What’s Your Game Plan?
Doctoring systems play an important role in removing excess ink, but because they are not perfect, converters need to strategize.
February 2007 by Missy Smith
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Anything in excess is never a good thing. Just like overdoing it by stuffing down that last bite of pie or filling your home with unnecessary material indulgences, printers can also overdo it with an excess amount of ink. Fortunately, this is where doctoring systems come in to save the day, and the printed material. But, like any piece of printing equipment, these systems are not problem-free. That is why converters need to be armed with the knowledge and skills necessary to make sure doctoring systems run properly and efficiently.
Happy medium
A doctoring blade can only do its job of wiping away excess ink if its contact angle is just right. Improper angles can lead to inconsistent printing and damage to anilox rolls or gravure cylinders.
When setting up a gravure print job, the press operator must adjust the doctor blade to the appropriate angle (between 55–65 degrees). With too low of an angle, an excess amount of ink passes under the doctor blade, carrying unwanted ink to the substrate, says Paul Sharkey, president, FLXON Inc. Too steep of an angle removes too much ink, he says. “A lot of the newer presses have gauges on the press to set the proper angles. The only information you will need is the cylinder diameter or circumference,” says Johnny Stamey, technical product manager, Max Daetwyler. If the press does not have gauges, he suggests using an angle measuring tool to set the proper angle based on the cylinder size. Sean Teufler, technical graphics advisor, Harper Graphic Solutions, recommends checking system alignment during preventative maintenance and at least once a week to ensure the lightest pressure is used without ink or coating leakage.
With flexography, press operators should not rely heavily on the automation of newer systems. “The details and care used in setting systems have become lost in the last 20 years since the introduction of ceramic anilox rolls that are more forgiving and allow for automated chamber systems that often have extra pressure to keep ink from leaking through end seals,” says Jean Jackson, technical account manager, Allison Systems. “This extra pressure is leading to flatter doctor blade contact angles that, on the newer high speed presses or with higher viscosity materials like UV, become even lower during the pressrun.” Most modern flexo presses are automatically aligned to 30-35 degrees, and if the chamber is not over-pressured, that is where blades should remain. When the angle decreases, dot gain will be the first sign of excess pressure, says Stamey. “Sending a set of used doctor blades to the blade supplier for angle analysis will determine if [too much pressure] is the cause of the problem,” he suggests. But, Norm Davister, senior sales engineer, Printco Industries, says, “Even if the doctor blade angle is set correctly by the equipment supplier, varying degrees of printing imperfections will result with the slightest blade angle changes caused by overloading the system, [which is] usually seen when the doctor blade has been worn beyond the intended life span. The doctor blade should be replaced at this point rather than adding extra blade pressure.”
Happy medium
A doctoring blade can only do its job of wiping away excess ink if its contact angle is just right. Improper angles can lead to inconsistent printing and damage to anilox rolls or gravure cylinders.
When setting up a gravure print job, the press operator must adjust the doctor blade to the appropriate angle (between 55–65 degrees). With too low of an angle, an excess amount of ink passes under the doctor blade, carrying unwanted ink to the substrate, says Paul Sharkey, president, FLXON Inc. Too steep of an angle removes too much ink, he says. “A lot of the newer presses have gauges on the press to set the proper angles. The only information you will need is the cylinder diameter or circumference,” says Johnny Stamey, technical product manager, Max Daetwyler. If the press does not have gauges, he suggests using an angle measuring tool to set the proper angle based on the cylinder size. Sean Teufler, technical graphics advisor, Harper Graphic Solutions, recommends checking system alignment during preventative maintenance and at least once a week to ensure the lightest pressure is used without ink or coating leakage.
With flexography, press operators should not rely heavily on the automation of newer systems. “The details and care used in setting systems have become lost in the last 20 years since the introduction of ceramic anilox rolls that are more forgiving and allow for automated chamber systems that often have extra pressure to keep ink from leaking through end seals,” says Jean Jackson, technical account manager, Allison Systems. “This extra pressure is leading to flatter doctor blade contact angles that, on the newer high speed presses or with higher viscosity materials like UV, become even lower during the pressrun.” Most modern flexo presses are automatically aligned to 30-35 degrees, and if the chamber is not over-pressured, that is where blades should remain. When the angle decreases, dot gain will be the first sign of excess pressure, says Stamey. “Sending a set of used doctor blades to the blade supplier for angle analysis will determine if [too much pressure] is the cause of the problem,” he suggests. But, Norm Davister, senior sales engineer, Printco Industries, says, “Even if the doctor blade angle is set correctly by the equipment supplier, varying degrees of printing imperfections will result with the slightest blade angle changes caused by overloading the system, [which is] usually seen when the doctor blade has been worn beyond the intended life span. The doctor blade should be replaced at this point rather than adding extra blade pressure.”
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