Impact of optical brightening agents on alkali-based inks in packaging: A comparative study on color accuracy

Abstract

Accurately assessing the color quality of printed products becomes intricate  when optical brightening agents (OBAs) are introduced in papers, as diverse interactions occur among different ink pigments and papers containing OBAs due to variations in ink formulation chemistries. Specifically, alkali-based pigments, commonly used as spot colors, are carefully formulated to ensure consistency across production batches. The presence of OBAs, which absorb ultraviolet light and emit it in the visible spectrum, significantly affects  color perception and accuracy on paper when interacting with these inks. This research marks an initial investigation into how OBAs in paper influence the color accuracy of five distinct alkali-based spot color paste inks using a Little Joe ink proofer. The research examines the physical, optical, and colorimetric  characteristics of two paper samples-one with OBA and one without- and analyzes the colorimetric changes occurring during the ink drying process. The results indicate that reflex blue, purple, and violet spot colors achieved acceptable delta E (ΔE₀₀) value of below 3 on non-OBA paper, with rubine red being on the borderline at 3.1 after 48 h. In contrast, purple, rhodamine red and violet achieved acceptable ΔE₀₀ below 3 on high OBA paper. The distinct behavior exhibited by certain inks led to the conclusion that achieving a consistent  proofing procedure across diverse alkali-based ink formulations is impractical.