SOME FACTORS INFLUENCING THE MORPHOLOGY OF FLEXO INK CALCIUM SOAP PARTICLES

The reaction between CaCl2 and various types of fatty acid soaps has b een studied by dynamic light scattering (DLS), transmission electron m icroscopy (TEM), light microscopy, and chemical analysis with regard t o 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 o f calcium to soap, the reaction between calcium and soap was found to be stoichiometric and reached equilibrium rapidly (< 4 min). Calcium s oap particles at low calcium to soap ratio (colloidally stable) were m ade and examined by TEM. Particles made with pure sodium oleate formed more regular structures with a narrow size distribution, whereas part icles made from soap mixtures (containing saturated and unsaturated fa tty acids) formed more amorphous structures of various sizes. The reac tion between a dispersed ink (flexo ink) and pre-made calcium soap par ticles was studied by light microscopy. The deposition of flexo ink on to the calcium soap particles was found to be very dependent on the fr ee calcium ion concentration in solution at 50 degrees C. At low calci um ion concentrations (< mmol/L), flexo ink did riot deposit onto the calcium soap particles, whereas at calcium concentrations between 1.5 and 4.4 mmol/L, several different aggregation processes (leading to di fferent structures) occurred in the mixture. The structures varied fro m small (< 50 mu m) homocoagulates of flexo ink to large (> 300 mu m) aggregates of flexo ink and calcium soap particles.