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DESCRIPTION JP2016063286

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DESCRIPTION JP2016063286
Abstract: To provide an electroacoustic transducing film and an electroacoustic transducer
capable of suppressing a reduction in conversion efficiency, a reduction in withstand voltage, a
reduction in flexibility, and the like even in an environment where temperature and humidity are
severe. A polymer composite piezoelectric body in which piezoelectric particles are dispersed in a
matrix made of a polymer material, a thin film electrode formed on both sides of the polymer
composite piezoelectric body, and a thin film electrode formed on the surface of the thin film
electrode The polymer composite piezoelectric material has a protective film, and the polymer
composite piezoelectric material contains the substance which is liquid at an SP value of less than
12.5 (cal / cm) and which is liquid at normal temperature in a mass ratio of 20 ppm to 500 ppm.
Solve the problem. [Selected figure] Figure 1
Electro-acoustic transducer film and electro-acoustic transducer
[0001]
The present invention relates to an electroacoustic conversion film used for an acoustic device
such as a speaker or a microphone.
[0002]
In order to correspond to the thinning of displays such as liquid crystal displays and organic EL
displays, weight reduction and thinning of speakers used for these thin displays are required.
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Furthermore, in the flexible display having flexibility, flexibility is also required in order to be
integrated into the flexible display without losing its lightness and flexibility. As such a
lightweight, thin and flexible speaker, it is considered to employ a sheet-like piezoelectric film
having a property of expanding and contracting in response to an applied voltage.
[0003]
For example, Patent Document 1 describes using, as a piezoelectric film, a uniaxially stretched
film of polyvinylidene fluoride (PVDF: Poly Vinyli Dene Fluoride) polarized with a high voltage. In
order to adopt such a piezoelectric film as a speaker, it is necessary to convert the stretching
movement along the film surface into the vibration of the film surface. The conversion from the
stretching movement to the vibration is achieved by holding the piezoelectric film in a curved
state, which enables the piezoelectric film to function as a speaker.
[0004]
However, since a piezoelectric film made of uniaxially stretched PVDF has in-plane anisotropy in
its piezoelectric characteristics, the sound quality is largely different depending on the bending
direction even with the same curvature. Furthermore, since PVDF has a small loss tangent
compared to a general speaker diaphragm such as cone paper, resonance tends to be strong and
frequency characteristics of severe undulations are obtained. Therefore, the amount of change in
sound quality when the lowest resonance frequency changes with the change in curvature also
increases. As described above, it was difficult to reproduce stable sound with a piezoelectric film
made of PVDF.
[0005]
Therefore, the applicant of the present application is a polymer material having visco-elasticity at
ordinary temperature, disclosed in Patent Document 2, as a speaker having flexibility and
capable of stably reproducing high-quality sound. Polymer composite piezoelectric body in which
piezoelectric particles are dispersed in a visco-elastic matrix, a thin film electrode formed on both
sides of the polymer composite piezoelectric body, and a protective layer formed on the surface
of the thin film electrode An acoustic conversion film was proposed.
[0006]
JP 2008-294493 JP 2014-14063 JP
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2
[0007]
The electroacoustic conversion film described in Patent Document 2 is hard against vibrations of
20 Hz to 20 kHz, and vibrations of several Hz or less by using the material of the piezoelectric
layer as a polymer material having viscoelasticity at normal temperature. It is possible for it to
behave softly, and has a moderate loss tangent for vibrations of all frequencies below 20 kHz.
Therefore, it is possible to output a sound that is excellent in flexibility and acoustic
characteristics and stable even when deformed.
[0008]
However, according to the study of the present inventors, when a temperature cycle test in which
heating and cooling were alternately repeated was performed on a piezoelectric film using a
polymer composite piezoelectric material in which piezoelectric particles are dispersed in a
matrix, the temperature was It has been found that after the cycle test, the conversion efficiency
of voltage and sound, the leakage of current, and the breakdown occur, that is, the breakdown
voltage may decrease.
That is, it has been found that there is a possibility that performance degradation may occur
under high temperature or low temperature environment. In addition, when a flexibility test was
performed under various environments, it was found that the piezoelectric layer may be cured
and the flexibility of the piezoelectric film may be reduced under low humidity.
[0009]
The object of the present invention is to solve the problems of the prior art, and the conversion
efficiency is lowered and the withstand voltage is lowered even under severe environments such
as a wide temperature range from high temperature to low temperature and a wide humidity
range. And providing an electroacoustic transducer film and an electroacoustic transducer
capable of suppressing a decrease in flexibility and the like.
[0010]
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In order to solve this problem, the inventors of the present invention have made a polymer
composite piezoelectric body formed by dispersing piezoelectric particles in a matrix made of a
polymer material, and thin film electrodes formed on both sides of the polymer composite
piezoelectric body. And a protective film formed on the surface of the thin film electrode, and the
polymer composite piezoelectric material has a SP value of less than 12.5 (cal / cm <3>) <1/2>
and is liquid at normal temperature. It has been found that, by containing 20 ppm to 500 ppm by
mass ratio, the reduction of conversion efficiency, the reduction of withstand voltage, the
reduction of flexibility and the like can be suppressed even under severe environments such as
temperature and humidity. The present invention has been completed.
That is, the present invention provides an electroacoustic transducer film and an electroacoustic
transducer having the following configurations.
[0011]
(1) A polymer composite piezoelectric body formed by dispersing piezoelectric particles in a
matrix made of a polymer material, a thin film electrode formed on both sides of the polymer
composite piezoelectric body, and a protection formed on the surface of the thin film electrode
And the polymer composite piezoelectric material has an SP value of less than 12.5 (cal / cm
<3>) <1/2>, and contains 20 ppm to 500 ppm by mass ratio of a substance liquid at normal
temperature Electro-acoustic conversion film. (2) The electroacoustic conversion film as
described in (1) whose content of a substance is 100 ppm-400 ppm. (3) The electroacoustic
transducer film according to (1) or (2), wherein the matrix is a polymer material having
viscoelasticity at ordinary temperature. (4) The electroacoustic conversion film according to any
one of (1) to (3), wherein the thickness of the polymer composite piezoelectric material is 5 to
100 ?m. (5) The substance is methyl ethyl ketone, dimethylformamide, cyclohexanone, acetone,
cyclohexane, acetonitrile, 1 propanol, 2 propanol, 2 methoxy alcohol, diacetone alcohol,
diacetone alcohol, dimethyl acetamide, benzyl alcohol, n-hexane, toluene, o-xylene, acetate The
electro-acoustic transducer film as described in any one of (1) to (4), which is at least one
selected from the group consisting of ethyl, butyl acetate, diethyl ether and tetrahydrofuran. (6)
The maximum value at which the loss tangent Tan ? at a frequency of 1 Hz is 0.5 or more
according to dynamic viscoelastic measurement of the polymer material exists in the temperature
range of 0 to 50 ░ C. in any of (1) to (5) Electro-acoustic conversion film described in. (7) The
electroacoustic conversion film according to any one of (1) to (6), wherein the polymer material
has a cyanoethyl group. (8) The electroacoustic transducer film according to any one of (1) to (7),
wherein the polymer material is cyanoethylated polyvinyl alcohol. (9) An electroacoustic
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transducer which has an electroacoustic transducing film in any one of (1)-(8), and the
supporting member which supports an electroacoustic transducing film.
[0012]
According to the electro-acoustic transducer film and the electro-acoustic transducer of the
present invention, it is possible to suppress the decrease in conversion efficiency, the decrease in
withstand voltage, the decrease in flexibility, etc., even in an environment where temperature and
humidity are severe. it can.
[0013]
It is a conceptual diagram which shows an example of the electroacoustic conversion film of this
invention.
FIGS. 2A to 2E are conceptual views showing an example of a method of producing the
electroacoustic conversion film shown in FIG. FIG. 3A to FIG. 3C are conceptual diagrams for
explaining an example of a piezoelectric speaker using the electroacoustic conversion film of the
present invention.
[0014]
Hereinafter, the electro-acoustic transducer film and the electro-acoustic transducer 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.
[0015]
In FIG. 1, an example of the electroacoustic transducing film of this invention is shown notionally.
An electroacoustic conversion film 10 (hereinafter referred to as a conversion film 10) shown in
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FIG. 1 basically includes a piezoelectric layer 12 made of a polymer composite piezoelectric
material, a thin film electrode 14 provided on one surface of the piezoelectric layer 12 and A thin
film electrode 16 provided on the other surface, and a protective layer 18 provided on the
surface of the thin film electrode 14 and a protective layer 20 provided on the surface of the thin
film electrode 16 are configured.
[0016]
Such conversion film 10 generates (reproduces) sound due to vibration according to an electrical
signal, and sounds in various acoustic devices (audio equipment) such as speakers, microphones,
and pickups used for musical instruments such as guitars. Is used to convert the vibration caused
by the
[0017]
In the conversion film 10 of the present invention, as described above, the piezoelectric layer 12
is made of a polymer composite piezoelectric material.
In the present invention, the polymer composite piezoelectric material forming the piezoelectric
material layer 12 is obtained by uniformly dispersing the piezoelectric particles 26 in a matrix 24
made of a polymer material, and the SP value is 12 in the matrix 24. .5 (cal / cm <3>) <1/2> Less
than 20% to 500 ppm by mass ratio of substance which is liquid at normal temperature. In
addition, preferably, the piezoelectric layer 12 is subjected to polarization processing. In the
present specification, ?normal temperature? refers to a temperature range of about 0 to 50 ░
C.
[0018]
Here, as a material of the matrix 24 (a matrix and a binder) of the polymer composite
piezoelectric material constituting the piezoelectric layer 12, it is preferable to use a polymer
material having viscoelasticity at normal temperature. The conversion film 10 of the present
invention is suitably used as 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. Therefore, as a
material having the following requirements, it is preferable to use a polymer material having
viscoelasticity at ordinary temperature.
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[0019]
(I) Flexibility For example, when holding in a loosely bent state in a document sense like a
newspaper or magazine for portable use, constantly receiving a relatively slow, large bending
deformation of several Hz or less from the outside 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) The sound quality 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.
[0020]
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.
[0021]
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
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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 ordinary temperature, that is, 0 to 50 ░ C.,
as the matrix of the polymer composite piezoelectric material, in that this behavior suitably
appears. .
[0022]
Various known materials can be used as the polymer material having viscoelasticity at normal
temperature. Preferably, at normal temperature, that is, 0 to 50 ░ C., a polymer material having
a maximum value of 0.5 or more of loss tangent Tan ? at a frequency of 1 Hz according to a
dynamic viscoelasticity test 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.
[0023]
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.
[0024]
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
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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.
[0025]
Examples of polymer materials that satisfy such conditions include cyanoethylated polyvinyl
alcohol (cyanoethylated PVA), polyvinyl acetate, polyvinylidene chloride coacrylonitrile,
polystyrene-vinyl polyisoprene block copolymer, polyvinyl methyl ketone, and polybutyl. A
methacrylate etc. are illustrated. Moreover, as these high molecular materials, commercially
available products such as HYBLER 5127 (manufactured by Kuraray Co., Ltd.) can be suitably
used. Among them, it is preferable to use a material having a cyanoethyl group, and it is
particularly preferable to use a 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.
