TW202323051A - Piezoelectric device and piezoelectric speaker - Google Patents

Abstract

The present invention addresses the problem of providing: a piezoelectric element in which a piezoelectric film is laminated, the piezoelectric element enabling suitable winding of a piezoelectric speaker when used as an exciter in the piezoelectric speaker; and a piezoelectric speaker in which this piezoelectric element is used. This problem is solved by a piezoelectric element that is obtained by laminating a plurality of layers of the piezoelectric film and affixing adjacent piezoelectric films using an affixing layer, wherein, when the piezoelectric element is cut to a size of 20*50 mm, a 100 g weight is attached to each of the 20 mm sides, and the piezoelectric element is hung and suspended from a round bar having a radius of 2.5 mm, the distance between piezoelectric elements at the lower end part of the round bar is 9.5 mm or less.

Description

Piezoelectric elements and piezoelectric speakers

The present invention relates to a piezoelectric element and a piezoelectric speaker using the piezoelectric element.

A so-called exciter (exciton) that vibrates and emits sound by being attached to various objects is used for various purposes. For example, in the office, when conducting on-site presentations and conference calls, etc., by installing exciters on conference tables, whiteboards, and screens, sound can be output instead of speakers. In vehicles such as automobiles, guide sounds, warning sounds, music, etc. can be emitted by installing exciters in consoles, A-pillars, ceilings, and the like. Also, in the case of a car that does not emit engine sound, such as a hybrid car or an electric car, the vehicle approach notification sound can be emitted from the bumper or the like by installing an exciter in the bumper or the like.

In such an exciter, known variable elements that generate vibration include combinations of coils and magnets, vibration motors such as eccentric motors and linear resonance motors, and the like. It is difficult to reduce the thickness of these variable elements. In particular, the vibration motor has the following difficulties: in order to increase the vibration force, it is necessary to increase the mass body, and the frequency modulation for adjusting the vibration level is difficult and the response speed is slow.

On the other hand, in recent years, for example, a speaker has been required to be flexible, for example, in response to a demand for a display having flexibility. However, it is difficult to match such a structure composed of exciter and vibrating plate with a flexible speaker.

It is also conceivable to provide a flexible speaker by affixing a flexible exciter to a flexible diaphragm. For example, in Patent Document 1, as a speaker having a diaphragm and an exciter, a speaker (electro-acoustic transducer) is described in which the loss tangent at a frequency of 1 Hz based on the dynamic viscoelasticity measurement of the exciter is in the range of 0 to 50 It has a maximum value in the temperature range of °C, and its maximum value is above 0.08. Furthermore, the product of the thickness of the exciter and the storage elastic coefficient at a frequency of 1 Hz and 25 °C based on the dynamic viscoelasticity measurement is the thickness of the vibrating plate and the Young's modulus less than 3 times the product of the quantities. In Patent Document 1, as an exciter suitable for the speaker, a laminated piezoelectric element is exemplified in which electrode layers are provided on both sides of a piezoelectric body layer, and a plurality of layers of piezoelectric films with protective layers are laminated, followed by cover the electrode layer. Further, as a preferable piezoelectric film, a piezoelectric film is exemplified in which a piezoelectric layer is a polymer composite piezoelectric body in which piezoelectric particles are dispersed in a matrix containing a polymer material.

In the multilayer piezoelectric element in which the piezoelectric film is laminated, the piezoelectric film expands and contracts in the plane direction when the piezoelectric film is energized. Therefore, it is possible to realize a piezoelectric speaker in which the laminated piezoelectric element is attached to the vibration plate as an exciter, and the vibration plate is bent by the expansion and contraction movement of the laminated piezoelectric film and is perpendicular to the plate surface. Vibrates in the direction so that the vibrating plate outputs sound.

[Patent Document 1] International Publication No. 2020/179353

The multilayer piezoelectric element used as an actuator described in Patent Document 1 has very good flexibility. In particular, a piezoelectric film and a laminated piezoelectric element in which a piezoelectric film using a polymer composite piezoelectric body as a piezoelectric layer is laminated has particularly good flexibility. Therefore, the piezoelectric speaker described in Patent Document 1 can realize not only bending, bending, folding, etc. but also a coiled piezoelectric speaker by using a diaphragm having good flexibility.

As a method of winding a piezoelectric speaker in which a laminated piezoelectric element is pasted on a flexible diaphragm, for example, a winding core is provided at the end of the diaphragm, and the winding core is rotated by power to wind up the piezoelectric speaker. The method of electric loudspeaker. In addition, regarding the winding of such a piezoelectric speaker, it is preferable to properly wind it on a winding core having a small diameter with a relatively small force.

However, in the conventional multilayer piezoelectric element, even when a sufficiently high-flexibility diaphragm is used, there are cases where, for example, unwinding and unwinding of the wound piezoelectric speaker occur depending on the diameter of the winding core. And/or the gap between the winding layers, which is a sign of loose winding, cannot perform sufficient and good winding.

The object of the present invention is to solve the problems of the prior art, and to provide a piezoelectric element and a piezoelectric speaker using the piezoelectric element. The piezoelectric element is a piezoelectric element on which a piezoelectric film is laminated. When the exciter is attached to the vibration plate of the piezoelectric speaker using the vibration plate that can be rolled up, the piezoelectric speaker can be wound up preferably.

In order to achieve this object, the present invention has the following constitutions. [1] A piezoelectric element, which is formed by laminating a plurality of piezoelectric films and pasting the laminated and adjacent piezoelectric films with an adhesive layer, wherein The distance in the horizontal direction of the position of the lower end of the round rod when it is cut into 20×50 mm, placed a weight of 100 g on both sides of 20 mm, and hung on a round rod with a radius of 2.5 mm is 9.5 mm or less. [2] The piezoelectric element as described in [1], wherein The thickness of the adhesive layer pasting adjacent piezoelectric films is 10 μm or less. [3] The piezoelectric element according to any one of [1] or [2], wherein The piezoelectric film has a piezoelectric layer, electrode layers provided on both surfaces of the piezoelectric layer, and a protective layer provided to cover the electrode layers. [4] The piezoelectric element as described in [3], wherein The thickness of the piezoelectric layer is 45 μm or more. [5] The piezoelectric element described in [3] or [4], wherein The piezoelectric layer is a polymer composite piezoelectric body having piezoelectric particles in a polymer material. [6] The piezoelectric element as described in [5], wherein The polymer material has a cyanoethyl group. [7] The piezoelectric element as described in [6], wherein The polymer material is cyanoethylated polyvinyl alcohol. [8] The piezoelectric element according to any one of [1] to [7], in which a plurality of piezoelectric films are laminated by folding back one piezoelectric film. [9] A piezoelectric speaker comprising the piezoelectric element described in any one of [1] to [8] bonded to a flexible diaphragm. [10] The piezoelectric speaker as described in [9], wherein The vibrating plate is a display element. [Invention effect]

According to the present invention, in the piezoelectric element on which the piezoelectric film is laminated, when the diaphragm of the piezoelectric speaker using the diaphragm that can be wound is pasted as the exciter, the piezoelectric speaker can be wound up preferably. .

Hereinafter, the piezoelectric element and the piezoelectric speaker 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. Moreover, the figure shown below is a schematic diagram for demonstrating the piezoelectric element and piezoelectric speaker of this invention. Therefore, the size, thickness, shape, and positional relationship of each member and each part are different from the actual object.

In the present invention, the numerical range represented by "-" means a range including the numerical values described before and after "-" as the lower limit and the upper limit. Furthermore, in the present invention, first and second added to electrode layers, protective layers, etc. refer to those added for the convenience of distinguishing two members that are basically the same, and for describing the piezoelectric element and piezoelectric speaker of the present invention. Therefore, the first and second of these components have no technical significance, and have nothing to do with the actual use status and mutual positional relationship.

An example of the piezoelectric element of the present invention is schematically shown in FIG. 1 . The piezoelectric element 10 shown in FIG. 1 is one in which a plurality of piezoelectric films 12 are laminated by folding a flexible piezoelectric film 12 multiple times in a bellows shape. The piezoelectric film 12 has a first electrode layer 28 on one side of the piezoelectric body layer 26, a second electrode layer 30 on the other side, a first protective layer 32 on the surface of the first electrode layer 28, and a second electrode layer on the second electrode layer. A second protective layer 34 is provided on the surface of the layer 30 . In addition, in the piezoelectric element 10 , the adjacent piezoelectric films 12 laminated by folding are adhered by the adhesive layer 20 .

Details will be described later. Regarding the piezoelectric element (multilayer piezoelectric element) of the present invention, when it is cut into 20×50 mm, a weight of 100 g is applied to both sides of 20 mm, and it is hung on a round rod with a radius of 2.5 mm, the lower end of the round rod The distance between the piezoelectric elements in the horizontal direction of the position is 9.5 mm or less. By having such a constitution, the piezoelectric element 10 of the present invention, for example, can be wound up with a small-diameter core when it is attached as an exciter to the vibration plate of a piezoelectric speaker using a flexible vibration plate. In the case of a piezoelectric speaker, it is also possible to prevent unwinding of the piezoelectric speaker being wound up and gaps between winding layers that may be a sign of unwinding of the piezoelectric speaker being wound up. This point will be described in detail later.

