WO2020261963A1 - 高分子複合圧電体および圧電フィルム - Google Patents
高分子複合圧電体および圧電フィルム Download PDFInfo
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- WO2020261963A1 WO2020261963A1 PCT/JP2020/022535 JP2020022535W WO2020261963A1 WO 2020261963 A1 WO2020261963 A1 WO 2020261963A1 JP 2020022535 W JP2020022535 W JP 2020022535W WO 2020261963 A1 WO2020261963 A1 WO 2020261963A1
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Definitions
- the present invention relates to a polymer composite piezoelectric body and a piezoelectric film using this polymer composite piezoelectric body.
- the speakers used in these thin displays are also required to be lighter and thinner. Further, in a flexible display having flexibility, flexibility is also required in order to integrate into the flexible display without impairing lightness and flexibility. As such a lightweight, thin and flexible speaker, it is considered to adopt a sheet-shaped piezoelectric film having a property of expanding and contracting in response to an applied voltage.
- Patent Document 1 describes a polymer composite piezoelectric body in which piezoelectric particles are dispersed in a matrix made of a polymer material, thin film electrodes formed on both sides of the polymer composite piezoelectric body, and surfaces of the thin film electrodes.
- the polymer composite piezoelectric material has a protective layer formed in, and has an SP value of less than 12.5 (cal / cm 3 ) 1/2 and is a liquid substance at room temperature of 20 ppm to 500 ppm in terms of mass ratio.
- the piezoelectric conversion film contained is described.
- the piezoelectric powder is contained in the organic substrate in a volume ratio of 65% or more, and the relative density (percentage of the measured density ⁇ meas to the theoretical density ⁇ cal ) is 93.00 to 97.00%.
- a piezoelectric composite material having pores formed so as to be formed is vulture-molded into a flat plate by applying pressure in the thickness direction, then polarized in the pressure-applied direction, and electrodes are arranged on the front and back surfaces thereof.
- the piezoelectric element for the underwater acoustic converter is described.
- the polymer composite piezoelectric material of the electroacoustic conversion film described in Patent Document 1 contains a substance having an SP value of less than 12.5 (cal / cm 3 ) 1/2 and a liquid at room temperature from 20 ppm by mass ratio. By containing 500 ppm, it is possible to suppress a decrease in conversion efficiency, a decrease in withstand voltage, a decrease in flexibility, and the like even in an environment where the temperature and humidity are severe.
- the SP value of the polymer composite piezoelectric material is less than 12.5 (cal / cm 3 ) 1/2 , and the content of a liquid substance at room temperature exceeds 500 ppm. In a temperature cycle test in which heating and cooling were repeated, a decrease in piezoelectric conversion efficiency was observed.
- the above substance is contained in a paint that becomes a polymer composite piezoelectric material with a solvent. Therefore, after applying the paint, it is necessary to dry the paint to control the content of the above substances in the polymer composite piezoelectric body. However, after applying the paint, it takes time to dry the substance to reduce the content of the above substance to 500 ppm or less, which causes a problem of poor productivity.
- An object of the present invention is to solve such problems of the prior art, that is, a polymer composite piezoelectric material and a piezoelectric material capable of suppressing a decrease in piezoelectric conversion efficiency in an environment with high productivity and severe temperature and humidity. To provide the film.
- the present invention has the following configuration.
- the polymer composite piezoelectric material contains a substance having an SP value of less than 12.5 (cal / cm 3 ) 1/2 and a liquid substance at room temperature in a mass ratio of more than 500 ppm and 10,000 ppm or less.
- Voids are formed in the polymer composite piezoelectric body
- [2] The polymer composite piezoelectric material according to [1], wherein the area ratio of the voids is 0.1% or more and less than 5%.
- [3] The polymer composite piezoelectric body according to [1] or [2], wherein the polymer composite piezoelectric body is polarized in the thickness direction.
- [4] The polymer composite piezoelectric material according to any one of [1] to [3], which has no in-plane anisotropy in the piezoelectric characteristics.
- [5] The polymer composite piezoelectric material according to any one of [1] to [4], wherein the content of the substance is more than 500 ppm and 1000 ppm or less.
- the polymer composite piezoelectric material according to any one of [1] to [5], wherein the polymer material has viscoelasticity at room temperature.
- the substances are methyl ethyl ketone, dimethylformamide, cyclohexanone, acetone, cyclohexane, acetonitrile, 1propanol, 2propanol, 2methoxy alcohol, diacetone alcohol, dimethylacetamide, benzyl alcohol, n-hexane, toluene, o-xylene, acetic acid.
- the piezoelectric film according to [8] which has a protective layer laminated on a surface of the electrode layer opposite to the surface on the polymer composite piezoelectric body side.
- a polymer composite piezoelectric body and a piezoelectric film capable of suppressing a decrease in piezoelectric conversion efficiency in an environment with high productivity and severe temperature and humidity.
- the description of the constituent elements described below may be based on typical embodiments of the present invention, but the present invention is not limited to such embodiments.
- the numerical range represented by using "-" means the range including the numerical values before and after "-" as the lower limit value and the upper limit value.
- the polymer composite piezoelectric material of the present invention A polymer composite piezoelectric body containing piezoelectric particles in a matrix containing a polymer material.
- the polymer composite piezoelectric material has an SP value (solubility parameter) of less than 12.5 (cal / cm 3 ) 1/2 and contains a substance that is liquid at room temperature in a mass ratio of more than 500 ppm and less than 10,000 ppm. Voids are formed in the polymer composite piezoelectric body, It is a polymer composite piezoelectric body in which the area ratio of voids in the cross section of the polymer composite piezoelectric body is 0.1% or more and 20% or less.
- the piezoelectric film of the present invention is With the above polymer composite piezoelectric material A piezoelectric film having electrode layers formed on both sides of a polymer composite piezoelectric body.
- FIG. 1 conceptually shows an example of the piezoelectric film of the present invention having the polymer composite piezoelectric material of the present invention by a cross-sectional view.
- the piezoelectric film 10 is laminated on a piezoelectric layer 20 which is a sheet-like material having piezoelectricity, a lower electrode 24 laminated on one surface of the piezoelectric layer 20, and a lower electrode 24. It has a lower protective layer 28, an upper electrode 26 laminated on the other surface of the piezoelectric layer 20, and an upper protective layer 30 laminated on the upper electrode 26.
- the piezoelectric layer 20 contains the piezoelectric particles 36 in the matrix 34 containing the polymer material.
- the piezoelectric layer 20 is the polymer composite piezoelectric material in the present invention. Further, the lower electrode 24 and the upper electrode 26 are the electrode layers in the present invention. Further, the lower protective layer 28 and the upper protective layer 30 are protective layers in the present invention. As will be described later, the piezoelectric film 10 (piezoelectric layer 20) is preferably polarized in the thickness direction.
- Such a piezoelectric film 10 is, for example, Various sensors such as sound sensor, ultrasonic sensor, pressure sensor, tactile sensor, distortion sensor and vibration sensor, Acoustic devices such as microphones, pickups, speakers and exciters (specifically, noise cancellers (used for cars, trains, airplanes, robots, etc.), artificial voice bands, buzzers to prevent pests and beasts from entering, furniture, wallpapers, etc. Photos, helmets, goggles, signage, robots, etc.), Haptics used for automobiles, smartphones, smart watches, games, etc. Ultrasonic transducers and ultrasonic transducers such as hydrophones, actuators used for water droplet adhesion prevention, transportation, stirring, dispersion, polishing, etc.
- Damping materials used for sports equipment such as containers, vehicles, buildings, skis and rackets, and It can be suitably used as a vibration power generator used by applying it to roads, floors, mattresses, chairs, shoes, tires, wheels, personal computer keyboards, and the like.
- the piezoelectric layer 20 which is the polymer composite piezoelectric material of the present invention, contains the piezoelectric particles 36 in the matrix 34. Further, the piezoelectric layer 20 contains a substance having an SP value of less than 12.5 (cal / cm 3 ) 1/2 and a liquid at room temperature in the matrix 34 in a mass ratio of more than 500 ppm and 10,000 ppm or less. There is.
- voids 35 are formed in the piezoelectric layer 20, and the area ratio of the voids in the cross section of the polymer composite piezoelectric body is 0.1% or more and 20% or less.
- "normal temperature” refers to a temperature range of about 0 to 50 ° C.
- the piezoelectric film 10 of the present invention is suitably used for a speaker having flexibility such as a speaker for a flexible display.
- the polymer composite piezoelectric body (piezoelectric layer 20) used for the flexible speaker has the following requirements. Therefore, it is preferable to use a polymer material having viscoelasticity at room temperature as a material satisfying the following requirements.
- (Ii) Sound quality A speaker vibrates piezoelectric particles at a frequency in the audio band of 20 Hz to 20 kHz, and the vibration energy causes the entire polymer composite piezoelectric body (piezoelectric film) to vibrate as a unit to reproduce sound. To. Therefore, in order to increase the transmission efficiency of vibration energy, the polymer composite piezoelectric material is required to have an appropriate hardness. Further, if the frequency characteristic of the speaker is smooth, the amount of change in sound quality when the minimum resonance frequency changes with the change in curvature also becomes small. Therefore, the loss tangent of the polymer composite piezoelectric material is required to be moderately large.
- the polymer composite piezoelectric material is required to behave hard against vibrations of 20 Hz to 20 kHz and soft against vibrations of several Hz or less. Further, the loss tangent of the polymer composite piezoelectric body is required to be appropriately large with respect to vibrations of all frequencies of 20 kHz or less.
- polymer solids have a viscoelastic relaxation mechanism, and large-scale molecular motion decreases (Relaxation) or maximizes loss elastic modulus (absorption) as the temperature rises or the frequency decreases.
- Relaxation large-scale molecular motion decreases
- absorption loss elastic modulus
- main dispersion the relaxation caused by the micro-Brownian motion of the molecular chain in the amorphous region is called main dispersion, and a very large relaxation phenomenon is observed.
- the temperature at which this main dispersion occurs is the glass transition point (Tg), and the viscoelastic relaxation mechanism appears most prominently.
- the polymer composite piezoelectric body (piezoelectric 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, for vibration of 20 Hz to 20 kHz.
- a polymer composite piezoelectric material that is hard and behaves softly against slow vibrations of several Hz or less is realized.
- the polymer material having viscoelasticity at room temperature various known materials can be used as long as they have dielectric properties.
- a polymer material having a maximum loss tangent value of 0.5 or more at a frequency of 1 Hz by a dynamic viscoelasticity test at room temperature, that is, 0 ° C. to 50 ° C. is used.
- the polymer material preferably has a storage elastic 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.
- E' storage elastic modulus
- the polymer material has a relative permittivity of 10 or more at 25 ° C.
- a voltage is applied to the polymer composite piezoelectric body, a higher electric field is applied to the piezoelectric particles in the matrix, so that a large amount of deformation can be expected.
- the polymer material has a relative permittivity of 10 or less at 25 ° C.
- polymer material satisfying such conditions examples include cyanoethylated polyvinyl alcohol (cyanoethylated PVA), polyvinyl acetate, polyvinylidene chloride core acrylonitrile, polystyrene-vinyl polyisoprene block copolymer, polyvinyl methyl ketone, and polybutyl. Examples include methacrylate. Further, as these polymer materials, commercially available products such as Hybler 5127 (manufactured by Kuraray Co., Ltd.) can also be preferably used.
- Hybler 5127 manufactured by Kuraray Co., Ltd.
- the polymer material it is preferable to use a material having a cyanoethyl group, and it is particularly preferable to use cyanoethylated PVA.
- a material having a cyanoethyl group it is preferable to use cyanoethylated PVA.
- only one kind of these polymer materials may be used, and a plurality of kinds may be used in combination (mixing).
- a plurality of polymer materials may be used in combination, if necessary. That is, in addition to the polymer material having viscoelasticity at room temperature, other dielectric polymer materials may be added to the matrix 34 for the purpose of adjusting the dielectric properties and mechanical properties. ..
- dielectric polymer material examples include polyvinylidene fluoride, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, and polyvinylidene fluoride-trifluoroethylene copolymer.
- fluoropolymers such as polyvinylidene fluoride-tetrafluoroethylene copolymer, vinylidene cyanide-vinyl acetate copolymer, cyanoethyl cellulose, cyanoethyl hydroxysaccharose, cyanoethyl hydroxycellulose, cyanoethyl hydroxypurrane, cyanoethyl methacrylate, cyanoethyl acrylate, cyanoethyl.
- Cyano groups such as 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 saccharose and cyanoethyl sorbitol.
- polymers having a cyanoethyl group synthetic rubbers such as nitrile rubber and chloroprene rubber, and the like are exemplified. Among them, a polymer material having a cyanoethyl group is preferably used. Further, in the matrix 34 of the piezoelectric layer 20, the dielectric polymer material added in addition to the polymer material having viscoelasticity at room temperature such as cyanoethylated PVA is not limited to one type, and a plurality of types are added. You may.
- the matrix 34 contains a thermoplastic resin such as vinyl chloride resin, polyethylene, polystyrene, methacrylic resin, polybutene, and isobutylene, and phenol for the purpose of adjusting the glass transition point.
- a resin, a urea resin, a melamine resin, an alkyd resin, and a thermosetting resin such as mica may be added.
- a tackifier such as rosin ester, rosin, terpene, terpene phenol, and petroleum resin may be added.
- the amount to be added when a material other than the viscoelastic polymer material such as cyanoethylated PVA is added is not particularly limited, but is 30% by mass or less in proportion to the matrix 34. Is preferable. As a result, the characteristics of the polymer material to be added can be exhibited without impairing the viscoelastic relaxation mechanism in the matrix 34, so that the dielectric constant can be increased, the heat resistance can be improved, and the adhesion to the piezoelectric particles 36 and the electrode layer can be improved. In this respect, favorable results can be obtained.
- the piezoelectric layer 20 is a polymer composite piezoelectric body containing piezoelectric particles 36 in such a matrix 34.
- the piezoelectric particles 36 are made of ceramic particles having a perovskite-type or wurtzite-type crystal structure. Examples of the ceramic particles constituting the piezoelectric particles 36 include lead zirconate titanate (PZT), lead zirconate titanate (PLZT), barium titanate (BaTIO 3 ), zinc oxide (ZnO), and zinc oxide (ZnO). Examples thereof include a solid solution (BFBT) of barium titanate and bismuth ferrite (BiFe 3 ). Only one type of these piezoelectric particles 36 may be used, or a plurality of types may be used in combination (mixed).
- the particle size of the piezoelectric particles 36 is not limited, and may be appropriately selected depending on the size and application of the polymer composite piezoelectric body (piezoelectric film 10).
- the particle size of the piezoelectric particles 36 is preferably 1 to 10 ⁇ m. By setting the particle size of the piezoelectric particles 36 in this range, it is possible to obtain preferable results in that the polymer composite piezoelectric body (piezoelectric film 10) can achieve both high piezoelectric characteristics and flexibility.
- the piezoelectric particles 36 in the piezoelectric layer 20 are uniformly and regularly dispersed 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 irregularly dispersed in the matrix 34 as long as they are preferably uniformly dispersed.
- the amount ratio of the matrix 34 and the piezoelectric particles 36 in the piezoelectric layer 20 is not limited, and the size and thickness of the piezoelectric layer 20 in the plane direction are not limited.
- the suitable setting may be made according to the application of the polymer composite piezoelectric body and the characteristics required for the polymer composite piezoelectric body.
- 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 more preferably 50 to 80%.
- the thickness of the piezoelectric layer 20 is not limited, and may be appropriately set according to the application of the polymer composite piezoelectric body, the characteristics required for the polymer composite piezoelectric body, and the like.
- the thickness of the piezoelectric layer 20 is preferably 10 to 300 ⁇ m, more preferably 20 to 200 ⁇ m, and even more preferably 30 to 150 ⁇ m.
- the matrix 34 of the piezoelectric layer 20 contains a substance having an SP value of less than 12.5 (cal / cm 3 ) 1/2 and a liquid substance at room temperature in a mass ratio of more than 500 ppm and 10,000 ppm or less. .. Further, voids 35 are formed in the matrix 34 of the piezoelectric layer 20, and the area ratio of the voids 35 in the cross section of the piezoelectric layer 20 is 0.1% or more and 20% or less.
- Specific examples of the substance having an SP value of less than 12.5 (cal / cm 3 ) 1/2 and liquid at room temperature include methyl ethyl ketone, dimethylformamide, cyclohexanone, acetone, cyclohexane, acetonitrile, 1propanol, and 2propanol. , 2 methoxy alcohol, diacetone alcohol, dimethylacetamide, benzyl alcohol, n-hexane, toluene, o-xylene, ethyl acetate, butyl acetate, diethyl ether, tetrahydrofuran and other organic compounds.
- the above-mentioned substances are generally used as organic solvents.
- the polymer composite piezoelectric body contains an organic solvent having an SP value of less than 12.5 (cal / cm 3 ) 1/2 and a liquid at room temperature at a mass ratio of 500 ppm. Contains super 10,000 ppm or less.
- the polymer composite piezoelectric body By containing the above substance in the polymer composite piezoelectric body, it is possible to prevent the polymer composite piezoelectric body from drying and curing even under low humidity. As a result, it is possible to prevent the flexibility from being lowered under low humidity.
- the polymer composite piezoelectric body has an SP value of 12.5 (cal / cm 3 ) 1/2 or more and contains a substance that is liquid at room temperature
- the polymer composite piezoelectric body It is possible to prevent curing due to drying.
