Office copiers and laser printers both use an electrostatic process to produce their image. Although the term photocopy is often used in relation to office copies it is actually inaccurate and refers to an older obsolete process.
This advice explains the technologies and their suitability for creating records for long-term retention.
Xerography, the most common photocopying process, uses the basic principles of static electricity to create an image on a sensitised surface and then transfer it to paper, as described below.
The laser printing process is very similar to the xerographic process. The major difference is that the exposure step for laser printers employs a laser beam to record the image onto the sensitised surface to form the latent electrostatic image.
A typical toner for both xerography and laser printing is composed of a heat-sensitive polymer, such as acrylic or styrene - or both, and a pigment such as carbon black.
Some toners may have an additive known as a 'carrier' added. A carrier is typically an iron powder, which may be coated with resin and is added to improve the ability of the toner to attach to the charged area of the paper. The presence of carriers in the image on paper may adversely affect the longevity of documents.
Full-colour photocopying uses the same principles as single-colour photocopying except that the process is repeated for each colour – yellow, magenta and cyan, and then black. That is, each colour is separately laid onto the paper.
The physical durability of a photocopy depends primarily on how well the toner adheres to the paper. Most copy machines ensure good adhesion but a poorly adjusted or malfunctioning machine may produce poorly adhered images which flake off or smudge.
Full-colour images are thicker than black toner images because they are composed of four distinct layers of toner. Consequently, adhesion is not as good, and the thicker layer is more prone to cracking and flaking during flexing or folding.
The durability of photocopied and laser-printed documents depends largely on the quality of the paper used, as well as the degree to which the paper and toner adhere after processing.
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