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FLEXO Magazine : June 2012
45-DEGREE QUAD In the mid-1980s, the main cell geometry that was being en- graved in chrome anilox rollers was the 45-degree pyramid or quad cell (Figure 5). When ceramic surfaced laser engraved anilox rollers were first produced, the 45-degree was the first geometric achievement. This cell structure has a four-sided cell with considerably wide walls. Flexible packaging and the label market went to this ge- ometry as they transitioned from chrome anilox rollers to the ceramic surfaced rollers. This geometry was the cell of choice for the flexo industry for most ceramic surfaces. The 45-degree roller is still chiefly utilized in coating ap- plications. High volume applications above 25 bcm are where this geometry is best applied. The quad cell can be used for OGR coatings, lamination adhesives, and blister coatings are just a few of the application types. The volume range on this geometry would be 85 bcm. 30-DEGREE HEX The 30-degree hex (Figure 10 and 11) has a natural channel created by nature in the orientation of that cell. The channel can be manipulated to some degree. It can help ink to wetout better as it is being transferred from the anilox to plate. Ink type, viscosity and ink rheology can change or affect the way the ink transfers. Experience proves that this geometry works best—with better holdout—on coated papers, films, foils and substrates. When running with uncoated materials, the ink can saturate into the substrate, and if it dries too quickly, a slightly ribbed affect may be seen. This geometry can and is used to lessen the spitting phe- nomenon that happens when using UV inks. It will also print adequately with UV inks, thanks to the drying rate of UV inks, which is slower and runs cleaner than most water and solvent systems. The 30-degree engraving needs to be evaluated if being considered for water or solvent systems. The 30-degree hex is especially useful when running opaque white inks on films and foils. The channel allows the ink to wetout slightly better than 60 degree. Subsequently, this lessens the amount of visible pinholing that can occur and runs better with UV whites, rather than water and solvent white inks. It may help to make sure curing lamps are spaced to allow ink to wetout the most before initiating cure. NOTE: On flexo applications, you should test thoroughly be- fore transitioning to any new geometry. Make sure the optimal stickyback choice has been made to help support the change. 30-DEGREE CHANNEL This channeled engraving has a few common uses. It was initially popular for UV spitting issues. The channel minimizes some of the pressure that builds up, due to UV ink viscosity behind the doctor blade. The build up can force the blade to bow causing the front edge of the doctor blade to intermittently discharge ink. UV ink spitting is a phenomenon that all printers struggle with and there is no definite cure. This geometry is just one of the components that may help avoid the problem. When used for printing a standard flexo graphic, it will yield an acceptable result, however, it is not as sharp as the 60 degree geometry. Note Figure 12: the 10 point type at an 8 bcm will print open, but does show some hallowing with the 30-degree channel. The 30-degree channel is also very useful when running high volume UV white application on films. There is an inter- est for this in the label industry on narrow web presses where they may want to simulate the rotary screen ink thickness. This geometry can work well as a substitute. The success of this application may vary, depending on the components in the flexo process—from stickybacks to ink manufacturers. Changing any variable may yield a different result. Testing and standardization of all components is imperative. TRiHELiCAL CHANNEL: XTR The trihelical (Figures 13-16) is a constant channel around the anilox roller or sleeve. This geometry comes in three vari- ations: 45-degree, 75-degree and 89-degree. Because it is an open channel, it is speed sensitive. This would be used mainly on high volume coating applications. Certain coatings—due to viscosity or rheology—may be sensitive to misting, which is a very fine mist that gets released from the cell channel while running at an extreme speed. That speed designation may vary due to the ink or coating’s viscosity. Also, due to the direction and angle of the channel, the 45-degree geometry tends to naturally push inks and coatings to one side of the ink chamber. One possible solution is the 75-degree or 89-degree variation. The 89-degree is almost lin- FiGURE 7 FiGURE 8 FiGURE 9 FiGURE 10 FiGURE 11 FiGURE 12 72 FLEXO june 2012 www.flexography.org