JP6523205B2 - Corrosion test method and corrosion test apparatus - Google Patents

Description

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

  In order to evaluate the resistance to corrosion of steel materials used for a long time outdoors or of a coating film of steel materials, a composite cycle test defined in JIS, ISO, etc. has been widely applied. In this test, a cycle consisting of three steps of a salt spray step, a drying step, and a wetting step is repeated on a steel material which is a sample (see Non-Patent Document 1).

JIS K5600-7-9 cycle corrosion test method, [March 31, 2016 search], Internet <URL: http://kikakurui.com/k5/K5600-7-9-2006-01.html> Suga Satoshi, "Automotive material, corrosion test method for parts and new test method by its application", Anticorrosion control, 1994-4, pp. 26 to 36, 1994 R. Lindstrom, "The Atmospheric Corrosion of Zinc in the Presence of NaCI The Influence of Carbon Dioxide and Temperature", Journal of the Electrochemical Society, 147 (5), pp. 1751-1757, 2000 Kobayashi Hiroaki et al., "Corrosion evaluation of high corrosion resistance coating film by AC impedance method", Aichi National Institute of Advanced Industrial Science and Technology Research Report, No. 1, p. 6-9, 2012 Kobayashi Hiroaki et al., “Corrosion Evaluation of Anticorrosion Coatings by AC Impedance Method,” Research Report of Aichi Industrial Research Institute, No. 10, p. 38-39, 2011 Kubota Hiroshi et al., "Deterioration prediction of coated steel surface materials by AC impedance measurement", Taisei Construction Technology Center Report, No. 43, 17-1 to 17-5, 2010 Hiroyuki Tajima et al., “Development of a device for diagnosing corrosion of metal under a coating,” DNT Coating Technical Report, No. 1, p. 13-17, October 2001 Iwase Yoshiyuki, Durability and anticorrosion course (6th lecture), "Maintenance management of steel structures by coating film diagnosis", Journal of the Japan Society of Color Material. 88 [3], pp. 85-89, 2015 Keita Kachi et al., "Measurement of Internal Impedance of Lead Acid Battery by AC Impedance Method and Phase Detection Method", [March 28, 2016 Search], 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 to simulate an environment used for a long time outdoors. For example, in cycle A of JIS K 5600-7-9 described above, a cycle consisting of three steps of a salt spray step (2 hours), a drying step (4 hours), and a wetting step (2 hours) Needs to be repeated 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-described problems, the present invention is a method for testing corrosion on paint, wherein a steel material coated with the paint, which is a sample, and a coated electrode coated with the same paint specifications as the steel material After the salt spray step of spraying salt water and the salt spray step, drying of the sample and the painted electrode is started, and the electrochemical measurement is performed at predetermined time intervals on the painted electrode which has started the drying, and the unit A drying step for terminating the drying of the sample when the change amount of at least one of the impedance, the coating resistance and the capacitance of the coating electrode per time becomes equal to or less than a predetermined value; And D. wetting the sample to a predetermined temperature and humidity.

  According to the present invention, it is possible to shorten the time required for the corrosion test of the paint used for steel materials and the like.

FIG. 1 is a view showing a configuration example of a test apparatus. FIG. 2 is a view showing a configuration example of a painting electrode. FIG. 3 is a flowchart showing a test procedure by the test apparatus. FIG. 4 is a diagram showing test conditions of the corrosion test. FIG. 5 is a diagram showing test results of the corrosion test. FIG. 6 is a view showing an example of arrangement of electrodes in the prior art electrochemical measurement. FIG. 7 is a view showing a modified example of the arrangement of electrodes in the prior art electrochemical measurement. FIG. 8 is a view showing an arrangement example of the electrodes in the test apparatus of the present embodiment. FIG. 9 is a view showing a modified example 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, an article including a steel (painted steel) coated with a paint to be tested, or a coated steel. If the test target is a resin, the sample uses a metal lined with a resin, an article containing this metal in the structure, or the like.

  The corrosion test is performed on the sample by repeating a cycle consisting of three steps of salt spray, drying and wetting. 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 paint electrode 115 in the test tank 11 in which the sample is stored, and repeats the cycle consisting of the above three steps on the sample and the paint electrode 115. Then, the test apparatus 10 performs the electrochemical measurement of the paint (coating film) of the coating electrode 115 in the drying step, and when the change of the impedance or the coating resistance per unit time of the coating electrode 115 becomes gentle, It is judged that the drying of is completed. That is, when drying of the coating film on the coating electrode 115 is completed, the test apparatus 10 determines that the coating film of the sample is also dried, and proceeds to the next step (wetting step).

