WO2021225075A1 - 高分子圧電フィルム - Google Patents
高分子圧電フィルム Download PDFInfo
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- WO2021225075A1 WO2021225075A1 PCT/JP2021/016180 JP2021016180W WO2021225075A1 WO 2021225075 A1 WO2021225075 A1 WO 2021225075A1 JP 2021016180 W JP2021016180 W JP 2021016180W WO 2021225075 A1 WO2021225075 A1 WO 2021225075A1
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- piezoelectric
- piezoelectric film
- layer
- polymer
- film
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- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
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- H10N30/883—Additional insulation means preventing electrical, physical or chemical damage, e.g. protective coatings
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- B32B2264/00—Composition or properties of particles which form a particulate layer or are present as additives
- B32B2264/10—Inorganic particles
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- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
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- B32B2307/40—Properties of the layers or laminate having particular optical properties
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- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
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- B32B27/06—Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material
- B32B27/08—Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material of synthetic resin
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- B32B27/00—Layered products comprising a layer of synthetic resin
- B32B27/36—Layered products comprising a layer of synthetic resin comprising polyesters
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F2810/00—Chemical modification of a polymer
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2329/00—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by an alcohol, ether, aldehydo, ketonic, acetal, or ketal radical; Hydrolysed polymers of esters of unsaturated alcohols with saturated carboxylic acids; Derivatives of such polymer
- C08J2329/02—Homopolymers or copolymers of unsaturated alcohols
- C08J2329/04—Polyvinyl alcohol; Partially hydrolysed homopolymers or copolymers of esters of unsaturated alcohols with saturated carboxylic acids
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- C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
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- 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
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- C08K2201/001—Conductive additives
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- 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
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R17/00—Piezoelectric transducers; Electrostrictive transducers
- H04R17/005—Piezoelectric transducers; Electrostrictive transducers using a piezoelectric polymer
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R2499/00—Aspects covered by H04R or H04S not otherwise provided for in their subgroups
- H04R2499/10—General applications
- H04R2499/15—Transducers incorporated in visual displaying devices, e.g. televisions, computer displays, laptops
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R31/00—Apparatus or processes specially adapted for the manufacture of transducers or diaphragms therefor
- H04R31/003—Apparatus or processes specially adapted for the manufacture of transducers or diaphragms therefor for diaphragms or their outer suspension
Definitions
- the present invention relates to a polymer piezoelectric film used for an electroacoustic conversion film used for a speaker, a microphone, or the like.
- Patent Document 1 describes a polymer composite piezoelectric body in which piezoelectric particles are dispersed in a matrix made of a polymer material having viscoelasticity at room temperature, and a piezoelectric material provided so as to sandwich the polymer composite piezoelectric body.
- a polymer piezoelectric film electroacoustic conversion film having a body layer and having an area fraction of piezoelectric particles on a contact surface with an electrode layer of 50% or less is also described.
- the polymer composite piezoelectric material described in Patent Document 1 has excellent piezoelectric properties. Further, since this polymer composite piezoelectric body is obtained by dispersing lead zirconate titanate particles in a polymer material with cyanoethylated polyvinyl alcohol, the piezoelectric layer made of this polymer composite piezoelectric body is good. Has flexibility. Therefore, according to the polymer piezoelectric film using this polymer composite piezoelectric material, for example, an electroacoustic conversion film having flexibility and having good piezoelectric characteristics that can be used for a flexible speaker or the like can be obtained. Be done.
- An object of the present invention is to solve such a problem of the prior art, and is a polymer piezoelectric film having a piezoelectric layer containing lead zirconate titanate particles in a matrix containing a polymer material. It is an object of the present invention to provide a polymer piezoelectric film which exhibits higher piezoelectric characteristics.
- the present invention has the following configuration.
- It has a piezoelectric layer containing lead zirconate titanate particles in a matrix containing a polymer material, and electrode layers provided on both sides of the piezoelectric layer.
- a polymer piezoelectric film in which the Raman shift of the maximum peak existing in the range of 190 to 215 cm -1 in the Raman spectrum of the piezoelectric layer is 205 cm -1 or less.
- the polymer piezoelectric film according to [1] which has a protective layer covering an electrode layer.
- [3] The polymer piezoelectric film according to [1] or [2], wherein the lead zirconate titanate particles have an arithmetic mean diameter of 1 to 10 ⁇ m.
- the peak intensity of the maximum peak existing in the range of 90 cm -1 or more and less than 120 cm -1 is I100, and the peak intensity of the maximum peak existing in the range of 120 to 150 cm -1 is I130.
- the peak intensity of the maximum peak existing in the range of 490 to 650 cm -1 is I550 and the peak intensity of the maximum peak existing in the range of 700 to 750 cm -1 is I725.
- a polymer piezoelectric film having excellent piezoelectric properties which has a piezoelectric layer containing lead zirconate titanate particles in a matrix containing a polymer material.
- FIG. 1 is a diagram conceptually showing an example of the polymer film of the present invention.
- FIG. 2 is a conceptual diagram for explaining a method for producing the piezoelectric film shown in FIG.
- FIG. 3 is a conceptual diagram for explaining a method for producing the piezoelectric film shown in FIG.
- FIG. 4 is a conceptual diagram for explaining a method for producing the piezoelectric film shown in FIG.
- FIG. 5 is a diagram conceptually showing an example of a piezoelectric speaker using the piezoelectric film shown in FIG.
- FIG. 6 is a conceptual diagram for explaining a method of measuring a Raman spectrum in an embodiment.
- FIG. 7 is a conceptual diagram for explaining a method of measuring the sound pressure of the piezoelectric speaker in the embodiment.
- the description of the constituent elements described below may be based on typical embodiments of the present invention, but the present invention is not limited to such embodiments.
- the numerical range represented by using "-" means a range including the numerical values before and after "-" as the lower limit value and the upper limit value.
- the figures shown below are conceptual diagrams for explaining the present invention. Therefore, the thickness of each layer, the size of the piezoelectric particles, the size of the constituent members, and the like are different from the actual ones.
- FIG. 1 conceptually shows an example of the polymer piezoelectric film of the present invention.
- the polymer piezoelectric film 10 includes a first electrode layer 14 laminated on one surface of the piezoelectric layer 12 and a first protective layer 18 laminated on the surface of the first electrode layer 14.
- the second electrode layer 16 is laminated on the other surface of the piezoelectric layer 12, and the second protective layer 20 is laminated on the surface of the second electrode layer 16.
- the piezoelectric layer 12 is polarized in the thickness direction.
- the polymer piezoelectric film 10 is also referred to as a piezoelectric film 10.
- the piezoelectric layer 12 preferably contains lead zirconate titanate particles 26, which are piezoelectric particles, in a matrix 24 containing a polymer material, as conceptually shown in FIG. ..
- lead zirconate titanate is also referred to as PZT.
- the piezoelectric layer 12 has a Raman shift of the maximum peak existing in the range of 190 to 215 cm -1 in the Raman spectrum of 205 cm -1 or less.
- the piezoelectric film 10 of the present invention exhibits high piezoelectric characteristics by having such a configuration, and for example, when used for an electroacoustic conversion film, a high sound pressure can be obtained.
- the piezoelectric layer 12 is formed by dispersing PZT particles 26, which are piezoelectric particles, in a matrix 24 containing a polymer material. That is, the piezoelectric layer 12 is a polymer composite piezoelectric body.
- the polymer composite piezoelectric body preferably has the following requirements.
- the normal temperature is 0 to 50 ° C.
- Flexibility For example, when gripping in a state of being loosely bent like a document like a newspaper or a magazine for carrying, it is constantly subjected to a relatively slow and large bending deformation of several Hz or less from the outside. become.
- the polymer composite piezoelectric body is required to have appropriate softness. Further, if the strain energy can be diffused to the outside as heat, the stress can be relaxed. Therefore, it is required that the loss tangent of the polymer composite piezoelectric body is appropriately large.
- the speaker vibrates the piezoelectric particles at a frequency in the audio band of 20 Hz to 20 kHz, and the vibration energy causes the entire diaphragm (polymer composite piezoelectric material) to vibrate as a unit, thereby reproducing the sound.
- the polymer composite piezoelectric material is required to have an appropriate hardness.
- the frequency characteristic of the speaker is smooth, the amount of change in sound quality when the minimum resonance frequency f 0 changes with the change in curvature also becomes small. Therefore, the loss tangent of the polymer composite piezoelectric material is required to be moderately large.
- the minimum resonance frequency f 0 of the speaker diaphragm is given by the following equation.
- s is the stiffness of the vibration system and m is the mass.
- m is the mass.
- the flexible polymer composite piezoelectric material used as an electroacoustic conversion film is required to behave hard against vibrations of 20 Hz to 20 kHz and soft against vibrations of several Hz or less. Further, the loss tangent of the polymer composite piezoelectric body is required to be appropriately large for vibrations of all frequencies of 20 kHz or less.
- a polymer solid has a viscoelastic relaxation mechanism, and a large-scale molecular motion causes a decrease in storage elastic modulus (Young's modulus) (relaxation) or a maximum loss elastic modulus (absorption) as the temperature rises or the frequency decreases.
- Young's modulus storage elastic modulus
- laxation maximum loss elastic modulus
- absorption maximum loss elastic modulus
- main dispersion the relaxation caused by the micro-Brownian motion of the molecular chain in the amorphous region
- the temperature at which this main dispersion occurs is the glass transition point (Tg), and the viscoelastic relaxation mechanism appears most prominently.
- the polymer composite piezoelectric body (piezoelectric layer 12), by using a polymer material having a glass transition point at room temperature for the matrix, it is hard for vibrations of 20 Hz to 20 kHz and for slow vibrations of several Hz or less. Is realized by a polymer composite piezoelectric material that behaves softly. In particular, in terms of preferably expressing this behavior, it is preferable to use a polymer material having a glass transition point at a frequency of 1 Hz at room temperature, that is, at 0 to 50 ° C. for the matrix of the polymer composite piezoelectric material.
- the polymer material having a glass transition point at room temperature is, in other words, a polymer material having viscoelasticity at room temperature.
- the polymer material having viscoelasticity at room temperature various known materials can be used.
- the polymer material having viscoelasticity at room temperature preferably has a storage elastic modulus (E') at a frequency of 1 Hz as measured by dynamic viscoelasticity measurement of 100 MPa or more at 0 ° C. and 10 MPa or less at 50 ° C.
- E' storage elastic modulus
- the polymer material having viscoelasticity at room temperature has a relative permittivity of 10 or more at 25 ° C.
- a voltage is applied to the polymer composite piezoelectric body, a higher electric field is applied to the piezoelectric particles in the polymer matrix, so that a large amount of deformation can be expected.
- the polymer material has a relative permittivity of 10 or less at 25 ° C.
- polymer material having viscoelasticity at room temperature satisfying such conditions examples include cyanoethylated polyvinyl alcohol (cyanoethylated PVA), polyvinyl acetate, polyvinylidene chloride core acrylonitrile, polystyrene-vinyl polyisoprene block copolymer, and polyvinylmethyl. Examples thereof include ketones and polybutyl methacrylate. Further, as these polymer materials, commercially available products such as Hybler 5127 (manufactured by Kuraray Co., Ltd.) can also be preferably used.
- Hybler 5127 manufactured by Kuraray Co., Ltd.
- the polymer material it is preferable to use a material having a cyanoethyl group, and it is particularly preferable to use cyanoethylated PVA.
- the matrix 24 only one of these polymer materials may be used, or a plurality of types may be used in combination (mixed).
- a plurality of polymer materials may be used in combination, if necessary. That is, in the matrix 24, in addition to a polymer material having viscoelasticity at room temperature such as cyanoethylated PVA for the purpose of adjusting dielectric properties and mechanical properties, other dielectric polymer materials are added as needed. It may be added.
- dielectric polymer material examples include polyvinylidene fluoride, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, and vinylidene fluoride-trifluoroethylene copolymer.
- fluoropolymers such as polyvinylidene fluoride-tetrafluoroethylene copolymer, vinylidene cyanide-vinyl acetate copolymer, cyanoethyl cellulose, cyanoethyl hydroxysaccharose, cyanoethyl hydroxycellulose, cyanoethyl hydroxypurrane, cyanoethyl methacrylate, cyanoethyl acrylate, cyanoethyl.
- Cyano groups such as hydroxyethyl cellulose, cyanoethyl amylose, cyanoethyl hydroxypropyl cellulose, cyanoethyl dihydroxypropyl cellulose, cyanoethyl hydroxypropyl amylose, cyanoethyl polyacrylamide, cyanoethyl polyacrylate, cyanoethyl pullulan, cyanoethyl polyhydroxymethylene, cyanoethyl glycidolpulrane, cyanoethyl saccharose and cyanoethyl sorbitol.
- a polymer having a cyanoethyl group a synthetic rubber such as a nitrile rubber or a chloroprene rubber, and the like are exemplified.
- a polymer material having a cyanoethyl group is preferably used.
- 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 a plurality of types may be added. ..
- the matrix 24 contains a vinyl chloride resin, a thermoplastic resin such as polyethylene, polystyrene, methacrylic resin, polybutene and isobutylene, and a phenol resin for the purpose of adjusting the glass transition point Tg.
- a thermoplastic resin such as polyethylene, polystyrene, methacrylic resin, polybutene and isobutylene
- a phenol resin for the purpose of adjusting the glass transition point Tg.
- Urea resin, melamine resin, alkyd resin, thermosetting resin such as mica and the like
- a tackifier such as rosin ester, rosin, terpene, terpene phenol, and petroleum resin may be added.
- the amount to be added when a material other than the polymer material having viscoelasticity at room temperature such as cyanoethylated PVA is added is not particularly limited, but is 30 mass in proportion to the matrix 24. It is preferably% or less. As a result, the characteristics of the polymer material to be added can be exhibited without impairing the viscoelastic relaxation mechanism in the matrix 24, so that the dielectric constant can be increased, the heat resistance can be improved, and the adhesion to the PZT particles 26 and the electrode layer can be improved. In terms of points, favorable results can be obtained.
