CN118020316A - Piezoelectric element and piezoelectric speaker - Google Patents
Piezoelectric element and piezoelectric speaker Download PDFInfo
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- CN118020316A CN118020316A CN202280065087.3A CN202280065087A CN118020316A CN 118020316 A CN118020316 A CN 118020316A CN 202280065087 A CN202280065087 A CN 202280065087A CN 118020316 A CN118020316 A CN 118020316A
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Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R17/00—Piezoelectric transducers; Electrostrictive transducers
-
- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N30/00—Piezoelectric or electrostrictive devices
- H10N30/50—Piezoelectric or electrostrictive devices having a stacked or multilayer structure
-
- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N30/00—Piezoelectric or electrostrictive devices
- H10N30/80—Constructional details
- H10N30/85—Piezoelectric or electrostrictive active materials
Landscapes
- Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Acoustics & Sound (AREA)
- Signal Processing (AREA)
- Piezo-Electric Transducers For Audible Bands (AREA)
- Diaphragms For Electromechanical Transducers (AREA)
Abstract
The object is to provide a piezoelectric element in which piezoelectric films are laminated, and a piezoelectric speaker using the piezoelectric element, which can be suitably wound when used as an exciter in the piezoelectric speaker. The piezoelectric element of the present invention solves the problems by: the piezoelectric element is formed by laminating a plurality of piezoelectric films and adhering adjacent piezoelectric films by using an adhesive layer, wherein the distance between the piezoelectric element and the lower end of a round bar when the piezoelectric element is cut into a round bar with a radius of 2.5mm and a weight of 100g is applied to the side of 20mm by 20X 50mm is less than 9.5 mm.
Description
Technical Field
The present invention relates to a piezoelectric element and a piezoelectric speaker using the same.
Background
So-called exciters (excitons) that vibrate and sound an article by contacting and mounting the article are used for various purposes.
For example, when a user performs a live conference or a teleconference in an office, an exciter is attached to a conference table, a whiteboard, a screen, or the like, so that a sound can be output instead of a speaker. In a vehicle such as an automobile, an exciter can be attached to a console, an a-pillar, a ceiling, or the like to generate a guide sound, a warning sound, music, or the like. In addition, in the case of an automobile that does not emit an engine sound, such as a hybrid automobile or an electric automobile, an exciter is attached to a bumper or the like, so that a vehicle approach notification sound can be emitted from the bumper or the like.
In such an exciter, as a variable element for generating vibration, a combination of a coil and a magnet, a vibration motor such as an eccentric motor and a linear resonance motor, and the like are known.
These variable elements are difficult to thin. In particular, the following difficulties exist with respect to vibration motors: in order to increase the vibration force, it is necessary to increase a mass body, frequency modulation for adjusting the degree of vibration state is difficult, response speed is slow, and the like.
On the other hand, in recent years, for example, a speaker is also required to have flexibility in response to a demand for a display having flexibility, or the like. However, such a structure composed of the exciter and the diaphragm is difficult to match with a speaker having flexibility.
A speaker having flexibility is also considered to be provided by attaching an exciter having flexibility to a diaphragm having flexibility.
For example, patent document 1 describes, as a speaker having a diaphragm and an exciter, a speaker (electroacoustic transducer) of the following type: the loss tangent at a frequency of 1Hz measured by dynamic viscoelasticity of the exciter has a maximum value of 0.08 or more in a temperature range of 0 to 50 ℃, and the product of the thickness of the exciter and the storage modulus at a frequency of 1Hz and 25 ℃ measured by dynamic viscoelasticity is 3 times or less the product of the thickness of the vibration plate and Young's modulus.
Patent document 1 discloses a laminated piezoelectric element as an exciter applied to the speaker, including: a laminated piezoelectric element is formed by laminating a plurality of layers of piezoelectric films, each of which has electrode layers provided on both surfaces of a piezoelectric layer and a protective layer so as to cover the electrode layers. In addition, as a preferable piezoelectric film, a piezoelectric film in which piezoelectric particles are dispersed in a matrix containing a polymer material is exemplified as the piezoelectric layer.
The laminated piezoelectric element in which the piezoelectric film is laminated expands and contracts in the plane direction by energizing the piezoelectric film. Thus, the following piezoelectric speaker can be realized: the laminated piezoelectric element is attached to a vibration plate as an exciter, and the vibration plate is bent by the stretching motion of the laminated piezoelectric film and vibrates in a direction orthogonal to the plate surface, whereby the vibration plate outputs sound.
Technical literature of the prior art
Patent literature
Patent document 1: international publication No. 2020/179353
Disclosure of Invention
Technical problem to be solved by the invention
The laminated piezoelectric element used as an actuator described in patent document 1 has very good flexibility. In particular, a laminated piezoelectric element in which a piezoelectric film in which a polymer composite piezoelectric body is used as a piezoelectric layer is laminated on a piezoelectric film has particularly good flexibility.
Therefore, the piezoelectric speaker described in patent document 1 can realize not only bending, folding, and the like, but also a rollable piezoelectric speaker by using a diaphragm having excellent flexibility.
As a winding method of a piezoelectric speaker in which a piezoelectric element is laminated on a flexible diaphragm, for example, a method of winding a piezoelectric speaker by providing a winding core at an end of the diaphragm and rotating the winding core with power is exemplified.
In addition, regarding the winding of such a piezoelectric speaker, it is preferable to properly wind with a small force on a winding core of a small diameter.
However, in the conventional laminated piezoelectric element, even when a vibration plate having a sufficiently high flexibility is used, there are cases where: for example, the winding of the piezoelectric speaker to be wound and the gap between winding layers, which is a sign of the winding, are generated according to the diameter of the winding core, and thus sufficient and satisfactory winding cannot be performed.
The present invention has been made to solve the above-described problems of the related art, and an object of the present invention is to provide a piezoelectric element in which piezoelectric films are laminated, and a piezoelectric speaker using the piezoelectric element, which can appropriately wind a piezoelectric speaker when, for example, the piezoelectric element is attached as an exciter to a diaphragm of the piezoelectric speaker using a diaphragm that can be wound.
Means for solving the technical problems
In order to achieve this object, the present invention has the following structure.
[1] A piezoelectric element is formed by laminating a plurality of piezoelectric films and attaching the laminated piezoelectric films to each other by an adhesive layer,
When the piezoelectric film is cut into a round bar having a radius of 2.5mm by applying a weight of 100g to two sides of 20mm by cutting the piezoelectric film into 20×50mm, the distance of the piezoelectric film in the horizontal direction at the position of the lower end of the round bar is 9.5mm or less.
[2] The piezoelectric element according to [1], wherein,
The thickness of the adhesive layer for adhering the 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 sides of the piezoelectric layer, and a protective layer provided so as to cover the electrode layers.
[4] The piezoelectric element according to [3], wherein,
The thickness of the piezoelectric layer is 45 μm or more.
[5] The piezoelectric element according to [3] or [4], wherein,
The piezoelectric layer is a polymer composite piezoelectric body having piezoelectric particles in a polymer material.
[6] The piezoelectric element according to [5], wherein,
The polymer material has cyanoethyl groups.
[7] The piezoelectric element according to [6], wherein,
The high polymer material is cyanoethylated polyvinyl alcohol.
[8] The piezoelectric element according to any one of [1] to [7], which is a piezoelectric element in which a multilayer film is laminated by folding back 1 piezoelectric film.
[9] A piezoelectric speaker in which the piezoelectric element described in any one of [1] to [8] is attached to a vibrating plate having flexibility.
[10] The piezoelectric speaker of [9], wherein,
The vibration plate is a display device.
Effects of the invention
According to the present invention, in a piezoelectric element in which piezoelectric films are laminated, when the piezoelectric element is attached as an exciter to a diaphragm of a piezoelectric speaker using a diaphragm that can be wound, the piezoelectric speaker can be wound appropriately.
Drawings
Fig. 1 is a schematic view showing an example of a piezoelectric element according to the present invention.
Fig. 2 is a view schematically showing another example of the piezoelectric element of the present invention.
Fig. 3 schematically shows an example of a piezoelectric film used in the piezoelectric element of the present invention.
Fig. 4 is a conceptual diagram illustrating an example of a method for producing a piezoelectric film.
Fig. 5 is a conceptual diagram illustrating an example of a method for producing a piezoelectric film.
Fig. 6 is a conceptual diagram illustrating an example of a method for producing a piezoelectric film.
Fig. 7 is a conceptual diagram illustrating an example of the piezoelectric element of the present invention.
Fig. 8 schematically illustrates another example of the piezoelectric element of the present invention.
Fig. 9 schematically shows an example of a piezoelectric speaker according to the present invention.
Detailed Description
The piezoelectric element and the piezoelectric speaker according to the present invention will be described in detail below based on preferred embodiments shown in the drawings.
The following description of the constituent elements is sometimes made based on the representative embodiments of the present invention, but the present invention is not limited to these embodiments.
The drawings shown below are conceptual views for explaining the piezoelectric element and the piezoelectric speaker according to the present invention. Therefore, the size, thickness, shape, positional relationship, and the like of each member and each portion are different from those of an actual object.
In the present invention, the numerical range indicated by the term "to" means a range including the numerical values before and after the term "to" as the lower limit value and the upper limit value.
Further, in the present invention, the 1 st and 2 nd elements added to the electrode layer, the protective layer, and the like are 2 parts which are substantially identical for convenience of distinction, and the piezoelectric element and the piezoelectric speaker of the present invention will be described. Therefore, the 1 st and the 2 nd of these components are not technically significant, and are not related to the actual use state, the mutual positional relationship, and the like.
Fig. 1 schematically shows an example of the piezoelectric element of the present invention.
