Printer's Mottle and Ink Trap Mottle on Coated and Un-Coated Paper in Single Colour Sheet Fed Offset Press

Mottling is the uneven appearance of print, particularly in solid areas, small dark and light areas appearing in the surface of paper or paper board. Print mottle is influenced by many parameters, but the most important one is the type of paper which is used for printing. Variations in the surface characteristics such as absorption and smoothness play an important role while analysis of the mottle. Print mottle can occur in sheet-fed offset due to several reasons related to both the paper and its coating and the printing press. The aim of the research work was to improve our knowledge of the influence on mottle related to the different paper surfaces (both coated and un-coated paper) in single colour sheet fed offset press. Both the coated and un-coated papers were used with different gram mage for printing with the help of a specially designed test form. The results from the print trials show that fountain solution from the previous printing unit can cause a decreased print density and dot gain. The structure of the paper coating, uneven porosity distribution has high influence oil water induced mottle while the effect of the surface chemistry is low.