The piezoelectric element 10 of the illustrated example is a piezoelectric film 12 in which five layers are stacked by folding a rectangular (rectangular) piezoelectric film 12 four times at equal intervals.

In addition, in the piezoelectric element 10 of the present invention, in the case of folding back the rectangular piezoelectric film 12 , the folding line formed by the folding of the piezoelectric film 12 can extend along the length in the planar shape of the piezoelectric element 10 . The sides are in the same direction, and can also be in the same direction along the short side. In addition, the planar shape of the piezoelectric element 10 refers to the shape of the piezoelectric element 10 when viewed from the lamination direction of the piezoelectric film 12 . In the following description, the folded line formed by the folded back of the piezoelectric film 12 , that is, the top line outside the end of the folded portion is also referred to as a “ridge line” for convenience. For example, if a rectangular piezoelectric film of 25 x 20 cm is folded four times in the direction of 25 cm at intervals of 5 cm, a piezoelectric film with five layers laminated can be obtained as a rectangle with a planar shape of 5 x 20 cm and ridges and long sides. Piezoelectric elements with the same direction of 20cm (see Figure 9). In addition, if a piezoelectric film of 100 x 5 cm is folded four times in the direction of 100 cm at intervals of 20 cm, a rectangular piezoelectric film of 5 x 20 cm with the same planar shape and ridgelines can be obtained among five piezoelectric films laminated. A piezoelectric element corresponding to 5cm in the short side direction.

In addition, as a preferred mode, the piezoelectric element 10 shown in FIG. 1 is manufactured by folding back a rectangular piezoelectric film 12 so that its planar shape is rectangular. However, in the piezoelectric element of the present invention, the shape of the piezoelectric film 12 is not limited to a rectangle, and various shapes can be utilized. As an example, polygons such as a circle, a rounded rectangle (long ellipse), an ellipse, and a hexagon are exemplified.

As described above, the piezoelectric element 10 is laminated by folding the piezoelectric film 12 a plurality of times. In the piezoelectric element 10 of the illustrated example, five piezoelectric films 12 are laminated by folding the piezoelectric film 12 four times. Also, the piezoelectric films 12 stacked and adjacent to each other are bonded by the bonding layer 20 . In the piezoelectric element 10 of the present invention, by laminating a plurality of piezoelectric films 12 and adhering adjacent piezoelectric films 12 in this way, compared with the case of using one piezoelectric film, the number of piezoelectric elements can be increased. Stretch force. As a result, for example, the diaphragm to be described later can be bent with a large force to output high sound pressure sound.

In addition, the piezoelectric element of the present invention is not limited to the configuration in which piezoelectric films 12 laminated and adjacent to one piezoelectric film 12 are pasted by the adhesive layer 20 . That is, as schematically shown in FIG. 2, the piezoelectric element (laminated piezoelectric element) of the present invention can be pasted by laminating a plurality of cut sheets (sheet-shaped) through the adhesive layer 20. The configuration of the piezoelectric film 12 and the adjacent piezoelectric film 12.

As in the piezoelectric element 10 of the illustrated example, the piezoelectric film 12 is stacked by folding one piezoelectric film 12. Although a plurality of piezoelectric films 12 are stacked, it can also be set in each electrode layer described later. One piezoelectric element 10 is the extraction of the electrode for driving the piezoelectric film 12 . As a result, the piezoelectric element 10 stacked by folding back one piezoelectric film 12 can simplify the configuration and electrode wiring, and furthermore, has excellent productivity. In addition, since the piezoelectric element 10 is laminated by folding back one piezoelectric film 12 , electrode layers facing adjacent piezoelectric films have the same polarity by lamination. As a result, this piezoelectric element 10 is also advantageous from the viewpoint that a short circuit does not occur even if the electrode layers are in contact with each other.

In the piezoelectric element 10 of the present invention, the number of layers of the piezoelectric film 12 in the piezoelectric element 10 is not limited to five layers as shown in the illustration. That is, in the piezoelectric element 10 of the present invention, the piezoelectric film 12 may be stacked with 4 or less layers of piezoelectric film 12 folded back three times or less, or may be stacked with 6 or more layers of piezoelectric film 12 folded back 5 or more times. 12 of the piezoelectric film. In the piezoelectric element of the present invention, the number of layers of the piezoelectric film 12 is not limited, but is preferably 2 to 10 layers, more preferably 3 to 7 layers, and still more preferably 4 to 6 layers. In this regard, the configuration of laminating the diced sheet-shaped piezoelectric film 12 shown in FIG. 2 is also the same.

In the piezoelectric element 10 of the present invention, the larger the number of layers of the piezoelectric film 12 is, the higher the output of the piezoelectric element is. For example, when used as an actuator of a piezoelectric speaker, high sound pressure can be output. On the contrary, the smaller the number of stacked layers, for example, the more favorable the winding of the piezoelectric speaker which will be described later. Therefore, the number of laminated layers of the piezoelectric film 12 in the piezoelectric element 10 of the present invention depends on the firmness of the vibrating plate to be pasted, the size of the vibrating plate to be pasted, the sticking position to the vibrating plate, and the piezoelectric film 12. The firmness of the piezoelectric element 10, the size of the piezoelectric film surface direction, the output (power) required for the piezoelectric element 10, the required winding performance, the diameter of the winding core, the size of the power used for winding and What is necessary is just to set appropriately, such as the limitation of the required thickness.

In the piezoelectric element 10 , among the piezoelectric films 12 laminated by folding back, the piezoelectric films 12 adjacent in the lamination direction are adhered to each other by the adhesive layer 20 . Adhering the adjacent piezoelectric films 12 in the stacking direction with the adhesive layer 20 can directly transmit the expansion and contraction of each piezoelectric film 12, and can be driven without waste as a laminated body on which the piezoelectric films 12 are stacked.

In the present invention, as long as the adjacent piezoelectric films 12 can be bonded, various known adhesives (adhesive materials) can be used for the adhesive layer 20 . Therefore, the adhesive layer 20 may be a layer composed of an adhesive (adhesive material), may also be a layer composed of an adhesive (adhesive material), or may be a layer composed of a material having the characteristics of both the adhesive and the adhesive. . In addition, the adhesive refers to an adhesive that has fluidity when pasted and then becomes solid. In addition, the adhesive refers to an adhesive that is a gel-like (rubber-like) soft solid at the time of bonding, and the gel-like state does not change after that. In addition, the adhesive layer 20 may be formed by applying a fluid adhesive such as a liquid, or may be formed using a sheet-like adhesive.

Among them, the piezoelectric element 10 is used as an actuator as an example. That is, the piezoelectric element 10 expands and contracts itself by expanding and contracting the plurality of stacked piezoelectric films 12 , for example, bending and vibrating the vibrating plate 62 as will be described later to generate sound. Therefore, in the piezoelectric element 10, it is preferable that the expansion and contraction of the laminated piezoelectric films 12 be directly transmitted. If there is a viscous substance between the piezoelectric films 12 to dampen the vibration, the transmission efficiency of the expansion and contraction energy of the piezoelectric film 12 will be lowered, and the driving efficiency of the piezoelectric element 10 will be lowered. In consideration of this point, the adhesive layer 20 is preferably an adhesive layer composed of an adhesive that can obtain a solid and relatively hard adhesive layer 20 rather than an adhesive layer composed of an adhesive. As the more preferable adhesive layer 20 , specifically, an adhesive layer composed of a thermoplastic adhesive such as a polyester-based adhesive and a styrene-butadiene rubber (SBR)-based adhesive can be preferably 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".

In the piezoelectric element 10 , the thickness of the adhesive layer 20 is not limited, as long as the thickness can be appropriately set to exhibit sufficient adhesive force according to the forming material of the adhesive layer 20 . Among them, regarding the piezoelectric element 10 , the thinner the adhesive layer 20 is, the better the transmission effect of the expansion and contraction energy (vibration energy) of the piezoelectric layer 26 is, and energy efficiency can be improved. Also, if the adhesive layer 20 is thick and rigid, expansion and contraction of the piezoelectric film 12 may be restricted. Taking this point into consideration, it is preferable that the adhesive layer 20 is thinner than the piezoelectric layer 26 . That is, in the piezoelectric element 10, the adhesive layer 20 is preferably hard and thin. Specifically, the thickness of the adhesive layer 20 after pasting is preferably 0.1-50 μm, more preferably 0.1-30 μm, and even more preferably 0.1-10 μm. In particular, from the viewpoint that the distance D (horizontal distance D) shown in FIG. 7 described later can be preferably set to 9.5 mm or less, the thickness of the adhesive layer 20 is preferably 10 μm or less in terms of the thickness after sticking. , 5 μm or less is better.

In the piezoelectric element of the present invention, various known piezoelectric films 12 can be used as long as the piezoelectric film 12 is flexible and can be bent and stretched. 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.

In the piezoelectric element 10 of the present invention, the piezoelectric film 12 preferably has an electrode layer provided on both surfaces of the piezoelectric layer 26 and a protective layer provided to cover the electrode layer. An example of the piezoelectric film 12 is schematically shown in FIG. 3 with a cross-sectional view. In FIG. 3 and the like, hatching is omitted in order to simplify the drawing and clearly show the configuration. In addition, in the following description, unless otherwise specified, "cross-section" means a cross-section in the thickness direction of the piezoelectric film. The thickness direction of the piezoelectric film is the lamination direction of the piezoelectric film.

