Accelerated deterioration test method for coating films

Abstract

To provide an accelerated deterioration test method for a coating film capable of sufficiently reproducing deterioration in the coating film in corrosive dust environment.SOLUTION: A test piece 3 in which a coating film is disposed on a surface of a metal plate is buried in corrosive dust 4 containing a corrosive component, and the coating film of the test piece 3 is brought into contact with the corrosive dust 4 (a burying step). Water 9 is sprayed to the corrosive dust 4 to make the corrosive dust 4 contain moisture (a spraying step). Temperatures of the test piece 3 and the corrosive dust 4 is raised to promote absorption of the moisture of the corrosive dust 4 by the coating film of the test piece 3 (a wetting step). The test piece 3 and the corrosive dust 4 are dried (a drying step).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for accelerated deterioration testing of coating films. [Background technology]

[0002] In steel mills, raw materials such as ore, coal, and coke are unloaded and transported using conveyor belts to produce crude steel. During this process, raw materials may spill from the belt (conveyor belt) and accumulate as dust on the conveyor belt and / or the frame of the rack. Such dust (also called "corrosive dust") contains corrosive components such as sulfur components, and is therefore highly corrosive to metal plates such as steel plates that make up the building frame.

[0003] Dust accumulated on the structure absorbs moisture when water is supplied by rainfall or the like. In this case, due to the corrosive components of the dust and the increased wetness time due to the moisture in the dust, corrosion of the structure progresses at a rate up to approximately 10 times faster than in a typical outdoor environment.

[0004] To prevent corrosion of the skeleton, it is effective to use stainless steel for the structural members, but this is not practical from a cost perspective. For this reason, for example, members made of low-carbon steel with the surface covered with a paint film are used. Since the progression of deterioration of a coating film takes a long time, the performance of the coating film is evaluated by a coating film deterioration acceleration test, which artificially accelerates the deterioration of the coating film (see Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-185502 Summary of the Invention [Problem to be solved by the invention]

[0006] Conventional accelerated coating deterioration tests are designed to simulate deterioration of coatings under general outdoor exposure environments, and therefore cannot adequately reproduce deterioration of coatings under corrosive dust environments. Therefore, an object of the present invention is to provide a method for testing accelerated deterioration of a coating film, which can adequately reproduce deterioration of the coating film in a corrosive dust environment. [Means for solving the problem]

[0007] As a result of extensive research, the present inventors have found that the above object can be achieved by employing the following configuration, and have completed the present invention. That is, the present invention provides the following [1] to [7]. [1] A method for accelerated deterioration testing of a coating film, comprising: an embedding step of embedding a test piece having a coating film disposed on the surface of a metal plate in corrosive dust containing a corrosive component to bring the coating film into contact with the corrosive dust; a spraying step of spraying water onto the corrosive dust to moisten the corrosive dust; a wetting step of increasing the temperature of the test piece and the corrosive dust to promote absorption of the moisture in the corrosive dust by the coating film; and a drying step of drying the test piece and the corrosive dust. [2] The accelerated deterioration test method for a coating film according to [1] above, wherein the corrosive component is a sulfur component. [3] The accelerated deterioration test method for a coating film according to [1] or [2] above, wherein the water sprayed in the spraying step is pure water. [4] The method for accelerated deterioration testing of a coating film according to any one of [1] to [3] above, wherein in the spraying step, the water content of the corrosive dust is saturated. [5] The accelerated deterioration test method for a coating film according to any one of [1] to [4] above, wherein the metal plate is a steel plate. [6] The accelerated deterioration test method for a coating film according to any one of [1] to [5] above, wherein the spraying step, the wetting step, and the drying step are carried out under the following conditions, respectively: The above spraying process: Temperature 25-60℃, time 8-16 hours The above moistening process: temperature 40-60°C, relative humidity 90-100%, time 8-16 hours The drying process: Temperature 50-70°C, relative humidity 45-55%, time 20-28 hours [7] The accelerated deterioration test method for a coating film according to any one of [1] to [6] above, wherein the spraying step, the wetting step, and the drying step are carried out under the following conditions, respectively. The above spraying process: Temperature 35℃, time 12 hours The above humidification process: temperature 50℃, relative humidity 95%, time 12 hours The above drying process: temperature 60℃, relative humidity 50%, time 24 hours [Effects of the Invention]

[0008] According to the present invention, deterioration of a coating film in a corrosive dust environment can be sufficiently reproduced. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a cross-sectional view schematically showing a testing machine used in a coating film deterioration acceleration test. [Figure 2] 1 is a graph showing the relationship between the diffusion coefficient of a coating film and temperature. [Figure 3] 1 is a graph showing the results of a water absorption and drying behavior test. [Figure 4] 1 is a graph showing the relative life spans of test pieces for standard use and specifications 1 to 3. DETAILED DESCRIPTION OF THE INVENTION

