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DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an acoustic
vibration material, in particular, an acoustic vibration material having 84C (boron carbide)
suitable as a constituent material of a diaphragm diaphragm of a speaker, a cantilever of a
cartridge, and the like. The criteria for selection as acoustic vibration materials are: (i) large
Young's modulus E (, small specific gravity 、 and large ratio E / ρ, (ii) cracks against
mechanical vibration which is inevitably added, There are no cracks and no brittleness, (iii)
stability and no secular change in environmental test such as humidity resistance, humidity
temperature cycle, salt water spray etc., (iv) excellent productivity, etc. . Among these, the
property of (i) is important. The following lists possible acoustic vibration materials and those
currently used. As can be seen from this table, 84C is an extremely excellent acoustic vibration
material. In the past, attempts have been made to apply to diaphragm materials focusing on the
characteristics of the 84C, but none of them have been satisfactory and have not been put to
practical use. As the prior art, for example, in the electric field evaporation method and the
electron beam evaporation method, the raw material 84C is heated and evaporated by an
electron beam heat source, and evaporation is carried out by simple evaporation or -2 in an
electric field of about ν. However, in this case, since the melting point of 84C is extremely high
at 2450 ° C., so-called splash phenomenon easily occurs when the raw material 84C is
irradiated with the electron beam, and the scattered 84C penetrates through the deposition
substrate of Ti or the like to open a hole. In addition, when the raw material 84G evaporates, it is
easy to decarburize, and the film deposited on the deposition substrate has a composition of B
(boron) excess rather than the stoichiometric 84C. Furthermore, the particle energy of the
evaporation particles is as small as 0.1 to 1 eV as compared with the ion plating method
described later, and therefore the adhesion strength is small and the throwing power is not good.
Also, although the high frequency sputtering method is a method of performing high frequency
sputtering of a B4C raw material target, the deposition rate is as small as 0.01 to 1 μ / sin, and
the practicality is poor particularly for a diaphragm requiring a film thickness of several μ or
more. . The adhesion strength is improved since the particle energy is 1 to 10 eV. In the 84C film
formation method by CVD method, mixed gas of hydrocarbons such as BCl 2 and CH 4 which are
constituents of 84 C is introduced onto a substrate heated to several thousand ° C., and B 4 C is
deposited by thermal decomposition reaction. It is a kind of so-called chemical vapor deposition.
Since the temperature of the substrate is high, aluminum and aluminum alloys can not be melted
and can be used, and the substrate of a titanium type is also easily deformed, so it is considered
effective only for high melting point metals such as tungsten.
Moreover, since tungsten and the like have a large specific gravity 振動 (−19, 3), they are not
suitable as substrates for acoustic vibration materials. As described above, the technology for
forming the film of 84 C as an acoustic vibration material has not yet been realized and has not
been commercialized. The present invention provides a novel acoustic vibration material which
has 84C as a constituent material in view of the above-mentioned point. The acoustic vibration
material of the present invention comprises a first film formed on a surface of a substrate and
made of a material having a large ratio of Young's modulus to specific gravity, and boron carbide
formed on the first film. It is characterized by comprising the second film made of (l (4C). As a
specific material of the first film, B may be selected based on the table on page 2 of the present
specification. That is, when the first film is formed of B, the Young's modulus and specific gravity
of the second film is relatively large with 84C, so that separation between the films occurs when
the produced vibrating material vibrates. Since the difference in propagation of the sound
velocity is unlikely to occur, it is possible to prevent the deterioration of the sound velocity (in
the case of the speaker) due to the multi-layering and the deterioration of the responsiveness (in
the case of the cantilever). The second film according to the present invention basically gasifies
elemental boron alone, while converting a hydrocarbon gas such as acetylene and methane into a
plasma, and in the plasma, the boron element and the carbon element are chemically reacted (air
The phase reaction is carried out to synthesize 84C, and the synthesized 84C is accelerated by a
high electric field and deposited on the required substrate surface to form an 84C film. In this
case, the stoichiometry (B: 78.3 wt%, C: 21.7 wt%) can be obtained by optimally selecting the
reaction conditions such as the evaporation rate of boron and the hydrocarbon gas pressure, (gas
concentration), etc. Close B and C films are obtained. As means for gasifying the boron element,
there are heating evaporation or sputtering, and as the heating evaporation source, laser beam,
high frequency induction heating, electron beam heating or the like is used. The melting point of
elemental boron has conventionally been reported in a large number of values in the range of
2300 ° C. to 2500 ° C. However, in the latest research, the value of 2075 ° C. is the most
reliable. This value is much lower than the melting point 2450 ° C. of 84 C, which is much
easier than the above-mentioned prior art which evaporates 84 C itself. It was also found that the
boron element can be melted cleanly and the splash phenomenon can be avoided by optimally
selecting the crucible material, beam diameter, beam scanning method and heating rate during
melting. As a raw material of carbon C which is another constituent element of 84 C, saturated
and unsaturated hydrocarbons of 0 to 4 are selected.
