Multilayer piezoelectric element

Abstract

Provided is a multilayer piezoelectric element in which heat generation can be reduced while a good piezoelectric property is maintained. This multilayer piezoelectric element is a laminate of a plurality of piezoelectric films each having a piezoelectric body layer having a macromolecular complex piezoelectric body containing piezoelectric body particles in a matrix including a macromolecular material, and electrode layers formed on both sides of the piezoelectric body layer. When a value obtained by dividing a capacitive reactance Xc of the piezoelectric films at a frequency of 1 kHz by an equivalent series resistance ESR is 1, a value XE20 obtained by dividing the capacitive reactance Xc at a frequency of 20 kHz by the equivalent series resistance ESR is in the range of 0.6 to 1.5.

Description

[Technical Field]

[0001] The present invention relates to a multilayer piezoelectric element. [Background technology]

[0002] As displays, such as liquid crystal displays and organic electroluminescence (EL) displays, become thinner, the speakers used in these displays must also be lighter and thinner. Furthermore, flexible displays must be flexible enough to be integrated into the displays without losing their lightness and flexibility. One promising lightweight, thin, and flexible speaker is a sheet-shaped piezoelectric film that expands and contracts in response to an applied voltage.

[0003] It has also been considered to create a flexible speaker by attaching a flexible exciter to a flexible diaphragm. An exciter is an exciter that, when attached to a variety of objects, vibrates the object to produce sound.

[0004] It has been proposed to use a composite piezoelectric material containing piezoelectric particles in a matrix as such a flexible sheet-like piezoelectric film or exciter.

[0005] For example, Patent Document 1 describes a piezoelectric film having a polymer composite piezoelectric element formed by dispersing piezoelectric particles in a viscoelastic matrix made of a polymer material that has viscoelasticity at room temperature, thin-film electrodes formed on both sides of the polymer composite piezoelectric element, and a protective layer formed on the surface of the thin-film electrodes. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-014063 DISCLOSURE OF THE INVENTION [Problem to be solved by the invention]

[0007] In such piezoelectric films, if the electrode layer is too thick, the deformation (vibration) of the piezoelectric layer is hindered, resulting in a decrease in output. Therefore, the electrode layer is formed very thin. However, according to the inventors' investigations, it was found that a thinner electrode layer results in a problem of increased heat generation.

[0008] SUMMARY OF THE INVENTION An object of the present invention is to solve the problems of the prior art and to provide a multilayer piezoelectric element that can suppress heat generation while maintaining good piezoelectric characteristics. [Means for solving the problem]

[0009] In order to solve such problems, the present invention has the following configuration. [1] A multilayer piezoelectric element formed by laminating multiple layers of piezoelectric films each having a piezoelectric layer made of a polymer composite piezoelectric material containing piezoelectric particles in a matrix containing a polymer material, and electrode layers formed on both sides of the piezoelectric layer, When the value obtained by dividing the capacitance reactance Xc of a piezoelectric film at a frequency of 1 kHz by the equivalent series resistance ESR is set to 1, the value obtained by dividing the capacitance reactance Xc at a frequency of 20 kHz by the equivalent series resistance ESR is XE. 20 is in the range of 0.6 to 1.5. [2] The multilayer piezoelectric element according to [1], wherein the polymer material has viscoelasticity at room temperature. [3] XE 20 The multilayer piezoelectric element according to [1] or [2], wherein is in the range of 0.8 to 1.3. [4] The multilayer piezoelectric element according to any one of [1] to [3], wherein the thickness of the electrode layer is 1 μm or less. [5] At least the piezoelectric film laminated on the outermost layer of the multilayer piezoelectric element has a protective layer laminated on the surface of the electrode layer on the outermost layer side opposite to the piezoelectric layer, the protective layer has holes penetrating from the surface to the electrode layer; a conductive member disposed within the hole; The multilayer piezoelectric element according to any one of [1] to [4], further comprising a conductive wire disposed on the surface of the hole in the protective layer and electrically connected to the electrode layer via a conductive member. [6] If the opening area of ​​the hole is A, the thickness of the electrode layer is t, and the capacitance of the multilayer piezoelectric element is F, then F / (A×t) is 260 μF / mm 3 The multilayer piezoelectric element according to [5], [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a multilayer piezoelectric element that can suppress heat generation while maintaining good piezoelectric characteristics. [Brief explanation of the drawings]

[0011] [Figure 1] 1A and 1B are diagrams conceptually illustrating an example of a multilayer piezoelectric element according to the present invention. [Figure 2] FIG. 1 is a diagram conceptually illustrating an example of a piezoelectric film. [Figure 3] 1 is a graph showing the relationship between frequency and capacitive reactance Xc and equivalent series resistance ESR. [Figure 4] 1A to 1C are conceptual diagrams for explaining an example of a method for producing a piezoelectric film. [Figure 5] 1A to 1C are conceptual diagrams for explaining an example of a method for producing a piezoelectric film. [Figure 6] 1A to 1C are conceptual diagrams for explaining an example of a method for producing a piezoelectric film. [Figure 7] 10A and 10B are diagrams conceptually showing another example of the multilayer piezoelectric element of the present invention. [Figure 8] 1 is a graph showing the relationship between frequency and capacitive reactance Xc and equivalent series resistance ESR. [Figure 9] 1 is a graph showing the relationship between frequency and capacitive reactance Xc and equivalent series resistance ESR. [Figure 10] 1 is a graph showing the relationship between frequency and capacitive reactance Xc and equivalent series resistance ESR. [Figure 11] 1 is a graph showing the relationship between frequency and capacitive reactance Xc and equivalent series resistance ESR. [Figure 12] 1 is a graph showing the relationship between frequency and capacitive reactance Xc and equivalent series resistance ESR. [Figure 13] 1 is a graph showing the relationship between frequency and capacitive reactance Xc and equivalent series resistance ESR. [Figure 14] 1 is a graph showing the relationship between frequency and capacitive reactance Xc and equivalent series resistance ESR. [Figure 15] FIG. 10 is a plan view conceptually showing another example of the multilayer piezoelectric element of the present invention. [Figure 16] FIG. 16 is a side view of FIG. [Figure 17] FIG. 17 is a partially enlarged cross-sectional view of line BB in FIG. [Figure 18] FIG. 4 is a partially enlarged view of another example of the multilayer piezoelectric element of the present invention. [Figure 19] FIG. 3 is a partially enlarged view of another example of a piezoelectric film used in the multilayer piezoelectric element of the present invention. [Figure 20] FIG. 20 is a cross-sectional view taken along line CC in FIG. 19. DETAILED DESCRIPTION OF THE INVENTION

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The multilayer piezoelectric element of the present invention will now be described in detail with reference to preferred embodiments shown in the accompanying drawings.

[0013] The following description of the components may be based on typical embodiments of the present invention, but the present invention is not limited to such embodiments. In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits.

[0014] [Multilayer piezoelectric element] The multilayer piezoelectric element of the present invention comprises: A multilayer piezoelectric element is formed by laminating a plurality of piezoelectric layers, each layer having a polymer composite piezoelectric material containing piezoelectric particles in a matrix containing a polymer material, and a piezoelectric film having electrode layers formed on both sides of the piezoelectric layer, When the value obtained by dividing the capacitance reactance Xc of a piezoelectric film at a frequency of 1 kHz by the equivalent series resistance ESR is set to 1, the value obtained by dividing the capacitance reactance Xc at a frequency of 20 kHz by the equivalent series resistance ESR is XE. 20 is in the range of 0.6 to 1.5.

[0015] FIG. 1 conceptually shows an example of the multilayer piezoelectric element of the present invention. The multilayer piezoelectric element 50 shown in FIG. 1 has a configuration in which three piezoelectric films 10 are stacked together, each having a first electrode layer 24 on one side of a piezoelectric layer 20 and a second electrode layer 26 on the other side, and adjacent piezoelectric films are attached with an adhesive layer (sticking layer) 19. The configuration of the piezoelectric films 10 will be described in detail later. Each piezoelectric film 10 is connected in parallel to a power supply. That is, the first electrode layer 24 of each piezoelectric film 10 is electrically connected by wiring to one electrode of the power supply, and the second electrode layer 26 of each piezoelectric film 10 is electrically connected by wiring to the other electrode of the power supply. Although the first protective layer 28 and the second protective layer 30 of each piezoelectric film 10 are not shown in FIG. 1, each piezoelectric film 10 may have the first protective layer 28 and the second protective layer 30.

[0016] 1 is formed by laminating three layers of piezoelectric film 10, but the present invention is not limited to this. That is, as long as the multilayer piezoelectric element of the present invention is formed by laminating multiple layers of piezoelectric film, the number of laminated piezoelectric film layers may be two, or four or more. This also applies to the multilayer piezoelectric element described below.

[0017] 1 is preferably stacked such that the polarization directions of adjacent piezoelectric films 10 are opposite to each other, as indicated by the arrows on the piezoelectric layers 20. However, the multilayer piezoelectric element 50 of the present invention is not limited to this, and adjacent piezoelectric films 10 may have the same polarization direction.

[0018] 1, the laminated piezoelectric element 50 is adhered to the diaphragm 12 by an adhesive layer 16 and is used as an exciter for generating sound from the diaphragm 12. In other words, the diaphragm 12 and the piezoelectric film 10 are fixed in contact with each other via the adhesive layer 16, and the piezoelectric film 10 acts as an exciter for generating sound from the diaphragm 12.

[0019] The multilayer piezoelectric element 50 is formed by laminating a plurality of piezoelectric films 10. Therefore, even if each piezoelectric film 10 has low rigidity and small stretching force, stacking the piezoelectric films 10 increases the rigidity and increases the stretching force of the multilayer piezoelectric element 50. As a result, even if the diaphragm 12 has a certain degree of rigidity, the multilayer piezoelectric element 50 can sufficiently deflect the diaphragm 12 with a large force, sufficiently vibrate the diaphragm 12 in the thickness direction, and generate sound from the diaphragm 12.

[0020] Furthermore, the thicker the piezoelectric layer 20, the greater the expansion and contraction force of the piezoelectric film, but the greater the drive voltage required to expand and contract the piezoelectric film by the same amount. As will be described later, the preferred thickness of the piezoelectric layer 20 in the piezoelectric film 10 is approximately 300 μm at most, so that the piezoelectric film can be expanded and contracted sufficiently even if the voltage applied to each piezoelectric film is small.

[0021] A power supply that applies a driving voltage that expands and contracts the piezoelectric film 10 is connected to the first electrode layer 24 and the second electrode layer 26 of each piezoelectric film 10. There are no limitations on the power source, and either a DC or AC power source may be used. The drive voltage may also be set appropriately depending on the thickness and material of the piezoelectric layer 20 of each piezoelectric film, so that the drive voltage can properly drive each piezoelectric film.

[0022] Furthermore, as shown in Figure 1, it is preferable to connect each piezoelectric film to a power source so that the polarization direction of each piezoelectric film and the polarity of the electrode layer are the same for all piezoelectric films. This allows voltages of the same phase to be applied to each piezoelectric film. In other words, when voltage is applied to a piezoelectric film, the expansion and contraction behavior of all piezoelectric films is in the same phase. This allows the expansion and contraction of each piezoelectric film to reinforce each other, increasing the deformation (output) of the entire piezoelectric film. In other words, high piezoelectric properties can be obtained.

