Highly filled resins for DLP-based printing of low density, high modulus materials

Abstract

Digital Light Processing (DLP)-based 3D printing enables the fabrication of complex structures from a broad range of neat and filled resin formulations, yet mass sensitive applications in the automotive, aerospace, and electronics industries are hindered by the lack of low-density resins. This paper investigates the formulation of a resin suitable for DLP-based fabrication of low density, high modulus structures with fine resolution of negative and positive features. An acrylate-based resin is loaded with a high-volume fraction (50 vol%) of hollow glass microspheres achieving adequate cured depth to fabricate 25 µm layer thicknesses. The suspension stability over typical multi-hour DLP print durations is verified. The filled resin exhibited a viscosity less than 5 Pa-s, which is below the upper limit of viscosity to recoat the Polydimethylsiloxane (PDMS) window between layers. The printed material possesses a uniform density distribution of 0.81 g cm−3 investigated using thermogravimetric analysis (TGA) and micro-Computed Tomography (micro-CT) imaging. The minimum feature sizes for the formulation are demonstrated as 400 µm for internal cavities (negative features) and 250 µm for protruding features (positive features). An example of a structure with an intricate geometry is created by printing a repeating mechanical metamaterial unit cell.