There is no particular selectivity if it is a gas at normal temperature and does not contain
nitrogen N, oxygen 0, sulfur S1 halogen, etc. in its molecule. In order to adjust the gas pressure, it
is also possible to mix an inert gas such as Ar or IIs which is not directly related to the reaction.
In addition, it is possible to react with boron vapor to some extent to synthesize 84C simply by
introducing a hydrocarbon gas, but it is more effective to make 84 C the reaction efficiency by
converting the introduced carbon hydrogen gas into plasma Can be generated. As means for
plasmatizing the introduced hydrocarbon gas, an activated reaction deposition (ARE) method, a
low pressure plasma deposition (LPPD) method, a high frequency coil method or the like is
adopted. Also, by applying a high DC voltage of minus several hundred volts to minus several
kilovolts to the base material on which the 84C film is to be applied and using so-called ion
plating method together, the particle energy becomes about several 10 to 1000 eV. Adhesion
strength on the substrate of the Cleaning of the substrate is crucial to the adhesion strength of
the BH3 film. This is usually (i) ultrasonic cleaning with a halogenated carbon solvent, steam
cleaning, (ii) dehydrating by heating to 100 ° C. to several 100 ° C. in high vacuum (1 o-5 to 1
O6 Torr). By taking steps such as bonding by gas, inert gas plasma such as (iii) Ar, etc., the
adhesive strength of the 84C film to be sufficiently satisfactory can be obtained. Next,
experimental results on the process and characteristics of the second film made of 84C according
to the present invention will be shown. FIG. 1 shows an activated reactive ion plating apparatus
applied to the present invention. In the figure, (11 is a vacuum chamber, a crucible (3) containing
a raw element of boron (21) in the chamber ill and a base material formed in a predetermined
shape on which an 84C film is deposited opposite to the crucible A substrate holder (5) for
holding (4) is disposed. The holder (5) is provided with a planetary jig, and the base material (4)
is rotated and revolved. The boron element (2) is evaporated by irradiation heating by the
electron beam (6). Between the crucible (3) and the base material (4), a ring-like gas inlet (7)
having a porous inside is arranged for introducing a hydrocarbon gas such as acetylene gas ((:
282), A ring-shaped electrode (8) is provided for plasmatizing the introduced acetylene gas. The
electrode ill is connected to the ARE power supply, and for example +1 oov is applied. On the
other hand, a direct current voltage of about 1 kV to -2 kV is applied to each base material (4)
through the holder (5).
