Piezoelectric film

Abstract

The invention provides a piezoelectric film capable of further improving sound pressure. A piezoelectric film comprises: a piezoelectric body layer comprising a polymer composite piezoelectric body in which piezoelectric body particles are included in a matrix comprising a polymer material; and two electrode layers provided on both surfaces of the piezoelectric layer, in which 10 regions having the same width as the thickness of the cross-section of the piezoelectric layer are continuously obtained by observing the cross-section of the piezoelectric layer in the thickness direction by a scanning electron microscope, and each region is divided into 10 regions in the in-plane direction, the piezoelectric film satisfies 1 < = in-plane standard deviation < = 3, where the standard deviation when the area ratio of the piezoelectric particles in each of 100 partitions is calculated is defined as in-plane standard deviation, and each of the regions is divided into 10 regions in the thickness direction. The piezoelectric film satisfies 0.5 < = standard thickness deviation < = 2, where the standard deviation when the area ratio of the piezoelectric particles in each of 100 partitions is calculated is defined as the standard thickness deviation.

Description

Technical Field

[0001] The present invention relates to a piezoelectric film. Background Art

[0002] As displays such as liquid crystal displays and organic EL displays become thinner, the speakers used in these thin displays are also required to be lightweight and thinner. In addition, in flexible displays with flexibility, in order to integrate the speaker with the flexible display without compromising the lightweight and flexibility, the speaker is also required to be flexible. As such a lightweight and thin flexible speaker, a sheet-like piezoelectric film (electroacoustic converter film) having the property of expanding and contracting in response to an applied voltage can be considered.

[0003] As a sheet-like piezoelectric film, for example, a film made of a material having piezoelectricity such as PVDF (polyvinylidene fluoride) is known. In addition, the applicant has proposed a piezoelectric film which is sheet-like and flexible, and which is a piezoelectric film capable of stably reproducing high-quality sound, and uses a polymer composite piezoelectric body in which piezoelectric particles are dispersed in a matrix composed of a polymer material as a piezoelectric layer.

[0004] For example, Patent Document 1 describes a piezoelectric film comprising: a polymer composite piezoelectric body comprising piezoelectric particles in a matrix comprising a polymer material; and electrode layers disposed on both surfaces of the polymer composite piezoelectric body. The cross section in the thickness direction is observed using a scanning electron microscope, the polymer composite piezoelectric body is divided into 10 equal parts in the thickness direction, and the area ratio of the piezoelectric particles in the two most separated regions is measured. When the area ratio of the piezoelectric particles in the region with a low area ratio is set to 1, the area ratio of the piezoelectric particles in the region with a high area ratio is greater than 1.2.

[0005] Previous technical literature

[0006] Patent Literature

[0007] Patent Document 1: International Publication No. 2021 / 157288 Summary of the invention

[0008] Technical issues to be solved by the invention

[0009] This piezoelectric film is required to further increase the sound pressure.

[0010] An object of the present invention is to solve the problems of the prior art and to provide a piezoelectric film capable of further improving the sound pressure.

[0011] Means for solving technical problems

[0012] In order to solve the above-mentioned problems, the present invention has the following configuration.

[0013] [1] A piezoelectric film comprising: a piezoelectric layer composed of a polymer composite piezoelectric body containing piezoelectric particles in a matrix containing a polymer material; and two electrode layers provided on both sides of the piezoelectric layer, wherein:

[0014] The cross section of the piezoelectric layer in the thickness direction is observed by a scanning electron microscope, 10 regions with the same width as the thickness of the cross section of the piezoelectric layer are continuously obtained, and each region is divided into 10 in the in-plane direction. When the standard deviation of the area ratio of the piezoelectric particles in each of the 100 partitions is calculated as the in-plane standard deviation, the piezoelectric film satisfies 1≤in-plane standard deviation≤3.

[0015] Each region is divided into 10 in the thickness direction. When the standard deviation of the area ratio of the piezoelectric particles in each of the 100 partitions is calculated as the thickness standard deviation, the piezoelectric film satisfies 0.5≤thickness standard deviation≤2.

[0016] [2] The piezoelectric film according to [1], which satisfies 1.7≤in-plane standard deviation≤2.8 and 0.6≤thickness standard deviation≤1.3.

[0017] [3] The piezoelectric film according to [1] or [2], wherein

[0018] The average area ratio of the piezoelectric particles in the 100 regions in total was 40% to 90%.

[0019] Effects of the Invention

[0020] According to the present invention, it is possible to provide a piezoelectric film capable of further improving sound pressure. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a diagram schematically showing an example of the piezoelectric film of the present invention.

[0022] Figure 2 yes Figure 1 A partial enlarged view of the piezoelectric film shown.

[0023] Figure 3 This is a schematic diagram for explaining a method for calculating the in-plane standard deviation.

[0024] Figure 4 This is a schematic diagram for explaining a method for calculating the thickness standard deviation.

[0025] Figure 5 This is a schematic diagram for explaining an example of a method for producing a piezoelectric film.

[0026] Figure 6 This is a schematic diagram for explaining an example of a method for producing a piezoelectric film.

[0027] Figure 7 This is a schematic diagram for explaining an example of a method for producing a piezoelectric film.

[0028] Figure 8 This is a schematic diagram for explaining an example of a method for producing a piezoelectric film.

[0029] Fig. 9 This is a graph plotting the in-plane standard deviation and thickness standard deviation of Examples and Comparative Examples.

[0030] Fig.10 This is a schematic diagram for explaining a conventional piezoelectric film.

[0031] Fig.11 This is a schematic diagram for explaining another example of a conventional piezoelectric film. DETAILED DESCRIPTION

[0032] Hereinafter, the piezoelectric film of the present invention will be described in detail based on preferred embodiments shown in the drawings.

[0033] Although the description of the constituent elements described below may be made based on representative embodiments of the present invention, the present invention is not limited to such embodiments.

[0034] In addition, in this specification, the numerical range expressed using "to" indicates a range including the numerical values ​​described before and after "to" as the lower limit and the upper limit.

[0035] [Piezoelectric film]

[0036] The piezoelectric film of the present invention has:

[0037] A piezoelectric film comprises: a piezoelectric layer, which is composed of a polymer composite piezoelectric body containing piezoelectric particles in a matrix containing a polymer material; and two electrode layers, which are arranged on both sides of the piezoelectric layer, wherein:

[0038] The cross section of the piezoelectric layer in the thickness direction is observed by a scanning electron microscope, 10 regions with the same width as the thickness of the cross section of the piezoelectric layer are continuously obtained, and each region is divided into 10 in the in-plane direction. When the standard deviation of the area ratio of the piezoelectric particles in each of the 100 partitions is calculated as the in-plane standard deviation, the piezoelectric film satisfies 1≤in-plane standard deviation≤3.

[0039] Each region is divided into 10 in the thickness direction. When the standard deviation of the area ratio of the piezoelectric particles in each of the 100 partitions is calculated as the thickness standard deviation, the piezoelectric film satisfies 0.5≤thickness standard deviation≤2.

[0040] exist Figure 1 2 is a diagram schematically showing an example of the piezoelectric film of the present invention.

[0041] exist Figure 1 The piezoelectric film 10 shown in FIG. 1 includes: a piezoelectric layer 20, which is a sheet-like object having piezoelectricity; a first electrode layer 24, which is stacked on one surface of the piezoelectric layer 20; a first protective layer 28, which is stacked on the surface of the first electrode layer 24 opposite to the piezoelectric layer 20; a second electrode layer 26, which is stacked on the other surface of the piezoelectric layer 20; and a second protective layer 30, which is stacked on the surface of the second electrode layer 26 opposite to the piezoelectric layer 20. That is, the piezoelectric film 10 has a structure in which the piezoelectric layer 20 is sandwiched between the electrode layers, and the protective layer is stacked on the surface of the electrode layer that is not in contact with the piezoelectric layer.

[0042] The first and second in the first electrode layer 24 and the first protective layer 28 and the second electrode layer 26 and the second protective layer 30 are indicated for convenience in describing the piezoelectric film 10. Therefore, the first and second in the present invention have no technical significance and are irrelevant to actual use.

