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JP2015006011

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DESCRIPTION JP2015006011
PROBLEM TO BE SOLVED: To provide a polymer speaker which can be reduced in weight and
thickness and can obtain practical sound pressure in a wide frequency range from low frequency
to high frequency. SOLUTION: A polymer speaker 1 is configured by including an electrostrictive
element 10 having a dielectric layer 11 made of an elastomer or resin, and a plurality of
electrode layers 12a and 12b disposed on both sides of the dielectric layer 11. . In the polymer
speaker 1, the electrode layers 12a and 12b include a polymer binder and a conductive material
and are made of a conductive material having an elastic modulus of 100 MPa or less, and the
volume resistivity of the electrode layers 12a and 12b is 200 Ω · cm or less. The spring constant
of the electrostrictive element 10, which is the sum of the spring constant of the dielectric layer
11 and the spring constant of the electrode layers 12a and 12b, is 3000 N / m or less. [Selected
figure] Figure 3
Polymer speaker
[0001]
The present invention relates to a polymer speaker using an electrostrictive element in a
vibrating portion.
[0002]
A dynamic speaker unit is known as a speaker for converting an electrical signal into sound.
05-05-2019
1
The dynamic speaker unit is composed of a permanent magnet, a voice coil, a diaphragm and the
like. According to the dynamic speaker unit, the phases of sound are reversed in front of and
behind the diaphragm. For this reason, when the sound emitted from the rear turns to the front,
the front sound and the rear sound cancel each other, resulting in a small sound. Therefore, in
order to block forward turning of the sound emitted from the rear, the dynamic speaker unit is
used in a state incorporated in the enclosure. In this case, it is necessary to prevent air in the
enclosure from obstructing the movement of the diaphragm. Therefore, the enclosure is easily
enlarged.
[0003]
On the other hand, a piezoelectric speaker using a piezoelectric material such as lead zirconate
titanate or polyvinylidene fluoride resin has been developed as a thin speaker (see, for example,
Patent Documents 2 and 3). However, since the piezoelectric body has high rigidity, there is a
problem that it is difficult to make sound in a low frequency region. On the other hand, Patent
Documents 4 and 5 disclose a transducer configured by arranging a pair of electrodes on both
sides of a dielectric dielectric layer made of elastomer. In this type of transducer, when the
voltage applied between the electrodes is increased, the electrostatic attraction between the
electrodes is increased, and the dielectric layer sandwiched between the electrodes is compressed
from the thickness direction. This reduces the thickness of the dielectric layer. As the dielectric
layer becomes thinner, the dielectric layer extends in the surface direction accordingly. On the
other hand, when the voltage applied between the electrodes is reduced, the electrostatic
attraction between the electrodes is reduced, and the compressive force on the dielectric layer is
reduced. For this reason, the dielectric layer becomes thick. As the dielectric layer becomes
thicker, the dielectric layer contracts in the surface direction accordingly. The change in
thickness of the dielectric layer with respect to voltage can be used to use the transducer as a
speaker.
[0004]
JP 2007-312094 JP JP 2006-5800 JP JP 2007-74502 JP JP-2007-524278 JP JP 2011-72112
JP
[0005]
When the above-mentioned transducer is used as a speaker, an alternating voltage as an electric
signal of sound is superimposed in a state where a bias voltage is applied to the dielectric layer.
05-05-2019
2
Under the present circumstances, according to the electrostatic attraction between electrodes, a
dielectric layer repeats expansion-contraction. However, if the electrode is hard, the movement of
the dielectric layer is blocked by the electrode and sufficient sound pressure can not be obtained.
Also, when the dielectric layer is stretched, the electrode may be cracked. In this case, the
conductivity is lowered and can not play a role as an electrode. Also, as described below, the
harder the electrode, the less likely it is for the sound pressure in the low frequency region to be
emitted.
