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FLEXO Magazine : July 2013
of up to 80 percent can be achieved. Additional time is saved during the engraving operation when areas of solid print are “skipped” by the laser, which passes quickly over these areas in non-operational mode. At the end of the engraving operation, any burnt dust residue remaining on the surface of the plate is removed, by means of a simple water cleaning operation that does not use any solvents. As the elastomer does not shrink and is stable in all dimensions, exact and repeatable repro- duction of the image can be achieved. When the material is pre-mounted on the sleeve before engraving, as is the case with a plate-on-sleeve, this saves the printer the need to mount plates and enables precise registration to be achieved on the press. PROFILING PERFORMANCE With laser engraving, plate characteristics can be realized that are not possible with exposed and processed photopolymer plate systems. The “PremiumProfiler ” is the part of the system that derives these benefits. The laser can be used to reduce the relief height of the smallest halftone dots and very fine elements on the plate, while maintaining the height of the rest of the plate. This pro- duces what is in effect a 3D plate. Reducing the height of the highlight dots means that when the print impression is set up, all other elements of the plate print before the highlight dots. This makes it possible to get good pinhole-free solids and minimize highlight dot gain. Dot gain can be reduced further by changing the profile of the halftone dots. This is achieved by making the final few microns of the dot shoulder just below the print surface perpendicular. This means the dot does not spread as much under impression and there is less opportunity for ink to build up around the edges of the dot. Highlight dots can be provided with more support by increasing the shoulder angle. As part of the laser production parameters, the undercut requirement, first profile step, and the shoulder angle can all be set improving the printability and durability of fine highlight dots. Where fine unsupported ele- ments of the design are concerned, a contoured shoulder can be built up, so as to provide sufficient support during printing. With laser engraving, there is no compromise where fine positive and fine reverse elements need to be produced on the same plate. Where photopolymer plates are concerned, fine positive line detail and fine halftone screens are often enhanced at the expense of fine reverse element and extreme shadow detail by increasing the exposure time. This has the adverse effect of decreasing the relief depth of the reverses and fills in the extreme shadow tones. n About the Author & Technology: David Atkinson has spent the last 36 years working in the flexo industry. After gaining a BSc Hons from London University, he spent 13 years in the flexible packaging industry as a flexographic print manager. In 1990, he joined PIRA, the UK printing industry research as- sociation, and worked there until 2003 as researcher, present- er, trainer and consultant responsible for all flexo activities. Since becoming an independent consultant in 2003, he has been a regular contributor to various trade publications. Hell Gravure Systems, part of Heliograph Holding, has developed a high resolution direct engraving process called PremiumFlexo that brings together their PremiumProfiler and PremiumSetter with the latest in elastomeric plate materials developed by ContiTech, a subsidiary of Continental. • CONTI Laserline CSX has been developed for use with mounting adapters that have a built in cushion • CONTI Laserline CSL has been optimized for varnishing applications • CONTI Laserline CSC, which is supplied with a built in compressible layer, offers the flexo printer two major ad- ditional advantages. Hell and Contitech have recently brought this technology to the USA, in partnership with Daetwyler Corp. in Huntersville, NC. A recently opened demo center affords printers a closer, more practical look at this new technology. Dot gain can be further minimized by changing the profile of the halftone dots. A contoured shoulder can be built up, so as to provide sufficient support during printing. 52 FLEXO July 2013 www.flexography.org