Demystifying Resin Handling for 3D Printing

by Christopher Lannon July 17, 2023

Resin-based 3D printers like SLA and DLP have become increasingly popular for hobbyists and professionals alike. The stunning detail and smooth surface finish achievable with resin printing comes from the unique photopolymerization process. But working with liquid resin also introduces some specific handling considerations compared to filament-based printing. Properly managing uncured resin can make the difference between a smooth printing experience versus one plagued by failed prints, contamination issues, and resin waste. This guide covers everything you need to know about resin handling for 3D printing.

Storing and Disposing of Resin

Photopolymer resin has a limited shelf life. With exposure to light and oxygen, the reactive chemicals that allow resin to solidify when cured will start to break down over time. Resin left sitting in vats or bottles will expire after 6-12 months typically. Old expired resin is likely to produce failed prints with cured resin that is soft, gummy, or uncured.

To prolong the life of your resin, store bottles in a cool, dark place away from sunlight. Opaque black bottles also help block light exposure. Refrigerated storage can extend the shelf life for some specialty resins, but check manufacturer guidelines. Let refrigerated resin come completely to room temperature before printing to avoid temperature-related viscosity issues.

Once resin expires past the point of printing reliably, disposal is the only option. Because cured and uncured resin contains chemicals hazardous to aquatic life, resin should never be poured down the drain. Check local regulations, as rules differ regionally on resin disposal. Many municipalities allow depositing small amounts of cured resin in regular landfill trash. Larger amounts may require specially designated hazardous waste facilities. Bottles of expired uncured resin can be solidified by curing with UV light before disposal.

Proper storage and timely disposal of expired resin helps avoid unnecessary waste and potential environmental hazards. Planning your purchases to match your printing needs reduces how much resin expires before use.

Avoiding Resin Contamination

Keeping resin free of contaminants is crucial for successful prints. Any debris, dust, dirt, oils from skin contact, or other foreign substances in the resin tank will leave flaws on printed surfaces or cause curing failures. Here are tips to avoid contaminating your liquid resin.

Carefully pour resin into the tank to prevent splashing and minimize bubbles. Let resin sit for a few minutes so bubbles can rise to the surface before printing.
Wipe down the outside of resin bottles before opening to avoid dust and particles falling in.
Never put used resin back into the bottle. The uncured resin remaining in the tank will introduce contaminants.
Cover idle resin tanks or vats when not printing to prevent airborne dust from landing in the resin.
Avoid touching the liquid resin with bare hands. Wear gloves and use tools to remove prints to limit oil and skin contact.
Place printers in a dust-free space away from high traffic areas to keep airborne particles away.
Filter resin before each print using mesh filters or coffee filters to catch particles.

Catching and preventing contamination keeps resin pure for higher quality prints. But if resin does become contaminated, filters can only catch particulates. Resin that appears cloudy or discolored needs replacement.

Monitoring Temperature Effects on Resin

Resin viscosity - the thickness and flow - changes with temperature. In warm environments, resin becomes thinner and flows more easily. Cooler temperatures make the resin more viscous and syrupy. This significantly affects the 3D printing process. Thinner warmer resin will spread more and lose fine details. Thick cold resin can impede resin flow across the build plate.

Ideally, keep ambient temperatures around the resin printer between 20-25°C (68-77°F). Monitor conditions with a thermometer, and adjust as needed. Enclosing the printer or using cooling/heating fans helps regulate the temperature. For cold conditions down to about 15°C, a space heater to gently warm the resin can help. Refrain from printing when ambient temperatures exceed 30°C.

Many manufacturers also recommend pre-warming the resin bottle before use in cold rooms by submerging it in warm water for 10-15 minutes. This brings the resin closer to the ideal printing viscosity before loading it into the printer. Avoid drastic temperature swings either colder or warmer during printing for best results.