[0026]
Such a matrix 24 using a polymer material having viscoelasticity at normal temperature may use
a plurality of polymer materials in combination, if necessary. That is, in addition to the viscoelastic material such as cyanoethylated PVA, other dielectric polymer materials may be added to
the matrix 24 for the purpose of adjusting the dielectric properties and mechanical properties.
[0027]
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. And fluorinated polymers
such as polyvinylidene fluoride-tetrafluoroethylene copolymer, vinylidene cyanide-vinyl acetate
copolymer, cyanoethyl cellulose, cyanoethyl hydroxysaccharose, cyanoethyl hydroxycellulose,
cyanoethyl hydroxy pullulan, cyanoethyl methacrylate, cyanoethyl acrylate, cyanoethyl acrylate
Hydroxyethyl cellulose, cyanoethyl amylose, cyanoethyl hydroxypropyl cellulose, cyanoethyl
dihydroxypropyl cellulose, Polymers having cyano group or cyanoethyl group such as noethyl
hydroxypropyl amylose, cyanoethyl polyacrylamide, cyanoethyl polyacrylate, cyanoethyl
pullulan, cyanoethyl polyhydroxy methylene, cyanoethyl glycidol pullulan, cyanoethyl saccharose
and cyanoethyl sorbitol, synthesis of nitrile rubber, chloroprene rubber, etc. Rubber etc. are
14-04-2019
9
illustrated. Among them, a polymeric material having a cyanoethyl group is suitably used.
Further, the dielectric polymer added to the material having viscoelasticity at normal
temperature such as cyanoethylated PVA in the matrix 24 of the piezoelectric layer 12 is not
limited to one type, and plural types may be added. .
[0028]
In addition to dielectric polymers, thermoplastic resins such as vinyl chloride resin, polyethylene,
polystyrene, methacrylic resin, polybutene, isobutylene, phenol resin, urea resin, melamine resin,
for the purpose of adjusting the glass transition point Tg. A thermosetting resin such as alkyd
resin or mica 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.
[0029]
The amount of addition of a polymer other than a viscoelastic material such as cyanoethylated
PVA in the matrix 24 of the piezoelectric layer 12 is not particularly limited, but is 30% by
weight or less in the proportion to the matrix 24 preferable. As a result, the characteristics of the
polymer material to be added can be expressed without impairing the viscoelastic relaxation
mechanism in the matrix 24, so that the dielectric constant can be improved, the heat resistance
can be improved, and the adhesion with the piezoelectric particles 26 and the electrode layer can
be improved. Favorable results can be obtained in terms of
[0030]
In the present invention, the material of the matrix 24 is not limited to a polymer material having
viscoelasticity at normal temperature, and the above-mentioned dielectric polymer can also be
used.
[0031]
The piezoelectric particles 26 are made of ceramic particles having a perovskite or wurtzite
crystal structure.
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Examples of ceramic particles constituting the piezoelectric particles 26 include lead zirconate
titanate (PZT), lead zirconate titanate zirconate (PLZT), barium titanate (BaTiO3), zinc oxide
(ZnO), and titanium. Examples include a solid solution (BFBT) of barium acid and bismuth ferrite
(BiFe3).
[0032]
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 ?m is preferable. By setting the particle diameter of the piezoelectric particles
26 in the above range, preferable results can be obtained in that high piezoelectric
characteristics and flexibility can be compatible.
[0033]
In FIG. 1, the piezoelectric particles 26 in the piezoelectric layer 12 are irregularly dispersed in
the matrix 24, but may be uniformly dispersed with regularity.
[0034]
In the conversion film 10 of the present invention, the ratio of the matrix 24 to the piezoelectric
particles 26 in the piezoelectric layer 12 is 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. It may
be set appropriately according to the characteristics required of
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 matrix 24 and the
piezoelectric particles 26 in the above range, preferable results can be obtained in that high
piezoelectric characteristics and flexibility can be compatible.
[0035]
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11
Here, in the conversion film 10 of the present invention, the piezoelectric layer 12 which is a
polymer composite piezoelectric body formed by dispersing piezoelectric particles in a matrix
has an SP value (solubility parameter) of 12.5 (cal / cm). <3>) Less than <1/2> and containing a
liquid substance at a normal temperature and a mass ratio of 20 ppm to 500 ppm. Specific
examples of the substance having an SP value of 12.5 (cal / cm <3>) <1/2> or less and being
liquid at normal temperature include methyl ethyl ketone, dimethylformamide, cyclohexanone,
acetone, cyclohexane, acetonitrile, 1 Organic compounds such as propanol, 2-propanol, 2methoxy alcohol, diacetone alcohol, dimethyl acetamide, benzyl alcohol, n-hexane, toluene, oxylene, ethyl acetate, butyl acetate, diethyl ether, tetrahydrofuran and the like can be mentioned.
The above substances are generally used as organic solvents. That is, according to the present
invention, the piezoelectric layer 12 contains 20 ppm to 500 ppm by mass ratio of the organic
solvent which is liquid at normal temperature and has an SP value of less than 12.5 (cal / cm
<3>) <1/2>. It is something to do.
[0036]
As described above, by forming the piezoelectric layer into a polymer composite piezoelectric
body in which piezoelectric particles are dispersed in a matrix made of a polymer material having
viscoelasticity at normal temperature, excellent in flexibility and acoustic characteristics, In
addition, it is possible to obtain a conversion film that can output a stable sound even if it is
deformed. However, according to the study of the present inventors, when a temperature cycle
test was alternately performed on a piezoelectric film using a polymer composite piezoelectric
material in which piezoelectric particles are dispersed in a matrix, heating and cooling were
alternately repeated, After the temperature cycle test, it was found that the conversion efficiency
of voltage and sound, the leak of current, and the breakdown occur, that is, the withstand voltage
may decrease. Moreover, when the flexibility test was conducted under various environments, it
was found that the piezoelectric layer (matrix) may be dried and cured under low humidity, and
the flexibility of the piezoelectric film may be reduced. The
[0037]
On the other hand, in the conversion film 10 of the present invention, the polymer composite
piezoelectric material (piezoelectric material layer 12) has an SP value of less than 12.5 (cal / cm
<3>) <1/2> and a normal temperature. The composition contains a liquid substance at a mass
ratio of 20 ppm to 500 ppm. When the polymer composite piezoelectric material contains the
above-described substance, it is possible to prevent the polymer composite piezoelectric material
from being dried and cured even under low humidity. As a result, the decrease in flexibility under
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low humidity can be prevented. In order to exhibit such an effect, the polymer composite
piezoelectric material needs to contain 20 ppm or more of the above-mentioned substance.
[0038]
Here, even in the case where the polymer composite piezoelectric material has a SP value of 12.5
(cal / cm 3) 2 <1/2> or more and contains a substance which is liquid at normal temperature, the
polymer It is possible to prevent the curing due to drying of the composite piezoelectric body.
However, when a substance having an SP value of 12.5 (cal / cm <3>) <1/2> or more is
contained, the substance is not uniformly dispersed in the polymer composite piezoelectric
material but is aggregated. It is estimated that Therefore, when exposed to high temperature and
the substance inside the piezoelectric body evaporates, a relatively large void is generated, and
the interface between the piezoelectric particles and the matrix is peeled off. As a result, the
vibration of the piezoelectric particles is not transmitted to the matrix, so that the conversion
efficiency of the voltage and the sound may be reduced, or the current may be leaked or the
dielectric breakdown may occur. On the other hand, in the present invention, by setting the SP
value of the substance to be contained in the polymer composite piezoelectric layer to less than
12.5 (cal / cm <3>) <1/2>, the substance can be made high. Since it can be uniformly dispersed
in the molecular composite piezoelectric material, generation of large voids is suppressed when
the substance inside the polymer composite piezoelectric material is evaporated by being
exposed to a high temperature, and piezoelectric particles and a matrix Can be prevented from
peeling off. Therefore, a reduction in conversion efficiency and a reduction in withstand voltage
can be suppressed.
[0039]
In addition, even when the content of the above-mentioned substance is too large, when the
substance inside the polymer composite piezoelectric body evaporates, a void is easily generated,
so the interface between the piezoelectric particles and the matrix is peeled off, and the
conversion efficiency And a reduction in withstand voltage. Therefore, in the present invention,
by setting the content of the above-mentioned substance to 500 ppm or less, when the substance
inside the polymer composite piezoelectric body evaporates, generation of large voids is
suppressed, and piezoelectric particles and matrix are Can be prevented from peeling off.
Therefore, a reduction in conversion efficiency and a reduction in withstand voltage can be
suppressed.
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[0040]
The piezoelectric layer SP value 12.5 (cal / cm <3) in the polymer composite piezoelectric
material is used from the viewpoint of preventing the decrease in flexibility and the prevention of
the decrease in conversion efficiency and the decrease in voltage resistance. It is preferable that
the content of the substance which is liquid at less than <1/2> and at normal temperature is 100
ppm to 400 ppm.
[0041]
In addition, from the viewpoint of preventing a decrease in conversion efficiency and a decrease
in withstand voltage, the SP value of the above-described substance is preferably 9.0 to 12.3 (cal
/ cm 3) 2 .1 (cal / cm <3>) <1/2> is more preferable.
[0042]
Here, the content of the substance in the polymer composite piezoelectric material is measured
by gas chromatography.
At that time, the value when the sample is left for 24 hours in an environment of temperature 50
░ C. and humidity 10% RH is taken as the content of the above-mentioned substance.
[0043]
There is no particular limitation on the method of containing the above-mentioned substance at a
predetermined concentration in the polymer composite piezoelectric body, and for example,
when preparing a paint to be a polymer composite piezoelectric body, a predetermined amount
of the above-mentioned substance may be added.
Preferably, the substance is used as a solvent of the paint to be prepared, and the drying
conditions after applying the paint are adjusted to control the content of the substance in the
polymer composite piezoelectric body. Drying conditions at that time may be appropriately set
according to the type of the substance, the desired content, the type of the matrix, the thickness
of the piezoelectric layer, and the like.
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[0044]
Further, in the conversion film 10 of the present invention, the thickness of the piezoelectric
layer 12 is not particularly limited, and depending on the size of the conversion film 10, the
application of the conversion film 10, the characteristics required of the conversion film 10, etc.
It may be set as appropriate. Here, according to the study of the present inventor, the thickness
of the piezoelectric layer 12 is preferably 5 to 100 ?m, more preferably 5 to 50 ?m, and
particularly preferably 5 to 30 ?m. By setting the thickness of the piezoelectric layer 12 in the
above range, when the content of the substance is controlled by drying as described above, the
thickness can be adjusted more easily. Further, the concentration of the substance in the
piezoelectric layer 12 can be made more uniform. In addition, by setting the thickness of the
piezoelectric layer 12 in the above-mentioned range, preferable results can be obtained also in
terms of coexistence of securing of rigidity and appropriate flexibility. As described above, the
piezoelectric layer 12 is preferably subjected to polarization processing (poling). The polarization
process will be described in detail later.
[0045]
As shown in FIG. 1, the conversion film 10 of the present invention has a configuration in which
the piezoelectric layer 12 is sandwiched between the thin film electrodes 14 and 16, and the
laminate is sandwiched between protective layers 18 and 20. In the conversion film 10, the
protective layers 18 and 20 play a role in providing the polymer composite piezoelectric body
with appropriate rigidity and mechanical strength. That is, in the conversion film 10 of the
present invention, the polymer composite piezoelectric (piezoelectric layer 12) composed of the
matrix 24 and the piezoelectric particles 26 has extremely excellent flexibility against slow
bending deformation. However, depending on the application, rigidity and mechanical strength
may be insufficient. The conversion film 10 is provided with protective layers 18 and 20 to
compensate for it.
