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Cleaner Technology Projects in Denmark 1996

VOC Reduction in the Printing Industry

Each chapter covers each printing method and the activities, which contribute to the VOC emissions. Subsequently, the cleaner technologies which can reduce the emissions immediately, and the technologies which imply certain changes of technical, economic or developing characters are described. At the end of each chapter, the traditional cleaning technologies are briefly mentioned as an alternative if the suggested cleaner technology solution is not sufficient.

Today, prepress work is mainly made on computers (electronic data processing) but the processes still include use of photographic materials. For the development of these, the use of VOC is insignificant.

Flexographic printing is the most widely used relief printing method, especially for printing on packaging made of corrugated cardboard, paper and plastics and for wrapping paper, bags, labels, etc. As suppliers develop water washout printing plates the VOC-emission from plate making can be reduced. It is possible to change from solvent-based to water-based flexo inks when printing on paper, cardboard and corrugated board. The use of water-based flexo inks for printing on plastics is possible to a certain degree but a wider use of the technology demands further development. It is expected that it will soon be possible to increase the use of UV-curing flexo inks but development of know-how and large investments are necessary.

As for replacement of VOC rinsing of the flexo machine parts, either high-pressure flushing or ultrasound rinsing can be used under certain conditions.

Letterset is used for printing on plastic buckets and cups. Today, the printing inks are UV-curing and do not contain VOC. However, VOC is used for rinsing the printing machines. Vegetable oil can be used instead when rinsing printing plates, rubber blankets, and inking rollers.

Letterpress is used for printing adhesive labels. The plates for letterpress printing are today washed out with pure water and the printing inks are UV-curing without solvents. The consumption of VOC for rinsing is minor and can be substituted with vegetable oil.

Offset in different forms is used for printing leaflets, catalogues, books, newspapers, magazines, cardboard boxes, tin cans, etc. The emission of VOC derives from alcohol in the fountain water and the use of white spirit and the like for the cleaning of the machines. In tin printing, varnishing causes emission of VOC. However, at manual rinsing it is possible to reduce the use of VOC by substituting white spirit with vegetable oils. The use of VOC in automatic rinsing can be reduced as new machines fit for cleaning with vegetable oils are introduced.

It is possible to reduce the amount of alcohol in the fountain water or to avoid the use of alcohol in web offset. If the necessary know-how is developed and investments are made on equipment for temperature control, the companies can use a relatively new method, waterless offset where fountain water - and consequently alcohol - is not used.

When successfully developed, water-based or UV-curing varnishes presumably will be used for the varnishing in tin printing.

There is a distinction between publication gravure and packaging gravure when it comes to machines and printing inks. Publication gravure is used for printing magazines while packaging gravure is used for long-term printing of flexible packaging made of paper, plastics, metal foil, and laminates. The emission from publication gravure is reduced by recovering the solvent from the printing ink. The solvents from packaging gravure cannot be recovered.

Cylinder making implies only sporadic use of organic solvents if any.

Water-based printing ink is a potential possibility for VOC-reduction in publication as well as in packaging gravure but the inks are still in the experimental stage. UV-curing gravure inks have not yet been tested.

Powder cleaning or even ultrasound cleaning can be used for cleaning machine parts under certain conditions.

Screen-printing is used for printing signs, posters, labels, t-shirts, etc. It can be used for printing on paper, plastics, textiles, glass and metal. Solvents are only used sporadically for the stencil making.

It is possible to use water reducible screen printing inks for printing on thick paper and cardboard. Water reducible as well as UV-curing inks can be used for printing on certain types of plastics (PVC, PC, PS, acrylics and possibly more) if the surface is well treated. The use of UV-curing inks implies investments in UV-lamps and can cause health problems for the workers. The use of water-based or certain water-reducible UV-curing screen printing inks open a possibility for using waterbased cleaning agents.

Solvent waste from the cleaning of screen printing frames can be regenerated if the necessary equipment is installed.

Finishing of printed matter includes gluing, varnishing and laminating. Gluing causes an insignificant use of solvents.

VOC emission can occur from the adhesive when printed paper is laminated with a thin plastic film. There is no immediately useable solution in the form of cleaner technology.

Author/ institution

Susanne Møller, Dansk Teknologisk Institut.
Erik Silfverberg, Gitte Gladding og Rikke Dreyer; Den Grafiske Højskole.

This report is subsidies by the National Council for Recycling and Cleaner Technology.

ISSN no. 0908-9195
ISBN no. 87-7810-541-2

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