- the piezoelectric layer 12 contains PZT particles 26 in such a matrix 24.
- the PZT particles 26 are particles containing PZT (lead zirconate titanate) as a main component.
- the main component indicates a component contained most in the substance, preferably a component containing 50% by mass or more, and more preferably a component containing 90% by mass or more.
- the PZT particles 26 preferably contain only the constituent elements of PZT, excluding impurities that are inevitably mixed.
- PZT is a solid solution of lead zirconate (PbZrO 3 ) and lead titanate (PbTIO 3 ), and is represented by the general formula Pb (Zr x Ti 1-x ) O 3 .
- this general formula Pb (Zr x Ti 1-x ) O 3 is also referred to as “general formula [I]”.
- x is an elemental ratio (molar ratio) of zirconium and titanium, that is, Zr / (Zr + Ti).
- x in the general formula [I] is not limited. As described above, it is known that a ferroelectric substance having a perovskite structure such as PZT can obtain high piezoelectric characteristics by setting the composition to a phase transition boundary (MPB (morphotropic phase boundary)) composition.
- the MPB composition of PZT is a composition in which x of the general formula [I] is around 0.52. That is, the MPB composition of PZT has a general formula [I] near "Pb (Zr 0.52 Ti 0.48 ) O 3 ". Therefore, x in the general formula [I] is preferably close to 0.52. Specifically, x in the general formula [I] is preferably 0.50 to 0.54, more preferably 0.51 to 0.53, and even more preferably 0.52.
- the piezoelectric layer 12 has a maximum Raman shift of 205 cm -1 or less in the range of 190 to 215 cm -1 in the Raman spectrum.
- the piezoelectric film 10 of the present invention exhibits high piezoelectric characteristics by having such a configuration, and when used for an electroacoustic conversion film, for example, a high sound pressure can be obtained.
- the piezoelectric layer 12 is formed by dispersing PZT particles 26 in a matrix 24 containing a polymer material. Therefore, in the Raman spectrum of the piezoelectric layer 12, a peak derived from the polymer material and a peak derived from PZT occur. In the Raman spectrum, peaks originating in the range of 190 to 215 cm -1 are peaks derived from PZT, and peaks derived from polymer materials do not occur in this wavenumber range. That is, in the piezoelectric film 10 of the present invention, the Raman shift of the maximum peak existing in the range of 190 to 215 cm -1 in the Raman spectrum of the PZT particles 26 constituting the piezoelectric layer 12 is 205 cm -1 or less. be.
- the present inventor has made extensive studies on a structure that can obtain high piezoelectric properties for a piezoelectric film using a piezoelectric layer (polymer composite piezoelectric material) in which PZT particles are dispersed in a matrix containing a polymer material. As a result, it was found that the distortion of the crystal lattice of the PZT particles constituting the piezoelectric layer is the cause of the deterioration of the piezoelectric characteristics.
- a piezoelectric film in which electrode layers are provided on both sides of a polymer composite piezoelectric body in which PZT particles are dispersed in a matrix containing a molecular material, the electrode layers are energized and an electric field is applied to the PZT particles to obtain PZT particles. It expands and contracts (expands / contracts).
- the piezoelectric film is used as an electroacoustic conversion film, the piezoelectric film is expanded and contracted by the expansion and contraction of the PZT particles, so that the piezoelectric film is vibrated in a direction orthogonal to the surface and sound is output.
- the piezoelectric film 10 of the present invention is a piezoelectric film 10 in which the piezoelectric layer 12 containing the PZT particles 26 in the matrix 24 containing the polymer material is used, and the piezoelectric layer 12, that is, 190 of the Raman spectrum of the PZT particles 26.
- the maximum peak Raman shift present at ⁇ 215 cm -1 is 205 cm -1 or less. That is, the piezoelectric film 10 of the present invention can exhibit high piezoelectric characteristics by using PZT particles 26 having extremely little distortion of the crystal lattice that causes deterioration of the piezoelectric characteristics. Therefore, the piezoelectric film 10 of the present invention can output high sound pressure sound by using it as, for example, an electroacoustic conversion film.
- the Raman shift of the maximum peak existing in 190 to 215 cm -1 of the Raman spectrum of the piezoelectric layer 12 exceeds 205 cm -1 , the distortion of the crystal lattice of the PZT particles 26 is large and sufficient. Problems such as not being able to obtain piezoelectric characteristics and not being able to obtain a large sound pressure as a speaker vibrating plate when used as an electroacoustic conversion film or the like occur.
- the Raman spectrum of the piezoelectric layer 12 preferably has a maximum peak in the range of 195 to 200 cm -1 in the range of 190 to 215 cm -1 , and a maximum peak in the range of 195 to 198 cm -1 . More preferred.
- the peak intensity of the maximum peak existing in the range of 90 cm -1 or more and less than 120 cm -1 is I100, and the maximum peak existing in the range of 120 to 150 cm -1.
- the peak intensity of is I130
- the peak intensity ratio I130 / I110 is preferably 1.05 or more.
- the peak intensity of the maximum peak existing in the range of 490 to 650 cm -1 is set to the peak intensity of the maximum peak existing in the range of I550 and 700 to 750 cm -1.
- the peak intensity ratio I725 / I550 is preferably 0.25 or more.
- the piezoelectric film 10 of the present invention preferably has a peak intensity ratio of I130 / I110 of 1.05 or more and a peak intensity ratio of I725 / I550 of 0.25 or more in the Raman spectrum of the piezoelectric layer 12. Satisfy at least one of the above.
- the piezoelectric film 10 of the present invention more preferably satisfies both of the conditions of this peak intensity ratio.
- the piezoelectric film 10 of the present invention in addition to suppressing distortion of the crystal lattice, better piezoelectric characteristics can be obtained by the PZT particles 26 having less lead atom defects.
- the peak intensity ratio I130 / I110 is more preferably 1.1 or more, and even more preferably 1.2 or more.
- the peak intensity ratio I725 / I550 is more preferably 0.4 or more, and further preferably 0.5 or more.
- the upper limit of the peak intensity ratio I130 / I110 is not limited, but is usually 1.3 or less.
- the upper limit of the peak intensity ratio I725 / I550 is also not limited, but is usually 0.8 or less.
- the particle size of the PZT particles 26 is not limited, and may be appropriately selected depending on the size of the piezoelectric film 10 and the intended use.
- the particle size of the PZT particles 26 is preferably 1 to 10 ⁇ m in arithmetic mean diameter.
- the particle size of the PZT particles 26 indicates the arithmetic mean diameter of the PZT particles 26.
- the arithmetic mean diameter of the PZT particles 26 is measured as follows. First, the piezoelectric film 10 is cut at an arbitrary position in the thickness direction.
- the thickness direction is the stacking direction of the piezoelectric layer 12, the first electrode layer 14, the first protective layer 18, the second electrode layer 16, and the second protective layer 20 in the piezoelectric film 10. It is the vertical direction of FIG.
- the cross section of the piezoelectric film 10 in the thickness direction is observed with a scanning electron microscope including the upper and lower ends of the piezoelectric layer 12 in the field of view, and the area ratio of the PZT particles 26 in the piezoelectric layer 12 is analyzed by image analysis of the microscope image. To calculate.
- the area ratio of the PZT particles 26 is divided by the number of PZT particles 26 in the microscope image, and the particle size of the PZT particles 26 is calculated by converting into yen.
- the particle size of the PZT particles 26 is calculated for the five cross sections arbitrarily selected in the piezoelectric film 10, and the average value of the particle sizes of the five cross sections is calculated as the particle size (arithmetic mean) of the PZT particles 26 in the piezoelectric film 10. Diameter).
- the particle size of the PZT particles 26 By setting the particle size of the PZT particles 26 to 1 ⁇ m or more, it is preferable in that high vibration energy transmission efficiency can be obtained.
- the PZT particles 26 that contribute to the roughness of the surface facing the electrode layer, which will be described later, can be reduced to obtain good piezoelectric characteristics, which can be used as an electroacoustic conversion film or the like. In this case, it is preferable in that the desired output characteristics can be stably obtained regardless of the curved state.
- the particle size of the PZT particles 26 is more preferably 1.5 to 7 ⁇ m, even more preferably 2 to 5 ⁇ m.
- the PZT particles 26 in the piezoelectric layer 12 are irregularly dispersed in the matrix 24, but the present invention is not limited to this. That is, the PZT particles 26 in the piezoelectric layer 12 may be regularly dispersed in the matrix 24 as long as they are preferably uniformly dispersed. Further, the PZT particles 26 may or may not have the same particle size.
- the amount ratio of the matrix 24 and the PZT particles 26 in the piezoelectric layer 12 there is no limitation on the amount ratio of the matrix 24 and the PZT particles 26 in the piezoelectric layer 12, the size and thickness of the piezoelectric film 10 in the plane direction, the use of the piezoelectric film 10, and the piezoelectricity. It may be appropriately set according to the characteristics required for the film 10.
- the volume fraction of the PZT particles 26 in the piezoelectric layer 12 is preferably 30 to 80%, more preferably 50% or more, still more preferably 50 to 80%.
- the thickness of the piezoelectric layer 12 is not particularly limited, and may be appropriately set according to the application of the piezoelectric film 10, the characteristics required for the piezoelectric film 10, and the like.
- the thickness of the piezoelectric layer 12 is preferably 8 to 300 ⁇ m, more preferably 8 to 200 ⁇ m, further preferably 10 to 150 ⁇ m, and particularly preferably 15 to 100 ⁇ m.
- the piezoelectric layer 12 is preferably polarized (polled) in the thickness direction.
- the polarization treatment will be described in detail later.
- the piezoelectric film 10 of the illustrated example has a first electrode layer 14 on one surface of such a piezoelectric layer 12, a first protective layer 18 on the surface thereof, and a piezoelectric layer.
- the other surface of the twelve has a second electrode layer 16 and a second protective layer 20 on the surface thereof.
- the first electrode layer 14 and the second electrode layer 16 form an electrode pair. That is, the piezoelectric film 10 sandwiches both sides of the piezoelectric layer 12 between electrode pairs, that is, the first electrode layer 14 and the second electrode layer 16, and this laminated body is sandwiched between the first protective layer 18 and the second protective layer. It has a structure sandwiched between 20 and 20. In such a piezoelectric film 10, the region held by the first electrode layer 14 and the second electrode layer 16 is expanded and contracted according to the applied voltage.
- the first electrode layer 14 and the first protective layer 18, and the first and second elements in the second electrode layer 16 and the second protective layer 20 are for convenience in order to explain the piezoelectric film 10.
- the name is given according to the drawing. Therefore, the first and second piezoelectric films 10 have no technical meaning and are irrelevant to the actual usage state.
- the first protective layer 18 and the second protective layer 20 have a role of covering the first electrode layer 14 and the second electrode layer 16 and imparting appropriate rigidity and mechanical strength to the piezoelectric layer 12. Is responsible for. That is, in the piezoelectric film 10, the piezoelectric layer 12 composed of the matrix 24 and the PZT particles 26 exhibits extremely excellent flexibility with respect to slow bending deformation, but on the other hand, depending on the application, the rigidity may be increased. Mechanical strength may be insufficient.
- the piezoelectric film 10 is provided with a first protective layer 18 and a second protective layer 20 to supplement the piezoelectric film 10.
- the laminate of the piezoelectric layer 12 and the electrode layer is sandwiched so as to correspond to both the first electrode layer 14 and the second electrode layer 16.
- a first protective layer 18 and a second protective layer 20 are provided.
- the first protective layer 18 and the second protective layer 20 are provided as preferred embodiments. Therefore, the piezoelectric film of the present invention may not have the first protective layer 18 and the second protective layer 20, or may have only one of the first protective layer 18 and the second protective layer 20.
- the laminate of the piezoelectric layer 12 and the electrode layer is sandwiched like the piezoelectric film 10 of the illustrated example. It is preferable to provide the first protective layer 18 and the second protective layer 20.
- the first protective layer 18 and the second protective layer 20 are not limited, and various sheet-like materials can be used.
- various resin films are preferably exemplified.
- PET polyethylene terephthalate
- PP polypropylene
- PS polystyrene
- PC polycarbonate
- PPS polyphenylene sulfide
- PMMA polymethylmethacrylate
- PEI Polyetherimide
- PEI polyimide
- PEN polyethylene naphthalate
- TAC triacetyl cellulose
- a resin film made of a cyclic olefin resin or the like are preferably used.
- the thickness of the first protective layer 18 and the second protective layer 20 there is no limitation on the thickness of the first protective layer 18 and the second protective layer 20. Further, the thicknesses of the first protective layer 18 and the second protective layer 20 are basically the same, but may be different. Here, if the rigidity of the first protective layer 18 and the second protective layer 20 is too high, not only the expansion and contraction of the piezoelectric layer 12 is restrained, but also the flexibility is impaired. Therefore, the thinner the first protective layer 18 and the second protective layer 20, the more advantageous it is, except when mechanical strength and good handleability as a sheet-like material are required.
- the thickness of the first protective layer 18 and the second protective layer 20 is twice or less the thickness of the piezoelectric layer 12, the rigidity can be ensured and the appropriate flexibility can be achieved. A favorable result can be obtained in terms of points.
- the thickness of the first protective layer 18 and the second protective layer 20 is preferably 100 ⁇ m or less. 50 ⁇ m or less is more preferable, and 25 ⁇ m or less is further preferable.
- a first electrode layer 14 is provided between the piezoelectric layer 12 and the first protective layer 18, and a second electrode layer 16 is provided between the piezoelectric layer 12 and the second protective layer 20. It is formed.
- the first electrode layer 14 is also referred to as the first electrode layer 14
- the second electrode layer 16 is also referred to as the second electrode layer 16.
