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BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
diaphragm for electroacoustic conversion excellent in 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 the periphery
of the edge 11 is fixed to the speaker frame 20 by a gasket 21. A center cap 30 is disposed at the
center of the inside of the diaphragm 10, and a voice coil 32 is wound around a coil bobbin 31
connected to the center cap 30. 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 the damper which supports
the coil bobbin 31. FIG.
The following characteristics are required as materials of the diaphragm 10 and the center cap
30 incorporated in the speaker. Small mass or density ρ to improve efficiency and improve
transient characteristics. The Young's modulus E should be large in order to widen the
reproduction range of the frequency, improve the transient characteristics, and extend the high
range. Having adequate internal loss in order to suppress split vibration, reduce peak dip of high
sound resonance, and flatten sound pressure frequency characteristics.
By the way, there is paper mainly composed of wood pulp as a representative one which has
been conventionally used as a diaphragm material. Paper diaphragms are useful because they
have a large degree of freedom in design. However, the paper diaphragm has a disadvantage that
the specific elastic modulus E / ρ is not so large and the reproduction frequency sound pressure
level is low. In addition, the physical properties are unstable due to the influence of humidity.
In order to eliminate these drawbacks, diaphragms made of metal such as titanium and beryllium
and diaphragms made of plastics such as polypropylene have come to be used. However,
although the metal diaphragm is excellent in the point of rigidity, it is disadvantageous that the
density is large and heavy. Also, the internal loss is small. On the other hand, although the
diaphragm made of plastics has a low density, it has to be thickened and used because of its low
rigidity, resulting in an increase in weight. Moreover, heat resistance is also inferior.
From this point of view, at present, the paper diaphragms mainly made of wood pulp are still
used in consideration of the degree of freedom of design. Then, it has been studied to improve
the physical properties of the paper diaphragm by mixing, for example, carbon fibers, aramid
fibers, etc. with wood pulp based on the paper diaphragm.
As an example, an attempt to apply an aromatic polyester fiber to a speaker diaphragm is
proposed, for example, in Japanese Patent Application Laid-Open No. 62-36999. This proposal
has the same tendency as the contents disclosed in Japanese Patent Application Laid-Open Nos.
56-48798 and 56-57395, and aromatic polyester fibers, carbon fibers, aramid fibers and glass
fibers. Some binders are required to form fibers that do not have self-binding ability. Therefore,
synthetic pulp such as polyethylene is used.
[Problems to be Solved by the Invention] When synthetic pulp is used, its melting point is as low
as 130 to 140 ° C., and thus the obtained diaphragm for a speaker is also regulated to the
melting point of synthetic pulp and is low temperature Limited to the use of In addition, since the
wood pulp and the like can not be dyed or sized, the degree of freedom in design is low, which
restricts the assembly of the speaker. In addition, since the binder effect of the synthetic pulp is
expressed by melting, the obtained diaphragm has a higher density than a paper cone. And when
heat-drying after papermaking, if the drying temperature is set above the melting point of the
synthetic pulp, there is a problem in production as it can not be taken out from the mold unless it
is cooled below the melting point.
However, the vibration absorption characteristics of the aromatic polyester are suitable as the
speaker diaphragm. Therefore, if it is possible to give the aromatic polyester a bonding force
without causing the defects found in synthetic pulp, a diaphragm having excellent properties can
be obtained.
The present invention was devised to meet such a demand, and by using an aromatic polyester
fiber having a specified repeating unit, it is possible to improve not only the frequency sound
pressure vibration characteristic but also the heat resistance. It is an object of the present
invention to provide a diaphragm having excellent physical properties in moisture resistance,
dimensional stability and the like.
SUMMARY OF THE INVENTION In order to achieve the object of the diaphragm for
electroacoustic conversion of the present invention, 10 to 50 of wholly aromatic polyester fibers
are used alone or as a mixture of wood pulp and natural fibers. It is characterized in that it is
obtained by forming into a composition which is compounded by weight and further to which a
fixing agent and a sizing agent are added.
The aromatic polyester used in the present invention is a so-called wholly aromatic polyester
consisting of the repeating units of the above-mentioned formulas I to IX.
Representative ones are those consisting of a combination of Formula I and Formula II.
In this combination, it is preferable to use the repeating unit of the formula I as a major
component and the repeating unit of the formula II as a minor component also from the
viewpoint of the synthesis reaction of the polyester and the thermal characteristics of the
obtained diaphragm. . It is also possible to use polyesters suitably copolymerized with other
recurring units as minor constituents, as long as they are based on recurring recurring units
consisting of a combination of formula I and formula II.
The fiber of this wholly aromatic polyester is suitable as a diaphragm material for an
electroacoustic transducer because the strength of the yarn is about 20 g / d or more and the
Young's modulus is about 600 g / d or more. In particular, since the larger the Young's modulus
is, the more excellent the diaphragm is as the diaphragm is exhibited, the Young's modulus is
adjusted to 800 to 900 g / d by further copolymerizing Formula III or Formula V, for example. Is
Fully aromatic polyester fibers consisting of a combination of Formula I and Formula II have a
specific gravity of about 1.4 and are less hygroscopic compared to conventional poly (pphenylene terephthalamide) fibers and have degraded performance under dry cycling conditions
Less is. This point corresponds well to the actual use conditions of the diaphragm material for an
electroacoustic transducer, and is a desirable characteristic.
