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

Standard architectural powder coatings based upon acid functional polyester resin cured with either TGIC or Primid crosslinking agents ore characteris ed by having very good mechanical properties but limited exterior durabilit y performance (eg about two years Florida exposure to 50 % loss of gloss). These characteristics, whilst being sufficient to provide satisfactory outd oor performance for ten years or more in European climates, ore not enough to allow their use in more tropical climates. Superdurable polyesters, base d upon similar resin technology, exist which provide improved exterior dura bility at the expense of the mechanical properties. This work has used tigh t stabilisers (UV absorbers and hindered amine stabilisers) to produce 'sta ndard' polyester systems which have goad mechanical properties coupled with improved exterior durability characteristics. Although these improved weat herability polyesters do not match the weather resistance of the superdurab les, their performance is greatly improved relative to unstabilised systems . Furthermore, as their mechanical properties are effectively unaltered by the addition of the light stabilisers, these new polyester coatings could s till find commercial applications. Finally, the effect of each of the addit ives on the final coating performance has been discussed with respect to a range of selection criteria, which must be considered before the final addi tive choice can be made.