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JPWO2015011903

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DESCRIPTION JPWO2015011903
Abstract A loudspeaker diaphragm includes a base layer containing natural fibers, and a coating
layer formed of cellulose nanofibers. The coating layer is formed on at least one side of the
substrate layer. The modulus of elasticity of the cellulose nanofibers is larger than that of the
base layer, and the internal loss of the cellulose nanofibers is smaller than the internal loss of the
base layer.
Loudspeaker diaphragm, loudspeaker using the diaphragm, electronic device, mobile device
[0001]
The present invention relates to a loudspeaker diaphragm having a coating layer containing
nanofibers, a loudspeaker using the diaphragm, an electronic device, and a mobile device.
[0002]
A conventional loudspeaker diaphragm includes a base layer and a coating layer.
The base material layer is produced, for example, by papermaking of natural fibers. For example,
wood-based pulp can be used as the natural fiber.
[0003]
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1
The coating layer is formed on one side of the substrate layer. The coating layer contains
bacterial cellulose. Bacterial cellulose is produced by fermentation using bacteria. Examples of
bacteria producing cellulose include, for example, Diplodia natalensis, Actinomucor elegans,
Rhizopus oligosporus and the like.
[0004]
The coating layer is formed by applying a dispersion containing bacterial cellulose to the
substrate layer and drying.
[0005]
As prior art document information related to the invention of this application, for example,
Patent Document 1 is known.
[0006]
Unexamined-Japanese-Patent No. 5-7393
[0007]
The loudspeaker diaphragm of the present invention has a base layer containing natural fibers
and a coating layer composed of cellulose nanofibers.
The coating layer is formed on at least one side of the substrate layer.
The modulus of elasticity of the cellulose nanofibers is larger than that of the base layer, and the
internal loss of the cellulose nanofibers is smaller than the internal loss of the base layer.
[0008]
As described above, the loudspeaker diaphragm of the present invention can be made to have
high elasticity and to be able to suppress the reduction of internal loss.
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2
Furthermore, the diaphragm for loudspeakers of the present invention can increase the adhesion
between the base layer and the coating layer. As a result, the vibration of the voice coil coupled
to the diaphragm is well transmitted to the diaphragm.
[0009]
FIG. 1A is a view showing an image of a cross section of a loudspeaker diaphragm according to
an embodiment of the present invention observed by a scanning electron microscope (SEM). FIG.
1B is a schematic view showing a part of FIG. 1A. FIG. 2 is a diagram showing sound speed
characteristics of the loudspeaker diaphragm according to the embodiment of the present
invention. FIG. 3 is a diagram showing the internal loss of the loudspeaker diaphragm according
to the embodiment of the present invention. FIG. 4 is a cross-sectional view of another
loudspeaker diaphragm according to an embodiment of the present invention. FIG. 5 is a crosssectional view of a loudspeaker according to an embodiment of the present invention. FIG. 6 is a
conceptual view of the electronic device according to the embodiment of the present invention.
FIG. 7 is a conceptual view of a mobile device according to an embodiment of the present
invention.
[0010]
Prior to the description of the embodiments of the present invention, problems in the
conventional loudspeaker diaphragm will be described.
[0011]
The material used for the loudspeaker diaphragm preferably has a large elastic modulus and a
large internal loss.
Therefore, the bacterial cellulose used in the conventional diaphragm has both the elastic
modulus and the internal loss greater than the material of the base layer.
[0012]
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However, bacterial cellulose, in which both the elastic modulus and the internal loss are larger
than the material of the base layer, has a low flow rate. Therefore, conventional bacterial
cellulose is associated with anxiety in stable supply. Also, conventional bacterial cellulose is
expensive. As a result, conventional bacterial cellulose has good characteristics as a diaphragm,
but is not a material that can be used commercially.
[0013]
Therefore, the present invention solves this problem, and provides a low-cost loudspeaker
diaphragm for loudspeakers in which the decrease in internal loss is suppressed while enhancing
the elasticity.
