Method and system for evaluating state of coating film

Abstract

To provide a method for evaluating the state of a coating film capable of accurately grasping the state of the coating film deteriorated due to environmental exposure or the like.SOLUTION: A method for evaluating the state of a coating film comprises: an analysis step of obtaining a relaxation time distribution function spectrum [τ-γ(τ)] related to a relaxation time (τ) from an impedance spectrum [f-Z] obtained by applying an alternating current (frequency f) to the coating film; and an evaluation step of grasping a state of the coating film by comparing a specific relaxation time (τp), when the relaxation time distribution function spectrum becomes a local maximum or maximum, with a predetermined reference relaxation time (τs). Furthermore, the state of the coating film may be grasped by comparing a specific impedance (|Za|) related to the predetermined specific frequency (fa) with a predetermined reference impedance (|Zs|).SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a method for grasping the state of a coating film (for example, history, deterioration, etc.).

Background Art

[0002] In order to ensure corrosion resistance, designability, etc., the surfaces of members, structures, etc. are painted. The coating film (especially a resin coating film) is exposed to the actual external environment (sunlight, wind and rain, corrosive gas, etc.) and deteriorates (or ages) over time, and its function may decline.

[0003] If the state of the coating film (degree of function decline, alteration, etc.) can be accurately grasped (evaluated), effective maintenance (repair, replacement, etc.) of the painted object is possible, which also contributes to a circular economy. For this reason, proposals related to the evaluation of painted objects have been made. For example, there are descriptions related to the following documents.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] Conventionally, the coating film has been diagnosed and evaluated based on impedance measured electrochemically. However, it has been found that it is difficult to accurately grasp the state of a coating film with a history of being subjected to a large stress from the past exposure environment by evaluation only using impedance (spectrum) based on an assumed equivalent circuit.

[0006] The present invention has been made in view of such circumstances, and an object thereof is to provide a new evaluation method or the like that can more accurately grasp the state of a coating film.

Means for Solving the Problem

[0007] As a result of intensive research, the present inventor has found that even in a coating film whose impedance (|Z|) has significantly decreased in the past, the impedance can recover after a long period of time. It has been discovered that the state of such a coating film is difficult to grasp only by impedance, but can be grasped by paying attention to the relaxation time. By developing such results, the present invention described below has been completed.

[0008] 《Coating Film State Evaluation Method》 (1) The present invention includes an analysis step of obtaining a relaxation time distribution function spectrum [τ-γ(τ)] related to the relaxation time (τ) from an impedance spectrum [f-Z] obtained by applying an alternating current (frequency f) to a coating film, and an evaluation step of grasping the state of the coating film by comparing a specific relaxation time (τp) when the relaxation time distribution function (γ(τ)) reaches a maximum or a maximum with a predetermined reference relaxation time (τs). It is a coating film state evaluation method.

[0009] (2) According to the present invention, it is possible to more accurately and non-destructively grasp the state of a coating film that cannot be grasped only by the magnitude of the impedance. The mechanism by which such an effect is obtained is not necessarily clear, but currently, it is speculated as follows.

[0010] A coating film exposed to an actual environment where wetting and drying are repeated generally has an increasing amount of moisture contained therein as it deteriorates, and the impedance in at least a specific frequency range can decrease (gradually decrease) over time. However, conversely, since the impedance is greatly affected by the amount of moisture in the coating film at the time of measurement, it does not necessarily accurately indicate the state of the coating film. For example, even if the material (such as resin) of the coating film has changed (such as being altered or deteriorated) due to the history of stress (such as changes in heat and humidity) received by the coating film, if the amount of moisture in the coating film happens to be small at the time of measurement, a large impedance may be measured, resulting in a possibility of misidentifying the state of the coating film.

[0011] On the one hand, the relaxation time can vary depending on the state of the material (such as the state of molecules or crystals). Therefore, the relaxation time distribution function spectrum can reflect the state of the material at the time of measurement. For this reason, even when the material of the coating film has changed due to stress or the like received from the environment to which it was exposed in the past, it is considered that by taking into account the relaxation time distribution function spectrum, the state of the coating film at the time of measurement can be grasped more accurately.

