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Description of Autophoretic®
Performance Characteristics
Performance Comparison
Autophoretic® 900 Coatings

 

 

Autophoretic®, also known as autodepostion or A-coat, is a waterborne process which depends on chemical reactions to achieve deposition. This process has been in commercial use since 1975. Since then, Autophoretic® has grown and matured. Since its inception, this unique process has been employed to coat billions of square feet of surface. Presently, there are numerous installations in operation, both captive and job-shop, coating a variety of fabricated steel parts for the automotive and general industry markets.

An Autophoretic® bath consists of a mildly acidic latex emulsion polymer, DI water, and other proprietary ingredients. The bath solids are normally between 3% and 5% by weight. The bath viscosity is close to that of water with little or no organic solvents in the coating bath. Another characteristic of the Autophoretic® coating process is that is quite simple in comparison to other coating systems. The mildly acid bath liberates a small amount of iron from the steel parts being immersed, causing an immediate surface reaction that releases iron ions. These ions interact with the latex in solution 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 a film with a high degree of surface protection and corrosion resistance.

The coating thickness of the autodeposited film is time and temperature related. The film thickness continues to grow as long as ionic species are being produced at the coating/metal interface. Initially, the deposition process is quite rapid, but slows down as the film increases in thickness. Typically, film thickness is controlled from 0.6 to 1.0 mil.

A unique feature of the Autophoretic® process is the formation of a very uniform film over the entire surface of the workpiece, even in difficult-to-reach areas. This allows the coating dispersion to flow into and around the most complex shapes. Unlike coating processes that require a charge to deposit the coating (i.e., where electrical energy is required to "throw" the coating into recessed areas) Autophoretic® will coat tubular, assembled, or intricate-design areas uniformly. Autophoretic® coating film thickness is controlled by diffusion of reactants in the bath and through the coating already formed on the surface of the substrate. This diffusion control leads to a uniform coating thickness on complex shapes and in recessed areas.

The film formed by the Autophoretic® process is most unique for a latex vehicle. Latex films form by coalescence. However, the degree to which the film forms in the Autophoretic® process via the coalescing action, is the basis for its uniqueness. Parts coated via Autophoretic® can be water rinsed immediately after leaving the bath with very little material loss. 

On leaving the bath, the coating consists of two layers; one is a very cohesive reacted layer; while the other is composed of undeposited excess polymer and activator from the bath. The chemical reaction continues in the second layer, which results in film deposition and increased film thickness instead of solids loss to dragout. This unusual feature strongly limits carryover of coating chemicals into the rinse tanks and greatly reduces the demand for waste treatment.

It should also be mentioned that the Autophoretic® process does not require a chemical conversion coating (such as zinc or iron phosphate) stage or, in the case of an Autophoretic® process using Autophoretic® 800 Series coating chemical, even a heavy metal final rinse stage. The elimination of these stages leads to considerable savings in required floor space, energy, and operating costs, as well as the total elimination of toxic metals from the process. Considerably lower temperatures are required to cure the autodeposited parts. These are just some of the many advantages of using the Autophoretic® process.

Autophoretic® is a registered trademark of Henkel Surface Technologies