JP5993772B2 - Electroacoustic conversion film, flexible display, vocal cord microphone and instrument sensor - Google Patents

Description

  The present invention relates to an electroacoustic conversion film used for an acoustic device such as a speaker or a microphone. Specifically, the electroacoustic conversion film is excellent in flexibility and acoustic characteristics, can output a stable sound even if deformed, and can realize a flexible speaker that can be suitably used for a flexible display, and the like, and The present invention relates to a flexible display, vocal cord microphone, and instrument sensor using the electroacoustic conversion film.

In recent years, research on flexible displays using flexible substrates such as plastics has been advanced.
As a substrate for such a flexible display, for example, Patent Document 1 discloses a flexible display substrate in which a gas barrier layer and a transparent conductive layer are laminated on a transparent plastic film.
A flexible display has superiority in lightness, thinness, flexibility, and the like as compared with a display using a conventional glass substrate, and can be provided on a curved surface such as a cylinder. In addition, since it can be rolled up and stored, it does not impair portability even on a large screen, and has attracted attention as a display device for posting advertisements, PDAs (personal digital assistants) and the like.

When such a flexible display is used as an image display device and a sound generation device that reproduces sound together with an image, such as a television receiver, a speaker that is an acoustic device for generating sound is required.
Here, as a conventional speaker shape, a so-called cone-shaped funnel shape, a spherical dome shape, or the like is common. However, if these speakers are incorporated in the flexible display described above, the lightness and flexibility that are the advantages of the flexible display may be impaired. Further, when a speaker is externally attached, carrying and the like are troublesome, and it is difficult to install the speaker on a curved wall, which may impair the beauty.

Under such circumstances, for example, Patent Document 2 discloses that a flexible piezoelectric film in the form of a sheet is employed as a speaker that can be integrated into a flexible display without impairing lightness and flexibility. Yes.
The piezoelectric film is a uniaxially stretched film of polyvinylidene fluoride (PVDF) that is polarized at a high voltage, and has a property of expanding and contracting in response to an applied voltage.

In order to employ a piezoelectric film as a speaker, it is necessary to convert expansion / contraction motion 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.
Incidentally, it is well known that the minimum resonance frequency f ₀ of the speaker diaphragm is given by the following equation. Here, s is the stiffness of the vibration system, and m is the mass.
At this time, since the mechanical stiffness s decreases as the degree of bending of the piezoelectric film, that is, the radius of curvature of the bending portion increases, the minimum resonance frequency f ₀ decreases. That is, the sound quality (volume and frequency characteristics) of the speaker changes depending on the curvature radius of the piezoelectric film.
In order to solve this problem, Patent Document 2 includes a sensor for measuring the degree of bending of the piezoelectric film, and corrects the amplitude by increasing / decreasing the amplitude by a predetermined amount according to the frequency band of the audio signal according to the degree of bending of the piezoelectric film. Enables stable sound output.

By the way, a flexible display with an integrated speaker made of piezoelectric film and rectangular in plan view is gripped in a loosely bent state like a newspaper or magazine for portable use, and the screen display is switched between portrait and landscape. In this case, it is preferable that the image display surface can be curved not only in the vertical direction but also in the horizontal direction.
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 lowest resonance frequency f ₀ changes with the change in curvature also increases.
As described above, due to the problems inherent in PVDF, it has been difficult for the sound quality correction means disclosed in Patent Document 2 described above to reproduce stable sound.

On the other hand, examples of the sheet-like flexible piezoelectric material having no in-plane anisotropy in piezoelectric characteristics include a polymer composite piezoelectric material in which piezoelectric ceramics are dispersed in a polymer matrix.
In the case of a polymer composite piezoelectric body, since the piezoelectric ceramic is hard but the polymer matrix is soft, energy may be absorbed before the vibration of the piezoelectric ceramic is transmitted to the whole. This is called mechanical vibration energy transmission efficiency. In order to improve this transmission efficiency, it is necessary to harden the polymer composite piezoelectric material. For this purpose, the piezoelectric ceramic is contained in the matrix in a volume fraction of at least 40. It is necessary to put ~ 50% or more.

For example, Non-Patent Document 1 discloses that a polymer composite piezoelectric material obtained by mixing a PZT ceramic powder, which is a piezoelectric material, with PVDF by solvent casting or hot kneading exhibits the flexibility of PVDF and the high piezoelectric properties of PZT ceramics. It is disclosed that both are compatible to some extent.
However, there is a mechanical disadvantage that if the proportion of PZT ceramic is increased in order to increase the piezoelectric characteristics, that is, the transmission efficiency, it becomes hard and brittle.

In order to solve this problem, for example, Non-Patent Document 2 discloses an attempt to maintain flexibility by adding fluororubber to PVDF.
This method has a certain effect in terms of flexibility. However, in general, rubber has a very low Young's modulus of 1 to 10 MPa, and therefore, the addition of rubber lowers the hardness of the polymer composite piezoelectric material, resulting in a decrease in vibration energy transmission efficiency.

  Thus, when a conventional polymer composite piezoelectric body is used as a diaphragm for a speaker, if it is intended to have flexibility, a decrease in energy efficiency is inevitable and sufficient performance as a speaker for a flexible display is exhibited. I couldn't.

JP 2000-338901 A JP 2008-294493 A

Toyoki Kitayama, 1986 Proceedings of the IEICE General Conference, 366 (1971) Seiichi Shirai, Hiroaki Nomura, Toshiro Oga, Takeshi Yamada, Nobuki Oguchi, IEICE Technical Report, 24, 15 (1980)

As mentioned above, it is preferable that the polymer composite piezoelectric material used as a speaker for a flexible display has 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 to 20 kHz, and the vibration plate (polymer composite piezoelectric material) 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.

(Iii) Moisture resistance The polymer material of the polymer composite piezoelectric material expands and contracts when it absorbs moisture. Therefore, in the case of a polymer material having high hygroscopicity, the performance may change due to environmental changes or changes with time. In general, a material having a higher relative dielectric constant tends to absorb moisture. Therefore, in consideration of ensuring good moisture resistance, the polymer material is required to have a low relative dielectric constant.

  In summary, the polymer composite piezoelectric material used as a speaker for a flexible display is required to behave hard to vibrations of 20 to 20 kHz and soft to 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. Further, the relative dielectric constant of the polymer material is required to be less than 10 at 25 ° C.

  The present invention was devised in view of the above-mentioned problems, and as a speaker that can be integrated into a flexible display without impairing lightness and flexibility, it has a large frequency dispersion in storage elastic modulus (E ′) near room temperature. Electroacoustic conversion film comprising a polymer composite piezoelectric material having a maximum loss tangent (Tanδ) and high moisture resistance, and a flexible display, vocal cord microphone, and musical instrument using the electroacoustic conversion film The purpose is to provide a sensor.

