A brief discussion on the history of defoaming agents
The development of modern science and technology has put forward high-quality and high-efficiency requirements for the coating industry. That is, water-based paints and solvent-based paints should use various additives in the formula, including additives that help the pigments to be moist and dispersed; there are additives that improve the storage stability of the finished paint, and there are additives that adjust the smooth appearance of the paint film; there are also Some additives that achieve special functions. Most of the above-mentioned additives are surfactants, which can change the surface tension of the paint, causing the paint itself to have internal factors that are prone to foaming or stabilize the foam.
Various high-speed mixers are required in the coating manufacturing process, such as three-roller machines, sand mills, and ball mills. Various methods used in coating, such as air spray, airless spray, roller coating, flow coating and shower coating, etc. During these processes, the free energy of the coating system will be increased to varying degrees and help generate foam, which is an external factor that generates foam.
In the paint industry, the foam problem of water-based latex paint is the most prominent, which is caused by its special formula and special production process. (1) Latex paint uses water as the diluent. During emulsion polymerization, a certain amount of emulsifier must be used to prepare a stable aqueous dispersion. The use of emulsifiers greatly reduces the surface tension of the emulsion system, which is the main reason for foaming. (2) The wetting agents and dispersants used to disperse pigments in latex paint are also substances that reduce the surface tension of the system and contribute to the generation and stability of foam. (3) The low viscosity of latex paint makes it difficult to construct. The use of thickeners thickens the film wall of the foam and increases its elasticity, making the foam stable and difficult to eliminate. (4) Extraction of free monomers when producing emulsion; adjustment, dispersion and stirring when preparing latex paint; spraying, brushing, roller and other operations during the construction process.
All of these can change the free energy of the system to varying degrees and promote the generation of foam. The foam problem of latex paint makes production operations difficult. The air in the foam will not only hinder the dispersion of pigments or fillers, but also cause insufficient utilization of equipment and affect output; multiple fillings are required due to foam during canning. The bubbles left in the paint film during construction cause surface defects, which not only damages the appearance, but also affects the anti-corrosion and weather resistance of the paint film.