Mixing Multi-Part Resins

Specialized resins like flexible, heat resistant, or medical resins use two-part formulas requiring mixing before use. Ensure you have the correct mixing ratio specified by the manufacturer, usually 1:1 or 10:1 ratios depending on resin chemistry. Measure out each part carefully by volume using graduated cylinders or by weight on a scale for the most precise mixture.

Thoroughly stir, scrape the sides, and mix again to fully combine the two parts. Mix for the recommended duration, normally 3-5 minutes. Mixing too little produces resin that does not cure properly. Over-mixing can actually start curing the resin prematurely. Stick to the mixing guidelines, and remix the resin at least once during longer print jobs.

Caring for the Resin Vat

The transparent resin vat or tank is crucial for allowing UV light to pass through and cure the resin. But the thin plastic film (FEP) at the bottom needs special care to prevent damage and maximize its lifespan. Here are some resin vat care tips:

Avoid exposing the resin vat to sunlight when not installed in the printer. The UV can degrade the film over time.
Check the film periodically for small holes or tears which would allow resin to leak. Replace the film if needed.
Lightly coat the film with lubricants like PTFE or FEP release spray. This prevents resin from strongly bonding and pulling up chunks of film.
Carefully remove solidified resin stuck to the film after prints using plastic or wooden tools. Avoid scraping with metal objects.
Replace the film roughly every 200 print hours or when damage, cloudiness, or resin adhesion occur frequently.

With proper care, the resin vat film can last through dozens of prints before needing replacement. Taking caution with the film saves money and avoids resin leaks.

Dealing with Resin Waste

Despite best practices, some amount of resin waste is inevitable. Spills, failed prints, emptied vats, and filtration all generate waste resin and materials to dispose of properly. Here are tips for handling resin waste:

Cure any liquid resin waste fully before disposal by exposing to UV light. This solidifies it for safe handling.
Resin-contaminated materials like gloves, filters, and paper towels also require curing before trashing.
Small amounts of cured resin can go in regular trash. For larger amounts, check local hazardous waste disposal regulations.
Reuse disposable resin filters by washing thoroughly in isopropyl alcohol and allowing to fully dry before reuse.
Limit waste by carefully pouring and not overfilling tanks. Plan supports and prints to minimize failures.
Explore recycling options for empty resin bottles depending on your region. Some suppliers accept returns.

Responsible resin waste management reduces environmental impact and keeps printing areas clean. With care and planning, hobbyists can minimize unnecessary waste.

Resin Handling FAQs

How long does unopened resin last before expiration?

Most resins expire 6-12 months after the bottling date if kept sealed and stored properly away from light and heat. Always check manufacturer date guides. Some may last 9-18 months or more refrigerated.

Can expired resin make you sick?

Uncured expired resin contains the same hazardous chemicals as regular resin. There is no evidence expired resin is more dangerous, but sensitivities may vary. Use PPE like gloves and a respirator when handling old resin and avoid skin contact. Cure resin fully before disposal.

Should resin be stored in the freezer?

Freezer storage can extend shelf life for some resins if permitted by the manufacturer, but is not required. Allow resin to reach room temperature before printing if refrigerated. Repeated freezing and thawing hastens expiration.

How do you thin too-viscous resin?

Gently warming resin to 25-30°C in a warm water bath can lower viscosity of resins that are too thick for printing. Take care not to overheat or shake resin violently. Avoid chemical thinning agents not approved for the specific resin.

Can expired resin be reused if filtered?

No, unfortunately once resin has expired its chemical composition has degraded too far. Filtering cannot rejuvenate old resin. Dispose of expired resin properly after fully curing any remainders with UV light.

Proper resin handling may seem daunting at first, but just follows common sense precautions. Storing resin properly, avoiding contamination, mixing 2-part resins correctly, caring for the resin vat, dealing with waste, and understanding temperature effects will help you avoid many beginner pitfalls. With experience, careful resin handling will become second nature!