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JP2010147526

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DESCRIPTION JP2010147526
The present invention provides a method of manufacturing an electro-acoustic transducer
diaphragm having excellent acoustic characteristics with adjusted elastic modulus and loss
coefficient. SOLUTION: In order to control the acoustic characteristics of a diaphragm made of
natural pulp material, a functional group which is hydrogen-bonded to pulp is used on the
surface of CNT, carbon fiber and nanodiamond. By adding functional groups, it is possible to
simultaneously control the elastic modulus and the loss factor and to improve the acoustic
characteristics without damaging the temperature characteristics of the pulp material. [Selected
figure] Figure 5
Method of manufacturing diaphragm for electro-acoustic transducer and speaker incorporating
the same
[0001]
The present invention relates to a diaphragm for an electroacoustic transducer, particularly to a
method for manufacturing a high performance diaphragm made of natural fiber pulp suitable for
speakers such as audio and the like, and a speaker incorporating the diaphragm manufactured by
the method.
[0002]
Heretofore, diaphragms made of natural fiber pulp have been widely used because of their mild
tone quality, changes in elastic modulus and loss coefficient due to temperature, and little aging
change during use.
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1
However, since the strength is insufficient when the acoustic output increases, recently, a
diaphragm (patent document 1) or a carbon nanotube-containing carbon fiber resin molded body
in which carbon fibers or high elastic fiber Kepler or the like are fixedly molded with resin is
sintered. A diaphragm (patent document 2) came to be used.
[0003]
The elastic modulus and loss factor of the material, which are mechanical properties required for
the speaker diaphragm, are important factors. A large elastic modulus is required to improve the
reproduction frequency band, and a large loss factor is required to reduce acoustic distortion. In
general, it is difficult to match both the elastic modulus and the loss coefficient of the material
because the elastic modulus and the loss coefficient of the material have a large negative
correlation.
[0004]
Carbon fiber, carbon nanotube (hereinafter referred to as CNT). ) Is compounded with a high
elastic fiber such as Kepler and resin molded (generally the resin crystallinity is poor), the Tg
temperature is low at around room temperature, and the binder resin is used in the use
environment as a speaker Since the change in elastic modulus and loss coefficient is large and
the sound quality changes, there remain problems for high-end speakers. In addition, in terms of
sound quality, the loss coefficient is low, high-order resonance modes are easily generated, and
high-order acoustic distortion is easily generated as compared with a natural fiber pulp
diaphragm.
[0005]
The speaker made by mixing and molding CNT and carbon fiber with thermosetting resin and
sintering it at a temperature around 1000 ° C has a large elastic modulus, and since the
components other than carbon are removed by sintering, the density decreases and regeneration
Although it is advantageous to increase the frequency band, it tends to have a porous structure in
which air bubbles are removed at the time of sintering. The holes are filled with resin or the like,
but since the loss coefficient is low, high-order resonance modes are easily generated, and there
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2
is also a problem in sound quality.
[0006]
For this reason, in recent years, a speaker diaphragm using a thin sheet of wood has begun to be
used in place of a resin composite molded diaphragm in which the sound quality is close and the
sound quality is not good and the crystallinity is not good. Wood has better crystallinity than
synthetic fibers such as Kepler etc., resin adhesive, etc., so the temperature change of elastic
modulus and loss coefficient is small and it has appropriate strength and loss coefficient, and
natural pulp is also sound quality It has a tone similar to that of wood (Patent Documents 3 and
4).
[0007]
However, it is difficult to form and process an integral wood thin plate diaphragm, and in order
to make a dome-shaped diaphragm, the strength of wood thin plate is lowered, and it is easy to
bend and form the wood thin plate as a wetting agent butylnaphthalene sulfone. The resin is
dipped in acid soda to soften it, then, a thermosetting resin or the like is applied and hot press
molding (heating and pressure molding) is performed to mold it into a predetermined shape. If
strength is required, it is lined with a highly elastic fiber cloth or a synthetic resin film and
molded. When wood is soaked in a moistening agent, it expands, weakens the bond between
wood fibers, and often does not sufficiently return to its original properties even by heat and
pressure molding. In addition, since synthetic fiber materials or synthetic resin films are used as
an adhesive with poor crystallinity and a backing layer, problems occur easily in mechanical
characteristics due to aging such as changes in elastic coefficient due to temperature
characteristics and humidity, and the process is complicated. As a result, there was a problem in
cost.
