In the last article we discussed high-speed dispersion. In this article we will continue the discussion on dispersion, this time using a quick screening method I developed using a dual axial centrifuge. This procedure saves time and allows significantly higher output. During the development of this process, I used a lab sandmill and high-speed disperser to make grinds, and compared the results to those made with the new method. The method was adjusted until results for several different dispersants coincided. Differences in tint strength and grinds were within error of the test.
Pigment dispersants are tested by adding standard or predicted amounts of dispersants to pigment/water or pigment/resin blends by varying the levels of dispersant with relation to the amount of pigment. Dispersant is added on a percent-actives basis with regard to the amount of pigment solids. These mixtures are subsequently dispersed using mechanical energy, with a high-speed blade for inorganic or extender pigments or a media mill for organic and carbon black pigments. The particle size of the mixture is then measured. When an optimal particle size is achieved, the viscosity of the grind is measured. The usage versus viscosity curve resulting from measurement of the viscosity of various levels of dispersant in a pigment identifies the potential of the molecule as a dispersant and the optimal level of dispersant.