[0012] 《Coating Film State Evaluation System》 The present invention can also be understood as an evaluation system for the state of a coating film. For example, the present invention may be a coating film state evaluation system including an electrode attached to the coating film, a measuring means for applying an alternating current to the electrode to obtain an impedance spectrum of the coating film, an analyzing means for obtaining a relaxation time distribution function spectrum from the impedance spectrum, and an evaluating means for evaluating the state of the coating film based on the impedance spectrum and / or the relaxation time distribution function spectrum.

[0013] 《Others》 (1) As used in this specification, "~means" and "~step" can be read interchangeably with each other, whereby the components of "object (system, device)" and the components of "method" can be made compatible. Steps and means may also be realized by executing a computer program.

[0014] (2) Unless otherwise specified, "x~y" as used in this specification includes the lower limit value x and the upper limit value y. Using any numerical value included in the various numerical values or numerical ranges described in this specification as a new lower limit value or upper limit value, a range such as "a~b" can be newly established.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Mode for Carrying Out the Invention

[0016] One or more components arbitrarily selected from this specification can be added to the components of the present invention described above. The content described in this specification may be appropriately applicable not only to "things" but also to "methods". Whether any embodiment is the best depends on the object, required performance, etc.

[0017] 《Impedance Spectrum》 The impedance spectrum [f-Z] is obtained by measuring the impedance (Z) obtained by applying an alternating current (frequency f) between electrodes in contact with the coating film using an LCR meter or the like (measuring means / measuring step). The applied voltage (amplitude / maximum value) of the alternating current applied during measurement may be, for example, 0.05 to 2 V, 0.1 to 1 V, or 0.3 to 0.7 V in consideration of measurement stabilization and damage prevention to the resin.

[0018] The frequency range (range) of the alternating current application may be, for example, 10 -3 ~10 7 Hz, 10 -2 ~10 6 Hz or 10 -1 ~10 5 Hz according to the type and form of the coating film. If the characteristics (frequency characteristics, etc.) of the coating film are known in advance, the impedance may be measured only in a specific frequency range (for example, 10 -2 ~10 3 Hz or 10 -1 ~10 2 Hz).

[0019] The measurement interval may be, for example, 1 to 100 point / dec or 2 to 10 point / dec in consideration of damage to the coating film and the time required for measurement. Note that 1 dec (decade) means one scale on the common logarithm scale (10 times in terms of frequency ratio).

[0020] "Spectrum of Relaxation Time Distribution Function" The spectrum of the relaxation time distribution function [τ-γ(τ)] is obtained by performing relaxation time distribution analysis (DRT: Distribution of Relaxation Time) based on the impedance spectrum [f-Z] (analysis step). This analysis method is well-known. The specific γ(τ) can be obtained, for example, using DRT tools.m (https: / / github.com / ciuccislab / DRTtools), etc. (analysis means).

[0021] "Evaluation" The state of the coating film is grasped, for example, as follows.

[0022] (1) Relaxation time Based on the spectrum of the relaxation time distribution function [τ-γ(τ)], the specific relaxation time (τp) when the relaxation time distribution γ reaches a peak (maximum or largest) is obtained. When there are multiple peaks (maxima) within the measurement range or observation range, it is advisable to select the largest peak within that range and specify τp.

[0023] Compare that τp with a reference relaxation time (τs) preset according to the coating film. τs may be set considering the τp (appropriately denoted as τp0) of the coating film ("initial coating film") before environmental exposure (initial state). However, it is not necessary to set τp0 as τs. Usually, τs may be a value smaller than τp0.

[0024] The τp of the coating film to be evaluated ("test coating film") usually becomes smaller (shorter) corresponding to the environmental exposure history and thus the state change (deterioration). Therefore, usually, if τp≦τs, it can be evaluated (judged) that the test coating film is in a deteriorated state compared to the desired state (evaluation step).

[0025] However, the set value of τs, the comparison (magnitude relationship) between τp and τs, etc. may be appropriately set according to the type of coating film, the specification (lifetime) of the coating film, etc. As an example, in the case of a rust-preventive coating film formed on a steel plate, the reference relaxation time (τs) may be a value selected from 0.5 to 5 seconds or 1 to 3 seconds (for example, any of τs = 1 second, 1.5 seconds, 2 seconds).

