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JPH09284884

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DESCRIPTION JPH09284884
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
diaphragm for an electroacoustic transducer such as a speaker or a microphone used for an
electroacoustic transducer, and more specifically, it has a large specific elastic modulus and an
appropriate internal loss. The present invention relates to an excellent diaphragm for an
electroacoustic transducer.
[0002]
2. Description of the Related Art As a physical property required for a diaphragm for an
electroacoustic transducer used for a speaker, a microphone, etc., the specific elastic modulus is
large, the internal loss is appropriate, the mechanical fatigue is small, and the weather resistance
is excellent. And the like. In order to meet such needs, materials such as various metals, ceramics,
synthetic resins, synthetic fibers, plant cellulose (wood, non-wood pulp), and microbial cellulose
fibers have been proposed and processed using various processing methods. It has been used.
[0003]
Among them, metals and ceramics have high elastic modulus but high density and low internal
loss, so they are relatively good for high-frequency reproduction, but for mid-low range and all
bands where light weight and high rigidity are required Is inappropriate.
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[0004]
In addition, paper diaphragms mainly composed of various cellulose fibers have suitable internal
loss but their specific elastic modulus is not so large, and they are weak against water and
humidity, so they are exposed to rain outdoors. There was a problem for use in vehicles and for
vehicles that require water during washing.
[0005]
On the other hand, diaphragms made of synthetic fibers are made of synthetic resin alone, a base
resin mixed with a filler (filler), an alloy with another resin (alloy), etc. Vacuum molded), and
pellets which are injection molded by an injection molding machine.
These resin diaphragms have a high specific elastic modulus, have appropriate internal loss, are
also resistant to water and humidity, and have a relatively excellent performance because they
have little variation during mass production. It can be said.
[0006]
Among them, a mixture of a fibrous filler with a synthetic resin based on a polyolefin polymer
(mainly polypropylene) as a base material utilizes a fiber orientation in injection molding, and a
diaphragm having particularly excellent performance. You are getting
Furthermore, since the performance (mainly the elastic modulus) depends on the performance of
the filler to be added, at present, the one using carbon fiber is a relatively excellent diaphragm.
[0007]
However, in the case of using carbon fiber, the conductivity of carbon is not fatal in itself due to
the structure of the speaker, but particularly the insulation treatment at the time of
manufacturing the speaker is an obstacle in terms of cost. ing. Furthermore, many of the high
elasticity type carbon fibers do not have sufficient strength, and there is a problem that breakage
of the fibers often occurs during mixing with the resin and injection molding, which also causes
product variation.
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[0008]
The present invention has been made in view of these points, and provides a diaphragm for an
electroacoustic transducer using a fiber having high elasticity, high strength, high internal loss,
and high toughness and having no conductivity. The purpose is
[0009]
SUMMARY OF THE INVENTION Polyparaphenylene benzbisthiazole (PBT) is an organic fiber
having an elastic modulus substantially equal to that of carbon fiber (about twice that of aramid
fiber), high strength, high internal loss, and high toughness. And a polybenzazole (PBO) fiber
such as polyparaphenylene benzbisoxazole (PBO) are mixed with a polyolefin polymer, and a
diaphragm for an electroacoustic transducer is formed using an injection molding method.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION The diaphragm for electroacoustic transducer
according to the present invention is characterized in that it is formed by injection molding
method by mixing 5% by weight or more of polybenzazole fiber with a polyolefin polymer.
[0011]
Further, in the diaphragm for electroacoustic transducer according to the present invention, the
polyolefin polymer is a polymer of an aliphatic olefin such as polypropylene, poly (4methylpentene-1), polyethylene or the like, or an alloy thereof, further, the polymer It is
characterized in that it is a copolymer having as its main component the constituent monomer of
[0012]
Furthermore, the diaphragm for an electroacoustic transducer according to the present invention
is characterized in that the polybenzazole fiber has a tensile strength of 4.0 GPa or more and an
initial tensile elastic modulus of 140 GPa or more.
[0013]
An embodiment of the present invention will be described below with reference to the drawings.
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FIG. 1 is a front view of a half cross section of a diaphragm according to the present invention.
1 is a diaphragm and 2 is an edge.
1.
20% by weight of polyparaphenylene benzbisoxazole (PBO) fiber with a tensile modulus of 250
GPa cut to 3 mm fiber length and 80% by weight of polypropylene (Mitsubishi Polypro BC2A) by
melt mixing at 230 ° C. using a single screw extruder A pellet was made.
