PVDF / Kynar® vs. Powder coating

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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.

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A. Hi Atul.

Kynar® is a trade name for PVDF based coatings. The general idea behind them is that the carbon-fluorine bond is impervious to UV radiation and several other factors which cause coating degradation, so very long service life in exterior applications is often possible. As for application methods, there are videos for application to asphalt roofs, etc., the gist of which are that Kynar is a proprietary product offered with a warranty which is only applicable if it is applied in full accord with the manufacturer's specifications, including an elastomer base coat under it. Only licensees can apply it.

Other types of Kynar and PVDF coatings can be sprayed or roll coated onto metal sheet material in the factory. Please explain the application you have in mind, and where you fit into the situation (for example, are you wanting to coat metal individual items with Kynar yourself, or looking to job out that portion, or looking to buy precoated sheet you can fabricate, etc.) ... Kynar, due to complexity and license issues is perhaps not an ideal coating for onesy-twosy pieces. Thanks!

Luck & Regards,


Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

A. Joe, please read Drew's and Sheldon's entry carefully because they cover some stuff that experts like them realize, but many people don't: it's largely 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 won't be either. Steel parts require a well done phosphatizing step before powder coating, and ideally also will also include electropaint priming. 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 have been heat cured 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 make 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 are thin (a few mils) whereas thermoplastic coatings are much heavier; thermoset materials are almost always applied by electrostatic spray, while thermoplastics are usually applied by immersion into a fluidized bed.

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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.

Ed. note: Apologies, but yes, threads do become convoluted as readers read something interesting and then extend the question in various directions :-)

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, nor necessarily be easy. Repainting of either to accommodate color changes is probably a pretty big deal, best avoided, but farmed out to experienced parties if necessary. For example, Kynar is a non-stick surface probably requiring an exacting process to obtain good adhesion. Firms who offer both can probably advise the details of repainting the various finishes.

Regards,

A. Hi Saravana,

Getting paint to stick to PVDF will be an issue because it is a non-stick finish somewhat similar to Teflon. Suppliers like Kynar offer instructions to do spot repairs, but it may involve heating or other requirements which you may find impractical for your situation.

If this is just a routine repainting of commonplace doors, there are specialty adhesive coatings that can be applied, followed by repainting. But if this is an extreme exposure which justified PVDF in the first place, and/or you need to maintain the warranty, you'll have to follow the exacting instructions from the original supplier.

Luck & Regards,


Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

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 any painting or powder coating. Best of luck.

Regards,

A. Hi again Eric. EPA regulations are "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 find out from EPA or 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 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 absolutely can't prep and paint such 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. Kynar can only be applied by licensees, so insuring that you will be able to get a license is step one. Secondly, I'm not quibbling over words but concepts when I say you don't "clean" aluminum for painting or powder coating, you "pretreat" it ... which involves a lot more that just cleaning.

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. It's not like residential sanitary waste where you just flush; rather a company is not allowed to discharge industrial process waste to the sewer except in accordance with their discharge permit. So your best next step is probably to contact your local POTW and find out what "category" they consider you to be and what the effluent limitations for that category are, and to start applying for a discharge permit.

It is a possibility, but not likely, that you can discharge all of your pretreatment and (non-hexavalent) chromate conversion coating wastes to the sewer under the terms of your permit. It's more likely that you'll have to have an industrial waste pretreatment system. There are probably things like solvents, stripping solutions, dregs from your paint drums, etc. which you cannot discharge but which must be hauled by a licensed disposal company ... and there may be regulations regarding not just the eventual disposal, but accumulation & storage & record keeping for these wastes. Environmental compliance is unfortunately not a simple, cheap, straightforward thing -- which is why there are environmental consultants and attorneys in every geographical area if you want to start there ... but again it's not a matter of figuring out what you can discharge to the sewer without a permit, you can't discharge any industrial waste into a sewer except in accord with a discharge permit. Best of luck.

Regards,