TW202315173A - Piezoelectric element and electroacoustic transducer - Google Patents

Abstract

Provided are a piezoelectric element and an electro-acoustic converter with which it is possible to achieve both a high sound pressure and good productivity, the piezoelectric element being formed by stacking a piezoelectric film. The piezoelectric element is formed by stacking a plurality of layers of the piezoelectric film, which comprises a piezoelectric layer, electrode layers provided on both surfaces of the piezoelectric layer, and protective layers provided on the electrode layers, by folding back the piezoelectric film one or more times, wherein: the piezoelectric element includes an adhesive layer for bonding the stacked layers of the piezoelectric film to one another; and a ratio of a bonding surface area of the adhesive layer to the surface area of a stacked portion of the piezoelectric film when seen from a stacking direction of the piezoelectric film lies in a range of 0.85 to 0.99.

Description

Piezoelectric elements and electroacoustic transducers

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

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

As a piezoelectric element, the use of a piezoelectric film in which a piezoelectric layer is sandwiched between electrode layers and protective layers has been proposed. Also, it has been proposed to laminate a plurality of piezoelectric films to be used as piezoelectric elements.

For example, Patent Document 1 describes a piezoelectric film comprising: a polymer composite piezoelectric body in which piezoelectric particles are dispersed in a matrix containing a polymer material; and an electrode layer formed on the aforementioned polymer material. Both sides of the composite piezoelectric body, in which the loss tangent at a frequency of 1 kHz in the measurement of dynamic viscoelasticity has a maximum value of 0.1 or more in the temperature range of more than 50°C and less than 150°C, and the value at 50°C 0.08 or more. Also, Patent Document 1 describes a piezoelectric element in which a plurality of piezoelectric films are stacked by folding back the piezoelectric film once or more.

[Patent Document 1] International Publication No. 2020/196850

In the case of using a piezoelectric film as a piezoelectric element, the piezoelectric element emits sound from the vibrating plate by being attached to the vibrating plate to vibrate the vibrating plate, but in the case of a single layer, the output of the piezoelectric element is small and cannot Sufficiently vibrating the diaphragm results in lower sound pressure. Therefore, as described above, by folding the piezoelectric film into multiple layers, the output of the piezoelectric element can be increased, and the diaphragm can be sufficiently vibrated to obtain a high sound pressure.

When the piezoelectric film is multilayered, it is necessary to bond the layers of the piezoelectric film with an adhesive layer to propagate the stress generated in each layer to the vibrating plate. When the bonding area by the bonding layer is large, the loss of stress propagation between the layers is small, and thus a higher sound pressure is obtained. However, if the bonding area by the bonding layer is too large, there is a problem that the adhesive protrudes from the layered part when the piezoelectric film is laminated, and the surface of the press machine is contaminated, resulting in a decrease in productivity.

The object of the present invention is to solve the problems of the prior art, and to provide a piezoelectric element and an electroacoustic transducer capable of achieving both high sound pressure and productivity among piezoelectric elements formed by laminating piezoelectric films.

In order to solve the above-mentioned problems, the present invention has the following configurations. [1] A piezoelectric element in which a piezoelectric film is laminated by folding one or more piezoelectric films including a piezoelectric layer, electrode layers provided on both surfaces of the piezoelectric layer, and a protective layer provided on the electrode layer It is made up of plural layers, among which, The piezoelectric element has an adhesive layer for bonding interlayers of laminated piezoelectric films, When viewed from the lamination direction of the piezoelectric film, the ratio of the bonding area of the adhesive layer to the area of the lamination portion of the piezoelectric film is in the range of 0.85 to 0.99. [2] The piezoelectric element as described in [1], wherein The adhesive force between the adhesive layer and the piezoelectric film exceeds 0.1N/cm. [3] The piezoelectric element described in [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 in which the piezoelectric element described in any one of [1] to [4] is adhered to a vibrating plate. [Invention effect]

According to the present invention, it is possible to provide a piezoelectric element and an electroacoustic transducer capable of achieving both high sound pressure and productivity among piezoelectric elements formed by laminating piezoelectric films.

Hereinafter, the piezoelectric element and the electroacoustic transducer of the present invention will be described in detail based on preferred embodiments shown in the attached drawings.

The description of the constituent requirements described below may be based on representative embodiments of the present invention, but the present invention is not limited to these embodiments. In addition, in this specification, the numerical range represented using "-" means the range which includes the numerical value described before and after "-" as a lower limit and an upper limit.

[Piezoelectric element] A piezoelectric element according to the present invention, in which a piezoelectric film is laminated by folding back a piezoelectric film having a piezoelectric layer, electrode layers provided on both surfaces of the piezoelectric layer, and a protective layer provided on the electrode layer at least once. It is made up of plural layers, among which, The piezoelectric element has an adhesive layer for bonding interlayers of laminated piezoelectric films, When viewed from the lamination direction of the piezoelectric film, the ratio of the bonding area of the adhesive layer to the area of the lamination portion of the piezoelectric film is in the range of 0.85 to 0.99.

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 . In addition, the top view is a view viewed from the lamination direction of the lamination of the plurality of piezoelectric films 10 .

The piezoelectric element 50 shown in FIGS. 1 to 3 is one in which five piezoelectric films 10 are laminated by folding one rectangular piezoelectric film 10 four times in one direction. That is, the piezoelectric element 50 is a multilayer piezoelectric element in which five piezoelectric films 10 are laminated. In FIG. 2 , the structure of the piezoelectric element 50 is omitted for simplification of the drawing, but the piezoelectric film 10 has electrode layers on both sides of the piezoelectric layer 20 and covers both electrode layers to have protection. layers. This point is also the same in FIG. 7 and FIG. 14 . In addition, in the following description, the direction in which the piezoelectric film 10 folds back (horizontal direction in FIG. 1 ) is referred to as the folded-back direction.

As shown in FIG. 1 , the piezoelectric element 50 has a protruding portion 10 a protruding outward in the plane direction from a laminated portion 10 b of piezoelectric films 10 stacked in five layers. That is, the piezoelectric element 50 is one in which the protruding portion 10a is provided in such a manner that when one piezoelectric film 10 is folded back four times, in FIG. The lengths in the directions are substantially the same, the piezoelectric film 10 of the uppermost layer is longer than the piezoelectric films 10 of other layers, and one end in the folding direction does not overlap with the piezoelectric films 10 of other layers.

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

In the present invention, the laminated portion 10 b refers to a region where two or more layers of piezoelectric films overlap when the piezoelectric element is viewed from above (or below) in plan view, that is, in FIG. 1 . That is, as shown in FIG. 3 , a region where five layers of the piezoelectric film 10 are stacked is the laminated portion 10 b.

On the other hand, the protruding portion 10a refers to a region that protrudes from the layered portion 10b in the surface direction, and is a region that does not overlap with other layers in plan view. In the example shown in FIG. 1 , the right end portion of the uppermost layer in the figure is the protruding portion 10 a.

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

In the connection part 40 , the wires connected to the external power supply are connected by filling known conductive materials such as conductive metal paste such as silver glue, conductive carbon paste, and conductive nano-ink. In addition, the connection method of the electrode and wiring in the protrusion part 10a is not limited, Well-known various methods can be utilized.

In the piezoelectric element 50 of the present invention, the piezoelectric element 50 is driven by applying a voltage to the electrode layer using an external power source through the connection portion 40 provided on the protruding portion 10a. When the piezoelectric element 50 is driven, the piezoelectric element 50 expands and contracts in the plane direction, and bends the vibrating plate on which the piezoelectric element 50 is pasted. As a result, the vibrating plate vibrates to generate sound. The vibrating plate vibrates according to the magnitude of the driving voltage applied to the piezoelectric film 50 and emits a sound corresponding to the driving voltage applied to the piezoelectric film 50 . That is, the piezoelectric element 50 can be used as an actuator.

However, in the present invention, the ratio of the bonding area of the bonding layer 14 to the area of the buildup portion 10b is within a range of 0.85 to 0.99. FIG. 4 is a diagram schematically showing a plan view of the piezoelectric film 10 and the adhesive layer 14 in the laminated portion 10b. As schematically shown in FIG. 4 , the adhesive layer 14 is smaller than the piezoelectric film 10 in the build-up portion 10b, and the adhesive layer 14 is formed on the edge of the piezoelectric film 10 on three sides except the side that becomes the folded portion. inside. In addition, in FIG. 4 , each side of the adhesive layer 14 is shown as a linear diagram, but it is not limited thereto. Like the example shown in FIG. 5 , each side of the adhesive layer 14 may have an irregular shape.

