WO2022209854A1 - 圧電フィルム - Google Patents

圧電フィルム Download PDF

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Publication number
WO2022209854A1
WO2022209854A1 PCT/JP2022/011628 JP2022011628W WO2022209854A1 WO 2022209854 A1 WO2022209854 A1 WO 2022209854A1 JP 2022011628 W JP2022011628 W JP 2022011628W WO 2022209854 A1 WO2022209854 A1 WO 2022209854A1
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Prior art keywords
piezoelectric
layer
film
piezoelectric film
electrode layer
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English (en)
French (fr)
Japanese (ja)
Inventor
美里 成林
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Fujifilm Corp
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Fujifilm Corp
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Priority to KR1020237032267A priority Critical patent/KR20230147697A/ko
Priority to CN202280023915.7A priority patent/CN117044238A/zh
Priority to JP2023510884A priority patent/JPWO2022209854A1/ja
Publication of WO2022209854A1 publication Critical patent/WO2022209854A1/ja
Priority to US18/478,009 priority patent/US20240023451A1/en
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    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N30/00—Piezoelectric or electrostrictive devices
    • H10N30/80—Constructional details
    • H10N30/85—Piezoelectric or electrostrictive active materials
    • H10N30/852—Composite materials, e.g. having 1-3 or 2-2 type connectivity
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/18—Oxygen-containing compounds, e.g. metal carbonyls
    • C08K3/20—Oxides; Hydroxides
    • C08K3/22—Oxides; Hydroxides of metals
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS
    • H04R17/00—Piezoelectric transducers; Electrostrictive transducers
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS
    • H04R17/00—Piezoelectric transducers; Electrostrictive transducers
    • H04R17/005—Piezoelectric transducers; Electrostrictive transducers using a piezoelectric polymer
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N30/00—Piezoelectric or electrostrictive devices
    • H10N30/01—Manufacture or treatment
    • H10N30/05—Manufacture of multilayered piezoelectric or electrostrictive devices, or parts thereof, e.g. by stacking piezoelectric bodies and electrodes
    • H10N30/057—Manufacture of multilayered piezoelectric or electrostrictive devices, or parts thereof, e.g. by stacking piezoelectric bodies and electrodes by stacking bulk piezoelectric or electrostrictive bodies and electrodes
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N30/00—Piezoelectric or electrostrictive devices
    • H10N30/01—Manufacture or treatment
    • H10N30/06—Forming electrodes or interconnections, e.g. leads or terminals
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N30/00—Piezoelectric or electrostrictive devices
    • H10N30/01—Manufacture or treatment
    • H10N30/09—Forming piezoelectric or electrostrictive materials
    • H10N30/092—Forming composite materials
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N30/00—Piezoelectric or electrostrictive devices
    • H10N30/50—Piezoelectric or electrostrictive devices having a stacked or multilayer structure
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N30/00—Piezoelectric or electrostrictive devices
    • H10N30/704—Piezoelectric or electrostrictive devices based on piezoelectric or electrostrictive films or coatings
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N30/00—Piezoelectric or electrostrictive devices
    • H10N30/80—Constructional details
    • H10N30/87—Electrodes or interconnections, e.g. leads or terminals
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/18—Oxygen-containing compounds, e.g. metal carbonyls
    • C08K3/20—Oxides; Hydroxides
    • C08K3/22—Oxides; Hydroxides of metals
    • C08K2003/2244—Oxides; Hydroxides of metals of zirconium
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K2201/00—Specific properties of additives
    • C08K2201/001—Conductive additives
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K2201/00—Specific properties of additives
    • C08K2201/002—Physical properties
    • C08K2201/005—Additives being defined by their particle size in general

Definitions

  • the present invention relates to piezoelectric films.
  • the speakers used in these thin displays are also required to be lighter and thinner.
  • flexible displays are also required to be flexible in order to be integrated into flexible displays without impairing lightness and flexibility.
  • a lightweight, thin and flexible speaker it is considered to employ a sheet-like piezoelectric film having a property of expanding and contracting in response to an applied voltage.
  • An exciter is an exciter that vibrates and emits sound by being attached to various articles in contact with them.
  • Patent Document 1 discloses a polymer composite piezoelectric body in which piezoelectric particles are dispersed in a viscoelastic matrix made of a polymer material having viscoelasticity at room temperature, and a polymer composite piezoelectric body formed on both sides of the polymer composite piezoelectric body.
  • a piezoelectric film is described that has a thin film electrode and a protective layer formed on the surface of the thin film electrode.
  • a polymer composite piezoelectric body in which piezoelectric particles are dispersed in a matrix made of a polymer material, and electrode layers formed on both sides of the polymer composite piezoelectric body. It was found that repeated bending and stretching of the piezoelectric film reduces the sound pressure and causes a problem of durability.
  • the object of the present invention is to solve the problems of the prior art, and to provide a highly durable piezoelectric film that can suppress a drop in sound pressure even after repeated bending and stretching.
  • a piezoelectric layer made of a polymer composite piezoelectric material containing piezoelectric particles in a matrix containing a polymer material, and electrode layers formed on both sides of the piezoelectric layer, having a plurality of recesses with a depth of 1 ⁇ m or more on at least one surface of the piezoelectric layer; The number density of the recesses is 100 to 1000/mm 2 , A piezoelectric film having a surface kurtosis Rku of 2.9-25.
  • FIG. 1 is a diagram conceptually showing an example of a piezoelectric film of the present invention
  • FIG. 4 is a partial enlarged view conceptually showing the surface shape of a piezoelectric layer
  • FIG. 2 is a conceptual diagram for explaining kurtosis Rku
  • FIG. 2 is a conceptual diagram for explaining kurtosis Rku
  • FIG. 4 is a diagram for explaining the state of stress when the piezoelectric film is bent
  • FIG. 3 is a partial enlarged view conceptually showing the surface shape of a conventional piezoelectric layer.
  • FIG. 4 is a partial enlarged view conceptually showing the surface shape of a piezoelectric layer when Rku is large.
  • a numerical range represented by "-" means a range including the numerical values before and after "-" as lower and upper limits.
  • the piezoelectric film of the present invention is A piezoelectric layer made of a polymer composite piezoelectric material containing piezoelectric particles in a matrix containing a polymer material, and electrode layers formed on both sides of the piezoelectric layer, having a plurality of recesses with a depth of 1 ⁇ m or more on at least one surface of the piezoelectric layer; The number density of the recesses is 100 to 1000/mm 2 , The piezoelectric film has a surface kurtosis Rku of 2.9-25.
  • FIG. 1 conceptually shows an example of the piezoelectric film of the present invention.
  • the piezoelectric film 10 includes a piezoelectric layer 20 which is a sheet-like material having piezoelectric properties, a first electrode layer 24 laminated on one surface of the piezoelectric layer 20, and a first electrode layer. 24 , a second electrode layer 26 laminated on the other surface of the piezoelectric layer 20 , and a second protective layer 30 laminated on the second electrode layer 26 .
  • the piezoelectric layer 20 is composed of a polymer composite piezoelectric body containing piezoelectric particles 36 in a matrix 34 containing a polymer material.
