The role and types of leveling agents in coating systems
In coating formulations, the role of leveling agents is to efficiently disperse, balance wetting leveling effects, solve shrinkage and fisheye phenomena. However, the types of leveling agents used vary depending on the coating system. One type works by adjusting the viscosity of the paint film and leveling time. These leveling agents are mostly high boiling organic solvents or their mixtures, such as isophorone and diacetone alcohol. Another type of leveling agent works by adjusting the surface properties of the paint film. Generally, what people refer to as leveling agents mostly refer to this type of leveling agent, which migrates to the surface of the paint film through limited compatibility, affecting surface properties such as interfacial tension of the paint film, and achieving good leveling of the paint film.
According to different mechanisms of action, leveling agents can be divided into surface state controlled leveling agents and flow and leveling accelerators. Surface state control leveling agent can reduce the surface tension of the coating and prevent defects such as shrinkage, ripple, Benel vortex, flower, orange peel, etc; Leveling promoter has the function of promoting the flow and leveling of the coating, and facilitating the disappearance of brush marks, rolling marks, and indentation marks. According to their different chemical structures, leveling agents are currently mainly divided into three categories: acrylic, organosilicon, and fluorocarbon.
1、 Acrylic ester polymers
Acrylic ester polymers do not reduce the surface tension of the system and are flow and leveling accelerators; The disadvantage is that it is powerless in terms of short wave leveling and solving shrinkage problems.
2、 Organic silicon
Organic silicon leveling agents can significantly reduce surface tension, better wet the coated substrate, and enhance the adhesion of the paint film to the substrate. In addition, these leveling agents can quickly migrate to the surface of the paint film by relying on low surface tension, forming an extremely thin monolayer. On the one hand, it slows down the evaporation rate of the solvent and prolongs the leveling time of the wet film; On the other hand, low surface tension monolayers can eliminate surface tension gradients and Bernoulli vortices, making the surface tension uniform, thereby eliminating surface defects such as shrinkage, orange peel, coating marks, and floating colors on the paint film.
Polyether modified siloxane leveling agent is a widely used and important type of leveling agent, and one of its important characteristics is the ability to reduce the surface tension of coatings. Depending on the chemical structure, the degree of surface tension reduction also varies. In terms of cost-effectiveness, it is a very good leveling agent.
3、 Fluorocarbon compounds
Fluorocarbon leveling agent is characterized by high efficiency, but expensive. It is generally used when acrylic leveling agent and silicone leveling agent are difficult to play a role. However, there is a tendency to stabilize foam and affect the adhesion between layers.
