CN118044227A

CN118044227A - Piezoelectric film and laminated piezoelectric element

Info

Publication number: CN118044227A
Application number: CN202280065086.9A
Authority: CN
Inventors: 岩本崇裕
Original assignee: Fujifilm Corp
Current assignee: Fujifilm Corp
Priority date: 2021-09-28
Filing date: 2022-08-17
Publication date: 2024-05-14
Also published as: TW202315174A; WO2023053758A1

Abstract

The invention provides a piezoelectric film and a laminated piezoelectric element capable of suppressing generation of wrinkles when the temperature and/or humidity of the environment repeatedly change. The piezoelectric film of the present invention has: a piezoelectric layer containing piezoelectric particles in a matrix containing a polymer material; electrode layers arranged on both sides of the piezoelectric layer; and a protective layer provided on a surface of the electrode layer opposite to the piezoelectric layer, wherein the number density of spots on the surface of the electrode layer is 250 pieces/cm ² or less.

Description

Piezoelectric film and laminated piezoelectric element

Technical Field

The present invention relates to a piezoelectric film used for an electroacoustic conversion film or the like, and a laminated piezoelectric element in which the piezoelectric film is laminated.

Background

Flexible displays using flexible substrates such as plastic, such as organic EL displays, are being developed.

In the case of using such a flexible display as an image display device and sound generation device that reproduce sound together with an image, such as a television receiver, a speaker that is an acoustic device for generating sound is required.

Among them, as a conventional speaker shape, a funnel-shaped dome shape such as a cone shape and a sphere shape is general. However, if these speakers are to be built in the above-described flexible display, light weight and flexibility, which are advantages of the flexible display, may be impaired. Also, when the speaker is mounted outside, it is inconvenient to carry and the like, and it is difficult to be provided on a curved wall, which may impair the beauty.

In contrast, as a speaker that can be integrated into a flexible display without impairing the light weight and flexibility, a piezoelectric film having flexibility has been proposed.

For example, patent document 1 discloses an electroacoustic conversion film (piezoelectric film) comprising: a polymer composite piezoelectric body (piezoelectric layer) in which piezoelectric particles are dispersed in a viscoelastic matrix made of a polymer material having viscoelasticity at ordinary temperature; thin film electrodes (electrode layers) provided on both sides of the polymer composite piezoelectric body; and the protective layer is arranged on the surface of the film electrode.

Technical literature of the prior art

Patent literature

Patent document 1: international publication No. 2013/047875

Disclosure of Invention

Technical problem to be solved by the invention

Patent document 1 describes the following: since the piezoelectric particles are dispersed in the viscoelastic matrix made of the polymer material having viscoelasticity at normal temperature and the internal loss at the frequency of 1Hz based on the dynamic viscoelasticity test becomes a maximum value of 0.1 or more at normal temperature (0 to 50 ℃), the piezoelectric particles exhibit extremely excellent flexibility against deformation which is gradually performed from the outside and can be mounted on a flexible device.

Here, according to the study of the present inventors, it is known that the following problems occur: a piezoelectric film using a polymer composite piezoelectric body using a polymer material as a matrix as a piezoelectric layer generates wrinkles by repeated changes in the temperature and/or humidity of the environment.

The present invention has been made to solve the above-described problems of the related art, and an object of the present invention is to provide a piezoelectric film and a laminated piezoelectric element capable of suppressing the occurrence of wrinkles even when the temperature and/or humidity of the environment change repeatedly.

Means for solving the technical problems

In order to achieve the above object, the present invention has the following structure.

[1] A piezoelectric film, comprising: a piezoelectric layer containing piezoelectric particles in a matrix containing a polymer material; electrode layers disposed on both sides of the piezoelectric layer; and a protective layer provided on a surface of the electrode layer opposite to the piezoelectric layer,

The number density of spots on the surface of the electrode layer is 250 spots/cm ² or less.

[2] The piezoelectric film of [1], wherein,

At the spot position, the proportion of organic nuclei in the piezoelectric layer, which have a region inscribable by a minimum circumscribed circle having a diameter of 10 μm or more, is 20% or less.

[3] A laminated piezoelectric element comprising 2 or more layers of the piezoelectric film according to [1] or [2 ].

[4] The laminated piezoelectric element according to [3], wherein the piezoelectric film is laminated by at least 2 layers by folding the piezoelectric film 1 or more times.

Effects of the invention

According to the present invention, a piezoelectric film and a laminated piezoelectric element can be provided that can suppress the occurrence of wrinkles in the case of repeated changes in the temperature and/or humidity of the environment.

Drawings

Fig. 1 is a conceptual diagram of an example of a piezoelectric film of the present invention.

Fig. 2 is a diagram for explaining spots generated in the electrode layer.

Fig. 3 is a conceptual diagram for explaining an example of a method of producing a piezoelectric film.

Fig. 4 is a conceptual diagram for explaining an example of a method of producing a piezoelectric film.

Fig. 5 is a conceptual diagram for explaining an example of a method of producing a piezoelectric film.

Fig. 6 is a conceptual diagram for explaining an example of a method of producing a piezoelectric film.

Fig. 7 is a conceptual diagram of an example of a laminated piezoelectric element according to the present invention.

Fig. 8 is a conceptual diagram of another example of the laminated piezoelectric element of the present invention.

Detailed Description

Hereinafter, the piezoelectric film and the laminated piezoelectric element according to the present invention will be described in detail based on preferred embodiments shown in the attached drawings.

The following description of the constituent elements is sometimes made based on the representative embodiments of the present invention, but the present invention is not limited to such embodiments.

In the present specification, the numerical range indicated by the term "to" means a range including the numerical values before and after the term "to" as a lower limit value and an upper limit value.

The drawings shown below are conceptual diagrams for explaining the present invention, and the thickness of each layer, the size of the piezoelectric particles, the size of the constituent members, and the like are different from those of an actual object.

[ Piezoelectric film ]

The piezoelectric film of the present invention has:

A piezoelectric layer containing piezoelectric particles in a matrix containing a polymer material; electrode layers disposed on both sides of the piezoelectric layer; and a protective layer provided on a surface of the electrode layer opposite to the piezoelectric layer,

The number density of spots on the surface of the piezoelectric film is 250 pieces/cm ² or less.

Fig. 1 schematically shows an example of the piezoelectric film of the present invention.

As shown in fig. 1, the piezoelectric film 10 includes a piezoelectric layer 12, a1 st electrode layer 14 laminated on one surface of the piezoelectric layer 12, a1 st protective layer 18 laminated on the surface of the 1 st electrode layer 14, a2 nd electrode layer 16 laminated on the other surface of the piezoelectric layer 12, and a2 nd protective layer 20 laminated on the surface of the 2 nd electrode layer 16. That is, the piezoelectric film 10 has the following structure: the piezoelectric layer 12 is sandwiched between electrode layers, and a protective layer is laminated on the surface of the electrode layers which is not in contact with the piezoelectric layer.

In the piezoelectric film 10, as schematically shown in fig. 1, the piezoelectric layer 12 includes piezoelectric particles 26 in a matrix 24 including a polymer material. As described later, the piezoelectric film 10, that is, the piezoelectric layer 12 is preferably polarized in the thickness direction.

In the present invention, the 1 st and 2 nd electrode layers 14 and 16, and the 1 st and 2 nd protective layers 18 and 20 are simply added to distinguish 2 identical components of the piezoelectric film 10. That is, the 1 st and 2 nd elements of the piezoelectric film 10 are not technically defined. Therefore, a paint for forming the piezoelectric layer 12 described later may be applied to either the 1 st electrode layer 14 or the 2 nd electrode layer 16.

In the following description, the electrode layer and the protective layer will be abbreviated as "electrode layer" and "protective layer" respectively unless it is necessary to distinguish between the 1 st and the 2 nd.

