JP6505845B2 - Electro-acoustic conversion film - Google Patents

Description

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

  In response to the reduction in thickness and weight of displays such as liquid crystal displays and organic EL (Electro Luminescence) displays, weight reduction and thickness reduction are also required for speakers used for these thin displays. In addition, in response to the development of a flexible display using a flexible substrate such as plastic, flexibility is also required for a speaker used therein.

  The shape of a conventional speaker is generally a funnel-shaped so-called cone shape, a spherical dome shape or the like. However, when such a speaker is to be incorporated into the above-described thin display, it can not be made sufficiently thin, and there is a possibility that the lightness and flexibility may be impaired. In addition, when the speaker is externally attached, carrying and the like is troublesome.

  Therefore, as a thin speaker that can be integrated with a thin display or flexible display without losing its lightness and flexibility, it has sheet-like flexibility and has the property of expanding and contracting in response to an applied voltage. It has been proposed to use a piezoelectric film.

  For example, the applicant of the present application proposes the electroacoustic transducing film disclosed in Patent Document 1 as a piezoelectric film which is sheet-like, flexible, and capable of stably reproducing high-quality sound. did. The electroacoustic conversion film disclosed in Patent Document 1 comprises a polymer composite piezoelectric body (piezoelectric body layer) formed by dispersing piezoelectric body particles in a viscoelastic matrix made of a polymer material having viscoelasticity at normal temperature. It has a thin film electrode formed on both sides of a molecular composite piezoelectric material and a protective layer formed on the surface of the thin film electrode.

JP, 2014-14063, A

With such a piezoelectric film, it is required to further enhance the sound pressure level by increasing the conversion efficiency between electricity and sound, and to reduce the unevenness of the peak and dip in the sound pressure level in the frequency characteristic and to broaden the band . In general, in a piezoelectric body, the conversion efficiency between electricity and pressure depends on the dielectric constant of the piezoelectric body, and the conversion efficiency improves as the dielectric constant increases.
Patent Document 1 discloses increasing the dielectric constant by adding a dielectric polymer material to a visco-elastic matrix, but to improve conversion efficiency and to broaden the bandwidth, it is disclosed that It has not been sufficiently studied whether to add a polymer material.

  The object of the invention is to solve the problems of the prior art as described above, and it is possible to improve the sound pressure level by increasing the conversion efficiency of electricity and sound, and to peak or dip the sound pressure level in the frequency characteristic. An object of the present invention is to provide an electroacoustic transducing film which has less unevenness and can be broadened in bandwidth.

As a result of intensive studies to solve the above problems, the inventors of the present invention have found that a polymer composite piezoelectric formed by dispersing piezoelectric particles in a viscoelastic matrix having a polymeric material having a cyanoethyl group exhibiting viscoelasticity at normal temperature. And two thin film electrodes laminated on both sides of the polymer composite piezoelectric material and two protective layers laminated respectively on the two thin film electrodes, and the viscoelastic matrix has a relative dielectric constant of 10 or more The inventors have found that the above-mentioned problems can be solved by containing an additive polymer material which is a polymer material of the present invention, and the present invention has been completed.
That is, the present invention provides an electroacoustic transducing film having the following configuration.

(1) A polymer composite piezoelectric body formed by dispersing piezoelectric particles in a viscoelastic matrix containing a polymeric material having a cyanoethyl group exhibiting viscoelasticity at normal temperature.
Two thin film electrodes stacked on both sides of the polymer composite piezoelectric material,
And two protective layers respectively stacked on two thin film electrodes,
The viscoelastic matrix contains an additive polymer material which is a polymer material having a dielectric constant of 10 or more and dielectric particles having a dielectric constant of 80 or more ,
A volume fraction of dielectric particles is 5 to 45% with respect to the total volume of a viscoelastic matrix and dielectric particles .
(2) The electroacoustic transducer film according to (1), wherein the loss tangent at 25 ° C. and 20 Hz of the added polymer material is 0.05 or less.
(3) The electroacoustic transducer film according to (1) or (2), wherein the volume resistance of the added polymer material is 1 × 10 ¹² Ω · cm or more.
(4) The electroacoustic conversion film according to any one of (1) to (3), wherein the proportion of the added polymer material in the viscoelastic matrix is 60% by mass or less.
(5) The electroacoustic transducer film according to any one of (1) to (4), wherein the proportion of the added polymer material in the viscoelastic matrix is 10% by mass to 30% by mass.
(6) The electroacoustic conversion film according to any one of (1) to (5), wherein the polymer material having a cyanoethyl group is cyanoethylated polyvinyl alcohol.
(7) The electroacoustic transducer film according to any one of (1) to (6), wherein the additive polymer material is cyanoethyl pullulan.
(8) The electroacoustic conversion film according to any one of (1) to (7), wherein the average particle diameter of the dielectric particles is 0.5 μm or less.

  According to the present invention, it is possible to improve the sound pressure level by increasing the conversion efficiency of electricity and sound, and to increase the sound pressure level in the frequency characteristic, thereby reducing the unevenness of the peak and dip in the sound pressure level and broadening the band. Can be provided.

It is sectional drawing which shows notionally an example of the electroacoustic transducing film of this invention. It is a conceptual diagram for demonstrating an example of the preparation methods of an electroacoustic transducer film. It is a conceptual diagram for demonstrating an example of the preparation methods of an electroacoustic transducer film. It is a conceptual diagram for demonstrating an example of the preparation methods of an electroacoustic transducer film. It is a conceptual diagram for demonstrating an example of the preparation methods of an electroacoustic transducer film. It is a conceptual diagram for demonstrating an example of the preparation methods of an electroacoustic transducer film. It is a top view which represents typically an example of an electroacoustic transducer using the electroacoustic conversion film of this invention. It is the BB sectional drawing of FIG. 3A. It is sectional drawing for demonstrating another example of an electroacoustic transducer. It is sectional drawing for demonstrating another example of an electroacoustic transducer. It is sectional drawing for demonstrating another example of an electroacoustic transducer. It is sectional drawing which shows another example of an electroacoustic transducer.

Hereinafter, the electroacoustic conversion film of the present invention will be described in detail based on the preferred embodiments shown in the attached drawings.
Although the description of the configuration requirements described below may be made based on the representative embodiments of the present invention, the present invention is not limited to such embodiments.
In addition, in this specification, the numerical range represented using "-" means the range which includes the numerical value described before and after "-" as a lower limit and an upper limit.

FIG. 1 is a cross-sectional view schematically showing an example of the electroacoustic transducer film of the present invention.
Such an electroacoustic transducing film is used as a diaphragm of an electroacoustic transducer, as described later.
In the electroacoustic transducer, when the electroacoustic transducing film is stretched in the in-plane direction by voltage application to the electroacoustic transducer film, the electroacoustic transducing film is above (sound radiation direction) to absorb the stretched portion. When the electroacoustic transducing film is contracted in the in-plane direction by voltage application to the electroacoustic transducing film, the electroacoustic transducing film is directed downward (case side) to absorb the contraction. Moving. The electroacoustic transducer converts vibration (sound) and an electrical signal by vibration due to the repetition of expansion and contraction of the electroacoustic transducer film.
Such electroacoustic transducers are used as various acoustic devices such as full range speakers, speakers such as tweeters, squawkers and woofers, speakers for headphones and earphones, noise cancelers, microphones, and pickups used for musical instruments such as guitars. Used to input an electrical signal to the electroacoustic transducing film to reproduce sound by vibration according to the electrical signal, or to convert the vibration of the electroacoustic transducing film by receiving a sound wave into an electrical signal It is

  An electroacoustic conversion film (hereinafter also referred to as “conversion film”) 10 shown in FIG. 1 includes a piezoelectric layer 12 which is a sheet-like material having piezoelectricity, and a lower thin film electrode 14 provided on one surface of the piezoelectric layer 12 An upper thin film electrode 16 provided on the other surface, and a lower protective layer 18 provided on the surface of the lower thin film electrode 14 and an upper protective layer 20 provided on the surface of the upper thin film electrode 16 are configured.

In the conversion film 10, the piezoelectric layer 12 is made of a polymer composite piezoelectric material.
As conceptually shown in FIG. 1, the polymer composite piezoelectric material forming the piezoelectric material layer 12 is obtained by dispersing the piezoelectric material particles 26 in a viscoelastic matrix 24 containing a polymer material having a cyanoethyl group. is there.
Here, in the present invention, an additive polymer material which is a polymer material having a dielectric constant of 10 or more is contained in the viscoelastic matrix 24 constituting the polymer composite piezoelectric material.
The electro-acoustic conversion film of the present invention having such a configuration can increase the conversion efficiency of electricity and sound, and can improve the sound pressure level, and peak in the sound pressure level in the frequency characteristic, The unevenness of the dip can be reduced to widen the band.
This point will be described in detail later.
In addition, preferably, the piezoelectric layer 12 is subjected to polarization processing.

