JPH0360083A - Method for manufacturing piezoelectric protective film - Google Patents

Abstract

PURPOSE:To form a piezoelectric element protective film having high adhesive properties with a base material without pinhole and to prevent its electric insulation from decreasing under water by coating the base material with a silane coupling agent, drying it, and then coating it with electrically insulating polymer resin by a thermal CVD method. CONSTITUTION:A ceramic cylindrical bass material 1 in which a silver electrode is baked to inner and outer wall faces is cleaned with chlorocene, and dried. Then, leads 4a, 4b are respectively soldered to inner and outer electrodes 2a, 2b, dipped in silicone oil to be polarized, and then left to stand in the silicone oil. Then, it is cleaned with chlorocene, and dried. Thereafter, it is dipped in solution mixed with silane coupling agent. Subsequently, it is dried, coated with electrically insulating polymer resin by a thermal CVD method to form a protective film 3. Eventually, the parts soldered with the leads are reinforced with epoxy resin to complete a piezoelectric element. Thus, an underwater acoustic sensor having high sensitivity and long lifetime can be realized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for manufacturing a piezoelectric protective film, and particularly to a method for forming a protective film on a piezoelectric film for an underwater acoustic sensor.

[Prior Art] Generally, piezoelectric devices are made by coating electrodes on both sides of a base material such as ceramic, and polarizing the base material to create a piezoelectric effect. Furthermore, in applications such as underwater acoustic sensors, the entire base material is usually covered with a coating material to improve moisture resistance.

FIG. 2 shows a schematic cross-sectional view of a cylindrical piezoelectric device, which is used in many underwater acoustic sensors.

A ceramic material 1 is generally used as the base material, and barium titanate or lead zirconate titanate is generally used as the ceramic material 1. The ceramic material 1 is formed into a cylindrical shape, and an inner electrode 2a is formed on its inner wall surface, and an outer mold ti2b is formed on its outer wall surface. Silver is usually used as the material for these electrodes tif1.2a and 2b. After forming the electrodes in this way, an electrostatic field is applied between the inner electrode 2a and the outer electrode 2b at high temperature to polarize the ceramic material 1.The polarized ceramic material 1 exhibits piezoelectric properties and has no mechanical strain. Once applied, this will be detected as a voltage.

The inner and outer wall surfaces of the cylindrical piezoelectric element 11 thus formed are covered with a protective film 3 for electrical insulation. Also, a lead wire 4 is connected from the inner electrode 2a and the outer electrode 2b.
a and 4b are derived.

FIG. 3 shows a schematic cross-sectional view of an underwater acoustic sensor 10 using the cylindrical piezoelectric element 11 shown in FIG.
In order to create an air chamber 13 inside the cylindrical piezoelectric element 11, spacers 12a and 12b are inserted at both ends of the piezoelectric element.

Note that the air chamber 13 plays the role of acoustically shielding the inside of the cylindrical piezoelectric element 11 from the applied sound field. Cylindrical piezoelectric element 11 with air chamber 13 formed inside in this way
is embedded in the mold 14 and sealed to form the underwater acoustic sensor 20.

Next, a conventional method for manufacturing a piezoelectric element having such a structure will be explained with reference to the process diagram shown in FIG.

First, after cleaning and drying a base material such as ceramic (steps 400 and 401), a seal is applied to prevent resin from adhering to the part where the electrode lead wire is soldered (step 402). Resin coating and thermal curing is generally performed before polarization (step 40:l 404), since heating reduces the piezoelectric sensitivity.
As the coating material, resins with high moisture resistance, such as epoxy resins, phenol resins, urethane resins, and silicone resins, which are commonly used as resins for coating electronic components, are used. As a coating method, a brush coating method, a dipping method, a spray method, an electrostatic coating method, etc. are used.

The thickness of the protective film is generally selected to be 30 to 50 μm because if it is too thick, the piezoelectric sensitivity will be greatly reduced. Next, peel off the soldering seal (step 405).
After cleaning and drying (step 406), lead wires that will become electrodes are soldered (step 407), and then an electrostatic voltage is applied between the inner and outer electrodes via the lead wires to bond the base material to the base material. Polarization processing is performed (step 408).

After that, washing and drying are performed (step 409).
The lead wire portion is reinforced (step 410) and the piezoelectric element is completed (step 411).

[Problems to be Solved by the Invention] However, in the conventional manufacturing method described above, the protective film formed on the surface of the base material is formed by dissolving the coating material in a solvent and applying it by brushing, dipping, spraying, or electrostatic coating. Since the coating is applied using a method such as a method, pinholes are likely to form in the protective film when air is drawn in when the coating material is dissolved in a solvent or when the solvent flies off, which can cause a decline in electrical insulation properties in water. was. That is, when the protective film 3 is exposed to water due to water absorption by the molding material 14 or other causes, the water penetrates into the vicinity of the electrodes through the pinholes.

An electrolytic reaction occurs in the electrode portion, and its products grow to the surface of the protective film 3 over time. Therefore, the electrical insulation properties are reduced.

Further, in the conventional manufacturing method, there was a problem that the adhesion between the base material and the protective film was insufficient, and the protective film peeled off, resulting in a decrease in electrical insulation properties in water.

