WO2022190715A1

WO2022190715A1 - Piezoelectric film

Info

Publication number: WO2022190715A1
Application number: PCT/JP2022/003906
Authority: WO
Inventors: 裕介香川; 輝男芦川
Original assignee: 富士フイルム株式会社
Priority date: 2021-03-11
Filing date: 2022-02-02
Publication date: 2022-09-15
Also published as: TW202236704A; JPWO2022190715A1

Abstract

Provided is a highly-flexible piezoelectric film capable of sufficiently ensuring conduction through an electrode layer. The piezoelectric film comprises a piezoelectric layer, electrode layers respectively formed on both sides of the piezoelectric layer, and protective layers, each laminated on the surface of each electrode layer on the reverse side of the surface on the piezoelectric layer side, wherein one protective layer has a hole portion that passes through to an electrode layer from the surface and has a flexible conductive member that is disposed inside the hole portion and includes at least one of a conductive fabric, a metal fabric and a conductive urethane foam which electrically connects the electrode layer and a conductor.

Description

piezoelectric film

The present invention relates to piezoelectric films.

In response to the thinning of displays such as liquid crystal displays and organic EL displays, the speakers used in these thin displays are also required to be lighter and thinner. Furthermore, in a flexible display having flexibility, the speaker is also required to be flexible in order to integrate the speaker into the flexible display without impairing light weight and flexibility. As such a lightweight, thin and flexible speaker, it is considered to employ a sheet-like piezoelectric film (electroacoustic conversion film) having a property of expanding and contracting in response to an applied voltage.

A piezoelectric film having electrode layers and protective layers on both sides of a piezoelectric layer has been proposed as such a flexible sheet-like piezoelectric film.

For example, Patent Document 1 discloses a dielectric layer, thin film electrodes formed on both sides of the dielectric layer (piezoelectric layer), and protective layers formed on the surfaces of both thin film electrodes. Furthermore, an electroacoustic conversion film is disclosed in which at least one of the protective layers has a thin layer portion thinner than the peripheral portion.

In such an electroacoustic conversion film, it is necessary to make the thickness of the electrode layer very thin in order to vibrate the electroacoustic conversion film by applying a voltage to the electrode layer. For example, a deposited film having a thickness of 1 μm or less is suitable for the electrode layer.

On the other hand, in order to mount the electroacoustic conversion film as a speaker or the like, it is necessary to pull out the electrode layer and connect wiring there.
However, it is difficult to extract a thin electrode layer such as a deposited film out of the plane of the electroacoustic conversion film. In addition, if a thin electrode such as a deposited film is exposed to the outside for connection with wiring and stored in this state, the electrode may be oxidized depending on the storage environment, resulting in a decrease in conductivity.

On the other hand, it has been proposed to provide a hole in the protective layer, insert a conductive material into the hole, and connect the lead wire to the conductive material.

For example, Patent Document 1 describes a configuration in which a recess is provided in a protective layer, a conductive material is inserted into the recess, and a lead wiring for electrically connecting an electrode layer and an external device is connected to the conductive material. It is It is described that, as a result, the electrical connection between the electrode layer and the lead wiring can be ensured, and the electrode layer can be prevented from being deteriorated due to oxidation or the like because the electrode layer is entirely covered with the protective layer. ing.

JP 2016-015354 A

Patent Document 1 describes electrically connecting an electrode layer and a wiring by inserting a conductive paste containing a conductive filler, a metal member, or the like into a hole provided in a protective layer.

When a conductive paste is used, the paint of the conductive paste is applied to the inside of the hole and then dried before use. There is a problem that the thickness of the conductive paste afterward becomes thinner than the protective layer, and the contact area between the filler and the electrode layer and/or the wiring decreases, and sufficient conduction with the wiring may not be obtained. .

Also, when a solid metal member is used, there is a problem that the flexibility of the piezoelectric film is lowered. It is conceivable to use solder to electrically connect the electrode layer and the wiring. .

An object of the present invention is to solve the problems of the prior art, and to provide a piezoelectric film that has high flexibility and can sufficiently ensure electrical connection to the electrode layer.

In order to solve the problems described above, the present invention has the following configurations.
[1] A piezoelectric film having a piezoelectric layer, electrode layers formed on both sides of the piezoelectric layer, and a protective layer laminated on a surface of the electrode layer opposite to the surface of the electrode layer,
The protective layer has a hole penetrating from the surface to the electrode layer,
A piezoelectric film having a soft conductive member including at least one of a conductive cloth, a metal cloth, and a conductive urethane foam disposed in the hole and electrically connecting the electrode layer and the conductive wire.
[2] The piezoelectric film according to [1], which has a sealing member that covers the connection position between the soft conductive member and the lead wire.
[3] The piezoelectric film according to [2], wherein the thickness of the soft conductive member before being covered with the sealing member is thicker than the thickness of the protective layer.
[4] The piezoelectric film according to any one of [1] to [3], which has a conductive adhesive tape placed between the soft conductive member and the conductor.
[5] The piezoelectric film according to any one of [1] to [4], wherein the piezoelectric layer is composed of a polymeric composite piezoelectric body containing piezoelectric particles in a matrix containing a polymeric material.

According to the present invention, it is possible to provide a piezoelectric film that has high flexibility and can sufficiently ensure electrical connection to the electrode layer.

1 is a plan view schematically showing an example of the piezoelectric film of the present invention; FIG. FIG. 2 is a cross-sectional view taken along the line AA of FIG. 1; FIG. 2 is a cross-sectional view taken along line BB of FIG. 1; It is a conceptual diagram for explaining an example of a method of manufacturing a piezoelectric film. It is a conceptual diagram for explaining an example of a method of manufacturing a piezoelectric film. It is a conceptual diagram for explaining an example of a method of manufacturing a piezoelectric film. It is a conceptual diagram for explaining an example of a method of manufacturing a piezoelectric film. It is a conceptual diagram for explaining an example of a method of manufacturing a piezoelectric film. It is a conceptual diagram for explaining an example of a method of manufacturing a piezoelectric film. It is a conceptual diagram for explaining an example of a method of manufacturing a piezoelectric film.

The piezoelectric film of the present invention will be described in detail below based on preferred embodiments shown in the accompanying drawings.

The description of the constituent elements described below may be made based on representative embodiments of the present invention, but the present invention is not limited to such embodiments.
In this specification, a numerical range represented by "-" means a range including the numerical values before and after "-" as lower and upper limits.

[Piezoelectric film]
The piezoelectric film of the present invention is
A piezoelectric film having a piezoelectric layer, electrode layers formed on both sides of the piezoelectric layer, and a protective layer laminated on a surface of the electrode layer opposite to the surface of the electrode layer,
The protective layer has a hole penetrating from the surface to the electrode layer,
A piezoelectric film having a soft conductive member including at least one of a conductive cloth, a metal cloth and a conductive urethane foam disposed in a hole and electrically connecting an electrode layer and a conductive wire.

FIG. 1 shows a plan view schematically showing an example of the piezoelectric film of the present invention. FIG. 2 shows a cross-sectional view of the piezoelectric film of FIG. 1 taken along the line AA. FIG. 3 shows an enlarged cross-sectional view of a part of the piezoelectric film of FIG. 1 taken along line BB.

The piezoelectric film 10 shown in FIGS. 1 to 3 includes a piezoelectric layer 20 which is a sheet-like material having piezoelectric properties, a lower electrode layer 24 laminated on one side of the piezoelectric layer 20, and a lower electrode layer 24 laminated on the lower electrode layer 24. an upper protective layer 26 laminated on the other surface of the piezoelectric layer 20; an upper protective layer 30 laminated on the upper electrode layer 26; a soft conductive member 70; , a sealing member 74 and a conductor 76 .

As shown in FIG. 2, the piezoelectric layer 20 includes piezoelectric particles 36 in a matrix 34 containing polymeric material. Also, the lower electrode layer 24 and the upper electrode layer 26 are electrode layers in the present invention. Also, the lower protective layer 28 and the upper protective layer 30 are protective layers in the present invention.
As will be described later, the piezoelectric film 10 (piezoelectric layer 20) is preferably polarized in the thickness direction.