[0010] FIG. 1 is a cross-sectional view that schematically shows a testing machine 7 used in the accelerated coating deterioration test. First, the test box 1 and the dust pan 2 arranged inside the tester 7 will be described. The test box 1 is a container with an open top, and a drain hole 6, which is a through hole, is formed in the bottom. The material of the test box 1 is, for example, a resin such as polypropylene. Although the test box 1 shown in Fig. 1 has a rectangular parallelepiped shape, the shape of the test box 1 is not limited to this.

[0011] The dust receiver 2 is a container with an open top, similar to the test box 1. However, the dust receiver 2 does not have a through-hole formed in the bottom surface. The material, shape, etc. of the dust pan 2 may be the same as those of the test box 1. The dust pan 2 shown in FIG.

[0012] More specifically, as shown in Fig. 1, first, a dust tray 2 is placed on the bottom surface inside the tester 7, and then the test box 1 is placed on top of that. Next, a mesh 5 is placed on the bottom surface of the test box 1. The material of the mesh 5 is, for example, a resin such as polypropylene. A portion of the dust 4 is spread on top of the net 5 as bedding. Next, the test specimen 3 is placed on top of the bedding (dust 4). After that, the remaining dust 4 is placed inside the test box 1 to cover the test specimen 3. In this way, the dust 4 is contained inside the test box 1 with the test specimen 3 buried inside.

[0013] The dust 4 is corrosive dust containing corrosive components such as sulfur components, and is derived from raw materials such as ore, coal, and coke that are transported using conveyer belts in steel mills to produce crude steel, for example. Specifically, among these raw materials, those that fall off the belt during transportation and accumulate on the frame of the belt conveyor or the like can be used as the corrosive dust. For example, dust derived from coke (coke dust) contains sulfur components as corrosive components.

[0014] The test piece 3 is assumed to be a part of a member constituting the frame of a belt conveyor or the like, and has a metal plate and a coating film disposed on its surface (one side or both sides). Examples of metal plates include conventionally known steel plates used for the frame, and specific examples thereof include low-carbon steel plates such as SS material (rolled steel for general structure) and SM material (rolled steel for welded structure).SPCC material (cold-rolled steel plate), which has almost the same chemical composition as these low-carbon steel plates, may also be used. As the paint to be applied to the coating film, for example, a conventionally known paint such as a modified epoxy resin paint, a polyurethane resin paint, a silicone resin paint, an organic zinc-rich paint, or an inorganic zinc-rich paint may be appropriately used, and commercially available products may also be used. The coating film may be a multi-layer coating film formed by sequentially applying two or more types of coating material. The thickness of the coating film (film thickness) is, for example, 100 to 400 μm, but is not limited to this.

[0015] Incidentally, the test box 1 has a drain hole 6 formed in the bottom surface thereof, which is a through hole, so that the dust 4 contained inside the test box 1 can fall through the drain hole 6. However, since a net 5 is placed on the bottom surface of the test box 1, the dust 4 is prevented from falling by the net 5. For this reason, it is preferable to appropriately select the size and shape of the mesh of the net 5 so that the dust 4 cannot easily pass through.

[0016] A spraying device 8 is provided on the upper surface side inside the testing machine 7. The spraying device 8 sprays water 9 downward. As the water 9, pure water is used, not salt water. The tester 7 may be any device capable of driving the spraying equipment 8 and appropriately changing the internal conditions such as temperature and humidity, and may be, for example, a tester conforming to JIS K 5600-7-9 (such as a CCT tester).

[0017] In this configuration, to conduct a coating deterioration acceleration test, first, as described above, the test piece 3 is buried in the dust 4 contained in the test box 1, and the coating of the test piece 3 is brought into contact with the dust 4 (burying process).

[0018] In this state, the spraying equipment 8 of the tester 7 is driven to spray water 9 onto the dust 4 contained in the test box 1, thereby moistening the dust 4 (spraying step). In the spraying process, it is preferable to moisten the dust 4 until the moisture content of the dust 4 reaches saturation. Note that in the spraying process, not only the dust 4 but also the coating film of the test piece 3 may be moistened. Excess water 9 that is not absorbed by the dust 4 passes through drainage holes 6 formed in the bottom of the test box 1 and falls into the dust receiver 2.

