JP2016063286A - Electroacoustic conversion film and electroacoustic converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electroacoustic conversion film and electroacoustic converter, capable of suppressing degradation in a conversion efficiency, a voltage resistance and flexibility even under environments where temperatures and humidities are severe.SOLUTION: The electroacoustic conversion film includes: a polymer composite piezoelectric body formed by dispersing piezoelectric material particles into a matrix comprised of polymeric material; a film electrode formed on both surfaces of the polymer composite piezoelectric body; and a protective film formed on a surface of the film electrode. The polymer composite piezoelectric body can solve the above problems by containing a liquid substance having SP value of less than 12.5(cal/cm)at a normal temperature, at a mass ratio of 20 ppm-500 ppm.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an electroacoustic conversion film used for an acoustic device such as a speaker or a microphone.

  In response to the thinning of displays such as liquid crystal displays and organic EL displays, the speakers used in these thin displays are also required to be light and thin. Furthermore, in a flexible display having flexibility, flexibility is also required in order to integrate the flexible display without impairing lightness and flexibility. As such a lightweight, thin and flexible speaker, it is considered to employ a sheet-like piezoelectric film having a property of expanding and contracting in response to an applied voltage.

For example, Patent Document 1 describes that a piezoelectric film obtained by subjecting a uniaxially stretched film of polyvinylidene fluoride (PVDF) to polarization treatment at a high voltage is used.
In order to employ such a piezoelectric film as a speaker, it is necessary to convert expansion / contraction movement along the film surface into vibration of the film surface. This conversion from expansion / contraction motion to vibration is achieved by holding the piezoelectric film in a curved state, thereby enabling the piezoelectric film to function as a speaker.

However, a piezoelectric film made of uniaxially stretched PVDF has in-plane anisotropy in its piezoelectric characteristics, so that the sound quality varies greatly depending on the direction of bending even with the same curvature.
Furthermore, since PVDF has a smaller loss tangent than a general speaker diaphragm such as cone paper, resonance is likely to occur strongly and the frequency characteristics are severe. Therefore, the amount of change in sound quality when the minimum resonance frequency changes with the change in curvature also increases.
As described above, it is difficult to reproduce a stable sound with a piezoelectric film made of PVDF.

  Therefore, the applicant of the present application is a speaker that has flexibility and is capable of stably reproducing high-quality sound from a polymer material having viscoelasticity at room temperature, disclosed in Patent Document 2. An electric device having a polymer composite piezoelectric material in which piezoelectric particles are dispersed in a viscoelastic matrix, a thin film electrode formed on both surfaces of the polymer composite piezoelectric material, and a protective layer formed on the surface of the thin film electrode An acoustic conversion film was proposed.

JP 2008-294493 A JP 2014-14063 A

  The electroacoustic conversion film described in Patent Document 2 is a high-viscosity material at room temperature, and is hard against vibrations of 20 Hz to 20 kHz and vibrations of several Hz or less. It can behave softly, and has an appropriate loss tangent for vibrations of all frequencies below 20 kHz. Therefore, it is excellent in flexibility and acoustic characteristics, and stable sound output is possible even if it is deformed.

However, according to the study by the present inventors, a temperature cycle test in which heating and cooling are alternately repeated was performed on a piezoelectric film using a polymer composite piezoelectric material obtained by dispersing piezoelectric particles in a matrix. After the cycle test, it was found that the conversion efficiency between voltage and sound, current leakage, and dielectric breakdown may occur, that is, the withstand voltage may decrease. That is, it has been found that there is a risk of performance degradation in a high or low temperature environment.
Moreover, when the flexibility test was performed under various environments, it was found that the piezoelectric layer might be cured and the flexibility of the piezoelectric film might be lowered under low humidity.

  An object of the present invention is to solve such problems of the prior art. Even in severe environments such as a wide temperature range from a high temperature to a low temperature and a wide humidity range, the conversion efficiency is lowered and the withstand voltage is lowered. Another object of the present invention is to provide an electroacoustic transducer film and an electroacoustic transducer that can suppress a decrease in flexibility.

In order to solve this problem, the present inventors have provided a polymer composite piezoelectric material in which piezoelectric particles are dispersed in a matrix made of a polymer material, and a thin film electrode formed on both surfaces of the polymer composite piezoelectric material. And a protective film formed on the surface of the thin film electrode. The polymer composite piezoelectric material has a SP value of less than 12.5 (cal / cm ³ ) ^1/2 and is liquid at room temperature. It has been found that the inclusion of 20 ppm to 500 ppm by mass ratio can suppress a decrease in conversion efficiency, a decrease in withstand voltage, a decrease in flexibility, and the like even under severe environments such as temperature and humidity, and the present invention has been completed. I let you.
That is, this invention provides the electroacoustic conversion film and electroacoustic transducer of the following structures.

(1) A polymer composite piezoelectric body in which piezoelectric particles are dispersed in a matrix made of a polymer material, a thin film electrode formed on both surfaces of the polymer composite piezoelectric body, and a protection formed on the surface of the thin film electrode And having a layer
The polymer composite piezoelectric material is an electroacoustic conversion film having an SP value of less than 12.5 (cal / cm ³ ) ^1/2 and a substance that is liquid at room temperature in a mass ratio of 20 ppm to 500 ppm.
(2) The electroacoustic conversion film as described in (1) whose content of a substance is 100 ppm-400 ppm.
(3) The electroacoustic conversion film according to (1) or (2), wherein the matrix is a polymer material having viscoelasticity at room temperature.
(4) The electroacoustic conversion film according to any one of (1) to (3), wherein the thickness of the polymer composite piezoelectric material is 5 to 100 μm.
(5) The substance is methyl ethyl ketone, dimethylformamide, cyclohexanone, acetone, cyclohexane, acetonitrile, 1 propanol, 2 propanol, 2 methoxy alcohol, diacetone alcohol, dimethylacetamide, benzyl alcohol, n-hexane, toluene, o-xylene, acetic acid The electroacoustic conversion film according to any one of (1) to (4), which is at least one selected from the group consisting of ethyl, butyl acetate, diethyl ether, and tetrahydrofuran.
(6) Any one of (1) to (5), wherein a maximum value at which a loss tangent Tan δ at a frequency of 1 Hz measured by dynamic viscoelasticity measurement of the polymer material is 0.5 or more exists in a temperature range of 0 to 50 ° C. The electroacoustic conversion film according to 1.
(7) The electroacoustic conversion film according to any one of (1) to (6), wherein the polymer material has a cyanoethyl group.
(8) The electroacoustic conversion film according to any one of (1) to (7), wherein the polymer material is cyanoethylated polyvinyl alcohol.
(9) An electroacoustic transducer having the electroacoustic transducer film according to any one of (1) to (8) and a support member that supports the electroacoustic transducer film.

  According to the electroacoustic conversion film and the electroacoustic transducer of the present invention, 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 temperature and humidity are severe. it can.

It is a conceptual diagram which shows an example of the electroacoustic conversion film of this invention. 2A to 2E are conceptual diagrams illustrating an example of a method for producing the electroacoustic conversion film illustrated in FIG. FIGS. 3A to 3C are conceptual diagrams for explaining an example of a piezoelectric speaker using the electroacoustic conversion film of the present invention.

Hereinafter, the electroacoustic conversion film and the electroacoustic transducer of the present invention will be described in detail based on preferred embodiments shown in the accompanying drawings.
The description of the constituent elements described below may be made based on typical embodiments of the present invention, but the present invention is not limited to such embodiments.
In the present specification, a numerical range expressed using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value.