The piezoelectric film of the present invention has a structure in which the number density of spots on the surface of the electrode layer is 250 spots/cm ² or less.

The spots in the present invention are granular spots detected by scanning the surface of the electrode layer with a resist layer at a resolution of 600dpi or more using ImageJ at 8bit and grayscale, setting the Threshold value to 121 to 255 in the range of 3cm×3cm, and performing analysis of particles. Fig. 2 shows an example of an image obtained by performing particle analysis on an image of the surface of the electrode layer with ImageJ. In fig. 2, the black dots are spots in the present invention. In addition, fig. 2 is a black-and-white reversed image.

Such spots are detected due to irregularities in the micro-deformed portions of the electrode layer.

The number density of spots was calculated by counting spots detected in the above-described manner over a range of 3cm×3 cm.

In addition, regarding selection of a range of 3cm×3cm, it is sufficient to perform Rectangle selection of an image portion by Area Selection Tools (region selection tool) and extract an image by Crop (clipping).

In addition, the size of the spots is not limited when counting the spots. In addition, the Exclude on edges (boundary exclusion) is selected, and particles that contact the boundary of the selection range are ignored. In addition, the processing is performed in a state where noise is not eliminated.

The number density of the spots was measured at 5 of the electrode layer, and the average value was set as the number density of the spots. In the present invention, the number density of spots in the electrode layers on both sides of each piezoelectric film is set to 250 spots/cm ² or less.

Points having a size of 0.5mm ² or less were regarded as spots, and points larger than the spots were excluded.

The apparatus for scanning the surface of the electrode layer is not particularly limited, and for example, a color compound machine ApeosC5570 manufactured by FUJIFILM Business Innovation corp. In addition, the electrode layer surface is scanned in color and output in Jpeg format.

As described above, according to the study of the present inventors, it is known that the following problems occur: a piezoelectric film in which polymer composite piezoelectric particles are dispersed with a polymer material as a matrix, which is used as a piezoelectric layer, is wrinkled by repeated changes in the temperature and/or humidity of the environment. In this regard, as a result of further studies by the present inventors, it is presumed that wrinkles are generated by the following mechanism.

The polymer material contained in the piezoelectric layer easily absorbs moisture, and the polymer material absorbs or emits moisture according to a change in temperature and/or humidity of the atmosphere environment, so that the piezoelectric layer expands or contracts. However, when the organic material as a matrix in the piezoelectric layer is unevenly distributed, undissolved nuclei of the organic material are present, and the piezoelectric particles are aggregated, if the temperature and/or humidity of the environment change, the portions of the uneven distribution of the organic material (hereinafter, also referred to as organic material nuclei) and the aggregated portions and other portions of the piezoelectric particles become causes of different degrees of expansion and contraction of the piezoelectric layer. Therefore, it is presumed that: if the temperature and/or humidity of the environment repeatedly change, the piezoelectric film repeatedly expands and contracts to different degrees in a portion or the like where the distribution of the organic substance is uneven and other portions, and thus wrinkles are generated in the piezoelectric film.

Among them, the inventors found the following: if there is a portion of the piezoelectric layer where the organic material as a matrix is unevenly distributed or the piezoelectric particles are aggregated, spots due to fine deformation can be detected on the surface of the electrode layer. As will be described in detail later, a piezoelectric film is produced by applying a paint as a piezoelectric layer over one electrode layer to form a piezoelectric layer, and then laminating an electrode layer and a protective layer over the piezoelectric layer and thermally pressurizing the same. In the piezoelectric layer, it is known that when the organic nuclei and/or aggregates of the piezoelectric particles are present, the electrode layer at the positions of the organic nuclei and/or aggregates of the piezoelectric particles is deformed finely when the piezoelectric layer is thermally pressurized because the organic nuclei and/or aggregates of the piezoelectric particles have a hardness different from that of other portions. By performing image analysis on the surface of the electrode layer by the above method, fine deformation of the electrode layer can be detected as speckles.

Therefore, in the piezoelectric film of the present invention in which the number density of spots on the surface of the electrode layer is as low as 250 spots/cm ² or less, the occurrence of wrinkles in the piezoelectric film can be suppressed even when the temperature and/or humidity of the environment repeatedly change, because the number of organic nuclei and/or aggregates of piezoelectric particles in the piezoelectric layer is reduced.

From the viewpoint of further preferably suppressing the occurrence of wrinkles, the number density of spots on the surface of the electrode layer is preferably 200/cm ² or less, more preferably 150/cm ² or less.

In the spot position, the proportion of the organic nuclei in the region of the piezoelectric layer where the minimum circumscribed circle having a diameter of 10 μm or more can be inscribed is preferably 20% or less. As described above, since the polymer material absorbs or emits moisture according to a change in temperature and/or humidity, the organic matter expands or contracts. The spots are more likely to wrinkle when caused by the organic nuclei than when caused by the aggregates of the piezoelectric particles. Therefore, by reducing the proportion of the organic nuclei present at the positions of the spots, the occurrence of wrinkles of the piezoelectric film can be further preferably suppressed.

The proportion of organic nuclei in the region where the minimum circumscribed circle having a diameter of 10 μm or more can be inscribed in the piezoelectric layer was measured at the position of the spot in the following manner.

First, a sample of the piezoelectric film is attached to a support. A coating layer is provided on a surface of the piezoelectric film opposite to the support. As the coating layer, a film having a smooth surface and a thickness of several μm to several tens μm, and metal, glass, resin, or the like is used as a material.

Then, a section having a width of about 1mm was processed using a microtome (for example, EMUC manufactured by HITACHI HIGH-Tech Corporation). Conducting treatment is performed as needed.

Using the sample after the cross-sectional processing, an EDS (energy dispersive X-ray spectroscopy) based component analysis was performed, and an elemental mapping (atomic number concentration quantitative map) image was obtained. The image was captured at 1500 times magnification to obtain an image.

The element map is analyzed for composition from the organic component, and the size is determined as an organic core if there is a region inscribable by a minimum circumscribed circle having a diameter of 10 μm or more in the organic region.

Such measurement is performed on 50 or more (total number of spots when the number of spots is less than 50), and the ratio of the spots in which the organic nuclei are present to the number of measured spots is calculated.

From the viewpoint of further preferably suppressing the occurrence of wrinkles, the proportion of spots in which the organic nuclei are present is preferably 17% or less, more preferably 15% or less, and particularly preferably 0%.

The constituent elements of the piezoelectric film of the present invention will be described in detail below.

As described above, in the piezoelectric film 10 of the present invention, the piezoelectric layer 12 is formed by dispersing the piezoelectric particles 26 in the matrix 24 containing the polymer material. That is, the piezoelectric layer 12 is a polymer composite piezoelectric body.

Here, the polymer composite piezoelectric body (piezoelectric layer 12) preferably has the following requirements. In the present invention, the normal temperature is 0 to 50 ℃.

(I) Flexibility of

For example, when a portable article such as a newspaper or a magazine is held in a gently curved state like a document, a relatively slow and large bending deformation of several Hz or less is continuously applied from the outside. At this time, when the polymer composite piezoelectric body is hard, a corresponding large bending stress is generated, and cracks are generated at the interface between the polymer matrix and the piezoelectric body particles, and as a result, the breakage may occur. Therefore, the polymer composite piezoelectric body is required to have appropriate flexibility. Further, if strain energy can be diffused as heat to the outside, stress can be relaxed. Therefore, the loss tangent of the polymer composite piezoelectric body is required to be appropriately large.

