Digital printing ink

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Digital printing inks , including inkjet printing inks, are printing inks that have been specially developed for inkjet printers. They have a viscosity of about 12-20 mPaS and are therefore practically water-thin. There are aqueous, UV-curable and solvent-based systems. Digital printing inks are specially adapted to print heads and are therefore quite different from printer to printer.

Composition of digital printing inks

Like classic printing inks, digital printing inks consist of:

Binding agents, resins (solid resins, acrylate resins) to wet the color pigments and to attach them to the printing material, depending on the system: UV monomers , also reactive thinners (acrylate monomers) or solvents or deionized water photoinitiators (radical formers, go in through UV radiation the excited state and start the UV curing according to the mechanism of radical chain polymerization) Additives (additives such as defoamers, leveling additives, dispersing additives for setting the rheological properties, influencing drying, gloss, surface quality, etc.) Organic colored pigments , carbon black and titanium dioxide as white pigment.

Manufacture of digital printing inks

Digital printing inks are mixed with the powdered pigments or pigment pastes and the auxiliary materials in a dissolver , a huge agitator. In further processing steps in a bead mill or a three-roll mill, an attempt is made to fully disperse the pigments. Additional manufacturer-specific ingredients are added between the individual steps. Finally, the finished digital printing ink is filled into the sales container, filtered and delivered to the customer.

Quality inspection of digital printing inks

Most test methods for printing inks do not measure individual physical quantities, but are practical, application-oriented test methods. The printing process in a printing press is a very complex process with many variable parameters and, therefore, has not yet been able to be reproduced with a printing test.

Suitable test methods must therefore require constant test conditions and parameters. As a rule, every test method includes the substrate , the printing plate and the dampening solution. Only a few test methods are certified by DIN or ISO.

The test areas of printing technology are rheology , coloristics , simulation of the printing process, homogeneity of the printing ink and the drying behavior.

Print finishing

Print finishing represents the treatment of the substrate after the actual printing. It contributes to better durability and a better appearance of the printed material. Print finishing is mainly used when a certain rub resistance is to be achieved. In order to carry out this process, the printing ink must be completely dry. It is also important that the substrate is free of abrasion protection pastes, silicones and waxes. It should be noted that due to the subsequent treatment of the printing material, color tones can be changed.

A distinction is made between printing varnishes , oil-based matt pastes, dispersion varnishes and UV varnishes. Furthermore, special forms of lacquering are scented lacquers and gumming as well as scratch-off lacquers.

During print varnishing, matt varnishes, matt pastes and glossy printing varnishes are applied to the printed sheet. This is done in the same way as the printing ink is applied in the printing machine. The lacquer layer has no special properties and has to dry for a few hours. Dusting is used to prevent the individual sheets of paper from sticking together. The disadvantage of these paints is their yellowing. They provide sufficient protection against moisture.

UV varnishes can only be applied to the substrate in special coating units or printing machines. The prerequisite for using these coatings is that the printing inks are gas and nitrofast. Painting with a UV varnish has several advantages. On the one hand, the paint dries very quickly. It also offers an excellent glossy or matte finish. The lacquer film is extremely resistant. After the lacquer has been applied, the printing material can be treated with a calender . Disadvantages are yellowing and an odor.

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