Most people accept that recycling is a good thing. Take paper for instance: in 2011 70% of European waste paper was recycled. Logistics and sorting can be complex, but of equal concern is how waste paper gets prepared for its reincarnation and a new life. The removal of printing ink from substrates, the deinking process, is key to waste paper’s reuse. However there are lots of ways of doing it and limited consensus on how it should be done.
Deinking has to be thorough if the pulp is to be useful for different applications. Recovered paper pulps must have the optical characteristics required for different market sectors, from newspapers to high grade tissues. It probably doesn’t matter much if the recycled pulp used to produce cardboard boxes is a bit drab and dingy, but lack of brightness is a serious problem for graphic papers. Recycled papers and board can be deinked and turned into something useful, but there is no standard method to provide benchmark quality control that ensures pulp meets the needs of different target uses.
Around the world regions and plants use their own deinking methods according to the type of pulp the plant is producing. Some digital, flexo and UV inks cannot be easily removed and so require a far more vigorous deinking process than is required for offset inks, and this may not be environmentally or economically worthwhile.
Successful deinking for all end uses inevitably depends on the technology and chemical recipes involved. Not all methods work for all printing inks. Ingede, a European association representing 33 paper companies, including many European paper mills and one from Pakistan, has developed various methods relating to paper deinking. There’s a method to measure the optical characteristics of pulps and one for assessing amounts of adhesive residues in a batch of recycled pulp. Ingede’s highest profile method is its Method 11, a deinkability test used to assess a print product’s recyclability. Ingede’s Method 11 outlines how to evaluate a print’s deinkability using alkaline flotation, a widely used deinking method using a standard deinking recipe. However alternatives abound because not all inks can be removed with Method 11.
There is some degree of consensus on the basics such as flotation tanks for the pulp that gets mixed up with chemicals to remove the ink, dirt and glues, but little else. As the quality of the raw material entering the recycling streams gets more diverse, with higher proportions of inks that cannot be easily deinked matters are getting complicated. The market might appreciate ISO standards that help account for the diversity of raw materials and facilitate the labelling of recycled papers according to their deinkability. We are working with Verdigris members, Ingede and the Digital Printing Deinking Alliance to explore how this might be achieved.
– Laurel Brunner