FUD: Painting? Post-cure?

Discussion in 'Finishing Techniques' started by patmat2350, Nov 29, 2015.

  1. patmat2350
    patmat2350 Well-Known Member
    I've had difficulty painting my FUD models... the issue usually was that the paint wouldn't cure.

    Parts were thoroughly cleaned in a variety of ways, using brushing/scrubbing with solvents as strong as lacquer thinner, and/or ultrasonics with strong aqueous cleaners. I'm confident that the parts were free of process wax, oil, water, etc. Yet any solvent based hobby paints and primers would stay gummy on the parts, and just wipe off.
    Then I found that water based acrylic hobby paints worked just fine- they dried quickly and hard. Yet sometimes, especially with flat paints, I'd notice a staining of the paint, as if something was leaching out of the plastic into the paint.

    But elsewhere I've read that ANY paint, including solvent based enamel, would work on FUD plastic.

    So this makes me think- Does FUD need a post-cure under sunlight or a UV lamp? This is standard practice with UV cured SLA parts.. why wouldn't Multi-jet parts also need a post-cure?

    So my latest batch of parts spent an hour under a florescent 15W flourescent UV lamp, as well as receiving a thorough cleaning. Just hit a sample part with spray can enamel primer... seems to have dried nicely and quickly, so I'll see how it looks after an overnight drying.


    Anyone else having similar issues, and/or trying DIY post cure?
     
  2. Baywing
    Baywing Member
    One thought I have is that the solvent you used for cleaning was partially absorbed by the FUD and was leaching out over time. That might explain why the solvent based paint wouldn't cure and the acrylic would. Not sure what the UV lamp would do for that other than extra time and a little heat to let any solvent evaporate out. I'd be curious to know what solvents you used and the soak times. It seems like Bestine comes up most often and from my limited experience with it, it is highly volitile which means it is not likely to leave a residue.
    Another thought is that there is still some wax leaching to the surface. I soaked a few pieces in Bestine for 24 hours and they have been sitting out for about a week and I noticed yesterday a few areas that feel a bit sticky that didn't feel that way a week a ago.
    I really wish Shapeways would step up and gives us some ideas of what works instead of making us guess.
     
  3. patmat2350
    patmat2350 Well-Known Member
    For the parts that exhibited staining of the flat acrylic paint (water based hobby paint), the FUD parts *may* have been cleaned first with paint thinner (spirits), which is pretty mild to most plastics; but definitely finished with warm water/Simple Green (an aqueous household cleaner) in an ultrasonic cleaner, followed by warm water flush and gentle brushing. Shapeways uses the same cleaner. So I doubt that anything was absorbed into the plastic... and even if it was, the paint thinner would be bad for my water based acrylic. The acrylic dried just fine, and the subsequent staining was like an oily material leaching into the paint.

    The UV post cure is standard practice for SLA parts, which also use UV cured resin. Having worked with SLA parts directly off an industrial SLA printer as well as from a Form1, I can attest to how the post cure offers further hardening and removes the surface tackiness of "green" SLA parts.
    >> I can't understand why SLA would need post cure and multi-jet wouldn't.

    If you don't have a UV lamp, try leaving your test parts out in the sun for a few hours. If the tacky spots harden up, they were due to uncured resin.

    I too would like to hear from Shapeways and/or 3D Systems about the potential need to post-cure multi-jet parts.