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New plastic de-inking method yields ‘near virgin transparency’

Recycling firm APK AG and printing inks producer Siegwerk successfully completed de-inking trials of twofold printed low density polyethylene (LDPE) films.

The strategic collaboration between the two companies, which started in October 2019, is said to hold the key to facilitating the efficient recycling of flexible packaging applications.

In spring 2020, the Research- and Development unit of APK AG tested a number of LDPE-film samples, which had been printed twofold with yellow, red, black and blue inks of Siegwerk. The test series aimed to establish, whether APK AG’s solvent-based recycling technology Newcycling could fully remove Siegwerk’s inks from the polymer matrix.

The film samples were treated with the Newcycling solvent and dissolved. The obtained polymer solution still contained printing ink-components. The dispersed inks were then removed with a filter unit explicitly designed for the process step of de-inking, featuring a very high selectivity level.

The de-inking tests of the red, black and blue samples produced a ‘near-virgin’ transparency. In case of the film printed with yellow ink a marginal yellowness remained after the treatment.

‘Design for recycling is crucial to closing the loop for flexible packaging. For Siegwerk this means providing innovative printing inks and lacquers, which facilitate high-quality recycling – for example by allowing easy de-inking while keeping full performance during the use phase‘, says Alina Marm, head of circular economy hub at Siegwerk. 

She notes printing inks play a vital role in the manufacture of plastic packaging. But they also represent a ‘major challenge’ when it comes to manufacturing a plastic recyclate of sound quality from post-consumer packaging waste.

‘The goal of a quality-driven recycling process is to create a recyclate, which is as transparent as feasible and which can once more be reused in packaging applications. Successful de-inking is essential‘, observes Klaus Wohnig, ceo of APK AG.

‘We consider the entire life cycle of the packaging – from design, to use phase and finally recycling,’ adds Ralf Leineweber, head of global technology development at Siegwerk. ‘We are very pleased that printing inks from Siegwerk have proven to be suitable for solvent-based recycling processes. We have mastered a much-discussed challenge for efficient recycling of flexible packaging.’

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