Dynamics of Ink Gloss Influence of Latex Type Over a Range of Pigment Volume Concentration, 1998 Coating Conference Proceedings

The evolution of wet ink gloss of model pigmented latex coatings is recorded immediately after printing every 0.1 second and followed for 60 seconds. Two distinct types of latex are used: a latex that interacts with the ink vehicle components and a latex relatively inert to the ink vehicle components. The ink gloss dynamics of both latexes, interactive vs. non-interactive, mixed with three distinct spherical polystyrene pigment sizes, at five Pigment Volume Concentrations (PVC) are compared. In addition, the latex films with no pigment are tested. A novel gloss-meter device is used for the first time to investigate the influence of the latex type and latex level on the ink gloss dynamics.

The type of latex in the coating has a dramatic influence on the print gloss dynamics. For pure latex films, the interactive latex retards print gloss development at short times and results in low print gloss while the non-interactive latex allowed the development of significantly higher print gloss. When the non-interactive latex is combined with a plastic pigment that is also non-interactive with the ink, the print gloss develops at a faster rate and to a significantly higher level over a wide PVC range than the print gloss of the interactive latex. With the interactive latex coating, the print gloss is significantly lower and from the low PVC level increases slowly to a maximum before decreasing as the PVC increases further. With the non-interactive latex coating, the print gloss remains significantly higher over that of the interactive one and decreases as the PVC level increases. At highest PVC level, both latex types result in comparable results. At higher PVC levels, coatings with the smaller size pigment produce lower gloss compared to the larger pigment size.

Two different mechanisms seem to be responsible for stopping the leveling of the ink film defects and reducing the print gloss. The mobile phase of the ink (ink solvent and low molecular weight fraction of polymer) penetrates into the coating pore structure at very high PVC levels. At lower PVC levels, the ink mobile phase penetrates into latex binder due to diffusion. Both mechanisms play a role in determining the final print gloss. At any given PVC level, both mechanisms could play a role depending on the amount of latex binder present at the surface of the coating.