Maintaining Print: Keeping the Same Color Over Time
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The Need for Accurate Color
For many printers and print buyers, accurate color and the ability to match the proof are important. The goal of accurate printing seems basic and fundamental, but it is not as easy as it seems. Printers and their clients often complain about the challenges of matching color. While print today has moved much closer to manufacturing, perfect color is still not guaranteed. For this article, we will explore why calibration is essential, what happens after we calibrate, the print condition and its relationship with maintenance, and finally how to implement a robust process control loop.
Why We Calibrate
We calibrate (and profile) to get the color to be accurate. Calibration itself is quite important as it determines the parameters and quality of the printing method that we are using, as well as aims the printing machine to the target print condition. Quite a bit of emphasis is placed on performing a correct calibration and learning the proper method. Calibration is important, but I often tell my customers— that’s the easy part. Maintaining the calibration is the real challenge.
What Happans After We Calibrate?
Immediately after calibration, the color match is normally good. Color metrics are often within tolerance, and the visual match is good. What happens next over time are subtle (as well as not-so-subtle) changes in the printing process. These subtle things can be changes in raw materials, with substrate being a primary area of change. Other consumables, such as inks, chemistry, and mechanical components, such as nozzles, blankets, and rollers all can change over time. When any of these components alter, this can cause a color change. The end result of these changes is known as drift – where we suddenly are no longer matching the print condition. Depending on the printing process, the drift can be barely noticeable, or it can be quite dramatic. For example, with inkjet, if the print heads are clean and the substrate has not shifted, results can be quite consistent over time. But even with inkjet, a simple clogged nozzle or change in substrate coating can cause a major shift in color. For more of a mechanical process such as litho printing, there are a much larger number of mechanical variables that can change and cause drift. For example, just with a shift change, a new operator changing how they run water, or pressure they use can affect a dramatic color change.
What is Process Control?
The way that we control printing machines is through process control. Process control is a systematic approach used to maintain the accuracy and consistency of color. The act of process control is defined as the monitoring and influencing of an activity to maintain a desired output. It involves watching and managing the entire color reproduction process to ensure that it stays within defined tolerances. Process control helps maintain color consistency not only between different devices, but also over time as equipment ages or environmental conditions change. We simply measure the printed output and watch to see if there are changes or drift. Most printing machines have a degree of normal variation, and as long as we are operating within those limits, we can expect consistent color. Some devices like litho, flexo, or gravure have higher levels of variation, but also dramatically high levels of production speed. Other devices like inkjet have less variation, but currently less speed than more traditional methods of print.
The Process Control Loop
One key idea with process control is the process control loop. This is the idea that you will monitor or measure print at a specific interval. Once you have measured it you will compare it to your target reference values. If the measurements are within tolerance, you record them and continue. If the measurements are outside of tolerance, then you stop and make corrections. This could be as simple as recalibrating or could require repairing a mechanical component that is causing the drift. For example, on an inkjet where the paper may have changed or a thermal print headed degraded, a simple calibration may pull you back into tolerance. On a traditional press, it may require a mechanical change such as adjusting roller stripes or changing blankets. Either way, the big idea is to measure at frequent intervals and make corrections when you notice drift.
The Relationship Between Maintenance and Drift
One thing I notice as I travel into different printing facilities is the direct relationship between maintenance and drift. At the average litho plant, there is normally some degree of drift that recalibrating helps with. I have a handful of litho customers who do exceptional maintenance, and who do not require recalibration each year. The presses are immaculately maintained, with scheduled roller and other part replacements. These sites have used the same plate curves, presses, and consumables for multiple years with no changes required. When I arrive and run test forms using the old plate curves, I get the same passing result as the run the prior year. In the inkjet world the maintenance is easier, but still just as important. The better shops are performing process control and monitoring color, and the adjustments are simple and routine. In the shops that don’t perform maintenance, the heads are often clogged, and they will have to spend hours cleaning prior to any type of calibration or certification to be performed. There is a clear relationship between maintenance and maintaining a print condition.
Implementing the Process Control Loop
Below are some steps on how to implement the process control loop:
- You will need to have the equipment and software to measure with. These typically include spectrophotometers, software to analyze the measurements, and keeping a record of the print conditions over time.
- You will also need to define precise color standards that align with your press and that are used in your industry. To monitor a machine, we need to know how that machine prints when correctly calibrated. When we calibrate, we need to aim a relevant industry standard.
- You will also need to calibrate regularly. Prior to performing process control, you will need to perform initial calibrations as well as follow a schedule for routine maintenance and recalibration as needed.
- During the process control loop, you will need to continuously monitor color output and adjust devices when needed to maintain accuracy.
- While doing all this you will need to document and analyze print data. This involves keeping records of calibration and measurement data for analysis and trend identification.
Color Accuracy is Paramount
In a world where color quality means higher-value products and customers, accurate color is paramount. Calibration, along with a robust process control loop, is the key to ensuring that colors appear as intended across various devices and applications. By investing in the right equipment, establishing standards, and implementing regular maintenance and monitoring, professionals can maintain precise color consistency and produce visually stunning results. Calibration is not merely a technical process; it is an art and science that bridges the gap between creative vision and tangible reality, ensuring that what we see is what we get.
About the author:
Ron Ellis is a consultant specializing in color management, automation, and workflow integration. An Idealliance BrandQ Expert, BrandQ Expert Trainer, G7 Expert, G7 Process Control Expert, G7 Expert Trainer, and chair of the Print Properties Committee (PPC). Ron has performed hundreds of G7 training and calibrations. He has conducted training and consulting for a wide range of customers in Europe, Asia, and North America. Well-versed in ISO standards, Ron specializes in creating and implementing working spaces for brands and agencies that allow them to work more efficiently with vendors, saving both time and money.
Learn with Ron during Idealliance G7® Training & Certification, find a calendar of upcoming training here –www.idealliance.org/g7training, or at iLEARNING+ as part of Color Management Professional® Offset Training & Certification and Packaging Print Essentials.