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JPH04367197

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DESCRIPTION JPH04367197
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
speaker diaphragm having excellent acoustic characteristics.
[0002]
2. Description of the Related Art The acoustic characteristics of an electroacoustic transducer
represented by an electrodynamic speaker mainly depend on the physical characteristics of a
vibration system. Above all, the diaphragm is an important member that greatly affects the
performance of the speaker.
[0003]
For example, as shown in FIG. 1, the diaphragm 10 is formed in a cone shape, and is fixed to the
speaker frame 20 by a gasket 21 around the edge 11. A center cap 30 is disposed at the center
of the inside of the diaphragm 10, and a voice coil 32 is wound around the coil bobbin 31. A
magnetic circuit is formed by the center pole 41, the yoke 42, the magnet 43 and the plate 44,
which are internally mounted on the coil bobbin 31, and the voice coil 32 is movable in the
middle of the magnetic circuit, that is, between the center pole 41 and the plate 44. Place on In
addition, the code | symbol 12 shows a damper.
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[0004]
The following characteristics are required for the materials used as the diaphragm 10 and the
center cap 30 incorporated in the speaker. ■ Low density ρ to improve efficiency. ■ The
specific modulus E / ρ should be large to widen the regeneration zone. ■ To have a moderate
internal loss to damp resonance and flatten the sound pressure frequency characteristics.
[0005]
As materials that satisfy these requirements, molded articles of prepreg sheets typified by cross
carbon, molded articles of sheets mainly made of polypropylene, injection molded articles mainly
made of polypropylene, etc. are conventional paper and pulp. It has come to be used as a
substitute for etc.
[0006]
Problems to be solved by the invention: Molded articles of prepreg sheet represented by cross
carbon, molded articles of polypropylene sheet, injection molded articles, etc. are compared with
paper, pulp etc. It can be said that it is a diaphragm material that satisfies the accompanying
required characteristics.
However, these materials have advantages and disadvantages, and there is room for
improvement in density 余地, specific elastic modulus E / ρ, internal loss, and the like.
[0007]
For example, although a molded prepreg sheet is excellent in rigidity, it has a large density が
and a small internal loss. In addition, in the case of molded articles such as polypropylene sheets,
it is necessary to blend carbon fibers, mica, whiskers, etc. in order to increase the rigidity more
than paper, pulp etc. However, this formulation increases the density. Moreover, polypropylene
sheets have the fatal disadvantage of being vulnerable to heat.
[0008]
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On the other hand, the conventional diaphragm made of paper, pulp or the like has a low density,
and has appropriate rigidity and internal loss. Moreover, since it manufactures by papermaking,
it is excellent in the freedom degree of material selection. Therefore, the diaphragm of this
system is used even now. However, a diaphragm made of paper, pulp or the like is weak to
humidity, and for example, it is impossible to cope with the rigidity of the pulp alone in order to
make the speaker compatible with digital. In order to solve this defect, it is introduced in
Japanese Patent Application Laid-Open Nos. 61-245791 and 61-245797, that carbon fiber or
aramid fiber is mixed with paper, pulp or the like. However, since carbon fibers, aramid fibers
and the like do not have a self-bonding force, the Young's modulus of the diaphragm tends to
decrease as the fibers are blended.
[0009]
The present invention has been made to solve the above problems, and when using inorganic
fibers, organic synthetic fibers, inorganic scale-like substances, etc. as a diaphragm for speakers
by papermaking, it is possible to use polymetaphenylene iso. An object of the present invention is
to provide a speaker diaphragm having excellent density, specific elastic modulus, heat
resistance, moisture resistance and the like and having a suitable internal loss by using
phthalamide fine fibers as a binder.
[0010]
[Means for Solving the Problems] In order to achieve the object, the diaphragm for a speaker
according to the present invention is made of a material suspension mainly composed of wood
pulp, bast, seed hair fiber, etc. It is characterized in that it is obtained by forming a mixture of
fibrillated poly (metaphenylene isophthalamide) with a fine fiber.
[0011]
As the raw material suspension, mineral fibers, organic synthetic fibers or blends of these fibers,
raw material suspensions mainly composed of scaly inorganic substances and the like are also
used.
In addition, two or three of these raw material suspensions may be blended, and a mixture of fine
fibers of highly fibrillated polymetaphenylene isophthalamide may be formed into a sheet.
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Further, a thermoplastic resin or a thermosetting resin may be attached to the formed
diaphragm. The diaphragm of the present invention is used as the diaphragm 10 and the center
cap 30 shown in FIG.
[0012]
The polymetaphenylene isophthalamide has the following structure and is particularly excellent
in thermal characteristics. For example, the thermal contraction at 250 ° C. is 1% or less, and
the thermal contraction at 300 ° C. is 5 to 6%. Therefore, sufficient resistance is exhibited also
when using it continuously by about 200 degreeC atmosphere.
[0013]
[Chem. 1]
[0014]
When this isophthalamide is spun using conventional spinning nozzles, so-called yarns are
obtained.
