Electroacoustic conversion film and electroacoustic converter

Abstract

Provided is an electroacoustic conversion film and an electroacoustic converter that can suppress a decrease in piezoelectric conversion efficiency when used in a high-temperature environment. The electroacoustic conversion film has a polymer composite piezoelectric body containing piezoelectric body particles in a matrix containing a polymer material and electrode layers formed on both surfaces of the polymer composite piezoelectric body, and the coefficient of thermal expansion of the electroacoustic conversion film is 12 ppm / °C to 100 ppm / °C.

Description

Technical Field

[0001] This invention relates to an electroacoustic conversion film and an electroacoustic converter. Background Technology

[0002] To address the trend towards thinner displays such as LCDs and OLEDs, the speakers used in these thin displays also require lightweight and thin design. Furthermore, in flexible displays, flexibility is also required to maintain lightweightness or to flexibly integrate with the flexible display. As such a lightweight, thin, and flexible speaker, a sheet-like electroacoustic conversion film with the property of expanding and contracting in response to applied voltage is being considered.

[0003] As a flexible, sheet-like electroacoustic conversion film, a technique using composite piezoelectrics containing piezoelectric particles in a matrix has been proposed.

[0004] For example, Patent Document 1 describes an electroacoustic conversion film comprising: a polymer composite piezoelectric body, wherein piezoelectric particles are dispersed in a viscoelastic matrix composed of a polymer material that is viscoelastic at room temperature; a thin film electrode formed on both sides of the polymer composite piezoelectric body; and a protective layer formed on the surface of the thin film electrode.

[0005] Furthermore, it is also being considered to create a flexible loudspeaker by attaching a flexible exciter to a flexible diaphragm. An exciter is an exciter that vibrates and produces sound by contacting various objects.

[0006] For example, Patent Document 2 describes a flexible display that integrates a flexible display, such as an organic electroluminescent display, with a flexible speaker consisting of a piezoelectric film, such as polyvinylidene fluoride (PVDF), held between electrodes. This flexible speaker can be positioned as an exciter-type speaker, which uses PVDF as an exciter (exciter) and the display as a vibrating plate to output sound.

[0007] Previous technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Application Publication No. 2014-014063

[0010] Patent Document 2: Japanese Patent Application Publication No. 2008-294493 Summary of the Invention

[0011] The technical problem to be solved by the invention

[0012] Here, according to the inventor's research, it is known that when using an electroacoustic conversion film of a polymer composite piezoelectric containing piezoelectric particles in a matrix as a loudspeaker, if used in a high-temperature environment, the distance between piezoelectric particles widens due to the thermal expansion of the polymer in the polymer composite piezoelectric, making it difficult for the deformation of the piezoelectric particles to be transmitted into the polymer composite piezoelectric, resulting in a decrease in sound pressure.

[0013] Furthermore, when using an exciter attached to a flexible diaphragm to function as a flexible loudspeaker, it is considered to use an electroacoustic conversion film containing piezoelectric particles within a polymer composite piezoelectric material matrix as the exciter. However, in this case, it is also known that if used in a high-temperature environment, the thermal expansion of the polymer in the polymer composite piezoelectric material widens the distance between the piezoelectric particles, making it difficult for the deformation of the piezoelectric particles to be transmitted within the polymer composite piezoelectric material, resulting in a decrease in sound pressure.

[0014] The objective of this invention is to address the problems of the prior art by providing an electroacoustic conversion film and an electroacoustic converter that can suppress the reduction of piezoelectric conversion efficiency when used in high-temperature environments.

[0015] means for solving technical problems

[0016] To address the aforementioned issues, the present invention has the following structure.

[0017] [1] An electroacoustic conversion film having a polymer composite piezoelectric body containing piezoelectric particles in a matrix containing polymer material and electrode layers formed on both sides of the polymer composite piezoelectric body.

[0018] The coefficient of thermal expansion of the electroacoustic conversion film is 12ppm / ℃~100ppm / ℃.

[0019] [2] The electroacoustic conversion film according to [1] has the following characteristics:

[0020] A protective layer is laminated on the surface of the electrode layer opposite to the surface of the polymer composite piezoelectric body.

[0021] [3] The electroacoustic conversion film according to [1] or [2], wherein,

[0022] The polymer composite piezoelectric is polarized in the thickness direction.

[0023] [4] The electroacoustic conversion film according to any one of [1] to [3], wherein,

[0024] Polymer composite piezoelectrics do not exhibit in-plane anisotropy in their piezoelectric properties.

[0025] [5] The electroacoustic conversion film according to any one of [1] to [4], wherein,

[0026] Polymer materials exhibit viscoelasticity at room temperature.

[0027] [6] An electroacoustic transducer having:

[0028] An electroacoustic conversion film comprising a polymer composite piezoelectric body containing piezoelectric particles within a polymer matrix and electrode layers formed on both sides of the polymer composite piezoelectric body; and

[0029] A vibrating plate, layered on an electroacoustic conversion film.

[0030] The coefficient of thermal expansion of the electroacoustic transducer is 12ppm / ℃~100ppm / ℃.

[0031] [7] According to the electroacoustic converter described in [6], wherein,

[0032] The absolute value of the difference between the thermal expansion coefficient of the electroacoustic conversion film and the thermal expansion coefficient of the vibrating plate is 0ppm / ℃~80ppm / ℃.

[0033] [8] The electroacoustic converter according to [6] or [7], wherein,

[0034] The coefficient of thermal expansion of the electroacoustic conversion film is 12ppm / ℃~100ppm / ℃.

[0035] [9] The electroacoustic converter according to any one of [6] to [8], wherein,

[0036] The loss tangent (Tanδ) of the electroacoustic conversion film at a frequency of 1 Hz and 60 °C, as measured by dynamic viscoelasticity, is greater than 0.03.

[0037]

[10] The electroacoustic converter according to any one of [6] to [9], wherein,

[0038] The electroacoustic conversion film has a protective layer on the surface of the electrode layer opposite to the surface of the polymer composite piezoelectric body.

[0039] Invention Effects

[0040] According to the present invention, an electroacoustic conversion film and an electroacoustic converter are provided that can suppress the reduction of piezoelectric conversion efficiency when used in a high-temperature environment. Attached Figure Description

[0041] Figure 1 This is a conceptual diagram of an example of the electroacoustic conversion film of the present invention.

[0042] Figure 2This is a conceptual diagram illustrating an example of a method for manufacturing an electroacoustic conversion thin film.

[0043] Figure 3 This is a conceptual diagram illustrating an example of a method for manufacturing an electroacoustic conversion thin film.

[0044] Figure 4 This is a conceptual diagram illustrating an example of a method for manufacturing an electroacoustic conversion thin film.

[0045] Figure 5 Is using Figure 1 A conceptual diagram of an example of a piezoelectric loudspeaker with an electroacoustic conversion film.

[0046] Figure 6 This is a conceptual diagram of an example of an electroacoustic transducer using an electroacoustic conversion film.

[0047] Figure 7 This is a conceptual diagram of an example of an electroacoustic transducer using a stacked piezoelectric element made of a stacked electroacoustic conversion film.

[0048] Figure 8 This is a conceptual diagram of another example of a stacked piezoelectric element.

[0049] Figure 9 This is a conceptual diagram of another example of a stacked piezoelectric element. Detailed Implementation

[0050] Hereinafter, the electroacoustic conversion film and electroacoustic converter of the present invention will be described in detail with reference to the preferred embodiments shown in the accompanying drawings.

[0051] The following description of the constituent elements is sometimes based on representative embodiments of the present invention, but the present invention is not limited to such embodiments.

[0052] In addition, in this specification, the numerical range indicated by “~” refers to the range of values ​​included before and after “~” as the lower and upper limits.

[0053] [Electroacoustic conversion film]

[0054] The electroacoustic converter of the present invention is an electroacoustic converter having:

[0055] An electroacoustic conversion film comprising a polymer composite piezoelectric body containing piezoelectric particles within a polymer matrix, and electrode layers formed on both sides of the polymer composite piezoelectric body.

[0056] The coefficient of thermal expansion of the electroacoustic conversion film is 12ppm / ℃~100ppm / ℃.

[0057] Figure 1 The image below is a conceptual illustration of an example of the electroacoustic conversion film of the present invention, shown in a cross-sectional view.

[0058] like Figure 1 As shown, the electroacoustic conversion film 10 has: a piezoelectric layer 20 as a sheet with piezoelectricity; a lower electrode 24 stacked on one surface of the piezoelectric layer 20; a lower protective layer 28 stacked on the lower electrode 24; an upper electrode 26 stacked on the other surface of the piezoelectric layer 20; and an upper protective layer 30 stacked on the upper electrode 26.

[0059] The piezoelectric layer 20 is formed by containing piezoelectric particles 36 in a matrix 34 containing a polymer material. That is, the piezoelectric layer 20 is a polymer composite piezoelectric material according to the present invention. Furthermore, the lower electrode 24 and the upper electrode 26 are electrode layers according to the present invention. And the lower protective layer 28 and the upper protective layer 30 are protective layers according to the present invention.

[0060] As described later, the electroacoustic conversion film 10 (piezoelectric layer 20) is preferably polarized in the thickness direction.

[0061] This electroacoustic conversion film 10, as an example, is used in various acoustic devices (acoustic equipment) such as pickups used in musical instruments such as loudspeakers, microphones, and guitars to generate (reproduce) sound caused by vibrations based on electrical signals, or to convert vibrations caused by sound into electrical signals.

[0062] In addition, electroacoustic conversion films can also be used in pressure sensors and power generation components.

[0063] [Piezoelectric layer]

[0064] The piezoelectric layer 20 is a polymer composite piezoelectric material in this invention, containing piezoelectric particles 36 in a matrix 34 containing polymer materials.

[0065] The matrix 34 (matrix and adhesive) constituting the polymer composite piezoelectric body of the piezoelectric layer 20 is preferably a polymer material that has viscoelasticity at room temperature.

[0066] The electroacoustic conversion film 10 of the present invention is preferably used in flexible loudspeakers, such as loudspeakers for flexible displays. Here, the polymer composite piezoelectric material (piezoelectric layer 20) used in the flexible loudspeaker preferably possesses the following characteristics. Therefore, as a material possessing these characteristics, a polymer material having viscoelasticity at room temperature is preferred.

[0067] Additionally, in this instruction manual, "normal temperature" refers to a temperature range of approximately 0 to 50°C.

[0068] (i) Flexibility

[0069] For example, when held loosely like a newspaper or magazine for carrying, it is constantly subjected to relatively slow but large bending deformations below a few Hz from the outside. If the polymer composite piezoelectric is too stiff, a correspondingly large bending stress will be generated, leading to cracking at the interface between the matrix and the piezoelectric particles, potentially causing damage. Therefore, the polymer composite piezoelectric requires appropriate flexibility. Furthermore, if the strain energy can diffuse outwards as heat, the stress can be relaxed. Therefore, the loss tangent of the polymer composite piezoelectric requires a suitable large value.

[0070] (ii) Sound quality

[0071] The loudspeaker vibrates piezoelectric particles in the 20Hz–20kHz audio frequency band. This vibrational energy causes the entire polymer composite piezoelectric material (electroacoustic conversion film) to vibrate as a single unit, thereby reproducing sound. Therefore, to improve the efficiency of vibrational energy transmission, the polymer composite piezoelectric material needs to have appropriate rigidity. Furthermore, if the loudspeaker's frequency response is smooth, the change in sound quality when the lowest resonant frequency changes with curvature is also smaller. Therefore, the polymer composite piezoelectric material needs to have a sufficiently large loss tangent.

[0072] In summary, the polymer composite piezoelectric material is required to become stiffer for vibrations in the 20Hz–20kHz range and softer for vibrations below a few Hz. Furthermore, for vibrations at all frequencies below 20kHz, the loss tangent of the polymer composite piezoelectric material is required to be appropriately large.

[0073] Typically, polymeric solids possess viscoelastic relaxation mechanisms. As temperature increases or frequency decreases, large-scale molecular motion is observed as a decrease in storage modulus (Young's modulus) (relaxation) or a maximization of loss modulus (absorption). Among these, relaxation caused by the micro-Brownian motion of molecular chains in amorphous regions is called principal dispersion, and very large relaxation phenomena are observed. The temperature at which this principal dispersion occurs is the glass transition point (Tg), where the viscoelastic relaxation mechanism is most pronounced.

[0074] In the polymer composite piezoelectric (piezoelectric layer 20), a polymer composite piezoelectric that hardens for vibrations from 20 Hz to 20 kHz and softens for slow vibrations below a few Hz is achieved by using a polymer material with a glass transition temperature at room temperature—in other words, by using a polymer material that is viscoelastic at room temperature as the matrix. In particular, to preferably exhibit this operation, the glass transition temperature at 1 Hz is room temperature; that is, a polymer material with a temperature between 0 and 50°C is preferably used as the matrix of the polymer composite piezoelectric.

[0075] As a viscoelastic polymer material at room temperature, it is possible to use various known materials as long as it has dielectric properties. Preferred polymer materials are those that, at room temperature (0°C to 50°C), have a maximum loss tangent of 0.5 or higher at a frequency of 1 Hz based on dynamic viscoelasticity testing.

[0076] Therefore, when the polymer composite piezoelectric material is slowly bent by external force, the stress concentration at the interface between the matrix and the piezoelectric particles in the part of maximum bending moment is relaxed, resulting in good flexibility.

[0077] Furthermore, the preferred polymer material has a storage modulus (E') at a frequency of 1 Hz obtained by dynamic viscoelasticity measurement that is above 100 MPa at 0 °C and below 10 MPa at 50 °C.

[0078] Therefore, it is possible to reduce the bending moment generated when the polymer composite piezoelectric body is slowly bent due to external force, and to harden for acoustic vibrations of 20Hz to 20kHz.

[0079] Furthermore, the relative permittivity of the polymer material is preferably 10 or higher at 25°C. Therefore, when a voltage is applied to the polymer composite piezoelectric, a higher electric field is applied to the piezoelectric particles in the matrix, thus allowing for a larger deformation.

[0080] However, on the other hand, considering the need to ensure good moisture resistance, it is preferable that the relative permittivity of the polymer material is 10 or less at 25°C.

[0081] Examples of polymeric materials that meet these conditions include cyanoethylated polyvinyl alcohol (cyanoethylated PVA), polyvinyl acetate, polyvinylidene chloride-acrylonitrile, polystyrene-vinyl polyisoprene block copolymer, polyvinyl methyl ketone, and polybutyl methacrylate. Furthermore, commercially available products such as HYBRAR5127 (manufactured by KURARAY CO.,LTD) are preferably used as these polymeric materials. Among these, materials containing cyanoethyl groups are preferred, and cyanoethylated PVA is particularly preferred.

[0082] In addition, these polymer materials can be used in single-component or mixed-component methods.

[0083] The matrix 34 using this polymer material allows for the simultaneous use of multiple polymer materials as needed.

[0084] That is, for the purpose of adjusting dielectric or mechanical properties, in addition to viscoelastic polymer materials at room temperature, other dielectric polymer materials can be added to the matrix 34 as needed.

