JP2017194377A - Corrosion test method and corrosion test device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the time needed for testing the corrosion of a paint used for steels, etc.SOLUTION: A test device 10 executes: a salt water spray step for spraying salt water for a prescribed time to a steel coated with a paint that is a sample, and to a coating electrode 115 coated with the same coating specification as for the steel; a drying step for commencing drying of the sample and the coating electrode after the salt water spray step, carrying out electrochemical measurement on the coating electrode 115 for which drying is commenced, and terminating drying of the sample when at least one of the amounts of change of the impedance, coating film resistance and electrostatic capacitance of the coating electrode 115 per unit time drops to or below a prescribed value; and a wetting step for placing the sample in a wet state of prescribed temperature and humidity after the drying step.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a corrosion test method and a corrosion test apparatus.

  In order to evaluate the resistance of steel materials used outdoors for a long time and corrosion of coating films of steel materials, combined cycle tests defined in JIS, ISO, and the like have been widely applied. In this test, a cycle consisting of three steps of a salt water spraying step, a drying step, and a wetting step is repeated for a steel material as a sample (see Non-Patent Document 1).

JIS K5600-7-9 Cycle Corrosion Test Method, [Search on March 31, 2016], Internet <URL: http://kikakurui.com/k5/K5600-7-9-2006-01.html> Suga Satoshi, "Corrosion test methods for automotive materials and parts and new test methods based on their application," rust prevention management, 1994-4, p.26-36, 1994 R. Lindstrom, “The Atmospheric Corrosion of Zinc in the Presence of NaCl The Influence of Carbon Dioxide and Temperature”, Journal of The Electrochemical Society, 147 (5), p.1751-1757, 2000 Hiroaki Kobayashi et al., “Corrosion Resistance Evaluation of High Corrosion Resistance Coating Film by AC Impedance Method”, Aichi Industrial Science and Technology Research Center Research Report, No.1, p.6-9, 2012 Hiroaki Kobayashi et al., “Evaluation of corrosion resistance of anticorrosion coating by AC impedance method”, Aichi Prefectural Institute of Industrial Technology, No.10, p.38-39, 2011 Hiroshi Kubota et al., “Prediction of steel surface coating deterioration by AC impedance measurement”, Taisei Construction Technology Center Bulletin No. 43, 17-1-17-5, 2010 Hiroyuki Tanabe et al., “Development of under-coating metal corrosion diagnostic equipment”, DNT Coating Technical Report, No.1, p.13-17, October 2001 Yoshiyuki Iwase, Durability / Corrosion Prevention Course (Lecture 6), “Maintenance and Management of Steel Structures by Coating Film Diagnosis”, Journal of the Japan Society of Color Material.88 [3], p.85-89, 2015 Keita Kaji et al., “Measurement of internal impedance of lead-acid battery by AC impedance method and phase detection method”, [Search on March 28, 2016], Internet <URL: http://iyokan.lib.ehime-u.ac .jp / dspace / bitstream / iyokan / 3412/1 / AA12158096_2013_12-138.pdf>

  However, in the above test, there is a problem that the test takes a long time because it simulates an environment used for a long time outdoors. For example, in cycle A of the above JIS K5600-7-9, a cycle consisting of three steps, a salt spray step (2 hours), a drying step (4 hours), and a wetting step (2 hours), is performed for a long time ( For several hundred to several thousand hours). Then, this invention makes it a subject to solve the above-mentioned problem and to shorten the time which the corrosion test of the coating material used for steel materials etc. requires.

  In order to solve the above-mentioned problems, the present invention is a corrosion test method for a paint, wherein a steel material coated with the paint, which is a sample, and a painted electrode coated with the same coating specifications as the steel material are used for a predetermined time. A salt spray step for spraying salt water, and after the salt spray step, drying of the sample and the coated electrode is started, and electrochemical measurement is performed on the coated electrode on which the drying has started every predetermined time. When the amount of change of at least one of the impedance of the coating electrode, the coating film resistance, and the capacitance per time is equal to or less than a predetermined value, a drying step for terminating the drying of the sample, and after the drying step, And a wetting step for bringing the sample into a moist state at a predetermined temperature and humidity.

  ADVANTAGE OF THE INVENTION According to this invention, the time which the corrosion test of the coating material used for steel materials etc. requires can be shortened.

FIG. 1 is a diagram illustrating a configuration example of a test apparatus. FIG. 2 is a diagram illustrating a configuration example of the painted electrode. FIG. 3 is a flowchart showing a test procedure by the test apparatus. FIG. 4 is a diagram showing test conditions for the corrosion test. FIG. 5 is a diagram showing test results of the corrosion test. FIG. 6 is a diagram illustrating an arrangement example of electrodes in the conventional electrochemical measurement. FIG. 7 is a diagram showing a modified example of electrode arrangement in the conventional electrochemical measurement. FIG. 8 is a diagram illustrating an arrangement example of electrodes in the test apparatus of the present embodiment. FIG. 9 is a view showing a modification of the arrangement of the electrodes in the test apparatus of the present embodiment.

