Dispersant Choice

With any effective polymeric dispersant, the two-component structure is made up from a polymeric chain and a pigment affinic anchor group. The nature of the polymeric chain is critical to the performance of the dispersant. If the chains are not sufficiently solvated, they will collapse on to the pigment surface, allowing the particles to aggregate or flocculate. This need for compatibility with the medium extends throughout the final drying stages of any applied coating. Whereas if it ceases to be compatible, flocculation may occur leading to reduced gloss and tinctorial strength. In order to meet the need for good compatibility, different polymer chains can be used effectively, covering the variety of solvents encountered. The structure of some dispersing additives can be described as one or more spacially close anchor groups with a number of polymer chains. Other dispersing additives are designed to improve the flocculation resistance of pigments (non-polar, organic pigments) and have higher molecular weights through the attainment of more complex polymer like structures. The molecular weight of the dispersant is sufficient to provide polymer chains of optimum length to overcome Van der Waals forces of attraction between pigment particles. If the chains are too short, they will not be able to provide a sufficient thick barrier in order to prevent flocculation. This will inevitably lead to an increase in viscosity and a loss of tinctorial properties. Dispersant choice involves a number of criteria such as the nature of the pigment, the resin involved and the solvent which can all affect the performance of the polymeric additive.

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