  • the first electrode layer 24 and the second electrode layer 26 are electrode layers in the present invention.
  • the piezoelectric film 10 (piezoelectric layer 20) is preferably polarized in the thickness direction.
  • Such a piezoelectric film 10 is used, for example, in various acoustic devices (acoustic equipment) such as speakers, microphones, and pickups used in musical instruments such as guitars to generate (reproduce) sounds by vibrating in response to electrical signals. It is also used to convert sound vibrations into electrical signals.
  • the piezoelectric film can also be used for pressure sensors, power generation elements, and the like.
  • the piezoelectric film can be used as an exciter that vibrates the article and emits sound by attaching it to various articles in contact therewith.
  • the second electrode layer 26 and the first electrode layer 24 form an electrode pair. That is, in the piezoelectric film 10 , both surfaces of the piezoelectric layer 20 are sandwiched between electrode pairs, that is, the first electrode layer 24 and the second electrode layer 26 , and this laminate is formed into the first protective layer 28 and the second protective layer 30 . It has a configuration sandwiched between.
  • the region sandwiched between the first electrode layer 24 and the second electrode layer 26 expands and contracts according to the applied voltage.
  • the first electrode layer 24 and the first protective layer 28, and the second electrode layer 26 and the second protective layer 30 are named according to the polarization direction of the piezoelectric layer 20. Therefore, the first electrode layer 24 and the second electrode layer 26 as well as the first protective layer 28 and the second protective layer 30 basically have the same configuration.
  • the piezoelectric film 10 may have, for example, an insulating layer or the like that covers the area where the piezoelectric layer 20 is exposed, such as the side surface, to prevent short circuits or the like.
  • the piezoelectric film 10 when a voltage is applied to the first electrode layer 24 and the second electrode layer 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) shrinks in the thickness direction. At the same time, due to the Poisson's ratio, the piezoelectric film 10 also expands and contracts in the in-plane direction. This expansion and contraction is about 0.01 to 0.1%. In addition, it expands and contracts isotropically in all directions in the in-plane direction.
  • the thickness of the piezoelectric layer 20 is preferably about 10-300 ⁇ m. Therefore, the expansion and contraction in the thickness direction is as small as about 0.3 ⁇ m at maximum.
  • the piezoelectric film 10, that is, the piezoelectric layer 20 has a size much larger than its thickness in the planar direction. Therefore, for example, if the length of the piezoelectric film 10 is 20 cm, the piezoelectric film 10 expands and contracts by about 0.2 mm at maximum due to voltage application. Also, when pressure is applied to the piezoelectric film 10, the action of the piezoelectric particles 36 generates electric power. By utilizing this, the piezoelectric film 10 can be used for various applications such as speakers, microphones, and pressure sensors, as described above.
  • the piezoelectric film 10 has a plurality of recesses with a depth of 1 ⁇ m or more on at least one surface of the piezoelectric layer 20, that is, the contact surface of the piezoelectric layer 20 with the electrode layer. is 100 to 1000/mm 2 , and the kurtosis Rku of the surface is 2.9 to 25.
  • FIG. 2 is a diagram omitting the second protective layer 30 and the second electrode layer 26 from the piezoelectric film 10 .
  • the surface of the piezoelectric layer 20 has fine recesses 21 at a predetermined number density, and the kurtosis Rku in the roughness curve due to the unevenness is -2.9 to 25.
  • the kurtosis Rku represents the square mean of Z(x) in the reference length dimensionless by the square root height (Zq) raised to the fourth power.
  • a piezoelectric film having a polymer composite piezoelectric body in which piezoelectric particles are dispersed in a matrix made of a polymer material and electrode layers formed on both sides of the polymer composite piezoelectric body is repeatedly bent and stretched.
  • the sound pressure decreased and there was a problem in durability.
  • the compressive stress when the surface of the piezoelectric layer is flat like the conventional piezoelectric film shown in FIG.
  • the piezoelectric particles may come into contact with each other and damage the crystals of the piezoelectric particles, making it impossible to obtain proper piezoelectric characteristics. Therefore, it is considered that the sound pressure is lowered.
  • the tensile stress even if the surface of the piezoelectric layer has a concave portion, as shown in FIG. 7, if the concave portion is sharp, that is, if the kurtosis Rku is too large, When a tensile stress is applied to a nearby region, stress concentration occurs at the tip of the recess, damaging the piezoelectric layer. Therefore, it is considered that appropriate piezoelectric characteristics cannot be obtained and the sound pressure is lowered.
  • the piezoelectric film of the present invention has a plurality of recesses with a depth of 1 ⁇ m or more on at least one surface of the piezoelectric layer 20, and the number density of the recesses is 100 to 1000/mm 2 , Moreover, the kurtosis Rku of this surface is 2.9-25.
  • the piezoelectric film of the present invention has a large number of recesses on the surface of the piezoelectric layer, so that it can absorb compressive stress when the piezoelectric film is bent. , can suppress stress concentration when subjected to tensile stress.
  • the piezoelectric layer it is possible to prevent the piezoelectric layer from being damaged due to repeated bending and stretching of the piezoelectric film, thereby preventing a decrease in sound pressure and providing a highly durable piezoelectric film.
  • the filling rate of the piezoelectric layer is ensured and sufficient piezoelectric characteristics are obtained, so that a piezoelectric film with high sound pressure (high conversion efficiency) can be obtained. be able to.
  • the kurtosis Rku is preferably 3 to 22, more preferably 4 to 20, and even more preferably 4.5 to 10.
  • the kurtosis Rku is determined according to JISB0601:2013 by exposing the surface of the piezoelectric layer in contact with the electrode layer and measuring profile data of the surface roughness of the piezoelectric layer.
  • a 5 mol/L NaOH aqueous solution is added dropwise to the protective layer at 15 to 25°C to dissolve it.
  • the electrode layer may be partially dissolved, but the piezoelectric layer is left to stand for a period of time during which the aqueous NaOH solution does not come into contact with the piezoelectric layer.
  • the NaOH aqueous solution left standing is washed with pure water, and the exposed electrode layer is dissolved in a ferric chloride aqueous solution of 0.01 mol/L to 0.1 mol/L. Dissolution of the aqueous ferric chloride solution should not exceed 5 minutes after exposure of the piezoelectric layer.
  • the exposed piezoelectric layer is washed with pure water and dried at 30° C. or less.
  • the number density of the concave portions is large.
  • the number density of the recesses is too high, the filling rate of the piezoelectric layer will be low, and there is a possibility that sufficient sound pressure cannot be obtained.
  • the number density of recesses having a depth of 1 ⁇ m or more is preferably 150 to 800/mm 2 , more preferably 200 to 600/mm 2 , and even more preferably 300 to 400/mm 2 .
  • the number density of the recesses is obtained by dissolving the protective layer and the electrode layer in the same manner as the Kurtsis Rku measurement described above, measuring the surface of the exposed piezoelectric layer with a non-contact three-dimensional surface profile roughness meter, and correcting the inclination. , Gaussian process regression fitting, and calculated from the obtained surface roughness.