[0019] Furthermore, the temperature inside the testing machine 7 (i.e., the test piece 3 and the dust 4) is raised above room temperature (e.g., 25°C) to cause the moisture in the dust 4 to be absorbed into the coating film of the test piece 3 and promote this absorption (wetting process). The spraying step and the wetting step may be the same step. Thereafter, the test piece 3 (particularly the coating film) and the dust 4 are dried (drying step).

[0020] Here, the reasons for carrying out the spraying step, wetting step, and drying step will be explained.

[0021] First, we define an environment with precipitation > 0 mm / h or relative humidity (RH) > 80% as a "wet" environment, while an environment that does not meet the wetness criteria as a "dry" environment. The coating on the test specimen absorbs water in a wet environment and dries in a dry environment.

[0022] The present inventors placed the coating film in contact with water in a constant temperature and humidity chamber, measured the change in the coating film mass over time at each temperature in a wet environment and a dry environment, and calculated the water content of the coating film. Furthermore, the diffusion coefficient D (unit: m 2 / s). (M t / M ∞ )=(4 / L)×(Dt / π) 2 t: Elapsed time (unit: s) M t : Moisture content of coating film at elapsed time t M ∞ : Saturated moisture content of coating film L: Coating thickness (unit: m) D: Diffusion coefficient (unit: m / s 2 )

[0023] FIG. 2 is a graph showing the relationship between the diffusion coefficient of the coating film and the temperature. As shown in Figure 2, the diffusion coefficient increases with increasing temperature, both when the coating film absorbs water and when it dries. When comparing at the same temperature, the diffusion coefficient tends to be larger when the coating film is drying than when it absorbs water. When a coating film absorbs water, the water molecules penetrate into the coating film while expanding the polymer network of the coating film, which is made of polymers, and the diffusion coefficient is thought to be relatively small.On the other hand, when a coating film dries, the water molecules are expelled from the expanded polymer network, and the diffusion coefficient is thought to be relatively large. Considering this difference in diffusion coefficient, it is clear that the water absorption behavior is greatly affected by the duration of the continuous wet environment (continuous wetting time).

[0024] In actual environments, the continuous wetting period is often 24 to 48 hours. Therefore, in order to reproduce the actual environment, a test (water absorption and drying behavior test) was conducted in which a test specimen buried in dust was exposed to a wet environment that met the following conditions, and then exposed to a dry environment that met the following conditions. Wet environment: Temperature 25°C, relative humidity 95%, time 48 hours Dry environment: Temperature 30°C, relative humidity 60%, time 120 hours

[0025] Figure 3 is a graph showing the results of the water absorption and drying behavior test. The horizontal axis shows the elapsed time (unit: h), and the vertical axis shows the moisture saturation rate of the coating and dust. The moisture saturation rate is the ratio of the moisture content at each elapsed time to the saturated moisture content. In the water absorption and drying behavior test, water was first supplied to the dust in which the test specimen was embedded at the start of the wet environment. The dust layer was set to a thickness of 35 mm, simulating the dust that accumulates on the body of a belt conveyor transporting coke. In a wet environment, not only the coating but also the dust absorbs water. For this reason, as shown in Figure 3, even after the environment is changed to a dry environment, the coating continues to absorb the moisture from the dust, and the coating continues to absorb water (the moisture saturation rate of the coating increases) for a certain amount of time.

[0026] Based on the relationship between the diffusion coefficient of the coating film and temperature (FIG. 2) and the results of the water absorption and drying behavior test (FIG. 3), the inventors came up with the idea of ​​carrying out the spraying step, wetting step, and drying step described above. By carrying out these steps, the water absorption and drying behavior of the coating film and dust in a real environment can be reproduced, making it possible to sufficiently reproduce the deterioration of the coating film in a corrosive dust environment in a short period of time while having a high correlation with the real environment.

[0027] The conditions for the spraying, wetting, and drying steps, such as temperature, humidity, and time, are appropriately set based on the properties of the coating film, but it is preferable to perform each step under the following conditions, which will allow the deterioration of the coating film in a corrosive dust environment to be more fully reproduced (see Examples below).

[0028] The temperature in the spraying step is preferably 25 to 60° C., more preferably 30 to 40° C., and even more preferably 35° C. The time for the spraying step is preferably 8 to 16 hours, more preferably 10 to 14 hours, and even more preferably 12 hours. The temperature in the wetting step is preferably 40 to 60° C., more preferably 45 to 55° C., and even more preferably 50° C. The relative humidity in the wetting step is preferably 90 to 100%, more preferably 93 to 98%, and even more preferably 95%. The duration of the wetting step is preferably 8 to 16 hours, more preferably 10 to 14 hours, and even more preferably 12 hours. The temperature in the drying step is preferably 50 to 70° C., more preferably 55 to 65° C., and even more preferably 60° C. The relative humidity in the drying step is preferably 45 to 55%, more preferably 48 to 53%, and even more preferably 50%. The time for the drying step is preferably 20 to 28 hours, more preferably 22 to 26 hours, and even more preferably 24 hours. [Example]

[0029] The present invention will be specifically described below with reference to examples, but the present invention is not limited to the examples described below.

