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Field of the Invention The present invention relates to an electroacoustic transducer with
excellent acoustic characteristics used as a speaker diaphragm or the like. 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 influences the performance of the picker.
The characteristics required for this type of diaphragm include (1) a small density ρ to improve
efficiency, (2) a large specific elastic modulus E / 拡 to expand a regeneration zone, and (3)
resonance In order to make the sound pressure frequency characteristic flat, it may have a
proper internal loss. Also, as the diaphragms conventionally used, various materials are used as
listed below, but there are merits and demerits respectively. Sulfate pulp (KP), sulfite pulp (SP),
seed wool fiber, cotton pulp, kapok fiber, bast fiber, natural fibers such as Mishima and Ramie,
and inorganic fibers, chemical fibers, etc. And resin-treated if necessary. In a diaphragm made of
such natural fibers or the like, there are limits to the values of specific modulus E / 内部 and
internal loss. Therefore, the required sound pressure frequency characteristics could not be
obtained. What formed films, such as polyethylene and polypropylene, into a desired shape. In
the diaphragm of this system, the density is relatively large, the efficiency tends to decrease, and
high Young's modulus E can not be expected. Press-molded light metal materials such as
aluminum, titanium, and beryllium. A cloth made of carbon fiber, glass fiber, etc. is made into a
prepreg, and is formed into a desired shape by heating and pressing. The diaphragms formed
with these metal materials and fiber reinforced plastics have very high specific elastic modulus E
/ ρ (E: Young's modulus, は: density) and show good values. However, the internal loss is low
and the sound pressure frequency characteristic is not flattened. In addition, there are problems
such as difficulty in processing and high cost. Table 1 shows typical physical property values of
the diaphragms listed above. Thus, conventional diaphragm materials still do not fully satisfy the
required characteristics. Therefore, research and development of new diaphragm materials are
being conducted. For example, Japanese Patent Application Laid-Open No. 63-1297 discloses a
diaphragm having performance improved at various points mentioned above by devising the
diameter, length and cross-sectional shape of the regenerated fiber. There is. Further, Japanese
Patent Application No. 62-191852 discloses a method of manufacturing a composite diaphragm
material by continuous spinning method.
Further, Japanese Patent Application Laid-Open No. 63-131800 shows an example in which the
range of application of those is expanded and used as a diaphragm material. [Problems to be
Solved by the Invention] However, with the diaphragm disclosed in JP-A-63-1297, particularly
when using gel-based recycled paper, significant shrinkage occurs during paper drying.
Therefore, the deformation in the drying step is large, and the dimensional stability is poor. In
addition, the obtained diaphragm has high hygroscopicity, and there is a problem in use as a
speaker. On the other hand, in Japanese Patent Application No. 62-191852, fiber strength is
reduced and yarn breakage is caused by including different kinds of materials. Therefore, the
blending of different materials was limited to a very small amount. Furthermore, in JP-A-63131800, a complex operation consisting of multiple steps of continuous spinning-cuttingdisintegration-screen is required. The present invention applies the flash spinning method
(Japanese Patent Application No. Hei 1-77363) which can prepare alginic acid fibers by a simpler
process (spinning-fibrillation) instead of the conventional diaphragm material as described above.
It is an object of the present invention to provide an electroacoustic transducer such as a
diaphragm which is balanced among density, specific elastic modulus and internal loss and has
excellent acoustic characteristics. [Means for Solving the Problems] In order to achieve the
object, the electroacoustic transducer of the present invention is knitted with alginate fibers spun
by a flash spinning method. Here, the alginic acid fiber can contain fine powders of inorganic and
/ or organic substances. In addition, it may be mixed and knitted with alginic acid fibers including
fine powders of inorganic and / or organic substances and a stock made of inorganic fibers and /
or organic fibers. Incidentally, as the fine powder, one selected from fibrous, whisker-like and
powdery substances, or a mixture of two or more can be used. [Operation] In the flash spinning
method, fibers are produced by contact between the injected alginic acid-based dope and the
coagulating solution. Therefore, it is possible to freely produce fibers having the required
diameter, size and the like by adjusting the discharge conditions of the alginate-based dope,
without requiring the fiber strength as in the continuous spinning apparatus in spinning. It also
has the advantage that it is easy to include foreign materials such as microparticles. At this time,
the physical properties can be adjusted over a wide range, and a high internal loss value is
maintained by changing the type and the comprehensive amount of the particles. Alginic acid is a
polysaccharide mainly contained in brown algae, and is a block copolymer of D-mannuronic acid
and L-guluronic acid, mainly based on β-1,4 bond.
