Insight into Set-off Phenomenon in Coldset Offset (CSWO) Printing

During the last decade the number of 4-colour pages in newspapers has increased rapidly. Concurrently, the print density level has risen to achieve better print quality. These developments have increased ink volume on paper and smearing. Smearing deteriorates print quality. Different explanations have been given for the smearing defined as set-off. The study concentrates on finding different parameters important for the set-off phenomenon. In the presentation the following factors are discussed: 1) location of printing ink on and in the surface structure of paper, 2) setting of ink during the time period between printing nip and set-off situation, and 3) creation of the contact between facing paper and ink layer on printed sheet.