Electronic devices and assemblies are getting smaller and more powerful. As a result, they generate more heat during operation that has to be dissipated. The demand for thermally conductive thermoplastics for housings therefore has risen sharply in recent years. LANXESS in response is putting together a new line of polyamide products called Durethan TC (thermally conductive) for the thermal management of devices. The first representatives of this line are two easy-flow polyamide 6 variations, which will be marketed in the future under the names Durethan BTC65 H3.0 EF and BTC75 H3.0 EF. Their high thermal conductivity is based on reinforcement with 65 and 75 percent of a special mineral. “Both materials display a very good balance between high thermal conductivity, outstanding mechanical properties and good processing behavior. They have since been successfully tested and approved by two international automotive suppliers and are poised for use in full-scale production,” explains Dr. Tobias Benighaus, Durethan product development specialist.
Alternative to compounds with boron nitride or aluminum oxide
The thermal conductivity of the two materials was determined by the Nanoflash test method. In the case of the polyamide with 65 percent mineral reinforcement, this value is 1.0 W/mK, or three times higher than that of Durethan BKV 30 H2.0, a polyamide 6 already established in industries such as automotive engineering. The material with a 75 percent mineral content tested at 1.5 W/mK, meaning it is even 4.7 times more conductive. The two materials conduct heat as efficiently as polyamides containing boron nitride or aluminum oxide as thermally conductive filler. “However, aluminum oxide systems have the disadvantage of being very abrasive, which quickly causes damage to the injection mold. Compared to boron nitride systems, our materials are significantly less expensive and have better mechanical properties. Furthermore, their thermal conductivity is not anisotropic, but virtually the same in all directions,” Benighaus says.
The materials also have the potential to replace pure metals. Compared to die-cast aluminum, housings can be fabricated from the two thermoplastics much more cost-efficiently, particularly in the case of high production volumes, and they yield more lightweight components. The precondition for substitutions of this kind is that the thermal conductivity of the metals is not fully utilized in these applications.
High tensile strength, elongation at break and impact resistance
The greatest advantage of these two innovative products is their good mechanical properties on par in some cases with those of Durethan BKV 30 H2.0 despite a high filler content. For example, Durethan BTC65 H3.0 EF is equally as stiff and displays a similar elongation at break of three percent. Its tensile strength is 90 MPa, which also is very high. “The Izod impact strength is excellent for a thermally conductive compound at 35 kJ/m2 and more than twice as high as in comparable polyamide compounds with aluminum oxide filler,” Benighaus explains. Furthermore, the mechanical property set of the polyamide 6 variation with 75 percent mineral reinforcement is superior to that of corresponding aluminum oxide compounds.
Wide processing window
The new, thermally conductive polyamides can be efficiently injection-molded in a wide processing window and a reliable process despite their high mineral content. Durethan BTC65 H3.0 EF, for instance, displays melt viscosities similar to those of the established compound Durethan DP BKV60 H2.0 EF, which already is used to fabricate numerous components, including thin-walled ones.
LANXESS (lanxess.com) is a leading specialty chemicals company with sales of EUR 9.1 billion in 2012 and roughly 17,500 employees in 31 countries. The company is currently represented at 52 production sites worldwide. The core business of LANXESS is the development, manufacturing and marketing of plastics, rubber, intermediates and specialty chemicals. LANXESS is a member of the leading sustainability indices Dow Jones Sustainability Index (DJSI) World and FTSE4Good as well as the Carbon Disclosure Leadership Index (CDLI).