Page 149 - DLIS006_INFORMATION SOURCES AND SERVICES

Information Sources and Services

Notes 7.5.3 Copiers

Because a copier is a machine that reproduces copies directly from an original document, the
copies are commonly referred to as photocopies. While some machines must be fed (the copy
must be inserted into the machine), other machines can copy such documents as pages from
books when the original is laid on top of the machine.

The copying process, like photography, is based on the sensitivity of a surface (either in the
machine or in the copying paper or master) to light or heat radiation. The light or heat in the
machine reacts with chemicals, either in the machine or in the paper or master, to produce an
image. Dry-process copiers operate with dry chemicals only, while wet-process copiers operate
with liquid chemicals. Most copy machines today use a dry process, such as an electrostatic
process or thermography; while some older machines use a wet process, such as diffusion
transfer or stabilization. The diazo process can be either dry or wet.

Electrostatic Processes
There are two common electrostatic processes: the transfer process, also known as the xerographic
process, which is used in plain-paper copiers (PPCs), and the direct image process, also known
as the Electrofax process, which is used in coated-paper copiers (CPCs). A fine black powder,
called toner, forms the image on a copy made by either electrostatic process.
Figure 7.1: A Convenience Copier: The Xerox 660 Plain-paper Copier.
(Courtesy of Xerox Corporation)

Source: 210.46.97.180/zonghe/book/197-office%20procedure/chapter6.htm
In both electrostatic processes, the image is exposed to a photoconductor (hence the common
terminology of “photocopier”) to develop the image. In the PPCs, a coated metal plate or drum
serves as the photoconductor; in the CPCs, a special coating on the copy paper serves as the
photoconductor. CPCs generally produce better halftones (shaded areas) and sharp images, but
the coating on the paper is difficult to write on, and the paper is more expensive than that used
in the PPCs.

Thermographic Process

In thermography, a heat-sensitive sheet and the original arc exposed to infrared light. The
heat-sensitive sheet is placed on top of the original before both are inserted into the machine.

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