Nylon Reaction to Resin

[Melona]

Ill TLDR first then fuller exploration of the issues
I'm making large dolls out of Elegoo Resin, These dolls are setup to use Mega-blocks Struxx Nylon joints. Some of the Ends of the Struxx are sort of melting. I was wondering how and if anyone has seem such issues?

Hi I'm Melona, English is not my best language,,,

I love my Elegoo Mars printer, I have even secured a Saturn, My Mars ran non stop for over 6 months strait!! except for repairs, 7 fep sheets on 3 vats and 6 lcd screens later I really like printing figures at very large scales I even occasionally sell some to make affording printer supplies and resin easier.
I starting making some BJD's they are pretty cool but I hate the strings so I got to work finding a alternative. Struxx are a ball joint toy made by Mega-blocks with some careful measuring I made a "3d model of these joints" a plug to use in some select dolls, the dolls are made 4 of them now and after being together for about a week to 10 days, standing up one of the dolls fell over the joint had given way it was gooey and gross so I popped out all the joints in that doll to find about half of them has this sort of melting nylon im pretty sure struxx is nylon, I went in with a Qtip and 91% to be sure no left over uncured resin was present and focused the light down these holes for about a half hour this seemed to clear it up,,, well at first.

I then let dry some more and got the doll back together and for the most part the problem seemed gone, I set aside the doll and left her sit for 2 weeks and pulled all the joints to my dismay a very select few of them look melty again. The first doll I made was solid and the joints manually drilled she didnt have the same problem? But this newer high tech doll did, I pulled apart the other 2 and one of them only had the problem in 2 joints the other was fine, all where printed in skin color. I printed a different doll in white and had the same issue.

I really want my dolls to work I wonder what i can do to better cure the resin down the holes or what better cleaning method after many washings and recuring the issue seems to be slowly going away. I cant know about the longevity of these dolls. I would like to sell some cause they are awesome 1/3 scale dolls, but they got to be right first.

Is the Nylon just not compatible with cured resin?
Is there a better way to cure deep in parts?
Will a added layer of spray paint or sealer help?
Anyone else had anything similar happen?

Im thinking of trying water curing the parts i have heard that can help

Settings
initial layer 60 seconds
layers 8 seconds
Clean model with Mean green and 91% as needed

[cliffyk]

Are you doing any post-printing curing?  Formlabs has a great white paper reporting their experiments using a 10 W 405 nm lamp for final curing. They found that it took 60 minutes exposure to that light source to achieve full curing and optimal mechanical properties.

I have found, using the 30 W 405 nm curing chamber I made from an old microwave oven, that it takes 25 to 35 minutes to fully cure a printed model.

It may well be that until such a full cure has been attained the epoxy acrylate resins retain some characteristic to which nylon is susceptible?

[Melona]

Are you doing any post-printing curing?  Formlabs has a great white paper reporting their experiments using a 10 W 405 nm lamp for final curing. They found that it took 60 minutes exposure to that light source to achieve full curing and optimal mechanical properties.

I have found, using the 30 W 405 nm curing chamber I made from an old microwave oven, that it takes 25 to 35 minutes to fully cure a printed model.

It may well be that until such a full cure has been attained the epoxy acrylate resins retain some characteristic to which nylon is susceptible?

I do think the nylon is reacting to uncured resin, but how to cure down a hole?
I did buy a probable solution more on that in a second,,,

I did forget to mention that I have 2 , 36 watt Nail Drying stations that are linked together for a total of 72 watts of UV 405nM so * 8bulbs at 9 watts each, It will cure a small pieces in under 5 minutes but i usually leave larger peices in for 30 minutes or so, I have re-baked these parts a few times with the holes right up the light.

I might have found a way to ensure the inside holes are cured. 3mm 12v UV LED's they are not as powerful as a cure chamber but i can shove them down in the holes for extended periods they can stay down in the holes for a hour or so each. They come in a 30 pack so i could do a whole model at once. Its hard to know just the nm of the lights (but they are UV) but for 7 bucks i will try them. beats throwing away a hundred bucks in resin.

[cliffyk]

Having 405 nm light (which is not really UV) for curing is important, the Formlabs testing included 365 and 385 nm (which are UV) and found neither to work as well as 405 nm light--which makes sense as the photo initiators selected for use in these resins are intended to be activated by 405 nm light,

[Melona]

Ok i got a answer on the leds and the company said they are between 385 and 395 which is close, I think they will work better than doing nothing, or trying to make light go around corners. i will report back for sure tho it might take some time to know.

[cliffyk]

Do you know what wavelength light your nail drying stations actually emit? A very brief web search indicated that many operate at 365 to 385 nm--too short to properly cure 405 nm rated SLA resin.

Have you tried 8-10 hours exposure to direct sunlight?

