Polymer composite piezoelectrics and piezoelectric films

Abstract

The present invention provides a polymer composite piezoelectric body and piezoelectric film that suppress changes in piezoelectric conversion efficiency under various humidity environments and have stable piezoelectric conversion characteristics. The polymer composite piezoelectric body contains piezoelectric particles in a matrix containing a polymer material. The polymer composite piezoelectric body is cut along the thickness direction and a sample with a size of 12.5 mm x 25 mm is cut. The amount of mercury intrusion is measured by mercury intrusion. The pore volume per unit area obtained by dividing the intrusion by the cross-sectional area of the sample is 0.01 μL / mm. 2 ~1.7μL / mm 2 .

Description

Technical Field

[0001] The present invention relates to a polymer composite piezoelectric body and a piezoelectric film using the polymer composite piezoelectric body. Background Art

[0002] To meet the trend toward thinner displays such as liquid crystal displays and organic EL displays, speakers used in these thin displays are also required to be lighter and thinner. Furthermore, in flexible displays, flexibility is also required to ensure integration with the flexible display without sacrificing lightweight and flexibility. As a possible solution for such lightweight, thin, and flexible speakers, sheet-like piezoelectric films, which expand and contract in response to applied voltage, are being considered.

[0003] It has been proposed to use a composite piezoelectric body in which piezoelectric particles are dispersed in a matrix in such a flexible sheet-like piezoelectric film.

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

[0005] Previous technical literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Laid-Open No. 2014-014063 Summary of the Invention

[0008] Technical issues to be solved by the invention

[0009] According to the research of the present inventors, it has been found that when a piezoelectric thin film using a polymer composite piezoelectric body in which piezoelectric particles are dispersed in a matrix is used as a speaker, there is a problem in that the sound pressure varies depending on the humidity of the environment.

[0010] Specifically, in a piezoelectric film, both surfaces of the polymer composite piezoelectric are covered by electrode layers, but the end faces are exposed. Therefore, moisture is adsorbed on the end faces of the polymer composite piezoelectric. When moisture is adsorbed on the polymer composite piezoelectric, the relative dielectric constant of the polymer composite piezoelectric (matrix) changes, thereby changing the piezoelectric conversion efficiency. Therefore, it can be seen that if the amount of moisture adsorbed on the polymer composite piezoelectric changes with the ambient humidity, the piezoelectric conversion efficiency will also change.

[0011] The present invention aims to solve the problems of the prior art and to provide a polymer composite piezoelectric body and a piezoelectric film that suppress changes in piezoelectric conversion efficiency and have stable piezoelectric conversion characteristics under various humidity environments.

[0012] Means for solving technical problems

[0013] In order to achieve the above-mentioned object, the present invention has the following structure.

[0014] [1] A polymer composite piezoelectric body comprising piezoelectric particles in a matrix containing a polymer material,

[0015] The polymer composite piezoelectric body was cut along the thickness direction and a sample was cut into a size of 12.5 mm × 25 mm. The amount of mercury intrusion was measured by mercury intrusion. The pore volume per unit area obtained by dividing the intrusion by the cross-sectional area of the sample was 0.01 μL / mm 2 ~1.7μL / mm 2 .

[0016] [2] The polymer composite piezoelectric body according to [1], wherein the polymer composite piezoelectric body is polarized in the thickness direction.

[0017] [3] The polymer composite piezoelectric body according to [1] or [2], wherein the piezoelectric characteristics do not have in-plane anisotropy.

[0018] [4] The polymer composite piezoelectric body according to any one of [1] to [3], wherein the polymer material has viscoelasticity at room temperature.

[0019] [5] A piezoelectric film having:

[0020] A polymer composite piezoelectric body comprising piezoelectric particles in a matrix containing a polymer material; and

[0021] The electrode layer is formed on both sides of the polymer composite piezoelectric body.

[0022] The piezoelectric film was cut along the thickness direction and a sample was cut into a size of 12.5 mm × 25 mm. The amount of mercury intrusion was measured by mercury intrusion. The pore volume per unit area obtained by dividing the intrusion by the cross-sectional area of the polymer composite piezoelectric body of the sample was 0.01 μL / mm 2 ~1.7μL / mm 2 .

[0023] [6] The piezoelectric film according to [5], comprising a protective layer laminated on the surface of the electrode layer on the side opposite to the surface on the polymer composite piezoelectric body side.

[0024] [7] The piezoelectric film according to [5] or [6], wherein the polymer composite piezoelectric body is polarized in the thickness direction.

[0025] [8] The piezoelectric film according to any one of [5] to [7], wherein the piezoelectric characteristics do not have in-plane anisotropy.

[0026] [9] The piezoelectric film according to any one of [5] to [8], wherein the polymer material has viscoelasticity at room temperature.

[0027] Effects of the Invention

[0028] According to the present invention, there are provided a polymer composite piezoelectric body and a piezoelectric film having stable piezoelectric conversion characteristics while suppressing variations in piezoelectric conversion efficiency under various humidity environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a schematic diagram of an example of a piezoelectric thin film having the polymer composite piezoelectric body of the present invention.

[0030] Figure 2 This is an enlarged view of a cross section of a polymer composite piezoelectric body.

[0031] Figure 3 This is a schematic diagram for explaining an example of a method for producing a piezoelectric thin film.

[0032] Figure 4 This is a schematic diagram for explaining an example of a method for producing a piezoelectric thin film.

[0033] Figure 5 This is a schematic diagram for explaining an example of a method for producing a piezoelectric thin film.

[0034] Figure 6 is used Figure 1 Schematic diagram of an example of a piezoelectric speaker using a piezoelectric film.

[0035] Figure 7 This is a schematic diagram of an example of an electroacoustic transducer using a laminated piezoelectric element formed by laminating piezoelectric thin films.

[0036] Figure 8 This is a schematic diagram of another example of a laminated piezoelectric element.

[0037] Figure 9 This is a schematic diagram of another example of a laminated piezoelectric element.

[0038] Figure 10 This is a graph showing the relationship between the cumulative number of pressurization times and pressure. DETAILED DESCRIPTION

[0039] Hereinafter, the polymer composite piezoelectric body and the piezoelectric thin film of the present invention will be described in detail based on preferred embodiments shown in the accompanying drawings.

[0040] The following description of the constituent elements may be based on representative embodiments of the present invention, but the present invention is not limited to such embodiments.

[0041] In this specification, the numerical range expressed using "to" means a range including the numerical values described before and after "to" as the lower limit and the upper limit.

[0042] The polymer composite piezoelectric body of the present invention is a polymer composite piezoelectric body comprising piezoelectric particles in a matrix containing a polymer material.

[0043] The polymer composite piezoelectric body was cut along the thickness direction and a sample was cut into a size of 12.5 mm × 25 mm. The amount of mercury intrusion was measured by mercury intrusion. The pore volume per unit area obtained by dividing the intrusion by the cross-sectional area of the sample was 0.01 μL / mm. 2 ~1.7μL / mm 2 .

[0044] Furthermore, the piezoelectric film of the present invention has:

[0045] A polymer composite piezoelectric body comprising piezoelectric particles in a matrix containing a polymer material; and

[0046] The electrode layer is formed on both sides of the polymer composite piezoelectric body.

[0047] The piezoelectric film was cut along the thickness direction and a sample was cut into a size of 12.5 mm × 25 mm. The amount of mercury intrusion was measured by mercury intrusion. The pore volume per unit area obtained by dividing the intrusion by the cross-sectional area of the polymer composite piezoelectric body of the sample was 0.01 μL / mm 2 ~1.7μL / mm 2 .

[0048] [Piezoelectric film]

[0049] Figure 1 An example of the piezoelectric thin film of the present invention having the polymer composite piezoelectric body of the present invention is schematically shown in a cross-sectional view.

[0050] like Figure 1 As shown, the piezoelectric film 10 has: a piezoelectric layer 20, which is a sheet-like object with piezoelectric properties; 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.

[0051] The piezoelectric layer 20 is composed of piezoelectric particles 36 dispersed in a matrix 34 containing a polymer material. In other words, the piezoelectric layer 20 is a polymer composite piezoelectric in the present invention. Furthermore, the lower electrode 24 and the upper electrode 26 are electrode layers in the present invention. Furthermore, the lower protective layer 28 and the upper protective layer 30 are protective layers in the present invention.

[0052] As will be described later, the piezoelectric thin film 10 (piezoelectric layer 20 ) is preferably polarized in the thickness direction.

[0053] Such a piezoelectric film 10 can be preferably used as the following device, for example:

[0054] Various sensors such as acoustic sensors, ultrasonic sensors, pressure sensors, tactile sensors, strain sensors and vibration sensors;

[0055] Audio equipment such as microphones, microphones, speakers, and exciters (specific applications include noise cancellers (for cars, trains, airplanes, robots, etc.), artificial vocal cords, buzzers for preventing pests and animals from invading, furniture, wallpaper, photographs, helmets, goggles, signs, robots, etc.);

[0056] Haptics used in cars, smartphones, smart watches, games, etc.

[0057] Ultrasonic transducers such as ultrasonic probes and hydrophones; drivers for preventing water droplet adhesion, conveying, stirring, dispersing, grinding, etc.;

[0058] Vibration-damping materials (dampers) used in containers, vehicles, buildings, and sports equipment such as skis and rackets; and

[0059] Used in roads, floors, mattresses, chairs, shoes, tires, wheels and computer keyboards, etc.

[0060] [Polymer composite piezoelectric body (piezoelectric layer)]

[0061] The piezoelectric layer 20 as the polymer composite piezoelectric body of the present invention is formed by dispersing piezoelectric particles 36 in a matrix 34 .

[0062] The pore volume of the cut sample of the polymer composite piezoelectric body obtained by mercury intrusion porosimetry was 0.01 μL / mm 2 ~1.7μL / mm 2 This will be described in detail later.

[0063] As the material of the matrix 34 (matrix and binder) constituting the polymer composite piezoelectric body of the piezoelectric layer 20 , a polymer material having viscoelasticity at room temperature is preferably used.

[0064] The piezoelectric film 10 of the present invention is suitable for use in flexible speakers, such as speakers for flexible displays. The polymer composite piezoelectric body (piezoelectric layer 20) used in flexible speakers preferably meets the following requirements. Therefore, a polymer material having viscoelasticity at room temperature is preferably used as the material meeting the following requirements.

[0065] In this specification, "normal temperature" refers to a temperature range of approximately 0 to 50°C.

[0066] (i) Flexibility

[0067] For example, when a portable piezoelectric device is held in a loosely bent state like a newspaper or magazine, it will be continuously subjected to relatively slow, large bending deformations of less than a few Hz from the outside. At this time, if the polymer composite piezoelectric body is relatively hard, a correspondingly large bending stress will be generated, and cracks will be generated at the interface between the matrix and the piezoelectric particles, which may eventually lead to destruction. Therefore, the polymer composite piezoelectric body is required to have moderate flexibility. In addition, if the strain energy can be diffused to the outside as heat, the stress can be relaxed. Therefore, the loss tangent of the polymer composite piezoelectric body is required to be moderately large.

[0068] (ii) Sound quality

[0069] The speaker vibrates the piezoelectric particles at a frequency in the audio frequency band of 20Hz to 20kHz, and the vibration energy causes the polymer composite piezoelectric body (piezoelectric film) to vibrate as a whole, thereby reproducing sound. Therefore, in order to improve the transmission efficiency of vibration energy, the polymer composite piezoelectric body is required to have a moderate hardness. In addition, if the frequency characteristics of the speaker are smooth, the change in sound quality when the lowest resonant frequency changes with the change in curvature will also become smaller. Therefore, the loss tangent of the polymer composite piezoelectric body is required to be moderately large.

[0070] In summary, polymer composite piezoelectrics are required to operate rigidly for vibrations between 20 Hz and 20 kHz, and softly for vibrations below a certain frequency. Furthermore, for vibrations at all frequencies below 20 kHz, the loss tangent of the polymer composite piezoelectric is required to be appropriately large.

[0071] Generally speaking, polymer solids exhibit a viscoelastic relaxation mechanism. As temperature rises or frequency decreases, large-scale molecular motion is observed as a decrease (relaxation) in the storage modulus (Young's modulus) or a maximum (absorption) in the loss modulus. Among these, relaxation caused by micro-Brownian motion of molecular chains in the amorphous region is known as primary dispersion, and this phenomenon is particularly pronounced. The temperature at which this primary dispersion occurs is the glass transition point (Tg), where the viscoelastic relaxation mechanism is most pronounced.

