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FLEXO Magazine : September 2009
FLEXO SEPTEMBER 2009 www.flexography.org DURING THE RUN When prepress run considerations have been reviewed and inks have been prepared as needed, there are several things to consider during the live pressrun. As we know, many variables contribute to the success of any job. The following highlights how these variables can affect the successful run of spot colors: Printing Ink. Ink technology, adjustments to the ink, care of ink in the sump/pan, and ink temperature can all affect color. First and foremost, make sure that your shipment of ink for the live pressrun are the same inks (formulas, not necessarily lot numbers) used in the initial drawdowns/standards. How to "control" inks during a run will vary depending on the ink technology. UV inks are very press stable and require little to no press-side maintenance. Water-based and solvent-based inks may require a bit more maintenance. When adjusting water-based inks, adjust pH first, then viscosity; when adding any "additives" to the ink sump/pan, do so in small increments---large additions could shift color. It is very important to ensure all materials added to the inks are compatible with the ink system; be sure to follow usage guidelines as provided by your ink manufacturer. Water-based and solvent-based inks in the sump/pan will need constant agitation so inks stay mixed and homo- geneous; also, sumps/pans should be covered to reduce evaporation during the pressrun. With water-based and solvent-based inks, temperature is critical. As ink tempera- tures increase, viscosity decreases and colors change. Anilox Selection and Care. Press operators should work with ink technicians to ensure that the correct anilox has been selected for the ink technology. Make sure that all anilox roll- ers have been cleaned prior to the live pressrun and that they are in good working condition. Dirty rolls can adversely affect the actual cell volume, which will affect color strength. For repeat jobs, make sure you use the exact same anilox rollers that were used in prior runs---not just the same specifi- cations, but the exact same rollers. This will provide the most consistent print from job to job. If the inks being used are "fast-drying" (i.e. water-based film ink), make sure the anilox and meter roll are consistently turned; otherwise, inks might dry themselves to the anilox and ink volume will be lost. Be sure that air is not blowing on anilox or plates, as this could cause premature drying, and colors will shift. Doctor Blades. Keep the doctor blade setting consistent between operators and jobs. Ensure that operators use the exact same doctor blades for repeat runs. Always set with proper pressure so the blade is not wearing. Follow the rec- ommended processes and maintenance procedures defined by the doctor blade suppliers. Substrate. The substrate used can have a significant affect on color. Be sure that the substrate used in the live pressrun is the same material used in proofing the inks. Color will vary from substrate to substrate. Be sure to test any substrates where multiple lot numbers may be used. And, if possible, plan you jobs using the same lot number. The surface of any film material can affect flow and transfer of the inks, affecting the final color. Corona treated versus non-corona treated material may affect end results, as well as top coated versus non-top coated material. The variables within substrates may impact your end result. Even utilizing different substrates with the same color will impact color. For example, semi-gloss material from one substrate supplier may have a different effect on color than semi-gloss material from a different supplier. This applies to all types of materials. Being aware of all aspects will help control color from start to finish. Mounting Tape. During press setup, make sure there are no bubbles between the tape and the plates; this could create darker or lighter spots on the final printed material. Setting impression is very important---set to optimum impression to keep even appearance of inks. Kiss impression may need to be adjusted during long runs, avoid crushing the mounting tape, which will affect bounce back and color. The Press. Always make sure your press is in good working condition. Conduct preventative maintenance on a regular basis. Job planners/schedulers should try to plan jobs to run on the same press to alleviate the variables when changing jobs press to press. This will help achieve consistent results on repeat orders. Keep in mind that the forces of gravity do affect laydown and final print results. Run your press at the same speed at which your job was signed off; as you increase or decrease press speeds your color may be affected due to changes in flow, leveling and ink transfer. In addition, if the press is stopped for any reason during a run, inks and press setting will need to be re-checked when the press is started again. Operator. Press operators should be trained to use con- sistent and correct press procedures. Consistency in press procedures from press to press and job to job is key to a successful end result. In addition, press operation should be uniform across shifts. This requires good communication from among all operators using the same press. All press personnel need to keep the press in good condi- tion. Regular maintenance programs for each printing press are essential for smooth running jobs and will save money in alleviating waste and saving time. Operators also need to ensure that inks are maintained press-side. Pay attention to usage guides provided by ink manufacturers. Press personnel should be trained in the use of ink measurement tools; understanding color will allow greater success in running a job. Ultimately, all variables and ancillary aspects in a pressrun will affect color control throughout the run. Consider each and every piece of the press and its affect on color control. This article touches on several aspects, but most likely not all. As with all successful operations, communication is key! Ink technicians, job planners/schedulers, and press operators need to fully communicate plans for the job; and suppliers of inks, materials, and equipment should be called upon to help in questionable areas. OH, ONE LAST THING... Remember that color might change when applied to the end package. For example, if you are working with a purple bottle, you should apply that newly printed label on the bottle to ensure that color is still correct and matches approved standards. ABOUT THE AUTHOR: Deanna Whelan manages marketing communications and customer relations in the U.S. for Flint Group Narrow Web. For further information on Flint Group, please visit www.flintgrp.com.