Need help painting polypropylene

toymaker · Post by **toymaker** » Thu Aug 06, 2015 9:57 am

I have a kit that has polypropylene parts I need to paint. Has anyone had success with getting paint to stick well? I have tried Rustoleum plastic primer but it didn't work.

Kylwell · Post by **Kylwell** » Thu Aug 06, 2015 1:10 pm

Polypropylene is near impossible to paint. Some suggest coating the part with cyanoacrylate glue then painting but don't flex the part or the glue will crack off. There are primers made for promoting paint adhesion but they are seriously nasty to work with.

But... if all you need is a decent coat that will never be flexed or rubbed I suggest Mr. Surfacer 1000 built up in very thin coats.

toymaker · Post by **toymaker** » Thu Aug 06, 2015 1:18 pm

Unfortunately some of these parts need to have a little bit of give.

Kylwell · Post by **Kylwell** » Thu Aug 06, 2015 1:50 pm

Well try the thin coats of Mr. Surfacer. I've got a polyvinyl piece painted with it that has survived a bit of flex & handling w/o issue.

The problem with polypropylene is that it falls into the class of low energy plastics, meaning it's inert and highly stable. This is why it gets used in so many applications. Those same properties make it difficult to get anything to stick to it so you need a highly energetic bonding agent which lacquer is. The step up would be something like self-etching primer but since that's made to work with metal it may or may not work, depending on the primer & type of polypropylene. You could also try Mr. Primer Surfacer (as opposed to Mr. Surfacer Primer) which is much hotter.

http://robot4less.com/mr-primer-surface ... e-mr-hobby

modelnutz · Post by **modelnutz** » Thu Aug 06, 2015 4:33 pm

When I was working with Fisher-Price , I had to do a lot of re-painting of production toys that were made from Polypropylene.
The only way to get paint to reliably adhere was to sandblast the parts first.
This created a rough surface for the paint to "grab" on to.

Once this step was done , I could use almost any good quality primer/paint system with confidence.

Brucebruce · Post by **Brucebruce** » Fri Aug 14, 2015 10:29 am

I was just about to post a question about paining a toy of the Milano from the Guardians of the Galaxy. I am having trouble painting it, is this why? Or is it made from something else? The box is no help!

Kylwell · Post by **Kylwell** » Fri Aug 14, 2015 12:45 pm

Quite possibly. You may be able to get some grab by sanding the hard outer surface down with some fine sandpaper. It all depends on the plastic, the paint and how it's applied.

toymaker · Post by **toymaker** » Thu Sep 03, 2015 1:43 am

I found an automotive spray can product from Duplicolor seems to do the trick. It's called adhesion promoter spray. It works amazing. I'm

Kylwell · Post by **Kylwell** » Thu Sep 03, 2015 9:49 am

Just read the health hazards on that. The ones I know of are exceedingly hazardous to health and require spraying in an open area with a respirator @ minimum.

kenlilly106 · Post by **kenlilly106** » Thu Sep 03, 2015 5:50 pm

Good grief it's not that bad.

Look at the MSDS, it's basically MEK and Acetone:
link

Methyl Ethyl Ketone 52.2%
Acetone 19.0%
Propane 11.7%
Butane 11.3%
Xylene 3.6%
Ethylbenzene 0.6%

Kylwell · Post by **Kylwell** » Mon Sep 07, 2015 3:45 pm

Now go look up the MSDS on MEK & Xylene.

http://www.sciencelab.com/msds.php?msdsId=9927358

kenlilly106 · Post by **kenlilly106** » Mon Sep 07, 2015 6:40 pm

And how is it worse than lacquer thinner?

Kylwell · Post by **Kylwell** » Mon Sep 07, 2015 6:59 pm

kenlilly106 wrote:And how is it worse than lacquer thinner?

Lacquer thinner is largely acetone which while hasty is actually pretty tame compared to some of the other chems we modelers play with. It flushes from the body easily and breaks down in the air to water largely. It'll make you sick but won't kill you or cause brain damage.

http://www.sciencelab.com/msds.php?msdsId=9927062

srspicer · Post by **srspicer** » Tue Apr 26, 2016 4:05 pm

Wasn't there a discussion on MEK a while back and how nasty it is!?

Good advice suggested already.

There is also an automotive product called 'flex-ilizer'. It is made for bumper covers and all of the softer plastic parts that are supposed to flex in a collision. It is an additive for standard automotive paints. You can get it a automotive suppliers. It may be expensive, I have never had to purchase any on my own.

Max Nex · Post by **Max Nex** » Wed Apr 27, 2016 3:44 pm

...and don't forget this one...

http://www.sciencelab.com/msds.php?msdsId=9923958