  Hereinafter, embodiments (embodiments) for carrying out the present invention will be described with reference to the drawings. The present invention is not limited to this embodiment.

(Embodiment)
First, the structure of the corrosion test apparatus (test apparatus) 10 of this embodiment is demonstrated. The test apparatus 10 performs a paint corrosion test. The sample used for the corrosion test is, for example, a steel material (painted steel material) coated with a coating material to be tested, or an article including a coated steel material. If the test object is a resin, the sample is a resin-lined metal or an article containing the metal in its configuration.

  The corrosion test is performed by repeating a cycle consisting of three steps of a salt spray step, a drying step, and a wetting step on the sample. Here, the test apparatus 10 determines the timing when the drying of the sample is completed using the coating electrode 115 having the same coating specification and film thickness as the sample, and proceeds to the next step (wetting step). That is, the test apparatus 10 installs the coating electrode 115 in the test tank 11 in which the sample is stored, and repeats the cycle including the above three steps for the sample and the coating electrode 115. Then, the test apparatus 10 performs electrochemical measurement of the paint (coating film) of the paint electrode 115 in the drying process, and when the change in impedance or paint film resistance per unit time of the paint electrode 115 becomes gradual, It is judged that the drying of is completed. That is, when the drying of the coating film on the coating electrode 115 is completed, the test apparatus 10 determines that the drying of the coating film of the sample has been completed, and proceeds to the next process (wetting process).

  Thereby, the test apparatus 10 can shorten the test time of the corrosion test. In the following, the test apparatus 10 will be described with respect to the case where the impedance of the coating film of the paint electrode 115 is measured by the AC impedance method, but is not limited thereto. For example, the test apparatus 10 may measure the impedance of the coating film of the painted electrode 115 by other electrochemical measurement, for example, the AC chemical impedance method. Further, the test apparatus 10 may measure the coating film resistance of the painted electrode 115. As the electrochemical measurement in this case, for example, a DC coating resistance measurement method, a current interrupter method, or the like is used.

  As shown in FIG. 1, the test apparatus 10 includes a test tank 11, an air supply unit 12, a salt water tank 13, a control unit 14, a humidification unit 15, a heating unit 16, and a measurement unit 17. The test tank 11 is a tank for performing a corrosion test of a sample. A pure water supply unit 20 is connected to the test apparatus 10. Although not shown, the test tank 11 is provided with a drain outlet for draining salt water sprayed on the sample and an exhaust outlet for exhausting air supplied into the test tank 11. ing. Note that the air concentration sensor 113 indicated by a broken line may or may not be installed in the test apparatus 10 and will be described later.

  The test tank 11 is a tank for performing a corrosion test on a sample. The air supply unit 12 supplies air into the test tank 11.

  The salt water tank 13 supplies salt water to the salt spray unit 112. For example, the salt water tank 13 supplies salt water by adding sodium chloride (NaCl) to water supplied from a pure water supply unit 20 installed outside the test apparatus 10. The salt water tank 13 is provided with a heater 131, and the temperature of the salt water is adjusted by the heater 131.

  The control unit 14 controls the entire test apparatus 10. Here, the control unit 14 mainly controls each step performed in the order of the salt spraying process of the sample → the drying process → the wetting process.

  First, the control unit 14 performs a salt spray process. That is, the control unit 14 supplies salt water at a predetermined temperature from the salt water tank 13 to the salt spray unit 112, and causes the salt spray unit 112 to spray salt water on the sample for a predetermined time.

  Next, the control part 14 performs a drying process. That is, the control unit 14 adjusts the temperature and humidity in the test tank 11 using the heating unit 16 and the humidification unit 15, and dries the sample and the painted electrode 115. Specifically, the control unit 14 monitors the temperature and humidity in the test tank 11 with the temperature / humidity sensor 114, and controls the heating unit 16 and the humidification unit 15 so that the temperature and humidity in the test tank 11 become predetermined values. To do.

  Further, the control unit 14 obtains the measurement result of the impedance of the paint electrode 115 from the measurement unit 17 every predetermined time after the drying of the sample and the paint electrode 115 is started. And when the control part 14 judges that the change of the impedance of the coating electrode 115 per unit time became less than predetermined value, the heating part 16 and the humidification part 15 are stopped. That is, the control unit 14 determines that the drying of the sample is completed when the amount of change in the impedance of the painted electrode 115 per unit time is equal to or less than a predetermined value after starting the drying of the sample, and ends the drying process. Let

  Next, the control unit 14 performs a wetting process. That is, the control unit 14 adjusts the temperature and humidity in the test tank 11 using the heating unit 16 and the humidification unit 15, and shifts the sample and the painted electrode 115 to a wet state. Specifically, the control unit 14 monitors the temperature and humidity in the test tank 11 with the temperature / humidity sensor 114, and controls the heating unit 16 and the humidification unit 15 so that the temperature and humidity in the test tank 11 become predetermined values. Then, the sample and the painted electrode 115 are in a wet state for a predetermined time. The control unit 14 repeats a cycle composed of the three steps of the salt spray step, the drying step, and the wetting step.

