Metal doped UV lamps were already being used in the nineteen seventies to ensure a thorough cure of difficult to process inks and varnishes. In those days UV system manufacturer IST METZ GmbH was supplying this technology mainly to the wood-processing industry. In comparison to today, however, this was in very modest quantities. Since then most of the metal doped UV lamps have been installed as so-called Deep Cure Lamps in the graphic arts sector. Printing on increasingly thin, non-absorbent substrates and the increasing use of special inks (e.g. opaque white, gold, silver, metallic inks) has also finally had an effect on the equipment for printing presses. Metal doped lamps are being used more and more often in web printing. UV system manufacturer IST METZ GmbH alone has installed more than 1,000 UV systems using this technology in the last five years. The company has introduced a product range, which has been designed specifically to cure inks that are difficult to process. This applies particularly to applications using opaque white, which require customised UV technology to guarantee a total cure of these inks even at higher production speeds. The two key elements of the system are specially doped metal halogen lamps and cold-mirror UV reflectors, which are both customised to meet the needs of each specific application.
The UV supplier, based in Nürtingen near Stuttgart, has therefore introduced this range as difficult to process colours are being used increasingly inline. Standard UV systems soon reach the limits of their performance capability with this application, as their UV energy is partially reflected off the surface of the ink. The system therefore uses doped UV lamps with an emission spectrum that is specially adapted to ensure a thorough cure of inks that are difficult to process. They emit a high proportion of longwave energy in the UV-A range, which is not reflected off the surface of the ink, but penetrates deep into the ink layer. This ensures a complete cure and guarantees excellent adhesion of the opaque white layer to the substrate.
Furthermore, the emission range of these UV lamps also includes wavelengths beyond 380 nanometers, i.e. into the visible light spectrum. This is beneficial because the photoinitiators used⿿ unlike those used in process colour inks - also react to this wavelength range. This means that higher production speeds can be achieved using this system and prevents the output losses associated with difficult inks. In addition to UV lamps, which have been customised to cure opaque white, there are also other types of doped lamps available. This means that a UV lamp can be selected that has been specially adapted to other difficult to cure inks.
The extended emission range is used even more effectively in the curing process as the reflectors are also designed specifically to match the output of the UV lamps. The reflector technology for the Deep Cure Lamps provides a high degree of reflection for the emission range of the UV lamps and at the same time minimises the effect of the IR energy (heat) on the substrate. The heat produced is removed from the system into the water-cooled reflector profile via a special coating system.
Deep Cure Lamp technology can easily be retrofitted into existing UV systems. For IST units which are already equipped with URS reflectors it is simply a case of changing the UV lamps. This can be carried out in a few seconds with the cable-free FLC Fast Change Lamp system. It is therefore simple to switch between Deep Cure and standard operation. IST Metz can advise customers whether new reflectors are needed in addition to new lamps to operate with Deep Cure Lamps. All that is needed is the unit reference number from the customer⿿s existing IST system.
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