PHOTOSTABILIZATION AND PHOTODEGRADATION IN ORGANIC COATINGS CONTAINING A HINDERED AMINE LIGHT STABILIZER .5. INFRARED SPECTROSCOPIC MEASUREMENTS OF HINDERED AMINE EFFECTIVENESS

The effectiveness of hindered amine light stabilizers in reducing carbonyl formation during ultraviolet light exposure of an acrylic melamine coating has been measured by infrared spectroscopy for both a harsh and near-ambient exposure. The four hindered amines studied are all based on 2,2,6,6 tetramethylpiperidine, and have the following substitutents on the piperidine nitrogen: H, CH3, CH2CH2-polymer, and COCH3. The inhibition of photo-oxidation provided by a given hindered amine varies with exposure condition. Harsh, accelerated tests can lead to inaccurate predictions of the performance of hindered amines in coatings exposed to sunlight. Under the near-ambient exposure used here, stabilizers based on NH and NCH3 functionality are found to provide higher levels of inhibition, especially during the early stages of exposure, than the other stabilizers in the acrylic melamine coating studied. © 1990.