  The test conditions such as the required time, the concentration of salt water, the temperature in the test tank 11 and the humidity in each of the three steps of the salt water spraying step, the drying step, and the wetting step are stored in the test condition storage unit 141. The test conditions used shall be used. This test condition is input by an administrator of the test apparatus 10 or the like.

  The humidification unit 15 performs humidification in the test tank 11 based on an instruction from the control unit 14. The heating unit 16 heats the test chamber 11 based on an instruction from the control unit 14.

  The measurement unit 17 performs electrochemical measurement of the painted electrode 115. For example, the measurement unit 17 measures the impedance of the paint electrode 115 every predetermined time. For example, a potentiostat with a built-in FRA (frequency response analyzer) is used as the measurement unit 17.

  Next, the test tank 11 will be described in detail. In the test tank 11, a sample holder 111, a salt spray unit 112, a temperature / humidity sensor 114, and a coating electrode 115 are installed.

  The sample holder 111 is a holder for storing a sample. The salt spray unit 112 sprays the salt water supplied from the salt water tank 13 on the sample on the sample holder 111 and the coating electrode 115 based on an instruction from the control unit 14. The temperature / humidity sensor 114 measures the temperature and humidity in the test chamber 11.

  The painted electrode 115 is an electrode for performing an electrochemical measurement of the paint. For example, as shown in FIG. 2, the coating electrode 115 is a comb-shaped electrode disposed between a reference electrode and a counter electrode and coated with the same coating specifications as the sample. The coated electrode 115 is insulated by connecting the comb electrode, the reference electrode, and the counter electrode with lead wires, and sealing the portion other than the painted region with a resin or the like.

  Thus, by using a comb-type electrode for the painted electrode 115, the surface area of the electrode when measuring impedance or coating film resistance can be increased. Further, since the distance between the electrodes can be shortened, impedance and coating resistance can be easily measured even when a highly insulating paint is applied.

  In addition, when using a comb-type electrode for the painting electrode 115, it is desirable that this comb-type electrode is as close as possible to the distance between the electrodes. For example, the distance between the electrodes is 10 μm or less, more desirably 3 μm or less. Further, the frequency when impedance measurement is performed on such a painted electrode 115 is preferably about 0.01 Hz to 1000 Hz, for example. This is because if the distance between the electrodes is too long, the resistance and impedance become too high, making it impossible to measure the resistance and impedance, and it is possible to measure in the high resistance / high impedance region near the measurable limit. This is because the accuracy may be poor.

  Next, the operation procedure of the test apparatus 10 will be described with reference to FIG. First, the test apparatus 10 sprays salt water on the sample and the coating electrode 115 by the salt spray unit 112 for a predetermined time (for example, 2 hours) (S1: salt spray step).

  For example, the control unit 14 transmits a salt spray start signal to the salt spray unit 112, and the salt spray unit 112 that has received the signal starts salt spray on the sample and the coating electrode 115. At this time, the control unit 14 adjusts the output of the heater 131 in the heating unit 16 and the salt water tank 13 while obtaining the temperature information in the test bath 11 from the temperature / humidity sensor 114, and sets the temperature in the test bath 11 to a predetermined setting. Control to a value (for example, 35 ° C.). And the control part 14 stops the salt spray of the salt spray part 112 after predetermined time (for example, 2 hours) progress from the start of salt spray.

  After S1, the test apparatus 10 dries the sample and the painted electrode 115 (S2: drying step).

  For example, the control unit 14 adjusts the outputs of the heating unit 16 and the humidifying unit 15 while obtaining temperature information and humidity information in the test tank 11 from the temperature / humidity sensor 114, and dries the temperature and humidity in the test tank 11. The sample and the painted electrode 115 are dried by controlling the set values of the environment (for example, temperature: 60 ° C., humidity: 30%, etc.). In addition, the control unit 14 monitors the impedance of the painted electrode 115 that has started drying by the measurement unit 17. Then, when the change in the absolute value | Z | of the impedance (Z) of the painted electrode 115 per unit time becomes a predetermined value or less (for example, the logarithm of the absolute value of the impedance in 5 minutes (log) When the change of | Z |) is 0.05 or less), the drying by the heating unit 16 and the humidifying unit 15 is stopped assuming that the drying of the sample is completed.

For example, let us consider a case in which a coated electrode 115 is formed by connecting a lead wire to a comb-shaped electrode having a comb interval of 3 μm and coating an epoxy resin paint. In this case, it is assumed that the coated electrode 115 is sufficiently impregnated with water and the absolute value | Z | of the impedance between the electrodes measured at a frequency of 1 Hz indicates “10 ⁷ ”.