[0006]
FIG. 1 shows a schematic view of sound pressure frequency characteristics of an arbitrary
speaker. As shown in FIG. 1, in the low frequency region, the sound pressure increases in
proportion to the frequency. Here, the frequency at which the sound pressure is maximized is
referred to as a primary resonance frequency (f 0). The primary resonance frequency is derived
by the following equation (1). As shown in equation (1), the primary resonance frequency is
proportional to the spring constant (k) of the vibrating portion of the speaker. The spring
constant is proportional to the elastic modulus of the vibrating portion. Therefore, if the elastic
modulus of the vibrating portion is large, in other words, if a hard material is used for the
vibrating portion, the primary resonance frequency becomes large. That is, in FIG. 1, the primary
resonance frequency (f 0) shifts to the right (high frequency side). When this happens, the sound
pressure in the low frequency region decreases. Therefore, when an electrostrictive element in
which a dielectric layer is interposed between electrodes is used as the vibrating portion of the
speaker, if the spring constant of the electrode is large, it is difficult to make sound in the low
frequency region.
[0007]
As described in Patent Document 5, the electrode of the speaker can be formed of, for example, a
conductive material in which a conductive material is mixed with a polymer binder. In this case, if
the compounding amount of the conductive material is reduced, the elastic modulus of the
conductive material is reduced, so that a flexible electrode can be formed. However, when the
blending amount of the conductive material is small, the electrical resistance of the electrode
becomes large. If the electrical resistance of the electrode is large, as described below, it is
difficult to make sound in the high frequency region.
05-05-2019
3
[0008]
In a speaker using an electrostrictive element in which a dielectric layer is interposed between
electrodes, the electrode layer and the dielectric layer virtually constitute a low pass filter in
which an electric resistance and a capacitor are connected in series. Therefore, the cutoff
frequency (f c) at which the sound pressure to be output is reduced by 3 db is derived by the
following equation (2). As shown in equation (2), the cutoff frequency is inversely proportional to
the electrical resistance (R) of the electrode and the capacitance (C) of the dielectric layer.
Therefore, if the electrical resistance of the electrode is large, the cut-off frequency will be small.
That is, in FIG. 1, the cutoff frequency (f c) shifts to the left (the low frequency side). When this
happens, the sound pressure in the high frequency region decreases.
[0009]
The present invention has been made in view of such circumstances, and it is possible to reduce
the weight and thickness, and to obtain a practical sound pressure in a wide frequency range
from low frequency to high frequency. The challenge is to provide
[0010]
In order to solve the above problems, a polymer speaker according to the present invention
comprises a polymer speaker having an electrostrictive element having a dielectric layer made of
an elastomer or resin and a plurality of electrode layers disposed on both sides of the dielectric
layer. The electrode layer comprises a polymer binder and a conductive material and is made of a
conductive material having a modulus of elasticity of 100 MPa or less, the volume resistivity of
the electrode layer is 200 Ω · cm or less, and the spring constant of the dielectric layer The
spring constant of the electrostrictive element, which is the sum of the spring constant of the
electrode layer, is 3000 N / m or less.
[0011]
In the polymer speaker of the present invention, when an alternating voltage as an electrical
signal of sound is applied between the electrode layers, the thickness of the dielectric layer
changes in accordance with the electrostatic attractive force between the electrode layers,
whereby the dielectric layer vibrates. .
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4
As a result, sound is generated from both the front and back sides of the electrostrictive element.
The phase of the generated sound is the same on the front side and the back side of the
electrostrictive element. For this reason, unlike the conventional dynamic type speaker unit, even
if the sound emitted from the rear side turns to the front side, they do not cancel each other.
Therefore, no enclosure is required. The electrostrictive element is composed of a dielectric layer
made of elastomer or resin and an electrode layer. For this reason, the polymer speaker of the
present invention is thin and light as compared with a conventional dynamic speaker unit having
a permanent magnet and a voice coil. Also, it can be manufactured at relatively low cost. Thus,
the polymer speaker of the present invention is lightweight, can be thinned, and is relatively
inexpensive. "Elastomer or resin" means that the base material of the dielectric layer is an
elastomer or a resin. Therefore, in addition to the elastomer or the resin component, other
components such as additives may be included. Elastomers include rubber and thermoplastic
elastomers.
