An autodesposition bath consists of a mildly acidic latex emulsion polymer, RO water, and other proprietary ingredients. The bath solids are normally between 4% and 6% by weight. The bath viscosity is close to that of water with little or no organic solvents. Another characteristic of the autodeposition (autophoretic) coating process is quite simple. The mildly acidic bath liberates a small amount of iron from the steel parts immersed, causing coating deposition on the surface of the steel parts. The newly deposited organic film is adherent yet quite porous. This allows the chemical activators to diffuse rapidly in the film and etch the surface of the metal. The continuous formation of coating provides the film with a high degree of surface protection and corrosion resistance.
The coating thickness of the autodesposition film is time and temperature related. The film thickness continues to grow as long as the ionic species are being produced at the coating/metal interface. Initially, the deposition process is quite rapid but slows down as the film increases thickness.
A unique feature of the autodeposition process is the formation of a very uniform film over the entire surface of the work piece, even in the most difficult-to-reach areas. This allows the coating dispersion to flow into and around the most complex shapes. Unlike coating processes that require the charge to deposit the coating, (i.e. where electrical energy is required to “throw” the coating into recessed areas), autodeposition will coat tubular, assembled or intricate-design areas uniformly.