  In this case, if the absolute value | Z | of the impedance is measured every predetermined time (for example, at an interval of 10 minutes) while the painted electrode 115 is dried, the absolute value | Z | When dry, the increase stops. At this time, the control unit 14 considers that the drying of the sample has been completed when the amount of change in impedance per unit time is equal to or less than a predetermined value, but the impedance depends on the type of paint or additive. The change of the value when containing water is very large. For this reason, the control unit 14 may consider that the drying is completed when the change in the logarithm (log | z |) of the absolute value of the impedance, not the absolute value | Z | For example, when the change per unit time of the logarithm (log | z |) of the absolute value of impedance becomes 0.05 or less, the control unit 14 may consider that the drying of the sample is completed.

  In the drying process of S2 described above, the test apparatus 10 prepares a plurality of combinations of the sample holder 111 and the measurement unit 17, and the control unit 14 causes the impedance change per unit time to be predetermined in all the sample holders 111. When the value falls below the value, the drying process may be terminated assuming that the drying of the sample is completed.

  In the step S2, the control unit 14 changes the impedance (initial impedance change) of the paint electrode 115 until a predetermined time (for example, 30 minutes) elapses from the start of drying of the sample and the paint electrode 115, The change of the impedance of the coating electrode 115 is obtained every predetermined time (for example, every 10 minutes). And the control part 14 is a time when the change of the impedance of the coating electrode 115 becomes below a predetermined ratio with respect to the initial impedance change (for example, 1/20 or less with respect to the first 30 minutes of impedance change). The drying process may be terminated assuming that the drying of the sample is completed.

  In addition, there may be individual differences in the thickness of the coating film between the coating electrode 115 and the sample, or the behavior when water present in the coating film is dried may be slightly different. Therefore, in order to completely dry the sample, the control unit 14 may end the drying process after a predetermined time has elapsed (for example, after 10 minutes) when the change in the impedance of the paint electrode 115 becomes a predetermined ratio or less. Good.

  Further, when the measurement unit 17 performs measurement of AC impedance, for example, if three different frequencies are measured as shown in Non-Patent Document 9, the control unit 14 determines whether the painted electrode is based on the measurement result of the absolute value of impedance. The electrostatic capacity of the coating film existing in 115 can be obtained. Here, the relative dielectric constant of the polymer material including the paint is about “5”, whereas the relative dielectric constant of water is about “78”. The capacity changes. Therefore, the control unit 14 considers that the drying of the sample is completed when the change in capacitance per unit time of the painted electrode 115 obtained from the measurement result of the absolute value of the impedance is equal to or less than a predetermined value, and the drying process. May be terminated.

  After S2, the control unit 14 puts the sample in a wet state for a predetermined time (for example, 2 hours) (S3: wet process).

  For example, the control unit 14 adjusts the outputs of the heating unit 16 and the humidifying unit 15 while obtaining temperature information and humidity information in the test tank 11 from the temperature / humidity sensor 114, and sets the temperature and humidity in the test tank 11 to a humid environment. (For example, temperature: 50 ° C., humidity: 98%, etc.). And the control part 14 complete | finishes the wetting process of S3, after setting predetermined temperature (for example, 2 hours), after setting the temperature and humidity in the test tank 11 to the setting value of a moist environment. Thereafter, the control unit 14 determines whether or not a predetermined time has elapsed since the start of the test (S4). If the predetermined time has not yet elapsed (No in S4), the control unit 14 returns to the salt spraying process of S1. On the other hand, if the predetermined time has already elapsed since the start of the test (Yes in S4), the test is terminated. Note that the control unit 14 may end the test when a cycle including the steps S1 to S3 is executed a predetermined number of times.

  The test apparatus 10 advances the corrosion of the sample by repeating the steps S1 to S3.

  Thus, since the test apparatus 10 ends the drying when the impedance change of the coating electrode 115 becomes a predetermined value or less in the drying process of S2, the time required for the drying process can be shortened.

  That is, in the conventional corrosion test (see Non-Patent Document 1), a longer drying time (4 hours) is set in the drying process in consideration of the use of a sample that is difficult to dry. The sample may be completely dried. Therefore, the test apparatus 10 measures the change in the impedance of the paint electrode 115 in the drying process, and determines that the drying of the sample has been completed when the change in the impedance per unit time of the sample becomes a predetermined value or less. Then, the drying process is terminated, and the process proceeds to the next wetting process. As a result, the test apparatus 10 can move to the next wet process in a short drying time while reliably drying various samples.

  Further, as in the drying process of S2, when the test apparatus 10 changes the impedance of the coating electrode 115 to a predetermined value or less, the drying time is about 100 to 200 μm, for example, by terminating the drying of the sample. In the case of a coating film (undercoat / intercoat: epoxy resin paint, topcoat: polyurethane resin paint), it is shortened from 4 hours to about 1 hour. As a result, for example, in the prior art (see Non-Patent Document 1), a salt spray process (temperature: 35 ° C., time: 2 hours) → drying process (temperature: 60 ° C.) on a coated steel material having a thickness of about 100 to 200 μm. , Time: 4 hours) → wetting process (temperature: 50 ° C., humidity 95% or more, time: 2 hours), the test apparatus 10 has a salt spray process (temperature: 35 ° C., time: 2 hours). ) → Drying process (temperature: 60 ° C., time: 1 hour) → wetting process (temperature: 50 ° C., humidity 95% or more, time: 2 hours). That is, since the time required for one cycle is reduced from 8 hours to 5 hours, the test time until the corrosion of the sample progresses to about 5/8 as much as in the prior art. In other words, when the corrosion test of this embodiment is performed for the same time as the corrosion test of the prior art, the sample can be corroded by about 8/5 (1.6) times compared to the corrosion test of the prior art. Therefore, the corrosion rate of the corrosion test of this embodiment is 1.6 times that of the prior art.