[0023] In the present invention, the polarization direction of the piezoelectric film can be detected by a d33 meter or the like. Alternatively, the polarization direction of the piezoelectric layer 20 may be determined from the processing conditions of the corona poling process described above.

[0024] [Piezoelectric film] FIG. 2 is a cross-sectional view conceptually showing an example of a piezoelectric film. As shown in FIG. 2, the piezoelectric film 10 includes a piezoelectric layer 20, which is a sheet-like material having piezoelectric properties, a first electrode layer 24 laminated on one side of the piezoelectric layer 20, a first protective layer 28 laminated on the first electrode layer 24, a second electrode layer 26 laminated on the other side of the piezoelectric layer 20, and a second protective layer 30 laminated on the second electrode layer 26. The piezoelectric layer 20 is made of a polymer composite piezoelectric material containing piezoelectric particles 36 in a matrix 34 containing a polymer material. The first electrode layer 24 and the second electrode layer 26 are electrode layers according to the present invention. As will be described later, the piezoelectric film 10 (piezoelectric layer 20) is preferably polarized in the thickness direction.

[0025] Such piezoelectric film 10 is used, for example, in various acoustic devices (acoustic equipment) such as speakers, microphones, and pickups used in musical instruments such as guitars, to generate (reproduce) sound by vibrating in response to an electrical signal, or to convert sound vibrations into an electrical signal. In addition, the piezoelectric film can also be used in pressure sensors, power generation elements, and the like. Alternatively, the piezoelectric film can be used as an exciter by attaching it to various objects in contact with them, causing the objects to vibrate and produce sound.

[0026] In the piezoelectric film 10, the second electrode layer 26 and the first electrode layer 24 form an electrode pair. That is, the piezoelectric film 10 has a configuration in which both sides of the piezoelectric layer 20 are sandwiched between an electrode pair, i.e., the first electrode layer 24 and the second electrode layer 26, and this laminate is sandwiched between a first protective layer 28 and a second protective layer 30.

[0027] In this way, in the piezoelectric film 10, the region sandwiched between the first electrode layer 24 and the second electrode layer 26 expands and contracts in response to the applied voltage.

[0028] The first electrode layer 24 and the first protective layer 28, as well as the second electrode layer 26 and the second protective layer 30, are named according to the polarization direction of the piezoelectric layer 20. Therefore, the first electrode layer 24 and the second electrode layer 26, as well as the first protective layer 28 and the second protective layer 30, have basically the same configuration.

[0029] In addition to these layers, the piezoelectric film 10 may also have an insulating layer that covers the areas where the piezoelectric layer 20 is exposed, such as the side surfaces, to prevent short circuits.

[0030] When a voltage is applied to the first electrode layer 24 and the second electrode layer 26 of such a piezoelectric film 10, the piezoelectric particles 36 expand and contract in the polarization direction in response to the applied voltage. As a result, the piezoelectric film 10 (piezoelectric layer 20) contracts in the thickness direction. At the same time, due to the Poisson's ratio, the piezoelectric film 10 also expands and contracts in the in-plane direction. This expansion and contraction is approximately 0.01 to 0.1%. Note that the expansion and contraction is isotropic in all in-plane directions. The thickness of the piezoelectric layer 20 is preferably about 10 to 300 μm, and therefore the expansion and contraction in the thickness direction is extremely small, at a maximum of about 0.3 μm. In contrast, the piezoelectric film 10, i.e., the piezoelectric layer 20, has a size in the planar direction that is much larger than its thickness. Therefore, for example, if the length of the piezoelectric film 10 is 20 cm, the piezoelectric film 10 will expand and contract by a maximum of about 0.2 mm when a voltage is applied. Furthermore, when pressure is applied to the piezoelectric film 10, the piezoelectric particles 36 act to generate electricity. By utilizing this, the piezoelectric film 10 can be used for various applications such as speakers, microphones, and pressure-sensitive sensors, as described above.

[0031] In the present invention, when the value obtained by dividing the capacitive reactance Xc at a frequency of 1 kHz by the equivalent series resistance ESR is set to 1, the value obtained by dividing Xc at a frequency of 20 kHz by the equivalent series resistance ESR is XE 20 is in the range of 0.6 to 1.5. This point will be explained with reference to FIG.

[0032] FIG. 3 is a graph conceptually showing the frequency characteristics of the capacitive reactance Xc and the equivalent series resistance ESR of the piezoelectric film 10. In FIG. A configuration in which a dielectric piezoelectric layer is sandwiched between a pair of electrodes can be represented by an equivalent circuit in which capacitance, equivalent series inductance, and equivalent series resistance are connected in series, similar to a capacitor, etc. Here, since equivalent series inductance does not contribute in the audible range (20 Hz to 20 kHz) in which the piezoelectric film of the present invention is used, the piezoelectric film 10 can be represented by an equivalent circuit in which capacitance C and equivalent series resistance ESR are connected in series.

[0033] In such an equivalent circuit, the capacitive reactance Xc = 1 / (2π × f × C) due to the electrostatic capacitance C is inversely proportional to the power supply frequency f, so as the frequency increases, the capacitive reactance Xc decreases, as shown in Figure 3. This capacitive reactance Xc is the ratio of the voltage to the current when driving the piezoelectric layer.

[0034] On the other hand, equivalent series resistance (ESR) corresponds to heat generation due to resistance components. ESR is caused by the resistance components of the piezoelectric layer and the electrode layer. Heat generation from the piezoelectric layer is thought to occur as frictional heat when the piezoelectric particles contained in the piezoelectric layer cause domain motion. In such a piezoelectric layer, when the frequency of the power supply increases, the movement of the domain motion cannot keep up with the frequency, and therefore frictional heat generated by domain motion is thought to decrease.

[0035] Furthermore, the resistance component of the electrode layer is almost constant regardless of frequency, so as shown in Figure 3, the equivalent series resistance ESR decreases as the frequency increases, and becomes almost constant above a certain frequency.

[0036] From the viewpoint of suppressing heat generation in the piezoelectric layer, it is sufficient to reduce the equivalent series resistance ESR. Generally, the more active the domain motion in a piezoelectric material, the higher its piezoelectric performance. In other words, piezoelectric materials with high piezoelectric performance tend to generate more heat. Therefore, it is difficult to suppress heat generation from the piezoelectric layer without sacrificing piezoelectric performance. Therefore, it is difficult to reduce the equivalent series resistance (ESR) in the low-frequency region where the contribution of the piezoelectric layer is large.

[0037] On the other hand, in the high frequency range (10 kHz to 20 kHz), the contribution of the piezoelectric layer becomes relatively small, and the contribution of the resistance components of the electrode layer and the like becomes large.

[0038] Incidentally, the equivalent series resistance ESR changes depending on factors such as the size of the piezoelectric film. On the other hand, the capacitive reactance Xc also depends on factors such as the size of the piezoelectric film. Therefore, by evaluating the ratio between the equivalent series resistance ESR and the capacitive reactance Xc, it is possible to evaluate the resistance component without the influence of size.

[0039] In the present invention, when the value XE1 obtained by dividing the capacitive reactance Xc of the piezoelectric film at a frequency of 1 kHz by the equivalent series resistance ESR is set to 1, the value XE obtained by dividing Xc at a frequency of 20 kHz by the ESR is20 is in the range of 0.6 to 1.5. That is, the value XE at a frequency of 20 kHz 20 By setting XE1 close to the value XE1 at a frequency of 1 kHz, the ratio of the input energy used for the piezoelectric effect to the energy generated as heat at a frequency of 20 kHz is set to a value close to that at a frequency of 1 kHz. This makes it possible to suppress heat generation while maintaining good piezoelectric properties.

[0040] Since 20kHz is the frequency with the largest current flowing within the audio band, XE 20 If the value is less than 0.6, the heat generation will increase and, in the worst case, thermal runaway will occur. On the other hand, the value XE 20 When the ratio exceeds 1.5, for example, if the electrode layer is made very thick, the ESR at 30 kHz will decrease, but the ESR at 20 kHz will hardly change, so it is thought that there will be no practical benefit within the audio band of 20 kHz.

[0041] From the above perspective, XE 20 is preferably in the range of 0.6 to 1.5, more preferably in the range of 0.8 to 1.3, and even more preferably in the range of 1.0 to 1.1.

[0042] The changes in the capacitive reactance Xc and the equivalent series resistance ESR with respect to frequency can be measured using, for example, an Impedance Analyzer 4294A manufactured by Agilent.

[0043] XE 20 In order to keep the resistance of the electrode layer within the above range, it is preferable to reduce the resistance of the electrode layer. Possible methods for suppressing the resistance of the electrode layer include, for example, increasing the thickness of the electrode layer, shortening the path length through which the current flows, using a material with a low volume resistivity as the material for the electrode layer, and controlling the film quality of the electrode layer. Furthermore, when using a plurality of piezoelectric films stacked together as in the multilayer piezoelectric element of the present invention, the resistance of the entire piezoelectric element can also be reduced by connecting a plurality of piezoelectric films in parallel. Furthermore, a combination of these methods can be used to reduce the resistance of the XE 20may be within the above range.

[0044] As mentioned above, if the electrode layer is too thick, the deformation (vibration) of the piezoelectric layer is hindered, resulting in a decrease in output (piezoelectric characteristics). Therefore, it is preferable to make the electrode layer thick enough so that the piezoelectric characteristics are not reduced. However, it is not possible to achieve the desired XE by simply adjusting the thickness. 20 It is difficult to keep the XE within the above range. In addition, the length of the path through which the current flows can be adjusted by devising the connection position between the electrode and the wiring from the power supply, but depending on the size of the piezoelectric film, it is difficult to make it sufficiently short. 20 It is difficult to keep the above range. Therefore, it is necessary to combine multiple methods mentioned above to 20 is preferably within the above range.

[0045] <Piezoelectric layer> The piezoelectric layer is a layer made of a polymer composite piezoelectric material containing piezoelectric particles in a matrix containing a polymer material, and is a layer that exhibits a piezoelectric effect of expanding and contracting when a voltage is applied.

[0046] In a preferred embodiment of the piezoelectric film 10, the piezoelectric layer 20 is made of a polymer composite piezoelectric material in which piezoelectric particles 36 are dispersed in a matrix 34 made of a polymer material that has viscoelasticity at room temperature. In this specification, "room temperature" refers to a temperature range of approximately 0 to 50°C.

[0047] Here, the polymer composite piezoelectric material (piezoelectric material layer 20) preferably satisfies the following requirements. (i) Flexibility For example, when a portable piezoelectric material is held loosely bent like a newspaper or magazine, it is constantly subjected to relatively slow, large bending deformation from the outside at frequencies below a few Hz. If the polymer composite piezoelectric material is too hard, a correspondingly large bending stress will be generated, which can lead to cracks at the interface between the polymer matrix and the piezoelectric particles, eventually leading to fracture. Therefore, polymer composite piezoelectric materials must be moderately flexible. Furthermore, if the strain energy can be diffused to the outside as heat, stress can be alleviated. Therefore, the loss tangent of the polymer composite piezoelectric material must be moderately large.

