CN118044228A

CN118044228A - Piezoelectric element and electroacoustic transducer

Info

Publication number: CN118044228A
Application number: CN202280065364.0A
Authority: CN
Inventors: 小泽荣贵; 岩本崇裕
Original assignee: Fujifilm Corp
Current assignee: Fujifilm Corp
Priority date: 2021-09-29
Filing date: 2022-08-15
Publication date: 2024-05-14
Also published as: TW202315173A; WO2023053751A1

Abstract

Provided are a piezoelectric element and an electroacoustic transducer which can achieve both high sound pressure and productivity in a piezoelectric element formed by laminating piezoelectric films. A piezoelectric element is formed by folding back a piezoelectric film having a piezoelectric layer, electrode layers provided on both sides of the piezoelectric layer, and a protective layer provided on the electrode layers 1 or more times to laminate the piezoelectric film in a plurality of layers, wherein the piezoelectric element has an adhesive layer that adheres between layers of the laminated piezoelectric film, and a ratio of an adhesion area of the adhesive layer to an area of a laminate portion of the piezoelectric film is in a range of 0.85 to 0.99 when viewed from a lamination direction of the piezoelectric film.

Description

Piezoelectric element and electroacoustic transducer

Technical Field

The present invention relates to a piezoelectric element and an electroacoustic transducer.

Background

Piezoelectric elements are used in various applications as so-called exciters (excitons) which are mounted in contact with various articles to vibrate the articles and emit sound. For example, it is possible to make these vibrations emit sound instead of a speaker by installing an exciter in an image display panel, a screen, or the like.

As the piezoelectric element, a piezoelectric film in which a piezoelectric layer is sandwiched between an electrode layer and a protective layer has been proposed. In addition, it has been proposed to use a piezoelectric element in which piezoelectric films are laminated in a plurality of layers.

For example, patent document 1 describes a piezoelectric film including: a polymer composite piezoelectric body in which piezoelectric particles are dispersed in a matrix containing a polymer material; and electrode layers formed on both sides of the polymer composite piezoelectric body, wherein the loss tangent at a frequency of 1kHz at the time of measuring dynamic viscoelasticity has a maximum value of 0.1 or more in a temperature range of more than 50 ℃ and 150 ℃ or less, and a value of 0.08 or more at 50 ℃. Patent document 1 describes a piezoelectric element in which piezoelectric films are folded back 1 or more times and laminated in a plurality of layers.

Technical literature of the prior art

Patent literature

Patent document 1: international publication No. 2020/196850

Disclosure of Invention

Technical problem to be solved by the invention

In the case of using a piezoelectric film as the piezoelectric element, the piezoelectric element emits sound from the vibration plate by being attached to the vibration plate to vibrate the vibration plate, but in the case of a single layer, the output of the piezoelectric element is small and the vibration plate cannot be sufficiently vibrated, resulting in a low sound pressure. Therefore, as described above, by folding back the piezoelectric film and making it multilayered, the output of the piezoelectric element can be increased, and the diaphragm can be sufficiently vibrated, so that a high sound pressure can be obtained.

When the piezoelectric film is multilayered, it is necessary to adhere the layers of the piezoelectric film with an adhesive layer and to transmit stress generated in each layer to the vibration plate. The larger the bonding area of the adhesive layer, the smaller the loss of stress propagation between layers, and thus higher sound pressure can be obtained. However, if the bonding area by the adhesive layer is set to be excessively large, there is a problem that: when laminating the piezoelectric film, the adhesive is caused to protrude from the lamination portion, and the surface of the laminator is contaminated, resulting in a decrease in productivity.

The present invention has been made to solve the problems of the conventional art, and an object of the present invention is to provide a piezoelectric element and an electroacoustic transducer which can achieve both high sound pressure and productivity in a piezoelectric element formed by laminating piezoelectric films.

Means for solving the technical problems

In order to solve the above problems, the present invention has the following configuration.

[1] A piezoelectric element is formed by laminating a plurality of piezoelectric films by folding back the piezoelectric film having a piezoelectric layer, electrode layers provided on both sides of the piezoelectric layer, and a protective layer provided on the electrode layers 1 or more times,

The piezoelectric element has an adhesive layer for bonding between layers of laminated piezoelectric films,

The ratio of the bonding area of the adhesive layer to the area of the laminated portion of the piezoelectric film is in the range of 0.85 to 0.99 when viewed from the lamination direction of the piezoelectric film.

[2] The piezoelectric element according to [1], wherein,

The adhesion of the adhesive layer to the piezoelectric film exceeds 0.1N/cm.

[3] The piezoelectric element according to [1] or [2], wherein,

The ratio of the cross-sectional area of the gap formed in the folded portion of the piezoelectric film to the area of the laminated portion is 0.04 or less.

[4] The piezoelectric element according to any one of [1] to [3], wherein,

The piezoelectric layer is composed of a polymer composite piezoelectric body including piezoelectric particles in a matrix including a polymer material.

[5] An electroacoustic transducer formed by attaching the piezoelectric element described in any one of [1] to [4] to a vibration plate.

Effects of the invention

According to the present invention, a piezoelectric element and an electroacoustic transducer that can achieve both high sound pressure and productivity in a piezoelectric element formed by laminating piezoelectric films can be provided.

Drawings

Fig. 1 is a schematic view showing an example of a piezoelectric element according to the present invention.

Fig. 2 is a perspective view of the piezoelectric element shown in fig. 1.

Fig. 3 is a plan view of the piezoelectric element shown in fig. 1.

Fig. 4 schematically shows an example of the state of the adhesive layer.

Fig. 5 is a diagram schematically showing an example of the state of the adhesive layer.

Fig. 6 is a diagram for explaining a calculation method of the ratio of the bonding area of the adhesive layer to the area of the laminated portion of the piezoelectric film.

Fig. 7 is a diagram for explaining a calculation method of the ratio of the bonding area of the adhesive layer to the area of the laminated portion of the piezoelectric film.

Fig. 8 is a diagram for explaining a method of measuring the adhesion force.

Fig. 9 is a diagram schematically showing a graph in which the adhesion force is measured.

Fig. 10 schematically shows an example of a piezoelectric film.

Fig. 11 is a conceptual diagram for explaining an example of a method of producing a piezoelectric film.

Fig. 12 is a conceptual diagram for explaining an example of a method of producing a piezoelectric film.

Fig. 13 is a conceptual diagram illustrating an example of a method for producing a piezoelectric film.

Fig. 14 schematically shows an example of an electroacoustic transducer of the present invention having a piezoelectric element of the present invention.

Fig. 15 is a diagram illustrating the slope of the roller.

Detailed Description

Hereinafter, the piezoelectric element and the electroacoustic transducer according to the present invention will be described in detail based on preferred embodiments shown in the 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 these 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 the lower limit value and the upper limit value.

[ Piezoelectric element ]

A piezoelectric element of the present invention is a piezoelectric element in which piezoelectric films each having a piezoelectric layer, electrode layers provided on both sides of the piezoelectric layer, and a protective layer provided on the electrode layers are laminated by folding back the piezoelectric films 1 or more times,

Fig. 1 is a side view schematically showing an example of the piezoelectric element of the present invention. Fig. 2 shows a perspective view of the piezoelectric element of fig. 1. Fig. 3 shows a plan view of the piezoelectric element of fig. 1. The plan view is a view from the lamination direction in which the piezoelectric film 10 is laminated in a plurality of layers.

The piezoelectric element 50 shown in fig. 1 to 3 stacks 5-layered piezoelectric films 10 by folding back 1 piece of rectangular piezoelectric film 10 4 times in one direction. That is, the piezoelectric element 50 is a laminated piezoelectric element in which 5 laminated films 10 are laminated.

