Printouts' Quality Depending on Too Small Pressure of a Blanket Cylinder Against an Impression Cylinder and a Plate Cylinder in Offset Machine

It has been written in many books that correct setting of clamp in a printing offset machine has impact on wear of consumables and machine elements, and quality of printouts. However there has been no clear recipe to do that. In our article we present research on effect of too small pressure between a blanket cylinder against a plate cylinder and an impression cylinder. The challenge was to find method for gaining results of printing with different clamp but with the same printing conditions. During printing, especially when the printing machine stops and starts, a balance between ink and dampening solution is changing. To obtain the same printing conditions with different clamp on the blanket cylinder under blanket, there were fixed underlay sheets with the same thickness and width but different length. To reduce influence of variable thickness of glue the underlay sheets was glued to each other only on the one edge. We printed on two kind of papers: coated and uncoated. The amount of ink transported on paper was adjusted by changing rotation of the ink fountain roller. The spectrophotometer was used to measure optical density. The tone value increase was computed with Murray-Davies equation. While the tone value increase and optical density are very important printout parameters, our research shows how change of pressure changes printing quality. Our results also help to understand behavior of ink under pressure. Depending on paper and clamp ink could penetrate into the paper or spreads on the paper surface