Press Optimization: Setting the Foundation for Quality Print
What is an optimization? Simply put, it’s a print test to identify the print components that will result in the best-looking print. A press optimization is an extremely important foundational requirement for accurate repeatable print.
If you were to open a new print shop, buy a new press, or get a new line of business, do you know what anilox roll CPI and BCM you would use? What about the density of your mounting tape? Would you know what ink or coating to use? How about the best plate cell patterning to use?
If you answered “Yes” to these questions, my next question would be “How do you know?”
If your answers are, “This is my favorite anilox roll” or “This is what we did at the last place I worked,” then try again…
However, if you can say, “We use a 900cpi 3.0bcm anilox roll because it achieves the desired ink density and print quality,” then BAM! Now, we have some quantifiable metrics on which the component selection was based. I will note that an optimization is not required if components are standardized and/or if sufficient experience or historical data is available. This data is typically derived from a previously accomplished optimization.
There is actually a book that has lots of great information regarding an optimization — FIRST (Flexographic Image Reproduction Specification and Tolerances). FIRST defines the goal of optimization as: To identify the best combination of print variables to achieve design requirements. I strongly encourage you to read the section on optimization in the FIRST book if you are optimizing your process.
Press optimizations will allow you to know without a doubt, how to choose the best anilox roll engravings, the optimal mounting tape density to select, and the best ink for a job. However, most people I talk to are either unsure of how to properly complete an optimization or don’t see the importance of it. This is most likely due to:
- Infrequent Practice. Press optimizations are performed infrequently, so operators don’t have exposure to the incredible benefits.
- Insecurity. In conjunction with the lack of frequency, the data derived from the optimization is highly critical to the success of the print job. This sounds well and good, but if employees running or evaluating the optimization have little experience doing so, they can be squeamish under the pressure. Operators fear that if they make a mistake the print results will suffer and their jobs will surely come to an end.
Don’t fret! If you follow the steps below you should be able to flawlessly execute and analyze an optimization test.
Communication and planning are the first and most important steps in the process. Before you run the press, you need to plan the optimization. I recommend getting all the parties involved together, including suppliers, prepress and press supervisors, and operators.
- Identify the components that you will be testing. Resist the urge to test everything under the sun, because you will need to evaluate all of the samples and it can quickly get out of hand. For instance, if you have a banded roll with five bands and you are testing four colors, and you pull five samples and evaluate 20 spots on each sample (four per band) you have to evaluate 2,000 data points. Now if you also look at three different tape densities, the evaluation skyrockets to 9,000 data points. It is easier to run a few smaller optimizations than one large one.
- Before you run any optimization, discuss the objectives of the test and the information you want to get from it with your team. Include how you will evaluate the print sample: Will you be using a loupe, density, dot gain, or Lab*measurements?
- Furthermore, identify the targets you will be aiming for. These could be FIRST Densities, ISO 12647-6, Lab* targets or your own specifications.
- If you are using a measurement instrument, take some time to identify the measurement procedure: specify the backing, observer angle, if you are using Status T or E, and other various measurement variables. Don’t forget to calibrate the instrument before using it.
- Plan for the evaluation. Take into consideration how the final sample will be evaluated. If you are reverse printing over white, the white print is critical and should have been optimized first. If the sample is reverse printed, what backing will you use to read it on? Will you be reading through the film to evaluate the print sample?
Planning for One-Color or Four-Color Optimizations: Some people complete an optimization with only one color to increase productivity. Depending on what you are evaluating, this can be acceptable. If you are looking at the impact of different mounting tape densities, the tape should have the same effect on all colors, so one color is fine. However, if you are determining what anilox rolls CPI and volume you want to use on your CMYK inks to achieve FIRST densities, I recommend running all four colors.
The plate elements and layout depend on what you are evaluating. In most cases, the layout will include solids, tints, vignettes positive and reverse lines and type. There is no right or wrong answer on what should be included on the plates; you just need to make sure you can get the data you require to make a decision on the components that you are evaluating. If you are running a banded anilox roll I recommend including the anilox band specifics (CPI, BCM, and engraving angle) on the plate so they are on the print sample. This can save you lots of time when evaluating.
Now that all of the planning has been done, we can run the optimization test. It is critical that the press run is done under normal repeatable conditions. This means your anilox rolls should be clean, doctor blades should be new, the ink should be in spec (pH and or viscosity). To assure repeatability, you should use the same material you will use in production. The list goes on and on.
Now, where many printers get into trouble is they take great care to prepare the press for the optimization, yet when they run production, they use dirty anilox rolls and ink that is out of spec. If you can’t repeat the results of the press optimization, don’t even waste your time doing one. It’s really that easy.
When you run the optimization trial, run at normal production speeds and run for more than 60 seconds. In most cases, production runs are more than 60 seconds long. It is not uncommon that after 20 minutes of runtime, screens printed with water-based ink can start to get dirty and print quality can decrease. This may cause you to reevaluate your optimization data. If possible, it is best to let the press run for 20 minutes or more to get the most repeatable results. I understand this is not always possible, but avoid running the press for only 60 seconds to get your print samples. It is best to collect and analyze samples throughout the press run to best capture the natural variations of the press.
I will note that an optimization and fingerprint are two different press runs. For the best results, you should optimize and then fingerprint. The optimization will identify the components to achieve your desired print results. During the fingerprint, you see how those components (determined during the optimization) print. The fingerprint data is used to adjust your curves getting the press in its sweet spot. Cutting corners will only decrease your success in the long run.
I bet you still have more questions, but I hope this gets you thinking about the optimization process and the planning that should be completed PRIOR to throwing some plates on the press and expecting amazing results. Remember, if you have questions about the optimization refer to the FIRST book or ask your suppliers. The optimization will ultimately result in the purchase of their products so it is in their best interest to help you out.
Shawn Oetjen is the flexo trainer at Flexographic Tech in Minneapolis, where he oversees the unique cooperative training program founded by AWT Labels & Packaging and Computype. He graduated from Clemson University with a B.S. in Graphic Communications and also holds two associate’s degrees; one in graphics and packaging and another in computer networking, both from Dunwoody College of Technology. Oetjen possess a wealth of knowledge and experience from working in various capacities within the flexographic industry including education, production, technical service and sales. He has a keen knowledge and understanding of the flexographic process from start to finish. Oetjen is actively involved with the Flexographic Technical Association and received the FTA’s president’s award in 2010. Shawn Oetjen is on the Executive Committee for the Flexographic Quality Consortium and is the president of the Twin Cities Flexo Association.