In fig. 2, although the structure of the piezoelectric element 50 is omitted for the sake of simplifying the drawing, the piezoelectric film 10 has electrode layers on both sides of the piezoelectric layer 20, and has a protective layer by covering both electrode layers. The same applies to fig. 7 and 14.

In the following description, the direction in which the piezoelectric film 10 is folded (horizontal direction in fig. 1) is referred to as a folding direction.

As shown in fig. 1, the piezoelectric element 50 has a protruding portion 10a protruding outward in the plane direction from the laminated portion 10b of the laminated 5-layer piezoelectric film 10. That is, in the piezoelectric element 50, when 1 piezoelectric film 10 is folded back 4 times, the length in the folding back direction is made substantially the same among the 4 layers from the layer on the lower surface side in fig. 1, so that the length of the piezoelectric film 10 which is the layer on the uppermost surface side is made longer than the piezoelectric films 10 of the other layers, and one end in the folding back direction is made not to overlap the piezoelectric films 10 of the other layers.

The layers of the piezoelectric film 10 adjacent to each other in the laminated portion 10b are adhered to each other by the adhesive layer 14.

In the present invention, the lamination portion 10b is a region where the piezoelectric film is overlapped by 2 layers or more in plan view, that is, when the piezoelectric element is viewed from above (or below) in fig. 1. That is, as shown in fig. 3, the region where the layers of the piezoelectric film 10 overlap by 5 layers is the lamination portion 10b.

On the other hand, the protruding portion 10a is a region protruding in the planar direction from the laminated portion 10b, and is a region that does not overlap with another layer in a plan view. In the example shown in fig. 1, the right end of the uppermost layer in the drawing is a protruding portion 10a.

As shown in fig. 3, a connection portion 40 for connecting the 1 st electrode layer 24 and the 2 nd electrode layer 26 (hereinafter, also referred to as electrode layers) and the external electrode is formed in the protruding portion 10 a. In the illustrated example, the connection portion 40 is provided by forming a through hole in the protective layers (the 1 st protective layer 28 and the 2 nd protective layer 30) of the protruding portion 10a and exposing the electrode layer. The method of forming the through hole is not limited, and may be performed by a known method such as laser processing, dissolution removal using a solvent, and mechanical processing such as mechanical polishing, depending on the material for forming the protective layer.

The connection portion 40 is filled with a known conductive material such as a conductive metal paste such as silver paste, a conductive carbon paste, or a conductive nano ink, and is connected to a wiring connected to an external power source.

The connection method between the electrode and the wiring in the protruding portion 10a is not limited, and various known methods can be used.

The piezoelectric element 50 of the present invention drives the piezoelectric element 50 by applying a voltage to the electrode layer using an external power source through the connection portion 40 provided in the protruding portion 10 a. When the piezoelectric element 50 is driven, the piezoelectric element 50 expands and contracts in the plane direction, and the vibration plate to which the piezoelectric element 50 is attached is bent, and as a result, the vibration plate vibrates to emit sound. The vibration plate vibrates according to the magnitude of the driving voltage applied to the piezoelectric film 50, and emits sound corresponding to the driving voltage applied to the piezoelectric film 50.

That is, the piezoelectric element 50 can function as an exciter.

In the present invention, the ratio of the bonding area of the adhesive layer 14 to the area of the laminated portion 10b is in the range of 0.85 to 0.99. Fig. 4 is a plan view schematically showing the piezoelectric film 10 and the adhesive layer 14 in the laminated portion 10 b. As schematically shown in fig. 4, the adhesive layer 14 is smaller than the area of the piezoelectric film 10 of the laminated portion 10b, and the adhesive layer 14 is formed at an inner side position than the end edge of the piezoelectric film 10 among 3 sides other than the side to be the folded-back portion. In fig. 4, each side of adhesive layer 14 is illustrated as a straight line, but not limited thereto, and each side of adhesive layer 14 may be irregularly shaped as in the example illustrated in fig. 5.

As described above, in the case where the piezoelectric film is used as an actuator, since a larger output is required, it is possible to consider that a multilayered laminated piezoelectric element is manufactured by folding back the piezoelectric film a plurality of times. At this time, in order to transmit the vibration of each of the laminated piezoelectric films to the outside (vibration plate), the piezoelectric films are adhered to each other by an adhesive layer. The adhesion of the piezoelectric films to each other is performed using a laminator or the like.

In order to reduce the transmission loss of vibration and increase the output, the bonding area based on the adhesive layer is preferably large. However, if the bonding area by the adhesive layer is excessively large, when the piezoelectric films are bonded to each other by the adhesive layer by folding back the piezoelectric film in the production of the piezoelectric element, the adhesive protrudes from the lamination portion, and the adhesive adheres to the surface of the laminator or the like, thereby causing contamination of the surface of the laminator or the like, resulting in a problem of reduced productivity.

In contrast, in the piezoelectric element 50 of the present invention, the ratio of the bonding area of the adhesive layer 14 to the area of the laminated portion 10b is 0.85 or more, so that the increase in transmission loss of vibration due to the reduction of the bonding area of the adhesive layer can be suppressed, and the output can be reduced. In addition, when the piezoelectric films are bonded to each other by the adhesive layer, the adhesive can be prevented from protruding from the laminated portion and the surface of the laminator or the like can be prevented from being contaminated, which results in a reduction in productivity, by setting the ratio of the bonding area to 0.99 or less.

The ratio of the bonding area of the adhesive layer 14 to the area of the laminated portion 10b is measured as follows.

First, as shown by a broken line in fig. 6, the rectangular laminated portion 10b is cut into 10 sections obliquely with respect to one side. At this time, the cut surfaces are parallel and equally spaced. The 4 sides of the laminated portion 10b were each cut at 1.

The dicing method is not particularly limited, and a method is preferable in which the cross section after dicing can be observed, and deformation and fracture of the electrode layer, deformation and fracture of the piezoelectric layer, deformation and fracture of the protective layer, and the like are not caused. For example, after the observation site is dried and cured using EB cured resin, a method of cutting by a single-blade razor can be utilized.

Next, each cut surface was observed at a magnification of 50 times using SEM (scanning electron microscope).

Fig. 7 shows a schematic view of a section of the line B-B of fig. 6.

As shown in fig. 7, a gap is generated between the piezoelectric film 10 and the adhesive layer 14. Specifically, the voids include a void 17 formed at an end (open end) opposite to the folded portion, a void 18 formed inside, and a void 19 formed at the folded portion. The lengths of these voids were measured, and the ratio of the bonding area to the area of the laminated portion 10b was calculated from the ratio of the lengths to the bonding layer 14.

Specifically, in fig. 7, if the piezoelectric films are set to the 1 st to 5 th layers from the upper side toward the lower side, the lengths of the voids 17 to 19 are measured on the lower surface side of the 1 st layer. In the example of the figure, an open-end void 17a and an internal void 18a are present on the lower surface of the 1 st layer, and the respective lengths are S ₁ and S ₂. On the other hand, the length L ₁ up to the folded-back end of the 1 st layer of the laminated portion 10b is set to the length of the laminated portion 10 b. Since the value obtained by subtracting the length of the void from the length of the laminated portion 10b is the length of the bonded portion, the value obtained by dividing the length of the laminated portion 10b by the length is regarded as the ratio of the bonded areas. That is, the ratio of the bonding area was calculated (L ₁-(S₁+S₂))/L₁ as the ratio of the bonding area) on the lower surface of the 1 st layer in the illustrated example.

Next, the lengths of the voids 17 to 19 were measured on the upper surface side of the layer 2. In the illustrated example, the open-end void 17a and the internal void 18b are provided on the upper surface of the 2 nd layer, and the respective lengths are S ₁ and S ₃. On the other hand, the length L ₁ up to the folded-back end of the 1 st layer of the laminated portion 10b becomes the length of the laminated portion 10 b. Thus, at the upper surface of layer 2 of the drawing example, a (L ₁-(S₁+S₃))/L₁ as a ratio of the bonding area was calculated.

