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JP2014050046

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DESCRIPTION JP2014050046
Abstract: [Problem] To provide a new electrostatic speaker that does not require a high voltage
application device by having a self-charging characteristic by friction between a diaphragm and a
buffer member. An electrostatic speaker includes: a vibrating membrane made of a thin film-like
member; a conductive flat electrode having acoustic transparency disposed opposite to the
vibrating membrane; and the vibrating membrane and the flat electrode And a buffer member
formed of a material having a cationic functional group introduced on the surface thereof.
[Selected figure] Figure 1
Electrostatic speaker
[0001]
The present invention relates to an electrostatic speaker that is excellent in flexibility, does not
require a high voltage, can maintain excellent sound quality even when used for a long time, and
can provide stable sound quality in various environments.
[0002]
Conventionally, an electrostatic speaker is known as one of the speakers.
This electrostatic speaker is composed of a vibrating membrane, and flat electrodes or the like
which are disposed in parallel to each other on both sides of the vibrating membrane with a
predetermined gap therebetween. By applying a drive current to the flat electrode, the vibrating
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film vibrates to generate a sound. The vibrating film is used by forming a conductive thin film on
the surface of a thin polymer film of about 10 μm by vacuum evaporation, sputtering or the like.
Since a high voltage is applied to the vibrating film to cause the vibrating film to be efficiently
vibrated to generate sound, it is a feature of the electrostatic speaker that power consumption
can be reduced. Furthermore, since the sound is propagated by plane waves, there is almost no
attenuation due to distance. In addition, since the sound source is wide, feedback peaks are not
concentrated on a specific frequency, and there are various excellent features such as not
causing a housing.
[0003]
However, in the conventional electrostatic speaker, since a high voltage is applied to the
vibrating membrane, a safety issue remains, and a transformer for applying the high voltage is
also required. Furthermore, when used for a long time in a dry environment, dust adheres to the
surface of the vibrating membrane and the buffer member, causing the vibration of the vibrating
membrane to be disturbed or causing discharge, which affects the sound quality and the volume.
In addition, when left in an environment with high humidity for a long time, the charged
vibrating film is discharged to reduce charging, which causes problems such as difficulty in
producing sound.
[0004]
As a method of solving such a problem, a method of suppressing the influence of humidity by
using a film obtained by treating the surface of a polymer film with a conductive polymer as a
vibrating film (Patent Document 1) or a member having a dust collecting function A method of
installing to suppress adhesion of dust (Patent Document 2), a method of making it difficult to
generate a discharge by not forming a conductive film formed on the surface of a vibrating film
(Patent Documents 3 and 4), etc. Has been proposed. JP-A-7-0446697 JP-A 2008-148195 JP-A
2010-016603 JP-A 2010-021646
[0005]
However, a method of using the film in which the polymer film surface has been treated with a
conductive polymer as a vibrating film to suppress the influence of humidity can take measures
against humidity, but dust and the like over time of use Dust adhesion occurs. In addition, it is
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also necessary to apply a high potential for charging, which is not a fundamental measure. In
addition, in a method of installing a member having a dust collection function to suppress
adhesion of dust and dirt, and a method of making it difficult to generate a discharge by not
forming a conductive film formed on the surface of a vibrating film, etc. The structure becomes
complicated and the speaker system becomes thick. Although the discharge can be partially
mitigated, it is impossible to prevent the discharge from the vibrating film surface. Furthermore,
since it is necessary to apply a high voltage as a system, it is not a fundamental improvement at
present.
[0006]
Therefore, the present invention has been made to solve the above-mentioned problems, and it is
an object of the present invention to provide an electrostatic speaker having a lower applied
voltage which needs to be applied to a vibrating membrane in order to generate sound. To aim.
[0007]
That is, according to the first aspect of the present invention, there is provided a vibrating
membrane made of a thin film-like member, a conductive flat electrode having acoustic
transparency disposed opposite to the vibrating membrane, and a portion between the vibrating
membrane and the flat electrode. A buffer member for charging the vibrating membrane by
contact with the vibrating membrane, and the buffer member is characterized in that at least a
surface thereof has a cationic functional group.
[0008]
In the second invention, the cationic functional group of the buffer member is any one of an
amino group, an ammonium group, a sulfonium group, and a phosphonium group according to
the first invention described in the first invention. It is an electronic speaker.
[0009]
Furthermore, according to the third invention, the amount of the cationic functional group per
unit mass of the buffer member is 0.5 mmol / g or more and 3.0 mmol / g or less. Of electrostatic
type.
[0010]
Furthermore, according to a fourth invention, in the electrostatic loudspeaker according to any
one of the first to third inventions, the functional group introduction method of the buffer
member is a radiation graft polymerization method.
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[0011]
Furthermore, according to a fifth invention, the air permeability of the buffer member is 150 cm
<3> / cm <2> / sec or more and 400 cm <3> / cm <2> / sec or less. It is an electrostatic type
speaker in any one of the 4th inventions.
[0012]
Furthermore, according to a sixth aspect of the present invention, a thin film containing
inorganic fine particles or polymer fine particles and a binder component and / or a silane
monomer is formed on the surface of the buffer member facing at least the vibrating film. It is an
electrostatic speaker according to any one of the first to fifth inventions characterized by the
features.
[0013]
Furthermore, in the seventh invention according to any one of the first to sixth inventions, the
vibrating film has a layer containing a fluorine-based polymer formed on at least a part of the
surface. Of electrostatic type.
[0014]
In the electrostatic loudspeaker according to the present invention, when the buffer member has
a cationic functional group, the charge amount of the vibrating membrane is further increased by
triboelectricity due to the vibration of the vibrating membrane.
Therefore, the same effect as in the case where a high potential is applied is obtained, and in
particular, the acoustic characteristics on the low frequency range side are excellent.
From this, it is possible to lower the applied voltage required when outputting the sound,
eliminate the possibility of electric shock due to the high potential, and significantly improve the
sound in the bass range.
[0015]
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Furthermore, the adhesion of dust and dirt to the surface is suppressed by the formation of a fine
particle layer composed of inorganic fine particles and polymer fine particles on the surface of
the buffer member and the formation of fine irregularities on the surface of the vibrating film.
Even if dust or dirt adheres, the contact area is extremely low and it is easily detached from the
surface of the vibrating membrane by the vibration of the vibrating membrane, so changes in
sound quality and volume reduction are suppressed even when used for a long period of time it
can.
Accordingly, it is possible to provide an electrostatic speaker that is less susceptible to the
adhesion of dust and dirt even when used for a long time.
