Polyester/TGIC Powder Coating Based on 1,3 Propanediol (PDO)
Carboxyl functional polyesters have been prepared from 1,3-propanediol (PDO), neopentyl glycol (NPG), and a 76/24 terephthalic/isophthalic acid (TPA/IPA) combination. These polyesters were formulated with triglycidyl isocyanurate (TGIC) resins for evaluation as powder coatings. Coatings based on polyesters with PDO provided superior impact resistance and flexibility over those that contained no PDO. Overall, properties including hardness, adhesion, and chemical resistances are retained over a broad range of PDO concentrations. In addition, the viscosity of the polyester decreased as the level of PDO increased.
All the materials were initially premixed in a high-speed mixer for 2 minutes to ensure homogeneous mixing, and the solids were then fragmented into small particles. The resulting intimate mixture was then continuously processed through a twin-screw extruder to produce a uniform viscous melt. The extrusion temperature was maintained at 80?C in both zones 1 and 2 at a processing speed of 120 rpm. Molten extrudates passed through a pair of water-cooled squeeze rolls afforded a friable product. The products were then pulverized using a hammer mill with liquid nitrogen fed slowly into the grinding chamber. Classification on an Alpine sieve afforded powders with particle sizes of 105 microns or less.