[0025] Before introducing the paint blistering test method of the present invention, the process of finding the cause of the paint blistering defect is first introduced. Finding the cause of blistering defects in paint is as important as proposing paint blistering test methods.
[0026] In order to find the cause of the blistering defect of the paint surface, first collect a large amount of data on the blistering defect of the paint surface. Through the analysis of big data, it is obtained that the blistering defect of the paint surface has the following characteristics:
[0027] ●From the appearance, the blisters on the paint surface are densely raised, similar to pore clusters. The blistered area as a whole presents the outline of a handprint or has obvious or polished wipe marks, indicating that the defect area has obvious traces of manual operation.
[0028] ●In terms of location, most of the blistering defects are located at the height of the hand. Indicates that the defect may be related to the operator's hand contact.
[0029] ●From the point of view of the process, the defect is limited to paint workshops of certain specific processes. Explain that the defect may be related to a certain process or a certain composition of paint.
[0030] ●From the point of view of defect manifestation time, the defect has not been reported and found in the finishing line of the paint shop, and the defect is gradually revealed 1-2 days after the completion of painting. It shows that the defect is not produced during spraying, but gradually appears after spraying.
[0031] The sample was further selected for microstructure analysis, and it was found that the specific location of the blistering defect was between the middle coating and the electrophoretic layer. In areas with blistering defects on the paint surface, it can be found that the middle coating layer and the electrophoretic layer are significantly separated, with gaps or cavities in the middle, but no obvious residues are found in the gaps or cavities. The colored paint layer and the varnish layer above the middle coating layer are normal and there is no defect. It can be seen from the microstructure analysis that the cause of the defect is likely to be between the electrophoretic layer and the middle coating. It may be that some impurities are mixed between the electrophoretic layer and the middle coating layer, or there are defects in the processing technology of the two layers.
[0032] Combined with the specific manufacturing process, the processes that need to be implemented between the electrophoretic layer and the middle coating layer are inner cavity modification, car body surface polishing, and cleaning. After the above work is completed, paint the car body and apply the middle coat.
[0033] After obtaining the above clues, a careful analysis of the entire process of interior modification, surface polishing, and cleaning of the car body revealed the following phenomena:
[0034] ●Operators will habitually prop up their hands on the car body during the work of interior modification, surface polishing and cleaning of the car body, and the position of the hand support will correspond to the high incidence area of blistering defects.
[0035] ●Because the workshop environment is closed and the temperature is high, the operators sweat a lot, and the sweat on the hands will stick to the position of the hand support on the car body. In the subsequent process, the sweat was not wiped off, and the sweat remained in the fingerprints or sanding marks.
[0036] ●Because this model is a new model, its paint composition is different from that used in other models before, and the painting process is also slightly different.
[0037] Based on the above phenomena, combined with the aforementioned characteristics of the paint surface blistering defect, it is speculated that the cause of the paint surface blistering defect may be as follows: a certain paint composition or spray paint process reacts with residual sweat, in the high temperature and high humidity environment of the subsequent process In this reaction, gaps and cavities appear between the electrophoretic layer and the middle coating layer, resulting in blistering defects on the paint surface.
[0038] In order to verify the above conjecture, the following experiments were further carried out:
[0039] The specific components of each person’s sweat are slightly different, but the main components are similar. Most of the human body’s sweat is water, and the remaining components account for a small part, including: sodium, chloride, potassium, urea, protein, lipids , Amino acids, calcium, phosphorus and iron. The most important components are sodium chloride (NaCl), disodium hydrogen phosphate and hydrate (NaCl). 2 HPO 4 ·12H 2 O) and acetate CH 3 COOH. The above three components will remain on the solid surface in the form of salt after the water in the sweat volatilizes. The remaining salt in the high temperature and high humidity environment will re-absorb the moisture in the surrounding environment and expand in volume. After the high temperature and high humidity disappears, the moisture will volatilize again. However, the process of volume expansion will form gaps or cavities between the layers of paint, which is consistent with the defect structure observed by microscopic analysis. In order to make the test more stable, it is necessary to prepare artificial sweat with fixed components and test with fixed components.
[0040] In order to determine the composition of artificial sweat, first select the sweat of a large number of employees as the alternative, stick the sweat of these employees on the electrophoresis sample plate, and then apply the middle coat, colored paint and varnish. The coating thickness of the intermediate coating is 35 microns, which is consistent with the thickness of the intermediate coating in actual production. After the painting is finished, the sample is placed in a high temperature and high humidity environment for a long enough time to simulate the working environment of the actual production line after the painting process. In the test, the samples were placed in different constant temperature and constant humidity environments for different periods of time. Then observe the blistering of the paint on the sample.
[0041] Tests have proved that sweat does cause the defect of paint blistering, and the manifestation of the defect is consistent with the previously observed manifestation. Therefore, it can be inferred that the aforementioned blistering defect of paint is caused by residual sweat. However, the severity of defects revealed by a large number of sweat samples is different, some defects are minor or even no defects, and some defects are significant. From the perspective of testing, the sweat with the most significant defects should be selected, and artificial sweat should be prepared according to its composition.
[0042] According to the composition analysis, in the sweat with the most significant defects, the weight ratio of the main components sodium chloride, disodium hydrogen phosphate and hydrate, and acetic acid is 5:10:3. Therefore, in the prepared artificial sweat, the weight ratio of sodium chloride, disodium hydrogen phosphate and hydrate, and acetic acid was also determined to be 5:10:3.