[0016]
The cross-sectional schematic diagram of the electrostatic-type speaker in this invention The
cross-sectional schematic diagram of the buffer member of the electrostatic-type speaker of this
embodiment The cross-sectional schematic diagram of the other example of the buffer member
of the electrostatic-type speaker of this embodiment A cross-sectional schematic diagram of a
diaphragm of the electro-speaker Cross-sectional schematic diagram of another example of the
diaphragm of the electrostatic speaker according to the embodiment A graph showing frequency
characteristics of an example and a comparative example
[0017]
Hereinafter, the electrostatic loudspeaker according to the embodiment of the present invention
will be described in detail.
[0018]
FIG. 1 is a schematic view enlarging a part of the cross section of the electrostatic speaker 100
according to the embodiment of the present invention.
The electrostatic loudspeaker 100 according to the present embodiment includes the planar
electrode 1, the buffer member 2, and the diaphragm 3 which is a thin film member.
[0019]
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The flat electrodes 1 are a pair of electrodes that apply a voltage to the vibrating membrane 3.
The flat electrode 1 is a conductive member provided opposite to the vibrating membrane 3 and
has acoustic transparency.
By supplying electric power from the AC power supply to the flat electrode 1, a voltage is applied
between the flat electrode 1 and the vibrating membrane 3, and the vibrating membrane 3 can
be vibrated to make a sound.
As a flat electrode, for example, a conductive material is treated by applying or sputtering to a
conductive material such as a metal material such as copper, stainless steel, iron or aluminum, or
a conductive material such as carbon or a resin or ceramic. Any material may be used as long as
it has conductivity, such as the above materials.
[0020]
In the buffer member 2, the vibrating membrane 3 and the flat electrode 1 are in direct contact
with each other, and the charge stored in the vibrating membrane 3 is discharged, and the
vibrating membrane 3 and the flat electrode are avoided for the purpose of avoiding scraping
and breakage due to friction. Placed between 1 and
In addition, the buffer member 2 is frictionally charged with the vibrating membrane 3 and has
acoustic transparency, vibration damping, and electrical insulation.
Since the buffer member 2 and the vibrating membrane 3 need to be frictionally charged, the
buffer member 2 is disposed in contact with the vibrating membrane 3 or at least in a positional
relationship in which the vibrating membrane 3 contacts when vibrating. .
The buffer member 2 is preferably made of a material separated from the material of the
vibrating membrane 3 on the charge train. The buffer member 2 is not limited to the case where
the entire buffer member is separated from the vibrating membrane 3 on the charging train, and
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at least the surface portion of the buffer member 2 facing the vibrating membrane 3 is separated
from the vibrating membrane 3 on the charging train. It may be formed including the above
materials. For example, even if the base material of the buffer member 2 and the vibrating
membrane 3 are the same material, a layer of material separated from the vibrating membrane 3
on the charging train is formed on the side of the buffer member 2 facing the vibrating
membrane 3 , Materials on the charging train may be included. Similarly, when the surface
portion of the vibrating membrane 3 facing the buffer member 2 is made of a material different
from the other portions, the buffer member 2 is a surface portion of the vibrating membrane 3
facing the buffer member. It may be made of a material separated from the charging train.
[0021]
Here, the charge train of the material is one in which the polarity caused by charging is arranged
in the positive and negative order with respect to the phenomenon that one side is charged to the
positive side and the other is charged to the negative side when the polymer films and fibers are
rubbed against each other. It is. As a charging train, Lehmicke's charging train and a charging
train by J. Henniker are known, and are widely used as a measure against static electricity.
[0022]
As positive ones in the charging series, acrylic (PMMA), polyamide (nylon), wool and formalin
resin are known, and polyethylene and polyvinyl chloride are well known as those located on the
negative side, especially poly Tetrafluoroethylene (PTFE) is considered to be one of the most
strongly negatively charged materials.
[0023]
Since the buffer member 2 is a material different from the vibrating membrane 3 on the charging
train, when the vibrating membrane 3 vibrates, the vibrating membrane 3 is charged by the
friction with the buffer member 2.
Then, if the buffer member 2 is further apart from the vibrating membrane 3 on the charge train,
the charge amount of the vibrating membrane becomes larger, and the same effect as the case
where a high potential is applied can be obtained. Therefore, if the buffer member 2 and the
vibrating membrane 3 are formed of materials separated from each other on the charging train,
sound can be generated even with a lower applied voltage, and electric shock due to high
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potential is caused. There is no risk of
[0024]
The buffer member 2 used in the present embodiment is not particularly limited as long as the
material is made of a material that is separated from the vibrating membrane 3 in the charge
train, and, for example, polyethylene resin, polypropylene resin, polystyrene resin,
Polymethylpentene resin, polyvinylidene chloride resin, methyl polyacrylate resin, polyamide
resin, polyimide resin, polyethylene terephthalate resin, polybutylene terephthalate resin,
polyarylate resin, polyether phenyl ether sulfone resin Thermoplastic resins such as
polyvinylidene fluoride resin, PVF, FEP, ETFE, PTFE, and PVDF, polyarylates, polymeric materials
such as molten liquid crystal polymers such as PPTA, and inorganic substances such as glass and
ceramics Materials, carbon or bamboo or silk or cotton Natural materials may be used. These
materials may be used singly or in combination of two or more kinds by laminating, coating,
impregnating, kneading or the like, and in particular, it is desirable to use a composite in the case
of inorganic materials.
[0025]
And the buffer member 2 of this embodiment has a cationic functional group at least on the
surface. The presence of a chemically positive functional group on the surface or inside of the
buffer member 2 makes it possible to increase the amount of positive charge of the buffer
member 2. If the buffer member 2 has a cationic functional group, the method of introduce ¦
transducing a cationic functional group is not specifically limited. For example, a surface
modification method by chemical reaction of a monomer, a chemical graft polymerization
method, a radiation graft polymerization method and the like can be mentioned. In particular, it
is particularly preferable to use the radiation graft polymerization method, since it is possible to
uniformly impart many cationic functional groups to the inside of the buffer member 2 as well as
the surface thereof.
[0026]
The buffer member 2 having a cationic functional group improves the charging performance
more than the buffer member having no cationic functional group. Therefore, it is possible to
obtain the same effect as using a more distant member on the charging train. That is, when the
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same vibration film 3 performs the same friction, the buffer member 2 having the cationic
functional group has more charge than the buffer member having the same material and no
cationic functional group. It will be charged. As the chargeability is improved, the charge amount
of the vibrating membrane 3 also becomes larger, and the effect of exhibiting an excellent
acoustic characteristic with the applied voltage can be obtained.