  Thereby, the test apparatus 10 can shorten the test time of the corrosion test. In addition, although the test device 10 demonstrates the case where the impedance of the coating film of the coating electrode 115 is measured by an alternating current impedance method below, it is not limited to this. For example, the test apparatus 10 may measure the impedance of the coating of the painted electrode 115 by another electrochemical measurement, such as an AC chemical impedance method. The test apparatus 10 may also measure the coating film resistance of the coating electrode 115. As the electrochemical measurement in this case, for example, a direct current film resistance measurement method, a current interrupter method or the like is used.

  The test apparatus 10 is provided with the test tank 11, the air supply part 12, the salt water tank 13, the control part 14, the humidification part 15, the heating part 16, and the measurement part 17 as shown in FIG. The test tank 11 is a tank for performing a corrosion test of a sample. Further, the pure water supply unit 20 is connected to the test apparatus 10. Although not shown, the test tank 11 is provided with a drainage port for draining salt water sprayed on the sample and an exhaust port for exhausting the air supplied into the test tank 11. ing. The air concentration sensor 113 indicated by a broken line may or may not be equipped with the test apparatus 10, and will be described later when it is equipped.

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

  The control unit 14 controls the entire test apparatus 10, and here mainly controls each process performed in the order of the salt spray process of the sample → the drying process → the wet process.

  First, the control unit 14 performs a salt spray process. That is, the control unit 14 supplies salt water of 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 unit 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 humidifying unit 15 to dry the sample and the painting electrode 115. Specifically, the control unit 14 monitors the temperature and humidity in the test tank 11 by the temperature and humidity sensor 114, and controls the heating unit 16 and the humidifying unit 15 so that the temperature and humidity in the test tank 11 become predetermined values. Do.

  In addition, the control unit 14 obtains the measurement result of the impedance of the painting electrode 115 from the measuring unit 17 every predetermined time after the start of drying of the sample and the painting electrode 115. When the control unit 14 determines that the change in the impedance of the coating electrode 115 per unit time has become smaller than a predetermined value, the heating unit 16 and the humidifying unit 15 are stopped. That is, when the amount of change in impedance of the coating electrode 115 per unit time becomes equal to or less than a predetermined value after the start of drying of the sample, the control unit 14 determines that the drying of the sample is completed 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 the humidity in the test tank 11 using the heating unit 16 and the humidifying unit 15 to shift the sample and the painting electrode 115 to the wet state. Specifically, the control unit 14 monitors the temperature and humidity in the test tank 11 by the temperature and humidity sensor 114, and controls the heating unit 16 and the humidifying unit 15 so that the temperature and humidity in the test tank 11 become predetermined values. The sample and the painting electrode 115 are wetted for a predetermined time. The control unit 14 repeats a cycle consisting of the above-described three steps of the salt spray step, the drying step, and the wetting step.

  The test condition storage unit 141 stores test conditions such as required time, concentration of salt water, temperature in the test tank 11, and humidity in each of the above-described three steps of the salt spray step, the drying step, and the wetting step. Test conditions shall be used. The test conditions are input by the administrator of the test apparatus 10 or the like.

  The humidifying unit 15 humidifies the inside of the test tank 11 based on an instruction from the control unit 14. The heating unit 16 heats the inside of the test tank 11 based on an instruction from the control unit 14.

  The measurement unit 17 performs electrochemical measurement of the painting electrode 115. For example, the measuring unit 17 measures the impedance of the painting electrode 115 every predetermined time. For example, a potentiostat built in an 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 and humidity sensor 114, and a painting electrode 115 are installed.

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

  The paint electrode 115 is an electrode for performing an electrochemical measurement of a 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 is coated according to the same coating specifications as the sample. In addition, after connecting a comb-type electrode, a reference electrode, and a counter electrode with a lead wire, the coating electrode 115 seals and insulates with resin etc. except the range which coated.

  As described above, by using the comb-shaped electrode as the painting electrode 115, the surface area of the electrode in the measurement of the impedance or the coating resistance can be increased. In addition, since the distance between the electrodes can be shortened, the impedance and the coating resistance can be easily measured even when a paint having a high insulating property is applied.

