Coalescents

In aqueous coating formulations, coalescents play a crucial role. They facilitate film formation significantly below the polymer's minimum film forming temperature. This is achieved through the coalescing agent inducing swelling in the dispersed polymer particles, coupled with a slight reduction in the glass transition temperature. This combination enables the polymer particles to coalesce effectively. There's a common belief that coalescents remaining in the film post-formation can lead to diminished film properties, such as tackiness, blocking, and increased dirt pickup. However, in a well-formulated coating, the amount of coalescent used is very small. This minimal usage typically has little to no impact on the film's hardness. Generally, plasticizer loadings range from about 8 to 50%, while coalescent loadings are usually less than 8%, relative to the binder. Traditionally, high VOC coalescents were expected to evaporate from the film post-coalescence, thereby reinforcing the film's strength. In contrast, modern low VOC coalescents, often similar to commercial plasticizers, remain within the film and contribute to the film solids. Their optimized low-level usage ensures the film's integrity remains intact.