The piezoelectric element 10 shown in fig. 1 is formed by laminating a plurality of laminated films 12 by folding back a piezoelectric film 12 having flexibility in a bellows shape a plurality of times. In the piezoelectric film 12, the 1 st electrode layer 28 is provided on one surface of the piezoelectric layer 26, the 2 nd electrode layer 30 is provided on the other surface, the 1 st protective layer 32 is provided on the surface of the 1 st electrode layer 28, and the 2 nd protective layer 34 is provided on the surface of the 2 nd electrode layer 30.
In the piezoelectric element 10, the piezoelectric film 12 stacked and adjacent by folding back is attached by the attaching layer 20.
As will be described in detail later. In the piezoelectric element (laminated piezoelectric element) of the present invention, when the piezoelectric element is cut into a round bar having a radius of 2.5mm and a weight of 100g is applied to both sides of 20mm by cutting into 20×50mm, the distance between the piezoelectric elements in the horizontal direction at the position of the lower end of the round bar is 9.5mm or less.
By having such a structure, for example, in the case where the piezoelectric element 10 of the present invention is attached as an exciter to a diaphragm of a piezoelectric speaker using a diaphragm having flexibility, even when the piezoelectric speaker is wound with a winding core having a small diameter, it is possible to prevent occurrence of backlash of the wound piezoelectric speaker, a gap between winding layers which becomes a sign of backlash of the wound piezoelectric speaker, and the like.
This will be described in detail later.
The piezoelectric element 10 illustrated in the drawing is a piezoelectric element in which rectangular (oblong) piezoelectric films 12 are folded back 4 times at equal intervals to laminate 5 layers of piezoelectric films 12.
In the piezoelectric element 10 of the present invention, when the rectangular piezoelectric film 12 is folded back, the folded back line formed by folding back the piezoelectric film 12 may be aligned in the longitudinal direction or in the short direction in the planar shape of the piezoelectric element 10. The planar shape of the piezoelectric element 10 is a shape when the piezoelectric element 10 is viewed from the lamination direction of the piezoelectric films 12.
In the following description, a folded line formed by folding back the piezoelectric film 12, that is, a line at the top outside the end of the folded back portion is also referred to as a "ridge line" for convenience.
For example, when rectangular piezoelectric films of 25×20cm are folded back in the direction of 25cm at 5cm intervals 4 times, a piezoelectric element (see fig. 9) in which 5 layers of piezoelectric films are laminated, the rectangular shape of 5×20cm in plan view and the ridge lines coincide with 20cm in the longitudinal direction can be obtained. Further, when rectangular piezoelectric films of 100×5cm are folded back in the direction of 100cm at intervals of 20cm 4 times, a piezoelectric element having a rectangular shape of 5×20cm, in which the same planar shape is laminated with 5 layers of piezoelectric films, and the ridge lines coincide with 5cm in the short side direction can be obtained.
In addition, the piezoelectric element 10 shown in fig. 1 is preferably a piezoelectric element having a rectangular planar shape, which is produced by folding back a rectangular piezoelectric film 12. 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, a circle, a rounded rectangle (oblong), an ellipse, a hexagon, or the like is exemplified.
As described above, the piezoelectric element 10 is formed by folding back the film 12 a plurality of times and stacking it. The piezoelectric element 10 of the example of the drawing stacks 5 layers of piezoelectric films 12 by folding back the piezoelectric films 124 times. The laminated and adjacent piezoelectric films 12 are bonded by the adhesive layer 20.
The piezoelectric element 10 of the present invention stacks a plurality of piezoelectric films 12 in this way and attaches adjacent piezoelectric films 12, so that the stretching force as a piezoelectric element can be increased as compared with the case where 1 piezoelectric film is used. As a result, for example, a diaphragm described later can be bent with a large force, and a high-pitched sound can be output.
The piezoelectric element of the present invention is not limited to a structure in which 1 piezoelectric film 12 is folded back and laminated, and adjacent piezoelectric films 12 are bonded by the adhesive layer 20.
That is, as schematically shown in fig. 2, the piezoelectric element (laminated piezoelectric element) of the present invention may be configured such that a plurality of piezoelectric films 12 in a cut sheet form (sheet-by-sheet form) are laminated, and adjacent piezoelectric films 12 are bonded by the adhesive layer 20.
As in the piezoelectric element 10 illustrated in the drawing, by folding back 1 piezoelectric film 12 to laminate the piezoelectric films 12, although a plurality of piezoelectric films 12 are laminated, the extraction of the electrode for driving the piezoelectric film 12, that is, the extraction of the electrode for driving the piezoelectric element 10 can be set at 1 in each electrode layer described later. As a result, the piezoelectric element 10 stacked by folding back 1 piezoelectric film 12 can simplify the structure and wiring of the electrodes, and further, the productivity is also excellent.
In addition, since 1 piezoelectric film 12 is folded back and laminated in this piezoelectric element 10, electrode layers facing each other by lamination of adjacent piezoelectric films have the same polarity. As a result, the piezoelectric element 10 is advantageous from the standpoint that no short circuit occurs even when 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 5 layers in the example of the figure. That is, the piezoelectric element 10 of the present invention may be formed by folding the piezoelectric film 12 3 times or less to laminate 4 layers or less of the piezoelectric film 12, or may be formed by folding the piezoelectric film 12 5 times or more to laminate 6 layers or more of the piezoelectric film 12.
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 even more preferably 4 to 6 layers.
In this regard, the structure of laminating the cut sheet-like piezoelectric film 12 shown in fig. 2 is also the same.
In the piezoelectric element 10 of the present invention, as the number of layers of the piezoelectric film 12 increases, the output as the piezoelectric element increases, and for example, when the piezoelectric element is used as an exciter of a piezoelectric speaker, a high sound pressure can be output. In contrast, the smaller the number of layers, for example, the more advantageous the winding of a piezoelectric speaker to be described later.
Accordingly, the number of layers of the piezoelectric film 12 in the piezoelectric element 10 of the present invention may be appropriately set according to the degree of firmness of the bonded diaphragm, the size of the bonded diaphragm, the bonding position to the diaphragm, the firmness of the piezoelectric film 12, the dimension in the piezoelectric film surface direction of the piezoelectric element 10, the required output (power) of the piezoelectric element 10, the required winding property, the winding core diameter, the amount of power used for winding, and the required thickness limitation.
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.
By attaching the piezoelectric films 12 adjacent to each other in the stacking direction through the adhesive layer 20, the expansion and contraction of each piezoelectric film 12 can be directly transmitted, and the piezoelectric film 12 can be driven without waste as a stacked body in which the piezoelectric films 12 are stacked.
In the present invention, as long as the adjacent piezoelectric film 12 can be adhered, various known adhesives (adhesive materials) can be used for the adhesive layer 20.
Accordingly, the adhesive layer 20 may be a layer made of an adhesive (adhesive material), or a layer made of a material having characteristics of both an adhesive and an adhesive. The adhesive means an adhesive agent which has fluidity at the time of bonding and becomes a solid. The adhesive is a soft solid in the form of gel (rubber-like) at the time of bonding, and the gel state does not change.
The adhesive layer 20 may be formed by applying a flowable adhesive such as a liquid, or may be formed by using a sheet-like adhesive.
The piezoelectric element 10 is used as an exciter, for example. That is, in the piezoelectric element 10, the laminated plurality of piezoelectric films 12 are stretched to expand and contract themselves, and for example, the vibration plate 62 is bent and vibrated as described later to generate sound. Therefore, in the piezoelectric element 10, the expansion and contraction of each of the laminated piezoelectric films 12 is preferably directly transmitted. If a viscous substance such as a vibration damping substance is present between the piezoelectric films 12, the transmission efficiency of the expansion and contraction energy of the piezoelectric films 12 is lowered, and the driving efficiency of the piezoelectric element 10 is lowered.
In view of this, the adhesive layer 20 is preferably an adhesive layer composed of an adhesive, and the adhesive layer can obtain a solid and hard adhesive layer 20 as compared with an adhesive layer composed of an adhesive. More preferably, the adhesive layer 20 is preferably formed of a thermoplastic type adhesive such as a polyester type adhesive and a styrene-butadiene rubber (SBR) type adhesive.
Bonding is useful when a high bonding temperature is required, unlike bonding. In addition, thermoplastic type adhesives are preferred because they combine "relatively low temperature, short time, and strong adhesion".
In the piezoelectric element 10, the thickness of the adhesive layer 20 is not limited, and the thickness capable of exhibiting a sufficient adhesive force may be appropriately set according to the material forming the adhesive layer 20.
In the piezoelectric element 10, the thinner the adhesive layer 20 is, the more the transmission effect of the expansion and contraction energy (vibration energy) of the piezoelectric layer 26 is improved, and the energy efficiency can be improved. In addition, if the adhesive layer 20 is thick and has high rigidity, the expansion and contraction of the piezoelectric film 12 may be restricted.
In view of this, the adhesive layer 20 is preferably 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 is 0.1 to 50 μm, more preferably 0.1 to 30 μm, still more preferably 0.1 to 10 μm in terms of the thickness after the adhesion.
In particular, from the viewpoint that the distance D (horizontal direction distance D) shown in fig. 7 described later can be appropriately set to 9.5mm or less, the thickness of the adhesive layer 20 is preferably 10 μm or less, more preferably 5 μm or less in terms of the thickness after adhesion.
In the piezoelectric element of the present invention, any known piezoelectric film 12 can be used as long as the piezoelectric film 12 has flexibility and can be bent and stretched.
In the present invention, the term "flexible" means capable of bending and flexing as commonly interpreted as having flexibility, and specifically, capable of bending and stretching without breaking or damaging.
