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The Danish banknotes are like most other banknotes printed with offset and intaglio printing. The
offset is the background consistent of fine lines. The portrait, the rosette, the latent image and the
denomination in words are all printed in intaglio. Contrary to the majority of banknote printers who print their banknotes in sheets the Danmarks Nationalbank prints its banknotes on a web printing press. Previously the offset printing was 4 colours on each side printed with conventional oxidative drying dry offset inks. At a later stage one of these colours was changed to a wet ink. The intaglio was printed with heat-set inks dried with gas burners headed directly towards the paper. Using the gas burners the paper was completely dried out and had to be remoistened before the next print in order to obtain good register between the prints and a good printability of the paper. The intaglio technique is used in banknote printing to obtain a tactile appearance of the print. Ink is applied to a printing cylinder from an ink duct. The excessive amount of ink is removed with paper wiping. The remaining ink in the engravings is transferred to the banknote paper with a pressure of about 0.3 tonnes/cm. Printing under the above mentioned conditions created severe problems. Set-off of the offset inks and difficulties with printing in register were the primary reasons to search for new types of printing inks. Furthermore it was seen that UV-curable offset inks could cure almost instantaneously when exposed to UV-light leading to a high printing speed. Since UV-inks do not contain any volatile organic compounds the dry film thickness is identical to the wet film thickness and no atmospheric pollution is created inside or outside the Printing works. UV-inks have, however, two main disadvantages concerning the costs of buying and installing the UV driers and the cost of the UV inks. A further disadvantage was that the varnish and photoinitiator for the inks was known to cause skin irritation. Following well established codes of practice the risk to cause skin irritation on the printers and the ink makers was minimized.
