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
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®
Autophoretic® is a registered trademark of Henkel Surface