  When a comb-shaped electrode is used as the painting electrode 115, it is desirable that the distance between the electrodes be as short as possible. For example, the distance between the electrodes is 10 μm or less, more preferably 3 μm or less. Moreover, as for the frequency in the case of implementing an impedance measurement to such a coating electrode 115, about 0.01 Hz-about 1000 Hz are preferable, for example. This is because if the distance between the electrodes is too long, the resistance and impedance may 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. Because the accuracy may be bad.

  Next, an 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 painted 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 receiving the start signal starts salt spray on the sample and the paint 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 temperature information in the test tank 11 from the temperature and humidity sensor 114, and sets the temperature in the test tank 11 to a predetermined value. Control to a value (eg 35 ° C. etc.). Then, the control unit 14 stops the salt spray of the salt spray unit 112 after a predetermined time (for example, 2 hours) has elapsed from the start of the 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 the temperature information and the humidity information in the test tank 11 from the temperature and humidity sensor 114, and dries the temperature and the humidity in the test tank 11. The sample and the painting electrode 115 are dried by controlling the setting value of the environment (for example, temperature: 60 ° C., humidity: 30%, etc.). Further, the control unit 14 monitors the impedance of the coating electrode 115 which has started drying by the measuring unit 17. Then, when the change in the absolute value | Z | of the impedance (Z) of the coating electrode 115 per unit time becomes equal to or less than a predetermined value, the control unit 14 (for example, the logarithm of the absolute value of impedance in 5 minutes (log ), 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, it is assumed that a lead wire is connected to a comb-shaped electrode having a distance of 3 μm between combs and coated with an epoxy resin paint as the coating electrode 115. In this case, it is assumed that the paint 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, when the absolute value | Z | of the impedance is measured at predetermined time intervals (for example, at intervals of 10 minutes) while drying the painting electrode 115, the absolute value of the impedance | Z | As it dries, the increase stops. At this time, the control unit 14 considers that the drying of the sample is completed when the amount of change in impedance per unit time becomes equal to or less than a predetermined value, but the impedance depends on the type of the paint or the additive. And the change in water value is very large. Therefore, the control unit 14 may consider that the drying has ended when the change in the logarithm (log | z |) of the absolute value of the impedance (log | z |) instead of the absolute value | Z | of the impedance becomes equal to or less than a predetermined value. For example, when the change per unit time of the logarithm (log | z |) of the absolute value of the impedance becomes 0.05 or less, the control unit 14 may consider that the drying of the sample is completed.

  In the above-described drying step of S2, the test apparatus 10 prepares a plurality of combinations of the sample holder 111 and the measurement unit 17, and in the control unit 14, the change in impedance per unit time is predetermined for all 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.

  Further, in the above-described step S2, the control unit 14 changes the impedance of the paint electrode 115 (initial impedance change) until a predetermined time (for example, 30 minutes) elapses from the start of drying of the sample and the paint electrode 115; The change in impedance of the paint electrode 115 is obtained every predetermined time (for example, every 10 minutes). When the control unit 14 determines that the change in impedance of the coating electrode 115 is less than or equal to a predetermined ratio (for example, 1/20 or less of the change in impedance for the first 30 minutes) with respect to the initial 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 of water present in the coating film may differ slightly. Therefore, in order to completely dry the sample, the control unit 14 changes the impedance of the coating electrode 115 to a predetermined ratio or less, and ends the drying process after a predetermined time (for example, 10 minutes). Good.

  Furthermore, 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 from the measurement result of the absolute value of the impedance that the paint electrode The capacitance of the coating present at 115 can be determined. Here, while the relative dielectric constant of the polymer material containing the paint is about "5", the relative dielectric constant of water is about "78", and in the process in which the dried coating film is hydrated, electrostatic The capacity changes. Therefore, when the change of the capacitance per unit time of the coating electrode 115 obtained from the measurement result of the absolute value of the impedance becomes a predetermined value or less, the control unit 14 considers that the drying of the sample is completed and the drying process You may terminate the

  After S2, the control unit 14 wets the sample for a predetermined time (for example, 2 hours) (S3: wetting step).

