The anilox roll and doctor blades are designed to work together to deliver a precise amount of ink to the plate. It is important to take time during a doctor blade installation in order to ensure print quality.
A doctor blade that’s installed correctly will have uniform, balanced contact with the anilox roll and remove ink consistently across its surface. Blade positioning, orientation, angle and pressure will aﬀect the delivery of a precise amount of ink to the plate, and proper installation will give the printer control over consistent, repeatable print quality.
Doctor Blade Installation
Positioning and Orientation
It is essential that the metering and containment blades be positioned correctly when they are installed. Depending on the rotation of the anilox roll, the metering blade could be positioned on the top or the bottom of the chamber. Keep in mind that the metering blade is always the last blade to contact the roll before the ink transfers to the plate. The containment blade is installed in the opposite location. If the two blades are installed in reverse, the metering blade will not achieve the appropriate point of contact with the roll and remove the correct amount of ink before transfer. It is important to remember that the MicroTip or bevel should point away from the roll or towards the chamber (as shown below) to prevent streaking.
The angle at which the blade comes into contact with the anilox roll is also crucial to proper doctor blade installation and optimum blade performance. Ideally, the contact angle should be 30° tangent to the anilox roll circumference. In reverse angle and chamber blade applications, the doctor blade angle should be between 28° and 32°. If the blade angle drops below 28°, a larger part of the blade’s edge will come into contact with the roll. When this happens, the contact area is too big to meter eﬀectively and the blade may allow ink to pass underneath or “hydroplane” at high speeds. If the angle exceeds 32°, it will result in faster wear on the blade.
When a doctor blade chamber is properly aligned, light pressure between the anilox roll and doctor blade is all that’s needed to produce a clean wiping action. In fact, applying the lightest possible pressure necessary to maintain sealing and metering will produce the best results. Excess pressure can cause a deterioration in print quality, wasted ink and substrate, and accelerated
blade and anilox wear. A good way to tell if you’re using the correct amount of doctor blade pressure is to look at the roll once it’s inked. Before increasing pressure, the anilox roll will appear glossy. This is a sign that too much ink is remaining on the surface. Pressure should be increased gradually until a satin ﬁnish appears on the surface of the roll. A satin ﬁnish is a good indication that the correct amount of pressure has been achieved and the doctor blade is eﬀectively shearing the excess ink from the roll. If pressure is increased beyond this point, the doctor blade edge will bend and hydroplane. The roll will again begin to look glossy because it is ﬂooded with too much ink.
The doctor blade plays a key role in the performance of the anilox roll and the printer’s control over print quality. Take the time to double-check blade positioning, orientation, pressure and angle during doctor blade installation to guarantee that the anilox roll delivers the precise volume of ink for which it was designed.