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JPH09107595

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DESCRIPTION JPH09107595
[0001]
The present invention relates to a diaphragm for an electroacoustic transducer such as a speaker
or a microphone used in an electroacoustic apparatus, and more specifically, it has a large
specific elastic modulus, an appropriate internal loss, and excellent weather resistance etc. The
present invention relates to a 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), microbial cellulose
fibers, etc. 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 can be used for high-frequency reproduction but are unsuitable for mid-low range
and all bands where light weight and high rigidity are required It is.
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1
[0004]
In addition, those using synthetic resin are made of synthetic resin alone, those based on resin
mixed with filler (filler), those that are alloyed with other resins (alloy), etc. are made into sheets,
which are molded and processed (mainly vacuum) There are molded ones and pellets which are
injection molded by an injection molding machine.
Although these resin diaphragms have relatively high specific elastic modulus, suitable internal
loss, and small variation during mass production, they have relatively excellent properties, but
they are vulnerable to heat and thickness control is not easy. The low design freedom is a
drawback.
[0005]
On the other hand, although the paper diaphragm obtained by paper-making using cellulose
fibers of various plants has a high degree of freedom in design and has an appropriate internal
loss, the specific modulus is not so large, and this specific modulus is In order to improve the
properties of various synthetic fibers, in particular, a mixture of aramid fibers and carbon fiber
ceramic fibers has been proposed.
[0006]
[Problems to be Solved by the Invention] A mixture of aramid fibers with cellulose fibers (generic
name of plant cellulose fibers and microbial cellulose fibers) has an improved specific modulus as
compared with cellulose fibers alone, and a suitable internal loss However, in the specific
modulus of elasticity, a mixture of carbon fibers is excellent.
However, although a mixture of carbon fibers has a specific elastic modulus greater than that of
aramid fibers, there is a disadvantage that the internal loss is not so large. In addition, the
conductivity of carbon has a problem that the structure of the speaker itself is not fatal. In
particular, the insulation process at the time of manufacturing the speaker is an obstacle in terms
of cost. Furthermore, many of the high elasticity type carbon fibers do not have sufficient
strength, and the fibers are often broken at the time of paper making, and such bending has a
disadvantage that it causes deterioration of physical properties and also causes product variation.
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[0007]
The present invention has been made in view of the above-mentioned point, and in order to
compensate for the above-mentioned conventional defects, the object of the present invention is
to make the internal loss approximately equal to that of carbon fiber (about twice that of aramid
fiber) Organic fibers with high strength and high heat resistance, such as polybenzimidazole
(PBZ) fibers such as polyparaphenylene benzbisthiazole (PBT) and polyparaphenylene
benzbisoxazole (PBO), and cellulose fibers It is providing the diaphragm for electroacoustic
transducers by mixing.
[0008]
[Means for Solving the Problems] In order to solve the above problems, the present invention is
to mix cellulose fibers with polybenzazole fibers having a tensile strength of 4.0 GPa or more and
an initial tensile modulus of 140 GPa or more.
[0009]
The polybenzazole fiber has a fiber length of 0.1 to 10 mm.
[0010]
In addition, the mixing ratio of cellulose fiber is 30 to 99% by weight, and polybenzazole fiber is
1 to 70% by weight.
[0011]
Also, the diaphragm was obtained by a wet paper-making method.
[0012]
Moreover, the said cellulose fiber is a cellulose producing microbe (Acetobacter xylinum etc.
It is decided that it is the microbial cellulose fiber obtained from the microorganism which is).
[0013]
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BEST MODE FOR CARRYING OUT THE INVENTION Next, an embodiment of the present invention
will be described.
A polybenzazole (PBZ) fiber having a tensile strength of 4.0 GPa or more and an initial elastic
modulus of 140 GPa or more is cut into a fiber length of 0.1 to 10 mm, preferably 2 to 4 mm,
and mixed with cellulose fiber to form a diaphragm. .
[0014]
Here, polybenzazole (PBZ) fiber refers to a fiber made of polybenzoxazole (PBZ) or
polybenzthiazole (PBT), or a random or block copolymer thereof.
[0015]
Thus, it is an ideal to have a large specific elastic modulus (sound velocity) and a large internal
loss by combining the goodness of the diaphragm made by mixing conventional aramid fiber and
cellulose fiber and the diaphragm made by mixing carbon fiber and cellulose fiber I got an
excellent diaphragm close by.
[0016]
Figure 1 compares the physical properties of the mixed pulp of wood pulp and high modulus
fiber, which is such cellulose fiber, where a is a PBZ fiber blend, b is a carbon fiber blend, c is a paramid fiber blend, d is It is 100% wood pulp (NBKP).
The vertical axis represents the velocity of sound (m / s), and the horizontal axis represents the
internal loss (tan δ × 10 -2).
And it will approach an ideal characteristic as it goes to the upper right direction of this figure.
[0017]
In addition, although the above-mentioned cellulose fiber uses the plant cellulose which uses
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wood etc. as a raw material, For example, the biocellulose obtained by cellulose producing
bacteria which is described in Unexamined-Japanese-Patent No. 61-281800 is used. It is also
possible to use.
By using such biocellulose, it is possible to obtain an excellent diaphragm having both the
physical properties of biocellulose having high Young's modulus (10 to 30 times that of
conventional corn paper) and high internal loss and the physical properties of PBZ fiber. Can.
[0018]
By the way, conventional polybenzazole (PBZ) fibers may have voids (Void) at the time of fiber
production and post-processing, and the water resistance tends to decrease. Therefore, they are
excellent immediately after production by hydrolysis. It has been difficult to maintain
performance for a long time.
