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JP2005260546

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DESCRIPTION JP2005260546
[PROBLEMS] To obtain a loudspeaker diaphragm which is environmentally friendly and which is
free from color and high in gloss on its surface. A speaker diaphragm (10) is made of both
biodegradable plastic and kenaf fibers, and the ratio of the weight of kenaf fibers to the total
weight of the both materials is 5% or more and 20% or less. The biodegradable plastic is
preferably polylactic acid. In the method of manufacturing the speaker diaphragm 10, the ratio
of the weight of kenaf fiber to the total weight of both materials in the state of the molded body
in the range of 5% to 20% of the biodegradable plastic and the kenaf fiber Mixing the mixture so
as to obtain the predetermined value, melting the mixture after the mixing, placing the melted
mixture in a mold of the speaker diaphragm, and curing the mixture put in the mold And.
Speaker diaphragm and method of manufacturing speaker diaphragm
[0001]
The present invention relates to a speaker diaphragm which is a sound wave generator of a
speaker used for an audio device or the like, and a method of manufacturing the speaker
diaphragm.
[0002]
The speaker diaphragm is made of a material in consideration of functionality such as density,
sound velocity, elastic modulus and internal loss, economy, processability, design and the like.
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Typical materials for the speaker diaphragm include industrial plastics such as polypropylene
and polystyrene, wood pulp and kenaf pulp (see, for example, Patent Document 1).
[0003]
When producing a speaker diaphragm with industrial plastic, the heated and melted fluid-like
industrial plastic is injected from an injection device into a mold for molding at high pressure,
and cooled to harden the industrial plastic. The speaker diaphragm can be obtained by taking it
out of the mold.
[0004]
When the speaker diaphragm is made of natural fibers such as wood pulp or kenaf pulp, trees or
kenaf are harvested, sufficiently dried, crushed to a size of about several centimeters, dispersed
in water and made into paper Thereafter, the speaker diaphragm is obtained by hot air drying as
it is or by heat pressing.
[0005]
JP-A-6-253390 (abstract)
[0006]
A speaker diaphragm made of industrial plastic such as polypropylene or polystyrene is often
difficult to be recycled, and therefore often used in landfills in the ground.
Industrial plastic speaker diaphragms buried in the ground are not broken down by
microorganisms in the ground and remain in the ground for a long time.
Therefore, the environmental evaluation of the loudspeaker diaphragm made of industrial plastic
is low.
[0007]
On the other hand, since a speaker diaphragm made of fibers such as wood pulp or kenaf pulp is
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2
degraded by microorganisms in the ground even if disposed in landfills, its evaluation against the
environment is high.
However, due to the nature of the fiber itself, it is difficult to obtain a free color tone due to the
coloring by the addition of a pigment or the like in the manufacturing process or the coloring by
the surface coating after manufacturing due to the nature of the fiber itself. . Moreover, the
speaker diaphragm made of fiber is difficult to mold. For this reason, it is difficult to impart high
gloss of the surface of an industrial plastic speaker diaphragm obtained by molding with a mirror
surface mold to a fiber speaker diaphragm.
[0008]
The present invention has been made in view of the above problems, and is a speaker diaphragm
and a speaker diaphragm which are environmentally friendly and excellent in design that can
give free tone and high glossiness to the surface thereof. The purpose is to provide a
manufacturing method.
[0009]
In order to achieve the above object, the speaker diaphragm of the present invention is made of
both biodegradable plastic and kenaf fiber, and the ratio of the weight of kenaf fiber to the total
weight of both materials is 5% or more and 20% or less It is.
The biodegradable plastic can adopt a configuration that is polylactic acid. In addition, a
configuration in which the thickness of the speaker diaphragm is 0.2 mm or more and 0.4 mm or
less can be adopted.
[0010]
The method for producing a speaker diaphragm according to the present invention is
characterized in that the ratio of the weight of kenaf fiber to the total weight of both materials in
the state of a molded body is in the range of 5% to 20%. A mixing step of mixing to reach a
predetermined value, a step of melting the mixture after the mixing step, a step of putting the
melted mixture into a mold of the speaker diaphragm, a step of curing the mixture put into the
mold, The Moreover, it has the process of producing the pellet of biodegradable plastics prior to
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a mixing process, and the process of mixing a pigment can employ | adopt the method of mixing
a coloring agent.