[0046]
The protective layers 18 and 20 are not particularly limited, and various sheet-like materials can
be used. As an example, various resin films (plastic films) are suitably 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),
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polyethylene naphthalate (PEN), triacetyl cellulose (TAC), and cyclic olefin resins are preferably
used.
[0047]
The thickness of the protective layers 18 and 20 is not particularly limited. Also, 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 will be restrained but also the flexibility will be lost, so the mechanical
strength and the good handling property as a sheet are required. Except where noted, protective
layers 18 and 20 are advantageously thinner.
[0048]
Here, according to the study of the present inventor, if the thickness of the protective layers 18
and 20 is equal to or less than twice the thickness of the piezoelectric layer 12, it is possible to
secure both rigidity and appropriate flexibility, etc. Favorable results can be obtained in terms of
points. For example, when the thickness of the piezoelectric layer 12 is 50 ?m and the
protective layers 18 and 20 are made of PET, the thickness of the protective layers 18 and 20 is
preferably 100 ?m or less, more preferably 50 ?m or less, and in particular 25 ?m or less Is
preferred
[0049]
Further, as described above, the polymer material used in the present invention has a low relative
dielectric constant and is excellent in moisture resistance, so it is not necessary to form a
protective layer for moisture resistance. Therefore, the protective layer can be thin or eliminated,
and the flexibility can be improved.
[0050]
In the conversion film 10 of the present invention, the thin film electrode 14 is formed between
the piezoelectric layer 12 and the protective layer 18, and the thin film electrode 16 is formed
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between the piezoelectric layer 12 and the protective layer 20. Thin film electrodes 14 and 16
are provided to apply a voltage to conversion film 10.
[0051]
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 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.
[0052]
Further, the method of forming the thin film electrodes 14 and 16 is not particularly limited, and
a film formed by vapor deposition (vacuum film forming method) such as vacuum evaporation or
sputtering or a film formed by plating, or a foil formed of the above material is attached Various
known methods such as a method of wearing can be used.
[0053]
Above all, a thin film of copper or aluminum formed by vacuum evaporation is suitably used as
the thin film electrodes 14 and 16 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
thin film electrodes 14 and 16 is not particularly limited. Also, the thicknesses of the thin film
electrodes 14 and 16 are basically the same but may be different.
[0054]
Here, as in the case of the protective layers 18 and 20 described above, when 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 restrained but also the flexibility is impaired. 16 is advantageous as thin
as long as the electrical resistance does not become too high.
14-04-2019
17
[0055]
Here, according to the study of the 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. It is
preferable because it does not happen.
For example, when protective layers 18 and 20 are a combination of PET (Young's modulus:
about 6.2 GPa) and thin film electrodes 14 and 16 are copper (Young's modulus: about 130 GPa),
the thickness of protective layers 18 and 20 is 25 ?m. If so, the thickness of the thin film
electrodes 14 and 16 is preferably 1.2 ?m or less, more preferably 0.3 ?m or less, and
particularly preferably 0.1 ?m or less.
[0056]
In addition, the thin film electrode 14 and / or the thin film electrode 16 need not necessarily be
formed corresponding to the entire surface of the piezoelectric layer 12 (the 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, for example, the piezoelectric layer 12, and the piezoelectric layer 12 may be in
direct contact with the protective film at the periphery of the conversion film 10. .
[0057]
Alternatively, the protective layer 18 and / or 20 having the thin film electrode 14 and / or the
thin film electrode 16 formed on the entire surface does not have to be formed correspondingly
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 layers 18 and / or 20.
[0058]
As described above, the conversion film 10 of the present invention is obtained by dispersing the
piezoelectric particles 26 in the matrix 24 and contains a substance having an SP value of less
14-04-2019
18
than 12.5 (cal / cm <3>) <1/2>. The piezoelectric layer 12 (polymer composite piezoelectric
body) is sandwiched between the thin film electrodes 14 and 16, and the laminated body is
further sandwiched by the protective layers 18 and 20. In such a conversion film 10 of the
present invention, it is preferable that a maximum value at which a loss tangent (Tan ?) at a
frequency of 1 Hz by dynamic viscoelasticity measurement is 0.5 or more exists 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
[0059]
Moreover, as for the conversion film 10 of this invention, it is preferable that the storage elastic
modulus (E ') in frequency 1 Hz by dynamic-viscoelasticity measurement is 10-30 GPa in 0
degreeC, and 1-10 GPa in 50 degreeC. 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.
[0060]
In addition, the conversion film 10 of the present invention has a product of the thickness and
the storage elastic modulus (E ?) at a frequency of 1 Hz measured by dynamic viscoelasticity
measurement: 1.0 О 10 6 <~2.0 at 0 ░ C. О 10 <6> (1.0E + 06 to 2.0E + 06) N / m at 50 ░ C.
1.0 О 10 <5> to 1.0 О 10 <6> (1.0E + 05 to 1.0E + 06) N / Preferably it is m. Thereby,
appropriate rigidity and mechanical strength can be provided as long as the conversion film 10
does not lose flexibility and acoustic characteristics.
[0061]
Furthermore, the conversion film 10 of the present invention preferably has a loss tangent (Tan
?) of 0.05 or more at 25 ░ C. and a frequency of 1 kHz in a master curve obtained from
dynamic viscoelasticity measurement. As a result, the frequency characteristics of the speaker
using the conversion film 10 become smooth, and the amount of change in sound quality when
the minimum resonance frequency f 0 changes with the change in curvature of the speaker can
be reduced.
14-04-2019
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[0062]
Next, an example of the manufacturing method of the electroacoustic transducing film of this
invention is demonstrated with reference to FIG. 2 (A)-FIG.2 (E). First, as shown in FIG. 2A, the
sheet-like material 10a in which the thin film electrode 14 is formed on the protective layer 18 is
prepared. The sheet 10a may be manufactured 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 is poor, the 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. The separator may be removed
after thermocompression bonding of the thin film electrode and the protective layer.
Alternatively, a commercially available product in which a copper thin film or the like is formed
on the protective layer 18 may be used as the sheet 10a.
[0063]
On the other hand, a polymer material to be a matrix material such as cyanoethylated PVA is
dissolved in an organic solvent, and further, piezoelectric particles 26 such as PZT particles, and
an SP value of 12.5 (cal / day) liquid at normal temperature. Substances less than cm <3>) <1/2>
are added and stirred to prepare a paint. In addition, there is no limitation in particular as an
organic solvent, Although various organic solvents can be utilized, it is preferable to use the said
substance as an organic solvent as mentioned above. After preparing the above-mentioned sheet
10a and preparing a paint, the paint is cast (coated) on the sheet 10a, and the organic solvent is
evaporated to dryness. As a result, as shown in FIG. 2B, a laminate 10b having the thin film
electrode 14 on the protective layer 18 and the piezoelectric layer 12 formed on the thin film
electrode 14 is manufactured. Here, as described above, the drying conditions of the paint are
adjusted, and the above-described substance (organic solvent) of 20 ppm to 500 ppm by mass
ratio is left in the piezoelectric layer 12.
[0064]
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.
[0065]
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20
As described above, in the conversion film 10 of the present invention, a polymeric piezoelectric
material such as PVDF may be added to the matrix 24 in addition to the viscoelastic material
such as cyanoethylated PVA.
When adding these polymeric piezoelectric materials to the matrix 24, the polymeric
piezoelectric materials added to the above-mentioned paint may be dissolved. Once the laminate
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 fabricated, preferably the polarization process (poling) of
the piezoelectric layer 12 is performed. .
[0066]
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 FIG. 2 (C) and FIG. 2 (D) are exemplified.
[0067]
In this method, as shown in FIGS. 2 (C) and 2 (D), a gap g is opened by, for example, 1 mm on the
upper surface 12a of the piezoelectric layer 12 of the laminate 10b, and movement is performed
along this upper surface 12a. A possible rod-like or wire-like corona electrode 30 is provided.
Then, the corona electrode 30 and the thin film electrode 14 are connected to a DC power supply
32. Furthermore, a heating means for heating and holding the laminate 10b, for example, a hot
plate is prepared.
[0068]
Then, while heating and holding the piezoelectric layer 12 at a temperature of 100 ░ C., for
example, by heating means, a few kV, for example, 6 kV is applied between the thin film
electrode 14 and the corona electrode 30 from the DC power supply 32. A direct current 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
14-04-2019
21
piezoelectric layer 12.
[0069]
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 10b, and
the stacked body 10b may be moved for polarization processing. Also for the movement of the
laminate 10b, 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 thin film electrode 16
before the polarization process. 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
performing this calendering process, the thermocompression bonding process described later
can be smoothly performed.
[0070]
Thus, while the polarization process of the piezoelectric material layer 12 of the laminated body
10b is performed, the sheet-like article 10c in which the thin film electrode 16 is formed on the
protective layer 20 is prepared. The sheet 10c may be manufactured by forming a copper thin
film or the like as the thin film electrode 16 on the surface of the protective layer 20 by vacuum
deposition, sputtering, plating or the like. Next, as shown in FIG. 2E, the thin film electrode 16 is
directed to the piezoelectric layer 12, and the sheet 10c is laminated on the laminate 10b after
the polarization process of the piezoelectric layer 12 is completed. Further, the laminated body of
the laminated body 10b and the sheet-like material 10c is thermocompression-bonded by a
heating press device, a heating roller pair or the like so as to sandwich the protective layer 20
and the protective layer 18 as shown in FIG. The conversion film of the present invention is
produced.
[0071]
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22
Next, the electroacoustic transducer of the present invention using the conversion film 10 will be
described. FIG. 3 (B) is a top view showing an example of the electro-acoustic transducer of the
present invention, and FIG. 3 (A) is a cross-sectional view taken along the line aa of FIG. 3 (B).
The electroacoustic transducer 40 shown in FIGS. 3A and 3B is a flat piezoelectric speaker using
the above-described conversion film 10 of the present invention as a speaker diaphragm for
converting an electric signal into vibration energy. is there. The piezoelectric speaker 40 can also
be used as a microphone or a sensor.
[0072]
The piezoelectric speaker 40 of the illustrated example 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 cylindrical case which is formed of plastic or the like and which is open on one side. In
the piezoelectric speaker using the conversion film of the present invention, the case 42 (i.e., the
piezoelectric speaker) is not limited to a square cylindrical shape, and is a case of various shapes
such as a cylindrical shape or a rectangular square rectangular bottom surface. Is available. The
frame 48 is a plate having a through hole at the center and having the same shape as the upper
end surface (open surface side) of the case 42. Furthermore, the visco-elastic support 46 has
appropriate viscosity and elasticity, supports the conversion film 10, and does not waste the
stretching movement of the conversion film by providing a constant mechanical bias anywhere
on the conversion film. It is for conversion into back and forth movement (movement in the
direction perpendicular to the plane of the film). As an example, nonwoven fabric such as wool
felt, wool felt including rayon and PET, glass wool, foam material such as polyurethane (foam
plastic), a plurality of sheets of paper, paint, etc. are exemplified. In the illustrated example, the
viscoelastic support 46 is a square prism having a bottom shape slightly larger than the bottom
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,
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>.
