Process control for narrow web flexo.

Author:O'Brien, Patrick J.

We have discussed the concept of process control in several previous articles. Most of the focus from our perspective has been on the prepress end of the business. We need to review the downstream operations beyond prepress to understand the reality of how process control is being implemented. Along this journey, we will identify those areas where, from the author's perspective, more focus is required in order to develop a "front to back" system which is truly under control.


So what is process control anyway? In fact, it is many things to many different people. And it can be a very simple approach to monitoring the repeatability of a process to a wildly sophisticated and complex web of interweaving systems and procedures that control an entire manufacturing process from beginning to end.

For the purposes of this discussion we will fix our attention on the prepress through printing process within the narrow web flexo pressure sensitive label market. Our eye will be on the process control as it is aimed at the ability to control color, both process and spot, utilizing control marks and targets from graphic file development through prepress proofing to on press monitoring and controls.

Let it also be known that the comments herein are a reflection based on the author's experience in the global market as a whole, not just specific to the United States.

What is required at this stage of the process in order to ensure that the intent of the label design will be maintained throughout and executed to the delight of the end user?

In order that process colors of CMYK and additional spot colors can be monitored for accuracy, a representation of these colors needs to be added to the file. These are typically a small square or circular target which is added to the file so that when the layout is finalized through the plate setter, they appear in the trim of the job. These should be representative of how the print is actually going to take place. In other words, if the color is to be printed directly on a metalized or clear substrate, the target should be represented that way. When the color is being printed over white on these substrates, the target needs to be represented over white. If additional spot colors are being built from combinations of CMYK, these combinations need to be presented accordingly. The targets need to be of a size that is readable by the control device used to monitor color within the process. In narrow web...

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