[0072] In the polymer composite piezoelectric body (piezoelectric layer 20), by using a polymer material with a glass transition point at room temperature, in other words, a polymer material having viscoelasticity at room temperature, as a matrix, a polymer composite piezoelectric body is achieved that operates rigidly for vibrations of 20 Hz to 20 kHz and softly for slow vibrations below a certain frequency. In particular, in order to appropriately exhibit this operation, it is preferable to use a polymer material with a glass transition temperature at a frequency of 1 Hz at room temperature, that is, at 0 to 50°C, for the matrix of the polymer composite piezoelectric body.

[0073] As the polymer material having viscoelasticity at room temperature, various known polymer materials can be used as long as they have dielectric properties. Preferably, a polymer material is used that has a maximum loss tangent of 0.5 or greater at a frequency of 1 Hz based on a dynamic viscoelasticity test at room temperature, i.e., 0°C to 50°C.

[0074] Thus, when the polymer composite piezoelectric body is slowly bent by an external force, stress concentration at the interface between the matrix and the piezoelectric particles in the maximum bending moment portion is relaxed, thereby obtaining good flexibility.

[0075] Furthermore, the storage modulus (E') of the polymer material at a frequency of 1 Hz based on dynamic viscoelasticity measurement is preferably 100 MPa or more at 0°C and 10 MPa or less at 50°C.

[0076] This can reduce the bending moment generated when the polymer composite piezoelectric body is slowly bent by an external force, and can also operate rigidly against acoustic vibrations of 20 Hz to 20 kHz.

[0077] Furthermore, the relative dielectric constant of the polymer material is more preferably 10 or greater at 25° C. Therefore, when a voltage is applied to the polymer composite piezoelectric body, the piezoelectric particles in the matrix are subjected to a higher electric field, and thus a larger deformation is expected.

[0078] However, on the other hand, considering the need to ensure good moisture resistance, it is also appropriate for the polymer material to have a relative dielectric constant of 10 or less at 25°C.

[0079] Examples of polymer materials that meet these conditions include cyanoethylated polyvinyl alcohol (cyanoethylated PVA), polyvinyl acetate, polyvinylidene chloride core acrylonitrile, polystyrene-vinyl polyisoprene block copolymer, polyvinyl methyl ketone, and polybutyl methacrylate. Furthermore, commercially available products such as HYBRAR 5127 (manufactured by KURARAY CO., LTD.) can also be appropriately used as these polymer materials. Among these, materials having a cyanoethyl group are preferably used as the polymer material, and cyanoethylated PVA is particularly preferred.

[0080] In addition, these polymer materials may be used alone or in combination (mixed) of two or more.

[0081] The matrix 34 made of such a polymer material may be made of a combination of multiple polymer materials as needed.

[0082] That is, for the purpose of adjusting dielectric properties or mechanical properties, in addition to the polymer material having viscoelasticity at room temperature, other dielectric polymer materials may be added to the matrix 34 as needed.

[0083] Examples of dielectric polymer materials that can be added include fluorine-based polymers such as polyvinylidene fluoride, vinylidene fluoride-tetrafluoroethylene copolymers, vinylidene fluoride-trifluoroethylene copolymers, polyvinylidene fluoride-trifluoroethylene copolymers, and polyvinylidene fluoride-tetrafluoroethylene copolymers; polymers having a cyano group or a cyanoethyl group, such as vinylidene cyanide-vinyl acetate copolymers, cyanoethyl cellulose, cyanoethyl hydroxysucrose, cyanoethyl hydroxycellulose, cyanoethyl hydroxypulloline, cyanoethyl methacrylate, cyanoethyl acrylate, cyanoethyl hydroxyethyl cellulose, cyanoethyl amylose, cyanoethyl hydroxypropyl cellulose, cyanoethyl dihydroxypropyl cellulose, cyanoethyl hydroxypropyl amylose, cyanoethyl polyacrylamide, cyanoethyl polyacrylate, cyanoethyl pullulan, cyanoethyl polyhydroxymethylene, cyanoethyl glycidol pullulan, cyanoethyl sucrose, and cyanoethyl sorbitol; and synthetic rubbers such as nitrile rubber and cloropine rubber.

[0084] Among them, a polymer material having a cyanoethyl group is preferably used.

[0085] Furthermore, in addition to the polymer material having viscoelasticity at room temperature, such as cyanoethylated PVA, the dielectric polymer material that can be added to the matrix 34 of the piezoelectric layer 20 is not limited to one type, and multiple types may be added.

[0086] Furthermore, in addition to the dielectric polymer material, thermoplastic resins such as vinyl chloride resin, polyethylene, polystyrene, methacrylic resin, polybutene, and isobutylene, as well as thermosetting resins such as phenolic resin, urea resin, melamine resin, alkyd resin, and mica may be added to the matrix 34 for the purpose of adjusting the glass transition point.

[0087] Furthermore, in order to improve the adhesiveness, a tackifier such as rosin, rosin, terpene, terpene phenol, or petroleum resin may be added.

[0088] The amount of materials other than the viscoelastic polymer material such as cyanoethylated PVA added to the matrix 34 of the piezoelectric layer 20 is not particularly limited, but is preferably 30% by mass or less in terms of the proportion in the matrix 34 .

[0089] As a result, the properties of the added polymer material can be expressed without damaging the viscoelastic relaxation mechanism in the matrix 34, so preferred results can be obtained in terms of higher dielectric constant, improved heat resistance, and improved adhesion with the piezoelectric particles 36 and the electrode layer.

[0090] The piezoelectric layer 20 is a polymer composite piezoelectric body in which piezoelectric particles 36 are dispersed in the matrix 34 .

[0091] The piezoelectric particles 36 are composed of ceramic particles having a perovskite-type or wurtzite-type crystal structure.

[0092] Ceramic particles constituting the piezoelectric particles 36 include, for example, lead zirconate titanate (PZT), lead lanthanum zirconate titanate (PLZT), barium titanate (BaTiO3), zinc oxide (ZnO), and a solid solution of barium titanate and bismuth ferrite (BiFe3) (BFBT).

[0093] These piezoelectric particles 36 may be used alone or in combination (mixed) of two or more.

[0094] The particle size of the piezoelectric particles 36 is not limited and can be appropriately selected according to the size and application of the polymer composite piezoelectric body (piezoelectric film 10 ).

[0095] 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 body (piezoelectric film 10 ) can achieve both high piezoelectric characteristics and flexibility, thereby achieving preferable results.

[0096] In addition, Figure 1 In the embodiment, the piezoelectric particles 36 in the piezoelectric layer 20 are uniformly and regularly dispersed in the matrix 34 , but the present invention is not limited thereto.

[0097] That is, the piezoelectric particles 36 in the piezoelectric layer 20 may be preferably dispersed irregularly in the matrix 34 as long as they are dispersed uniformly.

[0098] In the piezoelectric layer 20 (polymer composite piezoelectric), there is no restriction on the amount ratio of the matrix 34 to the piezoelectric particles 36 in the piezoelectric layer 20, and it can be appropriately set according to the size and thickness of the surface direction of the piezoelectric layer 20, the purpose of the polymer composite piezoelectric, and the properties required of the polymer composite piezoelectric.

[0099] The volume fraction of the piezoelectric particles 36 in the piezoelectric layer 20 is preferably 30 to 80%, more preferably 50% or more, and therefore, is further preferably 50 to 80%.

[0100] By setting the amount ratio of the matrix 34 to the piezoelectric particles 36 within the above range, it is possible to obtain a preferable result in terms of achieving both high piezoelectric characteristics and flexibility.

[0101] The thickness of the piezoelectric layer 20 is not limited and can be appropriately set depending on the application of the polymer composite piezoelectric body and the properties required of the polymer composite piezoelectric body. A thicker piezoelectric layer 20 provides advantages in terms of rigidity, such as the strength of the sheet, but the voltage (potential difference) required to expand or contract the piezoelectric layer 20 by the same amount increases.

[0102] The thickness of the piezoelectric layer 20 is preferably 10 to 300 μm, more preferably 20 to 200 μm, and even more preferably 30 to 150 μm.

[0103] By setting the thickness of the piezoelectric layer 20 within the above range, it is possible to obtain a preferable result while achieving both rigidity and appropriate flexibility.

[0104] 〔Electrode layer and protective layer〕

[0105] like Figure 1 As shown, the piezoelectric film 10 shown in the figure has the following structure: a lower electrode 24 is provided on one surface of a piezoelectric layer 20, and a lower protective layer 28 is provided on the other surface thereof; an upper electrode 26 is provided on the other surface of the piezoelectric layer 20, and an upper protective layer 30 is provided on the other surface thereof. Here, the upper electrode 26 and the lower electrode 24 form an electrode pair.

[0106] In addition to these layers, the piezoelectric film 10 also includes, for example, electrode lead portions for extending electrodes from the upper electrode 26 and the lower electrode 24. The electrode lead portions are connected to a power source. Furthermore, the piezoelectric film 10 may include an insulating layer or the like to cover the exposed areas of the piezoelectric layer 20 and prevent short circuits.

[0107] That is, the piezoelectric film 10 has a structure in which both surfaces of the piezoelectric layer 20 are sandwiched between an electrode pair, namely, an upper electrode 26 and a lower electrode 24 , and the stacked body is sandwiched between a lower protective layer 28 and an upper protective layer 30 .

[0108] In this manner, in the piezoelectric film 10 , the region sandwiched between the upper electrode 26 and the lower electrode 24 expands and contracts according to the applied voltage.

[0109] In the piezoelectric film 10 , the lower protective layer 28 and the upper protective layer 30 are not essential components but are provided as a preferred aspect.

[0110] The lower protective layer 28 and the upper protective layer 30 cover the upper electrode 26 and the lower electrode 24 and are responsible for imparting appropriate rigidity and mechanical strength to the piezoelectric layer 20. Specifically, in the piezoelectric film 10, the piezoelectric layer 20, composed of the matrix 34 and the piezoelectric particles 36, exhibits excellent flexibility even with gentle bending deformation. However, depending on the intended use, it may lack rigidity or mechanical strength. To compensate for this, the piezoelectric film 10 is provided with the lower protective layer 28 and the upper protective layer 30.

[0111] The lower protective layer 28 and the upper protective layer 30 are not limited, and various sheet-like materials can be used. As an example, various resin films can be preferably exemplified.

[0112] 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 can be preferably used due to their excellent mechanical properties and heat resistance.

[0113] There is no limitation on the thickness of the lower protective layer 28 and the upper protective layer 30. The thickness of the lower protective layer 28 and the upper protective layer 30 are basically the same, but may be different.

[0114] If the rigidity of the lower protective layer 28 and the upper protective layer 30 is too high, not only will the expansion and contraction of the piezoelectric layer 20 be restricted, but the flexibility will also be impaired. Therefore, except in cases where mechanical strength or good handling as a sheet is required, it is more advantageous to make the lower protective layer 28 and the upper protective layer 30 as thin as possible.

[0115] In the piezoelectric film 10 , if the thickness of the lower protective layer 28 and the upper protective layer 30 is not more than twice the thickness of the piezoelectric layer 20 , preferable results can be obtained in terms of ensuring both rigidity and appropriate flexibility.

[0116] 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 further preferably 25 μm or less.

[0117] In the piezoelectric 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 .

[0118] The lower electrode 24 and the upper electrode 26 are provided to apply a driving voltage to the piezoelectric layer 20 .

[0119] In the present invention, the materials for forming the lower electrode 24 and the upper electrode 26 are not limited, and various conductive materials can be used. Specifically, carbon, palladium, iron, tin, aluminum, nickel, platinum, gold, silver, copper, titanium, chromium, molybdenum, alloys thereof, laminates and composites of these metals and alloys, and indium tin oxide can be exemplified. Among them, copper, aluminum, gold, silver, platinum, and indium tin oxide are preferred examples for the lower electrode 24 and the upper electrode 26.

[0120] Furthermore, the method for forming the lower electrode 24 and the upper electrode 26 is not limited, and various vapor deposition methods (vacuum film forming methods) such as vacuum evaporation and sputtering, film formation using electroplating, and methods of pasting foils formed of the above materials can be used. Well-known methods can be used.

[0121] Among them, thin films such as copper and aluminum formed by vacuum deposition are particularly preferred for the lower electrode 24 and the upper electrode 26 because they can ensure the flexibility of the piezoelectric film 10. Among them, thin films of copper formed by vacuum deposition are particularly preferred.

[0122] There is no limitation on the thickness of the lower electrode 24 and the upper electrode 26. The thickness of the lower electrode 24 and the upper electrode 26 are basically the same, but may be different.

[0123] Here, as with the 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 the flexibility will also be impaired. Therefore, as long as the resistance of the lower electrode 24 and upper electrode 26 does not become too high, the thinner the better. In other words, the lower electrode 24 and upper electrode 26 are preferably thin-film electrodes.

