Every thing You All the time Needed to Know About Resins and Security SLA Printing (However Had been Afraid to Ask)


At present, we’re celebrating an anniversary – it has been precisely one yr since we launched our first SLA resin! Thus far, we’ve got launched Prusament Resin Robust, a cloth completely appropriate for terribly quick, detailed and dependable 3D printing of visible fashions similar to motion figures, busts, prototypes, casting molds, and so on. With the launch of our first resin, security was the best precedence together with extraordinarily excessive reactivity and determination. Nevertheless, we really feel that resin issues of safety should not careworn sufficient among the many customers and we wish to tackle the problems similar to: What are stereolithographic resins, what are their well being hazards and what may be accomplished to extend security?

With this text, we take our probability to enlighten you on some critically necessary facets. Additionally, you’ll be able to take a look at some great benefits of utilizing our resins over the competitors’s.

A little bit little bit of chemistry in the beginning

First, we have to make clear some primary chemical ideas of how stereolithography resins really work and what their composition is. This temporary lecture is important to completely perceive the problems we’re addressing not solely on this article but in addition throughout your work with the resin. Buckle up, right here comes the chemistry.

The most typical chemical mechanism for the solidification of liquid stereolithography resin into strong objects is a course of known as radical photopolymerization which is triggered by gentle of a sure wavelength penetrating into the resin by the LCD. After the sunshine absorption by photoinitiator molecules, initiating species are fashioned. These species are known as radicals and provoke chain progress polymerization through attacking the double bonds in monomer molecules. In consequent reactions, monomers are linked collectively by the double bonds forming the polymer community and strong objects (schematically depicted in Fig. 1). This course of is repeated layer by layer throughout 3D printing. The most typical and essentially the most reactive monomers may be discovered among the many acrylates, methacrylates, or acrylamides. Varied photopolymer constructions are fashioned primarily based on the variety of reactive teams per monomer molecule, from linear photopolymer chains to densely cross-linked photopolymer networks. The group of probably used photoinitiators is equally intensive and their description is past the aim of this text.

Fig. 1: Schematic depiction of chain progress photopolymerization

Whereas monomers and photoinitiators contribute primarily to reactivity, mechanical properties and toxicology, resins additionally comprise different necessary chemical parts similar to pigments or dyes, fillers, stabilizers and components required for general efficiency. These parts should be completely balanced. In our uncooked supplies selecting course of, three major standards should be met to be able to introduce a high quality product: extraordinarily excessive reactivity of the resin, appropriate mechanical properties which you’re in search of, and lowest potential toxicity.

Well being hazards of the stereolithography resins

To acquire just a little notion about resin toxicity, we introduce you to a system known as Globally Harmonized System of Classification and Labelling of Chemical substances (GHS) which covers the classification of the chemical substances substances and mixtures, common warning pictograms, and harmonized security information sheets. Pictograms beneath needs to be the primary signal of the resin hazard and visibly labeled on the bottle on your warning. Whereas a few of the pictograms may be irrelevant for the stereolithography resins, similar to GHS01 or GHS04, the remainder would possibly seem on frequent resins.

GHS01
Explosive

GHS02
Flammable

GHS03
Oxidizing

GHS04
Compressed fuel

GHS05
Corrosive

GHS06
Poisonous

GHS07
Dangerous

GHS08
Well being Hazard

GHS09
Environmental Hazard

It must be careworn that resin hazard classification relies on the substances used and their concentrations. And be aware that the hazard of the liquid resin is often greater than the hazard of the printed and post-cured resin. A whole listing of Hazard (Bodily, Well being and Environmental) may be discovered right here whereas Precautionary statements may be discovered right here. Security information sheets additional outline an inventory of hazards and precautions on your resin.

A few of the typical suspects

Stereolithography resin may comprise a lot of harmful chemical substances. On your precaution and warning, we’ve got picked a few of the commonest chemical substances posing a threat to human well being. Word that the next chemical substances are being utilized in powerful resins regularly so it may be time to begin paying very shut consideration to security information sheets and secure resin dealing with!

Colorless photoinitiator

Diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide or TPO is a generally used photoinitiator for its distinctive mixture of excessive reactivity at 405 nm wavelengths and its capability to create colorless to off-white formulations. Whereas different photoinitiators at 405 nm trigger important yellow colour or undergo from low reactivity, this substance is abundantly utilized in clear, white, blue, grey, beige, or pink-colored resins (gentle and chilly shades). Regardless of the advantages, the substance is suspected of damaging fertility, it might harm fertility or have an effect on unborn kids (ECHA) and its presence needs to be said within the SDS. Evaluation of assorted commercially obtainable resins (primarily from China) through UV/VIS absorption signifies the presence of the substance within the resin whereas SDS didn’t state the substance. We’re engaged on intensive analysis to exchange this substance whereas getting related and even higher properties.

