Water-based invisible green flexographic ink for anti-counterfeit applications

Developing chemical molecules with exceptional features as colorants in security inks for information storage has garnered significant research interest. In the quest of smart fluorescent pigments, a pyrene-based pigment- bis(pyren-1-ylmethylene)ethane-1,2-diamine (PDA), which exhibited mechanochromism feature was synthesized and characterized using spectral techniques. The feebly fluorescent pigment exhibited intense green fluorescence upon grinding, and reverted back to less-emissive state when heated and fumed. With PDA as pigment, the water-based flexographic ink formulation was coated on security paper and printed on boards, security and packaging papers. The printed substrates were invisible under day light and displayed green fluorescence upon excitation under UV light. The ink's gloss, lightfastness, colorimetric values and abrasion resistance suggested that PDA might be used as an invisible fluorescent ink with mechanochromic properties for security printing. An ink-less rewritable paper on which written letters and patterns using pressure can be easily erased upon suitable stimuli was developed showing real-life application in information security.