[0073]
In the piezoelectric speaker 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
14-04-2019
23
periphery of the conversion film 10 is The frame 48 is fixed to the case 42 in a state of being
pressed to the upper end face. The method for fixing the frame 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, a
method using a fixing jig, and the like can be used.
[0074]
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, in the state before the conversion film 10 and the frame 48 are
fixed, the visco-elastic support 46 protrudes from the upper surface of the case 42. There is.
Therefore, in the piezoelectric speaker 40, the viscoelastic support 46 is pressed downward by
the conversion film 10 as it gets closer to the peripheral portion of the viscoelastic support 46,
and is held in a state in which the thickness is reduced. That is, the main surface of the
conversion film 10 is held in a curved state. In this case, it is preferable to press the entire
surface of the visco-elastic support 46 in the surface direction of the conversion film 10 so that
the entire thickness is reduced. That is, it is preferable that the entire surface of the conversion
film 10 be pressed and supported by the viscoelastic support 46.
[0075]
In the piezoelectric speaker 40 using the conversion film 10 of the present invention, the
pressing force of the viscoelastic support 46 by the conversion film 10 is not particularly limited,
but the surface pressure is 0.02 to 0 at a low surface pressure. It is preferable to set it to about 2
MPa. The height difference of the conversion film 10 incorporated into the piezoelectric speaker
40, and in the illustrated example, the distance between the nearest and the farthest to the
bottom of the frame 48 is not particularly limited, but a thin flat speaker is obtained. It is
preferable to set the diameter to about 1 to 50 mm, particularly about 5 to 20 mm, in that
sufficient conversion of the conversion film 10 up and down is possible. 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.
[0076]
In such a piezoelectric speaker 40, when the conversion film 10 expands in the in-plane direction
14-04-2019
24
by applying a voltage to the piezoelectric layer 12, the conversion film 10 is positioned above
(radial direction of sound) to absorb the expansion. Move to Conversely, when the conversion
film 10 contracts in the in-plane direction by voltage application to the piezoelectric layer 12, the
conversion film 10 moves downward (to the case 42 side) to absorb the contraction. The
piezoelectric speaker 40 generates a sound by the vibration due to the repetition of expansion
and contraction of the conversion film 10.
[0077]
In the piezoelectric speaker 40, the visco-elastic support 46 is compressed in the thickness
direction as it approaches the frame 48. However, the static visco-elastic effect (stress relaxation)
mechanically biases the conversion film 10 anywhere. 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
piezoelectric speaker 40 excellent in acoustic characteristics can be obtained.
[0078]
Here, although the piezoelectric speaker 40 of the illustrated example presses the entire
peripheral area of the conversion film 10 against the case 42 (that is, the viscoelastic support 46)
by the frame 48, the present invention is not limited to this. That is, the electroacoustic
transducer using the conversion film 10 of the present invention does not have the frame 48, for
example, at four corners of the case 42, with the conversion film 10 by screws, bolt nuts, jigs, etc.
A configuration in which the upper surface of the case 42 is pressed / fixed may be used. 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.
[0079]
Further, the electroacoustic transducer using the conversion film 10 may be configured to have a
support plate on which the visco-elastic support 46 is placed, instead of the case 42
accommodating the visco-elastic support 46. That is, the visco-elastic support 46 is placed on a
rigid support plate, the visco-elastic support 46 is covered, the conversion film 10 is placed, and
14-04-2019
25
the same frame 48 as above is placed on the periphery of the conversion film 10 It is also
possible to use a configuration in which the visco-elastic support 46 is pressed by the conversion
film 10 together with the frame 48 by fixing the frame 48 to the support plate with a screw or
the like to bend the conversion film 10 It is. Further, even in a configuration without such a case
42, the conversion film 10 may be held in a state in which the viscoelastic support 46 is pressed
and thinned by a screw or the like without using the frame 48. The vibration of the conversion
film 10 may be further amplified by using various diaphragms such as polystyrene, foamed PET,
or carbon fiber as the material of the support plate.
[0080]
Furthermore, the electro-acoustic transducer using the conversion film 10 is not limited to the
configuration for pressing the periphery, for example, a location other than the periphery of the
laminate of the visco-elastic support 46 and the conversion film 10 by some means A
configuration in which at least a part of the conversion film 10 is held in a curved state by
pressing can also be used. Alternatively, a resin film may be attached to the conversion film 10 to
apply (hold) tension. 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.
[0081]
Further, the electro-acoustic transducer of the present invention is not limited to the
configuration using the viscoelastic support 46. For example, as the case, using an airtight
material having the same shape as the case 42, the open end of the case is covered with the
conversion film 10 and closed, and gas is introduced into the case to apply pressure to the
conversion film 10 It may be configured to be held in a convexly bulging state.
[0082]
In addition, in the structure which applies an internal pressure, a distortion component may
increase by the influence of an air spring, and there exists a possibility that a sound quality may
fall. On the other hand, in the case of a structure in which the conversion film 10 is supported by
a visco-elastic support such as glass wool or felt, since viscosity is given, it is preferable without
an increase in distortion component. Also, the case may be filled with gas other than gas, and
14-04-2019
26
magnetic fluid and paint can be used as long as appropriate viscosity can be given. Further, the
configuration using the viscoelastic support and the configuration applying pressure inside may
be combined.
[0083]
The electroacoustic conversion film and the electroacoustic transducer of the present invention
can be suitably used as a speaker in combination with a flexible display such as an organic EL
display. Further, since the electro-acoustic conversion film and the electro-acoustic transducer of
the present invention are thin, they can be suitably combined with thin display devices such as
liquid crystal display devices, electronic paper, and screens for projectors. Such a configuration
can improve the design and entertainability of the converted film. Further, by integrating the
conversion film as a speaker with the screen or the display, the 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.
[0084]
Further, as described above, in the conversion film 10 of the present invention, the piezoelectric
layer 12 also has the ability to convert vibrational energy into an electrical signal. Therefore, the
conversion film 10 of the present invention can be suitably used also for a microphone or a
sensor (pickup) for musical instruments by using this. For example, since the conversion film 10
of the present invention has flexibility, it can be attached to the throat of a person having a
complicated curved surface, and acts as a vocal cord microphone only by being attached near the
vocal cords.
[0085]
Although the electro-acoustic transducer film and the electro-acoustic transducer of the present
invention have been described above in detail, the present invention is not limited to the abovedescribed example, and various improvements and modifications can be made without departing
14-04-2019
27
from the scope of the present invention. Of course it is good.
[0086]
Hereinafter, the present invention will be described in more detail by way of specific examples of
the present invention.
[0087]
Example 1 The conversion film 10 of the present invention shown in FIG. 1 was produced by the
method shown in FIG.
First, cyanoethylated PVA (CR-V, manufactured by Shin-Etsu Chemical Co., Ltd.) was dissolved in
methyl ethyl ketone (MEK) at the following composition ratio.
Thereafter, PZT particles were added to 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. и и и и и и и и и и и и и и PZT particles и и и и и и и и и и и и 300 parts by weight и
cyanoethylated PVA и и и и и и и и и и 30 parts by weight и MEK и и и и и и и и и и и и и и 70 parts by weight The
PZT particles were obtained by sintering a commercially available PZT raw material powder at
1000 to 1200 ░ C., and then crushing and classifying this to an average particle diameter of 5
?m.
[0088]
On the other hand, sheet-like materials 10a and 10c were prepared by vacuum-depositing a 0.1
?m thick copper thin film on a 4 ?m thick PET film. That is, in this example, the thin film
electrodes 14 and 16 are copper-deposited thin films with a thickness of 0.1 m, and the
protective layers 18 and 20 are PET films with a thickness of 4 ?m. On the thin film electrode
14 (copper vapor deposition thin film) of the sheet 10a, a coating for forming the previously
prepared piezoelectric layer 12 was applied using a slide coater. The paint was applied such that
the thickness of the coating after drying was 40 ?m. Next, the paint applied on the sheet 10 a
was dried by heating on a hot plate at 100 ░ C. for 30 minutes to evaporate a part of MEK. As a
result, a laminate 10b having a thin film electrode 14 made of copper on a protective layer 18
made of PET, and a piezoelectric layer 12 (piezoelectric layer) having a thickness of 40 ?m
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28
formed thereon was produced.
[0089]
The piezoelectric layer 12 of the laminate 10b was subjected to polarization treatment by the
aforementioned corona poling shown in FIGS. 2 (C) and 2 (D). 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 thin film electrode 14 and the corona electrode 30 to cause
corona discharge.
[0090]
The sheet-like material 10c was laminated on the polarization-processed laminate 10b with the
thin film electrode 16 (copper thin film side) facing the piezoelectric layer 12. Next, the laminate
of the laminate 10 b and the sheet 10 c is thermocompression bonded at 120 ░ C. using a
laminator device to bond the piezoelectric layer 12 and the thin film electrodes 14 and 16,
thereby the conversion film 10. Was produced.
[0091]
Here, MEK used as the solvent has a SP value (solubility parameter) of 9.3 (cal / cm <3>) <1/2>
and is liquid at normal temperature. That is, the substance having an SP value of less than 12.5
(cal / cm <3>) <1/2> and being liquid at normal temperature in Example 1 is MEK. A sample of
the piezoelectric layer 12 was partially cut out to 5 cm square from the produced conversion film
10, and the content of MEK (the above-mentioned substance) was measured. For measurement, a
gas chromatograph (7890A GC-System, manufactured by Agilent) was used, and the column was
RESTEK Stabilwax 0.53 mm? О 30 m film 1.0 ?m. First, the sample was sealed in a vial and
heated to 160 ░ C. for 30 minutes, after which MEK was quantified. After leaving the sample to
stand for 24 hours in an environment of temperature 50 ░ C. and humidity 10% RH, the content
of MEK (the above-mentioned substance) was measured. As a result of measurement, the content
of MEK was 30 ppm.
[0092]
[Examples 2 to 7] A conversion film 10 was produced in the same manner as in Example 1 except
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29
that the drying conditions of the coated material to be the piezoelectric layer 12 were changed to
the conditions shown in Table 1 below.
[0093]
[Examples 8 to 9] A conversion film 10 was produced in the same manner as in Example 1 except
that the thickness of the piezoelectric layer 12 and the drying conditions were changed to the
conditions shown in Table 1 below.
[0094]
[Examples 10 to 14] The solvent is changed to DMF (dimethylformamide SP value: 12.1 (cal / cm
<3>) <1/2>), and the thickness of the piezoelectric layer 12 and the drying conditions are
changed. A conversion film 10 was produced in the same manner as in Example 1 except that the
conditions shown in Table 1 below were respectively changed.
[0095]
Example 15 An example was prepared except that the solvent was changed to cyclohexanone (SP
value: 9.9 (cal / cm 3)) <1/2> and the drying conditions were changed to the conditions shown in
Table 1 below. A conversion film 10 was produced in the same manner as in 1.
[0096]
[Example 16] An example was prepared except that the solvent was changed to acetone (SP
value: 9.9 (cal / cm 3)) <1/2> and the drying conditions were changed to the conditions shown in
Table 1 below. A conversion film 10 was produced in the same manner as in 1.
[0097]
Comparative Examples 1 and 2 A conversion film was produced in the same manner as in
Example 1 except that the drying conditions were changed to the conditions shown in Table 1
below.
[0098]
Comparative Examples 3 to 4 A conversion film was produced in the same manner as in Example
10 except that the drying conditions were changed to the conditions shown in Table 1 below.