The lengths of the voids 17 to 19 were measured on the lower surface of the layer 2, the upper and lower surfaces of the layer 3, the upper and lower surfaces of the layer 4, and the upper surface of the layer 5 in the same manner as described above, and the ratio of the bonding areas was calculated. For example, on the lower surface of layer 3, there are open-end voids 17b, internal voids 18c, and folded-back portion voids 19, and if the respective lengths are S ₄、S₅ and S ₆, the ratio of the bonding area is calculated (L ₁-(S₄+S₅+S₆))/L₁).

In this way, the ratio of the bonding area was calculated on the upper and lower surfaces of each layer of the piezoelectric film of each section, and the average value of all the values of 10 sections was defined as "ratio of the bonding area of the adhesive layer to the area of the laminated portion of the piezoelectric film when viewed from the lamination direction of the piezoelectric film" according to the present invention.

From the viewpoint of both output and productivity, the ratio of the bonding area of the adhesive layer 14 to the area of the laminated portion 10b is preferably 0.8 to 0.99, more preferably 0.9 to 0.99.

In addition, if the adhesive force between the adhesive layer 14 and the piezoelectric film 10 is weak, the laminated piezoelectric film 10 may be peeled off, and the output may be reduced. Therefore, from the viewpoint of suppressing the decrease in output, the adhesion force between the adhesive layer 14 and the piezoelectric film 10 is preferably more than 0.1N/cm, more preferably 0.2N/cm or more, and even more preferably 0.5N/cm or more. The upper limit of the binding force is not particularly limited.

The method of measuring the adhesion force between the adhesive layer 14 and the piezoelectric film 10 is as follows.

A sample of 1cm×5cm was partially cut out from the laminated portion 10b of the piezoelectric element 50 b. As shown in fig. 8, one surface of the sample of the piezoelectric element 50 cut out is stuck to the smooth base B by the double-sided adhesive tape TP ₂. The surface of the susceptor B is preferably made of stainless steel, metal, glass, or the like. Further, it is preferable to use a double-sided adhesive tape having an adhesive force of 10N/cm or more with respect to the double-sided adhesive tape TP ₂ in which air bubbles cannot enter between the double-sided adhesive tape TP ₂.

Further, a single-sided adhesive tape TP ₁ was attached to the other side of the sample, and the single-sided adhesive tape TP ₁ was folded back, and the folded back portion was sandwiched by STROGRAPH P (for example, TOYO SEIKI co., ltd. Manufactured No. 260 STROGRAPH). The base B was subjected to a peel test in which the base B was stretched in the parallel direction, a graph of the distance and the peel force was obtained (see fig. 9), and the peak value of the peel force was read from the graph. When peeling occurs between the piezoelectric film 10 and the double-sided adhesive layer or the single-sided double-sided adhesive layer, it is determined that the adhesion force between the adhesive layer 14 and the piezoelectric film is a value larger than that of the double-sided adhesive layer.

The peak value of the peeling force divided by the width of the measured sample is taken as the adhesion force (N/cm) of the adhesive layer 14 to the piezoelectric film 10.

From the viewpoint of suppressing a decrease in output, the ratio of the cross-sectional area of the gap of the folded portion to the cross-sectional area of the laminated portion 10b is preferably 0.04 or less, more preferably 0.03 or less, and still more preferably 0.02 or less.

The ratio of the cross-sectional area of the gap of the folded portion to the cross-sectional area of the laminated portion 10b is a value obtained by dividing the length of the folded portion gap 19, in which the length measurement is performed, by the length of the laminated portion 10b in the measurement of the ratio of the bonding area of the adhesive layer 14. The ratio of the lengths of the folded-back portion gaps 19 was calculated on the upper and lower surfaces of each layer of the piezoelectric film of each cross section, and the average value of all the values of 10 cross sections was obtained.

In the example shown in fig. 1, the lamination portion 10b has a protruding portion 10a protruding outward in the planar direction, but the present invention is not limited to this, and may have a configuration without a protruding portion.

The shape of the protruding portion 10a is not limited to a rectangle, and may be a polygon such as a hexagon, or may be various shapes such as a substantially circular shape, a semicircular shape, an elliptical shape, and an irregular shape.

In the example shown in fig. 1 and the like, the protruding portion 10a is configured to protrude in the folding-back direction from the laminated portion 10b, but the present invention is not limited thereto. The protruding portion 10a may protrude from the laminated portion 10b in the width direction orthogonal to the folding-back direction.

In the example shown in fig. 1 and the like, the piezoelectric element has a structure having 1 protruding portion, but the present invention is not limited to this, and may have a structure having 2 or more protruding portions.

In addition, although the piezoelectric element 50 shown in fig. 1 is formed by stacking 5 layers of the piezoelectric film 10, the present invention is not limited thereto. That is, the piezoelectric element may have 2 to 4 layers of the piezoelectric film 10, or may have 6 or more layers of the piezoelectric film 10.

The following describes the constituent elements of the piezoelectric element of the present invention.

A part of the piezoelectric film 10 is shown enlarged in fig. 10.

The piezoelectric film 10 shown in fig. 10 has: a piezoelectric layer 20 that is a sheet having piezoelectricity; a2 nd electrode layer 26 laminated on one surface of the piezoelectric layer 20; a2 nd protective layer 30 laminated on the surface of the 2 nd electrode layer 26 opposite to the piezoelectric layer 20; a1 st electrode layer 24 laminated on the other surface of the piezoelectric layer 20; the 1 st protective layer 28 is laminated on the surface of the 1 st electrode layer 24 opposite to the piezoelectric layer 20. That is, the piezoelectric film 10 has a structure in which the piezoelectric layer 20 is sandwiched between electrode layers, and a protective layer is laminated on a surface of the electrode layers, which is not in contact with the piezoelectric layer.

In the present invention, various known piezoelectric layers can be used for the piezoelectric layer 20.

In the present invention, as schematically shown in fig. 10, the piezoelectric layer 20 is preferably a polymer composite piezoelectric body including piezoelectric particles 36 in a matrix 34 including a polymer material.

As a material of the matrix 34 (matrix binder) of the polymer composite piezoelectric body constituting the piezoelectric layer 20, a polymer material having viscoelasticity at normal temperature is preferably used. In the present specification, "normal temperature" means a temperature range of about 0 to 50 ℃.

Among them, the polymer composite piezoelectric body (piezoelectric layer 20) preferably has the following requirements.

(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.

As described above, a flexible polymer composite piezoelectric body used as an exciter 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.

Further, it is preferable that the spring constant is easily adjusted by laminating the adhesive materials (diaphragm) according to the rigidity (hardness, stiffness, spring constant), and in this case, the thinner the adhesive layer 104 is, the higher the energy efficiency can be.

In general, a polymer solid has a viscoelastic relaxation mechanism, and a large-scale molecular motion is observed as a decrease (relaxation) in storage modulus (young's modulus) or an maximization (absorption) in loss 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 20), 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, which is obtained by a dynamic viscoelasticity test at normal temperature, that is, at 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 matrix, and thus a larger 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.

As the polymer material having viscoelasticity at normal temperature, a polymer material having cyanoethyl group is preferably used, and cyanoethylated PVA is particularly preferably used. That is, in the present invention, the piezoelectric layer 20 preferably uses a polymer material having cyanoethyl groups as the substrate 34, and particularly preferably uses cyanoethylated PVA.

In the following description, the above polymer materials represented by cyanoethylated PVA are also collectively referred to as "polymer materials having viscoelasticity at ordinary temperature".