In the piezoelectric element 10 of the present invention, the piezoelectric film 12 preferably includes electrode layers provided on both sides of the piezoelectric layer 26 and a protective layer provided to cover the electrode layers.
Fig. 3 schematically shows an example of the piezoelectric film 12 in a cross-sectional view. In fig. 3 and the like, hatching will be omitted in order to simplify the drawings to clearly show the structure.
In the following description, unless otherwise specified, the "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 example of the drawing includes a piezoelectric layer 26, a1 st electrode layer 28 laminated on one surface of the piezoelectric layer 26, a1 st protective layer 32 laminated on the 1 st electrode layer 28, a2 nd electrode layer 30 laminated on the other surface of the piezoelectric layer 26, and a2 nd protective layer 34 laminated on the 2 nd electrode layer 30.
As described above, the piezoelectric element 10 of the present invention stacks the piezoelectric film 12 by folding back 1 piezoelectric film 12.
Therefore, even if a plurality of piezoelectric films 12 are stacked, the electrode for driving the piezoelectric element 10, that is, the electrode for driving the piezoelectric film 12 can be drawn out at one place in each electrode layer described later. As a result, the structure of the piezoelectric element 10 and the electrode wiring can be simplified, and further, the productivity is also excellent. In addition, since 1 piezoelectric film 12 is folded and laminated, electrode layers facing each other through lamination of adjacent piezoelectric films have the same polarity, and thus short-circuiting does not occur 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, the polymer composite piezoelectric body (piezoelectric layer 26) preferably has the following requirements. In the present invention, the normal temperature is 0 to 50 ℃.
(I) Flexibility of
For example, when a portable article such as a newspaper or a magazine is held in a gently curved state like a document, a relatively slow and large bending deformation of several Hz or less is continuously applied from the outside. At this time, when the polymer composite piezoelectric body is hard, a corresponding large bending stress is generated, and cracks are generated at the interface between the polymer matrix and the piezoelectric body particles, and as a result, the breakage may occur. Therefore, the polymer composite piezoelectric body is required to have appropriate flexibility. Further, if strain energy can be diffused as heat to the outside, stress can be relaxed. Therefore, the loss tangent of the polymer composite piezoelectric body is required to be appropriately large.
(Ii) Sound quality
The speaker vibrates the piezoelectric particles at a frequency in the audio frequency band of 20Hz to 20kHz, and the entire diaphragm (polymer composite piezoelectric body) is vibrated by the vibration energy, thereby reproducing sound. Therefore, in order to improve the efficiency of vibration energy transmission, the polymer composite piezoelectric body is required to have an appropriate hardness. Further, if the frequency characteristic of the speaker is smooth, the amount of change in sound quality when the lowest resonance frequency f 0 changes with a change in curvature also becomes small. Therefore, the loss tangent of the polymer composite piezoelectric body is required to be appropriately large.
As is well known, the lowest resonance frequency f 0 of the speaker diaphragm is given by the following formula. Here, s is the stiffness of the vibration system and m is the mass.
[ Number 1]
Lowest resonance frequency
At this time, the mechanical rigidity s decreases as the degree of bending of the piezoelectric film, that is, the radius of curvature of the bending portion increases, and therefore the lowest resonance frequency f 0 decreases. That is, the sound quality (volume, frequency characteristics) of the speaker varies according to the radius of curvature of the piezoelectric film.
As described above, the polymer composite piezoelectric body is required to operate relatively hard against vibrations of 20Hz to 20kHz and to operate relatively soft against vibrations of several Hz or less. In addition, the loss tangent of the polymer composite piezoelectric body is required to be appropriately large for vibrations at all frequencies of 20kHz or less.
In general, a polymer solid has a viscoelastic relaxation mechanism, and large-scale molecular motion is observed as a decrease (relaxation) in storage modulus (young's modulus) or an maximization (absorption) of loss elastic modulus with an increase in temperature or a decrease in frequency. Among them, alleviation caused by Micro Brownian (Micro Brownian) motion of molecular chains of amorphous regions is called primary dispersion, and a very large alleviation phenomenon can be observed. The temperature at which this primary dispersion occurs is the glass transition point (Tg), and the viscoelastic mitigation mechanism appears most pronounced.
In the polymer composite piezoelectric body (piezoelectric layer 26), a polymer material having a glass transition point at normal temperature, in other words, a polymer material having viscoelasticity at normal temperature is used in the matrix, whereby the polymer composite piezoelectric body is realized which operates relatively hard against vibrations of 20Hz to 20kHz and operates relatively soft against slow vibrations of several Hz or less. In particular, from the viewpoint of preferably exhibiting such an action, a polymer material having a glass transition point Tg at a frequency of 1Hz at room temperature is preferably used in the matrix of the polymer composite piezoelectric body.
The maximum value of the loss tangent Tan δ at a frequency of 1Hz based on the dynamic viscoelasticity test is preferably 0.5 or more at normal temperature of the polymer material serving as the polymer matrix 38.
Accordingly, when the polymer composite piezoelectric body is gently bent by an external force, stress concentration at the interface between the polymer matrix and the piezoelectric body particles in the maximum bending moment portion is relaxed, and high flexibility can be expected.
In addition, in the polymer material to be the polymer matrix 38, the storage modulus (E') at a frequency of 1Hz, which is measured based on dynamic viscoelasticity, is preferably 100MPa or more at 0℃and 10MPa or less at 50 ℃.
This can reduce bending moment generated when the polymer composite piezoelectric body is slowly bent by an external force, and can operate harder against acoustic vibrations of 20Hz to 20 kHz.
Further, it is more preferable that the polymer material to be the polymer matrix 38 has a relative dielectric constant of 10 or more at 25 ℃. Accordingly, when a voltage is applied to the polymer composite piezoelectric material, a higher electric field is required for the piezoelectric particles in the polymer matrix, and thus a larger deformation amount can be expected.
However, on the other hand, if it is considered to ensure good moisture resistance or the like, it is also preferable that the relative dielectric constant of the polymer material is 10 or less at 25 ℃.
As the polymer material satisfying these conditions, cyanoethylated polyvinyl alcohol (cyanoethylated PVA), polyvinyl acetate, polyvinylidene chloride acrylonitrile, polystyrene-vinyl polyisoprene block copolymer, polyvinyl methyl ketone, polybutylmethacrylate, and the like are preferably exemplified.
Further, commercial products such as HYBRAR5127 (KURARAY co., LTD) can be suitably used as the polymer material.
As the polymer material constituting the polymer matrix 38, a polymer material having cyanoethyl groups is preferably used, and cyanoethylated PVA is particularly preferably used. That is, in the piezoelectric film 12, the piezoelectric layer 26 is preferably made of a polymer material having cyanoethyl groups, and cyanoethylated PVA is particularly preferably used as the polymer matrix 38.
In the following description, the above polymer materials represented by cyanoethylated PVA are also collectively referred to as "polymer materials having viscoelasticity at ordinary temperature".
In addition, only 1 kind of these polymer materials having viscoelasticity at normal temperature may be used, or a plurality of kinds may be used in combination (mixture).
In the piezoelectric film 12, the polymer matrix 38 of the piezoelectric layer 26 may be made of a plurality of polymer materials in combination as needed.
That is, in order to adjust the dielectric properties, mechanical properties, and the like, other dielectric polymer materials may be added to the polymer matrix 38 constituting the polymer composite piezoelectric body as needed, in addition to the polymer materials having viscoelasticity at the above-described normal temperature.
Examples of the dielectric polymer material that can be added include fluorine-based polymers such as polyvinylidene fluoride, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, polyvinylidene fluoride-trifluoroethylene copolymer, and polyvinylidene fluoride-tetrafluoroethylene copolymer, polymers having cyano groups or cyano groups such as vinylidene fluoride-vinyl ester copolymer, cyanoethyl cellulose, cyanoethyl hydroxy sucrose, cyanoethyl hydroxy cellulose, cyanoethyl hydroxy fullerene, cyanoethyl methacrylate, cyanoethyl acrylate, cyanoethyl hydroxyethyl cellulose, cyanoethyl amylose, cyanoethyl hydroxypropyl cellulose, cyanoethyl dihydroxypropyl cellulose, cyanoethyl hydroxypropyl amylose, cyanoethyl polyacrylamide, cyanoethyl polyethyl polyacrylate, cyanoethyl fullerene, cyanoethyl polyhydroxymethylene, cyanoethyl glycidyl fullerene, cyanoethyl sucrose and cyanoethyl sorbitol, and synthetic rubbers such as nitrile rubber and chloroprene rubber.
Among them, a polymer material having cyanoethyl groups can be preferably used.
The number of these dielectric polymer materials is not limited to 1, and a plurality of dielectric polymer materials may be added to the polymer matrix 38 of the piezoelectric layer 26.
In addition, in order to adjust the glass transition point Tg of the polymer matrix 38, a thermoplastic resin such as a vinyl chloride resin, polyethylene, polystyrene, methacrylic resin, polybutylene, and isobutylene, a thermosetting resin such as a phenol resin, a urea resin, a melamine resin, an alkyd resin, and mica, and the like may be added in addition to the dielectric polymer material.
Further, for the purpose of improving the adhesiveness, a tackifier such as rosin ester, rosin, terpenes, terpene phenol, and petroleum resin may be added.
The amount of polymer material other than the polymer material having viscoelasticity at ordinary temperature added to the polymer matrix 38 of the piezoelectric layer 26 is not limited, and the ratio of the polymer matrix 38 is preferably 30 mass% or less.
As a result, the characteristics of the polymer material to be added can be expressed without impairing the viscoelastic relaxation mechanism in the polymer matrix 38, and therefore preferable results can be obtained in terms of improvement of dielectric constant, heat resistance, adhesion to the piezoelectric particles 40 or the electrode layer, and the like.
