Patent Application
20240032431
The present invention relates to a piezoelectric film.
With reduction in thickness of displays such as liquid crystal displays or organic EL displays, speakers used in these thin displays are also required to be lighter and thinner. Further, in flexible displays having flexibility, speakers are also required to have flexibility in order to be integrated with flexible displays without impairing lightness and flexibility. As such lightweight, thin, and flexible speakers, it is considered to employ sheet-like piezoelectric films having a property of stretching and contracting in response to an applied voltage.
It is also considered that a speaker having flexibility is obtained by bonding an exciter having flexibility to a vibration plate having flexibility. The exciter is an exciter that vibrates an article and produces a sound by being brought into contact with various articles and being attached thereto.
It has been suggested to use a piezoelectric composite material containing piezoelectric particles in a matrix as a sheet-like piezoelectric film having flexibility or an exciter.
For example, JP2014-212307A describes an electroacoustic conversion film including a polymer-based piezoelectric composite material obtained by dispersing piezoelectric particles in a viscoelastic matrix consisting of a polymer material having a viscoelasticity at room temperature, and electrode layers provided to sandwich the polymer-based piezoelectric composite material, in which an area fraction of the piezoelectric particles in a contact surface with an electrode layer is 50% or less.
There has been a demand for such a piezoelectric film to have higher conversion efficiency between electrical energy and mechanical energy, that is, higher piezoelectric performance.
An object of the present invention is to solve such a problem of the related art and to provide a piezoelectric film having high piezoelectric performance.
In order to achieve the above-described object, the present invention has the following configurations.
[1] A piezoelectric film comprising: a piezoelectric layer consisting of a polymer-based piezoelectric composite material that contains piezoelectric particles in a matrix containing a polymer material; and electrode layers formed on both surfaces of the piezoelectric layer, in which the piezoelectric particles are particles containing lead zirconate titanate, and in a cross section of the piezoelectric layer in a thickness direction, a ratio of an area of a region where Pb/(Pb+Zr) is 90% or greater to an area of the lead zirconate titanate particles is in a range of 0.2% to 4%.
[2] The piezoelectric film according to [1], in which the lead zirconate titanate contained in the piezoelectric particles is represented by General Formula Pb(ZrXTi1−X)O3, where X represents 0.52±0.1.
[3] The piezoelectric film according to [1] or [2], in which the piezoelectric particles have an average particle diameter of 1 μm to 10 μm.
[4] The piezoelectric film according to any one of [1] to [3], in which the polymer material contains a cyanoethyl group.
[5] The piezoelectric film according to any one of [1] to [4], in which the polymer material contains cyanoethylated polyvinyl alcohol.
[6] The piezoelectric film according to any one of [1] to [5], in which the piezoelectric layer is polarized in the thickness direction.
According to the present invention as described above, it is possible to provide a piezoelectric film having high piezoelectric performance.
Hereinafter, a piezoelectric film according to an embodiment of the present invention will be described in detail based on preferred embodiments illustrated in the accompanying drawings.
The description of configuration requirements described below may be made based on typical embodiments of the present invention, but the present invention is not limited to such embodiments.
In addition, in the present specification, a numerical range shown using “to” indicates a range including numerical values described before and after “to” as a lower limit and an upper limit.
A piezoelectric film according to the embodiment of the present invention is a piezoelectric film including a piezoelectric layer consisting of a polymer-based piezoelectric composite material that contains piezoelectric particles in a matrix containing a polymer material, and electrode layers formed on both surfaces of the piezoelectric layer, in which the piezoelectric particles are particles containing lead zirconate titanate, and in a cross section of the piezoelectric layer in a thickness direction, a ratio of an area of a region where Pb/(Pb+Zr) is 90% or greater to an area of the lead zirconate titanate particles is in a range of 0.2% to 4%.
As illustrated in
The piezoelectric layer 20 consists of a polymer-based piezoelectric composite material containing the piezoelectric particles 36 in a matrix 34 containing a polymer material. In addition, the first electrode layer 24 and the second electrode layer 26 are electrode layers of the present invention.
As described below, the piezoelectric film 10 (piezoelectric layer 20) is polarized in the thickness direction as a preferred embodiment.
As an example, the piezoelectric film 10 is used in various acoustic devices (audio equipment) such as speakers, microphones, and pickups used in musical instruments such as guitars, to generate (reproduce) a sound due to vibration in response to an electrical signal or convert vibration due to a sound into an electrical signal.
Further, the piezoelectric film can also be used in pressure sensitive sensors, power generation elements, and the like in addition to the examples described above.
Alternatively, the piezoelectric film can also be used as an exciter that vibrates an article and generates a sound by being brought into contact with and attached to various articles.
In the piezoelectric film 10, the second electrode layer 26 and the first electrode layer 24 form a pair of electrodes. That is, the piezoelectric film 10 has a configuration in which both surfaces of the piezoelectric layer 20 are sandwiched between the electrode pair, that is, the first electrode layer 24 and the second electrode layer 26, and this laminate is further sandwiched between the first protective layer 28 and the second protective layer 30.
As described above, in the piezoelectric film 10, the region sandwiched between the first electrode layer 24 and the second electrode layer 26 stretches and contracts according to the applied voltage.
Further, the first electrode layer 24 and the first protective layer 28, and the second electrode layer 26 and the second protective layer 30 are named according to the polarization direction of the piezoelectric layer 20. Therefore, the first electrode layer 24 and the second electrode layer 26, and the first protective layer 28 and the second protective layer 30 have configurations that are basically the same as each other.
Further, in addition to the above-described layers, the piezoelectric film 10 may include an insulating layer that covers a region where the piezoelectric layer 20 on a side surface or the like is exposed for preventing a short circuit or the like.
In a case where a voltage is applied to the first electrode layer 24 and the second electrode layer 26 of the piezoelectric film 10, the piezoelectric particles 36 stretch and contract in the polarization direction according to the applied voltage. As a result, the piezoelectric film 10 (piezoelectric layer 20) contracts in the thickness direction. At the same time, the piezoelectric film 10 stretches and contracts in the in-plane direction due to the Poisson's ratio. The degree of stretch and contraction is approximately in a range of 0.01% to 0.1%. In the in-plane direction, the stretch and contraction are isotropically made in all directions.
The thickness of the piezoelectric layer 20 is preferably approximately in a range of 10 to 300 μm. Therefore, the degree of stretch and contraction in the thickness direction is as extremely small as approximately 0.3 μm at the maximum.
On the contrary, the piezoelectric film 10, that is, the piezoelectric layer 20, has a size much larger than the thickness in the plane direction. Therefore, for example, in a case where the length of the piezoelectric film 10 is 20 cm, the piezoelectric film 10 stretches and contracts by a maximum of approximately 0.2 mm by the application of a voltage.
Further, in a case where a pressure is applied to the piezoelectric film 10, electric power is generated by the action of the piezoelectric particles 36.
By utilizing this, the piezoelectric film 10 can be used for various applications such as a speaker, a microphone, and a pressure sensitive sensor as described above.
