Doctor blades are designed to meter the ink as it flows from the chamber to the anilox roll, making sure the exact volume of ink passes to the cells. The blades constantly wipe the surface of the rotating anilox during the printing run, so that the ink delivered to the printing plate is equivalent to the anilox cell volume.
According to Henrik Kristensen, vice president at Tresu Ancillary, doctor blades also act as a barrier to prevent air from contaminating the ink, as well as leakage. “The doctor blade maintains a wall of ink between the blade and the anilox to ensure desired levels of coverage,” he says. “Correct positioning of the blade is essential: positioned too close to the anilox roll, or at the wrong angle, will accelerate wear of both the blade and the anilox.
Kristensen adds that the blade can best fulfil its purpose at faster printing speeds, in situations where the ink supply to the flexo press is fully enclosed. The other components of an enclosed ink supply are a chamber doctor blade and an ink supply system.
Tresu has developed several products to help converters with doctor blade technology. “At Tresu we take these challenges very seriously and to address them, we have developed the inkLINK concept – a complete package of solutions, fine-tuned to the converter’s needs, linking the flow of ink through the print facility – from the ink supplier’s container to the point where it is applied to the substrate,” explains Kristensen. “The inkLink concept creates an efficient, automated and user-friendly solution, for regulating ink flow, ink pressure, pH level, temperature and viscosity – the latter via the patented ViscoFLOW.”
Maintaining the pressure level assures the formation of a wall of ink between the blade and the rotating anilox, which prevents air from entering the chamber. This prevents ink blistering on the substrate, and ultimately, clean, uniform ink coverage.
Kirstensen also details the clamping systems specific to these products. “Eccentric and pneumatic clamping systems allow the blade to be easily and safely slotted into position or removed within one minute,” he notes.
The eccentric clamp is used to exchange narrow width blades that are held in place by an oval-shaped tube. To exchange, the lever is inserted at the end of the tube and then turned clockwise from the 12 o’clock to the three o’clock position. Pressure is released on the blade holder, allowing its release. In order to secure, the lever is pulled 90° anti-clockwise, creating the tension to hold the blade in place.
“Pneumatic clamps, for wider widths, use a flow of air to operate the clamping system,” he adds.
Tresu provides stainless steel and plastic doctor blades in rolls of 100 meters. Rolls of stainless steel doctor blades are available in 35mm or 45mm length and 0.13mm thickness. Plastic blades are available in 35mm length and 0.35mm thickness.
“Stainless steel blades are most suitable for abrasive inks, especially white inks, but these can cause wear when using with ceramic anilox rolls,” says Kristensen. “Coated blades offer the greatest resistance to corrosion and also reduce friction between the blade and the anilox roll, allowing a cleaner wipe and lower blade pressure.”
Tresu also offers a program of chamber doctor blades in aluminum, carbon fiber and ceramic varieties. Available in widths from 185mm to beyond 6000mm, the chambers cover all flexo printing and coating applications and ink sets. There are closed-cassette chambers for label presses and wider variations for folding carton, flexible packaging, corrugated board and tissue converting.
Tresu’s SAVEink chamber for water-based and UV-curable narrow web applications is available at up to 800mm wide. The chamber profile has larger volume as it acts like an integrated ink reservoir, eliminating the need for a connected pumping system. The chamber is easily locked into place and is removed without ink spillage in seconds. The SAVEink chamber features Tresu’s seal system and E-Line quick-blade change system.