FIG. 1 conceptually shows an example of the electroacoustic conversion film of the present invention.
An electroacoustic conversion film 10 (hereinafter referred to as a conversion film 10) shown in FIG. 1 basically includes a piezoelectric layer 12 made of a polymer composite piezoelectric body, a thin film electrode 14 provided on one surface of the piezoelectric layer 12, and The thin film electrode 16 provided on the other surface, the protective layer 18 provided on the surface of the thin film electrode 14, and the protective layer 20 provided on the surface of the thin film electrode 16 are configured.

  Such a conversion film 10 is used in various acoustic devices (acoustic equipment) such as speakers, microphones, and pickups used for musical instruments such as guitars, to generate (reproduce) sound due to vibration according to electrical signals, It is used to convert the vibration caused by the above into an electrical signal.

In the conversion film 10 of the present invention, the piezoelectric layer 12 is made of a polymer composite piezoelectric body as described above.
In the present invention, the polymer composite piezoelectric material forming the piezoelectric layer 12 is obtained by uniformly dispersing piezoelectric particles 26 in a matrix 24 made of a polymer material, and the SP value is 12 in the matrix 24. 0.5 (cal / cm ³ ) ^1/2 and a substance that is liquid at room temperature contains 20 ppm to 500 ppm in mass ratio.
Preferably, the piezoelectric layer 12 is polarized.
In this specification, “room temperature” refers to a temperature range of about 0 to 50 ° C.

Here, as a material of the matrix 24 (matrix and binder) of the polymer composite piezoelectric body constituting the piezoelectric layer 12, a polymer material having viscoelasticity at room temperature is preferably used.
The conversion film 10 of the present invention is suitably used for a flexible speaker such as a speaker for a flexible display. Here, the polymer composite piezoelectric body (piezoelectric layer 12) used for the flexible speaker preferably has the following requirements. Therefore, it is preferable to use a polymer material having viscoelasticity at room temperature as a material having the following requirements.

(I) Flexibility For example, when gripping in a loosely bent state like a newspaper or a magazine for portable use, it is constantly subject to a relatively slow and large bending deformation of several Hz or less from the outside. become. At this time, if the polymer composite piezoelectric material is hard, a large bending stress is generated, and a crack is generated at the interface between the polymer matrix and the piezoelectric particles, which may eventually lead to destruction. Accordingly, the polymer composite piezoelectric body is required to have an appropriate softness. Further, if the strain energy can be diffused to the outside as heat, the stress can be relaxed. Accordingly, it is required that the loss tangent of the polymer composite piezoelectric material is appropriately large.
(Ii) Sound quality The speaker vibrates the piezoelectric particles at an audio band frequency of 20 Hz to 20 kHz, and the vibration plate (polymer composite piezoelectric body) vibrates as a whole by the vibration energy, so that sound is reproduced. The Accordingly, in order to increase the transmission efficiency of vibration energy, the polymer composite piezoelectric body is required to have an appropriate hardness. Further, if the frequency characteristic of the speaker is smooth, the amount of change in the sound quality when the lowest resonance frequency f ₀ with the change in the curvature is changed becomes small. Therefore, the loss tangent of the polymer composite piezoelectric material is required to be moderately large.

  In summary, a polymer composite piezoelectric body used for a flexible speaker is required to be hard for vibrations of 20 Hz to 20 kHz and to be soft for vibrations of several Hz or less. In addition, the loss tangent of the polymer composite piezoelectric body is required to be reasonably large with respect to vibrations of all frequencies of 20 kHz or less.

In general, polymer solids have a viscoelastic relaxation mechanism, and as the temperature increases or the frequency decreases, large-scale molecular motion decreases (relaxes) the storage elastic modulus (Young's modulus) or maximizes the loss elastic modulus (absorption). As observed. Among them, 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 remarkably.
In the polymer composite piezoelectric material (piezoelectric layer 12), a polymer material having a glass transition point at room temperature, in other words, a polymer material having viscoelasticity at room temperature is used for a vibration at 20 Hz to 20 kHz. A polymer composite piezoelectric material that is hard and softly behaves with respect to slow vibrations of several Hz or less is realized. In particular, a polymer material having a glass transition temperature at a frequency of 1 Hz at room temperature, that is, 0 to 50 ° C., is preferably used for the matrix of the polymer composite piezoelectric material in terms of suitably exhibiting this behavior.

Various known materials can be used as the polymer material having viscoelasticity at room temperature. Preferably, a polymer material having a maximum value of a loss tangent Tanδ at a frequency of 1 Hz in a dynamic viscoelasticity test at room temperature, that is, 0 to 50 ° C., is 0.5 or more.
As a result, when the polymer composite piezoelectric body is slowly bent by an external force, the stress concentration at the polymer matrix / piezoelectric particle interface at the maximum bending moment portion is alleviated, and high flexibility can be expected.

The polymer material preferably has a storage elastic modulus (E ′) at a frequency of 1 Hz as measured by dynamic viscoelasticity of 100 MPa or more at 0 ° C. and 10 MPa or less at 50 ° C.
As a result, the bending moment generated when the polymer composite piezoelectric body is bent slowly by an external force can be reduced, and at the same time, it can behave hard against an acoustic vibration of 20 Hz to 20 kHz.

Further, it is more preferable that the polymer material has a relative dielectric constant of 10 or more at 25 ° C. As a result, when a voltage is applied to the polymer composite piezoelectric material, a higher electric field is applied to the piezoelectric particles in the polymer matrix, so that a large amount of deformation can be expected.
However, in consideration of ensuring good moisture resistance, the polymer material preferably has a relative dielectric constant of 10 or less at 25 ° C.

Polymer materials satisfying such conditions 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. Moreover, as these polymer materials, commercially available products such as Hibler 5127 (manufactured by Kuraray Co., Ltd.) can be suitably used. Among these, it is preferable to use a material having a cyanoethyl group, and it is particularly preferable to use cyanoethylated PVA.
In addition, these polymeric materials may use only 1 type, and may use multiple types together (mixed).

The matrix 24 using the polymer material having viscoelasticity at room temperature may use a plurality of polymer materials in combination as necessary.
That is, other dielectric polymer materials may be added to the matrix 24 as needed in addition to viscoelastic materials such as cyanoethylated PVA for the purpose of adjusting dielectric properties and mechanical properties.

Examples of dielectric polymer materials that can be added include polyvinylidene fluoride, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, and polyvinylidene fluoride-trifluoroethylene copolymer. Fluorine polymers such as polyvinylidene fluoride-tetrafluoroethylene copolymer, vinylidene cyanide-vinyl acetate copolymer, cyanoethyl cellulose, cyanoethyl hydroxy saccharose, cyanoethyl hydroxy cellulose, cyanoethyl hydroxy pullulan, cyanoethyl methacrylate, cyanoethyl acrylate, cyanoethyl Hydroxyethyl cellulose, cyanoethyl amylose, cyanoethyl hydroxypropyl cellulose, cyanoethyl dihydroxypropyl cellulose, Synthesis of polymers having cyano groups or cyanoethyl groups, such as noethyl hydroxypropyl amylose, cyanoethyl polyacrylamide, cyanoethyl polyacrylate, cyanoethyl pullulan, cyanoethyl polyhydroxymethylene, cyanoethyl glycidol pullulan, cyanoethyl saccharose and cyanoethyl sorbitol, nitrile rubber, chloroprene rubber, etc. Examples thereof include rubber.
Among these, a polymer material having a cyanoethyl group is preferably used.
In addition, the dielectric polymer added to the matrix 24 of the piezoelectric layer 12 in addition to the material having viscoelasticity at room temperature such as cyanoethylated PVA is not limited to one type, and a plurality of types may be added. .