  • the surface roughness Ra of at least one of the piezoelectric layers is preferably 10 nm to 200 nm, more preferably 30 nm to 240 nm, and more preferably 65 nm to 230 nm. More preferred.
  • the surface roughness Ra is obtained by dissolving the protective layer and the electrode layer in the same manner as the measurement of Kurtsis Rku described above, measuring the surface of the exposed piezoelectric layer with a non-contact three-dimensional surface profile roughness meter, and correcting the inclination. , Gaussian process regression is performed to determine the surface roughness, and Ra is calculated. Ra is measured in each of ten observation fields of view, and an average value is obtained.
  • the piezoelectric layer is composed of a single layer of polymer composite piezoelectric material containing piezoelectric particles in a matrix containing a polymer material, but the present invention is not limited to this.
  • the piezoelectric layer may include a piezoelectric layer main body and an intermediate layer.
  • the piezoelectric layer main body is a layer made of a polymeric composite piezoelectric body containing piezoelectric particles in a matrix containing a polymeric material.
  • the intermediate layer is a layer other than the layer composed of the polymer composite piezoelectric material, and includes, for example, an adhesive layer that bonds the piezoelectric layer main body and the electrode layer, and a layer containing piezoelectric particles having an average particle diameter different from that of the piezoelectric layer main body. etc. are exemplified.
  • the adhesive layer for example, the same material as the matrix of the piezoelectric layer or a similar material can be used. Alternatively, a material that can be used as a matrix, which will be described later, may be used as the adhesive layer.
  • a layer containing piezoelectric particles having an average particle diameter different from that of the piezoelectric layer main body is formed on the piezoelectric layer main body as an intermediate layer, for example, as a layer whose average particle diameter of the piezoelectric particles is smaller than that of the piezoelectric layer main body.
  • the piezoelectric film has a configuration in which a first protective layer, a first electrode layer, a piezoelectric layer main body, an intermediate layer, a second electrode layer, and a second protective layer are laminated in this order. have.
  • the surface of the intermediate layer should have 100 to 1000 recesses/mm 2 with a depth of 1 ⁇ m or more, and the kurtosis Rku should be ⁇ 2.9 to 25.
  • the piezoelectric layer is a layer made of a polymeric composite piezoelectric body containing piezoelectric particles in a matrix containing a polymeric material, and is a layer that exhibits a piezoelectric effect that expands and contracts when a voltage is applied.
  • the piezoelectric layer 20 is composed of a polymeric composite piezoelectric body in which piezoelectric particles 36 are dispersed in a matrix 34 made of a polymeric material having viscoelasticity at room temperature.
  • ordinary temperature refers to a temperature range of about 0 to 50.degree.
  • the piezoelectric film 10 of the present invention is suitably used for speakers having flexibility, such as speakers for flexible displays.
  • the polymeric composite piezoelectric material (piezoelectric layer 20) used in the flexible speaker preferably satisfies the following requirements. Therefore, it is preferable to use a polymeric material having viscoelasticity at room temperature as a material that satisfies the following requirements.
  • (ii) Sound quality Speakers vibrate piezoelectric particles at frequencies in the audio band of 20 Hz to 20 kHz, and the vibration energy causes the entire polymer composite piezoelectric material (piezoelectric film) to vibrate as one to reproduce sound. be. Therefore, the polymer composite piezoelectric body is required to have appropriate hardness in order to increase the transmission efficiency of vibration energy. Also, if the frequency characteristics of the speaker are smooth, the amount of change in sound quality when the lowest resonance frequency changes as the curvature changes becomes small. Therefore, the loss tangent of the polymer composite piezoelectric body is required to be moderately large.
  • the polymer composite piezoelectric body is required to behave hard against vibrations of 20 Hz to 20 kHz and softly against vibrations of several Hz or less. Also, the loss tangent of the polymer composite piezoelectric body is required to be moderately large with respect to vibrations of all frequencies of 20 kHz or less.
  • polymer solids have a viscoelastic relaxation mechanism, and as the temperature rises or the frequency decreases, large-scale molecular motion causes a decrease (relaxation) in the storage elastic modulus (Young's modulus) or a maximum loss elastic modulus (absorption). is observed as Among them, the relaxation caused by the micro-Brownian motion of the molecular chains in the amorphous region is called principal dispersion, and a very large relaxation phenomenon is observed.
  • the temperature at which this primary dispersion occurs is the glass transition point (Tg), and the viscoelastic relaxation mechanism appears most prominently.
  • the polymer composite piezoelectric body (piezoelectric layer 20), by using a polymer material having a glass transition point at room temperature, in other words, a polymer material having viscoelasticity at room temperature as a matrix, it is possible to suppress vibrations of 20 Hz to 20 kHz. This realizes a polymer composite piezoelectric material that is hard at first and behaves softly with respect to slow vibrations of several Hz or less.
  • a polymer material having a glass transition point at room temperature ie, 0 to 50° C. at a frequency of 1 Hz, for the matrix of the polymer composite piezoelectric material, because this behavior is favorably expressed.
  • polymer materials having viscoelasticity at room temperature Preferably, a polymer material having a maximum value of 0.5 or more in loss tangent Tan ⁇ at a frequency of 1 Hz in a dynamic viscoelasticity test at normal temperature, ie, 0 to 50° C., is used.
  • a polymer material having a maximum value of 0.5 or more in loss tangent Tan ⁇ at a frequency of 1 Hz in a dynamic viscoelasticity test at normal temperature, ie, 0 to 50° C. is used.
  • the stress concentration at the interface between the polymer matrix and the piezoelectric particles at the maximum bending moment is relaxed, and high flexibility can be expected.
  • the polymer material having viscoelasticity at room temperature preferably has a storage modulus (E') at a frequency of 1 Hz measured by dynamic viscoelasticity of 100 MPa or more at 0°C and 10 MPa or less at 50°C.
  • E' storage modulus
  • the polymer material having viscoelasticity at room temperature has a dielectric constant of 10 or more at 25°C.
  • a voltage is applied to the polymer composite piezoelectric material, a higher electric field is applied to the piezoelectric particles in the polymer matrix, so a large amount of deformation can be expected.
  • the polymer material in consideration of ensuring good moisture resistance and the like, it is also suitable for the polymer material to have a dielectric constant of 10 or less at 25°C.
  • polymeric materials having viscoelasticity at room temperature examples include cyanoethylated polyvinyl alcohol (cyanoethylated PVA), polyvinyl acetate, polyvinylidene chloride core acrylonitrile, polystyrene-vinylpolyisoprene block copolymer, and polyvinylmethyl.
  • cyanoethylated polyvinyl alcohol cyanoethylated PVA
  • polyvinyl acetate polyvinylidene chloride core acrylonitrile
  • polystyrene-vinylpolyisoprene block copolymer examples include ketones and polybutyl methacrylate.
  • Commercially available products such as Hybler 5127 (manufactured by Kuraray Co., Ltd.) can also be suitably used as these polymer materials.
  • the polymer material it is preferable to use a material having a cyanoethyl group, and it is particularly preferable to use cyanoethylated PVA. These polymer materials may be used singly or in combination (mixed).
