Film characteristic measuring method and film characteristic measuring device

Abstract

To provide a film characteristic measuring method and a film characteristic measuring device capable of deriving information for grasping the conditions of the deepest part of a coating film, which is the part of the coating film closest to the steel material, and the vicinity of the steel material surface underneath. [Solution] The film characteristic measurement method uses electrochemical impedance analysis to measure the characteristics of a film having a base formed on a steel material and an outer layer formed on the base, and includes the steps of applying an AC voltage between an electrode formed on the film and the steel material and measuring the AC current, and deriving impedance from the AC voltage and AC current, wherein the area of ​​the electrode is sized according to the thickness of the film.

Description

[Technical field]

[0001] The present invention relates to a film characteristic measuring method and a film characteristic measuring apparatus. [Background technology]

[0002] Marine steel structures need to maintain their functionality for a long time in a severe corrosive environment. In the splash zone of marine steel structures that are expected to last more than 30 years, ultra-thick epoxy resin coating is often applied. Ultra-thick epoxy resin coating improves impact resistance against drifting objects with a coating thickness of more than 2.5 mm. In addition, the thick coating of ultra-thick epoxy resin coating can extend the time it takes for water, oxygen, and chloride ions, which are corrosion factors, to reach the steel surface. Furthermore, by forming a thick coating, the necessary thickness is secured against the decrease in the coating thickness due to wear caused by ultraviolet rays. In this way, ultra-thick epoxy resin coating ensures the long-term durability of steel by making the coating thicker. The first application of this coating has now passed its expected life of 30 years, and is clearly deteriorated from the outside, with cracks and micropores all over the surface.

[0003] The corrosion prevention performance of coating films exposed to the ocean for 30 years has been investigated (see, for example, Non-Patent Document 1). The items investigated in the corrosion prevention performance investigation include destructive testing by measuring the appearance, film thickness, and adhesion strength of the coating film, and measurements by electrochemical impedance spectroscopy (EIS). The corrosion prevention performance investigation is carried out in a narrow frequency range of 200 Hz to 1 kHz, and by measuring the electrochemical impedance spectrum characteristics for three frequencies, 200 Hz, 500 Hz, and 1 kHz, to evaluate the deterioration state of the coating film. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Nobuhiro Sasaki, Hirotaka Sato, Sayaka Morita, "Corrosion prevention performance of ultra-thick epoxy resin coating after 26 years", Rust Prevention Management, 2018, vol.62, no.5, p.159-168 Summary of the Invention [Problem to be solved by the invention]

[0005] Electrochemical impedance spectroscopy is one of the non-destructive testing methods that can evaluate the deterioration of a coating film in the depth direction. The electrochemical impedance spectrum characteristics are explained by an electrical equivalent circuit, and the parameters of the equivalent circuit change with the deterioration of the coating film. The parameters of the equivalent circuit are derived by fitting circuit elements to the Bode plot and Nyquist plot obtained from the measured electrochemical impedance spectrum characteristics. The derived parameters and the curve change tendency of the Bode plot and Nyquist plot are the deterioration indicators. If deterioration diagnosis using electrochemical impedance spectroscopy is applied to ultra-thick epoxy resin coatings, the general deterioration trend of the coating can be grasped by measuring the impedance in the narrow frequency range of 200 Hz to 1 kHz. However, in the low frequency range below 200Hz, which indicates the state of the deepest part of the paint film closest to the steel material and the interface between the paint film and the steel material, even if the paint film of an ultra-thick epoxy resin coating deteriorates, the insulation is high, so the S / N ratio is poor and the electrochemical impedance spectrum characteristics may be buried in noise. In this case, it is impossible to obtain actual data from which the parameters of the equivalent circuit can be derived, making deterioration diagnosis impossible.

[0006] The present invention has been made in consideration of the above-mentioned circumstances, and has an object to provide a coating film characteristic measuring method and coating film characteristic measuring device that can derive information to grasp the condition of the deepest part of a coating film, which is the part closest to the steel material of a coating film with a film thickness exceeding 1.5 mm at the time of inspection, and the condition of the area below that near the steel material surface. [Means for solving the problem]

[0007] (1) A coating property measuring method according to one aspect of the present invention comprises the steps of: A coating film characteristic measuring method performed by a coating film characteristic measuring device that measures coating film characteristics using electrochemical impedance spectroscopy, comprising: The coating film is a coating film in which a corrosion-resistant base such as a zinc-rich primer is applied to a steel material, and then a corrosion-resistant layer is formed by applying a super-thick epoxy resin at a predetermined interval. The coating film characteristic measuring method includes the steps of applying an AC voltage between an electrode formed on the coating film and the steel material, and measuring an AC current obtained by frequency sweeping the AC voltage; and deriving impedance based on the measurement results of the AC voltage and the AC current. 2 That's all.

[0008] According to this invention, the coating film characteristic measuring method uses electrochemical impedance spectroscopy to measure the AC current obtained by frequency sweeping an AC voltage between an electrode formed on the coating film and a steel material. The area of ​​the electrode is 0.05 m 2 That's it. The area of ​​the electrode is 0.05 m 2 By doing as described above, the coating film property measuring method can derive the impedance on the low frequency side based on the measurement results of the AC voltage and AC current applied between the electrode and the steel material. The impedance on the low frequency side indicates the state of the deep part close to the steel material side of the corrosion protection layer made of ultra-thick epoxy resin and the corrosion protection base (zinc-rich primer) on the steel material. Therefore, it is possible to derive information to grasp the situation from deep inside the coating film near the steel material surface.

[0009] (2) A coating characteristic measuring method according to one embodiment of the present invention is the coating characteristic measuring method according to (1) above, wherein in the measuring step, an AC voltage is frequency swept in a frequency range including a frequency range below 1 Hz.

[0010] In this case, the coating film characteristic measuring method frequency-sweeps an AC voltage between the electrode formed on the coating film and the steel material in a frequency range including a frequency range of less than 1 Hz. By frequency-sweeping an AC voltage in a frequency range including a frequency range of less than 1 Hz, the coating film characteristic measuring method can derive the impedance on the low frequency side. The impedance on the low frequency side less than 1 Hz indicates the state of the corrosion-protective base applied to the steel material. Therefore, the situation near the steel material surface can be understood from the information indicating the state of the corrosion-protective base.

[0011] (3) A coating property measuring method according to one aspect of the present invention is the coating property measuring method according to the above (1) or (2), The method includes the steps of: plotting a Nyquist diagram based on the impedance derived in the deriving step; and judging a state of the coating film based on the Nyquist diagram plotted in the plotting Nyquist diagram step.

[0012] The Nyquist diagram of a deteriorated thick coating film obtained by plotting impedance includes a first semicircle and a second semicircle. The second semicircle is found on the higher resistance side (lower frequency side) than the first semicircle. As the epoxy resin corrosion protection layer deteriorates, the radius of the first semicircle decreases, but as long as the corrosion protection base such as zinc-rich primer is sound, the radius of the second semicircle remains constant and does not decrease. Therefore, the coating film characteristic measurement method can determine the condition of the epoxy resin corrosion protection layer formed on the corrosion protection base such as zinc-rich primer based on the radius of the first semicircle shown in the Nyquist diagram.

[0013] (4) A coating film characteristic measuring method according to one embodiment of the present invention is the coating film characteristic measuring method described in (3) above, wherein in the judging step, the state of the corrosion-resistant base such as a zinc-rich primer is judged based on a semicircle representing the state of the corrosion-resistant base such as a zinc-rich primer shown in the Nyquist diagram.

[0014] The Nyquist diagram obtained by plotting impedance includes a first semicircle and a second semicircle. The second semicircle is on the higher resistance side than the first semicircle. As the epoxy resin corrosion protection layer deteriorates, the radius of the first semicircle decreases, but the radius of the second semicircle does not decrease as long as the corrosion protection base such as zinc-rich primer is sound. When the radius of the first semicircle becomes smaller and the ratio of the radius of the first semicircle to the radius of the second semicircle becomes about 3:1, the results of destructive testing by measuring the adhesion of the coating film with this characteristic show zinc cohesive failure. In other words, it is believed that corrosion factors such as water, oxygen, and chloride ions have reached the corrosion-resistant base, or at least the deepest part of the corrosion-resistant layer directly above the corrosion-resistant base. However, when the ratio of the radius of the first semicircle to the radius of the second semicircle is 3:1, the potential measurement result of the corrosion-resistant base (zinc-rich primer) is less noble than -0.9V (based on saturated silver-silver chloride electrode), which indicates that the zinc-rich primer is in good condition, and it can be confirmed from the appearance that the zinc-rich primer is not corroded at all. From this, it is clear that when the ratio of the radius of the first semicircle to the radius of the second semicircle is 3:1, the corrosion-resistant base is in good condition. As the corrosion protection layer deteriorates further and the radius of the first semicircle becomes smaller, the radius of the first semicircle becomes the same as that of the second semicircle. When the ratio of the radius of the first semicircle to that of the second semicircle becomes 1:1, the results of a destructive test using adhesion measurements of a coating film with this characteristic indicate zinc cohesive failure. In other words, it is believed that corrosion factors such as water, oxygen, and chloride ions have reached the corrosion protection base, or at least the deepest part of the corrosion protection layer directly above the corrosion protection base. However, when the ratio of the radius of the first semicircle to the radius of the second semicircle is 1:1, the potential measurement result of the corrosion-resistant base (zinc-rich primer) is less noble than -0.9V (based on saturated silver-silver chloride electrode), which indicates that it is a sound zinc-rich primer, and it can be confirmed from the appearance that the zinc-rich primer is not corroded at all, so it is determined that the corrosion-resistant base is sound when the ratio of the radius of the first semicircle to the radius of the second semicircle is 1:1.In this way, the soundness of the corrosion-resistant base is confirmed until the ratio of the radius of the first semicircle to the radius of the second semicircle becomes 1:1. Therefore, the coating film characteristic measuring method can determine the state of a corrosion-resistant base such as a zinc-rich primer based on the radius of the first semicircle and the radius of the second semicircle shown in the Nyquist diagram.

[0015] (5) A coating film characteristic measuring method according to one embodiment of the present invention is a coating film characteristic measuring method as described in (3) or (4) above, which includes a step of determining whether or not it is time for repair based on the condition of the corrosion-resistant base determined in the determining step.

[0016] The Nyquist diagram obtained by plotting impedance includes a first semicircle and a second semicircle. The second semicircle is on the higher resistance side (lower frequency side) than the first semicircle. As the coating deteriorates, the radius of the first semicircle decreases, but the radius of the second semicircle does not decrease. When the radius of the first semicircle and the radius of the second semicircle become the same, it is considered that the corrosive factors such as water and salt have already reached deep into the epoxy resin corrosion protection layer. In this case, repair is preferable to prevent the corrosive factors from reaching the steel material. Therefore, the coating film property measurement method can determine whether or not it is time for repair based on whether the radius of the first semicircle and the radius of the second semicircle have become the same.