[0085] Examples of dielectric polymer materials that can be added include fluorinated polymers such as polyvinylidene fluoride, polyvinylidene fluoride-tetrafluoroethylene copolymer, polyvinylidene fluoride-trifluoroethylene copolymer, polyvinylidene fluoride-trifluoroethylene copolymer, and polyvinylidene fluoride-tetrafluoroethylene copolymer; vinylidene cyanide-vinyl acetate copolymer; cyanoethyl cellulose; cyanoethyl hydroxysucrose; cyanoethyl hydroxyamylopectin; cyanoethyl methacrylate; cyanoethyl acrylate; cyanoethyl hydroxyethyl cellulose; cyanoethyl linear starch; cyanoethyl hydroxypropyl cellulose; cyanoethyl dihydroxypropyl cellulose; cyanoethyl hydroxypropyl linear starch; cyanoethyl polyacrylamide; cyanoethyl polyacrylate; cyanoethyl amylopectin; cyanoethyl polyhydroxymethylene; cyanoethyl glycidol amylopectin; cyanoethyl sucrose; and cyanoethyl sorbitol, as well as synthetic rubbers such as nitrile rubber or chloropine rubber.

[0086] Among them, polymeric materials containing cyanoethyl groups are preferred to be used.

[0087] Furthermore, in the matrix 34 of the piezoelectric layer 20, the dielectric polymer materials that can be added, besides viscoelastic polymer materials such as cyanoethylated PVA at room temperature, are not limited to one type, but can include multiple types.

[0088] In addition to dielectric polymer materials, thermoplastic resins such as vinyl chloride resin, polyethylene, polystyrene, methacrylic resin, polybutene and isobutene, as well as thermosetting resins such as phenolic resin, urea resin, melamine resin, alkyd resin and mica can be added to the matrix 34 for the purpose of adjusting the glass transition point.

[0089] Furthermore, to improve adhesion, tackifiers such as rosin, rosin, terpenes, terpene phenols, and petroleum resins can be added.

[0090] There is no particular limitation on the amount of materials other than viscoelastic polymers such as cyanoethylated PVA added to the matrix 34 of the piezoelectric layer 20, but it is preferably set to 30% by mass or less based on the proportion in the matrix 34.

[0091] Therefore, the properties of the added polymer material can be exhibited without damaging the viscoelastic relaxation mechanism in the matrix 34, thus achieving preferred results in terms of high dielectric constant, improved heat resistance, and improved adhesion to the piezoelectric particles 36 and the electrode layer.

[0092] The piezoelectric layer 20 is a polymeric composite piezoelectric material containing piezoelectric particles 36 in this matrix 34.

[0093] The piezoelectric particles 36 are composed of ceramic particles with perovskite or wurtzite crystal structures.

[0094] Examples of ceramic particles constituting piezoelectric particles 36 include lead zirconate titanate (PZT), lanthanum lead zirconate titanate (PLZT), barium titanate (BaTiO3), zinc oxide (ZnO), and a solid solution of barium titanate and bismuth ferrite (BiFe3) (BFBT).

[0095] These piezoelectric particles 36 can be used in single or multiple ways (mixed).

[0096] There is no limitation on the particle size of this piezoelectric particle 36; it can be appropriately selected according to the size and application of the polymer composite piezoelectric (electroacoustic conversion film 10).

[0097] 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, the polymer composite piezoelectric material (electroacoustic conversion film 10) can achieve a combination of high-voltage characteristics and flexibility, resulting in an optimal outcome.

[0098] In addition, Figure 1 In the piezoelectric layer 20, the piezoelectric particles 36 are uniformly and regularly dispersed in the matrix 34, but the present invention is not limited thereto.

[0099] That is, the piezoelectric particles 36 in the piezoelectric layer 20 can be irregularly dispersed in the matrix 34 as long as they are uniformly dispersed.

[0100] In the piezoelectric layer 20 (polymer composite piezoelectric), the ratio of matrix 34 to piezoelectric particles 36 is not limited. It can be appropriately set according to the size and thickness of the piezoelectric layer 20 in the surface direction, the application of the polymer composite piezoelectric, and the required characteristics of the polymer composite piezoelectric.

[0101] The volume fraction of piezoelectric particles 36 in the piezoelectric layer 20 is preferably 30-80%, more preferably 50% or more, and therefore, it is even more preferably set to 50-80%.

[0102] By setting the ratio of matrix 34 to piezoelectric particles 36 within the above range, an optimal result can be obtained that balances high voltage characteristics and flexibility.

[0103] There is no limit to the thickness of the piezoelectric layer 20. It can be appropriately set according to the application of the polymer composite piezoelectric material and the required characteristics of the polymer composite piezoelectric material. The thicker the piezoelectric layer 20, the more advantageous it is in terms of rigidity, such as the rigidity of the so-called sheet. However, the voltage (potential difference) required to make the piezoelectric layer 20 expand and contract by the same amount becomes larger.

[0104] The thickness of the piezoelectric layer 20 is preferably 10-300 μm, more preferably 20-200 μm, and even more preferably 30-150 μm.

[0105] By setting the thickness of the piezoelectric layer 20 within the aforementioned range, an optimal result can be obtained while ensuring rigidity and appropriate flexibility.

[0106] [Electrode layer and protective layer]

[0107] like Figure 1 As shown, the electroacoustic conversion film 10 of the example figure has a structure in which a lower electrode 24 is provided on one surface of the piezoelectric layer 20, and a lower protective layer 28 is provided on its surface; and an upper electrode 26 is provided on the other surface of the piezoelectric layer 20, and an upper protective layer 30 is provided on its surface. Here, the upper electrode 26 and the lower electrode 24 form an electrode pair.

[0108] In addition to these layers, the electroacoustic conversion film 10 also has electrode leads, for example, from the upper electrode 26 and the lower electrode 24, which are connected to a power source. Furthermore, the electroacoustic conversion film 10 may also have an insulating layer that covers the exposed area of ​​the piezoelectric layer 20 to prevent short circuits, etc.

[0109] That is, the electroacoustic conversion film 10 has a structure in which the piezoelectric layer 20 is sandwiched between two sides by an electrode pair, namely an upper electrode 26 and a lower electrode 24, and the laminate is sandwiched between a lower protective layer 28 and an upper protective layer 30.

[0110] Thus, in the electroacoustic conversion film 10, the area held by the upper electrode 26 and the lower electrode 24 expands and contracts according to the applied voltage.

[0111] In the electroacoustic conversion film 10, the lower protective layer 28 and the upper protective layer 30 are not essential components, but are provided as a preferred embodiment.

[0112] The lower protective layer 28 and the upper protective layer 30 cover the upper electrode 26 and the lower electrode 24, and also serve to impart appropriate rigidity and mechanical strength to the piezoelectric layer 20. That is, in the electroacoustic conversion film 10, the piezoelectric layer 20, composed of the matrix 34 and piezoelectric particles 36, exhibits excellent flexibility for slow bending deformation; however, depending on the application, its rigidity or mechanical strength may sometimes be insufficient. To compensate for this, the electroacoustic conversion film 10 is provided with a lower protective layer 28 and an upper protective layer 30.

[0113] There are no restrictions on the lower protective layer 28 and the upper protective layer 30; various sheet materials can be used. For example, various resin films can be preferably exemplified.

[0114] Among them, resin films composed of polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS), polycarbonate (PC), polyphenylene sulfide (PPS), polymethyl methacrylate (PMMA), polyetherimide (PEI), polyimide (PI), polyethylene naphthalate (PEN), triacetyl cellulose (TAC), and cyclic olefin resins are preferred due to their excellent mechanical properties and heat resistance.

[0115] There are no restrictions on the thickness of the lower protective layer 28 and the upper protective layer 30. Furthermore, the thicknesses of the lower protective layer 28 and the upper protective layer 30 are basically the same, but they can also be different.

[0116] If the lower protective layer 28 and the upper protective layer 30 are too rigid, not only will the expansion and contraction of the piezoelectric layer 20 be restricted, but its flexibility will also be compromised. Therefore, unless mechanical strength or good operability as a sheet is required, it is more advantageous for the lower protective layer 28 and the upper protective layer 30 to be as thin as possible.

[0117] In the electroacoustic conversion film 10, if the thickness of the lower protective layer 28 and the upper protective layer 30 is less than twice the thickness of the piezoelectric layer 20, then an optimal result can be obtained while ensuring rigidity and appropriate flexibility.

[0118] For example, when the thickness of the piezoelectric layer 20 is 50 μm and the lower protective layer 28 and the upper protective layer 30 are made of PET, the thickness of the lower protective layer 28 and the upper protective layer 30 is preferably 100 μm or less, more preferably 50 μm or less, and even more preferably 25 μm or less.

[0119] In the electroacoustic conversion film 10, a lower electrode 24 is formed between the piezoelectric layer 20 and the lower protective layer 28, and an upper electrode 26 is formed between the piezoelectric layer 20 and the upper protective layer 30.

[0120] The lower electrode 24 and the upper electrode 26 are provided to apply a driving voltage to the piezoelectric layer 20.

[0121] In this invention, the materials used to form the lower electrode 24 and the upper electrode 26 are not limited, and various conductors can be used. Specifically, examples include carbon, palladium, iron, tin, aluminum, nickel, platinum, gold, silver, copper, titanium, chromium, and molybdenum, their alloys, laminates and composites of these metals and alloys, and indium tin oxide. Among these, copper, aluminum, gold, silver, platinum, and indium tin oxide are preferably exemplified as the lower electrode 24 and the upper electrode 26.

[0122] Furthermore, there are no restrictions on the method of forming the lower electrode 24 and the upper electrode 26. Various known methods can be used, such as vacuum evaporation and sputtering vapor deposition (vacuum film formation), electroplating film formation, and bonding of foils formed from the above materials.

[0123] In particular, copper and aluminum films deposited by vacuum evaporation are preferably used as the lower electrode 24 and the upper electrode 26, for reasons such as ensuring the flexibility of the electroacoustic conversion film 10. In particular, copper films formed by vacuum evaporation are preferred.

[0124] There is no limitation on the thickness of the lower electrode 24 and the upper electrode 26. Furthermore, the thickness of the lower electrode 24 and the upper electrode 26 can be substantially the same, but they can also be different.

[0125] Similar to the aforementioned lower protective layer 28 and upper protective layer 30, if the rigidity of the lower electrode 24 and upper electrode 26 is too high, not only will the expansion and contraction of the piezoelectric layer 20 be restricted, but its flexibility will also be impaired. Therefore, the thinner the lower electrode 24 and upper electrode 26 are, the more advantageous it is, as long as the resistance does not become too high. That is, it is preferable that the lower electrode 24 and upper electrode 26 are thin-film electrodes.

[0126] In the electroacoustic conversion film 10, if the product of the thickness of the lower electrode 24 and the upper electrode 26 and the Young's modulus is less than the product of the thickness of the lower protective layer 28 and the upper protective layer 30 and the Young's modulus, the flexibility will not be greatly impaired, and therefore it is preferred.

[0127] For example, in the case where the lower protective layer 28 and the upper protective layer 30 are made of PET (Young's modulus: about 6.2 GPa) and the lower electrode 24 and the upper electrode 26 are made of copper (Young's modulus: about 130 GPa), if the thickness of the lower protective layer 28 and the upper protective layer 30 is 25 μm, then the thickness of the lower electrode 24 and the upper electrode 26 is preferably 1.2 μm or less, more preferably 0.3 μm or less, and preferably 0.1 μm or less.

[0128] Preferably, the maximum value of the loss tangent (Tanδ) of the electroacoustic conversion film 10 at a frequency of 1 Hz, as measured by dynamic viscoelasticity, exists at room temperature, and more preferably, the maximum value of 0.1 or higher exists at room temperature.

[0129] Therefore, even if the electroacoustic conversion film 10 is subjected to relatively slow but large bending deformation below a few Hz from the outside, it can effectively diffuse the strain energy to the outside as heat, thus preventing cracking at the interface between the matrix and the piezoelectric particles.

[0130] The preferred electroacoustic conversion film 10 has a storage modulus (E') at a frequency of 1 Hz, measured by dynamic viscoelasticity, that is 10 GPa to 30 GPa at 0 °C and 1 GPa to 10 GPa at 50 °C. Furthermore, the piezoelectric layer 20 also has the same conditions.

[0131] Therefore, the energy storage modulus (E') of the electroacoustic conversion film 10 can have a large frequency dispersion. That is, it can become stiff for vibrations in the range of 20Hz to 20kHz and become soft for vibrations below a few Hz.

[0132] Furthermore, the product of the thickness of the preferred electroacoustic conversion film 10 and the storage modulus at a frequency of 1 Hz based on dynamic viscoelasticity measurement is preferably 1.0 × 10⁻⁶ at 0°C. 5 ~2.0×10 6 (1.0E+05~2.0E+06) N / m, 1.0×10 at 50℃ 5 ~1.0×10 6 (1.0E+05~1.0E+06) N / m. Furthermore, the same conditions apply to piezoelectric layer 20.

[0133] Therefore, the electroacoustic conversion film 10 can possess appropriate rigidity and mechanical strength without compromising its flexibility and acoustic properties.

[0134] Furthermore, in the master curve obtained by dynamic viscoelasticity measurement, the loss tangent of the electroacoustic conversion film 10 is preferably 0.05 or higher at 25°C and 1 kHz. The same condition applies to the piezoelectric layer 20.

[0135] As a result, the frequency response of the loudspeaker using the electroacoustic conversion film 10 becomes smooth, which can reduce the change in sound quality when the lowest resonant frequency f0 changes with the curvature of the loudspeaker.

[0136] Furthermore, in this invention, the storage modulus (Young's modulus) and loss tangent of the electroacoustic conversion film 10 and the piezoelectric layer 20 can be measured by known methods. As an example, the dynamic viscoelasticity measuring device DMS6100 manufactured by SII NanoTechnology Inc. can be used for measurement.

[0137] As an example, the measurement conditions can be exemplified as follows: measurement frequency of 0.1Hz to 20Hz (0.1Hz, 0.2Hz, 0.5Hz, 1Hz, 2Hz, 5Hz, 10Hz and 20Hz), measurement temperature of -50 to 150℃, heating rate of 2℃ / min (in a nitrogen atmosphere), sample size of 40mm × 10mm (including the clamping area), and distance between suction cups of 20mm.

[0138] Here, the coefficient of thermal expansion of the electroacoustic conversion film of the present invention is 12ppm / ℃~100ppm / ℃.

[0139] As mentioned above, according to the inventors' research, when using an electroacoustic conversion film of a polymer composite piezoelectric material containing piezoelectric particles in a matrix as a loudspeaker, there is a problem of reduced sound pressure when used in a high-temperature environment.

[0140] Further research on this point reveals that if the temperature of the polymer composite piezoelectric increases, the polymer material serving as the matrix expands due to heat, thereby widening the distance between the piezoelectric particles contained in the matrix.

