2014 Volume 51 Issue 3 Pages 191-195
The fountain solution (FS) is one of the important parameters affecting the quality of offset printing. It can be controlled by adjusting the output of the FS motor, but it is quite difficult to measure the amount on the surface of paper, and thus, comparison of the efficiencies of different types of FSs is also difficult to achieve. Therefore, we have developed a quantitative method for determining the amount of FS on a surface by incorporating a fluorescent dye into the FS. There are many problems related to FSs, including greasing, registration errors, and snowflaking. We applied this method to the phenomenon of wet-printing mottle (WPM), which is an uneven print density caused by an excessive amount of FS, to understand the effect of the FS properties. We succeeded in establishing a quantitative method by extracting fluorescent dye from the printed matter and measuring the fluorescent intensity. We confirmed that one of the reasons for the occurrence of WPM was the non-uniformity of water absorption by the paper surface. When less FS was absorbed, the dynamic surface tension and dynamic contact angle of the FS were both smaller, and the WPM was better. We deduced that an effective means of improving the WPM is to use a paper for which there is little unevenness in the water absorption, to use an FS with a low dynamic surface tension, to minimize the amount of FS being used, and to print at low speed.
