Molecular charge control agents (CCAs) of different physical states, ranging from molecular adsorption on the silica surface to particulate mixture with silica particles, were prepared by treating a hydrophobic silica (Aerosil R972 from Degussa), with various CCA coating solutions. The CCAs studied are 3,5-di-t-butylsalicylic acid (t-BSA), potassium bis(3,5-di-t-butylsalicylato)borate (LR120), and potassium tetraphenylborate (KTPB). The physical states of the CCAs in the silica samples are controlled by careful manipulation of the coating solvent (system). The models and assumptions used in the solution coating experiments are discussed and are verified in the case of t-BSA. Studies of the charging properties of the synthesized CCA-modified silicas in styrene-butadiene toner against a series of polymer-coated metal beads show that higher toner charges and shorter admix times are consistently obtained when the CCA is molecularly adsorbed on the silica surface. Since the surface area of the CCA is largest when it is molecularly adsorbed on the silica surface, the high toner charge obtained when these surface modified silicas is incorporated in toner is attributable to a surface area effect. The short admix time can also be attributed to the surface area effect, either due to the rapid charging or to the rapid charge exchange between CCA sites.
Kock-Yee Law, Ihor W. Tarnawskyj, "Effect of Coating Solvent on the Morphology and Charging Properties of Charge-Control-Agent-Modified Silicas in Toners" in Journal of Imaging Science and Technology, 1998, pp 577 - 583, https://doi.org/10.2352/J.ImagingSci.Technol.1998.42.6.art00018