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JP2005101889

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DESCRIPTION JP2005101889
PROBLEM TO BE SOLVED: To provide a speaker diaphragm which is lightweight and excellent in
balance between rigidity and internal loss, and a simple and inexpensive method of
manufacturing such a speaker diaphragm. SOLUTION: The speaker diaphragm of the present
invention has at least a base layer containing a woven fabric of polyethylene naphthalate fibers
and a thermosetting resin impregnated in the woven fabric, and a thermoplastic resin layer.
Preferably, this thermoplastic resin layer is made of nylon, polyester, polyolefin, polystyrene,
polyvinyl chloride, polyurethane, polysulfone, polyether ketone, polyether ether ketone,
polyacetal, polyarylate, polyamide, polyamide imide, polycarbonate, modified polyphenylene
ether And at least one selected from polyphenylene sulfide, polyacrylate, polymethyl
methacrylate, polyether imide, polyether sulfone, polytetrafluoroethylene and liquid crystal
polymer. [Selected figure] Figure 1
Speaker diaphragm and method of manufacturing the same
[0001]
The present invention relates to a speaker diaphragm and a method of manufacturing the same.
More particularly, the present invention relates to a speaker diaphragm that is lightweight and
has excellent balance between rigidity and internal loss, and a simple and inexpensive method of
manufacturing such a speaker diaphragm.
[0002]
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1
Generally, the characteristics required for the speaker diaphragm include high Young's modulus
(elastic modulus, rigidity) and having a proper internal loss (tan δ). As a means to improve
Young's modulus, typically, a diaphragm using FRP made of a combination of carbon fiber and
epoxy resin is mentioned. As a means for improving the internal loss, typically, a diaphragm
using a synthetic resin such as polypropylene can be mentioned.
[0003]
Each of the above-mentioned diaphragms has a problem. Specifically, although the FRP
diaphragm has a high Young's modulus, the internal loss of the epoxy resin which is a matrix
resin is small, and as a result, the internal loss of the whole diaphragm is reduced. Therefore,
such a diaphragm is likely to generate resonance, have frequency characteristics with many peak
dips, and it is difficult to prevent the generation of the sound unique to the material. Synthetic
resin diaphragms often have good frequency characteristics due to large internal loss, but they
have insufficient rigidity and heat resistance.
[0004]
As a means for improving the rigidity (Young's modulus) and internal loss in a well-balanced
manner, a diaphragm using a film of polyethylene naphthalate has been proposed (see, for
example, Patent Documents 1 and 2). JP-A-1-67099 JP-A-6-181598
[0005]
Furthermore, in recent years, the demand for weight reduction of the speaker diaphragm has
been increased, and various means have been studied. For example, by using a thermoplastic
resin to which a foaming agent is added, the mold clamping force and the mold clearance applied
to the mold cavity at the time of injection molding are adjusted to obtain a lightweight structure
having an unfoamed structure at the surface and a foamed structure at the center. A vibrating
diaphragm has been proposed (see Patent Document 3). Alternatively, as an attempt to achieve
both strength and weight reduction, a resin foam including two types of cell structures having
different foam densities has been proposed (see Patent Document 4). This resin foam is obtained
by impregnating a resin with carbon dioxide gas in a supercritical state having a concentration
gradient, and heating the resin to foam it. Patent No. 3135482 Unexamined-Japanese-Patent No.
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2
11-80408
[0006]
However, the techniques described in these documents each have the following problems. The
techniques described in Patent Documents 1 and 2 can be applied only to small diameter
speakers (so-called micro speakers). Specifically, according to the techniques described in Patent
Documents 1 and 2, although a diaphragm sufficient for both rigidity and internal loss can be
obtained in the micro speaker application, the internal loss is extremely high in the large
aperture speaker application. It is insufficient, and a diaphragm which can withstand practical
use can not be obtained.
[0007]
The technique described in Patent Document 3 is extremely difficult to adjust the time for
foaming the foaming agent and the time for changing the clamping force and the mold clearance,
so a diaphragm having an excellent balance of strength and weight. It is difficult to get stable.
Since the technique described in Patent Document 4 impregnates a resin molded body (for
example, a sheet) with a gas, it takes a very long time to fully impregnate the gas. For example, in
the case of using a highly crystalline resin to enhance strength, it may take 100 hours or more to
impregnate. Therefore, this technique is not practical at all.
