Adhesion and thermal stability of thickness insensitive spectrally selective (TISS) polyurethane-based paint coatings on copper substrates

Thickness insensitive spectrally selective (TISS) paint coatings based on a polyurethane polymeric binder deposited on copper substrates were investigated to obtain information about their service lifetime. The degradation of TISS paint coatings was performed according to the methodology worked out within Task 10 of the IEAʹs Solar heating and the cooling programme. The activation energy (Ea) for the degradation process was derived from vibrational band changes of the polyurethane binder recorded in the infrared hemispherical reflectance spectra of TISS paint coatings exposed to different thermal loads. The results of the vibrational band analysis were correlated with cross-cut tests, showing that the coatings started to lose integrity at 190 °C but protected the copper substrate against oxidation perfectly even at 200 °C (15 days). An accelerated test procedure confirmed that TISS coatings could be safely used in solar collectors for at least 45 years.