In order to solve this problem, the present inventors have focused on viscoelastic materials that have a large frequency dispersion in the storage elastic modulus E ′ near room temperature and at the same time have a maximum value in the loss tangent Tanδ and a low relative dielectric constant. Then, intensive studies were made to apply this to the matrix material.
As a result, it is hard for vibrations of 20 to 20 kHz, can behave softly for vibrations of several Hz or less, and has an appropriate loss tangent for vibrations of all frequencies of 20 kHz or less, The inventors have come up with the idea of an electroacoustic conversion film made of a polymer composite piezoelectric material having a relative dielectric constant of less than 10 at 25 ° C.

  That is, the electroacoustic conversion film of the present invention comprises a polymer composite piezoelectric material obtained by dispersing piezoelectric particles in a viscoelastic matrix made of a polymer material having viscoelasticity at room temperature, and both surfaces of the polymer composite piezoelectric material. And an electroacoustic conversion film, wherein the polymer material has a relative dielectric constant of less than 10 at 25 ° C.

  In such an electroacoustic conversion film of the present invention, the polymer material is one or more of polyvinyl acetate, polyvinylidene chloride coacrylonitrile, polystyrene-vinyl polyisoprene block copolymer, polyvinyl methyl ketone, and polybutyl methacrylate. Is preferred.

Moreover, it is preferable to have a protective layer for imparting mechanical strength to at least one surface of the thin film electrode.
Moreover, it is preferable that the glass transition temperature in the frequency of 1 Hz of a polymeric material is 0-50 degreeC.
In addition, it is preferable that the maximum value at which the loss tangent (Tan δ) at a frequency of 1 Hz measured by dynamic viscoelasticity measurement of the electroacoustic conversion film is 0.5 or more is in the temperature range of 0 to 50 ° C.

Moreover, it is preferable that the storage elastic modulus (E ') in the frequency of 1 Hz by the dynamic viscoelasticity measurement of an electroacoustic conversion film is 10-30 GPa at 0 degreeC, and 1-10 GPa at 50 degreeC.
Further, the product of the thickness of the electroacoustic conversion film and the storage elastic modulus (E ′) at a frequency of 1 Hz by dynamic viscoelasticity measurement is 1.0 × 10 ^{6 to} 2.0 × 10 ⁶ N / m at 0 ° C. It is preferably 1.0 × 10 ^{5 to} 1.0 × 10 ⁶ N / m at 50 ° C.
Further, in the master curve obtained from the dynamic viscoelasticity measurement of the electroacoustic conversion film, the loss tangent (Tanδ) at 25 ° C. and the frequency of 1 kHz is preferably 0.05 or more.
Further, it is preferable that the maximum value at which the 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.
Further, the storage elastic modulus (E ′) at a frequency of 1 Hz as measured by dynamic viscoelasticity measurement of the polymer material is preferably 100 MPa or more at 0 ° C. and 10 MPa or less at 50 ° C.

  Further, the volume fraction of the piezoelectric particles in the polymer composite piezoelectric material is preferably 50% or more.

The piezoelectric particles are preferably ceramic particles having a perovskite type or wurtzite type crystal structure.
The ceramic particles are preferably any of lead zirconate titanate, lead lanthanum zirconate titanate, barium titanate, zinc oxide, and a solid solution of barium titanate and bismuth ferrite.

Moreover, it is preferable that the thickness of the protective layer is not more than twice the thickness of the polymer composite piezoelectric material.
The product of the thickness of the thin film electrode and the Young's modulus is preferably less than the product of the thickness of the protective layer and the Young's modulus.
The protective layer is preferably formed of any one of polyethylene terephthalate, polypropylene, polystyrene, polycarbonate, polyphenylene sulfite, polymethyl methacrylate, polyetherimide, polyimide, polyethylene naphthalate, and cyclic olefin resin.
The thin film electrode is preferably formed of any one of copper, aluminum, gold, silver, platinum, and indium tin oxide.

Moreover, the flexible display of this invention provides the flexible display which attached the electroacoustic conversion film of this invention to the surface on the opposite side to the image display surface of a flexible display which has flexibility.
Moreover, the vocal cord microphone of the present invention provides a vocal cord microphone characterized by using the electroacoustic conversion film of the present invention as a sensor.
Furthermore, the musical instrument sensor of the present invention provides a musical instrument sensor characterized by using the electroacoustic conversion film of the present invention as a sensor.

In the present invention, a polymer composite piezoelectric material in which piezoelectric particles are dispersed in a viscoelastic matrix made of a polymer material having viscoelasticity at room temperature, and thin film electrodes formed on both surfaces of the polymer composite piezoelectric material, The electroacoustic conversion film characterized in that the dielectric constant of the polymer material is less than 10 at 25 ° C. has a large frequency dispersion in the elastic modulus and is resistant to vibrations of 20 to 20 kHz. Is hard, can behave softly for vibrations of several Hz or less, and has an appropriate loss tangent for vibrations of all frequencies of 20 kHz or less. Further, since the relative dielectric constant is low, the moisture resistance is excellent.
Therefore, according to the electroacoustic conversion film of the present invention, it is excellent in flexibility and acoustic characteristics, can output stable sound even when deformed, has excellent moisture resistance, and can be suitably used for a flexible display or the like. An electroacoustic conversion film capable of realizing a flexible speaker and the like, and a flexible speaker that can be integrated into a flexible display without impairing lightness and flexibility can be realized.
In addition, the flexible display of the present invention in which the electroacoustic conversion film of the present invention is attached to a flexible display (flexible image display device) is excellent in flexibility, Stable audio output can be performed regardless of the bending direction and the amount of bending depending on the state held by the hand and the place of use.
Furthermore, the vocal tract microphone and the musical instrument sensor of the present invention using the electroacoustic conversion film of the present invention as a sensor have excellent flexibility, a small and simple configuration, and a bending direction and a bending depending on the place of use. Regardless of the amount, it is possible to reproduce the sound of the real voice and musical instrument faithfully.

It is a conceptual diagram which shows an example of the electroacoustic conversion film of this invention. (A)-(E) are the conceptual diagrams which show an example of the manufacturing method of the electroacoustic conversion film shown in FIG. (A)-(C) are the conceptual diagrams for demonstrating an example of the piezoelectric speaker using the electroacoustic conversion film of this invention. It is a figure which shows notionally another example of the piezoelectric speaker using the electroacoustic conversion film of this invention. (A)-(C) are the conceptual diagrams for demonstrating another example of the piezoelectric speaker using the electroacoustic conversion film of this invention. BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows an example of the flexible display of this invention, (A) is an organic electroluminescent display, (B) is an electronic paper, (C) is a liquid crystal display. It is a figure which shows notionally the structure of the general vocal cord microphone.