As described above, when a piezoelectric film is used as an actuator, a larger output is required, so it is conceivable to form a multilayer laminated piezoelectric element by folding the piezoelectric film several times. At this time, in order to transmit the vibration of the stacked piezoelectric films to the outside (vibration plate), the piezoelectric films are bonded to each other with an adhesive layer. The piezoelectric films are pasted together using a laminator or the like.

In order to reduce the transmission loss of vibration and increase the output, it is preferable that the bonding area of the bonding layer is large. However, if the adhesive area of the adhesive layer is too large, when the piezoelectric film is folded back to bond the piezoelectric film to each other by the adhesive layer when the piezoelectric element is manufactured, the adhesive protrudes from the lamination part, and the surface of the laminator, etc. Adhesive adheres to the surface of the laminator, etc., and causes a problem of lower productivity.

In contrast, the piezoelectric element 50 of the present invention can suppress transmission of vibration by reducing the bonding area of the bonding layer by setting the ratio of the bonding area of the bonding layer 14 to the area of the laminated portion 10b to 0.85 or more. Loss increases and output decreases. In addition, by setting the bonding area ratio to 0.99 or less, when the piezoelectric films are bonded by bonding, it is possible to prevent the bonding agent from protruding from the layered part, and the surface of the layering machine and the like being contaminated to reduce productivity.

The measurement method of the ratio of the bonding area of the bonding layer 14 with respect to the area of the laminated part 10b is as follows. First, as shown by the dotted line in FIG. 6 , ten cross-sections are cut obliquely with respect to one side of the rectangular build-up part 10 b. At this time, each cutting surface was made parallel and equidistant. Moreover, the four sides of the laminated part 10b were each cut at one place. The cutting method is not particularly limited, and a method that allows observation of the cross section after cutting and does not cause deformation or breakage of the electrode layer, deformation or breakage of the piezoelectric layer, or deformation or breakage of the protective layer is preferable. For example, after drying and curing the observation site using EB hardening resin, a method of cutting with a single-edged razor can be used.

Next, each cut surface was observed at a magnification of 50 times using a SEM (scanning electron microscope). FIG. 7 is a diagram schematically showing a B-B line cross-section in FIG. 6 . As shown in FIG. 7 , a gap is generated between the piezoelectric film 10 and the bonding layer 14 . Specifically, as voids, there are voids 17 formed at the end (open end) opposite to the folded portion, voids 18 formed inside, and voids 19 formed in the folded portion. The lengths of these voids were measured, and the ratio of the bonding area to the area of the buildup portion 10 b was calculated from the ratio to the length of the bonding layer 14 .

Specifically, in FIG. 7 , when each piezoelectric film is defined as the first layer to the fifth layer from the upper side toward the lower side, the lengths of the voids 17 to 19 are respectively measured on the lower surface side of the first layer. In the illustrated example, open end voids 17a and internal voids 18a exist on the lower surface of the first layer, and the respective lengths are S ₁ and S ₂ . On the other hand, let the length _L1 of the first layer of the build-up part 10b to the folded-back end be the length of the build-up part 10b. Since the length of the laminated portion 10b minus the length of the void is the length of the bonding portion, the value divided by the length of the laminated portion 10b is regarded as the ratio of the bonded area. That is, (L ₁ −(S ₁ +S ₂ ))/L ₁ is calculated as the ratio of the bonded area on the lower surface of the first layer in the illustrated example.

Next, the lengths of the voids 17 to 19 were measured on the upper surface side of the second layer. In the illustrated example, open-end voids 17a and internal voids 18b exist on the upper surface of the second layer, and the respective lengths are S ₁ and S ₃ . On the other hand, the length _L1 of the first layer of the build-up part 10b to the folded end is the length of the build-up part 10b. Therefore, on the upper surface of the second layer in the illustrated example, (L ₁ −(S ₁ +S ₃ ))/L ₁ is calculated as a ratio of the bonding area.

In the lower surface of the second layer, the upper surface and the lower surface of the third layer, the upper surface and the lower surface of the fourth layer, and the upper surface of the fifth layer, the lengths of the gaps 17-19 are measured in the same manner as above, Calculates the ratio of the bonded area. For example, on the lower surface of the third layer, there are open end voids 17b, internal voids 18c, and folded portion voids 19. If the respective lengths are S ₄ , S ₅ , and S ₆ , then (L ₁ −(S ₄ +S ₅ +S ₆ ))/L ₁ is calculated as a ratio of the bonded area.

In this way, on the upper surface and lower surface of each layer of the piezoelectric film in each section, the ratio of the bonding area is calculated, and the average value of all the values of the 10 cross-sections is taken as the "adhesion when viewed from the lamination direction of the piezoelectric film" of the present invention. The ratio of the bonded area of the layer to the area of the laminated part of the piezoelectric film".

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

Also, if the adhesive force between the adhesive layer 14 and the piezoelectric film 10 is weak, the laminated piezoelectric film 10 will be peeled off, which may result in a decrease in output. Therefore, from the viewpoint of suppressing a drop in output, the adhesive force between the adhesive layer 14 and the piezoelectric film 10 is preferably more than 0.1 N/cm, more preferably 0.2 N/cm or more, and still more preferably 0.5 N/cm or more. The upper limit of the adhesive force is not particularly limited.

Here, the method of measuring the adhesive force between the adhesive layer 14 and the piezoelectric film 10 is as follows. A sample of 1 cm×5 cm was cut out from the laminated portion 10b of the piezoelectric element 50b. As shown in FIG. 8 , one side of the cut out sample of the piezoelectric element 50 was adhered to a smooth base B by means of a double-sided adhesive tape TP ₂ . The surface of the base B is preferably made of stainless steel, metal and glass. Moreover, it is preferable to use double-sided adhesive tape TP ₂ installed so that air bubbles do not enter between the double-sided adhesive tape TP ₂ and the adhesive force of 10 N/cm or more is used.

Furthermore, the single-sided adhesive tape TP ₁ is attached to the other surface of the sample, the single-sided adhesive tape TP ₁ is folded back, and the folded portion is clamped by a spectrometer P (for example, No260 STROGRAPH manufactured by TOYO SEIKI CO., LTD.). Carry out a peeling test of the base B pulled out in a parallel direction, obtain the graph of the distance and the peeling force (see Figure 9), and read the peak value of the peeling force from the graph. In the case of peeling from the double-sided adhesive tape or the single-sided adhesive tape, it was determined that the adhesive force between the adhesive layer 14 and the piezoelectric film 10 was greater than that of the adhesive tape. The value obtained by dividing the peak value of the peeling force by the measured width of the sample was defined as the adhesive force (N/cm) between the adhesive layer 14 and the piezoelectric film 10 .

Also, from the viewpoint of suppressing reduction 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, 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 defined as the measurement of the ratio of the bonded area of the above-mentioned adhesive layer 14 by dividing the length of the folded portion gap 19 for length measurement by the value of the laminated portion 10b. The value of the length. The ratio of the lengths of the folded portion gaps 19 in the upper surface and the lower surface of each layer of the piezoelectric film in each section was calculated, and the average value of all the values of the 10 sections was obtained.

Here, in the example shown in FIG. 1, although it has the structure which has the protrusion part 10a which protrudes outward in the surface direction from the laminated part 10b, it is not limited to this, The structure which does not have a protrusion part may be sufficient. The shape of the protruding portion 10a is not limited to a rectangle, and may be a polygon such as a hexagon, or may have various shapes such as a substantially circle, a semicircle, an ellipse, and an irregular shape.

Moreover, in the example shown in FIG. 1 etc., although the protruding part 10a was made into the structure which protruded from the laminated part 10b in the folding direction, it is not limited to this. The protruding part 10a may be configured to protrude from the lamination part 10b in the width direction perpendicular to the folding direction.

In addition, in the example shown in FIG. 1 etc., although the piezoelectric element is made into the structure which has one protrusion part, it is not limited to this, You may make it into the structure which has two or more protrusion parts.

In addition, the piezoelectric element 50 shown in FIG. 1 is formed by laminating five piezoelectric films 10, but the present invention is not limited thereto. That is, the piezoelectric element may have two to four piezoelectric films 10 , or may have six or more piezoelectric films 10 .

Hereinafter, the constituent elements of the piezoelectric element of the present invention will be described.

