Eco-friendly flexographic ink from fluorene-based Schiff base pigment for anti-counterfeiting and printed electronics applications

The challenge to prevent the counterfeiting of documents and the development of flexible printed electronics are two thrust research areas that demand innovative techniques. This study reports the use of fluorene-based Schiff base (FBH) prepared via a simple, one-step and cost-effective method as a thermally stable and biocompatible pigment for environment-friendly, water-based flexographic ink for potential application in security printing and flexible printed electronics. The flexo ink coating and print on the UV dull security paper were invisible in the daylight but displayed bluish-green fluorescence under UV light. Moreover, the emission colour of the print was sensitive to changing pH, which further imparted the eco-friendly ink formulation an excellent covert perfor-mance that could be exploited for anti-counterfeit application. The functional ink formulation can also be smartly-utilized in stamp/ink pads to obtain invisible fingerprint for detecting forgery. The colorimetric, and densitometry studies, abrasion resistance and surface morphology analysis of both the coated and printed paper samples were also investigated. The electrical measurements of the prints on flexible and low-cost paper sub-strates with good mechanical properties exhibited high charge carrier mobility with p-type semiconductivity for use in organic printed transistors. This new functional ink could thus be a promising candidate for anti-counterfeiting applications, including food packaging, documents, labels and ink pads, as well as in secure printed electronics.

Automated summary

The study introduces the use of FBH pigment for eco-friendly flexographic ink, which displayed bluish-green fluorescence under UV light, making it suitable for security printing and flexible printed electronics. The ink formulation also showed excellent covert performance, especially with invisible fingerprint detection for forgery prevention.