[0043] The first protective layer 28 and the second protective layer 30 are basically identical in structure except for their different positions. Therefore, in the following description, when there is no need to distinguish between the first protective layer 28 and the second protective layer 30, both are collectively referred to as protective layers.

[0044] Similarly, the first electrode layer 24 and the second electrode layer 26 are basically the same except that the positions are different. Therefore, in the following description, when there is no need to distinguish between the first electrode layer 24 and the second electrode layer 26, both components are collectively referred to as electrode layers.

[0045] In the present invention, if Figure 1 As shown schematically, the piezoelectric layer 20 is a polymer composite piezoelectric body including piezoelectric particles 36 in a matrix 34 made of a polymer material. The piezoelectric particles 36 are piezoelectrics having piezoelectricity that expands and contracts according to an applied voltage. The piezoelectric layer 20 is a layer having flexibility and piezoelectricity by dispersing such piezoelectric particles 36 in the matrix 34.

[0046] The piezoelectric film 10 is driven as a piezoelectric body by applying a voltage to the first electrode layer 24 and the second electrode layer 26 to expand and contract the piezoelectric layer 20. When the piezoelectric film 10 is driven, the piezoelectric film 10 expands and contracts in the in-plane direction, and as a result, the piezoelectric film 10 vibrates in the thickness direction to generate sound. The piezoelectric film 10 vibrates according to the magnitude of the applied driving voltage, thereby generating sound corresponding to the applied driving voltage.

[0047] Here, in the piezoelectric film of the present invention, a cross section of the piezoelectric layer 20 in the thickness direction is observed by a scanning electron microscope (SEM), 10 regions having the same width as the thickness of the cross section of the piezoelectric layer 20 are continuously obtained, and each region is divided into 10 in the in-plane direction, and the area ratio of the piezoelectric particles 36 of each of the 100 partitions is calculated. When the standard deviation of the area ratio of the piezoelectric particles 36 is set as the in-plane standard deviation, the piezoelectric film satisfies 1≤in-plane standard deviation≤3,

[0048] Each region is divided into 10 in the thickness direction, and the area ratio of the piezoelectric particles 36 in each of the 100 partitions is calculated. When the standard deviation of the area ratio of the piezoelectric particles 36 is set as the thickness standard deviation, the piezoelectric film satisfies 0.5≤thickness standard deviation≤2.

[0049] like Figure 2 As schematically shown, the piezoelectric layer 20 that satisfies the above-mentioned ranges of the in-plane standard deviation and the thickness standard deviation is a state in which the piezoelectric particles are present unevenly and have a certain degree of unevenness in the in-plane direction.

[0050] As described above, when a voltage is applied to the piezoelectric film 10, the piezoelectric layer 20 expands and contracts in the in-plane direction, thereby vibrating in the thickness direction and generating sound. That is, in order to increase the sound pressure, the expansion and contraction of the piezoelectric layer 20 in the in-plane direction can be increased. The expansion and contraction of the piezoelectric particles 36 plays a role in the expansion and contraction of the piezoelectric layer 20. In order to increase the expansion and contraction of the piezoelectric particles 36, when a certain voltage is applied to the piezoelectric film 10, a larger voltage can be applied to the piezoelectric particles 36.

[0051] Here, according to the research of the present inventors, it is known that in order to apply a larger voltage to the piezoelectric particles 36, as shown in FIG. Figure 2 As shown in FIG. 1 , the piezoelectric particles 36 are concentrated (connected) in the thickness direction of the piezoelectric layer 20, which is better than Fig.10 The piezoelectric particles 136 are uniformly present as in the conventional piezoelectric film shown in FIG. If the piezoelectric particles 36 are concentrated in the thickness direction of the piezoelectric layer 20 , the voltage applied to the piezoelectric particles 36 increases, and the expansion and contraction of the piezoelectric particles 36 can be increased.

[0052] On the other hand, Fig.11 As shown in FIG. 1 , it is known that if the piezoelectric particles 136 are excessively concentrated in the thickness direction of the film and become columnar, Fig.11 As shown, a region where the piezoelectric particles 136 exist at a small ratio is generated in the in-plane direction, so that the expansion and contraction cannot be effectively transmitted in the in-plane direction, resulting in a decrease in sound pressure.

[0053] Therefore, the inventors set the in-plane standard deviation and thickness standard deviation of the area ratio of the piezoelectric particles 36 in the piezoelectric layer 20 within the above ranges, so that the piezoelectric particles 36 in the piezoelectric layer 20 are concentrated in the thickness direction within an appropriate range, and the voltage applied to the piezoelectric particles 36 can be increased, and the connectivity between the piezoelectric particles 36 in the in-plane direction can be suppressed from becoming smaller, thereby effectively transmitting the expansion and contraction in the in-plane direction. As a result, the piezoelectric film 10 of the present invention can increase the sound pressure when the same voltage is applied.

[0054] The in-plane standard deviation and the thickness standard deviation were calculated as follows.

[0055] First, in order to observe the cross section of the piezoelectric film, the film is cut in the thickness direction, for example, by installing a 8 mm wide histo blade manufactured by Drukker on RM2265 manufactured by Leica Biosystems, and cutting is performed at a speed of 1 on the controller scale and a meshing amount of 0.25 to 1 μm.

[0056] The cross section thereof is observed by SEM (for example, manufactured by Hitachi High-Tech Corporation., SU8220).

[0057] An example of observation conditions using SEM is shown below.

[0058] The samples were treated for conductivity by platinum evaporation, and the working distance was set to 8 mm.

[0059] The observation conditions are SE (secondary-electron) image (Upper), acceleration voltage: 0.5kV, and the clearest image is produced through focus adjustment and astigmatism adjustment. Automatic brightness adjustment is performed when the piezoelectric film becomes the entire screen (automatically setting brightness: 0, contrast: 0).

[0060] The imaging magnification is set such that the first electrode layer and the second electrode layer are contained in one screen and the width between the two electrode layers is more than half of the screen. In addition, the imaging is performed so that the two electrode layers are horizontal to the lower part of the image.

[0061] Ten consecutive fields of view at any position of any cross section of the piezoelectric layer are photographed by SEM.

[0062] In the obtained SEM image, the thickness of the cross section of the piezoelectric layer is measured at 10 or more points at 1 μm intervals to obtain the average value. The same width as the average value of the thickness is taken as one area, and 10 continuous areas in the SEM image are obtained. Figure 3As shown, the 10 regions obtained are divided into 10 in the in-plane direction, and the area ratio of the piezoelectric particles in one partition 21 relative to the geometric area of ​​one partition 21 is calculated in the total 100 partitions of the 10 regions. The standard deviation is calculated based on the area ratio of the piezoelectric particles in the total 100 partitions, and the in-plane standard deviation is obtained.

[0063] And, if Figure 4 As shown, the 10 regions obtained in the above manner are divided into 10 regions along the thickness direction, and the area ratio of the piezoelectric particles in one partition 22 is calculated relative to the geometric area of ​​one partition 22 in a total of 100 partitions of the 10 regions. The standard deviation is calculated based on the area ratio of the piezoelectric particles in the total of 100 partitions, and the thickness standard deviation is obtained.

[0064] in addition, Figure 3 and Figure 4 This is a diagram schematically showing one region of the piezoelectric layer 20, and illustration of piezoelectric particles is omitted.

[0065] From the viewpoint of further improving the sound pressure, the in-plane standard deviation preferably satisfies 1.7≤in-plane standard deviation≤2.8, more preferably 2.0≤in-plane standard deviation≤2.5. Furthermore, the thickness standard deviation preferably satisfies 0.6≤thickness standard deviation≤1.3, more preferably 0.6≤thickness standard deviation≤1.0.

[0066] The in-plane standard deviation and thickness standard deviation of the area ratio of the piezoelectric particles in the piezoelectric layer 20 of the piezoelectric film 10 can be adjusted by the type and quantitative ratio of the solvent in the coating (composition) used to form the piezoelectric layer 20, the coating coating method, the coating film drying method, the calendering treatment of the coating film, etc.