A part of the piezoelectric film 10 is enlarged in FIG. 10 . The piezoelectric film 10 shown in FIG. 10 has: a piezoelectric layer 20, which is a piezoelectric sheet; a second electrode layer 26, laminated on one surface of the piezoelectric layer 20; a second protective layer 30 , laminated on the surface of the second electrode layer 26 opposite to the piezoelectric layer 20; the first electrode layer 24, laminated on the other surface of the piezoelectric layer 20; the first protective layer 28, laminated on the first electrode layer 24 on the side 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 the surfaces of the electrode layers that are 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 the material of the matrix 34 (matrix and binder) of the polymer composite piezoelectric body constituting the piezoelectric layer 20 , a polymer material having viscoelasticity at room temperature is preferably used. In addition, in this specification, "normal temperature" means the temperature range of about 0-50 degreeC.

Among them, the polymer composite piezoelectric body (piezoelectric body layer 20 ) is preferably one that satisfies the following requirements. (i) Flexibility For example, when a portable document such as a newspaper or magazine is held in a state where it feels slowly bent, a relatively slow and large bending deformation of several Hz or less is continuously received from the outside. At this time, if the polymer composite piezoelectric body is hard, a relatively large bending stress may be generated to cause cracks at the interface between the polymer matrix and the piezoelectric body particles, which may eventually lead to destruction. Therefore, appropriate flexibility is required for the polymer composite piezoelectric body. Moreover, if strain energy can be diffused to the outside as heat, stress can be relaxed. Therefore, the loss tangent of the polymer composite piezoelectric body is required to be appropriately large.

In conclusion, the flexible polymer composite piezoelectric body used as an actuator is required to operate relatively hard for vibrations of 20 Hz to 20 kHz, and to operate relatively softly for vibrations of several Hz or less. In addition, the loss tangent of the polymer composite piezoelectric body is required to be appropriately large with respect to vibrations at all frequencies below 20 kHz. Furthermore, it is preferable to easily adjust the spring constant by laminating according to the rigidity (hardness, rigidity, spring constant) of the adhered object material (vibration plate). In this case, the thinner the adhesive layer 104, the more energy efficiency.

Generally, polymer solids have a viscoelastic relaxation mechanism, and as the temperature increases or the frequency decreases, large-scale molecular motion acts as a decrease (relaxation) of the storage elastic coefficient (Young's modulus) or a maximization of the loss elastic coefficient (absorption ) was observed. Among them, the relaxation caused by the Micro Brownian motion of the molecular chains in the amorphous region is called the main dispersion, and a very large relaxation phenomenon can be observed. The temperature at which this primary dispersion occurs is the glass transition point (Tg), where the viscoelastic relaxation mechanism appears most clearly. In the polymer composite piezoelectric body (piezoelectric body layer 20), by using a polymer material with a glass transition point at room temperature, in other words, a polymer material with viscoelasticity at room temperature, for the matrix, it is possible to realize the performance for 20 Hz to 20 Hz. A polymer composite piezoelectric body that operates hard at vibrations of 20kHz and soft at slow vibrations below a few Hz. In particular, it is preferable to use a polymer material having a glass transition point at room temperature, ie, 0 to 50° C. at a frequency of 1 Hz, for the matrix of the polymer composite piezoelectric body, in terms of appropriately expressing such an operation.

As the polymer material having viscoelasticity at normal temperature, various known ones can be used. It is preferable to use a polymer material having a maximum loss tangent Tanδ at a frequency of 1 Hz obtained based on a dynamic viscoelasticity test at room temperature, that is, 0 to 50° C., of 0.5 or more. Thereby, when the polymer composite piezoelectric body is slowly bent by an external force, the stress concentration at the interface between the polymer matrix and the piezoelectric body particles in the maximum bending moment portion is relieved, and high flexibility can be expected.

In addition, a polymer material having viscoelasticity at room temperature is preferably as follows, that is, the storage elastic coefficient (E') at a frequency of 1 Hz based on dynamic viscoelasticity measurement is 100 MPa or more at 0°C, and at 50°C The lower is below 10MPa. Thereby, the bending moment generated when the polymer composite piezoelectric body is slowly bent by an external force can be reduced, and at the same time, it can operate relatively hard against acoustic vibrations of 20 Hz to 20 kHz.

Moreover, it is more preferable that the relative permittivity of the polymer material which has viscoelasticity at normal temperature is 10 or more at 25 degreeC. Thereby, when a voltage is applied to the polymer composite piezoelectric body, a higher electric field is applied to the piezoelectric body 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 preferable that the relative dielectric constant of the polymer material is 10 or less at 25° C.

Examples of viscoelastic polymer materials at room temperature that satisfy these conditions include cyanoethylated polyvinyl alcohol (cyanoethylated PVA), polyvinyl acetate, polyvinylidene chloride acrylonitrile, polystyrene - Vinyl polyisoprene block copolymer, polyvinyl methyl ketone, polybutyl methacrylate, etc. In addition, commercially available products such as Hibler 5127 (manufactured by KURARAY CO., LTD.) can also be preferably used as such 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 a cyanoethylated PVA.

As a polymer material having viscoelasticity at room temperature, it is preferable to use a polymer material having cyanoethyl groups, and it is particularly preferable to use cyanoethylated PVA. That is, in the present invention, it is preferable to use a polymer material having a cyanoethyl group for the piezoelectric layer 20 as the matrix 34 , and it is particularly preferable to use cyanoethylated PVA. In the following description, the above-mentioned polymer materials represented by cyanoethylated PVA are collectively referred to as "polymer materials having viscoelasticity at room temperature".

In addition, these polymer materials having viscoelasticity at normal temperature may be used alone, or a plurality of them may be used in combination (mixed).

The matrix 34 using these polymer materials having viscoelasticity at room temperature can use multiple types of polymer materials in combination as needed. That is, for the purpose of adjusting dielectric properties or mechanical properties, other dielectric polymer materials may be added to the matrix 34 as needed, in addition to viscoelastic materials such as cyanoethylated PVA.

As an example, polyvinylidene fluoride, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, polyvinylidene fluoride- Fluorine-based polymers such as trifluoroethylene copolymer and polyvinylidene fluoride-tetrafluoroethylene copolymer, vinylidene-vinyl ester copolymer, cyanoethyl cellulose, cyanoethyl hydroxy sucrose, cyanoethyl hydroxy fiber cyanoethyl hydroxyfullerene, cyanoethyl methacrylate, cyanoethyl acrylate, cyanoethyl hydroxyethyl cellulose, cyanoethyl amylose, cyanoethyl hydroxypropyl cellulose, cyanoethyl Dihydroxypropyl cellulose, cyanoethyl hydroxypropyl amylose, cyanoethyl polyacrylamide, cyanoethyl polyethylacrylate, cyanoethyl fullerene, cyanoethyl polyhydroxymethylene, cyanide Polymers with cyano or cyanoethyl groups such as ethyl glycidyl fullerene, cyanoethyl sucrose and cyanoethyl sorbitol, and synthetic rubber such as nitrile rubber or chloroprene rubber. Among them, polymer materials having cyanoethyl groups can be preferably used. In addition, in the matrix 34 of the piezoelectric layer 20, the dielectric polymer material is not limited to one kind, and plural kinds may be added.

In addition, for the purpose of adjusting the glass transition point Tg, in addition to the dielectric polymer material, thermoplastic resins such as vinyl chloride resin, polyethylene, polystyrene, methacrylic resin, polybutylene, and isobutylene may be added to the matrix 34. And thermosetting resins such as phenolic resin, urea resin, melamine resin, alkyd resin and mica. Furthermore, for the purpose of improving the tackiness, tackifiers such as rosin esters, rosin, terpenes, terpene phenols, and petroleum resins may be added.

In the matrix 34 of the piezoelectric layer 20, the amount of addition of a material other than a viscoelastic polymer material such as cyanoethylated PVA is not particularly limited, but it is 30% by mass based on the ratio in the matrix 34. Below % is better. Thereby, the characteristics of the added polymer material can be exhibited without damaging the viscoelastic relaxation mechanism in the matrix 34, so it is possible to increase the dielectric constant, improve the heat resistance, and closely adhere to the piezoelectric particles 36 and the electrode layer. Better results can be obtained in aspects such as sexual enhancement.

