An evaluation of the effect of light stabilisers on the exterior durability of polyester powder coatings for the architectural market

The use of light stabilisers in traditional powder coatings cured with either TGIC or Primid can result in systems with greatly improved weathering resistance. This improvement in weatherability does not reach the level of performance given by superdurable polyesters, however, when coupled with their superior mechanical properties (cf superdurables) but these systems could still be of commercial interest.

The selection of the light stabiliser has also been shown to be an important process, with many factors requiring consideration before the final choice. This was illustrated by the choice of the UV absorber (primarily responsible for the improvement in performance). For example, UVA 1 had relatively poor volatility characteristics coupled with inferior UV absorption characteristics, which resulted in no real improvement in weathering. UVA 2, on the other hand, had better UV absorption and was of low volatility, characteristics which led to a great increase in the UV durability of the polyesters containing this product. The drawback with UVA 2 was that it imparted colour to the coating, in particular during overbake testing, which was large enough to cause potential problems if used commercially. UVA 3, which also had very good UV absorption and good volatility, performed much better in terms of overbake yellowing and also had improved UV durability.