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JPH1169483

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DESCRIPTION JPH1169483
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
diaphragm for a speaker, which comprises a resin foam sheet comprising a cell layer having a
very large number of fine cells with a cell diameter of 100 μm or less and a cell density of 10 9
cells / cm 3 or more By configuring the plate, the specific elastic modulus of the diaphragm is
increased, and the reproduction frequency range from the low range to the high range is
expanded.
[0002]
[0002] A speaker diaphragm (hereinafter referred to as a diaphragm). The resin foam sheet is
well known as JP-A-59-39199 and JP-A-57-24197. However, in the diaphragms of these prior
inventions, the specific elastic modulus (the elastic modulus divided by the specific gravity) is
low, and the improvement in the sound quality is insufficient. This is because by using the resin
foam sheet, although the specific gravity can be reduced significantly, the elastic modulus of the
resin foam sheet sharply decreases with the foaming, and the specific elastic modulus can not be
increased.
[0003]
Generally, when the specific elastic modulus of the material constituting the diaphragm is
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increased, the resonance frequency of the diaphragm is increased, and the piston movement area
(frequency) at the time of driving the diaphragm is expanded, thereby widening the reproduction
frequency band Are known. Therefore, the diaphragm made of the conventional resin foam sheet
has a drawback that the reproduction frequency range is not sufficiently wide.
[0004]
SUMMARY OF THE INVENTION It is therefore an object of the present invention to obtain a
diaphragm made of a resin foam sheet which has a wide reproduction frequency range and good
sound rise and elongation.
[0005]
This problem is solved by forming a diaphragm with a resin foam sheet having a cell layer with a
cell diameter of 100 μm or less and a cell density of 109 cells / cm 3 or more and a skin layer.
Furthermore, an inorganic layer such as beryllium may be provided on at least one side of the
resin foam sheet.
[0006]
BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in
detail below. FIG. 1 shows an example of the diaphragm of the present invention, and in the
figure, reference numeral 1 denotes a diaphragm. The diaphragm 1 is made of a resin foam
sheet. This foamed resin sheet has a three-layer structure comprising a central cell layer 2 and
skin layers 3 formed on both surfaces of the cell layer 2 and having a total thickness of 0.2 to 2
mm. It is.
[0007]
The cell layer 2 is a bubble layer in which extremely fine cells (bubbles) having a cell diameter of
100 μm or less are dispersed in an extremely large number of cell densities of 10 9 cells / cm 3
or more, and occupies 60 to 99% of the thickness of the entire sheet. . When the cell diameter of
the cell layer 2 exceeds 100 μm, the elastic modulus of the resin foam sheet is rapidly reduced,
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and the specific elastic modulus can not be increased. If the cell density is less than 10 9 cells /
cm 3, the number of cells as a whole is insufficient, making it difficult to reduce the weight (lower
the specific gravity), and it becomes impossible to increase the specific elastic modulus. The skin
layers 3 and 3 are substantially non-foamed resin layers, and the two layers together constitute 1
to 40% of the total thickness.
[0008]
Such a resin foam sheet is, for example, one obtained by foaming at least one of resins such as
polyethylene, polypropylene, polyurethane, polymethacrylamide, polyvinyl chloride, ABS resin,
AS resin, polycarbonate, liquid crystal polymer by various foaming means However, among these
resins, a resin foam sheet comprising polystyrene, polycarbonate, AS resin and liquid crystal
polymer having high elastic modulus is preferable.
[0009]
The production of such a diaphragm 1 is performed by, for example, an injection molding
method.
An injection molding machine having a screw in which a plasticizing screw portion and a mixing
screw portion are connected uniaxially is used, and a resin as a raw material is charged from a
hopper of the screw and heated and melted in the plasticizing screw portion. In addition, high
pressure liquefied carbon dioxide gas is pressed into the mixing screw portion, carbon dioxide
gas is brought into a supercritical state in the cylinder, and permeated into the molten resin. By
injecting a molten resin impregnated with carbon dioxide gas into a molding die having a cavity
of the diaphragm and cooling it, the carbon dioxide gas is vaporized and the resin is foamed to
obtain a desired diaphragm.
