Daetwyler SwissTec celebrates 50 years of lamella doctor blades
Who invented it? The Swiss, of course!
von Ansgar Wessendorf,
In principle, the lamella doctor blade is nothing more than a thin, resilient strip of alloyed steel. But with this ingenious invention, the Swiss companies Ringier and Daetwyler not only revolutionised gravure printing 50 years ago. Without the development of this high-end tool, high-quality flexo printing would not be where it is today. The high-precision application of different coating media such as adhesives or varnishes would also often not be possible without the use of coated lamella doctor blades. It is thus one of the most important elements not only of gravure presses but also of flexo printing and coating lines.
Particularly in gravure printing, the doctor blade is a decisive factor in achieving consistently high print quality. It is therefore often referred to as the “soul of gravure”. The fact that this doctor blade does indeed have a decisive influence on the print result is also proven by the numerous innovative development projects over the past decades that Daetwyler has brought to market maturity.
How it all began – the invention of the lamella doctor blade
As early as 1922, the then Ringier print shop in Zofingen, Switzerland, began printing “Ringiers Unterhaltungs-Blätter” (Ringiers Entertainment Magazine), also known as “RUB” for short. Called “Das Gelbe Heft” (The Yellow Magazine) because of its colour, the publication quickly became Ringier’s flagship product due to its hot topics, illustrated short stories and novellas. For a long time, therefore, it remained one of the publishing house’s most financially successful print products.
– The challenge
The lettering “Ringiers Unterhaltungs-Blätter” to be printed on the yellow title page was specified in a brown colour. However, this colour was so difficult to print that undesirable but then unavoidable streaking occurred. In addition, the permanent wear of the wedge doctor blade used at the time rapidly increased the contact area between the doctor blade and the cylinder surface and severely impaired the quality of the doctoring. All in all, printing the “Gelbe Hefte” was a real challenge and satisfactory quality was not easy to achieve. Ringier, as the largest gravure printing company in Switzerland at the time, urgently needed a solution and therefore began to work closely with Daetwyler.
– The initial situation or: When does the doctor blade need to be grinded?
The doctor blade in gravure printing is a steel band grinded like a knife. At the beginning of its development, the doctor blade therefore had a wedge-shaped cross-section. “At that time, gravure printers still grinded their doctor blades themselves, which, however, led to tonal value fluctuations due to the low precision. In addition, the contact surface was permanently enlarged due to wear and tear and therefore the printed ink tone was constantly changing”, says Olaf Segbert, Marketing Manager at Daetwyler SwissTec, describing the situation at the time.
This change in the contact zone “doctor blade/gravure cylinder” also has consequences for the line pressure in the gravure press. The line pressure in this context describes the physical pressure with which the doctor blade and the cylinder are pressed against each other in the contact area. With a constant contact pressure and depending on the service life (duration of doctor blade use), the associated enlargement of the contact zone area leads to a permanent reduction in the line pressure. This results in an increase in the transferred ink amount (dot gain). At that time, this could only be counteracted by regrinding the doctor blade.
This weak point of the printing process was countered by former Ringier employee Hans Burgener with the idea of a lamellar doctor blade, thus opening a new chapter in the history of this tool. Together with Hans Burgener, Daetwyler recognised the fundamental problem of conventional doctor blades and participated in transforming his idea of a lamella blade into a technically practicable solution. In this context, the term lamella means the bevelled scraper edge of the doctor blades, i.e. the actual functional area.
– An ingenious idea and first steps
Hans Burgener refined the newly developed doctor blade with an etching solution and thus achieved the first improvements in gravure printing, as the contact zone surface remained virtually unchanged throughout the entire print run. But at that time this new type of doctor blade was produced almost exclusively for printing the “Yellow Magazine”.
Nevertheless, Ringier was not yet fully satisfied with this new development. Although they were aware of the great potential that lay in further development and perfection, the publishing house had to admit that neither time nor staff were available for this.
At that time Daetwyler was known worldwide for its etching machines for the production of gravure cylinders. Since they therefore had the corresponding know-how in etching technology, Ringier transferred the further development and patenting of the lamellar doctor blade to the then company Max Daetwyler + Co (today Daetwyler SwissTec).
Max Daetwyler immediately recognised the hidden potential of this invention and within a very short time a wide variety of test stations were set up. )n the years that followed this led to a momentum of successive development stages and new ideas.
– The solution to the problem
After an initial period of “fiddling around”, it became increasingly obvious that the etching technique would not be a viable option in connection with the lamella doctor blade. In the meantime, the high precision blade grinding with self-developed automatic grinding machines achieved ever more consistent and better printing results. Parallel to the development of this very special grinding technology, the so-called “doctor blade steel” was also subjected to various strict tests and its composition constantly improved.
“Compared to the conventional doctor blade, the lamella type offers the great advantage that the actual doctoring zone of the blade is no longer grinded at a specific angle, but in a lamella shape”, explains Olaf Segbert. “Due to the special shape, the contact zone remains the same over the entire width of the lamella and thus also the line pressure, which leads to stable tonal values. Since this doctor blade also requires weaker contact pressure, cylinder wear is also reduced. All this combined ensures consistent print quality across the entire run.”
– The final breakthrough
In 1972, Daetwyler achieved the great breakthrough with the lamella doctor blade. The know-how gained through in-house development could now be used to manufacture innovative and practical doctor blade products. At the same time, this also marked the beginning of Daetwyler’s unstoppable rise to become the world market leader in the field of doctor blades.
However, an effective distribution network had to be established to sell this new product. As a successful supplier of machines and systems for gravure forme production, Daetwyler had no lack of contacts at the time, so that worldwide distribution structures were gradually established.
The development of the first coated lamella doctor blade and the introduction of the MDC Longlife product variant in 1991 were further outstanding milestones. “These developments hat a quite revolutionary impact on gravure printing. Increases in print quality and process efficiency were achieved that were previously thought not possible”, says Olaf Segbert. “The service live of doctor blades was significantly extended and gravure printing was raised to an even higher level of quality.”
The introduction of the “Longlife” lamellar doctor blades – Daetwyler’s most successful doctor blade type to date – was the basis for a unique success story that continues to this day. At the same time, “Longlife” also initiated the foundation of Daetwyler SwissTec AG in 2007.
Daetwyler SwissTec AG is intensively and exclusively engaged in the development and manufacture of doctor blades. Today, these products are used not only for a wide variety of applications in gravure printing, but also for flexo printing, printed electronics and the coating industry. However, the basis of all these customised doctor blade solutions is still the lamella doctor blade, which started its triumph 50 years ago.
Where does the term “doctor blade” comes from?
The basic task of the doctor blade is to wipe off excess low-viscosity inks, varnishes or coating media from the surfaces of gravure cylinders or anilox rollers so that only the ink required for printing, the varnish to be transferred or the coating medium to be applied remains in the cells of the impression cylinder or anilox roller. After removing the excess, the surface of the cell walls should be free and the cells optimally filled. This function is also the origin of the name “doctor blade”, which goes back to the French verb “racler” (= to wipe off, to brush off).