In addition to dielectric polymers, for the purpose of adjusting the glass transition point Tg, thermoplastic resins such as vinyl chloride resin, polyethylene, polystyrene, methacrylic resin, polybutene, isobutylene, phenol resin, urea resin, melamine resin, Thermosetting resins such as alkyd resins and mica may be added.
Furthermore, for the purpose of improving the tackiness, a tackifier such as rosin ester, rosin, terpene, terpene phenol, petroleum resin, etc. may be added.

In the matrix 24 of the piezoelectric layer 12, there is no particular limitation on the addition amount when a polymer other than a viscoelastic material such as cyanoethylated PVA is added, but it is 30% by weight or less in the ratio of the matrix 24. preferable.
Thereby, the characteristics of the polymer material to be added can be expressed without impairing the viscoelastic relaxation mechanism in the matrix 24, so that the dielectric constant is increased, the heat resistance is improved, the adhesion with the piezoelectric particles 26 and the electrode layer is improved, and the like. In this respect, preferable results can be obtained.

  In the present invention, the material of the matrix 24 is not limited to a polymer material having viscoelasticity at room temperature, and the above-described dielectric polymer can also be used.

The piezoelectric particles 26 are made of ceramic particles having a perovskite type or wurtzite type crystal structure.
Examples of the ceramic particles constituting the piezoelectric particles 26 include lead zirconate titanate (PZT), lead lanthanum zirconate titanate (PLZT), barium titanate (BaTiO3), zinc oxide (ZnO), and titanium. Examples thereof include a solid solution (BFBT) of barium acid and bismuth ferrite (BiFe3).

The particle size of the piezoelectric particles 26 may be appropriately selected according to the size and application of the conversion film 10, but is preferably 1 to 10 μm according to the study of the present inventors.
By setting the particle size of the piezoelectric particles 26 within the above range, a favorable result can be obtained in terms of achieving both high piezoelectric characteristics and flexibility.

  In FIG. 1, the piezoelectric particles 26 in the piezoelectric layer 12 are irregularly dispersed in the matrix 24, but may be uniformly dispersed with regularity.

Further, in the conversion film 10 of the present invention, the amount ratio between the matrix 24 and the piezoelectric particles 26 in the piezoelectric layer 12 is the size and thickness in the surface direction of the conversion film 10, the use of the conversion film 10, the conversion film 10. What is necessary is just to set suitably according to the characteristic etc. which are requested | required.
Here, according to the study of the present inventor, the volume fraction of the piezoelectric particles 26 in the piezoelectric layer 12 is preferably 30 to 70%, particularly preferably 50% or more, and therefore 50 to 50%. 70% is more preferable.
By setting the quantity ratio between the matrix 24 and the piezoelectric particles 26 within the above range, a favorable result can be obtained in terms of achieving both high piezoelectric characteristics and flexibility.

Here, in the conversion film 10 of the present invention, the piezoelectric layer 12 which is a polymer composite piezoelectric material obtained by dispersing piezoelectric particles in a matrix has an SP value (solubility parameter) of 12.5 (cal / cm). ³ ) A substance which is less than ^1/2 and is liquid at room temperature is contained in a mass ratio of 20 ppm to 500 ppm.
Specific examples of substances that have an SP value of less than 12.5 (cal / cm ³ ) ^1/2 and are liquid at room temperature include methyl ethyl ketone, dimethylformamide, cyclohexanone, acetone, cyclohexane, acetonitrile, 1 propanol, and 2 propanol. Examples include organic compounds such as 2-methoxy alcohol, diacetone alcohol, dimethylacetamide, benzyl alcohol, n-hexane, toluene, o-xylene, ethyl acetate, butyl acetate, diethyl ether, and tetrahydrofuran.
The above substances are generally used as organic solvents. That is, the present invention is that the piezoelectric layer 12 contains an organic solvent that has an SP value of less than 12.5 (cal / cm ³ ) ^1/2 and is liquid at room temperature in a mass ratio of 20 ppm to 500 ppm. is there.

As described above, the piezoelectric layer is excellent in flexibility and acoustic characteristics by being a polymer composite piezoelectric body in which piezoelectric particles are dispersed in a matrix made of a polymer material having viscoelasticity at room temperature, In addition, a conversion film capable of outputting stable sound even when deformed can be obtained.
However, according to the study by the inventors, a piezoelectric film using a polymer composite piezoelectric body in which piezoelectric particles are dispersed in a matrix was subjected to a temperature cycle test in which heating and cooling were alternately repeated. After the temperature cycle test, it was found that the conversion efficiency of voltage and sound, current leakage, and dielectric breakdown may occur, that is, the withstand voltage may decrease.
In addition, when the flexibility test was performed under various environments, it was found that the piezoelectric layer (matrix) may be dried and cured under low humidity, which may reduce the flexibility of the piezoelectric film. It was.

In contrast, in the conversion film 10 of the present invention, the polymer composite piezoelectric material (piezoelectric layer 12) has a SP value of less than 12.5 (cal / cm ³ ) ^1/2 and is a liquid at room temperature. In a mass ratio of 20 ppm to 500 ppm.
When the polymer composite piezoelectric material contains the above substance, the polymer composite piezoelectric material can be prevented from being dried and cured even under a low humidity. As a result, it is possible to prevent the flexibility from being lowered under low humidity. In order to exhibit such an effect, the polymer composite piezoelectric body needs to contain 20 ppm or more of the above substance.

Here, even when the polymer composite piezoelectric material has a SP value of 12.5 (cal / cm ³ ) ^1/2 or more and contains a liquid substance at room temperature, Curing by drying can be prevented. However, when a substance having an SP value of 12.5 (cal / cm ³ ) ^1/2 or more is contained, it is estimated that the substance is not uniformly dispersed in the polymer composite piezoelectric material but aggregates. The Therefore, when exposed to a high temperature and the substance inside the piezoelectric body evaporates, a relatively large gap is generated, and the interface between the piezoelectric particles and the matrix is peeled off. As a result, the vibration of the piezoelectric particles is not transmitted to the matrix, so that the conversion efficiency between voltage and sound is reduced, current leakage or dielectric breakdown occurs.
On the other hand, in the present invention, the material is contained in the polymer composite piezoelectric layer by setting the SP value of the material to less than 12.5 (cal / cm ³ ) ^1/2 , thereby making the material a polymer composite piezoelectric material. Since it can be uniformly dispersed inside, the interface between the piezoelectric particles and the matrix is peeled off by suppressing the formation of large voids when the material inside the polymer composite piezoelectric material evaporates when exposed to high temperatures. Can be prevented. Accordingly, it is possible to suppress a decrease in conversion efficiency and a decrease in withstand voltage.

In addition, even when the content of the above substance is too large, voids are likely to occur when the substance inside the polymer composite piezoelectric material evaporates, and the interface between the piezoelectric particles and the matrix peels off, resulting in conversion efficiency. Lowering or withstand voltage will occur.
Therefore, in the present invention, by setting the content of the substance to 500 ppm or less, it is possible to suppress the formation of large voids when the substance inside the polymer composite piezoelectric material evaporates, and the piezoelectric particles and the matrix. Can be prevented from peeling off. Accordingly, it is possible to suppress a decrease in conversion efficiency and a decrease in withstand voltage.

In addition, from the viewpoint of preventing the decrease in flexibility, and preventing the decrease in conversion efficiency and the breakdown voltage, the piezoelectric layer SP value in the polymer composite piezoelectric body is 12.5 (cal / cm ³ ). The content of the substance which is less than ^1/2 and which is liquid at normal temperature is preferably 100 ppm to 400 ppm.

