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I needed to know if typical UV curing resins, such as the ones from Anycubic, can withstand solar radiation over extended periods of time with little to no degradation. It has been quite difficult to find information about the subject online, so I'm wondering whether anyone here has experience here to share.

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  • $\begingroup$ Are you asking about the stability of cured or uncured resin? $\endgroup$
    – Caleb
    Mar 3 at 22:50
  • $\begingroup$ cured resin of course $\endgroup$
    – diegogmx
    Mar 4 at 10:17
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Yes, it is actually pretty hard to find that information. First thing is that the resin never stops curing. Additional exposure to UV will continue to degrade the material over time. This is true of even plastics (and human flesh), however, in the case of UV resins we're talking about years not weeks. Each manufacturer of resin, even from different batches, will exhibit different performance characteristics with their formulation. As a general rule of thumb resin prints should not be used as an end product. They are used to either create a mould for the final object or used as a fitness test where the dimensions and tolerances are tight. The cured resin is typically not 100% safe to handle, and as such should not be used on bare skin or inside the human body or as any form of eating or cooking utensil. Colour degradation of resins (they become cloudy) will also occur for resins that were once colourless.

EDIT: (Didn't want to expand this but it seems I have to) Companies that release 3d printed with branded resins have custom formulas to match their printers. This is perhaps to ensure that the customer keeps coming back for the consumables. These custom formulations are most undoubtedly patented, however, it seems that they are keeping the formula a secret (until you reproduce it and they claim you've breached their patent). Due to the fact that the formula is unknown to the end-user no one can certify that the cured resin is 100% non-toxic and safe for contact with skin; either on the outside of the body or the inside ;) Speciality dental adhesives have different formulas (and are perhaps more expensive than) 3d printing resins.

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    $\begingroup$ Do you have a reference for your "cured resin is typically not 100% safe to handle" claim? I have seen plenty of information about uncured resin, but nobody saying that finished prints were in any way unsafe to touch. $\endgroup$
    – Tal
    Mar 3 at 18:44
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    $\begingroup$ the resin will stop curing once there is no photoactive monomer left. But before that point, other spectrums of the UV will start to break polymer bonds, especially in the color molecules, which can degrade the plastic. Those are different processes. $\endgroup$
    – Trish
    Mar 3 at 21:24
  • $\begingroup$ Nope, no references. There is simply no way I can find that dude's video after so many years. $\endgroup$
    – user77232
    Mar 4 at 3:55
  • $\begingroup$ UV-cured polymers are used in dentistry as fillings, sealants, and glue, and the dentists seem to feel that it’s 100% safe for contact and that it’s completely cured after about 60 seconds of intense UV exposure. Those compounds aren’t printing resin, but they’re probably work the same way. Without some reference to an authoritative source your answer based on an unknown, years-old video isn’t very convincing. $\endgroup$
    – Caleb
    Mar 4 at 14:07
  • $\begingroup$ Well, that's a -1 from me. Saying that fully-cured resin isn't safe for skin contact is just fearmongering, and bad info, unless you can find some kind of useful reference about it. $\endgroup$
    – Tal
    Mar 4 at 18:03
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What seems to be a difficulty is the stabilizers for plastic absorb UV. So if added to UV resin, they probably greatly increase the exposure time needed.

The following show characteristics of some plastics, taken from https://www.coleparmer.com/tech-article/uv-properties-of-plastics

Unmodified types of plastics that are regarded as having unacceptable resistance to UV are POM (Acetal), PC, ABS and PA6/6. Other plastics such as PET, PP, HDPE, PA12, PA11, PA6, PES, PPO, PBT and PPO are regarded as fair. Note that a PC/ABS alloy is also graded as fair. Good resistance to ultraviolet rays can be achieved from polymers extruded by Zeus such as PTFE, PVDF, FEP, and PEEKTM. The only plastics found with excellent resistance are the imides, Polyimide (PI) as used in the Hubble Space Telescope and Polyetherimide (PEI).

PTFE has particularly good UV resistance because of its very strong carbon- fluorine (C-F) bond [almost 30% higher than the carbon-hydrogen (C-H) bond], which is the common side bond that surrounds the carbon (C-C) backbone in a helix and protects it. Most fluoropolymers also do not have the light absorbing chromophore impurities in their structure that can act as an initiator for photo-oxidation.

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Sunlight contains the full spectrum of electromagnetic radiation, including the wavelength to photoinitiate your resin. Most UV-curable materials are kept in opaque containers for this reason. The extent to which your material is crosslinked will depend on your material and how much sunlight it receives.

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