Glueing and painting polypropylene

[Zafarelli]

As I've seen so many great builds made from PP shampoo bottles and the like, I'd like to ask you guys what materials you use for glueing and painting. Up to now, I've had no luck at all, neither with CA glue nor two part epoxy. For painting, I had moderate success when I sanded the material very thoroughly prior to priming, but could still scrape the paint off with a fingernail.

Any advice will be greatly appreciated

[Mitch K]

Something like EvoStik is probably the best option, or the really evil solvent-based construction adhesives like original Gripfill - be warned if you haven't used it before: the latter is not subtle.

For painting, way back in the stone age Airfix used to recommend scrubbing the toy soldiers with soapy water then giving them a coat of PVA glue before painting them to allow the paint to key. I'm not sure where they were PP or HDPE or a.n. other polyolefin, but the general advice ought to work.

[zizi666]

Something like EvoStik is probably the best option, or the really evil solvent-based construction adhesives like original Gripfill - be warned if you haven't used it before: the latter is not subtle.

Froget the solvents. PP is unusually resistant to many chemical solvents, bases and acids. (quote wikipedia). I don't know what material white spirit containers are made of, but I'll bet you it's PP.

For painting, way back in the stone age Airfix used to recommend scrubbing the toy soldiers with soapy water then giving them a coat of PVA glue before painting them to allow the paint to key. I'm not sure where they were PP or HDPE or a.n. other polyolefin, but the general advice ought to work.

The airfix figures were made of PE.

On the topic of washing models : ALWAYS wash plastics and resins. chances are, the manufacturer uses a mold releasing agent that leaves some (greasy) particles on the model. some say to wash everything, even metal figs.

For painting, I had moderate success when I sanded the material very thoroughly prior to priming, but could still scrape the paint off with a fingernail.

Maybe a layer of varnish over the primer could help reinforce it ?
Also, I've heard that in the automobile sector they have to put special additives in the paints to lacquer plastic parts (like bumpers)
I believe I was told the additives make the paint flexible. Ofcourse this is hearsay and you might want to check that out with a genuine car painting specialist.

[Zafarelli]

No luck with the PVA coating, but I have found a something to prep PP for glueing, the main ingredient being sulphuric acid However, this still leaves the problem of painting. I think the only choice is to make a mold and cast the bloody thing in resin. It's even easier than using the primer stuff...

[Mitch K]

Froget the solvents. PP is unusually resistant to many chemical solvents, bases and acids. (quote wikipedia). I don't know what material white spirit containers are made of, but I'll bet you it's PP.

Zizi, I know more than enough about the chemistry of polyolefins for my own peace of mind ! I spent years working on plastics and plastic additives, and very dull it was too, I can assure you

Evostik and Gripfill, whilst solvent-based, don't rely on the action of the solvent to dissolve the substrate, effectively "welding" it together. They're solutions / suspensions of elastomers that rely on "tack" to form an initial bond, then de-solvent to leave the elastomer layer to hold things in place.

You're right that nothing works that well on PO's, but my experience is that these are about the least-worst option.

The airfix figures were made of PE.

On the topic of washing models : ALWAYS wash plastics and resins. chances are, the manufacturer uses a mold releasing agent that leaves some (greasy) particles on the model. some say to wash everything, even metal figs.

Maybe a layer of varnish over the primer could help reinforce it ?
Also, I've heard that in the automobile sector they have to put special additives in the paints to lacquer plastic parts (like bumpers)
I believe I was told the additives make the paint flexible. Ofcourse this is hearsay and you might want to check that out with a genuine car painting specialist.

Flexible primers / paints, adhesion promoters, two-pack epoxy paints... All tricky stuff. And a lot of car bumpers are colour moulded to start with

[Mitch K]

No luck with the PVA coating, but I have found a something to prep PP for glueing, the main ingredient being sulphuric acid However, this still leaves the problem of painting. I think the only choice is to make a mold and cast the bloody thing in resin. It's even easier than using the primer stuff...

TBH, unless it's concentrated sulphuric, the resin casting process involves stuff that's at least as noxious. It's all 'orrible, in its own special little ways...

Sorry the PVA didn't work - it was a long shot.

[zizi666]

Zizi, I know more than enough about the chemistry of polyolefins for my own peace of mind ! I spent years working on plastics and plastic additives, and very dull it was too, I can assure you

Heh, I guess I'm a little better off as I "just" have to process 'em into houshold containers and lids 

[Mitch K]

Heh, I guess I'm a little better off as I "just" have to process 'em into houshold containers and lids 

As they say, Hobson's choice...

At least I was indoors and could sit down

[snitcythedog]

For painting, you can try Krylon Fusion.  It is a spray paint made to adhere to plastics.  Might just do the trick.

Hope that helps.
Snitchy sends.

[dijit]

So far superglue has worked for me for glueing, painting is another matter altogether. Having just undercoated my spaceship built from plastic bottles, the paint is already pealing off.
Duncan

[Zafarelli]

Thanks, people! By now, I have resorted to molding and casting, will post pictures once I have something worth showing.

Sorry to hear about your spaceship, Duncan