[0141] As mentioned earlier, in the electroacoustic conversion film using a polymer composite piezoelectric containing piezoelectric particles in a matrix containing polymer materials, by applying a voltage to the electrode layers stacked on both sides of the polymer composite piezoelectric, the piezoelectric particles in the polymer composite piezoelectric are deformed (vibrated), and the deformation of the piezoelectric particles is transmitted to the matrix, thereby deforming (vibrating) the electroacoustic conversion film as a whole.

[0142] If the distance between the piezoelectric particles contained in the matrix becomes wider, the deformation of the piezoelectric particles when a voltage is applied to the electrodes of the electroacoustic conversion film is difficult to be transmitted to the matrix, resulting in a decrease in piezoelectric conversion efficiency.

[0143] Therefore, under high temperature conditions, the piezoelectric conversion efficiency of the electroacoustic conversion film decreases, resulting in a decrease in sound pressure when the electroacoustic conversion film is used as a loudspeaker.

[0144] In contrast, in the electroacoustic conversion film of the present invention, by setting the coefficient of thermal expansion of the electroacoustic conversion film to 12ppm / ℃ to 100ppm / ℃, the matrix expansion of the polymer composite piezoelectric is suppressed under high-temperature conditions, and the widening of the distance between the piezoelectric particles contained in the matrix is ​​suppressed. As a result, since the deformation (vibration) of the piezoelectric particles is more preferably transmitted to the matrix, the reduction in the piezoelectric conversion efficiency of the electroacoustic conversion film can be suppressed.

[0145] Furthermore, if the coefficient of thermal expansion of the electroacoustic conversion film is less than 12 ppm / ℃, the piezoelectric layer becomes brittle and may be damaged. Therefore, the coefficient of thermal expansion of the electroacoustic conversion film is set to be 12 ppm / ℃ or higher.

[0146] From the viewpoint that it can better suppress the decrease in piezoelectric conversion efficiency of the electroacoustic conversion film under high temperature environment and suppress the damage of piezoelectric layer, the coefficient of thermal expansion of the electroacoustic conversion film is preferably 12ppm / ℃ to 100ppm / ℃, more preferably 16ppm / ℃ to 70ppm / ℃, and even more preferably 18ppm / ℃ to 55ppm / ℃.

[0147] Here, the coefficient of thermal expansion of the electroacoustic conversion film is determined, for example, by measuring the thermomechanical properties using a thermomechanical analysis apparatus (TMA4000SE manufactured by TMA NETZSCH). The measurement conditions are as follows: sample size is 5mm × 20mm, distance between suction cups is 15mm, and the length of the suction cup portion is 2.5 ± 0.5mm both vertically and horizontally. The temperature is changed at a rate of 5℃ / min within the range of -20℃ to 60℃, and the displacement of the distance between the suction cups is measured. Furthermore, a constant weight of 3g is applied to the sample for measurement. Next, the slope of an approximate straight line representing the displacement data from -20℃ to 60℃ is calculated, thereby determining the displacement per 1℃ temperature change. Then, by dividing this slope by the distance between the suction cups when the sample is placed, i.e., 15mm, the coefficient of thermal expansion can be calculated.

[0148] One method for setting the coefficient of thermal expansion of the electroacoustic conversion film within the aforementioned range is as follows: During the fabrication of the electroacoustic conversion film, a coating is applied to form a piezoelectric layer (polymer composite piezoelectric), dried, and then subjected to a polarization treatment (described later). After laminating the upper electrode layer (and the upper protective layer), an aging treatment is performed by heating. The aging treatment varies depending on the substrate material, but can be performed at a temperature of 40°C to 70°C for 12 to 72 hours. Alternatively, the aging treatment can be performed before laminating the upper electrode layer (and the upper protective layer) or before the polarization treatment.

[0149] By undergoing aging treatment, the entanglement of the polymer material serving as the matrix of the polymer composite piezoelectric material is carried out, becoming stronger and more stable, and the coefficient of thermal expansion decreases compared to the case without aging treatment.

[0150] Alternatively, as a method to set the coefficient of thermal expansion of the electroacoustic conversion film within the aforementioned range, one approach is to apply a coating that forms a piezoelectric layer (polymer composite piezoelectric) and dry it, followed by vacuum drying. By performing vacuum drying, residual voids (air) in the piezoelectric layer are removed, thereby reducing the coefficient of thermal expansion of the electroacoustic conversion film.

[0151] Vacuum drying can be carried out at a temperature of 25℃~40℃, a pressure of 10Pa~50Pa, and for 48 hours~144 hours.

[0152] Alternatively, as a method to set the coefficient of thermal expansion of the electroacoustic conversion film within the aforementioned range, one approach is to increase the ratio of piezoelectric particles in the polymer composite piezoelectric. Compared to piezoelectric particles, the polymer material serving as the matrix has a higher coefficient of thermal expansion; therefore, by increasing the ratio of piezoelectric particles and decreasing the ratio of the matrix (polymer material), the coefficient of thermal expansion of the electroacoustic conversion film can be reduced.

[0153] From this perspective, it is preferable that the ratio of piezoelectric particles in the polymer composite piezoelectric is set to 30-80%, and more preferably 50-80%.

[0154] Regarding the humidity expansion coefficient of the electroacoustic conversion film of the present invention, it is preferably set to 1 to 30 ppm / %RH at a temperature of 25°C, and more preferably to 3 to 20 ppm / %RH. Furthermore, at a temperature of 60°C, it is preferably set to 3 to 40 ppm / %RH, and more preferably to 5 to 30 ppm / %RH. By setting the humidity expansion coefficient within this range, the reduction in sound pressure in high humidity environments can be suppressed.

[0155] The following is for reference. Figures 2-4 An example of a method for manufacturing the electroacoustic conversion film 10 will be described.

[0156] First, such as Figure 2 As shown, a sheet 10a is prepared to form a lower electrode 24 above the lower protective layer 28. This sheet 10a can be fabricated as the lower electrode 24 by forming a copper thin film on the surface of the lower protective layer 28 through vacuum evaporation, sputtering, electroplating, etc.

[0157] When the lower protective layer 28 is very thin and has poor operability, a lower protective layer 28 with an attached spacer (temporary support) can be used as needed. Alternatively, a PET material with a thickness of 25μm to 100μm can be used as the spacer. After heat-pressing the upper electrode 26 and the upper protective layer 30, the spacer can be removed before stacking any components on the lower protective layer 28.

[0158] On the other hand, a polymer material that dissolves in an organic solvent to form a matrix is ​​prepared, and then piezoelectric particles such as PZT particles are added, and the mixture is stirred and dispersed to form a coating.

[0159] There are no restrictions on organic solvents other than those mentioned above; a variety of organic solvents can be used.

[0160] Furthermore, as mentioned earlier, since the coefficient of thermal expansion of the electroacoustic conversion film varies depending on the ratio of piezoelectric particles in the polymer composite piezoelectric, coatings can be prepared to make the ratio of piezoelectric particles in the polymer composite piezoelectric to a desired ratio.

[0161] After preparing sheet material 10a and the coating, the coating is cast (coated) onto sheet material 10a, the organic solvent is evaporated, and the material is dried. Thus, as... Figure 3As shown, a laminate 10b is formed by having a lower electrode 24 above the lower protective layer 28 and a piezoelectric layer 20 formed above the lower electrode 24. Note that the lower electrode 24 refers to the electrode on the substrate side when the piezoelectric layer 20 is coated, and does not refer to the vertical position within the laminate.

[0162] As mentioned earlier, in order to reduce the coefficient of thermal expansion of the electroacoustic conversion film, vacuum drying can be performed after coating and drying. By performing vacuum drying, the voids (air) remaining in the piezoelectric layer can be removed, thereby reducing the coefficient of thermal expansion of the fabricated electroacoustic conversion film.

[0163] There are no restrictions on the casting method of this coating; all known methods (coating devices) such as sliding coating machines and doctor blades can be used.

[0164] As described above, in the electroacoustic conversion film 10, in the matrix 34, in addition to viscoelastic materials such as cyanoethylated PVA, dielectric polymer materials may also be added.

[0165] When adding these polymeric materials to matrix 34, it is sufficient to dissolve the polymeric materials added to the coating as described above.

[0166] After forming a laminate 10b with a lower electrode 24 above the lower protective layer 28 and a piezoelectric layer 20 above the lower electrode 24, it is preferable to perform a polarization treatment on the piezoelectric layer 20.

[0167] There are no restrictions on the method of polarization treatment of the piezoelectric layer 20; known methods can be used.

[0168] Alternatively, prior to this polarization treatment, a calendering process can be performed to smooth the surface of the piezoelectric layer 20 using a heated roller or similar device. By performing this calendering process, the hot pressing process described later can be carried out smoothly.

[0169] Thus, the piezoelectric layer 20 of the laminate 10b is polarized, and on the other hand, a sheet 10c for forming an upper electrode 26 is prepared above the upper protective layer 30. This sheet 10c can be fabricated as the upper electrode 26 by forming a copper thin film on the surface of the upper protective layer 30 through vacuum evaporation, sputtering, electroplating, etc.

[0170] Next, as Figure 4 As shown, with the upper electrode 26 facing the piezoelectric layer 20, the sheet 10c is stacked on the laminate 10b after the polarization treatment of the piezoelectric layer 20 is completed.

[0171] Then, the laminate of the laminate 10b and the sheet 10c is heat-pressed by means of clamping the upper protective layer 30 and the lower protective layer 28, using a heating pressing device or heating rollers.

[0172] Here, as mentioned above, after hot-pressing the laminate 10b and the sheet 10c, it is preferable to perform an aging treatment by heating. By performing the aging treatment, the coefficient of thermal expansion of the electroacoustic conversion film can be reduced.

[0173] The electroacoustic conversion film 10 is manufactured through the above process. The manufactured electroacoustic conversion film 10 can also be cut into the desired shape according to various applications.

[0174] The stacked piezoelectric element 14 described later has a structure in which the electroacoustic conversion film 10 of the present invention is stacked, preferably bonded by an adhesive layer 19. Figure 7 The stacked piezoelectric element 14 shown is preferably configured such that, as indicated by the arrow attached to the piezoelectric layer 20, the polarization directions of adjacent electroacoustic conversion films 10 are opposite to each other.

[0175] Typical piezoelectric elements made of stacked piezoelectric ceramics undergo polarization treatment after the piezoelectric ceramic stack is fabricated. Only a common electrode exists at the interfaces of each piezoelectric layer; therefore, the polarization directions of each piezoelectric layer alternate along the stacking direction.

[0176] In contrast, the stacked piezoelectric element using the electroacoustic conversion film 10 of the present invention can be polarized in the state of the electroacoustic conversion film 10 before stacking. Preferably, the piezoelectric layer 20 is polarized before the upper electrode 26 and the upper protective layer 30 are stacked.

[0177] Therefore, the piezoelectric element using the electroacoustic conversion film of the present invention can be fabricated by stacking polarized electroacoustic conversion films 10. Preferably, a long strip of electroacoustic conversion film (large area electroacoustic conversion film) subjected to polarization treatment is fabricated, and after being cut to form individual electroacoustic conversion films 10, the electroacoustic conversion films 10 are stacked to form a piezoelectric element 14.

[0178] Therefore, using the stacked piezoelectric element of the electroacoustic conversion film of the present invention, the polarization directions of adjacent electroacoustic conversion films 10 can be such that... Figure 9 As shown in the diagram, the stacked piezoelectric element 60 is aligned in the stacking direction, and can also be aligned as follows: Figure 7 The stacked piezoelectric elements 14 shown are alternated.

[0179] Furthermore, it is known that conventional electroacoustic conversion films made of polymer materials such as PVDF (polyvinylidene fluoride) undergo uniaxial stretching after polarization treatment, resulting in molecular chain orientation relative to the stretching direction and consequently, a large piezoelectric property in the stretching direction. Therefore, conventional electroacoustic conversion films exhibit in-plane anisotropy in their piezoelectric properties and anisotropy in the amount of planar stretching when a voltage is applied.

[0180] In contrast, the electroacoustic conversion film of the present invention, which contains piezoelectric particles 36 in the matrix 34, exhibits greater piezoelectric properties even without stretching after polarization treatment. Therefore, in the present invention, the polymeric composite piezoelectric material does not exhibit in-plane anisotropy in its piezoelectric properties, and when a driving voltage is applied as described later, it stretches isotropically in all directions in the in-plane direction.

[0181] The electroacoustic conversion film 10 of this invention can be manufactured using cut sheet materials, but roll to roll (hereinafter also referred to as RtoR) is preferred.

[0182] As is well known, RtoR is a manufacturing method in which raw materials are drawn out from a roll formed by winding long strips of raw materials, conveyed along the length direction, and subjected to various treatments such as film formation or surface treatment, and then the treated raw materials are wound back into a roll.

[0183] When manufacturing the electroacoustic conversion film 10 using the aforementioned manufacturing method via RtoR, a first roller is used, which is formed by a sheet 10a that forms a lower electrode 24 above the lower protective layer 28 of a long strip, and a second roller is used, which is formed by a sheet 10c that forms an upper electrode 26 above the upper protective layer 30 of a long strip.

[0184] The first and second rollers can be exactly the same.

[0185] Sheet 10a is drawn out from the roller, conveyed along the length direction, and coated with a coating containing matrix 34 and piezoelectric particles 36. It is dried by heating or the like, and a piezoelectric layer 20 is formed above the lower electrode 24 as the aforementioned laminate 10b.

[0186] Next, the piezoelectric layer 20 undergoes a polarization treatment. Here, the piezoelectric layer 20 is polarized during the fabrication of the electroacoustic conversion film 10 using the RtoR process. Additionally, as mentioned earlier, a calendering process can be performed prior to this polarization treatment.

[0187] Next, sheet 10c is drawn out from the second roller, and sheet 10c and laminate are conveyed. Using a known method such as using bonding rollers, as described above, the upper electrode 26 is oriented toward the piezoelectric layer 20, and sheet 10c is laminated on top of laminate 10b.

[0188] Then, the stacked body 10b and sheet 10c are clamped by heated rollers and heat-pressed to complete the electroacoustic conversion film 10 of the present invention, and the electroacoustic conversion film 10 is wound into a roll.

[0189] Furthermore, in the above example, the electroacoustic conversion film 10 of the present invention is produced by conveying the sheet (laminated body) along the length direction only once via RtoR, but it is not limited to this.

[0190] For example, after forming the aforementioned laminate 10b and performing polarization treatment, a laminate roller is formed to wind the laminate into a roll in one go. Next, the laminate is drawn out from the laminate roller, conveyed along the length direction, and as described above, a sheet-like object forming the upper electrode 26 is laminated on top of the upper protective layer 30, thereby completing the electroacoustic conversion film 10, which is then wound into a roll.

[0191] In this electroacoustic conversion film 10, if a voltage is applied to the lower electrode 24 and the upper electrode 26, the piezoelectric particles 36 stretch and contract in the polarization direction according to the applied voltage. As a result, the electroacoustic conversion film 10 (piezoelectric layer 20) contracts in the thickness direction. Simultaneously, due to Poisson's ratio, the electroacoustic conversion film 10 also stretches and contracts in the in-plane direction. This stretching and contraction is approximately 0.01% to 0.1%. Furthermore, as described above, it stretches and contracts isotropically in all directions in the in-plane direction.