[0067] This point will be described later.

[0068] Furthermore, from the viewpoint that the sound pressure can be further improved when the in-plane standard deviation and thickness standard deviation of the area ratio of the piezoelectric particles are set within the above-mentioned range, the average value of the area ratio of the piezoelectric particles in 100 segments is preferably 40 to 90, more preferably 50 to 80, and even more preferably 60 to 75.

[0069] Furthermore, from the perspective that the sound pressure can be further increased when the in-plane standard deviation and thickness standard deviation of the area ratio of the piezoelectric particles are set within the above range, the particle size of the piezoelectric particles is preferably 0.5 μm to 30 μm, more preferably 1 μm to 20 μm, and even more preferably 2 μm to 10 μm.

[0070] Furthermore, from the perspective that the sound pressure can be further increased when the in-plane standard deviation and thickness standard deviation of the area ratio of the piezoelectric particles are set within the above range, the thickness of the piezoelectric layer is preferably 1 μm to 200 μm, more preferably 5 μm to 150 μm, and even more preferably 10 μm to 100 μm.

[0071] Hereinafter, constituent elements of the piezoelectric film of the present invention will be described in more detail.

[0072] <Piezoelectric layer>

[0073] In the present invention, if Figure 1 As schematically shown, the piezoelectric layer 20 is a polymer composite piezoelectric body in which piezoelectric particles 36 are contained in a matrix 34 made of a polymer material.

[0074] As the material of the base 34 (base and binder) of the polymer composite piezoelectric body constituting the piezoelectric layer 20, a polymer material having viscoelasticity at room temperature is preferably used. In this specification, "room temperature" refers to a temperature range of about 0 to 50°C.

[0075] Here, the polymer composite piezoelectric body (piezoelectric layer 20) preferably meets the following requirements.

[0076] (i) Flexibility

[0077] For example, when a document is held in a state where it feels slowly bent, such as a newspaper or magazine, it is constantly subjected to relatively slow and large bending deformation of less than a few Hz from the outside. At this time, if the polymer composite piezoelectric body is hard, a correspondingly large bending stress is generated, and cracks are generated at the interface between the polymer matrix and the piezoelectric particles, which may result in damage. Therefore, appropriate flexibility is required for the polymer composite piezoelectric body. In addition, if the strain energy can be diffused to the outside as heat, the stress can be relaxed. Therefore, the loss tangent of the polymer composite piezoelectric body is required to be appropriately large.

[0078] (ii) Sound quality

[0079] The speaker vibrates the piezoelectric particles at a frequency in the audio frequency band of 20Hz to 20kHz, and through its vibration energy, the polymer composite piezoelectric body (piezoelectric film) vibrates as a whole, thereby reproducing the sound. Therefore, in order to improve the transmission efficiency of vibration energy, the polymer composite piezoelectric body requires appropriate hardness. In addition, if the frequency characteristics of the speaker are smooth, the change in sound quality when the lowest resonance frequency changes with the change of curvature also becomes smaller. Therefore, the loss tangent of the polymer composite piezoelectric body is required to be moderately large.

[0080] In summary, the polymer composite piezoelectric body is required to be rigid for vibrations of 20 Hz to 20 kHz and flexible for vibrations of several Hz or less. In addition, the polymer composite piezoelectric body is required to have a suitably large loss tangent for vibrations of all frequencies below 20 kHz.

[0081] In addition, when a piezoelectric film is used as a piezoelectric element (exciter), it is preferred to simply adjust the spring constant by stacking it according to the rigidity (hardness, toughness, spring constant) of the attached pairing material (vibration plate). In this case, the thinner the bonding layer, the higher the energy efficiency.

[0082] Generally, polymer solids have a viscoelastic relaxation mechanism, and as the temperature rises or the frequency decreases, large-scale molecular motion is observed as a decrease (relaxation) in the storage modulus (Young's modulus) or a maximization (absorption) in the loss modulus. Among them, the relaxation caused by the micro-Brownian motion of the molecular chains in the amorphous region is called the main dispersion, and a very large relaxation phenomenon can be seen. The temperature that causes this main dispersion is the glass transition point (Tg), and the viscoelastic relaxation mechanism is most prominent.

[0083] In the polymer composite piezoelectric body (piezoelectric body layer 20), by using a polymer material having a glass transition point at room temperature, in other words, a polymer material having viscoelasticity at room temperature in the matrix, a polymer composite piezoelectric body that exhibits hardness for vibrations of 20 Hz to 20 kHz and softness for slow vibrations below several Hz is realized. In particular, from the perspective of preferably exhibiting the action, it is preferred to use a polymer material having a glass transition point at room temperature, i.e., 0 to 50° C., at a frequency of 1 Hz in the matrix of the polymer composite piezoelectric body.

[0084] As the polymer material having viscoelasticity at room temperature, various known polymer materials can be used, but preferably a polymer material having a maximum value of a 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. is used.

[0085] Thus, when the polymer composite piezoelectric body is slowly bent by an external force, stress concentration at the interface between the polymer matrix and the piezoelectric particles in the maximum bending moment portion is relaxed, and high flexibility can be expected.

[0086] Furthermore, the storage modulus (E') at a frequency of 1 Hz obtained by dynamic viscoelasticity measurement of the polymer material having viscoelasticity at room temperature is preferably 100 MPa or more at 0°C and 10 MPa or less at 50°C.

[0087] This can reduce the bending moment generated when the polymer composite piezoelectric body is slowly bent by an external force, and can also exhibit rigidity against acoustic vibrations of 20 Hz to 20 kHz.

[0088] Furthermore, if the polymer material has viscoelasticity at room temperature, the relative dielectric constant is more preferably 10 or more at 25° C. Therefore, when a voltage is applied to the polymer composite piezoelectric body, a higher electric field acts on the piezoelectric particles in the matrix, and a large deformation amount can be expected.

[0089] However, on the other hand, considering the need to ensure good moisture resistance, the relative dielectric constant of the polymer material is preferably 10 or less at 25°C.

[0090] As the polymer material having viscoelasticity at room temperature that satisfies such conditions, cyanoethylated polyvinyl alcohol (cyanoethylated PVA), polyvinyl acetate, polyvinylidene chloride acrylonitrile, polystyrene-vinyl polyisoprene block copolymer, polyvinyl methyl ketone and polybutyl methacrylate etc. can be exemplified. Moreover, as these polymer materials, commercial products such as HYBRAR5127 (manufactured by KURARAY CO., LTD) can also be appropriately utilized. Among them, as the polymer material, it is preferred to use a material having a cyanoethyl group, and it is particularly preferred to use cyanoethylated PVA.

[0091] As the polymer material having viscoelasticity at room temperature, a polymer material having cyanoethyl group is preferably used, and cyanoethylated PVA is particularly preferably used. That is, in the present invention, the piezoelectric layer 20 as the base 34 preferably uses a polymer material having cyanoethyl group, and cyanoethylated PVA is particularly preferably used.

[0092] In the following description, the above-mentioned polymer materials represented by cyanoethylated PVA are also collectively referred to as "polymer materials having viscoelasticity at room temperature".

[0093] These polymer materials having viscoelasticity at room temperature may be used alone or in combination (mixed) of two or more.

[0094] The base 34 made of such a polymer material having viscoelasticity at room temperature may be made of a plurality of polymer materials at the same time as required.

[0095] That is, for the purpose of adjusting dielectric properties and mechanical properties, in addition to the viscoelastic material such as cyanoethylated PVA, other dielectric polymer materials may be added to the base 34 as needed.

[0096] As a dielectric polymer material that can be added, as an example, there can be exemplified 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, cyanoethyl hydroxyethyl cellulose, cyanoethyl amylose, cyanoethyl hydroxypropyl cellulose, cyanoethyl dihydroxypropyl cellulose, cyanoethyl hydroxypropyl amylose, cyanoethyl polyacrylamide, cyanoethyl polyacrylate, cyanoethyl pullulan, cyanoethyl polyhydroxymethylene, cyanoethyl glycidyl pullulan, cyanoethyl sucrose, cyanoethyl sorbitol and other polymers having a cyano group or cyanoethyl group, and synthetic rubbers such as nitrile rubber and chloroprene rubber.