(Ii) Sound quality

The speaker vibrates the piezoelectric particles at a frequency in the audio frequency band of 20Hz to 20kHz, and the entire diaphragm (polymer composite piezoelectric body) is vibrated by the vibration energy, thereby reproducing sound. Therefore, in order to improve the efficiency of vibration energy transmission, the polymer composite piezoelectric body is required to have an appropriate hardness. Further, if the frequency characteristic of the speaker is smooth, the amount of change in sound quality when the lowest resonance frequency f ₀ changes with a change in curvature also becomes small. Therefore, the loss tangent of the polymer composite piezoelectric body is required to be appropriately large.

As is well known, the lowest resonance frequency f ₀ of the speaker diaphragm is given by the following formula. Here, s is the stiffness of the vibration system and m is the mass.

[ Number 1]

At this time, the mechanical rigidity s decreases as the degree of bending of the piezoelectric film, that is, the radius of curvature of the bending portion increases, and therefore the lowest resonance frequency f ₀ decreases. That is, the sound quality (volume, frequency characteristics) of the speaker varies according to the radius of curvature of the piezoelectric film.

As described above, the flexible polymer composite piezoelectric body used for the electroacoustic transducer film is required to operate relatively hard against vibrations of 20Hz to 20kHz and to operate relatively soft against vibrations of several Hz or less. In addition, the loss tangent of the polymer composite piezoelectric body is required to be appropriately large for vibrations at all frequencies of 20kHz or less.

In general, a polymer solid has a viscoelastic relaxation mechanism, and large-scale molecular motion is observed as a decrease (relaxation) in storage modulus (young's modulus) or an maximization (absorption) of loss elastic modulus with an increase in temperature or a decrease in frequency. Among them, alleviation caused by Micro Brownian (Micro Brownian) motion of molecular chains of amorphous regions is called primary dispersion, and a very large alleviation phenomenon can be observed. The temperature at which this primary dispersion occurs is the glass transition point (Tg), and the viscoelastic mitigation mechanism appears most pronounced.

In the polymer composite piezoelectric body (piezoelectric layer 12), a polymer material having a glass transition point at normal temperature, in other words, a polymer material having viscoelasticity at normal temperature is used in a matrix, whereby a polymer composite piezoelectric body which operates relatively hard against vibrations of 20Hz to 20kHz and operates relatively soft against slow vibrations of several Hz or less is realized. In particular, in order to properly exhibit such an action, a polymer material having a glass transition point at a frequency of 1Hz at normal temperature, that is, at 0 to 50 ℃ is preferably used in the matrix of the polymer composite piezoelectric body.

As the polymer material having viscoelasticity at normal temperature, various known polymer materials can be used. It is preferable to use a polymer material having a maximum value of Tan delta at a frequency of 1Hz of 0.5 or more, which is obtained by a dynamic viscoelasticity test at normal temperature, that is, 0 to 50 ℃.

Accordingly, when the polymer composite piezoelectric body is gently bent by an external force, stress concentration at the interface between the polymer matrix and the piezoelectric body particles in the maximum bending moment portion is relaxed, and high flexibility can be expected.

The storage modulus (E') of the polymer material having viscoelasticity at normal temperature at a frequency of 1Hz, which is measured based on dynamic viscoelasticity, is preferably 100MPa or more at 0℃and 10MPa or less at 50 ℃.

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

It is more preferable that the relative dielectric constant of the polymer material having viscoelasticity at ordinary temperature is 10 or more at 25 ℃. Thus, when a voltage is applied to the polymer composite piezoelectric body, a higher electric field is applied to the piezoelectric particles in the polymer matrix, and thus a large deformation amount can be expected.

However, on the other hand, if it is considered to ensure good moisture resistance or the like, it is also preferable that the relative dielectric constant of the polymer material is 10 or less at 25 ℃.

Examples of the polymer material having viscoelasticity at ordinary temperature satisfying these conditions include cyanoethylated polyvinyl alcohol (cyanoethylated PVA), polyvinyl acetate, polyvinylidene chloride acrylonitrile, polystyrene-vinyl polyisoprene block copolymer, polyvinyl methyl ketone, and polybutylmethacrylate. Further, commercial products such as HYBRAR5127 (KURARAY co., LTD) can be suitably used as the polymer material. Among them, as the polymer material, a material having cyanoethyl groups is preferably used, and cyanoethylated PVA is particularly preferably used.

In the matrix 24, only 1 kind of these polymer materials may be used, or a plurality of kinds may be used in combination (mixture).

In addition to the polymer material having viscoelasticity at normal temperature, a polymer material having no viscoelasticity at normal temperature may be added to the matrix 24 as needed.

That is, for the purpose of adjusting the dielectric characteristics, mechanical characteristics, and the like, in addition to the polymer material having viscoelasticity at normal temperature such as cyanoethylated PVA, other dielectric polymer materials may be added to the matrix 24 as needed.

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, polymers having cyano groups or cyano groups such as vinylidene fluoride-vinyl ester copolymer, cyanoethyl cellulose, cyanoethyl hydroxy sucrose, cyanoethyl hydroxy cellulose, cyanoethyl hydroxy fullerene, cyanoethyl methacrylate, cyanoethyl acrylate, cyanoethyl hydroxyethyl cellulose, cyanoethyl amylose, cyanoethyl hydroxypropyl cellulose, cyanoethyl dihydroxypropyl cellulose, cyanoethyl hydroxypropyl amylose, cyanoethyl polyacrylamide, cyanoethyl polyethyl polyacrylate, cyanoethyl fullerene, cyanoethyl polyhydroxymethylene, cyanoethyl glycidyl fullerene, cyanoethyl sucrose, cyanoethyl sorbitol, and synthetic rubbers such as nitrile rubber and chloroprene rubber.

Among them, a polymer material having cyanoethyl groups can be preferably used.

The dielectric polymer to be added to the matrix 24 of the piezoelectric layer 12 is not limited to 1, and a plurality of dielectric polymers may be added, except for materials having viscoelasticity at normal temperature, such as cyanoethylated PVA.

In addition, in order to adjust the glass transition point Tg, a thermoplastic resin such as a vinyl chloride resin, polyethylene, polystyrene, methacrylic resin, polybutylene, and isobutylene, and a thermosetting resin such as a phenol resin, a urea resin, a melamine resin, an alkyd resin, and mica may be added to the matrix 24 in addition to the dielectric polymer material.

Further, for the purpose of improving the adhesiveness, a tackifier such as rosin ester, rosin, terpenes, terpene phenol, and petroleum resin may be added.

The amount of the material other than the polymer material having viscoelasticity at normal temperature, such as cyanoethylated PVA, added to the matrix 24 of the piezoelectric layer 12 is not particularly limited, but is preferably 30 mass% or less based on the amount of the material in the matrix 24.

As a result, the characteristics of the polymer material to be added can be expressed without impairing the viscoelastic relaxation mechanism in the matrix 24, and therefore preferable results can be obtained in terms of improvement of dielectric constant, heat resistance, adhesion to the piezoelectric particles 26 and the electrode layer, and the like.

Among them, since the glass transition point of a polymer material having viscoelasticity at normal temperature is in the temperature range of 0 to 50 ℃ at a frequency of 1Hz, expansion and contraction are easily performed when the temperature and/or humidity are changed in the vicinity of normal temperature. Therefore, a piezoelectric film using a polymer material having viscoelasticity at normal temperature as a substrate is likely to wrinkle due to repeated changes in the temperature and/or humidity of the environment. Therefore, in the piezoelectric film using a polymer material having viscoelasticity at normal temperature as a substrate, the occurrence of wrinkles can be suitably suppressed by setting the number density of spots on the surface of the electrode layer to 250 pieces/cm ² or less.

In the piezoelectric film 10 of the present invention, the piezoelectric layer 12 includes the piezoelectric particles 26 in the matrix 24. Specifically, the piezoelectric layer 12 is a polymer composite piezoelectric body in which piezoelectric particles 26 are dispersed in the matrix 24.

