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JPS59119997

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DESCRIPTION JPS59119997
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
method of manufacturing a diaphragm for a condenser microphone, and more particularly to a
method of manufacturing a diaphragm for a condenser microphone having a low fundamental
resonance frequency. [Technical background of the invention and its problems] Conventionally,
the electret-condenser type microphone shown in FIG. 1 has been widely used as a small-sized
microphone incorporated in a cassette type tape recorder, a portable video camera or the like. In
the figure, 1 is a vibration II which receives and vibrates a sound wave, 2 is a diaphragm ring for
stretching the layer 1, 3 is a pressure contact ring, 4 is an electret electrode used as a fixed
electrode, and 5 is for impedance matching. IC 6 is a microphone unit case, 7 is a polycarbonate
(PC) plate, and 8 is a resin mold. The vibrating film used here is usually manufactured using the
jig shown in FIG. That is, after the raw material film 9 for a vibrating membrane is fixed to the
vibrating membrane stretching frame 10, this is placed on the vibrating membrane stretching
base 11, and the wrinkles of the L refilm 9 are determined by the weight of the frame 10. The
film 9 is removed to keep a uniform tension applied to the film 9. Next, the vibrating membrane
stretching ring 2 is placed on the film 9, and after bonding the both using a conductive adhesive,
the film 9 is It is a method of cutting along the outer periphery of the ring 2. In recent years, with
the miniaturization of cassette-type tape recorders and portable video cameras etc., it has
become necessary to miniaturize the microphone itself. For this reason, a microminiature electret
condenser type microphone with an outer diameter of about six days is also in the stage of
practical use. However, although it is necessary to use a diaphragm with a small diameter for the
manufacture of a microminiature condenser type microphone, if the diameter of the membrane is
made smaller, the fundamental resonance frequency of the membrane becomes higher, and as a
result, the microminiature using this Unidirectional microphones have had the disadvantage that
their sensitivity to low frequency sounds is significantly reduced. That is, the fundamental
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resonance frequency fo of the circular vibrating membrane fixed at the periphery is expressed by
the following equation:% equation% (where a represents the radius of the vibrating membrane,
and T represents the tension applied to the vibrating membrane , M represents the mass per unit
area of the vibrating membrane, so in order to keep the radius a of the vibrating membrane at a
constant size and to lower the fundamental resonance frequency of the membrane, the tension T
applied to the film is small There is a need to. However, in the conventional manufacturing
method shown in FIG. 2, since it is necessary to remove the wrinkles of the material film 9 for a
diaphragm, the tension T applied to the film can be made equal to or less than a certain value. As
a result, it was not possible to make the fundamental resonant frequency of the vibrating
membrane equal to or less than a certain value.
On the other hand, it is also conceivable to make the mass m dog-friendly, but in this case,
although fo is lowered, it is not preferable because the transient characteristic of the microphone
is lowered. For this reason, it was not possible to manufacture an ultra-compact condenser type
microphone excellent in frequency characteristics and excellent in single directional
characteristics. SUMMARY OF THE INVENTION It is an object of the present invention to provide
a method of manufacturing a diaphragm for a condenser type microphone having a small
diaphragm radius and a low fundamental resonance frequency. [Summary of the invention] In the
method of manufacturing a diaphragm for a condenser microphone according to the present
invention, the conductive diaphragm is irradiated with an electromagnetic wave having a
wavelength of 0-10 to 10 "'m to form a molecule of the constituent polymer of the layer. It is
characterized in that the chain is partially cut, thereby lowering the fundamental resonance
frequency of the layer at the time of stretching. Hereinafter, the present invention will be
described in more detail. The conductive vibrating film used in the present invention is generally
used as a vibrating film for a condenser type microphone, and when irradiated with an
electromagnetic wave in the γ-ray to ultraviolet region in a state where a certain constant
tension is applied, Young's modulus Any polymer can be used as long as it decreases. Specific
examples include polyethylene terephthalate and polyethylene terephthalate. These may be used
in the form of a thin film, and a metal such as aluminum may be coated (for example, by vacuum
deposition) on one side, but usually at least one side is conductive. According to the method of
the present invention, usually, a conventional jig shown in FIG. 2 is used to apply tension not to
cause wrinkles and to lower the fundamental resonance frequency as much as possible, thereby
making the rail After making a diaphragm for condenser type microphone by fixing to a tension
ring, electromagnetic wave is irradiated to the surface side of the layer not covered with metal,
and the tension applied to the layer is relaxed. Thereby reducing the fundamental resonant
frequency of the layer. Usable electromagnetic waves are r-rays, X-rays and ultraviolet rays, of
which ultraviolet rays are most preferred. The irradiation intensity and the irradiation time of the
electromagnetic wave are not constant depending on the thickness of the vibrating film, the
tension when fixed to the tension ring, the material of the vibrating film, etc., and are
appropriately determined according to the fundamental resonant frequency of the intended
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vibrating film. Set to Generally, as the light intensity (dose) is stronger and the irradiation time is
longer, the fundamental resonance frequency is lowered. In the case where ultraviolet light is
irradiated, the vibrating film is heated by the heat generated by the light source, but the basic
resonance frequency of the vibrating film can not be reduced by the heating.