[0008]
A diaphragm in which ribbon-like microfibers produced by microorganisms are reinforced with
CNT has also been reported (Patent Document 5). Polysaccharides containing cellulose (bacterial
cellulose) microbiologically produced by bacteria are composed of highly crystalline cellulose
and have high strength and hydrogen bonding like wood pulps. Although it is mixed and molded
with a usual fiber material as a diaphragm, in order to further improve this strength, not a usual
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carbon fiber but CNT is used. Bacterial cellulose is expensive compared to ordinary pulp
cellulose, and CNTs have good crystallinity, so that they are difficult to hydrogen bond with
cellulose, so their performance can not be fully achieved. JP 2003-319488 JP JP 2004-32425 JP
JP 2008-278457 JP JP 2008-236213 JP JP 2004-023509 JP
[0009]
The present invention has been made in view of the above-described problems of the prior art,
and its main object is to provide a method of manufacturing an electroacoustic transducing
diaphragm having excellent acoustic characteristics with adjusted elastic modulus and loss factor.
It is in. In other words, the present invention improves the properties of pulp materials used in
diaphragms made of natural fibers that are used as woofers that are mainly responsible for the
low frequency range of the reproduction frequency in audio speakers. In addition, an additional
problem of the present invention is that the vibration plate made of pulp material excellent in
acoustic characteristics by the same process as the conventional Japanese paper manufacturing
method is made of pulp material suitable for woofer etc. at low cost without special incidental
equipment. It is in providing a board. The basic technical concept of the means for solving the
problems of the present invention is CNT, carbon fiber or nano diamond (hereinafter referred to
as "functionalized" on the surface to hydrogen bond with cellulose which is a basic constituent of
wood or non-wood pulp). It is simply called nano diamond. Or a mixture thereof to pulp material
and molding it in one piece.
[0010]
Natural pulp materials have higher crystallinity than Kepler and other synthetic fibers, so Tg
temperature (glass transition temperature) is high, temperature coefficient of elastic modulus is
almost zero, and secular change is not seen, and appropriate loss It has been widely used because
it has coefficients. However, in order to cope with recent high-power amplifiers, it is required to
increase the strength of pulp materials, and a diaphragm with a sandwich structure in which high
elastic fiber cloth such as Kepler is sandwiched between pulp materials and fixed with a synthetic
resin adhesive. Or the diaphragm which mix | blends a carbon fiber raw material with a pulp
material, and carries out integral molding similarly with a synthetic resin adhesive agent is used.
When a synthetic resin adhesive is used, the apparent strength increases under measurement
conditions that cause large mechanical strain such as DMA (dynamic viscoelasticity), but the loss
coefficient decreases significantly, and higher-order vibration modes as a diaphragm This
increases the acoustic distortion and lowers the natural goodness of natural pulp, making it
difficult to balance the reproduced sound.
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[0011]
When operating as the diaphragm of a speaker, it is the strength of the membrane bending
moment of the diaphragm that is related to the higher order vibration modes of the diaphragm.
Even if you put high elasticity fiber like Kepler in the middle and sandwich structure, the effect is
thin. This is because although the strain characteristic by mechanical measurement of the
material is usually measured by stretching 0.1% of the length of the material, the strain given to
the material is much smaller in the actual operation mode of the diaphragm. The adhesive
strength is also apparently reduced. As shown in the acoustic mass law, all materials are known
to become strain in the region acting as a perfect elastic body when the strain is reduced, and
loss is related only to mass, and the elastic modulus as a diaphragm is also increased. In addition,
the loss factor is also reduced, which is not preferable acoustically.
[0012]
The present invention has been made based on the above findings. That is, in order to solve the
above-mentioned main problems, the present invention provides a method for producing an
electroacoustic transducing diaphragm made of natural fiber pulp cone paper molded into a
predetermined shape, wherein CNTs and carbon shorts are produced when natural fiber pulp
cone paper is produced. It is characterized in that fibers or nanodiamonds or a mixture thereof is
blended to control the elastic modulus and the loss factor (claim 1).
[0013]
The present invention may also be referred to as CNT, carbon fiber, nano diamond or a mixture
thereof (hereinafter referred to as CNT etc.) in order to solve the above-mentioned additional
problems. The surface of the polymer cellulose is modified to provide a functional group which is
directly bonded via a hydrogen ion to a pulp made of polymer cellulose which is a matrix (claim
2). That is, the present invention provides a stable carbon atom surface of CNTs or
nanodiamonds by attaching a functional group to be bonded to cellulose pulp and hydrogen ions
via pulp ion, and directly bonding to pulp without using a synthetic resin adhesive. , The problem
is to be solved. According to the present invention, since CNTs or nanodiamonds are directly
bonded to pulp cellulose without the use of a poorly crystalline polymer adhesive, temperature
change of elastic modulus and aging are eliminated, and stable regenerated sound can be
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obtained.
