A cross-linking strategy with moderated pre-polymerization of resin for stereolithography

Compared with parts fabricated via traditional methods, such as injection or compression molding, polymeric parts produced by 3D stereolithography (SLA) have poorer mechanical properties. Here, we demonstrate a cross-linking strategy used in the coating field to attain long chains for resin pre-polymerization to obtain final resin parts which can expand the application of SLA. Isophorone diisocyanate (IPDI), 2-hydroxyethyl methacrylate (HEMA) and polyethylene glycol (PEG)-based prepolymer have long chains, making it easier for them to form dense structures. However, the prepolymer has high viscosity and can solidify in the absence of a laser. Thus, three kinds of adjuvants were added to dilute the prepolymer to make the slurry suitable for 3D-printing. Slurries were cured with different laser powers and scanning speeds. Diluents are found to affect the curing properties differently. With the diluent 2-hydroxyethyl acrylate added into the prepolymer, shrinkage of printed parts is lower than 1.3%. With the diluent ethylene glycol monophenyl ether, the density range of printed parts is between 1.187 g cm^-3 and 1.195 g cm^-3, which is higher than that of commercial PVC and PET. The three resins vary in density and hardness within a small range when the scanning speeds change. A relatively flat surface, high density and hardness can be obtained when the laser power is at 195.5-350 mW. Resin with this cross-linking strategy can expand the underutilized stereolithography's application from prototyping to actual parts by producing more functional components with excellent performance.