JPH0432982B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention relates to a coating film measuring probe, and in particular to a coating film suitable for electrochemically detecting and evaluating deterioration of a coating film applied to a metal surface for purposes such as rust prevention and aesthetic finishing. Concerning membrane measurement probes. [Technical Background of the Invention] Generally, when detecting and evaluating the deterioration of a coating film on a metal surface, an electrochemical evaluation method using a configuration as shown in the conceptual diagram of FIG. 5 is implemented. As shown in the figure, for evaluation, a measuring electrode 4 such as Al foil is brought into contact with a coating film 2 to be evaluated, which is coated on a base metal 1, via a conductive gel 3. next,
An alternating voltage is applied between the base metal 1 and the measurement electrode 4 using a current power source 6 via an ammeter 5. The voltage applied at this time is applied to the base metal 1 and the measurement electrode 4.
The voltage is read by a voltmeter 7 connected between the two. Generally, the coating film 2 has a very high electrical resistance in a normal state immediately after coating, and has a DC resistance of 10 ⁸ Ω-cm or more. When the paint film 2 is normal, the electrical equivalent circuit of the paint film 2 is represented by a parallel circuit of a resistor Rf and a capacitor Cf, as shown in the equivalent circuit diagram of FIG. On the other hand, as the coating film 2 deteriorates, this resistance Rf decreases, and a complex impedance with multiple time constants can be changed from a simple equivalent circuit as shown in FIG. It will come as shown. However, at the initial stage of deterioration, it is possible to treat it as a parallel circuit of a resistor Rf and a capacitor Cf. The impedance Z (jω) of the coating film 2 is determined based on the voltage and current measured through the configuration shown in FIG.
It can be obtained from equation (1). Z(jω) = e(jω)/i(jω) ...(1) where ω is the angular frequency, e(jω) is the voltage, i
(jω) is the current. Further, tan δ, which is another index of deterioration, can be obtained from equation (2). tanδ=|Zm|/|Ze|...(2) Here, Zm is the imaginary part of impedance, and Ze is the real part of impedance. Incidentally, the real part is the phase component when impedance is obtained by pure resistance. When the paint film deteriorates, the 6th
When the resistance Rf in the figure decreases and the same AC voltage e(jω) is applied, i(jω) increases and the impedance Z(jω) decreases. Similarly, as resistance Rf decreases, |Ze| decreases and tanδ increases.
By measuring the impedance or tan δ of the paint film 2 in this manner, deterioration of the paint film can be detected. The characteristic diagrams of FIG. 7 and FIG. 8 show changes in impedance before and after deterioration of the coating film 2. Incidentally, FIG. 7 is a plot of the absolute value of impedance versus frequency (logarithm), and is generally referred to as a Bode diagram. As the paint film deteriorates, the impedance decreases more markedly on the lower frequency side as shown by curve b, compared to the impedance curve a of the undegraded paint film. Therefore, when detecting deterioration only from the absolute value of impedance, it is more effective to measure at a lower frequency. On the other hand, FIG. 8 shows the impedance as a real part and an imaginary part, which is generally expressed as a complex diagram in a form called a Nyquist diagram. As the paint film 2 deteriorates, the semicircle of the impedance locus d becomes smaller and the circle becomes deformed compared to the normal case (curve c). The degree of deterioration of the paint film can be estimated from this shape. [Problems of Background Art] As described above, deterioration of the coating film 2 can be detected from the results of measuring the impedance of the coating film 2 through the configuration shown in the conceptual diagram of FIG. However, in order to carry out accurate measurements using such a method, it is necessary that the measuring electrode 4 made of aluminum foil or the like be brought into close contact with the coating film 2. For this reason, conventional measures have been taken to reduce measurement errors by applying conductive gel 3 to the surface to be measured. However, when the surface to be measured on the coating film 2 corresponds to a ceiling surface or a concave surface, the ninth
As shown in Figures a and b, air bubbles M are inside the conductive gel 3.
This tends to result in a situation where it is extremely difficult to remove the bubbles M that have formed. In this case, the conductive gel 3 is not present on the entire surface of the coating film 2 to be measured, and the measurement area between the measurement electrode 4 and the coating film 2 is not constant. This causes an error in the impedance measurement result, making it impossible to measure the original impedance of the paint film 2, and making it impossible to accurately detect the deterioration of the paint film 2. [Object of the Invention] Therefore, the object of the present invention is to solve the above-mentioned problems of the prior art and to make it possible to accurately and easily detect and evaluate the deterioration of a paint film applied to the surface of a metal structure. To provide coating measurement probes. [Summary of the Invention] In order to achieve the above object, the present invention provides a coating comprising a sponge-like electrode disposed on a surface facing the coating film, and a container containing a conductive gel to be impregnated into the sponge-like electrode. A membrane measurement probe is provided. [Embodiments of the Invention] Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of a coating film measuring probe according to an embodiment of the present invention, in which FIG. 1A shows a cross-sectional view, and FIG. 1B shows a bottom view. On the other hand, FIG. 2 is an explanatory diagram showing a state in which the coating film impedance of a concave portion of the coating film is measured using the coating film measurement probe shown in FIG. 1. Now, as shown in FIG. 1, a perforated plate 10 with a bellows 9 attached thereto is disposed inside the probe body 8, and a sponge-like electrode 11 with a convex outer surface (surface to be measured) is disposed at the tip. installed.
Further, an air vent hole 12 is provided in the upper part of the bellows 9 of the probe body 8, and a gel injection port 13 for injecting the conductive gel 3 is provided in the side surface.
The conductive gel 3 is inserted into the sponge-like electrode 1 from the injection port 13.
1, a perforated plate 10, and a bellows 9. A covered copper wire 14 is connected to the conductive gel 3 as a lead wire. Incidentally, as the conductive gel 3, a solution prepared by adding 3% thickener (carboxymethyl cellulose) to 3% saline can be used. Note that a magnet 15 is attached to the lower end of the probe body 8 for fixing the probe body 8 to the paint film when measuring the paint film impedance. The operation of this configuration will now be explained with reference to the explanatory diagram of FIG. 2. When the coating film measurement probe configured as shown in FIG. Even if air bubbles occur between the coating film 2 and the sponge-like electrode 11,
This is pushed out to the outer periphery. Therefore, the sponge-like electrode 11 is finally
is fully in close contact with the surface to be measured of the coating film 2, and the magnet 15
It is fixed by the magnetic adsorption force between the base metal 1 and the base metal 1. The conductive gel 3 soaks into the sponge-like electrode 11 and adheres to the entire surface of the coating film to be measured. Furthermore, changes in the pressure within the gel bath that occur when the sponge electrode 11 is pressed against or peeled off from the surface to be measured are buffered by the expansion and contraction of the bellows 9. Since the probe body 8 is fixed by the magnet 15 during measurement, it can be securely fixed on any slope, vertical surface, or ceiling surface, making it possible to easily and reliably measure the coating film impedance. Now, the results of measuring the coating film impedance of the epoxy thick film paint using the coating film measuring probe of this example are shown in Table 1 below. As is clear from Table 1, the measurement results are almost the same as those obtained when aluminum foil electrodes are used, and the coating film measurement probe of this example works effectively in measuring coating film impedance.

