After the coating is applied, there is a flowing and drying film forming process, and then a flat, smooth and uniform coating film is gradually formed. Whether the coating film can achieve flatness and smoothness is called leveling.

In the actual construction process of coatings, the coating film defects often appear are orange peel, fish eyes, shrinkage holes, pinholes, shrink edges, Benard swirls, airflow sensitivity and because of poor leveling, brush marks appear during brushing. The roll marks that occur when roller coating is called poor leveling. These phenomena reduce the decorative and protective functions of the coating.

There are many factors that affect the leveling of coatings, such as the solvent's volatilization gradient and dissolution performance, the surface tension of the coating, the wet film thickness and surface tension gradient, the coating's rheology, the construction process and the environment, etc., the most important factor is the surface Tension, the surface tension gradient generated by the wet film during film formation, and the surface tension uniformity of the wet film surface layer. To improve the leveling property of the coating, adjustment of the formulation and the addition of appropriate additives are needed to make the coating have the proper surface tension and the ability to reduce the surface tension gradient.