[0017] (6) A coating film characteristic measuring device according to one aspect of the present invention is a coating film characteristic measuring device that measures the characteristics of a coating film using electrochemical impedance spectroscopy, the coating film being a corrosion-resistant layer of epoxy resin formed on a corrosion-resistant base such as a zinc-rich primer that coats a steel material, the coating film characteristic measuring device comprising: a measurement unit that performs frequency sweeping of an AC voltage between an electrode formed on the coating film and the steel material and measures an AC current obtained by frequency sweeping the AC voltage; and a processing unit that derives impedance based on the measurement results of the AC voltage and the AC current, the area of ​​the electrode being 0.05 m or less. 2 That's all.

[0018] According to this invention, the coating film property measuring device uses electrochemical impedance spectroscopy to measure the AC current obtained by frequency sweeping an AC voltage between an electrode formed on the coating film and a steel material. The area of ​​the electrode is 0.05 m 2 That's it. The area of ​​the electrode is 0.05 m 2 By doing so, the coating film property measuring device can derive the impedance on the low frequency side based on the measurement results of the AC voltage and AC current applied between the electrode and the steel material. The impedance on the low frequency side indicates the state of the corrosion-resistant base, such as a zinc-rich primer that coats the steel material. Therefore, information can be derived to grasp the situation near the steel surface under the corrosion-resistant base. That is, if the corrosion-resistant base is sound, the steel material underneath is not corroded. On the other hand, if the corrosion-resistant base is deteriorated, the steel material underneath may be corroded. Or, there is a high possibility that the steel material will corrode in the near future. Effect of the Invention

[0019] According to an embodiment of the present invention, it is possible to grasp the deterioration status of the epoxy resin corrosion protection layer and the soundness of the corrosion protection base such as zinc-rich primer that coats the steel material underneath, and it is also possible to grasp the situation near the surface of the steel material underneath the corrosion protection base from the soundness of the corrosion protection base. [Brief description of the drawings]

[0020] [Figure 1] 1 is a diagram showing a coating film characteristic measuring system according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a diagram showing an example of a coating film CF. [Diagram 3] FIG. 4 is a diagram illustrating an example of a relationship between frequency and current amplitude. [Figure 4] FIG. 13 is a diagram illustrating an example of a relationship between frequency and impedance amplitude. [Diagram 5] FIG. 2 is a diagram showing an example of an electrical equivalent circuit of a coating film CF. [Figure 6] FIG. 13 is a diagram showing an example of the relationship between the electrode area ratio and the current ratio. [Figure 7]FIG. 13 is a diagram showing an example of the relationship between the electrode area ratio and the current ratio. [Figure 8] FIG. 1 is a diagram illustrating Example 1 of the relationship between AC resistance and capacitive reactance. [Figure 9] FIG. 11 is a diagram illustrating a second example of the relationship between AC resistance and capacitive reactance. [Figure 10] FIG. 11 is a diagram illustrating Example 3 of the relationship between AC resistance and capacitive reactance. [Figure 11] 1 is a block diagram showing a control and analysis device constituting a coating property measuring system according to an embodiment of the present invention. FIG. [Figure 12] FIG. 4 is a diagram showing an example of a deterioration state of a coating film classified by a control and analysis device according to an embodiment of the present invention. [Figure 13] FIG. 1 is a diagram showing Example 1 of a Nyquist diagram. [Figure 14] FIG. 13 is a diagram showing Example 2 of the Nyquist diagram. [Figure 15] FIG. 13 is a diagram showing Example 3 of the Nyquist diagram. [Figure 16] FIG. 11 is a diagram showing Example 4 of the Nyquist diagram. [Figure 17] FIG. 11 is a diagram showing Example 5 of the Nyquist diagram. [Figure 18] FIG. 1 is a diagram showing an example of the relationship between the deterioration state of a coating film classified by the control and analysis device according to an embodiment of the present invention and a Nyquist diagram. [Figure 19] FIG. 13 is a diagram showing an example of a coating deterioration degree determination table. [Figure 20] FIG. 2 is a diagram showing an example of a Bode plot derived by the control and analysis device according to the embodiment of the present invention. [Figure 21] FIG. 2 is a diagram showing an example of a Nyquist diagram derived by the control and analysis device according to the embodiment of the present invention. [Figure 22] FIG. 2 is a flow chart showing an example of the operation of the coating property measuring system according to the embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Next, a coating property measuring method and a coating property measuring device according to the present embodiment will be described with reference to the drawings. The embodiment described below is merely an example, and the embodiment to which the present invention is applied is not limited to the following embodiment. In addition, in all the drawings for explaining the embodiments, the same reference numerals are used for the parts having the same functions, and the repeated explanation is omitted. In addition, "based on XX" in this application means "based on at least XX," and includes cases where it is based on other elements in addition to XX. Furthermore, "based on XX" is not limited to cases where XX is used directly, but also includes cases where it is based on XX that has been calculated or processed. "XX" is any element (for example, any information).

[0022] (Embodiment) (Paint film characteristic measurement system) FIG. 1 is a diagram showing a coating film characteristic measuring system according to an embodiment of the present invention. The coating film property measuring system 1 according to this embodiment diagnoses the coating film covering the steel material by electrochemical impedance spectroscopy (EIS). Electrochemical impedance spectroscopy is an impedance spectroscopy method used to analyze the interface between an electrode and an electrolyte, and can also be applied to the deterioration diagnosis of the coating film. The coating film characteristic measuring system 1 applies a sine wave AC voltage to the coating film, sweeps it, and measures the AC current, which is the frequency response caused by applying and sweeping the sine wave AC voltage. The coating film characteristic measuring system 1 derives the ratio (impedance) between the AC voltage and the AC current by dividing the AC voltage by the AC current, based on the sine wave AC voltage applied to the coating film and the AC current obtained by measuring it. The coating film characteristic measurement system 1 utilizes the fact that by applying a sinusoidal AC voltage to the coating film and sweeping it, and measuring the AC current, which is the frequency response resulting from applying and sweeping the sinusoidal AC voltage, the impedance corresponding to various reactions from the coating film to the steel surface can be separated and measured.

[0023] Here, the coating film CF will be described. 2 is a diagram showing an example of a coating film CF. The coating film CF is formed on one surface of a steel material 10. An example of the steel material 10 is a marine structure. In this embodiment, as an example, the case where the steel material 10 is a marine structure will be described. The coating film CF is formed thick to improve impact resistance against drifting debris. The coating film CF is formed thick to lengthen the time it takes for corrosion factors such as oxygen, water, and chloride ions to reach the surface of the steel material 10. By forming the coating film CF thick, a necessary thickness is ensured against the film thickness reduction caused by ultraviolet ray attenuation. One example of the coating film CF includes a corrosion-resistant base 20a formed on the steel material 10, and a corrosion-resistant layer 20b formed on the corrosion-resistant base 20a. One example of the anticorrosive base 20a is a zinc-rich primer. The zinc-rich primer is a primer that contains a large amount of zinc dust. The zinc-rich primer protects the steel material from rust and serves as a base for the anticorrosive layer 20b. The steel material to which the zinc-rich primer is applied is subjected to surface preparation such as blasting. The blasting process results in a surface that is free of mill scale, rust, paint, foreign matter, oil, grease, and mud visible without a magnifying glass. Any remaining dirt is only visible as slight spots or streaks. In this embodiment, as an example, the case where the rust removal degree is Sa2 1 / 2 is described. An example of the thickness of the zinc-rich primer is 10 μm to 75 μm, and in this embodiment, the case where the thickness of the zinc-rich primer is 20 μm is described. An example of the anticorrosion layer 20b is epoxy resin. An example of the film thickness of the epoxy resin is 0.2 mm to 3 mm, and in this embodiment, the description will be continued for the case where the epoxy resin has a thickness of 2 mm. Here, the coating film CF may have an initial thickness of 0.3 mm to 3 mm, including a corrosion-resistant base layer 20a such as a zinc layer and a corrosion-resistant layer 20b such as an epoxy resin. In addition, a weather-resistant coating film may be formed on the top of the corrosion-resistant layer 20b. Preferably, the coating film CF may have a thickness of 1.0 mm to 2.5 mm, which is a combination of the corrosion-resistant base layer 20a such as a zinc layer and the corrosion-resistant layer 20b of an epoxy resin.

[0024] FIG. 2 further shows a conductive paste 30 and an electrode 40 that are formed when diagnosing the coating film CF. The conductive paste 30 electrically connects the anticorrosive layer 20b and the electrode 40, and forms an electrolyte that permeates the coating film CF. One example of the conductive paste 30 is one in which carboxymethyl cellulose (CMC) is dissolved in a 3% sodium chloride aqueous solution. An AC voltage is applied to the electrode 40 from a coating film property measuring device 100 described later. The electrode 40 is preferably a metal foil such as aluminum foil or stainless steel foil, and an example of the electrode 40 is aluminum foil. The area of ​​the electrode 40 is 0.05 m 2 More than 1m 2 More preferably, 0.1 m 2 More than 0.3m 2 In this embodiment, the area of ​​the electrode 40 is 0.3 m 2 The explanation will be continued for the case where

[0025] Here, the area S of the electrode 40 will be described. Fig. 3 is a diagram showing an example of the relationship between frequency and amplitude of AC current. Fig. 3 shows the relationship between frequency and amplitude of AC current obtained when the area S of the electrode 40 is made variable. In Fig. 3, the horizontal axis is frequency [Hz], and the vertical axis is amplitude [A] of the AC current. Both the horizontal and vertical axes are expressed in logarithm. The area S of the electrode 40 is 0.01 m 2 , 0.02m 2 , 0.03m 2 , 0.1m 2 , 0.2m 2 , 0.3m 2 It was decided. 3, it can be seen that the amplitude of the AC current increases as the area S of the electrode 40 increases. 2 And, 0.02m 2 It can be seen that the amplitude of the current value varies greatly between 10 Hz and 1 kHz when the area S of the electrode 40 is 0.03 m 2 In this case, the area S of the electrode 40 is 0.01 m 2 And, 0.02m 2 3, when the area S of the electrode 40 is 0.1 m, the variation in the amplitude of the current is smaller than that when the area S of the electrode 40 is 0.1 m. 2 Above this, no variation in the amplitude of the current value is observed, so the threshold value of the electrode area at which no variation in the amplitude of the current value is observed is 0.03 m 2 From 0.1m 2 The threshold value, not shown in the figure, is 0.05 m. 2 It was.

