Digital Print for Food-Safe Packaging

Migration and what to do

In simplest terms, ink migration is the transfer of unwanted substances from the printed surface to the product.

Migration results from four primary causes: diffusion, set-off, vapor phase, and condensation extraction. Each presents unique challenges.

Packaging safety is determined by substrate type and thickness, ink laydown and print coverage, end-use conditions, and the foodstuff itself. Each step of the manufacturing process impacts compliance, including package design.

Converters install controls on press to prevent non-visible set-off, and ensure full ink and varnish curing and drying. For water- and solvent-based inks, any residual solvents and volatile substances can be controlled. For UV-curable inks, full curing must be assured.

For example, Screen’s (Booth 10951) Truepress Jet L350UV+LM UV inkjet press features inks and a nitrogen purge mechanism to reduce extractable ink components, and mitigate diffusion migration risks. Because oxygen interferes with the curing process and prohibits full polymerization, nitrogen is used to purge oxygen, and sensors shut-down the press when it is detected.

Ultimately, ink innovation ensures packaging compliance. Because UV inkjet ink’s nano-sized Initiators and monomers can penetrate general packaging when insufficiently cured, Screen’s LM ink works with the nitrogen purge mechanism to accelerate and deepen UV curing, minimize odors, and eliminate impact on food flavor. Third-party testing laboratory Triskelion (TNO) in The Netherlands have certified these results.

Testing shows Screen’s LM inks can be used without migration risk with a PET layer greater than 25 microns, or a 40 micron PP barrier for non-fatty dry food. Additionally, functional barriers prevent migration in use and during processing.

Non-print factors may also affect chemical migration from contact materials to food. Subsequently, testing laboratories work closely with ink manufacturers. Screen, for example, has worked with laboratories TNO and Swiss Quality Testing Services (SQTS).