PC and PMMA components can be lighter and thinner than glass, and offer design flexibility. In addition, the components have been cost effectively scaled to production volumes using injection-molding processes. Relative to PMMA, polycarbonate benefits from greater heat resistance, higher impact strength and increased resistance to breakage. PC is also more flame-retardant. Benefits of PMMA over PC include its higher light transmission (> 92%) and better resistance to UV radiation.

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The project partners chose to use fiber-reinforced, thermosetting plastics that offer high-temperature resistance and high resistance to aggressive coolants. Unlike thermoplastics, thermosets do not swell when they come into contact with chemicals.

By dissipating the heat close to where it is generated, the project partners were able to construct the entire motor and housing from polymer materials, leading to further advantages. “Polymer housings are lightweight and easier to produce than aluminum housings. They also lend themselves to complex geometries without requiring post-processing, so we made some real savings on overall weight and cost,” Maertens says. The metal currently required as a heat conductor can be replaced by polymer materials, which have a low thermal conductivity compared to metals.

In order for polycarbonate to be used as a reflector, it can be colored or light-reflecting pigments can be added to the material. This produces a product that reflects light diffusely.

Special grades of PC have a light transmission in the visible-wavelength range just under 90%, but they absorb radiation in the UV as well as mid- and far-IR regions. UV exposure will damage standard grades of PC, resulting in an increasing yellowness that impairs the transparency of lenses and covers for lighting fixtures. To counter this phenomenon, a new infusion process has been developed to concentrate UV protection at the surface of PC products (see sidebar).

The two key components of an electric drive train are the electric motor and the battery. And there are three issues that play a particularly important role when it comes to using an electric motor for eco-friendly mobility: high power density, a compact configuration that fits snugly within the electric vehicle, and high levels of efficiency. As part of the DEmiL project – a German acronym that stands for directly-cooled electric motor with integrated lightweight housing – researchers at Fraunhofer ICT in Pfinztal are now working with the Institute of Vehicle System Technology (FAST) and the Institute of Electrical Engineering (ETI) at Karlsruhe Institute of Technology KIT to develop a novel approach that incorporates direct cooling of the stator and rotor. “An electric motor consists of a rotating rotor and a static stator. The stator contains the copper windings that the electricity flows through – and this is where the majority of electrical losses occur. The novel aspects of our new concept lie in the stator,” says Robert Maertens, a researcher at Fraunhofer ICT.

Stephen has been with PlasticsToday and its preceding publications Modern Plastics and Injection Molding since 1992, throughout this time based in the Asia Pacific region, including stints in Japan, Australia, and his current location Singapore. His current beat focuses on automotive. Stephen is an avid folding bicycle rider, often taking his bike on overseas business trips, and is a proud dachshund owner.

Polycarbonate lenses represent a current area of research and development. At Bayer’s Technical Service Center in Leverkusen, Germany, it is testing collimator lenses (Fig. 6), typically focusing lenses with free-form surfaces and asymmetrical geometries. One target application is automotive LED headlamps using a single-lens design. Today, LED headlamps are comprised of several separate components that are heavier than polycarbonate-based lenses.

Advanced polycarbonate materials can bring desirable properties to LED lamp and luminaires, including design flexibility, low weight and UV protection. To date, indoor LED troffers, alternative heat sinks and LED street-light covers have been optimized using these materials.

Electric motors have a high efficiency of over 90 percent, which means that a high proportion of the electrical energy is converted into mechanical energy. The remaining 10 percent or so of the electrical energy is lost in the form of heat. To prevent the motor from overheating, the heat in the stator is currently conducted through a metal housing to a cooling sleeve filled with cold water. In this project, the team of researchers have replaced the round wire with rectangular flat wire that can be wound more tightly in the stator. This creates more space for the cooling channel next to the flat wire winding phases. “In this optimized design, the heat losses can be dissipated through the cooling channel inside the stator, eliminating the need to transport the heat through the metal housing to an exterior cooling sleeve. In fact, you no longer need a cooling sleeve at all in this concept. It offers other benefits, too, including lower thermal inertia and higher continuous output from the motor,” says Maertens, explaining some of the advantages of the new system. In addition, the new design incorporates a rotor cooling solution that also allows the rotor’s heat loss to be dissipated directly within the motor.

To further optimize the injection-molding process, modeling of the multi-layer process makes it possible to calculate the necessary adjustment of temperature-dependent factors that impact component quality, such as warpage, shrinkage, stresses, and creep behavior. The next step will involve the use of simulation to fully optimize PC component quality.

PC grades can also be optimized for flame-retardant characteristics. For example, TerraGlo’s Alba Series of luminaires (Fig. 3) are designed with the driver circuitry and LED board underneath the fixture enclosure. As a result, the fixtures needed an enclosure material that was rated to the flammability standard UL94 5VA. The company selected a 3-mm transparent lens cover made from Makrolon FR7087 polycarbonate. The material has been tested by UL including glow-wire flammability and ignition testing.

The polymer housing is produced in an automated injection molding process. The cycle time for manufacturing the prototypes is currently four minutes. The stators themselves are overmolded with a thermally conductive epoxy resin molding compound in a transfer molding process. The team of researchers chose a design and manufacturing process for the electric motor that will allow it to be mass-produced.

