Light stabilisation of polymers by radiation-cured acrylic coatings

The light stability of macromolecular materials has been substantially increased by protecting their surface with a UV-cured acrylic coating containing both a UV absorber and a HALS. The liquid resin, made of a telechelic polyurethane-acrylate, was transformed into a highly crosslinked polymer within a fraction of a second upon intense illumination. The cure kinetics was followed in real-time by infrared spectroscopy. Acylphosphine oxide compounds proved to be the most efficient photoinitiators. The light-fastness of the UV-cured polymer was evaluated by monitoring the chemical modifications occurring upon accelerated QUV ageing. It was greatly increased by the addition of small amounts of a HALS radical scavenger. Clear poly(vinyl chloride) plates have been effectively protected against photodegradation by a 50 mu m thick UV-cured coating. The greatest stabilisation efficiency was obtained by using as UV absorber either a hydroxyphenyltriazine or an in situ photogenerated hydroxyphenylbenzotriazole. An additional advantage of this method of photostabilisation is an improvement in the surface properties of the coated material, which becomes more resistant to solvents, chemicals as well as to abrasion and scratching.