Printing inks usually account for only a tiny fraction of the total weight of flexible packaging – yet they determine whether a recyclate can be reused for high-quality applications or becomes unusable. However, there is often a gap between the strict requirements of the European Packaging and Packaging Waste Regulation (PPWR), new CEN standards such as EN 18120, and the technical reality in the pressroom. In the 45th INNO-Talk, Ewald Rempel (Sun Chemical) and André Altevogt (Follmann) joined host Karsten Schröder to discuss how solvent- and water-based ink systems perform in the recycling process, why carbon black pigments can become a knockout criterion, and what surprising performance advantages modern water-based inks offer when sealing recyclates.
Regulatory Pace-Setter: PPWR, EN 18120 and the 55% Recycling Target
The European Packaging and Packaging Waste Regulation (PPWR) sets ambitious targets for the flexpack industry: By 2030, all packaging must be designed for recyclability, combined with mandatory recycling targets of 55 % for plastics. In parallel, European standardization – in particular EN 18120 (“Design for Recycling of plastic packaging”) – defines concrete rules for printing inks, binders, and pigments.
For printing ink manufacturers and converters, this means a fundamental shift in priorities: While the focus used to be exclusively on gloss, abrasion resistance, rub resistance, and chemical resistance to packaged goods, recyclability has now become the central mandatory task. After collection, the printed packaging undergoes a demanding chain: from automated sorting plants (Material Recovery Facility, MRF) through hot and cold washing stages to melt extrusion at over 230 °C to 260 °C.
NIR Detectability: Why Standard Black Stops Sorting
Ewald Rempel, Head of Application Engineering Packaging Inks EMEA at Sun Chemical, shed light on the hurdles of modern sorting plants. The automated separation of plastic fractions in sorting facilities is based on near-infrared spectroscopy (NIR). An optical sensor scans the packaging, identifies the polymer-specific reflection spectrum (e.g., polyethylene or polypropylene), and instructs compressed air jets to eject the item into the correct material stream.
Here lies one of the biggest pitfalls:
- The problem with carbon black: Conventional carbon black pigments (Pigment Black 7) absorb NIR radiation almost completely. The scanner receives no reflected signal from the underlying substrate – the packaging remains “invisible” and ends up as sorting residue in thermal recovery.
- Clear criteria according to EN 18120: In surface printing, carbon black is considered non-recyclable. In reverse printing (intermediate layer in laminates), carbon black is only conditionally tolerated at a surface coverage of less than 1 %.
- Alternatives and their limits: While multichromatic black mixtures (cyan, magenta, yellow) enable NIR detection, they often appear milky-brown in the print result and drive up ink application rates. High-quality NIR-transparent specialty pigments or special Soot-free alternative inorganic black pigments offer colorimetrically brilliant results and full transparency for infrared rays, but their raw material prices are significantly higher than conventional carbon black.
Deinking vs. Melt: “Gray is the New Green”
Another frequently misunderstood topic is the deinking of printed films. While deinking has been standard in the paper industry for decades, industrial film recycling faces completely different challenges. Ewald Rempel clarified:
“Industrially, film deinking currently works essentially only for surface-printed mono-films. In the case of laminated structures with reverse printing, the laminate would first have to be mechanically or chemically delaminated prior to washing – which is feasible on a laboratory scale, but far from an industrial standard on a large scale.”
Ewald Rempel, Sun Chemical
In practice, the vast majority of flexible packaging is regranulated without prior deinking. The printing ink goes directly into the extruder and is homogenized with the polymer. The recyclate inevitably turns gray (“Gray is the new green”). For the ink binder systems, this entails extremely harsh thermal requirements:
- Risk of decomposition with nitrocellulose (NC): Conventional NC binders tend to thermally decompose at extrusion temperatures above 200 °C, leading to gelling, unpleasant odors, and discoloration.
- Stability through polyurethanes (PU): Modern PU systems and thermally modified binders stably withstand extrusion temperatures up to 260 °C without generating significant odor or degradation effects in the recyclate.
Water-based Printing Inks: The 1:1 Practical Comparison at Follmann
André Altevogt, Head of Water-based Printing Inks Europe at Follmann (Minden), presented the results of an in-depth comparative study. Follmann compared the recyclate quality of two identical polyethylene films printed with the same print design and identical ink coverage – one with a modern solvent-based ink system, the other with water-based printing inks.
Both film samples were regranulated under identical conditions into 100 % post-consumer recyclate (PCR) and extruded into new blown films. The quality testing revealed remarkable differences:
1. Particle and Gel Formation
In the extrusion process, incompletely melted ink particles or binder reactions caused inhomogeneities in the film. While the regranulates of the solvent-based ink exhibited around 849 particles per square meter (of which around 9 % were larger than 500 µm), the film made from the water-based ink recyclate showed a drastically more homogeneous structure with only 5 particles over 500 µm per square meter. Large gels are feared in blown film extrusion as they lead to thin spots, bubble tears, and pinhole formation.
2. Surprise in Heat Seal Strength (DIN Testing)
Particularly relevant in practice were the heat sealing properties determined according to DIN in the accredited testing laboratory of Innoform Testservice. Recyclates frequently suffer from altered rheological properties and narrowed process windows during packaging. However, the series of measurements presented a surprisingly clear picture in favor of the water-based variant:
- Lower seal initiation temperature (SIT): The recyclate, made from film printed with water-based ink, began to seal reliably at just 110 °C.
- 3-fold strength at 115 °C: While the solvent-based recyclate achieved a seal force of only around 5 N at 115 °C, the recyclate from the water-based ink was already above 15 N – a threefold increase.
- Wider process window: At 120 °C, the water-based sample exhibited around 30 % higher strength. Only at 140 °C and above did both variants reach a comparable level at around 25 N (substrate tear).
For converters and packers operating vertical and horizontal form-fill-seal machines (FFS), this difference is crucial: A material that seals reliably at temperatures 10 to 15 °C lower enables faster cycle times, consumes less energy, and tolerates temperature fluctuations in the sealing tool.
Market Trend: Is Surface Printing Making a Comeback?
In the subsequent discussion with participants, Karsten Schröder picked up on an interesting market development: surface printing. For years, reverse printing in multi-layer laminates was considered the unchallenged standard in flexographic printing to embed the ink layer safely between the substrate and sealing film.
Today, surface printing with protective overprint varnishes (OPV) is regaining importance – for two main reasons:
- Recyclability: Inks in surface printing are significantly more accessible to deinking solutions during hot washing processes than ink layers encapsulated within a laminate.
- Agility and lead time for converters: European packaging printers compete with high-volume imports from overseas. Those who stock unprinted mono-film or laminate semi-finished products and apply customized surface printing shortly before delivery can fulfill orders in days rather than months.
Conclusion: Printing Inks as Enablers for Functioning Circular Economies
The summary of the 45th INNO-Talk is encouraging: The printing ink industry has done its homework and offers recycle-ready solutions for almost every requirement profile. Whether modern PU solvent systems with temperature-stable resins or highly developed water-based inks without VOC emissions – the key lies in the interaction of all components:
- NIR-transparent pigments ensure sortability in the first step of the circular economy.
- Thermally robust binders prevent quality degradation and odors in the recyclate.
- Water-based systems can positively influence heat sealing behavior through more homogeneous recyclate structures.
Anyone looking to fit their packaging for the PPWR should no longer view printing inks as an isolated decorative layer, but as an active functional component of the recycling system.