The piezoelectric particles 26 are composed of ceramic particles having a perovskite-type or wurtzite-type crystal structure.

Examples of the ceramic particles constituting the piezoelectric particles 26 include lead zirconate titanate (PZT), lead lanthanum zirconate titanate (PLZT), barium titanate (BaTiO ₃), zinc oxide (ZnO), and a solid solution (BFBT) of barium titanate and bismuth ferrite (BiFe ₃).

The piezoelectric particles 26 may be used in an amount of 1, or may be used in combination (mixture).

The particle diameter of the piezoelectric particles 26 is not limited, and may be appropriately selected according to the size, the application, and the like of the piezoelectric film 10.

The particle diameter of the piezoelectric particles 26 is preferably 1 to 10. Mu.m. By setting the particle diameter of the piezoelectric particles 26 within this range, preferable results can be obtained in terms of the piezoelectric film 10 being able to achieve both high-voltage characteristics and flexibility.

In fig. 1, the piezoelectric particles 26 in the piezoelectric layer 12 are irregularly dispersed in the matrix 24, but the present invention is not limited thereto.

That is, the piezoelectric particles 26 in the piezoelectric layer 12 may be dispersed in the matrix 24 regularly, preferably as long as they are uniformly dispersed.

Further, the piezoelectric particles 26 may have the same particle size or may have different particle sizes.

In the piezoelectric film 10, the amount ratio of the matrix 24 and the piezoelectric particles 26 in the piezoelectric layer 12 is not limited, and may be appropriately set according to the size and thickness of the piezoelectric film 10 in the plane direction, the use of the piezoelectric film 10, the characteristics required for the piezoelectric film 10, and the like.

The volume fraction of the piezoelectric particles 26 in the piezoelectric layer 12 is preferably 30 to 80%, more preferably 50% or more, and thus, more preferably 50 to 80%.

When the amount ratio of the matrix 24 to the piezoelectric particles 26 is within the above range, preferable results can be obtained in terms of both high-voltage characteristics and flexibility.

In the piezoelectric film 10, the thickness of the piezoelectric layer 12 is not particularly limited, and may be appropriately set according to the application of the piezoelectric film 10, the characteristics required for the piezoelectric film 10, and the like.

The thicker the piezoelectric layer 12 is, the more advantageous it is in terms of rigidity such as toughness strength of a so-called sheet, but the larger the voltage (potential difference) required to expand and contract the piezoelectric film 10 by the same amount.

The thickness of the piezoelectric layer 12 is preferably 8 to 300. Mu.m, more preferably 8 to 200. Mu.m, still more preferably 10 to 150. Mu.m, particularly preferably 15 to 100. Mu.m.

By setting the thickness of the piezoelectric layer 12 within the above range, preferable results can be obtained in terms of both securing rigidity and appropriate flexibility.

The piezoelectric layer 12, that is, the piezoelectric film 10, is preferably polarized (polarized) in the thickness direction. The polarization process will be described in detail later.

As shown in fig. 1, the piezoelectric film 10 illustrated in the drawing has a structure in which the 1 st electrode layer 14 is provided on one surface of the piezoelectric layer 12, the 1 st protective layer 18 is provided on the surface thereof, the 2 nd electrode layer 16 is provided on the other surface of the piezoelectric layer 12, and the 2 nd protective layer 20 is provided on the surface thereof.

Wherein the 1 st electrode layer 14 and the 2 nd electrode layer 16 form an electrode pair. That is, the piezoelectric film 10 has a structure in which the piezoelectric layer 12 is sandwiched between the 1 st electrode layer 14 and the 2 nd electrode layer 16, which are electrode pairs, and the laminate is sandwiched between the 1 st protective layer 18 and the 2 nd protective layer 20.

In this piezoelectric film 10, the region sandwiched between the 1 st electrode layer 14 and the 2 nd electrode layer 16 expands and contracts according to the applied voltage.

In the piezoelectric film 10, the 1 st protective layer 18 and the 2 nd protective layer 20 cover the 1 st electrode layer 14 and the 2 nd electrode layer 16, and also function to impart appropriate rigidity and mechanical strength to the piezoelectric layer 12. That is, in the piezoelectric film 10, the piezoelectric layer 12 composed of the matrix 24 and the piezoelectric particles 26 exhibits very excellent flexibility against slow bending deformation, but may be insufficient in rigidity or mechanical strength depending on the application. In the piezoelectric film 10, the 1 st protective layer 18 and the 2 nd protective layer 20 are provided to compensate for this.

The 1 st protective layer 18 and the 2 nd protective layer 20 are not limited, and various kinds of sheet-like materials can be used, and as an example, various kinds of resin films are preferably exemplified.

Among them, for reasons of excellent mechanical properties and heat resistance, a resin film composed of polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS), polycarbonate (PC), polyphenylene Sulfide (PPs), polymethyl methacrylate (PMMA), polyetherimide (PEI), polyimide (PI), polyethylene naphthalate (PEN), triacetyl cellulose (TAC), a cyclic olefin resin, and the like is preferably used.

The thickness of the 1 st protective layer 18 and the 2 nd protective layer 20 is not limited. The 1 st protective layer 18 and the 2 nd protective layer 20 have substantially the same thickness, but may be different.

Here, if the rigidity of the 1 st and 2 nd protective layers 18 and 20 is too high, not only the expansion and contraction of the piezoelectric layer 12 but also the flexibility are impaired. Therefore, in addition to the case where mechanical strength and good handleability as a sheet are required, the thinner the 1 st protective layer 18 and the 2 nd protective layer 20 are, the more advantageous.

In the piezoelectric film 10, if the thickness of the 1 st protective layer 18 and the 2 nd protective layer 20 is 2 times or less the thickness of the piezoelectric layer 12, preferable results can be obtained in terms of both securing rigidity and appropriate flexibility.

For example, when the thickness of the piezoelectric layer 12 is 50 μm and the 1 st and 2 nd protective layers 18 and 20 are made of PET, the thickness of the 1 st and 2 nd protective layers 18 and 20 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 1 st electrode layer 14 is formed between the piezoelectric layer 12 and the 1 st protective layer 18, and the 2 nd electrode layer 16 is formed between the piezoelectric layer 12 and the 2 nd protective layer 20.

The 1 st electrode layer 14 and the 2 nd electrode layer 16 are provided for applying a voltage to the piezoelectric layer 12 (piezoelectric film 10).

In the present invention, the materials for forming the 1 st electrode layer 14 and the 2 nd electrode layer 16 are not limited, and various electric conductors can be used. Specifically, metals such as carbon, palladium, iron, tin, aluminum, nickel, platinum, gold, silver, copper, titanium, chromium, and molybdenum, alloys thereof, laminates and composites of these metals and alloys, indium tin oxide, and the like are exemplified. Among them, copper, aluminum, gold, silver, platinum, and indium tin oxide are preferably exemplified as the 1 st electrode layer 14 and the 2 nd electrode layer 16.

The method for forming the 1 st electrode layer 14 and the 2 nd electrode layer 16 is not limited, and a known method can be used. As an example, a film formation by a vapor deposition method (vacuum film formation method) such as vacuum vapor deposition and sputtering, a film formation by electroplating, a method of adhering a foil formed of the above-described materials, and the like are illustrated.

Among these, for reasons such as ensuring flexibility of the piezoelectric film 10, it is particularly preferable to use thin films of copper, aluminum, or the like formed by vacuum deposition as the 1 st electrode layer 14 and the 2 nd electrode layer 16. Among them, copper thin films formed by vacuum vapor deposition are particularly suitable for use.

