Piezoelectric Film

Abstract

The preset invention provides a piezoelectric film which has high piezoelectric performance. This piezoelectric film comprises: a piezoelectric layer that is composed of a polymer composite piezoelectric body which contains piezoelectric particles in a matrix that contains a polymer material; and electrode layers that are formed on both surfaces of the piezoelectric layer. With respect to this piezoelectric film, the piezoelectric particles contain lead zirconate titanate; and the ratio of the area of a region where Pb / (Pb + Zr) is 90% or more to the area of the lead zirconate titanate particles in a cross-section of the piezoelectric layer in the thickness direction is from 0.2% to 4%.

Description

[Technical Field]

[0001] The present invention relates to a piezoelectric film. [Background technology]

[0002] As displays such as liquid crystal displays and organic electroluminescence (EL) displays become thinner, the speakers used in these displays must also be lighter and thinner. Furthermore, flexible speakers are also required to be flexible so that they can be integrated into flexible displays without compromising their lightness and flexibility. One approach to achieving such lightweight, thin, and flexible speakers is to use sheet-shaped piezoelectric film, which expands and contracts in response to an applied voltage.

[0003] It has also been considered to create a flexible speaker by attaching a flexible exciter to a flexible diaphragm. An exciter is an exciter that, when attached to a variety of objects, vibrates the object to produce sound.

[0004] It has been proposed to use a composite piezoelectric material containing piezoelectric particles in a matrix as such a flexible sheet-like piezoelectric film or exciter.

[0005] For example, Patent Document 1 describes an electroacoustic converter film having a polymer composite piezoelectric element in which piezoelectric particles are dispersed in a viscoelastic matrix made of a polymer material that has viscoelasticity at room temperature, and electrode layers arranged to sandwich the polymer composite piezoelectric element, in which the area fraction of the piezoelectric particles on the contact surface with the electrode layer is 50% or less. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-212307 DISCLOSURE OF THE INVENTION [Problem to be solved by the invention]

[0007] In such piezoelectric films, there has been a demand for higher conversion efficiency between electrical energy and mechanical energy, that is, higher piezoelectric performance.

[0008] An object of the present invention is to solve the problems of the prior art and to provide a piezoelectric film having high piezoelectric performance. [Means for solving the problem]

[0009] In order to solve such problems, the present invention has the following configuration. [1] A piezoelectric element having a piezoelectric layer made of a polymer composite piezoelectric material containing piezoelectric particles in a matrix containing a polymer material, and electrode layers formed on both sides of the piezoelectric layer, the piezoelectric particles are particles containing lead zirconate titanate, A piezoelectric film in which the ratio of the area of ​​a region where Pb / (Pb+Zr) is 90% or more to the area of ​​lead zirconate titanate particles in a cross section in the thickness direction of the piezoelectric layer is 0.2 to 4%. [2] The lead zirconate titanate contained in the piezoelectric particles has the general formula Pb(Zr X Ti 1-X )O3, and X is 0.52±0.1. [3] The piezoelectric film according to [1] or [2], wherein the average particle size of the piezoelectric particles is 1 μm to 10 μm. [4] The piezoelectric film according to any one of [1] to [3], wherein the polymer material has a cyanoethyl group. [5] The piezoelectric film according to any one of [1] to [4], wherein the polymer material contains cyanoethylated polyvinyl alcohol. [6] The piezoelectric film according to any one of [1] to [5], wherein the piezoelectric layer is polarized in the thickness direction. [Effects of the Invention]

[0010] According to the present invention, a piezoelectric film having high piezoelectric performance can be provided. [Brief explanation of the drawings]

[0011] [Figure 1] 1A and 1B are diagrams conceptually illustrating examples of the piezoelectric film of the present invention. [Figure 2] FIG. 2 is a partially enlarged view of a cross section of a piezoelectric layer. [Figure 3] 1A to 1C are conceptual diagrams for explaining an example of a method for producing a piezoelectric film. [Figure 4] 1A to 1C are conceptual diagrams for explaining an example of a method for producing a piezoelectric film. [Figure 5] 1A to 1C are conceptual diagrams for explaining an example of a method for producing a piezoelectric film. [Figure 6] 1 is a diagram conceptually illustrating an example of a piezoelectric element having a piezoelectric film of the present invention. [Figure 7] FIG. 2 is a diagram conceptually illustrating another example of a piezoelectric element having a piezoelectric film of the present invention. [Figure 8] 1 is a graph showing the relationship between high Pb ratio and sound pressure. DETAILED DESCRIPTION OF THE INVENTION

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The piezoelectric film of the present invention will be described in detail below with reference to preferred embodiments shown in the accompanying drawings.

[0013] The following description of the components may be based on typical embodiments of the present invention, but the present invention is not limited to such embodiments. In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits.

[0014] [Piezoelectric film] The piezoelectric film of the present invention is The piezoelectric element has a piezoelectric layer made of a polymer composite piezoelectric material containing piezoelectric particles in a matrix containing a polymer material, and electrode layers formed on both sides of the piezoelectric layer, the piezoelectric particles are particles containing lead zirconate titanate, In the cross section of the piezoelectric layer in the thickness direction, the ratio of the area of ​​the region where Pb / (Pb+Zr) is 90% or more to the area of ​​the lead zirconate titanate particles is 0.2 to 4%.

[0015] FIG. 1 conceptually shows an example of the piezoelectric film of the present invention. As shown in FIG. 1, the piezoelectric film 10 includes a piezoelectric layer 20, which is a sheet-like material having piezoelectric properties, a first electrode layer 24 laminated on one side of the piezoelectric layer 20, a first protective layer 28 laminated on the first electrode layer 24, a second electrode layer 26 laminated on the other side of the piezoelectric layer 20, and a second protective layer 30 laminated on the second electrode layer 26. The piezoelectric layer 20 is made of a polymer composite piezoelectric material containing piezoelectric particles 36 in a matrix 34 containing a polymer material. The first electrode layer 24 and the second electrode layer 26 are electrode layers according to the present invention. As will be described later, the piezoelectric film 10 (piezoelectric layer 20) is preferably polarized in the thickness direction.

[0016] Such piezoelectric film 10 is used, for example, in various acoustic devices (acoustic equipment) such as speakers, microphones, and pickups used in musical instruments such as guitars, to generate (reproduce) sound by vibrating in response to an electrical signal, or to convert sound vibrations into an electrical signal. In addition, the piezoelectric film can also be used in pressure sensors, power generation elements, and the like. Alternatively, the piezoelectric film can be used as an exciter by attaching it to various objects in contact with them, causing the objects to vibrate and produce sound.

[0017] In the piezoelectric film 10, the second electrode layer 26 and the first electrode layer 24 form an electrode pair. That is, the piezoelectric film 10 has a configuration in which both sides of the piezoelectric layer 20 are sandwiched between an electrode pair, i.e., the first electrode layer 24 and the second electrode layer 26, and this laminate is sandwiched between a first protective layer 28 and a second protective layer 30.

[0018] In this way, in the piezoelectric film 10, the region sandwiched between the first electrode layer 24 and the second electrode layer 26 expands and contracts in response to the applied voltage.