[0008]
As described above, a speaker diaphragm that is lightweight and has an excellent balance
between rigidity and internal loss in any applications (that is, regardless of the large aperture
speaker application and the small aperture speaker application) and such speaker vibration
There is a strong demand for a simple and inexpensive method of manufacturing plates.
[0009]
The present invention has been made to solve the above-described conventional problems, and
its object is to provide a speaker diaphragm which is lightweight and excellent in balance
between rigidity and internal loss in any application and the speaker diaphragm It is to provide a
simple and inexpensive method of manufacturing such a speaker diaphragm.
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[0010]
The speaker diaphragm of the present invention has at least a base layer containing a woven
fabric of polyethylene naphthalate fibers and a thermosetting resin impregnated in the woven
fabric, and a thermoplastic resin layer.
[0011]
In a preferred embodiment, the thermoplastic resin layer is nylon, polyester, polyolefin,
polystyrene, polyvinyl chloride, polyurethane, polysulfone, polyether ketone, polyether ether
ketone, polyacetal, polyarylate, polyamide, polyamide imide, polycarbonate, And at least one
selected from the group consisting of modified polyphenylene ether, polyphenylene sulfide,
polyacrylate, polymethyl methacrylate, polyether imide, polyether sulfone,
polytetrafluoroethylene, liquid crystal polymer and thermoplastic elastomer.
[0012]
In a preferred embodiment, the speaker diaphragm of the present invention further comprises a
thermoplastic elastomer layer.
[0013]
In a preferred embodiment, the thermoplastic elastomer layer comprises at least one selected
from the group consisting of polyester elastomers, polyurethane elastomers and polyolefin
elastomers.
[0014]
In a preferred embodiment, the thermoplastic resin layer has a micro-foamed structure.
[0015]
In a preferred embodiment, the average diameter of the cells in the fine foam structure is 10 to
60 μm.
[0016]
According to another aspect of the present invention, a method of manufacturing a speaker
diaphragm is provided.
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This manufacturing method comprises the steps of: impregnating and curing a thermosetting
resin in a woven fabric of polyethylene naphthalate fibers to form a substrate layer; and adding
an inert gas in a supercritical state to the molten thermoplastic resin, And extruding a
thermoplastic resin to which an inert gas is added at a predetermined temperature and pressure
to form a thermoplastic resin layer; and laminating the base material layer and the thermoplastic
resin layer.
[0017]
According to still another aspect of the present invention, a speaker is provided.
This speaker comprises the above-mentioned speaker diaphragm.
[0018]
As described above, according to the present invention, by providing the base layer containing
the woven fabric of polyethylene naphthalate fiber, the thermosetting resin impregnated in the
woven fabric, and the thermoplastic resin layer, it is lightweight In addition, it is possible to
obtain a speaker diaphragm excellent in balance between rigidity and internal loss, and a simple
and inexpensive method of manufacturing such a speaker diaphragm.
[0019]
Hereinafter, preferred embodiments of the present invention will be described with reference to
the drawings, but the present invention is not limited to these embodiments.
[0020]
FIG. 1 is a schematic cross-sectional view of a speaker diaphragm according to a preferred
embodiment of the present invention.
The diaphragm 100 has a base layer 1 and a thermoplastic resin layer 2.
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Furthermore, this diaphragm 100 optionally has a thermoplastic elastomer layer 3.
In the speaker diaphragm of the present invention, it is preferable that the base material layer 1
is the outermost layer (the side which emits a sound wave).
It is because the speaker diaphragm which has the appearance of a glossy fiber pattern excellent
in the designability is obtained.
There is no particular limitation on the stacking order of the layers.
Therefore, as shown in FIG. 1, the order may be in the order of the base material layer, the
thermoplastic resin layer and the thermoplastic elastomer layer, or in the order of the base
material layer, the thermoplastic elastomer layer and the thermoplastic resin layer.
[0021]
The base layer 1 contains a woven fabric of polyethylene naphthalate (PEN) fibers and a
thermosetting resin impregnated in the woven fabric.
The thermosetting resin is preferably unsaturated polyester resin or melamine resin, although
any appropriate thermosetting resin may be employed.
