Dye-free and reprintable multi-color DLP 3D printing using ZnCl₂-based polymerizable deep eutectic solvents and type I photoinitiators

The current multi-color digital light processing (DLP) relies on different dyes and complex resin exchange/cleaning equipment to fabricate multi-color objects. Here, we developed a novel and simple approach to print multi-color objects using a conventional DLP printer with acrylic acid (AA)/ZnCl₂/H₂O (AZH)-based polymerizable deep eutectic solvents (PDESs) and type I photoinitiators, eliminating the need for dyes. The coloration of the printed objects is achieved by the molecular isomerization of type I photoinitiators remaining in the cured material. Furthermore, the color tuning range of the printed objects with this approach is close to the full-color gamut. Another advantage of this approach is that the printed objects can be recycled and reused to prepare the precursor solution for new multi-color DLP printing, making it a more sustainable and environmentally-friendly method. Finally, the potential application of multi-color objects in information encryption and decryption has been demonstrated, which opens new possibilities for the use of multi-color DLP printing in security and other areas. This novel multi-color DLP printing strategy utilizing residual photoinitiators represents a significant advancement in 3D printing technology, offering a simpler, more flexible, and more sustainable approach to achieving multi-color printing.