- a substance having an SP value of 12.5 (cal / cm 3 ) 1/2 or more it is presumed that the substance does not disperse uniformly in the polymer composite piezoelectric body and aggregates. To. Therefore, when the substance inside the piezoelectric body evaporates when exposed to a high temperature, relatively large voids are generated and the interface between the piezoelectric particles and the matrix is peeled off.
- the SP value of the substance contained in the polymer composite piezoelectric layer is set to less than 12.5 (cal / cm 3 ) 1/2 to make the substance a polymer composite piezoelectric. Since it can be uniformly dispersed in the polymer, when the substance inside the polymer composite piezoelectric body is exposed to high temperature and the substance is evaporated, it is possible to suppress the formation of large voids and the interface between the piezoelectric particles and the matrix is peeled off. It can be prevented from doing so. Therefore, it is possible to suppress a decrease in conversion efficiency and a decrease in withstand voltage.
- the P value is less than 12.5 (cal / cm 3 ) 1/2 , and the content of the liquid substance at room temperature is 500 ppm or less, so that the substance inside the polymer composite piezoelectric body is used. Evaporates, it suppresses the formation of large voids, prevents the interface between the piezoelectric particles and the matrix from peeling off, and suppresses a decrease in conversion efficiency and a decrease in withstand voltage.
- the above-mentioned substance is contained in a coating material as a polymer composite piezoelectric material as a solvent. Therefore, after applying the paint, it is necessary to dry the paint to control the content of the above substances in the polymer composite piezoelectric body. However, after applying the paint, it takes time to dry the substance to reduce the content of the above substance to 500 ppm or less, which causes a problem of poor productivity. In particular, in order to improve productivity, when a polymer composite piezoelectric material is continuously produced, it is necessary to slow down the line speed or lengthen the drying process for drying, which is said to be poor in productivity. There was a problem.
- the polymer composite piezoelectric material of the present invention contains a substance having an SP value of less than 12.5 (cal / cm 3 ) 1/2 and a liquid at room temperature in a mass ratio of more than 500 ppm and 10,000 ppm or less.
- voids are formed, and the area ratio of the voids in the cross section of the polymer composite piezoelectric material is 0.1% or more and 20% or less.
- the polymer composite piezoelectric material of the present invention has a void area ratio of 0.1% or more and 20% or less in the cross section of the polymer composite piezoelectric body, that is, by reducing the voids, evaporation of the above substance due to drying is suppressed.
- the polymer composite piezoelectric material of the present invention contains the above substances in a mass ratio of more than 500 ppm and 10,000 ppm or less, the drying time after applying the coating material to be the polymer composite piezoelectric material can be shortened. Therefore, the line speed can be increased and the length of the drying process can be shortened, so that the productivity can be improved.
- the area ratio of the voids in the cross section of the polymer composite piezoelectric material is less than 0.1%, that is, when the voids are too small, there is no way for the substance to escape when dried, which causes expansion and cracking. It becomes. Therefore, the area ratio of the voids in the cross section of the polymer composite piezoelectric body is 0.1% or more.
- the area ratio of the voids in the cross section of the polymer composite piezoelectric material is preferably 0.1% or more and less than 5% from the viewpoint of more preferably suppressing the decrease in conversion efficiency and suppressing the evaporation of the above substance due to drying. More preferably, it is 0.1% or more and 2% or less.
- the method for measuring the area ratio of the voids in the cross section of the polymer composite piezoelectric body is as follows. Cut in the thickness direction to observe the cross section of the polymer composite piezoelectric body. For cutting, a Leica Biosystem RM2265 is attached with a Drukker histo knife blade width of 8 mm, and the speed is set to the controller scale 1 and the meshing amount is set to 0.25 ⁇ m to 1 ⁇ m to obtain a cross section. The cross section is observed with a scanning electron microscope (SEM) (SU8220 manufactured by Hitachi High-Technologies Corporation). The sample is conductively treated by Pt vapor deposition, and the work distance is 8 mm.
- SEM scanning electron microscope
- the observation conditions are SE image (Upper), acceleration voltage: 0.5 kV, sharp image is output by focus adjustment and astigmatism adjustment, and automatic brightness adjustment (auto) with the polymer composite piezoelectric part covering the entire screen.
- the magnification of photography is such that the electrodes at both ends fit on one screen and the width between the electrodes is more than half of the screen.
- Image analysis software ImageJ is used to binarize the image, the lower limit of Thrashold is set to the maximum value at which the protective layer is not colored, and the upper limit of Thrashold is set to the maximum set value of 255.
- the area of the colored part between the electrodes is defined as the area of the void and is defined as the molecule, the vertical width is defined as the space between the electrodes, and the horizontal width is defined as both ends of the SEM image.
- the area ratio of the voids to the area of the composite piezoelectric part is calculated. This is performed on any 10 cross sections, and the average value of the area ratio is taken as the area ratio of the voids in the cross section of the polymer composite piezoelectric body.
- the amount of air bubbles that escape during drying can be adjusted by adjusting the size of air bubbles in the paint by changing the processing time and rotation speed of lymixing.
- the processing time and rotation speed of line mixing are determined by the desired void area ratio, matrix type, solvent (the substance) type, solvent ratio, paint viscosity, thickness of polymer composite piezoelectric material to be formed, etc. It may be set as appropriate according to the above.
- the SP value is less than 12.5 (cal / cm 3 ) 1/2 and
- the content of the substance liquid at room temperature is preferably more than 500 ppm and 10000 ppm or less, more preferably more than 500 ppm and 1000 ppm or less, and further preferably more than 500 ppm and 700 ppm or less in terms of mass ratio.
- the content of the above substance in the polymer composite piezoelectric material is measured by gas chromatography. At that time, the value at the time when the sample is left for 24 hours in an environment of a temperature of 25 ° C. and a humidity of 50% RH is defined as the content of the above substance.
- the content of the above substance is measured as follows. A part of the sample is cut out from the polymer composite piezoelectric body into an 8 ⁇ 8 mm square, and the content of the above substance is measured using a gas chromatograph device (GC-12A manufactured by Shimadzu Corporation). The column is 221-14368-11 manufactured by Shimadzu Corporation, and the filler is Chromosorb 101 manufactured by Shinwa Kako.
- the temperature of the sample vaporization chamber and the detector is 200 ° C., the column temperature is constant at 160 ° C., and 0.4 MPa of helium is used as the carrier gas for measurement. If a module or the like containing a protective layer located outside the electrode layer is adhered with an adhesive layer containing an organic solvent, it will affect the measurement. The content of the solvent is measured. The mass of the cut sample is measured before performing the gas chromatograph measurement. After the gas chromatograph measurement, the polymer composite piezoelectric body is removed from the same sample using an organic solvent or the like, and the mass of the remaining protective layer or the module containing the protective layer is measured and measured before the gas chromatograph measurement. The net mass of the polymer composite piezoelectric is calculated by subtracting from the mass. The content-mass ratio of the substance is calculated by dividing the mass of the substance obtained by the gas chromatograph measurement by the net mass of the polymer composite piezoelectric body.
- the method for containing the substance at a predetermined concentration in the polymer composite piezoelectric body is not particularly limited.
- the substance when preparing a coating material to be a polymer composite piezoelectric body, the substance may be added in a predetermined amount.
- the substance is used as a solvent for the coating material to be prepared, and the drying conditions after the coating material is applied are adjusted to control the content of the substance in the polymer composite piezoelectric body.
- the drying conditions at that time may be appropriately set according to the type of the substance, the desired content, the type of the matrix, the thickness of the piezoelectric layer, and the like.
- known drying methods such as heat drying with a heater and heat drying with warm air can be used.
- the SP value of the above substance is preferably 9.0 to 12.3 (cal / cm 3 ) 1/2 , and 9.3 to 12.1 (cal / cm 3 ). 1/2 is more preferable.
- the thickness of the piezoelectric layer 20 is not particularly limited, and may be appropriately set according to the size of the piezoelectric film 10, the application of the piezoelectric film 10, the characteristics required for the piezoelectric film 10, and the like.
- the thickness of the piezoelectric layer 20 is preferably 10 ⁇ m to 300 ⁇ m, more preferably 20 ⁇ m to 200 ⁇ m, and particularly preferably 30 ⁇ m to 150 ⁇ m.
- the piezoelectric layer 20 is preferably polarized (polled).
- the piezoelectric film 10 of the illustrated example has a lower electrode 24 on one surface of such a piezoelectric layer 20, a lower protective layer 28 on the surface thereof, and the other of the piezoelectric layer 20. It has a structure having an upper electrode 26 on the surface of the surface and an upper protective layer 30 on the surface thereof. Here, the upper electrode 26 and the lower electrode 24 form an electrode pair.
- the piezoelectric film 10 has, for example, an upper electrode 26 and an electrode drawing portion for drawing out the electrode from the lower electrode 24, and the electrode drawing portion is connected to a power source. Further, the piezoelectric film 10 may have an insulating layer or the like that covers a region where the piezoelectric layer 20 is exposed to prevent a short circuit or the like.
- the piezoelectric film 10 has a structure in which both sides of the piezoelectric layer 20 are sandwiched between electrode pairs, that is, the upper electrode 26 and the lower electrode 24, and the laminate is sandwiched between the lower protective layer 28 and the upper protective layer 30. Has. As described above, in the piezoelectric film 10, the region held by the upper electrode 26 and the lower electrode 24 is expanded and contracted according to the applied voltage.
- the lower protective layer 28 and the upper protective layer 30 are provided as a preferred embodiment rather than an essential constituent requirement.
- the lower protective layer 28 and the upper protective layer 30 cover the upper electrode 26 and the lower electrode 24, and play a role of imparting appropriate rigidity and mechanical strength to the piezoelectric layer 20. That is, in the piezoelectric film 10, the piezoelectric layer 20 composed of the matrix 34 and the piezoelectric particles 36 exhibits extremely excellent flexibility against slow bending deformation, while being rigid depending on the application. And mechanical strength may be insufficient.
- the piezoelectric film 10 is provided with a lower protective layer 28 and an upper protective layer 30 to supplement the piezoelectric film 10.
- the lower protective layer 28 and the upper protective layer 30 are not limited, and various sheet-like materials can be used, and various resin films are preferably exemplified as an example.
- various resin films are preferably exemplified as an example.
- PET polyethylene terephthalate
- PP polypropylene
- PS polystyrene
- PC polycarbonate
- PPS polyphenylene sulfide
- PMMA polymethylmethacrylate
- PET polyethylene terephthalate
- PET polypropylene
- PS polystyrene
- PC polycarbonate
- PPS polyphenylene sulfide
- PMMA polymethylmethacrylate
- PEI Polyetherimide
- PI Polystyrene
- PEN Polyethylene Naphthalate
- TAC Triacetyl Cellulose
- a resin film made of a cyclic olefin resin or the like are preferably used.
- the thickness of the lower protective layer 28 and the upper protective layer 30 there is also no limitation on the thickness of the lower protective layer 28 and the upper protective layer 30. Further, the thicknesses of the lower protective layer 28 and the upper protective layer 30 are basically the same, but may be different. Here, if the rigidity of the lower protective layer 28 and the upper protective layer 30 is too high, not only the expansion and contraction of the piezoelectric layer 20 is restricted, but also the flexibility is impaired. Therefore, the thinner the lower protective layer 28 and the upper protective layer 30, the more advantageous it is, except when mechanical strength and good handleability as a sheet-like material are required.
- the thickness of the lower protective layer 28 and the upper protective layer 30 is twice or less the thickness of the piezoelectric layer 20, it is possible to ensure both rigidity and appropriate flexibility. Preferred results can be obtained.
- the thickness of the piezoelectric layer 20 is 50 ⁇ m and the lower protective layer 28 and the upper protective layer 30 are made of PET
- the thickness of the lower protective layer 28 and the upper protective layer 30 is preferably 100 ⁇ m or less, more preferably 50 ⁇ m or less. It is preferable, and more preferably 25 ⁇ m or less.
- a lower electrode 24 is formed between the piezoelectric layer 20 and the lower protective layer 28, and an upper electrode 26 is formed between the piezoelectric layer 20 and the upper protective layer 30.
- the lower electrode 24 and the upper electrode 26 are provided to apply a driving voltage to the piezoelectric layer 20.
- the materials for forming the lower electrode 24 and the upper electrode 26 are not limited, and various conductors can be used. Specifically, alloys such as carbon, palladium, iron, tin, aluminum, nickel, platinum, gold, silver, copper, titanium, chromium and molybdenum, laminates and composites of these metals and alloys, and Examples thereof include indium tin oxide. Among them, copper, aluminum, gold, silver, platinum, and indium tin oxide are preferably exemplified as the lower electrode 24 and the upper electrode 26.
- a vapor phase deposition method such as vacuum deposition and sputtering, a film formation by plating, and a foil formed of the above materials
- Various known methods such as a method of sticking can be used.
- thin films such as copper and aluminum formed by vacuum vapor deposition are preferably used as the lower electrode 24 and the upper electrode 26 because the flexibility of the piezoelectric film 10 can be ensured.
- a copper thin film produced by vacuum deposition is preferably used.
- the thickness of the lower electrode 24 and the upper electrode 26 There is no limitation on the thickness of the lower electrode 24 and the upper electrode 26. Further, the thicknesses of the lower electrode 24 and the upper electrode 26 are basically the same, but may be different.
- the lower electrode 24 and the upper electrode 26 are thinner as long as the electric resistance does not become too high. That is, the lower electrode 24 and the upper electrode 26 are preferably thin film electrodes.
- the flexibility is increased. It is suitable because it does not damage it.
- the lower protective layer 28 and the upper protective layer 30 are made of PET (Young's modulus: about 6.2 GPa) and the lower electrode 24 and the upper electrode 26 are made of copper (Young's modulus: about 130 GPa)
- the lower protective layer 28 Assuming that the thickness of the upper protective layer 30 is 25 ⁇ m, the thickness of the lower electrode 24 and the upper electrode 26 is preferably 1.2 ⁇ m or less, more preferably 0.3 ⁇ m or less, and particularly preferably 0.1 ⁇ m or less.
- the piezoelectric film 10 preferably has a maximum value of loss tangent (Tan ⁇ ) at a frequency of 1 Hz as measured by dynamic viscoelasticity measurement at room temperature, and more preferably has a maximum value of 0.1 or more at room temperature.
- Tan ⁇ loss tangent
- the piezoelectric film 10 preferably has a storage elastic modulus (E') at a frequency of 1 Hz measured by dynamic viscoelasticity measurement of 10 GPa to 30 GPa at 0 ° C. and 1 GPa to 10 GPa at 50 ° C. Regarding this condition, the same applies to the piezoelectric layer 20. As a result, the piezoelectric film 10 can have a large frequency dispersion in the storage elastic modulus (E'). That is, it can behave hard for vibrations of 20 Hz to 20 kHz and soft for vibrations of several Hz or less.
- E' storage elastic modulus
- the product of the thickness and the storage elastic modulus at a frequency of 1 Hz measured by dynamic viscoelasticity is 1.0 ⁇ 10 5 to 2.0 ⁇ 10 6 (1.0E + 05 to 2.) At 0 ° C. It is preferably 0E + 06) N / m, preferably 1.0 ⁇ 10 5 to 1.0 ⁇ 10 6 (1.0E + 05 to 1.0E + 06) N / m at 50 ° C. Regarding this condition, the same applies to the piezoelectric layer 20. As a result, the piezoelectric film 10 can be provided with appropriate rigidity and mechanical strength as long as the flexibility and acoustic characteristics are not impaired.
- the piezoelectric film 10 preferably has a loss tangent of 0.05 or more at 25 ° C. and a frequency of 1 kHz in the master curve obtained from the dynamic viscoelasticity measurement. Regarding this condition, the same applies to the piezoelectric layer 20. As a result, the frequency characteristics of the speaker using the piezoelectric film 10 are smoothed, and the change in sound quality when the minimum resonance frequency f 0 changes with the change in the curvature of the speaker can be reduced.
- the storage elastic modulus (Young's modulus) and the loss tangent of the piezoelectric film 10 and the piezoelectric layer 20 and the like may be measured by a known method.
- the measurement may be performed using a dynamic viscoelasticity measuring device DMS6100 manufactured by SII Nanotechnology Inc. (manufactured by SII Nanotechnology Inc.).
- the measurement frequency is 0.1 Hz to 20 Hz (0.1 Hz, 0.2 Hz, 0.5 Hz, 1 Hz, 2 Hz, 5 Hz, 10 Hz and 20 Hz)
- the measurement temperature is -50 to 150 ° C.
- the temperature rise rate is 2 ° C./min (in a nitrogen atmosphere)
- the sample size is 40 mm ⁇ 10 mm (including the clamp region)
- the inter-chuck distance is 20 mm.
- a sheet-like object 10a in which the lower electrode 24 is formed on the lower protective layer 28 is prepared.
- the sheet-like material 10a may be produced by forming a copper thin film or the like as the lower electrode 24 on the surface of the lower protective layer 28 by vacuum deposition, sputtering, plating or the like.
- a polymer material to be a matrix material is dissolved in an organic solvent, and piezoelectric particles 36 such as PZT particles are added and stirred to prepare a dispersed coating material.
- the organic solvent it is preferable to use a substance that is liquid at room temperature and has an SP value of less than 12.5 (cal / cm 3 ) 1/2. However, when an organic solvent other than this substance is used, this substance is used. It may be added to the paint. There are no restrictions on the organic solvent other than the above substances, and various organic solvents can be used.
- a line mixing process is performed before applying the prepared paint.
- the air bubbles in the coating material are made finer and easily removed from the surface before drying, so that the area ratio of the voids in the produced polymer composite piezoelectric material can be reduced.
