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UV-Technology in Flexo Printing

UV-light curing that started to be popular in the seventies has become a high-tech application within short time. Year by year, there is a two-digit growth rate in this sector covering more and more application fields. The importance of UV-curing also applies to flexographic printing, especially with reference to narrow web presses. e.g. for rotary label printing. In the field of wide web printing, however, there is an ambiguous development of UV-flexo. While the big break-through for central cylinder presses didn’t yet happen, UV-curing has meanwhile become dominant for unit presses.

The BHS Printing and Converting Company in Weiherhammer has successfully concentrated on this press type. Some 80% of the flexo printing presses supplied by BHS are equipped with UV-units. Beside wood industry, the graphics sector has been among the earliest application fields in UV-technology. According to Dirk Jaegers, manager at IST, the initially reluctant attitude towards UV-curing of inks and varnishes has been meanwhile given up by most printers. The company group IST METZ, system supplier of UV, IR and warm air dryers, maintains that the average growth rate of this market sector is at 10% per year. In the end of the eighties, the UV-process in flexo printing of packagings was of in the center of interest as an alternative to exhaust air cleaning of the commonly used solvent-based ink systems. In practise, however, this expectation hasn’t yet been fulfilled. Priorities have changed According to BHS, the estimation of UV-flexo printing has changed with reference to one essential point. For the customer printing quality is on top of the priority list. The ecological point of view comes second to the demand of gaining lucrative orders from the competing sectors of offset and gravure printig. The quality benefits of UV-printing are a welcome supplement to the technical programme at BHS.

With the help of a sprocket-free direct drive of the impression cylinder, the enterprise had already had an important success against the competition of gravure printing. Variable size printing was possible from then on with flexography as well. Furthermore it was an advantage for BHS that the principle of unit presses is very well suited for an incorporation of UV-systems. There is enough space for a useful positioning of UV-modules allowing a full exploitation of power at full-surface printing and a high brilliance thanks to sufficient distances before curing. The well-known expenditure of a heat discharge out of the central cylinder area in CI-presses is not required for unit presses. The quality of flexographic printing has benefited from the use of light curing inks. This fact is regularly confirmed by the reports BHS managing director Wolfgang Ehrling receives from print shops. The decisive point is that the proprietary article industry meanwhile estimates the quality of UV-flexo printing as comparible to gravure printing. As a consequence the discussion has more and more focussed on the issue of economy. UV as a safe option in future As UV-Flexo-printing has meanwhile been accepted in the market, the users are starting to increase their capacities by investing in a second or third press. At a first installation, the printers often decided to buy units limiting the risk through an interchangeability between UV-curing and conventional production. In the meantime the users completely trust in UV.

At the moment about 70-80% of the customers order their presses with UV-equipment from BHS. The remaining customers, said Wolfgang Ertl, demand (without exception) a guarantee for being able to re-equip the presses without any problems in the future. The current main application fields of the BHS-presses are flexible packaging for pet food, yoghurt lids, cartons for liquids, etc. The vast majority of the users see the future in UV-Flexo printing on unit presses. Most of the printing companies assume that light-curing systems will determine the quality-level of this market-segment in a few years’ time. Those who are still afraid of working with UV-Flexo will still have the possibility of updating in future. The unit press design makes such an updating easily and calculable in costs. UV-Flexo is fast The list of advantages of UV-Flexo is very extensive. An obvious reason is the possibility of immediate processing. Here Wolfgang Ertl refers to a current example. Because of the increasing number of small orders a printing shop decided to add a flexo press to gravure printing exclusively used on one location until recently. The installation was carried out only after the company had been convinced that the printing quality would not be worse. As a result, the pass time (from printing to delivery) of small editions was reduced from 6 to an average of 1 ½ days. The fold-box sector which is also interested in reducing pass times due to the market demand of Just-in-Time delivery, has therefore been considering UV-flexo-printing for a long time. In addition to a reduction of process steps, fold-box manufacturers expect from Inline-processing space economy making a temporary storage unnecessary. A disadvantage of the conventional production is the high capital commitment caused by the stored material. The lasting topic of fold boxes in flexographic prinitng According to BHS the fold box market is a large potential for flexo printing. Offset printers who went deeper into the matter are convinced that today’s flexo printing is able to produce 70% to 80% of the orders in a quality that can be compared to offset. The remaining share could also be produced in the required quality, but at extensive costs. For BHS UV-technology is the key word for the achievement of offset or gravure quality required by proprietary articles. Ink manufacturers also do believe that UV-flexo printing will continue increasing its market share in various sectors. The offered range of radiation curing inks and varnishes is therefore growing. The development has been strongly driven forward in this sector. Especially for radically curing products the forced development has brought about a considerable progress, as cationic inks had hit the headlines due to benzole problems. Rocketing development of UV-units Beside inks, the UV-systems have made a large progress. The development of UV-modules working in oxygen-reduced atmosphere is specially interesting for flexo printing.

