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JPS55157224

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DESCRIPTION JPS55157224
Specification L Title of Invention
Method of manufacturing electret
8. Detailed Description of the Invention The present invention relates to a method of
manufacturing an electret. The electret is defined as a substance characterized by applying an
electrical polarization which is permanently connected to a dielectric substance having no
spontaneous polarization. As well known, electrets include an electret that can use
piezoelectricity or pyroelectricity, and an electret that can use an electrostatic field, and in
particular, an electret that can use an electrostatic field includes electrostatic microphones and
electrostatic headphones. Besides being used as a polarization voltage source, electrostatic
electro-mechanical conversion. It can be used for most devices that require mechanical-electrical
conversion operation, and has a high utility value. The conversion efficiency of the electrostatic
electro-mechanical converter and the electrostatic mechanical-electrical converter can be
obtained as the polarization voltage increases, and electrets for electrets used for these devices
The need for high voltage and the fact that the voltage values of each single electret are equal to
each other is necessary to improve the uniformity of the performance and quality of the nine
instruments. Furthermore, since the life of the electret voltage directly determines the service life
of the device using the electret, it is also an important requirement to have a uniform long life. As
methods for obtaining such electrets, conventionally (1) thermal electretization method, c2)
electro electretization method, (8) mechano electretization method, (4) photo electretization
method. Basic electrets such as (5) radio electretization methods, (6) magnetic fist electretization
methods and the like, and a number of electretization methods combining these methods have
been attempted. For example, the thermal electretization method and the electro-electretization
method are industrially used because they are easy to control the degree of polarization or the
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amount of charge and thus to control the electret voltage value, but they are practically used in
terms of stability, life, etc. It was not enough. Furthermore, in order to improve the stability, life
and the like, electretizing a dielectric surface having an uneven surface has also been tried in JPB-51-15599 and the like. In practice, sufficient performance could not always be obtained.
Furthermore, in these electretization methods, at the time of electretization, since the electret
surface contains an unstable charged component, a stabilization treatment as shown in, for
example, JP-A-47-48999 and JP-B-50-19860 is indispensable It was a process.
In view of the above-described points, the present invention aims to provide a manufacturing
method capable of easily obtaining a stable electret having a uniform electret voltage value and a
long life electret voltage without any need for a stabilization treatment step. I assume. The
method of the present invention is a method for producing an electret in which plastic
deformation is given to the surface of the dielectric material for electretization to form a
stretched region and a compressed region, and in the step of dispersing and forming the
stretched region and the compressed region, This is a method of manufacturing an electret in
which a pressing and deforming jig is brought into pressure contact with and peeled off from the
surface of the dielectric material for electretization. That is, in the method of the present
invention, as shown in cross section in FIGS. 1 (a) and 1 (b), a pressure deformation jig C) having
many irregularities is pressed against the surface of the dielectric material for electretization (1).
The peeled area (4) and the compressed area (G) are dispersedly formed. At this time, it has been
found that extremely stable electric charges are held in the stretched area (4) and the
compressed area (G). Note that the charging mechanism that generates this stable charge is the
charge (8) between the electret dielectric material (1) and the pressure deformation jig (2) when
forming the extension area (4) and the compression area (G). It is considered that the alignment
state of the molecular structure of the dielectric material for rubbing, peeling and electretizing is
locally changed. Examples of the dielectric material for electretization used in the method of the
present invention include ethylene tetrafluoride-hexafluoride-butylidene copolymer (hereinafter
referred to as FEP Teflon), polytetrafluoroethylene, polyperfluoroalkoxy and the like. , Also
polyethylene terephthalate. It is also possible to use a laminate obtained by coating FEP Teflon,
polytetrafluoroethylene or the like on the surface of polyimide, polyvinyl chloride, polyvinylidene
fluoride or the like. Further, the pressure deformation jig may be made of a material different
from the dielectric material for electretization and the charge sequence, and in practical use, it is
preferable to use a mold whose surface is covered with plating or the like. The electret voltage
can be easily controlled by appropriately selecting the forming material of the surface of the
pressure deformation jig. Furthermore, as the large number of irregularities provided on the
surface of the pressure forming jig, for example, trapezoidal projections (8) as shown in a bottom
plan view and a side view in FIG. 2 or 2 (Fig. 8 (a) K) (4). Such conical projections (8), etc., and
any other prism (Fig. 8 (b)), hemisphere (Fig. 8 (Fig. 8 (f)) as long as it is a shape capable of
forming plastic deformation having a stretched area and a compressed area by pressure welding.
