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JP2004023509

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DESCRIPTION JP2004023509
An object of the present invention is to use a carbon nanotube, which is a carbon-based material,
a carbon nanotube having a structure different from that of a high elastic modulus carbon fiber,
carbon whisker, or carbon graphite as a reinforcing material of bacterial cellulose. The present
invention provides a diaphragm for an electro-acoustic transducer with good sound quality,
having an internal loss of A diaphragm for an electroacoustic transducer according to the present
invention is characterized in that a bacterial cellulose composed of ribbon microfibrils produced
by a microorganism is molded of a composite material reinforced with carbon nanotubes. In this
case, 5 to 90% by weight of the carbon nanotube serving as a reinforcing material is added. The
diaphragm is light in weight, highly rigid, has a suitable internal loss, and can obtain good sound
quality. In addition, it is possible to produce a diaphragm having a complex shape, which is
excellent in plastic deformation. [Selected figure] Figure 1
Electroacoustic transducer diaphragm
The present invention relates to a diaphragm for an electroacoustic transducer such as a speaker
or a microphone, and more specifically, a lightweight and high-weight composite material in
which ribbon-like microfibrils produced by microorganisms are reinforced with carbon
nanotubes. The present invention relates to a diaphragm for an electroacoustic transducer
excellent in rigidity and the like. 2. Description of the Related Art The physical properties
required of a diaphragm for an electroacoustic transducer are to have a low density, a high
Young's modulus, and an appropriate internal loss. Various synthetic resin and paper diaphragms
are used to satisfy the above physical properties. Although these diaphragms have a large
internal loss, they have a problem that the Young's modulus is small. As a diaphragm having a
large Young's modulus, there are a metal diaphragm and a ceramic diaphragm, but these have a
problem of being heavy and having a small internal loss because of their large density. In order
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to solve the above problems, a diaphragm made of a composite material in which various
synthetic resins are reinforced with carbon fibers having a high elastic modulus, scaly mica, etc.
has been proposed and used. Japanese Patent Publication No. 6-39552 proposes that a mixture
of polypropylene and a polyamide resin uses carbon fibers and flaky graphite powder as a
reinforcing material. Further, as disclosed in JP-A-9-284885, in a speaker diaphragm in which
mica as a reinforcing material is filled and mixed in a polyolefin matrix resin, the acoustic
characteristic is improved and the pearl gloss is vivid. A speaker diaphragm has also been
proposed and used which is colored to improve the design as well. However, since these
synthetic resin based diaphragms have smaller Young's modulus and internal loss than paper
diaphragms, it is difficult to obtain good acoustic characteristics. Since the paper diaphragm
made of plant fibers such as wood pulp is natural fibers, the physical properties of single fibers
are limited. The single fiber is beaten with a beater in order to increase the interfiber bond
strength and the bond area in order to improve the physical properties, but if the beating process
proceeds, the physical properties of the single fiber decrease and vibration The internal loss
decreases as the density as the plate increases. In order to improve these properties, JP-B-5346088 proposes and uses a method of incorporating aromatic polyamide fibers with good single
fiber physical properties into pulp and natural fibers to improve the physical properties of the
diaphragm. It is done. However, since natural fibers for pulp and papermaking have a weak interfiber bonding strength with aromatic polyamide fibers, adding 10% or more of aromatic
polyamide fibers reduces the Young's modulus of the diaphragm, resulting in a sufficient
composite effect. There was a problem that it could not be obtained.
In JP-A-61-281800, it has been proposed and used to improve the characteristics of a papermade diaphragm without using carbon fibers or aramid fibers having a high elastic modulus. The
above proposal is that polysaccharides containing cellulose (bacterial cellulose) produced
microbiologically by bacteria are composed of highly crystalline cellulose and have high strength,
as well as ordinary cellulose fibers (wood pulp etc. And hydrogen bond, to obtain a highly rigid
corn paper without using non-cellulosic materials such as aromatic polyamide fibers. That is, the
above proposal is a proposal of an acoustic diaphragm in which bacterial cellulose is used as a
reinforcing material of a cellulose fiber body. However, bacterial cellulose has a moderate
internal loss, but the speed of sound is 4980 m / s, which is equivalent to the speed of sound of
aluminum. Therefore, composite diaphragms such as Japanese Patent No. 3048757, Japanese
Patent No. 3073608, and Japanese Patent Application Laid-Open No. 6-125593 have been
proposed as improved physical properties of the bacterial cellulose-based diaphragm. However,
the sound velocity of the above-described diaphragm combined with bacterial cellulose is from
3500 to 6000 m / s, which is insufficient for improvement of the acoustic characteristics. The
present invention has been proposed in view of the above, and the object of the present invention
is a carbon-based material, even though it is a carbon-based material, a carbon nanotube having
a structure different from that of a high elastic modulus carbon fiber, carbon whisker, or carbon
graphite. It is an object of the present invention to provide an electro-acoustic transducer
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diaphragm which is light in weight, has high rigidity, has a suitable internal loss, and has a good
sound quality, by using Another object of the present invention is to provide a diaphragm for an
electroacoustic transducer which can be easily fabricated in a complicated shape and has a good
processability. The present invention achieves the above object by producing a diaphragm of a
composite material in which bacterial cellulose is reinforced with carbon nanotubes. Further, in
this case, it is characterized in that 5 to 90% by weight of the addition amount of carbon
nanotubes as a reinforcing material is added. BEST MODE FOR CARRYING OUT THE INVENTION
A specific embodiment of the diaphragm for electroacoustic transducer according to the present
invention will be described below. Bacterial cellulose or deagglomerated material used in the
present invention includes cellulose produced by a microorganism and / or a
heteropolysaccharide containing cellulose as a main chain and / or β-1, 8, β-1, 2 etc. The
disintegrants are those obtained by mechanically disintegrating them.