[0048] In summary, the flexible polymer composite piezoelectric material used as an exciter must be rigid for vibrations between 20 Hz and 20 kHz, and flexible for vibrations below a few Hz. The loss tangent of the polymer composite must also be appropriately large for vibrations of all frequencies below 20 kHz. Furthermore, it is preferable to be able to easily adjust the spring constant by laminating the material to match the rigidity (hardness, stiffness, spring constant) of the material to which it is attached (the diaphragm).In this case, the thinner the adhesive layer, the higher the energy efficiency can be.

[0049] In general, polymer solids have a viscoelastic relaxation mechanism, and large-scale molecular motion is observed as a decrease (relaxation) in the storage modulus (Young's modulus) or a maximum (absorption) in the loss modulus with increasing temperature or decreasing frequency. Among these, relaxation caused by the micro-Brownian motion of molecular chains in the amorphous region is called primary dispersion, and a very large relaxation phenomenon is observed. The temperature at which this primary dispersion occurs is the glass transition point (Tg), where the viscoelastic relaxation mechanism is most prominent. In the polymer composite piezoelectric body (piezoelectric layer 20), by using a polymer material whose glass transition point is at room temperature, in other words, a polymer material that has viscoelasticity at room temperature, as the matrix, a polymer composite piezoelectric body that behaves hard to vibrations of 20 Hz to 20 kHz and soft to slow vibrations of a few Hz or less is realized. In particular, in order to favorably exhibit this behavior, it is preferable to use a polymer material whose glass transition point at a frequency of 1 Hz is at room temperature, i.e., 0 to 50°C, as the matrix of the polymer composite piezoelectric body.

[0050] As the polymer material having viscoelasticity at room temperature, various known materials can be used. Preferably, a polymer material is used that has a maximum value of loss tangent Tanδ of 0.5 or more at a frequency of 1 Hz in a dynamic viscoelasticity test at room temperature, i.e., 0 to 50°C. This reduces stress concentration at the interface between the polymer matrix and the piezoelectric particles at the maximum bending moment when the polymer composite piezoelectric body is slowly bent by an external force, and high flexibility can be expected.

[0051] Furthermore, the polymeric material having viscoelasticity at room temperature preferably has a storage modulus (E') at a frequency of 1 Hz measured by dynamic viscoelasticity measurement of 100 MPa or more at 0°C and 10 MPa or less at 50°C. This reduces the bending moment that occurs when the polymer composite piezoelectric body is slowly bent by an external force, and at the same time, allows the body to behave rigidly against acoustic vibrations of 20 Hz to 20 kHz.

[0052] Furthermore, it is more preferable for the polymer material that has viscoelasticity at room temperature to have a relative dielectric constant of 10 or more at 25°C. This means that when a voltage is applied to the polymer composite piezoelectric material, a higher electric field is applied to the piezoelectric particles in the polymer matrix, and a large amount of deformation can be expected. However, on the other hand, in order to ensure good moisture resistance, it is also preferable that the polymer material has a relative dielectric constant of 10 or less at 25°C.

[0053] Examples of polymeric materials that satisfy these conditions and have viscoelasticity at room temperature include cyanoethylated polyvinyl alcohol (cyanoethylated PVA), polyvinyl acetate, polyvinylidene chloride-co-acrylonitrile, polystyrene-vinyl polyisoprene block copolymer, polyvinyl methyl ketone, and polybutyl methacrylate. Commercially available products such as Hybrar 5127 (manufactured by Kuraray Co., Ltd.) can also be suitably used as these polymeric materials. Of these, it is preferable to use a material having a cyanoethyl group as the polymeric material, and it is particularly preferable to use cyanoethylated PVA. These polymer materials may be used alone or in combination (mixture) of two or more kinds.

[0054] The matrix 34 using such a polymeric material having viscoelasticity at room temperature may use a plurality of polymeric materials in combination as required. That is, in addition to a viscoelastic material such as cyanoethylated PVA, other dielectric polymer materials may be added to the matrix 34 as needed for the purpose of adjusting the dielectric properties and mechanical properties.

[0055] 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, vinylidene cyanide-vinyl acetate copolymer, cyanoethyl cellulose, cyanoethyl hydroxysucrose, cyanoethyl hydroxycellulose, cyanoethyl hydroxypullulan, cyanoethyl methacrylate, cyanoethyl acrylate, Examples include polymers having a cyano group or a cyanoethyl group, such as cyanoethyl hydroxyethyl cellulose, cyanoethyl amylose, cyanoethyl hydroxypropyl cellulose, cyanoethyl dihydroxypropyl cellulose, cyanoethyl hydroxypropyl amylose, cyanoethyl polyacrylamide, cyanoethyl polyacrylate, cyanoethyl pullulan, cyanoethyl polyhydroxymethylene, cyanoethyl glycidol pullulan, cyanoethyl sucrose, and cyanoethyl sorbitol, as well as synthetic rubbers such as nitrile rubber and chloroprene rubber. Among these, polymeric materials having a cyanoethyl group are preferably used. Furthermore, the dielectric polymer added to the matrix 34 of the piezoelectric layer 20 in addition to the material having viscoelasticity at room temperature, such as cyanoethylated PVA, is not limited to one type, and multiple types may be added.

[0056] In addition to the dielectric polymer, the matrix 34 may contain thermoplastic resins such as vinyl chloride resin, polyethylene, polystyrene, methacrylic resin, polybutene, and isobutylene, as well as thermosetting resins such as phenolic resin, urea resin, melamine resin, alkyd resin, and mica, in order to adjust the glass transition temperature Tg. Furthermore, for the purpose of improving adhesiveness, a tackifier such as rosin ester, rosin, terpene, terpene phenol, or petroleum resin may be added.

[0057] When adding a material other than a viscoelastic polymer material such as cyanoethylated PVA to the matrix 34 of the piezoelectric layer 20, there is no particular limitation on the amount of the material added, but it is preferable that the amount be 30 mass % or less in terms of the proportion of the matrix 34. This allows the properties of the added polymer material to be expressed without impairing the viscoelastic relaxation mechanism in the matrix 34, thereby achieving favorable results in terms of increasing the dielectric constant, improving heat resistance, and improving adhesion with the piezoelectric particles 36 and the electrode layer.

[0058] The piezoelectric particles 36 are made of ceramic particles having a perovskite or wurtzite crystal structure. Examples of ceramic particles that make up the piezoelectric particles 36 include lead zirconate titanate (PZT), lead lanthanum zirconate titanate (PLZT), barium titanate (BaTiO3), zinc oxide (ZnO), and a solid solution of barium titanate and bismuth ferrite (BiFe3) (BFBT).

[0059] There are no restrictions on the particle size of the piezoelectric particles 36, and it may be selected appropriately depending on the size of the piezoelectric film 10 and the intended use of the piezoelectric film 10. The particle size of the piezoelectric particles 36 is preferably 1 to 10 μm. By setting the particle size of the piezoelectric particles 36 within this range, it is possible to obtain favorable results in that the piezoelectric film 10 can achieve both high piezoelectric properties and flexibility.

[0060] In FIG. 2, the piezoelectric particles 36 in the piezoelectric layer 20 are dispersed uniformly and regularly in the matrix 34, but the present invention is not limited to this. That is, the piezoelectric particles 36 in the piezoelectric layer 20 may be dispersed irregularly in the matrix 34, as long as they are preferably dispersed uniformly.

[0061] In the piezoelectric film 10, there is no restriction on the quantitative ratio of the matrix 34 to the piezoelectric particles 36 in the piezoelectric layer 20, and it may be set appropriately depending on the size and thickness of the piezoelectric film 10 in the planar direction, the use of the piezoelectric film 10, and the properties required of the piezoelectric film 10. The volume fraction of the piezoelectric particles 36 in the piezoelectric layer 20 is preferably 30 to 80%, more preferably 50% or more, and therefore, is even more preferably 50 to 80%. By setting the ratio of the matrix 34 to the piezoelectric particles 36 within the above range, favorable results can be obtained in terms of achieving both high piezoelectric properties and flexibility.

[0062] In a preferred embodiment of the piezoelectric film 10 described above, the piezoelectric layer 20 is a polymer composite piezoelectric layer formed by dispersing piezoelectric particles in a viscoelastic matrix containing a polymer material that has viscoelasticity at room temperature. However, the present invention is not limited to this, and a polymer composite piezoelectric material formed by dispersing piezoelectric particles in a matrix containing a polymer material, which is used in known piezoelectric elements, can be used as the piezoelectric layer.

[0063] In the piezoelectric film 10, the thickness of the piezoelectric layer 20 is not particularly limited, and may be set appropriately depending on the application of the piezoelectric film 10, the number of layers of the piezoelectric film 10 in the piezoelectric element described below, the characteristics required of the piezoelectric film 10, etc. The thicker the piezoelectric layer 20, the more advantageous it is in terms of stiffness, such as the stiffness of the sheet-like material, but the voltage (potential difference) required to expand and contract the piezoelectric film 10 by the same amount becomes larger. The thickness of the piezoelectric layer 20 is preferably 10 to 300 μm, more preferably 20 to 200 μm, and even more preferably 30 to 150 μm. By setting the thickness of the piezoelectric layer 20 within the above range, it is possible to obtain favorable results in terms of ensuring both rigidity and appropriate flexibility.

[0064] <Protective layer> In the piezoelectric film 10, the first protective layer 28 and the second protective layer 30 cover the second electrode layer 26 and the first electrode layer 24, and also serve to provide the piezoelectric layer 20 with appropriate rigidity and mechanical strength. That is, in the piezoelectric film 10, the piezoelectric layer 20, which is made up of the matrix 34 and the piezoelectric particles 36, exhibits excellent flexibility with respect to slow bending deformation, but may lack rigidity or mechanical strength depending on the application. The first protective layer 28 and the second protective layer 30 are provided in the piezoelectric film 10 to compensate for this.

[0065] There are no limitations on the first protective layer 28 and the second protective layer 30, and various sheet-like materials can be used, and suitable examples include various resin films. Among these, resin films made of polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS), polycarbonate (PC), polyphenylene sulfite (PPS), polymethyl methacrylate (PMMA), polyetherimide (PEI), polyimide (PI), polyethylene naphthalate (PEN), triacetyl cellulose (TAC), and cyclic olefin resins are preferably used because of their excellent mechanical properties and heat resistance.

[0066] There is no limitation on the thickness of the first protective layer 28 and the second protective layer 30. The thickness of the first protective layer 28 and the second protective layer 30 is basically the same, but may be different. Here, if the rigidity of the first protective layer 28 and the second protective layer 30 is too high, not only will it restrict the expansion and contraction of the piezoelectric layer 20, but it will also impair flexibility. Therefore, except for cases where mechanical strength or good handleability as a sheet-like material is required, it is more advantageous for the first protective layer 28 and the second protective layer 30 to be as thin as possible.

[0067] In the piezoelectric film 10, if the thickness of the first protective layer 28 and the second protective layer 30 is not more than twice the thickness of the piezoelectric layer 20, favorable results can be obtained in terms of ensuring both rigidity and appropriate flexibility. For example, if the thickness of the piezoelectric layer 20 is 50 μm and the first protective layer 28 and the second protective layer 30 are made of PET, the thickness of the first protective layer 28 and the second protective layer 30 is preferably 100 μm or less, more preferably 50 μm or less, and even more preferably 25 μm or less.

