Concentration Change
Unintended fluctuation in the ratio of non volatile components to the total weight of a liquid formulation occurs during extended production runs. Evaporation of water or solvents from an open ink fountain or a coating pan leads to a gradual increase in the density of the material. This solids content drift directly impacts the viscosity and the coat weight applied to the substrate.
Rheological Shift
Viscosity increases as the liquid phase disappears and the remaining particles are forced closer together. Managing solids content drift is necessary to maintain consistent color and drying speeds throughout a shift. Automated dosing systems often monitor the density of the fluid and add small amounts of water or solvent to compensate for the loss.
If the concentration rises too high, the coating may become too thick to level properly or might even plug the anilox cells in a flexographic press. Lowering the solids below the target level results in weak colors and potentially poor adhesion as the binder concentration becomes insufficient.
Stability Limit
Chemical balance of the mixture can be upset by the constant addition of fresh components. When solids content drift exceeds the tolerance of the formulation, the particles may begin to clump or settle out of the suspension.
