Fine Detail Plastic Crystallization Formation

Discussion in 'Finishing Techniques' started by Model_Monkey, Dec 5, 2016.

  1. Model_Monkey
    Model_Monkey Well-Known Member
    A customer (Mark) who has much experience with FUD and FXD products recently sent me this message:

    "I moved from Wisconsin to Arizona in July. My stuff sat in a warehouse for about 3 months. When I unpacked my Pennsylvania stuff [3D-printed models for the battleship USS Pennsylvania] I noticed that the 3D printed stuff had formed a light crystal like surface. I managed to brush a lot of it off and with light airbrushing I should be able to cover almost all if it. I did clean the stuff pretty good and let it cure. Have you had any experience with this?"

    I have not heard of this happening before. Do any of you have any thoughts about crystals forming on top of paint some time after painting?

    Here's the advice I provide to customers with each product description and Mark has followed this advice to good effect on other products in the past without any crystalline surface problems occurring:

    "Some part cleanup will be necessary. During the 3D printing process, a waxy substance is used to support certain part features. Although the parts are cleaned by Shapeways afterwards, some waxy residue may remain. It can be safely removed with water and a mild aqueous detergent like “Dawn” dishwashing detergent, baby shampoo (no conditioner) or "Simple Green" using an old, soft toothbrush, Q-tips or pipe cleaners.

    During the printing process, liquid resin is cured by ultraviolet light. Microscopic bits of resin may remain uncured. Let your parts sit in direct sunlight for a few hours to fully cure the resin before painting.

    Once your parts are fully cured, if desired, careful use of an inexpensive “air eraser” emitting common household baking soda can help smooth surfaces and remove any unwanted “frost”. Similar to an airbrush but much cheaper, air erasers can be found on Amazon.com. Models by Harbor Freight and Paasche are popular.

    Water-based acrylic paints meant for plastics is strongly recommended. Other paints, especially enamels, may not cure on Frosted Detail 3D-printed plastics."*


    *Some forms of liquid resin naturally harden very quickly. To keep those resins in a liquid state so that they can extruded by a 3D printer, a chemical inhibitor is added to the resin at the factory. UV light destroys the inhibitor allowing the resin to naturally harden. The inhibitor can also prevent enamel paint from hardening. Post-curing the model by exposing it to UV light before painting can prevent problems with enamel paints.
     
    Last edited: Dec 25, 2018
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  2. Shea_Design
    Shea_Design Well-Known Member
    I have a pretty big part here ($700 2pcs) that I wet sanded to near perfection and then let sit for about a year now. A few days ago I also noticed what looked like crystals, not on the surface but sparkly in some areas, I can not feel them and nothing transfers to my finger so it is more like a subsurface metal flake effect. I also discovered that there is some goo gone in the garage, I will probably use that not to clean the surface but to make the part opaque as I understand it has that effect. -S
     
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  3. Model_Monkey
    Model_Monkey Well-Known Member
    Thanks for your description! The crystals you noticed on the inside of the parts is very interesting. I hope that we are not seeing a breakdown of the plastic over time. If, like concrete, the plastic is further hardening over time, that would be great, but a breakdown, not so much.

    Please let me know how the Goo Gone works for you.

    Cheers!
     
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  4. he6agon
    he6agon Well-Known Member
    I get the metallic sparkly stuff on several of my parts after a few weeks of storage. I have daughters so I thought the glittery stuff was their doing at first, but after keeping the parts stored in closed containers and seeing the sparkles come out again, I figure it must be from the plastic. I simply brush it off and wait for it to reappear.

    It's worth mentioning that all these parts are FUD, were all cleaned with either acetone, Simple Green or a combination of the two, and have all been painted with various brands of enamel paints.

    I hope the plastic is not failing, but I am afraid that is the case. If so, it is a serious problem. I have a lot of money tied up in these parts for them to only be temporary.
     
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  5. Andrewsimonthomas
    Andrewsimonthomas Well-Known Member
    Can you guys share some images of what they look like?
     
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  6. Model_Monkey
    Model_Monkey Well-Known Member
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  7. Model_Monkey
    Model_Monkey Well-Known Member
    Mark (the customer) sent the following photo. The paint he used was Tamiya Acrylics thinned with Methyl Ethyl Ketone, (MEK). Mark reports that there was no adverse affect to the material and the paint dried quickly with good sticking properties. The crystal shows up clearly against the Tamiya "XF-24 Dark Gray" acrylic.

