A Comparative Study of Offset Plate Quality Parameters using Image Processing and Analytical Methods

Printing plate performance is one of the crucial factors affecting the printed product quality. In particular, when producing printing plates for larger print runs, a rigorous quality control has to be performed, since any bulk and surface imperfection can have a large detrimental effect on print sharpness, contrast, non-uniformity, colour gamut, and other print properties. In our research two characteristics of an aluminium-based offset printing plate after 0, 123,000, 177,000 and 300,000 runs were studied: surface topography and contact angle. Each was determined using two assessment methods. For the surface roughness determination, the conventional mechanical profilometry and scanning electron microscope (SEM) imaging followed by an implementation of a texture analysis method Gray level co-occurrence matrix (GLCM) were applied. The contact angle of a printing plate with water was acquired by the sessile drop method using a DataPhysics OCA30 instrument and, alternatively, by implementing image analysis routines on a sequence of images captured by a simple image acquisition system. Image analysis for both surface topography and contact angle assessment was accomplished using ImageJ, a public domain Java image processing program. Both image analysis-based evaluation methods proved to be a viable alternative to the two established ones, providing a reliable tool for the monitoring of the wearing and other surface changes of a printing plate during the print run.