For this reason, the temperature is not particularly limited. As a light source to be used, in the
case of ultraviolet light, a high pressure mercury lamp, a metal halide lamp, a xenon lamp, an aclamp, etc. are exemplified, and in the case of X-ray, an X-ray tube etc. is exemplified. The
radioactive isotopes of and the like are exemplified. When ultraviolet light is irradiated, a
vibrating film having a fundamental resonance frequency of 4 to 61 Lchz can be obtained usually
by irradiation at an intensity of 30 to 300 mW / cm 2 for 1 to 10 minutes. Further, in the present
invention, in the conventional method, the material film for vibrating membrane is fixed to the
stretching frame and tension is applied to the layer, and after being irradiated with
electromagnetic waves in this state, the conductive adhesive is attached to the film. The vibrating
membrane may be manufactured by bonding a tension ring through an agent. As described
above, according to the present invention, it is a vibrating film having a desired fundamental
resonant frequency that can be irradiated with electromagnetic waves in a state where the
vibrating film is fixed by applying a constant tension to the tension ring or the tension frame. In
principle, by applying electromagnetic waves to the vibrating film without applying tension, the
basic resonance frequency is lower than before by adhering the layer to the tension ring. It is
possible to obtain a vibrating membrane. The jig shown in FIG. 2 is an example of an apparatus
that can be used in the present invention, and any apparatus can be used without being limited to
the jig as long as it can apply a constant tension to the vibrating membrane. It is. The constituent
polymer of the vibrating membrane obtained in the present invention has a structure in which
the main chain portion is partially cut by irradiation of electromagnetic waves, and this structure
can be obtained by the conventional method of simply stretching or by heating. I can not get it.
The vibrating membrane according to the present invention has a partially cut polymer structure,
whereby the tension applied to the layer is relaxed and the fundamental resonance frequency is
lowered. According to the method of the present invention, it is possible to manufacture a
vibrating membrane for a condenser type microphone having a fundamental resonance
frequency which is so low as can not be obtained by the conventional manufacturing method. For
this reason, it is possible to manufacture an ultra-compact condenser type microphone
diaphragm in which the diameter of the diaphragm is 4 基本 or less and the fundamental
resonance frequency of the layer is 6 kHz or less. Further, according to the present invention, it
is sufficient to prepare an electromagnetic wave irradiation device in addition to the vibrating
film manufacturing jig, and no special expensive equipment is required. Furthermore, since the
fundamental resonance frequency of the diaphragm decreases with the irradiation time of the
electromagnetic wave, it can be adjusted to be a diaphragm having a desired fundamental
resonance frequency. [Examples of the Invention] A polyethylene terephthalate film having a
thickness of 4 μm, on one side of which aluminum is vacuum-deposited, is fixed to a diaphragm
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supporting frame 10 having an inner diameter of 13 crn as shown in FIG. The film was placed on
a 12 crn vibrating membrane stretching stand 11 to remove wrinkles on the polyethylene
terephthalate film surface.