[0099]
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30
Comparative Examples 5 to 6 A conversion film was produced in the same manner as in Example
15, except that the drying conditions were changed to the conditions shown in Table 1 below.
[0100]
Comparative Examples 7 to 8 A conversion film was produced in the same manner as in Example
16 except that the drying conditions were changed to the conditions shown in Table 1 below.
[0101]
Comparative Example 9 Except that the solvent was changed to furfuryl alcohol (SP value: 12.5
(cal / cm <3>) <1/2>) and the drying conditions were changed to the conditions shown in Table 1
below, A conversion film was produced in the same manner as in Example 1.
[0102]
Comparative Example 10 Except that the solvent was changed to MEK + ethylene glycol (SP
value: 14.6 (cal / cm <3>) <1/2>), and the drying conditions were changed to the conditions
shown in Table 1 below, A conversion film was produced in the same manner as in Example 1.
Since ethylene glycol has a higher boiling point than MEK, only ethylene glycol remains in the
piezoelectric layer after drying of the paint.
[0103]
Reference Example 1 A conversion film was produced in the same manner as in Example 1
except that PVDF containing no piezoelectric particles was used as the piezoelectric layer, and
the drying conditions were changed to the conditions shown in Table 1 below.
In addition, the piezoelectric material layer which consists of PVDF was formed by the method
similar to Example 1 except having prepared the coating material which contains PVDF and MEK
of the following composition ratio.
ииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииии 300
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31
[0104]
[Reference Examples 2 to 3] Converted films were produced in the same manner as Reference
Example 1 except that the drying conditions were changed to the conditions shown in Table 1
below.
[0105]
[Evaluation] [Temperature cycle test] First, the conversion efficiency and the withstand voltage of
the produced conversion film were measured.
The conversion efficiency was evaluated by speaker performance by incorporating the produced
conversion film into a piezoelectric speaker.
First, a circular test piece of ? 150 mm was produced from the produced conversion film.
The test piece was fixed so as to cover the opening surface of a plastic round case with an inner
diameter of 138 mm and a depth of 9 mm, and the pressure inside the case was maintained at
1.02 atm.
Thereby, the conversion film was bent in a convex shape like a contact lens.
The sound pressure level-frequency characteristics of the thin piezoelectric speaker produced in
this manner were measured by sine wave sweep measurement using a constant current power
amplifier.
The measurement microphone was placed at a position 10 cm immediately above the center of
the piezoelectric speaker.
The withstand voltage was an effective voltage when no sound was generated by applying an
alternating voltage to the conversion film.
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[0106]
Next, a temperature cycle test was performed on the converted film.
The temperature cycle test was conducted in accordance with JIS C60068-2-14. After heating at
a temperature of 85 ░ C for 10 minutes, it was cooled at a temperature of -33 ░ C for 10
minutes. After repeating this heating and cooling five times, the conversion efficiency and the
withstand voltage were measured in the same manner as described above. The ratio of the
conversion efficiency after heating and cooling (after the temperature cycle test) to the
conversion efficiency immediately after the preparation (before the temperature cycle test) was
determined and evaluated as follows. A: 95% or more. B: 90% or more and less than 95%. C: less
than 90%.
[0107]
Similarly, the ratio of the withstand voltage after heating and cooling (after the temperature cycle
test) to the withstand voltage immediately after the preparation (before the temperature cycle
test) was determined and evaluated as follows. A: 90% or more. B: 70% or more and less than
90%. C: less than 70%.
[0108]
[Flexibility Test Under Low Humidity] A 1 cm О 15 cm strip-shaped test piece was produced
from the produced conversion film. After leaving this in an environment of humidity 10% RH and
temperature 25 ░ C. for 6 hours, in this environment, a predetermined radius of curvature (r = 5
cm, r = 2.5 cm and r = 0.5 cm) After rounding to 10 times and returning to the original state were
repeated 10 times, changes in the electrical characteristics (capacitance and dielectric loss) and
appearance were examined. When no change was seen in the electrical characteristics and
appearance, A was taken, and when no change was seen in the electrical characteristics but
marks such as folds remained, it was taken as B. When a change in the electrical characteristics
was seen, it was taken as C. The results of the evaluation and the content of the solvent are
shown in Table 1.
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[0109]
[0110]
From Table 1, the polymer composite piezoelectric material contains 20 ppm to 500 ppm by
mass ratio of substance having a SP value of less than 12.5 (cal / cm <3>) <1/2> and liquid at
normal temperature. In Examples 1 to 16, in comparison with Comparative Examples 1 to 10,
even if there is a drastic temperature change, the decrease in conversion efficiency and the
decrease in withstand voltage is small, and the decrease in flexibility under low humidity is It
turns out that it can suppress.
Further, it is understood from the comparison between Examples 1 to 4 and Examples 5 to 7 and
the comparison between Example 10 and Example 11 that the content of the above-mentioned
substance is preferably 100 ppm to 400 ppm.
[0111]
Further, Comparative Examples 1, 3, 5, 7 show that when the content of the substance is less
than 20 ppm, the flexibility under low humidity decreases. Further, Comparative Examples 2, 4,
6, 8 show that, when the content of the above-mentioned substance is more than 500 ppm, the
conversion efficiency and the withstand voltage decrease when the temperature changes.
Further, from Comparative Examples 9 and 10, in the case of containing a substance having an
SP value of 12.5 (cal / cm <3>) <1/2> or more, even if the content is within the above range, the
temperature is It can be seen that, when there is a change, the conversion efficiency and the
withstand voltage decrease.
[0112]
From the reference examples 1 to 3, the decrease in flexibility under low humidity, the
conversion efficiency due to the temperature change, and the decrease in withstand voltage are
obtained by dispersing the piezoelectric particles in the matrix made of the polymer material. It
can be seen that this is a problem unique to composite piezoelectric materials. From the above
results, the effects of the present invention are clear.
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[0113]
DESCRIPTION OF SYMBOLS 10 Electro-acoustic conversion film 12 Piezoelectric layer 14, 16
Thin film electrode 18, 20 Protective layer 24 Matrix 26 Piezoelectric particle 30 Corona
electrode 32 DC power supply 40 Piezoelectric speaker 42 Case 46 Viscoelastic support 48
Frame
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35
e electroacoustic conversion film according to any
one of (1) to (3), wherein the thickness of the polymer composite piezoelectric material is 5 to
100 ?m. (5) The substance is methyl ethyl ketone, dimethylformamide, cyclohexanone, acetone,
cyclohexane, acetonitrile, 1 propanol, 2 propanol, 2 methoxy alcohol, diacetone alcohol,
diacetone alcohol, dimethyl acetamide, benzyl alcohol, n-hexane, toluene, o-xylene, acetate The
electro-acoustic transducer film as described in any one of (1) to (4), which is at least one
selected from the group consisting of ethyl, butyl acetate, diethyl ether and tetrahydrofuran. (6)
The maximum value at which the loss tangent Tan ? at a frequency of 1 Hz is 0.5 or more
according to dynamic viscoelastic measurement of the polymer material exists in the temperature
range of 0 to 50 ░ C. in any of (1) to (5) Electro-acoustic conversion film described in. (7) The
electroacoustic conversion film according to any one of (1) to (6), wherein the polymer material
has a cyanoethyl group. (8) The electroacoustic transducer film according to any one of (1) to (7),
wherein the polymer material is cyanoethylated polyvinyl alcohol. (9) An electroacoustic
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4
transducer which has an electroacoustic transducing film in any one of (1)-(8), and the
supporting member which supports an electroacoustic transducing film.
[0012]
According to the electro-acoustic transducer film and the electro-acoustic transducer of the
present invention, it is possible to suppress the decrease in conversion efficiency, the decrease in
withstand voltage, the decrease in flexibility, etc., even in an environment where temperature and
humidity are severe. it can.
[0013]
It is a conceptual diagram which shows an example of the electroacoustic conversion film of this
invention.
FIGS. 2A to 2E are conceptual views showing an example of a method of producing the
electroacoustic conversion film shown in FIG. FIG. 3A to FIG. 3C are conceptual diagrams for
explaining an example of a piezoelectric speaker using the electroacoustic conversion film of the
present invention.
[0014]
Hereinafter, the electro-acoustic transducer film and the electro-acoustic transducer 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.
[0015]
In FIG. 1, an example of the electroacoustic transducing film of this invention is shown notionally.
An electroacoustic conversion film 10 (hereinafter referred to as a conversion film 10) shown in
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5
FIG. 1 basically includes a piezoelectric layer 12 made of a polymer composite piezoelectric
material, a thin film electrode 14 provided on one surface of the piezoelectric layer 12 and A thin
film electrode 16 provided on the other surface, and a protective layer 18 provided on the
surface of the thin film electrode 14 and a protective layer 20 provided on the surface of the thin
film electrode 16 are configured.
[0016]
Such conversion film 10 generates (reproduces) sound due to vibration according to an electrical
signal, and sounds in various acoustic devices (audio equipment) such as speakers, microphones,
and pickups used for musical instruments such as guitars. Is used to convert the vibration caused
by the
[0017]
In the conversion film 10 of the present invention, as described above, the piezoelectric layer 12
is made of a polymer composite piezoelectric material.
In the present invention, the polymer composite piezoelectric material forming the piezoelectric
material layer 12 is obtained by uniformly dispersing the piezoelectric particles 26 in a matrix 24
made of a polymer material, and the SP value is 12 in the matrix 24. .5 (cal / cm <3>) <1/2> Less
than 20% to 500 ppm by mass ratio of substance which is liquid at normal temperature. In
addition, preferably, the piezoelectric layer 12 is subjected to polarization processing. In the
present specification, ?normal temperature? refers to a temperature range of about 0 to 50 ░
C.
[0018]
Here, as a material of the matrix 24 (a matrix and a binder) of the polymer composite
piezoelectric material constituting the piezoelectric layer 12, it is preferable to use a polymer
material having viscoelasticity at normal temperature. The conversion film 10 of the present
invention is suitably used as 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. Therefore, as a
material having the following requirements, it is preferable to use a polymer material having
viscoelasticity at ordinary temperature.
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[0019]
(I) Flexibility For example, when holding in a loosely bent state in a document sense like a
newspaper or magazine for portable use, constantly receiving a relatively slow, large bending
deformation of several Hz or less from the outside 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) The sound quality 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.
[0020]
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.
[0021]
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
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7
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 ordinary temperature, that is, 0 to 50 ░ C.,
as the matrix of the polymer composite piezoelectric material, in that this behavior suitably
appears. .
[0022]
Various known materials can be used as the polymer material having viscoelasticity at normal
temperature. Preferably, at normal temperature, that is, 0 to 50 ░ C., a polymer material having
a maximum value of 0.5 or more of loss tangent Tan ? at a frequency of 1 Hz according to a
dynamic viscoelasticity test 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.
[0023]
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.
[0024]
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
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8
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.
[0025]
Examples of polymer materials that satisfy such conditions include cyanoethylated polyvinyl
alcohol (cyanoethylated PVA), polyvinyl acetate, polyvinylidene chloride coacrylonitrile,
polystyrene-vinyl polyisoprene block copolymer, polyvinyl methyl ketone, and polybutyl. A
methacrylate etc. are illustrated. Moreover, as these high molecular materials, commercially
available products such as HYBLER 5127 (manufactured by Kuraray Co., Ltd.) can be suitably
used. Among them, it is preferable to use a material having a cyanoethyl group, and it is
particularly preferable to use a 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.