    He used the same paint on injection-molded polystyrene parts that shared storage with the FUD part you see below (the very light gray tripod mast parts you see at the very top in the photo are polystyrene and the railings are brass). No crystalline powder formed on the Tamiya-painted polystyrene or their brass details, just the FUD parts.

    Crystals.jpg
     
    Last edited: Dec 7, 2016
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  8. mkroeker
    mkroeker Well-Known Member
    I imagine it would be important to know if these "crystals" are also observed on untreated parts - MEK being "acetone's big brother" this could be the same effect (chemical corrosion of the acrylic?) that turns FUD parts white and fuzzy after prolonged solvent exposure (recommended by some here to make it easier to apply paint apparently). Note the MEK may
    even be the active ingredient of the "acetone-free nail polish remover" implicated in this very similar old thread:
    https://www.shapeways.com/forum/t/crystalline-corrosion-on-fd-fud-and-fxd.29505/#post-125009
     
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  9. Model_Monkey
    Model_Monkey Well-Known Member
    Excellent feedback. Sounds like MEK is the culprit. There was no crystalline formation on the polystyrene or brass and other modelers using water or alcohol as a thinner for acrylic paint are not experiencing the crystal powder formation.

    Since frosted detail plastics are new to most of us, modelers are using finishing techniques successful with polystyrene not knowing acrylic plastic has different characteristics and vulnerabilities.

    Simon,

    Can Shapeways include some finishing advice with frosted detail products when they ship? Perhaps posting some advice as part of the material description for frosted detail plastics on the Shapeways website may be helpful.

    Here's the advice I now offer customers. You might find something appropriate within the following:

    "Cleaning your parts: during the 3D printing process, a waxy substance is used to support certain part features. Although the parts are cleaned by Shapeways afterwards, some waxy residue may remain. It can be safely removed with water and a mild water-based detergent like "Dawn" dishwashing detergent, baby shampoo (no conditioner), or "Simple Green" using an old, soft toothbrush, Q-tips or pipe cleaners. Do NOT use any cleaner containing acetone, acetate or thinner containing methyl ethel ketone (MEK). Acetone will attack acrylic plastic and damage it.

    "Curing and smoothing surfaces: during the "Frosted Detail" printing process, liquid resin is cured by ultraviolet light. Microscopic bits of resin may remain uncured. Let your parts sit in direct sunlight or under a UV or fluorescent lamp for a few hours to fully cure the resin. After your parts have fully cured, if desired, careful use of an inexpensive "air eraser" emitting common household baking soda can help smooth surfaces of Frosted Detail parts and remove any unwanted "frost" without harming detail. An air eraser, like an airbrush but much cheaper, can be found on Amazon.com. Models by Harbor Freight and Paasche are popular.

    "Primer and painting: for primer on "Frosted Detail" acrylic plastic, Tamiya "fine gray" is a good choice. Only acrylic paints meant for plastic are recommended. Enamel paint may not harden on "Frosted Detail" plastic. For "Strong and Flexible" products, a kind of nylon, only primers and paints intended specifically for use on nylon should be used. Other hobby paints may not adhere. Simply Google "primer for nylon" and "paint for nylon" for several good choices. Do NOT use any cleaner containing acetone, acetate or thinner containing methyl ethel ketone (MEK). Acetone will attack acrylic plastic and damage it."
     
    Last edited: Dec 22, 2018
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  10. stannum
    stannum Well-Known Member
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  11. Model_Monkey
    Model_Monkey Well-Known Member
    The more I learn about MEK the less I like it.
     
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  12. he6agon
    he6agon Well-Known Member
    I am not using MEK to clean my parts and I get the powder. I use Simple Green, typically a two or three minute soak followed by a scrub with Dawn detergent and a rinse of cool water. Then I prime and paint the parts using Testors enamels or Tamiya primer then enamels.
     