The piezoelectric layer 20 is a layer composed of a polymer composite piezoelectric body including piezoelectric particles 36 in such a matrix 34 . Piezoelectric particles 36 are dispersed in matrix 34 . It is preferable that the piezoelectric particles 36 are uniformly (approximately 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 piezoelectric particles 36 include lead zirconate titanate (PZT), lead lanthanum zirconate titanate (PLZT), barium titanate (BaTiO ₃ ), zinc oxide (ZnO), and barium titanate and iron Bismuth bismuth (BiFe ₃ ) solid solution (BFBT), etc.

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 and the application of the piezoelectric element 50 . The particle size of the piezoelectric particles 36 is preferably 1 to 10 μm. By setting the particle size of the piezoelectric particles 36 within this range, a favorable result can be obtained in that the piezoelectric film 10 can achieve both high piezoelectric characteristics and flexibility.

In addition, 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 in the piezoelectric layer 20 to the piezoelectric particles 36 is not limited, as long as it depends on the size and thickness of the piezoelectric film 10 in the plane direction, the application of the piezoelectric element 50, and What is necessary is just to set suitably with respect to the characteristic etc. which are required for the piezoelectric element 50. The volume fraction of the piezoelectric particles 36 in the piezoelectric layer 20 is preferably 30 to 80%, more preferably 50% or more, and is further preferably 50 to 80%. By setting the amount ratio of the matrix 34 to the piezoelectric particles 36 within the above-mentioned range, a good result can be obtained in terms of both high piezoelectric characteristics and flexibility.

In the piezoelectric film 10, the thickness of the piezoelectric body layer 20 is not particularly limited, and may vary depending on the application of the piezoelectric element 50, the number of layers of piezoelectric films in the piezoelectric element 50, and the characteristics required for the piezoelectric film 10. Set appropriately. The thicker the piezoelectric layer 20 is, the more advantageous it is in terms of rigidity such as the stiffness of the so-called sheet, but the voltage (potential difference) required to expand and contract the piezoelectric film 10 by the same amount becomes larger. The thickness of the piezoelectric layer 20 is preferably from 10 to 300 μm, more preferably from 20 to 200 μm, and still more preferably from 30 to 150 μm. By setting the thickness of the piezoelectric layer 20 within the above range, a favorable result can be obtained in terms of ensuring rigidity, appropriate flexibility, and the like.

In addition, it is preferable that the piezoelectric layer 20 is polarized in the thickness direction.

In addition, in the present invention, the piezoelectric layer 20 is not limited to the one containing the piezoelectric particles 36 in the matrix 34 composed of a polymer material having viscoelasticity at room temperature such as cyanoethylated PVA as described above. Polymer composite piezoelectric body. That is, in the piezoelectric film 10 of the present invention, various known piezoelectric layers can be used for the piezoelectric layer.

As an example, the same compressive force can also be used in a substrate comprising the above-mentioned dielectric polymer materials such as polyvinylidene fluoride, vinylidene chloride-tetrafluoroethylene copolymer, and vinylidene chloride-trifluoroethylene copolymer. Electrode particles 36 polymer composite piezoelectric body, piezoelectric layer made of polyvinylidene fluoride, piezoelectric layer made of fluororesin other than polyvinylidene fluoride, and film made of poly-L-lactic acid laminated And the piezoelectric layer of the film composed of poly-D lactic acid, etc. However, as described above, from the viewpoint of being able to operate relatively hard for vibrations of 20 Hz to 20 kHz, and for relatively slow vibrations of several Hz or less, it can be operated relatively softly, and can obtain excellent acoustic characteristics and excellent flexibility. In the matrix 34 composed of a polymer material having viscoelasticity at room temperature, such as cyanoethylated PVA, a polymer composite piezoelectric body including piezoelectric particles 36 can be preferably used.

As shown in FIG. 10, the piezoelectric film 10 has the second electrode layer 26 on one surface of the piezoelectric layer 20, the second protective layer 30 thereon, and the first electrode layer 26 on the other surface of the piezoelectric layer 20. The electrode layer 24 has a first protective layer 28 thereon. Among them, the first electrode layer 24 and the second electrode layer 26 form an electrode pair.

That is, the piezoelectric film 10 has both surfaces of the piezoelectric layer 20 sandwiched between the second electrode layer 26 and the first electrode layer 24 as an electrode pair, and the laminated layer is sandwiched between the second protective layer 30 and the first protective layer 28 . The composition of the body. In this way, in the piezoelectric film 10 , the region sandwiched between the second electrode layer 26 and the first electrode layer 24 expands and contracts in accordance with the applied voltage. In addition, the second electrode layer 26 and the second protective layer 30 , and the first electrode layer 24 and the first protective layer 28 are added for convenience of description of the piezoelectric film 10 . Therefore, the terms 1 and 2 in the present invention have no technical meaning, and have nothing to do with actual usage conditions.

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 can be an adhesive or an adhesive. In addition, the same material as the matrix 34 , which is a polymer material from which the piezoelectric particles 36 are removed from the piezoelectric layer 20 , can also be preferably used for the adhesive. In addition, the adhesive layer may be provided on both the first electrode layer 24 side and the second electrode layer 26 side, or may be provided on only one of the first electrode layer 24 side and the second electrode layer 26 side.

In the piezoelectric film 10 , the second protective layer 30 and the first protective layer 28 cover the first electrode layer 24 and the second electrode layer 26 and serve 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 sometimes has insufficient rigidity or mechanical strength depending on the application. The piezoelectric film 10 is provided with the second protective layer 30 and the first protective layer 28 to compensate for this. The first protective layer 28 and the second protective layer 30 have the same configuration except for the arrangement position. Therefore, in the following description, when there is no need to distinguish the first protective layer 28 and the second protective layer 30, both members are collectively referred to as a protective layer.

The second protective layer 30 and the first protective layer 28 are not limited, and various sheets can be used, and various resin films are preferably illustrated as examples. Among them, polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS), polycarbonate (PC), polyphenylene sulfide ( PPS), polymethyl methacrylate (PMMA), polyether imide (PEI), polyimide (PI), polyethylene naphthalate (PEN), triacetyl cellulose (TAC) and A resin film composed of a cyclic olefin resin or the like is preferably used.

The thicknesses of the second protective layer 30 and the first protective layer 28 are also not limited. Moreover, although the thickness of the 2nd protective layer 30 and the 1st protective layer 28 are basically the same, they may differ. However, if the rigidity of the second protective layer 30 and the first protective layer 28 is too high, not only the expansion and contraction of the piezoelectric layer 20 will be restricted, but also the flexibility will be impaired. Therefore, unless mechanical strength or good handleability as a sheet is required, it is more advantageous that the second protective layer 30 and the first protective layer 28 be thinner.

In the piezoelectric film 10, if the thicknesses of the second protective layer 30 and the first protective layer 28 are not more than twice the thickness of the piezoelectric layer 20, it is preferable to achieve both rigidity and appropriate flexibility. the result of. For example, when the thickness of the piezoelectric layer 20 is 50 μm and the second protective layer 30 and the first protective layer 28 are made of PET, the thickness of the second protective layer 30 and the first protective layer 28 is preferably 100 μm or less. It is more preferably not more than 50 μm, and is still more preferably not more than 25 μm.

In the piezoelectric film 10 , the second electrode layer 26 is formed between the piezoelectric layer 20 and the second protective layer 30 , and the first electrode layer 24 is formed between the piezoelectric layer 20 and the first protective layer 28 . The second electrode layer 26 and the first electrode layer 24 are provided to apply a voltage to the piezoelectric layer 20 (piezoelectric film 10 ).

The first electrode layer 24 and the second electrode layer 26 are basically the same except for their positions. Therefore, in the following description, when there is no need to distinguish the first electrode layer 24 and the second electrode layer 26, the two members are also collectively referred to as electrode layers.

In the present invention, the materials for forming the second electrode layer 26 and the first electrode layer 24 are not limited, and various 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 are exemplified. and indium tin oxide etc. Alternatively, conductive polymers such as PEDOT/PPS (polyethylenedioxythiophene-polystyrenesulfonic acid) are also exemplified. Among them, copper, aluminum, gold, silver, platinum, and indium tin oxide are preferably exemplified as the second electrode layer 26 and the first electrode layer 24 . Among them, copper is more preferable from the viewpoints of conductivity, cost, and flexibility.

Also, the method for forming the second electrode layer 26 and the first electrode layer 24 is not limited, and various vapor deposition methods (vacuum film formation methods) such as vacuum evaporation and sputtering, film formation by electroplating, and Well-known methods, such as the method of sticking the foil which consists of the said material, etc. are used.