[0026]
Such a matrix 24 using a polymer material having viscoelasticity at normal temperature may use
a plurality of polymer materials in combination, if necessary. That is, in addition to the viscoelastic material such as cyanoethylated PVA, other dielectric polymer materials may be added to
the matrix 24 for the purpose of adjusting the dielectric properties and mechanical properties.
[0027]
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. And fluorinated polymers
such as polyvinylidene fluoride-tetrafluoroethylene copolymer, vinylidene cyanide-vinyl acetate
copolymer, cyanoethyl cellulose, cyanoethyl hydroxysaccharose, cyanoethyl hydroxycellulose,
cyanoethyl hydroxy pullulan, cyanoethyl methacrylate, cyanoethyl acrylate, cyanoethyl acrylate
Hydroxyethyl cellulose, cyanoethyl amylose, cyanoethyl hydroxypropyl cellulose, cyanoethyl
dihydroxypropyl cellulose, Polymers having cyano group or cyanoethyl group such as noethyl
hydroxypropyl amylose, cyanoethyl polyacrylamide, cyanoethyl polyacrylate, cyanoethyl
pullulan, cyanoethyl polyhydroxy methylene, cyanoethyl glycidol pullulan, cyanoethyl saccharose
and cyanoethyl sorbitol, synthesis of nitrile rubber, chloroprene rubber, etc. Rubber etc. are
14-04-2019
9
illustrated. Among them, a polymeric material having a cyanoethyl group is suitably used.
Further, the dielectric polymer added to the material having viscoelasticity at normal
temperature such as cyanoethylated PVA in the matrix 24 of the piezoelectric layer 12 is not
limited to one type, and plural types may be added. .
[0028]
In addition to dielectric polymers, thermoplastic resins such as vinyl chloride resin, polyethylene,
polystyrene, methacrylic resin, polybutene, isobutylene, phenol resin, urea resin, melamine resin,
for the purpose of adjusting the glass transition point Tg. A thermosetting resin such as alkyd
resin or mica 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.
[0029]
The amount of addition of a polymer other than a viscoelastic material such as cyanoethylated
PVA in the matrix 24 of the piezoelectric layer 12 is not particularly limited, but is 30% by
weight or less in the proportion to the matrix 24 preferable. As a result, the characteristics of the
polymer material to be added can be expressed without impairing the viscoelastic relaxation
mechanism in the matrix 24, so that the dielectric constant can be improved, the heat resistance
can be improved, and the adhesion with the piezoelectric particles 26 and the electrode layer can
be improved. Favorable results can be obtained in terms of
[0030]
In the present invention, the material of the matrix 24 is not limited to a polymer material having
viscoelasticity at normal temperature, and the above-mentioned dielectric polymer can also be
used.
[0031]
The piezoelectric particles 26 are made of ceramic particles having a perovskite or wurtzite
crystal structure.
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10
Examples of ceramic particles constituting the piezoelectric particles 26 include lead zirconate
titanate (PZT), lead zirconate titanate zirconate (PLZT), barium titanate (BaTiO3), zinc oxide
(ZnO), and titanium. Examples include a solid solution (BFBT) of barium acid and bismuth ferrite
(BiFe3).
[0032]
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 ?m is preferable. By setting the particle diameter of the piezoelectric particles
26 in the above range, preferable results can be obtained in that high piezoelectric
characteristics and flexibility can be compatible.
[0033]
In FIG. 1, the piezoelectric particles 26 in the piezoelectric layer 12 are irregularly dispersed in
the matrix 24, but may be uniformly dispersed with regularity.
[0034]
In the conversion film 10 of the present invention, the ratio of the matrix 24 to the piezoelectric
particles 26 in the piezoelectric layer 12 is 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. It may
be set appropriately according to the characteristics required of
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 matrix 24 and the
piezoelectric particles 26 in the above range, preferable results can be obtained in that high
piezoelectric characteristics and flexibility can be compatible.
[0035]
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11
Here, in the conversion film 10 of the present invention, the piezoelectric layer 12 which is a
polymer composite piezoelectric body formed by dispersing piezoelectric particles in a matrix
has an SP value (solubility parameter) of 12.5 (cal / cm). <3>) Less than <1/2> and containing a
liquid substance at a normal temperature and a mass ratio of 20 ppm to 500 ppm. Specific
examples of the substance having an SP value of 12.5 (cal / cm <3>) <1/2> or less and being
liquid at normal temperature include methyl ethyl ketone, dimethylformamide, cyclohexanone,
acetone, cyclohexane, acetonitrile, 1 Organic compounds such as propanol, 2-propanol, 2methoxy alcohol, diacetone alcohol, dimethyl acetamide, benzyl alcohol, n-hexane, toluene, oxylene, ethyl acetate, butyl acetate, diethyl ether, tetrahydrofuran and the like can be mentioned.
The above substances are generally used as organic solvents. That is, according to the present
invention, the piezoelectric layer 12 contains 20 ppm to 500 ppm by mass ratio of the organic
solvent which is liquid at normal temperature and has an SP value of less than 12.5 (cal / cm
<3>) <1/2>. It is something to do.
[0036]
As described above, by forming the piezoelectric layer into a polymer composite piezoelectric
body in which piezoelectric particles are dispersed in a matrix made of a polymer material having
viscoelasticity at normal temperature, excellent in flexibility and acoustic characteristics, In
addition, it is possible to obtain a conversion film that can output a stable sound even if it is
deformed. However, according to the study of the present inventors, when a temperature cycle
test was alternately performed on a piezoelectric film using a polymer composite piezoelectric
material in which piezoelectric particles are dispersed in a matrix, heating and cooling were
alternately repeated, After the temperature cycle test, it was found that the conversion efficiency
of voltage and sound, the leak of current, and the breakdown occur, that is, the withstand voltage
may decrease. Moreover, when the flexibility test was conducted under various environments, it
was found that the piezoelectric layer (matrix) may be dried and cured under low humidity, and
the flexibility of the piezoelectric film may be reduced. The
[0037]
On the other hand, in the conversion film 10 of the present invention, the polymer composite
piezoelectric material (piezoelectric material layer 12) has an SP value of less than 12.5 (cal / cm
<3>) <1/2> and a normal temperature. The composition contains a liquid substance at a mass
ratio of 20 ppm to 500 ppm. When the polymer composite piezoelectric material contains the
above-described substance, it is possible to prevent the polymer composite piezoelectric material
from being dried and cured even under low humidity. As a result, the decrease in flexibility under
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12
low humidity can be prevented. In order to exhibit such an effect, the polymer composite
piezoelectric material needs to contain 20 ppm or more of the above-mentioned substance.
[0038]
Here, even in the case where the polymer composite piezoelectric material has a SP value of 12.5
(cal / cm 3) 2 <1/2> or more and contains a substance which is liquid at normal temperature, the
polymer It is possible to prevent the curing due to drying of the composite piezoelectric body.
However, when a substance having an SP value of 12.5 (cal / cm <3>) <1/2> or more is
contained, the substance is not uniformly dispersed in the polymer composite piezoelectric
material but is aggregated. It is estimated that Therefore, when exposed to high temperature and
the substance inside the piezoelectric body evaporates, a relatively large void is generated, and
the interface between the piezoelectric particles and the matrix is peeled off. As a result, the
vibration of the piezoelectric particles is not transmitted to the matrix, so that the conversion
efficiency of the voltage and the sound may be reduced, or the current may be leaked or the
dielectric breakdown may occur. On the other hand, in the present invention, by setting the SP
value of the substance to be contained in the polymer composite piezoelectric layer to less than
12.5 (cal / cm <3>) <1/2>, the substance can be made high. Since it can be uniformly dispersed
in the molecular composite piezoelectric material, generation of large voids is suppressed when
the substance inside the polymer composite piezoelectric material is evaporated by being
exposed to a high temperature, and piezoelectric particles and a matrix Can be prevented from
peeling off. Therefore, a reduction in conversion efficiency and a reduction in withstand voltage
can be suppressed.
[0039]
In addition, even when the content of the above-mentioned substance is too large, when the
substance inside the polymer composite piezoelectric body evaporates, a void is easily generated,
so the interface between the piezoelectric particles and the matrix is peeled off, and the
conversion efficiency And a reduction in withstand voltage. Therefore, in the present invention,
by setting the content of the above-mentioned substance to 500 ppm or less, when the substance
inside the polymer composite piezoelectric body evaporates, generation of large voids is
suppressed, and piezoelectric particles and matrix are Can be prevented from peeling off.
Therefore, a reduction in conversion efficiency and a reduction in withstand voltage can be
suppressed.
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13
[0040]
The piezoelectric layer SP value 12.5 (cal / cm <3) in the polymer composite piezoelectric
material is used from the viewpoint of preventing the decrease in flexibility and the prevention of
the decrease in conversion efficiency and the decrease in voltage resistance. It is preferable that
the content of the substance which is liquid at less than <1/2> and at normal temperature is 100
ppm to 400 ppm.
[0041]
In addition, from the viewpoint of preventing a decrease in conversion efficiency and a decrease
in withstand voltage, the SP value of the above-described substance is preferably 9.0 to 12.3 (cal
/ cm 3) 2 .1 (cal / cm <3>) <1/2> is more preferable.
[0042]
Here, the content of the substance in the polymer composite piezoelectric material is measured
by gas chromatography.
At that time, the value when the sample is left for 24 hours in an environment of temperature 50
░ C. and humidity 10% RH is taken as the content of the above-mentioned substance.
[0043]
There is no particular limitation on the method of containing the above-mentioned substance at a
predetermined concentration in the polymer composite piezoelectric body, and for example,
when preparing a paint to be a polymer composite piezoelectric body, a predetermined amount
of the above-mentioned substance may be added.
Preferably, the substance is used as a solvent of the paint to be prepared, and the drying
conditions after applying the paint are adjusted to control the content of the substance in the
polymer composite piezoelectric body. Drying conditions at that time may be appropriately set
according to the type of the substance, the desired content, the type of the matrix, the thickness
of the piezoelectric layer, and the like.
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14
[0044]
Further, in the conversion film 10 of the present invention, the thickness of the piezoelectric
layer 12 is not particularly limited, and depending on the size of the conversion film 10, the
application of the conversion film 10, the characteristics required of the conversion film 10, etc.
It may be set as appropriate. Here, according to the study of the present inventor, the thickness
of the piezoelectric layer 12 is preferably 5 to 100 ?m, more preferably 5 to 50 ?m, and
particularly preferably 5 to 30 ?m. By setting the thickness of the piezoelectric layer 12 in the
above range, when the content of the substance is controlled by drying as described above, the
thickness can be adjusted more easily. Further, the concentration of the substance in the
piezoelectric layer 12 can be made more uniform. In addition, by setting the thickness of the
piezoelectric layer 12 in the above-mentioned range, preferable results can be obtained also in
terms of coexistence of securing of rigidity and appropriate flexibility. As described above, the
piezoelectric layer 12 is preferably subjected to polarization processing (poling). The polarization
process will be described in detail later.
