Powder coatings are currently one of the most environmentally friendly coating systems due to their complete absence of organic solvents and low VOC (Volatile Organic Compound) emissions during curing. The so-called leveling property of the coating refers to the smooth and smooth state of the coating film after the coating is applied. The surface with good leveling property should have no irregularities such as orange peel, brush marks, ripples, and shrinkage holes.

Generally, the method of direct observation with the naked eye is to compare the sample and the standard sample in parallel to judge the pros and cons of the leveling of the coating film. This method varies from person to person and is highly subjective. The wavelength scanning method used in the automobile industry is used to characterize the surface state of the coating film, which has a semi-quantitative effect. Long-wave (10-0.6mm) and short-wave (0.6-0.1mm) are used for scanning, and the measured value is between 0 and 100. The lower the value, the smoother the surface of the coating film and the better the leveling.

The factors that affect the leveling of powder coatings mainly include three aspects. One is leveling additives. Add appropriate leveling additives to the formula of powder coatings, such as GL588 of Nanhai Company, H98 of Leith Company, and of Worlee-chemie Company. PV88, etc., when the powder coating is melted, these additives can quickly reduce the surface tension of the coating, promote the rapid flow of the coating before curing and film formation, and eliminate or reduce surface defects such as orange peel, brush marks, ripples, and shrinkage craters; the second is the powder coating. The melt viscosity of the coating, for thermosetting powder coatings, in the melt flow process, along with the cross-linking curing reaction, the higher the temperature, the faster the curing reaction, the faster the system viscosity rises, the shorter the flow time, and the more restricted the leveling. .

Therefore, the melt viscosity of the powder coating cannot accurately reflect the final leveling property of the coating film, and the influence of the baking process, heating rate, cross-linking curing temperature, etc. on the leveling property of the coating film must be considered at the same time; the third is the baking process. There is a heating process when powder coating is baked, and the heating rate has a considerable influence on the leveling of the coating. The trend of dynamic viscosity changes with temperature is basically the same, that is, the viscosity decreases with the increase of temperature at the beginning and reaches the minimum value, and then the viscosity increases with the increase of temperature, which is caused by the cross-linking reaction. More importantly, the faster the heating rate, the smaller the minimum value of the viscosity, and the higher the corresponding temperature, the better the curing of the coating film and the better the leveling of the coating film.

The leveling of powder coatings is restricted by the structure and curing mechanism of leveling aids, film-forming resins. With appropriate leveling additives, resin system with low melt viscosity and matching curing process (UV curing), a coating film with excellent leveling performance can be obtained.