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Whether as a full-area protective coating, a spot coating, or a scented coating, whether a matt, glossy or structured coating - the inline finishing of print products in an inline coating unit belongs to the daily business of many offset printing shops today.
The inline coating of a printing substrate in the direct printing process requires a harmonious coat transfer from the anilox roller to the coating plate. Doctor blades ensure that the anilox roller transfers the right amount of coating by scraping surplus coating from it. A precise and uniform doctoring is a crucial factor for the quality of the coating.
There are some important factors in the printing application environment that must be considered in order to ensure an optimal doctoring in the chamber system. This includes the type of coating, i.e. whether aqueous, UV or even Iriodin coatings are being used. Furthermore, the utilized capacity of the coating unit plays a role, i.e. whether sporadic printing jobs are coated or if the unit runs three shifts. Our customers’ demands towards the doctor blades’ lifespan and cost-ratio performance are also crucial factors.
Based on our long experience in the finishing industry, we have developed four types of doctor blades (steel and plastic) that are are adjusted especially for the different inline coating applications for sheet fed offset printing machines.
Our steelBLADE S doctor blades made out of high quality stainless steel are all-rounders in an offset coating unit. Thanks to their resistance to corrosion, they can be used for water based coatings as well as other types of coatings.
A thin grinded lamella is responsible for an optimal contact zone with the anilox roller, so that the doctor blade produces high doctoring results throughout its lifespan. Even if some print products do not require coating, the steelBLADE S can continue to be used afterwards until the lamella has lapsed since there is no risk of corrosion.
For the models of the brands Heidelberg, Komori and manroland, which have TRESU chamber doctor blade systems, the steeLBLADE S doctor blades usually require the dimensions 35 x 0.20 mm. For KBA, Komori and Ryobi with Harris & Bruno chambers, the doctor blades usually have the dimensions 28 x 0.20 mm or 25 x 0.20mm.
Optimum doctor blade for UV coatings
Our steelBLADE C doctor blades also have a thin grinded lamella like the steelBLADE S doctor blades. These are responsible for a precise doctoring in the chamber. These blades out of carbon steel are a good alternative for UV coatings due to their cost-performance ratio. The use of these doctor blades with other types of coatings can only be recommended for special applications, such as when the blades are run in three shifts with no downtime so that no risk of corrosion arises.
steelBLADE C doctor blades are also used in the ink chambers of the Heidelberg SM Anicolor and KBA Genius 52UV machines, which use oil based or UV inks.
Our steelBLADE T doctor blades are manufactured from premium tooling steel and have been developed especially for finishing applications with highly abrasive coatings such as Iriodin or opaque white. Due to their higher degree of hardness, the steelBLADE T doctor blades ensure an optimal doctoring also with coatings that have a grinding effect. When used under the same conditions, the steelBLADE T lasts about three times longer in comparison to the steelBLADE S.
Our fiberBLADE U doctor blades are manufactured from fiber-reinforced plastic. These doctor blades are highly wear resistant and have a wedge-shaped bevel. Plastic blades are by nature anticorrosive and are therefore suitable for all coating applications.
For coating units with TRESU chambers (usually Heiderlberg, manrolang and Komori), the dimensions for the fiberBLADE U doctor blades are usually 35 mm wide, while Harris & Bruno chambers mostly require blades with 28 mm width.
Opposite to the doctor blade lies the retaining blade. While the end seals have a sealing function at both sides of the chamber, the retaining blade seals the chamber along the anilox roller.
Many coating units use the same material for the doctoring and retaining blade. Due to the geometry of the chamber, the retaining blade is positioned in a rather steep angle to the anilox roller. In some coating units the retaining blade is located face down, e.g. in many Heidelberg models. A standard steel blade has a high stiffness when positioned in a steel angle. Thus, a retaining blade which is faced downwards partially doctors coating from the anilox roller instead of letting it flow back into the chamber. This leads to coating drops forming underneath the chamber, which affects the printing quality and costs time and money for cleaning and paper waste.
Our special retaining blade solutions act against this phenomenon:
Our polyBLADE S retaining blades are manufactured from a wear resistant plastic. Due to its high material elasticity, this flexible blade keeps permanent contact with the anilox roller and thus ensures a recirculation of the coating from not emptied cells into the chamber. This way the appearance of coating drops is almost completely eliminated.
Since the function of the retaining blade does not require a specific blade profile and since plastic is a lower priced raw material compared to steel, our polyBLADE S doctor blades are an effective alternative for coating units with an excellent cost-performance ratio.
Another alternative is a special version of our steelBLADE S doctor blade, which has increased in popularity lately. This retaining blade solution is also based on the flexibility of the material, thus we use 0.10 or 0.15 mm thick steel instead. On top of that, the retaining blade is oversized so that the blade surface seals the chamber instead of the blade edge.
This leads to the blade opening slightly and giving surplus coating the possibility to circulate back into the chamber.
All our doctor and retaining blades can either be delivered in 100m rolls or cut to length to fit your specific machine model. This saves you from measuring and cutting the right length in the printing shop and you can take the readily cut doctor blades out of the packaging and insert it directly into the chamber instead. Further advantages for cut to length doctor blades are:
protect you against cut injuries when handling doctor blades.
Our safety gloves are available in the sizes 8, 9 and 10 and deliver high quality protection while at the same time providing a high flexibility for all fingers.