Blog: Properly Installing TruPoint Doctor Blades

Alles, was sein Streben nach einwandfreiem Druck und effizienter Ausgabe verlangsamt oder unterbricht, wird vom Drucker verschmäht. Dazu gehört auch die Rückenbeschneidung, die verschwenderisch und störend ist und generell nervt. Die gute Nachricht ist, dass sie mit dem richtigen Rakelmesser leicht überwunden werden kann.

Rückenbeschneidung erklärt

No one would debate that back doctoring (also referred to as “trail doctoring”) is a nuisance. What operator wants to stop and clean the press more often than he already has to? It is also an expensive problem. Lost press time and wasted ink and substrate cost money – and delivering output with print defects costs customers.

Um die Rückwärtsbearbeitung zu erklären, vergleichen wir, was eigentlich passieren sollte und was tatsächlich passiert.

Der Traum

Both the metering blade and the containment blade are thin strips of material that play a key role in transferring ink from the anilox roll to the substrate. But the two blades have very different purposes. In order for the doctor blade chamber to function optimally, each blade has to be chosen carefully.

Ideally, the reverse angle blade acts as the true doctor blade responsible for delivering a precise amount of ink to the plate and ultimately, the substrate. It is designed to wipe the excess ink from the anilox roll before the transfer takes place to ensure that the correct volume of ink is transferred. Metering blades need to be stiff and rigid to prevent hydraulic pressure from lifting the blade as the roll turns, letting ink pass underneath and over-inking the anilox roll.

The trailing blade acts as a capture or containment blade and holds the ink within the confines of the chamber. Essentially, you want the containment blade to function in the opposite way in terms of how it interacts with the ink. Located in the opposing position in the chamber, its function is to collect and contain the excess ink from the roll after the transfer takes place. In this case, you want the hydraulic force from the rotation of the roll to lift the tip of the containment blade, letting the ink flow underneath – in one direction – and back into the chamber where it is reclaimed for future use. Whereas stiffness and rigidity are required of the metering blade for effective wiping, the containment blade should be thin and flexible in order to create a one-way “valve.”

Die Realität

Back doctoring occurs when the containment blade meters – or ”doctors” – the ink instead of allowing it to re-enter the chamber/funneling it back into the chamber. A containment blade that’s too stiff or rigid (such as steel) will prevent the ink from passing under the blade and being reclaimed. The “back-doctored” ink builds up on the outside of the blade, pools at the ends of the chamber and eventually slings onto the press and web. (This occurs more frequently when the containment blade is installed in the bottom position of the chamber where gravity pulls the ink downward.) The resulting mess requires the press to be shut down, cleaned and reset by the operator before he can continue with the print job. At higher press speeds or smaller anilox diameters, the centrifugal force of the roll as it turns is greater and the problem is even worse.

Wie man das Rückenkraulen stoppt

Der Schlüssel zur Beseitigung von Rückenkratzern ist die Verwendung der richtigen Eindämmungsklinge.

The ideal containment blade should be thin and flexible enough (such as plastic) to lift and create a one-way path for the ink to return to the chamber. Unlike the metering blade, where a precise area of contact enhances metering performance, a fine contact area with the roll is not required (why pay for a bevel when it’s not needed?) for the containment blade to perform its function. Choosing a straight or radius edge will optimize blade life and cost.

Polyester Eindämmungsflügel

Polyester ist aufgrund seiner Flexibilität und Stabilität bei dünnen Dicken seit langem das bevorzugte Material für die Eindämmung. Das Material hat einen niedrigen Reibungskoeffizienten und ist sehr lösungsmittelbeständig. Polyester Klingen kosten wesentlich weniger als Stahlklingen (etwa ein Drittel bis die Hälfte) und sind für das Druckpersonal sicherer zu handhaben. Das Material ist weich und enthält keine scharfen Fragmente, die abbrechen, sich an der Rasterwalze festsetzen und die Oberflächengravur beim Drehen der Walze zerstören könnten. Das Material ist auch nicht abrasiv und verursacht keine übermäßige Abnutzung der Walze.

Back doctoring is a common pressroom problem that, fortunately (but less commonly), has an easy fix: converting to a plastic containment blade. By choosing plastic, a printer can ensure that the containment blade will succeed in doing its job – keeping unused in ink the chamber and preventing it from escaping and making a mess – even at high press speeds.

Read our blog post, “Top 5 Reasons to Switch to Polyester Containment Blades” to learn more about the benefits of using plastic containment blades.

Fordern Sie ein kostenloses Muster von TruPoint an Polyester