[0026] FIG. 4 is a diagram showing an example of the relationship between frequency and impedance amplitude. FIG. 4 shows the relationship between frequency and impedance amplitude obtained when the area S of the electrode 40 is made variable. In FIG. 4, the horizontal axis is frequency [Hz], and the vertical axis is impedance amplitude [Ω]. Both the horizontal and vertical axes are expressed logarithmically. The area S of the electrode 40 is 0.01 m 2 , 0.02m 2 , 0.03m 2 , 0.1m 2 , 0.2m 2 , 0.3m 2 It was decided. 4, it can be seen that the amplitude of the impedance decreases as the area S of the electrode 40 increases. 2 And, 0.02m 2 It can be seen that the impedance amplitude varies greatly between 10 Hz and 1 kHz when the area S of the electrode 40 is 0.03 m 2 In this case, the area S of the electrode 40 is 0.01 m 2 And, 0.02m2 4, when the area S of the electrode 40 is 0.1 m2, the variation in the impedance amplitude is smaller than that when the area S of the electrode 40 is 0.1 m2, but the variation in the impedance amplitude is smaller than that when the area S of the electrode 40 is 0.1 m2, ... and the variation in the impedance amplitude is smaller than that when the area S of the electrode 40 is 0.1 m2. 2 Above this, no variation in the impedance amplitude is observed, so the threshold electrode area at which no variation in the impedance amplitude is observed is 0.03 m, similar to the current amplitude. 2 From 0.1m 2 The threshold value, not shown in the figure, is 0.05 m. 2 It was.

[0027] The electrochemical impedance characteristics (hereinafter also referred to as "EIS characteristics") are reproduced by an equivalent circuit combining elements such as resistance and capacitance, and the equivalent circuit is analyzed from the resistance and capacitance values, thereby making it possible to grasp the deterioration of the coating film CF and the corrosion state in the vicinity of the steel material below the coating film CF. From the results so far, it has been found that over a period of 30 years or so, the corrosion of the steel material 10 is not observed because the corrosion protection layer 20b deteriorates while the corrosion protection base 20a is almost sound. The corrosion protection layer 20b is divided into a sound portion and a defective portion, and the sound corrosion protection base 20a is connected in series to the corrosion protection layer 20b. As the deterioration of the corrosion protection layer 20b progresses, the defective portion becomes dominant in the circuit of the corrosion protection layer. Fig. 5 is a diagram showing an example of an electrical equivalent circuit of a coating film. In addition to the electrical equivalent circuit of the coating film CF, Fig. 5 also shows the electrical equivalent circuit of the conductive paste 30. The resistance of the conductive paste 30 is very small, so it can be ignored in the analysis. The electrical equivalent circuit of the coating film CF includes, for the corrosion-resistant layer 20b, a coating capacitance C1 [F] of the corrosion-resistant layer 20b and a coating resistance R1 [Ω] of the corrosion-resistant layer 20b, and for the corrosion-resistant base 20a, a coating capacitance C2 [F] of the corrosion-resistant base 20a and a coating resistance R2 [Ω] of the corrosion-resistant base 20a. When the frequency is f [Hz] and the angular frequency is ω = 2πf [rad / s], the impedance Z is expressed by the following equation (1).

[0028] Z=(R1 / (1+ω 2 +C1 2 +R1 2 ))-j(ωC1R1 2 / (1+ω2 +C1 2 +R1 2 ))+(R2 / (1+ω 2 +C2 2 +R2 2 ))-j(ωC2R2 2 / (1+ω 2 +C2 2 +R2 2 )) (1)

[0029] In equation (1), "(R1 / (1+ω 2 +C1 2 +R1 2 ))-j(ωC1R1 2 / (1+ω 2 +C1 2 +R1 2 ))" corresponds to the impedance of the corrosion protection layer 20b, and "(R2 / (1+ω 2 +C2 2 +R2 2 ))-j(ωC2R2 2 / (1+ω 2 +C2 2 +R2 2 )) corresponds to the impedance of the corrosion-resistant base 20a. In the electrical equivalent circuit of the coating film CF, the elements through which AC current flows change between high frequency and low frequency ranges. Capacitive reactance Xc is expressed by equation (2). According to equation (2), the higher the frequency, the smaller the capacitive reactance Xc, so in the high frequency range, AC current flows through the capacitor element and does not flow through the resistor. Conversely, the lower the frequency, the larger the capacitive reactance Xc, so in the low frequency range, AC current does not flow much through the capacitor element and mainly flows through the resistor.

[0030] The relationship between the capacitor element and frequency, and the relationship between the capacitor element and the electrode area are expressed by equations (2) and (3). The relationship between the resistor element and the electrode area is expressed by equation (4). Xc=1 / 2πfC [Ω] (2) C = ε × (S / d) [F] (3) R = (1 / σ) × (d / S) [Ω] (4)

[0031] In equations (2), (3), and (4), Xc is the capacitive reactance [Ω], f is the frequency [Hz], C is the capacitance [F], ε is the dielectric constant [F / m], S is the electrode area [m2], d is the coating thickness [m], R is the resistance [Ω], and σ is the conductivity [S / m]. According to equation (3), capacitance C is proportional to area S of electrode 40, and according to equation (4), resistance is inversely proportional. If area S of electrode 40 becomes N times larger (N is an integer larger than 0), capacitance C becomes N times larger according to equation (3). When capacitance C becomes N times larger, capacitive reactance Xc becomes 1 / N times larger according to equation (2), and as a result, the AC current flowing through capacitance C becomes N times larger. The dielectric constant ε in formula (3) is characterized by increasing due to moisture absorption by the coating film CF. The dielectric constant ε also changes with frequency, and generally shows a small and constant value in the high frequency range, but as the frequency decreases, it increases sharply at a certain frequency and then remains high and constant at an even lower frequency. On the other hand, according to formula (4), when the area S of the electrode 40 becomes N times larger, the resistance R becomes 1 / N times larger, and the AC current flowing through the resistance R becomes N times larger. Note that the conductivity σ in formula (4) has the characteristic of increasing due to moisture absorption by the coating film CF.

[0032] Next, the relationship between the area S of the electrode 40 and the AC current will be described. Fig. 6 is a diagram showing an example of the relationship between the ratio of electrode areas and the ratio of AC currents. Fig. 6 shows a case where the frequency is 100 kHz. When the frequency is 100 kHz, since it is on the high frequency side, the capacitive reactance Xc becomes small, and AC current flows through the capacitor element, and almost no AC current flows through the resistor side. 6, the horizontal axis represents the ratio of electrode areas. Here, the ratio of electrode areas is calculated when the area S of electrode 40 is 0.01 m 2 6, the vertical axis represents the AC current ratio, and here, the AC current ratio is calculated when the area S of the electrode 40 is 0.01 m 2 It is expressed as a ratio to the AC current that flows when The frequency is 100 kHz, and the area S of the electrode 40 is 0.01 m 2When this occurs, the AC current that flows is approximately 136 μA. According to Fig. 6, at a frequency of 100 kHz, the magnitude of the AC current ratio increases in the same way as the electrode area (area S of electrode 40) ratio increases, so if the electrode area ratio is increased by a factor of N, the AC current ratio also becomes N times, and it can be seen that the increase in current due to the increase in electrode area is in line with theory. In the high frequency range, the dielectric constant is small and constant, so there is almost no effect of the dielectric constant, and it is thought that the increase in AC current is only due to the increase in electrode area.

[0033] Fig. 7 is a diagram showing an example of the relationship between the ratio of electrode areas and the ratio of AC currents. Fig. 7 shows the case where the frequency is 0.1 Hz. When the frequency is 0.1 Hz, since it is on the low frequency side, the capacitive reactance Xc becomes large, and in the low frequency range, almost no AC current flows through the capacitor element, but flows through the resistor side. In FIG. 7, the horizontal axis represents the ratio of electrode areas. Here, the ratio of electrode areas is calculated when the area S of electrode 40 is 0.01 m 2 7, the vertical axis represents the AC current ratio, and here, the AC current ratio is calculated when the area S of the electrode 40 is 0.01 m 2 It is expressed as a ratio to the AC current that flows when The frequency is 0.1 Hz, and the area S of the electrode 40 is 0.01 m 2 In this case, the AC current that flows is about 0.07 μA. 7, it can be seen that at a frequency of 0.1 Hz, the AC current ratio increases more than the increase in the electrode area ratio (area S of electrode 40). If the electrode area ratio is set to N times, it can be seen that the current ratio is about one order of magnitude larger than the N times value. The reason for this is believed to be that the larger the electrode area, the easier it is for the conductive paste (electrolyte) to penetrate into the coating film CF, and the larger the electrode area, the higher the conductivity σ, and the greater the AC current, in addition to the electrode area effect. If the electrode area is small, the heat storage and wind in the coating film CF promote drying from the periphery of the electrode area, which hinders the coating film CF from absorbing moisture, but if the electrode area is large, the effect of drying can be almost ignored, and it is believed that the penetration of the electrolyte is promoted. Therefore, at a frequency of 0.1 Hz, it is believed to be about one order of magnitude larger than the value of the increase N times the ratio of the electrode areas.

[0034] Next, the relationship between the area S of the electrode 40 and the EIS characteristics will be described. Here, as an example of the EIS characteristics, the relationship between AC resistance and capacitive reactance, that is, the case where a Nyquist diagram is used, will be described. FIG. 8 is a Nyquist diagram showing Example 1 of the relationship between AC resistance and capacitive reactance. The left diagram in FIG. 8 shows the area S of the electrode 40 as 0.01 m 2 In the left diagram of Figure 8, the horizontal axis is AC resistance [Ω] and the vertical axis is capacitive reactance [Ω]. The right diagram in FIG. 8 shows the area S of the electrode 40 as 0.02 m 2 In the right diagram of Figure 8, the horizontal axis is AC resistance [Ω] and the vertical axis is capacitive reactance [Ω]. According to the left diagram of FIG. 8 and the right diagram of FIG. 8, the area S of the electrode 40 is 0.01 m 2 and 0.02m 2 It can be seen that impedance is obtained in quadrants other than the first quadrant when the area S of the electrode 40 is 0.01 m. Also, according to the left diagram of FIG. 8 and the right diagram of FIG. 8, when the area S of the electrode 40 is 0.01 m, 2 and 0.02m 2 It can be seen that when

[0035] FIG. 9 is a Nyquist diagram showing Example 2 of the relationship between AC resistance and capacitive reactance. The left diagram in FIG. 9 shows the area S of the electrode 40 as 0.03 m 2In the left diagram of Fig. 9, the horizontal axis represents AC resistance [Ω] and the vertical axis represents capacitive reactance [Ω]. The right diagram in FIG. 9 shows the area S of the electrode 40 when it is 0.1 m 2 In the right diagram of Figure 9, the horizontal axis is AC resistance [Ω] and the vertical axis is capacitive reactance [Ω]. According to the left diagram of FIG. 9, the area S of the electrode 40 is 0.03 m 2 9, when the area S of the electrode 40 is 0.03 m, impedance is obtained in other quadrants as well. 2 It can be seen that when , the impedance varies greatly. According to the right diagram of FIG. 9, the area S of the electrode 40 is 0.1 m 2 9, the impedance is contained in the first quadrant when the area S of the electrode 40 is 0.1 m 2 In this case, the area S of the electrode 40 is 0.01 m 2 , 0.02m 2 , 0.03m 2 It can be seen that the impedance variation is smaller than when