As shown in FIG. 3 , the piezoelectric film 12 of the illustrated example has a piezoelectric layer 26 , a first electrode layer 28 laminated on one surface of the piezoelectric layer 26 , and a first protective layer 32 laminated on the first electrode layer 28 . , the second electrode layer 30 laminated on the other surface of the piezoelectric layer 26 , and the second protective layer 34 laminated on the second electrode layer 30 .

As described above, in the piezoelectric element 10 of the present invention, the piezoelectric film 12 is laminated by folding one piezoelectric film 12 back. Therefore, even if a plurality of piezoelectric films 12 are laminated, one location for drawing electrodes for driving the piezoelectric element 10 , that is, the piezoelectric film 12 , can be provided in each electrode layer described later. As a result, the configuration and electrode wiring of the piezoelectric element 10 can be simplified, and the productivity is also excellent. In addition, since one piezoelectric film 12 is folded back, the electrode layers of adjacent piezoelectric films facing each other become the same polarity by lamination, and thus no short circuit occurs even if the electrode layers are in contact with each other.

In the piezoelectric film 12 , various known piezoelectric layers can be used for the piezoelectric layer 26 . In the piezoelectric film 12, as schematically shown in FIG. 3, the piezoelectric layer 26 is preferably a polymer composite piezoelectric body including piezoelectric particles 40 in a polymer matrix 38 including a polymer material.

Among them, it is preferable that the polymer composite piezoelectric body (piezoelectric body layer 26 ) has the following requirements. In addition, in this invention, normal temperature means 0-50 degreeC. (i) Flexibility For example, when a portable document such as a newspaper or a magazine is held in a state where it feels like it is being bent slowly, 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. Also, 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. (ii) Acoustic quality The speaker vibrates piezoelectric particles at a frequency in the audio frequency range of 20 Hz to 20 kHz, and the vibrating energy vibrates the vibration plate (polymer composite piezoelectric body) as a whole to reproduce sound. Therefore, in order to improve the transmission efficiency of vibration energy, appropriate hardness is required for the polymer composite piezoelectric body. Also, if the frequency characteristics of the speaker are smooth, the amount of change in sound quality when the lowest resonance frequency f ₀ changes with changes in the curvature is also small. Therefore, the loss tangent of the polymer composite piezoelectric body is required to be appropriately large.

此時，由於壓電膜的彎曲程度亦即彎曲部的曲率半徑變得越大，則機械剛性s下降，因此最低共振頻率f ₀變小。亦即，有時依據壓電膜的曲率半徑而揚聲器的音質（音量、頻率特性）改變。 As is well known, the lowest resonance frequency f ₀ of a speaker diaphragm is given by the following equation. Among them, s is the rigidity of the vibration system, and m is the mass. [Formula 1]

At this time, as the degree of curvature of the piezoelectric film, that is, the radius of curvature of the bent portion increases, the mechanical rigidity s decreases, and therefore the minimum resonance frequency f ₀ decreases. That is, the sound quality (volume, frequency characteristics) of the speaker may change depending on the curvature radius of the piezoelectric film.

To sum up, it is required that the polymer composite piezoelectric body exhibits rigidity for vibrations of 20 Hz to 20 kHz and softness 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.

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) in 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 the main dispersion occurs is the glass transition point (Tg), where the viscoelastic relaxation mechanism is most evident. In the polymer composite piezoelectric body (piezoelectric body layer 26), 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 achieve a frequency range of 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 Tg at room temperature at a frequency of 1 Hz for the matrix of the polymer composite piezoelectric body, from the viewpoint of expressing the motion preferably.

It is preferable that the maximum value of the loss tangent Tanδ at a frequency of 1 Hz based on a dynamic viscoelasticity test of the polymer material used as the polymer matrix 38 is 0.5 or more at room temperature. Thereby, when the polymer composite piezoelectric body is slowly bent by an external force, the stress concentration at the interface of the polymer matrix/piezoelectric body particle in the maximum bending moment portion is alleviated, and high flexibility can be expected.

In addition, the polymer material used as the polymer matrix 38 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 It 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 be rigid to the acoustic vibration of 20 Hz to 20 kHz.

Moreover, it is more preferable that the relative permittivity of the polymer material used as the polymer matrix 38 is 10 or more at 25°C. Accordingly, when a voltage is applied to the polymer composite piezoelectric body, a higher electric field is required for the piezoelectric particles in the polymer matrix, and thus a large amount of deformation can be expected. However, on the other hand, in consideration of ensuring good moisture resistance, etc., at 25° C., the number of polymer materials is preferably 10 or less.

Examples of polymer materials satisfying these conditions include cyanoethylated polyvinyl alcohol (cyanoethylated PVA), polyvinyl acetate, polyvinylidene chloride acrylonitrile, polystyrene-vinyl polyvinyl alcohol, and polystyrene-vinyl polyvinyl alcohol. Isoprene block copolymer, polyvinyl methyl ketone and polybutyl methacrylate, etc. In addition, commercially available items such as Hibler 5127 (manufactured by KURARAY CO., LTD.) can also be preferably used as such polymer materials.

As the polymer material constituting the polymer matrix 38, it is preferable to use a polymer material having a cyanoethyl group, and it is particularly preferable to use cyanoethylated PVA. That is, in the piezoelectric film 12, it is preferable to use a polymer material having a cyanoethyl group as the polymer matrix 38 for the piezoelectric layer 26, 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 in combination (mixed) in plural.

In the piezoelectric film 12, the polymer matrix 38 of the piezoelectric layer 26 may use a plurality of polymer materials in combination as necessary. That is, for the purpose of adjusting dielectric properties or mechanical properties, etc., in addition to the polymer material having viscoelasticity at the above normal temperature, other dielectric materials can also be added to the polymer matrix 38 constituting the polymer composite piezoelectric body as required. Electrical polymer materials.

As dielectric polymer materials that can be added, 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 rubbers such as nitrile rubber and chloroprene rubber. Among them, polymer materials having cyanoethyl groups can be preferably used. In addition, in the polymer matrix 38 of the piezoelectric layer 26, 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 of the polymer matrix 38, in addition to the dielectric polymer material, vinyl chloride resin, polyethylene, polystyrene, methacrylic resin, polybutylene, isobutylene, etc. may be added. Thermoplastic resins and thermosetting resins such as phenolic resins, urea resins, melamine resins, alkyd resins, 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 polymer matrix 38 of the piezoelectric layer 26, there is no limit to the amount of the polymer material other than the polymer material having viscoelasticity at room temperature, and the proportion of the polymer matrix 38 is set to 30% by mass. Below % is better. Thereby, the properties of the added polymer material can be discovered without damaging the viscoelastic relaxation mechanism in the polymer matrix 38, so it is possible to increase the dielectric constant, improve heat resistance, and piezoelectric particles 40 or electrode layers. Better results can be obtained in terms of improved adhesion.

The polymer composite piezoelectric system to be the piezoelectric layer 26 includes piezoelectric particles 40 in such a polymer matrix. The piezoelectric particles 40 are dispersed in the polymer matrix, preferably uniformly (approximately uniformly). The piezoelectric particles 40 are preferably composed of ceramic particles having a perovskite-type or wurtzite-type crystal structure. Examples of ceramic particles constituting piezoelectric particles 40 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 40 may be appropriately selected according to the size and application of the piezoelectric film 12 . The particle size of the piezoelectric particles 40 is preferably 1 to 10 μm. By setting the particle size of the piezoelectric particles 40 within the above-mentioned range, a favorable result can be obtained in terms of both high piezoelectric characteristics and flexibility.

In the piezoelectric film 12, the quantitative ratio between the polymer matrix 38 and the piezoelectric particles 40 in the piezoelectric layer 26 depends only on the size and thickness of the piezoelectric film 12 in the plane direction, the application of the piezoelectric film 12, and the piezoelectric film. The characteristics required in 12 can be set appropriately. The volume fraction of the piezoelectric particles 40 in the piezoelectric layer 26 is preferably 30 to 80%, more preferably 50 to 80%. By setting the amount ratio of the polymer matrix 38 to the piezoelectric particles 40 within the above-mentioned range, a good result can be obtained in terms of both high piezoelectric characteristics and flexibility.

In addition, in the piezoelectric film 12, the thickness of the piezoelectric layer 26 is not limited, as long as it is appropriately set according to the size of the piezoelectric film 12, the application of the piezoelectric film 12, and the characteristics required for the piezoelectric film 12. . The thickness of the piezoelectric layer 26 is preferably from 8 to 300 μm, more preferably from 8 to 200 μm, still more preferably from 10 to 150 μm, and most preferably from 15 to 100 μm. By setting the thickness of the piezoelectric layer 26 within the above-mentioned range, favorable results can be obtained in terms of ensuring rigidity, appropriate flexibility, and the like.

