Flexo printing - rotary die-cutting inline process

The flexo printing and rotary die-cutting inline process is the combination in one pass of two operations, delivering multi-out and multi-up, flat, die-cut trays and boxes, along with wrap-arounds and large point of purchase/point of sale (POS/POP) displays.

The main elements of a rotary die-cutter are:

• Feeder: which stacks and squares the incoming board before introducing it into the machine at the required speed
• Several flexographic print units, one for each color required
• A rotary die-cut unit comprising of a tool holding cylinder, mounted with a die, and an anvil cylinder. The anvil acts as a cutting plate, allowing the cutting knives to penetrate the corrugated substrate and the creasing rules to create well defined creases
• Waste stripping section: utilizing an oscillating belt and rotating brushes to remove residual waste
• Bundle stacker: comprising a stacker and lift-table with four squaring sides which separate multi-ups and form bundles
• Breaker and turntable: for the creation of optimum palletization patterns

In a modern flexographic press, each print unit comprises of:

• Anilox roller: a cylinder of highly engineered metal and/or ceramic, which is laser engraved with minute cells of a given angle, line screen, and volume to deliver the required fineness of print
• Chambered doctor blade system: a device that delivers a measured amount of ink to the cells of the anilox roller
• Plate cylinder: which the printing plate is mounted upon
• Impression cylinder: a sleeve that supports the substrate as the printing plate is pressed against it
• Inking system: ink holding tank, ink pump with delivery and return ink lines, plus other elements to ensure the maintenance of ink supply and viscosity

Between the print units, driers may be installed so that subsequent colors can be applied to the substrate without merging into those previously printed. These driers may utilize hot air, infra red, or ultra-violet light, depending on the application.

During the printing process, the ink is pumped into the ink chamber of the doctor blade system. Two blades within the ink chamber, the barrier blade and the doctor blade, seal either end and confine the ink to the chamber while it is in contact with the anilox roller.

As the anilox roller rotates, the cells in contact with the doctor blade system collect ink, then any surface excess is removed as the roller passes under the doctor blade.

As the anilox rotates, its surface comes into contact with the raised areas of the printing plates mounted on the plate cylinder, transferring the ink.

The printing plate then rotates and transfers the image onto the substrate.

Carrying out flexo printing and rotary die-cutting inline produces complex packaging or displays in a single pass and at high speed.

Today’s markets demand increasingly high quality graphics, which in turn means tighter registration and improved color consistency is needed. BOBST is at the forefront of developing rotary die-cutters in 'high graphics' configurations for the printing of four color process, pantone colors, and varnish onto coated paper.