[0014]
In order to attach a functional group, any one of the following methods can be used suitably. 1) A
method of plasmatizing F gas, N gas, etc. and reacting them with CNT etc. by active energy. 2) A
method in which a compound typified by berfluoroazoalkane C8F17N, aliphatic nitrile CH3
(CH2) nCN, etc. and CNT etc. are reacted with ultraviolet energy. 3) A method of oxidizing the
surface of CNTs or the like using concentrated inorganic acid, attaching a carboxyl group with
acetic anhydride or the like, and attaching a predetermined functional group by multistage
reaction (Non-patent Document 1). Nanocomposite materials Akihisa Inoue Fronthea Publishing
2005 Since the surface of the nanodiamond is usually covered with the SP2 graphite layer,
reactive groups are attached in the same process as CNT.
[0015]
As a specific functional group which can be easily dispersed in an aqueous solution used at the
time of production of pulp corn paper, any one of the functional groups (a) to (o) shown in Table
1 is preferable (claim 3). The functional group is appropriately selected according to the pressure
applied to the pulp material to be used, the heating temperature, the treatment time, the pH of
the dispersion, and the composition, but generally, it has hydrogen ions at the terminal of the
functional group (a), (B), (c), (f) etc. are desirable.
[0016]
As a method of manufacturing a diaphragm molded into a predetermined shape, an aqueous
solution of a predetermined concentration containing a predetermined amount of a pulp material
crushed and processed with a beater in advance and a functional group-attached CNT, carbon
fiber or nanodiamond or a mixture thereof The mixture is stirred and mixed, stirred for a
predetermined period of time and homogenized, and then adsorbed in a predetermined coneshaped mold, and after removing water, it is characterized in that a diaphragm is manufactured
by pressure heating and molding (hot press). I assume. The blending amount of CNT, carbon fiber
or nano diamond is effective to 1 wt% or more and 30 wt% or less with respect to the pulp
material (claim 4). If the amount is less than 1 wt%, the elastic modulus and the loss coefficient
are not sufficiently improved. If the amount exceeds 30 wt%, the weight is increased, the acoustic
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conversion efficiency is reduced, and the cost is increased.
[0017]
The invention of claim 4 can also be configured from the following steps (claim 5). (A) Select
CNTs grown in a predetermined shape, carbon fibers, or nanodiamonds of a predetermined
particle size, and described in the table below for binding pulp cellulose and hydrogen ions to the
surface of selected CNTs or nanodiamonds. A surface modification step of attaching any one of
the functional groups. (B) A step of blending a predetermined amount of pulp materials such as
wood pulp, cotton pulp, jute non-wood pulp having a large strength according to the required
acoustic characteristics, and crushing with a beater. (C) A predetermined amount of crushed pulp
material and surface-modified CNTs, carbon fibers or nanodiamonds are put in a stirring tank
and stirred in an aqueous solution for a predetermined time to make them uniform. (D) A step of
transferring the uniformed material to a molding tank by a pump, dewatering the porous metal
mold set in the lower part of the molding tank for a predetermined time, and wet-molding the
diaphragm. (E) A step of placing a mold carrying a diaphragm containing water in an electric
furnace, and performing pressure molding (hot press) at a predetermined temperature and a
predetermined pressure for a predetermined time.
[0018]
As hot press conditions, a heating temperature of 100 to 250 ° C., a pressure of 0.05 to 10
MPa, and a pressurization time of 10 to 120 seconds are preferable (claim 6). If the temperature
is less than 100 ° C., the pulp material can not be sufficiently dewatered, and if it exceeds 250
° C., the possibility of deterioration of the pulp material increases. If the pressure is less than
0.05 MPa, molding is difficult, and if it exceeds 10 MPa, the density is too high and the sound
quality is degraded. If the pressure heating time is less than 10 sec, dehydration can not be
sufficiently performed, and if it exceeds 120 sec, productivity is reduced. In general, the optimum
range is about 210 ° C., 0.1 MPa, and about 20 sec.
[0019]
The diaphragm manufactured by the method of the present invention is suitable for a bass
speaker having a reproduction acoustic frequency of 3000 Hz or less (claim 7).
