Inks, Adhesives and Coatings: Where Substances of Concern Hide

When a packaging line fails a substance screen, the base material is seldom the cause. The finding lives in the applied chemistry: pigments in the inks (the cadmium and lead story of the metals guide), solvents and photoinitiators in UV-cured print, plasticisers and tackifiers in adhesives, greaseproof and release coatings carrying PFAS, lacquers and varnishes with their own additive families. Article 5 applies to packaging and its components without exempting the thin layers, and the thin layers are where formulation chemistry concentrates.

The specification consequence: a packaging specification that names only the substrate is a specification of the part least likely to fail. This guide walks the applied layers in the order a specification review should reach them.

Printing inks carry the metals legacy (pigment chemistry), the mineral-oil story (MOSH and MOAH in recycled-board food packaging, a member-state-regulated concern that has shaped board sourcing for a decade), and photoinitiators in UV systems, several of which sit in the concern classifications. Food-contact printing has no single harmonised Union positive list; the German printing inks ordinance is the framework most often borrowed as the working standard in specifications, alongside the Swiss ordinance's lists and industry exclusion policies maintained by the ink associations. A specification that names the applicable ink standard - rather than 'food-safe inks' - converts this whole area from negotiation to verification. For direct food contact and set-off risk (print transferring to the contact face in the reel or stack), the assessment belongs with the food-contact file, not the artwork approval.

Adhesives hide twice: between layers, where composition is least visible, and in their migration behaviour through the substrates they join. Laminating adhesives in flexible food packaging carry their own regulatory history (aromatic amines from incompletely cured polyurethane systems are the textbook case), and hot-melts, cold-seal coatings and pressure-sensitive label adhesives each bring additive families of their own. The specification asks are standardisable: adhesive identity and supplier, food-contact status and its basis, curing and production conditions that the compliance assumes (an adhesive compliant when cured is not compliant in your process if your curing differs), and the change-notification clause - adhesive reformulation is frequent, quiet and consequential.

Functional coatings are applied chemistry by definition: grease barriers (the PFAS story), moisture barriers, heat-seal lacquers, release coatings (silicones and, historically, fluorinated agents), anti-fog and antistatic treatments. Each function has a chemistry, and each chemistry has a concern profile the inventory must record. The review questions are functional: is the coating's chemistry the only route to the function (dispersion barriers, clay and mineral coatings, and mechanical grease resistance have all widened the alternative set), and is the coated substrate's end-of-life still coherent - a coated board that defeats repulping pays for its coating twice, once in chemistry and once in grade. Specify the function, let suppliers propose chemistries against it, and score the proposals on concern profile and grade effect together.

Decorative layers close the tour: overprint varnishes, metallised films and foils, glitter and special-effect finishes on premium and seasonal packaging. Their substance significance is disproportionate to their mass - metals in effect pigments, the component-separability cost the grading station prices, and a tendency to escape the specification system entirely because they are chosen in design studios rather than engineering reviews. The change gate from the formats station should name decorative finishes expressly: a foil change is a component change, with a substance review attached, however it was briefed creatively.

Compress this guide into the artefact it exists to produce: a one-page applied-chemistry annex to every packaging specification. Rows: ink system and its standard; adhesive identity and cure conditions; each functional coating and its chemistry family; varnish and decorative finishes; and for each row, the evidence held and the change-notification term. One page, because a specification annex longer than that stops being read at the converter's desk. The annex travels with the artwork and the purchase order, which is how applied chemistry stops being the layer nobody specified.