The thicknesses of the 1 st electrode layer 14 and the 2 nd electrode layer 16 are not limited. The thicknesses of the 1 st electrode 14 and the 2 nd electrode 16 are substantially the same, but may be different.

Here, if the rigidity of the 1 st electrode layer 14 and the 2 nd electrode layer 16 is too high, the flexibility is impaired as well as the expansion and contraction of the piezoelectric layer 12, similarly to the 1 st protective layer 18 and the 2 nd protective layer 20. Therefore, the thinner the 1 st electrode layer 14 and the 2 nd electrode layer 16, the more advantageous the resistance will not become too high.

In the piezoelectric film 10, it is preferable that the product of the thickness of the 1 st electrode layer 14 and the 2 nd electrode layer 16 and the young's modulus is lower than the product of the thickness of the 1 st protective layer 18 and the 2 nd protective layer 20, since flexibility is not seriously impaired.

For example, in the case of a combination in which the 1 st protective layer 18 and the 2 nd protective layer 20 are made of PET (Young's modulus: about 6.2 GPa) and the 1 st electrode layer 14 and the 2 nd electrode layer 16 are made of copper (Young's modulus: about 130 GPa), if the thickness of the 1 st protective layer 18 and the 2 nd protective layer 20 is 25 μm, the thickness of the 1 st electrode layer 14 and the 2 nd electrode layer 16 is preferably 1.2 μm or less, more preferably 0.3 μm or less, and particularly preferably 0.1 μm or less.

As described above, the piezoelectric film 10 has a structure in which the 1 st electrode layer 14 and the 2 nd electrode layer 16 sandwich the piezoelectric layer 12 having the piezoelectric particles 26 in the matrix 24 containing the polymer material, and the 1 st protective layer 18 and the 2 nd protective layer 20 sandwich the laminate.

In the piezoelectric film 10 of the present invention, the maximum value of the loss tangent (Tan δ) at the frequency of 1Hz, which is obtained by dynamic viscoelasticity measurement, is preferably present at normal temperature, and more preferably, the maximum value of 0.1 or more is present at normal temperature.

Accordingly, even when the piezoelectric film 10 receives relatively slow and large bending deformation of several Hz or less from the outside, strain energy can be efficiently diffused to the outside as heat, and thus occurrence of cracks at the interface between the polymer matrix and the piezoelectric particles can be prevented.

The piezoelectric film 10 of the present invention preferably has a storage modulus (E') at a frequency of 1Hz, which is measured based on dynamic viscoelasticity, of 10 to 30GPa at 0℃and 1 to 10GPa at 50 ℃.

Thus, the piezoelectric film 10 can have a large frequency dispersion in the storage modulus (E') at normal temperature. That is, the vibration damper can operate relatively hard against vibrations of 20Hz to 20kHz and relatively soft against vibrations of several Hz or less.

In addition, the piezoelectric film 10 of the present invention is preferably such that the product of the thickness and the storage modulus (E') at a frequency of 1Hz, which is measured based on dynamic viscoelasticity, is 1.0X10 ⁶～2.0×10⁶ N/m at 0℃and 1.0X10 ⁵～1.0×10⁶ N/m at 50 ℃. The conditions are also similar to those of the piezoelectric layer 12.

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

Further, in the piezoelectric film 10, the loss tangent (Tan δ) at a frequency of 1kHz at 25 ℃ is preferably 0.05 or more in the main curve obtained from dynamic viscoelasticity measurement. The conditions are also similar to those of the piezoelectric layer 12.

As a result, the frequency characteristic of the speaker using the piezoelectric film 10 becomes smooth, and the amount of change in sound quality when the lowest resonance frequency f ₀ changes with a change in curvature of the speaker can be reduced.

In the present invention, the storage modulus (young's modulus) and loss tangent of the piezoelectric film 10, the piezoelectric layer 12, and the like may be measured by a known method. As an example, measurement may be performed using a dynamic viscoelasticity measurement device DMS6100 manufactured by SII Nano Technology inc.

As an example of the measurement conditions, the following are illustrated respectively: the measurement frequency is 0.1 Hz-20 Hz (0.1 Hz, 0.2Hz, 0.5Hz, 1Hz, 2Hz, 5Hz, 10Hz and 20 Hz), the measurement temperature is-50-150 ℃, the heating rate is 2 ℃/min (in nitrogen atmosphere), the sample size is 40mm multiplied by 10mm (including the splint region), and the space between chucks is 20mm.

Further, the piezoelectric film 10 of the present invention may include, in addition to these layers, an insulating layer or the like for preventing short circuits or the like by covering the electrode lead-out portion for leading out the electrodes from the 1 st electrode layer 14 and the 2 nd electrode layer 16 and the exposed region of the piezoelectric layer 12.

The method for extracting the electrodes from the 1 st electrode layer 14 and the 2 nd electrode layer 16 is not limited, and various known methods can be used.

As examples, a method of providing a portion protruding outward in the surface direction of the piezoelectric layer 12 in the electrode layer and the protective layer, a method of connecting a conductor such as copper foil to the 1 st electrode layer 14 and the 2 nd electrode layer 16 to lead out an electrode to the outside, a method of forming a through hole in the 1 st protective layer 18 and the 2 nd protective layer 20 by laser or the like, and filling a conductive material into the through hole to lead out an electrode to the outside, and the like are illustrated.

Examples of preferred electrode extraction methods include the method described in Japanese patent application laid-open No. 2014-209724 and the method described in Japanese patent application laid-open No. 2016-015354.

The number of electrode lead-out portions in each electrode layer is not limited to 1, and may be 2 or more. In particular, in the case of a configuration in which the hole portion is formed by inserting a conductive material by removing a part of the protective layer, it is preferable to have 3 or more electrode lead portions in order to ensure more reliable energization.

The power source connected to the piezoelectric film 10 is not limited, and may be a direct current power source or an alternating current power source. The driving voltage may be appropriately set so that the piezoelectric film 10 can be driven accurately according to the thickness of the piezoelectric layer 12 of the piezoelectric film 10, the material to be formed, and the like.

An example of the method of manufacturing the piezoelectric film 10 shown in fig. 1 will be described below with reference to conceptual diagrams of fig. 3 to 6.

First, as shown in fig. 3, a sheet 34 having the 2 nd electrode layer 16 formed on the 2 nd protective layer 20 is prepared. The sheet 34 can be produced by forming a copper thin film or the like as the 2 nd electrode layer 16 on the surface of the 2 nd protective layer 20 by vacuum deposition, sputtering, plating, or the like.

When the 2 nd protective layer 20 is extremely thin and has poor operability, etc., the 2 nd protective layer 20 with a separator (pseudo support) may be used as needed. Further, PET having a thickness of 25 to 100 μm or the like can be used as the separator. After the 2 nd electrode layer 16 and the 2 nd protective layer 20 are thermally bonded and before any component is laminated with the 2 nd protective layer 20, the separator may be removed.

On the other hand, a coating material is prepared by dissolving a polymer material having viscoelasticity at normal temperature, such as cyanoethylated PVA, in an organic solvent, and further adding piezoelectric particles 26, such as PZT particles, and dispersing the mixture by stirring.

The organic solvent is not limited, and various organic solvents such as Dimethylformamide (DMF), methyl ethyl ketone, and cyclohexanone can be used.

In the present invention, the number density of spots on the surface of the electrode layer can be set to 250 pieces/cm ² or less and the presence ratio of organic nuclei at the spots can be set to 20% or less by appropriately setting the dissolution time, the dissolution temperature, and the like when the polymer material is dissolved in the organic solvent. In order to further reduce the number density of spots and the presence ratio of organic nuclei, it is preferable to further lengthen the dissolution time and to further increase the dissolution temperature.

