Factors of the Fluting of Coated Paper in Web-Offset Printing

Abstract

The factors affecting on the fluting of the coated paper in the web-offset printing are discussed.In the early part of the drying process of the web-offset printing, moisture contained in the coated paper evaporates rapidly from a non-imaged area, resulting a large shrinkage in the cross direction of the coated paper in the non-imaged area. On the contrary, moisture of the coated paper lying under an imaged area evaporates slowly because a printed ink layer on the coated paper acts as heat transfer and moisture evaporation barrier, resulting a small shrinkage in the cross direction of the coated paper in the imaged area. As a result, the non-imaged area of the coated paper compresses the adjoining imaged area in the cross direction during the drying process leading to the buckling of the imaged area. It is the flutes of the coated paper in the web-offset printing.In this case, number of the flutes in the imaged area is defined by three parameters: Pc is the compressive force that acts to the imaged area, S is Gurley stiffness of the coated paper in the cross direction and b is size of the imaged area, as shown in formula (1). If these parameters of the coated paper which some flutings are shown on is fluctuated, the change of number of the fluting is predicted.