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JPH08126090

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This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
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DESCRIPTION JPH08126090
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
method of forming a waterproof protective film according to the manufacture of an ultrasonic
ultrasonic receiving element using a porous piezoelectric element used for a fish finder or a
sonar or the like.
[0002]
2. Description of the Related Art Conventionally, piezoelectric ceramics have been used as
underwater ultrasonic transmitting and receiving elements such as fish finders or sonars. In
particular, porous piezoelectric ceramics have a lower dielectric constant ε, maintain the same
electromechanical coupling coefficient, lower acoustic impedance, and lower mechanical quality
factor QM than in the case of a dense body, and therefore reception for a wide range of
frequencies It is effective as an element.
[0003]
Because these devices are used underwater, they need to be completely waterproofed.
Conventional waterproofing methods include a method of placing an insulating body in a strong
outer shell and placing an element in the liquid, and a method of molding a rubber-like elastic
film such as silicon or urethane. (For example, Akio Hasegawa, Tetsu Yoshii, Toshio Kikuchi,
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Journal of the Japan Society of Ocean Acoustics, Vol. 18, No. 3, pp 154-164)
[0004]
However, in the conventional waterproofing method, the ultrasonic wave receiving vibration is
largely attenuated in the waterproofing phase, or uneven distribution is caused due to refraction,
deflection or the like. As a result, sensitivity is reduced. Also, the waterproofing method is
complicated and expensive. Therefore, establishment of a method for waterproofing without
causing a decrease in sensitivity is desired.
[0005]
[Problems to be Solved by the Invention] In view of the above problems, the inventor of the
present invention has completed the present invention as a result of earnest research, and the
object of the present invention is that it causes a decrease in sensitivity. It is an object of the
present invention to provide a simple and inexpensive waterproof protective film forming
method.
[0006]
[Means for Solving the Problems] The above-mentioned object relates to the manufacture of an
ultrasonic ultrasonic receiving element using a porous piezoelectric element, and an ultrasonic
wave is applied to a rubber-like elastic film having a thickness of 10 to 100 μm on the receiving
surface. It is achieved by a waterproof protective film forming method characterized in that it is
attached to a receiving surface.
[0007]
Unlike the conventional waterproofing method, the waterproof protective film forming method of
the present invention adheres a rubber-like elastic film.
Further, the thickness of the rubber-like elastic film can be defined, and the attenuation of
ultrasonic vibration can be suppressed as much as possible.
[0008]
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The protective film of the present invention is a so-called rubber-like elastic film having rubberlike elasticity.
The rubber-like elasticity of the protective film allows the internal piezoelectric element to
vibrate freely without being restricted by the protective film. When the protective film does not
have rubbery elasticity, the piezoelectric element and the protective film integrally vibrate to
result in an apparent increase in acoustic impedance, which is not preferable. Further, the
protective film of the present invention must exhibit a waterproof effect completely, but by using
a rubbery elastic film, the waterproof property can be maintained against external damage and
impact.
[0009]
The thickness of the protective film of the present invention is in the range of 10 to 100 μm.
When the thickness of the protective film is less than 10 μm, a scratch is likely to be generated
due to an impact from the outside and the like, and there is some fear in waterproofing, which is
not preferable. On the other hand, when the thickness exceeds 100 μm, the attenuation of the
ultrasonic vibration becomes large, which is not preferable.
[0010]
Any material may be used as the material of the protective film as long as it has rubbery
elasticity at the temperature used (generally 0 to 40 ° C.) and the thickness is within the above
range. For example, silicone rubber, polyisoprene (natural rubber), polybutadiene, styrenebutadiene-styrene triblock copolymer, and the like can be mentioned. Among them, polyisoprene
which is inexpensive and easily processed to the thickness defined in the present invention is
preferable.
[0011]
The protective film of the present invention is formed by sticking on the receiving surface of the
piezoelectric element. By sticking, a protective film is formed with a fixed thickness. That is, when
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silicone rubber etc. were molded like before, it was very difficult to form the thickness uniformly.
