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JPH0484599

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DESCRIPTION JPH0484599
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
method of manufacturing an acoustic diaphragm used for a speaker, a microphone or the like. 2.
Related Art In recent years, digitization of sound 9 equipment has progressed, and performance
requirements for diaphragms such as skaters have 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, the 0 strength is large, and the like. However, there is a relationship of V- (E / ρ)
+7 among V, E, and ρ. Of course, in addition to these conditions, it is required that molding is
possible, that manufacture is easy, and that it is stable against external conditions such as heat
and humidity. Conventionally, paper, plastic, aluminum, titanium, beryllium, boron, 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
do not have sufficient characteristics such as Young's modulus, density, and sound velocity as a
diaphragm, and the frequency characteristics particularly in a high frequency band are extremely
inferior, and sound quality is clear as a diaphragm such as a tweeter. It was difficult to get In
addition, aluminum, magnesium, titanium, etc., although the sound velocity is quite good, but the
internal loss of vibration is small, so high frequency resonance phenomenon occurs, which too
can not be obtained only as a high frequency diaphragm. . On the other hand, boron, beryllium,
and the like have physical property values superior to those of the above-mentioned materials,
and therefore, it is possible to express a high quality sound as a diaphragm. However, boron and
bryllium have the disadvantage that they are extremely expensive and their processability is
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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
is to use the dirt as a diaphragm utilizing the excellent physical property values of carbon (graph
eye l-). There are the following methods for obtaining such a diaphragm material.
(1) 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 film by heat treatment.
Among these, as a typical one obtained by the method (1), 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 as
a diaphragm 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 heattreating 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
increasing the carbon yield as an organic material and preventing shrinkage and deformation
during heat treatment, and a diaphragm having excellent characteristics can be obtained. In the
case of the method of (3), some polymer films have been studied, but most polymer films are
excellent because they belong to so-called non-graphitizable materials which do not turn into
middle-sized graphite even when heat-treated at high temperatures. It was difficult to obtain an
acoustic diaphragm. However, the acoustic diaphragm according to the method of (1) is inferior
in humidity and temperature characteristics, and the vibration characteristics are significantly
deteriorated at 30 ° C. or higher. The methods of (2) all require complicated manufacturing
steps, and industrial G is extremely disadvantageous in mass production. 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 sheet in the plane
direction of the sheet]. Although the diaphragms obtained by these methods have extremely
excellent properties not found in the prior art, their properties are slightly inferior to beryllium,
which is currently said to be the best property, The theoretical elastic modulus 1020 GPa of the
single crystal was beyond the drawing.
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The method (3) is based on the recent finding that some of condensation polymers are so-called
graphitizable materials which are graphitized by heat treatment at high temperature. However,
the diaphragm obtained by this method was limited to a planar one. This is because the polymer
film as the raw material is extremely difficult to be molded. The flat acoustic diaphragm, for
example, has inferior sound pressure compared to the dome-shaped diaphragm, and has a
disadvantage that particularly high sound can not be heard when used in a large room. In view of
such circumstances, it is an object of the present invention to provide a method capable of easily
obtaining an acoustic diaphragm made of a dome-shaped or cone-shaped graphite having
excellent acoustic characteristics. Means for Solving the Problems In order to achieve the above
object, in the method of manufacturing an acoustic diaphragm according to the first to third
aspects of the present invention, when converting polyamic acid to polyimide by thermal
condensation polymerization, a dome shape or cone shape The polymer film pressure-molded is
subjected to heat treatment to reach a temperature range of 2000.degree. C. or more in an inert
atmosphere to cause graphitization. When the shape added in the molding step is dome-shaped,
it is not limited to a true spherical surface, and may be a flat elliptic surface. And the imidization
in this invention heats the film obtained by casting and removing a part of solvent by casting the
solution containing a polyamic acid at 70-400 degreeC like Claim 2, for example. To do. In the
case of the present invention, as described in claim 3, it is preferable to press Fill 1 in a
temperature range of 2000 ° C. or higher. In addition, the acoustic diaphragm obtained does
not need to be 100% graphite, and some non-graph eye] and carbon may remain. The polymer
film pressure-formed into a dome shape or cone shape used in the present invention is a
polyimide, particularly preferably an aromatic polyimide. The aromatic polyimides include, for
example, the following compounds. Mono-aromatic polyimide 11] 1 where R, is a substituent R 2
below is not a substituent The above-mentioned aromatic polyimide can be obtained, for
example, as follows. First, the following (formula 81 is used and pyromellitic anhydride and the
following (bJ formula is used and diaminophenyl ether is used. (A) (b)] 111 The two are reacted
to synthesize soluble polyamic acid which is not (C) below. Next, using a polyamic acid solution, a
polyamic acid film is produced by Cass I method or the like.