  Further, as a result of shortening the test time, the use time of the heating unit 16 and the heater 131 of the test apparatus 10 is also shortened, so that the power consumption required for the corrosion test can be reduced.

(Other embodiments)
In addition, you may make it the air supply part 12 of the test apparatus 10 supply the air which raised oxygen concentration in the test tank 11 during implementation of a corrosion test (namely, in each process of S1-S3). In this case, the air supply unit 12 uses, for example, an oxygen cylinder or an oxygen concentrator. The test apparatus 10 further includes an air concentration sensor 113 indicated by a broken line in FIG. The air concentration sensor 113 measures the oxygen concentration and the like in the test tank 11. Then, during the execution of the corrosion test, the control unit 14 monitors the oxygen concentration in the test tank 11 with the air concentration sensor 113 and controls the air supply unit 12 so that the oxygen concentration in the test tank 11 becomes a predetermined value. . That is, the air supply unit 12 supplies air having a higher oxygen concentration than the atmosphere into the test tank 11 during the corrosion test based on an instruction from the control unit 14.

  The oxygen concentration here is preferably about twice (about 40%) the oxygen concentration in normal air, for example. By increasing the oxygen concentration of the air supplied into the test chamber 11 in this way, it is possible to shorten the time until the corrosion of the sample proceeds to the same extent as in the conventional technique.

  In addition, when the coating material to be tested includes a metal such as zinc in which the presence or absence of carbon dioxide greatly affects the corrosion rate, the air supply unit 12 of the test apparatus 10 also supplies carbon dioxide to the air supplied into the test tank 11. It is better to include it. For example, the air supply unit 12 sets the concentration ratio of oxygen and carbon dioxide in the air supplied into the test tank 11 to about 200000: 350, which is close to the actual atmospheric concentration ratio. In this way, if the sample to be tested contains a metal whose presence or absence of carbon dioxide such as zinc greatly affects the corrosion rate, conduct a corrosion test that simulates the corrosion of the sample in an actual outdoor environment. Can do.

  When the air supply unit 12 includes carbon dioxide in the air supplied into the test tank 11 as described above, the air concentration sensor 113 measures the oxygen and carbon dioxide concentrations in the test tank 11. Then, the control unit 14 adjusts the oxygen and carbon dioxide concentrations in the air supply unit 12 while obtaining the oxygen concentration information and the carbon dioxide concentration information in the test tank 11 from the air concentration sensor 113, for example, the test tank 11 is controlled to have an oxygen concentration of 40% and a carbon dioxide concentration of about 700 ppm. In this case, the air supply unit 12 uses, for example, an oxygen cylinder, a carbon dioxide cylinder, and a blender. And the air supply part 12 blends general air with a blender, and adjusts to about 40% of oxygen and about 700 ppm of carbon dioxide.

  The air supply unit 12 may use an oxygen concentrator. In this case, the oxygen concentrator is preferably a hollow fiber membrane type. This is because in a hollow fiber membrane type oxygen concentrator, oxygen, carbon dioxide, etc. with a small molecular diameter are discharged to the outside of the membrane, and nitrogen with a large molecular diameter passes through the hollow fiber as it is. This is because if the collected gas is collected, air having a high concentration of oxygen and carbon dioxide is obtained.

  In addition, since oxygen concentration devices of other methods often reduce the concentration of carbon dioxide even if the concentration of oxygen can be increased, in order to obtain a gas in which both oxygen and carbon dioxide are highly concentrated, The hollow fiber membrane type oxygen concentrator is desirable. Further, in the case of a hollow fiber membrane type oxygen concentrator, the concentration efficiency of oxygen and carbon dioxide is different, so the concentration ratio of oxygen: carbon dioxide is slightly different from 200000: 350 which is close to the actual atmospheric value, but only oxygen is concentrated. Compared with the case where carbon dioxide is used, since carbon dioxide is also concentrated, corrosion in an actual outdoor environment can be simulated relatively well.

  In this way, the test apparatus 10 also includes carbon dioxide in the air supplied into the test tank 11, so that the actual corrosion test of a sample containing a metal whose presence or absence of carbon dioxide such as zinc greatly affects the corrosion rate can be realized. A corrosion test simulating the corrosion of a sample in an outdoor environment can be performed. Moreover, the test time of a corrosion test can be shortened by raising also the carbon dioxide concentration of the air which the test apparatus 10 supplies in the test tank 11. FIG.

