Charge control agent

There are two types of colored molecule that are used in the toner, namely the colorant and the charge control agent (CCA). The colorant is used to impart color to the toner whereas the CCA is used to help impart and especially control the triboelectric charge on the toner particles. 

Charge control agents (CCAs) can be either colored or colorless and are mainly metal complex dyes rather than pigments. Colored CCAs are more effective than colorless CCAs but, because of their color, are restricted to black toners. Colorless CCAs are needed for yellow, magenta, and cyan toners. 

A powder coating is the result of the application of a powder binder system, which generally consists of a resin, a crosslinker, flow additives, degassing agents, pigments or dyes, charge control agents, etc. Such a binder system is ap-pHed to the substrate as a fine, extruded powder (Fig. 20, step A), then melted at... 

Figure 2.38 Some examples of charge control agents (CCAs).

Boron complex (charge control agent) 2 Quinacridone master batch (pigment) 12... 

In this experiment the optical and electrical transients were recorded simultaneously for a dispersion containing relatively high particle concentration. The current-time curve reveals that in the initial movement, two species transit the cell at different times. Clearly both cannot be due to the movement of the particles across the cell the simultaneous optical measurement demonstrates that the motion of the charged particles is contributing only to the second maximum. The first peak is due to excess ions in the suspension, presumably the charge control agent which is put in specifically to assure proper charging of the suspended particles. 

Frictional Forces. Dyes have been designed to produce an electrostatic charge when frictional forces are applied. Such dyes, known as charge-control agents, are used in the toners for photocopiers and laser printers to both produce and regulate the triboelectric charge on the toner particles. 

Let us list the interfaces which govern the behavior of such a system. The first one is that which exists between the pigment and its medium polymeric dispersants and charge control agents are used to stabilize the suspension, and to assure that particles which are not illuminated will follow the field to the positive transparent electrode. Exposure in the strong electric field applied in the imaging zone generates hole-electron pairs within the phthalocyanine. The electrons are injected into the fluid, captured by impurities, and carried off towards the tin oxide electrode in the form of ions. 

When the electric field E in the colloid is uniform, the conductivities can be simply determined from the measured current densities I, as a = I/E. The transition from LC into the IC regime can be somewhat arbitrarily set at a, = 10- n lm-l LC colloids can be prepared by chemical attachment to the particles of charge control agent (cca) or other ionizable species or by irreversible physical adsorption of cca onto particle surfaces. Typical physically adsorbed colloids will have some cca remaining in solution at dynamic equilibrium and, as a result, will fall generally into the category of IC colloids. 

Figure 7. Typical adsorption isotherm of charge control agent on oxide particles in nonaqueous media. Key and O, atomic absorption electrical conductivity A, IR absorption and ,... 

Figure 8. Dependence of average particle size on the concentration of charge control agent in nonaqueous media.

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