Painting soft plastic
#1
Got a question, I'm using some sheet plastic for my new building. As near as I can find out, it's made from a mix of recycled Polyethylene and Polypropylene. It is thin, (.05"), soft, cuts easily, has a rough texture but doesn't adhere paint very well. It resists sanding too, (100 grit belt sander barely takes the texture off one side). It can be painted, but scratches and flakes off if you're not careful. I've been using acrylics. I like it for my building because, it cuts easily and the texture resembles stucco in N scale.

Has anyone used this stuff and painted it? If so, does a primer work, or do I need to use an oil-based paint or even a rattle can? I would not think a clear coat would help since the problem is one of adhesion. I like acrylics because I can mix my colors. I've already used this plastic for my backdrop, a scratch or flake isn't as big a deal on a 36" x 36" painting as it is on an N scale structure.
Don (ezdays) Day
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founder of the CANYON STATE RAILROAD
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#2
Hello Don,

Bad, but true facts: Polyethylene (PE) is not really paintable. PE belongs to the group of Polyolefines.

Wikipedia says:  Polyolefin surfaces are not effectively joined together by solvent welding because they have excellent chemical resistance and are unaffected by common solvents. They can be adhesively bonded after surface treatment (they inherently have very low surface energies and don't wet-out well (the process of being covered and filled with resin)), and by some superglues (cyanoacrylates) and reactive (meth)acrylate glues. They are extremely inert chemically but exhibit decreased strength at lower and higher temperatures.

In other words; not really glueable. Of course you can try to glue it, but do not look too sharp onto it and don't cough. It may fall apart into pieces again.

Exact the same behavior is with paint, dye and all other laquer stuff. The adhesion of paint is based onto wet-out effects and a not so chemical resisting surface of the plastic (bonding). The chemical resistance of PE also here makes sure that no paint will stick firmly onto the surface. Here too don't look too sharp onto it, don't cough in the same room, avoid draft and do not move the painted PE parts. Flaking off paint will be the inevitable result. 

Make a test: https://www.bottompaintstore.com/blog/bo...bt-blends/

There are further possiblities of treatments for the stubborn PE surface, including electrical corona Eek discharge, flame treatment, cold gas plasma, and ultraviolet irradiation. But this are industrial grade procedures and not acessible for hobby model railroaders.

Lutz
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#3
Thank you Lutz, I was also concerned about gluing and with good reason. You've got me thinking, I got "C" in chemistry, but "A" in determination, and so I've got enough material to experiment with. I'm going over to Home Depot tomorrow and check out the label on a sheet, (I've destroyed the one on my sheet), and so it may give me a hint where I'm at. If it's what I think it is, (Plas-Tex®), it says that panel adhesive is recommended for gluing, but says nothing about painting. By definition, "PLAS-TEX® is made up of recycled plastics such as Polyethylene, Polyolefin, and Polypropylenes", so it could be any or all of the above if that's what I'm using...

Thanks again Lutz, your response have been very helpful. I'll see where I can go, but one thing I won't do is to act like the Big Bad Wolf and huff and puff and blow the house down..... Nope
Don (ezdays) Day
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founder of the CANYON STATE RAILROAD
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#4
I forget what it was, but there was a paint made for really slippery things like loco handrails.
David
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Esquesing & Chinguacousy Radial Railway
In model railroading, there are between six and two hundred ways of performing a given task.
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#5
(12-29-2020, 10:01 PM)BR60103 Wrote: I forget what it was, but there was a paint made for really slippery things like loco handrails.

The paint used on radio controlled automobiles will work on the slippery plastic, but I've also found that pre-painting with Tamiya paint will allow paints such as Pollyscale or ModelMaster to adhere better, but those items should be handled as little as possible.
You can also buy a product that I have in my hand, although it's not clear what the actual name of it is. 
It was originally developed for painting things on your car which are made from engineering plastics of various types, such as the side-mirror housings, or the bumpers and plastic trim that's the same colour as the car itself.
The product is from Sherwin-Williams, and the label reads, from top-down...


       SPECIALTY

        UP07228  

Low VOC Adhesion Promoter


It's a spray can with a 15oz. capacity, and while it was bought several years ago, I've not had need to use it.

Here's a LINK to some info on it.