The unsaturated polyester resin is easy to manufacture because of its high curing speed and low
curing temperature, and a speaker diaphragm having excellent internal loss can be obtained.
Melamine resin greatly contributes to the improvement of strength.
[0022]
The base layer 1 contains a woven fabric of PEN fibers. As a weave structure of this PEN woven
fabric, any suitable structure (for example, plain weave, twill weave, satin weave, a combination
thereof) can be adopted, but preferably it is plain weave. This is because the vertical / horizontal
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strength is strong and it is easy to perform deep drawing. Therefore, it is particularly preferable
in large aperture cone diaphragm applications. The weave density (grain weight) in the case of
plain weave is preferably 150 to 190 g / m <2>, more preferably 160 to 180 g / m <2>. This
range of weave density is significantly larger than that of ordinary woven fabrics, so the effect of
increasing the strength is large. Furthermore, it is because it is excellent in moldability.
[0023]
Preferably, PEN fibers constituting the woven fabric are non-twisted fibers (untwisted fibers). By
using non-twisted fibers, the thickness per layer can be extremely reduced, and as a result, it is
possible to obtain a diaphragm that is lightweight and has very excellent strength. For example,
plain thermoplastic resin fibers are twisted, and the thickness of the woven fabric is about 1 mm
when the basis weight is about 170 g / m <2>, but plain weave woven fabric of non-twisted PEN
fibers is The thickness of the same basis weight is about 0.18 mm, which is less than one-fifth.
Furthermore, if such a woven fabric is used, the amount of the impregnated resin can be
significantly reduced (as the fiber / resin ratio of the base layer can be significantly increased),
the internal loss is significantly improved. (Details of the resin ratio will be described later). The
thickness of the PEN fibers is preferably 800 to 1200 denier although fibers of any appropriate
thickness may be employed depending on the purpose. When the thickness of the fiber is less
than 800 denier, the basis weight often decreases and the strength is often insufficient. When the
thickness of the fiber exceeds 1200 denier, the weight increases and as a result, the sound
pressure often decreases. Preferably, the PEN fibers are monofilaments. By using a monofilament,
diffuse reflection occurs on the inner surface of the fiber, so that a speaker diaphragm having an
excellent appearance (specifically, a glossy fiber pattern) can be obtained.
[0024]
Preferably, at least a portion of the PEN fiber is coated with a second thermosetting resin. As the
second thermosetting resin, any appropriate thermosetting resin other than the above-mentioned
impregnated thermosetting resin may be employed. For example, if the thermosetting resin to be
impregnated is an unsaturated polyester resin, the preferred second thermosetting resin is an
epoxy resin or a melamine resin. By coating with an epoxy resin or a melamine resin, the
wettability of the PEN fiber surface to the unsaturated polyester resin is improved, so the degree
of fiber reinforcement of the unsaturated polyester resin with PEN fibers becomes very large. As
a result, a speaker diaphragm having a very good Young's modulus can be obtained. On the other
hand, proper internal loss is maintained because the coated PEN fibers and the unsaturated
polyester resin are properly displaced during vibration. Such coating is carried out by a
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conventional impregnation operation. The amount of coating is adjusted by changing the amount
of resin to be impregnated. As an example of the suitable coating amount, the resin amount is 3
to 7 parts by weight, preferably about 5 parts by weight, with respect to 100 parts of the
substrate.
[0025]
The fiber / resin ratio of the base material layer 1 is preferably in the range of 60/40 to 80/20,
and more preferably in the range of 70/30 to 80/20. By using a base material layer having a
high fiber / resin ratio, a speaker diaphragm having extremely excellent internal loss can be
obtained without lowering the Young's modulus. Here, the fiber / resin ratio is the ratio of the
weight of the woven fabric before impregnation to the weight of the impregnated resin. As
described above, such an extremely high fiber / resin ratio is achieved by making the fibers (PEN
fibers) constituting the substrate non-twisting fibers.