Among them, because the flexibility of the piezoelectric film 10 can be ensured, thin films such as copper and aluminum formed by vacuum deposition are particularly preferably used as the second electrode layer 26 and the first electrode layer 24 . Among them, it is particularly preferable to use a thin film of copper formed by vacuum evaporation.

The thicknesses of the second electrode layer 26 and the first electrode layer 24 are not limited. Moreover, although the thickness of the 2nd electrode layer 26 and the 1st electrode layer 24 are basically the same, they may differ. Here, similarly to the above-mentioned second protective layer 30 and first protective layer 28, if the rigidity of the second electrode layer 26 and the first electrode layer 24 is too high, not only the expansion and contraction of the piezoelectric layer 20 will be restricted, but also the flexibility will be impaired. sex. Therefore, as long as the electrical resistance does not become too high, it is more advantageous for the second electrode layer 26 and the first electrode layer 24 to be thinner.

In the piezoelectric film 10, if the product of the thickness and Young's modulus of the second electrode layer 26 and the first electrode layer 24 is lower than the product of the thickness and Young's modulus of the second protective layer 30 and the first protective layer 28, then Flexibility is not seriously impaired, so it is preferable. For example, the second protective layer 30 and the first protective layer 28 are composed of PET (Young's modulus: about 6.2GPa) and the second electrode layer 26 and the first electrode layer 24 are made of copper (Young's modulus: about 130GPa) In the case where the thickness of the second protective layer 30 and the first protective layer 28 is 25 μm, the thickness of the second electrode layer 26 and the first electrode layer 24 is preferably 1.2 μm or less, more preferably 0.3 μm or less. Preferably, it is more preferably 0.1 μm or less.

As described above, the piezoelectric film 10 has the piezoelectric layer 20 in which the piezoelectric particles 36 are dispersed in the matrix 34 containing a polymer material sandwiched between the second electrode layer 26 and the first electrode layer 24. The protective layer 30 and the first protective layer 28 sandwich the laminate. Such a piezoelectric film 10 preferably has a maximum value of loss tangent (Tan δ ) at a frequency of 1 Hz obtained by dynamic viscoelasticity measurement at room temperature, and more preferably has a maximum value of 0.1 or more at room temperature. Thereby, even if the piezoelectric film 10 is subjected to 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, so that the deformation between the polymer matrix and the piezoelectric particles can be prevented. interface cracks.

The piezoelectric film 10 is preferably such that the storage elastic coefficient (E') at a frequency of 1 Hz based on dynamic viscoelasticity measurement is 10 to 30 GPa at 0°C and 1 to 10 GPa at 50°C. In addition, this condition is also the same as that of the piezoelectric layer 20 . Thereby, the piezoelectric film 10 can have a large frequency dispersion in the storage elastic coefficient (E') at normal temperature. That is, it can operate relatively hard for vibrations of 20 Hz to 20 kHz, and can operate relatively softly for vibrations of several Hz or less.

Also, it is preferable that the piezoelectric film 10 is such that the product of the thickness and the storage elastic coefficient (E') at a frequency of 1 Hz based on dynamic viscoelasticity measurement is 1.0×10 ⁵ to 2.0× 10 ⁶ N/m, 1.0×10 ⁵ to 1.0×10 ⁶ N/m at 50°C. In addition, this condition is also the same as that of the piezoelectric layer 20 . Accordingly, the piezoelectric film 10 can have appropriate rigidity and mechanical strength within a range that does not impair flexibility and acoustic characteristics.

Furthermore, the piezoelectric film 10 is preferably such that the loss tangent (Tan δ) at a frequency of 1 kHz at 25° C. is 0.05 or more in the main curve obtained from dynamic viscoelasticity measurement. This condition is also the same as that of the piezoelectric layer 20 . Thereby, the frequency characteristic of the speaker using the piezoelectric film 10 becomes smooth, and it is possible to reduce the amount of change in sound quality when the lowest resonance frequency f ₀ changes with changes in the curvature of the speaker.

In addition, in the present invention, the storage modulus (Young's modulus) and loss tangent of the piezoelectric film 10 and the piezoelectric layer 20 may be measured by known methods. As an example, it may be measured using a dynamic viscoelasticity measuring device DMS6100 manufactured by SII Nano Technology Inc. As the measurement conditions, as an example, the following are shown respectively: 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), the measurement temperature is -50 to 150 ° C, the temperature rise The speed is 2°C/min (in nitrogen atmosphere), the sample size is 40mm×10mm (including the splint area), and the distance between the chucks is 20mm.

In the piezoelectric element 50 , the second electrode layer 26 and the first electrode layer 24 of the piezoelectric film 10 are connected to a power source (external power source) for applying a driving voltage to expand and contract the piezoelectric film 10 , that is, supplying driving power. The power supply is not limited, and may be a DC power supply or an AC power supply. Also, regarding the driving voltage, it is only necessary to appropriately set a driving voltage at which the piezoelectric film 10 can be accurately driven according to the thickness of the piezoelectric layer 20 of the piezoelectric film 10 , the forming material, and the like.

As described above, when the electrodes are drawn out from the second electrode layer 26 and the first electrode layer 24 , it is done at the protruding portion 10 a. The method of drawing the electrodes from the second electrode layer 26 and the first electrode layer 24 is not limited, and various known methods can be used. As an example, a method of connecting conductors such as copper foil to the second electrode layer 26 and the first electrode layer 24 to draw electrodes outside, and a method of drawing electrodes on the second protective layer 30 and the first protective layer 28 by laser or the like are shown. A method of forming a through-hole, filling the through-hole with a conductive material, and drawing an electrode to the outside, etc. As a preferable electrode extraction method, the method described in Unexamined-Japanese-Patent No. 2014-209724, the method described in Unexamined-Japanese-Patent No. 2016-015354, etc. are illustrated.

Hereinafter, an example of a method for manufacturing the piezoelectric film 10 will be described with reference to FIGS. 11 to 13 .

First, as shown in FIG. 11 , a sheet-shaped object 12 a in which the second electrode layer 26 is formed on the surface of the second protective layer 30 is prepared. Furthermore, a sheet 12c in which the first electrode layer 24 is formed on the surface of the first protective layer 28 schematically shown in FIG. 13 is prepared.

What is necessary is just to form a copper film etc. as the 2nd electrode layer 26 on the surface of the 2nd protective layer 30 by vacuum evaporation, sputtering, electroplating, etc., and to produce the sheet-shaped object 12a. Similarly, a copper film or the like may be formed on the surface of the first protective layer 24 as the first electrode layer 28 by vacuum evaporation, sputtering, electroplating, or the like to produce the sheet-shaped object 12c. Alternatively, a commercially available sheet in which a copper film or the like is formed on a 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 very thin and the workability is poor, a protective layer with a spacer (temporary support) can be used as needed. In addition, PET or the like having a thickness of 25 to 100 μm can be used as the separator. What is necessary is just to remove a separator after thermocompression bonding of an electrode layer and a protective layer.

Next, as shown in FIG. 12 , the piezoelectric layer 20 is formed by coating the paint (coating composition) to be the piezoelectric layer 20 on the second electrode layer 26 of the sheet 12 a and curing it. Thereby, the piezoelectric laminated body 12b in which the sheet-shaped object 12a and the piezoelectric layer 20 were laminated|stacked was produced.

Various methods can be used to form the piezoelectric layer 20 depending on the material forming the piezoelectric layer 20 . As an example, first, a polymer material such as cyanoethylated PVA is dissolved in an organic solvent, and piezoelectric particles 36 such as PZT particles are added and stirred 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 paint is prepared, the paint is cast (coated) on the sheet 12a, the organic solvent is evaporated and dried. Thereby, as shown in FIG. 12 , the piezoelectric laminate 12 b having the second electrode layer 26 on the second protective layer 30 and the piezoelectric layer 20 stacked on the second electrode layer 26 is manufactured.

The casting method of the paint is not limited, and any known method (coating device), such as a bar coater, a slide coater, and a doctor knife, can be used. Alternatively, if the polymer material is a material capable of heating and melting, the polymer material can be heated and melted to produce a molten product in which piezoelectric particles 36 are added, and the molten material shown in FIG. 11 can be formed by extrusion molding or the like. The sheet-like object 12a shown is extruded into a sheet shape and cooled, thereby producing a piezoelectric laminate 12b as shown in FIG. 12 .

