Comparison of methods to assess pigment dispersion

Two inks made with different red pigments were evaluated by common methods to assess the degree of pigment dispersion. One pigment is more difficult to disperse than the other in the vehicle used. The five methods that could detect changes in dispersion with each pass over a three-roll mill were a light scattering particle size distribution analyzer, a NPIRI fineness of grind gauge, gloss, contrast ratio measurements, and rheology. The gloss and contrast ratio measurements could detect changes with each pass over a three-roll mill only with a significant reduction in pigment particle size.