Digital

In the graphic workflow digital technologies were first introduced in prepress, then printing, then gradually throughout the production chain.

Printing is the area which is most representative of the shift from analog to digital technologies.

Any form of computerized printing is by definition digital. A personal printer which costs € 89 performs digital printing in the same way as the Ink Jet Web Press introduced in 2008 which prints 3,300 pages per minute.

This definition refers to digital production printing which, since 1993, has been offering an alternative to offset printing and other so-called "traditional" printing technologies, i.e. letterpress, screen printing, flexography, etc.

The major difference between "digital" or "non-impact" printing technologies and "traditional" or "impact" printing technologies lies in the nature of the image carrier.

For digital printing the image carrier consists of dots (or digits) which may vary from one page to another, and which are sent by a computer to a printing system. These dots are then translated into electrical impulses and toner transfer and ink droplets on the paper.

For impact printing technologies, the image carrier is produced once, e.g. on an offset plate or a flexo block, then fitted on a press, and duplicated thousands or millions of times on paper.

In 2010, digital printing technologies can be classified into two major categories:

1. - Electrophotographic (xerographic) digital presses,
2. - Inkjet digital presses.

Electrophotographic presses use laser to form an image on the surface of a photoconductive drum. The sensitized areas of the drum electrically attract ink particles (toner or electro-ink) which are then transferred onto the paper either directly or via an intermediate device. Toner is then fixed to the paper via a fusing process which combines pressure and heat. This technology is mature and particularly well-suited for printing short high-quality runs.

Inkjet printing consists in transferring ink from print heads directly to paper.
 This ever-changing technology is used on high-quality plotters, on large format printers, and on a new generation of printing presses – flatbed or continuous-feed – which combine very high speed and high printing quality.

Digital printing is perfectly suited for variable data printing, very short runs, and print on demand. All types of prints from labels to books may be digitally printed if the number of copies and the printing cost permit it compared to traditional printing.

By Patrick CAHUET, market expert and GRAPHITEC consultant