  For example, the control unit 14 adjusts the outputs of the heating unit 16 and the humidifying unit 15 while obtaining the temperature information and the humidity information in the test tank 11 from the temperature and humidity sensor 114, and adjusts the temperature and the humidity in the test tank 11 Control to the set value of (eg, temperature: 50 ° C., humidity: 98%, etc.). Then, after setting the temperature and humidity in the test tank 11 to the set values of the wet environment, the control unit 14 ends the wetting step of S3 after a predetermined time (for example, 2 hours) has elapsed. Thereafter, the control unit 14 determines whether or not a predetermined time has elapsed from the start of the test (S4). If the predetermined time has not elapsed (No in S4), the process returns to the salt spray step of S1. On the other hand, if the predetermined time has already passed from the start of the test (Yes in S4), the test is ended. The control unit 14 may end the test when the cycle including the steps S1 to S3 has been performed a predetermined number of times.

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

  As described above, since the test apparatus 10 ends the drying when the change in the impedance of the coating electrode 115 becomes less than or equal to the predetermined value in the drying step of S2, the time required for the drying step 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 step in consideration of the use of a sample that is difficult to dry, but actually it is 4 hours Within some cases, drying of the sample may be completed. Therefore, the test apparatus 10 measures the change in impedance of the coating electrode 115 in the drying step, and determines that the drying of the sample is completed when the change in impedance per unit time of the sample becomes equal to or less than a predetermined value. Finish the drying step and move on to the next wetting step. As a result, the test apparatus 10 can move to the next wetting step in a short drying time while ensuring that the various samples are dried.

  In addition, as in the drying step of S2, when the change of the impedance of the coating electrode 115 becomes equal to or less than the predetermined value, the drying time of the test device 10 is about 100 to 200 μm, for example. In the case of a coated film (undercoating / intermediate coating: epoxy resin coating, top coating: polyurethane resin coating), the time 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 step (temperature: 60 ° C.) for coated steel of about 100 to 200 μm thickness The test apparatus 10 has a salt spray process (temperature: 35.degree. C., time: 2 hours), which is a cycle of time: 4 hours) to wet step (temperature: 50.degree. C., humidity 95% or more, time: 2 hours). → drying step (temperature: 60 ° C., time: 1 hour) → wetting step (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 can be reduced to about 5/8 as in the prior art. In other words, when the corrosion test of the present 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 the corrosion test of the prior art. Therefore, the corrosion rate of the corrosion test of the present embodiment is 1.6 times the corrosion rate of the prior art.

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

(Other embodiments)
The air supply unit 12 of the test apparatus 10 may supply air with an increased oxygen concentration into the test tank 11 during the corrosion test (that is, in each of the steps S1 to S3). In this case, the air supply unit 12 uses, for example, an oxygen cylinder, an oxygen concentrator, or the like. The test apparatus 10 further includes an air concentration sensor 113 shown by a broken line in FIG. The air concentration sensor 113 measures the oxygen concentration and the like in the test tank 11. Then, the control unit 14 monitors the oxygen concentration in the test tank 11 with the air concentration sensor 113 during the corrosion test, 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 the air whose concentration of oxygen is higher than the atmosphere into the test tank 11 during the corrosion test based on the instruction from the control unit 14.

  The oxygen concentration here is desirably, for example, about twice (about 40%) the oxygen concentration in the normal atmosphere. By increasing the oxygen concentration of the air supplied into the test tank 11 in this manner, it is possible to shorten the time until the corrosion of the sample progresses as in the case of the prior art.

  In addition, when the paint to be tested contains a metal whose presence or absence of carbon dioxide such as zinc 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. 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 200,000: 350, which is close to the concentration ratio of the actual atmosphere. 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 a real outdoor environment. Can.

  As described above, when the air supply unit 12 also includes carbon dioxide in the air supplied into the test tank 11, the air concentration sensor 113 measures the concentrations of oxygen and carbon dioxide in the test tank 11. Then, while obtaining the oxygen concentration information and the carbon dioxide concentration information in the test tank 11 from the air concentration sensor 113, the control unit 14 adjusts the concentrations of oxygen and carbon dioxide in the air supply unit 12, for example, The oxygen concentration in 11: 40% and the carbon dioxide concentration: about 700 ppm. In this case, the air supply unit 12 uses, for example, an oxygen cylinder, a carbon dioxide cylinder, and a blender. Then, the air supply unit 12 blends the general atmosphere with a blender to adjust to about 40% oxygen and about 700 ppm carbon dioxide.

