Tool coating systems and modified diamond-like carbon coatings (a-C:H:X) for polymer processing

The plastic processing industries have numerous applications for wear resistant anti-adhesion coatings. Such coatings avoid deposits on extrusion or die-casting tools. Thus not only cleaning and maintenance costs can be reduced, but also product quality will be significantly improved.

Amorphous hydrogenated diamond-like carbon films (a-C:H) are well known for their high hardness, high wear resistance and low friction coefficients. The incorporation of additional elements leads to considerable modifications of the coating properties. E.g. silicon containing a-C:H:Si or Si and O (a-C:H:Si:O) leads to hydrophobic coatings with lower surface energies (< 25 mN/m). Both types of coatings have anti-adhesive properties. Such modified DLC coatings were prepared by Plasma Enhanced Chemical Vapor Deposition (PECVD) processes in industrial scale coating machines. The different DLC modifications can be combined in a multilayer coating to optimize properties.

Promising results were obtained in the area of polymer fabrication. The advantages of wear-resistant non-sticking coatings could be demonstrated for different molding and extrusion tools. One example is a blow molding arbor for plastic foil (HDPE) manufacturing. The investigations had shown a reduction of the PE deposit on the surface of the DLC coated molding arbor by a factor 6 to 10 compared to other hard coatings.