[0019] The first electrode layer 24 and the first protective layer 28, as well as the second electrode layer 26 and the second protective layer 30, are named according to the polarization direction of the piezoelectric layer 20. Therefore, the first electrode layer 24 and the second electrode layer 26, as well as the first protective layer 28 and the second protective layer 30, have basically the same configuration.

[0020] In addition to these layers, the piezoelectric film 10 may also have an insulating layer that covers the areas where the piezoelectric layer 20 is exposed, such as the side surfaces, to prevent short circuits.

[0021] When a voltage is applied to the first electrode layer 24 and the second electrode layer 26 of such a piezoelectric film 10, the piezoelectric particles 36 expand and contract in the polarization direction in response to the applied voltage. As a result, the piezoelectric film 10 (piezoelectric layer 20) contracts in the thickness direction. At the same time, due to the Poisson's ratio, the piezoelectric film 10 also expands and contracts in the in-plane direction. This expansion and contraction is approximately 0.01 to 0.1%. Note that the expansion and contraction is isotropic in all in-plane directions.

[0022] The thickness of the piezoelectric layer 20 is preferably about 10 to 300 μm, and therefore the expansion and contraction in the thickness direction is extremely small, at a maximum of about 0.3 μm. In contrast, the piezoelectric film 10, i.e., the piezoelectric layer 20, has a size in the planar direction that is much larger than its thickness. Therefore, for example, if the length of the piezoelectric film 10 is 20 cm, the piezoelectric film 10 will expand and contract by a maximum of about 0.2 mm when a voltage is applied. Furthermore, when pressure is applied to the piezoelectric film 10, the piezoelectric particles 36 act to generate electricity. By utilizing this, the piezoelectric film 10 can be used for various applications such as speakers, microphones, and pressure-sensitive sensors, as described above.

[0023] In the present invention, the piezoelectric particles 36 are particles containing lead zirconate titanate (PZT), and in the 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 more to the area of ​​the entire lead zirconate titanate particles 36 is 0.2 to 4%.

[0024] Fig. 2 is a conceptual diagram showing an enlarged cross section of the piezoelectric layer 20 in the thickness direction. As shown in Fig. 2, when viewed in cross section of the piezoelectric layer 20, numerous piezoelectric particles 36 are observed. Some of these piezoelectric particles 36 are regions 36b (hereinafter also referred to as high-Pb regions) where the ratio of lead to the total of lead and zirconia, Pb / (Pb+Zr), is 90% or more, and the ratio of the area of ​​the high-Pb regions 36b to the area of ​​the entire lead zirconate titanate particle 36 is 0.2 to 4%. As shown in Fig. 2, in some cases, the entirety of one piezoelectric particle is made up of this high-Pb region 36b, and in other cases, only a portion of one piezoelectric particle is made up of this high-Pb region 36b.

[0025] As mentioned above, there has been a demand for improving the conversion efficiency between electrical energy and mechanical energy, i.e., the piezoelectric performance, in piezoelectric films having a polymer composite piezoelectric element formed by dispersing piezoelectric particles in a matrix of a polymer material and electrode layers formed on both sides of the polymer composite piezoelectric element.

[0026] In response to this, the inventors have conducted research and found that lead zirconate titanate is preferably used as the piezoelectric particles because it provides higher piezoelectric performance, but that when lead zirconate titanate is used as the piezoelectric particles, a portion of the lead zirconate titanate particles 36 becomes a high-Pb region 36b with a Pb / (Pb+Zr) ratio of 90% or more. The area ratio of this high-Pb region 36b to the entire lead zirconate titanate particles 36 varies depending on the conditions for producing the piezoelectric particles, and that a lower 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) results in higher piezoelectric performance.

[0027] Therefore, in the piezoelectric film of the present invention, by setting the ratio of the area of ​​the high Pb regions 36b, where Pb / (Pb+Zr) is 90% or more, to the area of ​​the entire lead zirconate titanate particles 36 in a cross section in the thickness direction of the piezoelectric layer to 0.2 to 4%, it is possible to obtain a piezoelectric film with higher conversion efficiency between electrical energy and mechanical energy and high piezoelectric performance.

[0028] The ratio (high Pb ratio) of the high Pb regions 36b, where Pb / (Pb+Zr) is 90% or more, to the entire lead zirconate titanate particles 36 is measured as follows.

[0029] First, the piezoelectric film is attached to a support, and a coating layer is applied to the other surface. The coating layer is a smooth film with a surface thickness of several μm to several tens of μm, and is made of metal, glass, resin, etc. After confirming that the coating layer is in close contact with the sample surface, a cross-section of approximately 500 μm in width is processed using a cross-sectional ion milling device (e.g., Hitachi High-Tech IM4000PLUS). If necessary, the sample is treated to be conductive.

[0030] Using the sample after cross-section processing, composition analysis is performed using EDS (energy dispersive X-ray spectroscopy), and elemental mapping (quantitative map of atomic concentration) images are obtained. The resolution of the quantitative map image is half that of the elemental mapping image. Simultaneously, SEM (scanning electron microscope) observation images are also obtained. The acceleration voltage for EDS composition analysis and SEM imaging is 5 kV, and a BSE detector (backscattered electron detector) and an SE detector (secondary electron detector) are used for SEM image observation, and a mixed image is obtained. For example, a Bruker AXS QUANTAX FlatQUAD EDS can be used for EDS analysis, and a Hitachi High-Tech SU8220 SEM can be used for SEM observation.

[0031] The imaging magnification is 1500x, and each field of view is approximately 45μm x 60μm, and five consecutive images are acquired. In this case, five images are acquired within a 350μm width. The imaging area is 640 x 480 pixels. SEM and mapping images of the same field of view are acquired and saved as text.

[0032] From the acquired SEM image, an image of only particles is extracted using ImageJ, and the area ratio of the region where the Pb / (Pb+Zr) ratio is 90% or more is calculated.

[0033] Specifically, import the SEM image saved in text format into ImageJ, extract the area of ​​the piezoelectric layer that does not contain the electrodes, and apply Gaussian Blur. Measure the mean gray value and standard deviation, and enter the mean gray value in Subtract and the standard deviation in Divide to normalize the gray value of the entire image to a mean of 0 and a standard deviation of 1. Open Threshold on the same image. Check Dark Background, check Select the area with higher brightness (make low-brightness areas the background), select and apply Otsu, and obtain a particle image by binarizing. Save the resulting image as a text file.

[0034] The EDS mapping data for lead (Pb) and zirconia (Zr) obtained from the same field of view as the SEM image above was converted into a text file, processed with Gaussian Blur in ImageJ, and saved as a text file.

[0035] The text files of the SEM image and EDS mapping are read, and pixels corresponding to particles in the SEM image with Pb=5atm% or less are excluded, and Pb / (Pb+Zr)×100% is calculated for each pixel.

[0036] A histogram is created for the calculated Pb / (Pb+Zr), and the area ratio of the region where the ratio is 90% or more is calculated.