Reflector films can also be produced with appropriate additives. Makrofol LM 327 polycarbonate, for example, is just 250-µm thick and easy to thermoform, yet its light reflection is ≥ 97% (based on ASTM E 1331, against a white background). Diffuser and reflector films have great potential for use in the backlight units of LCDs (Fig. 4).

A cross-sectional view of the electric motor. The core of the motor is a stator consisting of twelve individual teeth, which are wound upright using a flat wire.

The team has already completed the stator assembly and experimentally validated the cooling concept. "We used an electrical current to introduce the amount of heat in the copper windings that would be generated in real operation according to the simulation. We found that we can already dissipate over 80 percent of the expected heat losses. And we already have some promising approaches for dealing with the remaining heat losses of just under 20 percent, for example by optimizing the flow of coolant. We are now at the stage of assembling the rotors and will soon be able to operate the motor on the test bench at the Institute of Electrical Engineering and validate it in real operation,” says Maertens, summing up the project’s current status.

Light-directing films can also be made of polycarbonate. The required effect is achieved using a finely impressed grid of lines that also ensures good homogenization of the light. Applications include transparent covers for strip lighting and LED tubes. A newer application for PC films involves light-extraction films for organic LED (OLED) panels.

The increasing adoption of LED lighting creates applications for polycarbonates that were previously the preserve of materials such as glass and metal. For instance, because LEDs emit “cold” light without infrared (IR) radiation, thermal stress on the lamp components is reduced, making it possible to replace glass lenses with those made of transparent thermoplastics, most notably polycarbonate and polymethyl methacrylate (PMMA). PC and PMMA have already been applied to LED lamps and luminaires, especially as parts of housings or transparent covers.

An additional advantage to PC-based diffuser components is that they can provide a single-piece alternative to multi-component film and lens systems, thereby simplifying lamp assembly.

As PC grades are optimized further for specific applications, increased design flexibility will be brought to the makers of LED replacement lamps and luminaires.

Market demand for energy-efficient lighting solutions has been rising rapidly, and LED lighting products are the focus for the next-generation of fixtures in architectural, commercial, industrial, and residential lighting. New materials are playing a pivotal role in the optimization of these LED replacement lamps and outdoor fixtures (Fig. 1), driven by the specific thermal and mechanical needs of LED lighting.

Making electric cars lighter also entails reducing the weight of the batteries and electric motors used as their motive force. One way to achieve motor lightweighting is by constructing it from fiber-reinforced plastics. Researchers at Germany’s Fraunhofer Institute for Chemical Technology ICT are working together with the Karlsruhe Institute of Technology KIT to develop a new cooling concept that will enable polymers to be used as motor housing materials. This is not the only advantage of the new cooling concept: it also significantly increases the power density and efficiency of the motor compared to the current state-of-the-art designs.

If directed light from the LED source is required, a thin layer of metal can be applied to the surface of an injection-molded component. For example, the Makrolon and Bayblend (a blend of polycarbonate and acrylonitrile-butadiene-styrene copolymer) grades can reflect up to 95% of the incident light in such applications.

The diffusing effect is measured by using a goniophotometer to determine the half-value angle as defined in DIN 58161. This corresponds to the reflecting angle at which the luminance has fallen to half the light intensity passing through in a straight line from the diffuser component. The larger the half-value angle, the higher the light diffusion.

When PC is used for heat sinks there is greater design flexibility than can be accomplished using aluminum. Components with non-traditional shapes and more complex geometry can be fabricated. With injection molding, the heat sinks also can be lighter and don't require rework.

In many cases, it can make sense not to use injection molding to make PC components for LED lamps and luminaires, but rather semi-finished products such as thin films or sheets.

Multi-layer injection molding can result in improved component quality, lower yellowness index and less transmission loss. There are fewer defects such as shrinkage-related sink marks, for example, because a greater proportion of the shrinkage takes place during the premolding step. In addition, lower injection pressures result in lower internal stresses.

PC grades with high thermal conductivity have been developed to act as heat sinks in LED retrofit lamps. For example, at the Strategies in Light show in February, Bayer MaterialScience demonstrated a functional PAR30 LED replacement lamp with a PC heat sink and PC lens. The TC8060 PC features a thermal conductivity of 22 W/mK. The material is flame-retardant, complying with UL 94 V-0 rating at a thickness of 2.5 mm.

If PC is to be used in LED lenses, its optical properties must remain unchanged after long-term exposure to LED light. Testing has been performed on 4-mm thick polycarbonate lenses exposed to commercial LED lighting with an intensity of 46 lumens per square centimeter for over 6000 hours at 90°C. Light transmission, clouding and yellowing values (yellowness index, ASTM E 313) changed little under these conditions.

Solid polycarbonate diffuser sheets are compatible with flat cover designs. In some cases, modification of the color temperature is also possible. For instance, The Makrolon DX warm diffuser sheets convert cool LED light to a warmer light with a transmission of over 70%. The half-value angle is very high at more than 50°, which means that thin diffuser elements can be made. Possible applications of diffuser plates include large covers for LED street lights (Fig. 5), smaller LED indoor lamps and LED billboards or signposts.

PC reflectors can be more cost effective than metal reflectors, which often require expensive, time-consuming processes such as vacuum coating or wet-chemical electroplating. As with diffusers, additional cost reduction can result from designing the reflector and adjacent components into a single component.