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Where Next for Deinking?

Posted on: Friday, 26 August 2005, 03:01 CDT

Evolution must give way to revolution

DEINKED PULP (DIP) has become a principal raw material source for many European and global papermaking operations. In the newsprint sector, for example, the Confederation of European Paper Industries (CEPI) countries used 7.4 million tonnes of recovered paper in 2002 (17.1% of all recovered paper), much of which was deinked. Many newsprint and tissue grades commonly contain 100% deinked pulp and in many other grades, such as lightweight coated for offset and printing and writing papers for office and home use, DIP makes up a substantial proportion of the furnish.

The deinking process has evolved over many years to provide a means of ink removal from recovered paper, it involves a number of process stages that assist in the overall production process. There is some inherent flexibility in the process that enables the tailoring and optimization of systems to deal with the variability of incoming material.

Key to the deinking process is the ability to detach the ink from the fibers. This is achieved by a combination of mechanical action and chemical means. Mechanical action occurs in a pulper at high pulp consistencies. This can also be achieved later in a disperger, or in the kneading stages. The chemicals used for detachment are different surfactants, sodium silicate and sodium hydroxide.

THE SYSTEMS IN USE

Deinking systems have continued to develop and are based on either wash deinking or flotation deinking. Flotation deinking has become the major process in Europe and is carried out in numerous types of flotation systems, which consist essentially of multiple cells and injectors interconnected by pumps and pipes. The technology used is borrowed from the mineral processing industry of the 1960s. At the very basic level, the flotation process involves the passing of air bubbles through the wastepaper stock, which is in a liquid/slurry form. Ink particles dial attach to the air bubbles rise to the surface of the slurry for removal.

The flotation process can be influenced by the variance of physical, chemical and hydrodynamic factors. Physical variables include ink particle size and density, slurry stock concentration, and temperature. Chemical variables include water quality, slurry pH and surface tension values governed by flotation chemical agents such as frothers and collectors. Hydrodynamic factors include the flow patterns of air bubbles and the slurry in the flotation cell. All three factors can be manipulated according to the end use requirements, flotation cell design, deinking chemical selection and overall recycling system set-up.

Superficially the flotation deinking process seems very simple but in reality the deinking process is not well understood. It is an extremely complicated process to analyze and model. Many processes involving chemical, physical and hydrodynamic aspects occur simultaneously during flotation.

The process is then further complicated by the variability of the recovered papers. The variability stems from the range of printing processes used - including offset coldset, heat set offset, sheet fed offset, solvent- or water-based rotogravure, solvent- or water- based flexo, xerography, inkjet and other digital based processes - and the range of paper substrates, which enter the recycling loop with different degrees of ageing and pre-history. Coated, uncoated, mechanical, woodfree, calendered and surface treated are just some of the many types of substrate.

DRAWBACKS TO DEINKING

While existing technologies provide a satisfactory means of deinking the vast majority of printed output, there have been a number of notable print/ink systems that are increasingly causing problems for deinking operations. These include:

Flexo: The demking of flexo printed papers has been the subject of much research. Modifications and adaptations of conventional deinking processes have been proposed that have enabled small proportions of flexo-based material to be tolerated. Further, ink manufacturers have addressed the issue by seeking to formulate new inks that have at least some improved deinkability for newsprint and other applications.

Digital print: As digital printing technologies become more widespread and the printed output by such methods increases, more of this material will end up in recovered paper collections. The deinkability of such printed material could threaten the efficiency of current systems. It has already been shown that material printed using water-based, pigment-based ink-jet inks, as commonly found in a range of well known office and home based printers, is not deinkable. Worse still, researchers have shown dial the presence of around 10% of this material among other recovered papers will ruin the deinkability of the whole batch.

More attention has been paid to the deinking process as a result of a number of factors:

Inks are not the only problem facing papermakers using a DIP furnish: here are some of the items removed from the recovered fiber stream at Holmen Paper Braviken mill, Sweden

* The increasing reliance on DIP as a raw material

* The continued development of new printing engines and print vehicles: inks, toners, etc.

* The demand for less process waste, and

* Rising customer and end-use expectations.

Consequently, the need for effective and efficient deinking is more important than ever. In particular, there is a need to better understand the fundamentals of the deinking process, so that deinking operations can be better developed and optimized. This would enable paper mills to better deal with the changing nature of incoming material. Such knowledge would also have the potential to enable the development of inks and printing techniques that minimize deinking problems and maximize the efficiency of deinking technology.

The alternative approach to developing and refining current deinking technology would be to develop deinking friendly inks or printing techniques that would simplify the deinking process. Such an approach would require active input and involvement of ink manufacturers and printing machinery manufacturers. However, such a holistic approach, although longer term in nature, may ultimately be the best route forward for effective deinking, both in technological and economic terms.

Both such approaches are being investigated within a current European COST Action that is seeking to improve the understanding and use of deinking technology. The Action, which has active participation from universities, research institutes and companies across Europe started in 2004 and will continue through to 2007. The aims of the COST Action are to create:

* Improvements in the quality and uniformity of DIP

* More efficient and effective deinking operations

* Improvements in environmental credentials, and

* To enable the development of cost effective solutions for difficult to deink inks and toners.

The efficiency of a deinking operation can be affected by variability in the quality of incoming raw material and by changes arising from seasonal and climatic variations. Manipulation of deinking conditions and chemistry can limit such effects, as can improvements in the design and flexibility of the deinking hardware.

THE FUTURE OF DEINKING

Pira International predicts that:

* Deinking will be further developed and used for newsprint manufacture worldwide, particularly in Asia. Older deinking lines in Europe and elsewhere will be continually upgraded and expanded

* New developments will enable further use of recovered fiber in mechanical fiber-based publication grades

* Tissue grades will continue to use DIP. The market led requirements of properties such as softness and high absorbency may prevent the universal use of recovered fibers in all grades

* The use of recovered fiber in woodfree printing and writing grades is not going to increase much above existing levels unless there is legislative intervention.

Recent years have seen a steady increase in the use of recovered fiber in newsprint and other printing and writing grades, as well as a number of new and rebuilt deinking plants around the world. They have also seen the development and refinement of the deinking process. This has included dual loop water circuits; high speed disc dispersion and pre- and post-flotation. However much of this development could be described as evolution.

Developments in printing technologies have meant the arrival of new inks and toners in the recycling stream. To counter some of the potentially adverse effects of such materials, and to ensure the effective optimization and efficiency of the deinking process in the future, a revolution in deinking technology will be required.

Graham Moore is the Head of Pira International's Strategic Consultancy activity for the paper and board industry. He is also Vice Chairman of the COST Action on deinking. For further information please contact the author on +44 (0)1372 802127, or email grahamm@pira.co.uk

Copyright Paperloop, Inc. Jul 2005

Source: PPI; Pulp & Paper International

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