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JPH0484600

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DESCRIPTION JPH0484600
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
method of manufacturing an acoustic diaphragm used for an acoustic device such as a speaker
and a microphone. 2. Description of the Related Art In recent years, with the progress of
digitization of acoustic devices, the required performance for diaphragms such as speakers has
become rather severe. For example, it is required that the deformation due to external force is
small and the distortion of sound is small, and that the reproduction range is wide and clear
sound quality can be obtained, and for that purpose, it is required to be light and excellent in
elastic modulus and rigidity. . Summarizing this as the condition of specific physical property
values, ■ large Young's modulus (E), small density (ρ), large speed of sound (propagation speed
of sound wave), internal vibration The loss (tan δ) is appropriate, (2) strength is high, and (2)
molding into any shape is possible. However, there is a relationship of V- (E / ρ) 1 ′ ′ between
V, E, and ρ. Of course, it is needless to say that in addition to these conditions, it is required to
be easy to manufacture and to be stable to external conditions such as heat and humidity.
Conventionally, paper, plastic, aluminum, titanium, helilium, poron, silica and the like have been
used as the diaphragm material. These have been used alone or as a composite with glass fibers,
carbon fibers, etc., or in the form of metal alloys etc. However, paper and plastic have insufficient
characteristics such as Young's modulus, density, and sound velocity as a diaphragm, and
particularly the frequency characteristics in a high frequency band are extremely inferior, and as
a diaphragm such as a tweeter or a squawker, It was difficult to obtain clear sound quality. In
addition, aluminum, magnesium, titanium, etc., although the sound velocity is quite excellent, but
the internal loss of vibration is small, so that high frequency resonance phenomenon is
generated, which also can not be obtained only as a high frequency diaphragm. The On the other
hand, since Poron, Helilium, etc. have physical property values superior to the above-mentioned
materials, it is possible to express good sound quality as a diaphragm. However, poron and
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helirium are disadvantageous in that they are extremely expensive and their processing ability is
extremely inferior. A diaphragm using a carbon material has been developed with the aim of
overcoming the drawbacks of the conventional diaphragm materials as described above and
having excellent high-frequency characteristics and aiming to reproduce high-quality tones. This
utilizes the excellent physical property value of carbon (graphite) and uses it as a diaphragm.
There are the following methods for obtaining such a diaphragm material. (]) A method of
combining and integrating a graphite powder and a polymer resin. (2) A method in which a
graphite powder and a polymer resin are integrated and then sintered to form a graphite /
carbon composite type. (3) A method of carbonizing a polymer by heat treatment. Among these,
as a typical one obtained by the (+) method, there is a diaphragm in which a vinyl chloride resin
is used as a matrix and a graphite powder is composited thereto. This is known for diaphragms
with excellent properties. As a method of (2), there is a method of mixing graphite powder with
liquid crystal component of crude oil decomposition pitch and performing heat treatment
carbonization, or a method of adding a binder to the graphite powder to perform heat processing
carbonization. In the latter case, when carbonizing the binder, a method of heat-treating
carbonizing the monomer or prepolymer of the thermosetting resin in combination with a
thermoplastic resin having a functional group which decomposes upon heating and reacts with
each other to crosslink and cure. Etc. are known. These methods are developed for the purpose of
enhancing the carbon yield as an organic material and preventing shrinkage and deformation
during heat treatment, and a diaphragm having excellent characteristics can be obtained.
However, the diaphragm according to the method of (1) is inferior in humidity and temperature
characteristics, and its vibration characteristics are significantly deteriorated at 30 ° C. or more.
The methods (2) all require complicated manufacturing processes, and are industrially extremely
disadvantageous when mass-produced. That is, for example, in the production process, there is a
problem in that extremely complicated processes such as high temperature heat treatment and
solvent fractionation extraction are required to industrially obtain crude oil decomposition pitch
used as a raw material and its liquid crystal component. In the surface, the graphite powder and
the binder resin are sufficiently kneaded using a high shear kneader, and the graphite crystal and
the binder resin which are intercalated strongly by the mechanochemical reaction are mutually
affinity-dispersed and the crystal face of the graphite There is a problem in that advanced
technology is needed to orient the surface of the sheet in the plane direction of the sheet I.
