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DESCRIPTION JPH03198500

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DESCRIPTION JPH03198500
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
piezoelectric protective film, and more particularly to a piezoelectric protective film formed for
protecting piezoelectric electrons used in underwater acoustic sensors and the like. [Prior Art] As
an application of piezoelectrics, there is an underwater acoustic sensor used as an ultrasonic
transducer such as a fish finder or a soaker. In recent years, the demand in this field is
expanding, and a high sensitivity and long life underwater acoustic sensor is desired. FIG. 2 is a
schematic cross-sectional view of an underwater acoustic sensor using a cylindrical piezoelectric
which is conventionally used. In the figure, 11 is a cylindrical piezoelectric. Reference numerals
12 a and 12 b denote spacers for making the inside of the cylindrical piezoelectric electron 11 an
air chamber 13. The air chamber 13 serves to acoustically block the inside of the cylindrical
piezoelectric electrons 11 from the added sound field. 14 is a molding material. In general, the
molding material 11 is formed on a protective film (not shown) covering the cylindrical
piezoelectric element 11 with a resin having high moisture resistance so as to withstand use in
water. As is well known, in general, the cylindrical piezoelectric 11 is an electrostrictive material
typified by barium titanate to form a cylindrical vibrator, and it is vibrated in the radial direction
of the cylinder to transmit and receive ultrasonic waves. It is an element that performs waves.
There is a feature that the dimensions can be reduced for the low frequency-1 FIG. 3 is a
manufacturing process diagram showing a method of manufacturing piezoelectrics having a
general protective film containing cylindrical piezoelectrics as described above. After forming the
base material, ie, the piezoelectric body, piezoelectric electrons having a protective film are
formed by the steps of cleaning step (1) to lead wire portion reinforcing step (13) as shown in
the drawing. The forming process of the molding material 14 is omitted in FIG. As shown in FIG.
3, since heating at high temperature after polarization in the polarization step (10) lowers the
sensitivity of piezoelectric electrons, coating and thermal curing of the resin used for the
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protective film are generally performed in steps (4), (5) Generally, it takes place before
polarization as in). As the protective film, a highly moisture resistant resin used as a resin for
coating electronic parts such as epoxy resin, phenol resin, urethane resin, silicone resin,
polyimide and the like is used. As a resin coating method, 71 coating method, immersion method,
spray method, electrostatic coating, etc. are performed. When the thickness of the protective film
is too thick, the sensitivity of piezoelectric electrons is largely reduced, and therefore, the
thickness of the protective film is generally 30 to 50-. [Problems to be Solved by the Invention] In
the piezoelectric protective film of piezoelectricity obtained by the conventional manufacturing
method as described above, a void, a crack, a pinhole, etc. are generated in the protective film of
any of the above-mentioned resins <, There is a problem that it causes a decrease in the electrical
insulation in water.
As described above, when the protective film is exposed to water due to the water absorption of
the molding material and other causes, the water penetrates to the vicinity of the electrode
through the defects of the protective film such as the above-mentioned voids, cracks and pinballs.
At the electrode, an electrolytic reaction occurs, and the product grows to the surface of the
protective film with time. Therefore, the electrical insulation is reduced. In addition, the adhesion
between the substrate and the protective film is insufficient, the protective film is peeled off, and
the electrical insulation in water is lowered. The present invention has been made to solve the
problem of the decrease in the electrical insulation in water of the piezoelectric protective film
described above, and is free from defects such as voids, cracks, and pinholes, and also to a
substrate (cylindrical It is an object of the present invention to provide a piezoelectric protective
film having high adhesiveness to a (type [Means for Solving the Problems] The piezoelectric
protective film according to the present invention is any one or a mixture of an isoimide oligomer
and an imide oligomer having an acetylene end group bonded, which is a cured polymerizable
oligomer. A cylindrical piezoelectric is coated by coalescence. [Operation] In the present
invention, an isoimide oligomer or imide oligomer having an acetylene end group or a mixture
thereof is used as a material of a piezoelectric protective film, and such an oligomer is well
soluble in a common solvent, and Since the wettability and flatness are excellent and the reaction
proceeds without releasing water and alcohol, the oligomer can be cured or crosslinked without
voids, cracks, pinholes and the like. The cured polymer film has a three-dimensional structure
and can be a protective film having good physical properties, chemical properties and electrical
properties. Among the resins used conventionally, for example, polyimide is a material having no
reactive end group by thermal curing to form a material having only a reactive end group, so that
the polyimide has a two-dimensional structure and physical characteristics. In contrast, the
chemical and electrical properties are not always satisfactory, in contrast. [Example 1] Fig. 1 is a
schematic partial cross-sectional view showing an example of a cylindrical piezoelectric having
the piezoelectric protective film of the present invention. In the figure, reference numeral 1
denotes a cylindrical piezoelectric, which is generally formed of a ceramic material obtained by
firing an electrostrictive material such as barium titanate or lead zirconate titanate. Reference
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numeral 2a denotes an inner electrode on the inner surface side of the cylinder, and 2b denotes
an outer electrode on the outer surface side of the cylinder, both of which are generally formed
of a silver film. Cylindrical piezoelectric electrons 1 are obtained by polarizing a ceramic material
formed by applying an electrostatic field between the inner electrode 2a and the outer electrode
2b at a high temperature.