 

Diphenyl(2,4,6-trimethylbenzoyl)-phosphine oxide

 

H317 – Might trigger an allergic pores and skin response.

H361f – Suspected of damaging fertility.

H411 – Poisonous to aquatic life with long-lasting results.

Ultrastrong and ultrafast monomer

4-Acryloylmorpholine is used as a result of its wonderful mechanical robustness and intensely excessive reactivity. The substance’s drawbacks may be worse toxicology and attribute and unsightly odor. For us, these facets decide the utilization of this substance solely in particular, high-performance resins, primarily for engineering purposes.

4-Acryloylmorpholine

H302 – Dangerous if swallowed.

H317 – Might trigger an allergic pores and skin response.

H318 – Causes severe eye harm.

H373 – Might trigger harm to organs by
extended or repeated publicity.

Robust and quick monomers with some points

Poly(ethylene glycol) diacrylates are wonderful monomers for his or her flexibility, toughness, low viscosity and excessive reactivity. The properties may be tuned by the size of the polyethylene glycol unit. Sadly, the group of those chemical substances causes severe eye harm when uncovered to the substance. This leads to the classification of the substance as H318 (Severe eye harm – Class 1), which additionally signifies that the substance and consequently the resin will get a label GHS05 – Corrosive. And we don’t like that.

Poly(ethylene glycol) diacrylate

 

H315 – Causes pores and skin irritation.

H317 – Might trigger an allergic pores and skin response.

H318 – Causes severe eye harm.

An industrial commonplace with a controversial construction

There are numerous chemical constructions of bisphenols however the commonest is Bisphenol A. Typically, there are lots of sorts of Bisphenols and these could harm fertility, disrupt human and animal hormonal methods or trigger pores and skin allergic reactions in the event that they‘re in molecular type. In flip, the European Union included Bisphenol A amongst substances of very excessive concern.

The scenario for Bisphenol A monomers with double bonds similar to acrylate or methacrylates certain to it may be just a little totally different when in comparison with single molecular Bisphenols. These monomers often don’t pose well being dangers based on their Security Information Sheets. In reality, these monomers are industrial requirements or workhorses utilized in multi-purpose resin similar to dental filling or stereolithography purposes as a result of their excessive reactivity and mechanical robustness and their toxicology hazard may be questionable. For instance, Bisphenol A may be discovered additionally in thermoplastics similar to PC (Polycarbonate).

The final pattern is to keep away from such substances to lower any potential well being threat – in order that’s what we do. Possibly you may have observed merchandise of day by day use with a labeling Bisphenol A Free (BPA Free) and it’s one thing we are able to put our resins, too. You’ll be able to learn this ECHA article for more information about Bisphenol issues.

Bisphenol A

H317 – Might trigger an allergic pores and skin response.

H318 – Causes severe eye harm.

H335 – Might trigger respiratory irritation.

H360F – Might harm fertility.

H411 – Poisonous to aquatic life with long-lasting results.

Ethoxylated bisphenol A diacrylate

H315 – Causes pores and skin irritation.

H317 – Might trigger an allergic pores and skin response.

H319 – Causes severe eye irritation.

H335 – Might trigger respiratory irritation.

Our method

Common technique of our Pruscientists is to keep away from harmful substances, scale back the hazards and develop resins with low toxicological hazards with out sacrificing printing high quality and reliability. We expect that that is an particularly necessary rule for formulations of the resins for pastime, sculpting, quick and dependable prototyping usages, similar to our Prusament Resin Robust sequence. In different phrases, resins with excessive publicity of shoppers to liquid or cured type and for purposes that don’t require ultra-high mechanical efficiency needs to be made as secure as potential. On this case, the worst accepted classification for our Prusament Resin Robust is GHS07 or GHS09 that are nearly not possible to be averted for the ultimate resin formulation.

The utilization of extra harmful substances may be reasoned solely when there is no such thing as a different chemical counterpart and there’s merely no manner round primarily with regard to properties, for instance for high-performance resins.

Now, the query is are there any advantages and do we’ve got any outcomes that help our determination? Or is it simply us being too frightened of just a little little bit of chemistry? The brief reply is: sure, we’ve got accomplished some checks and it definitely is smart to be cautious. Let’s take a look at our information.

