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■ Diaphragm for electrostatic type acoustic equipment O Japanese Patent Application No. 451150540 Application No. 45 (1970) December 22 @ Inventor Present Katsuhiko Hamakita City
Yokosuka 1384 same village Yoshihiko Yoshihiko Hamamatsu city Nakazawacho 7 2 @ applicant
Japan The present invention relates to a diaphragm for an electrostatic type acoustic device, such
as a diaphragm for an electrostatic speaker, for example. Electrostatic loudspeakers are known as
dynamic loudspeakers (they are known to be free from labyrinth distortion, and their diaphragms
used to be old ones pasted with a thin film of lullamin foil or silver foil, but have recently been
used. On the top, aluminum is vapor-deposited on a thin film of polyester resin (for example,
Mylar film) to form a conductive coating, which is used as a diaphragm. In particular, a Mylar
film on which aluminum is vapor-deposited is light (it is strong, has no pinholes, and is excellent
in dielectric strength, and has been awarded as a diaphragm for electrostatic type acoustic
devices. However, in order to improve the efficiency of the electrostatic diaphragm, it is
preferable that the distance between the diaphragm and the fixed electrode be as narrow as
possible, and the DC bias voltage be as high as possible. I have a small hole. Mylar film is fixed
and tensioned at both ends, so the crack progresses from this hole and the whole is torn. For this
reason, the appearance of a diaphragm having high conductivity and not causing a crack is
desired. As a result of the present inventor's research on an electrostatic diaphragm that does not
have the disadvantages of such a conventional Mylar film diaphragm, the diaphragm composed
of a metal reinforced with carbon fiber is most suitable as the electrostatic diaphragm The
present invention has been made by finding [111111]. The carbon fibers used in the present
invention include natural or synthetic fibers such as rayon, polyacrylonitrile, lignin-poval, and
high modulus carbon fibers or graphite fibers obtained by carbonizing pitch fibers at a
temperature of 1800 ° C. or higher. say. These carbon fibers have (1) specific gravity or less, (2)
small thermal expansion coefficient, (3) high heat resistance, (4) electrical conductivity, (5) high
chemical resistance, etc. It has a feature. Carbon fibers having a denier of about 1 to about 10
denier are preferably used, particularly 2 to 5 denier. The proportion of carbon fibers in the final
diaphragm is preferably about 20 to 40% by weight. In the present invention, carbon fibers are
coated with a metal, which is heated by a hot press to fuse the metals and form a carbon fiber
reinforced metal foil. The most common methods for coating metals on carbon fibers are
immersion, plasma spraying and electro-coating.
The immersion method is a method of immersing carbon fibers in a molten metal bath, and the
plasma spraying method is a method of spraying a matrix metal by using a spray gun. According
to this method, fibers having complicated shapes can be coated well. Electroplating can be easily
plated in the usual way because the carbon fibers are conductive. The metal-coated carbon fibers
are layered and heated in a hot press to fuse and coalesce the metal to form a diaphragm. As the
metal, aluminum, duralumin and the like can be used. Example 1 strength 218.7 kg / mlt, elastic
modulus 36 t / m4, cutting elongation 0.60%, density 1.911? Aluminum was plasma sprayed
onto carbon fiber filaments of 1500 denier / 600 fil and / cf / l, cross section 62xio'-. That is,
using a mixed gas of 75 tons of nitrogen and 5 tons of water [111111] EndPage: 1 as a plasma
gas at 400 amps and 70 volts, using a METCo 3 MB type stripe spray gun, aluminum powder of
325 mesh as aluminum. The thermal spraying distance was 150 to 300 mm. The obtained
aluminum-coated carbon fiber was pressed at 1000 ° C. in an alumina die having a
predetermined shape in a nitrogen gas atmosphere to obtain a carbon fiber-reinforced aluminum
diaphragm. Example 23 A short fiber of copolymerized fiber consisting of 95% by weight of
denier acrylonitrile and 5% by weight of vinyl chloride (10 cm of plain woven fabric 10 crrLX
was placed in a quartz container and allowed to stand at 200 ° C. for 10 hours in an open tube)
Then air in the quartz tube is replaced with nitrogen gas, one end of the quartz tube is sealed,
and the other end is passed through a gas washing bottle containing pyrogallol / alkaline
solution for removing oxygen. Heat to 500 ° C. at an ascending rate of 50 ° C. in one hour to
800 ° C. at an ascending rate of 100 ° C. from 500 ° C. for one hour and then 1000 ° C. for
one hour in a carbon resistance furnace The temperature was raised to 2000 ° C., and heating
was continued at this temperature for 5 minutes to obtain cloth-like carbon fibers. This carbon
fiber retained the plain weave structure of the raw material acrylonitrile synthetic fiber cloth. The
carbon fiber fabric was plasma sprayed with aluminum. That is, a METCo 3 MB type stripe spray
gun, 400 amps, 70 volts, using a mixed gas of nitrogen at 75 t and hydrogen at 5 t per minute as
plasma gas, using aluminum powder of 325 mesh as aluminum, spraying distance 150 to 300 I
went with chopsticks.
The obtained carbon fiber woven fabric coated with aluminum was pressed at 1000 ° C. in an
alumina die in the shape of a flat plate speaker under a nitrogen gas atmosphere to obtain a
carbon fiber reinforced aluminum diaphragm. This carbon fiber reinforced aluminum diaphragm
has a carbon content of 30%, a specific gravity of 2.4, and a tensile elasticity of 9000 kg / 1 m! t,
which was suitable as an electrostatic speaker. The diaphragm of the present invention is suitable
as a diaphragm for electrostatic type acoustic equipment because the carbon fiber and the fused
metal are conductive, and since the carbon fiber is used, the strength is high and the peripheral
portion is tension fixed. Not only is it suitable for the purpose, but it can be operated in close
proximity to the fixed electrode without sparks and holes from the discharge. Furthermore, in the
case of Example 2, carbon is not pre-woven, but pre-woven fiber products are carbonized as such
into carbon fibers, which are coated with one metal. It has the advantage 1 that the fibers j are
not broken and the strength is not reduced.
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