Usually Polytetrafluoroethylene (PTFE) is not compatible to almost all other plastics. However, because of its lubricating effect PTFE is widely used as additive for sliding lacquers or materials with improved tribological behavior. But in all cases PTFE-powder is integrated only physically into the polymer matrix. For that reason larger PTFE-contents result in a deterioration of mechanical material properties and durability of coatings.So far typical antifriction coatings comprise a polymer matrix with physically homogenized antifriction additives (e.g.: PTFE, MoS2, Carbon black). Our aim was a chemical grafting (cg) of the lubricant with the polymer to enhance the resistance of lacquer films against wear and to improve the dispersion stability even in absence of dispersion additives.Thus, PTFE powder was modified using ?-beam irradiation, generating reactive functional groups and persistent radicals. The covalent bonding to Polyamideimide (PAI) was carried out by reactive extrusion in polymer melt and was proved by FTIR-spectroscopy. The thus obtained PAI-PTFE-cg pellets were used for the formulation of solvent-based antifriction coatings by varying PTFE-content and PTFE-type. Dispersions were characterized for their rheological properties, storage stability and particle distribution. It was found, that dispersions based on chemically coupled PAI-PTFE-cg are very steady for months in contrast to the physical mixture. Additionally, the particle size of PTFE in such chemically grafted systems is much lower.After application to steel test pieces and subsequent heat treatment, obtained films were characterized for their mechanical and tribological properties. Highly flexible films were obtained up to a PTFE-content of ~ 20 weight %. The coefficient of friction was about 0.15 and is nearly independent of the PTFE-content up to 25 weight % PTFE. However, the quietness of chemically grafted films is significantly higher than of commercially available antifriction coatings.Selected antifriction coatings were tested successfully as slide layer for hydrodynamic lubricating slide bearings.

Chemical grafted polyamideimide-PTFE for antifriction coatings

248th National Meeting (2014)

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