  Test conditions such as oxygen concentration and carbon dioxide concentration of the air supplied into the test tank 11 are set in the test condition storage unit 141.

(Experimental result)
Next, in order to verify the effect of the test method using the test apparatus 10 of the present embodiment, a comparison with a conventional test method (see Non-Patent Document 1) was performed.

  Here, the specimen can be corroded to the same degree as the conventional test method in a shorter test time compared to the conventional test method. This means that the degree of corrosion per unit time (corrosion rate) is that of the prior art. It is higher than the test method. That is, if it can be confirmed that the corrosion rate of the test method using the test apparatus 10 of the present embodiment is faster than the corrosion rate of the conventional test method, the test method using the test apparatus 10 of the present embodiment is effective. It can be confirmed that there is.

  Therefore, an experiment was conducted to compare the corrosion rate in the test method using the test apparatus 10 of the present embodiment with the corrosion rate of the conventional test method. Here, a steel plate and a zinc plate having a thickness of 7 cm × 15 cm × 2 mm were used as samples, and a paint comb electrode was used as the paint electrode 115. And the sample was corroded and the corrosion rate was compared with each of the test method using the test apparatus 10 of this embodiment, and the test method of a prior art.

  In this experiment, using the test apparatus 10, the coated comb-type electrode and the sample (steel plate and zinc plate) are subjected to a corrosion test at the same time, and the test is performed in the next step while electrochemically measuring the coated comb-type electrode. The corrosion rate of the sample at that time was compared with the test method of the prior art. The corrosion rate was a value obtained by dividing the weight loss of the sample after the test by the area of the sample and the test time. The test conditions are shown in FIG.

  As shown in FIG. 4, in the test method of the prior art, the oxygen and carbon dioxide concentrations in the air supplied into the test tank 11 in each step of the test are the same as in the general atmosphere, and the NaCl concentration of salt water in the salt spray step : 5 wt%, temperature in the test tank 11: 35 ° C, time: 2h. Further, the temperature in the test tank 11 in the drying process was 60 ° C. and the time was 4 h, and the temperature in the test tank 11 in the wetting process was 50 ° C. and the time was 2 h.

  In the pattern A in FIG. 4, the oxygen concentration and the carbon dioxide concentration of the air supplied into the test tank 11 in each step of the test are the same as those in the general atmosphere, but the coating electrode 115 per unit time in the drying step. Drying was terminated when the change in impedance became equal to or less than a predetermined value. For example, when the change in the logarithm (log | Z |) of the absolute value of the impedance in 5 minutes becomes 0.05 or less, the drying is terminated and the process proceeds to the next step. In the drying process of pattern A, the time until the change in the logarithm (log | Z |) of the absolute value of the impedance of the painted electrode 115 per unit time becomes 0.05 or less is about 1 hour from the start of the drying process. there were.

  Furthermore, in pattern B in FIG. 4, the concentration of oxygen and carbon dioxide in the air supplied into the test chamber 11 in each step of the test is twice that of the general atmosphere, and the drying process time is 4 as in the prior art. It was time.

  Also, pattern A + B in FIG. 4 is a pattern obtained by merging pattern A and pattern B together. That is, in the pattern A + B, the oxygen and carbon dioxide concentrations of the air supplied into the test tank 11 in each step of the test are double that of the general atmosphere, and the impedance change of the coating electrode 115 per unit time in the drying step. When the value became equal to or less than the predetermined value, drying was terminated. Moreover, in any of the patterns A, B, and A + B, the NaCl concentration in the salt water spraying process: 5 wt%, the temperature in the test tank 11: 35 ° C., the time: 2 h, and the temperature in the test tank 11 in the wetting process : 50 ° C, time: 2h. In the drying process of pattern A + B, the time until the change in impedance of the coating electrode 115 per unit time becomes equal to or less than a predetermined value is also about 1 hour from the start of the drying process.

  The test was conducted under the test conditions shown in FIG. 4, and the corrosion rate of the sample was determined from the weight reduction of the sample (steel and zinc) after the test was completed. The result is shown in FIG. As shown in FIG. 5, it was confirmed that the corrosion rates of the samples (steel and zinc) were faster than those of the prior art in any of the patterns A, B, and A + B.

Further, as shown in FIG. 5, in the conventional test method, the corrosion rate of steel was 80 (g / m ² / day), and the corrosion rate of zinc was 15 (g / m ² / day). It was. On the other hand, in the case of Pattern A, the corrosion rate of steel was 120 (g / m ² / day), and the corrosion rate of zinc was 21 (g / m ² / day). In other words, since the time required for the drying process was 4 hours in the prior art, the time required for one cycle of the corrosion test can be shortened from 8 hours to 5 hours in Pattern A because it can be shortened to 1 hour. The corrosion rate of the sample was improved.

