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2. Description of the Related Art Heretofore, as a speaker diaphragm, a large number of natural
fibers such as wood pulp are beaten with a beater and formed. Such a paper diaphragm made of
wood pulp or the like is subjected to resin processing to improve the water resistance, but the
water resistance is insufficient. In order to improve this, polypropylene resins and various liquid
crystal polymers have been proposed and used as diaphragm materials having Young's modulus
and internal loss equal to or higher than that of paper diaphragms.
However, a diaphragm made of a polypropylene resin has a disadvantage that its specific gravity
is as large as 0.85 or more as compared with a paper diaphragm, and it is heavy. In addition, it is
difficult to bond a polypropylene resin with a general adhesive, and the manufacturing process of
the speaker becomes complicated, which causes an increase in cost.
In addition, since the liquid crystal polymer has a large specific elasticity, the propagation speed
is as fast as about 4,000 m / s and the internal loss is as large as 0.55, but the specific gravity is
as large as 1.44. It has the disadvantage of being as heavy as the board.
Furthermore, in order to reduce the weight of the diaphragm, it has been proposed and used to
use a polystyrene-based resin foam.
However, since polystyrene has a low specific elasticity, the propagation speed is about 1,600 m
/ s, and the internal loss is also as small as 0.015.
In order to eliminate these disadvantages, natural fibers, chemical fibers, thermoplastic unfoamed
powder monomers such as polystyrene or vinylidene chloride, or polymers combined with other
resins are used as highly reactive binders such as polyethyl or imine. There is disclosed a
technique of bonding fibers in a beater and heating and foaming the same in a mold to obtain a
low density and light speaker diaphragm (Japanese Patent Application Laid-Open No. 51-327).
However, these complicate the manufacturing process and cause an increase in cost.
On the other hand, since expanded polystyrene contains a large amount of air, its fire resistance
is poor. In order to provide the diaphragm with fire resistance, a diaphragm added with borax,
hydrated aluminum, antimony trioxide or the like as a flame retardant. Are disclosed (JP-A-5142528). However, this method is also complicated in the manufacturing process and causes an
increase in cost.
The present invention has been proposed in view of the above, and the object of the present
invention is to provide a diaphragm which is lightweight, has appropriate rigidity and internal
loss, and has flame retardancy and chemical resistance at low cost. It is to do.
SUMMARY OF THE INVENTION The present invention is a diaphragm in which a vinylidene
chloride-based copolymer having an internal loss of 0.03 or more is foamed to have an apparent
density of 15 kg / m @ 2 to 80 kg / m @ 2. The above object is achieved by producing
Since the present invention uses the above-mentioned materials, it has flame resistance
equivalent to UL-94 · HF-1, has excellent oil resistance and chemical resistance, and has a small
amount of water absorption, The moisture permeability is also very small.
Also, it is flexible and does not break, and its recovery against deformation is large.
Furthermore, the dimensional accuracy of the molded article is good, the change with time is
small, the melting temperature is as high as 240 to 250 ° C., and the heat resistance is good.
Therefore, it is possible to obtain a diaphragm which is light in weight and has appropriate
rigidity and internal loss, and compared to the foam polystyrene diaphragm, the deformation to
the stress in the foam cell becomes smooth, and the distortion sound peculiar to the foam is
significantly reduced. In addition, since the product is made of a chemical resistant material,
control of frequency characteristics by application of a damping material or the like is easy.
EXAMPLES Examples of the present invention will be described below. A trade name Celmore
(manufactured by Asahi Kasei Kogyo Co., Ltd.) was used as a copolymer containing vinylidene
chloride as a main component. The vibration plate was formed by heating using a molding
machine for polystyrene with a predetermined mold. The molding conditions are a steam
pressure of 1 kg / cm 2 (absolute pressure) and a time of 3 seconds. Cooling was carried out
using a water cooling method. When the density of the molded part of CelloM is 40 kg / m @ 2, it
was almost equivalent to a cycle of 15 times of polystyrene of the same thickness. After molding,
water adhering to the molded product was removed by forced drying, and secondary processing
was performed to prepare a diaphragm.
FIG. 1 and FIG. 2 show the structure of the speaker attached with the diaphragm manufactured
as described above. The diaphragm 1 has a cone shape, has a skin material (PPS 50 μ) 2 on the
surface, and has a large number of honeycomb-shaped holes 3 on the inner side. FIG. 3 shows
frequency characteristics in the case of using the foam of the present invention and the case of
using expanded polystyrene resin as the diaphragm material of the 16 cm speaker. As apparent
from the figure, the diaphragm using the foam has less distortion in the high frequency region.
As described above, according to the present invention, beads formed by impregnating a foaming
agent with a copolymer containing vinylidene chloride as the main component are heat-molded
by a heat medium such as steam to be lightweight and appropriate. A diaphragm having stiffness
and internal loss, and having flame retardancy and chemical resistance can be obtained at low