Optimized dispersion of inorganic metal salts in photocurable resins for high-precision continuous 3D printing of complex metal structures

Emerging metal additive manufacturing (AM) technologies that incorporate metal precursors to fabricate both metal and alloy 3D objects has become an attractive method for producing complex metallic objects with microscale features. However, current metal precursor additive manufacturing technologies that operate in a layer-by-layer manner are limited by low solid loading, poor rheological performance, slow printing speed, and anisotropic physical properties from the stacking of individual layers. To circumvent these challenges, printing resin with high solid loading of metal precursors and excellent rheological behavior was developed and employed in a rapid, layer-less additive manufacturing process to fabricate metal precursor objects within minutes. Addition of BYK-2013 dispersant, an ionic copolymer, to aid in the homogeneous dispersion of metal salt precursor dispersion was able to achieve a high maximum copper precursor concentration of 60 % (w/w) while sustaining stable dispersion for more than 24 h without displaying significant particle sedimentation greater than 1 mm. Cross-linking characteristics were investigated to optimize surface quality and reduce printing times of 3D printed objects resulting in low surface roughness (0.986 μm) and printing speeds upwards of 20 μm s⁻¹. Additionally, experimental results indicated that resins containing BYK-2013 exhibited superior hydrophobicity with no rehydration of inorganic metal salts after 180 min while maintaining an excellent viscosity of approximately 0.16 Pa s. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) guided post-processing optimization was successfully conducted to promote stable thermal decomposition during the removal of organics, metal oxide formation, and metal oxide reduction leading to highly robust copper lattices with final concentration of copper upwards of 92.8 % and an overall average isotropic shrinkage of 62 %. Furthermore, the microstructure evinces that an either dense or porous microstructure can be realized by adjusting metal precursor concentration to generate tunable physical properties with the final copper part. This study provides a unique and cost-effective methodology for formulating photocurable metal precursor resins with exemplary rheological behavior to produce intricately designed metal and alloys for a wide range of industrial engineering applications.