In addition, wholly aromatic polyester fibers are superior in vibration damping characteristics to
carbon fibers and aramid fibers, for example. FIG. 2 is a graph showing the vibration absorption
characteristics of the drawn yarn of wholly aromatic polyester, and it is shown that the vibration
is attenuated in a short time. In addition, the vibration absorption characteristic of FIG. 2
prepares the test piece of the reinforced laminated board which attached the epoxy resin to the
thread of one direction, respectively so that it may be easy to compare and measure the
distortion vibration waveform of the cantilever by impact vibration. It did by doing. The
vibrational absorption characteristics of poly (p-phenylene terephthalamide) fibers and carbon
fibers as comparative materials were measured by the same test method, and the measurement
results are shown in FIGS. 3 and 4, respectively. As is apparent from the comparison of FIG. 2
with FIGS. 3 and 4, the wholly aromatic polyester fiber satisfies the requirements as a diaphragm
material for the electroacoustic transducer.
For the wholly aromatic polyester fiber, a yarn spun to 2 to 5 deniers, for example, is cut to 2 to
5 mm, and then mixed with wood pulp, and a fixing agent, a sizing agent and the like are added.
Generally, when spinning synthetic fibers, an appropriate oil is used to prevent yarn breakage.
However, the use of oil makes it difficult to uniformly disperse cut fibers in water. In this respect,
in the present invention, cut fibers of wholly aromatic polyester fibers are introduced into a highspeed mixer, for example, together with a cationic surfactant having a fiber ratio of 0.1% and a
wood pulp having a fiber ratio of 10%. After mixing and disintegrating, it is dewatered and
further washed with water, whereby a uniform composition can be obtained.
Cationic surfactants are used to break up the bundled fibers one by one. However, if the cationic
surfactant remains until the papermaking process of corn paper, it inhibits the binding of wood
pulp and reduces the strength of the obtained paper. The adverse effects caused by this cationic
surfactant can be removed by washing the composition with water. In addition, mixing of wood
pulp prevents entanglement and wrapping of wholly aromatic polyester fibers after dewatering
and water washing.
The compound prepared in this manner is formed into a sheet by a known method, and heatformed or heat-dried to produce a diaphragm for an electroacoustic transducer. In addition, after
heat molding or heat drying, the resin such as acrylic resin, nitrocellulose, silicone resin, butyl
rubber, chloroprene rubber or the like or a rubber may be impregnated to adjust the density,
rigidity and the like.
EXAMPLES The present invention will be described in more detail by way of the following
examples. Fiber of a wholly aromatic polyester having recurring units of Formula I and Formula
II at a ratio of 3: 1 (Yarn physical properties: 1000 d / 200 f, specific gravity 1.44, strength 25 g
/ d, Young's modulus 610 g / d) It was cut into 3 mm long. The resulting cut fibers were mixed
with NBKP beater at 20 ° SR. Table 1 shows the blending ratio at this time.
The prepared formulation was dispersed in water, a sizing agent and a fixing agent were added,
and paper-made to make a speaker cone with a diameter of 12 cm.
Physical properties such as density, Young's modulus, internal loss, propagation velocity and the
like of the obtained speaker cone were measured and are shown in Table 2 together with
Comparative Examples.
Generally, the physical properties required of the speaker cone are that the density is as small as
possible, the Young's modulus is as large as possible, the internal loss is as large as possible, and
the propagation speed is as large as described above.
A material satisfying all these requirements is ideal as a material for a speaker cone.
Among them, the Young's modulus term and the internal loss term are the most important
physical properties, and a speaker cone that is as large as possible is desired for both of these
From this point, it can be seen from the results in Table 2 that the speaker cones of Examples 1
to 4 have an overall balance of physical properties. In addition, when various tests were
performed on the speaker cones of Examples 1 to 4 under the following conditions, no change in
physical properties or deterioration was observed. Heat resistance test: 8 hours heating at 105 °
C Cold resistance test: Hold at -20 ° C for 48 hours Moisture resistance test: 95% relative
humidity, for 96 hours in an atmosphere at 45 ° C Water resistance test: 24 hours at 20 ° C
water column After standing, hold at 80 ° C for 4 hours Light resistance test: 200 hours
exposure to Xenon fade meter
Furthermore, when the frequency sound pressure characteristics of the speaker cones with a
diameter of 12 cm in Example 1 and Comparative Example 1 were measured, there was a
difference as shown in FIG. 5 between them. That is, in the speaker cone of Example 1, the
frequency sound pressure characteristic draws a flat curve, and it can be seen that the sound
quality is good. On the other hand, in the speaker cone of Comparative Example 1, a large
number of irregularities are observed in the frequency sound pressure characteristics, resulting
in an offensive sound quality.
As described above, in the present invention, since fibers of aromatic polyester consisting of
predetermined aromatic repeating units are used, it is suitable for electroacoustic transducers in
terms of density, Young's modulus, internal loss, etc. A diaphragm having excellent
characteristics can be obtained. Moreover, since this diaphragm is excellent also in durability,
heat resistance, moisture resistance, etc., even in a severe use atmosphere such as the inside of a
vehicle exposed to cold and warm temperatures, stable reproduction sound quality can be
obtained over a long period of time .
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