[0026] (2) Impedance From the impedance spectrum, a specific impedance (|Za|) related to a predetermined specific frequency (fa = ωa / 2π, ωa: specific angular frequency) is obtained. This |Za| is compared with a reference impedance (|Zs|) set in advance according to the coating film. |Zs| may be set in consideration of |Za| of the initial coating film (appropriately referred to as |Za0|). However, it is not necessary to set |Za0| as |Zs|. |Zs| may be a value smaller than |Za0|.

[0027] The |Za| of the test coating film also generally decreases over time due to deterioration or the like according to the environmental exposure history. Therefore, usually, if |Za| ≤ |Zs|, it can be evaluated (judged) that the test coating film is in a deteriorated state rather than the desired state (evaluation step).

[0028] |Zs| etc. may also be appropriately set according to the type of coating film, the specification (lifetime) of the coating film, etc. As an example, in the case of a rust-preventive coating film formed on a steel plate, the specific frequency (fa) for obtaining |Za| may be a value selected from 0.01 to 100 Hz or 0.1 to 10 Hz (for example, fa = 0.1 Hz, 1 Hz, 10 Hz). The |Zs| may be a value selected from 10 GΩ to 0.1 MΩ or 1 GΩ to 1 MΩ (for example, |Zs| = 1 GΩ, 10 MΩ, 1 MΩ).

[0029] Multiple |Zs| values may be set, and the state of the coating film may be classified into multiple levels and evaluated according to its degree of deterioration. For example, it may be divided into 2 to 5 levels or 3 to 4 levels to determine the state of the coating film. When |Za| is less than a predetermined value (for example, |Za| < 1 MΩ or |Za| < 0.1 MΩ), the coating film may be determined to have exceeded its lifetime (dysfunctional state).

[0030] The combination of the state evaluation based on the specific relaxation time (τp) and the state evaluation based on the specific impedance (|Za|), regardless of their priority or primary-secondary relationship. When evaluating the state of the coating film, in addition to using τp and |Za| as indicators at the same level, for example, τp can be used as the main indicator and |Za| as the subordinate indicator, or |Za| can be used as the main indicator and τp as the subordinate indicator, or only τp can be used as the indicator.

[0031] 《Coating Film》 The coating film, as long as it can conduct alternating current between the electrodes, regardless of its material, number of layers, presence or absence of substrate treatment (such as chemical conversion treatment, roughening, etc.). The coating film is composed of, for example, thermoplastic resin, thermosetting resin, rubber (including elastomer), etc. The coating film can be formed directly on the substrate surface or through an underlying film.

[0032] As a typical example of a coating film that undergoes state changes (such as deterioration, aging, etc.) due to exposure to the external environment, there is a coating film that covers a vehicle body, a ship hull, an aircraft body (substrate), etc. In the case of an automotive coating film, for example, electrocoating (rust-proof coating) for ensuring corrosion resistance, intermediate coating for ensuring pitch resistance, light shielding property, smoothness, etc., and top coating (usually a colored base coating and a transparent clear coating) for ensuring designability, weather resistance, etc. are successively applied to form the coating film. The rust-proof coating formed on a metal body often has an underlying layer (such as a chemical conversion coating).

[0033] 《Substrate》 The substrate on which the coating film is deposited is composed of, for example, an iron substrate, an aluminum substrate, a titanium substrate, a magnesium substrate, etc. The "substrate" includes pure metals, alloys, intermetallic compounds, or composites. Specific examples of the substrate include members and structures (such as vehicle bodies) made of steel plates (including plated steel plates), aluminum alloy plates, etc. In addition, a substrate made of metal can be used as one of the electrodes when applying alternating current to the coating film.

[0034] 《Electrode》 The electrode preferably has excellent conductivity and corrosion resistance, and also has flexibility to adhere to the coating film. Specific examples thereof include a foil-shaped electrode made of a noble metal, a rubber electrode, an electrolyte liquid (pressed cell), a sponge containing an electrolyte liquid, etc. A terminal or lead (such as a lead-out wire) for connecting to an external circuit is connected to the electrode.

[0035] The form (shape, size) and arrangement of the electrodes are not limited. Usually, a pair of electrodes is sufficient, but three or more electrodes may also be used. The distance between the electrodes arranged on the same surface of the coating film may be, for example, about 1 to 100 mm or 5 to 50 mm.

