Tresu’s MaxiPrint chambered doctor blade features a self-cleaning water jetting system
In flexo printing, controlling ink flow is crucial for reducing waste and improving productivity and it is using the right chambered doctor blades, in connection with a pumping system, which is the key to ink flow control. Michal Lodej reports.
Chambered doctor blades help to give converters greater control on production by providing a fully enclosed means of ink supply, which allows the precise regulation of flow, pressure and viscosity, to ensure uniform and precise ink density, even at faster speeds.
The ancillary programme from Tresu Group comprises of an ink supply, together with chamber doctor blade systems for narrow, mid and wide web flexo applications, providing a complete solution for regulating ink flow throughout the press, from bucket to substrate. This significantly reduces material and ink waste, setup times, emissions and labour and helps to achieve accurate colour targets at speeds that can reach up to 800m/min.
The company’s chamber programme includes lightweight, corrosion-resistant carbon fibre and ceramic variants and covers all flexo printing situations, in widths from 185mm to beyond 6000mm. Assisted by the company’s patented seals and constant pressure maintained by the supply system, the chambered doctor blades prevent leakage and air contamination, thereby ensuring clean, blister-free print results with fast drying characteristics, better reflection and higher gloss values. When doctor blades need replacing, the clamping systems enable safe blade changeovers in less than two minutes.
For wide web and corrugated flexo applications between 1600mm and 6000mm, the carbon fibre MaxiPrint Concept reduces cleaning time and improves colour quality and consistency. Comprising a closed chamber, an integrated ink supply unit and a cleaning cycle, the MaxiPrint Concept offers fast, automatic internal cleaning, corrosion-resistance, improved print quality consistency and reduced ink loss. The chamber’s cleaning nozzles with robustly designed water-shot mechanisms provide an ink change and cleaning cycle within 3-5 minutes.
Quick dry round
When using quick drying water-based inks for flexo printing, lumps of semi-dried ink tend to destroy the function of the end-seals. The new HumidFlow System from AkeBoose Graphic Products prevents water-based inks from drying up and pushing the end-seals out. This eliminates unplanned production stops due to clogged end-seals, ink dripping from the sealing blade or drying ink contaminating the linear bearings.
AkeBoose’s Nova XLS and HumidFlow fitted onto a Comexi FJ 2108
A popular design for inking and doctoring efficiency in flexo printing is an asymmetric chamber system such as the company’s Nova XLS, which works in combination with low-pressure doctoring. According to AkeBoose, the two principles allow the chamber to work with optimal blade angles for both working and sealing blade, which eliminates problems with back doctoring and ink spitting.
Today, with the use of quick drying water-based inks growing rapidly, the industry is facing new problems with the function of the chamber end-seals which are easily destroyed by lumps of semi-dried ink. Typically, the semi-dried ink builds up underneath the working blade, and thereby pushes the seal and the blade away from each other, allowing the ink in the chamber to flow out without restraint.
A double end-seal arrangement keeps the area around the seals at a high humidity, preventing the ink from drying in this area. This prevents unplanned production stops, due to heavy ink leakage at both ends of the chamber/screen roller and no more unnecessary cleaning work. This creates savings in manpower and running costs as well as a smaller risk of contaminating the linear bearings at each print deck. Ink should never be allowed to enter these bearings.
Get plenty of fibre
Typically today, doctor blade chambers are constructed from carbon fibre, however, Packaging Plast is emphasising that its doctor blade chambers are made from 100% carbon fibre. According to the company by using new moulding technology it is able to achieve an extremely lightweight system that does not suffer any torsion regardless of its length.
Packaging Plast systems can be installed on CI as well as in-line flexo presses and are suitable for the full spectrum of flexo printed products from corrugated board to flexible film, including tissue paper.
According to the company, building its chambers from nothing other than carbon fibre provides increased stiffness, removes corrosion, is easy to clean and can deliver ink and water savings.
The Italian OEM has also recently signed an agreement with Flexo Concepts, and will begin shipping all its chambers with the TruPoint Green doctor blade beginning in September 2017.
TruPoint Green is a next generation polymer doctor blade for corrugated printers producing mid-level graphics. The blade’s mechanical properties and composition allow it to meter more effectively than UHMW with significantly longer blade life than steel. TruPoint Green in combination with the carbon fibre chamber design delivers better print quality and
provides printers with considerable savings on the inking systems of their presses.
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Absolute Engineering has just completed the conversion to 2G Carbon Fibre chambers of a further two Bobst Bielefeld flexo presses for a manufacturer of paper sacks in
the UK.
East Riding Sacks (ERS) is the largest independent supplier of multi wall sacks in the UK and a key player in the European sack industry. Its relationship with Absolute has developed since 2015 when it was looking to replace the chambers on its six-colour F+K 16S. The existing systems were both heavy and worn and ERS wanted to use the upgrade as an opportunity to also improve both the performance and ergonomics of the press.
Jürgen Bopzin, technical engineering director, commented, ‘There are several suppliers of chambered doctor blades, and so we assessed the market alternatives, including the OEM alternatives and decided to try just one 2G Carbon Fibre chamber from Absolute. After a testing period we reviewed the performance and found that it gave us significant improvements in press cleanliness, speed of blade change and ergonomics and on this basis decided to replace the remaining seven units. We are really happy with both the technical expertise Absolute offers, as well as the service and support they have given us since.’
In fact such was the improvement that after several short months ERS decided to upgrade its eight-colour Bobst F+K 20SIX press as well. This installation has now been completed and has proven a similar hit with the operators and management. Antony Whiteside, managing director of Absolute is also happy with the outcome. ‘ERS are a progressive company, constantly investing in new equipment but also putting significant effort into upgrading the performance of existing equipment. This partnership is a great example of the excellent results that can be achieved when proactive like-minded partners work together. Absolute follow this model for both upgrades and new product developments.’
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