SubscribeZED instruments have been designing and manufacturing laser engravers for flexo and anilox plates for 25 years. Their newest ZEDMini range of direct digital laser engravers combines computer to plate technology in a compact, low cost, low maintenance, yet versatile machine, which enables them to expand into new markets.
In particular, they see direct digital laser engraving technology offering huge benefits in dry offset printing, where it enables the achievement of a quality normally associated only with waterless printing.
Drive for high quality
As brand owners vie for ever more sophisticated images, the print industry is only too familiar with the problems of producing high-quality print on non-absorbent substrates, such as plastic food and drink containers. The inherent limitations of dry offset have forced many printers into the use of waterless printing and in-mould labels. Both have disadvantages, but these are tolerated in the name of quality. Quality improvements in dry offset technology, with its existing advantages of speed and the robustness of relief plates, would be welcomed with open arms.
ZED Instruments' ZEDMini direct digital laser engraver
The old problem of high dot gain
It is difficult to produce traditional photopolymer relief plates without introducing some dot gain, which is especially problematic in the highlight areas.
The need to ensure minimum contact between the ink rollers and the plate, the plate to the blanket and the blanket to substrate is critical in trying to reduce the inevitable dot-gain. On set-up the printer will tend to use the solid density areas of the print for his ink and impression settings reference. The resultant dot-gain is then printed throughout the tonal range. This may be reduced at the plate-making stage by minimising exposure and wash times to reduce the dot shoulder angles, thereby reducing dot-gain on plate itself. Nevertheless, the result is inevitably a compromise between the quality of the solid densities and the highlight areas, which, of course, affects the entire tonal range. Dot gains of 20-30% in the highlight areas are quite common and this cannot be tolerated in today’s market.
Alternatives to dry offset
Waterless printing can achieve the image quality that brand owners now require, particularly on vignettes. However, short plate life has resulted in very frequent plate changes and, therefore, high wastage and increased production times.
In-mould labels are printed digitally or by other means, and can also deliver the required quality. The disadvantages here are the after-processes and time involved in moulding the label onto the container.
Revolution in dry offset technology
The dramatic improvements to dry offset image quality produced using polymer plates are made possible by two factors – laser engraving and precise digital control. It has been recognised for some time that laser engraving the polymer makes it possible to produce below-surface highlight dots in effect giving the plate a ‘built in make ready’ effect. However, early attempts to make use of this suffered from laser instability and limited control, with subsequent high variability in the exact below surface depth.
ZED Instruments' ZEDMini direct digital laser engraver
Now, using sealed lasers with digital switching of the output beam, the new ZEDMini series accomplishes the necessary consistency and ZED’s FlexoDirect integrated software package provides the control.
No compromise
Tone calibration of new plates is now precise and controllable. In addition to the normal range of dot areas from 1% to 100%, the first test plate includes a series of highlight dots whose surfaces are set progressively further below the print surface.
The printer uses this first test plate to set ink and roller settings for the best possible solid density/shadow areas as his reference without worrying about the highlight areas. The test print goes back to the engraver who measures the below-surface dot that is just starting to print at those settings, and defines that as the finest highlight dot. This not only ensures that the highlight areas in vignettes fade imperceptibly into the background, but also gives the maximum possible tonal range. Below surface depths and engraved dot sizes can be adjusted independently for accurate printing of percentages right across the tonal range.
Direct computer to plate
Direct digital laser engraving not only enables a dramatic improvement in the quality achievable with dry offset printing, but also increases productivity by eliminating the whole cycle of plate exposure, washing, drying and post exposure processes. Normal productivity is improved and rapid production of special editions becomes a viable possibility.
Direct computer to plate also means greater security, enabling centralised repro and direct electronic transmission of plate images to printing houses.
Dry offset plate engraved using the ZEDMini
The way ahead
With excellent image quality, line counts to equal waterless printing, increased productivity, and better security – the need to compromise is gone.
For further information please contact:
ZED Instruments
328 Molesey Road
Hersham
Surrey
KT12 3PD
UK
Tel: +44 (0)1932 228977
Fax:+44 (0)1932 243603