[0045]
As shown in FIG. 1, the conversion film 10 of the present invention has a configuration in which
the piezoelectric layer 12 is sandwiched between the thin film electrodes 14 and 16, and the
laminate is sandwiched between protective layers 18 and 20. In the conversion film 10, the
protective layers 18 and 20 play a role in providing the polymer composite piezoelectric body
with appropriate rigidity and mechanical strength. That is, in the conversion film 10 of the
present invention, the polymer composite piezoelectric (piezoelectric layer 12) composed of the
matrix 24 and the piezoelectric particles 26 has extremely excellent flexibility against slow
bending deformation. However, depending on the application, rigidity and mechanical strength
may be insufficient. The conversion film 10 is provided with protective layers 18 and 20 to
compensate for it.
[0046]
The protective layers 18 and 20 are not particularly limited, and various sheet-like materials can
be used. As an example, various resin films (plastic films) are suitably 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),
14-04-2019
15
polyethylene naphthalate (PEN), triacetyl cellulose (TAC), and cyclic olefin resins are preferably
used.
[0047]
The thickness of the protective layers 18 and 20 is not particularly limited. Also, 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 will be restrained but also the flexibility will be lost, so the mechanical
strength and the good handling property as a sheet are required. Except where noted, protective
layers 18 and 20 are advantageously thinner.
[0048]
Here, according to the study of the present inventor, if the thickness of the protective layers 18
and 20 is equal to or less than twice the thickness of the piezoelectric layer 12, it is possible to
secure both rigidity and appropriate flexibility, etc. Favorable results can be obtained in terms of
points. For example, when the thickness of the piezoelectric layer 12 is 50 ?m and the
protective layers 18 and 20 are made of PET, the thickness of the protective layers 18 and 20 is
preferably 100 ?m or less, more preferably 50 ?m or less, and in particular 25 ?m or less Is
preferred
[0049]
Further, as described above, the polymer material used in the present invention has a low relative
dielectric constant and is excellent in moisture resistance, so it is not necessary to form a
protective layer for moisture resistance. Therefore, the protective layer can be thin or eliminated,
and the flexibility can be improved.
[0050]
In the conversion film 10 of the present invention, the thin film electrode 14 is formed between
the piezoelectric layer 12 and the protective layer 18, and the thin film electrode 16 is formed
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16
between the piezoelectric layer 12 and the protective layer 20. Thin film electrodes 14 and 16
are provided to apply a voltage to conversion film 10.
[0051]
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 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.
[0052]
Further, the method of forming the thin film electrodes 14 and 16 is not particularly limited, and
a film formed by vapor deposition (vacuum film forming method) such as vacuum evaporation or
sputtering or a film formed by plating, or a foil formed of the above material is attached Various
known methods such as a method of wearing can be used.
[0053]
Above all, a thin film of copper or aluminum formed by vacuum evaporation is suitably used as
the thin film electrodes 14 and 16 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
thin film electrodes 14 and 16 is not particularly limited. Also, the thicknesses of the thin film
electrodes 14 and 16 are basically the same but may be different.
[0054]
Here, as in the case of the protective layers 18 and 20 described above, when 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 restrained but also the flexibility is impaired. 16 is advantageous as thin
as long as the electrical resistance does not become too high.
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17
[0055]
Here, according to the study of the 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. It is
preferable because it does not happen.
For example, when protective layers 18 and 20 are a combination of PET (Young's modulus:
about 6.2 GPa) and thin film electrodes 14 and 16 are copper (Young's modulus: about 130 GPa),
the thickness of protective layers 18 and 20 is 25 ?m. If so, the thickness of the thin film
electrodes 14 and 16 is preferably 1.2 ?m or less, more preferably 0.3 ?m or less, and
particularly preferably 0.1 ?m or less.
[0056]
In addition, the thin film electrode 14 and / or the thin film electrode 16 need not necessarily be
formed corresponding to the entire surface of the piezoelectric layer 12 (the 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, for example, the piezoelectric layer 12, and the piezoelectric layer 12 may be in
direct contact with the protective film at the periphery of the conversion film 10. .
[0057]
Alternatively, the protective layer 18 and / or 20 having the thin film electrode 14 and / or the
thin film electrode 16 formed on the entire surface does not have to be formed correspondingly
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 layers 18 and / or 20.
[0058]
As described above, the conversion film 10 of the present invention is obtained by dispersing the
piezoelectric particles 26 in the matrix 24 and contains a substance having an SP value of less
14-04-2019
18
than 12.5 (cal / cm <3>) <1/2>. The piezoelectric layer 12 (polymer composite piezoelectric
body) is sandwiched between the thin film electrodes 14 and 16, and the laminated body is
further sandwiched by the protective layers 18 and 20. In such a conversion film 10 of the
present invention, it is preferable that a maximum value at which a loss tangent (Tan ?) at a
frequency of 1 Hz by dynamic viscoelasticity measurement is 0.5 or more exists 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
[0059]
Moreover, as for the conversion film 10 of this invention, it is preferable that the storage elastic
modulus (E ') in frequency 1 Hz by dynamic-viscoelasticity measurement is 10-30 GPa in 0
degreeC, and 1-10 GPa in 50 degreeC. 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.
[0060]
In addition, the conversion film 10 of the present invention has a product of the thickness and
the storage elastic modulus (E ?) at a frequency of 1 Hz measured by dynamic viscoelasticity
measurement: 1.0 О 10 6 <~2.0 at 0 ░ C. О 10 <6> (1.0E + 06 to 2.0E + 06) N / m at 50 ░ C.
1.0 О 10 <5> to 1.0 О 10 <6> (1.0E + 05 to 1.0E + 06) N / Preferably it is m. Thereby,
appropriate rigidity and mechanical strength can be provided as long as the conversion film 10
does not lose flexibility and acoustic characteristics.
[0061]
Furthermore, the conversion film 10 of the present invention preferably has a loss tangent (Tan
?) of 0.05 or more at 25 ░ C. and a frequency of 1 kHz in a master curve obtained from
dynamic viscoelasticity measurement. As a result, the frequency characteristics of the speaker
using the conversion film 10 become smooth, and the amount of change in sound quality when
the minimum resonance frequency f 0 changes with the change in curvature of the speaker can
be reduced.
14-04-2019
19
[0062]
Next, an example of the manufacturing method of the electroacoustic transducing film of this
invention is demonstrated with reference to FIG. 2 (A)-FIG.2 (E). First, as shown in FIG. 2A, the
sheet-like material 10a in which the thin film electrode 14 is formed on the protective layer 18 is
prepared. The sheet 10a may be manufactured 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 is poor, the 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. The separator may be removed
after thermocompression bonding of the thin film electrode and the protective layer.
Alternatively, a commercially available product in which a copper thin film or the like is formed
on the protective layer 18 may be used as the sheet 10a.
[0063]
On the other hand, a polymer material to be a matrix material such as cyanoethylated PVA is
dissolved in an organic solvent, and further, piezoelectric particles 26 such as PZT particles, and
an SP value of 12.5 (cal / day) liquid at normal temperature. Substances less than cm <3>) <1/2>
are added and stirred to prepare a paint. In addition, there is no limitation in particular as an
organic solvent, Although various organic solvents can be utilized, it is preferable to use the said
substance as an organic solvent as mentioned above. After preparing the above-mentioned sheet
10a and preparing a paint, the paint is cast (coated) on the sheet 10a, and the organic solvent is
evaporated to dryness. As a result, as shown in FIG. 2B, a laminate 10b having the thin film
electrode 14 on the protective layer 18 and the piezoelectric layer 12 formed on the thin film
electrode 14 is manufactured. Here, as described above, the drying conditions of the paint are
adjusted, and the above-described substance (organic solvent) of 20 ppm to 500 ppm by mass
ratio is left in the piezoelectric layer 12.
[0064]
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.
[0065]
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20
As described above, in the conversion film 10 of the present invention, a polymeric piezoelectric
material such as PVDF may be added to the matrix 24 in addition to the viscoelastic material
such as cyanoethylated PVA.
When adding these polymeric piezoelectric materials to the matrix 24, the polymeric
piezoelectric materials added to the above-mentioned paint may be dissolved. Once the laminate
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 fabricated, preferably the polarization process (poling) of
the piezoelectric layer 12 is performed. .
[0066]
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 FIG. 2 (C) and FIG. 2 (D) are exemplified.
[0067]
In this method, as shown in FIGS. 2 (C) and 2 (D), a gap g is opened by, for example, 1 mm on the
upper surface 12a of the piezoelectric layer 12 of the laminate 10b, and movement is performed
along this upper surface 12a. A possible rod-like or wire-like corona electrode 30 is provided.
Then, the corona electrode 30 and the thin film electrode 14 are connected to a DC power supply
32. Furthermore, a heating means for heating and holding the laminate 10b, for example, a hot
plate is prepared.
[0068]
Then, while heating and holding the piezoelectric layer 12 at a temperature of 100 ░ C., for
example, by heating means, a few kV, for example, 6 kV is applied between the thin film
electrode 14 and the corona electrode 30 from the DC power supply 32. A direct current 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
14-04-2019
21
piezoelectric layer 12.
[0069]
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 10b, and
the stacked body 10b may be moved for polarization processing. Also for the movement of the
laminate 10b, 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 thin film electrode 16
before the polarization process. 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
performing this calendering process, the thermocompression bonding process described later
can be smoothly performed.
[0070]
Thus, while the polarization process of the piezoelectric material layer 12 of the laminated body
10b is performed, the sheet-like article 10c in which the thin film electrode 16 is formed on the
protective layer 20 is prepared. The sheet 10c may be manufactured by forming a copper thin
film or the like as the thin film electrode 16 on the surface of the protective layer 20 by vacuum
deposition, sputtering, plating or the like. Next, as shown in FIG. 2E, the thin film electrode 16 is
directed to the piezoelectric layer 12, and the sheet 10c is laminated on the laminate 10b after
the polarization process of the piezoelectric layer 12 is completed. Further, the laminated body of
the laminated body 10b and the sheet-like material 10c is thermocompression-bonded by a
heating press device, a heating roller pair or the like so as to sandwich the protective layer 20
and the protective layer 18 as shown in FIG. The conversion film of the present invention is
produced.
[0071]
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22
Next, the electroacoustic transducer of the present invention using the conversion film 10 will be
described. FIG. 3 (B) is a top view showing an example of the electro-acoustic transducer of the
present invention, and FIG. 3 (A) is a cross-sectional view taken along the line aa of FIG. 3 (B).
The electroacoustic transducer 40 shown in FIGS. 3A and 3B is a flat piezoelectric speaker using
the above-described conversion film 10 of the present invention as a speaker diaphragm for
converting an electric signal into vibration energy. is there. The piezoelectric speaker 40 can also
be used as a microphone or a sensor.
[0072]
The piezoelectric speaker 40 of the illustrated example 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 cylindrical case which is formed of plastic or the like and which is open on one side. In
the piezoelectric speaker using the conversion film of the present invention, the case 42 (i.e., the
piezoelectric speaker) is not limited to a square cylindrical shape, and is a case of various shapes
such as a cylindrical shape or a rectangular square rectangular bottom surface. Is available. The
frame 48 is a plate having a through hole at the center and having the same shape as the upper
end surface (open surface side) of the case 42. Furthermore, the visco-elastic support 46 has
appropriate viscosity and elasticity, supports the conversion film 10, and does not waste the
stretching movement of the conversion film by providing a constant mechanical bias anywhere
on the conversion film. It is for conversion into back and forth movement (movement in the
direction perpendicular to the plane of the film). As an example, nonwoven fabric such as wool
felt, wool felt including rayon and PET, glass wool, foam material such as polyurethane (foam
plastic), a plurality of sheets of paper, paint, etc. are exemplified. In the illustrated example, the
viscoelastic support 46 is a square prism having a bottom shape slightly larger than the bottom
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,
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>.
