The influence of pigment on the anti-corrosive properties of organic coating was investigated. The heavy duty anti-corrosion coatings were prepared with the resins such as alkyd and urethane, which are widely used for anti-corrosive coatings. The typical anti-corrosive pigments were zinc potassium chromate(ZPC), strontium chromate(STC) and Fe₂O₃. Accelerated deterioration tests were carried out to evaluate the anti-corrosive properties. During the deterioration tests, the coatings were exposed to immersion condition, or accelerated weathering conditions of xenon light irradiation in a Weather-O-Meter. The evaluation of the anti-corrosive properties of coatings was performed by means of electrochemical impedance spectroscopy. The relation between resin-pigment interaction and anti-corrosive properties of coatings was also studied. The interaction between resin and pigment was estimated from the sedimentation rate of pigment in resin solution, which was measured by using a Dynometer.
The extent of interaction between resin and pigment was found to follow the order : Fe₂O₃>ZPC>>STC with alkyd, and Fe₂O₃>>ZPC>STC with urethane resin. It was found from the impedance measurements that the anti-corrosive performance of coatings decreases with pigment used in the order of ZPC>Fe₂O₃>STC. From these results, it seemed that anti-corrosive properties of organic coating were affected by resin-pigment interaction and other properties of pigment, such as passivating ability and physical shape. It was also found that the coatings which were prepared by same pigment with different resins revealed different anti-corrosive properties, indicating that the properties of resin also influenced the anti-corrosive performance of organic coatings.