[0030] First, the dust and test specimens were prepared. As the dust, coke dust containing sulfur components was used. The metal plate for the test specimens was a steel plate (cold-rolled steel plate) made of SPCC material that had been subjected to blasting treatment. The paints shown in Table 1 below were applied to this steel plate to form coatings, and test specimens of standard specification and specifications 1 to 3 were obtained. The test specimens were processed to have artificial defects before being subjected to the tests described below.

[0031] [Table 1]

[0032] Using the test machine explained based on FIG. 1 (test machine conforming to JIS K 5600-7-9), a coating film deterioration acceleration test was carried out. That is, the test piece was buried in dust and pure water was sprayed from the spraying equipment (spraying process).Then, the temperature inside the testing machine was raised to promote the absorption of the moisture in the dust by the coating film (wetting process).After that, the test piece and dust were dried (drying process). The spraying step, wetting step and drying step were carried out under the following conditions. ·Spraying process: Temperature 35℃, time 12h Wetting process: Temperature 50℃, relative humidity 95%, time 12 hours Drying process: Temperature 60°C, relative humidity 50%, time 24 hours To shorten the time required for the spraying process, the dust thickness was set to 10 mm. In the spraying process, the amount of pure water sprayed was 3±1 mL / h / 80 cm. 2 Then, pure water was sprayed onto the dust until the moisture content of the dust reached saturation.

[0033] In addition to the accelerated coating deterioration test described above, a field exposure test was also conducted in which test specimens were buried in dust (thickness: 35 mm) and exposed to actual outdoor conditions. After the test, the blister area of ​​the artificial defect in the test piece was measured, and the ratio of the blister area to the blister area of ​​the standard specification was calculated as the relative life. FIG. 4 is a graph showing the relative lifespan of the standard use and the test pieces of specifications 1 to 3. As shown in Figure 4, the relationship between the relative lifespans of the standard specification and specifications 1 to 3 was almost the same between the example and the field exposure test. In other words, the accelerated coating degradation test of the example was able to sufficiently reproduce the degradation of the coating in a corrosive dust environment in a short period of time, while having a high correlation with the actual environment. [Explanation of symbols]

[0034] 1: Test box 2: Dust collector 3: Test piece 4: Dust (corrosive dust) 5: Net 6: Drain hole 7: Testing machine 8: Spray equipment 9:Water

Claims

1. an embedding step of embedding a test piece having a coating film disposed on the surface of a metal plate in corrosive dust containing a corrosive component to bring the coating film into contact with the corrosive dust; a spraying step of spraying water onto the corrosive dust to moisten the corrosive dust; a wetting step of increasing the temperature of the test piece and the corrosive dust to promote absorption of moisture from the corrosive dust by the coating; a drying step of drying the test piece and the corrosive dust; A coating film deterioration accelerated test method comprising:

2. The method for accelerated deterioration testing of a coating film according to claim 1, wherein the corrosive component is a sulfur component.

3. 3. The method for accelerated deterioration testing of a coating film according to claim 1, wherein the water sprayed in the spraying step is pure water.

4. 3. The accelerated deterioration test method for a coating film according to claim 1, wherein the spraying step is performed to saturate the moisture content of the corrosive dust.

5. The method for accelerated deterioration testing of a coating film according to claim 1 or 2, wherein the metal plate is a steel plate.

6. 3. The accelerated deterioration test method for a coating film according to claim 1, wherein the spraying step, the wetting step, and the drying step are each carried out under the following conditions: The spraying step: temperature 25 to 60°C, time 8 to 16 hours The moistening step: temperature 40 to 60°C, relative humidity 90 to 100%, time 8 to 16 hours The drying step: temperature 50 to 70°C, relative humidity 45 to 55%, time 20 to 28 hours

7. 3. The accelerated deterioration test method for a coating film according to claim 1, wherein the spraying step, the wetting step, and the drying step are each carried out under the following conditions: The spraying step: temperature 35°C, time 12 hours Wetting step: temperature 50°C, relative humidity 95%, time 12 hours Drying step: temperature 60°C, relative humidity 50%, time 24 hours

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