The relationship between current density and applied DC electric field was measured for carbon black-polyethylene composite films which contain large amounts of carbon black by volume fraction (vr =c 0.16-0.28). The curves relating the current density to the applied DC electric field for the samples show clearly that, at first, the current densities increase in proportion to the applied DC electric fields and then, after the greatest values, they decrease and show negative resistance at high applied DC electric fields. The shapes of the curves are very sensitive to the volume fraction of the carbon black, to a previously applied DC voltage during the sample film molding, and to the density of the matrix polyethylene; yet there is almost no influence due to the particle size of the carbon black or to the melt index of the matrix polyethylene. This finding can be explained well by the tunneling of carriers across the barriers and the generation of Coulomb forces among the carbon black particles.

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