X.X-post-print laser marking: A solution to the challenge of 100% calcium carbonate coating when using CO₂ lasers

Laser marking is a widely used technique to form individualised identification, such as product numbering or 2D coding. The technique is based on ink removal via laser ablation, which requires local heating with a laser beam, i.e. the coating layer must absorb at the particular wavelength of the laser to provide the heat to vaporise the ink layer. Calcium carbonate shows a very low absorption at the wavelength peaks of the typical CO₂ lasers used, which has led to the need to incorporate a threshold amount of other minerals, however generally at the cost of losing natural brightness. Post application of an ultrathin nanoclay or nanosilica layer onto a high brightness calcium carbonate coating is shown to support laser ablation of offset ink with all the standard laser wavelengths, without compromising the optical appearance.