Here, in the present invention, the piezoelectric particles 36 are particles containing lead zirconate titanate (PZT), and in a cross section of the piezoelectric film 10 in the thickness direction, the ratio of the area of the region where Pb/(Pb+Zr) is 90% or greater to the area of the entire lead zirconate titanate particles 36 is in a range of 0.2% to 4%.
As described above, the piezoelectric film including a polymer-based piezoelectric composite material formed by dispersing piezoelectric particles in a matrix consisting of a polymer material and electrode layers formed on both surfaces of the polymer-based piezoelectric composite material is required to have higher conversion efficiency between electrical energy and mechanical energy, that is, higher piezoelectric performance.
Meanwhile, as a result of examination conducted by the present inventors, lead zirconate titanate has been preferably used as piezoelectric particles from the viewpoint of obtaining higher piezoelectric performance, and it was found that in a case where lead zirconate titanate is used as the piezoelectric particles, parts of the lead zirconate titanate particles 36 have the high Pb region 36b where Pb/(Pb+Zr) is 90% or greater. It was found that the area ratio of the high Pb region 36b to the entire lead zirconate titanate particles 36 varies depending on the conditions for preparing the piezoelectric particles and that the piezoelectric performance is higher as the area ratio of the high Pb region 36b to the entire lead zirconate titanate particles 36 (hereinafter, also referred to as the high Pb ratio) decreases.
Therefore, in the piezoelectric film according to the embodiment of the present invention, a piezoelectric film having higher conversion efficiency between the electrical energy and the mechanical energy and high piezoelectric performance can be obtained by setting the ratio of the area of the high Pb region 36b where Pb/(Pb+Zr) is 90% or greater to the area of the entire lead zirconate titanate particles 36 to be in a range of 0.2% to 4% in a cross section of the piezoelectric layer in the thickness direction.
The area ratio (high Pb ratio) of the high Pb region 36b where Pb/(Pb+Zr) is 90% or greater to the entire lead zirconate titanate particles 36 is measured as follows.
First, the piezoelectric film is bonded to a support, and a coating layer is attached to the other surface of the support. The coating layer is a film having a smooth surface with a thickness of several μm to several tens of μm, and a metal, glass, a resin, or the like is used as the coating layer. After confirming that the coating layer is closely attached to the surface of the sample, a cross section with a width of approximately 500 μm is processed using a cross-sectional ion milling device (for example, IM4000PLUS, manufactured by Hitachi High-Tech Corporation). The sample is subjected to a conductive treatment as necessary.
A composition analysis is performed by energy dispersive X-ray spectroscopy (EDS) using the sample in which the processing of the cross section has been completed to acquire an element mapping (quantitative map of the atomic number concentration) image. The resolution of the quantitative map image here is set to ½ of the resolution of the element mapping image. Simultaneously, an image observed with a scanning electron microscope (SEM) is also acquired. A mixed image is acquired by performing composition analysis using EDS, setting the acceleration voltage in a case where an image is captured with an SEM to 5 kV, and observing the SEM image using a backscattered electron detector (BSE detector) and a secondary electron detector (SE detector). For example, QUANTAX FlatQUAD type EDS (manufactured by Bruker AXS GmbH) can be used for EDS analysis, and a SU8220 type SEM (manufactured by Hitachi High-Tech Corporation) can be used for SEM observation.
Five consecutive images are acquired by setting the imaging magnification to 1500 times and the size per visual field to approximately 45 μm×60 μm. In this case, five images are captured in a width of 350 μm. The imaging region is set to 640×480 pixels. An image of the SEM and mapping with the same visual field is acquired and saved as a text.
An image of only particles is extracted from the acquired SEM image by ImageJ, and the area ratio of the region where the ratio of Pb/(Pb+Zr) is 90% or greater is calculated.
Specifically, an SEM image saved in a text format is imported into (read by) ImageJ, a region of the piezoelectric layer that does not include an electrode is cut out, and Gaussian Blur (shading) is applied. Gray value (brightness values) of the entire image is standardized to an average of 0 and a standard deviation of 1 by measuring Mean gray value (average brightness) and Standard deviation and inputting the Mean gray value to Subtract (subtraction) and the Standard deviation to Divide (division). Threshold is opened on the same image. A particle image is acquired by checking Dark Background, checking “select a part with higher brightness (use a part with lower brightness as the background)”, selecting and applying Otsu, and performing binarization. The obtained image is saved in a text file.
The mapping data of lead Pb and zirconia Zr obtained by acquiring the EDS mapping with the same visual field as that of the SEM image is converted into a text file, subjected to Gaussian Blur processing by ImageJ, and saved as a text file.
The text files of the SEM image and the EDS mapping are read, pixels satisfying Pb=5 atm % or less are excluded from the pixels corresponding to the particles of the SEM image, and Pb/(Pb+Zr)×100% is calculated.
A histogram is created for the calculated Pb/(Pb+Zr), and the area ratio of the region where Pb/(Pb+Zr) is 90% or greater is calculated.
Here, from the viewpoints of obtaining higher piezoelectric performance and the production cost, the area ratio (high Pb ratio) of the high Pb region 36b where Pb/(Pb+Zr) is 90% or greater to the entire lead zirconate titanate particles 36 is preferably in a range of 0.2% to 3.5% and more preferably in a range of 0.2% to 3%.
Further, from the viewpoint of obtaining higher piezoelectric performance, it is preferable that the lead zirconate titanate contained in the entire lead zirconate titanate particles 36 is represented by General Formula Pb(ZrXTi1−X)O3 and that X represents 0.52±0.1.
The composition of the lead zirconate titanate contained in the piezoelectric particles 36 is determined by peeling off the protective layer and the electrode layer, scraping the piezoelectric particles from the piezoelectric layer, incinerating the piezoelectric particles, and performing quantitative analysis measurement using inductively coupled plasma (ICP) emission spectrometry.
The piezoelectric layer is a layer consisting of a polymer-based piezoelectric composite material that contains piezoelectric particles in a matrix containing a polymer material and is a layer that exhibits a piezoelectric effect in which the layer is stretched and contracted in a case where a voltage is applied.
In the piezoelectric film 10, as a preferred embodiment, the piezoelectric layer 20 consists of a polymer-based piezoelectric composite material in which piezoelectric particles 36 are dispersed in the matrix 34 consisting of a polymer material having viscoelasticity at room temperature. Further, in the present specification, “room temperature” indicates a temperature range of approximately 0° C. to 50° C.
The piezoelectric film 10 according to the embodiment of the present invention is suitably used for a speaker having flexibility such as a speaker for a flexible display. Here, it is preferable that the polymer-based piezoelectric composite material (piezoelectric layer 20) used for a speaker having flexibility satisfies the following requirements. Therefore, it is preferable that a polymer material having viscoelasticity at room temperature is used as a material satisfying the following requirements.
