Shielding coatings based on carbon–polymer composites

The protective coating against electromagnetic radiation (EMR) on the base of polymer composite filled with two types of graphite particles (ultra-disperse graphite C1 and graphite nanoplatelets — GNPs) had been prepared and investigated in the frequency range 25.5–37.5 GHz. The paint and epoxy resin were used as polymer matrix. The content of graphite filler in composite was 5–15 wt.% and composite layer was applied as a coating on polyethylene (PE) substrate. The small size of carbon fillers permits to prepare thin films of composites (beginning from 100 μm) on polyethylene substrate. The using of GNPs as filler in composite coating was found to be more promising for EMI shielding than the using of C1 graphite. The observed difference in the EMR shielding efficiency is related with the better electrical characteristics and low percolation threshold in polymer filled with GNPs (Ccr ≈ 5.43 wt.%) as compared with polymer containing conventional carbon fillers. The shielding efficiency SET increases with the content of graphite conductive component in CM coating and is equal to 8–10 dB for the composite layers 10 wt.%GNPs-epoxy (200–300 μm thick) on PE substrate. Good agreement between experimental and calculated within the model of double-layered medium data on SET for epoxy coatings with GNPs had been observed at the values of tan δ ranging within 0.15–0.28 and ε′ — within 17–35 for 5 and 10 wt.% of GNPs in CM-layer, respectively.