[0097] Among them, polymer materials having a cyanoethyl group are preferably used.

[0098] Furthermore, in the base 34 of the piezoelectric layer 20 , these dielectric polymer materials are not limited to one kind, and multiple kinds may be added.

[0099] Furthermore, in addition to the dielectric polymer material, thermoplastic resins such as vinyl chloride resin, polyethylene, polystyrene, methacrylic resin, polybutylene and isobutylene, and thermosetting resins such as phenolic resin, urea resin, melamine resin, alkyd resin and mica may be added to the matrix 34 for the purpose of adjusting the glass transition point Tg.

[0100] Furthermore, for the purpose of improving adhesion, a tackifier such as rosin ester, rosin, terpene, terpene phenol, or petroleum resin may be added.

[0101] The amount of material other than the polymer material having viscoelasticity such as cyanoethylated PVA added to the matrix 34 of the piezoelectric layer 20 is not particularly limited, but is preferably 30% by mass or less in terms of the proportion in the matrix 34 .

[0102] In this way, the characteristics of the added polymer material can be manifested without damaging the viscoelastic relaxation mechanism in the matrix 34, so that preferred results can be obtained from the perspectives of high dielectric constant, improved heat resistance, and improved adhesion with the piezoelectric particles 36 and the electrode layer.

[0103] The piezoelectric layer 20 is a layer composed of a polymer composite piezoelectric body including piezoelectric particles 36 in such a matrix 34. The piezoelectric particles 36 are dispersed in the matrix 34. It is preferable that the piezoelectric particles 36 are dispersed in the matrix 34 uniformly (substantially uniformly).

[0104] The piezoelectric particles 36 are composed of ceramic particles having a perovskite-type or wurtzite-type crystal structure.

[0105] Ceramic particles constituting the piezoelectric particles 36 include, for example, lead zirconate titanate (PZT), lead lanthanum zirconate titanate (PLZT), barium titanate (BaTiO3), zinc oxide (ZnO), and a solid solution (BFBT) of barium titanate and bismuth ferrite (BiFe3).

[0106] The particle size of the piezoelectric particles 36 is not limited, and may be appropriately selected according to the size of the piezoelectric film 10 , the purpose of the piezoelectric element 50 , and the like.

[0107] By setting the particle size of the piezoelectric particles 36 within this range, a preferable result can be obtained from the viewpoint that the piezoelectric film 10 can achieve both high piezoelectric characteristics and flexibility.

[0108] 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 can be appropriately set according to the size and thickness in the surface direction of the piezoelectric film 10, the purpose of the piezoelectric film 10, and the properties required in the piezoelectric film 10.

[0109] 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, further preferably 50 to 80%.

[0110] By setting the amount ratio of the matrix 34 to the piezoelectric particles 36 within the above range, a preferable result can be obtained from the viewpoint of being able to achieve both high piezoelectric characteristics and flexibility.

[0111] In the piezoelectric film 10 , the thickness of the piezoelectric layer 20 is not particularly limited and may be appropriately set according to the application of the piezoelectric film 10 , the number of stacked piezoelectric films in the piezoelectric element 50 , the characteristics required of the piezoelectric film 10 , and the like.

[0112] The thicker the piezoelectric layer 20 is, the more advantageous it is in terms of rigidity such as the strength 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.

[0113] The thickness of the piezoelectric layer 20 is as described above.

[0114] By setting the thickness of the piezoelectric layer 20 within the above range, a preferable result can be obtained from the viewpoint of ensuring both rigidity and appropriate flexibility.

[0115] Furthermore, the piezoelectric layer 20 is preferably subjected to polarization processing (polling) in the thickness direction.

[0116] like Figure 1As shown, the piezoelectric film 10 has the following structure: a first electrode layer 24 is provided on one side of the piezoelectric layer 20, a first protective layer 28 is provided thereon, and a second electrode layer 26 is provided on the other side of the piezoelectric layer 20, and a second protective layer 30 is provided thereon. Here, the first electrode layer 24 and the second electrode layer 26 form an electrode pair.

[0117] That is, the piezoelectric film 10 has a structure in which both surfaces of the piezoelectric body layer 20 are sandwiched between the first electrode layer 24 and the second electrode layer 26 , which are an electrode pair, and the stacked body is sandwiched between the first protective layer 28 and the second protective layer 30 .

[0118] In this manner, in the piezoelectric film 10 , a region sandwiched between the first electrode layer 24 and the second electrode layer 26 expands and contracts in accordance with an applied voltage.

[0119] In the present invention, the piezoelectric film 10 may have, in addition to these layers, for example, a bonding layer for bonding the electrode layer and the piezoelectric body layer 20 and a bonding layer for bonding the electrode layer and the protective layer.

[0120] The laminating agent may be an adhesive or a bonding agent. Furthermore, the laminating agent may preferably be made of the same material as the polymer material (i.e., the same material as the substrate 34) after the piezoelectric particles 36 are removed from the piezoelectric layer 20. In addition, the laminating layer may be provided on both sides of the first electrode layer 24 side and the second electrode layer 26 side, or may be provided on only one side of the first electrode layer 24 side and the second electrode layer 26 side.

[0121] In the piezoelectric film 10, the first protective layer 28 and the second protective layer 30 cover the first electrode layer 24 and the second electrode layer 26, and play a role in giving appropriate rigidity and mechanical strength to the piezoelectric layer 20. That is, in the piezoelectric film 10, the piezoelectric layer 20 composed of the matrix 34 and the piezoelectric particles 36 shows very excellent flexibility for slow bending deformation, but on the other hand, there is a case where the rigidity or mechanical strength is insufficient depending on the application. The piezoelectric film 10 is provided with the first protective layer 28 and the second protective layer 30 to compensate for this deficiency.

[0122] The first protective layer 28 and the second protective layer 30 are not limited, and various sheet-shaped materials can be used. As an example, various resin films can be preferably exemplified.

[0123] Among them, resin films composed of polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS), polycarbonate (PC), polyphenylene sulfide (PPS), polymethyl methacrylate (PMMA), polyetherimide (PEI), polyimide (PI), polyethylene naphthalate (PEN), triacetyl cellulose (TAC) and cyclic olefin resins can be preferably used due to their excellent mechanical properties and heat resistance.

[0124] There is no limitation on the thickness of the first protective layer 28 and the second protective layer 30. Furthermore, the thickness of the first protective layer 28 and the second protective layer 30 is basically the same, but may be different.

[0125] Here, if the rigidity of the first protective layer 28 and the second protective layer 30 is too high, not only the expansion and contraction of the piezoelectric layer 20 is restrained, but also the flexibility is impaired. Therefore, excluding the case where mechanical strength or good operability as a sheet is required, the thinner the first protective layer 28 and the second protective layer 30 are, the more advantageous it is.

[0126] 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 , a preferable result can be obtained from the viewpoints of ensuring both rigidity and appropriate flexibility.

[0127] For example, when 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 further preferably 25 μm or less.

[0128] 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).

[0129] In the present invention, there is no limitation on the materials for forming the first electrode layer 24 and the second electrode layer 26, and various conductors can be used. Specifically, metals such as carbon, palladium, iron, tin, aluminum, nickel, platinum, gold, silver, copper, titanium, chromium, and molybdenum, their alloys, laminates and composites of these metals and alloys, and indium tin oxide can be exemplified. Alternatively, conductive polymers such as PEDOT / PPS (polyethylene dioxythiophene-polystyrene sulfonic acid) can also be exemplified. Among them, copper, aluminum, gold, silver, platinum, and indium tin oxide can be preferably exemplified as the first electrode layer 24 and the second electrode layer 26. Among them, copper is more preferred from the viewpoints of conductivity, cost, flexibility, etc.

[0130] Furthermore, there is no limitation on the method for forming the first electrode layer 24 and the second electrode layer 26, and known methods such as various vapor deposition methods (vacuum film forming methods) such as vacuum evaporation and sputtering, film forming based on plating, and methods of bonding foils formed of the above materials can be used.