[0012]
The electrode layer of the polymer speaker of the present invention is formed of a conductive
material including a polymer binder and a conductive material. The elastic modulus of the said
conductive material is 100 Mpa or less. In the present specification, the elastic modulus of the
electrode layer and the dielectric layer is measured with a strip-shaped sample having a width
(w) of 10 mm and a length (l) of 25 mm, and the spring constant of the electrode layer and the
dielectric layer in the plane direction is It calculated by following Formula (3).
[0013]
The electrode layer is flexible. Therefore, the electrode layer is less likely to inhibit the expansion
and contraction of the dielectric layer, and less likely to crack even if it is stretched. Further,
since the spring constant in the surface direction of the electrode layer is small and the spring
constant in the surface direction of the electrostrictive element is 3000 N / m or less, the
primary resonance frequency in the electrostrictive element is reduced. That is, as indicated by a
dotted line in FIG. 2, the primary resonance frequency (f 0) shifts in the left direction (low
frequency side). For this reason, according to the polymer speaker of the present invention, it is
possible to output sound at the lower frequency side, and the sound pressure in the low
frequency region is increased. The plane direction is a direction orthogonal to the front and
back direction.
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[0014]
Moreover, the volume resistivity of the electrode layer of the polymer speaker of the present
invention is 200 Ω · cm or less. Since the electrical resistance of the electrode layer is small, the
cutoff frequency is increased. That is, as indicated by the one-dot chain line in FIG. 2, the cutoff
frequency (f c) shifts in the right direction (high frequency side). For this reason, according to the
polymer speaker of the present invention, it is possible to output sound at higher frequencies,
and the sound pressure in the high frequency region is increased. As described above, according
to the polymer speaker of the present invention, the reproducible frequency range can be
expanded by widening the distance between the primary resonance frequency and the cutoff
frequency. That is, a large sound pressure can be obtained in a wide frequency range from low
frequency to high frequency.
[0015]
It is a schematic diagram which shows the sound pressure frequency characteristic of arbitrary
speakers. It is a schematic diagram which shows the sound pressure frequency characteristic of
the polymer speaker of this invention. It is a perspective view of a polymer speaker of an
embodiment. It is IV-IV sectional drawing of FIG.
[0016]
Hereinafter, an embodiment of the polymer speaker of the present invention will be described.
[0017]
<Polymer Speaker> [Configuration] First, the configuration of a polymer speaker according to an
embodiment of the present invention will be described.
FIG. 3 shows a perspective view of the polymer speaker of the present embodiment. In FIG. 4, IVIV sectional drawing of FIG. 3 is shown. As shown in FIGS. 3 and 4, the polymer speaker 1
includes an electrostrictive element 10, a front side frame 20a, and a rear side frame 20b.
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[0018]
The front side frame 20a and the rear side frame 20b are respectively made of resin and have a
ring shape. The front side frame 20 a and the rear side frame 20 b are disposed to face each
other with the peripheral portion of the electrostrictive element 10 interposed therebetween. The
front side frame 20 a and the rear side frame 20 b are fixed by eight bolts 21 and eight nuts 22.
The set of bolt 21 -nut 22 is arranged at predetermined intervals in the circumferential
direction of the polymer speaker 1. The bolt 21 penetrates from the front surface of the front
side frame 20a to the rear surface of the back side frame 20b. The nut 22 is screwed to the
through end of the bolt 21.
[0019]
The electrostrictive element 10 is interposed between the front side frame 20a and the back side
frame 20b. The electrostrictive element 10 includes a dielectric layer 11 and a pair of electrode
layers 12a and 12b. The dielectric layer 11 is made of hydrogenated nitrile rubber (H-NBR)
having an elastic modulus of 3.5 MPa, and has a circular thin film shape. The planar spring
constant of the dielectric layer 11 is 75.6 N / m.