As shown in FIG. 3, the upper protective layer 30 has holes 31 penetrating from the surface to the upper electrode layer 26 . That is, the hole 31 is formed through the upper protective layer 30 from the surface opposite to the upper electrode layer 26 to the interface on the upper electrode layer 26 side. As shown in FIG. 1, the hole 31 is formed near the end of the upper protective layer 30 in the plane direction.
Although not shown, the lower protective layer 28 also has a hole penetrating from the surface to the lower electrode layer 24 in the same manner. That is, the hole portion of the lower protective layer 28 is formed through the lower protective layer 28 from the surface opposite to the lower electrode layer 24 to the interface on the lower electrode layer 24 side.

The soft conductive member 70 is filled in the hole 31 , is in contact with the upper electrode layer 26 inside the hole 31 , and is electrically connected to the upper electrode layer 26 . In the example shown in FIG. 3, the soft conductive member 70 is electrically connected to the conductive adhesive tape 72 provided in a preferred embodiment by contacting the surface opposite to the upper electrode layer 26 .

The soft conductive member 70 includes at least one of conductive cloth, metal cloth and conductive urethane foam. That is, the soft conductive member 70 may be made of a conductive cloth, a metal cloth, a conductive urethane foam, or a conductive cloth and a conductive material. Any of a combination with urethane foam, a combination of metal cloth and conductive urethane foam, and a combination of conductive cloth and metal cloth may be used, or a combination of conductive cloth, metal cloth and conductive urethane foam may be used. It can be anything. For example, the soft conductive member 70 may have a configuration in which conductive cloth is laminated on both sides of conductive urethane foam.

A conductive cloth is, for example, a woven or non-woven fabric woven from resin threads coated with a metal film by plating or the like. Various known conductive cloths can be used as the conductive cloth. For example, as the conductive cloth, a conductive cloth obtained by plating the surface of a thread made of PET with Cu or Ni is exemplified. Specifically, Sui-10-511M manufactured by Seiren Co., Ltd. can be used as the conductive cloth.

In the present invention, it is preferable to use a conductive cloth with low resistance and high flexibility. The surface resistivity of the conductive cloth is 0.1Ω/sq. The following is preferable, and 0.05Ω/sq. The following are more preferred. Moreover, as thickness of an electrically conductive cloth, 500 micrometers or less are preferable and 100 micrometers or less are more preferable.

A metal cloth is a woven or non-woven fabric woven with metal threads. Various known metal cloths can be used as the metal cloth. As an example, a plain weave wire mesh Φ0.05×200 m/s manufactured by Okutani Wire Net Mfg. Co., Ltd. can be used as the metal cloth.

Copper is preferable as the material for the metal cloth. The number of stitches per side (1 inch) of the metal cloth is preferably 100 or more, more preferably 200 or more.

　Conductive urethane foam is made by supporting conductive particles such as carbon black on soft urethane foam. Various known conductive urethane foams can be used as the conductive urethane foam.

It is preferable to use conductive urethane foam that has low resistance and is highly flexible. The surface resistivity of the conductive urethane foam is 0.1Ω/sq. The following is preferable, and 0.05Ω/sq. The following are more preferred. Also, the thickness of the conductive urethane foam is preferably 500 μm or less, more preferably 100 μm or less.

As shown in FIG. 3, the conductive adhesive tape 72 is adhered to a position overlapping the hole 31 of the upper protective layer 30 in the surface direction. That is, the conductive adhesive tape 72 contacts and is electrically connected to the soft conductive member 70 arranged in the hole 31 .

The conductive adhesive tape 72 has an adhesive layer provided on at least one surface of a conductive foil, and is attached to the upper protective layer 30 by being laminated with the adhesive layer facing the upper protective layer 30 . . In addition, the conductive adhesive tape 72 may be provided with adhesive layers on both sides of the conductive foil. 30, and the conductive wire 76 is adhered to the other adhesive layer.

A conductive wire 76 is arranged on the surface of the conductive adhesive tape 72 opposite to the upper protective layer 30 .

The conducting wire 76 is a conductive sheet-like or wire-like member. Conductive wire 76 is electrically connected to soft conductive member 70 via conductive adhesive tape 72 . Also, the above-described soft conductive member may be used as the lead wire 76 .

The sealing member 74 is an insulating sheet-like member, and is covered with an upper protective layer so as to cover at least a part of the positions where the flexible conductive member 70, the conductive adhesive tape 72, and the conductive wire 76 are laminated in the surface direction. 30 is laminated on. In the example shown in FIG. 3, the sealing member 74 is laminated so as to cover the entire surfaces of the soft conductive member 70 and the conductive adhesive tape 72 . A sealing member 74 can fix the soft conductive member 70 , the conductive adhesive tape 72 , and the lead wire 76 .

Although illustration is omitted, the holes of the lower protective layer 28 are similarly filled with the soft conductive member 70 on the lower protective layer 28 side, and the conductive adhesive tape 72 is attached to the lower protective layer 28 so as to cover the soft conductive member 70 . 28, the conductive wire 76 is placed on the conductive adhesive tape 72 and electrically connected to the soft conductive member 70, and the sealing member 74 is formed by the soft conductive member 70, the conductive adhesive tape 72 and the conductive wire. It is laminated so as to cover at least part of the position where 76 is laminated.

Thus, in the piezoelectric film 10, the conductor wire 76 is electrically connected to the conductive adhesive tape 72, the conductive adhesive tape 72 is electrically connected to the soft conductive member 70, and the soft conductive member 70 is the electrode. electrically connected to the layer. Therefore, the conducting wire 76 can be used as a lead wire, and wiring can be connected to the conducting wire 76 . Alternatively, the conductor 76 can be used as wiring.

Here, as described above, when the conductive paste containing the conductive filler is filled in the holes provided in the protective layer to electrically connect the electrode layer and the wiring, the conductive paste at the time of application Depending on the dispersion state of the conductive filler, the amount of the conductive filler may decrease, and the thickness of the conductive paste after drying may become thinner than the protective layer, resulting in insufficient electrical connection with the wiring. There was a problem.

Further, in the case where the hole provided in the protective layer is filled with a solid metal member or solder to electrically connect the electrode layer and the wiring, the flexibility of the piezoelectric film becomes low. There was a problem of hoarding.

On the other hand, in the piezoelectric film 10 of the present invention, the holes of the protective layer are filled with a soft conductive member 70 containing at least one of conductive cloth, metal cloth and conductive urethane foam, and the soft conductive member 70 is inserted between the holes. to electrically connect the electrode layer and the conductor 76 . Therefore, since there is no influence of the dispersed state of the conductive filler, the electrical connection between the electrode layer and the conductor wire 76 can be ensured. In addition, since the soft conductive member 70 is more flexible than a solid metal member or solder, the piezoelectric film has high flexibility without impairing the flexibility of the piezoelectric film. be able to.

Here, in the example shown in FIG. 3, the structure having the soft conductive member 70, the conductive adhesive tape 72, and the sealing member 74 adhered on the upper protective layer 30 so as to cover the conductive wire 76 is adopted. is not limited to For example, the piezoelectric film of the present invention does not have the sealing member 74, the conductive adhesive tape 72 has adhesive layers on both sides, and the conducting wire 76 is attached to the conductive adhesive tape 72. good.

Alternatively, the piezoelectric film of the present invention may have a configuration in which the sealing member 74 is not provided and the fixing member is adhered to the protective layer so as to cover the conductive wire 76 at a position not covering the soft conductive member 70 . .

In addition, by having the soft conductive member 70, the conductive adhesive tape 72, and the sealing member 74 adhered onto the upper protective layer 30 so as to cover the conductive wire 76, the conductive wire 76 can be replaced by the soft conductive member 70 (conductive By pressing it against the adhesive tape 72 ), the contact area can be increased, and stable electrical connection can be obtained between the soft conductive member 70 (electrode layer) and the lead wire 76 . In addition, by having the sealing member 74, when the piezoelectric film is bent, the positions of the soft conductive member 70, the conductive adhesive tape 72, and the lead wire 76 are displaced and the contact area is prevented from becoming small. and stable conduction can be obtained.

Also, in the example shown in FIG. 3, the configuration is such that the conductive adhesive tape 72 is arranged between the soft conductive member 70 and the lead wire 76, but the configuration is not limited to this. For example, the piezoelectric film of the present invention may have a configuration in which the conductive adhesive tape 72 is not provided and the soft conductive member 70 and the lead wire 76 are in direct contact and electrically connected.