[0027]
As a cationic functional group which the buffer member 2 of this embodiment has, an amino
group, an ammonium group, sulfonium volatilization, a phosphonium group etc. are mentioned.
An amino group is particularly preferable as the cationic functional group from the viewpoint of
productivity of the organic polymer fiber, charge amount and ease of introduction.
[0028]
In the present embodiment, the amount of the cationic functional group per unit mass of the
buffer member is preferably 0.5 mol / g or more and 3.0 mol / g or less. When the amount of
cationic functional groups is less than 0.5 mol / g, the amount of functional groups is small, so
the effect of increasing the charge amount by friction is not sufficient, and the effect of charging
the vibrating film, that is, the effect of improving acoustic characteristics is low. In addition, when
the amount of functional groups is more than 3.0 mol / g, the base material becomes brittle or
hard, for example, the mechanical physical properties are deteriorated and the flexibility is lost,
and thus the material is not suitable as a buffer material.
[0029]
In the present embodiment, the chemical graft polymerization method, radiation graft
polymerization method and the like are mentioned as a method of introducing a cationic
functional group into the buffer member 2, but radiation graft weight is preferred from the
viewpoint of simplicity of the polymerization process, production speed, etc. Legal is particularly
suitable. When an organic polymer base material is used as the material of the buffer member 2
in the radiation graft polymerization method, it is possible to introduce graft side chains from the
surface of the organic polymer base material to the inside, and introduce a cationic functional
group This is because the amount can be significantly improved. Here, as radiation used in graft
polymerization, α rays, β rays, γ rays, electron beams, ultraviolet rays and the like can be
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mentioned, but γ rays and electron beams are particularly suitable for use in the present
invention. There is. The radiation graft polymerization method can introduce a functional group
suitably by the method described below. The first preferred method is a simultaneous irradiation
graft polymerization method in which radiation is irradiated in the coexistence of a substrate and
a monomer, and the second preferred method is radiation such as gamma rays or electron beams
on the substrate surface in advance. In the prior art, there is a pre-irradiation graft
polymerization method in which a monomer is brought into contact with a monomer and then
reacted.
[0030]
The method of introducing a cationic functional group comprises graft polymerizing a monomer
having a cationic functional group or graft polymerizing a monomer having a functional group
that can be converted to a cationic functional group and then converting it to a cationic
functional group Any of the methods can be used.
[0031]
Examples of the monomer having a cationic functional group include diethylamine,
diethanolamine, and trimethylamine.
Moreover, as a monomer which has a functional group which can be converted into a cationic
functional group, glycidyl methacrylate, styrene, chloromethylstyrene, acrylonitrile, acrolein and
the like can be mentioned.
[0032]
The buffer member 2 only needs to electrically insulate the flat electrode 1 and the vibrating
membrane 3, and a through hole is formed by a film, sheet, non-woven, woven, mesh, knit, or
punching process. It can be used in any shape. Among these, from the viewpoint of flexibility and
uniformity of sound transmission, it is preferable to be a fiber structure of an organic polymer
such as non-woven fabric, woven fabric or mesh.
[0033]
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The buffer member 2 needs to have a function to transmit the vibration of air, which is the sound
generated by the vibration of the vibrating membrane, to the outside, and the air permeability of
the buffer member is 150 cm <3> / cm <2> / sec or more as this index. The thing of 400 cm <3>
/ cm <2> / sec or less is preferable. When the air permeability is higher than 400 cm <3> / cm
<2> / sec, the density as the buffer member decreases, so the air permeability, that is, the sound
transmission is excellent, but the insulation property and the damping property decrease. It will
When the air permeability is lower than 150 cm <3> / cm <2> / sec, the density of the buffer
member is too high, and although the insulation property is excellent, the air permeability is low
and the sound transmission is low. Not suitable as a shock absorber.
[0034]
In addition, on the surface of the buffer member 2 having a cationic functional group on at least
the surface according to the present embodiment, it is possible to form fine unevenness with
inorganic fine particles or polymer fine particles. FIG. 2 is a schematic cross-sectional view of the
buffer member 2 used in the electrostatic loudspeaker 100 according to the present
embodiment. FIG. 2 exemplifies one in which a thin film containing the inorganic fine particles
12 a and the polymeric fine particles 12 b is formed on the surface of the substrate 11 of the
buffer member using the binder component 14. Although the cationic functional group is not
shown in FIG. 2, the buffer member 2 has a cationic functional group at least on the surface, and
a thin film of the inorganic fine particles 12a and the polymer fine particles 12b is formed
thereon. It is formed.
[0035]
Due to the unevenness formed by the inorganic fine particles 12a and the polymer fine particles
12b, dust and dirt adhering to the surface of the buffer member 2 reduce the area with the buffer
member 2 in contact, and the effect by the vibration of the vibrating film 3 Synergistic and easy
detachment can suppress accumulation of dust and dirt. Further, by using the inorganic fine
particles 12a and the polymer fine particles 12b as dielectric materials, charging by friction
between the buffer member 2 and the vibrating film 3 is further facilitated, and the charged
charge is hard to discharge, which is an excellent acoustic. The effect is that permeability can be
maintained for a long time.
[0036]
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11
Examples of the inorganic fine particles 12a used for the thin film formed on the surface of the
buffer member 2 include Al2O3, TiO2, ZrO2, SnO2, FeO, Fe2O3, Fe3O4, Sb2O3, PbO, CuO, CuO,
NiO, Ni3O4, Ni2O3, CoO. And single inorganic oxides such as Co 3 O 4, Co 2 O 3, WO 3 and CeO
2. Further, as inorganic fine particles, for example, BaTiO 3, SrTiO 3, ZnFe 2 O 4, SiO 2 · Al 2 O 3,
SiO 2 · B 2 O 3, SiO 2 · P 2 O 3, SiO 2 · P 2 O 5, SiO 2 · TiO 2, SiO 2 · ZrO 2, Al 2 O 3 · TiO 2, Al 2
O 3 · ZrO 2, Al 2 O 3 · CaO, Al 2 O 3 · B 2 O 3 Al 2 O 3 · P 2 O 5, Al 2 O 3 · CeO 2, Al 2 O 3 · Fe 2
O 3, TiO 2 · CeO 2, TiO 2 · ZrO 2, SiO 2 · TiO 2 · ZrO 2, Al 2 O 3 · TiO 2 · ZrO 2, SiO 2 · Al 2 O 3 ·
TiO 2, SiO 2 · TiO 2 · CeO 2, TiC, TaC, KNbO3 Examples include complex oxides such as NaNbO3based ferroelectric ceramics, (Bi1 / 2Na1 / 2) TiO3-based ferroelectric ceramics, and tungsten
bronze-type ferroelectric ceramics.
