Electrically Conducting Rubber

In recent years the dangers and inconveniences arising from the presence of static electrical charges on rubber conveyor belts, rubber flooring, rubber-tired vehicles and the like, have aroused interest in the use of electrically conducting rubber as a means of minimizing the accumulation of static electricity. Conventional rubber compounds, which have electrical resistivities normally above 107 ohm-cm, and as high as 1014–1016 ohm-cm. for nonblack compositions, favor the accumulation of static charges. By using high loadings of channel black, the resistivity can be reduced considerably. If special types of carbon black are employed the resistivity can be reduced to a very low value ; in fact, the development of a compound with a resistivity of 1 ohm-cm. has been reported. A compound with a resistivity of about 10 ohm-cm., processible on ordinary factory-size rubber machinery, is described later in this paper. Rubber compounds with resistivities less than 107 ohm-cm. are generally grouped under the generic title of “electrically conducting rubbers”. The conduction of electricity through rubber-carbon black compositions is attributed to the ability of the carbon black to form chains of particles through the rubber. The formation of these chains depends on the particle size, crystal structure, and degree of dispersion of the black. The special types of black referred to above, termed conducting blacks, possess this ability for chain formation to an advanced degree. The work described below deals with the compounding of conducting rubbers, their application, and the methods used for testing. It appears under three main headings: measurement of resistivity; development of highly conducting rubber ; and development and testing of antistatic tires.