[0036] 《Applications》 According to the present invention, for example, it is possible to non-destructively and accurately grasp the state (such as the degree of deterioration) of a coating film applied to a subject such as a moving body (vehicle body, ship hull, aircraft body), a building, a bridge, or an infrastructure pipe. The inspection of the coating film may be performed temporarily, periodically, continuously, or cyclically. The same location of the coating film may be measured periodically to grasp its deterioration tendency over time. Such inspection of the coating film enables effective or efficient maintenance (inspection, repair, replacement, etc.) of the subject, and a circular economy can be realized.

Examples

[0037] The state of the rust-preventive coating film was evaluated based on AC characteristics. Based on such specific examples, the present invention will be described in more detail.

[0038] 《Subjects》 A rust-preventively painted steel plate (thickness 0.8 mm) was used as the subject. The coating film on the surface of the steel plate was obtained by applying an epoxy electrocoat after phosphating (substrate treatment). The thickness of the coating film was about 20 μm.

[0039] 《Measurement and Analysis》 A pair of electrodes (10 mm × 10 mm) was attached to each surface (the front and back painted surfaces) of a sample (70 mm × 140 mm) composed of the subject. Platinum was used for the electrodes. The electrodes were fixed to the painted surfaces (front and back surfaces) of the steel plate with a detachable insulating tape.

[0040] The lead (wiring) drawn from the electrode was connected to a measuring device (electrochemical analyzer (LCR meter): ModuLab manufactured by Solartron Analytical / measuring means), and alternating current was applied to measure the frequency identification of impedance (impedance spectrum) (measurement step).

[0041] The alternating current for energization was in the frequency range: 10 -1 ~10 6 Hz, the applied voltage (amplitude): 0.1 V, and the measurement interval: 10 point / dec. The relationship between the frequency and the magnitude of impedance |Z| (frequency characteristics of impedance) obtained by this measurement is shown in Fig. 1 in a double logarithmic display.

[0042] The impedance spectrum was subjected to relaxation time distribution analysis (DRT analysis) to obtain the relaxation time distribution function spectrum (analysis step). As the analysis device (software), open-source software DRT tools.m / MIT was used (analysis means). The relationship between the relaxation time (τ) and the relaxation time distribution γ (relaxation time distribution function spectrum) obtained by this analysis is shown in Fig. 2 in a logarithmic display of the horizontal axis.

[0043] 《Sample》 The above-mentioned measurement and analysis were performed on sample C0 composed of a test specimen in the initial state not subjected to the environmental test, sample 10 in which the test specimen was subjected to the environmental test described later, and sample 11 in which the test specimen was left in the room temperature atmosphere for 1 year after the environmental test.

[0044] The environmental test was performed by an environmental cycle test (CCT: Cyclic Corrosion Test) conforming to JASO M609. Specifically, the test specimen was exposed to thermal cycles in a corrosive environment. The corrosive environment was a mixed salt (NaCl - 1 mass% MgCl2 - 1 mass% CaCl2) applied to the painted surface at 1 cm 2It was sprayed at 40 mg per area, and the relative humidity (RH) was set to 95%. The thermal cycle was defined as 24 hours in total, with 12 hours at -10°C and 12 hours at 80°C as one cycle. In this example, the thermal cycle was repeated 50 times (cycles). After the test, the test specimens were washed with water as a whole and sufficiently dried in the air before being tested. Note that the electrode positions attached to the test specimens after the environmental test were made approximately the same for all samples.

[0045] 《Evaluation》 (1) Impedance |Z| As can be seen from Fig. 1, for the sample C0 in the initial state, the impedance |Z| changed almost linearly (logarithmic display) with respect to the frequency (f) in the entire frequency range, and the lower the frequency (f), the larger the impedance |Z|. For example, when fa = 0.1 Hz, the impedance |Za| was more than 10 9 Ω. Therefore, in this example, 10 9 Ω (1 GΩ) was set as the threshold value |Z s1 |.

[0046] For the sample 10 after the environmental test, the impedance |Z| in the low-frequency range (about 10 Hz or less) was smaller than that of the sample C0 and was flat. For example, when fa = 0.1 Hz, the impedance |Za| was 10 7 ~10 8 Ω. Therefore, in this example, 10 7 Ω (10 MΩ) was set as the threshold value |Z s2 |.

