Bleeding-Out Issue

Q.We see bleed-out after 2–3 days on our painted parts. The parts are steel substrate and we zinc phosphate and paint them. Our cycle is hot alkali cleaning, three rinses, pickle, three rinses, soak again, two rinses, zinc phosphate, rinse, sealer and dry. Then we paint and cure at 250°F for five minutes. There is a copper band on the outside circumference on the part which does not require painting so it is covered during paint process. We see very slight bleed-out from under this band after 2–3 days.
Also during crimping of the copper band over the steel part, the manufacturer uses an adhesive substance. But even if there is no adhesive under the copper band, there are still bleeding issues. H. K.

 

A. As I understand it, you are trapping aqueous pretreatment solutions or water under the copper band. The trapped material bleeds out after sitting for 2–3 days. Masking the parts may also help retain the residual solution.

To solve the problem you must drive the aqueous residue out from under the copper band. Obviously the dry-off stage of the pretreatment before painting is either not hot enough, not long enough or both. I suggest heating the parts at 250°F long enough to drive off all the aqueous residue before painting. Not knowing the size or mass of the parts, I really can’t suggest a dry-off time. You must do this by trial and error.