Measurements and dimensional scaling of spontaneous imbibition of inkjet droplets on paper

We investigate theoretically and experimentally the spontaneous imbibition of water based inkjet formulations utilizing paper capillary rise and imbibition of inkjet drops. We approximate the paper structure to a two dimensional anisotropic porous material, and using Darcy's law as a base, we derive dimensionless groups that scale drop imbibition. This derivation is based on a previous dimensional scaling of drop imbibition on thick isotropic porous material. We apply this scaling to a paper substrate by measuring the average drop imbibition rate, and perform paper capillary rise experiments to obtain the average system parameters required for the scaling. The results suggest that this approach is a valuable tool to predict drop imbibition rates on paper. We then continue and perform the same sets of experiments on a different paper with similar structure that is surface treated (surface sized) with CaCl2 salt, an additive that is known to improve print quality. We find that due to rapid aggregation of the colorant ink by the CaCl2, the imbibition rate is slowed down in the capillary rise experiments, i.e., on much larger scales compared to a single inkjet drop. However, the presence of CaCl2 has only minor effect over the average imbibition rates of single drops. Imbibition rates on the CaCl2 surface sized paper did not give adequate scaling as a result of the fact that the aggregation was not included the theoretical assumptions behind the scaling.
QC 20160407