The weight of the vibrating membrane stretching frame 10 required to remove wrinkles on the
polyethylene terephthalate film surface was 300 gr. A conductive adhesive made of brass
diaphragm ring 2 made of brass with an outer diameter of 6 mm and an inner diameter of 3.5
mb and a thickness of 1 + m is applied to the aluminum-deposited surface of polyethylene
terephthalate in the state of being stretched in this manner. The film was fixed by adhesion to
obtain a diaphragm for a condenser type microphone. The fundamental resonance frequency of
this vibrating membrane was 7 kHz. When the weight of the diaphragm stretching frame 10 is
less than 300 gr, many wrinkles remain on the surface of the polyethylene terephthalate film
fixed by the frame 10, and a vibrating membrane usable for a capacitor type microphone is
obtained. It was not done. That is, in the conventional vibrating membrane manufacturing
method, the fundamental resonant frequency of the vibrating membrane of a microminiature
capacitor type microphone having a vibrating partial diameter of 3.5 鰭 or less using a thin film
such as polyethylene terephthalate having a thickness of 4 μm is 7 kHz or less It turned out to
be impossible. Next, when the ultraviolet light was irradiated for 1 minute using the high
pressure mercury lamp on the polyethylene terephthalate side of the obtained vibrating
membrane, the fundamental resonance frequency of the vibrating membrane decreased to 6 kHz.
Further, when the ultraviolet light was irradiated for 2 minutes, the fundamental resonance
frequency of the vibrating film decreased to 5 kHz. The intensity of ultraviolet light on the
polyethylene terephthalate side was about 240 mW / cm 2. The relationship between the
ultraviolet irradiation time and the tensile modulus of elasticity when irradiated at this intensity
is shown in FIG. 4 to 6 show electret condenser microphones of the structure shown in FIG. 1
using diaphragms whose fundamental resonance frequencies are 7, 5 kHz,% 6.2 kHz and 5.0 kHz,
respectively. It shows the frequency characteristics of the microphone when configured. As
apparent from the figure, a microphone using a diaphragm having a fundamental resonance
frequency of 5 kI (z has flat frequency characteristics and excellent single directivity. Example 2
In the same manner as in Example 1, two types of vibrating membranes having a diameter of 3.5
vts and a thickness of 2.5 μm and 4 μm were produced. The layer was then irradiated with UV
light of intensity 180-200 mW / cttH under various conditions. The temperature of the vibrating
film at the time of ultraviolet irradiation was 80 to 100 c. FIG. 7 shows the relationship between
the ultraviolet irradiation time and the retention rate of the fundamental resonance frequency fO
for the vibrating film A having a thickness of 2.5 μm and the vibrating film B having a thickness
of 4 μm (hereinafter referred to as A) , B has the same meaning).
The fO of the vibrating film before the ultraviolet irradiation is 7.5 to 8.5 kHz in the case of the
vibrating film A and 8.4 to 9.4 kHz in the case of the vibrating film B. The retention rate
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corresponds to 1.0. FIG. 8 shows the vibration film A, in which the ultraviolet irradiation time is
1.5 minutes (curve C in the figure) and 2.5 minutes (curve D in the figure), respectively. The
relationship of f is shown. FIG. 9 shows the same relationship as above in the case where the
ultraviolet irradiation time is 2 minutes (curve in E in the figure) and 3 minutes (curve in F in the
figure) for the vibrating film B. It is. Example 3 The same two types of vibrating films A and H as
in Example 2 were irradiated with ultraviolet light of intensity 70 to 75 mW / cm. The
temperature of the vibrating membrane at the time of ultraviolet irradiation was about 800. FIG.