  In addition, the air supply unit 12 may use an oxygen concentrator. In this case, it is desirable that the oxygen concentration device be a hollow fiber membrane type. This is because in the hollow fiber membrane type oxygen concentrator, oxygen and carbon dioxide having a small molecular diameter are discharged to the outside of the membrane, and nitrogen having a large molecular diameter passes directly through the hollow fiber, so that it leaves the side of the membrane. The reason is that the collection of the new gas provides air having a high concentration of oxygen and carbon dioxide.

  In addition, since the concentration of carbon dioxide is often lowered even if the concentration of oxygen can be increased in other types of oxygen concentrators, in order to obtain a gas in which both oxygen and carbon dioxide are highly concentrated, The hollow fiber type oxygen concentrator described above is desirable. In addition, in the case of the hollow fiber membrane type oxygen concentrator, the concentration efficiency of oxygen and carbon dioxide is different, so the concentration ratio of oxygen: carbon dioxide deviates somewhat from 200,000: 350, which is close to the value of the actual atmosphere, but only oxygen is concentrated Since carbon dioxide is also concentrated as compared with the case where it is used, it can simulate corrosion in a real outdoor environment relatively well.

  As described above, by including carbon dioxide in the air supplied into the test chamber 11 by the test apparatus 10, the corrosion test of a sample containing a metal whose presence or absence of carbon dioxide such as zinc greatly affects the corrosion rate is also real. A corrosion test can be performed that simulates the corrosion of a sample in an outdoor environment. Moreover, the test apparatus 10 can shorten the test time of a corrosion test by raising also about the carbon dioxide concentration of the air supplied in the test tank 11. FIG.

  The test conditions such as the oxygen concentration and the 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 test method of the prior art (see Non-Patent Document 1) was performed.

  Here, the fact that the sample can be corroded to the same extent as the test method of the prior art in a test time shorter than that of the conventional test method is that the degree of corrosion per unit time (corrosion rate) 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 this embodiment is faster than the corrosion rate of the test method of the prior art, the test method using the test apparatus 10 of this embodiment is effective. It can be confirmed that there is.

  Then, the experiment which compared the corrosion rate in the test method using the test apparatus 10 of this embodiment with the corrosion rate of the test method of a prior art was performed. Here, as a sample, a steel plate of 7 cm × 15 cm × 2 mm thickness and a zinc plate were used, and a painted comb-type electrode was used as the painted electrode 115. And the sample was corroded and the corrosion rate was compared with the test method using the test apparatus 10 of this embodiment, and the test method of a prior art, respectively.

  In this experiment, using the test apparatus 10, the coated comb electrode and the sample (steel plate and zinc plate) are simultaneously subjected to a corrosion test, and the electrochemical measurement of the coated comb electrode is carried out while the test is performed in the next step. And the corrosion rate of the sample at that time was compared with the test method of the prior art. The corrosion rate was the weight loss of the sample after the test divided 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 concentration of oxygen and carbon dioxide in the air supplied into the test tank 11 in each test step is made the same as that in the general atmosphere, and the NaCl concentration of salt water in the salt spray step The temperature in the test tank 11 was 35 ° C., and the time was 2 h. Further, the temperature in the test tank 11 in the drying step: 60 ° C., the time: 4 h, and the temperature in the test tank 11 in the wetting step: 50 ° C., the time: 2 h.

  In addition, in the pattern A in FIG. 4, the concentration of oxygen and carbon dioxide in the air supplied into the test tank 11 in each step of the test is the same as that in the general atmosphere, but the coating electrode 115 per unit time in the drying step. When the change in the impedance of s. For example, the drying was terminated when the change in the logarithm (log | Z |) of the absolute value of the impedance over 5 minutes became 0.05 or less, and the process was advanced to the next step. In the drying process of this pattern A, the time until the change of the logarithm (log | Z |) of the absolute value of the impedance of the coating electrode 115 per unit time becomes 0.05 or less is about one 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 in the general atmosphere, and the time of the drying step is 4 as in the prior art. It was time.

  Further, pattern A + B in FIG. 4 is a pattern in which pattern A and pattern B are merged. That is, in the pattern A + B, the concentration of oxygen and carbon dioxide in the air supplied into the test tank 11 in each test step is twice that in the general atmosphere, and the change in impedance of the coated electrode 115 per unit time in the drying step When the value of was below the predetermined value, the drying was ended. Further, in any of the patterns A, B and A + B, the NaCl concentration in the salt water spray step is 5 wt%, the temperature in the test tank 11 is 35 ° C., and the time is 2 h. : 50 ° C., time: 2 h. In addition, the time until the change of the impedance of the coating electrode 115 per unit time becomes below in predetermined value in the drying process of this pattern A + B was also about 1 hour from the start of a 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 loss of the sample (steel and zinc) after the test. The results are 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.