[0037] From the viewpoints of obtaining higher piezoelectric performance and manufacturing costs, the area ratio (high Pb ratio) of the high Pb regions 36b, where Pb / (Pb+Zr) is 90% or more, to the entire lead zirconate titanate particle 36 is preferably 0.2 to 3.5%, and more preferably 0.2 to 3%.

[0038] In order to obtain higher piezoelectric performance, the lead zirconate titanate contained in the lead zirconate titanate particles 36 as a whole is represented by the general formula Pb(Zr XTi 1-X )O3, and X is preferably 0.52±0.1.

[0039] The composition of the lead zirconate titanate contained in the piezoelectric particles 36 is determined by peeling off the protective layer and electrode layer, scraping the piezoelectric particles from the piezoelectric layer, ashing the piezoelectric particles, and then performing quantitative analysis and measurement using ICP (inductively coupled plasma) optical emission spectroscopy.

[0040] <Piezoelectric layer> The piezoelectric layer is a layer made of a polymer composite piezoelectric material containing piezoelectric particles in a matrix containing a polymer material, and is a layer that exhibits a piezoelectric effect of expanding and contracting when a voltage is applied.

[0041] In a preferred embodiment of the piezoelectric film 10, the piezoelectric layer 20 is made of a polymer composite piezoelectric material in which piezoelectric particles 36 are dispersed in a matrix 34 made of a polymer material that has viscoelasticity at room temperature. In this specification, "room temperature" refers to a temperature range of approximately 0 to 50°C.

[0042] The piezoelectric film 10 of the present invention is suitable for use in flexible speakers, such as speakers for flexible displays. The polymer composite piezoelectric material (piezoelectric layer 20) used in flexible speakers preferably satisfies the following requirements: Therefore, it is preferable to use a polymer material that has viscoelasticity at room temperature as a material that satisfies the following requirements.

[0043] (i) Flexibility For example, when a portable piezoelectric material is held loosely bent like a newspaper or magazine, it is constantly subjected to relatively slow, large bending deformation from the outside at frequencies below a few Hz. If the polymer composite piezoelectric material is too hard, a correspondingly large bending stress will be generated, which can lead to cracks at the interface between the polymer matrix and the piezoelectric particles, eventually leading to fracture. Therefore, polymer composite piezoelectric materials must be moderately flexible. Furthermore, if the strain energy can be diffused to the outside as heat, stress can be alleviated. Therefore, the loss tangent of the polymer composite piezoelectric material must be moderately large.

[0044] (ii) Sound quality Speakers vibrate piezoelectric particles at frequencies in the audio band between 20 Hz and 20 kHz, and the resulting vibration energy causes the entire polymer composite piezoelectric material (piezoelectric film) to vibrate as a unit, reproducing sound. Therefore, polymer composite piezoelectric materials must have an appropriate level of hardness to increase the efficiency of vibration energy transmission. Furthermore, if the frequency characteristics of a speaker are smooth, the amount of change in sound quality when the lowest resonance frequency changes with changes in curvature will also be small. Therefore, the loss tangent of a polymer composite piezoelectric material must be appropriately large.

[0045] In summary, polymer composite piezoelectric materials are required to be rigid in response to vibrations between 20 Hz and 20 kHz, and flexible in response to vibrations below a few Hz. In addition, the loss tangent of the polymer composite piezoelectric material is required to be appropriately large for vibrations of all frequencies below 20 kHz.

[0046] In general, polymer solids have a viscoelastic relaxation mechanism, and large-scale molecular motion is observed as a decrease (relaxation) in the storage modulus (Young's modulus) or a maximum (absorption) in the loss modulus with increasing temperature or decreasing frequency. Among these, relaxation caused by the micro-Brownian motion of molecular chains in the amorphous region is called primary dispersion, and a very large relaxation phenomenon is observed. The temperature at which this primary dispersion occurs is the glass transition point (Tg), where the viscoelastic relaxation mechanism is most prominent.

[0047] In the polymer composite piezoelectric body (piezoelectric layer 20), by using a polymer material whose glass transition point is at room temperature, in other words, a polymer material that has viscoelasticity at room temperature, as the matrix, a polymer composite piezoelectric body that behaves hard to vibrations of 20 Hz to 20 kHz and soft to slow vibrations of a few Hz or less is realized. In particular, in order to favorably exhibit this behavior, it is preferable to use a polymer material whose glass transition point at a frequency of 1 Hz is at room temperature, i.e., 0 to 50°C, as the matrix of the polymer composite piezoelectric body.

[0048] Various known polymeric materials having viscoelasticity at room temperature can be used. Preferably, a polymeric material is used that has a maximum loss tangent (Tanδ) of 0.5 or more at a frequency of 1 Hz in a dynamic viscoelasticity test at room temperature, i.e., 0 to 50°C. This reduces stress concentration at the interface between the polymer matrix and the piezoelectric particles at the maximum bending moment when the polymer composite piezoelectric element is slowly bent by an external force, and high flexibility can be expected.

[0049] Furthermore, it is preferable that the polymer material having viscoelasticity at room temperature has a storage modulus (E') at a frequency of 1 Hz measured by dynamic viscoelasticity measurement of 100 MPa or more at 0° C. and 10 MPa or less at 50° C. This reduces the bending moment that occurs when the polymer composite piezoelectric body is slowly bent by an external force, and allows the body to behave rigidly against acoustic vibrations of 20 Hz to 20 kHz.

[0050] Furthermore, it is more preferable for a polymer material that has viscoelasticity at room temperature to have a relative dielectric constant of 10 or more at 25°C. This allows a higher electric field to be applied to the piezoelectric particles in the polymer matrix when a voltage is applied to the polymer composite piezoelectric, and a large amount of deformation can be expected. However, on the other hand, in order to ensure good moisture resistance, it is also preferable for the polymer material to have a relative dielectric constant of 10 or less at 25°C.

[0051] Examples of polymeric materials that satisfy these conditions and have viscoelasticity at room temperature include cyanoethylated polyvinyl alcohol (cyanoethylated PVA), polyvinyl acetate, polyvinylidene chloride-co-acrylonitrile, polystyrene-vinyl polyisoprene block copolymer, polyvinyl methyl ketone, and polybutyl methacrylate. Commercially available products such as Hybrar 5127 (manufactured by Kuraray Co., Ltd.) can also be used. Of these, it is preferable to use a material having a cyanoethyl group as the polymeric material, and cyanoethylated PVA is particularly preferable. These polymeric materials may be used alone or in combination (mixture) of multiple types.

[0052] Matrix 34 using such a polymeric material having viscoelasticity at room temperature may contain a plurality of polymeric materials in combination as needed. That is, in addition to a viscoelastic material such as cyanoethylated PVA, other dielectric polymeric materials may be added to matrix 34 as needed for the purpose of adjusting the dielectric properties and mechanical properties.

