| abstract |
An anti-corrosive coating composition comprises a pigment component dispersed in a film- forming binder, the pigment component comprising a salt of a polyvalent metal cation and an organic phosphonic acid containing at least two phosphonic acid groups. Generally, the molar ratio of polyvalent metal cations to phosphonate groups in the salt is at least 0.8/n:1, where n is the valency of the metal ion. However the composition may also include a corrosion passivator capable of modifying the metal oxide film on the metal to be protected to render it more protective, the ratio of the polyphosphonate salt to the passivator being 1:1 to 50:1 by weight, and in the latter alternative it is also possible to use a lower proportion of polyvalent metal cations. |