In addition, only 1 kind of these polymer materials having viscoelasticity at normal temperature may be used, or a plurality of kinds may be used in combination (mixture).

The substrate 34 using these polymer materials having viscoelasticity at ordinary temperature may be made of a plurality of polymer materials in combination as needed.

That is, in order to adjust the dielectric characteristics, mechanical characteristics, and the like, other dielectric polymer materials may be added to the substrate 34 as needed in addition to the viscoelastic material such as cyanoethylated PVA.

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 number of these dielectric polymer materials is not limited to 1, and a plurality of these dielectric polymer materials may be added to the substrate 34 of the piezoelectric layer 20.

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 34 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 material having viscoelasticity such as cyanoethylated PVA added to the matrix 34 of the piezoelectric layer 20 is not particularly limited, but is preferably 30 mass% or less based on the amount of the material in the matrix 34.

Accordingly, since the characteristics of the polymer material to be added can be exhibited without impairing the viscoelastic relaxation mechanism in the matrix 34, preferable results can be obtained in terms of improvement of dielectric constant, heat resistance, adhesion to the piezoelectric particles 36 and the electrode layer, and the like.

The piezoelectric layer 20 is a layer made of a polymer composite piezoelectric material including the piezoelectric particles 36 in the matrix 34. The piezoelectric particles 36 are dispersed in the matrix 34. Preferably, the piezoelectric particles 36 are uniformly (substantially uniformly) dispersed in the matrix 34.

The piezoelectric particles 36 are composed of ceramic particles having a perovskite-type or wurtzite-type crystal structure.

Examples of ceramic particles constituting the piezoelectric particles 36 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 particle size of the piezoelectric particles 36 is not limited, and may be appropriately selected according to the size of the piezoelectric film 10, the application of the piezoelectric element 50, and the like. The particle diameter of the piezoelectric particles 36 is preferably 1 to 10. Mu.m.

By setting the particle diameter of the piezoelectric particles 36 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.

The piezoelectric particles 36 in the piezoelectric layer 20 may be uniformly and regularly dispersed in the matrix 34, or may be irregularly dispersed in the matrix 34 as long as they are uniformly dispersed.

In the piezoelectric film 10, the amount ratio of the matrix 34 and the piezoelectric particles 36 in the piezoelectric layer 20 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 element 50, the characteristics required for the piezoelectric element 50, and the like.

The volume fraction of the piezoelectric particles 36 in the piezoelectric layer 20 is preferably 30 to 80%, more preferably 50% or more, and thus, more preferably 50 to 80%.

When the amount ratio of the matrix 34 to the piezoelectric particles 36 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 20 is not particularly limited, and may be appropriately set according to the application of the piezoelectric element 50, the number of layers of the piezoelectric film in the piezoelectric element 50, the characteristics required in the piezoelectric film 10, and the like.

The thicker the piezoelectric layer 20 is, the more advantageous the rigidity such as the rigidity of the 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 20 is preferably 10 to 300. Mu.m, more preferably 20 to 200. Mu.m, and still more preferably 30 to 150. Mu.m.

By setting the thickness of the piezoelectric layer 20 within the above range, preferable results can be obtained in terms of both securing rigidity and appropriate flexibility.

The piezoelectric layer 20 is preferably subjected to polarization (polarization) in the thickness direction.

In the present invention, the piezoelectric layer 20 is not limited to the polymer composite piezoelectric body including the piezoelectric particles 36 in the matrix 34 made of the polymer material having viscoelasticity at normal temperature such as cyanoethylated PVA as described above.

That is, in the piezoelectric film 10 of the present invention, various known piezoelectric layers can be used as the piezoelectric layer.

As an example, a polymer composite piezoelectric material including the same piezoelectric particles 36 in a matrix including the dielectric polymer material such as polyvinylidene fluoride, vinylidene chloride-tetrafluoroethylene copolymer, and vinylidene chloride-trifluoroethylene copolymer, a piezoelectric layer made of polyvinylidene fluoride, a piezoelectric layer made of a fluororesin other than polyvinylidene fluoride, a piezoelectric layer formed of a thin film made of poly-L-lactic acid, and a thin film made of poly-D-lactic acid, and the like can be used.

However, as described above, from the viewpoint of being able to operate relatively hard for vibrations of 20Hz to 20kHz, being able to operate relatively soft for vibrations of several Hz or less, and being able to obtain excellent acoustic characteristics, excellent flexibility, and the like, it is preferable to use the above-described polymer composite piezoelectric body including the piezoelectric particles 36 in the matrix 34 made of a polymer material having viscoelasticity at normal temperature, such as cyanoethylated PVA.

As shown in fig. 10, the piezoelectric film 10 has a structure in which one surface of the piezoelectric layer 20 has the 2 nd electrode layer 26, the 2 nd protective layer 30 is provided thereon, the 1 st electrode layer 24 is provided on the other surface of the piezoelectric layer 20, and the 1 st protective layer 28 is provided thereon. Wherein the 1 st electrode layer 24 and the 2 nd electrode layer 26 form an electrode pair.

That is, the piezoelectric film 10 has a structure in which the piezoelectric layer 20 is sandwiched between the electrode pairs, namely, the 2 nd electrode layer 26 and the 1 st electrode layer 24, and the laminate is sandwiched between the 2 nd protective layer 30 and the 1 st protective layer 28.

In this way, in the piezoelectric film 10, the region sandwiched between the 2 nd electrode layer 26 and the 1 st electrode layer 24 expands and contracts according to the applied voltage.

The 2 nd electrode layer 26 and the 2 nd protective layer 30, and the 1 st electrode layer 24 and the 1 st protective layer 28 are added for convenience of explanation of the piezoelectric film 10. Therefore, the 1 st and the 2 nd of the present invention have no technical significance and are not related to the actual use state.

In the present invention, the piezoelectric film 10 may have, for example, an adhesive layer for adhering the electrode layer and the piezoelectric layer 20 and an adhesive layer for adhering the electrode layer and the protective layer, in addition to these layers.

The adhesive may be an adhesive or an adhesive. The adhesive may be preferably the same as the substrate 34, which is a polymer material from which the piezoelectric particles 36 are removed from the piezoelectric layer 20. The adhesive layer may be provided on both the 1 st electrode layer 24 side and the 2 nd electrode layer 26 side, or may be provided on only one of the 1 st electrode layer 24 side and the 2 nd electrode layer 26 side.

In the piezoelectric film 10, the 2 nd protective layer 30 and the 1 st protective layer 28 cover the 1 st electrode layer 24 and the 2 nd electrode layer 26, and also function to impart appropriate rigidity and mechanical strength to the piezoelectric layer 20. That is, in the piezoelectric film 10, the piezoelectric layer 20 composed of the matrix 34 and the piezoelectric particles 36 exhibits very excellent flexibility against slow bending deformation, but may be insufficient in rigidity or mechanical strength depending on the application. The 2 nd protective layer 30 and the 1 st protective layer 28 are provided in the piezoelectric film 10 to compensate for this.

The 1 st protective layer 28 and the 2 nd protective layer 30 are identical in structure with only different arrangement positions. Therefore, in the following description, the two members are also collectively referred to as the protective layers without the need to distinguish between the 1 st protective layer 28 and the 2 nd protective layer 30.

The 2 nd and 1 st protective layers 30 and 28 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 2 nd and 1 st protective layers 30 and 28 is not limited. The thicknesses of the 2 nd and 1 st protective layers 30 and 28 are substantially the same, but may be different.

If the rigidity of the 2 nd and 1 st protective layers 30 and 28 is too high, the flexibility is impaired as well as the expansion and contraction of the piezoelectric layer 20 is restricted. Therefore, in addition to the case where mechanical strength and good handleability as a sheet are required, the thinner the 2 nd protective layer 30 and the 1 st protective layer 28 are, the more advantageous.