[0053] Examples of the dielectric polymer material that can be added include fluorine-based polymers such as polyvinylidene fluoride, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, polyvinylidene fluoride-trifluoroethylene copolymer, and polyvinylidene fluoride-tetrafluoroethylene copolymer, vinylidene cyanide-vinyl acetate copolymer, cyanoethyl cellulose, cyanoethyl hydroxysucrose, cyanoethyl hydroxycellulose, cyanoethyl hydroxypullulan, cyanoethyl methacrylate, cyanoethyl acrylate, Examples include polymers having a cyano group or a cyanoethyl group, such as 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, and cyanoethyl sorbitol, as well as synthetic rubbers such as nitrile rubber and chloroprene rubber. Among these, polymeric materials having a cyanoethyl group are preferably used.

[0054] Furthermore, the dielectric polymer added to the matrix 34 of the piezoelectric layer 20 in addition to the material having viscoelasticity at room temperature, such as cyanoethylated PVA, is not limited to one type, and multiple types may be added.

[0055] In addition to the dielectric polymer, in order to adjust the glass transition temperature Tg, thermoplastic resins such as vinyl chloride resin, polyethylene, polystyrene, methacrylic resin, polybutene, and isobutylene, and thermosetting resins such as phenolic resin, urea resin, melamine resin, alkyd resin, and mica may be added to the matrix 34. Furthermore, in order to improve adhesion, tackifiers such as rosin ester, rosin, terpene, terpene phenol, and petroleum resin may be added.

[0056] When a material other than a viscoelastic polymer material such as cyanoethylated PVA is added to the matrix 34 of the piezoelectric layer 20, there is no particular limitation on the amount of the material added, but it is preferable that the amount be 30 mass % or less in terms of the ratio to the matrix 34. This allows the properties of the added polymer material to be expressed without impairing the viscoelastic relaxation mechanism in the matrix 34, thereby achieving favorable results in terms of increasing the dielectric constant, improving heat resistance, and improving adhesion between the piezoelectric particles 36 and the electrode layer.

[0057] The piezoelectric layer 20 is a polymer composite piezoelectric material that contains piezoelectric particles 36 in such a matrix 34 .

[0058] The piezoelectric particles 36 are made of ceramic particles having a perovskite or wurtzite crystal structure. As described above, in the present invention, lead zirconate titanate (PZT) is used as the ceramic particles constituting the piezoelectric particles 36. The piezoelectric particles 36 may also contain piezoelectric particles made of other materials, such as lead lanthanum zirconate titanate (PLZT), barium titanate (BaTiO3), zinc oxide (ZnO), and a solid solution of barium titanate and bismuth ferrite (BiFe3) (BFBT).

[0059] There are no limitations on the particle size of the piezoelectric particles 36, and it may be selected appropriately depending on the size of the piezoelectric film 10 and the intended use of the piezoelectric film 10. The particle size of the piezoelectric particles 36 is preferably 1 to 10 μm. By setting the particle size of the piezoelectric particles 36 within this range, favorable results can be obtained in that the piezoelectric film 10 can achieve both high piezoelectric properties and flexibility.

[0060] 1, the piezoelectric particles 36 are shown as spherical, but the piezoelectric particles 36 are not limited to being perfectly spherical and may have various shapes. For example, as shown in FIG. 2, the piezoelectric particles 36 may have corners.

[0061] 1, the piezoelectric particles 36 in the piezoelectric layer 20 are uniformly and regularly dispersed in the matrix 34, but the present invention is not limited to this. That is, as shown in FIG. 2, the piezoelectric particles 36 in the piezoelectric layer 20 may be irregularly dispersed in the matrix 34, as long as they are preferably uniformly dispersed.

[0062] 1, the particle size of the piezoelectric particles 36 is shown as being uniform, but the present invention is not limited to this. That is, as shown in FIG. 2, the particle size of the piezoelectric particles 36 in the piezoelectric layer 20 may be non-uniform.

[0063] In the piezoelectric film 10, there are no limitations on the quantitative ratio of the matrix 34 to the piezoelectric particles 36 in the piezoelectric layer 20, and this may be set appropriately depending on the size and thickness of the piezoelectric film 10 in the plane direction, the application of the piezoelectric film 10, and the properties required of the piezoelectric film 10. The volume fraction of the piezoelectric particles 36 in the piezoelectric layer 20 is preferably 30 to 80%, more preferably 50% or more, and therefore even more preferably 50 to 80%. By setting the quantitative ratio of the matrix 34 to the piezoelectric particles 36 within the above range, favorable results can be obtained in terms of achieving both high piezoelectric properties and flexibility.

[0064] In a preferred embodiment of the piezoelectric film 10 described above, the piezoelectric layer 20 is a polymer composite piezoelectric layer formed by dispersing piezoelectric particles in a viscoelastic matrix containing a polymer material that has viscoelasticity at room temperature. However, the present invention is not limited to this, and a polymer composite piezoelectric material formed by dispersing piezoelectric particles in a matrix containing a polymer material, which is used in known piezoelectric elements, can be used as the piezoelectric layer.

[0065] There are no particular limitations on the thickness of the piezoelectric layer 20, and it may be set appropriately depending on the application of the piezoelectric film 10 and the properties required of the piezoelectric film 10. A thicker piezoelectric layer 20 is advantageous in terms of rigidity, such as the stiffness of the sheet-like material, but the voltage (potential difference) required to expand or contract the piezoelectric film 10 by the same amount increases. The thickness of the piezoelectric layer 20 is preferably 10 to 300 μm, more preferably 20 to 200 μm, and even more preferably 30 to 150 μm. By setting the thickness of the piezoelectric layer 20 within the above range, favorable results can be obtained in terms of ensuring both rigidity and appropriate flexibility.

[0066] <Protective layer> In the piezoelectric film 10, the first protective layer 28 and the second protective layer 30 cover the second electrode layer 26 and the first electrode layer 24, and also serve to provide the piezoelectric layer 20 with appropriate rigidity and mechanical strength. That is, in the piezoelectric film 10, the piezoelectric layer 20, which is made up of the matrix 34 and the piezoelectric particles 36, exhibits excellent flexibility with respect to slow bending deformation, but may lack rigidity or mechanical strength depending on the application. The first protective layer 28 and the second protective layer 30 are provided in the piezoelectric film 10 to compensate for this.

[0067] There are no limitations on the first protective layer 28 and the second protective layer 30, and various sheet-like materials can be used, with various resin films being preferred examples. Among these, resin films made of polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS), polycarbonate (PC), polyphenylene sulfite (PPS), polymethyl methacrylate (PMMA), polyetherimide (PEI), polyimide (PI), polyethylene naphthalate (PEN), triacetyl cellulose (TAC), cyclic olefin resins, and the like are preferred because of their excellent mechanical properties and heat resistance.

[0068] There are no limitations on the thickness of the first protective layer 28 and the second protective layer 30. The thicknesses of the first protective layer 28 and the second protective layer 30 are basically the same, but may be different. If the rigidity of the first protective layer 28 and the second protective layer 30 is too high, not only will it restrict the expansion and contraction of the piezoelectric layer 20, but it will also impair flexibility. Therefore, except in cases where mechanical strength or good handleability as a sheet-like material is required, it is more advantageous for the first protective layer 28 and the second protective layer 30 to be thinner.

