Types, action mechanism and application of leveling agent

Leveling agent is a kind of common coating additive, which can promote the coating to form a flat, smooth and even film in the process of drying and film formation With the improvement of coating appearance requirements, the amount and variety of leveling agent are increasing, and the consumption is increasing year by year According to the annual output of 5 million tons of various coatings in 2006, the average consumption is 2 ‰, and the annual consumption is about million tons There are many kinds of leveling agents, and the types of leveling agents used in different coatings are different The most commonly used leveling agent in oily coatings is acrylate polymer, which is usually used in solvent based coatings and powder coatings, especially in the production and application of powder coatings Polyurethane is the most commonly used leveling agent in waterborne coatings, especially in the middle and high-grade emulsion paint Other leveling agents include organosilicon and associated alkali swelling leveling thickeners The synthesis of acrylic acid leveling agent is generally initiated by polymerization of butyl acrylate with amines and alkyl esters The polymerization temperature of BPO and AIBN is generally controlled at 80-90 ℃ and the relative molecular weight of polymers such as toluene, xylene and cyclohexane is controlled at 4000-10000 The narrower the molecular weight distribution, the better the leveling effect Acrylic leveling agent is mainly used in the production and construction of powder coating Leveling agent is often used to improve the appearance of coating film and eliminate surface defects such as orange peel, shrinkage cavity, pinhole and shrinkage edge The leveling agent can reduce or change the surface tension and interface tension, and eliminate the surface defects of the film by promoting the surface tension homogenization during curing A high-quality leveling agent can reduce the melt viscosity of the system, which is helpful for melt mixing and pigment dispersion, improve the wettability of the substrate, improve the flow and leveling of the coating, help to remove surface defects and facilitate the release of air In powder coatings, the most commonly used leveling agents are acrylate homopolymer and copolymer and modified polysiloxane However, the sensitivity of polyacrylate leveling agent to excessive use and pollution is less than that of polysiloxane Therefore, acrylate polymer is still the most popular system in coating industry Organosilicon leveling agent can be used in oil-based coatings, some varieties can also be used in water-based coatings Due to the poor compatibility with the paint and its low surface tension, such as improper dosage or collocation, this kind of leveling agent is prone to quality defects In recent years, some auxiliary manufacturers have made various modifications to organosilicon leveling agent, which makes the compatibility increase and the application scope increase year by year And because of its small dosage and remarkable effect Therefore, in terms of consumption and development of new varieties, organosilicon leveling agents may have great development in the future Polyurethane leveling agent is generally used in waterborne coatings, especially in emulsion containing systems It has both leveling and thickening properties It is prepared by reacting polyoxirane with isocyanate and then modifying it with fat At present, there are many auxiliaries in China, and some of them are quite similar to those abroad The awareness of Pingji is gradually improved, and the consumption will increase year by year In addition, it is worth noting that many kinds of thickeners have certain leveling property through fat modification or other means Such as alkali swelling Association thickener, small molecular weight fat modified hydroxyethyl cellulose, etc