[0026]
The speaker diaphragm of the present invention has a thermoplastic resin layer 2. This is
because it becomes possible to prevent the generation of the inherent sound that is likely to
occur in the case of the base material layer alone, and it is possible to obtain a speaker
diaphragm having frequency characteristics without peak dip. The thermoplastic resin layer 2
may be in any form of woven fabric, non-woven fabric or film. For example, in the case where the
speaker diaphragm of the present invention has a two-layer structure of the base material layer 1
and the thermoplastic resin layer 2 or when the thermoplastic resin layer 2 is an intermediate
layer as shown in FIG. The thermoplastic resin layer 2 is preferably a film. Since it is easy to flow
into the gaps of the base material layer 1 at the time of molding, the wettability of the PEN fiber
surface constituting the base material layer 1 is improved, and as a result, a speaker diaphragm
having excellent rigidity (Young's modulus) is obtained. is there. For example, in the case where
the thermoplastic resin layer 2 is the innermost layer having a three-layer structure, the
thermoplastic resin layer 2 is preferably a woven or non-woven fabric. This is because the resin
of the intermediate layer easily flows into the gap of the thermoplastic resin layer 2.
[0027]
The resin constituting the thermoplastic resin layer 2 includes nylon (for example, nylon 6, nylon
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66), polyester (for example, polyethylene terephthalate, polybutylene terephthalate), polyolefin
(for example, polyethylene, ultra high molecular weight polyethylene, polypropylene, poly- 4Methylpentene-1), polystyrene, polyvinyl chloride, polyurethane, polysulfone, polyether ketone,
polyether ether ketone, polyacetal, polyarylate, polyamide, polyamideimide, polycarbonate,
modified polyphenylene ether, polyphenylene sulfide, polyacrylate, poly Methyl methacrylate,
polyether imide, polyether sulfone, polytetrafluoroethylene, liquid crystal polymer and
thermoplastic elastomer And the like. These may be used alone or in combination of two or more.
Alternatively, a copolymer of two or more of these resin monomers may be used. Preferred
thermoplastic resins are polyesters, nylons or polyolefins, and particularly preferred
thermoplastic resins are nylons or polyolefins. It is because it is excellent in vibration damping.
[0028]
Preferably, the thermoplastic resin layer 2 has a micro-foamed structure. The average diameter
of the cells in this fine foam structure is preferably 10 to 60 μm, more preferably 20 to 50 μm,
and most preferably 30 to 40 μm. It is because the speaker diaphragm which is excellent in
mechanical strength although it is lightweight can be obtained because the thermoplastic resin
layer 2 has a fine foam structure. In particular, such micro air bubbles are effective in improving
durability and reliability. In addition, such a minute air bubble has the effect of increasing the
internal loss (tan δ) that is regarded as important in the acoustic member, so it is possible to
reduce the unnecessary sound emitted when the diaphragm vibrates. . Further, the cell density of
the foam is preferably 10 <9> to 10 <15> cells / cm <3>, and more preferably 10 <10> to 10
<14> cells / cm <3>. . The expansion ratio corresponding to such a cell density is 1.2 to 3.0. By
having the cell density in such a range, the balance between strength and weight reduction can
be further improved.
[0029]
The manufacturing procedure of the said fine foam structure (foamed sheet) is as follows. First,
the resin sheet is placed in a high pressure container at room temperature. The high pressure
inert gas is then sufficiently dissolved in the high pressure vessel until a saturated solution is
reached. Representative examples of the inert gas include nitrogen, carbon dioxide, argon, neon,
helium, oxygen and mixed gas thereof. Nitrogen and carbon dioxide are preferred. It is because it
is inexpensive and easy to handle. Next, a state of gas supersaturation is created in the resin
sheet by rapidly depressurizing the gas pressure in the high-pressure vessel at room
temperature. At this time, the sheet is thermodynamically very unstable and bubble nuclei are
formed. This sheet is heated to a temperature above its softening temperature to grow cell nuclei,
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and then cooled to obtain a foamed sheet. Alternatively, the resin sheet is placed in a high
pressure vessel at high temperature, and the inert gas is sufficiently dissolved under the high
temperature and high pressure until reaching a saturated dissolution amount. Then, the gas
supersaturation, bubble nucleation and bubble growth are simultaneously advanced by rapidly
removing the gas, and then cooled to obtain a foam sheet.
