Principles of Leveling Agents

Overview of Leveling ​

After the application of coatings, there is a process of flow and drying into a film, which gradually forms a smooth, even, and uniform coating. The ability of the coating to achieve a flat and smooth surface is referred to as leveling property.

In practical coating applications, common defects such as orange peel, fish eyes , pinholes, shrinkage cavities, edge retraction, airflow sensitivity, as well as brush marks during brushing and roller marks during roller application—all resulting from poor leveling—are collectively termed poor leveling . These phenomena degrade the decorative and protective functions of the coating.

Numerous factors influence coating leveling, including solvent evaporation gradient and solubility, surface tension of the coating, wet film thickness and surface tension gradient, rheological properties of the coating, application techniques, and environmental conditions. Among these, the most critical factors are the surface tension of the coating, the surface tension gradient formed in the wet film during film formation, and the ​ability of the wet film surface to equalize surface tension.

Improving coating leveling requires adjusting the formulation and incorporating suitable additives to achieve an appropriate surface tension and reduce the surface tension gradient.

Function of Leveling Agents

A leveling agentn is an additive that controls the flow of a coating after it wets the substrate, guiding it toward a smooth, final finish. Leveling agents address the following issues:

Surface Tension Gradient–Air Interface

Turbulence caused by surface tension gradients between the inner and outer layers​Eliminating surface tension gradients is essential for achieving a smooth surface

Surface Tension Gradient–Substrate Interface

Lower surface tension than the substrate improves substrate wetting

Reducing the coating’s surface tension decreases intermolecular attraction on the surface, promoting better flow

Factors Affecting Leveling Speed

Higher viscosity → slower leveling

Thicker films → faster leveling

Higher surface tension → faster leveling