[Melona]

well i live in Central Florida and anyone whom has visited Disney mid summer can tell you "Sunlight is something we excel at having" I try not to leave the Models in the Sun, I'm pretty sure the driers I got said they where 405 but I cant go back to the page as the model I have where discontinued. They did claim you should wear gloves if you are to place your hands under the light which I can attest that it is painful to the skin to have your hands in this light for more than a few moments. and looking at the bulbs is something I would advise against strongly. it looks like replacement bulbs do normally run at 365 but it seems i can get 405NM bulbs also but they are LED not glass tube style. I know i can get fishtank bulbs at different wave lengths that are meant to kill bacteria and allege cause i have some UV filters on my fishs set up. This could be worth looking into ... If its anything i can cure nearly instantly any broken part by painting a bit of resin onto the broken area , hold the parts together and exposing them for 5 to 6 seconds and it will be dry and sandable. But I dont think i have any way to test the wave frequency,,, at least i dont think i do.

PS I do wear black rubber gloves and eye protection when working with those lights and resin.

[cliffyk]

well i live in Central Florida and anyone whom has visited Disney mid summer can tell you "Sunlight is something we excel at having" I try not to leave the Models in the Sun, I'm pretty sure the driers I got said they where 405 but I cant go back to the page as the model I have where discontinued. They did claim you should wear gloves if you are to place your hands under the light which I can attest that it is painful to the skin to have your hands in this light for more than a few moments. and looking at the bulbs is something I would advise against strongly. it looks like replacement bulbs do normally run at 365 but it seems i can get 405NM bulbs also but they are LED not glass tube style. I know i can get fishtank bulbs at different wave lengths that are meant to kill bacteria and allege cause i have some UV filters on my fishs set up. This could be worth looking into ... If its anything i can cure nearly instantly any broken part by painting a bit of resin onto the broken area , hold the parts together and exposing them for 5 to 6 seconds and it will be dry and sandable. But I dont think i have any way to test the wave frequency,,, at least i dont think i do.

PS I do wear black rubber gloves and eye protection when working with those lights and resin.

Hello, I am in Saint Augustine we've got that same sun;

Your comments re: the nature of the light lead me to believe it is of a wavelength shorter than 405 nm, real UV in the 365 to 375 nm range. 405 nm "UV" is really just relatively harmless very deep purple (violet) visible light.

I suspect it was specifically chosen for consumer-grade 3D printers because of it's fundamentally docile nature-photo-initiators are available in many "flavours".

I am a mechanical engineer (MSME MIT '71), not a chemist, however it is again not inconceivable that using real UV could cause chemical reactions making the resin attack the nylon--deep UV can be scary crap. The Formlabs people would know I'll see if I can get some info from them...

[cliffyk]

Are you certain the Struxx components are Nylon? That would be just about the most expensive material from which to mold something like that...

[Melona]

Cliffyk you are right i found this quote "MEGA Brands use injection-molded ABS" not nylon but yes indeed the uncured product eats the ABS. I dont know why I was under the impression Legos and Megablocks where nylon but now I know.

I got in 30 long pre-wired and pre-caped UV LEDS that are 395-400nm I stripped, soldiered and put them onto a molex to all plug into a 12v source and I printed a new set of parts lightly cleaned and cured, without really putting attention to the holes like i did before, then put the LEDs into the many orifices that the Megablocks go into. I let them cure this way for 2 hours. I left the parts in overnight and they dont seem melty at all. now i just sit and wait for a few days to see the outcome.

I still find it curious that the resin has such a bad reaction to ABS when in such little uncured quantity.

Ive been to Saint Augustine about 3 years ago it was fun we went on the haunted trolley super golf cart train thing. Visited Ripley's and the Fort.
There is alot of history packed into much a small area , I hope your summer has not been as hot as ours.
I live very close to Cocoa Beach area ,its fun living so close to so much fun things I cant wait till the kids all grow up so I can go do more of that!

I tested the UV LEDS at 3v , 7.4v , 9v , and 12v. They only run at full brightness on the 12V source, the package says they are 9-12 volt but 9v didnt seem to push them quite hard enough, this makes me happy because they are not just 3-5v lights with caps but rather a fairly serious and bright LED that uses the voltage pushed to them. I feel like this will be the trick.

And lastly I know real UV is bad stuff (for eyeballs and bacteria) Im not got any Applied Science Degrees but i have always pursued science, I study Astrology and have a dove unusually deep into Quantum Sciences , and have a good rounded base on general science and biology, at least as good as self taught. Its always funny when my college bound kids ask me very complex questions...

Anyhow ill report back in a day or 2 to see if its just uncured resin or the dry stuff or if my lights didnt work.
I did try Underwater UV Curing also and ill report on it next time (hint hint it does seem to work also) but I now need time to find out.