by clicking the arrows at the side of the page, or by using the toolbar.
by clicking anywhere on the page.
by dragging the page around when zoomed in.
by clicking anywhere on the page when zoomed in.
web sites or send emails by clicking on hyperlinks.
Email this page to a friend
Search this issue
Index - jump to page or section
Archive - view past issues
FLEXO Magazine : June 2012
Technologies & Techniques Chambered Doctor Blade Systems for Flexographic Printing Constant Changing Market Demands Require Continuous innovation By scott Michels At first glance, chambered doctor blade systems may seem fairly simple in construction. Yet through the years, this intricate piece of the flexographic printing process has repeatedly adapted to ever-changing market demands. Years of innovation have also improved under- standing and technology. Chambers have been used in the flexographic market since the early 1980s. They have earned industry-wide acceptance and are installed on countless applications in all segments of the flexographic printing and coating processes. The main objective of the chamber is to provide a closed loop ink supply to the anilox roll and then precisely meter the surface of the roll with a reverse angle doctoring blade. The enclosed chamber limits the ink’s exposure to the atmosphere, thereby reducing evaporation and keeping the ink in proper chemical balance. The end result allows for a consistent and repeatable ink film that’s critical to successful flexographic printing. Although the basic concept of applying ink to the anilox roll with a chamber sounds relatively simple, there are many vari- ables that demand constant innovation. Higher press speeds, demanding inks, and the continuous need for faster, more automated changeovers all require the chamber system – and its associated components – to continually evolve into the next generation of technologies. The basic construction of a chambered doctor blade system begins with a main cavity that holds the ink. Ink is fed to and returned from the cavity via inlet and outlet porting, which provides for a continuous closed-loop system. The chamber also has a means to clamp and hold consumable doctoring blades and end seals. Vari- ous pumping systems are then added to the chamber in order to complete the whole ink delivery and wash-up configuration. These individual compo- nents are pictured at right. CHAMBER CAVITY In the early days of the chamber, the consensus was that a large cavity and wide blade gap to the anilox roll offered the most efficient filling of the anilox roll cells. The thought was that this would allow more dwell time or ink exposure to the surface of the anilox roll. However, the truth is that larger cavity chambers have room inside for the ink to slosh around, which agitates the ink and allows air to enter the system. This can limit the ability for the cells to refill efficiently, making it more difficult to run up to speed. Ghosting and starvation (a shift back and forth from heavy ink coverage to light ink cover- age back to heavy ink coverage) issues also arise. Together, the anilox roll and chamber act like a small pump that tries to draw air into the system. Several items contrib- ute to this, including: large air pockets or turbulence inside the chamber, feed pumps, air getting pulled in from under The DocTor Is In • The main objective of the chamber is to provide a closed loop ink supply to the anilox roll • Higher press speeds, demanding inks, and the continuous need for faster, more automated changeovers all require the chamber system to continually evolve into the next generation of technologies • Larger cavity chambers have room inside for the ink to slosh around, which agitates the ink and allows air to enter the system • Newer chamber geometries are more circular in shape providing a smooth, laminar flow. • Although chambers may at first look relatively simple in construction, the reality is that there are a lot of complex fluid characteristics happening inside www.flexography.org june 2012 FLeXO 103