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DETAILED DESCRIPTION OF THE INVENTION (Field of Use on Sound Bundles) The present
invention relates to a diaphragm for a speaker. (Problems to be solved by the prior art and the
invention) Generally, the material of the speaker diaphragm is lighter in order to improve the
reproduction sound pressure level, that is, the density (ρ) is low. In order to lower the
reproduced sound pressure frequency, it is necessary to have a higher specific elastic modulus
[with] and to have a high sound velocity (V / B / ρ), and to reduce distortion and input
resistance. In order to achieve the improvement of (1), higher rigidity (high bending rigidity) is
required. Furthermore, in practical use, physical properties such as heat resistance and water
resistance are also required. At present, a foam made of a thermoplastic resin containing a large
amount of air layer has physical properties such as light weight, high rigidity and high specific
elastic modulus, and is considered to be used as a diaphragm for a speaker. This foam is made by
adding a foaming agent to a thermoplastic resin from the viewpoint of the production process
and thermally foaming it to react the two liquids with a polyethylene foam, a polypropylene
foam, a polystyrene foam, etc. containing a large amount of air layer. The gas can be roughly
classified into urethane foam and the like containing a large amount of air layer using the gas
generated at the time of However, in the case of the former foam utilizing the above-mentioned
foaming agent, it is necessary to obtain a foam whose foaming temperature is preferably several
tens of degrees higher than the melting point of the thermoplastic resin The heat resistance
temperature of the obtained foam is determined by the melting point of the thermoplastic resin
used since there is almost no blowing agent (at most 180 ° C.), and a foam having a large heat
resistance, about 140 ° C., is obtained. In addition, there was a natural limit to the heat
resistance of the speaker diaphragm. On the other hand, in the case of the latter foam using the
two-component reaction gas, uniform foaming is difficult if it is made thin, and the sheet
thickness required for the speaker diaphragm is 0.5 ++ t + ++ or less. It could not be applied to
the diaphragm for this purpose. Further, a proposal has been made in which air bubbles are
mechanically inserted into a thermoplastic resin having a melting point of 150 ° C. or higher,
and this air bubbled thermoplastic resin is molded to obtain a diaphragm for a speaker (Japanese
Patent Application Laid-Open No. 58-69197). ) Also. However, these conventional resin foams
have insufficient rigidity. In general, the imaging plate of the speaker has the same phase over
the entire frequency band to be used, that is, it is ideal that the piston vibrates, that is, the
pressure division characteristic, distortion factor The phase characteristics and the like
deteriorate to hinder high fidelity reproduction.
In order to solve these problems, flat diaphragms using a honeycomb sand-inch structure or the
like have recently been adopted. However, a flat diaphragm made of a honeycomb structure is
complicated in structure, and the cost is considerably high because it requires several tens of
manufacturing steps and many kinds of members, and the conventional cone paper is used. It
was difficult to make it cheaper than etc. In addition, since the material thickness of the
constituent material is limited in manufacture, it is difficult to reduce the weight of the moving
plate and the efficiency of the speaker is low. (Means for Solving the Problems) In order to solve
the above-mentioned problems, the present invention comprises the following constitution. That
is, the present invention is a diaphragm for a speaker comprising an aromatic polymer foam
which completely forms a liquid crystal phase in a molten state), and a foam layer comprising an
aromatic polymer which forms a liquid crystal phase in a molten state. A speaker diaphragm
made of a thin plate or a meet made of a material of the above, and a structure having a structure
of a sandwich. The aromatic pyromers that form liquid crystals in the molten state, ie
thermotropic liquid crystal polymers, used in the present invention are polymers that are liquid
crystalline (ie anisotropic) in the melt phase. Polymers of this type have been described in a
variety of terms, including 6 liquid crystalline "," liquid crystal "and" anisotropic ". Briefly stated,
this type of polymer is considered to take a regular parallel arrangement of molecular chains.
