A seal is a small component with a big impact.
The right seal reduces leaks, minimizes downtime, and keeps your printing process running efficiently.
In flexo printing, the closed doctor blade chamber is the system that manages the controlled transfer of ink onto the anilox roll. The side seals — positioned at the ends of the chamber — have a precise task: preventing ink leakage at the sides, maintaining uniform contact pressure along the entire width of the roll, and resisting the continuous action of solvents, inks, varnishes, and adhesives throughout every production shift.
It is not a component that is visible. But when it starts to deteriorate, the signs are clear: side leaks, contamination, unplanned downtime for cleaning or replacement.
The most common problem: the wrong material for the application
The market offers many types of seals compatible with the main doctor blade chambers available. The point is not finding a seal that physically fits into the housing: it is finding the one that lasts under the specific operating conditions of that machine, with that type of ink, at those temperatures.
A material with poor memory effect — that is, the ability to return to its original shape after compression — progressively loses its seal. The result is micro-leaks that are not always immediately visible, but which over time impact the productivity of the printing press and increase ink consumption.
Main material types and their applications
Doctor blade chamber seals are not interchangeable. Each material has specific characteristics designed for certain doctor blade chamber models and ink types. Here is an overview of the most common types:
EPDM Suitable for printing on film and paper. Good resistance to water-based and UV inks. Elastomer with fair flexibility.
XTREME and XTREME PLUS Developed for high-performance applications on film and paper. The XTREME PLUS 25 material offers greater wear resistance compared to the standard version, with superior memory effect.
LONG LIFE Versatile solution suitable for film, paper, and cardboard. Designed to extend the replacement interval in intensive production contexts.
FELT (impregnated) Used mainly on cardboard, coating, varnishing, and with white ink with high titanium dioxide content. Available with grease impregnation or specific sprays for water-based inks.
NBR / Molded rubber Suitable for cardboard, coating, and varnishing. Mold-produced, it guarantees precise geometries and excellent resistance to solvents. Available in versions compatible with the doctor blade chambers of the main manufacturers: Bobst, Tresu, Harris & Bruno, and Kroenert.
VULKOLLAN Specific material for the label sector. Offers high mechanical resistance and excellent behavior in high-speed processes.
PLASTAZOTE Suitable for paper and cardboard. Closed-cell material with good compressibility.
Inserts, milling, and special versions
In addition to the base material type, seals may require additional processing depending on the specifications of the doctor blade chamber:
- Teflon inserts (single or double milling)
- Inserts with double pin
- Rubber base with felt insert
- White teflon coatings
- UltraSeal for special applications
These processes are not optional: in many cases they are essential to ensure the correct seal with the specific geometry of the chamber.
Why cutting precision makes the difference
A seal made with quality material but with imprecise geometry does not seal correctly. Side leaks in the first cycles of use are, in many cases, not a material problem but a cutting tolerance problem.
Ulmex uses a latest-generation digital cutting center to ensure high perimeter precision across all types of seals produced in-house. This translates into correct geometry from the very first installation, without the need for adjustments.
Compatibility with the main flexo machine manufacturers
Ulmex seals are produced as compatible and equivalent for the closed doctor blade chambers of the following manufacturers, among others:
Windmöller & Hölscher, Uteco, Soma, KBA Flexotecnica, Bobst, Fischer & Krecke, Comexi, Allstein, TCE, Bobst Martin, Bobst Masterflex, Göpfer, EDF, Cellmach, Massenzana, Dong Fang, Omet, Gallus, Lombardi, Tresu, Curioni, Polytype, Kroenert, Harris & Bruno, Tresu.
Consultation before the product code
The most common mistake when purchasing seals is starting from the code of the old seal to be replaced, without verifying whether that material was actually the most suitable for the application.
The right question to ask the supplier is not “do you have the seal compatible with my machine?” but “what is the most suitable material for my application, my type of ink, and my production speed?”
We always start from here. Because selling the right seal means the customer doesn’t have to replace it every day!