François DE BUYL received his PhD in Organometallic Chemistry from University of Brussels, Belgium (1991) and an MSc in Advanced Material Sciences from University of Surrey, UK (2003). He joined Dow Corning Europe in 1991 and worked on various silicone based materials development and applications, such as, e.g., silicone sealant & adhesives, organosilanes, thermoplastics and rubbers reinforcements, coatings, before joining the Advanced Assembly Solution TS&D team, helping lighting and optical companies using silicone in their LED lamps and luminaires designs, with products such as, e.g., optical moldable silicones, thermal interface materials, adhesives and coatings for lighting fixtures protection and assembly.
Innovation in Water Purification Systems with UV-C LEDs and Silicone Optics
For more than a decade, silicone optical encapsulants have made possible to withstand the photo-thermal load of LEDs and to further accelerate the blue light revolution initiated by Nobel Prize winner Shuji Nakamura. The resistance of silicones against possible deterioration from ever increasing lumen flux density and heat has made recent innovative professional lighting solutions possible in applications such as, e.g. entertainments, sports halls, street and roadway lighting, architectural and industrial outdoors lighting as well as automotive lighting. Unleashing the benefits of silicones has inspired lighting fixtures developers to great new designs in so-called secondary optics applications.
In the present study, together with Philips Lighting we have further developed the concept using Dow Corning Moldable Silicone for application beyond lighting for illumination, such as, e.g., water and air sanitization systems. The quality of the water we drink and the air we breathe has a profound effect on our health and well-being. Households can purify their water by installing state of the art UV water purification systems developed by Philips Lighting using UV-C LEDs. Deep UV radiations can indeed inactivate bacteria, viruses and other micro-organisms in water in a cost-effective way, avoiding the use of chlorine. The small size of Philips UV-C module (see right picture below) provides a solution to disinfect water or air in places where relatively large conventional mercury discharge lamps are not practical. Examples of appliances where the UV-C LED module could be used are refrigerators, coffee machines, air humidifiers, drinking water fountains, ice makers, etc….
However, in order to design the most efficient and reliable water purification system, it was necessary to properly select the LED emitting at the appropriate wavelength and intensity in the deep UV region (<280nm), as well as selecting the appropriate material to fabricate optical lens capable of sustaining the exposure to UV-C radiations. Silicone lens molded by injection molding of Dow Corning MS-1003 (see left picture below) was found to be the most performing solution. The silicone lens made of this medium hardness (52 Shore A) optical grade moldable silicone have proven its performances after extensive testing completed by Philips Lighting team. Test results have confirmed that lenses made of MS-1003 have high transparency down to 270nm, and therefore does not deteriorate contrary to other optical materials such as, e.g., PC or PMMA. MS-1003 is also easy to use for designing and fabricating optical lenses in a cost-effective way by industrial injection molding process contrary to quartz lenses. The rubbery nature of optics made of MS-1003, as well as the high elasticity and high resistance against underwater immersion have demonstrated benefits for designing a water tight optic lens with negative draft angle, reliable against vibration and damp heat operating conditions, which therefore protect the whole UV-C LED and driving electronics. In addition, MS-1003 silicone lenses have a favorable health and safety profile that make them appropriate for food contact and drinking water applications.
Francois DE BUYL, Dow Corning Europe s.a., rue Jules Bordet, 7180 Seneffe, Belgium
Merlijn JANSSEN, Philips Lighting, ul. Kossaka 150, 64-920 Pila, Poland