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FIELD OF THE INVENTION The present invention relates to a diaphragm for audio equipment.
Specifically, the present invention has excellent acoustic characteristics because it has high
hardness, high strength, high elasticity and light weight as diaphragms for speakers and
microphones as compared to conventional diaphragm materials. The present invention relates to
a diaphragm for audio equipment having the same. In general, it is desirable that the following
conditions be satisfied as a diaphragm such as a speaker. (1) The density is low. (2) The Young's
modulus is large. (3) The propagation speed of longitudinal waves is high. (4) The internal loss of
vibration is moderately large. Furthermore, in order to increase the speed of sound from the
equation V = (E / 1) 1 ′ (where V: speed of sound: E: Young's modulus; :: density), a material
having a small density and a high Young's modulus is required. . Conventionally, as an acoustic
diaphragm having a large Young's modulus, there is one using a light metal such as aluminum,
titanium, magnesium, beryllium, or boron. However, acoustic diaphragms using aluminum,
titanium, magnesium or the like can not obtain a sufficiently satisfactory ratio Young's modulus E
/ 、, and acoustic diaphragms using beryllium, boron or the like have extremely large ratio
Young's modulus However, since these materials are extremely expensive and their processing is
extremely difficult industrially, there is a problem that they are extremely expensive in cost as
compared with other materials. (Problems to be solved by the invention) In view of the abovementioned drawbacks of the conventional diaphragm material, the object of the present
invention is to provide a diaphragm having excellent acoustic characteristics by making use of
the excellent physical properties of carbon. It is. (Means for Solving the Problems) As is well
known, carbon has extremely wide physical and chemical properties ranging from crystalline
carbon of diamond and graphite to non-crystalline carbon such as carbon black and charcoal.
doing. The inventor of the present invention has intensively studied to express various functional
properties aimed by designing and combining these carbon materials according to the required
functions, and first, thermosetting resin and carbon powder The present invention invented a
method for producing a all-carbon diaphragm obtained by forming a mixture of the above and
the mixture as a raw material, preforming it into a film, shaping it into a diaphragm, and firing it
in an inert atmosphere. (Japanese Patent Application Laid-Open No. 6O-121895). Furthermore,
the inventors of the present invention invented a method of manufacturing a glassy carbon
award diaphragm using only a thermosetting resin as a raw material, and applied for a patent
(Japanese Patent Application Laid-Open No. 6-65596). Although the diaphragms according to
these inventions can be manufactured at low cost industrially and have excellent physical
properties, the inventor of the present application has intensively studied to further improve the
physical properties of these diaphragms. Focusing on the fact that the theoretical elastic modulus
of diamond is as high as 1200 GPa, a diaphragm consisting of only the whole carbonaceous film
by vapor-depositing a diamond-like carbon film on the surface of the diaphragm material
consisting of the whole carbonaceous film We came to invent a diaphragm with better acoustic
characteristics than that.
In recent years, many proposals have been made for a method of synthesizing a diamond-like
carbon film from the gas phase, and the film structure is also gradually being clarified by analysis
methods such as X-ray and electron beam diffraction and Raman spectroscopy. Further, as a
known synthesis method, there are a CVD method, a plasma method, an ion beam evaporation
method and the like, and depending on the synthesis method and synthesis conditions, the
obtained thin film is also a mixture of amorphous carbon and polycrystalline diamond from
diamond crystal. There are a wide variety of things, including those that are mixed or mixed with
hydrogen. The CVD method is a method in which a hydrocarbon gas such as methane is
decomposed by heating at about 1000 ° C. under a reduced pressure to precipitate diamond,
and to deposit a diamond film on a substrate other than a single crystal of diamond. Mainly use
the thermal filament method. This method is a method in which a hydrocarbon gas diluted with
hydrogen gas is pyrolyzed by a tungsten filament heated to 2000 ° C. or more, and a diamondlike film is deposited on a substrate placed in the vicinity of the filament. The substrate is heated
to When the substrate temperature is lower than this range, mixing of
amorphous carbon and graphite increases. In the plasma CVD method, a mixture gas of
hydrocarbons diluted with hydrogen is plasma-decomposed by high frequency or microwave in
the process of pyrolysis of hydrocarbon gas, and a diamond is heated on a substrate heated to
700 to 1000 ° C. It is a method of depositing a glassy film. The structure of the film obtained in
this method depends on the heating temperature of the substrate, and a heating temperature of
700 ° C. or more is required to obtain a crystalline diamond film. At temperatures below 700 °
C., the films obtained are amorphous. Therefore, in order to obtain a crystalline diamond film, a
material that can withstand heat of 700 ° C. or more is required. One of the features of the
present invention is that, since the all-carbon thin film excellent in heat resistance is used as a
substrate, crystalline diamond can be deposited without deformation of the substrate
accompanying heating. The ion beam deposition method is famous for the method of Eisenhump
of America, but in principle, the target carbon is irradiated with an ion beam from an ion source
to sputter carbon. In this method, sputtered carbon is ionized into C 'in an arc discharge space,
and a diamond-like film is deposited on a substrate to which a negative potential is applied. In
this method, the substrate temperature can be set lower than other methods, and when deposited
at around normal temperature, amorphous carbon similar to the characteristics of diamond such
as specific resistance and hardness is often precipitated, Also called i-carbon.
