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This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
complete, reliable or fit for specific purposes. Critical decisions, such as commercially relevant or
financial decisions, should not be based on machine-translation output.
The present invention relates to a molding method for obtaining a conical vibration & from
thermoplastic resins or their foams. Conventionally, thermoplastic resins such as polystyrene. In
order to form a cone-shaped diaphragm from polypropylene, polystyrene, etc. or a foam thereof,
after forming the thermoplastic resin or foam thereof into a film, the diaphragm is formed by
vacuum, pressure or mold press. Method of molding or in-house production; The cost of molding
equipment is relatively low and the vehicle power is often used. The case where polypropylene is
used as the thermoplastic resin and vacuum forming is used as the forming method will be
described in more detail. In FIG. 1A, the polypropylene film 1 is uniformly preheated by a heater
2 in a clamped state so that sufficient elongation can be obtained at the time of vacuum forming.
The preheating temperature is raised to a rubbery temperature range about 50 ° C. higher than
the glass transition temperature. Next, as shown in FIG. 1-b, when the air in the mold 3 is
discharged by a vacuum pump (not shown), it is pressed by the softened polypropylene film IH
atmospheric pressure and adheres to the surface of the concave 3 of the cone shape. Do. Then, as
shown in FIG. 1C, the polypropylene film 1 molded into the diaphragm shape is peeled off from
the mold by feeding air into the mold 8 or the like, and the unnecessary portion is cut to obtain a
diaphragm. The thickness of the diaphragm thus obtained is the thinnest at the bottom of the
mold 3, that is, at the portion corresponding to the top of the diaphragm (FIG. 1-c A). C) It tends
to be thicker as it approaches FIG. B). This is L7) also due to the fact that the part has a large
displacement month at the time of molding, and as a result, the largest amount of stretching.
However, in the speaker diaphragm, it is known that the rigidity of the top of the diaphragm is
the most important for providing the speaker efficiency with high efficiency and excellent
frequency characteristics as it becomes smaller as it approaches the dog, the ear, and the outer
periphery most. There is. That is, it is desirable that the rigidity of the top portion, which is a joint
with the VC coil bobbin that transmits the vibration of the voice coil to the diaphragm without
loss, be high, and for the purpose of vibration short circuit energy, matching with the edge with
large compliance is taken. Therefore, it is desirable that K be as stiff or small as the outer
periphery (large compliance). Therefore, the rigidity of the diaphragm obtained by the above
molding method is smaller at the top (the thickness is smaller), and the rigidity does not become
smaller at the outer periphery as compared with that, which is contrary to the above-mentioned
requirements. Furthermore, the diaphragm made of the film made of the foam by the molding
method described above shows the change in thickness or the above-mentioned tendency, and
the hole in the top portion is most crushed 7 as a result. The internal loss caused by the
<<<reduction, the speaker incorporating such a diaphragm generates resonance at the root
portion of the diaphragm or the high-pitched sound reproduction area that mainly vibrates, and
this is a peak and dip harmful to frequency characteristics Cause of
Therefore, in the present invention, when the thermoplastic resin or the foam film thereof is
subjected to vacuum, pressure or mold press molding, heating is performed so that the
temperature becomes lower toward the center of the film in the preheating step. A method of
forming a diaphragm which is thicker as it approaches the top by suppressing the elongation of
the film, and in which a polypropylene film is used as a thermoplastic resin film and a vacuum
forming method is used as a forming method, will be described in detail. In FIG. 2, IU-clamped
polypropylene film, 2 is a heater, a three-piece mold and is identical to the conventional one. 21
is a heat shielding plate disposed between the heater 2 and the clamped polypropylene film at
the center of the polypropylene film, that is, the portion to be the top of the diaphragm. The heat
shield plate 21 shields the heat radiated from the heater 2 to some extent so that it can be heated
lower than the central portion of the shielded film or its outer peripheral portion. After such
preheating is complete, when the conventional forming step (FIG. 1-b) is performed, the
expansion of the central portion of the film 1 corresponding to the root portion of the diaphragm
is lower than that of the outer peripheral portion because the temperature is low. Small. Thus, the
diaphragm obtained by molding in this manner is thick because the height of its top portion is
small and thin because it is large at its outer peripheral portion. Also, since the foam film has a
similar thickness distribution and the rate of collapse of the pores in the top portion is extremely
smaller than that of the conventional molding method, the reduction of internal loss due to the
presence of the pores is extremely small. FIG. 3 shows another shielding plate 22 used for this
forming method, in which small holes 22a, 22b and 22c are drilled so as to reduce the shielding
ratio to the outer periphery of the plate 22. Since the temperature gradient of the film 1 is
further clarified, it is possible to obtain a diaphragm whose thickness is reduced sharply from the
top to the outer circumference. The above-mentioned shield plate 21.22 has an advantage that its
purpose can be achieved simply by adding it without modifying the conventional device, but it
can also be achieved by changing the heating temperature distribution of the heater 2. It is
obvious that the above-mentioned example is applicable to polypropylene films or other
thermoplastic resins or foam films thereof, and the forming method is not only vacuum forming,
but also compressed air pressure which causes pressure over atmospheric pressure. The same
applies to molding and die press molding in which a mold is pressed.
As described above, this invention vacuum-molds thermoplastic resins or their foam resin films.
In pressure forming or mold press forming, after obtaining the preheating step of heating so that
the temperature of the outer peripheral portion becomes higher than the portion corresponding
to the vicinity of the root of the diaphragm when formed on the diaphragm of the film . It is
possible to suppress the elongation at the time of molding of the portion corresponding to the
top portion as compared with the outer peripheral portion, and obtain a diaphragm which is
formed as thick as the top and thinner as the outer periphery by pressure molding or mold press
molding. It is. Further, in the case of the foam film, the ratio of the pressure at which the holes in
the root portion of the diaphragm are pressed is significantly reduced, so that it is possible to
provide the entire diaphragm having a high rigidity and a large root loss. . In addition, the
invention is extremely excellent in practical use, such as can be achieved by any modification or
slight improvement of the conventional device.
Brief description of the drawings
Th1-a, l-b, and l-C are cross-sectional views of the conventional apparatus showing a modified
airspace, and FIG. 3 is a perspective view of an embodiment shield used for this forming method.
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