We currently are looking into spraying some plastic chips and some other possible designs in our lab for an upcoming coating show but have been unsuccessful in finding a conductive primer. I contacted a major coating supplier after finding a tech data sheet online about a conductive primer they offered, but they no longer make it and told me they have nothing at all to offer that can go under powder.
Do you happen to know of anything that can be sprayed onto plastic objects prior to the powder being sprayed? Any help would be great.
A: Indeed, there are a couple options to make a plastic substrate conductive enough to electrostatically apply powder coating. First a few caveats:
1. Ensure that the plastic can take the powder bake cycle. Plastics are characterized by heat distortion temperature (HDT), which signifies the maximum temperature in which the plastic will maintain its integrity. At the HDT, the plastic will begin to soften and distort. Make sure that the HDT of the plastic to be used is at least 10°C higher than the powder bake temperature.
2. Make sure that the plastic is clean. Mold-release compounds are notorious for causing poor wetting and adhesion of powder coatings – and any other coating for that matter. You may want to clean the surface with an appropriate solvent prior to attempting to apply the powder.
3. Applying the powder is a little tricky. Make sure that the substrate has a good earth. In addition, reduce the kVs and amperage of the powder spray gun. I would start at 55 kVs and move higher or lower until you develop good, even deposition.
Now for the key component to make this work. I know of two approaches that provide sufficient conductivity on non-conductive substrates, which will facilitate electrostatic deposition of powder coatings. The first is Ransprep™ (available from a company called Chemical Technology Inc.).
The second approach involves applying an iodine-based solution. You can make your own solution by diluting tincture of iodine (alternately you can use a “teat dip” product). Use either isopropyl or ethyl alcohol for the dilution. I recommend a 1% concentration. The solution should be applied to the substrate by spray or dipping. Then thoroughly dry the substrate. This should provide the conductivity needed to apply the powder coating.