Water-based flexographic ink with tamper detection fluorescence for security printing applications

Smart luminescent materials are widely used in anticounterfeiting for their exceptional features that are easy to authenticate, but hard to duplicate. In order to tackle authentication issues and tamper-proofing of printed documents, a new fluorophore, 2-(2-aminoethyl)− 5-hydroxy-1H-benzo[de]isoquinoline-1,3(2H)-dione (HNEDA) was prepared as a pigment to formulate an ink with unique security features for flexographic printing. The naphthalimide-based molecule obtained through an easy one-pot synthetic procedure was structurally characterised through spectral techniques. HNEDA displayed good thermal stability and photo-physical features. The flexo prints achieved using the water-based formulation of HNEDA on a UV dull paper substrate demonstrated yellow-orange fluorescence when viewed under ultraviolet light. Moreover, secondary security features were explored through the application of various solvents, acids, and bases on the print proofs. A unique phenomenon of penetrating fluorescence on the rear side of the printed substrate, which is difficult to forge but easy to authenticate was observed. This feature provides a distinctive and secure authentication mark to detect tampering in documents/cheques/banknotes etc. Further, the surface morphology analysis, abrasion resistance, colorimetric, and densitometry studies of the prints were also investigated. Furthermore, the p-type semiconducting property and high charge carrier mobility of the prints obtained on low-cost paper substrates using the water-based ink with HNEDA as the functional pigment showcased promising opportunities in secure flexible electronics.