Furthermore, the thickness of the piezoelectric layer 26 is preferably 45 μm or more. Within the above range, the thickness of the piezoelectric layer 26 is more preferably 45 μm or more. By setting the thickness of the piezoelectric layer 26 to 45 μm or more, the piezoelectric element 10 with high output (strong stretching force) can be stably obtained, and the piezoelectric element can be thinned by reducing the number of layers of the piezoelectric film 12 , which can suppress It is preferable from the standpoint of power consumption when the piezoelectric element is driven. This point is the same even when the piezoelectric layer 26 is not a polymer composite piezoelectric body. However, in the case where the piezoelectric layer 26 is a polymer composite piezoelectric body, by setting the thickness of the piezoelectric layer 26 to 45 μm or more, it is possible to obtain sufficient strength of the piezoelectric film 12 while obtaining the advantages described above. From the viewpoint of flexibility, it is further preferable.

The piezoelectric layer 26 is preferably polarized in the thickness direction. The polarization treatment will be described in detail later.

In addition, in the piezoelectric film 12, the piezoelectric layer 26 is not limited to that described above, and the polymer matrix 38 composed of a polymer material having viscoelasticity at room temperature such as cyanoethylated PVA contains a piezoelectric material. The particle 40 is a polymer composite piezoelectric body. That is, in the piezoelectric film 12 , 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 particle 40 is a polymer composite piezoelectric body, a piezoelectric layer made of polyvinylidene fluoride, a piezoelectric layer made of fluororesin other than polyvinylidene fluoride, and a film made of poly-L-lactic acid. And the piezoelectric layer of the film composed of poly-D lactic acid, etc. However, as described above, from the viewpoint that it can operate hard for vibrations of 20 Hz to 20 kHz, and can operate softly for slow vibrations of several Hz or less, excellent acoustic characteristics, and excellent flexibility can be obtained. It is considered that in the above-mentioned polymer matrix 38 composed of a polymer material having viscoelasticity at room temperature such as cyanoethylated PVA, a polymer composite piezoelectric body including piezoelectric particles 40 can be preferably used.

The piezoelectric film 12 shown in FIG. 3 has a second electrode layer 30 on one side of the piezoelectric layer 26, a second protective layer 34 on the surface of the second electrode layer 30, and a second protective layer 34 on the other side of the piezoelectric layer 26. The first electrode layer 28 is provided on one surface, and the first protective layer 32 is provided on the surface of the first electrode layer 28 . In the piezoelectric film 12 , the first electrode layer 28 and the second electrode layer 30 form an electrode pair. In other words, the laminated film constituting the piezoelectric film 12 has both surfaces of the piezoelectric layer 26 sandwiched between the first electrode layer 28 and the second electrode layer 30 as electrode pairs, and further sandwiched by the first protective layer 32 and the second protective layer 34 . The composition of holding. In this way, the region sandwiched between the first electrode layer 28 and the second electrode layer 30 is driven according to the applied voltage.

In addition to these layers, the piezoelectric film 12 may have, for example, an adhesive layer for adhering the electrode layer and the piezoelectric layer 26 and an adhesive layer for adhering the electrode layer and the protective layer. The adhesive can be an adhesive or an adhesive. In addition, the same material as the polymer matrix 38 , which is a polymer material from which the piezoelectric particles 40 are removed from the piezoelectric layer 26 , can also be preferably used for the adhesive. In addition, the adhesive layer may be provided on both the first electrode layer 28 side and the second electrode layer 30 side, or may be provided on only one of the first electrode layer 28 side and the second electrode layer 30 side.

In the piezoelectric film 12 , the first protective layer 32 and the second protective layer 34 cover the first electrode layer 28 and the second electrode layer 30 and serve to impart appropriate rigidity and mechanical strength to the piezoelectric layer 26 . That is, in the piezoelectric film 12, the piezoelectric layer 26 including the polymer matrix 38 and the piezoelectric particles 40 exhibits very excellent flexibility against slow bending deformation, but rigidity or mechanical strength may be insufficient depending on the application. . The first protective layer 32 and the second protective layer 34 are provided on the piezoelectric film 12 to compensate for this. The first protective layer 32 and the second protective layer 34 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 32 and the second protective layer 34, both members are collectively referred to as a protective layer.

The protective layer is not limited, and various sheets can be used. As an example, various resin films are preferably illustrated. Among them, polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS), polycarbonate (PC), polyphenylene sulfide, etc. Ether (PPS), polymethylmethacrylate (PMMA), polyetherimide (PEI), polyimide (PI), polyamide (PA), polyethylene naphthalate (PEN), Resin films composed of triacetyl cellulose (TAC) and cyclic olefin resins are preferably used.

The thickness of the protective layer is also not limited. In addition, the thicknesses of the first protective layer 32 and the second protective layer 34 are basically the same, but may be different. If the rigidity of the protective layer is too high, not only the expansion and contraction of the piezoelectric layer 26 will be restricted, but also the flexibility will be impaired. Therefore, unless mechanical strength or good handleability as a sheet is required, the thinner the protective layer is, the more advantageous it is.

When the thicknesses of the first protective layer 32 and the second protective layer 34 are each less than twice the thickness of the piezoelectric layer 26 , favorable results can be obtained in terms of ensuring rigidity and appropriate flexibility. For example, when the thickness of the piezoelectric layer 26 is 50 μm and the first protective layer 32 and the second protective layer 34 are made of PET, the thicknesses of the first protective layer 32 and the second protective layer 34 are preferably 100 μm or less. , 50 μm or less is more preferable, and 25 μm or less is still more preferable.

In addition, in this invention, the 1st protective layer 32 and the 2nd protective layer 34 are used as a preferable aspect, and they are not essential components. Therefore, the piezoelectric film 12 may have only the first protective layer 32 , may have only the second protective layer 34 , or may have no protective layer. However, in consideration of the mechanical strength of the piezoelectric film 12, the protective properties of the electrode layers, etc., it is preferable that the piezoelectric film has at least one protective layer. A layer of protection is better.

In the piezoelectric film 12 , the first electrode layer 28 is provided between the piezoelectric layer 26 and the first protective layer 32 , and the second electrode layer 30 is provided between the piezoelectric layer 26 and the second protective layer 34 . The first electrode layer 28 and the second electrode layer 30 are for applying a voltage to the piezoelectric layer 26 . The piezoelectric film 12 expands and contracts by applying a voltage from the electrode layer to the piezoelectric layer 26 .

The first electrode layer 28 and the second electrode layer 30 are basically the same except for the position difference. Therefore, in the following description, when there is no need to distinguish between the first electrode layer 28 and the second electrode layer 30, the two members are also collectively referred to as electrode layers.

In the piezoelectric film, the material for forming the electrode layer is not limited, and various conductors can be used. Specifically, carbon, palladium, iron, tin, aluminum, nickel, platinum, gold, silver, copper, chromium, molybdenum, alloys thereof, indium tin oxide, and PEDOT/PPS (polyethylenedioxythiophene-polyethylene) are exemplified. Styrene sulfonic acid) and other conductive polymers. Among these, copper, aluminum, gold, silver, platinum, and indium tin oxide are preferably exemplified. Among them, copper is more preferable from the viewpoints of conductivity, cost, and flexibility.

In addition, the formation method of the electrode layer is not limited, and various vapor deposition methods (vacuum film formation methods) such as vacuum evaporation and sputtering, film formation by electroplating, or a method of adhering foil formed of the above materials can be used. A known method such as a coating method. Among them, for reasons such as ensuring the flexibility of the piezoelectric film 12 , as the electrode layer, especially thin films of copper and aluminum formed by vacuum evaporation can be preferably used. Among them, it is particularly preferable to use a thin film of copper formed by vacuum evaporation.

The thicknesses of the first electrode layer 28 and the second electrode layer 30 are not limited. In addition, the thicknesses of the first electrode 28 and the second electrode 30 are basically the same, but may be different. However, similarly to the above-mentioned protective layer, if the rigidity of the electrode layer is too high, not only the expansion and contraction of the piezoelectric layer 26 is restricted, but also the flexibility is impaired. Therefore, as long as the electrical resistance does not become too high, it is more advantageous for the electrode layer to be thinner.

In the piezoelectric film 12 , it is preferable that the product of the thickness of the electrode layer and the Young's modulus is lower than the product of the thickness of the protective layer and the Young's modulus since the flexibility will not be seriously impaired. For example, a case where the first protective layer 32 and the second protective layer 34 are PET, and the first electrode layer 28 and the second electrode layer 30 are copper is illustrated. At this time, the Young's modulus of PET is about 6.2 GPa, and the Young's modulus of copper is about 130 GPa. Therefore, if the thickness of the protective layer is set to 25 μm, the thickness of the electrode layer is preferably 1.2 μm or less, more preferably 0.3 μm or less, particularly preferably 0.1 μm or less.

The piezoelectric film 12 has a structure in which the piezoelectric layer 26 is sandwiched between the first electrode layer 28 and the second electrode layer 30 , and the laminate is further sandwiched between the first protective layer 32 and the second protective layer 34 . Such a piezoelectric film 12 preferably has a maximum value of loss tangent (Tan δ ) at a frequency of 1 Hz obtained based on dynamic viscoelasticity measurement at normal temperature of 0.1 or more. Thereby, even if the piezoelectric film 12 receives a relatively slow and large bending deformation of several Hz or less from the outside, the strain energy can be effectively diffused to the outside as heat, so that the deformation between the polymer matrix and the piezoelectric particles can be prevented. interface cracks.

The piezoelectric film 12 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. Thereby, the piezoelectric film 12 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 appear relatively soft for vibrations of several Hz or less.