- the first electrode layer 14 and the second electrode layer 16 are provided to apply a voltage to the piezoelectric layer 12 (piezoelectric film 10).
- the materials for forming the first electrode layer 14 and the second electrode layer 16 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, In addition, indium tin oxide and the like are exemplified. Among them, copper, aluminum, gold, silver, platinum, and indium tin oxide are preferably exemplified as the first electrode layer 14 and the second electrode layer 16.
- the method of forming the first electrode layer 14 and the second electrode layer 16 and the film formation by a vapor deposition method such as vacuum vapor deposition and sputtering, the film formation by plating, and the above.
- a vapor deposition method vacuum film deposition method
- Various known methods such as a method of attaching a foil formed of a material can be used.
- thin films such as copper and aluminum formed by vacuum deposition are preferably used as the first electrode layer 14 and the second electrode layer 16 because the flexibility of the piezoelectric film 10 can be ensured.
- NS Among them, a copper thin film produced by vacuum deposition is preferably used.
- the thickness of the first electrode layer 14 and the second electrode layer 16 There is no limitation on the thickness of the first electrode layer 14 and the second electrode layer 16. Further, the thicknesses of the first electrode layer 14 and the second electrode layer 16 are basically the same, but may be different.
- the rigidity of the first electrode layer 14 and the second electrode layer 16 is too high, not only the expansion and contraction of the piezoelectric layer 12 is restricted, but also the expansion and contraction of the piezoelectric layer 12 is restricted. Flexibility is also impaired. Therefore, the thinner the first electrode layer 14 and the second electrode layer 16 are, the more advantageous they are, as long as the electrical resistance does not become too high.
- the product of the thickness of the first electrode layer 14 and the second electrode layer 16 and Young's modulus is less than the product of the thickness of the first protective layer 18 and the second protective layer 20 and Young's modulus.
- the first protective layer 18 and the second protective layer 20 are PET
- the first electrode layer 14 and the second electrode layer 16 are copper.
- PET has a Young's modulus of about 6.2 GPa
- copper has a Young's modulus of about 130 GPa.
- the thickness of the first protective layer 18 and the second protective layer 20 is 25 ⁇ m
- the thickness of the first electrode layer 14 and the second electrode layer 16 is preferably 1.2 ⁇ m or less, preferably 0.3 ⁇ m or less. Is more preferable, and 0.1 ⁇ m or less is further preferable.
- the piezoelectric layer 12 having PZT particles 26 is sandwiched between the first electrode layer 14 and the second electrode layer 16 in a matrix 24 containing a polymer material having viscoelasticity at room temperature. Further, this laminated body has a structure in which the first protective layer 18 and the second protective layer 20 are sandwiched.
- the maximum value of the loss tangent (Tan ⁇ ) at a frequency of 1 Hz by dynamic viscoelasticity measurement exists at room temperature, and the maximum value of 0.1 or more exists at room temperature. More preferred.
- the piezoelectric film 10 is subjected to a relatively slow and large bending deformation of several Hz or less from the outside, the strain energy can be effectively diffused to the outside as heat. It is possible to prevent cracks from occurring at the interface of.
- the piezoelectric film 10 preferably has a storage elastic modulus (E') at a frequency of 1 Hz as measured by dynamic viscoelasticity measurement of 10 to 30 GPa at 0 ° C. and 1 to 10 GPa at 50 ° C.
- E' storage elastic modulus
- the piezoelectric film 10 can have a large frequency dispersion in the storage elastic modulus (E') at room temperature. That is, it can behave hard for vibrations of 20 Hz to 20 kHz and soft for vibrations of several Hz or less.
- the product of the thickness and the storage elastic modulus (E') at a frequency of 1 Hz measured by dynamic viscoelasticity is 1.0 ⁇ 10 6 to 2.0 ⁇ 10 6 N / m at 0 ° C. , It is preferably 1.0 ⁇ 10 5 to 1.0 ⁇ 10 6 N / m at 50 ° C.
- the piezoelectric film 10 can be provided with appropriate rigidity and mechanical strength as long as the flexibility and acoustic characteristics are not impaired.
- 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 the master curve obtained from the dynamic viscoelasticity measurement.
- Ton ⁇ loss tangent
- the frequency characteristics of the speaker using the piezoelectric film 10 are smoothed, and the amount of change in sound quality when the minimum resonance frequency f0 changes with the change in the curvature of the speaker can be reduced.
- the piezoelectric film 10 has, for example, a sticking layer for sticking the electrode layer and the piezoelectric layer 12 and a sticking layer for sticking the electrode layer and the protective layer. It may have a layer.
- the adhesive may be an adhesive or an adhesive. Further, as the adhesive, a polymer material obtained by removing the PZT particles 26 from the piezoelectric layer 12, that is, the same material as the matrix 24 can also be preferably used.
- the sticking layer may be provided on both the first electrode layer 14 side and the second electrode layer 16 side, or may be provided on only one of the first electrode layer 14 side and the second electrode layer 16 side. good.
- the piezoelectric film 10 covers the electrode drawing portion for drawing out the electrodes from the first electrode layer 14 and the second electrode layer 16 and the region where the piezoelectric layer 12 is exposed, and is short-circuited. It may have an insulating layer or the like to prevent the above.
- the electrode drawing portion for example, a portion where the electrode layer and the protective layer project convexly to the outside in the plane direction of the piezoelectric layer 12 may be provided, and this protruding portion may be used as the electrode drawing portion.
- a part of the protective layer is removed to form a hole, and a conductive material such as silver paste is inserted into the hole to electrically conduct the conductive material and the electrode layer to form an electrode extraction portion.
- each electrode layer the number of electrode extraction portions is not limited to one, and two or more electrode extraction portions may be provided.
- the number of electrode extraction portions is not limited to one, and two or more electrode extraction portions may be provided.
- a sheet-like object 34 in which the first electrode layer 14 is formed on the first protective layer 18 is prepared.
- the sheet-like material 34 may be produced by forming a copper thin film or the like as the first electrode layer 14 on the surface of the first protective layer 18 by vacuum deposition, sputtering, plating or the like.
- the first protective layer 18 with a separator temporary support
- PET or the like having a thickness of 25 to 100 ⁇ m can be used.
- the separator may be removed after the second electrode layer 16 and the second protective layer 20 are thermocompression bonded, and before any member is laminated on the first protective layer 18.
- PZT particles 26 are produced.
- the method for producing the PZT particles 26 may be basically the same as that for ordinary PZT particles.
- a lead oxide powder, a zirconium oxide powder, and a titanium oxide powder are mixed according to the composition of the target PZT to prepare a raw material mixed powder.
- the composition of PZT in the PZT particles 26 substantially matches the composition (preparation composition) of this raw material mixed powder.
- this raw material mixed powder is fired at about 700 to 800 ° C. for 1 to 5 hours to prepare a raw material for PZT. Make particles.
- the raw material particles obtained by firing are pulverized by a ball mill to obtain PZT particles 26 having a target particle size.
- the raw material particles obtained by firing are pulverized by a ball mill to obtain PZT particles 26 having a target particle size.
- strains and defects that cause deterioration of the piezoelectric characteristics occur in the crystal lattice of the PZT particles. That is, in order to obtain PZT particles in which distortion and deficiency of the crystal lattice are suppressed, it is necessary to appropriately set the conditions for pulverization by a ball mill. Specifically, crushing by a ball mill is controlled by the media diameter, filling rate, rotation speed, crushing time, and the like.
- the crushing proceeds by the collision of balls, and at that time, distortion and chipping of the crystal lattice occur.
- the collision between the powder with low internal defects and the media in the late stage of crushing is considered to be the cause of the distortion of the crystal lattice. It is effective to reduce the media diameter and the rotation speed in order to suppress the distortion and the defect of the crystal lattice.
- the media diameter is too small, the rotation speed is low, or the like, the energy required for crushing cannot be obtained, and the PZT particles 26 having the desired particle size cannot be obtained.
- the loss of atoms such as lead atoms is easily affected by shearing with the media. Reducing the filling rate of media is effective in suppressing the loss of atoms such as lead atoms.
- the media diameter, filling rate, rotation speed, and crushing time are appropriately adjusted to suppress distortion and chipping of the crystal lattice of the PZT particles 26 and to suppress the distortion and chipping of the crystal lattice of the PZT particles 26, and to suppress the distortion and chipping of the crystal lattice, and to suppress the distortion and chipping of the piezoelectric layer.
- a piezoelectric layer 12 having good piezoelectric characteristics can be obtained while reducing the particle size of the PZT particles 26, which contributes to the roughness of the surface facing the electrode layer of 12.
- the media diameter (ball diameter) is preferably 0.1 to 5 mm, more preferably 0.4 to 1.5 mm, still more preferably 0.8 to 1.2 mm.
- the filling rate is preferably 15 to 60%, more preferably 20 to 50%, still more preferably 25 to 35%.
- the rotation speed is preferably 20 to 80 rpm (revolutions per minute), more preferably 30 to 70 rpm, still more preferably 40 to 60 rpm.
- the pulverization time may be appropriately set according to the media diameter, the filling rate and the rotation speed.
- the crushing time is preferably 8 to 24 hr (hours), more preferably 10 to 20 hr, and even more preferably 12 to 15 hr.
- the media diameter, filling rate, rotation speed, and crushing time are appropriately adjusted as described above to suppress distortion and chipping of the crystal lattice and to suppress PZT.
- the particle size of the particles 26 is preferably controlled to suppress distortion and defects of the crystal lattice, and to suppress particles having a particle size that contributes to the roughness of the surface of the piezoelectric layer 12 facing the electrode layer.
- PZT particles 26 can be produced. That is, by appropriately adjusting the media diameter, filling ratio, rotation speed, and crushing time as described above, the target particle size, for example, the particle size is 1 to 10 ⁇ m, and 190 in the Raman spectrum.
- the Raman shift of the maximum peak existing in the range of ⁇ 215 cm -1 is 205 cm -1 or less, preferably the peak intensity ratio I130 / I110 described above is 1.05 or more and / or the peak intensity ratio I725 / I550 is 0.
- a piezoelectric layer satisfying .25 or more, that is, PZT particles 26 can be obtained.
- the PZT sintered body may be pulverized by a ball mill in a wet manner or a dry type, but a wet type is preferable.
- the liquid (solvent) used for pulverization is not limited, and examples thereof include acetone, methyl ethyl ketone (MEK), ethanol, isopropyl alcohol, ether, cyclohexane, toluene, and water.
- a polymer material having viscoelasticity at room temperature such as cyanoethylated PVA
- an organic solvent such as a cyanoethylated PVA
- PZT particles 26 are further added, and a coating material obtained by stirring and dispersing is obtained.
- a polymer material having viscoelasticity at room temperature such as cyanoethylated PVA
- a viscoelastic material is also referred to as a "viscoelastic material”.
- the organic solvent is not limited, and various organic solvents such as dimethylformamide (DMF), methylethylketone, and cyclohexanone can be used.
- the paint is cast (applied) to the sheet-like material 34 to evaporate and dry the organic solvent.
- a laminated body 36 having the first electrode layer 14 on the first protective layer 18 and forming the piezoelectric layer 12 on the first electrode layer 14 is produced. ..
- the first electrode layer 14 refers to the electrode on the base material side when the piezoelectric layer 12 is applied, and does not indicate the vertical positional relationship in the laminated body.
- the casting method of this paint is not particularly limited, and all known coating methods (coating devices) such as a slide coater and a doctor knife can be used.
- the viscoelastic material is a material that can be melted by heating, such as cyanoethylated PVA
- the viscoelastic material is heated and melted to prepare a melt obtained by adding / dispersing PZT particles 26 to the viscoelastic material, and then extruding.
- the first electrode layer 14 is provided on the first protective layer 18 as shown in FIG.
- the laminated body 36 formed by forming the piezoelectric layer 12 on the electrode layer 14 may be produced.
- a dielectric polymer material such as polyvinylidene fluoride may be added to the matrix 24 in addition to the viscoelastic material such as cyanoethylated PVA.
- the polymer piezoelectric materials to be added to the paint described above may be dissolved.
- the polymer piezoelectric material to be added may be added to the above-mentioned heat-melted viscoelastic material and heat-melted.
- the method for polarization treatment of the piezoelectric layer 12 is not limited, and known methods can be used.
- electric field polling in which a DC electric field is directly applied to an object to be polarized is exemplified.
- the first electrode layer 14 may be formed before the polarization treatment, and the electric field polling treatment may be performed using the first electrode layer 14 and the second electrode layer 16. ..
- the polarization treatment is performed in the thickness direction of the piezoelectric layer 12 rather than in the plane direction.
- a calendar treatment may be performed in which the surface of the piezoelectric layer 12 is smoothed by using a heating roller or the like. By performing this calendar processing, the thermocompression bonding process described later can be smoothly performed.
- the sheet-like material 38 in which the second electrode layer 16 is formed on the second protective layer 20 is prepared.
- the sheet-like material 38 may be produced by forming a copper thin film or the like as the second electrode layer 16 on the surface of the second protective layer 20 by vacuum deposition, sputtering, plating or the like.
- the second electrode layer 16 is directed toward the piezoelectric layer 12, and the sheet-like material 38 is laminated on the laminated body 36 which has completed the polarization treatment of the piezoelectric layer 12.
- the laminate of the laminate 36 and the sheet-like material 38 is thermocompression-bonded with a heating press device or a heating roller or the like so as to sandwich the second protective layer 20 and the first protective layer 18, and piezoelectric.
- Film 10 is made.
- the laminate 36 and the sheet-like material 38 may be bonded together using an adhesive, and preferably further pressure-bonded to produce the piezoelectric film 10.
- the piezoelectric film 10 produced in this way is polarized in the thickness direction instead of the plane direction, and large piezoelectric characteristics can be obtained without stretching treatment after the polarization treatment. Therefore, the piezoelectric film 10 has no in-plane anisotropy in the piezoelectric characteristics, and when a driving voltage is applied, the piezoelectric film 10 expands and contracts isotropically in all directions in the plane direction.
