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 printing, the targets are typically run as part of the bearer bars which have become a common “mark” on high quality print jobs. The bearer bar provides a means by which even impression settings can be maintained as the cylinder rotates during printing. In addition, where possible, the targets can be run in the matrix area so they can be monitored during printing but not remain as part of the finished label.

Once the proper targets are selected and applied to the design, they will remain with the file so that at each critical stage of the process, they can be evaluated to ensure that the process is in control and the expected results are being achieved. There are many good reasons for the targets, obviously, but think about the fact that we are under increasingly tightened timelines for producing labels these days. The targets allow us to ensure that we can pass from one process to the next and the next with confidence and control.

To understand this a bit more, let’s assume that a press characterization has been run. This is required when a key element of your process has changed, e.g., plates, inks, anilox manufacturer, even substrate type. Or if it’s a new press that will now be running a certain type of work that was previously run on another press. Whatever the reason, certain elements of the characterization, the square or circular targets, for example, will be used as ongoing process control targets for ongoing production runs.

These targets will assist the prepress provider in predicting the characteristics of this particular press. They will utilize these targets in proofing so that prior to going to press, a prediction can be made as to the result that can be expected once on press.

The profiles that are built from the press characterizations become the database to which all subsequent proofing and production runs are measured. If the prepress provider can monitor and maintain the level of reproducibility within his process by using common measuring targets and instrumentation, then the onus is on the printer to take the handoff, produce plates which reproduce the image accurately, and then execute the image on press as predicted by the proof.

In today’s market, the instrumentation is available and has been implemented in production environments around the world whereby each step of this process can be monitored, including images on relief plates.

Advancing flexo’s capabilities

Now we get on to the press, and this is where the fun starts. Video web inspection systems have been part of the press configuration for many years. Over the years they have increased in complexity. From the most simple registration control systems based on strobe lights to the most sophisticated defect detection systems, which stop a press dead in its tracks when a certain threshold of preprogrammed defect is exceeded.

Let’s look for a minute at the nature of the label printing market. As we all know, the quality of flexo has been improving steadily for many years, but at a very fast pace over the last decade with the advent of such technological advancements as UV inks, thin digitally imaged plates, finer anilox rolls and servo driven presses.

Flexo has reached a level of quality, predictability and consistency that can rival certain offset and gravure print performance. Consumer products companies (CPCs) are moving their label business to flexo because of the advancements in quality and technology, but a motivating factor for this migration continues to be the lower cost perception of flexo versus offset and gravure.

Label printers, in this author’s humble opinion, are not selling the value of the quality and the technology in which they have invested. It was this commitment and the associated investments that have allowed them to position their companies as competitive with the higher priced print processes, yet they have undersold the value that these investments have delivered.

Some market leading printers continue to have problems in implementing better process control in the area of color management on press as a result of their inability to sell the value of statistical process control to the CPCs.

For example, in order to ensure a quantifiable management of color on press, it is necessary to run color bars of the sort we have been talking about previously in this article. However, due to downward pricing pressure from the CPC, the printer decides that in order to remain profitable in the face of lowering the pricing to the CPC, he needs to optimize the material utilization by purchasing substrates such that there is no room for control targets anywhere on the web.

Consequently, the only color verification that is happening occurs when a sample is taken at the end of a roll when the roll is changed. This is not a good situation for obvious reasons. A color sign off by the CPC occurs at the beginning of the run, and they walk away happy. The printer carries on monitoring color occasionally during the run and adjusting from a visual inspection from time to time, and then a more detailed inspection occurs at a roll change.

The net result for the CPC is that it is saving money on its label purchases; the CPC thinks that it is receiving acceptable quality based on its sign-off, but by the time the finished labels get to the point of use, the variability is apparent and the complaints and rejections begin. This forces the printer to go back on press and re-run under similar conditions, so they back fill what was rejected with more suspect material. The adept CPC will recognize the defects, attribute them to flexo and go back to the previous supplier of the offset and gravure printed label. The aspect of this that everyone forgets is that the offset and gravure printer has built the same controls into their processes for years and would never relinquish this control for the sake of running a narrower web without the targets. They just wouldn’t.

Now if the flexo label printer was able to sell the value of process control and educate the CPC on the requirement to be able to monitor the process with the appropriate tools, the CPC would win because it gets the quality at a somewhat reduced price, and the printer will be able to control his process because he can run under control. The part that the flexo printer doesn’t recognize is that if he ran with control targets, he could get to color sooner, and maintain color during the run. Both would drive savings to the bottom line for the printer.

Having studied this scenario several times over the years in various situations in wide and narrow web, I have observed that it always plays out the same way. If the printer brings more control to his process, he will run a more efficient operation and deliver a less expensive but equally profitable product to the end user. And the interesting revelation that isn’t understood, and is always puzzling, is that given the education of the importance of process control, any CPC worth its salt will always opt to support the printer’s need for process control in order to deliver quality at a competitive price.

There are some emerging technologies which have been developed to further address the on-press process control capabilities from which narrow web printer converters will benefit over the next few years. Video web monitoring technology capable of analyzing spectral data is available today, and we need to engage these manufacturers so that the technology can come forward into the mainstream as rapidly as possible. [See Label Inspection, page 40.]

In the end, process control is essential to the ongoing drive for quality in narrow web flexo and to deliver flexo’s advantage of cost reduction versus offset and rotogravure. It begins in prepress and has to carry forward through the pressroom. When the prepress provider, the printer and the CPC work together and share innovative ideas among themselves, progress can be made in this area. Cooperation is the key and everyone benefits.

Patrick J. O’Brien has nearly 30 years experience in the flexographic printing and converting industry. His current area of focus is in the development of brand management solutions for major consumer products companies. He can be reached at 401-529-8864 or [email protected].