[0068] <Electrode layer> In the piezoelectric film 10, a first electrode layer 24 is formed between the piezoelectric layer 20 and the first protective layer 28, and a second electrode layer 26 is formed between the piezoelectric layer 20 and the second protective layer 30. The first electrode layer 24 and the second electrode layer 26 are provided to apply a voltage to the piezoelectric layer 20 (piezoelectric film 10).

[0069] In the present invention, there are no limitations on the materials for forming the first electrode layer 24 and the second electrode layer 26, and various conductors can be used. Specific examples include metals such as carbon, palladium, iron, tin, aluminum, nickel, platinum, gold, silver, copper, titanium, chromium, and molybdenum, alloys thereof, laminates and composites of these metals and alloys, and indium tin oxide. Among these, the aforementioned XE 20 From the viewpoint that it is easy to set the thickness within the above range, copper, aluminum, gold, silver, platinum, and indium tin oxide are suitable examples of materials for the first electrode layer 24 and the second electrode layer 26.

[0070] There are also no limitations on the method for forming the first electrode layer 24 and the second electrode layer 26, and various known methods can be used, such as vapor phase deposition methods (vacuum film formation methods) such as vacuum deposition, ion-assisted deposition, and sputtering, film formation by plating, or a method of adhering a foil formed from the above-mentioned materials.

[0071] Even when the same material is used for the electrode layer, the resistance varies depending on the film quality of the electrode layer (metal film). For example, the resistance increases when there are many grain boundaries and voids in the film. Therefore, it is preferable to adjust the film quality of the electrode layer by controlling the method and conditions for forming the electrode layer.

[0072] Ion-assisted deposition and sputtering are preferred deposition methods because they can produce films with good quality and low resistance. Metal thin films grown by vapor-phase deposition methods such as sputtering and vapor deposition generally have a columnar structure. Because the electrical resistance of these thin films is determined by the grain boundary density per unit area, a columnar structure with as thick individual grains as possible is ideal. For example, in the case of sputtering, a dense columnar structure with few voids and large grain size can be achieved by increasing the substrate temperature as much as possible to promote surface diffusion and reducing the gas pressure as much as possible to lengthen the mean free path and suppress the projection effect. Furthermore, it is also effective to promote surface diffusion by bombarding the substrate with high-speed charged particles, such as ion-assisted deposition.

[0073] There is no limitation on the thickness of the first electrode layer 24 and the second electrode layer 26. Furthermore, the thickness of the first electrode layer 24 and the second electrode layer 26 is basically the same, but may be different.

[0074] Here, similar to the first protective layer 28 and the second protective layer 30 described above, if the rigidity of the first electrode layer 24 and the second electrode layer 26 is too high, not only will it restrict the expansion and contraction of the piezoelectric layer 20, but it will also impair flexibility. Therefore, from the viewpoint of flexibility and piezoelectric properties, it is more advantageous for the first electrode layer 24 and the second electrode layer 26 to be thinner. On the other hand, if the first electrode layer 24 and the second electrode layer 26 are too thin, the electrical resistance will increase, resulting in the above-mentioned XE 20 It becomes difficult to meet the range. From the above viewpoints, the thickness of the first electrode layer 24 and the second electrode layer 26 is preferably 3 μm or less, more preferably 2 μm or less, and even more preferably 1 μm or less. The thickness of the first electrode layer 24 and the second electrode layer 26 is preferably 0.1 μm or more, more preferably 0.2 μm or more, and even more preferably 0.3 μm or more.

[0075] Wiring from a power source is connected to the first electrode layer 24 and the second electrode layer 26, and from the viewpoint of shortening the path length through which current flows, for example, when the planar shape of the piezoelectric film is rectangular, it is preferable to provide the connection points between the first electrode layer 24 and the wiring and the connection points between the second electrode layer 26 and the wiring on the long side. It is also preferable to connect each electrode layer to the wiring at multiple points.

[0076] As described above, the piezoelectric film 10 preferably has a configuration in which a piezoelectric layer 20, which is formed by dispersing piezoelectric particles 36 in a matrix 34 containing a polymeric material that has viscoelasticity at room temperature, is sandwiched between a first electrode layer 24 and a second electrode layer 26, and this laminate is further sandwiched between a first protective layer 28 and a second protective layer 30. In such a piezoelectric film 10, the loss tangent (Tan δ) at a frequency of 1 Hz measured by dynamic viscoelasticity measurement preferably has a maximum value at room temperature, and more preferably has a maximum value of 0.1 or more at room temperature. This allows the strain energy to be effectively diffused to the outside as heat, even if the piezoelectric film 10 is subjected to a relatively slow, large bending deformation of a few Hz or less from the outside, thereby preventing cracks from occurring at the interface between the polymer matrix and the piezoelectric particles.

[0077] The piezoelectric film 10 preferably has a storage modulus (E') of 10 to 30 GPa at 0°C and 1 to 10 GPa at 50°C at a frequency of 1 Hz as measured by dynamic viscoelasticity measurement. This allows the piezoelectric film 10 to have a large frequency dispersion in the storage modulus (E') at room temperature, i.e., it behaves hard against vibrations of 20 Hz to 20 kHz, but soft against vibrations of several Hz or less.

[0078] The piezoelectric film 10 has a thickness multiplied by a storage modulus (E') at a frequency of 1 Hz measured by dynamic viscoelasticity measurement of 1.0×10 6 ~2.0×10 6 N / m, 1.0 x 10 at 50°C 5 ~1.0×10 6 Preferably, it is N / m. This allows the piezoelectric film 10 to have appropriate rigidity and mechanical strength without impairing its flexibility and acoustic properties.

[0079] Furthermore, the piezoelectric film 10 preferably has a loss tangent (Tan δ) of 0.05 or more at 25° C. and a frequency of 1 kHz in a master curve obtained from dynamic viscoelasticity measurement. This makes it possible to smooth the frequency characteristics of a speaker using the piezoelectric film 10, and to reduce the amount of change in sound quality when the minimum resonance frequency f0 changes in accordance with a change in the curvature of the speaker.

[0080] An example of a method for manufacturing the piezoelectric film 10 will now be described with reference to FIGS.

[0081] 4, a sheet-like material 10a is prepared in which a first electrode layer 24 is formed on a first protective layer 28. This sheet-like material 10a may be produced by forming a copper thin film or the like as the first electrode layer 24 on the surface of the first protective layer 28 by vacuum deposition, sputtering, plating, or the like. If the first protective layer 28 is very thin and difficult to handle, a separator (temporary support) may be used as needed. The separator may be made of PET or the like having a thickness of 25 μm to 100 μm. The separator may be removed after the second electrode layer 26 and the second protective layer 30 are thermocompression bonded together and before any other member is laminated on the first protective layer 28.

[0082] On the other hand, a polymer material that will be the matrix material is dissolved in an organic solvent, and piezoelectric particles 36 such as PZT particles are further added and stirred to prepare a coating material that is dispersed. There are no limitations on the organic solvent other than the above substances, and various organic solvents can be used.

[0083] After preparing the sheet material 10a and preparing the coating material, the coating material is cast (applied) onto the sheet material 10a, and the organic solvent is evaporated and dried. As a result, as shown in Fig. 5, a laminate 10b is produced, which has a first electrode layer 24 on a first protective layer 28 and a piezoelectric layer 20 formed on the first electrode layer 24. Note that the first electrode layer 24 refers to the electrode on the substrate side when applying the piezoelectric layer 20, and does not indicate a vertical positional relationship in the laminate.

[0084] There is no limitation on the method for casting this coating material, and all known methods (coating devices) such as a slide coater and a doctor knife can be used.

[0085] As described above, in the piezoelectric film 10, a dielectric polymer material may be added to the matrix 34 in addition to the viscoelastic material such as cyanoethylated PVA. When adding these polymeric materials to the matrix 34, the polymeric materials to be added may be dissolved in the paint described above.

[0086] After fabricating the laminate 10b having the first electrode layer 24 on the first protective layer 28 and the piezoelectric layer 20 formed on the first electrode layer 24, the piezoelectric layer 20 is preferably subjected to a polarization treatment (poling).

[0087] There is no limitation on the method for polarization of the piezoelectric layer 20, and any known method can be used. Before the polarization treatment, the surface of the piezoelectric layer 20 may be smoothed by a calender treatment using a heated roller or the like. By performing the calender treatment, the thermocompression bonding step described below can be carried out smoothly.

[0088] While the piezoelectric layer 20 of the laminate 10b is polarized in this manner, a sheet-like material 10c is prepared in which a second electrode layer 26 is formed on the second protective layer 30. The sheet-like material 10c may be produced by forming a copper thin film or the like as the second electrode layer 26 on the surface of the second protective layer 30 by vacuum deposition, sputtering, plating, or the like. Next, as shown in FIG. 6, the sheet-like material 10c is laminated on the laminate 10b whose piezoelectric layer 20 has been subjected to polarization treatment, with the second electrode layer 26 facing the piezoelectric layer 20. Furthermore, the laminate of this laminate 10b and the sheet-like material 10c is thermocompressed with a heating press device or a pair of heating rollers so as to sandwich the second protective layer 30 and the first protective layer 28, and then cut into the desired shape to produce the piezoelectric film 10.

[0089] The steps up to this point can be performed using a web-like material, i.e., a long, continuous sheet wound up, while transporting it. The laminate 10b and the sheet-like material 10c can also be thermocompression bonded as described above while both are in web form. In this case, the piezoelectric film 10 is produced in web form at this point.

[0090] Furthermore, when laminating the laminate 10b and the sheet-like material 10c, a special adhesive layer may be provided. For example, an adhesive layer may be provided on the surface of the second electrode layer 26 of the sheet-like material 10c. The most suitable adhesive layer is made of the same material as the matrix 34. The same material may also be applied to the surface of the second electrode layer 26 and then laminated.

[0091] [Other aspects of the multilayer piezoelectric element] In the example shown in FIG. 1, the laminated piezoelectric element 50 is configured by stacking multiple piezoelectric films 10 (hereinafter also referred to as a sheet-type laminated piezoelectric element), but the laminated piezoelectric element of the present invention is not limited to this and various configurations can be used.

[0092] An example is shown in Fig. 7. Since the multilayer piezoelectric element 56 shown in Fig. 7 uses a plurality of the same members as the multilayer piezoelectric element 50 described above, the same members are given the same reference numerals, and the following description will mainly focus on the different portions. The multilayer piezoelectric element 56 shown in Fig. 7 is formed by folding a long piezoelectric film 10L in the longitudinal direction one or more times, preferably multiple times, to form multiple layers of piezoelectric films. As with the multilayer piezoelectric element 50 shown in Fig. 1, the piezoelectric element 56 shown in Fig. 7 also has, as a preferred embodiment, the folded piezoelectric films bonded together by an adhesive layer 19. By folding back and stacking a single long piezoelectric film 10L polarized in the thickness direction, the polarization directions of the piezoelectric films in adjacent (facing) parts in the stacking direction become opposite directions, as shown by the arrows in Figure 7. Although the first protective layer 28 and the second protective layer 30 of the piezoelectric film 10L are not shown in FIG. 7, the piezoelectric film 10L may have the first protective layer 28 and the second protective layer 30.

