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FLEXO Magazine : November 2010
LUX Technology Enables Better Flexo Print By Timothy Gotsick, Ph.D. Global Director of Innovation MacDermid Printing Solutions Flat-topped dots are not new. From the advent of photopoly- mer usage in flexo, everyone made flat-topped dots, because that was the only option. When you pull all the air from be- tween a negative placed on top of photopolymer, a flat-topped dot inevitably results. And there was a lot of good flexo printing done with analog flat-topped dots. But the more efficient digital platemaking workflow brought with it bullet-shaped dots, which could be made remarkably (if in many cases precariously) small, and which had the natural cutback curve that made their resulting print gain look so good. Both the ultra-small dots and the favorable print characteristics were fortuitous side ef- fects of oxygen inhibition of the photopolymerization reaction. However, despite the major advances that the standard digital workflow brought with it, there were sacrifices required. Most striking was the need for a large ‘bump’ curve to make up for the fact that very small holes in the digital mask were too small to let enough UV energy through to form usable dots, if any were created at all. In what has become standard practice, the work-around of chopping and stretching the tone curve to create small dots on the plate was adopted. Although effective in most cases, the ‘bump’ is yet another variable that has to be set and maintained in order to make plates print well. Plus, the structure of the very small dots that digital flexo platemaking yields adds another challenge – even if the smallest dots are held, their rounded tips and verti- cal shoulders make them very impression-sensitive and prone to folding over on press. Both of these issues can compromise the quality of the ‘fade to zero’ vignettes that such fine dots should make possible. Well, not for the first time in human history, we have made progress by learning from our past, and can now combine the best aspects of flat-top dot geometry and digital workflow into a new option that looks to be the next step in flexogra- phy’s technical evolution. By keeping the factors that make digital flexo successful (digital workflow, high-quality imagers, multiple plate options) and addressing the compromises previ- ously required (structurally weak highlight dots and a ‘bump’ curve), the new LUX platemaking process (Figure 1) from MacDermid Printing Solutions delivers a practical and simple option for those seeking to increase their print capability and take some business from gravure and offset. It is useful to explore the difficulties in standard digital flexo platemaking in order to understand how the LUX platemaking process addresses this situation. First, consider the highlight dot formed by a standard digital platemaking process (Figure 2). The dot has a rounded tip and steep shoulders. But where exactly is the inked/printing surface of this dot? In practice, it is process dependent; it varies with anilox-plate and plate- substrate impression levels. Push the plate harder into either the anilox or the substrate, and ink will be forced further and further down the rounded top surface of the dot. Compare this dot to the LUX digital dot (Figure 3), which has the same steep sides, but a well-defined top surface, as defined by the clear edge that distinguishes the top of the dot from the side. Once the dot’s printing surface (the top) and its support structure (the side) are clearly separated, they can be independently controlled and optimized. Figure 1 Digital Plate Ablate Image LUX Lamination LUX Membrane Expose Solvent Process LUX Digital Platemaking Workflow Remove Membrane fall conference eDITIon FLX_Nov10_mech.indd 18 11/1/10 2:19 PM
Sustainable Fall 2010