In addition, from the viewpoint of preventing a decrease in conversion efficiency and a decrease in withstand voltage, the SP value of the substance is preferably 9.0 to 12.3 (cal / cm ³ ) ^1/2 , and preferably 9.3 to 12.1 (cal / cm ³ ) ^1/2 is more preferred.

  Here, the content of the substance in the polymer composite piezoelectric material is measured by gas chromatography. At that time, the content when the sample is allowed to stand for 24 hours in an environment of temperature 50 ° C. and humidity 10% RH is defined as the content of the substance.

There is no particular limitation on the method of containing the substance in the polymer composite piezoelectric body at a predetermined concentration. For example, when preparing a coating material to be a polymer composite piezoelectric body, a predetermined amount of the substance may be added.
Preferably, the content of the substance in the polymer composite piezoelectric body is controlled by adjusting the drying conditions after applying the paint using the substance as a solvent for the paint to be prepared. What is necessary is just to set the drying conditions in that case suitably according to the kind of said substance, desired content, the kind of matrix, the thickness of a piezoelectric material layer, etc.

Further, in the conversion film 10 of the present invention, the thickness of the piezoelectric layer 12 is not particularly limited, depending on the size of the conversion film 10, the use of the conversion film 10, the characteristics required for the conversion film 10, etc. What is necessary is just to set suitably.
Here, according to the study of the present inventors, the thickness of the piezoelectric layer 12 is preferably 5 to 100 μm, more preferably 5 to 50 μm, and particularly preferably 5 to 30 μm.
By setting the thickness of the piezoelectric layer 12 in the above range, it can be more easily adjusted when the content of the substance is controlled by drying as described above. In addition, the concentration of the substance in the piezoelectric layer 12 can be made more uniform.
In addition, by setting the thickness of the piezoelectric layer 12 in the above range, a preferable result can be obtained in terms of ensuring both rigidity and appropriate flexibility.
The piezoelectric layer 12 is preferably polarized (polled) as described above. The polarization process will be described in detail later.

As shown in FIG. 1, the conversion film 10 of the present invention has a configuration in which a piezoelectric layer 12 is sandwiched between thin film electrodes 14 and 16 and this laminate is sandwiched between protective layers 18 and 20.
In the conversion film 10, the protective layers 18 and 20 have a role of imparting appropriate rigidity and mechanical strength to the polymer composite piezoelectric body. That is, in the conversion film 10 of the present invention, the polymer composite piezoelectric body (piezoelectric layer 12) composed of the matrix 24 and the piezoelectric particles 26 has very excellent flexibility against slow bending deformation. However, depending on the application, rigidity and mechanical strength may be insufficient. In order to compensate for the conversion film 10, protective layers 18 and 20 are provided.

  There is no limitation in particular in the protective layers 18 and 20, Various sheet-like materials can be utilized, and various resin films (plastic film) are suitably illustrated as an example. Among them, polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS), polycarbonate (PC), polyphenylene sulfite (PPS), polymethyl methacrylate (PMMA) due to excellent mechanical properties and heat resistance. ), Polyetherimide (PEI), polyimide (PI), polyethylene naphthalate (PEN), triacetyl cellulose (TAC), and cyclic olefin-based resin are preferably used.

The thickness of the protective layers 18 and 20 is not particularly limited. Further, the thicknesses of the protective layers 18 and 20 are basically the same, but may be different.
Here, if the rigidity of the protective layers 18 and 20 is too high, not only the expansion and contraction of the piezoelectric layer 12 is restricted, but also the flexibility is impaired, so mechanical strength and good handling properties as a sheet-like material are required. Except where it is done, the thinner protective layers 18 and 20 are advantageous.

Here, according to the study of the present inventor, if the thickness of the protective layers 18 and 20 is less than or equal to twice the thickness of the piezoelectric layer 12, it is possible to ensure both rigidity and appropriate flexibility. A favorable result can be obtained.
For example, when the thickness of the piezoelectric layer 12 is 50 μm and the protective layers 18 and 20 are made of PET, the thickness of the protective layers 18 and 20 is preferably 100 μm or less, more preferably 50 μm or less, and more preferably 25 μm or less. Is preferred

  In addition, as described above, the polymer material used in the present invention has a low relative dielectric constant and excellent moisture resistance, so that it is not necessary to form a protective layer for moisture resistance. Therefore, the protective layer can be made thin or eliminated, and flexibility can be improved.

In the conversion film 10 of the present invention, a thin film electrode 14 is formed between the piezoelectric layer 12 and the protective layer 18, and a thin film electrode 16 is formed between the piezoelectric layer 12 and the protective layer 20.
The thin film electrodes 14 and 16 are provided for applying a voltage to the conversion film 10.

  In the present invention, the material for forming the thin film electrodes 14 and 16 is not particularly limited, and various conductors can be used. Specific examples include carbon, palladium, iron, tin, aluminum, nickel, platinum, gold, silver, copper, chromium and molybdenum, alloys thereof, indium tin oxide, and the like. Among these, any one of copper, aluminum, gold, silver, platinum, and indium tin oxide is preferably exemplified.

  Further, the method for forming the thin film electrodes 14 and 16 is not particularly limited, and a vapor deposition method (vacuum film forming method) such as vacuum vapor deposition or sputtering, a film formed by plating, or a foil formed of the above material is pasted. Various known methods such as a method of wearing can be used.

In particular, a thin film of copper or aluminum formed by vacuum vapor deposition is preferably used as the thin film electrodes 14 and 16 because the flexibility of the conversion film 10 can be ensured. Among these, a copper thin film formed by vacuum deposition is particularly preferably used.
The thickness of the thin film electrodes 14 and 16 is not particularly limited. The thicknesses of the thin film electrodes 14 and 16 are basically the same, but may be different.

  Here, similarly to the protective layers 18 and 20 described above, if the thin film electrodes 14 and 16 are too rigid, not only the expansion and contraction of the piezoelectric layer 12 is restricted, but also the flexibility is impaired. The thickness of 16 is more advantageous as long as the electrical resistance is not too high.

Here, according to the study of the present inventor, if the product of the thickness of the thin film electrodes 14 and 16 and the Young's modulus is less than the product of the thickness of the protective layers 18 and 20 and the Young's modulus, the flexibility is greatly impaired. This is preferable because it does not occur.
For example, when the protective layers 18 and 20 are PET (Young's modulus: about 6.2 GPa) and the thin film electrodes 14 and 16 are made of copper (Young's modulus: about 130 GPa), the thickness of the protective layers 18 and 20 is 25 μm. If so, the thickness of the thin film electrodes 14 and 16 is preferably 1.2 μm or less, more preferably 0.3 μm or less, and particularly preferably 0.1 μm or less.

Further, the thin film electrode 14 and / or the thin film electrode 16 do not necessarily have to be formed corresponding to the entire surface of the piezoelectric layer 12 (protective layer 18 and / or 20).
That is, at least one of the thin film electrode 14 and the thin film electrode 16 may be smaller than the piezoelectric layer 12, for example, and the piezoelectric layer 12 and the protective film may be in direct contact with each other at the periphery of the conversion film 10. .

  Alternatively, the protective layers 18 and / or 20 having the thin film electrode 14 and / or the thin film electrode 16 formed on the entire surface do not need to be formed on the entire surface of the piezoelectric layer 12. In this case, a (second) protective layer that is in direct contact with the piezoelectric layer 12 may be separately provided on the surface side of the protective layer 18 and / or 20.

