Surface characterisation of components used in coil coating primers

Coil coating primer components were characterised by X-ray photoelectron spectroscopy (XPS) and inverse gas chromatography (IGC). The surface chemical composition of the various materials, i.e. two pigments and two organic compounds, one dispersing agent and one acrylic resin, were characterised with XPS. Then IGC has been performed with apolar n-alkane probes and polar probes of differing acidity and basicity in order to interrogate the London dispersive and Lewis acid–base properties. The value of the London component of the surface energy (γdS) at 45°C is 45.5±1.1 mJ/m2 for the two pigments and 31.0±1.0 mJ/m2 for the two organic compounds. The combination of the acid–base contributions to the free energy of adsorption (ΔGABa) of a Lewis acid (chloroform) and a Lewis base (methyl acetate) led to the conclusion that the two pigments behave predominantly as Lewis bases whilst they have a fairly low acidity by comparison with the organic materials.