No heated moods here: Heat conductive plastics for co-extruded linear LED lighting systems

Heat management is a crucial issue when designing and manufacturing LED light systems. Optimizing heat dissipation is essential to improving the light output and service life of LEDs and related electronic components. Temperature overloading is one of the main causes of failure in electronic circuitry. This is especially true when it comes to complex assemblies.

As such, choosing the right materials is key. Heat conductive plastics allow heat to flow more effectively, so that it can be drawn away from the heat source and contact surface.

ALBIS PLASTIC received a request from Gi Plast s.r.l., a manufacturer of plastic profiles for use in lighting technology, for a suitably heat-conductive material to use in replacing aluminum profiles with plastics-based LED light profiles in buses. A variety of products are currently available on the market for use in injection molding. With this particular application in linear LED lighting systems, however, co-extrusion is a well-established process, and the manufacturers were now looking for an appropriate heat-conductive grade that could be used in co-extrusion in combination with transparent or light-diffusing polycarbonate.

This specifications profile requires maximum possible thermal conductivity, good adhesion properties for co-extrusion, a smooth surface, and a high degree of impact resistance. At first glance, these properties seem like they could be combined into a single type—but the reality is just the opposite. “The plastics currently used in profile extrusion are all thermal insulators. So we were looking for an extrusion material, that combines the mutually influencing but in part, contradictory requirements,” explains Enrico Ghidi, President of Gi Plast s.r.l.

Increasing heat conductivity results in decreasing impact resistance, and also reduces surface quality, though extrudability remains guaranteed. On the other hand, improving impact resistance means lowering heat conductivity, which in turn has a positive effect on surface quality.

In response to this challenge, ALBIS developed extrusion grade that have heat conductivity ratings of 1.1 W/mK - 2.1 W/mK and are also suitable for co-extrusion. The material chosen was an ALCOM TC grade based on polycarbonate, whose temperature resistance and low moisture absorption fulfilled several other important considerations.

After the material had been selected, it underwent a series of comparison tests, and successfully outperformed competitor materials. The type selected won out due to its excellent adhesion to polycarbonate.However, there were additional requirements to cover as well, so the compound was then optimized to meet the customer’s specific requirements; subsequent extrusion trials proved successful.Finally, LED strips were mounted in the co-extruded profile . The important thing here was that no air got in between the plastic application and the LED strips. Air is an insulator, and would have resulted in heat not dissipating satisfactorily through the walls.

For this reason, with these types of projects, a final thermally conductive paste or thermally conductive film is used between the LED strips and the plastic profile. For comparison purposes: whereas heat-conductive film may have a thermal conductivity between 1 W/m K and 2.5 W /m K, air has a rating of just 0.02 W/m K.

Heat distribution across the surface (in plane) is key, as the greatest degree of heat conductivity can be achieved in the direction of flow. The fillers are packed close together in the direction of flow. The smaller the distance between the filling materials, the lower the proportion of plastic between them, thus minimizing its thermally insulating effect.

However, heat conductivity through plane (see graphic) is essential as well: in longitudinal cross section, fillers oriented through the wall mean greater polymer mass density transverse to the wall, which ultimately inhibits heat conductivity.

Moreover, when several heat sources (in this case, LEDs) are arranged close together, they can mutually influence one another in terms of heat dissipation.

As such, it is advisable to incorporate support ribs into the component design to provide better heat dissipation, provided that component size / available construction space permit. Ideally, the design would include such ribs on the thermal dissipative side.

Based on its findings during the product development process, ALBIS also developed a heat conductive compound that is suitable for extruding filaments for 3D printing. The ALCOM 3D product line is suitable for use in manufacturing the technical filaments used in the 3D printing process—among other things, for applications with requirements regarding thermal conductivity. This line of products combines the advantages of additive manufacturing with the sophisticated technical features the existing ALCOM portfolio offers. Their optimized formulations make these compounds suitable, for manufacturing filaments used in Fused Deposition Modeling (FDM). These technical properties open up new potential applications in areas such as the automotive industry and the E&E sector.

www.albis.com

Previously published in Plastverarbeiter in 11/2016

Author
Albis (UK) Ltd

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