Flexographic ink film's resistance to inkjet ink's solvent flow in Hybrid Printing

Through Darcy's permeability coefficient, K, one can evaluate the resistance of a flexographic ink film to the solvent penetration of an inkjet ink through a paper substrate. This resistance plays an important role for the print quality in hybrid printing applications where flexography and inkjet printing are combined. If this resistance is too high, K→0, the inkjet ink's solvent would not penetrate into the substrate and ink smearing would occur resulting in poor printability.Paper substrates were printed in a flexographic laboratory printing press. The flexographic printing dot area was varied to evaluate the influence of the full tone and halftone areas on K. These print outs were employed as filters for pigmented inkjet water based inks in a filtration setup. The inks had different pigment's mean particle size which allowed us to address the influence of this parameter on the filter cake build up and consequently, its impact on K. The dot area had indeed an impact in the ink's solvent penetration as we observed that the higher the dot area, the lower the K value, meaning that the resistance for ink's solvent flow was higher. The pigment's mean particle size also showed influence on K, as we observed that the bigger the pigment particles, the higher the K.The substrates were selected after a screening based on inkjet ink absorption speed evaluated through a print rub off test and line width measurements of printed lines.We also printed the pre-printed flexography images using a KM 512 piezoelectric printing head and one of the inks used during filtration to evaluate the inkjet printing quality for this hybrid printing approach. We observed wider, less blurry and ragged lines with increased dot area. No ink smearing was observed for the print outs.