The conversion film 10 is suitably used for a speaker having flexibility, such as a speaker for a flexible display. Here, it is preferable that the polymer composite piezoelectric material (piezoelectric material layer 12) used for the speaker having flexibility has the following requirements.
(I) Flexibility For example, when holding in a loosely flexed state like a document or magazine in a document sense for portable use, to be subjected to relatively slow, large bending deformation of several Hz or less from outside constantly become. At this time, if the polymer composite piezoelectric body 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 breakage. Therefore, the polymer composite piezoelectric body is required to have appropriate softness. In addition, if strain energy can be diffused to the outside as heat, stress can be relaxed. Therefore, it is required that the loss tangent of the polymer composite piezoelectric body be appropriately large.
(Ii) Sound quality The speaker vibrates the piezoelectric particles at a frequency of the audio band of 20 Hz to 20 kHz, and the vibration energy reproduces the sound by vibrating the entire diaphragm (polymer composite piezoelectric material) integrally. Ru. Therefore, in order to enhance the transmission efficiency of vibrational energy, the polymer composite piezoelectric body is required to have an appropriate hardness. In addition, if the frequency characteristic of the speaker is smooth, the amount of change in sound quality when the lowest resonance frequency f ₀ changes with the change in curvature also decreases. Therefore, the loss tangent of the polymer composite piezoelectric material is required to be moderately large.

  Summarizing the above, it is required that the polymer composite piezoelectric material used for the speaker having flexibility should be hard for vibrations of 20 Hz to 20 kHz, and be soft for vibrations of several Hz or less. In addition, the loss tangent of the polymer composite piezoelectric body is required to be appropriately large for vibrations of all frequencies of 20 kHz or less.

Generally, macromolecular solid has a viscoelastic relaxation mechanism, and large scale molecular motions decrease storage elastic modulus (Young's modulus) with the increase of temperature or decrease in frequency (relaxation) or maximum of loss elastic modulus (absorption) It is observed as Among them, the relaxation caused by the micro brown motion of molecular chains 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 notably.
In the polymer composite piezoelectric material (piezoelectric layer 12), by using a polymer material having a glass transition temperature at normal temperature, in other words, a polymer material having viscoelasticity at normal temperature as a matrix, against vibration of 20 Hz to 20 kHz A polymer composite piezoelectric material that is hard and behaves softly for slow vibrations of several Hz or less is realized. In particular, it is preferable to use a polymer material having a glass transition temperature at a frequency of 1 Hz at a normal temperature, that is, 0 to 50 ° C., as a matrix of the polymer composite piezoelectric material, in that this behavior suitably appears.
In the present specification, “normal temperature” refers to a temperature range of about 0 to 50 ° C.

As a polymer material having viscoelasticity at normal temperature, a material having a cyanoethyl group can be used.
Preferably, a polymer material having a maximum value of 0.5 or more of the loss tangent Tan δ at a frequency of 1 Hz in the dynamic viscoelasticity test at normal temperature, that is, 0 to 50 ° C. is used.
Thereby, when the polymer composite piezoelectric material is slowly bent by an external force, stress concentration at the polymer matrix / piezoelectric particle interface at the maximum bending moment portion is relaxed, and high flexibility can be expected.

Moreover, as for a polymeric material, it is preferable that the storage elastic modulus (E ') in frequency 1 Hz by dynamic-viscoelasticity measurement is 100 Mpa or more at 0 degreeC, and 10 Mpa or less at 50 degreeC.
As a result, the bending moment generated when the polymer composite piezoelectric material is slowly bent by an external force can be reduced, and at the same time, it can behave hard against acoustic vibration of 20 Hz to 20 kHz.

In addition, it is more preferable that the polymer material has a relative dielectric constant of 10 or more at 25 ° C. Thus, when a voltage is applied to the polymer composite piezoelectric material, a higher electric field is applied to the piezoelectric particles in the polymer matrix, and a large amount of deformation can be expected.
However, on the other hand, it is also preferable that the polymer material has a relative dielectric constant of 10 or less at 25 ° C. in consideration of securing of good moisture resistance and the like.

Preferred examples of the polymer material satisfying such conditions include cyanoethylated polyvinyl alcohol (cyanoethylated PVA). In addition to these, vinylidene cyanide-vinyl acetate copolymer, cyanoethyl cellulose, cyanoethyl hydroxysucrose, cyanoethyl hydroxy cellulose, cyanoethyl hydroxy pullulan, cyanoethyl methacrylate, cyanoethyl acrylate, cyanoethyl hydroxyethyl cellulose, cyanoethyl amylose, cyanoethyl hydroxypropyl cellulose, Cyanoethyl dihydroxypropyl cellulose, cyanoethyl hydroxypropyl amylose, cyanoethyl polyacrylamide, cyanoethyl polyacrylate, cyanoethyl pullulan, cyanoethyl polyhydroxy methylene, cyanoethyl glycidol pullulan, cyano group such as cyanoethyl saccharose and cyanoethyl sorbitol or cyanoe Polymers having a group, the polymeric material can be mentioned having a cyanoethyl group of synthetic rubbers such as nitrile rubber or chloroprene rubber.
Among them, it is preferable to use cyanoethylated PVA.
In addition, only 1 type may be used for these polymeric materials, and multiple types may be used together (mixing) and using them.

Moreover, the viscoelastic matrix 24 using the polymeric material which has such a cyanoethyl group may use together other polymeric materials which have viscoelasticity at normal temperature as needed.
Polyvinyl acetate, polyvinylidene chloride coacrylonitrile, polystyrene-vinyl polyisoprene block copolymer, polyvinyl methyl ketone, and polybutyl methacrylate etc. are illustrated as another polymer material which has viscoelasticity at normal temperature. Moreover, as these high molecular materials, commercially available products such as HYBLER 5127 (manufactured by Kuraray Co., Ltd.) can be suitably used.

  Here, in the present invention, a polymer material having a dielectric constant of 10 or more at 25 ° C. (hereinafter referred to as “added polymer material”) is a visco-elastic matrix 24 mainly containing such a cyanoethyl group-containing polymer material. (Also referred to as “)”.

As described above, the applicant of the present invention disperses piezoelectric particles in a visco-elastic matrix made of a polymer material having visco-elastic properties at normal temperature as a thin, piezoelectric film capable of stably reproducing high-quality sound. An electroacoustic transducing film is proposed having a polymer composite piezoelectric material (piezoelectric material layer), thin film electrodes formed on both sides of the piezoelectric material layer, and a protective layer formed on the surface of the thin film electrode.
The inventors of the present invention have made an electroacoustic transducing film using, as a piezoelectric layer, such a polymer composite piezoelectric material in which piezoelectric particles are dispersed in a visco-elastic matrix made of a polymer material having visco-elastic properties at normal temperature. Furthermore, in order to improve the conversion efficiency and to reduce the unevenness of the peaks and dips in the sound pressure level in the frequency characteristics, the band width was considered.

As a result of the examination, as in the present invention, an additive polymer material having a dielectric constant of 10 or more is added to the viscoelastic matrix 24 mainly composed of a polymer material having a cyanoethyl group exhibiting viscoelasticity at normal temperature. By increasing the dielectric constant of the visco-elastic matrix 24, the conversion efficiency between electricity and sound can be increased to improve the sound pressure, and the peak and dip unevenness of the sound pressure level can be reduced in the frequency characteristic. It has been found that the bandwidth can be increased.
The peak of the sound pressure level in the frequency characteristic is the maximum value of the sound pressure level in the graph representing the relationship between the frequency and the sound pressure level, and the dip is the minimum value next to this maximum value. That is, the smaller the difference between the peak and the dip of the sound pressure level, the smoother the frequency characteristic is, and the wider the band.

  From the viewpoint of further improving the dielectric constant of the viscoelastic matrix 24, the relative dielectric constant at 25 ° C. of the added polymer material is preferably 15 or more, more preferably 18 or more.

  As added polymer materials having a dielectric constant of 10 or more, cyanoethyl pullulan, cyanoethyl cellulose, nitrile rubber, cyanoethyl hydroxycellulose, cyanoethyl hydroxyethyl cellulose, cyanoethyl amylose, cyanoethyl hydroxypropyl cellulose, cyanoethyl dihydroxypropyl cellulose, cyanoethyl polyhydroxy methylene, cyanoethyl Examples include glycidol pullulan, cyanoethylsorbidol and the like.

