A team of researchers from the University of Texas at Austin have developed a novel photopolymer resin that makes high-resolution visible light curing significantly faster.
The panchromatic ‘rapid-cure’ material is curable in four different colors of light – violet, blue, green, and red – and contains a monomer, a photoredox catalyst, two co-initiators, and an opaquing agent. The scientists have stated that the resin could be integrable with a wide range of additives, including biological compounds, possibly paving the way for a new method of tissue engineering and medical device production.
UV curing vs. visible light curing
Photopolymerization systems are powered by one of two different types of printing engines: one that emits UV light and one that emits visible light. The more common high-power UV systems tend to be faster and more precise, but are limited in their material choice and subsequent applications. UV resins also suffer from degradation over time, and lend themselves to attenuation from absorption and scattering.
Lower-power visible light systems, on the other hand, offer opportunities for biocompatible materials, greater light penetration depths, lower costs, and even reduced light scattering at the cost of cure speeds and feature resolutions. Therefore, chemical innovations in the visible light spectrum could draw on the best of both worlds, enabling high-performance nanocomposites and multimaterial structures with all the benefits of UV-curing.
Panchromatic visible light resins
The team’s formulation relied on the PCR component absorbing visible light emitted by LEDs, which then catalyzes the process of electron transfer between the two co-initiators. This transfer is what generates radicals that cause the individual monomers to polymerize and form polymer chains. According to the paper, the use of both an electron-deficient and an electron-rich co-initiator was absolutely instrumental in surpassing the cure time limitations in the experiment.
When evaluating the material’s effect on part resolution, the scientists found that the opaquing agent had helped limit curing solely to the areas targeted by the projections, resulting in improved resolutions. When all was said and done, the novel mix of ingredients had been used to print both soft and stiff parts with mechanical isotropy and feature sizes in the sub-100 micron range.
Most importantly, the parts were built at speeds of up to 45mm/h. While this is still significantly slower than many UV-based systems, the next steps of the study involve increasing the light intensity and adding further components to improve the cure rate of the resin. The work marks a considerable step forward in enabling visible light technology to rival the throughput of UV 3D printing, with the potential for bio-printing and composite-printing just over the horizon.
Further details of the study can be found in the paper titled ‘Rapid High-Resolution Visible Light 3D Printing’. It is co-authored by Dowon Ahn, Lynn M. Stevens, Kevin Zhou, and Zachariah A. Page.
Just last month, 3D printer manufacturer Nanoscribe launched a new photopolymer resin for its two-photon lithography process. Dubbed IP-n162, the material features a high refractive index and disperses easily, making it great for microfabrication applications. The resin’s low absorption rate when exposed to infrared (IR) light also makes it well-suited to creating IR micro-optics such as optical communication products and photonic packaging.
Elsewhere, in China, researchers have previously formulated a high-strength vegetable oil-based photopolymer resin for UV-based SLA. By combining soybean oil with urethane epoxy and acrylates, the scientists managed to fabricate resin parts with high-performance mechanical properties without sacrificing biodegradability.
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Featured image shows a high-resolution octet truss 3D printed using the novel resin. Image via UT Austin.