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The present invention relates to an acoustic diaphragm represented by a speaker cone or the
like. Conventionally, paper has been mainly used as an electroacoustic transducer, in particular
as a diaphragm, but recently, excellent acoustic characteristics are obtained by a polyolefin
polymer film, and the processability of the diaphragm is good (mass production at low cost) It
has been attracting attention because of its ability (Japanese Patent Application Laid-Open Nos.
11152-145024, Japanese Patent Application Laid-Open No. 55-45226, Japanese Patent
Publication No. 55-44112). However, development of a diaphragm with a higher rigidity is
desired from the viewpoint of further enhancing the acoustic characteristics. Generally, in order
to improve the rigidity of a polymer material, compounding with a reinforcing filler is performed,
but a diaphragm formed using a fiber reinforcement such as glass fiber / carbon fiber is There is
a fight against the development of anisotropy in the performance of the diaphragm due to the
orientation of fibers during extrusion, and also glass flakes, lakes, and graphite. In the case of
using a flaky reinforcing material such as shellfish powder, although there is no anisotropy in
performance, the improvement effect of the rigidity is insufficient as a diaphragm. Therefore, as a
result of intensive research into the development of a diaphragm having no anisotropy and a
higher rigidity while maintaining the characteristics of a polyolefin polymer, the present
inventors have made it possible to obtain a specific shape of a poliorefne polymer. A diaphragm
made of a composite material having a specific Merck index obtained by compounding mica
powder meets these requirements, and in addition, it has been recognized that the formability
from the composite material to the diaphragm is suitable. The invention has been reached. That
is, the present invention comprises (i) 30 to 95 wt% of a polyolefin polymer and (ii) 70 to 5 wt%
of mica having a weight average flake diameter of 500 or less and a weight average aspect ratio
of 10 or more, And it is an acoustic diaphragm comprised with the composite material whose
Merck index is 3,5 fAOmin or less. The polyolefin polymers used in the present invention include
polyethylene (especially, high density diethylene), polypropylene (especially isotactic
polypropylene), polybutene, carbur (3-methylbutene-1), poly (4-methylpentene) 1) Polymers of
aliphatic olefins such as 1) or copolymers comprising the constituent monomers of the abovementioned polymers as main components. Other monomers constituting the copolymer include
other olefin monomers different from the main component monomer, vinyl acetate, maleic
anhydride, (meth) acrylic acid 駿 methyl, (meth) acrylic acid and the like, and their
copolymerization The monomer is used within a range not disturbing the crystallinity of the
polymer (usually 2096 or less).
As a copolymer, not only a random copolymer but also a block or graft copolymer may be used.
In addition, for the purpose of improving the adhesion to mica, so-called polarizable polyolefins
exemplified by the above-mentioned maleic acid and (meth) acrylic acid modified products etc.
may be used as Il & t in unmodified polyolefins. Among the above-mentioned polymers, isotactic
I-librobirene-based heavy weight is particularly preferable in the invention, which is an isotactic
polypropylene-based polymer which is excellent in moldability, low in price, and high in heat
resistance and high in bending speed. As coalescence, a copolymer having an ethylene content of
2 to 15% by weight is also preferably used. As micas used in the present invention, various micas
such as white mica (mascovite), gold mica (flogobite), and “synthetic” mica can be used, but as
the shape of mica, weight average flakes can be used. A diameter of 500 μm or less and a weight
average aspect ratio of 10 or more are required. In the present invention, the weight average
aspect ratio of mica is represented by the following formula weight aspect ratio '-7̶determined
by the diameter of the lake (D) /. At the bottom bl is the average diameter of one mica flake, '11
is the average thickness of that flake 1 m1 is the total weight of the flakes in the form of Dl h tl,
horse, t! , Town, Dll, t, m, have the same meaning. The average flake diameter of each of D, Dh +
++ ++-····, a is determined by π (D / 2) ′ ′ area of one flake. In the case where the diaphragm is
formed from a metal force having a weight average flake diameter of 500 μm or more, peeling
of the mica flakes from the surface of the diaphragm is apt to occur, or the like. Is often very
difficult, preferably the mica has a weight average flake diameter of 500 μm or less. When the
diaphragm is formed of flakes having a weight average aspect ratio of 10 or less, the effect of
improving the rigidity is small, and the acoustic characteristics are unsatisfactory. In the present
invention, the mixing ratio of the J polyolefin polymer and the mica is 50 to 95% by weight of the
polyolefin polymer and 5 to 70% by weight of the mica. When the mixing ratio of mica is 5% by
weight or less, the effect of improving the rigidity is unsatisfactory, while in the region where the
mixing ratio of mica exceeds 70% by weight, the formability when forming a sheet for a
diaphragm is It becomes difficult. Above all, 10 to 60% by weight of mica mixing ratio (f!