[0036] Fig. 10 is a Nyquist diagram showing Example 3 of the relationship between AC resistance and capacitive reactance. The left diagram in Fig. 10 shows the case where the area S of electrode 40 is 0.2 m2. In the left diagram in Fig. 10, the horizontal axis is AC resistance [Ω] and the vertical axis is capacitive reactance [Ω]. The right diagram in FIG. 10 shows the area S of the electrode 40 at 0.3 m 2 In the right diagram of Figure 10, the horizontal axis is AC resistance [Ω] and the vertical axis is capacitive reactance [Ω]. According to the left and right diagrams of FIG. 10, the area S of the electrode 40 is 0.2 m 2 and 0.3m 2 It can be seen that the impedance falls within the first quadrant when the area S of the electrode 40 is 0.2 m. Also, according to the left and right diagrams of FIG. 10, when the area S of the electrode 40 is 0.2 m, the impedance falls within the first quadrant. 2 and 0.3m 2 In this case, the area S of the electrode 40 is 0.01 m2 , 0.02m 2 , 0.03m 2 It can be seen that the impedance variation is smaller than when In Figures 8 to 10, the area S of the electrode 40 is 0.05 m 2 Although not shown, the case where the area S of the electrode 40 is 0.05 m 2 When the area S of the electrode 40 is 0.01 m, the impedance falls in the first quadrant, similar to when the area S of the electrode 40 is 0.1 m. 2 , 0.02m 2 , 0.03m 2 As a result, the impedance variation is smaller than that in the case of In Figures 8 to 10, the area S of the electrode 40 is 0.5 m 2 Although not shown, the case where the area S of the electrode 40 is 0.5 m 2 In this case, the area S of the electrode 40 is 0.3 m 2 As in the case where the impedance falls in the first quadrant and the area S of the electrode 40 is 0.01 m 2 , 0.02m 2 , 0.03m 2 As a result, the impedance variation is smaller than that in the case of From the above, the area S of the electrode 40 is 0.05 m 2 As a result, the impedance variation is reduced, and the signal-to-noise ratio (SN ratio) is 0.05 m 2 It can be seen that this is an improvement over the case where the electrode area is less than 1 m. 2 Although there is no problem with the signal-to-noise ratio when the electrode is attached or removed, the electrode area is set to 1 m from the viewpoint of workability because of the difficulty in handling the electrode attachment during EIS measurement. 2 was determined to be the upper limit. Therefore, the area S of the electrode 40 is 0.05 m 2 More than 1m 2 It is preferable that the distance is less than 0.1m from the viewpoint of the signal-to-noise ratio and workability. 2 More than 0.3m 2 It is more preferable that the following is true: Returning to FIG.

[0037] The coating film property measuring system 1 includes a coating film property measuring device 100 and a control and analysis device 200. The coating film property measuring device 100 includes a measurement unit 102 and a processing unit 104. An example of electrodes used by the coating film property measuring system 1 when performing measurement by electrochemical impedance spectroscopy is not three electrodes, but two electrodes using metal foil (electrode 40) as described above. An example of the measuring unit 102 is a potentio / galvanostat. In the present embodiment, as an example, the description will be continued for the case where the measuring unit 102 is a potentio / galvanostat. The measuring unit 102 includes a first counter electrode CE1 (counter electrode 1), a second counter electrode CE2 (counter electrode 2), a first working electrode WE1 (working electrode 1), and a second working electrode WE2 (working electrode 2). The first working electrode WE1 and the second working electrode WE2 are directly connected to the steel material 10 and are electrically connected thereto. The first counter electrode CE1 and the second counter electrode CE2 are connected to a measurement electrode attached on the conductive paste applied to the coating film, and are electrically connected to each other. Thus, the measurement unit 102 applies an AC voltage between the first counter electrode CE1 and the first working electrode WE1, and measures an AC current flowing between the second counter electrode CE2 and the second working electrode WE2.

[0038] The measurement unit 102 applies an AC voltage between the first counter electrode CE1 and the first working electrode WE1 via the processing unit 104 based on an output instructed by the control and analysis device 200. The measurement unit 102 applies and sweeps a sinusoidal AC voltage between the first counter electrode CE1 and the first working electrode WE1 based on measurement start information, which is information for starting measurement output by the processing unit 104, and based on information indicating the AC voltage to be applied between the first counter electrode CE1 and the first working electrode WE1 that has been received. The measurement unit 102 measures the AC current flowing between the second counter electrode CE2 and the second working electrode WE2, which is a frequency response obtained by applying and sweeping a sinusoidal AC voltage between the first counter electrode CE1 and the first working electrode WE1. The measurement unit 102 outputs to the processing unit 104 information indicating the sinusoidal AC voltage applied and swept between the first counter electrode CE1 and the first working electrode WE1 and a measurement result of the AC current flowing between the second counter electrode CE2 and the second working electrode WE2. Processing unit 104 acquires a measurement start request, which is information requesting the start of measurement output by control and analysis device 200, and outputs measurement start information to measurement unit 102 based on the acquired measurement start request. Processing unit 104 acquires information indicating the voltage of the sinusoidal AC output by measurement unit 102 and the measurement result of the current, and derives impedance by dividing the voltage value by the current value based on the acquired information indicating the voltage of the sinusoidal AC and the measurement result of the AC current. Processing unit 104 outputs information indicating the derived impedance to control and analysis device 200. Based on a user's operation, the control and analysis device 200 outputs a measurement start request to the coating film property measuring device 100. In addition, the control and analysis device 200 outputs measurement conditions including information indicating the AC voltage to be applied between the first counter electrode CE1 and the first working electrode WE1 and the AC current flowing between the second counter electrode CE2 and the second working electrode WE2 to the coating film property measuring device 100. The control and analysis device 200 acquires the measurement results including information indicating the impedance output by the coating film property measuring device 100, and analyzes the characteristics of the corrosion protection layer 20b based on the acquired measurement results.

[0039] Hereinafter, there will be described a control and analysis device 200 constituting the coating property measuring system 1. Fig. 11 is a block diagram showing a control and analysis device constituting the coating property measuring system according to an embodiment of the present invention. The control and analysis device 200 is realized by a device such as a personal computer, a server, or an industrial computer. The control and analysis device 200 comprises an IF 210, a memory unit 220, an information processing unit 230, an operation unit 240, a display unit 250, and a bus line 260 such as an address bus or a data bus for electrically connecting each component as shown in FIG. 11.

[0040] The IF 210 inputs and outputs information to and from the coating film property measuring device 100 . Specifically, the IF 210 acquires the measurement conditions output by the information processing unit 230, and outputs the acquired measurement conditions to the coating film property measuring apparatus 100. The IF 210 acquires the measurement start request output by the information processing unit 230, and outputs the acquired measurement start request to the coating film property measuring apparatus 100. The IF 210 acquires the measurement results output by the coating film property measuring apparatus 100, and outputs the acquired measurement results to the information processing unit 230.

[0041] The storage unit 220 is realized by, for example, a random access memory (RAM), a read only memory (ROM), a hard disk drive (HDD), a flash memory, or a hybrid storage device that combines a plurality of these. Instead of being provided as a part of the control and analysis device 200, a part or all of the storage unit 220 may be realized by an external device that the processor of the control and analysis device 200 can access via the network 50, such as a network attached storage (NAS) or an external storage server. The storage unit 220 stores a program 222 executed by the information processing unit 230, an application 224, measurement condition information 226, and a coating deterioration degree determination table 227. The program 222 is, for example, an operating system, which is positioned between the user or application programs and the hardware, and provides a standard interface for the user or application programs, while at the same time efficiently managing each resource such as the hardware. The application 224 causes the control and analysis device 200 to output the measurement conditions to the coating film characteristic measuring device 100 when the user operates the operation unit 240 to start the measurement. The application 224 causes the control and analysis device 200 to output a measurement start request to the coating film characteristic measuring device 100 when the user operates the operation unit 240 to start the measurement. The application 224 causes the control and analysis device 200 to accept the measurement results output by the coating film characteristic measuring device 100. The application 224 causes the control and analysis device 200 to derive a characteristic diagram based on the accepted measurement results. Examples of the characteristic diagram are a Bode diagram and a Nyquist diagram. The application 224 causes the control and analysis device 200 to determine the state (status) of the coating film CF based on the derived characteristic diagram. The measurement condition information 226 stores conditions for measuring impedance such as an AC voltage applied to the coating film CF when the coating film characteristic measuring device 100 diagnoses the coating film CF by electrochemical impedance spectroscopy. An example of the measurement condition is information indicating a sweep frequency and information indicating an applied voltage. In this embodiment, the description will continue for an example of the measurement condition in which the sweep frequency is 0.1 Hz to 100 kHz and the applied voltage is 1 V effective value, which is the maximum output of the device. In other words, the measurement condition includes information indicating a frequency range including a frequency range below 1 Hz.

[0042] The coating deterioration level determination table 227 will be described. First, the coating film deterioration level will be described. The deterioration state of the coating film CF is classified into a plurality of stages according to the degree of deterioration. In this embodiment, as an example, the description will be continued for a case where the deterioration state is classified into five stages from coating film deterioration level I to coating film deterioration level V. FIG. 12 is a diagram showing an example of the results of actual investigations of a coating film CF, such as an appearance investigation, a destructive inspection by measuring the adhesion strength of the coating film CF, and the state of infiltration of corrosion factors into the coating film CF, as well as an example of the deterioration state of a coating film CF classified by analysis of EIS data according to an embodiment of the present invention. Destructive testing by measuring the adhesion of the CF coating is carried out as follows: The coating surface is lightly polished with #240 sandpaper. After polishing, a φ20mm dolly (cylindrical tensile end) coated with epoxy resin adhesive is attached to the coating surface. After the adhesive has fully hardened, slits are made along the circumference of the dolly with a power tool. A vertical tensile force is applied to the dolly with a pull-off adhesion tester, and the adhesion strength is read when the CF coating peels off. The destruction mode of the peeled coating (corrosion prevention layer and corrosion prevention base) and the potential of the corrosion prevention base (zinc-rich primer layer) are also measured, and the presence or absence of corrosion of the zinc-zinc-rich primer layer and the steel surface are also observed. As shown in FIG. 12, the deterioration state of the coating film CF is classified into coating film deterioration level I to coating film deterioration level V, from a low deterioration state to a high deterioration state. Coating film deterioration level I is a state in which the initial state when the coating film CF was formed on the steel material 10 is maintained, and is a healthy state. In the state of coating film deterioration level I, in a healthy coating film, there is no penetration of corrosion factors into the coating film CF, and no surface deterioration of the coating film CF due to ultraviolet rays. Therefore, by measuring the adhesion force of the coating film CF, the dolly adhered to the coating film CF peels off at the adhesive without destroying the coating film CF (adhesive interface adhesion failure). In this case, the impedance obtained by measuring the coating film CF of coating film deterioration level I is a very high value. The coating deterioration level II is a state in which the surface of the corrosion protection layer 20b of the coating film CF starts to deteriorate due to corrosion factors such as ultraviolet rays, water, oxygen, and chloride ions. In the coating deterioration level II, the coating constituent molecules that absorb ultraviolet energy are activated and undergo chemical changes such as oxidative decomposition, the surface layer of the corrosion protection layer 20b starts to deteriorate, and water, salt, and oxygen start to penetrate through the surface layer of the corrosion protection layer 20b. In the coating deterioration level II, when a destructive inspection is performed by measuring the adhesion strength of the coating film CF, the coating film cohesive failure of the corrosion protection layer 20b occurs at a relatively shallow location a little in the depth direction from the surface layer, which is the position of the corrosion protection layer 20b where the corrosion factors have penetrated. The impedance obtained by measuring the coating film CF of the coating deterioration level II is lower than the impedance obtained by measuring the coating film CF of the coating deterioration level I.

