In general, a plastic film, such as a polyethylene terephthalate (PET) film, is widely used as a non-magnetic support for magnetic recording media. Such plastic films, however, have disadvantages in that they are readily electrostatically charged, thereby for example, causing dropout as a result of adhesion of dust.
In order to decrease the surface electric resistance of a magnetic recording tape, the use of a backing layer containing carbon black has been proposed.
However, the conventional backing layer formed by using only carbon black and a binder has disadvantages in that it is readily scratched and the formation of such scratches causes crumbling of the backing layer, thereby increasing drop out. Moreover, the coefficient of friction thereof is increased during repeated running.
For this reason, an abrasive agent is further added to the backing layer. However, since known abrasive agents, such as chromium oxide (Cr.sub.2 O.sub.3), alumina, silicon carbide, titanium carbide, silicon nitride, titanium nitride, and diamond are electrically non-conductive, the addition of such abrasive agents increases the surface electric resistance of the backing layer although it improves the running durability. The increase in the surface electric resistance, as described above, will lead to adhesion of dust, thereby, for example, increasing the drop out. If the amount of the added abrasive agent in the backing layer is decreased, the surface electric resistance thereof is decreased, but the durability deteriorates and the drop out is increased.
Accordingly, with conventional carbon black/binder/abrasive agent combinations, it has been very difficult to overcome both the problems of sufficient durability and surface electric resistance of the backing layer.