The next state is often referred to as the liquid crystal state or the nematic phase of the liquid
crystalline substance. Such polymers are generally elongated, flat, from monomers such as
having a plurality of chain extension bonds that are highly rigid and bulky along the long axis of
the molecule and are usually either coaxial or parallel. Manufactured. Such d trimers are easy to
form in the melt phase (ie, to form liquid crystals (ie exhibit anisotropy). Such properties can be
confirmed by conventional polarization inspection using crossed polarizers. More specifically,
confirmation of the anisotropy m (layer phase can be carried out by observing a sample mounted
on a Leitz hot stage using a Leitz polarization microscope at a magnification of 40 times under a
nitrogen atmosphere. The polymers of the invention are optically anisotropic. That is, light is
transmitted when inspected between orthogonal polarizers. If the sample is optically anisotropic,
it will transmit polarization even if it is stationary. As such a thermotropic night crystal polymer,
a copolymer obtained by a method of melt-blending p-hydroxybenzoic acid with polyethylene
terephthalate for transesterification reaction, or a method of directly copolymerizing the both is
well known. It has been announced by Kodak under the development name.
Also, aromatic polyesters having many copolymerization compositions mainly composed of phydroxybenzoic acid and 2-hydroxy-P-quinnaphtalin-6-carzene i'i2, and aromatics having an
amide bond introduced in part thereof Amide esters have been proposed, and recently several
compositions have become commercially available. That is, Dartco, Inc. is a trademark of Xyciar,
and Celanese, Inc. is a trademark of Vectri. As another thermotropic liquid crystal, there are JP-A51-138800 and other aromatic polyazomethines, which are used in the practice of the present
invention. Aromatic polymers suitable for use in the present invention tend to be substantially
insoluble in common solvents and are therefore unsuitable for solution processing. However,
these polymers can be easily processed by common melt processing methods. Fully aromatic
polyesters suitable for use in the present invention generally have a weight average molecular
weight of about 2,000 to 200,000, preferably about 10,000 to 50,000, and particularly
preferably about 20,000 to 25 000. is there. The speaker diaphragm made of the foam of the
thermotropic liquid crystal polymer of the present invention can be formed by any suitable
conventional method such as extrusion, injection molding and the like. For example, screw
extrusion of foam by mixing pellets of thermotropic liquid crystal polymer with powdery foaming
agent and extruding this mixture from a suitable orifice (eg slit die etc.) above the melting
temperature of the polymer used It can be formed by The blowing agent decomposes at the
extrusion temperature and a gas such as nitrogen or carbon dioxide is generated inside the
extruded polymer melt, thereby forming a foam. The extruded foamed polymer is quenched or
cooled by any suitable means such as forced air flow. The type of extrusion device used is not
particularly limited, and any suitable device can be used. The temperature and pressure
conditions under which the liquid crystal polymer can be extruded are not particularly limited in
the method of the present invention, and those skilled in the art can easily determine these
conditions. Generally, the extrusion of thermotropic liquid crystal polymer foam is at a
temperature in the range of about 250-390 ° C. (depending on the melting temperature of the
polymer) in the range of about 7.0-350 / di '/ cn12 It can be done under pressure. The
thermotropic liquid crystal polymer of the present invention is generally about 0.1 to 0.75 after
foaming. It has a density of / crn3. Preferably, the density of such foamed polymers is in the
range of about 0.3-0.
Also, the melting point of the foamed thermotropic liquid crystal polymer of the present
invention will be in the range of about 250 to 370 ': depending on the polymer used. The method
of forming the diaphragm for a speaker according to the present invention includes first a
method of extruding a foam in a sheet shape, and then forming and shaping the foam into a
predetermined shape, or directly forming a diaphragm for a speaker There is a method of
injection molding in a mold, and one of them can be selected according to the diameter,
performance, the number of production, etc. of the intended speaker. Conventional high
temperature blowing agents can be used to make the foamed polymers of the present invention.