The polymer composite piezoelectric material serving as the piezoelectric layer 26 contains piezoelectric particles 40 in such a polymer matrix. The piezoelectric particles 40 are dispersed in the polymer matrix, preferably uniformly (substantially uniformly) dispersed.
The piezoelectric particles 40 are preferably piezoelectric particles composed of ceramic particles having a perovskite-type or wurtzite-type crystal structure.
Examples of ceramic particles constituting the piezoelectric particles 40 include lead zirconate titanate (PZT), lead lanthanum zirconate titanate (PLZT), barium titanate (BaTiO 3), zinc oxide (ZnO), and solid solutions (BFBT) of barium titanate and bismuth ferrite (BiFe 3).
The particle diameter of the piezoelectric particles 40 may be appropriately selected according to the size and use of the piezoelectric film 12. The particle diameter of the piezoelectric particles 40 is preferably 1 to 10. Mu.m.
By setting the particle diameter of the piezoelectric particles 40 in the above range, preferable results can be obtained in terms of both high-voltage characteristics and flexibility.
In the piezoelectric film 12, the amount ratio of the polymer matrix 38 to the piezoelectric particles 40 in the piezoelectric layer 26 may be appropriately set according to the size and thickness of the piezoelectric film 12 in the plane direction, the use of the piezoelectric film 12, the characteristics required in the piezoelectric film 12, and the like.
The volume fraction of the piezoelectric particles 40 in the piezoelectric layer 26 is preferably 30 to 80%, more preferably 50 to 80%.
When the amount ratio of the polymer matrix 38 to the piezoelectric particles 40 is within the above range, preferable results can be obtained in terms of both high-voltage characteristics and flexibility.
In the piezoelectric film 12, the thickness of the piezoelectric layer 26 is not limited, and may be appropriately set according to the size of the piezoelectric film 12, the use of the piezoelectric film 12, the characteristics required for the piezoelectric film 12, and the like.
The thickness of the piezoelectric layer 26 is preferably 8 to 300. Mu.m, more preferably 8 to 200. Mu.m, still more preferably 10 to 150. Mu.m, particularly preferably 15 to 100. Mu.m.
By setting the thickness of the piezoelectric layer 26 within the above range, preferable results can be obtained in terms of both securing rigidity and appropriate flexibility.
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.
The piezoelectric element 10 having a thickness of 45 μm or more is preferable from the viewpoints of stably obtaining a high output (strong expansion/contraction force), reducing the thickness of the piezoelectric element by reducing the number of layers of the piezoelectric film 12, and suppressing the power consumption at the time of driving the piezoelectric element.
In this regard, the same applies 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, the thickness of the piezoelectric layer 26 is preferably 45 μm or more, so that the above advantage can be obtained and sufficient flexibility of the piezoelectric film 12 can be ensured.
The piezoelectric layer 26 is preferably polarized in the thickness direction (polarization). The polarization process will be described in detail later.
In the piezoelectric film 12, the piezoelectric layer 26 is not limited to the polymer composite piezoelectric body including the piezoelectric particles 40 in the polymer matrix 38 made of a polymer material having viscoelasticity at normal temperature, such as cyanoethylated PVA, as described above.
That is, various known materials can be used for the piezoelectric layer in the piezoelectric film 12.
As an example, a polymer composite piezoelectric material including the same piezoelectric particles 40, a piezoelectric layer made of polyvinylidene fluoride, a piezoelectric layer made of a fluororesin other than polyvinylidene fluoride, a piezoelectric layer formed of a thin film made of poly-L-lactic acid, and a thin film made of poly-D-lactic acid, or the like can be used in a matrix including the dielectric polymer materials such as polyvinylidene fluoride, vinylidene chloride-tetrafluoroethylene copolymer, and vinylidene chloride-trifluoroethylene copolymer.
However, as described above, from the viewpoints that the polymer matrix 38 made of a polymer material having viscoelasticity at normal temperature, such as cyanoethylated PVA, is hard to operate at vibrations of 20Hz to 20kHz, soft to operate at vibrations of several Hz or less, and excellent acoustic characteristics and flexibility are obtained, it is preferable to use a polymer composite piezoelectric body including piezoelectric particles 40.
The piezoelectric film 12 shown in fig. 3 has a structure in which the 2 nd electrode layer 30 is provided on one surface of the piezoelectric layer 26, the 2 nd protective layer 34 is provided on the surface of the 2 nd electrode layer 30, the 1 st electrode layer 28 is provided on the other surface of the piezoelectric layer 26, and the 1 st protective layer 32 is provided on the surface of the 1 st electrode layer 28. In the piezoelectric film 12, the 1 st electrode layer 28 and the 2 nd electrode layer 30 form an electrode pair.
In other words, the laminated film constituting the piezoelectric film 12 has a structure in which the piezoelectric layer 26 is sandwiched between the 1 st electrode layer 28 and the 2 nd electrode layer 30, which are electrode pairs, and further sandwiched between the 1 st protective layer 32 and the 2 nd protective layer 34.
In this way, the region sandwiched between the 1 st electrode layer 28 and the 2 nd electrode layer 30 is driven according to the applied voltage.
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, in addition to these layers.
The adhesive may be an adhesive or an adhesive. The adhesive may be preferably the same as the polymer matrix 38, which is a polymer material from which the piezoelectric particles 40 are removed from the piezoelectric layer 26. The adhesive layer may be provided on both the 1 st electrode layer 28 side and the 2 nd electrode layer 30 side, or may be provided on only one of the 1 st electrode layer 28 side and the 2 nd electrode layer 30 side.
In the piezoelectric film 12, the 1 st protective layer 32 and the 2 nd protective layer 34 cover the 1 st electrode layer 28 and the 2 nd electrode layer 30, and also function 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 may exhibit very excellent flexibility against slow bending deformation, but may have insufficient rigidity or mechanical strength depending on the application. The 1 st protective layer 32 and the 2 nd protective layer 34 are provided in the piezoelectric film 12 to compensate for this.
The 1 st protective layer 32 and the 2 nd protective layer 34 are identical in structure with only different arrangement positions. Therefore, in the following description, the two members are also collectively referred to as a protective layer without the need to distinguish between the 1 st protective layer 32 and the 2 nd protective layer 34.
The protective layer is not limited, and various kinds of sheet-like materials can be used, and as an example, various kinds of resin films are preferably exemplified. Among them, for the reason of having excellent mechanical properties, heat resistance, and the like, resin films composed of polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS), polycarbonate (PC), polyphenylene Sulfide (PPs), polymethyl methacrylate (PMMA), polyetherimide (PEI), polyimide (PI), polyamide (PA), polyethylene naphthalate (PEN), triacetyl cellulose (TAC), a cycloolefin resin, and the like are preferably used.
The thickness of the protective layer is not limited. The 1 st protective layer 32 and the 2 nd protective layer 34 have substantially the same thickness, 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 but also the flexibility is impaired. Therefore, in addition to the case where mechanical strength or good handleability as a sheet is required, the thinner the protective layer is, the more advantageous.
When the thickness of the 1 st protective layer 32 and the 2 nd protective layer 34 is 2 times or less the thickness of the piezoelectric layer 26, preferable results can be obtained in terms of securing rigidity and appropriate flexibility.
For example, when the thickness of the piezoelectric layer 26 is 50 μm and the 1 st protective layer 32 and the 2 nd protective layer 34 are made of PET, the thickness of each of the 1 st protective layer 32 and the 2 nd protective layer 34 is preferably 100 μm or less, more preferably 50 μm or less, and still more preferably 25 μm or less.
In the present invention, the 1 st protective layer 32 and the 2 nd protective layer 34 are preferably used, and are not essential. Thus, the piezoelectric film 12 may have only the 1 st protective layer 32, may have only the 2 nd protective layer 34, or may have no protective layer.
However, in consideration of the mechanical strength of the piezoelectric film 12, the protection of the electrode layers, and the like, the piezoelectric film preferably has at least 1 protective layer, and more preferably has 2 protective layers so as to cover two electrode layers, as in the illustrated example.
In the piezoelectric film 12, the 1 st electrode layer 28 is provided between the piezoelectric layer 26 and the 1 st protective layer 32, and the 2 nd electrode layer 30 is provided between the piezoelectric layer 26 and the 2 nd protective layer 34. The 1 st electrode layer 28 and the 2 nd electrode layer 30 are used to apply 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 1 st electrode layer 28 and the 2 nd electrode layer 30 are substantially identical except for their positions. Therefore, in the following description, the two members are also collectively referred to as electrode layers without the need to distinguish between the 1 st electrode layer 28 and the 2 nd electrode layer 30.
In the piezoelectric film, the material for forming the electrode layer is not limited, and various electric conductors can be used. Specifically, examples of the conductive polymer include carbon, palladium, iron, tin, aluminum, nickel, platinum, gold, silver, copper, chromium, molybdenum, an alloy of these, indium tin oxide, and PEDOT/PPS (polyethylene dioxythiophene-polystyrene sulfonic acid).
Among them, copper, aluminum, gold, silver, platinum, and indium tin oxide are preferably exemplified. Among them, copper is more preferable from the viewpoints of conductivity, cost, flexibility, and the like.
The method for forming the electrode layer is not limited, and various known methods such as a vapor deposition method (vacuum film forming method) such as vacuum vapor deposition and sputtering, a method of forming a film by electroplating, a method of adhering a foil made of the above materials, and a method of coating can be used.
Among them, for the reason that flexibility of the piezoelectric film 12 can be ensured, a thin film of copper and aluminum formed by vacuum deposition is particularly preferably used as the electrode layer. Among them, a thin film of copper formed by vacuum evaporation is particularly preferably used.
