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Applying laser engraving

March 19, 2007

Applying laser engraving
to high volume screen output
As is widely known, UV rotary screen is one of the prime processes for printing cosmetic and toiletries labels on flexo or offset combination presses. One of Europe’s largest users of the process is Rako Etiketten of Witzhave, near Hamburg, Germany. In fact, it markets primary labels under the High & Clear brand name that features screen’s ability to produce tactile varnish effects. Today it produces 12,000 rotary screens (Stork’s nickel RotaMesh), every year, up from 3,700 in 2003. With such a workload the risk of prepress bottlenecks and unwanted downtime at certain periods is obviously high. However, Rako believes it has licked the problem by adopting the latest direct laser engraving technology.
The company recently installed Stork’s new RotaLEN 5511 system. It has certainly impressed Stefan Behrens, prepress manager: “Engraving takes between 15 and 20 minutes on average, which is significantly less than the 90 minutes needed with the conventional exposure process. We can maintain fast turnarounds in a hectic prepress room, where sometimes we need up to 40 screens in a single day.” He adds that it is also a simpler and cleaner imaging process. Instead of films, chemicals, UV exposure, washing, and drying, the process involves the thermal decomposition of the positive area of the emulsion, leaving behind the stencil’s open areas.
The digital process is said to offer consistent quality. In the first month of production, no image defects occurred on any of the 400 screen cylinders that passed under the engraver’s laser beam. Behrens adds that conventional exposures would have resulted in reimaging some 5 to 8 percent of screens because of some defect. Now, all of Rako’s labels printed with laser engraved screens meet the high levels of consistency demanded by its international customer. In quality terms, the new method achieves a very high contrast — ideal for reproducing clear, small text and fine linework — with a wider range of angles than is possible by UV exposure.