In addition, as described above, in the piezoelectric layer 20 , in addition to the polymer material having viscoelasticity at room temperature, a polymer piezoelectric material such as PVDF may be added to the matrix 34 . When adding these piezoelectric polymer materials to the matrix 34, it is only necessary to dissolve the piezoelectric polymer materials added to the above-mentioned paint. Alternatively, it is sufficient to add the piezoelectric polymer material to be added to the viscoelastic polymer material that has been heated and melted at room temperature for heating and melting.

After the piezoelectric layer 20 is formed, a rolling treatment may be performed as necessary. The calendering treatment may be performed once or multiple times. As is well known, the calendering treatment refers to a treatment for flattening or the like by pressing while heating the surface to be treated with a hot press or a heating roll.

Next, the piezoelectric layer 20 of the piezoelectric laminate 12b having the second electrode layer 26 on the second protective layer 30 and the piezoelectric layer 20 formed on the second electrode layer 26 is polarized. . The polarization treatment of the piezoelectric layer 20 can be performed before the rolling treatment, and is preferably performed after the rolling treatment. The method of polarization treatment of the piezoelectric layer 20 is not limited, and known methods can be used. For example, electric field polarization processing in which a DC electric field is directly applied to an object to be polarized is exemplified. In addition, when the electric field polarization treatment is performed, the first electrode layer 24 may be formed before the polarization treatment, and the electric field polarization treatment may be performed using the first electrode layer 24 and the second electrode layer 26 . In addition, in the piezoelectric film 10 of the present invention, it is preferable to perform polarization treatment not in the plane direction of the piezoelectric layer 20 but in the thickness direction.

Next, as shown in FIG. 13 , on the piezoelectric layer 20 side of the piezoelectric laminate 12 b subjected to the polarization treatment, the previously prepared sheet 12 c is laminated with the first electrode layer 24 facing the piezoelectric layer 20 . Furthermore, by sandwiching the laminated body between the first protective layer 28 and the second protective layer 30, and performing thermocompression bonding using a thermocompression device, a heating roller, etc., the piezoelectric laminated body 12b and the sheet-shaped object 12c are bonded together, A piezoelectric film 10 as shown in FIG. 10 was fabricated. Alternatively, the piezoelectric laminate 12b and the sheet-like object 12c are bonded together using an adhesive, and it is preferable to further press them to manufacture the piezoelectric film 10 .

In addition, the piezoelectric film 10 can be manufactured using the sheet-like sheet 12 a and sheet 12 c , etc., which are diced, or can be manufactured by roll-to-roll (Roll to Roll).

The produced piezoelectric film can also be cut into desired shapes according to various purposes. The piezoelectric film 10 produced in this way is polarized not in the plane direction but in the thickness direction, and high piezoelectric characteristics can be obtained even without stretching treatment after the polarization treatment. Therefore, the piezoelectric film 10 has no 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 producing a piezoelectric element using the produced piezoelectric film will be described. The piezoelectric film 10 is bent so that the length of one end of the piezoelectric film 10 in the folding direction is the length of the laminated portion 10b. An adhesive sheet to be an adhesive layer is inserted between the bent piezoelectric films 10 . Alternatively, apply an adhesive.

Adhesive layer 14 for adhering piezoelectric films to each other can use various known materials as long as it can be used for adhering adjacent piezoelectric films 10 , and the same material as adhesive layer 104 for adhering vibrating plate and piezoelectric element described later can be used.

In addition, as the adhesive layer 14, an adhesive sheet that is solid in the form of a sheet and exhibits fluidity by heating can be used. By using the adhesive sheet, it is possible to better adjust the ratio of the adhesive area of the adhesive layer to the area of the laminated part. As the adhesive sheet, for example, TSU0041SI manufactured by TOYOCHEM CO., LTD. can be used.

The laminated portion of the piezoelectric film 10 is clamped from top to bottom by metal plates, and each metal plate is heat-pressed by a laminator. The metal plate is not particularly limited, and metal plates such as titanium and stainless steel can be used. Also, the thickness of the metal plate is preferably 0.2 mm to 0.4 mm.

The temperature at the time of hot pressing with a laminator is preferably 100°C to 120°C. Also, the roll speed of the laminator is preferably 0.04 m/s to 0.08 m/s.

After thermally pressing the entire surface, the laminated piezoelectric sheets are removed from between the metal plates.

The piezoelectric film is bent so as to be folded back into a bellows shape, and an adhesive sheet is inserted between the bent piezoelectric films 10 in the same manner as above, and heat press is performed with a laminator.

A bellows-type piezoelectric element is fabricated by repeating the above steps until a predetermined number of layers is obtained.

[Electro-acoustic converter] The electroacoustic transducer of the present invention is an electroacoustic transducer formed by adhering the above-mentioned piezoelectric element to a vibrating 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 above-described piezoelectric element 50 , a vibration plate 102 , and an adhesive layer 104 for adhering the piezoelectric element 50 to the vibration plate 102 . In the example shown in FIG. 14 , as a preferable aspect, the laminated portion 10 b on the surface side having the protruding portion 10 a of the piezoelectric element 50 is adhered to the vibrating plate 102 .

In such an electroacoustic transducer 100 , the piezoelectric film 10 expands and contracts in the plane 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 plane direction due to the expansion and contraction of the piezoelectric film 10 . telescopic. The vibration plate 102 bends due to the expansion and contraction of the piezoelectric element 50 in the plane direction, and as a result, the vibration plate 102 vibrates in the thickness direction. By this vibration in the thickness direction, the vibration plate 102 emits sound. The vibrating plate 102 vibrates according to the magnitude of the driving voltage applied to the piezoelectric film 10 , and emits a sound corresponding to the driving voltage applied to the piezoelectric film 10 .

As a preferred aspect, the vibrating plate 102 is flexible. In addition, in the present invention, "having flexibility" means being able to bend and bend, specifically, being able to bend and stretch without causing damage or damage.

The vibrating plate 102 is preferably not limited as long as it is flexible, and various sheets (plates, films) can be used. As an example, 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 cyclic olefin resins, etc. Film, foamed plastic composed of expanded polystyrene, expanded styrene and expanded polyethylene, and various corrugated paper materials made by pasting one or both sides of corrugated cardboard on other cardboard, etc.

Moreover, as long as the electroacoustic transducer 100 is flexible, an organic electroluminescence (OLED (Organic Light Emitting Diode)) display, a liquid crystal display, a micro LED (Light Emitting Diode: Light-emitting diode) displays and inorganic electroluminescent diode displays and other display elements.

In the electroacoustic transducer 100 , the vibrating plate 102 and the piezoelectric element 50 are pasted together by an adhesive layer 104 .

As long as the adhesive layer 104 can adhere the vibrating plate 102 and the piezoelectric element 50 , various well-known ones can be used. Therefore, the adhesive layer 104 may be a layer composed of an adhesive that has fluidity when pasted and then becomes solid, or may be a soft solid that is gel-like (rubber-like) when pasted and then maintains a gel. The layer composed of the adhesive in the form of the adhesive may be a layer composed of a material having both the characteristics of the adhesive and the adhesive.

Among them, in the electroacoustic transducer 100 , the vibration plate 102 is bent and vibrated by expanding and contracting the piezoelectric element 50 to generate sound. Therefore, in the electroacoustic transducer 100 , it is preferable that the expansion and contraction of the piezoelectric element 50 be directly transmitted to the vibrating plate 102 . If there is a viscous substance between the vibrating plate 102 and the piezoelectric element 50 to ease the vibration, the transmission efficiency of the expansion and contraction energy from the piezoelectric element 50 to the vibrating plate 102 will be reduced, and the electroacoustic transducer 100 will be reduced. driving efficiency. Considering this point, the adhesive layer 104 is preferably an adhesive layer that is made of an adhesive that can obtain a solid and hard adhesive layer 104 rather than an adhesive layer that is made of an adhesive. As the more preferable adhesive layer 104 , specifically, an adhesive layer composed of a thermoplastic type adhesive such as a polyester-based adhesive and a styrene-butadiene rubber (SBR)-based adhesive can be exemplified. Adhesion is different from adhesion, and it is useful when high adhesion temperature is required. In addition, thermoplastic type adhesives are preferred because they have both "relatively low temperature, short time and strong adhesion".