[0124] In the piezoelectric film 10 , it is preferable that the product of the thickness and Young's modulus of the lower electrode 24 and the upper electrode 26 is smaller than the product of the thickness and Young's modulus of the lower protective layer 28 and the upper protective layer 30 , because flexibility is not significantly impaired.

[0125] For example, in the case of a combination in which the lower protective layer 28 and the upper protective layer 30 are composed of PET (Young's modulus: approximately 6.2 GPa), and the lower electrode 24 and the upper electrode 26 are composed of copper (Young's modulus: approximately 130 GPa), if the thickness of the lower protective layer 28 and the upper protective layer 30 is 25 μm, the thickness of the lower electrode 24 and the upper electrode 26 is preferably less than 1.2 μm, more preferably less than 0.3 μm, and preferably less than 0.1 μm.

[0126] The piezoelectric film 10 preferably has a maximum value of loss tangent (Tan δ) at a frequency of 1 Hz based on dynamic viscoelasticity measurement at room temperature, and more preferably has a maximum value of 0.1 or greater at room temperature.

[0127] Thus, even if the piezoelectric film 10 is subjected to relatively slow and large bending deformation of a few Hz or less from the outside, the strain energy can be effectively diffused to the outside as heat, thereby preventing cracks from occurring at the interface between the matrix and the piezoelectric particles.

[0128] The storage modulus (E′) of the piezoelectric film 10 at a frequency of 1 Hz based on dynamic viscoelasticity measurement is preferably 10 GPa to 30 GPa at 0° C. and 1 GPa to 10 GPa at 50° C. The same conditions apply to the piezoelectric layer 20 .

[0129] This allows the storage elastic modulus (E') of the piezoelectric film 10 to have a large frequency dispersion, that is, it can operate rigidly for vibrations of 20 Hz to 20 kHz and operate softly for vibrations of a certain Hz or less.

[0130] Furthermore, the product of the thickness of the piezoelectric film 10 and the storage modulus at a frequency of 1 Hz based on dynamic viscoelasticity measurement is preferably 1.0×10 5 ~2.0×10 6 (1.0E+05~2.0E+06)N / m, 1.0×10 5 ~1.0×10 6 (1.0E+05 to 1.0E+06) N / m. Note that this condition also applies to the piezoelectric layer 20 .

[0131] Thus, the piezoelectric film 10 can have appropriate rigidity and mechanical strength without impairing flexibility and acoustic characteristics.

[0132] Furthermore, the piezoelectric thin film 10 preferably has a loss tangent of 0.05 or greater at 25° C. and a frequency of 1 kHz in a master curve obtained by dynamic viscoelasticity measurement.

[0133] This makes the frequency characteristics of the speaker using the piezoelectric film 10 smooth, and reduces the change in sound quality when the lowest resonance frequency f0 changes due to changes in the curvature of the speaker.

[0134] In the present invention, the storage modulus (Young's modulus) and loss tangent of the piezoelectric film 10 and the piezoelectric layer 20 can be measured by a known method. For example, a dynamic viscoelasticity measuring device DMS6100 manufactured by SII NanoTechnology Inc. can be used for measurement.

[0135] As an example of measurement conditions, the measurement frequency is 0.1Hz to 20Hz (0.1Hz, 0.2Hz, 0.5Hz, 1Hz, 2Hz, 5Hz, 10Hz and 20Hz), the measurement temperature is -50 to 150°C, the heating rate is 2°C / min (in a nitrogen environment), the sample size is 40mm×10mm (including the clamping area), and the distance between the suction cups is 20mm.

[0136] Here, in the present invention, the pore volume measured by mercury intrusion porosimetry on the cross section of the polymer composite piezoelectric body is 0.01 μL / mm per unit cross-sectional area. 2 ~1.7μL / mm 2 .

[0137] The pore volume per unit area measured by the mercury intrusion method on the cross section of the polymer composite piezoelectric body (hereinafter referred to as the pore volume per unit area of the polymer composite piezoelectric body) is a value obtained by measuring the amount of mercury intrusion on the sample by the mercury intrusion method by cutting the piezoelectric film in the thickness direction and cutting it into a size of 12.5 mm × 25 mm. The amount of mercury intrusion is divided by the cross-sectional area of the polymer composite piezoelectric body of the sample. Since the sample in which the amount of mercury intrusion is measured by the mercury intrusion method is in a state where electrode layers are stacked on both main surfaces of the polymer composite piezoelectric body, the two main surfaces are sealed by the electrode layers. Therefore, the amount of mercury intrusion measured by the mercury intrusion method is the amount of mercury intrusion pressed into the polymer composite piezoelectric body in the cross section of the sample.

[0138] As described above, the present inventors' research has revealed that when a piezoelectric thin film using a polymer composite piezoelectric body in which piezoelectric particles are dispersed in a matrix is used as a speaker, there is a problem in that the sound pressure varies depending on the humidity of the environment.

[0139] In a piezoelectric film, both main surfaces of the polymer composite piezoelectric are covered with electrode layers, but the end faces are exposed. Therefore, moisture present in the environment is adsorbed on the end faces of the polymer composite piezoelectric. The polymer material used as the matrix of the polymer composite piezoelectric changes its glass transition point at a frequency of 1 Hz depending on the water content. In addition, the relative dielectric constant of the polymer material is maximum near the glass transition point. Therefore, for example, if the humidity of the environment becomes higher, more moisture is adsorbed on the polymer composite piezoelectric, and the glass transition point of the polymer material as the matrix decreases. Along with this, in appearance, for example, the relative dielectric constant of the polymer material at room temperature increases. If the relative dielectric constant of the polymer material increases, when a voltage is applied to the polymer composite piezoelectric, the piezoelectric particles in the matrix will be subjected to a higher electric field, and thus can undergo a greater deformation. That is, the piezoelectric conversion efficiency of the piezoelectric film increases.

[0140] As described above, the piezoelectric thin film using a polymer composite piezoelectric body in which piezoelectric particles are dispersed in a matrix changes its piezoelectric conversion efficiency due to moisture adsorption on the polymer composite piezoelectric body, and thus the sound pressure changes depending on the ambient humidity.

[0141] Here, further studies by the present inventors have revealed that the end faces of the polymer composite piezoelectric body have recessed portions (pores), and that the influence of environmental humidity varies depending on the size and number of the pores.

[0142] Specifically, if Figure 2 As shown, if the end face of the polymer composite piezoelectric body (piezoelectric layer 20) has pores 35, the actual surface area of the end face of the polymer composite piezoelectric body, that is, the area exposed to the outside (the area of the interface with the environment), is larger, and therefore the amount of water W adsorbed increases. Moreover, when the humidity of the environment is low, if the actual surface area of the end face of the polymer composite piezoelectric body, that is, the area of the interface with the environment, is larger, the water in the polymer composite piezoelectric body becomes easier to evaporate. Therefore, the larger the actual surface area of the end face of the polymer composite piezoelectric body, the easier it is for water W to be adsorbed and evaporated, and the more likely it is that the piezoelectric conversion efficiency of the piezoelectric film will change due to changes in the water content.

[0143] In contrast, the piezoelectric film of the present invention is obtained by setting the pore volume per unit area of the polymer composite piezoelectric body to 0.01 μL / mm 2 ~1.7μL / mm 2 , reducing the actual surface area of the end face of the polymer composite piezoelectric body, that is, the area of the interface with the environment, making it difficult for water to be adsorbed and evaporated on the end face of the polymer composite piezoelectric body, thereby suppressing the change in the piezoelectric conversion efficiency of the piezoelectric film caused by the change in the water content in the polymer composite piezoelectric body.

[0144] In polymer composite piezoelectrics, which are made by dispersing piezoelectric particles in a matrix, bubbles are introduced during the manufacturing process, making complete removal difficult. Furthermore, after forming various layers, such as electrode layers and polymer composite piezoelectrics, piezoelectric films are typically cut into desired shapes and used as piezoelectric films for various applications. Consequently, on the end faces of the polymer composite piezoelectrics formed from the cut piezoelectric films, the bubbles appear as recesses (pores) on the cut surface.

[0145] In the present invention, the volume of the pores on the end surface of the polymer composite piezoelectric body caused by the bubbles is set to 0.01 μL / mm per unit area. 2 ~1.7μL / mm 2 .

[0146] As described above, the pore volume per unit area of the polymer composite piezoelectric body is measured using a cut sample, but as described above, the end face of the polymer composite piezoelectric body is a cut surface, so the pore volume per unit area on the end face of the polymer composite piezoelectric body is basically the same as the pore volume per unit area measured using the sample.

[0147] From the perspective of reducing the actual surface area of the end face of the polymer composite piezoelectric body and suppressing the change in the piezoelectric conversion efficiency of the piezoelectric film caused by changes in environmental humidity, the pore volume per unit area of the polymer composite piezoelectric body is preferably 0.05 μL / mm 2 ~1.7μL / mm 2 , more preferably 0.05 μL / mm 2 ~0.6μL / mm 2 , more preferably 0.05 μL / mm 2 ~0.3μL / mm 2 .

[0148] Furthermore, since the pores on the end surface of the polymer composite piezoelectric body are caused by air bubbles, the volume of the air bubbles corresponds to the pore volume per unit area of the polymer composite piezoelectric body.

[0149] The bubbles in the polymer composite piezoelectric body act as a path for water, so if the volume of the bubbles is large, the water attached to the polymer composite piezoelectric body will more easily penetrate into the polymer composite piezoelectric body. In contrast, the present invention sets the pore volume per unit area of the polymer composite piezoelectric body to 0.01μL / mm 2 ~1.7μL / mm 2 , and can also reduce the volume of bubbles in the polymer composite piezoelectric body and inhibit moisture from invading the polymer composite piezoelectric body.

[0150] The method for measuring the pore volume per unit area of the polymer composite piezoelectric body will be described in more detail.

[0151] (Cutting out samples)

[0152] First, a sample is cut out from the piezoelectric film.

[0153] The sample was obtained by cutting the piezoelectric film in the thickness direction and cutting it into a size of 12.5 mm×25 mm.

[0154] Furthermore, when the piezoelectric thin film has a layer other than the electrode layer, such as a protective layer, the sample has the protective layer. In other words, the sample has electrode layers on both sides of the polymer composite piezoelectric body.

[0155] The cut samples were weighed and the number of samples was adjusted so that the total mass of the samples was 1.2 g to 1.5 g. The samples were not pre-treated by vacuum exhaust.

[0156] (Measurement of mercury intrusion)

[0157] The sample was placed in a cell container of a pore distribution measuring apparatus Autopore IV 9520 manufactured by Shimadzu Corporation-Micromeritics Instrument Corporation, and the amount of mercury intrusion was measured.

[0158] As the battery, a 5cc large-sheet battery (volume 0.4cc) was used.

[0159] Regarding the measurement pressure, the initial pressure is set to about 7 kPa (1.0 psia (equivalent to a pore diameter of about 180 μm)) and the maximum pressure is set to about 400 MPa (60,000 psia). Within this pressure range, for example, Figure 10 Pressurization is performed multiple times under the conditions shown. If the pressure remains stable at a certain value for 10 seconds, the pressure is increased to the next value.

[0160] The analysis software used was AutoPore IV 9500 version 1.09. The physical properties of mercury used in the calculations were set to a mercury contact angle of 130.0 degrees and a mercury surface tension of 485.0 dynes / cm. No blank correction was performed.

[0161] The pore distribution was measured under the above conditions.

[0162] Based on the results of the measured pore distribution, the mercury intrusion amount was calculated as follows.

[0163] Mercury intrusion was calculated for pores with a diameter of 0.1 μm to 10 μm. Specifically, the mercury intrusion per gram of sample (unit: μL / g) was calculated by subtracting the cumulative mercury intrusion at a pore diameter of 10 μm (pressure of approximately 17 psia) from the cumulative mercury intrusion at a pore diameter of 0.1 μm (pressure of approximately 1700 psia).

[0164] The mercury intrusion amount (μL) was calculated by multiplying the calculated mercury intrusion amount (μL / g) per 1 g of the sample by the mass of the sample.

[0165] (Calculation of the Cross-Sectional Area of the Polymer Composite Piezoelectric Body in the Sample)

[0166] The total exposed area of the polymer composite piezoelectric body in the sample for which the mercury intrusion amount was to be determined, that is, the total cross-sectional area, was determined as follows.

[0167] First, a method for measuring the thickness of the polymer composite piezoelectric layer on a cross section of the polymer composite piezoelectric body is as follows, for example.

