Fraunhofer Institute for Surface Engineering and Thin Films IST
Fraunhofer Institute for Surface Engineering and Thin Films IST

Anti-adhesion coatings

Surfaces need to have good anti-adhesion properties in order to avoid deposits, contaminants, and adhesions or to meet demands for drop formation. In addition to low surface energy, the tools or components must also exhibit excellent wear resistance because of the heavy mechanical loads placed upon them. Hard coatings can possess not only high hardness but also anti-adhesion properties. Coatings consisting of modified diamond-like carbon (DLC), e. g. SICON® and also chromium nitride layers (CrN), are excellent examples for such a combination of properties.

Our Offer

  • Definded adjustment of surface energy or wetting behavior of coatings (adhesion and anti-adhesion layers)
  • Combination of wetting properties with high wear resistance
  • Combination of structured surfaces with pronounced anti-adhesion properties (Lotus effect)
  • Matching layer properties to customer-specific requirements
  • Process development, wear analysis and consulting

Properties and advtanges

The wetting behavior can be varied in a defined way by modifying the DLC coatings with nonmetallic elements. The elements fluorine and silicon significantly reduce surface energy and thus wettability (e. g. F‑DLC, SICON®, SICAN). Nitrogen, boron and oxygen cause the opposite effect, i. e. the surfaces could be wetted easily (e. g. N-DLC, B-DLC). DLC coatings modified with silicon and oxygen have good anti-adhesion properties similar to Teflon®, but a significantly higher wear resistance and temperature stability. Chromium-based layer systems (CrN and variations) also show favorable anti-adhesion as well as good mechanical and tribological properties. By variations of the deposition process parameters it is possible to adjust layer composition, structure and property profile to customer-specific requirements.

Properties of different coatings in comparison to PTFE and steel

Coatings Surface energy [mN/m] Hardness [GPa] Friction coefficient (against steel, dry)
DLC (a-C:H) 35 – 40 20 – 30 0.10 – 0.20
Me-DLC (a-C:H:Me) 40 – 45  15 – 20 0.15 – 0.20
SICAN (a-C:H:Si) 30 – 35 10 – 15 0.07 – 0.15
SICON® (a-C:H:Si:O) 22 – 26 7 – 9 0.50 – 0.60
F-DLC (a-C:H:F) 20 – 22 2 – 
CrN 30 – 75 18 – 20 0.50 –  0.80
PTFE (Teflon®) 18.5 0.3 0.10
Steel 100Cr6 > 1000 8 – 9 0.70 – 0.90

Applications

In the pharmaceutical industry, anti-adhesion coatings on press tools were applied successfully over many years in industrial use. By using SICON® coated tablet tools, the adhesion of strongly sticking powder mixtures can be completely avoided without any additional use of release-agents. The plastic processing industries have numerous applications for DLC-based anti-adhesion coatings as well as for CrN layers. Avoiding deposits on extrusion or die-casting tools not only reduces cleaning and maintenance costs, but also significantly improves product quality. A pronounced drop condensation e. g. in heat exchangers enables higher heat transfer coefficients and thus higher efficiency. SICON® layers enable heat flow densities to be an order of magnitude higher than those achieved with film condensation. The additional antifouling effect of the layer system reduces or even prevents lime deposits. Due to the relatively low process temperatures of only approx. 100 °C during the Plasma-assisted Chemical Vapor (PACVD) deposition process, theses coatings are suitable for further applications e. g. for temperature sensitive non-metallic tools and components. In addition the feasibility to adjust the coating property profile of modified DLC-coatings in a wide range, numerous further applications are possible, e. g. from easy-to-clean surfaces to electrical isolating purposes.