  Hereinafter, the electroacoustic conversion film, the flexible display, the vocal cord microphone, and the musical instrument sensor of the present invention will be described in detail based on preferred embodiments shown in the accompanying drawings.

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 viscoelastic matrix 24 made of a polymer material having viscoelasticity at room temperature. Preferably, the piezoelectric layer 12 is polarized.
In this specification, “room temperature” refers to a temperature range of about 0 to 50 ° C.

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.
The present invention uses a polymer material having a glass transition point at room temperature in a polymer composite piezoelectric body (piezoelectric layer 12), in other words, a polymer material having viscoelasticity at room temperature, so that the matrix is 20 to 20 kHz. Thus, a polymer composite piezoelectric body that is hard to the vibration of 1 and softly to the slow vibration 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 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 loss tangent Tanδ at a frequency of 1 Hz in a dynamic viscoelasticity test at room temperature 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 by dynamic viscoelasticity measurement 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 material is bent slowly by an external force can be reduced, and at the same time, it can behave hard with respect to 20 to 20 kHz acoustic vibration.

The polymer material has a relative dielectric constant of less than 10 at 25 ° C.
In general, since water molecules have polarity, a polymer material having a high relative dielectric constant tends to attract moisture and absorb moisture. For this reason, the polymer material may expand or contract due to moisture absorption or deteriorate, and the performance as a piezoelectric speaker may change. Therefore, in order to prevent performance deterioration due to environmental changes and changes with time, in consideration of ensuring good moisture resistance, the polymer material is required to have a relative dielectric constant of less than 10 at 25 ° C.
In addition, there is an advantage that it is not necessary to form a protective layer for moisture resistance by using a polymer material having a low relative dielectric constant and high moisture resistance.

Examples of the polymer material satisfying such conditions include polyvinyl acetate, polyvinylidene chloride core acrylonitrile, polystyrene-vinyl polyisoprene block copolymer, polyvinyl methyl ketone, and polybutyl methacrylate. Moreover, as these polymer materials, commercially available products such as Hibler 5127 (manufactured by Kuraray Co., Ltd.) can also be suitably used.
In addition, these polymeric materials may use only 1 type, and may use multiple types together (mixed).

In the present invention, the viscoelastic matrix 24 is not limited to a single viscoelastic material such as polyvinyl acetate alone.
That is, for the purpose of adjusting dielectric properties and mechanical properties, other dielectric polymer materials may be added to the viscoelastic matrix 24 as needed in addition to viscoelastic materials such as polyvinyl acetate. .

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 in the viscoelastic matrix 24 of the piezoelectric layer 12 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 viscoelastic matrix 24 of the piezoelectric layer 12, the addition amount when adding a polymer other than the viscoelastic material is not particularly limited, but is preferably 30% by weight or less in the proportion of the viscoelastic matrix 24. .
Thereby, the characteristics of the polymer material to be added can be expressed without impairing the viscoelastic relaxation mechanism in the viscoelastic matrix 24, so that the dielectric constant is increased, the heat resistance is improved, the moisture resistance is improved, the piezoelectric particles 26 and the electrodes. Desirable results can be obtained in terms of improving adhesion to the layer.

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).

In the present invention, the particle size of the piezoelectric particles 26 is not particularly limited. However, according to the study of the present inventors, the particle diameter of the piezoelectric particles 26 is preferably 1 to 10 μm.
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 and the like, the piezoelectric particles 26 in the piezoelectric layer 12 are dispersed with regularity in the viscoelastic matrix 24, but the present invention is not limited to this.
That is, the piezoelectric particles 26 in the piezoelectric layer 12 may be irregularly dispersed in the viscoelastic matrix 24 as long as it is preferably dispersed uniformly.

In the conversion film 10 of the present invention, the quantity ratio between the viscoelastic matrix 24 and the piezoelectric particles 26 in the piezoelectric layer 12 (polymer composite piezoelectric material) is not particularly limited. That is, the quantity ratio between the viscoelastic matrix 24 and the piezoelectric particles 26 depends on the size (size in the surface direction) and thickness of the conversion film 10, the use of the conversion film 10, the characteristics required for the conversion film 10, and the like. And may be set as appropriate.
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 viscoelastic matrix 24 and the piezoelectric particles 26 within the above range, a favorable result can be obtained in that high piezoelectric characteristics and flexibility can be achieved.

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 inventor, the thickness of the piezoelectric layer 12 is preferably 20 to 200 μm, particularly preferably 30 to 100 μm.
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 viscoelastic matrix 24 and the piezoelectric particles 26 has a very good resistance to slow bending deformation. While exhibiting flexibility, 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 an electric field 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, as with the protective layers 18 and 20 described above, if the rigidity of the thin film electrodes 14 and 16 is too high, 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 includes the piezoelectric layer 12 (polymer composite piezoelectric body) obtained by dispersing the piezoelectric particles 26 in the viscoelastic matrix 24 having viscoelasticity at room temperature, the thin film electrode 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 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. 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 having viscoelasticity such as polyvinyl acetate (hereinafter also referred to as viscoelastic material) such as polyvinyl acetate is dissolved in an organic solvent, and piezoelectric particles 26 such as PZT particles are added and stirred. A paint is prepared which is dispersed. The organic solvent is not particularly limited, and various organic solvents such as dimethylformamide (DMF), methyl ethyl ketone, and cyclohexanone can be used.
When the sheet-like material 10a is prepared and the 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.

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.
Alternatively, if the viscoelastic material is a material that can be heated and melted, the viscoelastic material is heated and melted, and a melt obtained by adding / dispersing the piezoelectric particles 26 to the melted material is prepared. By extruding the sheet-like material shown in (A) into a sheet shape and cooling, the thin-film electrode 14 is provided on the protective layer 18 as shown in FIG. A laminate 10b formed by forming the piezoelectric layer 12 may be produced.

As described above, in the conversion film 10 of the present invention, a polymer piezoelectric material such as PVDF may be added to the viscoelastic matrix 24 in addition to a viscoelastic material such as polyvinyl acetate.
When these polymer piezoelectric materials are added to the viscoelastic matrix 24, the polymer piezoelectric material added to the paint may be dissolved. Alternatively, the polymer piezoelectric material to be added may be added to the heat-melted viscoelastic material and heat-melted.
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 FIGS. 2 (C) and 2 (D), a gap g can be opened, for example, by 1 mm on the upper surface 12a of the piezoelectric layer 12 of the multilayer body 10b, and the movable body can move along the upper surface 12a. A 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.

