Print quality and the distribution of offset ink constituents in paper coatings.

Little is known about the distribution of offset ink components in coated paper, although this is likely to be critical to print quality. This work focused on two fundamental processes that cause differences in distribution of ink constituents into a coating structure during printing. In the first, adsorptive chromatographic fractionation, chemical components of an ink mixture separate on contact with the paper coating due to their different adsorption characters. These differences arise from coating pigment chemistry, surface area, and morphology variables. In the second, latex-oil diffusion, molecular movement due to a concentration gradient takes place as oil molecules penetrate into the polymer latex matrix. Our results indicated that adsorptive chromatographic fractionation, and the resulting distribution of ink constituents in a coating structure after printing, affected print quality parameters such as print gloss and density. Latex-oil diffusion and its constituents' distribution affected ink setting dynamics during printing, but did not influence print gloss or density. The inference is that adsorption onto the paper coating material surfaces delays permeation (sorption into the coating paper) of the slightly polar ink oils, hence delaying the concentration of solved ink resins on the ink-coating interface. Absorption through diffusion of ink oils by the paper coating latex internal matrix usually takes longer. In volumetric terms, it occurs away from the initial critical concentrating region of ink setting and cohesive ink tack build-up. Superimposed on these effects is the capillarity arising from the packing of pigments and binders. Application: Mills, converters, and printers can use the results from this study in optimizing the coating formulations for desired print quality, and in understanding how different coating chemistry changes the printing results. [ABSTRACT FROM AUTHOR]