Page 184 - Graphic Design and Print Production Fundamentals

172 Chapter 6. Imaging

Figure 6.8 Transfer

A more advanced method of transfer utilizes an intermediate transfer belt system. This is most common
on colour digital presses where four or more colours are transferred onto the belt before transferring the
complete image onto the sheet. Charge rollers beneath the belt, under each drum, pull off the developed
latent images of each separation directly onto the belt. In the transfer stage, a transfer charge roller
beneath the belt applies a negative charge to push the toner onto the sheet. A second roller, directly
beneath the first on the other side of the belt, applies pressure keeping the paper in contact with the
belt and aiding in transfer for more textured stocks. The lower roller may have a small positive charge
applied to it or may be grounded. Some systems can also alternate the charge applied to the transfer
charge roller to further aid toner application onto textured substrates.

After this stage, the sheet moves on to fusing where the toner permanently adheres to the substrate. The
next two stages described below are post-imaging steps that are necessary to prepare the drum surface
for the next print cycle.

Cleaning

After the transfer stage, some toner may be left behind on the surface of the drum. If left there, the
background of each successive print would slowly become darker and dirtier. To prevent this, a cleaning
blade removes any residual toner from the drum’s surface (see Figure 6.9). Some systems will recycle
this toner back to the developing unit, but mostly the waste toner is collected in a container for disposal.