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JPH0984175

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DESCRIPTION JPH0984175
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
acoustic diaphragm used for speakers, headphones, microphones and the like, and in particular,
so-called vibration for acoustic using a so-called bacterial cellulose produced by a fermentation
method using bacteria. It relates to the improvement of the board.
[0002]
BACKGROUND OF THE INVENTION Cellulose produced by fermentation using bacteria
(hereinafter referred to as bacterial cellulose). Since films and sheets obtained by drying (d) have
a high elastic modulus and a large internal loss, their use as acoustic diaphragms is expected, and
some of them are put to practical use.
[0003]
So far, the above-mentioned bacterial cellulose is prepared, for example, by press-drying a
cellulose sheet produced by bacteria in a gel form or disaggregating the gel-like cellulose as
proposed by the present applicants in Japanese Patent Publication No. 7-36636. , It is processed
into the diaphragm for sound.
[0004]
However, when it is attempted to manufacture an acoustic diaphragm made of bacterial cellulose
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by the above-mentioned method, various difficulties are involved.
[0005]
For example, according to the former method, a diaphragm made of a gelled cellulose sheet has
an extremely high elastic modulus and a large internal loss, but the shape and size in producing
gelled cellulose are limited, There is also a restriction on the shape and size of the diaphragm to
be
Further, even if it is intended to obtain a diaphragm having a constant weight, it is difficult to
adjust the production of gelled cellulose according to this, and there is also a problem that the
production cost is high.
[0006]
On the other hand, the diaphragm produced by the latter method of disaggregating and gelling
gel-like cellulose is not subject to limitations in producing gel-like cellulose or constraints in
producing a diaphragm, but the elastic modulus is There is a disadvantage that it is greatly
reduced compared to the above method.
[0007]
Therefore, an object of the present invention is to provide an acoustic diaphragm having high
elasticity and large internal loss, which is a feature of bacterial cellulose, as well as high
productivity and free from the restriction of shape and size. The purpose is to provide the
manufacturing method.
[0008]
[Means for Solving the Problems] Up to now, the expression of high elastic modulus and large
internal loss of bacterial cellulose has been considered to be largely due to a specific threedimensional network structure constructed by bacteria.
[0009]
However, as a result of detailed investigations by the present inventors, it became clear that the
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shrinkage of cellulose fibrils, which occurs in the process of obtaining sheets and films from
gelled cellulose, particularly in the drying process, greatly affects the elastic modulus. .
That is, it was found that the elastic modulus of the sheet and film dried in a state of freely
shrinking gelled cellulose is low, while the elastic modulus of the sheet and film dried in a state of
constraining gelled cellulose is high.
[0010]
The present invention has been completed based on such findings, and is characterized in that a
coating layer containing cellulose produced by a fermentation method using bacteria is formed
on a substrate. .
[0011]
Further, the production method of the present invention is characterized in that a disaggregation
solution containing cellulose produced by a fermentation method using bacteria is applied onto a
base material by a spray application method to form an applied layer, and this is dried. It is
[0012]
Bacterial cellulose applied to the substrate adheres to the surface of the substrate, and is dried in
a state where cellulose fibrils are restrained in the drying process, and a bacterial cellulose layer
having high elastic modulus and large internal loss is formed on the surface. Very good
diaphragm can be obtained.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION The acoustic diaphragm of the present
invention is formed by forming a coating layer containing bacterial cellulose on a substrate.
[0014]
As a base material, for example, a cellulose-based material such as paper or a polymer film such
as a polyethylene terephthalate film can be used.
[0015]
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Here, when a cellulose-based material is used as the base material, bacterial cellulose is
constrained by hydrogen bonding or the like, but when a polymer film is used, the restraint by
the hydrogen bond can not be expected. There is a risk that the binding force will be insufficient.
Then, when using a polymer film for a base material, it is preferable to use an adhesive together.
The amount of the adhesive used is preferably 5% by weight or more in consideration of
adhesion, but if the amount of the adhesive is too large, the characteristics of bacterial cellulose
can not be sufficiently exhibited. The upper limit is 50% by weight.
Moreover, as an adhesive agent used at this time, the thing with the adhesiveness with both a
cellulose and a polymer film is selected and used.
[0016]
On the other hand, bacterial cellulose used in the coating layer is microbiologically produced by
cultivating certain kinds of bacteria under predetermined conditions, is composed of highly
crystalline α-cellulose, and is very The orientation is strong and extremely fine, with a thickness
of 0.02 to 0.05 μm.
[0017]
As bacteria producing such bacterial cellulose, acetic acid bacteria are representative, and for
example, Acetobacter aceti (Acetobacter aceti), Acetobacter xylinum (Acetobacter xylinum),
Acetobacter lancens (Acetobacter rancens), Zaltina Bentrikuri (Sarcina ventriculi), a bacteria
xyloides (Bacterium xyloides), etc. are mentioned.
[0018]
By culturing these acetic acid bacteria using a medium containing organic matter, inorganic salts
and the like, extremely high-purity cellulose is produced.