For example, a polyamic acid solution is cast on a substrate and then dried (heated) to partially
remove the solvent to obtain a polyamic acid film. In this case, the solvent may, for example, be a
mixed solution of N-methylpyrrolidone, dimethylacetamide and an aromatic hydrocarbon. Then,
although it varies depending on the type of polyamic acid, it is usually thermally dehydrated and
imidized at a temperature in the range of 70 to 400 ° C. (preferably 120 to 300 ° C.) to give a
polyimide film of the following formula (d) Do. (D) And, according to the present invention,
instead of molding a film which has already been imidized, for example, as in claim 2, each time
the solution containing the polyamic acid is casted and part of the solvent is removed by
evaporation The resulting film is pressure molded at a temperature of 70-400 ° C. Usually,
molding is performed using a mold made of stainless steel or the like at a stage where imidization
has progressed to some extent (in the course of imidization), and heat treatment is further
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performed after molding to complete imidization. As the molded polyimide film is heat-treated as
it is and graphitized, it is easy to have wrinkles or lose its shape on the surface due to
dimensional shrinkage, so it is added at the heat treatment stage of graphite using a graphite
shape-retaining mold. It is preferable to press. The heat treatment performed in an inert (gas)
atmosphere is performed to reach 2000 'C (more preferably 2500 C) or more where
graphitization proceeds sufficiently, and after reaching 2000 C or more, it is usually 0 Apply a
pressure of about 1 to 200 kg / cJ. Pressure over 200 kg / ca is generally not necessary. This
pressurization not only has the function of preventing inconveniences such as the formation of
wrinkles in the obtained acoustic diaphragm, but also has the function of preventing the
generation of defects in the graphite crystal. In the method of manufacturing an acoustic
diaphragm according to the present invention, the dome-shaped or cone-shaped pressing is
performed in a stretchable state in the imidization progress stage where the imidization is
completed. It is easy to get one with a suitable shape, such as a cone. In addition, since the
polymer film is an aromatic polyimide material which is easy to graphitize, an excellent graphite
diaphragm can be obtained. EXAMPLES The present invention will be described in detail below.
Of course, the present invention is not limited to the following embodiment G. Examples 1 to 3
Using a polyamic acid solution (made by Toshi Co., Ltd., trade name: Trenyth), cast by a doctor
blade method to a glass substrate "2" with a thickness of 250 μm, heated to 120 ° C and
solvent (N-methylpyrrolidone And a mixture solution of dimethylacetamide and an aromatic
hydrocarbon was partially evaporated to obtain a polyamic acid film.
The obtained film is peeled off from the glass substrate, set in a stretching apparatus (Koyama
Scientific Machinery Co., Ltd. polymer stretching apparatus), and held for 10 minutes at a
temperature of 220 ° C. to proceed with imidization. Using a molding die (Example 1), diameter
30 mm 'T: R 25 rnm dome-shaped stainless steel molding die (Example 2), using a diameter of 30
angles and R 40 mm dome-shaped stainless steel molding die (Example 3) After pressure
molding, the temperature was raised to 350 ° C., and heat treatment was carried out for 10
minutes to complete imidization, to obtain a dome-shaped aromatic polyimide film. Next, using a
hot press furnace (G15X15HTB-Gll.III'15, manufactured by Chugai Chugai Kogyo Co., Ltd.), the
dome-shaped polyimide film thus obtained is raised to 2800 ° C at a heating rate of 20 ° C /
min in an argon atmosphere. Warm and at that temperature, a dome-shaped carbon shape
retaining mold with a diameter of 30 mm and R1, 5 mm (Example 1), a dome-shaped carbon
shape mold with a diameter of 30 mm and R25 + mn (Example 2), a diameter A dome-shaped
acoustic diaphragm was obtained by applying a pressure of 50 kg / c + Il and holding it for 2
hours using a dome-shaped carbon shape retaining mold (Example 3) of 30 mm and R 40 mm.
Example 4 Using a solution of polyamic acid (made by Toshi Co., Ltd., trade name: Trenyth), cast
by a thickness of 250 II II on a glass substrate by a doctor blade method and heat to 120 ° C. to
obtain a solvent (N-methylpyrrolidone And a mixture solution of dimethylacetamide and an
aromatic hydrocarbon was partially evaporated to obtain a polyamic acid film. The obtained film
is peeled off from the glass substrate, subjected to seso (˜) in a drawing apparatus (Kayama
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Scientific Machinery Co., Ltd. polymer drawing apparatus), and when it reaches a temperature of
120 ° C, it is subjected to 10% drawing in two axial directions. Using a dome-shaped stainless
steel mold with a diameter of 30 mm and a diameter of 100 mm from the lower side, and then
raising the temperature to 350 ° C. and heat treatment for 1 minute to complete imidization; An
aromatic polyimide film was obtained. Next, the obtained dome-like polyimide film is heated at
20 ° C./in an argon atmosphere using a hot press furnace (middle and outer furnace: G 2, 5 X),
5 II Tn-cp-npl, 5). (The temperature is raised to 280 (1 '(at the temperature, F' at 30 A pressure
of 50 kg / c% was applied and held for 2 hours using a 100 mm dome-shaped carbon shaperetaining mold to obtain a dome-shaped acoustic diaphragm.
With respect to the acoustic diaphragms of Examples 1 to 4, physical property values (sound
velocity, internal loss) were measured using a dynamic modular star 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 the acoustic diaphragms
of Examples 1 to 3 was cut out and the cross section was observed with a scanning electron
microscope (T- 300, manufactured by JEOL Ltd.), a layered structure unique to graphite was
observed. As shown in Table 1 and Table 1, the acoustic diaphragm of the embodiment has
excellent acoustic characteristics. Effects of the Invention As described above, in the method of
manufacturing an acoustic diaphragm according to the present invention, the polymer
diaphragm J has an appropriate shape for performing pressure molding in a stretchable state
before the end of imidization. , Is a polyimide that is easy to graphitize, and a graphite diaphragm
with good acoustic characteristics is obtained. Agent's name Attorney Attorney Shigetaka Hagino
1 person G
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