Electrocoat Q&A: Eco-Friendly Pretreatment Systems

Which pretreatments work with electrocoat systems?


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Q. We have been approached several times by pretreatment suppliers about the possibility of switching our zinc phosphate pretreatment to a more eco-friendly pretreatment for our electrocoat. Are those pretreatments compatible with electrocoat systems?

A. I believe that the pretreatments you are talking about are thin film pretreatments. Like zinc phosphate systems, thin film pretreatments provide enhanced adhesion to bare metallic substrates as well as additional corrosion protection when used with epoxy electrocoats. The thin film pretreatments were primarily developed for electrocoating systems processing mixed loads of ferrous and nonferrous metal substrates.

Thin films pretreatments deposit protective films between 10–50 mg/ft2 as opposed to the typical 200–400 mg/ft2 level for zinc phosphate systems. In addition to the lower coatings weights, thin film pretreatments produce almost zero sludge, less overall environmental footprint (no phosphates and no heavy metals) and lower application temperatures. Because of CAFE standards in the U.S., the resulting lower part weight is also a benefit to OEMs, because it reduces the overall weight of vehicles and increases fuel efficiencies. Adhesion, appearance, corrosion performance and cost are practically the same for both types of pretreatments.

When the low film pretreatments are formulated with hard metals such as titanium, zirconium or others, the thin film layer provides substrates with higher surface conductivities than substrates pretreated with a conventional zinc phosphate systems. This is excellent news for electrocoat systems. The increased conductivity of the substrate allows the electrocoat system to operate and deposit ecoat film at lower deposition voltages, and therefore operate at greater coating efficiencies and lower costs.

Many automotive OEMs are currently switching their body-in-white (BIW) lines from phosphate pretreatments to thin film pretreatments. These pretreatments have been gaining increased acceptance by OEMs lately, and the expectation is that this trend will continue to grow at an accelerated pace in the coming years. General purpose electrocoat part lines seem to be lacking behind on the technology transition efforts. 

Originally published in the December 2015 issue.