By having the conductive adhesive tape 72 arranged between the soft conductive member 70 and the conductive wire 76, the contact between the soft conductive member 70 and the conductive wire 76 can be reliably maintained, and the soft conductive member 70 and the conductive wire 76 can be kept in contact with each other. Stable conduction can be obtained by reducing the resistance between the conductors 76 .

Also, it is preferable that the soft conductive member 70 and the electrode layer are not adhered with a conductive adhesive tape or the like. When the soft conductive member 70 and the electrode layer are adhered to each other, when a pulling force is applied to the conductive wire 76 , a pulling force is also applied to the soft conductive member 70 connected to the conductive wire 76 . Since the electrode layer is very thin, if the electrode layer and the soft conductive member 70 are adhered, the electrode layer adhered to the soft conductive member 70 will be damaged when the soft conductive member 70 is pulled. There is a risk.

Also, the shape of the opening surface of the hole 31 of the protective layer is not limited, and may be various shapes such as circular, elliptical, rectangular, polygonal, and irregular. A circular shape is preferable from the viewpoint of ease of formation.

Further, the size of the opening surface of the hole 31 is not particularly limited as long as it is a size that can ensure electrical connection between the soft conductive member 70 and the electrode layer and allows the piezoelectric film to operate properly. The equivalent circle diameter of the opening surface of the hole is preferably 0.5 mm to 20 mm, more preferably 1.5 mm to 8 mm, and even more preferably 2 mm to 3 mm.

In addition, the size and shape of the soft conductive member 70 in plan view are not particularly limited as long as they can fill the holes 31 of the protective layer and can ensure electrical connection with the electrode layer. It is preferable that the size of the soft conductive member 70 approximately match the size and shape of the hole 31 of the protective layer.

Also, the thickness of the soft conductive member 70 before being covered with the sealing member 74 is preferably greater than the thickness of the protective layer. By making the thickness of the soft conductive member 70 thicker than the thickness of the protective layer and attaching the soft conductive member 70 so as to press it with the sealing member 74, the soft conductive member 70, the lead wire 76, and the soft conductive member 70 and the electrode layer can be reliably brought into contact with each other, and stable conduction can be obtained.

From the viewpoint of obtaining stable conduction, the thickness of the soft conductive member 70 before being covered with the sealing member 74 is preferably 1.1 times or more, more preferably 1.5 to 125 times the thickness of the protective layer. 1.5 times to 25 times is more preferable.

Here, in the example shown in FIG. 1, a conductor 76 electrically connected to the upper electrode layer 26 via the soft conductive member 70 and the conductive adhesive tape 72 on the side of the upper protective layer 30 and a conductor 76 on the side of the lower protective layer 28 In a preferred embodiment, the conductive wires 76 electrically connected to the lower electrode layer 24 via the soft conductive member and the conductive adhesive tape are arranged so as not to overlap each other in the plane direction. As a result, it is possible to prevent the conductive wire 76 on the upper electrode layer 26 side and the conductive wire 76 on the lower electrode layer 24 side from coming into contact with each other and causing a short circuit.

In the example shown in FIG. 1, each of the upper protective layer 30 and the lower protective layer 28 has one hole, and the electrode layer and the conductive wire 76 are connected through the flexible conductive member 70 arranged in each hole. Although it is configured to be electrically connected, it is not limited to this. It is good also as a structure connected to. That is, each electrode layer may be configured to be electrically connected to the conducting wire 76 at two or more locations.

Such a piezoelectric film 10 is used, for example, in various acoustic devices (acoustic equipment) such as speakers, microphones, and pickups used in musical instruments such as guitars to generate (reproduce) sounds by vibrating in response to electrical signals. It is also used to convert sound vibrations into electrical signals. In addition, the piezoelectric film can also be used for pressure sensors, power generation elements, and the like.

Each component of the piezoelectric film of the present invention will be described below.

[Piezoelectric layer]
The piezoelectric layer 20 may be a layer made of a known piezoelectric material. In the present invention, the piezoelectric layer 20 is preferably a polymeric composite piezoelectric body containing piezoelectric particles 36 in a matrix 34 containing a polymeric material.

As the material for the matrix 34 (matrix and binder) of the polymer composite piezoelectric material constituting the piezoelectric layer 20, it is preferable to use a polymer material having viscoelasticity at room temperature. In this specification, "ordinary temperature" refers to a temperature range of about 0 to 50.degree.

The piezoelectric film 10 of the present invention is suitably used for speakers having flexibility, such as speakers for flexible displays. Here, the polymeric composite piezoelectric material (piezoelectric layer 20) used in the flexible speaker preferably satisfies the following requirements. Therefore, it is preferable to use a polymeric material having viscoelasticity at room temperature as a material that satisfies the following requirements.

(i) Flexibility For example, when gripping a loosely bent state like a document like a newspaper or magazine for portable use, it is constantly subjected to a relatively slow and large bending deformation of several Hz or less from the outside. become. At this time, if the polymer composite piezoelectric material is hard, a correspondingly large bending stress is generated, and cracks occur at the interface between the matrix and the piezoelectric particles, which may eventually lead to destruction. Therefore, the polymer composite piezoelectric body is required to have appropriate softness. Moreover, stress can be relieved if strain energy can be diffused to the outside as heat. Therefore, it is required that the loss tangent of the polymer composite piezoelectric material is appropriately large.
(ii) Sound quality Speakers vibrate piezoelectric particles at frequencies in the audio band of 20 Hz to 20 kHz, and the vibration energy causes the entire polymer composite piezoelectric material (piezoelectric film) to vibrate as one to reproduce sound. be. Therefore, the polymer composite piezoelectric body is required to have appropriate hardness in order to increase the transmission efficiency of vibration energy. In addition, if the frequency characteristics of the speaker are smooth, the amount of change in sound quality when the lowest resonance frequency changes as the curvature changes becomes small. Therefore, the loss tangent of the polymer composite piezoelectric body is required to be moderately large.

In summary, the polymer composite piezoelectric body is required to behave hard against vibrations of 20 Hz to 20 kHz and softly against vibrations of several Hz or less. Also, the loss tangent of the polymer composite piezoelectric body is required to be moderately large with respect to vibrations of all frequencies of 20 kHz or less.

In general, polymer solids have a viscoelastic relaxation mechanism, and as the temperature rises or the frequency decreases, large-scale molecular motion causes a decrease (relaxation) in the storage elastic modulus (Young's modulus) or a maximum loss elastic modulus (absorption). is observed as Among them, the relaxation caused by the micro-Brownian motion of the molecular chains in the amorphous region is called principal dispersion, and a very large relaxation phenomenon is observed. The temperature at which this primary dispersion occurs is the glass transition point (Tg), and the viscoelastic relaxation mechanism appears most prominently.

In the polymer composite piezoelectric body (piezoelectric layer 20), by using a polymer material having a glass transition point at room temperature, in other words, a polymer material having viscoelasticity at room temperature, as a matrix, vibration of 20 Hz to 20 kHz is hard, and a polymer composite piezoelectric material that behaves softly against slow vibrations of several Hz or less is realized. In particular, it is preferable to use a polymeric material having a glass transition temperature of normal temperature, ie, 0 to 50° C. at a frequency of 1 Hz, for the matrix of the polymeric composite piezoelectric material in order that this behavior can be favorably expressed.

As the polymeric material having viscoelasticity at room temperature, various known materials can be used as long as they have dielectric properties. Preferably, the polymeric material used has a maximum loss tangent value of 0.5 or more at a frequency of 1 Hz according to a dynamic viscoelasticity test at room temperature, that is, at 0° C. to 50° C. As a result, when the polymer composite piezoelectric body is slowly bent by an external force, the stress concentration at the interface between the matrix and the piezoelectric particles at the maximum bending moment portion is relaxed, and good flexibility is obtained.

In addition, the polymer material preferably 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. As a result, the bending moment generated when the polymeric composite piezoelectric body is slowly bent by an external force can be reduced, and at the same time, it can behave rigidly against acoustic vibrations of 20 Hz to 20 kHz.

Further, it is more preferable that the polymer material has a dielectric constant of 10 or more at 25°C. As a result, when a voltage is applied to the polymer composite piezoelectric material, a higher electric field is applied to the piezoelectric particles in the matrix, so a large amount of deformation can be expected.

However, on the other hand, in consideration of ensuring good moisture resistance, etc., it is also suitable for the polymer material to have a dielectric constant of 10 or less at 25°C.

