Sidmadra
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Anyone ever cured PTFE with a heat gun?
I have a few metal parts I wanted to coat with PTFE and I found out the process isn't too terribly complicated. It involves phosphating the surface
with a typical metal-paint prep acid spray, spraying on the PTFE coating, and then curing(sintering) it at around 350-400C. I've found both PTFE
aqueous dispersions online (at 60% solids), as well as the typical PTFE aersol sprays.
Problem is most household ovens do not go above 550F/287C. I wonder if it would be feasible to blast the coated part with a heat gun, or even use a
variable controlled heatgun where I can set the temperature close to the cure temp, and let it heat the part directly for 10 minutes or so, simulating
the effect of a hot oven. PTFE doesn't really melt so I imagine it could withstand high temperatures easy enough to cure parts.
I did find this product online:
https://www.antiseize.com/ptfe-spray-heavy-coat-anti-seize-l...
Which indicates it can easily produce a heavy film of PTFE that doesn't easily come off, and it's only $10. It says it has an acrylic carrier, but I
didn't see this anywhere on the MSDS - unless it means "Butyl Acetate". Depending on the content, I worry the acrylic could melt and run the PTFE while heating it.
The plus side to using the 60% dispersion is that parts can be dip coated, potentially reaching crevices that a spray coating couldn't, however this
dispersions aren't cheap, as they start at around $90.
[Edited on 16-7-2018 by Sidmadra]
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wg48
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I purchased some micron sized powdered PTFE to coat poorly fitting male ground glass joints. Its available on Ebay about £5/100g https://www.ebay.co.uk/itm/100g-3-52-oz-Ultra-fine-1-6-Micro...
While waiting for it to arrive I discovered it does not melt before it thermally decomposes so its unlikely that it can be coated on to a hot object
the way some plastics can be ie dusting the powdered plastic on to a hot object. Apparently the way PTFE objects are created is by hot pressing the
powder not by injection moulding. So I suspect just heating an object coated with the powder will not work.
I may get round to making a mold to creating a pressed PTFE sleeve for an ground glass joint but its not a priority as I don’t think there is much
chance of success.
There are some other fluorinated plastics that can be injection mouldered so I would assume they melt for example PVDF(Polyvinylidene fluoride)
Apparently PVDF does melt and it can be welded with a hot air gun. You just need to find a source for small quantities.
From https://www.extremematerials-arkema.com/en/product-families/...
[Edited on 16-7-2018 by wg48]
Borosilicate glass:
Good temperature resistance and good thermal shock resistance but finite.
For normal, standard service typically 200-230°C, for short-term (minutes) service max 400°C
Maximum thermal shock resistance is 160°C
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Sidmadra
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What temperature did you take it up to?
PTFE doesn't melt at all, and will thermally decompose if you heat it too high. Rather, it's "melting point", is more of a sintering point, in which
it becomes sort of jelly like, but never will achieve a liquid flowing state. I believe FEP, which is another fluoropolymers, can melt. When you take
PTFE up to its melting point, any other PTFE nanoparticles it is in contact with will sort of fuse/defuse together on a molecular level, which allows
for it to be molded and formed. Pressure isn't necessarily required.
The technique definitely work as it is the industry standard for how many PTFE coatings are applied, though, they typically do it with temperature
controlled ovens. I am not too sure how well it will work on glass as I've only seen it done on metal surfaces which had been treated/phosphated
prior.
Here's a video example of one such Fluoropolymer coating:
https://www.youtube.com/watch?v=2VfyGg7zW-I
[Edited on 16-7-2018 by Sidmadra]
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unionised
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Be careful.
https://en.wikipedia.org/wiki/Polymer_fume_fever
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Sidmadra
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I have a highly ventilated area, but that's also why I think using a variable temperature heat gun would be useful. I used to own one that was very
precise at regulating the temperature of the air coming out. Plus I think PTFE can be cured at lower temperatures, it just takes longer.
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wg48
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No I have not tried to melt or sinter my PTFE powder as the literature on the subject suggests heat and pressure are required. I did try to dissolve
it in acids and alkali but they did not wet it. I wanted to check if it really was PTFE as I don’t trust Chinese ebay sellers.
That’s a video about a coating called Xylan. From Xylan literature its a coating containing PTFE and a thermosetting resin that’s why they refer
to curing the coating. So it does not show, prove or suggest you can melt or sinter PTFE particles together with just heat. It’s a thermosetting
paint/coating that contains PTFE powder
Borosilicate glass:
Good temperature resistance and good thermal shock resistance but finite.