C)), half (FIG. 8 (d)), spiral (FIG. 8 (e)), concentric circles (FIG. 8 (f)), etc. can be selected as
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appropriate.
Next, the influence of the dispersion density of asperities, the pressure applied to pressure
contact, and the change in thickness of the dielectric material for electretization on the electret
surface potential in the method of the present invention is examined. First, as shown in FIG. 4 (a),
a dielectric material (1) for electretization made of FF1P Teflon is provided on the surface of the
aluminum + aluminum substrate (4), and as shown in FIG. 4 (1)). An electret having a pyramidal
stretched region and a compressed region as shown in FIG. 4 (e) is obtained by pressing and
peeling a pressure deformation jig C) having a shape as shown in the figure against the surface of
the dielectric material for electretization (1). Manufacture. Then, when the electret surface
potential with respect to the change of the dispersion density of the protrusion provided on the
surface of the pressure deformation jig (2) was examined, the result as shown in FIG. 5 was
obtained. EndPage: 2 Using the same method as above, the relationship between the applied
pressure of the pressure welding of the pressure deformation jig and the change of the surface
potential of the electret to the change of the thickness of the dielectric material for electretization
is shown in FIG. 6 and FIG. In the measurement of FIG. 5, the conditions other than the dispersion
density of the irregularities are the same, in the measurement of FIG. 6, the conditions other than
the applied pressure are the same, and in the measurement of FIG. 7, the thickness of the electret
dielectric material Same except for sales. As a result, within the range in which plastic
deformation having a stretched region and a compressed region can be formed on the surface of
the dielectric material for electretization, the higher the dispersion density of the unevenness
(that is, the stretched region and the compressed region increase) It is apparent that the surface
potential of the electret is improved as the pressure increases and as the thickness of the electret
dielectric material increases. The dispersion density of the asperities, the applied pressure, and
the thickness of the dielectric material for electretization are appropriately selected according to
the required electret surface potential, the type of dielectric material for electretification, etc.
Practically when manufacturing an electret for electroacoustic transducers (electret surface
potential 12001 to +15001 V). The dispersion density of the unevenness is 2000 to 7500 pcs /
cr11. It is preferable that the application pressure be 10 to 75 kg / crl, the thickness of the
dielectric material for electretization be 50 ?m to 150 ?m, and the above conditions be
appropriately combined and selected as required. For example, in the case of an electret for
headphones having a surface potential of 500 to 100 OV, using a pressure deformation jig as
shown in FIG. 2, the dispersion density of irregularities is 5500 to 6000 pieces / d, applied
pressure 80 to 60 kg / d, dielectric for electretization Material (17 'BP Teflon) with a thickness of
50 to 100 ?m, and in the case of a cartridge electret with a surface potential of 800 to 800 V, 1
dispersion density 2000 to 8000 pieces / d applied pressure 20 to 60 kg / Cl 1 t dielectric
material for electretization The thickness of (FEB Teflon) is preferably 100 to 150 ?m.
The pressure contact speed at the time of pressure contact, the heating condition of the dielectric
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material for electretization, and the like can be appropriately selected according to the type of
the dielectric material for electretization and the like without departing from the scope of the
present invention. Next, the stability (lifetime) of the electret obtained by the method of the
present invention is examined. An electret (Example) made of F] i3P Teflon obtained by the
manufacturing method as described above and an electret provided with irregularities on the
surface without forming a stretched region and a compressed region in advance by a method
such as partial melting removal or cutting removal The lifespan of the electret (comparative
example) having the same surface potential as that of the electret obtained by the abovementioned method of the present invention obtained by applying the conventional thermal
electret method to the dielectric material is shown in FIG. . As an example, a pressure
deformation jig as shown in FIG. 2 (concave and convexity dispersion density 7000 pieces / crl)
as shown in FIG. 2 is brought into pressure contact with a 75 ?m thick dielectric material made
of FEP Teflon at 40 kg / crl and peeled off. As a comparative example, FEP Teflon was melted to
prepare the same shape as that of the electret obtained in the above example, and an electret
having the same surface potential by corona discharge was used as a comparative example. The
lifetime is indicated by the time (year) until the initial potential attenuates by 18 dB. The curve a
in FIG. 8 represents an example, and the curve a represents a comparative example. As a result, it
was confirmed that the life of the electret obtained by the method of the present invention is
significantly improved and the stability is excellent. In addition, curve 2 in FIG. 8 shows the life
when the same surface potential as in the above embodiment is obtained using FIG. 8 (b) or (C) as
a pressure deformation jig, and obtained by this It was also confirmed that the electret also had a
long life and excellent stability. In addition, it has been confirmed that the trapezoidal
deformation shown in FIG. 2 and the truncated cone-like projection shown in FIG. 8 (a) are most
preferable. Since the method of the present invention improves the characteristics of the electret
by applying plastic deformation to disperse and form the stretched region and the compressed
region on the surface of the dielectric material for electretization as described above, It is also
effective to add new charges by using EndPage: 3 by another means, and the effect of the present
invention can be obtained even if new charges are added by means on the back side after
removing the charges generated by pressure contact and peeling. Further, the effect of the
present invention can be obtained even if a voltage is applied to the metal pressure deformation
jig having a large number of irregularities during the pressure contact peeling process and the
conductive substrate of the electret.