Polymer materials that satisfy these conditions include cyanoethylated polyvinyl alcohol (cyanoethylated PVA), polyvinyl acetate, polyvinylidene chloride core acrylonitrile, polystyrene-vinylpolyisoprene block copolymer, polyvinylmethylketone, and polybutyl. Methacrylate and the like are exemplified. Commercially available products such as Hybler 5127 (manufactured by Kuraray Co., Ltd.) can also be suitably used as these polymer materials. Among them, as the polymer material, it is preferable to use a material having a cyanoethyl group, and it is particularly preferable to use cyanoethylated PVA. These polymer materials may be used singly or in combination (mixed).

The matrix 34 using such a polymer material may use a plurality of polymer materials together, if necessary. That is, for the purpose of adjusting the dielectric properties and mechanical properties of the matrix 34, in addition to the polymer material having viscoelasticity at room temperature, other dielectric polymer materials may be added as necessary. .

Examples of dielectric polymer materials that can be added include polyvinylidene fluoride, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, and polyvinylidene fluoride-trifluoroethylene copolymer. and fluorine-based polymers such as polyvinylidene fluoride-tetrafluoroethylene copolymer, vinylidene cyanide-vinyl acetate copolymer, cyanoethylcellulose, cyanoethylhydroxysaccharose, cyanoethylhydroxycellulose, cyanoethylhydroxypullulan, cyanoethylmethacrylate, cyanoethylacrylate, cyanoethyl Cyano groups such as hydroxyethylcellulose, cyanoethylamylose, cyanoethylhydroxypropylcellulose, cyanoethyldihydroxypropylcellulose, cyanoethylhydroxypropylamylose, cyanoethylpolyacrylamide, cyanoethylpolyacrylate, cyanoethylpullulan, cyanoethylpolyhydroxymethylene, cyanoethylglycidolpullulan, cyanoethylsaccharose and cyanoethylsorbitol. Alternatively, polymers having cyanoethyl groups, and synthetic rubbers such as nitrile rubber and chloroprene rubber are exemplified. Among them, polymer materials having cyanoethyl groups are preferably used.

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

In addition to the dielectric polymer material, the matrix 34 also contains thermoplastic resins such as vinyl chloride resin, polyethylene, polystyrene, methacrylic resin, polybutene, and isobutylene, and phenol for the purpose of adjusting the glass transition point. Thermosetting resins such as resins, urea resins, melamine resins, alkyd resins, and mica may be added. Furthermore, a tackifier such as rosin ester, rosin, terpene, terpene phenol, and petroleum resin may be added for the purpose of improving adhesiveness.

When adding a material other than a polymer material having viscoelasticity such as cyanoethylated PVA to the matrix 34 of the piezoelectric layer 20, there is no particular limitation on the amount of the material added, but the ratio of the material to the matrix 34 is 30% by mass or less. preferably. As a result, the characteristics of the polymer material to be added can be expressed without impairing the viscoelastic relaxation mechanism in the matrix 34, so that the dielectric constant can be increased, the heat resistance can be improved, and the adhesion between the piezoelectric particles 36 and the electrode layer can be improved. favorable results can be obtained in terms of

The piezoelectric layer 20 is a polymeric composite piezoelectric body containing piezoelectric particles 36 in such a matrix 34 .

The piezoelectric particles 36 are made of ceramic particles having a perovskite or wurtzite crystal structure. Examples of ceramic particles constituting the piezoelectric particles 36 include lead zirconate titanate (PZT), lead zirconate lanthanate titanate (PLZT), barium titanate (BaTiO ₃ ), zinc oxide (ZnO), and A solid solution (BFBT) of barium titanate and bismuth ferrite (BiFe ₃ ) is exemplified. Only one kind of these piezoelectric particles 36 may be used, or a plurality of kinds thereof may be used together (mixed).

The particle size of such piezoelectric particles 36 is not limited, and may be appropriately selected according to the size and application of the polymer composite piezoelectric material (piezoelectric film 10). The particle size of the piezoelectric particles 36 is preferably 1 to 10 μm. By setting the particle diameter of the piezoelectric particles 36 within this range, favorable results can be obtained in that the polymer composite piezoelectric body (piezoelectric film 10) can achieve both high piezoelectric characteristics and flexibility.

Although the piezoelectric particles 36 in the piezoelectric layer 20 are uniformly and regularly dispersed in the matrix 34 in FIG. 2, the present invention is not limited to this. That is, the piezoelectric particles 36 in the piezoelectric layer 20 may be randomly dispersed in the matrix 34, preferably uniformly dispersed.

In the piezoelectric layer 20 (polymer composite piezoelectric material), there is no restriction on the quantitative ratio between the matrix 34 and the piezoelectric particles 36 in the piezoelectric layer 20. It may be appropriately set according to the application of the composite piezoelectric material and the properties required for the polymer composite piezoelectric material. 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 50% to 80% is even more preferable. By setting the amount ratio between the matrix 34 and the piezoelectric particles 36 within the above range, favorable results can be obtained in terms of achieving both high piezoelectric properties and flexibility.

The thickness of the piezoelectric layer 20 is not limited, and may be appropriately set according to the application of the polymer composite piezoelectric material, the properties required for the polymer composite piezoelectric material, and the like. The thicker the piezoelectric layer 20 is, the more advantageous it is in terms of stiffness, such as stiffness of the so-called sheet, but the voltage (potential difference) required to expand and contract the piezoelectric layer 20 by the same amount is increased. The thickness of the piezoelectric layer 20 is preferably 10-300 μm, more preferably 20-200 μm, even more preferably 30-150 μm. By setting the thickness of the piezoelectric layer 20 within the above range, it is possible to obtain favorable results in terms of ensuring both rigidity and appropriate flexibility.

[Electrode layer and protective layer]
As shown in FIG. 2, the illustrated piezoelectric film 10 has a lower electrode layer 24 on one surface of the piezoelectric layer 20, a lower protective layer 28 on the surface thereof, and a lower protective layer 28 on the surface of the piezoelectric layer 20. It has an upper electrode layer 26 and an upper protective layer 30 on its surface. Here, the upper electrode layer 26 and the lower electrode layer 24 form an electrode pair.

That is, the piezoelectric film 10 has a piezoelectric layer 20 sandwiched between electrode pairs, that is, an upper electrode layer 26 and a lower electrode layer 24 , and this laminate sandwiched between a lower protective layer 28 and an upper protective layer 30 . have a configuration.
Thus, in the piezoelectric film 10, the region sandwiched between the upper electrode layer 26 and the lower electrode layer 24 expands and contracts according to the applied voltage.

The lower protective layer 28 and the upper protective layer 30 serve to cover the upper electrode layer 26 and the lower electrode layer 24 and to give the piezoelectric layer 20 appropriate rigidity and mechanical strength. That is, in the piezoelectric film 10, the piezoelectric layer 20 composed of the matrix 34 and the piezoelectric particles 36 exhibits excellent flexibility against slow bending deformation. May lack mechanical strength. The piezoelectric film 10 is provided with a lower protective layer 28 and an upper protective layer 30 to compensate.

There are no restrictions on the lower protective layer 28 and the upper protective layer 30, and various sheet-like materials can be used. As an example, various resin films are preferably exemplified. Among them, polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS), polycarbonate (PC), polyphenylene sulfite (PPS), polymethyl methacrylate (PMMA), due to their excellent mechanical properties and heat resistance. ), polyetherimide (PEI), polyimide (PI), polyethylene naphthalate (PEN), triacetyl cellulose (TAC), cyclic olefin resins, and the like are preferably used.

The thicknesses of the lower protective layer 28 and the upper protective layer 30 are also not limited. Also, although the thicknesses of the lower protective layer 28 and the upper protective layer 30 are basically the same, they may be different. Here, if the rigidity of the lower protective layer 28 and the upper protective layer 30 is too high, not only will the expansion and contraction of the piezoelectric layer 20 be restricted, but also the flexibility will be impaired. Therefore, the thinner the lower protective layer 28 and the upper protective layer 30 are, the better, except for cases where mechanical strength and good handling properties as a sheet-like article are required.

The thickness of the lower protective layer 28 and the upper protective layer 30 is preferably 3 μm to 100 μm, more preferably 3 μm to 50 μm, still more preferably 3 μm to 30 μm, and particularly preferably 4 μm to 10 μm.