For example, in a case of being gripped in a state of being loosely bent like a document such as a newspaper or a magazine as a portable device, the piezoelectric film is continuously subjected to large bending deformation from the outside at a relatively slow vibration of less than or equal to a few Hz. In this case, in a case where the polymer-based piezoelectric composite material is hard, a large bending stress is generated to that extent, and a crack is generated at the interface between a polymer matrix and piezoelectric particles, which may lead to breakage. Accordingly, the polymer-based piezoelectric composite material is required to have suitable flexibility. In addition, in a case where strain energy is diffused into the outside as heat, the stress is able to be relaxed. Therefore, the polymer-based piezoelectric composite material is required to have a suitably large loss tangent.
In a speaker, the piezoelectric particles vibrate at a frequency of an audio band of 20 Hz to 20 kHz, and the vibration energy causes the entire polymer-based piezoelectric composite material (piezoelectric film) to vibrate integrally so that a sound is reproduced. Therefore, in order to increase the transmission efficiency of the vibration energy, the polymer-based piezoelectric composite material is required to have appropriate hardness. In addition, in a case where the frequencies of the speaker are smooth as the frequency characteristic thereof, an amount of change in acoustic quality in a case where the lowest resonance frequency is changed in association with a change in the curvature of the speaker decreases. Therefore, the polymer-based piezoelectric composite material is required to have a suitably large loss tangent.
That is, the polymer-based piezoelectric composite material is required to exhibit a behavior of being hard with respect to a vibration of 20 Hz to 20 kHz and being flexible with respect to a vibration of less than or equal to a few Hz. In addition, the loss tangent of a polymer-based piezoelectric composite material is required to be suitably large with respect to the vibration of all frequencies of 20 kHz or less.
In general, a polymer solid has a viscoelasticity relaxing mechanism, and a molecular movement having a large scale is observed as a decrease (relief) in a storage elastic modulus (Young's modulus) or a maximal value (absorption) in a loss elastic modulus along with an increase in temperature or a decrease in frequency. Among these, the relaxation due to a microbrown movement of a molecular chain in an amorphous region is referred to as main dispersion, and an extremely large relaxing phenomenon is observed. A temperature at which this main dispersion occurs is a glass transition point (Tg), and the viscoelasticity relaxing mechanism is most remarkably observed.
In the polymer-based piezoelectric composite material (piezoelectric layer 20), the polymer-based piezoelectric composite material exhibiting a behavior of being rigid with respect to a vibration of 20 Hz to 20 kHz and being flexible with respect to a vibration of less than or equal to a few Hz is realized by using a polymer material whose glass transition point is room temperature, that is, a polymer material having a viscoelasticity at room temperature as a matrix. In particular, from the viewpoint that such a behavior is suitably exhibited, it is preferable that a polymer material in which the glass transition point at a frequency of 1 Hz is at room temperature, that is, in a range of 0° C. to 50° C. is used for a matrix of the polymer-based piezoelectric composite material.
As the polymer material having a viscoelasticity at room temperature, various known materials can be used. It is preferable that a polymer material in which the maximal value of a loss tangent Tan δ at a frequency of 1 Hz according to a dynamic viscoelasticity test at room temperature, that is, in a range of 0° C. to 50° C. is 0.5 or greater is used as the polymer material. In this manner, in a case where the polymer-based piezoelectric composite material is slowly bent due to an external force, stress concentration on the interface between the polymer matrix and the piezoelectric particles at the maximum bending moment portion is relaxed, and thus high flexibility can be expected.
In the polymer material having a viscoelasticity at room temperature, it is preferable that a storage elastic modulus (E′) at a frequency of 1 Hz according to the dynamic viscoelasticity measurement is 100 MPa or greater at 0° C. and 10 MPa or less at 50° C. In this manner, the bending moment generated in a case where the polymer-based piezoelectric composite material is slowly bent due to the external force can be reduced, and the polymer-based piezoelectric composite material can exhibit a behavior of being rigid with respect to an acoustic vibration of 20 Hz to 20 kHz.
In addition, it is more suitable that the relative dielectric constant of the polymer material having a viscoelasticity at room temperature is 10 or greater at 25° C. Accordingly, in a case where a voltage is applied to the polymer-based piezoelectric composite material, a higher electric field is applied to the piezoelectric particles in the polymer matrix, and thus a large deformation amount can be expected. However, in consideration of ensuring satisfactory moisture resistance and the like, it is suitable that the relative dielectric constant of the polymer material is 10 or less at 25° C.
Examples of the polymer material having a viscoelasticity at room temperature and satisfying such conditions include cyanoethylated polyvinyl alcohol (cyanoethylated PVA), polyvinyl acetate, polyvinylidene chloride-co-acrylonitrile, a polystyrene-vinyl polyisoprene block copolymer, polyvinyl methyl ketone, and polybutyl methacrylate. In addition, as these polymer materials, a commercially available product such as HYBRAR 5127 (manufactured by Kuraray Co., Ltd.) can also be suitably used. Among these, it is preferable to use a material containing a cyanoethyl group and particularly preferable to use cyanoethylated PVA as the polymer material. Further, these polymer materials may be used alone or in combination (mixture) of a plurality of kinds thereof.
In the matrix 34 for which such a polymer material having a viscoelasticity at room temperature is used, a plurality of polymer materials may be used in combination as necessary. That is, other dielectric polymer materials may be added to the matrix 34 for the purpose of adjusting dielectric properties or mechanical properties, in addition to the viscoelastic material such as cyanoethylated PVA as necessary.
Examples of the dielectric polymer material that can be added thereto include a fluorine-based polymer such as polyvinylidene fluoride, a vinylidene fluoride-tetrafluoroethylene copolymer, a vinylidene fluoride-trifluoroethylene copolymer, a polyvinylidene fluoride-trifluoroethylene copolymer, or a polyvinylidene fluoride-tetrafluoroethylene copolymer, a polymer containing a cyano group or a cyanoethyl group such as a vinylidene cyanide-vinyl acetate copolymer, cyanoethyl cellulose, cyanoethyl hydroxysaccharose, cyanoethyl hydroxycellulose, cyanoethyl hydroxypullulan, cyanoethyl methacrylate, cyanoethyl acrylate, cyanoethyl hydroxyethyl cellulose, cyanoethyl amylose, cyanoethyl hydroxypropyl cellulose, cyanoethyl dihydroxypropyl cellulose, cyanoethyl hydroxypropyl amylose, cyanoethyl polyacrylamide, cyanoethyl polyacrylate, cyanoethyl pullulan, cyanoethyl polyhydroxymethylene, cyanoethyl glycidol pullulan, cyanoethyl saccharose, or cyanoethyl sorbitol, and synthetic rubber such as nitrile rubber or chloroprene rubber. Among these, a polymer material containing a cyanoethyl group is suitably used.
Further, the number of kinds of the dielectric polymer materials to be added to the matrix 34 of the piezoelectric layer 20 in addition to the material having a viscoelasticity at room temperature, such as cyanoethylated PVA, is not limited to one, and a plurality of kinds of the materials may be added.
