| abstract |
A thermosetting, organic solvent-based, primer coating composition for protecting metal surfaces which includes a solvent solution of: (a) a hydroxy-functional polyester resin; (b) a thermosetting acrylic resin; (c) a hydroxy-terminal polybutadiene resin, a hydroxy-terminal epoxidized polybutadiene resin, or mixtures thereof; (d) a blocked isocyanate crosslinker including at least one dimethyl pyrazole blocked isocyanate; (e) an aminoplast crosslinker including at least one melamine-formaldehyde condensate; (f) a catalyst; and, (g) a pigment. The primer exhibits excellent flexibility after curing to allow the primer to be coil coated onto metals as a thicker film and to have the metal subsequently formed without film fracture or loss of adhesion. The primer also has improved solvent release properties during curing to allow volatiles to readily escape therefrom, which facilitates coil coating of the primer onto metals as thicker films that, when cured into thick film hardened surface finishes, do not exhibit the typical blisters, craters, pops, voids and other surface defects. The primer can be cured as well at reduced temperatures which contributes to the reduction in surface defects. A fluorocarbon topcoat is usually coil coated and cured over the non-blistering primer coating, to yield a composite coated metal substrate having a surface finish that is free of blisters, craters, pops, and voids, and other surface defects. |