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JPH04367198

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DESCRIPTION JPH04367198
[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 devised to solve such problems, and when inorganic fibers,
organic synthetic fibers, inorganic scale-like substances and the like are made into sheet
diaphragms for speakers by papermaking, it is possible to use bast fibers. 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 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 bast fibers with fine fibers.
[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 it may be
formed into a mixture of highly fibrillated bast fiber fine fibers with this.
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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, the center cap
30, etc. shown in FIG.
[0012]
As the microfibrillated cellulose-based binder, not only bast fibers but also those made from
wood pulp may be used. However, when using wood pulp as a starting material, it takes a long
time to fibrillate to a predetermined degree of beating.
[0013]
Wood fiber, as shown in FIG. 2, has an inner cell tissue C consisting of a secondary membrane S2
wrapped with a primary membrane S1. The secondary film S2 has a three-layer structure of an
outer layer S21, an intermediate layer S22 and an inner layer S23. When wood fibers having this
fiber structure are beaten with a disintegrator such as a beater, the beating degree is set to 30 °
SR or less in consideration of water retention. Under this condition, swelling and partial
fibrillation of the secondary membrane S2 take place with removal of the primary membrane S1.
However, in wood fibers, the angle at which the fibrils are wound with respect to the fiber
longitudinal direction is large, and the fibers tend to be cut before fibrillation. Therefore, as the
degree of beating is increased, the fiber form is broken.
[0014]
On the other hand, in bast fibers such as manila hemp, sasanmu, sisal, flax, burlap, rummy,
persimmon, persimmon, persimmon, corn, sweet potato, bamboo, esparto, etc. Running almost
parallel. Therefore, when the bast fibers are beaten, longitudinal cracks are likely to occur, and
fibrillation proceeds. For example, flax pulp having the fiber form shown in FIG. 7 in the
disaggregated state has the fibers beaten as shown in FIG. 8 at a freeness of 40.degree. SR and is
further microfibrillated as shown in FIG. Be done. However, if the bast fibers are simply beaten
with a beater or the like, a mixture of long fibers and short fibers is obtained, and the binder
effect varies.
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[0015]
Therefore, the present inventors examined the influence of the fiber length on the fibrillated bast
fibers. Flax highly fibrillated by a beater, using a sieving tester defined in JIS P-8207 “Testing
method for sieving pulp for paper pulp”, 20 mesh residue (second tank), 28 mesh It classified
into the residue (3rd tank), 48 mesh residue (4th tank), and 300 mesh residue (5th tank). The 20
mesh residue has a fiber length of about 1 to 1.5 mm, the 28 mesh residue has a fiber length of
about 0.7 to 1 mm, and the 48 mesh residue has a fiber length of about 0.3 to 0.7 mm, 300 The
mesh residue corresponds to a fiber length of about 0.05 to 0.3 mm. And 10 weight% of each
classification part was respectively added to what decomposed | disassembled N * BKP, and the
physical property was measured.
[0016]
The measurement results are shown in FIG. 3 and FIG. (A)-(d) of FIG. 3 show the value which
measured the density, Young's modulus, internal loss, and propagation velocity by the vibration
lead method, respectively. Also, (a) to (d) in FIG. 4 are the air permeability measured by JIS P8117 "Test method of air permeability of paper and paper board", JIS P-8112 "Mulen low
pressure test of paper and paper board" Resistance, measured by JIS P-8114 "Folding strength
test method using paper and paperboard Shopper type tester" and JIS P-8113, "Paper burst
strength test method" The breaking length measured by the tensile strength test method is
shown.
[0017]
Incidentally, F0, F20, F28 and F300 attached to the horizontal axes in FIG. 3 and FIG. 4 are those
obtained by deaggregating N · BKP, to which 10% by weight of 20 mesh residue is added, and 28
What added 10 weight% of mesh residues, what added 10 weight% of 48 mesh residues
similarly, and what added 10 weight% of 300 mesh residues similarly is shown. And, the larger
the mesh, the higher the degree of fibrillation to flax pulp.
