For thousands of years, humans have used pigmented paints, dyes, and inks that absorb light to create color. However, a Japanese researcher is pioneering a revolutionary approach by applying reflective color technology directly to 3D objects.
Traditional coloring methods, whether through paint, dyes, or inks, involve coating objects with materials that produce color by absorbing certain wavelengths of light. These methods serve purposes ranging from communication and decoration to weatherproofing.
However, they come with notable drawbacks: colors fade over time, necessitating regular reapplication; many pigments and solvents pose environmental and health hazards; and some methods require primers or thick coatings to be effective.
A New Color Technology
Now Sugimoto Hiroshi, a Kobe University researcher and material engineer, has produced a new method that fundamentally alters how humans produce color.
Conventional pigments absorb other colors from the light sprectrum, leaving only the color we see. Over time, reactions with sunlight, oxygen, and pollutants cause these pigments to degrade. As they degrade, less light is absorbed, washing out their effect.
Sugimoto’s new method uses a thin layer of nanometer silicon crystal spheres applied to a surface. The spheres reflect light instead of absorbing it. Through particular crystal arrangements, they only reflect the desired light color. The same principle imbues butterfly wings and peacock feathers with their brilliant colors in nature.
While the method may lead to some of the most vibrant colors in the natural world, reproducing it in manufacturing has been extremely difficult. Beyond difficulty in producing the correct color, the finish tends to be iridescent, relying on the viewing angle. Sugimoto’s true innovation was developing the precision control necessary to scatter light in specific wavelengths with a finish that would look the same from any angle. In a demonstration, just a thin coat on glass results in bright, vibrant colors.
“Using tiny silicon spheres of very consistent size, light can be scattered around these spheres so that only one color is reflected,” Sugimoto explained. “Then, we realized that this material lets us coat 3D objects in non-iridescent colors.”
Changing Color For Manufacturing
For the project’s next phase, Sugimoto worked with ANRI’s Kameda Takahiro, identifying paint markets for the practical implementation of his discovery. Kobe University Capital, which links discoveries at Kobe University to real-world use, worked alongside the pair to connect them to JST’s D-Global program, which granted them ¥300 million. Their first projects will include security inks and raw materials for cosmetics at a plant projected to be operational by 2027.
“With our nanospheres we can theoretically achieve printing resolutions of up to 50,000 dpi (your office printer has a resolution of 300 dpi) which is well beyond the 10,000 dpi required for the most advanced security inks. For the cosmetics industry, they are the only raw product that can combine the functions of pigments and concealers in foundations and sunscreens. Also, silicon being the second most abundant element in the Earth’s crust, humans are taking it in daily without any health effects,” explains Sugimoto.
Chrome Makes It Go Faster
Once those test cases prove the reliability of their production techniques and establish a sales infrastructure, the team plans to move on to the automotive industry. The current intent is to open a second plant in 2029 focused on this market. Sugimoto has several ideas on how his color technology can solve major automobile and airline manufacturing issues.
“Between a quarter and a third of the greenhouse gas emissions during the production of a car stem from the coloring process, because it takes so much energy to dry the thick layers of paint. Likewise, for airplane manufacturers, the thick layer of paint adds several hundreds of kilograms to the plane’s weight, which increases its fuel consumption, Sugimoto explained.
“In both cases, due to their opacity, our nanospheres would require a much thinner layer and so we can significantly reduce costs and environmental impact,” he said.
Environmentally Friendly Color Technology
Sugimoto quickly points out the many advantages of silicon for his nanospheres. Semiconductors, such as silicon, gain increasing importance annually as the basis for electronics, from smartphones to electric cars. The ever-increasing production processes for these devices may result in waste products that Sugimoto’s process can recycle, further increasing the environmental benefit.
“In addition to its low environmental impact, silicon is a fundamental material for the semiconductor industry, and therefore has a high affinity with industrial technology in addition to there already being abundant physical and chemical knowledge,” he said.
Many Applications
Sugimoto is thinking long-term, hoping to present an initial public offering by 2033. In addition to the many industrial applications he has presented to the public so far, he informed The Debrief that he has also developed consumer paint products.
“Our inks do not require the special machines for painting and can be processed with ordinary painting techniques including brushes and sprays. In addition to the monolayer coating, we developed a mixture of nanoparticles and binders in solution which can be used as a paint in a bottle like commercial ones,” Sugimoto explained.
The paper “Monolayer of Mie-Resonant Silicon Nanospheres for Structural Coloration” appeared on January 29, 2024 in the ACS Applied Nano Materials.
Ryan Whalen covers science and technology for The Debrief. He holds a BA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.