Kynar vs. Powder coating

A. Dear Tom:

Kynar is PVDF based coating which is guaranteed for 20 years of environmental exposure. Normal powder coatings are nowhere near it - to the best of my knowledge. I am afraid, you may not find what you are looking for.

A. Hi Tom,

With the correct pretreatment and application, powder coatings are available with a guarantee for 25 year environmental exposure. These powder coatings have been available for a long time and are common in Europe. Hope this helps.

A. PVDF or Kynar being a brand name, is a coating that can carry a lengthy warranty relating to color & gloss retention. A schedule of loss is applied to the product. Mechanical failure is generally not part of that. Warranties never apply to steel products. My advice is to sandblast the item white, handle minimally with clean gloves, Zinc prime, checking substrate temperature, powder coat with a finish product of SD quality polyester or TGIC free Sd polyester. Read any warranty. The 7 p's apply to powder coating. Prior Proper Planning Prevents Piss Poor Performance. Also know that Kynar or PVDF is not usually the recommended product on traffic & heavy contact areas by the reps I have dealt with. This comment is a personal opinion & not extended as fact.

Hi, Atul. Kynar is a powder coating, but it is thermoplastic rather than thermoset, and usually applied at far greater thicknesses than typical thermoset powder coatings. I have only seen Kynar coatings applied at one shop, so I am not really an expert on them, but they were applied from a fluidized bed rather than by electrostatic spray; my book knowledge supports that this is the typical approach.

Joe, please read Drew's entry very carefully because it implies some stuff that experts like him realize, but most people don't: it's all about the pretreatment! If appropriate and high quality powder coatings are applied to properly pretreated materials, the durability will be excellent. But no matter how exotic the paint or powder, if the pretreatment isn't good, the coating will be crummy. Steel parts require a well done phosphatizing step and possibly electropainting before powder coating. Good luck.

A. Hi, Zia. Thermoset plastics are plastics that cure into a different state than they started in. Sort of a one-way street. Once they are set they can never return to their original condition, you can't usefully melt them. Thermoplastic materials are plastics that soften with heat, repeatedly. If you formed a block of thermoset plastic, it would stay in that shape forever; if you formed a block of thermoplastic material you could, in theory at least, form it into a different shape the next time you applied heat.

When it comes to using these plastics in powder coating, the biggest differences seems to be that thermoset materials can be thin (a few mils) whereas thermoplastic coatings are much heavier; and thermoset materials are usually applied by electrostatic spray, while thermoplastics are usually applied by fluidized bed.

Regards,

Hi,

PVDF fluoropolymer based coatings are suitable for corrosion protection and making up to 15 mil film thickness. Teflon is a largest manufacturer of this type of coatings. Best luck.

A. Yes, if installed properly and well maintained it should last 5-10 years, maybe a little longer per BS4994. Halar (ECTFE) might be better but it is fairly expensive.

A. This thread is a little convoluted, so I answer what appears the central question. Kynar is a PPG trade mark for a PVDF resin system. PVDF is a fluorocarbon based polymer which when it comes to things like weathering properties is at the top of the food chain. This is why many architects specify it for buildings. Polyester is more of general purpose resin system used for more mundane, less critical, painting. Powder coating is paint that is applied without the use of solvent, though different resin systems can be used, including polyester.

When it comes to things thermoplastic to thermoset you learn quickly if you have a chemical like MEK on your hand don't pick up a phone or a plastic stopwatch, no chemical resistance.

A. Hi Greg. I think you can pick the railing material you wish (galvanized or aluminum), independently of which final finish you want (Kynar or a more mundane powder coating). I think I'd mix-&-match and go with the Kynar on the aluminum. But Kynar on galvanized should last the better part of forever.

A point we should continue to repeat in case there are any newbies reading this posting is that pretreatment is critical -- not only will the paint not stick properly to the aluminum if not pre-treated well, it will pull off the galvanizing in sheets :-)

Zinc phosphatizing is required for the galvanized, and chromate conversion coating for the aluminum. Best of luck.

Regards,

A. Hi again. Anything can require touch-up, and consequently there are touch up materials for either finish, although the touch-up may not have the durability and longevity of the oven-cured finish. Repainting of either to accommodate color changes is probably a pretty big deal, best avoided, but farmed out to experienced parties if necessary. Firms who offer both can probably advise the details of repainting the various finishes.

Regards,

A. Hi Eric. Kynar will outlast powder coating, but please remember that preparation/pretreatment provides about 80% of the durability and the paint/powder about 20% :-)

Are these T-tops, rails, etc., made of aluminum? If so, they should be properly prepped and chromate conversion coated (Alodine, Iridite, MIL-DTL-5541 [on DLA]) before painting or powder coating. Best of luck.

Regards,

A. Hi again Eric. EPA regulations are generally "categorically" based, meaning that an auto care center will have regs that are different from the regs a plating shop has, or a high school has, or an aluminum fabrication shop has, or other categories of businesses have. So you need to figure out exactly what category your business falls into.

Regardless of any of that though, aluminum should be non-etch cleaned, etched if necessary, desmutted/deoxidized, and chromate conversion coated. There are now chromate conversion coatings which comply with Mil DTL-5541 (meaning that they have been proven to offer good adhesion and good corrosion resistance) but which are free of hexavalent chromium (Type II coatings). These go by the slang name TCP (trivalent corrosion prevention) coatings, and are considered environmentally friendly.

I'm not saying you can't prep and paint these parts yourself, but usually such parts are handled in treatment lines which involve immersing the parts sequentially in tanks full of the chemicals I mentioned (with rinsing between each step).

Regards,

A. Hi again Eric. The EPA enforces discharge and performance standards on your local POTW (publicly owned treatment works / sewer system), and they in turn enforce standards on the businesses discharging to them. Basically you are not allowed to discharge to the sewer except in accordance with your discharge permit. So your best next step is probably to contact your POTW and find out what "category" they consider you to be and what the effluent limitations for that category are, and start applying for a discharge permit.

It is a possibility, but not a sure thing, that you can discharge all of your pretreatment and (non-hexavalent) chromate conversion coating wastes to the sewer under the terms of your permit. There are probably things like necessary solvents, stripping solutions, dregs from your paint drums, etc. which you cannot discharge but must have hauled by a licensed disposal company ... and there may be regulations regarding accumulation & storage of these wastes. Environmental permits are unfortunately not a simple, cheap, straightforward thing -- which is why there are environmental consultants and attorneys in every geographical area. Best of luck.

Regards,