[0093] According to this configuration, the laminated piezoelectric element 56 can be configured using only one long piezoelectric film 10L, only one power supply PS is required to apply the drive voltage, and the electrodes need only be drawn out from the piezoelectric film 10L at one location. Therefore, the multilayer piezoelectric element 56 shown in FIG. 7 can reduce the number of parts and simplify the configuration, improving the reliability of the piezoelectric element (module) and further reducing costs.

[0094] However, in such a structure in which one long piezoelectric film 10L is folded back (hereinafter also referred to as a bellows-type piezoelectric element), the path length through which the current flows tends to be long, and multiple piezoelectric films cannot be connected in parallel like in a sheet-type laminated piezoelectric element. 20 From the viewpoint of satisfying the above range, a single-wafer type multilayer piezoelectric element is preferable.

[0095] In a piezoelectric element 56 formed by folding back a long piezoelectric film 10L, such as the piezoelectric element 56 shown in FIG. 7, it is preferable to insert a core rod 58 into the folded portion of the piezoelectric film 10L in contact with the piezoelectric film 10L. As described above, the first electrode layer 24 and the second electrode layer 26 of the piezoelectric film 10L are formed of a metal vapor deposition film or the like. When a metal vapor deposition film is bent at an acute angle, cracks or the like are likely to occur, which may result in disconnection of the electrodes. That is, in the piezoelectric element 56 shown in FIG. 7, cracks or the like are likely to occur in the electrodes on the inside of the bent portion. In contrast, in a piezoelectric element 56 formed by folding a long piezoelectric film 10L, by inserting a core rod 58 into the folded portion of the piezoelectric film 10L, the first electrode layer 24 and the second electrode layer 26 can be prevented from being folded, and breakage can be suitably prevented.

[0096] <Adhesive layer> There are no limitations on the adhesive layer 19 that bonds the piezoelectric films 10 together, and the adhesive layer 16 that bonds the laminated piezoelectric element 50 and the vibration plate 12, and various known pressure-sensitive adhesives and adhesives can be used.

[0097] As the adhesive layer, various known adhesive layers can be used as long as they can bond the members together. Therefore, the adhesive layer may be a layer made of an adhesive that has fluidity when bonded and then becomes solid, a layer made of a pressure-sensitive adhesive that is a soft gel-like (rubber-like) solid when bonded and does not change to a gel-like state thereafter, or a layer made of a material that has the characteristics of both an adhesive and a pressure-sensitive adhesive.

[0098] Here, the laminated piezoelectric element 50 of the present invention generates sound by expanding and contracting the multiple laminated piezoelectric films 10, for example, to vibrate the diaphragm 12. Therefore, it is preferable that the expansion and contraction of each piezoelectric film 10 is transmitted directly. If a viscous substance that dampens vibration is present between the piezoelectric films 10, the transmission efficiency of the expansion and contraction energy of the piezoelectric films 10 will be reduced, and the driving efficiency of the piezoelectric films 10 will be reduced.

[0099] Considering this point, the adhesive layer is preferably an adhesive layer made of an adhesive, which provides a solid and hard adhesive layer, rather than an adhesive layer made of a pressure-sensitive adhesive.Specific examples of more preferable adhesive layers include adhesive layers made of thermoplastic adhesives such as polyester adhesives and styrene-butadiene rubber (SBR) adhesives. Unlike adhesives, adhesion is useful when high adhesion temperatures are required. Thermoplastic adhesives are suitable because they combine relatively low temperatures, short times, and strong adhesion.

[0100] There is no limitation on the thickness of the adhesive layer, and the thickness may be appropriately set depending on the material forming the adhesive layer so that sufficient adhesive strength (adhesion strength, cohesion strength) can be exhibited. Here, in the multilayer piezoelectric element 50 of the present invention, a thinner adhesive layer can improve the transmission effect of the expansion and contraction energy (vibration energy) of the piezoelectric layer 20, thereby increasing energy efficiency. Also, if the adhesive layer is thick and rigid, it may restrict the expansion and contraction of the piezoelectric film. Furthermore, in a configuration in which adjacent piezoelectric films 10 are stacked with their polarization directions reversed, as shown in Figure 1, there is no risk of adjacent piezoelectric films 10 shorting out, so the adhesive layer can be made thinner. Considering this point, it is preferable that the adhesive layer is thinner than the piezoelectric layer 20. That is, in the multilayer piezoelectric element 50 of the present invention, it is preferable that the adhesive layer is hard and thin. Specifically, the thickness of the adhesive layer after application is preferably 0.1 to 50 μm, more preferably 0.1 to 30 μm, and even more preferably 0.1 to 10 μm.

[0101] In the multilayer piezoelectric element 50 of the present invention, if the spring constant of the adhesive layer is high, it may restrict the expansion and contraction of the piezoelectric film 10. Therefore, it is preferable that the spring constant of the adhesive layer is equal to or less than the spring constant of the piezoelectric film 10. The spring constant is calculated by multiplying the thickness by Young's modulus.

[0102] Specifically, the product of the thickness of the adhesive layer and the storage modulus (E') at a frequency of 1 Hz determined by dynamic viscoelasticity measurement is 2.0 × 10 6N / m or less, 1.0 x 10 at 50°C 6 It is preferable that the resistance is N / m or less. Furthermore, it is preferable that the internal loss at a frequency of 1 Hz in dynamic viscoelasticity measurement of the adhesive layer is 1.0 or less at 25°C in the case of an adhesive layer made of a pressure-sensitive adhesive, and 0.1 or less at 25°C in the case of an adhesive layer made of an adhesive.

[0103] <Vibration plate> There are no limitations on the diaphragm 12, and various types of items can be used. Examples of the diaphragm 12 include plate materials such as resin plates and glass plates, advertising media such as signs, office equipment and furniture such as tables, whiteboards and projection screens, display devices such as organic electroluminescence (OLED (Organic Light Emitting Diode)) displays and liquid crystal displays, vehicle components such as consoles, A-pillars, ceilings and bumpers for automobiles, and building materials such as walls of houses.

[0104] The diaphragm 12 to which the multilayer piezoelectric element 50 of the present invention is attached is preferably flexible, and more preferably is rollable. A particularly suitable example of the flexible diaphragm 12 is a flexible panel-like display device such as a flexible display panel. It is more preferable that the display device is also rollable. Here, it is preferable that the multilayer piezoelectric element 50 bends together with the diaphragm 12 in accordance with the curvature of the diaphragm 12 when it is wound up, so that the multilayer piezoelectric element 50 does not peel off from the diaphragm 12. Since the piezoelectric film 10 has suitable flexibility, the multilayer piezoelectric element 50 of the present invention also basically exhibits good flexibility. In this case, the curvature of the diaphragm 12 when wound is basically a specific curvature, but the curvature of the diaphragm 12 when wound may be variable.

[0105] In the present invention, when the display device is the diaphragm 12, the laminated piezoelectric element 50 is preferably attached to the rear side of the display device, that is, the non-image display surface side of the display device. In this case, it is preferable that the size of the adhesive layer 16 in the planar direction is the same as or smaller than the size of the planar shape of the multilayered piezoelectric element 50 . When using a display device as the diaphragm 12, the display device itself, such as a flexible display panel, may be used as the diaphragm 12, or a plate-shaped member provided on the display device or a plate-shaped member that engages with the display device may be used as the diaphragm 12.

[0106] When the vibration plate 12 is retractable, it is preferable that a driving current is passed through the piezoelectric film 10 when the vibration plate 12 is not retracted, and that no current is passed through the piezoelectric film 10 when the vibration plate 12 is retracted. Furthermore, if the diaphragm 12 is electrically driven, such as in a display device, it is preferable that a driving current is passed through the piezoelectric film 10 and / or the diaphragm 12 when the diaphragm 12 is not wound up, and that no current is passed through the piezoelectric film 10 and / or the diaphragm 12 when the diaphragm 12 is wound up. As a method for switching between energized and de-energized states, various known methods can be used.

[0107] From the viewpoint of increasing sound pressure over a wide frequency band, the planar shape of the multilayer piezoelectric element is preferably rectangular (see FIG. 15). Furthermore, when the planar shape of the multilayer piezoelectric element is rectangular, sound pressure can be increased with the same applied voltage by increasing the length W2 of the long side without changing the length W1 of the short side. This allows the voltage required to obtain the same sound pressure to be lowered, thereby suppressing the amount of heat generated.

[0108] FIG. 15 shows a plan view of an example of a rectangular multilayer piezoelectric element. FIG. 16 shows a side view of FIG. 15 as viewed from the short side. In FIG. 16, the adhesive layer and the electrode lead-out portions are omitted. The example shown in FIGS. 15 and 16 is an example in which a long piezoelectric film 10L is folded multiple times to form a laminate. In the example shown in FIGS. 15 and 16, the direction in which it is folded multiple times is the short side direction.

[0109] 15 and 16, the folded layers are folded so that the lengths of the short sides of the folded layers are the same, but only the outermost layer has an end portion formed with a protruding portion 60 that protrudes from the laminated portion. As shown in Fig. 15, electrode lead portions (62, 64) are provided near both ends of the long side of the protruding portion 60.

[0110] In this way, the planar shape of the multilayer piezoelectric element is rectangular, and the length of the long side W2 is increased while the length of the short side W1 is not changed, thereby suppressing the amount of heat generated. This configuration may be combined with the multilayer piezoelectric element of the present invention described above.

[0111] From the viewpoint of suppressing the amount of heat generation while maintaining the sound pressure level, the ratio of the long side length W2 to the short side length W1 is preferably 3-30, more preferably 3-20, and even more preferably 3-10.

[0112] Here, for rectangular multilayer piezoelectric elements with the same short side length but different long side lengths, the manufacturing process can be further simplified by first fabricating a piezoelectric film laminate with the longer long side and then cutting it as needed. For example, by fabricating a piezoelectric film laminate with long sides of 46 cm and short sides of 3 cm and cutting it 20 cm from one short side, a multilayer piezoelectric element with long sides of 20 cm and short sides of 3 cm and a multilayer piezoelectric element with long sides of 26 cm and short sides of 3 cm can be fabricated.

[0113] FIG. 17 shows an enlarged view of a part of a cross section taken along line BB when a long piezoelectric film 10L is folded multiple times as shown in FIG. 16 to form a laminate and cut parallel to the paper surface.

[0114] When the piezoelectric film 10L is cut after being stacked, the short edge portions of each layer of the piezoelectric film 10L deform in the same direction, as shown in FIG. 17. In the illustrated example, the edge portions of each layer are deformed downward. In this way, the cut edges of each layer deform in the same direction, preventing contact between the electrode layers of each layer and causing a short circuit. In addition, because adhesive layers 19 are provided between each layer, the adhesive layers act as insulators, preventing contact between the electrode layers of each layer and causing a short circuit.