[0192] As described above, the thickness of the piezoelectric layer 20 is preferably about 10 to 300 μm. Therefore, the maximum stretching in the thickness direction is about 0.3 μm, which is very small.

[0193] In contrast, the electroacoustic conversion film 10, i.e., the piezoelectric layer 20, has a dimension in the planar direction that is much larger than its thickness. Therefore, for example, if the length of the electroacoustic conversion film 10 is 20 cm, the electroacoustic conversion film 10 can stretch or shrink by a maximum of about 0.2 mm when a voltage is applied.

[0194] Furthermore, when pressure is applied to the electroacoustic conversion film 10, electricity is generated through the action of the piezoelectric particles 36.

[0195] By utilizing this, as described above, the electroacoustic conversion film 10 can be used for various applications such as loudspeakers, microphones, and pressure sensors.

[0196] [Piezoelectric speaker]

[0197] Figure 5 A conceptual diagram showing an example of a planar piezoelectric loudspeaker having the electroacoustic conversion film 10 of the present invention.

[0198] The piezoelectric speaker 45 is a planar piezoelectric speaker that uses the electroacoustic conversion film 10 of the present invention as a vibrating plate to convert electrical signals into vibrational energy. In addition, the piezoelectric speaker 45 can also be used as a microphone and sensor.

[0199] The piezoelectric loudspeaker 45 is configured to have an electroacoustic conversion diaphragm 10, a housing 43, a viscoelastic support 46, and a frame 48.

[0200] The outer shell 43 is a thin, rectangular cylindrical shell with an open surface, formed of plastic or the like.

[0201] Furthermore, the frame 48 is a plate material with a through hole in the center and the same shape as the upper end face (open side) of the outer shell 43.

[0202] The viscoelastic support 46 has suitable viscosity and elasticity to support the electroacoustic conversion film 10, and by applying a constant mechanical bias at any point on the electroacoustic conversion film, the stretching motion of the electroacoustic conversion film 10 is effectively converted into forward and backward motion (motion in a direction perpendicular to the film surface). Examples include nonwoven fabrics such as wool felt, rayon, or PET-containing wool felt, and glass wool.

[0203] The piezoelectric speaker 45 is configured such that a viscoelastic support 46 is housed in the housing 43, the housing 43 and the viscoelastic support 46 are covered by an electroacoustic conversion film 10, and the frame 48 is fixed to the housing 43 while the periphery of the electroacoustic conversion film 10 is pressed against the upper surface of the housing 43 by the frame 48.

[0204] Here, in the piezoelectric loudspeaker 45, the viscoelastic support 46 is a square prism whose height (thickness) is thicker than the height of the inner surface of the outer shell 43.

[0205] Therefore, in the piezoelectric loudspeaker 45, the viscoelastic support 46 is held at its periphery while being pressed downwards by the electroacoustic conversion film 10, resulting in a thinner thickness. Furthermore, also at the periphery of the viscoelastic support 46, the curvature of the electroacoustic conversion film 10 changes abruptly, forming a raised portion 45a on the electroacoustic conversion film 10 that slopes downwards towards the periphery of the viscoelastic support 46. Moreover, the central region of the electroacoustic conversion film 10 is pressed down by the four-cornered prism-shaped viscoelastic support 46, becoming (slightly) planar.

[0206] In the piezoelectric loudspeaker 45, when a driving voltage is applied to the lower electrode 24 and the upper electrode 26, causing the electroacoustic conversion film 10 to elongate in the in-plane direction, the erected portion 45a of the electroacoustic conversion film 10 changes its angle in the erecting direction by means of the viscoelastic support 46 in order to absorb this elongation. As a result, the electroacoustic conversion film 10, which has a planar portion, moves upward.

[0207] Conversely, when a driving voltage is applied to the lower electrode 24 and the upper electrode 26, causing the electroacoustic conversion film 10 to contract inward, the upright portion 45a of the electroacoustic conversion film 10 changes its angle in the tilting direction (approaching the plane) to absorb the amount of contraction. As a result, the electroacoustic conversion film 10, which has a planar portion, moves downward.

[0208] The piezoelectric loudspeaker 45 generates sound through the vibration of the electroacoustic conversion diaphragm 10.

[0209] Furthermore, in the electroacoustic conversion film 10 of the present invention, the conversion from stretching motion to vibration can also be achieved by keeping the electroacoustic conversion film 10 in a bent state.

[0210] Therefore, the electroacoustic conversion film 10 of the present invention can function as a flexible speaker even if it is not such a piezoelectric speaker 45 but is simply kept in a bent state.

[0211] [Electroacoustic converter]

[0212] The electroacoustic converter of the present invention is an electroacoustic converter having:

[0213] An electroacoustic conversion film comprising a polymer composite piezoelectric body containing piezoelectric particles within a polymer matrix and electrode layers formed on both sides of the polymer composite piezoelectric body; and

[0214] A vibrating plate, layered on an electroacoustic conversion film.

[0215] The coefficient of thermal expansion of the electroacoustic transducer is 12ppm / ℃~100ppm / ℃.

[0216] Figure 6 This conceptually represents an example of an electroacoustic converter of the present invention having the electroacoustic conversion film of the present invention.

[0217] Figure 6 The electroacoustic transducer 51 shown has an electroacoustic conversion film 10 and a vibrating plate 12. The electroacoustic conversion film 10 is the electroacoustic conversion film of the present invention described above.

[0218] In the electroacoustic converter 51, the electroacoustic conversion film 10 and the vibrating plate 12 are bonded together by the adhesive layer 16.

[0219] A power supply PS for applying a driving voltage is connected to the electroacoustic conversion film 10 of the electroacoustic converter 51.

[0220] exist Figure 6 In this context, the electroacoustic conversion film 10 may have a lower protective layer 28 and an upper protective layer 30. However, in... Figure 6In the electroacoustic transducer 51 shown, the electroacoustic conversion film 10 may also be a structure without a lower protective layer 28 and / or an upper protective layer 30. As an example, in... Figure 6 In the example shown, it is also possible to have a structure that only has a lower protective layer 28 and does not have a protective layer (upper protective layer 30) on the side of the vibrating plate 12.

[0221] This electroacoustic transducer 51 applies a driving voltage to the electroacoustic conversion film 10, causing the film 10 to stretch and contract in the planar direction. This stretching and contraction of the film 10 causes the vibrating plate 12 to flex, resulting in vibration in the thickness direction. This vibration in the thickness direction generates sound. The vibrating plate 12 vibrates according to the magnitude of the driving voltage applied to the electroacoustic conversion film 10, producing sound corresponding to the applied driving voltage.

[0222] That is, the electroacoustic converter 51 is a loudspeaker that uses the electroacoustic conversion film 10 as an exciter.

[0223] In the electroacoustic converter 51, the vibrating plate 12 is preferably flexible. Furthermore, in this invention, "flexible" has the same meaning as in the usual interpretation, indicating the ability to bend and flex; specifically, it means the ability to bend and stretch without causing damage or harm.

[0224] The vibrating plate 12 is preferably flexible, and there are no restrictions as long as it satisfies the relationship with the electroacoustic conversion film 10 (or the laminated piezoelectric element 14 described later), and various sheet-like materials (plate-like materials, films) can be used.

[0225] Examples include resin films made of polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS), polycarbonate (PC), polyphenylene sulfide (PPS), polymethyl methacrylate (PMMA), polyetherimide (PEI), polyimide (PI), polyethylene naphthalate (PEN), triacetyl cellulose (TAC), and cyclic olefin resins; foamed plastics made of expanded polystyrene, expanded polystyrene, and expanded polyethylene; and various corrugated cardboard materials made by attaching other cardboard to one or both sides of a corrugated cardboard.

[0226] Furthermore, in the electroacoustic converter 51, as long as it is flexible, the vibrating plate 12 can preferably be a display device such as an organic light-emitting diode (OLED) display, a liquid crystal display, a micro LED (Light Emitting Diode) display, or an inorganic light-emitting diode display.

[0227] exist Figure 6 In the electroacoustic transducer 51 shown, the vibrating plate 12 and the electroacoustic conversion film 10 are preferably bonded together by an adhesive layer 16.

[0228] As long as the adhesive layer 16 can adhere the vibrating plate 12 and the electroacoustic conversion film 10, various known adhesive layers can be used.

[0229] Therefore, the adhesive layer 16 can be a layer composed of an adhesive that is fluid when bonded and then becomes solid, or it can be a layer composed of an adhesive that is a soft solid that is gel-like (rubber-like) when bonded and then remains gel-like, or it can be a layer composed of a material that has the characteristics of both an adhesive and an adhesive.

[0230] Here, in the electroacoustic transducer 51, sound is generated by stretching and contracting the electroacoustic conversion diaphragm 10, causing the vibrating plate 12 to flex and vibrate. Therefore, in the electroacoustic transducer 51, it is preferable that the stretching and contraction of the electroacoustic conversion diaphragm 10 is directly transmitted to the vibrating plate 12. If there is a viscous substance with relaxation vibration between the vibrating plate 12 and the electroacoustic conversion diaphragm 10, the energy transmission efficiency of the stretching and contraction of the electroacoustic conversion diaphragm 10 to the vibrating plate 12 is reduced, resulting in a decrease in the driving efficiency of the electroacoustic transducer 51.

[0231] With this in mind, the adhesive layer 16 is preferably an adhesive layer composed of an adhesive, which can result in a solid adhesive layer 16 that is harder than an adhesive layer composed of an adhesive. As a more preferred adhesive layer 16, specifically, an adhesive layer composed of thermoplastic adhesives such as polyester adhesives and styrene-butadiene rubber (SBR) adhesives can be exemplified.

[0232] Adhesion differs from bonding and is useful when high bonding temperatures are required. Furthermore, thermoplastic adhesives combine "relatively low temperature, short bonding time, and strong adhesion," making them a preferred choice.

[0233] There is no limit to the thickness of the adhesive layer 16. The thickness can be appropriately set to obtain sufficient adhesive force (bonding force, adhesion force) according to the material of the adhesive layer 16.

[0234] In the electroacoustic converter 51, the thinner the adhesive layer 16, the better the transmission effect of the stretching energy (vibration energy) of the electroacoustic conversion film 10 transmitted to the vibrating plate 12, thereby improving energy efficiency. However, if the adhesive layer 16 is thick and has high rigidity, the stretching of the electroacoustic conversion film 10 may be restricted.

[0235] With this in mind, it is preferable that the adhesive layer 16 is relatively thin. Specifically, the thickness of the adhesive layer 16, based on the thickness after adhesion, is preferably 0.1 to 50 μm, more preferably 0.1 to 30 μm, and even more preferably 0.1 to 10 μm.

[0236] In addition, in the electroacoustic converter 51, the adhesive layer 16 is provided as a preferred embodiment, but is not an essential component.

[0237] Therefore, the electroacoustic transducer 51 may also be without the adhesive layer 16, and the vibrating plate 12 and the electroacoustic transducer 10 may be fixed using known crimping, fastening, and fixing methods. For example, if the electroacoustic transducer 10 is rectangular, the four corners may be fastened using components such as bolts and nuts to form the electroacoustic transducer, or the four corners and the center may be fastened using components such as bolts and nuts to form the electroacoustic transducer.

[0238] However, in this case, when a driving voltage is applied from the power supply PS, the electroacoustic conversion diaphragm 10 stretches and contracts independently relative to the diaphragm 12. Depending on the situation, only the electroacoustic conversion diaphragm 10 flexes, and the stretching and contraction of the electroacoustic conversion diaphragm 10 is not transmitted to the diaphragm 12. Thus, when the electroacoustic conversion diaphragm 10 stretches and contracts independently relative to the diaphragm 12, the vibration efficiency of the diaphragm 12 caused by the electroacoustic conversion diaphragm 10 decreases, and the diaphragm 12 may not be able to vibrate sufficiently.

[0239] With this in mind, the vibrating plate 12 and the electroacoustic conversion film 10, as Figure 6 As shown, it is preferable to use adhesive layer 16 for pasting.

[0240] In the electroacoustic converter 51, a power supply PS is connected to the lower electrode 24 and the upper electrode 26 of the electroacoustic conversion film 10. The power supply PS applies a driving voltage to make the electroacoustic conversion film 10 expand and contract, that is, supplies driving power.

[0241] There are no restrictions on the power supply PS; it can be either a DC power supply or an AC power supply. Furthermore, the driving voltage can be appropriately set to accurately drive the electroacoustic conversion film 10, depending on the thickness and forming material of the piezoelectric layer 20 of the electroacoustic conversion film 10.

[0242] There are no restrictions on the method of drawing out electrodes from the lower electrode 24 and the upper electrode 26; various known methods can be used.

[0243] As an example, methods can be illustrated such as connecting a conductive material such as copper foil to the lower electrode 24 and the upper electrode 26 to lead the electrode outward, and forming through holes in the lower protective layer 28 and the upper protective layer 30 by means of a laser, and filling the through holes with conductive material to lead the electrode outward.

[0244] Preferred electrode extraction methods include those described in Japanese Patent Application Publication No. 2014-209724 and Japanese Patent Application Publication No. 2016-015354.

[0245] As described above, the piezoelectric layer 20 is formed by containing piezoelectric particles 36 in the matrix 34. Furthermore, the lower electrode 24 and the upper electrode 26 are provided such that the piezoelectric layer 20 is sandwiched in the thickness direction.

[0246] If a voltage is applied to the lower electrode 24 and upper electrode 26 of the electroacoustic conversion film 10 having this piezoelectric layer 20, the piezoelectric particles 36 stretch and contract in the polarization direction according to the applied voltage. As a result, the electroacoustic conversion film 10 (piezoelectric layer 20) contracts in the thickness direction. At the same time, due to Poisson's ratio, the electroacoustic conversion film 10 also stretches and contracts in the in-plane direction.

[0247] This expansion / contraction is approximately 0.01% to 0.1%.

[0248] As described above, the thickness of the piezoelectric layer 20 is preferably about 10 to 300 μm. Therefore, the maximum stretching in the thickness direction is about 0.3 μm, which is very small.

[0249] In contrast, the electroacoustic conversion film 10, i.e., the piezoelectric layer 20, has a dimension in the planar direction that is much larger than its thickness. Therefore, for example, if the length of the electroacoustic conversion film 10 is 20 cm, the electroacoustic conversion film 10 can stretch or shrink by a maximum of about 0.2 mm when a voltage is applied.

[0250] The vibrating plate 12 is attached to the electroacoustic conversion film 10 via the adhesive layer 16. Therefore, due to the expansion and contraction of the electroacoustic conversion film 10, the vibrating plate 12 flexes, resulting in the vibrating plate 12 vibrating in the thickness direction.

[0251] The vibrating plate 12 generates sound through vibration in the thickness direction. That is, the vibrating plate 12 vibrates according to the magnitude of the voltage (driving voltage) applied to the electroacoustic conversion film 10, producing sound corresponding to the driving voltage applied to the electroacoustic conversion film 10.