[0020]
Each of the electrode layers 12a and 12b is made of a conductive material containing acrylic
rubber and ketjen black. The elastic modulus of the said conductive material is 1.5 Mpa. The
spring constant in the surface direction of the electrode layers 12a and 12b is 3 N / m, and the
volume resistivity is 14 Ω · cm. The spring constant in the surface direction of the electrostrictive
element 10 is 81.6 (= 75.6 + 3 + 3) N / m. Each of the electrode layers 12 a and 12 b has a
circular thin film shape smaller in diameter than the dielectric layer 11. The electrode layers 12a
and 12b are arranged substantially concentrically with the dielectric layer 11, respectively. The
electrode layers 12a and 12b have terminal portions 120a and 120b, respectively. The terminal
portions 120a and 120b respectively project from the outer peripheral edge above the electrode
layers 12a and 12b in the radial direction. Each of the terminal portions 120a and 120b has a
strip shape. A direct current bias power supply 30 and an alternating current power supply 31
are connected to the terminal portions 120a and 120b through wires.
05-05-2019
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[0021]
[Manufacturing Method] Next, a method of manufacturing the polymer speaker of this
embodiment will be described. First, two release films are prepared, and a paint containing a
conductive material is printed on the surface of one of the films to form an electrode layer 12a.
Similarly, the electrode layer 12 b is formed on the surface of the other film. Next, one film is
attached to the surface of the dielectric layer 11, and the electrode layer 12 a formed on the film
is transferred to the surface of the dielectric layer 11. Further, the other film is attached to the
back surface of the dielectric layer 11, and the electrode layer 12 b formed on the film is
transferred to the back surface of the dielectric layer 11. Then, the two releasable films are
peeled off from the dielectric layer 11. Thus, the electrode layers 12a and 12b are formed on
both the front and back sides of the dielectric layer 11, and the electrostrictive element 10 is
manufactured. Next, the peripheral portion of the electrostrictive element 10 is held by the front
side frame 20a and the rear side frame 20b. In this state, the front side frame 20a and the rear
side frame 20b are fixed by eight bolts 21 and eight nuts 22. Thus, the polymer speaker 1 is
manufactured.
[0022]
[Motion] Next, the motion of the polymer speaker of this embodiment will be described. In the
initial state, a predetermined bias voltage is applied to the electrode layers 12a and 12b from the
DC bias power supply 30. In this state, an AC voltage based on the sound to be reproduced is
applied from the AC power supply 31 to the electrode layers 12a and 12b. Then, due to the
change in the film thickness of the dielectric layer 11, the electrostrictive element 10 vibrates in
the front-rear direction as shown by the white arrow in FIG. As a result, the air vibrates and a
sound is generated.
[0023]
[Operation and Effect] Next, the operation and effect of the polymer speaker of the present
embodiment will be described. In the polymer speaker 1 of the present embodiment, the
electrostrictive element 10 is composed of a dielectric layer 11 made of an elastomer and
electrode layers 12a and 12b formed on both the front and back sides. For this reason, the
polymer speaker 1 is thin and lightweight as compared with a conventional dynamic speaker unit
having a permanent magnet and a voice coil. Also, it can be manufactured at relatively low cost.
Furthermore, the polymer speaker 1 does not require an enclosure. Therefore, the polymer
05-05-2019
8
speaker 1 is lightweight, thin and relatively inexpensive.
[0024]
The dielectric layer 11 is made of H-NBR having a modulus of elasticity of 20 MPa or less.
Therefore, the dielectric layer 11 is flexible and excellent in stretchability. The electrode layers
12a and 12b contain acrylic rubber as a polymer binder, and are made of a conductive material
having an elastic modulus of 10 MPa or less. The spring constant in the surface direction of the
electrode layers 12a and 12b is 3 N / m. For this reason, the electrode layers 12 a and 12 b are
also flexible and can be expanded and contracted integrally with the dielectric layer 11. That is,
the electrode layers 12a and 12b are less likely to inhibit the movement of the dielectric layer
11, and are less likely to crack even when stretched. Further, the spring constant in the surface
direction of the electrode layers 12a and 12b is small, and the spring constant in the surface
direction of the electrostrictive element 10 is also 3000 N / m or less. For this reason, the
primary resonance frequency in the electrostrictive element 10 decreases. Therefore, the
polymer speaker 1 can output the sound at the lower frequency side, and the sound pressure in
the low frequency region becomes large.