- Such a piezoelectric film 10 may be manufactured by using a cut sheet-like sheet-like material 34, a sheet-like material 38, or the like, or by using roll-to-roll. May be good.
- FIG. 5 conceptually shows an example of a flat plate type piezoelectric speaker using the piezoelectric film 10 of the present invention.
- the piezoelectric speaker 40 is a flat plate type piezoelectric speaker that uses the piezoelectric film 10 as a diaphragm that converts an electric signal into vibration energy.
- the piezoelectric speaker 40 can also be used as a microphone, a sensor, or the like. Furthermore, this piezoelectric speaker can also be used as a vibration sensor.
- the piezoelectric speaker 40 includes a piezoelectric film 10, a case 42, a viscoelastic support 46, and a frame body 48.
- the case 42 is a thin housing made of plastic or the like and having one side open. Examples of the shape of the housing include a rectangular parallelepiped shape, a cubic shape, and a cylindrical shape.
- the frame body 48 is a frame material having a through hole having the same shape as the open surface of the case 42 in the center and engaging with the open surface side of the case 42.
- the viscoelastic support 46 has appropriate viscosity and elasticity, supports the piezoelectric film 10, and applies a constant mechanical bias to any part of the piezoelectric film to move the piezoelectric film 10 back and forth without waste.
- the back-and-forth movement of the piezoelectric film 10 is, that is, a movement in a direction perpendicular to the surface of the film.
- the viscoelastic support 46 include a non-woven fabric such as wool felt and wool felt containing PET and the like, glass wool and the like.
- the piezoelectric speaker 40 accommodates the viscoelastic support 46 in the case 42, covers the case 42 and the viscoelastic support 46 with the piezoelectric film 10, and surrounds the periphery of the piezoelectric film 10 with the frame 48 to form the upper end surface of the case 42.
- the frame body 48 is fixed to the case 42 while being pressed against the case 42.
- the height (thickness) of the viscoelastic support 46 is thicker than the height of the inner surface of the case 42. Therefore, in the piezoelectric speaker 40, the viscoelastic support 46 is held in a state of being thinned by being pressed downward by the piezoelectric film 10 at the peripheral portion of the viscoelastic support 46. Similarly, in the peripheral portion of the viscoelastic support 46, the curvature of the piezoelectric film 10 suddenly fluctuates, and the piezoelectric film 10 is formed with a rising portion that becomes lower toward the periphery of the viscoelastic support 46. Further, the central region of the piezoelectric film 10 is pressed by the viscoelastic support 46 having a square columnar shape to be (omitted) flat.
- the piezoelectric speaker 40 when the piezoelectric film 10 is stretched in the plane direction by applying a driving voltage to the first electrode layer 14 and the second electrode layer 16, the viscoelastic support 46 acts to absorb the stretched portion.
- the rising portion of the piezoelectric film 10 changes its angle in the rising direction.
- the piezoelectric film 10 having the flat portion moves upward.
- the piezoelectric film 10 contracts in the plane direction due to the application of the driving voltage to the second electrode layer 16 and the first electrode layer 14
- the rising portion of the piezoelectric film 10 collapses in order to absorb the contracted portion. Change the angle in the direction (the direction closer to the plane).
- the piezoelectric film 10 having the flat portion moves downward.
- the piezoelectric speaker 40 generates sound by the vibration of the piezoelectric film 10.
- the piezoelectric film 10 of the present invention the conversion from the stretching motion to the vibration can also be achieved by holding the piezoelectric film 10 in a curved state. Therefore, the piezoelectric film 10 of the present invention is not a flat plate-shaped piezoelectric speaker 40 having rigidity as shown in FIG. 5, but a piezoelectric speaker having flexibility even if it is simply held in a curved state, a vibration sensor, and the like. Can function as.
- a piezoelectric speaker using such a piezoelectric film 10 can be stored in a bag or the like by, for example, being rolled or folded, taking advantage of its good flexibility. Therefore, according to the piezoelectric film 10, it is possible to realize a piezoelectric speaker that can be easily carried even if it has a certain size. Further, as described above, the piezoelectric film 10 is excellent in flexibility and flexibility, and has no in-plane anisotropy of piezoelectric characteristics. Therefore, the piezoelectric film 10 has little change in sound quality regardless of which direction it is bent, and moreover, there is little change in sound quality with respect to a change in curvature.
- the piezoelectric speaker using the piezoelectric film 10 has a high degree of freedom in the installation location, and can be attached to various articles as described above.
- a so-called wearable speaker can be realized by attaching the piezoelectric film 10 to clothing such as clothes and portable items such as a bag in a curved state.
- the piezoelectric film of the present invention can be attached to a flexible display device such as a flexible organic EL display device and a flexible liquid crystal display device to obtain a display device. It can also be used as a speaker.
- the piezoelectric film 10 expands and contracts in the surface direction when a voltage is applied, and vibrates favorably in the thickness direction due to the expansion and contraction in the surface direction. It expresses good acoustic characteristics that can output sound.
- the piezoelectric film 10 Since the piezoelectric film 10 has good heat dissipation, it is possible to prevent its own heat generation even when it is laminated to form a piezoelectric vibrating element, and therefore it is possible to prevent heating of the diaphragm.
- the piezoelectric film may not have the first protective layer 18 and / or the second protective layer 20 if there is no possibility of a short circuit.
- a piezoelectric film having no first protective layer 18 and / or second protective layer 20 may be laminated via an insulating layer.
- a speaker in which a laminate of the piezoelectric films 10 is attached to a diaphragm and the diaphragm is vibrated by the laminate of the piezoelectric films 10 to output sound may be used. That is, in this case, the laminated body of the piezoelectric film 10 acts as a so-called exciter that outputs sound by vibrating the diaphragm.
- the laminated body of the piezoelectric film 10 acts as a so-called exciter that outputs sound by vibrating the diaphragm.
- the expansion and contraction of the laminate of the piezoelectric film 10 in the surface direction causes the diaphragm to which the laminate is attached to bend, and as a result, the diaphragm vibrates in the thickness direction.
- the vibration in the thickness direction causes the diaphragm to generate sound.
- the diaphragm vibrates according to the magnitude of the drive voltage applied to the piezoelectric film 10, and generates a sound according to the drive voltage applied to the piezoelectric film 10. Therefore, at this time, the piezoelectric film 10 itself does not output sound.
- the rigidity of the piezoelectric film 10 for each sheet is low and the elastic force is small, the rigidity is increased by laminating the piezoelectric film 10, and the elastic force of the laminated body as a whole is increased.
- the laminated body of the piezoelectric film 10 even if the diaphragm has a certain degree of rigidity, the diaphragm is sufficiently flexed with a large force to sufficiently vibrate the diaphragm in the thickness direction. Sound can be generated in the diaphragm.
- the number of laminated piezoelectric films 10 is not limited, and the number of sheets capable of obtaining a sufficient amount of vibration may be appropriately set according to, for example, the rigidity of the vibrating diaphragm.
- a single piezoelectric film 10 can be used as a similar exciter (piezoelectric vibrating element) as long as it has a sufficient stretching force.
- the diaphragm vibrated by the laminated body of the piezoelectric film 10 there is no limitation on the diaphragm vibrated by the laminated body of the piezoelectric film 10, and various sheet-like materials (plate-like material, film) can be used. Examples thereof include a resin film made of polyethylene terephthalate (PET) and the like, foamed plastic made of expanded polystyrene and the like, paper materials such as corrugated cardboard, glass plates, wood and the like. Further, a device such as a display device may be used as the diaphragm as long as it can be sufficiently bent.
- PET polyethylene terephthalate
- foamed plastic made of expanded polystyrene and the like
- paper materials such as corrugated cardboard, glass plates, wood and the like.
- a device such as a display device may be used as the diaphragm as long as it can be sufficiently bent.
- the laminate of the piezoelectric films 10 it is preferable that adjacent piezoelectric films are attached to each other with an adhesive layer (adhesive agent). Further, it is preferable that the laminate of the piezoelectric film 10 and the diaphragm are also attached by the attachment layer.
- the adhesive layer may be made of an adhesive or an adhesive.
- an adhesive layer made of an adhesive is used, which gives a solid and hard adhesive layer after application. The same applies to the above points in the laminated body formed by folding back the long piezoelectric film 10 described later.
- the polarization direction of each of the piezoelectric films 10 is the polarization direction in the thickness direction. Therefore, in the laminated body of the piezoelectric films 10, the polarization directions may be the same for all the piezoelectric films 10, and there may be piezoelectric films having different polarization directions.
- the piezoelectric films 10 in the laminated body of the piezoelectric films 10, it is preferable to laminate the piezoelectric films 10 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 12 depends on the polarization direction of the piezoelectric layer 12. Therefore, regardless of whether the polarization direction is from the first electrode layer 14 to the second electrode layer 16 or from the second electrode layer 16 to the first electrode layer 14, all the piezoelectric films 10 to be laminated have the first electrode.
- the polarity of the layer 14 and the polarity of the second electrode layer 16 are made the same.
- the laminate of the piezoelectric film 10 may be configured to laminate the plurality of piezoelectric films 10 by folding back the piezoelectric film 10 once or more, preferably a plurality of times.
- the structure in which the piezoelectric film 10 is folded back and laminated has the following advantages. That is, in a laminated body in which a plurality of cut sheet-shaped piezoelectric films 10 are laminated, it is necessary to connect the first electrode layer 14 and the second electrode layer 16 to the drive power source for each piezoelectric film. On the other hand, in the configuration in which the long piezoelectric film 10 is folded back and laminated, the laminated body can be formed only by one long piezoelectric film 10.
- the long piezoelectric film 10 is folded back and laminated, only one power source is required for applying the driving voltage, and the electrode may be pulled out from the piezoelectric film 10 at one place. Further, in the configuration in which the long piezoelectric films 10 are folded back and laminated, the polarization directions of the adjacent piezoelectric films 10 are inevitably opposite to each other.
- PZT particles were produced by pulverizing the produced raw material particles with a general ball mill.
- the ball mill was carried out under the conditions of a media diameter of 1 mm, a filling rate of 30%, a rotation speed of 45 rpm, and a crushing time of 15 hr.
- a piezoelectric film as shown in FIG. 1 was prepared by the methods shown in FIGS. 2 to 4.
- cyanoethylated PVA manufactured by CR-V Shin-Etsu Chemical Co., Ltd.
- DMF dimethylformamide
- the prepared PZT particles were added to this solution at the following composition ratio and stirred with a propeller mixer (rotation speed 2000 rpm) to prepare a coating material for forming a piezoelectric layer.
- two sheets prepared by vacuum-depositing a copper thin film having a thickness of 0.1 ⁇ m on a PET film having a thickness of 4 ⁇ m were prepared. That is, in this example, the first electrode layer and the second electrode layer are copper-deposited thin films having a thickness of 0.1 m, and the first protective layer and the second protective layer are PET films having a thickness of 4 ⁇ m.
- a paint for forming the previously prepared piezoelectric layer was applied using a slide coater. The paint was applied so that the film thickness of the coating film after drying was 40 ⁇ m.
- the sheet-like material coated with the paint was heated and dried on a hot plate at 120 ° C. to evaporate the DMF.
- a laminate having a copper second electrode layer on the PET second protective layer and a piezoelectric layer having a thickness of 40 ⁇ m was produced on the copper second electrode layer.
- the produced piezoelectric layer was polarized in the thickness direction.
- the laminate of the laminate and the sheet-like material is thermocompression-bonded at a temperature of 120 ° C. using a laminator device to adhere and bond the composite piezoelectric body and the first electrode layer, and FIG. A piezoelectric film as shown in the above was produced.
- the produced piezoelectric film was cut into a size of 40 ⁇ 40 mm with scissors at an arbitrary position.
- an iron chloride aqueous solution was prepared by mixing ferric chloride hexahydrate and pure water. The concentration of the iron chloride aqueous solution was 1.5 mol / L (liter). The cut piezoelectric film was immersed in the prepared iron chloride aqueous solution for 12 hours while hanging. Then, the immersed piezoelectric film was taken out and washed with pure water several times.
- the sheet-like material on the first electrode side was peeled off from the piezoelectric layer at a speed of about 4 mm / s to expose the piezoelectric layer.
- the sheet-like material is a sheet formed by vacuum-depositing a copper thin film having a thickness of 0.1 ⁇ m on a PET film having a thickness of 4 ⁇ m.
- the piezoelectric film from which the first electrode layer was peeled off was washed with pure water several times and then naturally dried for 24 hours. In this way, the first electrode layer was peeled off from the piezoelectric film, and the Raman scattered light of the exposed piezoelectric layer was measured to obtain a Raman spectrum. Raman scattering was measured using a Raman microscope with 532 nm excitation.
- FIG. 6 conceptually shows a measurement system for Raman scattered light.
- the linearly polarized laser light (excitation light having a wavelength of 532 nm) emitted by the laser light source 60 is reflected by the mirror 62, the mirror 64, and the mirror 68, passes through the objective lens 70 having a magnification of 100 times, and is linearly polarized (arrow a). It is incident on the surface of the piezoelectric layer S as incident light La in the direction).
- the Raman scattered light Lb by the piezoelectric layer S is reflected by the mirror 68 after passing through the objective lens 70, and after passing through the mirror 64, the excitation light is removed by the notch filter 72 and decomposed by the diffraction grating 74 for each wave number. After that, the light is measured by the detector 76.
- the Raman spectrum was obtained by removing noise from the photometric results by principal component analysis (PCA) processing and using components with an autocorrelation of 0.6 or more.
- PCA principal component analysis
- a region of 40 ⁇ 40 ⁇ m is arbitrarily selected on the surface of the exposed piezoelectric layer as described above, and the region is measured in 1 ⁇ m steps at 1681 points under the condition of 1 exposure point and 1 second. went.