As a sticking method, it is preferable to carry out using an adhesive material so as not to cause
air inside. As the adhesive, for example, any adhesive such as silicone resin, epoxy resin, acrylic
resin, melamine resin, urethane resin, emulsion of polyvinyl acetate and polychloroprene
adhesive, or hot melt adhesive may be used. From the viewpoint of long-term stability and
workability, silicone-based or epoxy-based adhesives are preferred.
[0012]
The device of the present invention is for the reception of ultrasonic waves in water. As it is an
element for reception, the attenuation, refraction and deflection of ultrasonic vibration greatly
affect the element performance. Therefore, when air is mixed in the protective film and the
piezoelectric element, nonuniformity of the received signal such as attenuation, refraction and
deflection of ultrasonic vibration may occur in that portion, and it is preferable to avoid it as
much as possible.
[0013]
The piezoelectric element of the present invention is a porous body. The properties required of
the piezoelectric element part for underwater ultrasonic wave receiving elements are: small
dielectric constant, large electromechanical coupling coefficient, small acoustic impedance
(ideally equivalent to acoustic impedance of water), mechanical quality coefficient It is small. A
porous piezoelectric material is most suitable as a piezoelectric element that satisfies these
conditions. (For example, Katsuyoshi Ina, Yoshimasa Mano, Seiji Omura, Kunihiro Nagata, Jpn. J.
Appl. Phys. Posting)
[0014]
The porosity of the porous piezoelectric material is preferably 30 to 80%. If the porosity is less
than 30%, the sensitivity as the receiving element is insufficient because the reduction of the
dielectric constant and the acoustic impedance is insufficient. On the other hand, when the
porosity exceeds 80%, the mechanical strength of the element itself is reduced, which causes a
practical problem. There is no restriction on the pore diameter.
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[0015]
Examples of the material of the piezoelectric element include lead titanate, lead zirconate, lead
zirconate titanate, lead magnesium niobate, barium titanate, cobalt niobate, lithium niobate,
lithium tantalate and the like. Among these, any material may be used if it is used as a general
piezoelectric ceramic, but it is preferable to use lead zirconate titanate having the highest
piezoelectric property.
[0016]
An example of the production of a porous piezoelectric material is shown. For the porous
piezoelectric material, at least a piezoelectric ceramic powder and spherical resin beads for
forming pores are prepared, and after mixing them (if necessary, a binder, a dispersing agent, etc.
are also mixed), dry pressing method, wet pressing method, It can be produced by molding a
precursor by a usual ceramic molding method such as a slurry casting method, an injection
molding method, etc. Then, resin beads are burned and removed together with firing (defatting)
and then this firing is carried out. At this time, the portions of the beads removed by incineration
become voids.
[0017]
As the spherical resin beads for pore formation, any resin which is usually commercially available
may be used. Specifically, polystyrene, polyethylene, polypropylene, acrylic and the like can be
mentioned. Moreover, in order to enlarge a pore diameter, the bead which expanded these can
also be used.
[0018]
The degreasing and firing of the porous piezoelectric material is carried out by a conventional
method. In the degreasing step, resin beads (and organic substances such as a binder and the
like) for pore formation are removed by raising the temperature to 500 to 600 ° C. at a
relatively moderate temperature rising rate. At this time, fresh air can be introduced into the
furnace to promote this. When using piezoelectric ceramics accompanied by evaporation at a
high temperature such as lead in firing, they are filled in a sealed container to compensate for
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this or in powder that generates evaporation substances, and a predetermined temperature
(usually Bake at 1350 ° C. Next, an electrode is placed on the porous piezoelectric body
manufactured in this manner, and polarization processing is performed to complete an element.
[0019]
Since the electrode is installed using a porous piezoelectric material, it is preferable to use a
metal foil in order to avoid contact failure due to the unevenness as much as possible. As the
metal foil electrode, any of noble metals such as gold, silver, platinum and palladium, base metals
such as aluminum and copper, or alloys thereof may be used, but copper which is inexpensive
and has excellent chemical stability Preferably, aluminum is used. Moreover, as for the adhesion |
attachment, it is preferable to use an electroconductive adhesive.
[0020]
As for the shape of the receiving element, as shown in FIG. 1, a shape in which vibration from a
predetermined direction is selectively received by a flat plate piezoelectric element, or as shown
in FIG. The present invention is applicable to any of the shapes for receiving.
