Q. We are in the process of upgrading our paint line. We are applying our primer on an old spray painting line and are looking at various options for replacing it. We have been considering the installation of an electrocoat line to replace spray priming. According to one of the suppliers, the processing cycle will be 3 to 3½ minutes. Based on your experience, what kind of trouble can we expect on startup?
- If there is any trouble on the conveyor system causing stoppages for 15 minutes or more, what will happen to coated parts remaining in the e-coat tank?
- When the parts are baked, will we get a normal paint film, or will there be defects?
- Is it true that we must use an acrylic-based paint as a topcoat?
- If we use other topcoats like alkyds or polyurethanes will we have problems with adhesion? L.S.
A. If the parts are in the coating tank during a conveyor line stoppage, shut off the coating power after a complete cycle (in your case 3 to 3½ minutes). The paint will not re-dissolve and there will be no film defects after baking. I would be more concerned about steel parts, which can rust if they reside in the pretreatment stages without going through the complete cycle during a conveyor line stoppage. If this occurs, the rust must be removed and the parts reprocessed. Another concern is parts residing in the oven for periods longer than their established over-bake resistance times.
Although the use of an e-coat primer is new to you, it is not new to the finishing world. Such primers have been used in the automotive industry for decades. While it is true that, in the automotive industry, parts have been topcoated using acrylics, which have excellent color and gloss retention, it is not true that they must be used over e-coat primers. Hence, the notion that acrylics must be used is bogus. You can safely apply any compatible topcoat.