Multi-Functional Optical Silicone-to-Thermoplastic Over-Molded Component for LED Lighting
Silicone optics have become quite well adopted in high end LED lamps & luminaires lighting applications, such as, e.g., automotive headlamps, outdoor streets, roadways and stadium as well as retails. Dow Silicones have largely contributed by demonstrating the benefits of silicones optics from various perspectives, such as, e.g., resistance to high heat and lumen fluxes, stability against UV radiation, high resistance against scratch and impact, good compression set, enhanced optics and free form lenses design capabilities, and opportunities to optimize manufacturing processes of optics at large volume industrial scales.
However, an area that was less explored until now was the possibilities to combine benefits of both thermoplastics and silicones in the design of optics for applications in LED lighting. Although over-molding of Liquid-Silicone-Rubber (LSR) on thermoplastics and composites, glass or metallic substrates is not new, Dow Silicones and Gaggione have decided to bring forwards this technology to the world of optics. The integration of silicone optics with thermosplatics enables to bring multiple functionalities into a single component with optimal performances: high grades optics – including accurate surface features, ingress protection (IP), impact protection (IK), rigidity, dimensional stability, and ease of assembling into LED lighting modules. The work presented here will describe how chemical adhesion of optical moldable silicones can be developed to a thermoplastic substrates, such as, e.g., polycarbonate (PC) or polybutylenetherephtalate (PBT) via an intermediate silicone coupling layer that is not impairing to the optical function of the assembly. Various scenari have been considered, taking into account variables and constraints dictated by injection molding processing for the over-molding steps and the mode of deposition of the intermediate silicone adhesive and coupling layer. The effect of thermoplastic pre-treatment, such as, e.g., UV or plasma will also be discussed with respect to their effects on adherence strength between the silicone optics and the thermoplastic substrates as well as their effects on surface chemistry and roughness.