[0043] The coating deterioration level III is a state in which the corrosion protection layer 20b of the coating film CF is further deteriorated than the coating deterioration level II by corrosion factors such as ultraviolet rays, water, oxygen, and chloride ions. In a state in which the surface of the corrosion protection layer 20b is worn away by ultraviolet rays, the corrosion protection layer 20b has microcracks and micropores, and voids are generated here and there. Therefore, the penetration of water, salt, and oxygen is further promoted than in the coating deterioration level II, and the penetration depth of the corrosion promotion factor is deeper than in the coating deterioration level II. In the coating deterioration level III, when a destructive inspection is performed by measuring the adhesion force of the coating film CF, cohesive failure of the corrosion protection layer 20b occurs in the deep part of the corrosion protection layer 20b where the corrosion factor has penetrated. The impedance obtained by measuring the coating film CF of the coating deterioration level III is lower than the impedance obtained by measuring the coating film CF of the coating deterioration level II. The coating deterioration level IV is a state in which the corrosion protection layer 20b of the coating film CF is further deteriorated than the coating deterioration level III due to corrosion factors such as ultraviolet rays, water, oxygen, and chloride ions. In the coating deterioration level IV, the corrosion protection layer 20b is further worn down due to ultraviolet deterioration than the coating deterioration level III, and the corrosion protection layer 20b has more cracks and small holes, and more voids are generated, allowing water, salt, and oxygen to reach the corrosion protection base 20a. In the coating deterioration level IV, when a destructive inspection is performed by measuring the adhesion force of the coating film CF, the corrosion protection base 20a has cohesive failure. In addition, the potential measurement of the corrosion protection base (zinc-rich primer) shows that it is a healthy zinc-rich primer (based on a saturated silver-silver chloride electrode), and from the appearance, the zinc-rich primer is not corroded at all, and the steel surface underneath is also not corroded at all. The impedance obtained by measuring the CF of a coating film at coating deterioration level IV is lower than the impedance obtained by measuring the CF of a coating film at coating deterioration level III. In the coating deterioration level V, after the corrosion-resistant base 20a corrodes, the corrosion protection by the zinc-rich primer disappears, and the steel material 10 corrodes. In the coating deterioration level V, water, salt, and oxygen reach the surface of the steel material 10. In the coating deterioration level V, when a destructive test is performed by measuring the adhesion strength of the coating film CF, the coating film CF peels off from the surface of the steel material, and a steel material interface adhesion failure occurs. In the potential measurement of the corrosion-resistant base (zinc-rich primer), the corrosion potential of the steel material is measured because the zinc has already disappeared. From the appearance, it is clear that the zinc-rich primer is corroded, and furthermore, the steel surface underneath it is also corroded. The impedance obtained by measuring the coating film CF is lower than the impedance obtained by measuring the coating film CF of the coating deterioration level IV.

[0044] Next, the Nyquist diagrams corresponding to each of the coating deterioration levels I to V will be described. Fig. 13 is a diagram showing Example 1 of the Nyquist diagram. Fig. 13 shows a Nyquist diagram obtained by actually measured EIS, which is reproduced by optimizing the values ​​of the circuit elements using formula (1) to match the Nyquist diagram of the actually measured EIS. Assuming that the corrosion-protective base 20a is sound, the coating resistance R2 of the corrosion-protective base 20a and the electrostatic capacitance C2 of the corrosion-protective base, as well as the coating capacitance C1 of the corrosion-protective layer 20b, which has little effect on the Nyquist diagram, are constant, and only the coating resistance R1 of the corrosion-protective layer 20b is reduced with deterioration. The upper diagram in Fig. 13 is a Nyquist diagram of the initial state in which a coating film CF is formed on a steel material 10. The coating film resistance is 100,000 [Ω]. According to the upper diagram in Fig. 13, one semicircle (hereinafter referred to as "first semicircle HC-1") is drawn on the Nyquist diagram. The lower diagram in Figure 13 is a Nyquist diagram of the state six months after the coating film CF was formed on the steel material 10. The coating film resistance is 50,000 [Ω]. According to the lower diagram in Figure 13, a first semicircle HC-1 is drawn on the Nyquist diagram. It can be seen that the radius of this first semicircle HC-1 is smaller than the radius of the first semicircle HC-1 in the upper diagram in Figure 13. FIG. 14 is a diagram showing a second example of the Nyquist diagram. FIG. 14 is a Nyquist diagram of a state in which several years to several decades have passed since the coating film CF was formed on the steel material 10. In the upper diagram of FIG. 14, the coating film resistance is 30,000 [Ω]. According to the upper diagram of FIG. 14, the first semicircle HC-1 is drawn on the Nyquist diagram, and it can be seen that the capacitive reactance on the high resistance side (low frequency side) of the first semicircle HC-1 protrudes from around 2000 Ω to 0. This is the appearance of the second semicircle. It can also be seen that the radius of the first semicircle HC-1 is smaller than the radius of the first semicircle HC-1 in the lower diagram of FIG. 13. In the lower diagram of FIG. 14, the coating film resistance is 20,000 [Ω]. In the lower diagram of Figure 14, the first semicircle HC-1 is drawn on the Nyquist diagram, and it can be seen that the protrusion of the capacitive reactance on the high resistance side (low frequency side) of the first semicircle HC-1 from around 1000 Ω to 0 is larger than in the upper diagram of Figure 14. It can also be seen that the radius of the first semicircle HC-1 is smaller than the radius of the first semicircle HC-1 in the upper diagram of Figure 14.

[0045] FIG. 15 is a diagram illustrating a third example of the Nyquist diagram. Figure 15 is a Nyquist diagram of the steel material 10 after several decades (approximately 30 years) have passed since the coating film CF was formed. In the upper diagram of Figure 15, the coating film resistance is 10,000 [Ω]. According to the left diagram of Figure 15, in addition to the first semicircle HC-1 seen in Figures 13 and 14, another semicircle (hereinafter referred to as the "second semicircle HC-2") appears on the high resistance side (low frequency side) of the first semicircle, making a total of two semicircles. It can be seen that the radius of this first semicircle HC-1 is smaller than the radius of the first semicircle HC-1 in the lower diagram of Figure 14. The lower diagram in Figure 15 shows that the coating resistance is 5000 [Ω]. According to the lower diagram in Figure 15, in addition to the first semicircle HC-1 seen in Figures 13 and 14, a second semicircle HC-2 appears on the high resistance side (low frequency side) of the first semicircle HC-1 in the Nyquist diagram, making a total of two semicircles. It can be seen that the radius of the second semicircle HC-2 is the same as in the upper diagram in Figure 15. It can be seen that the radius of this first semicircle HC-1 is smaller than the radius of the first semicircle HC-1 in the upper diagram in Figure 15. FIG. 16 is a diagram showing Example 4 of the Nyquist diagram. FIG. 16 is a Nyquist diagram of a state in which several decades (approximately 30 years) have passed since the coating film CF was formed on the steel material 10, as in FIG. 15, but compared to FIG. 15, the coating film CF has deteriorated further. In the upper diagram of FIG. 16, the coating film resistance is 3000 [Ω]. In the upper diagram of FIG. 16, a first semicircle HC-1 and a second semicircle HC-2 can be seen in the Nyquist diagram. It can be seen that the radius of the first semicircle HC-1 is smaller than that in the lower diagram of FIG. 15. It can also be seen that the radius of the second semicircle HC-2 is the same as that in the lower diagram of FIG. 15. The lower diagram of Figure 16 shows a coating resistance of 2000 [Ω]. In the lower diagram of Figure 16, the first semicircle HC-1 and the second semicircle HC-2 can be seen in the Nyquist diagram. It can be seen that the radius of the first semicircle HC-1 is smaller than that in the upper diagram of Figure 16. It can also be seen that the radius of the second semicircle HC-2 is the same as that in the upper diagram of Figure 16.

[0046] FIG. 17 is a diagram illustrating a fifth example of the Nyquist diagram. FIG. 17 is a Nyquist diagram of the steel material 10 after several decades (more than 30 years) have passed since the coating film CF was formed. The coating film resistance is 1000 [Ω]. According to FIG. 17, a first semicircle HC-1 and a second semicircle HC-2 are seen in the Nyquist diagram. It can be seen that the radius of the first semicircle HC-1 is smaller than that in the lower diagram of FIG. 16. It can also be seen that the radius of the second semicircle HC-2 is the same as that in the lower diagram of FIG. 16. Therefore, it can be seen that the radius of the first semicircle HC-1 and the radius of the second semicircle HC-2 are equal.