The present invention was made in order to improve the above-mentioned reduction in electrical MJI properties of the piezoelectric protective film in water.

It is an object of the present invention to provide a method for manufacturing a piezoelectric protective film that is free from pinholes and has high adhesion to a base material.

[Means for Solving the Problems] The present invention provides a method for manufacturing a piezoelectric protective film, in which the surface of a base material is coated with a silane coupling agent and dried, and then thermal CVD (Chemical Vap
The electrically insulating polymeric resin is coated using the our deposition method.

[Function] A silane coupling agent is an organic silicate polymer having two or more different reactive groups in its molecule.

One of the two reactive groups is a reactive group such as a methoxy group, ethoxy group, or silanol group that chemically reacts with inorganic substances, and the other one is a reactive group such as a methoxy group, an ethoxy group, or a silanol group.
The two reactive groups are vinyl groups, epoxy groups, methacrylic groups, amino groups, mercapto groups, etc. that chemically bond with organic agents, and chemically bond the piezoelectric substrate and protective film to improve adhesion. let

Further, the thermal CVD method is a method of activating raw material gas using thermal energy and polymerizing it on a substrate.

Since the thermal CVD method is solvent-free, does not require a catalyst, and does not require thermal curing, it is possible to form a pinhole-free polymer film with excellent electrical insulation properties.

[Example 1] Hereinafter, an example of the present invention will be described in detail in comparison with a comparative example.

FIG. 1 is a diagram showing the manufacturing process of the piezoelectric element of the present invention, and the following embodiments will be explained with reference to the diagram.

(Example 1) A cylindrical base material of lead zirconate titanate (outer diameter 38 mm, inner diameter 28 mm, height 30 mm) with silver electrodes about 20 μm thick baked on the inner and outer walls was coated with chlorocene. Wash and dry at 80°C (steps 100, 101
).

Next, solder the lead wires to the inner and outer electrodes (step 102), immerse them in silicone oil at 100°C and polarize them at 6 kV for 30 minutes (step 103),
Leave it in silicone oil at 0°C for 30 minutes. It is then washed with chlorocene and dried at 80°C (step 104).
). 1.5 ml of N-β (aminoethyl) γ-aminopropyltrimethoxysilane (Shin-Etsu Chemical Co., Ltd.) and 15 ml of pure water
0ml and 150ml of isopropyl alcohol for 30 minutes (step 105).
After that, it is dried at room temperature for 30 minutes and then at 80°C for 10 minutes (step 106). Using di-p-xylene as a raw material, a parylene vapor deposition device (manufactured by Tomoe Kogyo) is used to coat poly-p-xylylene to a thickness of 40 μm. (Step 1
07).

Finally, the portion to which the lead wires are soldered is reinforced with epoxy resin (step l○8), and the piezoelectric element is completed (step 109).

The parylene vapor deposition apparatus (Tomoe Kogyo) is a vapor deposition apparatus that coats an electrically insulating polymer material using a thermal CVD method.

(Example 2) Poly-monochloro-p-xylylene was prepared to a thickness of 40 Pm in the same process as in Example 1 except that di-monochloro-p-xylene was used instead of di-p-xylene used in Example 1. Coat.

(Example 3) Di-dichloro-P-xylene was used in place of the di-p-xylene used in Example 1, and poly-dichloro-P-xylylene was made to a thickness of 4 by the same method as in Example 1.
Coat 0 μm.

(Example 4) Instead of di-p-xylene used in Example 1,
Poly-tetrafluoro-p-xylylene is coated to a thickness of 40 μm using di-tetrafluoro-p-xylene, but in the same manner as in Example 1 except that di-tetrafluoro-p-xylene is used.

Next, in order to compare with the present invention, a protective film was formed by a manufacturing method different from that of the present invention, and this will be described as a comparative example.

(Comparative Example 1) Poly-p-xylylene was coated with a thickness of Coat 40 μm.

(Comparative Example 2) A cylindrical substrate similar to that used in Example 1 is washed with chlorocene and dried at 80°C. Next, seal the part where the lead wires will be soldered with polyimide tape. After that, epoxy resin (XW-2240 manufactured by Bellnox Japan) was applied using the dipping method.
) is coated on the surface of the cylindrical substrate. Further at room temperature 3
The epoxy resin is dried for 0 minutes and heat treated at 150'C for 30 minutes to cure the epoxy resin. Thereafter, the polyimide tape is removed, washed with chlorocene, and dried at 80°C. Lead wires are soldered to the inner and outer electrodes, 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. Thereafter, it is washed with chlorocene and dried at 80°C. The thickness of the epoxy resin after heat curing was approximately 40 μm.

Finally, reinforce the part where the lead wire is soldered with epoxy resin.

(Comparative Example 3) A 40 μm thick cylindrical base material surface is coated with a phenol resin using the same process except that a phenol resin (PC-1 manufactured by Sumitomo Bakelite) is used instead of the epoxy resin used in Comparative Example 2.