[0018]
As apparent from FIGS. 3 and 4, it can be seen that the short fibers have a greater binder action.
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Also, despite the improvement of Young's modulus, the internal loss is almost constant. In this
point, it usually shows a tendency different from that of a normal diaphragm material in which
the internal loss decreases as the Young's modulus increases. From this, what mixed the short
fiber means that it is optimal as a material used for a diaphragm for speakers.
[0019]
Also, the physical properties of fibrillated flax pulp added as a binder to N-UKP, N-BKP and BLT
(linter), and the amounts thereof changed, were measured by the same test method. 5 and 6
show the measurement results. Natural fibers themselves have self-bonding power and exhibit
predetermined physical properties and strength. However, it is shown in FIG. 6 that the strength
is further improved when fibrillated flax pulp is added thereto as a binder.
[0020]
From the above, it can be seen that as a suitable fiber length when using bast fibers as a binder,
48 to 300 mesh residue is more effective. However, from the viewpoint of cost, it is
advantageous to use 20 to 300 mesh residue.
[0021]
The comparison of physical properties in FIGS. 5 and 6 uses natural fibers such as N-UKP, N-BKP
and BLT (linter). However, since fibrillated bast fibers have a highly entangled fiber form, binders
for various fibers such as aramid, nylon, acrylic, polyester, aromatic polyester, carbon, glass,
phenol, ceramics, etc. having no self-bonding ability It is also effective. 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.
[0022]
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
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blended in papermaking, the yield is further improved.
[0023]
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.
[0024]
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 bast fibers. In addition, the binder fiber in
Table 1 shows the fine fiber which fibrillated the bast fiber.
[0025]
[Table 1]
[0026]
Further, those impregnated with an acrylic resin in Examples 1 to 10 were prepared as Examples
11 to 20, and those impregnated with an epoxy resin were prepared as Examples 21 to 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.
[0027]
The characteristics of the diaphragms obtained by forming these blends into sheets are shown in
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Tables 2 to 4. 【Table 2】
[0028]
[Table 3]
[0029]
[Table 4]
[0030]
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 bast fibers as a binder, it has become possible to form synthetic
fibers and inorganic fibers, which have conventionally been made into non-paper-making
materials.
[0031]
By the selection of the material, the diaphragms of Examples 1 to 8 and 10 have weather
resistance and good 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 11 to 30 can be made a
diaphragm excellent in flame retardance.
[0032]
Furthermore, the diaphragms of Examples 1 to 8, 10, 21 to 28 and 30 are heat resistant and
moisture resistant when they are treated with a heat resistant resin such as phenol resin or
melamine resin besides epoxy resin. Etc. can also be given.
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[0033]
As described above, according to the present invention, by using fibrillated bast fibers as a
binder, various types of fibers are compounded and formed into a speaker diaphragm. It can be
used safely in the vicinity of power supplies such as televisions and radios by taking advantage of
its flame retardancy.
Moreover, besides the diaphragm, it can be provided to the market as various prepreg materials.
[0034]
Brief description of the drawings
[0035]
Fig. 1 Schematic cross section showing the structure of an electrodynamic speaker Fig. 2 Model
showing the fiber structure of wood fibers Fig. 3 Graph showing the influence of the fiber length
of fibrillated flax pulp on the physical properties of N-BKP 4 fibrillation Figure 5 Graph showing
the effect of fiber length of flax pulp on other physical properties of N-BKP Figure 5 Graph
showing the effect of blending ratio of fibrillated flax pulp on physical property of N-BKP Figure
6 Fibrilized flax Graph showing the influence of the blend ratio of pulp on other physical
properties of N-BKP Fig. 7 Photograph showing the fiber shape of defibrated flax pulp Fig. 8
Indicates the fiber shape of flax pulp fibrillated at a freeness of 40 ° SR Photo
[0036]
Fig. 9 Photograph showing the fiber shape of flax pulp with 48-300 mesh residue fibrillated at a
freeness of 90 ° SR or more
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