In addition, for the purpose of adjusting the glass transition point Tg, a thermoplastic resin such as a vinyl chloride resin, polyethylene, polystyrene, a methacrylic resin, polybutene, or isobutylene, and a thermosetting resin such as a phenol resin, a urea resin, a melamine resin, an alkyd resin, or mica may be added to the matrix 34 in addition to the dielectric polymer materials. Further, for the purpose of improving the pressure sensitive adhesiveness, a viscosity imparting agent such as rosin ester, rosin, terpene, terpene phenol, or a petroleum resin may be added.
In the matrix 34 of the piezoelectric layer 20, the addition amount in a case of adding materials other than the polymer material having viscoelasticity such as cyanoethylated PVA is not particularly limited, but is preferably set to 30% by mass or less in terms of the proportion of the materials in the matrix 34. In this manner, the characteristics of the polymer material to be added can be exhibited without impairing the viscoelasticity relaxing mechanism in the matrix 34, and thus preferable results, for example, an increase in the dielectric constant, improvement of the heat resistance, and improvement of the adhesiveness between the piezoelectric particles 36 and the electrode layer can be obtained.
The piezoelectric layer 20 is a polymer-based piezoelectric composite material in which the piezoelectric particles 36 are dispersed in the matrix 34.
The piezoelectric particles 36 consist of ceramic particles having a perovskite type or wurtzite type crystal structure. In the present invention, lead zirconate titanate (PZT) is used as the ceramic particles constituting the piezoelectric particles 36 as described above. Further, the piezoelectric particles 36 may include piezoelectric particles consisting of other materials such as lead lanthanum zirconate titanate (PLZT), barium titanate (BaTiO3), zinc oxide (ZnO), and a solid solution (BFBT) of barium titanate and bismuth ferrite (BiFe3).
The particle diameter of such piezoelectric particles 36 is not limited, and may be appropriately selected depending on the size of the piezoelectric film 10, the applications of the piezoelectric film 10, and the like. The particle diameter of the piezoelectric particles 36 is preferably in a range of 1 to 10 μm. By setting the particle diameter of the piezoelectric particles 36 to be in this range, a preferable result is able to be obtained from a viewpoint of allowing the piezoelectric film 10 to achieve both high piezoelectric characteristics and flexibility.
Here, in the example illustrated in
In
Further, the particle diameters of the piezoelectric particles 36 are illustrated to be uniform in
In the piezoelectric film 10, the ratio between the amount of the matrix 34 and the amount of the piezoelectric particles 36 in the piezoelectric layer 20 is not limited and may be appropriately set according to the size and the thickness of the piezoelectric film 10 in the plane direction, the applications of the piezoelectric film 10, the characteristics required for the piezoelectric film 10, and the like. The volume fraction of the piezoelectric particles 36 in the piezoelectric layer 20 is preferably in a range of 30% to 80%, more preferably 50% or greater, and still more preferably in a range of 50% to 80%. By setting the ratio between the amount of the matrix 34 and the amount of the piezoelectric particles 36 to be in the above-described ranges, preferable results in terms of achieving both of excellent piezoelectric characteristics and flexibility can be obtained.
In the piezoelectric film 10 described above, as a preferred embodiment, the piezoelectric layer 20 is a polymer-based piezoelectric composite material in which piezoelectric particles are dispersed in the viscoelastic matrix containing a polymer material having viscoelasticity at room temperature. However, the present invention is not limited thereto, and a polymer-based piezoelectric composite material in which piezoelectric particles are dispersed in a matrix containing a polymer material, which is used in a known piezoelectric element, can be used as a piezoelectric layer.
Further, the thickness of the piezoelectric layer 20 is not particularly limited and may be appropriately set according to the applications of the piezoelectric film 10, the characteristics required for the piezoelectric film 10, and the like. The thicker the piezoelectric layer 20, the more advantageous it is in terms of rigidity such as the stiffness of a so-called sheet-like material, but the voltage (potential difference) required to stretch and contract the piezoelectric film 10 by the same amount increases. The thickness of the piezoelectric layer 20 is preferably in a range of 10 to 300 μm, more preferably in a range of 20 to 200 μm, and still more preferably in a range of 30 to 150 μm. By setting the thickness of the piezoelectric layer 20 to be in the above-described range, preferable results in terms of achieving both ensuring of the rigidity and moderate elasticity can be obtained.
The first protective layer 28 and the second protective layer 30 in the piezoelectric film 10 have a function of coating the second electrode layer 26 and the first electrode layer 24 and imparting moderate rigidity and mechanical strength to the piezoelectric layer 20. That is, the piezoelectric layer 20 consisting of the matrix 34 and the piezoelectric particles 36 in the piezoelectric film 10 exhibits extremely excellent flexibility under bending deformation at a slow vibration, but may have insufficient rigidity or mechanical strength depending on the applications. As a compensation for this, the piezoelectric film 10 is provided with the first protective layer 28 and the second protective layer 30.
The first protective layer 28 and the second protective layer 30 are not limited, and various sheet-like materials can be used, and suitable examples thereof include various resin films. Among these, from the viewpoints of excellent mechanical characteristics and heat resistance, a resin film consisting of polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS), polycarbonate (PC), polyphenylene sulfide (PPS), polymethylmethacrylate (PMMA), polyetherimide (PEI), polyimide (PI), polyethylene naphthalate (PEN), triacetyl cellulose (TAC), and a cyclic olefin-based resin is suitably used.
The thickness of the first protective layer 28 and the second protective layer 30 is not limited. In addition, the thicknesses of the first protective layer 28 and the second protective layer 30 are basically the same as each other, but may be different from each other. Here, in a case where the rigidity of the first protective layer 28 and the second protective layer 30 is extremely high, not only is the stretch and contraction of the piezoelectric layer 20 constrained, but also the flexibility is impaired. Therefore, it is advantageous that the thickness of the first protective layer 28 and the thickness of the second protective layer 30 decrease except for the case where the mechanical strength or satisfactory handleability as a sheet-like material is required.
In a case where the thickness of the first protective layer 28 and the second protective layer 30 in the piezoelectric film 10 is two times or less the thickness of the piezoelectric layer 20, preferable results in terms of achieving both ensuring of the rigidity and moderate elasticity can be obtained.
For example, in a case where the thickness of the piezoelectric layer 20 is 50 μm and the first protective layer 28 and the second protective layer 30 consist of PET, the thickness of the first protective layer 28 and the second protective layer 30 is preferably 100 μm or less, more preferably 50 μm or less, and still more preferably 25 μm or less.
In the piezoelectric film 10, the first electrode layer 24 is formed between the piezoelectric layer 20 and the first protective layer 28, and the second electrode layer 26 is formed between the piezoelectric layer 20 and the second protective layer 30. The first electrode layer 24 and the second electrode layer 26 are provided to apply a voltage to the piezoelectric layer 20 (piezoelectric film 10).
In the present invention, the material for forming the first electrode layer 24 and the second electrode layer 26 is not limited, and various conductors can be used as the material. Specific examples thereof include 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, and indium tin oxide. Among these, copper, aluminum, gold, silver, platinum, and indium tin oxide are suitable as the material of the first electrode layer 24 and the second electrode layer 26.