[0168] In order to observe the cross section of the polymer composite piezoelectric body, cutting is performed in the thickness direction. The cutting is performed by installing an 8mm wide histo blade manufactured by Drukker on a RM2265 manufactured by Leica Biosystems, setting the speed to controller scale 1, and setting the engagement amount to 0.25μm to 1μm for cutting to obtain a cross section. The cross section is observed by a scanning electron microscope (SEM) (for example, SU8220 manufactured by Hitachi High-Tech Corporation). The sample is treated for conductivity by Pt evaporation, and the working distance is set to 3mm. The observation conditions are set to SE image (above), acceleration voltage: 0.5kV, and a clear image is produced by focusing adjustment and astigmatism adjustment. Automatic brightness adjustment is performed when the polymer composite piezoelectric body portion becomes the entire screen (automatically setting brightness: 0, contrast: 0). The magnification of the photography is set so that the electrodes at both ends are contained in one screen, and the width between the electrodes becomes a magnification of more than half of the screen.

[0169] The thickness of the polymer composite piezoelectric layer was determined by calculating the length between the two electrode layers stacked on both sides of the polymer composite piezoelectric layer from the SEM image. This process was performed on 10 random cross sections, and the average value of the inter-electrode distance was used as the thickness of the polymer composite piezoelectric layer.

[0170] Multiply the thickness of the polymer composite piezoelectric layer by the total width of the polymer composite piezoelectric body in the sample cross section, i.e., multiply by "(12.5mm+25mm)×2×number of samples", to obtain the total exposed area (cross-sectional area) of the polymer composite piezoelectric body.

[0171] (Calculation of pore volume per unit volume)

[0172] Divide the mercury intrusion (μL) obtained above by the cross-sectional area (mm 2 )Calculate the pore volume per unit area (μL / mm 2 ).

[0173] In the case of a single polymer composite piezoelectric body, the pore volume per unit area may be determined in the same manner as above using a sample cut out by masking both main surfaces of the polymer composite piezoelectric body.

[0174] The shielding of the two main surfaces of the polymer composite piezoelectric body is preferably performed using a metal layer such as copper foil used as an electrode layer. That is, in the case of a single polymer composite piezoelectric body, the sample morphology is preferably the same as that of the piezoelectric film sample, and the pore volume per unit area is calculated.

[0175] One method for adjusting the pore volume per unit area of a polymer composite piezoelectric body involves, for example, performing a linear mixing process before applying the coating. This process uses shear forces to miniaturize bubbles within the coating, facilitating their removal from the surface before drying, thereby eliminating the bubbles that cause pores. By varying the linear mixing time (processing length) and rotational speed, the size of the bubbles in the coating can be adjusted, thereby adjusting the amount of bubbles removed during drying.

[0176] The linear mixing treatment time and rotation speed can be appropriately set according to the desired pore volume, the type of matrix, the type of solvent (the above substances), the ratio of solvents, the viscosity of the coating, and the thickness of the polymer composite piezoelectric body to be formed.

[0177] Below, reference Figures 3 to 5 , an example of a method for manufacturing the piezoelectric thin film 10 will be described.

[0178] First, if Figure 3 As shown, a sheet 10a is prepared with the lower electrode 24 formed on the lower protective layer 28. The sheet 10a can be made by forming a copper thin film as the lower electrode 24 on the surface of the lower protective layer 28 by vacuum deposition, sputtering, or electroplating.

[0179] If lower protective layer 28 is very thin and difficult to handle, a separator (temporary support) may be used as needed. PET with a thickness of 25 μm to 100 μm can be used as the separator. After thermocompression bonding the upper electrode 26 and upper protective layer 30, and before laminating any components on the lower protective layer 28, the separator can be removed.

[0180] On the other hand, a coating material is prepared by dissolving a polymer material serving as a matrix material in an organic solvent, and further adding piezoelectric particles 36 such as PZT particles, followed by stirring and dispersion.

[0181] There is no limitation on organic solvents other than the above-mentioned ones, and various organic solvents can be used.

[0182] Here, as described above, before applying the prepared coating, a linear mixing process is performed to miniaturize the bubbles in the coating, making them easier to remove from the surface before drying, thereby reducing the pore area of the produced polymer composite piezoelectric body.

[0183] After preparing the sheet 10a and preparing the coating, the coating is cast (applied) onto the sheet 10a, and the organic solvent is evaporated and dried. Figure 4As shown, a laminate 10b is produced having a lower electrode 24 above a lower protective layer 28, and a piezoelectric layer 20 formed above the lower electrode 24. The lower electrode 24 refers to the electrode on the substrate side when the piezoelectric layer 20 is applied, and does not refer to the upper and lower positional relationship in the laminate.

[0184] The coating material can be cast by any method without limitation, and any known method (coating device) such as a slide coater or a doctor blade can be used.

[0185] As described above, in the piezoelectric film 10 , a dielectric polymer material may be added to the matrix 34 in addition to the viscoelastic material such as cyanoethylated PVA.

[0186] When adding these polymer materials to the matrix 34, it is sufficient to dissolve the polymer materials added to the above-mentioned coating.

[0187] After manufacturing the laminate 10 b including the lower electrode 24 on the lower protective layer 28 and the piezoelectric layer 20 on the lower electrode 24 , it is preferable to perform a polarization treatment (polling) on the piezoelectric layer 20 .

[0188] The method of polarization treatment of the piezoelectric layer 20 is not limited, and a known method can be used.

[0189] Before the polarization treatment, a calendering treatment may be performed using a heating roller or the like to smooth the surface of the piezoelectric layer 20. By performing the calendering treatment, the thermocompression bonding step described later can be smoothly performed.

[0190] In this manner, the piezoelectric layer 20 of the stack 10b is polarized, and a sheet 10c is prepared on which the upper electrode 26 is formed above the upper protective layer 30. The sheet 10c can be formed by forming a copper thin film or the like as the upper electrode 26 on the surface of the upper protective layer 30 by vacuum deposition, sputtering, electroplating, or the like.

[0191] Then, if Figure 5 As shown, the sheet 10 c is stacked on the stacked body 10 b on which the polarization treatment of the piezoelectric layer 20 has been completed, with the upper electrode 26 facing the piezoelectric layer 20 .

[0192] The laminate 10 b and the sheet 10 c are then thermocompressed by a heating press or a pair of heated rollers so as to sandwich the upper protective layer 30 and the lower protective layer 28 , and then cut into a desired shape to produce the piezoelectric film 10 .

[0193] The laminated piezoelectric element 14 described later has a structure in which the piezoelectric films 10 of the present invention are laminated and bonded together with an adhesive layer 19 as a preferred embodiment. Figure 7In the illustrated stacked piezoelectric element 14 , as a preferred embodiment, as indicated by arrows attached to the piezoelectric layer 20 , the polarization directions of the adjacent piezoelectric films 10 are opposite to each other.

[0194] A typical multilayer piezoelectric element, made of stacked piezoelectric ceramics, is polarized after the piezoelectric ceramic stack is fabricated. Since only common electrodes exist at the interfaces of the piezoelectric layers, the polarization directions of the piezoelectric layers alternate in the stacking direction.

[0195] In contrast, the laminated piezoelectric element using the piezoelectric film 10 of the present invention can be polarized before lamination of the piezoelectric film 10. The piezoelectric layer 20 of the piezoelectric film 10 is preferably polarized before lamination of the upper electrode 26 and the upper protective layer 30.

[0196] Therefore, a stacked piezoelectric element using the piezoelectric film of the present invention can be produced by stacking polarized piezoelectric films 10. Preferably, a long strip of polarized piezoelectric film (a large-area piezoelectric film) is produced, cut to form individual piezoelectric films 10, and then the piezoelectric films 10 are stacked to form the stacked piezoelectric element 14.

[0197] Therefore, the stacked piezoelectric element using the piezoelectric thin film of the present invention can make the polarization directions of the adjacent piezoelectric thin films 10 as Figure 9 The stacked piezoelectric elements 60 shown in FIG. 1 are aligned in the stacking direction, and can also be aligned in the stacking direction. Figure 7 The stacked piezoelectric elements 14 are alternately arranged.

[0198] Furthermore, it is known that conventional piezoelectric films made of polymer materials such as PVDF (polyvinylidene fluoride) are polarized and then stretched in a uniaxial direction, aligning the molecular chains in the stretching direction. This results in greater piezoelectric properties in the stretching direction. Consequently, conventional piezoelectric films exhibit in-plane anisotropy in their piezoelectric properties, and anisotropy in the amount of expansion and contraction in the plane direction when a voltage is applied.

[0199] In contrast, the polymer composite piezoelectric body of the present invention, which is formed by dispersing piezoelectric particles 36 in a matrix 34, can exhibit significant piezoelectric properties even without undergoing a stretching treatment after a polarization treatment. Therefore, the polymer composite piezoelectric body of the present invention has no in-plane anisotropy in its piezoelectric properties and, as described later, expands and contracts isotropically in all in-plane directions when a driving voltage is applied.

[0200] The polymer composite piezoelectric body and the piezoelectric thin film 10 of the present invention can be produced using a cut sheet, but preferably using a roll-to-roll (hereinafter also referred to as RtoR) process.

[0201] As is well known, RtoR is a manufacturing method in which a raw material is drawn from a roll formed by winding a long raw material, transported in the longitudinal direction, subjected to various treatments such as film formation and surface treatment, and then the treated raw material is rewound into a roll.

[0202] When the piezoelectric film 10 is manufactured using the RtoR manufacturing method, a first roller is used, which is formed by winding a sheet 10a on top of a long lower protective layer 28 to form a lower electrode 24, and a second roller is used, which is formed by winding a sheet 10c on top of a long upper protective layer 30 to form an upper electrode 26.

[0203] The first roller and the second roller may be completely identical.

[0204] The sheet 10a is drawn out from the roller and conveyed in the longitudinal direction, and is coated with a coating material containing a matrix 34 and piezoelectric particles 36 and dried by heating etc., thereby forming the piezoelectric layer 20 on the lower electrode 24 as the laminate 10b.

[0205] Next, the polarization treatment is performed to polarize the piezoelectric layer 20. When the piezoelectric film 10 is manufactured by RtoR, the laminate 10b is transported while polarizing the piezoelectric layer 20. As described above, calendering may be performed before the polarization treatment.

[0206] Next, the sheet 10c is drawn out from the second roller, and the sheet 10c and the laminate are conveyed. As described above, the sheet 10c is laminated on the laminate 10b with the upper electrode 26 facing the piezoelectric layer 20 by a known method using laminating rollers or the like.

[0207] Then, the stacked laminate 10b and the sheet 10c are sandwiched and conveyed by a pair of heated rollers, thereby being thermocompression-bonded to complete the piezoelectric film 10 of the present invention. The piezoelectric film 10 is then wound into a roll.

[0208] In the above examples, the piezoelectric film 10 of the present invention is produced by transporting the sheet (laminated body) only once in the longitudinal direction using RtoR, but the present invention is not limited to this.

[0209] For example, the laminate 10b is formed and polarized, and then a roll of the laminate is formed. The laminate is then unwound from the roll, conveyed in the longitudinal direction, and laminated onto the upper protective layer 30 to form the sheet-like upper electrode 26 as described above. This completes the piezoelectric film 10, which is then wound into a roll.

[0210] In this piezoelectric film 10, when a voltage is applied to the lower electrode 24 and the upper electrode 26, the piezoelectric particles 36 expand and contract in the polarization direction according to the applied voltage. As a result, the piezoelectric film 10 (piezoelectric layer 20) contracts in the thickness direction. Simultaneously, due to the Poisson's ratio, the piezoelectric film 10 also expands and contracts in the in-plane direction. This expansion and contraction is approximately 0.01 to 0.1%. Furthermore, as described above, the in-plane expansion and contraction are isotropic in all directions.

[0211] As described above, the thickness of the piezoelectric layer 20 is preferably about 10 to 300 μm. Therefore, the maximum expansion and contraction in the thickness direction is approximately 0.3 μm, which is very small.

[0212] In contrast, the piezoelectric film 10, ie, the piezoelectric layer 20, has a dimension in the planar direction that is much greater than its thickness. Therefore, for example, if the piezoelectric film 10 is 20 cm long, the piezoelectric film 10 expands and contracts by a maximum of approximately 0.2 mm when a voltage is applied.

[0213] When pressure is applied to the piezoelectric thin film 10 , electricity is generated by the action of the piezoelectric particles 36 .

[0214] By utilizing this point, as described above, the piezoelectric film 10 can be used for various applications such as a speaker, a microphone, and a pressure sensor.

[0215] [Piezoelectric Speaker]

[0216] Figure 6 A schematic diagram showing an example of a flat-plate piezoelectric speaker including the piezoelectric film 10 of the present invention.