[0019]
Thus, it is already known that the acceleration of the hydrolytic action of polybenzazole (PBZ)
fibers is due to the ingress of water from relatively large voids, and by reducing the size of the
voids And the hydrolyzability is significantly improved.
As a method for reducing the diameter of the void to 25 Å or less, there is, for example, a means
described in JP-A-6-253389.
That is, when producing a fiber by spinning from a dope composed of a polymer containing PBZ
as a main component and polyphosphoric acid, the void diameter becomes 25 Å or less when the
concentration of phosphoric acid in the coagulation bath is 5% or more, See the same publication
for the details.
[0020]
Next, a preferred embodiment of the method of manufacturing the diaphragm 1 according to the
present invention will be described.
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In this example, the diaphragm 1 was manufactured by a wet sheet-forming method. That is,
polyparaphenylene benzbisoxazole (PBO) fiber cut to a predetermined length is added to wood
pulp beaten to a predetermined degree of beating, this is paper-made, dewatered, dried under
pressure, and the diaphragm 1 is made The details are described below.
[0021]
(1) A wood pulp was beaten to 500 ml of Canadian Standard 3 water degree, and 20 wt% of PBO
fibers cut into 3 mm fiber length were added to this natural cellulose fiber to prepare a solution
(slurry). (2) The solution (slurry) obtained in the above (1) was formed into a predetermined
shape (corn type in this example) on a wire mesh etc. and adjusted to an appropriate water
content in the dehydration step (this example 80%). (3) The sheet-formed product obtained in the
above (2) was pressurized, heated and dried using a mold having a predetermined shape (in this
example, a cone type), and then punched into a predetermined shape to obtain the diaphragm
main body 1a . The heating, heating, and drying conditions herein were 2 kg / m 2, 180 ° C.,
and 30 seconds. (4) The edge 2 made of synthetic rubber was attached to the diaphragm main
body 1a obtained in the above (3) to obtain a diaphragm 1 shown in FIG.
[0022]
Speakers with a diameter of 13 cm were produced and frequency characteristics were measured
using diaphragms manufactured in the same process using aramid fibers instead of the
diaphragm 1 manufactured in this manner and PBO fibers. The sound pressure-frequency
characteristic is shown in FIG. Here, the frequency characteristic of 500 Hz or more is shown for
comparison. In the figure, a is a speaker using the diaphragm according to the present invention,
and b is a speaker using a diaphragm of 80% natural cellulose fiber and 20% P-aramid fiber. As is
clear from this figure, it can be seen that the speaker using the diaphragm according to the
present invention extends in the high region and the high region characteristic is improved.
[0023]
Moreover, although the compounding ratio of PBZ fiber (PBO) was made into 20% with respect
to 80% of natural cellulose fiber in this example, it is not limited to this, The diaphragm of a
physical property which changes by changing the mixing ratio by the use etc. Is obtained. The
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relationship between the compounding ratio of the PBZ fiber and the physical properties is
shown in FIG. In the figure, a is Young's modulus, b is the speed of sound, and c is the internal
loss. As apparent from this figure, the mixing ratio of cellulose fiber and polybenzazole fiber (PBZ
fiber) is relatively balanced within the range of 99-30% by weight of cellulose fiber and 1-70% by
weight of polybenzazole fiber. Good physical properties can be obtained.
[0024]
In this example, a cone-shaped free edge diaphragm (using different materials for the diaphragm
main body and the edge portion) was manufactured, but a fixed edge diaphragm (one with the
diaphragm main body and the edge portion integrated) or It is also possible to apply the
diaphragm according to the present invention to a dome type diaphragm, a flat type diaphragm,
a center cap and the like.
[0025]
As described above, according to the diaphragm for an electroacoustic transducer according to
the present invention, since the specific elastic modulus is large and the internal loss is also
relatively large, it is difficult for split vibration to occur and flat from low to high Thus, a speaker
with a high reproduction limit can be obtained.
In addition, since there is no conductivity, no insulation process is required at the time of
manufacturing the speaker, and the manufacturing cost is reduced.
[0026]
Further, by setting the fiber length of the polybenzazole fiber to 0.1 to 10 mm, better physical
properties can be obtained.
[0027]
In addition, the above-mentioned good physical properties can be relatively easily obtained
within the range of a mixing ratio of 30 to 99% by weight of cellulose fiber and 1 to 70% by
weight of polybenzazole fiber.
[0028]
In addition, when the diaphragm is manufactured by a wet sheet-forming method, it is difficult
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for the carbon fiber to break like a carbon fiber, and a stable diaphragm with little variation in
physical properties can be obtained.
[0029]
In addition, by using cellulose fibers as microbial cellulose fibers obtained from microorganisms,
it is possible to obtain an excellent diaphragm having both physical properties of biocellulose
having high Young's modulus and high internal loss and physical properties of PBZ fibers.
[0030]
Brief description of the drawings
[0031]
FIG. 1 is a comparison of the physical properties of mixed pulp of wood pulp and high elastic
fiber, in which the vertical axis is the speed of sound (m / s) and the horizontal axis is the internal
loss (tan δ × 10 −2).
[0032]
2 is a cross-sectional view showing the appearance of the diaphragm according to the present
invention.
[0033]
3 is a diagram showing the sound pressure-frequency characteristics of each speaker using the
diaphragm according to the present invention and the diaphragm of the conventional natural
cellulose fiber 80%, P-aramid fiber 20%.
[0034]
Figure 4 shows the relationship between the compounding ratio of PBZ fiber and the physical
properties, the sound speed (m / s) on the vertical axis, Young's modulus (GPa), internal loss (tan
δ) on the horizontal axis, and the compounding ratio (%) of PBZ on the horizontal axis. It
represents.
[0035]
Explanation of sign
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[0036]
1 diaphragm 1a diaphragm main body 2 edge
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