[0037]
These inorganic fine particles 12a can be used alone or in combination of two or more. The
particle diameter of these inorganic fine particle particles is preferably 10 nm to 500 nm in order
to form minute irregularities.
[0038]
Also, as the polymer fine particles 12b used for the thin film formed on the surface of the buffer
member 2, for example, polyethylene resin, polypropylene resin, polystyrene resin,
polymethylpentene resin, polyvinylidene chloride resin, polyimide resin And thermoplastic resins
such as polyethylene terephthalate resin, polybutylene terephthalate resin, polyarylate resin,
polyvinylidene fluoride resin, PVF, FEP, ETFE, PTFE, and PVDF. These polymer fine particles may
be used alone or in combination of two or more. The particle diameter of these polymer fine
particles is preferably 10 nm to 1.0 μm in order to form minute irregularities.
[0039]
The inorganic fine particles 12a and the polymeric fine particles 12b may be fixed to the surface
of the buffer member 2, or a binder component may be included in the thin film in order to
impart water repellency, hydrophilicity or oil repellency. As the binder component 14, for
example, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltriacetoxysilane, N-β- (N-
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12
vinylbenzylaminoethyl) -γ-aminopropyltrimethoxysilane, N- (vinylbenzyl) Hydrochloride of 2aminoethyl-3-aminopropyltrimethoxysilane, 2- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, 3glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxy Silane, 3glycidoxypropyltriethoxysilane, p-styryltrimethoxysilane, 3methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3methacryloxypropylmethyldiethoxysilane, 3-methyl methacrylate Examples include silane
monomers such as acryloxypropyl triethoxysilane, 3-acryloxypropyl trimethoxysilane, 3isocyanatopropyltriethoxysilane and the like.
[0040]
In the case where the electrostatic speaker is used under a high humidity environment or an
environment in which condensation easily occurs due to a rapid temperature change, it is more
preferable to use a compound having water repellency as the binder component 14. The binder
component 14 having water repellency includes, for example, stearic acid acrylate, reactive
silicone oil, dimethyl silicone oil, methylphenyl silicone oil, methyl hydrogen silicone oil, reactive
silicone oligomer, etc. For example, Matsushita Electric Works The Fresser D ("Fresser" is a
registered trademark) manufactured by Corporation is used.
[0041]
Furthermore, as the binder component 14 having water repellency, acrylic monomers having a
perfluoroalkyl group, for example, 2- (perfluoropropyl) ethyl acrylate, 2- (perfluorobutyl) ethyl
acrylate, 2- ( Perfluoropentyl) ethyl acrylate, 2- (perfluorohexyl) ethyl acrylate, 2(perfluoroheptyl) ethyl acrylate, 2- (perfluorooctyl) ethyl acrylate, 2- (perfluoronolyl) ethyl
acrylate And 2- (perfluorodecyl) ethyl acrylate, 3-perfluorohexyl-2-hydroxypropyl acrylate,
perfluorooctylethyl methacrylate and 3-perfluorooctyl-2-hydroxypropyl acrylate , Fluorine-based
compounds such as 3-perfluorodecyl-2-hydroxypropyl acrylate are used.
[0042]
Furthermore, as the binder component 14 having water repellency, for example, 2perfluorooctylethanol, 2-perfluorodecylethanol, 2-perfluoroalkylethanol, perfluoro (propyl vinyl
ether), and perfluoroalkyliodide Alternatively, fluorine compounds such as
perfluorooctylethylene and 2-perfluorooctylethyl phosphonic acid may be used.
[0043]
Furthermore, as a binder component 14 having water repellency, a silane coupling agent having
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13
a perfluoroalkyl group, for example, CF 3 (CH 2) 2 Si (OCH 3) 3, CF 3 (CF 2) 5 (CH 2) 2 Si (OCH
3) 3, CF 3 (CF 2) 7 (CH 2) 2 Si (OCH 3) 3, CF 3 (CF 2) 11 (CH 2) 2 Si (OCH 3) 3, CF 3 (CF 2) 15
(CH 2) 2 Si (OCH 3) 3, CF 3 (CF 2) 7 (CH2) 2Si (OC2H5) 3, CF3 (CH2) 2SiCH3 (OCH3) 2, CF3
(CF2) 2 (CH2) 2SiCH3 (OCH3) 2, CF3 (CF2) 5 (CH2) 2SiCH3 (OCH3) 2, CF 3 (CF 2) 7 (CH 2) 2
SiCH 3 (OCH 3) 2 or CF 3 (CF 2) 7 (CH 2) 2 SiCH 3 (OC 2 H 5) 2, CF 3 (CF 2) 7 (CH 2) 2 Si (OCH
3) 3, CF 3 (CF 2) 7 (CH 2) 2 Si (OC 2 H 5) 3, CH 3 (CF 2) 9 (CH 2) 8 Si (OC 2 H 5) 3 or , CF 3 (CF
2) 7 CONH (CH 2) 3 Si (OCH 3) 3, CF 3 (CF 2) 7 CONH (CH 2) 2 SiCH 3 (OCH 3) 2, and oligomers
having a perfluoroalkyl group and a silanol group, such as KP-801M (Shin-Etsu Chemical
Industrial Co., Ltd., X-24-7890 (Shin-Etsu Chemical Co., Ltd.), perfluorobuteryl vinyl ether, its
polymer, etc. may be used.
[0044]
Furthermore, as another method in the case of fixing the inorganic fine particles 12a on the
surface of the buffer member 2 of the present embodiment, a silane having a unsaturated bond
portion and the surface of the inorganic fine particles 12a without using the binder component
14 It may be coated with a monomer, and the inorganic fine particles 12 a may be fixed to the
surface of the base 11 of the buffer member 2 by the silane monomer.
[0045]
FIG. 3 is a schematic cross-sectional view of the buffer member 2 in which the inorganic fine
particles 12a are fixed to the base 11 of the buffer member by the silane monomer 13 chemically
bonded to the surface of the inorganic fine particles 12a.
[0046]
The inorganic fine particles 12 a can be firmly fixed to the surface of the base 11 of the buffer
member 2 by using the inorganic fine particles 12 a coated with a silane monomer.
This is because the inorganic fine particles 12a in the thin film are chemically bonded to each
other by the unsaturated bond or reactive functional group of the silane monomer 13, and the
unsaturated bond or reaction of the silane monomer 13 is bonded to the inorganic fine particles
12a in the thin film. This is because the sex functional group chemically bonds to the surface
portion of the base 11 of the buffer member 2.
