Ruediger Baur

Charge control agents and triboelectrically-adjusted pigments in electrophotographic toner

Abstract In electrophotographic printing systems the print quality is strongly influenced by charge control agents (CCAs) and organic pigments used in the toner (electronic ink). Quaternary ammonium salts as CCAs exhibit a large potential both for positive and negative applications. Their triboelectric efficiency could be adjusted by varying chemical constitution and controlling solid-state parameters. Organic pigments provide the color of the toner. Additionally, they exhibit a certain triboelectric influence depending on their chemical constitution and solid-state properties. Low electrostatic influence together with appropriate “coloristic properties” (tinctorial strength, shade, transparency) are necessary. A specially-designed yellow benzimidazolone pigment meets these requirements. Both toner key ingredients - CCAs and pigments - have to be optimally dispersed into the polymer matrix (so-called binder or resin) in order to develop their desired electrostatic and coloristic properties. Finally, they work together perfectly if the optimum coloristic and electrostatic properties are fulfilled and if the appropriate process conditions (dispersion) are employed.

Charge stabilizers: properties and applications

Abstract Besides the well known charge control agents (also called charge additives, charge assistants or charge directing agents) for the specific charging of matrix systems like electrophotographic toners, there is a class of compounds which is able to stabilize triboelectric charge. These agents are called charge stabilizers. In comparison with charge control agents, charge stabilizers show lower charging magnitude but higher long term charge stability. A charge stabilizer can be applied within a matrix system or as an external additive which is simply mixed with the system. Surprisingly it is capable of stabilizing both negative as well as positive charges when used in combination with charge control agents. Different examples for the application of a special polymeric charge stabilizer will be presented in this contribution as well as its use with different carrier systems as an external additive. Furthermore, a concept is briefly introduced to explain the way charge stabilizers may work.