〔Effect of the invention〕

As described above, according to the present invention, when measuring paint film impedance, it is possible to measure paint film impedance regardless of whether the paint film surface to be measured is a slope, a vertical surface, a ceiling surface, or a concave or convex surface. Furthermore, even in areas where bubbles are likely to occur when applying conductive gel, it is possible to prevent bubbles from forming within the measurement surface, making it possible to accurately measure impedance to detect paint film deterioration. This makes it possible to obtain a coating film measurement probe that allows for the measurement of coatings.

[Brief explanation of drawings]

1a and 1b are cross-sectional views and bottom views of a coating film measurement probe according to an embodiment of the present invention, and FIG.
Explanatory diagram showing the state in which paint film deterioration is electrochemically evaluated using the paint film measurement probe shown in Figure 3.
Figures a and b are explanatory views showing other examples of electrode shapes, Figures 4 a and b are explanatory views showing other embodiments of the present invention and other examples, respectively, and Figure 5 is an explanatory view showing other examples of electrode shapes. A conceptual diagram showing a well-known method for electrochemical evaluation. Figure 6 is an electrical equivalent circuit diagram of a paint film. Figure 7 is a conceptual diagram showing a well-known method of electrochemical evaluation.
The figure is a characteristic diagram showing changes in the frequency dependence of impedance due to deterioration of the paint film, Figure 8 is a characteristic diagram representing Figure 7 on a complex plane, Figure 9 a and b are Al
It is an explanatory view showing a problem when using a foil electrode. DESCRIPTION OF SYMBOLS 1... Base metal, 2... Paint film, 3... Conductive gel, 8... Probe body, 9... Bellows, 10
... Porous plate, 11 ... Sponge-like electrode, 14 ...
Lead wire, 15...Magnet.

Claims (1)

[Scope of Claims] 1. A coating film measurement probe comprising: a sponge-like electrode disposed on a surface facing the coating film; and a container containing a conductive gel to be impregnated into the sponge-like electrode. . 2. The coating film measurement probe according to claim 1, characterized in that a magnet is arranged around the sponge-like electrode. 3. The coating film measurement probe according to claim 1, wherein the container is configured to absorb the pressure of the conductive gel. 4. The coating film measurement probe according to claim 1, wherein the container is configured in a bellows shape. 5. The coating film measurement probe according to claim 1, wherein the sponge-like electrode has a convex surface facing the coating film.