White nylon yellowing?

Discussion in 'General Discussion' started by tempusr94720_c557488ae6c, Nov 28, 2011.

  1. The subject more or less describes the problem.

    The white nylon inevitably turns yellow as time passes.

    Why does it happen? Exposure to sunlight? Exposure to the air? body oils? Why?

    How can it be prevented? I was thinking about putting a thin urethane coating over the part. Would this help to seal the nylon, and make it so it does not turn yellow?
     
  2. nervoussystem
    nervoussystem New Member
    exposure to UV light

    an anti-UV clear coat will prevent yellowing
     
    Creators_at_Heart likes this.
  3. Hey Nervoussystem,

    Thanks for the info!

    Do you know of any anti-UV clear coats that are on the market?

    What is the best way to apply the coating? Spray gun, paintbrush, dipping in a bucket of the coating?

    Thanks!
     
  4. roofoo
    roofoo Well-Known Member
  5. stannum
    stannum Well-Known Member
    Artist acrylic varnish will do, ask in art shops for the pots/bottles (Winsor, Liquitex, Vallejo, etc). First coat, water it down a bit more than normal, then dip in it and the material will drink it. Use a plate and a brush, no need to buy a bucket of varnish to give it a bath. Other layers can be applied with paintbrush or airbrush.

    White paint will also work, and can give you a stronger white, but reduce the translucency. Or any other acrylic color, if you want.
     
  6. Wow guys, thanks so much. This was extremely helpful.

    Do these coatings help to waterproof your parts and make them more resistant to getting dirty?

    Also, do they help to take away the abrasiveness of the material? As I'm sure you know, the SLS white (strong and flex) has a "grain" to it. This can be a little abrasive on the skin. I'm making a wearable product, so this can be a bit of a problem. Do you think if I added enough coats of the acrylic varnish it would help to smooth out the grain?
     
  7. roofoo
    roofoo Well-Known Member
    The floor wax won't smooth the model's texture. For that I would recommend getting Shapeways WSF polished material. Not sure about the varnish.
     
    Last edited: Nov 29, 2011
  8. stannum
    stannum Well-Known Member
    Yes, they will become watertight and stay clean, as you are filling the pores with the first coat(s) and then building an outer shell. If you apply a thick enough protection, the sandy texture will fade (as well as any fine detail). You can look up in one recent post in which someone used glue to achieve a similar result than with acrylic varnishes.

    You can just order WSFP if you want to save some time with the smoothing steps, as roofoo suggests, but you will need to coat it anyway to avoid the yellowing problem. Remember to wash WSFP perfectly, someone else has complained about paint not sticking (the polishing uses soap).
     
  9. Creators_at_Heart
    Creators_at_Heart New Member
  10. mkroeker
    mkroeker Well-Known Member
    Unfortunately that trick is not likely to work - note the article talks about restoring ABS material where the discoloration is (said to be) from traces of bromine released by fire-retardant additives. Shapeways' strong&flexible is Nylon, where a different reaction within the base material results in formation of trace amounts of an intensely yellow dye bonded to the nylon chains. (BTW that reaction is accelerated by heat or UV, but will occur in moderately lit and heated environments as well, just slower. Nylon switch plates in older houses are a typical example, though the problem may become apparent only when the surrounding paint or wallpaper is renewed)
     
    Last edited: Mar 29, 2017
  11. weijiazh
    weijiazh Member
    if I put the print in my office, not under direct sunlight, will it turn yellow anyway?
     
  12. mkroeker
    mkroeker Well-Known Member
    Yes, but it will take a couple of months or even years to become noticeable (easiest to see when you put a brand new print beside it, i think a few years back someone posted an anatomical model of a human skull where he had only been able to afford printing the lower yaw at first and managed to order the main part a year later). As noted above, the problem becomes invisible when you paint the model with standard acrylic paints (which will also serve to smooth out and seal the somewhat rough and porous surface of the sintered material).