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BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
diaphragm for a speaker which is good in sound quality and inexpensive and has little variation
in product lot. [Prior Art] As a performance required for a speaker diaphragm, the inelastic
modulus (E / ρ, E: elastic modulus, ρ: specific gravity) is large, and an appropriately large
internal loss (tan δ), and It is necessary that the weight of the diaphragm itself is light (if the
volume is the same, ρ is small). Conventionally, metal materials such as aluminum, beryllium,
and titanium have been known as materials with relatively small ρ and large E, and although
they have actually been used as diaphragms for speakers, there is a problem that tan δ is
extremely small. It existed. On the other hand, paper is well known as a material with a large tan
δ, but it has a low modulus of elasticity and is insufficient as a diaphragm for a speaker. In
recent years, carbon fiber has been mixed into paper for the purpose of improving modulus. It
has been taken. Plastic materials such as polypropylene and polyester are known to have
relatively large tan δ, and there is a possibility of mass production of uniform-quality
loudspeaker diaphragms at low cost by injection molding method. However, there is a problem
that the elastic modulus is low. In order to solve such problems, various methods of
incorporating fibrous or plate-like fillers have been proposed. However, the improvement effect
of the elastic modulus is not so large, and the melt viscosity is increased, and the flowability in
injection molding is lowered, so that the thickness of the diaphragm for the speaker must be
thickened. There is a drawback that the weight becomes heavy. Also, in recent years, a method of
forming a diaphragm for a speaker by curing an epoxy resin with a so-called carbon fiber epoxy
prepreg in which a carbon fiber woven fabric is impregnated with an epoxy resin has been
proposed, but the material cost is extremely expensive Not only that there is a problem that mass
production is difficult because the curing time is extremely long, but also variation in thickness
accuracy, curing density, etc. between product lots is likely to occur, resulting in a problem that
the sound quality is large. I had it. [Problems to be Solved by the Invention] On the other hand,
forming a diaphragm for a speaker from a thermotropic liquid crystal polymer is described, for
example, in JP-A-62-7, JP-A-62-2026, Tata-No. U.S. Pat. No. 5,095, 806, each of which relates to
a thermotropic liquid crystal polymer without fillers and to a thermotropic liquid crystal polymer
with fibrous fillers.
As a result of further investigations by the present inventors against the above-mentioned known
methods, the speaker formed by injection molding using the filler containing the thermotropic
liquid crystal polymer alone or a blend with other thermoplastic polymers is The surface
appearance of the diaphragm is so glossy and beautiful that the elastic modulus of the resin flow
direction is high, so it is recognized that the sound quality is extremely good as a speaker, but the
elastic modulus in the circumferential direction and the strength are low. When the speaker
pieces were punched out with a mold, cracks, cracks and the like were likely to occur, so that the
yield of split products was significantly reduced and the result was not obtained industrially
favorable. On the other hand, JP-A-62-2026? As described in No. 7, fibrous fillers such as carbon
fibers or glass fibers have the effect of stabilizing and uniformly orienting the polymer during
molding, and improve the elastic modulus in the radial direction and in the direction
perpendicular thereto. Was found to be effective. Furthermore, since the breaking strength is
also greatly improved, when the molded product was punched into a diaphragm for a speaker,
occurrence of cracks, cracks and the like was not recognized so much and was good.
Furthermore, for example, when carbon fiber is used as a filler, the radial elastic modulus is
extremely large, and the result is preferable. However, such a fibrous filler system has a large
effect of increasing the melt viscosity, and therefore the molding flowability is reduced, and the
thickness of the diaphragm becomes large when an actual speaker diaphragm is formed. The
speaker diaphragm not only causes problems for the purpose of making its weight as light as
possible, but from the aspect of injection molding technology, injection pressure and injection
speed are both limited in terms of equipment, and therefore larger-sized injection A molding
machine has to be used, and as a result, it is not always possible to obtain a speaker diaphragm
having a large aperture, which is not always preferable. [Means for Solving the Problems] In view
of the problems relating to the thermotropic liquid crystal polymer, the present inventors are
capable of mass production by injection molding and excellent in sound quality with a large E /
大 き い and tan δ. As a result of intensive investigations to obtain a diaphragm for a speaker, by
using a plate-like filler, the elastic modulus and strength in the direction perpendicular to the
flow direction of the resin are also improved, and cracking occurs in the die cutting step in the
secondary processing step. It has been found that the problem of cracking and the like does not
occur and the fluidity does not significantly decrease when using a fibrous filler, and reaches the
present invention. That is, the present invention relates to a speaker diaphragm formed by
injection molding of a resin composition containing 10% by weight or more of a thermotropic
liquid crystal polymer and 7% by weight or more of a plate-like filler.