- This measurement was performed at arbitrary two locations on the surface of the piezoelectric layer, and the average of the spectra of all 3362 was calculated to obtain a Raman spectrum of the produced piezoelectric layer.
- the Raman spectrum was created by applying baseline correction so that the intensity of 1000 cm -1 becomes 0, and using the baseline as a straight line with an intensity of 0.
- the Raman shift of the maximum peak present in the range of 190 ⁇ 215cm -1 in the Raman spectrum of the piezoelectric layer was 197.8cm -1.
- the peak intensity ratio I130 / I110 between the peak intensity I100 of the maximum peak existing in the range of 90 cm -1 or more and less than 120 cm -1 and the peak intensity I130 of the maximum peak existing in the range of 120 to 150 cm -1 is 1. It was .236.
- the peak intensity ratio I725 / I550 between the peak intensity I550 of the maximum peak existing in the range of 490 to 650 cm -1 and the peak intensity I725 of the maximum peak existing in the range of 700 to 750 cm -1 is 0.668. there were.
- the particle size of the PZT particles in the piezoelectric layer was measured.
- the produced piezoelectric film was cut at an arbitrary position in the thickness direction.
- the cross section in the thickness direction was observed with a scanning electron microscope including the upper and lower ends of the piezoelectric layer in the visual field, and the area ratio of PZT particles in the piezoelectric layer was calculated by image analysis.
- the area ratio of the PZT particles was divided by the number of PZT particles in the microscope image, and the particle size of the PZT particles was measured by yen conversion.
- the particle size of the PZT particles was measured on any of five cross sections, and the average value was taken as the particle size (arithmetic mean diameter) of the PZT particles in the piezoelectric film. As a result, the particle size of the PZT particles was 3.3 ⁇ m.
- Example 2 In crushing the raw material particles with a ball mill, PZT particles were produced in the same manner as in Example 1 except that the media diameter was changed to 0.5 mm and the crushing time was changed to 24 hr. A piezoelectric film was produced in the same manner as in Example 1 except that the PZT particles were used. For the produced piezoelectric film, the particle size of the PZT particles, the Raman shift of the maximum peak existing in the range of 190 to 215 cm -1 in the Raman spectrum, the peak intensity ratio I130 / I110, and the peak intensity ratio I725 / I550. It was measured.
- the particle size of the PZT particles was 10.7 ⁇ m
- the maximum peak Raman shift was 199.2 cm -1
- the peak intensity ratio I130 / I110 was 1.117
- the peak intensity ratio I725 / I550 was 0.672. ..
- Example 3 In the pulverization of the raw material particles by a ball mill, PZT particles were produced in the same manner as in Example 1 except that the filling rate was changed to 50% and the pulverization time was changed to 10 hr. A piezoelectric film was produced in the same manner as in Example 1 except that the PZT particles were used. For the produced piezoelectric film, the particle size of the PZT particles, the Raman shift of the maximum peak existing in the range of 190 to 215 cm -1 in the Raman spectrum, the peak intensity ratio I130 / I110, and the peak intensity ratio I725 / I550. It was measured.
- the particle size of the PZT particles was 3.5 ⁇ m
- the maximum peak Raman shift was 204.1 cm- 1
- the peak intensity ratio I130 / I110 was 1.044
- the peak intensity ratio I725 / I550 was 0.527.
- Example 4 PZT particles were produced in the same manner as in Example 1 except that the media diameter was changed to 0.5 mm, the filling rate was changed to 50%, and the rotation speed was changed to 60 rpm in the pulverization of the raw material particles by a ball mill.
- a piezoelectric film was produced in the same manner as in Example 1 except that the PZT particles were used.
- the particle size of the PZT particles, the Raman shift of the maximum peak existing in the range of 190 to 215 cm -1 in the Raman spectrum, the peak intensity ratio I130 / I110, and the peak intensity ratio I725 / I550 was measured.
- the particle size of the PZT particles was 3.2 ⁇ m
- the maximum peak Raman shift was 202.9 cm -1
- the peak intensity ratio I130 / I110 was 1.071
- the peak intensity ratio I725 / I550 was 0.240. ..
- Example 1 In crushing the raw material particles with a ball mill, PZT particles were produced in the same manner as in Example 1 except that the media diameter was changed to 30 mm and the crushing time was changed to 22 hr. A piezoelectric film was produced in the same manner as in Example 1 except that the PZT particles were used. For the produced piezoelectric film, the particle size of the PZT particles, the Raman shift of the maximum peak existing in the range of 190 to 215 cm -1 in the Raman spectrum, the peak intensity ratio I130 / I110, and the peak intensity ratio I725 / I550. It was measured.
- the particle size of the PZT particles was 3.4 ⁇ m
- the maximum peak Raman shift was 212.4 cm- 1
- the peak intensity ratio I130 / I110 was 1.088
- the peak intensity ratio I725 / I550 was 0.376. ..
- Example 2 In crushing the raw material particles with a ball mill, PZT particles were produced in the same manner as in Example 1 except that the media diameter was changed to 10 mm and the crushing time was changed to 18 hr. A piezoelectric film was produced in the same manner as in Example 1 except that the PZT particles were used. For the produced piezoelectric film, the particle size of the PZT particles, the Raman shift of the maximum peak existing in the range of 190 to 215 cm -1 in the Raman spectrum, the peak intensity ratio I130 / I110, and the peak intensity ratio I725 / I550. It was measured.
- the particle size of the PZT particles was 3.2 ⁇ m
- the maximum peak Raman shift was 209.0 cm- 1
- the peak intensity ratio I130 / I110 was 1.157
- the peak intensity ratio I725 / I550 was 0.213. ..
- Example 3 In crushing the raw material particles with a ball mill, PZT particles were produced in the same manner as in Example 1 except that the filling rate was changed to 50%, the rotation speed was changed to 60 rpm, and the crushing time was changed to 12 hr. A piezoelectric film was produced in the same manner as in Example 1 except that the PZT particles were used. For the produced piezoelectric film, the particle size of the PZT particles, the Raman shift of the maximum peak existing in the range of 190 to 215 cm -1 in the Raman spectrum, the peak intensity ratio I130 / I110, and the peak intensity ratio I725 / I550. It was measured.
- the particle size of the PZT particles was 3.2 ⁇ m
- the maximum peak Raman shift was 206.1 cm- 1
- the peak intensity ratio I130 / I110 was 1.032
- the peak intensity ratio I725 / I550 was 0.572. ..
- Example 4 In crushing the raw material particles with a ball mill, PZT particles were produced in the same manner as in Example 1 except that the rotation speed was changed to 60 rpm and the crushing time was changed to 12 hr. A piezoelectric film was produced in the same manner as in Example 1 except that the PZT particles were used. For the produced piezoelectric film, the particle size of the PZT particles, the Raman shift of the maximum peak existing in the range of 190 to 215 cm -1 in the Raman spectrum, the peak intensity ratio I130 / I110, and the peak intensity ratio I725 / I550. It was measured.
- the particle size of the PZT particles was 3.1 ⁇ m
- the maximum peak Raman shift was 207.8 cm -1