The thicknesses of the 1 st electrode layer 28 and the 2 nd electrode layer 30 are not limited. The thicknesses of the 1 st electrode 28 and the 2 nd electrode 30 are substantially the same, but may be different.
However, if the rigidity of the electrode layer is too high, the flexibility is impaired as well as the expansion and contraction of the piezoelectric layer 26 is restricted as in the case of the protective layer. Therefore, as long as the resistance does not become excessively high, it is more advantageous that the electrode layer is thinner.
In the piezoelectric film 12, the product of the thickness of the electrode layer and the young's modulus is preferably lower than the product of the thickness of the protective layer and the young's modulus, since flexibility is not seriously impaired.
For example, the case where the 1 st protective layer 32 and the 2 nd protective layer 34 are PET and the 1 st electrode layer 28 and the 2 nd electrode layer 30 are copper is illustrated. At this time, PET has a Young's modulus of about 6.2GPa, and copper has a Young's modulus of about 130GPa. Therefore, when the thickness of the protective layer is 25 μm, the thickness of the electrode layer is preferably 1.2 μm or less, more preferably 0.3 μm or less, and among these, is preferably 0.1 μm or less.
The piezoelectric film 12 has a structure in which the 1 st electrode layer 28 and the 2 nd electrode layer 30 sandwich the piezoelectric layer 26, and further, the 1 st protective layer 32 and the 2 nd protective layer 34 sandwich the laminate.
In the piezoelectric film 12, the loss tangent (Tan δ) at a frequency of 1Hz, which is measured based on dynamic viscoelasticity, is preferably a maximum value of 0.1 or more, and is preferably present at normal temperature.
Accordingly, even when the piezoelectric film 12 receives relatively slow and large bending deformation of several Hz or less from the outside, strain energy can be efficiently diffused to the outside as heat, and thus occurrence of cracks at the interface between the polymer matrix and the piezoelectric particles can be prevented.
In the piezoelectric film 12, the storage modulus (E') at a frequency of 1Hz, which is measured based on dynamic viscoelasticity, is preferably 10 to 30GPa at 0℃and 1 to 10GPa at 50 ℃.
Thus, the piezoelectric film 12 can have a large frequency dispersion in the storage modulus (E') at normal temperature. That is, the vibration damper can operate relatively hard against vibrations of 20Hz to 20kHz and relatively soft against vibrations of several Hz or less.
In addition, in the piezoelectric film 12, the product of the thickness and the storage modulus (E') at a frequency of 1Hz based on dynamic viscoelasticity measurement is preferably 1.0X10 6～2.0×106 N/m at 0℃and 1.0X10 5～1.0×106 N/m at 50 ℃.
Thus, the piezoelectric film 12 can have appropriate rigidity and mechanical strength without impairing flexibility and acoustic characteristics.
Further, in the piezoelectric film 12, in the main curve obtained by dynamic viscoelasticity measurement, the loss tangent (Tan δ) at a frequency of 1kHz at 25 ℃ is preferably 0.05 or more.
An example of a method for producing the piezoelectric film 12 will be described below with reference to fig. 4 to 6.
First, a sheet 42b having the 2 nd electrode layer 30 formed on the surface of the 2 nd protective layer 34 schematically shown in fig. 4 is prepared. Further, a sheet 42a having the 1 st electrode layer 28 formed on the surface of the 1 st protective layer 32 schematically shown in fig. 6 is prepared.
The sheet 42b can be produced by forming a copper thin film or the like as the 2 nd electrode layer 30 on the surface of the 2 nd protective layer 34 by vacuum evaporation, sputtering, plating, or the like. Similarly, the sheet 42a can be produced by forming a copper thin film or the like as the 1 st electrode layer 28 on the surface of the 1 st protective layer 32 by vacuum evaporation, sputtering, plating, or the like.
Alternatively, a commercially available sheet in which a copper film or the like is formed on the protective layer may be used as the sheet 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 extremely thin and the operability is poor, etc., a protective layer with a separator (temporary support) may be used as needed. Further, PET having a thickness of 25 to 100 μm or the like can be used as the separator. The separator may be removed after the thermocompression bonding of the electrode layer and the protective layer.
Next, as schematically shown in fig. 5, the piezoelectric layer 26 is formed on the 2 nd electrode layer 30 of the sheet 42b, and a laminate 46 is produced in which the sheet 42b and the piezoelectric layer 26 are laminated.
The piezoelectric layer 26 may be formed by a known method for the piezoelectric layer 26.
For example, as shown in fig. 3, if a piezoelectric layer (polymer composite piezoelectric layer) in which piezoelectric particles 40 are dispersed in a polymer matrix 38 is used, the following method is used as an example.
First, the above-mentioned polymer material such as cyanoethylated PVA is dissolved in an organic solvent, and piezoelectric particles 40 such as PZT particles are added thereto, followed by stirring to prepare a paint. The organic solvent is not limited, and various organic solvents such as Dimethylformamide (DMF), methyl ethyl ketone, and cyclohexanone can be used.
After the sheet 42b is prepared and the dope is prepared, the dope is cast (coated) on the sheet 42b, and the organic solvent is evaporated and dried. As a result, as shown in fig. 5, a laminate 46 is produced in which the 2 nd electrode layer 30 is provided on the 2 nd protective layer 34, and the piezoelectric layer 26 is laminated on the 2 nd electrode layer 30.
The method of casting the paint is not limited, and any known method (coating apparatus) such as a bar coater, a bevel blade coater (slidecoater), and a coater blade (doctorknife) can be used.
Alternatively, if the polymer material is a substance that can be melted by heating, a melt in which the piezoelectric particles 40 are added can be produced by melting the polymer material by heating, and the laminate 46 shown in fig. 5 can be produced by extruding the melt in a sheet form onto the sheet 42b shown in fig. 4 by extrusion molding or the like and cooling the extruded melt.
As described above, in addition to the polymer material having viscoelasticity at normal temperature, a polymer piezoelectric material such as PVDF may be added to the polymer matrix 38 in the piezoelectric layer 26.
When these polymer piezoelectric materials are added to the polymer matrix 38, the polymer piezoelectric materials added to the paint may be dissolved. Alternatively, the polymer piezoelectric material to be added may be added to the polymer material which is melted by heating and has viscoelasticity at ordinary temperature, and the polymer piezoelectric material may be melted by heating.
After the piezoelectric layer 26 is formed, a rolling treatment may be performed as needed. The rolling treatment may be performed 1 time or a plurality of times.
As is well known, the rolling treatment is a treatment of heating a surface to be treated by hot pressing, a heating roller, a pair of heating rollers, or the like, and simultaneously pressing to perform flattening or the like.
The piezoelectric layer 26 of the laminate 46 having the 2 nd electrode layer 30 on the 2 nd protective layer 34 and the piezoelectric layer 26 formed on the 2 nd electrode layer 30 is subjected to polarization treatment (polarization).
The method of polarizing the piezoelectric layer 26 is not limited, and a known method can be used. For example, electric field polarization in which a direct electric field is directly applied to an object to be subjected to polarization processing is exemplified. In the case of performing the electric field polarization treatment, the 1 st electrode layer 28 may be formed before the polarization treatment, and the electric field polarization treatment may be performed using the 1 st electrode layer 28 and the 2 nd electrode layer 30.
In addition, in manufacturing the piezoelectric film 12, the polarization treatment is preferably performed in the thickness direction, not in the plane direction of the piezoelectric layer 26.
Next, as schematically shown in fig. 6, the 1 st electrode layer 28 is laminated on the piezoelectric layer 26 side of the piezoelectric laminate 46 with the laminated body 42a prepared in advance facing the piezoelectric layer 26.
Further, the laminated body is sandwiched between the 1 st protective layer 32 and the 2 nd protective layer 34, and thermocompression bonding is performed using a hot press apparatus, a heating roller, or the like, so that the laminated body 46 is bonded to the sheet 42a.
Thus, the piezoelectric film 12 including the piezoelectric layer 26, the 1 st and 2 nd electrode layers 28 and 30 provided on both sides of the piezoelectric layer 26, and the 1 st and 2 nd protective layers 32 and 34 formed on the surfaces of the electrode layers was produced.
By polarizing the piezoelectric film 12 made in this way only in the thickness direction, not in the plane direction, and even if the stretching treatment is not performed after the polarizing treatment, a high piezoelectric characteristic can be obtained. Therefore, the piezoelectric film 12 does not have in-plane anisotropy in piezoelectric characteristics, and expands and contracts isotropically in all directions in the plane direction when a driving voltage is applied.
As described above, the piezoelectric element 10 is formed by laminating a plurality of layers by folding back the piezoelectric films 12, and attaching the laminated and adjacent piezoelectric films 12 to each other through the adhesive layer 20. Or as shown in fig. 2, a plurality of piezoelectric films 12 in the form of cut sheets are laminated, and the laminated and adjacent piezoelectric films 12 are adhered to each other by an adhesive layer 20.
As schematically shown in fig. 7, in the piezoelectric element 10 of the present invention, the distance D of the piezoelectric element 10 in the horizontal direction at the position of the lower end portion of the round bar 52 when the round bar 52 having a radius of 2.5mm is suspended by applying 100g of the weight 54 to the sides of 20mm cut into 20×50 mm.
With this configuration, the piezoelectric element 10 of the present invention can realize a piezoelectric speaker that can be properly wound without causing a backlash or a gap between winding layers that is a sign of backlash, for example, in a case where the piezoelectric speaker is attached as an exciter to a flexible and winding-able diaphragm, in a piezoelectric speaker having a diaphragm and an exciter attached to the diaphragm.