The dissolution time and the dissolution temperature may be appropriately set according to the type of the polymer material, the type and the mixing ratio of the organic solvent, and the like. For example, the dissolution time is preferably 1 hour or more, more preferably 1 hour to 24 hours, and still more preferably 5 hours to 24 hours. The dissolution temperature is preferably 30℃or higher, more preferably 30℃to 70℃and still more preferably 40℃to 70 ℃.

In the present invention, the number density of spots on the surface of the electrode layer can be adjusted according to the mixing time and the rotation speed at the time of mixing the piezoelectric particles in a solution in which the polymer material is dissolved in the organic solvent. In order to further reduce the number density of spots, it is preferable to further lengthen the mixing time and to further increase the rotational speed.

The stirring time and stirring speed may be appropriately set according to the type of piezoelectric particles, particle diameter, type of polymer material, type and mixing ratio of the organic solvent, and the like. For example, the mixing time is preferably 10 minutes or more, more preferably 10 minutes to 60 minutes, and still more preferably 15 minutes to 60 minutes. The rotation speed is preferably 500rpm or more, more preferably 500rpm to 1500rpm, and still more preferably 700rpm to 1500rpm.

The mixing time and the rotation speed are preferably set appropriately according to the type, size, and the like of the stirrer used for stirring. For example, it is known that when comparing the size of the disperser (EKO INSTRUMENTS co., ltd. Ae08) with the size of the disperser (PM 201 manufactured by AS ONE Corporation), the linear velocity applied to the outer periphery is reduced to generate unevenness because the disperser size is larger than the propeller mixer. Thus, longer mixing times and faster rotational speeds are not required.

After the sheet 34 is prepared and the paint is prepared, the paint is cast (coated) on the 2 nd electrode layer 16 of the sheet 34, and the organic solvent is evaporated and dried. As a result, as shown in fig. 4, a laminate 36 having the 2 nd electrode layer 16 on the 2 nd protective layer 20 and the piezoelectric layer 12 formed on the 2 nd electrode layer 16 was produced.

The casting method of the paint is not particularly limited, and any known coating method (coating apparatus) such as a tilted coater (slidecoater) and a coater blade (doctorknife) can be used.

Further, if the viscoelastic material is a substance that can be melted by heating, such as cyanoethylated PVA, a melt obtained by melting the viscoelastic material by heating and dispersing the piezoelectric particles 26 therein can be produced, and the melt can be extruded in a sheet form on the sheet 34 shown in fig. 3 by extrusion molding or the like and cooled, thereby producing a laminate 36 having the 2 nd electrode layer 16 on the 2 nd protective layer 20 and the piezoelectric layer 12 formed on the 2 nd electrode layer 16 as shown in fig. 4.

As described above, in the piezoelectric film 10, a dielectric polymer material such as polyvinylidene fluoride may be added to the substrate 24 in addition to the viscoelastic material such as cyanoethylated PVA.

When these polymer piezoelectric materials are added to the matrix 24, the polymer piezoelectric materials added to the paint may be dissolved. Or adding polymer piezoelectric material to be added to the above-mentioned heat-melted viscoelastic material, and heating and melting.

When the laminate 36 is produced, it is preferable to perform a rolling treatment for pressing the surface of the piezoelectric layer 12 by a heating roller or the like for the purpose of flattening the surface of the piezoelectric layer 12, adjusting the thickness of the piezoelectric layer 12, increasing the density of the piezoelectric particles 26 in the piezoelectric layer 12, and the like.

The method of the rolling treatment is not limited, and may be performed by a known method such as pressing by the above-mentioned heating roller or a treatment by a pressurizing machine.

The rolling treatment may be performed after the polarization treatment described later. However, if the rolling process is performed after the polarization process, the piezoelectric particles 26 pressed by the pressing are rotated, and the effect of the polarization process may be reduced. In view of this, the rolling treatment is preferably performed before the polarization treatment.

After the laminate 36 having the 2 nd electrode layer 16 on the 2 nd protective layer 20 and the piezoelectric layer 12 formed on the 2 nd electrode layer 16 is produced, it is preferable to perform polarization (polarization) of the piezoelectric layer 12 after the rolling process of the piezoelectric layer 12 is performed.

The method of polarizing the piezoelectric layer 12 is not limited, and a known method can be used. For example, electric field polarization in which a direct electric field is directly applied to an object to be subjected to polarization processing is exemplified. In addition, when electric field polarization is performed, the 1 st electrode layer 14 may be formed before the polarization treatment, and the electric field polarization treatment may be performed using the 1 st electrode layer 14 and the 2 nd electrode layer 16.

In addition, in manufacturing the piezoelectric film 10 of the present invention, the polarization treatment is preferably performed in the thickness direction, not in the plane direction of the piezoelectric layer 12.

On the other hand, a sheet 38 having the 1 st electrode layer 14 formed on the 1 st protective layer 18 is prepared. The sheet 38 can be produced by forming a copper thin film or the like as the 1 st electrode layer 14 on the surface of the 1 st protective layer 18 by vacuum evaporation, sputtering, plating, or the like. That is, the sheet 38 may be the same as the sheet 34 described above.

Next, as shown in fig. 5, the 1 st electrode layer 14 is oriented toward the piezoelectric layer 12, and the sheet 38 is laminated on the laminate 36.

Further, the piezoelectric film 10 shown in fig. 6 is produced by thermocompression bonding the laminate 36 and the laminate of the sheet 38 with a thermocompression bonding apparatus, a heating roller, and the like so as to sandwich the 2 nd protective layer 20 and the 1 st protective layer 18.

Alternatively, the laminate 36 and the sheet 38 are bonded, preferably further pressure bonded, with an adhesive to produce the piezoelectric film 10.

Such a piezoelectric film 10 may be manufactured using the sheet 34, the sheet 38, or the like which is cut into sheets, or may be manufactured using Roll-to-Roll (Roll to Roll).

The piezoelectric film thus produced may be cut into a desired shape according to various applications.

The piezoelectric film 10 manufactured in this way is polarized only in the thickness direction, not in the plane direction, and a high piezoelectric characteristic can be obtained even if the stretching treatment is not performed after the polarization treatment. Therefore, the piezoelectric film 10 does not have in-plane anisotropy in piezoelectric characteristics, and expands and contracts isotropically in all directions in the plane direction when a driving voltage is applied.

Such a piezoelectric film can be used for a piezoelectric speaker serving as a vibration plate in which the piezoelectric film itself vibrates. In addition, the piezoelectric speaker can also be used as a microphone, a sensor, or the like. Furthermore, the piezoelectric speaker can also be used as a vibration sensor.

The piezoelectric film can also be used as a so-called exciter that is attached to the diaphragm and vibrates the diaphragm. In the case where a piezoelectric film is used as an exciter, a laminated piezoelectric element in which piezoelectric films are laminated is preferable in order to obtain a higher output.

[ Multilayer piezoelectric element ]

The laminated piezoelectric element of the present invention is a laminated piezoelectric element in which the piezoelectric film is laminated by 2 or more layers.

Fig. 7 is a plan view schematically showing an example of the laminated piezoelectric element of the present invention.

The laminated piezoelectric element 50 shown in fig. 7 is formed by laminating a plurality of piezoelectric films 10. In the example shown in fig. 7, 3 piezoelectric films 10 are laminated. Adjacent piezoelectric films 10 are adhered to each other by the adhesive layer 72. In the example shown in fig. 7, the laminated piezoelectric element 50 is attached to the vibration plate 76 through the adhesive layer 74, and the electroacoustic transducer 70 is configured. A power source PS for applying a driving voltage is connected to each piezoelectric film 10. In addition, in the example shown in fig. 7, illustration of the protective layers of the respective piezoelectric films will be omitted, but as shown in fig. 1, the respective piezoelectric films have protective layers.

