Living hinges for resilient and recyclable paper-based flexible printed electronics

• Published in: Flexible and printed electronics Vol. 9; no. 4; pp. 45006 - 45015
• Main Authors: Wu, Flora, Graddage, Neil, Lee, James, Griffin, Ryan
• Format: Journal Article
• Language: English
• Published: IOP Publishing 01.12.2024
• Subjects: flexible printed electronics; living hinge; paper-based; recyclable; smart packaging
• ISSN: 2058-8585; 2058-8585
• DOI: 10.1088/2058-8585/ad8935

The ability to fabricate electronics by printing has enabled an array of technologies that can create intelligent or smart packaging; however, this can come at the cost of recyclability. Selection of materials compatible with recycling streams is possible, such as paperboard and carbon inks, but there is a trade-off in terms of performance, flexibility and reliability. A major challenge for the use of paperboard is delamination and deformation when subject to small bend radii. The substrate has a tendency to crease when bent beyond a critical radius, which can fracture the surface and any traces printed onto it, causing device failure. We have demonstrated that the use of kerf cuts to form a living hinge, similar to that used in woodworking, can increase the flexibility of paperboard and allow reliable bending of conductive traces. We have identified the key design parameters of such a living hinge and evaluated their effect on the flexibility of a typical paperboard used in packaging. We then demonstrated that conductive traces of silver or carbon can withstand repeated bending with 100% reliability, compared to a worst case of 16% of control sample traces surviving the same test. Additionally, we demonstrated that the hinges improve the consistency of the trace resistance when subject to repeat bending. The behaviour of the resistance change as a function of bending was seen to be dependent upon the ink material, likely due to differing morphologies. We demonstrate the applicability of this technique in a smart device for medication adherence packaging.