(91 is a heater which heats the substrate (4) to a predetermined temperature, and is controlled
by a thermocouple. (10) is a film thickness monitor (composed of a quartz oscillator) for
measuring the film thickness of the B4C film. EXPERIMENTAL EXAMPLE A base (4) made of
titanium Ti with a thickness of 20 μm press-formed into a dia-flar shape of a +11 coil is cleaned
with a fluorocarbon solvent and fixed to a holder (5) of the apparatus of FIG. C.) to degas the
chamber (1) to 1 × 10 = Torr. Next, Ar gas is introduced up to 8.times.10@-'Torr, plasma is
generated by a high frequency power supply of lk-, and bombarded cleaning is performed for 10
minutes. Stop Ar gas and set I X 10 = Torr high vacuum again. The temperature of the substrate
(4) is kept at 450 ° C. Next, the boron element (99, 9%) (2) in the refractory ceramic crucible (3)
is irradiated with the electron beam (6) of 5 at the same time, and simultaneously the acetylene
(C2H2) gas is passed through the gas introduction part (7) Is introduced to 2 × 10− ′ Torr,
and an acetylene plasma atmosphere (11) is created by the electrode (8). For example, a DC
voltage of -2 kV is applied to the base material (4). Then, after reaching a steady state, the
shutter (not shown) on the crucible (3) is opened, and an 84C film is deposited on the substrate
(4) by a method of so-called activated reactive ion plating. That is, when the boron element (2 ')
melted and evaporated by electron beam irradiation passes through the acetylene plasma
atmosphere (11), the boron element and the carbon element react in a gas phase to synthesize
B4C, and this 84C is It is accelerated by a direct current electric field applied to the substrate and
deposited on the substrate (4) as high energy molecules. A reaction of 12 minutes resulted in the
deposition of an 84 C film of 6.0 μ steel thickness on the substrate (4). Next, the base material
(4) was inverted and an 84 C film of 6.0 μm thickness was deposited on the back side in the
same manner. FIG. 2 shows a diaphragm of a coil obtained by depositing the 84C film (12) on the
front and back surfaces of the titanium (Ti) base material (4). This B4CII (12) had no crystallinity
in structural analysis by X-ray diffraction and had a completely amorphous structure. This is a
preferable property when viewed as a sound W vibration material without having structural
anisotropy. FIG. 3 is an X-ray diffraction of the 84C film deposited on the glass substrate by the
above-mentioned activation reactive ion plating, and it can be seen that the 84C film is an
amorphous film. The crystallinity of the 84C film (12) deposited on the substrate (4) is related to
the substrate temperature, and if it is about 1000 ° C. or less, it becomes an amorphous film
and becomes high temperature (temperature exceeding 1000 ° C.) Then it crystallizes.
EXPERIMENTAL EXAMPLE (2) A reaction product of B (boron) -C (carbon) system was deposited
on a substrate (4) of titanium Ti (10 μ foil) by the same method as that of the experimental
example (1). At this time, a sample in which the pressure of the acetylene plasma was changed in
the range of I x 10-'Torr to IOX 10-' Torr was prepared, and composition analysis and
measurement of the velocity of sound were performed. Fig. 4 is a characteristic diagram of
quantitative analysis of the reaction product film of the B-C system (However, in this
measurement, the substrate temperature is 450 ° C, the electronic heat output is 5 kW, the ARE
voltage is +100 v, and the substrate voltage is -1. Represents a relationship in which the content
of carbon C increases as the acetylene plasma pressure increases. As a result, when the electron
beam power 5 is-, B and C are quantitatively synthesized just at an acetylene plasma pressure of
2 X 10-'Torr. That is, the composition closest to the stoichiometric composition is synthesized.
FIG. 5 is a characteristic diagram showing the relationship between the velocity of sound and the
acetylene plasma pressure. From this curve (II), it was found that the velocity of sound is the
largest when the acetylene plasma pressure is 2 × 10 ′ ′ Torr. The straight line (I [I) is the
value of only the base material of titanium Ti (10 μ foil). The film structure in each case was
amorphous (the same as in Example 11. Experimental Example (3) A B4C film was deposited on a
substrate of titanium Ti1Oμ by the same method as in Experimental Example (ill). At this time, a
sample in which the substrate temperature was changed in the range of 150 ° C. to 550 ° C.
was made, and the speed of sound was measured. FIG. 6 is a characteristic diagram showing the
relationship between the substrate temperature and the speed of sound. As a result, the substrate
temperature does not increase the sound velocity on the low temperature side, and a large value
is 1 g at a temperature of 450 ° C. or higher. EXPERIMENTAL EXAMPLE (4) A simple substance
of boron was deposited to a thickness of 6.0 μm on both sides of a drawing diaphragm of 20
μm titanium Ti foil by a conventional ion plating method. A salt spray environment test based on
JIS 2371 was conducted simultaneously with this sample and the diaphragm on which the B4C
film according to Example (1) was deposited. As a result, the diaphragm on which the B4C film
was deposited was not found to be abnormal at all, but the diaphragm on which the boron single
film was deposited showed discoloration and deterioration of the surface roughness, and the
diaphragm of the 84C film deposition was It turned out to be strong in environmental testing.