Here, as the additive polymer material, it is preferable to use a polymer material whose loss tangent at 25 ° C. and 20 Hz is 0.05 or less.
In general, the smaller the loss tangent, the larger the mechanical quality factor (Q value), which is an index of the sharpness (resonance strength) of the resonance characteristic, that is, the resonance becomes sharper. Therefore, it has been found that when a polymer material having a loss tangent at 25 ° C. and 20 Hz of 0.05 or less as the additive polymer material is used, resonance becomes sharp in a high frequency band (1 kHz or more). It has been found that the sound pressure is improved by utilizing this resonance. In addition, when the resonance becomes sharp, the sound pressure level has unevenness in the frequency characteristics which is one of the indexes of the acoustic performance, and peaks and dips become apparent and the band is narrowed. It has been found that by adding it, smooth frequency characteristics can be obtained and the frequency band can be broadened without making peaks and dips apparent.

  Examples of the added polymer material having a loss tangent at 25 ° C. and 20 Hz of 0.05 or less include cyanoethyl pullulan, cyanoethyl cellulose and the like.

Further, as the additive polymer material, it is preferable to use a polymer material having a volume resistance of 1 × 10 ¹² Ω · cm or more.
By using a polymer material having a volume resistance of 1 × 10 ¹² Ω · cm or more as the additive polymer material, the withstand voltage of the piezoelectric layer 12 can be increased, and between the electrode pairs supporting the piezoelectric layer 12. Even when a high voltage is applied to (the lower thin film electrode 14 and the upper thin film electrode 16), the dielectric breakdown of the piezoelectric layer 12 is less likely to occur, and sound can be properly reproduced. In addition, since the dielectric breakdown does not easily occur, the piezoelectric layer 12 can be formed thinner, and the deflection due to its own weight can be reduced, and by making it lighter, the followability of the piezoelectric film to the applied voltage can be improved. Pressure and sound quality can be improved. Also, flexibility can be given.

Examples of the added polymer material having a volume resistance of 1 × 10 ¹² Ω · cm or more include cyanoethyl pullulan and the like.

Further, the addition amount of the added polymer material is not limited, but preferably 60% by mass or less, more preferably 10% by mass or more and 30% by mass or less in the proportion in the visco-elastic matrix 24 .
By setting the ratio of the added polymer material in the above range, it is possible to simultaneously improve the sound pressure, increase the frequency band, and improve the withstand voltage.

  Further, the viscoelastic matrix 24 exhibits viscoelasticity at normal temperature and has a cyanoethyl group-containing polymer material (viscoelastic material) for the purpose of adjustment of dielectric properties and mechanical properties, etc., and a high dielectric constant of 10 or more In addition to molecular materials, other polymer materials may be added as needed.

Examples of polymer materials that can be added include polyvinylidene fluoride, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, polyvinylidene fluoride-trifluoroethylene copolymer, and polyfluorocarbon as an example. Fluorinated polymers such as vinylidene fluoride-tetrafluoroethylene copolymer and synthetic rubbers such as chloroprene rubber are exemplified.
Moreover, in the visco-elastic matrix 24 of the piezoelectric layer 12, the polymer material to be added in addition to the material having visco-elastic properties at normal temperature such as cyanoethylated PVA is not limited to one type, and plural types are added It is also good.

In addition, for the purpose of adjusting the glass transition point Tg, thermoplastic resins such as vinyl chloride resin, polyethylene, polystyrene, methacrylic resin, polybutene, isobutylene, etc., phenol resin, urea resin, melamine resin, alkyd resin, mica, etc. A thermosetting resin may be added.
Furthermore, tackifiers such as rosin esters, rosins, terpenes, terpene phenols, petroleum resins and the like may be added for the purpose of improving the tackiness.

The amount of addition when adding a viscoelastic material such as cyanoethylated PVA and a polymer material other than an additive polymer material having a dielectric constant of 10 or more to the viscoelastic matrix 24 of the piezoelectric layer 12 is particularly limited. Although it does not exist, it is preferable to set it as 30 mass% or less in the ratio to 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 adjustment of the dielectric characteristics, the improvement of the heat resistance, the adhesion with the piezoelectric particles 26 and the electrode layer Favorable results can be obtained in terms of improvement and the like.

  In the present invention, the polymer material means one having a molecular weight of 10000 or more.

Further, in order to increase the dielectric constant of the piezoelectric layer 12, dielectric particles may be added to the viscoelastic matrix 24.
The dielectric particles are made of particles having a high relative dielectric constant of 80 or more at 25 ° C.
As dielectric particles, for example, lead zirconate titanate (PZT), barium titanate (BaTiO ₃ ), titanium oxide (TiO ₂ ), strontium titanate (SrTiO ₃ ), lead lanthanum zirconate titanate (PLZT) And zinc oxide (ZnO), a solid solution (BFBT) of barium titanate and bismuth ferrite (BiFeO ₃ ), and the like. Among them, it is preferable to use barium titanate (BaTiO ₃ ) as the dielectric particles in view of having a high relative dielectric constant.

The dielectric particles preferably have an average particle size of 0.5 μm or less.
The volume fraction of the dielectric particles is preferably 5 to 45%, more preferably 10 to 30%, and particularly preferably 20 to 30% of the total volume of the viscoelastic matrix and the dielectric particles.

The piezoelectric particles 26 are made of ceramic particles having a perovskite or wurtzite crystal structure.
Examples of ceramic particles constituting the piezoelectric particles 26 include lead zirconate titanate (PZT), lead zirconate titanate zirconate (PLZT), barium titanate (BaTiO ₃ ), zinc oxide (ZnO), and Examples thereof include a solid solution (BFBT) of barium titanate and bismuth ferrite (BiFe ₃ ).
The ceramic particles may be used alone or in combination of two or more.

The particle diameter of such piezoelectric particles 26 may be appropriately selected according to the size and application of the conversion film 10, but according to the study of the present inventor, 1 to 10 μm is preferable.
By setting the particle diameter of the piezoelectric particles 26 in the above-mentioned range, preferable results can be obtained in that high piezoelectric characteristics and flexibility can be compatible, and the withstand voltage can be improved.

Although the piezoelectric particles 26 in the piezoelectric layer 12 are dispersed uniformly and regularly in the viscoelastic matrix 24 in FIG. 1, 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 they are preferably dispersed uniformly.

In the conversion film 10, the ratio of the visco-elastic matrix 24 to the piezoelectric particles 26 in the piezoelectric layer 12 is required for the size and thickness in the plane direction of the conversion film 10, the application of the conversion film 10, and the conversion film 10 Depending on the characteristics of the
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%, and more preferably 50% or more. It is more preferable to make it 70%.
By setting the ratio of the viscoelastic matrix 24 to the piezoelectric particles 26 in the above range, preferable results can be obtained in that high piezoelectric characteristics and flexibility can be compatible.

In the conversion film 10, the thickness of the piezoelectric layer 12 is not particularly limited, and is appropriately set according to the size of the conversion film 10, the application of the conversion film 10, the characteristics required of the conversion film 10, etc. do it.
Here, according to the study of the present inventor, by reducing the thickness of the piezoelectric layer 12, the deflection due to its own weight is reduced, and by making it light, the followability of the piezoelectric film to the applied voltage is improved. Sound pressure and sound quality. Also, flexibility can be given. On the other hand, when the thickness of the piezoelectric layer 12 is too thin, local short circuit may occur when the voltage is applied continuously or when the rigidity is continuously applied. In addition, the rigidity may be reduced.
From the above viewpoint, the thickness of the piezoelectric layer 12 is preferably 5 μm to 100 μm, more preferably 8 μm to 50 μm, particularly preferably 10 to 40 μm, and particularly preferably 15 to 25 μm.
As described above, the piezoelectric layer 12 is preferably subjected to polarization processing (poling). The polarization process will be described in detail later.

As shown in FIG. 1, in the conversion film 10 of the present invention, the lower thin film electrode 14 is formed on one surface of such a piezoelectric layer 12, and the lower protective layer 18 is formed thereon. An upper thin film electrode 16 is formed on the other surface, and an upper protective layer 20 is formed thereon. Here, the upper thin film electrode 16 and the lower thin film electrode 14 form an electrode pair.
In addition to the layers, the conversion film 10 covers, for example, the upper thin film electrode 16 and an electrode lead-out portion for drawing out the electrode from the lower thin film electrode 14 and a region where the piezoelectric layer 12 is exposed. And an insulating layer or the like for preventing a short or the like.

As the electrode lead-out portion, a thin film electrode and a protective layer may be provided with a projecting portion projecting outward in the surface direction of the piezoelectric layer, or a part of the protective layer is removed to form a hole Then, a conductive material such as silver paste may be inserted into the hole to electrically conduct the conductive material and the thin film electrode to form an electrode lead-out portion.
In each thin film electrode, the number of electrode lead portions is not limited to one, and two or more electrode lead portions may be provided. In particular, in the case of a configuration in which a conductive material is inserted into the hole to remove a part of the protective layer to form an electrode lead-out part, three or more electrode lead-out parts are provided to ensure electric conduction more reliably. preferable.