[0115] In the present invention, after cutting a long piezoelectric film 10L, the cut piezoelectric film 10L may be folded back multiple times to form a laminate. In this case, as shown in FIG. 18, the short-side end of each layer of the piezoelectric film 10L is deformed in the opposite direction to the adjacent layer. In a configuration in which the piezoelectric film 10L is folded back multiple times and laminated, the facing electrode layers of adjacent layers are connected, so there is no problem even if they come into contact, and electrode layers with opposite polarities are unlikely to come into contact, preventing short circuits.

[0116] In the present invention, the method for connecting the electrode layer of the piezoelectric film to the wiring is not particularly limited, and various known methods can be used. For example, the electrode layer and the protective layer may have protruding portions on the outer side of the piezoelectric layer in the planar direction, and the wiring may be connected to the electrode layer at the protruding portion. Alternatively, as shown in FIGS. 19 and 20, a portion of the protective layer (second protective layer 30 in FIG. 20) may be removed to form a hole 70, and a conductive member 72 such as silver paste may be placed in this hole 70 to electrically connect the conductive member 72 to the electrode layer (second electrode layer 26 in FIG. 20). Wiring (conductor wire 74a) may then be connected to the electrode layer (second electrode layer 26) via the conductive member 72.

[0117] When the multilayer piezoelectric element is a single-layer type, it is preferable that a protective layer be disposed on the outermost electrode layer of at least the piezoelectric film disposed on the outermost layer of the multilayer piezoelectric element. Note that all of the piezoelectric films of the single-layer type multilayer piezoelectric element may have a protective layer.

[0118] In the multilayer piezoelectric element of the present invention, when at least one piezoelectric film has a protective layer having a hole penetrating from the surface to the electrode layer, a conductive member is disposed (filled) in the hole, and a conductor (wiring) is electrically connected to the electrode layer via the conductive member, C / (A×t) is 260 μF / mm 3 It is preferable that:

[0119] In a configuration in which holes are provided in the protective layer, conductive members are placed in the holes, and the conductors are connected to the electrode layers via the conductive members, all of the current applied to the multilayer piezoelectric element flows through the conductive members, which makes it easy for the conductive members and the electrode layers that come into contact with the conductive members (hereinafter also referred to as electrode contact portions) to generate heat due to current concentration.As a result, there is a risk that the temperature of the multilayer piezoelectric element will rise when the multilayer piezoelectric element is continuously driven, for example.

[0120] In contrast, C / (A×t) is set to 260 μF / mm 3 By doing the following, i.e., by lowering the capacitance of the multilayer piezoelectric element and / or increasing the volume of the electrode layer at the electrode contact portion, the current density at the electrode contact portion can be reduced, and local heat generation at the electrode contact portion can be suppressed.

[0121] From the viewpoint of heat suppression, C / (A×t) is 260μF / mm 3 Less than 150μF / mm is more preferable. 3 On the other hand, from the viewpoint of productivity, C / (A×t) is preferably 50 μF / mm 3 More than is preferable

[0122] The capacitance C of the multilayer piezoelectric element can be measured between the wirings drawn out from each electrode layer of the piezoelectric film constituting the multilayer piezoelectric element using an LCR meter (e.g., ZM2372 manufactured by NF Corporation) etc. The measurement was carried out at a measurement frequency of 1 kHz and a voltage of 5 V. In addition, when the laminated piezoelectric element is a sheet type, the capacitance C of the laminated piezoelectric element can be measured with the two electrode layers of each piezoelectric film connected to each other with the electrode layers of the same polarity, that is, with multiple piezoelectric films connected in parallel.

[0123] The capacitance C of the piezoelectric film is determined by the thickness, area, and dielectric constant of the piezoelectric layer. Therefore, by adjusting these, the capacitance C of the piezoelectric film can be adjusted.

[0124] The opening area A of the hole (area in a plan view) can be measured by removing the conductive wire and exposing the hole in the protective layer using a CNC image measuring device (such as Quick Vision manufactured by Mitutoyo Corporation). If the outline of the hole cannot be seen, the conductive material may be removed. In this case, it is necessary to select a method that does not damage the protective layer.

[0125] From the viewpoint of reducing C / (A×t), it is preferable that the opening area A of the hole is large. On the other hand, if the opening area A of the hole is too large, it is disadvantageous in terms of productivity.

[0126] Furthermore, the shape of the opening of the hole (shape in plan view) is not limited, and may be various shapes such as circular, elliptical, rectangular, polygonal, irregular, etc. From the viewpoint of ease of formation, a circular shape is preferred.

[0127] The method for forming the holes is not limited, and may be a known method depending on the material for forming the protective layer, such as laser processing, dissolving and removing using a solvent, or mechanical processing such as mechanical polishing.

[0128] The thickness of the electrode layer can be measured by cutting the piezoelectric film using an ultramicrotome (such as UC6 ​​manufactured by Leica) and then observing the cross section using an SEM (such as SU8220 manufactured by Hitachi High-Technologies).

[0129] As the conductive member, conductive paste such as silver paste, solder, conductive cloth, metal cloth, conductive urethane foam, etc. can be used. The conductive paste may be a material containing silver, copper, gold, carbon, nickel, solder, or the like as a filler. The conductive paste may be filled into the hole using a dispenser or the like. A sufficient amount of conductive paste is preferably filled to fill the hole. More preferably, the conductive paste is filled to an amount that bulges out of the hole, or the conductive paste is filled to an amount that overflows the hole.

[0130] The conductive fabric is, for example, a woven or nonwoven fabric made from resin threads whose surfaces are coated with a metal film by plating or the like. Various known conductive fabrics can be used as the conductive fabric. For example, conductive fabrics made from PET threads whose surfaces are plated with Cu or Ni can be used. Specifically, Sui-10-511M manufactured by Seiren Co., Ltd. can be used as the conductive fabric.

[0131] The metal cloth is a woven or nonwoven fabric made of metal thread. Various known metal cloths can be used as the metal cloth. As an example, a plain woven wire mesh (Φ0.05×200 m / s) manufactured by Okutani Wire Mesh Manufacturing Co., Ltd. can be used as the metal cloth.

[0132] The conductive urethane foam is a soft urethane foam carrying conductive particles such as carbon black, etc. As the conductive urethane foam, various known conductive urethane foams can be used.

[0133] Furthermore, the thickness of the conductive member is preferably greater than the thickness of the protective layer, thereby ensuring a reliable connection between the conductive member and the conductor.

[0134] The conductor may be a sheet (metal foil) or wire (metal wire) made of a conductive metal material. Suitable materials for the conductor include copper, aluminum, nickel, tin, gold, and silver. Alternatively, an FFC cable may be used as the conductor.

[0135] There are no particular limitations on the shape and size of the conductor wire, as long as it can be electrically connected to the conductive member and can be used as an extraction electrode.

[0136] Furthermore, the connection between the conductor and the conductive member may be performed by a known method. When the conductive member is a conductive paste, the conductor and the conductive member may be connected by contacting the conductor and the conductive paste and then curing the conductive paste. Alternatively, the conductor and the conductive member may be connected by covering at least a portion of the contact area with the conductor and the conductive member in contact with each other and adhering an adhesive tape onto the protective layer. Alternatively, the connection between the conductor and the conductive member may be fixed by adhering the protective layer to the conductor and the conductive member in contact with each other.

[0137] The multilayer piezoelectric element of the present invention has been described in detail above, but the present invention is not limited to the above examples, and various improvements and modifications may be made without departing from the spirit and scope of the present invention. [Example]

[0138] The present invention will be described in more detail below with reference to specific examples of the present invention. However, the present invention is not limited to these examples, and the materials, amounts used, ratios, processing details, processing procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention.

[0139] [Example 1] Sheets 10a and 10c were prepared by forming a 100 nm thick copper thin film on a 4 μm thick PET film by sputtering. That is, in this example, first electrode layer 24 and second electrode layer 26 were 100 nm thick copper thin films, and first protective layer 28 and second protective layer 30 were 4 μm thick PET films. The gas pressure when sputtering the copper thin film onto the PET film was 0.4 Pa, and the substrate temperature (temperature of the PET film) was 120° C. In the column for the electrode layer formation method in Table 1 below, the case where sputtering was performed under the same conditions as in Example 1 is represented as "Sputtering 1." To ensure good handling during the process, the PET film used had a 50 μm thick separator (PET temporary support), and the separators of each protective layer were removed after the sheet-like material 10c was thermocompression bonded.

[0140] First, cyanoethylated PVA (CR-V, manufactured by Shin-Etsu Chemical Co., Ltd.) was dissolved in methyl ethyl ketone (MEK) at the following composition ratio. Then, PZT particles were added to this solution at the following composition ratio and dispersed using a propeller mixer (rotation speed: 2000 rpm) to prepare a coating material for forming the piezoelectric layer 20. ·PZT particles 300 parts by mass Cyanoethylated PVA 15 parts by mass ·MEK·················85 parts by mass The PZT particles used were prepared by sintering commercially available PZT raw material powder at 1000 to 1200° C., followed by crushing and classifying the sintered powder to an average particle size of 5 μm.

[0141] The previously prepared coating material for forming the piezoelectric layer 20 was applied using a slide coater onto the first electrode layer 24 (thin copper film) of the previously prepared sheet material 10a. The coating material was applied so that the thickness of the coating film after drying would be 20 μm. Next, the sheet-like material 10a with the coating applied thereon was heated and dried on a hot plate at 120° C. to evaporate the MEK, thereby forming a laminate 10b.

[0142] The sheet-like material 10c was laminated on the laminate 10b with the second electrode layer 26 (thin copper film side) facing the piezoelectric layer 20, and was thermocompression bonded at 120°C. In this way, a piezoelectric film 10 was produced, which had the first protective layer 28, the first electrode layer 24, the piezoelectric layer 20, the second electrode layer 26, and the second protective layer 30 in this order.

[0143] The produced piezoelectric film was cut into a piece measuring 200 mm × 190 mm in plan view and folded four times in the longitudinal direction to produce a bellows-shaped piezoelectric element 56. The folded surfaces that came into contact were bonded together using a thermal adhesive sheet (FB-ML4 manufactured by Nitto Shinko Corporation). Furthermore, the first electrode layer 24 was connected to a wire at one end of the long side of the folded piezoelectric film, and the second electrode layer 26 was connected to a wire at the other end, as described below.

[0144] Holes were formed in the first and second protective layers using a laser processing machine. The opening shape of the holes was circular, and the opening area was 60 mm 2 A conductive paste containing Ni filler was used as the conductive member, and copper foil with a thickness of 35 μm was used as the wiring (conductor wire). After the conductive paste was filled into the holes using a dispenser, the wiring was brought into contact with the conductive paste, and the conductive paste was dried and hardened.

[0145] The capacitive reactance Xc and equivalent series resistance ESR of the fabricated piezoelectric element were measured using the method described above. A graph of the measured frequency and resistance value is shown in Figure 8. From Figure 8, the capacitive reactance Xc at 1 kHz was 148 Ω, and the equivalent series resistance ESR was 12.2 Ω. Therefore, the ratio of capacitive reactance Xc to equivalent series resistance ESR = Xc / ESR was 12.1. On the other hand, the capacitive reactance Xc at 20 kHz was 8.29 Ω, and the equivalent series resistance ESR was 0.77 Ω. Therefore, the ratio of capacitive reactance Xc to equivalent series resistance ESR = Xc / ESR was 10.8. When Xc / ESR at 1 kHz is set to 1, Xc / ESR at 20 kHz, that is, XE 20 was 0.89.