[0217] The piezoelectric speaker 45 is a flat-plate piezoelectric speaker that uses the piezoelectric film 10 of the present invention as a vibration plate for converting an electrical signal into vibration energy. The piezoelectric speaker 45 can also be used as a microphone, a sensor, or the like.

[0218] The piezoelectric speaker 45 includes a piezoelectric film 10 , a housing 43 , a viscoelastic support 46 , and a frame 48 .

[0219] The housing 43 is a thin rectangular cylindrical housing made of plastic or the like with one surface open.

[0220] The frame 48 is a plate having a through hole at the center and the same shape as the upper end surface (open surface side) of the housing 43 .

[0221] The viscoelastic support 46 has moderate viscosity and elasticity, and is used to support the piezoelectric film 10. By applying a constant mechanical bias to any portion of the piezoelectric film, the expansion and contraction motion of the piezoelectric film 10 is converted into forward and backward motion (motion perpendicular to the film surface) without waste. Examples of the viscoelastic support 46 include wool felt, non-woven fabrics such as rayon or PET-containing wool felt, and glass wool.

[0222] The piezoelectric speaker 45 is constructed by accommodating a viscoelastic support body 46 in a shell 43, covering the shell 43 and the viscoelastic support body 46 with a piezoelectric film 10, and fixing the frame 48 on the shell 43 while pressing the periphery of the piezoelectric film 10 against the upper end surface of the shell 43 through the frame 48.

[0223] Here, in the piezoelectric speaker 45 , the viscoelastic support body 46 has a quadrangular prism shape whose height (thickness) is thicker than the height of the inner surface of the housing 43 .

[0224] Therefore, in the piezoelectric speaker 45, the viscoelastic support 46 is held in a reduced thickness state while being pressed downward by the piezoelectric film 10 at the periphery of the viscoelastic support 46. Furthermore, the curvature of the piezoelectric film 10 changes dramatically at the periphery of the viscoelastic support 46, forming a rising portion 45a on the piezoelectric film 10 that becomes lower toward the periphery of the viscoelastic support 46. Furthermore, the central region of the piezoelectric film 10 is pressed by the quadrangular prism-shaped viscoelastic support 46, becoming (substantially) flat.

[0225] In the piezoelectric speaker 45, when a driving voltage is applied to the lower electrode 24 and the upper electrode 26, the piezoelectric film 10 expands in the in-plane direction. To absorb this expansion, the viscoelastic support 46 acts to cause the rising portion 45a of the piezoelectric film 10 to change its angle in the rising direction. As a result, the planar portion of the piezoelectric film 10 moves upward.

[0226] Conversely, when a driving voltage is applied to the lower electrode 24 and the upper electrode 26, causing the piezoelectric film 10 to contract in the in-plane direction, the rising portion 45a of the piezoelectric film 10 changes its angle in the direction of inclination (the direction toward the plane) to absorb this contraction. As a result, the planar portion of the piezoelectric film 10 moves downward.

[0227] The piezoelectric speaker 45 generates sound by the vibration of the piezoelectric film 10 .

[0228] Furthermore, in the piezoelectric film 10 of the present invention, conversion from expansion and contraction motion to vibration can also be achieved by maintaining the piezoelectric film 10 in a curved state.

[0229] Therefore, the piezoelectric film 10 of the present invention can function as a speaker having flexibility even if it is not such a piezoelectric speaker 45 but is simply kept in a bent state.

[0230] [Electroacoustic Converter]

[0231] Figure 7 An example of an electroacoustic transducer including the piezoelectric thin film 10 of the present invention is schematically shown.

[0232] Figure 7 The electroacoustic converter 50 shown has a laminated piezoelectric element 14 and a vibration plate 12. The laminated piezoelectric element 14 is formed by laminating a plurality of piezoelectric films of the present invention. Figure 7 In the example shown, the laminated piezoelectric element 14 is formed by laminating three layers of the piezoelectric thin films 10 of the present invention described above.

[0233] In the electroacoustic transducer 50 , the laminated piezoelectric element 14 and the vibration plate 12 are bonded together via an adhesive layer 16 .

[0234] A power supply PS for applying a driving voltage is connected to the piezoelectric film 10 of the laminated piezoelectric element 14 constituting the electroacoustic transducer 50 .

[0235] To simplify the drawings, Figure 7 The lower protective layer 28 and the upper protective layer 30 are omitted. Figure 7 In the illustrated laminated piezoelectric element 14 , as a preferred embodiment, all the piezoelectric films 10 have both a lower protective layer 28 and an upper protective layer 30 .

[0236] In addition, the stacked piezoelectric element is not limited to this, and a piezoelectric film with a protective layer and a piezoelectric film without a protective layer may be mixed. Furthermore, when the piezoelectric film has a protective layer, the piezoelectric film 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 can also be a structure in which the top piezoelectric film in the figure only has an upper protective layer 30, the middle piezoelectric film has no protective layer, and the bottom piezoelectric film only has a lower protective layer 28.

[0237] Regarding this point, the following Figure 8 The stacked piezoelectric element 56 and Figure 9 The same applies to the laminated piezoelectric element 60 shown.

[0238] As will be described in detail later, in the electroacoustic transducer 50 , a driving voltage is applied to the piezoelectric film 10 of the stacked piezoelectric element 14 , causing the piezoelectric film 10 to expand and contract in the planar direction. As a result of this expansion and contraction of the piezoelectric film 10 , the stacked piezoelectric element 14 expands and contracts in the planar direction.

[0239] The expansion and contraction of the laminated piezoelectric element 14 in the plane direction causes the vibration plate 12 to bend, resulting in the vibration of the vibration plate 12 in the thickness direction. This thickness-direction vibration generates sound in the vibration plate 12. The vibration of the vibration plate 12 is responsive to the magnitude of the driving voltage applied to the piezoelectric film 10, generating sound corresponding to the driving voltage applied to the piezoelectric film 10.

[0240] That is, the electroacoustic transducer 50 is a speaker using the laminated piezoelectric element 14 as an exciter.

[0241] In the electroacoustic transducer 50, the vibration plate 12 is preferably flexible. In the present invention, the term "flexible" has the same meaning as commonly understood, meaning capable of bending and flexing. Specifically, it means capable of bending and stretching without causing breakage or damage.

[0242] The vibration plate 12 preferably has flexibility, and is not limited as long as it satisfies the relationship with the laminated piezoelectric element 14 described later, and various sheet-shaped objects (plate-shaped objects, films) can be used.

[0243] As an example, there can be cited 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, foamed plastics composed of expanded polystyrene, expanded polystyrene and expanded polyethylene, and various corrugated cardboard materials obtained by pasting other cardboards on one or both sides of a corrugated cardboard.

[0244] Furthermore, in the electroacoustic transducer 50, as long as it is flexible, display devices such as an organic electroluminescent display (OLED (Organic Light Emitting Diode)), a liquid crystal display, a micro LED (Light Emitting Diode) display, and an inorganic electroluminescent display can also be appropriately used as the vibration plate 12.

[0245] exist Figure 7 In the illustrated electroacoustic transducer 50 , the vibration plate 12 and the laminated piezoelectric element 14 are preferably bonded together via an adhesive layer 16 .

[0246] As the adhesive layer 16 , various known adhesive layers can be used as long as they can adhere the vibration plate 12 and the laminated piezoelectric element 14 .

[0247] Therefore, the adhesive layer 16 can be a layer composed of an adhesive that has fluidity when adhered and then becomes solid, or it can be a layer composed of an adhesive that is a soft solid that is in a gel (rubber) state when adhered and then does not change its gel state, or it can be a layer composed of a material having the characteristics of both an adhesive and an adhesive.

[0248] Here, in the electroacoustic transducer 50, sound is generated by the expansion and contraction of the laminated piezoelectric element 14, which causes the vibration plate 12 to bend and vibrate. Therefore, in the electroacoustic transducer 50, it is preferable that the expansion and contraction of the laminated piezoelectric element 14 be directly transmitted to the vibration plate 12. If a viscous material with relaxation vibration exists between the vibration plate 12 and the laminated piezoelectric element 14, the efficiency of transmitting the expansion and contraction energy of the laminated piezoelectric element 14 to the vibration plate 12 decreases, resulting in a decrease in the driving efficiency of the electroacoustic transducer 50.

[0249] In view of this, the adhesive layer 16 is preferably an adhesive layer composed of an adhesive agent, which can obtain a harder solid adhesive layer 16 than an adhesive layer composed of an adhesive agent. More preferred adhesive layers 16 include, for example, adhesive layers composed of thermoplastic adhesives such as polyester adhesives and styrene-butadiene rubber (SBR) adhesives.

[0250] Bonding, unlike adhesion, is useful when a high bonding temperature is required. Furthermore, thermoplastic adhesives are suitable because they offer a combination of relatively low temperatures, short bonding times, and strong adhesion.

[0251] The thickness of the adhesive layer 16 is not limited, and can be appropriately set according to the material of the adhesive layer 16 so as to obtain sufficient adhesive force (adhesive force, cohesive strength).

[0252] Here, in the electroacoustic transducer 50, a thinner adhesive layer 16 can improve the transmission of the expansion and contraction energy (vibration energy) of the laminated piezoelectric element 14 to the diaphragm 12, thereby improving energy efficiency. Furthermore, a thicker and more rigid adhesive layer 16 can restrain the expansion and contraction of the laminated piezoelectric element 14.

[0253] In consideration of this, the adhesive layer 16 is preferably thin. Specifically, the thickness of the adhesive layer 16 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.

[0254] In the electroacoustic transducer 50 , the adhesive layer 16 is provided as a preferred embodiment and is not an essential component.

[0255] Therefore, the electroacoustic transducer 50 may not include the adhesive layer 16, but may use a known method such as crimping, fastening, or fixing to fix the vibration plate 12 and the laminated piezoelectric element 14. For example, if the laminated piezoelectric element 14 is rectangular, the electroacoustic transducer may be constructed by fastening the four corners with bolts and nuts, or by fastening the four corners and the center with bolts and nuts.

[0256] However, in this case, when a driving voltage is applied from the power supply PS, the stacked piezoelectric element 14 expands and contracts independently of the vibration plate 12. In some cases, only the stacked piezoelectric element 14 bends, and the expansion and contraction of the stacked piezoelectric element 14 is not transmitted to the vibration plate 12. In this way, when the stacked piezoelectric element 14 expands and contracts independently of the vibration plate 12, the vibration efficiency of the vibration plate 12 due to the stacked piezoelectric element 14 may be reduced, resulting in insufficient vibration of the vibration plate 12.

[0257] Considering this, the vibration plate 12 and the stacked piezoelectric element 14 are as follows. Figure 7 As shown, it is preferred to use an adhesive layer 16 for adhesion.

[0258] exist Figure 7 In the illustrated electroacoustic transducer 50, the laminated piezoelectric element 14 has a structure in which three piezoelectric films 10 are laminated and adjacent piezoelectric films 10 are bonded together by an adhesive layer 19. Each piezoelectric film 10 is connected to a power supply PS for applying a driving voltage to cause the piezoelectric film 10 to expand and contract.

[0259] in addition, Figure 7 The stacked piezoelectric element 14 shown is formed by stacking three layers of piezoelectric films 10, but the present invention is not limited to this. That is, as long as the stacked piezoelectric element is an element formed by stacking multiple layers of piezoelectric films 10, the number of layers of the piezoelectric films 10 may be 2, or may be 4 or more. Regarding this point, the following Figure 8 The stacked piezoelectric element 56 and Figure 9 The same applies to the laminated piezoelectric element 60 shown.

[0260] Furthermore, the electroacoustic transducer can also vibrate the diaphragm 12 with the same effect using the piezoelectric film of the present invention instead of the laminated piezoelectric element 14, thereby generating sound. That is, the electroacoustic transducer can also use the piezoelectric film of the present invention as an exciter.

[0261] Figure 7 The stacked piezoelectric element 14 shown in the figure preferably has the following structure: a plurality of layers are stacked so that the polarization directions of adjacent piezoelectric films 10 are opposite to each other. Figure 7 The example shown is a piezoelectric film 10 having three layers, and adjacent piezoelectric films 10 are bonded together using an adhesive layer 19 .

[0262] As the adhesive layer 19 , various known adhesive layers can be used as long as they can adhere the adjacent piezoelectric films 10 .

[0263] Therefore, the adhesive layer 19 may be a layer composed of the above-mentioned adhesive, a layer composed of an adhesive, or a layer composed of a material having characteristics of both an adhesive and an adhesive.

[0264] Here, the stacked piezoelectric element 14 generates sound by causing the stacked plurality of piezoelectric films 10 to expand and contract, thereby vibrating the diaphragm 12. Therefore, the stacked piezoelectric element 14 preferably directly transmits the expansion and contraction of each piezoelectric film 10. If a viscous substance with relaxation vibrations exists between the piezoelectric films 10, the efficiency of transmitting the energy of the expansion and contraction of the piezoelectric films 10 decreases, resulting in a decrease in the driving efficiency of the stacked piezoelectric element 14.

