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Description 1 Title of Invention
Speaker diaphragm
3. Detailed Description of the Invention The present invention relates to a speaker diaphragm
suitable for, for example, a dome-shaped speaker for middle and high frequency ranges. As is
well known, what is required as a diaphragm of a middle to high range speaker is that the mass is
small and the strength and rigidity are high. For this reason, light metals such as aluminum and
titanium have been widely used as speaker diaphragms in the past, but in recent years they have
been replaced with these recently to further increase the ratio E / p between Young's modulus (E)
and dense Ji (a) There is a movement in which a possible use of perillium glaze 9 or 9 forms a
coating layer such as ron and winter 9 or their alloys are used. However, in the case of using
beryllium, since it tends to give an ill effect IF to the human body in the manufacturing process, it
has been necessary to strictly implement its preventive measures, which has many problems in
manufacturing. In addition, the conventional chemical vapor deposition process which is
performed to obtain a coating layer such as melon has a disadvantage that it is easy to deform
the diaphragm on which it is formed because it takes a long time at high temperature. At the
same time, the power efficiency and mass productivity are low, and EndPage: 1 has the
disadvantage of becoming monovalent. Furthermore, in this case, since the surface is rough due
to evaporation, there are also problems with the appearance. Therefore, the present invention
has been made in view of the above points, and can be efficiently processed in a short time at a
low temperature by the microwave plasma i nitriding process, thereby avoiding the occurrence of
undesired deformation It is an object of the present invention to provide a very good loudspeaker
diaphragm which is inexpensive, has excellent characteristics, has a dense surface, and has a
desirable appearance. That is, the speaker diaphragm according to the present invention is a
discharge produced by transmitting microwaves into a processing chamber accommodating a
base such as a gold layer foil previously formed into a predetermined diaphragm shape and
introducing a mixed gas of nitrogen and hydrogen. It is noted that the nitriding treatment such as
sputtering of nitrogen component in the surface layer of the substrate is performed by plasma
processing. An embodiment of the present invention will now be described in detail with
reference to the drawings. That is, FIG. 1 shows a schematic example of a dome-shaped speaker
for middle to high frequency range to which the speaker diaphragm according to the present
invention is applied, and in the figure is a dome-shaped diaphragm, and (g) is a voice coil. , (S) is
a suspension wy, (P) is an edge backing, (F ') is 7 runs, (7) is a yoke, and (a) is a magnet. Then,
after the dome-shaped diaphragm in the above is made into a predetermined shape as a domeshaped substrate 17 made of, for example, titanium foil as shown in FIG. 2, microwave plasma
nitriding treatment as shown in FIG. Plural pieces are installed on the inner wall of the quartz
cylindrical body 16 in the vessel 5 which is the processing chamber of the apparatus.
That is, in FIG. 3, 1 is a microwave generation source, from which microwaves of, for example,
the frequency 2450 MEIz are generated and transmitted by the waveguide 2 (J [standard WRJ-2,
109 × 55 iaw)]. The waveguide 2 is provided with a matching section or plunger 3 and a three
stub tuner 4 in order to match the transmission of the microwaves. 6L waveguide 2) A plasma
generation chamber with a large diameter, that is, a stainless steel closed vessel (inner diameter:
30 mm, length: 50 an), a microwave non-transmissive member for preventing microwave
leakage, and energy injection efficiency is It is possible to prevent external influences such as
external impedance change. In addition, the closed container 5 may be made of non-metal coated
with a conductive film other than such metal, or made of non-metal in which a water layer is
provided on the outer wall. Here, the closed container 5 has an exhaust port 6 and a gas
introduction lower, and the exhaust port 6 has an exhaust device 8 having a diffusion bond fJla%
rotary pong 8 bs cold trap 8C with pulp 9 interposed therebetween. It is connected. In addition,
the gas introduction lower is pulp 10, nitrogen gas through flow meter 11? While the pump 12 is
connected, a hydrogen gas generator 15 is connected via a no-krub 13 and a flow meter 14. The
closed vessel 5 has a diameter of 1/2 or more of the microwave wavelength, in which a quartz
cylinder 16 (diameter 25 mm, length 30 cIL) is disposed, and the cylinder 16 is an insulator on
the inner wall thereof Thus, the plurality of dome-shaped substrates 17 described above are
installed in a state of being electrically suspended with respect to the case container 5.
Furthermore, 18 is an ionization vacuum gauge to check the degree of vacuum of the closed
vessel 5 at the time of exhaust, and 19 is a film pressure gauge to check the pressure in the
closed vessel 5 during processing. A cooling pipe 20 is provided around the closed vessel 5, and
cooling water is allowed to flow therethrough to cool the closed vessel 5 from the outside.
Further, the microwave transmitted through the waveguide 2 is taken out by the copper pipe
antenna 21 (outer diameter 61101%, inner diameter 4 m) inserted in the waveguide 2 and
introduced into the sealed container 5 It has become. The antenna 21 is surrounded by a quartz
cylinder 22 (201 m in thickness, 2 m in thickness) sealed on one side which transmits
microwaves, and is inserted into the center of the closed container 5. The space between the
quartz cylinder 22 and the closed vessel 6 is hermetically sealed by an O-ring 23. In addition,
non-oxidizing gas such as inert gas or nitrogen gas is flowed as an appropriate cooling gas 24
inside the antenna 2 so as to cool the antenna 2 and the cylinder 22 surrounding it and ending
Page: 2 ing.