- the paint is cast (coated) on the sheet-like material 10a to evaporate the organic solvent and dry it.
- a laminated body 10b having the lower electrode 24 on the lower protective layer 28 and forming the piezoelectric layer 20 on the lower electrode 24 is produced.
- the lower electrode 24 is an electrode on the base material side when the piezoelectric layer 20 is applied, and does not indicate the vertical positional relationship in the laminated body.
- the drying conditions of the paint are adjusted so that the above-mentioned substance (organic solvent) having a mass ratio of more than 500 ppm and 10000 ppm or less remains in the piezoelectric layer 20.
- a dielectric polymer material may be added to the matrix 34 in addition to the viscoelastic material such as cyanoethylated PVA.
- the polymer materials to be added to the paint described above may be dissolved.
- the polarization treatment (polling) of the piezoelectric layer 20 is preferably performed. Do.
- the method for polarization treatment of the piezoelectric layer 20 is not limited, and known methods can be used.
- a calendar treatment may be performed in which the surface of the piezoelectric layer 20 is smoothed by using a heating roller or the like. By performing this calendar processing, the thermocompression bonding process described later can be smoothly performed.
- a sheet-like material 10c in which the upper electrode 26 is formed on the upper protective layer 30 is prepared.
- the sheet-like material 10c may be produced by forming a copper thin film or the like as the upper electrode 26 on the surface of the upper protective layer 30 by vacuum deposition, sputtering, plating or the like.
- the upper electrode 26 is directed toward the piezoelectric layer 20, and the sheet-like material 10c is laminated on the laminated body 10b that has undergone the polarization treatment of the piezoelectric layer 20.
- the laminate of the laminate 10b and the sheet-like material 10c is thermocompression-bonded with a heating press device or a heating roller or the like so as to sandwich the upper protective layer 30 and the lower protective layer 28, and the piezoelectric film 10 is formed. To make.
- the laminated piezoelectric element 14 described later has a configuration in which such a piezoelectric film 10 of the present invention is laminated and bonded with a sticking layer 19 as a preferred embodiment.
- a general laminated ceramic piezoelectric element in which piezoelectric ceramics are laminated is subjected to a polarization treatment after producing a laminate of piezoelectric ceramics. Since only common electrodes exist at the interface of each piezoelectric layer, the polarization directions of each piezoelectric layer alternate in the stacking direction.
- the polarization treatment can be performed in the state of the piezoelectric film 10 before lamination. Therefore, the laminated piezoelectric element using the piezoelectric film of the present invention can be produced by laminating the polarization-treated piezoelectric film 10. Preferably, a long piezoelectric film (large-area piezoelectric film) subjected to polarization treatment is produced, cut into individual piezoelectric films 10, and then the piezoelectric films 10 are laminated to form a laminated piezoelectric element 14.
- the polarization directions of the adjacent piezoelectric films 10 can be aligned in the laminated direction as in the laminated piezoelectric element 60 shown in FIG. 8, and the laminated piezoelectric element shown in FIG. Like the element 14, it can be alternated.
- a general piezoelectric film made of a polymer material such as PVDF (polyvinylidene fluoride) the molecular chains are oriented in the stretching direction by stretching in the uniaxial direction after the polarization treatment, and as a result, the molecular chains are oriented in the stretching direction. It is known that large piezoelectric properties can be obtained. Therefore, a general piezoelectric film has in-plane anisotropy in the piezoelectric characteristics, and has anisotropy in the amount of expansion and contraction in the plane direction when a voltage is applied.
- PVDF polyvinylidene fluoride
- the polymer composite piezoelectric material of the present invention containing the piezoelectric particles 36 in the matrix 34 can obtain large piezoelectric properties without stretching treatment after polarization treatment. Therefore, the polymer composite piezoelectric material of the present invention has no in-plane anisotropy in the piezoelectric characteristics, and when a driving voltage is applied as described later, it expands and contracts isotropically in all directions in the in-plane direction.
- the polymer composite piezoelectric body and the piezoelectric film 10 of the present invention may be produced by using a cut sheet-like sheet, but preferably roll-to-roll or less. , Also called RtoR).
- RtoR is a raw material that has been processed by drawing out the raw material from a roll formed by winding a long raw material and carrying it in the longitudinal direction while performing various treatments such as film formation and surface treatment. This is a manufacturing method in which the material is wound into a roll again.
- a second roll formed by winding a sheet-like material 10c having an upper electrode 26 formed on a long upper protective layer 30 is used.
- the first roll and the second roll may be exactly the same.
- a sheet-like material 10a is pulled out from this roll, and while being conveyed in the longitudinal direction, a paint containing the matrix 34 and the piezoelectric particles 36 is applied, dried by heating or the like, and the piezoelectric layer is placed on the lower electrode 24. 20 is formed to form the above-mentioned laminated body 10b.
- the piezoelectric layer 20 is polarized.
- the piezoelectric film 10 is manufactured by RtoR
- the piezoelectric layer 20 is polarized in a direction orthogonal to the transport direction of the laminated body 10b while transporting the laminated body 10b.
- calendar processing may be performed before this polarization treatment.
- the sheet-like material 10c is pulled out from the second roll, and while the sheet-like material 10c and the laminated body are conveyed, the upper electrode 26 is subjected to the piezoelectric layer as described above by a known method using a bonding roller or the like.
- the sheet-like material 10c is laminated on the laminated body 10b toward 20.
- the laminated laminate 10b and the sheet-like material 10c are thermocompression-bonded by sandwiching and transporting them by a pair of heating rollers to complete the piezoelectric film 10 of the present invention, and the piezoelectric film 10 is wound in a roll shape. To do.
- the piezoelectric film 10 of the present invention is produced by transporting the sheet-like material (laminated body) only once in the longitudinal direction by RtoR, but the present invention is not limited to this.
- the laminated body roll is made by winding the laminated body once in a roll shape.
- the laminate is pulled out from the laminate roll, and while being conveyed in the longitudinal direction, the sheet-like material having the upper electrode 26 formed on the upper protective layer 30 is laminated as described above to form a piezoelectric film. 10 may be completed, and the piezoelectric film 10 may be wound in a roll shape.
- the piezoelectric film 10 when a voltage is applied to the lower electrode 24 and the upper electrode 26, the piezoelectric particles 36 expand and contract in the polarization direction according to the applied voltage. As a result, the piezoelectric film 10 (piezoelectric layer 20) shrinks in the thickness direction. At the same time, the piezoelectric film 10 expands and contracts in the in-plane direction due to the pore ratio. This expansion and contraction is about 0.01 to 0.1%. As described above, it expands and contracts isotropically in all directions in the in-plane direction. As described above, the thickness of the piezoelectric layer 20 is preferably about 10 to 300 ⁇ m. Therefore, the expansion and contraction in the thickness direction is very small, about 0.3 ⁇ m at the maximum.
- the piezoelectric film 10 that is, the piezoelectric layer 20, has a size much larger than the thickness in the plane direction. Therefore, for example, if the length of the piezoelectric film 10 is 20 cm, the piezoelectric film 10 expands and contracts by a maximum of about 0.2 mm when a voltage is applied. Further, when pressure is applied to the piezoelectric film 10, electric power is generated by the action of the piezoelectric particles 36. By utilizing this, the piezoelectric film 10 can be used for various purposes such as a speaker, a microphone, and a pressure-sensitive sensor as described above.
- FIG. 5 shows a conceptual diagram of an example of a flat plate type piezoelectric speaker having the piezoelectric film 10 of the present invention.
- the piezoelectric speaker 45 is a flat plate type piezoelectric speaker that uses the piezoelectric film 10 of the present invention as a diaphragm that converts an electric signal into vibration energy.
- the piezoelectric speaker 45 can also be used as a microphone, a sensor, or the like.
- the piezoelectric speaker 45 includes a piezoelectric film 10, a case 43, a viscoelastic support 46, and a frame body 48.
- the case 43 is a thin square-shaped tubular housing that is made of plastic or the like and has an open surface.
- the frame body 48 is a plate material having a through hole in the center and having the same shape as the upper end surface (open surface side) of the case 43.
- the viscoelastic support 46 has appropriate viscosity and elasticity, supports the piezoelectric film 10, and applies a constant mechanical bias to any part of the piezoelectric film to move the piezoelectric film 10 back and forth without waste. It is for converting into motion (movement in the direction perpendicular to the surface of the film).
- wool felt, non-woven fabric such as wool felt containing rayon and PET, glass wool and the like are exemplified.
- the piezoelectric speaker 45 accommodates the viscoelastic support 46 in the case 43, covers the case 43 and the viscoelastic support 46 with the piezoelectric film 10, and surrounds the periphery of the piezoelectric film 10 with the frame 48 to form the upper end surface of the case 43.
- the frame body 48 is fixed to the case 43 while being pressed against the case 43.
- the viscoelastic support 46 is a square columnar whose height (thickness) is thicker than the height of the inner surface of the case 43. Therefore, in the piezoelectric speaker 45, the viscoelastic support 46 is held in a state of being thinned by being pressed downward by the piezoelectric film 10 at the peripheral portion of the viscoelastic support 46. Similarly, in the peripheral portion of the viscoelastic support 46, the curvature of the piezoelectric film 10 suddenly fluctuates, and the piezoelectric film 10 is formed with a rising portion 45a that becomes lower toward the periphery of the viscoelastic support 46. Further, the central region of the piezoelectric film 10 is pressed by the viscoelastic support 46 having a square columnar shape to be (omitted) flat.
- the piezoelectric speaker 45 When the piezoelectric film 10 is stretched in the in-plane direction by applying a driving voltage to the lower electrode 24 and the upper electrode 26, the piezoelectric speaker 45 is made piezoelectric by the action of the viscoelastic support 46 in order to absorb the stretched portion.
- the rising portion 45a of the film 10 changes the angle in the rising direction.
- the piezoelectric film 10 having the flat portion moves upward.
- the piezoelectric film 10 contracts in the in-plane direction due to the application of the driving voltage to the lower electrode 24 and the upper electrode 26
- the rising portion 45a of the piezoelectric film 10 collapses in order to absorb the contracted portion. Change the angle in the direction closer to the plane).
- the piezoelectric film 10 having the flat portion moves downward.
- the piezoelectric speaker 45 generates sound by the vibration of the piezoelectric film 10.
- the conversion from the stretching motion to the vibration can also be achieved by holding the piezoelectric film 10 in a curved state. Therefore, the piezoelectric film 10 of the present invention can function as a flexible speaker by simply holding it in a curved state instead of such a piezoelectric speaker 45.
- FIG. 6 conceptually shows an example of an electroacoustic converter having the piezoelectric film 10 of the present invention.
- the electroacoustic transducer 50 shown in FIG. 6 has a laminated piezoelectric element 14 and a diaphragm 12.
- the laminated piezoelectric element 14 is formed by laminating a plurality of layers of the piezoelectric film of the present invention.
- the laminated piezoelectric element 14 is formed by laminating three layers of the above-mentioned piezoelectric film 10 of the present invention.
- the laminated piezoelectric element 14 and the diaphragm 12 are attached by an attachment layer 16.
- a power supply PS for applying a driving voltage is connected to the piezoelectric film 10 constituting the laminated piezoelectric element 14 of the electroacoustic converter 50.
- the lower protective layer 28 and the upper protective layer 30 are omitted for simplification of the drawings.
- all the piezoelectric films 10 have both the lower protective layer 28 and the upper protective layer 30.
- the laminated piezoelectric element is not limited to this, and a piezoelectric film having a protective layer and a piezoelectric film not having a protective layer may be mixed. Further, when the piezoelectric film has a protective layer, the piezoelectric film may have only the lower protective layer 28 or only the upper protective layer 30.
- the piezoelectric film in the uppermost layer in the figure has only the upper protective layer 30, and the piezoelectric film in the middle has no protective layer.
- the structure may be such that the lowermost piezoelectric film has only the lower protective layer 28.
- the piezoelectric film 10 expands and contracts in the plane direction by applying a driving voltage to the piezoelectric film 10 of the laminated piezoelectric element 14, and the expansion and contraction of the piezoelectric film 10 causes the piezoelectric film 10 to expand and contract.
- the laminated piezoelectric element 14 expands and contracts in the plane direction.
- the expansion and contraction of the laminated piezoelectric element 14 in the surface direction causes the diaphragm 12 to bend, and as a result, the diaphragm 12 vibrates in the thickness direction. Due to the vibration in the thickness direction, the diaphragm 12 generates a sound.
- the diaphragm 12 vibrates according to the magnitude of the drive voltage applied to the piezoelectric film 10, and generates a sound corresponding to the drive voltage applied to the piezoelectric film 10. That is, the electroacoustic converter 50 is a speaker that uses the laminated piezoelectric element 14 as an exciter.
- the diaphragm 12 is, in a preferred embodiment, flexible.
- having flexibility is synonymous with having flexibility in a general interpretation, and indicates that it can be bent and bent, specifically. Shows that it can be bent and stretched without causing breakage and damage.
- the diaphragm 12 is not limited as long as it is preferably flexible and satisfies the relationship with the laminated piezoelectric element 14 described later, and various sheet-like materials (plate-like materials, films) can be used. is there.
- PET polyethylene terephthalate
- PP polypropylene
- PS polystyrene
- PC polycarbonate
- PPS polyphenylene sulfide
- PMMA polymethylmethacrylate
- PEI polyetherimide
- PI polyimide
- PEN polyethylene naphthalate
- TAC triacetyl cellulose
- foamed plastic made of expanded polystyrene, expanded styrene, expanded polyethylene, etc., and other on one or both sides of wavy paperboard.
- cardboard materials and the like made by sticking the paperboard of the above are exemplified.
- the vibrating plate 12 includes an organic electroluminescence (OLED (Organic Light Emitting Diode)) display, a liquid crystal display, and a micro LED (Light Emitting Diode) display.
- OLED Organic Light Emitting Diode
- a display device such as an inorganic electroluminescent display can also be suitably used.
- such a diaphragm 12 and the laminated piezoelectric element 14 are attached by an attachment layer 16.
- the adhesive layer 16 has fluidity when bonded, and then becomes a solid. Even a layer made of an adhesive is a soft solid gel-like (rubber-like) when bonded, and then gels. It may be a layer made of a pressure-sensitive adhesive whose state does not change, or a layer made of a material having the characteristics of both an adhesive and a pressure-sensitive adhesive.
- the laminated piezoelectric element 14 is expanded and contracted to bend and vibrate the diaphragm 12 to generate sound.
- the adhesive layer 16 is preferably an adhesive layer made of an adhesive, which can obtain a solid and hard adhesive layer 16 rather than the adhesive layer made of an adhesive.
- the more preferable adhesive layer 16 include an adhesive layer made of a polyester adhesive and a thermoplastic type adhesive such as a styrene-butadiene rubber (SBR) adhesive. Adhesion, unlike adhesion, is useful when seeking high adhesion temperatures. Further, the thermoplastic type adhesive has "relatively low temperature, short time, and strong adhesion" and is suitable.
- SBR styrene-butadiene rubber
- the thickness of the sticking layer 16 is not limited, and a thickness at which sufficient sticking force (adhesive force, adhesive force) can be obtained may be appropriately set according to the material of the sticking layer 16.
- the thinner the adhesive layer 16 the higher the effect of transmitting the expansion / contraction energy (vibration energy) of the laminated piezoelectric element 14 transmitted to the diaphragm 12, and the higher the energy efficiency. ..
- the adhesive layer 16 is thick and has high rigidity, the expansion and contraction of the laminated piezoelectric element 14 may be restricted.
- the sticking layer 16 is preferably thin.
- the thickness of the sticking layer 16 is preferably 0.1 to 50 ⁇ m, more preferably 0.1 to 30 ⁇ m, and even more preferably 0.1 to 10 ⁇ m after sticking.
- the sticking layer 16 is provided as a preferred embodiment and is not an essential component. Therefore, the electroacoustic converter 50 does not have the bonding layer 16, and the diaphragm 12 and the laminated piezoelectric element 14 may be fixed by using known crimping means, fastening means, fixing means, and the like. ..
- the laminated piezoelectric element 14 is rectangular, the four corners may be fastened with members such as bolts and nuts to form an electroacoustic transducer, or the four corners and the central portion may be bolted and nuts.
- the electroacoustic converter may be formed by fastening with members.
- the laminated piezoelectric element 14 expands and contracts independently with respect to the diaphragm 12, and in some cases, only the laminated piezoelectric element 14 bends.
- the expansion and contraction of the laminated piezoelectric element 14 is not transmitted to the diaphragm 12.
- the vibration efficiency of the diaphragm 12 by the laminated piezoelectric element 14 decreases.
- the diaphragm 12 cannot be vibrated sufficiently.
- it is preferable that the diaphragm 12 and the laminated piezoelectric element 14 are attached by the attachment layer 16 as shown in FIG.
- the laminated piezoelectric element 14 has a configuration in which three piezoelectric films 10 are laminated and adjacent piezoelectric films 10 are attached by an attachment layer 19.
- a power supply PS for applying a driving voltage for expanding and contracting the piezoelectric film 10 is connected to each piezoelectric film 10.
- the laminated piezoelectric element 14 shown in FIG. 6 is formed by laminating three layers of the piezoelectric film 10, but the present invention is not limited to this. That is, as long as the laminated piezoelectric element is formed by laminating a plurality of layers of the piezoelectric film 10, the number of laminated piezoelectric films 10 may be two layers or four or more layers.
- the electroacoustic converter may be one that vibrates the diaphragm 12 with the same effect and effect by the piezoelectric film of the present invention instead of the laminated piezoelectric element 14 to generate sound. That is, the electroacoustic converter may use the piezoelectric film of the present invention as an exciter.