Since acetic acid bacteria are aerobic bacteria, supply of oxygen is necessary for their culture.
Therefore, as a method of producing bacterial cellulose, it is a gel-like substance having a certain
thickness at the interface between the culture medium and air. It is preferable to use a
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production method, aeration and agitation culture method, and the like.
[0019]
The thickness of the coating layer applied and formed on the substrate is arbitrary and may be
set according to the required characteristics etc., but even if the thickness of the coating layer is
too thick, the binding force is reduced. It is preferable to set the thickness to 25 μm or less
because the improvement of the characteristics can not be expected so much and the
manufacturing cost is increased.
If the thickness of the coating layer is too thin, it is preferable to set the thickness to 0.1 μm or
more because the characteristics such as high elastic modulus and large internal loss of bacterial
cellulose can not be sufficiently obtained.
[0020]
As a coating method of a coating layer, although a normal coating method is all employable, a
suitable coating state can be obtained by using a spray coating method.
[0021]
The acoustic diaphragm of the present invention realizes high elasticity and large internal loss
required for the diaphragm, and therefore is not limited to a speaker, and can be applied as a
diaphragm of acoustic devices such as headphones and microphones. is there.
[0022]
EXAMPLES Examples to which the present invention is applied will be described in detail based
on the specific experimental results.
[0023]
Preparation of bacterial cellulose 1 liter of culture medium having a composition comprising
sucrose 5 g / dl, yeast extract 0.5 g / dl, ammonium sulfate 0.5 g / dl, potassium hydrogen
phosphate 0.3 g / dl, and magnesium sulfate 0.005 g / dl It was embedded in a glass petri dish
having a diameter of 20 cm and a volume of 3 liters, and subjected to steam sterilization at 120
° C. for 20 minutes to prepare a culture solution.
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[0024]
In this culture broth, Acetobacter aceti was grown for three days at 30 ° C. in a test tube slope
agar medium 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. One platinum loop was inoculated with subsp. Xylinum (ATCC 10821)
and cultured at 30 ° C. for 30 days.
[0025]
Take out the white gel-like bacterial cellulose formed in the upper layer of the culture solution,
wash it with water, and immerse it in a 5% aqueous sodium hydroxide solution for 2 days at
room temperature to elute impurities mainly composed of bacteria and proteins derived from the
culture medium After washing, it was further washed with water to obtain gelled bacterial
cellulose.
[0026]
Difference in physical properties of gelled bacterial cellulose by constrained drying and free
drying Gelled cellulose (15 cm × 15 cm × 1 cm) on a Teflon resin plate is dried in a dryer at 90
° C. for about 48 hours, and the obtained sheet is In order to flatten it, it was immersed in water
for about 5 minutes, pressed between metal plates and pressed dry at 130 ° C. to obtain a
measurement sample.
(Free Drying) On the other hand, the same gel-like cellulose as used in free drying was
sandwiched between filter paper, water was squeezed out with a press, then sandwiched between
metal plates, and press dried at 130 ° C. to obtain a measurement sample.
(Constraint Drying) The elastic modulus of each of the obtained measurement samples was
measured by the vibration lead method, and it was 7.5 GPa for free drying, while it was 15.9 GPa
for constraint drying.
[0027]
From this result, it can be understood that the reason for the improvement of the elastic modulus
by the constraint drying is that when drying in a constrained state, tension is generated in the
cellulose fibrils by the drying shrinkage, and the cellulose fibrils form a plane orientation.
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[0028]
Preparation of defatted bacterial cellulose solution Gelled bacterial cellulose prepared in the
previous step was subjected to a maceration treatment for 15 minutes using a household mixer
to obtain a deflocculated bacterial cellulose having a concentration of 0.5%.
[0029]
Preparation and physical property measurement of bound dry film by disaggregated bacterial
cellulose From the previous examination, when disaggregated bacterial cellulose is dried on a
glass plate, hydrogen bonds are generated between the cellulose and the glass, and cellulose
fibrils are fixed and dried. It has been found that a constrained dry film can be obtained.
[0030]
Based on this finding, the disintegrating bacterial cellulose solution was poured into a glass petri
dish having a diameter of 15 cm to a depth of about 5 mm, and dried with a drier at 50 ° C. to
form a 10 μm thick film.
[0031]
Further, this film was immersed in water and dried without being restrained on a Teflon plate to
prepare a non-dried film, and physical properties were measured as a comparative sample.
The results are shown in Table 1.
[0032]
From the above results, it has been confirmed that, even with deaggregated cellulose in which the
specific three-dimensional structure constructed of bacteria has been destroyed, a high elastic
modulus can be obtained by constraining the cellulose fibrils.
[0033]
Example 1 Since a paper containing cellulose as a main component easily forms hydrogen bonds
with bacterial cellulose, it is expected to exhibit a high elastic modulus by applying this, as with a
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bound dry film using a glass plate. Ru.
This confirmation was performed using corn paper.
