UV-drying in Jumbo-format
Large-format sheet fed presses are often required for printing special products. Only a few press manufacturers are specialised in this market segment of Jumbo-presses. To name two of the most important ones, companies MAN Roland in Offenbach and the KBA-group in Würzburg, as well as their daughter company KBA-Planeta in Radebeul. Both KBA‘s large-size series including the model series Rapida 130 (max. paper format 910 x 1300 mm) to Rapida 162a (max. paper format 1200 x 1620 mm) and the Roland 900 machine series of the MAN Roland machine range covering the sector of 4-size format (max. format 820 x 1130 mm), 5-size format up to 6-size format (max. format 1000 x 1400 mm) and 6b-format (max. 1020 x 1420 mm) are used for printing various different substrates in a wide spectrum, such as extremely thin papers, for example for label printing, but also solid cardboard material and recently even corrugated cardboards with F- and G-profiles.
Key factors in package printing
The material mentioned above shows that package printing is a key factor in the fields of application of the Jumbo-presses. For many years, UV-curing has been recording a steady growth. Certain markets like the United States, Great Britain or France in Europe were heavily dependant on radiation curing. As a result, company IST Metz GmbH in Nürtingen has recently fitted a considerable number of large-size printing presses with UV-systems, most of them supplied to print houses in Great Britain. To name some of them, a MAN Roland 900 was delivered to Bonar Cereal near Manchester, another MAN Roland 900 to the print house Boxes, as well as a five-colour KBA Rapida 162 to Billboard Posters Limited/Augustus Martin and a six-colour KBA Rapida 142 to Imperial Litho.
This summary shows that most of the presses have five or six print units. Integration of coating units for a protective coating of the printed products, and also for optical effect, is virtually standard. All named users employ UV-radiation curing as the final drying procedure. Moreover, some installations are additionally equipped with IR-lamps or hot air in the gooseneck. Due to the heating of the coating, a better flow-out can be achieved and thus a perfect gloss result. The Rapida 162 double coater press for example, which was commissioned to a company in Great Britain, is fitted with four IR-lamps with together five blast nozzles in the intercoater dryer.
Flexible combinations and positioning
All named installations are fitted with 3-lamp end-of-press UV-dryers. The common lamp output is 160 W/cm. Furthermore, all presses can be equipped with either UV or IR interdeck dryers. Print houses which prefer radiation curing usually use interchangeable slide-in cassettes. Especially in the European countries, this technology has become a sort of standard. The user can have one or more UV-lamps which can be positioned independently, after any print group, in order to adapt the drying configuration to the individual demands of a print job. Contrary to this, North American print houses favour complete UV-equipment for their presses. The formats of these Jumbo-presses, with their large print widths, have extraordinarily high demands on the technique of lamp modules and UV-lamps. The longer the lamp length, the more important the temperature influence. For this reason, when manufacturing their lamp modules, IST always uses materials which comply with their high quality demands. Moreover, careful design and exact manufacturing techniques play an important role.
Cleverly thought-out cooling concepts
In printing production cooling of the individual UV components like lamp, reflector and lamp housing has an important influence on curing. In order to guarantee a constant UV emmission, the lamps have to be cooled consistently over the complete length. Additionally, the influence of infra-red lamps or hot air dryers combined with UV-curing have to be considered. Therefore UV manufacturers require today a broad expertise in this sector as well.
Very helpful in these situations are features like stepless control of the lamp output - which IST offers as SLC - as this feature guarantees that only the energy actually required is supplied and that unnecessary heat production is avoided. Especially effective is equipping the lamp modules with CMK reflectors. These cold mirror reflectors have a dichroic coating which selectively filters particular wave lengths. The reflection of the IR radiation, mainly responsible for the heat load of the substrate can therefore be reduced considerably. This is very important for the printing of large-sized printing material as distortion has a great influence on the acceptance of the finished product.
In order to guarantee sufficient cooling of the UV lamp modules, considerable supply and exhaust air volumes are required. Adjustment of the air flow on these machines is critical to minimise the effect on sheet travel especially when dealing with light weight stock, such as labels, or with sensitive surfaces such as aluminium vaporised board. Because of its long experience, particularly in the field of temperature management, IST Metz has developped cleverly thought and efficient cooling concepts.