[0069] In the piezoelectric film 10, if the thickness of the first protective layer 28 and the second protective layer 30 is not more than twice the thickness of the piezoelectric layer 20, favorable results can be obtained in terms of ensuring both rigidity and appropriate flexibility. For example, if the thickness of the piezoelectric layer 20 is 50 μm and the first protective layer 28 and the second protective layer 30 are made 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 even more preferably 25 μm or less.

[0070] <Electrode layer> In the piezoelectric film 10, a first electrode layer 24 is formed between the piezoelectric layer 20 and the first protective layer 28, and a 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).

[0071] In the present invention, there are no limitations on the materials for forming the first electrode layer 24 and the second electrode layer 26, and various conductors can be used. Specific examples 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. Of these, copper, aluminum, gold, silver, platinum, and indium tin oxide are preferred examples of materials for the first electrode layer 24 and the second electrode layer 26.

[0072] There are also no limitations on the method for forming the first electrode layer 24 and the second electrode layer 26, and various known methods can be used, such as vapor phase deposition methods (vacuum film formation methods) such as vacuum deposition, ion-assisted deposition, and sputtering, film formation by plating, or a method of adhering a foil formed from the above-mentioned materials.

[0073] Among these, thin films of copper, aluminum, or the like formed by vacuum deposition are particularly suitable for use as the first electrode layer 24 and the second electrode layer 26, because they can ensure the flexibility of the piezoelectric film 10. Among these, thin films of copper formed by vacuum deposition are particularly suitable for use.

[0074] There is no limitation on the thickness of the first electrode layer 24 and the second electrode layer 26. Furthermore, the thickness of the first electrode layer 24 and the second electrode layer 26 is basically the same, but may be different.

[0075] Here, similar to the first protective layer 28 and second protective layer 30 described above, if the first electrode layer 24 and the second electrode layer 26 are too rigid, not only will they restrict the expansion and contraction of the piezoelectric layer 20, but their flexibility will also be impaired. Therefore, from the standpoints of flexibility and piezoelectric properties, it is more advantageous for the first electrode layer 24 and the second electrode layer 26 to be thinner. In other words, the first electrode layer 24 and the second electrode layer 26 are preferably thin-film electrodes.

[0076] The thickness of the first electrode layer 24 and the second electrode layer 26 is thinner than the protective layer, and is preferably 0.05 μm to 10 μm, more preferably 0.05 μm to 5 μm, even more preferably 0.08 μm to 3 μm, and particularly preferably 0.1 μm to 2 μm.

[0077] Here, in the piezoelectric film 10, it is preferable that the product of the thickness and Young's modulus of the first electrode layer 24 and the second electrode layer 26 is less than the product of the thickness and Young's modulus of the first protective layer 28 and the second protective layer 30, since this does not significantly impair flexibility.

[0078] For example, in the case of 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 are made of copper (Young's modulus: approximately 130 GPa), if the thickness of the first protective layer 28 and the second protective layer 30 is 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 especially preferably 0.1 μm or less.

[0079] As described above, the piezoelectric film 10 preferably has a configuration in which a piezoelectric layer 20, which is formed by dispersing piezoelectric particles 36 in a matrix 34 containing a polymeric material that has viscoelasticity at room temperature, is sandwiched between a first electrode layer 24 and a second electrode layer 26, and this laminate is further sandwiched between a first protective layer 28 and a second protective layer 30.

[0080] In such piezoelectric film 10, the loss tangent (Tan δ) at a frequency of 1 Hz measured by dynamic viscoelasticity measurement preferably has a maximum value at room temperature, and more preferably a maximum value of 0.1 or greater at room temperature. This allows the strain energy to be effectively diffused to the outside as heat, even when piezoelectric film 10 is subjected to a relatively slow, large bending deformation at a frequency of a few Hz or less from the outside, thereby preventing cracks from occurring at the interface between the polymer matrix and the piezoelectric particles.

[0081] The piezoelectric film 10 preferably has a storage 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. This condition also applies to the piezoelectric layer 20. This allows the piezoelectric film 10 to have a large frequency dispersion in the storage modulus (E'). In other words, it behaves hard against vibrations of 20 Hz to 20 kHz and soft against vibrations of a few Hz or less.

[0082] The piezoelectric film 10 has a thickness multiplied by a storage modulus (E') at a frequency of 1 Hz measured by dynamic viscoelasticity measurement of 1.0×10 6 ~2.0×10 6 N / m, 1.0 x 10 at 50°C5 ~1.0×10 6 N / m. This condition also applies to the piezoelectric layer 20. This allows the piezoelectric film 10 to have appropriate rigidity and mechanical strength without impairing its flexibility and acoustic properties.

[0083] Furthermore, the piezoelectric film 10 preferably has a loss tangent (Tanδ) of 0.05 or more at 25°C and a frequency of 1 kHz in a master curve obtained from dynamic viscoelasticity measurement. This condition also applies to the piezoelectric layer 20. This smooths the frequency characteristics of a speaker using the piezoelectric film 10, and reduces the amount of change in sound quality when the minimum resonance frequency f0 changes with a change in the speaker curvature.

[0084] In the present invention, the storage modulus (Young's modulus) and loss tangent of the piezoelectric film 10, the piezoelectric layer 20, etc. may be measured by a known method, such as a dynamic viscoelasticity measuring device DMS6100 manufactured by SII NanoTechnology Inc.

[0085] Examples of 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 to 150°C, a temperature rise rate of 2°C / min (in a nitrogen atmosphere), a sample size of 40 mm x 10 mm (including the clamping area), and a chuck distance of 20 mm.

[0086] An example of a method for manufacturing the piezoelectric film 10 will now be described with reference to FIGS.

[0087] 3, a sheet-like material 10a is prepared in which a first electrode layer 24 is formed on a first protective layer 28. This sheet-like material 10a may be produced by forming a copper thin film or the like as the first electrode layer 24 on the surface of the first protective layer 28 by vacuum deposition, sputtering, plating, or the like. If the first protective layer 28 is very thin and difficult to handle, a separator (temporary support) may be used as needed. The separator may be made of PET or the like having a thickness of 25 μm to 100 μm. The separator may be removed after the second electrode layer 26 and the second protective layer 30 are thermocompression bonded together and before any other member is laminated on the first protective layer 28.

[0088] On the other hand, the piezoelectric particles 36 are produced. First, the starting materials are prepared by mixing powders of Pb oxide, Zr oxide, and Ti oxide, which are the main components, in a ratio that corresponds to the overall composition of the piezoelectric particles. The overall composition of the piezoelectric particles and the composition of the piezoelectric particles excluding the high-Pb region are approximately the same as the composition of this starting powder.

[0089] The raw material powder is prepared by wet mixing using a ball mill or the like to form mixed particles. After drying, the mixed particles are placed in a crucible or the like and fired. The average particle size of the mixed particles can be adjusted by the wet mixing time, the rotation speed of the ball mill, etc.

[0090] In the present invention, the ratio of the high Pb region to the lead zirconate titanate particles is adjusted by appropriately adjusting the average particle size of the mixed particles, the firing temperature, and other factors.