[0146] Furthermore, the capacitance between the wiring connected to the first electrode layer 24 and the wiring connected to the second electrode layer 26 of the fabricated multilayer piezoelectric element was measured using an LCR meter (for example, ZM2372 manufactured by NF Corporation), and was found to be 1.2 μF. Therefore, the capacitance C divided by the opening area A of the hole and the thickness t of the electrode layer, C / (A×t), was 200.0 μF / mm 3 It was.

[0147] [Example 2] A piezoelectric film was produced in the same manner as in Example 1, except that the thickness of the first electrode layer 24 and the second electrode layer 26 (copper thin film) was set to 150 nm.

[0148] The capacitive reactance Xc and equivalent series resistance ESR of the fabricated piezoelectric element were measured using the method described above. A graph of the measured frequency and resistance value is shown in Figure 9. From Figure 9, the capacitive reactance Xc at 1 kHz was 149 Ω, and the equivalent series resistance ESR was 12.3 Ω. Therefore, the ratio of capacitive reactance Xc to equivalent series resistance ESR = Xc / ESR was 12.1. On the other hand, the capacitive reactance Xc at 20 kHz was 8.32 Ω, and the equivalent series resistance ESR was 0.58 Ω. Therefore, the ratio of capacitive reactance Xc to equivalent series resistance ESR = Xc / ESR was 14.3. When Xc / ESR at 1 kHz is set to 1, Xc / ESR at 20 kHz, that is, XE 20 was 1.18.

[0149] The capacitance of the fabricated multilayer piezoelectric element was 1.2 μF, and C / (A×t) was 133.3 μF / mm 3 It was.

[0150] [Example 3] The piezoelectric film 10 produced in Example 1 was cut into five pieces measuring 200 mm × 38 mm in plan view, and the five cut-out piezoelectric films 10 were stacked to produce a sheet-type piezoelectric element 50. Adjacent piezoelectric films 10 were bonded to each other using a thermal adhesive sheet (FB-ML4 manufactured by Nitto Shinko Corporation). In addition, the first electrode layer 24 was connected to wiring on one side of each 200 mm side of each piezoelectric film 10 in the width direction, and the second electrode layer 26 was connected to wiring on the other side. That is, the first electrode layer 24 of each piezoelectric film 10 was connected to wiring at two points, and the second electrode layer 26 was connected to wiring at two points. In addition, the piezoelectric films 10 were connected in parallel.

[0151] The capacitive reactance Xc and equivalent series resistance ESR of the fabricated piezoelectric element were measured using the method described above. A graph of the measured frequency and resistance value is shown in Figure 10. From Figure 10, the capacitive reactance Xc at 1 kHz was 150 Ω, and the equivalent series resistance ESR was 12.1 Ω. Therefore, the ratio of the capacitive reactance Xc to the equivalent series resistance ESR, Xc / ESR, was 12.1. On the other hand, the capacitive reactance Xc at 20 kHz was 8.37 Ω, and the equivalent series resistance ESR was 0.70 Ω. Therefore, the ratio of the capacitive reactance Xc to the equivalent series resistance ESR, Xc / ESR, was 12.0. When Xc / ESR at 1 kHz is set to 1, Xc / ESR at 20 kHz, i.e., XE 20 was 0.99.

[0152] The capacitance of the fabricated multilayer piezoelectric element was 1.2 μF. C / (A×t) was 200.0 μF / mm 3 It was.

[0153] [Example 4] A single-wafer type piezoelectric element 50 was fabricated in the same manner as in Example 3, except that the copper thin film was formed by ion-assisted deposition to a thickness of 150 nm. The ion gun used for ion-assisted deposition of the copper thin film on the PET film was ST55 (1500 W, 7 A, 225 eV) manufactured by TELEMARK.

[0154] The capacitive reactance Xc and equivalent series resistance ESR of the fabricated piezoelectric element were measured using the method described above. A graph of the measured frequency and resistance value is shown in Figure 11. From Figure 11, the capacitive reactance Xc at 1 kHz was 148 Ω, and the equivalent series resistance ESR was 12.1. Therefore, the ratio of the capacitive reactance Xc to the equivalent series resistance ESR, Xc / ESR, was 12.2. On the other hand, the capacitive reactance Xc at 20 kHz was 8.28 Ω, and the equivalent series resistance ESR was 0.73 Ω. Therefore, the ratio of the capacitive reactance Xc to the equivalent series resistance ESR, Xc / ESR, was 11.4. When Xc / ESR at 1 kHz is set to 1, Xc / ESR at 20 kHz, i.e., XE 20 was 0.93.

[0155] The capacitance of the fabricated multilayer piezoelectric element was 1.2 μF, and C / (A×t) was 133.3 μF / mm 3 It was.

[0156] [Example 5] The opening area A of the hole is 40 mm 2 A bellows-type piezoelectric element was produced in the same manner as in Example 2, except that:

[0157] The capacitive reactance Xc and equivalent series resistance ESR of the fabricated piezoelectric element were measured using the method described above. The capacitive reactance Xc at 1 kHz was 147 Ω, and the equivalent series resistance ESR was 12.9 Ω. Therefore, the ratio of the capacitive reactance Xc to the equivalent series resistance ESR, Xc / ESR, was 11.4. On the other hand, the capacitive reactance Xc at 20 kHz was 8.36 Ω, and the equivalent series resistance ESR was 0.68 Ω. Therefore, the ratio of the capacitive reactance Xc to the equivalent series resistance ESR, Xc / ESR, was 12.3. When Xc / ESR at 1 kHz is set to 1, Xc / ESR at 20 kHz, i.e., XE 20 was 1.08.

[0158] The capacitance of the fabricated multilayer piezoelectric element was 1.2 μF, and C / (A×t) was 200.0 μF / mm 3 It was.

[0159] [Example 6] The thickness of the first electrode layer 24 and the second electrode layer 26 (copper thin film) is set to 300 nm, and the opening area A of the hole is set to 20 mm 2 A piezoelectric film was produced in the same manner as in Example 1, except that:

[0160] The capacitive reactance Xc and equivalent series resistance ESR of the fabricated piezoelectric element were measured using the method described above. The capacitive reactance Xc at 1 kHz was 145 Ω, and the equivalent series resistance ESR was 10.2 Ω. Therefore, the ratio of the capacitive reactance Xc to the equivalent series resistance ESR, Xc / ESR, was 14.2. On the other hand, the capacitive reactance Xc at 20 kHz was 8.44 Ω, and the equivalent series resistance ESR was 0.49 Ω. Therefore, the ratio of the capacitive reactance Xc to the equivalent series resistance ESR, Xc / ESR, was 17.2. When Xc / ESR at 1 kHz is set to 1, Xc / ESR at 20 kHz, i.e., XE 20 was 1.21.

[0161] The capacitance of the fabricated multilayer piezoelectric element was 1.2 μF, and C / (A×t) was 200.0 μF / mm 3 It was.

[0162] [Example 7] The opening area A of the hole is 30 mm 2 A piezoelectric film was produced in the same manner as in Example 6, except that:

[0163] The capacitive reactance Xc and equivalent series resistance ESR of the fabricated piezoelectric element were measured using the method described above. The capacitive reactance Xc at 1 kHz was 145 Ω, and the equivalent series resistance ESR was 10.0 Ω. Therefore, the ratio of the capacitive reactance Xc to the equivalent series resistance ESR, Xc / ESR, was 14.5. On the other hand, the capacitive reactance Xc at 20 kHz was 8.43 Ω, and the equivalent series resistance ESR was 0.44 Ω. Therefore, the ratio of the capacitive reactance Xc to the equivalent series resistance ESR, Xc / ESR, was 19.2. When Xc / ESR at 1 kHz is set to 1, Xc / ESR at 20 kHz, i.e., XE20 was 1.33.

[0164] The capacitance of the fabricated multilayer piezoelectric element was 1.2 μF, and C / (A×t) was 133.3 μF / mm 3 It was.

[0165] [Example 8] The opening area A of the hole is 15 mm 2 A piezoelectric film was produced in the same manner as in Example 6, except that:

[0166] The capacitive reactance Xc and equivalent series resistance ESR of the fabricated piezoelectric element were measured using the method described above. The capacitive reactance Xc at 1 kHz was 146 Ω, and the equivalent series resistance ESR was 10.4 Ω. Therefore, the ratio of the capacitive reactance Xc to the equivalent series resistance ESR, Xc / ESR, was 14.0. On the other hand, the capacitive reactance Xc at 20 kHz was 8.46 Ω, and the equivalent series resistance ESR was 0.54 Ω. Therefore, the ratio of the capacitive reactance Xc to the equivalent series resistance ESR, Xc / ESR, was 15.7. When Xc / ESR at 1 kHz is set to 1, Xc / ESR at 20 kHz, i.e., XE 20 was 1.12.

[0167] The capacitance of the fabricated multilayer piezoelectric element was 1.2 μF, and C / (A×t) was 266.6 μF / mm 3 It was.

[0168] [Comparative Example 1] A bellows-type piezoelectric element was produced in the same manner as in Example 1, except that the copper thin film was formed by vacuum deposition. The deposition source for vacuum deposition of copper thin film on PET film was a resistance heating type, the substrate temperature was 50°C, and the gas pressure was 5 × 10 -3 It was Pa.

[0169] The capacitive reactance Xc and equivalent series resistance ESR of the fabricated piezoelectric element were measured using the method described above. A graph of the measured frequency and resistance value is shown in Figure 12. From Figure 12, the capacitive reactance Xc at 1 kHz was 151 Ω, and the equivalent series resistance ESR was 11.8 Ω. Therefore, the ratio of the capacitive reactance Xc to the equivalent series resistance ESR, Xc / ESR, was 12.8. On the other hand, the capacitive reactance Xc at 20 kHz was 8.33 Ω, and the equivalent series resistance ESR was 1.25 Ω. Therefore, the ratio of the capacitive reactance Xc to the equivalent series resistance ESR, Xc / ESR, was 6.7. When Xc / ESR at 1 kHz is set to 1, Xc / ESR at 20 kHz, i.e., XE 20 was 0.52.

[0170] The capacitance of the fabricated multilayer piezoelectric element was 1.2 μF, and C / (A×t) was 200.0 μF / mm 3 It was.

[0171] Comparative Example 2 A bellows-type piezoelectric element was fabricated in the same manner as in Example 1, except that the gas pressure when sputtering a copper thin film onto the PET film was 1.2 Pa and the substrate temperature (temperature of the PET film) was 60° C. In the column for the electrode layer formation method in Table 1 below, the case where sputtering was performed under the same conditions as in Comparative Example 2 is represented as "Sputtering 2."

[0172] The capacitive reactance Xc and equivalent series resistance ESR of the fabricated piezoelectric element were measured using the method described above. A graph of the measured frequency and resistance value is shown in Figure 13. From Figure 13, the capacitive reactance Xc at 1 kHz was 152 Ω, and the equivalent series resistance ESR was 11.6 Ω. Therefore, the ratio of capacitive reactance Xc to equivalent series resistance ESR = Xc / ESR was 13.1. On the other hand, the capacitive reactance Xc at 20 kHz was 8.34 Ω, and the equivalent series resistance ESR was 1.15 Ω. Therefore, the ratio of capacitive reactance Xc to equivalent series resistance ESR = Xc / ESR was 7.25. When Xc / ESR at 1 kHz is set to 1, Xc / ESR at 20 kHz, i.e., XE 20 was 0.55.