[0252] As mentioned above, typical electroacoustic conversion films made of polymer materials such as PVDF exhibit in-plane anisotropy in piezoelectric properties and anisotropy in the amount of expansion and contraction in the plane direction when a voltage is applied.

[0253] In contrast, Figure 6 In the electroacoustic transducer 51 shown, the electroacoustic conversion film 10 has no in-plane anisotropy in its piezoelectric properties, but is isotropic in all directions in the in-plane direction. That is, in Figure 6 In the electroacoustic converter 51 shown, the electroacoustic conversion film 10 is isotropically stretched in two dimensions.

[0254] Compared to conventional electroacoustic conversion films such as PVDF that are stacked and stretch in only one direction, the isotropic two-dimensional electroacoustic conversion film 10 can vibrate the diaphragm 12 with greater force, producing a louder and more pleasant sound.

[0255] In addition, Figure 6 In this design, the size of the surface direction of the electroacoustic conversion film 10 and the size of the surface direction of the vibrating plate 12 are set to be approximately the same, but this is not a limitation. For example, the size of the surface direction of the electroacoustic conversion film 10 may also be smaller than the size of the surface direction of the vibrating plate 12.

[0256] In this invention, the coefficient of thermal expansion of the electroacoustic converter is 12ppm / ℃ to 100ppm / ℃.

[0257] Similar to the aforementioned electroacoustic conversion film, it can be seen that in electroacoustic converters with both an electroacoustic conversion film and a vibrating plate, a decrease in sound pressure also exists when used in a high-temperature environment. That is, the following problem also exists in electroacoustic converters: in a high-temperature environment, due to the expansion of the polymer composite piezoelectric matrix, the distance between the piezoelectric particles dispersed in the matrix widens, making it difficult for the deformation of the piezoelectric particles to be transmitted to the matrix, thereby reducing the piezoelectric conversion efficiency.

[0258] In contrast, in the electroacoustic transducer of the present invention, by setting the coefficient of thermal expansion of the transducer to 12ppm / ℃ to 100ppm / ℃, the matrix expansion of the polymer composite piezoelectric is suppressed in a high-temperature environment, and the widening of the distance between the piezoelectric particles dispersed in the matrix is ​​suppressed. As a result, since the deformation (vibration) of the piezoelectric particles is more preferably transmitted to the matrix, the reduction in the piezoelectric conversion efficiency of the transducer can be suppressed.

[0259] From the viewpoint that it is possible to more effectively suppress the decrease in piezoelectric conversion efficiency of the electroacoustic transducer under high temperature conditions and to suppress the damage to the piezoelectric layer, the coefficient of thermal expansion of the electroacoustic transducer is preferably 12ppm / ℃ to 100ppm / ℃, more preferably 16ppm / ℃ to 70ppm / ℃, and even more preferably 18ppm / ℃ to 55ppm / ℃.

[0260] Here, the thermal expansion coefficient of the electroacoustic converter can be measured by cutting out a sample at the location of the stacked electroacoustic conversion film and the vibrating plate, and using the same method as in the case of the electroacoustic conversion film.

[0261] One method to set the coefficient of thermal expansion of the electroacoustic transducer to the aforementioned range is to use an electroacoustic transducer film with a low coefficient of thermal expansion and a vibrating plate with a low coefficient of thermal expansion.

[0262] Specifically, as the electroacoustic conversion film, it is preferable to use an electroacoustic conversion film with a coefficient of thermal expansion in the range of 12 ppm / ℃ to 100 ppm / ℃. That is, it is preferable to use the electroacoustic conversion film of the present invention described above.

[0263] Furthermore, as a vibrating plate, vibrating plates with low coefficients of thermal expansion, such as polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS), polycarbonate (PC), polyphenylene sulfide (PPS), polymethyl methacrylate (PMMA), polyetherimide (PEI), polyimide (PI), polyethylene naphthalate (PEN), and triacetyl cellulose (TAC), are preferred.

[0264] Furthermore, inorganic films with low coefficients of thermal expansion, such as silicon oxide film and aluminum oxide film, can be formed on the surface of the vibrating plate to reduce the coefficient of thermal expansion of the vibrating plate.

[0265] Furthermore, display devices that use these vibrating plates as part of their components, such as organic light-emitting diode (OLED) displays, liquid crystal displays, micro LED (Light-Emitting Diode) displays, and inorganic light-emitting diode displays, can also be used as vibrating plates.

[0266] Furthermore, in the electroacoustic converter of the present invention, the coefficient of thermal expansion of the electroacoustic conversion film may be outside the range of 12ppm / ℃ to 100ppm / ℃, but in order to set the coefficient of thermal expansion of the electroacoustic converter to the above range, the coefficient of thermal expansion of the electroacoustic conversion film is preferably in the range of 12ppm / ℃ to 100ppm / ℃.

[0267] In this invention, the absolute value of the difference between the thermal expansion coefficient of the electroacoustic conversion film and the thermal expansion coefficient of the vibrating plate is preferably 0 ppm / ℃ to 80 ppm / ℃.

[0268] If the absolute value of the difference between the thermal expansion coefficients of the electroacoustic conversion film and the diaphragm (hereinafter also referred to as the difference in thermal expansion coefficients) is large, then under high-temperature conditions, the difference in thermal expansion between the electroacoustic conversion film and the diaphragm may generate internal stress at the interface between the electroacoustic conversion film and the diaphragm, leading to delamination at the interface. If the electroacoustic conversion film delaminates from the diaphragm, the vibration of the electroacoustic conversion film will be difficult to transmit to the diaphragm, thus potentially reducing acoustic performance (piezoelectric conversion efficiency). In particular, under repeated temperature changes, if the difference between the thermal expansion coefficients of the electroacoustic conversion film and the diaphragm is large, delamination is more likely to occur at the interface between the electroacoustic conversion film and the diaphragm.

[0269] In contrast, by setting the difference between the thermal expansion coefficient of the electroacoustic conversion film and the thermal expansion coefficient of the vibrating plate to 0ppm / ℃~80ppm / ℃, it is possible to suppress the peeling of the electroacoustic conversion film from the vibrating plate due to high temperature environment or repeated temperature changes, thereby suppressing the reduction of piezoelectric conversion efficiency.

[0270] From the viewpoint of being able to suppress the peeling of the electroacoustic conversion film from the diaphragm, the difference between the coefficient of thermal expansion of the electroacoustic conversion film and the coefficient of thermal expansion of the diaphragm is preferably 0 ppm / ℃ to 80 ppm / ℃, more preferably 0 ppm / ℃ to 50 ppm / ℃, and even more preferably 0 ppm / ℃ to 30 ppm / ℃.

[0271] The difference between the thermal expansion coefficient of the electroacoustic conversion film and the thermal expansion coefficient of the vibrating plate can be calculated by taking the electroacoustic conversion film and the vibrating plate out of the electroacoustic converter and measuring their respective thermal expansion coefficients using the method described above.

[0272] Furthermore, in the electroacoustic converter of the present invention, the loss tangent (Tanδ) of the electroacoustic conversion film at a frequency of 1 Hz and 60°C, as measured by dynamic viscoelasticity, is preferably 0.03 or higher.

[0273] By setting the loss tangent (Tanδ) of the electroacoustic conversion film at a frequency of 1Hz and 60℃ to 0.03 or higher, the electroacoustic conversion film exhibits viscosity under high-temperature conditions. Therefore, under high-temperature conditions or repeated temperature changes, the stress generated by the difference between the thermal expansion coefficient of the electroacoustic conversion film and the thermal expansion coefficient of the vibrating plate can be relaxed based on this viscosity, thereby suppressing the peeling of the electroacoustic conversion film from the vibrating plate.

[0274] From the viewpoint of being able to suppress the peeling of the electroacoustic conversion film from the diaphragm, the loss tangent (Tanδ) of the electroacoustic conversion film at a frequency of 1 Hz and 60°C, as measured by dynamic viscoelasticity, is preferably 0.03 or more, more preferably 0.04 or more, and even more preferably 0.07 or more.

[0275] exist Figure 6 The electroacoustic converter 51 shown is configured to have a structure with an electroacoustic conversion film 10, but is not limited to this.

[0276] Figure 7 This conceptually illustrates an example of an electroacoustic transducer having the electroacoustic conversion film 10 of the present invention.

[0277] Figure 7 The electroacoustic transducer 50 shown has a stacked piezoelectric element 14 and a vibrating plate 12. The stacked piezoelectric element 14 is formed by stacking multiple layers of the electroacoustic conversion film of the present invention. Figure 7 In the example shown, the stacked piezoelectric element 14 is formed by stacking three layers of the electroacoustic conversion film 10 of the present invention described above.

[0278] In the electroacoustic converter 50, the stacked piezoelectric element 14 and the vibrating plate 12 are bonded together by the adhesive layer 16.

[0279] A power supply PS for applying a driving voltage is connected to the electroacoustic conversion film 10 of the stacked piezoelectric element 14 constituting the electroacoustic converter 50.

[0280] in addition, Figure 7 The electroacoustic conversion film 10 is replaced by a stacked piezoelectric element 14, and in addition, it has the same... Figure 6 Since they have the same structure, the same symbols are used to mark the same parts. The following descriptions will mainly focus on the different parts.

[0281] To simplify the accompanying drawings, Figure 7 The lower protective layer 28 and the upper protective layer 30 are omitted. However, Figure 7 As a preferred embodiment, the stacked piezoelectric element 14 shown has both a lower protective layer 28 and an upper protective layer 30 in all electroacoustic conversion films 10.

[0282] Furthermore, the laminated piezoelectric element is not limited to this; it can contain a mixture of electroacoustic conversion films with and without protective layers. Moreover, when the electroacoustic conversion film has a protective layer, it may have only the lower protective layer 28 or only the upper protective layer 30. As an example, if... Figure 7 The three-layer stacked piezoelectric element 14 shown in the figure can also be a structure in which the uppermost electroacoustic conversion film has only an upper protective layer 30, the middle electroacoustic conversion film has no protective layer, and the lowermost electroacoustic conversion film has only a lower protective layer 28.

[0283] Regarding this point, as will be discussed later... Figure 8 The stacked piezoelectric element 56 shown is Figure 9 The same applies to the stacked piezoelectric element 60 shown.

[0284] As will be described in detail later, this electroacoustic transducer 50 applies a driving voltage to the electroacoustic transducer film 10 of the stacked piezoelectric element 14, causing the electroacoustic transducer film 10 to stretch and expand in the planar direction. Through the stretching and expansion of the electroacoustic transducer film 10, the stacked piezoelectric element 14 stretches and expands in the planar direction.

[0285] The vibrating plate 12 flexes due to the expansion and contraction of the laminated piezoelectric element 14 in the planar direction, resulting in vibration of the vibrating plate 12 in the thickness direction. This vibration in the thickness direction generates sound. The vibrating plate 12 vibrates according to the magnitude of the driving voltage applied to the electroacoustic conversion film 10, producing sound corresponding to the driving voltage applied to the electroacoustic conversion film 10.

[0286] That is, the electroacoustic converter 50 is a loudspeaker that uses the stacked piezoelectric element 14 as an exciter.

[0287] exist Figure 7 In the electroacoustic transducer 50 shown, the stacked piezoelectric element 14 has a structure in which three electroacoustic conversion films 10 are stacked and adjacent electroacoustic conversion films 10 are bonded together using an adhesive layer 19. A power supply PS is connected to each electroacoustic conversion film 10 to apply a driving voltage that causes the electroacoustic conversion film 10 to expand and contract.

[0288] in addition, Figure 7 The piezoelectric element 14 shown is formed by stacking three electroacoustic conversion films 10, but the present invention is not limited thereto. That is, as long as the piezoelectric element is formed by stacking multiple electroacoustic conversion films 10, the number of stacked electroacoustic conversion films 10 can be two layers, or it can be four or more layers. This will be discussed later. Figure 8 The stacked piezoelectric element 56 shown is Figure 9 The same applies to the stacked piezoelectric element 60 shown.

[0289] In this invention, the coefficient of thermal expansion of the electroacoustic converter is set to 12ppm / ℃ to 100ppm / ℃ in the electroacoustic converter 50 that uses a stacked piezoelectric element 14 with multiple stacked electroacoustic conversion films 10. This suppresses the reduction in the piezoelectric conversion efficiency of the electroacoustic converter.

[0290] In addition, the thermal expansion coefficient of an electroacoustic converter using a stacked piezoelectric element with multiple stacked electroacoustic conversion films can be measured by cutting out a sample at the location of the stacked electroacoustic conversion films (stacked piezoelectric elements) and the vibrating plate, using the same method as in the case of electroacoustic conversion films.

[0291] Figure 7 The stacked piezoelectric element 14 shown is preferably configured such that the polarization directions of adjacent electroacoustic conversion films 10 are opposite to each other, and multiple layers are stacked. Figure 7 The example shown is a 3-layer electroacoustic conversion film 10, with adjacent electroacoustic conversion films 10 bonded together using an adhesive layer 19.

[0292] As long as the adhesive layer 19 can adhere to the adjacent electroacoustic conversion film 10, various known adhesive layers can be used.

[0293] Therefore, the adhesive layer 19 can be a layer made of the aforementioned adhesive, or a layer made of an adhesive, or a layer made of a material having the characteristics of both an adhesive and a binder.

[0294] Here, the stacked piezoelectric element 14 generates sound by causing the vibrating plate 12 to vibrate through the expansion and contraction of the stacked multiple electroacoustic conversion films 10. Therefore, it is preferable that the stacked piezoelectric element 14 directly transmits the expansion and contraction of each electroacoustic conversion film 10. If there is a viscous substance with relaxation vibration between the electroacoustic conversion films 10, the energy transmission efficiency of the expansion and contraction of the electroacoustic conversion films 10 is reduced, resulting in a decrease in the driving efficiency of the stacked piezoelectric element 14.

[0295] With this in mind, the adhesive layer 19 is preferably an adhesive layer composed of an adhesive, which can result in a solid adhesive layer 19 that is harder than an adhesive layer composed of an adhesive. As a more preferred adhesive layer 19, specifically, an adhesive layer composed of thermoplastic adhesives such as polyester adhesives and styrene-butadiene rubber (SBR) adhesives can be preferably exemplified.

[0296] Adhesion differs from bonding and is useful when high bonding temperatures are required. Furthermore, thermoplastic adhesives combine "relatively low temperature, short bonding time, and strong adhesion," making them a preferred choice.

[0297] There is no limit to the thickness of the adhesive layer 19. The thickness can be appropriately set to exhibit sufficient adhesive force according to the material in which the adhesive layer 19 is formed.

[0298] Here, in Figure 7 In the stacked piezoelectric element 14 shown, the thinner the adhesive layer 19, the better the energy transfer effect of the electroacoustic conversion film 10, thereby improving energy efficiency. However, if the adhesive layer 19 is thick and has high rigidity, the expansion and contraction of the electroacoustic conversion film 10 may be restricted.

