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Thermally conductive thermoplastic polyester deployed in Audi lightweight LED lighting module

A heat-conducting Arnite XL-T grade from DSM Engineering Plastics based on a thermoplastic polyester has found commercial application in an LED/HID (high-intensity discharge) lamp lighting module used in the new Audi Q7's headlight. The superior performance of the grade, with a heat deflection temperature (HDT) of 250°C, low outgassing and excellent textured surface finish in dark colors reportedly offer designers and engineers extended freedom in headlight LED lamp module construction.

PlasticsToday Staff

September 17, 2015

2 Min Read
Thermally conductive thermoplastic polyester deployed in Audi lightweight LED lighting module

Headlights are a key distinguishing feature for a car's identity and currently LED lighting, with its excellent performance characteristics, is the cutting edge of automotive headlamp design. They are also a safety critical item and must perform to the highest international standards. LED, HID lamp and halogen lighting systems, often combined in one headlight assembly, offer excellent performance but also place more restrictions on the use of materials and design. Further, sunlight radiated into the multiple LED/HID lenses creates localized increases in thermal loadings in excess of 235°C.

Audi Q7 employs a thermally conductive polyester grade in its headlight module.

High sun loadings can cause heat distortion and outgassing of both functional and aesthetic components. To overcome this, exotic and expensive high performance polymers can be used or, alternatively, additional metal heat shields offer protection but add weight and cost as well as restricting design parameters.

Furthermore, components in the headlamp assembly such as the bezel, lensholders or frames can suffer from outgassing, become distorted, damaged or can even melt under such severe conditions. Aesthetic trim components extend the performance challenge in being able to meet the designer's requirement for exacting surface appearance in black or dark grey colors that increase the sun load issue.

Arnite has been used successfully for many years in lighting and many other automotive electrical and electronic applications that demand high heat performance and low outgassing characteristics. Through extensive experience and application understanding, DSM has developed proprietary technology that has extended the thermal conductivity of Arnite XL-T to outperform high heat resistance thermoplastics such as polyether sulfone (PES), polyetherimides (PEI) and polyphthalamides (PPA) without the exotic price tag or other issues like critical processing and water absorption. A key benefit of Arnite XL-T is said to be its outstanding surface finish when textured, even in glass fiber reinforced grades/variations/options.

Sylvana Wetscher, of the ZKW Group, a global provider of premium light systems for motor vehicles based in Wieselburg, Austria said, "Arnite XL-T enables us to design LED lighting modules that meet all the design criteria set by our OEM customers who have recognized the advantages it offers for sunload issues. Together with our partner DSM, we have achieved the ultimate goal of meeting the functional requirements of the headlamp module as well as conquering the issues of heat distortion and outgassing, without complex and costly redesigns for metal inserts or additional heat shields. This has kept the overall weight to a minimum, contributing to improved fuel economy and reducing the vehicle's carbon footprint."

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