Method for evaluating rime fog resistance of automobile paint film

Abstract

The invention discloses a method for evaluating the rime fog resistance of an automobile paint film. The evaluation method comprises the following steps: putting a test sample plate coated with an automobile paint film into a container filled with distilled water, ensuring that one part of the automobile paint film is soaked in the distilled water and the other part of the automobile paint film is exposed in the air, performing heat preservation soaking at 40-60 DEG C for 30-60 minutes, and taking out the test sample plate; then keeping the soaking state, transferring the test sample plate and the container to a low-temperature environment of-20 DEG C or below, freezing for 24-48 hours, naturally melting after freezing or washing the frozen part with low-temperature water until the test sample plate can be taken out, and observing the appearance of a paint film of the test sample plate by eyes; and when the surface of the automobile paint film soaked in the distilled water is white, judging that the anti-rime-fog performance of the paint film is unqualified, and otherwise, judging that the anti-rime-fog performance of the paint film is qualified. According to the evaluation method, the rime fog resistance of the automobile paint film can be accurately evaluated, and potential paint film problems can be effectively pre-judged in time.

Description

Technical Field

[0001] This invention relates to the field of performance testing of automotive paint films. More specifically, it relates to a method for evaluating the resistance of automotive paint films to white fog. Background Technology

[0002] Automobiles have become essential consumer goods and means of transportation for people's work and life. As a crucial factor affecting the appearance of automotive coatings, paint companies typically conduct rigorous standardized tests on various automotive coatings they develop, based on current national, industry, and enterprise standards, to ensure excellent automotive coating appearance. Currently available tests for evaluating paint film performance include gloss, color difference, appearance, cupping, adhesion, stone chip resistance, impact resistance, hardness, acid resistance, alkali resistance, water resistance, and gasoline resistance. Regarding paint film appearance, further refinement includes tests for cracking, loss of gloss, bubbling, runs, blistering, pinholes, fisheyes, haze, peeling, mottling, bursting, and particle formation. Generally, only automotive coatings that meet all the above test requirements are used in mass production lines and ultimately released to the market for sale.

[0003] However, based on feedback from car buyers, traditional paint film appearance testing is still relatively limited and not entirely accurate. Even paint films that pass initial evaluations often develop new appearance problems in real-world driving conditions. In other words, traditional paint film testing cannot fully reflect current real-world usage environments. After receiving consumer feedback, car companies will complain to upstream paint companies about the issues. At this point, it can be difficult for paint companies to adjust their paint formulations, and delayed remedial measures may result in lost orders and significant financial losses.

[0004] White fogging is a prominent issue that consumers have reported to car companies in recent years. This problem is a type of paint film defect, and currently there is no universally accepted name for it. It manifests as a whitish or whitish discoloration on the car's paint surface during normal use. It differs significantly from previously reported whitening or whitish discoloration at the painting site in the following ways: 1) Difficulty in removal: Once white fogging appears, it cannot be completely removed by washing (water or paint film cleaner) or polishing, severely affecting the overall appearance of the paint film. Traditional whitening or whitish discoloration can at least be cleaned with polishing; 2) Formation time: In northern winters, it sometimes appears overnight after washing the car or after it has been rained on, rather than during on-site painting. Further analysis revealed that this is because after washing or raining, a small amount of water remains in the car's drainage channels. This water freezes at night below 0°C and then thaws naturally the next day, leaving a noticeable whitish or whitish discoloration on the paint film in the areas where the water remained. Currently, paint companies have not disclosed any evaluation methods that can directly and effectively test the white fog resistance of paint films. Among the existing evaluation methods, such as water resistance (GWT A H20-46), temperature change resistance (GWT A H20-72), and damp heat resistance (GWT A H20-56), none of them can well reflect the white fog resistance performance of automotive paint films.

[0005] Therefore, there is an urgent need to develop an evaluation method for the anti-white fog of automotive paint films to fill the gap in the current automotive coating evaluation standards, thereby reducing complaints caused by white fog problems during vehicle use. Summary of the Invention

[0006] To address the aforementioned problems, the present invention aims to provide an evaluation method for the anti-white fog performance of automotive paint films. This evaluation method is simple to operate, accurately reflects the anti-white fog performance of automotive paint films, and automotive coatings evaluated using this method receive fewer related complaints.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] This invention discloses a method for evaluating the anti-white fog resistance of automotive paint films, characterized by comprising the following steps:

[0009] Place the test sample coated with automotive paint film into a container filled with distilled water, ensuring that part of the paint film is submerged in the distilled water while the other part is exposed to air. Keep it at 40-60℃ for 30-60 minutes. Then, while keeping it submerged, transfer the test sample and container to a low-temperature environment below -20℃ to freeze for 24-48 hours. After freezing, allow it to thaw naturally or rinse the frozen area with cold water until the test sample can be removed. Visually inspect the appearance of the paint film on the test sample.

