A comparison of reflectance properties on polymer micro-structured functional surface

In this study, a functional micro-structure surface has been developed as a combination of arrays of ridges. The scope of the surface is to achieve specific directional optical properties: that is, under constrained lighting, to maximize the reflectance from a certain viewing direction, and to minimize it from its horizontally orthogonal position, i.e. maximize the contrast between two horizontally orthogonal view positions at the same inclination. The sample is composed of 12 different anisotropic surfaces, designed as a combination of ridges defined by their pitch distance of 50, 75 and 100 μm, and their angle in respect to the surface of 5, 10, 15 and 20 degrees. The geometry was obtained by precision milling of a tool steel bar and replicated through silicone replica technology, in silicone thermoset material, and by hot embossing using Acrylonitrile Butadiene Styrene (ABS) thermoplastic material. Several colours of the silicone and of the ABS materials have been tested to characterize their influence on the reflectance. A digital microscope has been used as a gonioreflectometer to determine the directional surface reflectance of each surface at varying light and camera positions, allowing for determining optimum surface microstructure for maximizing contrast between two horizontally orthogonal views. This paper focuses on the optimum microstructure ridge parameters for maximizing orthogonal contrast on polymer replicas. The presented results show that the replication processes and the polymeric material have a strong impact on the contrast under constrained lightening. Specifically, the reflectance properties are strongly influenced by the geometry of the structure and by the colour. surface texture, anisotropic surface, hot embossing, sil icone replica