from the center of the diaphragm. It was measured. The average value of the sound pressure in the frequency range of 100 Hz to 5 kHz was calculated, and the difference with respect to the average sound pressure of Comparative Example 2 was evaluated using the average sound pressure of Comparative Example 2 as a reference. For the average value of the sound pressure, the maximum value was extracted in the frequency range of 100 Hz to 5 kHz, and the average value was taken as the average value.
The results are shown in Table 1. Further, FIG. 8 shows a graph in which the difference D and the difference in average sound pressure of Examples 1 to 8 and Comparative Examples 1 to 11 are plotted. In FIG. 8, black circles are examples, and black triangles are comparative examples.

From Table 1 and FIG. 8, it can be seen that the sound pressure of the example of the present invention is higher than that of the comparative example. Furthermore, from FIG. 8, it can be seen that the smaller the difference D, the higher the average sound pressure. Furthermore, regardless of the magnitude of the spring constant K ₁ of the deflection of the diaphragm, it is possible to increase the sound pressure by appropriately selecting the spring constant K ₂ of the adhesive layer and reducing the difference D. Recognize.
From the above, the effects of the present invention are clear.

10

piezoelectric film

11a, 11c sheet-like material 11b laminate 19, 104 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

Claims

An electroacoustic transducer comprising a flexible diaphragm and a flexible piezoelectric element attached to the diaphragm via an adhesive layer,
When the spring constant of the deflection of the diaphragm is K 1 (N/mm), the Young's modulus of the adhesive layer is E 2 (N/mm 2 ), and the thickness is h 2 (mm), |50× An electroacoustic transducer that satisfies K 1 −E 2 ×h 2 |≦2.5.
The electroacoustic transducer according to claim 1 , wherein the spring constant K1 of the deflection of the diaphragm is lower than 0.1 N/m.
The piezoelectric element includes 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 electroacoustic transducer according to claim 1 or 2.
The electroacoustic transducer according to claim 3, wherein the piezoelectric element is formed by laminating a plurality of layers of the piezoelectric film.