[0047]
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14
Here, the reason why the silane monomer 13 orients and bonds the unsaturated bond or reactive
functional group toward the outside of the inorganic fine particle 12a will be described in detail.
This is because the silanol group which is one end of the silane monomer 13 is hydrophilic, so it
is easily attracted to the surface of the inorganic fine particle 12a, which is also hydrophilic,
while the unsaturated bond or reactive functional group at the opposite end is Because it is
hydrophobic, it tends to leave the surface of the inorganic fine particles 12a.
For this reason, since the silanol group of the silane monomer 13 is covalently bonded to the
surface of the inorganic fine particle 12 a by a dehydration condensation reaction, the silane
monomer 13 tends to be oriented with the unsaturated bond portion or the reactive functional
group facing outward.
Therefore, for many silane monomers 13, unsaturated bonds or reactive functional groups are
directed outward to be covalently bonded to the inorganic fine particles.
[0048]
That is, the buffer member 2 on which the thin film of the inorganic fine particles 12a used in the
present embodiment is formed is made of a silane monomer having excellent reactivity with an
unsaturated bond portion or a reactive functional group, thereby achieving a chemical reaction
between silane monomers. The inorganic fine particles 12a on the buffer member 2 are bonded
to each other by bonding, and a chemical bond is formed between the silane monomer on the
surface of the inorganic fine particle 12a facing the buffer member 2 and the surface of the
buffer member 2 Can be firmly fixed on the buffer member 2.
[0049]
Examples of the unsaturated bond or reactive functional group possessed by the silane monomer
13 which is covalently bonded to the inorganic fine particles 12a by dehydration condensation
include vinyl group, epoxy group, styryl group, methacrylo group, acryloxy group and isocyanate
group.
[0050]
In the buffer member 2 in which the thin film made of the inorganic fine particles 12a used in
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the present embodiment is formed, examples of the silane monomer for covering the inorganic
fine particles 12a include vinyltrimethoxysilane, vinyltriethoxysilane, vinyltriacetoxysilane, N -Β(N-vinylbenzylaminoethyl) -γ-aminopropyltrimethoxysilane, hydrochloride of N- (vinylbenzyl) -2aminoethyl-3-aminopropyltrimethoxysilane, 2- (3, 4 epoxy) Cyclohexyl) ethyltrimethoxysilane, 3glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3glycidoxypropyltriethoxysilane, p-styryltrimethoxysilane, 3-methacryloxypropyl
Methyldimethoxysilane, 3 -Methacryloxypropyltrimethoxysilane, 3methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, 3acryloxypropyltrimethoxysilane, 3-isocyanatopropyltriethoxysilane, etc. may be mentioned.
[0051]
The amount of the silane monomer coated on the surface of the inorganic fine particles 12a may
be 0.1% by mass or more and 10% by mass or less based on the inorganic fine particles 12a.
When the content is 0.1% by mass or more, the bonding strength of the inorganic fine particles
12a onto the buffer member 2 becomes higher.
In addition, even if more than 10% by mass is supported, the bonding strength is almost
constant.
[0052]
Next, a method of manufacturing the buffer member 2 in which the inorganic fine particles 12a
whose surface is coated with the silane monomer shown in FIG. 3 is fixed will be described.
First, inorganic fine particles in which a silane monomer is chemically bonded to the surface are
mixed and dispersed in a dispersion medium such as methanol, ethanol, MEK, acetone, xylene or
toluene.
Here, in order to promote dispersion, surfactants, mineral acids such as hydrochloric acid and
sulfuric acid, and carboxylic acids such as acetic acid and citric acid may be added as necessary.
Subsequently, inorganic fine particles are crushed and dispersed in a dispersion medium using an
04-05-2019
16
apparatus such as a bead mill, a ball mill, a sand mill, a roll mill, a vibration mill, and a
homogenizer to prepare a slurry containing the inorganic fine particles.
[0053]
The covalent bond between the inorganic fine particles and the unsaturated monomer or the
silane monomer having a reactive functional group can be formed by a conventional method. For
example, the silane monomer is added to the dispersion of the inorganic fine particles, and then
refluxing is performed. A method of forming a thin film composed of a silane monomer by
covalently bonding a silane monomer to the surface of an inorganic fine particle by dehydration
condensation reaction while heating at a low temperature, or after adding the silane monomer to
a dispersion obtained by pulverizing by grinding Alternatively, a silane monomer is added and
pulverized to form fine particles, followed by solid-liquid separation and heating at 100 ° C. to
180 ° C. to covalently bond the silane monomer to the surface of the inorganic fine particles by
dehydration condensation reaction, The method of crushing and re-dispersing is mentioned.
[0054]
Here, after adding a silane monomer to the dispersion liquid obtained by atomization under
reflux or pulverization, or after adding a silane monomer and pulverizing by pulverization, solidliquid separation is carried out to 100 ° C. to 180 ° C. When the silane monomer is covalently
bonded to the surface of the inorganic fine particles by heating at 0 ° C., the amount of the
silane monomer depends on the weight of the inorganic fine particles, although it depends on the
average particle size of the inorganic fine particles. The content is preferably in the range of
mass% to 40.0 mass%, and particularly preferably in the range of 0.1 mass% to 10 mass% from
the viewpoint of the bonding strength between the inorganic fine particles and the buffer
member 2.
Also, there may be excess silane monomers that are not deposited in the bond.
[0055]
Subsequently, the slurry in which the inorganic fine particles obtained as described above are
dispersed is applied to the surface of the buffer member 2 on which the inorganic fine particles
are fixed. Specific methods for applying a slurry in which inorganic fine particles are dispersed
include spin coating, dip coating, spray coating, cast coating, bar coating, microgravure coating,
04-05-2019
17
and gravure coating, which are generally performed. There is no particular limitation as long as
the application suitable for the purpose can be performed.
[0056]
Next, if necessary, after removing the dispersion medium by heating and drying, the buffer
member 2 and the inorganic fine particles are chemically bonded. Specifically, while forming a
chemical bond between the silane monomers on the surface of the inorganic fine particles, the
inorganic fine particles are bonded to each other, and the bonded inorganic fine particles form a
chemical bond between the silane monomer and the surface of the buffer member. Fix it by
letting it
[0057]
In the present embodiment, it is preferable to use a bonding method by graft polymerization as a
method of chemically bonding the buffer member 2 and the silane monomer.
[0058]
Examples of graft polymerization that can be used in the present embodiment include graft
polymerization using a peroxide catalyst, graft polymerization using heat and light energy, graft
polymerization by radiation (radiation graft polymerization), etc., depending on the shape and
form. Therefore, it can be selected appropriately.