[0011]
According to the present invention, it is possible to obtain a speaker diaphragm which is
environmentally friendly and is also excellent in design in which a free color tone and high
glossiness can be given to the surface thereof.
[0012]
Hereinafter, embodiments of a speaker diaphragm and a method of manufacturing the speaker
diaphragm according to the present invention will be described with reference to the drawings.
[0013]
FIG. 1 is a cross-sectional view of a speaker 12 having a speaker diaphragm 10 according to an
embodiment of the present invention.
The speaker 12 includes a magnetic circuit 14, a voice coil 16, a damper 18, and a frame 20 in
addition to the speaker diaphragm 10.
[0014]
The magnetic circuit 14 has a first plate 22, a magnet 24 and a second plate 26.
The first plate 22 has a shape in which a toroidal disc is joined to the outside of one open end of
a cylinder.
[0015]
The magnet 24 is a ring-shaped magnetic body surrounding the center pole 28 which is a
cylindrical portion of the first plate 22 in a noncontact manner. The magnet 24 is adhesively
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fixed to the first plate 22 and supported.
[0016]
The second plate 26 has a ring shape surrounding the center pole 28 of the first plate 22 in a
noncontact manner, and is adhesively fixed to the magnet 24.
[0017]
The voice coil 16 is a coil formed by winding a conducting wire, and is disposed between the
outer wall of the center pole 28 of the first plate 22 and the inner wall of the second plate 26
without contacting them.
[0018]
The damper 18 has a donut shape having a concentric uneven surface on the surface.
Further, the damper 18 supports the voice coil 16 in the center portion of the voice coil 16 so as
to be able to be oscillated in the inner peripheral portion.
The outer peripheral portion of the damper 18 is connected to the inner wall of the frame 20.
[0019]
The speaker diaphragm 10 is in the shape of a megaphone in which one end is open in a small
circle and the other end is open in a large circle. The speaker diaphragm 10 is connected to the
voice coil 16 at the open end of a small circle. Also, the open end of the large circle of the
speaker diaphragm 10 is bent outward toward the open end of the small circle and fixed to the
front panel 29.
[0020]
The frame 20 is composed of a cup-shaped first frame 30 on the rear side of the speaker 12 and
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a megaphone-shaped second frame 32 on the front side of the speaker 12. The first frame 30
functions as a housing that encloses the first plate 22, the magnet 24 and the second plate 26.
[0021]
One end of the second frame 32 is fixed to the second plate 26, and the other end is fixed to the
front panel 29. The second frame 32 functions as a housing that covers the damper 18 and the
speaker diaphragm 10.
[0022]
Next, the operation of the speaker 12 will be described.
[0023]
An acoustic signal current is input to the voice coil 16 from the outside of the speaker 12.
The voice coil 16 oscillates in the central axis direction of the voice coil 16 according to the
current value input to the voice coil 16. The speaker diaphragm 10 also vibrates with the
amplitude of the voice coil 16. The vibration of the speaker diaphragm 10 generates a sound
wave by vibrating the ambient air.
[0024]
Therefore, since the speaker diaphragm 10 is a member that influences the acoustic
characteristics, the selection of the material is important. Further, for the speaker diaphragm 10,
it is necessary to select a material that takes into consideration not only acoustic characteristics
but also design and environmental load in recent years.
[0025]
The speaker diaphragm 10 according to the embodiment of the present invention is made of
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both materials of biodegradable plastic and kenaf fiber, and is manufactured by molding a
mixture of these materials. Since the speaker diaphragm 10 is broken down into water and
carbon dioxide by microorganisms even if discarded to the ground, the evaluation of the speaker
diaphragm 10 against the environment is high.
