This MIT-Developed 3D Printer Can Apply Varying Levels of Gloss to Printed Surfaces

Color graphics can reliably be defined by three characteristics: hue, saturation, and brightness. Two colors could have the exact same hue, but look completely different if their saturation and brightness don’t match. Similarly, the appearance of a physical surface is dependent on its color, texture, and reflectivity. For example, a car with a matte black paint job is easily distinguishable from a car with traditional glossy black paint job, purely because of how much light the paint reflects. To precisely control the reflectivity of physical objects, MIT engineers have developed a 3D printer that can apply varying levels of gloss to printed surfaces.

Today’s inkjet 3D printers can produce virtually any 3D geometry in a wide range of colors. They can even create a variety of textures on the surfaces of the printed objects. But they can’t vary the level of gloss on those surfaces — at least not within the same print job. Inkjet 3D printing works by spraying tiny droplets of a liquid binder — often colored — from an inkjet print head (similar to what you’d find on an inkjet printer) onto fine powder. The resulting material, and its reflectivity, is dependent on the binder and powder used. Generally, this means that the entire surface has the same level of gloss. That can be tweaked somewhat by altering the surface texture, but that isn’t visually predictable and could be undesirable in some circumstances.

This new system makes surface texture changes unnecessary by applying varnish to the part after printing. Varnish is too viscous to be sprayed through the inkjet head, so separate needle valve jets are used for this step. Three of these jets are fed from three pressurized reservoirs, which contain matte varnish, medium gloss varnish, and high gloss varnish, respectively. The software used to control the varnish application is capable of spraying these selectively in halftone patterns in order to create a “rainbow” of possible surface reflectivity. Before printing, varnish is sprayed on a small test part that is then inspected with a camera to calibrate the system. After calibration, it is capable of controlling the glossiness of any portion of a part’s surfaces — from completely matte to highly glossy. It is largely unnecessary for mechanical parts and prototypes, but this capability would be very useful for detailed models and reproducing three-dimensional artwork.