In the piezoelectric film 10, if the thickness of the 2 nd protective layer 30 and the 1 st protective layer 28 is 2 times or less the thickness of the piezoelectric layer 20, preferable results can be obtained in terms of both securing rigidity and appropriate flexibility.

For example, when the thickness of the piezoelectric layer 20 is 50 μm and the 2 nd and 1 st protective layers 30 and 28 are made of PET, the thickness of the 2 nd and 1 st protective layers 30 and 28 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 2 nd electrode layer 26 is formed between the piezoelectric layer 20 and the 2 nd protective layer 30, and the 1 st electrode layer 24 is formed between the piezoelectric layer 20 and the 1 st protective layer 28. The 2 nd electrode layer 26 and the 1 st electrode layer 24 are provided for applying a voltage to the piezoelectric layer 20 (piezoelectric film 10).

The 1 st electrode layer 24 and the 2 nd electrode layer 26 are substantially identical except for their positions. Therefore, in the following description, the two members are also collectively referred to as electrode layers without the need to distinguish between the 1 st electrode layer 24 and the 2 nd electrode layer 26.

In the present invention, the materials for forming the 2 nd electrode layer 26 and the 1 st electrode layer 24 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. Or also exemplified are conductive polymers such as PEDOT/PPS (polyethylene dioxythiophene-polystyrene sulfonic acid). Among them, copper, aluminum, gold, silver, platinum, and indium tin oxide are preferably exemplified as the 2 nd electrode layer 26 and the 1 st electrode layer 24. Among them, copper is more preferable from the viewpoints of conductivity, cost, flexibility, and the like.

The method for forming the 2 nd electrode layer 26 and the 1 st electrode layer 24 is not limited, and various known methods such as a vapor deposition method (vacuum film forming method) by vacuum vapor deposition, sputtering, and the like, a film forming method by electroplating, and a method of adhering a foil formed of the above materials can be used.

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 2 nd electrode layer 26 and the 1 st electrode layer 24. Among them, a thin film of copper formed by vacuum evaporation is particularly preferably used.

The thicknesses of the 2 nd electrode layer 26 and the 1 st electrode layer 24 are not limited. The thicknesses of the 2 nd electrode layer 26 and the 1 st electrode layer 24 are substantially the same, but may be different.

However, if the rigidity of the 2 nd electrode layer 26 and the 1 st electrode layer 24 is too high, the flexibility is impaired as well as the expansion and contraction of the piezoelectric layer 20 is restricted, similarly to the 2 nd protective layer 30 and the 1 st protective layer 28 described above. Therefore, the thinner the 2 nd electrode layer 26 and the 1 st electrode layer 24 are, the more advantageous as long as the resistance does not become excessively high.

In the piezoelectric film 10, it is preferable that the product of the thickness of the 2 nd electrode layer 26 and the 1 st electrode layer 24 and the young's modulus is lower than the product of the thickness of the 2 nd protective layer 30 and the 1 st protective layer 28, since flexibility is not seriously impaired.

For example, in the case of a combination in which the 2 nd protective layer 30 and the 1 st protective layer 28 are made of PET (Young's modulus: about 6.2 GPa) and the 2 nd electrode layer 26 and the 1 st electrode layer 24 are made of copper (Young's modulus: about 130 GPa), the thickness of the 2 nd protective layer 30 and the 1 st protective layer 28 is preferably 1.2 μm or less, more preferably 0.3 μm or less, and among these, 0.1 μm or less is preferable.

As described above, the piezoelectric film 10 has a structure in which the piezoelectric layer 20 in which the piezoelectric particles 36 are dispersed in the matrix 34 containing the polymer material is sandwiched between the 2 nd electrode layer 26 and the 1 st electrode layer 24, and the laminate is sandwiched between the 2 nd protective layer 30 and the 1 st protective layer 28.

In such a piezoelectric film 10, 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.

In the piezoelectric film 10, the storage modulus (E') at a frequency of 1Hz, which is measured based on dynamic viscoelasticity, is preferably 10 to 30GPa at 0℃and 1 to 10GPa at 50 ℃. The conditions are also similar to those of the piezoelectric layer 20.

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, in the piezoelectric film 10, the product of the thickness and the storage modulus (E') at a frequency of 1Hz, which is measured based on dynamic viscoelasticity, is preferably 1.0X10 ⁵～2.0×10⁶ 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 20.

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 20.

Thus, the frequency characteristic of the speaker using the piezoelectric film 10 is smoothed, 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 20, 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.

In the piezoelectric element 50, a power source (external power source) for applying a driving voltage for expanding and contracting the piezoelectric film 10, that is, supplying driving power, is connected to the 2 nd electrode layer 26 and the 1 st electrode layer 24 of the piezoelectric film 10.

The power supply is not limited, and may be a direct current power supply or an alternating current power supply. The driving voltage may be appropriately set according to the thickness of the piezoelectric layer 20 of the piezoelectric film 10, the material to be formed, and the like, so that the piezoelectric film 10 can be driven appropriately.

As described above, when the electrodes are extracted from the 2 nd electrode layer 26 and the 1 st electrode layer 24, the extraction is performed at the protruding portion 10 a. The method for extracting the electrodes from the 2 nd electrode layer 26 and the 1 st electrode layer 24 is not limited, and various known methods can be used.

As an example, a method of connecting a conductor such as copper foil to the 2 nd electrode layer 26 and the 1 st electrode layer 24 to draw out an electrode to the outside, a method of forming a through hole in the 2 nd protective layer 30 and the 1 st protective layer 28 by laser or the like, and filling a conductive material into the through hole to draw 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.

An example of a method for producing the piezoelectric film 10 will be described below with reference to fig. 11 to 13.

First, as shown in fig. 11, a sheet 12a having the 2 nd electrode layer 26 formed on the surface of the 2 nd protective layer 30 is prepared. Further, a sheet 12c schematically shown in fig. 13, in which the 1 st electrode layer 24 is formed on the surface of the 1 st protective layer 28, was prepared.

The sheet 12a may be produced by forming a copper film or the like as the 2 nd electrode layer 26 on the surface of the 2 nd protective layer 30 by vacuum deposition, sputtering, plating, or the like. Similarly, the sheet 12c may be produced by forming a copper film or the like as the 1 st electrode layer 28 on the surface of the 1 st protective layer 24 by vacuum deposition, sputtering, plating, or the like.

Alternatively, a commercially available sheet in which a copper film or the like is formed on the protective layer may be used as the sheet 12a and/or the sheet 12c.

The sheet 12a and the sheet 12c may be the same or different.

In addition, when the protective layer is extremely thin and the operability is poor, etc., a protective layer with a separator (temporary 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. The separator may be removed after the thermocompression bonding of the electrode layer and the protective layer.

Next, as shown in fig. 12, the coating material (coating composition) to be the piezoelectric layer 20 is applied to the 2 nd electrode layer 26 of the sheet 12a, and then cured to form the piezoelectric layer 20. Thus, the piezoelectric laminate 12b in which the sheet 12a and the piezoelectric layer 20 are laminated is produced.

The formation of the piezoelectric layer 20 can utilize various methods depending on the material forming the piezoelectric layer 20.

As an example, first, the above-mentioned polymer material such as cyanoethylated PVA is dissolved in an organic solvent, and piezoelectric particles 36 such as PZT particles are added thereto, followed by stirring to prepare a paint.

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

After the sheet 12a is prepared and the dope is prepared, the dope is cast (coated) on the sheet 12a, and the organic solvent is evaporated and dried. As a result, as shown in fig. 12, a piezoelectric laminate 12b having the 2 nd electrode layer 26 on the 2 nd protective layer 30 and the piezoelectric layer 20 laminated on the 2 nd electrode layer 26 was produced.