[0014]
Hereinafter, the loudspeaker diaphragm according to the present embodiment will be described
with reference to the drawings.
FIGS. 1A and 1B are each a schematic view showing an SEM observation image obtained by
enlarging a cross section of a loudspeaker diaphragm 11 (hereinafter, the diaphragm 11)
according to the present embodiment, and a part thereof. In addition, when observing the whole
of the thickness direction of the diaphragm 11 by a SEM observation image, it is preferable that
the magnification of a SEM observation image is about 100 times. Moreover, when observing the
coating layer 13 by a SEM image, it is preferable that the magnification of a SEM observation
image is about 300 times.
[0015]
The diaphragm 11 has a base layer 12 and a coating layer 13. The base layer 12 contains natural
fibers 22. The main component having the highest proportion of the material constituting the
base layer 12 is the natural fiber 22. Natural fibers 22 used for the base layer 12 include
cellulose. For example, wood pulp or non-wood pulp can be used as the natural fiber 22.
Alternatively, wood pulp and non-wood pulp may be used in combination. In addition, when
using non-wood pulp for the base material layer 12, it is preferable to use a bamboo fiber.
Bamboo has a short growing period, so it can control the depletion of forest resources. Therefore,
the diaphragm 11 can contribute to the suppression of the destruction of the global environment.
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[0016]
The coating layer 13 is formed on at least one side of the base layer 12. The main component
having the highest proportion of the material constituting the coating layer 13 is cellulose
nanofibers 23. The cellulose nanofibers 23 are nano level fibers containing cellulose. As
described above, since both the base layer 12 and the coating layer 13 contain cellulose, the base
layer 12 and the coating layer 13 firmly adhere to each other by the hydrogen bond between the
celluloses and the anchoring effect by the entanglement. The fiber diameter of the cellulose
nanofibers 23 is preferably in the range of about 5 nm or more and about 200 nm or less. In
addition, the said fiber diameter is the value observed by SEM.
[0017]
However, the cellulose nanofibers 23 have an elastic modulus greater than the elastic modulus of
the natural fiber 22, that is, the elastic modulus of the base layer 12. Furthermore, the cellulose
nanofibers 23 have an internal loss smaller than the internal loss of the natural fiber 22, that is,
the internal loss of the base layer 12. That is, the elastic modulus of the coating layer 13 is larger
than the elastic modulus of the base layer 12. Further, the internal loss of the coating layer 13 is
smaller than the internal loss of the base layer 12.
[0018]
Since the elastic modulus of cellulose nanofibers is high, the rigidity of the coating layer 13 can
be high even if the thickness of the coating layer 13 is thin. Therefore, the thickness of the
coating layer 13 can be reduced. As a result, the coating layer 13 can suppress the reduction of
the internal loss of the diaphragm 11.
[0019]
Also, the diaphragm 11 is provided using relatively cheap cellulose nanofibers. Therefore, the
diaphragm 11 has high elasticity, large internal loss, and low cost.
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[0020]
The coating layer 13 is preferably formed on the front side of the base layer 12, which is the
opposite surface on which the magnetic circuit of the loudspeaker is disposed when the
diaphragm 11 is incorporated in the loudspeaker. With this configuration, the coating layer 13 is
formed on the front surface side of the base material layer 12, so that the front surface of the
diaphragm 11 is glossy. Therefore, the front surface of the diaphragm 11 is very beautiful even if
the laminate film or the like is not attached to the front surface of the diaphragm 11, for
example. As a result, the diaphragm 11 is light and has a large sound velocity as compared with
the case where the laminate film is attached.
[0021]
Furthermore, the density of the cellulose nanofibers 23 in the coating layer 13 is very high. That
is, in the coating layer 13, the gap between the cellulose nanofibers 23 is very small. With this
configuration, the coating layer 13 suppresses the penetration of water droplets and the like into
the base layer 12. Therefore, it is not necessary to waterproof the diaphragm 11. Of course, the
diaphragm 11 may be waterproofed. In this case, the thickness of the waterproof film of the
diaphragm 11 can be suppressed. As a result, the diaphragm 11 is generally lighter and has a
higher sound velocity than when waterproofing is applied.
