Curing Characteristics of a Photopolymer Resin with Dispersed Glass Microspheres in Vat Polymerization 3D Printing

The curing characteristics of a photopolymer resin determine the relationship between the vat polymerization (VP) process parameters and the layer thickness, geometric accuracy, and surface roughness of the three-dimensional (3D) printed specimens. Dispersing a filler material into the photopolymer resin to modify the properties of the specimens changes the curing characteristics because the filler scatters, absorbs, and transmits light, which alters the photopolymerization reaction. However, the ability to cure the photopolymer resin with a high filler volume fraction is important to 3D print specimens for specific applications, such as composite and ceramic materials for biological and high-temperature environments. We specifically consider a translucent filler and methodically measure the curing characteristics of a diacrylate/epoxy photopolymer resin with dispersed translucent glass microspheres. Experiments relate the curing depth, degree-of-cure, geometric accuracy, and surface roughness to the exposure dose, filler fraction, and filler size distribution. The curing depth depends on two competing effects: light scattering and light transmission through the translucent filler, and it increases with increasing filler fraction for low exposure dose, which contrasts results documented by others for VP with an opaque filler. Furthermore, the degree-of-cure increases with increasing filler fraction for a constant exposure dose. The geometric accuracy and surface roughness of the 3D printed specimens decrease with increasing exposure dose and filler fraction. This work has implications for VP of photopolymer resins with high filler fraction in the context of manufacturing of engineered materials.