Upconversion particle-assisted near-infrared photopolymerization (UCAP) has shown promising applications in 3D printing. However

due to the low fluorescence efficiency of upconversion particles

the surface of the printed material suffers from severe oxygen inhibition effects. It reduces the printing speed and printing accuracy. In this study

we overcome this difficulty by introducing thiol-ene photopolymerization monomers into the ink design. By optimizing the printing ink formulation

it was found that the ink with secondary thiol-olefin monomer as the light-curing substrate and 4% thixotropic agent addition exhibited the best thermal stability and printing performance. By using this optimal ink formulation for 3D printing

fast printing of black lattice structures and unsupported spiral structures at 25 mm/s printing speed (1 mm diameter nozzle) was successfully achieved. The mechanical properties of the printed material were comparable to those of the molded material

with a tensile strength of 55 MPa.