A series hydrophobic silicas have been synthesized by reacting normal alcohols with hydrophilic fumed silica A130 (16-nm) at high temperature. Elemental analysis, solvent washing study and IR analysis suggest that alcohols molecules are grafted onto the silica surface. A rough estimation from the elemental data reveals that the surface area that is accessible for alcohol grafting is ∼ 4% and the grafting process is independent of the chain length of the normal alcohol. Water wetting tests indicate that the synthesized silicas are hydrophobic. Charging studies of the alcohol grafted silicas in unpigmented SPAR (a polyester) toner reveal that they generally charge to a higher charge level at both low (20%) and high (80%) relative humidity (RH). The charging process appears to be less humidity sensitive as compared to analogous, commercially available hydrophobic silica, e.g., R972, from Degussa. The length of the grafting group is shown to affect the charging performance and the molecular origin is proposed and discussed. Two strategies to further improve the charging performance of alcohol-grafted silicas were also studied in this work. We observed very similar charging levels and a reduction in humidity sensitivity when we grafted hydrophilic silica A130 with branched alcohols. We observed very interesting humidity effect when we modified a 1-dodecanol grafted A300 silica with 1-hexadecanol. Relatively speaking, the charge level of the modified silica is found to be lower than that of the unmodified grafted silica at 20% RH. The opposite is observed at 80% RH. This results in a developer that has very little humidity sensitivity in toner charging. The insensitivity of the toner charging process is rationalized.
K.-Y. Law, I. W. Tarnawskyj, "Effect of Alcohol Grafting on the Charging Characteristics of Silicas in Xerographic Toner" in Journal of Imaging Science and Technology, 1999, pp 300 - 305, https://doi.org/10.2352/J.ImagingSci.Technol.1999.43.3.art00019