Replication of nanopits and nanopillars by roll-to-roll extrusion coating using a structured cooling roll

Abstract

This paper investigates a novel, very high throughput, roll-to-roll (R2R) process for nanostructuring of polymer foils, called R2R extrusion coating. It has the potential to accelerate the integration of nanostructured materials in consumer products for a variety of applications, including optical, technical, and functional surfaces and devices. In roll-to-roll extrusion coating, a molten polymer film is extruded through a flat die forming a melt curtain, and then laminated onto a carrier foil. The lamination occurs as the melt curtain is pressed between a cooling roller and a counter roller. By mounting a nanostructured metal shim on the surface of the cooling roller, the relief structure from the shim can be replicated onto a thermoplastic foil. Among the benefits of Poil, the process are availability of a wide range of commercial extruders, off-the-shelf extrusion grade polymers, functional additives, polymeric materials with good diffusion barrier properties, and the overall maturity of the technology [S. H. Ahn and L. J. Guo, Adv. Mater. 20, 2044 (2008)]. In this article, the authors demonstrate replication of nanopits and nanopillars with diameters between 40 and 120 nm and depth/height of 100 nm. The best replication was achieved in polypropylene, by running at high roller line-speed of 60 m/min, and high cooling roller temperature of 70 °C. Replication in other common polymers like polyethylene and polystyrene was not possible for the parameter range used for the investigation.