[0030]
Alternatively, the micro-foamed structure can be formed simultaneously with sheet forming by
using an extruder, as shown in FIG. That is, the raw material thermoplastic resin 20 is introduced
from the hopper 21 of the extruder, and the thermoplastic resin is melted in the extruder 22
(typically at 180 to 220 ° C.), and the extruded resin center part 23 A predetermined amount
(typically, 10 to 30 parts by weight per 100 parts by weight of resin) of a supercritical state inert
gas (typically, nitrogen, carbon dioxide, argon, neon, helium, oxygen or a mixture thereof) ) Add.
Here, the reference numeral 24 represents an inert gas in a liquid state, and the reference
numeral 25 represents a super critical fluid (SCF) system that creates a supercritical state. Next,
the molten thermoplastic resin and the inert gas are kneaded while maintaining the foaming gas
in the extruder at a critical pressure or higher. By maintaining the foaming gas in the
supercritical state, the inert gas intrudes and disperses in the molten thermoplastic resin in a
very short time, and a very good compatible state is realized. In the supercritical state, the
viscosity is lower than in the liquid state, and the diffusivity is high. The molten thermoplastic
resin / inert gas mixture is supplied to the sheet forming die 26 at a predetermined temperature
(typically 130 to 150 ° C.) to form the foam sheet 27. The diaphragm of the present invention
can be manufactured by laminating such a foamed sheet (thermoplastic resin layer 2) and a PEN
woven fabric (base layer 1). In addition, a supercritical state means the state more than a critical
temperature and more than a critical pressure. The critical temperature of nitrogen gas is -127C,
the critical pressure is 3.5MPa, the critical temperature of carbon dioxide gas is 31C, and the
critical pressure is 7.4MPa.
[0031]
Even when the thermoplastic resin layer 2 has a fine foam structure, the above-mentioned
thermoplastic resin can be suitably used. In this case, a particularly preferred thermoplastic resin
is a polyolefin. It is because good fine foaming is possible.
[0032]
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The thermoplastic elastomer layer 3 may be in any form of woven fabric, non-woven fabric or
film. For example, as shown in FIG. 1, when the thermoplastic elastomer layer is the innermost
layer, the thermoplastic elastomer layer 3 is preferably a woven or non-woven fabric. Since the
resin constituting the thermoplastic resin layer 2 flows into the gaps of the thermoplastic
elastomer layer 3 at the time of molding, the wettability is improved, and as a result, a speaker
diaphragm having excellent rigidity (Young's modulus) is obtained. It is. For example, when the
thermoplastic elastomer layer is an intermediate layer, the thermoplastic elastomer layer 3 is
preferably a film. It is because it is easy to flow into the base material layer 1 and / or the
thermoplastic resin layer 2.
[0033]
The thermoplastic elastomer constituting the thermoplastic elastomer layer 3 includes polyester
elastomers, polyurethane elastomers and polyolefin elastomers. These may be used alone or in
combination of two or more. When the thermoplastic elastomer layer is the innermost layer,
preferably, these thermoplastic elastomers have a melting point higher than that of the resin
constituting the thermoplastic resin layer. By having such a relationship, the thermoplastic resin
is particularly likely to flow into the interstices of the elastomer layer during molding. On the
other hand, when the thermoplastic elastomer layer is an intermediate layer, preferably, these
thermoplastic elastomers have a melting point lower than that of the resin constituting the
thermoplastic resin layer. By having such a relationship, the thermoplastic elastomer is
particularly likely to flow into the interstices of the base layer and / or the thermoplastic resin
layer during molding. Particularly preferred thermoplastic elastomers are polyester elastomers. It
is because the speaker diaphragm which has the outstanding internal loss is obtained.
[0034]
The total thickness of the speaker diaphragm of the present invention is preferably 0.1 to 1 mm,
more preferably 0.2 to 0.6 mm. It considers practicality when incorporating it into a speaker unit.
The thickness of the base material layer 1 is preferably 0.05 to 0.4 mm, more preferably 0.1 to
0.25 mm. When the thickness of the base material layer is in such a range, a loudspeaker
diaphragm particularly excellent in balance between the rigidity and the internal loss can be
obtained. The thickness of the thermoplastic resin layer 2 is preferably 0.05 to 0.6 mm, more
preferably 0.1 to 0.35 mm. When the thermoplastic resin layer has a fine foam structure, the
thickness of the thermoplastic resin layer 2 is preferably 0.05 to 0.6 mm, more preferably 0.2 to
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0.4 mm. When the thickness of the thermoplastic resin layer has such a range, it is possible to
cope with speakers of various diameters while maintaining the balance between the rigidity and
the internal loss. Furthermore, when the thermoplastic elastomer layer 3 is provided, the
thickness of the thermoplastic elastomer layer 3 is preferably 0.01 to 0.1 mm, more preferably
0.04 to 0.08 mm.