[0022]
The position where the coating layer 13 is formed is not limited to the front side of the base layer
12. For example, the coating layer 13 may be formed on the back side of the base layer 12.
Furthermore, the coating layer 13 may be formed on both the front side and the rear side of the
base layer 12. However, by arranging at least on the front side of the base layer 12, the abovedescribed waterproof effect is exhibited.
[0023]
Hereinafter, the diaphragm 11 will be described in more detail. FIG. 2 is a diagram showing the
sound velocity characteristic of the diaphragm 11. FIG. 3 is a diagram showing the internal loss
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of the diaphragm 11. The horizontal axis in FIGS. 2 and 3 is the ratio of the thickness of the
coating layer 13 to the total thickness of the diaphragm 11. On the other hand, the vertical axis
in FIG. 2 is the value of the sound velocity of the diaphragm 11. Further, the vertical axis in FIG. 3
is the value of the internal loss of the diaphragm 11. The total thickness of the diaphragm 11 and
the thickness of the coating layer 13 are measured by observing the SEM image. The total
thickness of the diaphragm 11 is measured by setting the magnification of the SEM to 100 times.
On the other hand, the thickness of the coating layer 13 is measured by setting the magnification
of SEM to 300 times.
[0024]
As shown in FIG. 2, when the thickness of the coating layer 13 is 2% or more with respect to the
total thickness of the diaphragm 11, the increase in the velocity of sound of the diaphragm 11
sharply decreases. Furthermore, when the thickness of the coating layer 13 is 3.5% or more with
respect to the total thickness of the diaphragm 11, the increase in the speed of sound of the
diaphragm 11 is substantially saturated and stabilized. Although there is no actual measurement
data of the thickness of the coating layer 13 with respect to the total thickness of the diaphragm
11 corresponding to the above-mentioned numerical value 3.5%, the above-mentioned numerical
value 3.5% is derived from other actual measurement data shown in FIG. It is
[0025]
On the other hand, as shown in FIG. 3, when the thickness of the coating layer 13 is 8% or less of
the total thickness of the diaphragm 11, the decrease in internal loss of the diaphragm 11 is
small. In particular, when the thickness of the coating layer 13 is 6% or less of the total thickness
of the diaphragm 11, the change in the internal loss of the diaphragm 11 is very small.
Therefore, the thickness of the coating layer 13 is preferably 2% or more and 8% or less with
respect to the thickness of the diaphragm 11. By this configuration, the elastic modulus and the
sound velocity of the diaphragm 11 can be increased, and the decrease in internal loss of the
diaphragm 11 can be suppressed. In the present embodiment, the coating layer 13 is defined by
the thickness ratio, but is not limited thereto. For example, the weight ratio of the coating layer
13 to the total weight of the diaphragm 11 can also be defined. In this case, the weight of the
coating layer 13 is preferably 4% by weight or more and 8% by weight or less based on the total
weight of the diaphragm 11. Alternatively, the coating layer 13 may be defined by a specific
gravity value, an area density, or the like. In any of these, the ranges of specific gravity and
surface density can be calculated from the values of the thickness ratio and weight ratio.
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[0026]
The thickness of the coating layer 13 is more preferably 3.5% or more and 6% or less of the
thickness of the diaphragm 11. By this configuration, the elastic modulus and the sound speed of
the diaphragm 11 can be further increased, and the reduction of the internal loss of the
diaphragm 11 can be further suppressed.
[0027]
In this case, the internal loss of the cellulose nanofibers 23 is preferably 70% or more of the
internal loss of the natural fibers 22. With this configuration, even if the internal loss of the
cellulose nanofibers 23 is smaller than the internal loss of the natural fibers 22, it can be
suppressed that the internal loss of the diaphragm 11 becomes small.
