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BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
dust cap for a speaker, and more particularly to a dust cap molded of a novel material and a
method of manufacturing the same.
2. Description of the Related Art Conventionally, as a material of a dust cap for a speaker, the
dust cap is coupled to a diaphragm to contribute to acoustic radiation, and when it is reinforced
by being joined to a diaphragm or a voice coil bobbin coupling portion. In order to improve the
frequency characteristics of the speaker and to improve the reproduction sound pressure level, it
is lightweight, that is, the density (ρ) is low, and the specific elastic modulus (E It is required that
the ratio / ρ) is large and the rigidity is large in order to suppress distortion and improve input
resistance. In particular, as a material for a dust cap of a speaker used under a high temperature
and high humidity environment, in addition to the above-mentioned required characteristics, it is
necessary to have heat resistance and moisture resistance enough to withstand deformation
under high temperature and high humidity environment conditions. Conventionally, as a dust cap
material for such a use, a resin-impregnated paper, a glass or carbon fiber woven fabric
impregnated with an epoxy resin and thermoformed, or a thermoplastic polyimide (TPI) or other
super engineering plastic film is thermoformed Were used.
[Problems to be Solved by the Invention] Among conventional dust caps having such a structure,
those impregnated with resin in paper have low specific elastic modulus and rigidity, and
impregnated with epoxy resin in glass or carbon fiber woven fabric. Thermoforming dust caps
not only have a long molding time and cost increase, but also have the disadvantage that they
can not be used because the resin starts to decompose at high temperatures of 250 ° C. or
higher, and furthermore, thermoforming of super engineering plastic films There is a problem to
be solved that the dust cap can not be used because the resin softens at high temperature of 250
° C. or more and is deformed by vibration.
Therefore, the present invention solves the disadvantages of the prior art and heat-presses a
polymer alloy film of polyimide and aramid into a dust cap, and then heat-treated at a
temperature higher than the Tg of polyimide. An object of the present invention is to provide a
dust cap having a heat resistance much higher than that of aramid alone and a method of
manufacturing the same.
The dust cap for a speaker according to the present invention for achieving the above object and
the method of manufacturing the same will be described with reference to FIGS. 1 to 3 showing
an embodiment. It is a dust cap for speakers which is composed mainly of a polymer alloy of
polyimide and aramid.
A second invention is the dust cap for a speaker according to claim 1, wherein a mixing ratio of
the polyimide is 30% or more.
The third invention is a speaker dust characterized in that a polymer alloy of polyimide and
aramid is formed into a film by casting, the film is heat pressed to form a dust cap, and then heat
treated at a temperature higher than Tg of polyimide. It is a manufacturing method of a cap.
[Function] The change of the phase system of the single substance and the mixture is explained
by the DSC curve shown in FIG. 1 about the dust cap of such constitution and its production
method, curve A: single aramid, B: single polyimide, C is a DSC curve of what was heat-treated
only for the aramid / polyimide (50/50) blend and D was heat-treated at 330 ° C. for 12 hours
after casting.
In each curve, the point where the exotherm peaks is the temperature at which the crystal
structure changes, ie, it represents Tg.
Curves A and B show that Tg of aramid alone and polyimide alone is 240 ° C. and 280 ° C.
respectively, and in particular, aramid has an exothermic peak due to crystallization at 350 ° C.
or higher.
Also, in cast only (C), Tg of aramid single substance and polyimide single substance appear
respectively at 240 ° C and 280 ° C, and a peak of heat generation due to aramid
crystallization is seen above 350 ° C, these two components are phases It does not melt,
indicating that it is a two-phase system.
In the heat-treated product (D), a new Tg appears at 290 ° C. which is higher than the Tg of
each of the aramid simple substance and the polyimide simple substance, and the two Tg
appeared before the heat treatment change to one. It shows that it changed to one phase system.
From the above, aramid and polyimide, which were a two-phase system at the time of molding
the dust cap, are heat treated by heat treatment to break the hydrogen bond of the aramid to
form a one-phase system, and the two become compatible. Thus, a dust cap having high heat
resistance ( C.) can be obtained.