Components other than cellulose in the case of heteropolysaccharides are mannose, fructoma,
hexacarbon sugars such as galactose, xylose, arabinose, etc., five carbon sugars, organic acids
and the like. Microorganisms that produce bacterial cellulose are not particularly limited, but
there are no particular limitations, but bacterial cellulose such as Acetobacter aceti subspice
xylinam, Lances, Sarcina bentonicli, bacteria xyloides, Pseudomonas bacteria, Agrobacterium
bacteria, etc. You can use what produces. A device for applying mechanical shear such as a rotary
disintegrator, a mixer, a homogenizer, a beater, or a refiner can be used for the disintegration of
bacterial cellulose. Carbon nanotubes can be manufactured by arc discharge method,
hydrocarbon catalyst decomposition method, spinning method, etc., and form a seamless coaxial
cylinder of a sheet of hexagonal mesh plane of carbon atoms, and it is a machine of nanometer
size. It has excellent properties in mechanical strength. Although it is regarded as a kind of
whisker crystal from its unique structure, it is different from the conventional high modulus
carbon fiber because it gives rise to a unique mode of plastic deformation accompanied by
buckling when subjected to severe processing. Table 1 shows physical properties of sheets of
carbon nanotubes, PAN-based high modulus carbon fibers, and bacterial cellulose. As shown in
Table 1, the density of bacterial cellulose is 1180-1200 kg / m <3>, and the modulus of elasticity
is as shown in Table 1. <img class = "EMIRef" id = "197666862-000003" /> (Young's modulus) is
15 to 30 GPa. The sheet has a sound velocity of 3800 to 4990 m / s, which is lighter and faster
than the liquid crystal polymer having the largest Young's modulus among synthetic resins, and
has a value close to that of aluminum (5100 m / s). . Further, since the internal loss (tan δ) of
bacterial cellulose is 0.03 to 0.04, which is larger than the internal loss 0.002 of aluminum, it is
lighter than aluminum and has excellent acoustic characteristics. The invention relates to the
improvement of this bacterial cellulose diaphragm. In the present invention, a diaphragm made
of a composite material having the above-mentioned bacterial cellulose as a matrix and a carbon
nanotube having a larger Young's modulus than that of a high elastic modulus carbon fiber as a
reinforcing material is produced. The acoustic characteristics of the system diaphragm could be
significantly improved.
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The carbon nanotubes to be used preferably have a diameter of about 5 to 60 nm and a length of
about 0.5 to 5 μm, and they can be used even in a bundle of plural carbon nanotubes. Therefore,
this diaphragm is a composite of the matrix and the reinforcement in the nanometer size, so that
the addition amount of the reinforcement can be up to 90% by weight, and has high rigidity and
a moderate internal loss. A diaphragm can be obtained, and a diaphragm for an electroacoustic
transducer with excellent acoustic characteristics can be provided. The diaphragm for an
electroacoustic transducer according to the present invention has the biocellulose reinforced
with carbon nanotubes having light weight and high elastic modulus while securing the
advantage of bacterial cellulose as described above, so that compounding at the nano level is This
becomes a diaphragm which is easy, lightweight, has high rigidity, and has a suitable internal
loss. EXAMPLES The present invention will now be described by way of one example. In the
examples, all parts and percentages are by weight. Bacterial Cellulose and its Degraded
Preparation Example: 5 g / dl sucrose, 0.55 g / dl yeast extract, 0.5 g / dl ammonium sulfate, 0.3
g / dl potassium hydrogen phosphate, 0.05 g magnesium sulfate 50 ml of a crude medium (PH5)
consisting of dl was put into a 200 ml Erlenmeyer flask, and steam-sterilized at 120 ° C. for 20
minutes to prepare a culture solution. Then, this culture solution was prepared with a test tube
slant agar medium (PH 6.0) having a composition consisting of 0.5 g / dl of yeast extract, 0.3 g /
dl of peptone, and 2.5 g / dl of mannitol at 30 ° C., 3 One platinum loop of Acetobacter aceti
subsp. Xylinum (ATCC 10821) grown daily was inoculated and cultured at 30 ° C. After
culturing for 30 days under the above conditions, a gel-like film containing a white bacterial
cellulose polysaccharide was formed on the upper layer of the culture solution. The gelled
membrane of the cellulose polysaccharide was washed with water to obtain bacterial cellulose.