[0131] In particular, thin films of copper, aluminum, etc. formed by vacuum deposition are preferably used as the first electrode layer 24 and the second electrode layer 26 because flexibility of the piezoelectric film 10 can be ensured. In particular, thin films of copper formed by vacuum deposition are preferably used.

[0132] 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 are substantially the same, but may be different.

[0133] Here, similarly to the first protective layer 28 and the second protective layer 30, if the rigidity of the first electrode layer 24 and the second electrode layer 26 is too high, not only will the expansion and contraction of the piezoelectric layer 20 be restricted, but also the flexibility will be impaired. Therefore, as long as the resistance does not become too high, the thinner the first electrode layer 24 and the second electrode layer 26 are, the more advantageous it is.

[0134] In the piezoelectric film 10 , it is preferable that the product of the thickness and Young's modulus of the first electrode layer 24 and the second electrode layer 26 is lower than the product of the thickness and Young's modulus of the first protective layer 28 and the second protective layer 30 , because flexibility is not seriously impaired.

[0135] For example, in the case of a combination in which the first protective layer 28 and the second protective layer 30 are composed of PET (Young's modulus: approximately 6.2 GPa) and the first electrode layer 24 and the second electrode layer 26 are composed of copper (Young's modulus: approximately 130 GPa), if the thickness of the first protective layer 28 and the second protective layer 30 is 25 μm, the thickness of the first electrode layer 24 and the second electrode layer 26 is preferably 1.2 μm or less, more preferably 0.3 μm or less, and preferably 0.1 μm or less.

[0136] As described above, the piezoelectric film 10 has a structure in which the piezoelectric layer 20 in which the piezoelectric particles 36 are dispersed in the matrix 34 made of a polymer material is sandwiched between the first electrode layer 24 and the second electrode layer 26 , and the stacked body is further sandwiched between the first protective layer 28 and the second protective layer 30 .

[0137] Such a piezoelectric film 10 preferably has a local value of loss tangent (Tan δ) at a frequency of 1 Hz obtained by dynamic viscoelasticity measurement at room temperature, and more preferably has a local value of 0.1 or more at room temperature.

[0138] Thus, even if the piezoelectric film 10 is subjected to relatively slow and large bending deformation of several Hz or less from the outside, the strain energy can be effectively diffused to the outside as heat, thereby preventing cracks from being generated at the interface between the polymer matrix and the piezoelectric particles.

[0139] In the piezoelectric film 10 , the storage modulus (E′) at a frequency of 1 Hz obtained by dynamic viscoelasticity measurement is preferably 10 to 30 GPa at 0° C. and 1 to 10 GPa at 50° C. The conditions are the same as those for the piezoelectric layer 20 .

[0140] Thus, the piezoelectric film 10 can have a large frequency dispersion in the storage modulus (E′) at room temperature, that is, it can exhibit hardness for vibrations of 20 Hz to 20 kHz and exhibit softness for vibrations of several Hz or less.

[0141] In the piezoelectric film 10, the product of the thickness and the storage modulus (E') at a frequency of 1 Hz obtained by dynamic viscoelasticity measurement is preferably 1.0×10 5 ~2.0×10 6 N / m, 1.0×10 at 50°C 5 ~1.0×10 6 N / m. Note that this condition is also the same as that of the piezoelectric layer 20 .

[0142] Thus, the piezoelectric film 10 can have appropriate rigidity and mechanical strength within a range where flexibility and acoustic characteristics are not impaired.

[0143] In addition, for the piezoelectric film 10 , the loss tangent (Tan δ) at 25° C. and a frequency of 1 kHz in the master curve obtained by dynamic viscoelasticity measurement is preferably 0.05 or more. This condition is also the same as that of the piezoelectric layer 20 .

[0144] Thus, the frequency characteristics of the speaker using the piezoelectric film 10 become smooth, and the amount of change in sound quality when the lowest resonance frequency f0 changes with a change in the curvature of the speaker can be reduced.

[0145] In the present invention, the storage modulus (Young's modulus) and loss tangent of the piezoelectric film 10 and the piezoelectric layer 20 may be measured by a known method. For example, the dynamic viscoelasticity measuring device DMS6100 manufactured by SII Nano Technology Inc. may be used for the measurement.

[0146] As an example of the measurement conditions, they can be exemplified as follows: the measurement frequency is 0.1 Hz to 20 Hz (0.1 Hz, 0.2 Hz, 0.5 Hz, 1 Hz, 2 Hz, 5 Hz, 10 Hz and 20 Hz), the measurement temperature is -50 to 150°C, the heating rate is 2°C / minute (in a nitrogen atmosphere), the sample size is 40 mm × 10 mm (including the clamping plate area), and the chuck spacing is 20 mm.

[0147] A power source for applying a driving voltage for causing the piezoelectric film 10 to expand and contract, that is, supplying driving power, is connected to the first electrode layer 24 and the second electrode layer 26 of the piezoelectric film 10 .

[0148] The power source is not limited and may be a DC power source or an AC power source. Also, the driving voltage may be appropriately set according to the thickness and forming material of the piezoelectric layer 20 of the piezoelectric film 10 so as to appropriately drive the piezoelectric film 10 .

[0149] There is no limitation on the method of extracting electrodes from the first electrode layer 24 and the second electrode layer 26 , and various known methods can be used.

[0150] As an example, there can be exemplified a method of connecting a conductor such as copper foil to the first electrode layer 24 and the second electrode layer 26 to lead out the electrodes to the outside, and a method of forming through holes in the first protective layer 28 and the second protective layer 30 by a laser or the like and filling the through holes with a conductive material to lead out the electrodes to the outside.

[0151] Preferred methods for extracting electrodes include the method described in Japanese Patent Application Laid-Open No. 2014-209724 and the method described in Japanese Patent Application Laid-Open No. 2016-015354.

[0152] Here, as described above, the piezoelectric layer 20 includes the piezoelectric particles 36 in the matrix 34. Furthermore, the first electrode layer 24 and the second electrode layer 26 are provided so as to sandwich the piezoelectric layer 20 in the thickness direction.

[0153] When a voltage is applied to the first electrode layer 24 and the second electrode layer 26 of the piezoelectric film 10 having such a piezoelectric layer 20, the piezoelectric particles 36 expand and contract in the polarization direction according to the applied voltage. As a result, the piezoelectric film 10 (piezoelectric layer 20) contracts in the thickness direction. At the same time, due to the relationship of Poisson's ratio, the piezoelectric film 10 also expands and contracts in the in-plane direction. This expansion and contraction is about 0.01 to 0.1%.

[0154] As described above, the thickness of the piezoelectric layer 20 is preferably about 10 to 300 μm. Therefore, the expansion and contraction in the thickness direction is very small, and is only about 0.3 μm at most.

[0155] In contrast, the piezoelectric film 10, ie, the piezoelectric layer 20, has a dimension in the plane direction that is significantly larger than its thickness. Therefore, for example, if the length of the piezoelectric film 10 is 20 cm, the piezoelectric film 10 expands and contracts by a maximum of about 0.2 mm in the plane direction when a voltage is applied.

[0156] When pressure is applied to the piezoelectric film 10 , electricity is generated due to the action of the piezoelectric particles 36 .

[0157] By utilizing this technology, the piezoelectric film 10 can be used for various purposes such as a speaker, a microphone, and a pressure-sensitive sensor.

[0158] Below, reference Figures 5 to 8 , an example of a method for manufacturing the piezoelectric film 10 is described.

[0159] First, prepare Figure 5 The sheet 11a shown in FIG. 1 has a first electrode layer 24 formed on the surface of a first protective layer 28. Figure 8 Schematically shown in FIG. 1 is a sheet-like object 11 c in which the second electrode layer 26 is formed on the surface of the second protective layer 30 .

[0160] The sheet 11a can be produced by forming a copper thin film or the like on the surface of the first protective layer 28 by vacuum deposition, sputtering, plating, etc. as the first electrode layer 24. Similarly, the sheet 11c can be produced by forming a copper thin film or the like on the surface of the second protective layer 30 by vacuum deposition, sputtering, plating, etc. as the second electrode layer 26.

