Ink-paper interactions and effect on print quality in inkjet printing

Abstract: This thesis concerns paper and ink interactions related to inkjet printing. Themain purpose of this work was to gain a deeper understanding in whichparameters control the flow of ink into papers and how the ink interacts with thepaper surface. The overall objective was to find key parameters to optimize theprint quality in inkjet printing. Characterization of paper-surfaces in terms of porosity, surface roughness andsurface energy was made. Objective and subjective measurements were used forprint quality evaluation. Light microscopy imaging and SEM was used to see howink interacts with the paper surface in a printed image. A high speed camera wasused to study the absorption of picolitre sized inkjet droplets into fine papers.An initial study on the effect of paper properties on print quality was made.Result indicated that there were small differences in print quality for pilot paperswith different composition (in a specific parameter window) and the commercialpaper COLORLOK® reproduced a noticeable high colour gamut compared to theother samples.Research was made to see how surface fixation can affect the print quality forprintouts made with pigmented ink. Surface fixation promotes retention of thepigmented colorant in the outermost surface layer of the paper and has beendenoted “colorant fixation” in this thesis.It was shown that applying colorant fixation onto a paper surface beforeprinting can increase the detail reproduction in a printed image. Differentconcentrations of calcium chloride were applied onto the paper surface on fullscaleproduced non-commercial papers. Test printing was made with a SoHo(Small office/Home office) printer using pigmented ink and results showed thatusing calcium chloride as surface treatment can lead to aggregation of pigments atthe surface resulting in a higher detail reproduction.Fast absorption of the carrier liquid into the paper and fast fixation ofcolourants on the surface is important in inkjet printing to avoid colour to colourbleeding. These demands will be more pronounced when the printing speedincreases. It is important to understand which parameters affect the absorption process tobe able to control the mechanisms and to optimize the print quality.A study of absorption of picolitre size inkjet droplets into fine paper was madein this work. Theoretical equations describing fluid absorption into capillaries weretested and compared with experimental results. The result showed that the timedependence in the Lucas-Washburn (L-W) equation fits fairly well to data whereasthe L-W equation overestimates the penetration depth.The results are directly applicable to paper and printing industry and can beused as a base for future studies of absorption of picolitre sized droplets intoporous materials and for studies of aggregation of colloidal particles on surfaces.