[0025]
The volume resistivity of the electrode layers 12a and 12b is 200 Ω · cm or less. Since the
electrical resistance of the electrode layers 12a and 12b is small, the cutoff frequency is
increased. Therefore, in the polymer speaker 1, the sound on the higher frequency side can be
output, and the sound pressure in the high frequency region is increased. As described above,
according to the polymer speaker 1, a large sound pressure can be obtained in a wide frequency
range from low frequency to high frequency.
[0026]
In the above, one embodiment of the polymer speaker of the present invention has been
described. However, the embodiment of the polymer speaker of the present invention is not
limited to the above embodiment. Hereinafter, the electrostrictive element of the polymer
speaker of the present invention will be described in detail.
05-05-2019
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[0027]
<Electrostrictive Element> The electrostrictive element in the polymer speaker of the present
invention has a dielectric layer made of elastomer or resin, and a plurality of electrode layers
disposed on both the front and back sides of the dielectric layer.
[0028]
As suitable elastomers for the dielectric layer, hydrogenated nitrile rubber (H-NBR), nitrile rubber
(NBR), silicone rubber, ethylene-propylene-diene rubber (EPDM), acrylic rubber, urethane rubber,
epichlorohydrin rubber, chlorosulfone Polyethylene, chlorinated polyethylene and the like.
Alternatively, an elastomer modified by introducing a functional group may be used, such as an
epoxidized natural rubber, a carboxyl group-modified hydrogenated nitrile rubber (XH-NBR), or
the like. Alternatively, an elastomer to which a polar low molecular weight compound having a
polar functional group is added may be used.
[0029]
Suitable resins for the dielectric layer include polyethylene, polypropylene, polyurethane,
polystyrene (including crosslinked expanded polystyrene), polyvinyl chloride, vinylidene chloride
copolymer, ethylene-vinyl acetate copolymer and the like.
[0030]
Further, from the viewpoint of making the dielectric layer flexible and expanding the region
having a large sound pressure to the low frequency side, it is preferable to use an elastomer
material having a modulus of elasticity of 20 MPa or less for the dielectric layer.
In addition, when the thickness of the dielectric layer is reduced, more electric charges can be
stored, and thus the output sound pressure can be increased. In addition, the surface direction
spring constant of the dielectric layer can be reduced.
[0031]
05-05-2019
10
The dielectric layer may contain other components such as additives in addition to the elastomer
or resin component. For example, from the viewpoint of increasing the dielectric breakdown
resistance of the dielectric layer, an insulating inorganic filler can be blended. Examples of the
inorganic filler include silica, titanium oxide, barium titanate, calcium carbonate, clay, calcined
clay, and talc.
[0032]
The electrode layer is made of a conductive material including a polymer binder and a conductive
material. As the polymer binder, an elastomer, an oil or the like can be used. An elastomer is
preferable from the viewpoint of forming an electrode layer having stretchability. As the
elastomer, silicone rubber, NBR, EPDM, natural rubber, styrene-butadiene rubber (SBR), acrylic
rubber, urethane rubber, epichlorohydrin rubber, crosslinked rubber such as chlorosulfonated
polyethylene, chlorinated polyethylene and the like, styrene type, Thermoplastic elastomers, such
as olefin type, polyvinyl chloride type, polyester type, polyurethane type and polyamide type,
may be mentioned. Further, an elastomer modified by introducing a functional group may be
used, such as an epoxy group modified acrylic rubber, a carboxyl group modified hydrogenated
nitrile rubber and the like.
[0033]
The type of conductive material is not particularly limited. It may be appropriately selected from
carbon black, carbon nanotubes, carbon materials such as graphite, and metal powders such as
silver, gold, copper, nickel, rhodium, palladium, chromium, titanium, platinum, iron, and alloys
thereof. Also, coated particles in which the surface of particles other than metal is coated with
metal may be used. In this case, the specific gravity of the conductive material can be reduced as
compared to the case of using only metal. Therefore, when it is made a paint, the sedimentation
of the conductive material is suppressed, and the dispersibility is improved. Further, by
processing the particles, conductive materials of various shapes can be easily manufactured. In
addition, the cost of the conductive material can be reduced. As the metal to be coated, metal
materials such as silver listed above may be used. As particles other than metals, carbon
materials such as carbon black, metal oxides such as calcium carbonate, titanium dioxide,
aluminum oxide and barium titanate, inorganic substances such as silica, resins such as acrylic
and urethane, etc. may be used. . A conductive material may be used individually by 1 type, and
may mix and use 2 or more types.