[0073]
In the piezoelectric speaker 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
14-04-2019
23
periphery of the conversion film 10 is The frame 48 is fixed to the case 42 in a state of being
pressed to the upper end face. The method for fixing the frame 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, a
method using a fixing jig, and the like can be used.
[0074]
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, in the state before the conversion film 10 and the frame 48 are
fixed, the visco-elastic support 46 protrudes from the upper surface of the case 42. There is.
Therefore, in the piezoelectric speaker 40, the viscoelastic support 46 is pressed downward by
the conversion film 10 as it gets closer to the peripheral portion of the viscoelastic support 46,
and is held in a state in which the thickness is reduced. That is, the main surface of the
conversion film 10 is held in a curved state. In this case, it is preferable to press the entire
surface of the visco-elastic support 46 in the surface direction of the conversion film 10 so that
the entire thickness is reduced. That is, it is preferable that the entire surface of the conversion
film 10 be pressed and supported by the viscoelastic support 46.
[0075]
In the piezoelectric speaker 40 using the conversion film 10 of the present invention, the
pressing force of the viscoelastic support 46 by the conversion film 10 is not particularly limited,
but the surface pressure is 0.02 to 0 at a low surface pressure. It is preferable to set it to about 2
MPa. The height difference of the conversion film 10 incorporated into the piezoelectric speaker
40, and in the illustrated example, the distance between the nearest and the farthest to the
bottom of the frame 48 is not particularly limited, but a thin flat speaker is obtained. It is
preferable to set the diameter to about 1 to 50 mm, particularly about 5 to 20 mm, in that
sufficient conversion of the conversion film 10 up and down is possible. 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.
[0076]
In such a piezoelectric speaker 40, when the conversion film 10 expands in the in-plane direction
14-04-2019
24
by applying a voltage to the piezoelectric layer 12, the conversion film 10 is positioned above
(radial direction of sound) to absorb the expansion. Move to Conversely, when the conversion
film 10 contracts in the in-plane direction by voltage application to the piezoelectric layer 12, the
conversion film 10 moves downward (to the case 42 side) to absorb the contraction. The
piezoelectric speaker 40 generates a sound by the vibration due to the repetition of expansion
and contraction of the conversion film 10.
[0077]
In the piezoelectric speaker 40, the visco-elastic support 46 is compressed in the thickness
direction as it approaches the frame 48. However, the static visco-elastic effect (stress relaxation)
mechanically biases the conversion film 10 anywhere. 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
piezoelectric speaker 40 excellent in acoustic characteristics can be obtained.
[0078]
Here, although the piezoelectric speaker 40 of the illustrated example presses the entire
peripheral area of the conversion film 10 against the case 42 (that is, the viscoelastic support 46)
by the frame 48, the present invention is not limited to this. That is, the electroacoustic
transducer using the conversion film 10 of the present invention does not have the frame 48, for
example, at four corners of the case 42, with the conversion film 10 by screws, bolt nuts, jigs, etc.
A configuration in which the upper surface of the case 42 is pressed / fixed may be used. 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.
[0079]
Further, the electroacoustic transducer using the conversion film 10 may be configured to have a
support plate on which the visco-elastic support 46 is placed, instead of the case 42
accommodating the visco-elastic support 46. That is, the visco-elastic support 46 is placed on a
rigid support plate, the visco-elastic support 46 is covered, the conversion film 10 is placed, and
14-04-2019
25
the same frame 48 as above is placed on the periphery of the conversion film 10 It is also
possible to use a configuration in which the visco-elastic support 46 is pressed by the conversion
film 10 together with the frame 48 by fixing the frame 48 to the support plate with a screw or
the like to bend the conversion film 10 It is. Further, even in a configuration without such a case
42, the conversion film 10 may be held in a state in which the viscoelastic support 46 is pressed
and thinned by a screw or the like without using the frame 48. The vibration of the conversion
film 10 may be further amplified by using various diaphragms such as polystyrene, foamed PET,
or carbon fiber as the material of the support plate.
[0080]
Furthermore, the electro-acoustic transducer using the conversion film 10 is not limited to the
configuration for pressing the periphery, for example, a location other than the periphery of the
laminate of the visco-elastic support 46 and the conversion film 10 by some means A
configuration in which at least a part of the conversion film 10 is held in a curved state by
pressing can also be used. Alternatively, a resin film may be attached to the conversion film 10 to
apply (hold) tension. 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.
[0081]
Further, the electro-acoustic transducer of the present invention is not limited to the
configuration using the viscoelastic support 46. For example, as the case, using an airtight
material having the same shape as the case 42, the open end of the case is covered with the
conversion film 10 and closed, and gas is introduced into the case to apply pressure to the
conversion film 10 It may be configured to be held in a convexly bulging state.
[0082]
In addition, in the structure which applies an internal pressure, a distortion component may
increase by the influence of an air spring, and there exists a possibility that a sound quality may
fall. On the other hand, in the case of a structure in which the conversion film 10 is supported by
a visco-elastic support such as glass wool or felt, since viscosity is given, it is preferable without
an increase in distortion component. Also, the case may be filled with gas other than gas, and
14-04-2019
26
magnetic fluid and paint can be used as long as appropriate viscosity can be given. Further, the
configuration using the viscoelastic support and the configuration applying pressure inside may
be combined.
[0083]
The electroacoustic conversion film and the electroacoustic transducer of the present invention
can be suitably used as a speaker in combination with a flexible display such as an organic EL
display. Further, since the electro-acoustic conversion film and the electro-acoustic transducer of
the present invention are thin, they can be suitably combined with thin display devices such as
liquid crystal display devices, electronic paper, and screens for projectors. Such a configuration
can improve the design and entertainability of the converted film. Further, by integrating the
conversion film as a speaker with the screen or the display, the 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.
[0084]
Further, as described above, in the conversion film 10 of the present invention, the piezoelectric
layer 12 also has the ability to convert vibrational energy into an electrical signal. Therefore, the
conversion film 10 of the present invention can be suitably used also for a microphone or a
sensor (pickup) for musical instruments by using this. For example, since the conversion film 10
of the present invention has flexibility, it can be attached to the throat of a person having a
complicated curved surface, and acts as a vocal cord microphone only by being attached near the
vocal cords.
[0085]
Although the electro-acoustic transducer film and the electro-acoustic transducer of the present
invention have been described above in detail, the present invention is not limited to the abovedescribed example, and various improvements and modifications can be made without departing
14-04-2019
27
from the scope of the present invention. Of course it is good.
[0086]
Hereinafter, the present invention will be described in more detail by way of specific examples of
the present invention.
[0087]
Example 1 The conversion film 10 of the present invention shown in FIG. 1 was produced by the
method shown in FIG.
First, cyanoethylated PVA (CR-V, manufactured by Shin-Etsu Chemical Co., Ltd.) was dissolved in
methyl ethyl ketone (MEK) at the following composition ratio.
Thereafter, PZT particles were added to 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. и и и и и и и и и и и и и и PZT particles и и и и и и и и и и и и 300 parts by weight и
cyanoethylated PVA и и и и и и и и и и 30 parts by weight и MEK и и и и и и и и и и и и и и 70 parts by weight The
PZT particles were obtained by sintering a commercially available PZT raw material powder at
1000 to 1200 ░ C., and then crushing and classifying this to an average particle diameter of 5
?m.
[0088]
On the other hand, sheet-like materials 10a and 10c were prepared by vacuum-depositing a 0.1
?m thick copper thin film on a 4 ?m thick PET film. That is, in this example, the thin film
electrodes 14 and 16 are copper-deposited thin films with a thickness of 0.1 m, and the
protective layers 18 and 20 are PET films with a thickness of 4 ?m. On the thin film electrode
14 (copper vapor deposition thin film) of the sheet 10a, a coating for forming the previously
prepared piezoelectric layer 12 was applied using a slide coater. The paint was applied such that
the thickness of the coating after drying was 40 ?m. Next, the paint applied on the sheet 10 a
was dried by heating on a hot plate at 100 ░ C. for 30 minutes to evaporate a part of MEK. As a
result, a laminate 10b having a thin film electrode 14 made of copper on a protective layer 18
made of PET, and a piezoelectric layer 12 (piezoelectric layer) having a thickness of 40 ?m
14-04-2019
28
formed thereon was produced.
[0089]
The piezoelectric layer 12 of the laminate 10b was subjected to polarization treatment by the
aforementioned corona poling shown in FIGS. 2 (C) and 2 (D). 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 thin film electrode 14 and the corona electrode 30 to cause
corona discharge.
[0090]
The sheet-like material 10c was laminated on the polarization-processed laminate 10b with the
thin film electrode 16 (copper thin film side) facing the piezoelectric layer 12. Next, the laminate
of the laminate 10 b and the sheet 10 c is thermocompression bonded at 120 ░ C. using a
laminator device to bond the piezoelectric layer 12 and the thin film electrodes 14 and 16,
thereby the conversion film 10. Was produced.
[0091]
Here, MEK used as the solvent has a SP value (solubility parameter) of 9.3 (cal / cm <3>) <1/2>
and is liquid at normal temperature. That is, the substance having an SP value of less than 12.5
(cal / cm <3>) <1/2> and being liquid at normal temperature in Example 1 is MEK. A sample of
the piezoelectric layer 12 was partially cut out to 5 cm square from the produced conversion film
10, and the content of MEK (the above-mentioned substance) was measured. For measurement, a
gas chromatograph (7890A GC-System, manufactured by Agilent) was used, and the column was
RESTEK Stabilwax 0.53 mm? О 30 m film 1.0 ?m. First, the sample was sealed in a vial and
heated to 160 ░ C. for 30 minutes, after which MEK was quantified. After leaving the sample to
stand for 24 hours in an environment of temperature 50 ░ C. and humidity 10% RH, the content
of MEK (the above-mentioned substance) was measured. As a result of measurement, the content
of MEK was 30 ppm.
[0092]
[Examples 2 to 7] A conversion film 10 was produced in the same manner as in Example 1 except
14-04-2019
29
that the drying conditions of the coated material to be the piezoelectric layer 12 were changed to
the conditions shown in Table 1 below.
[0093]
[Examples 8 to 9] A conversion film 10 was produced in the same manner as in Example 1 except
that the thickness of the piezoelectric layer 12 and the drying conditions were changed to the
conditions shown in Table 1 below.
[0094]
[Examples 10 to 14] The solvent is changed to DMF (dimethylformamide SP value: 12.1 (cal / cm
<3>) <1/2>), and the thickness of the piezoelectric layer 12 and the drying conditions are
changed. A conversion film 10 was produced in the same manner as in Example 1 except that the
conditions shown in Table 1 below were respectively changed.
[0095]
Example 15 An example was prepared except that the solvent was changed to cyclohexanone (SP
value: 9.9 (cal / cm 3)) <1/2> and the drying conditions were changed to the conditions shown in
Table 1 below. A conversion film 10 was produced in the same manner as in 1.
[0096]
[Example 16] An example was prepared except that the solvent was changed to acetone (SP
value: 9.9 (cal / cm 3)) <1/2> and the drying conditions were changed to the conditions shown in
Table 1 below. A conversion film 10 was produced in the same manner as in 1.
[0097]
Comparative Examples 1 and 2 A c
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