Mechanism of coating leveling agent:
Leveling agent is a commonly used coating additive. After coating application, there is a flow and drying process to form a film, gradually forming a flat, smooth, and uniform coating. Whether the coating can achieve the characteristics of flatness and smoothness is called leveling. Shrinkage is one of the characteristic defects that occur during the leveling and film-forming process of coatings. In the actual construction process, due to poor leveling, there are brush marks during brushing, rolling marks during rolling, orange peel during spraying, shrinkage, pinholes, and sagging during drying, all of which are called poor leveling. These phenomena reduce the decorative and protective functions of the coating.
There are many factors that affect the leveling performance of coatings, including solvent evaporation gradient and solubility, surface tension of coatings, wet film thickness and surface tension gradient, rheological properties of coatings, construction technology and environment. Among them, the more important factors are the surface tension of coatings, the surface tension gradient generated by wet film during film formation, and the surface tension homogenization ability of wet film surface. Improving the leveling performance of coatings requires considering adjusting the formula and adding appropriate additives to give the coating a suitable surface tension and the ability to reduce surface tension gradients.
Types of paint leveling agents:
Paint leveling agents migrate to the surface of the paint film through limited compatibility, affecting surface properties such as interfacial tension, resulting in good leveling of the paint film. According to their different chemical structures, there are currently three main types of leveling agents: acrylic, fluorocarbon, and organosilicon.
1. Acrylic leveling agent
Acrylic leveling agents include pure acrylic leveling agents and modified acrylic leveling agents. Pure acrylic leveling agents include traditional non reactive acrylic leveling agents and novel reactive acrylic leveling agents containing tubular energy groups. This is a type of acrylic homopolymer or copolymer with varying molecular weights. These leveling agents only slightly reduce the surface tension of the coating, but can balance the difference in surface tension of the paint film and obtain a truly smooth, mirror like paint film surface. If the molecular weight is high enough, these leveling agents also have degassing and defoaming effects. The disadvantage of traditional non reactive acrylic leveling agents is that high molecular weight products may produce haze in the paint film, while low molecular weight products may reduce the surface hardness of the paint film. Acrylic leveling agents containing reactive functional groups can effectively solve this contradiction, providing good leveling performance without producing haze or reducing surface hardness, and sometimes even increasing surface hardness. The main types of modified acrylic leveling agents are fluorine modified acrylic leveling agents and phosphate modified acrylic leveling agents. Unlike pure acrylic leveling agents, modified acrylic leveling agents can significantly reduce the surface tension of coatings, resulting in good substrate wettability while maintaining leveling properties.
2. Fluorocarbon leveling agent
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.
3. Organic silicon leveling agent
Organic silicon leveling agents have two significant characteristics. One is to significantly reduce the surface tension of the coating, improve the substrate lubrication ability of the coating and the flowability of the paint film, eliminate Benard vortices, and prevent flower formation. The ability to reduce surface tension depends on its chemical structure. Another significant characteristic is the ability to improve the smoothness, anti scratch, and anti adhesion properties of the coating. The disadvantage of such leveling agents is that they tend to stabilize foam, affect the adhesion between layers, and some also pollute the construction environment, such as the oven. There are currently three main types of structures: polydimethylsiloxane, polymethylalkylsiloxane, and organic modified polysiloxane. Organic modified polysiloxane is more important, while pure polydimethylsiloxane is rarely used due to its poor compatibility with coating systems.
