The charged toner particles are first transferred in an electric field to a drum coated with a photo semiconductor. When the photo semiconductor is exposed to light, a latent image, in other words, areas of varying charge, is produced on the drum surface. To transfer the toner particles to the drum, a magnetic brush is used to bring these particles as close as possible to the photo semiconductor. The toner particles of two-component toners are located on the larger particles of the magnetic powder sticking to the brush. The magnetic powder is not transferred. The process can be controlled in such a way that toner particles are conveyed exclusively either to the exposed or to the unexposed regions of the drum. This forms the visible powder image. The dry toner is then transferred to another, more highly charged drum – the transfer drum. The paper is guided between the two rollers such that the dry toner is deposited in a targeted manner, and the powder on the paper is typically fixed at high temperature and pressure, once again using the rollers. The finished printout is thus produced.
Positively and Negatively Charged
Positively and negatively charged dry toners are available on the market. The underlying application process is similar in both cases. The dry toner is transferred to the paper by a non-contact process using electrical fields. The procedure is called non-impact printing.
During use, the dry toner is subject to mechanical stresses, for example, when mixing the toner and the magnetic powder in the charging process. Toners are also handled at different temperatures and air humidities. Throughout the application and under different ambient conditions, the dry toners and toner particles retain their clearly defined form, their outstanding flow properties and their triboelectric characteristics.
“We are able to customize the properties for the application by treating the surface with a wide range of silanes and siloxanes.”Dr. Ingmar Piglosiewicz Technical Marketing Manager for HDK®
This enables the toner additives to perform a range of functions. Silica as an “external additive” influences several properties, as lab manager Piglosiewicz explains: “hydrophobic silicas significantly reduce the moisture absorption of the toners. This enables the powder to remain free-flowing at any humidity and to retain its triboelectric chargeability. The printing process must function irrespective of the printing duration, temperature and air humidity.”
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