  • the matrix 34 using such a polymer material having viscoelasticity at room temperature may use a plurality of polymer materials together, if necessary. That is, in addition to a viscoelastic material such as cyanoethylated PVA, other dielectric polymer materials may be added to the matrix 34 as necessary for the purpose of adjusting dielectric properties and mechanical properties.
  • a viscoelastic material such as cyanoethylated PVA
  • other dielectric polymer materials may be added to the matrix 34 as necessary for the purpose of adjusting dielectric properties and mechanical properties.
  • dielectric polymer materials examples include polyvinylidene fluoride, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, and polyvinylidene fluoride-trifluoroethylene copolymer.
  • fluorine-based polymers such as polyvinylidene fluoride-tetrafluoroethylene copolymer, vinylidene cyanide-vinyl acetate copolymer, cyanoethylcellulose, cyanoethylhydroxysaccharose, cyanoethylhydroxycellulose, cyanoethylhydroxypullulan, cyanoethylmethacrylate, cyanoethylacrylate, cyanoethyl Cyano groups such as hydroxyethylcellulose, cyanoethylamylose, cyanoethylhydroxypropylcellulose, cyanoethyldihydroxypropylcellulose, cyanoethylhydroxypropylamylose, cyanoethylpolyacrylamide, cyanoethylpolyacrylate, cyanoethylpullulan, cyanoethylpolyhydroxymethylene, cyanoethylglycidolpullul
  • the dielectric polymer added in addition to the material having viscoelasticity at room temperature such as cyanoethylated PVA is not limited to one type, and plural types may be added. .
  • the matrix 34 may include thermoplastic resins such as vinyl chloride resin, polyethylene, polystyrene, methacrylic resin, polybutene, and isobutylene, and phenolic resin for the purpose of adjusting the glass transition point Tg. , urea resins, melamine resins, alkyd resins, and thermosetting resins such as mica may be added. Furthermore, a tackifier such as rosin ester, rosin, terpene, terpene phenol, and petroleum resin may be added for the purpose of improving adhesiveness.
  • the addition amount is not particularly limited, but the ratio of the material to the matrix 34 is 30% by mass or less. is preferable.
  • the characteristics of the polymer material to be added can be expressed without impairing the viscoelastic relaxation mechanism in the matrix 34, so that the dielectric constant can be increased, the heat resistance can be improved, and the adhesion between the piezoelectric particles 36 and the electrode layer can be improved. favorable results can be obtained in terms of
  • the piezoelectric layer 20 is a polymeric composite piezoelectric body containing piezoelectric particles 36 in such a matrix 34 .
  • the piezoelectric particles 36 are made of ceramic particles having a perovskite or wurtzite crystal structure.
  • ceramic particles constituting the piezoelectric particles 36 include lead zirconate titanate (PZT), lead zirconate lanthanate titanate (PLZT), barium titanate (BaTiO 3 ), zinc oxide (ZnO), and A solid solution (BFBT) of barium titanate and bismuth ferrite (BiFe 3 ) is exemplified. Only one kind of these piezoelectric particles 36 may be used, or a plurality of kinds thereof may be used together (mixed).
  • the particle size of the piezoelectric particles 36 is not limited, and may be selected as appropriate according to the size of the piezoelectric film 10, the application of the piezoelectric film 10, and the like.
  • the particle size of the piezoelectric particles 36 is preferably 0.5 to 5 ⁇ m. By setting the particle size of the piezoelectric particles 36 within this range, favorable results can be obtained in that the piezoelectric film 10 can achieve both high piezoelectric characteristics and flexibility.
  • the piezoelectric particles 36 are illustrated as being spherical, but the piezoelectric particles 36 are not limited to perfect spheres and have various shapes. For example, as shown in FIG. 3, it is a shape having corners.
  • the shape of the piezoelectric particles 36 the circularity of the piezoelectric particles observed in the cross section in the thickness direction of the piezoelectric layer is preferably 0.65 to 0.92.
  • the degree of circularity is expressed by 4 ⁇ (area) ⁇ (perimeter) 2 and represents the complexity of the shape. In the case of a perfect circle, the number is 1, and the more complicated the shape, the smaller the numerical value.
  • the piezoelectric particles 36 in the piezoelectric layer 20 are uniformly and regularly dispersed in the matrix 34 in FIG. 1, the present invention is not limited to this. That is, the piezoelectric particles 36 in the piezoelectric layer 20 may be dispersed irregularly in the matrix 34 as long as they are preferably uniformly dispersed.
  • the quantitative ratio of the matrix 34 and the piezoelectric particles 36 in the piezoelectric layer 20 is not limited. It may be appropriately set according to the properties required for the piezoelectric film 10 .
  • the volume fraction of the piezoelectric particles 36 in the piezoelectric layer 20 is preferably 30% to 80%, more preferably 50% or more, and therefore more preferably 50% to 80%.
  • the piezoelectric layer 20 is a polymer composite piezoelectric layer in which piezoelectric particles are dispersed in a viscoelastic matrix containing a polymer material having viscoelasticity at room temperature.
  • the present invention is not limited to this, and as the piezoelectric layer, a polymer composite piezoelectric body in which piezoelectric particles are dispersed in a matrix containing a polymer material, which is used in known piezoelectric elements, is used. It is possible.
  • the thickness of the piezoelectric layer 20 is not particularly limited, and may be set as appropriate according to the application of the piezoelectric film 10, the properties required of the piezoelectric film 10, and the like.
  • the thickness of the piezoelectric layer 20 is preferably 10 to 300 ⁇ m, more preferably 20 to 200 ⁇ m, even more preferably 30 to 150 ⁇ m.
  • the first protective layer 28 and the second protective layer 30 cover the second electrode layer 26 and the first electrode layer 24, and provide the piezoelectric layer 20 with appropriate rigidity and mechanical strength. is responsible for That is, in the piezoelectric film 10, the piezoelectric layer 20 made up of the matrix 34 and the piezoelectric particles 36 exhibits excellent flexibility against slow bending deformation, but depending on the application, the rigidity may increase. and mechanical strength may be insufficient.
  • the piezoelectric film 10 is provided with a first protective layer 28 and a second protective layer 30 to compensate.
  • first protective layer 28 and the second protective layer 30 there are no restrictions on the first protective layer 28 and the second protective layer 30, and various sheet materials can be used, and various resin films are suitable examples. Among them, polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS), polycarbonate (PC), polyphenylene sulfite (PPS), polymethyl methacrylate (PMMA), due to their excellent mechanical properties and heat resistance. ), polyetherimide (PEI), polyimide (PI), polyethylene naphthalate (PEN), triacetyl cellulose (TAC), cyclic olefin resins, and the like are preferably used.
