MPS can, in principle, use printing form sleeves on all machine models. However, the procedure whereby blocks are mounted on a sleeve and then fitted onto an air cylinder outside the machine so that it can be inserted into the printing unit like a conventional impression cylinder is only practical for endless motifs.

The setup advantages of sleeves only come into their own if sleeves can be changed directly in the machine on air axes that are installed as a standard feature. In the case of MPS, this is only possible with EF H model that has been designed as a hybrid machine.

Standards Are High in Narrow Web Printing
The fact that printing form sleeves have not been able to establish themselves in narrow web printing up to now may be related to a fact that has as yet been somewhat overlooked in public discussions. The majority of sleeves are matched to the requirements of wide web flexo printing. But completely different criteria are important in narrow web printing.

For example, higher demands are made on concentricity or dimensional stability in this market segment. This has various reasons. Thus, the standards for picture motif are higher than in wide web flexo. The images are generally smaller, calling for a higher print quality. What's more, narrow web printers use almost exclusively a No. 60 fine screen.

“At first glance, the narrow web widths implied that there would be hardly any problems with aspects such as register accuracy in sleeves for label printing,” says rotec CEO Mario Busshoff. But compared to packaging flexo printing on central cylinder machines, higher screen definitions are used as standards in label printing, meaning higher demands on the printing form.

Special Features of Narrow Web Printing
Users in the label sector are used to using the entire web width wherever possible when using impression cylinders. This is why the printing forms have to display a high dimensional stability right up to the edge zone.

The demands on concentricity and above all diameter accuracy have a maximum plus-minus tolerance of only one hundredth of a millimeter. It is much more difficult for plastic sleeves to fulfill these requirements than the impression cylinders of metal. And in the case of compressible sleeves, which can be used to positively influence the printing characteristics during flexo printing, these high accuracies have to be achieved despite the porous material structure.

Temperature changes that may occur, for example, through the production process in the printing press, should not affect the concentricity. The frequently used combination of several printing methods in one printing press is another reason why a high dimensional stability is very important in narrow web printing. Dimensional fluctuations in the flexo print sleeve would inevitably lead to register problems for the other printing methods.

Special Label Version Developed
Due to the requirements described above, a new sleeve has been developed especially for use in the label segment. The new product goes by the name of Blue Light Label and has a very high dimensional stability right through to the outer edge zones of the sleeve.

The printing characteristics and service life have been further improved compared to the standard version. The newly developed multilayer structure of synthetic resins and composite fibers guarantees constant characteristics even after intensive use. These include above all the greater dimensional stability, constant parallelism of the sleeve during printing, and the exact register behavior.

This is based on high-precision grinding that allows a TIR value (Total Indicator Reading, i.e., maximum deviation of the outer diameter during a 360 deg rotation) of below 0.025 mm – measured on a carrier cylinder with a TIR value of less than or equal to 0.005 mm.

The new sleeves are available from a wall thickness of 12 mm and up to a maximum face width of 600 mm. The sturdy yet at the same time lightweight sleeves are designed for conventional plate mounting with foamed adhesive tape. They are suitable for all plate and adhesive tape strengths and have an extremely resistant surface of polyurethane with a density of 75 Shore D. The surface is resistant to scratches and cuts as well as solvents and allows a simple removal of the adhesive tape.

During Labelexpo 2007, sleeves from this series were demonstrated on machines from Nilpeter, MPS, and Mark Andy. MPS also confirms that a noticeable improvement in quality can be achieved with the new type of sleeve.

Bert van den Brink compares the development of the sleeve to the history of UV flexo printing in the narrow web sector. The radiation-hardened printing inks also had to pass through a long phase of changing successes before they reached today's level.

He also believes that the adoption of the sleeve technology from the wide web sector has not yet been completed and still needs a little time. After all, there are numerous significant differences to the narrow web segment, e.g., as regard to printing inks, substrates, machine design, etc. In order to push the development faster in future, users are needed who will actively cooperate in the development.