[0020]
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According to the invention of claim 1, since the elastic modulus and the loss coefficient of the
natural pulp material diaphragm can be controlled to some extent independently, it is possible to
manufacture a diaphragm having the required acoustic characteristics.
Raw materials that have been modified with a functional group to blend only non-surfacemodified CNTs, carbon fibers or nano-diamonds or their mixtures to increase the loss factor, and
to increase the elastic modulus and loss factor together You can use In actual production,
depending on the required reproduction acoustic zone, both of the non-surface-modified material
and the surface-modified material are appropriately selected and used.
[0021]
According to the second aspect of the invention, since the diaphragm made of the composite
material can be manufactured without using a polymer adhesive, it is possible to obtain an
electroacoustic transducer which does not change acoustic characteristics in a wide temperature
range.
[0022]
According to the invention of claim 3, a specific functional group which is easily dispersed in
water is shown, which is appropriately selected according to the type of the opposite pulp
material and the production conditions, and the production becomes easy.
[0023]
According to the invention of claim 4, the required regeneration zone frequency and sound
quality can be obtained by changing the blending amount of CNT, carbon fiber or nano diamond,
or a mixture thereof by the ordinary method of manufacturing a pulp cone paper diaphragm. .
[0024]
According to the invention of claim 6, manufacturing conditions of the diaphragm made of CNT,
carbon fiber and nano diamond blended pulp cone paper can be defined.
[0025]
According to the invention of claim 7, it is possible to provide a speaker having excellent acoustic
characteristics.
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[0026]
Subsequently, an embodiment of the present invention will be described.
In the method for producing a composite diaphragm of CNT, carbon fiber or nanodiamond and
pulp according to the present invention, first, CNT, carbon fiber or nanodiamond having a
predetermined particle size grown into a predetermined shape is selected.
In order to improve the elastic modulus, fibrous nanocarbons and carbon fibers having a large
dimensional ratio are selected to be relatively spherical CNTs or nanodiamonds mainly to make
the pulp material slippery mainly when the loss factor is increased.
[0027]
Next, the surface of the selected CNTs, carbon fibers or nanodiamonds is provided with
functional groups for binding to pulp cellulose via hydrogen ions.
Usually, one of the methods described in paragraph 0014 is adopted for the addition of the
functional group.
Oxidation treatment of the surface with a strong acid and reaction with an acid having a
predetermined functional group is suitable for production.
[0028]
Pulp materials mix predetermined amounts of wood pulp, cotton pulp, and high strength jute
non-wood pulp according to the required acoustic characteristics, and break with a beater to
make it easy to intertwist fibers.
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In this case, depending on the selection of the pulp material, if the crushing time of the beater is
different, it is treated separately.
[0029]
Next, predetermined amounts of crushed pulp materials and surface-modified CNTs, carbon
fibers or nanodiamonds are placed in a stirring tank, mixed in an aqueous solution, and
homogenized. The pH of the aqueous solution, as well as the required additives, are chosen to
suit the pulp and the CNTs. Usually, the stirring time is about 30 minutes.
[0030]
The material which has been sufficiently homogenized is transferred to a molding tank by a
pump, dewatered on a porous mold set at the lower part of the molding tank for a predetermined
time, and wet molded, usually in 5-10 minutes A diaphragm having a shape defined by the mold
is formed on the mold, containing moisture of a predetermined thickness.
[0031]
Next, the mold on which the diaphragm containing water is placed is placed in an electric
furnace, and pressure molding (hot pressing) is performed for a predetermined time to obtain a
target composite diaphragm.
The temperature, pressure, and time which are the conditions of the hot press are appropriately
selected according to the pulp material and the functional group.
[0032]
[Example] A mixed pulp material consisting of two types of pulp is used as a raw material pulp
material, and 11 types of surface-modified CNTs and one type of non-surface-modified CNTs are
respectively prepared as raw material CNTs The mechanical properties of the formed coneshaped diaphragm were measured by DMA and central excitation method after mixing 5 wt%,
forming at a heating temperature of 21 ° C., applying pressure of 0.1 MPa and applying time of
20 sec. . The DMA measurement was performed at a temperature of 0 to 50 ° C. and a room
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temperature of 23 ° C. at a distortion rate of 0.1% at 10 Hz. The central excitation method
measured the resonant frequency and the loss factor at a frequency up to about 4000 Hz in the
seventh resonant mode at room temperature.