[0091] Specifically, if the average particle size of the mixed particles is too large, the proportion of high-Pb regions tends to increase, while if the average particle size of the mixed particles is too small, the piezoelectric properties deteriorate. From these points of view, the average particle size of the mixed particles is preferably 1 μm to 10 μm, more preferably 1.2 μm to 8 μm, and even more preferably 1.5 μm to 6 μm.

[0092] The average particle size of the mixed particles before firing may be determined as the volume average diameter MV value using a laser scattering particle size measuring device or the like.

[0093] If the firing temperature is too low, the components are not mixed sufficiently, and the proportion of high-Pb regions tends to increase, while if the firing temperature is too high, the fired particles become too large. From this point of view, the firing temperature is preferably 600°C to 1200°C, more preferably 700°C to 1150°C, and even more preferably 700°C to 1100°C.

[0094] If the firing time is too short, the components will not be mixed thoroughly, and the proportion of high-Pb regions will tend to increase, while if the firing time is too long, the fired particles will become too large. From this point of view, the firing temperature is preferably 1 to 200 hours, more preferably 2 to 170 hours, and even more preferably 2 to 150 hours.

[0095] After the firing is completed, the produced piezoelectric particles are crushed as needed. Crushing can be performed by a known method such as a method using a ball mill or a method in which the particles are placed on a mesh and pressure is applied from above to pass through the mesh.

[0096] Next, the paint for the piezoelectric layer is prepared by dissolving a polymeric material that will be the matrix material in an organic solvent, adding the piezoelectric particles 36, and stirring to disperse the mixture. There are no limitations on the organic solvent other than the above substances, and various organic solvents can be used.

[0097] After preparing the sheet material 10a and the paint, the paint is cast (applied) onto the sheet material 10a, and the organic solvent is evaporated to dry it, thereby producing a laminate 10b having a first electrode layer 24 on a first protective layer 28 and a piezoelectric layer 20 formed on the first electrode layer 24, as shown in FIG.

[0098] There is no limitation on the method for casting this coating material, and all known methods (coating devices) such as a slide coater and a doctor knife can be used.

[0099] As described above, in the piezoelectric film 10, a dielectric polymer material may be added to the matrix 34 in addition to the viscoelastic material such as cyanoethylated PVA. When adding these polymeric materials to the matrix 34, the polymeric materials to be added may be dissolved in the paint described above.

[0100] After fabricating the laminate 10b having the first electrode layer 24 on the first protective layer 28 and the piezoelectric layer 20 formed on the first electrode layer 24, the piezoelectric layer 20 is preferably subjected to polarization treatment (poling). There are no limitations on the method for poling the piezoelectric layer 20, and any known method can be used.

[0101] Before the polarization treatment, the surface of the piezoelectric layer 20 may be smoothed by a calender treatment using a heated roller or the like. By performing the calender treatment, the thermocompression bonding step described below can be carried out smoothly.

[0102] While the piezoelectric layer 20 of the laminate 10b is polarized in this manner, a sheet-like material 10c is prepared in which a second electrode layer 26 is formed on the second protective layer 30. The sheet-like material 10c may be produced by forming a copper thin film or the like as the second electrode layer 26 on the surface of the second protective layer 30 by vacuum deposition, sputtering, plating, or the like.

[0103] Next, as shown in FIG. 5, the sheet-like material 10c is laminated on the laminate 10b whose piezoelectric layer 20 has been subjected to polarization treatment, with the second electrode layer 26 facing the piezoelectric layer 20. Furthermore, the laminate of the laminate 10b and the sheet-like material 10c is thermocompressed with a heat press or a pair of heating rollers so as to sandwich the second protective layer 30 and the first protective layer 28, to produce the piezoelectric film 10. After thermocompression bonding, the laminate may be cut into a desired shape.

[0104] The steps up to this point can be performed using a web-like material, i.e., a long, continuous sheet wound up, while transporting it. The laminate 10b and the sheet-like material 10c can also be thermocompression bonded as described above while both are in web form. In this case, the piezoelectric film 10 is produced in web form at this point.

[0105] Furthermore, an adhesive layer may be provided when bonding the laminate 10b and the sheet-like material 10c together. 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 made of the same material as the matrix 34. The same material may be applied to the piezoelectric layer 20, or may be applied to the surface of the second electrode layer 26 and then bonded together.

[0106] Here, a typical piezoelectric film made of a polymer material such as PVDF (Polyvinylidene DiFluoride) has in-plane anisotropy in its piezoelectric properties, and there is anisotropy in the amount of expansion and contraction in the plane direction when a voltage is applied.

[0107] In contrast, the piezoelectric layer of the piezoelectric film of the present invention, which is made of a polymer composite piezoelectric material containing piezoelectric particles in a matrix containing a polymer material, has no in-plane anisotropy in its piezoelectric properties and expands and contracts isotropically in all in-plane directions. This type of isotropically expanding and contracting two-dimensionally can vibrate with greater force than common piezoelectric films such as PVDF, which only expand and contract in one direction, and can generate louder, more beautiful sounds.

[0108] Furthermore, for example, by adhering the piezoelectric film of the present invention to a flexible display device such as a flexible organic electroluminescence display or a flexible liquid crystal display, it can also be used as a speaker for the display device.

[0109] Furthermore, for example, when the piezoelectric film 10 is used in a speaker, it may be used to generate sound by the vibration of the film-like piezoelectric film 10 itself. Alternatively, the piezoelectric film 10 may be attached to a diaphragm and used as an exciter that generates sound by vibrating the diaphragm with the vibration of the piezoelectric film 10.

[0110] Furthermore, by laminating a plurality of piezoelectric films 10 of the present invention to form a laminated piezoelectric element, the film 10 also functions favorably as a piezoelectric vibration element that vibrates a vibrated body such as a vibration plate.

[0111] 6, a speaker may be formed by adhering a laminated piezoelectric element 50 formed by laminating piezoelectric films 10 to a diaphragm 12, and vibrating the diaphragm 12 with the laminated piezoelectric films 10 to output sound. That is, in this case, the laminated piezoelectric films 10 acts as a so-called exciter that vibrates the diaphragm 12 to output sound.

[0112] When a drive voltage is applied to a laminated piezoelectric element 50 made up of stacked piezoelectric films 10, each piezoelectric film 10 expands and contracts in its plane, and the expansion and contraction of each piezoelectric film 10 causes the entire laminate of piezoelectric films 10 to expand and contract in its plane. The expansion and contraction of the laminated piezoelectric element 50 in its plane causes the diaphragm 12 to which the laminate is attached to bend, causing the diaphragm 12 to vibrate in its thickness direction. This vibration in the thickness direction causes the diaphragm 12 to generate sound. The diaphragm 12 vibrates in accordance with the magnitude of the drive voltage applied to the piezoelectric film 10, and generates sound in accordance with the drive voltage applied to the piezoelectric film 10. Therefore, at this time, the piezoelectric film 10 itself does not output sound.