A chemical bond can be formed between the surface of the inorganic fine particles 2a and the
silane monomer by the treatment with a peroxide catalyst, the treatment with heat or light
energy, and the treatment with radiation.
[0059]
Here, in order to carry out graft polymerization of the silane monomer efficiently and uniformly,
the surface of the buffer member 2 is previously subjected to corona discharge treatment, plasma
discharge treatment, flame treatment, chromic acid, perchloric acid, etc. A hydrophilic treatment
such as a chemical treatment with an aqueous oxidizing acid solution or an alkaline aqueous
solution containing sodium hydroxide or the like may be performed.
04-05-2019
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[0060]
As described above, when the silane monomer 13 is chemically bonded to the surface of the
inorganic fine particle 12 a and the inorganic fine particle 12 a is fixed to the substrate 11 of the
buffer member 2 via the silane monomer 13, the inorganic fine particle 12 a As it is firmly held
on the buffer member 2, peeling and the like can be suppressed.
[0061]
In the present embodiment, a method of fixing the inorganic fine particles 12a to the buffer
member 2 with the binder component 14 and a method of fixing the inorganic fine particles 12a
to the buffer member 2 via the silane monomer 13 chemically bonded to the surface of the
inorganic fine particles 12a are described. However, it is not limited to this.
The inorganic fine particles 12 a may be fixed to the base 11 of the buffer member 2 using both
the binder component 14 and the silane monomer 13 chemically bonded to the surface of the
inorganic fine particles 12 a.
In this case, since the inorganic fine particles 12a are more firmly fixed to the base 11 of the
buffer member 2, the buffer member 2 having high durability can be formed.
[0062]
The method of forming the minute unevenness is not limited to the method of forming a film
including the inorganic fine particles 12a and the polymer fine particles 12b on the substrate 11
of the buffer member, and embossing, nanoimprinting, oxygen plasma The unevenness may be
formed by a physical method such as, or may be formed by a chemical method such as chemical
etching.
[0063]
Next, in the vibrating film 3, an electrostatic force (Coulomb force) acting on the vibrating film 3
is changed by a change in voltage applied from the flat electrode 1, and the electrostatic force
vibrates to generate a sound.
04-05-2019
19
By applying a voltage according to the acoustic signal, the diaphragm 3 emits an acoustic signal
corresponding to the acoustic signal. The vibrating film 3 of the present embodiment is a
vibrating plate of a method of self-charging by friction with the buffer member 2, and
electrostatic force acts on the vibrating film 3 when a voltage is marked on the flat electrode 1 by
frictional charging. And vibrate.
[0064]
The vibrating membrane 3 is preferably made of a material having excellent chargeability, and
for example, a film or sheet made of a polymer is preferable. As specific materials, for example,
polyethylene resin, polypropylene resin, polystyrene resin, polymethylpentene resin,
polyvinylidene chloride resin, polymethyl acrylate resin, polyamide resin, polyimide resin,
polyethylene terephthalate resin, , Polybutylene terephthalate resin, polyarylate resin, polyether
phenyl ether sulfone resin, polyvinylidene fluoride resin, PVF (poly vinyl fluoride), FEP
(fluorinated ethylene propylene copolymer), ETFE (ethylene tetra fluoroethylene) And
thermoplastic resins such as PTFE (polytetrafluoroethylene) and PVDF (poly vinylidene
difluoride), and polyarylate, and melt liquid crystal polymers such as PPTA (poly (p-phenylene
terephthalamide)).
[0065]
These materials may be used alone, or may be used as a substrate, and the surface may be used
by forming a polymer layer of another material. In particular, it is necessary that the vibrating
film be thin and light and have strength in terms of durability against vibration, and a fluorinebased material or a polymer film formed with a fluorine-based polymer layer is preferable.
Fluorine-based thin films tend to be negatively charged by friction. From this point, it is possible
to construct a speaker with better acoustic characteristics by selecting a member that tends to be
positively charged by the buffer member. .
[0066]
FIG. 4 is an enlarged view of a part of the cross section of the diaphragm 3 of the electrostatic
loudspeaker according to the embodiment of the present invention. The vibrating film 3 formed
of a thin film member is a polymer film formed of a material separated from the buffer member 2
04-05-2019
20
in which the cationic functional group is introduced on the surface of the organic polymer (fiber)
substrate. The fluorine-based polymer layer 15 is formed on the surface of the film substrate 16.
As a result, it is possible to construct an even more excellent electrostatic speaker having
features such as high water repellency and low dielectric constant possessed by the fluorinebased polymer.
[0067]
As a fluorine-based polymer used for the fluorine-based polymer layer 15 of the vibrating
membrane 3, for example, polyvinylidene fluoride resin, PVF, FEP, ETFE, thermoplastic resin such
as PTFE, PVDF, etc., amorphous fluorine, etc. Resin etc. can be used. Also, these fluorine-based
polymers may be used alone, or two or more of non-fluorine-containing polymers and fluorinebased polymers may be laminated or complexed by coating, etc., and the surface is a fluorinebased polymer Any configuration may be used as long as the vibrating membrane 3 is covered
with
[0068]
Furthermore, as shown in FIG. 5, dust and dirt adhering to the surface of the vibrating film 3 are
formed on the surface of the vibrating film 3 by forming fine irregularities having an arithmetic
average roughness Ra of 5 nm or more and 500 nm or less. Accumulation of dust and dirt can be
suitably suppressed by removing easily. As a method of forming the minute unevenness, physical
methods such as embossing, nano-imprinting, oxygen plasma, and chemical methods such as
chemical etching can be used.
[0069]
Further, as a method of forming irregularities on the surface of the vibrating film 3, a thin film
made of inorganic fine particles or polymer fine particles containing a binder component may be
formed on the surface of the vibrating film 3 as in the buffer member 2. Even in this case, the
effect of suppressing the adhesion of dust and dirt or causing the separation easily appears. The
surface of the vibrating film 3 is industrially difficult to control the arithmetic mean roughness
Ra to less than 5 nm, and when it is more than 500 nm, cotton dust which is routinely generated
in the living environment, so-called cotton linters It is not preferable because it easily adheres
and it becomes difficult to detach. Further, by forming minute irregularities on the surfaces of
04-05-2019
21
both the vibrating film 3 and the cushioning member 2, dust and dirt are less likely to be
attached, and even if they are attached, they are more easily removed. The characteristics are
maintained for a long time.
