Migration poor inks

The newly developed UV inkjet inks meet the stringent requirements for low-migration inks and can be used by all printhead manufacturers without any problems. The pigment-based UV inkjet inks have been optimized with regard to the substrates to be printed (paper, PET and glass) to create a color system of yellow, magenta, cyan and black for graphic color printing.

Digital printing systems are achieving ever higher printing speeds and print quality, making them competitive in many areas with traditional mass-market printing processes such as offset, gravure or flexographic printing. The printing industry has therefore been in a state of upheaval for years, and both the printing press market and the supplier market will change significantly as a result.

While printing inks for classic printing processes are offered by various suppliers with a wide choice of products, the situation is different for inkjet inks. Until now, these inks have had to be precisely adapted to the individual print heads of the various manufacturers in order to avoid misprints or print head failures. This also applies to UV-curable inkjet inks, which are used specifically in label printing. The complex design of these inkjet inks is made even more difficult by the high demands placedon the ink components, especially in the food, pharmaceutical and cosmetics sectors.

Migration in industrial printing

Conventional UV inks are made up of raw materials such as pigments, binders, photoinitiators and other additives which, due to their chemical structure, must not be used in sensitive areas such as food packaging. This is due to the risk that individual ink components of the printed food packaging may migrate into the food due to insufficient crosslinking. However, the numerous advantages of UV-curing inkjet inks (fast curing, wide range of application possibilities, high production numbers, ...) also make them very interesting in the food sector.

The legal requirements for the use of such inks in the food sector are specified by different regulations (e.g. the Swiss Consumer Goods Ordinance and the Nestle Guidance Note on Packaging Inks). These positive lists are therefore the basis for all paints, paints and varnishes for the food, pharmaceutical and cosmetics sectors.

The migratory capacity of a substance is determined, among other things, by the size of the molecule, its structural composition and the proportion and type of functional groups. For example, large and branched molecules tend not to penetrate the layers of the substrate as easily as unbranched and small molecules. Further, a high number of functional groups ensures sufficient cross-linking of the components in the ink, which can then prevent the migration of individual components. Such functional groups are, for example, double bonds ensuring that the molecules are co-crosslinked during radical polymerization and are thus bound in the polymer film.

In the research project, UV inkjet inks with low-migration properties have now been developed for the first time, which at the same time have the rheological and color properties of conventional inkjet inks and can thus be printed without problems with the inkjet print heads used in digital printing.