- the polarization directions of the adjacent piezoelectric films 10 are reversed from each other, and a plurality of layers (three layers in the example shown in FIG. 6) are laminated and adjacent to each other. It has a structure in which the piezoelectric film 10 is attached by the attachment layer 19.
- the adhesive layer 19 may be the above-mentioned layer made of an adhesive, a layer made of an adhesive, or a layer made of a material having the characteristics of both an adhesive and an adhesive.
- the laminated piezoelectric element 14 vibrates the diaphragm 12 by expanding and contracting the plurality of laminated piezoelectric films 10, and generates sound. Therefore, it is preferable that the expansion and contraction of each piezoelectric film 10 is directly transmitted to the laminated piezoelectric element 14.
- the adhesive layer 19 is preferably an adhesive layer made of an adhesive, which can obtain a solid and hard adhesive layer 19 rather than an adhesive layer made of an adhesive.
- an adhesive layer made of a polyester adhesive and a thermoplastic type adhesive such as a styrene-butadiene rubber (SBR) adhesive is preferably exemplified. Adhesion, unlike adhesion, is useful when seeking high adhesion temperatures. Further, the thermoplastic type adhesive has "relatively low temperature, short time, and strong adhesion" and is suitable.
- the thickness of the sticking layer 19 is not limited, and a thickness capable of exhibiting a sufficient sticking force may be appropriately set according to the material for forming the sticking layer 19.
- the adhesive layer 19 is thick and has high rigidity, the expansion and contraction of the piezoelectric film 10 may be restricted.
- the sticking layer 19 is preferably thinner than the piezoelectric layer 20. That is, in the laminated piezoelectric element 14, the bonding layer 19 is preferably hard and thin.
- the thickness of the sticking layer 19 is preferably 0.1 to 50 ⁇ m, more preferably 0.1 to 30 ⁇ m, and even more preferably 0.1 to 10 ⁇ m after sticking.
- the polarization directions of the adjacent piezoelectric films are opposite to each other, and there is no possibility that the adjacent piezoelectric films 10 are short-circuited, so that the bonding layer 19 can be made thin. ..
- the spring constant of the sticking layer 19 is equal to or less than the spring constant of the piezoelectric film 10.
- the product of the thickness of the adhesive layer 19 and the storage elastic modulus (E') at a frequency of 1 Hz by dynamic viscoelasticity measurement is 2.0 ⁇ 10 6 N / m or less at 0 ° C., 50. It is preferably 1.0 ⁇ 10 6 N / m or less at ° C.
- the internal loss at a frequency of 1 Hz by the dynamic viscoelasticity measurement of the adhesive layer is 1.0 or less at 25 ° C. in the case of the adhesive layer 19 made of an adhesive, and in the case of the adhesive layer 19 made of an adhesive. It is preferably 0.1 or less at 25 ° C.
- the bonding layer 19 is provided as a preferred embodiment and is not an essential component. Therefore, the laminated piezoelectric element constituting the electroacoustic converter does not have the bonding layer 19, and the piezoelectric film 10 is laminated and brought into close contact with each other by using known crimping means, fastening means, fixing means and the like.
- the laminated piezoelectric element may be configured. For example, when the piezoelectric film 10 is rectangular, the four corners may be fastened with bolts and nuts to form a laminated piezoelectric element, or the four corners and the central portion may be fastened with bolts and nuts to form a laminated piezoelectric element. May be configured.
- the laminated piezoelectric film 10 may be fixed by attaching an adhesive tape to the peripheral portion (end face) to form a laminated piezoelectric element.
- the individual piezoelectric films 10 expand and contract independently, and in some cases, each layer of each piezoelectric film 10 bends in the opposite direction to form a gap. It ends up.
- the drive efficiency of the laminated piezoelectric element decreases, the expansion and contraction of the laminated piezoelectric element as a whole becomes small, and the diaphragm and the like that come into contact with each other.
- the laminated piezoelectric element has a bonding layer 19 for bonding adjacent piezoelectric films 10 to each other, as in the laminated piezoelectric element 14 shown in FIG.
- a power supply PS is connected to the lower electrode 24 and the upper electrode 26 of each piezoelectric film 10 to apply a driving voltage for expanding and contracting the piezoelectric film 10, that is, to supply driving power.
- the power supply PS is not limited and may be a DC power supply or an AC power supply.
- the drive voltage capable of appropriately driving each piezoelectric film 10 may be appropriately set according to the thickness of the piezoelectric layer 20 of each piezoelectric film 10 and the forming material. As will be described later, in the laminated piezoelectric element 14, the polarization directions of the adjacent piezoelectric films 10 are opposite to each other.
- the lower electrodes 24 and the upper electrodes 26 face each other. Therefore, the power supply PS always supplies power of the same polarity to the facing electrodes regardless of whether it is an AC power supply or a DC power supply.
- the upper electrode 26 of the piezoelectric film 10 in the lowermost layer in the figure and the upper electrode 26 of the piezoelectric film 10 in the second layer (middle) always have the same polarity. Power is always supplied to the lower electrode 24 of the second layer piezoelectric film 10 and the lower electrode 24 of the uppermost piezoelectric film 10 in the drawing.
- the method of drawing the electrode from the lower electrode 24 and the upper electrode 26 is not limited, and various known methods can be used.
- An example is a method in which the through hole is filled with a conductive material and the electrode is pulled out to the outside.
- suitable electrode extraction methods include the methods described in JP-A-2014-209724 and the methods described in JP-A-2016-015354.
- the piezoelectric layer 20 contains the piezoelectric particles 36 in the matrix 34. Further, the lower electrode 24 and the upper electrode 26 are provided so as to sandwich the piezoelectric layer 20 in the thickness direction.
- the piezoelectric particles 36 expand and contract in the polarization direction according to the applied voltage.
- the piezoelectric film 10 shrinks in the thickness direction.
- the piezoelectric film 10 expands and contracts in the in-plane direction due to the pore ratio. This expansion and contraction is about 0.01 to 0.1%.
- the thickness of the piezoelectric layer 20 is preferably about 10 to 300 ⁇ m. Therefore, the expansion and contraction in the thickness direction is very small, about 0.3 ⁇ m at the maximum.
- the piezoelectric film 10, that is, the piezoelectric layer 20 has a size much larger than the thickness in the plane direction. Therefore, for example, if the length of the piezoelectric film 10 is 20 cm, the piezoelectric film 10 expands and contracts by a maximum of about 0.2 mm when a voltage is applied.
- the laminated piezoelectric element 14 is formed by laminating and adhering a piezoelectric film 10. Therefore, if the piezoelectric film 10 expands and contracts, the laminated piezoelectric element 14 also expands and contracts.
- the diaphragm 12 is attached to the laminated piezoelectric element 14 by the attachment layer 16. Therefore, the expansion and contraction of the laminated piezoelectric element 14 causes the diaphragm 12 to bend, and as a result, the diaphragm 12 vibrates in the thickness direction. Due to the vibration in the thickness direction, the diaphragm 12 generates a sound. That is, the diaphragm 12 vibrates according to the magnitude of the voltage (driving voltage) applied to the piezoelectric film 10 and generates a sound corresponding to the driving voltage applied to the piezoelectric film 10.
- a general piezoelectric film made of a polymer material such as PVDF has in-plane anisotropy in the piezoelectric characteristics, and has anisotropy in the amount of expansion and contraction in the plane direction when a voltage is applied. ..
- the piezoelectric film 10 of the present invention constituting the laminated piezoelectric element 14 has no in-plane anisotropy in the piezoelectric characteristics, and is equal in all directions in the in-plane direction. It expands and contracts in a direction. That is, in the electroacoustic converter 50 shown in FIG.
- the piezoelectric film 10 constituting the laminated piezoelectric element 14 expands and contracts isotropically and two-dimensionally.
- the laminated piezoelectric element 14 in which the piezoelectric film 10 that expands and contracts isotropically and two-dimensionally is laminated it is larger than the case where a general piezoelectric film such as PVDF that expands and contracts greatly in only one direction is laminated.
- the diaphragm 12 can be vibrated by force, and a louder and more beautiful sound can be generated.
- the laminated piezoelectric element 14 shown in FIG. 6 is formed by laminating a plurality of piezoelectric films 10.
- the laminated piezoelectric element 14 further adheres adjacent piezoelectric films 10 to each other with a bonding layer 19. Therefore, even if the rigidity of each piezoelectric film 10 is low and the stretching force is small, the rigidity is increased by laminating the piezoelectric films 10, and the stretching force of the laminated piezoelectric element 14 is increased.
- the laminated piezoelectric element 14 even if the diaphragm 12 has a certain degree of rigidity, the diaphragm 12 is sufficiently flexed by a large force to sufficiently vibrate the diaphragm 12 in the thickness direction.
- the preferable thickness of the piezoelectric layer 20 is about 300 ⁇ m at the maximum, so that even if the voltage applied to each piezoelectric film 10 is small, the piezoelectric layer is sufficiently piezoelectric.
- the film 10 can be expanded and contracted.
- the product of the thickness of the laminated piezoelectric element 14 and the storage elastic modulus at a frequency of 1 Hz and 25 ° C. measured by dynamic viscoelasticity measurement is 0.1 to 3 times the product of the thickness of the diaphragm 12 and Young's modulus. Is preferable.
- the piezoelectric film 10 of the present invention has good flexibility
- the laminated piezoelectric element 14 on which the piezoelectric film 10 is laminated also has good flexibility
- the diaphragm 12 has a certain degree of rigidity.
- the laminated piezoelectric element 14 having high rigidity is combined with such a diaphragm 12, it becomes hard and difficult to bend, which is disadvantageous in terms of flexibility of the electroacoustic converter 50.
- the thickness of the diaphragm 12 and Young's modulus measured by dynamic viscoelasticity is the thickness of the diaphragm 12 and Young's modulus. It is less than three times the product of the rate. That is, the laminated piezoelectric element 14 preferably has a spring constant of 3 times or less that of the diaphragm 12 for slow movement.
- the electroacoustic transducer 50 can behave softly against slow movements due to external forces such as bending and rolling, that is, good for slow movements. Expresses flexibility.
- the product of the thickness of the laminated piezoelectric element 14 and the storage elastic modulus at a frequency of 1 Hz and 25 ° C. measured by dynamic viscoelasticity measurement is twice the product of the thickness of the diaphragm 12 and Young's modulus. It is more preferably less than or equal to, more preferably 1 time or less, and particularly preferably 0.3 times or less.
- the product of the thickness of the laminated piezoelectric element 14 and the storage elastic modulus at a frequency of 1 Hz and 25 ° C. by dynamic viscoelasticity measurement. Is preferably 0.1 times or more the product of the thickness of the vibrating plate 12 and the Young's modulus.
- the product of the thickness of the laminated piezoelectric element 14 and the storage elastic modulus at a frequency of 1 kHz and 25 ° C. in the master curve obtained from the dynamic viscoelasticity measurement is the thickness of the diaphragm 12 and Young's modulus. It is preferably 0.3 to 10 times the product of. That is, the laminated piezoelectric element 14 preferably has a spring constant of 0.3 to 10 times that of the diaphragm 12 in a fast movement in a driven state.
- the electroacoustic converter 50 generates sound by vibrating the diaphragm 12 by expanding and contracting the laminated piezoelectric element 14 in the plane direction. Therefore, it is preferable that the laminated piezoelectric element 14 has a certain degree of rigidity (hardness, stiffness) with respect to the diaphragm 12 in the frequency of the audio band (20 Hz to 20 kHz).
- the electroacoustic transducer 50 combines the product of the thickness of the laminated piezoelectric element 14 and the storage elastic modulus at a frequency of 1 kHz and 25 ° C. in the master curve obtained from the dynamic viscoelasticity measurement with the thickness of the diaphragm 12 and Young's modulus.
- the product is preferably 0.3 times or more, more preferably 0.5 times or more, still more preferably 1 time or more. That is, the spring constant of the laminated piezoelectric element 14 is preferably 0.3 times or more, more preferably 0.5 times or more, and 1 times or more that of the diaphragm 12 for fast movement. It is more preferable to have it. As a result, in the frequency of the audio band, the rigidity of the laminated piezoelectric element 14 with respect to the diaphragm 12 is sufficiently secured, and the electroacoustic converter 50 can output a sound with high sound pressure with high energy efficiency.
- the product of the thickness of the laminated piezoelectric element 14 and the storage elastic modulus at a frequency of 1 kHz and 25 ° C. by dynamic viscoelasticity measurement. Is preferably 10 times or less the product of the thickness of the vibrating plate 12 and the Young's modulus.
- the product of the thickness and the storage elastic modulus described above is the same when the electroacoustic converter is configured by using the piezoelectric film 10 instead of the laminated piezoelectric element 14.
- the polarization directions of the piezoelectric layers 20 of the adjacent piezoelectric films 10 are opposite to each other.
- the polarity of the voltage applied to the piezoelectric layer 20 depends on the polarization direction. Therefore, the polarity of the applied voltage is the polarity of the electrode on the direction side (downstream side of the arrow) toward which the arrow points and the polarity of the electrode on the opposite side (upstream side of the arrow) in the polarization direction shown by the arrow in FIG. , Match with all piezoelectric films 10.
- the polarity of the voltage applied to the piezoelectric layer 20 depends on the polarization direction. Therefore, the polarity of the applied voltage is the polarity of the electrode on the direction side (downstream side of the arrow) toward which the arrow points and the polarity of the electrode on the opposite side (upstream side of the arrow) in the polarization direction shown by the arrow in FIG. , Match with all piezoelectric films 10.
- the electrode on the side in which the arrow indicating the polarization direction faces is the lower electrode 24, the electrode on the opposite side is the upper electrode 26, and in all the piezoelectric films 10, the upper electrode 26 and the lower electrode 24 are Make the polarity the same. Therefore, in the laminated piezoelectric element 14 in which the polarization directions of the piezoelectric layers 20 of the adjacent piezoelectric films 10 are opposite to each other, in the adjacent piezoelectric film 10, the upper electrodes 26 face each other on one surface and the other surface. The lower electrodes face each other. Therefore, in the laminated piezoelectric element 14, even if the electrodes of the adjacent piezoelectric films 10 come into contact with each other, there is no risk of short-circuiting.
- the adhesive layer 19 it is preferable to make the adhesive layer 19 thin so that the adhesive layer 19 does not interfere with the expansion and contraction of the piezoelectric layer 20.
- the adhesive layer 19 may not be provided, and the adhesive layer is preferable. Even if the number 19 is provided, the bonding layer 19 can be made extremely thin if the required bonding force is obtained. Therefore, the laminated piezoelectric element 14 can be expanded and contracted with high energy efficiency.
- the absolute amount of expansion and contraction of the piezoelectric layer 20 in the thickness direction is very small, and the expansion and contraction of the piezoelectric film 10 is substantially only in the plane direction. Therefore, even if the polarization directions of the laminated piezoelectric films 10 are opposite, all the piezoelectric films 10 expand and contract in the same direction as long as the polarities of the voltages applied to the lower electrode 24 and the upper electrode 26 are correct.
- the polarization direction of the piezoelectric film 10 may be detected by a d33 meter or the like. Alternatively, the polarization direction of the piezoelectric film 10 may be known from the processing conditions of the polarization treatment.
- the laminated piezoelectric element 14 shown in FIG. 6 preferably prepares a long (large area) piezoelectric film and cuts the long piezoelectric film into individual piezoelectric films 10 as described above. Therefore, in this case, the plurality of piezoelectric films 10 constituting the laminated piezoelectric element 14 are all the same. However, the present invention is not limited to this.
- the piezoelectric laminate has a structure in which piezoelectric films having different layer configurations such as a piezoelectric film having a lower protective layer 28 and an upper protective layer 30 and a piezoelectric film having no lower protective layer 30 are laminated, and piezoelectric Various configurations are available, such as a configuration in which piezoelectric films having different thicknesses of the body layer 20 are laminated.
- the laminated piezoelectric element 14 in the laminated piezoelectric element 14, a plurality of piezoelectric films 10 are laminated with adjacent piezoelectric films in opposite polarization directions, and as a preferred embodiment, the adjacent piezoelectric films 10 are laminated. Is attached with the attachment layer 19.
- the laminated piezoelectric element of the present invention is not limited to this, and various configurations can be used.
- FIG. 7 shows an example thereof. Since the laminated piezoelectric element 56 shown in FIG. 7 uses a plurality of the same members as the above-mentioned laminated piezoelectric element 14, the same members are designated by the same reference numerals, and the description will be given mainly to different parts.
- the laminated piezoelectric element 56 shown in FIG. 7 is a more preferable embodiment of the laminated piezoelectric element in the present invention.
- the piezoelectric film is formed by folding a long piezoelectric film 10L once or more, preferably a plurality of times in the longitudinal direction. It is a stack of a plurality of 10L layers. Further, similarly to the laminated piezoelectric element 14 shown in FIG.
- the piezoelectric film 10L laminated by folding back is attached by the attachment layer 19. There is.
- the polarization direction of the piezoelectric film 10L adjacent (facing) in the laminating direction is as shown by an arrow in FIG. , In the opposite direction.
- the laminated piezoelectric element 56 can be configured with only one long piezoelectric film 10L, only one power supply PS for applying a driving voltage is required, and an electrode from the piezoelectric film 10L is required.
- the drawer may be in one place. Therefore, according to the laminated piezoelectric element 56 shown in FIG. 7, the number of parts can be reduced, the configuration can be simplified, the reliability of the piezoelectric element (module) can be improved, and the cost can be further reduced. ..
