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FLEXO Magazine : August 2014
them over at the tip and increasing the contact area. As the blade tip bends, the contact area widens and the anilox ink lm deepens. Dot gain and dirty print soon follow. Chart 1 indicates the contact area at di er- ent contact angles when zero ex is present. WHEN MORE IS LESS When it comes to doctor blades, a thicker blade will o en result in a narrower contact area. A thicker blade had better resist exing when pressure is applied. Consider the gain seen in Chart 2 when moving from 0.006-in. thickness to 0.008-in.---that's 33 percent more material. ere are three types of doctor blade tips: • Radius For exo, this is the No. 1 choice. e polished true ra- dius edge is the best performer. It conforms to the anilox radius quickly, with no particular resistance. It is safer to handle and of- fers a longer run time, as you get a full measure of blade material from the outset. ere is also a small price advantage • Bevel ere are some advantages to using a beveled edged blade in label printing, especially when a single blade holder is used. Elongated bevels with angles less than 10 degrees require no break in time. e beveled edge is easier to see---not always the case at 30 degrees or 15 degrees. e operator should know the bevel must face away from the anilox and should exercise extreme caution when handling. Some wide web printers prefer to use the 2 degree bevel on their new HD exo applications • Lamella is is the most popular tip for rotogravure printing, because it easily exes. But remember, ex is a negative in exo. Lamella seems to be a favorite of press manufacturers. Yet when pressed, their technical sta admit they like the lamella for use in their demo center---where runs are 20 minutes. Otherwise, they would naturally use the radius or beveled tip. Many anilox rolls have been damaged when the lamella bends when pressured to produce large hair like strands of steel New generation high density doctor blade steels with hardness in the Vickers Pyramid Number range of 550-Hv. to 650-Hv. require little time to wear in and conform to the anilox radius. If breaking in a blade is taking too long, then check with your supplier to see if your steel is of the new generation. TO THE POINT Making the right choice isn't always obvious. Sometimes a thicker blade achieves a thinner contact area. Using the right blade material, thickness and tip can be critical to the success of a print program. Some blade suppliers o er assistance to help determine which tip and thickness is best for a given application. Anilox roll and ink suppliers also can assist in helping you decide. 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 exo process since 1976. He can be reached at psharkey@ xon.com. Contact Angle Blade Thickness 0.006-in. 0.008-in. Contact Areas 35 0.0106-in. 0.0136-in. 30 0.0120-in. 0.0155-in. 25 0.0145-in. 0.0183-in. 20 0.0179-in. 0.0220-in. Incremental Material Gain Resists Flex Blade Thickness Increase Over Prior % Increase Increase Over Base % Increase 0.006-in. 0 0 0 0 0.008-in. 0.002-in. 33 0.002-in. 33 0.010-in. 0.002-in. 25 0.004-in. 66 Chart 1 Chart 2 40 FLEXO | AUGUST 2014