Levelling agents 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 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 ptfe wax price can also be used in coating films.
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, 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.
2, 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.
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