Sensitive Detection of Pigment Particle Aggregation in Paints via Centrifugal Field-Flow Fractionation

Coatings add various functionalities to surfaces, providing a foundation for industries and society. In typical coating processes, pigment particles are dispersed in a resin solution with various additives, including thickeners and dispersants, and then applied to the surface, followed by drying and curing of the film. If pigment particle aggregation occurs during these steps, then the film quality degrades. However, an accurate assessment of pigment particle aggregation has been difficult because of the presence of large amounts of additives that are comparable in size to those of the pigment particles. Here, we investigated the use of centrifugal field-flow fractionation (CF3) to evaluate pigment particle aggregation in paints. Because CF3 classifies particles by mass, pigment particles are separated from the additives in a flow channel before detection, allowing for selective evaluation of particle aggregation. Carbon black particles were dispersed in water with different dispersants to produce two model paints. Despite having the same carbon black particle content, the paints showed different levels of darkness in the resulting films, as evidenced by the L* and Mc values. Although no sign of aggregation was observed between the two model paints using conventional dynamic light scattering, CF3 successfully detected aggregation in the paint with a lower darkness. Cryogenic transmission electron microscopy observations also confirmed the differences in the dispersion behavior of carbon black particles in the paint detected by CF3, validating the accuracy of the CF3-based evaluation. These results demonstrate that CF3 can be used as a simple and sensitive method to evaluate pigment particle aggregation in paints, which can lead to failure of the resulting films.