Лако-красочные материалы — производство

Alkyd emulsions are among the major developments in alkyd resins in the past few decades. Water-reducible alkyds contain considerable amounts of co-solvents that contribute to VOCs in the final compo­sitions, while alkyd emulsions are aqueous alkyd resins with little, if any, VOCs. They are prepared by emulsification of alkyd resins in water using emulsifiers (surfactants) and are normally supplied at 40 to 55 % solid content. They are generally prepared by a phase inversion technique in which water is added progressively to the molten resin containing the emulsifiers. Initially, a water-in-oil type of emulsion is formed that subsequently inverts to an oil-in-water type when a suffi­cient amount of water is added. This phase change is characterized by reduced particle size, homodispersity and good rheology of the alkyd emulsion. The particle size may range from 0.5 pm to 15 pm. The small particle size is desirable for good storage stability and better gloss. Important factors in the process are the phase inversion temperature, manufacturing controls, and engineering aspects of the process, such as the stirring method and impeller design, which govern the overall shear exerted during the emulsification process. In formulating alkyd emulsions, careful selection of type and amount of surfactants is very important to optimize their properties and performance. In order to obtain satisfactory water resistance and drying behavior, the content of emulsifiers should be kept as low as possible while maintaining good emulsion stability. Polymeric non-ionic surfactants are often the choice over normal anionic surfactants, especially when they contain autoxidizable reactivity (reactive emulsifiers). Alkyd emulsions are used in architectural coatings, wood coatings, and to some extent, corrosion protection coatings. Recently, there has been considerable interest in alkyd emulsions for direct-to-metal coatings.