Andy Kannurpatti & Brad Taylor
Ask any plate maker for their top three issues in the plateroom and you will get the following, in their order of preference: fulfill the day’s production needs, eliminate rework and quality issues, and enable the pressroom to deliver consistent print results.
At a high level, these make sense, as the plateroom is focused on delivering the plates needed on time to print consistently every time, while at the same time making improvements needed in the operation. If this is what motivates the plate maker, it is clear to see he/she could benefit from using the FIRST thought process in the plateroom.
FIRST (Flexographic Image Reproduction Specifications & Tolerances) is a methodology that provides best practices to improve print results and consistency run after run, with a focus on continuous improvement. The steps in the methodology are:
- Optimization
- Fingerprinting
- Process control
- Characterization
- Process improvement
While not all these steps may be directly translatable to plate making, many of them can be applied successfully.
In this article, we share a set of steps, much like the FIRST methodology, that can be applied in the plateroom. Although this is not an exhaustive summary of the more than 40 years of institutional knowledge our organization has gathered by working with customers, these steps are derived from that experience. We have chosen a digital photopolymer plate making process that uses thermal development for illustrative purposes; however, there is no reason one could not use it for other methods, such as solvent processing, laser engraving, analog plate making with film, or other variations used in the industry today.
Optimization
FIRST defines optimization as determining preferred operating parameters. This definition applies in the plateroom. A typical plate making process is shown in Image 1.
Understanding the key parameters that influence each step in the plate making process is the basis for determining the preferred operating parameters. These parameters need to be understood well by all personnel involved in the operation. Often, training is required to certify operators and other important individuals. For example, FTA offers certification programs for FIRST Prepress Operators. It may also be necessary to obtain additional training from suppliers on certain advanced equipment.
Optimization Procedures & Process Control Variables
Optimization procedures are important to follow in determining preferred operating parameters in the plate making process steps. The optimization is complete when the plate(s) tested are printed and the results are analyzed. In a sense, this is fingerprinting applied to plate making.
Image courtesy of DuPont
Here are key procedures that need to become standard practice in platerooms looking to deliver optimal printing plates to the pressroom. These optimization procedures, when performed on a routine basis, can ensure the plate making process is in control.
- Exposure bulb output measurement: High quality platerooms maintain a log of the exposure bulb output. These measurements can be made with a UV radiometer. The measurement is not only important to ensure operating parameters are within the preferred window, as maintaining a log can help identify issues when a plate is returned for rework
- Exposure bed temp measurement (optional): This is an optional measurement that can help ensure consistency of UV exposure. Some of the new exposure units have cooled beds with temperature control
- Imaging calibration check, stain and 50 percent: This ensures the digital imager creates the laser ablative mask with the correct percentage openings and appropriate energy (a similar check can be applied to film photo tools). The prevailing industry standard is to measure the transmitted optical density of a 100 percent cleared area (stain) referenced to the raw photopolymer (this requires removing the black ablative material over a small area), and a 50 percent dot area referenced to the 100 percent cleared area
- Imaging focus check: It is critical to make sure the digital imager is operating in proper focus for the gage of the plate being used. This primarily takes the form of ensuring the actual plate in the imager matches the selected gage of the plate when setting up the control software for the imager. It also includes periodic focus checks to correct any drift or changes in the focus for the machine
- BX and MX step test: The purpose of these step tests is to optimize the appropriate BX and MX time needed to produce the desired features on the plate. Manufacturers recommend plate makers test each batch for the correct BX and MX time to ensure the consistency of the results. This is a good test to check the exposure process is under control. Unexpected changes should also result in a double check of the exposure unit measurements
- Thermal processing program: It is important to work with the manufacturer to make sure the optimum processing conditions are programmed for the plate that is being used. Ensuring the software is of the latest version is important to make sure the process remains in control
- PX/LF tests: Finally, as with BX and MX tests, post exposure and light finishing tests need to be done to select the correct exposure times. The post cure and detack processes need to stay in control as well, to ensure plate to plate consistency
Process Control
Keeping the plate making process under control requires careful monitoring of results. Many platerooms will include a process control strip at the edge of a job that will not impact the package design or graphics. These control strips can include solids, halftones and some highlights. There are a variety of versions of these to choose from, but these strips are an inexpensive way to collect data on potential drifts in the process that need to be corrected.
Image courtesy of FTA
It is a standard recommendation that, at a minimum, a control strip should be used to apply two point control. This means examining and recording the processed plate dot size of every plate, or a sampling of plates, at a mid tone and a highlight value. It is critical to use the same digital file for the control strip at the two points being measured. These points provide a sensitive record of the plate making process—if it is out of control, it should show up here.
Many process deviations in printing that are caused by plates come from examples that were not demounted carefully or were stored incorrectly. Plates need to be handled appropriately when they are demounted and remounted. If the plate was not cleaned properly before storage, it will not deliver the same results. The pressroom operators need to help address this plateroom requirement for improved handling and storage.
Process Improvement
The typical plate maker faces ongoing challenges to improve cost, productivity and quality. A continuous improvement mindset is critical to success. In addition to identifying sources of inconsistency, it is important to identify opportunities to control, improve, measure and quantify day to day plate making. We recommend a Pareto analysis to identify areas of opportunities. Your statistical analysis should focus on:
- Status, changes, and control (modification as needed) of your operating parameters, and
- Accuracy (Are the results what you want?) and repeatability (Are the results changing?) of the important features on your finished plates
Creating focused programs to address these enables plate makers to deliver what’s needed in the pressroom. It is important to provide timely feedback to the plateroom, especially when there are complaints from customers or when the pressrun did not go as planned. There is a lot that can be learned from errors and it is critical to correct them in the future.
What About New Workflows?
We believe the fewer the number of steps in any process, the greater the consistency. This is a consequence of simplifying, as there are fewer opportunities for errors. Our newer technologies that deliver flat top dots built in the plates have focused on delivering plate making processes and plates that reduce the opportunities for error. The lack of additional process complexities, such as lamination or inert gas environment, enables customers to extract more from their plateroom. The efficiency, consistent quality and total cost productivity of our latest flat top dot technology (Cyrel EASY), users have commented, are achieved in part because of the workflow simplicity.
FIRST was developed to help flexographers deliver consistent quality prints to their customers. Clearly, the methodology and mindset can be applied to flexo plate making as well. Given the relevance of plate making to print quality and consistency, there are significant economic benefits to operations that apply this mindset of optimizing, controlling and continuously improving the process. While manufacturers continue to simplify the process to support the plate maker, adopting FIRST will help drive flexography forward.
About the Authors: Andy Kannurpatti is the global marketing manager – flexo & global strategy manager – DuPont Advanced Printing. One of the inventors of the Cyrel FAST thermal processing technology, Andy has worked in the industry since 1997. He received a Ph.D. in chemical engineering from the University of Colorado and an MBA in marketing from Drexel University’s LeBow College of Business.
Brad Taylor is a technical fellow for Cyrel Packaging Graphics Products, DuPont Advanced Printing, in Wilmington, DE. He has worked for DuPont for 28 years in various assignments in electronic imaging and imaging technology. He got his start in flexography as the technical team leader for Cyrel’s digital photopolymer plate development in 1995, and has continued to focus on new digital photopolymer product development and project management. Brad has a Ph.D. in electrical and computer engineering from Carnegie Mellon University.