On the other hand, the sheet-like object 10c in which the thin film electrode 16 is formed on the protective layer 20 is prepared. The sheet-like material 10c is the same as the above-described sheet-like material 10a.
As shown in FIG. 2E, the sheet-like material 10c is laminated on the laminated body 10b in which the polarization treatment of the piezoelectric layer 12 is finished with the thin film electrode 16 facing the piezoelectric layer 12.
Further, the laminated body of the laminated body 10b and the sheet-like material 10c is subjected to thermocompression bonding using a heating press device, a heating roller pair or the like so as to sandwich the protective layers 18 and 20, as shown in FIG. The conversion film 10 of the present invention is completed.

The conversion film 10 of the present invention may be manufactured using the cut sheet-like sheet material, but preferably roll-to-roll (hereinafter also referred to as RtoR). Is used.
As is well known, RtoR is a raw material that has been processed by performing various processes such as film formation and surface treatment while pulling out the raw material from a roll formed by winding a long raw material and transporting it in the longitudinal direction. Is a manufacturing method in which the material is wound into a roll again.

When the conversion film 10 is manufactured by the above-described manufacturing method using RtoR, a first roll formed by winding a sheet-like material 10a in which a thin film electrode 14 is formed on a long protective layer 18, and A second roll formed by winding a sheet-like material 10c on which a thin film electrode 16 is formed on a long protective layer 20 is used.
The first roll and the second roll may be exactly the same.

From the roll, the sheet-like material 10a is pulled out and conveyed in the longitudinal direction, and the coating material containing the viscoelastic matrix 24 and the piezoelectric particles 26 is applied and dried by heating or the like. A piezoelectric layer 12 is formed thereon to form the above-described laminated body 10b.
Next, the above-described corona poling is performed, and the piezoelectric layer 12 is polarized. Here, when the conversion film 10 is manufactured by RtoR, the rod-like corona electrode 30 is fixed by extending and fixing in the direction orthogonal to the conveyance direction of the laminate 10b while conveying the laminate 10b. Polarization processing of the piezoelectric layer 12 is performed. As described above, the calendar process may be performed before the polarization treatment.
Next, the sheet-like material 10c is pulled out from the second roll, and the sheet-like material 10c and the laminate are conveyed, and the thin-film electrode 16 is bonded to the piezoelectric layer by a known method using a bonding roller or the like as described above. The sheet-like object 10c is laminated on the laminated body 10b.
Thereafter, the protective layers 18 and 20 are sandwiched and conveyed by a pair of heating rollers to be thermocompression bonded to complete the conversion film 10 of the present invention, and the conversion film 10 is wound into a roll.

In the above example, the sheet-like material (laminated body) is conveyed only once in the longitudinal direction by RtoR to produce the conversion film 10 of the present invention. However, the present invention is not limited to this.
For example, after the laminate is formed and corona polling is performed, a laminate roll in which the laminate is wound once into a roll is obtained. Subsequently, the laminated body is pulled out from the laminated body roll and conveyed in the longitudinal direction, and as described above, the sheet-like material on which the thin film electrode 16 is formed on the protective layer 20 is laminated, thereby converting the conversion film 10. And the conversion film 10 may be wound into a roll.
Alternatively, the production by RtoR is not limited, and it may be produced by a single wafer type.

  FIGS. 3A and 3B are conceptual diagrams of an example of a flat plate type piezoelectric speaker using the conversion film 10 of the present invention. 3, (B) is a view as seen from the vibration direction (sound radiating direction) of the conversion film 10, and (A) is a view as seen from a direction orthogonal to (B). It is an aa sectional view taken on the line B).

The piezoelectric speaker 40 includes the piezoelectric layer 12, the thin film electrodes 14 and 16 provided on both surfaces of the piezoelectric layer 12, and the protective layers 18 and 20 provided on the surfaces of the thin film electrodes. This is a flat plate type piezoelectric speaker in which the conversion film 10 is used as a speaker diaphragm for converting an electric signal into vibration energy.
Note that both the piezoelectric speaker 40 (and a piezoelectric speaker 50 described later) can be used as a microphone or a sensor.

The illustrated piezoelectric speaker 40 basically includes the 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 vibrating body of the present invention, the case 42 (that is, the piezoelectric speaker) is not limited to a rectangular tube shape, and has various shapes such as a cylindrical shape and 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 anywhere on the piezoelectric film, so that the expansion and contraction motion of the conversion film can be avoided. 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 / cm 3, 100~300kg / cm} 3 is more preferable. When glass wool is used as the viscoelastic support, the specific gravity is preferably 20 to 100 kg / cm 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 viscoelastic support body 46 is held in a state where the viscoelastic support body 46 is pressed downward by the conversion film 10 and thinned at the peripheral portion of the viscoelastic support body 46. Similarly, the curvature of the conversion film 10 rapidly changes in the peripheral portion of the viscoelastic support 46, and the rising portion 40 a that decreases toward the periphery of the viscoelastic support 46 is formed in the conversion film 10. Further, the central region of the conversion film 10 is pressed by the quadrangular prism-like viscoelastic support 46 so as to be (substantially) planar.
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.

In addition, in the piezoelectric speaker 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 in terms of the surface pressure at the flat portion (flat portion). About 2 MPa is preferable.
The angle of the rising portion 40a (inclination angle with respect to the central plane portion (average inclination angle)) is not particularly limited, but is 10 to 90 ° in that the conversion film 10 can be sufficiently moved up and down. It is preferable to set the degree.
There is no particular limitation on the height difference of the conversion film 10 (in the illustrated example, the difference in distance between the lowest place and the farthest place on the bottom surface of the frame body 48), but there is no particular limitation. It is preferable that the thickness is about 1 to 10 mm in that sufficient vertical movement is possible.
In addition, the thickness of the viscoelastic support 46 is not particularly limited, but the thickness before pressing is preferably 1 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 rising portion 40a of the conversion film 10 rises in order to absorb this extension (see FIG. The angle is slightly changed to a direction in which the angle with respect to the surface direction of the conversion film 10 is close to 90 °. As a result, the conversion film 10 having a planar portion moves upward (in the sound emission direction).
Conversely, when the conversion film 10 contracts in the in-plane direction by applying a voltage to the piezoelectric layer 12, the rising portion 40 a of the conversion film 10 is tilted (in a direction close to a plane) in order to absorb this contraction. ) Slightly change the angle. As a result, the conversion film 10 having a planar portion moves downward.
The piezoelectric speaker 40 generates sound by the vibration of the conversion film 10.

