Upconversion 3D printing enhancement via silver sensitization to enable selective metallization

This work presents the synergistic effect of silver (Ag) ions to enhance the crosslinking of 3D printing photopolymers via near-infrared (NIR) to ultraviolet (UV)/visible light upconversion (UC) and allow selective metallization of multi-material parts. By incorporating a commercial micron-sized ytterbium-thulium co-doped sodium yttrium fluoride phosphor (NaYF4:Yb3+, Tm3+) into a photopolymer resin, a low-cost NIR laser is used to initiate curing exactly at the focal point in the depth of the vat, allowing voxel crosslinking in any point of the space at a depth in the centimeter scale, beyond the traditional layer-by-layer 2D scheme. This allows the printing with the presented resin on pre-existing printed parts, which is the basis for multi-material integration in 3D printing, beyond the 2D limitation. The addition of Ag(I) ions in the photopolymer enables improved photo-curing at 10-fold faster speeds, after printing through 10 mm of resin. In our approach, after the 3D printing process, the Ag(I) ions embedded into the photopolymer serve as seeding sites for electroless copper (Cu) plating, which allows the integration of metalized parts on different substrates, such as glass and 3D printed polymer. Finally, selective copper plating has enabled the manufacture of objects with metal (copper) and plastic (acrylic) surfaces.