During drupa 2000, the system supplier IST METZ has presented a new system called BLK-U. With this system, Rolf Müller from IST maintains, the proportion of photo initiators can be reduced. They are among the cost-intensive components of a UV-ink system. Their proportion can be reduced to roughly 10% of the original value in UV-coatings and to 20% in UV-inks improving the aspects of odour and yellowing. Further profits are resistance to chemicals, scratches and more brilliance. Economic efficiency A general statement regarding the economy of a printing method can scarcely be made according to Wolfhard Erling. In each individual case a large number of parameters has to be considered with reference to costs. Comparing various orders in packaging impression, both conventional flexo printing with hot air and gravure printing come second to UV-flexo printing according to calculations made by BHS. Despite increased ink costs, UV-printing turns out to be an economical method with the lowest allover costs. The higher ink price per kg is compensated by a lower ink consumption and balanced by the solvent proportion that evaporates at drying in conventional flexo printing. The possibility of reducing the number of colours has a positive effect on costs, supposed you have a competent partner from the repro part. Long termed practical investigations have shown that the handling of UV-inks by the operators (ink supply, cleaning, press stoppage, ink change, etc. ) can reduce ink consumption. Considering all parameters, UV-ink is more cost-effective than solvent-based inks. UV-inks require a careful handling leading to a clean ambience in the print shop. This has a positive side effect especially on food and pharmaceutical packagings making great demands on hygiene.

Tailor-made presses and UV units UV flexo presses from BHS can be divided into the sectors flexible packaging and cardboard products. Depending on the field of application, the company offers a particular press type. The UV unit configurations from IST METZ are also in tune with the different application fields. Three examples demonstrate the wide range: The French printing company Desmarescaux (DSA) prints with UV flexo printing aluminium foils with partially under 20 µm. International Paper in China prints drink packaging made of cardboard on a BHS press with the UV flexo printing. As the materials to be printed are not heat-sensitive, IST METZ accepted the customer's request to install a completely air-cooled system and therefore supplied lamp modules with aluminium reflector and air cooling. The new technology of light-curing under oxygen-reduced conditions is applied at the Italian printing company Alucap. The BHS press for this customer on which aluminium yoghurt tops are printed, is equipped with the BLK-U system from IST METZ. Due to the integration of a nitrogen supply, Alucap can optionally produce under oxygen-reduced conditions at the interdeck-dryings after each of the first seven printing units and at the 2-lamp end-of-press drying after the eighth printing unit. The customer mainly requested an odour reduction. Competent and reliable partner For the UV equipment of its printing presses, BHS concentrates on three suppliers. As the UV technology is a very young sector with a rapid developmental stage, BHS avoided consciously a too intensive relation to only one supplier. However, a big part of the installations were equipped through IST METZ.

The most important criterion for BHS is reliability. According to Wolfgang Ertl, this does not only include efficiency and durability of the unit technique - the same efficiency is expected from the supplier - but also service power. It is very important for the press manufacturer located in Weiherhammer that the customer gets on-site service support within few hours if requested. This demand can be met by most of the UV manufacturers at printing companies in Europe. However, for overseas installations in for example USA, Australia, Asia, etc., a partner company like IST METZ with a global sales and service net is necessary. One point where BHS expects a lot from IST METZ is the technical development in the field of the UV technology. According to Wolfhard Erling, the company located in Nürtingen is here leading on the graphic market.