Surface topography evolution through production of aluminium offset lithographic plates

The topographies of cold rolled, alkaline etched and electrograined specimens of AA1050 alloy have been examined by scanning electron microscopy, and ultra-low-noise inteferometry with data analysis by TalyMap software. The objectives of this work were to trace the topographical history contributing to the roughness parameters of fully convoluted, electrograined surfaces, to investigate the differences in pit shapes produced under different conditions and to explore their effect on the fluid retentive properties of the aluminium substrate. The analysis of 3D parameters, such as Sa, Ssk, Str, Sal, Sdr, Sku and Sv/Sz, disclosed the changes in typical topography from topography of rolling lines, with transverse tearing, to the topography of highly populated pits. Pit volumes were calculated after partitioning the surface by depth, using Sk functional parameters to define bearing area thresholds. Through this combined approach, simple functional void volume parameters and analysis of cross-sections at the top of the deepest layer (Svk) were sufficient to differentiate important features visible in plate topographies where roughness parameters had previously failed. Whilst amplitude parameters were sufficient to distinguish tearing or scallops after alkaline etching, the features of electrograining, such as double pit structures and shallow lateral pit development, were separated using analysis of Sk functional parameters, where the tips of deep pits that occupy the Svk layer revealed pit shape and were excellent indicators of the quality of the macroscopic electrograined surface.