Optimising returns through controlled flexo ink circulation. Henrik Kristensen, vice-president, TRESU Ancillary

In all areas of packaging converting, production run lengths are falling, as the supply chain meets the demand for just-in-time deliveries and greater brand variations.

To meet brand owners’ demands for strict colour consistency and to offer a flexible service, and remain profitable, it is imperative that printers take control of processes and automate wherever possible:  this is the key to eliminating waste from the workflow, in terms of materials, logistics, human intervention, energy, and – above all – time.

Controlling ink flow in the flexo press is vital for fast set-up times, quality consistency and  sustainability  At TRESU we not only manufacture ancillary equipment, offering programmes for almost every flexo printing application from labels to widths beyond six metres; we oversee retrofitting programmes to install the equipment on existing presses. This can bring presses in excess of 20 years old to the latest standards of performance.

Because of our retrofitting experience, we have observed significant shortcomings on presses with ink supply systems that allow ink to be exposed to the environment, or where ink is supplied manually. A mid-to-wide web flexo press typically runs at only 55 percent efficiency, with the remaining 45 percent being lost to setup times. Furthermore, over a quarter of time can be lost to adjusting viscosity, flow and pressure for repeat job start-ups and cleaning after production. And in solvent ink printing situations, escaping vapours present a serious health and fire hazard. The productivity problems can be more severe on common impression presses where it is difficult to prepare the printing units without a ladder.

Automate the ink supply!

The key to control is to enclose and automate the ink flow, from the bucket via an ink supply system, to the point at which it arrives in the cells of the anilox roll. This is the basis for a harmonious, precise regulation of flow, pressure and viscosity, which in turn determines ink density, uniformity of coverage and dot gain.

It includes the ink supply system, the chamber doctor blade, available in ceramic, aluminium or carbon fibre materials, and hoses.

The supply system, such as TRESU’s F10 iCon, automatically maintains a constant, pre-determined flow-rate, replenishing the chamber at finely calibrated rates, as the rotating anilox roll receives the ink into the cells. Its software stores job recipes comprising viscosity, flow rate and density presets that can be recalled. Calibration, therefore, is automatic. The supply system returns inks to the bucket and cleans the chamber without manual intervention.

Automation allows fast setups to occur simultaneously instead of consecutively. Cleaning cycles are at the most 15 minutes for all chambers – and with solvent inks this can be as low as five – saving hours of cleaning time per shift. Automation ensures exact proportions of water and detergent are used in the cleaning cycle.  Significant ink savings are achieved: volume measurement is accurate to one litre, enabling the return of about 90% of the ink or coating medium to the bucket after production per printing station.  This can bring five-figure savings sums annually.

Chamber Doctor Blades for a Cleaner, Safer Environment

The chamber doctor blade prevents leakage, splashing, vapour emissions and contamination of the ink by air. This is assisted by correct blade positioning, use of rubber seals, and precise regulation of flow pressure, forming a wall of ink between the blade and the rotating anilox roll, to stop air bubbles entering. A clamp allows the slotting of doctor blades into position and easy release, keeping changeover times as low as one minute.

Chamber doctor blades are available for all flexo applications, from closed-cassette chambers for label presses, to 6000mm-wide types for corrugated board printing. Carbon fibre chambers offer strength, lowest weight for better handling and optimum resistance against corrosive fluids with high pH values.

All-in-One Inking and Cleaning

The newest chamber for wide-web printing is an ‘all-in-one’ concept, comprising a chamber doctor blade, inking system and integrated cleaning system. One example is TRESU’s MaxiPrint carbon fibre chamber, available in widths from 1600mm to 6000mm. Its integrated cleaning nozzle with low-pressure water-shot mechanism cleans the chamber and anilox roll fast. It is emptied quickly so ink residue can be washed away afterwards before it dries.  Ink changes and cleaning cycles are typically completed within approximately five minutes.

Whether supplied with new presses or retrofitted to existing machines, the enclosed system offers myriad benefits:

• Cleaning times of minutes per job instead of hours
• Elimination of repeat entry of ink recipe data
• Consistent colour targets and even ink coverage throughout the job and from one job to the next
• Faster printing, in some cases more than 600m/min
• No evaporation: a safer, eco-friendlier working environment
• Reduced manual intervention, reduced chance of human error
• Significantly reduced solvent consumption and improved ink yields
• No splashing: a clean, presentable production floor.