Interview: „LED UV-curing systems are the technology of the future

The deinking process accounts for the most important part of processing waste paper. Until now, however, UV cured inks have only rarely fulfilled the criteria for a good recycling balance. Why is that?

Glaser: UV/LED UV inks form a solid, chemically and mechanically resistant layer after curing, comparable with adhesive plastic layers. Although this strong attachment of ink and paper fibers results in a preferable high stability of the ink film, it also complicates the removal of the ink during the recycling process. Until now, the cross-linked ink particles of standard UV/LED UV inks could not be sufficiently removed from the paper fiber mass, often leaving big dirt spots in the recycled paper visible to the naked eye as colored dots, thus diminishing the whiteness of the recycled pulp and consequently the quality of the recycled paper. 

You have now developed a UV/LED UV offset ink system with good deinking properties. On which aspects did you focus your efforts?

Thomas Glaser, head of the Sheetfed EMEA technology business unit, Siegwerk

Glaser: Our goal in the development was to formulate an ink system, which can clearly be deinked, or in other words removed from various types of paper. For the identification and assessment of the deinkability we’ve used the internationally recognized testing standards INGEDE method 11 as well as the EPRC scorecard. By now, three independent institutes have already confirmed the good deinking properties of the new ink system. In addition, we also aimed at gaining extensive knowledge for future developments. We wanted to understand what exactly needed to be done to adjust a UV/LED UV cured ink/varnish layer so that this can be sufficiently fragmented and effectively removed from the paper fiber pulp in the flotation cell.

What exactly is so special about the new ink system?

Glaser: Apart from delivering good deinking properties, the new Siegwerk ink series “Sicura Low NRGY UV/LED UV” features very good printability. In addition to considerable printing stability and high gloss levels, users confirm convincing dot sharpness and excellent flow properties as well as fast curing and good mechanical strength.

Which type of paper does your new development apply to? Is it only offered for newspaper print, or packaging print too?

Glaser: For deinking graphic papers are primarily used whereas cardboard packaging is not used at all. For our research project, we examined the deinkability on different types of paper. The new ink system achieved the overall result of “good deinkability” on wood-free coated paper, virgin fiber-based improved newsprint and coated mechanical as well as recycling paper. Today, our newly developed UV/LED UV ink is mainly used for commercial printing.

What are the disadvantages of the new ink system and what still needs to be readjusted?               

Glaser: Many users in Europe are already using the new ink series on different printing machines with a high degree of success. “Sicura Low NRGY UV/LED UV” has even been confirmed to be extremely suitable for alcohol-free printing. So far, no disadvantages have come to light that need addressing.

What difficulties are generally involved in paper recycling?

Glaser: In deinking plants, the high concentration of non-deinkable material can cause significant problems with dirt particles, which can lead to the production of rejects and thus a large economic loss. Each individual print product that is difficult to deink means higher costs for deinking plants as well as a huge extra expense in the manufacture of deinked pulp, in order to achieve the target values for whiteness and other quality parameters.

Which new areas of application result from the new ink system?

Glaser: As part of our research project with Stora Enso, we were able to prove that the new ink system shows good deinking properties with standard UV, LED UV and iron-doped UV curing such as LE-UV, H-UV, HR-UV and LEC-UV. For this reason, “Sicura Low NRGY UV/LED UV” can generally be used in any UV/LED UV commercial press.

What is the demand for UV cured inks and how will it develop in your opinion?

Glaser: The demand for UV cured inks is still high, especially LED UV curing systems are the technology of the future.

The interview was conducted by Kirsten Wrede.

Event tip

At the European Coatings Seminar Radiation Curing on 21 May in Amsterdam, your key-learnings will be how radiation curing works and which type of chemistry is important for this technology. Naturally, you will also find out about the components and parts of a UV curing facility.