UV Resin deserves respect not fear
Photopolymer resin is a fantastic tool for all of our creative and functional adventures, but like most things in life, it is only good in moderation. Working with UV resin implies that we will breath some in and get a bit on us at some point in time - the goal is to just reduce this as much as practically and economically possible. Wearing nitrile gloves prevents skin contact, having the printer in the garage prevents 24/7 exposure, wearing a respirator while interacting helps protect our lungs, and properly cleaning + curing + sealing/painting prints increases handling safety.
Everything can kill us, even the thing we are made 60% of. It is important to be informed that way we can respect the world around us instead of being consumed by fear or ignorance. In my personal life, I have spent a good chunk of my time in a house with interior lead paint and exterior asbestos siding, but my lead blood levels are good and I'm asbestos-free ... I hope - kidding aside, the asbestos panels are outside the house and stable unless they are drilled into or ripped off the wall.
Uncured resin can burn your skin
Hydrolytic degradation of resin monomers like methacrylate can form acid on your skin, which decreases your local PH level and can produce adverse effects1,2,6. This, among other reactions, is why any resin that gets on your skin should be wiped off and the area immediately washed with soap and water. Do not use IPA to clean the resin off of your skin.
To prevent exposure you can wear PPE such as longer/thicker gloves, safety glasses, and clothing protection (ie: lab coat, smock, or coveralls). It is a best practice to take a shower after interacting with resin to remove any unnoticed exposure.
Cleaning with IPA or Ethanol reduces handling toxicity
It is a common practice to clean finished resin prints with a solvent such as IPA to prevent them from being sticky and doing so makes them comparably safer.
Visijet Crystal is a biocompatible resin from 3D Systems that has a USP Class VI Certification for medical applications. One study exposed zebrafish embryos to Visijet Crystal cured discs that were either unwashed or washed with Ethanol. The embryos had a ≈59% survival rate when in contact with the unwashed disc and a ≈98% survival rate for the washed disc2. Visijet Crystal was the 'safest' resin in the study as the other resins used in the study had survival rates as low as ≈24%, yet it still resulted in sublethal effects such as lethargy, behavioral changes, and physical malformations.
Zebrafish embryos are ideal for testing toxicity since we share 70% of genes, 84% of our diseases have a zebrafish counterpart, the embryos are translucent, the studies are economical, and the fish are not aware for their first 120 hours2,3.
UCL Culture, CC BY 4.0 , via Wikimedia Commons20
Activated carbon filtration is not perfect
The good news is that activated carbon is an effective tool in mitigating resin fumes, but the efficiencies are not ideal. Every chemical compound is adsorbed at a different efficiency in carbon, which is why for industrial applications it is often impregnated with chemicals tailored to raise efficiencies and holding capacity for a target compound.
We recommend using ventilation as the primary means to prevent exposure to VOCs. This means placing the printer outside the residence (ie: garage, shed, or balcony), or it can be located inside a separate and sealed room that is vented out a window, ideally with an enclosure like a grow tent. Filtration can still be used as mitigation and a secondary defense but it should not be relied upon.
|Select VOC Removal Efficiencies4|
|Compound||1 Filter||2 Filters|
|IPA||42% ±14||63% ±34|
|Acetone||55% ±15||52% ±3|
|Styrene||55% ±9||63% ±4|
|Ethyl Acetate||66% ±6||76% ±7|
||72% ±6||74% ±6
The study measuring removal efficiencies used 4 mm diameter pellets with a filter thickness of 23 mm (0.9") - 2 filters would be 46 mm (1.8")4. Larger pellets will become saturated gradually over time, while granules are sudden. This means that granules will retain their efficiency but one day they will suddenly be full - the more you print the faster this happens.
Printing at higher temperatures may release more VOCs
There is a correlation between higher printing temperatures and growing emissions5. This is an important consideration for those printing indoors. Printing at 20°C instead of 30°C provides energy savings from heating and can reduce emissions at the cost of longer print time. Keep in mind that engineering resins may call for printing temperatures of 25°C, 30°C or beyond.