As described above, the conversion film 10 of the present invention is obtained by dispersing the piezoelectric particles 26 in the matrix 24 and containing a substance having an SP value of less than 12.5 (cal / cm ³ ) ^1/2. 12 (polymer composite piezoelectric body) is sandwiched between thin film electrodes 14 and 16, and the laminate is further sandwiched between protective layers 18 and 20.
The conversion film 10 of the present invention preferably has a maximum value at room temperature at which the loss tangent (Tanδ) at a frequency of 1 Hz by dynamic viscoelasticity measurement is 0.5 or more.
Thereby, even if the conversion film 10 is subjected to a relatively slow and large bending deformation of several Hz or less from the outside, the strain energy can be effectively diffused to the outside as heat, so that the polymer matrix and the piezoelectric particles It is possible to prevent cracks from occurring at the interface.

The conversion film 10 of the present invention preferably has a storage elastic modulus (E ′) at a frequency of 1 Hz as measured by dynamic viscoelasticity of 10 to 30 GPa at 0 ° C. and 1 to 10 GPa at 50 ° C.
Thereby, the conversion film 10 can have a large frequency dispersion in the storage elastic modulus (E ′) at room temperature. That is, it can behave hard for vibrations of 20 Hz to 20 kHz and soft for vibrations of several Hz or less.

The conversion film 10 of the present invention, the product of the thickness and the storage elastic modulus at a frequency 1Hz by dynamic viscoelasticity measurement (E ') is, 1.0 × 10 ⁶ to 2.0 × 10 at 0 ° C. ⁶ It is preferably (1.0E + 06 to 2.0E + 06) N / m, and 1.0 × 10 ^{5 to} 1.0 × 10 ⁶ (1.0E + 05 to 1.0E + 06) N / m at 50 ° C.
Thereby, in the range which does not impair flexibility and an acoustic characteristic, the conversion film 10 can be equipped with moderate rigidity and mechanical strength.

Furthermore, the conversion film 10 of the present invention preferably has a loss tangent (Tanδ) at 25 ° C. and a frequency of 1 kHz of 0.05 or more in the master curve obtained from the dynamic viscoelasticity measurement.
Thus, the conversion frequency characteristic of the loudspeaker using the film 10 becomes smooth, can vary the amount of sound is also small when the lowest resonance frequency f ₀ with the change in the curvature of the speaker has changed.

Next, an example of the manufacturing method of the electroacoustic conversion film of this invention is demonstrated with reference to FIG. 2 (A)-FIG.2 (E).
First, as shown in FIG. 2A, a sheet-like object 10a having a thin film electrode 14 formed on a protective layer 18 is prepared.
The sheet-like material 10a may be produced by forming a copper thin film or the like as the thin film electrode 14 on the surface of the protective layer 18 by vacuum deposition, sputtering, plating, or the like.
When the protective layer 18 is very thin and handling properties are poor, a protective layer 18 with a separator (temporary support) may be used as necessary. In addition, as a separator, 25-100 micrometers thick PET etc. can be used. In addition, what is necessary is just to remove a separator after the thermocompression bonding of a thin film electrode and a protective layer.
Or you may utilize the commercial item in which the copper thin film etc. were formed on the protective layer 18 as the sheet-like object 10a.

On the other hand, a polymer material that is a matrix material such as cyanoethylated PVA is dissolved in an organic solvent, and further, piezoelectric particles 26 such as PZT particles, and an SP value of 12.5 (cal / cm ³ ) Add a material of less than ^1/2 and stir and disperse to prepare a paint.
In addition, there is no limitation in particular as an organic solvent, Although various organic solvents can be utilized, As mentioned above, it is preferable to use the said substance as an organic solvent.
When the aforementioned sheet-like material 10a is prepared and a paint is prepared, the paint is cast (applied) on the sheet-like material 10a, and the organic solvent is evaporated and dried. Thereby, as shown in FIG. 2B, a laminated body 10b having the thin film electrode 14 on the protective layer 18 and the piezoelectric layer 12 formed on the thin film electrode 14 is manufactured.
Here, as described above, the drying condition of the coating material is adjusted, and the substance (organic solvent) having a mass ratio of 20 ppm to 500 ppm is left in the piezoelectric layer 12.

  The coating casting method is not particularly limited, and all known methods (coating apparatuses) such as a slide coater and a doctor knife can be used.

As described above, in the conversion film 10 of the present invention, a polymer piezoelectric material such as PVDF may be added to the matrix 24 in addition to a viscoelastic material such as cyanoethylated PVA.
When these polymer piezoelectric materials are added to the matrix 24, the polymer piezoelectric material to be added to the paint may be dissolved.
If the laminated body 10b which has the thin film electrode 14 on the protective layer 18, and forms the piezoelectric material layer 12 on the thin film electrode 14 is produced, Preferably, the polarization process (polling) of the piezoelectric material layer 12 is performed. .

  The method for polarization treatment of the piezoelectric layer 12 is not particularly limited, and a known method can be used. As a preferable method of polarization treatment, the method shown in FIGS. 2C and 2D is exemplified.

In this method, as shown in FIG. 2 (C) and FIG. 2 (D), the gap g is moved, for example, by 1 mm on the upper surface 12a of the piezoelectric layer 12 of the laminated body 10b, and moved along the upper surface 12a. A possible rod-shaped or wire-shaped corona electrode 30 is provided. The corona electrode 30 and the thin film electrode 14 are connected to a DC power source 32.
Furthermore, a heating means for heating and holding the laminated body 10b, for example, a hot plate is prepared.

  Then, the piezoelectric layer 12 is heated and held at, for example, a temperature of 100 ° C. by a heating means, and a direct current of several kV, for example, 6 kV, is provided between the thin film electrode 14 and the corona electrode 30 from the DC power source 32. A voltage is applied to cause corona discharge. Further, the corona electrode 30 is moved (scanned) along the upper surface 12a of the piezoelectric layer 12 while maintaining the gap g, and the piezoelectric layer 12 is polarized.

In such polarization treatment using corona discharge (hereinafter also referred to as corona poling treatment for convenience), the corona electrode 30 may be moved by using a known rod-like moving means.
In the corona poling process, the method for moving the corona electrode 30 is not limited. That is, the corona electrode 30 may be fixed and a moving mechanism for moving the stacked body 10b may be provided, and the stacked body 10b may be moved to perform the polarization treatment. The laminate 10b may be moved by using a known sheet moving means.
Furthermore, the number of corona electrodes 30 is not limited to one, and a plurality of corona electrodes 30 may be used to perform corona poling treatment.
Further, the polarization process is not limited to the corona polling process, and normal electric field poling in which a direct current electric field is directly applied to a target to be polarized can also be used. However, when performing this normal electric field poling, it is necessary to form the thin film electrode 16 before the polarization treatment.
In addition, you may perform the calendar process which smoothes the surface of the piezoelectric material layer 12 using a heating roller etc. before this polarization process. By applying this calendar process, the thermocompression bonding process described later can be performed smoothly.

Thus, while performing the polarization process of the piezoelectric body layer 12 of the laminated body 10b, the sheet-like object 10c in which the thin film electrode 16 was formed on the protective layer 20 is prepared. The sheet-like material 10c may be produced by forming a copper thin film or the like as the thin film electrode 16 on the surface of the protective layer 20 by vacuum deposition, sputtering, plating, or the like.
Next, as shown in FIG. 2E, the thin film electrode 16 is directed to the piezoelectric layer 12, and the sheet-like material 10c is stacked on the stacked body 10b after the polarization treatment of the piezoelectric layer 12 is completed.
Further, the laminate of the laminate 10b and the sheet-like material 10c is subjected to thermocompression bonding with a heating press device, a heating roller pair or the like so as to sandwich the protective layer 20 and the protective layer 18, and as shown in FIG. A conversion film of the present invention is prepared.

