Some factors influencing the morphology of flexo ink-calcium soap particles

The reaction between CaCl2 and various types of fatty acid soaps has been studied by dynamic light scattering (DLS), transmission electron microscopy (TEM), light microscopy, and chemical analysis with regard to the formation of colloidal particles and microscopic particles. The ratio of calcium to soap determines whether the particles formed small colloidally stable particles or larger precipitates. At high ratios of calcium to soap, the reaction between calcium and soap was found to be stoichiometric and reached equilibrium rapidly (<4 min). Calcium soap particles at low calcium to soap ratio (colloidally stable) were made and examined by TEM. Particles made with pure sodium oleate formed more regular structures with a narrow size distribution, whereas particles made from soap mixtures (containing saturated and unsaturated fatty acids) formed more amorphous structures of various sizes. The reaction between a dispersed ink (flexo ink) and premade calcium soap particles was studied by light microscopy. The deposition of flexo ink onto the calcium soap particles was found to be very dependent on the free calcium ion concentration in solution at 50°C. At low calcium ion concentrations (<1 mmol/L), flexo ink did not deposit onto the calcium soap particles, whereas at calcium concentrations between 1.5 and 4.4 mmol/L, several different aggregation processes (leading to different structures) occurred in the mixture. The structures varied from small (<50 μm) homocoagulates of flexo ink to large (>300 μm) aggregates of flexo ink and calcium soap particles.