In addition, it is preferable that the piezoelectric film 12 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 ⁶ to 2.0× 10 ⁶ N/m, 1.0×10 ⁵ to 1.0×10 ⁶ N/m at 50°C. Accordingly, the piezoelectric film 12 can have appropriate rigidity and mechanical strength within a range that does not impair flexibility and acoustic characteristics.

Furthermore, the piezoelectric film 12 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.

Hereinafter, an example of a method for manufacturing the piezoelectric film 12 will be described with reference to FIGS. 4 to 6 . First, a sheet 42b in which the second electrode layer 30 is formed on the surface of the second protective layer 34 schematically shown in FIG. 4 is prepared. Furthermore, a sheet 42a in which the first electrode layer 28 is formed on the surface of the first protective layer 32 schematically shown in FIG. 6 is prepared.

The sheet 42 b can be produced by forming a copper thin film or the like on the surface of the second protective layer 34 as the second electrode layer 30 by vacuum evaporation, sputtering, electroplating, or the like. Similarly, the sheet 42a can be produced by forming a copper thin film or the like on the surface of the first protective layer 32 as the first electrode layer 28 by vacuum evaporation, sputtering, electroplating, or the like. Alternatively, a commercially available sheet in which a copper thin film or the like is formed on a protective layer may be used as the sheet 42b and/or the sheet 42a. The sheet 42b and the sheet 42a may be the same or different.

In addition, when the protective layer is very thin and the handleability 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 schematically shown in FIG. 5 , the piezoelectric layer 26 is formed on the second electrode layer 30 of the sheet 42 b to fabricate a laminate 46 of the sheet 42 b and the piezoelectric layer 26 .

The piezoelectric layer 26 may be formed by a known method for the piezoelectric layer 26 . For example, in the piezoelectric layer (polymer composite piezoelectric layer) in which piezoelectric particles 40 are dispersed in the polymer matrix 38 shown in FIG. 3 , it is produced as follows as an example. First, a polymer material such as cyanoethylated PVA is dissolved in an organic solvent, and piezoelectric particles 40 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, and cyclohexanone can be used. After the sheet 42b is prepared and the paint is prepared, the paint is cast (coated) on the sheet 42b, and the organic solvent is evaporated and dried. Thereby, as shown in FIG. 5 , a laminate 46 having the second electrode layer 30 on the second protective layer 34 and laminating the piezoelectric layer 26 on the second electrode layer 30 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 that can be heated and melted, the polymer material can be heated and melted to produce a molten product in which piezoelectric particles 40 are added, and the molten material shown in FIG. 4 can be formed by extrusion molding or the like. The laminate 46 shown in FIG. 5 is manufactured by extruding the sheet-shaped object 42b shown in the sheet into a sheet shape and cooling it.

In addition, as described above, in the piezoelectric layer 26 , a polymer piezoelectric material such as PVDF may be added to the polymer matrix 38 in addition to the polymer material having viscoelasticity at room temperature. When adding these piezoelectric polymer materials to the polymer matrix 38, 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 26 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, a heating roll, a pair of heating rolls, and the like.

In addition, the piezoelectric layer 26 of the laminate 46 having the second electrode layer 30 on the second protective layer 34 and the piezoelectric layer 26 formed on the second electrode layer 30 is subjected to polarization treatment (polarization). The method of polarization treatment of the piezoelectric layer 26 is not limited, and a known method 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 performing the electric field polarization treatment, the first electrode layer 28 may be formed before the polarization treatment, and the electric field polarization treatment may be performed using the first electrode layer 28 and the second electrode layer 30 . In addition, when the piezoelectric film 12 is manufactured, it is preferable to perform polarization treatment not in the surface direction of the piezoelectric layer 26 but in the thickness direction.

Next, as schematically shown in FIG. 6 , the previously prepared laminate 42 a is laminated on the piezoelectric layer 26 side of the piezoelectric laminate 46 with the first electrode layer 28 facing the piezoelectric layer 26 . Furthermore, this laminated body is sandwiched between the first protective layer 32 and the second protective layer 34, and thermocompression bonding is performed using a heat press device, a heating roll, etc., so that the laminated body 46 and the sheet-like object 42a are bonded together. In this way, the piezoelectric body layer 26, the first electrode layer 28 and the second electrode layer 30 provided on both surfaces of the piezoelectric body layer 26, and the first protective layer 32 and the second protective layer 34 formed on the surface of the electrode layer were produced. The piezoelectric film 12.

By making the piezoelectric film 12 in this way polarized not only in the plane direction but also in the thickness direction, high piezoelectric characteristics can be obtained even without stretching treatment after the polarization treatment. Therefore, the piezoelectric film 12 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.

As described above, the piezoelectric element 10 is formed by laminating a plurality of layers by folding back the piezoelectric film 12 , and bonding the laminated and adjacent piezoelectric films 12 to each other with the adhesive layer 20 . Alternatively, as shown in FIG. 2 , the piezoelectric films 12 that are stacked and adjacent to each other are laminated by laminating a plurality of diced sheet-shaped piezoelectric films 12 with an adhesive layer 20 .

Among them, as schematically shown in FIG. 7 , the piezoelectric element 10 of the present invention is cut into 20×50 mm, a weight 54 of 100 g is applied to both sides of 20 mm, and a round rod with a radius of 2.5 mm is suspended. The distance D of the piezoelectric element 10 in the horizontal direction from the position of the lower end of the round rod 52 at 52 o'clock is 9.5 mm or less. The piezoelectric element 10 of the present invention has such a structure. For example, in a piezoelectric speaker having a vibrating plate and an exciter attached to the vibrating plate, a vibrator that is flexible and can be wound up is attached as an exciter. In the case of a plate, it is possible to realize a piezoelectric speaker that can be appropriately wound in a state where unwinding and/or gaps between winding layers that may be a sign of unwinding do not occur.

As described above, a flexible speaker can be realized by affixing a flexible exciter to a flexible diaphragm. A piezoelectric element (laminated piezoelectric element) 10 obtained by laminating a piezoelectric film 12 and pasting it with an adhesive layer 20, especially a piezoelectric element 10 in which a piezoelectric film 12 using a polymer composite piezoelectric body as a piezoelectric body layer is laminated has Very good flexibility. Therefore, by using a coilable diaphragm, it is possible to realize a coilable piezoelectric speaker.

As a winding method of a piezoelectric speaker that can be wound, for example, a method is exemplified in which a winding core is provided at the end of the diaphragm, and the winding core is rotated by power to wind the diaphragm and the laminated piezoelectric element. In addition, regarding the winding of such a piezoelectric speaker, it is preferable to properly wind it on a winding core having a small diameter with a relatively small force.

However, in the conventional piezoelectric speaker that can be rolled up using a piezoelectric element, even when a sufficiently high-flexibility diaphragm is used, for example, there is a case where the coiling is generated depending on the diameter of the winding core. Due to the unwinding of the piezoelectric speaker and/or the gap between the winding layers which is a sign of unwinding, sufficient good winding cannot be performed. In the following description, for convenience, the unwinding of the piezoelectric speaker and/or the generation of gaps between the winding layers are also referred to as "winding disorder". That is, even if the vibration plate has sufficient flexibility and is wound up in a state where winding disorder does not occur, the rigidity of the vibration plate and the rigidity of the piezoelectric element overlap at the bonding portion between the vibration plate and the piezoelectric element. Therefore, in this part, the wind-up of the piezoelectric speaker is hindered, and the force to restore the wound-up piezoelectric speaker to the original state becomes stronger. As a result, for example, when the winding core of the piezoelectric speaker has a small diameter, the piezoelectric speaker cannot be properly wound, and the winding of the piezoelectric speaker is disturbed.

On the other hand, as shown in FIG. 7 , when the piezoelectric element 10 of the present invention is cut into 20×50 mm, a weight 54 of 100 g is applied to both sides of 20 mm, and it is hung on a round rod 52 with a radius of 2.5 mm The distance D from the position of the lower end of the round rod 52 to the piezoelectric element 10 in the horizontal direction is 9.5 mm or less. In the following description, for convenience, the distance D is also referred to as "horizontal distance D". The piezoelectric element 10 of the present invention can perform preferable winding with a small force without causing winding disturbance even when the winding diameter is small. Therefore, according to the piezoelectric element 10 of the present invention, for example, when affixed as an exciter to a vibrating plate that can be wound up, a piezoelectric speaker that can be wound up preferably without causing winding disorder can be realized.

In the piezoelectric element 10 of the present invention, regarding the measurement of the distance D in the horizontal direction, after leaving the piezoelectric element 10 to be measured for more than 24 hours in an environment with a temperature of 23±3°C and a humidity of 65±20%RH , in this environment. In addition, the placement in this environment was performed after cutting the piezoelectric element 10 to be measured into 20×50 mm. In addition, cutting of the piezoelectric element 10 was performed so that the piezoelectric element cut into 20×50 mm was not included in the folded portion (ridge line) of the piezoelectric film 12 . Furthermore, the installation timing of the weight 54 is not limited, and it is preferable to carry out in this environment after leaving it in this environment. Also, the measurement of the distance D in the horizontal direction is carried out at a point in time of 10 to 60 seconds after the piezoelectric element 10 with the weight 54 attached is suspended behind the round rod 52 . The piezoelectric element 10 to which the weights 54 are attached is suspended from the round rod 52 so that the positions of the two weights 54 are at the same height in the vertical direction. That is, the measurement of the distance D in the horizontal direction is performed in a state where the heights in the vertical direction of the two weights 54 are equal. In other words, the measurement of the distance D in the horizontal direction is performed in a state where the direction of 50 cm suspended from the piezoelectric element 10 is divided into two by the round rod 52 .