In this electroacoustic transducer 70, the piezoelectric film 10 expands and contracts in the planar direction by applying a driving voltage to the piezoelectric film 10 of the laminated piezoelectric element 50, and the laminated piezoelectric element 50 expands and contracts in the planar direction by the expansion and contraction of the piezoelectric film 10.

As a result of the expansion and contraction of the laminated piezoelectric element 50 in the plane direction, the diaphragm 76 is bent, and as a result, the diaphragm 76 vibrates in the thickness direction. By this vibration in the thickness direction, the vibration plate 76 emits a sound. The vibration plate 76 vibrates according to the magnitude of the driving voltage applied to the piezoelectric film 10, and emits sound corresponding to the driving voltage applied to the piezoelectric film 10.

That is, the electroacoustic transducer 70 can be used as a speaker using the laminated piezoelectric element 50 as an exciter.

The laminated piezoelectric element 50 shown in fig. 1 is formed by laminating 3 laminated films 10, but the present invention is not limited to this. That is, if the piezoelectric element is formed by laminating 2 or more piezoelectric films 10, the number of layers of piezoelectric films 10 may be 2 or 4 or more. In this regard, the laminated piezoelectric element 56 shown in fig. 8 described later is also the same.

In the laminated piezoelectric element 50 shown in fig. 7, the polarization directions of the adjacent piezoelectric films 10 are opposite to each other as a preferable mode. Therefore, in the adjacent piezoelectric film 10, the 1 st electrode layer 14 and the 2 nd electrode layer 16 face each other. Therefore, the power source PS is an ac power source or a dc power source, and always supplies electric power of the same polarity to the opposing electrodes. For example, in the laminated piezoelectric element 50 shown in fig. 7, the same polarity of electric power is always supplied to the 2 nd electrode layer 16 of the lowermost piezoelectric film 10 and the 2 nd electrode layer 16 of the 2 nd (middle) piezoelectric film 10 in the drawing, and the same polarity of electric power is always supplied to the 1 st electrode layer 14 of the 2 nd piezoelectric film 10 and the 1 st electrode layer 14 of the top piezoelectric film 10 in the drawing. Therefore, in the laminated piezoelectric element 50, even if the electrodes of the adjacent piezoelectric films 10 are in contact with each other, short circuits (short circuits) are not generated.

In the laminated piezoelectric element 50, the polarization direction of the piezoelectric film 10 may be detected by a d33 Meter (Meter) or the like. Or the polarization direction of the piezoelectric film 10 may be known from the processing conditions of the polarization.

In the example shown in fig. 7, the adjacent piezoelectric films 10 have opposite polarization directions, but the present invention is not limited to this, and the polarization directions of the piezoelectric layers 12 may be all the same.

In the example shown in fig. 7, a plurality of single-leaf piezoelectric films 10 are laminated, but the present invention is not limited to this.

Fig. 8 shows another example of the laminated piezoelectric element. Note that, in the laminated piezoelectric element 56 shown in fig. 8, since a plurality of members similar to those of the laminated piezoelectric element 50 described above are used, the same members are denoted by the same reference numerals, and mainly different portions will be described.

The laminated piezoelectric element 56 shown in fig. 8 is formed by laminating 2 or more piezoelectric films by folding the elongated piezoelectric film 10L 1 or more times, preferably a plurality of times, in the longitudinal direction. The laminated piezoelectric element 56 is attached with the piezoelectric film 10L laminated by folding through the adhesive layer 72.

The elongated 1 piezoelectric film 10L polarized in the thickness direction is folded and laminated, whereby the polarization directions of the piezoelectric films adjacent (facing) in the lamination direction are opposite to each other as indicated by the arrows in fig. 8.

With this configuration, the laminated piezoelectric element 56 can be configured by only 1 long piezoelectric film 10L, and the number of power sources PS for applying the driving voltage may be 1, or only 1 electrode lead from the piezoelectric film 10L may be used.

Thus, according to the laminated piezoelectric element 56 shown in fig. 8, the number of components can be reduced, and the structure can be simplified to improve the reliability as a piezoelectric element (module), and further, the cost reduction can be realized.

As in the laminated piezoelectric element 56 shown in fig. 8, in the laminated piezoelectric element 56 formed by folding the elongated piezoelectric film 10L, the mandrel 58 is preferably inserted in the folded portion of the piezoelectric film 10L so as to be in contact with the piezoelectric film 10L.

The 1 st electrode layer 14 and the 2 nd electrode layer 16 of the piezoelectric film 10L are formed of a metal vapor deposited film or the like. If the metal deposited film is bent at an acute angle, cracks (cracks) or the like are likely to occur, and the electrode may be broken. That is, in the laminated piezoelectric element 56 shown in fig. 8, cracks or the like are likely to occur in the electrode inside the bent portion.

In contrast, in the laminated piezoelectric element 56 in which the elongated piezoelectric film 10L is folded, the mandrel 58 is inserted into the folded portion of the piezoelectric film 10L, whereby the 1 st electrode layer 14 and the 2 nd electrode layer 16 can be appropriately prevented from being bent and broken lines can be generated.

While the piezoelectric film and the laminated piezoelectric element according to the present invention have been described in detail, the present invention is not limited to the above examples, and various modifications and alterations can be made without departing from the spirit of the present invention.

Examples

Hereinafter, the present invention will be described in more detail with reference to specific examples thereof.

Example 1

A piezoelectric film as shown in fig. 1 was produced by the method shown in fig. 3 to 6.

First, cyanoethylated PVA (CR-V, shin-Etsu Chemical co., manufactured by ltd.) was dissolved in Dimethylformamide (DMF) at a composition ratio below at 50 ℃ for 12 hours.

Next, PZT particles were added as piezoelectric particles in the following composition ratio, and stirred for 10 minutes at a disperser size (EKO INSTRUMENTS co., ltd. AE08, rotation speed 1000 rpm) to prepare a paint for forming a piezoelectric layer.

PZT particle 300 parts by mass of

Cyanoethylated PVA & lt/EN & gt 30 parts by mass

DMF & lt/EN & gt 70 parts by mass

The PZT particles were obtained by calcining mixed powders of Pb oxide, zr oxide, and Ti oxide, which are main components, in a ball mill at 800 ℃ for 5 hours so as to be zr=0.52 mol and ti=0.48 mol with respect to pb=1 mol, and then pulverizing the mixed powders.

On the other hand, 2 sheets of copper film having a thickness of 0.1 μm were prepared by vacuum deposition on a PET film having a thickness of 4. Mu.m. That is, in this example, the 1 st electrode layer and the 2 nd electrode layer were copper vapor deposited films having a thickness of 0.1m, and the 1 st protective layer and the 2 nd protective layer were PET films having a thickness of 4 μm.

A coating material for forming a piezoelectric layer prepared in advance was applied to a copper thin film (2 nd electrode layer) of 1 sheet by using a slide coater. The coating material was applied so that the film thickness of the dried coating film became 30. Mu.m.

Subsequently, DMF was evaporated by heating and drying the coated material on the sheet on a heating plate of 120 ℃. Thus, a laminate was produced having a 2 nd electrode layer made of copper on a 2 nd protective layer made of PET and a piezoelectric layer (polymer composite piezoelectric layer) having a thickness of 30 μm thereon.

The piezoelectric layer produced was subjected to a rolling treatment using a heated roller.

The piezoelectric layer thus produced was subjected to polarization treatment in the thickness direction.

The same sheet obtained by vacuum deposition of a copper film on a PET film was laminated on the laminate subjected to the polarization treatment as shown in fig. 6.

