Painting PolyPropylene Canopy.

[wnor]

I am on a Quest to find a simple, durable, air-brush-free method of painting a polypropylene Raptor canopy. I've done some experimentation, not on a mere imitation, but on the genuine article, a Clorox bleach bottle. Here's what I have so far:

1. Wash in hot water with Joy dishwashing liquid, first with a sponge, then with a Scotchbrite pad.

2. Rub hard with Klean-Strip Bulldog Abrasive Bumper Cleaner, model number P-ABC-124, and a patch of bluejean cloth.

3. Let dry.

4. Prime with two coats of Klean-Strip Bulldog Adhesion Promoter, model number ETPO-123. This is a rattle-can.

5. Mask. Apply several coats of Krylon Fusion for Plastic 2330 Sunbeam. Steps 1-5 can all be done on the same day.

6. Wait 24 hours, then mask and apply several coats of Krylon Fusion for Plastic 2321 Gloss Black.

7. Let cure for one week.

The resulting paint job has excellent adhesion. Twisting and “oil-canning” the painted bleach-bottle material has no effect on the paint. BUT: Moistening a piece of paper towel with fuel (15% nitro) and rubbing the paint with it strips the paint right off. The paint does not come off in sheets like with a paint stripper, but the paint film progressively thins with rubbing until it disappears.

I have also painted a real, live Raptor canopy with similar results. After 20 flights, the paint is fine everywhere except where it has been splashed with fuel. Also, the area near the muffler exhaust shows some roughening and softening of the paint film – the paint still looks fine, but the most superficial layer is taking a bit of a beating.

So, that's as far as I've gotten: good adhesion, but not fuel-proof. Does anyone know of a fuel-proof clear top coat that is compatible with Krylon Fusion for Plastic, preferably a top coat available in a rattle-can? A very helpful technician at Krylon says that their clear coat is probably less fuel-resistant than the pigmented paints. I'm willing to haul out the bleach bottle and do the experiment if you have a suggestion.

[PaulH]

You might try one of the clear coats for R/C car bodies from your LHS. They are designed to be fuel proof and usually come in a spray can.

[edm3]

Would it be possible to fiberglass the shell?

Just a thought. I just bought a new canopy and am wondering how to make the paint stick. On my original canopy I lightly sanded it and used Krylon paint. The Krylon does chip off but it seems not to be affected by fuel.

Ed

[flyinfool]

You can't be building up 6, 8 or even more coats of anything and expect it to stay as flexible as a plastic canopy.
Think Thin.
Thin is also Light weight.
Primer is very heavy sand it down till its almost all gone.

My old rapy V1 lid from when the rapy first hit the market is still not chipping or pealing even after 5 crashes. It has holes punched in it and a lot of scrapes and scratches from years of hard use, but the paint still is stuck down.

I used the method;
Sand
Wash
flame
acetone wash
Adhesion promoter (1 light coat)
Flexible bumper primer (1 light coat)
Primer of choice (1 light coat)
color paint of choice (1 coat unless the color is a two part that requires a base coat)
Clear (1 wet coat)

[edm3]

Jeff,

What grit sand paper did you use and how did you flame the surface? Did you use a torch or hold it over the stove? Is acetone like MEK? As you can see I am a real novice when it comes to painting but I like the look over the stikers.

Thanks for your help and previos post.

Ed

[flyinfool]

I used 320 wet or dry and a propane torch.
acetone is not MEK.
MEK will clean off any oils present but I would test on the canopy cutout to be sure that it will not disolve the plastic.

[Seeker]

What is the process of flaming?

I understand from the post above, you use a torch... how do you do it?

Thanks,
Paul

[flyinfool]

It takes a little practice.
Using a propane torch I pass the flame all over the canopy. if you hold your hand on the inside surface while flaming you can tell if you are getting to hot (be careful). Also hold it to see a reflection from a good light source there will be a slight change in the surface appearance as you hit the right temp. You have to keep the flame moving at a good pace to avoid melting or distorting the plastic. Once you learn the technique it is a very quick and easy process.
I use a plumbers size torch, not the little pencil point type, the bigger torch is the same temperature as the pencil point but covers a bigger area.

Practice on the windshield cutout. A bleach bottle is a lot thicker than a canopy and can take a lot more flame before it melts.

[Seeker]

Cool... thanks!


Paul

[Mike Fortin]

How much weight does this process ad to the a stock plastic canopy? The ones that I have seen painted are pretty heavy for a canopy.

[flyinfool]

I do not have a scale to measure it with.

That is why in an earlier post I mentioned to keep it thin.
I have seen some really nice paint jobs that at least doubled the weight of the canopy.

If you think thin it can be done with very little extra weight.