Resin will release VOCs even when not printing
Resin can sit in the vat for weeks when not exposed to direct sunlight, but it will continuously offgass when not sealed. Any resin that sits dormant should be mixed, especially if it is pigmented or a concoction of budget and flexible resin.
This will be more of an issue for indoor users, but this does apply to printers in garages if people regularly use the space. A mitigation solution is to purchase or make a vat cover. The surefire way to prevent off-gassing is to put the resin back into the bottle via pouring or a baster.
Opening the enclosure and removing the printer cover releases a high concentration of pollutants
Initially, it might sound like a good idea (according to some Reddit users) to trap the fumes while printing if you do not have proper ventilation or filtration, but this releases a higher concentration of emissions all at once which can actually be an acute health hazard.
When you have the printer in the garage, it is totally fine to have it sealed in an enclosure to keep the heat in. Once you are ready to take the prints out, open up and air out the garage while wearing a respirator. If you have the printer indoors, it should be continuously ventilated to prevent buildups and leakage into the surrounding environment.
Resin can be hazardous to fetuses and children
Reproductive and developmental studies have not been conducted in humans for obvious reasons, but in animal studies, resin chemicals can cause developmental abnormalities1,2,7,8. Children and pregnant women should avoid exposure to photopolymer resin.
Plant-based resins are not safe or environmentally friendly
Plant materials such as soybean, corn, and sunflower oil can be used as resin ingredients, but vegetable oils in their natural state have a low reactivity towards photopolymerization9. Instead, the oils need to be epoxidized using a process that can include the addition of formic acid, sulfuric acid, hydrogen peroxide, sodium bicarbonate, ethyl acetate, and magnesium sulfate9,10. In the case of Anycubic's plant-based resin, the epoxidized soybean oil is only 45% of the total composition. The remaining 55% consists of higher reactivity monomers and photoinitiators which carry similar risks to standard resin.
Epoxy or vinyl ether is safer than acrylic and methacrylic based resins
The majority of MSLA resins utilize free-radical polymerization. Epoxies, vinyl ether, and propenyl ether can utilize cationic polymerization, and they are less toxic2,11,12. Some other advantages include: the ability to continue curing once the UV source has been turned off, better chemical resistance, higher HDTs, volumetric shrinkage of 2-6%, and the potential for faster curing times11,12.
The main downside is that the cationic resins are expensive for now - general (not designed for 3D printing) vinyl ether resin is ~$40 per liter. Another deal-breaker for many applications is that current blends of epoxy resin are rather brittle11. More research and development is needed in order to eventually bring commercially viable resins to market.
- 1) L. S. Andrews & John J. Clary (1986) Review of the toxicity of multifunctional acrylates, Journal of Toxicology and Environmental Health: Current Issues, 19:2, 149-164, DOI: 10.1080/15287398609530916.
- 2) Frank Alifui-Segbaya, Jasper Bowman, Alan R. White, Sony Varma, Graham J. Lieschke, Roy George, Toxicological assessment of additively manufactured methacrylates for medical devices in dentistry, Acta Biomaterialia, Volume 78, 2018, Pages 64-77, ISSN 1742-7061, https://doi.org/10.1016/j.actbio.2018.08.007.
- 3) Howe K, Clark MD, Torroja CF, Torrance J, Berthelot C, Muffato M, et al. The zebrafish reference genome sequence and its relationship to the human genome. Nature 2013; 496: 498-503.
- 4) E. Gallego, F.J. Roca, J.F. Perales, X. Guardino, Experimental evaluation of VOC removal efficiency of a coconut shell activated carbon filter for indoor air quality enhancement, Building and Environment, Volume 67, 2013, Pages 14-25, ISSN 0360-1323, https://doi.org/10.1016/j.buildenv.2013.05.003.
