UV curing in the printing industry dates back almost 40 years, at first with varnishes and then with inks for printing on carton board. The inks were cured immediately so did not permeate into the fibres of the board, enabling a dull material to carry a decent image as many records buyers of the 1970s can attest to. The same benefits were carried into food boxes, making these stand out, at least compared to their US counterparts where UV was not as widely used at that time.
Those early UV systems generated heat, a lot of it. The photoinitiators used could cause dermatological problems. The inks might cause damage if finding their way beyond the seals of press into more sensitive areas; rollers would glaze and powerful solvents were needed for cleaning.
The lamps needed to warm up to be effective and were always on. Any polymer bushes in the delivery would melt, so needed to be replaced by brass equivalents. Shuttering the lamps helped, as did water cooling, better reflectors and gradually UV was tamed into the safe process it is today. Some of the early names have disappeared. Baldwin revived the Spectral name last year, though not Wallace Knight.
Through this IST has mapped and led the changes, working closely with Heidelberg and other OEMs as well as supplying and servicing customers directly. Chris Schofield joined the UK arm of the German company 25 years ago as an engineer, installing and looking after the company’s installations. “The bulk of our business back then was on web offset forms presses, typically with ten or 12 lamp cassettes, although we did have quite a lot of sheet fed carton presses running in UV at the time.
“The forms presses were always relatively straight forward installations. However, sheetfed installs were carried out very differently to how it happens now. Whatever the press manufacturer, a UV supplier wasn’t allowed anywhere near until the press was just about built, and ready to run sheets.
“We would then arrive to cut holes through frame sides, to install the end of press UV, or through the footboards, to get the extraction in.”
Most presses today will come with the holes already cut in the frames ready to accommodate additional dryers, either of their own design or from a third party supplier. This has happened gradually as press manufacturers began to recognise that UV was not going to damage their presses, not was it going to fade away.
With the extension of UV printing into commercial printing, press manufacturers have been prepared and have worked with the lamp suppliers to achieve the best results. IST as a German supplier has a close relationship with Heidelberg for example.
In the early days relatively low lamp power was not a handicap as press speeds were low. But as these increased the sheet needed the power to be delivered more quickly and multiple lamp units followed. Lamps went from 80-100w/cm2 to 200-240W/cm2 with two or three lamps in the delivery not uncommon. Lamps could be designed to fit between print units to drive a white or coating before applying other inks. In packaging presses, there might be a number of such interdecks on a press, not all used concurrently.
Schofield moved into sales at the point that deflector design was able to aim the UV component of the energy generated at the substrate while absorbing and carrying away any heat generating IR energy. These were the so called ‘cold cure’ systems designed for films, foils and other heat sensitive materials. These allowed UV to extend into label printing with letterpress and flexo and more recently inkjet.
More recently still UV has broken free of the restraints it has in packaging to become a process for commercial printing. With turnaround times becoming shorter, the ability to print, process and invoice that UV curing allows, has been a boon. This comes from either a single doped conventional lamp or an LED array. There is no ozone generated, so no extraction equipment necessary; the inks respond only to a narrow wavelength so can be left on press overnight and energy consumption is 10Kw/hr compared to 80Kw/hr on an IR/hot IR system.
Label printers are now also being offered LED curing, so too flexible packaging converters, though low migration inks are not in general supply for carton producers. It has amounted to a rebirth for UV.
“Almost every project now involves the discussion of which system a printer should go for, and both have their pros and cons. Generally lower investment costs for the LE system (Low Energy UV lamp), and lower ink costs (compared to LED) suits many budgets. However, lower energy use and longer diode life can also push printers down the LED route,” he says.
“To combat the difficulty of deciding which system to invest in, at IST we have our ‘HotSwap’ technology, which allows a printer to invest in an LE system now, and easily swap to LED in the future.”
It is an approach that others are also taking. If the costs are too high currently, many, including IST, are sure that LED represents the future for UV printing and that it has a strong future across a broader spectrum of the entire print market.
Chris Schofield joined IST 25 years ago as an engineer, installing and looking after the company’s installations. After a well-timed move into sales, today he is optimistic for the opportunities that UV creates.