The characteristic of achieving a flat, smooth, and uniform coating after coating application is called leveling. Leveling is a very important issue in coating applications, as it affects the appearance and gloss of the coating. The additive that improves the leveling performance of coatings is leveling agent. Today, the editor of Jianyi Chemical will talk about the commonly used leveling agents, which can be divided into the following three types according to their composition.
(1) Leveling agent for modified polysiloxane
The main component is long-chain silicone resin with limited compatibility, which has the effect of controlling surface flow and improving leveling. In addition, silicone oil itself is a surfactant that can improve the wettability of the substrate, thereby enhancing its flowability. This type of leveling agent can strongly reduce the surface tension of the coating, improve the wettability of the coating to the substrate, and prevent shrinkage porosity; It can reduce the surface tension difference caused by solvent evaporation on the wet film surface, improve the surface flow state, and enable the coating to quickly level.
Organic silicon leveling agent is an important leveling agent. In any situation, organic silicon additives can reduce surface tension, enhance surface smoothness, especially avoid differences in surface tension, ensure surface leveling, and eliminate various defects. Organic silicon additives are derived from the basic structure of polydimethylsiloxane. Short chain organic silicon has good miscibility in coating systems and has the functions of improving flowability and low surface tension. Currently, diphenylpolysiloxane, methylphenylpolysiloxane, and organic modified siloxane are widely used.
(2) Long chain resin leveling agents with limited compatibility
The main component is long-chain resin with limited compatibility, which reduces the surface tension between the coating and the substrate and improves wettability. Due to its low molecular weight, it is not completely miscible with the resin in the coating, and its surface tension is low. It can seep out from the resin, wetting the coated object and eliminating gas molecules adsorbed on the solid surface of the coating as early as possible, thereby preventing surface defects in the coating film. Commonly used are acrylic homopolymers or copolymers, acetate cellulose, etc. They can reduce the surface tension between the coating and the substrate to a certain extent, improve wettability, and prevent shrinkage; And it can form a single-molecule layer on the surface of the coating to homogenize the surface tension of the coating, improve surface fluidity, suppress solvent evaporation rate, eliminate defects such as orange peel and brush marks, and make the coating smooth and flat.
(3) Leveling agent mainly composed of high boiling point solvents
This type of leveling agent can adjust the evaporation rate of the solvent, so that the coating has a relatively balanced evaporation rate and solubility during the drying process, preventing the flow of the coating from being hindered due to the rapid evaporation and high viscosity of the solvent, resulting in poor leveling. It can also prevent the shrinkage phenomenon caused by poor solubility and precipitation of the base material due to the rapid evaporation of the solvent. Common solvents are mainly composed of high boiling point solvent mixtures of aromatic hydrocarbons, ketones, esters, or multifunctional groups.
