Triboelectric charging control

Stricter control of particle size distribution improves powder handling (qv) and transport through the system, and appHcation efficiency. It also reduces blinding of the final filter (69). Additives have been developed which improve the triboelectric charging characteristics (70). 

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. 

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. 

The measurement of triboelectric charge generation is well known for its variability where relative humidity, surface contamination or abrasion, tress configuration, and other variables have to be strictly controlled. Even with the combing of up to five replicate tresses and five successive determinations, Lunn and Evans report a 95% confidence interval of 15%. The apparatus that Lunn and Evans used is shown in Figure 28. The insulated tress is combed with a hand-held insulated test comb, and after the appropriate number of strokes, the tress is released into a Faraday cage connected to an electrometer. The whole setup is enclosed in a box in which temperature and humidity are controlled. 

Control of triboelectric charging properties of polymers by chemical modification is the subject of a paper by Gibson, Bailey, and co-workers. The base polymer was a copolymer of styrene and butyl methacrylate. The latter comonomer units were subjected to aminolysis (ca. 30% conversion) with the 6-aminohexane derivatives RCCHjjjNHj, R = NHj, OH, H, and the resulting amino- and hydroxy-functional polymers were subjected to further reactions including acylation and coupling with dyes. 

Triboelectric separators for plastics have been described in detail (46,47). The separation efficiency in a triboelectric separator can be enhanced by adding media against which the components of the mixture will charge. As a result, random charging between the components of the mixture is reduced and controlled, and a predictable charging is achieved (47). 

A number of researchers have explored the use of triboelectric effects in measuring the properties of the pneumatic conveying systems [12, 13, 14]. Usually the researcher would like to eliminate these charges, but under controlled conditions they can be used to an advantage. Klinzing, et al. [15] have used a field probe that is both nonintrusive and effective in picking up the field variations in the flow of charged particles. 

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