painting plastic gas tanks??

#1
i recently just finished my nighthawk and did a slack ass job throwing a coat of black spray paint on my nighthawk tank... it started peeling about 1 day after i started riding haha..
what are your guys' experiences with painting plastic?
any processes that have proven to be successful? im thinking about dipping it like they do with motorcycle helmets.. like so

https://www.youtube.com/watch?v=_CA0DR4GSQg
 
#2
What type/brand of paint did you use? What I have learned from this forum is that you MUST uses a paint that is specially formulated to bond to plastic. Even with doing that, I wonder if there is a plastic paint that is gas resistant?
Michael
 
#3
It is quite possible to paint plastic with acrylic or urethanes. Paint over primer and it binds fine, as long as the prep work is up to snuff.

The problem with "gas tanks" however is that the plastic "supposedly" breathes and permeates the tank from inside. So it attacks any non catalyzed primer. The cure for that is a well and correct application of Caswells- the clear stuff, or the dragon blood.

Rattle can has no business on a gas tank of any material, unless you clear with two part urethane. Hydro is the same deal. Needs a clear coat. Not the stuff from the hardware store.
 

MB165

Active Member
#4
i dont think your going to have any luck painting a plastic gas tank. they will bubble up if you put gas in them....i did one and it looked good for a few months. it cleans off easy enough though.
 
#5
the only way to paint plastic is to scrub it real good with scotchbrite and use adhesion promoter and still you will get the gas permeating whatnot but ive had it last a lot longer than people say it does with lots of clear
 
#6
It is quite possible to paint plastic with acrylic or urethanes. Paint over primer and it binds fine, as long as the prep work is up to snuff.

The problem with "gas tanks" however is that the plastic "supposedly" breathes and permeates the tank from inside. So it attacks any non catalyzed primer. The cure for that is a well and correct application of Caswells- the clear stuff, or the dragon blood.

Rattle can has no business on a gas tank of any material, unless you clear with two part urethane. Hydro is the same deal. Needs a clear coat. Not the stuff from the hardware store.
Exactly right, Krylon Fusion is a plastic specific paint but it will not stick to a gas tank very well at all. The plastic evidently does breathe, that or the fumes just eat away at the paint over time. Either way I've had zero success painting plastic fuel tanks.
 
#7
This:

The problem with "gas tanks" however is that the plastic "supposedly" breathes and permeates the tank from inside. So it attacks any non catalyzed primer. The cure for that is a well and correct application of Caswells- the clear stuff, or the dragon blood.

If you don't line it first don't bother painting it....
 

markus

Well-Known Member
#8
I "stained" a couple of black ones in the past, I actually just started prepping another black tank last week and was going to do it again. I truly dont know how well they held up long term, both ones I did were bikes I owned for maybe a month or so after redoing them and they sold, did run fuel in them and ran/road the bikes alot in that time period though and no problems showed up. I actually am trying to get with the guy that did buy one of those bikes a few years ago about something else, so maybe I can find out what the long term effects were, but I am honestly not sure that that tank stayed on that bike or not.

http://www.oldminibikes.com/forum/general-minibike-talk/73969-getting-paint-plastic-tank.html

It would probably be a bitch to do on a large remote tank and keep it fluid and smooth though
 

Gatecrasher

Well-Known Member
#10
i recently just finished my nighthawk and did a slack ass job throwing a coat of black spray paint on my nighthawk tank... it started peeling about 1 day after i started riding haha..
what are your guys' experiences with painting plastic?
any processes that have proven to be successful? im thinking about dipping it like they do with motorcycle helmets.. like so
Different plastics require different preparation for paint. Some plastics are difficult for paint to adhere to. Due to the physical properties of various polymers, most motorcycle gas tanks are either made from high-density polyethylene (HDPE) or polypropylene (PP). They are used because of their chemical resistance and they also have good moisture-vapor barrier properties (MVTR). These two properties prevent the gas from evaporating and the plastic itself from dissolving from prolonged contact with the plastic.

Motorcycle helmets are generally made from polycarbonate (PC) which has better paint adhesion (and impact resistance). Polycarbonate requires less preparation and can more easily be painted.

The molecules in HDPE and PP have what is called a low "surface tension" which makes adhesion difficult. That's why they are difficult to glue too.

One way to prep HDPE and PP for decoration is to flame-treat the surface using a propane torch with a wide flaming head. You want to wave the flame over the surface quickly so the flame just "licks" it without melting it. This increases the surface tension by bringing carbon molecules to the surface and paints and inks will then adhere a lot better.

You can test the "dyne level" of the treated surface by dipping it in a tub of water and pulling it back out. The water will bead-up and just roll off an untreated surface (like a freshly-waxed car) but on a treated surface the water will stay more in sheets and not run right off (like an unwaxed car).

Another way to surface-treat olefins like HDPE and PP is to plasma-treat them but most people don't have that capability at home.