[0299] With this in mind, it is preferable that the adhesive layer 19 is thinner than the piezoelectric layer 20. That is, in the stacked piezoelectric element 14, it is preferable that the adhesive layer 19 is rigid and thin. Specifically, the thickness of the adhesive layer 19, measured by the thickness after adhesion, is preferably 0.1 to 50 μm, more preferably 0.1 to 30 μm, and even more preferably 0.1 to 10 μm.

[0300] Additionally, as will be discussed later, in Figure 7 In the stacked piezoelectric element 14 shown, the polarization directions of adjacent electroacoustic conversion films are opposite to each other, and it is possible that no adjacent electroacoustic conversion films 10 are short-circuited with each other, thus making the adhesive layer 19 thinner.

[0301] exist Figure 7 In the stacked piezoelectric element 14 shown, if the spring constant (thickness × Young's modulus) of the adhesive layer 19 is high, the expansion and contraction of the electroacoustic conversion film 10 may be restricted. Therefore, it is preferable that the spring constant of the adhesive layer 19 is the same as or lower than the spring constant of the electroacoustic conversion film 10.

[0302] Specifically, the product of the thickness of the adhesive layer 19 and the storage modulus (E') at a frequency of 1 Hz based on dynamic viscoelasticity measurements is 2.0 × 10⁻⁶ at 0 °C. 6 Below N / m, preferably 1.0 × 10 N / m at 50°C 6 Below N / m.

[0303] Furthermore, regarding the internal loss of the adhesive layer at a frequency of 1 Hz obtained by dynamic viscoelasticity measurement, in the case of adhesive layer 19 made of adhesive, it is 1.0 or less at 25°C, and in the case of adhesive layer 19 made of adhesive, it is preferably 0.1 or less at 25°C.

[0304] Furthermore, in the stacked piezoelectric elements 14 constituting the electroacoustic converter 50, the adhesive layer 19 is provided as a preferred embodiment, but is not an essential component.

[0305] Therefore, the laminated piezoelectric element constituting the electroacoustic transducer may also be constructed without the adhesive layer 19, by using known crimping, fastening, and fixing methods to laminate the electroacoustic conversion film 10 and seal it tightly. For example, when the electroacoustic conversion film 10 is rectangular, the laminated piezoelectric element can be constructed by fastening the four corners with bolts and nuts, or by fastening the four corners and the center with bolts and nuts. Alternatively, after laminating the electroacoustic conversion film 10, the laminated piezoelectric element can be constructed by attaching adhesive tape to the periphery (end face).

[0306] However, in this case, when a driving voltage is applied from the power supply PS, each electroacoustic conversion film 10 expands and contracts independently, and depending on the situation, each layer of each electroacoustic conversion film 10 flexes in opposite directions to form gaps. Thus, when each electroacoustic conversion film 10 expands and contracts independently, the driving efficiency as a stacked piezoelectric element decreases, and the overall expansion and contraction of the stacked piezoelectric element becomes smaller, potentially preventing the contacting vibrating plate or the like from vibrating sufficiently. In particular, when each layer of the electroacoustic conversion film 10 flexes in opposite directions to form gaps, the reduction in driving efficiency as a stacked piezoelectric element is significant.

[0307] Taking this into consideration, such as Figure 7 As shown in the laminated piezoelectric element 14, the laminated piezoelectric element preferably has an adhesive layer 19 for bonding adjacent electroacoustic conversion films 10 to each other.

[0308] As will be described later, in Figure 7In this configuration, the adjacent electroacoustic conversion films 10 of the stacked piezoelectric element 14 have opposite polarization directions. Therefore, in adjacent electroacoustic conversion films 10, the lower electrodes 24 are opposite to each other and the upper electrodes 26 are opposite to each other. Thus, whether the power supply PS is AC or DC, it always supplies power of the same polarity between the opposite electrodes. For example, in... Figure 7 In the stacked piezoelectric element 14 shown, the upper electrode 26 of the bottommost electroacoustic conversion film 10 and the upper electrode 26 of the second layer (in the middle) electroacoustic conversion film 10 are always supplied with the same polarity of electricity, and the lower electrode 24 of the second layer electroacoustic conversion film 10 and the lower electrode 24 of the topmost electroacoustic conversion film 10 are always supplied with the same polarity of electricity.

[0309] As previously described, when a voltage is applied to the lower electrode 24 and upper electrode 26 of the electroacoustic conversion film 10, the piezoelectric particles 36 stretch and contract in the polarization direction according to the applied voltage. As a result, the electroacoustic conversion film 10 (piezoelectric layer 20) contracts in the thickness direction. At the same time, due to Poisson's ratio, the electroacoustic conversion film 10 also stretches and contracts in the in-plane direction.

[0310] The stacked piezoelectric element 14 is formed by stacking and bonding the electroacoustic conversion film 10. Therefore, if the electroacoustic conversion film 10 expands or contracts, the stacked piezoelectric element 14 will also expand or contract.

[0311] The vibrating plate 12 is attached to the laminated piezoelectric element 14 via an adhesive layer 16. Therefore, due to the expansion and contraction of the laminated piezoelectric element 14, the vibrating plate 12 flexes, resulting in the vibrating plate 12 vibrating in the thickness direction.

[0312] The vibrating plate 12 generates sound through vibration in the thickness direction. That is, the vibrating plate 12 vibrates according to the magnitude of the voltage (driving voltage) applied to the electroacoustic conversion film 10, producing sound corresponding to the driving voltage applied to the electroacoustic conversion film 10.

[0313] Figure 7 The stacked piezoelectric element 14 shown is formed by stacking multiple electroacoustic conversion films 10. In a preferred embodiment, the stacked piezoelectric element 14 is further bonded to adjacent electroacoustic conversion films 10 using an adhesive layer 19.

[0314] Therefore, even if each individual electroacoustic conversion film 10 has low rigidity and small stretching force, by stacking the electroacoustic conversion films 10, the rigidity becomes higher, and the stretching force of the stacked piezoelectric element 14 becomes larger. As a result, in the stacked piezoelectric element 14, even if the vibrating plate 12 has a certain degree of rigidity, it can be fully flexed with a large force, causing the vibrating plate 12 to vibrate fully in the thickness direction, thereby generating sound.

[0315] Furthermore, the thicker the piezoelectric layer 20, the greater the stretching force of the electroacoustic conversion film 10, but correspondingly, the driving voltage required for its stretching and contraction increases by the same amount. As mentioned above, in the stacked piezoelectric elements 14, the thickness of the preferred piezoelectric layer 20 is at most about 300 μm, so even if the voltage applied to each electroacoustic conversion film 10 is small, the electroacoustic conversion film 10 can stretch and contract sufficiently.

[0316] Here, in the electroacoustic converter 50, it is preferable that the product of the thickness of the stacked piezoelectric element 14 and the energy storage modulus at a frequency of 1 Hz and 25°C, based on dynamic viscoelasticity measurements, is 0.1 to 3 times the product of the thickness of the vibrating plate 12 and the Young's modulus.

[0317] As described above, the electroacoustic conversion film 10 of the present invention has good flexibility, and the stacked piezoelectric element 14 formed by stacking the electroacoustic conversion film 10 also has good flexibility.

[0318] On the one hand, the vibrating plate 12 has a certain degree of rigidity. If a highly rigid stacked piezoelectric element 14 is combined on such a vibrating plate 12, it becomes stiff and difficult to bend, which is detrimental to the flexibility of the electroacoustic converter 50.

[0319] In contrast, the product of the thickness of the stacked piezoelectric element 14 and the storage modulus at a frequency of 1 Hz and 25°C, measured based on dynamic viscoelasticity, is preferably less than three times the product of the thickness of the vibrating plate 12 and the Young's modulus. That is, the spring constant of the stacked piezoelectric element 14 is preferably less than three times that of the vibrating plate 12 when it moves slowly.

[0320] With this structure, the electroacoustic transducer can operate smoothly to slow movements caused by external forces such as bending and rolling, that is, it exhibits good flexibility to slow movements.

[0321] In the electroacoustic converter, more preferably, the product of the thickness of the stacked piezoelectric element 14 and the energy storage modulus at a frequency of 1 Hz and 25°C based on dynamic viscoelasticity is less than twice the product of the thickness of the vibrating plate 12 and the Young's modulus, further preferably less than once, and especially preferably less than 0.3 times.

[0322] On the other hand, considering the materials used in the laminated piezoelectric element 14, the preferred structure of the laminated piezoelectric element 14, etc., it is preferred that the product of the thickness of the laminated piezoelectric element 14 and the energy storage modulus at a frequency of 1 Hz and 25°C based on dynamic viscoelasticity measurement is more than 0.1 times the product of the thickness of the vibrating plate 12 and the Young's modulus.

[0323] In the electroacoustic transducer, the product of the thickness of the stacked piezoelectric element 14 and the storage modulus at a frequency of 1 kHz and 25°C in the master curve obtained by dynamic viscoelastic measurement is preferably 0.3 to 10 times the product of the thickness of the vibrating plate 12 and the Young's modulus. That is, when the stacked piezoelectric element 14 moves rapidly in the driven state, the spring constant is preferably 0.3 to 10 times that of the vibrating plate 12.

[0324] As described above, the electroacoustic transducer causes the vibrating plate 12 to vibrate by the expansion and contraction of the laminated piezoelectric element 14 in the planar direction, thereby generating sound. Therefore, the laminated piezoelectric element 14 preferably has a certain degree of rigidity (hardness, stiffness) for the vibrating plate 12 at frequencies in the audio frequency band (20Hz to 20kHz).

[0325] In the electroacoustic transducer, the product of the thickness of the stacked piezoelectric element 14 and the energy storage modulus at a frequency of 1 kHz and 25°C in the master curve obtained by dynamic viscoelastic measurement is preferably 0.3 times or more, more preferably 0.5 times or more, and even more preferably 1 times or more, the product of the thickness of the vibrating plate 12 and the Young's modulus. That is, when the stacked piezoelectric element 14 moves rapidly, the spring constant is preferably 0.3 times or more, more preferably 0.5 times or more, and even more preferably 1 times or more.

[0326] Thus, at audio frequencies, the rigidity of the stacked piezoelectric element 14 relative to the diaphragm 12 is sufficiently ensured, enabling the electroacoustic converter to output high sound pressure with high energy efficiency.

[0327] On the other hand, considering the materials that can be used in the stacked piezoelectric element 14, the preferred structure of the stacked piezoelectric element 14, etc., it is preferable that the product of the thickness of the stacked piezoelectric element 14 and the energy storage modulus at a frequency of 1 kHz and 25°C based on dynamic viscoelasticity measurement is less than 10 times the product of the thickness of the vibrating plate 12 and the Young's modulus.

[0328] Regarding the product of the aforementioned thickness and energy storage modulus, in the case where an electroacoustic conversion film 10 is used to construct an electroacoustic converter instead of a multilayered piezoelectric element 14 (e.g., ... Figure 6 The same applies to that structure.

[0329] Figure 7 As a preferred embodiment, the electroacoustic converter 50 shown above has electroacoustic conversion films 20 of adjacent piezoelectric films 10 of the stacked piezoelectric elements 14 having opposite polarization directions.

[0330] In the electroacoustic conversion thin film 10, the polarity of the voltage applied to the piezoelectric layer 20 corresponds to the polarization direction. Therefore, the polarity of the applied voltage is... Figure 7In the polarization direction indicated by the middle arrow, the polarity of the electrode on the side in which the arrow points (downstream of the arrow) is consistent with the polarity of the electrode on the opposite side (upstream of the arrow) in all electroacoustic conversion films 10.

[0331] exist Figure 7 In the example shown, the electrode on the side where the arrow indicating the polarization direction points is designated as the lower electrode 24, and the electrode on the opposite side is designated as the upper electrode 26. In all electroacoustic conversion films 10, the upper electrode 26 and the lower electrode 24 are made to have the same polarity.

[0332] Therefore, in the stacked piezoelectric elements 14 where the polarization directions of the piezoelectric layers 20 of adjacent electroacoustic conversion films 10 are opposite to each other, the upper electrodes 26 of adjacent electroacoustic conversion films 10 face each other on one surface, and the lower electrodes face each other on another surface. Therefore, in the stacked piezoelectric elements 14, even if the electrodes of adjacent electroacoustic conversion films 10 are in contact with each other, it is possible that there is no short circuit.

[0333] As described above, in order to make the laminated piezoelectric element 14 stretch and contract with good energy efficiency, it is preferable to make the adhesive layer 19 thinner so that the adhesive layer 19 does not hinder the stretching and contraction of the piezoelectric layer 20.

[0334] In contrast, even if the electrodes of adjacent electroacoustic conversion films 10 are in contact with each other, there is a possibility of no short circuit. Figure 7 In the stacked piezoelectric element 14 shown, the adhesive layer 19 may not be present. As a preferred method, even when the adhesive layer 19 is present, it can be made extremely thin as long as the necessary adhesive force can be obtained.

[0335] Therefore, the stacked piezoelectric element 14 can be stretched or contracted with high energy efficiency.

[0336] Furthermore, as described above, in the electroacoustic conversion film 10, the absolute amount of stretching and contraction of the piezoelectric layer 20 in the thickness direction is very small, and the stretching and contraction of the electroacoustic conversion film 10 is essentially only in the planar direction.

[0337] Therefore, even if the polarization directions of the stacked electroacoustic conversion films 10 are opposite, as long as the polarity of the voltage applied to the lower electrode 24 and the upper electrode 26 is correct, all the electroacoustic conversion films 10 will stretch and contract in the same direction.

[0338] In addition, the polarization direction of the electroacoustic conversion film 10 in the stacked piezoelectric element 14 can be detected using a d33 measuring instrument or the like.

[0339] Alternatively, the polarization direction of the electroacoustic conversion film 10 can be determined from the above-mentioned polarization processing conditions.

[0340] Figure 7The stacked piezoelectric element 14 shown is preferably made by fabricating a long strip (large area) of electroacoustic conversion film as described above, and cutting the long strip of electroacoustic conversion film into individual electroacoustic conversion films 10. Therefore, in this case, all the multiple electroacoustic conversion films 10 constituting the stacked piezoelectric element 14 are identical.

[0341] However, the present invention is not limited thereto. That is, in the electroacoustic transducer, the piezoelectric laminate can be of various structures, such as a structure formed by laminating electroacoustic transducer films with different layer structures, such as electroacoustic transducer films having a lower protective layer 28 and an upper protective layer 30 and electroacoustic transducer films without these, and a structure formed by laminating electroacoustic transducer films with different thicknesses of piezoelectric layer 20.

[0342] exist Figure 7 In the electroacoustic converter 50 shown, the stacked piezoelectric element 14 is formed by stacking multiple electroacoustic conversion films 10 with opposite polarization directions between adjacent electroacoustic conversion films. Preferably, adjacent electroacoustic conversion films 10 are bonded together using an adhesive layer 19.

[0343] The stacked piezoelectric element of the present invention is not limited thereto and can utilize various structures.