As described above, the flexible speaker can be realized by attaching the flexible exciter to the flexible diaphragm.
The piezoelectric element (laminated piezoelectric element) 10, in particular, the piezoelectric element 10 in which the piezoelectric film 12 using the polymer composite piezoelectric body as the piezoelectric body layer is laminated with excellent flexibility by laminating the piezoelectric film 12 and adhering with the adhesive layer 20. Therefore, by using a coiled diaphragm, a coiled piezoelectric speaker can be realized.
As a winding method of a piezoelectric speaker capable of winding, for example, a method of winding a vibrating plate and a laminated piezoelectric element by providing a winding core at an end portion of the vibrating plate and rotating the winding core with power is illustrated.
In addition, regarding the winding of such a piezoelectric speaker, it is preferable to properly wind with a small force on a winding core of a small diameter.
However, in the conventional piezoelectric speaker using a piezoelectric element, even when a diaphragm having a sufficiently high flexibility is used, for example, the following may be used: the piezoelectric speaker wound by the diameter of the winding core is wound back and/or a gap between winding layers, which is a sign of the winding back, is generated, and thus satisfactory winding cannot be performed sufficiently. In the following description, for convenience, the rewinding of the piezoelectric speaker and/or the generation of a gap between winding layers is also referred to as "winding disorder".
That is, even when the diaphragm is sufficiently flexible and wound in a state where no winding disturbance occurs, the rigidity of the diaphragm overlaps the rigidity of the piezoelectric element at the adhesion portion of the diaphragm to the piezoelectric element. Therefore, the following is caused in this portion: the winding of the piezoelectric speaker is hindered, and the force that tries to restore the wound piezoelectric speaker to the original state is increased. As a result, for example, when the winding core of the piezoelectric speaker is small in diameter, the piezoelectric speaker cannot be wound appropriately, which results in disturbance of winding of the piezoelectric speaker.
On the other hand, as shown in fig. 7, in the piezoelectric element 10 of the present invention, the distance D of the piezoelectric element 10 in the horizontal direction at the position of the lower end portion of the round bar 52 when the round bar 52 having a radius of 2.5mm is hung by applying 100g of the weight 54 to the sides of 20mm cut into 20×50 mm.
In the following description, this distance D is also referred to as "horizontal direction distance D" for convenience.
The piezoelectric element 10 of the present invention can perform appropriate winding without causing winding disturbance with a small force even when the winding diameter is small. Therefore, according to the piezoelectric element 10 of the present invention, for example, when the piezoelectric element is attached as an exciter to a coiled diaphragm, a piezoelectric speaker that can be suitably coiled without causing any disturbance in the coiling can be realized.
In the piezoelectric element 10 of the present invention, the measurement of the horizontal distance D is performed after the piezoelectric element 10 to be measured is left for 24 hours or more in an environment where the temperature is 23±3 ℃ and the humidity is 65±20%rh.
In addition, the placement in this environment is performed after the piezoelectric element 10 to be measured is cut into 20×50 mm. The piezoelectric element 10 is cut so that the 20×50mm piezoelectric element is not included in the folded portion (ridge line) of the piezoelectric film 12. Further, the time of mounting the weight 54 is not limited, and is preferably performed in this environment after being placed in this environment.
Further, the measurement of the horizontal distance D is performed at a time point of 10 to 60 seconds after the piezoelectric element 10 to which the weight 54 is attached is suspended from the round bar 52.
The piezoelectric element 10 to which the weight 54 is attached is suspended from the round bar 52 so that the positions of the 2 weights 54 become the same height in the vertical direction. That is, the measurement of the horizontal direction distance D is performed in a state where the heights of the 2 weights 54 in the vertical direction are equal. In other words, the measurement of the horizontal distance D is performed in a state in which the direction of 50cm suspended from the piezoelectric element 10 is halved by the round bar 52.
As described above, in the piezoelectric element 10 of the present invention, as shown in fig. 7, the distance D (horizontal distance D) of the piezoelectric element 10 in the horizontal direction at the position of the lower end portion of the round bar 52 when the weight 54 having a weight of 100g is applied to the sides of 20mm cut into 20×50mm and the round bar 52 having a radius of 2.5mm is 9.5mm or less. Therefore, in the cut piezoelectric element 10, the 20mm side is the direction perpendicular to the paper surface of fig. 7, and the 50mm side is the side of the inverted U-shape in fig. 7.
The weight 54 may be mounted at any position as long as it is 20 cm-side, that is, the end in the longitudinal direction (50 cm direction), but is preferably mounted at the center of 20 cm-side.
The weight 54 may be directly attached to the 20cm side of the piezoelectric element 10 using an adhesive or an adhesive tape, or the weight 54 may be suspended from the 20cm side of the piezoelectric element 10 using a suspending member such as a hook, a string, or an adhesive tape.
However, since the weight of the suspension member such as a hook also affects the value of the distance D of the piezoelectric element 10 in the horizontal direction at the position of the lower end portion of the round bar 52, the suspension member is preferably a member of 2g or less. Or the total weight of the weight 54 and the suspension member may be set to 100g. That is, weight 54 may include a hanging member.
When the weight 54 is suspended from the 20cm side of the piezoelectric element, the engagement position between the suspension member such as a hook and the piezoelectric element 10 is set to be as close to the 20cm side as possible, that is, near the end of the cut piezoelectric element 10 in the longitudinal direction, depending on the suspension direction.
The distance D in the horizontal direction of the piezoelectric element 10 of the present invention is 9.5mm or less.
If the horizontal distance D exceeds 9.5mm, winding disturbance occurs when the piezoelectric element is wound, for example, when the diameter of the winding core is small. Therefore, when a piezoelectric speaker capable of winding is manufactured by attaching a piezoelectric element having a horizontal distance D exceeding 9.5mm to, for example, a windable diaphragm, the piezoelectric speaker is disturbed in winding according to the diameter of the winding core.
In the piezoelectric element 10 of the present invention, the horizontal distance D is preferably short, although it is only necessary to be 9.5mm or less. In the piezoelectric element 10 of the present invention, the horizontal direction distance D is preferably 8.5mm or less. In addition, the horizontal distance D is shortest 5mm.
In the piezoelectric element 10 of the present invention, the horizontal direction distance D can be controlled by various methods.
As an example, the horizontal distance D of the piezoelectric element 10 can be controlled by appropriately adjusting and/or selecting 1 or more of the number of layers of the piezoelectric film 12, the material for forming the adhesive layer 20 (the type of commercially available product), the thickness of the adhesive layer 20, the material for forming the piezoelectric layer 26, the thickness of the piezoelectric layer 26, the material for forming the electrode layer, the thickness of the electrode layer, and the like. In the case where the piezoelectric film 12 has a protective layer, the material for forming the protective layer and the thickness of the protective layer can be used as a means for controlling the distance D in the horizontal direction, in addition to the above.
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 having a high output, that is, a strong expansion force, and a good curl shape even when the diameter of the winding core is small can be obtained.
The piezoelectric element 10 of the present invention expands and contracts the piezoelectric layer 26 by applying a driving voltage to the 1 st electrode layer 28 and the 2 nd electrode layer 30. Therefore, the 1 st electrode layer 28 and the 2 nd electrode layer 30 need to be electrically connected to an external device such as an external power source.
The method of connecting the 1 st electrode layer 28 and the 2 nd electrode layer 30 to an external device can be any known method.
As an example, as schematically shown in fig. 8, the piezoelectric film 12 is extended at one end portion, and a protruding portion 12a protruding from the region where the piezoelectric film 12 is laminated is provided. Further, a method of providing a lead wire for electrical connection with an external device in the protruding portion 12a is exemplified.
In the present invention, the protruding portion specifically means a region which is a single layer that does not overlap with the other piezoelectric film 12 when viewed in the lamination direction, in terms of a planar shape.
Although fig. 8 illustrates the piezoelectric element 10 laminated by folding back 1 piezoelectric film 12 shown in fig. 1, even if the structure of the cut sheet-like piezoelectric film 12 shown in fig. 2 is laminated, a lead wire for connecting to an external device may be provided similarly for each piezoelectric film 12.
As shown in fig. 8, the 1 st lead 72 and the 2 nd lead 74 for electrically connecting to an external device such as a power supply device are connected to the protruding portion 12a of the piezoelectric element 10.
The 1 st lead 72 is a wiring electrically led out from the 1 st electrode layer 28, and the 2 nd lead 74 is a wiring electrically led out from the 2 nd electrode layer 30. In the following description, the 1 st lead 72 and the 2 nd lead 74 are also simply referred to as leads without distinction.
In the piezoelectric element 10 of the present invention, the method of connecting the electrode layer to the lead, that is, the extraction method is not limited, and various methods can be used.
As an example, the following method is illustrated: through holes are formed in the protective layer, electrode connection members made of metal paste such as silver paste are provided to fill the through holes, and lead wires are provided in the electrode connection members.
As another method, a method of providing a rod-like or sheet-like extraction electrode between an electrode layer and a piezoelectric layer or between an electrode layer and a protective layer and connecting a lead to the extraction electrode is exemplified. Alternatively, the lead may be directly interposed between the electrode layer and the piezoelectric layer or between the electrode layer and the protective layer, and connected to the electrode layer.
As other methods, the following methods are exemplified: a part of the protective layer and the electrode layer is protruded from the piezoelectric layer in the planar direction, and the lead is connected to the protruded electrode layer. The connection between the lead 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.
Examples of preferred electrode extraction methods include the method described in Japanese patent application laid-open No. 2014-209724 and the method described in Japanese patent application laid-open No. 2016-015354.