[0026]
Further, depending on the surface shape of the type of the speaker diaphragm 10, the surface of
the speaker diaphragm 10 can be made to be a high gloss surface, a half gloss surface or a matte
surface (mat surface). The speaker diaphragm 10 may be manufactured by thinly placing the
molten material on a base other than molding, for example, peeling it after curing, and cutting it
into the shape of the speaker diaphragm 10.
[0027]
In addition, since the speaker diaphragm 10 which consists only of biodegradable plastics has a
large density, the sound pressure by the sound wave generated from this speaker diaphragm 10
will become small. When the sound pressure is low, the volume at the sound source is attenuated
before reaching the listener. On the other hand, the speaker diaphragm 10 made of a material
obtained by adding kenaf fiber to biodegradable plastic is lighter than the speaker diaphragm 10
made only of the degradable plastic. Sound pressure does not decrease.
[0028]
The material having biodegradable plastic and kenaf fiber has an additive for enhancing molding
processability, an additive for strengthening the material, an additive for facilitating demolding, a
coloring agent such as a pigment or dye, and the like. You may
[0029]
In addition, the ratio of the weight of kenaf fiber to the total weight of biodegradable plastic and
kenaf fiber, that is, the weight of kenaf fiber / (weight of biodegradable plastic + weight of kenaf
fiber) is 5% or more and 20% or less Is preferred.
[0030]
When the proportion of the weight of kenaf fiber to the total weight of the biodegradable plastic
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and kenaf fiber exceeds 20%, the moldability by the mold decreases and the influence of the
color of the kenaf fiber increases, and the speaker diaphragm 10 The degree of freedom of the
color tone decreases.
[0031]
If the proportion of the weight of kenaf fibers to the total weight of the biodegradable plastic and
kenaf fibers is less than 5%, the weight reduction of the speaker diaphragm 10 can not be
achieved.
The ratio of the weight of kenaf fibers to the total weight of biodegradable plastics and kenaf
fibers is more preferably 15%.
[0032]
Examples of biodegradable plastics to be used as the material of the speaker diaphragm 10
include (1) chemical synthesis of polylactic acid, polycaprolactone, polybutylene succinate,
polybutylene succinate adipate, polybutylene succinate carbonate, polybutylene succinate
terephthalate, etc. Aliphatic polyesters and copolymers thereof, (2) biopolyesters such as
polyhydroxybutyrates produced by microorganisms, biocelluloses, polysaccharides or polyamino
acids, (3) modified starches produced by microorganisms or natural polymers, Etc. can be used.
[0033]
Among these, polylactic acid is inexpensive, easy to obtain, excellent in moldability by a mold,
strong in material strength, transparent, and easy to adjust color by coloring.
Therefore, polylactic acid is preferably used as the biodegradable plastic of the material of the
speaker diaphragm 10.
[0034]
The thickness of the speaker diaphragm 10 is preferably 0.2 mm or more and 0.4 mm or less.
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This is because the speaker diaphragm 10 thinner than 0.2 mm or thicker than 0.4 mm has
inferior acoustic characteristics.
Then, by setting the ratio of the weight of kenaf fiber to the total weight of the biodegradable
plastic and kenaf fiber of the material of the speaker diaphragm 10 to 20% or less, the speaker
having a thickness of 0.2 mm or more and 0.4 mm or less The diaphragm 10 can be
manufactured in a short time by molding. If this ratio exceeds 20%, the viscosity of the molten
material becomes high, and in the interior of the mold having a depth of 0.4 mm or less, the
molten material becomes difficult to spread, and the manufacturing efficiency is deteriorated.
[0035]
Next, a method of manufacturing the speaker diaphragm 10 according to the embodiment of the
present invention will be described.
[0036]
First, biodegradable plastic and kenaf fiber are uniformly mixed and processed into pellets.
Next, the pellet of the mixture of biodegradable plastic and kenaf fiber is heated and melted.
Next, the mixture of molten biodegradable plastic and kenaf fiber is filled into an injection device.
Next, a mixture of molten biodegradable plastic and kenaf fiber is injected into the mold of the
speaker diaphragm 10 under high pressure from an injection device.
