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Representation of the fiber distribution in the cross section of a plate.-(all images: KIMW) Representation of the fiber distribution in the cross section of a plate.-(all images: KIMW) Conductive plastics are considered promising materials for electromagnetic compatibility (EMC) applications because they combine the advantages of polymers with electrical conductivity. However, the high electrical resistance of the component surfaces remains a major challenge. The Plastics Institute Lüdenscheid (KIMW) is therefore investigating material concepts to improve surface conductivity as part of several research projects.
Compared to metallic materials, plastics offer advantages in terms of weight, production costs, CO₂ stability, recyclability and processing temperatures. to EMC applications, conductive compounds can basically achieve high electrical conductivity. In injection-molded, fiber-reinforced components, however, a multi-layer structure is created: While conductive fibers and particles combine predominantly in the core area to form a conductive network, the edge layer is dominated by the polymeric matrix and has a significantly reduce conductivity.
This inhomogeneous conductivity distribution can lead to EMC leaks, in particular in housings of several components. On the contact surfaces of the cover and the base body, the increased surface resistance can promote the penetration of electromagnetic waves.
Difference of conductivity by using metal alloy in edge and middle layer. Difference of conductivity by using metal alloy in edge and middle layer. Different material systems were therefore examined in three composite projects. Different plastics were utilized in combination with steel fibers, carbon fibers and nickel-plated carbon fibers as well as additives such as lead carbon, carbon nanostructures and copper-silver hybrid particles. The investigations confirmed a high conductivity in the interior of the components, however at the same time showed the dominant affect of the less conductive edge layers.
In the current joint project "EMV 4", the project group is pursuing a new approach. Low-melting metal alloys are introduced into the compounding process as additives. The alloys already melt at temperatures around 190 ° C and have an almost Newtonian flow behavior in the fluid state. As a result, they can increasingly reach the edge layer during the injection molding process and form a continuous conductive network there. The aim is to create a hybrid compound with as homogeneous conductivity as possible over the entire component cross-section.
According to KIMW, initial investigations show that with a carbon fiber reinforced polyamide compound, the conductivity of the edge layer could be increased by a factor of five compared to previous material systems. At the same time, the conductivity remained largely constant over the entire cross-section up to the core range.
In the further course of the project, additional plastic and fiber materials are to be examined. In addition, the project group deals with constructive solutions, including the integration of EMC seals by means of direct metal injections.
Interested companies are invited to join the project group and participate in the further research of this methodology.
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