In the case of Pattern B, the corrosion rate of steel was 150 (g / m ² / day), and the corrosion rate of zinc was 27 (g / m ² / day). In other words, by doubling the concentration of oxygen and carbon dioxide in the air supplied into the test chamber 11 in each test step, the corrosion rate is approximately doubled for both zinc and steel samples. We were able to. Thereby, it can be confirmed that the test method of the present embodiment improves the corrosion rate not only in steel materials not containing zinc, but also in steel materials containing zinc and coating tests containing zinc. It was.

In the case of pattern A + B, the corrosion rate of steel was 220 (g / m ² / day), and the corrosion rate of zinc was 36 (g / m ² / day). That is, in the case of the pattern A + B, the corrosion rate of the sample was further improved as compared with the case of the pattern A or the pattern B.

  That is, in the prior art, if the sample is dried for 4 hours in the drying process, most of the drying process is a time during which corrosion does not progress. On the other hand, since the pattern A detects the drying of the sample from the change in the impedance of the paint electrode 115 and moves to the next step, the time during which the corrosion of the sample does not proceed can be saved. As a result, the average corrosion rate of the entire test can be improved. Moreover, in pattern B, corrosion is accelerated | stimulated by high concentration oxygen, and a corrosion rate can be improved. Furthermore, in the pattern A + B, the combination of these can further improve the corrosion rate.

  That is, like the test apparatus 10 of the present embodiment, the concentration of oxygen and carbon dioxide in the air supplied into the test tank 11 in each step of the test is higher than that in the general atmosphere, and the coating per unit time in the drying step When the impedance change of the electrode 115 becomes a predetermined value or less, the sample corrosion rate can be improved by terminating the drying of the sample.

  In Non-Patent Document 2, in order to ensure the reliability of the corrosion test, the sample is in a wet state with respect to the time required for all steps of the salt spray step, the drying step, and the wet step (that is, salt spray). It is described as a condition that the time ratio of the step and the wetting step) is 50%. This means that if the time ratio of the wet sample is higher (more than 50%), the corrosion of the sample is further promoted, but corrosion that is significantly different from the corrosion that occurs in the actual environment occurs. This is based on the experimental result that the reliability of the corrosion test cannot be secured. From this, the sample of JIS test conditions described in Non-Patent Document 1, for example, salt spraying process (2 hours) → drying process (4 hours) → wetting process (2 hours) per cycle is conventionally wet. Test conditions with a state time ratio of 50% have been used.

  On the other hand, the inventor of the present invention considers that “the time the sample is continuously wet” is more important than the “time ratio of the state where the sample is wet” in the corrosion process of the coated steel sheet. Approximate to the corrosion that occurs in the actual environment even if the "wetting state time" is set to a predetermined time or less (4 hours in this embodiment) and the "time ratio when the sample is wet" is increased to enhance the acceleration. It was thought that highly reliable corrosion could be reproduced and the reliability of the test could be secured.

  Then, when the corrosion product of the coated steel plate corroded by the test method of this embodiment was identified by X-ray diffraction analysis, the same corrosion product as the coated steel plate corroded under the JIS test conditions described in Non-Patent Document 1 was obtained. It was confirmed that was generated. In other words, it was confirmed that even the test method of the present embodiment can reproduce the corrosion that occurs in the actual environment and the corrosion with high approximation.

  Here, in the test apparatus 10, the impedance of the coating electrode 115 is changed in the drying process of the corrosion test after setting “the time for which the sample is continuously wet (wetting process + salt spray process) is 4 hours”. When the drying process is terminated when the value is equal to or lower than the predetermined value, in many samples, the drying is completed in about 30 minutes to 2 hours. Therefore, the time ratio in a state where the sample is wet exceeds 50%. For this reason, according to the test method of this embodiment, the corrosion of the sample is promoted, and at the same time, the time during which the sample is continuously wet is equal to or less than a predetermined time. The time required for the process can be shortened. Therefore, the time for the corrosion test of the sample can be shortened.

  In addition, steel materials containing zinc and coating films containing zinc are affected by oxygen and carbon dioxide in an actual environment. Therefore, when carbon dioxide is included in the air supplied to the test tank 11, zinc oxide having a composition as shown in Table II of Non-Patent Document 3 is generated. Here, in the salt spray process of the corrosion test of the sample containing zinc, when carbon dioxide was not added with only oxygen in the air supplied to the test tank 11 having a high concentration, the composition analysis result of the corrosion product after the test was The oxide containing carbon (C) described in Table II of Non-Patent Document 3 could not be confirmed. That is, it was confirmed that a corrosion test simulating an actual environment can be realized by including carbon dioxide in the air supplied to the test tank 11 in a corrosion test for a steel material containing zinc or a coating film containing zinc.

  In addition, like the techniques shown in Non-Patent Documents 4 to 8, conventionally, in order to detect corrosion of steel materials and the like, many measurements of resistance and impedance of a coating film are performed by an electrochemical measurement method. However, these techniques are difficult to use to detect drying of the coating. The reason will be described below.