- the core rod 58 is inserted into the folded portion of the piezoelectric film 10L in contact with the piezoelectric film 10L.
- the lower electrode 24 and the upper electrode 26 of the piezoelectric film 10L are formed of a metal vapor-deposited film or the like. If the metal vapor-deposited film is bent at an acute angle, cracks and the like are likely to occur, and the electrodes may be broken. That is, in the laminated piezoelectric element 56 shown in FIG. 7, cracks or the like are likely to occur in the electrodes inside the bent portion.
- the lower electrode 24 and the upper electrode 26 are prevented from being bent by inserting the core rod 58 into the folded portion of the piezoelectric film 10L. Therefore, it is possible to preferably prevent the disconnection from occurring.
- the laminated piezoelectric element may use the adhesive layer 19 having conductivity.
- the adhesive layer 19 having conductivity is preferably used.
- the electrode is likely to be broken inside the bent portion that is folded back at an acute angle. Therefore, by sticking the laminated piezoelectric film 10L with the conductive sticking layer 19, even if the electrode is broken inside the bent portion, the sticking layer 19 can secure the continuity. This can be prevented and the reliability of the laminated piezoelectric element 56 can be significantly improved.
- the piezoelectric film 10L constituting the laminated piezoelectric element 56 preferably has a lower protective layer 28 and an upper portion so as to face the lower electrode 24 and the upper electrode 26 and sandwich the laminated body, as shown in FIG. It has a protective layer 30.
- the piezoelectric film 10L has a protective layer, through holes are provided in the lower protective layer 28 and the upper protective layer 30 in the region where the lower electrodes 24 and the upper electrodes 26 of the laminated piezoelectric films 10L face each other.
- the lower electrode 24 and the upper electrode 26 may be brought into contact with the conductive adhesive layer 19.
- the through holes formed in the lower protective layer 28 and the upper protective layer 30 are closed with a silver paste or a conductive adhesive, and an adjacent piezoelectric film 10L is attached by the conductive adhesive layer 19. To wear.
- the through holes of the lower protective layer 28 and the upper protective layer 30 may be formed by laser processing, removal of the protective layer by solvent etching, mechanical polishing, or the like.
- the through holes of the lower protective layer 28 and the upper protective layer 30 are preferably at one place other than the bent portion of the piezoelectric film 10L in the region where the lower electrodes 24 and the upper electrodes 26 of the laminated piezoelectric films 10L face each other. Often, there may be multiple locations.
- the through holes of the lower protective layer 28 and the upper protective layer 30 may be formed regularly or irregularly on the entire surface of the lower protective layer 28 and the upper protective layer 30.
- the adhesive layer 19 having conductivity is not limited, and various known ones can be used.
- the polarization direction of the laminated piezoelectric film 10 is opposite to that of the adjacent piezoelectric film 10, but the present invention is not limited to this. That is, in the present invention, in the laminated piezoelectric element in which the piezoelectric film 10 is laminated, the polarization directions of the piezoelectric layer 20 may be all the same as in the laminated piezoelectric element 60 shown in FIG. However, as shown in FIG. 8, in the laminated piezoelectric element 60 in which the polarization directions of the laminated piezoelectric films 10 are all the same, the lower electrode 24 and the upper electrode 26 face each other between the adjacent piezoelectric films 10.
- the bonding layer 19 cannot be thinned by the laminated piezoelectric element 60 in which the polarization directions of the laminated piezoelectric films 10 are all in the same direction, and the lamination shown in FIGS. It is disadvantageous in terms of energy efficiency compared to piezoelectric elements.
- Example 1 ⁇ Preparation of paint> First, cyanoethylated PVA (manufactured by CR-V Shin-Etsu Chemical Co., Ltd.) was dissolved in cyclohexanone (SP value: 9.9 (cal / cm 3 ) 1/2 ) at the following composition ratio. Then, PZT particles were added to this solution at the following composition ratio and dispersed by a propeller mixer (rotation speed 2000 rpm) to prepare a coating material for forming a piezoelectric layer. The process of passing this coating liquid through an in-line mixer (MX-F8 manufactured by OHR Fluid Engineering Laboratory Co., Ltd.) at a flow rate of 5 kg / min was repeated for 2 passes to refine the bubbles in the coating liquid.
- SP value 9.9 (cal / cm 3 ) 1/2
- PZT particles were added to this solution at the following composition ratio and dispersed by a propeller mixer (rotation speed 2000 rpm) to prepare a coating material for forming a piez
- a sheet-like material obtained by vacuum-depositing a copper thin film having a thickness of 0.1 ⁇ m on a PET film having a thickness of 4 ⁇ m was prepared. That is, in this example, the thin film electrode is a copper-deposited thin film having a thickness of 0.1 m, and the protective layer is a PET film having a thickness of 4 ⁇ m.
- a paint for forming the previously prepared piezoelectric layer was applied using a slide coater. The paint was applied so that the film thickness of the coating film after drying was 40 ⁇ m.
- ⁇ Drying paint> a part of cyclohexanone was evaporated by heating and drying the sheet-like material coated with the paint on a hot plate at 100 ° C. for 60 minutes. As a result, a laminate formed by having a copper thin film electrode on a PET protective layer and forming a piezoelectric layer (polymer composite piezoelectric body) having a thickness of 40 ⁇ m on the thin film electrode was produced.
- ⁇ Laminating sheet-like material> A sheet-like material was laminated on the polarized body with the thin film electrode (copper thin film side) facing the piezoelectric layer. Next, the laminate of the laminate and the sheet-like material was adhered to the piezoelectric layer and the thin film electrode using a laminator device. A piezoelectric film was produced by the above steps.
- a sample was cut out from the produced piezoelectric film, and the area ratio of voids in the polymer composite piezoelectric body was measured by the following method. It was cut in the thickness direction to observe the cross section of the polymer composite piezoelectric body.
- a Leica Biosystem RM2265 was attached with a Drukker histo knife blade width of 8 mm, and the speed was set to the controller scale 1 and the meshing amount was set to 0.25 ⁇ m to 1 ⁇ m to obtain a cross section.
- the cross section was observed by SEM (SU8220 manufactured by Hitachi High-Technologies Corporation).
- the sample is conductively treated by Pt vapor deposition, and the work distance is 8 mm.
- the observation conditions are SE image (Upper), acceleration voltage: 0.5 kV, sharp image is output by focus adjustment and astigmatism adjustment, and automatic brightness adjustment (auto) with the polymer composite piezoelectric part covering the entire screen.
- the setting brightness: 0, contrast: 0) was executed.
- the magnification of photography was set so that the electrodes at both ends fit on one screen and the width between the electrodes is more than half of the screen.
- Image analysis software ImageJ was used to binarize the image, the lower limit of Thrashold was set to the maximum value at which the protective layer was not colored, and the upper limit of Thrashold was set to the maximum set value of 255.
- the area of the colored part between the electrodes is defined as the area of the void and is defined as the molecule, the vertical width is defined as the space between the electrodes, and the horizontal width is defined as both ends of the SEM image.
- the area ratio of the voids to the area of the composite piezoelectric part was calculated. This was performed on any 10 cross sections, and the average value of the area ratio was calculated as the area ratio of the voids in the cross section of the polymer composite piezoelectric body. As a result, the area ratio of the voids in the cross section of the polymer composite piezoelectric body was 1.2%.
- a sample is cut out from the produced piezoelectric film, and a substance (solvent) having an SP value of less than 12.5 (cal / cm 3 ) 1/2 and a liquid at room temperature is contained in the polymer composite piezoelectric film by the following method. The amount was measured.
- a part of the sample was cut out from the polymer composite piezoelectric body into an 8 ⁇ 8 mm square, and the cyclohexanone content was measured using a gas chromatograph device (GC-12A manufactured by Shimadzu Corporation).
- the column used was 221-14368-11 manufactured by Shimadzu Corporation, and the filler used was Chromosorb 101 manufactured by Shinwa Kako.
- the temperature of the sample vaporization chamber and the detector was 200 ° C.
- the column temperature was constant at 160 ° C.
- 0.4 MPa of helium was used as the carrier gas for measurement.
- the mass ratio was calculated by dividing the mass of the obtained cyclohexanone by the net mass of the polymer composite piezoelectric material in the sample.
- the SP value of the polymer composite piezoelectric body was less than 12.5 (cal / cm 3 ) 1/2 , and the content of the substance (solvent) liquid at room temperature was 520 ppm.