[0070]
The electrostatic loudspeaker 100 according to the embodiment of the present invention
comprises a flat electrode 1 having acoustic conductivity and provided on the surface of an
organic polymer (fiber) substrate, which is provided opposite to a diaphragm 3 made of a thin
film member. A buffer member 2 having a cationic functional group introduced therein is
provided between the vibrating membrane 3 and the flat electrode 1. Here, the flat electrode 1
and the buffer member 2 may be configured independently or may be integrated.
[0071]
According to the present embodiment described above, the vibrating membrane 3 and the buffer
member 2 are rubbed by the vibration of the vibrating membrane, and the vibrating membrane 3
is charged. Further, in the present embodiment, since the vibrating membrane 3 has a cationic
functional group on the surface of the organic polymer (fiber) substrate, the charge amount of
the vibrating membrane 3 is further increased by frictional charging, and the planar electrode 1
is used. The same effect as when a high potential is applied, and particularly the acoustic
characteristics on the low frequency side are excellent. From this, it is possible to lower the
applied voltage required when outputting the sound, there is no possibility of an electric shock
due to the high potential, and the sound in the low range is significantly improved.
[0072]
Further, the formation of a fine particle layer composed of inorganic fine particles and polymer
fine particles on the surface of the buffer member 2 and the formation of fine irregularities on
the surface of the vibrating film suppress adhesion of dust and dirt to the surface. Even if dust or
dirt adheres, the contact area is extremely low, and it is easily detached from the surface of the
vibrating membrane by the vibration of the vibrating membrane 3. Therefore, even if it is used
for a long time, the sound quality changes or the volume decreases. Can be suppressed.
Therefore, it is possible to provide an electrostatic speaker that is less susceptible to the adhesion
of dust and dirt even when used for a long time.
04-05-2019
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[0073]
In the present embodiment, a speaker having a pair of the electrode (planar electrode 1) and the
buffer member 2 is exemplified, but the present invention is not limited to this, and one electrode
such as an electrode, the buffer member, and the diaphragm 3 is included. It may be a speaker
having only
[0074]
Next, the present invention will be more specifically described by way of examples.
However, the present invention is not limited to only these examples.
[0075]
(Production of Vibrating Film and Buffer Member) (Example 1) First, the vibrating film is a
polyester film (made by Toray Industries, Inc., 1.4 μm thick) as a fluorine-based film material,
CT-solv. 100 E ( Trade name: Cytop (trade name: CTL-102AE manufactured by Asahi Glass Co.,
Ltd.) diluted with Asahi Glass Co., Ltd. was applied by immersion and dried at 100 ° C. for 1
minute.
[0076]
Next, the buffer member was produced as follows.
First of all, using a non-woven nylon fabric (Asahi Kasei Corp., basis weight 40 g / m 2) in a
nitrogen atmosphere and using an electro curtain electron beam irradiation device CB250 /
15/180 L made by Iwasaki Electric Co., Ltd. accelerates the electron beam by 200 kV. The
voltage was irradiated at 20 Mrad. Then, the non-woven fabric was immersed in a 10% glycidyl
methacrylate solution to graft polymerize. At this time, the grafting ratio defined by the weight
increase rate ((nonwoven fabric weight after graft polymerization-graph and non-woven fabric
weight before polymerization) / nonwoven fabric weight before graft polymerization x 100 (%))
was 134%. The obtained non-woven fabric is called GMA graft polymerized non-woven fabric.
Then, the obtained GMA grafted nonwoven fabric was immersed in 10% diethylamine aqueous
04-05-2019
23
solution. By this reaction, the epoxy group in the graft polymer chain was converted to an amino
group to prepare a buffer member having an amino group introduced. The resulting buffer
member is referred to as an amino group introduction buffer member. The amount of cationic
functional groups was calculated by the following equation (1) from the weight increase of the
buffer member accompanying the reaction. Cationic functional group amount (mmol / g) = 1000
(W2-W1) / 73 / W1 (1) Here, W1 is the weight of GMA grafted nonwoven fabric (buffer member
before introduction of amino group), W2 is buffer for introduction of amino group It is the
weight of the member. Also, "73" is the molecular weight of diethylamine. From the above, the
cationic functional group content of the buffer member of Example 1 was calculated to be 2.1
mmol / g. In addition, when using monomers other than diethylamine as a cationic functional
group, it may change to "73" and should just use the molecular weight of the monomer for
calculation of the amount of cationic functional groups in (1) Formula.
[0077]
Example 2 The vibrating membrane is the same as in Example 1. The buffer member is the same
as that of Example 1 except that the irradiation amount of the electron beam to the nylon nonwoven fabric in Example 1 is 5 Mrad. The grafting ratio defined by the weight increase rate of
the obtained GMA non-woven fabric (buffer member before introduction of amino group) was
60%, and the amount of cationic functional group of the amino group introduction buffer
member was 0.6 mmol / g.
[0078]
Example 3 A vibrating membrane was produced in the same manner as in Example 1 except that
a PVDF film (made by Kureha, 4 μm in thickness) was used instead of the polyester film of
Example 1.
[0079]
The buffer member first uses a polypropylene non-woven fabric (manufactured by Asahi Kasei
Corp., basis weight 40 g / m <2>) in a nitrogen atmosphere using an electron curtain electron
beam irradiation apparatus CB250 / 15 / 180L manufactured by Iwasaki Electric Co., Ltd. 20
Mrad irradiation was performed at an acceleration voltage of 200 kV.
Then, the non-woven fabric was immersed in a 10% glycidyl methacrylate solution to carry out a
04-05-2019
24
graft polymerization reaction to obtain a polypropylene-made GMA grafted non-woven fabric
having a grafting ratio of 140% defined by a weight increase rate. Furthermore, this GMA grafted
nonwoven fabric was immersed in 10% diethylamine aqueous solution to introduce an amino
group to prepare a buffer member. The amount of cationic functional groups was 2.8 mmol / g.
[0080]
Example 4 The same vibrating membrane as in Example 1 was used. The buffer member had an
electron beam irradiation amount of 30 Mrad in the electron beam irradiation process in the first
embodiment. A buffer member was obtained by the same operation as in Example 1 except for
the above. In Comparative Example 2, the grafting ratio of GMA non-woven fabric was 198%, and
the amount of cationic functional group of the amino group introduced buffer member was 4.0
mmol / g.
[0081]
Example 5 The same vibrating membrane as in Example 1 was used. The buffer member has an
electron beam irradiation amount of 2 Mrad in the electron beam irradiation process in the first
embodiment. A shock absorbing material was obtained by the same operation as in Example 1
except for the above. The graft ratio of the GMA non-woven fabric obtained in Comparative
Example 3 was 15%, and the cationic functional group content of the amino group introduction
buffer was 0.2 mmol / g.
