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Description 1, title of the invention
Acoustic transducer diaphragm and method of manufacturing the same
3. Detailed Description of the Invention The present invention relates to a diaphragm of an
acoustic transducer such as a speaker or a microphone and a method of manufacturing the same.
A diaphragm such as a speaker or a microphone needs to have high elasticity and low density as
much as possible, and it is desirable that boron or beryllium can be easily used as a thin film in
order to radically improve the characteristics. However, it is not easy to form these materials into
thin films to form diaphragms. EndPage: 1 That is, in the case of manufacturing a diaphragm
made of beryllium or boron in the related art, a substrate such as aluminum, titanium or copper
is maintained at a high temperature of 3 ° C. or higher, and is placed on the substrate in a
vacuum of 10 Torr or less. Deposition O According to this method, it is batch production and the
production cost is high. In addition, the film quality of the obtained film is generally quite poor.
For example, the modulus of elasticity of the boron coating according to this method is about
20% smaller than that of boron. The same can be said for the IJIJ-um film. Furthermore, in the
case of the production of the IJIJium in the conventional method, vapor deposition is a poor
manufacturing process in terms of industrial hygiene in terms of the inherent toxicity of the
IJIJium. Also, in the case of vapor deposition of boron, the deposition rate of boron is generally
very slow, several μm / hour, which is a serious problem in terms of manufacturing cost. Thus,
although it is considered that boron or iron IJIJ is extremely excellent in physical properties, it is
considered to be an extremely excellent diaphragm material, but at the present time it has
considerable disadvantages in the manufacturing process or in the characteristics of the obtained
film. . Although aluminum plates and titanium plates are considerably used as materials for
diaphragms, they are generally considered to be still insufficient in terms of elastic modulus and
density. In view of the above-described drawbacks of the conventional diaphragm materials, the
inventor focused on aluminum boride, or a mixed crystal of aluminum boride and magnesium
boride as alternatives to these materials, and mainly composed these. The present invention
provides a diaphragm as an element and a method of manufacturing the same. Two main types
of substances are known as aluminum borides. That is, aluminum diboride 1 (AIB 2) and
aluminum 12 boride 1 (AIB + 2). AlB 2 is mainly identified, although some other phases are
observed in the result of X-ray diffraction measurement of the produced aluminum boride from
aluminum powder and boron powder and the manufactured diaphragm. The At temperatures
above 1400 ° C., AIB and 275 are synthesized at temperatures higher than this, and it seems
that AlB 2 tends to precipitate at temperatures lower than this.
Magnesium diboride (lqB,,) is known as magnesium boride. This substance is the same layered
structural compound as AIB. The inventors identified MqB synthesized from magnesium powder
and 46 W elemental powder by X-ray diffraction. At this time, the difference in the stability of the
MgB 2 in the high humidity atmosphere occurred due to the difference in the manufacturing
conditions. The inventors synthesized a mixed crystal compound of aluminum boride and
magnesium boride, that is, a ternary compound of aluminum, magnesium and boron, with
aluminum powder, magnesium powder and boron powder. The result of X-ray diffraction
measurement of this compound corresponds to the X-ray peak according to the shift of the
crystal lattice length of this compound as the amount of magnesium is increased relative to the
amount of aluminum in the raw material powder. The angle also shifted. In addition, when the
amount of magnesium powder is overwhelmingly larger than that of aluminum powder in the
raw material, the color of the surface slightly changes in a high humidity atmosphere depending
on the manufacturing conditions. Boron has a density of 2.36 C1 / cyA and a speed of sound of
approximately 13000 m / s (speed of sound <Q1. E is the elastic modulus, ρ is the density, and
in the following, the acoustic velocity is considered instead of the elastic modulus). This figure of
boron is close to the highest among substances. The density is 1, 82 q / cd, and the velocity of
sound is approximately 12,900 m / sec. In comparison with these, AIB + 2 exhibits the same
density and sound velocity as boron, and is excellent as a diaphragm material. AlB2 has a density
of 2.95 (J / clt * sound velocity of about 12000 m / IJ and is suitable for a diaphragm material.
