Influences of micro-ridges orientation and position on the replication of micro-structured surfaces by injection molding

In this work, directional optical properties were achieved with a microstructure composed of a close array of ridges, defined by their width and by the angle with respect to the main surface. Under constrained lighting, the reflectance was maximized from a certain viewing angle and direction, and minimized from its horizontally orthogonal position. The purpose was generating quick response codes (i.e. Data matrix) that could be easily scanned by means of commercially available software. The ridges were 1.2 mm long, 0.2 mm wide and with a 10° slope angle, for a depth of about 0.03 mm. Each code was defined by 10x10 modules, each composed of 6 ridges. The code was machined on a tool insert and replicated by means of Injection Moulding. This study investigated the effect of the ridge orientation with respect to flow front and the effect of the distance from the gate The inserts have then been replicated using Acrylonitrile butadiene styrene (ABS). Inserts and replicates were characterized using a Olympus Lext OLS4100 Laser Confocal microscope. Values of height, slope and roughness of the milled ridges and their replicates have been measured. The results showed that ridges parallel to the flow on the replicates had better replication accuracy and that, contrary to the expectations, ridges closer to the gate were replicated worse than the micro-structures far from the gate.