A high thermally conductive plastic is making LEDs more efficient and cheaper

The fluorescent light bulb was seen as a key step in reducing the energy consumption of consumers. Yet as incandescent light bulbs were phased out, increasing concerns were raised over the items environmental credentials.

Compact fluorescent light bulbs contain mercury as a vapour inside the glass tubing. Most contain around 3–5mg per bulb though some now contain as little as 1mg. Despite the small amount, the mass disposal of these light bulbs in landfills and incinerators is releasing the poisonous substances in to the air or water ways, making its environmentally credential somewhat questionable.

However, just as one technology has been phased in, it is fast becoming usurped by a cleaner and more efficient technology. LEDs have since shown themselves as a contender for being the lighting choice of the future and their use is fast becoming more widespread.

LEDs are much more efficient than conventional incandescent and florescent bulbs. Nonetheless, they still emit some of their energy in the form of heat, which must be dissipated via cooling elements to ensure a high light yield and long service life for the lamps. For this reason, and because of almost unlimited potential applications, Covestro has been supporting the energy-efficient technology with a range of material solutions. It has developed a special polycarbonate Makrolon TC8030, the TC standing for ‘thermally conductive’, which has a high thermal conductivity of 20W/m.K, similar to that of aluminium.

“Compared to the aluminium typically used, this plastic offers both thermal conductivity and a high degree of design freedom,” said Axel Wetzchewald, head of marketing for LED applications in the Europe, Middle East, Africa and Latin America regions at Covestro.

To better exploit the technical possibilities of Makrolon TC8030, Covestro has entered into collaboration with Karelia University of Applied Sciences (UAS) and injection moulding specialists Vesuto Oy. The initial objective of the project was to use the plastic to create cooling elements for LED lights that can be manufactured by injection moulding. These were compared with cooling elements made from other polymer-based materials and the results show the polycarbonate comfortably dissipates the heat generated by the LEDs.

Wetzchewald explains: “In general, [LED producers] are looking for lightweight materials that are easily shaped and cost-effective to process.

“Lenses should be as transparent as possible, so that the LED light can be used to its full extent. Light-diffusing materials are often required for indoor applications such as lamp covers, so that nobody is blinded by glare from the point light sources. For cooling elements, on the other hand, thermal conductivity has a higher priority. This is where plastics have a good chance of replacing existing materials.”

Luminaire designers are also looking at the Makrolon DX thermoformable material to generate warm or cool colour hues. The polycarbonate is adjusted to enable high light diffusion and light transmission. The material can also be formed into a variety of shapes, have special textures on the material’s surface to aid diffusion, provide a matte or glossy appearance or protect against UV radiation, chemicals, wear or scratching.

Covestro has been developing its polycarbonate for LED lighting for some time which has led to the development of Makrolon granules and sheets as well as a Makrofol films.

Polycarbonate is the natural choice for this application, as it is crystal-clear, extremely robust and can withstand high temperatures. It is also easy to shape and can be processed using extrusion and injection moulding just as effectively as other polycarbonates. It can also use special additives to give it light-diffusing or thermally conductive characteristics.

But critically what advantage does polycarbonate offer over aluminium for the cooling elements? Wetzchewald explains: “It is either impossible, or extremely difficult, to manufacture cooling elements with complex shapes using aluminium. The die-casting method most commonly used in this process is also not as cost-effective as manufacturing using injection moulding.”

Wetzchewald goes on to explain that one current trend is to manufacture parts with multiple optical functions. In vogue in architecture at the moment are de-glaring office lighting and multiple optical functions. One example is the new Makrolon SX Shark sheet with its concave linear-shaped prismatic optic on one side and a glossy surface on the other. This geometry combines high light permeability with excellent light guidance to give optimal glare-free light for indoor applications, especially within the office environment.

“When you consider the high impact resistance and its outstanding fire performance, there are clear advantages over similar products made from other thermoplastics or glass,” says Wetzchewald.

Materials key to high-efficiency solar

DuPont Microcircuit Materials recently collaborated with REC on its high-efficiency TwinPeak solar panels. The metallisation grid of the solar cells powering the TwinPeak solar panels is made using DuPont Solamet PV76x photovoltaic metallisation paste, an advanced front side silver material designed specifically to enhance the Passivated Emitter Rear Cell (PERC), a technology that delivers significantly higher efficiency and results in greater power output from solar sources.

“REC have focused on optimising successive generations of materials and manufacturing technologies so that they work better together,” says Thomas Lin, global photovoltaics marketing manager, DuPont Microcircuit Materials. “DuPont continues to innovate with Solamet pastes and bring the latest advanced materials to help improve the power output of solar panels even further.”

REC produces more than 15 million panels a year, all with integrated manufacturing from polysilicon to wafers, cells, panels and turnkey solar solutions. Its REC TwinPeak Series solar panels feature half cut cells, split junction boxes, four bus bars and PERC technology, resulting in higher overall energy yield.

DuPont Solamet PV76x paste is the latest in a series of products designed to enable cutting-edge PERC technology. DuPont Solamet integrated metallisation solutions for PERC have been demonstrated in production to deliver more than 0.15% significant efficiency gains for both multi- and mono-crystalline silicon PERC solar cells.

Justin Cunningham

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