Therefore, the manufacturing method of the present application is not only very convenient for
processing of the dust cap, but also can significantly improve the heat resistance of the product.
EXAMPLES Examples of the present invention will be described in detail with reference to FIGS. 1
to 3, which are polyimide (chemical formula 1) and aramid obtained by polymerizing
metaphenylene diamine and 3,4'-diaminophenyl ether (chemical formula 2) ) Was dissolved in Nmethylpyrrolidone with heating, and this solution was mixed so that the weight ratio of aramid /
polyimide = 50/50 was used to form a transparent cast film with a thickness of 40 μm by the
casting method. did.
This film is press-formed with a dome-shaped dust cap mold maintained at 250 ° C. to 280 °
C., and then held between stainless steel shape holding jigs of the same shape, and about 12 in
an electric furnace heated to 330 ° C. After heat treatment for a time, the product was returned
to room temperature and taken out of the jig to obtain a dome-shaped dust cap of the present
## STR1 ## To describe the mixing ratio of the polyimide in more detail, FIG. 2 shows the change
of Tg with respect to the ratio of polyimide when the polyimide is blended with aramid. In the
case of only casting shown by the dotted line, a polyimide ratio of 0 to 40% shows Tg at a
temperature (= 240 ° C) close to the aramid alone, and within 40 to 80% the aramid and
polyimide each close to Tg Tg appears at two points of temperature (240 ° C., 280 ° C.), and at
80 to 100%, Tg appears at a temperature (280 ° C.) close to that of the polyimide alone.
Therefore, since two types of Tg coexist between 40% / 80%, it can be molded at a temperature
near the lower Tg (240 ° C.).
The heat treatment at 330 ° C. for 12 hours shows a Tg higher by 40 to 50 ° C. than the Tg
before the heat treatment. In particular, when the proportion of the polyimide is 30% or more,
the Tg of the polymer alloy shows the Tg or more of the polyimide, and it can be seen that the
heat resistance is very excellent.
Although the dust cap for a speaker according to the present invention and the method for
producing the same have been described in detail based on an example considered to be
representative, the embodiments of the dust cap according to the present invention are: shape,
mixing ratio of polyimide and aramid, etc. The present invention is not limited to the structure of
the above-described embodiment, but includes the constituent requirements described in the
appended claims, exhibits the effects of the present invention, and has the effects described
below. It can be modified and implemented.
[Effects] In Fig. 3, only the cast C of aramid simple substance A, polyimide simple substance B,
and aramid / polyimide (50/50) blend is used, and the dynamic elastic modulus of heat treated D
at 330 ° C for 12 hours after casting. The result measured about temperature dependence is
When the aramid monomer A and the polyimide monomer B exceed their respective Tgs, the
elastic modulus begins to decrease sharply.
Also, in the case of cast only C, the same behavior is shown at a temperature between A and B.
The heat-treated product D shows a high elastic modulus even when it exceeds Tg (280 ° C.) of
the polyimide, and an elastic modulus of about 109 Pa is maintained even at 400 ° C. It can be
seen that heat resistance sufficient for practical use is exhibited even under severe environmental
conditions as indicated by the atmosphere.
The dust cap and the method of manufacturing the same according to the present invention have
the following effects. (1) In the manufacturing process, it can be easily molded at a temperature
of about 250 to 300 ° C. before heat treatment, and a dust cap having heat resistance of 400 °
C. or more can be obtained by applying the heat treatment. Therefore, it is very convenient for
processing of the dust cap. (2) The heat resistance of the product can be significantly improved
over the resin of the raw material. (3) Since polyimide is used as a base resin, it is flame
retardant, excellent in chemical resistance, acid / alkali resistance, water resistance, and solvent
resistance. Therefore, there is no deformation or deterioration even in continuous use in high
temperature steam or in high temperature COn / NOx gas.
From the above, the present invention is used as a sound source for active elimination of noise,
which is installed and used in a severe use environment where it is always exposed to a high
temperature of 200 to 400 ° C., for example, an automobile engine or exhaust pipe The present
invention has the effect of obtaining a dust cap suitable for use as a speaker.
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