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FLEXO Magazine : August 2010
Technologies & Techniques angle metering blade, and now also had a second blade con- tainment blade that would create a fountain effect by keeping ink on the anilox surface. This still exposed the ink and coat- ings to the atmosphere, and still needed a lot of ink, which in turn led to the final development of what is known today as the enclosed chamber blade system. The Roll SuRface Now, before we look at the newest systems in more detail, let’s take a step back and discuss the roll itself in a little more detail. Doctor blade technology certainly helped to remove the excess ink that would ride on the cell walls of the rather large land areas of the initial engraved anilox rolls. The problem was that with mechanical chrome rolls, the use of a blade, regardless of its material make up, was very prone to dramatically reducing the life of any anilox that it might be run against. It would be fine as long as a thin film of ink could be maintained between the tip of the blade and the roll, but turn your back and allow it to run dry then you had a disaster. In addition, any hardened particles of ink or other foreign debris that might get trapped between the blade and the chrome surface would immediately lead to scoring and se- vere damage to the engraved surface of the anilox. It is commonly claimed that a 1 percent loss off depth from a mechanically engraved cell can result in a loss of 25 percent of the individual cell’s volume carrying capacity due to its widest area being at the surface of the roll. Initially, the choice of engraving was severely limited to the tooling that the engraver might be able to offer and was usually very low line counts in the range of 150 to 250lpi, although counts up to 500lpi would eventually be made available. The screen angle was limited to 45 degrees with pyramid and quadrangular geometries being offered. As with every- thing where competition and a customer eager to improve his process is concerned, innovative new engravings such as tri- helical, channeled and other engraving angles of 30 and 60 degrees also quickly became available. The increased range of line counts and a wide variety of volumes also quickly led to the array of choices that the printer has to choose from right up to this day. The mechanical anilox, for all of its faults, really did allow the flexo industry to begin to move into many new markets, as new ink systems and new substrates were developed flexo grew at an incredible rate in every part of the world. Still, limitations included: • Limited range of screens and volumes available. • Limited resistance to wear. • Limited resistance to scoring and general mechanical damage. • Poor TIR due to the knurling process. • Inability to run with doctor blades. • Inconsistent volume release around and across face of roll. • Inconsistent chrome plating. Knowing that the chromed anilox engraved surface was susceptible to damage from most doctor blades even with the most skilful operator, the race was on to find a more durable surface. This led to a chaotic period of trial and error with ex- tra hard chromium surfaces, mechanically engraved ceramic coated surfaces, random sprayed ceramic surfaces, random engraved ceramic laser surfaces and, finally, the laser en- graved ceramic coated surface as we know it today, and the many benefits which include: • Almost unlimited screens and volumes availability. • Excellent resistance to wear. • Good resistance to scoring and mechanical damage. • Excellent TIR the laser is a non contact process. • Can be run with all types of blade material and configu- rations. • Very consistent ink volume release across face of roll. • Consistent coating thickness due to modern plasma coat- ing systems. It does not sound like a lot, but for many printers, engrav- ers and flexo print buyers alike, this caused a lot of frustra- tion. For opponents of the process, this proved that the only consistency in flexo was its inconsistency. This seems to have only driven the industry as a whole even harder to find the right formula. As such, just about every area of the process has seen dramatic improvements—ink formulations, plate materials, plate processing, software and hardware, mount- ing tapes, mounting equipment, and servo driven presses. Yet, during all these incredible developments, making the right line count, volume engraving choice appears to still cause considerable frustration to many printers in all flexo markets. So why is this? Like most things in life, having a choice is good. But having too wide a choice can lead to a lot of indecision and confusion. So it is with the modern doctor blade. One key factor that I be- lieve will help many printers when trying to make this decision is to understand that no one blade will suit every application, just as no one anilox will suit every requirement either. So let’s take a look at the many variables and consider each one in turn and how it will influence your choice of blade and anilox combination. DocToR BlaDe Tip pRofileS Square. This is the original shaped profile, and while it can be and is still used by printers running fairly coarse screen counts, it is more likely to be used as a retainer blade profile, again for lower line counts. It’s particularly prone to dragging any small ceramic particles, sometimes found on coarser no polished ceramic anilox, which when dragged around the cir- cumference of the anilox will cause light to heavy score lines. Beveled. The next evolution for the blade profile which for many years has dominated the market but due to the pro- gressive widening of the blade tip as it wears has now been superseded by the lamella and rounded profile blades. Lamella. The lamella profile, with its stepped thinner edge to the blade, is seen by many as the Rolls Royce of blade profiles and is used by many printers as the blade remains a constant thickness even as it wears, It also has more flexibility and yet can be gripped by standard blade holders, due to its thicker profile on the non-stepped edge. Advanced lamella. This is similar to the standard lamella blade, but as can be seen from the cross section, the blade increases in thickness as it moves away from the tip, giving it additional strength, yet being gradual does not cause undue changes in the blade thickness as it wears. Rounded. The rounded or radius blade is hailed by many as being much safer to install with both edges having a rounded edge. It is less prone to having any burrs due to the grinding square tip. Beveled tip. 92 FLeXO august 2010 www.flexography.org August2010_mech.indd 92 8/13/10 7:47 AM
Sustainable Summer 2010