[0082]
Example 6 The same vibrating membrane as in Example 1 was used. As a buffer member, first, a
nylon non-woven fabric (manufactured by Asahi Kasei Corp., basis weight 100 g / m <2>) under
a nitrogen atmosphere using an electron curtain electron beam irradiation apparatus CB250 / 15
/ 180L manufactured by Iwasaki Electric Co., Ltd. Was irradiated at an acceleration voltage of
200 kV for 20 Mrad. Then, the non-woven fabric was immersed in a 10% glycidyl methacrylate
solution to carry out a graft polymerization reaction, to obtain a nylon GMA-grafted non-woven
fabric having a graft ratio of 105% defined by a weight increase rate. Furthermore, the nonwoven fabric was immersed in a 10% aqueous solution of diethylamine to introduce an amino
group, a buffer member having a cationic functional group content of 2.6 mmol / g was obtained,
and the vibrating film was the same as that of Example 1.
04-05-2019
25
[0083]
Comparative Example 1 The same vibrating membrane as in Example 1 was used. As the buffer
member, the nylon non-woven fabric (manufactured by Asahi Kasei Corp., basis weight 40 g / m
<2>) used in Example 1 was used as the buffer member as it was.
[0084]
Comparative Example 2 The same vibrating membrane as in Example 3 was used. As the buffer
member, the polypropylene non-woven fabric (manufactured by Asahi Kasei Corp., basis weight
40 g / m <2>) used in Example 3 was used as it was as the buffer member.
[0085]
Comparative Example 3 The same vibrating membrane as in Example 1 was used. The nylon
nonwoven fabric (manufactured by Asahi Kasei Corp., basis weight 100 g / m <2>) used in
Example 6 was used as it was as a buffer member.
[0086]
The samples prepared above are shown in Table 1.
[0087]
[0088]
(Measurement of air permeability) The air permeability of the buffer member was measured by
JIS L 1096 (Frazil method).
[0089]
04-05-2019
26
(Speaker Frequency Characteristic Evaluation) The respective diaphragms and buffer members
were previously neutralized by a DC blower type static eliminator (manufactured by Kasuga
Denki, KD-410) to set the charge amount of the diaphragm and buffer members to approximately
0.0 nC. .
Thereafter, the flat electrodes were made of a mesh plate of SUS 325, and as shown in FIG. 1, the
buffer members of each of the example and the comparative example were provided between the
flat electrodes.
A voltage of 100 V with a sine wave of 20 Hz to 10 kHz was supplied between the electrodes of
the manufactured speaker, and the frequency characteristics were evaluated.
The frequency was evaluated with a sound level meter (NL-20 manufactured by Lion
Corporation) installed at a distance of 25 cm from the speaker.
[0090]
(Measurement of charge amount) Measurement of the charge amount of the diaphragm and the
buffer member is performed by supplying a voltage of 100 V with a sine wave of 100 Hz and 1
kHz to the speaker manufactured for frequency characteristic evaluation, and then taking out the
diaphragm from the speaker The amount of charge at each frequency was measured using an
electrostatic charge amount measuring device (Faraday cage type KQ-1400) connected with a
coulomb meter (NK-1001) manufactured by Corporation.
[0091]
Sound pressure characteristics with respect to the frequency of Example 1 and Comparative
Example 1 are shown in FIG. 6 as the measurement results of the noise level meter.
From this frequency characteristic result, it can be seen that particularly in the low frequency
region of 1 kHz or less, the frequency characteristic of the buffer member having a cationic
functional group introduced is excellent. Therefore, as an evaluation representative of frequency
characteristics, values of sound pressure at 100 Hz and 1 kHz are shown in Table 2 together with
measurement results of charge amounts of the buffer member and the vibrating film.
04-05-2019
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[0092]
[0093]
The order of the materials used in this example on the charge train is shown in Table 3.
The charge train in Table 3 is based on Lehmicke's charge train widely used in anti-static
technology, and nylon, which is the most easily charged material, and Teflon, which is the most
negatively charged material. As a reference material, and positioned by measuring the amount of
positive and negative charges and the amount of charge during mutual friction with the
reference material.
[0094]
[0095]
From the results in Table 2, when Examples 1 to 3 and Comparative Examples 1 and 2 are
compared, by introducing an amino group that is a cationic functional group into the buffer
member, the charge amount of the buffer member due to frictional charging increases. Along
with this, it is understood that the charge amount of the vibrating film also becomes high, and as
a result, the sound pressure is improved.
In particular, as shown by the frequency of 100 Hz as a representative value of the frequency
characteristics, it is understood that the improvement of the acoustic effect is remarkable by
introducing the cationic functional group in the low frequency region.
[0096]
Here, although the introduction amount of the amino group which is a cationic functional group
is increased in Example 4, the improvement of the charge amount and the sound pressure is
slightly smaller than that of Example 1. Although this increases the amount of electron beam
04-05-2019
28
irradiation to increase the grafting ratio, the amount of cationic functional groups is increased,
but the flexibility of the substrate is lost and the cushioning properties as a buffer member are
reduced by becoming hard. It is considered that the chargeability due to friction is adversely
affected. In addition, since physical properties such as strength and elongation of the base
material are adversely affected when the irradiation amount of the electron beam is increased,
attention must be paid to the durability of the acoustic characteristics of the speaker and the
handling property at the time of the speaker configuration. is there. Further, in Example 5, since
the introduction amount of the cationic functional group is small, the improvement effect of the
charge amount of the buffer member is limited to some extent, the change of the charge amount
of the vibrating film is not large, and the improvement of the acoustic characteristics is also
limited. It is thought that it became.
[0097]
Furthermore, as shown in Example 6, when the cushioning member having a low air permeability
is used, although the triboelectric charge amount and the acoustic characteristics are improved
as compared with Comparative Example 3 in which the cationic functional group is not
introduced, It can be seen that the effect of introducing the cationic functional group is
suppressed because the sound permeability is lowered.
[0098]
Therefore, by introducing a cationic functional group into the buffer member, the electrostatic
speaker obtained in the present invention can increase the frictional charge of the vibrating
membrane and the buffer member, and can significantly improve the acoustic characteristics.
Was confirmed.
[0099]
DESCRIPTION OF SYMBOLS 100 Electrostatic type speaker 2 Buffering member 3 Vibrating film
11 Base material of buffer member 12a Inorganic fine particle 12b Polymer fine particle 13
Silane monomer 14 Binder 15 Fluorinated polymer layer 16 Vibrating film base
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