The ceramic material thus polarized exhibits piezoelectric characteristics, and mechanical strain
can be detected as a voltage between the electrodes 2a and 2b through the lead wires 4a and 4b,
and functions as a piezoelectric electron 1. . Reference numeral 3 denotes a protective film
mainly for electrical insulation formed by covering cylindrical piezoelectrics including the
electrodes 2a and 2b s lead wires 4a and 4b, and in the description of the present invention, a
piezoelectric protective film (hereinafter referred to as protective film) Is called). The thickness of
the protective film 3 is formed in the range of 30 to 50 μm for the reasons described above. The
oligomer of the material forming the protective film 3 may be an isoimide oligomer or an imide
oligomer, or a mixture thereof. The above two oligomers are each represented by the following
structural formula (chemical formula). As evident from the above chemical formula, the end
group of these oligomers is an acetylene group. As such an oligomer, Thermid (trademark)
commercially available from Kanebo NSC can be used. The piezoelectric electrons of FIG. 1
having this thermid resin as a protective film are used as the sample of Example 1. In addition,
conventional piezoelectric electrons having an epoxy resin, a phenol resin, a urethane resin, and
a silicone resin, which have been conventionally used as piezoelectric protective films, are
produced as comparative examples 1.2 and 3.4, respectively, and implemented as comparative
samples. Performance comparison examination with the sample of Example 1 was conducted.
Example 1: As can be seen from the embodiment of FIG. 1 and the manufacturing process
diagram of FIG. 3, inner electrode 2a, outer electrode formed by baking a silver electrode film
(about 20 μm thick) on inner and outer surfaces The ceramic material of the cylindrical
piezoelectric 1 which is a cylindrical base material (outer diameter 38 + sm, inner diameter 28 +
om * height 30 mm) made of lead zirconate titanate having 2b is cleaned with chlorocene (step
1) and then at 80 ° C. Dried (Step 2) Furthermore, lead wire 4a (for inner electrode 28) with
polyimide tape, lead! The portion to be soldered (for the outer electrode 2b) was sealed (step 3).
Then, after soaking for 30 minutes in a solution of 150 ml of pure water and 150 ml of isopropyl
alcohol in 1.5 ml of N-β (aminoethyl) γ-aminopropyltrimethoxysilane (trademark: Shin-Etsu
Chemical Co., Ltd.), 30 minutes at room temperature It was dried for a minute and further dried
at 80 ° C. for 10 minutes. This was immersed in a 20% solution of the themid IP-fioO (isoimide
oligomer) in diglyme / THG (8/2) and pulled up at a rate of 20 cm / min.
The polyimide tape was peeled off, heat treated at 180 ° C. for 30 minutes, heat treated at 300
° C. for 30 minutes, and further heat treated at 400 ° C. for 15 minutes to cure and polymerize
the isoimide oligomer to form protective film 3 (step 4). Thereafter, the substrate was washed
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with chlorocene, and the lead wires 4a and 4b were soldered to the inner electrode 2a and the
outer electrode 2b, respectively (Steps 7 to 9). Subsequently, while immersed in silicone oil at
100 ° C., polarization was performed at 6 kV for 30 minutes (step 10), and left for 30 minutes
in silicone oil at 100 ° C. It was washed with chlorocene and dried at 80 ° C. (steps 11 to 12).
The portions where the lead wires 4a and 4b were soldered were reinforced with epoxy resin
(step 13). In the above, the manufacturing method of the piezoelectric electron which has a
piezoelectric protective film shown as Example 1 by this invention was shown. Comparative
Example 1 Here, a method of manufacturing piezoelectrics having a piezoelectric protective film
made of an epoxy resin by the same manufacturing method as that of the above-mentioned
Example 1 is shown, and this is taken as a sample of Comparative Example 1. A cylindrical
substrate similar to that used in Example 1 was washed with chlorocene and dried at 80 ° C.