Here, in the piezoelectric film 10, if the thickness of the lower protective layer 28 and the upper protective layer 30 is not more than twice the thickness of the piezoelectric layer 20, it is possible to ensure both rigidity and appropriate flexibility. favorable results can be obtained. For example, when the thickness of the piezoelectric layer 20 is 50 μm and the lower protective layer 28 and the upper protective layer 30 are made of PET, the thicknesses of the lower protective layer 28 and the upper protective layer 30 are preferably 100 μm or less, more preferably 50 μm or less. , 25 μm or less.

In the piezoelectric film 10, a lower electrode layer 24 is formed between the piezoelectric layer 20 and the lower protective layer 28, and an upper electrode layer 26 is formed between the piezoelectric layer 20 and the upper protective layer 30, respectively. A lower electrode layer 24 and an upper electrode layer 26 are provided for applying a drive voltage to the piezoelectric layer 20 .

In the present invention, the materials for forming the lower electrode layer 24 and the upper electrode layer 26 are not limited, and various conductors can be used. Specifically, carbon, palladium, iron, tin, aluminum, nickel, platinum, gold, silver, copper, titanium, chromium, molybdenum, etc., alloys thereof, laminates and composites of these metals and alloys, and Examples include indium tin oxide. Among them, copper, aluminum, gold, silver, platinum, and indium tin oxide are preferably exemplified as the lower electrode layer 24 and the upper electrode layer 26 .

In addition, the method of forming the lower electrode layer 24 and the upper electrode layer 26 is not limited. Various known methods, such as the method of applying foil, can be used.

Among others, thin films of copper, aluminum, etc. formed by vacuum deposition are preferably used as the lower electrode layer 24 and the upper electrode layer 26, for the reason that the flexibility of the piezoelectric film 10 can be ensured. Among them, a copper thin film formed by vacuum deposition is particularly preferably used.

The thicknesses of the lower electrode layer 24 and the upper electrode layer 26 are not limited. In addition, although the thicknesses of the lower electrode layer 24 and the upper electrode layer 26 are basically the same, they may be different.

Here, similarly to the lower protective layer 28 and the upper protective layer 30 described above, if the rigidity of the lower electrode layer 24 and the upper electrode layer 26 is too high, not only will the expansion and contraction of the piezoelectric layer 20 be restricted, but also the flexibility will be impaired. be Therefore, the thinner the lower electrode layer 24 and the upper electrode layer 26, the better, as long as the electrical resistance does not become too high. That is, the lower electrode layer 24 and the upper electrode layer 26 are preferably thin film electrodes.

The thickness of the lower electrode layer 24 and the upper electrode layer 26 is thinner than that of the protective layer, preferably 0.05 μm to 10 μm, more preferably 0.05 μm to 5 μm, further preferably 0.08 μm to 3 μm, further preferably 0.1 μm to 0.1 μm. 2 μm is particularly preferred.

Here, in the piezoelectric film 10, if the product of the thickness of the lower electrode layer 24 and the upper electrode layer 26 and the Young's modulus is less than the product of the thickness of the lower protective layer 28 and the upper protective layer 30 and the Young's modulus, This is preferable because it does not greatly impair flexibility.

For example, when the lower protective layer 28 and the upper protective layer 30 are made of PET (Young's modulus: about 6.2 GPa) and the lower electrode layer 24 and the upper electrode layer 26 are made of copper (Young's modulus: about 130 GPa), the lower protective layer Assuming that the thickness of the layer 28 and the upper protective layer 30 is 25 μm, the thickness of the lower electrode layer 24 and the upper electrode layer 26 is preferably 1.2 μm or less, more preferably 0.3 μm or less, especially 0.1 μm or less. is preferred.

The piezoelectric film 10 preferably has a maximum value of loss tangent (Tan δ) at a frequency of 1 Hz by dynamic viscoelasticity measurement at room temperature, and more preferably has a maximum value of 0.1 or more at room temperature. As a result, even if the piezoelectric film 10 is subjected to a relatively slow and large bending deformation of several Hz or less from the outside, the strain energy can be effectively diffused to the outside as heat. can prevent cracks from forming.

The piezoelectric film 10 preferably has a storage elastic modulus (E') at a frequency of 1 Hz measured by dynamic viscoelasticity measurement of 10 GPa to 30 GPa at 0°C and 1 GPa to 10 GPa at 50°C. Note that this condition applies to the piezoelectric layer 20 as well. This allows the piezoelectric film 10 to have a large frequency dispersion in the storage modulus (E'). That is, it can act hard against vibrations of 20 Hz to 20 kHz and soft against vibrations of several Hz or less.

In addition, the piezoelectric film 10 has a product of thickness and storage elastic modulus at a frequency of 1 Hz measured by dynamic viscoelasticity measurement at 0° C. of 1.0×10 ⁵ to 2.0×10 ⁶ (1.0E+05 to 2.0×10 6 ). 0E+06) N/m, preferably 1.0×10 ⁵ to 1.0×10 ⁶ (1.0E+05 to 1.0E+06) N/m at 50°C. Note that this condition applies to the piezoelectric layer 20 as well. As a result, the piezoelectric film 10 can have appropriate rigidity and mechanical strength within a range that does not impair flexibility and acoustic properties.

Furthermore, the piezoelectric film 10 preferably has a loss tangent of 0.05 or more at 25° C. and a frequency of 1 kHz in a master curve obtained from dynamic viscoelasticity measurement. Note that this condition applies to the piezoelectric layer 20 as well. As a result, the frequency characteristics of the speaker using the piezoelectric film 10 are smoothed, and the change in sound quality when the lowest resonance frequency f ₀ changes as the curvature of the speaker changes can be reduced.

In the present invention, the storage elastic modulus (Young's modulus) and loss tangent of the piezoelectric film 10, piezoelectric layer 20, etc. may be measured by known methods. As an example, the dynamic viscoelasticity measuring device DMS6100 manufactured by SII Nanotechnology Co., Ltd. (manufactured by SII Nanotechnology Co., Ltd.) may be used for measurement.

As an example of the measurement conditions, the measurement frequency is 0.1 Hz to 20 Hz (0.1 Hz, 0.2 Hz, 0.5 Hz, 1 Hz, 2 Hz, 5 Hz, 10 Hz and 20 Hz), and the measurement temperature is -50 to 150 ° C. , a heating rate of 2° C./min (in a nitrogen atmosphere), a sample size of 40 mm×10 mm (including the clamping area), and a distance between chucks of 20 mm.

[Conductive adhesive tape]
The conductive adhesive tape 72 has an adhesive layer on one surface of a conductive sheet, which is a sheet-shaped object made of a conductive metal material. Copper, aluminum, gold, silver and the like are preferably exemplified as the material of the conductive sheet.
The adhesive layer of the conductive adhesive tape 72 may be any material as long as it can adhere the conductive sheet and the protective layer. The material of the adhesive layer is suitably exemplified by a conductive acrylic adhesive material.

Also, the shape and size of the conductive adhesive tape 72 in plan view are not particularly limited. The conductive adhesive tape 72 may have any shape and size as long as it can cover the soft conductive member 70 , can be connected to the lead wire 76 , and does not restrict the driving of the piezoelectric film 10 .

Also, the thickness of the conductive adhesive tape 72 is not particularly limited as long as it can ensure electrical connection with the soft conductive member 70 and the lead wire 76 and does not restrict the driving of the piezoelectric film 10 .

[Sealing member]
The sealing member 74 is an insulating sheet-like member. The material of the sealing member 74 is exemplified by polyimide, heat-resistant PET, and the like.

Also, the shape and size of the sealing member 74 in plan view are not particularly limited. The shape and size of the sealing member 74 is such that it can cover at least a portion of the soft conductive member 70 and the conductive adhesive tape 72 to fix the soft conductive member 70 and the conductive wire 76 and does not restrict the driving of the piezoelectric film 10. and size. As described above, the sealing member 74 preferably covers the entire surface of the soft conductive member 70 and preferably covers the entire surface of the conductive adhesive tape 72 .

Also, the thickness of the sealing member 74 is not particularly limited as long as it does not restrict the driving of the piezoelectric film 10 .

The sealing member 74 may have an adhesive layer, or may be adhered to the protective layer with an adhesive or the like.

[Conducting wire]
The conducting wire 76 is a sheet-like or wire-like object made of a conductive metal material. Copper, aluminum, gold, silver, etc. are preferably exemplified as the material of the conductor wire 76 .

The shape and size of the conducting wire 76 are not particularly limited. The conductive wire 76 may have any shape and size as long as it can be electrically connected to the soft conductive member 70 directly or via the conductive adhesive tape 72 and can be used as an extraction electrode.