When an aqueous solution is prepared using this alginic acid as a water-soluble alkali salt, a
highly viscous alkali alginate solution is obtained. Examples of water-soluble alginic acid alkali
salts include lithium, sodium, potassium and ammonium of alginic acid. Examples of metal ions
having insoluble salt-forming ability with respect to alginate include ions of elements belonging
to the groups Ib, II, III, IV, VI, and VIIb of the periodic table and transition metals. Specifically, Ca
(II), Sr (II), Ba (II), Al (III), Sn (II), Pb (II), Mn (II), Cr (II), Fe (III), Co (II), Ni (II), Cu (II), Zn (II), Ag (I)
and the like are listed. Moreover, as an acid which forms the counter ion of these metal ions,
there exist inorganic acids, such as hydrochloric acid, nitric acid, and phosphoric acid, and
organic acids, such as formic acid and an acetic acid. The present invention will be specifically
described below by way of examples with reference to the drawings. The process of spinning
alginate fibers encasing fine inorganic and organic powders by flash spinning is carried out using
the apparatus outlined in FIG. As a material to be contained, a potassium titanate whisker having
an average fiber length of 20 to 30 μm is blended with sodium alginate to prepare a viscous
liquid. For example, 100 g of sodium alginate having a molecular weight of 6 × 10 5 is added to
10 l of water together with 100 g of potassium titanate whisker and stirred at high speed with a
mixer. As a result, sodium alginate and potassium titanate whiskers are dissolved and dispersed
in water as a solvent. Next, the resultant is filtered through a filter of about 60 mesh to remove
the non-dispersed lump whisker. The homogeneous dope obtained is filled into the pressure tank
1 of the dope injection part. An air pressure of about 3 to 4 kgf / cm 2 is applied to the pressure
tank 1. By this air pressure, the dope in the pressure tank 1 is injected from the injection nozzle 2
into the coagulation bath 3. In the coagulation bath, a solution of 3 kg of calcium chloride in 30
liters of water is filled as coagulation bath 3. The coagulation bath 3 is stirred by the stirring
blade 4 at a high speed of about 1000 rpm to prevent the binding of the spun alginic acid fiber.
In addition, this high-speed stirring also exhibits the action of cutting the alginic acid fiber into
an appropriate fiber length. The spun alginic acid fiber is sent out from the coagulation bath
through the discharge port 6 to the filtration / circulation tank. Then, the alginic acid fiber is
filtered and taken out in the filtration tank 5.
The filtrate after separation of the fibers is returned to the coagulation bath 3 by the circulation
pump 7 as a coagulation liquid. In the present embodiment, an injection nozzle 2 with a diameter
of 0.5 mm was used. Then, alginic acid fibers were injected into the coagulation bath at an
injection speed of about 1 ml / sec. At this time, even when potassium titanate whiskers were
mixed, calcium alginate fibers could be smoothly spun without causing any problems in
discharge and spinning of alginate based dope. After being washed with water, the spun alginic
acid fibers were manufactured into alginic acid fibers as a raw material of the diaphragm. Alginic
acid fibers encasing fine powder of potassium titanate whisker were weighed, and a
predetermined amount thereof was put into a beating machine. Then, it was defibrillated so as
not to damage the fiber form of the alginic acid fiber at a stock concentration of about 2.5%, and
the fiber lengths were appropriately aligned, and deaggregated and dispersed to a predetermined
beating degree by a beating degree measuring machine. The treated alginic acid fiber was dyed
using about 5% of a basic dye. Furthermore, in order to improve the wet strength, urea resin was
added to about 3% of the stock, and a sulfuric acid band was added to perform sizing to adjust
the pH value of the stock solution to about 5.0. Next, the adjusted stock was dispersed in water of
a paper making tank to prepare a suspension having a stock concentration of about 0.1%. Then,
this suspension was made into a diaphragm substrate using an appropriate paper making tool.
