Drying, Curing & UV
Examining the performance ofLED UV technologyon a newspaper press
IST METZused a Wifag OF-7 to test out the performance of its LED UV technology on a newspaper printing press, which is equipped with UV curing capabilities, located in the production hall of one of its customers in Switzerland
interest even in places where this alternative to classic UV curing has barely been used to date. Operators of fast-running web presses looking at investing in LED UV technology are especially keen to know exactly how a high-performance setup needs to be designed. “An ideal response to this question is resilient information about what printing speeds can actually be achieved in the field using an LED UV system as a function of the combination of printing ink and substrate,” explains Stefan Feil, director technical marketing at IST METZ. Experience with web printing applications
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comes primarily from narrow-web label printing to date. In this case, maximum press speed rarely exceeds a value of 200m/min. There was a general assumption that current performance is significantly higher, but there was no practical proof of this. IST METZ saw an opportunity to examine this question in newspaper printing. Centre d'impression et d'arts graphiques Pressor (Pressor) is a customer of the Nürtingen company and has a Wifag OF-7 printing press with a web width of 1,300mm and a section length of 940mm and equipped with UV technology. When it was installed in 2007, the UV equipment
originally consisted of BLK-3-type UV systems from IST METZ. With the rise in the low-energy variant of UV printing, Pressor switched to so-called LE UV technology, in which appropriately-adapted printing inks are used in addition to specially- doped UV lamps. The simultaneous benefit of this switch was that it was possible to reduce the previous number of three UV units for each side of the web to just one UV unit.
A UV MODULE FOR EACH SIDE OF THE WEB For the tests, one of the two LE UV radiators was replaced with an LEDcure system of the LUV 80 type (see right, an example of an LEDcure system). An important issue here was that the energy is focussed on the web by means of the special arrangement of the LEDs in a line. This accordingly provided separate UV units for the front and back, simultaneously allowing a comparison between low-energy UV and LED UV technology. With systems from IST METZ, the interchange
between different UV technologies is very simple by means of the Hot Swap concept. Last autumn at Labelexpo Europe, the company presented this for the first time. It allows UV units to be used interchangeably; a simple change from a
18 October 2016
he increasingly widespread nature of LED UV technology in various graphical applications is now piquing
LAMPcure to a LEDcure system and vice versa is possible. The peripheral equipment in the machine remains, a joint electrical supply is used.
SPEED INCREMENTALLY INCREASED During the test series with LED UV technology, the maximum mechanical speed of the machine - 35,000 revolutions/hour (which equates to a web speed of 548m/min) - was approached incrementally. Pressor usually achieves a speed of 32,000 revolutions/hour (500m/min) in practice.
THE EFFECT OF SUBSTRATE AND INK The right material for printing and the printing ink is important. The obvious choice for a newspaper press was a common 45 gsm newsprint paper. A 70 gsm matt-coated paper quality was tested as a second substrate; this has a more closed surface and thus reduced ink absorption properties. For printing inks, Pressor uses UV printing inks
from hubergroup designed for fast-running newspaper printing presses. The trials were performed with ‘advance samples’ of the four- colour process inks from this product family. The results showed that curing of the inks
when printing on newsprint paper was good across all the speeds tested. In this case, density values of 0.90 were specified as colour density for yellow, magenta and cyan, with 1.10 specified for black. The test results suggest that with an absorbent paper and low print densities, good curing results may also be achievable beyond the maximum speed of 500m/min tested. When printing on absorbent paper qualities, the good depth-curing properties of LED UV curing
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deliver an additional benefit, as ink which has been absorbed into the paper is reached better than by classic UV radiators. In analogy to classic UV curing, black ink also represents a bigger challenge than colour when LED UV radiators are used as black pigments absorb more energy from the UV spectrum than colour pigments.
SUITABILITY FOR HIGH PRINTING SPEEDS In summary, IST METZ says that when printing using LED UV inks, high production rates can now be achieved; surface speeds such as those usually achieved on presses for narrow-web label printing or in sheet-fed offset printing, were exceeded by a significant margin in the test runs on the newspaper press. To guarantee reliable curing, however, it should be ensured that an appropriately-modified speed is selected, especially when black ink is involved.
uwww.ist-uv.com
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