Also, as shown in FIG. 5, in the test method of the prior art, the corrosion rate of steel is 80 (g / m ² / day), and the corrosion rate of zinc is 15 (g / m ² / day) The 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). That is, although the time required for the drying step was 4 hours in the prior art, the pattern A could be shortened to 1 hour, and accordingly the time required for one cycle of the corrosion test could be shortened to 8 hours → 5 hours, The corrosion rate of the sample was improved.

Moreover, 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 tank 11 in each test step to that of the general atmosphere, the corrosion rate is approximately doubled for both zinc and steel samples. We were able to. Thereby, it is possible to confirm that the test method of the present embodiment improves the corrosion rate also in corrosion tests for steels not containing zinc but steels containing zinc and coatings containing zinc, for example. The

Moreover, 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 than in the case of the pattern A or the pattern B.

  That is, in the prior art, when the sample is dried for 4 hours in the drying step, most of the drying step is a time during which the corrosion does not progress. On the other hand, the pattern A detects the drying of the sample from the change in the impedance of the painting electrode 115 and moves to the next step, thereby saving the time when the corrosion of the sample does not progress. As a result, the average corrosion rate of the entire test can be improved. In addition, in the pattern B, the high concentration oxygen accelerates the corrosion, and the corrosion rate can be improved. Furthermore, in the pattern A + B, the corrosion rate can be further improved by these combinations.

  That is, as in 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 test step is higher than that in the general atmosphere, and painting per unit time is performed in the drying step. By terminating the drying of the sample when the change in impedance of the electrode 115 falls below a predetermined value, the corrosion rate of the sample can be improved.

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

  On the other hand, the inventor of the present invention considers that "the time for which the sample is continuously wetted" is more important than "the time ratio for the state where the sample is wetted" in the corrosion process of the coated steel sheet. Assuming that the time of wet state is less than a predetermined time (4 hours in this embodiment), the "proportion of time of wet state of sample" may be increased to promote acceleration by approximating the corrosion that occurs in a real environment It is thought that high corrosion can be reproduced and the reliability of the test can be ensured.

  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 test conditions of JIS described in Non-Patent Document 1 Was confirmed to be generated. That is, it has been confirmed that the test method of the present embodiment can also reproduce corrosion highly similar to the corrosion that occurs in a real environment.

  Here, in the test apparatus 10, after setting "the time for which the sample is continuously wet (wetting step + salt water spraying step) to 4 hours", the change in the impedance of the coating electrode 115 occurs in the drying step of the corrosion test. When the drying process is finished when the value is less than the predetermined value, the drying is finished in about 30 minutes to 2 hours for many samples, and the time ratio of the state in which the sample is wet is more than 50%. For this reason, according to the test method of the present embodiment, “corrosion of the sample is promoted and at the same time“ the time for which the sample is wet continuously is equal to or less than a predetermined time ””. The time required for the process can be shortened. Thus, the time for corrosion test of the sample can be shortened.

  In addition, steel materials containing zinc and coatings containing zinc are affected by oxygen and carbon dioxide in a real environment. Therefore, when carbon dioxide is included in the air supplied to the test chamber 11, a zinc oxide having a composition as shown in Table II of Non-Patent Document 3 is produced. Here, in the salt spray step of the corrosion test of the sample containing zinc, when only carbon dioxide of the air supplied to the test tank 11 was made high concentration and carbon dioxide was not added, the composition analysis result of the corrosion product after the test An oxide containing carbon (C) described in Table II of Non-Patent Document 3 could not be identified. That is, it has been confirmed that the corrosion test simulating the real environment can be realized by including carbon dioxide in the air supplied to the test tank 11 in the corrosion test for steel containing zinc and the coating film containing zinc.

  As in the techniques shown in Non-Patent Documents 4 to 8, in the past, for the detection of corrosion of steel materials and the like, it has been frequently performed to measure the resistance or impedance of a coating film by an electrochemical measurement method. However, these techniques are difficult to use to detect the drying of the coating. The reason is explained below.