As mentioned above, as shown in FIG. 7 , regarding the piezoelectric element 10 of the present invention, a weight 54 with a gravity of 100 g is applied to two sides of the piezoelectric element 10 cut into 20×50 mm, and the radius is 2.5 mm. The distance D (distance D in the horizontal direction) of the piezoelectric element 10 in the horizontal direction from the position of the lower end portion of the round rod 52 at 52 o'clock is 9.5 mm or less. Therefore, in the cut piezoelectric element 10, the side of 20 mm is the direction perpendicular to the paper of FIG. 7, and the side of 50 mm is the side of the inverted U shape in FIG. The installation position of the weight 54 can be any position as long as it is on the side of 20 cm, that is, the end in the long side direction (50 cm direction), but it is preferably installed in the center of the side of 20 cm. The weight 54 can be directly attached to the 20 cm side of the piezoelectric element 10 using adhesives and adhesive tapes, or hang the weight 54 from the 20 cm side of the piezoelectric element 10 using hanging components such as hooks, strings, and tapes. Wherein, the weight of the hanging member such as the hook also affects the value of the distance D of the piezoelectric element 10 in the horizontal direction from the position of the lower end of the round rod 52, so it is better to use a member of 2 g or less for the hanging member. Alternatively, the total weight of the weight 54 and the suspension member may be set to 100 g. That is, the weight 54 may include suspension members. In addition, in the case of hanging the weight 54 from the 20 cm side of the piezoelectric element, the engaging position of the hanging member such as a hook and the piezoelectric element 10 is set as close as possible to the side of the 20 cm, that is, cut Near the ends of the piezoelectric element 10 in the longitudinal direction.

The horizontal distance D of the piezoelectric element 10 of the present invention is 9.5 mm or less. When the distance D in the horizontal direction exceeds 9.5 mm, for example, when the diameter of the winding core is small, winding disorder occurs when winding up the piezoelectric element. Therefore, in the case of manufacturing a piezoelectric speaker that can be rolled up by attaching a piezoelectric element having a horizontal distance D exceeding 9.5 mm to, for example, a vibrating plate that can be rolled up, winding disorder occurs in the piezoelectric speaker depending on the diameter of the winding core. . In the piezoelectric element 10 of the present invention, the distance D in the horizontal direction may be 9.5 mm or less, but a shorter one is preferable. In the piezoelectric element 10 of the present invention, the distance D in the horizontal direction is preferably 8.5 mm or less. In addition, the shortest distance D in the horizontal direction is 5 mm.

In the piezoelectric element 10 of the present invention, the distance D in the horizontal direction can be controlled by various methods. As an example, by appropriately adjusting and/or selecting the number of layers of the piezoelectric film 12, the material for forming the adhesive layer 20 (commercially available), the thickness of the adhesive layer 20, the material for forming the piezoelectric layer 26, the piezoelectric The distance D in the horizontal direction of the piezoelectric element 10 is controlled by one or more of the thickness of the electrical body layer 26 , the material for forming the electrode layer, the thickness of the electrode layer, and the like. In addition, when the piezoelectric film 12 has a protective layer, the material for forming the protective layer and the thickness of the protective layer can also be used as means for controlling the distance D in the horizontal direction in addition to the above. In addition, as described above, the thickness of the piezoelectric layer 26 is preferably 45 μm or more. That is, by setting the thickness of the piezoelectric layer 24 to 45 μm or more, the piezoelectric element 10 can be obtained with a high output, that is, a strong stretching force, and a good curl shape even when the diameter of the winding core is small.

In the piezoelectric element 10 of the present invention, the piezoelectric layer 26 expands and contracts by applying a driving voltage to the first electrode layer 28 and the second electrode layer 30 . Therefore, it is necessary to electrically connect the first electrode layer 28 and the second electrode layer 30 to an external device such as an external power source. Various well-known methods can be used for connecting the first electrode layer 28 and the second electrode layer 30 to external devices.

As an example, as schematically shown in FIG. 8 , the piezoelectric film 12 is extended at one end, and a protrusion 12 a protruding from a region where the piezoelectric film 12 is laminated is provided. Moreover, the method of providing the lead wire for electrically connecting with an external device to this protrusion part 12a is shown as an example. In addition, in the present invention, the protruding portion specifically refers to a single-layer region that does not overlap with other piezoelectric films 12 in terms of planar shape, that is, when viewed from the lamination direction.

8 shows an example of a piezoelectric element 10 stacked by folding back one piezoelectric film 12 shown in FIG. As for the configuration, also for each piezoelectric film 12, a lead wire for connecting to an external device may be provided in the same manner.

As shown in FIG. 8 , a first lead 72 and a second lead 74 for electrically connecting to an external device such as a power supply device are connected to the protruding portion 12 a of the piezoelectric element 10 . The first lead 72 is a wiring electrically drawn out from the first electrode layer 28 , and the second lead 74 is a wiring electrically drawn out from the second electrode layer 30 . In the following description, when there is no need to distinguish the first lead 72 and the second lead 74, they are also simply referred to as leads.

In the piezoelectric element 10 of the present invention, the connection method of the electrode layer and the lead wire, that is, the drawing method is not limited, and various methods can be used. As an example, a method of forming a through hole in the protective layer, providing an electrode connection member made of metal paste such as silver glue to fill the through hole, and providing a lead wire in the electrode connection member is exemplified. As another method, a method of providing a rod-shaped or sheet-shaped lead-out electrode between the electrode layer and the piezoelectric layer or between the electrode layer and the protective layer, and connecting a lead wire to the lead-out electrode is exemplified. Alternatively, a lead wire may be directly inserted between the electrode layer and the piezoelectric body layer or between the electrode layer and the protective layer, and the lead wire may be connected to the electrode layer. As another method, a method is exemplified in which a part of the protective layer and the electrode layer protrudes from the piezoelectric layer in the direction along the plane, and a lead wire is connected to the protruding electrode layer. In addition, the connection between the lead wire and the electrode layer may be performed by a known method such as a method using a metal paste such as silver paste, a method using solder, or a method using a conductive adhesive. 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.

In addition, in the piezoelectric element 10, the end of the piezoelectric film 12 is not extended, and as shown in FIG. Protrusions such as islands protruding from the piezoelectric film are provided in the direction perpendicular to the direction, and lead-out wiring for connecting to external devices can be provided here. Furthermore, in the piezoelectric element of the present invention, a plurality of these protrusions may be used in combination as necessary.

As will be described later, the piezoelectric element 10 of the present invention can be used in various applications. Among them, the piezoelectric element 10 of the present invention is preferably used as an exciter that outputs sound by vibrating a diaphragm.

An example of the piezoelectric speaker of the present invention is schematically shown in FIG. 9 . The piezoelectric speaker of the present invention is used as an exciter that vibrates the diaphragm to output sound by affixing the piezoelectric element 10 of the present invention to the diaphragm. As shown in FIG. 9 , in the piezoelectric speaker 60 , the piezoelectric element 10 is adhered to the vibrating plate 62 through the adhesive layer 68 . In addition, in the piezoelectric speaker of the present invention, the number of piezoelectric elements attached to one diaphragm 62 is not limited to one, and a plurality of piezoelectric elements 10 may be attached to one diaphragm 62 . Also, for example, by providing two piezoelectric elements 10 on one vibration plate 62 and applying different driving voltages to the respective piezoelectric elements 10 , for example, stereo sound can be output from one vibration plate 62 .

In the piezoelectric speaker 60 of the present invention, the diaphragm 62 is not limited, and various sheet-shaped objects can be used as long as it functions as a diaphragm that outputs sound by vibration of the exciter.

In the piezoelectric speaker 60 of the present invention, as the diaphragm 62, polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS), polycarbonate (PC ), polyphenylene sulfide (PPS), polymethyl methacrylate (PMMA), polyetherimide (PEI), polyimide (PI), polyethylene naphthalate (PEN), triethylene Resin films composed of acyl cellulose (TAC) and cyclic olefin resins, foamed plastic sheets composed of expanded polystyrene, expanded styrene and expanded polyethylene, and sheets of corrugated cardboard A variety of corrugated paper materials made of one or both sides pasted on other cardboard. In addition, the piezoelectric speaker 60 of the present invention can also preferably utilize organic electroluminescent (OLED (Organic Light Emitting Diode)) displays, liquid crystal displays, micro LED (Light Emitting Diode: Light Emitting Diode) displays and inorganic electroluminescence. Various display elements such as a light-emitting display are used as the vibration plate 62 . Furthermore, the piezoelectric speaker 60 of the present invention can also preferably use electronic components such as personal computers such as smart phones, mobile phones, tablet terminals, and laptops, and portable devices such as smart watches as the vibration plate 62 . In addition, the piezoelectric speaker of the present invention can preferably use thin film metals composed of various metals and alloys such as stainless steel, aluminum, copper, and nickel as the vibration plate 62 .