[0021]
The present invention will be specifically described with reference to the following examples.
EXAMPLES Example 1 First, a porous piezoelectric material is prepared. Polystyrene spheres
classified to 150 μm in diameter and lead zirconate titanate (hereinafter referred to as “PZT”)
powder are dry-mixed at a volume ratio of 7: 3 and then press-molded with a molding die of 50
× 50 × 10 mm, porous A piezoelectric precursor was obtained. Next, the resultant was fired in
an electric furnace at 1200 ° C. for 2 hours to produce porous PZT having a porosity of 61%
and a pore diameter of 60 μm.
[0022]
Then, the porous PZT is cut into 20 × 20 × 4 mm, and a copper foil of 10 μm thickness is
attached with an adhesive having electrical conductivity (dotite, D-723S, manufactured by
Fujikura Kasei), and then 120 Polarized at 3 kv / mm in silicone oil for 20 minutes.
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[0023]
Next, a coaxial cable was installed and soldered to both electrodes for extracting signals.
Subsequently, as shown in FIG. 3, it installed in a 30x40x10 mm acrylic plate shape with a
double-sided tape via elastic rubber of thickness 2 mm. Next, a 5, 10, 50, 100, 200 μm thick
polyisoprene rubber is attached to the receiving surface with an epoxy adhesive (araldite), the
side of the porous PZT is molded with elastic silicone rubber, and the underwater ultrasonic wave
receiving element (Hydrophone element) was produced. For comparison, a device was also
prepared in which the receiving surface was not bonded with polyisoprene rubber, but was
molded entirely with silicone rubber, and a device molded with an epoxy resin having no rubbery
elasticity.
[0024]
The reception sensitivity of underwater ultrasonic waves was measured by the mutual calibration
method. (Ultrasonic Technology Handbook, Nikkan Kogyo Shimbun, p. 458) A sample is placed at
a sample distance of 1 m in a 1 × 3 × 7 m underwater tank, and the transmission voltage and
the reception voltage are measured. Calculated according to (7). In addition, the composite
(piezoelectric rubber) of PZT and resin was used as a calibration sample, and the impedance was
measured by YHP-4192A.
[0025]
S1 × M2 = E2 / E1S2 × M3 = E4 / E3S1 × M3 = E6 / E5S1 / M1 = H / Zf1S2 / M2 = H / Zf2S3
/ M3 = H / Zf3M32 = Zf2 / H × E1 / E2 × E4 / E3 × E6 / E5H = ρ × f / (2 × d) where S1:
transmission sensitivity of calibration sample 1 (piezoelectric rubber) S2: transmission sensitivity
of calibration sample 2 (piezoelectric rubber) S3: underwater ultrasonic wave reception Element
transmission sensitivity M1: Reception sensitivity of calibration sample 1 (piezoelectric rubber)
M2: Reception sensitivity of calibration sample 2 (piezoelectric rubber) S3: Reception sensitivity
of underwater ultrasonic wave reception element Z: Underwater impedance (fn: sample
Frequency dependency of n) H: calibration constant ρ: water density f: frequency d: inter-sample
distance Table 1 shows the peak sensitivity of underwater ultrasonic wave reception. An element
having a reception sensitivity of -185 dB or more is considered to be good. [Table 1] *:
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Comparative Example In the sample No. 1, the waterproof protective film was cracked by
external impact during use, and it was judged that it was difficult to use for a long time.
[0026]
From the results of FIG. 4, the thickness of the protective film is in the range of 10 to 100 μm.
[0027]
According to the waterproof protective film forming method of the present invention, it is
possible to produce an underwater ultrasonic wave receiving element excellent in waterproofness
without causing a decrease in sensitivity when ultrasonic waves are received in water.
[0028]
Brief description of the drawings
[0029]
1 is an explanatory view of the shape of a receiving element that selectively receives vibration
from a predetermined direction by a flat plate piezoelectric element.
[0030]
2 is an explanatory view of the shape of a receiving element that receives vibration from all
directions using a cylindrical piezoelectric element.
[0031]
Explanatory drawing of the shape of the receiving element of FIG. 3 Example 1. FIG.
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