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Case Study

Integrating Full-Color, Digital Inkjet with Flexo Label Printing Press – Case Study

The Goal – Like many label printing companies world wide Lundens Tryckeri were suffering due to customer demand for smaller order-quantities, with more variation, and so ever shorter run lengths. Setup time on their flexo presses already dominated job costs and the trend was very clear to Lundens’ director Bosse Andersson. Bosse was sure that Lundens needed to introduce digital printing but having studied the systems available he was also sure that a stand-alone digital system was going to require a very large up front investment and the kind of cost per print figures he was being quoted would make such a system viable only on very short runs of high value labels. In short, the return on investment would be long at best.

Bosse’s dream was of something different. He understood perfectly that his current flexo units deliver the low-cost and high quality that his customers demand, but ONLY when the print run is long enough that the setup costs become affordable. His idea was that what he really needed was a hybrid system: a fusion of digital and flexo. Basically a system that on long runs operates as a flexo label press, on short runs it becomes a pure digital system with zero setup time, and in the middle somewhere it could run as a mix of flexo on some colors and digital on the rest. The decision on any particular job should become purely economic – what is the lowest cost way to produce the job!… In summary what he wanted was to add a full color digital module to an existing flexo press.

By utilizing an existing press as a “base” unit, Bosse foresaw he should be able to achieve good savings in the system cost. He should not need to pay for the unwind-rewind system that is usually part of the digital printer, and in addition he could use the existing pre-treatment and finishing capabilities of one of his existing presses.
-Low investment cost
-Hybrid system allos optimum mix of flexo and digital for lowest cost per print
-Little or no increase in space requirements-
-Minimal retraining of staff

Adaptation Issues
Early on Bosse realized that the key issue in achieving a successful integration of the digital print unit would be the accuracy of the media movement under the colorprint module. IIJ had explained that their module is built up from a number of smaller inkjet printheads all contained in a single printhead unit. The individual printheads do not join end to end but are arranged in two rows per color and placed so that the print from one head merges seamlessly with that of its neighbor in the next row. The printheads used by IIJ (from Konica Minolta in Japan) are very slim, but the two rows are still 20mm apart. Roughly speaking this means that if the label stock moves under the inkjet unit at an angle then the print from adjacent heads will either not join together (leaving a white line) or will double up (creating a dark line). The first challenge was to ensure that the sideways movement of the label stock was controlled well enough that his would not be an issue.

A second issue was the cure delay of the inkjet ink on the media. IIJ had explained that on different label media the inkjet ink would wet out at different speeds. This means that the distance between the inkjet module and the UV lamp will need to be adjustable to achieve the best print quality on any different media. It was determined that the maximum gap between the lamp and the head should be 1 meter. A print base station or adapter was designed to ensure plenty of adjustment between the UV lamp and the inkjet module.

The next issue to be solved was to ensure that the print from the digital color label printer would register accurately to their die cut labels. The solution was simple. A photo-sensor was mounted after the in-line die cut. The sensor had no difficulty detecting labels against the background liner material. The result was a 100% regiter between die and print. The system was finally installed in April 2011.

Media Issues
During trials of different label stocks, Lundens realized that despite the print tests of different materials made earlier at IIJ, there were a lot of standard paper flexo stocks on which the inkjet print just did not work… Basically the inkjet ink tended to “reticulate” or “bead” on the gloss materials. Plastic films generally worked well, but many paper stocks did not work. The Mark Andy press was already fitted with a corona treatment unit but this was found to have little effect. Finally investigations found a pre-treatment coating can be applied inline by one of the existing flexo units on the press. This pre-treatment allows the inkjet to print on almost any stock with excellent definition and smoothness. At the same time the cost of the pre-treatment is sufficiently low that it does not significantly add to the overall cost per print of the digital system…

Result: Flexo vs UV Inkjet
The system has now been in use for around 2 years. It is used every day has proven to be reliable, easy to use and with an absolute minimum of maintenance. The combination of utilizing an existing flexomachine with the IIJ print unit created a complete unit for label production. With many options and possibilities and all produced in one single pass through the machine. No need for extra converting units.