Thus, the inside of the closed vessel 6 is evacuated, and by introducing nitrogen gas and
hydrogen gas at an appropriate mixing ratio and introducing microwave power) to generate the
plasma 25, each substrate 170 surface nitriding treatment Is done. At this time, the circle l116 in
which the respective substrates 17 are provided also serves to prevent the diffusion of the
plasma 25 to the wall surface of the closed container 5. In addition, the quartz cylinder 22
prevents the antenna 21 from being exposed to the plasma 26. Next, the plasma nitriding
process using this apparatus will be specifically described below including the procedure. First,
each base 17 is prepared, and is stored in the closed container 5 while being held on the wall of
the quartz cylinder 16 as shown in the figure. Then, the diffusion pump 8a built in the exhaust
unit 8 evacuates the pulp to about IX10-'Torr, and then the pulp of the diffusion pump 8 & is
closed, and the pal flO 13 is opened to put nitrogen gas and hydrogen gas The pressure was
about 1 + 5 Torr. In this case, the mixing ratio of nitrogen gas and hydrogen gas differs
depending on the degree of nitriding treatment α, but in this embodiment, it is 1: 1. The mixed
gas is adjusted at a flow rate of about 20 cc / min at a valve 9 so as to be replaced via a cold trap
8c cooled with liquid nitrogen by a rotary pump 8b in an exhaust system 8. On the other hand,
argon gas was used as a cooling gas flowing to the copper pipe antenna 21. In such a state, the
mixed gas is discharged by microwave power with a frequency of 2450 'MHz and an output of
850 W from the microwave generation source 1 to generate a guzz 26. The microwave discharge
plasma 25 generates active species such as nitrogen ions, nitrogen-hydrogen molecular ions, and
various radicals, which react with the respective substrates 12 to splay into their surface layers. .
After such a plasma reaction is sustained for a predetermined time of several tens of minutes to
several hours, the discharge is stopped, and when each substrate 17 is taken out while filling the
closed vessel 5 with nitrogen gas, the surface of each substrate is extremely dense. While
exhibiting a light gold color tone in the state, it was found from the cross-sectional photograph
by a metallographic microscope that a very hard nitrided layer was formed over about several
μm to several hundred μm. In the plasma processing apparatus of this embodiment, since the
closed vessel 5 constitutes a plasma generating chamber of a wide space separated from the
waveguide 2, firstly, a large-sized 9 large substrate obtained by processing a large number of
substrates simultaneously is used. It is easy to process. Second, even if the discharge plasma gas
pressure is changed in a wide range, the discharge can be stably maintained.
Therefore, application to various surface treatments and plasma reactions is also possible. In
particular, since the discharge space is wide and the discharge is stable even at a low pressure
(e.g. 10 -2 to 10 "-'Torr) due to the high frequency property of microwaves, the mean free path of
ions or radicals is large. Since a widely spread uniform plasma can be generated, processing of
uniform distribution can be easily performed. In addition, since microwave discharge is easy to
use, it is easy to match, and because it uses a waveguide and a metal antenna for microwave
transmission, the electromagnetic radiation loss is extremely small and the power efficiency is
good. There is also the advantage that it can be processed at low temperatures without
deformation of the substrate. And, since a large microwave can be easily injected into the plasma,
the processing speed can be increased and processing can be performed for a short time. FIG. 4
shows the characteristics of the case of applying to a dome-shaped speaker having a diameter of
251 m, and the one with a curved line is the characteristic of a titanium diaphragm with a
thickness of 20 μm which is not subjected to nitriding treatment. The characteristic is obtained
when nitriding treatment is performed to a depth of about 5 μm from the surface of the same
diaphragm (corresponding to the above-described base) K. That is, as is apparent from this
comparison, the speaker diaphragm made by the nitriding process according to the present
invention can flatten the frequency characteristics more than the one without the nitriding
process and at the same time the high frequency characteristic around 20 kHz. It is understood
that it can be extended. The speaker diaphragm formed by the nitriding treatment according to
the present invention is not limited to the above-described embodiment, and various
modifications and applications can be made within the EndPage: 3 range without departing from
the scope of the present invention. There is no point to say. For example, the substrate may be a
stainless steel foil other than titanium, an alloy foil containing aluminum, or an alloy foil
containing iron, as long as it is a metal material that can be nitrided. When stainless steel foil is
used as the substrate, there is an advantage that the nitriding treatment can be performed in a
very short time so that the entire nitriding can be completed within 30 minutes, for example,
with a thickness of 30 μm. Therefore, as described above in detail, according to the present
invention, microwave plasma nitriding can be efficiently performed at low temperature and in a
short period of time, thereby avoiding occurrence of undesired deformation and being
inexpensive It is possible to provide a very good loudspeaker diaphragm which has excellent
characteristics, a dense surface, and a desirable appearance.
4. Brief description of the drawings FIG. 1 is a cross-sectional view of a dome-shaped speaker to
which the speaker diaphragm according to the present invention is applied, and FIG. 2 is a
perspective view showing the base shape of the speaker diaphragm used in FIG. 3 is a block
diagram of an apparatus for applying microwave plasma nitriding treatment to the base of FIG. 2,
and FIG. 4 shows the characteristics of the speaker diaphragm according to one embodiment of
the present invention obtained by the apparatus of the third factor. It is a curve figure shown
contrasting with what before nitriding treatment. (B) ... diaphragm, 17 ... substrate. Applicants
Attorney Attorney Takehiko Suzue 11 m1 for citation Hz) EndPage: 4