Solid colour and PU-based ink systems
Effects in the context of recyclability
In addition to the material composition, the further development of the specifications for recyclable packaging is increasingly focussing on printing inks. For example, nitrocellulose (NC)-based printing inks are categorised as non-recyclable in certain combinations under certain conditions in the German minimum standard. Below you will find a summary of the background to the current status based on our cooperation and contacts with packaging licensors, recyclers and printing ink manufacturers.
Last update: 10 September 2024
Colour systems at ppg >
Due to our expertise in packaging solutions in the food sector, we use both NC and PU-based ink systems. We therefore have the necessary experience in processing both systems in our printing processes.
As the properties of individual colour tones differ in the systems, it is possible that the colour effect of a motif may change when switching from an NC-based to a PU-based ink system. Initial tests have shown that a direct changeover with existing print media can achieve good results in many cases .
However, whether a print motif or the corresponding print media are suitable or whether new print media are required must always be assessed on a case-by-case basis, as the shifts in the colour effect are uneven.
PU ink systems have usually only been used for special applications , making them more cost-intensive than NC-based systems due to their composition and lower availability .
Ink systems in recycling
Printing inks consist of pigments, solvents and binders. Standard pigments have a uniform effect on the quality of the recyclates in terms of discolouration. However, PU binders have been identified as more suitable in the recycling process compared to NC binders .
NC-based printing inks have a low temperature resistance. This leads to problems such as outgassing and a deterioration in recyclate quality during the process.
PU-based inks are more thermally stable , making them more suitable for the recycling process. This reduces the likelihood of degradation and release of harmful compounds during the recycling process.
Regardless of the composition of the colour system, it can be said that colours generally interfere with recycling, although PU-based systems do so less.
Ink systems in the german minimum standard
The consultation version of the update to the German minimum standard provides for NC-based colours in interlayer printing to be classified as non-recyclable for the entire PE-flex fraction. This year, a differentiation will only be made for sorting fractions, but not for recycling incompatibilities , with regard to the size of the packaging(< or > DIN A4) .
The background to this is that in the recycling industry, only the PE-flex fraction is fully allocated to high-quality material recycling. In principle, there are always certain periods of time between the recording of licensed quantities, their recycling and the corresponding reporting. This means that the minimum standard can only reflect the latest developments up to a certain point in time.
It is therefore assumed that the classification of NC-based inks in interlayer printing as non-recyclable will also apply to the PP-flex fraction in the medium term.
It remains to be seen when these changes will be adopted as a binding requirement in LEH style guides due to the market situation (availability and costs of PU-based inks).
It is important to note that the minimum standard is addressed to the dual systems and is thus less used as a regulatory instrument for the circular economy and much more as a driving force for the systems.
Impulses from the recycling industry:
Plastic Recyclers Europe
Plastic Recyclers Europe (PRE) - the representative body for plastics recycling in Europe - emphasises that thermally stable PU-based inks should be preferred as they have less impact on the quality of the recyclates .
NC-based inks , on the other hand, tend to degrade during the recycling process and release volatile components, which reduces the quality of the recycled material to a greater extent.
However, printing inks remain a disruptive factor in recycling and their impact, regardless of their composition, cannot be reduced without further measures such as de-inking and additional investment in recycling equipment.
Erema
Erema - the global market leader for recycling systems - has been involved in various projects on the recyclability of printing inks.
The different effects of NC-based and PU-based ink systems in mechanical recycling were also analysed.
The results showed that PU-based printing inks have a lower impact on the quality of the recyclates .
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