Including the case where the vibrating plate 62 is a display device or an electronic component, it is preferable that the vibrating plate 62 is flexible, and it is more preferable that the vibrating plate 62 can be wound. In the piezoelectric speaker of the present invention, the display element is preferably used as the vibrating plate 62, and among them, a display element having flexibility is preferable, and a display element that can be rolled up is particularly preferable. In addition, in the present invention, being able to be coiled means the same as the above-mentioned "having flexibility" and the meaning of being able to be coiled in general explanations, which means that it can be coiled by rolling up, and specifically means that it can be coiled by Coiling is carried out without damage and damage, and the coiled object becomes flat by unwinding.

In the piezoelectric speaker using the piezoelectric element as the diaphragm and the exciter, by using the diaphragm 62 which can be wound up and the piezoelectric element which can be wound up, the piezoelectric speaker which can be wound up can be realized. In the piezoelectric speaker that can be wound up, for example, a winding core is fixed at the end of the vibrating plate to use power such as a motor, or the winding core is manually rotated to wind up. Among them, as mentioned above, the piezoelectric speaker 60 of the present invention will be cut into 20×50mm, add a weight 54 of 100g, and hang it on a round rod 52 with a radius of 2.5mm, and the horizontal distance D will be 9.5mm or less. The inventive piezoelectric element 10 is used as an actuator. As described above, even if the piezoelectric element 10 of the present invention is a small-diameter winding core, it can be preferably wound without causing winding disorder. Therefore, even when the piezoelectric speaker 60 of the present invention has a small diameter, the piezoelectric speaker 60 can be preferably wound up in a state where winding disorder does not occur.

In the piezoelectric speaker 60 of the present invention, the adhesive layer 68 for bonding the vibrating plate 62 and the piezoelectric element 10 is not limited, as long as the vibrating plate 62 and the piezoelectric element 10 (piezoelectric film 12) can be bonded, Various adhesives can be used. In the piezoelectric speaker 60 of the present invention, the adhesive layer 68 for adhering the diaphragm 62 and the piezoelectric element 10 can use any of the same adhesive layers 20 as the adhesive layer 20 for adhering the above-mentioned adjacent piezoelectric films 12 . Also, the preferred adhesive layer 68 is also the same.

In the piezoelectric speaker 60 of the present invention, the thickness of the adhesive layer 68 is not limited, as long as the thickness can be appropriately set to exhibit sufficient adhesive force according to the forming material of the adhesive layer 68 . Among them, in the piezoelectric speaker 60 of the present invention, the thinner the adhesive layer 68 can improve the transmission effect of the stretching energy (vibration energy) of the piezoelectric film 12 and improve the energy efficiency. In addition, if the adhesive layer is thick and rigid, expansion and contraction of the piezoelectric element 10 may be limited. Taking this point into consideration, the thickness of the adhesive layer 68 for bonding the vibrating plate 62 and the piezoelectric element 10 is preferably 10 to 1000 μm, more preferably 30 to 500 μm, and still more preferably 50 to 300 μm. good.

As described above, in the piezoelectric element 10 of the present invention, the piezoelectric film 12 is formed by sandwiching the piezoelectric layer 26 between the first electrode layer 28 and the second electrode layer 30 . The piezoelectric layer 26 is preferably formed by dispersing piezoelectric particles 40 in the polymer matrix 38 .

When a voltage is applied to the second electrode layer 30 and the first electrode layer 28 of the piezoelectric film 12 having the piezoelectric layer 26 , the piezoelectric particles 40 expand and contract in the polarization direction according to the applied voltage. As a result, the piezoelectric film 12 (piezoelectric layer 26 ) shrinks in the thickness direction. At the same time, due to the relationship of Poisson's ratio, the piezoelectric film 12 also expands and contracts along the surface direction. This expansion and contraction is about 0.01 to 0.1%. As described above, the thickness of the piezoelectric layer 26 is preferably about 8 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 12 , that is, the piezoelectric layer 26 has a dimension significantly larger than its thickness in the plane direction. Therefore, for example, if the long side of the piezoelectric film 12 is 20 cm, the piezoelectric film 12 expands and contracts by a maximum of about 0.2 mm by applying a voltage.

As described above, the piezoelectric element 10 is formed by stacking five piezoelectric films 12 by folding back. In addition, the piezoelectric element 10 is adhered to the vibrating plate 62 via the adhesive layer 68 . As the piezoelectric film 12 expands and contracts, the piezoelectric element 10 also expands and contracts in the same direction. Due to the expansion and contraction of the piezoelectric element 10, the vibrating plate 62 bends, and as a result, vibrates in the thickness direction. The vibrating plate 62 emits sound by the vibration in the thickness direction. That is, the vibrating plate 62 vibrates according to the magnitude of the voltage (driving voltage) applied to the piezoelectric film 12 , and emits sound according to the driving voltage applied to the piezoelectric film 12 .

Among them, it is known that a general piezoelectric film composed of a polymer material such as PVDF aligns molecular chains in the direction of extension by performing an extension process in a uniaxial direction after polarization treatment, and as a result, a large piezoelectric film can be obtained in the direction of extension. Piezoelectric properties. Therefore, the piezoelectric properties of a general piezoelectric film have in-plane anisotropy, and the amount of expansion and contraction in the plane direction when a voltage is applied has anisotropy. In contrast, in the piezoelectric element 10, the piezoelectric film 12 composed of a polymer composite piezoelectric body in which piezoelectric particles 40 are dispersed in a polymer matrix 38 shown in FIG. Strong piezoelectric properties can be obtained without post-stretching treatment, so the piezoelectric properties do not have in-plane anisotropy, and expand and contract isotropically in all directions in the plane direction. That is, in the piezoelectric element 10 of the illustrated example, the piezoelectric film 12 shown in FIG. 3 constituting the piezoelectric element 10 expands and contracts isotropically in two dimensions. According to the piezoelectric element 10 laminated with the piezoelectric film 12 that expands and contracts isotropically in two dimensions, compared with the case of laminating a general piezoelectric film such as PVDF that expands and contracts greatly in only one direction, it can be The vibrating plate 62 is vibrated with a greater force, and a louder and more beautiful sound can be produced.

As described above, the piezoelectric element 10 of the illustrated example is formed by laminating five such piezoelectric films 12 . The piezoelectric element 10 of the example shown in the figure further adheres the adjacent piezoelectric films 12 to each other with an adhesive layer 20 . Therefore, even if the piezoelectric film 12 per sheet has low rigidity and a small tensile force, by laminating the piezoelectric film 12, the rigidity becomes high, and the tensile force as the piezoelectric element 10 also increases. As a result, even if the vibration plate 62 of the piezoelectric element 10 has a certain degree of rigidity, the vibration plate 62 can be sufficiently bent with a relatively large force to sufficiently vibrate the vibration plate 62 in the thickness direction, and the vibration plate 62 can be emitted. sound. Also, the thicker the piezoelectric layer 26 is, the larger the tensile force of the piezoelectric film 12 becomes, but the driving voltage required to expand and contract the piezoelectric film 12 by the same amount increases accordingly. Among them, as mentioned above, in the piezoelectric element 10 , the thickness of the piezoelectric layer 26 is preferably only about 300 μm at the maximum, so the piezoelectric film 12 can be stretched and stretched sufficiently even with a small voltage applied to each piezoelectric film 12 .

This piezoelectric element of the present invention can be preferably used in various sensors, acoustic components, tactile interfaces, ultrasonic transducers, actuators, vibration-damping materials ( Dampers) and vibration power generation devices and other applications. Specifically, as a sensor using the piezoelectric element of the present invention, an acoustic wave sensor, an ultrasonic wave sensor, a pressure sensor, a touch sensor, a strain sensor, a vibration sensor, etc. are exemplified. . The sensor using the piezoelectric film and the laminated piezoelectric element of the present invention is particularly useful in inspections at manufacturing sites such as inspections of infrastructure such as crack inspections and inspections of foreign matter incorporation. As an acoustic element using the piezoelectric element of the present invention, in addition to the piezoelectric speaker (exciter) described above, a speaker, a pickup, and various known speakers and exciters are exemplified. Specific applications of the acoustic element using the piezoelectric element of the present invention include noise cancellers used in cars, trains, airplanes, equipment, etc., artificial vocal cords, and buzzers for preventing the invasion of pests and harmful animals. And furniture, wallpapers, photos, helmets, goggles, headrests, signs and equipment with sound output functions. Examples of application of the tactile interface using the piezoelectric element of the present invention include automobiles, smart phones, smart watches, game machines, and the like. Examples of the ultrasonic transducer using the piezoelectric element of the present invention include an ultrasonic probe, an underwater wave receiver, and the like. Examples of applications of the actuator using the piezoelectric element of the present invention include prevention of water droplet adhesion, transportation, stirring, dispersion, and grinding. Examples of applications of vibration-damping materials using the piezoelectric element of the present invention include containers, vehicles, buildings, and sports equipment such as skis and rackets. Furthermore, as application examples of the vibration power generating device using the piezoelectric element of the present invention, roads, floors, mattresses, chairs, shoes, tires, wheels, computer keyboards, and the like are exemplified.