- Example 2 to 6 A piezoelectric film was produced in the same manner as in Example 1 except that the mixing method and the drying conditions of the paint used as the piezoelectric layer were changed to the conditions shown in Table 1 below.
- Example 7 Piezoelectric film in the same manner as in Example 1 except that the solvent contained in the paint to be the piezoelectric layer was dimethylformamide (DMF) (SP value: 12.1 (cal / cm 3 ) 1/2 ) instead of cyclohexanone. was produced.
- DMF dimethylformamide
- Example 8 The solvent contained in the paint to be the piezoelectric layer was changed to methyl ethyl ketone (MEK) (SP value: 9.3 (cal / cm 3 ) 1/2 ) instead of cyclohexanone, and the drying conditions of the paint were set to the conditions shown in Table 1 below.
- MEK methyl ethyl ketone
- Example 1 A piezoelectric film was produced in the same manner as in Example 1 except that the drying conditions were changed to the conditions shown in Table 1 below without mixing the paint to be the piezoelectric layer.
- Example 2 A piezoelectric film was produced in the same manner as in Example 1 except that the drying conditions of the paint to be the piezoelectric layer were changed to the conditions shown in Table 1 below.
- Example 3 A piezoelectric film was produced in the same manner as in Example 1 except that the mixing method and drying conditions of the paint used as the piezoelectric layer were changed to the conditions shown in Table 1 below.
- the piezoelectric film immediately after production was incorporated into the piezoelectric speaker to evaluate the speaker performance. Specifically, a circular test piece having a diameter of 150 mm was cut out from the produced piezoelectric film. This test piece was fixed so as to cover the opening surface of a plastic round case having an inner diameter of 138 mm and a depth of 9 mm, and the pressure inside the case was maintained at 1.02 atm. As a result, the conversion film was bent into a convex shape like a contact lens to form a piezoelectric speaker. The sound pressure level-frequency characteristics of the piezoelectric speaker thus produced were measured by sine wave sweep measurement using a constant current type power amplifier. The measurement microphone was placed at a position 10 cm directly above the center of the piezoelectric speaker.
- the piezoelectric film was removed from the piezoelectric speaker, and a temperature cycle test was conducted according to JISC6000068-2-14. After heating at a temperature of 85 ° C. for an exposure time of 10 minutes, the mixture was cooled at a temperature of ⁇ 33 ° C. for an exposure time of 10 minutes. This heating and cooling was repeated 5 times.
- the piezoelectric film was incorporated into the piezoelectric speaker again, and the sound pressure level-frequency characteristics of the piezoelectric speaker were measured by the above method.
- the ratio of the conversion efficiency of the piezoelectric speaker after the temperature cycle test to the conversion efficiency of the piezoelectric speaker immediately after fabrication (before the temperature cycle test) was calculated and evaluated according to the following criteria. A: 95% or more. B: 90% or more and less than 95%. C: Less than 90%. The results are shown in Table 1.
- Comparative Example 3 since the area ratio of the voids was less than 0.1%, it is considered that there was no escape route for the solvent when it was dried, expansion and cracking occurred, and the conversion efficiency decreased. Further, from the comparison of Examples 1 to 4, it can be seen that the area ratio of the voids is preferably 0.1% or more and less than 5%. From the above, the effect of the present invention is clear.
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Abstract
Description
[1] 高分子材料を含むマトリックス中に圧電体粒子を含む高分子複合圧電体であって、
高分子複合圧電体は、SP値が12.5(cal/cm3)1/2未満、かつ、常温で液体の物質を、質量比で500ppm超、10000ppm以下含有しており、
高分子複合圧電体内には空隙が形成されており、
高分子複合圧電体の断面における空隙の面積率が0.1%以上、20%以下である高分子複合圧電体。
[2] 空隙の面積率が0.1%以上、5%未満である[1]に記載の高分子複合圧電体。
[3] 高分子複合圧電体が厚さ方向に分極されたものである[1]または[2]に記載の高分子複合圧電体。
[4] 圧電特性に面内異方性を有さない[1]~[3]のいずれかに記載の高分子複合圧電体。
[5] 物質の含有量が500ppm超、1000ppm以下である[1]~[4]のいずれかに記載の高分子複合圧電体。
[6] 高分子材料が常温で粘弾性を有する[1]~[5]のいずれかに記載の高分子複合圧電体。
[7] 物質が、メチルエチルケトン、ジメチルホルムアミド、シクロヘキサノン、アセトン、シクロヘキサン、アセトニトリル、1プロパノール、2プロパノール、2メトキシアルコール、ジアセトンアルコール、ジメチルアセトアミド、ベンジルアルコール、n-ヘキサン、トルエン、o-キシレン、酢酸エチル、酢酸ブチル、ジエチルエーテル、テトラヒドロフランからなる群から選択される少なくとも1つである[1]~[6]のいずれかに記載の高分子複合圧電体。
[8] [1]~[7]のいずれかに記載の高分子複合圧電体と、
高分子複合圧電体の両面に形成された電極層とを有する圧電フィルム。
[9] 電極層の、高分子複合圧電体側の面とは反対側の面に積層された保護層を有する[8]に記載の圧電フィルム。
なお、本明細書において、「~」を用いて表される数値範囲は、「~」の前後に記載される数値を下限値および上限値として含む範囲を意味する。
高分子材料を含むマトリックス中に圧電体粒子を含む高分子複合圧電体であって、
高分子複合圧電体は、SP値(溶解度パラメーター)が12.5(cal/cm3)1/2未満、かつ、常温で液体の物質を、質量比で500ppm超、10000ppm以下含有しており、
高分子複合圧電体内には空隙が形成されており、
高分子複合圧電体の断面における空隙の面積率が0.1%以上、20%以下である高分子複合圧電体である。
上記高分子複合圧電体と、
高分子複合圧電体の両面に形成された電極層とを有する圧電フィルムである。
図1に、本発明の高分子複合圧電体を有する、本発明の圧電フィルムの一例を断面図によって概念的に示す。
図1に示すように、圧電フィルム10は、圧電性を有するシート状物である圧電体層20と、圧電体層20の一方の面に積層される下部電極24と、下部電極24に積層される下部保護層28と、圧電体層20の他方の面に積層される上部電極26と、上部電極26に積層される上部保護層30とを有する。
圧電体層20は、高分子材料を含むマトリックス34中に、圧電体粒子36を含むものである。すなわち、圧電体層20は、本発明における高分子複合圧電体である。また、下部電極24および上部電極26は、本発明における電極層である。また、下部保護層28および上部保護層30は、本発明における保護層である。
後述するが、圧電フィルム10(圧電体層20)は、好ましい態様として、厚さ方向に分極されている。
音波センサー、超音波センサー、圧力センサー、触覚センサー、歪みセンサーおよび振動センサー等の各種センサー、
マイクロフォン、ピックアップ、スピーカーおよびエキサイター等の音響デバイス(具体的な用途としては、ノイズキャンセラー(車、電車、飛行機、ロボット等に使用)、人工声帯、害虫・害獣侵入防止用ブザー、家具、壁紙、写真、ヘルメット、ゴーグル、サイネージ、ロボットなどが例示される)、
自動車、スマートフォン、スマートウォッチ、ゲーム等に適用して用いるハプティクス、
超音波探触子およびハイドロホン等の超音波トランスデューサ、水滴付着防止、輸送、攪拌、分散、研磨等に用いるアクチュエータ、
容器、乗り物、建物、スキーおよびラケット等のスポーツ用具に用いる制振材(ダンパー)、ならびに、
道路、床、マットレス、椅子、靴、タイヤ、車輪およびパソコンキーボード等に適用して用いる振動発電装置として好適に使用することができる。
本発明の高分子複合圧電体である圧電体層20は、マトリックス34に、圧電体粒子36を含むものである。
また、圧電体層20は、マトリックス34中に、SP値が12.5(cal/cm3)1/2未満、かつ、常温で液体の物質を、質量比で500ppm超、10000ppm以下含有している。
なお、SP値は、溶解パラメーターδであり、モル蒸発熱ΔHとモル体積Vよりδ={(ΔH-RT)/T}1/2で定義される。すなわち、1cm3の液体が蒸発するために必要な蒸発熱の平方根(cal/cm3)1/2から計算される。文献値としてはThe Three Dimensional Solubility Parameter and Solvent Diffusion Coefficient, Their Importance in Surface Coating Formulation(Charles M.Hansen)からも確認できる。
また、圧電体層20内には、複数の空隙35が形成されており、高分子複合圧電体の断面における空隙の面積率が0.1%以上、20%以下である。
なお、本明細書において、「常温」とは、0~50℃程度の温度域を指す。
本発明の圧電フィルム10は、フレキシブルディスプレイ用のスピーカなど、フレキシブル性を有するスピーカ等に好適に用いられる。ここで、フレキシブル性を有するスピーカに用いられる高分子複合圧電体(圧電体層20)は、次の用件を具備したものであるのが好ましい。従って、以下の要件を具備する材料として、常温で粘弾性を有する高分子材料を用いるのが好ましい。
例えば、携帯用として新聞や雑誌のように書類感覚で緩く撓めた状態で把持する場合、絶えず外部から、数Hz以下の比較的ゆっくりとした、大きな曲げ変形を受けることになる。この時、高分子複合圧電体が硬いと、その分大きな曲げ応力が発生し、マトリックスと圧電体粒子との界面で亀裂が発生し、やがて破壊に繋がる恐れがある。従って、高分子複合圧電体には適度な柔らかさが求められる。また、歪みエネルギーを熱として外部へ拡散できれば応力を緩和することができる。従って、高分子複合圧電体の損失正接が適度に大きいことが求められる。
(ii) 音質
スピーカは、20Hz~20kHzのオーディオ帯域の周波数で圧電体粒子を振動させ、その振動エネルギーによって高分子複合圧電体(圧電フィルム)全体が一体となって振動することで音が再生される。従って、振動エネルギーの伝達効率を高めるために高分子複合圧電体には適度な硬さが求められる。また、スピーカの周波数特性が平滑であれば、曲率の変化に伴い最低共振周波数が変化した際の音質の変化量も小さくなる。従って、高分子複合圧電体の損失正接は適度に大きいことが求められる。
高分子複合圧電体(圧電体層20)において、ガラス転移点が常温にある高分子材料、言い換えると、常温で粘弾性を有する高分子材料をマトリックスに用いることで、20Hz~20kHzの振動に対しては硬く、数Hz以下の遅い振動に対しては柔らかく振舞う高分子複合圧電体が実現する。特に、この振舞いが好適に発現する等の点で、周波数1Hzでのガラス転移温度が常温、すなわち、0~50℃にある高分子材料を、高分子複合圧電体のマトリックスに用いるのが好ましい。
これにより、高分子複合圧電体が外力によってゆっくりと曲げられた際に、最大曲げモーメント部におけるマトリックスと圧電体粒子との界面の応力集中が緩和され、良好な可撓性が得られる。
これにより、高分子複合圧電体が外力によってゆっくりと曲げられた際に発生する曲げモーメントが低減できると同時に、20Hz~20kHzの音響振動に対しては硬く振る舞うことができる。
しかしながら、その反面、良好な耐湿性の確保等を考慮すると、高分子材料は、比誘電率が25℃において10以下であるのも、好適である。
なお、これらの高分子材料は、1種のみを用いてもよく、複数種を併用(混合)して用いてもよい。
すなわち、マトリックス34には、誘電特性や機械的特性の調節等を目的として、常温で粘弾性を有する高分子材料に加え、必要に応じて、その他の誘電性高分子材料を添加しても良い。
中でも、シアノエチル基を有する高分子材料は、好適に利用される。
また、圧電体層20のマトリックス34において、シアノエチル化PVA等の常温で粘弾性を有する高分子材料に加えて添加される誘電性高分子材料は、1種に限定はされず、複数種を添加してもよい。
さらに、粘着性を向上する目的で、ロジンエステル、ロジン、テルペン、テルペンフェノール、および、石油樹脂等の粘着付与剤を添加しても良い。
これにより、マトリックス34における粘弾性緩和機構を損なうことなく、添加する高分子材料の特性を発現できるため、高誘電率化、耐熱性の向上、圧電体粒子36および電極層との密着性向上等の点で好ましい結果を得ることができる。
圧電体粒子36は、ペロブスカイト型またはウルツ鉱型の結晶構造を有するセラミックス粒子からなるものである。
圧電体粒子36を構成するセラミックス粒子としては、例えば、チタン酸ジルコン酸鉛(PZT)、チタン酸ジルコン酸ランタン酸鉛(PLZT)、チタン酸バリウム(BaTiO3)、酸化亜鉛(ZnO)、および、チタン酸バリウムとビスマスフェライト(BiFe3)との固溶体(BFBT)等が例示される。
これらの圧電体粒子36は、1種のみを用いてもよく、複数種を併用(混合)して用いてもよい。
圧電体粒子36の粒径は、1~10μmが好ましい。圧電体粒子36の粒径をこの範囲とすることにより、高分子複合圧電体(圧電フィルム10)が高い圧電特性とフレキシビリティとを両立できる等の点で好ましい結果を得ることができる。
すなわち、圧電体層20中の圧電体粒子36は、好ましくは均一に分散されていれば、マトリックス34中に不規則に分散されていてもよい。
圧電体層20中における圧電体粒子36の体積分率は、30~80%が好ましく、50%以上がより好ましく、従って、50~80%とするのが、さらに好ましい。
マトリックス34と圧電体粒子36との量比を上記範囲とすることにより、高い圧電特性と可撓性とを両立できる等の点で好ましい結果を得ることができる。
圧電体層20の厚さは、10~300μmが好ましく、20~200μmがより好ましく、30~150μmがさらに好ましい。
圧電体層20の厚さを、上記範囲とすることにより、剛性の確保と適度な柔軟性との両立等の点で好ましい結果を得ることができる。
また、圧電体層20のマトリックス34には、空隙35が形成されており、圧電体層20の断面における空隙35の面積率が0.1%以上、20%以下である。
上記物質は、一般に、有機溶媒として用いられるものである。すなわち、本発明は、高分子複合圧電体(圧電体層20)が、SP値12.5(cal/cm3)1/2未満で、かつ、常温で液体の有機溶媒を、質量比で500ppm超10000ppm以下含有する。
これに対して、本発明においては、高分子複合圧電体層中に含有させる物質のSP値を12.5(cal/cm3)1/2未満とすることで、物質を高分子複合圧電体中に均一に分散させることができるので、高温に曝されて高分子複合圧電体内部の物質が蒸発した際に、大きな空隙が生じるのを抑制して、圧電体粒子とマトリックスとの界面が剥離するのを防止することができる。従って、変換効率の低下や耐電圧の低下を抑制することができる。
本発明の高分子複合圧電体は、高分子複合圧電体の断面における空隙の面積率が0.1%以上、20%以下、すなわち、空隙を少なくすることで、乾燥による上記物質の蒸発を抑制する効果が得られる。これにより、上記物質が蒸発して、空隙が生じ、圧電体粒子とマトリックスとの界面が剥離して、変換効率が低下することを抑制できる。
また、本発明の高分子複合圧電体は、上記物質の含有量が質量比で500ppm超、10000ppm以下であるため、高分子複合圧電体となる塗料を塗布した後の乾燥時間を短くすることができるため、ライン速度を速くしたり、乾燥工程の長さを短くすることができるため、生産性を向上できる。
高分子複合圧電体の断面観察のため、厚さ方向に切削する。切削はライカバイオシステム社製RM2265にDrukker社製histoナイフ刃幅8mmを取り付け、スピードをコントローラー目盛り1、噛み合い量を0.25μm~1μmとして切削して断面を出す。その断面を走査型電子顕微鏡(SEM)(株式会社日立ハイテクノロジーズ社製SU8220)により観察する。サンプルはPt蒸着で導電処理し、ワークディスタンスは8mmとする。観察条件はSE像(Upper)、加速電圧:0.5kVとし、フォーカス調整と非点収差調整によりシャープな画像を出し、高分子複合圧電体部が画面全体になる状態で自動明るさ調整(オート設定 ブライトネス:0、コントラスト:0)を実行する。撮影の倍率は両端の電極が一画面に収まり、かつ電極間の幅が、画面の半分以上となる倍率とする。画像の2値化は画像解析ソフトImageJを使用し、Threshold下限は保護層が着色しない最大の値とし、Threshold上限は設定値最大255とする。電極間にて着色した箇所の面積を空隙の面積と定義して分子とし、縦方向幅を電極間、横方向幅をSEM画像の両端とした高分子複合圧電体の面積を分母とし、高分子複合圧電体部の面積に占める空隙の面積比率を計算する。これを任意の10断面において行い、面積比率の平均値を高分子複合圧電体の断面における空隙の面積率とする。
ラインミキシングの処理時間および回転数は、所望の空隙の面積率、マトリックスの種類、溶媒(上記物質)の種類、溶媒の比率、塗料の粘度、および、形成する高分子複合圧電体の厚さ等に応じて適宜、設定すればよい。
高分子複合圧電体からサンプルを8×8mm角に一部切り出し、ガスクロマトグラフ装置(島津製作所製 GC-12A)を用い、上記物質の含有量を測定する。カラムは島津製作所製221-14368-11、充填剤は信和加工製Chromosorb101を使用する。試料気化室および検出器温度は200℃、カラム温度は160℃一定とし、0.4MPaのヘリウムをキャリアガスとして使用し測定する。
