Thread: Advice sought on SG100

Let me start by saying that I paint a lot on ABS plastic and have been doing so for years. I like it using it because it is stiff and when coated with white primer is a nice surface to work on- similar to illustration board.

I mostly use PPG lacquers and water based acrylic paints and Lacquer clear coats on the stuff I paint whether it is a prototype model or a piece of artwork. I have used HOK urethane's a little here and there but just cleared with a lacquer clear as a urethane clear would be overkill.

So my problem is a ABS panel I painted with HOK urethanes bent after I cleared it with SG100. I have never had this happen before clearing with a lacquer clear coat. The SG100 wasn't sprayed on heavy just enough to coat my artwork. I think as it dried it shrunk because the panel was flat when I cleared it and when I came back to the paint booth a few hrs later my panel had curled. Can anyone with experience using SG100 give me any insight to this problem?
John

How thick is the panel?

Is the booth heated, or do you use heat lamps to speed up curing and drying?

Which way did the panel curl, towards the cleared finish, or away from it?

Heat tends to make the material expand, so putting a heat lamp or two facing one side will make that side of the panel expand, while the other (non heated) side stays the same (non-expanded), that makes it curl or bend away from the heat source.

If it is curling towards the cleared side (without heat being applied to the other side) then it may be your clear contracting/shrinking that causes it.

Its 72 degrees in the booth and no heat was used. it is curling towards the clear side. and I used the HOK 311 reducer to reduce hte SG100. The panel is .125" (1/8th)thick.

With ABS, adhesion is usually the biggest problem or issue.
If you sprayed the clear on lightly, then I doubt that it's contracting or srinking is the whole issue. It may*be the solvent in the reducer for the paint and or clearcoat. If it wasn't shrinking after the paint alone, then it may be just the clearcoat.
If you have some scrap of the material, I would do some tests with the paint alone, the clear alone, and the solvent used in the clear (probably MEK), and see if you can narrow down your problems.

Did you see any checking or distortions in the cleared side?

If you want to try rescuing this piece, you might try warming it up, and pressing it flat and letting it cool that way. Or, shoot the backside with the same clear and see if it causes the material to curl back to it's original shape.
Just a thought.

Thanks for the info. Unfortunately it warped enough for the underlying paint to crack. Personally I have never had an adhesion issue with ABS. As long as the surface is clean most paints stick to it.

Maybe my Sg100 is contaminated or something it has been sitting for over a year-still sealed in its can but who knows. I will spray it on a piece of ABS and see what happens.

I sprayed another piece of ABS with just the SG100 and the same thing has happened. It must shrink a little as it dries and since the plastic is thin enough to bend I assume this is what is happening. On Monday when I det back to work I shall try painting both sides and see what happens.