[0028]
For example, it is preferable that nata de coco powder, bamboo nano-fibers refined to nano level,
or the like be used as the cellulose nanofibers 23. Table 1 below shows values of elastic modulus
and internal loss of nata de coco flour, bamboo nanofibers, and common wood-based natural
pulps.
[0029]
[0030]
Natade coco powder is a biocellulose based nanofiber.
The nata de coco powder can be easily obtained, for example, by drying and crushing gelled nata
de coco. Nata de Coco is also used as a food and is easy to obtain. Therefore, nata de coco
powder can be obtained, for example, at about 1 yen / g. On the other hand, the price of bacterial
cellulose having a high internal loss is about 5 to 10 times the price of nata de coco powder
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8
cellulose nanofibers. Thus, nata de coco powder cellulose nanofibers are very cheap compared to
other bacterial celluloses.
[0031]
In addition, bamboo, which is a raw material of bamboo fiber refined to the nano level, is
inhabited worldwide, and its growth is very fast. Therefore, bamboo fiber is also easy to obtain.
Furthermore, the process of refining bamboo fibers to the nano level can divert most of the
process of microfibrillating existing bamboo fibers. Therefore, introduction of new equipment is
suppressed. Moreover, unlike bacterial cellulose, the cellulose nanofibers 23 do not require
culture of bacteria and the like. Therefore, the cellulose nanofibers 23 have much higher
productivity of bamboo fibers refined to the nano level than bacterial cellulose. As a result,
bamboo fiber refined to the nano level is much cheaper than bacterial cellulose.
[0032]
Next, a method of manufacturing the diaphragm 11 will be described. The base layer 12 is
formed by papermaking. The base layer 12 is produced by depositing a mixture of beaten natural
fibers 22 and water on a net. Thereafter, cellulose nanofibers 23 are applied to the deposit
constituting the substrate layer 12. The cellulose nanofibers 23 are mixed with water in advance.
Thereafter, the sediment and the cellulose nanofibers 23 are dehydrated by suction or the like.
Thereafter, the laminate of dewatered natural fibers and cellulose nanofibers 23 is dried and
shaped by heating and pressing. And the diaphragm 11 in which the coating layer 13 was
formed on the base material layer 12 is completed according to the above process.
[0033]
In this case, the cellulose nanofibers 23 are applied in a wet state of the deposit. Therefore, the
hydrogen bond of the cellulose of the cellulose nanofiber 23 and the cellulose of the natural fiber
22 can be enlarged. Therefore, the elastic modulus of the diaphragm 11 can be increased.
[0034]
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9
In addition, although the coating layer 13 is formed by apply | coating the cellulose nanofiber 23
to the non-dehydrated deposit, it is not restricted to this. For example, the coating layer 13 may
apply a liquid in which the cellulose nanofibers 23 are dispersed in the dehydrated deposit. In
this case, the deposit contains water since it is only dehydrated. Therefore, also in this case,
hydrogen bonding between the cellulose of cellulose nanofibers and the cellulose of natural
fibers can be increased.
[0035]
Alternatively, the base material layer 12 may be formed by dewatering only the deposit, and by
heating and pressing only the dewatered deposit in advance. In this case, the cellulose nanofibers
23 are applied to the base layer 12 which has been dried and shaped. Then, the coated cellulose
nanofibers 23 are dried. In this case, since the base material layer 12 is dry, breakage of the base
material layer 12 and the like hardly occur, and the productivity is good.
[0036]
FIG. 4 is a cross-sectional view of another diaphragm 11A in the embodiment of the present
invention. The coating layer 13 includes a first coating portion 13A and a second coating portion
13B. The second coating portion 13B is thicker than the first coating portion 13A. And it is
preferable to form the 2nd coating part 13B in the location which division resonance produces
with diaphragm 11A. As a result, in the second coating portion 13B, the strength of the
diaphragm 11A is increased, so that the occurrence of split resonance can be suppressed.
