Influence of pearlescent pigments on light-fastness of water-based flexographic inks

Abstract

The objective of the research was to investigate whether the addition of pearlescent plate-like parallel orientated particles have any impact on the light-fastness of the ink layer. Nine different pearlescent pigments were used in the studies, among them five silver, three gold and one red. Different amounts of these pigments such as 5%, 15% and 25% were added to the water-based flexographic ink. The samples were printed on two different bases, non-absorbent PE activated foil and absorbent gloss coated paper base then accelerated light aged in the Suntest CPS + device. The L∗, a∗, b∗ colour coordinates were measured and ΔE∗ab colour difference was calculated for different stages of light exposure. The total exposure time was 72 h.The novelty of this research is that it was proved that the majority of pearlescent pigments tested based on mica coated with metal oxides improve the light-fastness parameter. In the case of gold pearlescent pigment tested in the research by as much as up to 45%. This behaviour was observed especially with the greatest amount of pearlescent pigment added to the ink base especially those with high amounts of iron oxide (Fe2O3) and titanium dioxide (TiO2) platelets. It was also proved that the size of pearlescent pigments impacts the light stability. This results may have an application in the ink manufacturing process.The improvement of ink light-fastness parameter due to the pearlescent pigment presence may be caused by its specific ability to reflect light thus it could be a form of protection for other colour pigments in the ink composition.