Example In order to give a meaning as an environmental protection film to a B4C film based on
example experiment example (4), the acoustic vibration material which adhered-formed B film
and this on base material was produced. Specifically, a simple substance of boron is deposited on
a titanium titanium foil of 10 μm by a general ion plating method, and 84 C is further deposited
by an activation reactive ion plating method, and the sum of both films is 6 Three kinds of
samples which were made to be 0 μm were made on trial by changing the thickness balance.
Both films were of course applied to both sides of the titanium Ti foil. The three samples were
combined with the <84C simple substance film based on the experimental example +11 and the
boron simple substance film based on the experimental example (4) to measure the velocity of
sound. The results are shown in FIGS. 7 and 8. In both figures, a on the horizontal axis is an
acoustic vibration material in which only the B film is deposited on the substrate, b. c and d
indicate an acoustic vibration material in which a double film consisting of a B film and an 84C
film is deposited on the substrate, and e indicates an acoustic vibration material in which only the
84C film is deposited on the substrate. In FIG. 7, the curve (V) indicates the thickness of the B
film, and the curve (Vl) indicates the thickness of 84C. As can be seen from the curve (.box-solid.)
In FIG. Although the speed of sound tended to be large, the difference was very small. Further,
according to the same salt spray test as in the experimental example (4), no deterioration was
observed in any of the three samples in which 84C was deposited on the boron layer except for
the boron single film. From this experiment, it was found that the 84C film had a sufficient effect
as a protective film of a boron film. In the upper side, a B4C film is deposited on a base material
of titanium Ti to constitute an acoustic vibration material, but B4C is formed on an etchable base
material such as copper Cu, iron Fe, aluminum M or stainless SUS. After that, it is possible to
deposit on the substrate, etch away the substrate, and use it as a diaphragm and a cantilever of
84C film only. According to the present invention described above, 84C can be stably produced
by gasifying the boron element by heating evaporation, sputtering or the like, and reacting the
boron element and the carbon element in the plasma of hydrocarbon gas, and further, the ion
can be ionized. It is possible to form 54cl * with good adhesion by depositing 84 C as a high
energy molecule by accelerating 84 C by a direct current electric field applied to the base
material in combination with the plating method. Therefore, it is possible to produce an ideal
acoustic vibration material with high hardness and high sound velocity 84C. In particular, with
the multi-layer structure according to the present invention, the degree of freedom in setting the
elastic modulus, density, internal loss, etc. to predetermined values is expanded. As a diaphragm
of a speaker, it is desirable that the internal loss be relatively large. If it is large, control of the
internal loss is facilitated according to the required characteristics. The diaphragm that vibrates
by receiving the force from the voice coil needs to follow the movement of the voice coil, but
when the internal loss is small, it is likely to be vibrated by the natural vibration of the diaphragm
itself and has many peaks and dips. Become.
On the other hand, when it is large, the vibrational energy from the voice coil is attenuated until
it reaches all the way, and the characteristic becomes flat at first glance, but it becomes a duller
sound without lumps. Therefore, an appropriate value is required, but when it is made of a single
material, it is almost determined by the material, so it is difficult to control the internal loss, and
it is only possible to control by the structure, so the design freedom is reduced. On the other
hand, multi-layering as in the present invention provides an effect of broadening the degree of
Brief description of the drawings
FIG. 1 is a schematic view of an activated reactive ion plating apparatus generally used in the
present invention, FIG. 2 is a cross-sectional view of a diaflane having B + cF deposited on both
sides of a titanium substrate, and FIG. 3 is obtained by the present invention. Analysis of the B4C
film, Fig. 4 is a characteristic diagram of composition analysis of B-C reaction film when
acetylene plasma pressure is changed, and Fig. 5 is acetylene plasma in B-C reaction film
Characteristic diagram showing the relationship between pressure and sound velocity, FIG. 6 is a
characteristic diagram showing the relationship between substrate temperature and velocity of
sound, FIG. 7 is a graph showing the composition of the double film formed on the substrate, FIG.
The figure is a graph showing the sound velocity of the acoustically vibrating material.
(11) is a vacuum chamber, (2) is a single element of boron, (3) is a crucible, (4) is a base, (5) is a
holder, (6) is an electron beam, (7) is a hydrocarbon gas inlet, 8) is an electrode for plasma
formation, and (11) is a plasma atmosphere.
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