Leveling agent is a commonly used coating additive that can promote the formation of a flat, smooth, and uniform coating film during the drying and film-forming process of coatings. It is a common additive in paint construction. What is the function of leveling agent? Is leveling agent a hazardous material?
The function of leveling agent:
There are many types of leveling agents, and the types of leveling agents used in different coatings are also different. The commonly used leveling agent in oil-based coatings is acrylic polymer, which is usually used in solvent based coatings and powder coatings, especially in the production and application process of powder coatings. It is a necessary auxiliary agent. The commonly used leveling agent in water-based coatings is polyurethane, especially widely used in latex paints. Other leveling agents include organosilicon and associative alkali swelling leveling thickeners.
After coating application, there is a process of flow and drying to form a film, gradually forming a flat, smooth, and uniform coating. Whether the coating can achieve a smooth and even characteristic is called leveling. Shrinkage refers to the irregular, bowl shaped small depressions formed on the coating, which cause the coating to lose its flatness and often form a circular edge around a drop or small piece of impurities.
From the perspective of leveling, it is a special "point like" unevenness that occurs on the surface of the coating. Its shape can be divided into flat, volcano like, point like, exposed bottom like, bubble like, etc.
The synthesis of acrylic leveling agents generally involves the polymerization of butyl acrylate with amines and alkyl esters, with a polymerization temperature controlled at 80-90 ℃ and solvents such as toluene, xylene, cyclohexane, etc. The relative molecular weight of the polymer is controlled at 4000-10000. The narrower the molecular weight distribution, the better the leveling effect.
Acrylic leveling agents are mainly used in the production and construction process of powder coatings. Common leveling agents are used to improve the appearance of coatings, eliminate surface defects such as orange peel, shrinkage, pinholes, and shrinkage edges. Leveling agents eliminate surface defects in coatings by reducing or altering surface tension and interfacial tension, as well as promoting uniformity of surface tension during curing. A good leveling agent can reduce the melt viscosity of the system, thereby facilitating melt mixing and pigment dispersion, improving the wetting of the substrate, improving the flow and leveling of the coating, helping to remove surface defects, and facilitating air release.
In powder coatings, commonly used leveling agents include acrylic homopolymers and copolymers, as well as modified polydimethylsiloxane. However, polyacrylic acid ester leveling agents are less sensitive to excessive use and contamination compared to polydimethylsiloxane. Therefore, the popular system used in the coating industry is still acrylic polymer.
Organic silicone leveling agents can be used for oil-based coatings, and some varieties can also be used for water-based coatings. Due to poor compatibility with paint and its low surface tension, this type of leveling agent is prone to quality defects if used improperly or mixed improperly. In recent years, some additive manufacturers have made various modifications to organic silicon leveling agents, increasing their compatibility and application scope year by year. Also, due to its low dosage and significant effect. So, in terms of consumption and new product development, there may be significant growth in the use of organosilicon leveling agents in the future.
Polyurethane leveling agent is generally used for waterborne coatings, especially in systems containing lotion, which has both leveling and thickening properties. It is prepared by reacting polyepoxyethane with isocyanate and then fat modifying. At present, this leveling agent has been produced by many domestic auxiliary plants, some of which are equivalent to the foreign level. With the improvement of domestic auxiliary production level and variety, people's understanding of leveling agent is gradually improved, and the consumption will increase year by year.
It is also worth noting that many varieties of thickeners have a certain leveling property through fat modification or other means. For a given formulation system, suitable leveling agent varieties should be selected based on the properties of the formulation and the desired performance of the leveling agent, such as alkali swelling and binding thickeners, small molecular weight fat modified hydroxyethyl cellulose, etc.
