Ink Transfer Mechanism in Offset Printing Process

This paper describes the mechanisms of an ink transfer in offset printing process. It is found that the ink layer on the dot resin of PS plate is a mountain shape. The mountain shaped ink layer on resin dot is transferred to gum blanket by printing pressure, and at that time, the dot gain takes place. The square dot changes to the circular one on the blanket and increases about 10-25% in dot size. If other printing condition is constant, the supply variation of a fountain solution on the dampening rollers slightly influence to the total ink layer thickness on dot resin of PS plates. Therefore, the ink dot size on printed paper little changes, but the ink layer thickness and its shape of printed dot on paper is changed by the variation of the fountain solution on the dampening rollers. The ink transfer mechanisms at the three positions in lithographic printing, that is, the ink transfer from inking roller to PS plate to blanket and blanket to paper are discussed by phenomenological model.