  • PET polyethylene terephthalate
  • PP polypropylene
  • PS polystyrene
  • PC polycarbonate
  • PPS polyphenylene sulfite
  • PMMA polymethyl methacrylate
  • PET polyetherimide
  • PI polyimide
  • PEN polyethylene naphthalate
  • TAC tri
  • the thicknesses of the first protective layer 28 and the second protective layer 30 are also not limited. Also, the thicknesses of the first protective layer 28 and the second protective layer 30 are basically the same, but may be different. Here, if the rigidity of the first protective layer 28 and the second protective layer 30 is too high, not only will the expansion and contraction of the piezoelectric layer 20 be restricted, but also the flexibility will be impaired. Therefore, the thinner the first protective layer 28 and the second protective layer 30, the better, except for cases where mechanical strength and good handling properties as a sheet-like article are required.
  • the thickness of the first protective layer 28 and the second protective layer 30 is not more than twice the thickness of the piezoelectric layer 20, it is possible to ensure both rigidity and appropriate flexibility. favorable results can be obtained.
  • the thickness of the piezoelectric layer 20 is 50 ⁇ m and the first protective layer 28 and the second protective layer 30 are made of PET, the thicknesses of the first protective layer 28 and the second protective layer 30 are preferably 100 ⁇ m or less. 50 ⁇ m or less is more preferable, and 25 ⁇ m or less is even more preferable.
  • a first electrode layer 24 is provided between the piezoelectric layer 20 and the first protective layer 28, and a second electrode layer 26 is provided between the piezoelectric layer 20 and the second protective layer 30. It is formed. The first electrode layer 24 and the second electrode layer 26 are provided for applying voltage to the piezoelectric layer 20 (piezoelectric film 10).
  • the materials for forming the first electrode layer 24 and the second electrode layer 26 are not limited, and various conductors can be used. Specifically, metals such as carbon, palladium, iron, tin, aluminum, nickel, platinum, gold, silver, copper, titanium, chromium and molybdenum, alloys thereof, laminates and composites of these metals and alloys, Also, indium tin oxide and the like are exemplified. Among them, copper, aluminum, gold, silver, platinum, and indium tin oxide are suitable examples of materials for the first electrode layer 24 and the second electrode layer 26 .
  • the method of forming the first electrode layer 24 and the second electrode layer 26 is not limited, and vapor phase deposition methods (vacuum film formation methods) such as vacuum deposition, ion-assisted deposition, and sputtering, film formation by plating, Alternatively, various known methods such as a method of adhering a foil made of the above material can be used.
  • vapor phase deposition methods vacuum film formation methods
  • ion-assisted deposition ion-assisted deposition
  • sputtering film formation by plating
  • various known methods such as a method of adhering a foil made of the above material can be used.
  • a thin film of copper, aluminum, or the like formed by vacuum deposition is particularly preferably used as the first electrode layer 24 and the second electrode layer 26 because the flexibility of the piezoelectric film 10 can be ensured.
  • a copper thin film formed by vacuum deposition is particularly preferably used.
  • the thicknesses of the first electrode layer 24 and the second electrode layer 26 are not limited. Also, the thicknesses of the first electrode layer 24 and the second electrode layer 26 are basically the same, but may be different.
  • the first electrode layer 24 and the second electrode layer 26 are preferably thin film electrodes.
  • the thickness of the first electrode layer 24 and the second electrode layer 26 is thinner than that of the protective layer, preferably 0.05 ⁇ m to 10 ⁇ m, more preferably 0.05 ⁇ m to 5 ⁇ m, further preferably 0.08 ⁇ m to 3 ⁇ m, and 0.05 ⁇ m to 10 ⁇ m. 1 ⁇ m to 2 ⁇ m are particularly preferred.
  • the product of the thickness of the first electrode layer 24 and the second electrode layer 26 and the Young's modulus is the product of the thickness of the first protective layer 28 and the second protective layer 30 and the Young's modulus. is preferable because the flexibility is not greatly impaired.
  • the first protective layer 28 and the second protective layer 30 are made of PET (Young's modulus: about 6.2 GPa), and the first electrode layer 24 and the second electrode layer 26 are made of copper (Young's modulus: about 130 GPa).
  • the thickness of the first protective layer 28 and the second protective layer 30 is 25 ⁇ m
  • the thickness of the first electrode layer 24 and the second electrode layer 26 is preferably 1.2 ⁇ m or less, more preferably 0.3 ⁇ m or less. , it is preferably 0.1 ⁇ m or less.
  • the piezoelectric film 10 preferably includes the piezoelectric layer 20 formed by dispersing the piezoelectric particles 36 in the matrix 34 containing a polymer material having viscoelasticity at room temperature, the first electrode layer 24 and the second electrode layer 24 . It is sandwiched between the electrode layers 26, and further has a configuration in which this laminate is sandwiched between the first protective layer 28 and the second protective layer 30. As shown in FIG.
  • the maximum value of the loss tangent (Tan ⁇ ) at a frequency of 1 Hz by dynamic viscoelasticity measurement preferably exists at room temperature, and the maximum value of 0.1 or more exists at room temperature. more preferred.
  • the piezoelectric film 10 preferably has a storage elastic modulus (E') at a frequency of 1 Hz measured by dynamic viscoelasticity measurement of 10 to 30 GPa at 0°C and 1 to 10 GPa at 50°C. Note that this condition applies to the piezoelectric layer 20 as well. This allows the piezoelectric film 10 to have a large frequency dispersion in the storage modulus (E'). That is, it can act hard against vibrations of 20 Hz to 20 kHz and soft against vibrations of several Hz or less.
  • E' storage elastic modulus
  • the piezoelectric film 10 has a product of thickness and storage elastic modulus (E′) at a frequency of 1 Hz measured by dynamic viscoelasticity measurement of 1.0 ⁇ 10 6 to 2.0 ⁇ 10 6 N/m at 0° C. , 1.0 ⁇ 10 5 to 1.0 ⁇ 10 6 N/m at 50°C. Note that this condition applies to the piezoelectric layer 20 as well. As a result, the piezoelectric film 10 can have appropriate rigidity and mechanical strength within a range that does not impair flexibility and acoustic properties.
  • E′ thickness and storage elastic modulus
  • the piezoelectric film 10 preferably has a loss tangent (Tan ⁇ ) of 0.05 or more at 25° C. and a frequency of 1 kHz in a master curve obtained from dynamic viscoelasticity measurement. Note that this condition applies to the piezoelectric layer 20 as well. As a result, the frequency characteristics of the speaker using the piezoelectric film 10 are smoothed, and the amount of change in sound quality when the lowest resonance frequency f0 changes as the curvature of the speaker changes can be reduced.
  • Tan ⁇ loss tangent
  • the storage elastic modulus (Young's modulus) and loss tangent of the piezoelectric film 10, piezoelectric layer 20, etc. may be measured by known methods.
  • the dynamic viscoelasticity measuring device DMS6100 manufactured by SII Nanotechnology Co., Ltd. manufactured by SII Nanotechnology Co., Ltd. (manufactured by SII Nanotechnology Co., Ltd.) may be used for measurement.
  • the measurement frequency is 0.1 Hz to 20 Hz (0.1 Hz, 0.2 Hz, 0.5 Hz, 1 Hz, 2 Hz, 5 Hz, 10 Hz and 20 Hz), and the measurement temperature is -50 to 150 ° C. , a heating rate of 2° C./min (in a nitrogen atmosphere), a sample size of 40 mm ⁇ 10 mm (including the clamping area), and a distance between chucks of 20 mm.