[0010] Furthermore, if the paint film surface of a car becomes whitish after being soaked in distilled water, it is determined that the paint film's anti-white fog performance is unqualified; conversely, if it does not, it is determined that the paint film's anti-white fog performance is qualified.

[0011] Furthermore, in the test method, the automotive paint film exposed to air is used as the evaluation benchmark.

[0012] Furthermore, if the color difference ΔE between the paint film soaked in distilled water and the paint film exposed to air is greater than 0.5, the paint film is deemed to have unqualified anti-white fog performance; otherwise, the paint film is deemed to have qualified anti-white fog performance.

[0013] Furthermore, the temperature of the low-temperature environment is controlled at -20℃.

[0014] Furthermore, the freezing time is 24 hours.

[0015] Furthermore, the material of the test sample is selected from one of the following: tinplate, electrophoretic plate, phosphated steel plate, and galvanized steel plate.

[0016] Furthermore, the test sample coated with automotive paint film was prepared according to the following steps:

[0017] The test sample is pretreated, and the coating to be tested is applied to the test sample according to the coating process. The sample is then baked or cured according to the coating baking or curing conditions to obtain a test sample coated with automotive paint film.

[0018] Furthermore, the pretreatment involves wiping the test sample clean with a degreasing solvent or alcohol.

[0019] Furthermore, the low-temperature water is distilled water with a temperature not exceeding 23°C.

[0020] The beneficial effects of this invention are as follows:

[0021] Compared with traditional water resistance (GWT A H2O-46), temperature change resistance (GWT A H2O-72), and damp heat resistance (GWT A H2O-56) tests, the evaluation method provided by this invention can more accurately reflect the white fog resistance of the paint film. Therefore, paint companies can improve the white fog resistance of automotive paint films through design adjustments during the paint development stage, increasing the time for paint companies to remedy defects. This is expected to fundamentally eliminate a potential cause of poor paint film appearance during automobile use, and at the same time, fill the gap in the evaluation standard for automotive paints. Attached Figure Description

[0022] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0023] Figure 1The image shown is a photograph of the problem board taken during the evaluation experiment in Embodiment 1 of the present invention. Detailed Implementation

[0024] To more clearly illustrate the present invention, the following description, in conjunction with preferred embodiments and accompanying drawings, further explains the invention. Similar components in the drawings are indicated by the same reference numerals. Those skilled in the art should understand that the specific description below is illustrative rather than restrictive and should not be construed as limiting the scope of protection of the present invention.

[0025] This invention addresses the problem of white fog that occurs during vehicle use by providing a method for evaluating the white fog resistance of automotive paint films, comprising the following steps:

[0026] 1) Test sample pretreatment: Wipe the test sample clean with degreasing solvent or alcohol to obtain a clean test sample;

[0027] 2) Paint film preparation: The test sample is coated according to the paint application process. After the coating is completed, baking or curing is carried out according to the paint baking or curing conditions to ensure that the paint film formation process is prepared entirely according to the conditions of the mass production line operation site, and to eliminate errors in the paint film preparation process.

[0028] 3) Conduct evaluation tests: Place the test sample coated with automotive paint film into a container filled with distilled water, ensuring that part of the automotive paint film is immersed in the distilled water and the other part is exposed to the air. Keep it at 40-60℃ for 30-60 minutes, and then transfer the test sample and container to a low temperature environment below -20℃ for freezing for 24-48 hours while keeping it immersed. After freezing, allow it to thaw naturally or rinse the frozen area with low temperature water until the test sample can be removed. Visually observe whether the appearance of the paint film on the test sample has changed. In the above test method, the automotive paint film exposed to the air is used as the evaluation benchmark.