The part to which the lead wire was soldered was sealed with a polyimide tape. The epoxy resin
(Japanese Vernox Co., Ltd., trademark XW-2240) was coated by the immersion method. It was
dried at room temperature for 30 minutes and heat cured at 150 ° C. for 30 minutes. The
polyimide tape was peeled off, washed with chlorocene and dried at 80 ° C. Lead wires were
soldered to the inner and outer electrodes. It was immersed in silicone oil at 100 ° C., polarized
at 6 kV for 30 minutes, and left in silicone oil at 100 ° C. for 30 minutes. It was washed with
chlorocene and dried at 80 ° C. The thickness of the epoxy resin after heat curing was about 40. The part to which the lead wire was soldered was reinforced with epoxy resin. Comparative
Example 2 A phenolic resin was coated to a thickness of about 40 in the same process as
Comparative Example 1 except that a phenolic resin (Sumitomo Bakelite Co., Ltd., trade name: pc1) was used instead of the epoxy resin. Thus, piezoelectric electrons having a piezoelectric
protective film made of a phenol resin are used as a sample of Comparative Example 2.
Comparative Example 3 In the same process as Comparative Example 1 except that a urethane
resin (Toms Corp., trade name: S layer # 100) was used in place of the epoxy resin, a urethane
resin was coated to a thickness of about 40-. Piezoelectrics having a piezoelectric protective film
made of a urethane resin are used as a sample of Comparative Example 3. Comparative Example
4 In Comparative Example 1, a silicone resin (Shin-Etsu Chemical Co., Ltd., trade name: KR255)
was coated in a thickness of about 40 μm instead of the epoxy resin.
Piezoelectric electrons having a piezoelectric protective film made of a silicone resin are used as
a sample of Comparative Example 4. The following tests were conducted on the samples of
cylindrical piezoelectric electrons shown in Example 1 and Comparative Examples 1 to 4. First,
evaluation tests of the electrical insulation in water were conducted on cylindrical piezoelectric
electrons produced in Example 1 and Comparative Examples 1 to 4. With the cylindrical
piezoelectric electrons immersed in water at 20 ° C., the current value was measured 200
seconds after applying a direct current of 100 V to calculate the electrical resistance. The results
are as follows: Example 1 according to the invention retains excellent electrical insulation.
Example 1 1 X 1013 Ω Comparative Example 1 to 10 6 ··· 2 to 10 4 · · · 3 to 4 · 10 4 Next, the
cylindrical piezoelectric electrons of Example 1 having a high electric resistance in 60 ° C. warm
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water Soaked. After a certain time elapsed, it was removed from the hot water, cooled in water
for 1 hour, and the change with time of the electrical resistance was measured in water at 20 °
C. The results were as follows. After 10 hours 100 hours 1 [) 00 hour opening and closing
Example 1 1 x 10 12 Ω I x to 12 Ω 1 x 10 12 Ω From this result, in Example 1, high electrical
insulation is obtained without any change even after immersion in hot water of 60′C for 1000
hours. It has been shown that the piezoelectric protective film according to the present invention
functions as an excellent protective film. In addition, although the case where an isoimide
oligomer was used as a material of a protective film in Example 1 was shown, the same good
piezoelectric electron protective film can be obtained by using an imide oligomer or a mixture of
an isoimide oligomer and an imide oligomer instead. can get. Also, the piezoelectric electrons are
not limited to cylindrical piezoelectric electrons, but can be applied to piezoelectric electrons of
any shape. [Effects of the Invention] As described above, according to the present invention, an
isoimide oligomer imide oligomer having an acetylene end group, or a mixture thereof is used as
a starting material, which is excellent in water resistance and electrical insulation and has voids,
cracks and pins. Since a polymer film free of defects such as holes is used as a piezoelectric
protective film, piezoelectric electron retention excellent in electrical insulation in water:! ! l A
membrane is obtained. It is also excellent in heat resistance, chemical resistance and
environmental resistance. Therefore, there is an effect that a high sensitivity and long life
underwater acoustic sensor can be realized. Also, the piezoelectric protective film of the present
invention is applicable to piezoelectrics of any shape.
[0002]
Brief description of the drawings
[0003]
FIG. 1 is a schematic view of a piezoelectric protective film of cylindrical piezoelectric according
to an embodiment of the present invention, FIG. 2 is a schematic sectional view of a conventional
underwater acoustic sensor, and FIG. 3 has a conventional protective film It is a flowchart
showing a method of manufacturing piezoelectrics.
In the figure, 1 is a cylindrical piezoelectric electron, 2a is an inner electrode, 2b is an outer
electrode, 3 is a protective film, 4a and 4b are lead wires.
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