In addition, a method of forming the first electrode layer 24 and the second electrode layer 26 is not limited, and various known methods, for example, a vapor-phase deposition method (a vacuum film forming method) such as vacuum vapor deposition, ion-assisted vapor deposition, or sputtering, a film forming method of using plating, and a method of bonding a foil formed of the materials described above can be used.
Among these, particularly from the viewpoint of ensuring the flexibility of the piezoelectric film 10, a thin film made of copper, aluminum, or the like formed by vacuum vapor deposition is suitably used as the first electrode layer 24 and the second electrode layer 26. Among these, particularly a thin film made of copper formed by vacuum vapor deposition is suitably used.
The thicknesses of the first electrode layer 24 and the second electrode layer 26 are not limited. In addition, the thicknesses of the first electrode layer 24 and the second electrode layer 26 are basically the same as each other, but may be different from each other.
Here, similarly to the first protective layer 28 and the second protective layer 30 described above, in a case where the rigidity of the first electrode layer 24 and the second electrode layer 26 is extremely high, not only is the stretch and contraction of the piezoelectric layer 20 constrained, but also the flexibility is impaired. Therefore, from the viewpoints of the flexibility and the piezoelectric characteristics, the first electrode layer 24 and the second electrode layer 26 are more advantageous as the thicknesses thereof decrease. That is, it is preferable that the first electrode layer 24 and the second electrode layer 26 are thin film electrodes.
The thickness of each of the first electrode layer 24 and the second electrode layer 26 is less than the thickness of the protective layer, and is preferably in a range of 0.05 μm to 10 μm, more preferably in a range of 0.05 μm to 5 μm, still more preferably in a range of 0.08 μm to 3 μm, and particularly preferably in a range of 0.1 μm to 2 μm.
It is suitable that the product of the thickness and the Young's modulus of the first electrode layer 24 and the second electrode layer 26 of the piezoelectric film 10 is less than the product of the thickness and the Young's modulus of the first protective layer 28 and the second protective layer 30 from the viewpoint that the flexibility is not considerably impaired.
For example, in a combination in which the first protective layer 28 and the second protective layer 30 are made of PET (Young's modulus: approximately 6.2 GPa) and the first electrode layer 24 and the second electrode layer 26 consist of copper (Young's modulus: approximately 130 GPa), in a case where the thickness of the first protective layer 28 and the second protective layer 30 is assumed to be 25 μm, the thickness of the first electrode layer 24 and the second electrode layer 26 is preferably 1.2 μm or less, more preferably 0.3 μm or less, and still more preferably 0.1 μm or less.
As described above, it is preferable that the piezoelectric film 10 has a configuration in which the piezoelectric layer 20 obtained by dispersing the piezoelectric particles 36 in the matrix 34 containing the polymer material that has a viscoelasticity at room temperature is sandwiched between the first electrode layer 24 and the second electrode layer 26 and this laminate is sandwiched between the first protective layer 28 and the second protective layer 30.
It is preferable that, in such a piezoelectric film 10, the maximal value of the loss tangent (tan δ) at a frequency of 1 Hz according to dynamic viscoelasticity measurement is present at room temperature and more preferable that the maximal value at which the loss tangent is 0.1 or greater is present at room temperature. In this manner, even in a case where the piezoelectric film 10 is subjected to large bending deformation at a relatively slow vibration of less than or equal to a few Hz from the outside, since the strain energy can be effectively diffused to the outside as heat, occurrence of cracks at the interface between the polymer matrix and the piezoelectric particles can be prevented.
In the piezoelectric film 10, it is preferable that the storage elastic modulus (E′) at a frequency of 1 Hz according to the dynamic viscoelasticity measurement is in a range of 10 to 30 GPa at 0° C. and in a range of 1 to 10 GPa at 50° C. The same applies to the conditions for the piezoelectric layer 20. In this manner, the piezoelectric film 10 may have large frequency dispersion in the storage elastic modulus (E′). That is, the piezoelectric film 10 can exhibit a behavior of being rigid with respect to a vibration of 20 Hz to 20 kHz and being flexible with respect to a vibration of less than or equal to a few Hz.
In the piezoelectric film 10, it is preferable that the product of the thickness and the storage elastic modulus (E′) at a frequency of 1 Hz according to the dynamic viscoelasticity measurement is in a range of 1.0×106 to 2.0×106 N/m at 0° C. and in a range of 1.0×105 to 1.0×106 N/m at 50° C. The same applies to the conditions for the piezoelectric layer 20. In this manner, the piezoelectric film 10 may have moderate rigidity and mechanical strength within a range not impairing the flexibility and the acoustic characteristics.
Further, in the piezoelectric film 10, it is preferable that the loss tangent (Tan δ) at a frequency of 1 kHz at 25° C. is 0.05 or greater in a master curve obtained from the dynamic viscoelasticity measurement. The same applies to the conditions for the piezoelectric layer 20. In this manner, the frequency of a speaker formed of the piezoelectric film 10 is smooth as the frequency characteristic thereof, and thus an amount of a change in acoustic quality in a case where the lowest resonance frequency f0 is changed according to a change in the curvature of the speaker can be decreased.
In the present invention, the storage elastic modulus (Young's modulus) and the loss tangent of the piezoelectric film 10, the piezoelectric layer 20, and the like may be measured by a known method. As an example, the measurement may be performed using a dynamic viscoelasticity measuring device DMS6100 (manufactured by SII Nanotechnology Inc.).
Examples of the measurement conditions include a measurement frequency of 0.1 Hz to 20 Hz (0.1 Hz, 0.2 Hz, 0.5 Hz, 1 Hz, 2 Hz, 5 Hz, 10 Hz, and 20 Hz), a measurement temperature of −50° C. to 150° C., a temperature rising rate of 2° C./min (in a nitrogen atmosphere), a sample size of 40 mm×10 mm (including the clamped region), and a chuck-to-chuck distance of 20 mm.
Next, an example of the method of producing the piezoelectric film 10 will be described with reference to
First, a sheet-like material 10a in which the first electrode layer 24 is formed on the first protective layer 28 is prepared as illustrated in
In a case where the first protective layer 28 is extremely thin and thus the handleability is degraded, the first protective layer 28 with a separator (temporary support) may be used as necessary. Further, a PET having a thickness of 25 μm to 100 μm or the like can be used as the separator. The separator may be removed after thermal compression bonding of the second electrode layer 26 and the second protective layer 30 and before lamination of any member on the first protective layer 28.
On the other hand, the piezoelectric particles 36 are prepared.
First, powder of an oxide of Pb, an oxide of Zr, and an oxide of Ti, which are main components, is mixed as starting materials in an amount ratio according to the composition of the entirety of the piezoelectric particles to prepare raw material powder. Further, the entire composition of the piezoelectric particles and the composition of the piezoelectric particles excluding the high Pb region substantially match the composition of the raw material powder.
