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FLEXO Magazine : August 2010
Technologies & Techniques ferred to the surface of the printing plate will depend on sev- eral factors, such as surface tension, pigment concentration, pigment particle size, press speed, degree of plugging in cell, blade pressure, thickness of blade, angle of blade, reverse or positive blade, blade or wiper metering roll used. The truth is, there are even more factors, but I hope you will see that this is a very contentious area that printers and engravers rarely agree on, due to the multitude of factors involved. The one area, where most probably agree, is that there can be a huge difference between what is specified and what is achieved, if one does not take the factors mentioned into account. More to the point, if any of these elements change, again, the final volume of ink that is released to the plate will change as well. Because of the small dimensions involved with most en- graved cells, volume is generally measured in billion cubic microns (bcm) per square inch. One bcm is equal to one mi- croliter. In Europe and parts of Asia, it is referred to as cubic centimeters per square meter (cc/m2). Cell volume and volume to plate (VTP) is really what equates to the density and ink/coating film thickness that you will achieve, which is why this is a more important consider- ation than the cell count itself. Now that we have those simple factors straight, we can dis- cuss the choice of screen count. For most printers, this is another area of major frustration and confusion and is usually the first question asked of the engraver: “What do you recommend?” The response of most seasoned veterans is, “Well, what do you use now?” Now, for many printers, this does not seem like a fair question. The truth is, with so many variables involved in the process of selection, having a starting point, based on what you are presently using, gives a benchmark to work from. Clearly, if what you are using does not appear to be allow- ing you the chance to achieve the correct coat weight or den- sity, or is giving you too much dot gain, then it certainly helps to identify what is and is not working, and what you should consider changing. Do bear in mind, however, that one engraver ’s volume does not necessarily mean it will match another engraver’s , due to the differences in coating density, release characteristics, laser technology used, cell shape, actual line count and even volume measurement technique and instruments. FTA’s FQC is conducting a gauge reproducibility and repeatability study on volume measurement in response to this phenomenon. For more information, see FLEXO December 2009, page 8. It is for some of these reasons that, if you are satisfied with your print results from your existing anilox supplier, you need to consider long and hard about switching to another engraver just because your purchasing manager says it is cheaper. It is true that a good and experienced engraver will be ultimately able to match, and may even be able to improve on your print results and help reduce your ink or coating con- sumption. But you will need to be prepared for a learning curve Experience the science behind the service with Proline® anilox rolls Praxair Proline® laser engraved ceramic rolls deliver quality your printing operation can depend on. Whether you need extended life, improved ink laydown, better opacity, or more repeatable print results, Praxair Proline® series of engravings is for you. Our ART (Anilox Reverse Technology) and REV (Revolutionary Engraving) cell shapes and configurations continue our history of technical innovation to the flexographic industry that began with the introduction of the first laser engraved ceramic roll to the printing industry almost 30 years ago. You can see the results every time the press rolls. Improved printing quality. Consistent reproduction. Reduced maintenance downtime. And, better profitability. www.praxair.com/printing Call 1-800 -234-3131 for information on how we can help your business. www.flexography.org august 2010 FLeXO 95 August2010_mech.indd 95 8/13/10 7:47 AM
Sustainable Summer 2010