Experimental half

Cytotoxicity

Now we have carried out cytotoxicity checks for Prusament Resin Robust (Prusa Orange) and 4 different frequent competitors resins. The samples have been examined in a licensed testing laboratory, the place the impact of the resin and 3D printed objects on cell viability was measured.

Mice pores and skin fibroblasts have been used as testing cell tradition. Fluorescent dye is used for additional evaluation of the relative fluorescence depth as a sign of what number of cells survived or died in comparison with unexposed residing cells. The liquid resin or 3D printed objects have been immersed into the physiological resolution* supporting residing cells for twenty-four hours. After that time frame, extract with varied concentrations (100, 50, 25, 10 %) was put in touch with the cells for twenty-four hours. After that time frame, the relative variety of residing cells was measured.

*DMEM medium containing antibiotics with 10% inactivated veal serum

The specimens have been marked as extremely cytotoxic, reasonably cytotoxic, mildly cytotoxic and non-cytotoxic with the next share of residing cells:

  • Extremely cytotoxic: 0 % – 30 %
  • Reasonably cytotoxic: 30 % – 50 %
  • Mildly cytotoxic: 50 % – 70 %
  • Non-cytotoxic: 70 % and extra

These checks observe the usual testing process ISO 10993-5:2010.

Liquid resin comparability

To see what the resin does with residing cells, we ready samples of liquid, uncured and cured frequent powerful resins obtainable available on the market. In case you have a have a look at the outcomes beneath, you’ll see that all liquid resins are extremely cytotoxic. This underscores the need to deal with the resin with warning and as described within the security information sheet. And to restrict the publicity to liquid resin and its residues on the 3D printed fashions or within the washing resolution, whereas utilizing correct protecting tools, similar to gloves, goggles, and so on (as described in Security Information sheets). Principally, any form of extra security safety measures similar to elevated air flow or a fume field is barely a plus.

Fig. 2: The impact of extracts of assorted concentrations from 3D printing resins in liquid type on the cell viability of the mice fibroblasts (cytotoxicity). A lowering variety of residing cultivated mouse pores and skin cells have been noticed throughout a 24-hour interval at 37 °C on this check. Delicate, reasonable and excessive cytotoxicity ranges are represented by shades of gray.

Uncured and cured resin comparability

The outcomes for the liquid resins are fairly easy however issues get extra optimistic after the curing process. The cytotoxicity of the 3D printed and cured specimens is considerably decreased when in comparison with liquid resins. However most significantly, we are able to observe extra important variations between the examined manufacturers. For this check, we used two units of specimens: the primary was washed in pure isopropanol (IPA) whereas no heating and curing step was utilized (samples are marked as uncured), the second set was washed after which dried at 45 °C and cured in CW1S for 3 minutes (samples are marked as cured). Due to this fact, this check characterizes the cytotoxicity of 3D-printed components immediately after the 3D printing course of and components after the post-curing process.

The outcomes present that it’s somewhat unwise to the touch fashions with naked arms after printing, we advise doing so solely after extra curing when it’s secure. To get the bottom potential cytotoxicity, it’s essential to observe the producer’s directions for curing (curing temperature and time, curing machine utilization, and so on.). Our Prusament Resin Robust reveals low and fixed values for cytotoxicity even after one minute of curing!

Fig. 3: The impact of extracts of assorted concentrations from 3D printed and washed (additional uncured) components on the cell viability of the mice fibroblasts (cytotoxicity). A lowering variety of residing cultivated mouse pores and skin cells have been noticed throughout a 24-hour interval at 37 °C on this check. Delicate, reasonable and excessive cytotoxicity ranges are represented by shades of gray.

Fig. 4: The impact of extracts of assorted concentrations from 3D printed, washed, dried and additional cured components at 45°C for 3 minutes on the cell viability of the mice fibroblasts (cytotoxicity). A lowering variety of residing cultivated mouse pores and skin cells have been noticed throughout a 24-hour interval at 37 °C on this check. Delicate, reasonable and excessive cytotoxicity ranges are represented by shades of gray.

We discover it fairly fascinating (and alarming) that a few of the cured powerful resins present robust toxicity (for 100 % extract). Regarding our requirements, the Prusament resin powerful and specimen 4 are effectively throughout the limits.

