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JPH08340594

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DESCRIPTION JPH08340594
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
speaker diaphragm made of an injection-molded foam.
[0002]
2. Description of the Related Art In general, a speaker diaphragm material is required to have a
low density and a high Young's modulus (rigidity), to have an appropriate internal loss, to have
environmental resistance, and the like.
[0003]
The diaphragm of PP (polypropylene), which is an olefin resin, is used next to paper because it is
excellent in environmental resistance, particularly water resistance, good in appearance, large in
internal loss, and well balanced in physical properties as a speaker diaphragm. ing.
[0004]
However, PP's diaphragm has a specific gravity of 0.9 g / cm 3, is larger than that of paper, and
has a lower Young's modulus, so the rigidity is enhanced by reinforcing it with a filler such as
carbon fiber. Since the specific gravity is further increased, it is heavier than paper and the
sensitivity is lowered, and energy in the high frequency band is also difficult to release.
[0005]
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Therefore, although liquid crystal polymers and the like may be used as the diaphragm material
in order to increase the rigidity, there is a problem that the specific gravity is large and the
internal loss is also lower than PP. .
[0006]
There are also three-layered diaphragms in which a honeycomb structure and a foam are
sandwiched by flat skin layers are used as the diaphragms whose structural weight and high
rigidity are required. Since it is necessary to bond each layer, there is a problem that the cost
increases in the manufacturing process.
[0007]
The present invention has been made to cope with such a situation, and it is a speaker diaphragm
made of an injection foam molded body that can improve light weight, high internal loss, high
rigidity, and environmental resistance without increasing the cost. Intended to provide.
[0008]
According to the first aspect of the present invention, there is provided a three-layer structure in
which the inside is a foamed layer and the surface is an unfoamed layer by injection molding of a
resin containing a foaming agent. It features.
[0009]
The invention according to claim 2 is characterized in that the average foaming ratio of the entire
diaphragm including the non-foamed layer is approximately 1.1 to 3.0.
[0010]
The invention according to claim 3 is characterized in that the thickness of the non-foamed layer
is approximately 0.05 mm to 0.20 mm.
[0011]
The invention according to claim 4 is characterized in that the foam layer is oriented in the
thickness direction.
[0012]
In the speaker diaphragm of the injection foam molded article of the present invention, the resin
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containing the foaming agent is injection molded, and the inside is a foam layer and the surface is
a non-foamed layer having a three-layer structure. Because it can be made thicker, not only a
lightweight, high-rigidity diaphragm can be obtained, but because the surface is covered with an
unfoamed layer, it is excellent in environmental resistance, and it is necessary to bond three
layers as in the past. Can be manufactured at low cost.
[0013]
In addition, since the average foaming ratio of the entire diaphragm including the non-foamed
layer is approximately 1.1 to 3.0, it is possible to use the characteristics of the high rigidity by
foaming and the high internal loss to realize the physical properties of the diaphragm. Variation
can be reduced.
That is, when the expansion ratio is 1.1 times or more, the rigidity is increased and the internal
loss can be enhanced. However, when the expansion ratio exceeds 3.0 times, the expansion cells
become too large, and the dispersion of the expansion state becomes large. This is because the
variation in the physical properties of the diaphragm becomes large.
[0014]
Furthermore, since the thickness of the non-foamed layer is approximately 0.05 mm to 0.20 mm,
the balance of the physical properties of the diaphragm can be made good.
That is, in order to obtain a lightweight and highly rigid structure by sandwiching a foam layer
and an unfoamed layer, it is preferable to make the unfoamed layer as thin as possible within the
range that maintains the strength. If the unfoamed layer is too thin, there is a problem that the
unfoamed layer may be deformed or cracked easily when the mold is caused to recede and cause
foaming. This is because the effective foaming ratio can not be obtained (in other words, the
foaming ratio decreases).
From such a thing, the thickness of the most well-balanced unfoamed layer is about 1/3 of the
surface thickness before foaming, and it is a common unfoamed PP diaphragm used as a
diaphragm. Since the thickness is 0.15 mm to 0.6 mm, the thickness of the unfoamed layer is
0.05 mm to 0.2 mm.
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[0015]
Furthermore, since the foam cells of the foam layer are oriented in the thickness direction, the
unfoamed layer is reinforced, and the decrease in Young's modulus becomes moderate, and the
rigidity increase rate can be increased.