The thickness of the adhesive layer 104 is not limited, as long as the thickness can be appropriately set according to the material of the adhesive layer 104 to obtain sufficient adhesive force (adhesive force, adhesive force). Among them, regarding the electroacoustic transducer 100 , the thinner the adhesive layer 104 is, the better the transmission effect of stretching energy (vibration energy) is transmitted to the piezoelectric element 50 of the vibrating plate 102 , and energy efficiency can be improved. In addition, if the adhesive layer 104 is thick and rigid, expansion and contraction of the piezoelectric element 50 may be limited. In consideration of this point, it is preferable that the adhesive layer 104 is thin. Specifically, with regard to the thickness of the adhesive layer 104 , the pasted thickness is preferably 0.1-50 μm, more preferably 0.1-30 μm, and even more preferably 0.1-10 μm.

In addition, in the electroacoustic transducer 100, the adhesive layer 104 is provided as a preferred mode, and is not an essential component. Therefore, the electroacoustic transducer 100 does not have the adhesive layer 104 , and the vibrating plate 102 and the piezoelectric element 50 can be fixed by using known crimping mechanisms, fastening mechanisms, and fixing mechanisms. For example, when the piezoelectric element 50 is rectangular in plan view, the four corners can be fastened with bolts and nuts to form an electroacoustic transducer, or the four corners can be fastened with bolts and nuts. And the central part constitutes an electroacoustic transducer.

However, at this time, when a driving voltage is applied from a power source, the piezoelectric element 50 expands and contracts independently of the vibration plate 102 , depending on the case, 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 vibration plate 102 , the vibration efficiency of the vibration plate 102 by the piezoelectric element 50 decreases. There is a possibility that the vibrating plate 102 cannot be vibrated sufficiently. Taking this point into consideration, as shown in FIG. 14 , it is preferable to stick the vibrating plate 102 and the piezoelectric element 50 by the sticking layer 104 .

However, as described above, the piezoelectric layer 20 includes piezoelectric particles 36 in the matrix 34 . In addition, the second electrode layer 26 and the first electrode layer 24 are provided so as to sandwich the piezoelectric layer 20 in the thickness direction. When a voltage is applied to the second electrode layer 26 and the first 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 ) shrinks in the thickness direction. At the same time, due to the relationship of Poisson's ratio, the piezoelectric film 10 also expands and contracts along the in-plane direction. This 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 its thickness in the plane direction. Therefore, for example, if the length of the piezoelectric film 10 is 20 cm, the piezoelectric film 10 expands and contracts by a maximum of about 0.2 mm by applying a voltage.

The vibrating plate 102 is adhered to the piezoelectric film 10 through the adhesive layer 104 . Therefore, the vibration plate 102 bends due to expansion and contraction of the piezoelectric film 10 , and as a result, the vibration plate 102 vibrates in the thickness direction. By this vibration in the thickness direction, the vibration plate 102 emits sound. That is, the vibrating 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 .

Also, by adjusting the mass of the piezoelectric film 10 according to the spring constant of the vibrating plate 102, the sound pressure level can be improved. If the mass of the piezoelectric film 10 is large, the vibrating plate 102 will be bent, so it is possible to suppress the vibration of the vibrating plate 102 during driving. On the other hand, if the mass of the piezoelectric film 10 is small, the resonance frequency becomes high, and it is possible to suppress the vibration of the diaphragm 102 at a low frequency. Taking these points into consideration, it is preferable to appropriately adjust the mass of the piezoelectric film 10 according to the spring constant of the vibrating plate 102 .

As mentioned above, the piezoelectric element of the present invention has been described in detail, but the present invention is not limited to the above-mentioned examples, and it is a matter of course that various improvements and changes can be made without departing from the gist of the present invention. [Example]

Hereinafter, specific examples of the present invention are given, and the present invention will be described in more detail. In addition, this invention is not limited to this Example, Unless it deviates from the gist of this invention, the material, usage-amount, ratio, process content, process procedure etc. shown in the following Example can be changed suitably.

[Production of Piezoelectric Film] A piezoelectric film was produced by the method shown in FIGS. 11 to 13 described above. First, cyanoethylated PVA (manufactured by CR-V Shin-Etsu Chemical Co., Ltd.) was dissolved in dimethylformamide (DMF) at the following composition ratio. Then, to this solution, PZT particles were added as piezoelectric particles at the following composition ratio, and stirred with a propeller mixer (rotational speed: 2000 rpm) to prepare a coating material for forming a piezoelectric layer. ・PZT particles 300 parts by mass ·Cyanoethylated PVA...30 parts by mass ·DMF················· 70 parts by mass In addition, the PZT particle used commercially available PZT raw material powder after sintering at 1000-1200 degreeC, and pulverized and classified so that the average particle diameter might become 5 micrometers.

On the other hand, a sheet in which a copper film with a thickness of 0.3 μm was vacuum-deposited on a PET film with a thickness of 4 μm was prepared. That is, in this example, the first electrode layer and the second electrode layer are deposited copper films with a thickness of 0.3 μm, and the first protective layer and the second protective layer are PET films with a thickness of 4 μm. On the second electrode layer (copper-deposited film) of the sheet, the paint for forming the previously prepared piezoelectric layer was applied using a slant die coater. Moreover, the coating material was applied so that the film thickness of the coating film after drying might become 50 micrometers. Next, the DMF was evaporated by heating and drying the sheet-coated material on a hot plate at 120°C. In this way, a second electrode layer made of copper was provided on the second protective layer made of PET, and a piezoelectric laminate having a piezoelectric layer (polymer composite piezoelectric layer) having a thickness of 50 μm was produced thereon.

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

On the polarized piezoelectric laminate, the first electrode layer (copper film side) faces the piezoelectric layer, and a sheet in which the same thin film is vapor-deposited on the PET film is laminated. Next, by using a laminator, the laminate of the piezoelectric laminate and the sheet was thermocompressed at a temperature of 120°C, and the piezoelectric layer and the first electrode layer were bonded together to form a piezoelectric laminate. electric film.

[Example 1] The manufactured piezoelectric film was cut out to 170mm×150mm, folded back 4 times along the direction of the 170mm side, and a laminated part with a length of 30mm×width 150mm and a protruding part with a length of 20mm×width 150mm were produced. electrical components. When turning back, place an adhesive sheet (TSU0041SI manufactured by TOYOCHEM CO., LTD.) between the laminated piezoelectric films every time it is turned back, and sandwich the pasted film with a metal plate (made of Ti, thickness 0.3mm). Above and below the piezoelectric film, heat and press each metal plate with a laminator to bond the piezoelectric film to each other. The heating temperature during lamination was 120° C., and the heating time was 0.08 m/min. Also, the gap difference (T ₂ −T ₁ ) between both ends of the roller pair (R ₁ , R ₂ in FIG. 15 ) of the laminator is set to be 5 μm or less. Also, the area of the adhesive sheet before lamination was set to be 0.91 times the area of the lamination portion. By repeating the same folding process 4 times, a piezoelectric element with 5 piezoelectric films was produced.

The result of measuring the ratio of the bonding area of the bonding layer to the area of the laminated portion of the manufactured piezoelectric element by the above-mentioned method was 0.99. Also, as a result of measuring the adhesive force between the piezoelectric film and the adhesive layer by the method described above, the piezoelectric element and the support body B were peeled off. Since the adhesive force of the adhesive bonding the piezoelectric element and the support body B is approximately 10 N/cm, the adhesive force between the piezoelectric film and the adhesive layer exceeds 10 N/cm. Also, the result of calculating the ratio of the cross-sectional area of the gap of the folded portion by the above-mentioned method was zero.

[Example 2] A piezoelectric element was produced in the same manner as in Example 1, except that the difference in the gap between both ends of the roll of the laminator was 75 μm. The ratio of the bonding area of the bonding layer of the produced piezoelectric element to the area of the laminated part was 0.85. Also, the adhesive force of the adhesive layer exceeded 10 N/cm. Also, the ratio of the cross-sectional area of the gap in the folded portion is zero.

[Example 3] A piezoelectric element was fabricated 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 bonding layer of the produced piezoelectric element to the area of the laminated part was 0.97. Also, the adhesive force of the adhesive layer exceeded 10 N/cm. Also, the ratio of the cross-sectional area of the gap in the folded portion was 0.04.

[Example 4] A piezoelectric element was fabricated in the same manner as in Example 1 except that the heating temperature during lamination was set to 80°C. The ratio of the bonding area of the bonding layer of the produced piezoelectric element to the area of the laminated part was 0.99. Also, the adhesive force of the adhesive layer was 0.2 N/cm. Also, the ratio of the cross-sectional area of the gap in the folded portion is zero.