Next, the electroacoustic transducer of the present invention using the conversion film 10 will be described.
FIG. 3B is a top view showing an example of the electroacoustic transducer of the present invention, and FIG. 3A is a cross-sectional view taken along the line aa in FIG.
An electroacoustic transducer 40 shown in FIGS. 3A and 3B is a flat plate type piezoelectric speaker using the above-described conversion film 10 of the present invention as a speaker diaphragm for converting an electric signal into vibration energy. is there.
In addition, the piezoelectric speaker 40 can also be used as a microphone or a sensor.

The illustrated piezoelectric speaker 40 basically includes a conversion film 10 (piezoelectric film), a case 42, a viscoelastic support 46, and a frame 48.
The case 42 is a thin square tube-shaped housing that is made of plastic or the like and that is open on one side. In the piezoelectric speaker using the conversion film of the present invention, the case 42 (that is, the piezoelectric speaker) is not limited to a square tube shape, and various cases such as a cylindrical shape or a rectangular tube shape having a rectangular bottom surface. Is available.
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 42.
Furthermore, the viscoelastic support 46 has an appropriate viscosity and elasticity, supports the conversion film 10, and gives a constant mechanical bias everywhere on the conversion film, so that the expansion and contraction motion of the conversion film is not wasted. This is to convert the movement back and forth (movement in a direction perpendicular to the film surface). Examples include nonwoven fabrics such as wool felt, wool felt including rayon and PET, foamed materials (foamed plastics) such as glass wool or polyurethane, a laminate of a plurality of papers, paints, and the like.
In the illustrated example, the viscoelastic support 46 has a quadrangular prism shape having a bottom surface slightly larger than the bottom surface of the case 42.
The specific gravity of the viscoelastic support 46 is not particularly limited, and may be appropriately selected according to the type of the viscoelastic support. As an example, in the case of using a felt as a viscoelastic support, the specific gravity is preferably ^{50~500kg / m 3, 100~300kg / m} 3 and more preferably. Moreover, when glass wool is used as the viscoelastic support, the specific gravity is preferably 10 to 100 kg / m ³ .

In the piezoelectric speaker 40, the viscoelastic support 46 is accommodated in the case 42, the case 42 and the viscoelastic support 46 are covered with the conversion film 10, and the periphery of the conversion film 10 is surrounded by the frame 48. The frame 48 is fixed to the case 42 while being pressed against the upper end surface.
The method for fixing the frame body to the case 42 is not particularly limited, and various known methods such as a method using screws and bolts and nuts and a method using a fixing jig can be used.

Here, in the piezoelectric speaker 40, the viscoelastic support 46 has a quadrangular prism shape whose height (thickness) is thicker than the height of the inner surface of the case 42. That is, as schematically shown in FIG. 3C, the viscoelastic support 46 is in a state of protruding from the upper surface of the case 42 before the conversion film 10 and the frame 48 are fixed. Yes.
Therefore, in the piezoelectric speaker 40, the closer to the peripheral portion of the viscoelastic support body 46, the lower the viscoelastic support body 46 is pressed by the conversion film 10 and the thickness is reduced. That is, the main surface of the conversion film 10 is held in a curved state.
In this case, it is preferable to press the entire surface of the viscoelastic support 46 in the surface direction of the conversion film 10 so that the thickness of the entire surface becomes thin. That is, it is preferable that the entire surface of the conversion film 10 is pressed and supported by the viscoelastic support 46.

In addition, in the piezoelectric speaker 40 using the conversion film 10 of the present invention, the pressing force of the viscoelastic support 46 by the conversion film 10 is not particularly limited, but is 0.02 to 0 as the surface pressure at a position where the surface pressure is low. About 2 MPa is preferable.
Although there is no particular limitation on the height difference of the conversion film 10 incorporated in the piezoelectric speaker 40, in the illustrated example, there is no particular limitation on the distance between the position closest to the bottom surface of the frame body 48 and the position farthest from the bottom. The conversion film 10 is preferably 1 to 50 mm, particularly preferably about 5 to 20 mm, from the standpoint that a sufficient vertical movement of the conversion film 10 becomes possible.
In addition, the thickness of the viscoelastic support 46 is not particularly limited, but the thickness before being pressed is preferably 1 to 100 mm, particularly preferably 10 to 50 mm.

In such a piezoelectric speaker 40, when the conversion film 10 expands in the in-plane direction by applying a voltage to the piezoelectric layer 12, the conversion film 10 is upward (radiation direction of sound) to absorb this extension. Move to.
Conversely, when the conversion film 10 contracts in the in-plane direction by applying a voltage to the piezoelectric layer 12, the conversion film 10 moves downward (case 42 side) to absorb this contraction.
The piezoelectric speaker 40 generates sound by vibration caused by repeated expansion and contraction of the conversion film 10.

  In the piezoelectric speaker 40, the viscoelastic support 46 is compressed in the thickness direction as it approaches the frame body 48, but mechanical bias is applied everywhere on the conversion film 10 due to the static viscoelastic effect (stress relaxation). Can be kept constant. Thereby, since the expansion / contraction motion of the conversion film 10 is converted into the front-back motion without waste, the flat piezoelectric speaker 40 having a thin and sufficient sound volume and excellent acoustic characteristics can be obtained.

Here, in the illustrated piezoelectric speaker 40, the entire periphery of the conversion film 10 is pressed against the case 42 (that is, the viscoelastic support 46) by the frame 48, but the present invention is not limited to this.
That is, the electroacoustic transducer using the conversion film 10 of the present invention does not have the frame body 48, and the conversion film 10 is formed by screws, bolts and nuts, jigs, etc. at four corners of the case 42, for example. A configuration formed by pressing / fixing to the upper surface of the case 42 can also be used.
Further, an O-ring or the like may be interposed between the case 42 and the conversion film 10. By having such a configuration, a damper effect can be provided, vibrations of the conversion film 10 can be prevented from being transmitted to the case 42, and more excellent acoustic characteristics can be obtained.

In addition, the electroacoustic transducer using the conversion film 10 may include a support plate on which the viscoelastic support 46 is placed instead of the case 42 that houses the viscoelastic support 46.
In other words, the viscoelastic support 46 is placed on a rigid support plate, the viscoelastic support 46 is covered, the conversion film 10 is placed thereon, and the same frame 48 is placed on the periphery of the conversion film 10. It is also possible to use a configuration in which the conversion film 10 is curved by pressing the viscoelastic support 46 with the conversion film 10 together with the frame 48 by fixing the frame 48 to the support plate with screws or the like. It is.
Further, even in the configuration without the case 42, the conversion film 10 may be held in a state where the viscoelastic support 46 is pressed and thinned with a screw or the like without using the frame 48.
In addition, it is good also as a structure which further amplifies the vibration of the conversion film 10 by using various diaphragms, such as a polystyrene, foaming PET, or a carbon fiber, as a material of a support plate.

Furthermore, the electroacoustic transducer using the conversion film 10 is not limited to a configuration that presses the periphery. For example, a portion other than the periphery of the laminate of the viscoelastic support 46 and the conversion film 10 may be removed by some means. The structure formed by pressing and holding at least a part of the conversion film 10 in a curved state can also be used.
Or it is good also as a structure which affixes the tension | tensile_strength by sticking the resin film to the conversion film 10, and hold | maintains. It can be set as the structure hold | maintained with a resin film, and it can be set as a flexible speaker by enabling it to hold | maintain in the curved state.
Or it is good also as a structure which raised the conversion film 10 to the curved frame.