[0016]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be
described in detail with reference to the drawings.
FIG. 1 shows an embodiment of a speaker diaphragm according to the injection foam molded
article of the present invention.
As shown in the figure, the speaker diaphragm 1 made of an injection foam molded product
injects a resin mixture material obtained by adding a foaming agent to PP (polypropylene) into a
mold and immediately retracts the mold to cause foaming. As a result, the inside is foamed to
form the foamed layer 3 and the surface is in contact with the inner surface of the mold in the
process of being filled with the resin, so the skin layer 2 is unfoamed by solidifying before
foaming. It has a three-layer structure formed.
The thickness of the speaker diaphragm 1 is 0.17 mm to 1.8 mm, and the thickness of the skin
layer 2 is 0.05 mm to 0.2 mm.
[0017]
This is a dimension which can make the balance of the physical properties of the speaker
diaphragm 1 favorable, and the details thereof will be described later.
[0018]
FIG. 2 shows an injection molding machine for manufacturing the speaker diaphragm 1 by the
injection foam molded body of FIG.
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Further, the injection molding machine shown in the same figure has the molding characteristics
shown in FIG.
[0019]
The clamping pressure between the movable side mold 21 held by the movable platen 24 of the
mold 20 and the fixed side mold 22 held by the fixed platen 25 in the injection molding machine
shown in FIG. Controlled by the clamping cylinder 10 controlled by the.
[0020]
The injection port of the injection device 40 for injecting a resin mixture material obtained by
adding a foaming agent to PP (polypropylene) is inserted into the injection port of the fixed side
mold 22.
The injection device 40 is controlled by the injection conditions controlled by the injection
process control unit 31.
Further, information on the molding process is output from the injection device 40 side, and the
mold clamping pressure by the mold clamping pressure control unit 30 according to the
information and information on the distance on the movable platen 24 side, etc. Control is
performed.
[0021]
Then, the manufacturing method of the diaphragm by the injection molding machine of the
above structures is demonstrated.
[0022]
First, as shown in FIG. 3A, the movable mold 21 and the fixed mold 22 of the mold 20 are closed
by the mold clamping mechanism 10, and a foaming agent is put into PP (polypropylene) from
the injection device 40 Inject the resin mixture.
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[0023]
At this time, the temperature of the resin mixture is maintained at about 230 ° C. in the cylinder
10.
Also, the temperature of the cavity surface of the mold 20 is maintained at about 90.degree.
Furthermore, the clamping pressure by the mold clamping cylinder 10 controlled by the mold
clamping pressure control unit 30 is maintained at about 100 t.
Furthermore, the general thickness of the cavity formed by the movable side mold 21 and the
fixed side mold 22 of the mold 20 is about 0.3 mm.
[0024]
At this time, as shown in FIG. 6B, the resin mixture filled in the cavity between the movable mold
21 and the fixed mold 22 is solidified from the portion in contact with the mold 20. Beginning
the skin layer 2 is formed, and the melted part is pressed by the pressure from the screw and the
clamping pressure by the movable side mold 21 and the fixed side mold 22, the gas of the
decomposed foaming agent is compressed and the foaming is suppressed Solidification proceeds.
[0025]
Next, as shown in FIG. 6C, immediately after the filling of the resin mixture is completed, while
the foaming pressure of the foaming agent in the melting portion remains sufficient to push out
the surrounding skin layer (solidified portion) 2 The clamping pressure by the clamping cylinder
10 controlled by the mold clamping pressure control unit 30 is instantaneously dropped to near
0 t.
Thereby, the decomposition gas of the blowing agent which has been compressed at the melting
portion expands while spreading the resin around, and foaming is started.
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[0026]
Here, the mold opening timing of the movable side mold 21 will be described.
If the mold opening is performed before the resin filling is completely completed, the resin
mixture excessively enters the inside of the movable mold 21 and the fixed mold 22 of the mold
20 and the weight of the product increases. On the contrary, if the timing is late, solidification of
the resin proceeds too much, and the foaming agent completely solidifies without being able to
foam. In this case, open the mold 0.3 to 0.4 seconds after the start of injection. Is preferred.
However, these requirements vary depending on conditions such as the resin temperature of the
resin mixture, the temperature of the mold 20, the product thickness, and the amount of the
foaming agent added.
