JPS5831695

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DESCRIPTION JPS5831695
[0001]
The present invention relates to a speaker diaphragm, and an object thereof is to provide a
speaker diaphragm having a high specific elastic modulus and a large internal loss. In general,
the speaker characteristics have a large relationship with the physical properties of the
diaphragm used, the K wave number band is related to the specific elastic modulus (E / P), the
flatness of the frequency characteristics is related to the internal loss, and (tan δ). Ru.
Conventionally, a large amount of paper has been used as a speaker diaphragm, but in recent
years, a diaphragm made of a polymer material or a metal material has come to be used.
However, there is not found any one that can satisfy both of the specific elastic modulus required
for the speaker diaphragm and the internal loss at the same time. The specific modulus and the
internal loss are of opposite properties, and it is impossible to satisfy both at the same time with
a single material. A mixture of flakes with current resin is considered to be strong, but in this
case a high specific modulus can not be obtained unless the content of flakes is increased by 5 ".
This is because the aspect ratio of the flakes is small and the contribution to the elastic modulus
is small. And, such a material with a high content of flakes tends to cause brittle fracture of the
speaker diaphragm, and it has the disadvantage that a tear occurs even with a small impact, and
it is heavy when the content of flakes is high also in terms of weight The present invention,
which has the following disadvantages, overcomes these conventional disadvantages. The
speaker diaphragm of the present invention has a feature of simultaneously satisfying the
physical properties of high specific elastic modulus and high internal loss by containing aramid
fibers having a flat cross section. Here, the aramid fiber is an aromatic polyamide represented by,
for example, Kevtar-49 (trade name) of DuPont, USA, and the fiber is subjected to heat treatment
in a tension state after liquid crystal spinning to promote crystallization. Table 1 shows the
physical properties of various fibers. As apparent from Table 1, the aramid fiber has a small
specific gravity and an elastic modulus higher than that of glass fiber. Although the modulus of
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elasticity is slightly lower than carbon fiber, it has superior tensile strength and is nonconductive,
so it can be used for indirect lead type and has wide applications. In a composite material with a
resin, the cross-sectional shape of the aramid fiber is flat, so the inter-fiber gap in the composite
material is large. And since flake-like ones overlap layers, the surface is wide and internal loss is
large. Thus, by using aramid fibers having a flat cross-sectional profile as a reinforcing material,
it enables a lightweight, high specific elastic modulus, high internal loss speaker diaphragm
material to be obtained. 0 At this time, high internal loss is obtained It is desirable to use an
aramid fiber having at least a major axis / minor axis ratio of 3 or more.
FIG. 1 shows the relationship between the major axis / minor axis ratio of the aramid fiber and
the internal loss. As a method of producing an aramid fiber having a flat cross-sectional shape, a
spinning method using a flat nozzle. There are two ways to cut the film. Hereinafter, an
embodiment of the speaker diaphragm of the present invention will be described. Example 1 The
aramid fiber is spun using a nozzle having a major axis / minor axis ratio of 4 and this is further
drawn 10 times to form a cross section having a major axis of 10 μm, a minor axis of 10 μm,
and a major axis / minor axis ratio of 3 A flat aramid fiber was obtained. This flat aramid fiber
was cut to a fiber length of 1.6 and used as a reinforcing material. Using polyethylene as a base
material, the mixture was thoroughly kneaded with a flat aramid fiber at a ratio of 8: 2, and cut to
make a master pellet. A 0.2 m thick reinforced polyethylene sheet was obtained by an extruder
equipped with a T-die again using this master pellet. Next, this sheet was heated in a far infrared
ray for several seconds, and when it was softened, it was molded by a cold press to obtain a
diaphragm. Physical properties of this diaphragm are shown in Table 2. In addition,
polypropylene instead of polyethylene as a base material. Similar results were obtained using
thermoplastic resins such as TPX, polycarbonate, polyethylene terephthalate and the like.
Example 2 The aramid fiber is spun using a nozzle having a major axis / minor axis ratio of 4,
and this is further drawn 10 times to form a cross section with a major axis of 3 oμm, a minor
axis of 10 μm, and a major axis / minor axis ratio of 3 Gave a flat aramid fiber. A woven fabric is
made from this flat aramid fiber, and then this woven fabric is impregnated with a phenol resin,
the solvent is removed, and heat press molding is carried out at a mold temperature of 200 ° C.
The diaphragm obtained in 2 hours 0 The physical properties of this diaphragm are shown in
Table 2. Similar results were obtained with thermosetting resins such as epoxy as well as
phenolic resins. Example 3 The aramid fiber is spun using a nozzle having a major / minor axis
ratio of 4, and this is further drawn 10 times to have a cross-sectional shape with a major axis of
3 oμm, a minor axis of 10 μm, and a major / minor axis ratio of 3 A flat aramid fiber was
obtained. And this flat aramid fiber was cut into 1.5 m. Next, 20 wt% of this flat aramid fiber of
1.51111+ in fiber length and 80 wt% of wood pulp (NUKP) are mixed in a total aqueous solution
and formed into a cone shape to absorb water and then subjected to a hot press journey. I got a
diaphragm. The physical properties of this diaphragm are shown in Table 2. Example 4 The
aramid fiber is spun using a nozzle having a major axis / minor axis ratio of 4 and this is further
stretched 10 times to form a cross section with a major axis of 3011 m and a minor axis of 10 /
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jms with a major axis / minor axis ratio of 3. Gave a flat aramid fiber, which was cut to a length
of L5 m.
Then, 20 wt% of this flat aramid fiber with a fiber length of 5 m and 80 wt% of high density
polyethylene synthetic pulp are mixed in an aqueous solution. At this time, high density
polyethylene synthetic pulp having a beating degree of 210 mt was used, and was dispersed by
well stirring with flat aramid fibers. Thereafter, the sheet was formed by using a round mesh
cylinder, and then this sheet was heated by far infrared rays, and the sheet was formed by cold
pressing at a softening point to obtain a diaphragm. The physical properties of this diaphragm
are shown in Table 2. Further, the frequency characteristic of a 10w speaker using this
diaphragm is shown by curve A in FIG. Similar results were obtained using thermoplastic
synthetic pulp such as polypropylene and TPX instead of high density polyethylene synthetic
pulp. Curve B in FIG. 2 shows the frequency characteristics of the 103 speaker using the
conventional paper cone diaphragm. As apparent from the physical property values of the
margin Table 2 and Table 2 below, it is understood that the diaphragms of Examples 1 to 4
simultaneously satisfy the physical properties of high specific elastic modulus and high internal
loss in any case. Also, as is apparent from FIG. 2, the frequency characteristic is flat with little
unevenness and the high region is extended, and it can be seen that a flat aramid fiber is very
excellent as a diaphragm material for a speaker. As described above, according to the present
invention, since the aramid fiber having a flat cross-sectional shape is contained, physical
properties of high specific elastic modulus and high internal loss are simultaneously satisfied,
and a loudspeaker diaphragm having excellent frequency characteristics is obtained. It is possible
to
[0002]
Brief description of the drawings
[0003]
FIG. 1 is a graph showing the relationship between the major axis / short axis ratio of the aramid
fiber and the internal loss, and FIG. 2 is a graph comparing the frequency characteristics of the
speaker diaphragm of the second embodiment of the present invention and the conventional
paper cone diaphragm. It is.
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