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Plasticomp has formulated long-fibre thermoplastic materials (LFT) that provide up to 70dB shielding in the megahertz and higher frequency ranges for parts and enclosures in consumer electronics.

Traditionally, engineering thermoplastics are painted with conductive films or filled with conductive and metallic additives to provide electro-static dissipation (ESD) and electro-magnetic interference shielding (EMI).

Conductive carbon fibre is a suitable additive.

To increase shielding efficiency, carbon fibres are often coated with metals such as nickel.

However, these materials only achieve EMI shielding efficiencies in the 30 to 40dB range.

Moreover, the reinforcing carbon fibres lose mechanical properties and shielding efficiencies drop precipitously with the lowering of part sectional thicknesses.

Altogether, additions of specialised nickel-coated carbon fibre and secondary operations involving conductive paint are cost prohibitive.

Plasticomp was recently approached with a set of requirements for EMI applications.

These parts had to possess a stiffness of 35GPa or higher, provide 50dB or better EMI shielding and possess a surface resistivity of 5ohms/square or lower.

There were restraints on unit costs as well.

Thicknesses varied in part sections and were 1.5mm or less.

To meet these challenging requirements, Plasticomp chose a systemic approach that included structural and mould flow analyses to select a long carbon-fibre nylon that was tested to 50-70dB shielding effectiveness.

The retention of long-fibre lengths in these thin parts and additives were principally responsible in creating a conductive network of the reinforcing fibres, thus affording the high shielding effectiveness, as well as the high stiffness.

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