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FLEXO Magazine : July 2009
TECHNOLOGIES & TECHNIQUES magnifi cation/bar width reduction combinations. The primary variables that will be evaluated include: minimum dot size, dot gain, maximum color strength (saturation), minimum positive and reverse type size for serif and sans serif fonts, optimum line screen for vignettes and screen tints, and optimum bar code magnifi cation/BWR. The test target will be positioned within each band of the banded anilox roll design. CONDUCTING THE PRINT TRIAL Once the test plan has been established and documented, it is time to conduct the optimization print trial. The print trial provides physical samples to evaluate the performance of the printing system under the various conditions. As the printing manager, you schedule the print trial into the press production schedule, so that adequate time and resources are allocated. Schedule the print trial on the press that will run the live job. You brief the supervisor and press crew on the print trial objectives and on the procedures to follow prior to the pressrun. On the day of the print trial, all neces- sary participants, including the supplier team , as appropriate, are press side. The test variables (mounted plate cylinders, inks, banded anilox, etc.) are clearly labeled, staged and ready to go. All CoAs (Certifi cates of Analysis) have been received and reviewed to confi rm conformance to agreed-upon specifi cations. The press is clean and set up to run. You have established a production run speed target and a sampling plan. Care must be taken in setting the press to achieve the running conditions. Impression levels must be set evenly and optimally from gear side to operator side to yield effective ink transfer while avoiding excessive dot gain and squeeze. Impression and slur targets, solids, and halftone tints are placed on both sides of the test form, in the 1in. to 2in. control bands, to verify impression settings. Remember, the combination of print variables and settings defi ned during the optimization trial are what will need to be repeated on future runs. You are establishing the run conditions for all future runs. Once the press settings are properly set and the target run speed is achieved, it is time to begin sampling. There are no hard-fast rules on how 20 FLEXO JULY 2009 long to run or how many samples to take, but the goal is to run long enough to adequately sample the normal shortterm variation of the process and pull enough prints to have a statistically representative sampling. A possible starting point may be to run 30 minutes and pull 30 samples, but it depends on process variation and the expense of materials and press time. Finally, the materials, conditions, and various press settings all need to be meticulously documented. The goal is to be able to repeat all aspects of the run at a later date. the key print variables—a press operating data sheet. It should include job-specifi c print variables for each print deck: ink formulation, plate type, mounting tape, and anilox roll as well as settings for the more general press components print variables: tension settings, dryer settings, doctor blade settings, etc.The press operating data sheet is the document that will go to press with the fi ngerprint and characterization trials as well as with all future production orders for this new job. It informs the press crew how to setup the press to achieve optimum and repeatable results. Once the optimization process has identifi ed the optimum press setup conditions, you are ready to conduct the press fi ngerprint and characterization trials. These provide the prepress provider with the data necessary to create the fi les for the job tailored to your specifi c printing process, so that you can run the trial order with the live graphics and win that account! Tune in next month to follow this imaginary job through the fi ngerprint and characterization steps! ■ DATA & DOCUMENTATION Once the print trial is complete and samples have been pulled, labeled, and assembled with the run documentation, you are ready to begin the fi nal step of the optimization process—data collection and documentation. The data collection and documentation step consists of evaluating each print sample, measuring the print variables, and recording the measurements on a data collection form. First, evaluate each print sample. Ink lay, minimum type size, minimum line thickness, and other visual aspects should be evaluated. Next, measure the appropriate print variables for the job. Quantify solid ink densities, dot gains, overprint traps, colorimetric attributes, and other measureable print characteristics. Finally, record the measurements on a data collection form. Once all of the print samples have been evaluated and the data assembled, you are ready to statistically analyze the results. Based upon the statistical analysis of the data collected from the optimization print trial, the outcome of the optimization process is a document that describes the optimum settings for www. f le xography. org ABOUT THE AUTHORS: Michelle Warfford Beuscher earned a Bachelor’s (1989) and Master’s (1997) degree in Graphic Communications from Clemson University. She has been involved in the fl exographic printing industry since 1990, working in both wide-web paper and fi lm applications. She served on the FIRST Committee for the premier and second editions and as editor of the third edition. Currently, Beuscher is an independent consultant to the fl exographic industry specializing in training program development and implementation, printing process measurement, control and evaluation. She served as project manager and editor of FIRST 4.0. For more information, contact Michelle at firstname.lastname@example.org. Bill Pope is technical director for FTA. FIRST 4.0 Get Your Copy Today! FTA Members: $99.00 (Non-members: $198.00) Place your order online at www.ftastore.com or call FTA at 631-737-6020.
Sustainable Spring 2009