2. The pellet obtained in the above 1 was made into a predetermined shape (this time it was a
cone shape in FIG. 1) with a resin temperature of 240 ° C., an injection pressure of 100 MPa, an
injection time of 1 second, a mold temperature of 60 ° C., and a cooling time of 10 seconds. It
was injection molded. 3. The edge 2 was attached to the diaphragm 1 obtained in 2 above.
[0014]
The velocity of sound (the square root of the specific elastic modulus) and the internal loss (tan
δ) were measured for the three types of pellets (20 wt.% PBO fibers, 20 wt. Table 1 shows the
values. Although a cone-shaped diaphragm was manufactured this time, a dome-shaped
diaphragm, a flat diaphragm, a center cap, etc. are also possible. The measurement method is the
vibration lead method.
[0015]
FIG. 2 is a frequency characteristic diagram of the sound pressure of the speaker using the
diaphragm according to the present invention and the sound pressure of the speaker using the
100% polypropylene diaphragm. The solid line A in the figure is the invention according to the
present invention consisting of 20% by weight of polyparaphenylene benzbisoxazole (PBO) fiber
having a tensile modulus of 250 GPa cut to a fiber length of 3 mm and 80% by weight of
polypropylene (Mitsubishi Polypro BC2A). It is a sound pressure-frequency characteristic of a 13cm aperture speaker using a diaphragm. The broken line B represents the sound pressurefrequency characteristics of a 13-cm diameter loudspeaker using a diaphragm of the same shape
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manufactured using 100% polypropylene (Mitsubishi Polypropylene BC2A) containing no filler.
The solid line A has a large specific elastic modulus with respect to the broken line B, so that the
high frequency reproduction limit is extended.
[0016]
FIG. 3 is a frequency characteristic diagram of the sound pressure of the speaker using the
diaphragm according to the present invention and the sound pressure of the speaker using the
diaphragm of carbon fiber 20% and polypropylene 80%. The solid line A in the figure is the
invention according to the present invention consisting of 20% by weight of polyparaphenylene
benzbisoxazole (PBO) fiber having a tensile modulus of 250 GPa cut to a fiber length of 3 mm
and 80% by weight of polypropylene (Mitsubishi Polypro BC2A). It is a sound pressure-frequency
characteristic of a 13-cm aperture speaker using a diaphragm. The broken line C indicates the
sound pressure-frequency of a 13 cm diameter speaker using a diaphragm of the same shape
manufactured in the same process using carbon fiber (Mitsubishi Dielead K223, tensile modulus
of 220 GPa) instead of PBO fiber. It is a characteristic. Since there is almost no difference
between the specific elastic moduli of the two, the reproduction limit of the high region is almost
the same, but the solid line A has a larger internal loss and thus a flatter (flat) response is
obtained.
[0017]
As described above, the diaphragm for an electroacoustic transducer according to the present
invention is formed by injection molding method by mixing 5% by weight or more of
polybenzazole fiber with a polyolefin polymer, and the present invention is also applicable. In the
diaphragm for an electroacoustic transducer according to the invention, the polyolefin polymer is
a polymer of an aliphatic olefin such as polypropylene, poly (4-methylpentene-1), polyethylene or
the like, or an alloy of these, and further, a constituent monomer of the polymer In the
diaphragm for an electroacoustic transducer according to the present invention, the
polybenzazole fiber has a tensile strength of 4.0 GPa or more and an initial tensile modulus of
140 GPa or more. Since the elastic modulus is large and the internal loss is also relatively large, it
is difficult for split vibration to occur, and it is flat from the low band to the high band, and has a
high band reproduction limit. There can be obtained a speaker, also because there is no
conductive, insulated at the time of speaker manufacturing is not required, manufacturing cost is
inexpensive. Furthermore, in the manufacture of the diaphragm, since no breakage occurs as in
the case of carbon fibers, a stable diaphragm with little variation in physical properties can be
obtained.
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[0018]
Brief description of the drawings
[0019]
1 is a front view of one side cross section of the diaphragm according to the present invention.
[0020]
2 is a frequency characteristic diagram of the sound pressure of the speaker using the diaphragm
according to the present invention and the sound pressure of the speaker using the
polypropylene 100% diaphragm.
[0021]
3 is a frequency characteristic diagram of the sound pressure of the speaker using the diaphragm
according to the present invention and the sound pressure of the speaker using the diaphragm of
carbon fiber 20% and polypropylene 80%.
[0022]
Explanation of sign
[0023]
1 diaphragm 2 edge
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