In addition, the electroacoustic transducer of the present invention is not limited to the configuration using the viscoelastic support 46.
For example, as the case, an object having the same shape as the case 42 and having airtightness is used, the open end of the case is covered and closed with the conversion film 10, gas is introduced into the case, and pressure is applied to the conversion film 10. Alternatively, the structure may be held in a bulged state.

In addition, in the structure which applies a pressure inside, there exists a possibility that a distortion component may increase under the influence of an air spring and sound quality may fall. On the other hand, in the case of a configuration in which the conversion film 10 is supported by a viscoelastic support such as glass wool or felt, viscosity is imparted, which is preferable without increasing the distortion component.
The case may be filled with a gas other than gas, and a magnetic fluid or paint can be used as long as an appropriate viscosity can be imparted.
Moreover, you may combine the structure which utilizes a viscoelastic support body, and the structure which applies a pressure inside.

The electroacoustic conversion film and electroacoustic transducer of the present invention can be suitably used as a speaker in combination with a flexible display such as an organic EL display. In addition, since the electroacoustic conversion film and the electroacoustic transducer of the present invention are thin, they can be suitably combined with thin display devices such as liquid crystal display devices, electronic paper, and projector screens.
With such a configuration, the design and entertainment of the conversion film can be improved. Further, by integrating the conversion film as a speaker with a screen or a display, sound can be reproduced from the direction in which the image is displayed, and the sense of reality can be improved.
Further, since the projector screen is flexible, it can have a curvature. By giving the curvature to the image display surface, the distance from the observer to the screen can be made substantially uniform at the center and the end of the screen, and the sense of reality can be improved.
In addition, when the curvature is given to the image display surface in this way, the projected image is distorted. Therefore, it is preferable to perform image processing on the image data to be projected so as to reduce distortion in accordance with the curvature of the image display surface.

In addition, as described above, the conversion film 10 of the present invention has the performance that the piezoelectric layer 12 converts vibration energy into an electrical signal.
Therefore, the conversion film 10 of the present invention can be suitably used for a microphone or a sensor for a musical instrument (pickup) using this. For example, since the conversion film 10 of the present invention has flexibility, it can be attached to the throat of a person having a complicated curved surface, and acts as a vocal cord microphone simply by applying it near the vocal cords.

  The electroacoustic conversion film and the electroacoustic transducer of the present invention have been described in detail above. However, the present invention is not limited to the above-described examples, and various improvements and modifications are made without departing from the gist of the present invention. Of course, you may.

  Hereinafter, specific examples of the present invention will be given to explain the present invention in more detail.

[Example 1]
The conversion film 10 of the present invention shown in FIG. 1 was produced by the method shown in FIG.
First, cyanoethylated PVA (CR-V manufactured by Shin-Etsu Chemical Co., Ltd.) was dissolved in methyl ethyl ketone (MEK) at the following composition ratio. Thereafter, PZT particles were added to the solution at the following composition ratio and dispersed with a propeller mixer (rotation speed: 2000 rpm) to prepare a coating material for forming the piezoelectric layer 12.
・ PZT particles ・ ・ ・ ・ ・ ・ 300 parts by mass ・ Cyanoethylated PVA ・ ・ ・ ・ ・ ・ 30 parts by mass ・ MEK ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ 70 parts by mass The PZT particles used were obtained by sintering a commercially available PZT raw material powder at 1000 to 1200 ° C. and then crushing and classifying the PZT particles so as to have an average particle size of 5 μm.

On the other hand, sheet-like materials 10a and 10c were prepared by vacuum-depositing a 0.1 μm thick copper thin film on a 4 μm thick PET film. That is, in this example, the thin film electrodes 14 and 16 are 0.1 m thick copper vapor deposited thin films, and the protective layers 18 and 20 are 4 μm thick PET films.
On the thin film electrode 14 (copper-deposited thin film) of the sheet-like material 10a, a paint for forming the piezoelectric layer 12 prepared previously was applied using a slide coater. In addition, the coating material was apply | coated so that the film thickness of the coating film after drying might be set to 40 micrometers.
Next, a part of MEK was evaporated by heating and drying the sheet-like material 10a coated with a paint on a hot plate at 100 ° C. for 30 minutes. Thereby, the laminated body 10b which has the thin film electrode 14 made from copper on the protective layer 18 made from PET, and formed the piezoelectric material layer 12 (piezoelectric layer) with a thickness of 40 micrometers on it was produced.

  The piezoelectric layer 12 of the laminate 10b was subjected to polarization treatment by the above-described corona poling shown in FIGS. 2 (C) and 2 (D). The polarization treatment was performed by setting the temperature of the piezoelectric layer 12 to 100 ° C. and applying a DC voltage of 6 kV between the thin film electrode 14 and the corona electrode 30 to cause corona discharge.

A sheet-like material 10c was laminated on the laminated body 10b subjected to the polarization treatment with the thin film electrode 16 (copper thin film side) facing the piezoelectric body layer 12.
Subsequently, the laminated body of the laminated body 10b and the sheet-like material 10c is bonded by bonding the piezoelectric layer 12 and the thin film electrodes 14 and 16 by thermocompression bonding at 120 ° C. using a laminator device. Produced.

Here, MEK used as a solvent has an SP value (solubility parameter) of 9.3 (cal / cm ³ ) ^1/2 and is liquid at room temperature. That is, the SP value in Example 1 is less than 12.5 (cal / cm ³ ) ^1/2 and the substance that is liquid at room temperature is MEK.
A part of the sample of the piezoelectric layer 12 was cut into a 5 cm square from the produced conversion film 10, and the content of MEK (the above substance) was measured. For the measurement, a gas chromatograph apparatus (Agilent 7890A GC-System) was used, and the column was RESTEK Stabilwax 0.53 mmφ × 30 m film 1.0 μm. First, the sample was sealed in a vial, heated to 160 ° C. for 30 minutes, and then MEK was quantified. The sample was allowed to stand for 24 hours in an environment of a temperature of 50 ° C. and a humidity of 10% RH, and then the content of MEK (the above substance) was measured.
As a result of the measurement, the MEK content was 30 ppm.

[Examples 2 to 7]
A conversion film 10 was produced in the same manner as in Example 1 except that the drying conditions of the coated material to be the piezoelectric layer 12 were changed to the conditions shown in Table 1 below.

[Examples 8 to 9]
A conversion film 10 was produced in the same manner as in Example 1 except that the thickness of the piezoelectric layer 12 and the drying conditions were changed to the conditions shown in Table 1 below.

[Examples 10 to 14]
The solvent was changed to DMF (dimethylformamide SP value: 12.1 (cal / cm ³ ) ^1/2 ), and the thickness of the piezoelectric layer 12 and the drying conditions were changed to the conditions shown in Table 1 below, respectively. Produced a conversion film 10 in the same manner as in Example 1.

[Example 15]
A conversion film 10 was prepared in the same manner as in Example 1 except that the solvent was changed to cyclohexanone (SP value: 9.9 (cal / cm ³ ) ^1/2 ) and the drying conditions were changed to the conditions shown in Table 1 below. Produced.

[Example 16]
A conversion film 10 was prepared in the same manner as in Example 1 except that the solvent was changed to acetone (SP value: 9.9 (cal / cm ³ ) ^1/2 ) and the drying conditions were changed to the conditions shown in Table 1 below. Produced.

[Comparative Examples 1-2]
A conversion 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.

[Comparative Examples 3 to 4]
A conversion film was produced in the same manner as in Example 10 except that the drying conditions were changed to the conditions shown in Table 1 below.

