The main reasons for the foaming of paint coatings are as follows:
1. Foaming due to swelling of the film volume.
That is to say, polymer coatings used for anticorrosion usually absorb 0.1% - 3% (weight of coatings) of water when exposed to aqueous electrolyte solution for a long time. When the film is immersed or condensated in high humidity, it will swell and increase its volume after absorbing water. If this swelling occurs locally, bubbles will occur if the stress produced by the swelling is greater than the adhesion force. In time, the absorbed water does not really expand the coating, but also accumulates on some internal interfaces, resulting in foaming.
2. Bubbling due to gas inclusions or gas
During the process of film formation or cathodic protection, bubbles are produced because of the presence of volatile components or the formation of volatile components in the film. This composition may be air bubbles mixed in paint preparation or painting, some solvent inclusions brought in by phase separation or volatile condensation products. These bubbles may not necessarily limit the cup world surface, but should be seen in the whole Xu layer. It is easy to see bubbles with a wide range of internal and external causes. The bubbles may also precipitate f-rom the remaining 41 surface decomposition. If hydrogen is generated within noon, hydrogen is generated in the cathode when hydrogen ion thrives through the defect of capillary hole if the painted steel plate is immersed in acid medium towel.
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