The raw material powder is prepared by performing wet mixing using a ball mill or the like to form mixed particles. After the particles are dried, the mixed particles are put into a crucible or the like and calcined. The average particle diameter of the mixed particles can be adjusted by adjusting the wet mixing time, the rotation speed of the ball mill, or the like.
In the present invention, the proportion of the high Pb region in the lead zirconate titanate particles is adjusted by appropriately adjusting the average particle diameter, the calcining temperature, and the like of the mixed particles.
Specifically, the proportion of the high Pb region is likely to increase in a case where the average particle diameter of the mixed particles is extremely large, and the piezoelectric characteristics are degraded in a case where the average particle diameter of the mixed particles is extremely small. From the above-described viewpoints, the average particle diameter of the mixed particles is preferably in a range of 1 μm to 10 μm, more preferably in a range of 1.2 μm to 8 μm, and still more preferably in a range of 1.5 μm to 6 μm.
The average particle diameter of the mixed particles before calcination may be determined as a volume average diameter MV value using a laser scattering particle size measuring device or the like.
Further, the respective components are not sufficiently mixed and the proportion of the high Pb region is likely to increase in a case where the calcining temperature is extremely low, and the size of the calcined and solidified particles is extremely large in a case where the calcining temperature is extremely high. From this viewpoint, the calcining temperature is preferably in a range of 600° C. to 1200° C., more preferably in a range of 700° C. to 1150° C., and still more preferably in a range of 700° C. to 1100° C.
Further, the respective components are not sufficiently mixed and the proportion of the high Pb region is likely to increase in a case where the calcining time is extremely short, and the size of the calcined and solidified particles is extremely large in a case where the calcining time is extremely long. From this viewpoint, the calcining time is preferably in a range of 1 hour to 200 hours, more preferably in a range of 2 hours to 170 hours, and still more preferably in a range of 2 hours to 150 hours.
After completion of the calcination, the prepared piezoelectric particles are crushed as necessary. The crushing may be carried out by a known method such as a method using a ball mill or a method of placing particles on a mesh, applying a pressure thereto from above, and allowing the particles to pass through the mesh.
Next, a coating material that is formed into the piezoelectric layer is prepared. The coating material is prepared by dissolving a polymer material serving as a material of the matrix in an organic solvent, adding the piezoelectric particles 36 thereto, and stirring the solution for dispersion.
The organic solvent other than the above-described substances is not limited, and various organic solvents can be used.
In a case where the sheet-like material 10a is prepared and the coating material is prepared, the coating material is cast (applied) onto the sheet-like material 10a, and the organic solvent is evaporated and dried. In this manner, as illustrated in
A casting method of the coating material is not limited, and all known methods (coating devices) such as a slide coater or a doctor knife can be used.
As described above, in the piezoelectric film 10, in addition to the viscoelastic material such as cyanoethylated PVA, a dielectric polymer material may be added to the matrix 34.
In a case where the polymer material is added to the matrix 34, the polymer material added to the coating material may be dissolved.
In a case where the laminate 10b in which the first electrode layer 24 is provided on the first protective layer 28 and the piezoelectric layer 20 is formed on the first electrode layer 24 is prepared, it is preferable that the piezoelectric layer 20 is subjected to a polarization treatment (poling). A method of performing the polarization treatment on the piezoelectric layer 20 is not limited, and a known method can be used.
Before the polarization treatment, a calender treatment may be performed to smoothen the surface of the piezoelectric layer 20 using a heating roller or the like. By performing the calender treatment, a thermal compression bonding step described below can be smoothly performed.
In this manner, while the piezoelectric layer 20 of the laminate 10b is subjected to the polarization treatment, a sheet-like material 10c in which the second electrode layer 26 is formed on the second protective layer 30 is prepared. The sheet-like material 10c may be prepared by forming a copper thin film or the like as the second electrode layer 26 on the surface of the second protective layer 30 using vacuum vapor deposition, sputtering, plating, or the like.
Next, as illustrated in
Further, a laminate of the laminate 10b and the sheet-like material 10c is subjected to the thermal compression bonding using a heating press device, a pair of heating rollers, or the like such that the laminate is sandwiched between the second protective layer 30 and the first protective layer 28, to prepare the piezoelectric film 10. In addition, the laminate may be cut into a desired shape after the thermal compression bonding.
Further, the steps described so far can also be performed by using a web-like material, that is, a material wound up in a state where long sheets are connected without using a sheet-like material, during transport. Both the laminate 10b and the sheet-like material 10c have a web shape and can be subjected to thermal compression bonding as described above. In that case, the piezoelectric film 10 is prepared in a web shape at this time point.
Further, an adhesive layer may be provided in a case where the laminate 10b and the sheet-like material 10c are bonded to each other. For example, an adhesive layer may be provided on the surface of the second electrode layer 26 of the sheet-like material 10c. The most suitable adhesive layer is formed of the same material as the material of the matrix 34. The piezoelectric layer 20 may be coated with the same material or the surface of the second electrode layer 26 can be coated with the same material and bonded.
Here, a typical piezoelectric film consisting of a polymer material such as polyvinylidene difluoride (PVDF) has in-plane anisotropy as a piezoelectric characteristic and is anisotropic in the amount of expansion and contraction in the plane direction in a case where a voltage is applied.
On the contrary, the piezoelectric layer which is included in the piezoelectric film according to the embodiment of the present invention and consists of a polymer-based piezoelectric composite material that contains piezoelectric particles in a matrix containing a polymer material has no in-plane anisotropy as a piezoelectric characteristic and stretches and contracts isotropically in all directions in the in-plane direction. According to the piezoelectric film 10 that stretches and contracts isotropically and two-dimensionally as described above, the piezoelectric film can be vibrated with a larger force and a louder and more beautiful sound can be generated as compared with a case of a typical piezoelectric film formed of PVDF or the like that stretches and contracts greatly in only one direction.
Further, the piezoelectric film according to the embodiment of the present invention can also be used as a speaker of a display device, for example, by being bonded to a display device having flexibility such as an organic electroluminescence display having flexibility or a liquid crystal display having flexibility.
Further, for example, in a case where the piezoelectric film 10 is used as a speaker, the piezoelectric film 10 may be used as a speaker that generates a sound from the vibration of the film-like piezoelectric film. Alternatively, the piezoelectric film 10 may be used as an exciter that generates a sound by being attached to a vibration plate to vibrate the vibration plate, from the vibration of the piezoelectric film 10.
In addition, the piezoelectric film 10 according to the embodiment of the present invention satisfactorily functions as a piezoelectric vibrating element that vibrates a vibrating body such as a vibration plate by laminating a plurality of the piezoelectric films to obtain a laminated piezoelectric element.
