Modeling inkjet dots from drop spreading, absorption and evaporation – An engineering approach

Spreading and absorption of small liquid drops on porous substrates is of interest in a number of fields ranging from additive manufacturing and composite processing to inkjet printing. In inkjet printing, spreading and absorption processes determine the final area of a printed dot, which is decisive for print quality in terms of coverage and resolution. However, it is not fully understood how substrate and liquid properties influence the involved physical processes and the resultant printed dot area. In this work, the printed dot area of overall 140 paper-liquid pairings representative for the operational window of an inkjet printer is evaluated. The results are explained by a simple model including spreading, absorption, and evaporation. The surface tension and viscosity of the liquids, as well as the pore size and polarity of the substrates were varied systematically to represent the range of uncoated paper-liquid pairings applicable for inkjet printing. Results show that the printed dot area mainly depends on the wettability of the liquid-substrate pairing followed by penetration speed. Evaporation and volume reduction due to roughness filling had little impact. The modeling results are in line with empirical observations showing that the dot area is closely related to the contact angle.