[0027]
The opening amount of the above-mentioned mold 20 is about 0.1 to 1.5 mm, and it is necessary
to open it at a high speed of 0.04 to 0.05 seconds, so the mold 20 has about 0.0020 to 20 The
blowing agent, spring force and clamping pressure are controlled to open at a rate of 0.0375 mm
/ ms.
In order to form a thin foam-formed diaphragm, it is sufficient to open the mold at a speed of
about 0.001 mm / ms or more.
[0028]
Furthermore, if a spring is embedded between the movable side mold 21 and the fixed side mold
22 of the mold 20 to increase the opening force of the movable side mold 21 when the clamping
pressure is lowered, the expansion ratio is increased. You can raise it.
[0029]
Here, specific examples of the injection molding machine and the foaming agent employed in this
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embodiment will be described. As PP (polypropylene), one obtained by adding 7% of carbon fiber
to MA06 Mitsubishi Chemical Co., Ltd. is used as the foaming agent. As a mixture, the
compounding ratio made the foaming agent 0.1 weight part using the thing of EE-205 Eiwa
Chemical Industry Co., Ltd. product.
As the injection molding machine, Ultra 220 Sumitomo Heavy Industries, Ltd. was used.
[0030]
The characteristics of the product obtained by the method for forming a foam molded article as
described above are as shown in FIG. 5 to FIG.
[0031]
That is, FIG. 5 shows the measurement results of specific gravity, Young's modulus, internal loss,
surface thickness, and rigidity when various expansion ratios of products are changed while
keeping the product weight constant, and FIG. FIG. 7 shows the change in Young's modulus, FIG.
7 shows the change in internal loss according to the expansion ratio, and FIG. 8 shows the
change in rigidity due to the expansion ratio.
[0032]
As can be seen from these figures, as the expansion ratio is increased, the Young's modulus
decreases, but the specific gravity decreases and the surface thickness increases, so the stiffness
is proportional to the Young's modulus and proportional to the cube of the thickness. The rigidity
increases as the expansion ratio increases.
In addition, the internal loss also increases as the expansion ratio is increased.
[0033]
The expansion ratio is about 1.1 times and rigidity equivalent to that of the current PP cone (a
material with a Young's modulus of 6.4E + 9N / m2 and a face thickness of 0.3mm) is obtained,
the internal loss is increased, and the expansion ratio is further increased. The rigidity is
increased by
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[0034]
However, if the expansion ratio exceeds about 3.0 times, the expansion cells become too large,
which causes variation in the expansion state, and the dispersion of the physical properties of the
diaphragm increases, so the expansion ratio is 1.1 times to About 3.0 times is appropriate.
[0035]
Further, by setting the expansion ratio to 1.5 times or more, as shown in FIG. 1, the foam cells of
the foam layer 3 are longitudinally oriented with respect to the surface thickness direction and
the skin layer 2 is reinforced. The decrease in the rate becomes moderate and the rigidity
increase rate rises sharply.
This is also due to the mold 20 being retracted at a high speed and made by foam molding.
[0036]
On the contrary, when the expansion ratio exceeds 2.5 times, the resin density of the foam layer
3 for reinforcing the skin layer 2 becomes too small, the decreasing rate of Young's modulus
becomes large, and the variation of the rigidity of the product gradually becomes large It will
come.
Therefore, in order to effectively use the structural rigidity increase by the foam molding and
obtain a stable product, it is preferable to set the foaming ratio to 1.5 times to 2.5 times.
[0037]
Further, in order to obtain a lightweight and highly rigid structure having a sandwich structure of
the skin layer 2 and the foam layer 3, it is desirable to make the skin layer 2 as thin as possible
within the range in which the strength is maintained.
However, in the case of injection foam molding, if it is too thin, there is a problem that the skin
layer 2 is deformed or easily broken when the mold 20 is retracted to cause foaming.
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[0038]
On the other hand, when the thickness is increased, the resin for forming the foam layer 3 is
reduced, and an effective expansion ratio can not be obtained (in other words, the expansion
ratio is decreased).
From these facts, the thickness of the most well-balanced skin layer 2 is about 1/3 of the surface
thickness before foaming, and the thickness of a general unfoamed PP diaphragm used as a
diaphragm. The thickness of the skin layer is preferably 0.05 mm to 0.2 mm, because the
thickness of the skin layer is 0.15 mm to 0.6 mm.
