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FLEXO Magazine : August 2010
Technologies & Techniques 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for many years has dominated the market but due to the pro- gressive widening of the blade tip as it wears has now been superseded by the lamella and rounded profile blades.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 and honing process that it is subjected to. It is said to help reduce blade chatter and claimed to reduce scoring. As can be seen, there are a number of steel blade profile options as well as thickness that can range from 0.006in. to 0.080in., or even thicker when plastic and other synthetic ma- terials are considered as options. With such a wide choice of materials, including carbon steels, composites, hi-tech alloys, stainless, and plastics being available, what is right for you? It is generally acknowledged that steel blades give the most consistent metering and print results, generally when high-pu- rity Swedish steel is used. But newer hi-tech alloys are being touted for giving longer life when used with ceramic anilox and more abrasive inks and coatings. Composite blades also offer good resistance and there- fore longer life and are most often used with abrasive inks. They tend to be more rigid than cheaper plastic materials and also do not suffer from edge damage and material embedment in the tip of the blade that some plastic blades can suffer from. That said, plastic blades do have a lower coefficient of fric- tion on ceramic rolls and are very popular in the corrugated industry. These blades tend to be thicker than those used in higher graphic areas, and as a result, tend to leave between 5 and 10 percent ink on the anilox surface, leading to print inconsistencies. Polyester and or mylar blades tend to be the preference for most containment blades. Even if you make the right choice of blade material, ensur- ing the correct angle and pressure of the blade to the anilox Round tip. lamella tip. Advanced lamella tip. www.flexography.org August 2010 FLeXO 93 August2010_mech.indd 93 8/13/10 7:47 AM
Sustainable Summer 2010