For example, suitable blowing agents include those marketed under the following trade names,
including, but not limited to: Expandcx 5PT (consisting of 5-phenyl totelazole; sold 5tepan
Chemical Co. , Ficel T) (T (consists of Trichla radicoria); sold by Finons Industrial Chemical s),
Oelogen HT550 (consisting of hydrazine derivatives: sold TJ niroyal Chemical) and J (emtec 500
(sold by Sherwin-Williams Chemicals)). Such blowing agents decompose at temperatures within
the range of about 240-310 ° C. The decomposition of the blowing agent depends on
temperature as well as time. It is important to match the decomposition temperature with the
processing temperature of the polymer. If the blowing agent decomposes before the polymer is
sufficiently melted, the cell structure may be poor and an unsatisfactory surface appearance may
be obtained. The amount of blowing agent required will generally be in the range of about 0.1%
to a few percent by weight, depending on the gassing rate of the blowing agent and the rate of
density loss desired. Preferably, the amount of blowing agent used will be in the range of about
0.2 to 0.5% by weight. Also, with the proper choice of chemical blowing agents, control of the
temperature and / or pressure can control the foaming action. The control of the foaming action
by temperature is more reliable than the control by pressure, so the use of chemical blowing
agents is preferred. It is also possible to blow a suitable gas into the molten polymer to form a
foamed polymer. However, it is difficult to ensure sufficient dispersion of the gas by such a
method. Various fillers and reinforcements may be used to enhance the various properties of the
foamed polymer. For example, the foam can be reinforced using suitable reinforcements, such as
glass fiber, carbon fiber, fibrils, and the like. Such reinforcements may generally be used in
amounts of up to about 50% by weight, preferably about 10 to 50% by weight, based on the
weight of the foam.
Also, fillers such as pigments, antioxidants and nucleating agents may be added. Typical amounts
of such fillers are in the range of about 0.2 to 10 weight percent, preferably about 0.5 to 2
weight percent. However, the foam of the thermotropic liquid crystal polymer of the present
invention is self-reinforcing and has comparable corner mechanical properties to fiber reinforced
polymer materials. The orientation of the polymer molecules around the closed cell nocople is
caused by the field of the biaxially extensible flow of the expanding bubble during the foaming
process. The framer molecules of the liquid crystal polymer can be easily oriented by such flow
fields and can be held as such in the resulting biaxial orientation. It is also a preferred
embodiment that heat treatment is further performed after molding, and in these thermotropic
liquid crystal polymers, the effect of molecular weight increase is known along with removal of
anisotropy of molecular orientation at molding. The effect of improving the strength, the
crystallinity and the melting point, that is, the heat resistance can be expected. The heat
treatment of the foam can be carried out in an inert atmosphere (eg nitrogen, carbon dioxide,
argon, helium) or a flowing oxygen-containing atmosphere (eg air). The use of a non-oxidizing
atmosphere is preferred to avoid the possibility of thermal degradation. For example, the foam
may be heated to a temperature about 10 to 30 ° C. lower than the melting temperature of the
foamed liquid crystal polymer, at which temperature the foam remains a solid substance. The
heat treatment temperature is preferably as high as possible without exceeding the melting
temperature of the polymer. It is particularly preferred that the heat treatment temperature be
progressively raised accordingly as the melting temperature of the dimer increases during the
heat treatment. The heat treatment time is generally in the range of several minutes to several
days (or more), for example, 0.5 to 200 hours or more. Preferably the heat treatment is carried
out for 1 to 48 hours, typically about 5 to 30 hours. Generally, the heat treatment time varies
depending on the heat treatment temperature, and the higher the heat treatment temperature
used, the shorter the treatment time. Thus, polymers with high melting points can shorten the
time of heat treatment since they can be melted to apply higher heat treatment temperatures. In
the foam layer of the present invention, a thin plate or sheet made of a material having high
rigidity and a sand-in structure are also preferable embodiments, but the high rigidity material
referred to herein means Young modulus of thin plate or sheet. Refers to those showing 500 kg /
lyn "or more, preferably 750 k'J / va2 or more in any plane direction, and particularly preferably
a carbon fiber composite material with a small specific gravity, Alami 14 fiber Composite
materials, thermotropic aromatic fiber composite materials, gel-stretched high polymerization
degree polyethylene fiber composite fibers, Sue · ξ draw polio yan methin, fiber composite
materials, and the like.