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  13. mkroeker
    mkroeker Well-Known Member
    That would appear to still leave the solvents used in the enamels as a possible culprit - pulling up a few MSDS at random from http://www.testors.com/product-catalog/testors-brands/testors/enamel-paint/enamel-paints shows mainly "Stoddard solvent" (mineral spirit/white spirit - compare the effects of heptane/Bestine) and some (e.g. their "Sky Blue") also have "solvent naphtha", i.e. an ugly mix of benzene and naphthalene derivatives. Do you see any correlation between paint color and crystal formation ?
    And anybody here seeing "crystals" on parts painted with acrylic paint (and not using suspicious thinners) ?
     
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  14. he6agon
    he6agon Well-Known Member
    I haven't noticed any difference between colors, although the appearance of the crystals is exaggerated on dark colors. The iridescent nature of the crystals makes them visible on any background once light hits them. I don't have any examples to show right now since I've recently cleaned the models. I have a few primer gray parts that have the crystals, but I'll have to wait to take photos in the sun.

    I haven't used any acrylic paints, but I'd be willing to try an acrylic primer if one is available that is comparable to Tamiya primer in thickness and ease of application.
     
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  15. stannum
    stannum Well-Known Member
    Badger, Vallejo, Ammo Mig and others have water based primers. Tamiya, Gunze or MrHobby also have alcohol acrylics and some just use them directly. Airbrush recommended for all.
     
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  16. Model_Monkey
    Model_Monkey Well-Known Member
    Customers report no problems of any kind when using acrylic paints over an acrylic primer.

    I've used Testors "Polly Scale" acrylic paint over bare FUD plastic (no primer) and have no problems.

    Looks like Bestine (heptane) may be a problem, too.
     
    Last edited: Dec 14, 2016
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  17. he6agon
    he6agon Well-Known Member
    Sounds like I need to go shopping for new primer.
     
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  18. sbhunterca
    sbhunterca Well-Known Member
    I've never had this problem using acrylic model railroad paints airbrushed on, often without primer if the colour is dark.

    I clean my parts with Simple Green, followed by a quick rinse in warm clean water and a dip in 95% isopropyl alcohol, air dried.

    Could it be related to the enamel paint?

    Steve Hunter
     
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  19. he6agon
    he6agon Well-Known Member
    I'm guessing it must be the case, Steve. It sounds like it's the only difference between how you and I finish our parts. I wonder if Future would be a strong enough barrier between the acrylic and any paints that go on over it. If not, I'd like to see how some different acrylic primers work. Thirty years of airbrushing enamels without issue (until now) makes me hesitant to change, but if the material requires a change I'll give it a go.
     
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  20. Model_Monkey
    Model_Monkey Well-Known Member
    A customer posted this today, the same frosting occurred, but he experienced this with acrylic paints and had success with enamels. Although this customer is confident in enamels, nearly all others have had terrible experiences with them. Another customer followed exactly the same procedure this customer had success with (automotive primer followed by enamels) and ended up with non-hardened enamel that ruined the parts. I'm befuddled and more customers are becoming concerned. With conflicting solutions and increasingly uncertain causes, I fear sales are increasingly at risk. Here's his post from a forum on ModelWarships.com:

    "On a recent build (1941 Pennsy) using ModelMonkey's Super structure set in 1/350, I had the same "frosting" problems others have spoke of.

    "I had washed the parts with Simple Green in an ultra-sonic cleaner and placed it in window sill for 2 days and then airbrushed it with acrylics. The frosting showed up within days of being painted. My thinner was Water.

    "I then proceeded to strip the parts with goo-gone in the ultra-sonic cleaner and afterwards shot the parts with automotive primer and then Airbrushed with Enamels..

    "The paint dried in about 24 hours and so far has shown NO signs of Frosting. It's been a couple months now and still it shows no sign of Frosting. Yes the Enamel dried over the Primer.

    "I also had purchased the "Z" vents and crane assemblies for the same build and had absolutely NO problems at all with Frosting?

    "Maybe my Simple Green solution was too strong?

    "Maybe I didnt rinse it sufficiently?
    "Maybe as has been said there is a chemical residue in the Plastic itself?

    "The technology is still fairly new and am sure the process will only improve as time goes on and I will keep making purchases of Printed Parts. I will keep implementing work-a rounds like I did with the "Enamels" that are not supposed to work.

    "So I want to give a shout out to all the guys here who are involved in this new medium...well done and Many Thanks to you [​IMG]"
     
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