Flexo printing - rotary die-cutting inline process

With a background in the flexo printing and rotary die-cutting inline of corrugated board which stretches back to 1923, BOBST is perfectly placed to understand the requirements and expectations of manufacturers around the globe.

Alongside the development of rotary die-cutting machines that have pushed forward the boundaries of both high graphics printing and die-cutting, BOBST continues to pay close attention to the quality of the finished product and to the productivity and reliability of its equipment.

Rotary die-cutters are used in two main industries, these being the manufacture of corrugated packaging that has high printing and die-cutting requirements, and the production of in-store displays from corrugated board.

BOBST, through its Bobst Lyon product line, has been at the forefront of developing technology to help users exploit these growing markets, including the introduction of independent drives and closed inking circuits. BOBST production lines are designed to deliver accuracy, flexibility, performance, and ease of use, while the wide variety of sizes and levels of automation available suit the needs of a range of users.

Flexo printing and 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.

Rotary die-cutters

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

Flexographic printing units

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.

Process description

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.

Process advantages

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

BOBST expertise and knowledge

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.