Fig. 5: The impact of extracts of assorted concentrations from 3D printed components with varied post-processing protocols and post-curing time on the cell viability of the mice fibroblasts (cytotoxicity). A lowering variety of residing cultivated mouse pores and skin cells have been noticed throughout a 24-hour interval at 37 °C on this check. Delicate, reasonable and excessive cytotoxicity ranges are represented by shades of gray.

One other set of checks for the pores and skin irritation impact confirmed that brief exposition to a well-washed 3D print is effectively throughout the limits. Nevertheless, we advise curing fashions for at the least 3 minutes to get one of the best outcomes, regarding cytotoxicity.

Word that these checks don’t utterly mirror lengthy exposition in small doses. Though some resins could include good cytotoxicity, they could nonetheless trigger well being points after repeated publicity. Once more, because of this we don’t use extremely poisonous chemical substances as said above.

Pores and skin Irritation

Plates with dimensions 2.5×2.5 mm and thickness of 1.0 mm have been printed utilizing Authentic Prusa SL1S SPEED. The publicity time was 2 seconds per 50 um layer and 25 seconds for first layers whereas plates have been standing on the helps – thus investigated specimens have been totally printed with 2 seconds per layer. Additional samples have been washed in clear isopropanol for 3 minutes and post-cured for 0, 1, or 3 minutes. Ready samples have been utilized immediately on the pores and skin of 30 volunteers for the time frame 24±2, 48±2 and 72±2 hours. Sodium dodecyl sulfate was used as a optimistic pores and skin response reference (0,4 ml of 20% aqueous resolution was immediately utilized to the pores and skin of volunteers). After this time period, pores and skin response was evaluated with grating as follows:

0 – No Response;

1 – Weakly optimistic response (often characterised by delicate erythema and/or dryness throughout many of the remedy website);

2 – Reasonably optimistic response (often distinct erythema or dryness, probably spreading past of the remedy website);

3 – Strongly optimistic response (robust and infrequently spreading erythema with edema and/or eschar formation).

The process of the checks follows the usual testing process: Assessments for irritation in vivo (ISO 10993-23: 2021 Organic analysis of medical gadgets).

Whereas sodium dodecyl sulfate evoked a optimistic pores and skin response inside 1-3 grating scale amongst 30 volunteers (with no 0 consequence), analyzed samples 3D printed from Prusament Resin Robust Prusa Orange exhibited no pores and skin response with a pointy 0 grating consequence amongst all 30 volunteers no matter post-curing or utility time. The certificates of the evaluation from the licensed laboratory may be seen beneath.

 

Hold it clear

Talking about lengthy and brief exposures leads us to a correct office structure and precautions limiting publicity to harmful substances. If you wish to hold every part clear and secure, it’s best to observe these guidelines and proposals:

  • Work in a well-ventilated room. On the whole, protecting your printer and dealing with resins beneath a fume hood may be one of the best however for the frequent resins, open home windows or well-ventilated rooms needs to be sufficient.
  • Have your office set on an easy-cleanable floor. A clear desk would possibly work one of the best however you too can use disposable paper tablecloths that could be modified when polluted. Additionally, their sorption capability helps to forestall spilled resin from additional polluting.
  • Place the printer in a disposable tray. If the resin leaks from the vat, it received’t get far.
  • All the time have paper towels inside attain and each time you spill something, wipe it immediately.
  • All the time use disposable gloves and protecting eyewear. Some resins could set off an allergic response, particularly when you undergo from eczema or your pores and skin is delicate. And also you don’t wish to cope with resin in your eyes…
  • Get a lab coat or another working coat that protects you from publicity to chemical substances. Think about a scenario the place you shake a bottle of resin and rapidly discover out that the bottle is punctured or not correctly closed.

Fig. 6: An excellent instance of SLA office setup

Technical datasheets

Lastly, don’t overlook to learn the technical information sheet totally for the resin you purchase. Apart from mechanical properties, there must also be necessary info that’s carefully associated to well being security and data from the security information sheet. There needs to be beneficial printing instances, details about washing, drying and post-curing procedures. We came upon that for some resins, this info is commonly obtainable on-line on shared google sheets, typically it’s in a security information sheet and typically it’s incomplete or not obtainable in any respect. We consider that this needs to be clearly organized and said within the technical datasheet.

Primary utilization of SLA 3D printing will not be rocket science however there are clearly some guidelines price following to maintain it as secure as potential. All of it comes right down to studying datasheets totally to seek out whether or not it’s secure or not and utilizing the best safety. We hope this can enable you to to be as secure as potential when printing with SLA.

Completely happy printing!





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