Toner charging

Fig. 9. (a) Schematic of charged area development (CAD), using toner charged oppositely to that of the photoreceptor and resulting in a positive document (b) discharged area development (DAD), where the toner and photoreceptor polarity are the same, resulting in a negative document. 

A second adverse effect of van der Waals adhesion is a tendency of carrier and photoconductor surfaces to become coated with a thin film of toner residue—a film which progressively impairs the efficiency of toner charging and photoreceptor performance. Salaneck et al. (57) have reported that material transfer amounting to as little as 1 atom/10 surface sites is measurable as a shift in "triboelectric" charging behavior ... 

The electrophotographic system (102,103) involves two key physicochemical elements a photoreceptor and a toner. The minimum requirements of the process are (/) to charge a photoconductive photoreceptor uniformly (2) to illuminate selectively the photoreceptor to form a latent electrostatic image and (J) to develop the image by applying charged toner. These steps are illustrated in Figure 17. 

Liquid toners are suspensions of toner particles in a fluid carrier. The carrier is typically a hydrocarbon. Dielectric, chemical, and mechanical properties of the Hquid must be compatible with the photoreceptor, the suspended toner particles, and the materials of the development equipment. Liquid toners are capable of producing higher resolution than dry toners because of the smaller (3—5 -lm) particle size achievable. Development of the latent image occurs as it passes through a bath of toner and the charged particles are attracted to the oppositely charged surface. 

Triboelectricity. For development to occur, the toner particles must be reproducibly charged to the correct level and polarity for the specific photoreceptor. The phenomena of triboelectricity, which involves the transfer of charge from one soHd to another, are exceedingly complex, involving the surfaces of soHds and interaction of the surfaces with each other and with the ambient (52). Consequentiy, the specific experimental observations are highly sensitive to the nature and purity of the materials, the physical and chemical state of both surfaces, and the precise details of the experiments performed. 

Fig. 12. Charge-to-mass, /Af, distribution of individual (—) toner and (—) toner-carrier particles produced by milling. Particles are initially positively or...

Fig. 13. Two-component development involving competition between electrostatic and adhesive forces, where + outside and beneath the large circles represents the positively charged toner and the large circles containing negative signs represent carrier beads.

The electrostatic adhesive force is proportional to whereas the dispersion force F does not depend on the charge on the toner, and for a given set... 

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