Sub-micron silver wires on non-planar polymer substrates fabricated by thermal nanoimprint and back injection molding

Abstract

In back injection molding, a polymer film (most commonly a decorative label) is inserted into the mold and fused with the polymer product by injection of the polymer melt from behind. By placing a bendable film into a mold cavity and by injection of polymer melt, the film conforms to the outlines of the cavity, thus enabling the decoration of elements with non-planar surfaces. This technique allows for pre-patterning of films by a planar process, and then convert these into the surface skin of a non-planar molded part. In this research we demonstrate the integration of silver wires onto the surface of a curved polymer part. As an example, we used poly (methyl methacrylate) films of different thicknesses that were pre-structured with micrometer-sized V-grooves, filled with silver nanoparticle ink and placed into the cavity of a commercial injection molding tool. The effect of the back injection molding process on unfilled and filled V-grooves was evaluated for different process parameters. In most cases, the silver wires remained undamaged and their electrical conductivities remained essentially similar to those in planar films. The resulting surface-integrated silver wires were characterized by scanning electron microscopy and electrical resistivity measurements.

Keywords

• Printed flexible electronics
• Silver nanoparticles
• Conductive ink
• Nanoimprint lithography
• V-groove capillaries
• Back injection molding