Page 182 - Graphic Design and Print Production Fundamentals

170 Chapter 6. Imaging

Figure 6.5 Charge roller

Exposure

A laser is used to write the image onto the charged surface (see Figure 6.6). Because the photosensitive
coating on the drum becomes conductive when exposed to light, the charges on the surface of the drum
exposed to the laser conduct to the base layer, which is connected to a ground. The result is a near zero
volt image and a negative background. This is known as the latent image.

Figure 6.6 Exposure

Development

Many digital printers and presses use a dual component development system (see Figure 6.7). The
developer is a mixture of non-magnetic toner and a magnetic carrier. As the developer is stirred and
the particles rub up against each other, a triboelectric charge is generated between the them. The toner
becomes negatively charged while the carrier becomes positive. The opposite charges cause the toner to
be attracted to the carrier. A magnetic development roller holds the mostly iron carrier in alignment with
magnetic lines of force forming a magnetic brush. This magnetic brush in turn ‘carries’ the attracted
toner to the surface of the drum. A high negative bias is applied to the development roller repelling the