In the thermotropic liquid crystal polymer, its molecular chain is usually oriented in the flow
direction of the resin, and the orientation of the molecular chain is frozen in the course of cooling
and solidification of the crucible. The modulus of elasticity in the direction of orientation is
thereby significantly increased. In particular, in the case of forming the speaker diaphragm by
the injection molding method, it is preferable to set the thickness of the diaphragm to be a
clearance, and in such a case, the orientation obtained particularly easily in the flow process. The
modulus of elasticity of the plate also amounts to r-20 x / 0 'dyne / crd in the flow direction. In
addition, since the thermotropic liquid crystal polymer is also a kind of ordinary plastic, it
exhibits internal loss (tan δ) equal to or larger than, for example, polypropylene, polyamide and
the like. The thermotropic liquid crystal polymer used in the present invention can be optionally
selected from the group consisting of polyesters or polyesteramides comprising segments having
at least the following structure. l) Polyester-0-R-0-CO-R-CO-O-R-CO-2) Polyester amide 1-R-0-COR-CO-l-R-CO- NH-R-NH-NH-R-CO-R in the above structural formula can be each selected
arbitrarily from the following group. -CH2- (CHJ *-(CH2) 6-Hs, and hydrogen of these aromatic
ring group, alicyclic group or aliphatic residue may be substituted by various substituents.
Preferred examples of the substituent include an aromatic group such as a halogen atom such as
CI and Br, a linear or branched alkyl group having carbon number / j such as -CH11,-(CH3) 8, or
A phosphorus containing group is mentioned. The speaker diaphragm according to the present
invention is obtained from a composition containing at least 10% by weight or more of the
thermotropic liquid crystal polymer. If it is less than 10% by weight, the orientation of the liquid
crystal polymer is insufficient, and the effect of improving the elastic modulus is not good. The
present invention can also be achieved by blending such thermotropic liquid crystal polymers
with other thermoplastic resins. The thermoplastic resin can be optionally selected from
polyester, polycarbonate, polyamide, polyesteramide, polysulfone, polyarylate, polyimide,
polyamideimide, polyketones, polyolefin, polystyrene, polyparaphenylene sulfide, vinyl chloride
resin, etc. . Usually, a plate-like filler is a filler having a flat shape such as so-called mica, and its
flat ratio is.
It is defined by short diameter / thickness. In the present invention, as the plate-like filler to be
used together with the thermotropic liquid crystal polymer, one having a flatness of 10 or more
is preferable. If the flatness is smaller than / θ, the improvement effect of the elastic modulus
and the flowability are significantly reduced, and the plate thickness of the speaker diaphragm
can not be reduced, which is not preferable. Further, if the filling amount is less than 1% by
weight, the anisotropy is increased, and cracking occurs in the punching step of the speaker
diaphragm, which is not preferable because of generation of cracks and the like. If it exceeds 30%
by weight, the mechanical strength of the material is reduced, so that cracking also occurs in the
punching process, which is unsuitable. If it is a preferred plate-like filler, it can be selected and
used from mica, glass flakes and the like. The filler may have any diameter (minor diameter) as
long as the flatness is io or more. In the case of mica, there are two types, muscovite and
phlogopite, but phlogopite is preferably used because its flatness is generally larger. The average
particle diameter of the filler can be selected depending on the surface appearance of the
speaker diaphragm. However, when the average particle diameter exceeds / θQμ, the
appearance of the molded article is unfavorably deteriorated. Also, if it is less than 03 μ,
dispersion failure occurs, which is also a cause of appearance failure, which is not preferable. In
the present invention, a fibrous filler may be added in addition to the above-mentioned plate-like
filler. Hereinafter, the present invention will be more specifically described by way of examples,
but the present invention is not limited thereto. [Examples] A trade name N0VACCURATE E-322
(a thermotropic liquid crystal polymer consisting of a PET component and a parahydroxybenzoic
acid component) manufactured by Sanyo Kasei Co., Ltd. is used as a thermotropic liquid crystal
polymer, in contrast to Toho. For carbon fiber made of rayon ■ (trade name: HTA (jS) filled with
20% by weight, and mountain lomyca ■ made phlogopite (trade name: A, 2 /) 20 weight light
filled Injection molding was carried out using a speaker diaphragm mold of the shape shown in
FIG. The injection molding machine uses Sumitomo Heavy Industries n's Nestal (clamping force
iso ton), and injection speed, injection pressure, molding so that a diaphragm of 0.3 rran
thickness is obtained for each resin composition. The temperature was changed and examined.