According to the inventor, magnesium boride (consisting mainly of MgB) may have some
problems with moisture resistance, but the density is approximately 2.4 q / ca and the speed of
sound is 12500 m / IJ, It is a good number for the diaphragm. In the case of a mixed crystal
compound of magnesium boride and aluminum boride, the velocity of sound is substantially
distributed at 12000 to 12500 m / sec. The density of this mixed crystal compound is distributed
from 2.95 to 2.4. There is not much difference with AlB 2 etc. in the point of sound velocity, but
the density can be made smaller than in the case of AlB 2. This is very advantageous for EndPage:
2 in terms of diaphragm design. In addition, the moisture resistance of the diaphragm is
guaranteed against variations in manufacturing conditions as long as the amount of magnesium
in the raw material is not overwhelmingly increased relative to the amount of aluminum. With
regard to the moisture resistance of the diaphragm made of magnesium boride or the diaphragm
made of a mixed crystal compound of aluminum boride and magnesium boride, if necessary, a
coating of an inorganic substance, eg silicon oxide, or a coating of an organic resin is applied. Be
The synthesis of AIB, 2 requires high temperatures of over 1000 ° C. On the other hand, AlB 2
can be synthesized at a relatively low temperature and is likely to be scaly crystals, so it is
oriented and solidified by means such as pressing, and in the state of being a diaphragm
Considering that the -j property and elastic modulus of this diaphragm are improved, it is also
preferable to adopt AlB2 as aluminum boride, which is more preferable for magnesium 0 boride
or a mixed crystal compound of aluminum boride and magnesium boride. It is similar. That is,
scaly crystals of the AlB 2 type tend to precipitate at relatively low temperatures, and have the
same advantages as described above. That is, the present invention is made by paying attention
to a boride whose A- and B-faces are formed of at least one member and boron in the group
consisting of aluminum and magnesium. Next, an example for embodying the present invention
will be outlined. A metal powder and a boron powder at least one member of a group consisting
of aluminum powder and magnesium powder are uniformly mixed to obtain a mixture. At this
time, it is desirable that the total gram atomic ratio of the metal powder and the boron powder be
0.4 to 1 to 0.6 to 1. When the drum atomic ratio is out of the above range, unreacted metal and
boron are clearly recognized in the obtained diaphragm, and in some cases, it may be extremely
porous or the tensile strength may be extremely poor. In order to mix uniformly, the smaller the
particle size of metal powder and → boron powder, the better, and it is desirable that they have
substantially the same particle size. However, the finer the particle size, the higher the content of
impurities tends to be. Further, the particle size of magnesium powder and boron powder is
limited in commercial products. Powder production of magnesium and aluminum involves the
danger of k. However, according to the inventor's research, if the reaction time is sufficiently
long, the particle size of the raw material powder will not be an important factor in obtaining a
uniform diaphragm. It is desirable that the mixing of the raw material powder be made with a
roller or a ball mill. In this case, it is necessary to add 2 to 40 parts by weight to the raw material
powder of a lubricant which evaporates, evaporates, or decomposes, for example, alcohol or
paraffin, by heating or pressurization. If the amount of this lubricant is too large, the fluidity of
the mixture becomes a dog, which causes problems in the subsequent work. It is necessary for
the lubricant to act as a binder for the raw material powder in the next molding process (ie, some
higher alcohols and paraffins) or, otherwise, it is necessary to add a binder such as a higher
alcohol to the lubricant. There is.
This binding agent is effective in the next molding process, and is preferably 2 to 20 parts by
weight with respect to the raw material powder. It is desirable that the binder be vaporized,
evaporated or decomposed by heating or pressurizing 1 ° at the time of reaction. When the
amount of the binder is too small, molding in the next molding process becomes difficult, and
when it is too large, the porosity of the obtained diaphragm becomes a dog and the strength
becomes considerably inferior. In the case of kneading with a ball mill, the mixed wire
atmosphere should be set to about 10 Torr, or the mixture which is desirable for long-time
kneading should be embossed. Thereafter, the embossed product is maintained at a temperature
at which the lubricant and binder evaporate, evaporate or decompose. At this time, it may be
desirable to slightly pressurize the product. The atmosphere is preferably 10 Torr or a nitrogen
atmosphere. This process can be omitted if evaporation, evaporation or decomposition of the
lubricant or binder is rapid. The product obtained as described above is finally put in a high
pressure apparatus and kept at a pressure of 200 to 1000 "p / cA and a temperature of 750 to
900 DEG C for several minutes to several tens of minutes. Most of the soot product is reacted to
boron compound. Atmosphere EndPage: 3 atmosphere is desirable a nitrogen atmosphere or a
reduced pressure atmosphere of 10 Torr or less. Even in the case of the atmosphere in the air,
when the mixture does not contain magnesium, a good diaphragm can be obtained. In addition,
when the pressure was lower than 200 K // c4 or the temperature was lower than 750 ° C., the
mechanical properties of the diaphragm were inferior. If the pressure or temperature is too high,
the high pressure device becomes complicated. The diaphragm made in this way has the speed of
sound as described above. The density was lower than expected. This corresponds to a porosity
of 5 to 15%, and the Q value of the diaphragm has been lowered correspondingly. That is,
adjustment of the Q value of the diaphragm is possible to some extent by the porosity. As a result
of X-ray diffraction of such a diaphragm, it is considered that aluminum and magnesium
borohydride (AlB2 and IN / I1gB2), and mixed crystal compound ・ · et al of aluminum
borohydride and magnesium borohydride. Diffraction of the lines appeared as predicted by each
diaphragm. Apart from the above, some X-ray diffraction of silicon carbide (B4C) and boron was
observed, but no difference was observed in the characteristics of the diaphragm. The following
method of manufacturing the diaphragm is also mass-producible. Good diaphragm was obtained.