Therefore, it is possible to suppress the occurrence of peaks and dips in the sound pressure
frequency characteristics of the diaphragm 11A.
[0037]
FIG. 5 is a cross-sectional view of the loudspeaker 51 in the present embodiment. The
loudspeaker 51 includes a frame 52, a magnetic circuit 53 including a magnetic gap 53A, a voice
coil 54, and a diaphragm 11. The magnetic circuit 53 is coupled to the back side of the central
portion of the frame 52 and fixed to the frame 52. The outer peripheral portion of the diaphragm
11 is connected to the outer peripheral portion of the frame 52. The outer peripheral portion of
the diaphragm 11 and the outer peripheral portion of the frame may be connected via an edge.
The voice coil 54 includes a bobbin, and has a first end coupled to the central portion of the
10-05-2019
10
diaphragm 11 and a second end inserted into the magnetic gap 53A.
[0038]
As described above, since the elasticity and sound velocity of the diaphragm 11 are large, the
frequency range in which the loudspeaker 51 can reproduce is wide, and the sound pressure
level is also large. Further, since the reduction of the internal loss of the diaphragm 11 is
suppressed, the loudspeaker 51 has a sound pressure frequency characteristic in which the
occurrence of peaks and dips is suppressed. Furthermore, since the price of the diaphragm 11 is
low, the loudspeaker 51 is also low.
[0039]
Preferably, the coating layer 13 is formed on the inner peripheral portion including the central
portion of the diaphragm 11 to which the first end of the voice coil 54 is coupled. With this
configuration, the adhesion between the base material layer 12 and the coating layer 13 is large
at the location where the voice coil 54 is joined due to the hydrogen bond between the celluloses
and the anchor effect due to the entanglement. Therefore, the vibration of the voice coil 54 is
well transmitted to the diaphragm 11. As a result, the sound pressure output from the
loudspeaker 51 becomes large.
[0040]
When the second coating portion 13B is formed on the diaphragm 11, the first end of the voice
coil 54 is preferably coupled to the second coating portion 13B. Note that the first end of the
voice coil 54 is not limited to the configuration to be coupled to the second coating portion 13B,
but the surface opposite to the surface on which the second coating portion 13B is formed in the
range where the second coating portion 13B is formed It may be bonded to the layer 12). By
forming the second coating portion 13B on the diaphragm 11, the thickness of the diaphragm 11
to which the first end of the voice coil 54 is coupled is increased, so that the strength of the
coupled portion of the diaphragm 11 and the voice coil 54 is obtained. Becomes larger.
Therefore, the vibration of the voice coil 54 is well transmitted to the diaphragm 11. As a result,
the sound pressure output from the loudspeaker 51 becomes large. Furthermore, the coating
layer 13 is preferably formed on the front side of the diaphragm 11. With this configuration, the
appearance of the loudspeaker 51 is beautiful.
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11
[0041]
The peak and the dip can be further suppressed by using the diaphragm 11A instead of the
diaphragm 11.
[0042]
FIG. 6 is a conceptual view of the electronic device 101 according to the present embodiment.
The electronic device 101 includes a housing 102, a signal processing unit 103, and a
loudspeaker 51. The electronic device 101 is, for example, a component stereo.
[0043]
The signal processing unit 103 is housed in the housing 102. The signal processing unit 103
processes an audio signal. The signal processing unit 103 includes an amplification unit.
Furthermore, the signal processing unit 103 may include a sound source unit. In this case, the
sound source unit may include, for example, one or two or more of a CD player, an MP3 player, a
radio receiver, and the like.
[0044]
The electronic device 101 is not limited to component stereo. The electronic device 101 may be,
for example, a video device such as a television, a mobile phone or a smart phone, and further a
personal computer or a tablet terminal. In these cases, the electronic device 101 further includes
a display unit (not shown). In this case, in addition to the processing of the audio signal, the
signal processing unit 103 also performs processing of the video signal.
