Abstract: This invention provides a UV curable powder coating composition comprising a particulate blend of a non-crystalline unsaturated polyester base resin, a crystalline unsaturated crosslinker resin co-polymerizable with the base resin, and a photoinitiator, that exhibits reduced or eliminated hazing in the cured coating formed therefrom upon being cured at low temperatures demanded by certain heat sensitive substrates. This is accomplished by incorporating in the powder composition a recrystallization or haze inhibitor which is comprised of a crystalline epoxy resin. When this powder blend is melted for curing, the crystalline crosslinker resin visually appears to separate and recrystallize out of the molten powder less completely than it does in the absence of the recrystallization or haze inhibitor. This prevents a visible haze from developing on the surface of the coating upon curing with UV radiation.

Abstract: This invention provides a UV curable powder coating composition comprising a particulate blend of a non-crystalline unsaturated polyester base resin, a crystalline unsaturated crosslinker resin co-polymerizable with the base resin, and a photoinitiator, that exhibits reduced or eliminated hazing in the cured coating formed therefrom upon being cured at low temperatures demanded by certain heat sensitive substrates. This is accomplished by incorporating in the powder composition a recrystallization inhibitor which is comprised of a crystalline epoxy resin. When this powder blend is melted for curing, all of the crystalline resin species tend to separate and recrystallize out of the molten powder slower and less completely than they do in the absence of the recrystallization inhibitor. This prevents a visible haze from quickly developing on the surface of the molten coating before the coating can be cured with UV radiation.