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

Alternatively, if the polymer material is a substance that can be melted by heating, a melt in which the piezoelectric particles 36 are added can be produced by heating the polymer material, and the piezoelectric laminate 12b shown in fig. 12 can be produced by extruding the melt in a sheet form onto the sheet 12a shown in fig. 11 by extrusion molding or the like and cooling the extruded melt.

As described above, in addition to the polymer material having viscoelasticity at normal temperature, a polymer piezoelectric material such as PVDF may be added to the substrate 34 in the piezoelectric layer 20.

When these polymer piezoelectric materials are added to the substrate 34, the polymer piezoelectric materials added to the paint may be dissolved. Alternatively, the polymer piezoelectric material to be added may be added to the polymer material which is melted by heating and has viscoelasticity at ordinary temperature, and the polymer piezoelectric material may be melted by heating.

After the piezoelectric layer 20 is formed, a rolling treatment may be performed as needed. The rolling treatment may be performed 1 time or a plurality of times.

As is well known, the rolling treatment is a treatment of heating a surface to be treated by hot pressing, a heating roller, or the like, and simultaneously pressing to perform planarization or the like.

Next, polarization treatment (polarization) is performed on the piezoelectric layer 20 of the piezoelectric laminate 12b having the 2 nd electrode layer 26 on the 2 nd protective layer 30 and the piezoelectric layer 20 formed on the 2 nd electrode layer 26. The polarization treatment of the piezoelectric layer 20 may be performed before the rolling treatment, but is preferably performed after the rolling treatment is performed.

The method of polarizing the piezoelectric layer 20 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 the case of performing electric field polarization, the 1 st electrode layer 24 may be formed before the polarization treatment, and the electric field polarization treatment may be performed using the 1 st electrode layer 24 and the 2 nd electrode layer 26.

In the piezoelectric film 10 of the present invention, the polarization treatment is preferably performed not in the plane direction of the piezoelectric layer 20 but in the thickness direction.

Next, as shown in fig. 13, the 1 st electrode layer 24 is laminated on the piezoelectric layer 20 side of the piezoelectric laminate 12b subjected to the polarization treatment so as to face the piezoelectric layer 20, whereby the sheet 12c prepared in advance is laminated.

Further, the piezoelectric film 10 shown in fig. 10 is produced by sandwiching the laminate between the 1 st protective layer 28 and the 2 nd protective layer 30, and thermally bonding the piezoelectric laminate 12b to the sheet 12c by using a hot press device, a heating roller, or the like.

Or the piezoelectric laminate 12b and the sheet 12c are bonded (preferably further pressure-bonded) with an adhesive to produce the piezoelectric film 10.

The piezoelectric film 10 may be manufactured by cutting a sheet-like sheet 12a, a sheet 12c, or the like, or may be manufactured by 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.

Next, a method of manufacturing a piezoelectric element using the manufactured piezoelectric film will be described.

One end of the piezoelectric film 10 is folded so that the length in the folding-back direction becomes the length of the laminated portion 10 b. An adhesive sheet serving as an adhesive layer is interposed between the folded piezoelectric films 10. Or an adhesive may be applied.

In the adhesive layer 14 for adhering the piezoelectric films to each other, as long as the adjacent piezoelectric films 10 can be adhered, various known materials can be used, and the same materials as the adhesive layer 104 for adhering the vibration plate and the piezoelectric element described later can be used.

As the adhesive layer 14, an adhesive sheet which is sheet-shaped and exhibits fluidity by heating can be used. By using the adhesive sheet, the ratio of the adhesive area of the adhesive layer to the area of the laminated portion can be more preferably adjusted. As the adhesive sheet, for example, TOYOCHEM co., ltd.

The laminated portion of the piezoelectric film 10 is sandwiched by metal plates from above and below, and each metal plate is thermally pressurized by a laminator. The metal plate is not particularly limited, and a metal plate such as titanium or stainless steel can be used. The thickness of the metal plate is preferably 0.2mm to 0.4mm.

The temperature at which the heat pressurization is carried out by the laminator is preferably 100 to 120 ℃. The roll speed of the laminator is preferably 0.04m/s to 0.08m/s.

After the entire surface is thermally pressurized, the laminated piezoelectric sheet is taken out from between the metal plates.

The piezoelectric film was folded back into a bellows shape, and in the same manner as described above, an adhesive sheet was interposed between the folded piezoelectric films 10, and the lamination machine was used to thermally press the piezoelectric films.

The above steps are repeated until the number of layers becomes a predetermined number, thereby producing a bellows-type piezoelectric element.

[ Electroacoustic transducer ]

The electroacoustic transducer of the invention is that

An electroacoustic transducer formed by adhering the piezoelectric element to a vibration plate.

Fig. 14 is a diagram schematically showing an example of the electroacoustic transducer of the present invention having the piezoelectric element of the present invention.

The electroacoustic transducer 100 shown in fig. 14 has the piezoelectric element 50 described above, the vibration plate 102, and the adhesive layer 104 that adheres the piezoelectric element 50 to the vibration plate 102. In the example shown in fig. 14, the lamination portion 10b of the piezoelectric element 50 on the surface side having the protruding portion 10a is preferably adhered to the vibration plate 102.

In this electroacoustic transducer 100, the piezoelectric film 10 expands and contracts in the planar direction by applying a driving voltage to the piezoelectric film 10 of the piezoelectric element 50, and the 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 piezoelectric element 50 in the plane direction, the diaphragm 102 bends, and as a result, the diaphragm 102 vibrates in the thickness direction. By this vibration in the thickness direction, the vibration plate 102 emits sound. The vibration plate 102 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.

Preferably, the vibration plate 102 is a flexible member. In the present invention, the term "flexible" means capable of bending and flexing as commonly interpreted as having flexibility, and specifically, capable of bending and stretching without breaking or damaging.

The diaphragm 102 is not limited as long as it has flexibility, and various kinds of sheet-like objects (plate-like objects, films) can be used.

Examples of the resin film include 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), and a cyclic olefin resin, foamed plastic including foamed polystyrene, foamed styrene, and foamed polyethylene, and various corrugated paper materials obtained by bonding one side or both sides of a corrugated cardboard to other cardboard.

In addition, as long as the electroacoustic transducer 100 has flexibility, a display device such as an Organic LIGHT EMITTING Diode (OLED) display, a liquid crystal display, a micro LED (LIGHT EMITTING Diode) display, or an inorganic electroluminescent Diode display can be appropriately used as the vibration plate 102.

In the electroacoustic transducer 100, the vibration plate 102 and the piezoelectric element 50 are bonded by the bonding layer 104.

As long as the vibration plate 102 and the piezoelectric element 50 can be bonded, various known materials can be used for the bonding layer 104.

Accordingly, the adhesive layer 104 may be a layer made of an adhesive that has fluidity at the time of bonding and becomes solid after that, may be a layer made of an adhesive that is soft solid in a gel state (rubber-like) at the time of bonding and also remains in a gel state after that, or may be a layer made of a material having characteristics of both an adhesive and an adhesive.

In the electroacoustic transducer 100, the piezoelectric element 50 is stretched to bend the vibration plate 102, thereby vibrating the same to generate sound. Therefore, in the electroacoustic transducer 100, it is preferable that the expansion and contraction of the piezoelectric element 50 is directly transmitted to the vibration plate 102. If a viscous substance such as a vibration-reducing substance exists between the vibration plate 102 and the piezoelectric element 50, the transmission efficiency of the expansion and contraction energy of the piezoelectric element 50 to the vibration plate 102 is reduced, and the driving efficiency of the electroacoustic transducer 100 is reduced.

