Doctors Do Lots
While not a headline-catching subject, doctoring systems have a big impact on printing quality and overall production costs.
ALTHOUGH NOT A particularly glamorous topic, package printers know that doctoring systems represent a complex challenge. The selection, operation, and maintenance of these systems can have a major impact on consistent print quality, along with longer term cost issues when it comes to roll maintenance and life.
When selecting the right doctor blade for your application, there are any number of places to begin and approaches that can be taken. For starters, Perry Lichon, president of Retroflex, lists blade material composition, tip design, thickness, and width. He recommends having a doctor blade system manufacturer cover the available options, while pointing out the benefits and disadvantages of each type.
Even with a clear understanding of the options and tradeoffs, Lichon says that many times the best way to choose a doctor blade material is by trial and error. "Even small differences in anilox or gravure roll engraving, machine speed, fluid chemistry, blade system design, operator experience, and end-product requirements and expectations can result in a big difference when doctor blade materials are compared," he states.
Johnny Stamey, technical product manager for Max Daetwyler, says there are four basic doctor blade style/tip configurations to choose from for all printing applications. These include a straight steel blade with a square edge or no tip, a radius tip blade or round edge, a bevel blade, and a MDC lamella tip or stepped-edge blade. "These four types of blades range in thickness from .004˝-.012˝," says Stamey. "Nonmetallic or plastic blades have all the same tip configurations, but the blade thickness ranges from .007˝ up to 1/8˝, depending on the type of plastic."
As a starting point in choosing a blade combination for a particular application, Stamey points to the line screen of the anilox roll. "For anilox rollers up to 400 line screen, it is best to use straight steel or a radius blade," he says. "For line screens between 400-800, the radius edge or bevel blade is an appropriate choice, and if you stay to the higher side of 800, a lamella tip also works well."