  In the rising portion 40a of the conversion film 10, the viscoelastic support 46 is compressed in the thickness direction as it approaches the frame 48. However, due to the static viscoelastic effect (stress relaxation), the viscoelastic support 46 is placed anywhere in the piezoelectric film. The mechanical bias can be kept constant. As a result, the expansion and contraction motion of the piezoelectric film is converted into the back-and-forth motion without waste, so that a flat piezoelectric speaker having a thin and sufficient sound volume and excellent acoustic characteristics can be obtained.

The piezoelectric speaker 40 in the illustrated example presses the entire periphery of the conversion film 10 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 piezoelectric speaker using the conversion film 10 of the present invention does not have the frame body 48, and the conversion film 10 is framed by screws, bolts, nuts, jigs, etc. at four corners of the case 42, for example. A structure formed by pressing / fixing to the upper surface of 48 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 piezoelectric speaker using the conversion film 10 of the present invention may not have the case 42 that houses the viscoelastic support 46.
That is, in the cross-sectional view of the piezoelectric speaker 50 of FIG. 4, the viscoelastic support 46 is placed on the rigid support plate 52 and the viscoelastic support 46 is covered so as to conceptually show an example thereof. The conversion film 10 is placed, and the same frame 48 is placed on the periphery. Next, by fixing the frame body 48 to the support plate 52 with the screws 54, the viscoelastic support body 46 is pressed together with the frame body 48, the peripheral portion of the viscoelastic support body 46 is thinned, and the conversion film A configuration in which ten inclined portions are formed can also be used.
Even in such a configuration without the case 42, the viscoelastic support 46 may be pressed and thinned with a screw or the like without using the frame 48, and may be held.

Furthermore, the piezoelectric speaker using the conversion film 10 of the present invention is not limited to the configuration of pressing the periphery. For example, the center of the laminate of the viscoelastic support 46 and the conversion film 10 is pressed by some means. A configuration in which the viscoelastic support 46 is held in a thin state can also be used.
That is, the piezoelectric speaker using the conversion film 10 of the present invention maintains the state in which the viscoelastic support 46 is pressed by the conversion film 10 to reduce the thickness, and the pressing / holding causes the conversion film 10 to be thin. As long as the curvature of the film fluctuates rapidly and the rising portion 40a is formed on the conversion film 10, various configurations can 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. 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.

  The piezoelectric speaker shown in FIGS. 3 and 4 uses the viscoelastic support 46, but the piezoelectric speaker using the conversion film 10 of the present invention is not limited to this configuration.

For example, a piezoelectric speaker 56 shown in FIG.
First, as shown in FIG. 5A, the piezoelectric speaker 56 uses an airtight thing as a similar case 42 and is provided with a pipe 42 a for introducing air into the case 42.
An O-ring 57 is provided on the upper surface of the open end of the case 42, and the case 42 is covered with the conversion film 10 so as to close the open surface.

Next, as shown in FIG. 5B, a frame-shaped holding lid 58 having a substantially L-shaped cross section having an inner periphery substantially the same as the outer periphery of the case 42 is fitted to the outer periphery of the case 42. (The O-ring 57 is omitted in FIGS. 5B and 5C).
Thereby, the conversion film 10 is pressed and fixed to the case 42, and the inside of the case 42 is airtightly closed by the conversion film 10.

Further, as shown in FIG. 5C, air is introduced from the pipe 42a into the case 42 (closed space between the case 42 and the conversion film 10), and pressure is applied to the conversion film 10 to expand it into a convex shape. In this state, the piezoelectric speaker 56 is held.
There is no limitation on the pressure in the case 42, and it is sufficient if the conversion film 10 bulges outwardly so as to have an atmospheric pressure or higher.
The pipe 42a may be fixed or detachable. When removing the pipe 42a, it is natural that the attaching / detaching portion of the pipe is hermetically closed.

The flexible display of the present invention is a flexible sheet-like image display device using the above-described conversion film 10 (electroacoustic conversion film) of the present invention as a speaker.
Specifically, the back surface (image display surface) of a flexible sheet-like display device such as a flexible organic EL display device, a flexible liquid crystal display device, or flexible electronic paper. A speaker-mounted flexible display in which the conversion film 10 of the present invention is attached as a speaker to the surface opposite to the surface.
The flexible display of the present invention may be a color display or a monochrome display.

As described above, the conversion film 10 of the present invention is excellent in flexibility and flexibility, and has no in-plane anisotropy. Therefore, the conversion film 10 of the present invention has little change in sound quality regardless of which direction it is bent, and also has little change in sound quality with respect to the change in curvature.
Therefore, the speaker-mounted flexible display according to the present invention in which the vibration film 10 according to the present invention is attached to a flexible image display device is excellent in flexibility and is held in a hand. Regardless of the direction and amount of bending by (i.e., suitably corresponding to any deformation), it is possible to output sound with stable sound quality.

FIG. 6A conceptually shows an example in which the flexible display of the present invention is used for an organic EL (electroluminescence) display.
An organic EL display 60 shown in FIG. 6A is a speaker-mounted organic EL flexible display in which the conversion film 10 of the present invention is attached to the back surface of a flexible sheet-like organic EL display device 62. is there.

In the flexible display of the present invention, the method for attaching the conversion film 10 of the present invention to the back surface of a flexible sheet-like image display device such as the organic EL display device 62 is not limited. That is, all known methods for attaching (bonding) the sheet-like objects to face to face can be used.
As an example, a method of attaching with an adhesive, a method of attaching by thermal fusion, a method of using a double-sided tape, a method of using an adhesive tape, a plurality of stacked sheet-like materials such as a substantially C-shaped clamp, A method using a jig that holds the sheets by a side, a method that uses a jig that holds a plurality of stacked sheet-like objects such as rivets in a plane (excluding the image display surface), and protection from both sides of the laminated sheet-like objects Examples thereof include a method of sandwiching with a film (transparent at least on the image display side), a method of using these together, and the like.
In addition, when the display device and the conversion film 10 are pasted using an adhesive or the like, the four corners and the central portion, etc. are appropriately set, whether they are stuck all over or only the entire periphery of the end portion. These may be pasted in the form of dots at the locations where they are used, or they may be used in combination.

  In the organic EL display 60, the conversion film 10 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, a thin film electrode 16 provided on the other surface, and the thin film electrode 14. It is the (electroacoustic) conversion film 10 of the above-mentioned this invention comprised including the protective layer 18 provided in the surface of this, and the protective layer 20 provided in the surface of the thin film electrode 16. FIG.

