This is the fourth article in our series on additives, and will cover dispersants and surfactants used to stabilize pigments in coatings. Dispersion is the process where a non-soluble solid is suspended in a liquid and stabilized against settling, separation, agglomeration or aggregation. The concentration of solids in the liquid must be uniform during mixing. Once mixing is removed, the mixture must be stable. For paints and coatings, pigments are being dispersed into a resin/solvent matrix, and stability against settling, flooding, floating or flocculation is required.
Generally, pigments are divided into three main types: primary, extender and specialty. Primary pigments tend to be expensive and give coatings color and hiding. Extender pigments are added to control gloss, lower cost or influence other physical properties. Specialty pigments are added for a specific purpose and include anti-corrosive, effect pigments and nanoparticles. Since primary pigments tend to greatly affect the cost of a coating, using them optimally is necessary.