Recognition of laser-marked quick response codes on polypropylene surfaces

Polystyrene-grafted antimony trioxide (Sb2O3-g-PS) was prepared as a laser-marking additive by free radical polymerization. Fourier transform infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy were used to characterize the modified Sb2O3 particles with a core-shell structure. Composites of polypropylene (PP) and modified or unmodified Sb2O3 were laser-marked using a neodymium-doped yttrium aluminum garnet laser at 1064 nm. Compared with PP and unmodified Sb2O3 composites, the laser marking performance was dramatically improved for PP composites, with an equivalent amount of Sb2O3-g-PS. The marking patterns of quick response (QR) codes on the surface of PP composites containing Sb2O3-g-PS were clear and had a high contrast. The QR codes were easily and quickly recognized when the content of Sb2O3-g-PS reached 2.0 wt%. The laser-induced blackening on the surface of the PP/Sb2O3-g-PS composite was due to the synergistic effect of Sb2O3 photothermal conversion and PS carbonization, which can effectively improve the laser marking performance and QR code recognition. We believe that the application of this core-shell laser additive will become prominent in the field of QR code marking, for polyolefins that are poor absorbers of the 1064 nm wavelength.