On the other hand, the organic EL display device 62 is a known sheet-like organic EL display device (organic EL display panel) having flexibility.
That is, the organic EL display device 62 includes, for example, an anode 68 in which a pixel electrode having a switching circuit such as a TFT is formed on a substrate 64 such as a plastic film, and an organic EL material is formed on the anode 68. A light-emitting layer 70 to be used; a light-emitting layer 70 having a transparent cathode 72 made of ITO (indium tin oxide) or the like; and a cathode 72 having a transparent substrate 74 formed of a transparent plastic or the like. Configured.
Further, a hole injection layer or a hole transport layer may be provided between the anode 68 and the light emitting layer 70, and further, an electron transport layer or an electron injection is provided between the light emitting layer 70 and the cathode 72. You may have a layer. Furthermore, a protective film such as a gas barrier film may be provided on the transparent substrate 74.

In addition, although illustration is abbreviate | omitted, to the thin film electrode 14 and the thin film electrode 16 of the conversion film 10, the wiring for driving the conversion film 10, ie, a speaker, is connected. Furthermore, wiring for driving the organic EL display device 62 is connected to the anode 68 and the cathode 72.
The same applies to the electronic paper 78 and the liquid crystal display 94 described later.

FIG. 6B conceptually shows an example in which the flexible display of the present invention is used for electronic paper.
An electronic paper 78 shown in FIG. 6B is a speaker-mounted electronic paper in which the conversion film 10 of the present invention is attached to the back surface of a flexible sheet-like electronic paper device 80.

In the electronic paper 78, the conversion film 10 is the same as that described above.
On the other hand, the electronic paper device 80 is a known electronic paper having flexibility. That is, as an example, the electronic paper device 80 has a lower electrode 84 on which a pixel electrode having a switching circuit such as a TFT is formed on a substrate 82 such as a plastic film. A display layer 86 in which microcapsules 86a containing white and black pigments charged therein are arranged, a transparent upper electrode 90 made of ITO or the like on the display layer 86, and transparent on the upper electrode 90 And a transparent substrate 92 made of a plastic or the like.

Note that the example shown in FIG. 6B is an example in which the flexible display of the present invention is used for electrophoretic electronic paper using microcapsules, but the present invention is not limited to this.
In other words, the flexible display of the present invention includes an electrophoretic method that does not use microcapsules, an electrophoretic method, a chemical change method that uses an oxidation-reduction reaction, an electronic powder method, an electrowetting method, a liquid crystal method, and the like. Any known electronic paper can be used as long as it is a sheet having flexibility.

FIG. 6C conceptually shows an example in which the flexible display of the present invention is used for a liquid crystal display.
A liquid crystal display 94 shown in FIG. 6C is a speaker-mounted liquid crystal flexible display in which the conversion film 10 of the present invention is attached to the back surface of a flexible sheet-like liquid crystal display device 96.

In the liquid crystal display 94, the conversion film 10 is the same as that described above.
On the other hand, the liquid crystal display device 96 is a known sheet-like liquid crystal display device (liquid crystal display panel) having flexibility. That is, as an example, the liquid crystal display device 96 includes a flexible edge light type light guide plate 98 and a light source 100 that receives a backlight from an end portion of the light guide plate 98. For example, the liquid crystal display device 96 includes a polarizer 102 on a light guide plate 98, a transparent lower substrate 104 on the polarizer 102, and a switching circuit such as a TFT on the lower substrate 104. A transparent lower electrode 106 on which pixel electrodes are formed, a liquid crystal layer 108 on the lower electrode 106, a transparent upper electrode 110 made of ITO or the like on the liquid crystal layer 108, and an upper electrode A transparent upper substrate 112 is provided on 110, a polarizer 114 is provided on the upper substrate 112, and a protective film 116 is provided on the polarizer 114.

  Note that the flexible display of the present invention is not limited to an organic EL display, electronic paper, and liquid crystal display, and an image using various display devices as long as it is a flexible sheet-like display device (display panel). A display device is available.

It has a piezoelectric layer 12 in which piezoelectric particles are dispersed in a polymer matrix having viscoelasticity at room temperature, and a thin film electrode 14 and a thin film electrode 16 provided on the surface of the piezoelectric layer 12. In the conversion film 10 of the present invention having a dielectric constant of less than 10 at 25 ° C., the piezoelectric layer 12 also has a performance of converting vibration energy into an electric 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.
As an example, a vocal cord microphone is preferably exemplified.

FIG. 7 conceptually shows an example of a general vocal cord microphone.
As shown in FIG. 7, a conventional general vocal cord microphone 120 has a piezoelectric ceramic 126 such as PZT laminated on a metal plate 128 such as a brass plate, and an elastic cushion 130 is provided on the lower surface of the laminated body. The spring 132 is attached to the upper surface, supported in the case 124, and the signal lines 136 and 136 are drawn out from the case.

On the other hand, the vocal cord microphone of the present invention using the conversion film 10 of the present invention as a sensor for converting an audio signal into an electric signal is provided with, for example, an attaching means on the conversion film 10 and has a piezoelectric layer 12 (thin film). A vocal cord microphone can be configured with a simple configuration in which a signal line for extracting an electrical signal output from the electrode 14 and the thin film electrode 16) is provided.
In addition, the vocal cord microphone of the present invention having such a configuration functions as a vocal cord microphone by simply attaching the conversion film 10 to the vicinity of the vocal cord.

In addition, the conventional vocal cord microphone using the piezoelectric ceramic 126 and the metal plate 128 as shown in FIG. 7 has a very small loss tangent, so that the resonance is very strong and the frequency characteristics are undulating. Therefore, it tends to be a metallic tone.
On the other hand, as described above, the conversion film 10 of the present invention is excellent in flexibility and acoustic characteristics, and has little change in sound quality when deformed. Therefore, the conversion film 10 is affixed to the throat of a person having a complicated curved surface. Can be reproduced faithfully from low to high.
That is, according to the present invention, an ultra-lightweight and space-saving vocal cord microphone can be realized with a simple configuration that can output an audio signal very close to a real voice and does not give a feeling of wearing.

In the vocal cord microphone of the present invention, there are no particular limitations on the method for attaching the conversion film 10 to the vicinity of the vocal cords, and various known sheet-like material attaching methods can be used.
Further, instead of directly attaching the conversion film 10 to the vicinity of the vocal cords, the conversion film 10 may be accommodated in an extremely thin case or bag and attached to the vicinity of the vocal cords.

Further, the musical instrument sensor of the present invention using the conversion film 10 of the present invention as a sensor for converting an audio signal into an electric signal is provided with, for example, an attaching means on the conversion film 10 and the piezoelectric layer 12 (thin film electrode). 14 and the thin film electrode 16), the instrument sensor can be configured with a simple configuration simply by providing a signal line for taking out an electrical signal output from the thin film electrode 16).
In addition, the musical instrument sensor of the present invention having such a configuration functions as a pickup by simply attaching the conversion film 10 to the casing surface of the musical instrument.