The mixture ratio of 9 to 40% by weight of lyorefine polymer is particularly preferable. In
manufacturing the diaphragm in the present invention, fillers other than mica (for example, talc,
calcium carbonate, wollastonite, glass peas, magnesium hydroxide, silica, graphite, glass flakes,
varicam sulfate, alumina, titanium) Acid potassium fiber, processed mineral fiber M! (PMF), glass
fiber, carbon fiber, aramid delicate, etc.) may be used as a supplement. In addition, addition of an
additive (such as a silane cuff ring agent), a pigment, a plasticizer, a stabilizer, a lubricant and the
like for improving the interfacial adhesive strength between the polymer and the mica is also
appropriately carried out as necessary. In the present invention, the melt index of the above
composite material containing a polyolefin polymer and mica as main components is preferably
5.5 f / 10 n11 m or less. O9710 mln or less is more preferable, and 2.0 t 710 min or less is
particularly preferable. The melt index is a value measured according to TM 8TMD 1258, and
shows, for example, a melt flow rate (unit: nigeram / 10 minutes) at 230 ° C. when the
polyolefin is 1 propylene. When the melt index is 3.5 f / 10 win or more, problems such as
generation of wrinkles are likely to occur when the acoustic diaphragm is formed from the sheet
(vacuum forming, press forming, stamp forming, etc.). Composite materials with low melt index
are often obtained by employing low melt index lyorefine as a raw material. The diaphragm of
the present invention is obtained by first forming a composite sheet of a polyolefin polymer and
mica and then forming the composite sheet into 81 shapes by a vacuum forming method or the
like. The composite sheet is preferably formed by melt-mixing a polymer and mica, and extrusion
is carried out by a conventional method. According to such a method, the diaphragm of the
present invention can be obtained with good formability. The thickness of the diaphragm of the
present invention is not particularly limited, but 0.1 to 0.9, particularly 0.2 to 0.7, is useful.
When the thickness is less than 0.1, the strength of the plate is weak (or when it is thicker than
0, 9), the weight of the diaphragm becomes too large, requiring an expensive strong magnet,
which is not economical. . The diaphragm of the present invention obtained as described above is
significantly improved in rigidity as compared with a diaphragm formed only of a polyolefin
polymer, and thus is excellent as an acoustic diaphragm such as a speaker cone. It was
recognized that there was. Furthermore, since the diaphragm of the present invention is also
improved in heat resistance, when the temperature rise of the atmosphere during actual use of
the acoustic diaphragm and the acoustic device are assembled using the diaphragm, the
diaphragm is used as a substrate, for example. It is also effective against temperature rise when
bonding and processing.
Further, the present invention will be described in detail by way of examples. EXAMPLE 1
Surface-treated with r-aminopropyltriethoxysilane: Melt-blended phlogopite having an average
flake diameter of 21 .mu.m and crystalline l-librobilene (PF) (MI: 1 r 710 min) at 230 DEG C.
using a single screw extruder. The pellets obtained were again extruded into a sheet at 240 ° C.