The formed diaphragm base was dried with a mold having the same shape under heating and
pressurizing conditions at a temperature of about 180 ° C. and a pressure of about 3.0 kg / cm
2. Then, it cut ¦ disconnected to a predetermined ¦ prescribed dimension and obtained the
diaphragm for speakers made into the objective. At this time, inorganic fibers such as carbon
fibers, glass fibers, alumina fibers and metal fibers, or organic fibers such as wood pulp and
chemical fibers may be mixed with alginic acid fibers including fine particles. Further, for the
coloring of the diaphragm, in place of the basic dye, it is also possible to adopt a method of
impregnating with an oil-based dye or a method of directly including a pigment in alginic acid
fiber. As a second example, carbon fine fibers with an average thread length of 0.13 mm were
compounded in place of the potassium titanate whisker used in the first example, and filtered
through a 60 mesh filter to remove bulk components. I used one. The other steps are the same as
in the first embodiment. As a third example, a powder of carbon black having an average particle
diameter of 20 μm was included in alginic acid fibers. The process of obtaining the diaphragm
was performed under the same conditions as in the first embodiment. In the flash spinning
method, fibers are produced by contacting the injected alginic acid-based dope with a
coagulating solution.
Therefore, in spinning, no fiber strength as in a continuous spinning device is required.
Therefore, the inclusion amount of different types of materials is very flexible. For example, even
when experimentally blending up to 600% carbon black to sodium alginate, no problem affecting
the fiberization was confirmed. The dynamic physical property values of the obtained speaker
diaphragm are shown in Table 2. As apparent from the above description and Table 2, the use of
the flash spinning method makes it possible to easily incorporate different materials. In addition,
the inclusion of the fine particles in alginic acid enables the physical properties to be selected in
a wide range depending on the type and the amount of the fine particles, and at the same time,
the value of high internal loss is maintained. In particular, when incorporating fine fibers such as
potassium titanate whiskers, as shown in FIG. 2, the fibrous material is randomly dispersed inside
the alginic acid fiber, and acts as a reinforcing material. As a result, it was confirmed that the
shrinkage at the time of drying was suppressed, and that the dimensional stability had a great
effect. This is because, for example, when an amorphous substance such as carbon black is used,
there is no effect of preventing shrinkage even if its compounding amount is increased, and
particularly the characteristic effect by the substance having a fibrous form and Conceivable.
Table 3 shows, in a circular sheet having a diameter of 16 cm, the dimensional change with
shrinkage upon drying in terms of the area ratio based on 100 for conventional wood pulp, to
express this effect numerically. Thus, the inclusion of the fine fibers suppressed the contraction
and increased the reliability as the diaphragm material. In addition, in the alginate-based fiber
according to the present invention, the hygroscopic component occupied in total is reduced by
the inclusion of the fine particles. As a result, the hygroscopicity of the fiber was significantly
improved as shown in Table 4, and could be kept equal to or less than that of wood pulp which is
the mainstream of diaphragm materials at present. In the above embodiments, the diaphragm
formation by papermaking has been described. However, by applying the present invention, for
example, fine fibers such as whiskers can be easily taken in via alginic acid fibers, so that the
strength can be greatly improved by resin treatment, FRP formation, etc. . This indicates that the
present invention is not limited to the diaphragm, but can be applied in various other fields
where strength is to be improved by the use of fine fibers. Moreover, in the said Example,
inclusion of a fine fiber, a powder, etc. was demonstrated. However, as long as the substance is
not restricted to this and does not disturb alginic acid fiber spinning, any substance such as
emulsion, non-drying oil, perfume and the like can be included.
As a result, even substances that could not be incorporated conventionally can be easily
incorporated by fiberizing as alginic acid fibers by the flash spinning method, and can be
provided as entirely new fiber materials. [Effects of the Invention] As described above, according
to the present invention, physical properties can be freely selected by forming a material for an
electroacoustic transducer such as a diaphragm by paper-forming mainly using an alginate-based
fiber including fine particles Thus, an electroacoustic transducer with high internal loss can be
obtained. In addition, the inclusion of fine fibers, in particular, can suppress shrinkage, moisture
absorption, and the like during paper drying, and can provide an electroacoustic transducer
having stable quality and high reliability.
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