[0161] Alternatively, a commercially available sheet in which a copper thin film or the like is formed on a protective layer may be used as the sheet 11 a and / or the sheet 11 c .

[0162] The sheet-shaped object 11a and the sheet-shaped object 11c may be the same or different.

[0163] In addition, when the protective layer is very thin and has poor handling properties, a protective layer with a partition (pseudo-support) may be used as required. In addition, as a partition, PET with a thickness of 25 to 100 μm may be used. The partition may be removed after the electrode layer and the protective layer are thermocompressed.

[0164] Then, if Figure 6 As shown, a coating material (coating composition) to be the piezoelectric layer 20 is applied onto the first electrode layer 24 of the sheet 11a and then cured to form the piezoelectric layer 20. Thus, a laminate 11b in which the sheet 11a and the piezoelectric layer 20 are laminated is produced.

[0165] The piezoelectric layer 20 can be formed by various methods depending on the material forming the piezoelectric layer 20 .

[0166] As an example, first, the polymer material such as the cyanoethylated PVA described above is dissolved in an organic solvent, and then the piezoelectric particles 36 such as PZT particles are added and stirred to prepare a coating material.

[0167] The organic solvent is not limited, and various organic solvents such as dimethylformamide (DMF), methyl ethyl ketone (MEK), and cyclohexanone can be used.

[0168] After preparing the sheet 11a and the coating, the coating is cast (coated) on the sheet 11a, and the organic solvent is evaporated and dried. Thus, as shown in FIG. 15 , a laminate 11b having a first electrode layer 24 on a first protective layer 28 and a piezoelectric layer 20 stacked on the first electrode layer 24 is produced.

[0169] The coating material is not particularly limited in the pouring method, and any known method (coating device) such as a bar coater, a slide coater, or a doctor knife can be used.

[0170] Alternatively, if the polymer material is a substance that can be heated and melted, a melt can be prepared by heating and melting the polymer material and adding piezoelectric particles 36 thereto, and then extruded into a sheet on the sheet 11a shown in Figure 14 by extrusion molding, and cooled, thereby preparing a stacked body 11b as shown in Figure 15.

[0171] As described above, in the piezoelectric layer 20 , a polymer piezoelectric material such as PVDF (Poly Vinylidene DiFluoride) may be added to the base 34 in addition to the polymer material having viscoelasticity at room temperature.

[0172] When adding these polymer piezoelectric materials to the matrix 34, the polymer piezoelectric materials added to the coating material may be dissolved or added to the polymer material having viscoelasticity at room temperature after heating and melting, and then heated and melted.

[0173] Here, in the present invention, in order to adjust the in-plane standard deviation and thickness standard deviation of the area ratio of the piezoelectric particles within the above-mentioned range, it is preferred that cyclohexanone, DMF (N,N-dimethylformamide), etc. be included as an organic solvent in the coating for forming the piezoelectric layer 20. Cyclohexanone and the like have a higher boiling point than MEK and are less volatile, so after the coating is applied, if the organic solvent is evaporated and dried, more voids are likely to be generated in the coating. If the coating having many voids is subjected to the calendering treatment described later, the voids are flattened, so that the area ratio of the piezoelectric particles in the thickness direction at the position where the voids in the in-plane direction exist becomes relatively higher than the area ratio of the piezoelectric particles in the thickness direction at the position where the voids in the in-plane direction do not exist. As a result, Figure 2 As shown, the existence state of the piezoelectric particles can be set to a state having a certain degree of non-uniformity in the in-plane direction, and the in-plane standard deviation of the area ratio of the piezoelectric particles can be set to a high value of 1 or more.

[0174] From the viewpoint of forming voids in the coating film as described above, the proportion of cyclohexanone in all solvents in the coating material is preferably 82 to 97 mass %, more preferably 85 to 95 mass %, and even more preferably 88 to 93 mass %.

[0175] In order to adjust the in-plane standard deviation and thickness standard deviation of the area ratio of the piezoelectric particles within the above range, it is preferred to apply the coating for forming the piezoelectric layer 20 multiple times. By preparing coatings with different contents of piezoelectric particles, changing the type of coating to be applied and applying multiple times to form a coating film, the presence state of the piezoelectric particles can be set to a state with a certain degree of unevenness in the thickness direction, and the thickness standard deviation of the area ratio of the piezoelectric particles can be adjusted.

[0176] After the piezoelectric layer 20 (coating film) is formed, a calendering treatment may be performed as necessary. The calendering treatment may be performed once or multiple times.

[0177] As is known to all, calendering is a process of flattening a surface by heating it with a hot press or a heated roller, and pressing it. Figure 7 As shown, a calendering film 80 is placed on the surface of the piezoelectric layer 20 (coating film), and a roller is used to press the calendering film 80 from above. As a result, as described above, the voids in the piezoelectric layer 20 (coating film) can be flattened, so that the existence state of the piezoelectric particles becomes a state with a certain degree of unevenness in the in-plane direction.

[0178] The pressing pressure in the calendering treatment is preferably 0.1 MPa to 10 MPa.

[0179] Next, the piezoelectric layer 20 of the stacked body 11b having the first electrode layer 24 on the first protective layer 28 and the piezoelectric layer 20 formed on the first electrode layer 24 is polarized. The polarization of the piezoelectric layer 20 may be performed before the calendering treatment, but is preferably performed after the calendering treatment.

[0180] There is no limitation on the method of polarization treatment of the piezoelectric layer 20, and a known method can be used. For example, electric field polarization in which a direct current electric field is directly applied to the object to be polarized can be exemplified. In addition, when electric field polarization is performed, the second electrode layer 26 can be formed before the polarization treatment, and the electric field polarization treatment can be performed using the first electrode layer 24 and the second electrode layer 26.

[0181] Furthermore, in the piezoelectric film 10 of the present invention, it is preferable that the polarization treatment be performed in the thickness direction rather than in the surface direction of the piezoelectric layer 20 .

[0182] Then, if Figure 8 As shown in FIG. 1 , a sheet 11 c prepared in advance is stacked on the piezoelectric layer 20 side of the polarized stack 11 b with the second electrode layer 26 facing the piezoelectric layer 20 .

[0183] In addition, the laminate 11b and the sheet 11c are bonded together by heat pressing using a heat pressing device and a heating roller so as to sandwich the laminate 28 and the second protective layer 30, thereby producing a laminate 11b and a sheet 11c. Figure 1 The piezoelectric film 10.

[0184] Alternatively, the laminate 11b and the sheet 11c may be bonded together using an adhesive, and preferably, pressure-bonded to produce the piezoelectric film 10. The adhesive in this case may be the same material as that of the base of the piezoelectric layer 20.

[0185] The piezoelectric film 10 may be manufactured using the slice-shaped sheet 11 a and the sheet 11 c or the like, or may be manufactured using a roll-to-roll process.

[0186] The produced piezoelectric film can also be cut into a desired shape according to various uses. Furthermore, the heat treatment can also be performed after cutting.

[0187] The piezoelectric film 10 manufactured in this way is polarized in the thickness direction rather than in the plane direction, and can obtain a large piezoelectric property even without stretching after polarization. Therefore, the piezoelectric film 10 does not have in-plane anisotropy in terms of piezoelectric properties, and expands and contracts isotropically in all directions in the plane direction when a driving voltage is applied.

[0188] As an example, in various acoustic devices (acoustic equipment) such as speakers, microphones, and pickups in musical instruments such as guitars, the piezoelectric film 10 can be used to generate (reproduce) sound based on vibrations corresponding to electrical signals and convert vibrations caused by sound into electrical signals.

[0189] Furthermore, in addition to these, the piezoelectric film 10 can also be used for a pressure-sensitive sensor, a power generating element, and the like.

[0190] Alternatively, the piezoelectric film 10 can also be used as an exciter (exciter) that makes various objects vibrate and emit sound by being attached to the objects in contact with them.

[0191] Furthermore, the piezoelectric film 10 can be used in an integrated manner with a flexible display.

