The authors have recently proposed a novel charge-control mechanism that assumes an appreciable temperature increase at the "toner/carrier" interface due to the triboelectrification. In this model, the temperature dependence of the electrical conductivity of charge-control agents (CCAs) plays the crucial role. Therefore, electrical and thermal properties of azo-metal complexes used as CCAs have been investigated in order to provide additional evidence for our model as well as to study their high thermal stability. The electrical conductivity of a typical azo-Fe complex (i.e., T-77 from Hodogaya Chemical) is found to increase exponentially with temperature, and the value around 100° C is about two to three orders of magnitude higher than that at room temperature. This supports our charge-control mechanism. On the other hand, the structure analyses of T-77, sodium salt of T-77, and sodium salt of a Cr-complex revealed that there are intermolecular hydrogen-bond networks or coordination networks, in which each cation bridges neighboring anions. This type of network is found to be responsible for high thermal stability above 250° C.
Y. Sato, S. Ito, K. Uta, J. Mizuguchi, "Electrical and Thermal Properties of Azo-Metal Complexes used as Charge-Control Agents" in Journal of Imaging Science and Technology, 2009, pp 10504-1 - 10504-9, https://doi.org/10.2352/J.ImagingSci.Technol.(2009)53:1(010504)