That is, in the conversion film 10, both surfaces of the piezoelectric layer 12 are sandwiched by the electrode pair, that is, the upper thin film electrode 16 and the lower thin film electrode 14, and the laminate is sandwiched by the upper protective layer 20 and the lower protective layer 18. The configuration is as follows.
Thus, the region held by the upper thin film electrode 16 and the lower thin film electrode 14 is driven according to the applied voltage.

In the conversion film 10, the upper protective layer 20 and the lower protective layer 18 serve to cover the upper thin film electrode 16 and the lower thin film electrode 14 and to provide the piezoelectric layer 12 with appropriate rigidity and mechanical strength. . That is, in the conversion film 10 of the present invention, the piezoelectric layer 12 composed of the viscoelastic matrix 24 and the piezoelectric particles 26 exhibits very excellent flexibility against slow bending deformation, Depending on the application, rigidity and mechanical strength may be insufficient. The conversion film 10 is provided with the upper protective layer 20 and the lower protective layer 18 to compensate for it.
The lower protective layer 18 and the upper protective layer 20 are the same except that the arrangement position is different. Therefore, in the following description, it is not necessary to distinguish the lower protective layer 18 and the upper protective layer 20. The two members are collectively referred to as a protective layer.

The upper protective layer 20 and the lower protective layer 18 are not particularly limited, and various sheet materials can be used. As an example, various resin films are preferably exemplified. Among them, polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS), polycarbonate (PC), polyphenylene sulfide (PPS), polymethyl methacrylate (PMMA) and the like because of having excellent mechanical properties and heat resistance. And polyetherimide (PEI), polyimide (PI), polyamide (PA, aramid), polyethylene naphthalate (PEN), triacetyl cellulose (TAC), and cyclic olefin resins are preferably used.
Among them, polyamides, polyimides, polyetherimides, polycarbonates and triacetylcelluloses are preferably used from the viewpoint of exhibiting excellent heat resistance when the glass transition temperature Tg is 150 ° C. or more. From these, appearance damage due to heat generation at the time of voltage application can be prevented, and it is possible to withstand standing test under high temperature and driving test.

The thickness of the upper protective layer 20 and the lower protective layer 18 is not particularly limited. Also, the thicknesses of the upper protective layer 20 and the lower protective layer 18 are basically the same but may be different.
Here, when the rigidity of the upper protective layer 20 and the lower protective layer 18 is too high, not only the expansion and contraction of the piezoelectric layer 12 is restrained, but also the flexibility is impaired, so that the mechanical strength and the sheet-like material are good. The upper protective layer 20 and the lower protective layer 18 are more advantageously thinner, except when handling is required.

According to the study of the present inventor, if the thickness of the upper protective layer 20 and the lower protective layer 18 is not more than twice the thickness of the piezoelectric layer 12, compatibility between securing of rigidity and appropriate flexibility, etc. Favorable results can be obtained in terms of
For example, when the thickness of the piezoelectric layer 12 is 20 μm and the upper protective layer 20 and the lower protective layer 18 are made of PET, the thickness of the upper protective layer 20 and the lower protective layer 18 is preferably 40 μm or less, more preferably 20 μm or less Among them, the thickness is preferably 15 μm or less.

In the conversion film 10, an upper thin film electrode (hereinafter also referred to as an upper electrode) 16 is provided between the piezoelectric layer 12 and the upper protective layer 20, and a lower thin film electrode is provided between the piezoelectric layer 12 and the lower protective layer 18. (Hereinafter, it is also called a lower electrode) 14 is formed, respectively.
The upper electrode 16 and the lower electrode 14 are provided to apply an electric field to the conversion film 10 (piezoelectric layer 12).
The lower electrode 14 and the upper electrode 16 have the same structure except that the size and the arrangement position are different. Therefore, in the following description, the lower electrode 14 and the upper electrode 16 need not be distinguished from each other. Together, both members are also referred to as thin film electrodes.

  In the present invention, the materials for forming the upper electrode 16 and the lower electrode 14 are not particularly limited, and various conductors can be used. Specific examples thereof include carbon, palladium, iron, tin, aluminum, nickel, platinum, gold, silver, copper, chromium and molybdenum, alloys of these, indium tin oxide and the like. Among them, any of copper, aluminum, gold, silver, platinum and indium tin oxide is suitably exemplified.

  Further, the method of forming the upper electrode 16 and the lower electrode 14 is not particularly limited, and a film formed by vapor deposition (vacuum film forming method) such as vacuum evaporation or sputtering or film formed by plating, or a foil formed of the above material Various known methods such as a method of pasting can be used.

Above all, a thin film of copper or aluminum formed by vacuum deposition is suitably used as the upper electrode 16 and the lower electrode 14 because the flexibility of the conversion film 10 can be secured among others. Among them, a thin film of copper by vacuum evaporation is suitably used.
The thickness of the upper electrode 16 and the lower electrode 14 is not particularly limited. Also, the thicknesses of the upper electrode 16 and the lower electrode 14 are basically the same but may be different.

  Here, similarly to the upper protective layer 20 and the lower protective layer 18 described above, when the rigidity of the upper electrode 16 and the lower electrode 14 is too high, not only the expansion and contraction of the piezoelectric layer 12 is restricted but also the flexibility is impaired. Therefore, the upper electrode 16 and the lower electrode 14 are more advantageous as thin as long as the electrical resistance does not become too high.

Here, according to the study of the inventor, if the product of the thickness of the upper electrode 16 and the lower electrode 14 and the Young's modulus is less than the product of the thickness of the upper protective layer 20 and the lower protective layer 18 and the Young's modulus, It is preferable because the flexibility is not greatly impaired.
For example, when the upper protective layer 20 and the lower protective layer 18 are a combination of PET (Young's modulus: about 6.2 GPa) and the upper electrode 16 and the lower electrode 14 are copper (Young's modulus: about 130 GPa), the upper protective layer 20 When the thickness of the lower protective layer 18 is 25 μm, the thickness of the upper electrode 16 and the lower electrode 14 is preferably 1.2 μm or less, more preferably 0.3 μm or less, and particularly preferably 0.1 μm or less.

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

  Alternatively, the protective layer on which the thin film electrode is formed does not have to be formed corresponding to the entire surface of the piezoelectric layer 12. In this case, a second protective layer in direct contact with the piezoelectric layer 12 may be separately provided on the surface side of the protective layer.

Further, a coating layer may be further provided between the thin film electrode and the piezoelectric layer 12 for the purpose of improving adhesion and flexibility. In this case, the coating layer may be applied to either the thin film electrode or the piezoelectric layer 12.
In this case, as the polymer component, a thermoplastic resin such as poly (meth) acrylic, polyurethane, polyester polyolefin, PVA, polystyrene, or a thermosetting resin such as phenol resin or melamine resin can be used. Above all, a dielectric polymer is preferably used to improve the acoustic performance. Specifically, the aforementioned polymers can be preferably used. In addition to the polymer component, high dielectric particles, an antistatic agent, a surfactant, a thickener, a crosslinking agent and the like may be added.

  Further, in the illustrated example, the layer configuration of the conversion film 10 includes the piezoelectric layer 12, the lower thin film electrode 14 stacked on one surface of the piezoelectric layer 12, and the lower protective layer stacked on the lower thin film electrode 14. 18 and the upper thin film electrode 16 stacked on the other surface of the piezoelectric layer 12 and the upper protective layer 20 stacked on the upper thin film electrode 16, but the present invention is not limited thereto. In addition to the layers, for example, an insulating layer for preventing short circuit or the like, a colored layer for covering a thin film electrode, or the like may be provided to cover the region where the piezoelectric layer 12 is exposed.

For example, in the case of having a colored layer, the layer configuration includes a piezoelectric layer 12, a lower thin film electrode 14 stacked on one surface of the piezoelectric layer 12, and a lower colored layer stacked on the lower thin film electrode 14. A lower protective layer 18 stacked on the lower colored layer, an upper thin film electrode 16 stacked on the other surface of the piezoelectric layer 12, an upper colored layer stacked on the upper thin film electrode 16, and an upper colored layer And the upper protective layer 20 to be laminated on the substrate.
By having the colored layer, it is possible to make the rust of the upper thin film electrode 16 and the lower thin film electrode 14 invisible from the outside.

The transmission density of the colored layer is preferably 0.3 or more, more preferably 0.5 or more, from the viewpoint of preventing the rust of the thin film electrode from being visible from the outside.
The transmission density is an optical density measured as a ratio of transmitted light to incident light, and the transmittance at a transmission density of 0.3 is about 50%, and the transmittance at a transmission density of 0.5 Is about 30%.