For normal, standard service typically 200-230°C, for short-term (minutes) service max 400°C
Maximum thermal shock resistance is 160°C
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wg48
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If I did try heating it would be outside. I have already experienced the flu like symptoms of zinc fume fever after I watched the white zinc oxide
smoke raising from the zinc plated steel I was tig welding. I bit of zinc oxide dust is harmless I assumed incorrectly. Feeling like sh## for two
days a couple of times is very effective learning tool.
Borosilicate glass:
Good temperature resistance and good thermal shock resistance but finite.
For normal, standard service typically 200-230°C, for short-term (minutes) service max 400°C
Maximum thermal shock resistance is 160°C
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Sidmadra
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You should check out some of the below links. Sintering PTFE particles with just heat is very standard. This is only done in the form of coatings on
treated surfaces, as the surface holds the particles in place during the process. If you're trying to form an object, then you do need pressure.
"Curing" is the standard terminology when referring to sintering Fluoropolymer coatings, whether there is some other polymer mixed in there with it or
not. Or at least it is the standard terminology used on DuPont websites and such. Some of the blends do have other polymers, others don't. It is
important to note that for coating metals, phosphating the surface must be done, otherwise the coating is unlikely to stick: Here's some links for
reference.
https://www.coatingsolutions.com/dupont-teflon-coating-types...
https://www.chemours.com/Teflon_Industrial/en_US/products/se...
To create a dispersion for spraying they usually have to suspend it with some sort of surfactant. This here they use a nonionic surfactant to
stabilize the suspension.
http://www.fuelcellstore.com/teflon-disp30
The above website ^ sells both FEP and PTFE dispersions, and some others I think. These are in the pure form and also give instructions on how to use
them for coating metal objects, as well as preparing the surface and curing the coat.
You can also find discussions like this:
https://www.researchgate.net/post/What_are_the_steps_for_PTF...
Here's a quote from that page:
| Quote: | | you can dip/spray coat the substrate with PTFE dispersion. Dry it at 120°C then sinter it at temperature just above melting point of PTFE.
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Also check out:
http://www2.dupont.com/Teflon_Industrial/en_US/assets/downlo...
In this PDF it details the use of one of their fluoropolymer aqueous dispersions, which only contains 60% fluoropolymer, and 5% stabilizer, and is
used for coating purposes, after which it must be heat treated at the specified temperature. This just serving as another example that these
fluoropolymer do sinter/cure when heated to the necessary temperature.
| Quote: |
Teflon PFA TE-7224 is a general-purpose product used in a
variety of coating applications. It can also be used as a heat
sealable topcoat.
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[Edited on 16-7-2018 by Sidmadra]
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wg48
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Sidmadra:
I think you are correct several of those links state pure PTFE partcles can sinter. Curiously stating that the sinter (cure) temperature is above the
melting point. I assume the melting point is not defined as the point it turns into a liquid.
So now you have renewed my interest in coating glassware with PTFE. I guess I need a none ionic detergent that will also evaporate to get it in to
a water dispersion. One of the MSDS indicates Polyoxyethylene alkylether. That’s similar to breakfluid but probably with a longer chain. There are
probably other none ionic detergents that will work and evaporate at +300C.
Ok so back to your original question. I don’t think just using a heat gun to heat the object will work as it will be difficult to hold the
temperature at a specific value and duration. Apparently the time temperature profile is critical to achieve a coherent coating.
A temperature controlled heat gun blowing into an insulated chamber that contains the coated object would probably work. That’s effectively a
temperature-controlled oven. That would be ideal.
Borosilicate glass:
Good temperature resistance and good thermal shock resistance but finite.
For normal, standard service typically 200-230°C, for short-term (minutes) service max 400°C
Maximum thermal shock resistance is 160°C
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Sidmadra
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There seems to be a bit of flexibility with the cure temperature of PTFE. From what I read, it depends on how strong you want the layer to be, as well
as how thick the layer(s) is. A number of those links above aren't for PTFE, but are for other fluoropolymers.
I don't think you'll need a detergent that evaporates. After sintering the PTFE, most of the detergent would be trapped under the PTFE, and any that
is exposed can be washed off the surface, and at worst would have minimal/no effect on your reaction, as it would still be trapped within the PTFE
network. It's similar to how many of those PTFE coatings have dyes in them. Any dyes exposed on the surface would be washed off, but most of the dye
would remain protected under the PTFE surface, irrelevant to the chemicals at play.
With respect to the heat gun, if it's temperature controlled, wouldn't it be effective to just aim the heatgun at the object once the right heat
setting was discovered? I used to own one that cost about $60. I've tested it's accuracy. I think it had 10 heat settings from 100F up to 1400F, and
it was able to keep the output air temperature very consistent. I could use a infrared thermometer to monitor the temperature of the metal part.
Blowing the heat gun into an insulated chamber is also a good idea.
[Edited on 17-7-2018 by Sidmadra]
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