[0173] The capacitance of the fabricated multilayer piezoelectric element was 1.2 μF, and C / (A×t) was 200.0 μF / mm 3 It was.

[0174] Comparative Example 3 The piezoelectric film produced in Example 1 was cut into a size of 200 mm × 380 mm in plan view and folded nine times in the longitudinal direction to produce a bellows-shaped piezoelectric element 56. The surfaces that came into contact after folding were bonded together using a thermal adhesive sheet (FB-ML4 manufactured by Nitto Shinko Corporation). Furthermore, the first electrode layer 24 was connected to a wire at one end of the long side of the folded piezoelectric film, and the second electrode layer 26 was connected to a wire at the other end.

[0175] The capacitive reactance Xc and equivalent series resistance ESR of the fabricated piezoelectric element were measured using the method described above. A graph of the measured frequency and resistance value is shown in Figure 14. From Figure 14, the capacitive reactance Xc at 1 kHz was 64.1 Ω, and the equivalent series resistance ESR was 6.12 Ω. Therefore, the ratio of the capacitive reactance Xc to the equivalent series resistance ESR, Xc / ESR, was 10.5. On the other hand, the capacitive reactance Xc at 20 kHz was 3.66 Ω, and the equivalent series resistance ESR was 1.05 Ω. Therefore, the ratio of the capacitive reactance Xc to the equivalent series resistance ESR, Xc / ESR, was 3.49. When Xc / ESR at 1 kHz is set to 1, Xc / ESR at 20 kHz, i.e., XE 20 was 0.33.

[0176] The capacitance of the fabricated multilayer piezoelectric element was 2.4 μF, and C / (A×t) was 400.0 μF / mm 3 It was.

[0177] Comparative Example 4 The opening area A of the hole is 20 mm 2 A bellows-type piezoelectric element was produced in the same manner as in Comparative Example 2, except that:

[0178] The capacitive reactance Xc and equivalent series resistance ESR of the fabricated piezoelectric element were measured using the method described above. The capacitive reactance Xc at 1 kHz was 150 Ω, and the equivalent series resistance ESR was 13.5 Ω. Therefore, the ratio of the capacitive reactance Xc to the equivalent series resistance ESR, Xc / ESR, was 11.1. On the other hand, the capacitive reactance Xc at 20 kHz was 8.31 Ω, and the equivalent series resistance ESR was 1.41 Ω. Therefore, the ratio of the capacitive reactance Xc to the equivalent series resistance ESR, Xc / ESR, was 5.9. When Xc / ESR at 1 kHz is set to 1, Xc / ESR at 20 kHz, i.e., XE 20 was 0.53.

[0179] The capacitance of the fabricated multilayer piezoelectric element was 1.2 μF, and C / (A×t) was 600.0 μF / mm 3 It was.

[0180] Comparative Example 5 The thickness of the first electrode layer 24 and the second electrode layer 26 (copper thin film) is set to 300 nm, and the opening area A of the hole is set to 8 mm 2 A bellows-type piezoelectric element was produced in the same manner as in Comparative Example 2, except that:

[0181] The capacitive reactance Xc and equivalent series resistance ESR of the fabricated piezoelectric element were measured using the method described above. The capacitive reactance Xc at 1 kHz was 146 Ω, and the equivalent series resistance ESR was 12.2 Ω. Therefore, the ratio of the capacitive reactance Xc to the equivalent series resistance ESR, Xc / ESR, was 12.0. On the other hand, the capacitive reactance Xc at 20 kHz was 8.42 Ω, and the equivalent series resistance ESR was 1.22 Ω. Therefore, the ratio of the capacitive reactance Xc to the equivalent series resistance ESR, Xc / ESR, was 6.90. When Xc / ESR at 1 kHz is set to 1, Xc / ESR at 20 kHz, i.e., XE 20 was 0.58.

[0182] The capacitance of the fabricated multilayer piezoelectric element was 1.2 μF, and C / (A×t) was 500.0 μF / mm 3 It was.

[0183] [evaluation] The fabricated multilayer piezoelectric element was connected to a continuous drive tester (40 Vrms), suspended in the air, and the temperature reached by the multilayer piezoelectric element after one hour of continuous drive was measured. The input signal was an SN2 signal. The SN2 signal is a noise signal standard established by JEITA, and is a noise signal in which the high-frequency and low-frequency components of a white noise signal have been cut off. The frequency of the applied voltage was in the range of 20 Hz to 20 kHz. The temperature of the multilayer piezoelectric element was measured at an arbitrary position that showed the highest temperature reached. The results are shown in Table 1.

[0184] [Table 1]

[0185] Table 1 shows that the piezoelectric element of the present invention reaches a lower temperature than the comparative example, and can suppress heat generation. Furthermore, a comparison between Example 1 and Comparative Example 2 shows that even when the same film formation method is used, the film quality changes depending on the film formation conditions, and poor film quality increases heat generation. Furthermore, a comparison between Example 1 and Comparative Example 3 shows that the longer the path length through which the current flows, the greater the heat generation. Furthermore, a comparison between Example 1 and Example 3 reveals that when a piezoelectric element is formed by stacking piezoelectric films, it is preferable to connect the piezoelectric films in parallel.

[0186] Furthermore, a comparison between Example 2 and Example 5, and a comparison between Examples 6 to 8, shows that the smaller C / (A×t) is, the lower the reached temperature is, and 3 It is found that the following are preferred:

[0187] [Reference example 1] Sheets 10a and 10c were prepared by forming a 300 nm thick copper thin film on a 5 μm thick PET film by vacuum deposition. The conditions for vacuum deposition of the copper thin film were the same as those in Comparative Example 1. That is, in this example, first electrode layer 24 and second electrode layer 26 were copper thin films with a thickness of 300 nm, and first protective layer 28 and second protective layer 30 were PET films with a thickness of 5 μm.

[0188] Using these sheets 10a and 10c, a piezoelectric layer 20 having a thickness of 50 μm was formed in the same manner as in Example 1, to produce a long piezoelectric film 10L.

[0189] The fabricated piezoelectric film was cut into a size of 150 mm x 200 mm in plan view and folded four times in the 150 mm direction to fabricate a bellows-shaped multilayer piezoelectric element. That is, the short side of the multilayer piezoelectric element was 30 mm and the long side was 200 mm. The folded surfaces that came into contact were bonded together using a butadiene-based adhesive. The thickness of the adhesive layer was 30 μm.

[0190] Furthermore, the first electrode layer 24 was connected to a wire at one end of the long side of the folded laminated piezoelectric element, and the second electrode layer 26 was connected to a wire at the other end.

[0191] [Reference Examples 2 and 3] Multilayer piezoelectric elements were fabricated in the same manner as in Reference Example 1, except that the lengths of the long sides were set to 260 mm and 320 mm.

[0192] [evaluation] The fabricated laminated piezoelectric element was attached to a diaphragm as an exciter and the sound pressure was measured. The diaphragm was a duralumin plate with a thickness of 0.8 mm and dimensions of 450 mm x 500 mm. The laminated piezoelectric element was attached to the approximate center of the diaphragm, with the horizontal direction of the diaphragm aligned with the longitudinal direction of the laminated piezoelectric element.

[0193] The laminated piezoelectric element was connected to a continuous drive tester, driven with an applied voltage of 40 Vrms, and the sound pressure was measured using a microphone placed 1 m from the center of the diaphragm. The sound pressure measurement results for each frequency from 1 kHz to 20 kHz are shown in Table 2.

[0194] [Table 2]

[0195] From Table 2, it can be seen that by increasing the length of the long side, it is possible to uniformly improve the sound pressure mainly in the range of 1 kHz to 15 kHz.

[0196] Furthermore, when an applied voltage of 40 Vrms was applied, the temperature of a multilayer piezoelectric element with a long side length of 200 mm was approximately 40°C. The applied voltage was adjusted to a multilayer piezoelectric element with a long side length of 260 mm to obtain the same sound pressure as when an applied voltage of 40 Vrms was applied to a multilayer piezoelectric element with a long side length of 200 mm, and the result was 32 Vrms. At this time, the temperature of the multilayer piezoelectric element was approximately 33°C. In other words, when a multilayer piezoelectric element with a long side length of 260 mm was used to achieve the same sound pressure as when an applied voltage of 40 Vrms was applied to a 200 mm long side, the temperature of the multilayer piezoelectric element dropped by approximately 7°C.

[0197] From the above results, it can be seen that by increasing the length of the long side of the laminated piezoelectric element, it is possible to increase the sound pressure with the same applied voltage, and therefore it is possible to reduce the voltage required to obtain the same sound pressure, thereby further reducing heat generation. The above results clearly demonstrate the effectiveness of the present invention. [Explanation of symbols]

[0198] 10 Piezoelectric film 10a, 10c Sheet-like object 10b Laminate 12 Diaphragm 16, 19 Adhesive layer 20 Piezoelectric layer 24 1st electrode layer 26 Second electrode layer 28 1st protective layer 30 Second protective layer 34 Viscoelastic matrix 36 Piezoelectric particles 50, 56 Piezoelectric element 58 Core rod 60 overhang 62, 64 Electrode lead-out section 70 Hole 72 Conductive material 74a, 74b conductor

Claims

1. A multilayer piezoelectric element is formed by laminating a plurality of piezoelectric films each having a piezoelectric layer made of a polymer composite piezoelectric material containing piezoelectric particles in a matrix containing a polymer material, and electrode layers formed on both sides of the piezoelectric layer, When the value obtained by dividing the capacitive reactance Xc of the piezoelectric film at a frequency of 1 kHz by the equivalent series resistance ESR is set to 1, the value XE obtained by dividing the capacitive reactance Xc of the piezoelectric film at a frequency of 20 kHz by the equivalent series resistance ESR is 20 is in the range of 0.6 to 1.

5.

2. 2. The multilayer piezoelectric element according to claim 1, wherein the polymer material has viscoelasticity at room temperature.

3. The XE 20 3. The multilayer piezoelectric element according to claim 1, wherein the value of the saturation coefficient is in the range of 0.8 to 1.

3.

4. 4. The multilayer piezoelectric element according to claim 1, wherein the electrode layer has a thickness of 1 μm or less.

5. the piezoelectric film laminated on at least the outermost layer of the multilayer piezoelectric element has a protective layer laminated on a surface of the electrode layer on the outermost layer side opposite to the piezoelectric layer, the protective layer has a hole penetrating from a surface to the electrode layer, a conductive member disposed in the hole; 5. The multilayer piezoelectric element according to claim 1, further comprising: a conductive wire disposed on a surface of the hole in the protective layer and electrically connected to the electrode layer via the conductive member.

6. When the opening area of ​​the hole is A, the thickness of the electrode layer is t, and the capacitance of the laminated piezoelectric element is C, C / (A×t) is 260 μF / mm 3 6. The multilayer piezoelectric element according to claim 5, wherein:

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