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FLEXO Magazine : March 2014
But the most surprising thing to me is that every time I ask what Delta E I should expect if I print cyan in the upper den- sity tolerance and magenta in the lower limit, no one is able to answer me. Owners and sales people like to promise that they can print within a 2.0 Delta E. Unfortunately, this is not true in most cases, for most printers, because the way they control color today is not related to Delta E. So, finding this number for the density tolerance should be the starting point of any standardization process. Variances are part of any industrialized process and finding those variances is the first step. This will reduce waste and time in the future, and will offer an important tool for the prepress department to know if one color can be printed within customer expectations. This study will offer an idea of what to expect, and also de- fine a way to set proper tolerances as a starting point for any printer who wants to standardize its process. The paper will include research that can be used as a comparison of what to expect, depending on selected printed variables (methodolo- gy, substrate, ink). PROPOSED PROCEDURE This procedure is described for CMYK. It analyzes single inks, two ink overprint colors and three ink overprint grays for 100 percent overprint. The first step is to define the variables, since this process should be done for every set of relevant variables. We talk about: • Printing methodology • Press • Printing forms and accessories, (blankets for offset, an- ilox, tape, etc. for flexo) • Substrate The second step is to define the printing densities and cal- culate compensation curves for CMYK to match the selected printing standard (for example, an ISO curve or G7 methodol- ogy, or any other defined by the customer.) The third step is to run CMYK P2P with your own densities at upper and lower limits. In the example herein, we define the cyan target as 1.45 and tolerance as ±0.05. This means that you will print sets of cyan with 1.4 and 1.5 . When finished, do the same for magenta and yellow. When this is done, you will have eight printed samples to analyze (See Image 1). In the fourth step, using a comparison tool, calculate the difference between maximum cyan and minimum cyan in terms of Delta E and Delta E 2000. For our research, we used “Measure Tools and Esko Verification Tool” as indicated in Image 2. In the fifth step, complete the table depicted in Image 3. For our example, we completed the values for cyan, magen- ta and yellow. These are the tolerances to expect, depend- ing on the resultant color and how many colors we used to make the color build. Keep in mind that this is the minimum requirement to set basic differences. It is possible to extract more data for the colors and for the overprints if we analyze different tint values and combinations. It is also important to mention that the ink sequence should not be changed. RESEARCH RESULTS Our results can be seen in Image 4. Note that they should be used only as a reference. The values indicated are based on specific printing conditions and they may vary depending upon the different combinations of variables. STUDY TAKEAWAYS • Delta E tolerances should be defined in Delta E 2000. For most cases, Delta E 2000 will provide an acceptable difference for a single color, with a density tolerance between ±0.05 • Delta E will deliver a very large deviation, especially for yellow. Light colors don’t represent what humans see • For two color overprints, we can expect Delta E 2000 results between 2 and 10, depending on the printing variables Flexo -‐ Sample printer 1 Delta E 76 Delta E 2000 Cyan Mx vs Min 0.1 2.3 2.2 Magenta max vs min 0.1 3.08 2.17 Yellow min vs max 0.1 14.3 3.4 2 Colors overprint Cyan vs Mag 0.2 6.50 3.50 Yellow vs Cyan 0.2 3.0 1.0 Yellow vs Mag 0.2 6.7 3.1 3 colors Overprint 3 min v 3 max 0.3 5.2 4.0 Image 3 www.flexography.org MARCH 2014 FLEXO 41