(31b) Enhancing NIR Reflectance of Black Automotive Coating

Carbon black is usually used as a pigment in coatings to provide a deep black color in the automotive industry. The black automotive coating reflects less than 5% of light in both visible light (380nm – 750nm) and near-infrared (NIR) wavelength ranges (750 – 2500nm). However, a minimum of 10% reflectance in the NIR range is necessary to ensure safety for autonomous vehicles equipped with LiDAR technology, as the LiDAR sensors use signals at 905 or 1550 nm. Herein, we introduce two approaches to enhance the NIR reflectance for black coatings. The layer technology was utilized in the first approach by applying a multilayer plastic film on top of the black coating. The constructive interference at each interface between nanometer thin layers of two polymer contributed to very high reflectance (up to 98%) in the NIR wavelength range. But the wide adoption of this approach is very challenging, as it will add at least $2,000 additional cost for end consumers to cover the vehicle with such films. The second approach was to tailor carbon black’s optical band gap. Here in we present a modified carbon black with the optical band gap calculated based on Tauc’s plot increased from nearly zero to 0.7 eV. In comparison to the control carbon black, the modified carbon black in the acrylic coating exhibited more than 2 times higher total reflectance (12.9%) at 1550 nm wavelength. More importantly, the coating retained a deep visual blackness (My = 224). The technology of modified carbon black could be a pioneering solution to achieve high NIR reflectance while maintaining deep coating blackness. Additionally, the black pigments with enhanced NIR reflectance would contribute to improving the sorting and recyclability of black plastic parts.