05-05-2019
11
[0034]
The elastic modulus of the conductive material is 100 MPa or less. In order to form a more
flexible electrode layer, the elastic modulus of the conductive material is desirably 10 MPa or
less. On the other hand, the volume resistivity of the conductive material (electrode layer) is 200
Ω · cm or less. In order to reduce the electrical resistance of the electrode layer and increase the
sound pressure in the high frequency region, it is desirable to set the volume resistivity of the
electrode layer to 2 Ω · cm or less. The type, particle diameter, shape, compounding amount, and
the like of the conductive material may be determined so that the elastic modulus and the
conductivity of the conductive material can be compatible.
[0035]
The conductive material may contain, in addition to the polymer binder and the conductive
material, if necessary, additives such as a dispersant, a reinforcing agent, a plasticizer, an
antiaging agent, and a colorant. For example, when using an elastomer as a polymer binder, a
paint is prepared by adding a conductive material and, if necessary, an additive to a polymer
solution in which the polymer of the elastomer component is dissolved in a solvent, and stirring
and mixing. be able to. The electrode layer may be formed by directly applying the prepared
paint to both the front and back sides of the dielectric layer. Alternatively, a paint may be applied
to the release film to form an electrode layer, and the formed electrode layer may be transferred
to both the front and back surfaces of the dielectric layer.
[0036]
Various known methods can be adopted as a method of applying the paint. For example, in
addition to printing methods such as inkjet printing, flexographic printing, gravure printing,
screen printing, pad printing and lithography, dip method, spray method, bar coat method and
the like can be mentioned. For example, when the printing method is adopted, it is possible to
easily separate the application part and the non-application part. Also, printing of large areas,
thin lines, and complicated shapes is easy. Among the printing methods, the screen printing
method is preferable because a paint having a high viscosity can be used and the adjustment of
the thickness of the coating film is easy.
05-05-2019
12
[0037]
In order to reduce the surface direction spring constant of the electrode layer, it is desirable to
reduce the thickness of the electrode layer. Further, from the viewpoint of increasing the sound
pressure in the low frequency region, the spring constant of the electrostrictive element is set to
3000 N / m or less. The spring constant of the electrostrictive element is calculated by the sum
of the spring constant in the surface direction of the electrode layer and the spring constant in
the surface direction of the dielectric layer.
[0038]
The number of dielectric layers and electrode layers constituting the electrostrictive element is
not particularly limited. For example, as in the above embodiment, one electrode layer can be
disposed on each of the front and back surfaces of one dielectric layer. Alternatively, multiple
dielectric layers may be stacked via the electrode layer. In this case, the amount of deformation
of the electrostrictive element with respect to the applied voltage increases, and the sound
pressure to be output can be increased. In addition, the electrostrictive element may be fixed to a
support member such as a frame in a state in which the dielectric layer is expanded in the
surface direction.
[0039]
The size and shape of the electrode layer are not particularly limited as long as a voltage can be
applied to the dielectric layer. For example, the electrode layer may be disposed to cover the
entire surface of the dielectric layer. Also, a plurality of strip-shaped or ring-shaped electrode
layers may be disposed on both the front and back sides of the dielectric layer. In the polymer
speaker of the present invention, the overlapping portion of the electrode layer on the surface of
the dielectric layer, the dielectric layer, and the electrode layer on the back surface of the
dielectric layer functions as a speaker unit that outputs sound. The larger the area of the speaker
portion (overlapping portion), the larger the capacitance. As a result, the cutoff frequency is
shifted to the low frequency side, and the sound pressure in the low frequency region is
increased. Therefore, by adjusting the arrangement pattern of the electrode layers, a plurality of
speaker units capable of reproducing sound in different frequency regions may be set in one
polymer speaker.
