An Analysis of a Ghost Phenomenon on the Web Offset Printing

Abstract

On the web offset printing press, special kind of ghost phenomenon is known as a kind of printing defect. This printing defect is the blurred white image showed up within the half tone image printed on the web where printing plate of the corresponding position has no such image to print. This blurred white image is suspected to be that coming from the printing plate of the other side printing. Only a little has been reported regarding this printing defect. In this paper, this special ghost phenomenon on the web offset printing was studied. We have developed a method to reproduce the ghost phenomenon and the effects of the printing condition to the ghost were examined. These results indicate that this ghost on the web offset printing occurs by two steps. First step is the ink piling on the blanket cylinder of one side reflecting the image of the other side, and the second step is the formation of the ghost on the web due to the thinning of the half tone dots at the ink piled up position. The mechanism of ink piling is suggested to be strongly related to the tack balance between top and bottom blanket cylinders and the web.