[Example 5] A piezoelectric element was produced in the same manner as in Example 1 except that the heating temperature during lamination was set to 70°C. The ratio of the bonding area of the bonding layer of the produced piezoelectric element to the area of the laminated part was 0.99. Also, the adhesive force of the adhesive layer was 0.1 N/cm. Also, the ratio of the cross-sectional area of the gap in the folded portion is zero.

[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 bonding layer of the produced piezoelectric element to the area of the laminated part was 0.97. Also, the adhesive force of the adhesive layer exceeded 10 N/cm. Also, the ratio of the cross-sectional area of the gap in the folded portion was 0.05.

[Comparative example 1] A piezoelectric element was fabricated in the same manner as in Example 1 except that the area ratio of the bonding sheet was set to 1. The ratio of the bonding area of the bonding layer to the area of the laminated portion of the produced piezoelectric element was 1. Also, the adhesive force of the adhesive layer exceeded 10 N/cm. Also, the ratio of the cross-sectional area of the gap in the folded portion is zero. [Comparative example 2] A piezoelectric element was produced in the same manner as in Example 1, except that the difference in the gap between both ends of the roll of the laminator was 150 μm. The ratio of the bonding area of the bonding layer to the area of the laminated portion of the manufactured piezoelectric element was 0.84. Also, the adhesive force of the adhesive layer exceeded 10 N/cm. Also, the ratio of the cross-sectional area of the gap in the folded portion is zero.

[evaluate] The presence or absence of contamination on the surface of the laminator and the sound pressure were evaluated for the manufactured electroacoustic transducers of the Examples and Comparative Examples.

＜Pollution on the surface of the laminator＞ It was visually checked whether or not the adhesive adhered to the surface of the laminator after the piezoelectric film folded back was laminated when the piezoelectric element was produced.

＜Sound pressure＞ The surface of the produced piezoelectric element opposite to the protruding part was pasted on a vibrating plate to produce an electroacoustic transducer. As the vibrating plate, a plate-shaped member having a size of 500 mm×450 mm, a thickness of 0.8 mm, and a material of aluminum (A5052) was used. The horizontal direction of the vibrating plate was aligned with the longitudinal direction of the piezoelectric element, and the center of the vibrating plate was aligned with the center of the laminated part of the piezoelectric element. An acrylic adhesive is used as the adhesive layer for bonding the piezoelectric element and the vibration plate.

A sinusoidal sweep signal with a frequency of 1kHz to 20kHz and an applied voltage of 50Vrms is input to the piezoelectric element, and the sound pressure is measured with a loudspeaker located at a distance of 1m from the center of the vibrating plate. When the sound pressure at 3 kHz is 84 dB or more, it is evaluated that the desired characteristics are satisfied. The results are shown in Table 1.

[Table 1] Next method Then the part evaluate Heating temperature °C Heating time m/min Gap difference between both ends of the roller μm Adhesive sheet area (ratio of laminated part) Subsequent Area Ratio Adhesion force N/cm Cross-sectional area ratio of the turnback gap Sound pressure (@3kHz) dB Laminator Surface Contamination Example 1 120 0.08 ≤5 0.91 0.99 >10 0 85 none Example 2 120 0.08 75 0.91 0.85 >10 0 84 none Example 3 120 0.08 ≤5 0.88 0.97 >10 0.04 85 none Example 4 80 0.08 ≤5 0.91 0.99 0.2 0 85 none Example 5 70 0.08 ≤5 0.91 0.99 0.1 0 84 none Example 6 120 0.08 ≤5 0.87 0.97 >10 0.05 84 none Comparative example 1 120 0.08 ≤5 1.00 1.00 >10 0 85 have Comparative example 2 120 0.08 150 0.91 0.84 >10 0 82 none

From Table 1, it can be seen that the embodiment of the present invention does not contaminate the surface of the laminator during manufacture, and has a high sound pressure. It can be seen that in Comparative Example 1, since the ratio of the bonding area of the bonding layer was too large, the surface of the laminator was contaminated. It can be seen that the sound pressure of the adhesive layer of Comparative Example 2 was low because the ratio of the adhesive area was too small.

Also, from the comparison of Examples 1, 4, and 5, it can be known that the adhesive force of the adhesive layer is better than 0.1 N/cm. Also, from the comparison of Examples 1, 3, and 6, it can be seen that the ratio of the cross-sectional area of the gap in the folded portion is preferably 0.04 or less. From the above, it can be seen that the effect of the present invention is remarkable. [Industrial availability]

Regarding the piezoelectric element of the present invention, for example, it can be suitably used as various sensors such as an acoustic wave sensor, an ultrasonic sensor, a pressure sensor, a touch sensor, a strain sensor, and a vibration sensor. (Especially, it is useful for inspection of basic structures such as crack detection or detection of foreign matter intrusion, etc.), audio components such as microphones, pickups, speakers, and exciters (as specific applications, noise cancellers (used in Vehicles, commuter trains, airplanes, equipment, etc.), artificial vocal cords, buzzers for pest/harmful animal intrusion prevention, furniture, wallpaper, photos, helmets, goggles, headrests, signs, equipment, etc.), Suitable for tactile interfaces used in automobiles, smart phones, smart watches, game consoles, etc., ultrasonic transducers such as ultrasonic probes and underwater wave receivers, used to prevent water droplet adhesion, transportation, stirring, dispersion, grinding, etc. Vibration-absorbing materials (dampers) used in sports equipment such as actuators, containers, rides, buildings, skis, and rackets, and for roads, floors, mattresses, chairs, shoes, tires, wheels, and computer keyboards The vibration power generation device used.

10: Piezoelectric film 10a: protrusion 10b: Lamination department 12a, 12c: flakes 12b: Piezoelectric laminate 14: Adhesive layer 17: Open end gap 18: Internal void 19: Gap in the turning part 20: Piezoelectric layer 24: The first electrode layer 26: The second electrode layer 28: 1st protective layer 30: 2nd protective layer 34: matrix 36: Piezoelectric particles 40: Connecting part 50: piezoelectric element 100: electroacoustic converter 102: Vibration plate 104: Paste layer

FIG. 1 is a diagram schematically showing an example of a piezoelectric element of 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 is a diagram schematically showing an example of a state of an adhesive layer. FIG. 5 is a diagram schematically showing an example of a state of an adhesive layer. 6 is a diagram for explaining a method of calculating the ratio of the bonding area of the bonding layer to the area of the laminated portion of the piezoelectric film. 7 is a diagram for explaining a method of calculating the ratio of the bonding area of the bonding layer to the area of the laminated portion of the piezoelectric film. Fig. 8 is a diagram for explaining a method of measuring adhesive force. Fig. 9 is a diagram schematically showing a graph of measured adhesive force. FIG. 10 is a diagram schematically showing an example of a piezoelectric film. FIG. 11 is a schematic diagram for explaining an example of a method for producing a piezoelectric film. Fig. 12 is a schematic diagram for explaining an example of a method for producing a piezoelectric film. Fig. 13 is a schematic diagram for explaining an example of a method for producing a piezoelectric film. 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. Fig. 15 is a diagram for explaining the slope of the roller.

10: Piezoelectric film

10a: protrusion

10b: Lamination Department

14: Adhesive layer

20: Piezoelectric layer

24: The first electrode layer

26: The second electrode layer

28: 1st protective layer

30: 2nd protective layer

50: piezoelectric element

Claims (5)

A piezoelectric element in which the piezoelectric film is laminated by folding back a piezoelectric film having a piezoelectric layer, electrode layers provided on both surfaces of the piezoelectric layer, and a protective layer provided on the electrode layer at least once made up of plural layers, of which The piezoelectric element has an adhesive layer for bonding interlayers of the laminated piezoelectric film, The ratio of the bonding area of the adhesive layer to the area of the layered 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. The piezoelectric element according to claim 1, wherein The adhesive force between the adhesive layer and the piezoelectric film exceeds 0.1 N/cm. The piezoelectric element according to claim 1, wherein A 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. The piezoelectric element according to claim 1, wherein The piezoelectric layer is composed of a polymer composite piezoelectric body including piezoelectric particles in a matrix including a polymer material. An electroacoustic transducer, which is formed by adhering the piezoelectric element described in any one of claim 1 to claim 4 on a vibrating plate.

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