電極層の外側に位置する保護層を含むモジュール等が有機溶剤を含む粘着層で接着している場合は、測定に影響を及ぼすため、これらを剥離し粘着層を除去してから切り出し、上記物質の含有量測定を実施する。
切り出したサンプルは、ガスクロマトグラフ測定を実施する前に質量を測定しておく。ガスクロマトグラフ測定後、同じサンプルから有機溶剤等を使用して高分子複合圧電体を除去し、残された保護層もしくは保護層を含むモジュール等の質量を測定し、ガスクロマトグラフ測定前に測定していた質量から引くことで、高分子複合圧電体正味の質量を計算する。ガスクロマトグラフ測定により得られた上記物質の質量を、高分子複合圧電体正味の質量で除することで、上記物質の含有量質量比を計算する。
好ましくは、上記物質を、調製する塗料の溶媒として用いて、塗料を塗布した後の乾燥条件を調整して、高分子複合圧電体内の上記物質の含有量を制御する。その際の乾燥条件は、上記物質の種類、所望の含有量、マトリックスの種類、圧電体層の厚さ等に応じて適宜、設定すればよい。また、乾燥方法としては、ヒータによる加熱乾燥、温風による加熱乾燥等の公知の乾燥方法が利用可能である。
ここで、本発明者の検討によれば、前述のとおり、圧電体層20の厚さは10μm~300μmが好ましく、20μm~200μmがより好ましく、30μm~150μmが特に好ましい。
圧電体層20の厚さを上記範囲とすることで、上述のように乾燥によって上記物質の含有量を制御する際に、より容易に調整することができる。また、圧電体層20中での上記物質の濃度をより均一にすることができる。また、塗料を塗布した後、空隙の原因となる気泡が抜けやすくなり、空隙の面積率を小さく調整することができる。
また、圧電体層20の厚さを、上記範囲とすることにより、剛性の確保と適度な柔軟性との両立等の点でも好ましい結果を得ることができる。
なお、圧電体層20は、分極処理(ポーリング)されているのが好ましいのは、前述のとおりである。
図1に示すように、図示例の圧電フィルム10は、このような圧電体層20の一面に、下部電極24を有し、その表面に下部保護層28を有し、圧電体層20の他方の面に、上部電極26を有し、その表面に上部保護層30を有してなる構成を有する。ここで、上部電極26と下部電極24とが電極対を形成する。
なお、圧電フィルム10は、これらの層に加えて、例えば、上部電極26、および、下部電極24からの電極の引出しを行う電極引出し部を有し、電極引き出し部が電源に接続される。また、圧電フィルム10は、圧電体層20が露出する領域を覆って、ショート等を防止する絶縁層等を有していてもよい。
このように、圧電フィルム10において、上部電極26および下部電極24で挾持された領域は、印加された電圧に応じて伸縮される。
下部保護層28および上部保護層30は、上部電極26および下部電極24を被覆すると共に、圧電体層20に適度な剛性と機械的強度を付与する役目を担っている。すなわち、圧電フィルム10において、マトリックス34と圧電体粒子36とからなる圧電体層20は、ゆっくりとした曲げ変形に対しては、非常に優れた可撓性を示す一方で、用途によっては、剛性や機械的強度が不足する場合がある。圧電フィルム10は、それを補うために下部保護層28および上部保護層30が設けられる。
中でも、優れた機械的特性および耐熱性を有するなどの理由により、ポリエチレンテレフタレート(PET)、ポリプロピレン(PP)、ポリスチレン(PS)、ポリカーボネート(PC)、ポリフェニレンサルファイト(PPS)、ポリメチルメタクリレート(PMMA)、ポリエーテルイミド(PEI)、ポリイミド(PI)、ポリエチレンナフタレート(PEN)、トリアセチルセルロース(TAC)、および、環状オレフィン系樹脂等からなる樹脂フィルムが、好適に利用される。
ここで、下部保護層28および上部保護層30の剛性が高過ぎると、圧電体層20の伸縮を拘束するばかりか、可撓性も損なわれる。そのため、機械的強度やシート状物としての良好なハンドリング性が要求される場合を除けば、下部保護層28および上部保護層30は、薄いほど有利である。
例えば、圧電体層20の厚さが50μmで下部保護層28および上部保護層30がPETからなる場合、下部保護層28および上部保護層30の厚さは、100μm以下が好ましく、50μm以下がより好ましく、25μm以下がさらに好ましい。
下部電極24および上部電極26は、圧電体層20に駆動電圧を印加するために設けられる。
下部電極24および上部電極26の厚さには、制限はない。また、下部電極24および上部電極26の厚さは、基本的に同じであるが、異なってもよい。
例えば、下部保護層28および上部保護層30がPET(ヤング率:約6.2GPa)で、下部電極24および上部電極26が銅(ヤング率:約130GPa)からなる組み合わせの場合、下部保護層28および上部保護層30の厚さが25μmだとすると、下部電極24および上部電極26の厚さは、1.2μm以下が好ましく、0.3μm以下がより好ましく、中でも0.1μm以下とするのが好ましい。
これにより、圧電フィルム10が外部から数Hz以下の比較的ゆっくりとした、大きな曲げ変形を受けたとしても、歪みエネルギーを効果的に熱として外部へ拡散できるため、マトリックスと圧電体粒子との界面で亀裂が発生するのを防ぐことができる。
これにより、圧電フィルム10が貯蔵弾性率(E’)に大きな周波数分散を有することができる。すなわち、20Hz~20kHzの振動に対しては硬く、数Hz以下の振動に対しては柔らかく振る舞うことができる。
これにより、圧電フィルム10が可撓性および音響特性を損なわない範囲で、適度な剛性と機械的強度を備えることができる。
これにより、圧電フィルム10を用いたスピーカーの周波数特性が平滑になり、スピーカーの曲率の変化に伴い最低共振周波数f0が変化した際の音質の変化を小さくできる。
測定条件としては、一例として、測定周波数は0.1Hz~20Hz(0.1Hz、0.2Hz、0.5Hz、1Hz、2Hz、5Hz、10Hzおよび20Hz)が、測定温度は-50~150℃が、昇温速度は2℃/分(窒素雰囲気中)が、サンプルサイズは40mm×10mm(クランプ領域込み)が、チャック間距離は20mmが、それぞれ、例示される。
上記物質以外の有機溶媒としては制限はなく各種の有機溶媒が利用可能である。
ここで、前述のとおり、塗料の乾燥条件を調整して、質量比で500ppm超10000ppm以下の上記物質(有機溶媒)を、圧電体層20中に残存させる。
マトリックス34に、これらの高分子材料を添加する際には、上述した塗料に添加する高分子材料を溶解すればよい。
なお、分極処理の前に、圧電体層20の表面を加熱ローラ等を用いて平滑化する、カレンダー処理を施してもよい。このカレンダー処理を施すことで、後述する熱圧着工程がスムーズに行える。
次いで、図4に示すように、上部電極26を圧電体層20に向けて、シート状物10cを、圧電体層20の分極処理を終了した積層体10bに積層する。
さらに、この積層体10bとシート状物10cとの積層体を、上部保護層30と下部保護層28とを挟持するようにして、加熱プレス装置や加熱ローラ対等で熱圧着して、圧電フィルム10を作製する。
従って、本発明の圧電フィルムを用いる積層圧電素子は、分極処理済の圧電フィルム10を積層して作製できる。好ましくは、分極処理を施した長尺な圧電フィルム(大面積の圧電フィルム)を作製し、切断して個々の圧電フィルム10とした後に、圧電フィルム10を積層して積層圧電素子14とする。
そのため、本発明の圧電フィルムを用いる積層圧電素子は、隣接する圧電フィルム10における分極方向を、図8に示す積層圧電素子60のように積層方向で揃えることもできるし、図6に示す積層圧電素子14のように、交互にもできる。
これに対して、マトリックス34中に圧電体粒子36を含む本発明の高分子複合圧電体は、分極処理後に延伸処理をしなくても大きな圧電特性が得られる。そのため、本発明の高分子複合圧電体は、圧電特性に面内異方性がなく、後述するように駆動電圧を印加すると、面内方向では全方向に等方的に伸縮する。
周知のように、RtoRとは、長尺な原材料を巻回してなるロールから、原材料を引き出して、長手方向に搬送しつつ、成膜や表面処理等の各種の処理を行い、処理済の原材料を、再度、ロール状に巻回する製造方法である。
第1のロールおよび第2のロールは、全く、同じものでよい。
次いで、圧電体層20の分極処理を行う。ここで、RtoRによって圧電フィルム10を製造する際には、積層体10bを搬送しつつ、積層体10bの搬送方向と直交する方向に圧電体層20の分極処理を行う。なお、この分極処置の前に、カレンダー処理を行ってもよいのは、前述のとおりである。
次いで、第2のロールからシート状物10cを引き出し、このシート状物10cおよび積層体を搬送しつつ、貼り合わせローラ等を用いる公知の方法で、前述のように、上部電極26を圧電体層20に向けて、積層体10bの上にシート状物10cを積層する。
その後、加熱ローラ対によって、積層した積層体10bとシート状物10cとを挟持搬送することで熱圧着して、本発明の圧電フィルム10を完成し、この圧電フィルム10を、ロール状に巻回する。
例えば、上述した積層体10bを形成し、分極処理を行った後に、一度、ロール状に、この積層体を巻回した積層体ロールとする。次いで、この積層体ロールから積層体を引き出して、長手方向に搬送しつつ、前述のように、上部保護層30の上に上部電極26が形成されたシート状物の積層を行って、圧電フィルム10を完成し、この圧電フィルム10を、ロール状に巻回してもよい。
上述したように、圧電体層20の厚さは、好ましくは10~300μm程度である。従って、厚さ方向の伸縮は、最大でも0.3μm程度と非常に小さい。
これに対して、圧電フィルム10すなわち圧電体層20は、面方向には、厚さよりもはるかに大きなサイズを有する。従って、例えば、圧電フィルム10の長さが20cmであれば、電圧の印加によって、最大で0.2mm程度、圧電フィルム10は伸縮する。
また、圧電フィルム10に圧力を加えると、圧電体粒子36の作用によって、電力を発生する。
これを利用することで、圧電フィルム10は、上述のように、スピーカー、マイクロフォン、および、感圧センサ等の各種の用途に利用可能である。
図5に、本発明の圧電フィルム10を有する平板型の圧電スピーカーの一例の概念図を示す。
この圧電スピーカー45は、本発明の圧電フィルム10を、電気信号を振動エネルギーに変換する振動板として用いる、平板型の圧電スピーカーである。なお、圧電スピーカー45は、マイクロフォンおよびセンサー等として使用することも可能である。
ケース43は、プラスチック等で形成される、一面が開放する薄い正四角筒状の筐体である。
また、枠体48は、中央に貫通孔を有する、ケース43の上端面(開放面側)と同様の形状を有する板材である。
粘弾性支持体46は、適度な粘性と弾性を有し、圧電フィルム10を支持すると共に、圧電フィルムのどの場所でも一定の機械的バイアスを与えることによって、圧電フィルム10の伸縮運動を無駄なく前後運動(フィルムの面に垂直な方向の運動)に変換させるためのものである。一例として、羊毛のフェルト、レーヨンやPETを含んだ羊毛のフェルトなどの不織布、グラスウール等が例示される。
そのため、圧電スピーカー45では、粘弾性支持体46の周辺部では、粘弾性支持体46が圧電フィルム10によって下方に押圧されて厚さが薄くなった状態で、保持される。また、同じく粘弾性支持体46の周辺部において、圧電フィルム10の曲率が急激に変動し、圧電フィルム10に、粘弾性支持体46の周辺に向かって低くなる立上がり部45aが形成される。さらに、圧電フィルム10の中央領域は四角柱状の粘弾性支持体46に押圧されて、(略)平面状になっている。
逆に、下部電極24および上部電極26への駆動電圧の印加によって、圧電フィルム10が面内方向に収縮すると、この収縮分を吸収するために、圧電フィルム10の立上がり部45aが、倒れる方向(平面に近くなる方向)に角度を変える。その結果、平面状の部分を有する圧電フィルム10は、下方に移動する。
圧電スピーカー45は、この圧電フィルム10の振動によって、音を発生する。
従って、本発明の圧電フィルム10は、このような圧電スピーカー45ではなく単に湾曲状態で保持することでも、可撓性を有するスピーカーとして機能させることができる。
図6に、本発明の圧電フィルム10を有する電気音響変換器の一例を概念的に示す。
図6に示す電気音響変換器50は、積層圧電素子14と、振動板12とを有する。積層圧電素子14は、本発明の圧電フィルムを複数層、積層したものである。図6に示す例では、積層圧電素子14は、上述した本発明の圧電フィルム10を、3層、積層したものである。
電気音響変換器50において、積層圧電素子14と振動板12とは、貼着層16によって貼着されている。
電気音響変換器50の積層圧電素子14を構成する圧電フィルム10には、駆動電圧を印加するための電源PSが接続されている。
なお、積層圧電素子は、これに制限はされず、保護層を有する圧電フィルムと、有さない圧電フィルムとが混在してもよい。さらに、圧電フィルムが保護層を有する場合には、圧電フィルムは、下部保護層28のみを有してもよく、上部保護層30のみを有してもよい。一例として、図6に示すような3層構成の積層圧電素子14であれば、図中最上層の圧電フィルムが上部保護層30のみを有し、真ん中の圧電フィルムが保護層を有さず、最下層の圧電フィルムが下部保護層28のみを有するような構成でもよい。
この点に関しては、後述する図7に示す積層圧電素子56および図8に示す積層圧電素子60も、同様である。
この積層圧電素子14の面方向の伸縮によって、振動板12が撓み、その結果、振動板12が、厚さ方向に振動する。この厚さ方向の振動によって、振動板12は、音を発生する。振動板12は、圧電フィルム10に印加した駆動電圧の大きさに応じて振動して、圧電フィルム10に印加した駆動電圧に応じた音を発生する。
すなわち、この電気音響変換器50は、積層圧電素子14をエキサイターとして用いるスピーカーである。
振動板12は、好ましくは可撓性を有し、後述する積層圧電素子14との関係を満たすものであれば、制限はなく、各種のシート状物(板状物、フィルム)が利用可能である。
一例として、ポリエチレンテレフタレート(PET)、ポリプロピレン(PP)、ポリスチレン(PS)、ポリカーボネート(PC)、ポリフェニレンサルファイト(PPS)、ポリメチルメタクリレート(PMMA)、ポリエーテルイミド(PEI)、ポリイミド(PI)、ポリエチレンナフタレート(PEN)、トリアセチルセルロース(TAC)および環状オレフィン系樹脂等からなる樹脂フィルム、発泡ポリスチレン、発泡スチレンおよび発泡ポリエチレン等からなる発泡プラスチック、ならびに、波状にした板紙の片面または両面に他の板紙をはりつけてなる各種の段ボール材等が例示される。
また、電気音響変換器50では、可撓性を有するものであれば、振動板12として、有機エレクトロルミネセンス(OLED(Organic Light Emitting Diode))ディスプレイ、液晶ディスプレイ、マイクロLED(Light Emitting Diode)ディスプレイ、および、無機エレクトロルミネセンスディスプレイなどの表示デバイス等も好適に利用可能である。
従って、貼着層16は、貼り合わせる際には流動性を有し、その後、固体になる、接着剤からなる層でも、貼り合わせる際にゲル状(ゴム状)の柔らかい固体で、その後もゲル状の状態が変化しない、粘着剤からなる層でも、接着剤と粘着剤との両方の特徴を持った材料からなる層でもよい。
ここで、電気音響変換器50では、積層圧電素子14を伸縮させることで、振動板12を撓ませ振動させて、音を発生させる。従って、電気音響変換器50では、積層圧電素子14の伸縮が、直接的に振動板12に伝達されるのが好ましい。振動板12と積層圧電素子14との間に、振動を緩和するような粘性を有する物質が存在すると、振動板12への積層圧電素子14の伸縮のエネルギーの伝達効率が低くなってしまい、電気音響変換器50の駆動効率が低下してしまう。
この点を考慮すると、貼着層16は、粘着剤からなる粘着剤層よりも、固体で硬い貼着層16が得られる、接着剤からなる接着剤層であるのが好ましい。より好ましい貼着層16としては、具体的には、ポリエステル系接着剤およびスチレン・ブタジエンゴム(SBR)系接着剤等の熱可塑タイプの接着剤からなる貼着層が例示される。
接着は、粘着とは異なり、高い接着温度を求める際に有用である。また、熱可塑タイプの接着剤は『比較的低温、短時間、および、強接着』を兼ね備えており、好適である。
ここで、電気音響変換器50においては、貼着層16が薄い方が、振動板12に伝達する積層圧電素子14の伸縮エネルギー(振動エネルギー)の伝達効果を高くして、エネルギー効率を高くできる。また、貼着層16が厚く剛性が高いと、積層圧電素子14の伸縮を拘束する可能性もある。
この点を考慮すると、貼着層16は、薄い方が好ましい。具体的には、貼着層16の厚さは、貼着後の厚さで0.1~50μmが好ましく、0.1~30μmがより好ましく、0.1~10μmがさらに好ましい。
従って、電気音響変換器50は、貼着層16を有さず、公知の圧着手段、締結手段、および、固定手段等を用いて、振動板12と積層圧電素子14とを固定してもよい。例えば、積層圧電素子14が矩形である場合には、四隅をボルトナットのような部材で締結して電気音響変換器を構成してもよく、または、四隅と中心部とをボルトナットのような部材で締結して電気音響変換器を構成してもよい。
しかしながら、この場合には、電源PSから駆動電圧を印加した際に、振動板12に対して積層圧電素子14が独立して伸縮してしまい、場合によっては、積層圧電素子14のみが撓んで、積層圧電素子14の伸縮が振動板12に伝わらない。このように、振動板12に対して積層圧電素子14が独立して伸縮した場合には、積層圧電素子14による振動板12の振動効率が低下してしまい。振動板12を十分に振動させられなくなってしまう可能性がある。
この点を考慮すると、振動板12と積層圧電素子14とは、図6に示すように、貼着層16で貼着するのが好ましい。
なお、図6に示す積層圧電素子14は、圧電フィルム10を3層積層したものであるが、本発明は、これに制限はされない。すなわち、積層圧電素子は、圧電フィルム10を、複数層、積層したものであれば、圧電フィルム10の積層数は、2層でもよく、あるいは、4層以上であってもよい。この点に関しては、後述する図7に示す積層圧電素子56および図8に示す積層圧電素子60も、同様である。
また、電気音響変換器は、積層圧電素子14に変えて、本発明の圧電フィルムによって、同様の作用効果で振動板12を振動させて、音を発生するものであってもよい。すなわち、電気音響変換器は、本発明の圧電フィルムをエキサイターとして用いてもよい。
従って、貼着層19は、上述した、接着剤からなる層でも、粘着剤からなる層でも、接着剤と粘着剤との両方の特徴を持った材料からなる層でもよい。
ここで、積層圧電素子14は、積層した複数枚の圧電フィルム10を伸縮させることで、振動板12を振動させて、音を発生させる。従って、積層圧電素子14は、各圧電フィルム10の伸縮が、直接的に伝達されるのが好ましい。圧電フィルム10の間に、振動を緩和するような粘性を有する物質が存在すると、圧電フィルム10の伸縮のエネルギーの伝達効率が低くなってしまい、積層圧電素子14の駆動効率が低下してしまう。
この点を考慮すると、貼着層19は、粘着剤からなる粘着剤層よりも、固体で硬い貼着層19が得られる、接着剤からなる接着剤層であるのが好ましい。より好ましい貼着層19としては、具体的には、ポリエステル系接着剤およびスチレン・ブタジエンゴム(SBR)系接着剤等の熱可塑タイプの接着剤からなる貼着層が好適に例示される。
接着は、粘着とは異なり、高い接着温度を求める際に有用である。また、熱可塑タイプの接着剤は『比較的低温、短時間、および、強接着』を兼ね備えており、好適である。
ここで、図6に示す積層圧電素子14は、貼着層19が薄い方が、圧電フィルム10の伸縮エネルギーの伝達効果を高くして、エネルギー効率を高くできる。また、貼着層19が厚く剛性が高いと、圧電フィルム10の伸縮を拘束する可能性もある。
この点を考慮すると、貼着層19は、圧電体層20よりも薄いのが好ましい。すなわち、積層圧電素子14において、貼着層19は、硬く、薄いのが好ましい。具体的には、貼着層19の厚さは、貼着後の厚さで0.1~50μmが好ましく、0.1~30μmがより好ましく、0.1~10μmがさらに好ましい。
なお、後述するが、図6に示す積層圧電素子14は、隣接する圧電フィルムの分極方向が互いに逆であり、隣接する圧電フィルム10同士がショートする恐れが無いので、貼着層19を薄くできる。
具体的には、貼着層19の厚さと、動的粘弾性測定による周波数1Hzでの貯蔵弾性率(E’)との積が、0℃において2.0×106N/m以下、50℃において1.0×106N/m以下であるのが好ましい。
また、貼着層の動的粘弾性測定による周波数1Hzでの内部損失が、粘着剤からなる貼着層19の場合には25℃において1.0以下、接着剤からなる貼着層19の場合には25℃において0.1以下であるのが好ましい。
従って、電気音響変換器を構成する積層圧電素子は、貼着層19を有さず、公知の圧着手段、締結手段、および、固定手段等を用いて、圧電フィルム10を積層して、密着させて、積層圧電素子を構成してもよい。例えば、圧電フィルム10が矩形である場合には、四隅をボルトナット等で締結して積層圧電素子を構成してもよく、または、四隅と中心部とをボルトナット等で締結して積層圧電素子を構成してもよい。あるいは、圧電フィルム10を積層した後、周辺部(端面)に粘着テープを貼着することで、積層した圧電フィルム10を固定して、積層圧電素子を構成してもよい。
しかしながら、この場合には、電源PSから駆動電圧を印加した際に、個々の圧電フィルム10が独立して伸縮してしまい、場合によっては、各圧電フィルム10各層が逆方向に撓んで空隙ができてしまう。このように、個々の圧電フィルム10が独立して伸縮した場合には、積層圧電素子としての駆動効率が低下してしまい、積層圧電素子全体としての伸縮が小さくなって、当接した振動板等を十分に振動させられなくなってしまう可能性がある。特に、各圧電フィルム10各層が逆方向に撓んで空隙ができてしまった場合には、積層圧電素子としての駆動効率の低下は大きい。
