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FLEXO Magazine : September 2014
GRAPH EXPO 14 2014 Table 1 L*a*b* Delta E Comparisons Y M C K Film, low speed 6.157 1.746 7.823 0.943 Film, high speed 5.775 1.457 1.418 1.161 Paper, low speed 4.969 2.492 2.228 4.315 Paper, high speed 9.899 3.242 0.830 3.490 Delta E values calculated in Ta b l e 1 were compared to standards for color difference in Ta b l e 2 . These are industry accepted standards on where delta E values begin to differ. The two tables are used to compare whether there was a significant difference seen between the color values produced by the two different UV curing systems. Table 2 Delta E Value Meaning 0-1 A normally invisible difference 1-2 Very small difference, only obvious to a trained eye 2-3.5 Medium difference, also obvious to an untrained eye 3.5 -5 An obvious difference >6 A very obvious difference There were color differences in the conventional UV and LED UV samples detectable by the human eye. Looking at the first comparison in the table of run A (film, conventional UV, low speed) and run F (film, LED UV, low speed), there were significant differences in color for both the yellow and cyan color samples, while there were only negligible differences in magenta and black. Looking back at the ColorThink graphs, it is important to note that conventional UV reaches a purer color for both yellow and cyan. A significant difference in delta E values was also seen on the comparison of run D (paper, conventional UV, high speed) and run H (paper, LED UV, high speed), where the color differences for yellow were significant. This difference in color seen between the conventional UV and LED UV sam- ples is important when understanding the color reproduction capabilities of the press. The L*a*b* delta E data chart in Table 2 illustrates other areas in which the color differences were detectable to the human eye, both trained and untrained. A trained eye will notice slight color differences, while the untrained eye does not recognize these slight differences. Given these color differences and the graphical interpretations, it appears that conventional UV curing produces a wider color gamut. Further testing of ink formulations used for the two curing systems may reveal more valuable information about the impact on color gamuts. Both conventional UV and LED UV curing methods may not have an impact on the color produced by the UV inks. When cured, UV inks are solidified and bond to the substrate without any evapora- tion, which is typical of traditional flexo inks (“An Evaluation of Flexographic Inks on Wide Web Film”). Because of this, there may be properties inherent in the different ink formulations that should be further studied to better understand the differences in the color gamuts studied in this experiment. 70 FLEXO | SEPTEMBER 2014