Tech Notes: Autodeposition Update

In plating, there are two basic kinds of processes: electrolytic and electroless. The terms are pretty self-explanatory—electrolytic plating processes apply a current through the parts to attract the metal being plated, while in electroless processes plating occurs as a result of chemical processes only.

An analogous situation exists in organic coating with electrocoating and autodeposition paint processes. In e-coat, a current applied through the parts being coated attracts particles of paint with an opposite charge. In autodeposition, paint is deposited as the result of chemical reactions only. In e-coat, paint deposition stops when the current stops. In autodeposition, deposition stops when parts move to a rinse tank. Film thickness is self-limiting, ensuring uniform coating thickness on any part surface that can be wetted by the paint material.

Both processes are waterborne and use no organic solvents, so they require no air pollution controls. Both are effective for steel parts ranging from fasteners to auto bodies.

Now, advances in autodeposition coating materials and processes are making the process more competitive for a variety of part materials and applications, according to developer Henkel Corporation (Madison Height, MI). The company says its Aquence brand of autodeposition coating processes are now displacing conventional metal pretreatment and the electrocoat process for an entire automotive vehicle body.

According to Henkel, the process can allow customers to reduce capital expenditures and paint shop complexity, decrease energy consumption, eliminate heavy metal sludge, and improve inside-out corrosion performance compared with e-coat. Because it uses fewer stages than e-coat, the process also has a significantly smaller footprint, says Kevin Woock, global director, Aquence Coatings.

“E-coat systems normally include 12 or more stages to properly clean, rinse and coat a metal part,” Woock says. “The equivalent clean, rinse, and coat autodeposition coating process is seven stages—a 40% reduction in the number of steps needed to properly coat a part, and in the corresponding footprint of the process.”

According to Woock, Aquence coatings also offer more processing flexibility than Henkel’s earlier autodeposition materials, which were applicable only to steel substrates. “There are many small and large parts that cannot be coated with the traditional autodeposition coating process because they are made of materials other than ferrous metals—for example, aluminum and zinc components,” he says.

“Now Henkel is moving the product from a niche coating for steel parts to a more broadly applied immersion coating process for multi-metal applications, including zinc, aluminum and steel substrates,” he continues. “In addition, developments with other suppliers of top-coating technologies such as powder coatings will provide a cosmetic and functional performance coating for future applications.”

Woock believes ongoing development in autodeposition coating materials, processes and applications will allow the technology to make more inroads versus electrocoat. “Autodeposition coatings are currently used in more than 130 locations, in more than 20 countries, in every major manufacturing region of the world,” he says. “Henkel’s position as an automotive metal pretreatment supplier and our market presence with major automotive OEMs make us well suited to target this new technology into these same segments.”