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FLEXO Magazine : May 2012
Plants & Processes Consistency & Precision spot color reproduction starts in the Inkroom By rick rosenberger Just how accurate is it to produce a drawdown? This blending of ink bases and matching of colors away from press is imperative if time is to be saved. While many de- vices have been created to provide a consistent drawdown, the most basic is the mechanically engraved hand proofer. Testing suggests that the popular mechanically engraved anilox hand proofer, and even a bladed ceramic hand proofer, cannot suf- ficiently duplicate the anilox roll on press. In other words, a 440- cell count with a volume of five does not necessarily correlate to the same cell count volume on the press. Generally speaking, a drawdown is most likely equivalent to a volume of seven—no matter what kind of proofing method you are using. Don’t believe it? Simply have the inkroom draw down the same color with as many different hand proofers as are available. Each looks the same, from a volume of two all the way to a volume of seven. Many printers force inkrooms to provide dark ink, regardless of what the anilox volume is in an effort to extend ink back to the proper strength. But, this method does not always work. Many times, ink on press can remain even after numerous attempts to strengthen the tone. After being informed that the ink is weak, the inkroom takes a wet sample, draws it down and exclaims that the ink is many times too strong. This incurs numerous costs. Multiply that cost by the amount of times this problem happens and there is a serious amount of money being wasted. But, thankfully, all is not lost. There is a way to get ink right the first time and save thousands of dollars in wasted sub- strate and press time. The key to reliable spot color reproduction is a consistent and repeatable ink to press as compared to a standard; not ink designed to be lightened on press once you see what it looks like. Make the appropriate change to the ink before it goes to press, based on the banded roll test results, which will be expanded upon in this article. In other words, consistency to a standard means measur- ing to a standard and understanding the variables involved, which there are only a few of. One approach is a standard database of colors that have been measured with a spectro- photometer and recorded as ∆e. Another, and the most basic, is clean color standards in a cabinet. Today, the most efficient spot color technique is to compile a database of LabCH values for each color. Following this method will avoid bothering with faded colors. It is preferable to have software that manages the database but it can also be done manually utilizing an Excel spreadsheet. Whenever ink is mixed or blended, it should be drawn down by hand or with a device designed to give as consistent a draw as possible. One example is Parmarco’s precision proofer. It pro- vides excellent results but there are many products available that offer the same scores. What must be considered is the amount of drawdowns needed and how long it takes to clean up between colors. TOLERANCE Once the proper tools have been procured to create a drawdown, the next step is choosing a tolerance. A tolerance is the allowed deviation from the set upon standard color database. There is no industry standard for this kind of devia- tion. It is not in the Flexographic Image Reproduction Specifi- cations and Tolerances (FIRST) manual. Deviation needs to be worked out based on ability. A ∆e of 1.5 or better to the standard is a good starting point. But, while getting closer to ∆e 1.0 is possible, the tighter the tolerance, the more expensive and difficult it will be. It is DEMAND DEPENDABLE COLOR • An engraved anilox hand proofer or a bladed ce- ramic hand proofer cannot sufficiently duplicate the anilox roll on press • No matter what kind of proofing method you are using, the drawdown is most likely equivalent to a volume of seven • There is a way to get ink right the first time and save thousands of dollars in wasted substrate and press time • The key to reliable spot color reproduction is a con- sistent and repeatable draw down as compared to a standard • The most efficient spot color technique is to compile a database of LabCH values for each color 58 FLEXO may 2012 www.flexography.org