[0047] According to Figures 13 to 17, when six months have passed since the coating film CF was formed on the steel material 10, a first semicircle HC-1 is drawn, but when more than several years have passed since the coating film CF was formed on the steel material 10, both the first semicircle HC-1 and the second semicircle HC-2 are drawn. The first semicircle HC-1 reflects the electrochemical impedance of the corrosion protection layer 20b of the epoxy resin coating, and the radius of the first semicircle HC-1 decreases as the corrosion protection layer 20b deteriorates. The second semicircle HC-2 shows a locus in which the capacitive reactance starts to increase at 2 Hz to 20 Hz, reaches a maximum at 0.3 Hz to 0.5 Hz, and reaches a minimum again at 0.1 Hz. The radius of the second semicircle HC-2 remains the same even when the corrosion protection layer 20b of the coating CF deteriorates. From the frequency range in which the second semicircle HC-2 appears, it is assumed that the second semicircle HC-2 reflects the electrochemical impedance of the corrosion protection base 20a. Since the radius of the second semicircle HC-2 remains the same, it is inferred that the corrosion protection base 20a is sound. From the above, it is understood that the deterioration process of the anticorrosive layer 20b of the coating film CF can be grasped by the EIS characteristics with an increased electrode area. When the coating film CF is represented by an electrical equivalent circuit, if several decades have passed since the initial state in which the coating film CF was formed on the steel material 10, it is represented by a series circuit of the corrosion protection layer 20b, which is represented by a parallel circuit of AC resistance and capacitance, and the corrosion protection base 20a, which is represented by a parallel circuit of AC resistance and capacitance. The EIS characteristics obtained by actual measurement and the EIS characteristics reproduced by analyzing the electrical equivalent circuit are almost identical. The corrosion-resistant layer 20b of the coating CF decreases in resistance due to deterioration, but the change in capacitance of the corrosion-resistant layer 20b is small. Even after the passage of more than thirty years, the corrosion-resistant layer 20b of the coating CF has a sound corrosion-resistant base 20a, and the resistance and capacitance of the corrosion-resistant base 20a do not change from the initial values. The cause of the decrease in the resistance of the corrosion-resistant layer 20b is assumed to be that cracks and micropores are generated in the corrosion-resistant layer 20b by ultraviolet rays, causing a physical loss of volume, and that corrosion factors such as water, salt, and oxygen penetrate into the cracks and micropores. If corrosion occurs beneath the coating film CF due to corrosion of the corrosion-resistant base 20a, it is assumed that the resistance of the corrosion-resistant base 20a will increase.

[0048] Based on FIG. 13 to FIG. 17, the deterioration state of the coating film CF is correlated with the Nyquist diagram. Fig. 18 is a diagram showing an example of the relationship between the deterioration state of the coating film CF classified by the control and analysis device according to the embodiment of the present invention and the Nyquist diagram. In Fig. 18, the horizontal axis is AC resistance [Ω] and the vertical axis is capacitive reactance [Ω]. In the example shown in FIG. 18, Nyquist diagrams obtained by plotting AC resistance and capacitive reactance for each of coating deterioration levels I to IV are shown. The Nyquist diagram for coating deterioration level I, represented by "I", includes the first semicircle HC-11. The Nyquist diagram of coating deterioration level II, represented by "II", includes a first semicircle HC-12 and a second semicircle HC-22. The second semicircle HC-22 is drawn on the higher resistance side (lower frequency side) than the first semicircle HC-12. It can be seen that the radius of the first semicircle HC-12 is shorter than the radius of the first semicircle HC-11 in the Nyquist diagram of coating deterioration level I, and longer than the radius of the second semicircle HC-22. The Nyquist diagram of coating deterioration level III, represented by "III", includes a first semicircle HC-13 and a second semicircle HC-23. The second semicircle HC-23 is drawn on the higher resistance side (lower frequency side) than the first semicircle HC-13. It can be seen that the radius of the first semicircle HC-13 is shorter than the radius of the first semicircle HC-12 in the Nyquist diagram of coating deterioration level II, and longer than the radius of the second semicircle HC-23. The Nyquist diagram of the coating deterioration level IV, represented by "IV", includes the first semicircle HC-14 and the second semicircle HC-24. The second semicircle HC-24 is drawn on the higher resistance side (lower frequency side) than the first semicircle HC-14. It can be seen that the radius of the first semicircle HC-14 is shorter than the radius of the first semicircle HC-13 in the Nyquist diagram of the coating deterioration level III, and longer than the radius of the second semicircle HC-24. Hereinafter, any one of the first semicircles HC-11, HC-12, HC-13, and HC-14 will be referred to as the first semicircle HC-1. Also, any one of the first semicircles HC-22, HC-23, and HC-24 will be referred to as the second semicircle HC-2.

[0049] It can be seen that the radius of the first semicircle HC-1 decreases as the coating deterioration level changes from I to IV. In other words, the radius of the first semicircle HC-1 decreases as the degree of deterioration of the corrosion protection layer 20b of the coating CF increases. On the other hand, it can be seen that the radius of the second semicircle HC-2 does not change as the coating deterioration level changes from I to IV. In other words, even if the degree of deterioration of the corrosion protection layer 20b of the coating CF increases, the radius of the second semicircle HC-2 does not change. If the radius of the first semicircle HC-1 and the radius of the second semicircle HC-2 become the same, it is assumed that corrosion factors such as water, salt, and oxygen have reached the corrosion-protected base 20a. In this embodiment, each of the coating deterioration levels I to V is associated with the range of impedance obtained at each of the coating deterioration levels I to V, the range of radii of the first semicircle obtained at each of the coating deterioration levels I to V, and information indicating the presence or absence of the second semicircle obtained at each of the coating deterioration levels I to V.

[0050] FIG. 19 is a diagram showing an example of a coating deterioration degree determination table. The coating deterioration degree determination table 227 is information in a table format that associates the coating deterioration degree, the presence or absence of a second semicircle, and the ratio of the radius of the first semicircle to the radius of the second semicircle. Here, the radius of the first semicircle refers to the resistance value from 0 to the intersection of the first semicircle and the second semicircle on the X-axis of the Nyquist diagram, and the radius of the second semicircle refers to the resistance value from the intersection of the first semicircle and the second semicircle to the point where the second semicircle touches the X-axis. For example, in the case of the lower diagram of FIG. 16 (deterioration 7: coating resistance 2000Ω), the radius of the first semicircle is 2000Ω and the radius of the second semicircle is 1000Ω. The coating deterioration degree judgment table 227 is not limited to the association between the coating deterioration degree, the presence or absence of the second semicircle, and the ratio of the radius of the first semicircle to the radius of the second semicircle, but may also be table-format information associated with the destruction mode of the coating CF in the coating adhesion test, such as the impedance range and the change in the radius of the second semicircle. Further, the coating deterioration degree determination table 227 may be prepared for each steel material 10, or may be prepared for each thickness of the coating film CF. In these cases, the coating deterioration degree determination table 227 is configured to include a plurality of coating deterioration degree determination tables. Returning to FIG. 11, the description will be continued.

[0051] The information processing unit 230 is a functional unit (hereinafter referred to as a "software functional unit") that is realized by a processor such as a CPU (Central Processing Unit) executing a program 222 or an application 224 stored in the storage unit 220. Note that all or a part of the information processing unit 230 may be realized by hardware such as an LSI (Large Scale Integration), an ASIC (Application Specific Integrated Circuit), or an FPGA (Field-Programmable Gate Array), or may be realized by a combination of the software functional unit and hardware. The information processing unit 230 includes, for example, an instruction unit 231, a receiving unit 232, a processing unit 233, and an analysis unit 234. The instruction unit 231 acquires information indicating the start of measurement output from the operation unit 240 when the user performs an operation to start measurement on the operation unit 240. The instruction unit 231 acquires measurement condition information 226 stored in the storage unit 220 based on the acquired information indicating the start of measurement, and outputs the measurement conditions included in the acquired measurement condition information 226 to the IF 210. The instruction unit 231 creates a measurement start request based on the acquired information indicating the start of measurement, and outputs the created measurement start request to the IF 210.

[0052] The receiving unit 232 receives the measurement result output by the IF 210. The receiving unit 232 outputs the received measurement result to the processing unit 233. An example of information included in the measurement result is information indicating impedance. Below, a description will be given of the case where the information included in the measurement result is information indicating impedance. The processing unit 233 acquires the measurement results output by the receiving unit 232. The processing unit 233 processes information indicating impedance included in the measurement results based on the acquired measurement results. The processing unit 233 outputs the result of processing the information indicating impedance included in the measurement results to the analyzing unit 234. Specifically, the processing unit 233 acquires information indicating the impedance included in the measurement result output by the receiving unit 232, and derives one or both of a Bode plot and a Nyquist plot based on the acquired information indicating the impedance. In this embodiment, the description will continue with the case where the processing unit 233 derives the Bode plot and the Nyquist plot. The processing unit 233 outputs information indicating the derived Bode plot and information indicating the Nyquist plot to the analysis unit 234.

[0053] FIG. 20 is a diagram showing an example of a Bode plot derived by the control and analysis device according to an embodiment of the present invention. The left diagram in FIG. 20 is a Bode plot showing the frequency characteristics of impedance amplitude, and the right diagram in FIG. 20 is a Bode plot showing the frequency characteristics of impedance phase. In the left diagram of Figure 20, the horizontal axis is frequency [Hz] and the vertical axis is impedance amplitude [Ω]. In this case, both the horizontal and vertical axes are logarithmic. From the left diagram of Figure 20, it can be seen that there is no significant noise in any frequency range. In the right diagram of Figure 20, the horizontal axis is frequency [Hz] and the vertical axis is impedance phase [deg]. In this case, only the horizontal axis is displayed logarithmically. From the right diagram of Figure 20, it can be confirmed that there is no significant noise in all frequency ranges. FIG. 21 is a diagram showing an example of a Nyquist diagram derived by the control and analysis device according to the embodiment of the present invention. In FIG. 21, the horizontal axis is AC resistance [Ω], and the vertical axis is capacitive reactance [Ω]. According to FIG. 21, it can be confirmed that there is no significant noise in all frequency ranges in the Nyquist diagram. It can be confirmed that the impedance can be read even in the low frequency range of 0.1 Hz in this Nyquist diagram. In other words, it can be seen that the second semicircle HC-2 can be detected by performing measurements in a frequency range including a frequency range of less than 1 Hz in this Nyquist diagram.

[0054] The analysis unit 234 acquires the information indicating the Bode plot and the information indicating the Nyquist plot output by the processing unit 233. The analysis unit 234 grasps the state of the coating film CF based on the acquired information indicating the Bode plot and the information indicating the Nyquist plot. The explanation will be continued for the case where the analysis unit 234 acquires the Bode plot shown in FIG. 20 and the Nyquist plot shown in FIG. The analysis unit 234 refers to the coating deterioration level determination table 227 stored in the storage unit 220, and determines to which of the impedance ranges of coating deterioration levels I to V the impedance obtained from the acquired Bode plot falls. With this configuration, it is possible to check the impedance even in the low frequency range of 0.1 Hz, so that it is possible to determine whether or not the corrosion-resistant base 20a of the coating film CF and the surface of the steel material 10 are corroded. The analysis unit 234 refers to the coating deterioration level determination table 227 stored in the storage unit 220, and determines, based on the radius of the first semicircle HC-1 obtained from the acquired Nyquist diagram, which of the ranges of the radius of the first semicircle for each of the coating deterioration levels I to V the coating deterioration level falls into. With this configuration, it is possible to confirm the impedance even in the low frequency range of 0.1 Hz, and therefore it is possible to grasp the degree of deterioration of the corrosion protection layer 20b of the coating CF.