The thickness of the colored layer is preferably 1 μm or less, more preferably 100 nm or less, and particularly preferably 40 nm or less.
The colored layer preferably has a low electric resistivity, and preferably 1 × 10 ⁻⁷ Ωm or less.

The material for forming the colored layer is not particularly limited as long as it satisfies the above transmission density and does not change color due to rusting or the like.
Specifically, as a material for forming the colored layer, metals such as indium, nickel, titanium, aluminum, gold, platinum, chromium and the like, carbon black (CB), inorganic pigments such as titanium oxide, zinc oxide and barium sulfate, quinacridone Examples thereof include organic pigments of an azo type, a benzimidazolone type, a phthalocyanine type and an anthraquinone type, and a member having a light scattering property and having pores inside.
It is preferable to use a metal as a formation material of a colored layer from a viewpoint of the above-mentioned permeation | transmission density | concentration, thickness, and an electrical resistivity, and nickel is more preferable among them.

Moreover, there is no limitation in particular in the formation method of a colored layer, According to the said material, what is necessary is just to form by various well-known methods.
For example, in the case of using a metal as a material for forming the colored layer, a film formed by vapor deposition (vacuum film forming method) such as vacuum evaporation or sputtering or plating, or a foil formed of the above material is attached Methods etc. are available. It is more preferable to form by vacuum evaporation from the point which can be formed thinner.
Moreover, when using a pigment as a formation material of a colored layer, the apply | coating method, printing, etc. can be utilized.
Also, a method of transferring a previously formed colored layer can be used.

  Moreover, it is not limited to the structure which has a colored layer in each of the upper electrode 16 side and the lower electrode 14 side, You may be the structure which has a colored layer in at least one side.

As described above, the conversion film 10 includes the upper electrode 16 and the piezoelectric layer 12 formed by dispersing the piezoelectric particles 26 in the visco-elastic matrix 24 containing a polymer material having a cyanoethyl group exhibiting visco-elastic properties at normal temperature. It has a configuration formed by sandwiching the lower electrode 14 and further sandwiching the upper protective layer 20 and the lower protective layer 18.
It is preferable that such a conversion film 10 has a maximum value at which a loss tangent (Tan δ) at a frequency of 1 Hz determined by dynamic viscoelasticity measurement is 0.1 or more at normal temperature.
Thereby, even if the conversion film 10 is subjected to a relatively slow, large bending deformation of several Hz or less from the outside, 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 the occurrence of cracks at the interface of

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

The conversion film 10 thickness and the product of the storage modulus at a frequency 1 Hz (E ') by dynamic viscoelasticity ^{measurement, 1.0 × 10 6 ~2.0 × 10} 6 (1 at 0 ° C.. 0E + 06~2.0E + 06) N / m, at ^{50 ℃ 1.0 × 10 5 ~1.0 ×} 10 6 (1.0E + 05~1.0E + 06) is preferably N / m.
Thereby, appropriate rigidity and mechanical strength can be provided as long as the conversion film 10 does not lose flexibility and acoustic characteristics.

Furthermore, it is preferable that the conversion film 10 has a loss tangent (Tan δ) at 25 ° C. and a frequency of 1 kHz in a master curve obtained from dynamic viscoelasticity measurement, of 0.05 or more.
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.

  In the example shown in FIG. 1, the layer configuration of the conversion film 10 is formed on the piezoelectric layer 12, the lower thin film electrode 14 stacked on one surface of the piezoelectric layer 12, and the lower thin film electrode 14. Although the lower protective layer 18, the upper thin film electrode 16 stacked on the other surface of the piezoelectric layer 12, and the upper protective layer 20 stacked on the upper thin film electrode 16 are provided, the present invention is not limited thereto. In addition to these layers, for example, an insulating layer which covers a region where the piezoelectric layer 12 is exposed to prevent a short etc., or a thin film electrode is visually recognized from the outside between the protective layer and the thin film electrode. It may have a colored layer or the like that prevents

  Next, with reference to FIG. 2A-FIG. 2E, an example of the manufacturing method of the conversion film 10 is demonstrated.

First, as shown in FIG. 2A, the sheet-like material 11a in which the lower electrode 14 is formed on the lower protective layer 18 is prepared. The sheet-like material 11 a may be manufactured by forming a copper thin film or the like as the lower electrode 14 on the surface of the lower protective layer 18 by vacuum deposition, sputtering, plating or the like.
When the lower protective layer 18 is very thin and handling is poor, the lower protective layer 18 with a separator (temporary support) may be used as needed. In addition, PET etc. of 25-100 micrometers in thickness can be used as a separator. Note that the separator may be removed immediately after the side surface insulating layer, the second protective layer, and the like are formed after thermocompression bonding of the thin film electrode and the protective layer.
Alternatively, a commercial product having a copper thin film or the like formed on the lower protective layer 18 may be used as the sheet 11a.

On the other hand, a polymeric material having a cyanoethyl group such as cyanoethylated PVA (hereinafter also referred to as a viscoelastic material) and an additive polymeric material having a dielectric constant of 10 or more such as cyanoethyl pullulan are dissolved in an organic solvent, Further, piezoelectric particles 26 such as PZT particles are added, stirred and dispersed to prepare a paint. There is no particular limitation on the organic solvent, and various organic solvents such as dimethylformamide (DMF), methyl ethyl ketone and cyclohexanone can be used.
Once the sheet 11a is prepared and the paint is prepared, the paint is cast (coated) on the sheet and the organic solvent is evaporated to dryness. Thereby, as shown to FIG. 2B, the lower electrode 14 is on the lower protective layer 18, and the laminated body 11b formed by forming the piezoelectric material layer 12 on the lower electrode 14 is produced.

There is no particular limitation on the method of casting the paint, and all known methods (coating apparatus) such as a slide coater and a doctor knife can be used.
Alternatively, if the visco-elastic material is a heat-meltable material such as cyanoethylated PVA, a melt formed by heat-melting the visco-elastic material and adding / dispersing the additive polymer material and the piezoelectric particles 26 thereto. 2A, and the lower electrode 14 is formed on the lower protective layer 18 as shown in FIG. 2B by cooling. Alternatively, the laminate 11 b formed by forming the piezoelectric layer 12 on the lower electrode 14 may be manufactured.
Also, there is no particular limitation on the method of preparing the paint to be the piezoelectric layer 12, and after dissolving the polymer material having a cyanoethyl group and adding and stirring the additive polymer material, the piezoelectric particles 26 are further added. The composition may be stirred to prepare a paint.

As described above, in the conversion film 10, in addition to the viscoelastic material such as cyanoethylated PVA and the added polymer material such as cyanoethyl pullulan, the polymer piezoelectric material such as PVDF is added to the viscoelastic matrix 24. It is good.
When adding these polymeric piezoelectric materials to the viscoelastic matrix 24, the polymeric piezoelectric materials added to the above-mentioned paint may be dissolved. Alternatively, the polymer piezoelectric material to be added may be added to the heat-melted viscoelastic material and heat-melted.
Once the laminate 11b having the lower electrode 14 on the lower protective layer 18 and the piezoelectric layer 12 formed on the lower electrode 14 is produced, preferably, the polarization process (poling) of the piezoelectric layer 12 is performed. Do.

  There is no particular limitation on the method of polarization treatment of the piezoelectric layer 12, and a known method can be used. As a preferable polarization method, the methods shown in FIGS. 2C and 2D are exemplified.

In this method, as shown in FIGS. 2C and 2D, a bar or wire shape movable along the upper surface 12a with a gap g of, for example, 1 mm on the upper surface 12a of the piezoelectric layer 12 of the laminate 11b. The corona electrode 30 is provided. Then, the corona electrode 30 and the lower electrode 14 are connected to a DC power supply 32.
Further, a heating means for heating and holding the laminate 11b, for example, a hot plate is prepared.

  Then, while heating and holding the piezoelectric layer 12 at a temperature of 100 ° C., for example, by heating means, a DC voltage of several kV, eg, 6 kV between the lower electrode 14 and the corona electrode 30. Voltage is applied to cause corona discharge. Further, while maintaining the gap g, the corona electrode 30 is moved (scanned) along the upper surface 12 a of the piezoelectric layer 12 to polarize the piezoelectric layer 12.

In the polarization treatment using such corona discharge (hereinafter, also referred to as a corona poling treatment for convenience, for convenience), the movement of the corona electrode 30 may be performed using a known rod-like moving means.
Further, in the corona poling treatment, the method of moving the corona electrode 30 is not limited. That is, a moving mechanism may be provided to fix the corona electrode 30 and move the stacked body 11b, and the stacked body 11b may be moved for polarization processing. Also for the movement of the laminate 11b, a known sheet moving means may be used.
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 poling process, and a normal electric field poling in which a direct current electric field is directly applied to an object to be subjected to the polarization process can also be used. However, when performing this normal electric field poling, it is necessary to form the upper electrode 16 before the polarization processing.
A calendar process may be applied to smooth the surface of the piezoelectric layer 12 using a heating roller or the like before the polarization process. By applying this calendering treatment, the thermocompression bonding described later can be smoothly performed.