using an extruder to obtain a l-propylene Maika composite sheet having a phlogopite mixing
ratio of 60% by weight and a thickness of 300 μm. The weight-average diameter L / -size of
mica contained in the cough sheet was 4.118 μm, and the aspect ratio was 12. The dynamic
elastic modulus E 'and internal loss tan δ are measured at 20 ° C. at a frequency of 11 on using
Toyo Baldwin's Phybron DDV-2 with respect to the sheet. The density ρ was measured by the
specified method. We also measured the sound propagation velocity using Dynamic Modular Te
5ter. Furthermore from the temperature dependence of E '. The temperature at which E ′ was
10 @ dyne s / J was measured, and this value was used as the evaluation standard of heat
resistance. As shown in Table 1, the sheet had a very high specific modulus, sound velocity, tan
δ and heat resistance. Using the sheet, 20 speaker cones were formed at a temperature of 190
° C. by a vacuum forming method. The vacuum formability was good, and no defective product
was generated. Examples 2 and 5 The weight average flake diameter of phlogopite to be used is
401 m (Example 2) and 2 so tm (Example 3), and the mixing ratio of phlogopite is 30% by weight
(Example 2), 10 wt q 6 The performance was measured in the same manner as in Example 1
except that (Example 3) was used. The results are shown in Table 1. The specific modulus, the
velocity of sound, the tan J, the heat resistance and the vacuum formability were extremely good.
Example 4 30% by weight of phlogopite powder having an average heavy flake diameter of 90
μm is mixed with a propylene-ethylene block copolymer (ethylene 4%) resin of melt index s, st /
1 omaim, and the same as the case of Example 1 A sheet with a thickness of 200 μm was
produced by the method and conditions. The performance adjustment results are shown from
Table 1 in Table 1. The specific modulus of elasticity, sound velocity, internal loss, heat resistance
and vacuum formability U are very good. Comparative Examples 1 and 2 Melt index 5f / 10w1th
polypropylene (comparative f141) or propylene-ethylene flock valve type & (ethylene 6L $) tree
# (comparative # l12) with a 40 μm average flake diameter of a muscovite powder with a so
weight of 96m In the same manner as in Example 1, a sheet having a thickness 400- as shown in
Table 1 was obtained in the same manner as in Example 1. As shown in Table 1, the specific
elastic modulus, sound velocity and heat resistance of the sheets of Comparative Examples 1 and
2 were obtained. Although the flexibility was sufficient, it was found that there was sheeting as a
result of heating during vacuum forming when forming the sheet into a speaker cone, and it was
found that 20 speaker cones were formed for each of the comparative examples. In addition,
wrinkles were generated in the five sheets of the sheet of Comparative Example 1 and the four
speaker cones of the sheet of Comparative Example 2, and it was determined to be a defective
Comparative Examples 5 and 4 Polypropylene having a melt index of 1f / 10m1m1 is used, and
mica is not used at all (Comparative Example 3), or 4% by weight of phlogopite having an Mlk
average flake diameter of 90 μm is mixed (Comparative Example 4) The performance of the
sheet prepared in the same manner as in Example 1 is shown in Table 1. The sound velocity was
unsatisfactory as an acoustic diaphragm. Example 5 50% by weight of phlogopite powder having
a weight average flake diameter of 90 μm is mixed with high density polyethylene (] aDPE)
having a melt index of 2 f / 101 n and melted at 160 ° C. in the same manner as in Example 1.
The performance of the sheet obtained by performing the mixing and sheet extrusion is shown in
Table 1. Very good sheets of specific modulus, speed of sound, internal loss and heat resistance
were obtained. By vacuum forming the sheet at 150 ° C., the sheet can be easily formed into a
spring for forming a diaphragm for a cone speaker, and the vacuum formability thereof is
extremely good. Comparative Example 5 The performance of a sheet prepared only with the high
density polyethylene shown in the actual jII # 15 without using mica is shown in Table 1. The
specific elastic modulus, the speed of sound and the heat resistance were unsatisfactory as the
acoustic diaphragm. Patent Assignee R-Tare Co., Ltd. Agent 本 本 Procedure correction port
(spontaneous) Patent S 7th, S S Patent Secretary Secretary Harada Shimada 1, Indication of
Japanese Patent Application No. 56-1 oz 666 f2, Name of Invention Acoustic Diaphragm (108)
Co., Ltd. Representative approach i Tsukasa Okabayashi 4, representative telephone Tokyo 03
(27 n 31 825, date of correction instruction date 6, column 7 of detailed description of invention
of target specification of correction, Details of the correction (1) “Melt Index” of the
specification, page 3, line 4 is corrected to “melt index” k. (2) Correct "Baricam sulfate" in page
7, line 3 of the specification to "Barium sulfate".
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