  • FIG. 9 An example of a method for manufacturing the piezoelectric film 10 will be described below with reference to FIGS. 9 to 12.
  • FIG. 9 An example of a method for manufacturing the piezoelectric film 10 will be described below with reference to FIGS. 9 to 12.
  • a sheet-like object 10a having a first protective layer 28 and a first electrode layer 24 formed thereon is prepared.
  • This sheet-like object 10a may be produced by forming a copper thin film or the like as the first electrode layer 24 on the surface of the first protective layer 28 by vacuum deposition, sputtering, plating, or the like.
  • the first protective layer 28 with a separator temporary support
  • PET or the like having a thickness of 25 ⁇ m to 100 ⁇ m can be used.
  • the separator may be removed after the second electrode layer 26 and the second protective layer 30 are thermally compressed and before laminating any member on the first protective layer 28 .
  • a coating material is prepared by dissolving a polymer material as a matrix material in an organic solvent, adding piezoelectric particles 36 such as PZT particles, and stirring and dispersing the mixture.
  • Organic solvents other than the above substances are not limited and various organic solvents can be used.
  • the matrix 34 may be added with a dielectric polymer material other than a viscoelastic material such as cyanoethylated PVA.
  • a dielectric polymer material other than a viscoelastic material such as cyanoethylated PVA.
  • the piezoelectric layer 20 of the formed laminate 10b is calendered so that the surface shape of the piezoelectric layer 20 is made into a desired shape.
  • a calendering film 80 is placed on the surface of the piezoelectric layer 20, and the surface of the calendering film 80 is pressed by a roller from above the calendering film 80. is transferred to the surface of the piezoelectric layer 20 . That is, the calendering film 80 has projections with a height of 1 ⁇ m or more at a number density of 100 to 1000/mm 2 , and the kurtosis Rku of the surface of the piezoelectric layer 20 after transfer is 2.9 to 25. Anything can be used.
  • the surface of the piezoelectric layer 20 having a plurality of recesses with a depth of 1 ⁇ m or more, a number density of recesses of 100 to 1000/mm 2 , and a kurtosis Rku of 2.9 to 25. to form
  • calendering film 80 a PET film, a resin film such as polypropylene or polyvinyl chloride, a metal foil such as copper foil or aluminum foil, or the like can be used.
  • a method for making the surface shape of the calendering film 80 into a desired shape pre-calendering of the calendering film itself, processing with abrasive paper, or the like can be used.
  • the piezoelectric layer 20 is subjected to polarization treatment (poling) after calendering.
  • the method of polarization treatment of the piezoelectric layer 20 is not limited, and known methods can be used.
  • the sheet-like object 10c in which the second electrode layer 26 is formed on the second protective layer 30 is prepared.
  • This sheet-like object 10c may be produced by forming a copper thin film or the like as the second electrode layer 26 on the surface of the second protective layer 30 by vacuum deposition, sputtering, plating, or the like.
  • the second electrode layer 26 is directed toward the piezoelectric layer 20, and the sheet-like object 10c is laminated on the laminate 10b for which the polarization treatment of the piezoelectric layer 20 has been completed.
  • the laminate of the laminate 10b and the sheet-like material 10c is thermocompression-bonded by a heating press device, a pair of heating rollers or the like while sandwiching the second protective layer 30 and the first protective layer 28 to form a piezoelectric film. 10 is made. Alternatively, it may be cut into a desired shape after thermocompression bonding.
  • the processes up to this point can also be carried out while transporting a sheet that is not in the form of a sheet, but in the form of a web, that is, a sheet wound up in a long continuous state.
  • Both the laminate 10b and the sheet-like material 10c can be web-like and can be thermocompressed as described above. In that case, the piezoelectric film 10 is produced in web form at this point.
  • an adhesive layer may be provided when laminating the laminate 10b and the sheet-like material 10c.
  • an adhesive layer may be provided on the surface of the second electrode layer 26 of the sheet 10c.
  • the most preferred adhesive layer is the same material as matrix 34 .
  • the same material may be applied on the piezoelectric layer 20, or may be applied on the surface of the second electrode layer 26 and attached.
  • the surface of the adhesive layer has a roughness that follows the surface properties of the piezoelectric layer (piezoelectric layer main body) 20 of the laminate 10b described above. , the number density of recesses on the surface of the adhesive layer, and the kurtosis Rku are within the above ranges.
  • the method for adjusting the number density of concave portions on the surface of the piezoelectric layer and the kurtosis Rku within the above range is not limited to the above. , a method of transferring the surface shape of the roller by bringing it into contact with the piezoelectric layer, a method of patterning when applying the paint, a method of adjusting the drying conditions of the coating film that will become the piezoelectric layer, and adjusting the thickness of the piezoelectric layer. and a method of adjusting the viscosity and concentration of the paint that forms the piezoelectric layer. A plurality of these methods may be combined to adjust the number density of recesses and the kurtosis Rku.
  • a method of patterning when applying a coating material there are a method of making unevenness on a slide coater and making unevenness on the coating liquid (coating film) before drying, a method of transferring the uneven shape immediately after transporting the slide coater, and a method of having uneven shape. Examples include a method of scratching with a tool.
  • the number density of the recesses and the kurtosis Rku can be adjusted by the convection due to the temperature difference in the thickness direction in the coating film that becomes the piezoelectric layer.
  • the surface of the coating film is blown with air and/or the sheet-like object 10a is placed on a hot plate, and the thickness of the coating film that becomes the piezoelectric layer 20 is increased.
  • convection occurs in which the paint inside the coating film moves toward the surface side, and the roughness of the surface of the piezoelectric layer to be formed changes.
  • the irregularities formed on the surface of the coating film that will be the piezoelectric layer can be adjusted, and the number density of the concave portions and Kurtosis Rku can be adjusted.
  • one of the electrode layers (sheet-shaped material) and the piezoelectric layer are thermocompression bonded, but the present invention is not limited to this.
  • the piezoelectric film may be produced by thermocompression bonding a sheet material to both sides of the piezoelectric layer. In this case, it is preferable that the number density of concave portions on the surface and the kurtosis Rku are within the ranges described above on both surfaces of the piezoelectric layer.
  • PVDF PolyVinylidene DiFluoride
  • the piezoelectric layer of the piezoelectric film of the present invention which is composed of a polymer composite piezoelectric material containing piezoelectric particles in a matrix containing a polymer material, has no in-plane anisotropy in the piezoelectric properties, and has no in-plane anisotropy. In the inner direction, it expands and contracts isotropically in all directions. According to such a piezoelectric film 10 that expands and contracts isotropically two-dimensionally, it can vibrate with a larger force than a general piezoelectric film such as PVDF that expands and contracts greatly only in one direction. And it can produce beautiful sounds.
  • the piezoelectric film of the present invention can be used as a speaker of the display device. is also possible.
  • the piezoelectric film 10 when used for a speaker, the film-shaped piezoelectric film 10 itself may vibrate to generate sound.
  • the piezoelectric film 10 may be attached to a diaphragm and used as an exciter that vibrates the diaphragm by the vibration of the piezoelectric film 10 to generate sound.