[0113] Even if each individual piezoelectric film 10 has low rigidity and small stretching force, the laminated piezoelectric element 50 formed by stacking piezoelectric films 10 has high rigidity, and the laminate as a whole has a large stretching force. As a result, even if the diaphragm has a certain degree of rigidity, the laminated piezoelectric element 50 formed by stacking piezoelectric films 10 can sufficiently deflect the diaphragm 12 with a large force, causing the diaphragm 12 to vibrate sufficiently in the thickness direction, and causing the diaphragm 12 to generate sound.

[0114] In the laminated piezoelectric element 50 in which piezoelectric films 10 are laminated, there is no limit to the number of laminated piezoelectric films 10, and the number may be appropriately set to obtain a sufficient amount of vibration depending on, for example, the rigidity of the vibrating diaphragm 12. Note that a single piezoelectric film 10 can also be used as a similar exciter (piezoelectric vibration element) as long as it has sufficient stretching force.

[0115] There are no limitations on the diaphragm 12 that is vibrated by the laminated piezoelectric element 50 formed by laminating piezoelectric films 10, and various sheet-like materials (plate-like materials, films) can be used. Examples include resin films made of polyethylene terephthalate (PET) or the like, foamed plastics made of expanded polystyrene or the like, paper materials such as cardboard, glass plates, and wood. Furthermore, various devices such as display devices such as organic electroluminescence displays and liquid crystal displays may be used as the diaphragm as long as they can be sufficiently deflected.

[0116] In the multilayer piezoelectric element 50 formed by laminating piezoelectric films 10, adjacent piezoelectric films 10 are preferably bonded together with an adhesive layer 19 (adhesive). In addition, the multilayer piezoelectric element 50 and the diaphragm 12 are also preferably bonded together with an adhesive layer 16.

[0117] There are no limitations on the adhesive layer, and various types of layers that can bond objects to each other can be used. Therefore, the adhesive layer may be made of a pressure-sensitive adhesive or an adhesive. Preferably, an adhesive layer is used that provides a solid, hard adhesive layer after bonding. The above points also apply to a laminate formed by folding back a long piezoelectric film 10, which will be described later.

[0118] In a multilayer piezoelectric element 50 in which piezoelectric films 10 are stacked, there are no restrictions on the polarization direction of each of the stacked piezoelectric films 10. The piezoelectric film 10 of the present invention is preferably polarized in the thickness direction. Here, the polarization direction of the piezoelectric film 10 refers to the thickness direction. Therefore, in the multilayer piezoelectric element 50, the polarization direction may be the same for all of the piezoelectric films 10, or there may be piezoelectric films with different polarization directions.

[0119] In a laminated piezoelectric element 50 in which piezoelectric films 10 are stacked, the piezoelectric films 10 are preferably stacked so that the polarization directions of adjacent piezoelectric films 10 are opposite to each other. In the piezoelectric film 10, the polarity of the voltage applied to the piezoelectric layer 20 corresponds to the polarization direction of the piezoelectric layer 20. Therefore, whether the polarization direction is from the second electrode layer 26 to the first electrode layer 24 or from the first electrode layer 24 to the second electrode layer 26, the polarity of the second electrode layer 26 and the polarity of the first electrode layer 24 are the same in all of the stacked piezoelectric films 10. Therefore, by having the polarization directions opposite to each other in adjacent piezoelectric films 10, even if the electrode layers of adjacent piezoelectric films 10 come into contact with each other, the contacting electrode layers have the same polarity, so there is no risk of short-circuiting.

[0120] 7, a multilayer piezoelectric element formed by stacking piezoelectric films 10 may be configured by folding back a piezoelectric film 10L one or more times, preferably multiple times, to stack multiple piezoelectric films 10. A multilayer piezoelectric element 56 formed by folding back and stacking piezoelectric films 10 has the following advantages.

[0121] In a laminate in which multiple cut-sheet piezoelectric films 10 are stacked, the second electrode layer 26 and the first electrode layer 24 of each piezoelectric film must be connected to a drive power supply. In contrast, in a configuration in which a long piezoelectric film 10L is folded and stacked, the laminated piezoelectric element 56 can be formed using only one long piezoelectric film 10L. Therefore, in a configuration in which a long piezoelectric film 10L is folded and stacked, only one power supply is required to apply a drive voltage, and further, electrodes from the piezoelectric film 10L only need to be drawn out from one location. Furthermore, in a configuration in which a long piezoelectric film 10L is folded and stacked, the polarization directions of adjacent piezoelectric films are inevitably opposite to each other.

[0122] Such a laminated piezoelectric element, in which a piezoelectric film having an electrode layer and a protective layer provided on both sides of a piezoelectric layer made of a polymer composite piezoelectric material is laminated, is described in International Publication No. 2020 / 095812 and International Publication No. 2020 / 179353, among others.

[0123] The piezoelectric film of the present invention has been described in detail above, but the present invention is not limited to the above examples, and various improvements and modifications may be made within the scope of the present invention. [Example]

[0124] The present invention will be described in more detail below with reference to specific examples of the present invention. However, the present invention is not limited to these examples, and the materials, amounts used, ratios, processing details, processing procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention.

[0125] [Example 1] Sheets 10a and 10c were prepared by forming a 100 nm thick copper thin film on a 4 μm thick PET film by sputtering. That is, in this example, first electrode layer 24 and second electrode layer 26 were 100 nm thick copper thin films, and first protective layer 28 and second protective layer 30 were 4 μm thick PET films. To ensure good handling during the process, the PET film used had a 50 μm thick separator (PET temporary support), and the separators of each protective layer were removed after the sheet-like material 10c was thermocompression bonded.

[0126] On the other hand, as starting materials, powders of the main components, Pb oxide, Zr oxide, and Ti oxide, were wet mixed in ethanol in a ball mill for 12 hours. The amounts of each oxide were 1 mole of Pb, 0.52 moles of Zr, and 0.48 moles of Ti. The ball mill rotation speed was 60 rpm. This mixing resulted in the formation of mixed particles. The average particle size of the mixed particles was 1.5 μm.

[0127] Next, the resulting mixed particles were fired at 800° C. for 5 hours.

[0128] Next, cyanoethylated PVA (CR-V, manufactured by Shin-Etsu Chemical Co., Ltd.) was dissolved in methyl ethyl ketone (MEK) at the following composition ratio: Then, the piezoelectric particles obtained above were added to this solution at the following composition ratio and dispersed using a propeller mixer (rotation speed: 2000 rpm) to prepare a coating material for forming the piezoelectric layer 20. ·PZT particles 300 parts by mass Cyanoethylated PVA 15 parts by mass ·MEK·················85 parts by mass

[0129] The previously prepared coating material for forming the piezoelectric layer 20 was applied using a slide coater onto the first electrode layer 24 (thin copper film) of the previously prepared sheet material 10a. The coating material was applied so that the thickness of the coating film after drying would be 20 μm.

[0130] Next, the sheet-like material 10a with the coating applied thereon was placed on a hot plate at 120° C. to heat and dry the coating, thereby evaporating the MEK and forming a laminate 10b.

[0131] Next, the sheet-like material 10c was laminated on the laminate 10b with the second electrode layer 26 (thin copper film side) facing the piezoelectric layer 20, and thermocompression bonded at 120°C. In this way, a piezoelectric film 10 was produced, which had 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.

