Poor paint adhesion on cast resin

KnightTemplar5150

 Looks as if Johnny has done both already. 

The release agents used in rubber molds come in a lot of forms - some are petroleum based, others are silicon based, and there are a handful of companies using talc based releases. It's hard to tell what you're dealing with sometimes.

I couldn't agree more. Definitely sounds like a release agent issue. Heres the kicker, you need the correct product to help neutralise the agent. If the agent was solvent based, you need a solvent to remove it.... water or alcohol based methods wont touch it and vice versa. 

The trick to cleaning anything is wipe or spray on, wipe off. Cleaners, once applied, will lift the contaminants to the surface. They must then be cleaned off with a clean, dry wipe. If your cleaner is just wiped over and allowed to dry the contaminants sink back onto the surface. In the case of washing your model kits out the box if your using warm water and detergent and running them under water it will be dragging the contaminants away. Point is don't just wet a cloth and wipe parts over, it's achieving squat.

So I would try all 3, I would detergent wash, iso wipe down and wipe off, then try a solvent. Im not sure on the specific resins used in the parts you have but in the composites industry straight acetone is generally used for cleaning as it dries out almost immediately and draws any moisture out of the composite resin. I would do a solvent test on your resin first before getting too excited with acetone. The degreasers mentioned may be a good choice. 

Josh

Tamiya Gray primer is my standard for resin

Everything comes off, final paint and the primer I can use my fingernail and scratch down to the resin.

After cleaning, maybe switch the primer.

Also, you know it just may never be super bullet proof.

When you say "final" paint, is it the final coat that comes off of the primer, or the whole shebang?

Hi JohnnyK;

 Although I don't do resin often ( Allergies ), when I do, I wash it off with Bleche -White. Then Prime it with Rustoleum Dove grey primer. No Flaking problems yet ! T.B.  P.S. I forgot to mention this. Test the resin for reaction from any agent. If you use something like Lacquer thinner the stuff will or should help the paint bite the resin. DO NOT handle your resin model with bare hands after cleaning it! It will absorb any Body oil you think you don't have on your finger pads!

I use SuperClean, also sold in Walmart's automotive section, as my de-greaser.  It'll strip paint, too.  I use warm water and a couple of drops of SC, to clean resin parts, or styrene, too.

For priming, I also use Tamiya's fine surface primer, or automotive primers, or Rustoleum primer.  I've never had any problems with paint adhesion.

Much as I like Testors enamel for painting, I don't like the prime very well.  After washing resin I prime it with either Tamiya primer or auto body primer.

Purple Power is a good idea. I'll use that next time I paint resin.

JohnnyK

First I washed the part, then primed it with Testors spray primer. The final finish was Testors' spray lacquer. 

 

Looks as if Johnny has done both already. 

The release agents used in rubber molds come in a lot of forms - some are petroleum based, others are silicon based, and there are a handful of companies using talc based releases. It's hard to tell what you're dealing with sometimes.

I've been using the Purple Power degreaser from the automotive section of our local Walmart. Just a quick soak removes the petroleum and silicone releases. And, if I mess up my primer or color coats, I'll use the solution to strip things back to bare resin. Just wear gloves and eye protection - the stuff is pretty caustic.

Wash resin and prime resin before painting.

Westy’s Bleche White white wall tire cleaner from an auto supply store.  It’s a bit more aggressive in neutralizing the resin release material

Could be the wash.  I've had some resin parts coated in release agent.  Try dawn or an isopropyl alcohol wipe down.