- the peak intensity ratio I130 / I110 was 1.140
- the peak intensity ratio I725 / I550 was 0.434. ..
- the piezoelectric speaker shown in FIG. 5 was produced using the produced piezoelectric film. First, a rectangular test piece of 210 ⁇ 300 mm (A4 size) was cut out from the produced piezoelectric film. As shown in FIG. 5, the cut-out piezoelectric film is placed on a 210 ⁇ 300 mm case containing glass wool as a viscoelastic support in advance, and then the peripheral portion is pressed by a frame to give an appropriate tension to the piezoelectric film. By giving a curvature, a piezoelectric speaker as shown in FIG. 5 was manufactured. The depth of the case was 9 mm, the density of glass wool was 32 kg / m 3 , and the thickness before assembly was 25 mm.
- a 1 kHz sine wave was input to the produced piezoelectric speaker as an input signal through a power amplifier, and the sound pressure was measured with a microphone 50 placed at a distance of 50 cm from the center of the speaker, as conceptually shown in FIG. .. The results are shown in the table below.
- the piezoelectric films of the present invention having a maximum peak Raman shift of 205 cm -1 or less existing in the range of 190 to 215 cm -1 in the Raman spectrum of the piezoelectric layer are all 70 dB or more. It outputs a high sound pressure. That is, the piezoelectric film of the present invention has been shown to have good piezoelectric properties. Further, by comparing Example 1 and Example 2, a high sound pressure can be obtained by setting the particle size of the PZT particles in the range of 1 to 10 ⁇ m. By comparing Example 1 and Example 3, a high sound pressure can be obtained by setting the peak intensity ratio I130 / I110 to 1.05 or more.
- Example 1 a high sound pressure can be obtained by setting the peak intensity ratio I725 / I550 to 0.25 or more.
- the piezoelectric films of the comparative examples in which the Raman shift of the maximum peak existing in the range of 190 to 215 cm -1 in the Raman spectrum of the piezoelectric layer exceeds 205 cm -1 have a sound pressure of less than 70 dB. ..
- the piezoelectric films of Examples 1, 3 and 4 and the piezoelectric films of Comparative Examples 1 to 4 are similar in that the particle size of the PZT particles is 3.1 to 3.5 ⁇ m.
- the piezoelectric films of Examples 1, 3 and 4 are 205 cm -1 or less, whereas the comparative example. Piezoelectric films 1 to 4 exceed 205 cm -1. That is, in Examples 1, 3 and 4, and Comparative Examples 1 to 4, PZT particles having a target particle size are obtained, and the maximum existing in the Raman spectrum of the piezoelectric layer is in the range of 190 to 215 cm -1.
- electroacoustic converters such as speakers and vibration sensors.
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Abstract
Description
このようなフレキシブルディスプレイを、テレビジョン受像機等のように画像と共に音声を再生する画像表示装置兼音声発生装置として使用する場合、音声を発生するための音響装置であるスピーカーが必要である。
ここで、従来のスピーカー形状としては、漏斗状のいわゆるコーン型や、球面状のドーム型等が一般的である。しかしながら、これらのスピーカーを上述のフレキシブルディスプレイに内蔵しようとすると、フレキシブルディスプレイの長所である軽量性や可撓性を損なう虞れがある。また、スピーカーを外付けにした場合、持ち運び等が面倒であり、曲面状の壁に設置することが難しくなり美観を損ねる虞れもある。
例えば、特許文献1には、常温で粘弾性を有する高分子材料からなるマトリックス中に圧電体粒子を分散してなる高分子複合圧電体と、この高分子複合圧電体を挟むように設けられる圧電体層とを有し、電極層との接触面における圧電体粒子の面積分率が50%以下である高分子圧電フィルム(電気音響変換フィルム)も記載されている。
そのため、この高分子複合圧電体を用いる高分子圧電フィルムによれば、例えば、フレキシブルスピーカー等に利用可能な、可撓性を有し、かつ、良好な圧電特性を有する電気音響変換フィルム等を得られる。
[1] 高分子材料を含むマトリックス中にチタン酸ジルコン酸鉛粒子を含む圧電体層と、圧電体層の両面に設けられる電極層とを有し、
圧電体層のラマンスペクトルにおける190~215cm-1の範囲に存在する最大ピークのラマンシフトが、205cm-1以下である高分子圧電フィルム。
[2] 電極層を覆う保護層を有する、[1]に記載の高分子圧電フィルム。
[3] チタン酸ジルコン酸鉛粒子の算術平均径が1~10μmである、[1]または[2]に記載の高分子圧電フィルム。
[4] 圧電体層のラマンスペクトルにおいて、90cm-1以上120cm-1未満の範囲に存在する最大ピークのピーク強度をI100、120~150cm-1の範囲に存在する最大ピークのピーク強度をI130とした際に、ピーク強度比I130/I110が1.05以上である、[1]~[3]のいずれかに記載の高分子圧電フィルム。
[5] 圧電体層のラマンスペクトルにおいて、490~650cm-1の範囲に存在する最大ピークのピーク強度をI550、700~750cm-1の範囲に存在する最大ピークのピーク強度をI725とした際に、ピーク強度比I725/I550が0.25以上である、[1]~[4]のいずれかに記載の高分子圧電フィルム。
[6] 高分子材料がシアノエチル基を有する、[1]~[5]のいずれかに記載の高分子圧電フィルム。
[7] 高分子材料がシアノエチル化ポリビニルアルコールである、[6]に記載の高分子圧電フィルム。
[8] 圧電体層が厚さ方向に分極されている、[1]~[7]のいずれかに記載の高分子圧電フィルム。
本明細書において、「~」を用いて表される数値範囲は、「~」の前後に記載される数値を下限値および上限値として含む範囲を意味する。
また、以下に示す図は、いずれも、本発明を説明するための概念的な図である。従って、各層の厚さ、圧電体粒子の大きさ、および、構成部材の大きさ等は、実際の物とは異なる。
図1に示すように、高分子圧電フィルム10は、圧電体層12の一方の面に積層される第1電極層14と、第1電極層14の表面に積層される第1保護層18と、圧電体層12の他方の面に積層される第2電極層16と、第2電極層16の表面に積層される第2保護層20とを有する。後述するが、圧電体層12は、厚さ方向に分極されている。
以下の説明では、高分子圧電フィルム10を、圧電フィルム10ともいう。
以下の説明では、チタン酸ジルコン酸鉛をPZTともいう。
ここで、後に詳述するが、本発明の圧電フィルム10において、圧電体層12は、ラマンスペクトルにおける190~215cm-1の範囲に存在する最大ピークのラマンシフトが、205cm-1以下である。本発明の圧電フィルム10は、このような構成を有することにより、高い圧電特性を発現しており、例えば、電気音響変換フィルムに用いた場合に、高い音圧を得ることができる。
ここで、高分子複合圧電体(圧電体層12)は、次の用件を具備したものであるのが好ましい。なお、本発明において、常温とは、0~50℃である。
(i) 可撓性
例えば、携帯用として新聞や雑誌のように書類感覚で緩く撓めた状態で把持する場合、絶えず外部から、数Hz以下の比較的ゆっくりとした、大きな曲げ変形を受けることになる。この時、高分子複合圧電体が硬いと、その分大きな曲げ応力が発生し、高分子マトリックスと圧電体粒子との界面で亀裂が発生し、やがて破壊に繋がる恐れがある。従って、高分子複合圧電体には適度な柔らかさが求められる。また、歪みエネルギーを熱として外部へ拡散できれば応力を緩和することができる。従って、高分子複合圧電体の損失正接が適度に大きいことが求められる。
(ii) 音質
スピーカーは、20Hz~20kHzのオーディオ帯域の周波数で圧電体粒子を振動させ、その振動エネルギーによって振動板(高分子複合圧電体)全体が一体となって振動することで音が再生される。従って、振動エネルギーの伝達効率を高めるために高分子複合圧電体には適度な硬さが求められる。また、スピーカーの周波数特性が平滑であれば、曲率の変化に伴い最低共振周波数f0が変化した際の音質の変化量も小さくなる。従って、高分子複合圧電体の損失正接は適度に大きいことが求められる。
このとき、圧電フィルムの湾曲程度すなわち湾曲部の曲率半径が大きくなるほど機械的なスチフネスsが下がるため、最低共振周波数f0は小さくなる。すなわち、圧電フィルムの曲率半径によってスピーカーの音質(音量、周波数特性)が変わることになる。
高分子複合圧電体(圧電体層12)において、ガラス転移点が常温にある高分子材料をマトリックスに用いることで、20Hz~20kHzの振動に対しては硬く、数Hz以下の遅い振動に対しては柔らかく振舞う高分子複合圧電体が実現する。特に、この振舞いが好適に発現する等の点で、周波数1Hzでのガラス転移点が常温、すなわち、0~50℃にある高分子材料を、高分子複合圧電体のマトリックスに用いるのが好ましい。
なお、ガラス転移点が常温にある高分子材料とは、言い換えると、常温で粘弾性を有する高分子材料である。
これにより、高分子複合圧電体が外力によってゆっくりと曲げられた際に、最大曲げモーメント部における高分子マトリックスと圧電体粒子との界面の応力集中が緩和され、高い可撓性が期待できる。
これにより、高分子複合圧電体が外力によってゆっくりと曲げられた際に発生する曲げモーメントが低減できると同時に、20Hz~20kHzの音響振動に対しては硬く振る舞うことができる。
しかしながら、その反面、良好な耐湿性の確保等を考慮すると、高分子材料は、比誘電率が25℃において10以下であるのも、好適である。
なお、マトリックス24において、これらの高分子材料は、1種のみを用いてもよく、複数種を併用(混合)して用いてもよい。
すなわち、マトリックス24には、誘電特性や機械的特性の調節等を目的として、シアノエチル化PVA等の常温で粘弾性を有する高分子材料に加え、必要に応じて、その他の誘電性高分子材料を添加しても良い。
中でも、シアノエチル基を有する高分子材料は、好適に利用される。
また、圧電体層12のマトリックス24において、シアノエチル化PVA等の常温で粘弾性を有する材料に加えて添加される誘電性ポリマーは、1種に限定はされず、複数種を添加してもよい。
さらに、粘着性を向上する目的で、ロジンエステル、ロジン、テルペン、テルペンフェノール、および、石油樹脂等の粘着付与剤を添加しても良い。
これにより、マトリックス24における粘弾性緩和機構を損なうことなく、添加する高分子材料の特性を発現できるため、高誘電率化、耐熱性の向上、PZT粒子26および電極層との密着性向上等の点で好ましい結果を得ることができる。
PZT粒子26はPZT(ジルコン酸チタン酸鉛)を主成分とする粒子である。
なお、本発明において、主成分とは、物質中において、最も多く含まれる成分を示し、好ましくは50質量%以上を含む成分であり、より好ましくは90質量%以上を含む成分である。
本発明において、PZT粒子26は、不可避的に混入する不純物を除き、PZTの構成元素のみを含むのが好ましい。
一般式[I]において、x<1である。また、一般式[I]において、xは、ジルコニウムとチタンとの元素比(モル比)であり、すなわち、Zr/(Zr+Ti)である。
上述のように、PZTなどのペロブスカイト構造をとる強誘電体では、組成を相転移境界(MPB(モルフォトロピック相境界))組成とすることで、高い圧電特性が得られることが知られている。PZTのMPB組成は、一般式[I]のxが0.52付近の組成である。すなわち、PZTのMPB組成は、一般式[I]が『Pb(Zr0.52Ti0.48)O3』付近のである。
従って、一般式[I]のxは、0.52に近いのが好ましい。具体的には、一般式[I]のxは、0.50~0.54が好ましく、0.51~0.53がより好ましく、0.52がさらに好ましい。
本発明の圧電フィルム10は、このような構成を有することにより、高い圧電特性を発現しており、例えば電気音響変換フィルムに用いた場合に、高い音圧を得られる。
ラマンスペクトルにおいて、190~215cm-1の範囲に生じるピークは、PZTに由来するピークであり、高分子材料に由来するピークは、この波数の範囲には生じない。
すなわち、本発明の圧電フィルム10は、実質的に、圧電体層12を構成するPZT粒子26のラマンスペクトルにおける190~215cm-1の範囲に存在する最大ピークのラマンシフトが、205cm-1以下である。
その結果、圧電体層を構成するPZT粒子の結晶格子の歪みが、圧電特性の低下の原因であることを見出した。
ところが、本発明者の検討によれば、PZT粒子の結晶格子に歪みが生じると、電界を印加した場合の応答性が劣化する。その結果、結晶格子に歪みを有するPZT粒子を用いる高分子複合圧電体は、圧電特性が劣化してしまう。
ところが、PZT粒子の結晶格子に歪みが生じると、この200cm-1の付近のピークが、波数が高い側に移動する。このピークの移動は、結晶格子の歪みが大きいほど、高波数側になる。
すなわち、本発明の圧電フィルム10は、圧電特性の劣化の原因となる結晶格子の歪みが極めて少ないPZT粒子26を用いることにより、高い圧電特性を発現することができる。そのため、本発明の圧電フィルム10は、例えば、電気音響変換フィルムとして用いることにより、高い音圧の音声を出力できる。
圧電体層12のラマンスペクトルは、190~215cm-1の範囲内において、195~200cm-1の範囲に最大ピークを有するのが好ましく、195~198cm-1の範囲に最大ピークを有するのが、より好ましい。
また、本発明の圧電フィルム10は、圧電体層12のラマンスペクトルにおいて、490~650cm-1の範囲に存在する最大ピークのピーク強度をI550、700~750cm-1の範囲に存在する最大ピークのピーク強度をI725とした際に、ピーク強度比I725/I550が0.25以上であるのが好ましい。
