Patent ID: 7987717

Claim:
A method for determining the degree of hardening of one or more printed ink or coating films on a substrate selected from the group consisting of paper, cardboard, plastic film or composite materials, in an offset printing process, the method comprising: measuring a change of one of the mechanical and viscoelastic properties of the ink or coating films on the substrate by externally causing an ultrasonic oscillation or an ultrasound signal in the ink or coating film and analyzing the echo from the ultrasonic oscillation or ultrasound signal to determine mechanical or viscoelastic properties of the ink or coating film while the substrate is passing through a printing press used for the printing process; and determining the degree of hardening or drying of the printed ink or coating films via the measured change of mechanical or viscoelastic properties, wherein the ultrasound signal is externally caused by one of a laser beam and a laser pulse directed to the ink or coating film, wherein a rapid local expansion of the ink or coating film takes place due to the thermal energy of the laser beam or pulse, leading to the generation of ultrasound in the ink or coating film.