- 5) Yiran Yang, Lin Li, Total Volatile Organic Compound Emission Evaluation and Control for Stereolithography Additive Manufacturing Process, Journal of Cleaner Production (2017), doi: 10.1016/j.jclepro.2017.09.193.
- 6) Ali Bagheri and Jianyong Jin, Photopolymerization in 3D Printing, ACS Applied Polymer Materials 2019 1 (4), 593-611, DOI: 10.1021/acsapm.8b00165.
- 7) Dearfield KL, Millis CS, Harrington-Brock K, Doerr CL, Moore MM. Analysis of the genotoxicity of nine acrylate/methacrylate compounds in L5178Y mouse lymphoma cells. Mutagenesis. 1989 Sep;4(5):381-93. doi: 10.1093/mutage/4.5.381. PMID: 2687634.
- 8) Lin, J.S., Townsend, J.A., Humbyrd, C. et al. Is methylmethacrylate toxic during pregnancy and breastfeeding?--- a systematic review. Arthroplasty 3, 9 (2021). https://doi.org/10.1186/s42836-020-00059-z.
- 9) Diego Savio Branciforti, Simone Lazzaroni, Chiara Milanese, Marco Castiglioni, Ferdinando Auricchio, Dario Pasini, Daniele Dondi, Visible light 3D printing with epoxidized vegetable oils, Additive Manufacturing, Volume 25, 2019, Pages 317-324, ISSN 2214-8604, https://doi.org/10.1016/j.addma.2018.11.020.
- 10) Pimchanok Saithai, Jérôme Lecomte, Eric Dubreucq, Varaporn Tanrattanakul. Effects of different epoxidation methods of soybean oil on the characteristics of acrylated epoxidized soybean oil-co-poly(methyl methacrylate) copolymer. Express Polymer Letters, BME-PT Hungary, 2013, 7 (11), pp.910-924. ⟨10.3144/expresspolymlett.2013.89⟩. ⟨hal-01269361⟩.
- 11) Sangermano, Marco. "Advances in cationic photopolymerization" Pure and Applied Chemistry, vol. 84, no. 10, 2012, pp. 2089-2101. https://doi.org/10.1351/PAC-CON-12-04-11.
- 12) https://nvlpubs.nist.gov/nistpubs/SpecialPublications/NIST.SP.1500-17.pdf
- 13) A.B. Stefaniak, S Du Preez & JL Du Plessis (2021) Additive Manufacturing for Occupational Hygiene: A Comprehensive Review of Processes, Emissions, & Exposures, Journal of Toxicology and Environmental Health, Part B, 24:5, 173-222, DOI: 10.1080/10937404.2021.1936319.
- 14) https://www.osha.gov/annotated-pels/table-z-1
- 15) http://infocenter.3dsystems.com/materials/sites/default/files/sds-files/certvi/CIB%200912%20ProJet%20Class%20VI%20Cleaning%20VisiJet%20Crystal.pdf
- 16) https://infocenter.3dsystems.com/materials/sites/default/files/sds-files/professional/VisiJet_EX200/24184-S12-03-A%2CSDS%20GHS%2CEnglish%2CVisiJet%20EX%20200%20and%20M3%20Crystal.pdf
- 17) https://pacificbiolabs.com/usp-class-plastics
- 18) https://www.epa.gov/sites/production/files/2016-09/documents/methyl-methacrylate.pdf
- 19) Liu W, Mazumdar S, Zhang Z, Poussou SB, Liu J, Lin CH, Chen Q. State-of-the-art methods for studying air distributions in commercial airliner cabins. Build Environ. 2012 Jan;47:5-12. doi: 10.1016/j.buildenv.2011.07.005. Epub 2011 Jul 18. PMID:32288018; PMCID: PMC7126834.
- 20) https://commons.wikimedia.org/wiki/File:Zebrafish,_Benjamin_Lemaire.jpg
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