Digital printing

Digital printing is a combination of digital imaging and digital press. Digital imaging has already almost completely replaced conventional prepress. There are 3 types of digital imaging processes that create images directly on printing plates for conventional printing, or directly on plateless presses: computer-to-plate, computer-to-press, computer-to-print.

Computer-to-plate is the term used to describe the computer-controlled direct imaging of printing plates from digital data. CtP technology was first used by gravure and flexography in 1980s followed by lithography in 1990.

The first computer-to-press technology was introduced in 1991 using a spark discharge. It was replaced by thermal laser ablation in 1993. It uses non-processing plates which can be imaged directly on-press. Producing the image carrier on the press shortens makeready time significantly.

Computer-to-print technologies don`t require a printing plate at all. In general there are two types of printing processes: plate printing and plateless printing. Plate systems are the major printing processes: offset lithography, gravure, letterpress, flexography and screen printing. Plateless systems are the digital printing processes: electrophotography, ion or electron charge deposition, magnetography, ink-jet, thermal transfer and dye sublimation and electrocoagulation. Depending on the applied non-impact printing technology the image is either transferred to an intermediate carrier (as in electrophotography) or the image is transferred directly onto the substrate without any plate or carrier (as in ink-jet printing). Each printing cycle transfers a new image to the substrate. It can be the same or different than the previous image. These methods are used mainly for short runs, variable information or on-demand printing.

Electrophotography

Also known as xerography, is the most widespread of the plateless printing technologies. Electrophotographic printing system consists of a photoconductor which is charged. Charged surface is partly discharged by the exposure according to a printing image. So printing areas are charged and non-printing areas are discharged. Inking unit transfers dry or liquid toner on charged areas of the drum, so the latent image becomes visible. The image is transferred to a substrate and fixed.

Ink-jet printing

In addition to electrophotography, the most common non-impact technology is ink-jet printing. Ink-jet systems use jets of ink droplets sprayed from nozzles and driven by digital signals to print information directly on paper. The first plateless digital printing process was ink-jet introduced in 1970. Two basic types of ink-jet system are in use: continuous-jet in which drops are generated continuously but only part of them is directed on paper to produce an image, others are deflected; and drop-on-demand in which a drop is formed only on response of a digital signal.

Ion or electron charge deposition

This process uses an electron cartridge driven by digital files to produce negative charges on a drum with dielectric surface. The image is produced by a special magnetic toner that is fixed by cold fusion.

Magnetography

Magnetography is a digital printing technology similar to ion or electron charge deposition, except that a magnetic drum and special magnetic toners are used. A magnetic charge is produced on the drum by a digital file. Then toner is transferred to the latent image. Printed image is fixed by heat fusion.

Thermal transfer

This technology uses digital data to drive thermal print heads that melt spots of dry ink on a special donor ribbon and transfer them to a receiver to produce images. So, the ink is stored on a donor and is transferred to the substrate by the application of heat.

Thermal dye sublimation

This technology is similar to thermal transfer except the inks on the donor ribbons are replaced by sublimable dyes. The thermal heads convert the dyes to gas that condense on the receiver. So, the ink is transferred from the donor to the substrate by diffusion.

Electrocoagulation

It is a unique digital printing technology. It uses water-based ink sprayed on a release coating on a metallic cylinder. The image is produced by a digital print head that uses the cylinder as a positive electrode to coagulate the ink on the release coating. The coagulated ink image is transferred to the paper in printing.

Дата добавления: 2015-11-14