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FLEXO Magazine : June 2011
Technologies & Techniques Cell Count & Cell Volume The True Determiners of ink Film Thickness By shane Weber Flexo printing is ever evolving. Mechanical improve- ments now allow for high-end process printing to be run at speeds in excess of 1500 fpm. Exponential advance- ments in digital technology have paved the way for printing plates that can hold dots down to 0.25 percent at 240 lpi and beyond. Still, we’ve yet to succeed in establishing “one size fits all” flexo. Some, in fact, doubt that we ever will. Each system is unique and must be optimized with regard to inks, substrates, anilox rolls, photopolymer plates, etc. Companies that are willing to innovate and develop efficiency can use these advantages to remain profitable and competi- tive. Optimization of the relationship between the printing plate and anilox roll is critical for print-to-proof color repro- duction. It all begins with the anilox roll, which by simple definition is an engraved ink delivery roll designed to apply a specific ink film thickness to the printing plate. Essential terms associated with an anilox roll’s constitution are: 1. Cells: microscopic cups that carry ink. 2. Cell Count: Number of cells per linear inch on the angle of engraving. 3. Volume: Amount of ink contained per square inch of cell area. Specified as Billion Cubic Microns per square inch. 4. Angle: Angle at which the cells are engraved to horizon- tal roll axis. (30-, 45-,6 0 -degrees) The cell count and, more importantly, the cell volume of the anilox roll will determine the ink film thickness that is applied to the plate.There is a wide range of options for cell count and volume combinations. (See Table 1). In addition to cell count and volume combinations, there are new and advanced cell geometries available that offer benefits. Now, let’s briefly cover the various styles of anilox.The cur- rent standard for anilox roll engravings is what’s referred to as a 60-degree, laser-engraved, ceramic anilox roll.Differ- ent suppliers have various product names for their specific technology, but all are an arrangement of cells engraved at a 60-degree angle to the horizontal axis.The end result is similar to a honeycomb pattern. (See photo, page 61).This technol- ogy has been available since the late 1980s and continues to be the workhorse for laser-engraved anilox rolls. There are some newer styles of engravings available in the marketplace today. One of these engravings is an open cell geometry engraved in the pattern of an “S” and the other is an elongated variation of the 60-degree cell pattern. (See photo, page 61).They are designed to increase the range of printable graphic capabilities within the same anilox roll, the idea being to increase density delivery while maintaining fine detail in the highlights and mid-tones.Improvements of this kind can in fact increase the printable color space.More importantly, they can print better levels of contrast, giving the image more “POP” . Regardless of anilox roll cell geometry, the ink film thick- ness delivered by the anilox rolls needs to be predictable, repeatable, and manageable in order to print consistent brand colors. Minor shifts in the ink film thickness will add time to on press color matching and create headaches for the ink suppliers. Table 1 60 FLeXO June 2011 www.flexography.org Correct & Consistent • Optimization of the relationship between the printing plate and anilox roll is critical for print-to-proof color reproduction. • Regardless of cell geometry, the ink film thickness, delivered by the anilox roll, needs to be predictable, repeatable, and manageable in order to print consis- tent brand colors. • A banded anilox roll test is highly recommended to establish the anilox roll cell count and volume com- bination that will achieve the minimum target density and provide the best graphic reproduction. • Minimizing dot gain and maximizing density is a primary goal for selecting the correct anilox roll.
Sustainable Spring 2011