- November 01, 2003, Claudia Hine, Senior Editor
When I joined PFFC magazine, one of the first lessons editor Yolanda Simonsis taught me was to think of a “doctor” blade as something that “fixed” ink on the anilox roll. That simple lesson kept me from categorizing a doctor blade as a useful tool in the slitting process, and it's stuck with me all these years. But in preparing to write this column, I've discovered doctor blades can do a lot more than just “fix” the ink.
Advances in shapes, coatings, and wear-resistant material bases provide long blade life, more effective wiping, and longer engraving life, says Thomas K. Allison, president, Allison Systems Corp., Riverside, NJ (allisonblades.com). “New doctor blade holder, system, and chamber configurations that can prevent poor contact angles on both gravure and flexo doctor blades — while reducing changeover time and blade mounting problems — are as important as the new blades,” he says.
Developments in flexo ink metering systems specifically designed for one market segment are being shared with other market segments, Allison reports. “Plastic and precision composite blade materials that have been a standard product in the flexographic newspaper industry since the late 1980s now are being used in corrugated, flexible packaging, and labels. Automatic wash-up blade systems developed for the newspaper industry now are being run on packaging presses and entering the corrugated markets.”
Converters are turning to lightweight, yet durable, chambers in which blades can be changed without tools, reports Wally Nard, president, Novaflex, Carol Stream, IL (novaflex-inc.com). “You should be able to change the blades without tools safely in a manner that minimizes the chance of an operator getting injured,” he says.
The adoption of “holder bolt-free” doctor blade mounting systems on both flexo and gravure presses helps to minimize challenges for converters, adds Allison. “Some use air bladders; others use engineered uniform pressure spring clamping with a simple means of opening and cleaning. Blade holder screws and the tapped holes they engage are an enormous source of lost press time, labor costs, and printed waste.” Much time and effort are needed to tighten them without distorting the blade holder jaws and wrinkling the doctor blade.
Today's equipment manages ink flow without pressuring the ink inside the chamber, yet maintains enough ink throughout the speed range of the press. But that's not all, Nard says. “There are new managed ink flow systems that can clean the chamber and anilox roll automatically on press quickly and with the minimum consumption of solvents.”
Converters will appreciate a number of developments in the works. They include the use of doctor blade materials and coatings with low coefficients of friction that efficiently meter the rollers as well as increase the roll and doctor blade life, according to Allison. “Doctor blade assemblies will be designed with more automation, control, and repeatability of settings through advance finite element analysis of gravure and flexo doctor blade systems. The payback is good contact angles and a small blade footprint for better metering, instead of the low contact angles and resultant large blade footprint that contribute to ink drying, score lines, and wear on the flexo anilox rollers and to such gravure print problems as hazing and dragout.”
Modern controls will automate an old and variable process, says Allison. “As my father told me after I complained as I came out of my first printing plant at age 15: ‘Shh…Tom! Pressmen are frustrated artists!’ But in today's print world, that wonderful artistic skill and desire can and should be directed by doctoring equipment that can achieve the necessary process control.”
Restrictions of time and space limit the number of companies, products, and trends that we can discuss in these reports. For additional information, see PFFC's features and departments each month, consult the June Buyers Guide, and check pffc-online.com.