Flint Group’s Nilsson highlights UV flexo printed shrink sleeves

Nilsson said, “Impression catches the eye; a packaging has the ability to make you to take a decision within seconds. This is the power of labels.”

Nilsson cited the advantages of UV flexo technology being 100% VOC-free. “It is the fastest growing printing process in the narrow web industry. Not only is it environment friendly, but also it competes with offset and gravure quality of label printing with minimal dot gain,” informed Nilsson.

She added, “As compared to solvent-based and water-based inks, which release 60-70% and 40-50% VOCs respectively, UV curing inks use 20% less ink with the same anilox.”

While using UV inks for shrink sleeves, the major challenge according to Nillson is to maintain the ability of ink to shrink as ink is cross-linked when drying and curing.

Nilsson said, "Most of all, the inks must have good flexibility and should not become brittle after shrinking. Shrink inks should have excellent scratch resistance to withstand the sheathing process without scratching and damaging the inside/reverse printed area."

She further added, “There is a need to combine the conflicting parameters of ink such as high-speed curing and shrinkable ink films or scratch resistance and adhesion to film. The ink also must handle different surface slip characteristics as it needs to stick to various substrates such as PET, OPP, OPS, PVC, PLA etc without primer coating. Plus it has to scope with various degrees of shrinkages.”

The production of shrink sleeves requires a strict control over the coefficient of friction (COF) of the film. Nilsson explained the importance of calculating the static and dynamic COF. She said, “If the static and dynamic COF is too low it can be difficult to handle the reels before seaming. On the other hand, if the dynamic COF is too high, the sleeves will curl up and will not work on high speed bottlers.”

In the next part of Nilsson’s presentation, she focused on low migration inks. Explaining the concept of low migration, Nilsson, said, “Migration refers to transfer of substance from the packaging to the packed food product. The potential migrants include plasticisers from plastics or inks, residual monomers from plastics or coatings, solvents, washes and cleaning chemicals, oils and greases, low molecular weight components from substrates or adhesives, low molecular ink additives etc.”

According to Nilsson, migration can take place by two methods. “Through package migration, which occurs from the printed side through the packaging materials onto the unprinted side. Then there is direct contact migration from the printed side to the unprinted side of another sheet in a stack or roll, also known as set-off migration.”

The problem of migration can be countered with systematic approach. “All the members of food packaging chain must implement good manufacturing practices (GMP) and printers must maintain documented evidences for ink, batch, anilox, speed, humidity etc and trace it.”

In the final segment of her presentation, Nilsson highlighted some innovations developed by Flint Group to counter migration. These include low migration flexo ink, low migration offset ink and UV inks for LED.