Thus, while the polarization process of the piezoelectric material layer 12 of the laminated body 11b is performed, the sheet-like article 11c in which the upper electrode 16 is formed on the upper protective layer 20 is prepared. The sheet-like material 11 c may be manufactured by forming a copper thin film or the like as the upper electrode 16 on the surface of the upper protective layer 20 by vacuum deposition, sputtering, plating or the like.
Next, as shown in FIG. 2E, the sheet-like material 11c is laminated on the laminate 11b in which the polarization treatment of the piezoelectric layer 12 is finished, with the upper electrode 16 facing the piezoelectric layer 12.
Further, the laminated body of the laminated body 11b and the sheet-like material 11c is thermocompression-bonded by a heating press device, a heating roller pair or the like so as to sandwich the upper protective layer 20 and the lower protective layer 18 to convert the conversion film 10 Make

The conversion film 10 may be manufactured using the cut sheet-like sheet-like material, or may be performed by roll-to-roll (hereinafter also referred to as RtoR).
As is well known, with RtoR, raw materials are drawn from rolls made by winding long raw materials, and while being transported in the longitudinal direction, various processes such as film formation and surface treatment are performed, and processed raw materials are processed. Are rolled again in a roll shape.

Next, an electroacoustic transducer using such a conversion film as a diaphragm will be described.
The top view which represents typically an example of the electroacoustic transducer of this invention to FIG. 3A is shown, and the BB sectional drawing of FIG. 3A is shown to it at FIG. 3B.
The electroacoustic transducer 40 shown in FIGS. 3A and 3B uses the conversion film 10 as a diaphragm.

As shown in the figure, the electroacoustic transducer 40 is a flat panel speaker, and the vertical direction in FIG. 3B is the vibration direction of the conversion film 10, that is, the sound radiation direction. FIG. 3A is a view seen from the vibration direction of the conversion film 10.
The electroacoustic transducer 40 is configured to include the conversion film 10, the case 42, the viscoelastic support 46, and the pressing member 48.

The case 42 is a holding member that holds the conversion film 10 and the visco-elastic support 46 together with the pressing member 48. The case 42 is a box-shaped case which is formed of plastic, metal, wood or the like, and is open on one side. In the illustrated example, the case 42 has a thin hexahedron shape, and one of the largest surfaces is an open surface. Also, the open part is a square. The case 42 accommodates the visco-elastic support 46 therein.
In the electro-acoustic transducer of the present invention, the shape of the case 42 (that is, the shape of the electro-acoustic transducer) is not limited to a square cylinder, and various shapes such as a cylinder or a square cylinder having a rectangular bottom surface Is available.

The viscoelastic support 46 has appropriate viscosity and elasticity, holds the conversion film 10 in a curved state, and stretches the conversion film 10 by applying a constant mechanical bias anywhere on the conversion film 10 It is for converting motion into forward and backward motion (motion in the direction perpendicular to the surface of the conversion film) without waste.
In the illustrated example, the viscoelastic support 46 is in the form of a square pole having a bottom shape substantially equal to the bottom surface of the case 42. Also, the height of the visco-elastic support 46 is larger than the depth of the case 42.

The material of the viscoelastic support 46 is not particularly limited as long as it has appropriate viscosity and elasticity, and does not prevent the vibration of the piezoelectric film and deforms suitably. For example, nonwoven fabric such as wool felt, wool felt including rayon and PET, glass wool, foam material such as polyurethane (foam plastic), polyester wool, multiple sheets of paper, magnetic fluid, paint, etc. It is illustrated.
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, when using a felt as a visco-elastic support, 50-500 kg / m < ³ > is preferable and, as for specific gravity, 100-300 kg / m < ³ > is more preferable. When glass wool is used as the viscoelastic support, the specific gravity is preferably 10 to 100 kg / m ³ .

  The pressing member 48 is for supporting the conversion film 10 in a state where it is pressed against the viscoelastic support 46, and is formed of plastic, metal, wood or the like, and is a square plate having an opening at the center. Like members. The pressing member 48 has the same shape as the open surface of the case 42, and the shape of the opening is a square shape similar to the open portion of the case 42.

In the electroacoustic transducer 40, the visco-elastic support 46 is accommodated in the case 42, the case 42 and the visco-elastic support 46 are covered by the conversion film 10, and the case 42 is surrounded by the pressing member 48. The pressing member 48 is fixed to the case 42 in a state of being in contact with the open surface of the case.
The method for fixing the pressing member 48 to the case 42 is not particularly limited, and various known methods such as a method using a screw or a bolt and a nut, and a method using a fixing jig can be used.

In the electroacoustic transducer 40, the height (thickness) of the viscoelastic support 46 is larger than the height of the inner surface of the case 42. That is, in the state before the conversion film 10 and the pressing member 48 are fixed, the visco-elastic support 46 protrudes from the upper surface of the case 42.
Therefore, in the electroacoustic transducer 40, the viscoelastic support 46 is held by the conversion film 10 so as to be pressed downward by the conversion film 10 as it gets closer to the peripheral portion of the viscoelastic support 46 in a state where the thickness becomes thinner. That is, at least a part of the main surface of the conversion film 10 is held in a curved state. Thereby, a curved part is formed in at least one part of the conversion film 10. In the electroacoustic transducer 40, this curved portion is a vibrating surface. In the following description, the curved portion is also referred to as a vibrating surface.
Under the present circumstances, it is preferable to press the whole surface of the visco-elastic support 46 in the surface direction of the conversion film 10, and to make thickness whole thin. That is, it is preferable that the entire surface of the conversion film 10 be pressed and supported by the viscoelastic support 46.
In addition, it is preferable that the curvature of the curved portion formed in this manner gradually changes from the center toward the peripheral portion. As a result, the resonance frequency can be dispersed and the frequency band can be further increased.

  In the electroacoustic transducer 40, the viscoelastic support 46 is compressed in the thickness direction as it approaches the pressing member 48. However, due to the static viscoelastic effect (stress relaxation), which place of the conversion film 10 But mechanical bias can be kept constant. As a result, since the expansion and contraction movement of the conversion film 10 is converted to the back and forth movement without wasting, a thin, sufficient volume can be obtained, and the planar electroacoustic transducer 40 excellent in acoustic characteristics can be obtained.

In the electro-acoustic transducer 40 with such a configuration, a region of the conversion film 10 corresponding to the opening of the pressing member 48 is a curved portion that actually vibrates. That is, the pressing member 48 is a portion that defines the curved portion.
An electroacoustic conversion unit using a conversion film having piezoelectricity can easily make the relative size of the diaphragm to the size of the whole unit larger than that of a cone speaker in which the diaphragm generally has a circular shape. Is easy to
Moreover, from the said viewpoint, 20 mm or less is preferable and, as for the width | variety of the edge part of the press member 48, 1 mm-10 mm are preferable.

  Moreover, it is preferable that the surface by the side of the conversion film 10 of the electroacoustic transducer 40 and a curved part are similar. That is, it is preferable that the outer shape of the pressing member 48 and the shape of the opening be similar.

In the electroacoustic transducer 40, the pressing force of the visco-elastic support 46 by the conversion film 10 is not particularly limited, but the surface pressure at a position where the surface pressure is low is 0.005 to 1.0 MPa, particularly 0.02 It is preferable to set it as about -0.2MPa.
In addition, the thickness of the viscoelastic support 46 is not particularly limited, but the thickness before pressed is preferably 1 to 100 mm, particularly 10 to 50 mm.

In the illustrated example, the viscoelastic support 46 having viscoelasticity is used. However, the present invention is not limited to this, as long as the elastic support having at least elasticity is used.
For example, instead of the viscoelastic support 46, an elastic support having elasticity may be provided.
Examples of the elastic support include natural rubber and various synthetic rubbers.

Here, although the electroacoustic transducer 40 shown to FIG. 3A is pressing the peripheral region of the conversion film 10 on the case 42 by the press member 48, this invention is not limited to this.
That is, the electroacoustic transducer using the conversion film 10 does not have the pressing member 48, for example, at four corners of the case 42, the conversion film 10 is formed of the case 42 by screws, bolts, nuts and jigs. A configuration in which pressing / fixing to the upper surface is also available.
In addition, 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, and transmission of vibration of the conversion film 10 to the case 42 can be prevented, and more excellent acoustic characteristics can be obtained.