[0029] 4) Judgment: If the paint film surface of a car that has been soaked in distilled water appears whitish, specifically meaning that the water-soaked area of ​​the paint film appears whitish compared to the unsoaked area, then the paint film is deemed to have failed the white fog resistance test. This indicates that the paint film is prone to white fogging issues after washing the car in northern winters or after the car has been exposed to rain. If the paint film surface of a car that has been soaked in distilled water shows no obvious change, specifically meaning that the water-soaked area of ​​the paint film appears to have no difference in color compared to the unsoaked area, then the paint film is deemed to have passed the white fog resistance test. This indicates that the paint film is not prone to white fogging issues after washing the car in northern winters or after the car has been exposed to rain.

[0030] This invention utilizes a simple combination of heat preservation immersion and low-temperature freezing to effectively simulate the causes of white fogging in automotive paint films, thereby helping to guide technicians in evaluating the anti-white fogging performance of paint films.

[0031] To better evaluate the color change of the paint film, a colorimeter can be used in addition to visual observation. This allows for a better assessment of the paint film's anti-white fog performance when the color change is not very obvious. If the color difference ΔE between the paint film soaked in distilled water and the paint film exposed to air is greater than 0.5, the paint film is deemed to have failed the anti-white fog performance test. Conversely, if the color difference ΔE between the paint film soaked in distilled water and the paint film exposed to air is less than 0.5, the paint film is deemed to have passed the anti-white fog performance test.

[0032] In one specific embodiment, the temperature of the heat preservation soaking can be 40℃, 45℃, 50℃, 55℃, 60℃, etc., and the heat preservation soaking time can be 30min, 35min, 40min, 45min, 50min, 55min, 60min, etc.

[0033] In one specific embodiment, the temperature of the low-temperature environment is controlled at -20°C.

[0034] In one specific embodiment, the electrical conductivity of the distilled water is no greater than 5 μs / cm.

[0035] In one specific embodiment, the material of the test sample is selected from one of the following: tinplate, electrophoretic plate, phosphated steel plate, and galvanized steel plate.

[0036] In one specific embodiment, the test sample coated with automotive paint film is prepared according to the following steps:

[0037] The test sample is pretreated, and the coating to be tested is applied to the test sample according to the coating process. The sample is then baked or cured according to the coating baking or curing conditions to obtain a test sample coated with automotive paint film.

[0038] In one specific embodiment, the pretreatment involves wiping the test sample clean with a degreasing solvent or alcohol.

[0039] In one specific embodiment, the container is a glass instrument, such as a beaker, capable of holding a test sample.

[0040] In one specific embodiment, the freezing time can be 24h, 36h, 48h, etc.

[0041] In one specific embodiment, the low-temperature water is distilled water with a temperature not exceeding 23°C.

[0042] In one specific implementation, the appearance of the paint film on the test sample is visually observed in a well-lit environment.

[0043] The technical solution of the present invention will be further illustrated by specific examples below.

[0044] Preparation Example 1

[0045] This preparation example is used to simulate the condition of a paint film with white fogging issues, and its preparation process is as follows:

[0046] Wipe the test sample clean with degreasing solvent or alcohol to obtain a clean test sample;

[0047] Select a complete set of paint formulations for the problematic paint film, apply the paint to the test sample according to the paint application process, and continue to bake or cure the paint according to the paint baking or curing conditions after the coating is completed to ensure that the paint film formation process is prepared entirely according to the control conditions of the construction site, eliminate errors in the paint film preparation process, and obtain a test sample coated with automotive paint film, hereinafter referred to as the problem board;

[0048] The coating consists of electrophoresis + 3C1B1PH intermediate coat + color paint + clear coat. The 3C1B1PH intermediate coat has a film thickness of 10-12 micrometers, the color paint film thickness is generally 13-15 micrometers, and the clear coat film thickness is generally 50-60 micrometers.

[0049] The paint film was prepared by robotic spraying, and the specific process parameters are shown in Table 1 below.

[0050] Table 1

[0051]

[0052] Test case

[0053] The problematic board in Example 1 was subjected to relevant performance tests according to the methods provided in Table 2, and the results are shown in Table 2.

[0054] Table 2

[0055]

[0056]

[0057] The test results in Table 2 show that the paint films that exhibit white fogging issues in actual use all passed the tests for water resistance, alkali resistance, and acid resistance, and the paint films showed no abnormalities in appearance. This indicates that the current standards cannot accurately assess the anti-white fogging performance of the paint films, and there is a potential risk of white fogging issues.

