Solubility, dispersion and carbon adsorption of a chromium hydroxyazo complex in a toner

Abstract

In recent years organic salts such as chromium azo dyes have been used as additive to impart desired surface (tribo) charging properties of electrophotographic toners.1-4 In this study we have prepared solid blends consisting of a chromium hydroxyazoaryl complex salt (T-37 dye), Cr[-OC10H6-NN-C6H3 (Cl)O-]2 [NH4], in a styrene-hutyl methacrylate copolymer containing carbon black powder. We characterized the blends to determine the bulk and interface concentrations of the salt, and relate it to the contact charge. The salt has limited solubility in the copolymer and in organic solvents. It dissolves up to 1.7 μmoles/g at a slow rate in the viscous polymer melt at 190 °C. Solid blends with the chromium complex salt in excess of this amount also contain undissolved aggregates of various sizes depending on the preparation conditions. The chromium complex salt also adsorbs on the surface of carbon black up to a monolayer coverage. The carbon efficiently extracts the salt out of THF, and extracts it slowly out of the viscous polymer melt. The toners (10 pm size powder) develop a negative charge on contact. The charge scales with the amount of chromium complex salt in the blend and further varies depending on the proportion of the salt which is solubilized, exists as undissoled aggregates or is adsorbed on carbon. The chromium complex salt which is adsorbed on carbon is deactivated for charging by the carbon surface.