[0033]
[Measurement Results When CNTs Have No Surface Modification] The results of DMA
measurement and central excitation measurement of a diaphragm manufactured using CNTs not
subjected to surface modification are shown in FIGS.
[0034]
FIG. 1 is a graph showing in contrast the temperature characteristics of storage elastic modulus
in the case where the material of the corn paper produced is pulp only and in the case of the
composite material of CNT and pulp material without surface modification, and the sample The
numbers 0-1 and 0-2 and 0-3 are pulps, and C-1 and C-2 and C-3 are CNTs.
2 is a graph showing loss elastic modulus of each cone paper of FIG. 1, FIG. 3 is a graph showing
loss coefficient of each cone paper of FIG. 1, and FIG. 4 is a resonance frequency characteristic
diagram by central excitation measurement. It can be seen that the elastic modulus of the CNTblended product is somewhat greater than that of the case without. FIG. 5 is a graph showing the
loss factor obtained by the measurement of FIG.
[0035]
Since CNTs without surface modification have poor adhesion to pulp, the elastic modulus
measured at a large strain rate falls by about 40%, but a central excitation method close to the
operation mode of an actual diaphragm with a small strain rate In the measurement of, the
resonance frequency is slightly increased, and the deterioration of the elastic modulus is not
observed. The loss factor is up in any measurement, which is shown to be effective in reducing
high-order distortion as a diaphragm.
[0036]
[Measurement result in the case of surface modification of CNT] For the diaphragm
manufactured using 11 types of surface modified CNT, the same measurement as above is
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performed at room temperature to obtain CNT without surface modification. The results
normalized as a reference are shown in FIGS.
[0037]
FIG. 6 is a mechanical characteristic diagram of the surface modified CNT-blended pulp
composite (composite material) by DMA measurement, and FIGS. 7, 8 and 9 are graphs showing
the surface modified CNT composite normalized elastic modulus by central excitation
measurement. The resonant frequencies of the first, third, and fifth modes were about 200 Hz,
about 1200 Hz, and about 2500 Hz, respectively.
FIG. 10 is a graph showing the loss coefficient of the surface-modified CNT composite by central
excitation measurement.
[0038]
Since the adhesion between the pulp cellulose and the CNTs is improved by the surface
modification of the CNTs, mutual slippage is not recognized so much even by the DMA
measurement, and the elastic modulus is increased. The loss factor is improved in all processes.
Since the manufacturing conditions of the sample were made constant, the type of functional
group deviates from the optimum processing conditions, so the elastic modulus may be lowered
in this measurement. The normalized elastic modulus by the central excitation method is the
product number no. 1 is the best under this manufacturing condition, and is up about 30%. The
loss factor was substantially improved in all resonant modes. No1. The degradation of the
elastic modulus at 0-50 ° C. according to DMA measurement of the sample is about 4%, which is
far smaller than 10-40% of the diaphragm molded with the organic polymer adhesive.
[0039]
If the present invention is used, the ratio of both functionalized CNTs, carbon fibers and
nanodiamonds to those not attached with functional groups is appropriately selected to process
and shape a pulp cone paper diaphragm, mainly in the bass region. The characteristics of the
electroacoustic transducer in the frequency domain used can be controlled to form a high quality
audio system with low distortion corn pulp paper specific sound quality.
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[0040]
The graph which contrasts the temperature characteristic of the storage elastic modulus in the
case where the material of the manufactured corn paper is a pulp only, and in the case of the
composite material of CNT and a pulp material without surface modification.
The graph which shows the loss elastic modulus of each cone paper of FIG. The graph which
shows the loss coefficient of each corn paper of FIG. The resonance frequency characteristic
figure by the central excitation method measurement. The graph which shows the loss coefficient
by the measurement of FIG. Mechanical characteristics of surface-modified CNT-blended pulp
composite material by DMA measurement. The graph which shows surface-modified CNT
composite normalization elastic modulus 1st mode by central excitation method measurement.
The graph which shows surface-modified CNT composite normalization elastic modulus 3rd
mode by central excitation method measurement. The graph which shows surface-modified CNT
composite normalization elastic modulus 5th mode by central excitation method measurement.
The graph which shows the loss coefficient of surface-modified CNT composite by central
excitation measurement. The drawing substitute photograph which shows the surface structure
of the composite material of CNT and nano diamond. The drawing substitute photograph which
shows the surface structure of the aggregate of basic particles (20 nm) of nano diamond.
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