3D Printing ProcessesAdvanced MaterialsMaterialsPhotopolymer ResinsThermoplastic Polymers

Researches use thiol‐ene photoresins for volumetric AM

Look to expand the range of materials and properties available

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A study published on the Advanced Materials journal presented the first report of volumetric additive manufacturing (VAM) of thiol‐ene photoresins, combining the benefits from two high-potential areas in AM and material science.

The study expands the versatility of volumetric AM by introducing a new class of VAM‐compatible thiol‐ene resins and demonstrating the superior quality of these materials and – by extension – the advantages of the layerless volumetric process.

VAM prints were performed in a custom printer setup equipped with a 405 nm LED light engine (CEL5500, Digital Light Innovations), with a maximum intensity of 55 mW cm−2, illuminating a resin vial fixtured to a rotation mount (HDR50, ThorLabs).

Output of all light sources was measured using a Si photodiode power meter, and spectral distribution measured using a compact CCD spectrometer (PM100D with S120VC sensor, and CCS100, Thorlabs). Spectral information for all light sources is given in the study’s Supporting Information, along with methods for calculating wavelength‐dependent absorbed optical dose in each case.

Importantly, this work also established the first comprehensive framework for spatial-temporal control over volumetric energy distribution, demonstrating structures 3D printed in thiol‐ene resin by means of tomographic volumetric VAM.

Figure 1 Schematic of VAM hardware configuration. The insets at left present example projections from different angles, resulting in the structure shown in the right inset. Scale bar: 2 mm. b) Schematics of four formulations Ac‐a, Ac‐b, Th‐a, and Th‐f, with varying molecular network structure composed of five constituent monomers, with acrylate (green) and thiol‐ene (red/blue) functionality. Compositions are indicated by molar ratios of functional groups. A1—Triethylene glycol diacrylate (TEGDA), A2—Tris[2‐(acryloyloxy)ethyl] isocyanurate (TAE‐ICN), T1—Triethylene glycol diallyl ether (TEGDAE), T2—Tri‐allyl isocyanurate (TA‐ICN), and T3—Tris[2‐(3‐mercaptopropionyloxy)ethyl] isocyanurate (TME‐ICN). The 3D model of the ballerina in Figure 1a by Miguel Zavala is licensed under the CC BY Creative Commons Attribution 4.0 International license (https://creativecommons.org/licenses/by/4.0).

Emerged recently, volumetric additive manufacturing processes form complete 3D objects in a single photocuring operation, from tomographic data, without layering defects, enabling 3D printed polymer parts with mechanical properties similar to their bulk material counterparts. VAM could also lead to a broadening of the materials available for photopolymer 3D printing, having fewer constraints on viscosity and reactivity compared to layered 3D printing. Printing parts in a single step from tomographic data overcomes many of the drawbacks of layer‐based fabrication, such as long build times and rough surfaces.

Combined with thiol‐ene chemistry, VAM could move beyond the limitations of common acrylate photopolymer formulations. In other words, this study shows that not only volumetric 3D printing can be achieved – dramatically accelerating the build speed and improving on part properties by eliminating layers, but that using thiol-ene based chemistry it can open the door to a broader range of material possibilities.

By printing parts in a single step from tomographic-type data, VAM holds promise because it overcomes many of the drawbacks of layer‐based fabrication, such as long build times and rough surfaces.

Until now, VAM has been demonstrated with extremely soft hydrogels, and almost exclusively on acrylate‐based chemistry (almost all currently available commercial materials for photopolymerization are acrylates)

This is natural because the oxygen inhibition of acrylate polymerization provides the threshold behavior required for VAM and all continuous 3D printing processes (such as cDLM and DLS, for example). However, acrylate chemistry is in general limiting due to the brittle and glassy properties of the resulting materials. Accordingly, extensive efforts have been made to identify and target specific soft, elastic acrylate formulations.

Introducing alternative crosslinking chemistries to the VAM realm, as well as AM more broadly, is highly desirable as an alternative method to gain access to a wider range of mechanical, thermal, and optical performance. Thiol‐ene‐based polymers present more controllable, tunable mechanical properties and have shown promise for applications in adhesives, electronics, and as biomaterials.

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Davide Sher

Since 2002, Davide has built up extensive experience as a technology journalist, market analyst and consultant for the additive manufacturing industry. Born in Milan, Italy, he spent 12 years in the United States, where he completed his studies at SUNY USB. As a journalist covering the tech and videogame industry for over 10 years, he began covering the AM industry in 2013, first as an international journalist and subsequently as a market analyst, focusing on the additive manufacturing industry and relative vertical markets. In 2016 he co-founded London-based VoxelMatters. Today the company publishes the leading news and insights websites VoxelMatters.com and Replicatore.it, as well as VoxelMatters Directory, the largest global directory of companies in the additive manufacturing industry.

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