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The present invention relates to an acoustic diaphragm, which comprises an alumina ceramic
fiber, a binder not having a fiber structure, or a material further containing a metal oxide, and
has a high propagation speed. Also, it is an object of the present invention to provide an acoustic
diaphragm in which the internal loss is also large and which has extremely desirable
characteristics as an acoustic diaphragm. For example, an acoustic diaphragm formed by mixing
and making alumina fibers and fibers such as natural pulp has been proposed (Japanese Patent
Application Laid-Open No. 50-71318). However, although the acoustic diaphragm according to
this proposal contains 30% or more of organic fibers such as natural fibers as a binder and is
excellent in moldability, a portion without binder fibers, particularly a cross chain portion
between ceramic fibers In this case, most of the coupling is made, so that not only sufficient
homogeneous strength can not be obtained, but also frictional noise is generated in the noncoupled part, which is also a cause of an increase in distortion characteristics of the speaker. The
present invention eliminates the above-mentioned drawbacks and will be described in the
following. For example, a water-soluble organic substance is prepared by dispersing 100 parts of
a ceramic fiber (fiber diameter 0.5 to 4 μm 1 fiber length 0.1 to 10 crIL) containing 55 to 95%
of alumina in water and forming the same in water. A binder not having a fiber structure, for
example, about 50 to 100 parts of a water-soluble acrylamide resin (anionic resin with a
molecular weight of about 800,000 to 1,000,000), particularly about 80 parts, is added and
sufficiently stirred. Next, a sulfate is added to the above mixture to adjust to pH 4 to 6, and to
this, about 1 to 10 parts of a sizing agent is added and stirred, and immediately thereafter, it is
formed into a sheet with a desired diaphragm shape. Then, the wet ceramic fiber mat removed
from the papermaking net is heat-pressed and dried under conditions of a mold temperature of
140 to 200 ° C. and a pressing time of 3 to 15 minutes to constitute an acoustic diaphragm
according to the present invention. As described above, the acoustic diaphragm made of the
material including the alumina ceramic fiber and the binder having no fiber structure has a large
propagation speed desired for the characteristics of the alumina ceramic fiber as the diaphragm,
and Since those used as binders do not have a fiber structure, they do not cause defects when
there is little bonding in the cross section of aluminous ceramic fibers, and they have sufficiently
homogeneous strength as a whole. And increase the distortion characteristics of the speaker. And
the acoustic diaphragm of the said Example has a propagation velocity of 10-2 of the acoustic
diaphragm which used the natural bulb | bulb.
In contrast to OK n ∼ S, its propagation velocity is high at 2.2 to 2.6 K m / s, and the internal
loss (tan δ) of alumina bulk is 0.002 to O: 005. , 002 sufficiently large, and further, as shown by
the solid line in the drawing, the frequency characteristic of the speaker using this acoustic
diaphragm, the high frequency band limit frequency is 3.5 K Hz, while the paper pulp is used As
the frequency characteristic of the speaker is indicated by an alternate long and short dash line,
the upper limit frequency thereof is 2.6 KHz, and the acoustic diaphragm of the above
embodiment shows an excellent feature. Further, this acoustic diaphragm is flame-retardant, and
can be manufactured by the same manufacturing process as in the case of using a natural bulb,
and is also rich in formability and mass productivity. In the above embodiment, the alumina
ceramic fiber and the binder not having a fiber structure are used as the essential components of
the acoustic diaphragm. However, it is preferable to contain a metal oxide in the acoustic
vibration of preferable characteristics. A board is obtained. That is, the acoustic diaphragm
obtained in the above example is immersed, for example, in alumina sol (30% aqueous solution of
alumina) to impregnate the acoustic diaphragm material with alumina of not more than 30% by
weight, and then dried at about 100 to 160 ° C. By doing this, it is possible to obtain an acoustic
diaphragm excellent in characteristics such as a propagation velocity of 2.5 to 3.0 Km / s and an
internal loss of 0.01. As described above, since the acoustic diaphragm according to the present
invention is made of a material containing an alumina ceramic fiber and a binder having no fiber
structure, both the propagation speed and the internal loss are large, and the alumina ceramic
fiber is also Since the binder for bonding the fibers is not of fiber structure, it is possible to
obtain almost no bonding in the aluminous ceramic fibers, and to obtain homogeneous strength,
sufficient rigidity, and strain. The characteristics of the propagation velocity and the internal loss
can be balanced by adding the metal oxide in addition to the above-mentioned components
without increasing the characteristics and increasing the high frequency limit frequency. It has
features such as more preferable.
Brief description of the drawings
Drawing is a grab of the frequency characteristic of the speaker using the acoustic diaphragm of
this invention.
Patent Assignee Nippon Victor Co., Ltd. Atsushi Udaka 5, 5
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