Laser-assisted photonic crystal-based thermal printing: A technology with significant improvements in resolution, grayscale, color tuning, and compatibility with curved substrate

Structural-colored thermal printing using the “photonic crystal/phase change material” (PC/PCM) composites as thermal paper is a promising and feasible technique, which possesses superior color stability against chemicals and green characteristics for humans and the environment. However, there are still great challenges to limit its application, including the incapability of multi-color printing, unsatisfactory resolution, and limited greyscale levels. Here, a laser-assisted thermal printing process is developed based on the photothermal conversion from the laser irradiation and the thermochromic effect of the PC/PCM composites. Thanks to the intense laser heating in a small range, fine patterns with practical/theoretical resolution as high as 275/879 DPI can be obtained under fast laser scanning. Using precise control of the laser intensity or the visual fusion of microdots with tunable size and number, 36 greyscale levels are realized by “photomask” or “halftone” strategies. Multicolor patterns are fabricated by stacking the separately printed RGB sub-images, which vertically mix two or three of the RGB colors to produce abundant colors. Based on the tomographic deconstruction of the source image, a clear structural-colored pattern can be printed on the curved substrate by continuous tuning of the laser focal plane and multi-step laser printing on each slice.