[0192] Examples of flexible displays include display devices such as organic light emitting diode (OLED) displays, liquid crystal displays, micro LED (Light Emitting Diode) displays, and inorganic light emitting diode displays, and projector screens.

[0193] Furthermore, the piezoelectric film of the present invention can be stacked in multiple layers to be used as a piezoelectric element. The piezoelectric element is attached to a vibration plate to be used as an exciter.

[0194] The vibration plate may be flexible enough to be rolled up. In the present invention, flexibility is the same as the commonly interpreted meaning of flexibility, which means that it can be bent and flexed, and specifically, it can be bent and stretched without being broken or damaged.

[0195] The vibration plate is not limited, and various sheet-shaped objects (plate-shaped objects, films) can be used.

[0196] As an example, there can be illustrated resin films made of polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS), polycarbonate (PC), polyphenylene sulfide (PPS), polymethyl methacrylate (PMMA), polyetherimide (PEI), polyimide (PI), polyethylene naphthalate (PEN), triacetyl cellulose (TAC), and cyclic olefin resins, foamed plastics made of expanded polystyrene, expanded styrene, and expanded polyethylene, single board, cork board, leather such as cowhide, carbon sheet, various paperboards such as Japanese paper, various corrugated paperboards made by attaching other paperboards to one or both sides of corrugated paperboard, thin film metals made of various metals such as stainless steel, aluminum, copper, and nickel, and various alloys, etc. In addition, the vibration plate can be a composite material made by bonding a film-like object made of these materials.

[0197] Furthermore, display devices such as organic light emitting diode (OLED) displays, liquid crystal displays, micro LED (Light Emitting Diode) displays, and inorganic light emitting diode displays, and projector screens can also be preferably used as the vibration plate.

[0198] The piezoelectric element functions as a so-called exciter that exhibits piezoelectricity in response to an applied voltage and vibrates the vibration plate. The piezoelectric element and the vibration plate are bonded together by a bonding layer.

[0199] The piezoelectric element may have a structure in which a plurality of piezoelectric films 10 are stacked by folding a single rectangular long piezoelectric film 10 multiple times in one direction, or may have a structure in which a plurality of single-sheet piezoelectric films 10 are stacked.

[0200] Furthermore, in the case where the piezoelectric element is a structure in which the piezoelectric film is stacked by folding, it is preferred that the piezoelectric film on the outermost surface has a protrusion protruding outward in the surface direction from the stacked portion on which the piezoelectric film is stacked, and a connection portion for connecting the first electrode layer 24 and the second electrode layer 26 to a power source is formed in the protrusion. In addition, there is no limitation on the method of connecting the electrode layer and the wiring in the protrusion, and various known methods can be used.

[0201] The piezoelectric element obtained by folding and stacking long piezoelectric films has the following advantages.

[0202] That is, when stacking a plurality of slice-shaped piezoelectric films 10, it is necessary to connect the first electrode layer 24 and the second electrode layer 26 to the driving power source for each piezoelectric film. In contrast, in a structure in which a long piezoelectric film 10 is folded and stacked, a stack can be formed by only one long piezoelectric film 10. Furthermore, in a structure in which a long piezoelectric film 10 is folded and stacked, only one power source for applying a driving voltage is required, and further, only one electrode is required to be drawn out from the piezoelectric film 10.

[0203] Furthermore, in a structure in which the elongated piezoelectric films 10 are folded and stacked, the polarization directions of adjacent piezoelectric films are necessarily opposite to each other.

[0204] In the case of a structure in which a plurality of piezoelectric films 10 are stacked in the piezoelectric element, the piezoelectric films 10 are bonded together by a bonding layer. As the bonding layer for bonding the piezoelectric films 10 together, various known bonding layers can be used as long as the adjacent piezoelectric films 10 can be bonded together.

[0205] As for the bonding layer, various known bonding layers can be used as long as they can bond the vibration plate and the piezoelectric element or the piezoelectric film 10 to each other.

[0206] Therefore, the laminating layer may be a layer composed of an adhesive that has fluidity when laminating and then becomes solid, or a layer composed of an adhesive that is soft and solid in a gel (rubbery) state when laminating and does not change in the gel state, or a layer composed of a material having the characteristics of both an adhesive and an adhesive. Furthermore, the adhesive (adhesive) may be any one of a moisture-curing adhesive, a thermoplastic adhesive, and a thermosetting adhesive. Furthermore, as the laminating layer, a double-sided tape, an adhesive sheet, etc. may be used.

[0207] The vibration plate is bonded to the piezoelectric element via a bonding layer, so that the vibration plate is bent by the expansion and contraction of the piezoelectric element (piezoelectric film 10), and as a result, the vibration plate vibrates in the thickness direction.

[0208] The vibration plate generates sound by the vibration in the thickness direction. That is, the vibration plate vibrates according to the magnitude of the voltage (driving voltage) applied to the piezoelectric film 10 , and generates sound according to the driving voltage applied to the piezoelectric film 10 .

[0209] Furthermore, by adjusting the mass of the piezoelectric element according to the spring constant of the vibration plate, the sound pressure level can be increased. If the mass of the piezoelectric element is large, the vibration plate will bend, so it is possible to suppress the vibration of the vibration plate during driving. On the other hand, if the mass of the piezoelectric element is small, the resonance frequency becomes high, which may suppress the vibration of the vibration plate at low frequencies. Considering these points, it is preferable to appropriately adjust the mass of the piezoelectric element according to the spring constant of the vibration plate.

[0210] As mentioned above, the piezoelectric film of the present invention has been described in detail, but the present invention is not limited to the above-mentioned examples, and it is a matter of course that various improvements or changes can be made without departing from the scope of the present invention.

[0211] Example

[0212] Below, enumerate specific embodiment of the present invention, the present invention is described in more detail.In addition, the present invention is not limited to this embodiment, as long as do not depart from the gist of the present invention, then can suitably change the material shown in the following embodiment, usage, ratio, processing content, processing sequence etc.

[0213] [Example 1]

[0214] <Production of piezoelectric film>

[0215] Through the above Figures 5 to 8 The method shown in Figure 1 The piezoelectric film shown.

[0216] First, cyanoethylated PVA (CR-V Shin-Etsu Chemical Co., Ltd.) was dissolved in a mixed solvent of cyclohexanone and MEK at the following composition ratio. Then, PZT particles were added as piezoelectric particles to the solution at the following composition ratio, and the mixture was stirred using a propeller stirring mixer (rotation speed 2000 rpm) to prepare coatings A to C for forming a piezoelectric layer.

[0217] Paint A

[0218] ·PZT particles···········300 parts by mass

[0219] ·Cyanoethylated PVA···········15 parts by mass

[0220] ·Cyclohexanone··········85 parts by mass

[0221] ·MEK···········15 parts by mass

[0222] In coatings A to C, the ratio of cyclohexanone in all solvents was set to 85 mass %. In coating A, the concentration of PZT particles in the solid content was set to 95 mass %, in coating B, the concentration of PZT particles in the solid content was set to 96 mass %, and in coating C, the concentration of PZT particles in the solid content was set to 94 mass %.

[0223] In the following examples and comparative examples, the ratio of cyclohexanone was appropriately changed, but the concentration of PZT particles was 95 mass % for coating material A, 96 mass % for coating material B, and 94 mass % for coating material C, while the ratio of cyclohexanone was appropriately changed.

[0224] The PZT particles used were obtained by sintering commercially available PZT raw material powder at 1000 to 1200° C. and then pulverizing and classifying the powder so that the average particle size became 5 μm.

[0225] On the other hand, a sheet (first laminate) was prepared in which a copper thin film having a thickness of 0.3 μm was vacuum-deposited on a PET film having a thickness of 4 μm. That is, in this example, the first electrode layer and the second electrode layer were copper-deposited thin films having a thickness of 0.3 μm, and the first protective layer and the second protective layer were PET films having a thickness of 4 μm.

[0226] Using a slide coater, coating material B and coating material C prepared in advance for forming a piezoelectric layer were alternately applied four times starting from coating material B on the first electrode layer (copper vapor-deposited film) of the sheet.