これに対して、本発明の圧電フィルム10は、好ましくは、圧電体層12のラマンスペクトルにおいて、ピーク強度比I130/I110が1.05以上、および、ピーク強度比I725/I550が0.25以上の少なくとも一方を満たす。本発明の圧電フィルム10は、より好ましくは、このピーク強度比の条件を両方とも満たす。
これにより、本発明の圧電フィルム10は、より結晶格子の歪みの抑制に加え、鉛原子の欠損も少ないPZT粒子26によって、より良好な圧電特性を得られる。
他方、ピーク強度比I725/I550は、0.4以上がより好ましく、0.5以上がさらに好ましい。
なお、ピーク強度比I130/I110の上限には、制限はないが、通常、1.3以下である。他方、ピーク強度比I725/I550の上限にも、制限はないが、通常、0.8以下である。
PZT粒子26の粒径は、算術平均径で1~10μmが好ましい。以下の説明において、PZT粒子26の粒径と言った場合には、PZT粒子26の算術平均径を示す。
なお、本発明の圧電フィルム10において、PZT粒子26の算術平均径は、以下のように測定する。
まず、圧電フィルム10を任意の位置で厚さ方向に切断する。なお、厚さ方向とは、言い換えると、圧電フィルム10における、圧電体層12、第1電極層14、第1保護層18、第2電極層16および第2保護層20の積層方向であり、図1の上下方向である。
圧電フィルム10の厚さ方向の断面を、圧電体層12の上端と下端を視野に含めて走査型電子顕微鏡で観察し、圧電体層12におけるPZT粒子26の面積率を、顕微鏡画像を画像解析して算出する。このPZT粒子26の面積率を、顕微鏡画像中におけるPZT粒子26の個数で除し、円換算によってPZT粒子26の粒径を算出する。このようなPZT粒子26の粒径の算出を、圧電フィルム10において任意に選択した5つの断面で行い、5断面の粒径の平均値を、圧電フィルム10におけるPZT粒子26の粒径(算術平均径)とする。
PZT粒子26の粒径を1μm以上とすることにより、高い振動エネルギーの伝達効率を得られる等の点で好ましい。
PZT粒子26の粒径を10μm以下とすることにより、後述する電極層と対向する面の粗さに寄与するPZT粒子26を低減して良好な圧電特性を得られる、電気音響変換フィルム等として利用した場合に、湾曲の状態によらず、安定して目的とする出力特性が得られる等の点で好ましい。
PZT粒子26の粒径は、1.5~7μmがより好ましく、2~5μmがさらに好ましい。
すなわち、圧電体層12中のPZT粒子26は、好ましくは均一に分散されていれば、マトリックス24中に規則性を持って分散されていてもよい。
さらに、PZT粒子26は、粒径が揃っていても、揃っていなくてもよい。
圧電体層12中におけるPZT粒子26の体積分率は、30~80%が好ましく、50%以上がより好ましく、50~80%がさらに好ましい。
マトリックス24とPZT粒子26との量比を上記範囲とすることにより、高い圧電特性とフレキシビリティとを両立できる等の点で好ましい結果を得ることができる。
圧電体層12が厚いほど、いわゆるシート状物のコシの強さなどの剛性等の点では有利であるが、同じ量だけ圧電フィルム10を伸縮させるために必要な電圧(電位差)は大きくなる。
圧電体層12の厚さは、8~300μmが好ましく、8~200μmがより好ましく、10~150μmがさらに好ましく、15~100μmが特に好ましい。
圧電体層12の厚さを、上記範囲とすることにより、剛性の確保と適度な柔軟性との両立等の点で好ましい結果を得ることができる。
すなわち、圧電フィルム10は、圧電体層12の両面を電極対、すなわち、第1電極層14と第2電極層16とで挟持し、この積層体を、第1保護層18と第2保護層20とで挟持してなる構成を有する。
このような圧電フィルム10において、第1電極層14および第2電極層16で挾持された領域は、印加された電圧に応じて伸縮される。
本発明の圧電フィルム10において、第1保護層18および第2保護層20は、好ましい態様として設けられるものである。従って、本発明の圧電フィルムは、第1保護層18および第2保護層20を有さないものでも、第1保護層18および第2保護層20の一方のみを有するものでもよい。
しかしながら、圧電フィルムの機械的強度、剛性、および、耐久性等を考慮すると、本発明においては、図示例の圧電フィルム10のように、圧電体層12と電極層との積層体を挟持するように、第1保護層18および第2保護層20を設けるのが好ましい。
中でも、優れた機械的特性および耐熱性を有するなどの理由により、ポリエチレンテレフタレート(PET)、ポリプロピレン(PP)、ポリスチレン(PS)、ポリカーボネート(PC)、ポリフェニレンサルファイト(PPS)、ポリメチルメタクリレート(PMMA)、ポリエーテルイミド(PEI)、ポリイミド(PI)、ポリエチレンナフタレート(PEN)、トリアセチルセルロース(TAC)、および、環状オレフィン系樹脂等からなる樹脂フィルムが、好適に利用される。
ここで、第1保護層18および第2保護層20の剛性が高過ぎると、圧電体層12の伸縮を拘束するばかりか、可撓性も損なわれる。そのため、機械的強度やシート状物としての良好なハンドリング性が要求される場合を除けば、第1保護層18および第2保護層20は、薄いほど有利である。
例えば、圧電体層12の厚さが50μmで第1保護層18および第2保護層20がPETからなる場合、第1保護層18および第2保護層20の厚さは、100μm以下が好ましく、50μm以下がより好ましく、25μm以下がさらに好ましい。
第1電極層14および第2電極層16は、圧電体層12(圧電フィルム10)に電圧を印加するために設けられる。
中でも特に、圧電フィルム10の可撓性が確保できる等の理由で、真空蒸着によって成膜された銅およびアルミニウム等の薄膜は、第1電極層14および第2電極層16として、好適に利用される。その中でも特に、真空蒸着による銅の薄膜は、好適に利用される。
ここで、前述の第1保護層18および第2保護層20と同様に、第1電極層14および第2電極層16の剛性が高過ぎると、圧電体層12の伸縮を拘束するばかりか、可撓性も損なわれる。そのため、第1電極層14および第2電極層16は、電気抵抗が高くなり過ぎない範囲であれば、薄いほど有利である。
一例として、第1保護層18および第2保護層20がPETで、第1電極層14および第2電極層16が銅である組み合わせを考える。この組み合わせでは、PETのヤング率が約6.2GPaで、銅のヤング率が約130GPaである。従って、この場合、第1保護層18および第2保護層20の厚さが25μmだとすると、第1電極層14および第2電極層16の厚さは、1.2μm以下が好ましく、0.3μm以下がより好ましく、0.1μm以下がさらに好ましい。
このような圧電フィルム10は、動的粘弾性測定による周波数1Hzでの損失正接(Tanδ)の極大値が常温に存在するのが好ましく、0.1以上となる極大値が常温に存在するのがより好ましい。
これにより、圧電フィルム10が外部から数Hz以下の比較的ゆっくりとした、大きな曲げ変形を受けたとしても、歪みエネルギーを効果的に熱として外部へ拡散できるため、高分子マトリックスと圧電体粒子との界面で亀裂が発生するのを防ぐことができる。
これにより、常温で圧電フィルム10が貯蔵弾性率(E’)に大きな周波数分散を有することができる。すなわち、20Hz~20kHzの振動に対しては硬く、数Hz以下の振動に対しては柔らかく振る舞うことができる。
これにより、圧電フィルム10が可撓性および音響特性を損なわない範囲で、適度な剛性と機械的強度を備えることができる。
これにより、圧電フィルム10を用いたスピーカーの周波数特性が平滑になり、スピーカーの曲率の変化に伴って最低共振周波数f0が変化した際における音質の変化量も小さくできる。
貼着剤は、接着剤でも粘着剤でもよい。また、貼着剤は、圧電体層12からPZT粒子26を除いた高分子材料すなわちマトリックス24と同じ材料も、好適に利用可能である。なお、貼着層は、第1電極層14側および第2電極層16側の両方に有してもよく、第1電極層14側および第2電極層16側の一方のみに有してもよい。
電極引出し部としては、例えば、電極層および保護層が、圧電体層12の面方向外部に凸状に突出する部位を設け、この突出部を電極引出し部としても良い。あるいは、保護層の一部を除去して孔部を形成して、この孔部に銀ペースト等の導電材料を挿入して導電材料と電極層とを電気的に導通して、電極引出し部としてもよい。
なお、各電極層において、電極引出し部は1つには制限されず、2以上の電極引出し部を有していてもよい。特に、保護層の一部を除去して孔部に導電材料を挿入して電極引出し部とする構成の場合には、より確実に通電を確保するために、電極引出し部を3以上有するのが好ましい。
第1保護層18が非常に薄く、ハンドリング性が悪い時などは、必要に応じて、セパレータ(仮支持体)付きの第1保護層18を用いても良い。なお、セパレータとしては、厚さ25~100μmのPET等を用いることができる。セパレータは、第2電極層16および第2保護層20を熱圧着した後、第1保護層18に何らかの部材を積層する前に、取り除けばよい。
PZT粒子26の作製方法は、基本的に、通常のPZT粒子と同様でよい。
まず、目的とするPZTの組成に応じた鉛酸化物の粉末、ジルコニウム酸化物の粉末およびチタン酸化物の粉末を混合して原料混合粉を調製する。PZT粒子26におけるPZTの組成は、この原料混合粉の組成(仕込み組成)に、ほぼ一致する
次いで、この原料混合粉を700~800℃程度で1~5時間、焼成することで、PZTの原料粒子を作製する。
ここで、本発明者の検討によれば、このボールミルによる粉砕の際に、PZT粒子の結晶格子に、圧電特性の劣化の原因となる歪み、および、欠損が発生する。すなわち、結晶格子の歪みおよび欠損を抑制したPZT粒子を得るためには、ボールミルによる粉砕の条件を、適正に設定する必要がある。
具体的には、ボールミルによる粉砕はメディア径、充填率、回転数および粉砕時間等によって制御される。粉砕はボールの衝突により進行するが、その際に、結晶格子の歪みおよび欠損等を生じる。特に、粉砕後期における内部欠損の低い粉体とメディアとの衝突が、結晶格子の歪みの要因と考えられる。
この結晶格子の歪みおよび欠損の抑制には、メディア径および回転数の低減が有効である。その一方、ボールミルによる粉砕において、メディア径が小さ過ぎる、および、回転数が少ない等の場合には、粉砕に必要なエネルギーを得られず、目的とする粒径のPZT粒子26が得られない。
また、PZT粒子26において、鉛原子等の原子の欠損はメディアとのせん断の影響を受け易い。鉛原子等の原子の欠損の抑制にはメディアの充填率の低減が有効である。
ボールミルによるPZT焼結体の粉砕において、充填率は、15~60%が好ましく、20~50%がより好ましく、25~35%がさらに好ましい。
ボールミルによるPZT焼結体の粉砕において、回転数は20~80rpm(revolutions per minute)が好ましく、30~70rpmがより好ましく、40~60rpmがさらに好ましい。
さらに、ボールミルによるPZT焼結体の粉砕において、粉砕時間は、メディア径、充填率および回転数に応じて、適宜、設定すればよい。粉砕時間は、一例として、8~24hr(時間)が好ましく、10~20hrがより好ましく、12~15hrがさらに好ましい。
すなわち、メディア径、充填率、回転数、および、粉砕時間を、上述のように、適宜、調節することにより、目的とする粒径、例えば粒径が1~10μmで、かつ、ラマンスペクトルにおける190~215cm-1の範囲に存在する最大ピークのラマンシフトが、205cm-1以下であり、好ましくは、上述したピーク強度比I130/I110が1.05以上および/またはピーク強度比I725/I550が0.25以上を満たす圧電体層すなわちPZT粒子26を得ることができる。
その結果、例えば、本発明の圧電フィルム10を、電気音響変換フィルムに利用することにより、湾曲状態によらず、安定して高い出力特性を発現する電気音響変換フィルムを実現できる。
有機溶媒には制限はなく、ジメチルホルムアミド(DMF)、メチルエチルケトン、シクロヘキサノン等の各種の有機溶媒が利用可能である。
シート状物34を準備し、かつ、塗料を調製したら、この塗料をシート状物34にキャスティング(塗布)して、有機溶媒を蒸発して乾燥する。これにより、図3に示すように、第1保護層18の上に第1電極層14を有し、第1電極層14の上に圧電体層12を形成してなる積層体36を作製する。なお、上述のように、第1電極層14とは、圧電体層12を塗布する際の基材側の電極を差し、積層体における上下の位置関係を示すものではない。
なお、粘弾性材料がシアノエチル化PVAのように加熱溶融可能な物であれば、粘弾性材料を加熱溶融して、これにPZT粒子26を添加/分散してなる溶融物を作製し、押し出し成形等によって、図2に示すシート状物34の上にシート状に押し出し、冷却することにより、図3に示すような、第1保護層18の上に第1電極層14を有し、第1電極層14の上に圧電体層12を形成してなる積層体36を作製してもよい。
マトリックス24に、これらの高分子圧電材料を添加する際には、上述した塗料に添加する高分子圧電材料を溶解すればよい。または、上述した加熱溶融した粘弾性材料に、添加する高分子圧電材料を添加して加熱溶融すればよい。
第1保護層18の上に第1電極層14を有し、第1電極層14の上に圧電体層12を形成してなる積層体36を作製したら、圧電体層12の分極処理(ポーリング)を行う。
また、本発明の圧電フィルム10を製造する際には、分極処理は、圧電体層12の面方向ではなく、厚さ方向に分極を行うのが好ましい。
なお、この分極処理の前に、圧電体層12の表面を加熱ローラ等を用いて平滑化する、カレンダー処理を施してもよい。このカレンダー処理を施すことで、後述する熱圧着工程がスムーズに行える。
次いで、図4に示すように、第2電極層16を圧電体層12に向けて、シート状物38を、圧電体層12の分極処理を終了した積層体36に積層する。
さらに、この積層体36とシート状物38との積層体を、第2保護層20と第1保護層18とを挟持するようにして、加熱プレス装置や加熱ローラ対等で熱圧着して、圧電フィルム10を作製する。
あるいは、積層体36とシート状物38とを、接着剤を用いて貼り合わせて、好ましくは、さらに圧着して、圧電フィルム10を作製してもよい。
この圧電スピーカー40は、圧電フィルム10を、電気信号を振動エネルギーに変換する振動板として用いる、平板型の圧電スピーカーである。なお、圧電スピーカー40は、マイクロフォンおよびセンサー等として使用することも可能である。さらに、この圧電スピーカーは、振動センサーとしても利用可能である。
ケース42は、プラスチック等で形成される、一面が開放する薄い筐体である。筐体の形状としては、直方体状、立方体状、および、円筒状とが例示される。
また、枠体48は、中央にケース42の開放面と同形状の貫通孔を有する、ケース42の開放面側に係合する枠材である。
粘弾性支持体46は、適度な粘性と弾性を有し、圧電フィルム10を支持すると共に、圧電フィルムのどの場所でも一定の機械的バイアスを与えることによって、圧電フィルム10の伸縮運動を無駄なく前後運動に変換させるためのものである。なお、圧電フィルム10の前後運動とは、すなわち、フィルムの面に垂直な方向の運動である。
粘弾性支持体46としては、一例として、羊毛のフェルトおよびPET等を含んだ羊毛のフェルトなどの不織布、ならびに、グラスウール等が例示される。
そのため、圧電スピーカー40では、粘弾性支持体46の周辺部では、粘弾性支持体46が圧電フィルム10によって下方に押圧されて厚さが薄くなった状態で、保持される。また、同じく粘弾性支持体46の周辺部において、圧電フィルム10の曲率が急激に変動し、圧電フィルム10に、粘弾性支持体46の周辺に向かって低くなる立上がり部が形成される。さらに、圧電フィルム10の中央領域は四角柱状の粘弾性支持体46に押圧されて、(略)平面状になっている。
逆に、第2電極層16および第1電極層14への駆動電圧の印加によって、圧電フィルム10が面方向に収縮すると、この収縮分を吸収するために、圧電フィルム10の立上がり部が、倒れる方向(平面に近くなる方向)に角度を変える。その結果、平面状の部分を有する圧電フィルム10は、下方に移動する。
圧電スピーカー40は、この圧電フィルム10の振動によって、音を発生する。
従って、本発明の圧電フィルム10は、図5に示すような剛性を有する平板状の圧電スピーカー40ではなく、単に湾曲状態で保持することでも、可撓性を有する圧電スピーカー、および、振動センサー等として機能させることができる。
また、上述のように、圧電フィルム10は、柔軟性および可撓性に優れ、しかも、面内に圧電特性の異方性が無い。そのため、圧電フィルム10は、どの方向に屈曲させても音質の変化が少なく、しかも、曲率の変化に対する音質変化も少ない。従って、圧電フィルム10を利用する圧電スピーカーは、設置場所の自由度が高く、また、上述したように、様々な物品に取り付けることが可能である。例えば、圧電フィルム10を、湾曲状態で洋服など衣料品およびカバンなどの携帯品等に装着することで、いわゆるウエアラブルなスピーカーを実現できる。