[0037]
As the mold, a mold, a ceramic mold or a resin mold having a melting point higher than the
melting temperature of the mixture of biodegradable plastic and kenaf fiber can be used. Among
them, it is preferable to use a mold in consideration of the cost of the material, the machinability
of the material, the durability of the mold, and the easiness of removal of the molded body from
the mold.
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[0038]
Next, the mixture of biodegradable plastic and kenaf fiber injected into the mold is cooled and
cured. Then, the speaker diaphragm 10 can be obtained by removing the hardened mixture of
biodegradable plastic and kenaf fiber from the mold.
[0039]
In this manufacturing method, the surface of the speaker diaphragm 10 can be made a high gloss
surface, a half gloss surface or a matte surface (mat surface) by changing the surface shape of
the mold. In addition, in the process of uniformly mixing biodegradable plastic and kenaf fiber in
the manufacturing method and processing it into a pellet, if a coloring agent is added, the
speaker diaphragm 10 can be colored easily and in a desired color tone. can do. As a coloring
agent, a pigment, a dye, etc. can be used.
[0040]
The acoustic characteristics of the speaker diaphragm 10 can be evaluated by measuring density,
sound velocity, elastic modulus, internal loss, and the like.
[0041]
Hereinafter, examples of the present invention will be described.
First, 85 wt% of polylactic acid ("Lacia M151" from Mitsui Chemical Co., Ltd.), which is a
biodegradable plastic, and 15 wt% of kenaf fiber were uniformly mixed to form a mixed resin
pellet.
[0042]
Next, the mixed resin pellet was dried and then heated and melted. Next, the molten mixed resin
was filled into an injection device. Next, the molten mixed resin was injected from the injection
device into the mold of the heated speaker diaphragm 10 at high pressure.
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10
[0043]
Next, the mold was cooled to cure the mixed resin in the mold, and the cured mixed resin was
removed from the mold. Thus, a 0.3 mm-thick loudspeaker diaphragm 10 comprising 85% by
weight of polylactic acid of the example and 15% by weight of kenaf fibers was obtained.
[0044]
As Comparative Example 1, only polylactic acid was molded to manufacture a speaker diaphragm
10. Further, as Comparative Example 2, an industrial plastic consisting of 85% by weight of
polypropylene and 15% by weight of mica was molded to manufacture the speaker diaphragm
10.
[0045]
The speaker diaphragms 10 obtained in the example, the comparative example 1 and the
comparative example 2 were processed into a strip shape, and the density, the speed of sound,
the elastic modulus and the internal loss, which are indexes of acoustic characteristics, were
measured by the vibration lead method. The measurement results are shown in the table.
[0046]
[0047]
The density of the loudspeaker diaphragm 10 of the example was about 30% smaller than that of
the loudspeaker diaphragm of Comparative Example 1.
Therefore, the sound pressure of the sound wave generated from the speaker diaphragm 10 of
the embodiment is larger than the sound pressure of the sound wave generated from the speaker
diaphragm 10 of the comparative example 1.
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[0048]
The density of the loudspeaker diaphragm 10 of the example is slightly larger than that of the
loudspeaker diaphragm 10 of Comparative Example 2, but not as large as that of the loudspeaker
diaphragm 10 of Comparative Example 1. Moreover, compared with the speaker diaphragm 10
of the comparative example 2, the sound velocity, the elasticity modulus, and the internal loss of
the speaker diaphragm 10 of the Example were equivalent or more than that. Therefore, the
speaker diaphragm 10 of the embodiment is considered to have acoustic characteristics suitable
as a speaker diaphragm.
[0049]
INDUSTRIAL APPLICABILITY The present invention can be used for a speaker diaphragm which
is a sound wave generator of a speaker used for an acoustic device or the like, and its
manufacture.
[0050]
It is a sectional view of a speaker provided with a speaker diaphragm concerning an embodiment
of the invention.
Explanation of sign
[0051]
DESCRIPTION OF SYMBOLS 10 Speaker diaphragm 12 Speaker 14 Magnetic circuit 16 Voice coil
18 Damper 20 Frame 22 1st plate 24 Magnet 26 2nd plate 28 Center pole 29 Front panel
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