Pigment Dispersion Chemicals

High-molecular-weight polyacrylate and polyurethane-based dispersants with multiple anchor groups are most effective for organic pigments in waterborne systems. They provide steric stabilization around hydrophobic pigment surfaces, preventing flocculation. For carbon black, cationic or nonionic dispersants with amine groups offer strong surface affinity. The dispersant selection should be matched to the specific pigment surface chemistry and binder system.

Fineness of grind (FOG) is measured with a Hegman gauge (grindometer) — a steel block with tapered channels. The depth at which particles first appear corresponds to the grind fineness. Typical targets: architectural paints 40–60 µm (Hegman 4–5), industrial coatings 25–35 µm (Hegman 5.5–6), automotive coatings 10–15 µm (Hegman 7). Finer grind improves gloss, color development, and hiding power.

Flooding (uniform color shift) and floating (surface streaking) occur when pigments of different densities, particle sizes, or surface polarities separate in the wet film. Prevention strategies include: using compatible dispersants for each pigment, adding viscosity modifier to limit convection, selecting pigments with matched surface polarities, and pre-dispersing problem pigments separately before let-down into the base.