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FLEXO Magazine : June 2014
• Plastics In the past, plastics were used as con- tainment blade material because they are nat- urally more flexible than steel at thin gauge. But over time, problems surfaced such as: » Hard pigment and resin particles can easily imbed into soft plastic materials, allowing these particles to potentially imbed into cells or even contribute to anilox scoring » When plastics wear, the worn particles imbed into ceramic changing the surface dyne levels • Steel In recent years, the steels developed to meet the increased demands of HD flexo (high line anilox at high speed) are super re- fined, slower wearing materials. An additional advantage is that steel in the containment position will wear more in time with the doc- tor blade. Finally, steel will not imbed into the ceramic or harbor harmful hard non magnetic elements • Thickness The containment blade should be thinner and more flexing. The containment blade engages the anilox on its side or face with a wider contact area as compared to a doctor blade. Remember that we want ink to push the blade back away from the anilox, even at high speed, allowing all the surface ink back into the chamber • Contact Angle In the past, the preset contact angle for both top and bottom positions on many chambers was ±32 degrees. This meant chambers could be used on the up or down side of the CI drum. Unfortunately, back doctoring is more pronounced if the containment blade makes contact at ±32 degrees, which is the ideal angle for metering. Today, many chambers come with the containment blade set to make contact at ±20 degrees. In this angle range with a thinner blade, back doctoring is almost impossible • Width When the set angle of the containment blade is less than the doctoring blade, the width of the blade can be the same. However, when the set angle of both blades is the same—usually around 30 degrees—better results may be achieved by increasing the width of the containment by 0.125-in. This added width will cause the containment blade to make contact a bit closer in on the anilox, helping to reduce the actual contact angle. A word of caution: Changing blade width may alter the blade’s interface to the seal and may contribute to end seal leaking. This depends on the width and density of the seal • Beveled/Lamella/Radius Edge While a doctor blade may require a beveled or tapered edge to take a thicker more rigid material down to a reduced contact area, the containment blade functions well with a polished radius edge. Remember: We want the contact area of the containment blade to be wide OPTIMAL BLADE PREFERENCES The ideal containment blade should be: • High quality steel relative to the material used for doctoring • A thickness of 0.006 -in. or possibly 0.008 -in., depending on the thickness of the doctor blade • Radius edge • Depending on chambers set angle, the same or slightly wider than the doctor blade The good news is that while the cost of doctor blades has gone up over the years due to technology developments, the price for containment blades should be a bit less. To make sure the containment blade is op- timum and compatible with your application, consult with a qualified industry blade supplier. n About the Author: Paul Sharkey is the president and founder of FLXON Inc. He has been actively engaged in understanding and preventing the causes of waste in the flexo process since 1976. He can be reached at email@example.com . “The good news is that while the cost of doctor blades has gone up over the years, due to technology developments, the price for containment blades should be a bit less. ” 72 FLEXO | JUNE 2014