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Press Release 1/96

Printing inks leave traces in the deinking sludge

New printing inks could possibly prevent problems concerning the utilisation of deinking sludge. INGEDE plans to support a pilot project with new chlorine-free yellow ink

The key process in paper recycling is deinking: the printing ink is washed out of the wastepaper. This process leaves the so-called deinking sludge to dispose of. Over 50 per cent of this are natural minerals, such as kaolin or calcium carbonate. Kaolin is a clay mineral used, in particular, for the manufacture of porcelain and ceramics. Among the most familiar forms of calcium carbonate are marble, chalk or boiler scale (lime) in coffee machines. The paper industry applies kaolin and calcium carbonate as fillers and components of coating pastes filling the inter-fibre spaces and thus enhancing the writing and printing quality of the paper.

In addition to kaolin and lime, the remaining substances also contain waste fibres and insoluble, coloured or black printing ink components, namely pigments. These remaining substances constitute an excellent aggregate in cement and brick production. The fibres contained therein are particularly welcome here, since they burn in the brick kiln and leave pores reducing the brick's weight and enhancing its insulating properties. However, traces of chloric impurities in the deinking remaining substance as well as heavy-metal traces of copper and zinc may cause certain problems with regard to some forms of utilisation. The organic compounds of chlorine ("OX") stem from particular printing inks getting into the paper mill together with the wastepaper.

On behalf of the International Research Association Deinking Technology (INGEDE e. V.), the Papiertechnische Stiftung (PTS, Foundation of Paper Technology) in Munich examined the content of such impurities. The examination revealed that printing inks release an average of 75 milligrams of OX per kilogram wastepaper into the deinking process, since the desired concentration of printing inks in the deinking process also results in elevated levels of attendant material which, in turn, impair certain ways of utilisation.

Depending on the respective use, a substitution by chlorine-free printing inks turns out to be difficult. For yellow scale colours of all common printing processes, chloric pigments have been used so far all over the world. For many years now, these pigments have replaced plumbiferous yellow pigments commonly used in the past. Various companies have now developed yellow pigments which do not contain any organically-fixed chlorine. These pigments of different manufacturers which are all similar in structure are particularly suited for water-soluble colours, ultraviolet colours as well as solvent-containing package printing. However, these pigments have not been very common so far due to various reasons: Firstly, yellow printing inks containing these pigments do not always meet the required standards as to shade of colour, intensity of colour and light-fastness. Secondly, as in many development projects, a broader use is still too expensive.

INGEDE endeavours to launch a pilot project together with a manufacturer and a major user which is to examine various aspects of utilisation as well as effects on the deinking process and resulting remaining substances. Currently, talks are under way with a major environmental protection organisation interested in chlorine-free manufacture of its printing products. First printing test results are expected in the forthcoming months.

However, a final evaluation of these pigments is not yet available. It might be possible that the apparent advantages to the environment due to the use of chlorine-free substances are compensated or even overcompensated by their more expensive and complicated synthesis.

INGEDE is an association of leading European paper manufacturers aiming at promoting utilisation of wastepaper and improving the conditions for an extended use of wastepaper.

15 March 1996

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Last update: Feb 10, 1998