Partner Focus
Cutting edge advantages of DG-AUXO web-offset with electron beam curing
he potential reduction of energy consumption by switching to Electron Beam curing is a frequently recurring topic in the printing industry. However, EB curing in combination with web-offset has, besides energy savings, several additional advantages for printers and converters which will be highlighted in this article. EB curing of ink is a long-time proven technology dating back to the 1960s and 1970s, but with the development of web-offset sleeve cylinder technology, interest and the number of installations has risen significantly.
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A good example is the DG-AUXO web-offset press series that, when equipped with electron beam curing, offers packaging and label printers a number of significant advantages that go beyond low energy consumption and low carbon footprint.
ELECTRON BEAM, HOW IT WORKS The electron beam system exists of two main units, a high voltage (HV) transformer, and an electron gun. The electron gun contains tungsten filaments, placed in a vacuum chamber. A water-cooled copper window with a very thin titanium foil maintains the vacuum inside the chamber.
As filaments are heated up to their thermionic emission temperature they start emitting electrons. The HV transformer generates the required amount of kV to accelerate the electrons up to an energy level that can easily pass through the titanium foil and exit the vacuum chamber.
Hereafter the electrons hit and penetrate the wet ink layer on the moving web and start the free-radical polymerization reaction, causing instantaneous and full cure of the ink and varnish layers. The polymerization of the ink takes place under nitrogen inerted conditions, in order to prevent that oxygen from the air can inhibit the reaction. The two main parameters to control are the dose (or the amount of electrons emitted), and the acceleration voltage, that gives the speed to the
electrons. A higher dose allows higher print speeds. A higher voltage guarantees safe cure of thicker ink and varnish layers, as higher speed electrons have more energy and therefore penetrate deeper into ink and varnish layers.
EB systems are designed with a so-called self-shield,
Cross section of an Electron Beam accelerator.
preventing electrons and secondary X-rays to escape unintentionally, not even from the areas where the electrons exit from the vacuum chamber and impact the ink.
ADVANTAGES OF ELECTRON BEAM CURING Web-offset operations with Electron Beam curing of inks and varnishes have a number of advantages: O Web-offset EB curing inks are 100% VOC free O Web-offset EB inks do not contain photo initiators, thus eliminating hazardous health risks that are related to migration of photo initiators.
O EB provides a very robust cure through high conversion of bonds, allowing high printing speeds
O EB curing is color blind, meaning it easily cures thick ink layers, including whites
O The total energy consumption of an EB system is low
O EB curing has a low-temperature impact on the printed web
O EB curing is an on/off system. There is no radioactivity once the system is switched off
O EB inks and varnishes are available from most of the leading ink manufactures.
And besides, web-offset’s paste inks allow formulations with molecules of higher molecular weight and multiple reactive sites providing lowest migration ink formulations for food-safe packaging.
WET-TRAP PRINTING
The dimensions and pricing of an EB system make it unfavorable for intermediate drying. Therefore EB is typically operated as end-of-line curing equipment, which requires good wet-trap performance from the utilized EB inks.
It is this requirement of wet-trap performance that makes web-offset the ideal and best matching printing technology for EB curing. Other printing technologies, which require liquid inks, face hurdles regarding wet-trap performance and stability of the inks over time.
WEB-OFFSET WITH EB FROM DG PRESS DG press can integrate the EB systems from any of the leading EB equipment manufacturers. EB systems in the 70 kV – 150 kV range for curing inks and varnishes on DG-AUXO web-offset press series at the widths: 520 mm, 900 mm and 1050 mm and printing speeds up to 400 m/min.
The team from DG press ServiceS has long-time experience with EB system integrations on various web-offset press series for food packaging and label applications. Starting in 2005 with web-offset presses for liquid board packaging followed by web-offset presses with EB curing for the production of shrink sleeves and flexible packaging. To date, the counter stands at more than 25 EB web-offset integrations globally, varying in widths from 520 mm up to 1250 mm.
DG-AUXO Web-offset EB press with Flexo-EB downstream unit.
Xinfo@dgpress.nl X+31 (0)313 671 911
www.convertermag.com
September 2022
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