[0034]
The disaggregated bacterial cellulose solution prepared above was applied at a rate of 10 g / m 2
by a spray method onto a surface of corn paper mainly composed of kraft pulp obtained by a
normal papermaking process to prepare a diaphragm.
Physical properties of the obtained diaphragm were measured by a vibration lead method.
The results are shown in Table 2.
[0035]
From the above results, it is confirmed that the application of disintegrating bacterial cellulose
improves the elastic modulus by about 1.5 times, and the internal loss is also large.
[0036]
Therefore, using this coated cone paper and the non-coated cone paper, a full range speaker unit
having a diameter of 16 cm was made, and the characteristics were compared.
The results are shown in FIG.
[0037]
From FIG. 1, it was confirmed that the characteristic of the speaker using cone paper coated with
disaggregated bacterial cellulose is that the high frequency reproduction limit frequency is
shifted to the high frequency side, the reproduction frequency band is expanded, and the
characteristic is improved.
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[0038]
Example 2 A disaggregated bacterial cellulose solution was applied to both sides of a corn paper
mainly composed of kraft pulp used in Example 1 by a spray method at a rate of 10 g / m 2, and
its physical properties were measured by a vibration lead method. did.
The measurement results are shown in Table 3.
[0039]
As a result, it was confirmed that the elastic modulus was improved and the effect was also
effective in double-sided application.
[0040]
Preparation of Adhesive-Containing Disintegrated Biocellulose Liquid A polymeric material such
as polyethylene terephthalate (PET) is widely used as a diaphragm material.
[0041]
However, the polymer material does not form a hydrogen bond with cellulose, and the restraint
of cellulose fibrils by the hydrogen bond can not be expected, so that the improvement of the
elastic modulus can not be expected.
[0042]
In fact, the disintegrated bacterial cellulose solution prepared above was applied to a PET film
and tried to carry out, but the PET film and the bacterial cellulose did not adhere to each other,
and the compounding was difficult.
[0043]
Then, the adhesion between the PET film and the bacterial cellulose was examined, and it was
confirmed that the cellulose fibril can be restrained by using an adhesive (binder) for adhering
the cellulose fibril and the PET.
[0044]
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Table 4 shows a blending example of adhesive-containing disaggregated bacterial cellulose using
a polyester-based adhesive (trade name: Viroral MD 1330, manufactured by Toyobo Co., Ltd.)
having good adhesiveness to PET and cellulose.
[0045]
A surfactant (trade name Rapizole B-80, manufactured by Nippon Oil and Fats Co., Ltd.) was
added to improve the coating properties of the preparation.
[0046]
In addition, what is necessary is just to select the thing of adhesiveness with the material of a tobe-coated-article (base material), and an adhesive should just be selected, and it is not restricted
to what was used by this example.
[0047]
Example 3 The prepared adhesive-containing disaggregated bacterial cellulose solution was
applied to a PET film (thickness 25 μm) by a spray method, and then dried at 60 ° C. to form a
composite film.
[0048]
And the coating layer film thickness dependence of the longitudinal wave propagation speed in
this composite film was measured.
The results are shown in FIG.
[0049]
From the results shown in FIG. 2, it is also confirmed that the elastic modulus of the film is
improved by forming the coating layer also in the PET film.
In addition, the elastic modulus of bacterial cellulose determined from the composite law is as
high as 9.4 GPa, and it can be seen that surface orientation occurs in the cellulose fibrils and high
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elastic modulus is expressed.
[0050]
Then, the composite film (coated thickness 2.5 μm) and uncoated PET film (thickness 25 μm)
were vacuum molded at 180 ° C. to obtain a diaphragm for dome shape tweeter with a diameter
of 25 mm.
The frequency characteristic of the tweeter speaker using each diaphragm is shown in FIG.
[0051]
It can be seen from FIG. 3 that, in the speaker using the composite film coated with bacterial
cellulose as the diaphragm, the high frequency reproduction limit frequency is shifted to the high
frequency side, and the reproduction frequency band is expanded.
In addition, it can be seen that the characteristic peaks and dips are small, and the large internal
loss of bacterial cellulose is reflected.
[0052]
As apparent from the above description, it is possible to expand the reproduction frequency band
of the speaker and reduce the characteristic peak and dip by using the acoustic diaphragm of the
present invention coated with bacterial cellulose. Is possible.
[0053]
In addition, since the acoustic diaphragm of the present invention is manufactured by applying
bacterial cellulose, it has high productivity and is not restricted in shape or size.
[0054]
Brief description of the drawings
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[0055]
FIG. 1 is a characteristic diagram comparing the frequency characteristics of a 16 cm cone-type
full-range speaker using a diaphragm coated with bacterial cellulose and a diaphragm not coated
with bacterial cellulose.
[0056]
2 is a characteristic diagram showing the relationship between bacterial cellulose film thickness
and longitudinal wave propagation speed in a composite film obtained by applying bacterial
cellulose to a PET film.
[0057]
FIG. 3 is a characteristic diagram comparing the frequency characteristics of a 25 mm diameter
dome-shaped tweeter speaker using PET film coated with bacterial cellulose and uncoated PET
film.
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