[0055] The analysis unit 234 refers to the coating deterioration degree judgment table 227 stored in the memory unit 220, and judges whether the coating deterioration degree I to the coating deterioration degree V corresponds to the presence or absence of the second semicircle HC-2 and the increase or absence of the radius of the second semicircle HC-2 based on the presence or absence of the second semicircle HC-2 obtained from the acquired Nyquist diagram and the increase or absence of the radius of the second semicircle HC-2. By configuring in this way, it is possible to check the impedance even in the low frequency range of 0.1 Hz, so that it is possible to check the presence or absence of the second semicircle and the increase or absence of the radius of the second semicircle HC-2. Therefore, it is possible to grasp the degree of deterioration of the corrosion-resistant base 20a of the coating film CF. The analysis unit 234 determines whether the coating deterioration level falls into one of the coating deterioration levels I to V based on the results of determining the impedance obtained from the Bode plot, the radius of the first semicircle HC-1 obtained from the Nyquist plot, the presence or absence of the second semicircle HC-2 obtained from the Nyquist plot, and the presence or absence of an increase in the radius of the second semicircle HC-2. For example, the analysis unit 234 may determine the most deteriorated of the deterioration degrees of the coating film determined from the impedance obtained from the Bode plot, the radius of the first semicircle HC-1 obtained from the Nyquist plot, the presence or absence of the second semicircle HC-2 obtained from the Nyquist plot, and the presence or absence of an increase in the radius of the second semicircle HC-2. By configuring in this way, it is possible to quickly take measures against the deterioration of the coating film CF. The analysis unit 234 displays information indicating the result of judging the state of the coating film CF based on the Bode diagram and the Nyquist diagram on the display unit 250. Furthermore, the analysis unit 234 may perform the following process when it judges that the state of the coating film CF is coating film deterioration level IV. When the state of the coating film CF is coating film deterioration level IV, it is assumed that corrosion factors such as water and salt have reached the corrosion protection base 20a. In this case, it is preferable to perform repairs to prevent the corrosion factors from reaching the steel material. Therefore, when the analysis unit 234 judges that the state of the coating film CF is coating film deterioration level IV, it judges that it is time for repairs. For example, the time when the radius of the semicircle on the high frequency side and the radius of the semicircle on the low frequency side become 1:1 is set as the threshold value for the time for repairs. In this case, the analysis unit 234 outputs information indicating that it is time for repairs to the display unit 250. The repair time may be determined as III instead of IV.

[0056] The operation unit 240 is an input device that accepts user operations. Specifically, when the user operates the operation unit 240 to start measurement, the operation unit 240 creates information indicating the start of measurement and outputs the created information indicating the start of measurement to the information processing unit 230. The display unit 250 is configured, for example, by a touch panel. The display unit 250 displays a screen for diagnosing the coating film CF covering the steel material 10 by electrochemical impedance spectroscopy. The display unit 250 also displays a screen for displaying the diagnosis results of the coating film CF covering the steel material 10.

[0057] (Operation of coating film characteristic measurement system) FIG. 22 is a flow chart showing an example of the operation of the coating property measuring system according to the embodiment of the present invention. (Step S1) When a user operates the operation unit 240 of the control and analysis device 200 to start measurement, the operation unit 240 creates information indicating the start of measurement, and outputs the created information indicating the start of measurement to the information processing unit 230. (Step S2) The instruction unit 231 of the information processing unit 230 acquires information indicating the start of measurement output by the operation unit 240. The instruction unit 231 acquires the measurement condition information 226 stored in the storage unit 220 based on the acquired information indicating the start of measurement, and outputs the measurement conditions included in the acquired measurement condition information 226 to the IF 210. The IF 210 acquires the measurement conditions output by the information processing unit 230 , and outputs the acquired measurement conditions to the coating film property measuring apparatus 100 . (Step S3) The instruction unit 231 creates a measurement start request based on the acquired information indicating the start of measurement. (Step S4) The instruction unit 231 outputs the created measurement start request to the IF 210. The IF 210 acquires the measurement start request output by the information processing unit 230, and outputs the acquired measurement start request to the coating film property measuring apparatus 100. (Step S5) The processing unit 104 of the coating property measuring device 100 acquires the measurement start request output by the control and analysis device 200, and outputs a measurement start request to the measuring unit 102 based on the acquired measurement start request. The measurement unit 102 receives the measurement conditions output by the control and analysis device 200. The measurement unit 102 acquires information indicating the AC voltage to be applied between the first counter electrode CE1 and the first working electrode WE1, which is included in the received measurement conditions, based on a measurement start request output by the processing unit 104. The measurement unit 102 applies and sweeps a sinusoidal AC voltage between the first counter electrode CE1 and the first working electrode WE1, based on the acquired information indicating the AC voltage to be applied between the first counter electrode CE1 and the first working electrode WE1.

[0058] (Step S6) The measurement unit 102 measures an AC current flowing between the second counter electrode CE2 and the second working electrode WE2, which is a frequency response obtained by applying and sweeping a sinusoidal AC voltage between the first counter electrode CE1 and the first working electrode WE1. The measurement unit 102 outputs to the processing unit 104 information indicating the AC voltage swept with a sine wave between the first counter electrode CE1 and the first working electrode WE1 and the measurement result of the current. (Step S7) The processing unit 104 acquires information indicating the AC voltage output by the measurement unit 102 and the measurement results of the AC current, and derives the impedance by dividing the voltage value by the current value based on the acquired information indicating the AC voltage and the measurement results of the current. (Step S8) The processing unit 104 outputs information indicating the derived impedance to the control and analysis device 200. (Step S9) The IF 210 of the control and analysis device 200 acquires the measurement results output by the coating property measuring device 100 , and outputs the acquired measurement results to the information processing unit 230 . The receiving unit 232 of the information processing unit 230 receives the measurement result output by the IF 210. The receiving unit 232 outputs the received measurement result to the processing unit 233. The processing unit 233 acquires the measurement result output by the receiving unit 232. The processing unit 233 derives a Bode plot and a Nyquist plot based on information indicating the impedance included in the acquired measurement result. The processing unit 233 outputs information indicating the derived Bode plot and information indicating the Nyquist plot to the analysis unit 234. (Step S10) The analysis unit 234 acquires the information indicating the Bode plot and the information indicating the Nyquist plot output by the processing unit 233. The analysis unit 234 judges the state of the coating film CF based on the acquired information indicating the Bode plot and the information indicating the Nyquist plot. (Step S11) The analysis unit 234 displays on the display unit 250 information indicating the results of judging the state of the coating film CF based on the Bode plot and the Nyquist plot.

[0059] In the above-described embodiment, the coating film property measuring device 100 and the control and analysis device 200 are described as different devices, but this is not limited thereto. For example, the coating film property measuring device 100 and the control and analysis device 200 may be integrated together. That is, the coating film property measuring device 100 may include the control and analysis device 200. Furthermore, the measurement unit 102 and the processing unit 104 included in the coating film property measuring device 100 may be different devices. Furthermore, two of the measurement unit 102, the processing unit 104, and the control and analysis device 200 may be combined. In the above-described embodiment, the coating property measuring device 100 and the control and analysis device 200 may be connected by wire or wirelessly. In the above-described embodiments, the method for measuring impedance in the coating film characteristic measuring method and coating film characteristic measuring device involves applying an AC voltage between the electrode and the steel material across the coating film CF, sweeping the frequency, and measuring the AC current flowing between the electrode and the steel material across the coating film CF, which is the frequency response, to determine the impedance of the coating film CF. However, similar results can also be obtained conversely by passing an AC current between the electrode and the steel material across the coating film CF, sweeping the frequency, and measuring the AC voltage generated between the electrode and the steel material across the coating film CF, which is the frequency response, to determine the impedance. In the above-mentioned embodiment, the coating film CF includes the anticorrosive base 20a and the anticorrosive layer 20b, and the anticorrosive base 20a is an example of zinc-rich primer, and the anticorrosive layer 20b is an example of epoxy resin. However, the present invention is not limited to this example. For example, when the anticorrosive layer 20b deteriorates, the Nyquist diagram corresponding to the anticorrosive base 20a and the anticorrosive layer 20b becomes two semicircles, and while the anticorrosive base 20a is sound, only the diameter of the semicircle corresponding to the anticorrosive layer 20b becomes smaller, and the semicircle corresponding to the anticorrosive base 20a does not change. This phenomenon is assumed to be realized in a coating film that combines the anticorrosive base 20a and the anticorrosive layer 20b, which have two different electrical characteristics. This combination is a combination of the anticorrosive base 20a with a low resistance such as zinc-rich primer and the anticorrosive layer 20b with a high resistance such as epoxy resin. Here, the anticorrosion layer 20b may be made of a resin other than epoxy resin, and may be made of, for example, acrylic resin, urethane resin, or the like, which is used as the anticorrosion layer 20b of paint.

[0060] In the above-described embodiment, the coating film CF in which zinc and epoxy are combined may be used for the following purposes. (1) Ultra-thick epoxy resin coating (a) Organic zinc 20μm or more + epoxy resin 2500μm or more (total film thickness 2.52mm or more) (b) Organic zinc 20μm or more + epoxy resin 1250μm or more + weather-resistant paint 55μm or more (total film thickness 1.325mm or more) (2) Marine thick epoxy coating (a) Organic zinc 75μm or more + epoxy resin 480μm or more (total film thickness 0.555mm or more) (b) Organic zinc 75μm or more + epoxy resin 200μm or more + weather-resistant paint 55μm or more (total film thickness 0.33mm or more) (3) C5 paint Inorganic zinc 75μm or more + epoxy resin 120μm or more + weather-resistant paint 55μm or more (total film thickness 0.25mm or more) Here, (1) and (2) apply to marine steel structures, and (3) may be applied to large bridges. Here, the thickness of the coating film CF will be described. When the coating film CF is constructed based on (1) to (3), the coating film CF can also be applied when a weather-resistant paint is applied on the corrosion-resistant layer 20b, and includes a corrosion-resistant base 20a (zinc layer) and the corrosion-resistant layer 20b. In this case, the coating film CF has a film thickness of 250 μm or more and 3 mm or less. In this case, the corrosion-resistant layer 20b is not limited to epoxy resin. Specifically, the corrosion-resistant layer 20b may be an acrylic resin or a urethane resin. When the coating film CF is constructed based on (1) and (2), the coating film CF can also be applied when a weather-resistant paint is applied on the corrosion-resistant layer 20b, and includes a corrosion-resistant base 20a (zinc layer) and the corrosion-resistant layer 20b. In this case, the coating film CF has a film thickness of 300 μm or more and 3 mm or less. In this case, the corrosion-resistant layer 20b is not limited to epoxy resin. Specifically, the corrosion-resistant layer 20b may be an acrylic resin or a urethane resin. When the coating film CF is constructed based on (1), the coating film CF can also be applied when a weather-resistant paint is applied on the corrosion-resistant layer 20b, and includes a corrosion-resistant base 20a (zinc layer) and the corrosion-resistant layer 20b. In this case, the coating film CF has a film thickness of 1.325 mm or more and 3 mm or less. In this case, the corrosion-resistant layer 20b is not limited to epoxy resin. Specifically, the corrosion-resistant layer 20b may be an acrylic resin or a urethane resin.