As a result, in the case of 20% by weight of carbon fiber, the thickness of the molded article is
0.3! Only the tram's were obtained. It was possible to obtain a molded article having a thickness
of 0.30 rran filled with square mica. This means that when a plate-like filler is used, the
flowability of the resin decreases less than when a fibrous filler is used, and hence it is suitable
for a speaker diaphragm having an extremely thin plate thickness. Show that.
Moreover, although it shape | molded also about the natural resin which does not contain a filler,
the molded article of sufficient satisfactory thickness was able to be obtained. Example 2 The
molded product obtained in Example 2 was die-cut using a mold to obtain the shape shown in
FIG. The probability of cracking and cracking at the time of punching was as follows. Natural
resin 30% phlogopite 20 weight-related resin Q% carbon fiber 20 weight-related resin 0%
[Example 3] The diaphragms punched out in Example 2 were actually assembled into a speaker,
and a sound quality test was conducted. Also, samples were cut out from the diaphragm in the
circumferential direction and in the direction perpendicular thereto, and the dynamic elastic
modulus and tan δ were measured. /) Sound quality test Natural resin Very good phlogopite 20
weight-bearing resin Very good carbon fiber 20 weight-bearing resin Very good 2) Dynamic
modulus and using tanδ Orientic's Leo by Vibro DDV-2 EA type The dynamic modulus and tan
δ were evaluated at room temperature at a frequency of l10 Hz. The sound quality was found to
be extremely good for any of the measurement samples! The dynamic modulus of elasticity and
the ta opening δ were also good values. [Comparative Example 1] 20 weight by weight of the
same carbon fiber as used in Example / in polypropylene resin (trade name: N0VATEC-P% MI
(melt index) = ♂ '+ 7' / m1r1) manufactured by Mitsubishi Kasei ■ The light-filled material was
used to form a speaker diaphragm under the same conditions as in the example. As a result, a
molded article having a thickness of 0.2 r could be obtained. The obtained molded product was
punched out, and the sound quality test, the dynamic elastic modulus and the like were
evaluated. Sound quality test The sound quality in the middle to high range was inferior to that of
the speaker diaphragm using the thermotropic liquid crystal polymer although it was good.
Dynamic modulus of elasticity equal circumferential direction 乙 x / (7 'dyn / c! Right angle
direction μ, evening xto 'dyn / Cr1 tan δ 0. The measured values such as Ojt ♂ dynamic elastic
modulus were also inferior results to the diaphragm using liquid crystal polymer. According to
the present invention, the use of the plate-like filler makes it possible to reduce the decrease in
fluidity of the resin, so that a speaker diaphragm having a thin plate thickness can be obtained. In
addition, this diaphragm has few cracks and cracks at the time of molding, is excellent also in
elastic modulus and strength, and is excellent in sound quality.
Brief description of the drawings
FIG. 1 is a view showing the shape of a diaphragm die for a speaker used in Example 1 of the
present invention.
FIG. 2 is a view showing the shape of the speaker diaphragm after the molded product obtained
in the embodiment of the present invention is punched by a die.
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