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FLEXO Magazine : June2010
Technologies & Techniques Dirty Printing Plate-Based solutions By Wayde Clark Measure multiple spots of the exposure bed with a uV radiometer to calculate overall energy output throughout the field of exposure. All art courtesy DuPont Packaging graphics. FIRST says, Process improvement uses statistical analysis of printing process data to improve quality, ef- ficiency, and production yield. The database created as part of the process control step, is used to analyze the printing process to identify potential areas of improvement. Customer complaint data is another very useful tool when pursuing process improvement. TEST says, FIRST Methodology and CGATS TR 012-2003 both clearly identify a five-step process: • Optimization. • Fingerprinting. • Process Control. • Characterization. • Process Improvement. As most flexographers attempt to comply with FIRST, they often focus very heavily on fingerprinting and characterization, but never actually do anything with all of the data that is generated. Process Improvement is a key money maker for any flexo printer. This step allows you to evaluate your printing process, identify the improvement opportunities and quantify the results. For more information, see Section 19.5 (Page 163) of FIRST 4.0. Process Improvement What is FIRST The intention of FIRST is to provide all participants in the flexographic reproduction process with a common set of guidelines, tutorials and data that can be used as communication and production tools. The aim of FIRST is to create a common set of specifications and commu- nication protocols for the industry. This platform should establish common communication and identify the responsibility of the provider(s). To order FIRST, call 631-737-6020 or visit www.ftastore.com. What is TEST TEST is the educational arm of the Flexographic Technical Association. The aim of TEST is to align all of the training materials available through the FTA with the guidelines, tutorials and data identified in FIRST. TEST is focused on implementing new learning methodologies to reach out to a larger portion of the FTA membership. For more information on TEST, visit www.flexography.org. 48 FLeXO june 2010 www.flexography.org Asasenior technical support specialist for DuPont Cyrel® Packaging Graphics, I have been privileged to witness flexography ’s capability as a printing me- dium blossom into the versatile, powerful force it is in today ’s packaging marketplace. Yet, as much as our industry has advanced flexography in the past decade, and as much as we have lessened any previous objections to flexo across a multitude of applications, we still continue to tussle with some of the same issues that have hounded us for many years. When the FTA approached me about contributing an article for its troubleshooting guide, I wanted to choose a subject relevant to its members. I settled on dirty printing in the highlight tonal range, particularly as it relates to insufficient preparation of the printing plate. When I started to outline all of the potential contributors to dirty printing, the list grew quite quickly. Over-inking the printing plate, incorrect ink viscosity, use of slow solvents of the wrong type or ratio, silicone release agents on the plate surface, and so on and so on; can all be the culprit of dirty highlights. As such, we’ll focus on the platemaking factors that can contribute to dirty printing. A GooD FounDAtion As with any manufacturing process, solid measurement, management and modification (if needed) can eliminate variation in the overall workflow. The key is to break down each facet of the workflow and understand how to evaluate and control each part of the whole. In today ’s discussion we will review: • Proper UV exposure. • Evaluation and control of imaging. • Minimum dot size and bump curve selection. It may sound basic and obvious to reiterate the importance of proper back and main exposure testing and control. How- ever, I believe in the importance of creating a solid foundation for the elements on a printing plate. I use the analogy of build- ing a beautiful mansion on top of a swamp. In the long run, the structural integrity and the lifespan of the mansion will fall short of our expectations. Two main points of control in our exposure steps are quantifying the overall UV energy output from a set of lamps and providing support through proper floor height/relief depth ratios. Utilizing a calibrated UV radiometer on a scheduled basis allows us to quantify UV output and uniformity and to track any changes. Measuring multiple spots of the exposure bed (typically nine to 16 readings) with a UV radiometer allows us to calcu- late overall energy output, variability throughout the field of exposure and any changes over time. Fully polymerizing our plate floors and, thus, providing support for our printing ele- ments is a critical step toward minimizing dirty printing in the highlights. When the relief depth is too severe for a particular photopolymer plate, isolated elements and fine dots can be compromised. • Use a radiometer to measure the amount of energy being emitted by the exposure unit to ensure uniform and consistent exposure across the plate. • A focus or stain test will reveal problems in LAMS layer ablation. • Remember: Different durometer, gauges, relief depths, line screens, imaging resolutions, etc, can all impact the minimum printable dot. FLX_June2010_mech.indd 48 6/10/10 9:39 AM