Ask Joe Powder
I run a modest powder jobcoating shop. One of my suppliers keeps telling me that I should switch from using hybrids and polyesters to superdurable powders. What are superdurable powders, and should I spend the extra money that these command?
Lynn Laviere, Hartstown, Pa.
First of all, congratulations on running your own show. Small businesses have all sorts of challenges; hats off to those who take the plunge and live to tell about it.
Hybrid (epoxy polyester) and polyester powder technology are considered the stalwarts of the industry. Hybrids should only be used for applications where there will be no possibility of exposure to the outdoor elements. They are a great economical choice for most indoor applications; however, they will quickly chalk and fade if exposed to sunlight. Conversely, polyesters provide good exterior durability. You can expect to get up to two years of durability in a sun-soaked environment such as southern Florida before observing evidence of coating degradation.
Superdurables typically are polyester based (TGIC in North America and Primid™ in Western Europe) and offer enhanced exterior durability. The resin system alone can survive up to five years in Florida before gloss begins to deteriorate. Pigmented systems usually fade a little sooner, depending on the durability of the pigments used.
Superdurables do command a higher price tag. The resins used are more expensive than conventional polyesters, and the pigmentation can be more costly. In most cases, conventional polyesters will meet the general-purpose needs of a jobcoater. However, if one of your customers has a special application that warrants the higher expense - such as refurbishing a motorcycle or refinishing the exterior parts of a classic car - then I would definitely go with the superdurable technology.
I coat electronic cabinetry for a company that manufactures computer servers. The coating is a textured hybrid powder. Our customer applies a silk screen to the finish to identify control names, and they are having trouble getting the silk screen to adhere to the powder finish. Please help.
Stan Dubrowski, Parma, Ohio
Jak sie masz (How are you? in Polish), Stan? Perhaps not so good. I have encountered this problem many times in the field. Sporadic adhesion failure to textured powders can be caused by a couple of factors. The red flag in this case is the texture of the powder coating. Often a novice powder formulator will incorporate a texturing agent based on polytetrafluoroethylene (PTFE) (similar to DuPont's Teflon®), which creates texture because it doesn't melt. The powder begins to flow and level during the bake cycle; however, the PTFE restricts some of the flow, thereby creating a texture. It's a nice formulating technique - unless you want something to stick to the finish. As you might have guessed, things don't stick to PTFE.
Another possible cause could be a gross overbake condition. If the parts being coated are baked significantly beyond the time and/or temperature recommended by the powder supplier, the surface might present adherence challenges. Check to ensure that your bake conditions closely approximate the time and temperature prescribed by your supplier.
I would also ask your powder supplier whether any PTFE is present in the formula. Most powder formulators prefer to avoid discussion about a powder's ingredients; however, this situation is serious enough to warrant this conversation.
Powodzenia (Good luck), Stan. Let me know how you make out.