[0058] Example 1

[0059] This embodiment provides a method for evaluating the resistance of automotive paint films to white fog, including the following steps:

[0060] The preparation of the paint film is the same as that of the problem board in Example 1;

[0061] Place the problem board into a beaker containing distilled water at (23±2)℃. Insert the problem board into the beaker, with half of the problem board immersed in distilled water and the other half exposed to air. This allows the paint film exposed to air to be used as an evaluation benchmark and compared with the paint film immersed in distilled water in terms of color.

[0062] The temperature of the distilled water in the beaker was heated to 40°C in a water bath and kept constant throughout the test. The beaker was soaked for 30 minutes. After soaking, the problematic board was transferred to a -20°C freezer along with the beaker while still soaked. The board was frozen for 24 hours. After freezing, the board was removed and allowed to thaw naturally at room temperature. The problematic board was then removed and its paint film appearance was visually inspected.

[0063] The results are as follows Figure 1 As shown, the paint film soaked in distilled water was found to have an abnormally white surface color, which was significantly different from the paint film exposed to air. This was visible to the naked eye, and the color difference was measured to be △E=5.02. Furthermore, the white area could not be cleaned by washing with water or paint film cleaning agents, nor could it be removed by polishing. Ultimately, the problematic board was determined to be unqualified.

[0064] Subsequently, through research and analysis of the above-mentioned abnormal phenomena, the paint composition was adjusted in a targeted manner, a new paint was formulated, and the above test experiments were repeated. It was found that the surface of the new paint film did not show any whitening phenomenon, and the color of the paint film exposed to air was no different from that of the paint film by visual observation.

[0065] Example 2

[0066] This embodiment provides a method for evaluating the resistance of automotive paint films to white fog, including the following steps:

[0067] The preparation of the paint film is the same as that of the problem board in Example 1;

[0068] Place the problem board into a beaker containing distilled water at (23±2)℃. Insert the problem board into the beaker, with half of the problem board immersed in distilled water and the other half exposed to air. This allows the paint film exposed to air to be used as an evaluation benchmark and compared with the paint film immersed in distilled water in terms of color.

[0069] The temperature of the distilled water in the beaker was heated to 50°C in a water bath and kept constant throughout the test. The beaker was soaked for 50 minutes. After soaking, the problematic board was transferred to a -20°C freezer along with the beaker and kept soaked for 24 hours. The board was then removed and allowed to thaw naturally at room temperature. The problematic board was then removed and its paint film appearance was visually inspected.

[0070] The results showed that the paint film soaked in distilled water exhibited an abnormal phenomenon of obvious whitening on the surface, which was significantly different from the paint film exposed to air. This was visible to the naked eye, and the color difference was measured to be △E=5.05. Furthermore, the whitening area could not be cleaned by washing with water or paint film cleaning agents, nor could it be removed by polishing. Ultimately, the problematic board was determined to be unqualified.

[0071] Subsequently, through research and analysis of the above-mentioned abnormal phenomena, the paint composition was adjusted in a targeted manner, a new paint was formulated, and the above test experiments were repeated. It was found that the surface of the new paint film did not show any whitening phenomenon, and the color of the paint film exposed to air was no different from that of the paint film by visual observation.

[0072] Comparative Example 1

[0073] This comparative example provides a method for evaluating the resistance of automotive paint films to white fog, including the following steps:

[0074] The preparation of the paint film is the same as that of the problem board in Example 1;

[0075] Place the problem board into a beaker containing distilled water at (23±2)℃. Insert the problem board into the beaker, with half of the problem board immersed in distilled water and the other half exposed to air. This allows the paint film exposed to air to be used as an evaluation benchmark and compared with the paint film immersed in distilled water. Immerse at this temperature for 0 min.

[0076] Then, while still soaking, transfer the problematic board along with the beaker directly to a -20°C freezer for 48 hours. Remove it and allow it to thaw naturally at room temperature. Take out the problematic board and visually inspect the appearance of the paint film.

[0077] The results showed that the paint film soaked in distilled water did not change significantly in appearance, and there was no whitening. The color of the paint film was visually indistinguishable from that of the paint film exposed to air. The color difference was measured to be ΔE = 0.12, indicating that this method cannot accurately evaluate the anti-white fog performance of the paint film and there is a potential risk of white fog problem.