[0265] In view of this, the adhesive layer 19 is preferably an adhesive layer composed of an adhesive, which can obtain a harder solid adhesive layer 19 than an adhesive layer composed of an adhesive. As a more preferred adhesive layer 19, specifically, an adhesive layer composed of a thermoplastic adhesive such as a polyester adhesive and a styrene-butadiene rubber (SBR) adhesive can be preferably exemplified.

[0266] Bonding, unlike adhesion, is useful when a high bonding temperature is required. Furthermore, thermoplastic adhesives are suitable because they offer a combination of relatively low temperatures, short bonding times, and strong adhesion.

[0267] The thickness of the adhesive layer 19 is not limited, and may be appropriately set to a thickness that can exhibit sufficient adhesive strength, depending on the material forming the adhesive layer 19 .

[0268] Here, in Figure 7 In the laminated piezoelectric element 14 shown, a thinner adhesive layer 19 can enhance the transmission of the expansion and contraction energy of the piezoelectric film 10, thereby improving energy efficiency. Furthermore, a thicker and more rigid adhesive layer 19 can restrain the expansion and contraction of the piezoelectric film 10.

[0269] Taking this into consideration, the adhesive layer 19 is preferably thinner than the piezoelectric layer 20. That is, in the laminated piezoelectric element 14, the adhesive layer 19 is preferably hard and thin. Specifically, the thickness of the adhesive layer 19 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.

[0270] In addition, as mentioned later, Figure 7 In the stacked piezoelectric element 14 shown, the polarization directions of adjacent piezoelectric films are opposite to each other, and adjacent piezoelectric films 10 are prevented from short-circuiting, so that the adhesive layer 19 can be made thinner.

[0271] exist Figure 7In the laminated piezoelectric element 14 shown, if the spring constant (thickness x Young's modulus) of the adhesive layer 19 is high, the expansion and contraction of the piezoelectric film 10 may be restrained. Therefore, the spring constant of the adhesive layer 19 is preferably equal to or less than that of the piezoelectric film 10.

[0272] 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 measurement is preferably 2.0×10 6 N / m or less, 1.0×10 at 50°C 6 Below N / m.

[0273] Furthermore, the internal loss of the adhesive layer at a frequency of 1 Hz based on dynamic viscoelasticity measurement is preferably 1.0 or less at 25°C when the adhesive layer 19 is composed of a binder, and 0.1 or less at 25°C when the adhesive layer 19 is composed of an adhesive.

[0274] In the laminated piezoelectric element 14 constituting the electroacoustic transducer 50 , the adhesive layer 19 is provided as a preferred embodiment and is not an essential component.

[0275] Therefore, the stacked piezoelectric element constituting the electroacoustic transducer may not have the adhesive layer 19, but may be formed by stacking and adhering the piezoelectric films 10 using a known crimping method, fastening method, or fixing method. For example, if the piezoelectric film 10 is rectangular, the stacked piezoelectric element may be formed by fastening the four corners with bolts and nuts, or by fastening the four corners and the center with bolts and nuts. Alternatively, the stacked piezoelectric element may be formed by attaching adhesive tape to the peripheral portions (end faces) of the stacked piezoelectric films 10 after the piezoelectric films 10 are stacked.

[0276] However, in this case, when a driving voltage is applied from the power supply PS, each piezoelectric film 10 expands and contracts independently. In some cases, the layers of each piezoelectric film 10 may flex in opposite directions, forming gaps. This independent expansion and contraction of each piezoelectric film 10 reduces the driving efficiency of the stacked piezoelectric element, and the overall expansion and contraction of the stacked piezoelectric element decreases, potentially preventing sufficient vibration of an abutting vibration plate, etc. In particular, when the layers of each piezoelectric film 10 flex in opposite directions, forming gaps, the driving efficiency of the stacked piezoelectric element decreases significantly.

[0277] With this in mind, Figure 7 Like the illustrated laminated piezoelectric element 14 , the laminated piezoelectric element preferably includes an adhesive layer 19 in which adjacent piezoelectric films 10 are bonded to each other.

[0278] like Figure 7As shown, in the electroacoustic transducer 50 , a power source PS is connected to the lower electrode 24 and the upper electrode 26 of each piezoelectric film 10 . The power source PS applies a driving voltage for causing the piezoelectric film 10 to expand and contract, that is, provides driving power.

[0279] The power source PS is not limited and can be either a DC power source or an AC power source. Furthermore, the driving voltage can be appropriately set to a voltage that can appropriately drive each piezoelectric film 10 according to the thickness and forming material of the piezoelectric layer 20 of each piezoelectric film 10 .

[0280] As will be described later, the polarization directions of the adjacent piezoelectric films 10 of the stacked piezoelectric element 14 are opposite. Therefore, in the adjacent piezoelectric films 10, the lower electrodes 24 and the upper electrodes 26 are opposite to each other. Therefore, regardless of whether it is an AC power supply or a DC power supply, the power supply PS always supplies power of the same polarity to the opposing electrodes. For example, in Figure 7 In the stacked piezoelectric element 14 shown, electric power of the same polarity is always supplied to the upper electrode 26 of the bottom piezoelectric film 10 and the upper electrode 26 of the second (middle) piezoelectric film 10, and electric power of the same polarity is always supplied to the lower electrode 24 of the second piezoelectric film 10 and the lower electrode 24 of the top piezoelectric film 10 in the figure.

[0281] There is no limitation on the method of extracting electrodes from the lower electrode 24 and the upper electrode 26 , and various known methods can be used.

[0282] As an example, there can be cited a method of connecting a conductor such as copper foil to the lower electrode 24 and the upper electrode 26 to lead the electrodes to the outside, and a method of forming through holes in the lower protective layer 28 and the upper protective layer 30 by laser or the like, and filling the through holes with conductive material to lead the electrodes to the outside.

[0283] Preferred methods for extracting the electrodes include the method described in Japanese Patent Application Laid-Open No. 2014-209724 and the method described in Japanese Patent Application Laid-Open No. 2016-015354.

[0284] As described above, the piezoelectric layer 20 is formed by dispersing the piezoelectric particles 36 in the matrix 34. The lower electrode 24 and the upper electrode 26 are provided so as to sandwich the piezoelectric layer 20 in the thickness direction.

[0285] When a voltage is applied to the lower electrode 24 and upper electrode 26 of the piezoelectric film 10 having the piezoelectric layer 20, the piezoelectric particles 36 expand and contract in the polarization direction according to the applied voltage. As a result, the piezoelectric film 10 (piezoelectric layer 20) contracts in the thickness direction. Simultaneously, due to the Poisson's ratio, the piezoelectric film 10 also expands and contracts in the in-plane direction.

[0286] The expansion and contraction is approximately 0.01 to 0.1%.

[0287] As described above, the thickness of the piezoelectric layer 20 is preferably about 10 to 300 μm. Therefore, the maximum expansion and contraction in the thickness direction is approximately 0.3 μm, which is very small.

[0288] In contrast, the piezoelectric film 10, ie, the piezoelectric layer 20, has a dimension in the planar direction that is much greater than its thickness. Therefore, for example, if the piezoelectric film 10 is 20 cm long, the piezoelectric film 10 expands and contracts by a maximum of approximately 0.2 mm when a voltage is applied.

[0289] The laminated piezoelectric element 14 is formed by laminating and pasting the piezoelectric thin film 10. Therefore, when the piezoelectric thin film 10 expands or contracts, the laminated piezoelectric element 14 also expands or contracts.

[0290] The vibration plate 12 is adhered to the laminated piezoelectric element 14 via an adhesive layer 16. Therefore, the vibration plate 12 is bent by the expansion and contraction of the laminated piezoelectric element 14, and as a result, the vibration plate 12 vibrates in the thickness direction.

[0291] The vibration in the thickness direction generates sound from the vibration plate 12. That is, the vibration plate 12 vibrates according to the magnitude of the voltage (driving voltage) applied to the piezoelectric film 10, generating sound corresponding to the driving voltage applied to the piezoelectric film 10.

[0292] As described above, a typical piezoelectric film made of a polymer material such as PVDF has in-plane anisotropy in its piezoelectric characteristics and anisotropy in the amount of expansion and contraction in the plane direction when a voltage is applied.

[0293] In contrast, in Figure 7 In the electroacoustic transducer 50 shown, the piezoelectric film 10 of the present invention constituting the laminated piezoelectric element 14 has no in-plane anisotropy in its piezoelectric characteristics and expands and contracts isotropically in all directions in the in-plane direction. Figure 7 In the illustrated electroacoustic transducer 50 , the piezoelectric film 10 constituting the laminated piezoelectric element 14 expands and contracts isotropically and two-dimensionally.

[0294] The stacked piezoelectric element 14 formed by stacking such isotropically two-dimensionally expanding and contracting piezoelectric films 10 can vibrate the vibration plate 12 with greater force compared to stacking conventional piezoelectric films such as PVDF that expand and contract greatly in only one direction, thereby producing a louder and more beautiful sound.

[0295] Figure 7 The laminated piezoelectric element 14 shown is formed by laminating a plurality of piezoelectric films 10. In a preferred embodiment, the laminated piezoelectric element 14 is formed by laminating adjacent piezoelectric films 10 with an adhesive layer 19.

[0296] Therefore, even if the rigidity and expansion force of each individual piezoelectric film 10 are low, by stacking the piezoelectric films 10, the rigidity becomes higher, and the expansion force of the stacked piezoelectric element 14 becomes larger. As a result, in the stacked piezoelectric element 14, even if the vibration plate 12 has a certain degree of rigidity, the vibration plate 12 can be sufficiently bent with a large force, causing the vibration plate 12 to vibrate sufficiently in the thickness direction, thereby causing the vibration plate 12 to produce sound.

[0297] Furthermore, the thicker the piezoelectric layer 20, the greater the expansion and contraction force of the piezoelectric thin film 10. However, the driving voltage required to achieve the same amount of expansion and contraction also increases accordingly. As described above, in the stacked piezoelectric element 14, the preferred maximum thickness of the piezoelectric layer 20 is approximately 300 μm. Therefore, even with a low voltage applied to each piezoelectric thin film 10, the piezoelectric thin film 10 can still expand and contract sufficiently.

[0298] The product of the thickness of the laminated piezoelectric element 14 and the storage modulus at a frequency of 1 Hz and 25° C. based on dynamic viscoelasticity measurement is preferably 0.1 to 3 times the product of the thickness of the vibration plate 12 and the Young's modulus.

[0299] As described above, the piezoelectric film 10 of the present invention has excellent flexibility, and the laminated piezoelectric element 14 formed by laminating the piezoelectric films 10 also has excellent flexibility.

[0300] On the other hand, the vibration plate 12 has a certain degree of rigidity. If the highly rigid laminated piezoelectric element 14 is combined with such a vibration plate 12 , the plate becomes rigid and difficult to bend, which is disadvantageous in terms of the flexibility of the electroacoustic transducer 50 .

[0301] In contrast, for the electroacoustic transducer 50, the product of the thickness of the laminated piezoelectric element 14 and its storage modulus at a frequency of 1 Hz and 25°C, as measured by dynamic viscoelasticity, is preferably no greater than three times the product of the thickness of the diaphragm 12 and its Young's modulus. In other words, the spring constant of the laminated piezoelectric element 14 is preferably no greater than three times that of the diaphragm 12 for slow motion.

[0302] With such a structure, the electroacoustic transducer 50 can operate flexibly with respect to slow movements caused by external forces such as bending and rolling, that is, it can exhibit good flexibility with respect to slow movements.

[0303] In the electroacoustic transducer 50, the product of the thickness of the stacked piezoelectric element 14 and the storage modulus at a frequency of 1 Hz and 25°C based on dynamic viscoelasticity measurement is preferably less than 2 times the product of the thickness of the vibration plate 12 and the Young's modulus, further preferably less than 1 times, and particularly preferably less than 0.3 times.

[0304] On the other hand, considering the materials used for the stacked piezoelectric element 14, the preferred structure of the stacked piezoelectric element 14, etc., the product of the thickness of the stacked piezoelectric element 14 and the storage modulus at a frequency of 1 Hz and 25°C based on dynamic viscoelasticity measurement is preferably greater than 0.1 times the product of the thickness of the vibration plate 12 and the Young's modulus.