良好な音響特性すなわち圧電による高い伸縮性能を発現する圧電フィルム10は、複数枚を積層することにより、振動板等の被振動体を振動させる圧電振動素子としても、良好に作用する。圧電フィルム10は、放熱性が良好であるので、積層して圧電振動素子とした際にも、自身の発熱を防止でき、したがって、振動板の加熱を防止できる。
なお、圧電フィルム10を積層する際には、短絡(ショート)の可能性が無ければ、圧電フィルムは第1保護層18および/または第2保護層20を有さなくてもよい。または、第1保護層18および/または第2保護層20を有さない圧電フィルムを、絶縁層を介して積層してもよい。
積層した圧電フィルム10に駆動電圧を印加することで、個々の圧電フィルム10が面方向に伸縮し、各圧電フィルム10の伸縮によって、圧電フィルム10の積層体全体が面方向に伸縮する。圧電フィルム10の積層体の面方向の伸縮によって、積層体が貼着された振動板が撓み、その結果、振動板が、厚さ方向に振動する。この厚さ方向の振動によって、振動板は、音を発生する。振動板は、圧電フィルム10に印加した駆動電圧の大きさに応じて振動して、圧電フィルム10に印加した駆動電圧に応じた音を発生する。
従って、この際には、圧電フィルム10自身は、音を出力しない。
なお、十分な伸縮力を有するものであれば、1枚の圧電フィルム10を、同様のエキサイター(圧電振動素子)として用いることも可能である。
一例として、ポリエチレンテレフタレート(PET)等からなる樹脂フィルム、発泡ポリスチレン等からなる発泡プラスチック、段ボール材等の紙材、ガラス板、および、木材等が例示される。さらに、十分に撓ませることができるものであれば、振動板として、表示デバイス等の機器を用いてもよい。
貼着層には制限はなく、貼着対象となる物同士を貼着できるものが、各種、利用可能である。従って、貼着層は、粘着剤からなるものでも接着剤からなるものでもよい。好ましくは、貼着後に固体で硬い貼着層が得られる、接着剤からなる接着剤層を用いる。
以上の点に関しては、後述する長尺な圧電フィルム10を折り返してなる積層体でも、同様である。
従って、圧電フィルム10の積層体において、分極方向は、全ての圧電フィルム10で同方向であってもよく、分極方向が異なる圧電フィルムが存在してもよい。
圧電フィルム10において、圧電体層12に印加する電圧の極性は、圧電体層12の分極方向に応じたものとなる。従って、分極方向が第1電極層14から第2電極層16に向かう場合でも、第2電極層16から第1電極層14に向かう場合でも、積層される全ての圧電フィルム10において、第1電極層14の極性および第2電極層16の極性を、同極性にする。
従って、隣接する圧電フィルム10同士で、分極方向を互いに逆にすることで、隣接する圧電フィルム10の電極層同士が接触しても、接触する電極層は同極性であるので、ショート(短絡)する恐れがない。
圧電フィルム10を折り返して積層した構成は、以下のような利点を有する。
すなわち、カットシート状の圧電フィルム10を、複数枚、積層した積層体では、1枚の圧電フィルム毎に、第1電極層14および第2電極層16を、駆動電源に接続する必要がある。これに対して、長尺な圧電フィルム10を折り返して積層した構成では、一枚の長尺な圧電フィルム10のみで積層体を構成できる。また、長尺な圧電フィルム10を折り返して積層した構成では、駆動電圧を印加するための電源が1個で済み、さらに、圧電フィルム10からの電極の引き出しも、1か所でよい。
さらに、長尺な圧電フィルム10を折り返して積層した構成では、必然的に、隣接する圧電フィルム10同士で、分極方向が互いに逆になる。
酸化鉛粉末、酸化ジルコニウム粉末および酸化チタン粉末を、ボールミルで12時間、湿式混合して、原料混合粉を調製した。このとき、各酸化物の量は、Pb=1モルに対し、Zr=0.52モル、Ti=0.48モルとした。
この原料混合粉を、坩堝に投入して、800℃で5時間、焼成を行い、PZT粒子の原料粒子を作製した。
ボールミルは、メディア径1mm、充填率30%、回転数45rpm、粉砕時間15hrの条件で行った。
まず、下記の組成比で、シアノエチル化PVA(CR-V 信越化学工業社製)をジメチルホルムアミド(DMF)に溶解した。その後、この溶液に、作製したPZT粒子を下記の組成比で添加して、プロペラミキサー(回転数2000rpm)で攪拌して、圧電体層を形成するための塗料を調製した。
・PZT粒子・・・・・・・・・・・300質量部
・シアノエチル化PVA・・・・・・・30質量部
・DMF・・・・・・・・・・・・・・70質量部
1枚のシート状物の第2電極層(銅蒸着薄膜)の上に、スライドコーターを用いて、先に調製した圧電体層を形成するための塗料を塗布した。なお、塗料は、乾燥後の塗膜の膜厚が40μmになるように、塗布した。
次いで、シート状物に塗料を塗布した物を、120℃のホットプレート上で加熱乾燥することでDMFを蒸発させた。これにより、PET製の第2保護層の上に銅製の第2電極層を有し、その上に、厚さが40μmの圧電体層を有する積層体を作製した。
次いで、積層体とシート状物との積層体を、ラミネータ装置を用いて、温度120℃で熱圧着することで、複合圧電体と第1電極層とを貼着して接着して、図1に示すような圧電フィルムを作製した。
まず、作製した圧電フィルムを任意の位置において40×40mmサイズにハサミで裁断した。一方で、塩化第二鉄六水和物と純水とを混合した塩化鉄水溶液を調製した。塩化鉄水溶液の濃度は1.5mol/L(リットル)とした。
調製した塩化鉄水溶液中に裁断した圧電フィルムを吊るしながら12時間浸漬した。その後、浸漬した圧電フィルムを取り出し純水で数回洗浄した。洗浄した圧電フィルムの角をつまみ、4mm/s程度の速度で圧電体層から第1電極側のシート状物を剥離して、圧電体層を露出させた。シート状物とは、上述のように、厚さ4μmのPETフィルムに、厚さ0.1μmの銅薄膜を真空蒸着してなるシートである。
第1電極層を剥がした圧電フィルムを純水で、数回、洗浄した後、24時間自然乾燥させた。このようにして圧電フィルムから第1電極層を剥がして、露出した圧電体層のラマン散乱光を測定して、ラマンスペクトルを得た。
ラマン散乱の測定は、ラマン顕微鏡を用いて、532nm励起で行った。
レーザー光源60が出射した直線偏光のレーザー光(波長532nmの励起光)は、ミラー62、ミラー64およびミラー68で反射されて、倍率100倍の対物レンズ70を通過して、直線偏光(矢印a方向)の入射光Laとして圧電体層Sの表面に入射する。
圧電体層Sによるラマン散乱光Lbは、対物レンズ70を通過した後、ミラー68で反射され、ミラー64を通過した後、ノッチフィルター72によって励起光を除去され、回折格子74によって波数毎に分解された後、検出器76によって測光される。
測光結果を主成分分析(PCA)処理でノイズを除去し、自己相関0.6以上の成分を用いることで、ラマンスペクトルを得た。
この測定を、圧電体層の表面で任意の2か所で行い、全3362のスペクトルの平均を算出することで、作製した圧電体層のラマンスペクトルを得た。なお、ラマンスペクトルは、1000cm-1の強度が0になるようベースライン補正をかけ、ベースラインを強度0の直線として、作成した。
その結果、圧電体層のラマンスペクトルにおける190~215cm-1の範囲に存在する最大ピークのラマンシフトは197.8cm-1であった。
また、90cm-1以上120cm-1未満の範囲に存在する最大ピークのピーク強度I100と、120~150cm-1の範囲に存在する最大ピークのピーク強度I130とのピーク強度比I130/I110は、1.236であった。
さらに、490~650cm-1の範囲に存在する最大ピークのピーク強度I550と、700~750cm-1の範囲に存在する最大ピークのピーク強度I725とのピーク強度比I725/I550は、0.668であった。
作製した圧電フィルムを任意の位置で厚さ方向に切断した。厚さ方向の断面を、圧電体層の上端と下端を視野に含めて走査型電子顕微鏡で観察し、圧電体層におけるPZT粒子の面積率を画像解析により算出した。
このPZT粒子の面積率を、顕微鏡画像中のPZT粒子の個数で除し、円換算によってPZT粒子の粒径を測定した。
このようなPZT粒子の粒径の測定を、任意の5断面で行い、その平均値を圧電フィルムにおけるPZT粒子の粒径(算術平均径)とした。その結果、PZT粒子の粒径は3.3μmであった。
ボールミルによる原料粒子の粉砕において、メディア径を0.5mm、粉砕時間を24hrに変更した以外は、実施例1と同様にPZT粒子を作製した。
このPZT粒子を用いた以外は、実施例1と同様に、圧電フィルムを作製した。
作製した圧電フィルムについて、PZT粒子の粒径、ならびに、ラマンスペクトルにおける、190~215cm-1の範囲に存在する最大ピークのラマンシフト、ピーク強度比I130/I110、および、ピーク強度比I725/I550を測定した。
その結果、PZT粒子の粒径は10.7μm、最大ピークのラマンシフトは199.2cm-1、ピーク強度比I130/I110は1.117、ピーク強度比I725/I550は0.672、であった。
ボールミルによる原料粒子の粉砕において、充填率を50%、粉砕時間を10hrに変更した以外は、実施例1と同様にPZT粒子を作製した。
このPZT粒子を用いた以外は、実施例1と同様に、圧電フィルムを作製した。
作製した圧電フィルムについて、PZT粒子の粒径、ならびに、ラマンスペクトルにおける、190~215cm-1の範囲に存在する最大ピークのラマンシフト、ピーク強度比I130/I110、および、ピーク強度比I725/I550を測定した。
その結果、PZT粒子の粒径は3.5μm、最大ピークのラマンシフトは204.1cm-1、ピーク強度比I130/I110は1.044、ピーク強度比I725/I550は0.527であった。
ボールミルによる原料粒子の粉砕において、メディア径を0.5mm、充填率を50%、回転数を60rpmに変更した以外は、実施例1と同様にPZT粒子を作製した。
このPZT粒子を用いた以外は、実施例1と同様に、圧電フィルムを作製した。
作製した圧電フィルムについて、PZT粒子の粒径、ならびに、ラマンスペクトルにおける、190~215cm-1の範囲に存在する最大ピークのラマンシフト、ピーク強度比I130/I110、および、ピーク強度比I725/I550を測定した。
その結果、PZT粒子の粒径は3.2μm、最大ピークのラマンシフトは202.9cm-1、ピーク強度比I130/I110は1.071、ピーク強度比I725/I550は0.240、であった。
ボールミルによる原料粒子の粉砕において、メディア径を30mm、粉砕時間を22hrに変更した以外は、実施例1と同様にPZT粒子を作製した。
このPZT粒子を用いた以外は、実施例1と同様に、圧電フィルムを作製した。
作製した圧電フィルムについて、PZT粒子の粒径、ならびに、ラマンスペクトルにおける、190~215cm-1の範囲に存在する最大ピークのラマンシフト、ピーク強度比I130/I110、および、ピーク強度比I725/I550を測定した。
その結果、PZT粒子の粒径は3.4μm、最大ピークのラマンシフトは212.4cm-1、ピーク強度比I130/I110は1.088、ピーク強度比I725/I550は0.376、であった。
ボールミルによる原料粒子の粉砕において、メディア径を10mm、粉砕時間を18hrに変更した以外は、実施例1と同様にPZT粒子を作製した。
このPZT粒子を用いた以外は、実施例1と同様に、圧電フィルムを作製した。
作製した圧電フィルムについて、PZT粒子の粒径、ならびに、ラマンスペクトルにおける、190~215cm-1の範囲に存在する最大ピークのラマンシフト、ピーク強度比I130/I110、および、ピーク強度比I725/I550を測定した。
その結果、PZT粒子の粒径は3.2μm、最大ピークのラマンシフトは209.0cm-1、ピーク強度比I130/I110は1.157、ピーク強度比I725/I550は0.213、であった。
ボールミルによる原料粒子の粉砕において、充填率を50%、回転数を60rpm、粉砕時間を12hrに変更した以外は、実施例1と同様にPZT粒子を作製した。
このPZT粒子を用いた以外は、実施例1と同様に、圧電フィルムを作製した。
作製した圧電フィルムについて、PZT粒子の粒径、ならびに、ラマンスペクトルにおける、190~215cm-1の範囲に存在する最大ピークのラマンシフト、ピーク強度比I130/I110、および、ピーク強度比I725/I550を測定した。
その結果、PZT粒子の粒径は3.2μm、最大ピークのラマンシフトは206.1cm-1、ピーク強度比I130/I110は1.032、ピーク強度比I725/I550は0.572、であった。
ボールミルによる原料粒子の粉砕において、回転数を60rpm、粉砕時間を12hrに変更した以外は、実施例1と同様にPZT粒子を作製した。
このPZT粒子を用いた以外は、実施例1と同様に、圧電フィルムを作製した。
作製した圧電フィルムについて、PZT粒子の粒径、ならびに、ラマンスペクトルにおける、190~215cm-1の範囲に存在する最大ピークのラマンシフト、ピーク強度比I130/I110、および、ピーク強度比I725/I550を測定した。
その結果、PZT粒子の粒径は3.1μm、最大ピークのラマンシフトは207.8cm-1、ピーク強度比I130/I110は1.140、ピーク強度比I725/I550は0.434、であった。
作製した圧電フィルムを用いて、図5に示す圧電スピーカーを作製した。
まず、作製した圧電フィルムから、210×300mm(A4サイズ)の矩形試験片を切り出した。切り出した圧電フィルムを、図5に示すように、予め粘弾性支持体としてグラスウールを収納した210×300mmのケース上に載せた後、周辺部を枠体で押さえて、圧電フィルムに適度な張力と曲率を与えることで、図5に示すような圧電スピーカーを作製した。
なお、ケースの深さは9mmとし、グラスウールの密度は32kg/m3で、組立前の厚さは25mmとした。
結果を下記の表に示す。
また、実施例1と実施例2との比較により、PZT粒子の粒径を1~10μmの範囲とすることにより、高い音圧が得られる。実施例1と実施例3との比較により、ピーク強度比I130/I110を1.05以上とすることにより、高い音圧が得られる。さらに、実施例1と実施例4との比較により、ピーク強度比I725/I550を0.25以上とすることにより、高い音圧が得られる。
これに対して、圧電体層のラマンスペクトルにおける190~215cm-1の範囲に存在する最大ピークのラマンシフトが205cm-1以を超える比較例の圧電フィルムは、いずれも音圧が70dB未満である。
しかしながら、圧電体層のラマンスペクトルにおける190~215cm-1の範囲に存在する最大ピークのラマンシフトに関しては、実施例1、3および4の圧電フィルムは205cm-1以下であるのに対し、比較例1~4の圧電フィルムは205cm-1を超えている。
すなわち、実施例1、3および4、ならびに、比較例1~4は、目的とする粒径のPZT粒子を得、かつ、圧電体層のラマンスペクトルにおける190~215cm-1の範囲に存在する最大ピークのラマンシフトを205cm-1以下とするためには、ボールミルによる粉砕の際に、メディア径、メディアの充填率、回転数、および、粉砕時間を、それぞれ、適正に設定する必要があることを示している。
以上の結果より、本発明の効果は明らかである。
12 圧電体層
14 第1電極層
16 第2電極層
18 第1保護層
20 第2保護層
24 マトリックス
26 PZT粒子
34,38 シート状物
36 積層体
40 圧電スピーカー
42 ケース
46 粘弾性支持体
48 枠体
50 マイクロフォン
60 レーザー光源
62,64,68 ミラー
70 対物レンズ
72 ノッチフィルター
74 回折格子
76 検出器
Claims (8)
- 高分子材料を含むマトリックス中にチタン酸ジルコン酸鉛粒子を含む圧電体層と、前記圧電体層の両面に設けられる電極層とを有し、
前記圧電体層のラマンスペクトルにおける190~215cm-1の範囲に存在する最大ピークのラマンシフトが、205cm-1以下である高分子圧電フィルム。 - 前記電極層を覆う保護層を有する、請求項1に記載の高分子圧電フィルム。
- 前記チタン酸ジルコン酸鉛粒子の算術平均径が1~10μmである、請求項1または2に記載の高分子圧電フィルム。
- 前記圧電体層のラマンスペクトルにおいて、90cm-1以上120cm-1未満の範囲に存在する最大ピークのピーク強度をI100、120~150cm-1の範囲に存在する最大ピークのピーク強度をI130とした際に、ピーク強度比I130/I110が1.05以上である、請求項1~3のいずれか1項に記載の高分子圧電フィルム。
- 前記圧電体層のラマンスペクトルにおいて、490~650cm-1の範囲に存在する最大ピークのピーク強度をI550、700~750cm-1の範囲に存在する最大ピークのピーク強度をI725とした際に、ピーク強度比I725/I550が0.25以上である、請求項1~4のいずれか1項に記載の高分子圧電フィルム。
- 前記高分子材料がシアノエチル基を有する、請求項1~5のいずれか1項に記載の高分子圧電フィルム。
- 前記高分子材料がシアノエチル化ポリビニルアルコールである、請求項6に記載の高分子圧電フィルム。
- 前記圧電体層が厚さ方向に分極されている、請求項1~7のいずれか1項に記載の高分子圧電フィルム。
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