  For example, in these techniques, as shown in FIG. 6, electrodes are disposed in an aqueous solution on the surface side of a paint (coating film) and a steel material that is a coating substrate, and between the coating film surface and the coating substrate through the aqueous solution. The resistance and impedance are measured. Therefore, it is difficult to detect the drying of the coating film by measuring resistance and impedance.

  Further, as shown in FIG. 7, it is also conceivable to measure the resistance and impedance of the coating film with an electrode arranged so as not to pass through the aqueous solution and detect the drying of the coating film. However, since the electrode is present on the coating film (paint), it is difficult to dry or absorb water immediately below the electrode as compared with other portions of the coating film (portions not in contact with the electrode). Therefore, there is a high possibility that the drying of the coating film and the water absorption behavior cannot be accurately detected. Further, as shown in FIG. 7, according to the electrode arranged not to pass through the aqueous solution, the average drying of the entire coating film can be detected, but the drying and water absorption behavior near the interface with the steel material in the coating film. There is a high possibility that cannot be detected accurately.

  On the other hand, the test apparatus 10 of this embodiment uses the property that resistance and impedance between electrodes decrease when the coating film contains water, and resistance and impedance increase when the coating film dries. For example, as shown in FIG. 8, it arrange | positions inside a coating film (paint), and the resistance and impedance of the coating film between electrodes are measured. Thereby, it is possible to accurately monitor the drying and water absorption behavior at the interface of the coating film with the coating substrate (near the position where the electrode in the paint in FIG. 8 is disposed).

  In addition, when protecting a coated substrate (for example, steel) from corrosion by painting, the coated substrate is corroded if water does not reach the vicinity of the interface between the coated film and the coated substrate even if the surface of the coated film contains water. do not do. For this reason, it is more important to detect whether or not the vicinity of the interface with the coating substrate in the coating film is dried than the average water content of the coating film. For this reason, the application effect of the test apparatus 10 of this embodiment that can accurately monitor the drying and water absorption behavior in the vicinity of the interface with the coating substrate in the coating film is high.

  Moreover, as shown in FIG. 9, the test apparatus 10 arrange | positions an electrode in the several position (distance A, distance B, distance C) from which the depth (distance) from a coating-film surface differs, and in each depth You may monitor the behavior of drying and hydration. In this case, the depth from the coating film surface to the electrode may be measured with an eddy current film thickness meter or the like.

DESCRIPTION OF SYMBOLS 10 Test apparatus 11 Test tank 12 Air supply part 13 Salt water tank 14 Control part 15 Humidification part 16 Heating part 17 Measurement part 20 Pure water supply part 111 Sample holder 112 Salt water spray part 113 Air concentration sensor 114 Temperature / humidity sensor 115 Paint electrode 131 Heater 141 Test condition storage

Claims (6)

A corrosion test method for paints,
A salt water spraying step of spraying salt water for a predetermined time on a steel material coated with the paint as a sample, and a painted electrode coated with the same coating specifications as the steel material;
After the salt water spraying step, drying of the sample and the painted electrode is started, and an electrochemical measurement is performed every predetermined time on the dried coated electrode, and the impedance of the painted electrode per unit time, A drying step for ending the drying of the sample when the amount of change in at least one of the coating film resistance and the capacitance is equal to or less than a predetermined value;
After the drying step, a wetting step for bringing the sample into a wet state at a predetermined temperature and humidity;
A corrosion test method characterized by comprising:   The corrosion test method according to claim 1, wherein the painted electrode is a comb-shaped electrode painted with the same coating specifications as the steel material.   The corrosion test method according to claim 1, wherein the electrochemical measurement is at least one of an AC impedance method, a DC coating film resistance measurement method, a current interrupter method, and an AC chemical impedance method.   2. The corrosion test method according to claim 1, wherein in each step, the oxygen concentration in the air in the test tank in which the sample and the coating electrode are installed is set higher than the atmospheric concentration. When the paint contains zinc,
2. The method according to claim 1, wherein in each of the steps, the oxygen concentration and the carbon dioxide concentration in the air in the test tank in which the sample and the coating electrode are installed are set higher than the atmospheric concentration. Corrosion test method. A corrosion test apparatus for paint,
A test tank in which a steel material coated with the paint as a sample and a painted electrode coated with the same coating specifications as the steel material are installed;
A salt spray section for spraying salt water onto the sample and the coating electrode in the test tank;
An air supply unit for supplying air into the test chamber;
A heating unit for heating in the test chamber;
A humidifying section for humidifying the test chamber;
An electrochemical measurement is performed on the painted electrode, and a measurement unit that measures at least one of impedance, coating film resistance, and capacitance of the painted electrode;
The salt spray unit sprays salt water onto the sample and the coating electrode for a predetermined time, and after finishing spraying the salt water, causes the heating unit to start drying the sample and the coating electrode. When at least one change amount of impedance, coating film resistance, and capacitance of the painted electrode per unit time measured is a predetermined value or less, the drying of the sample by the heating unit is terminated, A corrosion test apparatus comprising: a control unit configured to bring the sample into a wet state at a predetermined temperature and humidity by a heating unit and the humidifying unit for a predetermined time.

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