[0061] According to the coating film property measuring system 1 of this embodiment, the coating film property measuring device 100 measures the properties of the coating film CF using electrochemical impedance spectroscopy. The coating film CF is a thick film formed on a corrosion-resistant base applied directly on a steel material and an anticorrosive layer applied on the corrosion-resistant base. The coating film property measuring system 1 applies an AC voltage between the steel material and an electrode formed on the anticorrosive layer, measures the AC current obtained by frequency sweeping the AC voltage, and derives the impedance based on the measurement results of the AC voltage and the AC current. The area of ​​the electrode is 0.1 m 2 More than 0.3m 2 The following is the result. By increasing the area of ​​the electrode, the capacitance increases, so the capacitive reactance can be reduced. In addition, by increasing the area of ​​the electrode, the AC resistance can be reduced. In addition, the degree of influence of drying from the coating film CF around the electrode is large when the electrode area is small, but when the electrode area is large, the influence of drying is almost eliminated, so the degree of moisture absorption of the conductive paste into the coating film CF is favorable for the electrode area. This suggests that at low frequencies, the current flows almost entirely through the resistance circuit, so the larger the electrode area, the lower the conductivity of the coating film CF. As mentioned above, by increasing the electrode area, in addition to the decrease in resistance and the decrease in capacitive reactance corresponding to the increase in the electrode area, an effective decrease in conductivity occurs. Therefore, by increasing the area of ​​the electrode, the signal current increases and the signal-to-noise ratio is improved, so information for obtaining a clear Nyquist diagram can be derived.

[0062] Moreover, according to the coating film property measuring system 1, the coating film property measuring device 100 performs frequency sweep of the AC voltage in a frequency range including a frequency range below 1 Hz. By increasing the area of ​​the electrode, it is possible to read the impedance even in the low frequency range below 1Hz. To grasp the condition near the surface of the steel material under the coating CF, it is necessary to measure the electrochemical impedance in the lower frequency range. By measuring the electrochemical impedance including the low frequency range below 1Hz, it is possible to confirm the semicircle that appears in the low frequency range in the Nyquist diagram. Since this semicircle that appears in the low frequency range is assumed to reflect the electrochemical impedance of the corrosion protection base, the condition of the corrosion protection base can be judged by this semicircle in the low frequency range. By configuring in this way, it is possible to evaluate the soundness of the corrosion protection base and the presence or absence of corrosion on the steel surface. In other words, it is possible to derive information for judging the condition of the corrosion protection base. In addition, by increasing the electrode area, it is possible to measure the EIS characteristics in the low frequency range without noise, so it is possible to fit the measured EIS with the EIS reproduced by the equivalent circuit. Furthermore, by fitting the measured EIS data of the coating CF with different deterioration progression to the equivalent circuit, the deterioration process of the coating CF can be clarified by the change in parameters and the change in the EIS curve shape. This makes it possible to determine whether the deterioration of the coating has progressed to the corrosion protection layer, whether the corrosion protection base underneath is corroding, or whether it has progressed further and the steel material underneath the corrosion protection film is corroding.

[0063] Moreover, according to the coating film characteristic measuring system 1, the coating film characteristic measuring system 1 plots a Nyquist diagram based on the derived impedance, and judges the state of the coating film CF based on the plotted Nyquist diagram. By configuring in this way, a clear Nyquist diagram can be obtained, and therefore the state of the coating film CF can be judged. Moreover, according to the coating film characteristic measuring system 1, the coating film characteristic measuring system 1 judges the state of the coating film CF based on the semicircle representing the state of the coating film CF shown in the Nyquist diagram. By configuring in this way, the state of the corrosion-protective base film can be judged because the state of the corrosion-protective base is represented by the semicircle in the low frequency range in the Nyquist diagram. Moreover, according to the coating film characteristic measuring system 1, the coating film characteristic measuring system 1 judges whether or not it is time for repair based on the state of the coating film CF. By configuring in this way, it is possible to judge whether or not it is time for repair based on the state of the coating film CF, so that it is possible to prevent corrosion factors from reaching the steel material. If the anticorrosive base is corroded, a large-scale repair with the entire coating film peeling off is required, but if the deterioration has reached the anticorrosive layer, it is possible to leave the coating film CF and limit the repair to a simple repair of penetrating into cracks and micropores, filling the gaps, and applying a topcoat of paint with good weather resistance, and it is possible to propose an appropriate time for repair. Although the embodiments have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, modifications, and combinations can be made without departing from the spirit of the invention. These embodiments are included in the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents described in the claims.

[0064] The above-mentioned control and analysis device 200 may be realized by a computer. In that case, a program for realizing the functions of each functional block is recorded on a computer-readable recording medium. The program recorded on the recording medium may be read into a computer system and executed by a CPU to realize the device. The term "computer system" as used herein includes hardware such as an OS (Operating System) and peripheral devices. In addition, "computer-readable recording media" refers to portable media such as flexible disks, optical magnetic disks, ROMs, CD-ROMs, etc. In addition, "computer-readable recording media" includes storage devices such as hard disks built into computer systems.

[0065] Furthermore, the term "computer-readable recording medium" may include a medium that dynamically stores a program for a short period of time, such as a communication line for transmitting a program via a network such as the Internet or a communication line such as a telephone line. Furthermore, the "computer-readable recording medium" may also include a storage medium that holds a program for a certain period of time, such as a volatile memory inside a computer system that is a server or a client. The program may be for implementing part of the functions described above. The program may be capable of implementing the functions described above in combination with a program already recorded in the computer system. The program may be implemented using a programmable logic device. An example of a programmable logic device is an FPGA (Field Programmable Gate Array).

[0066] The above-mentioned control and analysis device 200 has an internal computer. Each process of the above-mentioned control and analysis device 200 is stored in a computer-readable recording medium in the form of a program, and the above-mentioned processes are performed by the computer reading and executing this program. Here, computer-readable recording media refers to magnetic disks, magneto-optical disks, CD-ROMs, DVD-ROMs, semiconductor memories, etc. In addition, this computer program may be distributed to a computer via a communication line, and the computer that receives this distribution may execute the program. The program may be for implementing some of the functions described above, or may be a so-called differential file (differential program) that can implement the functions described above in combination with a program already recorded in the computer system. [Explanation of symbols]

[0067] 1. Coating film property measurement system 10 Steel material 20a Anti-corrosive Base 20b Anticorrosive layer 30 Conductive Paste 40 electrodes 100 Coating film characteristic measuring device 102 Measuring part 104 Processing section 200 Control and analysis equipment 210 IF 220 Storage section 222 Program 226 Measurement condition information 227 Paint Deterioration Determination Table 230 Information Processing Department 231 Instruction section 232 Reception 233 Processing section 234 Analysis Department 240 Operation section 250 Display section 260 Bus Line

Claims

1. A film characteristic measurement method for measuring characteristics of a film having a substrate formed on a steel material and an outer layer formed on the substrate by using an electrochemical impedance method, comprising: applying an AC voltage between an electrode formed on the film and the steel material and measuring an AC current; deriving an impedance from said AC voltage and said AC current; having The film characteristic measuring method further comprises determining a state of the base based on the impedance.

2. A film characteristic measurement method for measuring characteristics of a film having a substrate formed on a steel material and an outer layer formed on the substrate by using an electrochemical impedance method, comprising: applying an AC voltage between a first counter electrode connected to an electrode formed on the film and a first working electrode directly connected to the steel material, and measuring an AC current flowing between a second counter electrode connected to the electrode formed on the film and a second working electrode directly connected to the steel material; deriving an impedance from said AC voltage and said AC current; The film characteristic measuring method includes the steps of:

3. A film characteristic measurement method for measuring characteristics of a film having a substrate formed on a steel material and an outer layer formed on the substrate by using an electrochemical impedance method, comprising: applying an AC voltage between an electrode formed on the film and the steel material and measuring an AC current; deriving an impedance from said AC voltage and said AC current; having A film characteristic measuring method, wherein one Nyquist diagram drawn from the impedance includes a first semicircle and a second semicircle on a higher resistance side than the first semicircle.

4. The area of ​​the electrode is 0.01 m ２ The film characteristic measuring method according to claim 1 , wherein the film characteristic measuring method is a film characteristic measuring method according to claim 1 .

5. The film characteristic measuring method according to claim 1 , wherein in the measuring step, the AC voltage is frequency swept in a frequency range including a frequency range of less than 1 Hz.

6. A step of plotting a Nyquist diagram based on the impedance derived in the deriving step; determining a state of the film from the Nyquist diagram; The method for measuring film characteristics according to claim 1 , further comprising:

7. 7. The film characteristic measuring method according to claim 6, wherein in the determining step, the state of the base is determined from a semicircle representing the state of the base shown in the Nyquist diagram.

8. A step of determining whether or not it is time for repair based on the condition of the base determined in the step of determining. The film characteristic measuring method according to claim 6 or 7, comprising:

9. A film characteristic measuring device that uses an electrochemical impedance method to measure characteristics of a film having a base formed on a steel material and an outer layer formed on the base, A measurement unit that applies an AC voltage between an electrode formed on the film and the steel material and measures an AC current; A processing unit that derives an impedance from the AC voltage and the AC current; an analysis unit that determines a state of the substrate based on the impedance; A film characteristic measuring apparatus comprising:

10. A film characteristic measuring device that uses an electrochemical impedance method to measure characteristics of a film having a base formed on a steel material and an outer layer formed on the base, A first working electrode and a second working electrode directly connected to the steel material; A first counter electrode and a second counter electrode connected to the electrode formed on the membrane; a measurement unit that applies an AC voltage between the first counter electrode and the first working electrode and measures an AC current flowing between the second counter electrode and the second working electrode; a processing unit that derives impedance from the AC voltage and the AC current; A film characteristic measuring apparatus comprising:

11. A film characteristic measuring device that uses an electrochemical impedance method to measure characteristics of a film having a base formed on a steel material and an outer layer formed on the base, A measurement unit that applies an AC voltage between an electrode formed on the film and the steel material and measures an AC current; a processing unit that derives impedance from the AC voltage and the AC current and derives a Nyquist diagram from the impedance; an analysis unit that determines a state of the substrate from a Nyquist diagram including a first semicircle and a second semicircle on a higher resistance side than the first semicircle, the Nyquist diagram being derived from the impedance; A film characteristic measuring apparatus comprising:

Images