In the piezoelectric element 10, as shown in fig. 18 of international publication No. 2020/095812, a protruding portion such as an island protruding from the piezoelectric film is provided in the direction of the ridge line of the piezoelectric film 12, that is, in the direction orthogonal to the folding-back direction, and a lead-out wiring for connecting an external device may be provided therein, without extending the end portion of the piezoelectric film 12.
Further, in the piezoelectric element of the present invention, a plurality of these protruding portions 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 suitable for use as an exciter that outputs sound by vibrating a vibration plate.
Fig. 9 schematically shows an example of the piezoelectric speaker of the present invention.
The piezoelectric speaker of the present invention is used as an exciter for vibrating a diaphragm to output sound by attaching the piezoelectric element 10 of the present invention to the diaphragm.
As shown in fig. 9, the piezoelectric speaker 60 attaches the piezoelectric element 10 to the vibration plate 62 via the attaching layer 68. In the piezoelectric speaker of the present invention, the number of piezoelectric elements attached to 1 diaphragm 62 is not limited to 1, and a plurality of piezoelectric elements 10 may be attached to 1 diaphragm 62. In addition, for example, 2 piezoelectric elements 10 may be provided in 1 vibration plate 62, and different driving voltages may be applied to each piezoelectric element 10, so that, for example, stereo sound may be output from 1 vibration plate 62.
In the piezoelectric speaker 60 of the present invention, the diaphragm 62 is not limited, and various types of sheets can be used as long as it functions as a diaphragm that outputs sound by vibration of an exciter.
In the piezoelectric speaker 60 of the present invention, as the vibration plate 62, for example, polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS), polycarbonate (PC), polyphenylene Sulfide (PPs), polymethyl methacrylate (PMMA), polyetherimide (PEI), polyimide (PI), polyethylene naphthalate (PEN), a resin film composed of triacetyl cellulose (TAC), a cycloolefin resin, and the like, a foamed plastic sheet composed of foamed polystyrene, foamed styrene, foamed polyethylene, and the like, and various corrugated cardboard materials in which one side or both sides of a corrugated cardboard are adhered to other cardboard, and the like are illustrated.
In the piezoelectric speaker 60 of the present invention, various display devices such as an Organic LIGHT EMITTING (OLED) display, a liquid crystal display, a micro LED (LIGHT EMITTING) display, and an inorganic electroluminescence display can be suitably used as the vibration plate 62.
Further, the piezoelectric speaker 60 of the present invention can be suitably used as the vibration plate 62 for electronic devices such as personal computers including smart phones, mobile phones, tablet terminals, notebook computers, and wearable devices including smart watches.
In addition, the piezoelectric speaker of the present invention can preferably use a thin film metal such as stainless steel, aluminum, copper, or nickel, which is made of various metals, various alloys, or the like, as the diaphragm 62.
Including the case where the vibration plate 62 is a display device, an electronic component, or the like, the vibration plate 62 is preferably flexible, and more preferably can be wound. In the piezoelectric speaker of the present invention, a display device is preferably used as the vibration plate 62, wherein a display device having flexibility is preferable, and wherein a display device capable of being rolled up is particularly preferable.
In the present invention, the term "winding-up" means winding-up by winding up, in the same manner as the term "winding-up" described above, and means winding-up by winding up, specifically, winding-up can be performed without causing damage or injury, and winding-up is performed to form a wound object into a flat plate shape.
In a piezoelectric speaker using a piezoelectric element as a diaphragm and an exciter, a reelable piezoelectric speaker can be realized by using a reelable diaphragm 62 and a reelable piezoelectric element. The piezoelectric speaker capable of winding is wound by fixing a winding core to an end of a diaphragm, using power such as a motor, or manually rotating the winding core.
As described above, the piezoelectric speaker 60 of the present invention uses the piezoelectric element 10 of the present invention, which is cut into 20×50mm pieces, and added with 100g of weight 54, and suspended from a round bar 52 having a radius of 2.5mm, and has a horizontal distance D of 9.5mm or less, as an exciter. As described above, the piezoelectric element 10 of the present invention can be properly wound even with a small-diameter winding core without causing winding disturbance.
Therefore, the piezoelectric speaker 60 of the present invention can be properly wound without causing winding disturbance even when the winding core has a small diameter, for example.
In the piezoelectric speaker 60 of the present invention, the adhesive layer 68 for adhering the vibration plate 62 to the piezoelectric element 10 is not limited, and various adhesives can be used as long as the vibration plate 62 and the piezoelectric element 10 (piezoelectric film 12) can be adhered.
In the piezoelectric speaker 60 of the present invention, the adhesive layer 68 for adhering the vibration plate 62 to the piezoelectric element 10 can be made of various adhesive layers similar to the adhesive layer 20 for adhering the adjacent piezoelectric film 12. In addition, 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 capable of exhibiting a sufficient adhesive force is appropriately set according to the material forming the adhesive layer 68.
In the piezoelectric speaker 60 of the present invention, the thinner the adhesive layer 68 is, the more the transmission effect of the expansion and contraction energy (vibration energy) of the piezoelectric film 12 can be improved, and the energy efficiency can be improved. In addition, if the adhesive layer is thick and has high rigidity, expansion and contraction of the piezoelectric element 10 may be restricted.
In view of this, the thickness of the adhesive layer 68 for adhering the vibration plate 62 to the piezoelectric element 10 is preferably 10 to 1000 μm, more preferably 30 to 500 μm, and even more preferably 50 to 300 μm.
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 1 st electrode layer 28 and the 2 nd electrode layer 30.
The piezoelectric layer 26 is preferably a layer in which piezoelectric particles 40 are dispersed in a polymer matrix 38.
When a voltage is applied to the 2 nd electrode layer 30 and the 1 st electrode layer 28 of the piezoelectric film 12 having such a 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) contracts in the thickness direction. Meanwhile, the piezoelectric film 12 also expands and contracts in the plane direction due to the poisson's ratio.
The expansion and contraction is about 0.01 to 0.1%.
As described above, the thickness of the piezoelectric layer 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 the thickness in the planar direction. Therefore, for example, if the long side of the piezoelectric film 12 is 20cm, the piezoelectric film 12 stretches and contracts about 0.2mm at maximum by applying a voltage.
As described above, the piezoelectric element 10 is formed by folding back the piezoelectric film 12 and stacking 5 layers of the piezoelectric film 12. The piezoelectric element 10 is attached to the vibration plate 62 via the adhesive layer 68.
The piezoelectric element 10 also expands and contracts in the same direction by the expansion and contraction of the piezoelectric film 12. By the expansion and contraction of the piezoelectric element 10, the vibration plate 62 is bent, and as a result, vibrates in the thickness direction.
By this vibration in the thickness direction, the vibration plate 62 emits sound. That is, the vibration 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 typical piezoelectric film made of a polymer material such as PVDF is stretched in a uniaxial direction after polarization treatment to align molecular chains in the stretching direction, and as a result, a large piezoelectric characteristic in the stretching direction can be obtained. Therefore, the piezoelectric characteristics of a typical 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 formed of the polymer composite piezoelectric body in which the piezoelectric particles 40 are dispersed in the polymer matrix 38 shown in fig. 3 can obtain a strong piezoelectric characteristic even without the stretching treatment after the polarization treatment, and therefore does not have in-plane anisotropy and expands and contracts 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 in which the piezoelectric films 12 are laminated so as to extend and retract in two dimensions, the vibration plate 62 can be vibrated with a larger force and a larger sound can be emitted than a piezoelectric element in which normal piezoelectric films such as PVDF which extend and retract in only one direction are laminated.
As described above, the piezoelectric element 10 illustrated in the drawing is formed by stacking 5 layers of such piezoelectric films 12. In the piezoelectric element 10 of the illustrated example, the adjacent piezoelectric films 12 are further bonded to each other with the adhesive layer 20.
Therefore, even if the rigidity of the piezoelectric film 12 per 1 sheet is low and the tensile force is small, by stacking the piezoelectric films 12, the rigidity becomes high and the tensile force as the piezoelectric element 10 becomes large. As a result, in the piezoelectric element 10, even if the diaphragm 62 has a certain degree of rigidity, the diaphragm 62 is sufficiently bent with a large force and the diaphragm 62 is sufficiently vibrated in the thickness direction, so that the diaphragm 62 can emit sound.
In addition, the thicker the piezoelectric layer 26 is, the greater the tensile force of the piezoelectric film 12 becomes, but the driving voltage required to expand and contract the same amount becomes correspondingly greater. In the piezoelectric element 10, the thickness of the piezoelectric layer 26 is preferably only about 300 μm at the maximum, and thus the voltage applied to each piezoelectric film 12 is small, and the piezoelectric film 12 can be sufficiently stretched.
The piezoelectric element of the present invention can be preferably used in various applications such as various sensors, acoustic elements, tactile interfaces, ultrasonic transducers, actuators, vibration damping materials (dampers), and vibration power generation devices, in addition to the piezoelectric speaker described above.
Specifically, examples of the sensor using the piezoelectric element of the present invention include a sonic sensor, an ultrasonic sensor, a pressure sensor, a tactile sensor, a strain sensor, and a vibration sensor. The sensor using the piezoelectric film and the laminated piezoelectric element of the present invention is useful for inspection in manufacturing sites such as inspection of a base structure such as crack inspection and foreign matter contamination inspection.
As an acoustic element using the piezoelectric element of the present invention, a microphone, a sound pickup, various well-known speakers, exciters, and the like are exemplified in addition to the piezoelectric speaker (exciter) described above. Specific applications of the acoustic element using the piezoelectric element of the present invention include noise cancellers, artificial vocal cords, buzzers for preventing invasion of vermin and harmful animals, furniture, wallpaper, photographs, helmets, goggles, headrests, signs, robots, and the like used in vehicles, electric trains, airplanes, robots, and the like.
