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Inkjet printing:
Definition and application

In inkjet printing, individual drops of color are injected onto the printing material and the print image is thereby created. This method has been used since the 1980s and is the most common method in home printing devices. The inkjet process is a contactless printing technology (non-impact process). The smaller the amount of ink used, the smaller the color dots on the printing material, which can have a decisive influence on the resolution. The minimum drop size is therefore decisive for the quality of image details and contours. The amount of ink per drop in modern devices is in the picolitre range.

The exact and reproducible formation of the droplets is particularly important in the inkjet process. This can be done using various technological processes. In the industrial sector, continuous inkjet printers (CIJ) and Drop-on-Demand (DoD) are used. In the CIJ process, the inkjet is broken into individual droplets using rapidly deformable piezo elements. Electrodes add a charge to the droplets, directing them to their target point. Drops that are not required are reused by being caught by the printhead.

Drop on Demand (DoD) is another commonly used method of inkjet printing. In the Thermo-DoD process, the ink in the print head is heated. Droplets are separated and ejected by the cloud of steam. In the Piezo-DoD process, the ink jet is broken down into drops by rapidly deformable piezo elements.

Inkjet inks can consist of both dyes and pigments. With dye inks, the dye is dissolved in a carrier liquid. The advantages of these inks are their ease of manufacture and their high color sharpness. Furthermore, these inks do not clog the nozzles on the printhead. However, the low light resistance and the high solubility in water have a disadvantage.
Pigment inks, on the other hand, are based on water-insoluble pigments in the micrometer range, which are also added to a carrier liquid and ensure the color effect. The advantages of pigment inks are, in particular, more precise printing results, lightfastness and fast drying compared to dye inks. The possibility of blockages in the printhead nozzles has a disadvantageous effect.
As a carrier medium, a distinction can be made between water-based, solvent-based and UV-curing inks.