Fabrication of hydrophobic optical diffuser film for LED lights through induction-aided hot embossing using micro-textured mold fabricated by μ-WEDM: parametric analysis, wettability study and optical characterization

Abstract

This study used an in-house designed induction-aided hot embossing (IHE) setup to make polymer-based hydrophobic optical diffuser film for LED lights. Negative-featured micron sized V-shaped grooves (Width and depth −300 μm, angle −60°, adjacent distance-500 μm) were fabricated on the mold to develop the micro-textured mold required for the hot embossing via μ-WEDM. In this study, polyethylene terephthalate (PET), polymethyl methacrylate (PMMA), and polycarbonate (PC) were used as working substrates. Initially, the parametric investigation was carried out by considering the four main parameters of IHE, i.e., embossing temperature-(Te), pressure-(Pe), duration-(te), and deembossing temperature-(Tde). Parametric analysis shows that the height of the embossed micron-sized V-shaped-grooves on the polymer substrate significantly affects the embossed diffuser film’s wettability and lighting efficiency. Embossed PC diffuser film showed the highest height, WCA, and illumination in all parametric investigations. Finally, PC diffuser film was made with the optimal IHE parameters: Te−225 °C, Pe−40 Kg cm−2, te−600 s, Tde−30 °C. This set of settings resulted in a maximum V-groove height of 273.35 ± 4.71 μm and a 94.52% replication rate. Illumination analysis of embossed PC diffuser film (171×102 (lux)) compared to traditional/bare film (71×102 (lux)) revealed a 137.5% percentile gain in illumination. A laser-based optical system was employed for optical characterization, and the X-direction diffused light length on the white screen was measured. The best diffused light length was 109.35 mm for embossed PC diffuser film. To compare plain and embossed diffuser film lighting effectiveness, RGB photos captured by CCD-RGB camera were converted to HSI images to determine hue, saturation, and intensity. The intensity dropped most with embossed PC diffuser film. It shows that embossed PC diffuser sheet diffuses light better. Finally, wettability study showed that all embossed diffuser film surfaces are hydrophobic. Embossed PC diffuser film had the highest WCA (95.3°) and 27.71% higher wettability than bare film.