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BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
speaker diaphragm having excellent acoustic characteristics.
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.
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.
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.
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.
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.
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.
On the other hand, conventional diaphragms made of paper, pulp or the like have a low density,
and have 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 as a raw material
is weak to humidity and can not cope with the rigidity of pulp only when it is used as a speaker
compatible with digital, for example. 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.
The present invention has been made to solve such problems, and when inorganic fibers, organic
synthetic fibers, inorganic scale-like substances, etc. are made into a diaphragm for a speaker by
papermaking, phosphate ester cellulose is used. An object of the present invention is to provide a
speaker diaphragm having excellent density, specific elastic modulus, flame retardance, moisture
resistance and the like and having an appropriate internal loss by using fine fibers as a binder.
[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 phosphate ester cellulose with fine fibers.
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
It is also possible to form a mixture of two or three of these raw material suspensions and a
mixture of highly fibrillated phosphate ester cellulose fine fibers.
Further, a thermoplastic resin or a thermosetting resin may be attached to the formed
diaphragm. The diaphragm of the present invention includes the diaphragm 10, the center cap
30, and the like shown in FIG.
For example, phosphate ester cellulose is prepared as follows. First, several percent of urea is
further added to the solution of ammonium polyphosphate obtained by reacting urea and
phosphoric acid. The aqueous solution of phosphoric acid esterifying agent is impregnated into
cellulose fibers so that an effective adhesion amount of 20 to 30% by weight to cellulose ratio
can be obtained. As cellulose fiber, natural fibers such as wood pulp and paper can be used. After
the impregnation treatment, the cellulose fiber is dewatered with hot air at 100 ° C. or less, and
the subsequent esterification reaction is started by further heating to 140 ° C. or more.
[Chem. 1]
In the esterification reaction, the compound [II] is in an unstable state, so most of it becomes the
compound [I] after completion of the reaction.
The obtained phosphate ester cellulose is fibrillated when it is beaten with a disintegrator such as
a beater or refiner. For example, while wood pulp used as a raw material had the fiber state
shown in FIG. 2, the phosphate ester cellulose after beating is in the state shown in FIG.
At this time, the cellulose of the natural fiber has a crystalline region and a noncrystalline region,
and the crystalline region is broken by the esterification reaction to become a noncrystalline
region. Therefore, beating can be easily performed. In addition, in the present invention, it is
preferable to beat phosphate ester cellulose at a degree of beating of 90 ° SR or more in terms
of Shopper's Riglare freeness, in order to impart properties necessary as a binder.
When phosphate ester cellulose is dispersed in water, it exhibits cation behavior. And it works as
an effective binder for materials such as wood pulp, glass fiber, ceramic fiber, metal fiber, etc.
whose zeta potential is negative. In addition, entanglement with organic fibers such as nylon
fiber, acrylic fiber, polyester fiber, aramid fiber, PPS fiber, aromatic polyester fiber is also good.
That is, it acts as a binder for various fibers. Therefore, a wide range of fiber materials can be
used, and they can be optionally blended and manufactured by papermaking, so that it becomes
possible to obtain a new speaker diaphragm which has not hitherto been available.
In addition, phosphoric ester cellulose exhibits a flame retardancy in which, when exposed to
high temperatures, a phosphoric acid in the molecule is denatured and carbonized, causing
carbonization due to autolysis. Therefore, when a highly heat-resistant aramid fiber, a phenol
resin, an inorganic fiber or the like is used as a main material, it becomes a speaker diaphragm
having excellent flame resistance. With regard to mica, carbon graphite, various whiskers, etc., it
becomes possible to mix with high yield by the entanglement of microfibrils and mechanical
filtration. Furthermore, when an additive such as polyacrylamide which neutralizes the surface
charge is blended in papermaking, the yield is further improved.
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.
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
fibrillated phosphate ester cellulose fibrils as a binder. In addition, the binder fiber of Table 1
shows the fine fiber which fibrillated phosphate ester cellulose.
[Table 1]
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,
In addition, the epoxy resin in Examples 21-30 and the comparative example 3 was cured by the
heat processing hold | maintained at 210 degreeC for 2 minutes. As the impregnating resin, a
phenol resin or a melamine resin can be used, and the diaphragm obtained by this can be
imparted with flame retardancy.
The characteristics of the diaphragms obtained by forming these blends into sheets are shown in
Tables 2 to 4. 【Table 2】
[Table 3]
[Table 4]
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 phosphate ester cellulose as a binder, it has become possible to
form synthetic fibers and inorganic fibers, which have conventionally been regarded as nonpaper-making materials.
By the selection of the material, the diaphragms of Examples 1 to 8 and 10 have flame
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. 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.
As described above, according to the present invention, by using fibrillated phosphate ester
cellulose as a binder, various fibers are compounded and formed into a speaker diaphragm. It can
be used safely in the vicinity of power supplies such as TVs and radios by taking advantage of
flame retardancy. Since the degree of freedom of selection for this material is large, a diaphragm
excellent in moisture resistance and chemical resistance is obtained, and the diaphragm exhibits
sufficient characteristics over a long period of time even in a use environment exposed to a
seawater atmosphere.
Brief description of the drawings
Fig. 1 A schematic sectional view showing the structure of an electrodynamic speaker Fig. 2 A
photograph showing the fiber shape of wood pulp used as a fiber material
Fig. 3 Photograph showing the fiber shape of fibrillated phosphate ester cellulose
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