For substances that can be used as leveling agents in coating systems, the following two characteristics are required: first, it has a lower surface tension than the system, and second, its compatibility with the system is limited. These two factors work together to cause the leveling agent to self migrate to the surface of the paint film after being added to the coating system, and form a single molecular film with a fixed and uniform surface tension on the surface. This single molecular film ensures that the surface tension of the paint film does not change with the changes of the paint film (such as curing, solvent evaporation, etc.), thereby ensuring that the paint film can transform from uneven to flat under the action of surface tension. The common leveling agents mainly include organic silicon leveling agents and non silicon leveling agents.
Compared with non silicone leveling agents, organic silicone leveling agents often migrate to the surface of the paint film at a faster rate due to the low surface tension of their organic silicone segments and limited compatibility with the resin system, thus exhibiting a faster leveling speed; At the same time, due to the fact that organic silicon leveling agents can migrate to the surface of the paint film earlier than non silicon leveling agents, they are more helpful in eliminating the Bernal vortex caused by solvent evaporation during the initial drying stage of the paint film, which is often the fundamental cause of many paint film defects.
Commercialized organic silicon leveling agents mainly consist of various polyether modified silicone oils with different structures. For polyether modified silicone oil leveling agents, a series of organic silicon leveling agents with different properties can be obtained by changing the relative ratio of organic silicon to polyether and the ratio of different monomers in polyether; And there is a similar pattern for aromatic alkyl modified silicone oil.
From the perspective of performance, organic silicon leveling agents can mainly provide the following eight aspects of performance: leveling, leveling speed, wetting ability, recoating, compatibility, smoothness, low-temperature foaming, anti shrinkage porosity, and anti adhesion. And these properties are often closely related to the chemical structure of organic silicon leveling agents, among which the two most important indicators are silicon content and molecular weight. In a sense, choosing the appropriate organic silicon leveling agent is choosing organic silicon compounds with appropriate silicon content and molecular weight. When choosing leveling agents, one can choose according to the specific performance requirements of the leveling agent in their own formula. While optimizing the required performance, attention should be paid to avoiding some common side effects to achieve balance.