[Comparative Examples 5-6]
A conversion film was produced in the same manner as in Example 15 except that the drying conditions were changed to the conditions shown in Table 1 below.

[Comparative Examples 7-8]
A conversion film was produced in the same manner as in Example 16 except that the drying conditions were changed to the conditions shown in Table 1 below.

[Comparative Example 9]
A conversion film in the same manner as in Example 1 except that the solvent was changed to furfuryl alcohol (SP value: 12.5 (cal / cm ³ ) ^1/2 ) and the drying conditions were changed to the conditions shown in Table 1 below. Was made.

[Comparative Example 10]
Conversion film in the same manner as in Example 1 except that the solvent was changed to MEK + ethylene glycol (SP value: 14.6 (cal / cm ³ ) ^1/2 ) and the drying conditions were changed to the conditions shown in Table 1 below. Was made.
Since ethylene glycol has a higher boiling point than MEK, only ethylene glycol remained in the piezoelectric layer after the paint was dried.

[Reference Example 1]
A conversion film was produced in the same manner as in Example 1 except that PVDF containing no piezoelectric particles was used as the piezoelectric layer and the drying conditions were changed to the conditions shown in Table 1 below.
The piezoelectric layer made of PVDF was formed in the same manner as in Example 1 except that a paint containing PVDF and MEK having the following composition ratio was prepared.
・ PVDF ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ 100 parts by mass ・ MEK ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ 300 parts by mass

[Reference Examples 2-3]
A conversion film was produced in the same manner as in Reference Example 1 except that the drying conditions were changed to the conditions shown in Table 1 below.

[Evaluation]
[Temperature cycle test]
First, the conversion efficiency and the withstand voltage of the produced conversion film were measured.
The conversion efficiency was evaluated by speaker performance by incorporating the produced conversion film into a piezoelectric speaker.
First, a circular specimen having a diameter of 150 mm was produced from the produced conversion film. The 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. Thereby, the conversion film was bent into a convex shape like a contact lens.
The sound pressure level-frequency characteristics of the thin piezoelectric speaker thus fabricated were measured by sine wave sweep measurement using a constant current power amplifier. Note that the measurement microphone was placed 10 cm above the center of the piezoelectric speaker.
The withstand voltage was an effective voltage when an AC voltage was applied to the conversion film and no sound was produced.

Next, a temperature cycle test was performed on the conversion film. The temperature cycle test was conducted according to JIS C60068-2-14. After heating at a temperature of 85 ° C. for 10 minutes, the plate was cooled at a temperature of −33 ° C. for 10 minutes. After repeating this heating and cooling 5 times, the conversion efficiency and the withstand voltage were measured in the same manner as described above.
The ratio of the conversion efficiency after heating and cooling (after the temperature cycle test) to the conversion efficiency immediately after production (before the temperature cycle test) was determined and evaluated as follows.
A: 95% or more.
B: 90% or more and less than 95%.
C: Less than 90%.

Similarly, the ratio of the withstand voltage after heating and cooling (after the temperature cycle test) to the withstand voltage immediately after production (before the temperature cycle test) was determined and evaluated as follows.
A: 90% or more.
B: 70% or more and less than 90%.
C: Less than 70%.

[Flexibility test under low humidity]
A 1 cm × 15 cm strip-shaped test piece was produced from the produced conversion film.
This is left for 6 hours in an environment with a humidity of 10% RH and a temperature of 25 ° C., and under this environment, a predetermined radius of curvature (r = 5 cm, r = 2.5 cm and r = 0.5 cm) is obtained. After being rounded and returning to the original state 10 times, electrical characteristics (capacitance and dielectric loss) and changes in appearance were examined.
When there was no change in the electrical characteristics and appearance, it was A, when there was no change in the electrical characteristics but a trace such as a crease remained, and when there was a change in the electrical characteristics, it was C.
Table 1 shows the results of the evaluation and the content of the solvent.

From Table 1, the polymer composite piezoelectric material contains an SP value of less than 12.5 (cal / cm ³ ) ^1/2 and a substance that is liquid at room temperature in a mass ratio of 20 ppm to 500 ppm. 1 to 16, compared with Comparative Examples 1 to 10, it can be seen that even if there is a drastic temperature change, there is little decrease in conversion efficiency and withstand voltage, and it is possible to suppress a decrease in flexibility even under low humidity. .
Moreover, it turns out that content of the said substance has preferable 100 ppm-400 ppm from the comparison with Examples 1-4 and Examples 5-7, and the comparison with Example 10 and Example 11. FIG.

In addition, it can be seen from Comparative Examples 1, 3, 5, and 7 that when the content of the substance is less than 20 ppm, the flexibility under low humidity is lowered. In addition, it can be seen from Comparative Examples 2, 4, 6, and 8 that when the content of the substance exceeds 500 ppm, the conversion efficiency and the withstand voltage decrease when there is a temperature change.
Further, from Comparative Examples 9 and 10, when a substance having an SP value of 12.5 (cal / cm ³ ) ^1/2 or more was contained, there was a temperature change even if the content was within the above range. It can be seen that the conversion efficiency and the withstand voltage are reduced.

From Reference Examples 1 to 3, a decrease in flexibility under low humidity, a decrease in conversion efficiency due to a temperature change, and a decrease in withstand voltage are obtained by dispersing a polymer particle in a matrix made of a polymer material. It turns out that it is a problem peculiar to a composite piezoelectric material.
From the above results, the effect of the present invention is clear.

DESCRIPTION OF SYMBOLS 10 Electroacoustic conversion film 12 Piezoelectric layer 14,16 Thin film electrode 18,20 Protective layer 24 Matrix 26 Piezoelectric particle 30 Corona electrode 32 DC power supply 40 Piezoelectric speaker 42 Case 46 Viscoelastic support body 48 Frame body

Claims (9)

Polymer composite piezoelectric material in which piezoelectric particles are dispersed in a matrix made of a polymer material, thin film electrodes formed on both surfaces of the polymer composite piezoelectric material, and protective layer formed on the surface of the thin film electrode And
The polymer composite piezoelectric material has an SP value 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 20 ppm to 500 ppm. Sound conversion film.   The electroacoustic conversion film according to claim 1, wherein the content of the substance is 100 ppm to 400 ppm.   The electroacoustic conversion film according to claim 1 or 2, wherein the matrix is a polymer material having viscoelasticity at room temperature.   The electroacoustic conversion film according to any one of claims 1 to 3, wherein the polymer composite piezoelectric material has a thickness of 5 to 100 µm.   The substance is methyl ethyl ketone, dimethylformamide, cyclohexanone, acetone, cyclohexane, acetonitrile, 1 propanol, 2 propanol, 2 methoxy alcohol, diacetone alcohol, dimethylacetamide, benzyl alcohol, n-hexane, toluene, o-xylene, ethyl acetate, The electroacoustic conversion film according to any one of claims 1 to 4, which is at least one selected from the group consisting of butyl acetate, diethyl ether, and tetrahydrofuran.   6. The maximum value at which a loss tangent Tan δ at a frequency of 1 Hz measured by dynamic viscoelasticity measurement of the polymer material is 0.5 or more exists in a temperature range of 0 to 50 ° C. 6. Electroacoustic conversion film.   The electroacoustic conversion film according to claim 1, wherein the polymer material has a cyanoethyl group.   The electroacoustic conversion film according to claim 1, wherein the polymer material is cyanoethylated polyvinyl alcohol.   The electroacoustic transducer which has the electroacoustic conversion film of any one of Claims 1-8, and the supporting member which supports the said electroacoustic conversion film.

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