In the coating, ink, adhesive and other industries, the flatness and glossiness of the coating are key factors that determine the appearance and performance of the product. However, during the curing process, liquid coatings often form defects such as orange peel, shrinkage, and brush marks due to problems such as uneven surface tension and differences in solvent evaporation rates. At this time, a chemical additive called a silicone leveling agent quietly appeared on the scene, playing the role of a "surface smoothing magician". This article will analyze the scientific mysteries behind this material from the perspective of principles, applications and future trends.
1. What is a silicone leveling agent?
Silicone leveling agents are a type of surfactant with polysiloxane as the core structure. By regulating the surface tension of the coating and improving the rheological properties, the liquid coating is evenly spread before curing, and finally a smooth, defect-free film layer is formed. Its molecules are usually composed of a hydrophobic siloxane main chain and a hydrophilic modified group (such as polyether, amino, epoxy, etc.), which has the functions of reducing surface tension and adjusting compatibility.
The core functions can be summarized in two points:
Eliminate surface defects: Reduce shrinkage holes, fish eyes and other problems caused by local tension differences in the coating.
Improve gloss and touch: By promoting uniform flow of the coating, a mirror-like smooth surface is formed.
For example, in the spraying of automotive topcoat, adding 0.1%~0.5% of silicone leveling agent can significantly reduce the orange peel phenomenon and make the paint surface smooth as a mirror.
2. Scientific principle: How to "iron" the coating surface?
The effectiveness of the leveling agent comes from its regulation of the surface tension and rheological behavior of the liquid coating. The specific mechanism is as follows:
1. Surface tension homogenization
When the coating is cured, the volatilization of the solvent will cause a surface tension gradient (such as high edge tension and low center tension), triggering "Bénard cells" and forming an orange peel texture. The silicone leveling agent quickly migrates to the coating surface, reduces the overall surface tension and eliminates the gradient difference, allowing the liquid to flow evenly.
2. Reduce interfacial resistance
The hydrophobic siloxane segments of the leveling agent tend to be distributed at the interface between the coating and the air, forming a low surface energy film, reducing the flow resistance inside the liquid and extending the "leveling time window" of the coating.
3. Compatibility balance
Through the compatibility of the hydrophilic group with the coating system, the leveling agent can prevent "foam stabilization" or "shrinkage" caused by excessive migration. For example, in UV-curing coatings, the leveling agent needs to be well compatible with the resin and monomer to avoid affecting the curing efficiency.
Comparison of typical phenomena:
Without adding leveling agent: the coating surface is uneven, with brush marks or shrinkage.
After adding leveling agent: the coating self-levels to form a smooth surface, and the glossiness is increased by 20%~50%.
