Wing T. Luu

Date of Award

12-2010

Level of Access Assigned by Author

Campus-Only Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemical Engineering

Advisor

Douglas W. Bousfield

Second Committee Member

Adriaan R.P. van Heiningen

Third Committee Member

Michael D. Mason

Abstract

The setting and transfer of water-based inks is important in processes such as flexographic and ink-jet printing. Changes in ink chemistry or paper surface properties can have a significant impact on print quality, but a fundamental understanding is not clear in the literature. The setting and transfer of water-based flexographic inks on various uncoated papers were reported as a function of ink formulation and paper surface energy. Inks formulated with different binders and co-solvents were characterized for viscosity, surface tension and filtration resistance. Paper surface energy was changed with alkyl ketene dimer (AKD) size in hexane and characterized by contact angles. Interactions of co-solvents with paper were studied using inverse gas chromatography. Papers were printed with a laboratory flexographic press at different ink volumes. A model for water absorption into paper was proposed that accounted for capillary flow, diffusion into fibers, and surface roughness of the paper. A new method to improve ink-jet printing using nano-fibrillated cellulose (NFC) was proposed. Ink transfer and print density decreased with AKD treatment for some inks, while minimal differences were seen for other inks even though the inks had similar viscosities and surface tensions. Filtration resistance of the inks was found to explain the results. The change in surface energy had a large effect on ink transfer and print density for inks with low filtercake resistance. For inks with high filtercake resistance, paper surface energy had no effect on ink transfer. Interactions between co-solvents with AKD were quantified by the Flory-Huggins X interaction parameter. The value of % for MIBK was smaller than isopropanol. The strong interaction between MIBK and AKD may explain the increased ink penetration and lower print density compared to inks formulated with isopropanol. The proposed model predicted absorption rates that were consistent with experimental data. The primary mechanism for water absorption in sized papers was fiber diffusion, but surface roughness contributed a significant value at short contact times. A combination of NFC and AKD gave higher print density and reduced print-through for ink-jet printing. Microscopy revealed that for papers without NFC ink droplets contracted on the AKD hydrophobic surface, giving poor area coverage.

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