Onulis Wrap W7500

All resin-based 3D printing technologies produce waste resin. In its liquid form, resin is classified as a hazardous material. However, during the 3D printing process, resins are transformed from a liquid to a solid by being exposed to UV light.

Here is an overview of how waste resin is produced in the three most prolific resin 3D printing technologies:

PolyJet 3D Printing Technology

PolyJet 3D printers work by inkjet printing tiny droplets of resin one layer at a time on a build platform. The UV lights attached to the print head simultaneously cure the resin, forming a single, fully cured cross-section of the parts on the build platform. Once a cross-section is completed the build platform is lowered in the Z-direction, and the process is repeated for the next layer until the part is completed.

PolyJet waste resin is generated in the following three ways:

• Interval Cleaning: At pre-determined intervals during the print process, the print head travels to the side of the build platform and automatically jets small amounts of resin through the print head nozzles into a waste reservoir. This process clears the nozzles and, in effect, cleans the print heads. Although a very small amount of material gets wasted in each interval, this process continues, and waste accumulates over time.
  
  
• Material Changeover: When an operator loads the printer with a different resin there is a purge cycle to clear the printer of the previously used resin. For example, when changing from VeroBlack to VeroWhite, the VeroBlack that is residing in the printer’s heads and hoses are purged into the waste container.
  
  
• Expiration: PolyJet materials have a shelf life of 12 to 14 months and will expire if left unused. Each container has an RFID tag with an expiration date. This prevents damage to the printer since the material will coagulate and clog up the print heads.
  
  

SL (Stereolithography) 3D Printing Technology

SL 3D printers work by beaming a UV laser onto a vat filled with UV light-sensitive resin. When the laser hits the resin, it cures it from liquid to solid. After parts are printed and removed from the vat, the user must pour the additional resin into the vat to “top-it-off.” Typical vat volumes are anywhere from .2 Liters (Formlabs Form 2) to 400+ Liters (3D Systems ProX 800 and Stratasys Neo 800).

SL waste resin is generated in the following ways:

• Post Processing: When cleaning SL parts, the parts are bathed in IPA (Isopropanol), which removes any excess uncured waste resin. Over time, the IPA becomes semisaturated with uncured waste resin and must be disposed of.
  
  
• Contamination: SL systems utilize an open vat configuration. If the vat getscontaminated with foreign debris or partially cured remnants from previous print runs, then it needs to be replaced.
  
  
• Expiration: SL resins have a shelf life of 18 to 24 months. Upon expiration, the material must be disposed of properly.

DLP (Digital Light Projection) Technology

DLP 3D printers work by using a UV light projector and flashing an image onto a vat (build tray) filled with resin. When the UV light image is projected onto the resin, the resin is partially cured from a liquid to a solid. After parts are printed and removed from the vat, the user must pour the additional resin into the vat to “top-it-off.” Typical vat volumes are small which enables the user
to easily change build trays.

DLP resin is generated in the following ways:

• Post Processing: When cleaning DLP parts, the parts are bathed in IPA (Isopropanol), which removes any excess uncured waste resin. Over time, the IPA becomes semi-saturated with uncured waste resin and must be disposed of.
  
  
• Expiration: DLP resins are more unstable than SL resins and typically have shorter shelf lives. Some of the two-part resins, such as the EPX 82 from Carbon 3D, once mixed, only last for 24 hours and must be disposed of. Some Carbon 3D customers report disposing of as much as 1 gallon per month of uncured DLP resin.

All resin-based 3D printing technologies produce waste resin. Although waste resin is considered hazardous in its liquid form, there are several options available to deal with waste resin. This paper touches on most of the issues related to this subject and points out that users may be subject to a combination of federal, state, and local regulations.

Option 1: Hazardous Waste Disposal Service

The first option is to hire a Hazardous Waste Disposal Service (HWDS) to pick up your waste resin. Many different companies offer this service. Please note, providers in your area may or may not process waste locally.

US Environmental Protection Agency (EPA) Registration
HWDS companies require your registration with the EPA, which requires a one-page application and a $40 fee. This will classify your company as a generator of hazardous waste, and you will be required to file a biannual report and renew your registration annually.

Depending on how much waste resin is generated, users will be assigned a classification, such as Small Quantity Generator (SQG) >2,200 lbs. per year or Large Quantity Generator (LQG) <2,200 lbs. per year. Among other regulations, classification determines the length of time a waste generator is allowed to store hazardous waste onsite; an SQG has up to 180 days and an LQG has up to 90 days.

To manage and ship hazardous waste, most HWDS companies require customers to complete Resource Conservation and Recovery Act (RCRA) training. As the waste generator, the user maintains all liability for the storage drum and is required to complete a Uniform Hazardous Waste Manifest Form prior to sealing, labeling, and shipment. Additional documentation may be required based on a user’s location.

Material Safety Data Sheets (MSDS)
You will be asked to provide the MSDS of your resin to the HWDS. Their staff will review the MSDS and upon receipt of the waste resin, they will perform lab testing prior to disposal.

Type of Disposal
HWDS companies offer two types of waste resin disposal 1) Landfill and 2) Waste to Energy Incineration. The latter being the more expensive option. Depending on your area and HWDS, typical costs for disposal of a 55 gallon drum of waste resin could be $125 to $175 for landfill and $200 to $300 for incineration.

Other Considerations
Subject to location, HWDS companies are, by law, limited to storing hazardous waste at holding sites for a maximum of 10 days. In the current environment, many HWDS companies are backed up due to the overproduction of hand sanitizers, which, due to
high alcohol content and flammability, must be sent off to incinerators. For example, users located in California should consider how the timing of disposal may be impacted by the additional regulations for storage and shipment placed on HWDS companies, which must dispose of hazardous waste at sites located out of state. Also, storing location, floor space and general liability of hazardous waste storage should be considered.

Amount of Waste Resin
The amount of waste resin produced will determine the cost of your service. Typically, waste resin is stored in a 55 gallon drum ($75 to $300). Drums and storage containers can either be sourced through the HWDS or from an industrial equipment supplier, such as Grainger.

Other Fees
With each pickup, or “Milk Run,” there are several fees to be aware of, including: driver fees ($85 to $100 per hour, typically 2 hour minimum), manifest fees ($25 to $50), and environmental services charges (typically 15% surcharge).

Option 2: California Lunch Tray Method

The second option is a DYI process, in which users pour waste resin onto a lunch tray or metal baking pan and let it cure outside under sunlight. The UV light from the sun will slowly cure the resin. The resin must be poured periodically in thin layers to maximize the surface area of sun exposure. The user must periodically stir the waste resin to ensure that underlayers of uncured resin are exposed to UV light.

Face masks and gloves are required for protection from the caustic process. Processing times can vary, depending on temperature and weather. When cured, the solid resin can be disposed of as common household waste.

Option 3: Waste Resin Axial 3D Printing (WRAP) Technology

A third option is to use Waste Resin Axial 3D Printing (WRAP) Technology to cure waste resin. WRAP technology enables safe curing through a patented process in which a user pours the resin into the system’s vat. The resin is slowly dispensed in drips onto a disposable paper-based cylinder located in a chamber with high-powered UV lights. As the resin drips and the cylinder rotates, the resin is instantly cured. The process continues until the full volume of waste resin in the vat is exhausted, leaving a cylinder of cardboard and solid cured plastic stock. When cured, the solid resin can be disposed of as common household waste or repurposed for various applications, including low-cost media for CNC machining.