[0305] In the electroacoustic transducer 50, the product of the thickness of the laminated piezoelectric element 14 and the storage modulus at a frequency of 1 kHz and 25°C, as measured in the master curve obtained through dynamic viscoelasticity measurements, is preferably 0.3 to 10 times the product of the thickness of the diaphragm 12 and its Young's modulus. In other words, during rapid motion in a driven state, the laminated piezoelectric element 14 preferably has a spring constant 0.3 to 10 times that of the diaphragm 12.

[0306] As described above, the electroacoustic transducer 50 generates sound by vibrating the diaphragm 12 through the planar expansion and contraction of the laminated piezoelectric element 14. Therefore, the laminated piezoelectric element 14 preferably has a certain degree of rigidity (hardness, stiffness) relative to the diaphragm 12 at frequencies in the audio band (20 Hz to 20 kHz).

[0307] In the electroacoustic transducer 50, the product of the thickness of the laminated piezoelectric element 14 and the storage modulus at a frequency of 1 kHz and 25°C in the master curve obtained by dynamic viscoelasticity measurement is preferably set to be at least 0.3 times, more preferably at least 0.5 times, and even more preferably at least 1 times the product of the thickness of the diaphragm 12 and the Young's modulus. In other words, the spring constant of the laminated piezoelectric element 14 is preferably at least 0.3 times, more preferably at least 0.5 times, and even more preferably at least 1 times that of the diaphragm 12 for rapid motion.

[0308] Thus, the rigidity of the laminated piezoelectric element 14 relative to the diaphragm 12 is sufficiently ensured at frequencies in the audio band, and the electroacoustic transducer 50 can output sound at a high sound pressure with high energy efficiency.

[0309] On the other hand, considering the materials that can be used for the stacked piezoelectric element 14, the preferred structure of the stacked piezoelectric element 14, etc., the product of the thickness of the stacked piezoelectric element 14 and the storage modulus at a frequency of 1 kHz and 25°C based on dynamic viscoelasticity measurement is preferably less than 10 times the product of the thickness of the vibration plate 12 and the Young's modulus.

[0310] The product of the thickness and the storage modulus mentioned above also applies when the electroacoustic transducer is configured using the piezoelectric film 10 instead of the laminated piezoelectric element 14 .

[0311] As a preferred method, Figure 7 In the illustrated electroacoustic transducer 50 , as described above, the polarization directions of the piezoelectric layers 20 of the adjacent piezoelectric films 10 of the stacked piezoelectric element 14 are opposite to each other.

[0312] In the piezoelectric film 10, the polarity of the voltage applied to the piezoelectric layer 20 corresponds to the polarization direction. Figure 7 In the polarization direction indicated by the arrow, the polarity of the electrode on the arrow side (downstream side) and the polarity of the electrode on the opposite side (upstream side) are made consistent in all the piezoelectric films 10 .

[0313] exist Figure 7 In the example shown, the electrode on the side indicated by the arrow indicating the polarization direction is the lower electrode 24 , and the electrode on the opposite side is the upper electrode 26 . In all piezoelectric films 10 , the polarity of the upper electrode 26 and the polarity of the lower electrode 24 are the same.

[0314] Therefore, in a stacked piezoelectric element 14 in which the polarization directions of the piezoelectric layers 20 of adjacent piezoelectric films 10 are opposite to each other, the upper electrodes 26 of the adjacent piezoelectric films 10 face each other on one surface, and the lower electrodes face each other on the other surface. Therefore, in the stacked piezoelectric element 14, even if the electrodes of the adjacent piezoelectric films 10 come into contact with each other, a short circuit does not occur.

[0315] As described above, in order to expand and contract the multi-layer piezoelectric element 14 with good energy efficiency, it is preferable to make the adhesive layer 19 thinner so that the adhesive layer 19 does not hinder the expansion and contraction of the piezoelectric layer 20 .

[0316] On the other hand, even if the electrodes of the adjacent piezoelectric films 10 come into contact with each other, there is no short circuit. Figure 7 The illustrated laminated piezoelectric element 14 may not have the adhesive layer 19. As a preferred embodiment, even when the adhesive layer 19 is present, the adhesive layer 19 can be made extremely thin as long as the necessary adhesive force can be obtained.

[0317] Therefore, the laminated piezoelectric element 14 can be expanded and contracted with high energy efficiency.

[0318] Furthermore, as described above, in the piezoelectric film 10 , the absolute amount of expansion and contraction of the piezoelectric layer 20 in the thickness direction is very small, and the expansion and contraction of the piezoelectric film 10 occurs substantially only in the surface direction.

[0319] Therefore, even if the polarization directions of the stacked piezoelectric 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 piezoelectric films 10 expand and contract in the same direction.

[0320] In addition, in the laminated piezoelectric element 14 , the polarization direction of the piezoelectric thin film 10 can be detected using a d33 meter or the like.

[0321] Alternatively, the polarization direction of the piezoelectric film 10 may be known based on the processing conditions of the polarization treatment.

[0322] Figure 7 The stacked piezoelectric element 14 shown is preferably formed by manufacturing a long (large-area) piezoelectric film as described above and cutting the long piezoelectric film into individual piezoelectric films 10. Therefore, in this case, the plurality of piezoelectric films 10 constituting the stacked piezoelectric element 14 are all identical.

[0323] However, the present invention is not limited to this. Specifically, in the electroacoustic transducer, the piezoelectric stack can employ various structures, for example, a structure in which piezoelectric films having different layer structures are stacked, such as a piezoelectric film having a lower protective layer 28 and an upper protective layer 30 and a piezoelectric film not having these layers, or a structure in which piezoelectric films having different thicknesses of the piezoelectric layer 20 are stacked.

[0324] exist Figure 7 In the illustrated electroacoustic transducer 50 , the laminated piezoelectric element 14 is formed by laminating a plurality of piezoelectric films 10 with the polarization directions of adjacent piezoelectric films being opposite to each other. Preferably, the adjacent piezoelectric films 10 are bonded together using an adhesive layer 19 .

[0325] The multi-layer piezoelectric element of the present invention is not limited thereto, and various structures can be employed.

[0326] Figure 8 Indicates an example. Figure 8 The illustrated laminated piezoelectric element 56 uses a plurality of components identical to those of the laminated piezoelectric element 14 described above. Therefore, identical components are denoted by identical reference numerals, and the description will focus on different portions.

[0327] Figure 8 The stacked piezoelectric element 56 shown is a more preferred embodiment of the stacked piezoelectric element of the present invention, which is formed by folding the long piezoelectric film 10L back more than once in the longitudinal direction, preferably folding it back multiple times, and stacking multiple layers of piezoelectric films 10L. Figure 7 The same as the stacked piezoelectric element 14 shown in FIG. Figure 8 The laminated piezoelectric element 56 shown is also preferably formed by laminating the piezoelectric film 10L by folding and laminating them with the adhesive layer 19 .

[0328] By folding back a long piezoelectric film 10L polarized in the thickness direction and stacking them, the polarization directions of the piezoelectric films 10L adjacent (opposite) in the stacking direction are as follows: Figure 8 As shown by the arrow in the middle, it becomes the opposite direction.

[0329] According to this structure, the laminated piezoelectric element 56 can be formed of only one long piezoelectric film 10L, and only one power supply PS is required to apply a driving voltage. Furthermore, only one electrode can be drawn out from the piezoelectric film 10L.

[0330] Therefore, according to Figure 8 The stacked piezoelectric element 56 shown can reduce the number of parts and simplify the structure, thereby improving the reliability of the piezoelectric element (module) and achieving cost reduction.

[0331] like Figure 8 In the stacked piezoelectric element 56 formed by folding back a long piezoelectric film 10L as shown, it is preferable to insert a core rod 58 into the folded portion of the piezoelectric film 10L so as to abut against the piezoelectric film 10L.

[0332] As described above, the lower electrode 24 and the upper electrode 26 of the piezoelectric film 10L are formed of a metal vapor-deposited film or the like. If the metal vapor-deposited film is bent at an acute angle, cracks (fissures) are likely to occur, and the electrodes may be disconnected. Figure 8 In the illustrated laminated piezoelectric element 56 , cracks and the like easily penetrate into the electrodes on the inner side of the bent portion.

[0333] In contrast, in the stacked piezoelectric element 56 formed by folding the long piezoelectric film 10L, the core rod 58 is inserted into the folded portion of the piezoelectric film 10L to prevent the lower electrode 24 and the upper electrode 26 from being bent, thereby appropriately preventing the occurrence of disconnection.

[0334] In the present invention, the laminated piezoelectric element may also use the conductive adhesive layer 19. Figure 8 In the laminated piezoelectric element 56 formed by folding and laminating a single long piezoelectric film 10L, the conductive adhesive layer 19 can be preferably used.

[0335] In such Figure 7 and Figure 8 In the stacked piezoelectric element shown in which the polarization directions of the adjacent piezoelectric films 10 are opposite, electric power of the same polarity is supplied between the opposing electrodes in the stacked piezoelectric films 10. Therefore, a short circuit does not occur between the opposing electrodes.

[0336] On the other hand, as described above, in the laminated piezoelectric element 56 formed by folding and laminating the piezoelectric film 10L, disconnection of the electrodes is likely to occur inside the bent portion folded at an acute angle.

[0337] Therefore, by using the conductive adhesive layer 19 to adhere the stacked piezoelectric film 10L, even if the electrode is disconnected on the inner side of the bent portion, the adhesive layer 19 can ensure conductivity, thereby preventing disconnection and significantly improving the reliability of the stacked piezoelectric element 56.

[0338] Here, the piezoelectric film 10L constituting the stacked piezoelectric element 56 is preferably as follows: Figure 1As shown, a lower protective layer 28 and an upper protective layer 30 are provided so as to face the lower electrode 24 and the upper electrode 26 and sandwich the laminate.

[0339] In this case, even with the use of a conductive adhesive layer 19, conductivity cannot be ensured. Therefore, when the piezoelectric film 10L includes a protective layer, through-holes are provided in the lower protective layer 28 and the upper protective layer 30 in the regions where the lower electrodes 24 and the upper electrodes 26 of the stacked piezoelectric films 10L face each other, so that the lower electrodes 24 and the upper electrodes 26 are in contact with the conductive adhesive layer 19. Preferably, the through-holes formed in the lower protective layer 28 and the upper protective layer 30 are sealed with silver paste or a conductive adhesive, and then adjacent piezoelectric films 10L are bonded together using the conductive adhesive layer 19.

[0340] The through holes in the lower protective layer 28 and the upper protective layer 30 may be formed by removing the protective layers by laser processing, solvent etching, mechanical polishing, or the like.

[0341] The through-holes in the lower protective layer 28 and the upper protective layer 30 may be formed at one or more locations, in addition to the curved portion of the piezoelectric film 10L, in the regions where the lower electrodes 24 and the upper electrodes 26 of the stacked piezoelectric film 10L face each other. Alternatively, the through-holes in the lower protective layer 28 and the upper protective layer 30 may be formed regularly or irregularly over the entire surface of the lower protective layer 28 and the upper protective layer 30.

[0342] The conductive adhesive layer 19 is not limited, and various known adhesive layers can be used.

[0343] In the above-described stacked piezoelectric element, the polarization directions of the stacked piezoelectric films 10 are opposite to each other in adjacent piezoelectric films 10 , but the present invention is not limited to this.

[0344] That is, in the present invention, the laminated piezoelectric element formed by laminating the piezoelectric thin films 10 may also be Figure 9 As in the illustrated laminated piezoelectric element 60 , the polarization directions of all the piezoelectric layers 20 are in the same direction.

[0345] However, if Figure 9 As shown, in a stacked piezoelectric element 60 in which the polarization directions of all the stacked piezoelectric films 10 are in the same direction, the lower electrode 24 and the upper electrode 26 face each other between adjacent piezoelectric films 10. Therefore, if the adhesive layer 19 is not sufficiently thick, the lower electrodes 24 and the upper electrodes 26 of the adjacent piezoelectric films 10 may come into contact at the outer end portions in the surface direction of the adhesive layer 19, thereby causing a short circuit.

[0346] Therefore, if Figure 9As shown, in the stacked piezoelectric element 60 in which the polarization directions of the stacked piezoelectric films 10 are all in the same direction, the adhesive layer 19 cannot be made thinner. Figure 7 and Figure 8 The stacked piezoelectric element shown is disadvantageous in terms of energy efficiency.

[0347] While the polymer composite piezoelectric body and the piezoelectric thin film of the present invention have been described in detail above, the present invention is not limited to the above examples, and various improvements and modifications can of course be made without departing from the spirit of the present invention.

[0348] Example

[0349] Hereinafter, specific embodiments of the present invention are listed to describe the present invention in more detail.