An example of a method for manufacturing the piezoelectric film 10 will be described below with reference to FIGS. 4 to 10. FIG.

First, as shown in FIG. 4, a sheet-like object 10a having a lower electrode layer 24 formed on a lower protective layer 28 is prepared. This sheet-like object 10a may be produced by forming a copper thin film or the like as the lower electrode layer 24 on the surface of the lower protective layer 28 by vacuum deposition, sputtering, plating, or the like.

When the lower protective layer 28 is very thin and has poor handling properties, the lower protective layer 28 with a separator (temporary support) may be used as necessary. As the separator, PET or the like having a thickness of 25 μm to 100 μm can be used. The separator may be removed after the upper electrode layer 26 and the upper protective layer 30 are thermocompressed and before laminating any member on the lower protective layer 28 .

On the other hand, a coating material is prepared by dissolving a polymer material as a matrix material in an organic solvent, adding piezoelectric particles 36 such as PZT particles, and stirring and dispersing the mixture. Organic solvents other than the above substances are not limited and various organic solvents can be used.

After the sheet-like material 10a is prepared and the paint is prepared, the paint is cast (applied) on the sheet-like material 10a and dried by evaporating the organic solvent. As a result, as shown in FIG. 5, the laminate 10b having the lower electrode layer 24 on the lower protective layer 28 and the piezoelectric layer 20 on the lower electrode layer 24 is produced. The lower electrode layer 24 refers to the electrode on the base material side when the piezoelectric layer 20 is applied, and does not indicate the vertical positional relationship in the laminate.

There are no restrictions on the method of casting this paint, and all known methods (coating devices) such as slide coaters and doctor knives can be used.

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 these polymeric materials are added to the matrix 34, the polymeric materials to be added to the coating material described above may be dissolved.

After manufacturing the laminate 10b having the lower electrode layer 24 on the lower protective layer 28 and the piezoelectric layer 20 formed on the lower electrode layer 24, the piezoelectric layer 20 is preferably subjected to polarization treatment (poling). conduct.

The method of polarization treatment of the piezoelectric layer 20 is not limited, and known methods can be used. Before this polarization treatment, the surface of the piezoelectric layer 20 may be smoothed by using a heating roller or the like, which is a calendering treatment. By performing this calendering process, the thermocompression bonding process, which will be described later, can be performed smoothly.

While the piezoelectric layer 20 of the laminate 10b is subjected to polarization treatment in this manner, the sheet-like object 10c having the upper electrode layer 26 formed on the upper protective layer 30 is prepared. This sheet-like object 10c may be produced by forming a copper thin film or the like as the upper electrode layer 26 on the surface of the upper protective layer 30 by vacuum deposition, sputtering, plating, or the like.

Next, as shown in FIG. 6, the upper electrode layer 26 faces the piezoelectric layer 20, and the sheet-like material 10c is laminated on the laminate 10b for which the polarization treatment of the piezoelectric layer 20 has been completed.

Furthermore, the laminated body of the laminated body 10b and the sheet-like material 10c is thermocompression bonded by a hot press device, a pair of heated rollers, or the like, with the upper protective layer 30 and the lower protective layer 28 sandwiched therebetween.

Through the above steps, a laminate in which electrode layers and protective layers are laminated on both sides of the piezoelectric layer 20 is produced. The produced laminate may be cut into a desired shape according to various uses.

Such a laminate may be produced using a cut sheet-like sheet material, or may be produced by roll to roll (hereinafter also referred to as RtoR).

Next, a hole is provided in the protective layer of the laminate, a soft conductive member is filled in the hole, and a conductive adhesive tape is used to connect the conductive wire, and then the connection is sealed with a sealing member.

Specifically, first, as shown in FIG. 7, holes 31 are formed in the upper protective layer 30 . Similarly, holes are formed in the lower protective layer 28 (not shown).
The holes 31 may be formed by a method using laser processing (carbon dioxide laser or the like), a method of cutting the protective layer in the depth direction by press processing, and then peeling off the protective layer, or the like.

After forming the holes in the protective layer, the soft conductive member 70 is arranged in the holes 31 as shown in FIG. The soft conductive member 70 is preliminarily processed so that its size in plan view is equal to or smaller than the size of the hole 31 . Moreover, as described above, preferably, the thickness d2 of the soft conductive member ₇₀ is thicker _than the thickness d1 of the protective layer.

Next, as shown in FIG. 9, a conductive adhesive tape 72 is laminated on the protective layer so as to cover the soft conductive member 70 . Furthermore, a conductive wire 76 is arranged on the conductive adhesive tape 72 .

After laminating the conductive adhesive tape 72 on the protective layer, a sealing member 74 is laminated on the conductive adhesive tape 72 and the conductor 76 as shown in FIG. The sealing member 74 is adhered to the protective layer with an adhesive, an adhesive, or the like.

The piezoelectric film of the present invention is produced through the above steps.

In such a piezoelectric film 10, when a voltage is applied to the lower electrode layer 24 and the upper electrode layer 26, the piezoelectric particles 36 expand and contract in the polarization direction according to the applied voltage. As a result, the piezoelectric film 10 (piezoelectric layer 20) shrinks in the thickness direction. At the same time, due to the Poisson's ratio, the piezoelectric film 10 also expands and contracts in the in-plane direction. This expansion and contraction is about 0.01 to 0.1%. In addition, it expands and contracts isotropically in all directions in the in-plane direction.

As described above, the thickness of the piezoelectric layer 20 is preferably about 10-300 μm. Therefore, the expansion and contraction in the thickness direction is as small as about 0.3 μm at maximum.

On the other hand, the piezoelectric film 10, that is, the piezoelectric layer 20, has a size much larger than its thickness in the planar direction. Therefore, for example, if the length of the piezoelectric film 10 is 20 cm, the piezoelectric film 10 expands and contracts by about 0.2 mm at maximum due to voltage application.

Also, when pressure is applied to the piezoelectric film 10, the action of the piezoelectric particles 36 generates electric power. By utilizing this, the piezoelectric film 10 can be used for various applications such as speakers, microphones, and pressure sensors, as described above.

Here, a general piezoelectric film made of a polymeric material such as PVDF has in-plane anisotropy in piezoelectric properties, and anisotropy in the amount of expansion and contraction in the plane direction when a voltage is applied.

On the other hand, a piezoelectric layer composed of a polymer composite piezoelectric material containing piezoelectric particles in a matrix containing a polymer material has no in-plane anisotropy in the piezoelectric characteristics and is isotropic in all directions in the in-plane direction. stretches to Such a piezoelectric film 10 that expands and contracts isotropically two-dimensionally can vibrate with a greater force than when a general piezoelectric film such as PVDF that expands and contracts greatly in only one direction is laminated. , can produce a louder and more beautiful sound.

Further, for example, by attaching the piezoelectric film of the present invention to a flexible display device such as a flexible organic electroluminescence display and a flexible liquid crystal display, the film can be used as a speaker of the display device. is also possible.

Further, for example, when the piezoelectric film 10 is used for a speaker, the film-shaped piezoelectric film 10 itself may vibrate to generate sound. Alternatively, the piezoelectric film 10 may be attached to a diaphragm and used as an exciter that vibrates the diaphragm by the vibration of the piezoelectric film 10 to generate sound.

In addition, the piezoelectric film 10 of the present invention works well as a piezoelectric vibrating element for vibrating an object to be vibrated, such as a diaphragm, by forming a laminated piezoelectric element in which a plurality of sheets are laminated.

As an example, a laminated piezoelectric element in which piezoelectric films 10 are laminated may be attached to a diaphragm, and a speaker that outputs sound by vibrating the diaphragm with the laminate of piezoelectric films 10 may be used. That is, in this case, the laminate of the piezoelectric films 10 acts as a so-called exciter that outputs sound by vibrating the diaphragm.

By applying a driving voltage to the laminated piezoelectric element in which the piezoelectric films 10 are laminated, the individual piezoelectric films 10 expand and contract in the plane direction, and the expansion and contraction of each piezoelectric film 10 causes the entire laminate of the piezoelectric films 10 to expand and contract in the plane direction. do. The expansion and contraction of the laminated piezoelectric element in the planar direction bends the diaphragm to which the laminate is attached, and as a result, the diaphragm vibrates in the thickness direction. This vibration in the thickness direction causes the diaphragm to generate sound. The diaphragm vibrates according to the magnitude of the driving voltage applied to the piezoelectric film 10 and generates sound according to the driving voltage applied to the piezoelectric film 10 . Therefore, at this time, the piezoelectric film 10 itself does not output sound.