[0344] Figure 8 This is one example. Additionally, Figure 8 The stacked piezoelectric element 56 shown uses multiple components that are the same as those in the stacked piezoelectric element 14 described above. Therefore, the same components are labeled with the same symbols, and the different parts are mainly described.

[0345] Figure 8 The stacked piezoelectric element 56 shown is a more preferred embodiment of the stacked piezoelectric element in this invention, formed by stacking multiple layers of electroacoustic conversion films 10L by folding a long strip of electroacoustic conversion film 10L back and forth at least once, preferably multiple times, in the length direction. Furthermore, compared with the above... Figure 7 The stacked piezoelectric element 14 shown is the same as that shown. Figure 8 The stacked piezoelectric element 56 shown is also a preferred embodiment, in which an electroacoustic conversion film 10L formed by folding and stacking is attached using an adhesive layer 19.

[0346] By folding and stacking a long strip of electroacoustic conversion film 10L polarized in the thickness direction, the polarization directions of adjacent (opposite) electroacoustic conversion films 10L in the stacking direction are as follows: Figure 8 As indicated by the middle arrow, it becomes the opposite direction.

[0347] According to this structure, a stacked piezoelectric element 56 can be formed from a single long strip of electroacoustic conversion film 10L, and only one power supply PS is needed to apply the driving voltage. Furthermore, there can be one electrode leading out from the electroacoustic conversion film 10L.

[0348] Therefore, according to Figure 8 The stacked piezoelectric element 56 shown can reduce the number of parts, simplify the structure, improve the reliability of the piezoelectric element (module), and thus reduce costs.

[0349] like Figure 8 As shown in the laminated piezoelectric element 56, in the laminated piezoelectric element 56 formed by the folded-back elongated electroacoustic conversion film 10L, it is preferable to insert the core rod 58 by abutting the folded portion of the electroacoustic conversion film 10L against the electroacoustic conversion film 10L.

[0350] As described above, the lower electrode 24 and upper electrode 26 of the electroacoustic conversion film 10L are formed of a metal vapor-deposited film, etc. If the metal vapor-deposited film is bent at an acute angle, it is prone to cracking, and the electrode may break. That is, in Figure 8 In the stacked piezoelectric element 56 shown, cracks or other defects can easily enter the electrode on the inside of the bend.

[0351] In contrast, in the stacked piezoelectric element 56 formed by the folded-back elongated electroacoustic conversion film 10L, by inserting a core rod 58 into the folded portion of the electroacoustic conversion film 10L, bending of the lower electrode 24 and the upper electrode 26 can be prevented, thereby preferably preventing wire breakage.

[0352] In this invention, the laminated piezoelectric element can also use a conductive adhesive layer 19. In particular, in cases such as... Figure 8 In the stacked piezoelectric element 56 shown, which is formed by folding back and stacking a long strip of electroacoustic conversion film 10L, a conductive adhesive layer 19 can preferably be used.

[0353] In such Figure 7 and Figure 8 In the stacked piezoelectric elements with opposite polarization directions of the adjacent electroacoustic conversion films 10, the same polarity of electricity is supplied between the opposing electrodes in the stacked electroacoustic conversion films 10. Therefore, no short circuit occurs between the opposing electrodes.

[0354] On the other hand, as described above, the stacked piezoelectric element 56, which is formed by folding and stacking the electroacoustic conversion film 10L, is prone to electrode breakage on the inside of the bend at an acute angle.

[0355] Therefore, by using a conductive adhesive layer 19 to bond the laminated electroacoustic conversion film 10L, even if the electrode breaks on the inside of the bend, the adhesive layer 19 can ensure continuity, thus preventing breakage and significantly improving the reliability of the laminated piezoelectric element 56.

[0356] Here, the electroacoustic conversion film 10L constituting the laminated piezoelectric element 56 is preferably as follows: Figure 1As shown, the laminate has a lower protective layer 28 and an upper protective layer 30 such that it is opposite to and sandwiches the lower electrode 24 and the upper electrode 26.

[0357] In this case, even using a conductive adhesive layer 19 cannot guarantee conductivity. Therefore, when the electroacoustic conversion film 10L has a protective layer, through holes are provided in the lower protective layer 28 and upper protective layer 30 in the regions where the lower electrodes 24 and upper electrodes 26 of the stacked electroacoustic conversion films 10L are opposite each other, so that the lower electrodes 24 and upper electrodes 26 can contact the conductive adhesive layer 19. Preferably, the through holes formed in the lower protective layer 28 and upper protective layer 30 are blocked with silver paste or a conductive adhesive, and then adjacent electroacoustic conversion films 10L are adhered using the conductive adhesive layer 19.

[0358] The through holes in the lower protective layer 28 and the upper protective layer 30 can be formed by laser processing and removal of the protective layer based on solvent etching and mechanical polishing.

[0359] The through holes in the lower protective layer 28 and the upper protective layer 30 are preferably located in one or more areas where the lower electrodes 24 and the upper electrodes 26 of the stacked electroacoustic conversion film 10L are opposite each other, except at the curved portions. Alternatively, the through holes in the lower protective layer 28 and the upper protective layer 30 may be formed regularly or irregularly on the entire surface of the lower protective layer 28 and the upper protective layer 30.

[0360] There are no limitations on the conductive adhesive layer 19, and various known adhesive layers can be used.

[0361] In the above-described stacked piezoelectric elements, the polarization direction of the stacked electroacoustic conversion films 10 is opposite in adjacent electroacoustic conversion films 10, but the present invention is not limited thereto.

[0362] That is, in this invention, the stacked piezoelectric element formed by stacking the electroacoustic conversion thin film 10 can also be as follows: Figure 9 As shown in the stacked piezoelectric element 60, the polarization directions of all piezoelectric layers 20 are the same.

[0363] However, as Figure 9 As shown, in a stacked piezoelectric element 60 where all the polarization directions of the stacked electroacoustic conversion films 10 are the same, the lower electrode 24 and the upper electrode 26 of adjacent electroacoustic conversion films 10 are opposite each other. Therefore, if the adhesive layer 19 is not thick enough, the lower electrode 24 and the upper electrode 26 of adjacent electroacoustic conversion films 10 may come into contact at the outer end of the adhesive layer 19 in the planar direction, potentially causing a short circuit.

[0364] Therefore, as Figure 9 As shown, in a stacked piezoelectric element 60 where the polarization directions of all the stacked electroacoustic conversion films 10 are the same, the adhesive layer 19 cannot be thinned. Regarding energy efficiency, for Figure 7 and Figure 8 The stacked piezoelectric element shown is undesirable.

[0365] The electroacoustic conversion film and electroacoustic converter of the present invention have been described in detail above. However, the present invention is not limited to the above examples. Various improvements or modifications can be made without departing from the spirit of the present invention.

[0366] Example

[0367] The following are specific embodiments of the present invention to provide a more detailed description of the invention.

[0368] [Example 1-1]

[0369] <Preparation of Coatings>

[0370] First, cyanoethylated PVA (manufactured by CR-V Shin-Etsu Chemical Co., Ltd.) was dissolved in dimethylformamide (DMF) at the following composition ratio. Then, PZT particles were added to the solution at the following composition ratio and dispersed using a propeller mixer (2000 rpm) to prepare a coating for forming a piezoelectric layer.

[0371] (coating)

[0372] PZT particles... 300 parts by mass

[0373] • Cyanoethylated PVA……10 parts by weight

[0374] ·DMF……70 parts by weight

[0375] In addition, the PZT particles are made by sintering commercially available PZT raw material powder at 1000-1200℃, and then crushing and classifying it into particles with an average particle size of 5μm.

[0376] <Coating of Paint>

[0377] On one hand, a sheet-like material is prepared by vacuum evaporating a 0.1 μm thick copper film onto a 4 μm thick PET film. That is, in this example, the thin film electrode is a 0.1 μm thick copper vapor-deposited film, and the protective layer is a 4 μm thick PET film.

[0378] Above the thin-film electrode (copper vapor-deposited thin film) of the sheet-like material, a coating material for forming the previously prepared piezoelectric layer is applied using a sliding coating machine. Furthermore, the coating is applied so that the film thickness after drying is 40 μm.

[0379] <Drying of Coatings>

[0380] Next, the coating material is applied to the sheet and then heated and dried on a heating plate at 100°C, thereby causing the DMF to evaporate. This creates a laminate consisting of a copper thin-film electrode on top of a PET protective layer, and a 40 μm thick piezoelectric layer (polymer composite piezoelectric) formed thereon.

[0381] <Polarization Treatment>

[0382] Next, the piezoelectric layer of the stack was polarized.

[0383] <Layering of sheet-like objects>

[0384] Above the polarized laminate, the thin film electrode (copper film side) is aligned with the piezoelectric layer. Next, the laminate and the sheet are heat-pressed onto the piezoelectric layer and the thin film electrode at 120°C using a laminating apparatus.

[0385] <Aging Treatment>

[0386] Next, the hot-pressed laminate will be heat-treated at 75°C for 72 hours.

[0387] The electroacoustic conversion film was manufactured using the above process.

[0388] <Measurement of the coefficient of thermal expansion of electroacoustic conversion films>

[0389] Thermomechanical properties were measured using a thermomechanical analysis apparatus (TMA4000SE, manufactured by TMA NETZSCH). The sample size was set to 5 mm × 20 mm, the distance between the suction cups was set to 15 mm, and the length of the suction cups was set to 2.5 ± 0.5 mm both vertically and horizontally.

[0390] After the sample was installed, the temperature was changed at a rate of 5°C / min within the range of -20°C to 60°C, and the displacement of the distance between the suction cups was measured. Furthermore, regarding the load, a constant weight of 3g was applied to the sample, and measurements were performed.

[0391] Next, the slope of the approximate straight line representing the displacement data from -20℃ to 60℃ was determined, thus calculating the displacement per 1℃ temperature change. Then, the coefficient of thermal expansion was calculated by dividing this slope by the distance between the suction cups when the sample was placed, which was 15mm.

[0392] The measured coefficient of thermal expansion is 12 ppm / ℃.

[0393] [Examples 1-2]

[0394] The composition ratio of the coating that will become the piezoelectric layer is set as follows. Otherwise, an electroacoustic conversion film was made in the same manner as in Example 1-1.

[0395] (coating)

[0396] PZT particles... 300 parts by mass

[0397] • Cyanoethylated PVA……15 parts by weight

[0398] ·DMF……70 parts by weight

[0399] [Examples 1-3]

[0400] The composition ratio of the coating that will become the piezoelectric layer is set as follows. Otherwise, an electroacoustic conversion film was made in the same manner as in Example 1-1.

[0401] (coating)

[0402] PZT particles... 300 parts by mass

[0403] • Cyanoethylated PVA……30 parts by weight

[0404] ·DMF……70 parts by weight

[0405] [Examples 1-4]

[0406] The aging treatment conditions of the laminated body after hot pressing were changed to a heat treatment at 65°C for 72 hours. Otherwise, an electroacoustic conversion film was made in the same manner as in Examples 1-3.

[0407] [Examples 1-5]

[0408] The aging treatment conditions of the laminated body after hot pressing were changed to a heat treatment at 55°C for 72 hours. Otherwise, an electroacoustic conversion film was made in the same manner as in Examples 1-3.

[0409] [Comparative Example 1-1]

[0410] The composition ratio of the coating that will become the piezoelectric layer is set as follows. Otherwise, an electroacoustic conversion film was made in the same manner as in Example 1-1.

[0411] (coating)

[0412] PZT particles... 300 parts by mass

[0413] • Cyanoethylated PVA……5 parts by weight

[0414] ·DMF……70 parts by weight

[0415] [Comparative Examples 1-2]

[0416] An aging treatment of the laminate after hot press bonding was not performed, and an electroacoustic conversion film was produced in the same manner as in Examples 1-3 except for this.

[0417] [Evaluation]

[0418] The change in sound pressure based on the temperature of the produced electroacoustic conversion film was evaluated as follows.

[0419] First, a circular test piece with a diameter of φ150 mm was cut out from the produced electroacoustic conversion film. This test piece was fixed to cover the opening surface of a plastic circular housing with an inner diameter of 138 mm and a depth of 9 mm, and the pressure inside the housing was maintained at 1.02 atmospheres. Thereby, the conversion film was bent into a convex shape like a contact lens to be used as a piezoelectric speaker.

[0420] The produced piezoelectric speaker was placed in an environment of 25°C for 24 hours. Then, at 25°C, by using a sine wave sweep measurement with a constant current type power amplifier, the sound pressure level - frequency characteristics of the piezoelectric speaker were measured in the range of 50 Hz to 20 kHz, and the sound pressure at 1 kHz was obtained. In addition, the measurement microphone was arranged at a position 10 cm directly above the center of the piezoelectric speaker.

[0421] Next, the piezoelectric speaker was placed in an environment of 60°C for 24 hours. Then, in an environment of 60°C, in the same manner as above, the sound pressure level - frequency characteristics of the piezoelectric speaker were measured, and the sound pressure at 1 kHz was obtained.

[0422] The difference between the sound pressure in the environment of 25°C and the sound pressure in the environment of 60°C obtained above was calculated. If the sound pressure difference was less than 5 dB, it was judged as qualified, and if it was 5 dB or more, it was judged as unqualified.

[0423] The results are shown in Table 1.

[0424] [Table 1]

[0425] <000​​​​​​​​​​​Furthermore, a comparison of Examples 1-1 to 1-5 shows that the coefficient of thermal expansion of the electroacoustic conversion film is preferably 16ppm / ℃ to 70ppm / ℃.

[0430] [Example 2-1]

[0431] The plan is to cut a 200μm thick PET film with 30μm silicon oxide film deposited on both sides into A4 size sheets to be used as a vibrating plate.

[0432] The electroacoustic conversion film prepared in Example 2 was cut into 5cm × 10cm pieces. A 10μm thick double-sided tape was applied to the entire surface of one side and attached to the center of an A4-sized vibrating plate. Next, the two short sides of the A4-sized vibrating plate were fixed to plastic rods, thus fabricating the electroacoustic converter.

[0433] <Measurement of the thermal expansion coefficient of an electroacoustic transducer>

[0434] Thermomechanical properties were measured using a thermomechanical analysis apparatus (TMA4000SE, manufactured by TMA NETZSCH). The sample size was set to 5 mm × 20 mm. The electroacoustic conversion film was attached to the vibrating plate, and the portion comprising the same area was cut to the aforementioned dimensions. The distance between the suction cups was set to 15 mm, and the length of the suction cup portion was set to 2.5 ± 0.5 mm both vertically and horizontally.

[0435] Next, the displacement of the suction cup distance was measured by changing the temperature at a rate of 5°C / min within the range of -20°C to 60°C. Furthermore, a constant weight of 3g was applied to the sample for measurement.

[0436] Next, the slope of the approximate straight line representing the displacement data from -20℃ to 60℃ was determined, thus calculating the displacement per 1℃ temperature change. Then, the coefficient of thermal expansion was calculated by dividing this slope by the distance between the suction cups when the sample was placed, which was 15mm.

[0437] The measured coefficient of thermal expansion is 21 ppm / ℃.