Similar to the vocal cord microphone described above, the conversion film 10 of the present invention is thin and rich in flexibility. Therefore, the musical instrument sensor of the present invention is excellent in flexibility and acoustic characteristics and has little change in sound quality when deformed. Therefore, it can be attached to the casing surface of a musical instrument having a complicated curved surface, and the sound of the musical instrument can be faithfully reproduced from low to high.
Moreover, since the instrument sensor of the present invention has almost no mechanical restraint on the casing surface of the vibrating instrument, the influence on the original sound of the instrument by attaching the pickup can be minimized.

  Similar to the above vocal cord microphone, in the musical instrument sensor of the present invention, there are no particular limitations on the method for attaching the musical instrument, and various known sheet-like material attaching methods can be used. Moreover, the sensor for musical instruments of this invention may accommodate the conversion film 10 in a very thin case or bag body, and may affix it on a musical instrument.

  The electroacoustic conversion film, flexible display, vocal cord microphone, and instrument sensor of the present invention have been described in detail above, but the present invention is not limited to the above-described examples, Of course, improvements and changes may be made.

  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, polyvinyl acetate (manufactured by Aldrich) was dissolved in dimethylformamide (DMF) at the following composition ratio. Thereafter, the PZT particles after drying are added to this solution at the following composition ratio so that the volume fraction of the PZT particles becomes 60%, and dispersed with a propeller mixer (rotation speed 2000 rpm) to form the piezoelectric layer 12. A paint for was prepared.
・ PZT particles ・ ・ ・ ・ ・ ・ 200 parts by mass ・ Polyvinyl acetate ・ ・ ・ ・ ・ ・ 20 parts by mass ・ DMF ・ ・ ・ ・ ・ ・ 80 parts by mass Part PZT particles were obtained by sintering 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.
The glass transition temperature (Tg) of polyvinyl acetate is 30 ° C. The loss tangent Tanδ was measured by a dynamic viscoelasticity test and found to be 0.8 at 25 ° C. and 1 Hz.

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.
In addition, in order to obtain good handling during the process, a PET film with a 50 μm thick separator (temporary support PET) was used. After the thermocompression bonding of the thin film electrode and the protective layer, the separator of each protective layer was used. Removed.
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, the DMF was evaporated by heating and drying the product obtained by applying the paint on the sheet-like material 10a on a hot plate at 120 ° C. 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.

[Flexibility test]
A 1 cm × 15 cm strip-shaped test piece was produced from the produced conversion film 10.
This was rounded to a radius of curvature r = 0.5 cm and returned to the original state 10 times, and then the 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 marked as ◯, when there was no change in the electrical characteristics, but a mark such as a crease remained, and when there was a change in the electrical characteristics, it was marked as x.
The results are shown in Table 1.

[Relative permittivity measurement test]
A 2 cm × 4 cm strip-shaped test piece was produced from the produced conversion film 10.
The relative dielectric constant ε _r of this test piece was measured with an LCR meter. The measurement conditions are shown below.
Measurement temperature: 25 ° C
Measurement frequency: 1 kHz
The measurement results of the relative dielectric constant ε _r are shown in Table 1.

[Moisture resistance test]
A 2 cm × 4 cm strip-shaped test piece was produced from the produced conversion film 10.
This was left for 1 hour in an environment of 90% humidity and 50% temperature, and then the 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 marked as ◯, when there was no change in the electrical characteristics, but a mark such as a crease remained, and when there was a change in the electrical characteristics, it was marked as x.
The results are shown in Table 1.

[Example 2]
A conversion film 10 was produced in the same manner as in Example 1 except that a polystyrene-vinyl polyisoprene block copolymer (Hibler 5127, manufactured by Kuraray Co., Ltd.) was used as the viscoelastic matrix 24 and toluene was used as the solvent. Thereafter, the PZT particles are added to this solution at the following composition ratio so that the volume fraction of the dried PZT particles is 60%, and dispersed with a propeller mixer (rotation speed: 2000 rpm). A paint was prepared to form
・ PZT particles ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ 300 parts by weight ・ Hibler 5127 ・ ・ ・ ・ ・ ・ ・ ・ ・ 30 parts by weight ・ Toluene ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ 70 parts by weight Polystyrene -The glass transition temperature (Tg) of a vinyl polyisoprene block copolymer is 25 degreeC. The loss tangent Tanδ was measured and found to be 1.2 at 25 ° C. and 1 Hz.
The produced conversion film 10 was subjected to a flexibility test, a relative dielectric constant measurement test, and a moisture resistance test in the same manner as in Example 1.
The results are shown in Table 1.

[Example 3]
Example 2 except that as the viscoelastic matrix 24, a polystyrene-vinyl polyisoprene block copolymer (Hibler 5127 made by Kuraray Co., Ltd.) and polybutene (made by Kuraray Co., Ltd.) were mixed at a ratio of 70:30. Similarly to the above, conversion film 10 was prepared using toluene as a solvent so that the volume fraction of PZT particles after drying was 60%.
The glass transition temperature (Tg) of the mixture of polystyrene-vinyl polyisoprene block copolymer and polybutene is 10 ° C. The loss tangent Tanδ was measured and found to be 1.8 at 25 ° C. and 1 Hz.
The produced conversion film 10 was subjected to a flexibility test, a relative dielectric constant measurement test, and a moisture resistance test in the same manner as in Example 1.
The results are shown in Table 1.

[Example 4]
Except for using polyvinyl methyl ketone (manufactured by Aldrich) as the viscoelastic matrix 24, a conversion film was used so that the volume fraction of PZT particles after drying using DMF as a solvent was 60% as in Example 1. 10 was produced.
The glass transition temperature (Tg) of polyvinyl methyl ketone is 28 ° C. The loss tangent Tanδ was measured and found to be 0.9 at 25 ° C. and 1 Hz.
The produced conversion film 10 was subjected to a flexibility test, a relative dielectric constant measurement test, and a moisture resistance test in the same manner as in Example 1.
The results are shown in Table 1.

[Example 5]
Except that polybutyl methacrylate (Aldrich) was used as the viscoelastic matrix 24, a conversion film was used so that the volume fraction of PZT particles after drying using DMF as a solvent was 60% as in Example 1. 10 was produced.
The glass transition temperature (Tg) of polybutyl methacrylate is 35 ° C. The loss tangent Tanδ was measured and found to be 0.6 at 25 ° C. and 1 Hz.
The produced conversion film 10 was subjected to a flexibility test, a relative dielectric constant measurement test, and a moisture resistance test in the same manner as in Example 1.
The results are shown in Table 1.