この点を考慮すると、積層圧電素子は、図6に示す積層圧電素子14のように、隣接する圧電フィルム10同士を貼着する貼着層19を有するのが好ましい。
電源PSには、制限はなく、直流電源でも交流電源でもよい。また、駆動電圧も、各圧電フィルム10の圧電体層20の厚さおよび形成材料等に応じて、各圧電フィルム10を適正に駆動できる駆動電圧を、適宜、設定すればよい。
後述するが、積層圧電素子14は、隣接する圧電フィルム10の分極方向が逆である。そのため、隣接する圧電フィルム10では、下部電極24同士および上部電極26同士が対面する。従って、電源PSは、交流電源でも直流電源でも、対面する電極には、常に同じ極性の電力を供給する。例えば、図6に示す積層圧電素子14では、図中最下層の圧電フィルム10の上部電極26と、2層目(真ん中)の圧電フィルム10の上部電極26とには、常に同じ極性の電力が供給され、2層目の圧電フィルム10の下部電極24と、図中最上層の圧電フィルム10の下部電極24とには、常に同じ極性の電力が供給される。
一例として、下部電極24および上部電極26に銅箔等の導電体を接続して外部に電極を引き出す方法、および、レーザ等によって下部保護層28および上部保護層30に貫通孔を形成して、この貫通孔に導電性材料を充填して外部に電極を引き出す方法、等が例示される。
好適な電極の引き出し方法として、特開2014-209724号公報に記載される方法、および、特開2016-015354号公報に記載される方法等が例示される。
このような圧電体層20を有する圧電フィルム10の下部電極24および上部電極26に電圧を印加すると、印加した電圧に応じて圧電体粒子36が分極方向に伸縮する。その結果、圧電フィルム10(圧電体層20)が厚さ方向に収縮する。同時に、ポアゾン比の関係で、圧電フィルム10は、面内方向にも伸縮する。
この伸縮は、0.01~0.1%程度である。
上述したように、圧電体層20の厚さは、好ましくは10~300μm程度である。従って、厚さ方向の伸縮は、最大でも0.3μm程度と非常に小さい。
これに対して、圧電フィルム10すなわち圧電体層20は、面方向には、厚さよりもはるかに大きなサイズを有する。従って、例えば、圧電フィルム10の長さが20cmであれば、電圧の印加によって、最大で0.2mm程度、圧電フィルム10は伸縮する。
振動板12は、貼着層16によって積層圧電素子14に貼着されている。従って、積層圧電素子14の伸縮によって、振動板12は撓み、その結果、振動板12は、厚さ方向に振動する。
この厚さ方向の振動によって、振動板12は、音を発生する。すなわち、振動板12は、圧電フィルム10に印加した電圧(駆動電圧)の大きさに応じて振動して、圧電フィルム10に印加した駆動電圧に応じた音を発生する。
これに対して、図6に示す電気音響変換器50において、積層圧電素子14を構成する本発明の圧電フィルム10は、圧電特性に面内異方性がなく、面内方向では全方向に等方的に伸縮する。すなわち、図6に示す電気音響変換器50において、積層圧電素子14を構成する圧電フィルム10は、等方的に二次元的に伸縮する。
このような等方的に二次元的に伸縮する圧電フィルム10を積層した積層圧電素子14によれば、一方向にしか大きく伸縮しないPVDF等の一般的な圧電フィルムを積層した場合に比べ、大きな力で振動板12を振動することができ、より大きく、かつ、美しい音を発生できる。
そのため、1枚毎の圧電フィルム10の剛性が低く、伸縮力は小さくても、圧電フィルム10を積層することにより、剛性が高くなり、積層圧電素子14としての伸縮力は大きくなる。その結果、積層圧電素子14は、振動板12がある程度の剛性を有するものであっても、大きな力で振動板12を十分に撓ませて、厚さ方向に振動板12を十分に振動させて、振動板12に音を発生させることができる。
また、圧電体層20が厚い方が、圧電フィルム10の伸縮力は大きくなるが、その分、同じ量、伸縮させるのに必要な駆動電圧は大きくなる。ここで、上述したように、積層圧電素子14において、好ましい圧電体層20の厚さは、最大でも300μm程度であるので、個々の圧電フィルム10に印加する電圧が小さくても、十分に、圧電フィルム10を伸縮させることが可能である。
一方、振動板12は、ある程度の剛性を有するものである。このような振動板12に剛性の高い積層圧電素子14が組み合わされると、硬く、曲げにくくなり、電気音響変換器50の可撓性の点で不利である。
これに対して、電気音響変換器50は、好ましくは、積層圧電素子14の厚さと動的粘弾性測定による周波数1Hz、25℃での貯蔵弾性率との積が、振動板12の厚さとヤング率との積の、3倍以下である。すなわち、積層圧電素子14は、ゆっくりとした動きに対しては、バネ定数が、振動板12の3倍以下であるのが好ましい。
このような構成を有することにより、電気音響変換器50は、折り曲げる、および、丸める等の外力によるゆっくりした動きに対しては、柔らかく振舞うことができ、すなわち、ゆっくりとした動きに対して、良好な可撓性を発現する。
電気音響変換器50において、積層圧電素子14の厚さと動的粘弾性測定による周波数1Hz、25℃での貯蔵弾性率との積は、振動板12の厚さとヤング率との積の、2倍以下であるのがより好ましく、1倍以下であるのがさらに好ましく、0.3倍以下であるのが特に好ましい。
電気音響変換器50は、積層圧電素子14の厚さと動的粘弾性測定から得られたマスターカーブにおける周波数1kHz、25℃での貯蔵弾性率との積を、振動板12の厚さとヤング率との積の、好ましくは0.3倍以上、より好ましくは0.5倍以上、さらに好ましくは1倍以上とする。すなわち、積層圧電素子14は、早い動きに対しては、バネ定数が、振動板12の0.3倍以上であるのが好ましく、0.5倍以上であるのがより好ましく、1倍以上であるのがさらに好ましい。
これにより、オーディオ帯域の周波数において、振動板12に対する積層圧電素子14の剛性を十分に確保して、電気音響変換器50が、高いエネルギー効率で、高い音圧の音を出力できる。
圧電フィルム10において、圧電体層20に印加する電圧の極性は、分極方向に応じたものとなる。従って、印加する電圧の極性は、図6に矢印で示す分極方向において、矢印が向かう方向側(矢印の下流側)の電極の極性と、逆側(矢印の上流側)の電極の極性とは、全ての圧電フィルム10で一致させる。
図6に示す例においては、分極方向を示す矢印が向かう方向側の電極を下部電極24、逆側の電極を上部電極26として、全ての圧電フィルム10において、上部電極26と下部電極24との極性を同極性にする。
従って、隣接する圧電フィルム10の圧電体層20の分極方向が、互いに逆である積層圧電素子14においては、隣接する圧電フィルム10では、一方の面で上部電極26同士が対面し、他方の面で下部電極同士が対面する。そのため、積層圧電素子14では、隣接する圧電フィルム10の電極同士が接触しても、ショート(短絡)する恐れがない。
これに対して、隣接する圧電フィルム10の電極同士が接触しても、ショートする恐れが無い図6に示す積層圧電素子14では、貼着層19が無くてもよく、好ましい態様として貼着層19を有する場合でも、必要な貼着力が得られれば、貼着層19を極めて薄くできる。
そのため、高いエネルギー効率で積層圧電素子14を伸縮させることができる。
従って、積層される圧電フィルム10の分極方向が逆であっても、下部電極24および上部電極26に印加する電圧の極性さえ正しければ、全ての圧電フィルム10は同じ方向に伸縮する。
または、分極処理の処理条件から、圧電フィルム10の分極方向を知見してもよい。
しかしながら、本発明は、これに制限はされない。すなわち、電気音響変換器において、圧電積層体は、例えば、下部保護層28および上部保護層30を有する圧電フィルムと有さない圧電フィルムなど、異なる層構成の圧電フィルムを積層した構成、および、圧電体層20の厚さが異なる圧電フィルムを積層した構成等、各種の構成が利用可能である。
本発明の積層圧電素子は、これに制限はされず、各種の構成が利用可能である。
図7に示す積層圧電素子56は、本発明における積層圧電素子のより好ましい態様であり、長尺な圧電フィルム10Lを、長手方向に、1回以上、好ましくは複数回、折り返すことにより、圧電フィルム10Lを複数層、積層したものである。また、上述した図6等に示す積層圧電素子14と同様、図7に示される積層圧電素子56も、好ましい態様として、折り返しによって積層された圧電フィルム10Lを、貼着層19によって貼着している。
厚さ方向に分極された長尺な1枚の圧電フィルム10Lを、折り返して積層することで、積層方向に隣接(対面)する圧電フィルム10Lの分極方向は、図7中に矢印で示すように、逆方向になる。
そのため、図7に示す積層圧電素子56によれば、部品点数を低減し、かつ、構成を簡略化して、圧電素子(モジュール)としての信頼性を向上し、さらに、コストダウンを図ることができる。
上述したように、圧電フィルム10Lの下部電極24および上部電極26は、金属の蒸着膜等で形成される。金属の蒸着膜は、鋭角で折り曲げられると、ヒビ(クラック)等が入りやすく、電極が断線してしまう可能性がある。すなわち、図7に示す積層圧電素子56では、屈曲部の内側において、電極にヒビ等が入り易い。
これに対して、長尺な圧電フィルム10Lを折り返した積層圧電素子56において、圧電フィルム10Lの折り返し部に芯棒58を挿入することにより、下部電極24および上部電極26が折り曲げられることを防止して、断線が生じることを好適に防止できる。
図6および図7に示すような、隣接する圧電フィルム10の分極方向が逆である積層圧電素子においては、積層される圧電フィルム10において、対面する電極には、同じ極性の電力が供給される。従って、対面する電極間で短絡が生じることは無い。
一方で、上述したように、圧電フィルム10Lを、折り返して積層した積層圧電素子56は、鋭角的に折り返される屈曲部の内側において、電極の断線が生じやすい。
従って、導電性を有する貼着層19によって、積層した圧電フィルム10Lを貼着することにより、屈曲部の内側において電極の断線が生じても、貼着層19によって導通を確保できるので、断線を防止して、積層圧電素子56の信頼性を大幅に向上できる。
この場合には、導電性を有する貼着層19を用いても、導電性を確保できない。そのため、圧電フィルム10Lが保護層を有する場合には、積層される圧電フィルム10Lの下部電極24同士および上部電極26同士が対面する領域において、下部保護層28および上部保護層30に貫通孔を設けて、下部電極24および上部電極26と、導電性を有する貼着層19とを接触させればよい。好ましくは、下部保護層28および上部保護層30に形成した貫通孔を銀ペーストまたは導電性の貼着剤で塞ぎ、その上で、導電性を有する貼着層19で隣接する圧電フィルム10Lを貼着する。
下部保護層28および上部保護層30の貫通孔は、好ましくは圧電フィルム10Lの屈曲部以外で、積層される圧電フィルム10Lの下部電極24同士および上部電極26同士が対面する領域に1か所でもよく、複数個所でもよい。または、下部保護層28および上部保護層30の貫通孔は、下部保護層28および上部保護層30の全面に、規則的または、不規則に形成してもよい。
導電性を有する貼着層19には、制限はなく、公知のものが、各種、利用可能である。
すなわち、本発明において、圧電フィルム10を積層した積層圧電素子は、図8に示す積層圧電素子60のように、圧電体層20の分極方向が、全て同方向であってもよい。
ただし、図8に示すように、積層する圧電フィルム10の分極方向が、全て同方向である積層圧電素子60では、隣接する圧電フィルム10同士では、下部電極24と上部電極26とが対面する。そのため、貼着層19を十分に厚くしないと、貼着層19の面方向の外側の端部において、隣接する圧電フィルム10の下部電極24と上部電極26とが接触して、ショートしてしまう恐れがある。
そのため、図8に示すように、積層する圧電フィルム10の分極方向が、全て同方向である積層圧電素子60では、貼着層19を薄くすることができず、図6および図7に示す積層圧電素子に対して、エネルギー効率の点で、不利である。
<塗料の調製>
まず、下記の組成比で、シアノエチル化PVA(CR-V 信越化学工業社製)をシクロヘキサノン(SP値:9.9(cal/cm3)1/2)に溶解した。その後、この溶液に、PZT粒子を下記の組成比で添加して、プロペラミキサー(回転数2000rpm)で分散させて、圧電体層を形成するための塗料を調製した。
この塗布液をインラインミキサー(株式会社OHR流体工学研究所製 MX-F8)に流量5kg/minで通液する処理を2パス繰り返し、塗布液中の気泡を微細化した。
・PZT粒子・・・・・・・・・・・・・・・300質量部
・シアノエチル化PVA・・・・・・・・・・・30質量部
・シクロヘキサノン・・・・・・・・・・・・・70質量部
なお、PZT粒子は、市販のPZT原料粉を1000~1200℃で焼結した後、これを平均粒径5μmになるように解砕および分級処理したものを用いた。
一方、厚さ4μmのPETフィルムに、厚さ0.1μmの銅薄膜を真空蒸着してなるシート状物を用意した。すなわち、本例においては、薄膜電極は、厚さ0.1mの銅蒸着薄膜であり、保護層は厚さ4μmのPETフィルムとなる。
このシート状物の薄膜電極(銅蒸着薄膜)の上に、スライドコーターを用いて、先に調製した圧電体層を形成するための塗料を塗布した。なお、塗料は、乾燥後の塗膜の膜厚が40μmになるように、塗布した。
次いで、シート状物の上に塗料を塗布した物を、100℃のホットプレート上で60分間、加熱乾燥することでシクロヘキサノンの一部を蒸発させた。これにより、PET製の保護層の上に銅製の薄膜電極を有し、その上に、厚さが40μmの圧電体層(高分子複合圧電体)を形成してなる積層体を作製した。
次に、この積層体の圧電体層を、上述の方法で分極処理した。
分極処理を行った積層体の上に、薄膜電極(銅薄膜側)を圧電体層に向けてシート状物を積層した。次いで、積層体とシート状物との積層体を、ラミネータ装置を用いて圧電体層と薄膜電極とを接着した。
以上の工程によって、圧電フィルムを作製した。
作製した圧電フィルムからサンプルを切り出し、以下の方法で高分子複合圧電体中の空隙の面積率を測定した。
高分子複合圧電体の断面観察のため、厚さ方向に切削した。切削はライカバイオシステム社製RM2265にDrukker社製histoナイフ刃幅8mmを取り付け、スピードをコントローラー目盛り1、噛み合い量を0.25μm~1μmとして切削して断面を出した。その断面をSEM(株式会社日立ハイテクノロジーズ社製SU8220)により観察した。サンプルはPt蒸着で導電処理し、ワークディスタンスは8mmとする。観察条件はSE像(Upper)、加速電圧:0.5kVとし、フォーカス調整と非点収差調整によりシャープな画像を出し、高分子複合圧電体部が画面全体になる状態で自動明るさ調整(オート設定 ブライトネス:0、コントラスト:0)を実行した。撮影の倍率は両端の電極が一画面に収まり、かつ電極間の幅が、画面の半分以上となる倍率とした。画像の2値化は画像解析ソフトImageJを使用し、Threshold下限は保護層が着色しない最大の値とし、Threshold上限は設定値最大255とした。電極間にて着色した箇所の面積を空隙の面積と定義して分子とし、縦方向幅を電極間、横方向幅をSEM画像の両端とした高分子複合圧電体の面積を分母とし、高分子複合圧電体部の面積に占める空隙の面積比率を計算した。これを任意の10断面において行い、面積比率の平均値を高分子複合圧電体の断面における空隙の面積率として算出した。その結果、高分子複合圧電体の断面における空隙の面積率は、1.2%であった。
作製した圧電フィルムからサンプルを切り出し、以下の方法で高分子複合圧電体中の、SP値が12.5(cal/cm3)1/2未満、かつ、常温で液体の物質(溶媒)の含有量を測定した。
高分子複合圧電体からサンプルを8×8mm角に一部切り出し、ガスクロマトグラフ装置(島津製作所製 GC-12A)を用い、シクロヘキサノンの含有量を測定した。カラムは島津製作所製221-14368-11、充填剤は信和加工製Chromosorb101を使用した。試料気化室および検出器温度は200℃、カラム温度は160℃一定とし、0.4MPaのヘリウムをキャリアガスとして使用し測定した。得られたシクロヘキサノンの質量を、サンプル中の高分子複合圧電体正味の質量で除することで、その質量比を計算した。その結果、高分子複合圧電体中の、SP値が12.5(cal/cm3)1/2未満、かつ、常温で液体の物質(溶媒)の含有量は、520ppmであった。
圧電体層となる塗料のミキシング方法及び乾燥条件を下記表1に示す条件にそれぞれ変更した以外は、実施例1と同様にして圧電フィルムを作製した。
圧電体層となる塗料に含まれる溶媒をシクロヘキサノンに代えてジメチルホルムアミド(DMF)(SP値:12.1(cal/cm3)1/2)とした以外は実施例1と同様にして圧電フィルムを作製した。
圧電体層となる塗料に含まれる溶媒をシクロヘキサノンに代えてメチルエチルケトン(MEK)(SP値:9.3(cal/cm3)1/2)とし、塗料の乾燥条件を下記表1に示す条件に変更した以外は実施例1と同様にして圧電フィルムを作製した。
圧電体層となる塗料のミキシングを実施せず、乾燥条件を下記表1に示す条件に変更した以外は、実施例1と同様にして圧電フィルムを作製した。
圧電体層となる塗料の乾燥条件を下記表1に示す条件に変更した以外は、実施例1と同様にして圧電フィルムを作製した。
圧電体層となる塗料のミキシング方法及び乾燥条件を下記表1に示す条件に変更した以外は、実施例1と同様にして圧電フィルムを作製した。
作製した圧電フィルムの温度サイクル試験前後の変換効率の変化を評価した。
具体的には、作製した圧電フィルムから、φ150mmの円形試験片を切り出した。この試験片を、内径138mm、深さ9mmのプラスチック製の丸形のケースの開口面を覆うように固定して、ケース内部の圧力を、1.02気圧に維持した。これにより、変換フィルムをコンタクトレンズのように凸型に撓ませて圧電スピーカーとした。
このようにして作製した圧電スピーカーの音圧レベル-周波数特性を、定電流型パワーアンプを用いたサイン波スイープ測定によって測定した。なお、計測用マイクロフォンは、圧電スピーカーの中心の真上10cmの位置に配置した。
作製直後(温度サイクル試験前)の圧電スピーカーの変換効率に対する、温度サイクル試験後の圧電スピーカーの変換効率の比率を求めて以下の基準で評価した。
A:95%以上である。
B:90%以上95%未満である。
C:90%未満である。
結果を表1に示す。
比較例1は、高分子複合圧電体の断面における空隙の面積率が20%超であるため、乾燥により溶媒が蒸発して、空隙が生じ、圧電体粒子とマトリックスとの界面が剥離して、変換効率が低下したと考えられる。
比較例2は、溶媒の含有量が10000ppm超であるため、乾燥により溶媒が蒸発して、空隙が生じ、圧電体粒子とマトリックスとの界面が剥離して、変換効率が低下したと考えられる。
比較例3は、空隙の面積率が0.1%未満であるため、乾燥した際の溶媒の抜け道がなくなり、膨張、亀裂が発生し、変換効率が低下したと考えられる。
また、実施例1~4の対比から、空隙の面積率は、0.1%以上5%未満が好ましいことがわかる。
以上から本発明の効果は明らかである。
10a、10c シート状物
10b 積層体
12 振動板
14,56,60 積層圧電素子
16,19 貼着層
20 圧電体層
20a 上面
24 下部電極
26 上部電極
28 下部保護層
30 上部保護層
34 マトリックス
35 空隙
36 圧電体粒子
43 ケース
45 圧電スピーカー
45a 立ち上がり部
46 粘弾性支持体
48 枠体
50 電気音響変換器
58 芯棒
PS 電源
g 間隔
Claims (9)
- 高分子材料を含むマトリックス中に圧電体粒子を含む高分子複合圧電体であって、
前記高分子複合圧電体は、SP値が12.5(cal/cm3)1/2未満、かつ、常温で液体の物質を、質量比で500ppm超、10000ppm以下含有しており、
前記高分子複合圧電体内には空隙が形成されており、
前記高分子複合圧電体の断面における前記空隙の面積率が0.1%以上、20%以下である高分子複合圧電体。 - 前記空隙の面積率が0.1%以上、5%未満である請求項1に記載の高分子複合圧電体。
- 前記高分子複合圧電体が厚さ方向に分極されたものである請求項1または2に記載の高分子複合圧電体。
- 圧電特性に面内異方性を有さない請求項1~3のいずれか一項に記載の高分子複合圧電体。
- 前記物質の含有量が500ppm超、1000ppm以下である請求項1~4のいずれか一項に記載の高分子複合圧電体。
- 前記高分子材料が常温で粘弾性を有する請求項1~5のいずれか一項に記載の高分子複合圧電体。
- 前記物質が、メチルエチルケトン、ジメチルホルムアミド、シクロヘキサノン、アセトン、シクロヘキサン、アセトニトリル、1プロパノール、2プロパノール、2メトキシアルコール、ジアセトンアルコール、ジメチルアセトアミド、ベンジルアルコール、n-ヘキサン、トルエン、o-キシレン、酢酸エチル、酢酸ブチル、ジエチルエーテル、テトラヒドロフランからなる群から選択される少なくとも1つである請求項1~6のいずれか一項に記載の高分子複合圧電体。
- 請求項1~7のいずれか一項に記載の高分子複合圧電体と、
前記高分子複合圧電体の両面に形成された電極層とを有する圧電フィルム。 - 前記電極層の、前記高分子複合圧電体側の面とは反対側の面に積層された保護層を有する請求項8に記載の圧電フィルム。
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WO2022246821A1 (zh) * | 2021-05-28 | 2022-12-01 | 京东方科技集团股份有限公司 | 一种压电传感器、其制作方法及触觉反馈装置 |
WO2023047958A1 (ja) * | 2021-09-24 | 2023-03-30 | 富士フイルム株式会社 | 積層圧電素子および電気音響変換器 |
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