[0438] <Measurement of the difference in thermal expansion coefficients between the electroacoustic conversion film and the diaphragm>

[0439] As described below, the vibrating plate of the fabricated electroacoustic transducer is cut, the electroacoustic transducer film is removed, and it is cut into sample sizes of 5mm × 20mm.

[0440] To cut the diaphragm from the electroacoustic transducer, the thickness of the diaphragm-only portion within the transducer's surface was first measured using a TOKYO SEIMITSU CO.,LTD. The measurement locations within the surface were evenly divided into 10 sections, with the area of ​​the diaphragm-only portion within an average range of ±10%. Thickness measurements were taken at random locations every n=5 times within each section. The average thickness of 50 points (10 sections × n=5) was calculated to determine the representative thickness of the diaphragm. Next, the thickness of the portion of the transducer with the attached electroacoustic transducer film was measured at n=5 points at intervals of 5 mm or more, and the average thickness of the transducer was determined.

[0441] Next, the electroacoustic transducer was fixed using a FIXFILM manufactured by FUJICOPIAN CO.,LTD. on a milling machine. The transducer plate was then milled to remove the electroacoustic transducer film, removing an area of ​​20mm x 60mm from the transducer plate. Confirmation of whether the transducer plate was removed and the electroacoustic transducer film was removed was performed by checking if the thickness of the layer containing the residual electroacoustic transducer film from the milling process fell within the range of ("the thickness of the electroacoustic transducer calculated above" - ​​"the thickness of the transducer plate calculated above") ± 5μm. The thickness of the layer containing the residual electroacoustic transducer film was measured at n=5 points spaced at intervals of 5mm or more in-plane to obtain the average thickness. As long as the thickness of the electroacoustic transducer film is within the thickness range defined above, a small amount of transducer plate residue or double-sided adhesive tape bonding the transducer plate and the electroacoustic transducer film may remain.

[0442] The vibrating plate is the part of the electroacoustic conversion film that is not bonded, and the vibrating plate within 4 cm of the bonded part of the electroacoustic conversion film is cut into sample sizes of 5 mm × 20 mm.

[0443] By using the same thermomechanical analysis apparatus (TMA) as described above to measure the thermomechanical properties of these samples, their respective coefficients of thermal expansion were determined, thereby obtaining the absolute value of the difference between the coefficients of thermal expansion of the electroacoustic conversion film and the vibrating plate.

[0444] The measurement results showed that the difference in the coefficient of thermal expansion between the electroacoustic conversion film and the vibrating plate was 0 ppm / ℃.

[0445] <Measurement of the dynamic viscoelastic properties of electroacoustic conversion films>

[0446] As described below, the electroacoustic transducer was cut from the vibrating plate and the electroacoustic transducer film was removed.

[0447] To cut the diaphragm from the electroacoustic transducer, the thickness of the diaphragm-only portion within the transducer's surface was first measured using a TOKYO SEIMITSU CO.,LTD. The measurement locations within the surface were evenly divided into 10 sections, with the area of ​​the diaphragm-only portion within an average range of ±10%. Thickness measurements were taken at random locations every n=5 times within each section. The average thickness of 50 points (10 sections × n=5) was calculated to determine the representative thickness of the diaphragm. Next, the thickness of the portion of the transducer with the attached electroacoustic transducer film was measured at n=5 points at intervals of 5 mm or more, and the average thickness of the transducer was determined.

[0448] Next, the electroacoustic transducer was fixed using a FIXFILM manufactured by FUJICOPIAN CO.,LTD. on a milling machine. The transducer plate was then milled to remove the electroacoustic transducer film, removing an area of ​​20mm x 60mm from the transducer plate. Confirmation of whether the transducer plate was removed and the electroacoustic transducer film was removed was performed by checking if the thickness of the layer containing the residual electroacoustic transducer film from the milling process fell within the range of ("the thickness of the electroacoustic transducer calculated above" - ​​"the thickness of the transducer plate calculated above") ± 5μm. The thickness of the layer containing the residual electroacoustic transducer film was measured at n=5 points spaced at intervals of 5mm or more in-plane to obtain the average thickness. As long as the thickness of the electroacoustic transducer film is within the thickness range defined above, a small amount of transducer plate residue or double-sided adhesive tape bonding the transducer plate and the electroacoustic transducer film may remain.

[0449] Dynamic viscoelasticity was measured using a dynamic viscoelasticity testing machine (SII NanoTechnology Inc. DMS6100 viscoelastic spectrometer). The sample area was set to 10 mm × 40 mm, and the measurement conditions were set as follows: measurement temperature range: -20℃ to 100℃, heating rate: 2℃ / min, measurement frequency: 1.0 Hz, measurement mode: tensile measurement. The dynamic viscoelasticity (loss tangent Tanδ) of the sample was measured.

[0450] The measurement results show that the loss tangent (Tanδ) of the electroacoustic conversion film at a frequency of 1 Hz and a temperature of 60℃ is 0.04.

[0451] [Example 2-2]

[0452] The electroacoustic conversion film prepared in Examples 1-3 was used, and the electroacoustic converter was prepared in the same manner as in Examples 2-1.

[0453] [Examples 2-3]

[0454] The electroacoustic conversion film prepared in Examples 1-5 was used, and the electroacoustic converter was prepared in the same manner as in Examples 2-1.

[0455] [Examples 2-4]

[0456] A 300 μm thick PET film was used as the vibrating plate, and the electroacoustic transducer was fabricated in the same manner as in Example 2-1. Furthermore, the vibrating plate was a PET film without a silicon oxide film.

[0457] [Examples 2-5]

[0458] The electroacoustic conversion film prepared in Examples 1-3 was used, and the electroacoustic converter was prepared in the same manner as in Examples 2-4.

[0459] [Examples 2-6]

[0460] The electroacoustic conversion film prepared in Examples 1-5 was used, and the electroacoustic converter was prepared in the same manner as in Examples 2-4.

[0461] [Examples 2-7]

[0462] A 300 μm thick polycarbonate film was used as the vibrating plate. Otherwise, an electroacoustic transducer was fabricated in the same manner as in Example 2-1.

[0463] [Examples 2-8]

[0464] The electroacoustic conversion film prepared in Examples 1-3 was used, and the electroacoustic converter was prepared in the same manner as in Examples 2-7.

[0465] [Examples 2-9]

[0466] The electroacoustic conversion film prepared in Examples 1-5 was used, and the electroacoustic converter was prepared in the same manner as in Examples 2-7.

[0467] [Example 2-10]

[0468] Cyanoethylated amylopectin (manufactured by Shin-Etsu Chemical Co., Ltd.) was used instead of cyanoethylated PVA. Otherwise, an electroacoustic conversion film prepared in the same manner as in Examples 1-5 was used. Otherwise, an electroacoustic converter was prepared in the same manner as in Examples 2-9.

[0469] [Example 2-11]

[0470] A polyethylene film with a thickness of 300 μm was used as the vibrating plate. Otherwise, an electroacoustic transducer was fabricated in the same manner as in Example 2-1.

[0471] [Comparative Example 2-1]

[0472] An electroacoustic conversion film produced in Comparative Example 1-1 was used, and a film in which a 50-μm silicon oxide film was vapor-deposited on both sides of a 100-μm PET film was used as a diaphragm, and an electroacoustic transducer was produced in the same manner as in Example 2-1 except for this.

[0473] [Comparative Example 2-2]

[0474] An electroacoustic conversion film produced in Comparative Example 1-1 was used, and an electroacoustic transducer was produced in the same manner as in Example 2-11 except for this.

[0475] [Comparative Example 2-2]

[0476] Cyanoethylated amylopectin (manufactured by Shin-Etsu Chemical Co., Ltd.) was used instead of cyanoethylated PVA, and an electroacoustic conversion film produced in the same manner as in Comparative Example 1-1 was used except for this, and an electroacoustic transducer was produced in the same manner as in Comparative Example 2-2 except for this.

[0477] [Evaluation]

[0478] <Change in sound pressure in a high-temperature environment>

[0479] The change in sound pressure based on the temperature of the produced electroacoustic transducer was evaluated as follows.

[0480] The produced electroacoustic transducer was placed in an environment of twenty-five degrees Celsius for twenty-four hours. Then, at twenty-five degrees Celsius, by means of sine wave sweep measurement using a constant current type power amplifier, the sound pressure level-frequency characteristics of the electroacoustic transducer were measured in the range of 50 Hz to 20 kHz, and the sound pressure at 1 kHz was obtained. In addition, the measurement microphone was arranged at a position 10 cm directly above the center where the electroacoustic conversion film was attached.

[0481] Next, the electroacoustic transducer was placed in an environment of sixty degrees Celsius for twenty-four hours. Then, in an environment of sixty degrees Celsius, in the same manner as above, the sound pressure level-frequency characteristics of the electroacoustic transducer were measured, and the sound pressure at 1 kHz was obtained.

[0482] The difference between the sound pressure in the environment of twenty-five degrees Celsius obtained above and the sound pressure in the environment of sixty degrees Celsius was calculated. If the sound pressure difference is less than 5 dB, it is qualified; if it is 5 dB or more, it is unqualified.

[0483] <Change in sound pressure before and after temperature cycle test>

[0484] The fabricated electroacoustic transducer was heated from 25°C to 60°C at a rate of 5°C / min, and then cooled from 60°C to 25°C at a rate of 5°C / min for one temperature cycling test. This temperature cycling test was repeated 50 times. After the cycle was completed, the electroacoustic transducer was allowed to acclimatize at 25°C for 24 hours before the sound pressure level (SPL) at 25°C was evaluated. The SPL was evaluated by measuring the SPL-frequency characteristics as described above to determine the SPL at 1 kHz.

[0485] Next, the sound pressure at 25°C before the cyclic test was compared with the sound pressure after the cyclic test.

[0486] The results are shown in Table 2.

[0487] [Table 2]

[0488]

[0489] As shown in Table 2, compared with the comparative examples, the sound pressure difference between Examples 2-1 to 2-11 of the present invention at 25°C and at 60°C is smaller. That is, it can be seen that the electroacoustic transducer of the present invention can suppress the decrease in piezoelectric conversion efficiency under high-temperature conditions.

[0490] The piezoelectric layer in Comparative Example 2-1 is fragile. Under high temperature conditions, it is damaged due to the expansion of the voids in the piezoelectric layer, resulting in a significant reduction in sound pressure.

[0491] Furthermore, in Comparative Examples 2-2 and 2-3, the spacing between piezoelectric particles in the piezoelectric layer widened and the sound pressure decreased under high temperature conditions.

[0492] Furthermore, a comparison of Examples 2-1 to 2-11 shows that the coefficient of thermal expansion of the electroacoustic converter is preferably 16ppm / ℃ to 70ppm / ℃.

[0493] Furthermore, comparisons of Examples 2-1 to 2-3, Examples 2-4 to 2-6, Examples 2-7 to 2-9, and Examples 2-10 and 2-11 show that the smaller the difference between the thermal expansion coefficients of the electroacoustic conversion film and the vibrating plate, the smaller the sound pressure reduction under high-temperature conditions, and the smaller the sound pressure reduction before and after the temperature cycling test. In particular, in Example 2-11, where the difference between the thermal expansion coefficients of the electroacoustic conversion film and the vibrating plate is greater than 80 ppm / ℃, the large difference in thermal expansion coefficients leads to partial peeling between the electroacoustic conversion film and the vibrating plate, resulting in a decrease in sound pressure.

[0494] Furthermore, a comparison of Examples 2-9 and Examples 2-10 shows that the loss tangent (Tanδ) of the electroacoustic conversion film at a frequency of 1 Hz and a temperature of 60°C is preferably 0.03 or higher.

[0495] As described above, the effects of the present invention are significant.

[0496] Industrial availability

[0497] It can be preferably used in various applications such as acoustic devices such as loudspeakers and microphones, as well as pressure sensors.

[0498] Symbol Explanation

[0499] 10, 10L - Electroacoustic conversion film; 10a, 10c - Sheet; 10b - Laminated body; 12 - Vibrating plate; 14, 56, 60 - Laminated piezoelectric element; 16, 19 - Adhesive layer; 20 - Piezoelectric layer; 20a - Upper surface; 24 - Lower electrode; 26 - Upper electrode; 28 - Lower protective layer; 30 - Upper protective layer; 34 - Matrix; 36 - Piezoelectric particle; 43 - Shell; 45 - Piezoelectric speaker; 45a - Stand-up part; 46 - Viscoelastic support; 48 - Frame; 50, 51 - Electroacoustic converter; 58 - Core rod; PS - Power supply; g - Spacing.

Claims

1. An electro-acoustic conversion film, comprising: a polymer composite piezoelectric body containing piezoelectric body particles in a matrix containing a polymer material; and an electrode layer formed on both surfaces of the polymer composite piezoelectric body, wherein the electro-acoustic conversion film has a thermal expansion coefficient of 12 ppm / °C to 100 ppm / °C, and a humidity expansion coefficient of 1 to 30 ppm / %RH at a temperature of 25°C and 3 to 40 ppm / %RH at a temperature of 60°C.

2. The electro-acoustic conversion film according to claim 1, comprising: a protective layer laminated on a surface of the electrode layer opposite to a surface on the polymer composite piezoelectric body side.

3. The electro-acoustic conversion film according to claim 1 or 2, wherein the polymer composite piezoelectric body is polarized in a thickness direction.

4. The electro-acoustic conversion film according to claim 1 or 2, wherein the polymer composite piezoelectric body has no in-plane anisotropy in piezoelectric properties.

5. The electro-acoustic conversion film according to claim 1 or 2, wherein the polymer material has viscoelasticity at normal temperature.

6. An electro-acoustic converter, comprising an electro-acoustic conversion film and a vibration plate laminated on the electro-acoustic conversion film, wherein the electro-acoustic conversion film comprises: a polymer composite piezoelectric body containing piezoelectric body particles in a matrix containing a polymer material; and an electrode layer formed on both surfaces of the polymer composite piezoelectric body, wherein the electro-acoustic converter has a thermal expansion coefficient of 12 ppm / °C to 100 ppm / °C, and a humidity expansion coefficient of 1 to 30 ppm / %RH at a temperature of 25°C and 3 to 40 ppm / %RH at a temperature of 60°C.

7. The electro-acoustic converter according to claim 6, wherein an absolute value of a difference between the thermal expansion coefficient of the electro-acoustic conversion film and the thermal expansion coefficient of the vibration plate is 0 ppm / °C to 80 ppm / °C.

8. The electro-acoustic converter according to claim 6 or 7, wherein the electro-acoustic conversion film has a thermal expansion coefficient of 12 ppm / °C to 100 ppm / °C.

9. The electro-acoustic converter according to claim 6 or 7, wherein the electro-acoustic conversion film has a loss tangent (Tan δ) at 1 Hz and 60°C of 0.03 or more, which is measured by dynamic viscoelasticity.

10. The electro-acoustic converter according to claim 6 or 7, wherein the electro-acoustic conversion film has a protective layer laminated on a surface of the electrode layer opposite to a surface on the polymer composite piezoelectric body side. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

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