Even if the rigidity of each piezoelectric film 10 is low and the expansion/contraction force is small, the laminated piezoelectric element in which the piezoelectric films 10 are laminated has high rigidity, and the expansion/contraction force of the laminate as a whole is large. As a result, even if the diaphragm has a certain degree of rigidity, the laminated piezoelectric element in which the piezoelectric film 10 is laminated can sufficiently flex the diaphragm with a large force and sufficiently vibrate the diaphragm in the thickness direction. to make the diaphragm generate sound.

In the laminated piezoelectric element in which the piezoelectric films 10 are laminated, the number of laminated piezoelectric films 10 is not limited. Just do it. It should be noted that a single piezoelectric film 10 can be used as a similar exciter (piezoelectric vibrating element) as long as it has sufficient stretching force.

There are no restrictions on the vibration plate that is vibrated by the laminated piezoelectric element in which the piezoelectric film 10 is laminated, and various sheet-like objects (plate-like objects, films) can be used. Examples include resin films such as polyethylene terephthalate (PET), foamed plastics such as polystyrene foam, paper materials such as cardboard, glass plates, and wood. Furthermore, various devices such as display devices such as organic electroluminescence displays and liquid crystal displays may be used as the diaphragm as long as they can be bent sufficiently.

In the laminated piezoelectric element in which the piezoelectric films 10 are laminated, it is preferable that the adjacent piezoelectric films 10 are adhered with an adhesive layer (adhesive). Also, the laminated piezoelectric element and the diaphragm are preferably adhered with an adhesive layer.

There are no restrictions on the adhesive layer, and various types of materials that can be used to attach objects to be attached can be used. Therefore, the sticking layer may be made of a pressure-sensitive adhesive or an adhesive. Preferably, an adhesive layer is used which, after application, results in a solid and hard adhesive layer. The above points are the same for a laminated body formed by folding a long piezoelectric film 10 described later.

In the laminated piezoelectric element in which the piezoelectric films 10 are laminated, the polarization direction of each laminated piezoelectric film 10 is not limited. As will be described later, the piezoelectric film 10 of the present invention is preferably polarized in the thickness direction. Accordingly, the polarization direction of the piezoelectric film 10 referred to herein is the polarization direction in the thickness direction. Therefore, in the laminated piezoelectric element, all the piezoelectric films 10 may have the same polarization direction, or there may be piezoelectric films having different polarization directions.

In the laminated piezoelectric element in which the piezoelectric films 10 are laminated, it is preferable to laminate the piezoelectric films 10 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 depends on the polarization direction of the piezoelectric layer 20 . Therefore, regardless of whether the polarization direction is from the upper electrode layer 26 to the lower electrode layer 24 or from the lower electrode layer 24 to the upper electrode layer 26, the polarity and The polarity of the lower electrode layer 24 is made the same. Therefore, by reversing the polarization directions of the adjacent piezoelectric films 10, even if the electrode layers of the adjacent piezoelectric films 10 are in contact with each other, the contacting electrode layers have the same polarity, so a short circuit occurs. there is no fear of

The laminated piezoelectric element in which the piezoelectric films 10 are laminated may have a configuration in which a plurality of piezoelectric films 10 are laminated by folding the piezoelectric films 10 one or more times, preferably a plurality of times. The configuration in which the piezoelectric film 10 is folded and laminated has the following advantages.

In a laminate in which a plurality of cut sheet-like piezoelectric films 10 are laminated, it is necessary to connect the upper electrode layer 26 and the lower electrode layer 24 to the drive power source for each piezoelectric film. On the other hand, in the structure in which the long piezoelectric film 10 is folded and laminated, the laminated piezoelectric element can be configured with only one long piezoelectric film 10 . Therefore, in the configuration in which the long piezoelectric film 10 is folded and laminated, only one power source is required for applying the driving voltage, and the electrode may be led out from the piezoelectric film 10 at one point. Furthermore, in the structure in which the long piezoelectric films 10 are folded and laminated, the polarization directions of adjacent piezoelectric films 10 are inevitably opposite to each other.

Regarding such a laminated piezoelectric element in which piezoelectric films having electrode layers and protective layers provided on both sides of a piezoelectric layer made of a polymer composite piezoelectric body are laminated, International Publication No. 2020/095812 and International Publication No. 2020/ 179353 and the like.

The piezoelectric film of the present invention and the above-described laminated piezoelectric element can be used for various sensors such as sound wave sensors, ultrasonic sensors, pressure sensors, tactile sensors, strain sensors and vibration sensors (especially infrastructure inspection such as crack detection and foreign matter detection). etc.), acoustic devices such as microphones, pickups, speakers and exciters (specific applications include noise cancellers (used in cars, trains, airplanes, robots, etc.), artificial vocal cords, pests and Buzzers for preventing vermin intrusion, furniture, wallpaper, photographs, helmets, goggles, headrests, signage, robots, etc.), haptics used for applications such as automobiles, smartphones, smart watches, games, etc., ultrasonic probes and ultrasonic transducers such as hydrophones, actuators used for preventing adhesion of water drops, transportation, stirring, dispersion, polishing, etc., damping materials (dampers) used for containers, vehicles, buildings, sports equipment such as skis and rackets, and roads , floors, mattresses, chairs, shoes, tires, wheels, and personal computer keyboards.

Although the piezoelectric film of the present invention has been described in detail above, the present invention is not limited to the above examples, and various improvements and modifications may be made without departing from the gist of the present invention. is.

Hereinafter, the present invention will be described in more detail by giving specific examples of the present invention. The present invention is not limited to this example, and the materials, amounts used, proportions, processing details, processing procedures, etc. shown in the following examples can be changed as appropriate without departing from the gist of the present invention. can.

[Example 1]
A sheet 10a and a sheet 10c were prepared by vacuum-depositing a 0.1 μm thick copper thin film on a 4 μm thick PET film. That is, in this example, the upper electrode layer 26 and the lower electrode layer 24 are 0.1 μm-thick copper-deposited thin films, and the upper protective layer 30 and the lower protective layer 28 are 4 μm-thick PET films. In addition, in order to obtain good handling during the process, a PET film with a separator (temporary support PET) having a thickness of 50 μm was used, and the separator of each protective layer was removed after the sheet-like material 10c was thermocompressed. rice field.

First, cyanoethylated PVA (CR-V manufactured by Shin-Etsu Chemical Co., Ltd.) was dissolved in methyl ethyl ketone (MEK) at the following composition ratio. After that, PZT particles were added to this solution in the following compositional ratio and dispersed with a propeller mixer (rotation speed: 2000 rpm) to prepare a paint for forming the piezoelectric layer 20 .

・PZT particles・・・・・・・・・・300 parts by mass ・Cyanoethylated PVA・・・・・・・・15 parts by mass ・MEK・・・・・・・・・・・・85 parts by mass

The PZT particles used were obtained by sintering commercially available PZT raw material powder at 1000 to 1200° C. and then pulverizing and classifying the sintered particles to an average particle size of 5 μm.

On the lower electrode layer 24 (copper-deposited thin film) of the previously prepared sheet-like material 10a, the previously prepared paint for forming the piezoelectric layer 20 was applied using a slide coater. In addition, the paint was applied so that the thickness of the coating film after drying was 20 μm. Next, the sheet material 10a coated with the paint was dried by heating on a hot plate at 120° C. to evaporate the MEK, thereby forming the laminate 10b.

The sheet-like object 10c was laminated on the laminated body 10b with the upper electrode layer 26 (copper thin film side) side facing the piezoelectric layer 20, and was thermocompression bonded at 120°C. Thus, the piezoelectric layer 20, the upper electrode layer 26 and the upper protective layer 30, and the piezoelectric layer 20, the lower electrode layer 24 and the lower protective layer 28 are adhered.

Next, a voltage was applied between the lower electrode layer 24 and the upper electrode layer 26 to subject the piezoelectric layer 20 to electrical polarization treatment. The electric polarization treatment was performed by setting the temperature of the piezoelectric layer 20 to 100° C. on a hot plate and applying a DC voltage of 6 kV between the lower electrode layer 24 and the upper electrode layer 26 .

