How is PVDF Coating Done?

A. PVDF can be applied to the surface in three ways:

• Solvent copolymers are dispersed in a semi-solvent. Dissolved in a unpleasant solvent (dimethyle acetamide solvent).
• Fine powder used for dip coating.
• Electrostatic coating.

Hi, Nitin; hi, SP; welcome to the forum, cousins. PVDF means Polyvinylidene Fluoride, a thermoplastic fluoropolymer used for robust paints and powder coatings.

Our readers are usually generous in trying to help with both highly specific questions that can be answered in a paragraph or two, as well as requests for quick introductions to a technology . . . but please try to be a little bit realistic, folks :-).

What you are looking for would require a multi-day training course or a 150-page book. You can't expect a stranger, free of charge, to spend a week writing a customized booklet for you :-)

Please go to your library and obtain a few books about PVDF coatings for an introduction to coating procedures, machine settings, area calculations, material selection, etc., and then post any detailed questions in terms of your own experience with the process, or anything that the books failed to mention, and I'm confident you'll get lots of good help. Best of luck. Thanks!

Regards,

A. Hi, Abdul.

Sorry, but PVDF is a rather exotic fluoropolymer and is "better" for long-term outdoor use. Architectural sheet metal that is painted with Kynar or Halar (two brand names) is typically guaranteed for 20 years or more -- far longer than when painted with polyester powder coatings.

Regards,

A. Hi Hugh.

They are the same thing. My understanding is that PVF2 is just an acronym that came from the chemistry field rather than the coating field.

Regards,

A. Hi Alwyn. "Metal patination" is a bit vague, but in general it probably means to apply a "patina" (an aged look) to the metal. For example, if the item is copper, to apply a coating that either ages the copper by causing it to form some copper salts, or which includes a copper salt. The term usually applies more to copper, brass, and bronze than to aluminum or steel.

Plating means to apply a metallic coating via electrodeposition. There are many metals and alloys that can be plated, but it would be rare to expect plating to last as long as a good paint job in the absence of abrasion. As already mentioned, PVDF is an expensive and long lasting coating. I hate to use the word "better" because everything depends on the situation, but PVDF is more expensive and usually longer lasting than other paints.

Regards,

Hi Rahul. The GI should be properly pretreated; zinc phosphatizing is probably appropriate. It's probably not practical to apply 2-3 mm with wet paint, so you are probably talking about powder coating. To my limited knowledge, powder of this thickness is more appropriately applied in a fluidized bed than by electrostatic spray.

Regards,

Hi Ciamak. A picture is worth a thousand words. Please send a good photo or two so people can clearly understand what is not acceptable with the finish. Also, please tell us whether this is liquid electrostatic coating or powder coating.Thanks!

Regards,

A. Hi Abdul. In view of the previous responses, I don't immediately understand your questions ... they seem to be already asked and well answered. Please try your best to frame your question in terms of the answers that were already offered so we can understand what difficulties you are having in understanding. Thanks!

Regards,

A. The first question [Malik's]: 0.75 mils for the PVDF topcoat if coil coated.

Second question [Abdul's]: I take it you want a more general description of PVDF rather what it is chemically.

Coatings, like many things, can have a hierarchy determined by end use. For the end use in the painted siding or roofing industry, PVDF is the premium product. This is followed by urethanes, silicone polyesters, and polyesters. Many manufactures will give a 40-year warranty for their PVDF product for this end use. In my industry it is applied on coils of various substrates including HDG, galvanneal, aluminum.

! Hello,
0.75 mil thickness is too much. I think you mean 0.075 mil or 75 micro. Isn't it?

Hi Pouya. In the USA, "mil" means 1/1000 of an inch. So .75 mil means .00075", and would be equal to 19 micrometers.

I do not know enough about PVDF coatings to say whether 19 micrometers is too little or too much, but I think it's the right order of magnitude (the right number of zeros).

Regards,

Hi Gordon. I don't think you can take a qualitative issue like "any difference in the visual appearance" and quantify it to a yes/no answer. Are you implying that one item (the coil) is roll-coated with wet paint while the other is powder coated?

Regards,

A. Hi Bill. I'm quite confident that Kynar is a brand name of PVDF coatings even if your Kynar applicator hasn't studied the chemical nature of Kynar coatings :-)

My understanding is that alkyd paints are incompatible with galvanizing because it can saponify them, with the resultant soapy layer offering very low adhesion. I wouldn't have suspected the same problem with PVDF coatings, but I don't actually know enough about their formulation to know whether they will stick to a properly zinc phosphatized galvanized finish or suffer the same problem. Hopefully another reader will know :-)

Regards,

A. Hi Bill,
Adhesion and cosmetics could be a problem short or long term unless the existing zinc is removed. The applicator probably understands the risk and does not want to "go there".

A. Hi Ahmad. I think the reason you see the pattern you see is because the panels of the sandwich are probably only touching, and only glued, there -- there is no adhesive elsewhere to pull off anything. But it does look like the galvanizing is suffering from white rust. Unfortunately, these observations probably don't get you any closer to solving the problem. Sorry.

These two pictures are of the same panel (I've been working on jigsaw puzzles too much lately and couldn't help seeing it). Is there a picture of the "opposing panel", the one with white rust and from which the galvanized coating we are seeing here was ripped?

Regards,

A. Hi Denis. Sorry, I don't know. But that's at least the 3rd time the question has been asked on this thread, so I hope that somebody who knows will get back to us! :-)

Regards,

A. I wish to write an answer for the above question of
"How do you test a surface to see if the coating on it is PVDF?"
PVDF is highly reactive with Sodium Hydroxide; i.e., PVDF gets Dehydrofluorination (HF removal) and turns Black color. This may be used to test whether the coating is PVDF or NOT.