electrical and electronic | LEDs
ideal alternative to aluminium in heat sinks. Even though conductive compounds have much lower conductivity than aluminium, this is not so critical in applications such as this where the distances over which the heat has to be conducted are very short, says DSM’s Meijers. Overall heat transfer in these devices is often limited by convective air flows, and not by conductivity. A product environmental study conducted by SABIC
in partnership with GreenOrder, a leading sustainability consulting firm, showed that LED heat sinks made with SABIC’s Konduit compounds in place of die-cast aluminum can typically avoid 87% of the energy consumed and greenhouse gas emitted during manu- facturing and fabrication. (Konduit compounds, original- ly developed by LNP and now produced by Sabic, were the first thermally conductive compounds commercially available and are based on polyamides and polyphe- nylene sulphide, PPS.) Heat sinks using the compound with aluminium inserts avoid 69-77% of the energy consumed and 67-78% of the greenhouse gas emitted, according to the study. TC compounds from other suppliers yield similar results. DSM offers TC compounds based on its Stanyl
polyamide 46. The polymer has very good heat resist- ance, and compounds heavily loaded with the various fillers needed for the application – graphite conductive filler (or possibly a mineral, which is less thermally conductive but is also less electrically conductive), flame retardant, and fibre reinforcement – still have good flow and mechanical properties. Meijers does not divulge the filler content of Stanyl TC compounds, but generally such compounds contain over 50% by weight of additives.
DSM says that with Stanyl TC, designers can reduce
weight of lamps, while increasing electrical safety and productivity in manufacturing. Total system costs can be reduced by up to 30-40% compared with cast aluminum. Stanyl TC is already used in a wide range products such a as reflector lamps, conventional bulbs and LED modules. Numerous polymer suppliers and independent
compounders now offer thermally conductive com- pounds based on various resins, including polyamides, thermoplastic polyesters, polyphenylene sulphide (PPS), and polycarbonate (PC). PolyOne’s Therma-Tech range is typical in including electrically conductive and insulating grades. Heat sinks, sockets and bulb holders all require thermally conductive materials, but they don’t all want electrically conductive ones. Available thermal conduc- tivities range from 1-21 W/mK in the in-plane direction and 1-7 W/mK for the through-plane direction. Neil Hardwick, Conductive Products Marketing
24 INJECTION WORLD | April 2013
Manager for another TC compound supplier, RTP, says that as a custom compounder, it has the ability to modify these compounds to meet the performance requirements of specific LED lighting applications. A variety of additives achieve in-plane thermal conductivity up to 35 W/mK and allow the compounds to be either electrically insulative or conductive. Additionally, UL94 flame retardancy, white colors with reflectivity greater than 95% and UV resistance can be included to optimize each formulation. Cool Polymers also offers thermally conductive
compounds. E-Series grades in its CoolPoly range conduct electricity, while D-Series grades are electrical isolators. Polycarbonate TC grades are available from
Bayer MaterialScience (BMS). At 40 W/mK, for example, Makrolon TC8060 has a thermal conductivity around one hundred times higher than standard grades of this polycarbonate. It also has a UL 94 V-0 flammability classification at 1.5 mm.
Focus of development Unlike conventional incandescent light bulbs, LED devices emit light in one direction. While this is beneficial for some applications, for many others it is desirable to spread or diffuse the light and avoid pinpoint light spots, such as for broad area lighting, accent lighting and signage/displays. This effect can be incorporated into either primary or secondary lenses, housing covers and other optical features. The key to this application is to balance hiding power with light transmission so as to produce soft, uniform light with little loss in luminescence. OnCap light diffusion additives from PolyOne are
available for commonly used lens materials. Effects are realized at a low dosing rate so that physical properties of the base lens material are maintained. As compared to pre-compounded diffusion grade lens materials, customers can customize LED special effects without maintaining separate inventory of base material, simplifying manufacturing and reduced lead times. For example, different levels of diffusion can be achieved as desired or the same level of diffusion can be provided even though lens thickness varies. In addition, colour, antistatic and/or UV stabilizer can be included in the same masterbatch to fully meet other objectives and aesthetics for the application. RTP also provides LED light-diffusion solutions for
applications that incorporate LEDs. It notes that colour correction can moderate colour variations among LEDs. Sabic’s Lexan Lux polycarbonate resins feature a choice of transparencies, including high clarity for
www.injectionworld.com
Netherlands- based Fonckel uses Sabic’s Lexan FXD
polycarbonate
for the diffuser in its One lamp design, which it welds to the
luminaire back cover
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