[Comparative Example 1]
The volume fraction of PZT particles after drying using DMF as a solvent in the same manner as in Example 1 except that polyethyl methacrylate (made by Aldrich) having no viscoelasticity at room temperature was used as the viscoelastic matrix 24. The conversion film 10 was produced so that it might become 60%.
The glass transition temperature (Tg) of polyurethane is 65 ° C. Further, the loss tangent Tanδ was measured and found to be 0.6 at 25 ° C. and 1 Hz.
The produced conversion film 10 was subjected to a flexibility test, a relative dielectric constant measurement test, and a moisture resistance test in the same manner as in Example 1.
The results are shown in Table 1.

[Comparative Example 2]
The volume fraction of PZT particles after drying using DMF as a solvent in the same manner as in Example 1 except that cyanoethylated pullulan (manufactured by Shin-Etsu Chemical Co., Ltd.) having no viscoelasticity at room temperature was used as the viscoelastic matrix 24. The conversion film 10 was produced so that the rate might be 60%.
The glass transition temperature (Tg) of cyanoethylated pullulan is 120 ° C. The loss tangent Tan δ was measured and found to be 0.06 at 25 ° C. and 1 Hz.
The produced conversion film 10 was subjected to a flexibility test, a relative dielectric constant measurement test, and a moisture resistance test in the same manner as in Example 1.
The results are shown in Table 1.

From Table 1, Examples 1-5 which used the polymeric material which has viscoelasticity at normal temperature for a matrix are very excellent compared with the comparative examples 1 and 2 which used the polymeric material which does not have viscoelasticity for a matrix. It can be seen that it has flexibility.
Further, Examples 1 to 5 using a polymer material having a relative dielectric constant of less than 10 as a matrix have superior moisture resistance compared to Comparative Example 2 using a polymer material having a relative dielectric constant of 10 or more as a matrix. You can see that
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 Viscoelastic matrix 26 Piezoelectric particle 30 Corona electrode 32 DC power supply 40,50,56 Piezoelectric speaker 42 Case 46 Viscoelastic support body 48 Frame body 52 Support plate 54 Screw 57 O-ring 58 Holding lid 60 Organic EL display 62 Organic EL display device 64, 82, 104 Substrate 68 Anode 70 Light emitting layer 72 Cathode 74, 92 Transparent substrate 84, 106 Lower electrode 86 Display layer 86a Microcapsule 90 , 110 Upper electrode 98 Light guide plate 100 Light source 102, 114 Polarizer 108 Liquid crystal layer 112 Upper substrate 116 Protective film

Claims (19)

A polymer composite piezoelectric material in which piezoelectric particles are dispersed in a viscoelastic matrix made of a polymer material having viscoelasticity at room temperature, and thin film electrodes formed on both surfaces of the polymer composite piezoelectric material. ,
Ri der less than 10 relative permittivity at 25 ° C. of the polymer material,
Electroacoustic conversion film maxima loss tangent at the frequency 1 Hz (Tan?) Of 0.5 or more by dynamic viscoelasticity measurement is characterized that you present in a temperature range of 0 to 50 ° C..   The electroacoustic conversion according to claim 1, wherein the polymer material is one or more of polyvinyl acetate, polyvinylidene chloride coacrylonitrile, polystyrene-vinyl polyisoprene block copolymer, polyvinyl methyl ketone, and polybutyl methacrylate. the film.   The electroacoustic conversion film according to claim 1, further comprising a protective layer for imparting mechanical strength to at least one surface of the thin film electrode.   The electroacoustic conversion film according to claim 1, wherein the polymer material has a glass transition temperature of 0 to 50 ° C. at a frequency of 1 Hz. Storage modulus at frequency 1Hz by dynamic viscoelasticity measurement of the electroacoustic conversion film (E ') is, 10～30GPa at 0 ° C., any one of claims 1 to 4, which is a 1~10GPa at 50 ° C. The electroacoustic conversion film according to 1. The product of the thickness of the electroacoustic conversion film and the storage elastic modulus (E ′) at a frequency of 1 Hz by dynamic viscoelasticity measurement is 1.0 × 10 ^{6 to} 2.0 × 10 ⁶ N / m at 0 ° C. It is 1.0 * 10 < ⁵ > -1.0 * 10 < ⁶ > N / m in 50 degreeC, The electroacoustic conversion film of any one of Claims 1-5 . In master curve obtained from the dynamic viscoelasticity measurement of the electro-acoustic conversion film, 25 ° C., according to any one of claims 1-6 loss tangent at the frequency 1 kHz (Tan?) Is 0.05 or more Electroacoustic conversion film. Any one of claim 1 to 7, the maximum value the loss tangent at the frequency 1 Hz (Tan?) Of 0.5 or more by dynamic viscoelasticity measurement of the polymeric material is present in a temperature range of 0 to 50 ° C. The electroacoustic conversion film according to 1. Storage modulus at frequency 1Hz by dynamic viscoelasticity measurement of the polymeric material (E '), 0 ℃ 100MPa or more at, according to any one of claims 1-8 is 10MPa or less at 50 ° C. Electroacoustic conversion film. The electroacoustic conversion film according to any one of claims 1 to 9 , wherein a volume fraction of piezoelectric particles in the polymer composite piezoelectric body is 50% or more. The piezoelectric particles, electro-acoustic conversion film according to any one of claims 1 to 10 which is a ceramic particle having a perovskite or a wurtzite-type crystal structure. The electroacoustic according to claim 11 , wherein the ceramic particles are any one of lead zirconate titanate, lead lanthanum zirconate titanate, barium titanate, zinc oxide, and a solid solution of barium titanate and bismuth ferrite. Conversion film. The electroacoustic conversion film according to any one of claims 3 to 12 , wherein a thickness of the protective layer is not more than twice a thickness of the polymer composite piezoelectric body. The product of the thickness and Young's modulus of the thin-film electrode, the electro-acoustic conversion film according to any one of claims 1 to 13, below the product of the thickness and Young's modulus of the protective layer. The protective layer is a polyethylene terephthalate, polypropylene, polystyrene, polycarbonate, polyphenylene sulfide, polymethyl methacrylate, polyether imide, polyimide, polyethylene naphthalate, and claims 3-14, which is formed by either of the cyclic olefin-based resin The electroacoustic conversion film of any one of these. Wherein the thin film electrode, copper, aluminum, gold, silver, platinum, and electro-acoustic conversion film according to any one of claims 1 to 15, which is formed by any of indium tin oxide. A flexible display comprising the electroacoustic conversion film according to any one of claims 1 to 16 attached to a surface opposite to an image display surface of a flexible display having flexibility. A vocal fold microphone using the electroacoustic conversion film according to any one of claims 1 to 16 as a sensor. Musical instrument sensor which comprises using as a sensor electroacoustic conversion film according to any one of claims 1-16.