[0010]
In such a diaphragm 1, the cell layer 2 of the resin foam sheet forming the diaphragm 1 has a
cell diameter of 100 μm or less and a cell density of 109 cells / cm 3 or more. The specific
elastic modulus is increased because the specific gravity is reduced to about 30 to 50% of the
unfoamed resin. Moreover, bending rigidity becomes high compared with a non-foamed sheet.
Therefore, the resonance frequency of the diaphragm 1 is increased, the reproduction frequency
is extended to the high frequency range, and the rise and the extension of the sound are also
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improved.
[0011]
FIG. 2 shows another example of the diaphragm of the present invention, and the diaphragm 1 of
this example is characterized in that the inorganic layers 4 and 4 are provided on the surface of
the skin layers 3 and 3 of the resin foam sheet. It differs from the previous example. The
inorganic layer 4 is made of metal such as aluminum, beryllium, boron, titanium, nickel,
chromium and copper, crystalline carbon such as diamond and graphite, and metal oxide such as
beryllium oxide, magnesium oxide, alumina and silica. The thin layer having a thickness of 0.1 to
50 μm is formed by a thin film forming means such as a known vapor deposition method,
plating method, CVD method, sputtering method or the like.
[0012]
If the thickness of the inorganic layer 4 is less than 0.1 μm, it is too thin to obtain the effect of
the inorganic layer 4, and if it exceeds 50 μm, the specific gravity of the diaphragm 1 is too high
to improve the specific elastic modulus . The inorganic layer 4 may be formed only on one side of
the resin foam sheet.
[0013]
In the diaphragm 1 of this example, the presence of the inorganic layers 4 and 4 further
increases the specific elastic modulus, enabling reproduction to a higher tone range, and also
improving the expansion and the rise of the sound.
[0014]
Hereinafter, although an example is shown, the present invention is not limited to this example.
(Example 1) Pellets of liquid crystal polymer (product name "Novaculate E322" manufactured by
Mitsubishi Engineering Plastics Co., Ltd.) are put into the hopper of an injection molding machine
having a screw in which a plasticizing screw portion and a mixing screw portion are connected
uniaxially The plasticizing screw was heated at 280 ° C. to melt. Liquefied carbon dioxide gas
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was pressurized from the cylinder to 250 kg / cm 2 by a pressure pump and pressed into the
mixing screw portion. The introduced liquefied carbon dioxide gas was heated to 280 ° C. in a
cylinder, brought to a supercritical state, and impregnated into the molten liquid crystal polymer.
[0015]
The liquid crystal polymer in this state was injection molded in a molding die having a cavity of a
diaphragm. The temperature of the molding die was 100 ° C., and the cooling time was 60
seconds. Thus, a cone-shaped diaphragm having a diameter of 10 cm and a thickness of 0.5 mm
was obtained. The average thickness of the skin layer of this diaphragm was 20 μm, the cell
diameter of the cell layer was 10 μm on average, the cell density was 10 15 cells / cm 3, and the
specific gravity was 0.5. When this diaphragm was used, there were few noises, and the rising
and stretching of the sound were good, and reproduction up to the high range was possible.
[0016]
Further, beryllium was vacuum deposited to a thickness of 0.1 μm on both sides of the injectionmolded diaphragm to obtain a diaphragm provided with an inorganic layer. When this diaphragm
was used, reproduction to a higher frequency range was possible compared to the previous one,
and the extension and rise of the sound were even better.
[0017]
As described above, according to the diaphragm of the present invention, the specific elastic
modulus is increased, whereby the resonance frequency is increased, the reproduction frequency
range is extended to the high frequency range, and the sound is expanded. The effect is obtained
that the rise is excellent.
[0018]
Brief description of the drawings
[0019]
FIG. 1 is a schematic cross-sectional view showing an example of a diaphragm of the present
invention.
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[0020]
FIG. 2 is a schematic cross-sectional view showing another example of the diaphragm of the
present invention.
[0021]
Explanation of sign
[0022]
1 ... diaphragm, 2 ... cell layer, 3 ... skin layer, 4 ... inorganic layer
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