Coating Wet Adhesion

Finally, a special issue of coating adhesion is discussed: wet adhesion. Strictly speaking, coating adhesion should refer to the adhesion of coated metal exposed to high humidity environment or solution, commonly known as wet adhesion (wet adhesion), that is, after the coated metal is placed in a medium environment, it will show of adhesion. The reason for such a distinction is mainly due to the fact that most of the commonly used methods for measuring coating adhesion currently measure the value of the dry coating system, which is different from the wet adhesion of the coating. Because after the coating is in contact with the medium, its adhesion will undergo a series of changes, and these changes are closely related to the corrosion of the interface metal under the coating, especially the water disbondment.

When the painted sample is exposed to water or high humidity environment, its adhesion will inevitably be reduced, but this change will not immediately or immediately lead to complete peeling off of the coating, and there is often an intermediate transition state. At this stage, when the coating system is re-dried, adhesion may be partially regained. It has been reported in the literature that after one round of immersion/drying, the adhesion of the coating can be reduced by 15% of its original value, but after 20 rounds, it is only reduced by 50%. practical experience. Lin Changjian et al. used multiple internal reflection infrared spectroscopy to study in detail the penetration and depolarization of water molecules in the medium to the coating. The results showed that water entering the interface destroys the adhesive bond of the polymer to the metal substrate.

At the same time, the modern coating system has not only formed a barrier layer, but a comprehensive carrier with many additives with different functions. The anti-corrosion substances in it can effectively prevent the occurrence and development of metal corrosion under the coating, so that The intermediate process of adhesion decline lasts for a long time, such as effective coating corrosion inhibitor can obviously prolong the service life of the coating. In addition, we found in the research that although the effect of the corrosion inhibitor is not in doubt, when the adhesion of the dry coating is measured, the method of drawing a circle is often used to compare the adhesion of the original sample without the corrosion inhibitor. Good, but it does not mean that the corrosion resistance of this sample is better than that of the corrosion inhibitor sample. not comprehensive. Therefore, although the adhesion is the main factor determining the performance of the coating, the two must not be simply equated, because the accurate measurement of the interface force of the adhesion itself is very difficult, and the adhesion is in the coating. There may be changes in the actual use of the coating, and there is no unified adhesion test method at present, and an appropriate method should be selected for different research objects. (Adhesion Tester can be used for adhesion performance testing instrument)

For more information, please refer to the full text of "Research Progress on Adhesion between Coating and Substrate Metal" (Song Yusu, Yao Shuren)