Both of these techniques allow paints to adhere due to a change in the surface of the plastic on a molecular scale. That's the trick to making paint stick long-term.

If you are uncomfortable with torching your gas tank, you can also sand the surface and use special primers like are used by body shops to paint PP spoilers and front fascias that some cars have.

The best paints to use on HDPE and PP are the flexible polyurethanes.
 
#11
Mark G is correct. You need to seal the inside of tank first. Caswell makes a 2 part mix that is made for sealing tanks. Prep work is very important and follow the instructions to do it right. Caswell is not cheap but it is good stuff.
 

Gatecrasher

Well-Known Member
#12
I work in the plastics industry. Here is a surface-treatment system I helped design for the decoration of HDPE and PP bottles. It is a flaming conveyor belt. Bottles are fed through a series of propane flaming heads at a fairly rapid rate. The goal is to expose the surfaces to be decorated with the flame while not melting them. After the bottle goes through the first set of flaming heads it enters a bottle rotator which turns them 90 degrees before they go through a second set of flaming heads. This ensures full 360 degree coverage of the areas to be decorated.

MVC-009F.JPG

MVC-012F.JPG

MVC-006F.JPG

MVC-008F.JPG

MVC-002F.JPG

After surface-treatment, these HDPE bottles can then be decorated with paint, silk-screened inks, pad printing, inkject, or even have a pressure-sensitive label applied and they will all stick. If you were to attempt to decorate them without surface treatment, nothing would stick due to the low molecular surface tension. If you notice in the 3rd picture there is also a top flaming head that is not being used for this particular bottle. It is used for bottles that get a tamper-evident foil seal on the top so they will stick better too.

Here's a picture of some PP caps that are being flame-treated and printed with ink all in one process. You might recognize them. They are the caps used by Walmart Pharmacies on the amber prescription vials.

IMG_0100s.jpg

Without flame-treating anything made from HDPE or PP prior to decoration you would be able to wipe the paints and inks right off fairly easily. After flame treatment though, the molecular surface tension is increased and it sticks quite well.
 
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#14
#15
Caswell is a company out of New York. They make a lot of different specialty epoxy and coatings. They have a very good ceramic coating for headers. Elctro plating kits also. This company is not cheap on there prices. It is high quality materials. Look them up. Plating Kits Electroplating Kits Aluminum Anodizing Kits Gas Tank Sealer Metal Polishing And Buffing Supplies - Caswell Inc. the tank sealer works on steel,aluminum,fiberglass and plastic gas tanks
It was a smart assed joke Rick. Here's my post- #3 in this thread where I recommend Caswells.

I use the heck out of it after a "Ken's" failure. (Polymer) I found I can reduce Caswells using rubbing alcohol instead of acetone. I do two coats, but they're thin. Great stuff. Doesn't require a bunch of prep either. It also acts 100% like the epoxy resin I used to use on boats. (glasswork)

Now if you'll excuse me, I'm headed to the garage to use a blow torch on my expensive, hard to find Cat plastic gas tank. :laugh:
 

Gatecrasher

Well-Known Member
#16
It was a smart assed joke Rick. Here's my post
Now if you'll excuse me, I'm headed to the garage to use a blow torch on my expensive, hard to find Cat plastic gas tank. :laugh:
You can laugh if you want but that's what it is going to take for the paint to really adhere properly and last any length of time.

I'm an engineer by trade and have a BS degree in Plastics Engineering and studied organic polymer chemistry in college.

There is a new surface preparation device that is out now called the Electro-Treat that does the same thing chemically to the surface tension of olefins without the heat risk but it costs thousands of dollars.

If you doubt my expertise on this subject I suggest you try an experiment. Take an old polyethylene container of any type. A gas can will work but I would wash it out good so it doesn't explode. Take a propane torch with a wide flaming head and wave it across half of the surface of the container and leave the other half untreated. Then take a can of spray paint and paint the container. You'll see a big difference in paint adhesion between the two halves.
 

Midyrman

Well-Known Member
#17
Paint it with Krylon Plastic spray can and don't put gas in it.

Can't drive it but the tank looks like plastic.

This topic is a tough one. If only Tecumseh engineers knew what the future held for us restorers......
 

Gatecrasher

Well-Known Member
#19
That's why you take an old gas can or something and practice on it first. All that is required is a quick wave of the flame across it. You need a wide flaming head or fantail on your torch though. It's hard to do it with a regular propane torch that concentrates the flame in a pinpoint.

You have about 6 months to paint the tank after flame-treating it. If you let it sit any longer than that, you must re-flame it to regain the surface tension prior to painting.
 
#20
ill tell you what, if i paid 200 dollars for any piece of plastic id probly frame it cause thats ridiculous... thanks for the advice gatecrasher.. one thing i do have access to is a propane torch so ill definitely give it my best shot.
 
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