Pinholes (porosity) may develop during the curing process of powder coatings, usually due to the inability of small molecules trapped inside the coating to be released in time as the viscosity gradually increases. Here's what can cause foaming problems in powder coatings and how to fix them:
Cause analysis
Inherent features of powder coating systems: The loose structure of powder coatings creates a large number of voids between the particles, which may be filled by air after spraying, and as the temperature rises, the powder particles melt and the air fails to escape and pinholes are formed.
Small molecules produced by the curing reaction: Chemical reactions during curing can produce small molecules, such as moisture or solvents, which can also lead to pinhole formation if entrapped by the coating.
Substrate issues: Porous or highly reactive substrates and improper pre-treatment can also lead to pinholes.
Powder storage is damp: If the powder coating is exposed to moisture during storage, it will also increase the risk of air bubbles inside the coating.
Resolution
Optimize powder coating formulations: Reduce the production of small molecules during the curing process by improving the formulation, or add the appropriate defoamer to aid in the release of air bubbles.
Improved substrate handling: Ensure that the substrate is clean and free of oil, and that appropriate surface treatment methods are used to improve the adhesion of the coating to the substrate and reduce the occurrence of pinholes.
Use a defoamer: Add defoamers specially designed for powder coatings, these defoamers usually have the characteristics of high temperature resistance, acid and alkali resistance, and can effectively eliminate and inhibit the generation of foam without changing the basic properties of the coating system.
Pay attention to the amount of defoamer used: The amount of defoamer should be used in the right amount, too much may affect the leveling and other properties of the coating, too little may not achieve the desired defoaming effect. Therefore, it is advisable to conduct a test or consult a professional before use.
Storage conditions: Powder coatings and defoamers should be stored in a ventilated, dark and cool place, and should be sealed to avoid moisture and impurities to maintain their best performance.
In summary, solving the problem of defoaming powder coatings requires a combination of factors, from coating formulation to storage conditions, each of which needs to be carefully controlled to ensure the quality and performance of the coating.