[0043] Similarly, for the constant temperature and humidity environment and duration, the similar principle is to choose the most significant defect as the standard. It is determined that the high temperature environment is 38°C, the high humidity environment is 88% humidity, and the duration is 24 hours. It should be noted that other reference high temperature environment is 38° C., high humidity environment is 80% humidity or 85% humidity, and the duration is 8 hours or 16 hours. These high-temperature, high-humidity environments and storage time are also common working environments and process durations on production lines. Although they have not been determined as the optimal choice in current applications, they may be better in other applications. s Choice.
[0044] After determining that the sweat adhering to the car body during the process is the cause of the paint blistering defect, it is necessary to try to solve this problem.
[0045] There are two ways to solve this problem:
[0046] The first way is to prevent sweat from adhering to the car body. This approach requires strengthening the training and management of operating workers, or improving the working environment of the workshop and reducing the temperature of the workshop. From the actual situation, the control stability of the first approach is poor. In the construction site of a large number of operators, it is very difficult to completely prevent each operator from sticking sweat to the car body. Even if strict operating specifications are formulated and equipped with adequate protective equipment, sweat will still adhere to the car body under high-intensity working conditions.
[0047] The second way is to improve the paint formulation. Figure 2a with Figure 2b It reveals the cause of paint blistering defects. reference Figure 2a As shown, the sweat adheres to the car body and is actually located outside the electrophoretic layer 202. After the moisture in the sweat volatilizes, what remains on the electrophoretic layer is the salt 204 formed by various components in the sweat. After the subsequent spraying of the intermediate coating layer 206, the salt 204 is locked between the intermediate coating layer 206 and the electrophoretic layer 202. reference Figure 2b As shown, in the subsequent process, when the salt 204 is located in a high temperature and high humidity environment for a long enough time, the salt 204 re-absorbs the moisture in the environment and re-dissolves to form a liquid 208. In a high temperature environment, the liquid 208 expands, forming a gap between the midway layer 206 and the electrophoretic layer 202. When the water in the liquid volatilizes again, a cavity will be left between the middle coating 206 and the electrophoretic layer 202. If the composition of the middle coat can be adjusted to make it have better water resistance and prevent water from entering through the middle coat, it can prevent the salt from re-dissolving to form a liquid and swell. So as to avoid the defect of paint blistering. If the paint formula can be improved so that foaming can be avoided even when sweat is contaminated, the control stability can be greatly improved, and it is no longer necessary to restrict and manage the operation process of each operator.
[0048] How to adjust the components of the middle coating is not the focus of the present invention. The present invention focuses on the blistering test of a certain component of the middle coating to see if it can meet the requirements for preventing blistering. Requirements.
[0049] figure 1 A flowchart of a paint blistering test method according to an embodiment of the invention is disclosed. Such as figure 1 As shown, the present invention proposes a paint blistering test method, which includes the following steps:
[0050] 101. Polish the electrophoresis template to form a polishing mark on the template. In one embodiment, 400# water sandpaper is used to polish the electrophoresed template.
[0051] 102. Clean and dry the polished template.
[0052] 103. Configure the bubbling test liquid and smear the bubbling test liquid on the sample plate. The bubbling test liquid is artificial sweat. In one embodiment, the artificial sweat is a mixed solution of sodium chloride, disodium hydrogen phosphate and hydrate and acetic acid, wherein the weight ratio of sodium chloride, disodium hydrogen phosphate and hydrate and acetic acid is 5:10:3 . Specifically, the concentration of artificial sweat is 5 g/L of sodium chloride, 10 g/L of disodium hydrogen phosphate and hydrate, and 3 g/L of acetic acid.
[0053] 104. Dry the sample plate so that the components of the foaming test liquid adhere to the sanding print.
[0054] 105. Spraying and drying the middle coat, colored paint and varnish on the sample board at one time, where the middle coat, colored paint and varnish are all covered with a polished print. In one embodiment, the thickness of the middle coating is 35 microns, the thickness of the colored paint is 12 microns, and the thickness of the varnish is 35 microns.
[0055] 106. Bake the painted template for the first time. In one embodiment, the first time for baking the painted template is 1 hour.
[0056] 107. Place the baked template in a constant temperature and humidity environment for a second time. In one embodiment, the constant temperature and humidity environment is provided by a constant temperature and humidity hot box, the constant temperature and humidity environment is 38° C., 88% humidity, and the second time is 24 hours.
[0057] 108. Check whether the paint on the sample board is blistering. If there is no defect of paint blistering on the sample, it means that the composition of the halfway layer is qualified and can be used.
[0058] The paint foaming test method of the present invention can test the salt resistance ability of the paint. By selecting a paint with high salt resistance ability, the probability of paint foaming is reduced, even if a small amount of salt is mixed in the production process, it has high salt resistance ability The paint can still avoid the defect of large area paint blistering.
[0059] The above-mentioned embodiments are provided for those skilled in the art to implement or use the present invention. Those skilled in the art can make various modifications or changes to the above-mentioned embodiments without departing from the inventive idea of the present invention. The protection scope of the present invention is not limited by the above-mentioned embodiments, but should be the maximum scope that meets the innovative features mentioned in the claims.