However, when spinning is performed while rotating the spinning nozzle at high speed, the spun
fiber is divided by the centrifugal force of the spinning nozzle, and as shown in FIG. 2, it becomes
fibrillated in the case of wood pulp. This fibrillated isophthalamide fiber has a very large surface
area. When the isophthalamide fiber is dispersed in water and the freeness is measured, the
ordinary cut fiber has a freeness of 80 ° SR or more, while it is 8 to 9 ° SR. That is, the surface
area is large and the water retention capacity is large.
[0015]
Isophthalamide fibers are not only entangled with natural fibers such as wood pulp by
fibrillation, but also inorganic fibers such as glass fibers, ceramic fibers, carbon fibers, nylon
fibers, acrylic fibers, polyester fibers, aramid fibers, The entanglement with organic fibers such as
PPS fibers and aromatic polyester fibers is also good. That is, it acts as a binder for various fibers.
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Therefore, a wide range of fiber materials can be used, and they can be optionally blended, so
that it becomes possible to obtain a new speaker diaphragm which has not been used
conventionally.
[0016]
With regard to mica, carbon graphite, various whiskers, etc., it becomes possible to mix the paper
with high yield by the entanglement of the microfibrils and the mechanical filtration action.
Furthermore, when an additive such as polyacrylamide which neutralizes the surface charge is
blended in papermaking, the yield is further improved.
[0017]
Further, the rigidity, Young's modulus, density and the like of the diaphragm can be
appropriately adjusted by adhering a thermoplastic resin, a thermosetting resin or the like to the
diaphragm. These resins can be adhered to the diaphragm by immersing the diaphragm in a resin
solution dissolved or suspended in a solvent, or by spraying the resin solution on the diaphragm.
[0018]
EXAMPLES The present invention will be described in more detail by way of the following
examples. Table 1 shows the blend ratio of the material for producing a diaphragm using, as a
binder, fine fibers or the like obtained by fibrillating polymetaphenylene isophthalamide. In
addition, the binder fiber in Table 1 shows the fine fiber which fibrillated polymetaphenylene
isophthalamide.
[0019]
[Table 1]
[0020]
Further, those in which Examples 1 to 10 were impregnated with an acrylic resin were prepared
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as Examples 11 to 20, respectively.
In Examples 1 to 10 and Comparative Example 1, 0.2 wt% of polyacrylamide and 1.0 wt% of a
synthetic high molecular cation sizing agent were used. Moreover, what impregnated the epoxy
resin with Examples 1-10 was prepared as Examples 21-30, respectively. The epoxy resins in
Examples 21 to 30 and Comparative Example 3 were cured by heat treatment maintained at 210
° C. for 2 minutes.
[0021]
The characteristics of the diaphragms obtained by forming these blends into sheets are shown in
Tables 2 to 4. 【Table 2】
[0022]
[Table 3]
[0023]
[Table 4]
[0024]
As apparent from Tables 2 to 4, the diaphragms of the embodiments according to the present
invention show excellent characteristics in terms of density, Young's modulus, internal loss and
the like.
In addition, by using fibrillated polymetaphenylene isophthalamide as a binder, it has become
possible to form synthetic fibers and inorganic fibers, which have conventionally been made into
non-paper-making materials.
[0025]
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By the selection of the material, the diaphragms of Examples 1 to 8 and 10 have flame
retardancy.
Moreover, when using the thing excellent in the flame retardance as an acrylic resin and epoxy
resin which were used in Examples 11-20 and 21-30, or when using the acrylic resin and epoxy
resin which carried out the flame-retarding process, an Example Even in the case of 11 to 30, the
diaphragm can be made excellent in flame retardancy.
[0026]
Furthermore, the diaphragms of Examples 1 to 8, 10, 21 to 28 and 30 have durability to
withstand continuous use of 2000 hours or more exposed to a high temperature atmosphere of
200.degree. The same applies to the case where it is treated with a heat-resistant resin such as a
phenol resin or a melamine resin, in addition to the epoxy resin.
[0027]
As described above, according to the present invention, by using fibrillated polymetaphenylene
isophthalamide as a binder, various fibers are blended to form a diaphragm for a speaker. It can
be paper-made and can be used safely in the vicinity of power sources such as televisions and
radios by taking advantage of flame retardancy. Since the degree of freedom of selection for this
material is large, a diaphragm excellent in heat resistance and chemical resistance can be
obtained, and the diaphragm exhibits sufficient characteristics over a long period of time even in
a use environment exposed to a seawater atmosphere. In addition, since continuous use at high
temperature is also possible, it is also suitable as a diaphragm of a muffling speaker for exhaust
noise of an internal combustion engine such as a car.
[0028]
Brief description of the drawings
[0029]
Fig. 1 A schematic cross-sectional view showing the structure of an electrodynamic speaker Fig. 2
A photograph showing the fiber shape of fibrillated polymetaphenylene isophthalamide
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