[0047] For the sample 11 left for a long time after the environmental test, the impedance |Z| became unstable in the high-frequency range. Also, in the low-frequency range (about 10 3 Hz or less), similar to the sample C0, the lower the frequency (f), the larger the impedance |Z|. For example, when fa = 0.1 Hz, the impedance |Za| was about 10 9 Ω.

[0048] As is clear from the comparison between the sample 11 and the sample C0, just using the impedance |Z| in the low-frequency range could not appropriately distinguish between the two with different environmental exposure histories.

[0049] (2) Relaxation time (τ) As can be seen from Fig. 2, the relaxation time (ττp) when the relaxation time distribution γ reaches its peak (maximum value) differed for each sample. For example, for sample C0, 1 s < τp, and for sample 11, τp < 1 s (= τs). That is, it was found that it is possible to grasp the state of the coating film, which is impossible with only the impedance |Z|, by paying attention to the relaxation time distribution γ.

[0050] It was found that by paying attention to the specific relaxation time (τp) in this way, the state of the coating film reflecting the environmental exposure history can be grasped more appropriately.

[0051] (3) Classification If the specific relaxation time (τp) and the impedance |Za| are used as indices, the state (degree of deterioration) of the coating film can be determined more accurately. This is summarized in Fig. 3.

[0052] The coating film belonging to region A shown in Fig. 3 has τp ≧ τs (for example, 1 s), is close to the initial state, has not deteriorated significantly, and can be judged to be in a state with sufficient rust prevention effect. Such a coating film also has a sufficiently large impedance |Z|, for example, |Za| ≧ |Zs1| (for example, 1 GΩ).

[0053] The coating film belonging to region B1 has |Za| ≧ |Zs1|, but τp < τs, and can be judged to be in a state where deterioration has progressed more than the judgment based on impedance.

[0054] The coating film belonging to region B2 has |Zs1| > |Za| ≧ |Zs2| (for example, 10 MΩ), and can be judged to be in a state where deterioration has progressed more than the visual judgment and the remaining life is short.

[0055] The coating film belonging to region B3 has |Zs2| > |Za| ≧ |Zs3| (for example, 1 MΩ), and can be judged to be in a state where deterioration has progressed and the rust prevention effect is poor.

[0056] The coating film belonging to region C has |Zs3| > |Za|, and can be judged to be in a state where deterioration or aging has progressed considerably and there is no rust prevention effect.

[0057] Thus, according to the present invention, it was confirmed that the state of the coating film can be more appropriately grasped in consideration of the influence of stress history due to environmental exposure and the like.

Claims

1. An analysis step of obtaining a relaxation time distribution function spectrum [τ-γ(τ)] related to a relaxation time (τ) from an impedance spectrum [f-Z] obtained by applying an alternating current (frequency f) to a coating film, and An evaluation step of grasping the state of the coating film by comparing a specific relaxation time (τp) when the relaxation time distribution function (γ(τ)) reaches a maximum or a maximum with a predetermined reference relaxation time (τs), and A coating film state evaluation method comprising the above.

2. The coating film is a rust preventive coating film formed on a steel plate, The coating film state evaluation method according to Claim 1, wherein the reference relaxation time (τs) is selected from 0.5 to 5 seconds.

3. The evaluation step further includes determining the state of the coating film by comparing a specific impedance (|Za|) related to a predetermined specific frequency (fa) obtained from the impedance spectrum with a predetermined reference impedance (|Zs|). The coating film state evaluation method according to Claim 1 or 2.

4. The coating film is a rust preventive coating film formed on a steel plate, The coating film state evaluation method according to Claim 3, wherein the specific frequency is selected from 0.01 to 100 Hz.

5. The coating film state evaluation method according to Claim 4, wherein the reference impedance is selected from 10 GΩ to 0.1 MΩ.

6. A plurality of the reference impedances are set, The evaluation step classifies the state of the coating film into a plurality of layers based on the reference impedance. The coating film state evaluation method according to Claim 5.

7. An electrode attached to the coating film, Measuring means for applying an alternating current to the electrode to obtain an impedance spectrum of the coating film, Analysis means for obtaining a relaxation time distribution function spectrum from the impedance spectrum, Evaluation means for evaluating the state of the coating film based on the impedance spectrum and / or the relaxation time distribution function spectrum, A coating film state evaluation system comprising the above.

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