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

  Moreover, it is also conceivable to measure the resistance or impedance of the coating film with an electrode disposed without an aqueous solution as shown in FIG. 7 to detect the drying of the coating film. However, due to the presence of the electrode on the coating (paint), it is difficult to dry or absorb water directly below the electrode as compared to the other part of the coating (the part not in contact with the electrode). Therefore, there is a high possibility that the drying or water absorption behavior of the coating can not be accurately detected. In addition, as shown in FIG. 7, according to the electrode disposed so as not to intervene in the aqueous solution, the average drying of the entire coating can be detected, but the behavior of drying and water absorption near the interface with the steel material in the coating Is likely not to be detected accurately.

  On the other hand, the test apparatus 10 of this embodiment utilizes the property that the resistance and impedance between the electrodes decrease when the coating film is hydrated, and the resistance and impedance increase when the coating film is dried, and the electrode used for the coating electrode 115 For example, as shown in FIG. 8, the film is placed inside a coating (paint), and the resistance or impedance of the coating between the electrodes is measured. This makes it possible to accurately monitor the behavior of drying and water absorption at the interface with the coating substrate in the coating film (near the position where the electrode in the paint in FIG. 8 is disposed).

  When the coated substrate (for example, steel material) is protected from corrosion by coating, the coated substrate is corroded if water does not reach near the interface between the coated film and the coated substrate even if the film surface is hydrated. do not do. For this reason, it is important to detect whether or not the vicinity of the interface with the coating substrate in the coating has been dried, rather than the average water content of the coating. For this reason, the application effect of the test apparatus 10 of this embodiment which can monitor the behavior of drying and water absorption of interface vicinity with the coating base material in a coating film correctly is high.

  Further, as shown in FIG. 9, the test apparatus 10 arranges the electrodes at a plurality of positions (distance A, distance B, distance C) different in depth (distance) from the coating film surface, and the respective depths are different. You may monitor the behavior of dryness and moisture. In this case, the depth from the coating film surface to the electrode may be measured by 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 spray part 113 air concentration sensor 114 temperature / humidity sensor 115 painting electrode 131 heater 141 Test condition storage unit

Claims (6)

It is a corrosion test method to paint,
A salt spray step of spraying salt water for a predetermined time on a steel material coated with the paint as a sample and a coated electrode coated with the same paint specifications as the steel material;
After the salt spray step, drying of the sample and the painting electrode is started, and an electrochemical measurement is performed every predetermined time on the painting electrode which has started the drying, and the impedance of the painting electrode per unit time, A drying step for terminating the drying of the sample when the amount of change in at least one of the coating film resistance and the capacitance becomes equal to or less than a predetermined value;
Wetting the sample to a predetermined temperature and humidity after the drying step;
Corrosion test method characterized in that   The corrosion test method according to claim 1, wherein the coating electrode is a comb-shaped electrode coated with the same coating specification as the steel material.   The corrosion test method according to claim 1, wherein the electrochemical measurement is at least one of an alternating current impedance method, a direct current film resistance measurement method, a current interrupter method, and an AC chemical impedance method.   The corrosion test method according to claim 1, wherein in each of the steps, the concentration of oxygen in the air in the test tank in which the sample and the painting electrode are installed is made higher than the concentration in the atmosphere. If the paint contains zinc,
In each of the steps, the concentration of oxygen and the concentration of carbon dioxide in the air in the test tank in which the sample and the painting electrode are installed are set higher than the concentration in the atmosphere. Corrosion test method. It is a corrosion test device for paint,
A test tank in which a steel material coated with the paint, which is a sample, and a paint electrode coated with the same paint specification as the steel material are installed;
A salt spray section for spraying salt water on the sample and the painting electrode in the test tank;
An air supply unit for supplying air into the test tank;
A heating unit that heats the inside of the test chamber;
A humidifying unit for humidifying the inside of the test tank;
A measurement unit which performs electrochemical measurement on the painted electrode and measures at least one of the impedance, the coating film resistance, and the capacitance of the painted electrode;
After the salt water is sprayed to the sample and the painting electrode for a predetermined time in the salt water spraying portion and the spraying of the salt water is finished, the drying of the sample and the painting electrode is started by the heating portion. The drying of the sample by the heating unit is ended when the measured change amount of at least one of the impedance, the coating film resistance, and the capacitance of the coating electrode per unit time becomes less than a predetermined value, And a control unit for bringing the sample into a wet state at a predetermined temperature and humidity for a predetermined time by a heating unit and the humidifying unit.

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