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FLEXO Magazine : March 2011
THANK YOU FOR 100 YEARS OF TRUST AND PARTNERSHIP A century of printing inks under the Siegwerk brand. This is what we celebrate this year – together with our customers and friends. 180 years ago, we started as printers ourselves. In 1911, we brought our first print- ing inks to market. Sharing a great passion for packaging and publication ink solutions with our customers, we work together hand in hand. This is what we call: Ink, Heart & Soul. It is the formula for your success. As it is our ambition for the future. www.siegwerk.com SW_E_AZ_US-letter_full-page_bleed-size.indd 1 09.03.11 16:04 Technologies & Techniques tions include fan cooling and high efficiency. Vari- able speeds are usually achieved by an external AC inverter. Explosion- proof electric motors are similar to regular electric motors, except that they have been designed to run in the flammable atmospheres found when using solvent-based ink. Several ratings are available, so be sure to consult with your pump vendor. Tank. Four character- istics need to be consid- ered when choosing a tank: Size, shape, sump and material. Tanks should be sized to hold enough ink for a typical run. This avoids the need to refill the tank, possibly changing the viscosity and pH. Tanks are available in two common shapes, rectangular/ square and round/oval. The former is cheaper to fabricate, but ink tends to stagnate in the corners, leading to viscosity is- sues and pigment settling. Round and oval tanks allow better mixing, but they tend to cost more. The addition of a sump, created through either a welded-on round sump or through the use of a slanted bottom, allows better pump-down of ink. This reduces waste and changeover time but adds to the cost of the tank. Finally, there is a choice of materials. Most tanks come in stainless or regular steel. Stainless is more expensive but holds up to a wide variety of chemicals without rusting. Finally, many vendors offer plastic liners, either rigid reusable or thin disposable, for their tanks. Using liners dramatically speeds up changeover time. Filter. Filtration is a crucial step, but one that is frequently ignored. Filters remove two main types of contamination, me- tallic and non-metallic. Metallic particles come from doctor blade wear; as a doctor blade runs on an anilox, slivers and filings of metal come off. Metallic particles also come from solvent supply lines. These pipes are typically metal, and rust or deterioration on the inside can put metal into your “clean” solvent. Filters also remove non-metallic particles. Usually these are clusters of dried ink (most common with water-based inks) or foreign contamination such as dust from corrugated substrates. Filters designed for printing will feed in from the bottom and exit from the top, allowing easy draining of the ink after a run. Common options include a variety of mesh/micron sized cartridges and upgraded rare-earth magnets. Viscosity control. Viscosity control has become common in flexo and gravure printing. Holding the viscosity constant allows proper inking and color density. Viscometers are avail- able in bypass, in-tank and in-line configurations and are typically useful on longer runs, where pH and viscosity can drift and affect the print output. Temperature control. Temperature control is a new area of concern but one with potentially large savings. Several things happen as ink warms up during a run. First, viscosity is temperature-dependent: Fluids thin naturally with increasing temperature. However, most viscometers in a process environment will read a viscosity that is too low and not add enough solvent or water to thin out the ink. Because the “correct” viscosity was reached with less solvent or water than would have been added without the temperature-dependent thinning, the pigment ends up too dense. This results in increased ink consumption—up to twice as much in some cases. Second, because the ink is warm, it dries faster, leading to poor dot structure. Third, even though more ink is being consumed, the poor dot structure results in a lower reflective density. Temperature controls are widely available from a number of sources. Look for minimal pressure drop and easy cleaning. Fittings. Fittings such as tubing, pipes, barbed fittings and connectors are small, cheap and rarely warrant a second thought. That’s unfortunate, as they also have the capability to destroy the performance of an otherwise well-designed sys- tem. There are four rules to follow when choosing fittings. First, ensure compatibility. Select fittings that are not ad- versely affected by the chemicals in your specific ink. Many chemical compatibility charts are available online, and your ink vendor can give you a list of chemicals that you need to check against. Second, minimize the number of fittings and the lengths of tube. Every fitting, every bend, and every centimeter of tub- ing means more friction, which robs performance from your system and increases your energy costs. Replace 90o elbows with 45o elbows or eliminate bends altogether. Third, make the fittings as large as practical. Increasing the diameter of your tubes and fittings by 25 percent can cut the problem in half. Finally, ensure that all fittings are “full port.” Many cheaper fittings actually taper down, reducing the diameter and creat- ing a friction-inducing bottleneck. In our experience, we have seen poor fittings rob 80 percent of a pump’s performance. Don’t be afraid to ask questions and involve your vendors in these decisions. Chances are they have already seen some- thing similar and can help you work through optimizing a system to fit your specific needs. Additionally, most major ven- dors have the ability to design and fabricate custom systems to fit your needs if necessary. Remember that a well-designed system that matches what you are trying to accomplish with your press can make the difference between profit and loss. About the Author: Craig Shields is the president of Graymills Corp., Chicago, IL . He currently is a member of FTA’s Sup- plier Leadership Council. 38 FLeXO march 2011 www.flexography.org FLX_March11.indd 38 3/18/11 1:32 PM