Next, in each of the lower protective layer 28 and the upper protective layer 30, holes penetrating through the protective layer with a diameter of 5 mm were formed by laser processing.

As the soft conductive member 70, a conductive cloth of Sui-10-511M (woven cloth) manufactured by Seiren Co., Ltd. and having a thickness of 100 μm was prepared. This conductive cloth was cut out to have a diameter of 5 mm in plan view, and was placed in the hole of the protective layer.

As the conductive adhesive tape 72, 60382 manufactured by Tesa Tape Co., Ltd. was cut into a size of 10 mm x 10 mm. Also, as the conducting wire 76, a wire 76 made of copper and having a size of 12 mm×15 mm was prepared. As the sealing member 74, a 650R made by Teraoka Seisakusho Co., Ltd. cut out to a size of 15 mm×10 mm was used.

A conductive adhesive tape 72 was adhered to the protective layer so as to cover the entire surface of the conductive cloth (holes). Next, a part of the conducting wire 76 is placed in contact with the conductive adhesive tape 72 , and a sealing member 74 is placed so as to cover the entire surface of the conductive cloth and the conductive adhesive tape 72 . was attached to the protective layer. At that time, the sealing member 74 was adhered so as to compress the conductive cloth in the thickness direction. A piezoelectric film was produced as described above.

[Example 2]
A piezoelectric film was produced in the same manner as in Example 1, except that the conductive adhesive tape 72 was not used. That is, the conductive wire 76 was partially in contact with the conductive cloth, and the sealing member 74 was adhered to the protective layer so as to cover the contact position between the conductive cloth and the conductive wire 76, thereby producing the piezoelectric film.

[Example 3]
A piezoelectric film was produced in the same manner as in Example 1, except that the sealing member 74 was not provided.

[Example 4]
A piezoelectric film was produced in the same manner as in Example 1 except that the conductive adhesive tape 72 and the sealing member 74 were not provided. In addition, the conducting wire 76 was fixed to the protective layer using an adhesive tape at a position other than the position in contact with the conductive cloth.

[Example 5]
A piezoelectric film was produced in the same manner as in Example 4, except that a 70 μm-thick Si-80-301 (nonwoven fabric) conductive cloth manufactured by Seiren Co., Ltd. was used as the soft conductive member.

[Example 6]
A piezoelectric film was produced in the same manner as in Example 4, except that a 100 μm-thick plain-woven wire mesh Φ0.05×200 m/s (woven fabric) manufactured by Okutani Wire Net Mfg. Co., Ltd. was used as the soft conductive member.

[Example 7]
A piezoelectric film was produced in the same manner as in Example 4, except that a 100 μm-thick metal cloth of copper fiber nonwoven fabric manufactured by Nikko Techno Co., Ltd. was used as the soft conductive member.

[Example 8]
A piezoelectric film was produced in the same manner as in Example 4, except that SUI-70-5005A conductive urethane foam and conductive cloth having a thickness of 500 μm manufactured by Seiren Co., Ltd. were used as the soft conductive member.

[Example 9]
A piezoelectric film was produced in the same manner as in Example 4, except that the diameter of the conductive cloth in plan view was 2 mm.

[Comparative Example 1]
A piezoelectric film was produced in the same manner as in Example 4, except that a conductive paste was used instead of the soft conductive member.

Dotite D550 manufactured by Fujikura Kasei Co., Ltd. was used as the conductive paste. Also, the conductive paste was applied so as to fill the holes of the protective layer.

[Comparative Example 2]
A piezoelectric film was produced in the same manner as in Example 4, except that solder was used instead of the soft conductive member.

[evaluation]
The following items were evaluated for the produced piezoelectric film.

[resistance]
The electrical resistance of the piezoelectric film was measured 24 hours after it was produced using an LCR meter. In the evaluation, a lead wire for resistance measurement was attached in the same manner as in each example and comparative example on the same surface as each lead wire attachment surface for evaluation. At this time, the mounting position was set so that the distance between the centers of the holes in the protective layer was 30 mm. The measured resistance values were evaluated according to the following criteria.
・A: Less than 1 Ω ・B: 1 Ω or more and less than 5 Ω ・C: 5 Ω or more

[Flexibility]
The piezoelectric film was bent along a φ40 mm round bar so that the center of the hole formed in the protective layer was the bending center. At that time, it was confirmed whether the electrode was bent following the shape of a round bar, and whether the electrode returned to its original shape after being unbent and stretched was confirmed. A was given when the film was bent in the same manner as the piezoelectric film when bent and returned to its original state when stretched, and C was given when it did not bend when bent and did not stretch when stretched.

[Bending durability]
Twenty-four hours after the piezoelectric film was produced, it was bent along a round bar of φ40 mm so that the center of the hole formed in the protective layer was the center of the bending. The bending was repeated 30 times. Thereafter, an electrode for resistance measurement was attached in the same manner as in the above resistance evaluation, and evaluation was performed. The measured resistance values were evaluated according to the following criteria.
・A: Less than 1 Ω ・B: 1 Ω or more and less than 5 Ω ・C: 5 Ω or more

[Stability of amount of conductive material]
After the conductive member was supplied to the holes of the protective layer of the piezoelectric film whose weight had been measured in advance, the conductive member was allowed to stand for 24 hours while being exposed to the air, and the weight before and after was measured. In the measurement, the weight of 30 sheets was measured, the average of 30 sheets measured was A, the standard deviation was B, and the ratio of variation to the average was evaluated by B/A (%) according to the following criteria. For the conductive paste, 15 samples each were produced from the well-stirred liquid and the liquid that had been allowed to stand still for 24 hours after stirring and was used without re-stirring. . Each liquid was supplied by sucking the liquid on the liquid surface using a tube dispenser.
・A: Less than 10% ・C: 10% or more

The results are shown in Table 1.

From Table 1, the examples of the present invention have higher flexibility, higher bending durability, and higher stability of the amount of the conducting member than the comparative examples, that is, sufficient conduction is stable. I know you can get it. On the other hand, in Comparative Example 1, the conductive paste layer to be formed varied due to variations in concentration, so the amount of the conductive member was not stable. Therefore, sufficient conduction may not be obtained. Moreover, in Comparative Example 2, the flexibility was lowered due to the hardness of the solder, and the electrode layer was damaged after repeated bending, resulting in an increase in the resistance value.

Also, from the comparison between Example 1 and Examples 2 and 4, it can be seen that the resistance can be reduced by connecting the soft conductive member and the conductive wire via the conductive adhesive tape.

In addition, from the comparison between Example 1 and Examples 3 and 4, it was found that when the piezoelectric film was repeatedly bent due to the presence of the sealing member, the positions of the respective members were displaced and the conductive member and the electrode layer were displaced. It can be seen that the contact area can be prevented from becoming smaller due to a change in the contact due to the pressure between the conductor and the lead wire being not maintained, and stable conduction can be obtained.
From the above, the effect of the present invention is clear.

It can be suitably used for various purposes such as acoustic equipment such as speakers and microphones, and pressure sensors.

REFERENCE SIGNS LIST 10

piezoelectric films

10a, 10c sheet 10b laminate 20 piezoelectric layer 24 lower electrode layer 26 upper electrode layer 28 lower protective layer 30 upper protective layer 31 hole 34 matrix 36 piezoelectric particles 70 soft conductive member 72 conductive adhesive tape 74 Sealing member 76 conducting wire

Claims

A piezoelectric film having a piezoelectric layer, electrode layers formed on both sides of the piezoelectric layer, and a protective layer laminated on a surface of the electrode layer opposite to the surface of the electrode layer,
The protective layer has a hole penetrating from the surface to the electrode layer,
A piezoelectric film having a soft conductive member including at least one of a conductive cloth, a metal cloth, and a conductive urethane foam disposed in the hole and electrically connecting the electrode layer and the conductive wire.
The piezoelectric film according to claim 1, which has a sealing member that covers a connection position between the soft conductive member and the lead wire.
The piezoelectric film according to claim 2, wherein the thickness of the soft conductive member before being covered with the sealing member is thicker than the thickness of the protective layer.
The piezoelectric film according to any one of claims 1 to 3, having a conductive adhesive tape arranged between the soft conductive member and the conductor.
The piezoelectric film according to any one of claims 1 to 4, wherein the piezoelectric layer is composed of a polymer composite piezoelectric body containing piezoelectric particles in a matrix containing a polymer material.