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The present invention relates to improvement of a diaphragm for an electroacoustic transducer,
and more particularly to a diaphragm made of a material having high rigidity and which is very
easy to form. In recent years, in the diaphragm for electro-acoustic transducer, one using carbon
fiber as one member of the diaphragm-constituting material has been considered and put to
practical use for the purpose of mainly increasing the rigidity. An example of this type of
diaphragm is (1) after mixing the carbon fiber and the valve fiber, then forming the diaphragm
using a phenolic resin or the like (2) mixing the carbon fiber with a thermoplastic resin such as
polypropylene resin to obtain a sheet A thermosetting resin is impregnated into a woven or nonwoven fabric of non-woven or non-woven diaphragm (3) carbon fiber which is molded and
vacuum-molded the above-mentioned material or injection-molded the above material into a
prepreg, which is press molded Vibrating plates and the like have been put to practical use.
However, 'The above-mentioned conventional swing! Jl plates have various disadvantages. For
example, in (1), the high elastic properties characteristic of carbon fibers are not fully utilized,
and the Young's modulus is at most 5 × 1 even if it is mixed with δθ% t% carbon fiber. This is
the Young's modulus relative to the mixing ratio of carbon fibers and pulp fibers. This is because
peak values occur and the mixing ratio of carbon fibers is limited. In the case of (2), the amount
of carbon fiber mixed in is limited by the fluidity of the mixture at the time of sheet formation
and the size of the discharge nozzle. For example, in a 0.3 to 0.5 mm thick sheet, the mixing
amount of carbon fibers is at most 20 wt%. Moreover, the said mixing amount also receives the
restriction ¦ limiting from a vacuum forming process. On the other hand, in injection molding, the
mixing amount is at most 15 wt%. Therefore, the rigidity of the diaphragm can not be sufficiently
reduced. Furthermore, (3) gives a rigid diaphragm in comparison with the above two examples,
but carbon fiber is used to form a flat cloth once textured as a woven fabric into a cone or dome
shape. Because it is necessary to shape using the 1-m eye gap which can not expect the
expansion and contraction of itself, because it becomes possible to form through the various
processes such as preforming! ! The cost is very high, and it is difficult to form a diaphragm
having a complicated shape such as a shape with a large apex angle or integral formation of a
corrugation rib. The present invention is a diaphragm for an electroacoustic transducer which is
obtained by mixing whiskers in a composite material of a layered mineral, a thermosetting resin
and a carbon fiber in which a curing agent or a curing accelerator is adsorbed between layers
and mixing them with heat. For example, montmorillonite (A t 2 o 3 4 S i 20-n H 2 O, aka
bentonite), which is a kind of hydrous aluminum silicate, is a layered mineral in which the curing
agent or curing accelerator used in the diaphragm of the present invention is adsorbed between
layers. The solution is deposited ( C. for several hours) in a solution of the
montmorillonite in a curing agent or curing accelerator dissolved in a suitable solvent.
As a result, a curing agent or a curing accelerator is adsorbed between the silicate layers of
montmorillonite. The solution is washed and then dried to obtain a complex with a curing agent
or curing accelerator. Next, an embodiment of the diaphragm according to the present invention
using the composite will be described. [Examples] Diamino diphenylmethane adsorbed as a
complex curing agent 10 parts Epoxy resin monomer (trade name araldite 6071) 30 parts Curing
agent (diaminodiphenylsulfone) 4.4 parts Releasing agent (zinc stearate) 1 part Carbon fiber
(polyacrylonitrile-based carbon fiber average length 0.35 mm) 45 parts The above composition is
uniformly mixed by stirring under heating (85 ° C.), and then cooled and pulverized to a
powdery state The composite material of Silicon carbide whisker (m! In this composite material)
tttIO, 2-0, 5 H, m 2) lo parts are uniformly mixed and pressed with a mold of a predetermined
shape at a temperature of 160 ° C., a 585 kg / em brace, for a molding time of 10 minutes to
form a cone-shaped diaphragm Obtained. As a conventional diaphragm using the diaphragm
obtained in the above embodiment and carbon fiber [Conventional Example 1] A diaphragm
comprising a kraft valve δOut%, carbon fibers 35 nt%, and phenol resin 15 wt%. [Conventional
Example 2] A diaphragm formed by mixing 15 vt% of carbon fiber with polypropylene resin and
injection molding. As is apparent from the table of which physical properties (density 、, Young's
modulus E) are measured, the diaphragm according to the present invention has an extremely
high E / ρ. As a factor that the Young's modulus of the diaphragm of the invention of the
present invention increases remarkably, the montmorillonite-epoxy complex disperses so as to
fill the space of carbon fiber and whisker, and the epoxy polymer and montmorillonite which got
into the interlayer of montmorillonite become strong A bonded blend polymer is formed, and the
blend polymer is organized into a three-dimensional network so as to interweave carbon fibers
and whiskers, and the interstices between carbon fibers having a large fiber diameter are small
diameter whiskers of fiber diameter. Seems to be due to the distributed arrangement. In the
diaphragm of the present invention, the epoxy resin once melts in the press mold and becomes
low in viscosity and flows, but the curing agent or curing accelerator adsorbed between the
layers of montmorillonite up to a certain temperature (150 ° C.) Conventional epoxy resin,
hardener mixture that could be obtained with a diaphragm with a high dimensional accuracy,
even if it is a mold of complex shape as a result of maintaining a low viscosity fluid state as it
does not leach out In the case of molding the body, since curing starts immediately, only a short
time of molding can be performed, and it is difficult to fill the entire mold, and injection molding
and the like can not be performed. According to this, these drawbacks can be eliminated and the
diaphragm can be formed by injection molding.
In the above embodiment, the case where silicon carbide whiskers are used as the whiskers has
been described, but other whiskers usable in the present invention may be made of one or more
silkworms such as potassium titanate whiskers, silicon nitride whiskers and alumina whiskers. It
can be used together. Also, as a hard water accelerator to be adsorbed to a layered mineral, for
example, ethyl methyl imidazole can be used in combination with phthalic anhydride (hardening
agent). As described above, the present invention is mainly composed of a composite material
consisting of a layered mineral, a thermosetting resin monomer, and carbon fibers in which a
curing agent or a curing accelerator is adsorbed and a whisker as a main material, and a mixture
of the above materials A diaphragm for an electroacoustic transducer, characterized in that it is
formed by heating, and the rigidity and weight of the diaphragm can be increased, so that a
speaker having good frequency characteristics can be provided. Although the present invention
has been described as applied to a cone-shaped diaphragm, it is of course applicable to a domeshaped diaphragm and further to a center dome radiator. Patent Applicant Onkyo Co., Ltd.