[0078] Comparative Example 2

[0079] This comparative example provides a method for evaluating the resistance of automotive paint films to white fog, including the following steps:

[0080] The preparation of the paint film is the same as that of the problem board in Example 1;

[0081] Place the problem board into a beaker containing distilled water at (23±2)℃. Insert the problem board into the beaker, with half of the problem board immersed in distilled water and the other half exposed to air. This way, the half exposed to air can be used as an evaluation benchmark to compare with the paint film color immersed in distilled water. Immerse at this temperature for 60 minutes.

[0082] Then, while keeping the board submerged, transfer it along with the beaker to a -20°C freezer for 48 hours. Remove the board and allow it to thaw naturally at room temperature. Take out the board and visually inspect the appearance of the paint film.

[0083] The results showed that the paint film soaked in distilled water did not change significantly in appearance, and there was no whitening. The color of the paint film was visually indistinguishable from that of the paint film exposed to air. The color difference was measured to be ΔE=0.17, indicating that this method cannot accurately evaluate the anti-white fog performance of the paint film and there is a potential risk of white fog problem.

[0084] Comparative Example 3

[0085] This comparative example provides a method for evaluating the resistance of automotive paint films to white fog, including the following steps:

[0086] The preparation of the paint film is the same as that of the problem board in Example 1;

[0087] Place the problem board into a beaker containing distilled water at (23±2)℃. Insert the problem board into the beaker, with half of the problem board immersed in distilled water and the other half exposed to air. This allows the paint film exposed to air to be used as a reference for color comparison with the paint film immersed in distilled water.

[0088] The temperature of the distilled water in the beaker was heated to 40°C in a water bath and kept constant throughout the test. The beaker was soaked for 10 minutes. After soaking, the problematic board was transferred to a -20°C freezer along with the beaker while still soaked. The board was frozen for 4 hours, then removed and allowed to thaw naturally at room temperature. The problematic board was then removed and its paint film appearance was visually inspected.

[0089] The results showed that the appearance of the paint film soaked in distilled water did not change significantly, and it was extremely difficult to detect any whitening. The color of the paint film was almost indistinguishable from that of the paint film exposed to air. The color difference was measured to be ΔE = 0.31, indicating that this method cannot accurately evaluate the anti-white fog performance of the paint film and there is a potential risk of white fog problem.

[0090] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A method for evaluating the anti-white fog resistance of automotive paint films, characterized in that, Includes the following steps: Place the test sample coated with automotive paint film into a container filled with distilled water, ensuring that part of the paint film is submerged in the distilled water while the other part is exposed to air. Keep it at 40-60℃ for 30-60 minutes. Then, while keeping it submerged, transfer the test sample and container to a low-temperature environment below -20℃ to freeze for 24-48 hours. After freezing, allow it to thaw naturally or rinse the frozen area with cold water until the test sample can be removed. Visually inspect the appearance of the paint film on the test sample.

2. The evaluation method according to claim 1, characterized in that, If the paint film of a car turns white after being soaked in distilled water, the paint film is deemed to have failed the white fog resistance test; otherwise, the paint film is deemed to have passed the white fog resistance test.

3. The evaluation method according to claim 1, characterized in that, In the test method, the automotive paint film exposed to air is used as the evaluation benchmark.

4. The evaluation method according to claim 3, characterized in that, If the color difference ΔE between the paint film soaked in distilled water and the paint film exposed to air is greater than 0.5, the paint film is deemed to have failed the white fog resistance test; otherwise, the paint film is deemed to have passed the white fog resistance test.

5. The evaluation method according to claim 1, characterized in that, The temperature of the low-temperature environment is controlled at -20℃.

6. The evaluation method according to claim 1, characterized in that, The freezing time is 24 hours.

7. The evaluation method according to claim 1, characterized in that, The test sample is made of one of the following materials: tinplate, electrophoretic plate, phosphated steel plate, or galvanized steel plate.

8. The evaluation method according to claim 1, characterized in that, The test sample coated with automotive paint film was prepared according to the following steps: The test sample is pretreated, and the coating to be tested is applied to the test sample according to the coating process. The sample is then baked or cured according to the coating baking or curing conditions to obtain a test sample coated with automotive paint film.

9. The evaluation method according to claim 8, characterized in that, The pretreatment involves wiping the test sample clean with a degreasing solvent or alcohol.

10. The evaluation method according to claim 1, characterized in that, The low-temperature water is distilled water with a temperature not exceeding 23°C.

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