In view of this, the adhesive layer 104 is preferably an adhesive layer composed of an adhesive, and the adhesive layer can obtain a solid and hard adhesive layer 104 as compared with an adhesive layer composed of an adhesive. More preferred examples of the adhesive layer 104 include adhesive layers made of thermoplastic adhesives such as polyester adhesives and styrene-butadiene rubber (SBR) adhesives.

Bonding is useful when a high bonding temperature is required, unlike bonding. In addition, thermoplastic type adhesives are preferred because they combine "relatively low temperature, short time, and strong adhesion".

The thickness of the adhesive layer 104 is not limited as long as a thickness capable of obtaining a sufficient adhesive force (adhesive force, cohesive force) is appropriately set according to the material of the adhesive layer 104.

In the electroacoustic transducer 100, the thinner the adhesive layer 104 is, the more the transmission effect of the expansion and contraction energy (vibration energy) transmitted to the piezoelectric element 50 of the vibration plate 102 is improved, and the energy efficiency can be improved. In addition, if the adhesive layer 104 is thick and has high rigidity, expansion and contraction of the piezoelectric element 50 may be restricted.

In view of this, the adhesive layer 104 is preferably thin. Specifically, the thickness of the adhesive layer 104 is preferably 0.1 to 50 μm, more preferably 0.1 to 30 μm, and even more preferably 0.1 to 10 μm in terms of the thickness after adhesion.

In addition, in the electroacoustic transducer 100, the adhesive layer 104 is a layer provided as a preferable embodiment, and is not an essential constituent element.

Therefore, even if the electroacoustic transducer 100 does not include the adhesive layer 104, the vibration plate 102 and the piezoelectric element 50 may be fixed using a known pressure bonding mechanism, fastening mechanism, fixing mechanism, or the like. For example, in the case where the piezoelectric element 50 is rectangular in shape in plan view, the electroacoustic transducer may be configured by fastening four corners with members such as bolts and nuts, or may be configured by fastening four corners and a center portion with members such as bolts and nuts.

However, at this time, when the driving voltage is applied from the power supply, the piezoelectric element 50 expands and contracts independently from the vibration plate 102, and in some cases, only the piezoelectric element 50 bends and the expansion and contraction of the piezoelectric element 50 cannot be transmitted to the vibration plate 102. In this way, when the piezoelectric element 50 expands and contracts independently of the diaphragm 102, the vibration efficiency of the diaphragm 102 by the piezoelectric element 50 decreases. There is a possibility that the vibration plate 102 cannot be sufficiently vibrated.

In view of this, as shown in fig. 14, the vibration plate 102 and the piezoelectric element 50 are preferably bonded by the bonding layer 104.

Wherein, as described above, the piezoelectric layer 20 contains the piezoelectric particles 36 in the matrix 34. The 2 nd electrode layer 26 and the 1 st electrode layer 24 are provided so as to sandwich the piezoelectric layer 20 in the thickness direction.

When a voltage is applied to the 2 nd electrode layer 26 and the 1 st electrode layer 24 of the piezoelectric film 10 having such a piezoelectric layer 20, 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) contracts in the thickness direction. Meanwhile, the piezoelectric film 10 also stretches in the in-plane direction due to the poisson's ratio. The expansion and contraction is about 0.01 to 0.1%.

As described above, the thickness of the piezoelectric layer 20 is preferably about 10 to 300 μm. Therefore, the maximum expansion and contraction in the thickness direction is only about 0.3 μm, which is very small.

In contrast, the piezoelectric film 10, that is, the piezoelectric layer 20, has a dimension significantly larger than the thickness in the planar direction. Therefore, for example, when the length of the piezoelectric film 10 is 20cm, the piezoelectric film 10 stretches and contracts approximately 0.2mm at maximum by applying a voltage.

The vibration plate 102 is attached to the piezoelectric film 10 through the adhesive layer 104. Accordingly, the diaphragm 102 is bent by the expansion and contraction of the piezoelectric film 10, and as a result, the diaphragm 102 vibrates in the thickness direction.

By this vibration in the thickness direction, the vibration plate 102 emits sound. That is, the vibration plate 102 vibrates according to the magnitude of the voltage (driving voltage) applied to the piezoelectric film 10, and emits sound according to the driving voltage applied to the piezoelectric film 10.

In addition, by adjusting the mass of the piezoelectric film 10 according to the spring constant of the vibration plate 102, the sound pressure level can be improved. If the mass of the piezoelectric film 10 is large, the vibration plate 102 is bent, and therefore vibration of the vibration plate 102 at the time of driving may be suppressed. On the other hand, if the mass of the piezoelectric film 10 is small, the resonance frequency becomes high, and there is a possibility that the vibration of the vibration plate 102 at a low frequency is suppressed. Considering these points, it is preferable to appropriately adjust the mass of the piezoelectric film 10 according to the spring constant of the vibration plate 102.

While the piezoelectric element of the present invention has been described in detail, the present invention is not limited to the above examples, and various modifications and changes 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. The present invention is not limited to this embodiment, and materials, amounts of use, ratios, processing contents, processing sequences, and the like shown in the following embodiments can be appropriately changed without departing from the spirit of the present invention.

[ Production of piezoelectric film ]

The piezoelectric film was produced by the method shown in fig. 11 to 13 described above.

First, cyanoethylated PVA (CR-V Shin-Etsu Chemical Co., manufactured by Ltd.) was dissolved in Dimethylformamide (DMF) at the following composition ratio. Then, PZT particles were added as piezoelectric particles in the following composition ratio, and stirred with a propeller mixer (rotation speed 2000 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 are obtained by sintering a commercially available PZT raw material powder at 1000 to 1200 ℃ and then pulverizing and classifying the powder so that the average particle diameter becomes 5 μm.

On the other hand, a sheet of copper film having a thickness of 0.3 μm was vacuum deposited 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 0.3. Mu.m, and the 1 st protective layer and the 2 nd protective layer were PET films having a thickness of 4. Mu.m.

A coating material for forming a piezoelectric layer prepared in advance was applied to the 2 nd electrode layer (copper vapor deposited film) of the sheet-like material using a bevel blade coater. The coating material was applied so that the film thickness of the dried coating film became 50. Mu.m.

Subsequently, DMF was evaporated by heating and drying the coated material on the sheet on a heating plate of 120 ℃. Thus, a 2 nd electrode layer made of copper was provided on the 2 nd protective layer made of PET, and a piezoelectric laminate having a piezoelectric layer (polymer composite piezoelectric layer) with a thickness of 50 μm was produced thereon.

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

On the piezoelectric laminate subjected to the polarization treatment, a sheet-like material obtained by vapor deposition of the thin film on a PET film was laminated with the 1 st electrode layer (copper film side) facing the piezoelectric layer.

Next, the piezoelectric laminate and the laminate of the sheet were thermally bonded at a temperature of 120 ℃ using a lamination apparatus, and the piezoelectric layer and the 1 st electrode layer were bonded to each other, thereby producing a piezoelectric film.

Example 1

The piezoelectric film thus produced was cut out at 170mm×150mm and folded back 4 times in the direction of the 170mm side, to produce a piezoelectric element having a laminated portion having a length of 30mm×150mm and a protruding portion having a length of 20mm×150 mm.

At the time of folding, each time of folding 1 time, an adhesive sheet (TSU 0041SI manufactured by TOYOCHEMCO., LTD.) was disposed between the laminated piezoelectric films, and the upper and lower sides of the adhered piezoelectric films were sandwiched between metal plates (made of Ti and having a thickness of 0.3 mm), and each metal plate was thermally pressed by a laminator to adhere the piezoelectric films to each other. The heating temperature at the time of lamination was set to 120℃and the heating time was set to 0.08m/min. The gap difference (T ₂-T₁) between both ends of the pair of rolls (R ₁、R₂ in fig. 15) of the laminator was set to 5 μm or less. The area of the adhesive sheet before lamination was set to 0.91 times the area of the lamination portion.

