Powder coatings are completely solvent-free and emit low VOC (volatile organic compound) emissions during curing, making them one of the most environmentally friendly coating systems. Coating leveling refers to the smooth, even appearance of the coating film after application. A surface with good leveling should be free of irregularities such as orange peel, brush marks, ripples, and craters.

Generally, direct visual observation involves comparing a sample with a standard sample to assess the leveling properties of a coating. This method is subjective and varies from person to person. The wavelength scanning method, used in the automotive industry, provides a semi-quantitative approach to characterizing the surface condition of a coating. Long-wavelength (10-0.6 mm) and short-wavelength (0.6-0.1 mm) scanning is used, with measured values ranging from 0 to 100. Lower values indicate a smoother coating surface and better leveling properties.

The factors that affect the leveling of powder coatings mainly include three aspects. The first is the leveling agent. Appropriate leveling agents are added to the formula of powder coatings. When the powder coating is melted, these agents can quickly reduce the surface tension of the coating, promote the rapid flow of the coating before solidification and film formation, and eliminate or reduce surface defects such as orange peel, brush marks, ripples, and shrinkage holes; the second is the melt viscosity of the powder coating. For thermosetting powder coatings, during the melting flow process, it is accompanied by cross-linking and curing reactions. The higher the temperature, the faster the curing reaction, the faster the system viscosity rises, the flow time is shortened, and the leveling properties are restricted.

Therefore, the melt viscosity of powder coatings cannot accurately reflect the leveling properties of the coating. The effects of the baking process, heating rate, and crosslinking curing temperature on coating leveling must also be considered. Thirdly, the baking process.

Powder coatings undergo a temperature ramp during baking, and the rate of temperature ramp significantly influences the coating's leveling. The dynamic viscosity follows a similar trend with temperature: initially, the viscosity decreases with increasing temperature, then increases. This is due to the crosslinking reaction. More importantly, faster heating rates reduce viscosity, while higher temperatures promote film curing and improve coating leveling.

The leveling properties of powder coatings are influenced by the leveling agent, the structure of the film-forming resin, and the curing mechanism. Using an appropriate leveling agent, selecting a low-melt-viscosity resin system, and a matching curing process (UV curing) can produce a coating with excellent leveling properties.

These are the steps to improve the leveling properties of powder coatings. Have you learned?