[0035]
The speaker diaphragm of the present invention may further have any suitable layer. For
example, when the thermoplastic resin layer 2 has a micro-foamed structure, an adhesive layer or
another thermoplastic elastomer layer may be provided between the base material layer 1 and
the thermoplastic resin layer 2. It is because adhesion becomes strong and internal loss is further
improved.
[0036]
Hereinafter, the operation of the present invention will be described. According to the present
invention, there is provided a speaker diaphragm having a base layer comprising a woven fabric
of polyethylene naphthalate fibers and a thermosetting resin impregnated in the woven fabric,
and a thermoplastic resin layer. Such a speaker diaphragm is very excellent in the balance
between Young's modulus and internal loss. The details are as follows. By using a woven fabric as
the base material layer, the fibers are easily displaced at the time of vibration, so that vibration
energy is converted into heat energy and the internal loss is increased. Furthermore, since the
PEN woven fabric used in the present invention has a very high weave density, in the formed
diaphragm, the thermosetting resin as a binder is present only in a small amount between the
fibers constituting the woven fabric. As a result, in the base material layer, a laminated structure
having a woven layer and a resin layer is substantially formed, and such a structure contributes
to a further improvement of the internal loss. In addition, the very high weave density of PEN
woven fabric also maintains excellent Young's modulus. Therefore, coexistence with Young's
modulus and internal loss which were difficult in the prior art is achieved. Moreover, since the
speaker diaphragm of the present invention has the thermoplastic resin layer laminated on the
base material layer, it becomes possible to prevent the generation of the inherent sound that is
likely to occur in the case of the base material layer alone. As a result, a speaker diaphragm
having frequency characteristics without peak dip is obtained.
[0037]
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In a preferred embodiment, the thermoplastic resin layer has a micro-foamed structure. Since the
thermoplastic resin layer has a micro-foamed structure, a speaker diaphragm that is lightweight
but has excellent mechanical strength can be obtained. In particular, such micro air bubbles are
effective in improving durability and reliability. In addition, such a minute air bubble has the
effect of increasing the internal loss (tan δ) that is regarded as important in the acoustic
member, so it is possible to reduce the unnecessary sound emitted when the diaphragm vibrates.
. Moreover, according to the present invention, a simple and inexpensive method of
manufacturing such a diaphragm is provided. By using an inert gas in a supercritical state, it is
possible to simultaneously perform extrusion and foaming of a foam sheet (thermoplastic resin
layer) using an extruder for sheet formation. Such a manufacturing method does not require a
large-scale high-pressure equipment, and thus both cost and mass productivity are significantly
improved.
[0038]
EXAMPLES Hereinafter, the present invention will be specifically described by way of examples,
but the present invention is not limited to these examples. In the Examples and Comparative
Examples, parts and percentages are by weight unless otherwise indicated.
[0039]
A plain weave woven fabric of PEN fibers without twist (Teijin Limited, yarn count: 1100 × 1100
(dtex), density: 17 × 17 (book / inch), coating weight: 166 g / m <2>) It was impregnated and
cured to form a substrate layer. The amount of melamine resin impregnated was 30 parts by
weight with respect to 100 parts by weight of PEN woven fabric. Furthermore, a polyester
elastomer film (manufactured by Toyobo Co., Ltd., Perprene, thickness 80 μm) as a
thermoplastic resin layer, and a polyester elastomer non-woven fabric as a thermoplastic
elastomer layer (Toyobo Co., Ltd., Pelprene, basis weight: 110 g / m <2>) Was used. It laminated ¦
stacked in order of the base material layer, the thermoplastic resin layer, and the thermoplasticelastomer layer from the front side (the side which radiates an acoustic wave). Such non-woven
fabric is usually produced by a water jet method.