[wnor]

Here's another attempt to get a long-lasting, fuel-resistant paint job on a "Clorox bottle" Raptor canopy using (mostly) hardware store (True Value) rattle cans:

1.Wash in hot water with Joy dishwashing liquid, first with a sponge, then with a Scotchbrite pad.
2.Flame (see prior posts by other authors on this site).
3.Wipe down with acetone.
4.Rub hard with Klean-Strip Bulldog Abrasive Bumper Cleaner, model number P-ABC-124 (W.M. Barr Co, Memphis, TN) and a patch of bluejean cloth. Got this product at an auto parts store.
5.Wash in hot water with Joy. Let dry.
6.Wipe down with acetone.
7.Wipe down with tack rag.
8.Prime whole canopy with two coats of Klean-Strip Bulldog Adhesion Promoter, model number ETPO-123. This is a rattle can, purchased from an auto parts store.
9.Apply two coats of Premium Decor Satin to whole canopy, model number PDS-3 White (GPM, Cary, IL).
10. Wait 24 hours.
11. Mask.
12. Wipe with tack rag.
13. Spray with two coats Premium Decor Fluorescent, model number PDFL-6 Red Orange.
14. Wait 24 hours.
15. Mask.
16. Wipe with tack rag.
17. Spray with two coat Premium Decor Fluorescent, model number PDFL-5 Neon Blue.
18. Wait 24 hours.
19. Apply decals by floating them on over a layer of Glass Plus.
20. Rinse with water.
21. Let dry.
22. Wipe with tack rag.
23. Spray with Premium Decor Clear, model number PDS-7 Gloss, two "dusting" coats followed by one final "wet" coat.
24. Wait one week.
25. Fly.

Note that I did not sand between coats. Both the white satin base coat and the fluorescent colors dry to a dead-flat matte finish, so this did not seem necessary.

So far, I have 140 flights with 30% nitro fuel on a canopy painted as above. No crashes to date, but the paint has been subjected to some abuse by fuel and muffler leaks. Adhesion has been excellent. The clear topcoat is a little soft and extra-glossy in places, but not too bad in my view. A more fuel-proof topcoat would be nice, though.

[wnor]

Regarding message #37 above, after 550 flights (and two crashes) with 20-30% nitro fuel, the paint near the muffler became gummy like fly paper. I stripped the canopy with MEK, then redid the procedure described in message #37, except substituting Top Flite LustreKote Crystal Clear TOPR7501 for the clear coat. LustreKote seemed fully compatible with the Premium Decor color paints. On-line accounts of the durability of LustreKote Crystal Clear vary wildly. Guess I'll be finding out for myself.

[MartyH]

If I could clear up several things here.....First of all, the canopies are blow molded from HDPE (high density poly ethylene), they are not polypropylene. The process of going over the canopy with a torch is called flame treating and is the same thing we do in the blow molding industry on plastic containers so they can be printed. To test for proper flame treating, you dunk the completed canopy in tap water. When you remove it the water should at first uniformly coat the surface then the sheeting action will breakup and the water will run off. If the water instantly beads and immediately rolls off, the surface has not been properly treated. Finally, you will not dissolve or melt polyethylene with MEK or acetone.
I have been blow molding HDPE for 25 years. We flame treat every item and screen print them in enamels. Improper or no flame treating allows the enamel to scratch if not just about fall off of the plastic. A proper flame treated surface will provide "tooth" for the enamel to grab on to and once cured will not easily scratch off. Flame treating does have a limited shelf life so if you treat a part and a year later want to paint it or stick decals to it, reflame it first for better adhesion.

[wnor]

Concerning the recipe in post #38 above, after 100 flights (no crashes) with 20% nitro fuel, the finish is like new. Some caveats:

1. The paint film is quite soft for at least 2 days at 60 degrees F. Waiting at least a week before flying is probably a good idea.

2. I also used Premium Decor PDFL-3 Bright Yellow. After about two weeks it developed a strange, migratory, vague, measles-like rash that eventually coalesced into an acceptable finish after about 5 weeks. Perhaps this was a manifestation of the curing process. Beware.

3. I got curious concerning the fuel-proofness of hardware store rattle can clear coats. I tried a bunch, and all but one were total failures. Various posts suggest that Minwax Fast-Drying Polyurethane Clear Gloss (no part number that I can find) is fuel proof. After applying it to a paint base prepared per post #38, the clear coat bubbled right off when fuel was dripped on it after two days of curing. After a week, however, a drop of fuel left in place for 20 min, then washed off, did nothing to the clear coat. But a paper towel soaked in 20% nitro fuel and applied to the paint for 20 min stripped it. So, in a pinch, this top coat might work if the fuel contamination is not too severe.