A co-axial indirect transfer printing process technology applied to the production of flexible serpentine silver micro-nanowires

A co-axial indirect transfer printing technique is proposed for making serpentine silver micro-nanowires, which are suitable for the production of PET (Poly-Ethylene-Terephthalate) film circuits used in wearable devices. A tabletop co-axial indirect transfer printing system with Harmonic Cancellation Algorithms (HCA) is developed so that system vibration can be effectively suppressed while the diamond tool is performing simple harmony servo motion cutting. To obtain super fine serpentine silver micro-nanowires, a serpentine convex microrolling-tooth letterpress and wire transfer printing are designed on the same rolling system to minimize swaying errors. Various contact angles are created for silver paste by controlling the surface roughness of an in-situ ultra-precision cutting transfer roller. Silver paste can be smoothly transferred to the serpentine convex microrolling-tooth letterpress and then to the surface of PET film. Experimental results show that the consistent serpentine silver micro-nanowires with a wire-width of 35 µm and a wire-thickness of 1 µm can be transfer printed onto the PET film under a letterpress-width of 15 µm, a letterpress-gap of 1 µm, and a surface roughness of Ra 6 nm. Also, the transmittance of PET film can reach up to 89.9%. The maximum change in electrical resistance is merely 0.7% after the silver micro-nanowires on the PET film are subject to a test of 200 bending cycles. This technique features a high material use rate and low production costs. It is a high-precision, environment-friendly technical option for fast production of wearable devices.