Metal Paint

Metal paints are usually also distinguished from ordinary or decorative paints in a variety of subtle ways, they tend to have shorter oil lengths if the metal paint is based on a renewable resource like Soya bean oil or sunflower oil, these are then chemically modified by reaction with chain stopping agents such as benzoic acid to improve mechanical properties such as gloss and scratch resistance (for one coat direct to metal paints) or phenolic resins to improve chemical resistance in metal paints aimed at being over-coated with a finish. They can also be modified with silicone to improve durability or polyurethane to improve some chemicals and wear properties or even other monomers to improve application characteristics, often in well tried and tested smooth and hammer effect direct to metal paints this was styrene or vinyl toluene but more recently other techniques are used to make overcoating easier.

However, for a really efficient metal paint the choice of anti-corrosive pigment is also very important, some would argue the most critical aspect of the paint. Historically red lead was used and whilst this did indeed work it was found to be dangerous to health and eventually the government introduced lead at work regulations which have almost eliminated this technology. Higher performance products were introduced more than 50 years ago, originally based on zinc oxide derivatives such as zinc phosphate and zinc chromate and indeed even today on many older specifications people still ask for BS5493 zinc phosphate paint – even though this has been superseded by much more efficient and safer technologies. Higher specification products were based on derivatives of zinc and chromium but these derivates like zinc chromate, zinc tetraoxychromate and zinc potassium chromate all bring serious health risks all are carcinogenic and all are to a greater or lesser degree water soluble so easily migrate to the water supply. This in combination with progress on corrosion testing and the replacement of the highly ineffective B117 salt spray test with more realistic testing techniques including prohesion and cyclic testing with QUVB lead to the development around the world of several non-toxic environmentally friendly anti corrosive pigments for the metal paint formulator -the early products were based on calcium ion exchanged silica gel but these proved to be temperamental and were slowly replaced by alternative phosphates and modified phosphates based on nontoxic metals including calcium and magnesium sometimes in conjunction with other inhibitors  – one of the market leaders today in this technology is Nanoguard ACP and there are similar older generation versions of this technology still used in metal paints around the world. Nanoguard ACP was however, unique in its ability to offer a totally non toxic, safe, heavy metal free solution for the formulator of metal paints. Other similar technologies became available from other suppliers as people tried to copy the technology – with varying degrees of success.