Moreover, although the diaphragms obtained by these methods have extremely excellent
properties which have never been achieved before, their properties are slightly inferior to
helirium which is currently said to have the best properties, and so are graphite single crystals.
The theoretical elastic modulus of 1020 GPa is far less than that. In the method of (3), since the
conventional plastic films are all non-graphitizable materials, properties as originally expected
were not obtained. In addition, the carbon yield of the plastic material used is low, the
dimensional shrinkage at the time of heat treatment is large, and deformation, cracking and the
like often occur.
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That is, in this method, it has been difficult to obtain a diaphragm having an arbitrary shape, a
sufficient quality control, and excellent characteristics. SUMMARY OF THE INVENTION
Therefore, in order to solve the disadvantages of the method (3), the inventors obtained a
graphite by heat-treating a specific polymer in an inert gas and vibrated it. It proposed to use as
a board. However, the graphite obtained by this method has a small thickness, moreover, the
dimensional shrinkage at the time of heat treatment is still large, and deformation, cracking and
the like occur, so that it can not be formed into any shape. Had problems with As a result, this
method has the disadvantage that only a flat diaphragm can be produced, and even in terms of
strength, it can not be used as an acoustic diaphragm alone. In view of these circumstances, the
present invention solves the drawbacks of the graphite diaphragm developed by the inventors,
can be processed into an arbitrary shape by a very simple method, and can be further compared
to any conventional diaphragm. Another object of the present invention is to provide a graphite
diaphragm having excellent characteristics. Means for Solving the Problems In order to achieve
the above object, in a method of manufacturing an acoustic diaphragm according to the invention
of claims 1 to 3, at least one of an aromatic polyimide, a polyoxadiazole and an aromatic
polyamide When heat-treating and graphitizing the polymer film which consists of these, it is
made to press-mold in the temperature range 2000 degreeC or more. In the method for
producing an acoustic diaphragm according to the invention as set forth in claim 4, a graphite
film obtained by heat-treating a polymer film comprising at least one of an aromatic polyimide, a
polyoxadiazole and an aromatic polyamide is The pressure molding is performed in a
temperature range of 2000 ° C. or higher. According to the second aspect of the present
invention, it is preferable that the shape added in the molding step be a dome shape (not only a
spherical surface but also an elliptical surface) or a cone shape. Further, as in the third aspect, it
is preferable to press-mold the polymer film while applying tension. The following compounds
are illustrated as an aromatic polyimide, a polyoxadiazole, and an aromatic polyamide used by
this invention. Aromatic polyimide wherein R, R2 heat treats and graphitizes a polymer film in
the present invention, but in the heat treatment, it is made to reach a temperature range of 2000
° C. or more. If it is less than 2000 ° C., it is difficult to appropriately graphitize.
Press molding is performed in a temperature range of 2000 ° C. or higher. Below 2000 ° C.,
the film is still substantially in the form of hard carbon and is broken by pressure molding. In the
temperature range of 2000 ° C. or more, flexibility is obtained with graphitization, and it
becomes possible to press-mold. Conversely, it is desirable not to apply pressure substantially in
the temperature range below 2000 ° C. Here, the state in which the pressure is not substantially
applied refers to, for example, a state in which a pressure is applied only by the weight of the jig
for molding. The pressure for pressure molding requires a higher pressure depending on the film
thickness. Specifically, the magnitude of pressure per film is usually 0.2 kg / ci or more for a
thickness of 2571 m or less, and about 1.0 kg / cr1 or more for a thickness exceeding 25 μm. If
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the pressure is less than this, wrinkles will form in the dome-like or cone-like molded body. It is
preferred to apply tension to the film during pressure molding. As a method of applying tension,
a method of pulling a film during heat treatment from the side, a method of fixing a polymer film
to a frame, and a method of applying tension naturally due to film contraction by heat treatment
can be mentioned. In the method of manufacturing an acoustic diaphragm according to the
present invention, pressure molding is performed at the stage of flexibility on the film in the
temperature range of 2000 ° C. or more in the heat treatment of graphing, for example, dome
shape, cone shape The acoustic diaphragm of appropriate shape can be obtained. In addition,
since the polymer film is an easy-to-graphitize material such as aromatic polyimide,
polyoxadiazole or aromatic polyamide, an excellent graphite diaphragm can be obtained. The
inventors have found that a flat-type graphite diaphragm can not provide adequate performance,
and therefore, as a result of various studies, it is possible to find a method for obtaining an
acoustic diaphragm of an appropriate shape, for example, dome-like or cone-like. It was possible.