  • the piezoelectric film 10 of the present invention works well as a piezoelectric vibrating element for vibrating an object to be vibrated, such as a diaphragm, by forming a laminated piezoelectric element in which a plurality of sheets are laminated.
  • a laminated piezoelectric element 50 in which piezoelectric films 10 are laminated is attached to a diaphragm 12, and a speaker that outputs sound by vibrating the diaphragm 12 with the laminated body of the piezoelectric films 10 is produced.
  • the laminate of the piezoelectric films 10 acts as a so-called exciter that outputs sound by vibrating the diaphragm 12 .
  • the individual piezoelectric films 10 expand and contract in the plane direction, and the expansion and contraction of each piezoelectric film 10 causes the entire laminate of the piezoelectric films 10 to expand in the plane direction.
  • the diaphragm 12 vibrates according to the magnitude of the driving voltage applied to the piezoelectric film 10 and generates sound according to the driving voltage applied to the piezoelectric film 10 . Therefore, at this time, the piezoelectric film 10 itself does not output sound.
  • the laminated piezoelectric element 50 in which the piezoelectric films 10 are laminated has high rigidity, and the expansion/contraction force of the laminate as a whole is large.
  • the laminated piezoelectric element 50 in which the piezoelectric film 10 is laminated can sufficiently bend the diaphragm 12 with a large force even if the diaphragm has a certain degree of rigidity, and the diaphragm 12 is bent in the thickness direction. By vibrating sufficiently, the diaphragm 12 can generate sound.
  • the number of laminated piezoelectric films 10 is not limited. You can set it. It should be noted that a single piezoelectric film 10 can be used as a similar exciter (piezoelectric vibrating element) as long as it has sufficient stretching force.
  • the vibration plate 12 that is vibrated by the laminated piezoelectric element 50 in which the piezoelectric film 10 is laminated is also not limited, and various sheet-like objects (plate-like objects, films) can be used. Examples include resin films such as polyethylene terephthalate (PET), foamed plastics such as polystyrene foam, paper materials such as cardboard, glass plates, and wood. Furthermore, various devices such as display devices such as organic electroluminescence displays and liquid crystal displays may be used as the diaphragm as long as they can be bent sufficiently.
  • PET polyethylene terephthalate
  • foamed plastics such as polystyrene foam
  • paper materials such as cardboard, glass plates, and wood.
  • various devices such as display devices such as organic electroluminescence displays and liquid crystal displays may be used as the diaphragm as long as they can be bent sufficiently.
  • the adjacent piezoelectric films 10 are adhered with the adhesion layer 19 (adhesive). Also, the laminated piezoelectric element 50 and the diaphragm 12 are preferably attached with the adhesive layer 16 .
  • the sticking layer may be made of a pressure-sensitive adhesive or an adhesive.
  • an adhesive layer is used which, after application, results in a solid and hard adhesive layer. The above points are the same for a laminated body formed by folding a long piezoelectric film 10 described later.
  • the polarization direction of each laminated piezoelectric film 10 is not limited.
  • the piezoelectric film 10 of the present invention is preferably polarized in the thickness direction.
  • the polarization direction of the piezoelectric film 10 referred to here is the polarization direction in the thickness direction. Therefore, in the laminated piezoelectric element 50, all the piezoelectric films 10 may have the same polarization direction, or there may be piezoelectric films having different polarization directions.
  • the piezoelectric films 10 are preferably laminated so that the polarization directions of the adjacent piezoelectric films 10 are opposite to each other.
  • the polarity of the voltage applied to the piezoelectric layer 20 depends on the polarization direction of the piezoelectric layer 20 . Therefore, regardless of whether the polarization direction is from the second electrode layer 26 to the first electrode layer 24 or from the first electrode layer 24 to the second electrode layer 26, the second electrode is The polarity of layer 26 and the polarity of first electrode layer 24 are made the same.
  • the laminated piezoelectric element in which the piezoelectric films 10 are laminated may have a configuration in which a plurality of piezoelectric films 10 are laminated by folding the piezoelectric film 10L one or more times, preferably multiple times.
  • the laminated piezoelectric element 56 in which the piezoelectric film 10 is folded and laminated has the following advantages.
  • the laminated piezoelectric element 56 can be configured with only one long piezoelectric film 10L. Therefore, in the configuration in which the long piezoelectric film 10L is folded and laminated, only one power supply is required for applying the driving voltage, and the electrode from the piezoelectric film 10L can be led out at one place. Furthermore, in the structure in which the long piezoelectric films 10L are folded and laminated, the polarization directions of adjacent piezoelectric films are inevitably opposite to each other.
  • Sheets 10a and 10c were prepared by forming a copper thin film with a thickness of 100 nm on a PET film with a thickness of 4 ⁇ m by sputtering. That is, in this example, the first electrode layer 24 and the second electrode layer 26 are copper thin films with a thickness of 100 nm, and the first protective layer 28 and the second protective layer 30 are PET films with a thickness of 4 ⁇ m.
  • the gas pressure for sputtering the copper thin film onto the PET film was 0.4 Pa, and the substrate temperature (the temperature of the PET film) was 120°C.
  • a PET film with a separator temporary support PET having a thickness of 50 ⁇ m is used, and the separator of each protective layer is removed after the sheet-like material 10c is thermocompressed. rice field.
  • cyanoethylated PVA (CR-V, manufactured by Shin-Etsu Chemical Co., Ltd.) was dissolved in methyl ethyl ketone (MEK) at the following composition ratio.
  • PZT particles were added to this solution in the following composition ratio and dispersed with a propeller mixer (rotation speed: 2000 rpm) to prepare a paint for forming the piezoelectric layer 20 .
  • ⁇ PZT particles ⁇ 300 parts by mass
  • ⁇ Cyanoethylated PVA ⁇ 15 parts by mass ⁇ MEK ⁇ 85 parts by mass
  • the PZT particles used were obtained by sintering a commercially available PZT raw material powder at 1000 to 1200° C. and then pulverizing and classifying the sintered particles to an average particle size of 5 ⁇ m.
  • the previously prepared paint for forming the piezoelectric layer 20 was applied using a slide coater.
  • the paint was applied so that the thickness of the coating film after drying was 20 ⁇ m.
  • the sheet material 10a coated with paint was placed on a hot plate at 120°C, and the coating film was dried by heating. MEK was thereby evaporated to form a laminate 10b.
  • a calendering film 80 was placed on the surface of the formed piezoelectric layer 20, and calendering was performed using a roller.
  • the number density of 1 ⁇ m-high projections and the kurtosis Rku of the calendering film 80 were measured as follows.
  • the profile of the surface roughness of the calendering film 80 was measured using a non-contact three-dimensional surface roughness meter manufactured by Bruker, with a white LED light source (green filter), a 10x objective lens, a 0.55x internal lens, and a CCD: After measuring under the conditions of 1280 ⁇ 960 pixels, VSI / VXI, observation field of view 825.7 ⁇ m ⁇ 619.3 ⁇ m, cross-sectional sampling 0.645 ⁇ m, 0 is averaged, cylindrical, after tilt correction, fitting with Gaussian process regression, surface The roughness was obtained, and the number density of convex portions with a height of 1 ⁇ m and the kurtosis Rku were calculated. The number density of convex portions and Rku were measured in each of ten observation fields, and an average value was obtained. Table 1 shows the measurement results.
