ADDITIVES | POLYAMIDES
Right: Radiator end tanks need improved hydrolysis resistant PAs to operate at today’s elevated temperatures
Right: A thermally conductive polymer heat sink designed to optimize performance
Below: PA with high thermal conductivity fillers can replace metal heat sinks but part designs must typically be re-examined
cells, Ascend’s Director of Technology Dr Steve Manning said in a presen- tation at AMI’s Performance Polyamides conference in Pitts- burgh in the US last year that combustion-engine technology is also advancing rapidly, with higher powertrain efficien- cy and reduced emissions leading to downsized engine compartments that have higher thermal loads and more limited cooling space. This requires increasing the operating temperature of the cooling system, in turn calling for materials for radiator end tanks, for example, that must display improved hydrolysis resistance. Polyamides are already handling challenging conditions, and PA66 (mostly glass reinforced but some with alternative fillers) is widely used in power train and cooling systems as well as other areas, said Manning. To meet the new performance specifications presented by increased operating tempera- tures, Ascend has devel- oped its Vydyne HR (which stands for hydroly- sis resistant) series of PA66 compounds using a combination of technolo- gies, including glass fibre reinforcement and additives. The new material’s properties are said to approach those of PPA (polyphthalamide) but offering better weld strength. With the trend to increased temperatures and tighter spaces, additives that make polyamides more thermally conductive are growing in impor- tance in automotive and E&E components, and they can be used to tackle the increasing problem of malfunction or recalls caused by overheated electronics—or even an overheated battery—in a car, said Péter Sebö, Head of Marketing and Market Development at HPF The Mineral Engi- neers (a division of Quarzwerke), in a recent
conference presentation. Polyamides with thermally conductive additives can be used to replace metal for parts such as heat sinks for LED lamps and covers for batteries in electrical vehicles, but Sebö said that it is not just a simple material swap. Redesign of the part is typically necessary to take advantage of heat convection to obtain the thermal performance required. That redesign process can often also result in improved part functional- ity, ease of assembly and lighter weight.
Integrated solutions Another key application for thermally conductive polyamides is in integrated circuitry, for example, in
molded interconnect devices (MIDs) used in micro E&E components such as sensors and switches. These tiny parts are injection moulded before a metallic path for electrical conductivity is added on the surface, usually by some form of selective metal plating. The plastic material must be thermally conductive but electrically isolating, while the thermal expansion of the polymer should be as low as possible to minimise the difference between it and the metallic part. This is essential to avoid breakage at the polymer-metal interface, according to Dr Oliver Frey, Head of the Compounding Department at Ensinger in Germany. Additives such as graphite, copper, boron
nitride, and aluminum oxide can add thermal conductivity, says Frey. The company has evaluated mineral and ceramic fillers for reducing the coefficient of thermal expansion (CTE) of PPA and found that these fillers can be effective, depending on the use temperature of the part. Some fillers, such as aluminum oxide, can increase thermal conductivity and at the same time reduce CTE. Polyamides modified with additives are also enabling hydrogen tanks for fuel cell electrical vehicles (FCVs). Although FCVs are currently a niche area, they are growing in interest in various countries. Japan, for example, aims to build nearly 160 hydrogen stations and get 40,000 FCVs on the
18 COMPOUNDING WORLD | February 2018
www.compoundingworld.com
PHOTO: FOTOLIA
PHOTO: ASCEND PERFORMANCE MATERIALS
PHOTO: LPKF/SIEMENS AUDIOLOGISCHE
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