In the present invention, any of these known methods may be used to deposit the diamond
carbon film, but metal materials generally used for the diaphragm such as aluminum and
titanium are used under high temperatures of 700 ° C. or higher. Because of the deformation,
the depositable diamond-like film is usually amorphous. On the other hand, since the all-carbon
thin film substrate of the present invention has excellent heat resistance, it is possible to
selectively deposit a crystalline film or an amorphous film according to the purpose. It can be
said that it is the most suitable substrate material even if it is judged that the substrate alone has
excellent acoustic properties. EXAMPLES The present invention will be described in more detail
by way of examples, but the present invention is not limited by the examples. To 4% by weight of
50% methanol solution of p-toluenesulfonic acid as a curing agent is added to 100% by weight of
the initial condensation product (UF 502 manufactured by Hitachi Chemical side) of "Yoshi 1"
rainbow-1 furfuryl alcohol / furfural resin The mixture was sufficiently stirred by a mixer and
then coated on a bank sheet by a coater having a doctor blade and precured to obtain a B-staged
preformed sheet. Next, the back sheet was removed, and it was molded into a dome shape by a
vacuum molding machine, heat-cured, and demolded to obtain a diaphragm molded body. This
molded product is post-cured in an air oven at 150 ° C. for 5 hours, and then in a nitrogen gas
atmosphere furnace up to 500 ° C. at 15 ° C./hour, 500 to 1000 ° C. at 50 ° C./hour After
heating at a temperature rising rate of 0 ° C. and holding at 1000 ° C. for 3 hours, natural
cooling was carried out to complete firing. Using the glassy carbonaceous vibration plate of 25
mm in diameter and 50 μm in film thickness thus obtained as a substrate, a diamond-like film
was deposited by a known filament method. The synthesis conditions of the film are as follows: a
mixed gas is introduced into the purger under a pressure of 30 Torrs and a flow rate of 20 m1 /
min at a methane concentration to hydrogen of 5 Vol. On the other hand, deposition was
performed for 6 hours while maintaining the filament substrate distance 7 mm, the filament
temperature 2000 ° C., and the substrate temperature 800 ° C. The thickness of the obtained
film was 5.5 mm, and when the surface was analyzed by electron beam diffraction, it was
confirmed to be crystalline diamond. (2) Flame retardant-60% by weight of initial condensation
product of main furfuryl alcohol / furfural resin (UF502 manufactured by Hitachi Chemical side)
and 40% by weight of natural scaly graphite (average particle diameter 1 μm) in a Warner mixer
After uniformly dispersing, high-grade dispersion was performed using a three-roll mill for ink
kneading to obtain a raw material paste composition.
To 100% by weight of the raw material paste composition, 4% by weight of 50% methanol
solution of p-) luenesulfonic acid was added as a curing agent, and the same operation as in
Example 1 was carried out to obtain a total of 25 m + wφ and a film thickness of 40 μm. A
carbonaceous diaphragm was obtained. Using this all-carbon diaphragm as a base material,
deposition of a diamond-like film was performed by a known plasma CVD method. The synthesis
conditions of the film are such that a mixed gas is introduced into the purger under the
conditions of a pressure of 30 Torrs and a flow rate of 20 m1 / min at a concentration of
methane to hydrogen, IVolχ. On the other hand, while maintaining the substrate temperature at
900 ° C., plasma was induced by microwaves at 2.45 GH 8 °, and film deposition was
performed for 4 hours. The thickness of the obtained film was 0, and the surface was analyzed by
electron beam diffraction to confirm that it was a crystalline diamond. (Effects of the Invention)
The characteristics of the diaphragm obtained by the present invention are compared with those
of the conventional diaphragm material, and the results are shown in the following table.
Material Name Speed of sound Young's modulus Density Km / sec GPa d Aluminum 5.1? 0.0 2.7
Titanium 4.9 110.0 4.5 Beryllium 12.2 270.0 1.8 Example 1 (Base Material) 7.5 78.0 1.40
Example 2 (Base Material) 11 .0 1? 5.0 1.45 Example 1 (after deposition) 8.5 116.0 1.60
Example 2 (after deposition) 12.0 238.0 1.65 As judged from this table, Example 1 In both cases,
when physical properties of the substrate before vapor deposition are compared, the physical
properties are improved by 40 to 50% in elastic modulus and by about 10% in sound velocity.
The effect of the present invention is not limited to the above-described embodiment, and the
physical properties can be further improved by making the film thickness of the deposited film
thick. These excellent properties of the diaphragm in the present invention can be sufficiently
demonstrated as a diaphragm for recent digital audio equipment.