[0045]
Loudspeaker 51 is fixed to housing 102. For example, the frame 52 shown in FIG. 5 is fixed to
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12
the housing 102 by an adhesive, a screw or the like. The loudspeaker 51 is fixed to the housing
102 by this configuration. The housing 102 may be separated into a portion for housing the
signal processing unit 103 and a loudspeaker box for fixing the loudspeaker 51. The housing
102 may be integrated, and may have a structure in which the signal processing unit 103 is
housed and the loudspeaker 51 is fixed.
[0046]
The output side of the signal processing unit 103 is electrically connected to the loudspeaker 51.
In this case, the output side of the signal processing unit 103 is electrically connected to the
voice coil 54 shown in FIG. Therefore, the signal processing unit 103 supplies an audio signal to
the voice coil 54.
[0047]
In particular, in the electronic device 101, as shown in FIG. 1, the coating layer 13 is preferably
formed on the front surface of the diaphragm 11. With this configuration, even when the
diaphragm 11 is exposed from the housing 102, the diaphragm 11 can be prevented from
impairing the appearance of the electronic device 101.
[0048]
FIG. 7 is a conceptual view of the mobile device 111 in the present embodiment. The mobile
device 111 includes a main body unit 112, a drive unit 113, a signal processing unit 114, and a
loudspeaker 51. The mobile device 111 is not limited to a car. The mobile device 111 may be, for
example, a train, a motorcycle, a ship, or a vehicle for various operations.
[0049]
The drive unit 113 is mounted on the main body unit 112. The drive unit 113 may include, for
example, an engine, a motor, a tire, and the like. Then, the main body portion 112 can be moved
by the drive portion 113.
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13
[0050]
The signal processing unit 114 is housed in the main body unit 112. Further, the loudspeaker 51
is fixed to the main body 112. In this case, the frame 52 shown in FIG. 5 is fixed to the main body
112 by, for example, an adhesive or a screw. Therefore, the loudspeaker 51 is fixed to the main
body 112. Mobile device 111 is, for example, an automobile. And the main-body part 112 may
also include door 112A, motor room (or engine room) 112B, and side mirror part 112C. The
loudspeaker 51 may be accommodated in any of the door 112A, the motor room 112B, and the
side mirror portion 112C.
[0051]
The output side of the signal processing unit 114 is electrically connected to the loudspeaker 51.
In this case, the output side of the signal processing unit 114 is electrically connected to the
voice coil shown in FIG. Note that the signal processing unit 114 may constitute a part of a car
navigation system or a car audio. Further, the loudspeaker 51 may constitute a part of a car
navigation system or a car audio.
[0052]
In particular, in the movable body device 111, it is preferable that the coating layer 13 be formed
on the front side of the diaphragm 11 as shown in FIG. With this configuration, even when the
diaphragm 11 is exposed, it is possible to prevent the appearance of the inside of the mobile
device 111 from being impaired by the diaphragm 11.
[0053]
When the loudspeaker 51 is housed in the door 112A, the motor room 112B, the side mirror
portion 112C or the like, the loudspeaker 51 is likely to come in contact with rainwater.
Therefore, as shown in FIG. 1, the coating layer 13 is preferably formed on the front side of the
diaphragm 11. With this configuration, the coating layer 13 suppresses the entry of rainwater
into the interior of the loudspeaker 51.
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[0054]
The diaphragm for loudspeakers according to the present invention has the effects of high
elasticity and large internal loss, and is useful when used for loudspeakers mounted on electronic
devices, mobile devices, and the like.
[0055]
DESCRIPTION OF SYMBOLS 11 diaphragm 11A diaphragm 12 base material layer 13 coating
layer 13A 1st coating part 13B 2nd coating part 22 natural fiber 23 cellulose nanofiber 51
loudspeaker 52 frame 53 magnetic circuit 53A magnetic gap 54 voice coil 101 electronic device
102 case 103 Signal processing unit 111 Mobile unit 112 Main unit 112A Door 112B Motor
room 112C Side mirror unit 113 Drive unit 114 Signal processing unit
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