Next, the laminate of the laminate and the sheet was thermally bonded at 120 ℃ using a lamination apparatus, whereby a piezoelectric film as shown in fig. 1 was produced in which the piezoelectric layer was bonded to the 1 st electrode layer and the 2 nd electrode layer, the piezoelectric layer was sandwiched between the 1 st electrode layer and the 2 nd electrode layer, and the laminate was sandwiched between the 1 st protective layer and the 2 nd protective layer.

The number density of spots of the produced piezoelectric film was measured in the above-described manner and found to be 250 spots/cm ².

The proportion of organic nuclei at the spots was measured by the above method, and found to be 4%.

Example 2

A piezoelectric film was produced in the same manner as in example 1, except that the temperature at which cyanoethylated PVA was dissolved in DMF was changed to 70 ℃.

The number density of spots of the produced piezoelectric film was 45 spots/cm ². The proportion of organic nuclei at the spots was 0%,

Example 3

A piezoelectric film was produced in the same manner as in example 1, except that the temperature at which cyanoethylated PVA was dissolved in DMF was changed to 30 ℃ and the time was changed to 24 hours.

The number density of spots of the produced piezoelectric film was 40 spots/cm ². The proportion of organic nuclei at the spots was 0%,

Example 4

A piezoelectric film was produced in the same manner as in example 3, except that the rotation speed of the disperser at the time of mixing PZT particles was changed to 1500 rpm.

The number density of spots of the produced piezoelectric film was 10 spots/cm ². The proportion of organic nuclei at the spots was 0%,

Example 5

A piezoelectric film was produced in the same manner as in example 3, except that the mixing time when PZT particles were mixed was changed to 30 minutes.

The number density of spots of the produced piezoelectric film was 7 spots/cm ². The proportion of organic nuclei at the spots was 0%,

Example 6

A piezoelectric film was produced in the same manner as in example 3, except that the temperature at which cyanoethylated PVA was dissolved in DMF was changed to 70 ℃.

The number density of spots of the produced piezoelectric film was 3 spots/cm ². The proportion of organic nuclei at the spots was 0%,

Example 7

A piezoelectric film was produced in the same manner as in example 4, except that the time for dissolving cyanoethylated PVA in DMF was changed to 1 hour and the temperature was changed to 50 ℃.

The number density of spots of the produced piezoelectric film was 180 pieces/cm ². The proportion of organic nuclei at the spots was 20%.

Example 8

A piezoelectric film was produced in the same manner as in example 7, except that the time for dissolving cyanoethylated PVA in DMF was changed to 30 ℃.

The number density of spots of the produced piezoelectric film was 250 spots/cm ². The proportion of organic nuclei at the spots was 25%.

Comparative example 1

A piezoelectric film was produced in the same manner as in example 1, except that the temperature at which cyanoethylated PVA was dissolved in DMF was changed to 30 ℃ and the PZT particles were mixed by a propeller mixer (PM 201 manufactured by AS ONE Corporation).

The number density of spots of the produced piezoelectric film was 450 spots/cm ². The proportion of the organic nuclei at the spots was 10%.

Comparative example 2

A piezoelectric film was produced in the same manner as in comparative example 1, except that the temperature at which cyanoethylated PVA was dissolved in DMF was changed to 40 ℃.

The number density of spots of the produced piezoelectric film was 500 spots/cm ². The proportion of the organic nuclei at the spots was 6%.

Comparative example 3

A piezoelectric film was produced in the same manner as in comparative example 1, except that stirring was performed manually when PZT particles were mixed.

The number density of spots of the produced piezoelectric film was 2300 pieces/cm ². The proportion of the organic nuclei at the spots was 8%.

Comparative example 4

A piezoelectric film was produced in the same manner as in comparative example 1, except that the mixing time when PZT particles were mixed was changed to 2 minutes.

The number density of spots of the produced piezoelectric film was 1200 spots/cm ². The proportion of the organic nuclei at the spots was 8%.

Comparative example 5

A piezoelectric film was produced in the same manner as in comparative example 1, except that the time for dissolving cyanoethylated PVA in DMF was changed to 2 hours.

The number density of spots of the produced piezoelectric film was 400 spots/cm ². The proportion of organic nuclei at the spots was 15%.

Comparative example 6

A piezoelectric film was produced in the same manner as in comparative example 1, except that the time when cyanoethylated PVA was dissolved in DMF was changed to 1 time.

The number density of spots of the produced piezoelectric film was 350 spots/cm ². The proportion of organic nuclei at the spots was 30%.

[ Evaluation ]

The produced piezoelectric film was subjected to a cycle test to evaluate whether wrinkles were generated.

Appearance (with or without wrinkles)

The fabricated piezoelectric films were subjected to a cyclic test to evaluate whether or not there was any appearance defect after the cyclic test.

For the cyclic test, the piezoelectric film was placed in a laboratory, and the temperature was changed from-10℃to 65℃for 10 days under a humidity of 96% RH in the laboratory over 1 day.

The surface of the piezoelectric film after the cyclic test was visually observed, and the presence or absence of wrinkles was evaluated based on the following criteria. A: no wrinkles were observed. B: slight wrinkles were confirmed. C: wrinkles were confirmed.

The results are shown in table 1.

TABLE 1

As is clear from table 1, the piezoelectric film of the present invention can suppress the occurrence of wrinkles after the cycle test, as compared with the comparative example.

As is clear from the comparison between examples 1 and 7 and 8, the proportion of the organic nuclei present in the piezoelectric layer at the positions of the spots is preferably 20% or less.

The effect of the present invention is evident from the above results.

Industrial applicability

The piezoelectric film and the laminated piezoelectric element according to the present invention can be preferably used as various sensors (particularly useful for in-situ inspection of a base structure such as crack detection or foreign matter mixing detection), such as acoustic sensors, ultrasonic sensors, pressure sensors, tactile sensors, strain sensors, and vibration sensors, acoustic elements such as microphones, speakers, and exciters (specific applications are exemplified by noise cancellers (used for vehicles, electric buses, airplanes, robots, etc.), artificial vocal cords, buzzers for preventing invasion of pests/harmful animals, furniture, wallpaper, photographs, helmets, goggles, headrests, labels, robots, etc.), ultrasonic transducers such as automobile, smart phones, smart watches, tactile interfaces of game machines, ultrasonic probes, and underwater wave receivers; an actuator used for preventing adhesion, conveyance, stirring, dispersion, grinding, and the like of water droplets; damping materials (dampers) used in sports equipment such as containers, rides, buildings, snowboards, and rackets; and vibration power generation devices suitable for roads, floors, mattresses, chairs, shoes, tires, wheels, computer keyboards and the like.

Symbol description

10. 10L-piezoelectric film, 12-piezoelectric layer, 14-1 st electrode layer, 16-2 nd electrode layer, 18-1 st protective layer, 20-2 nd protective layer, 24-substrate, 26-piezoelectric particles, 34, 38-sheet, 36-laminate, 50, 56-laminate piezoelectric element, 58-mandrel, 70-electroacoustic transducer, 72, 74-adhesive layer.

Claims

1. A piezoelectric film, comprising:

a piezoelectric layer containing piezoelectric particles in a matrix containing a polymer material;

Electrode layers provided on both sides of the piezoelectric layer; and

A protective layer provided on a surface of the electrode layer opposite to the piezoelectric layer,

Wherein,

The number density of spots on the surface of the electrode layer is 250/cm ² or less.

2. The piezoelectric film of claim 1, wherein,

At the position of the spot, the proportion of organic nuclei in the piezoelectric layer, which have a region inscribable by a minimum circumscribed circle having a diameter of 10 μm or more, is 20% or less.

3. A laminated piezoelectric element comprising 2 or more layers of the piezoelectric film according to claim 1 or 2.

4. The laminated piezoelectric element according to claim 3, wherein the piezoelectric film is laminated by at least 2 layers by folding the piezoelectric film 1 or more times.