[0039]
As described above, in this embodiment, since the resin containing the foaming agent is injectionmolded and the foam layer 3 is covered with the skin layer 2 which is the non-foam layer, the
surface thickness is increased with low specific gravity. Not only is it possible to obtain a
lightweight and highly rigid diaphragm, but because the surface is covered with the skin layer 2,
it is excellent in environmental resistance, and there is no need to bond three layers as in the
prior art. , Can be manufactured at low cost.
[0040]
In addition, since the average foaming ratio of the entire speaker diaphragm 1 including the skin
layer 2 which is the non-foamed layer is approximately 1.1 to 3.0 times, the characteristics of
high rigidity and high internal loss due to the foaming are obtained. The variation in the physical
properties of the speaker diaphragm 1 can be reduced.
That is, when the expansion ratio is 1.1 times or more, the rigidity is increased and the internal
loss can be enhanced. However, when the expansion ratio exceeds 3.0 times, the expansion cells
become too large, and the dispersion of the expansion state becomes large. This is because the
variation in the physical properties of the diaphragm 1 becomes large.
[0041]
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Furthermore, since the thickness of the skin layer 2 is approximately 0.05 mm to 0.20 mm, the
balance of the physical properties of the speaker diaphragm 1 can be made favorable. That is, in
order to obtain a lightweight and highly rigid structure by the sandwich structure of the foam
layer 3 and the skin layer 2, it is preferable to make the skin layer 2 as thin as possible within the
range that maintains the strength. If the skin layer 2 is too thin, there is a problem that the skin
layer 2 is deformed or easily broken when the mold 20 is caused to retract and foam, and if it is
thick, the resin forming the foam layer 3 is It is because it decreases and an effective foaming
ratio can not be obtained.
[0042]
Furthermore, immediately after the foaming resin containing the foaming agent is injected into
the mold 20, the mold 20 is retracted at a high speed, so that the foam cells of the foam layer 3
are oriented in the thickness direction, and the skin layer is formed. Since it becomes a form
which reinforces 2, the fall of Young's modulus becomes loose, and it can raise a rigidity rise rate.
[0043]
In this example, immediately after injecting the resin mixture material obtained by adding a
foaming agent to PP (polypropylene) in the mold 20, mold opening is performed to obtain a
sandwich structure of the skin layer 2 and the foam layer 3 Although the method of molding the
speaker diaphragm 1 has been described, the present invention is not limited to this example, for
example, injection molding is performed at a resin temperature at which an unfoamed foaming
agent remains, and then a mold such as a heat press mold or a vacuum mold Alternatively, a
method may be used in which heating is performed above the decomposition temperature of the
foaming agent, and the foaming agent is foamed and molded.
[0044]
As described above, according to the speaker diaphragm of the injection foam molded article of
the present invention, the inside is a foam layer and the surface is a non-foam layer by injection
molding of a resin containing a foaming agent. It is formed in a layered structure, and since the
foam is sandwiched between the skin layers, it is possible to make a diaphragm with low specific
gravity and a large thickness, a lightweight and highly rigid diaphragm, and the surface is
covered with a skin layer. It is also excellent in quality and, unlike the prior art, it is not necessary
to bond three layers, so it can be manufactured at low cost.
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[0045]
Brief description of the drawings
[0046]
1 is a diagram showing an embodiment of a speaker diaphragm by the injection foam molded
article of the present invention.
[0047]
2 is a view showing an injection molding machine for manufacturing a speaker diaphragm by the
injection foam molded body of FIG.
[0048]
3 is a diagram showing a method of manufacturing a speaker diaphragm by the injection
molding machine of FIG.
[0049]
4 is a diagram showing the molding characteristics of the injection molding machine of FIG.
[0050]
5 is a diagram showing the change in the physical properties of the speaker diaphragm due to
the foaming ratio of the injection foam molded body of FIG.
[0051]
6 is a diagram showing a change in Young's modulus of the speaker diaphragm due to the
injection foam molded body of FIG.
[0052]
7 is a diagram showing the internal loss change by the expansion ratio of the speaker diaphragm
of FIG.
[0053]
8 is a diagram showing the change in rigidity according to the expansion ratio of the speaker
diaphragm of FIG.
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[0054]
Explanation of sign
[0055]
DESCRIPTION OF REFERENCE NUMERALS 10 mold clamping cylinder 20 mold 21 movable side
mold 22 fixed side mold 23 vacuum forming mold 24 movable platen 25 fixed platen 30 mold
clamping pressure control unit 31 injection process control unit 40 injection device
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