In addition, the electroacoustic transducer using the conversion film 10 may not have the case 42 for housing the viscoelastic support 46.
For example, the visco-elastic support is placed on a rigid support plate, the visco-elastic support is covered, the conversion film 10 is placed, and the same pressing member as described above is placed on the periphery. Then, a configuration in which the viscoelastic support is pressed together with the pressing member by fixing the pressing member to the support plate with a screw or the like can also be used.
The size of the support plate may be larger than that of the visco-elastic support, and the material of the support plate may be an electroacoustic transducer by using various diaphragms such as polystyrene, foamed PET, or carbon fiber. The effect of further amplifying the vibration of can also be expected.

Furthermore, the electro-acoustic transducer is not limited to the configuration for pressing the periphery, for example, a configuration in which the center of the laminate of the viscoelastic support 46 and the conversion film 10 is pressed by some means is also available. is there.
That is, as long as the electroacoustic transducer is configured to be held in a curved state of the conversion film 10, various configurations can be used.
Alternatively, the conversion film 10 may be attached to a resin film to apply tension (curve). A flexible speaker can be obtained by being configured to be held by a resin film and can be held in a curved state.
Alternatively, the conversion film 10 may be stretched on a curved frame.

  In the example shown in FIGS. 3A and 3B, the conversion film 10 is pressed against the viscoelastic support 46 and supported using the pressing member 48, but the invention is not limited thereto. For example, the case 42 The end of the conversion film may be fixed on the back surface side of the case 42 using the conversion film 10 larger than the opening surface of the above. That is, the case 42 and the visco-elastic support 46 disposed in the case 42 are covered with the conversion film 10 larger than the opening surface of the case 42, and the end of the conversion film 10 is pulled to the back side of the case 42. Alternatively, the conversion film 10 may be pressed against the viscoelastic support 46 to apply tension to be curved, and the end of the conversion film may be fixed on the back side of the case 42.

  Alternatively, using an airtight case, cover the open end of the case with a conversion film to close it, introduce a gas into the case, apply pressure to the conversion film, and hold it in a convexly expanded state It may be

For example, an electroacoustic transducer 56 shown in FIG. 4C is illustrated.
First, as shown in FIG. 4A, the electro-acoustic transducer 56 uses a similar airtight case 42, and a pipe 42a for introducing air into the case 42 is provided.
An O-ring 57 is provided on the upper surface of the open end of the case 42, and the O-ring 57 is covered with the conversion film 10 so as to close the open surface of the case 42.

Next, as shown in FIG. 4B, a frame-like presser 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 (FIG. 4B And in FIG. 4C, the O-ring 57 is omitted).
Thus, pressed and fixed to the case 42 to convert film 10, the conversion film 10, for closing the interior of the case 42 airtight.

Furthermore, as shown in FIG. 4C, air is introduced from the pipe 42a into the case 42 (the closed space by the case 42 and the conversion film 10), and pressure is applied to the conversion film 10 to expand in a convex shape. , Hold the electro-acoustic transducer 56.
The pressure in the case 42 is not limited, as long as the conversion film 10 bulges outward in a convex shape, as long as the pressure is equal to or higher than atmospheric pressure.
The pipe 42a may be fixed or detachable. When the pipe 42a is removed, it is natural that the pipe attaching / detaching portion is closed airtight.

  In FIG. 4C, pressure is applied to the inside of the case and held in a convexly expanded state. However, as shown in FIG. 4D, the case having the same airtightness as FIG. 4C is used. The open end may be covered and closed with a conversion film, and the inside of the case may be evacuated and a negative pressure may be applied to the conversion film to hold it in a concave state.

In the electroacoustic transducer 40 shown in FIGS. 3A and 3B, the conversion film 10 is configured to be pressed by the viscoelastic support 46 and held in a state where the main surface is curved in a convex shape, Thus, there is no limitation in particular in the structure which hold | maintains the conversion film 10 in the curved state.
For example, you may form a convex part in conversion film 10 itself. There is no limitation in particular as a formation method of a convex part, The processing method of various well-known resin films can be utilized. For example, the convex portion can be formed by a forming method such as a vacuum pressure molding method or embossing.

  The electroacoustic conversion film 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, the electroacoustic conversion film of the present invention may be combined with a screen for a projector.

This can improve the design and entertainability of the converted film. Further, by integrating the conversion film as a speaker with the screen or the flexible display, sound can be reproduced from the direction in which the image is displayed, and the sense of reality can be improved.
In addition, 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 between the center and the edge of the screen, and the sense of reality can be improved.
In addition, when the curvature is given to the image display surface as described above, distortion occurs in the projected image. Therefore, it is preferable to perform image processing on data of an image to be projected so as to reduce distortion in accordance with the curvature of the image display surface.

  The electro-acoustic transducer film of the present invention has been described above in detail, but the present invention is not limited to the above-described example, and various improvements and modifications may be made without departing from the scope of the present invention. Of course.

  Hereinafter, the present invention will be described in more detail by way of specific examples of the present invention.

Example 1
The conversion film 10 shown in FIG. 1 was produced by the method shown in FIGS. 2A to 2E described above.
First, cyanoethylated PVA (CR-V Shin-Etsu Chemical Co., Ltd.) and cyanoethyl pullulan (CR-S Shin-Etsu Chemical Co., Ltd.) were mixed with methyl ethyl ketone (MEK) and cyclohexanone (50 wt% each) at the following composition ratios: Dissolved in Thereafter, PZT particles as piezoelectric particles were added to this solution at the following composition ratio, and dispersed by a propeller mixer (rotation speed: 2000 rpm) to prepare a paint for forming the piezoelectric layer 12.
· PZT particles ............ 600 parts by cyanoethyl pullulan ....... 36 parts by mass cyanoethylated PVA ....... 24 parts by mass MEK · · · ···································································································· 170 parts by mass of PZT particles, after sintering commercially available PZT raw material powder at 1000 to This was crushed and classified so as to have an average particle diameter of 3.4 μm.
The proportion of the added polymer material (cyanoethyl pullulan) in the viscoelastic matrix 24 is 60% by mass.

On the other hand, sheet-like materials 11 a and 11 c 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 upper electrode 16 and the lower electrode 14 are a copper-deposited thin film having a thickness of 0.1 m, and the upper protective layer 20 and the lower protective layer 18 are a PET film having a thickness of 4 μm.
In addition, in order to obtain good handling during the process, a PET film with a 50 μm-thick separator (temporary support PET) is used, and after the thermocompression bonding of the thin film electrode and the protective layer, the separator of each protective layer is I removed it.

A paint for forming the previously prepared piezoelectric layer 12 was applied on the lower electrode 14 (copper vapor deposited thin film) of the sheet 11 a using a slide coater. The paint was applied such that the thickness of the coating after drying was 20 μm.
Next, the coating obtained on the sheet 11a was heated and dried in an oven at 120 ° C. to evaporate MEK and cyclohexanone. As a result, a laminate 11b was prepared which had the lower electrode 14 made of copper on the lower protective layer 18 made of PET, and the piezoelectric layer 12 (piezoelectric layer) having a thickness of 20 μm formed thereon. .

  The piezoelectric layer 12 of the laminate 11b was subjected to polarization treatment by the aforementioned corona poling shown in FIGS. 2C and 2D. The polarization process was performed by setting the temperature of the piezoelectric layer 12 to 100 ° C. and applying a DC voltage of 6 kV between the lower electrode 14 and the corona electrode 30 to generate a corona discharge.

A mixture of cyanoethylated pullulan and cyanoethylated PVA (CR-M, Shin-Etsu Chemical Co., Ltd.) is applied to 0.3 μm on the upper electrode 16 (copper thin film side) on the laminate 11b subjected to polarization treatment. The sheet-like material 11 c was laminated with the coated surface of the resulting film facing the piezoelectric layer 12.
Then, the laminate of the laminate 11b and the sheet 11c is thermocompression-bonded at 120 ° C. using a laminator device to bond the piezoelectric layer 12 to the upper electrode 16 and the lower electrode 14 for flat conversion Film 10 was produced.

[Examples 2 to 6]
An electroacoustic transducer film 10 was produced in the same manner as in Example 1 except that the proportion of the added polymer material (cyanoethyl pullulan) in the viscoelastic matrix 24 was changed as shown in Table 2 below.

[Example 7]
An electroacoustic transducer film 10 was produced in the same manner as in Example 1 except that cyanoethyl cellulose was used as the additive polymer material, and the proportion of the additive polymer material (cyanoethyl cellulose) in the viscoelastic matrix 24 was 20% by mass. .

[Example 8]
A nickel thin film with a thickness of 20 nm was formed by vacuum evaporation on a PET film with a thickness of 4 μm as sheet-like materials 11a and 11c, and a copper thin film with a thickness of 0.1 μm was vacuum-deposited on the nickel thin film. An electroacoustic transducing film 10 was produced in the same manner as in Example 6 (proportion of added polymer material: 20% by mass) except that the thing was used.

