Siegwerk has joined forces with INGEDE member Stora Enso, one of the leading provider of renewable products in packaging, biomaterials, wooden constructions and paper, to improve the deinkability of UV/LED cured prints.

First results of this cooperation have already marked a significant milestone towards more sustainable UV printing products in terms of deinkability in the paper recycling process. Based on these investigations Siegwerk has developed a new UV/LED offset ink system with impressive deinking properties on various paper grades even comparable to the deinkability of conventional oil-based sheetfed offset inks.

In general, paper that is printed with UV/LED inks shows poor deinkability as these inks form a solid, chemically and mechanically resistant layer after curing comparable with adhesive plastic layers. In other words, UV/LED inks are strongly attached to the paper fiber and therefore very hard to remove during the recycling process resulting in big color spots in the recycled paper. It is important that the cured ink film is fragmented into hydrophobic particles as small as possible during recycling in order to become detached and more easily separated from the paper fiber.

"Present standard UV/LED inks often lead to large hydrophilic particles leaving visible traces on the recycled paper. That’s why we have focused our research resources on finding enhanced solutions for this problem and improving the recycling of UV cured prints," said Thomas Glaser, head of technology Sheetfed at Siegwerk.

As low-energy curing UV inks (iron-doped UV, LED-UV) are gaining more and more market share, the problem has reached new dimensions and has increased the need for further advancements of UV inks and the UV printing process.

Since 2017, the partners have already investigated the deinkablilty of different ink formulations developed by Siegwerk and have examined the different inks’ behavior with standard UV, LED-UV as well as iron doped UV curing such as LE-UV, H-UV, HR-UV and LEC-UV.

"Our goal has been to develop UV/LED solutions for all UV technologies that show good deinkability similar to traditional offset and gravure inks without any loss in ink performance and printability," adds Glaser.

The deinkability has been checked using the INGEDE method 11 (01/2018) and the EPRC scorecard, the officially-approved industry standards for deinking testing and evaluation.

Based on extensive investigations, Siegwerk has succeeded in developing an enhanced UV/LED offset ink system with good deinking properties on both high- and low-weight coated paper as well as on uncoated virgin fiber-based newsprint (iNP). Therefore, existing Siegwerk inks like the L-NRGY series have been refined for good deinkability. The research project has already proven the suitability of the new ink system for commercial printing. The new UV/LED offset ink system is free of reclassified photoinitiators 369, EDB, EHA and PBZ and offers very good printing stability, high gloss levels, excellent dot sharpness and great flow properties as well as fast curing and good mechanical strength.