Examples of applications of the haptic interface using the piezoelectric element of the present invention include automobiles, smart phones, smart watches, and game machines.
An ultrasonic probe, an underwater wave receiver, and the like are exemplified as an ultrasonic transducer using the piezoelectric element of the present invention.
Examples of the application of the actuator using the piezoelectric element of the present invention include prevention of water droplet adhesion, conveyance, stirring, dispersion, polishing, and the like.
Examples of applications of the vibration damping material using the piezoelectric element of the present invention include containers, carriers, buildings, sports equipment such as snowboards and rackets, and the like.
Further, examples of applications of the vibration power generation device using the piezoelectric element of the present invention include roads, floors, mattresses, chairs, shoes, tires, wheels, computer keyboards, and the like.
While the piezoelectric element and the piezoelectric speaker according to the present invention have been described in detail, the present invention is not limited to the above examples, and various modifications and alterations can be made without departing from the spirit of the present invention.
Examples
Hereinafter, the present invention will be described in more detail with reference to specific examples thereof.
[ Production of piezoelectric film ]
A piezoelectric film as shown in fig. 3 was produced by the method shown in fig. 4 to 6.
First, cyanoethylated PVA (CR-V Shin-Etsu Chemical Co., manufactured by Ltd.) was dissolved in Dimethylformamide (DMF) at the following composition ratio. Then, PZT particles were added as piezoelectric particles in the following composition ratio, and stirred with a propeller mixer (rotation speed 2000 rpm) to prepare a paint for forming a piezoelectric layer.
PZT particle 300 parts by mass of
Cyanoethylated PVA & lt/EN & gt 30 parts by mass
DMF & lt/EN & gt 70 parts by mass
The PZT particles were obtained by calcining mixed powders of Pb oxide, zr oxide, and Ti oxide, which are main components, in a ball mill at 800 ℃ for 5 hours so as to be zr=0.52 mol and ti=0.48 mol with respect to pb=1 mol, and then pulverizing the mixed powders.
On the other hand, 2 sheets of copper film having a thickness of 0.1 μm were prepared by vacuum deposition on a PET film having a thickness of 4. Mu.m. That is, in this example, the 1 st electrode layer and the 2 nd electrode layer were copper vapor deposited films having a thickness of 0.1 μm, and the 1 st protective layer and the 2 nd protective layer were PET films having a thickness of 4 μm.
A coating material for forming a piezoelectric layer prepared in advance was applied to a copper thin film (2 nd electrode layer) of 1 sheet by using a slide coater.
Subsequently, DMF was evaporated by heating and drying the coated material on the sheet on a heating plate of 120 ℃. Thus, a 2 nd electrode layer made of copper was provided on the 2 nd protective layer made of PET, and a laminate having a piezoelectric layer (polymer composite piezoelectric layer) with a thickness of 50 μm was produced thereon.
The piezoelectric layers (laminate) thus produced were subjected to a rolling treatment using a pair of heated rolls. The temperature of the pair of heated rolls was set to 100 ℃.
After the rolling treatment, the piezoelectric layer thus produced was subjected to polarization treatment in the thickness direction.
Another sheet was laminated on the laminate so that the copper film (1 st electrode layer) faced the piezoelectric layer.
Next, the laminate of the laminate and the sheet was thermally bonded at a temperature of 120 ℃ by using a pair of heated rolls, whereby the piezoelectric layer and the 1 st electrode layer were bonded to each other, and a piezoelectric film as shown in fig. 3 was produced.
Example 1
The fabricated piezoelectric film was cut into a rectangle of 20X 25 cm.
The setting of the adhesive layer, folding back of the piezoelectric film 4 times, and pressing with a roller were repeated at 5cm intervals in the direction of 25cm to adhere the piezoelectric film. Thus, a piezoelectric element having a planar shape of 20×5cm, as shown in fig. 1, was produced by laminating 5 layers of piezoelectric films and bonding adjacent and laminated piezoelectric films. Therefore, the piezoelectric element has a length of 20cm and a ridge (folded line).
As the adhesive layer, NE-NCP3 (thickness: 3 μm) manufactured by NEION Film Coatings Corp. Was used.
Example 2
A piezoelectric element was produced 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) produced 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 produced in the same manner as in example 1, except that the adhesive layer was changed to TOYOCHEM co., ltd.
Comparative example 4
A piezoelectric element was produced in the same manner as in example 1, except that the adhesive layer was changed to FB-ML4-50S (thickness: 50 μm) produced by NITTO DENKO CORPORATION.
[ Evaluation of winding Property ]
A round rod having a diameter of 20mm was attached so as to cover the entire region of one 5cm side of the fabricated 5×20cm piezoelectric element. By rotating the round bar by hand, a piezoelectric element of 5×20cm was wound with the round bar as a winding core.
The wound piezoelectric element was evaluated for winding property (winding disorder) according to the following criteria.
A: no rollback occurs and there is no gap between layers that is a sign of rollback.
B: at least one of the rollback and the gap between the layers that becomes a precursor of the rollback is generated.
[ Measurement of horizontal distance D ]
The fabricated piezoelectric element of 5X 20cm was cut into 20X 50mm. The cuts were made using scissors. As described above, the dicing was performed so that the piezoelectric element cut into 20×50mm was not included in the folded portion (ridge line) of the piezoelectric film.
The cut piezoelectric element of 20X 50mm was stored for 27 hours at a temperature of 23℃and a humidity of 65% RH.
Then, in this environment, a weight of 100g was mounted at the center of the 20cm side of the cut piezoelectric element. The weight is mounted by cellophane tape.
Further, in this environment, in order to equalize the positions of the 2 weights in the vertical direction, the piezoelectric element was hung on a metal round bar having a radius of 5 mm.
After the suspension was started, a time point of 15 seconds elapsed, and a horizontal distance D of the position of the lower end portion of the round bar was measured using a steel rule.
The results are shown in the following table.
TABLE 1
In all piezoelectric elements, the number of laminated piezoelectric films was 5 layers
As shown in the table, the piezoelectric element of the present invention having a horizontal distance D of 9.5mm or less does not cause backlash or gaps between layers which are a sign of backlash, that is, winding disorder, when wound around a round bar of 20mm. Therefore, by attaching the piezoelectric element to the coiled diaphragm, a piezoelectric speaker capable of being coiled without generating a coil back and a gap between layers which is a sign of the coil back can be obtained.
In contrast, in the piezoelectric element of the comparative example in which the horizontal distance D exceeds 9.5mm, at least one of the winding back and the gap between the layers, which is a sign of the winding back, occurs, that is, the winding is disturbed when the piezoelectric element is wound around the round bar of 20 mm. Therefore, when the piezoelectric element is attached to a coiled diaphragm as a piezoelectric speaker, there is a possibility that a curl and/or a gap between layers, which is a sign of the curl, may occur when the piezoelectric speaker is coiled.
The effect of the present invention is evident from the above results.
Industrial applicability
The piezoelectric speaker and the like can be preferably used for various applications.
Symbol description
10-Piezoelectric element, 12-piezoelectric film, 20, 68-adhesive layer, 26-piezoelectric layer, 28-1 st electrode layer, 30-2 nd electrode layer, 32-1 st protective layer, 34-2 nd protective layer, 38-polymer matrix, 40-piezoelectric particles, 42a, 42 b-sheet, 46-laminate, 52-round bar, 54-weight, 60-piezoelectric speaker, 62-vibration plate, 72-1 st lead wire, 74-2 nd lead wire, M-thickest part.
Claims (10)
1. A piezoelectric element is formed by laminating a plurality of piezoelectric films and attaching the laminated piezoelectric films to each other by an adhesive layer,
When the piezoelectric film is cut into 20X 50mm, a weight of 100g is applied to two sides of 20mm, and the piezoelectric film is hung on a round bar having a radius of 2.5mm, the distance in the horizontal direction of the piezoelectric film at the position of the lower end of the round bar is 9.5mm or less.
2. The piezoelectric element according to claim 1, wherein,
The thickness of the adhesive layer for adhering the adjacent piezoelectric films is 10 μm or less.
3. The piezoelectric element according to claim 1, wherein,
The piezoelectric film includes a piezoelectric layer, electrode layers provided on both sides of the piezoelectric layer, and a protective layer provided so as to cover the electrode layers.
4. The piezoelectric element according to claim 3, wherein,
The thickness of the piezoelectric layer is 45 μm or more.
5. The piezoelectric element according to claim 3, wherein,
The piezoelectric layer is a polymer composite piezoelectric body having piezoelectric particles in a polymer material.
6. The piezoelectric element according to claim 5, wherein,
The polymer material has cyanoethyl groups.
7. The piezoelectric element according to claim 6, wherein,
The high polymer material is cyanoethylated polyvinyl alcohol.
8. The piezoelectric element according to claim 1, wherein,
The piezoelectric element is a piezoelectric element in which a plurality of piezoelectric films are laminated by folding back 1 sheet of the piezoelectric film.
9. A piezoelectric speaker in which the piezoelectric element according to any one of claims 1 to 8 is attached to a vibrating plate having flexibility.
10. The piezoelectric speaker of claim 9, wherein,
The vibration plate is a display device.
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| JP2021157585 | 2021-09-28 | ||
| JP2021-157585 | 2021-09-28 | ||
| PCT/JP2022/034128 WO2023053931A1 (en) | 2021-09-28 | 2022-09-13 | Piezoelectric element and piezoelectric speaker |
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| CN118020316A true CN118020316A (en) | 2024-05-10 |
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| TW202323051A (en) | 2023-06-16 |
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