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FLEXO Magazine : January 2008
. ... .. . I ' I. . J .. . .1 I .... ... . 'F1IIII . ... .. . I ' I I. '" J . I .... sistent usage of the same anilox speci- fications per cyan, magenta, yellow and black will go a long way in assuring a higher percentage of consistent print results. With the advancement of new anilox engraving technologies, choices should be made via a banded roll trail as to the necessary anilox specification for a target solid ink density, l*a*b* or L*c*h o value. In order to assure repeatability, it is imperative to consistently use the same cylinder with the same inks and keep as much of the parameters at the press level consistent. yield. When combined with all evaluated data, it will enable a quantified choice of anilox specification for specific solid ink density target. Along with the analysis of the tone-scales for press gain, analysis of the print contrast for comparison of printable three-quarter-tone detail was also conducted. TONESCALES Each column lists the engraving specifications (cells per inch and volume). Each chart highlights the 20 percent, SO percent and 70 percent areas, as well as that correlated directly with the climb in volume. See Figure 2. DENSITY AND CONTRAST The yellow hit the target with the vol- ume of 1.25bcm. The magenta is just be- low and above the target with the volume of 1.25bcm and 1.50bcm. That leaves a choice of either extending the magenta to achieve the solid ink density target us- ing the 1.50bcm volume or using an en- graving volume specification of 1.35bcm, which should hit the target solid ink density number of 1.40. The cyan and the FIGURE 2. To illustrate the point the following is an example of narrow-web print trials conducted using the latest ceramic anilox engraving technology, high density ink and digital polymer on a banded roll trial with cyan, magenta, yellow, and black inks. This example will illustrate the impact of new engraving technology in achieving solid ink density targets print- ed on high gloss stock with high-density inks and printed using high lines per inch on the polymer (175Ipi), using a me- dium durometer stickyback. The anilox engraving used was 1,600 cells per inch with a volume of 1.00bcm on the first band; the second band had 1,600 cells per inch with a volume of 1.25bcm; the third band had engraving specifications of 1,600 cells per inch with a volume of 1.5bcm. The solid ink density target was Y = 1.00, M = 1.40, C = 1.45, K = 1.60. Conducting the print trial gave the opportunity to analyze the tonescales to determine the press gain each differ- ent cells per inch and volumes would the quarter-tone, mid-tone and three- quarter-tone areas. These areas, along with the minimum dot percentages, are key location points in the tonescale ramp to monitor and track in order to assure consistent results once running in a pro- duction setting. See Figure 1. Looking at the change in anilox speci- fication per column, there is a direct cor- relation in dot gain and an increase in volume. In this instance, the difference is minimal. However, the difference can be magnified when the other variables of over impression, stickyback variation and wrong anilox selection are added to the equation. With a little extra squeeze of impression, the density numbers and press gain number can be dramatically affected. Additionally, the wrong choice in anilox volume selection will impact the printed result and can be compound- ed with over impression. Likewise to the tone-scale gain, the solid ink density values in comparison to the target had a similar upward range www.flexography.org black inks hit the solid ink density target with the anilox volume of 1.25bcm. Another area of the image evaluated was the print contrast. Print contrast is a reflection of the printable tone range between the solid areas and the shadow areas or the three-quarter-tone areas. In this case, it is a comparison of the 70-percent tone-scale to the 100-percent solid of the same color. Using the 1,600 engraving specification, the digital poly- mer and high strength ink, the value that was read was quite impressive. Traditionally, the print-contrast values have been anything above 20 percent. Looking at the print contrast values that were recorded, these values are signifi- cantly greater. Relative to the traditional 20-percent target, the results recorded are all desirable. See Figure 3. SMALLER AND SMALLER Not too many years ago, using a 1,600 anilox engraving, along with 175lpi poly- mer would be unheard of, or thought of 2008 - JANUARY FLEXO