Corrosion inhibition of brass and copper pigments by polymers

The oxygen corrosion of brass and copper pigments in aqueous alkaline medium can be inhibited by certain polymers and ink resins. The surprising result that the corrosion of brass pigment is sometimes inhibited more efficient by polymers when compared to copper pigment could be explained as follows: copper is certainly more noble as zinc but copper-polymer-complexes are more soluble as the respective zinc-complexes. Furthermore, it was shown that with brass as well as with the copper pigment the concentration of dissolved metal ions in the medium increases linear with the acid number of the added polymers and ink resins. This explains the empirical result that as a rule a low acid number is a necessary but not sufficient requirement for inhibition of the oxygen corrosion of brass and copper pigment.