As an example, as illustrated in
By applying a driving voltage to the laminated piezoelectric element 50 obtained by laminating the piezoelectric films 10, each of the piezoelectric films 10 stretches and contracts in the plane direction, and the entire laminate of the piezoelectric films 10 stretches and contracts in the plane direction due to the stretch and contraction of each of the piezoelectric films 10. The vibration plate 12 to which the laminate has been bonded is bent due to the stretch and contraction of the laminated piezoelectric element 50 in the plane direction, and as a result, the vibration plate 12 vibrates in the thickness direction. The vibration plate 12 generates a sound due to the vibration in the thickness direction. That is, the vibration plate 12 vibrates according to the magnitude of the driving voltage applied to the piezoelectric film 10, and generates a sound according to the driving voltage applied to the piezoelectric film 10. Therefore, the piezoelectric film 10 itself does not output sound in this case.
Therefore, even in a case where the rigidity of each piezoelectric film 10 is low and the stretching and contracting force thereof is small, the rigidity of the laminated piezoelectric element 50 obtained by laminating the piezoelectric films 10 is increased, and the stretching and contracting force as the entire laminate is increased. As a result, in the laminated piezoelectric element 50 obtained by laminating the piezoelectric films 10, even in a case where the vibration plate has a certain degree of rigidity, the vibration plate 12 is sufficiently bent with a large force and can be sufficiently vibrated in the thickness direction, and thus the vibration plate 12 can generate a sound.
In the laminated piezoelectric element 50 obtained by laminating the piezoelectric films 10, the number of laminated sheets of the piezoelectric films 10 is not limited, and the number of sheets set such that a sufficient amount of vibration is obtained may be appropriately set according to, for example, the rigidity of the vibration plate 12 to be vibrated. Further, one piezoelectric film 10 can also be used as a similar exciter (piezoelectric vibrating element) in a case where the piezoelectric film 10 has a sufficient stretching and contracting force.
The vibration plate 12 that is vibrated by the laminated piezoelectric element 50 obtained by laminating the piezoelectric films 10 is not limited, and various sheet-like materials (plate-like materials and films) can be used. Examples thereof include a resin film consisting of polyethylene terephthalate (PET) and the like, foamed plastic consisting of foamed polystyrene and the like, a paper material such as a corrugated cardboard material, a glass plate, and wood. Further, various machines (devices) such as display devices such as an organic electroluminescence display and a liquid crystal display may be used as the vibration plate as long as the devices can be sufficiently bent.
It is preferable that the laminated piezoelectric element 50 obtained by laminating the piezoelectric films 10 is formed by bonding the adjacent piezoelectric films 10 with a bonding layer 19 (bonding agent). Further, it is preferable that the laminated piezoelectric element 50 and the vibration plate 12 are also bonded with a bonding layer 16.
The bonding layer is not limited, and various layers that can bond materials to be bonded can be used. Therefore, the bonding layer may consist of a pressure sensitive adhesive or an adhesive. It is preferable that an adhesive layer consisting of an adhesive is used from the viewpoint that a solid and hard bonding layer is obtained after the bonding. The same applies to the laminate formed by folding back the long piezoelectric film 10 described below.
In the laminated piezoelectric element 50 obtained by laminating the piezoelectric films the polarization direction of each piezoelectric film 10 to be laminated is not limited. It is preferable that the piezoelectric film 10 according to the embodiment of the present invention is polarized in the thickness direction. The polarization direction of the piezoelectric film 10 here is a polarization direction in the thickness direction. Therefore, in the laminated piezoelectric element 50, the polarization directions may be the same for all the piezoelectric films 10, and piezoelectric films having different polarization directions may be present.
In a laminated piezoelectric element 50 obtained by laminating the piezoelectric films 10, it is preferable that the piezoelectric films 10 are laminated such that the adjacent piezoelectric films 10 have polarization directions opposite to each other. In the piezoelectric film 10, the polarity of the voltage to be applied to the piezoelectric layer 20 depends on the polarization direction of the piezoelectric layer 20. Therefore, even in a case where the polarization direction is directed from the second electrode layer 26 toward the first electrode layer 24 or from the first electrode layer 24 toward the second electrode layer 26, the polarity of the second electrode layer 26 and the polarity of the first electrode layer 24 in all the piezoelectric films 10 to be laminated are set to be the same as each other. Therefore, by reversing the polarization directions of the adjacent piezoelectric films 10, even in a case where the electrode layers of the adjacent piezoelectric films 10 come into contact with each other, the electrode layers in contact with each other have the same polarity, and thus there is no risk of a short circuit.
The laminated piezoelectric element obtained by laminating the piezoelectric films 10 may have a configuration in which a plurality of piezoelectric films 10 are laminated by folding a piezoelectric film 10L once or more times, preferably a plurality of times, as illustrated in
In the laminate in which a plurality of cut sheet-like piezoelectric films 10 are laminated, the second electrode layer 26 and the first electrode layer 24 need to be connected to a driving power supply for each piezoelectric film. On the contrary, in the configuration in which the long piezoelectric film 10L is folded back and laminated, only one sheet of the long piezoelectric film 10L can form the laminated piezoelectric element 56. Therefore, in the configuration in which the long piezoelectric film 10L is folded back and laminated, only one power source is required for applying the driving voltage, and the electrode may be led out from the piezoelectric film 10L at one site. Further, in the configuration in which the long piezoelectric film 10L is folded back and laminated, the polarization directions of the adjacent piezoelectric films are inevitably opposite to each other.
Further, such a laminated piezoelectric element obtained by laminating the piezoelectric film including electrode layers and protective layers provided on both surfaces of a piezoelectric layer consisting of a polymer-based piezoelectric composite material is described in WO2020/095812A and WO2020/179353A.
Hereinbefore, the piezoelectric film according to the embodiment of the present invention has been described in detail, but the present invention is not limited to the above-described examples, and various improvements or modifications may be made within a range not departing from the scope of the present invention.
Hereinafter, the present invention will be described in more detail with reference to specific examples of the present invention. Further, the present invention is not limited to the examples, and the materials, the used amounts, the proportions, the treatment contents, the treatment procedures, and the like shown in the following examples can be appropriately changed within a range not departing from the scope of the present invention.
Sheet-like materials 10a and 10c formed by sputtering a copper thin film having a thickness of 100 nm on a PET film having a thickness of 4 μm were prepared. That is, in the present example, the first electrode layer 24 and the second electrode layer 26 were copper thin films having a thickness of 100 nm, and the first protective layer 28 and the second protective layer 30 were PET films having a thickness of 4 μm.
Further, in order to obtain satisfactory handleability during the process, a film with a separator (temporary support PET) having a thickness of 50 μm was used as the PET film, and the separator of each protective layer was removed after the thermal compression bonding of the sheet-like material 10c.
In addition, as starting materials, powder of a Pb oxide, a Zr oxide, and a Ti oxide serving as the main components was wet-mixed in ethanol using a ball mill for 12 hours. Here, the amount of each oxide was set to Zr=0.52 mol and Ti=0.48 mol with respect to Pb=1 mol. Here, the rotation speed of the ball mill was set to 60 rpm. The powder was mixed to form mixed particles. The average particle diameter of the mixed particles was 1.5 μm.
