The doctor blade – a crucial factor in expanded gamut printing
von Ansgar Wessendorf,
Daetwyler SwissTec’s new MDC Gamutstar doctor blade is a specific response to the demands of customers working with an expanded colour gamut (ECG). ECG describes printing with an expanded palette of colours (gamut), where the gamut is standardised through the use of seven process colours: cyan, magenta, yellow, black, expanded to include the orange, green and violet. The doctor blade is a crucial factor for the successful use of ECG. But why is that?
Daetwyler SwissTec first encountered ECG through its US operation, partly because over recent years the use of ECG has grown steadily in the American flexographic printing market in particular. The company’s team of around 40 recognised printing technology experts provides daily support in the use of their presses to customers all around the world. This means that the technical support team is right at the heart of matters when it comes to using doctor blades correctly.
Not only are printing process problems solved through a joint effort, this also enables Daetwyler SwissTec to satisfy market demands more effectively and to ensure product development is customer oriented. The specifications for the doctor blade were developed through knowledge that had been gained in this way and then passed on to the company’s Swiss head office. Daetwyler SwissTec’s research & development department was then asked to develop a doctor blade that would meet the high demands of expanded gamut (ECG) printing.
Current market demands
The trend to more and more product variants and small batch sizes, presents packaging manufacturers with greater and greater challenges. Especially as every company would like to satisfy the vast array of customer wishes without incurring cost increases. Lean management is called for and process optimisation is the order of the day. ECG printing helps by increasing efficiency and saving costs thanks to the reduced use of ink, faster processes as well as shorter press down-times.
Printing with a fixed colour palette means that “colour mixing” on the press is a thing of the past. Orders can also be reproduced exactly at any time thanks to the standardised process colours, and this offers customers consistent product quality. But watch out: the use of standardised process colours does not guarantee the consistent ink transfer required for reproduction. So what do you have to watch out for?
The doctor blade – a crucial factor
Regardless of whether it’s a highly complicated special order or the simplest of jobs – it is crucially important to control? the thickness of the ink layer being transferred if high-quality, reproducible printing results are to be achieved. However, this requires the use of finely ruled anilox rollers. Here, it is very important to choose the right doctor blade. Its quality and configuration should suit the ruling of the anilox rollers and the order in question. As flexo doctor blades wear out, it is important that the angle of the blade to the anilox roller is kept constant over the whole lifespan of the doctor blade, so as to transfer an even ink layer thickness to the substrate.
Doctor blade designed especially for ECG printing
New doctor blade technology from Daetwyler SwissTec achieves precisely this. The concept for the MDC Gamutstar was developed especially for ECG printing and is based on customer feedback. Its design and the coating of this special type of doctor blade have been developed to ensure constant ink transfer and a long lifespan.
Right from its first contact with the anilox roller, the MDC Gamutstar offers an optimal blade angle, and so it is no longer necessary for the doctor blade to be run in. In addition, the new type of doctor blade promises a constant and clean blade angle over the whole printing process. Thanks to this, several orders can be printed one after the other without the doctor blade having to be changed, ensuring that the doctor blade plays its part in delivering the fundamental benefit of ECG: short changeover times and fast preparation.
The quality of repeat jobs can also be maintained thanks to consistent ink transfer. MDC Gamutstar has a low friction soft coating which has a positive influence on the ink wetting of the anilox roller and acts as a gentle lubricating film against the anilox roller. In addition, this approach largely prevents doctor blade streaking and reduces contact pressure to no more than the necessary minimum.
The doctor blade bevel should be chosen to suit the anilox roller ruling and Daetwyler SwissTec offers three different bevels – Lamella, Multiblade and Flexolife – to cover the whole spectrum of anilox roller rulings.
The interplay of blade chamber and end seal
When using a chambered doctor blade system in flexo printing, there is another factor that can cause ink transfer to vary, namely the interplay of the doctor blade and the end seal (seals). The end seals complement the doctor blade. In flexo printing they are needed to cleanly seal the doctor blade chamber and to prevent the ink from escaping. Doctor blades (working and closing blades), ink chambers and seals make up the chambered doctor blade system. Contact with the anilox roller means that doctor blade knives as well as the end seals of the wearing parts interact and heavily influence ink transfer.
Close interlocking of doctor blade knives and chambered seals has allowed Daetwyler SwissTec to develop a new concept for end seals. There are three categories of MDC end seals based on differing material properties: MDC Regular, MDC Advanced and MDC Expert. This allows the customer to select the right seal for the job based on the run time and the quality of the doctor blades being used.
The user benefits from doctor blades and end seals that are finely tuned to one another, offering clean and consistent printing behaviour during production printing. With ECG, press down time is reduced as you are only required to change one of the two wearing parts.
Successful market launch
The MDC Gamutstar has now been successfully launched in the flexo printing market, but the advantages of the new type of doctor blade should also be applicable to gravure printing. Daetwyler SwissTec is currently carrying out printing trials to see if this is so.
The MDC doctor blade family for flexo and gravure printing – as well as the globally successful MDC long-life doctor blade – now consists of a dozen differently coated doctor blades that are tailored to the most varied of printing and coating conditions. In this context it is worth noting that for Daetwyler SwissTec, instantaneous on-site technical support on the customer’s own press forms the basis for its research and development activities into new product solutions.