Laser engraving in gravure industry

Digital imaging methods like Computer to Plate (CTP) solutions are progressive technologies to improve the quality and efficiency of prepress and printing workflows. In this environment the application of lasers for print form fabrication plays an increasingly important role because of the high machining rate, the high spatial resolution, the achievable high energy densities by fine focusing and the ability of digital modulation. This paper gives an overview of our laser based processes in flexography and gravure with a focus on the precise micro structuring of gravure print forms by direct laser ablation. Direct laser engraving into metallic cylinders is performed with a high power Q-switched Nd:YAG laser system at 70 kHz repetition rate tuned for high reproducibility and stability of the mean pulse energy (σ2 < 0.8%). An exact modulation technique allows fast variation and precise calibration of the energy of each single laser pulse as well as active modulation of the intensity profile of the beam. This method permits to engrave with each single laser pulse a complete cell and to define diameter and depth of each cell (the aspect ratio and the cell shape) independently and freely from pulse to pulse at a rate of 70 kHz, controlled by digital image data. Thus the cell shape can be optimized for the best ink transfer characteristic on different print substrates. Future developments in gravure industry and the requirements on fiber lasers and ultra short pulse lasers for an efficient industrial engraving process of print cylinders are discussed.