Next, the obtained mixed particles were calcined at 800° C. for 5 hours.
First, cyanoethylated PVA (CR-V, manufactured by Shin-Etsu Chemical Co., Ltd.) was dissolved in methyl ethyl ketone (MEK) at the following compositional ratio. Thereafter, the piezoelectric particles obtained above were added to the solution at the following compositional ratio and dispersed using a propeller mixer (rotation speed of 2000 rpm), thereby preparing a coating material for forming a piezoelectric layer 20.
The first electrode layer 24 (copper thin film) of the sheet-like material 10a prepared in advance was coated with the coating material for forming the piezoelectric layer 20 prepared in advance using a slide coater. Further, the coating material was applied such that the film thickness of the coating film after being dried reached 20 μm.
Next, the material obtained by coating the sheet-like material 10a with the coating material was placed on a hot plate at 120° C., and the coating film was heated and dried. In this manner, MEK was evaporated to form a laminate 10b.
Next, the sheet-like material 10c was laminated on the laminate 10b in a state where the second electrode layer 26 (copper thin film side) side was directed toward the piezoelectric layer 20, and subjected to thermal compression bonding at 120° C.
In this manner, a piezoelectric film 10 including the first protective layer 28, the first electrode layer 24, the piezoelectric layer 20, the second electrode layer 26, and the second protective layer 30 in this order was prepared.
The area ratio (high Pb ratio) of the high Pb region where Pb/(Pb+Zr) was 90% or greater to the lead zirconate titanate particles in the piezoelectric layer 20 of the prepared piezoelectric film 10 was determined by the above-described method, and the high Pb ratio was 4.0%.
Further, the composition of the lead zirconate titanate contained in the piezoelectric particles 36 was determined by peeling off the protective layer and the electrode layer, scraping the piezoelectric particles from the piezoelectric layer, incinerating the piezoelectric particles, and performing quantitative analysis measurement using inductively coupled plasma (ICP) emission spectrometry, and Zr/(Zr+Ti)=X was 0.54.
A piezoelectric film was prepared in the same manner as in Example 1 except that the calcining time of the mixed particles to be formed into the piezoelectric particles was set to 10 hours. The high Pb ratio in the prepared piezoelectric film was 2.5%.
A piezoelectric film was prepared in the same manner as in Example 1 except that the calcining time of the mixed particles to be formed into the piezoelectric particles was set to 100 hours. The high Pb ratio in the prepared piezoelectric film was 1.0%.
A piezoelectric film was prepared in the same manner as in Example 1 except that the calcining time of the mixed particles to be formed into the piezoelectric particles was set to 200 hours. The high Pb ratio in the prepared piezoelectric film was 0.5%.
A piezoelectric film was prepared in the same manner as in Example 3 except that the calcining temperature of the mixed particles to be formed into the piezoelectric particles was set to 1000° C. The high Pb ratio in the prepared piezoelectric film was 0.2%.
A piezoelectric film was prepared in the same manner as in Example 3 except that the rotation speed of the ball mill in a case where the raw material powder to be formed into the piezoelectric particles was wet-mixed was set to 20 rpm. The average particle diameter of the mixed particles was 3.3 μm. The high Pb ratio in the prepared piezoelectric film was 2.5%.
A piezoelectric film was prepared in the same manner as in Example 6 except that the calcining temperature of the mixed particles to be formed into the piezoelectric particles was set to 1000° C. The high Pb ratio in the prepared piezoelectric film was 1.0%.
A piezoelectric film was prepared in the same manner as in Example 1 except that the calcining time of the mixed particles to be formed into the piezoelectric particles was set to 2 hours. The high Pb ratio in the prepared piezoelectric film was 4.5%.
A piezoelectric film was prepared in the same manner as in Example 1 except that the rotation speed of the ball mill in a case where the raw material powder to be formed into the piezoelectric particles was wet-mixed was set to 20 rpm. The average particle diameter of the mixed particles was 3.3 μm. The high Pb ratio in the prepared piezoelectric film was 8.0%.
A piezoelectric film was prepared in the same manner as in Example 7 except that the calcining time of the mixed particles to be formed into the piezoelectric particles was set to 5 hours. The high Pb ratio in the prepared piezoelectric film was 5.0%.
First, a rectangular test piece having a size of 210×300 mm (A4 size) was cut out from the prepared piezoelectric film. The cut-out piezoelectric film was placed on a case having an opening portion with a size of 210×300 mm in which glass wool was stored, the peripheral portion was pressed by a frame to impart an appropriate tension and a curvature to the piezoelectric film, thereby preparing a piezoelectric speaker. The depth of the case was set to 9 mm, the density of glass wool was set to 32 kg/m3, and the thickness before assembly was set to 25 mm.
A 1 kHz sine wave was input to the prepared piezoelectric speaker as an input signal through a power amplifier, and the sound pressure was measured with a microphone placed at a distance of 1 m from the center of the speaker.
The results are listed in Table 1 and illustrated in
As shown in Table 1 and
Based on the comparison between Examples 1 to 4, it was found that the high Pb ratio was decreased and the sound pressure was increased as the calcining time was increased.
Based on the comparison between Examples 3 and 5, it was found that the high Pb ratio was decreased and the sound pressure was increased as the calcining temperature was increased.
Based on the comparison between Example 3 and Example 6 and the comparison between Example 5 and Example 7, it was found that the high Pb ratio was decreased and the sound pressure was increased as the average particle diameter of the mixed particles before calcination was increased.
As shown in the above-described results, the effects of the present invention are evident.
The piezoelectric film according to the embodiment of the present invention can be suitably used for various applications, for example, various sensors (particularly useful for infrastructure inspection such as crack detection and inspection at a manufacturing site such as foreign matter contamination detection) such as sound wave sensors, ultrasound sensors, pressure sensors, tactile sensors, strain sensors, and vibration sensors, acoustic devices (specific applications thereof include noise cancellers (used for cars, trains, airplanes, robots, and the like), artificial voice cords, buzzers for preventing invasion of pests and harmful animals, furniture, wallpaper, photos, helmets, goggles, headrests, signage, and robots) such as microphones, pickups, speakers, and exciters, haptics used by being applied to automobiles, smartphones, smart watches, and game machines, ultrasonic transducers such as ultrasound probes and hydrophones, actuators used for water droplet adhesion prevention, transport, stirring, dispersion, and polishing, damping materials (dampers) used for containers, vehicles, buildings, and sports goods such as skis and rackets, and vibration power generation devices used by being applied to roads, floors, mattresses, chairs, shoes, tires, wheels, personal computer keyboards, and the like.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2021-064580 | Apr 2021 | JP | national |
This application is a Continuation of PCT International Application No. PCT/JP2022/013437 filed on Mar. 23, 2022, which claims priority under 35 U.S.C. § 119(a) to Japanese Patent Application No. 2021-064580 filed on Apr. 6, 2021. The above applications are hereby expressly incorporated by reference, in their entirety, into the present application.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2022/013437 | Mar 2022 | US |
| Child | 18481304 | US |
