Microbicides in paints - historical background

Traditionally, no special biocides were applied in the early times of industrial coating material production, because typical paints were based either on alkyd binders dissolved in organic solvents or on inorganic powdered materials which were used by the painter to prepare the paint at site by adding the appropriate quantity of water. 

The old alkyd paints contained heavy metal salts (lead) acting as curing catalysts which rendered the paint film microbicidal. It should not be under-emphasized that customer perception changed over the years as well and appearance of a paint film to be acceptable is different today from ancient times. 

Even the first emulsion paints emerging in the 1950s were not very susceptible to bacterial growth because the polyvinyl acetate binders used contained sufficient amounts of the free monomer vinylacetate and the hydrolysis product acetaldehyde (II, 2.2.) to prevent growth. In the 1950s phenylmercury compounds (II, 19.2.-3.) were used in low concentrations of 0.05 to 0.15% as a microbicide for the wet and the dry state, respectively. Alternatively, formaldehyde was very efficient to keep paints protected against bacterial growth, but in practice 

Two major trends were seen in the 1980s in the Americas and Europe The emerging of the isothiazolinones, especially 5-Chloro-2-methylisothiazolin-3-one/2-Methylisothiazolin-3-one 3 1 mixtures (CIT/MIT 3 1) (II, 15.3.) as in-can preservatives provided a new standard in paints as well as in other water based products. Due to the high performance at rather low cost only very few other molecules could keep their position in systems, the isothiazolinones were not stable enough in. Using CIT/MIT allowed paint makers to produce heavy metaland formaldehyde-free products. 

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