05-05-2019
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[0040]
Next, the present invention will be more specifically described by way of examples.
[0041]
<Electrode Layer> [Production of Electrode Layer] Various electrode layers were produced from
the electrode layer polymer shown in Table 1 below, a conductive material, and the like.
First, a polymer for electrode layer was dissolved in 1000 parts by mass of a solvent to prepare a
polymer solution. As a solvent, butyl cellosolve acetate (BCA) was used for Examples 1-11, and
toluene was used for Example 12. Next, a conductive material was added to the prepared
polymer solution at a predetermined mass ratio and dispersed to prepare a paint. About what
added the silver powder as a electrically conductive material, it was made to disperse ¦ distribute
by 3 roll, and it was made to disperse ¦ distribute by bead mill about others. For the electrode
layers 2 and 4, in addition to the conductive material, a polyester acid amide amine salt was also
added as a dispersant. For electrode layers 9-11, the polyisocyanate of the crosslinker was added
to the polymer solution. Then, the prepared coating was screen-printed on the surface of a
substrate made of acrylic resin, and heated at 150 ° C. for about 1 hour to produce a thin film
electrode layer. The electrode layer 7 was manufactured by screen-printing a commercially
available carbon paste ("JELCON CH-8" manufactured by Tojo Chemical Co., Ltd.) for comparison,
on the surface of the substrate.
[0042]
The thickness of the manufactured electrode layer is as shown in Table 1. The following
materials were used as the electrode polymer and the crosslinking agent. Epoxy group-containing
acrylic rubber: "Nipol (registered trademark) AR 42 W" manufactured by Nippon Zeon Co., Ltd.
Hydroxyl group-containing acrylic rubber A: A copolymer of n-ethyl acrylate (98% by mass) and
2-hydroxyethyl methacrylate (2% by mass) (mass molecular weight is about 900,000). Hydroxyl
group-containing acrylic rubber B: A copolymer of n-butyl acrylate (98% by mass) and 2hydroxyethyl methacrylate (2% by mass) (mass molecular weight is about 900,000).
Polyurethane-based thermoplastic elastomer: "Nipporan (registered trademark) 5193"
manufactured by Nippon Polyurethane Industry Co., Ltd. Silicone rubber: "KE-1935"
manufactured by Shin-Etsu Chemical Co., Ltd. Crosslinking agent: "Coronate (registered
trademark) HL" manufactured by Nippon Polyurethane Industry Co., Ltd.
05-05-2019
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[0043]
[Physical Properties of Electrode Layer] (1) Calculation of Spring Constant The manufactured
electrode layer was cut into a strip of 10 mm in width (w) and 25 mm in length (l) to prepare a
sample. And about the said sample, the tension test according to JISK7127 (1999) was done, and
the elasticity modulus was computed from the obtained stress-elongation curve. Moreover, the
calculated elastic modulus was substituted to the above-mentioned Formula (3), and the spring
constant of the surface direction of the said sample was computed. Table 1 shows the elastic
modulus and the spring constant of the electrode layer.
[0044]
(2) Measurement of Volume Resistivity The volume resistivity of the manufactured electrode
layer was measured according to the parallel terminal electrode method of JIS K6271 (2008).
Table 1 shows the volume resistivity of the electrode layer.
[0045]
<Dielectric Layer> [Production of Dielectric Layer] Various dielectric layers were produced from
the dielectric layer polymers shown in Table 2 below. For the dielectric layers 1 and 2, first, a
carboxyl group-containing hydrogenated nitrile rubber polymer ("Terban (registered trademark)
XT 8889" manufactured by LANXESS Corporation) was dissolved in acetylacetone. For the
dielectric layer 3, first, the same polymer and silica (wet silica "Nipsil (registered trademark)
VN3" manufactured by Tosoh Silica Corporation, pH 5.5 to 6.5, specific surface area 240 m <2> /
g) Were kneaded with a roll mill to prepare a rubber composition. Then, the prepared rubber
composition was dissolved in acetylacetone. Next, an organic metal compound tetrakis (2ethylhexyloxy) titanium was added to the obtained polymer solution and mixed. Then, the mixed
solution was screen-printed on the surface of an acrylic resin substrate and heated at 150 ° C.
for about 1 hour to produce a thin film dielectric layer. The thickness of the manufactured
dielectric layer is as shown in Table 2.
