Electromagnetic interference metal fillers

More recently, several novel conductive plastics have been introduced to provide shielding against electromagnetic interference (EMI). Filler and reinforcing materials contending for these applications include carbon fibers metallized mitrospheres aluminum fibers, flakes, and ribbon and aluminum-metallized glass fibers. 

Conductive composites are obtained when powered metal fillers, metal flakes, or metal-plated fillers are added to resins. These composites have been used to produce forming tools for the aircraft industry and to overcome electromagnetic interference in office machines. 

Some fillers impart specialist secondary functions to the polymer. Glass in the form of fibres, flakes and hollow microbaUoons or microspheres has been used to fill polymers (Walker and Shashoua, 1996). Metal flakes or powdered metals are used as fillers in electrically conductive plastics, which are used to overcome electromagnetic interference in office equipment. Carbon-filled polymers are good conductors of electricity and heat. 

To obtain the lowest electrical volume resistivities (in the 10 to 10 ohm-cm range) and the lowest contact resistances, polymer resins must be highly Ailed with 70-80% by weight (25-30% by volume) of metal particles and must be thoroughly cured. Silver and silver alloys are the most widely used fillers but, in specific applications, other metal fillers including gold, copper, nickel, and even carbon are used. Carbon-filled polymers are often used to dissipate static electricity or to protect from electromagnetic interference (EMI). 

Electrical Conductivity. This quality is important to bleed off static charge and to avoid electromagnetic interference (EMI) (Sec. 5.9). It can be produced by adding carbon black, graphite, and especially metallic fillers (Table 5.23). This requires particle-to-particle contact, so flakes are more efficient than simple powders, and fibers are most efficient of all (Table 5.24). 

EMS shields equipment that can produce electromagnetic interference (EMI) or that is affected by it (e.g., computers, television sets, telephones, etc.). Metal housings provide excellent shielding. However, conductive plastics offer lower part weight and greater facility of production. Very high conductivities have become achievable at low loading levels with some conductive metal fillers such as stainless steel fibers. 

On the electrical side, a variety of fillers may be used to produce statically-conductive plastics (metal powders), shielding of electromagnetic interference (carbon fibres) or magnetic composites (powdered Al/Ni alloys or barium ferrite). 

Keywords aluminum, automotive applications, carbon, conducting fillers, copper, cost, electromagnetic interference (EMI), electronic devices, fibers, flakes, metal, nickel, polyethersulfone (PES), safety, health and environment, solder-like alloys. 

Keywords antistatic, conductivity, insulator, electric resistance, electromagnetic shielding, EMI, radio-frequency interference shielding, RFI, percolation, carbon black, carbon fiber, fillers, BET surface, metal-coated fibers, semiconductor, antistatic compounds, conductive fillers. 

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