(Comparative Example 4) Urethane resin (Tom's ILS Leia #100) was used instead of the epoxy resin used in Comparative Example 2, and the urethane resin was coated to a thickness of about 40 μm in the same process except for the same procedure.

(Comparative Example 5) A silicone resin (Shin-Etsu Chemical Co., Ltd. KR255) was used instead of the epoxy resin used in Comparative Example 2, and the silicone resin was coated to a thickness of about 4 Opm using the same process except for the epoxy resin used in Comparative Example 2.

The cylindrical piezoelectric elements thus produced were subjected to an evaluation test for electrical insulation properties in water, and the results were measured for Examples 1 to 4 and Comparative Examples 1 to 5.

The evaluation test was carried out by applying a direct current of 100 V to the cylindrical piezoelectric device while immersing it in water at 20° C., measuring the current value after 200 seconds, and calculating the electrical resistance. The measurement results are as follows.

Example 1 1 X 1013 Ω Example 2 1XIO" Ω Example 3 1 Example 5 2X10'Ω Next, the cylindrical piezoelectric elements formed in Examples 1 to 4 and Comparative Example 1, which had high electrical resistance, were immersed in hot water at 60°C. After a certain period of time, take it out of the hot water and cool it in water for 1 hour.
Electrical resistance was measured in water at ℃. The results were as follows.

After 10 hours After 100 hours After 1000 hours Example 1
1 X 10"Ω lXl0"Ω lXl0"Ω Example 2 2 X 10"Ω 2 X 1012Ω 2 X
10"Ω Example 3 2X10th Q 2 X10'jQ
2 XIO”Ω Example 4 1 X 10”Q I
X 10"Q I X 10"Ω Comparative example 1 8X1
As is clear from the results of 0'Ω 5X107Ω 4 X 10'Ω or more, it can be seen that the piezoelectric elements created in Examples 1 to 4 maintain high electrical insulation properties even after being immersed in hot water at 60°C for 1000 hours. .

In addition, in the above-mentioned examples, N was used as the silane coupling agent.
-β(aminoethyl)γ-aminopropyltrimethoxysilane is used, but it is vinyl-based.

The same results as in this example can be obtained even if a methacryloxy, epoxy, amino, mercapto, or chlorovir silane coupling agent is used.

[Effects of the Invention] As described above in detail based on the examples, in the present invention, a silane coupling agent is coated on the surface of a base material as a pretreatment, and an electrically insulating polymer resin is coated on the surface by a thermal CVD method. Because it is coated, a protective film with excellent adhesion to the base material and no pinholes can be obtained.

Therefore, a piezoelectric protective film with excellent electrical insulation properties in water can be obtained.

This makes it possible to realize an underwater acoustic sensor with high sensitivity and long life.

Further, since the manufacturing method of the present invention can coat any location, it can be applied to any shape of piezoelectric element.

Furthermore, since no heat curing is required, coating can be applied after polarization. Therefore, there is an advantage that there is no need to expose the protective film to the polarization process performed at high temperature and high voltage.

It also has the advantage that the number of steps can be reduced compared to conventional manufacturing methods.

[Brief explanation of drawings]

Figure 1 is a manufacturing process diagram of a piezoelectric element according to the present invention, Figure 2 is a schematic cross-sectional view of a cylindrical piezoelectric element, Figure 3 is a schematic cross-sectional view of an underwater acoustic sensor, and Figure 4 is a conventional piezoelectric manufacturing process. It is a process diagram. 1...Ceramic material, 2a...Inner electrode, 2b...Outer electrode, 3...Protective film, 4a, 4b...Lead Line, 11...
Cylindrical piezoelectric, 20... Underwater acoustic sensor.

Claims (7)

[Claims] (1) A first step of forming an electrode on the piezoelectric substrate, applying an electrostatic field between the electrodes to polarize the piezoelectric substrate, and then drying the substrate, and then placing a silane cup on the piezoelectric substrate. a second step of coating and drying the ring agent;
and a third step of coating an electrically insulating polymer resin using a thermal CVD method. (2) The method for manufacturing a piezoelectric protective film according to claim (1), characterized in that N-β (aminoethyl)-aminopropyltrimethoxysilane is used as the silane coupling agent. (3) The method for producing a piezoelectric protective film according to claim (1), characterized in that a vinyl-based, methacryloxy-based, epoxy-based, amino-based, mercapto-based, or chloropyr-based silane is used as the silane coupling agent. (4) The method for manufacturing a piezoelectric protective film according to claim (1), characterized in that di-p-xylene is used as a raw material and poly-p-xylylene is coated as the insulating polymer resin. (5) Claim characterized in that di-monochloro-p-xylene is used as a raw material and poly-monochloro-p-xylylene is coated as the electrically insulating polymer resin (
1) The method for producing a piezoelectric protective film as described above. (6) Polyethylene using di-dichloro-p-xylene as a raw material
2. The method of manufacturing a piezoelectric protective film according to claim 1, wherein dichloro-p-xylylene is coated as the insulating polymer resin. (7) The piezoelectric protective film according to claim (1), wherein the electrically insulating polymer resin is coated with poly-tetrafluoro-p-xylylene using di-tetrafluoro-p-xylene as a raw material. Production method.