For these composite materials, it is convenient to use those which are commercially available as a
prepreg by laminating and curing them, but it is convenient to use a woven fabric, a papermaking
method, a spray method web, etc. of those fibers by a conventional method such as a vacuum
press method. It can also be produced by resin impregnation. A particular example is the film
produced from Alami P, which is preferred because it has the advantage of being thinner than
the above-described fiber defolding and having little in-plane anisotropy in the Young's modulus.
In the case of a tensilized type film, a plurality of sheets are used by laminating them with their
tensing axis shifted. (Function) According to the present invention, as a feature of the aromatic
polymer which forms a liquid crystal phase in a molten state, high molecular orientation is easily
achieved due to high crystallinity due to rigidity of the molecular chain and shear force and
elongation force by flow. As the molded product of high strength and high strength is provided,
by foaming the polymer, it is highly oriented to the foam cell wall, giving a high specific elastic
modulus as well as light weight preferable as a speaker diaphragm. Furthermore, by blending a
polymer with a reinforcing fiber such as glass fiber, it is possible to adjust the specific elastic
modulus and the rigidity by K. By forming a sand-in sheet of a thin plate or sheet of the foam
layer-divided rigid material of the present invention, the rigidity is further enhanced and is useful
for a large diameter woofer or the like. EXAMPLES The present invention will be described by
way of examples. Example 1 The logarithmic viscosity when dissolved at a concentration of 0.1
wt% in pentafluorophenol at 60 ° C., consisting of 25 mol% of 2-oxy-2-naphthoyl units and 75
mol% of p-oxybitenzoyl units Pellets of thermotropic liquid crystal polymer with η inh) of 8.5
are mixed with 0.5% by weight powdered Kemtec 500 blowing agent and 1.0% by weight talc
(nucleating agent). The mixture was extruded at 307 ° C. to produce a sheet. A static mixer was
used just prior to extruding the mixture from Gui to ensure uniform mixing of the blowing agent
and the melt. The obtained sheet was further formed into a 20 cT n aperture curve r cone for
woofer with a hot press. The diaphragm thus obtained has a density of 0.585 ′ ′ 7 cm 3, a
specific elastic modulus of 2 7 × 10 ′ ′ dyne 10 n ′ ′, a sound velocity (s / T 7 a) of 2.16 ×
10 5 cIn / see ′ ′ CA + ) Fc. By the way, conventional corn paper has a density of 0.4 to 0.8, a
specific elastic modulus of 0.8 to 2.5 × 10 ′ ′ ° ydne / cm 2, and an acoustic velocity of 0.5
to 1 × 105 m / see.
Example 2 A diaphragm was formed in the same manner as in Example 1 except that the polymer
of Example 1 was blended with glass chopped 22527210% by weight, density 0.75, specific
elastic modulus 8.62 × 10 ”dyne 7 cm 2, speed of sound 3, 39 X It was 105 cm / sec. Example
3 A foam was used to make a diaphragm by using a foam sheet, kneading with an alami 1,4 fiber
prepreg, and vacuum hot pressing between molds. A density of 0.81, specific modulus of 4.2 X It
was 10 "dyne 7 cm 2, speed of sound 2, 3 × 105 Crn / see. (Effects of the Invention) The
vibration for a speaker according to the present invention is lightweight, has a high specific
elastic modulus, and can be more easily molded than when using a conventional green core and
can provide a homogeneous diaphragm. Speakers with favorable sound quality can be
manufactured while guaranteeing stable performance.
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