Laura Cirstea, Anna Kolesova, Hammad Khan, Mohamed Abouelmagd, Swapnil Patel, Thomas Sprinzing, Matthias Galus and Armin Weichmann

Comparison of the performance of DLC to chromium as wear resistance layer on a gravure cylinder for printing fine line structures

For many decades in rotogravure electro plating a chromium layer on top of the copper surface which holds
the cells was used as wear protection for the print form cylinder. Recently, coating the copper with a layer
of diamond like carbon (DLC) presents an alternative with even higher wear protection. The price of a DLC
coating is significantly higher, so further advantages would be beneficial to justify its application. There were
indications that the ink accepting and releasing properties of the DLC are superior to chromium. This would be
especially useful for micro structures and fine lines. Therefore, we designed a print form including many differ-
ent small structures and manufactured two identical cylinders by laser mask etching, one electro plated with
chromium, one coated with DLC. A print trial was conducted on our industrial-scale gravure printing machine.
We compared the two surfaces with black ink on a white biaxially oriented polypropylene (BoPP) film under
varying ink viscosities, doctor blade materials and doctor blade angles. Analysis of print gradation, missing
dots and mottle was made, a visual assessment of a fine line star pattern was conducted and 15 μm, 20 μm, and
50 μm lines in and across the print direction were measured according to their average width and homogeneity.
Almost every evaluation shows the micro structures printed were significantly better with the DLC surface. The
influence of the surface surpassed by far the other parameters. The ink viscosity had surprisingly low influence.
This indicates that the difference of the surfaces in respect to print quality indeed is based on their different ink
releasing capabilities, constituting DLC superior to chromium.