A metal powder consisting of at least one of the group consisting of aluminum powder and
magnesium nide powder, boron powder, epoxy resin, and a curing agent are kneaded with a
roller and rolled to obtain a flat plate.
At this time, the atomic ratio of metal powder to boron powder is made to be 4 to 1 to 0.6 to 1,
and the epoxy resin / hardener is 2 to 20 weight based on the total amount of metal powder and
boron powder. Part. The epoxy resin and the curing agent serve as binders for the metal powder
and the boron powder. Next, if necessary, the epoxy resin k is heat-cured to some extent in a
reduced pressure atmosphere of 10 Torr or less or a nitrogen atmosphere if it is necessary, for
example, if the plate is made of magnesium or the like. Next, this is brought to a temperature in
the range of 750 to 90 ° C. while applying a pressure of 200 to 100 ° ν / cJ. The atmosphere
at this time may be a reduced pressure atmosphere of 10 Torr or less, or a nitrogen atmosphere,
if necessary, such as when magnesium is contained in the air or in a flat plate. The characteristics
of the diaphragm thus obtained had a slightly lower sound velocity than that described above.
The density was also evaluated as having a porosity of 5 to 20%. Accordingly, the Q value also
decreased slightly. As a result of X-ray diffraction measurement of such a diaphragm, diffraction
of X-rays of B4C and other unknown phases is recognized in addition to diborism. However, the
influence of this on the diaphragm characteristics was such that it could not be identified clearly.
The invention will now be elucidated by means of specific examples. [Example] Commercially
available aluminum powder 20q having an average particle size of approximately 1 to 5 μm and
purity of 99.9%, and commercially available magnesium powder (purity approximately 99%,
particle size of approximately 1 to 10μ) 46q, A powder obtained by dissolving boron powder
20CI having a diameter of about 2 μm and purity 99.9% and further 72.7 g of a commercially
available epoxy resin and a curing agent 19 in 100 cc of acetone is added and kneaded by a ball
mill. Next, this mixed material is air-dried, acetone is evaporated to some extent, and then
embossed. This product is kept at 80 ° C. for about 3 minutes in the atmosphere to obtain a
gripple. More desirably, the product may be air dried at room temperature to obtain a prepreg.
Next, this was placed in a vacuum hot press apparatus, and kept at a temperature of 80 ° C. for
10 minutes while applying a pressure of 600 ′ ′ t / ca while maintaining an atmosphere of
about 10 Torr by a rotary pump. The speed of sound of the product thus obtained was 12,450 m,
the density was 2.8, and it was excellent as a diaphragm. As a result of X-ray diffraction
measurement, in addition to a diffraction line assumed to be 7 borides, there were a line of B4C
and a considerable unknown phase. The diaphragm was also stable in air.
EndPage: 4 or more, although the present invention has been specifically described, the present
invention is not limited thereby. That is, even if the diaphragm contains some foreign matter, as
long as the characteristics of the diaphragm, particularly its sound velocity and density, are
dependent on the aluminum boride, magnesium boride or their mixed crystal compounds which
are constituents of the diaphragm, Such a diaphragm is included in the present invention. In
addition, when trying to obtain a diaphragm directly from boron by such a method, it is
presumed that a pressure of several tens of thousands of // cA and a high temperature of 1500
° C. or more are required. When beryllium is used as a raw material, its implementation is
difficult in terms of toxicity. That is, according to the present invention, an excellent diaphragm
can be obtained at a relatively low temperature, low pressure, and in a mass-producible method,
and its industrial value is thick. Name of Agent Attorney Nakao and 1 other EndPage: 5