STUDY OF COLOUR CHANGE IN THE COURSE OF DRYING ON PRINTS CREATED USING OFFSET PRINTING TECHNOLOGY

Abstract: The research presented in the article describes the colour changes resulting from the drying of printing ink. In technical terminology, this colour change is called dryback (Schulz et al, 2005). Different print technologies use different inks (solvent-based, inks dried by oxidation, inks dried by UV radiation), but all of them are affected by dryback. This means that the ink still wet after printing has colour properties different from ink after it is dried. During the printing process it is usually possible to measure the colour properties (lightness, blue-yellow, red-green content, density) of the still wet print by the machine. A polarizing filter is installed in spectrophotometers in order to perform this measurement, which tries to measure the colour characteristics of the print, eliminating surface reflection. The research is designed to determine the point when the paint can be considered dried on the carrier (paper), to describe – using mathematical equations – the changes in the colour characteristics during the drying process, and then to design a device which is able to determine – using the mathematical model – what colour characteristics the still wet print will have after complete drying. In our article we intend to describe the first tests and the resulting conclusions.