Enhancement of surface replication by gas assisted microinjection moulding.

Achieving perfect replication of micro- and nanostructured surfaces without creating sink marks in the parts is challenging. Therefore, gas assisted injection moulding (GAIM) was investigated as a method to enhance moulding quality in polypropylene, polymethylmethacrylate (PMMA) and thermoplastic polyurethane (TPU) parts. For all three polymers, the GAIM did not improve replication (depth ratios) of low aspect ratio microfeatures moulded using tooling with positive features, but did significantly enhance replication of higher aspect ratio trenches and tapered holes. The enhanced replication was attributed to better filling, and with the semicrystalline polymer, significantly less shrinkage. GAIM sometimes enhanced the edge definition of the features, and as expected, reduced sink marks in the polypropylene surfaces. [ABSTRACT FROM AUTHOR]