I don't recall the actual price, but do remember that it was not insignificant.  I got it at a nearby shop specialising in paint and protective finishes for automobiles.

Wayne
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#6
There's a Shewin-Williams store about a mile from my house. I've not heard of, or had a need for this product, but I'm sure I can expect to pay dearly for it there. On that same note, I have bought paint in a spray can that is formulated for plastic. I'm not sure, but there might even be a primer but I'm not sure if it will work with what I'm using. I'm heading to Home Depot today to check the label on what I have and if they have any kind of paint there that I can use as an undercoat. If it is Plas-Tex, I cannot find anywhere where they talk about painting it, I guess they assume you want bright white (or beige).

One other thought that I've had is to wash it with something that will take the slickness off the surface without melting it. Maybe Acetone, got to put on a white lab jacket, eye protectors and rubber gloves just like Dr. Nefario in "Despicable Me" and do some experimenting. Where are those Minions when you need them? Waiting

Thanks for you input guys, it's helped point me in the right direction.
Don (ezdays) Day
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founder of the CANYON STATE RAILROAD
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#7
Went to Home Depot, what I have is indeed, PLAS-TEX®. I then went to the paint dept and asked them what was the best primer for plastic and she pointed out the "2X", even though it was cheaper ($3.98) than the others. I then spent an abnormal amount of time looking over their glue stock and decided on this one. This time it was the most expensive one ($5.47) for less than one ounce, but they say it sets in 30 seconds and cures in 30 minutes and bonds just about anything.

I put on my Dr. Nefario coat, goggles and gloves, found a few minions that were willing to help and proceeded to do some testing. The paint dries to the touch in 20 minutes and fully in 24 hours, but they recommend 5-7 days for maximum adhesion  on plastic. Sorry Rust-Oleum, I have patience, but my minions start to get crazy after about two hours, so we'll start our experimenting with that in mind. Crazy 

   

   
Don (ezdays) Day
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founder of the CANYON STATE RAILROAD
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#8
The results of my experiments:

Model cement did not adhere well, but the new glue worked fine. When they say, "Bonds virtually anything", they're not kidding, fingers, tools, working surfaces all joined as one now. Icon_rolleyes

Moving on to the paint, acrylics scratched off easily without the primer. I sprayed the primer on a test piece and after two hours, it adhered just fine. Painting over the primer kept the acrylics from scratching or flaking, just that the darker grey bled through on most acrylics, even a white undercoat did not cure that completely. Either I use dark colors or try to find a lighter primer.

Again, I thank you all for your comments, they did get me pointed in the right direction.
Don (ezdays) Day
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founder of the CANYON STATE RAILROAD
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#9
You might try doing a test where you set the item aside for the 5-7 days, and check the result. If the off gasing of the paint continues for 5-7 days, that may be the cause of the bleed through.
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#10
(12-31-2020, 11:18 PM)Russ Bellinis Wrote: You might try doing a test where you set the item aside for the 5-7 days, and check the result.  If the off gasing of the paint continues for 5-7 days, that may be the cause of the bleed through.

Good point Russ, I guess that could be why they say to wait that long for maximum adherence to plastic. I did one other thing, I did find the same primer in white which could help conceal the bleed through. Several coats with the grey did not help, even with darker colors, so I'll give waiting longer a try regardless of which one I use.

Thanks, that's why we ask questions like this..... Worship Worship
Don (ezdays) Day
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founder of the CANYON STATE RAILROAD
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#11
one of the biggest problems i have found wiyh recycled plastic is that some recyclers don't prep  the stuff like they should found that a wash with MEK (not the California stuff ) helps with adhesion.
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#12
(01-02-2021, 09:31 PM)jim currie Wrote: one of the biggest problems i have found wiyh recycled plastic is that some recyclers don't prep  the stuff like they should found that a wash with MEK (not the California stuff ) helps with adhesion.

Thanks Jim, I mentioned Acetone earlier, MEK might be better. I think I have some to experiment with. My only though is what it might do to the plastic. We'll find out..
Don (ezdays) Day
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founder of the CANYON STATE RAILROAD
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#13
I've actually tried wiping plastic surfaces with acetone first to make them tacky, then quickly painting them with a rustoleum or krylon plastic primer. Most of that was in trying to repaint vinyl auto parts. It actually worked ok.
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