Charged area development

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 computer-controlled laser beam forms an image on a charged photosensitive drum. A carbon toner is applied and adheres to the charged areas, developing the image which is then transferred to the substrate and fixed with heat and pressure. Text, graphics and bar codes can all be produced this way. 

The most common form of gas sensor is based on a porous, sintered ceramic as shown schematically in Fig. 4.46. As adsorption occurs over the surface of the semiconductor grains, the barriers to charge transport develop, especially at the grain boundaries and at particle contact areas (the neck regions). 

For either conventional or digital xerography, the surface potential in the nonexposed and the latent image areas must be stable with time. The nonexposed areas must be stable for the time between charging and development and the exposed areas for the time between exposure and development (these are typically between 0.2 and 2 s). The need to determine latent image quality has resulted in the development of techniques to analyze both microscopic (Yarmchuck and Keefe, 1989, 1991) and macroscopic (Kogure, 1987 Miyasaka et al., 1991 Weiss et al.. 1996 Weiss and Young,... 

Figure 8 shows the xerographic process from the viewpoint of the toner. The material is fed into the development chamber, charged (usually by triboelectri-fication), and applied to the photoconductor surface. Powder which adheres to charged areas of the latent image is then transferred and fused to a sheet of paper or film the residue is cleaned off. Let us now consider these steps in greater detail. 

Ion deposition printers are used in similar circumstances, but their method of operation is different. A latent image is formed on a dielectric cylinder which is directly imaged by a projection of ions. Development is by a toner adhering to the charged areas and simultaneously transferred and fixed to the substrate under pressure. 

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