New printing process changes materials from black to clear

Credit: EPFL

EPFL researchers have developed a new printing process that involves removing material rather than depositing it. Their method could be particularly useful for printing banknotes and identity documents, for example.

“We have developed an entirely new printing process, turning Guttenberg’s concept on its head,” says Professor Olivier Martin, head of the Nanophotonics and Metrology Laboratory at EPFL’s Faculty of Engineering Sciences. Martin proudly displays a representation of the EPFL logo made using his team’s revolutionary method. The letters of the logo are transparent, while their edges are black or aluminum colored. The researchers’ initial goal was to develop a material that completely absorbs light. They created a material consisting of three layers – first aluminum, then magnesium fluoride (a dielectric compound) and finally chromium – resting on a Plexiglas substrate. Each layer is only a few nanometers thick. The end result is a black surface that absorbs all light waves. “Black is a very difficult color to get,” says Martin. “You usually end up with something that has bluish or purple undertones. But in our case, the black we got was really black. That means our material can capture 100% of the light it’s exposed to.”

A perfect mirror

Sebastian Mader, the Ph.D. student who led the project, wanted to see what would happen if he removed the top layer of the material: chrome. “Once I did that, all that was left was the dielectric compound and the aluminum,” he says. “Together, these two compounds form a perfect mirror. They reflect all wavelengths of light, absorbing none.” He then went a step further and removed these two layers, leaving only the Plexiglas substrate. “It gave us a fully transparent surface,” Mader explains.

New printing process changes materials from black to clear

Credit: Federal Polytechnic School of Lausanne

Drawing Transparency

The researchers removed the individual layers using a laser. It was so precise that they were able to fine-tune the layers as much or as little as they wanted in order to reproduce the full spectrum of shades between black and transparent. “The longer we left the laser in one place, the more material it removed,” says Martin. “We basically ‘draw’ lines of transparency rather than lines of color.” Their new method could be particularly useful in security applications and for printing banknotes. “Contrast is very important to our eyes, and since our method can produce both fully black and fully transparent areas, we can generate a lot of contrast,” says Martin. “For example, we can draw white letters on a black background, which makes the letters very easy to read.” Their study appears in Light: advanced manufacturing.


Fast, cheap and colorful 3D printing


More information:
Sebastian Mader et al, On-Demand Multistate Transparency Engineering, Light: advanced manufacturing (2021). DOI: 10.37188/lam.2021.026

Provided by the Federal Polytechnic School of Lausanne

Quote: New printing process changes materials from black to transparent (February 3, 2022) Retrieved February 3, 2022 from https://phys.org/news/2022-02-materials-black-transparent.html

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