For example, as shown in FIG. 9, after electretizing a FEP Teflon film (10) having no unevenness,
a Kapton film (trade name of Dupont Co., Ltd. for polyimide film) (11) is placed, and i! A
thermally stimulated current spectrum of the pole (12) and the line -a is obtained, and further,
the thermally stimulated current spectrum of the electret according to the method of the present
invention in which the metal pressing deformation jig is pressed into contact to form a large
number of irregularities become that way. Furthermore, after heat stimulation current spectrum
measurement (that is, after removing the charge obtained by the method of the present
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invention), the electret is obtained again by the electro electretization method. If a thermally
stimulated current is measured, 2 curves-can be obtained. That is, FIG. 10 shows that the stability
of the charge contained is different even in the electret having the same surface potential.
Another important effect of the present invention is to effectively contribute to improving the
flatness of the electret. At present, electrostatic microphones and electrostatic headphones are
mentioned as main uses of electrets. 1 For example, when used in electrostatic headphones, as
shown in FIG. 11, the vibrating electrode 14t from the surface of the electret 10) Although it is
possible to reduce the distance between the electrets 10 and 11 as much as possible in order to
enhance the electro-acoustic conversion efficiency, when the electret 10 and the vibrating
electrode 14 come into contact with each other in use of the headphones, the characteristics of
the headphones deteriorate significantly. Since there is a risk of damaging the headphones,
electrets with uniform flatness are used. In the method of the present invention, if the flatness of
the pressing and deforming jig is high, it has the same effect as embossing when pressing under
high pressure, and an electret having a high degree of flatness can be obtained. By using it as
shown in the figure, a stable turtle-shaped navel-acoustic transducer can be obtained. In the
figure, (15) indicates the spacer, (16) indicates the fixed electrode (conductive substrate), (17)
indicates the transformer, and (18) indicates the signal source by using the method of the
present invention. It is possible to obtain an electret having an extremely stable charge without
applying the stabilization process which has been conventionally required, and to significantly
extend the electret life. 0 Also, the dielectric material for electretization is pressure-deformed also
in the manufacturing process Since the required electret can be obtained only by pressure
welding and peeling with a jig, mass production is improved by simplifying the process. Further,
the charge distribution on the electret surface can also be easily controlled by the dispersion
density of the irregularities on the surface of the pressure deformation jig, and an electret having
a uniform surface potential can be easily obtained.
Furthermore, the surface potential itself of the electret can be easily controlled by the dielectric
material for electretization, the pressure deformation jig, the applied pressure, and the like.
4. Brief description of the drawings FIG. 1 is a cross-sectional view for explaining the method of
the present invention. 1 иии Dielectric material for electretization 2 и и и Jig for deformation under
pressure Figs. 2 and 8 are a bottom view and a side view showing an example of the structure of
the pressure deformation jig used in the method of the present invention, respectively. FIG. 4 is a
process diagram for explaining the method of the present invention, and FIGS. 5 to 8 are curves
showing characteristic examples of electrets obtained by the method of the present invention,
and FIG. FIG. 10 is a curve showing the thermal stimulation current spectrum of the electret, and
FIG. 11 is a schematic view of the configuration of an electrostatic headphone using the electret.
Attorney Attorneys General Attorney General's Law (1 other) EndPage: 41 wards H L L ?) H, U
? H ? to L)) 5 Taida Price (Park) ? ward ? H L L)) ?Area-M bad H H ? ? ? ? Waki-Haki
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EndPage: 6 Warning: Page Discontinuity Figure 9 Figure 10 Wt'ml Ha Figure 11 1015 n7EndPage: ?
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