[Example 9]
A 20 nm thick chromium thin film was formed by vacuum evaporation on a 4 μm thick PET film as sheet materials 11a and 11c, and a 0.1 μm thick copper thin film was vacuum deposited on the chromium thin film. An electroacoustic conversion film 10 was produced in the same manner as in Example 6 except that the thing was used.

[Example 10]
An electroacoustic conversion film 10 was produced in the same manner as in Example 6 except that an aramid film with a thickness of 4 μm was used as a protective layer.

[Example 11]
An electroacoustic transducing film 10 was produced in the same manner as in Example 4 except that BaTiO ₃ particles were added as dielectric particles to the paint for forming the piezoelectric layer 12.
As the BaTiO ₃ particles, BT-05 (manufactured by Sakai Chemical Co., Ltd., average particle diameter 0.5 μm) was used. The volume fraction of the piezoelectric particles in the piezoelectric layer was 15%.

[Example 12]
An electroacoustic transducer film 10 was produced in the same manner as in Example 1 except that a nitrile rubber was used as the additive polymer material and the proportion of the additive polymer material (nitrile rubber) in the viscoelastic matrix 24 was 20 mass%. .

Comparative Example 1
An electroacoustic conversion film was produced in the same manner as in Example 1 except that the additive polymer material was not added.

[Comparative Examples 2 to 6]
An electroacoustic transducing film was produced in the same manner as in Comparative Example 1 except that the polymer material shown in Table 2 below was used instead of cyanoethylated PVA as the viscoelastic matrix.

Comparative Example 7
An electroacoustic transducer film 10 is manufactured in the same manner as in Example 1 except that polyvinylidene fluoride is used as the additive polymer material and the proportion of the additive polymer material (polyvinylidene fluoride) in the viscoelastic matrix 24 is set to 20% by mass. Was produced.

Comparative Example 8
An electroacoustic transducer film 10 is produced in the same manner as in Example 1 except that chloroprene rubber is used as the additive polymer material and the proportion of the additive polymer material (chloroprene rubber) in the viscoelastic matrix 24 is set to 20% by mass. did.

  The relative dielectric constants, the loss tangent at 25 ° C. and 20 Hz, and the volume resistance of the added polymer materials used in the examples and comparative examples are shown in Table 1 below.

[Evaluation]
<Sound pressure>
(Production of electroacoustic transducer)
A circular test piece of 70 mm in diameter was cut out from the produced conversion film, and incorporated into case 42 to produce an electroacoustic transducer 56b as shown in FIG. 4D.
The case 42 is a cylindrical container whose one surface is open, and a metal cylindrical container having a diameter of 40 mm at an opening and a depth of 10 mm was used.
The conversion film 10 is disposed so as to cover the opening of the case 42 and the peripheral portion is fixed by the holding lid 58, and then the air in the case 42 is exhausted from the pipe 42a to maintain the pressure in the case 42 at -20 kPa. And the conversion film 10 was concavely curved. It was 4 mm when arrow height of the film at this time was measured with the laser displacement meter.

(Measurement of sound pressure)
The sound pressure level of the produced electroacoustic transducer was measured to determine the sound pressure sensitivity.
Specifically, a microphone is disposed at a distance of 0.1 m toward the center of the conversion film 10 of the electroacoustic transducer 56b, and 1 kHz, 10 V _op between the upper electrode and the lower electrode of the electroacoustic transducer. The sound pressure level was measured by inputting a sine wave of.
Based on the difference with the sound pressure level of the comparative example 1, it evaluated as follows.
When the difference in sound pressure level with Comparative Example 1 is +2 dB or more, “A”
When the difference in sound pressure level with Comparative Example 1 is more than +1 dB and less than +2 dB, "B"
When the difference in sound pressure level with Comparative Example 1 is more than −1 dB and less than +1 dB, “C”
When the difference in sound pressure level with Comparative Example 1 is less than −1 dB, “D”
It was evaluated.

<Frequency band>
The sound pressure level-frequency characteristics of the produced electroacoustic transducer were measured by sine wave sweep measurement using a constant current type power amplifier. The measurement microphone was disposed at a position 10 cm immediately above the center of the speaker. Moreover, the frequency was measured between 20 Hz and 20 kHz.
From the measurement result of this sound pressure level-frequency characteristic, the maximum value (peak) of the sound pressure level and the next very small value (dip) on the high frequency side of the peak are read, and the difference between these peak and dip is determined. It evaluated as follows based on.
"A" when the difference between the peak and the dip is less than 20 dB
"B" when the difference between the peak and the dip is more than 20 dB and less than 25 dB
"C" when the difference between peak and dip is more than 25 dB

<Withstand voltage>
The withstand voltage of the conversion film was measured using the produced electroacoustic transducer.
An alternating voltage is applied to the upper thin film electrode and the lower thin film electrode of the conversion film incorporated in the electroacoustic transducer, and when the abnormality occurs in the appearance of the film, the frequency is 10 kHz. And
The following evaluation was made based on the measured withstand voltage value.
When the difference in withstand voltage value with Comparative Example 1 is 10 V or more, "A"
When the difference in withstand voltage value with Comparative Example 1 is 5 V or more and less than 10 V, "B"
When the difference in withstand voltage value with Comparative Example 1 is 2 V or more and less than 5 V, "C"
When the difference in withstand voltage value with Comparative Example 1 is 0 V or more and less than 2 V, "D"
When the difference in withstand voltage value with Comparative Example 1 is less than 0 V, "E"
The results are shown in Table 2.

It can be seen from Table 2 that in the example of the electroacoustic conversion film of the present invention, the evaluation of the sound pressure and the frequency band is higher than that of the comparative example.
Further, from the comparison of Examples 1 to 6, it is understood that the proportion of the added polymer material is preferably 10% to 30%, and more preferably 15% to 20%.
Further, it is understood from the comparison of Examples 4, 7 and 12 that the sound pressure is improved and preferable by using the added polymer material whose loss tangent at 25 ° C. and 20 Hz is 0.05 or less. In addition, it is understood that the withstand voltage is improved and is preferable because the volume resistance of the added polymer material is 1 × 10 ¹² Ω · cm or more.
Further, from the comparison between Examples 4 and 10, it is understood that the use of an aramid film having a high heat resistance, that is, a glass transition temperature Tg of 270 ° C. or more as the protective layer, improves the withstand voltage and is preferable.
Also, from the comparison between Examples 4 and 11, it is understood that the dielectric strength is improved by dispersing the dielectric particles in the piezoelectric layer, which is preferable.
From the above results, the effects of the present invention are clear.

DESCRIPTION OF SYMBOLS 10 electroacoustic conversion film 11a, 11c sheet-like object 11b laminated body 12 piezoelectric material layer 14 lower thin film electrode 16 upper thin film electrode 18 lower protective layer 20 upper protective layer 24 viscoelastic matrix 26 piezoelectric particle 30 corona electrode 32 direct current power supply 40, 56 electro-acoustic transducer 42 case 42a pipe 46 visco-elastic support 48 pressing member 57 O-ring 58 pressing lid

Claims (8)

A polymer composite piezoelectric body formed by dispersing piezoelectric particles in a viscoelastic matrix containing a polymeric material having a cyanoethyl group exhibiting viscoelasticity at normal temperature;
Two thin film electrodes stacked on both sides of the polymer composite piezoelectric material;
And two protective layers respectively stacked on the two thin film electrodes;
The visco-elastic matrix contains an additive polymer material which is a polymer material having a dielectric constant of 10 or more and dielectric particles having a dielectric constant of 80 or more ,
A volume fraction of the dielectric particles relative to a total volume of the viscoelastic matrix and the dielectric particles is 5 to 45% .   The electroacoustic transducer film according to claim 1, wherein the loss tangent at 25 ° C and 20 Hz of the added polymer material is 0.05 or less. The electroacoustic transducer film according to claim 1, wherein a volume resistance of the added polymer material is 1 × 10 ¹² Ω · cm or more.   The ratio of the said addition polymeric material in the said viscoelastic matrix is 60 mass% or less, The electroacoustic transducer film as described in any one of Claims 1-3.   The ratio of the said addition polymeric material in the said visco-elastic matrix is 10 mass% or more and 30 mass% or less, The electroacoustic transducing film as described in any one of Claims 1-4.   The electro-acoustic transducer film according to any one of claims 1 to 5, wherein the polymer material having a cyanoethyl group is cyanoethylated polyvinyl alcohol.   The electroacoustic transducer film according to any one of claims 1 to 6, wherein the added polymer material is cyanoethyl pullulan.   The electro-acoustic transducer film according to any one of claims 1 to 7, wherein an average particle diameter of the dielectric particles is 0.5 μm or less.