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FLEXO Magazine : December 2012
Other approaches, such as that of the Australian Opaltone5 system focused on using standard Pantone® primaries, add- ing a Pantone® conventional spot color yellow shade red, a green made by mixing a yellow primary and a blue primary and a red shade blue primary. Following this logic, some brand owners in the U.K. and in the U.S. attempted to substitute a six- or seven-color pro- cess set in place of their traditional four-color process set and three brand colors. The thinking was that by using only process colors, the ink wells would be kept active and full and there would be an operating cost reduction due to not having to stop the press to change inks. Additionally, different products could be printed on a wide web at the same time, since all products, no matter what brand colors were needed, would be able to utilize the same ink sets. Flexo Quality Consortium (FQC) was charged with identifying a series of inks that could be combined with the FIRST process inks to give an extended color gamut process set. The exact combination of primaries would be left up to the converter or determined jointly between the converter and the print buyer. EXPERIMENT’s PLAN A survey was distributed to Flexographic Technical Associa- tion membership and a review of the concepts of Expanded Col- or Gamut (ECG) printing was undertaken. The survey showed that the majority of FTA members would choose an orange and a violet as the first two extended gamut primaries. Then there was an almost equal distribution for green, blue and red. So, the plan attempted to define carefully an orange primary and a violet primary and document the gamut gains. Then it added the green primary and documented the gamut gain, followed by substituting the red for the orange and the blue for violet. The color science of ECG gives guidelines on how to choose primaries. Figure1 shows a CIELAB a*, b* diagram with the positions of the standard ISO 12647-5 primaries shown. The theory is that one would want a secondary pri- mary that falls in the preferred location of an ideal two-color overprint, which never happens since the transfer of wet ink onto a previously printed ink (wet or dry) is never the same as the transfer of ink onto unprinted substrate. In Figure 1, we see the usual dilemma facing an ink sup- plier trying to select a set of two or three additional process primaries. The orange is a good complement to the cyan and will give a very large extension to the CMYK gamut. Similarly, the magenta is a good complement to the green primary and would be even better if the magenta were slightly more yellow, like most inks for use in light and solvent fast applications. Both of these new primaries show much better complements than they do for the two-color overprint colors. Unfortunately, neither blue-1 nor the violet is a good complement for the typical yellow, though the violet could be a good complement to the two-color overprint of a green primary and the yellow primary. Blue-2 , on the other hand, seems to provide a good aim for the yellow. So, the optimum set of primaries from the colorimetric point would be to add a bright orange, a bright green and a strong red-shade blue. FTA sponsored a student at Clemson University who sur- veyed four of the largest ink suppliers in North America6. The list of 24 pigments and inks that might be used as extended gamut primaries were tabulated and then documented in a manner similar to that used to document the four process primaries in the FIRST book7. Table I shows the results of the Clemson study. The student evaluated the impact of each new colorant using Esko Color Engine Pilot8 software by substituting each colorant, one at a time into an ICC profile for an ANSI CGATS9 IT8/7-4 chart for sheetfed commercial offset printing (GRACoL10). Thus, the addition of red was evaluated by replacing magenta with a Figure 2: Esko proposed approach for assessing gamut improvement. Colored solid shows extended gamut in the CGYK region due to addition of a green primary. This shows an increase from 591,000 CCU* to 712,000 CCU. *CCU is Cubic CIELAB Units (or a cube 1 CIELAB DE* on each side). www.flexography.org DECEmBEr 2012 FLEXO 13