Scientists have found a way to print full-color images using completely transparent ink

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Image for article titled Scientists have found a way to print full color images with completely transparent ink

image: Yanlin Song

To solve some of the many problems with printers, researchers at the Institute of Chemistry of the Chinese Academy of Sciences have found a way to use transparent inks to print images with a full spectrum of colors.

You don’t have to be an environmental scientist or engineer to understand why printers are problematic. The chemical processes required to make the pigments and inks used in the devices are not accurate environmentally friendly, and then there is the problem that if you do a lot of color printing, you have to keep replacing multiple ink cartridges even if the cartridges don’t seem to be completely empty. Where is all the leftover ink? Is it disposed of responsibly? There are many questions and concerns surrounding the printing industry that have encouraged researchers to find alternative ways of creating color images.

One approach is inspired by nature, in which creatures like butterflies and peacocks create shimmering colors by manipulating the way light is reflected by microscopic structures, a phenomenon known as structure color. In 2015, researchers from the Missouri University of Science and Technology created in an inkless printer alternative that uses a laser to print Perforate a metal material with thousands of tiny holes to create a microstructure that creates the same effect, resulting in a small range of visible colors.

In a recently published paper, however, a team from the Chinese Academy of Sciences describes a new approach to structural color technology that sounds much more promising for real-world applications because it can reproduce a wide range of colors and uses existing printer hardware. An inkjet printer – the color printer most people have in their homes – creates full-color images by shooting microscopic droplets of ink of various sizes and colors onto a sheet of paper. When viewed up close, the patterns of colored dots appear completely random, but from a distance a full-color image can be seen.

The researchers modified an inkjet printer to use only a single polymer ink that appears transparent to the human eye. Instead of paper, which absorbs most liquids easily, spreads and bleeds, glass with a hydrophobic surface was used so that the water-based ink droplets were repelled when applied, creating a structure that looked like a tiny dome. By harnessing the surface tension properties of liquids and the hydrophobic properties of glass, researchers were able to modify a printer to produce these microdomes of various sizes and shapes that cover a surface with essentially thousands and thousands of tiny lenses.

Since the microdome structures are only printed on one side of the glass, the imagery is only visible from this side;  viewed from the other side, it becomes completely transparent.

Since the microdome structures are only printed on one side of the glass, the imagery is only visible from this side; viewed from the other side, it becomes completely transparent.
image: Institute of Chemistry, Chinese Academy of Sciences

Each Microdome reflects a different wavelength of light depending on its size and shape, which means that the human eye perceives different colors. Grouped with thousands, a larger, full-color image can be created, just as colored dots of ink create images on paper (also like the colored pixels on an LCD screen). However, the effect only works in one direction, so that when the printed piece of glass is viewed from the other side, the ink is transparent again. One day entire skyscrapers could be covered in pictures, be it artistic designs, massive billboards or Protection for birdswithout obstructing the view from the inside.

Images by Audrey Hepburn and Isaac Newton demonstrate the high fidelity of this new approach to printing.

Images by Audrey Hepburn and Isaac Newton demonstrate the high fidelity of this new approach to printing.
image: Yanlin Song

By carefully manipulating the shape and patterned structure of the micro-domes, researchers believe they can fully control the saturation, brightness, and other aspects of the colors produced. For now, though, they’ve focused on recreating detailed, recognizable images with limited color palettes to demonstrate the potential of the new approach.

In addition to being compatible with existing printing hardware, including the printers used in larger commercial print shops, the new textured color process could potentially help reduce printing costs as it relies on a single ink. It also promises to last much longer for prints than using dyes and pigments, which naturally fade over time. Assuming that light continues to obey the laws of physics and as long as nothing affects the printed microdome structures, the visible colors will always look as vivid and saturated as when they were first printed.


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