[0350] [Example 1]

[0351] <Paint Preparation>

[0352] First, cyanoethylated PVA (CR-V Shin-Etsu Chemical Co., Ltd.) was dissolved in methyl ethyl ketone (MEK) according to the following composition ratio. PZT particles were then added to this solution at the following composition ratio and dispersed using a propeller mixer (2000 rpm) to prepare a coating for forming the piezoelectric layer.

[0353] The coating liquid was passed through an inline mixer (MX-F8 manufactured by OHR Laboratory Corporation) at a flow rate of 5 kg / min, and the bubbles in the coating liquid were miniaturized.

[0354] (coating)

[0355] ·PZT particles·············300 parts by mass

[0356] ·Cyanoethylated PVA···········30 parts by mass

[0357] MEK···············70 parts by mass

[0358] The PZT particles used were obtained by sintering commercially available PZT raw material powder at 1000 to 1200° C., and then pulverizing and classifying the powder to have an average particle size of 5 μm.

[0359] <Coating>

[0360] On the other hand, a sheet was prepared by vacuum-evaporating a 0.1 μm thick copper thin film onto a 4 μm thick PET film. That is, in this example, the thin film electrode was a 0.1 μm thick copper vapor-deposited film, and the protective layer was a 4 μm thick PET film.

[0361] The coating material for forming the piezoelectric layer prepared previously was applied onto the thin film electrode (copper vapor-deposited film) of the sheet using a slide coater. The coating material was applied so that the thickness of the coating film after drying would be 40 μm.

[0362] <Drying of paint>

[0363] Next, the coating was applied to the sheet and dried on a 100°C hot plate for 30 minutes to partially evaporate the MEK. This produced a laminate comprising a copper thin-film electrode on top of a PET protective layer, and a 40 μm-thick piezoelectric layer (polymer composite piezoelectric) formed thereon.

[0364] Polarization treatment

[0365] Next, the piezoelectric layer of the stacked body was subjected to polarization treatment.

[0366] <Lamination of Sheets>

[0367] The sheet-like object was stacked on the polarized laminate with the thin film electrode (copper thin film side) facing the piezoelectric layer. Next, a laminating device was used to bond the laminate and the sheet-like object to the piezoelectric layer and the thin film electrode.

[0368] The piezoelectric film was manufactured through the above steps.

[0369] <Measurement of pore volume per unit area>

[0370] (Cutting out samples)

[0371] A sample was cut out from the produced piezoelectric film, and the pore volume per unit area was measured by the following method.

[0372] The samples were cut into 12.5 mm x 25 mm pieces by cutting the piezoelectric film in the thickness direction. A craft cutter (product number: XB141) manufactured by OLFA CORPORATION was used as the cutter for cutting the samples. A new blade was prepared for each sample.

[0373] The cut samples were weighed using an electronic balance (AW220) manufactured by Shimadzu Corporation, and the number of samples was adjusted so that the total mass of the samples was 1.2 g to 1.5 g. In Example 1, the number of samples was 27. The total mass of the samples was 1.456 g.

[0374] Furthermore, the samples were not pre-treated by vacuum exhaust.

[0375] (Measurement of mercury intrusion)

[0376] The sample was placed in a unit container of a pore distribution measuring apparatus Autopore IV 9520 manufactured by Shimadzu Corporation-Micromeritics Instrument Corporation, and the amount of mercury intrusion was measured.

[0377] As the battery, a 5cc large-sheet battery (volume 0.4cc) was used.

[0378] Regarding the measurement pressure, the initial pressure was set to about 7 kPa (1.0 psia (equivalent to a pore diameter of about 180 μm)) and the maximum pressure was set to about 400 MPa (60,000 psia). Figure 10 Pressurization is performed multiple times under the conditions shown. If the pressure remains stable at a certain value for 10 seconds, the pressure is increased to the next value.

[0379] The analysis software used was AutoPore IV 9500 version 1.09. The mercury properties used in the calculations were set to a mercury contact angle of 130.0 degrees and a mercury surface tension of 485.0 dynes / cm. No blank correction was performed.

[0380] The pore distribution was measured under the above conditions.

[0381] Based on the results of the measured pore distribution, the mercury intrusion amount was calculated as follows.

[0382] Mercury intrusion was calculated for pores ranging from 0.1 μm to 10 μm. Specifically, the mercury intrusion per gram of sample (unit: μL / g) was calculated by subtracting the cumulative mercury intrusion at a pore diameter of 10 μm (at a pressure of approximately 17 psia) from the cumulative mercury intrusion at a pore diameter of 0.1 μm (at a pressure of approximately 1700 psia). In Example 1, the cumulative mercury intrusion at a pore diameter of 0.1 μm was 0.007422 μL / g, and the cumulative mercury intrusion at a pore diameter of 10 μm was 0.005179 μL / g.

[0383] The mercury intrusion amount (μL) was calculated by multiplying the calculated mercury intrusion amount (μL) per 1 g of the sample by the mass of the sample. The mercury intrusion amount (μL) of Example 1 was 3.2663 μL.

[0384] (Calculation of the Cross-Sectional Area of the Polymer Composite Piezoelectric Body in the Sample)

[0385] (Calculation of the Cross-Sectional Area of the Polymer Composite Piezoelectric Body in the Sample)

[0386] The total exposed area of the polymer composite piezoelectric body in the sample for which the mercury intrusion amount was to be determined, that is, the total cross-sectional area, was determined as follows.

[0387] First, a method for measuring the thickness of the polymer composite piezoelectric layer on a cross section of the polymer composite piezoelectric body is as follows, for example.

[0388] In order to observe the cross section of the polymer composite piezoelectric body, cutting is performed in the thickness direction. The cutting is performed by installing an 8mm wide histo blade manufactured by Drukker on a RM2265 manufactured by Leica Biosystems, setting the speed to controller scale 1, and setting the engagement amount to 0.25μm to 1μm to obtain a cross section. The cross section is observed by a scanning electron microscope (SEM) (for example, SU8220 manufactured by Hitachi High-Tech Corporation). The sample is treated for conductivity by Pt evaporation, and the working distance is set to 3mm. The observation conditions are set to SE image (above), acceleration voltage: 0.5kV, and a clear image is produced by focusing adjustment and astigmatism adjustment. Automatic brightness adjustment is performed when the polymer composite piezoelectric body portion becomes the entire screen (automatically setting brightness: 0, contrast: 0). The magnification of the photography is set so that the electrodes at both ends are contained in one screen, and the width between the electrodes becomes a magnification of more than half of the screen.

[0389] The thickness of the polymer composite piezoelectric layer was determined by calculating the length between the two electrode layers stacked on both sides of the polymer composite piezoelectric layer from the SEM image. This process was performed on 10 random cross sections, and the average value of the inter-electrode distance was used as the thickness of the polymer composite piezoelectric layer.

[0390] In Example 1, the thickness was 30.1 μm.

[0391] The thickness of the polymer composite piezoelectric layer is multiplied by the total width of the polymer composite piezoelectric layer in the sample cross section, that is, multiplied by "(12.5mm + 25mm) × 2 × the number of samples", and the total exposed area (cross-sectional area) of the polymer composite piezoelectric layer is obtained. In Example 1, the cross-sectional area is 60.75mm 2 .

[0392] (Calculation of pore volume)

[0393] Divide the mercury intrusion (μL) obtained above by the cross-sectional area (mm 2 ) The pore volume per unit area (μL / mm 2In Example 1, the pore volume per unit area is 0.05 μL / mm 2 .

[0394] [Examples 2 to 4, Comparative Example 1]

[0395] A piezoelectric thin film was produced in the same manner as in Example 1 except that the conditions for linear mixing of the coating material to be the piezoelectric layer were changed to the conditions shown in Table 1 below.

[0396] For each of the Examples and Comparative Examples, the pore volume per unit area was measured in the same manner as in Example 1.

[0397] [evaluate]

[0398] Changes in the thermoelectric conversion efficiency with respect to humidity conversion of the produced piezoelectric thin films were evaluated as follows.

[0399] First, a 150mm diameter circular test piece was cut from the prepared piezoelectric film. This test piece was fixed so that it covered the opening of a circular plastic housing with an inner diameter of 138mm and a depth of 9mm. The pressure inside the housing was maintained at 1.02 atmospheres. This caused the converter film to bend into a convex shape, similar to a contact lens, creating a piezoelectric speaker.

[0400] The fabricated piezoelectric speaker was placed in a temperature-controlled humidity chamber at 25°C and 50% humidity for 24 hours. Immediately after removal from the chamber, the sound pressure level-frequency characteristics of the piezoelectric speaker were measured over a range of 50 Hz to 20 kHz using a sine wave sweep measurement using a constant-current power amplifier. The sound pressure at 1 kHz was determined. A measurement microphone was positioned 10 cm directly above the center of the piezoelectric speaker. The measurement environment was maintained at a temperature of 25°C.

[0401] Next, the piezoelectric speaker was placed in a temperature- and humidity-controlled chamber at 25°C and 80% humidity for 24 hours. Immediately after removal from the chamber, the piezoelectric speaker's sound pressure level-frequency characteristics were measured using the same method as above, and the sound pressure at 1 kHz was determined.

[0402] The difference between the sound pressure after being placed in an environment with a humidity of 50% and the sound pressure after being placed in an environment with a humidity of 80% determined above was calculated and evaluated based on the following criteria.

[0403] A: Sound pressure difference is less than 2dB

[0404] B: The sound pressure difference is greater than 2dB and less than 3dB

[0405] C: Sound pressure difference is 3dB or more and less than 5dB

[0406] D: Sound pressure difference is 5dB or more

[0407] The results are shown in Table 1.

[0408] [Table 1]

[0409]

[0410] As shown in Table 1, the difference between the sound pressure after exposure to a 50% humidity environment and the sound pressure after exposure to an 80% humidity environment is smaller in Examples 1 to 4 of the present invention than in the comparative example. This indicates that the piezoelectric film of the present invention suppresses changes in piezoelectric conversion efficiency due to humidity, resulting in stable piezoelectric conversion characteristics.

[0411] Furthermore, from the comparison of Examples 1 to 4, it can be seen that the pore volume per unit area is preferably 0.6 μL / mm 2 the following.

[0412] As described above, the effects of the present invention are significant.

[0413] Industrial applicability

[0414] It can be suitably used in various applications, including audio devices such as speakers and microphones and pressure sensors.

[0415] [Explanation of symbols]

[0416] 10, 10L-piezoelectric 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, 35-pores, 36-piezoelectric particles, 43-shell, 45-piezoelectric speaker, 45a-rising portion, 46-viscoelastic support body, 48-frame, 50-electroacoustic converter, 58-core rod, PS-power supply, g-spacer.

Claims

1. A polymer composite piezoelectric body comprising piezoelectric particles in a matrix containing a polymer material. The pore volume per unit area of the polymer composite piezoelectric body is 0.01 μL / mm 2 ~1.7μL / mm 2 The pore volume per unit area is calculated as follows: the polymer composite piezoelectric body having electrode layers formed on both sides is cut in the thickness direction and a sample is cut out with a size of 12.5 mm × 25 mm. The amount of mercury intrusion into the sample is measured by mercury intrusion porosimetry, and the pore volume per unit area is calculated by dividing the intrusion amount by the cross-sectional area of the sample.

2. The polymer composite piezoelectric body according to claim 1, wherein: The polymer composite piezoelectric body is polarized in the thickness direction.

3. The polymer composite piezoelectric body according to claim 1 or 2, wherein: Piezoelectric properties do not have in-plane anisotropy.

4. The polymer composite piezoelectric body according to claim 1 or 2, wherein: The polymer material has viscoelasticity at room temperature.

5. A piezoelectric film comprising: A polymer composite piezoelectric body comprising piezoelectric particles in a matrix containing a polymer material; and The electrode layers are formed on both sides of the polymer composite piezoelectric body. The pore volume per unit area of the piezoelectric film is 0.01 μL / mm 2 ~1.7μL / mm 2 The pore volume per unit area is calculated as follows: the piezoelectric film is cut along the thickness direction and a sample is cut out with a size of 12.5 mm × 25 mm, the amount of mercury intrusion is measured by the mercury intrusion method, and the pore volume per unit area is calculated by dividing the intrusion amount by the cross-sectional area of the polymer composite piezoelectric body of the sample.

6. The piezoelectric film according to claim 5, comprising: The protective layer is laminated on a surface of the electrode layer opposite to the surface on the polymer composite piezoelectric body side.

7. The piezoelectric film according to claim 5 or 6, wherein: The polymer composite piezoelectric body is polarized in the thickness direction.

8. The piezoelectric film according to claim 5 or 6, wherein: Piezoelectric properties do not have in-plane anisotropy.

9. The piezoelectric film according to claim 5 or 6, wherein: The polymer material has viscoelasticity at room temperature.

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