ETH researchers produced complex and highly porous glass objects using a special resin that can be cured with UV light in a novel glass photopolymerization process. Although it is very common (or maybe because of that) glass is the hardest material to effectively 3D print. In the limited number of previous attempts, made by both researchers and companies like ExOne and Micron3D, some have made objects by printing molten glass while others have used powdered ceramic particles that can be printed at room temperature and then sintered later to create glass. There have also been some previous studies focusing on SLA photopolymerization. However, all of these approaches have shown limitations in terms of high-temperature management (for extrusion of molten glass) and transparency (for binder jetting and SLA).
Researchers from ETH Zurich have now used a new technique to produce complex glass objects using photopolymerization and specifically DLP photopolymerization. David Moore, Lorenzo Barbera, and Kunal Masania in the Complex Materials group led by ETH professor André Studart have developed a special resin that contains both plastic and organic molecules to which glass precursors are bonded. The researchers reported their results in the latest issue of the journal Natural Materials.
Light up the glass
The resin can be processed using commercially available Digital Light Processing technology. This involves irradiating the resin with UV light patterns. Wherever the light strikes the resin the plastic monomers combine to form a labyrinth-like structure, hardening and creating the polymer. The ceramic-bearing molecules fill the interstices of this labyrinth.
The researchers can change various parameters in each layer, including pore size: weak light intensity results in large pores; intense illumination produces small pores. “We discovered that by accident, but we can use this to directly influence the pore size of the printed object,” says Masania. The researchers are also able to modify the microstructure, layer by layer, by mixing silica with borate or phosphate and adding it to the resin. Complex objects can be made from different types of glass, or even combined in the same object using the technique.
The researchers then fire the blank produced in this way at two different temperatures: at 600˚C to burn off the polymer framework and then at around 1000˚C to densify the ceramic structure into glass. During the firing process, the objects shrink significantly but become transparent and hard just like window glass.
These 3D printed glass objects are still no bigger than a die. Large glass objects, such as bottles, drinking glasses or windowpanes, cannot be produced in this way – which was not actually the goal of the project, emphasizes Masania. The aim was rather to prove the feasibility of producing glass objects of complex geometry using a 3D printing process. However, this new approach is not just a gimmick. The researchers applied for a patent and are currently negotiating with a major Swiss glassware dealer who wants to use the technology for commercial applications.