[0132] The area ratio (high Pb ratio) of high Pb regions where Pb / (Pb+Zr) is 90% or more relative to the lead zirconate titanate particles in the piezoelectric layer 20 of the produced piezoelectric film 10 was determined using the method described above, and the high Pb ratio was 4.0%. Furthermore, the composition of the lead zirconate titanate contained in the piezoelectric particles 36 was determined by peeling off the protective layer and electrode layer, scraping the piezoelectric particles from the piezoelectric layer, ashing the piezoelectric particles, and then quantitatively analyzing and measuring them using ICP (inductively coupled plasma) optical emission spectroscopy, which revealed that Zr / (Zr+Ti)=X was 0.54.

[0133] [Example 2] Except for changing the firing time of the mixed particles that become the piezoelectric particles to 10 hours, a piezoelectric film was produced in the same manner as in Example 1. The high Pb ratio in the produced piezoelectric film was 2.5%.

[0134] [Example 3] Except for changing the firing time of the mixed particles that become the piezoelectric particles to 100 hours, a piezoelectric film was produced in the same manner as in Example 1. The high Pb ratio in the produced piezoelectric film was 1.0%.

[0135] [Example 4] Except for changing the firing time of the mixed particles that become the piezoelectric particles to 200 hours, a piezoelectric film was produced in the same manner as in Example 1. The high Pb ratio in the produced piezoelectric film was 0.5%.

[0136] [Example 5] A piezoelectric film was produced in the same manner as in Example 3, except that the firing temperature of the mixed particles that became the piezoelectric particles was set to 1000° C. The high Pb ratio in the produced piezoelectric film was 0.2%.

[0137] [Example 6] A piezoelectric film was produced in the same manner as in Example 3, except that the ball mill rotation speed during wet mixing of the raw material powders that would become the piezoelectric particles was set to 20 rpm. The average particle size of the mixed particles was 3.3 μm. The high Pb ratio in the produced piezoelectric film was 2.5%.

[0138] [Example 7] A piezoelectric film was produced in the same manner as in Example 6, except that the firing temperature of the mixed particles that became the piezoelectric particles was set to 1000° C. The high Pb ratio in the produced piezoelectric film was 1.0%.

[0139] [Comparative Example 1] Except for changing the firing time of the mixed particles that become the piezoelectric particles to 2 hours, a piezoelectric film was produced in the same manner as in Example 1. The high Pb ratio in the produced piezoelectric film was 4.5%.

[0140] Comparative Example 2 A piezoelectric film was produced in the same manner as in Example 1, except that the ball mill rotation speed during wet mixing of the raw material powders that would become the piezoelectric particles was set to 20 rpm. The average particle size of the mixed particles was 3.3 μm. The high Pb ratio in the produced piezoelectric film was 8.0%.

[0141] Comparative Example 3 A piezoelectric film was produced in the same manner as in Example 7, except that the mixed particles that would become the piezoelectric particles were fired for 5 hours. The high Pb ratio in the produced piezoelectric film was 5.0%.

[0142] [evaluation] First, a rectangular test piece measuring 210 x 300 mm (A4 size) was cut out from the fabricated piezoelectric film. The cut piezoelectric film was placed on a case with an opening of 210 x 300 mm and containing glass wool, and then the periphery was pressed with a frame to apply an appropriate tension and curvature to the piezoelectric film, thereby fabricating a piezoelectric speaker. The depth of the case was 9 mm, and the density of the glass wool was 32 kg / m 3 The thickness before assembly was 25mm.

[0143] A 1 kHz sine wave was input as an input signal to the fabricated piezoelectric speaker through a power amplifier, and the sound pressure was measured using a microphone placed 1 m away from the center of the speaker. The results are shown in Table 1 and FIG.

[0144] [Table 1]

[0145] From Table 1 and FIG. 8, it can be seen that the piezoelectric element of the present invention has higher sound pressure and higher piezoelectric performance than the comparative example.

[0146] Comparing Examples 1 to 4, it can be seen that the longer the firing time, the lower the high Pb ratio and the higher the sound pressure. Comparing Example 3 and Example 5, it is clear that the higher the firing temperature, the lower the high Pb ratio and the higher the sound pressure. Comparing Example 3 with Example 6 and Example 5 with Example 7, it is clear that the smaller the average particle size of the mixed particles before firing, the lower the high Pb ratio and the higher the sound pressure. The above results clearly demonstrate the effectiveness of the present invention. [Industrial Applicability]

[0147] The piezoelectric film of the present invention can be suitably used as, for example, various sensors such as sonic sensors, ultrasonic sensors, pressure sensors, tactile sensors, strain sensors, and vibration sensors (particularly useful for infrastructure inspections such as crack detection and manufacturing site inspections such as detecting foreign matter contamination), acoustic devices such as microphones, pickups, speakers, and exciters (specific applications include noise cancellers (used in cars, trains, airplanes, robots, etc.), artificial vocal cords, buzzers to prevent pests and vermin from entering, furniture, wallpaper, photographs, helmets, goggles, headrests, signage, and robots), haptics used in automobiles, smartphones, smart watches, games, etc., ultrasonic transducers such as ultrasonic probes and hydrophones, actuators used to prevent water droplet adhesion, transport, mixing, dispersion, polishing, etc., vibration-damping materials (dampers) used in containers, vehicles, buildings, and sporting equipment such as skis and rackets, and vibration-powered generators used in roads, floors, mattresses, chairs, shoes, tires, wheels, computer keyboards, etc. [Explanation of symbols]

[0148] 10, 10L piezoelectric film 10a, 10c Sheet-like object 10b Laminate 12 Diaphragm 16, 19 Adhesive layer 20 Piezoelectric layer 24 1st electrode layer 26 Second electrode layer 28 1st protective layer 30 Second protective layer 34 Matrix 36 Piezoelectric particles 36b High Pb region 50, 56 Multilayer piezoelectric element 58 Core rod

Claims

1. The piezoelectric element has a piezoelectric layer made of a polymer composite piezoelectric material containing piezoelectric particles in a matrix containing a polymer material, and electrode layers formed on both sides of the piezoelectric layer, the piezoelectric particles are particles containing lead zirconate titanate, a ratio of an area of ​​a region where Pb / (Pb+Zr) is 90% or more to an area of ​​the lead zirconate titanate particles in a cross section in the thickness direction of the piezoelectric layer of the piezoelectric film being 0.2 to 4%.

2. The lead zirconate titanate contained in the piezoelectric particles has the general formula Pb(Zr X Ti 1-X ) O 3 2. The piezoelectric film of claim 1, wherein X is 0.52±0.

1.

3. 3. The piezoelectric film according to claim 1, wherein the average particle size of the piezoelectric particles is 1 μm to 10 μm.

4. The piezoelectric film according to any one of claims 1 to 3, wherein the polymer material has a cyanoethyl group.

5. The piezoelectric film according to any one of claims 1 to 4, wherein the polymeric material comprises cyanoethylated polyvinyl alcohol.

6. The piezoelectric film according to any one of claims 1 to 5, wherein the piezoelectric layer is polarized in the thickness direction.

Images