Press Speeds
One of the most common causes of defects is an incorrect ink drying speed. As press speeds increase, the ink drying speed needs to be slower. Historically, inks that are based on ethanol tend to dry too fast, so as press speeds increase, a different combination of raw materials should be considered. Converters that are only moderately increasing press speeds may still use ethanol in some cases, but studies show that now more are using inks based with normal propanol, which dries slower. Diacetone alcohol and a variety of glycol ethers are solvents that would help slow down the drying of ink on press even further.
The key challenge is to develop an ink solvent blend that both meets the needs of high speed presses and maintains ink stability. Inks are typically not mono solvent, but contain a mix of solvents that can include a percentage of alcohol, acetates and glycol ethers.
High speed presses shear the inks more severely, thereby exacerbating the volatility of the solvents, and it is critical that the ratio of these ink blends stay the same during the pressrun. If the ink solvency changes over time during the pressrun, then the inks are not stable and equally capable of causing defects, even with a slower dry ink blend.
As press speeds increase, typically the anilox volumes must decrease. This is due to the defect of misting. Misting typically occurs when too much ink is applied, yielding a fine ink dust that settles on the press equipment.
Misting is seen when the deeper aniloxes are used (above 6.0 bcm to 7.0 bcm), so the best solution is to move to shallower rolls, which minimize the misting defect. However, even with a shallower anilox, the expectation is that the same color strength will need to be delivered. This forces the ink strength to be higher. In summary, using finer aniloxes to get the same color strength requires a stronger ink to be used.
Rework
No printer wants ink left on its shelves after a print job. It is for that reason that printers frequently rework colors from existing colors. If a printer has 7-g. of orange ink leftover and it needs a certain shade of red, it can calculate what is required to rework the ink so that it becomes the required shade.
The challenge is that this process does inherently create some variation. If one print job uses purple to develop the same red and the other uses blue to create the red, then there is a strong possibility that the red will be printed at a slightly different shade.
Color Management By The Numbers
It is important to understand that color is not subjective; every color that can be printed can also be measured, and its characteristics stored as a spectral curve that acts as the “DNA” of the color and serves as an exact specification for further reproduction. There is a supporting system that enables printers to reproduce any color as faithfully and efficiently as possible, whether on paper, board, film, plastic or any other substrate that can be thought of.
The key for such a system is to develop multiple libraries of colors that cover the majority of substrates used in the packaging industry, including corrugated kraft, transparent and white films, laminated films, carton board, paper and labels.
These libraries can capture the spectral curves of any color on the relevant substrate—from a physical print—and hold it in a database on the cloud, which can be referenced at each step of the packaging workflow when a brand owner needs to reproduce that color. The additional key enabler is a digital color communication tool that can link every part of the packaging workflow and share this color “DNA” with every participant.
The brand owner specifies the right color digitally. The designer creates the design file using that exact same color signature. Prepress adapts the file to the specific printer configuration based on that same color spectral curve. The ink manufacturer matches spectrally the right ink to that digital color specification. The printer ultimately reproduces the color on the final product and controls color quality by comparing directly to the original color spectral curves, as specified by the brand owner, and closes the loop for a seamless color approval.
This type of system allows everyone to work from the precise and unique color definition stored in the cloud, and enables users to operate seamlessly in a fully digital workflow to produce colors that will match the original specifications established from real examples on real substrates.
This tool has the scope to remove the margin for error in color reproduction from one packaging material to another, and to bring about far greater consistency through brand families and across multiple territories where substrates are often inconsistent.
About the Authors: Tom DeBartolo is the director of liquid ink technologies and Jim Felsberg is a field marketing manager at Sun Chemical. To learn more about how Sun Chemical can help brand owners and printers produce the same color consistently worldwide using a digitally color managed workflow with solutions that include SunColor Consulting, SunColorHouse, SunDigiGuide, and PantoneLIVE, call 708-236-3798 or email [email protected].