  • the sheet-like object 10c was laminated on the laminated body 10b with the second electrode layer 26 (copper thin film side) side facing the piezoelectric layer 20, and was thermocompression bonded at 120.degree.
  • the piezoelectric film 10 having the first protective layer 28, the first electrode layer 24, the piezoelectric layer 20, the second electrode layer 26 and the second protective layer 30 in this order was produced.
  • a 5 mol/L NaOH aqueous solution at a temperature of 15 to 25° C. was added dropwise to dissolve the second protective layer 30 of the piezoelectric film 10 thus produced.
  • the piezoelectric layer 20 was allowed to stand still for a period of time during which the aqueous NaOH solution did not come into contact with the piezoelectric layer 20 even if a portion of the second electrode layer 26 was dissolved.
  • the exposed second electrode layer 26 was dissolved in a 0.01 mol/L ferric chloride aqueous solution. The dissolution of the ferric chloride aqueous solution did not exceed 5 minutes after the piezoelectric layer 20 was exposed.
  • the exposed piezoelectric layer 20 was washed with pure water and dried at 30° C. or less.
  • the surface of the exposed piezoelectric layer 20 is measured by a non-contact three-dimensional surface profile roughness meter manufactured by Bruker Co., Ltd., with a white LED light source (green filter), a 10x objective lens, a 0.55x internal lens, and a CCD. : 1280 ⁇ 960 pixels, VSI / VXI, observation field of view 825.7 ⁇ m ⁇ 619.3 ⁇ m, cross-sectional sampling 0.645 ⁇ m After measurement, 0 is averaged, cylindrical, tilt corrected, fitted with Gaussian process regression, surface The roughness was determined, and the number density of recesses, Rku and Ra were calculated. The number density of concave portions, Rku and Ra were measured in each of ten observation fields, and the average value was obtained. Table 1 shows the measurement results.
  • the particle size of the piezoelectric particles 36 in the piezoelectric layer 20 was measured as follows.
  • a sample is cut from the piezoelectric film and cut in the thickness direction for cross-sectional observation. Cutting is carried out, for example, by attaching a histo knife blade width of 8 mm manufactured by Drukker to RM2265 manufactured by Leica Biosystems, setting the speed to 1 on the scale of the controller, and setting the meshing amount to 0.25 to 1 ⁇ m.
  • the cross section is observed by SEM (Scanning Electron Microscope).
  • SEM scanning Electron Microscope
  • S4800 manufactured by Hitachi High-Technologies Corporation can be used.
  • the sample may be conductively treated.
  • the sample may be conductively treated by platinum deposition and the working distance may be 2.8 mm.
  • SE secondary-electron
  • the imaging magnification is such that the first electrode layer and the second electrode layer fit in one screen, and the width between both electrodes is half or more of the screen. Moreover, at that time, the two electrode layers are photographed so as to be horizontal to the bottom of the image.
  • the image obtained as described above is binarized. Specifically, first, the image analysis software WinROOF is used to linearly convert the density range of the original imaging data to the range of 0 (dark) to 255 (bright) gradation to enhance the contrast. Subsequently, the piezoelectric layer is selected in a rectangular shape so that the selected area is maximized in a range not including the first electrode layer and the second electrode layer, and the density range of 110 to 255 gradations is binarized.
  • the average particle size of the piezoelectric particles is obtained by obtaining the circle-equivalent diameter of each piezoelectric particle using the image binarized by the above-described method, and calculating the average value.
  • the average particle size the N5 field of view of the cross section is also measured, and the average particle size is obtained for each measurement field, and is taken as the average particle size of the piezoelectric particles in the piezoelectric film. Table 1 shows the measurement results.
  • Example 2 A piezoelectric film was produced in the same manner as in Example 1, except that the average particle diameter of the PZT particles dispersed in the coating material forming the piezoelectric layer was 5.75 ⁇ m. The Rku and Ra of the piezoelectric layer of the produced piezoelectric film and the particle size of the piezoelectric particles were measured in the same manner as described above.
  • Example 3 A piezoelectric film was produced in the same manner as in Example 1, except that the calendering film 80 having the number density of protrusions and kurtosis Rku as described below was used. Table 1 shows the number density of protrusions and the kurtosis Rku of the calendering film 80 .
  • Piezoelectric films were produced in the same manner as in Example 1, except that different resin films were used as the calendering films 80 .
  • Table 1 shows the number density of protrusions and the kurtosis Rku of each calendering film 80 .
  • a 1 kHz sine wave was input as an input signal to the fabricated piezoelectric speaker through a power amplifier, and the sound pressure (initial sound pressure) was measured with a microphone placed 50 cm away from the center of the speaker.
  • the piezoelectric element of the present invention has a smaller difference in sound pressure after the endurance test than the initial sound pressure, and has high durability against bending and stretching, as compared with the comparative example.
  • the number density of the recesses was too large and the kurtosis Rku was too small, so it is considered that the filling rate of the piezoelectric layer was low and the initial sound pressure was low.
  • the kurtosis Rku was too large, stress concentration occurred at the tip portion of the recess, and the piezoelectric layer was damaged, so that the sound pressure after the durability test decreased.
  • Comparative Example 3 the kurtosis Rku was too small, the filling rate of the piezoelectric layer was low, and the initial sound pressure was low.
  • Comparative Example 4 the number density of the recesses was too small, and the piezoelectric particles were damaged when compressive stress was applied to the piezoelectric layer.
  • Comparative Example 5 the number density of the recesses was too large, so the filling rate of the piezoelectric layer was low, and the initial sound pressure was low.
  • the particle size of the piezoelectric particles is preferably 0.5 ⁇ m to 5 ⁇ m.
  • the surface roughness Ra of the piezoelectric layer is preferably 10 nm to 200 nm. From the above results, the effect of the present invention is clear.
  • the piezoelectric film of the present invention can be used, for example, in various sensors such as sound wave sensors, ultrasonic sensors, pressure sensors, tactile sensors, strain sensors and vibration sensors (especially for infrastructure inspection such as crack detection and manufacturing site inspection such as foreign matter contamination detection). useful), acoustic devices such as microphones, pickups, speakers and exciters (specific applications include noise cancellers (used in cars, trains, airplanes, robots, etc.), artificial vocal cords, buzzers for preventing insects and vermin from entering , furniture, wallpaper, photographs, helmets, goggles, headrests, signage, robots, etc.), automobiles, smartphones, smart watches, haptics used for games, etc.
  • sensors such as sound wave sensors, ultrasonic sensors, pressure sensors, tactile sensors, strain sensors and vibration sensors (especially for infrastructure inspection such as crack detection and manufacturing site inspection such as foreign matter contamination detection).
  • acoustic devices such as microphones, pickups, speakers and exciters (specific applications include noise cancellers (used in cars, trains, airplanes, robots,

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