In addition, when pressure molding is performed while applying tension to the polymer film,
graphitization is further promoted, and a graphite diaphragm having excellent acoustic
characteristics can be obtained. The obtained diaphragm can be used as a speaker, a microphone
or the like. EXAMPLES The present invention will be described in detail below. Of course, the
present invention is not limited to the following embodiments. Example 1 to 4 25 μm thick
(Example 1), 5011 m (Example 2), 75 μm (Example 3), 125 μm (Example 4) polyimide films
(trade name Kapton manufactured by Toray Dupont Co., Ltd.) Diameter: 30's, sandwiched by a
carbon molding jig having a dome-shaped portion of R 25 barrel, using a hot press furnace
(medium and outer furnace industrial type GI5X, 5 + 1T-BCP-HP15) in an argon atmosphere at
20 ° C. / The temperature was raised to 2800 ° C. at a temperature raising rate of 1 minute,
and then a pressure of 10 kg / cffl was applied and held for 2 hours to obtain a dome-shaped
acoustic diaphragm.
Example 5 A dome-shaped acoustic diaphragm was obtained in the same manner as in Example 1
except that a polyamide film having a thickness of 50 μm was used. Example 6 A dome-shaped
acoustic diaphragm was obtained in the same manner as in Example 1 except that a
polyoxadiazole film having a thickness of 50 μm was used. Example 7 A polyamide film having a
thickness of 50 μm was heat-treated at 2800 ° C. in an argon atmosphere using an ultra-high
temperature furnace (Type 45-6 manufactured by Shinsei Electric Furnace Mfg. Co., Ltd.) to
obtain a graphite film. Pressure molding was performed in a hot press furnace under the same
method and conditions to obtain a dome-shaped acoustic diaphragm. Example 8 A polyoxadiazole
film having a thickness of 50 μm is fixed to a frame made of graphite, and the temperature is
raised by 20 ° C./minute in an argon atmosphere using a hot press furnace (medium and outer
furnace industrial type G15X1511T-B-GP.1IP15) The temperature is raised to 2800 ° C. at a
heating rate, and then a pressure of 10 kg / Cd is applied and held for 2 hours with a carbon
molding jig having a dome-shaped portion with a diameter of 30 mm and R 25 mm. I got a board.
With respect to the acoustic diaphragms of Examples 1 to 8, physical property values (sound
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velocity, internal loss) were measured using a dynamic modulus square manufactured by Toyo
Seiki. Furthermore, a voice coil was attached and the (reproduction) limit frequency was
measured. The measurement results are shown in Table 1. In addition, when a part of acoustic
diaphragms of Examples 1 to 4 was cut out and the cross section was observed with a scanning
electron microscope (manufactured by JEOL Ltd. T-300), a layered structure unique to graphite
was observed. (Hereinafter, the margin) The diaphragm made from the first table is obtained. In
the method of manufacturing an acoustic diaphragm according to claim 2, in addition, since the
shape of the diaphragm to be obtained is a cone shape or a dome shape, a graphite diaphragm
having better acoustic characteristics can be obtained. In addition, according to the method of
manufacturing an acoustic diaphragm of the third aspect, a graphite diaphragm with better
acoustic characteristics, in which graphitization is sufficiently advanced, can be obtained. Name
of Agent As shown in Table 1 of Patent Attorney Shigetaka Ogino, one person, the acoustic
diaphragms of Examples 1 to 8 have excellent acoustic characteristics not found in the prior art.
Effect of the invention
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