10 shows the relationship between the ultraviolet irradiation time and the retention rate of the
fundamental resonance frequency fo for the vibrating films A and BK. The fo before irradiation
with ultraviolet light is the same as that shown in FIG. FIG. 11 shows the relationship between fo
before and after irradiation when the UV irradiation time is 5 minutes (curve in G in the figure)
and 10 minutes (curve in H in the figure) for vibration MA. It is. FIG. 12 shows the relationship
between fo before and after irradiation of the vibrating membrane B with ultraviolet light for 10
minutes. Example 4 A diaphragm similar to that of Example 1 was irradiated with r-rays of Co-60
except that the fundamental resonance frequency was 12.0 to 12-5 kHz. The relationship
between the irradiation dose and the fundamental resonance frequency f at this time is shown in
FIG. As is clear from the figure, it was found that it is possible to lower the fundamental
resonance frequency of the vibrating membrane if the radiation dose is constant or more even
when the r-ray is irradiated. Therefore, it is apparent that the fundamental resonant frequency of
the vibrating membrane can be lowered even when the X-ray existing in the intermediate region
between the r-ray and the ultraviolet light is irradiated. Reference Example The same vibrating
membrane as in Example 1 except that the fundamental resonance frequency was 10 to 11 kHz
was placed in a dryer and heated for 20 minutes under various temperatures. As a result, it was
examined whether ultraviolet light or heat was used to cut the constituent polymer of the
vibrating film when irradiated with ultraviolet light. The results are shown in FIG. The figure
shows the heating temperature and the fundamental resonance frequency f. And their
relationship with As is apparent from the figure, even when heated to around the melting point
of polyethylene terephthalate f. It has been found that it is the ultraviolet light, not the heat, that
causes the vibrating film's constituent polymer to be cut, since it does not drop so much.
From this experimental result, it is a vibrating membrane for a condenser type microphone
having a fundamental resonance frequency lower than that of the conventional one, in which the
constituent polymer of the layer is partially cut, the vibrating membrane manufactured according
to the present invention It can be said that
[0002]
Brief description of the drawings
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[0003]
FIG. 1 is a schematic sectional view of an electret condenser type microphone, and FIG. 2 is a
schematic sectional view of a manufacturing jig of a diaphragm for a conventional condenser
type microphone.
Fig. 3 shows the relationship between the irradiation time and the tensile modulus of elasticity
when the polyethylene terephthalate film is irradiated with ultraviolet light of about 240 mW /
cm2, and Figs. 4 to 6 respectively show the fundamental resonance frequency. The figure which
showed the frequency characteristic of the microminiature unidirectional electret condenser type
microphone which used the diaphragm which is 745 kHz and 6.2 kI (z, 5.0 kHz, and FIG. 7 and
FIG. 10 are respectively , 180-200 rrf N / cwt. The figure which showed the relationship between
the irradiation time and the retention of a fundamental resonance frequency at the time of
irradiating an ultraviolet-ray of 70-75 mW / cm, FIG. 8 and FIG. 9 irradiated the ultraviolet-ray of
180-200 mW / cm 2 The figure which showed the relationship of the fundamental resonance
frequency before and behind irradiation in the case. 11 and 12 show the relationship between
the fundamental resonance frequency before and after irradiation with ultraviolet light of 70 to
75 low, and FIG. 13 irradiates the vibrating film with γ-rays by Co-60. FIG. 14 shows the
relationship between the irradiation dose and the fundamental resonance frequency, and FIG. 14
shows the relationship between temperature and the fundamental resonance frequency when the
vibrating membrane is heated. DESCRIPTION OF SYMBOLS 1 ... diaphragm membrane, 2 ...
diaphragm ring ring, 3 ... pressure-contact ring, 4 ... electret electrode, 5 ... IC for impedance
matching, 6 ... microphone unit case, 7 ... · Polycarbonate (PC) plate, 8 · · · Resin mold, 9 · · · · · · · · ·
· · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · Fig. 1 Fig. 2 Fig. 3
g / m♂) 100 "0123456 UV light (remains of decoy)" Fig. 4 fo = 7.5 KHz Fig. 5 fo = 6.2 KHz Fig. 6
fo = 5, 0 KHz Fig. 7 Children 吋 rJ + UC 第 Fig. 32 Elbow front ty fo (KHz) Fig. 9 Terumura 荊 fo
(KHz) Fig. 10, cleavage (廻 Fig. 11; M @ Q fo (KHz) Fig. 12 p, Resistance to fo (KHz) Fig. 13 1
(Heavy punishment) 釉 f knee (rod)
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