[0040]
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Two jigs having a hole of about 13 cm in diameter were prepared in the central part of a
stainless plate of about 16 cm × 16 cm, and the laminate was sandwiched between the two jigs.
Next, it was preheated at 120 to 160 ° C. for 10 seconds using a far infrared heater, and a part
of the thermoplastic resin layer (polyester film) was allowed to flow into the gap between the
substrate layer and the thermoplastic elastomer layer. By performing preforming, molding time
can be shortened. Then, it was molded at a pressure of 90 to 140 kg / cm <2> at 130 ° C. for 30
seconds using a matched die mold of a predetermined shape. After the mold was cooled, the
mold was opened and the molded article was taken out. Thus, a speaker diaphragm having a
diameter of 12 cm and a thickness of 0.29 mm was obtained.
[0041]
The density, weight, Young's modulus and internal loss (tan δ) of the obtained diaphragm were
measured by a conventional method. The obtained results are shown in Table 1 below together
with the results of Examples 2 to 3 and Comparative Example 1 described later. Furthermore, the
frequency characteristic of the speaker using the obtained diaphragm was measured. The results
are shown in FIG.
[0042]
<img class = "EMIRef" id = "199049024-00003" />
[0043]
(Comparative example 1) Plain weave woven fabric of Kevlar fiber (made by Toray DuPont Co.,
Ltd., yarn count: 1100 × 1100 (dtex), density: 17 × 17 (book / inch), basis weight: 166 g / m
<2>) And a prepreg sheet impregnated with an epoxy resin, and molded at 130 ° C. for 5
minutes under a pressure of 90 to 140 kg / cm <2>.
The other detailed procedures were the same as in Example 1. As a result, a loudspeaker
diaphragm having a diameter of 12 cm and a thickness of 0.29 mm was obtained. The obtained
speaker diaphragm was subjected to the same evaluation as in Example 1. The results are shown
in Table 1 above. Furthermore, the frequency characteristic of the speaker using the obtained
diaphragm was measured. The results are shown in FIG.
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[0044]
A thermoplastic resin layer having a microfoamed structure was produced by the following
procedure. Polypropylene (Mitsubishi Chemical Corporation, MA06) was hot-air dried, charged
into an extruder controlled at 200 ° C., and melted. Next, carbon dioxide pressurized to 25 MPa
was pumped in from the center of the extruder. Carbon dioxide penetrated into the molten
polypropylene in a short time and dispersed. The molten mixture was extruded at a die
temperature of 140 ° C. and a discharge rate of 20 kg / h, and a foam sheet was obtained
through three rolls. The average diameter of the cells of the foam sheet was about 20 μm.
[0045]
A speaker diaphragm was produced in the same manner as in Example 1 except that this foam
sheet was used as a thermoplastic resin layer. The obtained speaker diaphragm was subjected to
the same evaluation as in Example 1. The results are shown in Table 1 above. Furthermore, the
frequency characteristic of the speaker using the obtained diaphragm was measured. The results
are shown in FIG.
[0046]
A speaker diaphragm was produced in the same manner as in Example 2 except that the base
material layer, the thermoplastic elastomer layer and the thermoplastic resin layer were
laminated in this order. The obtained speaker diaphragm was subjected to the same evaluation as
in Example 1. The results are shown in Table 1 above. Furthermore, the frequency characteristic
of the speaker using the obtained diaphragm was measured.
[0047]
As is clear from Table 1, it can be seen that the speaker diaphragm of the embodiment of the
present invention has a low density (that is, is lightweight), and is excellent in the balance
between the rigidity (Young's modulus) and the internal loss.
[0048]
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1 is a schematic cross-sectional view of a speaker diaphragm according to a preferred
embodiment of the present invention.
FIG. 5 is a schematic view illustrating a method of forming a thermoplastic resin layer of a
speaker diaphragm according to a preferred embodiment of the present invention. It is a graph
which shows the frequency characteristic of the speaker using the speaker diaphragm of the
Example of this invention. It is a graph which shows the frequency characteristic of the speaker
using the speaker diaphragm of a comparative example. It is a graph which shows the frequency
characteristic of the speaker using the speaker diaphragm of another Example of this invention.
Explanation of sign
[0049]
1 substrate layer 2 thermoplastic resin layer 3 thermoplastic elastomer layer 100 speaker
diaphragm
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