Printing of Ultra-thin Layers of Colloidal Inks using Nanoporous Stamps for High Resolution Flexography

There is a growing industrial need for manufacturing technologies that can print devices with high resolution (< 10 microns) and at high throughput. Conventional flexography is limited in resolution due to the instabilities in the ink loading and transfer mechanisms. A recent invention from our research group, engineered nanoporous stamps composed of polymer coated carbon nanotube (CNT) forests, are highly porous (>90%) and can retain the ink within their volume rather than on their surface only and has been used to print micron-scale features with highly uniform ink layer thickness (<100 nm). We conducted experiments using a custom-built printing apparatus which enables printing on flat and curved substrates by precisely controlling the force and printing speeds while observing the printing process in the time scales of milliseconds using a high magnification high speed imaging system. Using observations, we present the mechanics of spreading during contact and the evolution of a capillary liquid bridge which after rupture transfers liquid on a precursor film formed during contact. We study the influence of stamp design, ink properties, and printing speed on the ink transfer process, and present models to eludicate how printed layer thickness can be controlled precisely.