By repeating the same folding for 4 times, a piezoelectric element having 5 layers of piezoelectric films was produced.

The ratio of the bonding area of the adhesive layer to the area of the laminated portion of the fabricated piezoelectric element was measured by the above method and found to be 0.99. In addition, as a result of measuring the adhesion force of the piezoelectric film and the adhesive layer by the above method, the piezoelectric element and the support B are peeled off from each other. Since the adhesive force of the adhesive for bonding the piezoelectric element to the support B is approximately 10N/cm, the adhesive force of the piezoelectric film to the adhesive layer exceeds 10N/cm. The ratio of the cross-sectional area of the gap of the folded portion was found to be 0 by the above method.

Example 2

A piezoelectric element was produced in the same manner as in example 1, except that the difference in the gap between the both ends of the roller of the laminator was 75 μm.

The ratio of the bonding area of the adhesive layer of the fabricated piezoelectric element to the area of the laminated portion was 0.85. In addition, the adhesive force of the adhesive layer exceeds 10N/cm. The ratio of the cross-sectional area of the gap in the folded-back portion was 0.

Example 3

A piezoelectric element was produced in the same manner as in example 1, except that the area ratio of the adhesive sheet was set to 0.88.

The ratio of the bonding area of the adhesive layer of the fabricated piezoelectric element to the area of the laminated portion was 0.97. In addition, the adhesive force of the adhesive layer exceeds 10N/cm. The ratio of the cross-sectional area of the gap in the folded-back portion was 0.04.

Example 4

A piezoelectric element was produced in the same manner as in example 1, except that the heating temperature at the time of lamination was set to 80 ℃.

The ratio of the bonding area of the adhesive layer of the fabricated piezoelectric element to the area of the laminated portion was 0.99. In addition, the adhesive force of the adhesive layer was 0.2N/cm. The ratio of the cross-sectional area of the gap in the folded-back portion was 0.

Example 5

A piezoelectric element was produced in the same manner as in example 1, except that the heating temperature at the time of lamination was 70 ℃.

The ratio of the bonding area of the adhesive layer of the fabricated piezoelectric element to the area of the laminated portion was 0.99. In addition, the adhesive force of the adhesive layer was 0.1N/cm. The ratio of the cross-sectional area of the gap in the folded-back portion was 0.

Example 6

A piezoelectric element was produced in the same manner as in example 1, except that the area ratio of the adhesive sheet was set to 0.87.

The ratio of the bonding area of the adhesive layer of the fabricated piezoelectric element to the area of the laminated portion was 0.97. In addition, the adhesive force of the adhesive layer exceeds 10N/cm. The ratio of the cross-sectional area of the gap in the folded-back portion was 0.05.

Comparative example 1

A piezoelectric element was produced in the same manner as in example 1, except that the area ratio of the adhesive sheet was set to 1.

The ratio of the bonding area of the adhesive layer to the area of the laminated portion of the fabricated piezoelectric element was 1. In addition, the adhesive force of the adhesive layer exceeds 10N/cm. The ratio of the cross-sectional area of the gap in the folded-back portion was 0.

Comparative example 2

A piezoelectric element was produced in the same manner as in example 1, except that the difference in the gap between the both ends of the roller of the laminator was 150 μm.

The ratio of the bonding area of the adhesive layer to the area of the laminated portion of the fabricated piezoelectric element was 0.84. In addition, the adhesive force of the adhesive layer exceeds 10N/cm. The ratio of the cross-sectional area of the gap in the folded-back portion was 0.

[ Evaluation ]

The electroacoustic transducers of each of the examples and comparative examples were evaluated for contamination of the laminator surface and sound pressure.

< Contamination of laminator surfaces >

It was visually confirmed whether or not an adhesive was attached to the surface of the laminator after laminating the folded-back piezoelectric film at the time of manufacturing the piezoelectric element.

< Sound pressure >

An electroacoustic transducer was fabricated by attaching the surface of the fabricated piezoelectric element opposite to the protruding portion to a vibration plate. As the vibration plate, a plate-like member having a size of 500mm×450mm, a thickness of 0.8mm, and a material of aluminum (a 5052) was used. The widthwise direction of the vibration plate is aligned with the longitudinal direction of the piezoelectric element, and the center of the vibration plate is aligned with the center of the laminated portion of the piezoelectric element and bonded. As an adhesive layer for adhering the piezoelectric element and the vibration plate, an acrylic adhesive is used.

A sinusoidal sweep signal having a frequency of 1kHz to 20kHz and a voltage of 50Vrms was applied to the piezoelectric element, and the sound pressure was measured by a microphone located at a distance of 1m from the center of the diaphragm.

If the sound pressure at 3kHz is 84dB or more, it is evaluated that the desired characteristics are satisfied.

The results are shown in table 1.

TABLE 1

From table 1, it is clear that the examples of the present invention do not contaminate the laminator surface at the time of fabrication and that the sound pressure is high. It was found that the lamination machine surface was contaminated because the ratio of the bonding area of the adhesive layer of comparative example 1 was too large. It is found that the ratio of the bonding area of the adhesive layer of comparative example 2 is too small, and thus the sound pressure becomes low.

Further, as is clear from the comparison of examples 1, 4 and 5, the adhesive force of the adhesive layer is preferably more than 0.1N/cm.

As is clear from the comparison of examples 1, 3 and 6, the ratio of the cross-sectional area of the gap of the folded-back portion is preferably 0.04 or less.

From the above, the effects of the present invention are remarkable.

Industrial applicability

The piezoelectric element of the present invention can be preferably used for various sensors such as an acoustic wave sensor, an ultrasonic sensor, a pressure sensor, a tactile sensor, a strain sensor, and a vibration sensor (particularly, it is suitable for use in manufacturing site detection such as foundation point detection such as crack detection and foreign matter contamination detection); acoustic elements such as microphones, speakers, and exciters (specific applications include noise cancellers (used for vehicles, commuter electric vehicles, airplanes, robots, and the like), artificial vocal cords, buzzers for pest/pest intrusion prevention, furniture, wallpaper, photographs, helmets, goggles, headrests, signs, robots, and the like); a haptic interface for automobiles, smart phones, smart watches, gaming machines, etc.; ultrasonic transducers such as ultrasonic probes and wave receivers in water; 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 for roads, floors, mattresses, chairs, shoes, tires, wheels, computer keyboards, and the like.

Symbol description

10-Piezoelectric film, 10 a-protrusion, 10 b-lamination, 12a, 12 c-sheet, 12 b-piezoelectric lamination, 14-adhesive layer, 17-open-end void, 18-interior void, 19-folded-back void, 20-piezoelectric layer, 24-1 st electrode layer, 26-2 nd electrode layer, 28-1 st protective layer, 30-2 nd protective layer, 34-substrate, 36-piezoelectric particles, 40-connection portion, 50-piezoelectric element, 100-electroacoustic transducer, 102-vibration plate, 104-adhesive layer.

Claims

1. A piezoelectric element is formed by laminating a plurality of piezoelectric films by folding back the piezoelectric films each having a piezoelectric layer, electrode layers provided on both sides of the piezoelectric layer, and a protective layer provided on the electrode layers 1 or more times,

The piezoelectric element has an adhesive layer for bonding between layers of the laminated piezoelectric films,

2. The piezoelectric element according to claim 1, wherein,

The adhesion of the adhesive layer to the piezoelectric film exceeds 0.1N/cm.

3. The piezoelectric element according to claim 1, wherein,

4. The piezoelectric element according to claim 1, wherein,

5. An electroacoustic transducer formed by attaching the piezoelectric element according to any one of claims 1 to 4 to a vibration plate.