The role of leveling agents

2021-09-15   Pageview:399

Generally speaking, the main function of leveling agents is to prevent defects in the coating film (such as shrinkage, fish eyes, etc.) and to reduce orange peel. At the same time, the use of leveling agents helps to improve the dispersion of pigments and degassing during curing, increasing the flow of the effect. The good dispersion effect promotes the dispersion effect of pigments in the system, enhancing the uniformity of color and reducing processing time.












The leveling agents used today generally improve interfacial properties by eliminating (or compensating for) differences in surface tension. Typically, when/if an acrylic polymer additive is added, this excess leveling agent migrates to the surface of the molten resin (this migration is generally enhanced by its incompatibility with the coating system), thereby compensating for its chemical potential on the surface of the substrate and in the body. When this acrylic polymer reaches the surface, its polar backbone remains in the molten resin (or substrate), while the alkyl side chains tend to escape to the outside and reach some stable equilibrium. As a result, the entire surface tension tends to average out due to the high concentration of molecular structures oriented on the entire surface. This micronized ptfe wax concentration effect eliminates the unevenness of the original surface tension.

The film formation and flow of powder coatings are controlled by two main parameters, surface tension and melt viscosity. The surface tension (at a given temperature) is the main driving force for flow, while the only resistance to flow comes from the melt viscosity of the powder under baking conditions. The leveling agent can therefore be more precisely defined as a surface tension improver.

Theoretically, two prerequisites are necessary to control the flow of powder coatings:

( 1) high surface tension. However, in order to ensure sufficient wetting of the substrate, the surface tension must not be higher than the surface tension of the substrate.
(2) The surface tension must be partially homogeneous at the interface with the air. According to the current powder production process, the powder is generally non-homogeneous, so without the use of leveling agents, the second condition is almost impossible to achieve.




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