[0227] First, a coating material B prepared in advance for forming a piezoelectric layer was applied onto the first electrode layer (copper vapor-deposited film) of the sheet-like object using a slide coater. The coating material B was applied so that the film thickness after drying would be 10 μm.

[0228] Next, a coating material C for forming a piezoelectric layer prepared in advance was applied on the first coating film using a slide coater. The coating material C was applied so that the film thickness of the coating film after drying would be 10 μm.

[0229] Next, a coating material B for forming a piezoelectric layer prepared in advance was applied on the second coating film using a slide coater. The coating material B was applied so that the film thickness of the coating film after drying would be 10 μm.

[0230] Furthermore, the coating material C for forming the piezoelectric layer prepared in advance was applied on the third coating film using a slide coater. The coating material C was applied so that the film thickness of the coating film after drying would be 10 μm.

[0231] Next, the sheet-like object coated with the coating material was dried by heating on a hot plate at 50° C., thereby evaporating the organic solvent (cyclohexanone).

[0232] Thus, a laminated body was produced which had a first electrode layer made of copper on a first protective layer made of PET and a piezoelectric layer (polymer composite piezoelectric layer) having a thickness of 40 μm thereon.

[0233] The produced piezoelectric layer was subjected to calendering treatment using a 100 mm diameter roller and a pressing force of 1 MPa.

[0234] The produced piezoelectric layer was polarized in the thickness direction.

[0235] On the piezoelectric laminate subjected to the polarization treatment, a sheet in which the thin film was vapor-deposited on a PET film was laminated with the second electrode layer (copper thin film side) facing the piezoelectric layer.

[0236] Next, the piezoelectric laminate and the laminate of the sheet-like material were thermally pressed at a temperature of 120° C. using a laminating device, thereby laminating and bonding the piezoelectric layer and the second electrode layer to produce a Figure 1 The piezoelectric film shown.

[0237] <Measurement of in-plane standard deviation and thickness standard deviation>

[0238] A sample was cut from the produced piezoelectric film, cut in the thickness direction by the above method, and the cross section was observed by SEM (manufactured by Hitachi High-Tech Corporation, SU8220). Ten consecutive fields of view at any position of the cross section were photographed by SEM, and SEM images were obtained.

[0239] In the obtained SEM image, the thickness of the cross section of the piezoelectric layer was measured at 10 points at 1 μm intervals to find the average value. The thickness was 40 μm. Ten continuous regions in the SEM image were obtained, with the width equal to the average value of the thickness found being considered as one region.

[0240] like Figure 3As shown, the 10 regions obtained are divided into 10 in the in-plane direction, and the area ratio of the piezoelectric particles in one partition 21 relative to the geometric area of ​​one partition 21 is calculated in a total of 100 partitions of the 10 regions. The standard deviation is calculated based on the area ratio of the piezoelectric particles in the total of 100 partitions, and the in-plane standard deviation is obtained. The in-plane standard deviation is 1.02%. In addition, the average value of the area ratio of the piezoelectric particles in the 100 partitions is 64.93%.

[0241] And, if Figure 4 As shown, the 10 regions obtained were divided into 10 in the thickness direction, and the area ratio of the piezoelectric particles in one partition 22 relative to the geometric area of ​​one partition 22 was calculated in the total 100 partitions of the 10 regions. The standard deviation was calculated based on the area ratio of the piezoelectric particles in the total 100 partitions, and the thickness standard deviation was found. The thickness standard deviation was 1.93%.

[0242] [Examples 2 to 13, Comparative Examples 1 to 5]

[0243] A piezoelectric film was produced in the same manner as in Example 1 except that the ratio of cyclohexanone in the coating material, the type of coating material, the number of coatings, and the thickness of the piezoelectric layer were changed as shown in Table 1.

[0244] In the same manner as in Example 1, the in-plane standard deviation and the thickness standard deviation in each of Examples and Comparative Examples were measured.

[0245] [evaluate]

[0246] <Sound pressure>

[0247] A rectangular test piece of 210×300 mm (A4 size) was cut out from the produced piezoelectric film. After the cut piezoelectric film was placed on a box with an opening of 210×300 mm for accommodating glass wool, the periphery was pressed by the frame to apply appropriate tension and curvature to the piezoelectric film, thereby producing a piezoelectric speaker. In addition, the depth of the box was set to 9 mm, and the density of the glass wool was set to 32 kg / m 3 , the thickness before assembly is set to 25mm.

[0248] As an input signal, a 1 kHz sine wave was input to the piezoelectric speaker through a power amplifier, and the sound pressure was measured by a microphone placed 60 cm from the center of the speaker. In addition, the voltage of the input signal changes in intensity in proportion to the thickness of the piezoelectric layer.

[0249] The results are shown in Table 1. In addition, a graph in which the in-plane standard deviation and the thickness standard deviation of each example and comparative example are plotted is shown in Fig. 9 .

[0250] [Table 1]

[0251]

[0252] From Table 1 and Fig. 9 It is found that the sound pressure of the piezoelectric film of the example whose in-plane standard deviation and thickness standard deviation satisfy the range of the present invention is improved compared with the comparative example.

[0253] Furthermore, from the comparison between Examples 4, 6 to 8, and 10 and other Examples, it can be seen that the sound pressure is further improved by satisfying 1.7≤in-plane standard deviation≤2.8 and 0.6≤thickness standard deviation≤1.3.

[0254] The effects of the present invention are thus apparent.

[0255] Industrial Applicability

[0256] Regarding the piezoelectric film of the present invention, for example, it can be preferably used as various sensors such as sound wave sensors, ultrasonic sensors, pressure sensors, tactile sensors, strain sensors and vibration sensors (especially suitable for infrastructure inspections such as crack detection or manufacturing site inspections such as foreign matter mixing detection), acoustic devices such as microphones, pickups, speakers and exciters (as specific uses, noise eliminators (for cars, trains, airplanes, robots, etc.), artificial vocal cords, buzzers for preventing pests / animal invasion, furniture, wallpapers, photos, helmets, goggles, headrests, signs, robots, etc. can be exemplified), tactile feedback used in automobiles, smart phones, smart watches, game consoles, etc., ultrasonic transducers such as ultrasonic probes and hydrophones, actuators used in preventing water droplet adhesion, transportation, stirring, dispersion, grinding, etc., containers, vehicles, buildings, vibration damping materials (vibration dampers) used in sports equipment such as skis and rackets, and vibration power generation devices used in roads, floors, mattresses, chairs, shoes, tires, wheels and computer keyboards.

[0257] Explanation of symbols

[0258] 10-piezoelectric film, 11a, 11c-sheet-like objects, 11b-laminated body, 20-piezoelectric layer, 24-first electrode layer, 26-second electrode layer, 28-first protective layer, 30-second protective layer, 34-substrate, 36-piezoelectric particles, 80-film for calendering treatment.

Claims

1. A piezoelectric film, comprising: a piezoelectric layer composed of a polymer composite piezoelectric body containing piezoelectric particles in a matrix containing a polymer material; and Two electrode layers are provided on both sides of the piezoelectric layer, wherein: The cross section of the piezoelectric layer in the thickness direction is observed by a scanning electron microscope, 10 regions with the same width as the thickness of the cross section of the piezoelectric layer are continuously obtained, and each region is divided into 10 in the in-plane direction. When the standard deviation of the area ratio of the piezoelectric particles in each of the 100 partitions is calculated as the in-plane standard deviation, the piezoelectric film satisfies 1≤in-plane standard deviation≤3, Each of the regions is divided into 10 in the thickness direction, and when the standard deviation of the area ratio of the piezoelectric particles in each of the 100 partitions is calculated as the thickness standard deviation, the piezoelectric film satisfies 0.5≤thickness standard deviation≤2. 2 . The piezoelectric film according to claim 1 , which satisfies 1.7≤in-plane standard deviation≤2.8 and 0.6≤thickness standard deviation≤1.

3.

3. The piezoelectric film according to claim 1 or 2, wherein: The average area ratio of the piezoelectric particles in the 100 sections in total is 40% to 90%.

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