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

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

[Production of Piezoelectric Film] The piezoelectric film as shown in FIG. 3 was produced by the method shown in FIGS. 4 to 6 . 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, PZT particles are used so that Zr=0.52 mole and Ti=0.48 mole relative to Pb=1 mole, and Pb oxide, Zr oxide, and Ti, which are the main components, are oxidized at 800°C with a ball mill. The mixed powder obtained by wet mixing the powder of the product is calcined for 5 hours and then pulverized.

On the other hand, two sheets in which a copper thin film with a thickness of 0.1 μm was vacuum-deposited on a PET film with a thickness of 4 μm were prepared. That is, in this example, the first electrode layer and the second electrode layer are deposited copper films with a thickness of 0.1 μm, and the first protective layer and the second protective layer are PET films with a thickness of 4 μm. On the copper thin film (second electrode layer) of one sheet, the paint for forming the piezoelectric body layer prepared in advance was applied using a slant die coater. Next, the DMF was evaporated by heating and drying the sheet-coated material on a hot plate at 120°C. In this way, a laminate having a piezoelectric layer (polymer composite piezoelectric layer) having a thickness of 50 μm was formed on a second protective layer made of PET with a second electrode layer made of copper.

The produced piezoelectric layer (laminated body) was rolled using a pair of heating rollers. The temperature of the heating roller pair was set to 100°C. After the rolling treatment, the fabricated piezoelectric layer was subjected to polarization treatment in the thickness direction.

Laminate another sheet on the laminate so that the copper thin film (first electrode layer) faces the piezoelectric layer. Next, by thermocompression-bonding the laminated body and the laminated body of the sheet at a temperature of 120° C. by using a pair of heating rollers, the piezoelectric layer and the first electrode layer were bonded together to produce the one shown in FIG. 3 . piezoelectric film.

[Example 1] The fabricated piezoelectric film was cut into a rectangle of 20×25 cm. The piezoelectric film was pasted by repeatedly placing an adhesive layer at intervals of 5 cm in the direction of 25 cm, turning back the piezoelectric film 4 times, and pressing with a roller. Thereby, a piezoelectric element having a planar shape of 20×5 cm as shown in FIG. 1 was produced by laminating five piezoelectric films and adjacently stacking the piezoelectric films. Therefore, the side of the piezoelectric element with a length of 20 cm becomes a ridge line (return line). NE-NCP3 (thickness 3 μm) manufactured by NEION Film Coatings Corp. was used for the adhesive layer.

[Example 2] A piezoelectric element was fabricated in the same manner as in Example 1 except that the adhesive layer was changed to 68548 (thickness: 10 μm) manufactured by TESA Corporation.

[Comparative example 1] A piezoelectric element was produced in the same manner as in Example 1 except that the adhesive layer was changed to 5603 (thickness: 30 μm) manufactured by NITTO DENKO CORPORATION. [Comparative example 2] A piezoelectric element was produced in the same manner as in Example 1 except that the adhesive layer was changed to 5919ML (thickness: 50 μm) manufactured by NITTO DENKO CORPORATION. [Comparative example 3] A piezoelectric element was fabricated in the same manner as in Example 1 except that the adhesive layer was changed to TSU0041SI (thickness: 25 μm) manufactured by TOYOCHEM CO., LTD. [Comparative example 4] A piezoelectric element was fabricated in the same manner as in Example 1 except that the adhesive layer was changed to FB-ML4-50S (thickness: 50 μm) manufactured by NITTO DENKO CORPORATION.

[evaluation of winding characteristics] A round rod with a diameter of 20 mm was pasted over the entire area of one 5 cm side of the manufactured piezoelectric element of 5 x 20 cm. By rotating the round rod by hand, a piezoelectric element of 5×20 cm was wound up using the round rod as a winding core. Regarding the wound piezoelectric element, the winding property (winding disorder) was evaluated according to the following criteria. A: Loose laps did not occur, and there were no interlayer gaps that would be a sign of loose laps. B: At least one of gaps between layers that cause loose laps and a sign of loose laps.

[Measurement of the distance D in the horizontal direction] The fabricated piezoelectric element of 5×20 cm was cut into 20×50 mm. Cut with scissors. Also, as described above, the dicing was performed so that the piezoelectric element cut into 20×50 mm was not included in the folded portion (ridge line) of the piezoelectric film. The cut piezoelectric element of 20×50 mm was stored for 27 hours in an environment with a temperature of 23° C. and a humidity of 65% RH. Then, in this environment, a weight weighing 100 g was attached to the center of the 20 cm side of the cut piezoelectric element. The installation of the weight is carried out with cellophane tape. Further, in this environment, in order to make the positions of the two weights equal in the vertical direction, the piezoelectric element was suspended from a metal round rod with a radius of 5 mm. After 15 seconds had elapsed after the suspension was started, the distance D in the horizontal direction of the position of the lower end of the round bar was measured using a steel ruler. The results are shown in the following tables.

[Table 1] Sticky layer Horizontal distance D [mm] Coilability manufacturers model Thickness [μm] Example 1 NEION Film Coatings Corp. NE-NCP3 3 8.5 A Example 2 tesa tape KK 68548 10 9.5 A Comparative example 1 NITTO DENKO CORPORATION 5603 30 11.5 B Comparative example 2 NITTO DENKO CORPORATION 5919ML 50 13.5 B Comparative example 3 TOYOCHEM CO., LTD. TSU0041SI 25 13.5 B Comparative example 4 NITTO DENKO CORPORATION FB-ML4-50S 50 16.0 B In all piezoelectric elements, the number of laminated piezoelectric films is 5

As shown in the table, when the piezoelectric element of the present invention having a horizontal distance D of 9.5 mm or less is wound up to a 20 mm round rod, there is no unwinding or a gap between layers that is a sign of unwinding, that is, there is no Winding disorder. Therefore, by affixing this piezoelectric element to a reelable vibration plate, a piezoelectric speaker that can be rewound without causing unwinding or a gap between layers that may be a sign of unwinding can be obtained. On the other hand, when the piezoelectric element of the comparative example whose horizontal distance D exceeds 9.5 mm is wound up to a 20 mm round rod, at least one of unwinding and a gap between layers that is a sign of unwinding, that is, winding disorder occurs. . Therefore, when the piezoelectric element is attached to a reelable vibration plate to form a piezoelectric speaker, when the piezoelectric speaker is reeled up, unwinding and/or interlayer gaps that may be a sign of unwinding may occur. From the above results, the effect of the present invention is obvious. [Industrial availability]

It can be suitably utilized in various applications as a piezoelectric speaker and the like.

10: Piezoelectric element 12: Piezoelectric film 12a: protrusion 20,68: Paste layer 26: Piezoelectric layer 28: The first electrode layer 30: The second electrode layer 32: 1st protective layer 34: The second protective layer 38: polymer matrix 40: Piezoelectric particles 42a, 42b: flakes 46: laminated body 52: round rod 54: Heavy 60: Piezoelectric speaker 62: Vibration plate 72: 1st lead 74: 2nd lead D: Horizontal distance M: the thickest part

FIG. 1 is a diagram schematically showing an example of the piezoelectric element of the present invention. Fig. 2 is a diagram schematically showing another example of the piezoelectric element of the present invention. Fig. 3 is a diagram schematically showing an example of a piezoelectric film used in the piezoelectric element of the present invention. FIG. 4 is a schematic diagram for explaining an example of a method for producing a piezoelectric film. FIG. 5 is a schematic diagram for explaining an example of a method for producing a piezoelectric film. FIG. 6 is a schematic diagram for explaining an example of a method for producing a piezoelectric film. Fig. 7 is a schematic diagram illustrating an example of the piezoelectric element of the present invention. Fig. 8 is a diagram schematically showing another example of the piezoelectric element of the present invention. Fig. 9 is a diagram schematically showing an example of the piezoelectric speaker of the present invention.

10: Piezoelectric element

52: round rod

54: heavy objects

D: Horizontal distance

Claims (10)

A piezoelectric element, which is formed by pasting the aforementioned piezoelectric film laminated and adjacent to each other by laminating a plurality of piezoelectric films with an adhesive layer, wherein When cutting into 20×50mm, adding 100g weight on both sides of 20mm, and hanging on a round rod with a radius of 2.5mm, the distance in the horizontal direction of the position of the lower end of the above-mentioned round rod is 9.5mm or less. The piezoelectric element according to claim 1, wherein The thickness of the adhesive layer pasting the adjacent piezoelectric films is 10 μm or less. The piezoelectric element according to claim 1, wherein The piezoelectric film has a piezoelectric layer, electrode layers provided on both surfaces of the piezoelectric layer, and a protective layer provided to cover the electrode layers. The piezoelectric element according to claim 3, wherein The piezoelectric layer has a thickness of 45 μm or more. The piezoelectric element according to claim 3, wherein The aforementioned piezoelectric layer is a polymer composite piezoelectric body having piezoelectric particles in a polymer material. The piezoelectric element as described in Claim 5, wherein The aforementioned polymer material has a cyanoethyl group. The piezoelectric element according to claim 6, wherein The aforementioned polymer material is cyanoethylated polyvinyl alcohol. The piezoelectric element according to claim 1, which is a plurality of layers of the piezoelectric film laminated by folding back one of the piezoelectric films. A piezoelectric speaker, which is formed by pasting the piezoelectric element described in any one of claim 1 to claim 8 on a flexible vibration plate. The piezoelectric speaker as claimed in item 9, wherein The aforementioned vibrating plate is a display element.

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