[0046]
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[Physical Properties of Dielectric Layer] The manufactured dielectric layer was cut into strips of
width (w) 10 mm and length (l) 25 mm to prepare a sample. And about the said sample, the
tension test according to JISK7127 (1999) was done, and the elasticity modulus was computed
from the obtained stress-elongation curve. Moreover, the calculated elastic modulus was
substituted to the above-mentioned Formula (3), and the spring constant of the surface direction
of the said sample was computed. Table 2 shows the elastic modulus and the spring constant of
the dielectric layer.
[0047]
<Manufacture of Electrostrictive Element> Various electrostrictive elements were manufactured
by appropriately combining the manufactured electrode layer and dielectric layer. First, the
electrode layer was cut out in a circular shape of 50 mm in diameter together with the base
material. Next, the electrode layer was pasted together with the substrate on the front and back
surfaces of the dielectric layer peeled off from the substrate. Then, the base material was peeled
off from the electrode layer to produce an electrostrictive element consisting of electrode layer /
dielectric layer / electrode layer. The same type of electrode layer was attached to both front and
back surfaces of the dielectric layer. The spring constant of the electrostrictive element was
calculated from the sum of the spring constant of the dielectric layer and the spring constant of
the two electrode layers. Moreover, the surface resistivity of the electrostrictive element was
measured according to the double ring electrode method of JIS K6271 (2008). The spring
constant and surface resistivity of the electrostrictive element are shown in Table 3 below.
[0048]
<Evaluation of Electrostrictive Element> A DC bias voltage of 30 V / μm was applied to the
manufactured electrostrictive element with respect to the thickness of the dielectric layer. In this
state, a low frequency (200 Hz) AC voltage (3 V / μm) was applied to measure the sound
pressure to be output. Similarly, a high frequency (2000 Hz) AC voltage was applied to measure
the sound pressure output. The results are summarized in Table 3 above.
[0049]
As shown in Table 3, in the electrostrictive elements of Examples 1 to 13, large sound pressures
of 40 dB / m or more were obtained regardless of the frequency level. On the other hand, the
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sound pressure in the electrostrictive element of Comparative Examples 1 and 2 in which the
elastic modulus of the electrode layer (conductive material) exceeds 100 MPa and the spring
constant of the electrode layer is larger than the spring constant of the dielectric layer The
frequency was also less than 40 dB / m. Among the examples, in the electrostrictive elements of
Examples 1, 2, 4, 5, and 10 to 12, the sound pressure of the low frequency was 60 dB / m or
more. From this result, when the elastic modulus of the electrode layer (conductive material) is
10 MPa or less, the spring constant of the electrode layer is smaller than the spring constant of
the dielectric layer, and the spring constant of the electrostrictive element is 120 N / m or less It
can be seen that the sound pressure of the frequency is greater. In the electrostrictive devices of
Examples 2, 3, 5 and 7 to 9 provided with electrode layers 2 to 6 having a volume resistivity of 2
Ω · cm or less, the electrostrictive devices of the other embodiments have higher frequencies.
Sound pressure has increased. From this result, it can be understood that reducing the volume
resistivity of the electrode layer is effective to increase the sound pressure of high frequency.
[0050]
The polymer speaker of the present invention can be used, for example, as a headrest speaker, a
seat speaker, a ceiling speaker, a floor speaker, an instrument panel speaker, a door speaker, etc.
of an automobile. Of course, you may arrange ¦ position other than a vehicle. Moreover, the
polymer speaker of the present invention may be used as an active noise canceller as well as
reproducing sound.
[0051]
1: Polymer speaker, 10: Electrostrictive element, 11: Dielectric layer, 12a, 12b: Electrode layer,
120a, 120b: terminal portion, 20a: front side frame, 20b: back side frame, 21: bolt, 22: nut, 30 :
DC bias power supply, 31: AC power supply.
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