What is the main role of leveling agent?
The main function of the coating is to decorate and protect, if there are flow and leveling defects, not only affect the appearance, but also damage the protection function. Such as the formation of shrinkage caused by insufficient film thickness, the formation of pinholes will lead to the film of the discontinuity, which will reduce the protective film. Paint in the construction and film forming process, there will be some physical and chemical changes, these changes and the nature of the paint itself will significantly affect the flow of paint and leveling.
After the construction of the paint, there will be a new interface, under normal circumstances for the paint and the substrate between the liquid / solid interface and paint and air between the liquid / gas interface. If the interface between the paint and the substrate liquid / solid interface interface tension is higher than the critical surface tension of the substrate, the coating can not spread on the substrate, naturally there will be fisheye, shrinkage and other leveling defects.
The evaporation of the solvent during the drying of the paint film results in poor temperature, density and surface tension between the surface of the paint and the inside of the paint, which in turn results in turbulent motion inside the paint film, forming the so-called Benard vortex. Benard vortex will lead to the production of orange peel; in more than one pigment system, if the movement of pigment particles there are some differences, Benard vortex is also likely to lead to floating and hair, vertical surface construction will lead to silk pattern.
In the drying process of the paint film, some insoluble colloids are sometimes produced. The formation of insoluble colloids results in the formation of a surface tension gradient, which often leads to the generation of shrinkage in the film. For example, in a cross-linked cure system, the formulation contains more than one resin. During the drying of the paint film, insoluble particles may form a resin with poor solvent solubility and poor solubility. In addition, in the formulation containing the surfactant, if the surfactant is incompatible with the system or the concentration of the solvent fluctuates during the drying process, the solubility is changed to form incompatible droplets, Will also form a poor surface tension. These may lead to shrinkage generation.
Paint in the construction and film forming process, if there are external pollutants, may also lead to shrinkage, fish eyes and other leveling defects. These contaminants are usually from the air, construction tools and substrates of oil, dust, paint mist, water vapor and so on.