When Desktop Metal introduced its “office-friendly” Studio metal prototype printer earlier this year, the company renewed attention on the issue of safer materials for binder jetting, an additive manufacturing method. As it turns out, Desktop Metal (Burlington, MA) uses two binder jetting processes that differ from each other and from one typically used. Historically, binder has been extruded onto a bed of particulate sand, ceramic or metal to create layers of an object during 3D printing. It’s used for many applications, including foundry molds, as well as finished objects.
Among Desktop’s accomplishments are its proprietary binders, in that they can be used safely around humans, said Larry Lyons, head of product for the company. “On the Studio side, I can tell you they are much, much safer than [furan and phenol],” he said. “Our binders can come into contact with skin, do not require any safety goggles, any respirators, anything like that. They can be handled by hands, and there is no issue or safety concern with them.”
Desktop’s production system, which is still in development, is designed to isolate the user from the binder and metal powder at all stages of the process.
There are other safe binders on the market, including sodium silicate from ExOne (North Huntingdon, PA). When ExOne introduced sodium silicate in 2013, it also introduced a phenolic binder that eliminates the need for heat-treating but is not so human-friendly. Long-term exposure to phenol vapor is associated with cardiovascular disease and it can burn skin. Another binder, furan, is lumped with dioxin because their chemical structures are so similar. These substances have been linked with hormone changes and cancer.
While binder jetting was a leap forward for 3D printing when it was patented in 1993, the materials it uses for binders haven’t changed much since then. “The first materials and binders to be developed were metal and ceramic powders and sand used in conjunction with aqueous or organic binders, including furan and phenol,” said Bryony Core, a technology analyst for IDTechEx (Cambridge, England), in an email. She authored the market intelligence report 3D Printing Metals 2018–2028: Technology and Market Analysis. “Any less toxic alternative would be more desirable.”
Core might be interested in the work of Jim Bredt, R&D director at Viridis3D (Woburn, MA), who said, “One of the big complaints about the materials that are in the market now is that they’re all fairly toxic and, in some cases, somewhat unstable, and require a lot of effort in print head maintenance.”
Bredt, who worked as a grad student with MIT’s Ely Sachs, Desktop co-founder and binder jetting inventor, said furan is on its way out in the industry because of its toxicity.
“There are some regulations that are getting put in place against it in Europe and we’re also somewhat worried about its future in Canada,” he said.
When he handles furan, Bredt said he wears nitrile gloves, a lab coat and a p100 respirator with a charcoal filter. “Too much furan fumes will give you a headache,” Bredt said.
Viridis hopes to give manufacturing a better binder. “We’re working on a system that’s much less toxic than any of these, that can be used in the same material set, and that we’re pretty sure is going to be able to last a lot longer in the industry,” he said. “Right now, it’s still under development.”
Bredt is confident the new binder will be able to achieve a 300 dpi resolution.
Core said other developments are in store. “Looking to the future, binder jetting allows for multiple materials to be incorporated into one object through the addition of agents that modify the properties of the powder they are deposited into,” she wrote. “While this may be as straightforward as simply changing the color, it could extend to modifying the elasticity or conductivity of discrete areas of the total part.”