The deflocculated product was added with 100 times the dry weight of water, and was treated
for 10 minutes at 15000 rpm using an Excell autohomogenizer to prepare a 1.0% suspension of
bacterial cellulose deflocculated product. The carbon nanotubes used in this example were
produced by an arc discharge method. The carbon nanotube powder (about 5 to 60 nm in
diameter and about 0.5 to 5 μm in length) contains granular graphite and amorphous carbon as
impurities in addition to carbon nanotubes.
In this example, 5 to 90% of carbon nanotube powder was added to the above suspension of
bacterial cellulose, mixed thoroughly, and diluted with 10 to 100 times tap water to make a
sheet. Bacterial cellulose is a cellulose with a high degree of crystallinity, but since it is
hygroscopic, an alkyl ketene dimer (Acopel 12, manufactured by Dick Hercules) was used as a
sizing agent. After paper making, heat and pressure were applied using a predetermined die to
produce a diaphragm. The mold temperature at this time is 120 ° C., and the pressure is 4 kgf /
cm <2>. As a shape of the diaphragm, a flat plate, a cone, a dome or the like can be manufactured
through a mold. FIG. 1 shows a block diagram of the above process. Test pieces for measuring
the physical properties of the diaphragm were manufactured by the same method as the case of
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manufacturing the diaphragm for the electroacoustic transducer. The sound velocity and internal
loss of the test piece were determined by the vibration lead method. The measurement results
are shown in Table 2. As shown in Table 2, the addition amount of carbon nanotubes is 5 to 90%
with respect to bacterial cellulose. It is effective in the range. Physical properties at the time of
5% addition is the dry sheet physical properties (Young's modulus 29.8 GPa, sound velocity 4990
m / s, after treatment of bacterial cellulose gel with 0.5% sodium hypochlorite, 5% sodium
hydroxide mixed solution) Internal loss 0.042 This value is equivalent to the highest physical
property value of bacterial cellulose sheet), and it is a physical property of paper made of pulp
material (Young's modulus 0.3 to 6 GPa, sound velocity 1000 to 2800 m / s, internal loss The
physical properties are significantly improved as compared to 0.02 to 0.1). On the other hand, in
the case of 90% added, the influence of the interaction between the bacterial cellulose which is
the matrix and the interface of the carbon nanotube is small, and the physical property value is
lowered depending on the properties of the matrix is there. The present invention is not limited
to the above embodiments, and some modifications can be made without departing from the
spirit of the present invention. That is, although the above-mentioned Example demonstrated the
case where the disaggregated matter (disaggregated gel) of bacterial cellulose was used, carbon
nanotubes and bacterial cellulose are similar in size (diameter in nm and length in μm).
Therefore, compounding is easy by various methods.
It is also possible to use a carbon nanotube sheet and a biocellulose sheet laminated in layers,
and it is also possible to use the composite vibration base material after processing such as resin
processing and metal plating. Of course, carbon nanotubes produced by other methods may be
used. The carbon nanotube is a cage (cage structure) based on a network of graphite. However,
unlike carbon-graphite, there are one longitudinal wave, two transverse waves, and one torsional
acoustic mode, and the sound velocity of these four acoustic modes reflects the coupling of SP
<2> than the ordinary material Also the speed of sound is significantly increased. In the present
invention, since bacterial cellulose is reinforced with the above-mentioned carbon nanotubes, a
diaphragm which is lightweight, has high rigidity, and has a suitable internal loss can be
obtained. It is possible to expand the reproduction frequency band. In addition, since carbon
nanotubes have good plastic deformability and excellent processability, it is possible to easily
manufacture a small-sized and complicated diaphragm such as a microphone. BRIEF
DESCRIPTION OF THE DRAWINGS FIG. 1 shows a block diagram of the manufacturing process of
the present invention.
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