The leveling Principle of Silicone Leveling Agent

Mar 9, 2021

The leveling principle of silicone leveling agent: surface tension is the main driving force for the leveling of the coating film, but the poor surface tension is the main source of the surface defects of the coating film. Improve the surface tension of the coating film to achieve a balance of surface tension, which is very beneficial to the flow and leveling of the coating film, but it cannot be done. Therefore, people have to reduce the surface tension of the coating film to eliminate the difference in surface tension, control the surface state of the coating film, and eliminate surface defects.

Leveling principle
Surface tension is the main driving force for coating film leveling, but poor surface tension is the main source of coating film surface defects. Improve the surface tension of the coating film to achieve a balance of surface tension, which is very beneficial to the flow and leveling of the coating film, but it cannot be done. Therefore, people have to reduce the surface tension of the coating film to eliminate the difference in surface tension, control the surface state of the coating film, and eliminate surface defects. Such as eliminating the Benal vortex, preventing the production of flowers and orange peel. Eliminate the difference in surface tension gradient on the surface of the coating film, and prevent the generation of shrinkage holes and ripples. Reduce the interfacial tension between the coating and the substrate, enhance the spreadability of the coating, improve the adhesion, and reduce or eliminate the shrinkage caused by the substrate. Silicone oil and organically modified polysiloxane are a kind of surface condition control agent that has been used earlier and widely used in the coating industry, and can basically eliminate surface defects caused by poor surface tension.
The modification methods of organosilicon leveling agents are different, the modified materials are different, the structure is different, the molecular weight is different, and the application is also different. Therefore, pay attention to the following points when applying.

Choose leveling agent according to the problem
There is no "universal type" of silicon leveling agents that can solve any problems. If you choose improperly, it will bring negative effects. If you want to eliminate the difference in surface tension, it is best to choose a polyether-modified polysiloxane that reduces the surface tension, rather than an alkyl-modified polysiloxane. Requires high temperature baking. Can not choose polyether modified, to choose alkyl modified or polyester modified. It is required to have long-term smoothness and can not choose additive. It is necessary to choose reactive type, which requires improvement of interfacial relationship and reduction of interfacial tension. It is best to use a low molecular weight polyether-modified substrate wetting agent.

Foam stabilization
Almost reduce the surface tension, the stronger the leveling agent, the stronger the foam stability, especially the polyether-modified polysiloxane, it is easy to align at the air/liquid interface, and the air in the coating is leveled The agent "wrapped" and formed bubbles. Pay special attention to the application, you can choose unstable foam or low foam. MONENG-7003 is a product with low foam stability. Strongly reduce the surface tension and wet the substrate.

Thermal stability
When using in heating and solid-type coatings, you must pay attention to the heat resistance range of the leveling agent, and the baking temperature should be within the heat resistance range of the leveling agent, otherwise the leveling agent will decompose during overheating and baking, resulting in coating. The film has negative effects such as shrinkage, difficulty in recoating, and loss of gloss. Primer or secondary primer, it is best to use alkyl-modified polysiloxane that does not reduce surface tension, and topcoat can be polyester-modified polysiloxane that can be recoated
Other leveling agents

There are also fluorocarbons and high-boiling solvents. Fluorocarbon leveling agent has the highest surface activity and can reduce the surface tension of the coating to 16-18mN/m, so it has the strongest surface state control ability. In a nutshell, fluorocarbon leveling agents have all the functions of silicone leveling agents. Compared with silicone leveling agents, the ability to reduce surface tension is stronger and the effect of surface state control is better. But it also has its negative effects, like the adhesion between layers, and the foam stabilization is more difficult to overcome. Its price is also very expensive, which affects its application.

Solvent-based leveling agents are mostly mixtures of high-boiling solvents, and their main mechanism of action is to slow down the volatilization rate of solvents, reduce coating viscosity, and improve