Text 6 Modern printing techniques

Thermography In this process the image is first printed in the normal way by letterpress or offset using an adhesive ink. The ink image is then coated with a resmous (thermoplastic) powder and the surplus is shaken off (from the non-image areas). The printed sheets are subjected to heat, which fuses the thermoplastic resin with the ink to give a hard, raised image. The result is glossy and simulates the results of copper engraving, but is coarser and much cheaper. It is commonly used for invitations, business cards and letterheads,

Duplicating This process is used mainly in offices, rather than by commercial printers, to produce circulars, forms, price lists and other items with runs of perhaps a few hundred where quality is not a paramount consideration. The quality of duplicators has greatly improved, giving a much sharper, cleaner result, but is still inferior to offset duplicating.

'Offset duplicators' are, in fact, true offset machines and are called duplicators simply because they are small and used for short runs of black-and-white work.

Xerography This process gave its name to 'Xerox' - the photocopier manufacturer which developed the process commercially. It works by utilizing the physics of electrostatics: particles of matter that are charged negatively and positively are attracted to their opposites.

The modern development of the process uses a variation of the offset principle. The toner is deposited electrostatically on a selenium drum or belt which then prints on to plain paper. The process is also used to make plates for small offset machines.

This process has developed in a dramatic way in the last few years: the quality has improved to near-offset standard, speeds have increased to 7,000 copies per hour or more and the larger machines can collate, print both sides and insert staples. Developments in laser printing are likely to produce further advances.

Laser printing In laser printing, the image is produced by a laser beam, which can output computer files prepared using word processing or desk-top publishing software. Sophisticated laser printing machines such as the Xerox Docutech are now used for printing runs of up to 500 more economically than offset printing. Typical products of this process are workshop manuals, timetables and other items with short runs. The process can also be used for items such as address labels, direct-mail letters and bar-coded labels.

Digital printing This process has been developed recently with the introduction of machines such as Agfa, Xeikon and Indigo. These print either using electrostatics with toners or by using the ink-jet process. They take desk-top publishing disks or PostScript files and transfer the image digitally to the printing cylinder without requiring a plate to be made. These machines are ideal for short-run colour which would previously have been uneconomical.

Ink-jet printing Ink-jet heads deposit droplets of ink on paper, in response to instructions given by paper tape, magnetic tape or magnetic disk. The image is produced by means of a dot matrix, which creates the letter or graphic image. As in laser printing, this process is particularly useful for labels and direct-mail.

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